CALCINEURIN PREFERENTIALLY SYNERGIZES WITH PKC-THETA TO ACTIVATE JNK AND IL-2 PROMOTER IN T-LYMPHOCYTES

Costimulation of the T cell receptor (TCR) and CD28 is required for op timal interleukin-2 (IL-2) induction. These signals, which can be repl aced by the pharmacological agents phorbol ester (PMA) and Ca2+ ionoph ore, synergistically activate the mitogen-activated protein kinase (MA PK) JNK, Cyclosporin A, an inhibitor of the Ca2+-dependent phosphatase calcineurin which blocks IL-2 induction, abrogates Ca2+ triggered syn ergistic JNK activation. As protein kinase C (PKC) downregulation inhi bits PMA+ionophore-induced JNK activation, we examined whether a parti cular PKC isoform is preferentially involved in this response. We foun d that PKC-theta but neither PKC-alpha nor PKC-epsilon participates in JNK activation, whereas all three PKCs lead to ERK MAPK activation, P KC-theta specifically cooperates with calcineurin, and together their signals converge on (or upstream of) Pac leading to potent JNK activat ion. Similarly, calcineurin and PKC-theta specifically synergize to in duce transcription of reporters driven by the c-jun and IL-2 promoters . PKC-theta and calcineurin are also partially responsible for the syn ergistic activation of JNK following TCR and CD28 ligation, Preferenti al cooperation between PKC-theta and calcineurin is observed in Jurkat T cells but not in HeLa cells, These results indicate that PKC isozym es have distinct biological functions and suggest that synergistic JNK activation is an important function for PKC-theta in T-cell activatio n.