RGS4 controls Gαi3-mediated regulation of Bcl-2 phosphorylation on TGN38-containing intracellular membranes

Abstract

Intracellular pools of the heterotrimeric G-protein alpha-subunit, Gαi3, has been shown to promote growth factor signaling, while at the same time inhibiting the activation of JNK and autophagic signaling following nutrient starvation. The precise molecular mechanisms linking Gαi3 to both stress and growth factor signaling remain poorly understood. Importantly, JNK-mediated phosphorylation of Bcl-2 was shown to activate autophagic signaling following nutrient deprivation. Our data shows that activated Gαi3 decreases Bcl-2 phosphorylation, whereas biochemical inhibitors of Gαi3, such as RGS4 and AGS3, markedly increase the levels of phosphorylated Bcl-2. Manipulation of the palmitoylation status and intracellular localization of RGS4 suggests that Gαi3 modulates phosphorylated Bcl-2 levels and autophagic signaling from discreet TGN38-labelled vesicle pools. Consistent with an important role for these molecules in normal tissue responses to nutrient-deprivation, increased Gαi signaling within nutrient-starved adrenal glands from RGS4-KO mice resulted in a dramatic abrogation of autophagic flux, compared to wild type tissues. Together, these data suggest that the activity of Gαi3 and RGS4 from discreet TGN38-labelled vesicle pools are critical regulators of autophagic signaling via their ability to modulate phosphorylation of Bcl-2.