FEN1

Gene Summary

Gene:FEN1; flap structure-specific endonuclease 1
Aliases: MF1, RAD2, FEN-1
Location:11q12.2
Summary:The protein encoded by this gene removes 5' overhanging flaps in DNA repair and processes the 5' ends of Okazaki fragments in lagging strand DNA synthesis. Direct physical interaction between this protein and AP endonuclease 1 during long-patch base excision repair provides coordinated loading of the proteins onto the substrate, thus passing the substrate from one enzyme to another. The protein is a member of the XPG/RAD2 endonuclease family and is one of ten proteins essential for cell-free DNA replication. DNA secondary structure can inhibit flap processing at certain trinucleotide repeats in a length-dependent manner by concealing the 5' end of the flap that is necessary for both binding and cleavage by the protein encoded by this gene. Therefore, secondary structure can deter the protective function of this protein, leading to site-specific trinucleotide expansions. [provided by RefSeq, Jul 2008]
Databases:VEGA, OMIM, HGNC, Ensembl, GeneCard, Gene
Protein:flap endonuclease 1
Source:NCBIAccessed: 09 March, 2017

Ontology:

What does this gene/protein do?
Show (31)

Cancer Overview

Research Indicators

Publications Per Year (1992-2017)
Graph generated 10 March 2017 using data from PubMed using criteria.

Literature Analysis

Mouse over the terms for more detail; many indicate links which you can click for dedicated pages about the topic.

  • Cancer Gene Expression Regulation
  • Breast Cancer
  • Cell Cycle
  • Cell Proliferation
  • Flap Endonucleases
  • Lung Cancer
  • Mutation
  • Apoptosis
  • Gene Expression Profiling
  • DNA
  • Western Blotting
  • Cell Line
  • Genotype
  • Transfection
  • Drug Resistance
  • Immunohistochemistry
  • Signal Transduction
  • HeLa Cells
  • Oligonucleotide Array Sequence Analysis
  • Single Nucleotide Polymorphism
  • Molecular Sequence Data
  • Adenocarcinoma
  • Surveys and Questionnaires
  • Ubiquitin-Conjugating Enzymes
  • DNA Replication
  • Liver Cancer
  • Case-Control Studies
  • Colorectal Cancer
  • DNA Damage
  • Protein Kinases
  • Nuclear Proteins
  • Antineoplastic Agents
  • DNA Repair
  • Haplotypes
  • Chromosome 11
  • Genetic Predisposition
  • p53 Protein
  • Cell Cycle Proteins
  • Biomarkers, Tumor
  • Genetic Association Studies
  • DNA-Binding Proteins
Tag cloud generated 09 March, 2017 using data from PubMed, MeSH and CancerIndex

Specific Cancers (4)

Data table showing topics related to specific cancers and associated disorders. Scope includes mutations and abnormal protein expression.

Note: list is not exhaustive. Number of papers are based on searches of PubMed (click on topic title for arbitrary criteria used).

Latest Publications: FEN1 (cancer-related)

He L, Zhang Y, Sun H, et al.
Targeting DNA Flap Endonuclease 1 to Impede Breast Cancer Progression.
EBioMedicine. 2016; 14:32-43 [PubMed] Free Access to Full Article Related Publications
DNA flap endonuclease 1 (FEN1) plays critical roles in maintaining genome stability and integrity by participating in both DNA replication and repair. Suppression of FEN1 in cells leads to the retardation of DNA replication and accumulation of unrepaired DNA intermediates, resulting in DNA double strand breaks (DSBs) and apoptosis. Therefore, targeting FEN1 could serve as a potent strategy for cancer therapy. In this study, we demonstrated that FEN1 is overexpressed in breast cancers and is essential for rapid proliferation of cancer cells. We showed that manipulating FEN1 levels in cells alters the response of cancer cells to chemotherapeutic drugs. Furthermore, we identified a small molecular compound, SC13 that specifically inhibits FEN1 activity, thereby interfering with DNA replication and repair in vitro and in cells. SC13 suppresses cancer cell proliferation and induces chromosome instability and cytotoxicity in cells. Importantly, SC13 sensitizes cancer cells to DNA damage-inducing therapeutic modalities and impedes cancer progression in a mouse model. These findings could establish a paradigm for the treatment of breast cancer and other cancers as well.

Liu ZZ, Cui ST, Tang B, et al.
Identification of key biomarkers involved in osteosarcoma using altered modules.
Genet Mol Res. 2016; 15(3) [PubMed] Related Publications
The aim of this study was to screen for key biomarkers of osteosarcoma (OS) by tracking altered modules. Protein-protein interaction (PPI) networks of OS and normal groups were constructed and re-weighted using the Pearson correlation coefficient (PCC), respectively. The condition-specific modules were explored from OS and normal PPI networks using a clique-merging algorithm. Altered modules were identified by a maximum weight bipartite-matching method. The important biological pathways in OS were identified by a pathway-enrichment analysis using genes from disrupted modules. The most important genes in these pathways were selected as key biomarkers. Finally, the mRNA and protein expressions of hub genes in OS bone tissues were analyzed using reverse transcription-polymerase chain reaction and western blotting, respectively. We identified 703 and 2270 modules in normal and disease networks, respectively; 150 altered modules were identified from among these and explored. We identified 10 important pathways based on gene pairs with altered PCC > 1 in the disrupted modules (P < 0.01), and PCNA, ATP6V1C2, ATP6V1G3, FEN1, CDC7, and RPA3 (expressed in these pathways) were selected as key genes of OS. We observed that these genes (and the proteins they encoded) were differentially expressed between normal and OS samples (P < 0.01) (excluding ATP6V1C2, whose protein expression did not differ significantly). Therefore, we identified 5 gene signatures that may be potential biomarkers for the detection and effective therapy of OS.

Srihari S, Kalimutho M, Lal S, et al.
Understanding the functional impact of copy number alterations in breast cancer using a network modeling approach.
Mol Biosyst. 2016; 12(3):963-72 [PubMed] Related Publications
UNLABELLED: Copy number alterations (CNAs) are thought to account for 85% of the variation in gene expression observed among breast tumours. The expression of cis-associated genes is impacted by CNAs occurring at proximal loci of these genes, whereas the expression of trans-associated genes is impacted by CNAs occurring at distal loci. While a majority of these CNA-driven genes responsible for breast tumourigenesis are cis-associated, trans-associated genes are thought to further abet the development of cancer and influence disease outcomes in patients. Here we present a network-based approach that integrates copy-number and expression profiles to identify putative cis- and trans-associated genes in breast cancer pathogenesis. We validate these cis- and trans-associated genes by employing them to subtype a large cohort of breast tumours obtained from the METABRIC consortium, and demonstrate that these genes accurately reconstruct the ten subtypes of breast cancer. We observe that individual breast cancer subtypes are driven by distinct sets of cis- and trans-associated genes. Among the cis-associated genes, we recover several known drivers of breast cancer (e.g. CCND1, ERRB2, MDM2 and ZNF703) and some novel putative drivers (e.g. BRF2 and SF3B3). siRNA-mediated knockdown of BRF2 across a panel of breast cancer cell lines showed significant reduction in cell viability for ER-/HER2+ (MDA-MB-453) cells, but not in normal (MCF10A) cells thereby indicating that BRF2 could be a viable therapeutic target for estrogen receptor-negative/HER2-enriched (ER-/HER2+) cancers. Among the trans-associated genes, we identify modules of immune response (CD2, CD19, CD38 and CD79B), mitotic/cell-cycle kinases (e.g. AURKB, MELK, PLK1 and TTK), and DNA-damage response genes (e.g. RFC4 and FEN1). siRNA-mediated knockdown of RFC4 significantly reduced cell proliferation in ER-negative normal breast and cancer lines, thereby indicating that RFC4 is essential for both normal and cancer cell survival but could be a useful biomarker for aggressive (ER-negative) breast tumours.
AVAILABILITY: under NetStrat.

Xie C, Wang K, Chen D
Flap endonuclease 1 silencing is associated with increasing the cisplatin sensitivity of SGC‑7901 gastric cancer cells.
Mol Med Rep. 2016; 13(1):386-92 [PubMed] Related Publications
Flap endonuclease 1 (FEN1), which is key in DNA replication and repair, has been demonstrated to be intimately involved in the development and progression of cancer. Our previous study determined that the downregulation of FEN1 can suppress the proliferation of, and induce apoptosis in, gastric cancer SGC‑7901 cells. In addition, several FEN1 inhibitors have been identified to increase sensitisation to DNA injury agents. These results may provide a promising treatment method to enhance the traditional chemotherapeutics used for the treatment of gastric cancer. Thus, the aim of the present study was to determine the role of FEN1 in the chemosensitivity of SGC‑7901 cells. The protein expression levels of FEN1 in cisplatin (CDDP)‑treated SGC‑7901 cells were detected using western blot analysis. FEN1 was silenced via specific FEN1‑targeted small interfering RNAs (siRNA). The survival and apoptotic rates of the SGC‑7901 cells were assessed using an MTT assay and flow cytometry, respectively. Relevant apoptotic factors were detected using western blotting. The results showed that the expression of FEN1 was significantly induced by CDDP in a dose‑ and time‑dependent manner. The targeting of FEN1 in SGC‑7901 cells, in combination with CDDP treatment, significantly inhibited their proliferation and effectively increased their apoptotic rate. In addition, in the cells targeted with FEN1‑siRNA and exposed to CDDP, the levels of Bcl‑2‑associated X protein were significantly increased, whereas the expression levels of Bcl‑2 and Bcl‑extra large were effectively decreased, compared with the cells exposed to negative control‑siRNA and CDDP. These results suggest a potential chemotherapeutic target, which exhibits enhanced sensitivity to CDDP following FEN1 silencing in SGC‑7901 cells via decreased survival and increased apoptosis.

Jiao X, Wu Y, Zhou L, et al.
Variants and haplotypes in Flap endonuclease 1 and risk of gallbladder cancer and gallstones: a population-based study in China.
Sci Rep. 2015; 5:18160 [PubMed] Free Access to Full Article Related Publications
The role of FEN1 genetic variants on gallstone and gallbladder cancer susceptibility is unknown. FEN1 SNPs were genotyped using the polymerase chain reaction-restriction fragment length polymorphism method in blood samples from 341 gallbladder cancer patients and 339 healthy controls. The distribution of FEN1-69G > A genotypes among controls (AA, 20.6%; GA, 47.2% and GG 32.2%) was significantly different from that among gallbladder cancer cases (AA, 11.1%; GA, 48.1% and GG, 40.8%), significantly increased association with gallbladder cancer was observed for subjects with both the FEN1-69G > A GA (OR = 1.73, 95% CI = 1.01-2.63) and the FEN1-69G > A GG (OR = 2.29, 95% CI = 1.31-3.9). The distribution of FEN1 -4150T genotypes among controls (TT, 21.8%;GT, 49.3% and GG 28.9%) was significantly different from that among gallbladder cancer cases (TT, 12.9%; GT, 48.4% and GG 38.7%), significantly increased association with gallbladder cancer was observed for subjects with both the FEN1-4150T GT(OR = 1.93, 95% CI = 1.04-2.91) and the FEN1-4150T GG(OR = 2.56, 95% CI = 1.37-5.39). A significant trend towards increased association with gallbladder cancer was observed with potentially higher-risk FEN1-69G > A genotypes (P < 0.001, χ2 trend test) and FEN14150G > T (P < 0.001, χ2 trend test) in gallstone presence but not in gallstone absence (P = 0.81, P = 0.89, respectively). In conclusion, this study revealed firstly that FEN1 polymorphisms and haplotypes are associated with gallbladder cancer risk.

Alsubhi N, Middleton F, Abdel-Fatah TM, et al.
Chk1 phosphorylated at serine345 is a predictor of early local recurrence and radio-resistance in breast cancer.
Mol Oncol. 2016; 10(2):213-23 [PubMed] Related Publications
Radiation-induced DNA damage activates the DNA damage response (DDR). DDR up-regulation may predict radio-resistance and increase the risk of early local recurrence despite radiotherapy in early stage breast cancers. In 1755 early stage breast cancers, DDR signalling [ATM, ATR, total Ckh1, Chk1 phosphorylated at serine(345) (pChk1), Chk2, p53], base excision repair [PARP1, POLβ, XRCC1, FEN1, SMUG1], non-homologous end joining (Ku70/Ku80, DNA-PKcs) and homologous recombination [RAD51, BRCA1, γH2AX, BLM, WRN, RECQL5, PTEN] protein expression was correlated to time to early local recurrence. Pre-clinically, radio-sensitization by inhibition of Chk1 activation by ATR inhibitor (VE-821) and inhibition of Chk1 (V158411) were investigated in MDA-MB-231 (p53 mutant) and MCF-7 (p53 wild-type) breast cancer cells. In the whole cohort, 208/1755 patients (11.9%) developed local recurrence of which 126 (61%) developed local recurrence within 5 years of initiation of primary therapy. Of the 20 markers tested, only pChk1 and p53 significantly associated with early local recurrence (p value = 0.015 and 0.010, respectively). When analysed together, high cytoplasmic pChk1-nuclear pChk1 (p = 0.039), high cytoplasmic pChk1-p53 (p = 0.004) and high nuclear pChk1-p53 (p = 0.029) co-expression remain significantly linked to early local recurrence. In multivariate analysis, cytoplasmic pChk1 level independently predicted early local recurrence (p = 0.025). In patients who received adjuvant local radiotherapy (n = 949), p53 (p = 0.014) and high cytoplasmic pChk1-p53 (p = 0.017) remain associated with early local recurrence. Pre-clinically, radio-sensitisation by VE-821 or V158411 was observed in both MCF-7 and MDA-MB-231 cells and was more pronounced in MCF-7 cells. We conclude that pChk1 is a predictive biomarker of radiotherapy resistance and early local recurrence.

Hwang JC, Sung WW, Tu HP, et al.
The Overexpression of FEN1 and RAD54B May Act as Independent Prognostic Factors of Lung Adenocarcinoma.
PLoS One. 2015; 10(10):e0139435 [PubMed] Free Access to Full Article Related Publications
Synthetic lethality arises when a combination of mutations in two or more genes leads to cell death. However, the prognostic role of concordant overexpression of synthetic lethality genes in protein level rather than a combination of mutations is not clear. In this study, we explore the prognostic role of combined overexpression of paired genes in lung adenocarcinoma. We used immunohistochemical staining to investigate 24 paired genes in 93 lung adenocarcinoma patients and Kaplan-Meier analysis and Cox proportional hazards models to evaluate their prognostic roles. Among 24 paired genes, only FEN1 (Flap endonuclease 1) and RAD54B (RAD54 homolog B) were overexpressed in lung adenocarcinoma patients with poor prognosis. Patients with expression of both FEN1 and RAD54B were prone to have advanced nodal involvement and significantly poor prognosis (HR = 2.35, P = 0.0230). These results suggest that intensive follow up and targeted therapy might improve clinical outcome for patients who show expression of both FEN1 and RAD54B.

Narayan S, Sharma R
Molecular mechanism of adenomatous polyposis coli-induced blockade of base excision repair pathway in colorectal carcinogenesis.
Life Sci. 2015; 139:145-52 [PubMed] Free Access to Full Article Related Publications
Colorectal cancer (CRC) is the third leading cause of death in both men and women in North America. Despite chemotherapeutic efforts, CRC is associated with a high degree of morbidity and mortality. Thus, to develop effective treatment strategies for CRC, one needs knowledge of the pathogenesis of cancer development and cancer resistance. It is suggested that colonic tumors or cell lines harbor truncated adenomatous polyposis coli (APC) without DNA repair inhibitory (DRI)-domain. It is also thought that the product of the APC gene can modulate base excision repair (BER) pathway through an interaction with DNA polymerase β (Pol-β) and flap endonuclease 1 (Fen-1) to mediate CRC cell apoptosis. The proposed therapy with temozolomide (TMZ) exploits this particular pathway; however, a high percentage of colorectal tumors continue to develop resistance to chemotherapy due to mismatch repair (MMR)-deficiency. In the present communication, we have comprehensively reviewed a critical issue that has not been addressed previously: a novel mechanism by which APC-induced blockage of single nucleotide (SN)- and long-patch (LP)-BER play role in DNA-alkylation damage-induced colorectal carcinogenesis.

Wang J, Zhou L, Li Z, et al.
YY1 suppresses FEN1 over-expression and drug resistance in breast cancer.
BMC Cancer. 2015; 15:50 [PubMed] Free Access to Full Article Related Publications
BACKGROUND: Drug resistance is a major challenge in cancer therapeutics. Abundant evidence indicates that DNA repair systems are enhanced after repetitive chemotherapeutic treatments, rendering cancers cells drug-resistant. Flap endonuclease 1 (FEN1) plays critical roles in DNA replication and repair and in counteracting replication stress, which is a key mechanism for many chemotherapeutic drugs to kill cancer cells. FEN1 was previously shown to be upregulated in response to DNA damaging agents. However, it is unclear about the transcription factors that regulate FEN1 expression in human cancer. More importantly, it is unknown whether up-regulation of FEN1 has an adverse impact on the prognosis of chemotherapeutic treatments of human cancers.
METHODS: To reveal regulation mechanism of FEN1 expression, we search and identify FEN1 transcription factors or repressors and investigate their function on FEN1 expression by using a combination of biochemical, molecular, and cellular approaches. Furthermore, to gain insights into the impact of FEN1 levels on the response of human cancer to therapeutic treatments, we determine FEN1 levels in human breast cancer specimens and correlate them to the response to treatments and the survivorship of corresponding breast cancer patients.
RESULTS: We observe that FEN1 is significantly up-regulated upon treatment of chemotherapeutic drugs such as mitomycin C (MMC) and Taxol in breast cancer cells. We identify that the transcription factor/repressor YY1 binds to the FEN1 promoter and suppresses the expression of FEN1 gene. In response to the drug treatments, YY1 is dissociated from the FEN1 promoter region leading over-expression of FEN1. Overexpression of YY1 in the cells results in down-regulation of FEN1 and sensitization of the cancer cells to MMC or taxol. Furthermore, we observe that the level of FEN1 is inversely correlated with cancer drug and radiation resistance and with survivorship in breast cancer patients.
CONCLUSION: Altogether, our current data indicate that YY1 is a transcription repressor of FEN1 regulating FEN1 levels in response to DNA damaging agents. FEN1 is up-regulated in human breast cancer and its levels inversely correlated with cancer drug and radiation resistance and with survivorship in breast cancer patients.

Das D, Preet R, Mohapatra P, et al.
5-Fluorouracil mediated anti-cancer activity in colon cancer cells is through the induction of Adenomatous Polyposis Coli: Implication of the long-patch base excision repair pathway.
DNA Repair (Amst). 2014; 24:15-25 [PubMed] Free Access to Full Article Related Publications
Colorectal cancer (CRC) patients with APC mutations do not benefit from 5-FU therapy. It was reported that APC physically interacts with POLβ and FEN1, thus blocking LP-BER via APC's DNA repair inhibitory (DRI) domain in vitro. The aim of this study was to elucidate how APC status affects BER and the response of CRC to 5-FU. HCT-116, HT-29, and LOVO cells varying in APC status were treated with 5-FU to evaluate expression, repair, and survival responses. HCT-116 expresses wild-type APC; HT-29 expresses an APC mutant that contains DRI domain; LOVO expresses an APC mutant lacking DRI domain. 5-FU increased the expression of APC and decreased the expression of FEN1 in HCT-116 and HT-29 cells, which were sensitized to 5-FU when compared to LOVO cells. Knockdown of APC in HCT-116 rendered cells resistant to 5-FU, and FEN1 levels remained unchanged. Re-expression of full-length APC in LOVO cells caused sensitivity to 5-FU, and decreased expression of FEN1. These knockdown and addback studies confirmed that the DRI domain is necessary for the APC-mediated reduction in LP-BER and 5-FU. Modelling studies showed that 5-FU can interact with the DRI domain of APC via hydrogen bonding and hydrophobic interactions. 5-FU resistance in CRC occurs with mutations in APC that disrupt or eliminate the DRI domain's interaction with LP-BER. Understanding the type of APC mutation should better predict 5-FU resistance in CRC than simply characterizing APC status as wild-type or mutant.

Abdel-Fatah TM, Arora A, Alsubhi N, et al.
Clinicopathological significance of ATM-Chk2 expression in sporadic breast cancers: a comprehensive analysis in large cohorts.
Neoplasia. 2014; 16(11):982-91 [PubMed] Free Access to Full Article Related Publications
ATM-Chk2 network is critical for genomic stability, and its deregulation may influence breast cancer pathogenesis. We investigated ATM and Chk2 protein levels in two cohorts [cohort 1 (n = 1650) and cohort 2 (n = 252)]. ATM and Chk2 mRNA expression was evaluated in the Molecular Taxonomy of Breast Cancer International Consortium cohort (n = 1950). Low nuclear ATM protein level was significantly associated with aggressive breast cancer including larger tumors, higher tumor grade, higher mitotic index, pleomorphism, tumor type, lymphovascular invasion, estrogen receptor (ER)-, PR -, AR -, triple-negative, and basal-like phenotypes (Ps < .05). Breast cancer 1, early onset negative, low XRCC1, low SMUG1, high FEN1, high MIB1, p53 mutants, low MDM2, low Bcl-2, low p21, low Bax, high CDK1, and low Chk2 were also more frequent in tumors with low nuclear ATM level (Ps < .05). Low ATM protein level was significantly associated with poor survival including in patients with ER-negative tumors who received adjuvant anthracycline or cyclophosphamide, methotrexate, and 5-fluorouracil-based adjuvant chemotherapy (Ps < .05). Low nuclear Chk2 protein was likely in ER -/PR -/AR -; HER-2 positive; breast cancer 1, early onset negative; low XRCC1; low SMUG1; low APE1; low polβ; low DNA-PKcs; low ATM; low Bcl-2; and low TOPO2A tumors (P < .05). In patients with ER + tumors who received endocrine therapy or ER-negative tumors who received chemotherapy, nuclear Chk2 levels did not significantly influence survival. In p53 mutant tumors, low ATM (P < .000001) or high Chk2 (P < .01) was associated with poor survival. When investigated together, low-ATM/high-Chk2 tumors have the worst survival (P = .0033). Our data suggest that ATM-Chk2 levels in sporadic breast cancer may have prognostic and predictive significance.

Yong KJ, Milenic DE, Baidoo KE, Brechbiel MW
Impact of α-targeted radiation therapy on gene expression in a pre-clinical model for disseminated peritoneal disease when combined with paclitaxel.
PLoS One. 2014; 9(9):e108511 [PubMed] Free Access to Full Article Related Publications
To better understand the molecular basis of the enhanced cell killing effected by the combined modality of paclitaxel and ²¹²Pb-trastuzumab (Pac/²¹²Pb-trastuzumab), gene expression in LS-174T i.p. xenografts was investigated 24 h after treatment. Employing a real time quantitative PCR array (qRT-PCR array), 84 DNA damage response genes were quantified. Differentially expressed genes following therapy with Pac/²¹²Pb-trastuzumab included those involved in apoptosis (BRCA1, CIDEA, GADD45α, GADD45γ, GML, IP6K3, PCBP4, PPP1R15A, RAD21, and p73), cell cycle (BRCA1, CHK1, CHK2, GADD45α, GML, GTSE1, NBN, PCBP4, PPP1R15A, RAD9A, and SESN1), and damaged DNA repair (ATRX, BTG2, EXO1, FEN1, IGHMBP2, OGG1, MSH2, MUTYH, NBN, PRKDC, RAD21, and p73). This report demonstrates that the increased stressful growth arrest conditions induced by the Pac/²¹²Pb-trastuzumab treatment suppresses cell proliferation through the regulation of genes which are involved in apoptosis and damaged DNA repair including single and double strand DNA breaks. Furthermore, the study demonstrates that ²¹²Pb-trastuzumab potentiation of cell killing efficacy results from the perturbation of genes related to the mitotic spindle checkpoint and BASC (BRCA1-associated genome surveillance complex), suggesting cross-talk between DNA damage repair and the spindle damage response.

Abdel-Fatah TM, Perry C, Arora A, et al.
Is there a role for base excision repair in estrogen/estrogen receptor-driven breast cancers?
Antioxid Redox Signal. 2014; 21(16):2262-8 [PubMed] Free Access to Full Article Related Publications
Estrogen and estrogen metabolite-induced reactive oxygen species generation can promote oxidative DNA base damage. If unrepaired, base damaging lesions could accelerate mutagenesis, leading to a "mutator phenotype" characterized by aggressive behavior in estrogen-estrogen receptor (ER)-driven breast cancer. To test this hypothesis, we investigated 1406 ER(+) early-stage breast cancers with 20 years' long-term clinical follow-up data for DNA polymerase β (pol β), flap endonuclease 1 (FEN1), AP endonuclease 1 (APE1), X-ray cross-complementation group 1 protein (XRCC1), single-strand monofunctional uracil glycosylase-1 (SMUG1), poly (ADP-ribose) polymerase 1 (PARP1), ataxia telangiectasia mutated and Rad3 related (ATR), ataxia telangiectasia mutated (ATM), DNA-dependent protein kinase catalytic subunit (DNA-PKcs), Chk1, Chk2, p53, breast cancer susceptibility gene 1 (BRCA1), and topoisomerase 2 (TOPO2) expression. Multivariate Cox proportional hazards model was used to calculate a DNA repair prognostic index and correlated to clinicopathological variables and survival outcomes. Key base excision repair (BER) proteins, including XRCC1, APE1, SMUG1, and FEN1, were independently associated with poor breast cancer-specific survival (BCSS) (ps≤0.01). Multivariate Cox model stratified patients into four distinct prognostic sub-groups with worsening BCSS (ps<0.01). In addition, compared with prognostic sub-group 1, sub-groups 2, 3, and 4 manifest increasing tumor size, grade, mitosis, pleomorphism, differentiation, lymphovascular invasion, high Ki67, loss of Bcl-2, luminal B phenotype (ps≤0.01), and poor survival, including in patients who received tamoxifen adjuvant therapy (p<0.00001). Our observation supports the hypothesis that BER-directed stratification could inform appropriate therapies in estrogen-ER-driven breast cancers. Antioxid.

Zhang W, Gong W, Ai H, et al.
Gene expression analysis of lung adenocarcinoma and matched adjacent non-tumor lung tissue.
Tumori. 2014 May-Jun; 100(3):338-45 [PubMed] Related Publications
AIMS AND BACKGROUND: The aim of this study was to find disease-associated genes and gene functions in lung adenocarcinoma and matched adjacent non-tumor lung tissues with DNA microarray.
METHODS: We downloaded the gene expression profile GSE32863 from the Gene Expression Omnibus database including 58 lung adenocarcinoma and 58 adjacent non-tumor lung tissue samples. Data were preprocessed and the differentially expressed genes (DEGs) were identified using packages in the R computing language. The selected DEGs were further analyzed with bioinformatics methods. After the coexpression network of DEGs was constructed by STRING (Search Tool for the Retrieval of Interacting Genes/Proteins), we analyzed gene functions with DAVID (The Database for Annotation, Visualization and Integrated Discovery) and WebGestalt (WEB-based Gene Set Analysis Toolkit).
RESULTS: A total of 1429 genes were filtered as DEGs, including 873 downregulated genes and 556 upregulated genes, and the DEGs including CDC45, CCNB2, CDC20, MCM2, PTTG1, MCM4 and FEN1 were most significantly related to cell cycle and DNA replication.
CONCLUSION: The discovery of featured genes which were significantly related to cell cycle and DNA replication has potential for use in the clinic for the diagnosis of lung adenocarcinoma in the future. However, further experiments will be needed to confirm our result.

Xu J, Tian S, Yin Z, et al.
MicroRNA-binding site SNPs in deregulated genes are associated with clinical outcome of non-small cell lung cancer.
Lung Cancer. 2014; 85(3):442-8 [PubMed] Related Publications
BACKGROUND: Single-nucleotide polymorphisms (SNPs) in 3'-untranslated regions of cancer-related genes might affect regulation by microRNAs and contribute to cancer patients' outcome.
METHODS: We used public databases to identify SNPs within miRNA-binding sites in deregulated genes in non-small cell lung cancer (NSCLC). A total of 13 SNPs in 10 genes were included and genotyped by SNaPshot assay in 576 NSCLC patients. Associations between SNPs, overall survival (OS) and chemotherapy response were evaluated by Cox regression and logistic regression. We then examined the functionality of the significant polymorphisms.
RESULTS: Two SNPs (TYMS rs2790 and MICA rs9266825) were significantly associated with OS. In the combined analysis, an increasing number of unfavorable loci was associated with a poorer prognosis (P for trend<0.001) and patients having 2-3 unfavorable loci had a 1.61-fold elevated risk of death (95% confidence interval: 1.20-2.15), compared with those carrying 0-1 unfavorable loci. A significant effect of SNPs on platinum-based chemotherapy response was observed among 296 advanced NSCLC patients without surgical operation: rs2790, rs4246215 and rs1882. Further analysis using mRNA expression data from the HapMap suggested that these significant loci (FEN1 rs4246215, HDAC2 rs11391, MICA rs1882 and rs9266825) were closely associated with host genes expression. In vitro functional study for TYMS rs2790 was carried out. Luciferase assay showed a lower expression level for rs2790 G allele as compared with A allele, and the hsa-miR-1248 had an effect on modulation of TYMS gene.
CONCLUSION: Our data indicate that miRNA-binding site SNPs in deregulated genes may serve as candidate prognostic markers of NSCLC clinical outcome.

Abdel-Fatah TM, Russell R, Albarakati N, et al.
Genomic and protein expression analysis reveals flap endonuclease 1 (FEN1) as a key biomarker in breast and ovarian cancer.
Mol Oncol. 2014; 8(7):1326-38 [PubMed] Free Access to Full Article Related Publications
FEN1 has key roles in Okazaki fragment maturation during replication, long patch base excision repair, rescue of stalled replication forks, maintenance of telomere stability and apoptosis. FEN1 may be dysregulated in breast and ovarian cancers and have clinicopathological significance in patients. We comprehensively investigated FEN1 mRNA expression in multiple cohorts of breast cancer [training set (128), test set (249), external validation (1952)]. FEN1 protein expression was evaluated in 568 oestrogen receptor (ER) negative breast cancers, 894 ER positive breast cancers and 156 ovarian epithelial cancers. FEN1 mRNA overexpression was highly significantly associated with high grade (p = 4.89 × 10(-57)), high mitotic index (p = 5.25 × 10(-28)), pleomorphism (p = 6.31 × 10(-19)), ER negative (p = 9.02 × 10(-35)), PR negative (p = 9.24 × 10(-24)), triple negative phenotype (p = 6.67 × 10(-21)), PAM50.Her2 (p = 5.19 × 10(-13)), PAM50. Basal (p = 2.7 × 10(-41)), PAM50.LumB (p = 1.56 × 10(-26)), integrative molecular cluster 1 (intClust.1) (p = 7.47 × 10(-12)), intClust.5 (p = 4.05 × 10(-12)) and intClust. 10 (p = 7.59 × 10(-38)) breast cancers. FEN1 mRNA overexpression is associated with poor breast cancer specific survival in univariate (p = 4.4 × 10(-16)) and multivariate analysis (p = 9.19 × 10(-7)). At the protein level, in ER positive tumours, FEN1 overexpression remains significantly linked to high grade, high mitotic index and pleomorphism (ps < 0.01). In ER negative tumours, high FEN1 is significantly associated with pleomorphism, tumour type, lymphovascular invasion, triple negative phenotype, EGFR and HER2 expression (ps < 0.05). In ER positive as well as in ER negative tumours, FEN1 protein overexpression is associated with poor survival in univariate and multivariate analysis (ps < 0.01). In ovarian epithelial cancers, similarly, FEN1 overexpression is associated with high grade, high stage and poor survival (ps < 0.05). We conclude that FEN1 is a promising biomarker in breast and ovarian epithelial cancer.

Zhang B, Jia WH, Matsuda K, et al.
Large-scale genetic study in East Asians identifies six new loci associated with colorectal cancer risk.
Nat Genet. 2014; 46(6):533-42 [PubMed] Free Access to Full Article Related Publications
Known genetic loci explain only a small proportion of the familial relative risk of colorectal cancer (CRC). We conducted a genome-wide association study of CRC in East Asians with 14,963 cases and 31,945 controls and identified 6 new loci associated with CRC risk (P = 3.42 × 10(-8) to 9.22 × 10(-21)) at 10q22.3, 10q25.2, 11q12.2, 12p13.31, 17p13.3 and 19q13.2. Two of these loci map to genes (TCF7L2 and TGFB1) with established roles in colorectal tumorigenesis. Four other loci are located in or near genes involved in transcriptional regulation (ZMIZ1), genome maintenance (FEN1), fatty acid metabolism (FADS1 and FADS2), cancer cell motility and metastasis (CD9), and cell growth and differentiation (NXN). We also found suggestive evidence for three additional loci associated with CRC risk near genome-wide significance at 8q24.11, 10q21.1 and 10q24.2. Furthermore, we replicated 22 previously reported CRC-associated loci. Our study provides insights into the genetic basis of CRC and suggests the involvement of new biological pathways.

Duan F, Song C, Dai L, et al.
The significance of Exo1 K589E polymorphism on cancer susceptibility: evidence based on a meta-analysis.
PLoS One. 2014; 9(5):e96764 [PubMed] Free Access to Full Article Related Publications
The exonuclease1 (Exo1) gene is a key component of mismatch repair (MMR) by resecting the damaged strand, which is the only exonuclease involved in the human MMR system. The gene product is a member of the RAD2 nuclease family and functions in DNA replication, repair and recombination. However, whether Exo1 is required to activate MMR-dependent DNA damage response (DDR) remains unknown, the conclusions of the Exo1 polymorphisms on cancer susceptibility studies were not consistent. We carried out a meta-analysis of 7 case-control studies to clarify the association between the Exo1 K589E polymorphism and cancer risk. Overall,a significant association of the Exo1 K589E polymorphism with cancer risk in all genetic models (Lys vs Glu: OR = 1.51, 95%CI:1.39-1.99, P<0.01; Glu/Lys vs Glu/Glu: OR = 1.43, 95%CI:1.28-1.60, P<0.01; Lys/Lys vs Glu/Glu: OR = 2.45, 95%CI:1.90-3.17, P<0.01; Lys/Lys+Glu/Lys vs Glu/Glu: OR = 1.53, 95%CI:1.38-1.71, P<0.01; Glu/Glu vs Glu/Lys+Lys/Lys: OR =  2.27, 95%CI:1.79-2.89, P<0.01). In the stratified analysis by ethnicity, significantly increased risk was observed in Asian population (Lys vs Glu: OR = 1.53, 95%CI:1.39-1.69, P<0.01; Glu/Lys vs Glu/Glu: OR = 1.50, 95%CI:1.34-1.69, P<0.01; Lys/Lys vs Glu/Glu: OR = 2.48, 95%CI:1.84-3.34, P<0.01; Lys/Lys+Glu/Lys vs Glu/Glu: OR = 1.58, 95%CI:1.41-1.78, P<0.01; Glu/Glu vs Glu/Lys+Lys/Lys: OR = 2.18, 95%CI:1.62-2.93, P<0.01). Subgroup analysis based on smoking suggested Exo1 K589E polymorphism conferred significant risk among smokers (Lys/Lys+Glu/Lys vs Glu/Glu: OR = 2.16, 95%CI:1.77-2.63, P<0.01), but not in non-smokers (Lys/Lys+Glu/Lys vs Glu/Glu: OR = 0.89, 95%CI:0.64-1.24, P = 0.50). In conclusion, Exo1 K589E Lys allele may be used as a novel biomarker for cancer susceptibility, particularly in smokers.

Wang K, Xie C, Chen D
Flap endonuclease 1 is a promising candidate biomarker in gastric cancer and is involved in cell proliferation and apoptosis.
Int J Mol Med. 2014; 33(5):1268-74 [PubMed] Related Publications
As a DNA repair protein, flap endonuclease 1 (FEN1), a structure-specific 5' nuclease, plays pivotal roles in the maturation of Okazaki fragments, long-patch base excision repair, restarting of stalled replication forks and telomere maintenance. FEN1 possesses 5' endonuclease, 5' exonuclease and gap-endonuclease activities, which render it an essential node in maintaining genome fidelity. The aim of this study was to investigate the association between the expression level of FEN1 and gastric cancer and to explore the role of FEN1 in carcinogenesis and the progression of gastric cancer. The mRNA and protein expression of FEN1 in 42 matched pairs of human gastric tumor tissues and corresponding normal tissues were measured by semiquantitative reverse transcription-PCR and immunohistochemical staining. FEN1 expression was downregulated in the SGC-7901 gastric cancer cells following transfection with siRNA targeting the FEN1 gene. Western blot analysis was used to evaluate the protein expression of FEN1 in SGC-7901 human gastric cancer cells in order to verify the transfection efficiency of FEN1 siRNA. Moreover, cell proliferation was analyzed by MTS assay. The apoptosis of the cells was determined by flow cytometry. Our results revealed that FEN1 was overexpressed in gastric cancer in comparison to the corresponding normal gastric tissues (P<0.01). We further confirmed that FEN1 expression has a positive correlation with the degree of differentiation (P=0.027), lymphatic metastasis (P=0.001), tumor size (P=0.026) and TNM stage (P=0.020) of gastric cancer. A high FEN1 expression in SGC-7901 cells can be effectively downregulated by siRNA constructed to target the FEN1 gene. Moreover, the inhibition of FEN1 expression suppressed the proliferation and induced the apoptosis of SGC-7901 cells. Taken together, our results indicate that FEN1 may be a promising biomarker for the diagnosis of gastric cancer and individual therapy.

Chen B, Zhang Y, Wang Y, et al.
Curcumin inhibits proliferation of breast cancer cells through Nrf2-mediated down-regulation of Fen1 expression.
J Steroid Biochem Mol Biol. 2014; 143:11-8 [PubMed] Related Publications
Curcumin can inhibit cell proliferation of breast cancer, but the mechanism for this inhibition remains unclear. Over-expression of Flap endonuclease 1 (Fen1), a DNA repair-specific nuclease, is involved in the development of breast cancer. Nrf2 is a master regulator of cellular antioxidant defense systems. Curcumin can induce the expression of Nrf2 in both non-breast cancer cells and breast cancer cells. However, whether curcumin-induced inhibition of breast cancer cell proliferation may involve Nrf2-mediated Fen1 expression is not yet understood. In this study, we demonstrated that curcumin inhibited Fen1-dependent proliferation of MCF-7 cells and significantly induced Nrf2 protein expression while inhibiting Fen1 protein expression. Curcumin could down-regulate Fen1 gene expression in a Nrf2-dependent manner. Further investigation revealed that curcumin could lead to Nrf2 translocation from the cytoplasm to the nucleus and decrease Fen1 promoter activity by decreasing the recruitment of Nrf2 to the Fen1 promoter. These data suggest that curcumin may inhibit the proliferation of breast cancer cells through Nrf2-mediated down-regulation of Fen1 expression, which may be a new mechanism of curcumin-induced tumor growth inhibition.

Lv Z, Liu W, Li D, et al.
Association of functional FEN1 genetic variants and haplotypes and breast cancer risk.
Gene. 2014; 538(1):42-5 [PubMed] Related Publications
AIM: As a tumor suppressor, FEN1 plays an essential role in preventing tumorigenesis. Two functional germline variants (-69G>A and 4150G>T) in the FEN1 gene have been associated with DNA damage levels in coke-oven workers and multiple cancer risk in general populations. However, it is still unknown how these genetic variants are involved in breast cancer susceptibility.
METHODS: We investigated the association between these polymorphisms and breast cancer risk in two independent case-control sets consisted of a total of 1100 breast cancer cases and 1400 controls. The influence of these variations on FEN1 expression was also examined using breast normal tissues.
RESULTS: It was found that the FEN1-69GG genotypes were significantly correlated to increased risk for developing breast cancer compared with the -69AA genotype in both sets [Jinan set: odds ratios (OR)=1.41, 95% confidence interval (CI)=1.20-1.65, P=1.9×10(-5); Huaian set: OR=1.51, 95% CI=1.22-1.86, P=1.7×10(-4)]. Similar results were observed for 4150G>T polymorphism. The genotype-phenotype correlation analyses demonstrated that the -69G or 4150G allele carriers had more than 2-fold decreased FEN1 expression in breast tissues compared with -69A or 4150T carriers, suggesting that lower FEN1 expression may lead to higher risk for malignant transformation of breast cells.
CONCLUSION: Our findings highlight FEN1 as an important gene in human breast carcinogenesis and genetic variants in FEN1 confer susceptibility to breast cancer.

Abdel-Fatah TM, Perry C, Moseley P, et al.
Clinicopathological significance of human apurinic/apyrimidinic endonuclease 1 (APE1) expression in oestrogen-receptor-positive breast cancer.
Breast Cancer Res Treat. 2014; 143(3):411-21 [PubMed] Related Publications
Oestrogen metabolites can induce oxidative DNA base damage and generate potentially mutagenic apurinic sites (AP sites) in the genomic DNA. If unrepaired, mutagenic AP sites could drive breast cancer pathogenesis and aggressive phenotypes. Human apurinic/apyrimidinic endonuclease 1 (APE1) is a key DNA base excision repair (BER) protein and essential for processing AP sites generated either directly by oestrogen metabolites or during BER of oxidative base damage. Our hypothesis is that altered APE1 expression may be associated with aggressive tumour biology and impact upon clinical outcomes in breast cancer. In the current study, we have investigated APE1 protein expression in a large cohort of breast cancers (n = 1285) and correlated to clinicopathological features and survival outcomes. Low APE1 protein expression was associated with high histological grade (p < 0.000001), high mitotic index (p < 0.000001), glandular de-differentiation (p < 0.000001), pleomorphism (p = 0.003), absence of hormonal receptors (ER-/PgR-/AR-) (p < 0.0001) and presence of triple negative phenotype (p = 0.001). Low APE1 protein expression was associated with loss of BRCA1, low XRCC1, low FEN1, low SMUG1 and low pol β (ps < 0.0001). High MIB1 (p = 0.048), bcl-2 negativity (p < 0.0001) and low TOP2A (p < 0.0001) were likely in low APE1 tumours. In the ER-positive sub-group, specifically, low APE1 remains significantly associated with high histological grade, high mitotic index, glandular de-differentiation (ps < 0.00001) and poor breast cancer specific survival (p = 0.007). In the ER-positive cohort that received adjuvant endocrine therapy, low APE1 protein expression is associated with poor survival (p = 0.006). In multivariate analysis, low APE1 remains independently associated with poor survival in ER-positive tumours (p = 0.048). We conclude that low APE1 expression may have prognostic and predictive significance in ER-positive breast cancers.

Hu X, Xing L, Jiao Y, et al.
BTG2 overexpression increases the radiosensitivity of breast cancer cells in vitro and in vivo.
Oncol Res. 2013; 20(10):457-65 [PubMed] Related Publications
Antiproliferative gene B-cell translocation gene, member 2 (BTG2) is a member of the BTG/TOB antiproliferative gene family. In this study, we investigated the effect of BTG2 gene overexpression on the radiosensitivity of breast cancer cells in vitro and in vivo. Results show that in human breast cancer cell line MCF-7 stably overexpressing BTG2 gene, cell sensitivity to ionizing radiation increased. The MCF-7-BTG2 cells were more susceptible to radiation-caused apoptosis with decreased cyclin B1, cyclin D1, Ku70, FEN-1, and XRCC1 protein expression as well as increased BAX protein expression. The findings indicate for the first time that BTG2 can improve the radiosensitivity of breast cancer cells by affecting cell cycle distribution, enhancing radiation-induced apoptosis, and inhibiting DNA repair-related protein expression.

Qian L, Luo Q, Zhao X, Huang J
Pathways enrichment analysis for differentially expressed genes in squamous lung cancer.
Pathol Oncol Res. 2014; 20(1):197-202 [PubMed] Related Publications
Squamous lung cancer (SQLC) is a common type of lung cancer, but its oncogenesis mechanism is not so clear. The aim of this study was to screen the potential pathways changed in SQLC and elucidate the mechanism of it. Published microarray data of GSE3268 series was downloaded from Gene Expression Omnibus (GEO). Significance analysis of microarrays was performed using software R, and differentially expressed genes (DEGs) were harvested. The functions and pathways of DEGs were mapped in Gene Otology and KEGG pathway database, respectively. A total of 2961 genes were filtered as DEGs between normal and SQLC cells. Cell cycle and metabolism were the mainly changed functions of SQLC cells. Meanwhile genes such as MCM, RFC, FEN1, and POLD may induce SQLC through DNA replication pathway, and genes such as PTTG1, CCNB1, CDC6, and PCNA may be involved in SQLC through cell cycle pathway. It is demonstrated that pathway analysis is useful in the identification of target genes in SQLC.

Chen Y, Zhu M, Zhang Z, et al.
A NEIL1 single nucleotide polymorphism (rs4462560) predicts the risk of radiation-induced toxicities in esophageal cancer patients treated with definitive radiotherapy.
Cancer. 2013; 119(23):4205-11 [PubMed] Related Publications
BACKGROUND: To assess the association between single nucleotide polymorphisms (SNPs) of base-excision repair genes and clinical outcomes, the roles of genetic variants of 3 selected genes-flap structure-specific endonuclease 1 (FEN1), 8-hydroxyguanine DNA glycosylase (hOGG1), and nei endonuclease VIII-like 1 (NEIL1)--were investigated in radiation-induced esophageal toxicity (RIET), radiation pneumonitis (RP), and overall survival (OS) after radio(chemo)therapy in patients with esophageal squamous cell carcinoma (ESCC).
METHODS: NEIL1 reference SNP 4462560 (rs4462560) and rs7402844, hOGG1 rs1052133 and rs293795, and FEN1 rs4246215 and rs174538 were genotyped in 187 patients with ESCC who received definitive radiotherapy with or without chemotherapy. Kaplan-Meier cumulative probabilities and Cox proportional hazards regression models were used to assess the effect of the genotypes on the risk of RIET, RP, and OS.
RESULTS: The authors observed that patients who had the NEIL1 rs4462560 GC/CC genotype had a statistically significantly lower risk of both grade ≥ 2 acute radiation-induced esophageal toxicity (RIET) (adjusted hazard ratio [HR], 0.421; 95% confidence interval [CI], 0.207-0.856; P = .017) and grade ≥ 2 acute radiation pneumonitis (RP) (adjusted HR, 0.392; 95% CI, 0.163-0.946; P = .037) compared with patients who had the GG genotype, but the genotype did not affect OS (adjusted HR, 0.778; 95% CI, 0.471-1.284; P = .326). There were no significant findings for other the SNPs under investigation.
CONCLUSIONS: The NEIL1 rs4462560 SNP may serve as a predictor of acute RIET and RP risk but not of OS. Larger prospective studies are needed to validate these findings.

Corral R, Lewinger JP, Joshi AD, et al.
Genetic variation in the base excision repair pathway, environmental risk factors, and colorectal adenoma risk.
PLoS One. 2013; 8(8):e71211 [PubMed] Free Access to Full Article Related Publications
Cigarette smoking, high alcohol intake, and low dietary folate levels are risk factors for colorectal adenomas. Oxidative damage caused by these three factors can be repaired through the base excision repair pathway (BER). We hypothesized that genetic variation in BER might modify colorectal adenoma risk. In a sigmoidoscopy-based study, we examined associations between 182 haplotype tagging SNPs in 14 BER genes, and colorectal adenoma risk, and examined their potential role as modifiers of the effect cigarette smoking, alcohol intake, and dietary folate levels. Among all individuals, no statistically significant associations between BER SNPs and adenoma risk persisted after correction for multiple comparisons. However, among Asian-Pacific Islanders we observed two SNPs in FEN1 and one in NTHL1, and among African-Americans one SNP in APEX1 that were associated with colorectal adenoma risk. Significant associations were also observed between SNPs in the NEIL2 gene and rectal adenoma risk. Three SNPS modified the effect of smoking (MUTYH interaction p = 0.002; OGG1 interaction p = 0.013); FEN1 interaction p = 0.013)), one SNP in LIG3 modified the effect of alcohol consumption (interaction p = 0.024) and two SNPs in LIG3 modified the effect of dietary folate (interaction p = 0.001 and p = 0.08) on colorectal adenoma risk. These findings support a role for genetic variants in the BER pathway as potential modifiers of colorectal adenoma risk. Our findings strengthen the role of oxidative damage induced by key lifestyle and dietary risk factors in colorectal adenoma formation.

De Luca P, Moiola CP, Zalazar F, et al.
BRCA1 and p53 regulate critical prostate cancer pathways.
Prostate Cancer Prostatic Dis. 2013; 16(3):233-8 [PubMed] Related Publications
BACKGROUND: Loss or mutations of the BRCA1 gene are associated with increased risk of breast and ovarian cancers and with prostate cancer (PCa) aggressiveness. Previously, we identified GADD153 as a target of BRCA1 protein, which increases doxorubicin sensitivity in human p53 -/- PCa cells (PC3). Considering that p53 is a crucial target in cancer therapy, in this work we investigated p53 role in the regulation of transcription of GADD153.
METHODS: We performed reverse transcription quantitative PCR (RT-qPCR), western blot and luciferase assays to analyze GADD153 and/or BRCA1 expression in response to ultraviolet or doxorubicin exposure in PC3 p53 stable-transfected cells and LNCaP (p53+/+) cells. BRCA1 protein recruitment to GADD153 promoter was studied by chromatin immunoprecipitation-qPCR. To assess expression of BRCA1 and/or p53 target genes, we used a panel of stable-transfected PCa cell lines. We finally analyzed these genes in vivo using BRCA1-depleted PCa xenograft models.
RESULTS: We found that GADD153 was highly induced by doxorubicin in PC3 cells; however, this response was totally abolished in LNCaP (p53wt) and in p53-restituted PC3 cells. Furthermore, BRCA1 protein associates to GADD153 promoter after DNA damage in the presence of p53. Additionally, we demonstrated that BRCA1 and/or p53 modulate genes involved in DNA damage and cell cycle regulation (cyclin D1, BLM, BRCA2, DDB2, p21(WAF1/CIP1), H3F3B, GADD153, GADD45A, FEN1, CCNB2), EMT (E-cadherin, β-catenin, vimentin, fibronectin, slug, snail) and Hedgehog pathways (SHH, IHH, DHH, Gli1, PATCH1). Furthermore, xenograft studies demonstrated that BRCA1 knockdown in PC3 cells increased tumor growth and modulated these genes in vivo.
CONCLUSIONS: Although BRCA1 induces GADD153 in a p53 independent manner, p53 abolished GADD153 induction in response to DNA damage. In addition, several important PCa targets are modulated by BRCA1 and p53. Altogether, these data might be important to understand the therapy response of PCa patients.

Li WQ, Hu N, Hyland PL, et al.
Genetic variants in DNA repair pathway genes and risk of esophageal squamous cell carcinoma and gastric adenocarcinoma in a Chinese population.
Carcinogenesis. 2013; 34(7):1536-42 [PubMed] Free Access to Full Article Related Publications
The DNA repair pathways help to maintain genomic integrity and therefore genetic variation in the pathways could affect the propensity to develop cancer. Selected germline single nucleotide polymorphisms (SNPs) in the pathways have been associated with esophageal cancer and gastric cancer (GC) but few studies have comprehensively examined the pathway genes. We aimed to investigate associations between DNA repair pathway genes and risk of esophageal squamous cell carcinoma (ESCC) and GC, using data from a genome-wide association study in a Han Chinese population where ESCC and GC are the predominant cancers. In sum, 1942 ESCC cases, 1758 GC cases and 2111 controls from the Shanxi Upper Gastrointestinal Cancer Genetics Project (discovery set) and the Linxian Nutrition Intervention Trials (replication set) were genotyped for 1675 SNPs in 170 DNA repair-related genes. Logistic regression models were applied to evaluate SNP-level associations. Gene- and pathway-level associations were determined using the resampling-based adaptive rank-truncated product approach. The DNA repair pathways overall were significantly associated with risk of ESCC (P = 6.37 × 10(-4)), but not with GC (P = 0.20). The most significant gene in ESCC was CHEK2 (P = 2.00 × 10(-6)) and in GC was CLK2 (P = 3.02 × 10(-4)). We observed several other genes significantly associated with either ESCC (SMUG1, TDG, TP53, GTF2H3, FEN1, POLQ, HEL308, RAD54B, MPG, FANCE and BRCA1) or GC risk (MRE11A, RAD54L and POLE) (P < 0.05). We provide evidence for an association between specific genes in the DNA repair pathways and the risk of ESCC and GC. Further studies are warranted to validate these associations and to investigate underlying mechanisms.

van Pel DM, Barrett IJ, Shimizu Y, et al.
An evolutionarily conserved synthetic lethal interaction network identifies FEN1 as a broad-spectrum target for anticancer therapeutic development.
PLoS Genet. 2013; 9(1):e1003254 [PubMed] Free Access to Full Article Related Publications
Harnessing genetic differences between cancerous and noncancerous cells offers a strategy for the development of new therapies. Extrapolating from yeast genetic interaction data, we used cultured human cells and siRNA to construct and evaluate a synthetic lethal interaction network comprised of chromosome instability (CIN) genes that are frequently mutated in colorectal cancer. A small number of genes in this network were found to have synthetic lethal interactions with a large number of cancer CIN genes; these genes are thus attractive targets for anticancer therapeutic development. The protein product of one highly connected gene, the flap endonuclease FEN1, was used as a target for small-molecule inhibitor screening using a newly developed fluorescence-based assay for enzyme activity. Thirteen initial hits identified through in vitro biochemical screening were tested in cells, and it was found that two compounds could selectively inhibit the proliferation of cultured cancer cells carrying inactivating mutations in CDC4, a gene frequently mutated in a variety of cancers. Inhibition of flap endonuclease activity was also found to recapitulate a genetic interaction between FEN1 and MRE11A, another gene frequently mutated in colorectal cancers, and to lead to increased endogenous DNA damage. These chemical-genetic interactions in mammalian cells validate evolutionarily conserved synthetic lethal interactions and demonstrate that a cross-species candidate gene approach is successful in identifying small-molecule inhibitors that prove effective in a cell-based cancer model.

Chen YD, Zhang X, Qiu XG, et al.
Functional FEN1 genetic variants and haplotypes are associated with glioma risk.
J Neurooncol. 2013; 111(2):145-51 [PubMed] Related Publications
As a tumor suppressor, FEN1 plays an essential role in keeping genomic instability and preventing tumorigenesis. There are two functional genetic variants (-69G>A and 4150G>T) in the FEN1 gene, which have been associated with DNA damage levels in coke-oven workers as well as risks of lung cancer, hepatocellular carcinoma, esophageal cancer, gastric cancer and colorectal cancer in general populations. However, it is still unknown how these polymorphisms and their haplotypes are associated with glioma risk. Therefore, we investigated the role of these polymorphisms in glioma development using a case-control design in a Chinese population. The impact of the haplotypes constructed by these two polymorphisms on glioma risk was also examined. It was observed that the FEN1-69GG or 4150GG genotype were significantly associated to increased glioma risk compared with the -69AA or 4150TT genotype [Odds ratios (OR) = 1.87, 95 % confidence interval (CI) = 1.23-2.85, P = 0.003; or OR = 1.87, 95 % CI = 1.23-2.84, P = 0.003). The associations were more pronounced among female subjects (For -69AG or GG genotype: OR = 2.35, 95 % CI = 1.22-4.52; for 4150TG or GG genotype: OR = 2.33, 95 % CI = 1.21-4.48) and patients with grade 1 or 2 disease (For -69AG or GG genotype: OR = 2.21, 95 % CI = 1.20-4.05; for 4150TG or GG genotype: OR = 2.45, 95 % CI = 1.31-4.58). Additionally, the G(-69)G(4150) haplotype was also significantly associated with increased glioma risk compared with the A(-69)T(4150) haplotype. Our results suggest that FEN1 polymorphisms and haplotypes are associated with glioma risk.

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