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Vol. 18, Issue 8, 3026-3038, August 2007

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Phosphatidylinositol-4,5 Bisphosphate Produced by PIP5KI Regulates Gelsolin, Actin Assembly, and Adhesion Strength of N-Cadherin Junctions

T. Y. El Sayegh^*, P. D. Arora^*, K. Ling, C. Laschinger^*, P. A. Janmey, R. A. Anderson, and C. A. McCulloch^*

*Canadian Institutes of Health Research Group in Matrix Dynamics, University of Toronto, Toronto, Ontario, Canada M5S 3E2; Department of Pharmacology, University of Wisconsin Medical School, Madison, WI 53706; and Institute for Medicine and Engineering, Department of Physiology, University of Pennsylvania, Philadelphia, PA 19104

Submitted December 29, 2006; Revised April 16, 2007; Accepted May 22, 2007
Monitoring Editor: Asma Nusrat

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)P₂ or transfection with GFP-PH-PLC showed that PI(4,5)P₂ was 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 PIP5KI was spatially associated with N-cadherin–Fc beads. Association of PIP5KI with N-cadherin adhesions was in part dependent on the activation of RhoA. Transfection with catalytically inactive PIP5KI blocked the enrichment of PI(4,5)P₂ around beads. Catalytically inactive PIP5KI 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)P₂ binding region, demonstrated intercellular adhesion strength similar to wild-type transfected controls. We conclude that PIP5KI-mediated generation of PI(4,5)P₂ at sites of N-cadherin contacts regulates intercellular adhesion strength, an effect due in part to PI(4,5)P₂-mediated regulation of gelsolin.

The online version of this article contains supplemental material at MBC Online (http://www.molbiolcell.org).

Address correspondence to: T. Y. El Sayegh (t.elsayegh{at}utoronto.ca).