Identification of phosphorylation sites in GIT1.

G protein-coupled receptor kinaseinteracting protein 1 (GIT1) was originally identified as an ADP ribosylation factor GTPase-activating protein (ARF-GAP) that binds Gprotein-coupled receptor kinases (GRKs) and regulates membrane trafficking (Premont et al., 1998). Subsequent studies have shown a much broader function for GIT1 and GIT2/PKL as regulators of migrationrelated processes, including adhesion and cytoskeletal organization (Manabe et al., 2002; Mazaki et al., 2001; West et al., 2001; Zhao et al., 2000). GIT function and localization are most likely mediated through its interaction with various signaling molecules, including paxillin, p21-activated kinase interacting exchange factor (PIX), focal adhesion kinase (FAK), phospholipase C (PLC ) and mitogen-activated protein kinase kinase 1 (MEK1) (Bagrodia et al., 1999; Haendeler et al., 2003; Manabe et al., 2002; West et al., 2001; Yin et al., 2004; Zhao et al., 2000). In fibroblasts and epithelial cells, GIT1 regulates migration and protrusive activity by assembling and targeting multi-protein signaling complexes that contain actin regulators, such as PIX and the Rac/Cdc42 effector p21-activated kinase (PAK), to adhesions and the leading edge of a protrusion (Di Cesare et al., 2000; Manabe et al., 2002). Another GIT family member, PKL, which is the chicken homolog of GIT2, also recruits PIX and PAK to adhesions through its interaction with paxillin (Brown et al., 2002). Once in adhesions, GIT1 promotes their disassembly through a PIX-dependent mechanism and stimulates motility (Zhao et al., 2000).