FIGURE 1.

The PI3K/Akt signaling pathway inhibits MST1 cleavage and MST1-induced cell death. A, MST1 cleavage was inhibited by IGF-1. HeLa cells were treated with STS (300 μm) for 1 h after exposure to IGF-1 (50 μm) or/and LY294002 (20 μm) for 30 min and then immunoblotted with indicated antibodies (bottom). Apoptosis was analyzed with annexin V labeling/fluorescence-activated cell sorting. The experiment was repeated three times in triplicate (top). B, activation of PI3K/Akt reduces MST1 cleavage and apoptosis. COS7 cells were transfected/treated with indicated plasmids and reagents. Immunoblot was detected with anti-FLAG antibody (top). The apoptosis was assessed as described in panel A. C, elevated level of pMST-Thr¹⁸³ in Akt1-deficient MEFs. Akt1-knockout MEFs were transfected with Akt1 or vector alone, treated with STS (300 μm) for 1 h, and then immunoblotted with indicated antibodies. D, knockdown of AKT2 induced pMST1-Thr¹⁸³. OVCAR8 cells were transfected with small interference RNA AKT2. After 72-h incubation, the cells were lysed and immunoblotted with indicated antibodies.