Association of a functional RAD52 genetic variant locating in a miRNA binding site with risk of HBV-related hepatocellular carcinoma

Novel Insights into RAD52’s Structure, Function, and Druggability for Synthetic Lethality and Innovative Anticancer Therapies

In recent years, the RAD52 protein has been highlighted as a mediator of many DNA repair mechanisms. While RAD52 was initially considered to be a non-essential auxiliary factor, its inhibition has more recently been demonstrated to be synthetically lethal in cancer cells bearing mutations and inactivation of specific intracellular pathways, such as homologous recombination. RAD52 is now recognized as a novel and critical pharmacological target. In this review, we comprehensively describe the available structural and functional information on RAD52. The review highlights the pathways in which RAD52 is involved and the approaches to RAD52 inhibition. We discuss the multifaceted role of this protein, which has a complex, dynamic, and functional 3D superstructural arrangement. This complexity reinforces the need to further investigate and characterize RAD52 to solve a challenging mechanistic puzzle and pave the way for a robust drug discovery campaign.

Updated review of advances in microRNAs and complex diseases: experimental results, databases, webservers and data fusion

MicroRNAs (miRNAs) are gene regulators involved in the pathogenesis of complex diseases such as cancers, and thus serve as potential diagnostic markers and therapeutic targets. The prerequisite for designing effective miRNA therapies is accurate discovery of miRNA-disease associations (MDAs), which has attracted substantial research interests during the last 15 years, as reflected by more than 55 000 related entries available on PubMed. Abundant experimental data gathered from the wealth of literature could effectively support the development of computational models for predicting novel associations. In 2017, Chen et al. published the first-ever comprehensive review on MDA prediction, presenting various relevant databases, 20 representative computational models, and suggestions for building more powerful ones. In the current review, as the continuation of the previous study, we revisit miRNA biogenesis, detection techniques and functions; summarize recent experimental findings related to common miRNA-associated diseases; introduce recent updates of miRNA-relevant databases and novel database releases since 2017, present mainstream webservers and new webserver releases since 2017 and finally elaborate on how fusion of diverse data sources has contributed to accurate MDA prediction.

Circ_0006404 enhances hepatocellular carcinoma progression by regulating miR-624

Growing studies have demonstrated that circRNAs (circular RNAs) act potential roles in tumor metastasis and progression. However, the expression and function of circ_0006404 in hepatocellular carcinoma (HCC) remain to be investigated. The expression of circ_0006404 and miR-624 was detected by qRT-PCR. CCK-8 assay, flow cytometry, and wound healing were performed to determine cell proliferation, cycle, and migration. The target of circ_0006404 was studied by bioinformatics and luciferase activity analysis. Our data indicated that circ_0006404 was overexpressed in HCC specimens and cells and ectopic expression of circ_0006404 increased HCC cell growth, cycle, and migration. Moreover, we showed that miR-624 was downregulated in HCC specimens and cells and miR-624 expression was negatively correlated with circ_0006404 expression in HCC specimens. Circ_0006404 sponged miR-624 in HCC cell, and the overexpression of circ_0006404 suppressed miR-624 expression in HCC cell. Furthermore, circ_0006404 induced HCC cell growth, cycle, and migration via regulating miR-624. These results elucidated that circ_0006404 facilitated HCC progression and might act as one new biomarker for this carcinoma.

Genetic polymorphisms in DNA repair genes and hepatocellular carcinoma risk

Hepatocellular carcinoma (HCC) is one of the most frequent types of tumors worldwide. Its occurrence and development have been related to various risk factors, such as chronic infection with hepatitis B or C viruses and alcohol addiction. DNA repair systems play a critical role in maintaining the integrity of the genome. Defects in these systems have been related to increased susceptibility to various types of cancer. Multiple genetic polymorphisms in genes of DNA repair systems have been reported that may affect DNA repair capacity (DRC) and modulate risk to cancer. Several studies have been conducted to assess the role of polymorphisms of DNA repair genes on the HCC risk. Identifying these polymorphisms and their association with HCC risk may help to improve prevention and treatment strategies. In this study, we review investigations that evaluated the association between genetic polymorphisms of DNA repair genes and risk of HCC.

Von Hippel-Lindau gene single nucleotide polymorphism (rs1642742) may be related to the occurrence and metastasis of HBV-related hepatocellular carcinoma

It is well-known that microRNAs are able to regulate the expression of target mRNAs through complementary base-pairing to their 3'-untranslated regions (3'UTR) sequences. This study aimed to investigate whether single nucleotide polymorphisms resided in the 3'UTR sequences in patients with chronic hepatitis B viruses (HBV) infection are associated with the development and metastasis of hepatocellular carcinoma (HCC). Seventeen single nucleotide polymorphisms in the 3'UTR sequence of 10 genes regulated or affected by hepatitis B virus X protein were found by bioinformatics methods. Two hundred fifteen patients with HBV-related HCC and 216 patients with chronic HBV infection were recruited. Through case-control study, only found that the von Hippel-Lindau gene rs1642742 (G>A) may be associated with the occurrence and metastasis of HCC. The ORs of the frequencies of rs1642742 A allele versus G allele were 1.424 (P = .038, 95% confidence interval [CI] = 1.019-1.989) between HBV-related HCC and chronic HBV infection group and were 2.004 (P = .037, 95%CI = 1.031-3.895) between tumor metastasis and non-metastasis group, respectively. Through multivariate regression analysis, we also found that rs1642742 AA genotype was an independent risk factor for tumor metastasis (odds ratio = 2.227, 95% CI = 1.043-4.752, P = .038) in HBV-related HCC group. Our study suggested that Von Hippel-Lindau rs1642742 contributed to susceptibility to developing HCC and correlated with tumor metastasis.

Identification of a novel heterozygous germline RAD52 missense mutation in a patient with gallbladder carcinoma: A case report

RATIONALE

Gallbladder carcinoma is a malignant biliary tract tumor which is characterized by poor prognosis. Recent advances in genomic medicine have identified a few novel germline mutations that contribute to the increased risk of gallbladder carcinoma. RAD52 is a crucial human deoxyribonucleic acid (DNA) repair gene involved in maintaining genomic stability and preventing tumor occurrence.

PATIENT CONCERNS

A 57-year-old man was hospitalized for space-occupying lesions in the gallbladder.

DIAGNOSIS

A diagnosis of gallbladder adenocarcinoma was made based on computed tomography, B-ultrasound, blood tests, and postoperative pathology.

INTERVENTIONS

Next-generation sequencing using a 599-gene panel and Sanger sequencing were performed to validate the mutation in the proband and his family members, respectively.

OUTCOMES

A novel potentially pathogenic heterozygous germline RAD52 missense mutation (c.276T > A: p.N92K) was identified in the patient. Sanger sequencing revealed that this variation was not observed in unaffected family members.

LESSONS

We identified a novel heterozygous germline RAD52 missense mutation in a patient with gallbladder carcinoma. Our results added to the current body of knowledge. It also provides new insights into genetic counseling and targeted therapeutic strategies for patients with gallbladder carcinoma.

The Role of RNA in DNA Breaks, Repair and Chromosomal Rearrangements

Incorrect reparation of DNA double-strand breaks (DSB) leading to chromosomal rearrangements is one of oncogenesis's primary causes. Recently published data elucidate the key role of various types of RNA in DSB formation, recognition and repair. With growing interest in RNA biology, increasing RNAs are classified as crucial at the different stages of the main pathways of DSB repair in eukaryotic cells: nonhomologous end joining (NHEJ) and homology-directed repair (HDR). Gene mutations or variation in expression levels of such RNAs can lead to local DNA repair defects, increasing the chromosome aberration frequency. Moreover, it was demonstrated that some RNAs could stimulate long-range chromosomal rearrangements. In this review, we discuss recent evidence demonstrating the role of various RNAs in DSB formation and repair. We also consider how RNA may mediate certain chromosomal rearrangements in a sequence-specific manner.

The role of DNA damage and repair in liver cancer

Hepatocellular carcinoma is rapidly becoming a major cause of global mortality due to the ever-increasing prevalence of obesity. DNA damage is known to play an important role in cancer initiation, however DNA repair systems are also vital for the survival of cancer cells. Given the function of the liver and its exposure to the gut, it is likely that DNA damage and repair would be of particular importance in hepatocellular carcinoma. However, many contemporary reports have neglected the role of individual pathways of DNA damage and repair in their hypotheses. This review, therefore, aims to provide a concise overview for researchers in the field of liver cancer to understand the pathways of DNA damage and repair and their individual roles in hepatocellular carcinoma.

Association between Single-Nucleotide Polymorphism in MicroRNA Target Site of DDB2 and Risk of Hepatocellular Carcinoma in a Southern Chinese Population

Damage-specific DNA-binding protein 2 (DDB2) is a DNA repair protein mainly involved in nucleotide excision repair, which plays a pivotal role in maintaining genomic stability. In this study, we evaluated the association of single-nucleotide polymorphism (SNP) rs1050244 in miRNA target site of DDB2 gene with risk of hepatocellular carcinoma (HCC) among 1073 HCC patients and 1119 cancer-free controls in a southern Chinese population. Our results showed that no statistically significant association was found between DDB2 rs1050244 and HCC risk. In further analysis stratified by age, sex, smoking, alcohol drinking, and HBV infection status, we found that individuals carrying the CT/TT genotypes of SNP rs1050244 had a significantly decreased risk of HCC compared with those with the CC genotype among non-HBV infected population (adjusted OR = 0.31, 95% CI = 0.13–0.72), and a significant interaction was found between this SNP and HBV infection (P_interaction=0.002). Our results suggested that the DDB2 rs1050244 C>T polymorphism was associated with the decreased risk of HCC among non-HBV infected population. Further studies with larger sample sizes are needed to validate our findings.

Evaluating the role of RAD52 and its interactors as novel potential molecular targets for hepatocellular carcinoma

Background

Radiation sensitive 52 (RAD52) is an important protein that mediates DNA repair in tumors. However, little is known about the impact of RAD52 on hepatocellular carcinoma (HCC). We investigated the expression of RAD52 and its values in HCC. Some proteins that might be coordinated with RAD52 in HCC were also analyzed.

Methods

Global RAD52 mRNA levels in HCC were assessed using The Cancer Genome Atlas (TCGA) database. RAD52 expression was analyzed in 70 HCC tissues and adjacent tissues by quantitative real-time PCR (qRT-PCR), Western blotting and immunohistochemistry. The effect of over-expressed RAD52 in Huh7 HCC cells was investigated. The String database was then used to perform enrichment and functional analysis of RAD52 and its interactome. Cytoscape software was used to create a protein–protein interaction network. Molecular interaction studies with RAD52 and its interactome were performed using the molecular docking tools in Hex8.0.0. Finally, these DNA repair proteins, which interact with RAD52, were also analyzed using the TCGA dataset and were detected by qRT-PCR. Based on the TCGA database, algorithms combining ROC between RAD52 and RAD52 interactors were used to diagnose HCC by binary logistic regression.

Results

In TCGA, upregulated RAD52 related to gender was obtained in HCC. The area under the receiver operating characteristic curve (AUC) of RAD52 was 0.704. The results of overall survival (OS) and recurrence-free survival (RFS) indicated no difference in the prognosis between patients with high and low RAD52 gene expression. We validated that RAD52 expression was increased at the mRNA and protein levels in Chinese HCC tissues compared with adjacent tissues. Higher RAD52 was associated with older age, without correlation with other clinicopathological factors. In vitro, over-expressed RAD52 significantly promoted the proliferation and migration of Huh7 cells. Furthermore, RAD52 interactors (radiation sensitive 51, RAD51; X-ray repair cross complementing 6, XRCC6; Cofilin, CFL1) were also increased in HCC and participated in some biological processes with RAD52. Protein structure analysis showed that RAD52–RAD51 had the firmest binding structure with the lowest E-total energy (− 1120.5 kcal/mol) among the RAD52–RAD51, RAD52–CFL1, and RAD52–XRCC6 complexes. An algorithm combining ROC between RAD52 and its interactome indicated a greater specificity and sensitivity for HCC screening.

Conclusions

Overall, our study suggested that RAD52 plays a vital role in HCC pathogenesis and serves as a potential molecular target for HCC diagnosis and treatment. This study’s findings regarding the multigene prediction and diagnosis of HCC are valuable.

Inhibition of RAD54B suppresses proliferation and promotes apoptosis in hepatoma cells

RAD54 homolog B is a central motor protein of homologous recombination (HR), which plays an important role in the development and evolution of human cancer. Recent studies have indicated that RAD54B is aberrantly expressed in a variety of cancers and exhibits numerous biological functions, including participating in the repair of DNA double strand breaks. However, the expression and function of RAD54B in liver cancer have not yet been reported. The aim of the present study was to investigate the expression of RAD54B and elucidate its role in liver cancer cell lines by inhibiting RAD54B using a lentivirus-mediated shRNA interference system. We also assessed the effect of RAD54B on cell proliferation, colony formation, cell cycle distribution and cell apoptosis in BEL-7404 and SMMC-7721 cell lines using shRAD54B or shCtrl transfection. Furthermore, we analyzed the relationship between the expression of RAD54B protein, as measured by immunohistochemical staining, and the prognosis of patients with hepatoma. We found that RAD54B was highly expressed in liver cancer cell lines compared with the normal hepatic cell line LO2. Similarly, positive expression of RAD54B, which is associated with poor prognosis, was also observed in 52/83 samples of liver cancer tissue. Additionally, RAD54B downregulation significantly inhibited cell proliferation and colony formation, while also inducing G1/S cell cycle arrest and apoptosis in BEL-7404 and SMMC-7721 cells. These results indicated that RAD54B has oncogenic properties, and may be a potential treatment target for liver cancer patients.

LncRNA GAS5 Indel Genetic Polymorphism Contributes to Glioma Risk Through Interfering Binding of Transcriptional Factor TFAP2A

Long noncoding RNA (lncRNA) growth arrest-specific 5 (GAS5) accumulates in growth-arrested cells and plays a crucial role in progression of multiple cancers, including glioma. There is a functional GAS5 rs145204276 indel genetic polymorphism in the promoter region. However, it is still largely unknown how the GAS5 indel genetic polymorphism is involved in etiology of glioma. We evaluated the association between the GAS5 indel genetic polymorphism and glioma development in a Chinese population. Odds ratios (ORs) and 95% confidence intervals (CIs) were estimated by logistic regression adjusted by age and sex. We found that carriers of the GAS5 del allele was significantly associated with elevated risk of glioma (OR = 1.71, 95% CI = 1.34-2.18, p = 1.7 × 10^-5). Compared with the GAS5 ins/ins genotype, the ins/del genotype or the del/del genotype was significantly associated with 1.57-fold or 2.61-fold increased glioma susceptibility (p = 0.001 or p = 9.0 × 10^-6). When patients were stratified by disease subtypes, The GAS5 indel polymorphism was not significantly associated with risk of oligodendroglial tumor (p = 0.353). Integrated analyses indicated that the GAS5 indel polymorphism might alert the binding of transcriptional factor TFAP2A and activation of its expression based on ENCODE and REMBRANDT databases. Our results highlight the importance and potential of the biological relevance of the GAS5 indel genetic variant in glioma predisposition.

MicroRNA-Related Polymorphisms in Infectious Diseases-Tiny Changes With a Huge Impact on Viral Infections and Potential Clinical Applications

MicroRNAs (miRNAs) are single-stranded sequences of non-coding RNA with approximately 22 nucleotides that act posttranscriptionally on gene expression. miRNAs are important gene regulators in physiological contexts, but they also impact the pathogenesis of various diseases. The role of miRNAs in viral infections has been explored by different authors in both population-based as well as in functional studies. However, the effect of miRNA polymorphisms on the susceptibility to viral infections and on the clinical course of these diseases is still an emerging topic. Thus, this review will compile and organize the findings described in studies that evaluated the effects of genetic variations on miRNA genes and on their binding sites, in the context of human viral diseases. In addition to discussing the basic aspects of miRNAs biology, we will cover the studies that investigated miRNA polymorphisms in infections caused by hepatitis B virus, hepatitis C virus, human immunodeficiency virus, Epstein–Barr virus, and human papillomavirus. Finally, emerging topics concerning the importance of miRNA genetic variants will be presented, focusing on the context of viral infectious diseases.

Association of the GLB1 rs4678680 genetic variant with risk of HBV-related hepatocellular carcinoma

Accumulated evidences demonstrated that GLB1 is involved in cell senescence and cancer development. The GLB1 rs4678680 single nucleotide polymorphism (SNP) has been identified as a hepatocellular carcinoma (HCC) susceptibility polymorphism by a genome-wide association study in Korean population previously. However, little or nothing was known about its involvement and functional significance in hepatitis B viruses (HBV)-related HCC in Chinese. Therefore, we investigated the association between the GLB1 rs4678680 SNP and HBV-related HCC risk as well as its biological function in vivo. Genotypes were determined in two independent case-control sets from two medical centers of China. Odds ratios (ORs) and 95% confidence intervals (CIs) were estimated by logistic regression. The potential regulation role the rs4678680 genetic variant on GLB1 expression was examined with HCC and normal liver tissues. We found that The rs4678680 G allele was showed to be risk allele; individuals with the TG genotype had an OR of 1.51 (95% CI = 1.10–2.07, P = 0.010, Shandong set) or 1.49 (95% CI = 1.11–1.99, P = 0.008, Jiangsu set) for developing HBV-related HCC, respectively, compared with individuals with the TT genotype. This association was more pronounced in males, individuals aged older than 57 years and drinkers (all P < 0.05). In the genotype-phenotype correlation analyses of fifty-six human liver tissue samples, rs4678680 TG or GG was associated with a statistically significant increase of GLB1 mRNA expression (P < 0.05). Our data indicated that the GLB1 rs4678680 SNP contributes to susceptibility to develop HBV-related HCC, highlighting the involvement of GLB1 and cell senescence in etiology of HCC.

A non-synonymous polymorphism in NBS1 is associated with progression from chronic hepatitis B virus infection to hepatocellular carcinoma in a Chinese population

PURPOSE

Nijmegen breakage syndrome 1 (NBS1) has a vital role in DNA double-strand break (DSB) repair, functioning as a sensor to identify and repair DNA damage and maintaining genomic stability by participating in the intra-S-phase checkpoint. Polymorphisms of NBS1 have been investigated in multiple cancers with variable results. To our best knowledge, no previous study has focused on the association between NBS1 single-nucleotide polymorphisms (SNPs) and hepatitis B virus (HBV)-related hepatocellular carcinoma (HCC).

PATIENTS AND METHODS

Five NBS1 SNPs were selected based on their potential functional impact. A hospital-based cohort, comprising 481 patients with HBV-related HCC, 508 patients with chronic hepatitis B virus infection (CHB), and 581 healthy controls, was recruited for genotyping analysis.

RESULTS

After quality control, four SNPs were successfully genotyped (rs10464867, rs1063053, rs1805794, and rs709816), none of which were significantly associated with HCC or CHB compared with those of healthy controls. Similarly, the combined HBV-infected group (including the HCC and CHB groups) exhibited no significant associations with these SNPs compared with healthy controls. In contrast, comparison of the frequency of rs1805794 between patients with CHB and those with HCC identified a significant association (P=2.99E-03, odds ratio =1.31, 95% confidence interval =1.10-1.56).

CONCLUSION

These findings suggest that, as a non-synonymous SNP, the rs1805794 C/G polymorphism may play a role in the progression from CHB to HCC.

Clinical Implications of the Autophagy Core Gene Variations in Advanced Lung Adenocarcinoma Treated with Gefitinib

EGFR-TKIs show dramatic treatment benefits for advanced lung adenocarcinoma patients with activating EGFR mutations. Considering the essential role of autophagy in EGFR-TKIs treatments, we hypothesized that genetic variants in autophagy core genes might contribute to outcomes of advanced lung adenocarcinoma treated with gefitinib. We systematically examined 27 potentially functional genetic polymorphisms in 11 autophagy core genes among 108 gefitinib-treated advanced lung adenocarcinoma patients. We found that ATG10 rs10036653, ATG12 rs26538, ATG16L1 rs2241880 and ATG16L2 rs11235604 were significantly associated with survival of lung adenocarcinoma patients (all P < 0.05). Among EGFR-mutant patients, ATG5 rs688810, ATG5 rs510432, ATG7 rs8154, ATG10 rs10036653, ATG12 rs26538, ATG16L1 rs2241880 and ATG16L2 rs11235604 significantly contributed to disease prognosis. We also found that ATG5 rs510432, ATG5 rs688810, ATG10 rs10036653 and ATG10 rs1864182 were associated with primary or acquired resistance to gefitinib. Functional analyses of ATG10 rs10036653 polymorphism suggested that ATG10 A allele might increase transcription factor OCT4 binding affinity compared to the T allele in lung cancer cells. Our results indicate that autophagy core genetic variants show potential clinical implications in gefitinib treatment, especially among advanced lung adenocarcinoma patients, highlighting the possibility of patient-tailored decisions during EGFR-TKIs based on both germline and somatic variation detection.

RAD52 gene polymorphisms are associated with risk of colorectal cancer in a Chinese Han population

Upward trends in the incidence and mortality rates of colorectal cancer (CRC) in China over the past decade mean that it is critical to improve survival outcomes for patients with this malignancy. Analysis of genetic variants may identify biomarkers that have a role in CRC susceptibility and clinical outcomes in Chinese patients with CRC. RAD52 is a key mediator during DNA strand exchange and homologous recombination within mammalian cells. In this study, we explored the effects of RAD52 single nucleotide polymorphisms (SNPs) in the susceptibility and clinicopathological characteristics of Chinese Han patients with CRC. Five RAD52 SNPs (rs1051669, rs10774474, rs11571378, rs6489769, and rs7963551) were analyzed using TaqMan SNP genotyping in 281 patients with CRC and 309 healthy controls. Among those aged over 60 years in the total population, carriers of the variant C allele or at least one T allele of the rs1051669 SNP were at a lower risk of CRC than carriers of the wild-type CC variant of rs1051669, while in those carrying the rs7963551 SNP, the GT or GT+GG alleles were associated with an increased risk of CRC compared with patients carrying TT alleles. We indicated a significant correlation between RAD52 rs7963551 polymorphism and lymph node metastasis in CRC patients. In all patients, the T-T-T-T-T, C-T-T-T-T, and C-T-A-C-T haplotypes were associated with an increasing risk of CRC. Our findings suggest that 4 RAD52 SNPs (rs1051669, rs10774474, rs11571378, and rs6489769) might contribute to the prediction of CRC susceptibility. In conclusion, our study demonstrated that RAD52 polymorphisms were associated with CRC in a Chinese Han cohort.

CHST9 rs1436904 genetic variant contributes to prognosis of triple-negative breast cancer

Triple-negative breast cancer (TNBC) refers to one aggressive histological subtype of breast cancer with high heterogeneity and poor prognosis after standard therapy. Lack of clearly established molecular mechanism driving TNBC progression makes personalized therapy more difficult. Thus, identification of genetic variants associated with TNBC prognosis will show clinic significance for individualized treatments. Our study is aimed to evaluate the prognostic value of the genome wide association study (GWAS)-identified CHST9 rs1436904 and AQP4 rs527616 genetic variants in our established early-stage TNBC sample database. Cox regression was used to estimate hazard ratios (HRs) and 95% confidence intervals (CIs). CHST9 rs1436904G allele was significantly associated with decreased disease-free survival time (DFS) (8.5 months shorter in GG genotype carriers compared to TT genotype carriers, HR = 1.70, 95% CI = 1.03–2.81, P = 0.038). Stratified analyses showed an increased risk of cancer progression in CHST9 rs1436904G allele carriers harboring larger tumor (tumor size > 2 cm), without lymph-node metastasis, being premenopausal at diagnosis or with vascular invasion (P = 0.032, 0.017, 0.008 or 0.003). Our findings demonstrate that the GWAS-identified 18q11.2 CHST9 rs1436904 polymorphism significantly contributes to prognosis of early-stage TNBC, suggesting its clinical potential in the screening of high-risk TNBC patients for recurrence and the possibility of patient-tailored therapeutic decisions.

Corrupting the DNA damage response: a critical role for Rad52 in tumor cell survival

The DNA damage response enables cells to survive, maintain genome integrity, and to safeguard the transmission of high-fidelity genetic information. Upon sensing DNA damage, cells respond by activating this multi-faceted DNA damage response leading to restoration of the cell, senescence, programmed cell death, or genomic instability if the cell survives without proper repair. However, unlike normal cells, cancer cells maintain a marked level of genomic instability. Because of this enhanced propensity to accumulate DNA damage, tumor cells rely on homologous recombination repair as a means of protection from the lethal effect of both spontaneous and therapy-induced double-strand breaks (DSBs) in DNA. Thus, modulation of DNA repair pathways have important consequences for genomic instability within tumor cell biology and viability maintenance under high genotoxic stress. Efforts are underway to manipulate specific components of the DNA damage response in order to selectively induce tumor cell death by augmenting genomic instability past a viable threshold. New evidence suggests that RAD52, a component of the homologous recombination pathway, is important for the maintenance of tumor genome integrity. This review highlights recent reports indicating that reducing homologous recombination through inhibition of RAD52 may represent an important focus for cancer therapy and the specific efforts that are already demonstrating potential.

Let-7a enhances the sensitivity of hepatocellular carcinoma cells to cetuximab by regulating STAT3 expression

Background

Let-7 miRNAs are reported to play an inhibitory role in carcinogenesis, tumor progression, recurrence, and pluripotency of cancer. However, few studies have reported the relationship between let-7 and drug sensitivity, especially for let-7a (a subtype of let-7). This study aimed to investigate the function of let-7a in regulating the sensitivity of hepatocellular carcinoma (HCC) cell lines to cetuximab.

Methods

The cytotoxicity of cetuximab on HCC cell lines (Huh7, Hep3B, HepG2, SNU449, and SNU387) was evaluated using a cell viability assay (the Cell Counting Kit-8 assay) and a cell proliferation assay (the Click-iT EdU Imaging Kit) in the presence of a control, a let-7a mimic, and a let-7a inhibitor. Small interfering RNA to knockdown the expression of signal transducer and activator of transcription 3 (STAT3) were employed. Protein and mRNA expression levels were determined using quantitative polymerase chain reaction and Western blot analysis.

Results

It was found that let-7a enhances the sensitivity of HCC cells with an epithelial phenotype (Huh7, Hep3B, and HepG2) to cetuximab, but has no effect on cells with the mesenchymal phenotype (SNU449 and SNU387). It was determined that STAT3 was a target mRNA of let-7a using TargetScan. Expression of STAT3 and let-7a mRNA were negatively correlated in HCC cell lines. Moreover, let-7a altered the protein and mRNA expression of STAT3. Furthermore, STAT3 knockdown enhanced the function of cetuximab on HCC cell lines with epithelial phenotypes, but not on HCC cell lines with mesenchymal phenotypes. Finally, a rescue experiment confirmed that let-7a affected the sensitivity of HCC cell lines to cetuximab by interacting with STAT3.

Conclusions

There is a functional link between let-7a and STAT3 in enhancing the sensitivity of HCC cells with an epithelial phenotype to cetuximab. Our results provide novel insight into new methodologies for combating HCC drug resistance.

MiRNA-binding site functional polymorphisms in DNA repair genes RAD51, RAD52, and XRCC2 and breast cancer risk in Chinese population

RAD51, RAD52, and XRCC2 are all involved in DNA homologous recombinational repair, and there are interactions among those genes. Polymorphisms in 3'-UTR of DNA repair genes may change DNA repair capacity by regulating gene expression. However, potential regulatory variants affecting their expression remain largely unexplored. Five miRNA-binding site SNPs (rs7180135 and rs45549040 in RAD51, rs1051669 and rs7963551 in RAD52 and rs3218550 in XRCC2) selected by bioinformatics method were genotyped in 498 breast cancer (BC) patients and 498 matched controls in Chinese population. Association between SNPs and BC risk was analyzed by adjusted odds ratios (ORs) and 95 % confidence intervals (CIs) in unconditional logistic regression model. Quantitative real-time (qRT) PCR and Western Blot assays were used to calculate the relative expression of RAD52 in recombinant plasmid-pGenesil-1-let-7b group and let-7b-inhibitor group. Gene-reproductive factors interactions were evaluated by multifactor dimensionality reduction (MDR) method. We found that individuals with AC (OR 0.684, 95%CI 0.492-0.951) and CC (OR 0.317, 95%CI 0.200-0.503) genotypes of rs7963551 had a significantly lower risk of breast cancer and qRT-PCR and Western Blot revealed that let-7b might downregulate the expression of RAD52 in MCF-7 and SKBR-3 cells. A significant interaction between the number of pregnancy (≥2) and rs7963551 (Ars7963551) was found to increase breast cancer risk by 2.63-fold (OR 2.63; 95%CI 2.03-3.42). In summary, the miRNA-binding SNPs in DNA repair genes RAD51, RAD52, and XRCC2 and their interaction with reproductive factors might play important roles in the development of BC, and let-7b might downregulate RAD52 expression in MCF-7 and SKBR-3 cells.

53BP1 fosters fidelity of homology-directed DNA repair

Repair of DNA double-strand breaks (DSBs) in mammals is coordinated by the ubiquitin-dependent accumulation of 53BP1 at DSB-flanking chromatin. Owing to its ability to limit DNA-end processing, 53BP1 is thought to promote nonhomologous end-joining (NHEJ) and to suppress homology-directed repair (HDR). Here, we show that silencing 53BP1 or exhausting its capacity to bind damaged chromatin changes limited DSB resection to hyper-resection and results in a switch from error-free gene conversion by RAD51 to mutagenic single-strand annealing by RAD52. Thus, rather than suppressing HDR, 53BP1 fosters its fidelity. These findings illuminate causes and consequences of synthetic viability acquired through 53BP1 silencing in cells lacking the BRCA1 tumor suppressor. We show that such cells survive DSB assaults at the cost of increasing reliance on RAD52-mediated HDR, which may fuel genome instability. However, our findings suggest that when challenged by DSBs, BRCA1- and 53BP1-deficient cells may become hypersensitive to, and be eliminated by, RAD52 inhibition.

Functional BCL-2 regulatory genetic variants contribute to susceptibility of esophageal squamous cell carcinoma

B-cell lymphoma-2 (BCL-2) prevents apoptosis and its overexpression could promote cancer cell survival. Multiple functional BCL-2 genetic polymorphisms, such as rs2279115, rs1801018 and rs1564483, have been identified previously and might be involved in cancer development through deregulating BCL-2 expression. Therefore, we examined associations between these three polymorphisms and esophageal squamous cell carcinoma (ESCC) susceptibility as well as its biological function in vivo. Genotypes were determined in two independent case-control sets consisted of 1588 ESCC patients and 1600 controls from two regions of China. Odds ratios (ORs) and 95% confidence intervals (CIs) were calculated by logistic regression. The impact of the rs2279115 polymorphism on BCL-2 expression was detected using esophagus tissues. Our results demonstrated that the BCL-2 rs2279115 AA genotype was significantly associated with decreased ESCC risk compared with the CC genotype (OR = 0.72, 95% CI = 0.57–0.90, P = 0.005), especially in nonsmokers (OR = 0.42, 95% CI = 0.29–0.59, P = 0.001) or nondrinkers (OR = 0.44, 95% CI = 0.32–0.62, P = 0.002). Genotype-phenotype correlation studies demonstrated that subjects with the rs2279115 CA and AA genotypes had a statistically significant decrease of BCL-2 mRNA expression compared to the CC genotype in both normal and cancerous esophagus tissues. Our results indicate that the BCL-2 rs2279115 polymorphism contributes to ESCC susceptibility in Chinese populations.

Evaluation of miRNA-binding-site SNPs of MRE11A, NBS1, RAD51 and RAD52 involved in HRR pathway genes and risk of breast cancer in China

MiRNA-binding-site single nucleotide polymorphisms (SNPs) in homologous recombination repair (HRR) pathway genes may change DNA repair capacity and affect susceptibility to cancer though complex gene-gene and gene-reproductive factors interactions. However, these SNPs associated with breast cancer (BC) are still unclear in Chinese women. Therefore, we conducted a case-control study to evaluate the genetic susceptibility of the five miRNA-binding-site SNPs in HRR pathway genes (MRE11A rs2155209, NBS1 rs2735383, RAD51 rs963917 and rs963918 and RAD52 rs7963551) in the development of BC. MRE11A rs2155209 and RAD52 rs7963551 were found to be associated with BC risk (ORadjusted: 1.87; 95 % CI: 1.23-2.86 and ORadjusted: 0.36; 95 % CI: 0.24-0.58). NBS1 rs2735383, RAD51 rs963917 and rs963918 were associated with BC risk after stratification according to reproductive factors. Haplotypes of Crs963917Ars963918 decreased the risk of BC (ORadjusted: 0.53; 95 % CI: 0.4-0.68), while the Trs963917Ars963918 and Trs963917Grs963918 haplotypes could increase the risk of BC (ORadjusted: 1.28; 95 % CI: 1.05-1.57 and ORadjusted: 1.31; 95 % CI: 1.09-1.62). Combined effect of risk alleles showed that the five SNPs were associated with increased BC risk in a dose-dependent manner (P trend = 0.003). The GC genotype of rs2735383, AG + GG genotype of rs963918 and AC + CC genotype of rs7963551 were associated with PR positivity of BC patients. These findings suggest that the miRNA-binding-site SNPs involved in HRR pathway genes may affect susceptibility of BC in Chinese women; moreover, the interactions of gene-gene and gene-reproductive factors play vital roles in the progression of BC. Further functional studies with larger sample are needed to support and validate these findings.

The functional BRCA1 rs799917 genetic polymorphism is associated with gastric cancer risk in a Chinese Han population

BRCA1 is a crucial tumor suppressor which plays an essential role in maintaining genomic stability and integrity. Accumulated evidences demonstrated that there is frequent chromosome loss of BRCA1 or significant BRCA1 down-regulation via hypermethylation of its promoter in human gastric cancer specimens, highlighting the tumor-suppressing function of BRCA1 in gastric carcinogenesis. There is an rs799917 T>C single nucleotide polymorphism (SNP) located in the BRCA1 coding sequence (CDS). This SNP can disturb the interaction between BRCA1 mRNA and miR-638 and result in significantly decreased BRCA1 expression among carriers of rs799917C allele. In this study, we investigated the association between rs799917 and gastric cancer risk in a Chinese Han population using a case-control design. A total of 660 gastric cancer patients and 800 controls were enrolled and genotyped. Odds ratios (ORs) and 95 % confidence intervals (CIs) were calculated by logistic regression. We found that individuals with the rs799917 CT genotype was significantly associated with gastric cancer risk (OR = 1.81, 95 % CI = 1.28-2.56; P = 0.001). Individuals having the rs799917 CC genotype had an OR of 1.40 (95 % CI = 1.17-1.68; P = 2.2 × 10(-4)) for developing gastric cancer, compared with individual having the rs799917 TT genotype. However, stratified analyses did not find any evident gene-covariates interaction. Our results for the first time indicate that the functional BRCA1 rs799917 polymorphism contributes to gastric cancer susceptibility.