The orphan receptor Rev-ErbA alpha activates transcription via a novel response element.
ABSTRACT Rev-ErbA alpha (Rev-Erb) is a nuclear hormone receptor-related protein encoded on the opposite strand of the alpha-thyroid hormone receptor (TR) gene. This unusual genomic arrangement may have a regulatory role, but the conservation of human and rodent Rev-Erb amino acid sequences suggests that the protein itself has an important function, potentially as a sequence-specific transcriptional regulator. However, despite its relationship to the TR, Rev-Erb bound poorly to TR binding sites. To determine its DNA-binding specificity in an unbiased manner, Rev-Erb was synthesized in Escherichia coli, purified, and used to select specific binding-sites from libraries of random double-stranded DNA sequences. We found that Rev-Erb binds to a unique site consisting of a specific 5-bp A/T-rich sequence adjacent to a TR half-site. Rev-Erb contacts this entire asymmetric 11-bp sequence, which is the longest nonrepetitive element specifically recognized by a member of the thyroid/steroid hormone receptor superfamily, and mutations in either the A/T-rich or TR half-site regions abolished specific binding. The binding specificity of wild-type Rev-Erb was nearly identical to that of C- and N-terminally truncated forms. This binding was not enhanced by retinoid X receptor, TR, or other nuclear proteins, none of which formed heterodimers with Rev-Erb. Rev-Erb also appeared to bind to the selected site as a monomer. Furthermore, Rev-Erb activates transcription through this binding site even in the absence of exogenous ligand. Thus, Rev-Erb is a transcriptional activator whose properties differ dramatically from those of classical nuclear hormone receptors, including the TR encoded on the opposite strand of the same genomic locus.
Full-textDOI: · Available from: Mitchell A Lazar, May 12, 2015
SourceAvailable from: Kazuhiko Imaizumi[Show abstract] [Hide abstract]
ABSTRACT: It is now evident that many nuclear hormone receptors can modulate target gene expression. REV-ERBα, one of the nuclear hormone receptors with the capacity to alter clock function, is critically involved in lipid metabolism, adipogenesis, and the inflammatory response. Recent studies suggest that REV-ERBα plays a key role in the mediation between clockwork and inflammation. The purpose of the current study was to investigate the role of REV-ERBα in the regulation of interleukin-6 (il6) gene expression in murine macrophages. REV-ERBα agonists, or overexpression of rev-erb α in the murine macrophage cell line RAW264 cells, suppressed the induction of il6 mRNA following a lipopolysaccharide (LPS) endotoxin challenge. Also, rev-erb α overexpression decreased LPS-stimulated nuclear factor κB (NFκB) activation in RAW264 cells. We showed that REV-ERBα represses il6 expression not only indirectly through an NFκB binding motif but also directly through a REV-ERBα binding motif in the murine il6 promoter region. Furthermore, peritoneal macrophages from mice lacking rev-erb α increased il6 mRNA expression. These data suggest that REV-ERBα regulates the inflammatory response of macrophages through the suppression of il6 expression. REV-ERBα may therefore be identified as a potent anti-inflammatory receptor and be a therapeutic target receptor of inflammatory diseases.01/2014; ２０１４(Article ID 685854):10 pages. DOI:10.1155/2014/685854
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ABSTRACT: Little is known about molecular links between circadian clocks and steroid hormone signalling, although both are important for normal physiology. Here we report a circadian function for a nuclear receptor, ecdysone-induced protein 75 (Eip75/E75), which we identified through a gain-of-function screen for circadian genes in Drosophila melanogaster. Overexpression or knockdown of E75 in clock neurons disrupts rest:activity rhythms and dampens molecular oscillations. E75 represses expression of the gene encoding the transcriptional activator, CLOCK (CLK), and may also affect circadian output. PER inhibits the activity of E75 on the Clk promoter, thereby providing a mechanism for a previously proposed de-repressor effect of PER on Clk transcription. The ecdysone receptor is also expressed in central clock cells and manipulations of its expression produce effects similar to those of E75 on circadian rhythms. We find that E75 protects rhythms under stressful conditions, suggesting a function for steroid signalling in the maintenance of circadian rhythms in Drosophila.Nature Communications 12/2014; 5:5697. DOI:10.1038/ncomms6697 · 10.74 Impact Factor