Non-canonical ubiquitination of the cholesterol-regulated degron of squalene monooxygenase

Chua, Ngee Kiat; Hart‐Smith, Gene; Brown, Andrew

doi:10.1074/jbc.ra119.007798

Cited by 38 publications

(29 citation statements)

References 94 publications

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“…Of note, the transferable SM N100 degron still behaves as such even when all five of its lysine residues are mutated to arginine [38]. Recently, a careful investigation of SM N100 serine residues identified Ser59, Ser61, Ser83 and Ser87 as critical for cholesterol-induced degradation and provided direct MS-based evidence that Ser83 is a site for ubiquitination; the evidence in this study also suggests that both MARCH6 and catalytically active Ube2j2 are important for this process [39]. Overall, these studies support that SQLE is capable of undergoing non-lysine-dependent degradation, which is facilitated by Ube2j2 and MARCH6.…”

Section: Non-lysine Ubiquitination Targets a Variety Of Cellular Procmentioning

confidence: 82%

Cellular functions and molecular mechanisms of non-lysine ubiquitination

2019

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Protein ubiquitination is of great cellular importance through its central role in processes such as degradation, DNA repair, endocytosis and inflammation. Canonical ubiquitination takes place on lysine residues, but in the past 15 years non-lysine ubiquitination on serine, threonine and cysteine has been firmly established. With the emerging importance of non-lysine ubiquitination, it is crucial to identify the responsible molecular machinery and understand the mechanistic basis for non-lysine ubiquitination. Here, we first provide an overview of the literature that has documented non-lysine ubiquitination. Informed by these examples, we then discuss the molecular mechanisms and cellular implications of non-lysine ubiquitination, and conclude by outlining open questions and future perspectives in the field.

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Section: Non-lysine Ubiquitination Targets a Variety Of Cellular Procmentioning

confidence: 82%

Cellular functions and molecular mechanisms of non-lysine ubiquitination

2019

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“…Beyond transcriptional regulation, we investigated the post-translational regulation of LSS and LDM. We have previously characterised pre-lanosterol (SM [7,31,[53][54][55][56]) and the terminal (DHCR7 [8,47,57,58] and DHCR24 [9,46,59]) enzymes of cholesterol synthesis. However, little research has been conducted on the intermediate enzymes within the pathway.…”

Section: Discussionmentioning

confidence: 99%

The cholesterol synthesis enzyme lanosterol 14α-demethylase is post-translationally regulated by the E3 ubiquitin ligase MARCH6

Scott

Sharpe

Capell-Hattam

et al. 2020

Biochemical Journal

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Cholesterol synthesis is a tightly controlled pathway, with over 20 enzymes involved. Each of these enzymes can be distinctly regulated, helping to fine-tune the production of cholesterol and its functional intermediates. Several enzymes are degraded in response to increased sterol levels, whilst others remain stable. We hypothesised that an enzyme at a key branch point in the pathway, lanosterol 14α-demethylase (LDM) may be post-translationally regulated. Here, we show that the preceding enzyme, lanosterol synthase is stable, whilst LDM is rapidly degraded. Surprisingly, this degradation is not triggered by sterols. However, the E3 ubiquitin ligase membrane-associated ring-CH-type finger 6 (MARCH6), known to control earlier rate-limiting steps in cholesterol synthesis, also control levels of LDM and the terminal cholesterol synthesis enzyme, 24-dehydrocholesterol reductase. Our work highlights MARCH6 as the first example of an E3 ubiquitin ligase that targets multiple steps in a biochemical pathway and indicates new facets in the control of cholesterol synthesis.

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“…NB-598 and Squalene Stabilize SM-N100 by Blunting MARCH6 Interaction and Ubiquitination. MARCH6 is an ER-resident E3 ubiquitin ligase, which ubiquitinates SM (9) at the SM-N100 regulatory domain, targeting it for degradation (10,11). Therefore, we hypothesized that squalene accumulation may stabilize SM-N100 by disrupting its MARCH6-mediated degradation.…”

Section: Nb-598-mediated Stabilization Is Dependent On the Availabilimentioning

confidence: 99%

“…SM senses excess cholesterol in the endoplasmic reticulum (ER) membrane through its N-terminal 100-residue regulatory region (SM-N100), and alters its own stability depending on the cholesterol concentration (5,7,8). Membrane-associated ring-CH type finger 6 (MARCH6) is the cognate E3 ligase for SM (9,10), catalyzing its ubiquitination in the N100 region (11).…”

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confidence: 99%

A key mammalian cholesterol synthesis enzyme, squalene monooxygenase, is allosterically stabilized by its substrate

Yoshioka

Coates

Chua

et al. 2020

Proc. Natl. Acad. Sci. U.S.A.

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Cholesterol biosynthesis is a high-cost process and, therefore, tightly regulated by both transcriptional and posttranslational negative feedback mechanisms in response to the level of cellular cholesterol. Squalene monooxygenase (SM, also known as squalene epoxidase or SQLE) is a rate-limiting enzyme in the cholesterol biosynthetic pathway and catalyzes epoxidation of squalene. The stability of SM is negatively regulated by cholesterol via its N-terminal regulatory domain (SM-N100). In this study, using a SM-luciferase fusion reporter cell line, we performed a chemical genetics screen that identified inhibitors of SM itself as up-regulators of SM. This effect was mediated through the SM-N100 region, competed with cholesterol-accelerated degradation, and required the E3 ubiquitin ligase MARCH6. However, up-regulation was not observed with statins, well-established cholesterol biosynthesis inhibitors, and this pointed to the presence of another mechanism other than reduced cholesterol synthesis. Further analyses revealed that squalene accumulation upon treatment with the SM inhibitor was responsible for the up-regulatory effect. Using photoaffinity labeling, we demonstrated that squalene directly bound to the N100 region, thereby reducing interaction with and ubiquitination by MARCH6. Our findings suggest that SM senses squalene via its N100 domain to increase its metabolic capacity, highlighting squalene as a feedforward factor for the cholesterol biosynthetic pathway.

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Non-canonical ubiquitination of the cholesterol-regulated degron of squalene monooxygenase

Cited by 38 publications

References 94 publications

Cellular functions and molecular mechanisms of non-lysine ubiquitination

Cellular functions and molecular mechanisms of non-lysine ubiquitination

The cholesterol synthesis enzyme lanosterol 14α-demethylase is post-translationally regulated by the E3 ubiquitin ligase MARCH6

A key mammalian cholesterol synthesis enzyme, squalene monooxygenase, is allosterically stabilized by its substrate

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