Phosphatidylinositol-4,5 Bisphosphate Produced by PIP5KIγ Regulates Gelsolin, Actin Assembly, and Adhesion Strength of N-Cadherin Junctions

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Abstract
Phosphoinositides regulate several actin-binding proteins but their role at intercellular adhesions has not been defined. We found that phosphatidylinositol 4,5-bisphosphate (PI(4,5)P2) was generated at sites of N-cadherin–mediated intercellular adhesion and was a critical regulator of intercellular adhesion strength. Immunostaining for PI(4,5)P2or transfection with GFP-PH-PLCδ showed that PI(4,5)P2was enriched at sites of N-cadherin adhesions and this enrichment required activated Rac1. Isoform-specific immunostaining for type I phosphatidylinositol 4-phosphate 5 kinase (PIP5KI) showed that PIP5KIγ was spatially associated with N-cadherin–Fc beads. Association of PIP5KIγ with N-cadherin adhesions was in part dependent on the activation of RhoA. Transfection with catalytically inactive PIP5KIγ blocked the enrichment of PI(4,5)P2around beads. Catalytically inactive PIP5KIγ or a cell-permeant peptide that mimics and competes for the PI(4,5)P2-binding region of the actin-binding protein gelsolin inhibited incorporation of actin monomers in response to N-cadherin ligation and reduced intercellular adhesion strength by more than twofold. Gelsolin null fibroblasts transfected with a gelsolin severing mutant containing an intact PI(4,5)P2binding region, demonstrated intercellular adhesion strength similar to wild-type transfected controls. We conclude that PIP5KIγ-mediated generation of PI(4,5)P2at sites of N-cadherin contacts regulates intercellular adhesion strength, an effect due in part to PI(4,5)P2-mediated regulation of gelsolin.