PIPKIγ regulates β-catenin transcriptional activity downstream of growth factor receptor signaling

Increased β-catenin transcriptional activity downstream of the Wnt/Wingless signaling pathway has been observed in many human tumors, most notably colorectal carcinomas. However, β-catenin activation is also observed in many human malignancies with no observable Wnt activity. Wnt-independent pathways that activate β-catenin remain undefined, yet have the potential to play a significant role during tumorigenesis. Here, we report that phosphotidylinositol phosphate kinase Iγ (PIPKIγ), an enzyme that generates phosphoinositide messengers in vivo, directly associates with β-catenin and increases β-catenin activity downstream of growth factor stimulation. PIPKIγ expression and kinase activity enhance β-catenin phosphorylation on residues that promote nuclear importation and transcriptional activity. Lastly, we show that β-catenin is required for PIPKIγ-dependent increased cell proliferation. These results reveal a novel mechanism in which PIPKIγ expression and catalytic activity enhance β-catenin nuclear translocation and expression of its target genes to promote tumorigenic phenotypes.