Hm. Miettinen et M. Jalkanen, THE CYTOPLASMIC DOMAIN OF SYNDECAN-1 IS NOT REQUIRED FOR ASSOCIATION WITH TRITON X-100-INSOLUBLE MATERIAL, Journal of Cell Science, 107, 1994, pp. 1571-1581
Cell surface heparan sulfate proteoglycans such as syndecan-1 bind var
ious extracellular matrix proteins and have been suggested to interact
with the cytoskeleton. Such interactions are thought to be important
for stabilizing cell morphology. Syndecan-1 resists extraction with Tr
iton X-100. This insolubility was reported not to be affected by remov
al of the glycosaminoglycan chains, suggesting that the insolubility i
s not due to binding to the extracellular matrix, but rather to an ass
ociation with the actin cytoskeleton (Rapraeger, A., Jalkanen, M. and
Bernfield, M. (1986) J. Cell Biol. 103, 2683-2696). To examine further
the interaction of syndecan-1 with the Triton X-100-insoluble residue
, we expressed wild-type mouse syndecan-1 and a cytoplasmic deletion m
utant (tail-less) in Chinese hamster ovary cells. We observed that bot
h the wild-type and the tail-less syndecan-1 were partly insoluble in
Triton X-100. The insolubility was not affected by increasing temperat
ure (37 degrees C or 50 degrees C) or by cytochalasin D. Removal of th
e glycosaminoglycan chains from the ectodomain, however, resulted in c
omplete Triton X-100 solubility, unlike previous reports, Syndecan-1 c
ould also be released into the Triton X-100-soluble fraction by additi
on of heparin or heparan sulfate to the extraction medium. We conclude
that the cytoplasmic domain of syndecan-1 is not responsible for Trit
on X-100 insolubility. Instead, our results indicate that Triton X-100
insolubility is caused by an interaction of syndecan-1 molecules with
other cellular and/or extracellular molecules mediated by the heparan
sulfate chains.