Role of DNA methylation and non‑coding RNAs expression in pathogenesis, detection, prognosis, and therapy‑resistant ovarian carcinoma (Review)

Ovarian cancer is the deadliest gynecological cancer globally, with epithelial ovarian cancer (EOC) comprising up to 90% of cases. A molecular characterization linking the histological subtypes with tumor grade in EOC has been suggested. Variations in genetic biomarkers such as BRCA1/2, MSH2, MLH1/6, BRIP1, and RAD51C/D have been studied in EOC. In addition, molecular characteristics, including DNA methylation and RNA transcription, are being explored as potential new biomarkers for the diagnosis and prognosis of this type of neoplasia. The present review focused on the role of DNA methylation and non‑coding RNA expression in the development of ovarian carcinomas and their association with diagnosis, prognosis, and the resistance of cancer cells to radiotherapy and chemotherapy. The present review considered the transition from the DNA structure to the RNA expression in ovarian carcinoma.

Pan-cancer analysis of the prognostic and immunological role of Fanconi anemia complementation group E

Fanconi anemia (FA) genes contribute to tumorigenesis by regulating DNA repair. Despite its importance for assembly and functionality of the FA core complex, no pan-cancer analysis of FANCE was performed. We aimed to provide a comprehensive understanding of the role of FANCE in cancers. Based on The Cancer Genome Atlas (TCGA), Cancer Cell Line Encyclopedia (CCLE), Genotype Tissue-Expression (GTEx), Human Protein Atlas (HPA), Gene Expression Omnibus (GEO), and Cancer Single-cell Atlas (CancerSEA) databases, we investigated the carcinogenicity of FANCE using various bioinformatics methods, including FANCE expression and prognosis, immune invasion, tumor mutation burden, microsatellite instability, and neoantigens. We monitored Fance mutations in mice that caused tumorigenesis. FANCE expression and activity scores were upregulated in 15 and 21 cancers. High expression of FANCE affected shorter overall survival (OS) in seven cancers and longer overall survival in three cancers. It was correlated with shorter overall survival and progression-free interval (PFI) in endometrial cancer and longer overall survival and PFI in cervical cancer. FANCE expression negatively correlated with stromal/immune scores in 21 cancers including cervical cancer, endometrial cancer, and ovarian cancer. FANCE expression negatively correlated with CD8 T cells in endometrial cancer and positively correlated with M1 macrophages in cervical cancer, possibly related to cancer prognosis. FANCE positively correlated with immune checkpoint inhibitors PD-1, PD-L1, and CTLA4 in endometrial cancer and ovarian cancer. FANCE expression positively correlated with microsatellite instability, tumor mutational burden, and neoantigens in 7, 22, and five cancers, especially in endometrial cancer, potentially increasing the effectiveness of immunotherapy. Single-cell sequencing data showed FANCE was primarily expressed in cancer cells in cervical and ovarian cancer, and in fibroblasts in endometrial cancer. Fance heterozygous mutant mice had increased tumor incidences and shorter overall survival and tumor-free survival (TFS) than Fance homozygous mutant mice and wild-type mice. Conclusively, FANCE potential to serve as a biomarker for cancer prognosis and may predict cancer immunotherapy responses. Fance heterozygous mutant resulted in increased tumorigenesis and poor prognosis in mice.

Homologous Recombination Deficiency in Ovarian, Breast, Colorectal, Pancreatic, Non-Small Cell Lung and Prostate Cancers, and the Mechanisms of Resistance to PARP Inhibitors

Homologous recombination (HR) is a highly conserved DNA repair mechanism that protects cells from exogenous and endogenous DNA damage. Breast cancer 1 (BRCA1) and breast cancer 2 (BRCA2) play an important role in the HR repair pathway by interacting with other DNA repair proteins such as Fanconi anemia (FA) proteins, ATM, RAD51, PALB2, MRE11A, RAD50, and NBN. These pathways are frequently aberrant in cancer, leading to the accumulation of DNA damage and genomic instability known as homologous recombination deficiency (HRD). HRD can be caused by chromosomal and subchromosomal aberrations, as well as by epigenetic inactivation of tumor suppressor gene promoters. Deficiency in one or more HR genes increases the risk of many malignancies. Another conserved mechanism involved in the repair of DNA single-strand breaks (SSBs) is base excision repair, in which poly (ADP-ribose) polymerase (PARP) enzymes play an important role. PARP inhibitors (PARPIs) convert SSBs to more cytotoxic double-strand breaks, which are repaired in HR-proficient cells, but remain unrepaired in HRD. The blockade of both HR and base excision repair pathways is the basis of PARPI therapy. The use of PARPIs can be expanded to sporadic cancers displaying the “BRCAness” phenotype. Although PARPIs are effective in many cancers, their efficacy is limited by the development of resistance. In this review, we summarize the prevalence of HRD due to mutation, loss of heterozygosity, and promoter hypermethylation of 35 DNA repair genes in ovarian, breast, colorectal, pancreatic, non-small cell lung cancer, and prostate cancer. The underlying mechanisms and strategies to overcome PARPI resistance are also discussed.

The Fanconi anemia pathway and Breast Cancer: A comprehensive review of clinical data

The development of breast cancer depends on several risk factors, including environmental, lifestyle and genetic factors. Despite the evolution of DNA sequencing techniques and biomarker detection, the epidemiology and mechanisms of various breast cancer susceptibility genes have not been elucidated yet. Dysregulation of the DNA damage response causes genomic instability and increases the rate of mutagenesis and the risk of carcinogenesis. The Fanconi Anemia (FA) pathway is an important component of the DNA damage response and plays a critical role in the repair of DNA interstrand crosslinks and genomic stability. The FA pathway involves 22 recognized genes and specific mutations have been identified as the underlying defect in the majority of FA patients. A thorough understanding of the function and epidemiology of these genes in breast cancer is critical for the development and implementation of individualized therapies that target unique tumor profiles. Targeted therapies (PARP inhibitors) exploiting the FA pathway gene defects have been developed and have shown promising results. This narrative review summarizes the current literature on the involvement of FA genes in sporadic and familial breast cancer with a focus on clinical data derived from large cohorts.

FANCF hypomethylation is associated with colorectal cancer in Han Chinese

BACKGROUND/AIMS

Fanconi anemia complement group F (FANCF) is known to be involved in DNA repair, and the overexpression of FANCF protein leads to cell proliferation and ultimately to cancer. The purpose of this study was to assess whether FANCF methylation was associated with colorectal cancer (CRC).

MATERIALS AND METHODS

A case-control experiment was conducted to study the association between FANCF methylation and CRC. We used quantitative methylation-specific PCR to measure the FANCF promoter methylation, and the percentage of methylation reference (PMR) to quantify the FANCF promoter methylation level. To investigate the effect of the selected FANCF fragment on gene expression regulation, we also performed a dual-luciferase reporter gene assay.

RESULTS

The results indicated that FANCF methylation in CRC tumor tissues was significantly lower than that in the nontumor tissues (median PMR: 44.86% vs. 65.77%, p=0.00001). Analysis of receiver-operating characteristic curves showed that FANCF hypomethylation had a diagnostic value for CRC (area under curve [AUC]: 0.670, sensitivity: 55.8%, specificity: 71.7%, p=0.00001). The dual-luciferase reporter assay showed that the FANCF fragment upregulated gene expression (fold change: 1.93, p=0.002).

CONCLUSION

Research demonstrates for the first time that FANCF hypomethylation is significantly associated with CRC risk. FANCF hypomethylation may ultimately increase the risk of CRC by upregulating the expression of FANCF.

Role of DNA Methylation in the Resistance to Therapy in Solid Tumors

Despite the recent advances in chemotherapeutic treatments against cancer, some types of highly aggressive and invasive cancer develop drug resistance against conventional therapies, which continues to be a major problem in the fight against cancer. In recent years, studies of alterations of DNA methylome have given us a better understanding of the role of DNA methylation in the development of tumors. DNA methylation (DNAm) is an epigenetic change that promotes the covalent transfer of methyl groups to DNA. This process suppresses gene expression through the modulation of the transcription machinery access to the chromatin or through the recruitment of methyl binding proteins. DNAm is regulated mainly by DNA methyltransferases. Aberrant DNAm contributes to tumor progression, metastasis, and resistance to current anti-tumoral therapies. Aberrant DNAm may occur through hypermethylation in the promoter regions of tumor suppressor genes, which leads to their silencing, while hypomethylation in the promoter regions of oncogenes can activate them. In this review, we discuss the impact of dysregulated methylation in certain genes, which impact signaling pathways associated with apoptosis avoidance, metastasis, and resistance to therapy. The analysis of methylome has revealed patterns of global methylation, which regulate important signaling pathways involved in therapy resistance in different cancer types, such as breast, colon, and lung cancer, among other solid tumors. This analysis has provided gene-expression signatures of methylated region-specific DNA that can be used to predict the treatment outcome in response to anti-cancer therapy. Additionally, changes in cancer methylome have been associated with the acquisition of drug resistance. We also review treatments with demethylating agents that, in combination with standard therapies, seem to be encouraging, as tumors that are in early stages can be successfully treated. On the other hand, tumors that are in advanced stages can be treated with these combination schemes, which could sensitize tumor cells that are resistant to the therapy. We propose that rational strategies, which combine specific demethylating agents with conventional treatment, may improve overall survival in cancer patients.

Hypermethylation of tumor suppressor genes is a risk factor for poor prognosis in ovarian cancer: A meta-analysis

OBJECTIVE

DNA methylation is the earliest and most studied epigenetic modification in cancer. The literature reported that the abnormal methylation level of multiple genes was associated with poor prognosis in ovarian cancer. However, due to a small sample size, the results reported in the literature vary widely. In this study, the correlation between aberrant methylation level of genes and poor prognosis of ovarian cancer was reviewed in order to clarify the role of DNA methylation in the prognosis of ovarian cancer.

METHODS

A systematic research of PubMed, EMbase, Cochrane Library, China Biology Medicine disc (CBMdisc), China National Knowledge Infrastructure (CNKI), Wanfang databases, and EMBASE was performed, and calculated the hazard ratio (HR) of overall survival (OS) and progression-free survival (PFS) and its 95% confidence interval.

RESULTS

HR of the OS obtained of target genes was 2.32 (95% CI: 1.54-3.48, P = .000); HR of the PFS obtained of target genes was 1.318 (95% CI: 0.848-2.050, P = .220). HR of OS achieved by tumor suppressor genes was 3.09 (95% CI 1.80 - 5.30, P = .000).

CONCLUSION

Hypermethylation of tumor suppressor genes indicate poor prognosis of ovarian cancer.

Epigenetic regulation of DNA repair genes and implications for tumor therapy

DNA repair represents the first barrier against genotoxic stress causing metabolic changes, inflammation and cancer. Besides its role in preventing cancer, DNA repair needs also to be considered during cancer treatment with radiation and DNA damaging drugs as it impacts therapy outcome. The DNA repair capacity is mainly governed by the expression level of repair genes. Alterations in the expression of repair genes can occur due to mutations in their coding or promoter region, changes in the expression of transcription factors activating or repressing these genes, and/or epigenetic factors changing histone modifications and CpG promoter methylation or demethylation levels. In this review we provide an overview on the epigenetic regulation of DNA repair genes. We summarize the mechanisms underlying CpG methylation and demethylation, with de novo methyltransferases and DNA repair involved in gain and loss of CpG methylation, respectively. We discuss the role of components of the DNA damage response, p53, PARP-1 and GADD45a on the regulation of the DNA (cytosine-5)-methyltransferase DNMT1, the key enzyme responsible for gene silencing. We stress the relevance of epigenetic silencing of DNA repair genes for tumor formation and tumor therapy. A paradigmatic example is provided by the DNA repair protein O⁶-methylguanine-DNA methyltransferase (MGMT), which is silenced in up to 40% of various cancers through CpG promoter methylation. The CpG methylation status of the MGMT promoter strongly correlates with clinical outcome and, therefore, is used as prognostic marker during glioblastoma therapy. Mismatch repair genes are also subject of epigenetic silencing, which was shown to correlate with colorectal cancer formation. For many other repair genes shown to be epigenetically regulated the clinical outcome is not yet clear. We also address the question of whether genotoxic stress itself can lead to epigenetic alterations of genes encoding proteins involved in the defense against genotoxic stress.

TET1 inhibits cell proliferation by inducing RASSF5 expression

Tet methylcytosine dioxygenases (TETs) catalyze the oxidative reactions of 5-methylcytosine to 5-hydroxymethylcytosine (5hmC). However, TET1 roles in ovarian cancer cell growth are unknown. Here, we show that ectopic expression of TET1 increased 5hmC levels, and inhibited proliferation and colony formation in ovarian cancer cell lines. Furthermore, in vitro and in vivo functional studies demonstrated that TET1 overexpression is necessary for the suppression of ovarian cancer growth, whereas depletion of TET1 expression had the opposite effect. Furthermore, the results of RNA-seq and qRT-PCR analyses identified a tumor suppressor, Ras association domain family member 5 (RASSF5), as the key downstream target of TET1. TET1 promotes RASSF5 expression by demethylating a CpG site within RASSF5 promoter. Up-regulated RASSF5 expression leads to the suppression of ovarian cancer cells growth. Additionally, we demonstrated that inhibition of CUL4-DDB1 ubiquitin ligase complex decrease 5hmC levels in ovarian cancer cells. These results provide new insights into the understanding of how ovarian cancers develop and grow, and identify TET1 as a key player in this process.