The RET proto-oncogene encodes two
isoforms of a receptor type
tyrosine kinase which plays a role in neural crest and kidney development. Distinct germ-line mutations of RET have been associated with the inherited
cancer syndromes
MEN2A,
MEN2B and FMTC as well as with the
congenital disorder Hirschsprung disease (HSCR), whereas somatic rearrangements (RET/PTCs) have been frequently detected in the
papillary thyroid carcinoma. Despite these findings, suggesting a relevant role for RET product in development and
neoplastic processes, little is known about the signalling triggered by this receptor. In this study, we have demonstrated that the transducing adaptor molecule Shc is recruited and activated by both Ret
isoforms and by the rearranged cytoplasmatic Ret/ptc2
oncoproteins as well as by the membrane bound receptor activated by
MEN2A or by
MEN2B associated mutations. Moreover, our analysis has identified the Ret
tyrosine residue and the Shc domains involved in the interaction. In fact, here we show that both the
phosphotyrosine binding domains of Shc, PTB and SH2, interact with Ret/ptc2 in vitro. However, PTB domain binds 20 folds higher amount of Ret/ptc2 than SH2. The putative binding site for either SH2 and PTB domains has been identified as Tyr586 of Ret/ptc2 (Tyr1062 on proto-Ret). In keeping with this finding, by using RET/PTC2-Y586F mutant, we have demonstrated that this
tyrosine residue, the last
amino acid but one before the divergence of the two Ret
isoforms, is the docking site for Shc.