Hypertrophic responses of cardiomyocytes induced by endothelin-1 through the protein kinase C-dependent but Src and Ras-independent pathways

We have previously shown that endothelin-1 (ET-1) modulates mechanical stre tch-induced hypertrophic responses such as extracellular signal-regulated p rotein kinase (ERK) activation in cardiac myocytes. This study was undertak en to elucidate the ET-1 evoked signal transduction pathways leading to ERK activation. ET-1 was added to cultured cardiac myocytes of neonatal rats w ith or without a variety of inhibitors. ET-1 activated ERKs, which were fol lowed by an increase in protein synthesis, and inhibition of protein kinase C activities by calphostin C completely suppressed the ET-1-induced ERK ac tivation. We next examined whether tyrosine kinases or Ras are involved in ET-1-induced signaling pathways in cardiomyocytes. Pretreatment with a rece ptor tyrosine kinase inhibitor did not attenuate ET-1-induced activation of ERKs, Also, co-transfection of the dominant-negative mutant of Ras or acti ve mutant of C-terminal Src kinase, a tyrosine kinase which inhibits Src fa mily tyrosine kinases, with hemagglutinin-tagged ERK2 had no effects on ET- 1-induced ERK2 activation. On the other hand, blockade of Raf-1 kinase func tion by overexpression of the dominant-negative mutant of Raf-1 kinase comp letely inhibited ET-1-induced ERK2 activation. These results suggest that p rotein kinase C and Raf-1 kinase, but not Src or Ras, are critical to ET-1- induced ERK activation in cardiac myocytes.