Transactivation of the epidermal growth factor receptor in endothelin-1-induced mitogenic signaling in human ovarian carcinoma cells

Endothelin (ET)-1 is produced in ovarian carcinoma cells and is known to ac t through ETA receptors as an autocrine growth factor in vitro and in vivo. In OVCA 433 human ovarian carcinoma cells, ET-1 caused phosphorylation of the epidermal growth factor receptor (EGF-R) that was accompanied by phosph orylation of Shc and its recruitment complexed with Grb2. These findings su ggested that an EGF-R/ras-dependent pathway may contribute to the activatio n of mitogen-activated protein kinase (MAPK)/extracellular signal-regulated kinase (Erk) 2 and mitogenic signaling induced by ET-1 in these cells. Spe cific inhibition of EGF-R kinase activity by tyrphostin AG1478 prevented ET -1-induced transactivation of the EGF-R, as well as Shc phosphorylation and recruitment with Grb2. Furthermore, ET-1-induced activation of Erk 2 was p artially inhibited by tyrphostin AG1478. In accord with this finding, the m itogenic action of ET-1 in OVCA 433 cells was also significantly reduced by a concentration of tyrphostin AG1478 that abolished the growth response of EGF-stimulated cells. Inhibition of protein kinase C activity, which contr ibutes to the proliferative action of ET-1 in OVCA 433 cells, had no effect on the activation of Erk 2 by ET-1, which suggests that this effect of pro tein kinase C does not involve ras-independent activation of Erk 2. Inhibit ion by wortmannin of PI3-kinase activity, which has been implicated in ET-1 and other G protein-coupled receptor (GPCR)-mediated signaling pathways, r educed Erk 2 activation by ET-1 but had no effect on ET-1-induced EGF-R and Shc phosphorylation. These findings indicate that ET-1-induced stimulation of Erk 2 phosphorylation, and mitogenic responses in OVCA 433 ovarian canc er cells are mediated in part by signaling pathways that are initiated by t ransactivation of the EGF-R.