ASSOCIATION OF THE AMINO-TERMINAL HALF OF C-SRC WITH FOCAL ADHESIONS ALTERS THEIR PROPERTIES AND IS REGULATED BY PHOSPHORYLATION OF TYROSINE-527

We have characterized the mechanism by which the subcellular distribut ion of c-Src is controlled by the phosphorylation of tyrosine 527. Mut ation of this tyrosine dramatically redistributes c-Src from endosomal membranes to focal adhesions. Redistribution to focal adhesions occur s independently of kinase activity and cellular transformation. In cel ls lacking the regulatory kinase (CSK) that phosphorylates tyrosine 52 7, c-Src is also found predominantly in focal adhesions, confirming th at phosphorylation of tyrosine 527 affects the location of c-Src insid e the cell. The first 251 amino acids of c-Src are sufficient to allow association with focal adhesions, indicating that at least one signal for positioning c-Src in focal adhesions resides in the amino-termina l half. Point mutations and deletions in the first 251 amino acids of c-Src reveal that association with focal adhesions requires the myrist ylation site needed for membrane attachment, as well as the SH3 domain . Expression of the aminoterminal region alters both the structural an d biochemical properties of focal adhesions. Focal adhesions containin g this non-catalytic portion of c-Src are larger and exhibit increased levels of phosphotyrosine staining. Our results suggest that c-Src ma y regulate focal adhesions and cellular adhesion by a kinase-independe nt mechanism.