RAPID TYROSINE PHOSPHORYLATION OF GRB2 AND SHC IN T-CELLS EXPOSED TO ANTI-CD3, ANTI-CD4, AND ANTI-CD45 STIMULI - DIFFERENTIAL-EFFECTS OF AGING

Two adapter proteins, Grb2 and Shc, have recently been implicated in t he transmission of activation signals from the stimulated T cell recep tor to Ras. We show here that in vitro stimulation of mouse splenic T cells with crosslinked anti-CD3 antibody leads within 30 s to phosphor ylation of both Grb2 and Shc. Treatment with crosslinked anti-CD45 ant ibody leads to phosphorylation of Grb2 and also to a slight retardatio n in the mobility of this protein in an SDS polyacrylamide gel; both c hanges are seen within 30 s of crosslinking. Crosslinked anti-CD4 anti body leads to phosphorylation of Shc and to the phosphorylation of a 3 0-kDa protein that cross-reacts with anti-Grb2 antibodies. Aging leads to a decline in CD3-stimulated phosphorylation of Shc (but not Grb2), and to an increase in CD4-stimulated phosphorylation of Grb2, Shc, an d the 30-kDa Grb2-like protein. Increased tyrosine-phosphorylation of Grb2 after exposure to either anti-CD3 or anti-CD45 suggests that Grb2 may be a common substrate for both CD3-linked kinases and the CD45 ph osphatase. The differences between T cells from young and old mice sug gest that aging may lead to a set of alterations in kinase/substrate c oupling that contribute to immune dysfunction in the elderly, and that activation of the Ras pathway might be impaired by aging in T lymphoc ytes.