Kim So Young, Seo Miran, Oh Jung Min, Cho Eun Ah, Juhnn Yong Sung
Department of Biochemistry and Molecular Biology, Cancer Research Institute, Seoul National University, College of Medicine, Seoul 110-799, Korea.
Exp Mol Med. 2007 Oct 31;39(5):583-93. doi: 10.1038/emm.2007.64.
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.
异源三聚体GTP结合蛋白（G蛋白）通过激活包括催化cAMP形成的腺苷酸环化酶在内的效应分子，将细胞外信号转导为细胞内信号，从而调节各种细胞反应，如代谢、增殖和凋亡。据报道，cAMP信号通路可保护细胞免受电离辐射诱导的凋亡，但其保护机制尚不清楚。因此，本研究旨在探讨介导cAMP信号系统在辐射诱导凋亡中抗凋亡作用的信号分子和机制。持续激活的Gas突变体（GalphasQL）的稳定表达可保护γ射线诱导的凋亡，这通过分析PARP、caspase-9和caspase-3的裂解以及SH-SY5Y人神经母细胞瘤细胞中细胞色素C的释放来评估。GasQL抑制γ射线诱导的Bcl-xL蛋白下调，但转染Bcl-xL siRNA可增加γ射线诱导的凋亡并消除GasQL的抗凋亡作用。GasQL降低了Bcl-xL蛋白的降解率，并且通过增加电离辐射后的稳定性，还抑制了Bcl-xL mRNA的减少。此外，发现激活Gas的前列腺素E2可保护γ射线诱导的凋亡，而EP2/4R亚型特异性前列腺素受体拮抗剂处理可消除这种保护作用。此外，抑制cAMP信号通路的腺苷A1受体特异性激动剂可增强γ射线诱导的凋亡。从本研究得出结论，Galphas-cAMP信号系统可部分通过抑制Bcl-xL表达的下调来保护SH-SY5Y细胞免受γ射线诱导的凋亡，这表明辐射诱导的凋亡可通过GPCR配体进行调节，以提高放射治疗的效率。
