Ezrin interacts with focal adhesion kinase and induces its activation independently of cell-matrix adhesion

Ezrin, a membrane-cytoskeleton linker, is required for cell morphogenesis, motility, and survival through molecular mechanisms that remain to be eluci dated. Using the N-terminal domain of ezrin as a bait, we found that p125 f ocal adhesion kinase (FAR) interacts with ezrin. We show that the two prote ins coimmunoprecipitate from cultured cell lysates. However, FAK does not i nteract with full-length ezrin in vitro, indicating that the FAK binding si te on ezrin is cryptic. Mapping experiments showed that the entire N-termin al domain of FAK (amino acids 1-376) is required for optimal ezrin binding. While investigating the role of the ezrin-FAK interaction, we observed tha t, in suspended kidney-derived epithelial LLC-PK1 cells, overproduction of ezrin promoted phosphorylation of FAK Tyr-397, the major autophosphorylatio n site, creating a docking site for FAK signaling partners. Treatment of th e cells with a Src family kinase inhibitor reduced the phosphorylation of T yr-577 but not that of Tyr-397, indicating that ezrin-mediated FAK activati on does not require the activity of Src kinases. Altogether, these observat ions indicate that ezrin is able to trigger FAK activation in signaling eve nts that are not elicited by cell-matrix adhesion.