TYROSINE PHOSPHORYLATION OF A 94-KDA PROTEIN ASSOCIATED WITH GRB2 ASHIS IMPLICATED IN THE SIGNAL-TRANSDUCTION OF HEMATOPOIETIC SURVIVAL FACTORS/

Grb2/Ash is an adapter molecule that contains Src-homology (SH) 2 and 3 domains. We have examined Grb2/Ash-associated proteins in hematopoie tic cells, and have noted a 94-kDa phosphotyrosine-containing protein (pp94) among them. It was shown that the SH2 domain of Grb2/Ash is nec essary for the binding of pp94 to Grb2/Ash from the binding experiment s using the GST fusion proteins and the phosphotyrosine analogue pheny lphosphate. Tyrosine phosphorylation of pp94 was rapid and transient, and was only observed when the cells were stimulated with factors that were absolutely required for survival of the cells (survival factors) . The kinase inhibitors, staurosporine and genistein, inhibit the prol iferation of UT-7 cells. However, genistein does not inhibit the survi val of the cells while staurosporine inhibits both the proliferation a nd the survival of the cells. Tyrosine phosphorylation of pp94 was sen sitive to staurosporine but resistant to genistein. It is possible tha t tyrosine phosphorylation of pp94 might be related to the survival ra ther than to the proliferation of the cells. (C) 1996 Academic Press. Inc.