Gαq Signaling Activates β-Catenin-Dependent Gene Transcription

Background: The canonical Wnt signal transduction or the Wnt/beta-catenin pathway plays a crucial role in both carcinogenesis and development of animals. Activation of the G alpha q class of G alpha proteins positively regulates Wnt/beta-catenin pathway, and expression of G alpha q in HEK293T cells or Xenopus oocytes leads to the inhibition of GSK-3 beta and cellular accumulation of beta-catenin. This study investigated whether G alpha q-mediated cellular accumulation of beta-catenin could affect the transcriptional activity of this protein.Methods: HEK-293T and HT-29 cells were used for cell culture and transfection. Protein localization and quantification were assessed by using immunofluorescence microscopy, cell fractionation assay, and Western blotting analysis. Gene expression at the transcription level was examined by quantitative reverse transcriptase/real-time PCR method.Results: Transcription of two cellular beta-catenin target genes (c-MYC and CCND1) and the beta-catenin/TCF reporter luciferase gene (TopFlash plasmid) significantly increased by G alpha q activation. The G alpha q-mediated increase in the expression level of the beta-catenin-target genes was sensitive to the expression of a minigene encoding a specific G alpha q blocking peptide. The results of cell fractionation and Western blotting experiments showed that activation of G alpha q signaling increased the intracellular beta-catenin protein level, but it blocked its membrane localization.Conclusion: Our results reveal that the G alpha q-dependent cellular accumulation of beta-catenin can enhance beta-catenin transcriptional activity.