TOB, A NOVEL PROTEIN THAT INTERACTS WITH P185(ERBB2), IS ASSOCIATED WITH ANTIPROLIFERATIVE ACTIVITY

We have molecularly cloned a cDNA for a novel protein termed Tob (Tran sducer of ErbB-2) that interacts with the c-erbB-2 gene product p185(e rbB2). Nucleotide sequencing reveals that the Tob protein is a 45 kDa protein that does not contain either SH2 (Src Homology 2) or SH3 domai n but is homologous to the previously characterized anti-proliferative gene product BTG-1 at its amino-terminal half. The carboxyl-terminal half of Tob is characterized by the presence of a sequence rich in pro line and glutamine and shows no homology to known proteins. Like BTG-1 , exogenously expressed Tob is able to suppress growth of NIH3T3 cells , but the growth suppression is hampered by the presence of kinase-act ive p185(erbB2). By using the GST-Tob protein that contains either ful l length or amino-terminal half of Tob, we show that the carboxyl-term inal half of Tob is relevant to its interaction with p185(erbB2). Furt hermore, we could co-immunoprecipitate the Tob protein with anti-ErbB- 2 antibody, and reciprocally the p185(erbB2). With anti-Tob antibodies . These data suggest that p185(erbB2) negatively regulates the Tob-med iated anti-proliferative pathway through its interaction with Tob, res ulting possibly in growth stimulation by p185(erbB2). Finally, express ion of the Tob mRNA is observed in various cell types and is not corre lated with expression of c-erbB-2, suggesting that other receptor-type protein-tyrosine kinases are also involved in the Tob-mediated regula tion of cell growth.