Glucocorticoid receptor down-Regulates c-jun amino terminal kinases induced by tumor necrosis factor ? in fetal rat hepatocyte primary cultures

Abstract

The effect of dexamethasone on Jun N-terminal kinase (JNK) activity was assayed by using fetal hepatocytes in primary culture. The addition of tumor necrosis factor ␣ (TNF-␣) caused an increase in JNK in a dose-and timedependent manner. We show that activation of JNK by this extracellular signal is inhibited by dexamethasone in a dose-dependent fashion. This inhibitory effect was observed in cells treated for 10 minutes with dexamethasone in the presence of protein phosphatase inhibitors such as orthovanadate or okadaic acid, or in cells previously treated with actinomycin D. Glucocorticoid receptor (GR) can be precipitated with the fusion protein, GST-c-Jun (1-79), bound to agarose beads. However, the inhibitory effect of glucocorticoids on JNK activity was also observed using ATF-2 as substrate. In addition, dexamethasone inhibits JNK phosphorylation induced by TNF-␣. Finally, we show that GR can also be phosphorylated in tyrosine residues in response to TNF-␣ and epidermal growth factor (EGF) upon ligand-binding. Our results suggest that the antiinflammatory effect of glucocorticoids on the inflammatory pathways induced by TNF-␣ can be explained, at least in part, by modulating JNK activity through a direct proteinprotein interaction; the JNK phosphorylation and tyrosinephosphorylation state of GR may be regulatory steps also involved in that effect. (HEPATOLOGY 1999;29:849-857.)

Recovery of Mature Hepatocytic Phenotype following Bile Ductular Transdifferentiation of Rat Hepatocytes in Vitro

“…7 Dex inhibits the phosphorylation of JNK via a direct interaction with the glucocorticoid receptor in rat hepatocytes. 22 However, interestingly, Dex decreased JNK at the protein level in our experiments, suggesting that this may be a long-term effect of Dex in the regulation of JNK activity.…”

Dexamethasone Causes Sustained Expression of Mitogen-Activated Protein Kinase (MAPK) Phosphatase 1 and Phosphatase-Mediated Inhibition of MAPK p38

“…Inhibition of MAPK function by glucocorticoids has been described elsewhere (10,27,30,31,40,73). In a mast cell line, dexamethasone induced the expression of MKP-1 within 5 h, but inhibition of ERK function was observed only at much later time points (35).…”

“…However, glucocorticoids also posttranscriptionally repress a number of proinflammatory genes, several of which are known targets of the p38 pathway (3,26,48,60,67). As glucocorticoids have been shown to inhibit other members of the MAPK family (10,27,30,31,35,73), we hypothesized that posttranscriptional effects of dexamethasone involve the inhibition of p38 function. The synthetic glucocorticoid dexamethasone was demonstrated to inhibit p38 activity in a manner requiring ongoing, glucocorticoid receptor-mediated gene expression (40).…”

Activation of Potassium and Chloride Channels by Tumor Necrosis Factor α

“…In liver, TNF exhibits pleiotropic effects, ranging from reduction of bile flow to hepatocellular apoptosis (10 -12). Experimental evidence supports several mechanisms to account for such effects, including activation of caspases and kinases, generation of free radicals, and down-regulation of membrane organic solute transporters (13)(14)(15)(16)(17). Despite this body of evidence, there remain significant gaps in our knowledge regarding the responsible pathways that couple TNF to liver damage.…”