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The sterol-responsive RNF145 E3 ubiquitin ligase mediates the degradation of HMG-CoA reductase together with gp78 and Hrd1.

ABSTRACT: Mammalian HMG-CoA reductase (HMGCR), the rate-limiting enzyme of the cholesterol biosynthetic pathway and the therapeutic target of statins, is post-transcriptionally regulated by sterol-accelerated degradation. Under cholesterol-replete conditions, HMGCR is ubiquitinated and degraded, but the identity of the E3 ubiquitin ligase(s) responsible for mammalian HMGCR turnover remains controversial. Using systematic, unbiased CRISPR/Cas9 genome-wide screens with a sterol-sensitive endogenous HMGCR reporter, we comprehensively map the E3 ligase landscape required for sterol-accelerated HMGCR degradation. We find that RNF145 and gp78 independently co-ordinate HMGCR ubiquitination and degradation. RNF145, a sterol-responsive ER-resident E3 ligase, is unstable but accumulates following sterol depletion. Sterol addition triggers RNF145 recruitment to HMGCR via Insigs, promoting HMGCR ubiquitination and proteasome-mediated degradation. In the absence of both RNF145 and gp78, Hrd1, a third UBE2G2-dependent E3 ligase, partially regulates HMGCR activity. Our findings reveal a critical role for the sterol-responsive RNF145 in HMGCR regulation and elucidate the complexity of sterol-accelerated HMGCR degradation.

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This article has been through an editorial process in which the authors decide how to respond to the issues raised during peer review. The Reviewing Editor's assessment is that all the issues have been addressed (see decision letter).

SUBMITTER: Menzies SA

PROVIDER: S-EPMC6292692 | biostudies-literature | 2018 Dec

REPOSITORIES: biostudies-literature

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The sterol-responsive RNF145 E3 ubiquitin ligase mediates the degradation of HMG-CoA reductase together with gp78 and Hrd1.

Menzies Sam A SA Volkmar Norbert N van den Boomen Dick Jh DJ Timms Richard T RT Dickson Anna S AS Nathan James A JA Lehner Paul J PJ

eLife 20181213

Mammalian HMG-CoA reductase (HMGCR), the rate-limiting enzyme of the cholesterol biosynthetic pathway and the therapeutic target of statins, is post-transcriptionally regulated by sterol-accelerated degradation. Under cholesterol-replete conditions, HMGCR is ubiquitinated and degraded, but the identity of the E3 ubiquitin ligase(s) responsible for mammalian HMGCR turnover remains controversial. Using systematic, unbiased CRISPR/Cas9 genome-wide screens with a sterol-sensitive endogenous HMGCR re ...[more]

PMID: 30543180

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Project description:HMG-CoA reductase (HMGR) is the target of statins, cholesterol-lowering drugs prescribed to millions of patients worldwide. More recent research indicates that HMGR could be a useful target in the development of antimicrobial agents. Over the last seven decades, researchers have proposed a series of increasingly complex reaction mechanisms for this biomedically important enzyme. The maturation of the mechanistic proposals for HMGR have paralleled advances in a diverse set of research areas, such as molecular biology and computational chemistry. Thus, the development of the HMGR mechanism provides a useful case study for following the advances in state-of-the-art methods in enzyme mechanism research. Similarly, the questions raised by these mechanism proposals reflect the limitations of the methods used to develop them. The mechanism of HMGR, a four-electron oxidoreductase, is unique and far more complex than originally thought. The reaction contains multiple chemical steps, coupled to large-scale domain motions of the homodimeric enzyme. The first proposals for the HMGR mechanism were based on kinetic and labeling experiments, drawing analogies to the mechanism of known dehydrogenases. Advances in molecular biology and bioinformatics enabled researchers to use site-directed mutagenesis experiments and protein sequencing to identify catalytically important glutamate, aspartate, and histidine residues. These studies, in turn, have generated new and more complicated mechanistic proposals. With the development of protein crystallography, researchers solved HMGR crystal structures to reveal an unexpected lysine residue at the center of the active site. The many crystal structures of HMGR led to increasingly complex mechanistic proposals, but the inherent limitations of the protein crystallography left a number of questions unresolved. For example, the protonation state of the glutamate residue within the active site cannot be clearly determined from the crystal structure. The differing protonation state of this residue leads to different proposed mechanisms for the enzyme. As computational analysis of large biomolecules has become more feasible, the application of methods such as hybrid quantum mechanics/molecular mechanics (QM/MM) calculations to the HMGR mechanism have led to the most detailed mechanistic proposal yet. As these methodologies continue to improve, they prove to be very powerful for the study of enzyme mechanisms in conjunction with protein crystallography. Nevertheless, even the most current mechanistic proposal for HMGR remains incomplete due to limitations of the current computational methodologies. Thus, HMGR serves as a model for how the combination of increasingly sophisticated experimental and computational methods can elucidate very complex enzyme mechanisms.

Dataset Information

The sterol-responsive RNF145 E3 ubiquitin ligase mediates the degradation of HMG-CoA reductase together with gp78 and Hrd1.

Editorial note

Publications

The sterol-responsive RNF145 E3 ubiquitin ligase mediates the degradation of HMG-CoA reductase together with gp78 and Hrd1.

Similar Datasets

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