AKT is translocated to the mitochondria during etoposide-induced apoptosis of HeLa cells

Abstract

Akt, or protein kinase B, is a key serine-threonine kinase, which exerts anti-apoptotic effects and promotes cell proliferation in response to various stimuli. Recently, however, it was demonstrated that Akt exhibits a proapoptotic role in certain contexts. During etoposide-induced apoptosis of He La cells, Akt enhances the interaction of second mitochondria-derived activator of caspases/direct IAP binding protein with low pI (Smac/DIABLO) and X-linked inhibitor of apoptosis protein by phosphorylating Smac at serine 67, and thus promotes apoptosis. However, the detailed mechanisms underlying Akt regulation in etoposide-mediated apoptosis remain to be determined. The present study investigated whether etoposide triggers the translocation of Akt into the mitochondria. It was found that Akt activity was increased and sustained during apoptosis triggered by etoposide in He La cells. During apoptosis, Akt was translocated from the cytoplasm into the mitochondria in a phosphoinositide 3-kinase-dependent manner at the early and late stages of apoptosis. Concomitantly, the depletion of Akt in the nuclear fraction was observed after etoposide treatment from analysis of confocal microscopy. The results suggest that etoposide-stimulated Akt is translocated into the mitochondria, thereby possibly enhancing its interaction with Smac and promoting apoptosis in He La cells. These results indicate that Akt may be a promising candidate for a pro-apoptotic approach in cancer treatment.