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Papers In Press, published online ahead of print June 28, 2006
Baylor College of Medicine, Houston, TX 77030
Corresponding Author: pwpark{at}bcm.tmc.edu
Syndecans comprise a major family of cell surface heparan sulfate proteoglycans (HSPGs). Syndecans bind and modulate a wide variety of biological molecules through their heparan sulfate (HS) moiety. Although all syndecans contain the ligand-binding HS chains, they likely perform specific functions in vivo because their temporal and spatial expression patterns are different. However, how syndecan expression is regulated has yet to be clearly defined. In this study, we examined how syndecan-1 expression is regulated in epithelial cells. Our results showed that among several bioactive agents tested, only forskolin and three isoforms of TGFß (TGFß1-TGFß3) significantly induced syndecan-1, but not syndecan-4, expression on various epithelial cells. Steady-state syndecan-1 mRNA was not increased by TGFß treatment and cycloheximide did not inhibit syndecan-1 induction by TGFß, indicating that TGFß induces syndecan-1 in a post-translational manner. However, TGFß induction of syndecan-1 was inhibited by transient expression of a dominant-negative construct of protein kinase A (PKA) and by specific inhibitors of PKA. Further, i) syndecan-1 cytoplasmic domains were Ser-phosphorylated when cells were treated with TGFß and this was inhibited by a PKA inhibitor, ii) PKA was co-immunoprecipitated from cell lysates by anti-syndecan-1 antibodies, iii) PKA phosphorylated recombinant syndecan-1 cytoplasmic domains in vitro, and iv) expression of a syndecan-1 construct with its invariant 286Ser replaced with a Gly was not induced by TGFß. Together, these findings define a regulatory mechanism where TGFß signals through PKA to phosphorylate the syndecan-1 cytoplasmic domain and increases syndecan-1 expression on epithelial cells.
J. Biol. Chem, 10.1074/jbc.M509320200
Submitted on August 24, 2005
Revised on June 15, 2006
Accepted on June 28, 2006
Syndecan-1 expression in epithelial cells is induced by TGF
through a PKA-dependent pathway
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