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Orozco Rodriguez JM, Krupinska E, Wacklin-Knecht H, Knecht W. Protein production, kinetic and biophysical characterization of three human dihydroorotate dehydrogenase mutants associated with Miller syndrome. NUCLEOSIDES, NUCLEOTIDES & NUCLEIC ACIDS 2022; 41:1318-1336. [PMID: 35094635 DOI: 10.1080/15257770.2021.2023749] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/14/2023]
Abstract
Miller syndrome is a rare Mendelian disorder caused by mutations in the gene encoding human dihydroorotate dehydrogenase (DHODH). Human DHODH, a Class II DHODH, is an integral protein of the inner mitochondrial membrane (IMM) catalyzing the fourth step of the de novo pyrimidine biosynthesis pathway. Here we present a summary of the state of knowledge regarding Miller syndrome in the absence of any current review on the topic. We then describe the production and characterization of three distinct DHODH missense mutations (G19E, E52G, R135C) associated with Miller syndrome by means of enzyme kinetics and biophysical techniques. These human DHODH mutants were produced both in E. coli and in insect cells using the baculovirus expression vector system. We can show that the effects of these mutations differ from each other and the wild-type enzyme with respect to decreased enzymatic activity, decreased protein stability and probably disturbance of the correct import into the IMM. In addition, our results show that the N-terminus of human DHODH is not only a structural element necessary for correct mitochondrial import and location of DHODH on the outer side of the IMM, but also influences thermal stability, enzymatic activity and affects the kinetic parameters.Supplemental data for this article is available online at https://doi.org/10.1080/15257770.2021.2023749 .
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Affiliation(s)
| | - Ewa Krupinska
- Department of Biology & Lund Protein Production Platform, Lund University, Lund, Sweden
| | - Hanna Wacklin-Knecht
- Department of Chemistry, Division of Physical Chemistry, Lund University, Lund, Sweden.,European Spallation Source ERIC, Lund, Sweden
| | - Wolfgang Knecht
- Department of Biology & Lund Protein Production Platform, Lund University, Lund, Sweden
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Zhou Y, Tao L, Zhou X, Zuo Z, Gong J, Liu X, Zhou Y, Liu C, Sang N, Liu H, Zou J, Gou K, Yang X, Zhao Y. DHODH and cancer: promising prospects to be explored. Cancer Metab 2021; 9:22. [PMID: 33971967 PMCID: PMC8107416 DOI: 10.1186/s40170-021-00250-z] [Citation(s) in RCA: 39] [Impact Index Per Article: 13.0] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/29/2020] [Accepted: 03/10/2021] [Indexed: 02/08/2023] Open
Abstract
Human dihydroorotate dehydrogenase (DHODH) is a flavin-dependent mitochondrial enzyme catalyzing the fourth step in the de novo pyrimidine synthesis pathway. It is originally a target for the treatment of the non-neoplastic diseases involving in rheumatoid arthritis and multiple sclerosis, and is re-emerging as a validated therapeutic target for cancer therapy. In this review, we mainly unravel the biological function of DHODH in tumor progression, including its crucial role in de novo pyrimidine synthesis and mitochondrial respiratory chain in cancer cells. Moreover, various DHODH inhibitors developing in the past decades are also been displayed, and the specific mechanism between DHODH and its additional effects are illustrated. Collectively, we detailly discuss the association between DHODH and tumors in recent years here, and believe it will provide significant evidences and potential strategies for utilizing DHODH as a potential target in preclinical and clinical cancer therapies.
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Affiliation(s)
- Yue Zhou
- State Key Laboratory of Biotherapy and Cancer Center, West China Hospital, Sichuan University, and Collaborative Innovation Center for Biotherapy, Chengdu, 610041, China
| | - Lei Tao
- State Key Laboratory of Biotherapy and Cancer Center, West China Hospital, Sichuan University, and Collaborative Innovation Center for Biotherapy, Chengdu, 610041, China
| | - Xia Zhou
- State Key Laboratory of Biotherapy and Cancer Center, West China Hospital, Sichuan University, and Collaborative Innovation Center for Biotherapy, Chengdu, 610041, China
| | - Zeping Zuo
- The Laboratory of Anesthesiology and Critical Care Medicine, Translational Neuroscience Center, State Key Laboratory of Biotherapy, West China Hospital, Sichuan University, Chengdu, 610041, Sichuan, China
| | - Jin Gong
- State Key Laboratory of Biotherapy and Cancer Center, West China Hospital, Sichuan University, and Collaborative Innovation Center for Biotherapy, Chengdu, 610041, China
| | - Xiaocong Liu
- State Key Laboratory of Biotherapy and Cancer Center, West China Hospital, Sichuan University, and Collaborative Innovation Center for Biotherapy, Chengdu, 610041, China
| | - Yang Zhou
- State Key Laboratory of Biotherapy and Cancer Center, West China Hospital, Sichuan University, and Collaborative Innovation Center for Biotherapy, Chengdu, 610041, China
| | - Chunqi Liu
- State Key Laboratory of Biotherapy and Cancer Center, West China Hospital, Sichuan University, and Collaborative Innovation Center for Biotherapy, Chengdu, 610041, China
| | - Na Sang
- State Key Laboratory of Biotherapy and Cancer Center, West China Hospital, Sichuan University, and Collaborative Innovation Center for Biotherapy, Chengdu, 610041, China
| | - Huan Liu
- West China School of Pharmacy, Sichuan University, Chengdu, 610041, China
| | - Jiao Zou
- State Key Laboratory of Biotherapy and Cancer Center, West China Hospital, Sichuan University, and Collaborative Innovation Center for Biotherapy, Chengdu, 610041, China
| | - Kun Gou
- State Key Laboratory of Biotherapy and Cancer Center, West China Hospital, Sichuan University, and Collaborative Innovation Center for Biotherapy, Chengdu, 610041, China
| | - Xiaowei Yang
- State Key Laboratory of Biotherapy and Cancer Center, West China Hospital, Sichuan University, and Collaborative Innovation Center for Biotherapy, Chengdu, 610041, China
| | - Yinglan Zhao
- State Key Laboratory of Biotherapy and Cancer Center, West China Hospital, Sichuan University, and Collaborative Innovation Center for Biotherapy, Chengdu, 610041, China. .,West China School of Pharmacy, Sichuan University, Chengdu, 610041, China.
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Zhao J, Yang L. Broad-spectrum next-generation sequencing-based diagnosis of a case of Nager syndrome. J Clin Lab Anal 2020; 34:e23426. [PMID: 32537850 PMCID: PMC7521291 DOI: 10.1002/jcla.23426] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/29/2020] [Revised: 05/18/2020] [Accepted: 05/19/2020] [Indexed: 12/27/2022] Open
Abstract
BACKGROUND Nager syndrome is a rare genetic syndrome characterized by craniofacial and preaxial limb anomalies. Haploinsufficiency of the SF3B4 gene has been identified as a significant reason for Nager syndrome. Treacher Collins syndrome (TCS) has similar facial features; however, the TCOF1, POLR1D, and POLR1C genes have been reported as the critical disease-causing genes. Similar phenotypes make it easy to misdiagnose. CASE REPORT In this report, we have presented a case of one newborn with acrofacial dysostosis, who was first diagnosed with TCS. Expanded next-generation sequencing eventually detected a (c.1A>G) heterozygous mutation in the SF3B4 gene at chr1:149899651 that was confirmed by Sanger sequencing. Combined with his preaxial limb anomalies discovered after his death, a diagnosis of Nager syndrome was made. CONCLUSIONS This report presents one patient with Nager syndrome who was initially misdiagnosed with TCS. Correct genetic testing will be beneficial to future prenatal diagnosis.
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Affiliation(s)
- Jue Zhao
- Department of Obstetrics, Zhejiang Provincial People's Hospital, People's Hospital of Hangzhou Medical College, Hangzhou, China
| | - Liwei Yang
- Department of Obstetrics, Zhejiang Provincial People's Hospital, People's Hospital of Hangzhou Medical College, Hangzhou, China
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Jones CC, Bradford Y, Amos CI, Blot WJ, Chanock SJ, Harris CC, Schwartz AG, Spitz MR, Wiencke JK, Wrensch MR, Wu X, Aldrich MC. Cross-Cancer Pleiotropic Associations with Lung Cancer Risk in African Americans. Cancer Epidemiol Biomarkers Prev 2019; 28:715-723. [PMID: 30894353 PMCID: PMC6449205 DOI: 10.1158/1055-9965.epi-18-0935] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/29/2018] [Revised: 11/02/2018] [Accepted: 12/31/2018] [Indexed: 12/13/2022] Open
Abstract
BACKGROUND Identifying genetic variants with pleiotropic associations across multiple cancers can reveal shared biologic pathways. Prior pleiotropic studies have primarily focused on European-descent individuals. Yet population-specific genetic variation can occur, and potential pleiotropic associations among diverse racial/ethnic populations could be missed. We examined cross-cancer pleiotropic associations with lung cancer risk in African Americans. METHODS We conducted a pleiotropic analysis among 1,410 African American lung cancer cases and 2,843 controls. We examined 36,958 variants previously associated (or in linkage disequilibrium) with cancer in prior genome-wide association studies. Logistic regression analyses were conducted, adjusting for age, sex, global ancestry, study site, and smoking status. RESULTS We identified three novel genomic regions significantly associated (FDR-corrected P <0.10) with lung cancer risk (rs336958 on 5q14.3, rs7186207 on 16q22.2, and rs11658063 on 17q12). On chromosome16q22.2, rs7186207 was significantly associated with reduced risk [OR = 0.43; 95% confidence interval (CI), 0.73-0.89], and functional annotation using GTEx showed rs7186207 modifies DHODH gene expression. The minor allele at rs336958 on 5q14.3 was associated with increased lung cancer risk (OR = 1.47; 95% CI, 1.22-1.78), whereas the minor allele at rs11658063 on 17q12 was associated with reduced risk (OR = 0.80; 95% CI, 0.72-0.90). CONCLUSIONS We identified novel associations on chromosomes 5q14.3, 16q22.2, and 17q12, which contain HNF1B, DHODH, and HAPLN1 genes, respectively. SNPs within these regions have been previously associated with multiple cancers. This is the first study to examine cross-cancer pleiotropic associations for lung cancer in African Americans. IMPACT Our findings demonstrate novel cross-cancer pleiotropic associations with lung cancer risk in African Americans.
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Affiliation(s)
- Carissa C Jones
- Department of Thoracic Surgery, Vanderbilt University Medical Center, Nashville, Tennessee
- Vanderbilt Genetics Institute, Vanderbilt University Medical Center, Nashville, Tennessee
| | - Yuki Bradford
- School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania
| | | | - William J Blot
- Division of Epidemiology, Department of Medicine, Vanderbilt University Medical Center, Nashville, Tennessee
| | - Stephen J Chanock
- Division of Cancer Epidemiology and Genetics, NCI, Bethesda, Maryland
| | | | - Ann G Schwartz
- Karmanos Cancer Institute, Wayne State University, Detroit, Michigan
| | - Margaret R Spitz
- Department of Medicine, Baylor College of Medicine, Houston, Texas
| | - John K Wiencke
- Department of Neurological Surgery, University of California San Francisco, San Francisco, California
| | - Margaret R Wrensch
- Department of Neurological Surgery, University of California San Francisco, San Francisco, California
- Department of Epidemiology and Biostatistics, University of California San Francisco, San Francisco, California
- Institute of Human Genetics, University of California San Francisco, San Francisco, California
| | - Xifeng Wu
- Department of Epidemiology, Division of Cancer Prevention and Population Sciences, University of Texas MD Anderson Cancer Center, Houston, Texas
| | - Melinda C Aldrich
- Department of Thoracic Surgery, Vanderbilt University Medical Center, Nashville, Tennessee.
- Vanderbilt Genetics Institute, Vanderbilt University Medical Center, Nashville, Tennessee
- Division of Epidemiology, Department of Medicine, Vanderbilt University Medical Center, Nashville, Tennessee
- Department of Biomedical Informatics, Vanderbilt University Medical Center, Nashville, Tennessee
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Löffler M, Carrey EA, Zameitat E. New perspectives on the roles of pyrimidines in the central nervous system. NUCLEOSIDES NUCLEOTIDES & NUCLEIC ACIDS 2018; 37:290-306. [PMID: 29693489 DOI: 10.1080/15257770.2018.1453076] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Since 1956, when exogenous uridine and cytidine were found to be necessary for the maintenance of perfused rat brain function, the co-existence of de novo synthesis, salvage pathways and removal of pyrimidine bases in the CNS has been a controversial subject. Here, we review studies on metabolites and enzymes of pyrimidine metabolism through more than 60 years. In view of known and newly-described inherited pyrimidine and purine disorders - some with complex clinical profiles of neurological impairments - we underline the necessity to investigate how the different pathways work together in the developing brain and then sustain plasticity, regeneration and neuro-transmission in the adult CNS. Experimentally, early incorporation studies in animal brain slices and homogenates with radio-labelled nucleosides or precursors demonstrated salvage activity or de novo synthesis. Later, the nucleoside transporters and organic anionic transporters underlying uptake of metabolites and anti-pyrimidine drugs in the CNS were identified. Recently, the expression of de novo enzymes in glial cells and neurons was verified using (immuno) histochemical and in-situ-hybridization techniques. Adult brain was shown to take up or produce all pyrimidine (deoxy) ribonucleosides or, after uptake and phosphorolysis of nucleosides, to make use of ribose for different purposes, including energy. More recently, non-canonical pyrimidine bases (5mC, 5hmC) have been found most notably in brain, pointing to considerable postreplicative DNA metabolism, with the need for pyrimidine-specific enzymes. Even more perspectives are emerging, with advances in genome analysis and in the manipulation of expression from the gene.
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Affiliation(s)
- M Löffler
- a Institute of Physiological Chemistry, Faculty of Medicine, Philipps-University Marburg , Marburg , Germany
| | - E A Carrey
- b Institute of Child Health, University College London , GB
| | - E Zameitat
- a Institute of Physiological Chemistry, Faculty of Medicine, Philipps-University Marburg , Marburg , Germany
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Broeckx BJG, Peelman L, Saunders JH, Deforce D, Clement L. Using variant databases for variant prioritization and to detect erroneous genotype-phenotype associations. BMC Bioinformatics 2017; 18:535. [PMID: 29191167 PMCID: PMC5710091 DOI: 10.1186/s12859-017-1951-y] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/14/2017] [Accepted: 11/22/2017] [Indexed: 01/08/2023] Open
Abstract
Background In the search for novel causal mutations, public and/or private variant databases are nearly always used to facilitate the search as they result in a massive reduction of putative variants in one step. Practically, variant filtering is often done by either using all variants from the variant database (called the absence-approach, i.e. it is assumed that disease-causing variants do not reside in variant databases) or by using the subset of variants with an allelic frequency > 1% (called the 1%-approach). We investigate the validity of these two approaches in terms of false negatives (the true disease-causing variant does not pass all filters) and false positives (a harmless mutation passes all filters and is erroneously retained in the list of putative disease-causing variants) and compare it with an novel approach which we named the quantile-based approach. This approach applies variable instead of static frequency thresholds and the calculation of these thresholds is based on prior knowledge of disease prevalence, inheritance models, database size and database characteristics. Results Based on real-life data, we demonstrate that the quantile-based approach outperforms the absence-approach in terms of false negatives. At the same time, this quantile-based approach deals more appropriately with the variable allele frequencies of disease-causing alleles in variant databases relative to the 1%-approach and as such allows a better control of the number of false positives. We also introduce an alternative application for variant database usage and the quantile-based approach. If disease-causing variants in variant databases deviate substantially from theoretical expectancies calculated with the quantile-based approach, their association between genotype and phenotype had to be reconsidered in 12 out of 13 cases. Conclusions We developed a novel method and demonstrated that this so-called quantile-based approach is a highly suitable method for variant filtering. In addition, the quantile-based approach can also be used for variant flagging. For user friendliness, lookup tables and easy-to-use R calculators are provided. Electronic supplementary material The online version of this article (doi: 10.1186/s12859-017-1951-y) contains supplementary material, which is available to authorized users.
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Affiliation(s)
- Bart J G Broeckx
- Laboratory of Animal Genetics, Faculty of Veterinary Medicine, Ghent University, Heidestraat 19, B-9820, Merelbeke, Belgium.
| | - Luc Peelman
- Laboratory of Animal Genetics, Faculty of Veterinary Medicine, Ghent University, Heidestraat 19, B-9820, Merelbeke, Belgium
| | - Jimmy H Saunders
- Department of Medical Imaging and Orthopedics, Faculty of Veterinary Medicine, Ghent University, Merelbeke, Belgium
| | - Dieter Deforce
- Laboratory of Pharmaceutical Biotechnology, Faculty of Pharmaceutical Sciences, Ghent University, Ghent, Belgium
| | - Lieven Clement
- Department of Applied Mathematics, Computer Science and Statistics, Faculty of Sciences, Ghent University, Ghent, Belgium
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Human teratogens and genetic phenocopies. Understanding pathogenesis through human genes mutation. Eur J Med Genet 2016; 60:22-31. [PMID: 27639441 DOI: 10.1016/j.ejmg.2016.09.011] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/25/2016] [Accepted: 09/12/2016] [Indexed: 12/27/2022]
Abstract
Exposure to teratogenic drugs during pregnancy is associated with a wide range of embryo-fetal anomalies and sometimes results in recurrent and recognizable patterns of malformations; however, the comprehension of the mechanisms underlying the pathogenesis of drug-induced birth defects is difficult, since teratogenesis is a multifactorial process which is always the result of a complex interaction between several environmental factors and the genetic background of both the mother and the fetus. Animal models have been extensively used to assess the teratogenic potential of pharmacological agents and to study their teratogenic mechanisms; however, a still open issue concerns how the information gained through animal models can be translated to humans. Instead, significant information can be obtained by the identification and analysis of human genetic syndromes characterized by clinical features overlapping with those observed in drug-induced embryopathies. Until now, genetic phenocopies have been reported for the embryopathies/fetopathies associated with prenatal exposure to warfarin, leflunomide, mycophenolate mofetil, fluconazole, thalidomide and ACE inhibitors. In most cases, genetic phenocopies are caused by mutations in genes encoding for the main targets of teratogens or for proteins belonging to the same molecular pathways. The aim of this paper is to review the proposed teratogenic mechanisms of these drugs, by the analysis of human monogenic disorders and their molecular pathogenesis.
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Orotic Acid, More Than Just an Intermediate of Pyrimidine de novo Synthesis. J Genet Genomics 2015; 42:207-19. [DOI: 10.1016/j.jgg.2015.04.001] [Citation(s) in RCA: 49] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/30/2014] [Revised: 04/04/2015] [Accepted: 04/09/2015] [Indexed: 01/21/2023]
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Abstract
We report a new case of postaxial acrofacial dysostosis (Miller) syndrome with expanded profile. The patient presented with unusual orofacial and digital anomalies along with mental retardation. This report emphasizes the recognized features of the syndrome as well as describes intraoral findings that could aid in the diagnosis and management of these patients.
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Affiliation(s)
- Aadithya B Urs
- Department of Oral Pathology, Maulana Azad Institute of Dental Sciences, New Delhi, India
| | - Priya Kumar
- Department of Oral Pathology, Maulana Azad Institute of Dental Sciences, New Delhi, India
| | - Kalpana Nunia
- Department of Oral Pathology, Maulana Azad Institute of Dental Sciences, New Delhi, India
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Shawky RM, Amr N, Salah H, Gad S. Bilateral absence of fifth ray in feet, cleft palate, malformed ears, and corneal opacity in a patient with Miller syndrome. EGYPTIAN JOURNAL OF MEDICAL HUMAN GENETICS 2014. [DOI: 10.1016/j.ejmhg.2013.12.004] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022] Open
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Protein instability and functional defects caused by mutations of dihydro-orotate dehydrogenase in Miller syndrome patients. Biosci Rep 2013; 32:631-9. [PMID: 22967083 PMCID: PMC3497730 DOI: 10.1042/bsr20120046] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
Miller syndrome is a recessive inherited disorder characterized by postaxial acrofacial dysostosis. It is caused by dysfunction of the DHODH (dihydroorotate dehydrogenase) gene, which encodes a key enzyme in the pyrimidine de novo biosynthesis pathway and is localized at mitochondria intermembrane space. We investigated the consequence of three missense mutations, G202A, R346W and R135C of DHODH, which were previously identified in patients with Miller syndrome. First, we established HeLa cell lines stably expressing DHODH with Miller syndrome-causative mutations: G202A, R346W and R135C. These three mutant proteins retained the proper mitochondrial localization based on immunohistochemistry and mitochondrial subfractionation studies. The G202A, R346W DHODH proteins showed reduced protein stability. On the other hand, the third one R135C, in which the mutation lies at the ubiquinone-binding site, was stable but possessed no enzymatic activity. In conclusion, the G202A and R346W mutation causes deficient protein stability, and the R135C mutation does not affect stability but impairs the substrate-induced enzymatic activity, suggesting that impairment of DHODH activity is linked to the Miller syndrome phenotype.
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Dihydro-orotate dehydrogenase is physically associated with the respiratory complex and its loss leads to mitochondrial dysfunction. Biosci Rep 2013; 33:e00021. [PMID: 23216091 PMCID: PMC3564035 DOI: 10.1042/bsr20120097] [Citation(s) in RCA: 82] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Some mutations of the DHODH (dihydro-orotate dehydrogenase) gene lead to postaxial acrofacial dysostosis or Miller syndrome. Only DHODH is localized at mitochondria among enzymes of the de novo pyrimidine biosynthesis pathway. Since the pyrimidine biosynthesis pathway is coupled to the mitochondrial RC (respiratory chain) via DHODH, impairment of DHODH should affect the RC function. To investigate this, we used siRNA (small interfering RNA)-mediated knockdown and observed that DHODH knockdown induced cell growth retardation because of G2/M cell-cycle arrest, whereas pyrimidine deficiency usually causes G1/S arrest. Inconsistent with this, the cell retardation was not rescued by exogenous uridine, which should bypass the DHODH reaction for pyrimidine synthesis. DHODH depletion partially inhibited the RC complex III, decreased the mitochondrial membrane potential, and increased the generation of ROS (reactive oxygen species). We observed that DHODH physically interacts with respiratory complexes II and III by IP (immunoprecipitation) and BN (blue native)/SDS/PAGE analysis. Considering that pyrimidine deficiency alone does not induce craniofacial dysmorphism, the DHODH mutations may contribute to the Miller syndrome in part through somehow altered mitochondrial function.
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