ACTIVATION-DEPENDENT TYROSINE PHOSPHORYLATION OF FYN-ASSOCIATED PROTEINS IN T-LYMPHOCYTES

While previous studies have implicated the tyrosine protein kinase p60(fyn) in antigenic activation of T lymphocytes, it is clear that signal transduction initiated through the antigen receptor requires the concerted actions of several proteins. Here, we report our finding that the activation of p60(fyn) following TcR cross-linking results in the tyrosine phosphorylation of two Fyn-associated proteins of 82 and 116 kDa. In the cells analyzed, p116 appears to represent one of the major substrates of T-cell antigen receptor mediated tyrosine phosphorylation In activated T-cells, the interaction of these proteins is specific for p60(fyn) since neither p56(lck) nor p62(c-yes) were found to detectably associate with p82 or p116. Furthermore, the p60(fyn)-p82/p116 complex could be dissociated and then reconstituted in vitro using purified recombinant Fyn. Using this technique we demonstrated that both p82 and p116 were capable of binding to the Fyn SH2 domain while p82 was to some extent capable of independent binding to the Fyn SH3 domain. An association between p60(fyn) and phosphoproteins possibly related to the T-cell p82 and p116 was also observed in other hematopoietic cells. Thus, the activation-induced phosphorylation of the p60(fyn)-associated proteins p116 and p82 and the wide distribution of potentially similar p60(fyn)-associated proteins in hematopoietic cells suggest that p116 and p82 may play a role as physiological substrates and/or regulators of p60(fyn).