INVOLVEMENT OF PROTEIN-KINASE-C AND CA2-II-INDUCED MITOGENESIS OF CARDIAC FIBROBLASTS( IN ANGIOTENSIN)

Angiotensin (ANG) II has been previously shown to stimulate proliferat ion of neonatal rat cardiac fibroblasts via AT(1) receptors. Here we c onducted studies to assess involvement in this process of two second m essengers linked to AT(1) receptors, protein kinase C (PKC) and Ca2+. Several findings argue against a dominant role for PKC in ANG II-induc ed mitogenesis: 1) [Sar(1)]ANG II, which produced a modest, transient increase in PKC activity, was equally effective in inducing thymidine incorporation into DNA in PKC-depleted cells, whereas the effect of pl atelet-derived growth factor (PDGF)-BB on thymidine incorporation was reduced to the level observed with [Sar(1)]ANG II; 2) phorbol 12-myris tate 13-acetate (PMA), a potent PKC stimulator, was ineffective in sti mulating thymidine incorporation; and 3) PKC downregulation or the hig hly specific PKC inhibitor, compound 3, eliminated PMA-induced mitogen -activated protein (MAP) kinase activity but did not affect comparable increases induced by [Sar(1)]ANG II or PDGF-EE. Increased intracellul ar Ca2+ may be sufficient to account for [Sar(1)]ANG II-induced MAP ki nase activity because ionomycin also increased MAP kinase activity and chelation of intracellular Ca2+ eliminated [Sar(1)]ANG II-induced act ivity in PKC-depleted fibroblasts. However, Ca2+ chelation did not pre vent [Sar(1)]ANG II-induced MAP kinase activity in non-PKC-depleted fi broblasts. Thus ANG II can activate MAP kinases in cardiac fibroblasts by either Ca2+- or PKC-dependent pathways, and whereas the full effec t of PDGF-BB on thymidine incorporation and cell proliferation require s a phorbol ester-sensitive PKC, the hyperplastic growth effect of ANG II does not.