The Glu346Lys polymorphism and frameshift mutations of the Methyl-CpG Binding Domain 4 gene in gastrointestinal cancer

Meta-analysis of the association between MBD4 Glu346Lys polymorphism and cancer risk

OBJECTIVE

The purpose of this study was to systematically evaluate the association between methyl-CpG binding domain 4, DNA glycosylase (MBD4) Glu346Lys polymorphism and cancer risk.

METHODS

A comprehensive document retrieval from the Chinese National Knowledge Infrastructure (CNKI), EMBASE, and PubMed databases was performed through 1 September 2019. The strength of the correlation was assessed using the pooled odds ratio (ORs) and 95% confidence interval (CIs).

RESULTS

Five relevant studies were retrieved following screening, including 1804 cases and 2193 controls. We found no association between MBD4 Glu346Lys polymorphism and cancer risk under all genetic models. Nevertheless, a subgroup analysis based on country showed a strong association in the Chinese population. Under the recessive model, Chinese individuals with the Lys/Lys genotype had a higher risk of cancer (OR = 1.37, 95% CI = 1.11-1.70).

CONCLUSION

Analysis of the MBD4 Glu346Lys polymorphism in different populations will help to elucidate the pathogenesis of cancer. The polymorphism can be utilized as a biomarker for cancer susceptibility among Chinese people.

Association of DNA repair gene polymorphisms with colorectal cancer risk and treatment outcomes

Colorectal cancer (CRC) is the third most common carcinoma worldwide. Despite the progress in screening and treatment, CRC remains a leading cause of cancer-related mortality. Alterations to normal nucleic acid processing may drive neoplastic transformation of colorectal epithelium. DNA repair machinery performs an essential function in the protection of genome by reducing the number of genetic polymorphisms/variations that may drive carcinogenicity. Four essential DNA repair systems are known which include nucleotide excision repair (NER), base excision repair (BER), mismatch repair (MMR), and double-strand break repair (DSBR). Polymorphisms of DNA repair genes have been shown to influence the risk of cancer development as well as outcomes of treatment. Several studies demonstrated the association between genetic polymorphism of DNA repair genes and increased risk of CRC in different populations. In this review, we have summarized the impact of DNA repair gene polymorphisms on risk of CRC development and treatment outcomes. Advancements of the current understanding for the impact of DNA repair gene polymorphisms on the risk and treatment of CRC may support diagnostic and predictive roles in patients with CRC.

The Mbd4 DNA glycosylase protects mice from inflammation-driven colon cancer and tissue injury

Much of the global cancer burden is associated with longstanding inflammation accompanied by release of DNA-damaging reactive oxygen and nitrogen species. Here, we report that the Mbd4 DNA glycosylase is protective in the azoxymethane/dextran sodium sulfate (AOM/DSS) mouse model of inflammation-driven colon cancer. Mbd4 excises T and U from T:G and U:G mismatches caused by deamination of 5-methylcytosine and cytosine. Since the rate of deamination is higher in inflamed tissues, we investigated the role of Mbd4 in inflammation-driven tumorigenesis. In the AOM/DSS assay, Mbd4-/- mice displayed more severe clinical symptoms, decreased survival, and a greater tumor burden than wild-type (WT) controls. The increased tumor burden in Mbd4-/- mice did not arise from impairment of AOM-induced apoptosis in the intestinal crypt. Histopathological analysis indicated that the colonic epithelium of Mbd4-/- mice is more vulnerable than WT to DSS-induced tissue damage. We investigated the role of the Mbd4-/- immune system in AOM/DSS-mediated carcinogenesis by repeating the assay on WT and Mbd4-/- mice transplanted with WT bone marrow. Mbd4-/- mice with WT bone marrow behaved similarly to Mbd4-/- mice. Together, our results indicate that the colonic epithelium of Mbd4-/- mice is more vulnerable to DSS-induced injury, which exacerbates inflammation-driven tissue injury and cancer.

Methyl-CpG-Binding Protein (MBD) Family: Epigenomic Read-Outs Functions and Roles in Tumorigenesis and Psychiatric Diseases

Epigenetics is the study of the heritable changes on gene expression that are responsible for the regulation of development and that have an impact on several diseases. However, it is of equal importance to understand how epigenetic machinery works. DNA methylation is the most studied epigenetic mark and is generally associated with the regulation of gene expression through the repression of promoter activity and by affecting genome stability. Therefore, the ability of the cell to interpret correct methylation marks and/or the correct interpretation of methylation plays a role in many diseases. The major family of proteins that bind methylated DNA is the methyl-CpG binding domain proteins, or the MBDs. Here, we discuss the structure that makes these proteins a family, the main functions and interactions of all protein family members and their role in human disease such as psychiatric disorders and cancer.

Involvement of MBD4 inactivation in mismatch repair-deficient tumorigenesis

The DNA glycosylase gene MBD4 safeguards genomic stability at CpG sites and is frequently mutated at coding poly-A tracks in mismatch repair (MMR)-defective colorectal tumors (CRC). Mbd4 biallelic inactivation in mice provided conflicting results as to its role in tumorigenesis. Thus, it is unclear whether MBD4 alterations are only secondary to MMR defects without functional consequences or can contribute to the mutator phenotype. We investigated MBD4 variants in a large series of hereditary/familial and sporadic CRC cases. Whereas MBD4 frameshifts were only detected in tumors, missense variants were found in both normal and tumor DNA. In CRC with double-MBD4/MMR and single-MBD4 variants, transition mutation frequency was increased, indicating that MBD4 defects may affect the mutational landscape independently of MMR defect. Mbd4-deficient mice showed reduced survival when combined with Mlh1^−/− genotype. Taken together, these data suggest that MBD4 inactivation may contribute to tumorigenesis, acting as a modifier of MMR-deficient cancer phenotype.

Gut Microbiota Imbalance and Base Excision Repair Dynamics in Colon Cancer

Gut microbiota are required for host nutrition, energy balance, and regulating immune homeostasis, however, in some cases, this mutually beneficial relationship becomes twisted (dysbiosis), and the gut flora can incite pathological disorders including colon cancer. Microbial dysbiosis promotes the release of bacterial genotoxins, metabolites, and causes chronic inflammation, which promote oxidative DNA damage. Oxidized DNA base lesions are removed by base excision repair (BER), however, the role of this altered function of BER, as well as microbiota-mediated genomic instability and colon cancer development, is still poorly understood. In this review article, we will discuss how dysbiotic microbiota induce DNA damage, its impact on base excision repair capacity, the potential link of host BER gene polymorphism, and the risk of dysbiotic microbiota mediated genomic instability and colon cancer.

The MBD4 Glu346Lys polymorphism is associated with the risk of cervical cancer in a Chinese population

OBJECTIVE

Methyl-CpG binding domain 4 (MBD4) protein functions as a DNA repair enzyme and plays an important role in maintaining genome integrity and carcinogenesis. The polymorphisms in the MBD4 gene may be associated with differences in DNA repair capacity and thereby influence an individual's susceptibility to cervical cancer. To verify this hypothesis, we examined the potential association between the MBD4 Glu346Lys polymorphism (rs140693, G>A) and the risk of cervical cancer in a Chinese population.

METHODS

We genotyped the MBD4 Glu346Lys polymorphism in 146 cervical cancer cases and 320 healthy female subjects using polymerase chain reaction-based restriction fragment length polymorphism method. Unconditional logistic regression analysis was used to estimate the association between the genotypes and the risk of cervical cancer.

RESULTS

We observed a significantly decreased risk of cervical cancer associated with the heterozygous Lys/Glu genotype (odds ratio [OR], 0.60; 95% confidence interval [CI], 0.36-0.99; P = 0.046) and the homozygous Glu/Glu genotype (OR, 0.52; 95% CI, 0.30-0.89; P = 0.018), compared with the Lys/Lys homozygotes. Moreover, the reduced cervical cancer risk was more predominant among younger subjects or human papillomavirus-positive individuals carrying Glu/Glu genotypes (OR, 0.33; 95% CI, 0.14-0.78, P = 0.011; and OR, 0.27; 95% CI, 0.09-0.75, P = 0.013, respectively).

CONCLUSIONS

The MBD4 codon 346 polymorphism may play a role in cervical cancer susceptibility in the Chinese population. Further larger case-control and functional studies are needed to validate these findings.

Survivin -31G>C polymorphism and gastrointestinal tract cancer risk: a meta-analysis

Background

Emerging evidence showed that common functional −31G>C polymorphism (rs9904341 G>C) in the promoter region of the survivin gene is involved in the regulation of survivin expression, thus increasing an individual’s susceptibility to gastrointestinal tract (GIT) cancer; but individually published results are inconclusive. The aim of this systematic review and meta-analysis was to derive a more precise estimation of the association between survivin −31G>C polymorphism and GIT cancer risk.

Methods

A literature search of PubMed, Embase, Web of Science and CBM databases was conducted from inception through July 1st, 2012. Crude odds ratios (ORs) with 95% confidence intervals (CIs) were used to assess the strength of association.

Results

Nine case-control studies were included with a total of 2,231 GIT cancer cases and 2,287 healthy controls. The results indicated that survivin −31G>C polymorphism was associated with increased risk of GIT cancer. In the stratified analysis by cancer types, significant associations were observed between survivin −31G>C polymorphism and increased risk of colorectal and gastric cancers. However, the lack of association of survivin −31G>C polymorphism with esophageal cancer risk may be due to a lack of a sufficient number of eligible studies and the influence of different genetic and environmental factors.

Conclusion

Results from the current meta-analysis suggests that survivin −31G>C polymorphism might increase the risk of GIT cancer, especially among gastric and colorectal cancers.

Base excision repair and cancer

Base excision repair is the system used from bacteria to man to remove the tens of thousands of endogenous DNA damages produced daily in each human cell. Base excision repair is required for normal mammalian development and defects have been associated with neurological disorders and cancer. In this paper we provide an overview of short patch base excision repair in humans and summarize current knowledge of defects in base excision repair in mouse models and functional studies on short patch base excision repair germ line polymorphisms and their relationship to cancer. The biallelic germ line mutations that result in MUTYH-associated colon cancer are also discussed.