G-Alpha Subunit Abundance and Activity Differentially Regulate β -Catenin Signaling

Abstract

ABSTRACTHeterotrimeric G proteins are signal transduction proteins involved in regulating numerous signaling events. In particular, previous studies have demonstrated a role for G-proteins in regulating ?-catenin signaling. However, the link between G-proteins and ?-catenin signaling is controversial and appears to depend on G-protein specificity. We describe a detailed analysis of a link between specific G-alpha subunits and ?-catenin using G-alpha subunit genetic knockout and knockdown approaches. The Pasteurella multocida toxin was utilized as a unique tool to activate G-proteins, with LiCl treatment serving as a ?-catenin signaling agonist. The results show that Pasteurella multocida toxin (PMT) significantly enhanced LiCl-induced active ?-catenin levels in HEK293T cells and mouse embryo fibroblasts. Evaluation of the effect of specific G-alpha proteins on the regulation of ?-catenin showed that Gq/11 and G12/13 knockout cells had significantly higher levels of active and total ?-catenin than wild-type cells. The stimulation of active ?-catenin by PMT and LiCl was lost upon both constitutive and transient knockdown of G12 and G13 but not Gq. Based on our results, we conclude that endogenous G-alpha proteins are negative regulators of active ?-catenin; however, PMT-activated G-alpha subunits positively regulate LiCl-induced ?-catenin expression in a G12/13-dependent manner. Hence, G-alpha subunit regulation of ?-catenin is context dependent.