Inhibition of gamma ray-induced apoptosis by stimulatory heterotrimeric GTP binding protein involves Bcl-xL down-regulation in SH-SY5Y human neuroblastoma cells.
Heterotrimeric GTP-binding proteins (G proteins) transduce extracellular signals into intracellular signals by activating effector molecules including adenylate cyclases that catalyze cAMP formation, and thus regulate various cellular responses such as metabolism, proliferation, and apoptosis. cAMP signaling pathways have been reported to protect cells from ionizing radiation-induced apoptosis, but however, the protective mechanism is not clear. Therefore, this study aimed to investigate the signaling molecules and the mechanism mediating the anti-apoptotic action of cAMP signaling system in radiation-induced apoptosis. Stable expression of a constitutively active mutant of Gas (GalphasQL) protected gamma ray-induced apoptosis which was assessed by analysis of the cleavages of PARP, caspase-9, and caspase-3 and cytochrome C release in SH-SY5Y human neuroblastoma cells. GasQL repressed the gamma ray-induced down-regulation of Bcl-xL protein, but transfection of Bcl-xL siRNA increased the gamma ray-induced apoptosis and abolished the anti-apoptotic effect of GasQL. GasQL decreased the degradation rate of Bcl-xL protein, and it also restrained the decrease in Bcl-xL mRNA by increasing the stability following ionizing irradiation. Furthermore, prostaglandin E2 that activates Gas was found to protect gamma ray-induced apoptosis, and the protective effect was abolished by treatment with prostanoid receptor antagonist specific to EP2/4R subtype. Moreover, specific agonists for adenosine A1 receptor that inhibits cAMP signaling pathway augmented gamma ray-induced apoptosis. From this study, it is concluded that Galphas-cAMP signaling system can protect SH-SY5Y cells from gamma ray-induced apoptosis partly by restraining down-regulation of Bcl-xL expression, suggesting that radiation-induced apoptosis can be modulated by GPCR ligands to improve the efficiency of radiation therapy.
Department of Biochemistry and Molecular Biology, Cancer Research Institute, Seoul National University, College of Medicine, Seoul 110-799, Korea.
So Young
SY
Kim
Miran
M
Seo
Jung Min
JM
Oh
Eun Ah
EA
Cho
Yong Sung
YS
Juhnn
D017209:Apoptosis / Q000502:physiology* / Q000528:radiation effects*; D001483:Base Sequence; D045744:Cell Line, Tumor; D000242:Cyclic AMP / Q000378:metabolism; D017931:DNA Primers / Q000235:genetics; D015536:Down-Regulation / Q000528:radiation effects; D019205:GTP-Binding Protein alpha Subunits, Gs / Q000378:metabolism*; D005720:Gamma Rays; D006801:Humans; D009447:Neuroblastoma / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D034741:RNA, Small Interfering / Q000235:genetics; D015398:Signal Transduction; D051020:bcl-X Protein / Q000235:genetics / Q000378:metabolism*
C494811:BCL2L1 protein, human; D017931:DNA Primers; D034741:RNA, Small Interfering; D051020:bcl-X Protein; D000242:Cyclic AMP; D019205:GTP-Binding Protein alpha Subunits, Gs