Diminished tyrosine protein kinase activity in I cells unresponsive to TCR stimulation

bstract: Tyrosine phosphorylation is thought to be one f the earliest steps in antigenic activation of T cells. hree nonreceptor tyrosine kinases, �S6Ith, p6O�"�, and AP-70, are known to be involved in T cell receptor TCR) signaling, albeit their functional roles appear to be ifferent. Whereas p60w and ZAP-70 are functionally ssociated with the T cell antigen receptor, p56� is es- ential for TCR signaling without being directly coupled o the TCR. We have studied a mutant variant of the Jur- kat T cell line 032-3.2), in which basal activities of �56k1c and p6VY#{176} are 2- to 2.5-fold reduced relative to those in its parental line (J32) while basal activity of ZAP-70 remains unchanged, and compared responses of J32-3.2 and J32 to TCR stimulation. We have demon- strated that tyrosine phosphorylation following CD3 cross-linking in J32-3.2 cells was extremely short-lived and thus insufficient for the induction of subsequent physiological responses. This was at least partially due to the diminished tyrosine kinase activity in these cells. A decrease in the activity of src-related kinases was caused primarily by their lower expression, whereas expression of ZAP-70 was unchanged but its response to CD3 cross- linking was diminished, correlating with the deficient tyrosine phosphorylation of the CD3 c-chain, recently observed in J32-32. These data are consistent with the idea that src-related kinases phosphorylate the c-chain, which in turn recruits ZAP-70 required to sustain the sig- nal. J. Leukoc. Biol. 55: 289-298; 1994.