PKCδ is necessary for Smad3 expression and transforming growth factor β-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)beta 1 regulates the synthesis of the extracellular matrix protein fibronectin (FN). Methods and Results-TGF beta 1 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 TGF beta 1-induced FN expression, whereas expression of Smad7 eliminated the TGF beta response. Because TGF beta activated PKC delta in SMCs, we tested the role of PKC delta in regulation of FN expression. Inhibition of PKC delta activity by rottlerin or dominant-negative adenovirus (AdPKC delta DN) blocked TGF beta 1's induction of FN, whereas overexpression of PKC delta enhanced TGF beta's effect. Moreover, aortic SMCs isolated from PKC delta(-/-) mice exhibited diminished FN induction in response to TGF beta. Furthermore, we found that Smad3 protein and mRNA were markedly reduced in AdPKC delta DN-treated A10 cells and in PKC delta null cells. Finally, restoring Smad3 in rottlerin-treated A10 and PKC delta null cells rescues the ability of TGF beta to upregulate FN protein and mRNA expression. Conclusion-Our data suggest that TGF beta-activated PKC delta is critical to maintain normal expression of Smad3, which in turn is required for the induction of fibronectin. PKC delta represents a promising target for treating the fibroproliferative response after arterial injury.