Constitutively active α subunits of G q/11 and G 12/13 families inhibit activation of the pro‐survival Akt signaling cascade

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 Gα 11 , Gα 14 , Gα 16 , Gα 12 , or Gα 13 (Gα 11 QL, Gα 14 QL, Gα 16 QL, Gα 12 QL and Gα 13 QL, 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 Gα s mutant (Gα s QL). Additional experiments showed that Gα 11 QL, Gα 14 QL, Gα 16 QL, Gα 12 QL and Gα 13 QL, but not Gα 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 G q family members was independent of phospholipase Cβ activation and calcium signaling because Gα 11 QL, Gα 14 QL and Gα 16 QL 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 Gα 12 QL‐ and Gα 13 QL‐mediated inhibition, suggesting that activated Gα 12 and Gα 13 inhibit Akt signaling via RhoA. Collectively, this study demonstrated the inhibitory effect of activated Gα 11 , Gα 14 , Gα 16 , Gα 12 and Gα 13 on pro‐survival Akt signaling.