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

The mechanisms by which DNA interstrand cross-links (ICLs) are repaired in mammalian cells are unclear. Studies in bacteria and yeasts indicate that both nucleotide excision repair (NER) and recombination are required for their removal and that double-strand breaks are produced as repair intermediates in yeast cells. The role of NER and recombination in the repair of ICLs induced by nitrogen mustard (HN2) was investigated using Chinese hamster ovary mutant cell lines. XPF and ERCC1 mutants (defective in genes required for NER and some types of recombination) and XRCC2 and XRCC3 mutants (defective in RAD51-related homologous recombination genes) were highly sensitive to HN2. Cell lines defective in other genes involved in NER (XPB, XPD, and XPG), together with a mutant defective in nonhomologous end joining (XRCC5), showed only mild sensitivity. In agreement with their extreme sensitivity, the XPF and ERCC1 mutants were defective in the incision or "unhooking" step of ICL repair. In contrast, the other mutants defective in NER activities, the XRCC2 and XRCC3 mutants, and the XRCC5 mutant all showed normal unhooking kinetics. Using pulsed-field gel electrophoresis, DNA double-strand breaks (DSBs) were found to be induced following nitrogen mustard treatment. DSB induction and repair were normal in all the NER mutants, including XPF and ERCC1. The XRCC2, XRCC3, and XRCC5 mutants also showed normal induction kinetics. The XRCC2 and XRCC3 homologous recombination mutants were, however, severely impaired in the repair of DSBs. These results define a role for XPF and ERCC1 in the excision of ICLs, but not in the recombinational components of cross-link repair. In addition, homologous recombination but not nonhomologous end joining appears to play an important role in the repair of DSBs resulting from nitrogen mustard treatment.
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PMID:Defining the roles of nucleotide excision repair and recombination in the repair of DNA interstrand cross-links in mammalian cells. 1102 68

Fanconi anemia (FA) is a cancer-predisposition syndrome characterized by hypersensitivity to interstrand-cross-link (ICL) inducers. FA hypersensitivity to ICL has been correlated with alterations in homologous recombination, non-homologous end-joining, telomere maintenance, DNA-damage assessment and checkpoint regulation, processes in which the components of the RAD50/MRE11/NBS1 (RMN) complex are involved. To better characterize the mechanisms by which ICL are processed in human cells and to gain insight into their toxicity in FA, we examined (i). the RMN complex assembling in response to the ICL inducers mitomycin C (MMC) and photoactivated 8-methoxypsoralen and (ii). the proficiency of FA cells to perform RMN activation in response to ICL inducers. We show here that ICL activates the assembly of the RMN proteins into subnuclear foci, and that their formation proceeds independently of ICL incision, a step mainly dependent on XP-F/ERCC1 heterodimer activity. Interestingly, FA cells were unable to form RMN foci in response to either ICL inducer. Analysis by pulsed-field gel electrophoresis and single-cell gel electrophoresis of MMC-treated cells showed that FA cells from complementation group C (FA-C cells, defective in the FANCC gene) form double-strand breaks and unhook MMC-induced ICL similarly to FANCC wild-type cells. These observations imply that the absence of RMN assembly in FA-C cells is not simply due to the absence of DNA ends produced as intermediates of ICL processing, and indicates a direct role for FANCC in RMN focus assembly in response to ICL inducers. Moreover, we show that the formation of foci, including BRCA1 and/or RAD51 proteins, is significantly delayed in FA cells. These alterations in the assembly of DNA-repair proteins in FA provide an interpretation for the DNA-damage processing anomalies observed in FA cells and for the genetic instability and the cancer predisposition of the syndrome.
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PMID:DNA cross-link-dependent RAD50/MRE11/NBS1 subnuclear assembly requires the Fanconi anemia C protein. 1235 79

In C. elegans, DOG-1 prevents deletions that initiate in polyG/polyC tracts (G/C tracts), most likely by unwinding secondary structures that can form in G/C tracts during lagging-strand DNA synthesis. We have used the dog-1 mutant to assay the in vivo contribution of various repair genes to the maintenance of G/C tracts. Here we show that DOG-1 and the BLM ortholog, HIM-6, act synergistically during replication; simultaneous loss of function of both genes results in replicative stress and an increase in the formation of small deletions that initiate in G/C tracts. Similarly, we demonstrate that the C. elegans orthologs of the homologous recombination repair genes BARD1, RAD51, and XPF and the trans-lesion synthesis polymerases poleta and polkappa contribute to the prevention of deletions in dog-1 mutants. Finally, we provide evidence that the small deletions generated in the dog-1 background are not formed through homologous recombination, nucleotide excision repair, or nonhomologous end-joining mechanisms, but appear to result from a mutagenic repair mechanism acting at G/C tracts. Our data support the hypothesis that absence of DOG-1 leads to replication fork stalling that can be repaired by deletion-free or deletion-prone mechanisms.
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PMID:Homologous recombination is required for genome stability in the absence of DOG-1 in Caenorhabditis elegans. 1654 95

Nucleotide excision repair is the principal mechanism for the removal of bulky DNA adducts caused by a range of chemotherapeutic drugs, and contributes to cisplatin resistance. In this study, we used synthetic siRNAs targeted to XPA and ERCC1 and compared their effectiveness in sensitising mismatch repair deficient prostate cancer cell lines to cisplatin and mitomycin C. Downregulation of ERCC1 sensitised DU145 and PC3 cells to cisplatin and mitomycin C. In contrast, XPA downregulation did not sensitise either cell line to mitomycin C, and only sensitised DU145 cells to cisplatin. The effects of ERCC1 downregulation may be due to its role in homologous recombination repair. Excision repair of cisplatin adducts in PC3 cells was attenuated to a similar extent by XPA and ERCC1 downregulation. Downregulation of XPA but not ERCC1 caused an increase in the number of cisplatin-induced RAD51 foci in PC3 cells, suggesting that HRR is able to substitute for NER in these cells. We observed co-localisation of ERCC1 and RAD51 in cisplatin treated PC3 cells by immunofluorescence and co-immunoprecipitation, which may represent recruitment of ERCC1/XPF to sites of recombination repair. These results indicate that ERCC1 is a broader therapeutic target than XPA with which to sensitise cancer cells to chemotherapy because of its additional role in recombination repair.
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PMID:XPA versus ERCC1 as chemosensitising agents to cisplatin and mitomycin C in prostate cancer cells: role of ERCC1 in homologous recombination repair. 1675 62

Analysis of the combined effects of polymorphisms in genes encoding xenobiotic metabolizing enzymes (XMEs) and DNA repair proteins may be a key to understanding the role of these genes in the susceptibility of individuals to mutagens. In the present study, we performed an in vitro experiment on lymphocytes from 118 healthy donors that measured the frequency of diepoxybutane (DEB) induced sister chromatid exchanges (SCEs) in relation to genetic polymorphisms in genes coding for XMEs (CYP1A1, CYP2E1, GSTT1, EPHX, and NAT2), as well as DNA repair proteins (XRCC1, XRCC2, XRCC3, XPD, XPA, XPC, XPG, XPF, ERCC1, BRCA1, NBS1, and RAD51). We found that GSTT1(-) and CYP2E1 c1/c2 polymorphisms were associated with higher DEB-induced SCE frequencies, and that NAT2 G(590)A was associated with lower SCE induction by DEB. Analysis of the effect of pairs of genes showed that for a fixed GSTT1 genotype, the SCE level increased with an increasing number of Tyr alleles in EPHX codon 113. We found that among GSTT1(+) individuals the DEB-induced SCE level was significantly lower when the EPHX 139 codon was His/Arg rather than His/His. An interaction between polymorphisms in CYP2E1 and at EPHX codon 113 was also observed. The results of our study confirm observations in cancer patients and in people exposed to xenobiotics indicating that sensitivity to mutagens depends upon a combined effect of a variety of "minor impact" genes. Moreover, our results indicate that polymorphisms in genes coding for XMEs have a greater influence on the genotoxic activity of DEB, measured by DEB-induced SCE frequency, than polymorphisms in genes encoding DNA repair proteins.
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PMID:Influence of polymorphisms in xenobiotic-metabolizing genes and DNA-repair genes on diepoxybutane-induced SCE frequency. 1707 1

Chromosomal aberrations (CAs) are important genetic alterations in the development and progression of the majority of human cancers. The frequency with which such alterations occur depends to a large extent on polymorphisms of DNA-repair genes and in genes coding for xenobiotic metabolizing enzymes, which are involved in the processes of activation and inactivation of xenobiotics. The frequency of bleomycin (BLM)-induced CAs is an indirect measure of the effectiveness of DNA repair mechanisms, and a predictor of environment-related risk of cancer. Our study was conducted on the human peripheral blood lymphocytes of 82 healthy volunteers. The aim of the study was to elucidate whether the frequency of BLM-induced CAs is correlated with polymorphisms of selected genes involved in different mechanisms of DNA repair such as: XRCC1 [base excision repair]; XPA, XPC, XPG, XPD, XPF, ERCC1 [nucleotide excision repair], NBS1, RAD51, XRCC2, XRCC3, RAD51, and BRCA1 [homologous recombination], as well as in genes encoding xenobiotic metabolizing enzymes, such as CYP1A, CYP2E1, NAT2, GSTT1, and EPHX (mEH). Our study indicated that, of the polymorphisms studied, only XPC (exon 15 and intron 11) is associated with BLM-induced CAs, suggesting a role of the NER pathway in the repair of BLM-induced chromosomal aberrations.
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PMID:Polymorphism in nucleotide excision repair gene XPC correlates with bleomycin-induced chromosomal aberrations. 1768 59

Both the ERCC1-XPF complex and the proteins involved in homoIogous recombination (HR) have critical roles in inter-strand cross-link (ICL) repair. Here, we report that mitomycin C-induced lesions inhibit replication fork elongation. Furthermore, mitomycin C-induced DNA double-strand breaks (DSBs) are the result of the collapse of ICL-stalled replication forks. These are not formed through replication run off, as we show that mitomycin C or cisplatin-induced DNA lesions are not incised by global genome nucleotide excision repair (GGR). We also suggest that ICL-lesion repair is initiated either by replication or transcription, as the GGR does not incise ICL-lesions. Furthermore, we report that RAD51 foci are induced by cisplatin or mitomycin C independently of ERCC1, but that mitomycin C-induced HR measured in a reporter construct is impaired in ERCC1-defective cells. These data suggest that ERCC1-XPF plays a role in completion of HR in ICL repair. We also find no additional sensitivity to cisplatin by siRNA co-depletion of XRCC3 and ERCC1, showing that the two proteins act on the same pathway to promote survival.
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PMID:The ERCC1/XPF endonuclease is required for completion of homologous recombination at DNA replication forks stalled by inter-strand cross-links. 1971 38

Replication inhibitors cause replication fork stalling and double-strand breaks (DSB) that result from processing of stalled forks. During recovery from replication blocks, the homologous recombination (HR) factor RAD51 mediates fork restart and DSB repair. HR defects therefore sensitize cells to replication inhibitors, with clear implications for cancer therapy. Gemcitabine is a potent replication inhibitor used to treat cancers with mutations in HR genes such as BRCA2. Here, we investigate why, paradoxically, mutations in HR genes protect cells from killing by gemcitabine. Using DNA replication and DNA damage assays in mammalian cells, we show that even short gemcitabine treatments cause persistent replication inhibition. BRCA2 and RAD51 are recruited to chromatin early after removal of the drug, actively inhibit replication fork progression, and promote the formation of MUS81- and XPF-dependent DSBs that remain unrepaired. Our data suggest that HR intermediates formed at gemcitabine-stalled forks are converted into DSBs and thus contribute to gemcitabine-induced cell death, which could have implications for the treatment response of HR-deficient tumors.
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PMID:BRCA2 and RAD51 promote double-strand break formation and cell death in response to gemcitabine. 2505 26

A xenobank of patient-derived (PDX) ovarian tumor samples has been established consisting of tumors with different sensitivity to cisplatin (DDP), from very responsive to resistant. As the DNA repair pathway is an important driver in tumor response to DDP, we analyzed the mRNA expression of 20 genes involved in the nucleotide excision repair, fanconi anemia, homologous recombination, base excision repair, mismatch repair and translesion repair pathways and the methylation patterns of some of these genes. We also investigated the correlation with the response to platinum-based therapy. The mRNA levels of the selected genes were evaluated by Real Time-PCR (RT-PCR) with ad hoc validated primers and gene promoter methylation by pyrosequencing. All the DNA repair genes were variably expressed in all 42 PDX samples analyzed, with no particular histotype-specific pattern of expression. In high-grade serous/endometrioid PDXs, the CDK12 mRNA expression levels positively correlated with the expression of TP53BP1, PALB2, XPF and POLB. High-grade serous/endometrioid PDXs with TP53 mutations had significantly higher levels of POLQ, FANCD2, RAD51 and POLB than high-grade TP53 wild type PDXs. The mRNA levels of CDK12, PALB2 and XPF inversely associated with the in vivo DDP antitumor activity; higher CDK12 mRNA levels were associated with a higher recurrence rate in ovarian patients with low residual tumor. These data support the important role of CDK12 in the response to a platinum based therapy in ovarian patients.
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PMID:Platinum sensitivity and DNA repair in a recently established panel of patient-derived ovarian carcinoma xenografts. 2987 99