The Degron Architecture of Squalene Monooxygenase and How Specific Lipids Calibrate Levels of This Key Cholesterol Synthesis Enzyme

2020 ◽  
Author(s):  
Ngee Kiat Chua ◽  
Andrew J. Brown
Keyword(s):  
Cholesterol Synthesis ◽  
Specific Lipids ◽  
Squalene Monooxygenase

Squalene monooxygenase: a journey to the heart of cholesterol synthesis

2020 ◽  
Vol 79 ◽  
pp. 101033 ◽  
Author(s):  
Ngee Kiat Chua ◽  
Hudson W. Coates ◽  
Andrew J. Brown
Keyword(s):  
Cholesterol Synthesis ◽  
Squalene Monooxygenase

Increased cholesterol synthesis via squalene monooxygenase to predict lethal prostate cancer.

2016 ◽  
Vol 34 (2_suppl) ◽  
pp. 77-77 ◽  
Author(s):  
Konrad Hermann Stopsack ◽  
Travis Gerke ◽  
James Robert Cerhan ◽  
Lorelei A. Mucci ◽  
Jennifer R. Rider
Keyword(s):  
Prostate Cancer ◽  
Cancer Progression ◽  
Cholesterol Synthesis ◽  
Watchful Waiting ◽  
Prostate Tissue ◽  
Health Study ◽  
Squalene Monooxygenase ◽  
Increased Risk ◽  
The Mean ◽  
Benign Prostate

77 Background: Prostate cancer cells rely on cholesterol for proliferation and androgen production. We recently demonstrated that increased expression of the second key enzyme of cholesterol synthesis, squalene monooxygenase (SQLE), is associated with higher prostate cancer-specific mortality (PCSM). We here validate findings in two additional prospective studies and investigate putative mechanisms. Methods: We analyzed the prospective prostatectomy cohorts within the Health Professionals Follow-up Study (HPFS) and the Physicians’ Health Study (PHS) as well as initially expectantly managed patients in the Swedish Watchful Waiting Study (SWWS). 258 lethal cancer cases and 469 patients who survived > 8 years without metastases were included. SQLE mRNA was measured in tumor specimens at diagnosis of all patients and in benign prostate tissue of 197 patients. Markers of tumor angiogenesis were assessed via immunohistochemistry in 169 HPFS patients. We estimated multivariable-adjusted odds ratios (ORs) and 95% confidence intervals (CIs) using logistic regression. Results: Higher SQLE expression was confirmed to be predictive of higher PCSM in the validation prostatectomy cohort PHS. Combining the two prostatectomy cohorts, men with high SQLE expression ( > 1 standard deviation above the mean) were 6.7 times (95% CI, 2.9 to 15.8; p < 0.001) more likely to die from their cancer compared to men with the mean level of SQLE expression. A 10% higher ratio of SQLE mRNA expression in tumor vs. benign prostate tissue of the same patient was predictive of 42% higher PCSM (95% CI, 15% to 74%). Higher SQLE expression was strongly associated with increased angiogenesis markers (all p ≤ 0.001). This increased risk associated with high SQLE expression was not modified by statin use (p ≥ 0.52). In initially untreated patients in SWWS, a more modest association of tumor SQLE expression with PCSM was observed (p = 0.047). Conclusions: SQLE, the second rate-limiting enzyme of cholesterol synthesis, is associated with prostate cancer progression. Its expression at cancer diagnosis is predictive of lethal disease both after curative-intent prostatectomy and in a watchful waiting setting, possibly by facilitating micrometastatic disease.

scholarly journals The mammalian cholesterol synthesis enzyme squalene monooxygenase is proteasomally truncated to a constitutively active form

2020 ◽  
Author(s):  
Hudson W. Coates ◽  
Andrew J. Brown
Keyword(s):  
Cholesterol Synthesis ◽  
Catalytic Domain ◽  
Active Form ◽  
Feedback Regulation ◽  
Intrinsically Disordered ◽  
Additional Layer ◽  
Squalene Monooxygenase ◽  
Lipid Sensing ◽  
The Stability ◽  
Constitutively Active

AbstractSqualene monooxygenase (SM) is a rate-limiting enzyme of cholesterol synthesis that is oncogenic in a range of cancer types. SM is subject to feedback regulation via cholesterol-induced degradation, which depends on its lipid-sensing N terminal regulatory domain. Here, we characterize an endogenous truncated form of SM and show that it is cholesterol-resistant, and therefore constitutively active. Truncation of SM occurs during its endoplasmic reticulum-associated degradation and requires the proteasome, which partially degrades the SM N-terminus and eliminates cholesterol-sensing elements within this region. Using mutagenesis studies, we demonstrate that partial degradation of SM depends on both an intrinsically disordered region near the truncation site and the stability of the adjacent catalytic domain. Finally, truncation converts SM from an integral to a peripheral ER membrane protein. These findings uncover an additional layer of complexity in the cellular control of cholesterol synthesis and establish SM as the first eukaryotic enzyme known to undergo proteasomal truncation.

Valosin-containing protein mediates the ERAD of squalene monooxygenase and its cholesterol-responsive degron

2019 ◽  
Vol 476 (18) ◽  
pp. 2545-2560 ◽  
Author(s):  
Ngee Kiat Chua ◽  
Nicola A. Scott ◽  
Andrew J. Brown
Keyword(s):  
Endoplasmic Reticulum ◽  
Cholesterol Synthesis ◽  
Protein Quality ◽  
Extraction Process ◽  
Dependent Manner ◽  
Amphipathic Helix ◽  
Extraction Mechanism ◽  
Cholesterol Levels ◽  
Squalene Monooxygenase ◽  
Rate Limiting

Abstract Squalene monooxygenase (SM) is an essential rate-limiting enzyme in cholesterol synthesis. SM degradation is accelerated by excess cholesterol, and this requires the first 100 amino acids of SM (SM N100). This process is part of a protein quality control pathway called endoplasmic reticulum-associated degradation (ERAD). In ERAD, SM is ubiquitinated by MARCH6, an E3 ubiquitin ligase located in the endoplasmic reticulum (ER). However, several details of the ERAD process for SM remain elusive, such as the extraction mechanism from the ER membrane. Here, we used SM N100 fused to GFP (SM N100-GFP) as a model degron to investigate the extraction process of SM in ERAD. We showed that valosin-containing protein (VCP) is important for the cholesterol-accelerated degradation of SM N100-GFP and SM. In addition, we revealed that VCP acts following ubiquitination of SM N100-GFP by MARCH6. We demonstrated that the amphipathic helix (Gln62–Leu73) of SM N100-GFP is critical for regulation by VCP and MARCH6. Replacing this amphipathic helix with hydrophobic re-entrant loops promoted degradation in a VCP-dependent manner. Finally, we showed that inhibiting VCP increases cellular squalene and cholesterol levels, indicating a functional consequence for VCP in regulating the cholesterol synthesis pathway. Collectively, we established VCP plays a key role in ERAD that contributes to the cholesterol-mediated regulation of SM.

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

2020 ◽  
Vol 117 (13) ◽  
pp. 7150-7158 ◽  
Author(s):  
Hiromasa Yoshioka ◽  
Hudson W. Coates ◽  
Ngee Kiat Chua ◽  
Yuichi Hashimoto ◽  
Andrew J. Brown ◽  
...  
Keyword(s):  
Biosynthetic Pathway ◽  
Cholesterol Synthesis ◽  
Cholesterol Biosynthesis ◽  
Squalene Epoxidase ◽  
Reporter Cell ◽  
Accelerated Degradation ◽  
Squalene Monooxygenase ◽  
Cholesterol Biosynthetic Pathway ◽  
The Stability ◽  
Rate Limiting

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.

scholarly journals Post-translational control of the long and winding road to cholesterol

2020 ◽  
Vol 295 (51) ◽  
pp. 17549-17559 ◽  
Author(s):  
Laura J. Sharpe ◽  
Hudson W. Coates ◽  
Andrew J. Brown
Keyword(s):  
Translational Control ◽  
Cholesterol Synthesis ◽  
Future Research ◽  
The Road ◽  
Squalene Monooxygenase ◽  
Ubiquitin Proteasome ◽  
Health And Disease ◽  
Proteasome Pathway ◽  
The Rich ◽  
Coa Reductase

The synthesis of cholesterol requires more than 20 enzymes, many of which are intricately regulated. Post-translational control of these enzymes provides a rapid means for modifying flux through the pathway. So far, several enzymes have been shown to be rapidly degraded through the ubiquitin–proteasome pathway in response to cholesterol and other sterol intermediates. Additionally, several enzymes have their activity altered through phosphorylation mechanisms. Most work has focused on the two rate-limiting enzymes: 3-hydroxy-3-methylglutaryl CoA reductase and squalene monooxygenase. Here, we review current literature in the area to define some common themes in the regulation of the entire cholesterol synthesis pathway. We highlight the rich variety of inputs controlling each enzyme, discuss the interplay that exists between regulatory mechanisms, and summarize findings that reveal an intricately coordinated network of regulation along the cholesterol synthesis pathway. We provide a roadmap for future research into the post-translational control of cholesterol synthesis, and no doubt the road ahead will reveal further twists and turns for this fascinating pathway crucial for human health and disease.

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