Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

---

Query: UMLS:C0043346 (xeroderma pigmentosum)
2,924 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

We have devised a method to evaluate the capacity of mammalian cell extracts to incise damaged DNA in vitro. The assay uses damaged-plasmid DNA as a substrate for nucleotide excision repair by cell extracts. During this process, enzymatic incision of the damaged DNA is followed by DNA resynthesis. Under our assay conditions, the DNA synthesis stage of excision repair is prevented by limiting dNTP concentration and including the specific DNA polymerase inhibitor aphidicolin. Incisions are quantitatively detected by [alpha-32P]dAMP incorporation catalysed by the Klenow fragment of E. coli DNA pol I at nicked sites in plasmids purified from incision reactions. Lesion-specific incision is an ATP-dependent process; it was observed in plasmids modified with three different DNA damaging agents and damage-dependent incisions were abolished with extracts from xeroderma pigmentosum excision-repair deficient cell lines, indicating that this in vitro incision assay is dealing with true nucleotide excision repair.
...
PMID:Measurement of damage-specific DNA incision by nucleotide excision repair in vitro. 804 50

The Saccharomyces cerevisiae RAD30 gene encodes a novel eukaryotic DNA polymerase, pol eta that is able to replicate across cis-syn cyclobutane pyrimidine dimers both accurately and efficiently. Very recently, a human homolog of RAD30 was identified, mutations in which result in the sunlight-sensitive, cancer-prone, Xeroderma pigmentosum variant group phenotype. We report here the cloning and localization of a second human homolog of RAD30. Interestingly, RAD30B is localized on chromosome 18q21.1 in a region that is often implicated in the etiology of many human cancers. The mouse homolog (Rad30b) is located on chromosome 18E2. The human RAD30B and mouse Rad30b mRNA transcripts, like many repair proteins, are highly expressed in the testis. In situ hybridization analysis indicates that expression of mouse Rad30b occurs predominantly in postmeiotic round spermatids. Database searches revealed genomic and EST sequences from other eukaryotes such as Aspergillus nidulans, Schizosaccharomyces pombe, Brugia malayi, Caenorhabditis elegans, Trypanosoma cruzi, Arabidopsis thaliana, and Drosophila melanogaster that also encode putative homologs of RAD30, thereby suggesting that Rad30-dependent translesion DNA synthesis is conserved within the eukaryotic kingdom.
...
PMID:Novel human and mouse homologs of Saccharomyces cerevisiae DNA polymerase eta. 1045 7

The human disease xeroderma pigmentosum (XP) involves DNA repair and replication deficiencies that predispose homozygous individuals to a 1000-fold increase in nonmelanoma and melanoma skin cancers. Two major forms of XP are known with different biochemical defects: one form lacks nucleotide excision repair (NER); the other lacks the capacity to replicate damaged DNA. Since the clinical symptoms of both kinds of patients are almost the same, the different cellular defects must be reconciled with common clinical outcomes. An additional question among the NER defective patients is how to reconcile widely different skin and central nervous system symptoms with mutations in the same biochemical pathway. XP involves seven genes of the NER system (XPA through G). The XPA gene codes for a protein that is central to NER and binds to a variety of UV light and chemical damage to DNA. It also acts as a nucleation center for other repair proteins to attach and carry out excision and replacement synthesis. Mutations in XPA that are within the DNA binding site produce more severe CNS disorders, than mutations in the C-terminal region of the protein that interacts with the TFIIH complex. In contrast, mutations in two members of the TFIIH complex, the XPB and XPD genes are generally very severe with both skin and CNS disorders. Missense mutations within the helicase regions of these genes are associated with DNA repair deficiencies and XPD; mutations elsewhere in these genes are correlated with symptoms of XP and Cockayne syndrome and trichothiodystrophy. This raises the question whether the CNS disorders of XPA, XPB, and XPD patients are similar, or whether a careful clinical evaluation might reveal different mechanisms of development. The XP variant lacks the capacity to replicate damaged DNA due to mutations in hRad30, a damage-specific polymerase eta. The phenotype of XP variant cells becomes unstable and the cells become much more UV-sensitive when they are transformed by methods that inactivate p53. On a p53 negative background, the induction of recombination between sister chromatids occurs much more extensively than in normal cells, and we have evidence that DNA double strand breaks which trigger an apoptotic pathway involving caspase-3 are involved. The pathway for UV carcinogenesis may be the same for all XP patients if the ultimate cause of genomic instability is an increase in replication of damaged DNA by the error-prone polymerase zeta. The presence of unrepaired damage in the NER defective groups of XP would present more substrate for the error-prone system leading to increased mutation rates. The absence of pol eta would require cells to use the error-prone pol zeta pathway, also increasing mutation rates from UV damage. A common pathway for increased mutagenesis therefore underlies both forms of XP.
...
PMID:Common pathways for ultraviolet skin carcinogenesis in the repair and replication defective groups of xeroderma pigmentosum. 1069 59

When chromosomal replication is impeded in the presence of DNA damage, members of a newly discovered UmuC/DinB/Rev1/Rad30 superfamily of procaryotic and eucaryotic DNA polymerases catalyze translesion synthesis at blocked replication forks. Although these polymerases share sequence elements essentially unrelated to the standard replication and repair enzymes, some of them (such as the SOS-induced Escherichia coli pol V) catalyze 'error-prone' translesion synthesis leading to large increases in mutation, whereas others (an example being the Xeroderma pigmentosum variant gene product XPV pol eta) carry out aberrant, yet nonmutagenic translesion synthesis. Ongoing studies of these low fidelity polymerases could provide new insights into the mechanism of somatic hypermutation, a key element in the immune response.
...
PMID:Sloppier copier DNA polymerases involved in genome repair. 1075 75

Cockayne syndrome (CS) is a human hereditary disorder characterized by UV sensitivity, developmental abnormalities and premature aging. CS cells display a selective deficiency in transcription-coupled repair (TCR), a subpathway of nucleotide excision repair (NER) that preferentially removes lesions from transcribed strands. Following UV irradiation, the recovery of RNA synthesis is abnormally delayed in CS cells in conjunction with TCR deficiency. To date, TCR has been detected in cultured cells, but not in cell-free systems. In this study, we constructed an assay system using isolated nuclei. RNA synthesis catalyzed by RNA polymerases (pol I and II) was measured in nuclei prepared from UV-irradiated cells. In nuclei isolated from HeLa and xeroderma pigmentosum (XP) group C cells, RNA synthesis was relatively resistant to UV irradiation. In contrast, RNA synthesis by pol I and, in particular, pol II in CS-B nuclei was significantly inhibited upon UV irradiation. Our data support the utility of this assay system for the in vitro detection of the recovery of RNA synthesis in cultured cells.
...
PMID:Detection of reduced RNA synthesis in UV-irradiated Cockayne syndrome group B cells using an isolated nuclear system. 1237 75

Acrolein, which is widely spread in the environment and is produced by lipid peroxidation in cells, reacts with DNA to form two exocyclic 1,N2-propanodeoxyguanosine (PdG) adducts. To establish their relative contribution to the acrolein mutagenicity, the genotoxic properties of alpha-OH-PdG and gamma-OH-PdG together with their model DNA adduct, PdG, were studied in human cells. DNA adducts were incorporated site-specifically into a SV40/BK virus origin-based shuttle vector and replicated in xeroderma pigmentosum complementation group A (XPA) cells. Analysis of progeny plasmid revealed that alpha-OH-PdG and PdG strongly block DNA synthesis and that both adducts induced base substitutions with G --> T transversions predominating. Primer extension studies, catalyzed by the 3'-->5' exonuclease-deficient Klenow fragment of Escherichia coli pol I, revealed limited extension from the 3' primer termini opposite these two adducts. In contrast, gamma-OH-PdG did not strongly block DNA synthesis or miscode in XPA cells. Primer extension from a dC terminus opposite gamma-OH-PdG was much more efficient than that opposite alpha-OH-PdG or PdG. These results indicate that the minor alpha-OH-PdG adduct is more genotoxic than the major gamma-OH-PdG. Furthermore, experiments using a HeLa whole cell extract indicate that all three DNA adducts are not efficiently removed from DNA by base excision repair.
...
PMID:Mutagenesis by acrolein-derived propanodeoxyguanosine adducts in human cells. 1242 46

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.
...
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

Xeroderma pigmentosum variant (XPV) cells lack the damage-specific polymerase eta and undergo a protracted arrest at the S phase checkpoint(s) following UV damage. The S phase checkpoints encompass several qualitatively different processes, and stimulate downstream events that are dependent on the functional state of p53. Primary fibroblasts with wild-type p53 arrest in S, and require a functional polymerase eta (pol eta) to carry out bypass replication, but do not recruit recombination factors for recovery. XPV cells with non-functional p53, as a result of transformation by SV40 or HPV16 (E6/E7), recruit the hMre11/hRad50/Nbs1 complex to arrested replication forks, coincident with PCNA, whereas normal transformed cells preferentially use the pol eta bypass replication pathway. The formation of hMre11 foci implies that arrested replication forks rapidly undergo a collapse involving double strand breakage and rejoining. Apoptosis occurs after UV only in cells transformed by SV40, and not in normal or XPV fibroblasts or HPV16 (E6/E7) transformed cells. Conversely, ultimate cell survival in XPV cells was much less in HPV16 (E6/E7) transformed cells than in SV40 transformed cells, indicating that apoptosis was not a reliable predictor of cell survival. Inhibition of p53 transactivation by pifithrin-alpha or inhibition of protein synthesis by cycloheximide did not induce hMre11 foci or apoptosis in UV damaged fibroblasts. Inhibition of kinase activity with wortmannin did not increase killing by UV, unlike the large increase seen with caffeine. Since HPV16 (E6/E7) transformed XPV cells were highly UV sensitive and not further sensitized by caffeine, it appears likely that caffeine sensitization proceeds through a p53 pathway. The S phase checkpoints are therefore, a complex set of different checkpoints that are coordinated by p53 with the capacity to differentially modulate cell survival, apoptosis, bypass replication and hMre11 recombination.
...
PMID:Polymerase eta and p53 jointly regulate cell survival, apoptosis and Mre11 recombination during S phase checkpoint arrest after UV irradiation. 1250 96

Ultraviolet light damages DNA by catalysing covalent bond formation between adjacent pyrimidines, generating cis-syn cyclobutane pyrimidine dimers (CPDs) as the most common lesion. CPDs block DNA replication by high-fidelity DNA polymerases, but they can be efficiently bypassed by the Y-family DNA polymerase pol eta. Mutations in POLH encoding pol eta are implicated in nearly 20% of xeroderma pigmentosum, a human disease characterized by extreme sensitivity to sunlight and predisposition to skin cancer. Here we have determined two crystal structures of Dpo4, an archaeal pol eta homologue, complexed with CPD-containing DNA, where the 3' and 5' thymine of the CPD separately serves as a templating base. The 3' thymine of the CPD forms a Watson-Crick base pair with the incoming dideoxyATP, but the 5' thymine forms a Hoogsteen base pair with the dideoxyATP in syn conformation. Dpo4 retains a similar tertiary structure, but each unusual DNA structure is individually fitted into the active site for catalysis. A model of the pol eta-CPD complex built from the crystal structures of Saccharomyces cerevisiae apo-pol eta and the Dpo4-CPD complex suggests unique features that allow pol eta to efficiently bypass CPDs.
...
PMID:Replication of a cis-syn thymine dimer at atomic resolution. 1290 19

Mutations in the XPD subunit of the transcription/repair factor TFIIH cause the Xeroderma pigmentosum disorder. We show that in some XP-D deficient cells, transactivation by the vitamin D receptor (VDR) is selectively inhibited for a subset of responsive genes, such as CYP24, and that the XPD/R683W mutation prevents VDR recruitment on its promoter. Contrary to other nuclear receptors, VDR, which lacks a functional A/B domain, is not phosphorylated and consequently not regulated by the cdk7 kinase of TFIIH. In fact, we demonstrate that the VDR transactivation defect resides in Ets1, another activator that cannot be phosphorylated by TFIIH in XP-D cells. Indeed, the phosphorylated Ets1 seems to promote the binding of VDR to its responsive element and trigger the subsequent recruitment of coactivators and RNA pol II. We propose a model in which TFIIH regulates the activity of nuclear receptors by phosphorylating either their A/B domain or an additional regulatory DNA binding partner.
...
PMID:Selective regulation of vitamin D receptor-responsive genes by TFIIH. 1549 6


1 2 3 Next >>

---