IN-VIVO ASSOCIATION OF GRB2 WITH PP116, A SUBSTRATE OF THE T-CELL ANTIGEN RECEPTOR-ACTIVATED PROTEIN-TYROSINE KINASE

Numerous recent studies have implicated the src homology 2 and 3 domai n-containing protein, Grb2, in coupling protein tyrosine kinase signal ing pathways with the Res signaling pathway. Ligation of the T cell an tigen receptor results in the activation of both a PTK, and Ras; there fore, we investigated whether Grb2 may serve a similar function in T c ells. Here we report that a GST/Grb2 fusion protein associates with se veral tyrosine phosphoproteins from lysates of T cell antigen receptor -stimulated Jurkat T cells. Two of these proteins, pp36 and pp116, bin d to the Grb2 fusion protein with high affinity. Through the use of mu tated Grb2 fusion proteins, we demonstrate that pp116 binds the amino- terminal src homology 3 domain of Grb2, the same domain of Grb2 though t to be primarily responsible for its inter action with SOS. We demons trate further that pp116 associates with Grb2 in vivo, and we provide evidence that in the Jurkat T cell line Grb2 may exist complexed with either pp116 or with SOS.