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J. Biol. Chem., Vol. 277, Issue 44, 42171-42177, November 1, 2002
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From the Chondrocyte proliferation is important for
skeletal development and growth, but the mechanisms regulating it are
not completely clear. Previously, we showed that syndecan-3, a cell
surface heparan sulfate proteoglycan, is expressed by proliferating
chondrocytes in vivo and that proliferation of cultured
chondrocytes in vitro is sensitive to heparitinase
treatment. To further establish the link between syndecan-3 and
chondrocyte proliferation, additional studies were carried out in
vivo and in vitro. We found that the topographical
location of proliferating chondrocytes in developing chick long bones
changes with increasing embryonic age and that syndecan-3 gene
expression changes in a comparable manner. For in vitro
analysis, mitotically quiescent chondrocytes were exposed to increasing
amounts of fibroblast growth factor-2 (FGF-2). Proliferation was
stimulated by as much as 8-10-fold within 24 h; strikingly, this
stimulation was significantly prevented when the cells were treated
with both fibroblast growth factor-2 (FGF-2) and antibodies against
syndecan-3 core protein. This neutralizing effect was dose-dependent and elicited a maximum of 50-60%
inhibition. To establish specificity of neutralizing effect, cultured
chondrocytes were exposed to FGF-2, insulin-like growth
factor-1, or parathyroid hormone, all known mitogens for
chondrocytes. The syndecan-3 antibodies interfered only with FGF-2
mitogenic action, but not that of insulin-like growth factor-1 or
parathyroid hormone. Protein cross-linking experiments indicated that
syndecan-3 is present in monomeric, dimeric, and oligomeric forms on
the chondrocyte surface. In addition, molecular modeling indicated that
contiguous syndecan-3 molecules might form stable complexes by parallel
pairing of
Syndecan-3 Is a Selective Regulator of Chondrocyte
Proliferation*
§,
, and
Department of Orthopaedics, University of
Maryland School of Medicine, Baltimore, Maryland 21201 and the
Departments of ¶ Anatomy and Cell Biology and
Biochemistry,
School of Dental Medicine, University of Pennsylvania,
Philadelphia, Pennsylvania 19104
-sheet segments within the ectodomain of the core
protein. In conclusion, the results suggest that syndecan-3 is a direct
and selective regulator of the mitotic behavior of chondrocytes and its
role may involve formation of dimeric/oligomeric structures on their
cell surface.
*
This work was supported by National Institutes of Health
Grants AR46245 (to T. K.) and AR45302 (to M. P.).The costs of publication of this
article were defrayed in part by the
payment of page charges. The article
must therefore be hereby marked
"advertisement" in accordance with 18 U.S.C. Section
1734 solely to indicate this fact.
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