GIT2 represses Crk- and Rac1-regulated cell spreading and Cdc42-mediated focal adhesion turnover

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Abstract
G protein‐coupled receptor kinase interactors (GITs) regulate focal adhesion (FA) turnover, cell spreading, and motility through direct interaction with paxillin and the Rac‐exchange factor Pak‐interacting exchange factor β ( β PIX). However, it is not clear whether GITs function to activate or repress motility or if the predominant GIT forms, GIT1 and GIT2, serve distinct or redundant roles. Here we demonstrate an obligatory role for endogenous GIT2 in repression of lamellipodial extension and FA turnover by Rac1‐ and Cdc42‐dependent signaling pathways, respectively. Moreover, we show that the SH2–SH3 adaptor protein Crk is an essential target of GIT2 inhibition. Unexpectedly, we find that β PIX is dispensable for the effects elicited by knockdown of GIT2. Finally, we show that loss of GIT2 is sufficient to induce migration of the nontransformed epithelial cell line MCF10A. These results suggest that inactivation of GIT2 function is a required step for induction of cell motility and that GIT2 may be a target of oncogenic signaling pathways that regulate cell migration.