Interleukin 4 inhibits IL-2-induced proliferation of a human t-leukemia cell line without interfering with p56-LCK kinase activation

Recently we described the establishment in culture and the immunophenotypic and functional characteristics of a human T-leukemia line TALL-103/2 derived from the T-cell receptor (TCR)- γ δ subset of T-lymphocytes. TALL-103/2 cells are absolutely dependent on interleukin 2 (IL-2) for their growth and survival in culture and thus provide a model cell line for studies of IL-2 signal transduction in a TCR- γ δ T-cell. In this report, we focus on the regulation of SRC-family protein tyrosine kinases (PTKs) by IL-2. TALL-103/2 cells were found to contain p56-LCK, p59-FYN, p62-YES and p53/56-LYN. Stimulation of growth factor-deprived TALL-103/2 cells with IL-2, however, induced increases in the relative activity only of the p56-LCK kinase. This IL-2-mediated increase in LCK kinase activity was manifested both by increased kinase autophosphorylation and by increased phosphorylation of the exogenous substrate enolase during in vitro kinase assays. Furthermore, immunoblot assays determined that the levels of p56-LCK protein were unaltered by IL-2-treatment, indicating that the measured elevations in LCK kinase activity reflected an increase in the specific activity of this PTK. In TALL-103/2 cells, IL-2 stimulated concentration-dependent increases in p56-LCK activity that displayed rapid and transient kinetics: detectable increases occurred within 1 minute after IL-2 stimulation, peaked at 10 minutes, and declined to baseline levels by 30 minutes. Treatment of TALL-103/2 cells with IL-4 abrogated IL-2-initiated proliferation, but did not inhibit IL-2-mediated activation of p56-LCK. These findings demonstrate that, like previous results obtained with TCR- α β T-cells and NK-like cell lines, IL-2 specifically regulates the activity of the p56-LCK kinase in this TCR- γ δ T-cell line. The results obtained when TALL-103/2 cells were exposed to IL-4, however, argue that IL-2-mediated increases in p56-LCK kinase activity can be insufficient for IL-2-driven proliferation.