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

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Query: EC:2.7.7.7 (DNA polymerase)
17,007 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Mutations are a hallmark of cancer. Normal cells minimize spontaneous mutations through the combined actions of polymerase base selectivity, 3' --> 5' exonucleolytic proofreading, mismatch correction, and DNA damage repair. To determine the consequences of defective proofreading in mammals, we created mice with a point mutation (D400A) in the proofreading domain of DNA polymerase delta (poldelta, encoded by the Pold1 gene). We show that this mutation inactivates the 3' --> 5' exonuclease of poldelta and causes a mutator and cancer phenotype in a recessive manner. By 18 months of age, 94% of homozygous Pold1(D400A/D400A) mice developed cancer and died (median survival = 10 months). In contrast, only 3-4% of Pold1(+/D400A) and Pold1(+/+) mice developed cancer in this time frame. Of the 66 tumors arising in 49 Pold1(D400A/D400A) mice, 40 were epithelial in origin (carcinomas), 24 were mesenchymal (lymphomas and sarcomas), and two were composite (teratomas); one-third of these animals developed tumors in more than one tissue. Skin squamous cell carcinoma was the most common tumor type, occurring in 60% of all Pold1(D400A/D400A) mice and in 90% of those surviving beyond 8 months of age. These data show that poldelta proofreading suppresses spontaneous tumor development and strongly suggest that unrepaired DNA polymerase errors contribute to carcinogenesis. Mice deficient in poldelta proofreading provide a tractable model to study mechanisms of epithelial tumorigenesis initiated by a mutator phenotype.
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PMID:High incidence of epithelial cancers in mice deficient for DNA polymerase delta proofreading. 1242 60

Two isoforms of the CCAAT-displacement protein/cut homeobox (CDP/Cux) transcription factor have been characterized thus far. The full length protein, p200, which contains four DNA binding domains, transiently binds to DNA and carries the CCAAT-displacement activity. The p110 isoform is generated by proteolytic processing at the G1-S transition and is capable of stable interaction with DNA. Here we demonstrate the existence of a shorter CDP/Cux isoform, p75, which contains only two DNA binding domains, Cut repeat 3 and the Cut homeodomain, and binds more stably to DNA. CDP/Cux p75 was able to repress a reporter carrying the promoter for the cyclin-dependent kinase inhibitor p21 gene and to activate a DNA polymerase alpha gene reporter. Expression of CDP/Cux p75 involved a novel mechanism: transcription initiation within intron 20. The intron 20-initiated mRNA (I20-mRNA) was expressed at higher level in the thymus and in CD4+/CD8+ and CD4+ T cells. I20-mRNA was expressed only weakly or not at all in normal human mammary epithelial cells and normal breast tissues but was detected in many breast tumor cells lines and breast tumors. In invasive tumors a significant association was established between higher I20-mRNA expression and a diffuse infiltrative growth pattern (n = 41, P = 0.0137). In agreement with these findings, T47D breast cancer cells stably expressing p75 could not form tubule structures in collagen but rather developed as solid undifferentiated aggregates of cells. Taken together, these results suggest that aberrant expression of the CDP/Cux p75 isoform in mammary epithelial cells may be associated with the process of tumorigenesis in breast cancer.
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PMID:Characterization of a tissue-specific CDP/Cux isoform, p75, activated in breast tumor cells. 1243 59

The Pulmonary adenoma resistance 2 (Par2) locus of the BALB/cByJ mouse, located within 0.5 cM of chromosome 18, is responsible for reducing the mean multiplicity of urethane-induced lung tumors relative to those in C57BL/6J, A/J and C3H/HeJ mice. Thus, BALB/B6-Par2 congenic strain genetically identical to BALB/cByJ except carrying C57BL/6J Par2 alleles develops seven times more tumors than BALB/cByJ. To gain clues for identification of Par2 candidate genes, we analysed lung tumorigenesis in BALB/cByJ<-->BALB.B6-Par2 chimeric animals. Of 100 tumors induced by urethane in 16 chimeras, 82 originated from BALB.B6-Par2 cells, indicating the Par2 phenotype to be cell-autonomous. In addition, the BALB.B6-Par2- and BALB/cByJ-derived tumors were similar in mean size, implying that the phenotype is primarily expressed during initiation rather than in the promotion stage of carcinogenesis. Given these results, we surveyed a comprehensive mouse genome database and physically mapped Par2 within a 2.3 Mbp segment containing three known genes, Poli, Mbd2 and Dcc. Among those, the Poli seemed to be the most reasonable Par2 candidate, since it encodes an extremely error-prone DNA polymerase preferentially incorporating G or T opposite template T in vitro, reminiscent of the Kras2 activation because of an A to G or T point mutation within codon 61 with which most urethane-induced lung tumors are initiated. Indeed, our sequencing of Poli cDNAs from BALB/cByJ, C57BL/6J, A/J and C3H/HeJ lungs revealed 21 BALB/cByJ-specific single-nucleotide polymorphisms in the coding region accompanied by seven amino-acid substitutions and an elevated frequency of alternative splicing, while no polymorphisms associated with tumor susceptibility were found for either Mbd2 or Dcc. Notably, we obtained evidence that BALB/cByJ Par2 alleles may selectively decrease the frequency of Kras2-mutated tumors compared with C57BL/6J alleles. Consequently, the Poli is an intriguing Par2 candidate clearly deserving further evaluation.
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PMID:Analysis of lung tumorigenesis in chimeric mice indicates the Pulmonary adenoma resistance 2 (Par2) locus to operate in the tumor-initiation stage in a cell-autonomous manner: detection of polymorphisms in the Poli gene as a candidate for Par2. 1270 Jun 72

Telomeres are primarily controlled by a highly specialized DNA polymerase, termed telomerase. In early studies, high levels of telomerase activity were detected in cancer cells, but no activity was found in most normal somatic cells, leading to the speculation that telomerase might be required for tumor growth. Recent studies have demonstrated that introduction of the telomerase catalytic component (TERT) into telomerase- negative cells activates telomerase and extends cell lifespan, whereas mice lacking telomerase activity revealed impaired cell proliferation in some organs as well as reduced tumorigenesis. These findings suggest that telomerase plays an important role in long-term cell viability and cell proliferation. We have recently demonstrated a crucial role of telomerase activation in the regulation of vascular smooth muscle cell (VSMC) proliferation and clarified the mechanisms by which telomerase is activated in the process of VSMC growth. Moreover, increasing evidence suggests that telomerase activity contributes to the vascular pathophysiology. Thus, further understanding of the role of telomerase and telomere function would provide new insights into the treatment of human vascular disorders.
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PMID:The role of telomerase activation in the regulation of vascular smooth muscle cell proliferation. 1294 50

In this study, we performed systematic candidate gene analyses of the Pulmonary adenoma resistance 2 locus. Differential gene expression in lung tissues and nucleotide polymorphisms in coding regions between A/J and BALB/cJ mice were examined using reverse transcription-PCR and direct sequencing. Although not all genes in the interval were analyzed at this moment due to the recent database updating, we have found that the Pol iota gene, encoding the DNA polymerase iota, contains 25 nucleotide polymorphisms in its coding region between A/J and BALB/cJ mice, resulting in a total of ten amino acid changes. Primer extension assays with purified BALB/cJ and A/J proteins in vitro demonstrate that both forms of Pol iota are active but that they may differ in substrate discrimination, which may affect the formation of Kras2 mutations in mouse lung tumors. Altered expression of POL iota protein and an amino acid-changing nucleotide polymorphism were observed in human lung cancer cells, suggesting a possible role in the development of lung cancer. Thus, our data support the Pol iota gene as a modifier of lung tumorigenesis by altering DNA polymerase activity.
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PMID:Pol iota is a candidate for the mouse pulmonary adenoma resistance 2 locus, a major modifier of chemically induced lung neoplasia. 1502 25

DNA polymerase (Pol) is an error-prone repair DNA polymerase that has been shown to create genetic instability and tumorigenesis when overexpressed by only 2-fold in cells, suggesting that a rigorous regulation of its expression may be essential in vivo. To address this question, we have generated mice which express a transgene (Tg) bearing the Pol cDNA under the control of the ubiquitous promoter of the mouse H-2K gene from the major histocompatibility complex. These mice express the Tg only in thymus, an organ which normally contains the most abundant endogenous Pol mRNA and protein, supporting the idea of a tight regulation of Pol in vivo. Furthermore, we found no tumor incidence, suggesting that the single Pol overexpression event is not sufficient to initiate tumorigenesis in vivo.
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PMID:Evidence of finely tuned expression of DNA polymerase beta in vivo using transgenic mice. 1514 85

DNA polymerase beta (Polbeta) is a DNA repair protein that functions in base excision repair and meiosis. The enzyme has deoxyribose phosphate lyase and polymerase activity, but it is error prone because it bears no proofreading activity. Errors in DNA repair can lead to the accumulation of mutations and consequently to tumorigenesis. Polbeta expression has been found to be higher in tumors, and deregulation of its expression has been found to induce chromosomal instability, a hallmark of tumorigenesis, but the underlying mechanisms are unclear. In the present study, we have investigated whether ectopic expression of Polbeta influences the stability of chromosomes in a murine mammary cell line. The results demonstrate a telomere dysfunction phenotype: an increased rate of telomere loss and chromosome fusion, suggesting that ectopic expression of Polbeta leads to telomere dysfunction. In addition, Polbeta interacts with TRF2, a telomeric DNA binding protein. Colocalization of the two proteins occurs at nontelomeric sites and appears to be influenced by the change in the status of the telomeric complex.
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PMID:DNA polymerase beta interacts with TRF2 and induces telomere dysfunction in a murine mammary cell line. 1517 90

Overexpression of DNA polymerase beta (polbeta), an error-prone DNA repair enzyme, has been shown to result in mutagenesis, aneuploidy and tumorigenesis. To further investigate the molecular basis leading to cancer-associated genetic changes, we examined whether the DNA polbeta could affect homologous recombination (HR). Using mammalian cells carrying an intrachromosomal recombination marker we showed that the DNA polbeta overexpression increased the HR mostly by enhancing gene conversion. Concomitantly, we observed the generation of DNA strand breaks as well as a DNA polbeta-dependent formation of Rad51 foci. The stimulation of HR was abolished by the coexpression of a dominant negative form of Rad51, suggesting that the Rad51 was involved in the increased HR events. The expression of different DNA polbeta mutants lacking polymerase activity did not result in HR stimulation, indicating that the DNA synthesis activity of DNA polbeta was related to this phenotype. These results provide new insights into the molecular mechanisms of the genetic instability observed in DNA polbeta overexpressing tumour cells.
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PMID:DNA polymerase beta overexpression stimulates the Rad51-dependent homologous recombination in mammalian cells. 1545 77

Herein we report Xiphophorus DNA polymerase beta (XiphPolbeta) mRNA and protein expression levels in brain, liver, gill, and testes tissues from Xiphophorus maculatus, Xiphophorus helleri, and Xiphophorus couchianus parental line fish and two different tumor-bearing Xiphophorus interspecies hybrids. Polymerase beta protein levels in the Xiphophorus tissues were measured by Western blot, and mRNA was measured with a quantitative real time RT-PCR method which employed cRNA construction to produce accurate calibration curves. We found significant differences in both mRNA and protein levels between the tumor-bearing hybrid animals and the three parental species. However, there were no significant differences in either mRNA levels or protein expression observed between the parental species. Thus, interspecies hybridization results in dysregulation of Polbeta expression and this may manifest a modulation in DNA repair capability and susceptibility to latent tumorigenesis.
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PMID:DNA polymerase beta mRNA and protein expression in Xiphophorus fish. 1553 90

Specialized DNA polymerases are required to bypass DNA damage lesions that would otherwise cause replication arrest and cell death. When operating on non-canonical templates, such as undamaged DNA or on non-cognate lesions, these polymerases exhibit considerably reduced fidelity, resulting in the generation of mutations. Ectopic overexpression of these polymerases can also lead to an increased mutation rate and an enhanced capability of DNA repair, suggesting that they could potentially act as oncogenes if they were overexpressed in cancers. Here, we examine expression patterns of DNA polymerases in matched normal and tumor samples from a diverse range of tissues. As well as investigating the specialized polymerases beta, lambda, iota and kappa, we also investigate the expression of the replicative polymerases alpha, delta and epsilon. The data presented provide evidence for the overexpression of specialized polymerases in tumors, with more than 45% of the 68 tumor samples studied demonstrating greater than two-fold enhanced expression of at least one specialized polymerase. Of particular note, DNA polymerase beta (pol beta) was found to be overexpressed at both the mRNA and protein level in approximately one third of all tumor types studied, with overexpression being particularly frequent in uterus, ovary, prostate and stomach samples. Pols lambda, and iota were also found to be overexpressed to a significant extent in a range of tumor types, albeit less frequently than pol beta. In contrast, pol kappa was rarely found to be overexpressed in tumors but was found to be commonly underexpressed in many samples. Downregulation of pol beta expression by siRNA resulted in an increased sensitivity to the chemotherapeutic agent cisplatin, suggesting a role for this polymerase in providing tolerance to cisplatin-induced damage. These observations suggest that specialised DNA polymerases, and particularly pol beta, could be considered both as caretaker genes altered during tumorigenesis, and as potential drug targets to sensitise tumors to chemotherapy.
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PMID:The overexpression of specialized DNA polymerases in cancer. 1581 30


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