Heterotrimeric stimulatory
GTP-binding protein (G(s)) stimulates adenylate cyclases to activate the cAMP signaling pathway. Although the cAMP 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 alpha subunit of G(s) (Galpha(s)) in the ROS-induced apoptosis of
cancer cells. The stable expression of constitutively active Galpha(s) (Galpha(s)QL) 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 Galpha(s)QL, but Bak
small interfering RNA decreased
hydrogen peroxide-induced apoptosis. Galpha(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-kappaB, and NFAT. Moreover, Galpha(s) also inhibited the
hydrogen peroxide-induced binding of AP1,
NF-kappaB, and NFAT to the Bak promoter. Furthermore,
hydrogen peroxide-induced apoptosis was reduced by treating cells with
prostaglandin E(2), which activates Galpha(s), but this was augmented by CCPA, which activates Galpha(i) causing a decrease in cAMP levels. From the results, we conclude that Galpha(s) protects
neuroblastoma cells from
hydrogen peroxide-induced apoptosis by repressing Bak induction, which is mediated by the inhibition of the
hydrogen peroxide-induced activations of AP1,
NF-kappaB, and NFAT through cAMP-PKA-CREB signaling system.