Protein kinase C theta cooperates with calcineurin to induce pas ligand expression during activation-induced T cell death

Activation-induced cell death is mediated by the TCR-induced expression of the Fas ligand (FasL) on the surface of T cells, followed by binding to its receptor Fas, Fast expression is induced by stimulating T cells with a com bination of phorbol ester and Ca2+ ionophore, implicating a role for protei n kinase C (PKC) in this process. However, the precise mechanisms that regu late Fast expression, including the contribution of distinct T cell-express ed PKC isoforms, are poorly understood. Herein, we report that PKC theta, a Ca2+-independent PKC isoform that we have previously isolated as a PKC enz yme selectively expressed in T cells, plays an important role in these proc esses, A constitutively active PKC theta mutant preferentially induced Fast expression and activated the corresponding gene promoter; conversely, a do minant-negative PKC theta mutant blocked Fast expression induced by anti-CD 3 or PMA plus ionomycin stimulation, Furthermore, PKC theta synergized with calcineurin to provide a potent stimulus for Fast promoter activation, Ful l activation of the promoter required its binding sites for the transcripti on factors NF-AT, AP-1, and NF-KB, The biological significance of these fin dings is implicated by the finding that rottlerin, a selective PKC theta in hibitor, blocked Fast induction by anti-CD3 or PMA plus ionomycin stimulati on and, consequently, protected human Jurkat T cells and the mouse T cell h ybridoma A1.1 from activation-induced cell death.