Signal transduction mechanisms linking increased extracellular calcium to proliferation in ovarian surface epithelial...

Although ovarian surface epithelial (OSE) cells are the cell type responsible for malignant ovarian carcinoma, relatively little is known about either the extracellular stimuli or the intracellular signaling mechanisms responsible for regulating proliferation in these cells. We have demonstrated that OSE cells proliferate in response to elevation of extracellular calcium and that OSE cells express functional calcium-sensing receptors (CaR). Here we show that agonists of the CaR increase the kinase activity of Src and ERKs (extracellular signal-regulated kinases) in rat OSE cells and promote association between tyrosine-phosphorylated Shc and p120rasGAP. Expression of an interfering mutant CaR inhibited the proliferative response to elevated extracellular calcium, as well as CaR agonist-induced tyrosine phosphorylation and ERK activation. Transfection with dominant negative mutants of Ras, Raf, and MKK1 also inhibited the increase in ERK activity in response to calcium, as did treatment with herbimycin, a selective inhibitor for Src family kinases. These results indicate that the ability of OSE cells to proliferate in response to increases in extracellular calcium involves cross-talk between the G-protein-coupled CaR and the activation of a tyrosine kinase-dependent Ras-Raf-ERK signaling pathway.