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The heme-regulatory motif of nuclear receptor Rev-erb? is a key mediator of heme and redox signaling in circadian rhythm maintenance and metabolism.

ABSTRACT: Rev-erb? is a heme-responsive transcription factor that regulates genes involved in circadian rhythm maintenance and metabolism, effectively bridging these critical cellular processes. Heme binding to Rev-erb? indirectly facilitates its interaction with the nuclear receptor co-repressor (NCoR1), resulting in repression of Rev-erb? target genes. Fe³⁺-heme binds in a 6-coordinate complex with axial His and Cys ligands, the latter provided by a heme-regulatory motif (HRM). Rev-erb? was thought to be a heme sensor based on a weak K_d value for the Rev-erb?·heme complex of 2 ?m determined with isothermal titration calorimetry. However, our group demonstrated with UV-visible difference titrations that the K_d value is in the low nanomolar range, and the Fe³⁺-heme off-rate is on the order of 10^-6 s^-1 making Rev-erb? ineffective as a sensor of Fe³⁺-heme. In this study, we dissected the kinetics of heme binding to Rev-erb? and provided a K_d for Fe³⁺-heme of ?0.1 nm Loss of the HRM axial thiolate via redox processes, including oxidation to a disulfide with a neighboring cysteine or dissociation upon reduction of Fe³⁺- to Fe²⁺-heme, decreased binding affinity by >20-fold. Furthermore, as measured in a co-immunoprecipitation assay, substitution of the His or Cys heme ligands in Rev-erb? was accompanied by a significant loss of NCoR1 binding. These results demonstrate the importance of the Rev-erb? HRM in regulating interactions with heme and NCoR1 and advance our understanding of how signaling through HRMs affects the major cellular processes of circadian rhythm maintenance and metabolism.

SUBMITTER: Carter EL

PROVIDER: S-EPMC5500795 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:Ultraviolet B radiation (UVB) exerts pleiotropic effects on human skin. DNA damage response and repair pathways are activated by UVB; if damage cannot be repaired, apoptosis ensues. Although cumulative UVB exposure predisposes to skin cancer, UVB phototherapy is widely used as an effective treatment for psoriasis. Previous studies defined the therapeutic action spectrum of UVB and showed that psoriasis is resistant to apoptosis. This study aimed to investigate early molecular responses within psoriasis plaques following irradiation with single equi-erythemogenic doses of clinically-effective (311 nm, narrow-band) compared to clinically-ineffective (290 nm) UVB. Forty-eight micro-dissected epidermal samples from 20 psoriatic patients were analyzed using microarrays. Our bioinformatic analysis compared gene expression between 311 nm irradiated, 290 nm irradiated and control psoriasis epidermis to specifically identify 311 nm UVB differentially expressed genes (DEGs) and their upstream regulatory pathways. Key DEGs and pathways were validated by immunohistochemical analysis. There was a dynamic induction and repression of 311 nm UVB DEGs between 6 h and 18 h, only a limited number of DEGs maintained their designated expression status between time-points. Key disease and function pathways included apoptosis, cell death, cell migration and leucocyte chemotaxis. DNA damage response pathways, NRF2-mediated oxidative stress response and P53 signalling were key nodes, interconnecting apoptosis and cell cycle arrest. Interferon signalling, dendritic cell maturation, granulocyte adhesion and atherosclerotic pathways were also differentially regulated. Consistent with these findings, top transcriptional regulators of 311 nm UVB DEGs related to: a) apoptosis, DNA damage response and cell cycle control; b) innate/acquired immune regulation and inflammation; c) hypoxia/redox response and angiogenesis; d) circadian rhythmicity; f) EGR/AP1 signalling and keratinocyte differentiation; and g) mitochondrial biogenesis. This research provides important insights into the molecular targets of 311 nm UVB, underscoring key roles for apoptosis and cell death. These and the other key pathways delineated may be central to the therapeutic effects of 311 nm in psoriasis.

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The heme-regulatory motif of nuclear receptor Rev-erb? is a key mediator of heme and redox signaling in circadian rhythm maintenance and metabolism.

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