PKCdelta is necessary for Smad3 expression and transforming growth factor beta-induced fibronectin synthesis in vascular smooth muscle cells.

OBJECTIVE: The purpose of these studies is to investigate the mechanism by which transforming growth factor (TGF)beta1 regulates the synthesis of the extracellular matrix protein fibronectin (FN). METHODS AND
RESULTS: TGFbeta1 elicited a time-dependent induction of FN protein and mRNA in A10 rat aortic smooth muscle cells (SMCs). Ectopic expression of Smad3 in A10 cells stimulated both basal and TGFbeta1-induced FN expression, whereas expression of Smad7 eliminated the TGFbeta response. Because TGFbeta activated PKCdelta in SMCs, we tested the role of PKCdelta in regulation of FN expression. Inhibition of PKCdelta activity by rottlerin or dominant-negative adenovirus (AdPKCdelta DN) blocked TGFbeta1's induction of FN, whereas overexpression of PKCdelta enhanced TGFbeta's effect. Moreover, aortic SMCs isolated from PKCdelta(-/-) mice exhibited diminished FN induction in response to TGFbeta. Furthermore, we found that Smad3 protein and mRNA were markedly reduced in AdPKCdelta DN-treated A10 cells and in PKCdelta null cells. Finally, restoring Smad3 in rottlerin-treated A10 and PKCdelta null cells rescues the ability of TGFbeta to upregulate FN protein and mRNA expression.
CONCLUSIONS: Our data suggest that TGFbeta-activated PKCdelta is critical to maintain normal expression of Smad3, which in turn is required for the induction of fibronectin. PKCdelta represents a promising target for treating the fibroproliferative response after arterial injury.