GSK3 promotes arsenite-induced apoptosis via facilitation of mitochondria disruption

Arsenic is an environmental toxicant that recently has been shown to have anticancer activity against a number of types of cancer cells by inducing apoptosis. Glycogen synthase kinase-3 (GSK3), a serine/threonine kinase, is an important pro-apoptotic signaling enzyme. Although GSK3 has been shown to promote apoptosis caused by a wide variety of insults, a role for GSK3 in arsenic-induced apoptosis has not yet been identified. Investigation of the involvement of GSK3 in arsenite-induced apoptosis demonstrated that arsenite induced apoptosis in SH-SY5Y human neuroblastoma cells, activating the executioner caspase-3 which caused cleavage of poly-ADP ribose-polymerase (PARP). Two selective GSK3 inhibitors, lithium and SB216763, attenuated caspase-3 activation and PARP cleavage induced by arsenite treatment indicating that GSK3 contributed to arsenite-induced apoptosis. Apoptotic signaling following exposure to arsenite involved cytochrome C release from mitochondria, and this was reduced by inhibition of GSK3 indicating that GSK3 promotes arsenite-induced apoptotic signaling upstream of mitochondrial disruption. Moreover, arsenite induced the translocation of Bax and p53 to the mitochondria and the activation-associated oligomerization of Bax, and these crucial events were reduced by inhibition of GSK3, indicating that GSK3 promotes arsenite-induced apoptosis by facilitating signals leading to mitochondrial apoptotic events. Taken together, the findings from this study reveal that GSK3 promotes arsenite-induced apoptosis by facilitating signaling leading to disruption of mitochondria.