MAP KINASE MEDIATES EPIDERMAL GROWTH FACTOR-AND PHORBOL ESTER-INDUCEDPROSTACYCLIN FORMATION IN CARDIOMYOCYTES

We studied the role of protein kinase C (PKC) and mitogen-activated pr otein kinase (MAPK) in epidermal growth factor (EGF)-induced prostacyc lin (PGI(2)) production in cultured, spontaneously-beating neonatal ve ntricular rat cardiomyocytes. To this purpose, the effect of EGF on ca rdiomyocyte MAPK phosphorylation, MAPK activity and PGI(2)-production were investigated, and compared to those induced by the PKC activator 4 beta phorbol 12-myristate 13-acetate (PMA). Both EGF (0.1 mu M) and PMA (0.1 mu M) induced the rapid and reversible phosphorylation of 42 KDa-MAPK in ventricular cardiomyocytes, responses that were accompanie d by transient increases in MAPK activity (190-230% of control values within 5 min), and two-to three-fold increases in PGI(2) formation. Th e tyrosine kinase inhibitors lavendustin (1 mu M) and genistein (10 mu M) strongly inhibited EGF-induced MAPK activation and PGI(2)-formatio n, but had no effect on PMA-stimulated responses. Experiments with the PKC inhibitor CGP 41251 (1 mu M) or with PKC-downregulated cells demo nstrated that in contrast to the PMA-stimulated responses, EGF-induced MAPK activation and PGI(2)-production were PKC-independent processes. Investigating the role of MAPK in EGF-and in PMA-promoted PGI(2)-form ation, we found that the MAPK-inhibitor 6-thioguanine (500 mu M), as w ell as the MAPK-kinase-inhibitor PD98059 (50 mu M) abolished both EGF- and PMA-stimulated PGI(2)-production in cardiomyocytes. Our results i ndicate that MAPK-activation is at the basis of both growth factor rec eptor and PKC-dependent eicosanoid-formation in ventricular cardiomyoc ytes, where EGF-induced prostaglandin-production takes place via a PKC -independent pathway. (C) 1998 Academic Press Limited.