Tyrosine phosphorylation of Shc proteins and formation of Shc/Grb2 complex correlate to the transformation of NIH3T3 cells mediated by the point-mutation activated neu.

PLC-gamma, ras-GAP and Shc have been proposed to be in vivo substrates for the neu-encoded p185neu receptor tyrosine kinases. We compared the tyrosine phosphorylation levels of PLC-gamma, ras-GAP and Shc in two NIH3T3 derived cell lines, transformed B104-1-1 and non-transformed DHFR/G8 cells in which point-mutation activated and normal rat neu genes were transfected and expressed, respectively. We found that tyrosine phosphorylation of Shc and formation of Shc/Grb2 complex were more significant in B104-1-1 cells than in DHFR/G8 cells, while no obvious difference could be detected for the tyrosine phosphorylation levels of ras-GAP and PLC-gamma between these two cell lines. Furthermore, we observed that association with Shc was severely impaired by deletion of most of the major autophosphorylation sites of the point-mutated neu. The truncated neu product, however, fully retained its ability to transform NIH3T3 cells, induce Shc tyrosine phosphorylation and Shc/Grb2 complex formation. Our results suggest that tyrosine phosphorylation of Shc which allows formation of Shc/Grb2 complex may play an important role for cell transformation induced by the point mutation-activated neu, and that stable binding to mutant p185neu may not be necessary for Shc to mediate this signaling pathway.