The Structural Basis of Gas-Responsive Transcription by the Human Nuclear Hormone Receptor REV-ERBβ

Abstract

Heme is a ligand for the human nuclear receptors (NR) REV-ERBα and REV-ERBβ, which are transcriptional repressors that play important roles in circadian rhythm, lipid and glucose metabolism, and diseases such as diabetes, atherosclerosis, inflammation, and cancer. Here we show that transcription repression mediated by heme-bound REV-ERBs is reversed by the addition of nitric oxide (NO), and that the heme and NO effects are mediated by the C-terminal ligand-binding domain (LBD). A 1.9 Å crystal structure of the REV-ERBβ LBD, in complex with the oxidized Fe(III) form of heme, shows that heme binds in a prototypical NR ligand-binding pocket, where the heme iron is coordinately bound by histidine 568 and cysteine 384. Under reducing conditions, spectroscopic studies of the heme-REV-ERBβ complex reveal that the Fe(II) form of the LBD transitions between penta-coordinated and hexa-coordinated structural states, neither of which possess the Cys384 bond observed in the oxidized state. In addition, the Fe(II) LBD is also able to bind either NO or CO, revealing a total of at least six structural states of the protein. The binding of known co-repressors is shown to be highly dependent upon these various liganded states. REV-ERBs are thus highly dynamic receptors that are responsive not only to heme, but also to redox and gas. Taken together, these findings suggest new mechanisms for the systemic coordination of molecular clocks and metabolism. They also raise the possibility for gas-based therapies for the many disorders associated with REV-ERB biological functions.

Structure of REV-ERBβ Ligand-binding Domain Bound to a Porphyrin Antagonist

“…Heme binds directly to the REV-ERB ligand-binding domain (LBD) and regulates the ability of REVERBs to recruit NR corepressors such as NCoR to target gene promoters and repress transcription of downstream genes (4,10). A crystal structure of heme bound within the ligand-binding pocket of REV-ERB␤ has also been described confirming these biological observations (11). The apparent constitutive repressor effect previously noted for the REV-ERBs is most likely due to the fact that all cells have some level of intracellular heme present, thus providing the ligand-dependent repression activity of these receptors.…”

A circadian clock in hippocampus is regulated by interaction between oligophrenin-1 and Rev-erbα

“…For example, it has been shown that Rev-erbα's nuclear repressor activity depends on the oxidation state of its heme moiety and the ability of nitric oxide (NO) to bind heme 16 in reducing conditions. Since NO is a neurotransmitter involved in long term potentiation 28 we speculate that a similar mechanism might occur in synapses: by binding to Rev-erbα heme, NO might regulate the transcriptional repressor activity of Rev-erbα in target neurons to influence the expression of protein complexes in the dendritic spines and long-term synaptic plasticity.…”

20-Hydroxyecdysone (20E) Primary Response Gene E75 Isoforms Mediate Steroidogenesis Autoregulation and Regulate Developmental Timing in Bombyx

“…E75 binds to heme, which responds to gases NO and CO (7)(8)(9)(10)(11)(12). The E75 orthologs in mammals are Rev-erb ␣ (NR1D1) and Rev-erb ␤ (NR1D2), and NR1D2 binds to heme, responds to NO, and regulates circadian rhythm (13)(14)(15).…”