ORCID Profile
0000-0002-6506-5249
Current Organisation
University of Cambridge
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Publisher: Elsevier BV
Date: 12-2020
Publisher: Springer Science and Business Media LLC
Date: 16-01-2023
Publisher: Elsevier BV
Date: 07-2020
Publisher: eLife Sciences Publications, Ltd
Date: 19-01-2023
DOI: 10.7554/ELIFE.82843
Abstract: Cholesterol synthesis is both energy- and oxygen-intensive, yet relatively little is known of the regulatory effects of hypoxia on pathway enzymes. We previously showed that the rate-limiting and first oxygen-dependent enzyme of the committed cholesterol synthesis pathway, squalene monooxygenase (SM), can undergo partial proteasomal degradation that renders it constitutively active. Here, we show hypoxia is a physiological trigger for this truncation, which occurs through a two-part mechanism: (1) increased targeting of SM to the proteasome via stabilization of the E3 ubiquitin ligase MARCHF6 and (2) accumulation of the SM substrate, squalene, which impedes the complete degradation of SM and liberates its truncated form. This preserves SM activity and downstream pathway flux during hypoxia. These results uncover a feedforward mechanism that allows SM to accommodate fluctuating substrate levels and may contribute to its widely reported oncogenic properties.
Publisher: Elsevier BV
Date: 12-2022
DOI: 10.1016/J.JLR.2022.100295
Abstract: The enzymatic pathway of cholesterol biosynthesis has been well characterized. However, there remain several potential interacting proteins that may play ancillary roles in the regulation of cholesterol production. Here we identified ERG28 (C14orf1), a homologue of the yeast protein Erg28p, as a player in mammalian cholesterol synthesis. ERG28 is conserved from yeast to humans, but has been largely overlooked in mammals. Using qRT-PCR, luciferase assays, and publicly available ChIP-seq data, we found that transcription of this gene is driven by the transcription factor SREBP-2, akin to the vast majority of cholesterol synthesis enzymes, as well as identifying sterol responsive elements and co-factor binding sites in its proximal promoter. Based on a split luciferase system, ERG28 interacted with itself and two enzymes of cholesterol synthesis (NSDHL and SC4MOL). Huh7 ERG28-knockout cell-lines were generated, revealing reduced total cholesterol levels in sterol-depleted environments. Additionally, radiolabeled metabolic flux assays showed a 60 to 75% reduction in the rate of cholesterol synthesis in the knockout versus wild-type cells, which could be rescued by expression of ectopic ERG28. Unexpectedly, knockout of ERG28 also impaired the activation of SREBP-2 under sterol replete conditions, by a yet-to-be defined mechanism. These results indicate that ERG28 is clearly involved in cholesterol synthesis, although the precise role this non-catalytic protein plays in this complex metabolic pathway remains to be fully elucidated. A deeper understanding of ERG28, and other ancillary proteins of cholesterol synthesis, may help inform therapeutic strategies for diseases associated with aberrant cholesterol metabolism.
Publisher: American Association for the Advancement of Science (AAAS)
Date: 18-04-0011
DOI: 10.1126/SCITRANSLMED.AAT3741
Abstract: A key enzyme in cholesterol synthesis is placed firmly on the oncogenic map and demonstrated to be a potential therapeutic target in liver cancer by repurposing a common antifungal agent (Liu et al ., this issue).
Publisher: eLife Sciences Publications, Ltd
Date: 30-11-2022
Publisher: Elsevier BV
Date: 10-2019
Publisher: Informa UK Limited
Date: 07-0022
Publisher: Elsevier
Date: 2021
Publisher: Proceedings of the National Academy of Sciences
Date: 13-03-2020
Abstract: 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.
Publisher: Elsevier BV
Date: 11-2019
DOI: 10.1016/J.BBALIP.2019.08.006
Abstract: Cholesterol accumulation is a hallmark of prostate cancer (PCa) enabled by the upregulation of its synthesis, which presents a potential therapeutic target. This pathway is suppressed by the E3 ubiquitin ligase membrane-associated RING-CH-type finger 6 (MARCH6) however, little is known of MARCH6 regulation, particularly at the transcriptional level. Here, we consulted large transcriptomic PCa datasets to investigate transcription factors and DNA sequence elements that regulate the MARCH6 gene. Amongst 498 primary PCa tissues of The Cancer Genome Atlas, we identified a striking positive correlation between MARCH6 and androgen receptor (AR) gene expression (r = 0.81, p < 1 × 10
Publisher: Routledge
Date: 12-2009
Publisher: American Association for the Advancement of Science (AAAS)
Date: 05-03-2021
Abstract: Cholesterol levels in cells are controlled by the sterol regulatory element–binding protein (SREBP) pathway. When the cell has sufficient cholesterol, the transcription factor that regulates cholesterol metabolism is sequestered at the endoplasmic reticulum membrane, but when cholesterol is depleted, the transcription factor is released to activate the expression of genes involved in cholesterol synthesis and uptake. Yan et al. determined the structure of a central complex in human SREBP containing the proteins Scap and Insig-2. These two membrane-embedded proteins undergo 25-hydroxycholesterol (25HC)–dependent association and must dissociate for the pathway to be activated. The structure shows that 25HC is sandwiched between Scap and Insig-2 to facilitate their association. A mutational analysis is consistent with the structural model. Science , this issue p. eabb2224
Publisher: Cold Spring Harbor Laboratory
Date: 19-08-2022
DOI: 10.1101/2022.08.18.504470
Abstract: Cholesterol synthesis is both energy- and oxygen-intensive, yet relatively little is known of the regulatory effects of hypoxia on pathway enzymes. We previously showed that the rate-limiting and first oxygen-requiring enzyme of the committed cholesterol synthesis pathway, squalene monooxygenase (SM), can undergo partial proteasomal degradation that renders it constitutively active. Here, we show that hypoxia is the physiological trigger for this truncation, which occurs through a two-part mechanism: (1) increased targeting of SM to the proteasome via stabilization of the E3 ubiquitin ligase MARCHF6, and (2) accumulation of the SM substrate, squalene, which impedes the complete degradation of SM and liberates its truncated form. Truncation of SM is also increased in endometrial cancer tissues, where it correlates with levels of hypoxia-inducible factor−1α. These results uncover a feedforward mechanism that enables SM to accommodate fluctuations in substrate levels yet is also a likely contributor to its widely reported oncogenic properties.
Publisher: Cold Spring Harbor Laboratory
Date: 12-10-2020
DOI: 10.1101/2020.10.12.335414
Abstract: Squalene 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.
Publisher: Elsevier BV
Date: 2021
Location: United Kingdom of Great Britain and Northern Ireland
No related grants have been discovered for Hudson W. Coates.