Triptolide (TPL) has been shown to inhibit cell proliferation and induce apoptosis in various human
cancer cells; however, the precise mechanism of apoptosis induced by TPL in human
melanoma cells has not yet been elucidated. In this study, we investigated the precise mechanism underlying cytocidal effects of TPL on human
melanoma cells. Treatment of human
melanoma cells with TPL significantly inhibited cell growth and induced apoptosis, as evidenced by flow cytometry and
annexin V-
fluorescein isothiocyanate analyses. TPL increased the levels of Fas and Fas-associated death domain (FADD) and induced cleavage of Bid by activation of
caspase-8 and
cytochrome c release from mitochondria to the cytosol, which resulted in activation of
caspase-9 and
caspase-3. Moreover, TPL-induced apoptosis in SK-MEL-2 cells was mediated through dephosphorylation of
focal adhesion kinase (FAK) and its cleavage by caspase-8-mediated
caspase-3 activation via upregulation of Fas expression. We also found that TPL mediated the dissociation of
receptor-interacting protein (RIP) from FAK and enhanced the formation of RIP/Fas complex formation initiating cell death. In conclusion, our data firstly demonstrated that TPL induces apoptosis by both extrinsic and intrinsic apoptosis pathways in human
melanoma cells and identified that RIP shuttles between Fas and FAK to mediate apoptosis.