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

作者：Carter Eric L; Gupta Nirupama; Ragsdale Stephen W^*

来源：JOURNAL OF BIOLOGICAL CHEMISTRY, 2016, 291(5): 2196-2222.

DOI：10.1074/jbc.M115.670281

Rev-erb beta and Rev-erb beta 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 beta 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 beta (FLRev-erb beta) and an NCoR1 construct encompassing all three NR interaction domains. NCoR1 tightly binds both apo- and heme-replete FLRev-erb beta.DNA complexes; furthermore, heme, at high concentrations, destabilizes the FLRev-erb beta-NCoR1 complex. The interaction between FLRev-erb beta and NCoR1 as well as Rev-erb beta 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 beta 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 beta rules out a prior proposal that Rev-erb beta acts as an intracellular heme sensor.

• 出版日期2016-1-29