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Glucocorticoid receptor [alpha] (GR[alpha]) and peroxisome proliferator-activated receptor [alpha] (PPAR[alpha]) are transcription factors with clinically important immune-modulating properties. Either receptor can inhibit cytokine gene expression, mainly through interference with nuclear factor [kappa]B (NF-[kappa]B)-driven gene expression. The present work aimed to investigate a functional cross-talk between PPAR[alpha]- and GR[alpha]-mediated signaling pathways. Simultaneous activation of PPAR[alpha] and GR[alpha] dose-dependently enhances transrepression of NF-[kappa]B-driven gene expression and additively represses cytokine production. In sharp contrast and quite unexpectedly, PPAR[alpha] agonists inhibit the expression of classical glucocorticoid response element (GRE)-driven genes in a PPAR[alpha]-dependent manner, as demonstrated by experiments using PPAR[alpha] wild-type and knockout mice. The unclerlying mechanism for this transcriptional antagonism relies on a PPAR[alpha]-mediated interference with the recruitment of GR[alpha], and concomitantly of RNA polymerase II, to GRE-driven gene promoters. Finally, the biological relevance of this phenomenon is underscored by the observation that treatment with the PPAR[alpha] agonist fenofibrate prevents glucocorticoid-induced hyperinsulinemia of mice fed a high-fat diet. Taken together, PPAR[alpha] negatively interferes with GRE-mediated GR[alpha] activity while potentiating its antiinflammatory effects, thus providing a rationale for combination therapy in chronic inflammatory disorders. cross-talk | gluconeogenesis | inflammation | hyperinsulinema | side effects

The localization and identification of the photoreceptor cell-specific nuclear gene NR2E3 as a novel disease locus and gene for 'autosomal dominant retinitis pigmentosa' (adRP) is described. A different pathogenetic mechanism is proposed for these distinct dominant and recessive phenotypes, which is attributed to the dual key role of NR2E3 in the regulation-specific genes during rod development and maintenance.

Glucocorticoids exert multiple anti-inflammatory activities, one of which is the inhibition of transcription dependent on the nuclear factor (NF)-[Kappa]B. It has been suggested that the effect of dexamethasone (DEX), a glucocorticoid analog, is attributed to an increased production of the inhibitory I[Kappa]B molecule, which in turn would bind and remove activated, DNA-bound NF-[Kappa]B complexes in the cell nucleus. Upon investigating DEX-mediated repression of interleukin-6 expression induced by tumor necrosis factor, DEX treatment was found to act directly on NF-[Kappa]B-dependent transcription, without changing the expression level of I[Kappa]B. Neither the mRNA of I[Kappa]B nor the protein was significantly elevated by a combined treatment with tumor necrosis factor and DEX of murine endothelial or fibroblast cells. The DNA-binding activity of induced NF-[Kappa]B also remained unchanged after stimulation of cells with DEX. Evidence for a direct nuclear mechanism of action was obtained by analysis of cell lines stably expressing a fusion protein between the DNA-binding domain of the yeast Gal4 protein and the transactivating p65 subunit of NF-[Kappa]B. Expression of a Gal4-dependent luciferase reporter gene activated by this nuclear fusion protein was also strongly repressed after addition of DEX. Because the DNAbinding activity of the Gal4 fusion protein was not affected by DEX, it can be concluded that the reduction of gene activation was caused by interference of the activated glucocorticoid receptor with the transactivation potential of the NF-[Kappa]B p65 subunit.

Abstract Background Multidrug resistance (MDR) is a major obstacle in cancer treatment and is often the result of overexpression of the drug efflux protein, P-glycoprotein (P-gp), as a consequence of hyperactivation of NFκB, AP1 and Nrf2 transcription factors. In addition to effluxing chemotherapeutic drugs, P-gp also plays a specific role in blocking caspase-dependent apoptotic pathways. One feature that cytotoxic treatments of cancer have in common is activation of the transcription factor NFκB, which regulates inflammation, cell survival and P-gp expression and suppresses the apoptotic potential of chemotherapeutic agents. As such, NFκB inhibitors may promote apoptosis in cancer cells and could be used to overcome resistance to chemotherapeutic agents. Results Although the natural withanolide withaferin A and polyphenol quercetin, show comparable inhibition of NFκB target genes (involved in inflammation, angiogenesis, cell cycle, metastasis, anti-apoptosis and multidrug resistance) in doxorubicin-sensitive K562 and -resistant K562/Adr cells, only withaferin A can overcome attenuated caspase activation and apoptosis in K562/Adr cells, whereas quercetin-dependent caspase activation and apoptosis is delayed only. Interestingly, although withaferin A and quercetin treatments both decrease intracellular protein levels of Bcl2, Bim and P-Bad, only withaferin A decreases protein levels of cytoskeletal tubulin, concomitantly with potent PARP cleavage, caspase 3 activation and apoptosis, at least in part via a direct thiol oxidation mechanism. Conclusions This demonstrates that different classes of natural NFκB inhibitors can show different chemosensitizing effects in P-gp overexpressing cancer cells with impaired caspase activation and attenuated apoptosis.

Glucocorticoids (GCs) are used to combat inflammatory diseases. Their beneficial effect relies mainly on the inhibition of NF-[Kappa]B-and/or AP-1-driven proinflammatory gene expression. Previously, we have shown that GCs repress tumor necrosis factor-induced IL-6 gene expression by an NF-[Kappa]B-dependent nuclear mechanism without changing the DNA-binding capacity of NF-[Kappa]B or the expression levels of the cytoplasmic inhibitor of NF-[Kappa]B (I[Kappa]B-[Alpha]). In the present work, we investigate the effect of GC repression on different natural and/or recombinant NF-[Kappa]B-driven reporter gene constructs in the presence of increasing amounts of various coactivator molecules, such as CREB-binding protein (CBP), p300, and SRC-1. We found that GCs maintain their repressive capacities, irrespective of the amount of cofactor present in the cell. Similar results were obtained for the reciprocal transrepression of a GC receptor (GR) element-driven reporter gene by p65. We demonstrate that neither the expression levels of p65 and CBP nor their physical association are affected by activated GR. Using Gal4 chimeras, we show that repression by GCs is specific for p65-mediated transactivation, ruling out competition for limiting nuclear factors as the major underlying mechanism of gene repression. In addition, the transactivation potential of a point-mutated Ga14-p65 variant with a decreased CBP interaction capability is still repressed by GR. Finally, we present evidence that the specificity of GC repression on p65-driven gene expression is codetermined by the TATA box context.