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Abstract
The XPG/ERCC5 endonuclease was originally identified as the causative gene for Xeroderma Pigmentosum complementation group G. Ever since its discovery, in depth biochemical, structural and cell biological studies have provided detailed mechanistic insight into its function in excising DNA damage in nucleotide excision repair, together with the ERCC1–XPF endonuclease. In recent years, it has become evident that XPG has additional important roles in genome maintenance that are independent of its function in NER, as XPG has been implicated in protecting replication forks by promoting homologous recombination as well as in resolving R-loops. Here, we provide an overview of the multitasking of XPG in genome maintenance, by describing in detail how its activity in NER is regulated and the evidence that points to important functions outside of NER. Furthermore, we present the various disease phenotypes associated with inherited XPG deficiency and discuss current ideas on how XPG deficiency leads to these different types of disease.
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Feltes BC. Revisiting the structural features of the xeroderma pigmentosum proteins: Focus on mutations and knowledge gaps. MUTATION RESEARCH. REVIEWS IN MUTATION RESEARCH 2022; 789:108416. [PMID: 35690419 DOI: 10.1016/j.mrrev.2022.108416] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/01/2021] [Revised: 03/23/2022] [Accepted: 03/24/2022] [Indexed: 06/15/2023]
Abstract
The nucleotide excision repair pathway is a broadly studied DNA repair mechanism because impairments of its key players, the xeroderma pigmentosum proteins (XPA to XPG), are associated with multiple hereditary diseases. Due to the massive number of novel mutations reported for these proteins and new structural data published every year, proper categorization and discussion of relevant observations is needed to organize this extensive inflow of knowledge. This review aims to revisit the structural data of all XP proteins while updating it with the information developed in of the past six years. Discussions and interpretations of mutation outcomes, mechanisms of action, and knowledge gaps regarding their structures are provided, as well as new perspectives based on recent research.
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Affiliation(s)
- Bruno César Feltes
- Department of Theoretical Informatics, Institute of Informatics, Department of Theoretical Informatics, Federal University of Rio Grande do Sul, Porto Alegre, RS, Brazil; Department of Genetics, Institute of Bioscience, Federal University of Rio Grande do Sul, Porto Alegre, RS, Brazil; Department of Biophysics, Institute of Bioscience, Federal University of Rio Grande do Sul, Porto Alegre, RS, Brazil.
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Tsutakawa SE, Bacolla A, Katsonis P, Bralić A, Hamdan SM, Lichtarge O, Tainer JA, Tsai CL. Decoding Cancer Variants of Unknown Significance for Helicase-Nuclease-RPA Complexes Orchestrating DNA Repair During Transcription and Replication. Front Mol Biosci 2021; 8:791792. [PMID: 34966786 PMCID: PMC8710748 DOI: 10.3389/fmolb.2021.791792] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/09/2021] [Accepted: 11/16/2021] [Indexed: 01/13/2023] Open
Abstract
All tumors have DNA mutations, and a predictive understanding of those mutations could inform clinical treatments. However, 40% of the mutations are variants of unknown significance (VUS), with the challenge being to objectively predict whether a VUS is pathogenic and supports the tumor or whether it is benign. To objectively decode VUS, we mapped cancer sequence data and evolutionary trace (ET) scores onto crystallography and cryo-electron microscopy structures with variant impacts quantitated by evolutionary action (EA) measures. As tumors depend on helicases and nucleases to deal with transcription/replication stress, we targeted helicase–nuclease–RPA complexes: (1) XPB-XPD (within TFIIH), XPF-ERCC1, XPG, and RPA for transcription and nucleotide excision repair pathways and (2) BLM, EXO5, and RPA plus DNA2 for stalled replication fork restart. As validation, EA scoring predicts severe effects for most disease mutations, but disease mutants with low ET scores not only are likely destabilizing but also disrupt sophisticated allosteric mechanisms. For sites of disease mutations and VUS predicted to be severe, we found strong co-localization to ordered regions. Rare discrepancies highlighted the different survival requirements between disease and tumor mutations, as well as the value of examining proteins within complexes. In a genome-wide analysis of 33 cancer types, we found correlation between the number of mutations in each tumor and which pathways or functional processes in which the mutations occur, revealing different mutagenic routes to tumorigenesis. We also found upregulation of ancient genes including BLM, which supports a non-random and concerted cancer process: reversion to a unicellular, proliferation-uncontrolled, status by breaking multicellular constraints on cell division. Together, these genes and global analyses challenge the binary “driver” and “passenger” mutation paradigm, support a gradient impact as revealed by EA scoring from moderate to severe at a single gene level, and indicate reduced regulation as well as activity. The objective quantitative assessment of VUS scoring and gene overexpression in the context of functional interactions and pathways provides insights for biology, oncology, and precision medicine.
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Affiliation(s)
- Susan E Tsutakawa
- Molecular Biophysics and Integrated Bioimaging, Lawrence Berkeley National Laboratory, Berkeley, CA, United States
| | - Albino Bacolla
- Department of Molecular and Cellular Oncology, University of Texas M.D. Anderson Cancer Center, Houston, TX, United States
| | - Panagiotis Katsonis
- Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, TX, United States
| | - Amer Bralić
- Laboratory of DNA Replication and Recombination, Biological and Environmental Sciences and Engineering Division, King Abdullah University of Science and Technology (KAUST), Thuwal, Saudi Arabia
| | - Samir M Hamdan
- Laboratory of DNA Replication and Recombination, Biological and Environmental Sciences and Engineering Division, King Abdullah University of Science and Technology (KAUST), Thuwal, Saudi Arabia
| | - Olivier Lichtarge
- Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, TX, United States
| | - John A Tainer
- Molecular Biophysics and Integrated Bioimaging, Lawrence Berkeley National Laboratory, Berkeley, CA, United States.,Department of Molecular and Cellular Oncology, University of Texas M.D. Anderson Cancer Center, Houston, TX, United States.,Department of Cancer Biology, University of Texas M.D. Anderson Cancer Center, Houston, TX, United States
| | - Chi-Lin Tsai
- Department of Molecular and Cellular Oncology, University of Texas M.D. Anderson Cancer Center, Houston, TX, United States
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Human XPG nuclease structure, assembly, and activities with insights for neurodegeneration and cancer from pathogenic mutations. Proc Natl Acad Sci U S A 2020; 117:14127-14138. [PMID: 32522879 PMCID: PMC7321962 DOI: 10.1073/pnas.1921311117] [Citation(s) in RCA: 33] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
DNA repair is essential to life and to avoidance of genome instability and cancer. Xeroderma pigmentosum group G (XPG) protein acts in multiple DNA repair pathways, both as an active enzyme and as a scaffold for coordinating with other repair proteins. We present here the structure of the catalytic domain responsible for its DNA binding and nuclease activity. Our analysis provides structure-based hypotheses for how XPG recognizes its bubble DNA substrate and predictions of the structural impacts of XPG disease mutations associated with two phenotypically distinct diseases: xeroderma pigmentosum (XP, skin cancer prone) or Cockayne syndrome (XP/CS, severe progressive developmental defects). Xeroderma pigmentosum group G (XPG) protein is both a functional partner in multiple DNA damage responses (DDR) and a pathway coordinator and structure-specific endonuclease in nucleotide excision repair (NER). Different mutations in the XPG gene ERCC5 lead to either of two distinct human diseases: Cancer-prone xeroderma pigmentosum (XP-G) or the fatal neurodevelopmental disorder Cockayne syndrome (XP-G/CS). To address the enigmatic structural mechanism for these differing disease phenotypes and for XPG’s role in multiple DDRs, here we determined the crystal structure of human XPG catalytic domain (XPGcat), revealing XPG-specific features for its activities and regulation. Furthermore, XPG DNA binding elements conserved with FEN1 superfamily members enable insights on DNA interactions. Notably, all but one of the known pathogenic point mutations map to XPGcat, and both XP-G and XP-G/CS mutations destabilize XPG and reduce its cellular protein levels. Mapping the distinct mutation classes provides structure-based predictions for disease phenotypes: Residues mutated in XP-G are positioned to reduce local stability and NER activity, whereas residues mutated in XP-G/CS have implied long-range structural defects that would likely disrupt stability of the whole protein, and thus interfere with its functional interactions. Combined data from crystallography, biochemistry, small angle X-ray scattering, and electron microscopy unveil an XPG homodimer that binds, unstacks, and sculpts duplex DNA at internal unpaired regions (bubbles) into strongly bent structures, and suggest how XPG complexes may bind both NER bubble junctions and replication forks. Collective results support XPG scaffolding and DNA sculpting functions in multiple DDR processes to maintain genome stability.
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Chikhaoui A, Elouej S, Nabouli I, Jones M, Lagarde A, Ben Rekaya M, Messaoud O, Hamdi Y, Zghal M, Delague V, Levy N, De Sandre-Giovannoli A, Abdelhak S, Yacoub-Youssef H. Identification of a ERCC5 c.2333T>C (L778P) Variant in Two Tunisian Siblings With Mild Xeroderma Pigmentosum Phenotype. Front Genet 2019; 10:111. [PMID: 30838033 PMCID: PMC6383105 DOI: 10.3389/fgene.2019.00111] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2018] [Accepted: 01/30/2019] [Indexed: 11/22/2022] Open
Abstract
Xeroderma pigmentosum (XP) is a rare autosomal recessive disorder due to a defect in the nucleotide excision repair (NER) DNA repair pathway, characterized by severe sunburn development of freckles, premature skin aging, and susceptibility to develop cancers at an average age of eight. XP is an example of accelerated photo-aging. It is a genetically and clinically heterogeneous disease. Eight complementation groups have been described worldwide. In Tunisia, five groups have been already identified. In this work, we investigated the genetic etiology in a family with an atypically mild XP phenotype. Two Tunisian siblings born from first-degree consanguineous parents underwent clinical examination in the dermatology department of the Charles Nicolle Hospital on the basis of acute sunburn reaction and mild neurological disorders. Blood samples were collected from two affected siblings after written informed consent. As all mutations reported in Tunisia have been excluded using Sanger sequencing, we carried out mutational analysis through a targeted panel of gene sequencing using the Agilent HaloPlex target enrichment system. Our clinical study shows, in both patients, the presence of achromic macula in sun exposed area with dermatological feature suggestive of Xeroderma pigmentosum disease. No developmental and neurological disorders were observed except mild intellectual disability. Genetic investigation shows that both patients were carriers of an homozygous T to C transition at the nucleotide position c.2333, causing the leucine to proline amino acid change at the position 778 (p.Leu778Pro) of the ERCC5 gene, and resulting in an XP-G phenotype. The same variation was previously reported at the heterozygous state in a patient cell line in Europe, for which no clinical data were available and was suggested to confer an XP/CS phenotype based on functional tests. This study contributes to further characterization of the mutation spectrum of XP in consanguineous Tunisian families and is potentially helpful for early diagnosis. It also indicates that the genotype-phenotype correlation is not always coherent for patients with mild clinical features. These data therefore suggest that targeted NGS is a highly informative diagnostic strategy, which can be used for XP molecular etiology determination.
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Affiliation(s)
- Asma Chikhaoui
- Laboratoire de Génomique Biomédicale et Oncogénétique, Institut Pasteur de Tunis, Université de Tunis El Manar, Tunis, Tunisia
| | - Sahar Elouej
- Laboratoire de Génomique Biomédicale et Oncogénétique, Institut Pasteur de Tunis, Université de Tunis El Manar, Tunis, Tunisia.,Aix Marseille Univ, Inserm, MMG, U 1251, Marseille, France
| | - Imen Nabouli
- Laboratoire de Génomique Biomédicale et Oncogénétique, Institut Pasteur de Tunis, Université de Tunis El Manar, Tunis, Tunisia
| | - Meriem Jones
- Laboratoire de Génomique Biomédicale et Oncogénétique, Institut Pasteur de Tunis, Université de Tunis El Manar, Tunis, Tunisia.,Service de Dermatologie, Hôpital Charles Nicolle, Tunis, Tunisia
| | - Arnaud Lagarde
- Aix Marseille Univ, Inserm, MMG, U 1251, Marseille, France
| | - Meriem Ben Rekaya
- Laboratoire de Génomique Biomédicale et Oncogénétique, Institut Pasteur de Tunis, Université de Tunis El Manar, Tunis, Tunisia
| | - Olfa Messaoud
- Laboratoire de Génomique Biomédicale et Oncogénétique, Institut Pasteur de Tunis, Université de Tunis El Manar, Tunis, Tunisia
| | - Yosr Hamdi
- Laboratoire de Génomique Biomédicale et Oncogénétique, Institut Pasteur de Tunis, Université de Tunis El Manar, Tunis, Tunisia
| | - Mohamed Zghal
- Service de Dermatologie, Hôpital Charles Nicolle, Tunis, Tunisia
| | | | - Nicolas Levy
- Aix Marseille Univ, Inserm, MMG, U 1251, Marseille, France.,Département de Génétique Médicale, AP-HM, Hôpital la Timone, Marseille, France
| | - Annachiara De Sandre-Giovannoli
- Aix Marseille Univ, Inserm, MMG, U 1251, Marseille, France.,Département de Génétique Médicale, AP-HM, Hôpital la Timone, Marseille, France
| | - Sonia Abdelhak
- Laboratoire de Génomique Biomédicale et Oncogénétique, Institut Pasteur de Tunis, Université de Tunis El Manar, Tunis, Tunisia
| | - Houda Yacoub-Youssef
- Laboratoire de Génomique Biomédicale et Oncogénétique, Institut Pasteur de Tunis, Université de Tunis El Manar, Tunis, Tunisia
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Drury S, Boustred C, Tekman M, Stanescu H, Kleta R, Lench N, Chitty LS, Scott RH. A novel homozygous ERCC5 truncating mutation in a family with prenatal arthrogryposis--further evidence of genotype-phenotype correlation. Am J Med Genet A 2014; 164A:1777-83. [PMID: 24700531 DOI: 10.1002/ajmg.a.36506] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/08/2013] [Accepted: 01/30/2014] [Indexed: 11/10/2022]
Abstract
We report on a family with five fetuses conceived to first cousin parents presenting with abnormal ultrasound findings including contractures and microcephaly. Cerebellar hypoplasia and ventriculomegaly were also present in two and fetal edema developed in the one fetus that survived beyond 24 weeks of gestation. Linkage studies of 15 members of the family, including four affecteds, were undertaken followed by exome sequencing of one affected individual and their parents. Analysis of exome data was restricted to the 9.3 Mb largest shared region of homozygosity identified by linkage; a single novel homozygous mutation in the proband that was heterozygous in the parents (ERCC5 c.2766dupA, p.Leu923ThrfsX7) was identified. This segregated with disease. ERCC5 is a component of the nucleotide excision repair machinery and biallelic mutations in the gene have previously been associated with xeroderma pigmentosum (group G), Cockayne syndrome and the more severe cerebrooculofacioskeletal syndrome. The phenotype in the family we report on is consistent with a severe manifestation of cerebrooculofacioskeletal syndrome. Our data broaden the reported clinical spectrum of ERCC5 mutations and provide further evidence of genotype-phenotype correlation with truncating mutations being associated with severe phenotypes. They also demonstrate the molecular diagnostic power of a combined approach of linkage studies and exome sequencing in families with rare, genetically heterogeneous disorders and a well described pedigree.
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Affiliation(s)
- Suzanne Drury
- NE Thames Regional Genetics Service, Great Ormond Street Hospital for Children, London, United Kingdom
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7
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Brooks BP, Thompson AH, Bishop RJ, Clayton JA, Chan CC, Tsilou ET, Zein WM, Tamura D, Khan SG, Ueda T, Boyle J, Oh KS, Imoto K, Inui H, Moriwaki SI, Emmert S, Iliff NT, Bradford P, Digiovanna JJ, Kraemer KH. Ocular manifestations of xeroderma pigmentosum: long-term follow-up highlights the role of DNA repair in protection from sun damage. Ophthalmology 2013; 120:1324-36. [PMID: 23601806 DOI: 10.1016/j.ophtha.2012.12.044] [Citation(s) in RCA: 55] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/23/2012] [Revised: 12/13/2012] [Accepted: 12/20/2012] [Indexed: 11/29/2022] Open
Abstract
OBJECTIVE Xeroderma pigmentosum (XP) is a rare autosomal recessive disease caused by mutations in DNA repair genes. Clinical manifestations of XP include mild to extreme sensitivity to ultraviolet radiation resulting in inflammation and neoplasia in sun-exposed areas of the skin, mucous membranes, and ocular surfaces. This report describes the ocular manifestations of XP in patients systematically evaluated in the Clinical Center at the National Institutes of Health. DESIGN Retrospective observational case series. PARTICIPANTS Eighty-seven participants, aged 1.3 to 63.4 years, referred to the National Eye Institute (NEI) for examination from 1964 to 2011. Eighty-three patients had XP, 3 patients had XP/Cockayne syndrome complex, and 1 patient had XP/trichothiodystrophy complex. METHODS Complete age- and developmental stage-appropriate ophthalmic examination. MAIN OUTCOME MEASURES Visual acuity; eyelid, ocular surface, and lens pathology; tear film and tear production measures; and cytologic analysis of conjunctival surface swabs. RESULTS Of the 87 patients, 91% had at least 1 ocular abnormality. The most common abnormalities were conjunctivitis (51%), corneal neovascularization (44%), dry eye (38%), corneal scarring (26%), ectropion (25%), blepharitis (23%), conjunctival melanosis (20%), and cataracts (14%). Thirteen percent of patients had some degree of visual axis impingement, and 5% of patients had no light perception in 1 or both eyes. Ocular surface cancer or a history of ocular surface cancer was present in 10% of patients. Patients with an acute sunburning skin phenotype were less likely to develop conjunctival melanosis and ectropion but more likely to develop neoplastic ocular surface lesions than nonburning patients. Some patients also showed signs of limbal stem cell deficiency. CONCLUSIONS Our longitudinal study reports the ocular status of the largest group of patients with XP systematically examined at 1 facility over an extended period of time. Structural eyelid abnormalities, neoplasms of the ocular surface and eyelids, tear film and tear production abnormalities, ocular surface disease and inflammation, and corneal abnormalities were present in this population. Burning and nonburning patients with XP exhibit different rates of important ophthalmologic findings, including neoplasia. In addition, ophthalmic characteristics can help refine diagnoses in the case of XP complex phenotypes. DNA repair plays a major role in protection of the eye from sunlight-induced damage.
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Affiliation(s)
- Brian P Brooks
- National Eye Institute, National Institutes of Health, Bethesda, Maryland 20892, USA.
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Characterization of three XPG-defective patients identifies three missense mutations that impair repair and transcription. J Invest Dermatol 2013; 133:1841-9. [PMID: 23370536 DOI: 10.1038/jid.2013.54] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Only 16 XPG-defective patients with 20 different mutations have been described. The current hypothesis is that missense mutations impair repair (xeroderma pigmentosum (XP) symptoms), whereas truncating mutations impair both repair and transcription (XP and Cockayne syndrome (CS) symptoms). We identified three cell lines of XPG-defective patients (XP40GO, XP72MA, and XP165MA). Patients' fibroblasts showed a reduced post-UVC cell survival. The reduced repair capability, assessed by host cell reactivation, could be complemented by XPG cDNA. XPG mRNA expression of XP165MA, XP72MA, and XP40GO was 83%, 97%, and 82.5%, respectively, compared with normal fibroblasts. XP165MA was homozygous for a p.G805R mutation; XP72MA and XP40GO were both compound heterozygous (p.W814S and p.E727X, and p.L778P and p.Q150X, respectively). Allele-specific complementation analysis of these five mutations revealed that p.L778P and p.W814S retained considerable residual repair activity. In line with the severe XP/CS phenotypes of XP72MA and XP165MA, even the missense mutations failed to interact with the transcription factor IIH subunits XPD and to some extent cdk7 in coimmunoprecipitation assays. Immunofluorescence techniques revealed that the mutations destabilized early recruitment of XP proteins to localized photodamage and delayed their redistribution in vivo. Thus, we identified three XPG missense mutations in the I-region of XPG that impaired repair and transcription and resulted in severe XP/CS.
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Thorel F, Constantinou A, Dunand-Sauthier I, Nouspikel T, Lalle P, Raams A, Jaspers NGJ, Vermeulen W, Shivji MKK, Wood RD, Clarkson SG. Definition of a short region of XPG necessary for TFIIH interaction and stable recruitment to sites of UV damage. Mol Cell Biol 2004; 24:10670-80. [PMID: 15572672 PMCID: PMC533987 DOI: 10.1128/mcb.24.24.10670-10680.2004] [Citation(s) in RCA: 59] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
XPG is the human endonuclease that cuts 3' to DNA lesions during nucleotide excision repair. Missense mutations in XPG can lead to xeroderma pigmentosum (XP), whereas truncated or unstable XPG proteins cause Cockayne syndrome (CS), normally yielding life spans of <7 years. One XP-G individual who had advanced XP/CS symptoms at 28 years has been identified. The genetic, biochemical, and cellular defects in this remarkable case provide insight into the onset of XP and CS, and they reveal a previously unrecognized property of XPG. Both of this individual's XPG alleles produce a severely truncated protein, but an infrequent alternative splice generates an XPG protein lacking seven internal amino acids, which can account for his very slight cellular UV resistance. Deletion of XPG amino acids 225 to 231 does not abolish structure-specific endonuclease activity. Instead, this region is essential for interaction with TFIIH and for the stable recruitment of XPG to sites of local UV damage after the prior recruitment of TFIIH. These results define a new functional domain of XPG, and they demonstrate that recruitment of DNA repair proteins to sites of damage does not necessarily lead to productive repair reactions. This observation has potential implications that extend beyond nucleotide excision repair.
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Affiliation(s)
- Fabrizio Thorel
- Department of Microbiology and Molecular Medicine, University Medical Centre, 1 rue Michel-Servet, 1211 Geneva 4, Switzerland
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Emmert S, Slor H, Busch DB, Batko S, Albert RB, Coleman D, Khan SG, Abu-Libdeh B, DiGiovanna JJ, Cunningham BB, Lee MM, Crollick J, Inui H, Ueda T, Hedayati M, Grossman L, Shahlavi T, Cleaver JE, Kraemer KH. Relationship of neurologic degeneration to genotype in three xeroderma pigmentosum group G patients. J Invest Dermatol 2002; 118:972-82. [PMID: 12060391 DOI: 10.1046/j.1523-1747.2002.01782.x] [Citation(s) in RCA: 77] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
We studied three newly diagnosed xeroderma pigmentosum complementation group G patients with markedly different clinical features. An Israeli-Palestinian girl (XP96TA) had severe abnormalities suggestive of the xeroderma pigmentosum/Cockayne syndrome complex including sun sensitivity, neurologic and developmental impairment, and death by age 6 y. A Caucasian girl (XP82DC) also had severe sun sensitivity with neurologic and developmental impairment and died at 5.8 y. In contrast, a mildly affected 14-y-old Caucasian female (XP65BE) had sun sensitivity but no neurologic abnormalities. XP96TA, XP82DC, and XP65BE fibroblasts showed marked reductions in post-ultraviolet cell survival and DNA repair but these were higher in XP65BE than in XP82DC. XP96TA fibroblasts had very low XPG mRNA expression levels whereas XP65BE fibroblasts had nearly normal levels. Host cell reactivation of an ultraviolet-treated reporter assigned all three fibroblast strains to the rare xeroderma pigmentosum complementation group G (only 10 other patients previously reported). XP96TA and XP82DC cells had mutations in both XPG alleles that are predicted to result in severely truncated proteins including stop codons and two base frameshifts. The mild XP65BE patient had an early stop codon mutation in the paternal allele. The XP65BE maternal allele had a single base missense mutation (G2817A, Ala874Thr) that showed residual ability to complement xeroderma pigmentosum complementation group G cells. These observations agree with earlier studies demonstrating that XPG mutations, which are predicted to lead to severely truncated proteins in both alleles, were associated with severe xeroderma pigmentosum/Cockayne syndrome neurologic symptoms. Retaining residual functional activity in one allele was associated with mild clinical features without neurologic abnormalities.
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Affiliation(s)
- Steffen Emmert
- Basic Research Laboratory, Center for Cancer Research, National Cancer Institute, Bethesda, Maryland 20892, USA
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Lalle P, Nouspikel T, Constantinou A, Thorel F, Clarkson SG. The founding members of xeroderma pigmentosum group G produce XPG protein with severely impaired endonuclease activity. J Invest Dermatol 2002; 118:344-51. [PMID: 11841555 DOI: 10.1046/j.0022-202x.2001.01673.x] [Citation(s) in RCA: 39] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Of the eight human genes implicated in xeroderma pigmentosum, defects in XPG produce some of the most clinically diverse symptoms. These range from mild freckling to severe skeletal and neurologic abnormalities characteristic of Cockayne syndrome. Mildly affected xeroderma pigmentosum group G patients have diminished XPG endonuclease activity in nucleotide excision repair, whereas severely affected xeroderma pigmentosum group G/Cockayne syndrome patients produce truncated XPG proteins that are unable to function in either nucleotide excision repair or the transcription-coupled repair of oxidative lesions. The first two xeroderma pigmentosum group G patients, XP2BI and XP3BR, were reported before the relationship between xeroderma pigmentosum group G and Cockayne syndrome was appreciated. Here we provide evidence that both patients produce truncated proteins from one XPG allele. From the second allele, XP2BI generates full-length XPG of 1186 amino acids containing a single L858P substitution that has reduced stability and greatly impaired endonuclease activity. In XP3BR, a single base deletion and alternative splicing at a rare noncanonical AT-AC intron produces a 1185 amino acid protein containing 44 internal non-XPG residues. This protein is stably expressed but it also has greatly impaired endonuclease activity. These four XPG products can thus account for the severe ultraviolet sensitivity of XP2BI and XP3BR fibroblasts. These cells, unlike those from xeroderma pigmentosum group G/Cockayne syndrome patients, are capable of limited transcription-coupled repair of oxidative lesions. Our results suggest that the L858P protein in XP2BI and the almost full-length XPG protein in XP3BR are responsible for this activity and for the absence of severe early onset Cockayne syndrome symptoms in these patients.
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Affiliation(s)
- Philippe Lalle
- Department of Genetics and Microbiology, Centre Médical Universitaire (CMU), Geneva, Switzerland
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Zafeiriou DI, Thorel F, Andreou A, Kleijer WJ, Raams A, Garritsen VH, Gombakis N, Jaspers NG, Clarkson SG. Xeroderma pigmentosum group G with severe neurological involvement and features of Cockayne syndrome in infancy. Pediatr Res 2001; 49:407-12. [PMID: 11228268 DOI: 10.1203/00006450-200103000-00016] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
We describe a premature, small for gestational age infant girl with micropthalmia, bilateral congenital cataracts, hearing impairment, progressive somatic and neurodevelopmental arrest, and infantile spasms. She presented a massive photosensitive reaction with erythema and blistering after minimal sun exposure, which slowly gave place to small skin cancers. Her skin fibroblasts were 10-fold more sensitive than normal to UV exposure due to a severe deficiency in nucleotide excision repair. By complementation analysis, the patient XPCS4RO was assigned to the very rare xeroderma pigmentosum (XP) group G (XP-G). One allele of her XPG gene contained a 526C-->T transition that changed Gln-176 to a premature UAG stop codon. Only a minor fraction of XPG mRNA was encoded by this allele. The second, more significantly expressed XPG allele contained a 215C-->A transversion. This changed the highly conserved Pro-72 to a histidine, a substitution that would be expected to seriously impair the 3' endonuclease function of XPG in nucleotide excision repair. In cases suspected of having XP and/or early-onset Cockayne syndrome, extensive DNA repair studies should be performed to reach a correct diagnosis, thereby allowing reliable genetic counseling and prenatal diagnosis.
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Affiliation(s)
- D I Zafeiriou
- First Department of Pediatrics, Aristotle University of Thessaloniki, Greece
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Rapin I, Lindenbaum Y, Dickson DW, Kraemer KH, Robbins JH. Cockayne syndrome and xeroderma pigmentosum. Neurology 2000; 55:1442-9. [PMID: 11185579 PMCID: PMC4459578 DOI: 10.1212/wnl.55.10.1442] [Citation(s) in RCA: 159] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
Abstract
OBJECTIVES To review genetic variants of Cockayne syndrome (CS) and xeroderma pigmentosum (XP), autosomal recessive disorders of DNA repair that affect the nervous system, and to illustrate them by the first case of xeroderma pigmentosum-Cockayne syndrome (XP-CS) complex to undergo neuropathologic examination. METHODS Published reports of clinical, pathologic, and molecular studies of CS, XP neurologic disease, and the XP-CS complex were reviewed, and a ninth case of XP-CS is summarized. RESULTS CS is a multisystem disorder that causes both profound growth failure of the soma and brain and progressive cachexia, retinal, cochlear, and neurologic degeneration, with a leukodystrophy and demyelinating neuropathy without an increase in cancer. XP presents as extreme photosensitivity of the skin and eyes with a 1000-fold increased frequency of cutaneous basal and squamous cell carcinomas and melanomas and a small increase in nervous system neoplasms. Some 20% of patients with XP incur progressive degeneration of previously normally developed neurons resulting in cortical, basal ganglia, cerebellar, and spinal atrophy, cochlear degeneration, and a mixed distal axonal neuropathy. Cultured cells from patients with CS or XP are hypersensitive to killing by ultraviolet (UV) radiation. Both CS and most XP cells have defective DNA nucleotide excision repair of actively transcribing genes; in addition, XP cells have defective repair of the global genome. There are two complementation groups in CS and seven in XP. Patients with the XP-CS complex fall into three XP complementation groups. Despite their XP genotype, six of nine individuals with the XP-CS complex, including the boy we followed up to his death at age 6, had the typical clinically and pathologically severe CS phenotype. Cultured skin and blood cells had extreme sensitivity to killing by UV radiation, DNA repair was severely deficient, post-UV unscheduled DNA synthesis was reduced to less than 5%, and post-UV plasmid mutation frequency was increased. CONCLUSIONS The paradoxical lack of parallelism of phenotype to genotype is unexplained in these disorders. Perhaps diverse mutations responsible for UV sensitivity and deficient DNA repair may also produce profound failure of brain and somatic growth, progressive cachexia and premature aging, and tissue-selective neurologic deterioration by their roles in regulation of transcription and repair of endogenous oxidative DNA damage.
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Affiliation(s)
- I Rapin
- Department of Neurology, Rose F. Kennedy Center for Research in Mental Retardation and Human Development, Albert Einstein College of Medicine,Bronx, NY, USA.
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Cleaver JE, Thompson LH, Richardson AS, States JC. A summary of mutations in the UV-sensitive disorders: xeroderma pigmentosum, Cockayne syndrome, and trichothiodystrophy. Hum Mutat 2000; 14:9-22. [PMID: 10447254 DOI: 10.1002/(sici)1098-1004(1999)14:1<9::aid-humu2>3.0.co;2-6] [Citation(s) in RCA: 177] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
The human diseases xeroderma pigmentosum, Cockayne syndrome, and trichothiodystrophy are caused by mutations in a set of interacting gene products, which carry out the process of nucleotide excision repair. The majority of the genes have now been cloned and many mutations in the genes identified. The relationships between the distribution of mutations in the genes and the clinical presentations can be used for diagnosis and for understanding the functions and the modes of interaction among the gene products. The summary presented here represents currently known mutations that can be used as the basis for future studies of the structure, function, and biochemical properties of the proteins involved in this set of complex disorders, and may allow determination of the critical sites for mutations leading to different clinical manifestations. The summary indicates where more data are needed for some complementation groups that have few reported mutations, and for the groups for which the gene(s) are not yet cloned. These include the Xeroderma pigmentosum (XP) variant, the trichothiodystrophy group A (TTDA), and ultraviolet sensitive syndrome (UVs) groups. We also recommend that the XP-group E should be defined explicitly through molecular terms, because assignment by complementation in culture has been difficult. XP-E by this definition contains only those cell lines and patients that have mutations in the small subunit, DDB2, of a damage-specific DNA binding protein.
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Affiliation(s)
- J E Cleaver
- UCSF Cancer Center and Department of Dermatology, University of California, San Francisco 94143-0808, USA.
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Constantinou A, Gunz D, Evans E, Lalle P, Bates PA, Wood RD, Clarkson SG. Conserved residues of human XPG protein important for nuclease activity and function in nucleotide excision repair. J Biol Chem 1999; 274:5637-48. [PMID: 10026181 DOI: 10.1074/jbc.274.9.5637] [Citation(s) in RCA: 79] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The human XPG endonuclease cuts on the 3' side of a DNA lesion during nucleotide excision repair. Mutations in XPG can lead to the disorders xeroderma pigmentosum (XP) and Cockayne syndrome. XPG shares sequence similarities in two regions with a family of structure-specific nucleases and exonucleases. To begin defining its catalytic mechanism, we changed highly conserved residues and determined the effects on the endonuclease activity of isolated XPG, its function in open complex formation and dual incision reconstituted with purified proteins, and its ability to restore cellular resistance to UV light. The substitution A792V present in two XP complementation group G (XP-G) individuals reduced but did not abolish endonuclease activity, explaining their mild clinical phenotype. Isolated XPG proteins with Asp-77 or Glu-791 substitutions did not cleave DNA. In the reconstituted repair system, alanine substitutions at these positions permitted open complex formation but were inactive for 3' cleavage, whereas D77E and E791D proteins retained considerable activity. The function of each mutant protein in the reconstituted system was mirrored by its ability to restore UV resistance to XP-G cell lines. Hydrodynamic measurements indicated that XPG exists as a monomer in high salt conditions, but immunoprecipitation of intact and truncated XPG proteins showed that XPG polypeptides can interact with each other, suggesting dimerization as an element of XPG function. The mutation results define critical residues in the catalytic center of XPG and strongly suggest that key features of the strand cleavage mechanism and active site structure are shared by members of the nuclease family.
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Affiliation(s)
- A Constantinou
- Department of Genetics and Microbiology, University Medical Centre, 9 ave de Champel, 1211 Geneva 4, Switzerland
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16
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Abstract
Studies with patients having the inherited DNA repair disorders xeroderma pigmentosum (XP), Cockayne syndrome (CS), and sun-sensitive trichothiodystrophy (TTD) have shown that neither the defect in repair nor the consequent elevated frequency of sunlight-induced mutations in the skin is sufficient to account for the classically high incidence of skin cancer in XP patients. The possible ways in which different mutations in the XP(D) gene and deficiencies in the immune system may be involved are discussed.
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Affiliation(s)
- B A Bridges
- MRC Cell Mutation Unit, University of Sussex, Brighton, Great Britain, UK.
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17
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Okinaka RT, Perez-Castro AV, Sena A, Laubscher K, Strniste GF, Park MS, Hernandez R, MacInnes MA, Kraemer KH. Heritable genetic alterations in a xeroderma pigmentosum group G/Cockayne syndrome pedigree. Mutat Res 1997; 385:107-14. [PMID: 9447232 DOI: 10.1016/s0921-8777(97)00031-1] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
A search for genetic alterations within the XPG gene has been conducted on skin and blood cells cultured from a newly characterized xeroderma pigmentosum (XP) patient (XP20BE). This patient is the ninth known case that falls into the extremely rare XP complementation group G. Four genetic markers within the XPG gene (including two polymorphisms) demonstrated the Mendelian distribution of this gene from the parents to the patient and to an unaffected sibling. The patient (XP20BE) inherited a G to T transversion from his father in exon 1 of the XPG gene that resulted in the conversion of a glutamic acid at codon 11 to a termination codon. The patient also inherited an XP-G allele from his mother that produces an unstable or poorly expressed message. The cause of the latter defect is still uncertain. In addition to these alterations, XP20BE cDNA contained an mRNA species with a large splicing defect that encompassed a deletion from exon 1 to exon 14. This splicing defect, however, appears to be a naturally occurring low-frequency event that results from abnormal splicing that occurs between certain conserved non-consensus splicing signals within the human XPG gene.
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Affiliation(s)
- R T Okinaka
- Life Sciences Division, Los Alamos National Laboratory, NM 87545, USA.
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18
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Park MS, Valdez J, Gurley L, Kim CY. Characterization of a putative helix-loop-helix motif in nucleotide excision repair endonuclease, XPG. J Biol Chem 1997; 272:27823-9. [PMID: 9346928 DOI: 10.1074/jbc.272.44.27823] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
Complementation group G of xeroderma pigmentosum (XPG) is one of the most rare and pathophysiologically heterogeneous forms of this inherited disease. XPG patients exhibit varying phenotypes, from having a very mild defect in DNA repair to being severely affected, and a few cases are also associated with the neurological degeneracy and growth retardation of Cockayne's syndrome. The XPG gene encodes a 134-kDa nuclear protein that is essential for the incision steps of nucleotide excision repair. XPG protein contains a putative helix-loop-helix (HLH) motif in the region that is most conserved among the members of structure-specific endonuclease family. To establish the functional significance of the HLH motif, we used several approaches, including theoretical modeling, functional complementation assay, structure-specific endonuclease assay, and DNA binding assay. A secondary structure of the motif was predicted by energy minimization and the Monte Carlo simulation and empirically proven using the circular dichroism to contain a high content of alpha-helix. When an XPG mutant lacking the HLH was overexpressed in UV135 cells, which have defects in the hamster homolog of XPG, the mutant gene failed to confer to the hamster cells the resistance to UV light. A recombinant XPG protein lacking the HLH motif was purified from insect cells and tested for a structure-specific endonuclease activity. The mutant protein failed to cleave the flap strand. A recombinant peptide containing the HLH (amino acids 758-871) was expressed in and purified from bacteria, tested for DNA binding activity, and found to bind to a DNA substrate with the flap structure. These results suggest that the HLH motif is required for the catalytic and DNA binding activities of XPG.
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Affiliation(s)
- M S Park
- Life Sciences Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA.
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Nouspikel T, Lalle P, Leadon SA, Cooper PK, Clarkson SG. A common mutational pattern in Cockayne syndrome patients from xeroderma pigmentosum group G: implications for a second XPG function. Proc Natl Acad Sci U S A 1997; 94:3116-21. [PMID: 9096355 PMCID: PMC20331 DOI: 10.1073/pnas.94.7.3116] [Citation(s) in RCA: 126] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/06/1996] [Accepted: 01/14/1997] [Indexed: 02/04/2023] Open
Abstract
Xeroderma pigmentosum (XP) patients have defects in nucleotide excision repair (NER), the versatile repair pathway that removes UV-induced damage and other bulky DNA adducts. Patients with Cockayne syndrome (CS), another rare sun-sensitive disorder, are specifically defective in the preferential removal of damage from the transcribed strand of active genes, a process known as transcription-coupled repair. These two disorders are usually clinically and genetically distinct, but complementation analyses have assigned a few CS patients to the rare XP groups B, D, or G. The XPG gene encodes a structure-specific endonuclease that nicks damaged DNA 3' to the lesion during NER. Here we show that three XPG/CS patients had mutations that would produce severely truncated XPG proteins. In contrast, two sibling XPG patients without CS are able to make full-length XPG, but with a missense mutation that inactivates its function in NER. These results suggest that XPG/CS mutations abolish interactions required for a second important XPG function and that it is the loss of this second function that leads to the CS clinical phenotype.
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Affiliation(s)
- T Nouspikel
- Department of Genetics and Microbiology, University Medical Centre (CMU), Geneva 4, Switzerland
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Cooper PK, Nouspikel T, Clarkson SG, Leadon SA. Defective transcription-coupled repair of oxidative base damage in Cockayne syndrome patients from XP group G. Science 1997; 275:990-3. [PMID: 9020084 DOI: 10.1126/science.275.5302.990] [Citation(s) in RCA: 252] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
In normal human cells, damage due to ultraviolet light is preferentially removed from active genes by nucleotide excision repair (NER) in a transcription-coupled repair (TCR) process that requires the gene products defective in Cockayne syndrome (CS). Oxidative damage, including thymine glycols, is shown to be removed by TCR in cells from normal individuals and from xeroderma pigmentosum (XP)-A, XP-F, and XP-G patients who have NER defects but not from XP-G patients who have severe CS. Thus, TCR of oxidative damage requires an XPG function distinct from its NER endonuclease activity. These results raise the possibility that defective TCR of oxidative damage contributes to the developmental defects associated with CS.
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Affiliation(s)
- P K Cooper
- Life Sciences Division, Building 934, Lawrence Berkeley National Laboratory, University of California, 1 Cyclotron Road, Berkeley, CA 94720, USA
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Moriwaki S, Stefanini M, Lehmann AR, Hoeijmakers JH, Robbins JH, Rapin I, Botta E, Tanganelli B, Vermeulen W, Broughton BC, Kraemer KH. DNA repair and ultraviolet mutagenesis in cells from a new patient with xeroderma pigmentosum group G and cockayne syndrome resemble xeroderma pigmentosum cells. J Invest Dermatol 1996; 107:647-53. [PMID: 8823375 DOI: 10.1111/1523-1747.ep12584287] [Citation(s) in RCA: 46] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
Xeroderma pigmentosum (XP)/Cockayne syndrome (CS) complex is a combination of clinical features of two rare genetic disorders in one individual. A sun-sensitive boy (XP20BE) who had severe symptoms of CS, with dwarfism, microcephaly, retinal degeneration, and mental impairment, had XP-type pigmentation and died at 6 y with marked cachexia (weight 14.5 lb) without skin cancers. We evaluated his cultured cells for characteristic CS or XP DNA-repair abnormalities. The level of ultraviolet (UV)-induced unscheduled DNA synthesis was less than 5% of normal, characteristic of the excision-repair defect of XP. Cell fusion studies indicated that his cells were in XP complementation group G. His cells were hypersensitive to killing by UV, and their post-UV recovery of RNA synthesis was abnormally low, features of both CS and XP. Post-UV survival of plasmid pSP189 in his cells was markedly reduced, and post-UV plasmid mutation frequency was higher than with normal cells, as in both CS and XP. Sequence analysis of the mutated plasmid marker gene showed normal frequency of plasmids with multiple base substitutions, as in CS, and an abnormally increased frequency of G:C-->A:T mutations, a feature of XP. Transfection of UV-treated pRSVcat with or without photoreactivation revealed that his cells, like XP cells, could not repair either cyclobutane pyrimidine dimers or non-dimer photoproducts. These results indicate that the DNA-repair features of the XP20BE (XP-G/CS) cells are phenotypically more like XP cells than CS cells, whereas clinically the CS phenotype is more prominent than XP.
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Affiliation(s)
- S Moriwaki
- Laboratory of Molecular Carcinogenesis, National Cancer Institute, Bethesda, MD 20892, USA
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23
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O'Donovan A, Davies AA, Moggs JG, West SC, Wood RD. XPG endonuclease makes the 3' incision in human DNA nucleotide excision repair. Nature 1994; 371:432-5. [PMID: 8090225 DOI: 10.1038/371432a0] [Citation(s) in RCA: 366] [Impact Index Per Article: 12.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
Humans with a defect in the XPG protein suffer from xeroderma pigmentosum (XP) resulting from an inability to perform DNA nucleotide excision repair properly. Here we show that XPG makes a structure-specific endonucleolytic incision in a synthetic DNA substrate containing a duplex region and single-stranded arms. One strand of the duplex is cleaved at the border with single-stranded DNA. A cut with the same polarity is also made in a bubble structure, at the 3' side of the centrally unpaired region. Normal cell extracts introduce a nick 3' to a platinum-DNA lesion, but an XP-G cell extract is defective in making this incision. These data show that XPG has a direct role in making one of the incisions required to excise a damaged oligonucleotide, by cleaving 3' to DNA damage during nucleotide excision repair.
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Affiliation(s)
- A O'Donovan
- Imperial Cancer Research Fund, Clare Hall Laboratories, South Mimms, Herts, UK
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O'Donovan A, Scherly D, Clarkson S, Wood R. Isolation of active recombinant XPG protein, a human DNA repair endonuclease. J Biol Chem 1994. [DOI: 10.1016/s0021-9258(17)33956-x] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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O'Donovan A, Wood RD. Identical defects in DNA repair in xeroderma pigmentosum group G and rodent ERCC group 5. Nature 1993; 363:185-8. [PMID: 8483505 DOI: 10.1038/363185a0] [Citation(s) in RCA: 98] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
Humans with the complementation group G form of the inherited syndrome xeroderma pigmentosum (XP) are hypersensitive to solar ultraviolet light because of a defect in nucleotide-excision repair of DNA. Some individuals are also affected with Cockayne's syndrome, and have neurological abnormalities. Here we report that the DNA repair deficiency of XP-G cell extracts can be corrected by addition of protein fractions from normal cells. Repair proficiency can also be restored by mixing XP-G cell extracts with extracts from different repair-defective cell lines, with one exception. Extracts from cells representing group 5 of a set of ultraviolet-sensitive rodent mutants fail to complement XP-G extracts. XP-G and group 5 correcting activities co-elute after approximately 1,000-fold purification from HeLa cells. An antibody directed against a recombinant fragment of the XP-G complementing protein (XPGC) inhibits excision repair by normal cell extracts, and activity can be restored with an XP-G/group 5 complementing fraction. These data strongly suggest that the XPGC and group 5 correcting (ERCC5) proteins are identical.
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Affiliation(s)
- A O'Donovan
- Imperial Cancer Research Fund, Clare Hall Laboratories, South Mimms, Herts, UK
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Cole J, Arlett CF, Norris PG, Stephens G, Waugh AP, Beare DM, Green MH. Elevated hprt mutant frequency in circulating T-lymphocytes of xeroderma pigmentosum patients. ACTA ACUST UNITED AC 1992; 273:171-8. [PMID: 1372100 DOI: 10.1016/0921-8777(92)90078-h] [Citation(s) in RCA: 22] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
The mutant frequency to 6-thioguanine resistance in circulating T-lymphocytes from 10 xeroderma pigmentosum patients (including complementation groups D and G and XP variants) has been determined. A highly significantly elevated frequency was observed, compared to age-matched, non-smoking control donors (x 2.1-fold higher than the mutant frequency in normal control donors, adjusted for age and cloning efficiency, p less than 0.001). The mutant frequency of 5 XP heterozygotes was in the normal range, when age, smoking habit and log cloning efficiency were taken into account. A number of possible factors which may account for the elevated mutant frequency seen in the XP donors (including an elevated spontaneous mutation rate, UV mutagenesis of the T-cells as they pass through the skin, an effect of environmental mutagens such as tobacco smoke, or as a consequence of immune deficiency) are discussed.
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Affiliation(s)
- J Cole
- MCR Cell Mutation Unit, University of Sussex, Falmer, Brighton, Great Britain
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