Biology of Sialyl GlycansPart 3: New thinking in function and glycan biosynthesis
Joseph Lau
ST6Gal-1
X3Q O H X1a X1bL X2 IIII II IV V VI
P3 P4 P2b P1 P2a P2c
• A single copy gene (Siat1)
• Transcription starts from six physically distinct promoters
• Generation of the identical ST6Gal-1 protein
• Differential regulation in different tissues and cells
• Feature conserved across mammalian species
α2,6
β1,4test
es
kid
ne
y
mu
scle
liv
er
lun
g
sple
en
bra
in
he
art
P1
ST6Gal-1 deficient mice have moresevere acute inflammatory response
Ce
lls
x 1
0-3
* p <0.003
*
*
0
5 00
1 00 0
1 50 0
2 00 0
t ota l eos neu CD8 CD4 B DC
w t
dP1
Eos Ly6Gpos CCR3pos
Neu Ly6Gpos CCR3neg
;
;
Bone niches govern
hematopoietic stem cell activities-- interactions between “seeds” and “soil”--
- from Yin & Li (2006) J Clin Invest. 116: 1195-1201
;
Hematopoietic stem and progenitor cells
LSKLin neg
cKit ++
Sca-1 +
LKLin neg
cKit +
Sca-1 neg
Lin pos
Lin neg
cKit lo
Sca-1 lo
;
HSPCs from ST6Gal-1 deficient (∆P1) animals
proliferate and differentiate faster ex vivo
Total
Lin - - + +
Sca1 + - - -
cKit + + + -
WT
∆P1
*
*
**
A B
cell
s x 1
05
differentiation
HSC MPP
CLP
GMP
MKEPCMP
OPPLSK
LK
lymph
neu
mono
RBC
platelet
differentiation
;
Recombinant ST6Gal-1 can suppress ex vivo
HSPC proliferation and differentiation !!
cells x 106
Total LSK LKCD11b+
cKit +
CD11b+
cKit -
no addition
rST6Gal
differentiation
HSC MPP
CLP
GMP
MKEPCMP
OPPLSK
LK
lymph
neu
mono
RBC
platelet
differentiation
;
ST6Gal-1 Expression
ST6Gal-1
circulation
liver
α2,6 sialylated
hepatic glycoproteins
bone marrow
Proliferation, Differentiation
;
Challenging the Traditional ParadigmChallenging the Traditional Paradigm
T T
T
T
TTT
� Each cell always makes its own glycans
� Glycans can be made by non-self enzymes!
T T
T
T
TTT
secreted ST6
;
HSPCs have cell surface α2,6-sialic acids,
but do not express the ST6Gal-1 to make them
rela
tive
ab
un
da
nce
ST6Gal-1 mRNA
ST6Gal-1 enzyme activity
Cell surface α2,6 Sia
;
Cell surface α2,6-SA is constructed by
extrinsic ST6Gal-1
α2,6 sialic acid on cells?
KO > KO
WT > KO WT > WT
KO > WT
Mice strains:WT= wild-type mice with intact ST6Gal-1KO= mutant mice with defective ST6Gal-1
KO
donor
recipient
KO
WT
donor
recipient
KO
WT
donor
recipient
WT
KO
donor
recipient
WT
;
SummaryGlycans as mediators between cell (“seed”) and niche (“soil”)
SummaryGlycans as mediators between cell (“seed”) and niche (“soil”)
� Glycans occupy critical intersection between cells and their outside
environment.
� Existence of a novel, “extrinsic” glycosylation pathway
� Extrinsic ST6Gal-1 can alter hematopoietic activity
Current Questions:
� What is mechanism of ST6Gal-1 action?
• How can this be exploited for therapeutic benefit?
� Do other glycosyltransferases act by the “extrinsic” pathway?
• Do they possess clinically useful properties?