The Differential Effects of pp120 (Ceacam 1) on the Mitogenic Action of Insulin and Insulin-Like Growth Factor 1 Are Regulated by the Nonconserved Tyrosine 1316 in the Insulin Receptor

Abstract

pp120 (Ceacam 1) undergoes ligand-stimulated phosphorylation by the insulin receptor, but not by the insulin-like growth factor 1 receptor (IGF-1R). This differential phosphorylation is regulated by the C terminus of the β-subunit of the insulin receptor, the least conserved domain of the two receptors. In the present studies, deletion and site-directed mutagenesis in stably transfected hepatocytes derived from insulin receptor knockout mice (IR^−/−) revealed that Tyr¹³¹⁶, which is replaced by the nonphosphorylatable phenylalanine in IGF-1R, regulated the differential phosphorylation of pp120 by the insulin receptor. Similarly, the nonconserved Tyr¹³¹⁶ residue also regulated the differential effect of pp120 on IGF-1 and insulin mitogenesis, with pp120 downregulating the growth-promoting action of insulin, but not that of IGF-1. Thus, it appears that pp120 phosphorylation by the insulin receptor is required and sufficient to mediate its downregulatory effect on the mitogenic action of insulin. Furthermore, the current studies revealed that the C terminus of the β-subunit of the insulin receptor contains elements that suppress the mitogenic action of insulin. Because IR^−/− hepatocytes are derived from liver, an insulin-targeted tissue, our observations have finally resolved the controversy about the role of the least-conserved domain of insulin and IGF-1Rs in mediating the difference in the mitogenic action of their ligands, with IGF-1 being more mitogenic than insulin.

ACKNOWLEDGMENTS

We thank Richard A. Roth (Stanford University), Jerrold M. Olefsky (University of California, San Diego), Derek LeRoith (NIDDK, NIH), and Domenico Accili (NICHD, NIH) for providing recombinant hIR-hIRRK, Y1316F/Y1322F hIR, F1310Y hIGF-1R, and Δ43 hIR mutant receptors, respectively. We also thank D. Accili for providing us with the IR^−/− hepatocytes, Myrna Saouda for her technical assistance with cloning experiments, and Curtis V. Choice and Yan Yang for their technical assistance in transfection experiments.

This work was supported by the National Science Foundation (grant MCB-9601427 to S.M.N.)