The earliest demonstrable biochemical event that occurs as a consequence of antigen recognition by the T-cell antigen receptor (TCR) is activation of a non-receptor protein tyrosine kinase (PTK). The TCR as well as the accessory molecules CD4 and CD8 are physically associated with src family PTKs, the fyn and lck encoded kinases, respectively. We have developed a model system to elucidate the function of src family PTK in T cell function by expressing prototypic PTKs in an antigen specific T-cell hybridoma. We demonstrated that expression of v-src results in constitutive interleukin 2 (IL-2) production which is inhibitable by cyclosporin A. These cells have constitutively high nuclear levels of the transcription factor NFKappaB and other DNA binding proteins. The induction of NFKappaB is independent of protein kinase C. Other genes are induced by v-src including the IL-2RAlpha chain and the HTLV1-LTR. Additionally, we observed that v-src expressing T cells have marked potentiation of TCR mediated calcium mobilization which appears to be independent of phosphoinositol levels. We have demonstrated that the NK cell Fc receptor, FcGammaRIIIA, is a multimeric receptor complex comprising a ligand binding molecule associated with the Zeta chain and FcEpsilon Gamma chains and is coupled to a PTK. Like the TCR, the Zeta chain was phosphorylated upon perturbation of FcGammaRIIIA. We showed that pharmacologically blocking PTK activity abrogated FcR dependent calcium mobilization and induction of the IL-RAlpha and IFN-Gamma genes. We found that PTK inhibition also blocked cytotoxicity mediated by FcGammaRIIIA or antibody dependent cellular cytotoxicity (ADCC). We also found that PTK inhibition blocks other modes of cytotoxicity including NK mediated cytotoxicity and LAK. Studies are underway to elucidate the structure/function relationships among src family PTK and how they influence receptor mediated signaling and gene induction.
