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Andrew J Brown - One of the best experts on this subject based on the ideXlab platform.
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the mammalian cholesterol synthesis enzyme Squalene Monooxygenase is proteasomally truncated to a constitutively active form
Journal of Biological Chemistry, 2021Co-Authors: Hudson W Coates, Isabelle M Capellhattam, Andrew J BrownAbstract:Squalene Monooxygenase (SM, also known as Squalene epoxidase) is a rate-limiting enzyme of cholesterol synthesis that converts Squalene to monooxidoSqualene and is oncogenic in numerous cancer types. SM is subject to feedback regulation via cholesterol-induced proteasomal degradation, which depends on its lipid-sensing N-terminal regulatory domain. We previously identified an endogenous truncated form of SM with a similar abundance to full-length SM, but whether this truncated form is functional or subject to the same regulatory mechanisms as full-length SM is not known. Here, we show that truncated SM differs from full-length SM in two major ways: it is cholesterol resistant and adopts a peripheral rather than integral association with the endoplasmic reticulum membrane. However, truncated SM retains full SM activity and is 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 disrupts cholesterol-sensing elements within the regulatory domain. Furthermore, truncation relies on a ubiquitin signal that is distinct from that required for cholesterol-induced degradation. Using mutagenesis, we demonstrate that partial proteasomal degradation of SM depends on both an intrinsically disordered region near the truncation site and the stability of the adjacent catalytic domain, which escapes degradation. These findings uncover an additional layer of complexity in the post-translational regulation of cholesterol synthesis and establish SM as the first eukaryotic enzyme found to undergo proteasomal truncation.
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the mammalian cholesterol synthesis enzyme Squalene Monooxygenase is proteasomally truncated to a constitutively active form
bioRxiv, 2020Co-Authors: Hudson W Coates, Andrew J BrownAbstract: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.
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the degron architecture of Squalene Monooxygenase and how specific lipids calibrate levels of this key cholesterol synthesis enzyme
Advances in Experimental Medicine and Biology, 2020Co-Authors: Ngee Kiat Chua, Andrew J BrownAbstract:Cholesterol synthesis is a fundamental process that contributes to cellular cholesterol homeostasis. Cells execute transcriptional and post-translational mechanisms to control the abundance of enzymes of the cholesterol synthesis pathway, consequently affecting cholesterol production. One such highly tuned enzyme is Squalene Monooxygenase (SM), which catalyzes a rate-limiting step in the pathway. A well-characterized mechanism is the cholesterol-mediated degradation of SM. Notably, lipids (cholesterol, plasmalogens, Squalene, and unsaturated fatty acids) can act as cellular signals that either promote or reduce SM degradation. The N-terminal region of SM consists of the shortest known cholesterol-responsive degron, characterized by atypical membrane anchoring structures, namely a re-entrant loop and an amphipathic helix. SM also undergoes non-canonical ubiquitination on serine, a relatively uncommon attachment site for ubiquitination. The structure of the catalytic domain of SM has been solved, providing insights into the catalytic mechanisms and modes of inhibition by well-known SM inhibitors, some of which have been effective in lowering cholesterol levels in animal models. Certain human cancers have been linked to dysregulation of SM levels and activity, further emphasizing the relevance of SM in health and disease.
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Squalene Monooxygenase a journey to the heart of cholesterol synthesis
Progress in Lipid Research, 2020Co-Authors: Ngee Kiat Chua, Hudson W Coates, Andrew J BrownAbstract:Squalene Monooxygenase (SM) is a vital sterol synthesis enzyme across eukaryotic life. In yeast, it is a therapeutic target for treating certain fungal infections, and in mammals it is a rate-limiting enzyme that represents a key control point in the cholesterol synthesis pathway. SM introduces an oxygen atom to Squalene, which becomes the signature oxygen of the hydroxyl group in cholesterol. Our knowledge of SM has advanced tremendously since its initial cloning and characterization. Early research developed mammalian SM inhibitors to target SM for cholesterol-lowering purposes. The substrate Squalene has gained considerable interest for its health benefits and in nanomedicine for delivery of drugs. More recently, SM has been implicated as a key dysregulated component in certain cancers. In this review, we summarize our present knowledge of SM, focusing on the regulation of SM and the gene encoding it, SQLE. Furthermore, we offer insights into the role of SM across different organisms and its significance in human health and disease.
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a key mammalian cholesterol synthesis enzyme Squalene Monooxygenase is allosterically stabilized by its substrate
Proceedings of the National Academy of Sciences of the United States of America, 2020Co-Authors: Hiromasa Yoshioka, Ngee Kiat Chua, Andrew J Brown, Hudson W Coates, Yuichi Hashimoto, Kenji OhganeAbstract: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.
Todd D Porter - One of the best experts on this subject based on the ideXlab platform.
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New insights into the role of cytochrome P450 reductase (POR) in microsomal redox biology
Acta Pharmaceutica Sinica B, 2012Co-Authors: Todd D PorterAbstract:Cytochrome P450 reductase (POR) is an essential electron transfer protein located on the endoplasmic reticulum of most cell types, and has long been appreciated for its role in cytochrome P450-mediated drug metabolism. Additional roles and electron acceptors for POR have been described, but it is largely with the recent availability of POR-null tissues that these supplemental roles for POR have been able to be explored. These studies have confirmed POR as the principal redox partner for the microsomal P450s responsible for drug and xenobiotic metabolism as well as cholesterol and bile acid synthesis, and for heme oxygenase, which catalyzes the initial step in the breakdown of heme. Surprisingly, these studies have revealed that Squalene Monooxygenase, an enzyme essential to cholesterol synthesis, has a second unknown redox partner in addition to POR, and that 7-dehydrocholesterol reductase, previously proposed to require POR as an electron donor, functions fully independently of POR. These studies have also helped define the role of cytochrome b5 in P450 catalysis, and raise the question as to the extent to which POR contributes to b5-dependent redox pathways.
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hepatic cytochrome p450 reductase null mice reveal a second microsomal reductase for Squalene Monooxygenase
Archives of Biochemistry and Biophysics, 2007Co-Authors: Todd D PorterAbstract:Squalene Monooxygenase is a microsomal enzyme that catalyzes the conversion of Squalene to 2,3(s)-oxidoSqualene, the immediate precursor to lanosterol in the cholesterol biosynthesis pathway. Unlike other flavoprotein Monooxygenases that obtain electrons directly from NAD(P)H, Squalene Monooxygenase requires a redox partner, and for many years it has been assumed that NADPH-cytochrome P450 reductase is this requisite redox partner. However, our studies with hepatic cytochrome P450-reductase-null mice have revealed a second microsomal reductase for Squalene Monooxygenase. Inhibition studies with antibody to P450 reductase indicate that this second reductase supports up to 40% of the Monooxygenase activity that is obtained with microsomes from normal mice. Studies carried out with hepatocytes from CPR-null mice demonstrate that this second reductase is active in whole cells and leads to the accumulation of 24-dihydrolanosterol; this lanosterol metabolite also accumulates in the livers of CPR-null mice, indicating that cholesterol synthesis is blocked at lanosterol demethylase, a cytochrome P450.
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supernatant protein factor stimulates hmg coa reductase in cell culture and in vitro
Archives of Biochemistry and Biophysics, 2005Co-Authors: Vishwesh Mokashi, Dev K Singh, Todd D PorterAbstract:Abstract Supernatant protein factor (SPF) is a 46-kDa cytosolic protein that stimulates Squalene Monooxygenase in vitro and, unexpectedly, cholesterol synthesis in cell culture. Because Squalene Monooxygenase is not thought to be rate-limiting with regard to cholesterol synthesis, we investigated the possibility that SPF might stimulate other enzymes in the cholesterol biosynthetic pathway. Substitution of [ 14 C]mevalonate for [ 14 C]acetate in McARH7777 hepatoma cells expressing SPF reduced the 1.8-fold increase in cholesterol synthesis by half, suggesting that SPF acted on or prior to mevalonate synthesis. This conclusion was supported by the finding that substitution with [ 14 C]mevalonate completely blocked an SPF-induced increase in Squalene synthesis. Evaluation of 2,3-oxidoSqualene synthesis from [ 14 C]mevalonate demonstrated that SPF also stimulated Squalene Monooxygenase (1.3-fold) in hepatoma cells. Immunoblot analysis showed that SPF did not increase HMG-CoA reductase or Squalene Monooxygenase enzyme levels, indicating a direct effect on enzyme activity. Addition of purified recombinant SPF to rat liver microsomes stimulated HMG-CoA reductase by about 1.5-fold, and the SPF-concentration/activation curve paralleled that for the SPF-mediated stimulation of Squalene Monooxygenase. These results reveal that SPF directly stimulates HMG-CoA reductase, the rate-limiting step of the cholesterol biosynthetic pathway, as well as Squalene Monooxygenase, and suggest a new means by which cholesterol synthesis can be rapidly modulated in response to hormonal and environmental signals.
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rat supernatant protein factor like protein stimulates Squalene Monooxygenase and is activated by protein kinase a
Biochemical and Biophysical Research Communications, 2004Co-Authors: Vishwesh Mokashi, Dev K Singh, Todd D PorterAbstract:Rat supernatant protein factor-like protein (SPF2) shares 90% sequence identity with rat SPF and 77% identity with human SPF, both of which have been shown to stimulate Squalene Monooxygenase in the cholesterol biosynthetic pathway. SPF2 appears to be predominantly expressed in respiratory and epithelial tissues, whereas SPF is expressed in liver. To determine if SPF2 was also able to stimulate Squalene Monooxygenase activity, we have cloned, expressed, and purified the protein following heterologous expression in Escherichia coli. SPF2 was only half as effective as SPF in stimulating Squalene epoxidation and was more strongly inhibited by GTP and GDP. The inhibition by guanine nucleotides was fully prevented by α-tocopherol, a reported ligand for these proteins. Incubation of SPF2 with protein kinase A and ATP increased its activity by about twofold, has been found for SPF. These results indicate that SPF2 activity is modulated by guanine nucleotides and α-tocopherol, as well as by phosphorylation.
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phosphorylation of supernatant protein factor enhances its ability to stimulate microsomal Squalene Monooxygenase
Journal of Biological Chemistry, 2003Co-Authors: Dev K Singh, Vishwesh Mokashi, Lee C Elmore, Todd D PorterAbstract:Supernatant protein factor is a 46-kDa cytosolic protein that stimulates Squalene Monooxygenase, a downstream enzyme in the cholesterol biosynthetic pathway. The mechanism of stimulation is poorly understood, although supernatant protein factor belongs to a family of lipid-binding proteins that includes Sec14p and alpha-tocopherol transfer protein. Because recombinant human supernatant protein factor purified from Escherichia coli exhibited a relatively weak ability to activate microsomal Squalene Monooxygenase, we investigated the possibility that cofactors or post-translational modifications were necessary for full activity. Addition of ATP to rat liver cytosol increased supernatant protein factor activity by more than 2-fold and could be prevented by the addition of inhibitors of protein kinases A and C. Incubation of purified recombinant supernatant protein factor with ATP and protein kinases A or C delta similarly increased activity by more than 2-fold. Addition of protein phosphatase 1 gamma, a serine/threonine phosphatase, to rat liver cytosol reduced activity by 50%, suggesting that supernatant protein factor is partially phosphorylated in vivo. To determine whether dietary cholesterol influenced the phosphorylation state, cytosols were prepared from livers of rats fed a high fat diet. Although supernatant protein factor activity was reduced by more than one-half, it could not be restored by the addition of ATP or protein kinase C delta with ATP, suggesting that dietary cholesterol reduced the expression of this protein. Supernatant protein factor thus appears to be regulated both post-translationally through phosphorylation and at the level of expression. Phosphorylation may provide a means for the rapid short term modulation of cholesterol synthesis.
Ngee Kiat Chua - One of the best experts on this subject based on the ideXlab platform.
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the degron architecture of Squalene Monooxygenase and how specific lipids calibrate levels of this key cholesterol synthesis enzyme
Advances in Experimental Medicine and Biology, 2020Co-Authors: Ngee Kiat Chua, Andrew J BrownAbstract:Cholesterol synthesis is a fundamental process that contributes to cellular cholesterol homeostasis. Cells execute transcriptional and post-translational mechanisms to control the abundance of enzymes of the cholesterol synthesis pathway, consequently affecting cholesterol production. One such highly tuned enzyme is Squalene Monooxygenase (SM), which catalyzes a rate-limiting step in the pathway. A well-characterized mechanism is the cholesterol-mediated degradation of SM. Notably, lipids (cholesterol, plasmalogens, Squalene, and unsaturated fatty acids) can act as cellular signals that either promote or reduce SM degradation. The N-terminal region of SM consists of the shortest known cholesterol-responsive degron, characterized by atypical membrane anchoring structures, namely a re-entrant loop and an amphipathic helix. SM also undergoes non-canonical ubiquitination on serine, a relatively uncommon attachment site for ubiquitination. The structure of the catalytic domain of SM has been solved, providing insights into the catalytic mechanisms and modes of inhibition by well-known SM inhibitors, some of which have been effective in lowering cholesterol levels in animal models. Certain human cancers have been linked to dysregulation of SM levels and activity, further emphasizing the relevance of SM in health and disease.
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Squalene Monooxygenase a journey to the heart of cholesterol synthesis
Progress in Lipid Research, 2020Co-Authors: Ngee Kiat Chua, Hudson W Coates, Andrew J BrownAbstract:Squalene Monooxygenase (SM) is a vital sterol synthesis enzyme across eukaryotic life. In yeast, it is a therapeutic target for treating certain fungal infections, and in mammals it is a rate-limiting enzyme that represents a key control point in the cholesterol synthesis pathway. SM introduces an oxygen atom to Squalene, which becomes the signature oxygen of the hydroxyl group in cholesterol. Our knowledge of SM has advanced tremendously since its initial cloning and characterization. Early research developed mammalian SM inhibitors to target SM for cholesterol-lowering purposes. The substrate Squalene has gained considerable interest for its health benefits and in nanomedicine for delivery of drugs. More recently, SM has been implicated as a key dysregulated component in certain cancers. In this review, we summarize our present knowledge of SM, focusing on the regulation of SM and the gene encoding it, SQLE. Furthermore, we offer insights into the role of SM across different organisms and its significance in human health and disease.
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a key mammalian cholesterol synthesis enzyme Squalene Monooxygenase is allosterically stabilized by its substrate
Proceedings of the National Academy of Sciences of the United States of America, 2020Co-Authors: Hiromasa Yoshioka, Ngee Kiat Chua, Andrew J Brown, Hudson W Coates, Yuichi Hashimoto, Kenji OhganeAbstract: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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valosin containing protein mediates the erad of Squalene Monooxygenase and its cholesterol responsive degron
Biochemical Journal, 2019Co-Authors: Ngee Kiat Chua, Nicola A Scott, Andrew J BrownAbstract: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. However, several details of the ERAD process for SM remain elusive, such as the extraction mechanism from the endoplasmic reticulum 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.
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Non-canonical ubiquitination of the cholesterol-regulated degron of Squalene Monooxygenase
The Journal of biological chemistry, 2019Co-Authors: Ngee Kiat Chua, Gene Hart-smith, Andrew J BrownAbstract:Squalene Monooxygenase (SM) is a rate-limiting enzyme in cholesterol synthesis. The region comprising the first 100 amino acids, termed SM N100, represents the shortest cholesterol-responsive degron and enables SM to sense excess cholesterol in the endoplasmic reticulum (ER) membrane. Cholesterol accelerates the ubiquitination of SM by membrane-associated ring-CH type finger 6 (MARCH6), a key E3 ubiquitin ligase involved in ER-associated degradation. However, the ubiquitination site required for cholesterol regulation of SM N100 is unknown. Here, we used SM N100 fused to GFP as a model degron to recapitulate cholesterol-mediated SM degradation and show that neither SM lysine residues nor the N terminus impart instability. Instead, we discovered four serines (Ser-59, Ser-61, Ser-83, and Ser-87) that are critical for cholesterol-accelerated degradation, with MS analysis confirming Ser-83 as a ubiquitination site. Notably, these two clusters of closely spaced serine residues are located in disordered domains flanking a 12-amino acid-long amphipathic helix (residues Gln-62-Leu-73) that together confer cholesterol responsiveness. In summary, our findings reveal the degron architecture of SM N100, introducing the role of non-canonical ubiquitination sites and deepening our molecular understanding of how SM is degraded in response to cholesterol.
Masanori Honsho - One of the best experts on this subject based on the ideXlab platform.
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plasmalogen homeostasis regulation of plasmalogen biosynthesis and its physiological consequence in mammals
FEBS Letters, 2017Co-Authors: Masanori HonshoAbstract:Plasmalogens, mostly ethanolamine-containing alkenyl ether phospholipids, are a major subclass of glycerophospholipids. Plasmalogen synthesis is initiated in peroxisomes and completed in the endoplasmic reticulum. The absence of plasmalogens in several organs of peroxisome biogenesis-defective patients suggests that the de novo synthesis of plasmalogens plays a pivotal role in its homeostasis in tissues. Plasmalogen synthesis is regulated by modulating the stability of fatty acyl-CoA reductase 1 on peroxisomal membranes, a rate-limiting enzyme in plasmalogen synthesis, by sensing plasmalogens in the inner leaflet of plasma membranes. Dysregulation of plasmalogen homeostasis impairs cholesterol biosynthesis by altering the stability of Squalene Monooxygenase, a key enzyme in cholesterol biosynthesis, implying physiological consequences of plasmalogen homeostasis with respect to cholesterol metabolism in cells, as well as in organs such as the liver.
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Dataset for: Plasmalogen homeostasis: regulation of plasmalogen biosynthesis and its physiological consequence in mammals
2017Co-Authors: Masanori Honsho, Yukio FujikiAbstract:Plasmalogens, mostly ethanolamine-containing alkenyl ether phospholipids, are a major sub-class of glycerophospholipids. Plasmalogen synthesis is initiated in peroxisomes and completed in endoplasmic reticulum. The absence of plasmalogens in several organs of peroxisome biogenesis-defective patients suggests that de novo synthesis of plasmalogens plays a pivotal role in the plasmalogen homeostasis in tissues. Plasmalogen synthesis is regulated by modulating the stability of fatty acyl-CoA reductase 1 on peroxisomal membrane, a rate-limiting enzyme in plasmalogen synthesis, by sensing plasmalogens in the inner leaflet of plasma membranes. Dysregulation of plasmalogen homeostasis impairs cholesterol biosynthesis by altering the stability of Squalene Monooxygenase, a key enzyme in the cholesterol biosynthesis, implying physiological consequences of plasmalogen homeostasis in cholesterol metabolism in cells and organs such as liver
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dysregulation of plasmalogen homeostasis impairs cholesterol biosynthesis
Journal of Biological Chemistry, 2015Co-Authors: Masanori HonshoAbstract:Plasmalogen biosynthesis is regulated by modulating fatty acyl-CoA reductase 1 stability in a manner dependent on cellular plasmalogen level. However, physiological significance of the regulation of plasmalogen biosynthesis remains unknown. Here we show that elevation of the cellular plasmalogen level reduces cholesterol biosynthesis without affecting the isoprenylation of proteins such as Rab and Pex19p. Analysis of intermediate metabolites in cholesterol biosynthesis suggests that the first oxidative step in cholesterol biosynthesis catalyzed by Squalene Monooxygenase (SQLE), an important regulator downstream HMG-CoA reductase in cholesterol synthesis, is reduced by degradation of SQLE upon elevation of cellular plasmalogen level. By contrast, the defect of plasmalogen synthesis causes elevation of SQLE expression, resulting in the reduction of 2,3-epoxySqualene required for cholesterol synthesis, hence implying a novel physiological consequence of the regulation of plasmalogen biosynthesis.
Konrad H Stopsack - One of the best experts on this subject based on the ideXlab platform.
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cholesterol metabolism and prostate cancer lethality
Cancer Research, 2016Co-Authors: Konrad H Stopsack, Travis Gerke, Jennifer A Sinnott, Kathryn L Penney, Svitlana Tyekucheva, Howard D SessoAbstract:Cholesterol metabolism has been implicated in prostate cancer pathogenesis. Here, we assessed the association of intratumoral mRNA expression of cholesterol synthesis enzymes, transporters, and regulators in tumor specimen at diagnosis and lethal prostate cancer, defined as mortality or metastases from prostate cancer in contrast to nonlethal disease without evidence of metastases after at least 8 years of follow-up. We analyzed the prospective prostate cancer cohorts within the Health Professionals Follow-up Study (n = 249) and the Physicians' Health Study (n = 153) as well as expectantly managed patients in the Swedish Watchful Waiting Study (n = 338). The expression of Squalene Monooxygenase (SQLE) was associated with lethal cancer in all three cohorts. Men with high SQLE expression (>1 standard deviation above the mean) were 8.3 times (95% confidence interval, 3.5 to 19.7) more likely to have lethal cancer despite therapy compared with men with the mean level of SQLE expression. Absolute SQLE expression was associated with lethal cancer independently from Gleason grade and stage, as was a SQLE expression ratio in tumor versus surrounding benign prostate tissue. Higher SQLE expression was tightly associated with increased histologic markers of angiogenesis. Collectively, this study establishes the prognostic value of intratumoral cholesterol synthesis as measured via SQLE, its second rate-limiting enzyme. SQLE expression at cancer diagnosis is prognostic for lethal prostate cancer both after curative-intent prostatectomy and in a watchful waiting setting, possibly by facilitating micrometastatic disease. Cancer Res; 76(16); 4785-90. ©2016 AACR.
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abstract 60 pten expression cholesterol metabolism and lethal prostate cancer
Cancer Research, 2016Co-Authors: Konrad H Stopsack, Travis Gerke, Lorelei A Mucci, Jennifer R RiderAbstract:BACKGROUND: We previously showed that mRNA expression of Squalene Monooxygenase (SQLE), part of the cholesterol synthesis pathway, is associated with lethal prostate cancer. In-vitro studies suggest that loss of PTEN expression and resulting PI3K pathway activation drive cholesterol ester accumulation in aggressive prostate cancers through sterol regulatory element-binding protein (SREBP) and acyl coenzyme A-cholesterol acyltransferase (ACAT1) activity. In two prospective cohorts, we studied whether lower PTEN expression is associated with cholesterol metabolism and how this relates to lethal prostate cancer. METHODS: We analyzed men with prostate cancer from the prospective prostatectomy Health Professionals Follow-up Study and Physicians’ Health Study. 105 men had lethal cancer and 284 men non-lethal disease without metastases at 8 years of follow-up. Whole-transcriptome mRNA expression profiling data was available from diagnostic prostate tumor specimens. Linear regression models were used to assess continuous and categorical associations, and Pearson correlation coefficients were calculated. Logistic regression was used to obtain odds ratios (ORs) and 95% confidence intervals (CIs) of lethal prostate cancer. RESULTS: Both lower PTEN and higher SQLE expression were associated with higher Gleason grade (p trend 0.05). Adjusting for PTEN mildly attenuated the association of SQLE with lethal cancer (OR, 2.07; 95% CI, 1.57 to 2.73), as did additional adjustment for age, Gleason grade, and stage (SQLE: OR, 1.75; 95% CI, 1.29 to 2.40). In the lowest quartile of PTEN expression, SQLE was less strongly associated with lethal cancer (OR 1.74; 95% CI, 1.20 to 2.52) compared to the upper three quartiles (OR 2.47; 95% CI, 1.69 to 3.60; p interaction = 0.2). CONCLUSION: Low PTEN mRNA expression and high SQLE are features of aggressive prostate cancers. However, at the time of prostatectomy, SREBF1/2 expression and resulting ACAT1 expression do not appear to be major characteristics of prostate cancers with lethal outcomes. Citation Format: Konrad H. Stopsack, Travis A. Gerke, Lorelei A. Mucci, Jennifer R. Rider. PTEN expression, cholesterol metabolism, and lethal prostate cancer. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 60.
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increased cholesterol synthesis via Squalene Monooxygenase to predict lethal prostate cancer
Journal of Clinical Oncology, 2016Co-Authors: Konrad H Stopsack, Travis Gerke, Lorelei A Mucci, James R Cerhan, Jennifer R RiderAbstract: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%...