Md. Schaller et al., AUTOPHOSPHORYLATION OF THE FOCAL ADHESION KINASE, PP125(FAK), DIRECTSSH2 DEPENDENT BINDING OF PP60(SRC), Molecular and cellular biology, 14(3), 1994, pp. 1680-1688
The phosphorylation of protein tyrosine kinases (PTKs) on tyrosine res
idues is a critical regulatory event that modulates catalytic activity
and triggers the physical association of PTKs with Src homology 2 (SH
2)-containing proteins. The integrin-linked focal adhesion kinase, ppl
25(FAK), exhibits extracellular matrix-dependent phosphorylation on ty
rosine and physically associates with two nonreceptor PTKs, pp6O(src)
and pp59(fyn), via their SH2 domains. Herein, we identify Tyr-397 as t
he major site of tyrosine phosphorylation on ppl25(FAK) both in vivo a
nd in vitro. Tyrosine 397 is located at the juncture of the N-terminaI
and catalytic domains, a novel site for PTK autophosphorylation. Muta
tion of Tyr-397 to a nonphosphorylatable residue dramatically impairs
the phosphorylation of ppl25(FAK) on tyrosine in vivo and in vitro. Th
e mutation of Tyr-397 to Phe also inhibits the formation of stable com
plexes with pp60(src) in cells expressing Src and FAK(397F) suggesting
that autophosphorylation of ppl25(FAK) may regulate the association o
f pp125(FAK) with Src family kinases in vivo. The identification of Ty
r-397 as a major site for FAK autophosphorylation provides one of the
first examples of a cellular protein containing a high-affinity bindin
g site for a Src family kinase SH2 domain. This finding has implicatio
ns for models describing the mechanisms of action of pp125(FAK), the r
egulation of the Src family of PTKs, and signal transduction through t
he integrins.