Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C0043346 (xeroderma pigmentosum)
 2,924 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The skin-cancer-prone hereditary disease xeroderma pigmentosum is typically characterized by defective nucleotide excision repair (NER) of DNA. However, since all subunits of the core basal transcription factor TFIIH are required for both RNA polymerase II basal transcription and NER, some mutations affecting genes that encode TFIIH subunits can result in clinical phenotypes associated with defective basal transcription. Among these is a syndrome called trichothiodystrophy (TTD) in which the prominent features are brittle hair and nails, and dry scaly skin. A recent study provides dramatic support for the so-called transcription hypothesis of TTD.(1) Specifically, several patients have been shown to carry a mutation in the XPD gene, which encodes a thermolabile form of XPD protein, resulting in loss of hair during febrile episodes.
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PMID:Hot news: temperature-sensitive humans explain hereditary disease. 1149 13

Here, we describe the assembly of the nucleotide excision repair (NER) complex in normal and repair-deficient (xeroderma pigmentosum) human cells, employing a novel technique of local UV irradiation combined with fluorescent antibody labeling. The damage recognition complex XPC-hHR23B appears to be essential for the recruitment of all subsequent NER factors in the preincision complex, including transcription repair factor TFIIH. XPA associates relatively late, is required for anchoring of ERCC1-XPF, and may be essential for activation of the endonuclease activity of XPG. These findings identify XPC as the earliest known NER factor in the reaction mechanism, give insight into the order of subsequent NER components, provide evidence for a dual role of XPA, and support a concept of sequential assembly of repair proteins at the site of the damage rather than a preassembled repairosome.
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PMID:Sequential assembly of the nucleotide excision repair factors in vivo. 1151 74

Damaged DNA-binding protein, DDB, is a heterodimer of p127 and p48 with a high specificity for binding to several types of DNA damage. Mutations in the p48 gene that cause the loss of DDB activity were found in a subset of xeroderma pigmentosum complementation group E (XP-E) patients and have linked to the deficiency in global genomic repair of cyclobutane pyrimidine dimers (CPDs) in these cells. Here we show that with a highly defined system of purified repair factors, DDB can greatly stimulate the excision reaction reconstituted with XPA, RPA, XPC.HR23B, TFIIH, XPF.ERCC1 and XPG, up to 17-fold for CPDs and approximately 2-fold for (6-4) photoproducts (6-4PPs), indicating that no additional factor is required for the stimulation by DDB. Transfection of the p48 cDNA into an SV40-transformed human cell line, WI38VA13, was found to enhance DDB activity and the in vivo removal of CPDs and 6-4PPs. Furthermore, the combined technique of recently developed micropore UV irradiation and immunostaining revealed that p48 (probably in the form of DDB heterodimer) accumulates at locally damaged DNA sites immediately after UV irradiation, and this accumulation is also observed in XP-A and XP-C cells expressing exogenous p48. These results suggest that DDB can rapidly translocate to the damaged DNA sites independent of functional XPA and XPC proteins and directly enhance the excision reaction by core repair factors.
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PMID:DDB accumulates at DNA damage sites immediately after UV irradiation and directly stimulates nucleotide excision repair. 1170 87

The xeroderma pigmentosum group D (XPD) protein is a subunit of transcription factor TFIIH with DNA helicase activity. TFIIH has two functions, in basal transcription and nucleotide excision repair. Mutations in XPD that affect DNA repair but not transcription result in the skin cancer-prone disorder, xeroderma pigmentosum (XP). If transcription is also affected, the result is the multi-system disorder trichothiodystrophy (TTD), in which there is no skin cancer predisposition, or in rare cases, XP combined with Cockayne syndrome. Up till now there have been no reports of combined clinical features of XP and TTD. We have now identified two patients with some features of both these disorders. One of these, XP189MA, a 3-year-old girl with sun sensitivity, mental and physical developmental delay, has XPD mutations not previously reported, and barely detectable levels of nucleotide excision repair. The other, XP38BR, a 28-year-old woman with sun sensitivity, pigmentation changes and skin cancers typical of XP, has a mutation that has been identified previously, but only in TTD patients with no features of XP. The level of repair of UV damage in XP38BR is substantially higher than that in other patients with the same mutation. With both patients, polarized light microscopy revealed a 'tiger-tail' appearance of the hair, and amino acid analysis of the hair shafts show levels of sulfur-containing proteins intermediate between those of normal and TTD individuals. Our findings highlight the complexities of genotype-phenotype relationships in the XPD gene.
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PMID:Two individuals with features of both xeroderma pigmentosum and trichothiodystrophy highlight the complexity of the clinical outcomes of mutations in the XPD gene. 1170 41

The transcription factor TFIIH is involved in both basal transcription and DNA repair. Mutations in the XPD helicase component of TFIIH can result in the diverse clinical features associated with xeroderma pigmentosum (XP) and trichothiodystrophy (TTD). It is generally believed that the multi-system abnormalities associated with TTD are the result of a subtle deficiency in basal transcription. However, to date, there has been no clear demonstration of a defect in expression of any specific gene in individuals with these syndromes. Here we show that the specific mutations in XPD that cause TTD result in reduced expression of the beta-globin genes in these individuals. Eleven TTD patients with characterized mutations in the XPD gene have the haematological features of beta-thalassaemia trait, and reduced levels of beta-globin synthesis and beta-globin mRNA. All these parameters were normal in three patients with XP. These findings provide the first evidence for reduced expression of a specific gene in TTD. They support the hypothesis that many of the clinical features of TTD result from inadequate expression of a diverse set of highly expressed genes.
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PMID:Mutations in the general transcription factor TFIIH result in beta-thalassaemia in individuals with trichothiodystrophy. 1173 44

Inherited mutations in the XPD subunit of the general transcription/repair factor TFIIH yield the rare genetic disorder Xeroderma pigmentosum (XP), the phenotypes of which cannot be explained solely on the basis of a DNA repair defect. In cells derived from XP-D patients, we observed a reduction of the ligand-dependent transactivation mediated by several nuclear receptors (RARalpha, ERalpha, and AR). We demonstrate that the XPD mutation alters cdk7 function in RARalpha phosphorylation. Transactivation is restored upon overexpression of either the wild-type XPD or the RARalphaS77E (a mutation which mimics phosphorylated RARalpha). Thus, we demonstrate that the cdk7 kinase of TFIIH phosphorylates the nuclear receptor, then allowing ligand-dependent control of the activation of the hormone-responsive genes.
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PMID:XPD mutations prevent TFIIH-dependent transactivation by nuclear receptors and phosphorylation of RARalpha. 1195 52

Mutations in XPB and XPD TFIIH helicases have been related with three hereditary human disorders: xeroderma pigmentosum, Cockayne syndrome, and trichothiodystrophy. The dual role of TFIIH in DNA repair and transcription makes it difficult to discern which of the mutant TFIIH phenotypes is due to defects in any of these different processes. We used haywire (hay), the Drosophila XPB homolog, to dissect this problem. Our results show that when hay dosage is affected, the fly shows defects in structures that require high levels of transcription. We found a genetic interaction between hay and cdk7, and we propose that some of these phenotypes are due to transcriptional deficiencies. We also found more apoptotic cells in imaginal discs and in the CNS of hay mutant flies than in wild-type flies. Because this abnormal level of apoptosis was not detected in cdk7 flies, this phenotype could be related to defects in DNA repair. In addition the apoptosis induced by p53 Drosophila homolog (Dmp53) is suppressed in heterozygous hay flies.
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PMID:DNA repair and transcriptional effects of mutations in TFIIH in Drosophila development. 1222 Nov 29

Trichothiodystrophy (TTD) is a rare hereditary multisystem disorder associated with defects in nucleotide excision repair (NER) as a consequence of mutations in XPD, XPB or TTDA, three genes that are all related to TFIIH, the multiprotein complex involved in NER and transcription. Here we show that all the mutations found in TTD cases, irrespective of whether they are homozygotes, hemizygotes or compound heterozygotes, cause a substantial and specific reduction (by up to 70%) in the cellular concentration of TFIIH. Intriguingly, the degree of reduction in the level of TFIIH does not correlate with the severity of the pathological phenotype, suggesting that the severity of the clinical features in TTD cannot be related solely to the effects of mutations on the stability of TFIIH. We have also measured TFIIH levels in cells in which different mutations in the XPD gene are associated with clinical symptoms not of TTD but of the highly cancer-prone disorder xeroderma pigmentosum (XP). We have found mild reductions (up to 40%) in TFIIH content in some but not all of these cell strains. We conclude that the severity of the clinical features in TTD patients and the clinical outcome of differentially mutated XPD proteins is likely to depend both on the effects that each mutation has on the stability of TFIIH and on the transcriptional activity of the residual TFIIH complexes.
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PMID:Reduced level of the repair/transcription factor TFIIH in trichothiodystrophy. 1239 3

TFIIH is a multiprotein complex that has a central role in the RNA pol II mediated transcription, in DNA repair and in the control of the cell cycle. Mutations in some components of TFIIH are associated with three hereditary human syndromes: xeroderma pigmentosum (XP), Cockayne syndrome (CS) and trichothiodystrophy (TTD). The p62 protein is a structural component of the TFIIH core and no syndromes have been identified up to date by mutations in this human gene. In this work we report the molecular and genetic characterization of the Drosophila melanogaster p62 gene (Dmp62). The Dmp62 gene product shows high identity with its human and mouse homologues. Using computer analysis we identified several common motifs in the p62 proteins from different organisms, suggesting that these motifs could be involved in possible protein-protein interactions within the TFIIH complex or with other transcription and DNA repair factors. The Dmp62 transcript is expressed at similar levels throughout development, although there is a significant increase of the transcript level during the late embryogenesis and in the adult male. The analysis of a Drosophila line with a P-element enhancer trap insertion at the Dmp62 5'-UTR that directs the lac-Z expression from the Dmp62 promoter, showed a high level of expression in the gut, the testis and the pericardial cells. A P-element that disrupts the Dmp62 gene (Dmp62mut) produces early embryo lethality in homozygous flies. Heterozygous Dmp62mut larvae are more sensitive to UV light irradiation, and those individuals that are able to develop into adults have severe abdominal cuticular damage after UV light irradiation.
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PMID:Molecular characterization and developmental expression of the TFIIH factor p62 gene from Drosophila melanogaster: effects on the UV light sensitivity of a p62 mutant fly. 1250 40

Mutations in the XPD gene result in xeroderma pigmentosum (XP) and trichothiodystrophy (TTD), the phenotypes of which are often intricate. To understand the genotype/phenotype relationship, we engineered recombinant TFIIHs in which XPD subunits carry amino acid changes found in XPD patients. We demonstrate that all the XPD mutations are detrimental for XPD helicase activity, thus explaining the NER defect. We also show that TFIIH from TTD patients, but not from XP patients, exhibits a significant in vitro basal transcription defect in addition to a reduced intracellular concentration. Moreover, when XPD mutations prevent interaction with the p44 subunit of TFIIH, transactivation directed by certain nuclear receptors is inhibited, regardless of TTD versus XP phenotype, thus explaining the overlapping symptoms. The implications of these mutations are discussed using a structural model of the XPD protein. Our study provides explanations for the nature and the severity of the various clinical features.
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PMID:Basal transcription defect discriminates between xeroderma pigmentosum and trichothiodystrophy in XPD patients. 1282 Sep 75


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