ENDOTHELIN-1-INDUCED MITOGENIC RESPONSES OF CHINESE-HAMSTER OVARY CELLS EXPRESSING HUMAN ENDOTHELIN(A) - THE ROLE OF A WORTMANNIN-SENSITIVESIGNALING PATHWAY

In the current study, endothelin-l (ET-I) worked as a mitogen on Chine se hamster ovary cells stably expressing human endothelin,; when appli ed to serum-deprived cells, ET-I caused dose-dependent increases in [H -3]thymidine incorporation and cell proliferation. No synergism was ob served between the effect of ET-1 and that of insulin-like growth fact or-1/basic fibroblast growth factor. Both the inhibition of intracellu lar Ca2+ response by phospholipase C inhibitor U73122 and the downregu lation of protein kinase C (PKC) by pretreatment with phorbol 12-myris tate-13-acetate (PMA) partially blocked the ET-l-induced mitogenic res ponses. Wortmannin, a phosphatidylinositol-3-kinase inhibitor, caused dose-dependent inhibition of the ET-l-induced mitogenic responses in b oth PMA-treated and -untreated cells. Wortmannin also inhibited ET-1-i nduced increase in phosphatidylinositol trisphosphate formation and ac tivation of mitogen-activated protein kinase (MAPK), whereas it failed to inhibit PMA-induced activation of MAPK. In accordance with its eff ect on MAPK activation, wortmannin inhibited ET-I-induced activation o f Raf-B, whereas it failed to inhibit the effect of PMA. These results suggested the role of a Ca2+/PKC-independent, wortmannin-sensitive si gnaling pathway that linked ET(A) and MAPK cascade in the mitogenic si gnaling activated by ET(A).