Chapter 15

Cellular Signal Transduction

The biochemistry and molecular biology department of CMU

2. Intracellular receptor (transcription regulated recepto

r) Intracellular R is trans-acting

elememt cis-acting element gene expression

Localized in the cytosol and/or in the nucleus.

ligand: Steroid H, VD3, Thyroxine

3. Properties of binding of H and R

• highly specificity

• highly affinity

• saturation

• reversible binding

• special function model

4. Control of receptor activity

• Phosphorylation or dephosphorylation of R

• Phospholipid of membrane

• Enzyme catalyzed hydrolysis

• G protein regulation

(1) Recognize the special ligand

(2) Binding to special ligand

(3) Signal transduction biological effect

5. Function of receptor

§3 Pathway of Signal

Transduction

Signal transduction mediated by membrane receptor

• cAMP dependent-protein kinase A pathway

• cGMP dependent PKG pathway 　• Ca2+ dependent PK pathway 　• Tyrosine protein Kinase pathway

• NF-κB pathway 　• TGF- βpathway

1. cAMP dependent-protein kinase A pathway

H R

G protein

Phosphorylation of Es or functional proteins

Biological effects

PKA

cAMPAC

(1) cAMP metabolism

ATPMg2+

PPi

cAMP

H2OMg2+ 5'-AMP

AC PDE

AC ： Adenylate cyclase

PDE ： Phosphodiesterase

PDE

H2O

N

N N

N

NH2

O

H

OHOH

CH2

H

H H

OPO

O

O

PO

O

O

P

O

O

O ATP

ACPPi

N

N N

N

NH2

O

H

OHO

CH2

H

H H

O

PO

O

cAMP

N

N N

N

NH2

O

H

OHOH

CH2

H

H H

OPO

O

O

5'-AMP

(2) Mechanism of cAMP effect

Activate cAMP-dependent protein kinase (PKA).

(3) PKA effect

Phosphorylate specifically Ser/

Thr residues in several proteins

（ 1 ） Regulation of metabolism

（ 2 ） Regulation of gene e

xpression

hormons: glucagon, epinephrine

inactive AC active AC

ATP cAMP

inactive PKA active PKA

phosphorylase b kinase

phosphorylase b kinase

P

ATP

ADP

H2O

Pi

phosphorylase b

P

P

ATP ADP

Pi

H2OATP ADP

glycogen synthase

glycogen synthase

P

H2OPi protein phosphatase-1

(active) (inactive)

inhibitor-1 (active)

inhibitor-1 (inactive)

phosphorylase a

ATP

CRE : cAMP response element (T

GACGTCA)

CREB: CRE binding protein

DNACRE

CREB

PKA

Ｐ

Transcription

mRNA

CREB

PKA

Ｐ

CREBＰ

CR

EBＰ

CR

EB

Ｐ

CREBＰ

CR

EB

Ｐ

CR

EB

Ｐ

2. Ca2+ dependent PK pathway

(1) Ca2+ -DAG -dependent PKC pathway

H R

PIP2

G protein PLC

IP3 DG

ERPKC

Ca2+ PS

Biological effects

Phosphorylation of Es or functional proteins

[Ca 2+]i 0.01-1 mol/L （ 10-7 mol/L ）

[Ca 2+]o 2.5mmol/L （ 10-3 mol/L ）

5000~10000×

1 ） Function of DG and IP3

IP3 + R→open of Ca2 ＋ channel →[Ca2 ＋ ]↑

PS, Ca2 ＋DG PKC ↑

2 ） Function of PKC

• regulation of metabolism

PKC →Ser/Thr-P of R, enzyme,

Protein of Mb.

• Gene expression 　

Late response:

Trans-acting factor-P

Third messengerImmediate early genes

Third messenger-P

Activate genes

Cell proliferation

PKC

PKC

Early response:

(2) Ca2 ＋ -CaM dependent protein kinase pathway

H R G protein PLC

IP3

Ca2+ CaM

CaMK

Biological effects

Phosphorylation of Es or functional proteins

Calmodulin (CaM ）： Ca2 ＋ binding protein

4 Ca2 ＋ + CaM → Ca2 ＋ - CaM

↓ CaM kinase↑

↓ 　 Ser/Thr - P ↓

Ca2 ＋ pump, AC ↑ GC ↑

Es (glycogen synthase, phosphorylase kinase)

3. cGMP-dependent PKG pathway

Biological effects

Phosphorylation of Es or functional proteins

ANPNO, CO

Soluble GC

PKG

cGMPReceptor-linked GC

(1) cGMP

(2) Function of PKG

Ser/Thr- P of protein and E

Mg2+

PPi H2O

Mg2+GTP cGMP 5'-GMP

GC PDE

GC: Guanylate cyclase

ANP （ atrial natriuretic peptides ） ↓

GC NO

↓

cGMP

↓

PKG

↓

Vascular dilatation

cis-acting elementnucleus

expression

cell memberane

phosphorylation of enzymes or proteins effects

CaM-PK

Ca2+-CaMCa2+

IP3DGcAMP cGMP

PKA PKG PKC

ATP GTP PIP2(PC)

G AC GC G PL

peptide hormonesneurotransmitters AFP

neurotransmittershypothalamic pituitrin

Ptrans-acting factor

4. Tyrosine-protein kinase pathway (TPK)

• TPK receptor is related to proliferation, differentiation, dissociation, carcinomatous change.

• TPK：receptor TPK ： Mb.

non receptor TPK ： cytosol

(1) Receptor TPK － Ras － MAPK pathway

• GRB2, SOS, Ras, Raf

• Small G protein: Ras

• MAPK (mitogen-activated protein kinase)：

MAPK、MAPKK、MAPKKK

ÊÜÌå ÐÍTPKϸ°ûĤ

EGF, PDGF

receptor TPK Ras － GTPSOS － PGRB2 － P

Raf － P

MAPKK － P

MAPK － Ptrans-acting factor

expression

nucleus

－ P

(2) JAKs － STAT pathway

ligand

non TPK receptor

JAKs STAT

gene expression

• JAKs

• STAT: Signal transductors and activa

tor of transcription

ÖÊĤ

¸ÉÈÅËØÓ¦´ð Ôª¼þ

ºËĤ

»ùÒò

£ PP£

JAK

11391

84

48

113

P

91P 84 P

48

113

91 84P P

P

interferons

inactive STAT

Plasma membrane

STAT complex

Nuclear membrane

geneInterferons response element

transcription

Dimerization of Receptor

Interferon

Autophosphorylation of JAK

Phosphorylation of STAT

Nuclear translocation of STAT

Interferon response element

Expression of gene

5. Nuclear factor-κB pathway

6. TGF-βpathway

Intracellular receptor (DNA transcription regulated

receptor)

• Steroid H, VD3, Thyroxine

• Cytosolic R: glycocorticosteroid H

• Nuclear R: thyroxine, estrogen, androgen, progesterone

Serum binding proteinWith bound bormone