Cell Cycle Regulatory Proteins in Renal Disease

8/13/2019 Cell Cycle Regulatory Proteins in Renal Disease

1/16

278:515-529, 2000.Am J Physiol Renal PhysiolStuart J. Shankland and Gunter Wolf

You might find this additional information useful...

144 articles, 40 of which you can access free at:This article cites

http://ajprenal.physiology.org/cgi/content/full/278/4/F515#BIBL

35 other HighWire hosted articles, the first 5 are:This article has been cited by

[PDF][Full Text][Abstract], October 1, 2008; 19 (10): 1965-1974.J. Am. Soc. Nephrol.

DoucetJ. P. D. Van Huyen, L. Cheval, M. Bloch-Faure, M. F. Belair, D. Heudes, P. Bruneval and A.

GDF15 Triggers Homeostatic Proliferation of Acid-Secreting Collecting Duct Cells

[PDF][Full Text][Abstract], November 1, 2008; 295 (5): F1563-F1573.Am J Physiol Renal Physiol

Gianiorio, F. Tosetti, U. Weiss, P. Traverso, M. Mji, G. Deferrari and G. GaribottoD. Verzola, M. T. Gandolfo, G. Gaetani, A. Ferraris, R. Mangerini, F. Ferrario, B. Villaggio, F.

Accelerated senescence in the kidneys of patients with type 2 diabetic nephropathy

[PDF][Full Text][Abstract], November 1, 2008; 295 (5): C1409-C1416.Am J Physiol Cell Physiol

R. Tao, C.-P. Lau, H.-F. Tse and G.-R. Livolume-sensitive chloride channels in mouse mesenchymal stem cellsRegulation of cell proliferation by intermediate-conductance Ca2+-activated potassium and

[PDF][Full Text][Abstract], January 1, 2009; 24 (1): 52-61.Nephrol. Dial. Transplant.

D. Sabuda-Widemann, B. Grabensee, C. Schwandt and C. Blumeexpression of Egr-1 in rat mesangial cellsMycophenolic acid inhibits the autocrine PDGF-B synthesis and PDGF-BB-induced mRNA

[PDF][Full Text][Abstract], March 1, 2009; 174 (3): 797-807.Am. J. Pathol.

RemuzziD. Macconi, F. Sangalli, M. Bonomelli, S. Conti, L. Condorelli, E. Gagliardini, G. Remuzzi and A.

InhibitionPodocyte Repopulation Contributes to Regression of Glomerular Injury Induced by Ace

on the following topics:http://highwire.stanford.edu/lists/artbytopic.dtlcan be found atMedline items on this article's topics

Physiology .. ApoptosisMedicine .. HypertrophyOncology .. CDKPhysiology .. Cell Cycle RegulatorsBiochemistry .. Kinase InhibitionBiochemistry .. Kinases

including high-resolution figures, can be found at:Updated information and services

http://ajprenal.physiology.org/cgi/content/full/278/4/F515

can be found at:AJP - Renal PhysiologyaboutAdditional material and information

http://www.the-aps.org/publications/ajprenal

This information is current as of February 28, 2009 .

http://www.the-aps.org/.American Physiological Society. ISSN: 0363-6127, ESSN: 1522-1466. Visit our website at(monthly) by the American Physiological Society, 9650 Rockville Pike, Bethesda MD 20814-3991. Copyright 2005 by therespective cells and vasculature, as well as to the control of body fluid volume and composition. It is published 12 times a year

publishes original manuscripts on a broad range of subjects relating to the kidney, urinary tract, and theirAJP - Renal Physiology
http://ajprenal.physiology.org/cgi/content/full/278/4/F515#BIBLhttp://www.jasn.org/cgi/reprint/19/10/1965http://www.jasn.org/cgi/content/full/19/10/1965http://www.jasn.org/cgi/content/full/19/10/1965http://www.jasn.org/cgi/content/abstract/19/10/1965http://ajprenal.physiology.org/cgi/reprint/295/5/F1563http://ajprenal.physiology.org/cgi/content/full/295/5/F1563http://ajprenal.physiology.org/cgi/content/full/295/5/F1563http://ajprenal.physiology.org/cgi/content/abstract/295/5/F1563http://ajpcell.physiology.org/cgi/reprint/295/5/C1409http://ajpcell.physiology.org/cgi/content/full/295/5/C1409http://ajpcell.physiology.org/cgi/content/full/295/5/C1409http://ajpcell.physiology.org/cgi/content/abstract/295/5/C1409http://ndt.oxfordjournals.org/cgi/reprint/24/1/52http://ndt.oxfordjournals.org/cgi/content/full/24/1/52http://ndt.oxfordjournals.org/cgi/content/full/24/1/52http://ndt.oxfordjournals.org/cgi/content/abstract/24/1/52http://ndt.oxfordjournals.org/cgi/reprint/24/1/52http://ndt.oxfordjournals.org/cgi/content/abstract/24/1/52http://ndt.oxfordjournals.org/cgi/content/full/24/1/52http://ndt.oxfordjournals.org/cgi/reprint/24/1/52http://ajp.amjpathol.org/cgi/reprint/174/3/797http://ajp.amjpathol.org/cgi/content/full/174/3/797http://ajp.amjpathol.org/cgi/content/full/174/3/797http://ajp.amjpathol.org/cgi/content/abstract/174/3/797http://ajp.amjpathol.org/cgi/content/full/174/3/797http://ajp.amjpathol.org/cgi/reprint/174/3/797http://ajp.amjpathol.org/cgi/content/abstract/174/3/797http://ajp.amjpathol.org/cgi/content/full/174/3/797http://highwire.stanford.edu/lists/artbytopic.dtlhttp://highwire.stanford.edu/lists/artbytopic.dtlhttp://ajprenal.physiology.org/cgi/content/full/278/4/F515http://www.the-aps.org/publications/ajprenalhttp://www.the-aps.org/http://www.the-aps.org/http://www.the-aps.org/http://www.the-aps.org/publications/ajprenalhttp://ajprenal.physiology.org/cgi/content/full/278/4/F515http://highwire.stanford.edu/lists/artbytopic.dtlhttp://www.jasn.org/cgi/reprint/19/10/1965http://www.jasn.org/cgi/content/full/19/10/1965http://www.jasn.org/cgi/content/abstract/19/10/1965http://ajprenal.physiology.org/cgi/reprint/295/5/F1563http://ajprenal.physiology.org/cgi/content/full/295/5/F1563http://ajprenal.physiology.org/cgi/content/abstract/295/5/F1563http://ajpcell.physiology.org/cgi/reprint/295/5/C1409http://ajpcell.physiology.org/cgi/content/full/295/5/C1409http://ajpcell.physiology.org/cgi/content/abstract/295/5/C1409http://ndt.oxfordjournals.org/cgi/reprint/24/1/52http://ndt.oxfordjournals.org/cgi/content/full/24/1/52http://ndt.oxfordjournals.org/cgi/content/abstract/24/1/52http://ajp.amjpathol.org/cgi/reprint/174/3/797http://ajp.amjpathol.org/cgi/content/full/174/3/797http://ajp.amjpathol.org/cgi/content/abstract/174/3/797http://ajprenal.physiology.org/cgi/content/full/278/4/F515#BIBL


2/16

invited review

Cell cycle regulat ory proteins in rena l disea se:role in hypertrophy, proliferation, and apoptosis

STU ART J . SH ANKL AND 1 AND GUNTER WOLF 2

1Departm ent of M edi cine, Di vision of N ephr ology, Un iversity of Washi ngton Seattl e,

Washington 98195-6521; and 2Departm ent of M edi cin e, D ivi sion of N ephrology

and Osteology, Universi ty of Hamburg, D-20146 Hamburg, Germany

Shankland, Stuart J ., and Gunter Wolf. Cell cycle regula t oryproteins in rena l disease: role in hypertrophy, proliferat ion, and apopto-sis. Am J Physiol Renal Physiol278: F515F529, 2000.The response to

g l om e r ul a r a n d t u b u loi n t er s t i t ia l ce ll i n ju r y i n m os t f or m s of r e n a ldisease includes cha nges in cell number (proliferation a nd a poptosis)a ndcell s ize (hyerpt rophy). Thes e event s t ypica lly precede a nd ma y berepons ible for t he a ccumula t ion of ext ra cellula r ma t rix prot eins t ha tl ea d s t o a d e cr e a s e i n r e n a l f u n ct i on . Th e r e i s i n cr e a s in g e vi d en ceshowing that positive (cyclins and cyclin-dependent kinases) and nega-tive (cyclin-dependent kinase inhibitors) cell cycle regulatory proteinsha ve a crit ical role in regulat ing these fundam enta l cellular responses toimmune a nd nonimmune forms of injury. Da t a now s how t ha t a l t eringspecific cell cycle proteins affects renal cell proliferation and improvesr e na l f u n ct i on . E q u a l l y e xci t i ng i s t h e e xp a n d i ng b od y o f l i t er a t u r eshowing novel biological r oles for cell cycle proteins in the regulat ion ofcell hypert rophy a nd a popt os is . Wit h increa s ing unders t a nding of t herole for cell cyle regulatory proteins in rena l disease comes the hope forpotentia l thera peutic inverventions.

cyclin; cell cycle; kidney; glomerulus; mesangial cell

D U R I N G D E V E L OP M E N T, K I D N E Y g rowt h is in i t ial ly d u e toan in cre ase in g lo m e ru lar an d tu b u lar e p ith e lial ce l lnumber because of proliferation. Thereafter, there is aphysiologica l increa se in cell size. Thus kidney sizedepends on cell number a nd on t he individual cell sizea nd ma ss (10). Cell number reflects t he bala nce of newcell generation by proliferation and loss by apoptosis(99). There is very little cell turnover in the matureadult kidney under normal physiological circumstances(81). However, cell number and cell size may changea f t e r m a n y f or m s of p a t h ol og ica l r e na l i n ju r y. F orexample, glomerulonephritis can be a ssociat ed wit h a nincrease in glomerular cell number due to proliferation(47), wh ereas increa sed a poptosis aft er uretera l obstr uc-tion and acute tubular necrosis are initially associatedw ith a decrease in tubula r epithelia l cell number (59).M ore over, re n al cel l p rol iferat ion an d ap op tosis ar eoften closely linked within a given renal cell popula-t io n , an d th e b alan ce o f th e se g ro wth an d d e ath p ro -cesses ultimately determines renal cell number. Cer-ta in forms of renal injury such as dia betic nephropat hy

an d a r eduction in nephron number a re associat ed withan increase individual cell size by hypertrophy ratherth a n a n increa se in cell number (42, 90).

Th u s, d e pe n d in g on th e u n d erlyin g fo rm of re n alinjury, proliferation, hypertrophy, and apoptosis maycon t r i bu t e t o t h e d ev el op me nt of r e na l s ca r r i n g i ng lom e ru lar an d tu b u loin te rst i t ial d isease s. Alth ou g hs u ch d i ve r se p r oce ss es a p pe a r t o h a v e n ot h i n g i ncom m o n at th e fi rst g la n ce, th is re vie w w ill sh ow th a tthe ultima te fa te of a cell is regulat ed at the level of the

cell cycle by a complex interaction of specific cell cycleregulatory proteins.

THE CELL CYCLE

It has been known for more than 100 years that cellp ro l i fe rat io n is u l t im ate ly a n u cle ar e ve n t an d is d i-vided into different pha ses in wha t is now called the cellcycle (72, 74) (Fig. 1). Nondividing (quiescent) cells arein G 0 p h ase a n d e n te r t h e cel l cycle a t G 1, followed bythe S phase, w here DNA replica tion occurs. Cells thenp rog re ss th ro u gh G 2, a n d en t e r m i t os is (M p ha s e ),

Am J Ph ysiol Renal Physiol278: F515F 529, 2000.

0363-6127/00 $5.00 C opyr igh t 2000 t h e Am er ica n P hysiologica l S ociet y F 515ht tp://w w w.a jprena l.org


3/16

w hich is furt her subdivided into propha se, metapha se,anaphase, and telophase, which is followed by cytokine-sis (cell divis ion). Tra nsit ion from one cell cycle pha se toa nother is a coordinated, sequentia l, and syn chronizedp r oces s t h a t occu r s w i t h p r eci se t i m in g i n a w e ll -d e fi n e d o rd er to e n su re th a t th e cel lular m a ch in ery isready for DNA replica tion, tha t D NA replicat ion occursonly once in each cycle, that DNA replication is com-pleted before mitosis star ts, a nd th a t chromosomes a rere plicate d in to id en tical se ts in d au g h te r ce lls (31).After pa ssing a rest riction point in la te G 1, cells ar e nolonger responsive to extracellular signals and complete

the cell cycle under the control of specific cell cycleregulatory proteins. The average cell cycle time is 12 hfor G 1, 6 h for S , G 2last s 6 h, a nd mit osis is completed in30 mi n (70).

Renal injury can result in proliferation, hypertrophy,or apoptosis, wh ich we believe a re linked at th e level ofthe cell cycle (101). Proliferation requires normal pro-g re ssion th ro u g h th e cel l cycle; h yp ertro ph y occu rswhen cells engage the cell cycle but cannot progressb e yo n d late G 1 (G 1/S a rrest); a poptosis is a ssociat edw ith exit from the cell cycle, which t ypica lly occurs inG 1. Thus t hese processes ma y sha re common pat hw ay sand may explain why certain cell populations undergoproliferation and apoptosis, whereas proliferation and

hypertrophy a re independent events.Cell Cycle Regulat or y Protein s

The cell cycle is ultimately controlled by cell cycleregulatory proteins, which localize predominantly inthe nucleus. Tra nsition betw een each pha se of the cellcycle is positively regulated by the kina se a ctivity of ad ist in ct h oloe n zym e , wh ich is com p ose d of tw o su b -units: cyclins and their partner, cyclin-dependent ki-na ses (CD K) (65, 112, 114) (Ta ble 1). C yclins ha ve ver ysh ort h al f-l ive s (30 60 m i n ), a n d l ev el s fl u c t u a t ethroughout the cell cycle (84). In contrast, CDK pro-

teins a re constit uitively expressed, a nd levels typicallyremain unchanged throughout the cell cycle (57). How-ever, CDK are posttranslationally activated on bindingby a part ner cyclin (118). C DK inhibitors n egat ivelyregula te cell cycle progression by inh ibiting cyclin-CD Kcomplexes, resulting in cell cycle arrest (115).

En tr y of Qui escent Cells In to the Cell Cycle

Entry of quiescent cells (G 0) i n t o ea r l y G 1 requiresD-ty pe cyclins (D1, D 2, D3) (6), w hich a re expressed in

a cell-t ype-specifi c ma nner (48). D-cyclins a re tr a nscr ip-tionally regulated, and levels are increased by specificmitogens such a s growth factors (6). D -cyclin levelsd e cre ase o n m itog en with d ra wa l (114), an d g rowt hinhibitors such as interferon (127) and transformingg ro wth facto r- (TGF-) (28) suppress D-type cyclintranscription.

D-type cyclins associa te with a nd activa te CDK 4 a nd6 in G 1(112, 113). A critica l subst ra te for cyclin D-CDKis the 110-kDa protein product of the retinoblastomagene (pRb) (8), w hich regula tes G 1/S t ra ns it ion (96, 133)(F ig . 2). p Rb is h yp op h osp h orylat e d d u rin g G 0 a n de arly G 1 an d is g rowt h r e strict ive b y se qu e ste rin g th etra nscription fa ctor E2F (133). C yclin D phosphory-

Fig. 1. Overview of different pha ses of cell cycle. Quiescent cells arein G 0phase, an d reenter cell cycle at G 1, which prepa res cell for DNAs y n t h e sis . Af t er p a s s in g t h e r e s t r ic t ion p oin t in la t e G 1, c e l ls a r ecommitted to enter the S phase, where DNAreplication occurs. In G 2,cells prepare for mitosis (M phase), where cells divide. Cell cycleprogression is controlled by positive [cyclins and cyclin-dependentkinases (CDK)] and negat ive (CDK inhibitors) cell cycle regulatoryproteins.

Ta ble 1. Pr in cipal cell cycle r egulat ory pr otein s

C ell C ycle P ha se C y clin C D K C D K I n hibit or

E a r l y G 1 D 1 , D 2 , D 3 4 , 6 p 15, p 16, p 18 , p 19 , p 20p21, p27, p57

L a t e G 1 E 1, E 2 2 p21, p27, p57S A 2 p21, p27, p57M A, B cdc2 p21

A specific cyclin binds to and activates a partner cyclin-dependentkinase (CDK) in each pha se of the cell cycle. CD K inh ibitors bind t oan d inhibit t he activit y of cyclin-CD K complexes.

Fig. 2. P hosphorylat ion of ret inoblastoma (Rb) gene protein. G rowthfactor induces cyclin D synth esis, lead ing to forma tion of active cyclinD-CDK 4 complexes. H ypophosphorylated Rb binds t ran script ionfactor E2F, and is growth restrict ive. Cyclin D -CDK 4 phosphorylatesR b (g r ow t h p er m is s iv e ), lea d in g t o r e le a s e of E2 F. I n a d d i t ion t obinding to several target genes required for G 1-phase progression,E2F a lso binds to an d increases synt hesis of cyclin E. Increased cyclinE a ct ivates CDK 2, which also phosphorylates Rb.

F516 INVITED REVIEW


4/16

lat es some of the sites on pRb, but only t o the point inwh ich p Rb is s t i l l h yp op h osp h orylat e d , a ct ive , a n dgrowth restrictive. Cyclin E phosphorylat es the remain-ing sites, so tha t pRb is now hyperphosphoryla ted pRb,i n a ct i v e, a n d g r ow t h p er m i ss iv e a n d r e le a s es E 2 F,which binds to the promoter regions of several targetgenes essential for further cell cycle progression, includ-i n g i m m ed ia t e e a r ly g en es , t h y m i di n e k i n a s e, a n d

dihydrofolat e reductase.

G1/ S Tr an si t i on

The transition from late G 1 in to th e S p h ase d e te r-mines the cells growth characteristics. For example, G 1a rrest results in a ntiproliferat ion or hypertrophy (90),G 1 exi t is asso ciate d with ap o pto sis (64), an d G 1/Stra n si t ion re sults in D N A syn th e sis an d p roliferat ion(112). Cycl in E leve ls in cre ase in late G 1, w h e r e i tasso ciate s w ith a n d a ctivat e s CD K 2, th e reb y p layin g apivotal role in G 1/S t ra nsit ion (77, 78). Cy clin E in duc-tion is less dependent on exogenous growth factors andis regulated by intrinsic factors of the cell cycle such as

E2F. Cyclin E-CD K 2 also p h osp h orylat e s p Rb (se eabove), and a positive cyclin E-synthesis feedback loopexists through the phosphorylation of pRb, leading torelease of E2F (Fig. 2). Recently, a novel cyclin E2 wascloned, wh ich associat es wit h CD K2 (32).

Cyclin A levels peak in late G1, are maximal duringthe S phase, and persist through G2. Cyclin A a ctivat esCDK2 (15), which is essential for DNA synthesis (29).Forced overexpression of cyclin A induces DNA syn th e-sis, a nd reducing cyclin A levels prevents cell prolifera-t ion (29, 82).

E n t r y I n t o M i t o si s

Alth ough mitosis is t he fi na l pha se of th e cell cycle,

i t w a s t h e fi r s t p ha s e t o b e ca r e f ul ly d el in ea t e d , a n df r om t h e se s t u d ie s h a s a r i s en m u ch of ou r p r es en tunderstanding of cell cycle proteins (76, 89). The firstcycl in id e n tifi e d was cycl in B , wh ich is re qu ire d fo r

mitosis (16). C yclin B levels fluctua te due t o synth esisan d d e g rad atio n , wh e re as i ts p artn e r, cd c2 ( fo rm e rlycalled CDK1), does not (Fig. 3). Cyclin B-cdc2 activity,similar t o CDK2, depends on its phosphorylat ion sta tus(17).

Monomeric cdc2 is unphosphorylated and inactive.cdc2 undergoes a conforma tional change on binding tocy cl in B , w h i ch r es u lt s i n t h e p hos ph or y l a t i on on

threonine 14 (Thr 14), tyrosine 15 (Tyr 15), and Thr 161amino acid residues on cdc2 (89). Phosphorylation ofThr 14 and Tyr 15 by t he kinases Wee1 a nd Myt 1 ar egrowt h inhibit ory, wh ich domina tes over Thr 161 phos-phoryla tion, which is growt h a ctivat ing. Consequently,the triple phosphorylated cdc2-cyclin B heterodimer isinactive. D ephosphorylat ion of Thr 14 an d Tyr 15 byth e d u al-sp ecifi c p h osp h ata se cdc25 is e sse n tial forentr y int o mitosis. Active cdc2-cyclin B phosphoryla tessubstrates (H1 histone, laminins, nucleolin) requiredfor chromosome condensa tion, nuclea r envelope break-d o wn , an d fo rm atio n o f th e m ito tic sp in d le (30). Oncom p le tion of m itosis , cycl in B is d e g rad e d via th eubiquitin-protea some pat hw a y, leading t o the dissocia-tion and inactivation of the complex (69), and cdc2 isfinally dephosphorylated by kinase-associated phospha-t a s e .

CDK I nhi bi tors: N egative Regulators of th e Cel l Cycle

Cyclin-CDK complexes are negatively regulated bycell cycle proteins called CD K inhibit ors (20, 87, 115).CD K inhibitors are relat ively sma ll molecules tha t bindto specifi c cyclin-CD K complexes a nd in so doing inh ibittheir a ctivity. There ar e tw o families of CD K inhibitors,wh ich a re based on the ta rget cyclin-CD K t hey inhibit,a nd on sha red homologous sequences. Individua l CD Ki n hi bi t or s a r e n a m e d a c cor d in g t o t h e ir m ol ecu la r

we ig h t . T h e I N K 4 fam ily o n ly in h ib i t cycl in D - CD Kcomplexes a nd sha re a n a nkyrin repea t. The C ip/Kipfamily a re more promiscuous a nd inhibit CD K 2, 4, a nd6, a nd sha re a CD K2-binding doma in (39) (Ta ble 1).

Fig. 3. Ph osphorylat ion of cyclin B-cdc2i nmitosis. Synthesis of cyclin B during inter-phase and binding to cdc2 induces phos-phorylation on 3 sites: phosphorylation ont h r e on in e 1 4 (T1 4) a n d t h r e on in e 1 61(T161) by Wee1 (Y15) an d M yt 1 (T15, Y15)is inhibitory, and phosphorylation on tyro-sine 14 (Y14) by CDK-activating kinase isact ivat ing. Dephosphorylat ion of inhibi-

tory sites by dua l-specific cdc25phospha-tase leads t o act ivat ion of cyclin B-cdc2. Apositive feedba ck loop (not sh own) leads t ocyclin B-cdc2-mediated phosphorylation ofcdc25 w i t h f u r t h er g e n er a t ion of a c t ivecyclin B-cdc2 complexes. Furthermore, in-hibit ion of Wee1/Myt 1 thr ough ph osphory -lat ion of kinases prevents deact ivat ion ofcyclin B-cdc2. Autophosphorylation of cy-clin B leads to ubiquit in-mediated degrada-t ion of cyclin B protein. Fina lly, cdc2 isd e p h os p h or y la t e d b y k in a s e -a s s oc ia t e dphosphatase (KAP).

F517INVITED REVIEW


5/16

T h e m o le cu lar m e ch an ism s wh e re b y CD K in h ib ito rsinhibit cyclin-CD K complexes a re still incompletelyunderstood.

C I P / K I P F a m i l y o f C D K I n h i b i t o r s

p21. Th e CD K in h ib itor p 21Cip1,WAF1,SD I1 (p21), a21-kDa protein, is th e founding m ember of t he C ip/Kip

fam ily. p 21 is tra n scription al ly re g ulate d in a p 53-dependent (18) a nd a p53-independent ma nner (19).How ever, p21 expression can a lso be modula ted t hroughposttranslational mechanisms (3). In addition to bind-ing CD Ks, p21 can a lso a ssociat e with P CNA, a proces-sivity factor of DNA polymerase , through the COOH-termina l doma in, which ma y be sufficient for G 1arre st(132). Asomewha t sur prising observat ion w a s tha t p21expression increases during proliferat ion a nd t ha t p21remains bound to CDK complexes in proliferating cells(152). p21 may therefore act as a scaffold to facilitateth e asse m b ly o f cycl in s an d CD K s re qu ire d fo r D N As y n t h es is . R ece nt s t u d ie s h a v e d e m on s t r a t e d t h a t asingle p21 molecule is sufficient for CD K inhibition

(38). B ecause p21-knockout mice do not ha ve d evelop-m e n tal d e fi cie n cie s o r tu m o rs, i t h as b e e n su g g e ste dthat the role of p21 is check-point control of G 1/S -ph a setran si t io n rath e r th an with d rawal f ro m th e ce l l cyclean d d i ffere n tiat ion (7). M ore re ce n tly, s tu d ies h aveshown tha t p21 inhibits G 2/M pha se of th e cell cyclea n d t h u s m a y a l s o r e gu la t e m i t os is , w h i ch f ur t h e rdistinguishes it from other members of t he C ip/Kipfam ily of CDK inhibitors.

p27. The 27-kDa protein p27Kip1 (p27) is widelyexpressed in nonproliferat ing (quiescent) rena l (11,107) and nonrenal cells (75). In contrast to p21, p27expression is postranscriptionally regulated by changesi n p r ot e in t r a n s l a t i on a n d d eg r a d a t i on t h r ou g h t h e

u b iqu it in p rote olytic p ath w ay (73, 130) an d is alsopostt ra nslat iona lly modified by phosphoryla tion (111).Thus, in contr a st to p21, p27 is not r egula ted by p53.p 27 r eg u la t e s g r ow t h a r r e s t i n r es pon s e t o TG F -,ra p am ycin , cAM P, an d con ta ct in h ib i t ion (75). Th einteraction of p27 with cyclin-CDK complexes is morecomplicated than previously thought because p27 canbe both a n inhibitor and a substra te for cyclin E-CD K2.Cyclin E- CD K 2 m ay b e in h ib i te d in G 0 by p27. How-ever, after growth factor-mediated activation of cyclinD-CD K4, p27 preferentia lly binds to these complexesand redistribution of p27 to cyclin D-CDK4 results inactivation of cyclin E-CDK2 with subsequent phosphor-ylation of p27, which enhances p27 degradation (111).

Th e fi n a l r e su lt m a y b e a ct i v a t i on of m or e cy cl inE-CD K2, which facilita tes G 1progression. Low levels ofp 27 h a ve b ee n sh own in a varie ty o f tu m o rs, an d p 27levels a re critical in rena l cell differentia tion, apoptosis,prolifera tion, a nd hypert rophy (see below ) (102).

p57. The CDK inhibitor p57Kip2 (p57) is expressed inm a n y d i f f e r e n t i a t e d c e l l s a n d i n m a n y a d u l t t i s s u e s(153). p57 binds CDK2, 3, and 4, and overexpressionleads to G 1ar rest (154). Furt her st udies suggest a closecooperation of p27 and p57 to control proliferation anddifferentiation in multiple tissues during development(154). However, the precise function of p57 in cell cycle

regulation, and in particular in the kidney, remains tobe elucidated.

I N K 4 F a m i l y o f CD K I n h i b i t or s

The INK4 family (p15, p16, p18, p19, p20) consist off ou r or m or e a n k y r in r e pe a t s a n d i n hi bi t C D K 4 a n dCD K6 complexes in G 1(116). In contr a st to t he C ip/Kip

fam ily, I N K 4 m e m be rs ar e tu m o r su pp ressor g en e s(12), where p15 and p16 are deleted and mutated in avariety of tumors, and the selected disruption of p19 inmice predisposes to tu mor development (150). TG F--mediated induction of p15 blocks activation of cyclinD-CDK4 complexes by displacement of p27 from thesecom p le xe s to d own st re am b in d in g an d in h ib i t ion ofcyclin E-CDK 2 het erodimers (95). The expression ofI N K 4 C D K i n hi bi t or s m a y b e r e q ui r ed t o m a i n t a i nquiescent cells in G 0(36).

CELL CYCLE REGULATION OF RENAL

CELL HYPERTROPHY

What I s H ypert rophy?

An orga n can increa se in size a t t he cellular level dueto a n increas e in cell number (increas ed prolifera tion ordecreased apoptosis) or an increase in individual cellsize (hypertrophy). C ell hypert rophy is defi ned a s celle n larg e m e n t d u e to an in cre ase in p ro te in an d RN Acontent without DNA replication (21, 22) and can bedue to cell cycle-dependent or -independent mecha -nisms (60, 90). Norma l entr y into G 1 phase of the cellcycle is asso ciate d with in cre ase d p rote in a n d RN Asynt hesis, which occurs in a nt icipat ionof DNA synt he-sis in the S phase. The present par ad igm suggests t ha th yp ertro ph y is a n act ive p rocess r e qu irin g e n try in tothe cell cycle, w ithout progression through t he S phase

(134, 136) (F ig . 4). He n ce h yp ertro ph y can also b ed e fi n e d as G 0/G 1-phase arrest (91), which explains whyhypertrophy and proliferat ion a re exclusive at a singlecell level. Thus certa in growt h fa ctors, hormones, extr a -cellula r m a trix, mechanical forces, a nd h yperglycemiath at in d u ce h yp e rtro p h y faci l i tate e n try in to th e ce l lcycle. In contr ast , t ubular cell hypertrophy can be cellcycle in d ep en d e n t d u e to th e in h ib i t ion of p rote indegra da tion (25).

Glomeru lar Cel l H ypert rophy

G lo m eru lar cel l h yp e rtro ph y occurs d u rin g m a n yfo rm s o f ch ro n ic re n al d ise ase an d m ay an te ce d e th edevelopment of glomerulosclerosis (27, 42, 151). G lo-

merular diseases a ssociat ed with glomerular hypertro-phy include dia betic nephropa th y (155), relapsin g mini-m a l c ha n g e n e ph r op a t h y (1 29 ), f oca l s eg m en t a lglomerular sclerosis (24, 68), and a reduction of neph-ron ma ss due to disease, surgery, or congenital a plasia(120). The consequence of glomerula r hypert rophy de-p en d s on th e u n d erlyin g d ise ase a n d is con sid ere dco m p e n sato ry af te r a d e cre ase in re n al m ass su ch asu n in ep h recto m y an d is n o t th e re fore a ssociat e d w ithglomerulosclerosis. In contrast, glomerular hypertro-p h y in d iab e tic n e p h ro p ath y an te ce d e s an d p ro b ab lyunderlies the development of glomerulosclerosis (93).

F518 INVITED REVIEW


6/16

Di abeti c nephr opathy. A c h a r a c t er i st i c fi n d i n g i nearly diabetic nephropathy is glomerular hypertrophy,which predominantly involves the mesangial cell butcan also involve the glomerular endothelial cell (51,144). This contrasts to most forms of mesangial cellinjury that are associated with proliferation (47). Glo-meruli from diabetic rats and cultured mesangial cellsgrown in high-glucose concentra tions a re a ssocia tedw i t h a n i n cr e a s e i n e xp r es s ion of i m m ed ia t e e a r l y-response genes (52, 108). That immediate early genes

are e xp re sse d in th e e arly G 1 phase of the cell cycle(137) su g g ests th a t h ig h g lu cose in d u ce s qu iesce n tglomerula r cells to actively ent er t he cell cycle.

Although short-term exposure of mesangial cells tohigh glucose levels induces a limited proliferat ion invitro (13) and in vivo (149), prolonged exposure to highglucose ha s t w o effects on mesangia l cell growth. First,glucose inhibits mesangial cell proliferation (142) and,second, glucose induces hypertrophy (110). Cell cycleanalysis reveals glucose arrests cells in the G 1 phase,an e f fe ct m e d iate d in p art b y th e au to crin e syn th e sisa n d a c t i va t i on of TG F - (142). Indeed, glomerularTGF- expression increa ses in vivo during th e phase ofhypert rophy (109, 148), a nd a pplicat ion of neutr a lizing

anti-TGF- an t ib od ies a t te n u at e s h yp ertro ph y in d ia-bet ic m ice (110).

A body of litera tu re is emerging on the role of specifi ccell cycle proteins in diabetic glomerular hypertrophy(Ta bles 2 a nd 3). F irst , glucose-induced mesa ngia l cellhypertrophy in vitro is not associated with an increasein the protein expression for cyclin E or CDK2 (56). Weha ve also been una ble to show a significan t increase inglomerular expression for G 1- and S-phase cyclins inexperimental diabetic nephropa thy (56), a nd glomeru-lar expression of the retinoblastoma protein gene prod-u ct r e m a i ns i n a n u n d er p hos ph or y l a t e d (g r ow t h -

restrictive) sta te (104), consistent wit h G 1/S a rrest . Incontrast, Huang and Preisig (44) showed that cyclin Dkinase is activated during tubular epithelial hypertro-phy in experimenta l dia betes. Ta ken together, t hesestudies suggest that hyperglycemia does not typicallyincrease the mesangial cell expression of cyclins andCDKs required for DNAsynthesis.

Fig. 4. Schema of cell cycle-induced renal cell

hypertrophy. Cell cycle engagement after renalcell injury is associated with increased proteina n d R N A s y n t h e sis . P r ogr e s sion t h r ou gh c el lcycle leads to DNA synthesis and cell prolifera-t ion. Hypertrophic factors such as ANG II , t ran s-f or m in g g r ow t h f a c t or - (TG F-), and glucoseincrease levels of CDK inhibitors , which causescell cycle arrest (G 1), preventing DNA synthesis .This is associated with an increase in protein andRNAcontent without an increase in DNA synthe-sis, an d an increase in cell size (hypert rophy).

Ta ble 2. Expr ession an d activi ty of cell cycle pr otein sin r enal cel l s in vi tr o

CellType

Cyclin-CDKComplex

C D KInhibitor

MitogensP D G F , b F G F , ET-1 M C >D1 (43, 46, 100) >p21

>E (100, 107) A (109) &p57>CDK2 activity (100,

109)>CDK4 activity (122)

AntimitogensTGF- MC p21

p27 (109)


7/16

Th e se stu d ie s h a ve lead to t h e h yp oth e sis th a t g lu -cose-induced glomerular cell hypertrophy is regulatedby CDK inhibitors at the level of the cell cycle (Fig. 4).Incubation of mouse mesangial cells in high-glucosemedium stimulates p27 protein expression, indepen-dent of mRNA a bunda nce (141). H igh-glucose-st imu-lat ed expression of p27 involves the activa tion of pro-

t e in k in a s e C (P K C ) a n d i s p a r t l y d ep en d en t on t h einduction of TGF-. The increase in p27 preferentiallyassociates with CDK2 (141), which differs from ANGI I -m e d iat e d h yp ertro ph y, wh e re p 27 asso ciate s withcyclin D-CD K4 (143). Low ering p27 levels w ith specifi ca ntisense oligonucleotides, but not contr ol missense,inhibited high-glucose-stimula ted hypertrophy a nd fa-cilita ted cell cycle progression (141). A similar role forp27 has been shown in vivo. The glomerular levels forp 27 are e n h an ce d in d b / d b m ice (m o d e l o f typ e I Id iab e tes m e ll itu s), a n d th e in crease wa s re stricte d t omesangia l cells (140). Furt hermore, mesangia l cellscultured from d b / d b mice grown in medium containingnormal glucose concentr a tions display ed n o difference

in p27 expression compared with mesangial cells ob-ta ined from nondiabeticd b/ a nima ls (140). H owever,ra ising glucose concentr at ions to 275450 mg/dl in-duced cell cycle arrest and increased the expression ofp27 (140). These st udies indica te t ha t high glucose wa sthe primary stimulus for p27 induction.

To furt her cha ra cterize t he role of p27 in high -glucose-in d u ce d h yp ertro ph y, we stu d ied cultu re d m e san g ialcells derived from p27-knockout (p27/) m i c e a n dcont rol p27 w ild-ty pe (p27/) animals. Our prelimi-nary studies showed that high glucose concentrations(450 mg/dl) stimu la ted hypert rophy in p27/ m e san -

gial cells compared with control p27/ cells grown innorm a l glucose concent ra t ions (100 mg/dl) (G .Wolf an dS . J . S h a n k lan d , u n p ub lish ed ob servat ion s). I n con -tra st , in p 27/ mesangial cells, high glucose concen-trations caused cell cycle progression with DNAsynthe-sis, but not cell hypertr ophy. However, wh en p27 levelsw ere reconstit uted in p27/ m e san g ial cel ls with a ninducible expression vector, high glucose concentra -

tions arrested cells at G 1 and induced cell hypertrophyin a s im ilar m an n e r to p 27/ cells. Ta ken together,th ese studies sh ow a critica l role for p27 in the develop-ment of diabetic glomerular hypertrophy.

I n a d d i t i on t o r e gu la t i n g p 27, h i gh g lu cos e a l s oincreases p21 expression in cultured mesangial cells(56). Moreover, there is an increase in glomerular p21immunostaining in experimental diabetes (streptozoto-cin model) during the phase of early glomerular hyper-tr ophy (56). Recent st udies ha ve shown t ha t st reptozoto-cin -in d u ce d d iab e tes is asso ciate d with g lom e ru larhypertrophy in p21/ m i c e b u t t h a t t h e s a m e i n -cre ase in h yp erg lyce m ia wa s n o t asso ciate d with g lo-merular hypertrophy in diabetic p21/ mice (4).

We p rop ose th e fol lowin g p ath w ay of cel l cycle -dependent regulation of glomerular cell hypertrophy indiabetes (Fig. 4). High ambient glucose in vivo or invitro st im u lat e s G 1 entr y. After one or tw o completionsthrough the cell cycle leading to a limited proliferation,the concomitant induction of TGF-, most likely medi-ate d b y PK C activat io n , s t im u late s an in cre ase in th eCD K inhibitors p21 and p27. CD K inhibitors preferen-tia lly bind to a nd ina ctivat e cyclin E-CD K2 complexes,re su lt in g in u n d e rp h o sp h o rylat io n o f p Rb . T h e fi n alresult is G 1-phase arrest with increased protein contenta nd cellular enlar gement, w ithout DNA synthesis (hy-pertrophy).

Redu ced n ephr on m ass.Areduction in nephron num-ber induces compensatory glomerular hypertrophy inthe remaining nephrons (120). Uninephrectomy doesnot infl uence t he protein expression of cyclins D 1 a ndD 2 , n or of C D K 2 a n d 4, w h en t ot a l r en a l l y s a t e s a r es t u d i e d a t d a y 7 (85). However, wh en specific rena lcom p a r t m en t s w e r e e xa m i n ed , s t u d ie s s h ow e d t h a tcycl in E- CD K 2, b u t n o t cycl in D 1- CD K 4, was act iveduring compensatory hypertrophy induced by surgicaluninephrectomy (61). However, severe renal ablationsuch a s a 5/6 nephrectomy is a lso accompanied by a nearly glomerular cell proliferative response, which isa ssocia ted w ith a n increase in cyclin E expression a ndthe phosphorylation of pRb (105).

A picture is t hus emerging from cell cultur e experi-ments demonstrating how cell cycle proteins regulatehypertrophy. H owever, studies a re necessa ry to char a c-terize the role of these heterogeneous components inrenal hypertrophy in vivo.

Tubular Epithel ial Cel l Hypertrophy

The capability of the a dult kidney t o grow to replacelost tiss ue w a s fi rst recognized by Arist otle (384322B C ), w h o s h ow e d t h a t a n i ma l s b or n w i t h a s in g lek id n ey h a v e a l a r g er or g a n com p a r ed w i t h a n i m a l swit h tw o kidneys (145). Furt her studies ha ve shown a n

Ta ble 3. Cell cycle regul atory protein s inexperimental renal disease

Experimental ModelCell

Type C y clin s C D KC D K

Inhibitor

Proliferation

GlomerulusTh y1 MC >D1 (146) >CD K4 (146) >p15 (146)

>>>A (108) >>>CD K2 (108) >p21 (108)A >C D K 2An t ig lom e r u la r V EC >A >C D K 2P H N VE C >A (106) >CD K2 (106) >>>p21 (106)

>>>p27 (106)&p15, &p57

Tubulointerst itiumIschemia >D1 (147) >p21 (63)U r e t e r a l

obstruction >CD K2 (80) >p21 (66, 67)Cisplat inum >p21 (62)

Hy p e r t r o p h y

GlomerulusSTZ-diabetes &E, A (56) &CD K2 (56) >>>p21 (56)

d b / d b r a t >>>p27 (140)Uninephrectomy &p57

>>>p27

GEN, glomerular endothelial cell ; VEC, podocyte; PHN, passiveHeyma nn nephrit is; STZ, streptozotocin;>, mild increase;>>>, markedincrease; &, no charge;


8/16

increase in renal size, predominantly due to proximaltu b u lar e pith e lial ce ll h yp ertro ph y, in th e re m ain in gk id n ey a f t e r a d ecr e a s e i n n ep hr on n u m be r d u e t odisease or surgical resection (93). The initial tubularepithelial cell hypertrophy is considered compensa-tory a nd a da ptive hypert rophy (134, 135, 145). H ow-ever over t ime, tubu la r cell hypertr ophy becomes ma l-a da ptive(42, 50)a nd is a ssociat ed with the subsequentin fi l tra t ion of m acrop h ag e s/m on ocytes, T cel ls , an dfi b rob lasts in to th e tu b u loin te rst i t ial sp ace , wh ich re -sults in tubular atrophy and tubulointerstitial fibrosis,wh ich are th e u l t im ate co m m o n e n d p o in ts o f m an yrenal diseases with diverse etiologies. The biochemicalasp e cts , g ro wth factors , a n d p ote n tial s ig n al tra n sd u c-tion pathw a ys of rena l hypertr ophy ha ve been reviewedelsewhere (21, 22, 93).

AN G I I - induced tubul ar cel l hypert rophy. To iden t ifyp ote n tial m olecular m e ch an ism s u n d erlyin g tu b u larepithelial cell hypertrophy, we induced proximal tubu-la r cell hypert rophy in vit ro w ith ANG II (139; Ta ble 2).I n th is m od e l, AN G I I s t im u late d th e e xp ression of

immediate early genes, which is consistent with a cellG 0/G 1 phenotype. However, ANG II-induced G 1 arre stwas asso ciate d with in cre ase d p ro te in syn th e sis an dcellular enlargement but not progression through thecell cycle and DNA synthesis, fin dings consistent wit hhy pert rophy (139, 143).

ANG II t reat ment of proximal t ubular cells increasedthe protein levels for the CDK inhibitor p27, withoutaltering the mRNA abundance (143). More recently, weshowed tha t ANG II -induced p27 expression wa s mediat edby s uperoxide a nions genera ted/produced by membra ne-bound NAD(P)H oxida se (35). Moreover, p27 preferent ia llya ssociat ed w ith cyclin D-CD K4 complexes, which inhibitedthe kinase activity (143). Lowering p27 levels in proximal

tu bula r cells with p27 a nt isense oligonucleotides a bolishedANG II-mediated G 1-phase arrest and hypertrophy andfacilitated entry into the S phase, thereby converting ahypert rophic phenoty pe to a prolifera tive one (143). Recentpreliminary dat a suggest tha t ANG II also induces p21expression via a J AK2-STAT1 pat hw a y t o mediat e proxi-ma l tubula r cell hypert rophy (124). Interest ingly, Tera da etal. (123) showed that the forced overexpression of p21a nd p27, but not p16, induces hypertr ophy in t ubula r cells.

T G F - -induced tubular cell hypertrophy. The role ofthe cytokine TG F- in inducing hypertrophy is a lso ofparticular interest to nephrologists (9). For example,we showed that ANG II-induced proximal tubular cellhypertrophy depends on the concomitant induction of

endogenous TG F- (138). In t he model of TG F- convert-ing mitogen-induced tubular epithelial cell prolifera-t ion to h yp e rtro ph y, F ra n ch e t a l . (26) sh owe d th a tTGF- prevents entr y into the S-phase by ma inta iningp Rb in an u n d e rp h o sp h o rylate d state . T G F - h a d n oe ffect on cyclin D -CD K 4 activi ty, b u t ra th e r TG F -prevented cyclin E kina se act ivity (26).

CELL CYCLE CONTROL OF RENAL CELL PROLIFERATION

In contrast to other organs such as the gastrointesti-na l tra ct or liver, there is very little cell turnover in the

normal a dult kidney (81). La beling murine glomerularcells with [3H]thymidine, a marker of DNA synthesis,showed th a t only 12%of cells of glomerular endothe-l ia l a n d , t o a m u ch l es s er e xt e n t , m e s a n g ia l ce ll s,proliferate, whereas podocytes do not (81). The calcu-lated mean lifespan of glomerular cells is 5100 day s(81). Ab ou t on e tu b u lar e pith e lial cel l p er h u m ann e ph ron slou g h s in to t h e u rin e d a i ly u n d er n orm a lphysiological conditions (92), w hich explains w hy t hereis very little prolifera tion in the norma l huma n kidney.

In contrast to normal physiological conditions, glo-m e ru lar an d tu b u lar e p ith e lial ce l l p ro l i fe rat io n an dcellularity increase in pathological situations such asrenal injury. Addis (18811949) and the pathologistOlivier (2) su g g este d th a t p rol ifera t ion of in trin sicglomerular cells contributes to the overall cellularityunder cert a in pa th ological conditions (2). In deed, prolif-erat ion of intrinsic glomerular cells such a s mesa ngialce l ls is th e ch aracte rist ic re sp o n se to m an y fo rm s o fimmune (IgA nephropathy, lupus, membranoprolifera-tive glomerulonephritis)-, meta bolic (diabetes)-, a nd

hemodynamic (remnant kidney)-mediated glomerularinjury (for review, see Ref. 47). Moreover, glomerularcell proliferat ion is a lso closely linked t o extra cellularm atrix p ro te in accu m u latio n an d th e su b se qu e n t d e -cline in renal function. The regulation of glomerularce l l p ro l i fe rat io n b y g ro wth facto rs an d in trace l lu larsig n al in g p ath ways h as b e e n re vie we d e lse wh e re (1,119), and blocking mesangial cell proliferation at theselevels decreases glomerular matrix protein accumula-tion.

M esangial Cel l Prol i ferat ion: Cycl i ns and CD Ks

Mesangial cell proliferation induced by a variety of

known mitogens in vitro is associated with changes inspecifi c cell cycle proteins (Ta ble 2). For example,platelet-derived growth factor, endothelin-1, and basicfi b rob last g ro wth factor (bF G F ) are asso ciate d w ith a nincrease in D-type cyclins (43, 46, 100) in early G 1,cyclin E in la te G 1(100, 105), a nd cyclin Ain t he S pha se(107). Lowerin g cyclin D1 levels w ith a nt isense reducesDNA synthesis. Mitogens also increase the activity ofCD K4 (100) a nd C DK 2 in mesang ia l cells in vitro (107),a n d a n t i m it og en s s uch a s TG F -1 (100, 107) a n dsecreted protein acidic and rich in cysteine (H. Sage,personal communication) reduce mesangial cell prolif-erat ion by decreasing CD K4 and C DK2 a ctivity, therebypreventing phosphoryla tion of pRb, w hich cau ses G 1/S

arrest. Finally, Riley et al . (97) showed that the phos-p h orylat io n sta tu s of p RB d e term in es t h e m e san g ialcells prolifera tive r esponse t o mitogens.

The expression of positive cell cycle proteins ha s a lsobeen shown in experimental glomerular diseases in th ep a s t f ew y ea r s (Ta b l e 3 ). C y cl in s D , E , a n d A a r eincreased in glomerular disea ses cha ra cterized by m es-angial cell proliferation such as experimental mesan-gial proliferat ive glomerulonephritis (Thy1 nephritis)(106, 121, 146). CDK2 protein levels and activity arealso increased in Thy1 (106). Furthermore, inhibitingCD K 2 activi ty with sp e cifi c p u rin e an alo g s, with o u t

F521INVITED REVIEW


9/16

a ltering CD K2 protein levels, ma rkedly decreases mes-angial cell proliferation (88). Moreover, inhibiting CDK2a c t i vi t y a l s o d e cr ea s e s t h e a c cu m u la t i on of m a t r i xp rote in s a n d im proves re n al fu n ction com p are d withcontrol subjects (88). More recently, we have also shownthat inhibiting CDK2 activity reduces glomerular cellp rol iferat ion in an o th e r m o de l of im m u n e-m e d iat e dglomerular injury. These studies provide potential tar-

gets for future t herapeutic interventions in glomerulardiseases a ssociat ed wit h mesa ngial cell prolifera tion.

M esangial Cel l Pr ol i ferat ion: CDK I nhi bi tors

C D K i n hi bi t or s a r e cr i t ica l d et e r m in a n t s f or t h eon se t an d m ag n itu d e of re n al ce ll p rol i fe rat io n . A l-though t here a re t wo fa milies of C DK inhibitors (115),most renal studies reported have focused on the Cip/Kip family (p21, p27, p57). The CDK inhibitor p21 isnormally only present in low abundance in quiescentglomerular cells (106). However, p21 levels increa seduring mitogen-induced mesangia l cell prolifera tion.Studies in nonrenal cell have suggested p21 provides a

f ram e wo rk fo r th e asse m b ly o f cycl in s, CD K s, an dP CNA required for DNA synt hesis. We have shown t ha tthe a ntimit ogen TG F-1 increases p21 levels in mesa n-gial cells in vitr o, and Terada et a l . (125) showed t ha tforced overexpression of p16 a nd p21 reduces m itogen-induced m esangia l cell prolifera tion in vit ro. Int erest-in g ly, th e re is a d e n ovo e xpre ssion of p 21 in Th y1glomerulonephrit is tha t coincides with increa sed TG F-expression and the resolution of mesangial cell prolifera-tion in th is model (106). From a t hera peutic sta ndpoint,it should be noted t ha t glucocorticoids increase p21levels directly in mesangia l cells (79). F urth er st udiesa re required t o determine the defi nitive role for p21 inmesa ngia l cell prolifera tion in vivo.

In contr a st to p21, p27 is const ituit ively expressed innormal quiescent mesangial cells in vitro (107). Theonset of mesangia l cell proliferat ion in vitro induced bysp ecifi c m ito g en ic g rowt h factors is a ssociat e d w ith adecrease in p27 protein levels (109). F urt hermore, p27dissocia tes from cyclin A-CD K2 complexes on m itogenstimulation, which coincides with increased A-CDK2a ctivity. The onset a nd ma gnitude of mitogen-inducedm e san g ial ce l l p ro l i fe rat io n in vi tro are fu rth e r au g -m e n te d wh e n p 27 le ve ls are lo we re d with an tise n se(107). However, lowering the levels of p27 by itself, inth e ab se n ce o f m itog en ic sig n als , is n ot su ff icie n t toinduce mesangial cell proliferation.

p27 is also constituitively expressed in normal glo-

merular cells (106), and mesangial cell proliferation invivo also correlat es closely w ith p27 levels. The peak ofmesangia l cell proliferat ion in experimenta l mesangia lproliferative glomerulonephritis coincides with almostund etect a ble p27 levels (106). To deter min e th e role ofp 27 in g lo m e ru lar ce l l p ro l i fe rat io n in in flam m ato ryrena l disease, immune-mediat ed glomerulonephritiswas induced in p27/ and p27/ mice. The lack ofp 27 re sulte d in a m ark e d in crease in th e o n set an dma gnitude of glomerular cell prolifera tion in nephriticp27/ mice compared w ith cont rol an ima ls (80). Thiswas asso ciate d with an in cre ase in g lo m e ru lar m atrix

p rote in s in n e ph ri t ic p 27/ m i ce com pa r e d w i t hcont rol mice. Tubula r cell prolifera tion w a s a lso mar k-edly increased after non-immune-mediated injury inp27/ m ice com p are d with con tro l an im a ls (80).Ta ken together, these results show t ha t t he level of theCD K inhibitor p27 is a critical determinan t in the rena lresponse to immune and nonimmune forms of injury.Te rad a e t a l . (122) showe d th a t lovasta t in in h ibi te d

mesangia l cell proliferat ion by increasing the levels ofp27 in vitro and in vivo (personal communication). Weh ave r e ce n tly sh o wn th a t p reven tin g p 27 d eg rad a tionb y b lo ck in g th e u b iqu it in p ath way in h ib i ts m ito g e n -induced mesan gia l cell prolifera tion in vitr o.

L ack of Podocyte Pr oliferati on: Role of Cell Cycle Proteins

In contrast to mesangial and glomerular endothelialcells, adult visceral glomerular epithelial cells (VEC;also cal le d p od ocytes) d o n ot re ad ily p rol ifera te inresponse to the same forms of injury (53). However,during glomerulogenesis VEC prolifera te dur ing t he

S-shaped phase, which ceases during the comma phase.The cessat ion of VEC prolifera tion coincides w ith thede novo expression of the CDK inhibitors p27 (11) andp57 in VEC (71). Nagata et al. (71) showed that p21 isa lso tr a nsiently expressed by VEC during glomerulogen-e sis . Th e se stu d ie s sh ow th a t th e t ran si t io n from ap rol if er a t i n g i m m a t u r e V E C p he not y p e t o a m a t u r enonproliferating and quiescent phenotype during glo-merulogenesis coincides wit h, a nd ma y be due to, the denovo expression of specifi c C DK inhibitors (Fig. 5).Interestingly, p57/ m ice are b o rn with fu se d fo o tp rocesses (153), su g g estin g th a t th is CD K in h ib itormay be more critical for VEC development than othermembers of this family of CDK inhibitors, as p21/

an d p 27/ mice have a normal glomerular develop-m e n t.

I n con tra st to m e san g ial cel ls, m a tu re V EC u n d erg olitt le, if a ny, prolifera tion in vivo in response to immun e(m e m b ran ou s n e ph rop ath y, m in im a l ch an g e), m e ta-bolic (dia betes), hemodyn a mic (reduced nephron ma ss)a nd oth er (foca l segment a l glomerulosclerosis) forms ofinjury (53). Kriz (53), Kriz et a l . (54), Rennke (94),P a v en s t a d t (86), a n d ot h e r s h a v e p r op os ed t h a t t h einability of VEC t o proliferat e an d replace VEC lost bydeta chment a fter injury results in a denuded glomeru-lar basement membra ne, which underlies t he develop-ment of glomerulosclerosis in these diseases. However,in certain forms of VEC injury such as collapsing glo-

merulopat hy, VEC proliferat ion is prominent a nd ma ybe associat ed with a ra pid decline in renal function thatchar a cterizes t his form of foca l glomerulosclerosis (14).

Wh y d o V E C n ot p r ol if er a t e i n m os t g lom e ru la rdiseases, yet do prolifera te in others? In experimenta lmembranous nephropathy, complement-mediated VECinjury is associated with a slight increase in expressionfor cyclin A and its partner, CDK2 (103). Thus VEChave the nuclear machinery capable of undergoingD N A syn th e sis . Ho we ve r, th e an swe r to th e re lat ivelack of VEC proliferation probably lies with the CDKin h ib itors . Co m plem e n t-m e d iat e d in ju ry to VEC wa s

F522 INVITED REVIEW


10/16

a ssociat ed with a ma rked increase in expression for theCD K in h ib itors p 21 a n d p 27 in VEC in e xpe rim e n talmembranous nephropathy (103). Moreover, both theseinhibitors were bound t o a nd inhibited cyclin A-CD K2activity (103).

Kriz et al. (55) and Floege et al. (23) showed that the

mitogen bFGF increases DNAsynthesis in VEC in ratsw ith membra nous nephropat hy. To determine wh etherth is w as d u e to ch an g e s in t h e le ve ls o f sp ecifi c CD Kin h ibitors , we a d m in iste red b F G F t o rats with p assiveHe ym an n n e ph ri t is . Ou r re su lts sh owe d t h at , in d e ed ,t h e i n c r e a s e i n V E C D N A s y n t h e s i s w a s a s s o c i a t e dw ith a decrease in levels of p21, but not p27 (103). Tofurther determine w hether levels of the C DK inhibitorp21 determine the capa city of mat ure VEC t o reenga geth e cel l cycle an d p roli fe rate in vivo, e xp erim en ta lglomerulonephritis w a s induced in p21/ a nd p21/m i ce w i t h a n a n t i gl om e r ul a r a n t i bod y. N ep h r it i c

p21/ h ad a m ar k ed in cre ase in V EC D N A syn th e sisco m p are d with co n tro l m ice , an d th is was asso ciate dwit h a n increase in the number of multilayered cells inB o wm an s sp ace (49). T h is was also asso ciate d within cre ase d g lom e ru lar tu f t col lap se , a n d a d e cl in e inr en a l f un ct i on , s om ew h a t a n a l og ou s t o t h a t s ee n i n

collapsing glomerulonephritis. Interestingly, VEC pro-liferation was associated with the loss of VEC-specificma rkers (such a s WT-1, GL EP P -1), suggesting tha t ifVEC dedifferentia ted a fter injury, they can r eenter t hecell cycle and proliferate (49). Thus it is tempting tosp ecu late th a t th e m a rk ed V EC p roli fe rat io n in n e -phritic p21/ mice ocurs because p21 inhibits bothG 1/S a nd M pha ses of the cell cycle.

As sta ted earlier, p57 is constituitively expressed inquiescent ma ture huma n VEC (71), an d we ha ve shownth at p 57 is also e xp re sse d in ro d e n t V EC in cu ltu re .Interestingly, p57-knockout mice are born with fused

Fig. 5. Cell cycle proteins an d lack of podocyte prolifera-tion. During glomerulogenesis, the switch from an imma -ture proliferating podocyte [also called visceral epithe-l ia l c el l (V EC)] p h e n ot y p e t o a m a t u r e , t e r m in a l lydifferentiated, a nd quiescent phenotype is a ssociatedw it h d e n ov o e xp r es s ion of s p e cifi c CD K in h ibi t or s .Levels of CDK inhibitors determine proliferative capac-ity of mature VEC after injury. Thus increased levels ofCDK inhibitors prevent VEC proliferat ion after injury,whereas a decrease in CDK inhibitor levels is associatedwith VEC proliferat ion.

F523INVITED REVIEW


11/16

foot processes (153). We have recently shown that p57le ve ls d e cre ase in V EC th at h ave re e n g ag e d th e ce l lcycle af te r an t ib od y-in d u ce d in ju ry in e xp erim en ta lglomerulonephritis. Further studies are ongoing to testt h e h y pot h es is t h a t p 57 i s r eq u ir ed t o m a i nt a i n aterm ina lly differentia ted an d quiescent VEC phenotype.

I n s u m m a r y, t h e se s t u d ie s s h o w t h a t s pe ci fi c ce llcycle proteins have two important roles in VEC biology

(Fig. 5). First, the switch to a quiescent VEC pheno-type during glomerulogenesis coincides with de novoexpression of specific CDK inhibitors (p21, p27, p57),and maintaining a quiescent and terminally differenti-a t e d VE C p hen ot y pe m a y b e d u e t o p 27 a n d p57.S e con d , th e in ab ili ty of m a tu re te rm in ally d i ffere n ti-a t e d VE C t o p r ol if er a t e a f t er i nju r y i s d u e t o a nu p re g u lat io n o f CD K in h ib ito rs p 21 an d p 27 an d th em a in te n an ce o f p 57 e xpre ssion , an d lowe rin g th e selevels is a ssociat ed wit h VEC prolifera tion.

CELL CYCLE AND TUBULOINTERSTITIAL

PROLIFERATION

In contrast to tubular epithelial cell hypertrophy inchronic rena l disease, t ubular epithelial cell prolifera -t ion is th e m ajor g rowt h r e spon se af te r acu te t u b u larinjury such a s ischemia or obstruction (128). Aftera cute tubular ischemia , surviving tubular cells migrat ea long t he basement m embran e, prolifera te, a nd differ-e n tiate to h ig h ly sp e cial iz e d ce l ls o f th e ap p ro p riatenephron segment, a process th at can be a ccelera ted bythe administration of exogenous growth factors (98).These studies show t ha t cell prolifera tion is essent ia l inthe restoration and repair of renal function after acuteinjury (34, 41).

Cycl i ns and CD Ks in Tubuloint ersti t i a l

Cell Proliferation

C y cl in s D a n d A, a n d C D K 2 a n d 4, i ncr ea s e i np roliferat in g tu b u lar e pith e lial cel ls af te r isch e m icinjur y (147). The role of CD K inh ibit ors ha s been show nin tu b u loin te rst i t ial cel l in ju ry. M eg ye si e t a l . (63)showed t ha t cisplatinum-induced injury ca used a p53-in d ep en d e n t in cre ase in p 21 e xp ression in tu b u larepithelial cells and that p21 increased in acute ische-mic tubular injury. The same group showed a markedincrease in tubular cell proliferation in p21/ miceafter cisplatinum-induced injury compared with con-trol p21/ mice (62). Morissey et al. (66, 67) showedtha t p21 increased aft er ureteral obstruction. However,

wh e n u re te ral o b stru ctio n was p e rfo rm e d in p 21/mice, a somewha t surprising fi nding wa s tha t prolifera-t ion wa s m a rk ed ly in crease d in th e m yo fi b ro b last cel lp op ul a t i on , r a t h e r t h a n t u b u la r ce ll s i n ob s t r uct e dp21/ mice compared with obstructed p21/ mice(45). Finally, tubular cell DNAsynthesis is significantlyincreased in hyperglycemic p21/ mice compar edwith h yp erg lyce m ia p 21/ mice (4). These result ssuggest th a t the r ole of p21 may depend on t he type oftubulointerst itial injury a nd on the cell type injured.

Alth o ug h tu b u loin te rst i t ial cel l p rol i fe rat io n an dapoptosis characterize unilateral ureteral obstruction,

the contralateral kidney undergoes compensatory hy-pertr ophy. Morissey et al. (66) reported tha t p21 mRNAle ve ls d o n o t in cre ase in th e co n tralate ral k id n e y atd ays 1 8postobstr uction. Tubula r epithelial cell prolif-e rat io n o f th e ob stru cte d k idn e y is con sid era b ly in -creased in p27/ mice compared with p27/ mice(80). We ha ve extended these st udies to t he contr a lat -e ral k id n e y, a n d a l th ou g h w e d e te cte d a h ig h p rote in

expression of p21 and p27 in the obstructed kidney byWestern blott ing, there wa s no increase in the contra lat -e ral k id n e y d u rin g th e e arly p h ase o f co m p e n sato ryhypertrophy (J . Gerth and G. Wolf, unpublished obser-vat ion s). Th is so m ewh a t su rp risin g fi n d in g m a y in d i-cate th at co m p e n sato ry h yp e rtro p h y in th e co n tralat-e ra l k id n ey a f t e r u n il a t e r a l u r et e r a l ob s t r uct i on i sindependent of these specific CDK inhibitors.

CELL CYCLE PROTEINS AND RENAL CELL APOPTOSIS

As sta ted earlier, tota l orga n cell number reflects t heb alan ce of p rol ifera t ion an d ap op tosis (p rog ram m e dce ll d e ath ) a n d m a n y form s of g lom e ru lar an d tu b u lar

cell injury are associated with increased proliferationand apoptosis (59, 131). However, the consequence ofglomerular cell apoptosis depends on the type of glo-m e ru lar in ju ry an d th e g lo m e ru lar ce l l typ e in ju re d .F o r e xam p le , ap o p to sis m ay b e b e n e fi cial d u rin g th eresolution phase of mesangia l prolifera tive glomerulo-n e ph ri t is t o n o rm aliz e th e in cre ase in m e san g ial cel lnumber (5). In contrast, a decrease in mesangial celln u m ber d u e t o e xces s a p op t os i s m a y u n d er l ie t h edevelopment of glomerulosclerosis after a decrease innephron number (37). Likewise, endothelial cell apopto-sis results in a denuded capillary lumen in t hromboticmicroa ngiopat hy (R. J ohnson, unpublished observa-tions) a nd in oth er forms of endothelia l injury (117) a nd

m ay p red ispose to th e d e ve lop m en t of p rog re ssiveglomerulosclerosis. Podocyte loss in diabetes (83) andmembra nous nephropa thy (103) ma y a lso underlie thedevelopment of glomerulosclerosis. Fina lly, prolifera -tion a nd a poptosis ha ve also been reported in proximala n d d i s t a l t u b u l a r e p i t h e l i a l c e l l s i n m a n y t y p e s o facute and chronic tubulointerstitial diseases. Apopto-sis, in excess of proliferation, decreases cell number,leadin g to inters tit ia l fi brosis (59, 126).

These studies show a possible link between certaingrowth (proliferation) and death (apoptosis) pathwaysin renal disease. How a re these processes linked at thele ve l o f th e ce l l cycle ? I n co n trast to tran si t io n an dp rog re ssion th ro u gh th e cel l cycle th a t occu rs with

p roli fe rat io n , in vi tro stu d ies h ave sh own th a t cel lstyp ical ly e xi t th e cel l cycle in late G 1 p h ase d u rin gapoptosis. However, apoptotic cells can exit during anypha se of t he cell cycle (64).

CDK I nhi bi tors in Renal Cel l Apoptosis

The fi rst clue to a possible role for cell cycle proteinsin glomerular cell apoptosis came from the observationtha t the peak in mesa ngial cell apoptosis in experimen-ta l (Thy1) glomerulonephritis coincided w ith th e ma xi-mum decrease in p27 levels (106). Moreover, apoptosis

F524 INVITED REVIEW


12/16

w a s m a r k ed ly i n cr ea s e d i n n ep hr i t ic p 27/ micecompa red w ith contr ol p27/ mice (80). Furthermore,tubulointerstitial cell apoptosis was also increased inp27/ a fter unilat eral uretera l obstruction compa redwith control mice (80). In contrast, apoptosis is not amarked feature of glomerular diseases associated withincreased p27 levels, such as membranous nephropa-thy and diabetic nephropathy (56).

To determine w heth er th e CD K inh ibitor p27 indeedp rote cts m e san g ial ce lls f rom ap o pto sis , we stu d iedm es a n g i a l ce ll s i n v it r o d er i ve d f r om p 27/ a n dp27/mice. Apoptosis induced by grow th fa ctor depri-vat ion or cycloh e xam id e wa s m ar k ed ly in cre ase d inp27/ mesangial cells compared with p27/ cells(40). Moreover, reconstituting p27 levels in p27/cells rescued cells from a poptosis. An increa se in growt hfactor-deprived induced apoptosis was also observed inra t mesangia l cells when p27 levels were lowered withp27 a ntisense compar ed w ith contr ol r a ts (40). Recentstu d ie s in n o n re n al ce l ls sh o we d th at th e COOH te r-m i ni of p 21 a n d p 27 a r e t r u n ca t e d b y ca s p a s es i na poptotic cells (58). Ta ken t ogeth er, in a ddit ion to it srole in proliferat ion an d hy pertr ophy (105), our st udiesshowed tha t a novel function for the CD K inhibitor p27is t o protect rena l cells from a poptosis (Fig. 6).

CDKs in Renal Cell Apoptosis

The r ole for cyclin dependent kinase 2 (CDK2) inDNA synt hesis has been w ell esta blished. However, wean d oth e rs h ave re ce n tly sh own th a t C D K 2 a lso h as acri t ical ro le in ap o pto sis . I n g rowt h factor-d e privedp27/ mesangial cells undergoing apoptosis, CDK2activi ty wa s m a rk ed ly in cre ase d with o u t a n y in creasein CDK2 protein levels (40). Moreover, CDK2 activityin cre ase d in th e ab se n ce o f D N A syn th esis . F u rth e r-

m ore , in h ib it in g CD K 2 activi ty p h arm a colog ical ly orwith a d om in an t n e g ative m u tan t d e cre ase d ap o pto sisin grow th fa ctor-deprived mesa ngia l cells (40). We ha vealso shown t ha t t ubular epithelial cell apoptosis in vivo

after ureteral obstruction is associated with increasedCD K 2 activi ty (80). M ore re ce n tly, s tu d ies h ave alsos h o w n t h a t C D K 2 a c t i v i t y i s i n c r e a s e d i n a p o p t o t i cnonr ena l cells (33, 58).

As discussed earlier, normal cell cycle progression(a nd DNA synt hesis) requires the sequentia l activa tionof CD K2 by cyclin E in la te G 1phase, an d cyclin Ain t heS p h a s e (112 ). To d et e r m i ne w h e t h e r t h e C D K 2 -d ep en d en t m e sa n g i a l ce ll a p op t os is w a s d u e t o t h ea ctiva tion of CD K2 by a specific cyclin, tota l cell proteinwa s im m u n op recip ita te d with an t ib od ies to cyclin s Ean d A, the part ners for CD K2. Our results showed tha tapoptosis was due to increased cyclin A-CDK2 activity,without a preceding increase in cyclin E-CDK2 activity.These studies suggest that an unscheduled and uncoor-dinated increase in cyclin A-CDK2 activity (without ap reced in g cycl in E -CD K 2 activat ion ) m a y lead to acatastrophic G 1/S ph a se, resu lt ing in a poptosis (40).

These studies show that growth (proliferation) andd e ath (ap o p to sis) p ath ways sh are co m m o n ce l l cyclepat hw a ys (Fig. 6) a nd ma y provide a n explana tion why

glomerular cell proliferation and apoptosis are oftenclosely linked in man y forms of glomerular disea se.

CONCLUSIONS

The progressive decline in r ena l function in g lomeru-lar an d tu b u lo in te rst i t ial d ise ase is u l t im ate ly d u e toth e in cre ase in e xtrace l lu lar m atrix p ro te in s, wh ichl e a d s t o s c a r r i n g . H o w e v e r , t h e s e l a t e c h a n g e s a r epreceded by, a nd a re closely linked to, cha nges in cellnumber (ba la nce of prolifera tion a nd a poptosis) and/orcell size (hypert rophy). It ha s only recently been recog-n i ze d t h a t t h e se e a r l ie r ce ll ul a r e ven t s a r e cl os el yl in k ed to t h e ce ll cycle in p ath o log ical s ta te s su ch asoccur in ma ny forms of renal disease. Recognition tha tth e g rowt h (p roli fe rat io n ) an d d e ath (ap o pto sis) re -sp o n se s to in ju ry sh are co m m o n ce l l cycle p ath waysm ay e xp lain wh y th e se p rocesses ar e o f te n close lylinked in renal disease. Furthermore, our understand-ing of the cell cycle also explains why proliferation andhypertrophy a re exclusive within the sa me cell.

There are a number of compelling reasons to studyce ll cycle re g u lat ory p rote in s in re n al d isease . F irst ,a lthough cell proliferat ion, a poptosis, a nd hypertrophya r e r eg u la t e d b y g r ow t h f a ct or s , s i g n a l in g p a t h w a y s ,and extracellular matrix and immediate response genes,the ultima te fat e of the cellsr esponse to injury ma y begoverned by cell cycle regulatory proteins within the

n u cleu s. S e con d , e ach re n al cel l t yp e h a s a d i ffere n tconstitutive expression pattern of cell cycle proteins.Third, the role of each cell cycle protein is probably cellty pe specifi c and a lso depends on the form of injury, an dhence its role in renal diseas e is not a lwa ys predicta ble.F in al ly, m a n y n e w an d e xcit in g th e ra p eu tic s tra te g ie sa re being developed to ta rget specifi c cell cycle proteinsan d fu rth e r re se arch in to th e se ap p licat io n s in re n aldisea se ma y provide some hope to our pa tient s.

Original work by S. J . Shankland is supported by Public HealthService G ra nts DK -34198, DK-47659, D -K52121, D-K51096 an d t heGeorge OBrien Kidn ey Cent er. Origina l work by G . Wolf is supported

Fig. 6. Growth and death pathways are linked at level of cell cycle.Injury to mesangial cells increases activity of CDK2, which coincideswith a decrease in levels of CDK inhibitor p27. Normal progressionthrough cell cycle leads to proliferation, whereas a catastrophic entryinto G 1/S is associat ed wit h cell cycle exit, a nd a poptosis.

F525INVITED REVIEW


13/16

by the Deutsche Forschungsgemeinschaft Wo 460/24, 24 and aHeisenberg Grant .

Ad d r es s f or r e pr i n t r e q u es t s a n d ot h er c or r e s pon de n ce : S . J .Sha nkla nd, U niv. of Wash ington Medical C enter, Div. of Nephrology,B ox 356521, 1959 NE P a cifi c Ave., S eat tle, WA 98195-6521 (E -ma il:[email protected]).

REFERENCES

1. Abboud HE. Gr owth factors in glomerulonephrit is .Kid n ey I n t 43: 252267, 1993.

2. Addis T and Oliver J . Th e Renal Lesion i n Br ights Di sease.New York: H oeber, 1931.

3. Akashi M, Osawa Y, Koeffler HP, and Hachiya M. AcadEmerg Med p53: importa nt role of RNA stabilizat ion. Biochem-is t r y 337: 607616, 1999.

4. Al-Douahji M, Brugarolis J , Brown PAJ , Stehman-BreenCO,Alpers CE, and Shankland SJ . The cyclin kina se inhibi-tor p21WAF/CI P 1 is required for glomerular hypertrophy in experi-mental diabetic nephropathy.Kid n ey I n t 56: 16911699, 1999.

5. Baker AJ ,MooneyA, Hughes J ,L ombardi D,J ohnson RJ ,and Savill J . Mesangial cell a poptosis : the major mechanismfor resolut ion of glomerular hypercellularity in experimentalmesangial proliferat ive nephrit is .J Cl in I n v e st 94: 21052116,1994.

6. Baldin V, Lukas J , Marcote MJ , Pagano M, and DraettaG. Cyclin D1 is a protein required for cell cycle progression inG 1. Genes Dev7: 812821, 1993.

7. Brugarolas J , Chandrasekaran C, Gordon J I, Beach D,J acks T, and Hannon GJ . Radiation-induced cell cycle arrestcomprim ised by p21-defi ciency.N a t u r e 377: 552557, 1995.

8. Buchkovich K, Duffy LA, and Harlow E. The retinoblas-toma pr otein is phosphoryla ted durin g specifi c pha ses of the cellcycle.Cell58: 10971105, 1989.

9. Choi ME, Eung-Gook K, HuangQ, and Ballerman BJ . Ra tmesangial cell hypertrophy in response to tra nsforming growthfactor-1. Ki d n ey I n t 44: 948958, 1993.

10. Conion I andRaff M.Size control in animal development. Cell96: 235244, 1999.

11. Coombs HL, Shankland SJ , Setzer SV, Hudkins KL, andAlpers CE. Expression of the cyclin kina se inhibitor, p27kip1, indevelopeing and mature human kidney.Ki d n ey I n t 53: 892896,

1998.12. Cordon-Cardo C. Mutation of cell cycle regulators. Biologicaland clinical implications for human neoplasia. Am J Pathol147:545560, 1995.

13. Cosio FG. Effects of high glucose concentrat ions on humanmesangial cell proliferat ion. J Am Soc Nep h r o l 5: 16001609,1995.

14. DAgati V.The ma ny ma sks of focal segmenta l glomerulosclero-sis.Ki d n ey I n t 46: 12231241, 1994.

15. DeBondt HL , Rosenblatt J , J ancarik J , J ons HD, andMorgon DO. Crystal s tructure of cyclin dependent kinase 2.N a t u r e 363: 595602, 1993.

16. Draetta B. cdc2 act ivat ion: the interplay of cyclin binding a ndThr161 phosphoryla tion. Trends Cell Bi ol3: 287289, 1993.

17. Draetta G and Beach D. Activat ion of cdc2 protein kinaseduring mitosis in human cells: cell cycle-dependent phosphory-lat ion and subunit rearrangement. Cell 54: 1726, 1988.

18. El-Deiry WS,Tokino T, Velculescu VE, Levy DB, ParsonsR, Trent J M, Lin D, Mercer WE, Kinzler KW, and Vogel-stein B. p21WAF1, a potentia l media tor of p53 tumor suppres-sion.Cell75: 817825, 1993.

19. ElbendaryA, Berchuck A,DavisP,Havrilesky L, Bast RC,Iglehart D, and Marks J R. Tran sforming growth factor 1can induce C IP 1/WAF1 expression independent of the p53p a t h w a y in ov a r ia n c a n ce r c e lls . Ce l l Gr o wt h Dif f e r 5: 13011307, 1994.

20. ElledgeSJ ,andHarper J W. CDK inhibitors : on th e thresholdof checkpoints and development. C u r r O p i n C el l B i o l 6: 847852, 1994.

21. Fine LG. The biology of renal hypertrophy. K i d n e y I n t 29:619634, 1986.

22. FineL G andNorman J . Cellular events in renal hypertrophy.Annu Rev Physiol 51: 1932, 1989.

23. Floege J , K riz W, Schulze M, Susani M, Kerjaschki D,Mooney A, Couser WG, and K och KM. B a s ic fi b r ob la s tgrowth factor augments podocyte injury and induces glomerulo-sclerosis in rat s w ith experimental membranous n ephrology. JClin Invest96: 28092819, 1996.

24. Fogo A, Hawkins EP, Berry PL, Glick AD, Chiang ML,MacDonell RC, and Ichikawa I. Glomerular hy pertrophy inm in im a l c h a n g e d ise a s e p r ed ict s s u b se q u en t p r og r e ss ion t ofocal glomerula r sclerosis.Ki d n ey I n t 38: 115123, 1990.

25. Franch HA, Alpern RJ , and Preisig PA. Alkalinization ofa c idic v e sicu la r c om p a r t m e n t s in d u ce s h y p er t r oph y in t h eabsence of cell entry (Abstra ct). J A m Soc N ephr ol5: 692, 1994.

26. Franch HA, Alpern RJ , and Preisig PA. TGF convertsEGF-induced hyperplasia to hypertrophy by inhibit ing CDK2/cyclin E kinase a ct ivity (Abstract) . J Am So c Ne p h r o l 6: 767,1995.

27. Fries J LW, Sandstrom DJ , Meyer TW, and R ennke HG.G lom er u la r h y p er t r oph y a n d e pi t h el ia l c el l in ju r y m od ula t eprogressive glomerulosclerosis in the rat. Lab Invest 60: 205218, 1989.

28. Geng Y, and Weinberg RA. Transforming growth factor effects on expression of G 1 cyclins a nd cyclin-dependent ki-nases. Proc N atl A cad Sci U SA 90: 1031510319, 1993.

29. Girard F, Strausfeld U, Fernandez A, and Lamb N. CyclinA is required for the onset of DNA replicat ion in mammalianfibroblasts . Cell67: 11691179, 1991.

30. Glotzer M. The mechanism and control of cytokinesis . C u r r Opin Cell Biol9: 815823, 1997.

31. Grana X, and Reddy EP. Cell cycle control in mammaliancells: role of cyclins, cyclin-dependent kinases (CDKs), growthsuppressor genes and cyclin-dependent kina se inhibitors (CKIs).Oncogene11: 211219, 1995.

32. Gudas J M,Payton S,Thukras S,Chen E, Mass M,Robin-son MO,and Coats S.Cyclin E2, a novel G1 cyclin th at bindsCDK2 and is aberrantly expressed in human cancers. M o l Cel l Bio l 19: 612622, 1999.

33. Hakem A, Sasaki T, Kozieradzki I , and Penninger J M..The cyclin-dependent kina se CD K2 regula tes th ymocyte apopto-sis.J E x p Med 189: 957967, 1999.

34. Hammerman MR. Gr owth factors and a poptosis in acute renalinjury. Curr Opin Nephrol Hypertens7: 419424, 1998.

35. Hannken T,Schroeder R, Stahl RAK, and Wolf G.Angioten-sin I I-mediated expression of p27(Kip1) and induction of cellu-lar hypertrophy in renal t ubular cells depend on the generat ionof oxygen radicals. Ki d n ey I n t 54: 19231933, 1998.

36. Hara E, Smith R, Parry D,Tahara H, StoneS,and PetersG. Regulat ion of p16(CD KN2) expression an d its implication forcell immortalization and senescence. Mol Cell Bi ol16: 859867,1996.

37. Hattori T, Shindo S, and Kawamura H. Apoptosis ande x p r e s s ion of B a x p r ot e in a n d F a s a n t ig e n in g lom e r u li of aremnant-kidney model.N ephr on79: 186191, 1998.

38. Hengst L, Gopfert U, Lashuel HA, and Reed SI. Completeinhibition of CD K/cyclin by one molecule of p21Cip1. Genes Dev12: 38823888, 1998.

39. Hengst L, and Reed SI. Inh ibitors of t he C ip/Kip fa mily.C u r r Top M ic r o bio l I mm u n o l 227: 2541, 1998.

40. Hiromura K, Pippin J W, Fero ML, Roberts J M, andShankland SJ . Modulation of apoptosis by the cyclin-depen-dent kinase inhibitor p27Kip1.J Cl in I n v est 103: 597604, 1999.

41. Hi rschberg R and Ding H. G r ow t h f a c t or s a n d a c u t e r e n a lfailure.Semi n N ephrol18: 191207, 1998.

42. Hostetter TH. Progression of renal disease and renal hypertro-phy. Annu Rev Physiol57: 263278, 1995.

43. HuangH and WangH. Cyclin D1, CD K4 expression an d cyclinD1 upregulat ion by endothelin-1 in rat mesangial cells (Ab-stract) .J A m Soc Nephr ol7: 1658, 1996.

44. HuangHC and Preisig P. Cyclin D kinase is act ivated in a lldiabetic renal growt h, while cyclin E kinase determines wheth ert h e g r ow t h p a t t er n w i l l b e b y h y pe r pl a s ia or h y pe rt r op hy(Abstract). J A m Soc Nephr ol9: A2252, 1998.

45. Hughes J , Brown P, and Shankland SJ . Cy c lin k in a s einhibitor p21CI P 1/WAF1 l im it s in t e r st i t ia l b u t n ot t u b u la r c el l

F526 INVITED REVIEW


14/16

proliferat ion after ureteric obstruct ion. A m J P h ysi o l R en a l Physiol277: F948 F956, 1999.

46. Inoshita S, Terada Y, Ymamda T, Nakashima O, Sasaki S,and Marumo F. Mitogenic signa ling of endothelin-1 is regu-lated by cyclin D1, p16 and the phosphorylat ion of ret inoblas-toma gene product in r at mesangial cells (Abstra ct). J Am So c Nephrol7: 1564, 1996.

47. J ohnson J . The glomerular response to injury: progression orresolution?Kid n ey I n t 45: 17691782, 1994.

48. Kato J and Sherr J . Inhibit ion of granulocyte differentiat ionby G1 cyclins D2 and D 3 but not D1 C. Proc Natl Acad Sci USA90: 1151311517, 1993.

49. Kim Y-G, Alpers CE , Brugarolas J , J ohnson RJ , CouserWG, and Shankland SJ . The cyclin kina se inhibit or p21Cip1/WAF1 limits glomerula r epithelia l cell proliferat ion in experi-mental glomerulonephrit is .Ki d n ey I n t 55: 23492361, 1999.

50. Klahr S, Schreiner G, and Ichikawa I. Pr ogression in rena ldisease. N En g l J M ed 318: 16571666, 1988.

51. Kreisberg J I, and Ayo SH. The glomerular mesangium indiabetes mellitus.Ki d n ey I n t 43: 109113, 1993.

52. Kreisberg J I, Radnik RA, Ayo SH, Garoni J , and Saiku-mar P. High glucose elevates c-fos an d c-jun tr anscripts andproteins in mesangial cell cultures. K i d n e y I n t 46: 105112,1994.

53. K riz W. Progressive renal fa ilureinability of podocytes toreplicate and the consequences for development of glomeruloscle-rosis.Ne p r h ol D ia l Tr a n sp la n t 11: 17381742, 1996.

54. Kriz W, Gretz N, and Lemley KV. Pr ogression of glomerulardiseases: is the podocyte the culprit? K i d n e y I n t 54: 687687,1998.

55. K riz W, Hahnel B, R osener S, and Elger M. Long-termtrea tment of rat s with FG F-2 results in focal segmental glomeru-losclerosis. Ki d n ey I n t 48: 14351450, 1995.

56. Kuan CJ , Al-Douahji M, and Shankland SJ . The cyclink in a s e in h ibi t or p 21WA F 1, C IP1 is in cr e a s ed in e xp er im e n t a ldiabetic nephropathy: potential role in glomerular hypertrophy.J A m Soc N ephr ol 9: 986993, 1998.

57. Lees E. Cyclin dependent kinase regulat ion. C u r r O p i n C e l l Bio l 7: 773 780, 1995.

58. Levkau B,K oyama H, Raines EW, Clurman BE, Herren B,Orth K, R oberts J M, and Ross R. Cleavage of p21 (Cip1/Waf1) an d p27 (Kip1) mediat es a poptosis in endothelial cellsthrough a ct ivat ion of CDK2: role of a caspase cascade. Mol Cell 1: 553563, 1998.

59. Lieberthal W, and Levine J S. Mechanisms of apoptosis a ndits potential role in renal tubular epithelia l cell injury. A m JPhysiol Renal Fluid Electrolyte Physiol271: F477F488, 1996.

60. Liu B and Preisig P. Compensatory renal hypertrophy (CRH)is mediated by both cell cycle-dependent and -independentgrowt h processes (Abstract).J A m Soc N ephrol9: 444A, 1998.

61. L iu B andPreisigP. Renal hypertrophy following uninephrec-tomy (Unx) is associated with act ivat ion of CDK 2-cyclin E, butnot CD K4/cyclin D1 kin ase (Abstract). J Am Soc Ne ph r o l 8:A1966, 1997.

62. Megyesi J , Safirstein R L, and Price P M. Induction ofp21WAF1/CI P 1/SD I1 in kid ney t ubule cells a ffects th e course ofcisplatin-induced acute renal failure. J Cli n In vest101: 77782,1998.

63. Megyesi J , Udvarhelyi N, Safirstein RL , and Pri ce PM.The p53-independent activa tion of tr an scription of p21WAF1/CIP 1/SDI1 a fter a cute renal fa ilure. Am J Ph y s io l Re n a l Flu id ElectrolytePhysiol 271: F1211F1216, 1996.

64. Meikrantz W and Schegal R. Apoptosis an d t he cell cycle.JCell Biochem 58: 160174, 1995.

65. Morgan DO. Principles of CDK regulat ion. N a t u r e 374: 131134, 1995.

66. Morrissey J J , I shidoya S, McCracken R, and Klahr S.Control of p53 a nd p21 (WAF1) expression during unilatera lureteral obstruct ion.Ki d n ey I n t 50: S84S92, 1996.

67. Morrissey J J , IshidoyaS, McCracken R, and Klahr S.Theeffect of ACE inhibitors on the expression of m atr ix genes andthe r ole of p53 an d p21 (WAF1) in experimenta l rena l fi brosis.Ki d n ey I n t 4 9, Su p p l 54: S83S87, 1996.

68. Muda AO, Feriozzi S, Cinotti GA, and Faraggiana T.G lom er u l a r h y p er t r oph y a n d c h r on ic r e n a l f a i lur e in f oc a l

segmental glomerulosclerosis. A m J K i d n ey D i s 23: 237241,1994.

69. Murray A. Cyclin ubiquit inat ion: the destruct ive end of mito-sis.Cell81: 149152, 1995.

70. Murray A and Hunt T. The Cell Cycle. An Introduction. N ewYork: Oxford Univ. Press, 1993.

71. NagataM, Nakayama K, TeradaY,H oshi S,and WatanabeT. Ce l l c y cle r e g u la t ion a n d d i ff er e n t ia t ion in t h e h u m a npodocyte lin eage. Am J Pa t h o l 153: 15111520, 1998.

72. Nasmyth K. Viewpoint: putting the cell cycle in order. Science274: 16431645, 1996.

73. Nguyen H, Gitig DM, and Koff A.Cell-free degrada t ion ofp27(Kip1), a G 1 cyclin-dependent kin ase inhibitor, is d ependento n C D K 2 a c t iv it y a n d t h e p r ot e a som e . M o l C el l B i ol 19:11901201, 1999.

74. Norbury C and Nurse P. Animal cell cycles and their control.Annu Rev Biochem 61: 441471, 1992.

75. Nourse J , Firpo E, Flanagan WM, Coats S,Polyak K, LeeM,MassagueJ ,C rabtreeGR, and RobertsJ M.Interleukin-2-mediat ed elimina tion of th e p27kip1 cyclin-dependent kina seinhibitor prevented by r apam ycin.N a t u r e 372: 570573, 1994.

76. Nurse P. U n iv er s a l c on t r ol m e c h a n is m r e g ula t in g on se t ofM-phase.N a t u r e 344: 503508, 1990.

77. Ohtsubo M and Roberts M. Cyclin-dependent regulation ofG 1 in m a m m a lia n fi b r ob la s t s .Science259: 19081912, 1993.

78. Ohtsubo M, Theodoras AM, Schumacher J , Roberts J M,and Pagano M. Human cyclin E, a nuclear protein essentailfor the G 1-to-S phase transition. Mo l Ce l l Bio l 15: 26122624,1995.

79. Okado T, Terada Y, Inoshita S, Nakashima O, KuwaharaM,Sasaki S,andMarumo F.Glucorticoids stimulate p21(Cip1)gene promoter activity a nd inhibit m esan gial cell cycle: involve-ment of C/EB P alpha in tr an scription oif p21(Cip1) (Abstract).JAm Soc N ephr ol9: 444A, 1998.

80. Ophascharoensuk V, Fero ML , Hughes J , R oberts J M,and Shankland SJ . Th e c y cl in -k in a s e in h ib i t or p 27Kip1

s a f e ga u r d s a g a in s t in fla m m a t or y in j u r y. N a t M ed 4: 575580,1998.

81. Pabst R and Sterzel B. Cell renewa l of glomerular cell typesin normal rats R. An autoradiographic analysis . Kid n e y I n t 24:626631., 1983.

82. PaganoM, pepperkok R, VerdeF,AnsorgeW, and DraettaG. Cyclin A is required at two points in the human cell cycle.E M B O J 11: 961971, 1992.

83. Pagtalunan ME, Miller PL, J umping-Eagle S,Nelson RG,Myer BD, Rennke HG, Coplon NS, Sun L, and Meyer TW.P od oc yt e los s a n d p r og r e ss ive g lom e r u la r in ju r y in t y p e I Idiabetes. J Clin Invest99: 342348, 1997.

84. Pardee B. G1 events and regulat ion of cell proliferat ion A.Science246: 603608, 1989.

85. Park SK, Kang SK, Lee DY, Kang MJ , Kim SH, and KohGY. Temporal expression of cyclins an d cyclin-dependent ki-n a s e s d u r in g r e n a l d e ve lopm e n t a n d c om p en s a t or y g r ow t h .Ki d n ey I n t 51: 762769, 1997.

86. P avenstadt H. The podocyte-a neglected play er in g lomerularinjury? Ne p h r ol D ia l Tr a n s p la n t 10: 147161, 1995.

87. Peter M and Herskowitz I . J oining the complex: cyclin-dependent kinase inhibitory proteins and the cell cycle. Cell7 9:181184, 1994.

88. Pippin J W, Qu Q, Meijer L , and Shankland SJ . Direct invivo inhibition of the nuclear cell cycle cascade in experimentalmesangial proliferat ive glomerulonephrit is w ith roscovit ine, anovel cyclin-dependent kinase ant agonist . J C l i n I n v est 100:25122520, 1997.

89. Piwnica-Worms H. Reversible phosphorylat ion and mitot iccontrol.J L a b Cl in M ed 128: 350354, 1996.

90. Preisig P A,and Franch H A. Renal epithelia l cell hyperpla-sia and hypertrophy. Semi n N ephr ol 15: 327340, 1995.

91. Preisig PA,andFranch HA.Renal epithelia l hyperplasia a ndhypertrophy. Semi n N ephr ol15: 327 340., 1995.

92. Prescott LF. Th e n or m a l u r in a r y e xc r et ion r a t e s of r e n a ltubular cells, leukocytes, and red blood cells. Cl i n Sci ( Colc h ) 31: 425435, 1966.

93. Rabkin R, and Fervenza F C. Renal hypertrophy and kidneydisease in diabetes.D iabetes M etab R ev12: 217241, 1996.

F527INVITED REVIEW


15/16

94. RennkeHG.How d oes glomerula r epithelial cell injury contrib-ute to progressive glomerular da mage? Ki d n ey I n t 45: S58S 63,1994.

95. Reynisdottir I, Polyak K , I avarone A, and Massague J .Kip/Cip a nd I NK4 C DK inhibitors cooperat e to induce cell cyclearrest in response to TGFbeta. Genes Dev9: 18311845, 1995.

96. Riley DJ , Lee EY-HP, and Lee W-H. The ret inoblastomaprotein: more tha n a tumor suppressor. Annu Rev Cell Biol 10:129, 1994.

97. Riley DJ , Nikitin AY, Frank MA, and Lee W-H. Control ofm e s a n g ia l c el l p r ol i fe r a t ion b y c on d it ion a l e xp r es s ion of aret inoblastoma tra nsgene (Abstract) . J A m S oc N ep h r ol 9:445A, 1998.

98. Safirstein R. Gene expression in nephrotoxic and ischemicacute renal injury.J A m Soc N ephr ol4: 13871395, 1994.

99. Savill J . Apoptosis in resolution of inflammation.J L eukoc Biol61: 375380, 1997.

100. Schoecklmann HO, Rupprecht HD, Zauner I, and SterzelRB. TGF beta-1-induced cell cycle a rrest in renal mesangialcells involves inhibition of cyclin E-CDK2 a ctivat ion and r etino-blastoma protein phosphorylat ion. K i d n e y I n t 51: 12281236,1997.

101. Shankland SJ . Cell cycle control and renal disease. Ki d n ey I n t 52: 294308, 1997.

102. Shankland SJ . The growin g role for the cyclin kinase inhibit orp27 Kip1 in renal disease.Ki d n ey I n t 54: 22412242, 1998.

103. ShanklandSJ ,F loegeJ ,T homasSE, NangakuM, Hugo C,Pippin J , Henne K, Hockenberry DM, J ohnson RJ , andCouser WG. Cy cl i n k in a s e in h ib it or s a r e in cr e a s ed d u r in gexperimental m embranous nephropathy: potential r ole in limit-ing glomerular epithelia l cell proliferat ion in vivo. K i d n ey I n t 52: 404413, 1997.

104. Shankland SJ , Hamel PA, and Scholey J W.Phosphoryla-t ion of ret inoblastoma protein in glomeruli of normal, dia beticand renal-ablated rats (Abstract) . J Am Soc Nep h r o l 5: 701,1994.

105. Shankland SJ , H amel PA, and Scholey J W. Cy c l in a n dcyclin dependent kinase expression in the remnant glomeru-lus.J A m Soc N ephr ol 8: 368375, 1996.

106. Shankland SJ , Hugo C, Coats SR, Nangaku M, Pichl

Date post:	04-Jun-2018
Category:	Documents
Upload:	chizda-msii
View:	219 times
Download:	0 times

Cell Cycle Regulatory Proteins in Renal Disease

Documents