High Affinity Heme Binding to a Heme Regulatory Motif on the Nuclear Receptor Rev-erb? Leads to Its Degradation and Indirectly Regulates Its Interaction with Nuclear Receptor Corepressor.

ABSTRACT: Rev-erb? and Rev-erb? are heme-binding nuclear receptors (NR) that repress the transcription of genes involved in regulating metabolism, inflammation, and the circadian clock. Previous gene expression and co-immunoprecipitation studies led to a model in which heme binding to Rev-erb? recruits nuclear receptor corepressor 1 (NCoR1) into an active repressor complex. However, in contradiction, biochemical and crystallographic studies have shown that heme decreases the affinity of the ligand-binding domain of Rev-erb NRs for NCoR1 peptides. One explanation for this discrepancy is that the ligand-binding domain and NCoR1 peptides used for in vitro studies cannot replicate the key features of the full-length proteins used in cellular studies. However, the combined in vitro and cellular results described here demonstrate that heme does not directly promote interactions between full-length Rev-erb? (FLRev-erb?) and an NCoR1 construct encompassing all three NR interaction domains. NCoR1 tightly binds both apo- and heme-replete FLRev-erb?·DNA complexes; furthermore, heme, at high concentrations, destabilizes the FLRev-erb?·NCoR1 complex. The interaction between FLRev-erb? and NCoR1 as well as Rev-erb? repression at the Bmal1 promoter appear to be modulated by another cellular factor(s), at least one of which is related to the ubiquitin-proteasome pathway. Our studies suggest that heme is involved in regulating the degradation of Rev-erb? in a manner consistent with its role in circadian rhythm maintenance. Finally, the very slow rate constant (10(-6) s(-1)) of heme dissociation from Rev-erb? rules out a prior proposal that Rev-erb? acts as an intracellular heme sensor.

SUBMITTER: Carter EL 

PROVIDER: S-EPMC4732205 | biostudies-literature | 2016 Jan

REPOSITORIES: biostudies-literature