EVIDENCE FOR PHOSPHATIDYLINOSITOL 3-KINASE-DEPENDENT T-CELL ANTIGEN RECEPTOR (TCR) SIGNAL-TRANSDUCTION

Recent evidence implicates PI 3-kinase in TCR signal transduction. The fungal metabolite wortmannin is a specific inhibitor of PI 3-kinase b oth in vitro and in vivo when used at nanomolar concentrations. Theref ore, we examined the effect of wortmannin on stimulation of primary T cells and T cell lines. Wortmannin had a dose-dependent inhibitory eff ect on TCR-dependent primary T cell proliferation with IC50 in the nan omolar range. Furthermore, activation of T cell lines independently of antigen presenting cells and, therefore of any CD28 co-stimulatory si gnaling, was also sensitive to wortmannin. As expected, phorbol ester stimulation bypassed PI 3-kinase signal transduction. Importantly, the effect of wortmannin correlated with inhibition of activation of PI 3 -kinase in stimulated T cells. The earliest step in T cell activation, tyrosine kinase activation, was not significantly affected by wortman nin. We conclude that a wortmannin-sensitive enzyme, probably PI 3-kin ase, acting downstream of tyrosine kinases, but independently of the p horbol ester activated pathway, is necessary for stimulation of T cell s via the TCR, and that this requirement is independent of any role of PI S-kinase in co-stimulation via CD28 coreceptor. PI 3-kinase is mos t probably involved in generation of 3-phosphorylated lipid products, and is not merely an adaptor. (C) 1997 Elsevier Science Ltd.