Regulation of GSK-3beta and beta-Catenin by Galphaq in HEK293T cells.

Recent studies have shown that heterotrimeric G proteins are involved in the regulation of the canonical Wnt/beta-Catenin pathway. However, the mechanism(s) behind this involvement is (are) poorly understood. Our previous results have shown that activation of Galphaq in Xenopus oocytes leads to inhibition of GSK-3beta and stabilization of the beta-Catenin protein, suggesting that Galphaq might stabilize beta-Catenin via inhibition of GSK-3beta. In this study, we have observed similar results in HEK293T cells. In these cells optimal activation of endogenous Galphaq by expressing M3-muscarinic acetylcholine receptor (with or without carbachol treatment), or exposing the cells to thrombin led to an increase of 2 to 3-fold in endogenous cytoplasmic beta-Catenin protein levels. In addition, expression of the activated mutant of Galphaq (GalphaqQL) dramatically enhanced accumulation of exogenous beta-Catenin with no effect on beta-catenin (CTNNB1) gene transcription. The Galphaq-mediated cellular accumulation of beta-Catenin was blocked by expression of a minigene encoding a Galphaq specific inhibitory peptide but not by a minigene encoding a Galphas blocking peptide. Also, expression of GalphaqQL led to a significant reduction in GSK-3beta kinase activity, supporting the idea that the positive role of Galphaq signaling in inducing cellular accumulation of beta-Catenin is mediated through inhibition of GSK-3beta. Copyright (c) 2010 Elsevier Inc. All rights reserved.