Calcineurin preferentially synergizes with PKC-θ to activate JNK and IL-2 promoter in T lymphocytes

Costimulation of the T cell receptor (TCR) and CD28 is required for optimal interleukin-2 (IL-2) induction. These signals, which can be replaced by the pharmacological agents phorbol ester (PMA) and Ca²⁺ ionophore, synergistically activate the mitogen-activated protein kinase (MAPK) JNK. Cyclosporin A, an Ca²⁺-dependent phosphatase calcineurin which blocks IL-2 induction, abrogates Ca²⁺ triggered synergistic JNK activation. As protein kinase C (PKC) downregulation inhibits PMA + ionophore-induced JNK activation, we examined whether a particular PKC isoform is preferentially involved in this response. We found that PKC-θ but neither PKC-α nor PKC-ε participates in JNK activation, whereas all three PKCs lead to ERK MAPK activation. PKC-θ specifically cooperates with calcineurin, and together their signals converge on (or upstream of) Rac leading to potent JNK activation. Similarly, calcineurin and PKC-θ specifically synergize to induce transcription of reporters driven by the c-jun and IL-2 promoters. PKC-θ and calcineurin are also partially responsible for the synergistic activation of JNK following TCR and CD28 ligation. Preferential cooperation between PKC-θ and calcineurin is observed in Jurkat T cells but not in HeLa cells. These results indicate that PKC isozymes have distinct biological functions and suggest that synergistic JNK activation is an important function for PKC-θ in T-cell activation.