(A) The effect of transiently transfected MST1 on cell death. HEK-293 cells were transfected with empty FLAG vector or FLAG-MST1 vector. The cells were incubated for 36 h, and then cisplatin was added. After another 6 h of incubation, the cells were collected and analyzed for apoptosis by Annexin-V/PI. Cell lysates were subjected to immunoblot analysis with anti-FLAG antibody and with anti-β-actin as a loading control (bottom). (B) The effect of transient transfection with hWW45 on cell death. HEK-293 cells were transfected with empty HA vector or vector encoding HA-hWW45. After incubation, the cells were collected and analyzed for apoptosis as in A. (C) The effect of hWW45 over-expression on apoptosis induced by MST1. HEK-293 cells were transfected with plasmids encoding hWW45 and/or MST1 in the amounts indicated. After incubation, the cells were collected and analyzed for apoptosis as in A. The protein levels in the HEK-293 cells after transfection are shown at the bottom. (D) The effect of knocking down endogenous hWW45 via small interfering RNAs (siRNAs) on MST1-induced apoptosis. HEK-293 cells were transfected with siRNA duplexes capable of targeting the hWW45 and/or FLAG-MST1 plasmids, in the amounts indicated. After incubation, the cells were collected and analyzed for apoptosis as in A. Immunoblots for hWW45 and MST1 expression are shown at the bottom. *, p < 0.05. All data are expressed as means ± SEM.