Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: UMLS:C0596263 (carcinogenesis)
 64,820 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

We have studied reversion in DNA repair deficient EM9 cells, by selection for ethylmethanesulfonate (EMS) resistance. EM9 is a mutant CHO cell line that is hypersensitive to killing by EMS and X-rays and deficient in DNA single-strand break (SSB) repair. EM9 cells were transfected with DNA from a cosmid library, and transfectants resistant to EMS were isolated. Four revertant lines were obtained, which varied in their sensitivity to killing by EMS, ionizing radiation and other genotoxic agents. When the cell lines were analyzed for resistance to killing by chlorodeoxyuridine (CldUrd) or N-methyl-N'-nitro-N-nitrosoguanidine (MNNG), a different relative ranking among the cell lines was observed. The recently cloned human XRCC1 gene is capable of correcting the deficiencies of the EM9 cell line. Using the human XRCC1 cDNA (pXR1-30) as a probe, we determined that the resistant-transfectant cell lines contained only the endogenous hamster XRCC1 gene, implying that a hamster XRCC1 gene was altered during the transfection/selection procedure and was responsible for the EMS resistance. In these cells the levels of XRCC1 mRNA corresponded roughly to the degrees of resistance of the reverted cell lines to killing by EMS or X-rays. The degree of increased resistance to killing by EMS or X-rays also roughly correlated with increased SSB repair. These results suggest that increased cellular levels of the endogenous XRCC1 gene mRNA may largely, though not completely, explain the phenotypes of revertant, EMS-resistant EM9 cell lines.
Carcinogenesis 1991 May
PMID:Characterization of revertants of the CHO EM9 mutant arising during DNA transfection. 202 44

Hybrids formed between HeLa cells and fibroblasts from xeroderma pigmentosum group D show either HeLa sensitivity or XPD-like hypersensitivity to u.v. radiation and corresponding high or low excision repair capability. Hybrids with low repair are presumed to have lost, via chromosome segregation, the HeLa wild type D alleles. In this paper we analyse the u.v. sensitivity and excision repair capability of another hybrid, HD1A, derived spontaneously from the normally sensitive hybrid HD1. While HD1A closely resembles the XPD phenotype in terms of u.v. sensitivity and excision repair it differs from XPD because of its ability to reactivate u.v.-irradiated adenovirus 2 to an extent similar to that of its HeLa parent. This capacity functionally dissociates excision repair of chromatin-based damage from damage in a viral environment. Moreover, on the basis of complementation studies the excision repair of genomic damage by HD1A is subtly different from that of a true XPD-like hybrid, HD2. The data are discussed in terms of a second change in the defective D allele of the HD1A cell.
Carcinogenesis 1986 Oct
PMID:Analysis of DNA repair in XP-HeLa hybrids; lack of correlation between excision repair of u.v. damage and adenovirus reactivation in an XP(D)-like cell line. 375 74

Nucleotide-excision repair (NER) is an important cellular defence mechanism against mutagenesis and carcinogenesis. The essential yeast genes RAD3 (ref. 2) and SSL2 (RAD25), homologues of the human xeroderma pigmentosum genes XPD and XPB respectively, have been implicated in NER in yeast. The products of these genes are also subunits of (Rad3 protein) or associate with (Ssl2 protein) purified yeast RNA polymerase II transcription initiation factor b, the counterpart of human TFIIH. Rad3 and Ssl2 proteins may participate directly in NER. Alternatively, they may function exclusively as transcription factors that support NER by influencing the expression of other NER genes. Here we show that defective NER in rad3 mutant extracts can be specifically complemented by purified transcription factor b. Similarly, defective NER in ssl2 mutant extracts is corrected by purified factor b/Ssl2 complex. These results support a direct role of factor b during NER in yeast. Hence, factor b (TFIIH) has a dual role in transcription and NER.
 ...
PMID:Transcription factor b (TFIIH) is required during nucleotide-excision repair in yeast. 810 88

The p53 tumor suppressor gene product is a transcriptional transactivator and a potent apoptotic inducer. The fact that many of the DNA tumor virus oncoproteins bind to p53 and affect these p53 functions indicates that this interaction is an important step in oncogenic transformation. We and others have recently demonstrated that the hepatitis B virus oncoprotein, HBx, can form a complex with p53 and inhibit its DNA consensus sequence binding and transcriptional transactivator activity. Using a microinjection technique, we report here that HBx efficiently blocks p53-mediated apoptosis and describe the results of studies exploring two possible mechanisms of HBx action. First, inhibition of apoptosis may be a consequence of the failure of p53, in the presence of HBx, to upregulate genes, such as p21WAF1, Bax, or Fas, that are involved in the apoptotic pathway. Data consistent with this hypothesis include HBx reduction of p53-mediated p21WAF1 expression. Alternatively, HBx could affect p53 binding to the TFIIH transcription-nucleotide excision repair complex as HBx binds to the COOH terminus of p53 and inhibits its binding to XPB or XPD. Binding of p53 to these constituents of the core TFIIH is a process that may be involved in apoptosis. Because the HBx gene is frequently integrated into the genome of hepatocellular carcinoma cells, inhibition of p53-mediated apoptosis by HBx may provide a clonal selective advantage for hepatocytes expressing this integrated viral gene during the early stages of human liver carcinogenesis.
 ...
PMID:Abrogation of p53-induced apoptosis by the hepatitis B virus X gene. 852 83

It has recently been reported that the XPD (ERCC2) gene is an integral component of the basal transcription factor TFIIH. We have studied the direct role of this repair gene on the fine structure of DNA repair in hamster cells. The gene and strand specific DNA repair of UV induced pyrimidine dimers was determined in wild-type hamster cells, in hamster cells harboring a mutation in the gene homologous to the XPD gene and in mutant cells transfected with the human XPD gene. In the mutant cells, strand specific repair was severely deficient. In the transfected cells, preferential and strand specific gene repair were restored to wild-type levels. The results of the current study clearly demonstrate a direct role for the XPD gene product both in the preferential repair and bulk repair of pyrimidine dimers as well as its high functional conservation between rodent and human cells. An in vitro transcription assay was employed to investigate whether RNA polymerase II mediated transcription was also affected by the transfection with the XPD gene. No change in transcription between the mutant and transfected cells was observed. This suggests that the role of XPD in repair can be distinguished from its role in TFIIH dependent transcription initiation. Different functional domains of XPD appear to be necessary for repair versus transcription.
Carcinogenesis 1997 Apr
PMID:Restoration of preferential and strand specific gene repair in group 2 Chinese hamster ovary mutants (UV5) by the XPD (ERCC2) gene. 911 Dec

DNA repair enzymes play a pivotal role in the maintenance of chromosome integrity and in the elimination of premutagenic lesions from DNA by patrolling the genome; nuclear import mechanisms are implicated in molecular carcinogenesis. We have attempted to predict cell trafficking and the nuclear importation of proteins involved in DNA repair by sequence analysis aimed at identifying karyophilic clusters (arginines, lysines, histidines) flanked by the helix breakers proline or glycine that could function as nuclear localization signals (NLSs). Most mammalian proteins that participate in DNA repair pathways seem to possess NLS peptides. Repair proteins with multiple nuclear signals are the ERCC6 helicase (eight signals), the XPC protein involved in the repair of the transcribed strand in active genes (eight strong and seven weak signals), and the Rep-3/Duc-1 mismatch repair protein (five strong one weak signal). We propose that it is unlikely to identify mutations on the genes encoding these proteins resulting in cytoplalsmic retention. However, a number of mammalian DNA repair proteins lack NLS clusters; these proteins include ERCC1, ERCC2 (XPD), mouse RAD51, and the HHR23B/p58 and HHR23A subunits of XPC. NLS-less S. cerevisiae proteins include both RAD51 and RAD52 that function in the recombination and in the repair of double-strand breaks as well as the RAD23 and HRR25 molecules. We propose that these proteins depend on their complexation with other proteins in the cytoplasm for their nuclear localization. The hMSH2 human mismatch repair protein linked to the hereditary nonpolyposis colon cancer gene, has a weak nuclear signal containing two histidines.
 ...
PMID:Nuclear import of DNA repair proteins. 913 18

Among the major responses of human cells to DNA damage is accumulation of the p53 tumor suppressor protein, which plays a crucial role as a cell-cycle checkpoint. We have already shown that this response is different in cells from the UV-hypersensitive human syndromes xeroderma pigmentosum (XP) and trichothiodystrophy (TTD), which overlap with each other and arise from mutations in genes involved in nucleotide excision repair. In this paper we report that correction of the repair defect by retroviral-mediated transduction of the wild-type XPD gene in XP-D and TTD/XP-D untransformed primary fibroblasts leads to a normal p53 response in these cells. Thus, the complemented cells, like normal human fibroblasts, require higher UV doses (10 J/m2) for p53 induction than the parental repair-deficient XP-D or TTD/XP-D cells (both mapping at the XPD locus), which accumulate p53 protein at very low UV doses (2.5 and 5 J/m2). The p53 protein levels return to normal 24 h after irradiation when UV-induced lesions have been efficiently repaired by the restored NER activity. These data confirm our earlier results that p53 accumulation following UV treatment is directly related to the presence of unrepaired cyclobutane dimers on the transcribed strand of active genes.
Carcinogenesis 1998 Sep
PMID:Recovery of the normal p53 response after UV treatment in DNA repair-deficient fibroblasts by retroviral-mediated correction with the XPD gene. 977 45

Human hepatitis B virus (HBV) is a major risk factor of human hepatocellular carcinoma. Both in vivo and in vitro studies have shown that HBV X protein (HBx) can bind to the p53 tumor-suppressor protein and interfere with the role that p53 plays in the cellular response to DNA damage. Our previous work has shown that HBx protein inhibits p53 sequence-specific transcriptional activation, p53-mediated apoptosis and p53 binding to the TFIIH transcription-nucleotide excision repair (NER) factors, including XPB and XPD. To investigate whether HBx interferes with the NER pathway, we utilized cell-proliferation and colony-formation assays to determine if cells expressing HBx are more sensitive to UVC-induced DNA damage. NER was also measured by a plasmid host cell re-activation assay using a vector containing a luciferase reporter gene. UV-irradiated plasmids were transfected into a human RKO colon carcinoma cell line that contains wild-type (wt) p53 as well as its derivatives, either mutant p53-143ala (RKO-143ala) or human papillomavirus E6 (RKO-E6, a wt p53 protein that is rapidly degraded and non-functional). We found that cells expressing HBx are more sensitive to UVC-induced killing. Moreover, expression of HBx resulted in a reduction of NER efficiency in RKO cells to 52 +/- 2% (compared with control), RKO-143a1a cells to 46 +/- 3% and RKO-E6 cells to 60 +/- 3%. Similar results were also obtained with a HepG2 hepatoblastoma cell line carrying wt p53. In addition, we found that HBx bound directly to either XPB or XPD DNA helicase in vitro. Thus, our data indicate that HBx may interfere with the NER pathway through both p53-dependent and p53-independent mechanisms. Because HBx binds to TFIIH-associated proteins, we propose that HBx may interfere with the NER pathway also through binding to and altering the activities of helicases necessary for NER and, thereby, increase the mutation rate induced by chemical carcinogens, such as aflatoxin B1, during human liver carcinogenesis.
 ...
PMID:Hepatitis B virus X protein inhibits nucleotide excision repair. 1007 21

Patients with the nucleotide excision repair (NER) disorder xeroderma pigmentosum (XP) are highly predisposed to develop sunlight-induced skin cancer, in remarkable contrast to photosensitive NER-deficient trichothiodystrophy (TTD) patients carrying mutations in the same XPD gene. XPD encodes a helicase subunit of the dually functional DNA repair/basal transcription complex TFIIH. The pleiotropic disease phenotype is hypothesized to be, in part, derived from a repair defect causing UV sensitivity and, in part, from a subtle, viable basal transcription deficiency accounting for the cutaneous, developmental, and the typical brittle hair features of TTD. To understand the relationship between deficient NER and tumor susceptibility, we used a mouse model for TTD that mimics an XPD point mutation of a TTD patient in the mouse germline. Like the fibroblasts from the patient, mouse cells exhibit a partial NER defect, evident from the reduced UV-induced DNA repair synthesis (residual repair capacity approximately 25%), limited recovery of RNA synthesis after UV exposure, and a relatively mild hypersensitivity to cell killing by UV or 7,12-dimethylbenz[a]anthracene. In accordance with the cellular studies, TTD mice exhibit a modestly increased sensitivity to UV-induced inflammation and hyperplasia of the skin. In striking contrast to the human syndrome, TTD mice manifest a dear susceptibility to UV- and 7,12-dimethylbenz[a]anthracene-induced skin carcinogenesis, albeit not as pronounced as the totally NER-deficient XPA mice. These findings open up the possibility that TTD is associated with a so far unnoticed cancer predisposition and support the notion that a NER deficiency enhances cancer susceptibility. These findings have important implications for the etiology of the human disorder and for the impact of NER on carcinogenesis.
 ...
PMID:Mouse model for the DNA repair/basal transcription disorder trichothiodystrophy reveals cancer predisposition. 1041 15

Mouse mutants as model for human ageing disorders. Defective transcription and premature ageing. DNA damage has been implicated in carcinogenesis and ageing. Our group examines the nucleotide excision DNA repair (NER) process, which can detect and repair various UV- and chemically-induced DNA damages, in addition to some types of oxidative DNA damage. Recently, two mouse models were generated with a defect in one of the NER genes (XPD and CSB), displaying distinctive symptoms of premature ageing. Remarkably, in both cases the NER gene plays an additional role in transcription. Research using these mouse models aims to investigate the link between premature ageing and molecular defects in NER and transcription.
 ...
PMID:[Mutant mice as a model of human diseases of aging. Defective transcription and premature aging]. 1048 22


1 2 3 4 5 6 7 8 Next >>