Abstract
Abstract
Intracellular signal transduction has been reported to be triggered by phosphorylation of interleukin-2 (IL-2) receptor by IL–2. In order to clarify the effect of tyrosine phosphorylation of IL–2 receptors on cell-mediated cytotoxicity by natural killer (NK) cells, we studied the effect of a tyrosine kinase inhibitor, genistein, on the lethal effects of NK-rich cells for K562 cells. Exposure of NK-rich ceils to IL-2 (100 U/ml) for 3 days increased their cytotoxicities against K562 cells. The effect was reduced in the presence of 10 μg/ml of genistein.
Samples Immunoprecipitated by anti-IL-2Rβ antibodies were prepared from NK-rich fractions with or without exposure to IL-2 and/or genistein. Coprecipitated proteins with 75, 65, and 56 kDa were detected with an antiphosphotyrosine antibody. The amount of phosphorylated tyrosine residues of 56-kDa protein, which was predominantly detected in NK-rich cells, was remarkably increased by IL-2 treatment. The enhanced phosphorylation of 56-kDa protein was reduced by the presence of genistein. These results suggested that IL-2 increased tyrosine phosphorylation and the affinity to IL-2Rβ of the 56-kDa proteins in NK-rich cells. Immunoprecipitated samples by anti-IL-2Rβ were reblotted with anti-p56lck antibody and revealed that the 56-kDa protein was Identified to be p56lck. The increase of coprecipitated p56lck with anti-IL-2Rβ antibody by the treatment with IL-2 suggested that the affinity of p56lck to IL-2Rβ was increased by IL-2 in NK-rich cells. The amount of coprecipitated p56lck with IL-2Rβ was reduced in the sample exposed to genistein. The affinity of p56lck to IL-2Rβ was considered to be regulated by IL-2-induced tyrosine phosphorylation. Our results demonstrated a potential role for tyrosine kinase, p56lck, in the signaling events that regulate the cytotoxicity by NK-rich cells.
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