Apoptosis and tumorigenesis in human cholangiocarcinoma cells involvement of Fas/APO-1 (CD95) and calmodulin

We have previously demonstrated that tamoxifen inhibits the growth of human cholangiocarcinoma cells in culture and inhibits tumor growth when cells a re injected into nude mice. However, the mechanism of action of tamoxifen r emains unknown. Here we demonstrate that tamoxifen and trifluoperazine, bot h potent calmodulin antagonists, induce apoptosis in vitro, probably acting via the Fas system, in human cholangiocarcinoma cells. Human cholangiocarc inoma cell lines heterogeneously express Fas antigen on their surface. Fas- negative and Fas-positive surface-expressing cells were isolated, cloned, a nd cultured. Fas antibody, tamoxifen, and trifluoperazine induced dose-depe ndent apoptosis only in Fas-positive cells; Fas-negative cells were unaffec ted. Furthermore, apoptosis induced by tamoxifen in Fas-positive cells was blocked by an inhibitory Fas antibody. Tamoxifen was not acting through an anti-estrogenic mechanism, because neither Fas-negative nor Fas-positive ce lls expressed estrogen receptors and the pure anti-estrogen compound, ICI 1 82780, did not induce apoptosis in either cell line. Fas-negative cells, bu t not Fas-positive cells, were able to produce tumors when subcutaneously i njected into nude mice. These findings suggest Fas may be a candidate oncog ene involved in the pathogenesis of cholangiocarcinoma. Furthermore, the si milarity between the proapoptotic effects of tamoxifen and trifluoperazine support an underlying molecular mechanism for Fas-mediated apoptosis that i nvolves calmodulin.