Opposing effects of delta- and zeta-protein kinase C isozymes on cardiac fibroblast proliferation: use of isozyme-selective inhibitors.

Neonatal primary cardiac fibroblasts in defined medium continue to proliferate. Here, we show that phorbol ester inhibited and transforming growth factor-beta1 (TGFbeta1) stimulated this fibroblast proliferation. Cardiac fibroblasts contain six protein kinase C (PKC) isozymes: alpha-, delta-, epsilon-, betaI-, betaII-, and zeta-PKC. To evaluate the effect of different PKC isozymes on the proliferation of these cells, we used isozyme-selective PKC inhibitors. Inhibition of endogenous delta-PKC with deltaV1-1, an isozyme-selective translocation inhibitor, resulted in increased basal thymidine incorporation by 58 +/- 12% of control cells, but did not affect TGFbeta1-induced cell growth. Inhibition of endogenous zeta-PKC in neonatal rat cardiac fibroblasts with zeta-pseudosubstrate, a selective inhibitor for the atypical PKC isozymes, revealed an opposite effect; this inhibitor reduced basal growth to 45 +/- 11% and TGFbeta1-induced growth to 61 +/- 10%. Other isozyme-specific inhibitors used in this study did not alter basal or TGFbeta1-stimulated fibroblast growth. Taken together, our data provide evidence that delta-PKC inhibits and zeta-PKC stimulates proliferation of neonatal rat cardiac fibroblasts.