PIPKIγ Regulates Focal Adhesion Dynamics and Colon Cancer Cell Invasion

Focal adhesion assembly and disassembly are essential for cell migration and cancer invasion, but the detailed molecular mechanisms regulating these processes remain to be elucidated. Phosphatidylinositol phosphate kinase type I gamma (PIPKI gamma) binds talin and is required for focal adhesion formation in EGF-stimulated cells, but its role in regulating focal adhesion dynamics and cancer invasion is poorly understood. We show here that overexpression of PIPKI gamma promoted focal adhesion formation, whereas cells expressing either PIPKI gamma(K188,200R) or PIPKI gamma(D316K), two kinase-dead mutants, had much fewer focal adhesions than those expressing WT PIPKI gamma in CHO-K1 cells and HCT116 colon cancer cells. Furthermore, overexpression of PIPKI gamma, but not PIPKI gamma(K188,200R), resulted in an increase in both focal adhesion assembly and disassembly rates. Depletion of PIPKI gamma by using shRNA strongly inhibited formation of focal adhesions in HCT116 cells. Overexpression of PIPKI gamma(K188,200R) or depletion of PIPKI gamma reduced the strength of HCT116 cell adhesion to fibronection and inhibited the invasive capacities of HCT116 cells. PIPKI gamma depletion reduced PIP2 levels to similar to 40% of control and PIP3 to undetectable levels, and inhibited vinculin localizing to focal adhesions. Taken together, PIPKI gamma positively regulates focal adhesion dynamics and cancer invasion, most probably through PIP2-mediated vinculin activation.