ASSOCIATION OF INSULIN-RECEPTOR SUBSTRATE-1 WITH SIMIAN-VIRUS-40 LARGE T-ANTIGEN

Mouse embryo cells expressing a wild-type number of insulin-like growt h factor I receptors (IGF-IR) (W cells) can be transformed either by s imian virus 40 large T antigen (SV40 T) or by overexpressed insulin re ceptor substrate 1 (IRS-1), singly transfected. Neither SV40 T antigen nor IRS-1, individually, can transform mouse embryo cells with a targ eted disruption of the IGF-IR genes (R(-) cells). However, cotransfect ion of SV40 T antigen and IRS-1 does transform R(-) cells. In this stu dy, using different antibodies and different cell lines, we found that SV40 T antigen and IRS-1 are coprecipitated from cell lysates in a sp ecific fashion, regardless of whether the lysates are immunoprecipitat ed with an antibody to SV40 T antigen or an antibody to IRS-1. The sam e antibody to SV40 T antigen, however, fails to coprecipitate another substrate ofIGF-IR, the transforming protein She, and two other signal -transducing molecules, Grb2 and Sos. Finally, an SV40 T antigen lacki ng the amino-terminal 250 amino acids fails to coprecipitate IRS-1 and also fails to transform R(-) cells overexpressing mouse IRS-1. These experiments indicate that IRS-1 associates with SV40 T antigen and tha t this association plays a critical role in the combined ability of th ese proteins to transform R(-) cells, This finding is discussed in lig ht of the crucial role of the IGF-IR in the establishment and maintena nce of the transformed phenotype.