Protein tyrosine phosphorylation is an early and requisite event in receptor-mediated signaling in T cells and NK cells. We have shown that expression of an active cytoplasmic protein tyrosine kinase (PTK), v-src in T cells has several striking effects including spontaneous calcium oscillations and enhanced T-cell receptor (TCR)-dependent, inositol phosphate independent, calcium mobilization, and constitutive interleukin-2 (IL-2) secretion. Moreover, expression of transmembrane (EGFR) and cytoplasmic PTK lead to phosphorylation of many of the same substrates including TCR-zeta. However the existence of TCR-specific substrates was shown using these systems. Expression of v-src leads to the activation of the promoter/enhancer elements of several genes including IL-2, IL-2R receptor alpha chain, HIV-1, and HTLV-1. We demonstrated that v-src expression leads to the constitutive nuclear expression of the p65 subunit of NFkappaB and NFAT transcription factors. Mutation of the NFkappaB element abrogates v-src induction of transcription mediated by promoters with this element. A synthetic enhancer composed of a multimer of the NFAT motif responded to v-src expression. However v-src also activated the HTLV-1 LTR which does not contain bonafide NFAT or NFkappaB elements. The v-src effect also did not map to the tax responsive elements. Pharmacologic induction of protein phosphorylation using pervanadate also resulted in activation of normal human T cells both biochemically and functionally. We have demonstrated that the Fc receptor (FcR) like the TCR, comprises Fcepsilon and TCRzeta subunits and receptor-mediated signaling is PTK- dependent. Unlike T cells however, NK cells have higher basal protein tyrosine phosphorylation which is not due to elevated expression of the src family PTK pp56lck or pp59fyn. Rather, it may be due to expression of a novel PTK. We have also recently demonstrated that T lymphocytes from tumor-bearing mice have impaired cytolytic function. This is correlated with impaired TCR-dependent calcium mobilization and aberrant expression of T-cell signaling molecules. T lymphocytes from tumor- bearing mice also have depressed levels of TCR-zeta and the PTK pp56lck and pp59fyn.
