Glucocorticoids antagonize AP-1 by inhibiting the activation/phosphorylation of JNK without affecting its subcellular distribution

The immunosuppressive and antiinflammatory actions of glucocorticoid hormon es are mediated by their transrepression of activating protein-1 (AP-1) and nuclear factor-kappa B (NF kappa B) transcription factors. Inhibition of t he c-Jun NH2-terminal kinase (JNK) signaling pathway, the main mediator of AP-1 activation, has been described in extracts of hormone-treated cells. H ere, we show by confocal laser microscopy, enzymatic assays, and immunoblot ting that the synthetic glucocorticoid dexamethasone inhibited tumor necros is factor alpha (TNF-alpha)-induced phosphorylation and activation of JNK i n the cytoplasm and nucleus of intact HeLa cells. As a result, c-Jun NH2-te rminal domain phosphorylation and induction were impaired. Dexa methasone d id not block the TNF-alpha-induced JNK nuclear translocation, but rather in duced, per se, nuclear accumulation of the enzyme. Consistently with previo us findings, a glucocorticoid receptor mutant (GRdim), which is deficient i n dimerization, DNA binding, and transactivation, but retains AP-1 transrep ressing activity, was as efficient as wild-type GR in mediating the same ef fects of dexamethasone on JNK in transfected Cos-7 cells. Our results show that glucocorticoids antagonize the TNF-alpha-induced activation of AP-1 by causing the accumulation of inactive JNK without affecting its subcellular distribution.