Phosphatidylinositol-4-phosphate 5-kinase γ is associated with cell-cell junction in A431 epithelial cells

Cell to cell contact in epithelial cells is crucial for tissue integrity and is maintained by junctional complexes, such as the adherens junction (AJ). Actin polymerization has been shown to be important for AJ formation; however, the molecular mechanisms have yet to be clarified. It has been shown that increased phosphatidylinositol-4,5-bisphosphate (PIP2) induces actin polymerization. It is thus of interest to know more about the production of PIP2 during cell-cell adhesion formation in epithelial cells. The distribution of phosphatidylinositol-4-phosphate 5-kinase γ635 (PIP5Kγ635), an isoform of the PIP2 synthesizing enzymes, was examined in epithelial cell line A431. It was found that, in non-contact cells, PIP5Kγ635 was not concentrated at the plasma membrane. However, in cells that were in contact, PIP5Kγ635 localized to the intercellular contact sites and colocalized with E-cadherin and β-catenin, two components of AJ, and with polymerized actin, but did not colocalize with focal adhesion, integrin-mediated cell-substratum complex. Decreasing calcium ion concentration induced both disruption of intercellular adhesion and the dissociation of both PIP5Kγ635 and actin from the contact site. These results suggest that PIP5K has an important role in actin polymerization in epithelial cell-cell adhesion.