Gαq Signaling Activates β-Catenin-Dependent Gene Transcription

ABSTRACT BACKGROUND: The canonical Wnt signal transduction or the Wnt/β-catenin pathway plays a crucial role in both carcinogenesis and development of animals. Activation of the Gαq class of Gα proteins positively regulates Wnt/β-catenin pathway, and expression of Gαq in HEK293T cells or Xenopus oocytes leads to the inhibition of GSK-3β and cellular accumulation of β-catenin. This study investigated whether Gαq-mediated cellular accumulation of β-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 β-catenin target genes (c-MYC and CCND1) and the β-catenin/TCF reporter luciferase gene (TopFlash plasmid) significantly increased by Gαq activation. The Gαq-mediated increase in the expression level of the β-catenin-target genes was sensitive to the expression of a minigene encoding a specific Gαq blocking peptide. The results of cell fractionation and Western blotting experiments showed that activation of Gαq signaling increased the intracellular β-catenin protein level, but it blocked its membrane localization. CONCLUSION: Our results reveal that the Gαq-dependent cellular accumulation of β-catenin can enhance β-catenin transcriptional activity.