THE HIGH TRANSFORMING POTENCY OF ERBB-2 AND RET IS ASSOCIATED WITH PHOSPHORYLATION OF PAXILLIN AND A 23 KDA PROTEIN

Two-dimensional gel maps of proteins phosphorylated by the epidermal g rowth factor receptor (EGFR) and erbB-2 kinases were obtained, to inve stigate the molecular basis of the different biological properties of these two molecules. Several proteins were phosphorylated by EGFR or e rbB-2 with different stoichiometry. Differences were either quantitati ve or qualitative. In NIH3T3 cells, erbB-2 is 100-fold more transformi ng than EGFR. In the same cell line several proteins were preferential ly phosphorylated by erbB-2, as compared to EGFR. To identify which of these substrates might be directly involved in mitogenic signaling, w e obtained two-dimensional maps of proteins phosphorylated on tyrosine by EGFR/ret and an EGFR/erbB-2(TK) chimeric receptors. Both these chi merae behaved indistinguishably from erbB-2 in a number of bioassays a nd potently transformed NIH3T3 cells. Paxillin and a 23 kDa substrate were invariably phosphorylated to higher stoichiometry whenever potent mitogenic and transforming signals were activated. We propose that pa xillin and the 23 kDa substrate are important elements in the erbB-2 a nd ret-activated mitogenic and transforming signaling.