G-alpha subunit abundance and activity differentially regulate β-catenin signalling.

Heterotrimeric 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 β-catenin signaling. However, the link between G-proteins and β-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 β-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 β-catenin signaling agonist. The results show that PMT significantly enhanced LiCl-induced active β-catenin levels in HEK293T cells and mouse embryo fibroblasts. Evaluation of the effect of specific G-alpha proteins on the regulation of β-catenin showed that Gq/11 and G12/13 knockout cells had significantly higher levels of active and total β-catenin compared to wild-type cells. The stimulation of active β-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 β-catenin; however, PMT activated G-alpha subunits positively regulates LiCl-induced β-catenin expression, in a G12/13 -dependent manner. Hence G-alpha subunit regulation of β-catenin is context-dependent.