title: Inhibition of extracellular signal-regulated kinase (ERK) signaling participates in repression of nuclear factor (NF)-kappaB activity by glucocorticoids.
abstract: Glucocorticoid (GC) effects are mediated via the GC-receptor (GR), which either stimulates or represses gene expression. Repression of target genes often involves negative cross-talk between the GR and other transcription factors e.g. NF-kappaB, important for gene activation. Using HEK293 cells we here describe that repression of NF-kappaB requires functions of the GR that are dependent on the signaling pathways employed to activate NF-kappaB. While a GR mutant was able to repress NF-kappaB activity following activation by TNFalpha, it did not so following activation by the phorbol ester TPA. In these cells, TPA stimulation but not TNFalpha, activated extracellular signal-regulated kinase (ERK). We demonstrated that the ability of the dexamethasone activated GR mutant to repress TPA-induced NF-kappaB activity was restored in conjunction with ERK1/2 inhibition. Previous reports have shown GC-mediated inhibition of ERK1/2 phosphorylation to involve GC induction of MAPK phosphatase-1 (MKP-1). Here, we demonstrated that the GRR488Q mutant was incapable of inducing gene expression of endogenous MKP-1 following dexamethasone treatment, in contrast to the GRwt. However, TPA treatment alone resulted in much stronger MKP-1 expression in both GRwt and GRR488Q containing cells than that of dexamethasone suggesting that the inability of GRR488Q to inhibit TPA-induced NF-kappaB activity did not involve a lack of MKP-1 expression. In line with this, RNAi targeted towards MKP-1 did not abolish or inhibit the ability of the GRwt to repress NF-kappaB activity. Importantly, we observed no difference in activated ERK1/2 (phospho-ERK1/2) expression over time between GRwt and GRR488Q containing cells following co-treatment with TPA and dexamethasone. Based on these results we suggest that GRwt does not directly regulate ERK1/2 but rather alters ERK1/2-mediated effects allowing it to repress NF-kappaB activity, a capacity lacked by the GRR488Q mutant.
authors.affiliation: Department of Biosciences and Nutrition, Karolinska Institutet, Novum, Huddinge, Sweden.
authors.forename: Lars-Göran
authors.initials: LG
authors.lastname: Bladh
authors.forename: Krishan
authors.initials: K
authors.lastname: Johansson-Haque
authors.forename: Ingalill
authors.initials: I
authors.lastname: Rafter
authors.forename: Stefan
authors.initials: S
authors.lastname: Nilsson
authors.forename: Sam
authors.initials: S
authors.lastname: Okret
mesh_terms: D003907:Dexamethasone / Q000494:pharmacology; D054638:Dual Specificity Phosphatase 1 / Q000235:genetics / Q000378:metabolism; D048049:Extracellular Signal-Regulated MAP Kinases / Q000037:antagonists & inhibitors* / Q000378:metabolism; D005938:Glucocorticoids / Q000494:pharmacology*; D006801:Humans; D020935:MAP Kinase Signaling System; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D016328:NF-kappa B / Q000037:antagonists & inhibitors* / Q000378:metabolism; D014162:Transfection
chemical_list: D005938:Glucocorticoids; D016328:NF-kappa B; D003907:Dexamethasone; D048049:Extracellular Signal-Regulated MAP Kinases; D020928:Mitogen-Activated Protein Kinases; C517019:DUSP1 protein, human; D054638:Dual Specificity Phosphatase 1