Constitutively active α 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 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.

Gq Protein-induced Apoptosis Is Mediated by AKT Kinase Inhibition That Leads to Protein Kinase C-induced c-Jun N-terminal Kinase Activation

“…Interestingly, although this pathway seems to be activated by most G q PCRs (11), some reports showed that activation of certain G q proteins actually reduces AKT activation. These include a GnRH receptor that counteracts IGF-1 in ␣T3-1 cells (23), a m1 muscarinic receptor that counteracts insulin in HeLa cells (24), and constitutively active G q that counteracts EGF in HEK293 cells (25). However, the mechanism of G q PCRs effect on growth factor-induced AKT activation is not fully elucidated.…”

Tuberin: A Stimulus-Regulated Tumor Suppressor Protein Controlled by a Diverse Array of Receptor Tyrosine Kinases and G Protein-Coupled Receptors

“…Likewise, luteinizing hormone-releasing hormone receptor strongly diminishes the anti-apoptotic effect of IGF-1 through inhibition of Akt activation. Our recent experimental results also demonstrated that other activated ␣ subunits of the G q family (G ␣ 11 , G ␣ 14 , and G ␣ 16 ) can attenuate basal and EGF-induced Akt activities and the phosphorylation of tuberin in a PLC ␤ -and Ca 2+ mobilization-independent manner [109] . In agreement, a number of recent studies have shown that the pro-apoptotic effect of G q/11 is neither dependent on PLC ␤ activity [110] nor on the elevation of intracellular calcium [111] .…”

“…Some of our current experimental data demonstrated that activated G 12 and G 13 are able to inhibit Akt and tuberin phosphorylation via RhoA [109] . Overexpression of the constitutively active G ␣ 12 and G ␣ 13 (G ␣ 12 QL and G ␣ 13 QL) is apparently sufficient to inhibit the EGF-induced Akt activation and tuberin phosphorylation in human embryonic kidney (HEK293) cells.…”

The T393C polymorphism in the gene GNAS1 of G protein is associated with survival of patients with invasive breast carcinoma

“…The gene GNAS1 encodes the ubiquitously expressed G(alpha)s (Gas) subunit of heterotrimeric G proteins. In vitro experiments suggest, that increased expression of Gas is associated with enhanced apoptosis and that the second messenger, cyclic AMP (cAMP), which functions downstream the G proteins, plays a major role in pro-apoptotic processes [5][6][7][8][9]. We have recently shown that genotypes of the common T393C single nucleotide polymorphism (SNP) of the GNAS1 gene are significantly associated with the clinical outcome of patients suffering from bladder cancer [10], colorectal cancer [11], clear cell renal cell carcinoma [12], and B-cell chronic lymphocytic leukaemia [13].…”