Gene Summary

Gene:POLB; DNA polymerase beta
Summary:The protein encoded by this gene is a DNA polymerase involved in base excision and repair, also called gap-filling DNA synthesis. The encoded protein, acting as a monomer, is normally found in the cytoplasm, but it translocates to the nucleus upon DNA damage. Several transcript variants of this gene exist, but the full-length nature of only one has been described to date. [provided by RefSeq, Sep 2011]
Databases:OMIM, HGNC, Ensembl, GeneCard, Gene
Protein:DNA polymerase beta
Source:NCBIAccessed: 31 August, 2019


What does this gene/protein do?
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Pathways:What pathways are this gene/protein implicaed in?
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Cancer Overview

Research Indicators

Publications Per Year (1994-2019)
Graph generated 31 August 2019 using data from PubMed using criteria.

Literature Analysis

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Tag cloud generated 31 August, 2019 using data from PubMed, MeSH and CancerIndex

Latest Publications: POLB (cancer-related)

Putri JF, Widodo N, Sakamoto K, et al.
Induction of senescence in cancer cells by 5'-Aza-2'-deoxycytidine: Bioinformatics and experimental insights to its targets.
Comput Biol Chem. 2017; 70:49-55 [PubMed] Related Publications
5'-Aza-2'-deoxycytidine (5-Aza-dC) is a demethylating drug that causes genome-wide hypomethylation resulting in the expression of several tumor suppressor genes causing growth arrest of cancer cells. Cancer is well established as a multifactorial disease and requires multi-module therapeutics. Search for new drugs and their approval by FDA takes a long time. Keeping this in view, research on new functions of FDA-approved anticancer drugs is desired to expand the list of multi-module functioning drugs for cancer therapy. In this study, we conducted an analysis for new functions of 5-Aza-dC by applying bio-chemo-informatics approach. The potential of 5-Aza-dC bioactivity was analyzed by PASS online and Molinspiration. Target proteins were predicted by SuperPred. The protein networks and biological processes were analyzed by Biological Networks using Gene Ontology tool, BINGO, based on BIOGRID database. Interactions between 5-Aza-dC and targeted proteins were examined by Autodoc Vina integrated into pyrx software. Induction of p53 by 5-Aza-dC was tested in vitro using cancer cells. Bioinformatics analyses predicted that 5-Aza-dC functions as a p53 inducer, radiosensitizer, and inhibitor of some enzymes. It was predicted to target proteins including MDM2, POLA1, POLB, and CXCR4 that are involved in the induction of DNA damage response and p53-HDM2-p21 signaling. In this study, we provide experimental evidence showing HDM2 is one of the targets of 5-AZA-dC leading to activation of p53 pathway and growth arrest of cells. Furthermore, we found that the combinatorial treatment of 5-AZA-dC with three other drugs caused drug resistance. We discuss that 5-Aza-dC-induced senescence is a multi-module drug that controls cell proliferation phenotype not only by proteins but also by noncoding miRNAs. Further studies are warranted to dissect these mechanisms and establish 5-Aza-dC as an effective multi-module anticancer reagent.

Ramakodi MP, Devarajan K, Blackman E, et al.
Integrative genomic analysis identifies ancestry-related expression quantitative trait loci on DNA polymerase β and supports the association of genetic ancestry with survival disparities in head and neck squamous cell carcinoma.
Cancer. 2017; 123(5):849-860 [PubMed] Free Access to Full Article Related Publications
BACKGROUND: African Americans with head and neck squamous cell carcinoma (HNSCC) have a lower survival rate than whites. This study investigated the functional importance of ancestry-informative single-nucleotide polymorphisms (SNPs) in HNSCC and also examined the effect of functionally important genetic elements on racial disparities in HNSCC survival.
METHODS: Ancestry-informative SNPs, RNA sequencing, methylation, and copy number variation data for 316 oral cavity and laryngeal cancer patients were analyzed across 178 DNA repair genes. The results of expression quantitative trait locus (eQTL) analyses were also replicated with a Gene Expression Omnibus (GEO) data set. The effects of eQTLs on overall survival (OS) and disease-free survival (DFS) were evaluated.
RESULTS: Five ancestry-related SNPs were identified as cis-eQTLs in the DNA polymerase β (POLB) gene (false discovery rate [FDR] < 0.01). The homozygous/heterozygous genotypes containing the African allele showed higher POLB expression than the homozygous white allele genotype (P < .001). A replication study using a GEO data set validated all 5 eQTLs and also showed a statistically significant difference in POLB expression based on genetic ancestry (P = .002). An association was observed between these eQTLs and OS (P < .037; FDR < 0.0363) as well as DFS (P = .018 to .0629; FDR < 0.079) for oral cavity and laryngeal cancer patients treated with platinum-based chemotherapy and/or radiotherapy. Genotypes containing the African allele were associated with poor OS/DFS in comparison with homozygous genotypes harboring the white allele.
CONCLUSIONS: Analyses show that ancestry-related alleles could act as eQTLs in HNSCC and support the association of ancestry-related genetic factors with survival disparities in patients diagnosed with oral cavity and laryngeal cancer. Cancer 2017;123:849-60. © 2016 American Cancer Society.

Chang JG, Chen CC, Wu YY, et al.
Uncovering synthetic lethal interactions for therapeutic targets and predictive markers in lung adenocarcinoma.
Oncotarget. 2016; 7(45):73664-73680 [PubMed] Free Access to Full Article Related Publications
Two genes are called synthetic lethal (SL) if their simultaneous mutation leads to cell death, but mutation of either individual does not. Targeting SL partners of mutated cancer genes can selectively kill cancer cells, but leave normal cells intact. We present an integrated approach to uncover SL gene pairs as novel therapeutic targets of lung adenocarcinoma (LADC). Of 24 predicted SL pairs, PARP1-TP53 was validated by RNAi knockdown to have synergistic toxicity in H1975 and invasive CL1-5 LADC cells; additionally FEN1-RAD54B, BRCA1-TP53, BRCA2-TP53 and RB1-TP53 were consistent with the literature. While metastasis remains a bottleneck in cancer treatment and inhibitors of PARP1 have been developed, this result may have therapeutic potential for LADC, in which TP53 is commonly mutated. We also demonstrated that silencing PARP1 enhanced the cell death induced by the platinum-based chemotherapy drug carboplatin in lung cancer cells (CL1-5 and H1975). IHC of RAD54B↑, BRCA1↓-RAD54B↑, FEN1(N)↑-RAD54B↑ and PARP1↑-RAD54B↑ were shown to be prognostic markers for 131 Asian LADC patients, and all markers except BRCA1↓-RAD54B↑ were further confirmed by three independent gene expression data sets (a total of 426 patients) including The Cancer Genome Atlas (TCGA) cohort of LADC. Importantly, we identified POLB-TP53 and POLB as predictive markers for the TCGA cohort (230 subjects), independent of age and stage. Thus, POLB and POLB-TP53 may be used to stratify future non-Asian LADC patients for therapeutic strategies.

Zhang Y, Zhang D, Li Q, et al.
Nucleation of DNA repair factors by FOXA1 links DNA demethylation to transcriptional pioneering.
Nat Genet. 2016; 48(9):1003-13 [PubMed] Related Publications
FOXA1 functions in epigenetic reprogramming and is described as a 'pioneer factor'. However, exactly how FOXA1 achieves these remarkable biological functions is not fully understood. Here we report that FOXA1 associates with DNA repair complexes and is required for genomic targeting of DNA polymerase β (POLB) in human cells. Genome-wide DNA methylomes demonstrate that the FOXA1 DNA repair complex is functionally linked to DNA demethylation in a lineage-specific fashion. Depletion of FOXA1 results in localized reestablishment of methylation in a large portion of FOXA1-bound regions, and the regions with the most consistent hypermethylation exhibit the greatest loss of POLB and are represented by active promoters and enhancers. Consistently, overexpression of FOXA1 commits its binding sites to active DNA demethylation in a POLB-dependent manner. Finally, FOXA1-associated DNA demethylation is tightly coupled with estrogen receptor genomic targeting and estrogen responsiveness. Together, these results link FOXA1-associated DNA demethylation to transcriptional pioneering by FOXA1.

Kabzinski J, Mucha B, Cuchra M, et al.
Efficiency of Base Excision Repair of Oxidative DNA Damage and Its Impact on the Risk of Colorectal Cancer in the Polish Population.
Oxid Med Cell Longev. 2016; 2016:3125989 [PubMed] Free Access to Full Article Related Publications
DNA oxidative lesions are widely considered as a potential risk factor for colorectal cancer development. The aim of this work was to determine the role of the efficiency of base excision repair, both in lymphocytes and in epithelial tissue, in patients with CRC and healthy subjects. SNPs were identified within genes responsible for steps following glycosylase action in BER, and patients and healthy subjects were genotyped. A radioisotopic BER assay was used for assessing repair efficiency and TaqMan for genotyping. Decreased BER activity was observed in lymphocyte extract from CRC patients and in cancer tissue extract, compared to healthy subjects. In addition, polymorphisms of EXO1, LIG3, and PolB may modulate the risk of colorectal cancer by decreasing (PolB) or increasing (LIG3 and EXO1) the chance of malignant transformation.

Chantre-Justino M, Alves G, Britto C, et al.
Impact of reduced levels of APE1 transcripts on the survival of patients with urothelial carcinoma of the bladder.
Oncol Rep. 2015; 34(4):1667-74 [PubMed] Free Access to Full Article Related Publications
Molecular evidence indicates that alterations in genes involved in the maintenance of genome stability may be related to susceptibility to bladder carcinoma. Our goal was to evaluate the prognostic role of base excision repair (BER) genes in a cohort of patients diagnosed with primary urothelial carcinoma of the bladder (UCB). The levels of all APE1, XRCC1 and POLB transcripts were detected by quantitative real-time PCR (qPCR) technique in tumor samples from 52 patients undergoing transurethral resection (TUR) for primary UCB at the Department of Urology, Brazilian National Cancer Institute, Rio de Janeiro. Increased levels of APE1, XRCC1 and POLB transcripts were significantly associated with high-grade tumors when compared to these levels in low-grade tumors (p<0.01) and could be attributed to different mechanisms of transcriptional regulation as a response to tumorigenesis and oxidative stress. By analyzing the collected data in the present study, regardless of pathological grade or stage, univariate analysis revealed that the reduced levels of APE1 transcripts were significantly associated with cancer-specific mortality (p=0.032). Furthermore, the variant genotype (TG/GG) of the APE1 T1349G polymorphism was observed in 75% of a subset of patients who concomitantly experienced reduced levels of the APE1 transcript and death and/or recurrence events. Taken together, our data reinforce the idea that human DNA repair mechanisms must be finely regulated in order to avoid instability leading to tumorigenesis and poor clinical outcomes in UCB patients.

Tan X, Wang H, Luo G, et al.
Clinical significance of a point mutation in DNA polymerase beta (POLB) gene in gastric cancer.
Int J Biol Sci. 2015; 11(2):144-55 [PubMed] Free Access to Full Article Related Publications
Gastric cancer (GC) is a major cause of global cancer mortality. Genetic variations in DNA repair genes can modulate DNA repair capability and, consequently, have been associated with risk of developing cancer. We have previously identified a T to C point mutation at nucleotide 889 (T889C) in DNA polymerase beta (POLB) gene, a key enzyme involved in base excision repair in primary GCs. The purpose of this study was to evaluate the mutation and expression of POLB in a larger cohort and to identify possible prognostic roles of the POLB alterations in GC. Primary GC specimens and their matched normal adjacent tissues were collected at the time of surgery. DNA, RNA and protein samples were isolated from GC specimens and cell lines. Mutations were detected by PCR-RFLP/DHPLC and sequencing analysis. POLB gene expression was examined by RT-PCR, tissue microarray, Western blotting and immunofluorescence assays. The function of the mutation was evaluated by chemosensitivity, MTT, Transwell matrigel invasion and host cell reactivation assays. The T889C mutation was detected in 18 (10.17%) of 177 GC patients. And the T889C mutation was associated with POLB overexpression, lymph nodes metastases and poor tumor differentiation. In addition, patients with- the mutation had significantly shorter survival time than those without-, following postoperative chemotherapy. Furthermore, cell lines with T889C mutation in POLB gene were more resistant to the treatment of 5-fluorouracil, cisplatin and epirubicin than those with wild type POLB. Forced expression of POLB gene with T889C mutation resulted in enhanced cell proliferation, invasion and resistance to anticancer drugs, along with increased DNA repair capability. These results suggest that POLB gene with T889C mutation in surgically resected primary gastric tissues may be clinically useful for predicting responsiveness to chemotherapy in patients with GC. The POLB gene alteration may serve as a prognostic biomarker for GC.

Chan N, Ali M, McCallum GP, et al.
Hypoxia provokes base excision repair changes and a repair-deficient, mutator phenotype in colorectal cancer cells.
Mol Cancer Res. 2014; 12(10):1407-15 [PubMed] Related Publications
UNLABELLED: Regions of acute and chronic hypoxia exist within solid tumors and can lead to increased rates of mutagenesis and/or altered DNA damage and repair protein expression. Base excision repair (BER) is responsible for resolving small, non-helix-distorting lesions from the genome that potentially cause mutations by mispairing or promoting DNA breaks during replication. Germline and somatic mutations in BER genes, such as MutY Homolog (MUTYH/MYH) and DNA-directed polymerase (POLB), are associated with increased risk of colorectal cancer. However, very little is known about the expression and function of BER proteins under hypoxic stress. Using conditions of chronic hypoxia, decreased expression of BER proteins was observed because of a mechanism involving suppressed BER protein synthesis in multiple colorectal cancer cell lines. Functional BER was impaired as determined by MYH- and 8-oxoguanine (OGG1)-specific glycosylase assays. A formamidopyrimidine-DNA glycosylase (Fpg) Comet assay revealed elevated residual DNA base damage in hypoxic cells 24 hours after H2O2 treatment as compared with normoxic controls. Similarly, high-performance liquid chromatography analysis demonstrated that 8-oxo-2'-deoxyguanosine lesions were elevated in hypoxic cells 3 and 24 hours after potassium bromate (KBrO3) treatment when compared with aerobic cells. Correspondingly, decreased clonogenic survival was observed following exposure to the DNA base damaging agents H2O2 and MMS, but not to the microtubule interfering agent paclitaxel. Thus, a persistent downregulation of BER components by the microenvironment modifies and facilitates a mutator phenotype, driving genetic instability and cancer progression.
IMPLICATIONS: Aberrant BER is a contributing factor for the observed genetic instability in hypoxic tumor cells.

Tiong KL, Chang KC, Yeh KT, et al.
CSNK1E/CTNNB1 are synthetic lethal to TP53 in colorectal cancer and are markers for prognosis.
Neoplasia. 2014; 16(5):441-50 [PubMed] Free Access to Full Article Related Publications
Two genes are called synthetic lethal (SL) if their simultaneous mutations lead to cell death, but each individual mutation does not. Targeting SL partners of mutated cancer genes can kill cancer cells specifically, but leave normal cells intact. We present an integrated approach to uncovering SL pairs in colorectal cancer (CRC). Screening verified SL pairs using microarray gene expression data of cancerous and normal tissues, we first identified potential functionally relevant (simultaneously differentially expressed) gene pairs. From the top-ranked pairs, ~20 genes were chosen for immunohistochemistry (IHC) staining in 171 CRC patients. To find novel SL pairs, all 169 combined pairs from the individual IHC were synergistically correlated to five clinicopathological features, e.g. overall survival. Of the 11 predicted SL pairs, MSH2-POLB and CSNK1E-MYC were consistent with literature, and we validated the top two pairs, CSNK1E-TP53 and CTNNB1-TP53 using RNAi knockdown and small molecule inhibitors of CSNK1E in isogenic HCT-116 and RKO cells. Furthermore, synthetic lethality of CSNK1E and TP53 was verified in mouse model. Importantly, multivariate analysis revealed that CSNK1E-P53, CTNNB1-P53, MSH2-RB1, and BRCA1-WNT5A were independent prognosis markers from stage, with CSNK1E-P53 applicable to early-stage and the remaining three throughout all stages. Our findings suggest that CSNK1E is a promising target for TP53-mutant CRC patients which constitute ~40% to 50% of patients, while to date safety regarding inhibition of TP53 is controversial. Thus the integrated approach is useful in finding novel SL pairs for cancer therapeutics, and it is readily accessible and applicable to other cancers.

Sarker AH, Chatterjee A, Williams M, et al.
NEIL2 protects against oxidative DNA damage induced by sidestream smoke in human cells.
PLoS One. 2014; 9(3):e90261 [PubMed] Free Access to Full Article Related Publications
Secondhand smoke (SHS) is a confirmed lung carcinogen that introduces thousands of toxic chemicals into the lungs. SHS contains chemicals that have been implicated in causing oxidative DNA damage in the airway epithelium. Although DNA repair is considered a key defensive mechanism against various environmental attacks, such as cigarette smoking, the associations of individual repair enzymes with susceptibility to lung cancer are largely unknown. This study investigated the role of NEIL2, a DNA glycosylase excising oxidative base lesions, in human lung cells treated with sidestream smoke (SSS), the main component of SHS. To do so, we generated NEIL2 knockdown cells using siRNA-technology and exposed them to SSS-laden medium. Representative SSS chemical compounds in the medium were analyzed by mass spectrometry. An increased production of reactive oxygen species (ROS) in SSS-exposed cells was detected through the fluorescent detection and the induction of HIF-1α. The long amplicon-quantitative PCR (LA-QPCR) assay detected significant dose-dependent increases of oxidative DNA damage in the HPRT gene of cultured human pulmonary fibroblasts (hPF) and BEAS-2B epithelial cells exposed to SSS for 24 h. These data suggest that SSS exposure increased oxidative stress, which could contribute to SSS-mediated toxicity. siRNA knockdown of NEIL2 in hPF and HEK 293 cells exposed to SSS for 24 h resulted in significantly more oxidative DNA damage in HPRT and POLB than in cells with control siRNA. Taken together, our data strongly suggest that decreased repair of oxidative DNA base lesions due to an impaired NEIL2 expression in non-smokers exposed to SSS would lead to accumulation of mutations in genomic DNA of lung cells over time, thus contributing to the onset of SSS-induced lung cancer.

Corral R, Lewinger JP, Van Den Berg D, et al.
Comprehensive analyses of DNA repair pathways, smoking and bladder cancer risk in Los Angeles and Shanghai.
Int J Cancer. 2014; 135(2):335-47 [PubMed] Free Access to Full Article Related Publications
Tobacco smoking is a bladder cancer risk factor and a source of carcinogens that induce DNA damage to urothelial cells. Using data and samples from 988 cases and 1,004 controls enrolled in the Los Angeles County Bladder Cancer Study and the Shanghai Bladder Cancer Study, we investigated associations between bladder cancer risk and 632 tagSNPs that comprehensively capture genetic variation in 28 DNA repair genes from four DNA repair pathways: base excision repair (BER), nucleotide excision repair (NER), non-homologous end-joining (NHEJ) and homologous recombination repair (HHR). Odds ratios (ORs) and 95% confidence intervals (CIs) for each tagSNP were corrected for multiple testing for all SNPs within each gene using pACT and for genes within each pathway and across pathways with Bonferroni. Gene and pathway summary estimates were obtained using ARTP. We observed an association between bladder cancer and POLB rs7832529 (BER) (pACT = 0.003; ppathway = 0.021) among all, and SNPs in XPC (NER) and OGG1 (BER) among Chinese men and women, respectively. The NER pathway showed an overall association with risk among Chinese males (ARTP NER p = 0.034). The XRCC6 SNP rs2284082 (NHEJ), also in LD with SREBF2, showed an interaction with smoking (smoking status interaction pgene = 0.001, ppathway = 0.008, poverall = 0.034). Our findings support a role in bladder carcinogenesis for regions that map close to or within BER (POLB, OGG1) and NER genes (XPC). A SNP that tags both the XRCC6 and SREBF2 genes strongly modifies the association between bladder cancer risk and smoking.

Yamtich J, Nemec AA, Keh A, Sweasy JB
A germline polymorphism of DNA polymerase beta induces genomic instability and cellular transformation.
PLoS Genet. 2012; 8(11):e1003052 [PubMed] Free Access to Full Article Related Publications
Several germline single nucleotide polymorphisms (SNPs) have been identified in the POLB gene, but little is known about their cellular and biochemical impact. DNA Polymerase β (Pol β), encoded by the POLB gene, is the main gap-filling polymerase involved in base excision repair (BER), a pathway that protects the genome from the consequences of oxidative DNA damage. In this study we tested the hypothesis that expression of the POLB germline coding SNP (rs3136797) in mammalian cells could induce a cancerous phenotype. Expression of this SNP in both human and mouse cells induced double-strand breaks, chromosomal aberrations, and cellular transformation. Following treatment with an alkylating agent, cells expressing this coding SNP accumulated BER intermediate substrates, including single-strand and double-strand breaks. The rs3136797 SNP encodes the P242R variant Pol β protein and biochemical analysis showed that P242R protein had a slower catalytic rate than WT, although P242R binds DNA similarly to WT. Our results suggest that people who carry the rs3136797 germline SNP may be at an increased risk for cancer susceptibility.

Murphy DL, Donigan KA, Jaeger J, Sweasy JB
The E288K colon tumor variant of DNA polymerase β is a sequence specific mutator.
Biochemistry. 2012; 51(26):5269-75 [PubMed] Free Access to Full Article Related Publications
DNA polymerase β (pol β) is the main polymerase involved in base excision repair (BER), which is a pathway responsible for the repair of tens of thousands of DNA lesions per cell per day. Our recent efforts in sequencing colon tumors showed that 40% of the tumors sequenced possessed a variant in the coding region of the POLB gene; one of these variants is E288K. Expression of the E288K variant in cells leads to an increase in the frequency of mutations at AT base pairs. In vitro, the E288K variant is as active as and binds one-base-gapped DNA with the same affinity as wild-type pol β. Single-turnover kinetic data for the E288K variant show that its mutator phenotype is specific for misincorporating opposite template A up to 6-fold more than the wild-type enzyme and that this is due to a decrease in the degree of discrimination in nucleotide binding. Molecular modeling suggests that the substitution of Lys at position 288 causes the polymerase to adopt a more open conformation, which may be disrupting the nucleotide binding pocket. This may explain the reduced degree of discrimination at the level of nucleotide binding. The enhanced mutagenesis of the E288K variant could lead to genomic instability and ultimately a malignant tumor phenotype.

Donigan KA, Sun KW, Nemec AA, et al.
Human POLB gene is mutated in high percentage of colorectal tumors.
J Biol Chem. 2012; 287(28):23830-9 [PubMed] Free Access to Full Article Related Publications
Previous small scale sequencing studies have indicated that DNA polymerase β (pol β) variants are present on average in 30% of human tumors of varying tissue origin. Many of these variants have been shown to have aberrant enzyme function in vitro and to induce cellular transformation and/or genomic instability in vivo, suggesting that their presence is associated with tumorigenesis or its progression. In this study, the human POLB gene was sequenced in a collection of 134 human colorectal tumors and was found to contain coding region mutations in 40% of the samples. The variants map to many different sites of the pol β protein and are not clustered. Many variants are nonsynonymous amino acid substitutions predicted to affect enzyme function. A subset of these variants was found to have reduced enzyme activity in vitro and failed to fully rescue pol β-deficient cells from methylmethane sulfonate-induced cytotoxicity. Tumors harboring variants with reduced enzyme activity may have compromised base excision repair function, as evidenced by our methylmethane sulfonate sensitivity studies. Such compromised base excision repair may drive tumorigenesis by leading to an increase in mutagenesis or genomic instability.

Kazma R, Babron MC, Gaborieau V, et al.
Lung cancer and DNA repair genes: multilevel association analysis from the International Lung Cancer Consortium.
Carcinogenesis. 2012; 33(5):1059-64 [PubMed] Free Access to Full Article Related Publications
Lung cancer (LC) is the leading cause of cancer-related death worldwide and tobacco smoking is the major associated risk factor. DNA repair is an important process, maintaining genome integrity and polymorphisms in DNA repair genes may contribute to susceptibility to LC. To explore the role of DNA repair genes in LC, we conducted a multilevel association study with 1655 single nucleotide polymorphisms (SNPs) in 211 DNA repair genes using 6911 individuals pooled from four genome-wide case-control studies. Single SNP association corroborates previous reports of association with rs3131379, located on the gene MSH5 (P = 3.57 × 10-5) and returns a similar risk estimate. The effect of this SNP is modulated by histological subtype. On the log-additive scale, the odds ratio per allele is 1.04 (0.84-1.30) for adenocarcinomas, 1.52 (1.28-1.80) for squamous cell carcinomas and 1.31 (1.09-1.57) for other histologies (heterogeneity test: P = 9.1 × 10(-)(3)). Gene-based association analysis identifies three repair genes associated with LC (P < 0.01): UBE2N, structural maintenance of chromosomes 1L2 and POLB. Two additional genes (RAD52 and POLN) are borderline significant. Pathway-based association analysis identifies five repair pathways associated with LC (P < 0.01): chromatin structure, DNA polymerases, homologous recombination, genes involved in human diseases with sensitivity to DNA-damaging agents and Rad6 pathway and ubiquitination. This first international pooled analysis of a large dataset unravels the role of specific DNA repair pathways in LC and highlights the importance of accounting for gene and pathway effects when studying LC.

Donigan KA, Hile SE, Eckert KA, Sweasy JB
The human gastric cancer-associated DNA polymerase β variant D160N is a mutator that induces cellular transformation.
DNA Repair (Amst). 2012; 11(4):381-90 [PubMed] Free Access to Full Article Related Publications
Approximately 30% of human tumors sequenced to date harbor mutations in the POLB gene that are not present in matched normal tissue. Many mutations give rise to enzymes that contain non-synonymous single amino acid substitutions, several of which have been found to have aberrant activity or fidelity and transform cells when expressed. The DNA Polymerase β (Pol β) variant Asp160Asn (D160N) was first identified in a gastric tumor. Expression of D160N in cells induces cellular transformation as measured by hyperproliferation, focus formation, anchorage-independent growth and invasion. Here, we show that D160N is an active mutator polymerase that induces complex mutations. Our data support the interpretation that complex mutagenesis is the underlying mechanism of the observed cellular phenotypes, all of which are linked to tumorigenesis or tumor progression.

Varadi V, Bevier M, Grzybowska E, et al.
Genetic variation in genes encoding for polymerase ζ subunits associates with breast cancer risk, tumour characteristics and survival.
Breast Cancer Res Treat. 2011; 129(1):235-45 [PubMed] Related Publications
Chromosomal instability is a known hallmark of many cancers. DNA polymerases represent a group of enzymes that are involved in the mechanism of chromosomal instability as they have a central function in DNA metabolism. We hypothesized that genetic variation in the polymerase genes may affect gene expression or protein configuration and by that cancer risk and clinical outcome. We selected four genes encoding for the catalytic subunits of the polymerases β, δ, θ and ζ (POLB, POLD1, POLQ and REV3L, respectively) and two associated proteins (MAD2L2 and REV1) because of their previously reported association with chromosomal instability and/or tumorigenesis. We selected potentially functional and most informative tagging single nucleotide polymorphisms (SNPs) for genotyping in a population-based series of 783 Swedish breast cancer (BC) cases and 1562 controls. SNPs that showed a significant association in the Swedish population were additionally genotyped in a Polish population consisting of 506 familial/early onset BC cases and 568 controls. SNPs in all three polymerase ζ subunit genes associated either with BC risk or prognosis. Two SNPs in REV3L and one SNP in MAD2L2 associated with BC risk: rs462779 (multiplicative model: OR 0.79, 95% CI 0.68-0.92), rs3204953 (dominant model: OR 1.28, 95% CI 1.05-1.56) and rs2233004 (recessive model: OR 0.49, 95% CI 0.28-0.86). Homozygous carriers of the minor allele C of the third SNP in REV3L, rs11153292, had significantly worse survival compared to the TT genotype carriers (HR 2.93, 95% CI 1.34-6.44). Minor allele carriers of two REV1 SNPs (rs6761391 and rs3792142) had significantly more often large tumours and tumours with high histological grade and stage. No association was observed for SNPs in POLB, POLQ and POLD1. Altogether, our data suggest a significant role of genetic variation in the polymerase ζ subunit genes regarding the development and progression of BC.

Martin SA, McCabe N, Mullarkey M, et al.
DNA polymerases as potential therapeutic targets for cancers deficient in the DNA mismatch repair proteins MSH2 or MLH1.
Cancer Cell. 2010; 17(3):235-48 [PubMed] Free Access to Full Article Related Publications
Synthetic sickness/lethality (SSL) can be exploited to develop therapeutic strategies for cancer. Deficiencies in the tumor suppressor proteins MLH1 and MSH2 have been implicated in cancer. Here we demonstrate that deficiency in MSH2 is SSL with inhibition of the DNA polymerase POLB, whereas deficiency in MLH1 is SSL with DNA polymerase POLG inhibition. Both SSLs led to the accumulation of 8-oxoG oxidative DNA lesions. MSH2/POLB SSL caused nuclear 8-oxoG accumulation, whereas MLH1/POLG SSL led to a rise in mitochondrial 8-oxoG levels. Both SSLs were rescued by silencing the adenine glycosylase MUTYH, suggesting that lethality could be caused by the formation of lethal DNA breaks upon 8-oxoG accumulation. These data suggest targeted, mechanism-based therapeutic approaches.

Iwatsuki M, Mimori K, Yokobori T, et al.
A platinum agent resistance gene, POLB, is a prognostic indicator in colorectal cancer.
J Surg Oncol. 2009; 100(3):261-6 [PubMed] Related Publications
BACKGROUND: Recent progress in chemotherapy with platinum agents has improved clinical outcome in colorectal cancer (CRC), but there are no useful markers to predict the efficacy of such agents. DNA polymerase beta (POLB) mediates the efficacy of chemotherapy through DNA repair machinery. We analyzed the significance of POLB expression in CRC chemotherapy and its potential as a prognostic indicator.
METHODS: Using microarray, POLB was found to be overexpressed in CRC cells compared with corresponding normal colon epithelial cells. We determined the susceptibility of POLB-suppressed cells to cisplatin and oxaliplatin. We evaluated POLB mRNA expression in 97 CRC cases to determine the clinicopathologic significance of POLB expression.
RESULTS: We found the suppression of POLB altered the in vitro susceptibility to cisplatin but not to oxaliplatin. In 97 CRC cases, lymph node metastasis, distant metastasis and TNM classification were significantly greater in the high POLB group than in the low group (P < 0.05). Patients with high POLB expression had significantly poorer prognosis than those with low expression (P < 0.05).
CONCLUSIONS: The data indicate POLB is overexpressed in CRC cases with high malignant potential. We suggest POLB could be useful as a predictive marker for selection of patients responsive to cisplatin.

Michiels S, Laplanche A, Boulet T, et al.
Genetic polymorphisms in 85 DNA repair genes and bladder cancer risk.
Carcinogenesis. 2009; 30(5):763-8 [PubMed] Related Publications
Several defense mechanisms have been developed and maintained during the evolution to protect human cells against damage produced from exogenous or endogenous sources. We examined the associations between bladder cancer and a panel of 652 polymorphisms from 85 genes involved in maintenance of genetic stability [base excision repair, nucleotide excision repair, double-strand break repair (DSBR) and mismatch repair, as well as DNA synthesis and cell cycle regulation pathways] in 201 incident bladder cancer cases and 326 hospital controls. Score statistics were used to test differences in haplotype frequencies between cases and controls in an unconditional logistic regression model. To account for multiple testing, we associated to each P-value the expected proportion of false discoveries (q-value). Haplotype analysis revealed significant associations (P < 0.01) between bladder cancer and two genes (POLB and FANCA) with an associated q-value of 24%. A permutation test was also used to determine whether, in each pathway analyzed, there are more variants whose allelic frequencies are different between cases and controls as compared with what would be expected by chance. Differences were found for cell cycle regulation (P = 0.02) and to a lesser extent for DSBR (P = 0.05) pathways. These results hint to a few potential candidate genes; however, our study was limited by the small sample size and therefore low statistical power to detect associations. It is anticipated that genome-wide association studies will open new perspectives for interpretation of the results of extensive candidate gene studies such as ours.

Li D, Suzuki H, Liu B, et al.
DNA repair gene polymorphisms and risk of pancreatic cancer.
Clin Cancer Res. 2009; 15(2):740-6 [PubMed] Free Access to Full Article Related Publications
PURPOSE: The current research was undertaken to examine the association between genetic variations in DNA repair and pancreatic cancer risk.
EXPERIMENTAL DESIGN: We analyzed 9 single nucleotide polymorphisms of 7 DNA repair genes (LIG3, LIG4, OGG1, ATM, POLB, RAD54L, and RECQL) in 734 patients with pancreatic adenocarcinoma and 780 healthy controls using the Taqman method. Information on cigarette smoking, alcohol consumption, medical history, and other risk factors was collected by personal interview.
RESULTS: The homozygous mutant genotype of LIG3 G-39A [odds ratio (OR), 0.23; 95% confidence interval (CI), 0.06-0.82; P = 0.027] and ATM D1853N (OR, 2.55; 95% CI, 1.08-6.00; P = 0.032) was significantly associated with altered risk for pancreatic cancer. A statistically significant interaction of ATM D1853N and LIG4 C54T genotype with diabetes on the risk of pancreatic cancer was also detected. Compared with nondiabetics with the ATM D1853N GG genotype, nondiabetics with the GA/AA, diabetics with the GG, and diabetics with the GA/AA genotypes, respectively, had ORs (95% CI) of 0.96 (0.74-1.24), 1.32 (0.89-1.95), and 3.23 (1.47-7.12; P(interaction) = 0.032, likelihood ratio test). The OR (95% CI) was 0.91 (0.71-1.17), 1.11 (0.73-1.69), and 2.44 (1.34-4.46) for nondiabetics carrying the LIG4 CT/TT genotype, diabetics with the CC genotype, and diabetics carrying the CT/TT genotype, respectively, compared with nondiabetics carrying the CC genotype (P(interaction) = 0.02).
CONCLUSIONS: These observations suggest that genetic variations in DNA repair may act alone or in concert with other risk factors on modifying a patient's risk for pancreatic cancer.

Liu SN, Bai WY, Frye RM, et al.
Specific up-regulation of DNA polymerase by human papillomavirus 16.
Chin Med Sci J. 2008; 23(2):108-12 [PubMed] Related Publications
OBJECTIVE: To analyze how the infection of human papillomavirus 16 (HPV16) affects expression of DNA polymerase beta (DNA polB) with the aim of probing the mechanism of over-expression of DNA polB in human cancers.
METHODS: Four fragments of human DNA polB promoter were amplified and constructed into luciferase reporter vector pGL-Basic, generating pGL-BP, pGL-BMH, pGL-BMS, and pGL-BAT constructs respectively, and co-transfected with HPV16 or HPV6 into Hep2 cells. Luciferase activity was assayed 48 hours after transfection. Semi-quantitative RT-PCR was used to measure mRNA expression of endogenous DNA polB. Immunohistochemistry and in situ hybridization were used to analyze DNA polB expression and HPV16 or HPV6 infection in 38 cases of cervical lesions respectively.
RESULTS: With co-transfection of HPV16 and DNA polB promoter-driving reporters into Hep2 cells, pGL-BP reporter in full-length DNA polB promoter presented markedly elevated luciferase activities (P < 0.05). However, the other three mutant reporters: pGL-BMH, pGL-BMS, and pGL-BAT, generated no reporting activities in the presence of HPV16 (P > 0.05). On the contrary, all of polB promoter reporters were little stimulated in co-transfection of HPV6 (P > 0.05). The transfection of HPV16 could enhance the endogenous polB mRNA expression compared with that of HPV6 (3.42 vs. 0.80, P < 0.05). The DNA polB expression was found in 8 of 10 HPV16-positive cervical intraepithelial neoplasia grade III (CIN III) cases, while was only found in 3 of 11 HPV6-positive condyloma accuminatum cases, but was negative in all chronic cervicitis cases. The correlation of DNA polB expression with HPV16 infection in cervical lesions was significant (P < 0.05).
CONCLUSIONS: HPV16 is able to specifically stimulate the expression of DNA polB in human epithelial cells through interaction with the core upstream regulatory sequences of DNA polB promoter. Over-expression of DNA polB might be an explanation for the molecular mechanism underlying HPV-related human cancers.

Konkimalla VS, Wang G, Kaina B, Efferth T
Microarray-based expression of DNA repair genes does not correlate with growth inhibition of cancer cells by natural products derived from traditional Chinese medicine.
Cancer Genomics Proteomics. 2008 Mar-Apr; 5(2):79-84 [PubMed] Related Publications
Drug resistance represents a major obstacle in cancer chemotherapy. As chemically characterized compounds derived from plants used in traditional Chinese medicine (TCM) may have molecular targets different from those of standard antitumor drugs, they might be attractive candidates for novel therapeutics with improved pharmacological features. DNA repair is frequently involved in the development of resistance to established anticancer drugs, e.g. alkylating agents. Using a database of 531 chemically characterized TCM compounds from medicinal plants recently established by us, the IC50 values of 60 N.C.I. tumor cell lines for these 531 natural products were tested for correlation with the microarray-based mRNA expression of six genes involved in nucleotide excision repair (ERCC1, XPA, XPC, DDB2, ERCC4, ERCC5). No compound correlated with the expression of these genes, indicating that mRNA expression of these genes is not associated with resistance of the cell lines to these TCM compounds. The same is true for another six genes of the base excision repair pathway (MPG, APEX1, OGG1, XRCC1, LIG3, POLB). Microarray-based COMPARE analyses were performed to identify other candidate genes that are able to predict responsiveness of tumor cells to TCM-derived natural products. As an example, diallyl disulfide from garlic (Allium sativum L., Chinese name: dashuan) was chosen. Eighteen genes were identified whose mRNA expression predicted sensitivity or resistance to diallyl disulfide in hierarchical cluster analyses. Apart from some genes with still unknown function, genes were identified from different functional groups, e.g. signal transducers, regulators of GTPase activity, those associated with cytoskeleton formation and regulation, constituents of the ribosome. Remarkably, none of these genes have been described to be involved in DNA repair. In conclusion, our data indicate that TCM-derived natural products are worth being further investigated as novel compounds to eradicate tumors which reveal resistance to established anti-cancer drugs.

Sellick GS, Wade R, Richards S, et al.
Scan of 977 nonsynonymous SNPs in CLL4 trial patients for the identification of genetic variants influencing prognosis.
Blood. 2008; 111(3):1625-33 [PubMed] Related Publications
To identify genetic variants associated with outcome from chronic lymphocytic leukemia (CLL), we genotyped 977 nonsynonymous single nucleotide polymorphisms (nsSNPs) in 755 genes with relevance to cancer biology in 425 patients participating in a phase 3 trial comparing the efficacy of fludarabine, chlorambucil, and fludarabine with cyclophosphamide as first-line treatment. Selection of nsSNPs was biased toward those likely to be functionally deleterious. SNP genotypes were linked to individual patient outcome data and response to chemotherapy. The effect of genotype on progression-free survival (PFS) and overall survival (OS) was assessed by Cox regression analysis adjusting for treatment and clinico-pathologic variables. A total of 78 SNPs (51 dominantly acting and a further 27 recessively acting) were associated with PFS (9 also affecting OS) at the 5% level. These included SNPs mapping to the immune-regulation genes IL16 P434S (P = .03), IL19 S213F (P = .001), LILRA4 P27L (P = .004), KLRC4 S29I (P = .007), and CD5 V471A (P = .002); and DNA response genes POLB P242R (P = .04) and TOPBP1 S730L (P = .02), which were all independently prognostic of immunoglobulin heavy-chain variable region (IgV(H)) mutational status. The variants identified warrant further evaluation as promising prognostic markers of patient outcome. To facilitate the identification of prognostic markers through pooled analyses, we have made all data from our analysis publicly available.

Matakidou A, el Galta R, Webb EL, et al.
Genetic variation in the DNA repair genes is predictive of outcome in lung cancer.
Hum Mol Genet. 2007; 16(19):2333-40 [PubMed] Related Publications
To assess whether DNA repair gene variants influence the clinical behaviour of lung cancer we examined the impact of a comprehensive panel of 109 non-synonymous single-nucleotide polymorphisms (nsSNPs) in 50 DNA repair genes on overall survival (OS) in 700 lung cancer patients. Fifteen nsSNPs were associated with OS, significantly greater than that expected (P = 0.04). SNPs associated with prognosis mapped primarily to two repair pathways--nucleotide excision repair (NER): ERCC5 D1104H (P = 0.004); ERCC6 G399D (P = 0.023), ERCC6 Q1413R (P = 0.025), POLE (P = 0.014) and base excision repair: APEX1 D148E (P = 0.028); EXO1 E670G (P = 0.007); POLB P242R (P = 0.018). An increasing number of variant alleles in EXO1 was associated with a poorer prognosis [hazard ratio (HR) = 1.24; P = 0.0009]. A role for variation in NER and BRCA2/FA pathway genes as determinants of OS was provided by an analysis restricted to the 456 patients treated with platinum-based agents. Our data indicate that the pathway-based approach has the potential to generate prognostic markers of clinical outcome.

Berndt SI, Huang WY, Fallin MD, et al.
Genetic variation in base excision repair genes and the prevalence of advanced colorectal adenoma.
Cancer Res. 2007; 67(3):1395-404 [PubMed] Related Publications
Base excision repair (BER) corrects DNA damage caused by oxidative stress and low folate intake, which are putative risk factors for colorectal neoplasia. To examine the relationship between genetic variation in BER genes and colorectal adenoma risk, we conducted a case-control study of 767 cases of advanced colorectal adenoma and 773 controls from the baseline screening exam of the Prostate, Lung, Colorectal, and Ovarian Cancer Screening Trial. Cases included participants diagnosed with advanced left-sided adenoma, and controls were subjects without evidence of a left-sided polyp by sigmoidoscopy, frequency-matched to cases on race and gender. Twenty single nucleotide polymorphisms were genotyped in four BER genes (APEX1, PARP1, POLB, and XRCC1), and conditional logistic regression was used to estimate odds ratios (OR) and 95% confidence intervals (95% CI) for the association with colorectal adenoma. Two variants with possible functional significance were associated with risk. The APEX1 51H variant was associated with a borderline significant decreased risk of colorectal adenoma (OR, 0.66; 95% CI, 0.44-1.00), and the XRCC1 399Q variant was inversely associated with risk among Caucasians (OR, 0.80; 95% CI, 0.64-0.99). Homozygotes at two PARP1 loci (A284A and IVS13+118G>A) were also associated with a decreased risk of colorectal adenoma compared with wild-type carriers (OR, 0.70; 95% CI, 0.49-0.98 for both), which was restricted to advanced adenomas displaying histologically aggressive characteristics (OR, 0.51; 95% CI, 0.33-0.78, P = 0.002 for PARP1 A284A). This study suggests that polymorphisms in APEX1, XRCC1, and PARP1 may be associated with advanced colorectal adenoma.

Li D, Li Y, Jiao L, et al.
Effects of base excision repair gene polymorphisms on pancreatic cancer survival.
Int J Cancer. 2007; 120(8):1748-54 [PubMed] Free Access to Full Article Related Publications
To explore the association between single nucleotide polymorphisms of DNA repair genes and overall survival of patients with pancreatic cancer, we conducted a study in 378 cases of pancreatic adenocarcinoma who were treated at The University of Texas M. D. Anderson Cancer Center between February 1999 and October 2004 and were followed up to April 2006. Genotypes were determined using genomic DNA and the MassCode method. Overall survival was analyzed using the Kaplan-Meier plot, log-rank test and Cox regression. We observed a strong effect of the POLB A165G and T2133C genotypes on overall survival. The median survival time (MST) was 35.7 months for patients carrying at least 1 of the 2 homozygous variant POLB GG or CC genotypes, compared with 14.8 months for those carrying the AA/AG or TT/TC genotypes (p = 0.02, log rank test). The homozygous variants of hOGG1 G2657A, APEX1 D148E and XRCC1 R194W polymorphisms all showed a weak but significant effect on overall survival as demonstrated by either log rank test or multivariate COX regression after adjusting for other potential confounders. In combined genotype analysis, a predominant effect of the POLB homozygous variants on survival was observed. When POLB was not included in the model, a slightly better survival was observed among those carrying none of the adverse genotypes than those carrying at least one of the adverse genotypes. These observations suggest that polymorphisms of base excision repair genes significantly affect the clinical outcome of patients with pancreatic cancer. These observations need to be confirmed in a larger study of homogenous patient population.

Figueroa JD, Malats N, Real FX, et al.
Genetic variation in the base excision repair pathway and bladder cancer risk.
Hum Genet. 2007; 121(2):233-42 [PubMed] Related Publications
Genetic polymorphisms in DNA repair genes may impact individual variation in DNA repair capacity and alter cancer risk. In order to examine the association of common genetic variation in the base-excision repair (BER) pathway with bladder cancer risk, we analyzed 43 single nucleotide polymorphisms (SNPs) in 12 BER genes (OGG1, MUTYH, APEX1, PARP1, PARP3, PARP4, XRCC1, POLB, POLD1, PCNA, LIG1, and LIG3). Using genotype data from 1,150 cases of urinary bladder transitional cell carcinomas and 1,149 controls from the Spanish Bladder Cancer Study we estimated odds ratios (ORs) and 95% confidence intervals (CIs) adjusting for age, gender, region and smoking status. SNPs in three genes showed significant associations with bladder cancer risk: the 8-oxoG DNA glycosylase gene (OGG1), the Poly (ADP-ribose) polymerase family member 1 (PARP1) and the major gap filling polymerase-beta (POLB). Subjects who were heterozygous or homozygous variant for an OGG1 SNP in the promoter region (rs125701) had significantly decreased bladder cancer risk compared to common homozygous: OR (95%CI) 0.78 (0.63-0.96). Heterozygous or homozygous individuals for the functional SNP PARP1 rs1136410 (V762A) or for the intronic SNP POLB rs3136717 were at increased risk compared to those homozygous for the common alleles: 1.24 (1.02-1.51) and 1.30 (1.04-1.62), respectively. In summary, data from this large case-control study suggested bladder cancer risk associations with selected BER SNPs, which need to be confirmed in other study populations.

Yu J, Mallon MA, Zhang W, et al.
DNA repair pathway profiling and microsatellite instability in colorectal cancer.
Clin Cancer Res. 2006; 12(17):5104-11 [PubMed] Related Publications
BACKGROUND: The ability to maintain DNA integrity is a critical cellular function. DNA repair is conducted by distinct pathways of genes, many of which are thought to be altered in colorectal cancer. However, there has been little characterization of these pathways in colorectal cancer.
METHOD: By using the TaqMan real-time quantitative PCR, RNA expression profiling of 20 DNA repair pathway genes was done in matched tumor and normal tissues from 52 patients with Dukes' C colorectal cancer.
RESULTS: The relative mRNA expression level across the 20 DNA repair pathway genes varied considerably, and the individual variability was also quite large, with an 85.4 median fold change in the tumor tissue genes and a 127.2 median fold change in the normal tissue genes. Tumor-normal differential expression was found in 13 of 20 DNA repair pathway genes (only XPA had a lower RNA level in the tumor samples; the other 12 genes had significantly higher tumor levels, all P<0.01). Coordinated expression of ERCC6, HMG1, MSH2, and POLB (RS>or=0.60) was observed in the tumor tissues (all P<0.001). Apoptosis index was not correlated with expression of the 20 DNA repair pathway genes. MLH1 and XRCC1 RNA expression was correlated with microsatellite instability status (P=0.045 and 0.020, respectively). An inverse correlation was found between tumor MLH1 RNA expression and MLH1 DNA methylation (P=0.003).
CONCLUSION: Our study provides an initial characterization of the DNA repair pathways for understanding the cellular DNA damage/repair system in human colorectal cancer.

Kokkinakis DM, Brickner AG, Kirkwood JM, et al.
Mitotic arrest, apoptosis, and sensitization to chemotherapy of melanomas by methionine deprivation stress.
Mol Cancer Res. 2006; 4(8):575-89 [PubMed] Related Publications
Methionine deprivation stress (MDS) eliminates mitotic activity in melanoma cells regardless of stage, grade, or TP53 status, whereas it has a negligible effect on normal skin fibroblasts. In most cases, apoptosis accounts for the elimination of up to 90% of tumor cells from the culture within 72 hours after MDS, leaving a scattered population of multinucleated resistant cells. Loss of mitosis in tumor cells is associated with marked reduction of cyclin-dependent kinase (CDK) 1 transcription and/or loss of its active form (CDK1-P-Thr(161)), which is coincident with up-regulation of CDKN1A, CDKN1B, and CDKN1C (p21, p27, and p57). Expression of the proapoptotic LITAF, IFNGR, EREG, TNFSF/TNFRSF10 and TNFRSF12, FAS, and RNASEL is primarily up-regulated/induced in cells destined to undergo apoptosis. Loss of Aurora kinase B and BIRC5, which are required for histone H3 phosphorylation, is associated with the accumulation of surviving multinucleated cells. Nevertheless, noncycling survivors of MDS are sensitized to temozolomide, carmustin, and cisplatin to a much greater extent than normal skin fibroblasts possibly because of the suppression of MGMT/TOP1/POLB, MGMT/RAD52/RAD54, and cMET/RADD52, respectively. Sensitivity to these and additional genotoxic agents and radiation may also be acquired due to loss of cMET/OGG1, reduced glutathione reductase levels, and a G(2)-phase block that is a crucial step in the damage response associated with enhancement of drug toxicity. Although the genes controlling mitotic arrest and/or apoptosis in response to low extracellular methionine levels are unknown, it is likely that such control is exerted via the induction/up-regulation of tumor suppressors/growth inhibitor genes, such as TGFB, PTEN, GAS1, EGR3, BTG3, MDA7, and the proteoglycans (LUM, BGN, and DCN), as well as the down-regulation/loss of function of prosurvival genes, such as NFkappaB, MYC, and ERBB2. Although MDS targets several common genes in tumors, mutational variability among melanomas may decide which metabolic and signal transduction pathways will be activated or shutdown.

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