High Affinity Heme Binding to a Heme Regulatory Motif on the Nuclear Receptor Rev-erbβ Leads to Its Degradation and Indirectly Regulates Its Interaction with Nuclear Receptor Corepressor
High Affinity Heme Binding to a Heme Regulatory Motif on the Nuclear Receptor Rev-erbβ Leads to Its Degradation and Indirectly Regulates Its Interaction with Nuclear Receptor Corepressor
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DOI：
10.1074/jbc.m115.670281
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发表时间：
2016-01-29
影响因子：
4.8
通讯作者：
Ragsdale, Stephen W.
中科院分区：
文献类型：
--
作者：
Carter, Eric L.;Gupta, Nirupama;Ragsdale, Stephen W.
Rev-erb beta和Rev-erb beta是血红素结合核受体（NR），抑制参与调节代谢、炎症和生物钟的基因的转录。先前的基因表达和免疫共沉淀研究导致了一个模型，其中血红素结合Rev-erb β招募核受体辅阻遏物1（NCoR 1）进入活性阻遏物复合物。然而，在矛盾，生物化学和晶体学研究表明，血红素降低了NCoR 1肽的配体结合域的Rev-erb NR的亲和力。这种差异的一种解释是，用于体外研究的配体结合结构域和NCoR 1肽不能复制细胞研究中使用的全长蛋白质的关键特征。然而，本文所述的体外和细胞结果表明，血红素并不直接促进全长Rev-erb β（FLRev-erb β）和包含所有三个NR相互作用结构域的NCoR 1构建体之间的相互作用。NCoR 1与富含载脂蛋白和血红素的FLRev-erb β DNA复合物紧密结合;此外，高浓度的血红素使FLRev-erb β-NCoR 1复合物不稳定。FLRev-erb β和NCoR 1之间的相互作用以及Bmal 1启动子处的Rev-erb β抑制似乎受到另一种细胞因子的调节，其中至少一种与泛素-蛋白酶体途径相关。我们的研究表明，血红素参与调节Rev-erb β的降解，其方式与其在昼夜节律维持中的作用一致。最后，血红素从Rev-erb β解离的非常慢的速率常数（10（-6）s（-1））排除了先前的提议，即Rev-erb β作为细胞内血红素传感器。
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.