Stimulatory heterotrimeric GTP-binding protein inhibits hydrogen peroxide-induced apoptosis by repressing BAK induction in SH-SY5Y human neuroblastoma cells

Heterotrimeric stimulatory GTP-binding protein (G_s) stimulates adenylate cyclases to activate the cAMP signaling pathway. Although thec AMP pathway has been reported to be involved in apoptosis, the role of the G _s-cAMP signaling pathway during reactive oxygen species (ROS)-mediated apoptosis, which is involved in the resistance of cancer cells to chemotherapy and radiation, is not clearly understood. Thus, in this study we aimed to investigate the role of the α subunit of Gs (Gα _s) in the ROS-induced apoptosis of cancer cells. The stable expression of constitutively active Gα_s (Gα _sQL) inhibited the hydrogen peroxide-induced apoptosis of SH-SY5Y human neuroblastoma cells and reduced the hydrogen peroxide-induced increase in Bak and the decrease in Bcl-x_L protein expression. Exogenous Bak expression abolished these inhibitory effects of Gα_sQL, but Bak small interfering RNA decreased hydrogen peroxide-induced apoptosis. Gα_s repressed hydrogen peroxide-induced Bak expression by inhibiting the transcription of Bak mRNA, which resulted from the inhibition of the hydrogen peroxide-induced activation of transcription factors such as AP1, NF-κB, and NFAT. Moreover, Gα_s also inhibited the hydrogen peroxide-induced binding of AP1, NF-κB, and NFAT to the Bak promoter. Furthermore, hydrogen peroxide-induced apoptosis was reduced by treating cells with prostaglandin E₂, which activates Gα_s, but this was augmented by CCPA, which activates Gα_i causing a decrease in cAMP levels. From the results, we conclude that Gα_s protects neuroblastoma cells from hydrogen peroxide-induced apoptosis by repressing Bak induction, which is mediated by the inhibition of the hydrogenperoxide-induced activations of AP1, NF-κB, and NFAT through cAMP-PKA-CREB signaling system.