Key role of Shc signaling in the transforming pathway triggered by Ret/ptc2 oncoprotein

The RET/PTC oncogenes, generated by chromosomal rearrangements in papillary thyroid carcinomas, are constitutively activated versions of protoRET, a g ene encoding two protein isoforms of a transmembrane tyrosine kinase recept or, By using Ret/ptc2 short isoform (iso9), we have previously demonstrated that Tyr586 (Tyr1062 of protoRet) is the docking site for both the PTB and the SH2 domains of Shc. To determine the relevance of this interaction for the transforming activity of Ret/ptc oncogenes, we have generated and char acterized novel Ret/ptc mutants unable to activate Shc: Ret/ptc2 long isofo rm (iso51)-Y586F and both isoforms of Ret/ptc2-N583A, These mutants neither activate Shc nor transform NIH3T3 cells. Since Tyr1062 shows features of a multifunctional docking site, we have used a Shc mutant (Shc Y317F) to dir ectly assess Shc role, We have demonstrated that in our cell syst-ern Shc Y 317F behaves like a dominant interfering mutant on the activation of the Gr b2-Sos pathway by endogenous Shc triggered by Ret/ptc2, A strong reduction of the transforming activity of Ret/ptc2 in presence of this mutant was als o demonstrated. Our data suggest that Shc activation play a key role in the transforming pathways triggered by Ret/ptc oncoproteins. Moreover, we have shown that coexpression of the Shc-Y317F mutant with Ret/ptc2 specifically causes apoptosis, and that the surviving cells lose the long-term expressi on of one of the two genes.