Expression Of FEN1 Research Articles

The hijacking of HBV by small extracellular vesicles inhibits M1 macrophages to facilitate immune evasion

Small extracellular vesicles (sEVs) have the ability to transfer genetic material between cells, but their role in mediating HBV infection and regulating M1 macrophages to promote immune evasion remains unclear. In this study, we utilized PMA + LPS + IFN-γ to induce THP-1 into M1 macrophages. We then extracted sEVs from HepG2.2.15 cell and treated the M1 macrophages with these sEVs. QPCR detection revealed the presence of HBV-DNA in the M1 macrophages. Additionally, RT-qPCR and WB analysis demonstrated a significantly decreased in the expression of TLR4, NLRP3, pro-caspase-1, caspase-1p20, IL-1β and IL-18 in the M1 macrophages (P < 0.05). Furthermore, RT-qPCR results displayed high expression levels of that miR-146a and FEN-1 in the sEVs derived from HepG2.2.15 cells (P < 0.01). RT -qPCR and WB analysis showed that these sEVs enhanced the expression of FEN-1 or miR-146a in the M1 macrophages through miR-146a or FEN-1 (P < 0.05), while simultaneously reducing the expression of TLR4, NLRP3, caspase-1p20, IL-1β and IL-18 in the M1 macrophages (P < 0.05). In summary, our findings indicate that sEVs loaded with HBV inhibit the inflammatory function of M1 macrophages and promote immune escape. Additionally, miR-146a and FEN-1 present in the sEVs play a crucial role in this process.

Harmine inhibits pulmonary fibrosis through regulating DNA damage repair-related genes and activation of TP53-Gadd45α pathway

BackgroundHarmine has many pharmacological activities and has been found to significantly inhibit the fibrosis of keloid fibroblasts. DNA damage repair (DDR) is essential to prevent fibrosis. This study aimed to investigate the effects of harmine on pulmonary fibrosis and its underlying mechanisms. MethodsBleomycin and TGF-β1 were used to construct pulmonary fibrosis models in vivo and in vitro, then treated with harmine to explore harmine’s effects in treating experimental pulmonary fibrosis and its related mechanisms. Then, RNA sequencing was applied to investigate further the crucial DDR-related genes and drug targets of harmine against pulmonary fibrosis. Finally, the expression levels of DDR-related genes were verified by real-time quantitative PCR (RT-qPCR) and western blot. ResultsOur in vivo experiments showed that harmine treatment could improve weight loss and lung function and reduce tissue fibrosis in mice with pulmonary fibrosis. The results confirmed that harmine could inhibit the viability and migration of TGF-β1-induced MRC-5 cells, induce their apoptosis, and suppress the F-actin expression, suggesting that harmine could suppress the phenotypic transition from lung fibroblasts to lung myoblasts. In addition, RNA sequencing identified 1692 differential expressed genes (DEGs), and 10 DDR-related genes were screened as critical DDR-related genes. RT-qPCR and western blotting showed that harmine could down-regulate the expression of CHEK1, ERCC1, ERCC4, POLD1, RAD51, RPA1, TOP1, and TP53, while up-regulate FEN1, H2AX and GADD45α expression. ConclusionsHarmine may inhibit pulmonary fibrosis by regulating DDR-related genes and activating the TP53-Gadd45α pathway.

27-hydroxycholesterol and DNA damage repair: implication in prostate cancer.

We previously reported that cholesterol homeostasis in prostate cancer (PC) is regulated by 27-hydroxycholesterol (27HC) and that CYP27A1, the enzyme that converts cholesterol to 27HC, is frequently lost in PCs. We observed that restoring the CYP27A1/27HC axis inhibited PC growth. In this study, we investigated the mechanism of 27HC-mediated anti-PC effects. We employed in vitro models and human transcriptomics data to investigate 27HC mechanism of action in PC. LNCaP (AR+) and DU145 (AR-) cells were treated with 27HC or vehicle. Transcriptome profiling was performed using the Affymetrix GeneChip™ microarray system. Differential expression was determined, and gene set enrichment analysis was done using the GSEA software with hallmark gene sets from MSigDB. Key changes were validated at mRNA and protein levels. Human PC transcriptomes from six datasets were analyzed to determine the correlation between CYP27A1 and DNA repair gene expression signatures. DNA damage was assessed via comet assays. Transcriptome analysis revealed 27HC treatment downregulated Hallmark pathways related to DNA damage repair, decreased expression of FEN1 and RAD51, and induced "BRCAness" by downregulating genes involved in homologous recombination regulation in LNCaP cells. Consistently, we found a correlation between higher CYP27A1 expression (i.e., higher intracellular 27HC) and decreased expression of DNA repair gene signatures in castration-sensitive PC (CSPC) in human PC datasets. However, such correlation was less clear in metastatic castration-resistant PC (mCRPC). 27HC increased expression of DNA damage repair markers in PC cells, notably in AR+ cells, but no consistent effects in AR- cells and decreased expression in non-neoplastic prostate epithelial cells. While testing the clinical implications of this, we noted that 27HC treatment increased DNA damage in LNCaP cells via comet assays. Effects were reversible by adding back cholesterol, but not androgens. Finally, in combination with olaparib, a PARP inhibitor, we showed additive DNA damage effects. These results suggest 27HC induces "BRCAness", a functional state thought to increase sensitivity to PARP inhibitors, and leads to increased DNA damage, especially in CSPC. Given the emerging appreciation that defective DNA damage repair can drive PC growth, future studies are needed to test whether 27HC creates a synthetic lethality to PARP inhibitors and DNA damaging agents in CSPC.

Identification of FEN1 as a prognostic marker and novel therapeutic target in gastric cancer harboring TP53 mutations.

e16057 Background: As a common tumor suppressor gene, TP53 gene mutation leads to persistent activation of multiple downstream effectors that drive the cancer phenotype. Approximately 50% of gastric cancer (GC) patients harbor TP53 mutations, which confer stronger tumor biology and shorter overall survival (OS). Given that TP53-mutated proteins have proven difficult to target directly, identifying genes that function closely with TP53 and targeting these genes appears to be a promising therapeutic strategy for TP53-mutated GC patients. Methods: TP53 functionally sensitive genes were identified by evaluating the correlation between gene-dependent scores from CRISPR knockout screens and TP53 mRNA expression in TP53 mutant GC cell lines in the Cancer Cell Line Encyclopedia (CCLE) database. If the correlation coefficient is ≥0.6, the gene was considered as TP53 functional sensitive gene. Then TP53 functionally sensitive genes associated with prognosis were screened out in The Cancer Genome Atlas (TCGA). PockDrug-Server was used to predict drug susceptibility of candidate genes. Results: The results showed that in 9 GC cell lines with TP53 mutations and 14 with TP53 wild-type, 4 genes (KLF5, FEN1, CCNA2, CCNB1) were identified as TP53 functional sensitive genes. Among the 4 genes, only FEN1 expression was significantly correlated with OS (HR=1.85, 95CI 1.06−3.26, P=0.029). Multivariate Cox regression analysis showed that high FEN1 expression was an independent predictor of prognosis in TP53-mutated GC. Pocket druggability prediction analysis presented that FEN1 had 8 drug-able pockets, four of which all have a druggability score of 0.8 or higher, including one pocket with a score of 1. Conclusions: These findings suggested that FEN1 was promising prognostic marker and therapeutic target in TP53-mutated GC.

RNA G-Quadruplex within the 5′-UTR of FEN1 Regulates mRNA Stability under Oxidative Stress

Reactive oxygen species (ROS) are a group of highly oxidative molecules that induce DNA damage, affecting DNA damage response (DDR) and gene expression. It is now recognized that DNA base excision repair (BER) is one of the important pathways responsible for sensing oxidative stress to eliminate DNA damage, in which FEN1 plays an important role in this process. However, the regulation of FEN1 under oxidative stress is still unclear. Here, we identified a novel RNA G-quadruplex (rG4) sequence in the 5'untranslated region (5'UTR) of FEN1 mRNA. Under oxidative stress, the G bases in the G4-forming sequence can be oxidized by ROS, resulting in structural disruption of the G-quadruplex. ROS or TMPyP4, a G4-structural ligand, disrupted the formation of G4 structure and affected the expression of FEN1. Furthermore, pull-down experiments identified a novel FEN1 rG4-binding protein, heterogeneous nuclear ribonucleoprotein A1 (hnRNPA1), and cellular studies have shown that hnRNPA1 plays an important role in regulating FEN1 expression. This work demonstrates that rG4 acts as a ROS sensor in the 5'UTR of FEN1 mRNA. Taken together, these results suggest a novel role for rG4 in translational control under oxidative stress.

Abstract 5342: Identifying therapeutic targets in combination with PARP inhibitors using a 63-gene signature in triple-negative breast cancer

Abstract Triple-negative breast cancer (TNBC) is a difficult-to-treat breast cancer with limited therapeutic options. PARP inhibitors (PARPi) have emerged as a promising targeted therapeutic for TNBC patients with germline mutations in BRCA1/2, recently demonstrating inhibition of micrometastatic disease. However, studies have also suggested that PARPi may have efficacy in TNBC, regardless of BRCA mutation status. We have previously identified a 63-gene signature associated with the DNA damage response to PARPi, with an overall accuracy of 86% in a cohort of patient-derived xenografts and a predicted sensitivity to PARPi in 45% of untreated TNBC patients. Additionally, our 63-gene signature can be used to identify genes implicated in intrinsic resistance. Therefore, we hypothesize that genes from our 63-gene signature can be used to identify potential targets for combination therapies with PARPi. We selected six candidate genes from our 63-gene signature: BARD1, BUB1, FEN1, RRM2, EXO1, and USP1. For each of the selected genes, we performed siRNA knockdown experiments in MDAMB231, a TNBC cell line. Using flow cytometry, we found that talazoparib, a potent PARPi plus siBARD1, increased the proportion of cells in G2 phase, with 80% γ-H2AX-positive cells and 60% cleaved-caspase-3-positive cells. Interestingly, the DNA damage response was comparable to what was observed with the combination of talazoparib and carboplatin. Talazoparib + siBUB1 also induced DNA damage in 51% of cells (P&amp;lt;0.001), and apoptosis in 20% of cells (P=0.002). Similar effects for enhanced DNA damage and apoptosis with talazoparib was observed for siUSP1, siFEN1, and siEXO1. Furthermore, the combination of siBARD1 + talazoparib resulted in a 49% reduction in cell migration in comparison to siBARD1 alone (P=0.0008), and the combination of siBUB1 and talazoparib demonstrated a 44% reduction in cell migration in comparison to talazoparib alone (P=0.04). Moreover, we evaluated gene expression in different breast cancer subtypes, and correlated with prognosis in a cohort of 881 untreated breast cancer patients. We found elevated expression of RRM2, FEN1, and EXO1 amongst more aggressive breast cancer subtypes (basal and HER2), and that their overexpression were associated with a poorer 10-year distant metastasis-free survival (RRM2, P&amp;lt;0.00001; FEN1, P=0.00012; EXO1, P&amp;lt;0.00001). Taken together, genes from our 63-gene signature can be used to identify therapeutic targets that have demonstrated either enhanced DNA damage, cell death, or cell migration in combination with PARPi. With prognostic implications, these targets also demonstrate therapeutic potential in the clinic and warrant further investigation. Citation Format: Audrey Hubert, Alexia Cotte, Nelly Bechir, Takrima Haque, Saima N. Hassan. Identifying therapeutic targets in combination with PARP inhibitors using a 63-gene signature in triple-negative breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 5342.

FEN1 Status and Its Correlation with Clinicopathologic Characteristic in Colorectal Cancer.

The goal of this study was to investigate the status of FEN1 in colorectal cancer (CRC) and determine the potential correlation between FEN1 expression level and clinicopathological parameters in CRC patients. Expression of FEN1 in CRC tissue on tissue microarray was detected using immunohistochemistry (IHC). The relationship between FEN1 expression status and clinicopathologic characteristics of CRC was analyzed by the Chi-square test. The survival data of TCGA Colon Cancer (COAD) were obtained from ucsc xena browser (https://xenabrowser.net/). Patients were separated into higher and lower expression groups by median FEN1 expression. The association with prognosis of CRC patients was determined by Kaplan-Meier survival analysis with Log-rank test. FEN1expression level and cellular localization had wide variability among different individuals; we classified the staining results into four types: both positive in nucleus and cytoplasm, both negative in nucleus and cytoplasm, only positive in the nucleus, only positive in the cytoplasm. Moreover, FEN1 expression status only correlated with patient's metastasis status, and the patients in the NLCL group showed more risk of cancer cell metastasis. Our results indicate that FEN1 expression level and cellular localization had wide variability in CRC and is not a promising biomarker in CRC.

Downregulation of MEIS1 mediated by ELFN1-AS1/EZH2/DNMT3a axis promotes tumorigenesis and oxaliplatin resistance in colorectal cancer

Oxaliplatin is widely used in the frontline treatment of colorectal cancer (CRC), but an estimated 50% of patients will eventually stop responding to treatment due to acquired resistance. This study revealed that diminished MEIS1 expression was detected in CRC and harmed the survival of CRC patients. MEIS1 impaired CRC cell viabilities and tumor growth in mice and enhanced CRC cell sensitivity to oxaliplatin by preventing DNA damage repair. Mechanistically, oxaliplatin resistance following MEIS1 suppression was critically dependent on enhanced FEN1 expression. Subsequently, we confirmed that EZH2-DNMT3a was assisted by lncRNA ELFN1-AS1 in locating the promoter of MEIS1 to suppress MEIS1 transcription epigenetically. Based on the above, therapeutics targeting the role of MEIS1 in oxaliplatin resistance were developed and our results suggested that the combination of oxaliplatin with either ELFN1-AS1 ASO or EZH2 inhibitor GSK126 could largely suppress tumor growth and reverse oxaliplatin resistance. This study highlights the potential of therapeutics targeting ELFN1-AS1 and EZH2 in cell survival and oxaliplatin resistance, based on their controlling of MEIS1 expression, which deserve further verification as a prospective therapeutic strategy.

MiR-4324 inhibits ovarian cancer progression by targeting FEN1

BackgroundOvarian cancer is one of the most lethal malignancies, with a 1.9% mortality rate worldwide. The dysregulation of the FEN1 gene and miR-4324 has been associated with cancer progression. However, the relationship between miR-4324 and-FEN1 requires further investigation.MethodsmiR-4324 and FEN1 expressions in ovarian cancer tissues and cell lines were measured via RT-qPCR. The interaction between miR-4324 and FEN1 was assessed using luciferase and RNA pull-down assays. The effects of miR-4324 and FEN1 on cell proliferation, adhesion and apoptosis were determined by CCK-8, BrdU, colony formation, cell adhesion, Caspase-3 and western blot assays in ovarian cancer cell lines CaOV3 and OVCAR3, respectively.ResultsThe results showed that miR-4324 expression was significantly decreased and FEN1 expression was enhanced in ovarian cancer tissues and cell lines. miR-4324 inhibitor promoted cell proliferation, adhesion and migration, and prevented apoptosis. Furthermore, the downregulation of FEN1 inhibited ovarian cancer cell growth and increased apoptosis. miR-4324 inhibited FEN1 expression and repressed ovarian cancer progression.ConclusionOur study found that miR-4324 inhibited FEN1 expression, suppressed cell growth, and increased apoptosis in ovarian cancer cells. Therefore, we identified miR-4324 and FEN1 as potential therapeutic targets for ovarian cancer treatment.

PARP inhibitor BMN-673 induced apoptosis by trapping PARP-1 and inhibiting base excision repair via modulation of pol-β in chromatin of breast cancer cells

PARP inhibitors emerged as clinically effective anti-tumor agents in combination with DNA damaging agents but the toxicity of DNA damaging agents and their off-target effects caused serious problems in cancer therapy. They confer cytotoxicity in cancer cells both by catalytic inhibition and trapping of PARP-1 at the DNA damage site. There is a lack of direct evidence to quantitatively determine the trapped PARP-1 in cellular DNA. Here, we have precisely evaluated the mechanism of PARP trapping mediated anti-cancer action of Quinacrine (QC), BMN-673, and their combination (QC + BMN-673) in breast cancer cells. We introduced a strategy to measure the cellular PARP trapping potentiality of BMN-673 in QC pretreated cells using a fluorescence-based assay system. It was found that QC+ BMN-673 induced apoptosis by triggering DNA damage in breast cancer cells. Treatment with QC + BMN-673 stimulated the expression of PARP-1 in the chromatin compared to that of PARP-2 and PARP-3. QC + BMN-673 treatment also caused a dose-dependent and time-dependent accumulation of PARP-1 and inhibition of PARylation in the chromatin. Upregulation of BER components (pol-β and FEN-1), an unchanged HR and NHEJ pathway proteins, and reduction of luciferase activity of the cells transfected with R-p21-P (LP-BER) were noted in combined drug-treated cells. Interestingly, silencing of pol-β resulted in unchanged PARP-1 trapping and PAR activity in the chromatin with increasing time after QC + BMN-673 treatment without altering APC and FEN-1 expression. Thus, our data suggested that the QC + BMN-673 augmented breast cancer cell death by pol-β mediated repair inhibition primarily through trapping of PARP-1 besides PARP-1 catalytic inhibition.

Ginger modulates gene expression of oxidative stress, single and double DNA strand breaks, and micronucleus induced by variant durations and doses of monosodium glutamate in mice

This study aims to compare the genotoxic effects of low and high MSG doses in short and long term (6-12 weeks) exposure, as well as to investigate the potential protective effect of ginger co-administration against MSG genotoxicity. The expression of antioxidant genes (GST, MT1, CAT) and single and double strand DNA repair genes (XRCC1, FEN1) were analyzed also to detect DNA damage using the micronucleus assay. 120 Swiss albino male mice were allocated into six groups for each time interval exposure. Group 1 (Control), Group 2 received daily 160 mg/kg b.wt ginger, Group 3 (100 mg/kg b.wt MSG), Group 4 (240 mg/kg b.wt MSG), Group 5 (100 mg/kg b.wt MSG and 160 mg/kg b.wt ginger) and Group 6 (240 mg/kg b.wt MSG and 160 mg/kg b.wt ginger). Results revealed that high dose of MSG significantly increased GST expression in short- and long-term exposure. While short-term exposure to MSG both doses induced significant upregulation of CAT expression. The expression level of XECC1 was significantly increased by the MSG high dose in short-term treatment. Both doses significantly increased FEN1 expression level, particularly high dose of MSG in long-term exposure. The expressions of antioxidant genes and DNA repair genes are significantly downregulated in short and long exposure by both doses when co-administered with ginger. Moreover, long-term MSG exposure is associated with an increase micronucleus frequency. We concluded that MSG induced oxidative stress and DNA damage in mice. Additionally, ginger could be a potential candidate agent for reducing the genotoxicity caused by MSG.

Prec-O1-01 - Increased chlormethine induced DNA double stranded breaks in malignant T cells from mycosis fungoides skin lesions

<h3>Background:</h3> Cutaneous T-cell lymphoma (CTCL) is a heterogeneous group of extranodal non-Hodgkin's lymphoma. Mycosis fungoides (MF) is the most common types of CTCL and considered as a malignancy of skin-resident T cells. Chlormethine (CL), also known as mechlorethamine or nitrogen mustard, is a synthetic agent with well-known alkylating capacity. Its topical application has a long tradition in dermatology, as CL-containing products have been used for the treatment of MF since 1940. Recently, a novel CL gel formulation has been approved for the treatment of skin lesions in MF adult patients. <h3>Objective:</h3> Here we aim to study the impact of CL on malignant skin T cells regarding their susceptibility to treatment, proliferation, DNA double strand breaks and the expression of alkylated-nucleotides-excision genes. <h3>Methods:</h3> Tumour blood or skin T cells were isolated by magnetic-activated cell (MACS) sorting. Susceptibility to CL exposure was evaluated by MTT assay. Proliferation and DNA double strand breaks upon CL exposure were detected by BrdU proliferation assay and flowcytometry for γH2AX Ser139. Expression of alkylated-nucleotides-excision genes was measured by reverse transcription quantitative PCR (RT-qPCR). <h3>Results:</h3> While CL exposure in vitro decreased time- and dose-dependently total blood T-cell viability, it did not statistically significantly influence neither blood nor skin T-cell proliferation. Of interest, when acting on skin T cells, CL induce DNA double stranded breaks predominately in the subpopulation of MF clonal malignant skin T cells but not the non-tumoral healthy T cells. Quantitative real-time PCR uncovered that several important genes involved in rescue of alkylated nucleotides were generally decreased in tumor T cells and CL exposure in vitro further significantly decreased the expression of FEN1 and BRCA2, two major alkylated-nucleotides-excision-repair genes. <h3>Conclusion:</h3> This study sheds light on how CL affects malignant skin T cells from patients with MF and provides additional rationale for considering it as an early and valuable skin-directed treatment option for skin lymphoma.

Late p65 nuclear translocation in glioblastoma cells indicates non-canonical TLR4 signaling and activation of DNA repair genes

Glioblastoma (GBM) is the most aggressive brain primary malignancy. Toll-like receptor 4 (TLR4) has a dual role in cell fate, promoting cell survival or death depending on the context. Here, we analyzed TLR4 expression in different grades of astrocytoma, and observed increased expression in tumors, mainly in GBM, compared to non-neoplastic brain tissue. TLR4 role was investigated in U87MG, a GBM mesenchymal subtype cell line, upon LPS stimulation. p65 nuclear translocation was observed in late phase, suggesting TLR4-non-canonical pathway activation. In fact, components of ripoptosome and inflammasome cascades were upregulated and they were significantly correlated in GBMs of the TCGA-RNASeq dataset. Moreover, an increased apoptotic rate was observed when the GBM-derived U87MG cells were co-treated with LPS and Temozolomide (TMZ) in comparison to TMZ alone. Increased TLR4 immunostaining was detected in nuclei of U87MG cells 12 h after LPS treatment, concomitant to activation of DNA repair genes. Time-dependent increased RAD51, FEN1 and UNG expression levels were confirmed after LPS stimulation, which may contribute to tumor cell fitness. Moreover, the combined treatment with the RAD51 inhibitor, Amuvatinib in combination with, TMZ after LPS stimulation reduced tumor cell viability more than with each treatment alone. In conclusion, our results suggest that stimulation of TLR4 combined with pharmacological inhibition of the DNA repair pathway may be an alternative treatment for GBM patients.

Proteomic Analyses Identify Differentially Expressed Proteins and Pathways Between Low-Risk and High-Risk Subtypes of Early-Stage Lung Adenocarcinoma and Their Prognostic Impacts

AbstractThe histopathological subtype of lung adenocarcinoma (LUAD) is closely associated with prognosis. Micropapillary or solid predominant LUAD tends to relapse after surgery at an early stage, whereas lepidic pattern shows a favorable outcome. However, the molecular mechanism underlying this phenomenon remains unknown. Here, we recruited 31 lepidic predominant LUADs (LR: low-risk subtype group) and 28 micropapillary or solid predominant LUADs (HR: high-risk subtype group). Tissues of these cases were obtained and label-free quantitative proteomic and bioinformatic analyses were performed. Additionally, prognostic impact of targeted proteins was validated using The Cancer Genome Atlas databases (n = 492) and tissue microarrays composed of early-stage LUADs (n = 228). A total of 192 differentially expressed proteins were identified between tumor tissues of LR and HR and three clusters were identified via hierarchical clustering excluding eight proteins. Cluster 1 (65 proteins) showed a sequential decrease in expression from normal tissues to tumor tissues of LR and then to HR and was predominantly enriched in pathways such as tyrosine metabolism and ECM-receptor interaction, and increased matched mRNA expression of 18 proteins from this cluster predicted favorable prognosis. Cluster 2 (70 proteins) demonstrated a sequential increase in expression from normal tissues to tumor tissues of LR and then to HR and was mainly enriched in pathways such as extracellular organization, DNA replication and cell cycle, and high matched mRNA expression of 25 proteins indicated poor prognosis. Cluster 3 (49 proteins) showed high expression only in LR, with high matched mRNA expression of 20 proteins in this cluster indicating favorable prognosis. Furthermore, high expression of ERO1A and FEN1 at protein level predicted poor prognosis in early-stage LUAD, supporting the mRNA results. In conclusion, we discovered key differentially expressed proteins and pathways between low-risk and high-risk subtypes of early-stage LUAD. Some of these proteins could serve as potential biomarkers in prognostic evaluation.

Impairment of Pol β-related DNA base-excision repair leads to ovarian aging in mice

The mechanism underlying the association between age and depletion of the human ovarian follicle reserves remains uncertain. Many identified that impaired DNA polymerase β (Pol β)-mediated DNA base-excision repair (BER) drives to mouse oocyte aging. With aging, DNA lesions accumulate in primordial follicles. However, the expression of most DNA BER genes, including APE1, OGG1, XRCC1, Ligase I, Ligase α, PCNA and FEN1, remains unchanged during aging in mouse oocytes. Also, the reproductive capacity of Pol β+/- heterozygote mice was impaired, and the primordial follicle counts were lower than that of wild type (wt) mice. The DNA lesions of heterozygous mice increased. Moreover, the Pol β knockdown leads to increased DNA damage in oocytes and decreased survival rate of oocytes. Oocytes over-expressing Pol β showed that the vitality of senescent cells enhances significantly. Furthermore, serum concentrations of anti-Müllerian hormone (AMH) indicated that the ovarian reserves of young mice with Pol β germline mutations were lower than those in wt. These data show that Pol β-related DNA BER efficiency is a major factor governing oocyte aging in mice.

IGF2BP2 Promotes Liver Cancer Growth Through an m6A-FEN1-Dependent Mechanism.

Hepatocellular carcinoma (HCC) is one of the most common malignant tumors in China. N6−methyladenosine (m6A) plays an important role in posttranscriptional gene regulation. METTL3 and IGF2BP2 are key genes in the m6A signal pathway and have recently been shown to play important roles in cancer development and progression. In our work, higher METTL3 and IGF2BP2 expression were found in HCC tissues and were associated with a poor prognosis. In addition, IGF2BP2 overexpression promoted HCC proliferation in vitro and in vivo. Mechanistically, IGF2BP2 directly recognized and bound to the m6A site on FEN1 mRNA and enhanced FEN1 mRNA stability. Overall, our study revealed that METTL3 and IGF2BP2, acting as an oncogene, maintained FEN1 expression through an m6A-IGF2BP2-dependent mechanism in HCC cells, and indicated a potential biomarker panel for prognostic prediction in liver cancer.

Jianpi-yangwei decoction inhibits DNA damage repair in the drug resistance of gastric cancer by reducing FEN1 expression

BackgroundFlap Endonuclease 1(FEN1) has been considered as a new tumor marker in recent years and Jianpi Yangwei Decoction (JPYW) is a basic Traditional Chinese Medicine (TCM) for the treatment of gastric cancer. This study aimed to explore the role of FEN1-mediated DNA damage repair in the drug resistance of gastric cancer and the effect of JPYW on it by employing BGC823/5-Fu drug-resistant cell model.MethodsThe DNA repair efficiency of BGC823 and BGC823/5-Fu was compared intracellularly and extracellularly using an extrachromosomal assay system and the reconstituted base excision repair assay. By comparing gene and protein expression and identifying cell survival rates after knockdown or high expression of FEN1, the correlation between FEN1 high expression and 5-Fluorouracil (5-Fu) drug resistance was revealed. The effect of JPYW on DNA damage repair and FEN1 expression was observed by the degree of γ-H2AX phosphorylation in the cells, DNA repair efficiency and enzyme activity, et al.ResultsBGC823/5-Fu had a higher DNA repair efficiency than BGC823(P < 0.001), which proved to be both intracellular and extracellular. FEN1 was highly expressed in BGC823/5-Fu regardless of gene level(P < 0.001) or protein level. Furthermore, manipulating FEN1 altered the sensitivity of cancer cells to chemotherapeutic drug 5-Fu. Different concentrations of JPYW were used to investigate the inhibitory effect on the expression of FEN1 and DNA damage repair. JPYW inhibited DNA damage repair both intracellularly and extracellularly: the phosphorylation of γ-H2AX increased, with more DNA damage in the cells; the synthetic 8-oxo dG damage repair was reduced; and the ability of cell lysates to repair DNA damage decreased. The decrease of FEN1 expression in BGC823/5-Fu had a concentration dependent relationship with JYPW. In addition, JPYW inhibited the activity of FEN1 at the enzymatic level, as the amount of cut-off synthetic 32p labeled DNA substrates were decreased.ConclusionFEN1 was highly expressed in drug-resistance gastric cancer cells BGC823/5-Fu, which leading to BGC823 resistant to (5-Fu) by acting on DNA damage repair. JPYW inhibited DNA damage repair and reversed 5-Fu drug resistance by reducing FEN1 expression and inhibiting FEN1 functional activity.

FEN1 inhibitor increases sensitivity of radiotherapy in cervical cancer cells.

BackgroundCervical cancer is one of the most common causes of cancer‐associated mortality among affected women in the world. At present, treatment with weekly cisplatin plus ionizing radiation (IR) therapy is the standard regimen for cervical cancer, especially for locally advanced cervical cancer. The purpose of this study is to determine whether FEN1 inhibitors could enhance the therapeutic effect of IR therapy.MethodsWestern blot was applied to determine the expression of FEN1‐ and apoptosis‐related proteins. Cell growth inhibition assay and colony formation assay were used to determine the effects of FEN1 inhibitor and IR exposure for Hela cells in vitro. CRISPR technology was used to knockdown FEN1 expression level of 293T cells, and tumor xenograft in nude mice was employed to determine the effects of FEN1 inhibitor and IR exposure on tumor growth in vivo.ResultsOur data revealed that FEN1 is overexpressed in HeLa cell and can be upregulated further by IR. We also demonstrated that FEN1 inhibitor enhances IR sensitivity of cervical cancer in vitro and in vivo.ConclusionFEN1 inhibitor SC13 could sensitize radiotherapy of cervical cancer cell.

Identification of Flap endonuclease 1 as a potential core gene in hepatocellular carcinoma by integrated bioinformatics analysis.

Hepatocellular carcinoma (HCC) is a common yet deadly form of malignant cancer. However, the specific mechanisms involved in HCC diagnosis have not yet fully elucidated. Herein, we screened four publically available Gene Expression Omnibus (GEO) expression profiles (GSE14520, GSE29721, GSE45267 and GSE60502), and used them to identify 409 differentially expressed genes (DEGs), including 142 and 267 up- and down-regulated genes, respectively. The DAVID database was used to look for functionally enriched pathways among DEGs, and the STRING database and Cytoscape platform were used to generate a protein-protein interaction (PPI) network for these DEGs. The cytoHubba plug-in was utilized to detect 185 hub genes, and three key clustering modules were constructed with the MCODE plug-in. Gene functional enrichment analyses of these three key clustering modules were further performed, and nine core genes including BIRC5, DLGAP5, DTL, FEN1, KIAA0101, KIF4A, MCM2, MKI67, and RFC4, were identified in the most critical cluster. Subsequently, the hierarchical clustering and expression of core genes in TCGA liver cancer tissues were analyzed using the UCSC Cancer Genomics Browser, and whether elevated core gene expression was linked to a poor prognosis in HCC patients was assessed using the GEPIA database. The PPI of the nine core genes revealed an interaction between FEN1, MCM2, RFC4, and BIRC5. Furthermore, the expression of FEN1 was positively correlated with that of three other core genes in TCGA liver cancer tissues. FEN1 expression in HCC and other tumor types was assessed with the FIREBROWSE and ONCOMINE databases, and results were verified in HCC samples and hepatoma cells. FEN1 levels were also positively correlated with tumor size, distant metastasis and vascular invasion. In conclusion, we identified nine core genes associated with HCC development, offering novel insight into HCC progression. In particular, the aberrantly elevated FEN1 may represent a potential biomarker for HCC diagnosis and treatment.

Letrozole improves the sensitivity of breast cancer cells overexpressing aromatase to cisplatin via down-regulation of FEN1

PurposeFlap endonuclease 1 (FEN1) is up-regulated by estrogen (17β-estradiol, E2) and related to cisplatin resistance of human breast cancer cells. Letrozole, an aromatase inhibitor, suppresses the change of testosterone into estrogen and is frequently used to treat breast cancer. However, the effects of letrozole on FEN1 expression and cisplatin sensitivity in breast cancer cells overexpressing aromatase have not been revealed.MethodsThe expression of FEN1 and the proteins in ERK/Elk-1 signaling were evaluated by RT-PCR and Western blot. Cisplatin sensitivity was explored through CCK-8 and flow cytometry analysis, respectively. FEN1 siRNAs and FEN1 expression plasmid were transfected into cells to down-regulate or up-regulate FEN1 expression. The promotor activity of FEN1 was detected using luciferase reporter assay.ResultsFEN1 down-regulation improved cisplatin sensitivity of breast cancer cells overexpressing aromatase. Letrozole down-regulated FEN1 expression and increased cisplatin sensitivity. The sensitizing effect of letrozole to cisplatin was dependent on FEN1 down-regulation. FEN1 overexpression could block the sensitizing effect of letrozole to cisplatin. Testosterone up-regulated the promotor activity, protein expression of FEN1, and phosphorylation of ERK/Elk-1, which could be eliminated by both letrozole and MEK1/2 inhibitor U0126. Letrozole down-regulated FEN1 expression in an ERK/Elk-1-dependent manner.ConclusionsOur findings clearly demonstrate that letrozole improves cisplatin sensitivity of breast cancer cells overexpressing aromatase via down-regulation of FEN1 and suggest that a combined use of letrozole and cisplatin may be a potential treatment protocol for relieving cisplatin resistance in human breast cancer.