Focal adhesion kinase and Src mediate integrin regulation of insulin receptor phosphorylation

We show here that phosphorylation of the insulin receptor and insulin receptor substrate-1 is increased when suspended cells are replated on fibronectin. This is not due to decreased numbers of cell surface receptors, alteration of insulin binding, or stimulation of a phosphatase activity in non-adherent cells. Expression of Src together with focal adhesion kinase (FAK) in suspended cells restores insulin-induced receptor autophosphorylation to levels observed in fibronectin-attached cells. Conversely, expression of dominant-negative mutants of either Src or FAK abolishes potentiation of insulin receptor phosphorylation by cell adhesion. The results suggest that both Src and FAK participate in integrin-mediated regulation of insulin receptor signal.