Endothelin-1 enhances proliferation of lung cancer cells by increasing intracellular free Ca2+

Endothelin-1 (ET-1), the most potent vasoconstrictor, has been shown to be mitogenic in many tumor cells as well as in vascular cells. It was previously reported that the mRNA of ET-1 and endothelin receptors (ETRs) are expressed in lung cancer cells. However, their biological role in lung cancer remains to be explored. The purpose of this study was to determine whether ET-1 stimulates proliferation of the human lung adenocarcinoma cell SPC-A1 and probe its cellular mechanism. Reverse-transcription polymerase chain reaction and Western blot analysis showed that both the mRNA and protein of ET-1, ET A R and ET B R are expressed in SPC-A1 cells. Application of ET-1 at 10(-15)-10(-8) M caused a dose-dependent cell proliferation and an increase in intracellular free Ca2+ concentration ([Ca2+]i). This ET-1-induced cell proliferation and [Ca2+]i increase were completely abolished by BQ123, a selective ET A R antagonist, but not by BQ788, a selective ET B R antagonist. Furthermore, it was significantly reduced by U73122, a specific inhibitor of phospholipase C (PLC), but not by U73433, the structural isomer of U73122. Chelating extracellular Ca2+ or blocking voltage dependent calcium channels by nifedipine also significantly reduced the mitogenic effect of ET-1 and [Ca2+]i increase in SPC-A1 cells. These results indicate that ET-1 acts as an autocrine growth factor and enhances proliferation of SPC-A1 cells via activation of ET A R. The phosphoinositol/Ca2+ pathway and Ca2+ influx through voltage dependent Ca2+ channels activated by ET A R contribute to this process.