Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: UMLS:C0268140 (XPF)
 549 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Fusion between HeLa and fibroblasts from complementation group D xeroderma pigmentosum (XPD) followed by challenge with small doses of ultraviolet light (u.v.) results in the production of hybrid cells expressing either HeLa (HD1) or XPD-like (HD2) sensitivity to u.v. and related repair capacity. Assays used included unscheduled DNA synthesis (UDS), DNA break accumulation in the presence of inhibitors of DNA repair synthesis and host cell reactivation of irradiated adenovirus. Complementation assay in heterokaryons reveals limited ability of HD2 to restore UDS in XPD nuclei. We believe this complementation is more apparent than real since proliferating hybrids of HD2 and XPD parentage are without exception u.v.-sensitive and express limited excision repair. On the other hand hybrids between HD2 and XPC, XPE or XPF fibroblasts show true complementation resulting in a return to normal u.v. sensitivity and elevated repair ability.
 ...
PMID:Xeroderma pigmentosum D-HeLa hybrids with low and high ultraviolet sensitivity associated with normal and diminished DNA repair ability, respectively. 406 82

Nucleotide excision repair is the principal way by which human cells remove UV damage from DNA. Human cell extracts were fractionated to locate active components, including xeroderma pigmentosum (XP) and ERCC factors. The incision reaction was then reconstituted with the purified proteins RPA, XPA, TFIIH (containing XPB and XPD), XPC, UV-DDB, XPG, partially purified ERCC1/XPF complex, and a factor designated IF7. UV-DDB (related to XPE protein) stimulated repair but was not essential. ERCC1- and XPF-correcting activity copurified with an ERCC1-binding polypeptide of 110 kDa that was absent in XP-F cell extract. Complete repair synthesis was achieved by combining these factors with DNA polymerase epsilon, RFC, PCNA, and DNA ligase I. The reconstituted core reaction requires about 30 polypeptides.
 ...
PMID:Mammalian DNA nucleotide excision repair reconstituted with purified protein components. 769 16

Human cells from patients suffering with xeroderma pigmentosum (XP) characterized by extreme sensitivity to UV light and a high incidence of skin tumors fall into seven complementation groups, XPA to XPG, and are lacking a functional helicase, endonuclease, or lesion-recognizing protein involved in the initial steps during nucleotide excision repair (NER); a number of proteins involved in DNA repair are termed XPA to XPG depending on which one is defective in a particular complementation group of XP and include: (i) proteins involved in the recognition of (6-4) photoproducts (XPE) and of a broad range of lesions such as pyrimidine dimers (XPA); (ii) proteins that are DNA helicases and integral parts of the general transcription factor TFIIH functioning in both transcription and repair (XPB, XPD); (iii) endonucleases that perform the two incisions, the XPG incising six nucleotides (nt) to the 3' side from a photodimer and the ERCC1-XPF protein complex incising 22 nt to the 5' side of the lesion; and (iv) single-strand DNA-binding proteins (XPC). The ERCC6 helicase is largely responsible for coupling transcription to repair whereas XPC seems to be responsible for the repair of the inactive parts of the genome as well as for the repair of the nontranscribed strand in active genes. p53 recognizes insertion/deletion mismatches as well as free ends of DNA produced by ionizing radiation to arrest the cell cycle. Most of the human DNA repair proteins have their counterparts in both budding and fission yeasts and some of them also in E. coli evoking an evolutionary conservation of DNA repair pathways. Accumulation of mutations within repair genes in single cells followed by their escape from the immune surveillance and in clonal expansion may greatly contribute to the appearance and development of human cancers.
 ...
PMID:Xeroderma pigmentosum and molecular cloning of DNA repair genes. 868 16

The repair-deficient mutant rodent cell lines UV20 and UV41, which are defective in the ERCC1/ERCC4[XPF]-mediated 5'-endonuclease activity, are unusually sensitive to gamma-irradiation under hypoxic (but not oxic) conditions. Because this 5'-endonuclease appears to be involved in two distinct (but overlapping) DNA-repair pathways-the nucleotide excision repair pathway and the recombination-dependent pathway for the removal of DNA interstrand cross-links-it is unclear which of these defective activities is responsible for the hypoxic radiosensitivity of UV20 and UV41 cells. Accordingly, we have extended these measurements to the UV5 and UV24 lines which carry mutations in the ERCC2[XPD] and ERCC3[XPB] genes, respectively; both of these genes encode DNA helicases. These two mutants display a sensitivity to ultraviolet light that is similar to that of UV20 and UV41 cells, reflecting their defect in the incision step of the nucleotide excision repair pathway. However, neither UV5 nor UV24 cells are especially cross-sensitive to agents that produce DNA interstrand cross-links, suggesting that the ERCC2 and ERCC3 activities are not crucial for the repair of these lesions. We show that neither UV5 nor UV24 cells exhibit the unusual hypoxic radiosensitivity that characterizes UV20 and UV41 cells. Based on these data and on a comparison of the patterns of cross-sensitivity of these various mutants to other DNA-damaging agents, we conclude that the increased hypoxic radiosensitivity observed in the UV20 and UV41 mutants is due to a defect in the ERCC1/ERCC4-dependent pathway for the repair of DNA cross-links and not in the nucleotide excision repair pathway. The evidence suggests that this sensitivity may be mediated by some type of radiation-induced cross-links, possibly DNA-protein cross-links.
 ...
PMID:The importance of the ERCC1/ERCC4[XPF] complex for hypoxic-cell radioresistance does not appear to derive from its participation in the nucleotide excision repair pathway. 896 Jan 33

During nucleotide excision repair in human cells, a damaged DNA strand is cleaved by two endonucleases, XPG on the 3' side of the lesion and ERCC1-XPF on the 5' side. These structure-specific enzymes act at junctions between duplex and single-stranded DNA. ATP-dependent formation of an open DNA structure of approximately 25 nt around the adduct precedes this dual incision. We investigated the mechanism of open complex formation and find that mutations in XPB or XPD, the DNA helicase subunits of the transcription and repair factor TFIIH, can completely prevent opening and dual incision in cell-free extracts. A deficiency in XPC protein also prevents opening. The absence of RPA, XPA or XPG activities leads to an intermediate level of strand separation. In contrast, XPF or ERCC1-defective extracts open normally and generate a 3' incision, but fail to form the 5' incision. This same repair defect was observed in extracts from human xeroderma pigmentosum cells with an alteration in the C-terminal domain of XPB, suggesting that XPB has an additional role in facilitating 5' incision by ERCC1-XPF nuclease. These data support a mechanism in which TFIIH-associated helicase activity and XPC protein catalyze initial formation of the key open intermediate, with full extension to the cleavage sites promoted by the other core nucleotide excision repair factors. Opening is followed by dual incision, with the 3' cleavage made first.
 ...
PMID:Mechanism of open complex and dual incision formation by human nucleotide excision repair factors. 935 36

The removal or repair of DNA damage has a key role in protecting the genome of the cell from the insults of cancer-causing agents. This was originally demonstrated in individuals with the rare genetic disease xeroderma pigmentosum, the paradigm of cancer genes, and subsequently in the relationship between mismatch repair and colon cancer. Recent reports suggest that individuals with less dramatic reductions in the capacity to repair DNA damage are observed at polymorphic frequency in the population; these individuals have an increased susceptibility to breast, lung, and skin cancer. We report initial results from a study to estimate the extent of DNA sequence variation among individuals in genes encoding proteins of the DNA repair pathways. Nine different amino acid substitution variants have been identified in resequencing of the exons of three nucleotide excision repair genes (ERCC1, XPD, and XPF), a gene involved in double-strand break repair/recombination genes (XRCC3), and a gene functioning in base excision repair and the repair of radiation-induced damage (XRCCI). The frequencies for the nine different variant alleles range from 0.04 to 0.45 in a group of 12 healthy individuals; the average allele frequency is 0.17. The potential that this variation, and especially the six nonconservative amino acid substitutions occurring at residues that are identical in human and mouse, may cause reductions in DNA repair capacity or the fidelity of DNA repair is intriguing; the role of the variants as cancer risk factors or susceptibility alleles remains to be addressed.
 ...
PMID:Nonconservative amino acid substitution variants exist at polymorphic frequency in DNA repair genes in healthy humans. 948 7

DNA repair has been proposed to be an important determinant of cancer cell sensitivity to alkylating agents and cisplatin (DDP). Nucleotide excision repair (NER), which represents one of the most important cellular DNA repair processes able to remove a broad spectrum of DNA lesions, is involved in the recognition and repair of the crosslinks caused by DDP and melphalan (L-PAM). In this study, the mRNA levels of the different genes involved in NER (ERCC1, XPA, XPB, XPC, XPD, XPF) were examined in a panel of eight different human cancer cell lines, together with the overall DNA repair capacity using a host cell reactivation assay of a damaged plasmid. A statistically significant correlation was observed between the relative expression of XPA/XPC (P < 0.05) and ERCC1/XPC (P < 0.05) mRNAs. No correlation was found between the DDP and L-PAM IC50S and the relative mRNA expression of the tested NER genes. When the overall cellular DNA repair capacity was studied, carcinomas seemed to have a higher repair activity than leukaemias; but this repair DNA activity correlated neither with the mRNA expression of the different NER genes nor with DDP and L-PAM IC50S. These data seem to suggest that even if the NER pathway is an important determinant for the cytotoxicity of alkylating agents, as demonstrated by the extremely high sensitivity to alkylating agents in cells lacking this repair system, other factors have to play a role in regulating the cellular sensitivity/resistance to these antitumour drugs.
 ...
PMID:Expression of genes involved in nucleotide excision repair and sensitivity to cisplatin and melphalan in human cancer cell lines. 989 69

For the bulk of mammalian DNA, the core protein factors needed for damage recognition and incision during nucleotide excision repair (NER) are the XPA protein, the heterotrimeric RPA protein, the 6 to 9-subunit TFIIH, the XPC-hHR23B complex, the XPG nuclease, and the ERCC1-XPF nuclease. With varying efficiencies, NER can repair a very wide range of DNA adducts, from bulky helical distortions to subtle modifications on sugar residues. Several of the NER factors have an affinity for damaged DNA. The strongest binding factor appears to be XPC-hHR23B but preferential binding to damage is also a property of XPA, RPA, and components of TFIIH. It appears that in order to be repaired by NER, an adduct in DNA must have two features: it must create a helical distortion, and there must be a change in DNA chemistry. Initial recognition of the distortion is the most likely function for XPC-hHR23B and perhaps XPA and RPA, whereas TFIIH is well-suited to locate the damaged DNA strand by locating altered DNA chemistry that blocks translocation of the XPB and XPD components.
 ...
PMID:DNA damage recognition during nucleotide excision repair in mammalian cells. 1021 8

During human nucleotide excision repair, damage is recognized, two incisions are made flanking a DNA lesion, and residues are replaced by repair synthesis. A set of proteins required for repair of most lesions is RPA, XPA, TFIIH, XPC-hHR23B, XPG, and ERCC1-XPF, but additional components have not been excluded. The most complex and difficult to analyze factor is TFIIH, which has a 6-subunit core (XPB, XPD, p44, p34, p52, p62) and a 3-subunit kinase (CAK). TFIIH has roles both in basal transcription initiation and in DNA repair, and several inherited human disorders are associated with mutations in TFIIH subunits. To identify the forms of TFIIH that can function in repair, recombinant XPA, RPA, XPC-hHR23B, XPG, and ERCC1-XPF were combined with TFIIH fractions purified from HeLa cells. Repair activity coeluted with the peak of TFIIH and with transcription activity. TFIIH from cells with XPB or XPD mutations was defective in supporting repair, whereas TFIIH from spinal muscular atrophy cells with a deletion of one p44 gene was active. Recombinant TFIIH also functioned in repair, both a 6- and a 9-subunit form containing CAK. The CAK kinase inhibitor H-8 improved repair efficiency, indicating that CAK can negatively regulate NER by phosphorylation. The 15 recombinant polypeptides define the minimal set of proteins required for dual incision of DNA containing a cisplatin adduct. Complete repair was achieved by including highly purified human DNA polymerase delta or epsilon, PCNA, RFC, and DNA ligase I in reaction mixtures, reconstituting adduct repair for the first time with recombinant incision factors and human replication proteins.
 ...
PMID:Nucleotide excision repair of DNA with recombinant human proteins: definition of the minimal set of factors, active forms of TFIIH, and modulation by CAK. 1067 6

We have previously observed that the mRNA of selected genes involved in nucleotide excision repair appear to be coordinately expressed in human tissues from patients with ovarian cancer, testicular cancer, malignant brain tumors, and other malignancies. Such genes include ERCC1, XPA, XPB, XPD, XPF, and XPG. Coordinate mRNA expression appears to be most impressive in non-malignant tissues. We therefore began to explore possible reasons why such coordinate expression should occur. DNA sequences for the above noted genes were obtained from GeneBank. Two different software programs were applied to the DNA sequence, to the area 5' to the start of exon I of each gene. Analyses were performed by computer. The length of the 5' area assessed, was based on previous reports that determined what portion of the genomic sequence comprised the 5' UTR of the promoter of the respective gene. Based on this approach, potential DNA binding sites for no less than three dozen proteins, were identified in the 5'-flanking region of each of the NER genes studied. For each gene, potential binding sites for activator proteins and for repressor proteins were identified. The 5'-flanking regions for each gene noted above, had binding sites in common for 14 proteins with transcription modulatory activity. Eleven of these proteins are known for activator activity; two are reported to have repressor activity, and one has both repressor and activator function. These data suggest a possible molecular basis for the previously observed coordinate mRNA expression of selected NER genes in human tissue specimens.
 ...
PMID:Computer based analyses of the 5'-flanking regions of selected genes involved in the nucleotide excision repair complex. 1089 49


1 2 3 4 5 6 7 8 Next >>