Differential implication of protein kinase C isoforms in cytotoxic T lymphocyte degranulation and TCR-induced Fas ligand expression

Abstract

CD8+ cytotoxic T lymphocyte (CTL) clones are able to exert both perforin- and Fas-dependent cytotoxicity. We show in the present work that phosphatidylinositol 3-kinase (PI3K) inhibitors wortmannin and LY294002 prevent TCR/CD3-induced functional Fas ligand (FasL) expression, but not perforin-dependent cytotoxicity. The specific inhibitor of classical protein kinase C (PKC) isoforms, Gö6976, completely inhibited perforin-dependent cytotoxicity and only affected slightly TCR/CD3-induced FasL expression, while the opposite was observed using rottlerin, an inhibitor with higher specificity for PKCθ. To address further the dependence of FasL expression on PI3K, a luciferase reporter controlled by the FasL promoter was used. Reporter gene induction by anti-CD3 mAb was abolished in cells transfected with dominant-negative PI3K (PI3K-DN) and increased in cells transfected with constitutively active PI3K (PI3K*). Transfection with constitutively active mutants (A/E) of PKCε, and especially of PKCθ, improved anti-CD3 mAb-induced reporter expression and completely abolished inhibition by wortmannin, while transfection with dominant-negative (K/R) PKCθ prevented the induction of the reporter. Finally, transfection with PKCα A/E, but not with PKCθ A/E, cooperated with ionomycin to induce degranulation in the CTL line 1.3E6SN. Altogether, the results suggest that TCR/CD3-induced FasL gene transcription is controlled by PI3K and PKCθ activation, while this signaling pathway is not implicated in CTL degranulation, which is rather dependent on the activation of classical PKC isoforms.