Pertussis toxin-sensitive Gi/o proteins are involved in nerve growth factor-induced pro-survival Akt signaling cascade in PC12 cells

In Gαz-deficient mice, survival of sympathetic neurons is significantly attenuated in the presence of pertussis toxin (PTX). This suggests that Gi/o proteins may have distinct roles in neuronal survival. Here, we investigated the possible involvement of Gi/o proteins in nerve growth factor (NGF)-induced pro-survival phosphatidylinositol-3-kinase (PI3K)/Akt signaling in rat pheochromocytoma PC12 cells. Treatment of PC12 cells with NGF increased the Akt phosphorylation level in a time- and dose-dependent manner. The NGF-dependent Akt activation was partially attenuated by PTX or overexpression of regulators of G protein signaling Z1 (RGSZ1) and Gα-interacting protein (GAIP)), indicating the participation of Gi/o proteins. In contrast, epidermal growth factor (EGF)-mediated Akt phosphorylation was unaffected by PTX or RGSZ1 and GAIP. Expression of PTX-resistant mutants of Gαi1, Gαi3, GαoA, and GαoB, but not Gαi2, abolished the inhibitory effect of PTX on NGF-induced Akt activation. The use of transducin as a Gβγ scavenger further revealed that Gβγ subunits rather than Gαi/o acted as the signal transducer. The activation profiles of Akt-regulated downstream effectors such as Bad, IKK, and nuclear factor-κB (NFκB) were also examined. NGF-stimulated phosphorylation of Bad and IKK and transcriptional activity of NFκB were indeed sensitive to treatments with PTX. This is the first study that demonstrates the involvement of Gi/o proteins in NGF-induced Akt signaling.