The Fyn tyrosine kinase binds Irs-1 and forms a distinct signaling complex during insulin stimulation

Abstract

Irs-proteins link the receptors for insulin/IGF-1, growth hormones, and several interleukins and interferons to signaling proteins that contain Src homology-2 (SH2). To identify new Irs-1-binding proteins, we screened a mouse embryo expression library with recombinant [32P]Irs-1, which revealed a specific association between p59(fyn) and Irs-1. The SH2 domain in p59(fyn) bound to phosphorylated Tyr895 and Tyr1172, which are located in YXX(L/I) motifs. Mutation of p59(fyn) at the COOH-terminal tyrosine phosphorylation site (Tyr531) enhanced its binding to Irs-1 during insulin stimulation. Binding experiments with various SH2 proteins revealed that Grb- 2 was largely excluded from Irs-1 complexes containing p59(fyn), whereas Grb- 2 and p85 occurred in the same Irs-1 complex. By comparison with the insulin receptor, p59(fyn) kinase phosphorylated a unique cohort of tyrosine residues in Irs-1. These results outline a role for p59(fyn) or other related Src- kinases during insulin and cytokine signaling.