Glucocorticoids Antagonize Ap-1 by Inhibiting the Activation/Phosphorylation of Jnk without Affecting Its Subcellular Distribution

Abstract

The immunosuppressive and antiinflammatory actions of glucocorticoid hormones are mediated by their transrepression of activating protein-1 (AP-1) and nuclear factor-kappa B (NFκB) transcription factors. Inhibition of the c-Jun NH2-terminal kinase (JNK) signaling pathway, the main mediator of AP-1 activation, has been described in extracts of hormone-treated cells. Here, we show by confocal laser microscopy, enzymatic assays, and immunoblotting that the synthetic glucocorticoid dexamethasone inhibited tumor necrosis factor α (TNF-α)–induced phosphorylation and activation of JNK in the cytoplasm and nucleus of intact HeLa cells. As a result, c-Jun NH2-terminal domain phosphorylation and induction were impaired. Dexamethasone did not block the TNF-α–induced JNK nuclear translocation, but rather induced, per se, nuclear accumulation of the enzyme. Consistently with previous findings, a glucocorticoid receptor mutant (GRdim), which is deficient in dimerization, DNA binding, and transactivation, but retains AP-1 transrepressing activity, was as efficient as wild-type GR in mediating the same effects of dexamethasone on JNK in transfected Cos-7 cells. Our results show that glucocorticoids antagonize the TNF-α–induced activation of AP-1 by causing the accumulation of inactive JNK without affecting its subcellular distribution.

Cross-talk between glucocorticoid receptor and AP-1

“…Rather ligandinduced GR or an associated factor seems to downmodulate JNK enzyme activity. In addition, JNK activity was inhibited in both cytoplasm and nucleus and nuclear uptake of JNK was not a ected (Gonza lez et al, 2000). Although it is disturbing that in these experiments hormone was added 45 min prior to treatment with the JNK activating agent, the inhibition may be`immediate' which is in contrast to the delayed e ect mentioned above which requires more than 6 h of hormone pretreatment.…”

“…All nuclear receptors including the GR inhibit AP-1 target gene transcription SchuÈ le et al, 1990;Yang-Yen et al, 1990;Shemshedini et al, 1991). Although in the initial studies no interference with Jun or Fos phosphorylation was discovered (Jonat, 1990;Jonat et al, 1990), a rapid and transcription-independent inhibition of Jun phosphorylation and of JNK activity has been reported (Caelles et al, 1997;Gonza lez et al, 2000). As JNK activity was determined by immune precipitate assay with an excess of GST-Jun as substrate, it is unlikely that the substrate was shielded from enzyme action by GR bound to the substrate.…”

Nontranscriptional actions of the glucocorticoid receptor

“…Acute Dex treatment interfered with JNK activation in the cytoplasm and nucleus without altering JNK subcellular distribution. These effects did not involve direct interaction between JNK and GR and were independent of DNA binding, since a dimerization defective GR mutant, which lacks transcriptional capacity, is still able to suppress JNK activation in response to Dex [63].…”

Jun, the oncoprotein

“…The following are some examples: The glucocorticoid receptor interferes with Jun activity, but under certain conditions can also exert an enhancing e ect (Diamond et al, 1990;Schule et al, 1990;Teurich and Angel, 1995;Yang-Yen et al, 1990). The mechanism of this interaction is complex; it may involve the regulation of JNK (Gonzalez et al, 2000). The inhibition of Jun induced by the glucocorticoid receptor a ects oncogenic transformation: it interferes with Jun induced transormation and secondarily with transformation by oncoproteins that depend on Jun, e.g.…”