title: Constitutively active alpha subunits of G(q/11) and G(12/13) families inhibit activation of the pro-survival Akt signaling cascade.
abstract: Accumulating evidence indicates that G protein signaling plays an active role in the regulation of cell survival. Our previous study demonstrated the regulatory effects of G(i/o) proteins in nerve growth factor-induced activation of pro-survival Akt kinase. In the present study we explored the role of various members of the G(s), G(q/11) and G(12/13) subfamilies in the regulation of Akt in cultured mammalian cells. In human embryonic kidney 293 cells transiently expressing constitutively active mutants of G alpha11, G alpha14, G alpha16, G alpha12, or G alpha13 (G alpha11QL, G alpha14QL, G alpha16QL, G alpha12QL and G alpha13QL, respectively), basal phosphorylation of Akt was attenuated, as revealed by western blotting analysis using a phosphospecific anti-Akt immunoglobulin. In contrast, basal Akt phosphorylation was unaffected by the overexpression of a constitutively active G alpha(s) mutant (G alpha(s)QL). Additional experiments showed that G alpha11QL, G alpha14QL, G alpha16QL, G alpha12QL and G alpha13QL, but not G alpha(s)QL, attenuated phosphorylation of the Akt-regulated translation regulator tuberin. Moreover, they were able to inhibit the epidermal growth factor-induced Akt activation and tuberin phosphorylation. The inhibitory mechanism of Gq family members was independent of phospholipase Cbeta activation and calcium signaling because G alpha11QL, G alpha14QL and G alpha16QL remained capable of inhibiting epidermal growth factor-induced Akt activation in cells pretreated with U73122 and the intracellular calcium chelator, BAPTA/AM. Finally, overexpression of the dominant negative mutant of RhoA blocked G alpha12QL- and G alpha13QL-mediated inhibition, suggesting that activated G alpha12 and G alpha13 inhibit Akt signaling via RhoA. Collectively, this study demonstrated the inhibitory effect of activated G alpha11, G alpha14, G alpha16, G alpha12 and G alpha13 on pro-survival Akt signaling.
authors.affiliation: Department of Biochemistry, the Molecular Neuroscience Center, and the Biotechnology Research Institute, Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong, China.
authors.forename: Eddy H T
authors.initials: EH
authors.lastname: Wu
authors.forename: Becky H L
authors.initials: BH
authors.lastname: Tam
authors.forename: Yung H
authors.initials: YH
authors.lastname: Wong
mesh_terms: D002460:Cell Line; D002470:Cell Survival; D000242:Cyclic AMP / Q000378:metabolism; D004789:Enzyme Activation; D004791:Enzyme Inhibitors; D044365:GTP-Binding Protein alpha Subunits, G12-G13 / Q000378:metabolism*; D043802:GTP-Binding Protein alpha Subunits, Gq-G11 / Q000378:metabolism*; D006801:Humans; D007668:Kidney; D010766:Phosphorylation; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism*; D015398:Signal Transduction; D014162:Transfection
chemical_list: D004791:Enzyme Inhibitors; D000242:Cyclic AMP; D051057:Proto-Oncogene Proteins c-akt; D044365:GTP-Binding Protein alpha Subunits, G12-G13; D043802:GTP-Binding Protein alpha Subunits, Gq-G11