Constitutively active α subunits of Gq/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 Gi/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 Gs, Gq/11 and G12/13 subfamilies in the regulation of Akt in cultured mammalian cells. In human embryonic kidney 293 cells transiently expressing constitutively active mutants of Gα11, Gα14, Gα16, Gα12, or Gα13 (Gα11QL, Gα14QL, Gα16QL, Gα12QL and Gα13QL, 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 Gαs mutant (GαsQL). Additional experiments showed that Gα11QL, Gα14QL, Gα16QL, Gα12QL and Gα13QL, but not GαsQL, 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 Cβ activation and calcium signaling because Gα11QL, Gα14QL and Gα16QL 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 Gα12QL- and Gα13QL-mediated inhibition, suggesting that activated Gα12 and Gα13 inhibit Akt signaling via RhoA. Collectively, this study demonstrated the inhibitory effect of activated Gα11, Gα14, Gα16, Gα12 and Gα13 on pro-survival Akt signaling. © 2006 The Authors.