CD45 tyrosine phosphatase-activated p59 super(fyn) couples the T cell antigen receptor to pathways of diacylglycerol production, protein kinase C activation and calcium influx

The role of the CD45 phosphotyrosine phosphatase in coupling the T cell antigen receptor complex (TCR) to intracellular signals was investigated. CD45 super(-) HPB-ALL T cells were transfected with cDNA encoding the CD45RA super(+)B super(+)C- isoform. The tyrosine kinase activity of p59 super(fyn) was found to be 65% less in CD45 super(-) cells than in CD45 super(+) cells, whereas p56 super(lck) kinase activity was comparable in both sub-clones. In CD45 super(-) cells the TCR was uncoupled from protein tyrosine phosphorylation, phospholipase C sub( gamma 1) regulation, inositol phosphate production, calcium signals, diacylglycerol production and protein kinase C activation. Restoration of TCR coupling to all these pathways correlated with the increased p59 super(fyn) activity observed in CD45-transfected cells. Co-aggregation of CD4- or CD8-p56 super(lck) kinase with the TCR in CD45 super(-) cells restored TCR-induced protein tyrosine phosphorylation, phospholipase C sub( gamma 1) regulation and calcium signals. Receptor-mediated calcium signals were largely due (60-90%) to Ca super(2+) influx, and only a minor component (10-40%) was caused by Ca super(2+) release from intracellular stores. Maximal CD3-mediated Ca super(2+) influx occurred at CD3 mAb concentrations at which inositol phosphate produced was non-detectable. The results indicate that CD45-regulated p59 super(fyn) plays a critical role in coupling the TCR to specific intracellular signalling pathways and that CD4- or CD8-p56 super(lck) can only restore signal transduction coupling in CD45 super(-) cells when brought into close association with the TCR. (DBO)