The Drosophila Nuclear Receptor E75 Contains Heme and Is Gas Responsive

Abstract

Nuclear receptors are a family of transcription factors with structurally conserved ligand binding domains that regulate their activity. Despite intensive efforts to identify ligands, most nuclear receptors are still "orphans." Here, we demonstrate that the ligand binding pocket of the Drosophila nuclear receptor E75 contains a heme prosthetic group. E75 absorption spectra, resistance to denaturants, and effects of site-directed mutagenesis indicate a single, coordinately bound heme molecule. A correlation between the levels of E75 expression and the levels of available heme suggest a possible role as a heme sensor. The oxidation state of the heme iron also determines whether E75 can interact with its heterodimer partner DHR3, suggesting an additional role as a redox sensor. Further, the E75-DHR3 interaction is also regulated by the binding of NO or CO to the heme center, suggesting that E75 may also function as a diatomic gas sensor. Possible mechanisms and roles for these interactions are discussed.

Fin de l’orphelinat pour les récepteurs nucléaires REVERB

“…Cette approche peut permettre l'identification de ligands. C'est ainsi que Reinking et al, en exprimant dans E. coli le LBD de E75 [10], l'orthologue unique chez la drosophile des deux REVERB, ont obtenu une protéine purifiée de couleur rouge, suggérant une co-purification avec un chromophore. Les analyses ont montré qu'il s'agissait de la protoporphyrine IX couplée à un ion Fe 2+ , communément appelée hème.…”

The effects of chronic carbon monoxide treatment on diet-induced obesity and Rev-erb-alpha target gene expression in adipose tissue

“…Rev-erb-α is a gas responsive transcriptional repressor that has been shown to regulate circadian rhythms, metabolism, and adiposity [10,13,14]. Because CO is thought to bind Rev-erb and promote transcriptional repression [10], we examined the mRNA expression of Rev-erb-α targets in EWAT from mice with pre-existing diet-induced obesity that were treatment with CO for six weeks.…”

“…Because CO is thought to bind Rev-erb and promote transcriptional repression [10], we examined the mRNA expression of Rev-erb-α targets in EWAT from mice with pre-existing diet-induced obesity that were treatment with CO for six weeks. CO treatment did not alter the expression of the Rev-erb-α targets Bmal1, Pparγ, and Pgc-1α ( Figures 4A-4C).…”

“…Rev-erb-α is a ligand regulated transcription factor that acts as a transcriptional repressor [11,12] regulating circadian rhythms and metabolism [13,14]. Although heme has been identified as the ligand for Rev-erb-α [15,16], evidence suggests the Drosophila orthologue to Rev-erb-α binds CO and represses gene expression [10]. Whether or not the expression of Rev-erb-α targets is altered in tissues following CO treatment is not known, although a Rev-erb agonist has been shown to promote weight loss and suppress PGC-1α mRNA expression, an established target of Rev-erb-α [14].…”

“…CO may bind to the nuclear receptor Rev-erb-α [10]. Rev-erb-α is a ligand regulated transcription factor that acts as a transcriptional repressor [11,12] regulating circadian rhythms and metabolism [13,14].…”