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Forbes D. Porter - One of the best experts on this subject based on the ideXlab platform.
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altered cerebrospinal fluid proteins in smith lemli opitz syndrome patients
American Journal of Medical Genetics Part A, 2016Co-Authors: Stephanie M Cologna, Christopher A. Wassif, Simona Bianconi, Christine Shieh, Cynthia L Toth, Antony Cougnoux, Kathryn R Burkert, Forbes D. PorterAbstract:Smith-Lemli-Opitz syndrome (SLOS) is an autosomal recessive, multiple malformation syndrome with neurocognitive impairment. SLOS arises from mutations in the 7-Dehydrocholesterol Reductase gene which results in impaired enzymatic conversion of 7-Dehydrocholesterol to cholesterol. In the current work, we sought to measure proteins that were altered in the cerebrospinal fluid from SLOS patients compared to pediatric controls. Using a multi-analyte antibody-based assay, we found that 12 proteins are altered in SLOS patients. Validation studies were carried out and the findings from this study suggest alterations in extracellular matrix remodeling and further evidence of oxidative stress within the disease pathophysiology. The results of this study will be used to explore biological pathways altered in SLOS and identifies a set of CSF proteins that can be evaluated as biomarkers in future therapeutic trials. © 2016 Wiley Periodicals, Inc.
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Altered cerebrospinal fluid proteins in Smith–Lemli–Opitz syndrome patients
American journal of medical genetics. Part A, 2016Co-Authors: Stephanie M Cologna, Christopher A. Wassif, Simona Bianconi, Christine Shieh, Cynthia L Toth, Antony Cougnoux, Kathryn R Burkert, Forbes D. PorterAbstract:Smith-Lemli-Opitz syndrome (SLOS) is an autosomal recessive, multiple malformation syndrome with neurocognitive impairment. SLOS arises from mutations in the 7-Dehydrocholesterol Reductase gene which results in impaired enzymatic conversion of 7-Dehydrocholesterol to cholesterol. In the current work, we sought to measure proteins that were altered in the cerebrospinal fluid from SLOS patients compared to pediatric controls. Using a multi-analyte antibody-based assay, we found that 12 proteins are altered in SLOS patients. Validation studies were carried out and the findings from this study suggest alterations in extracellular matrix remodeling and further evidence of oxidative stress within the disease pathophysiology. The results of this study will be used to explore biological pathways altered in SLOS and identifies a set of CSF proteins that can be evaluated as biomarkers in future therapeutic trials. © 2016 Wiley Periodicals, Inc.
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Discordant phenotype and sterol biochemistry in Smith-Lemli-Opitz syndrome.
American journal of medical genetics. Part A, 2010Co-Authors: Grace Koo, Christopher A. Wassif, Sandra K Conley, Forbes D. PorterAbstract:Smith-Lemli-Opitz syndrome (SLOS) is a malformation syndrome resulting from mutations of the 7-Dehydrocholesterol Reductase (DHCR7) gene. During cholesterol biosynthesis, DHCR7 catalyzes the conversion of 7-Dehydrocholesterol (7DHC) to cholesterol. A clinical diagnosis of SLOS is confirmed biochemically by the presence of elevated levels of 7DHC. Phenotypic severity of SLOS has previously been shown to correlate with the 7DHC/cholesterol ratio. We describe a patient with a severe SLOS phenotype, but a very low serum 7DHC/cholesterol ratio. We show that this discordance is due to alternative splicing of a previously unreported IVS5+3 A>T mutation. This mutation results in the transcription of both normal and mutant mRNA transcripts. We postulate that alternative splicing of the IVS5+3 A>T results in insufficient DHCR7 activity during embryogenesis, but sufficient DHCR7 activity once cholesterol synthetic rates decrease postnatally. This unique case underscores the adjunctive use of fibroblast and molecular testing in ambiguous cases of SLOS and may provide insight into the potential efficacy of therapeutic interventions altering postnatal cholesterol biosynthesis.
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Smith–Lemli–Opitz syndrome: pathogenesis, diagnosis and management
European Journal of Human Genetics, 2008Co-Authors: Forbes D. PorterAbstract:Smith–Lemli–Opitz syndrome (SLOS) is a malformation syndrome due to a deficiency of 7-Dehydrocholesterol Reductase (DHCR7). DHCR7 primarily catalyzes the reduction of 7-Dehydrocholesterol (7DHC) to cholesterol. In SLOS, this results in decreased cholesterol and increased 7DHC levels, both during embryonic development and after birth. The malformations found in SLOS may result from decreased cholesterol, increased 7DHC or a combination of these two factors. This review discusses the clinical aspects and diagnosis of SLOS, therapeutic interventions and the current understanding of pathophysiological processes involved in SLOS.
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smith lemli opitz syndrome pathogenesis diagnosis and management
European Journal of Human Genetics, 2008Co-Authors: Forbes D. PorterAbstract:Smith-Lemli-Opitz syndrome (SLOS) is a malformation syndrome due to a deficiency of 7-Dehydrocholesterol Reductase (DHCR7). DHCR7 primarily catalyzes the reduction of 7-Dehydrocholesterol (7DHC) to cholesterol. In SLOS, this results in decreased cholesterol and increased 7DHC levels, both during embryonic development and after birth. The malformations found in SLOS may result from decreased cholesterol, increased 7DHC or a combination of these two factors. This review discusses the clinical aspects and diagnosis of SLOS, therapeutic interventions and the current understanding of pathophysiological processes involved in SLOS.
Andrew J Brown - One of the best experts on this subject based on the ideXlab platform.
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DHCR7: A vital enzyme switch between cholesterol and vitamin D production.
Progress in lipid research, 2016Co-Authors: Anika V Prabhu, Laura J Sharpe, Winnie Luu, Andrew J BrownAbstract:The conversion of 7-Dehydrocholesterol to cholesterol, the final step of cholesterol synthesis in the Kandutsch-Russell pathway, is catalyzed by the enzyme 7-Dehydrocholesterol Reductase (DHCR7). Homozygous or compound heterozygous mutations in DHCR7 lead to the developmental disease Smith-Lemli-Opitz syndrome, which can also result in fetal mortality, highlighting the importance of this enzyme in human development and survival. Besides serving as a substrate for DHCR7, 7-Dehydrocholesterol is also a precursor of vitamin D via the action of ultraviolet light on the skin. Thus, DHCR7 exerts complex biological effects, involved in both cholesterol and vitamin D production. Indeed, we argue that DHCR7 can act as a switch between cholesterol and vitamin D synthesis. This review summarizes current knowledge about the critical enzyme DHCR7, highlighting recent findings regarding its structure, transcriptional and post-transcriptional regulation, and its links to vitamin D synthesis. Greater understanding about DHCR7 function, regulation and its place within cellular metabolism will provide important insights into its biological roles.
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Phosphorylation regulates activity of 7-Dehydrocholesterol Reductase (DHCR7), a terminal enzyme of cholesterol synthesis.
The Journal of steroid biochemistry and molecular biology, 2016Co-Authors: Anika V Prabhu, Laura J Sharpe, Winnie Luu, Andrew J BrownAbstract:Cholesterol is essential for survival, but too much or too little can cause disease. Thus, cholesterol levels must be kept within close margins. 7-Dehydrocholesterol Reductase (DHCR7) is a terminal enzyme of cholesterol synthesis, and is essential for embryonic development. Largely, DHCR7 research is associated with the developmental disease Smith-Lemli-Opitz syndrome, which is caused by mutations in the DHCR7 gene. However, little is known about what regulates DHCR7 activity. Here we provide evidence that phosphorylation plays a role in controlling DHCR7 activity, which may provide a means to divert flux from cholesterol synthesis to vitamin D production. DHCR7 activity was significantly decreased when we used pharmacological inhibitors against two important kinases, AMP-activated protein kinase and protein kinase A. Moreover, mutating a known phosphorylated residue, S14, also decreased DHCR7 activity. Thus, we demonstrate that phosphorylation modulates DHCR7 activity in cells, and contributes to the overall synthesis of cholesterol, and probably vitamin D.
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Cholesterol-mediated Degradation of 7-Dehydrocholesterol Reductase Switches the Balance from Cholesterol to Vitamin D Synthesis
The Journal of biological chemistry, 2016Co-Authors: Anika V Prabhu, Laura J Sharpe, Winnie Luu, Andrew J BrownAbstract:Cholesterol is detrimental to human health in excess but is also essential for normal embryogenesis. Hence, enzymes involved in its synthesis possess many layers of regulation to achieve balanced cholesterol levels. 7-Dehydrocholesterol Reductase (DHCR7) is the terminal enzyme of cholesterol synthesis in the Kandutsch-Russell pathway, converting 7-Dehydrocholesterol (7DHC) to cholesterol. In the absence of functional DHCR7, accumulation of 7DHC and a lack of cholesterol production leads to the devastating developmental disorder, Smith-Lemli-Opitz syndrome. This study identifies that statin treatment can ameliorate the low DHCR7 expression seen with common Smith-Lemli-Opitz syndrome mutations. Furthermore, we show that wild-type DHCR7 is also relatively labile. In an example of end-product inhibition, cholesterol accelerates the proteasomal degradation of DHCR7, resulting in decreased protein levels and activity. The loss of enzymatic activity results in the accumulation of the substrate 7DHC, which leads to an increased production of vitamin D. Thus, these findings highlight DHCR7 as an important regulatory switch between cholesterol and vitamin D synthesis.
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The terminal enzymes of cholesterol synthesis, DHCR24 and DHCR7, interact physically and functionally.
Journal of lipid research, 2015Co-Authors: Winnie Luu, Laura J Sharpe, Gene Hart-smith, Andrew J BrownAbstract:Cholesterol is essential to human health, and its levels are tightly regulated by a balance of synthesis, uptake, and efflux. Cholesterol synthesis requires the actions of more than twenty enzymes to reach the final product, through two alternate pathways. Here we describe a physical and functional interaction between the two terminal enzymes. 24-Dehydrocholesterol Reductase (DHCR24) and 7-Dehydrocholesterol Reductase (DHCR7) coimmunoprecipitate, and when the DHCR24 gene is knocked down by siRNA, DHCR7 activity is also ablated. Conversely, overexpression of DHCR24 enhances DHCR7 activity, but only when a functional form of DHCR24 is used. DHCR7 is important for both cholesterol and vitamin D synthesis, and we have identified a novel layer of regulation, whereby its activity is controlled by DHCR24. This suggests the existence of a cholesterol #x201C;metabolon#x201D;, where enzymes from the same metabolic pathway interact with each other to provide a substrate channeling benefit. We predict that other enzymes in cholesterol synthesis may similarly interact, and this should be explored in future studies.
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the sterol based transcriptional control of human 7 dehydrocholesterol Reductase dhcr7 evidence of a cooperative regulatory program in cholesterol synthesis
Biochimica et Biophysica Acta, 2014Co-Authors: Anika V Prabhu, Laura J Sharpe, Andrew J BrownAbstract:Abstract The enzyme 7-Dehydrocholesterol Reductase (DHCR7) catalyzes the final step of cholesterol synthesis via the Kandutsch–Russell pathway, and is crucial in maintaining cellular cholesterol levels. Its absence leads to the devastating fetal developmental disorder Smith–Lemli–Opitz Syndrome (SLOS). How this enzyme is regulated has implications in controlling not only cholesterol synthesis, but also the synthesis of Vitamin D — another product of 7-Dehydrocholesterol. In this study, we look specifically at how DHCR7 is regulated by the sterol regulatory element–binding protein-2 (SREBP-2) transcription factor. Sterol regulation has previously been studied in the rat DHCR7 promoter, but we have found that its regulatory elements are not all conserved in humans. Rather, the human promoter contains two binding sites for SREBP-2 (at − 155 and − 55) and a binding site for the nuclear factor-Y (NF-Y) cofactor (at − 136). The − 155 site is a particularly responsive sterol regulatory element (SRE) which is well conserved in mammals, and was possibly overlooked in the rat promoter study. The exact location of the weaker − 55 site (close to the known rat SRE) may have shifted during evolution. Furthermore, we established that the two SREs that bind SREBP-2 work in cooperation to synergistically activate DHCR7. We have previously characterized the SREs in DHCR24, the final enzyme in the alternate Bloch pathway of cholesterol synthesis. Here, comparison of the sterol regulation of these terminal enzymes demonstrates the unique cooperative system that helps to control cholesterol synthesis.
Young Ki Paik - One of the best experts on this subject based on the ideXlab platform.
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Methylation of CpG islands in the rat 7-Dehydrocholesterol Reductase promoter suppresses transcriptional activation.
Molecules and cells, 2005Co-Authors: Jai-hyun Kim, Eun-ha Hwang, Hye-jung Park, Young Ki Paik, Yhong-hee ShimAbstract:In mammals, 7-Dehydrocholesterol Reductase (Dhcr7) is the terminal enzyme in cholesterol biosynthesis. We previously reported that the Dhcr7 proximal promoter (-179 to +1), which contains CpG islands, is responsible for sterol-mediated expression of the rat gene. In the present study, we examined whether methylation of this region affects the transcriptional activity of the Dhcr7 gene. In vitro DNA methylation of the Dhcr7 promoter and luciferase-reporter assays showed that DNA methylation of the CpG islands suppressed transcription. Furthermore, treatment of the methylated Dhcr7 promoter with the demethylating agent, 5-aza-2'-deoxycytidine (5-Aza-CdR), reversed the suppression of promoter activity. These results indicate that methylation of the CpG islands is an important transcriptional regulatory mechanism in the Dhcr7 promoter.
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A novel mutation of the human 7-Dehydrocholesterol Reductase gene reduces enzyme activity in patients with holoprosencephaly
Biochemical and biophysical research communications, 2004Co-Authors: Yhong-hee Shim, Jai-hyun Kim, Soo-han Bae, Kyu-rae Kim, Chong Jai Kim, Young Ki PaikAbstract:Defects in cholesterol biosynthesis genes are recognized as a leading cause for holoprosencephaly (HPE). Previous reports suggest that mutations of human 7-Dehydrocholesterol Reductase (Dhcr7), which catalyzes the final step of cholesterol biosynthesis, may cause HPE [Clin. Genet. 53 (1998) 155]. To determine whether Dhcr7 mutations are involved in HPE pathogenesis, we analyzed the sequence of exon 9, which contains both a catalytic domain and a mutational hot spot. We examined 36 prematurely terminated fetuses with HPE at their gestation ages in the range from 21 to 33 weeks by single strand conformation polymorphism analysis and DNA sequencing. A novel missense mutation was identified: G344D. Dhcr7 enzyme assays using overexpressed recombinant mutant proteins revealed altered enzyme activity. Mutant G344D harbored less than 50% of enzyme activity compared with the control. Two previously reported mutations, R404C and G410S, abolished enzyme activity. These results suggest that mutation of the Dhcr7 gene is involved in HPE pathogenesis.
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Structure and alternative splicing of the rat 7-Dehydrocholesterol Reductase gene.
Biochimica et biophysica acta, 2002Co-Authors: Joon No Lee, Soo-han Bae, Young Ki PaikAbstract:The enzyme 7-Dehydrocholesterol Reductase (Dhcr7) catalyzes the reduction of 7-Dehydrocholesterol (DHC), the terminal reaction of the pathway of cholesterol biosynthesis. We report the isolation and characterization of the genomic DNA encoding rat Dhcr7 that contains nine exons and eight introns distributed over 15944 nucleotides (nts) and a consensus GT-AG at each exon/intron junction. Unexpectedly, we have found the occurrence of at least five isoforms of Dhcr7, designated as Dhcr7-AS (alternatively spliced)-1 (1474 nts), -2 (1595 nts), -3 (1602 nts), -4 (1723 nts) and -5 (1287 nts), which was believed to be caused by alternative usage of three 5' noncoding exons. Furthermore, Dhcr7-AS-1 was found to be differentially expressed in six tissues examined while Dhcr7-AS-2 was expressed mainly in liver and brain. Interestingly, human Dhcr7 gene in HepG2 cells produced no detectable isoform while mouse Dhcr7 gene in L929 cells produced three isoforms, suggesting a difference in alternative splicing between species. Thus, regulation of Dhcr7 through the combined mechanisms of tissue-specific transcription and differential alternative splicing appears unique among enzymes characterized from the entire post-lanosterol pathway in cholesterol biosynthesis.
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cholesterol biosynthesis from lanosterol a concerted role for sp1 and nf y binding sites for sterol mediated regulation of rat 7 dehydrocholesterol Reductase gene expression
Journal of Biological Chemistry, 2001Co-Authors: Young Ki PaikAbstract:Abstract The 7-Dehydrocholesterol Reductase (Dhcr7) is the terminal enzyme in the pathway of cholesterol biosynthesis. We have previously reported that sterol depletion in vivo caused a significant induction of both liver mRNA and enzyme activity of Dhcr7 (Bae, S.-H., Lee, J. N., Fitzky, B. U., Seong, J., and Paik, Y.-K. (1999) J. Biol. Chem. 274, 14624–14631). In this paper, we also observed liver cell-specific sterol-mediated Dhcr7 gene induction in vitro by sterol depletion in rat hepatoma cells, suggesting the presence of sterol-mediated regulatory elements in the Dhcr7 gene. To understand the mechanisms responsible for regulating Dhcr7 expression, we have isolated the 5′-flanking region of the gene encoding rat Dhcr7 and have characterized the potential regulatory elements of the gene that are responsible for sterol-mediated regulation. The Dhcr7 promoter contains binding sites for Sp1 (at −177, −172, −125, and −20), NF-Y (at −88 and −51), and SREBP-1 or ADD1 (at −33). Deletion analysis of the Dhcr7 gene promoter (−1053/+31), employing a nested series of Dhcr7-luciferase constructs, demonstrated that the −179 upstream region of the gene is necessary and sufficient for optimal efficient sterol-regulated transcription. DNase I footprinting and electrophoretic mobility shift assay showed that the SRE1/E box (−33/−22) involved in sterol response of many sterol-related enzyme genes was protected specifically by the overexpressed recombinant ADD1. Mutational analysis for the functional relationship between the identified cis-elements in this region indicate that one of the binding sites for Sp1 (GC box at −125) and NF-Y (CCAAT box at −88) plays a cooperative role in the sterol-mediated activation, in which the latter site also acts as a co-regulator for SREBP-activated Dhcr7 promoter activity. We believe that Dhcr7 is the first enzyme characterized with a sterol-regulatory function in the post-lanosterol pathway. This may be important for understanding the coordinated control of cholesterol biosynthesis as well as the molecular mechanism of Smith-Lemli-Opitz syndrome-related protein in mammals.
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cholesterol biosynthesis from lanosterol molecular cloning tissue distribution expression chromosomal localization and regulation of rat 7 dehydrocholesterol Reductase a smith lemli opitz syndrome related protein
Journal of Biological Chemistry, 1999Co-Authors: Barbara U Fitzky, Jekyung Seong, Young Ki PaikAbstract:Abstract The cDNA encoding the 471-amino acid rat 7-Dehydrocholesterol Reductase (DHCR), an enzyme that has been implicated in both cholesterol biosynthesis and developmental abnormalities (e.g. Smith-Lemli-Opitz syndrome) in mammals, has been cloned and sequenced, and the primary structure of the enzyme has been deduced. The DHCR gene was mapped to chromosome 8q2.1 by fluorescence in situ hybridization. Rat DHCR, calculated molecular mass of 54.15-kDa polypeptide, shares a close amino acid identity with mouse and human DHCRs (96 and 87%, respectively) as compared with its other related proteins (e.g. fungal sterol Δ14-Reductase) and exhibits high hydrophobicity (>68%) with 9 transmembrane domains. Five putative sterol-sensing domains were predicted to be localized in transmembrane domains 4–8, which are highly homologous to those found in 3-hydroxymethylglutaryl-CoA Reductase, sterol regulatory element-binding protein cleavage-activating protein, and patched protein. The polypeptide encoded by DHCR cDNA was expressed in yeast as a 55.45-kDa myc-tagged fusion protein, which was recognized with anti-myc monoclonal antibody 9E10 and shown to possess full DHCR activity with respect to dependence on NADPH and sensitivity to DHCR inhibitors. Northern blot analysis indicates that the highest expression of DHCR mRNA was detected in liver, followed by kidney and brain. In rat brains, the highest level of mRNA encoding DHCR was detected in the midbrain, followed by the spinal cord and medulla. Feeding rats 5% cholestyramine plus 0.1% lovastatin in chow resulted in both approximately a 3-fold induction of DHCR mRNA and a 5-fold increase of the enzymic activity in the liver. When rats were fed 0.1% (w/w) AY-9944 (in chow) for 14-days, a complete inhibition of DHCR activity and a significant reduction in serum total cholesterol level were observed. However, the level of hepatic DHCR mRNA fell only slightly, suggesting that AY-9944 may act more rapidly at the protein level than at the level of transcription of the DHCR gene under these conditions.
Anika V Prabhu - One of the best experts on this subject based on the ideXlab platform.
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DHCR7: A vital enzyme switch between cholesterol and vitamin D production.
Progress in lipid research, 2016Co-Authors: Anika V Prabhu, Laura J Sharpe, Winnie Luu, Andrew J BrownAbstract:The conversion of 7-Dehydrocholesterol to cholesterol, the final step of cholesterol synthesis in the Kandutsch-Russell pathway, is catalyzed by the enzyme 7-Dehydrocholesterol Reductase (DHCR7). Homozygous or compound heterozygous mutations in DHCR7 lead to the developmental disease Smith-Lemli-Opitz syndrome, which can also result in fetal mortality, highlighting the importance of this enzyme in human development and survival. Besides serving as a substrate for DHCR7, 7-Dehydrocholesterol is also a precursor of vitamin D via the action of ultraviolet light on the skin. Thus, DHCR7 exerts complex biological effects, involved in both cholesterol and vitamin D production. Indeed, we argue that DHCR7 can act as a switch between cholesterol and vitamin D synthesis. This review summarizes current knowledge about the critical enzyme DHCR7, highlighting recent findings regarding its structure, transcriptional and post-transcriptional regulation, and its links to vitamin D synthesis. Greater understanding about DHCR7 function, regulation and its place within cellular metabolism will provide important insights into its biological roles.
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Phosphorylation regulates activity of 7-Dehydrocholesterol Reductase (DHCR7), a terminal enzyme of cholesterol synthesis.
The Journal of steroid biochemistry and molecular biology, 2016Co-Authors: Anika V Prabhu, Laura J Sharpe, Winnie Luu, Andrew J BrownAbstract:Cholesterol is essential for survival, but too much or too little can cause disease. Thus, cholesterol levels must be kept within close margins. 7-Dehydrocholesterol Reductase (DHCR7) is a terminal enzyme of cholesterol synthesis, and is essential for embryonic development. Largely, DHCR7 research is associated with the developmental disease Smith-Lemli-Opitz syndrome, which is caused by mutations in the DHCR7 gene. However, little is known about what regulates DHCR7 activity. Here we provide evidence that phosphorylation plays a role in controlling DHCR7 activity, which may provide a means to divert flux from cholesterol synthesis to vitamin D production. DHCR7 activity was significantly decreased when we used pharmacological inhibitors against two important kinases, AMP-activated protein kinase and protein kinase A. Moreover, mutating a known phosphorylated residue, S14, also decreased DHCR7 activity. Thus, we demonstrate that phosphorylation modulates DHCR7 activity in cells, and contributes to the overall synthesis of cholesterol, and probably vitamin D.
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Cholesterol-mediated Degradation of 7-Dehydrocholesterol Reductase Switches the Balance from Cholesterol to Vitamin D Synthesis
The Journal of biological chemistry, 2016Co-Authors: Anika V Prabhu, Laura J Sharpe, Winnie Luu, Andrew J BrownAbstract:Cholesterol is detrimental to human health in excess but is also essential for normal embryogenesis. Hence, enzymes involved in its synthesis possess many layers of regulation to achieve balanced cholesterol levels. 7-Dehydrocholesterol Reductase (DHCR7) is the terminal enzyme of cholesterol synthesis in the Kandutsch-Russell pathway, converting 7-Dehydrocholesterol (7DHC) to cholesterol. In the absence of functional DHCR7, accumulation of 7DHC and a lack of cholesterol production leads to the devastating developmental disorder, Smith-Lemli-Opitz syndrome. This study identifies that statin treatment can ameliorate the low DHCR7 expression seen with common Smith-Lemli-Opitz syndrome mutations. Furthermore, we show that wild-type DHCR7 is also relatively labile. In an example of end-product inhibition, cholesterol accelerates the proteasomal degradation of DHCR7, resulting in decreased protein levels and activity. The loss of enzymatic activity results in the accumulation of the substrate 7DHC, which leads to an increased production of vitamin D. Thus, these findings highlight DHCR7 as an important regulatory switch between cholesterol and vitamin D synthesis.
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the sterol based transcriptional control of human 7 dehydrocholesterol Reductase dhcr7 evidence of a cooperative regulatory program in cholesterol synthesis
Biochimica et Biophysica Acta, 2014Co-Authors: Anika V Prabhu, Laura J Sharpe, Andrew J BrownAbstract:Abstract The enzyme 7-Dehydrocholesterol Reductase (DHCR7) catalyzes the final step of cholesterol synthesis via the Kandutsch–Russell pathway, and is crucial in maintaining cellular cholesterol levels. Its absence leads to the devastating fetal developmental disorder Smith–Lemli–Opitz Syndrome (SLOS). How this enzyme is regulated has implications in controlling not only cholesterol synthesis, but also the synthesis of Vitamin D — another product of 7-Dehydrocholesterol. In this study, we look specifically at how DHCR7 is regulated by the sterol regulatory element–binding protein-2 (SREBP-2) transcription factor. Sterol regulation has previously been studied in the rat DHCR7 promoter, but we have found that its regulatory elements are not all conserved in humans. Rather, the human promoter contains two binding sites for SREBP-2 (at − 155 and − 55) and a binding site for the nuclear factor-Y (NF-Y) cofactor (at − 136). The − 155 site is a particularly responsive sterol regulatory element (SRE) which is well conserved in mammals, and was possibly overlooked in the rat promoter study. The exact location of the weaker − 55 site (close to the known rat SRE) may have shifted during evolution. Furthermore, we established that the two SREs that bind SREBP-2 work in cooperation to synergistically activate DHCR7. We have previously characterized the SREs in DHCR24, the final enzyme in the alternate Bloch pathway of cholesterol synthesis. Here, comparison of the sterol regulation of these terminal enzymes demonstrates the unique cooperative system that helps to control cholesterol synthesis.
Laura J Sharpe - One of the best experts on this subject based on the ideXlab platform.
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DHCR7: A vital enzyme switch between cholesterol and vitamin D production.
Progress in lipid research, 2016Co-Authors: Anika V Prabhu, Laura J Sharpe, Winnie Luu, Andrew J BrownAbstract:The conversion of 7-Dehydrocholesterol to cholesterol, the final step of cholesterol synthesis in the Kandutsch-Russell pathway, is catalyzed by the enzyme 7-Dehydrocholesterol Reductase (DHCR7). Homozygous or compound heterozygous mutations in DHCR7 lead to the developmental disease Smith-Lemli-Opitz syndrome, which can also result in fetal mortality, highlighting the importance of this enzyme in human development and survival. Besides serving as a substrate for DHCR7, 7-Dehydrocholesterol is also a precursor of vitamin D via the action of ultraviolet light on the skin. Thus, DHCR7 exerts complex biological effects, involved in both cholesterol and vitamin D production. Indeed, we argue that DHCR7 can act as a switch between cholesterol and vitamin D synthesis. This review summarizes current knowledge about the critical enzyme DHCR7, highlighting recent findings regarding its structure, transcriptional and post-transcriptional regulation, and its links to vitamin D synthesis. Greater understanding about DHCR7 function, regulation and its place within cellular metabolism will provide important insights into its biological roles.
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Phosphorylation regulates activity of 7-Dehydrocholesterol Reductase (DHCR7), a terminal enzyme of cholesterol synthesis.
The Journal of steroid biochemistry and molecular biology, 2016Co-Authors: Anika V Prabhu, Laura J Sharpe, Winnie Luu, Andrew J BrownAbstract:Cholesterol is essential for survival, but too much or too little can cause disease. Thus, cholesterol levels must be kept within close margins. 7-Dehydrocholesterol Reductase (DHCR7) is a terminal enzyme of cholesterol synthesis, and is essential for embryonic development. Largely, DHCR7 research is associated with the developmental disease Smith-Lemli-Opitz syndrome, which is caused by mutations in the DHCR7 gene. However, little is known about what regulates DHCR7 activity. Here we provide evidence that phosphorylation plays a role in controlling DHCR7 activity, which may provide a means to divert flux from cholesterol synthesis to vitamin D production. DHCR7 activity was significantly decreased when we used pharmacological inhibitors against two important kinases, AMP-activated protein kinase and protein kinase A. Moreover, mutating a known phosphorylated residue, S14, also decreased DHCR7 activity. Thus, we demonstrate that phosphorylation modulates DHCR7 activity in cells, and contributes to the overall synthesis of cholesterol, and probably vitamin D.
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Cholesterol-mediated Degradation of 7-Dehydrocholesterol Reductase Switches the Balance from Cholesterol to Vitamin D Synthesis
The Journal of biological chemistry, 2016Co-Authors: Anika V Prabhu, Laura J Sharpe, Winnie Luu, Andrew J BrownAbstract:Cholesterol is detrimental to human health in excess but is also essential for normal embryogenesis. Hence, enzymes involved in its synthesis possess many layers of regulation to achieve balanced cholesterol levels. 7-Dehydrocholesterol Reductase (DHCR7) is the terminal enzyme of cholesterol synthesis in the Kandutsch-Russell pathway, converting 7-Dehydrocholesterol (7DHC) to cholesterol. In the absence of functional DHCR7, accumulation of 7DHC and a lack of cholesterol production leads to the devastating developmental disorder, Smith-Lemli-Opitz syndrome. This study identifies that statin treatment can ameliorate the low DHCR7 expression seen with common Smith-Lemli-Opitz syndrome mutations. Furthermore, we show that wild-type DHCR7 is also relatively labile. In an example of end-product inhibition, cholesterol accelerates the proteasomal degradation of DHCR7, resulting in decreased protein levels and activity. The loss of enzymatic activity results in the accumulation of the substrate 7DHC, which leads to an increased production of vitamin D. Thus, these findings highlight DHCR7 as an important regulatory switch between cholesterol and vitamin D synthesis.
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The terminal enzymes of cholesterol synthesis, DHCR24 and DHCR7, interact physically and functionally.
Journal of lipid research, 2015Co-Authors: Winnie Luu, Laura J Sharpe, Gene Hart-smith, Andrew J BrownAbstract:Cholesterol is essential to human health, and its levels are tightly regulated by a balance of synthesis, uptake, and efflux. Cholesterol synthesis requires the actions of more than twenty enzymes to reach the final product, through two alternate pathways. Here we describe a physical and functional interaction between the two terminal enzymes. 24-Dehydrocholesterol Reductase (DHCR24) and 7-Dehydrocholesterol Reductase (DHCR7) coimmunoprecipitate, and when the DHCR24 gene is knocked down by siRNA, DHCR7 activity is also ablated. Conversely, overexpression of DHCR24 enhances DHCR7 activity, but only when a functional form of DHCR24 is used. DHCR7 is important for both cholesterol and vitamin D synthesis, and we have identified a novel layer of regulation, whereby its activity is controlled by DHCR24. This suggests the existence of a cholesterol #x201C;metabolon#x201D;, where enzymes from the same metabolic pathway interact with each other to provide a substrate channeling benefit. We predict that other enzymes in cholesterol synthesis may similarly interact, and this should be explored in future studies.
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the sterol based transcriptional control of human 7 dehydrocholesterol Reductase dhcr7 evidence of a cooperative regulatory program in cholesterol synthesis
Biochimica et Biophysica Acta, 2014Co-Authors: Anika V Prabhu, Laura J Sharpe, Andrew J BrownAbstract:Abstract The enzyme 7-Dehydrocholesterol Reductase (DHCR7) catalyzes the final step of cholesterol synthesis via the Kandutsch–Russell pathway, and is crucial in maintaining cellular cholesterol levels. Its absence leads to the devastating fetal developmental disorder Smith–Lemli–Opitz Syndrome (SLOS). How this enzyme is regulated has implications in controlling not only cholesterol synthesis, but also the synthesis of Vitamin D — another product of 7-Dehydrocholesterol. In this study, we look specifically at how DHCR7 is regulated by the sterol regulatory element–binding protein-2 (SREBP-2) transcription factor. Sterol regulation has previously been studied in the rat DHCR7 promoter, but we have found that its regulatory elements are not all conserved in humans. Rather, the human promoter contains two binding sites for SREBP-2 (at − 155 and − 55) and a binding site for the nuclear factor-Y (NF-Y) cofactor (at − 136). The − 155 site is a particularly responsive sterol regulatory element (SRE) which is well conserved in mammals, and was possibly overlooked in the rat promoter study. The exact location of the weaker − 55 site (close to the known rat SRE) may have shifted during evolution. Furthermore, we established that the two SREs that bind SREBP-2 work in cooperation to synergistically activate DHCR7. We have previously characterized the SREs in DHCR24, the final enzyme in the alternate Bloch pathway of cholesterol synthesis. Here, comparison of the sterol regulation of these terminal enzymes demonstrates the unique cooperative system that helps to control cholesterol synthesis.
