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Although CTLA-4 (CD152) has potent inhibitory effects on T cell function, the signaling events affected by this coreceptor remain to be fully defined. Mitogen-activated protein kinases (MAPK) extracellular signal-regulated kinase (ERK) and c-Jun N-terminal kinase (JNK) act as crucial regulators of multiple aspects of cell function. Ab ligation studies have reported an inhibitory effect of CTLA-4 on TCR-induced ERK and JNK activation. In this study, we have re-examined the specificity of CTLA-4 inhibition of MAPKs by using natural ligand with ex vivo-purified CD4(+) T cells deficient in CD80 and CD86 (double knockout), or CTLA-4, CD80, and CD86 (triple knockout). Under these conditions, CTLA-4 ligation was found to up-regulate and sustain JNK activation, while inhibiting ERK activity. At the same time, JNK activation could not account for CTLA-4 induction of TGF-beta production. Our findings demonstrate that CTLA-4 cosignaling is more complex than previously appreciated, with an ability to differentially regulate members of the MAPK family in T cells.
Schneider et al. (Tue,) studied this question.