Stimulatory heterotrimeric GTP-binding protein inhibits gamma ray-induced apoptosis in SH-SY5Y human neuroblastoma cells Free

LB-39

Heterotrimeric GTP-binding proteins (G proteins) transduce extracellular signals into intracellular signals by activating effector molecules including adeylatate cyclase and phospholipase C beta, and thus regulate various cellular responses such as metabolism, proliferation, and apoptosis. However, it is unknown how G prtoeins signaling pathways regulates ionizing radiation-induced apoptosis in cancer cells. Therefore, in thisstudy we have investigated the effects of stimulatory G protein signaling on gamma ray-induced apoptosis of SH-SY5Y human neuroblastoma cells. The expression of a constitutively active mutant of stimulatory G protein alpha subunit (GαsQL) in SH-SY5Y cells protected gamma ray-induced apoptosis when the cleavage of PARP and caspase-9,-3, and cytochrome c release were analyzed. Expression of GαsQL repressed the decrease in Bcl-xL protein and the increase in Bak protein caused bygamma ray irradiation, compared with vector-transfected control. The transfection of Bcl-xL siRNA or transient expression of Bak abolished the protective effect of GαsQL against gamma ray-induced apoptosis. GαsQL increased the gamma ray-induced Bcl-xL expression by inducing transcription of Bcl-xL gene. Furthermore, we have shown that ionizing irradiation-induced apoptosis was reduced by treatment with prostaglandin E2 (PGE2) that activates Gαs. The protective effect of PGE2 was abolished by treatment with specific EP2/4R antagonist or A1R agonist. From this study, we concluded that Gαs signaling pathway can protect SH-SY5Y cells against gamma ray-induced apoptosis by inducing Bcl-xL expression and repressing Bak expression in SH-SY5Y neuroblastoma cells, implying that modulation of G protein signaling activity might enhance the cancer cell killing effects of radiation therapy.