Activated lek Tyrosine Protein Kinase Stimulates AntigenIndependent Interleukin-2 Production in T Cells

Abstract

p56^lck a member of the src family of cytoplasmic tyrosine kinases, is expressed predominantly in T cells where it associates with the T-cell surface molecules CD4 and CD8. Mutants of CD4 and CD8 that have lost the ability to associate with p56^lck no longer enhance antigen-induceu T-cell activation. This suggests that p56^lck plays an important role during T-cell activation. In an effort to understand the function of p56^lck in T cells, a constitutively activated lck gene (F505lck) was introduced into T-helper hybridoma cell lines by retroviral infection. In four T-cell lines we examined, the activated lck protein stimulated interleukin-2 (IL-2) production, a hallmark of T-cell activation, in the absence of antigenic stimulation. In addition, a marked increase in antigen-independent IL-2 production was apparent when T cells infected with a temperature-sensitive F505lck were shifted to the permissive temperature. Only one cell line expressing F05lck exhibited increased sensitivity to antigenic stimulation. The SH3 domain of p56^lck was dispensable for the induction of antigen-independent IL-2 production. In contrast, deletion of the majority of the SH2 domain of p56^F50lck reduced its ability to induce spontaneous IL-2 production markedly. Activated p60^c-src also induced antigen-independent IL-2 production, whereas two other tyrosine kinases, v-abl and the platelet-derived growth factor receptor, did not. Tyrosine phosphoiylation of a 70-kDa cellular protein was observed after cross-linking of CD4 in T cells expressing F505lck but not in cells expressing F527src.