Identification of the APS protein as a novel insulin receptor substrate

In order to identify novel substrates involved in insulin receptor signalin g, a yeast two-hybrid 3T3-L1 adipocyte cDNA library was screened with the c ytoplasmic domain of the human insulin receptor as bait. Here we describe t he isolation and characterization of an interacting protein, APS, which con tains pleckstrin homology and Src homology 2 domains and several potential tyrosine phosphorylation sites. APS mRNA and protein are expressed primaril y in skeletal muscle, heart, and adipose tissue, and in differentiated 3T3- L1 adipocytes, We show that APS associates with phosphotyrosines situated w ithin the activation loop of the insulin receptor via the APS Src homology 2 domain. Insulin stimulation of 3T3-L1 adipocytes resulted in rapid tyrosi ne phosphorylation of endogenous APS on tyrosine 618, whereas platelet-deri ved growth factor treatment resulted in no APS phosphorylation, In summary, we have identified a new insulin receptor substrate that is primarily expr essed in insulin-responsive tissues and in 3T3-L1 adipocytes whose phosphor ylation shows insulin receptor specificity. These findings suggest a potent ial role for APS in insulin-regulated metabolic signaling pathways.