Influence of cancer-related gene polymorphisms on clinicopathological features in colorectal cancer

Association between three exonuclease 1 polymorphisms and cancer risks: a meta-analysis

To date, the results of studies exploring the relation between exonuclease 1 (Exo1) polymorphisms and cancer risks have differed. In this study, we performed a meta-analysis to investigate the effect of the three most extensively studied Exo1 polymorphisms (Pro757Leu, Glu589Lys, and Glu670Gly) on cancer susceptibility. The related studies published before August 5, 2015, were collected by searching the PubMed and EMBASE databases. We found 16 publications containing studies that were eligible for our study, including 10 studies for Pro757Leu polymorphism (4,093 cases and 3,834 controls), 12 studies for Glu589Lys polymorphism (6,479 cases and 6,550 controls), and 7 studies for Glu670Gly polymorphism (3,700 cases and 3,496 controls). Pooled odds ratios and 95% confidence intervals were used to assess the strength of the associations, and all the statistical analyses were calculated using the software program STATA version 12.0. Our results revealed that the Pro757Leu polymorphism was significantly associated with a reduced cancer risk, whereas an inverse association was found for the Glu589Lys polymorphism. Furthermore, subgroup analysis of smoking status indicated that the Glu589Lys polymorphism was significantly associated with an increased cancer risk in smokers, but not in nonsmokers. However, no evidence was found for an association between the Glu670Gly polymorphism and cancer risk. In conclusion, this meta-analysis suggests that the Pro757Leu polymorphism may provide protective effects against cancer, while the Glu589Lys polymorphism may be a risk factor for cancer. Moreover, the Glu670Gly polymorphism may have no influence on cancer susceptibility. In the future, large-scaled and well-designed studies are needed to achieve a more precise and comprehensive result.

Role of genetic variants of deleted in colorectal carcinoma (DCC) polymorphisms and esophageal and gastric cancers risk in Kashmir Valley and meta-analysis

Genetic alterations in the deleted in colorectal carcinoma (DCC) gene have been a priori reported to associate with metastasis in variety of human cancers. We investigated the association between potentially functional SNPs in DCC and susceptibility to esophageal (EC) and gastric (GC) cancers in Kashmir Valley. We genotyped two SNPs DCC rs714 (A>G) and DCC rs2229080 (C>G) of DCC in 135 EC patients, 108 GC patients, and 195 controls matched by age and sex in Kashmir Valley by polymerase chain reaction-RFLP method. Risk for developing EC and GC was estimated by binary logistic regression by using SPSS. We also performed a meta-analysis on DCC rs714 (A>G) and evaluated the association between the DCC rs714 (A>G) polymorphisms and cancer risk. A significant difference in DCC rs714 (A>G) genotype distribution between EC and GC cases and corresponding control groups was observed (odds ratio (OR) = 1.92; P = 0.03; P-trend = 0.04; false discovery rate (FDR) Pcorr = 0.03: OR = 2.15; P = 0.02; P-trend = 0.01; FDR Pcorr = 0.03). But no such association was observed in DCC rs2229080 (C>G). Further, DCC rs714 (A>G) AA genotype showed significantly increased risk for both gastric squamous cell carcinoma (OR = 5.63; P = 0.02; FDR Pcorr = 0.01) and gastric adenocarcinoma (OR = 2.15; P = 0.02; FDR Pcorr = 0.01). Smoking and salted tea are independently associated with both EC and GC, but gene-environment interaction did not further modulate the risk. Meta-analysis also suggested both independent and overall association of DCC rs714 (A>G) polymorphism with cancer (P = 0.000). In conclusion, genetic variations in DCC rs714 (A>G) modulate risk of EC and GC in high-risk Kashmir population.

A genome-wide association study identifies SNP in DCC is associated with gallbladder cancer in the Japanese population

Gallbladder cancer (GC) is a relatively uncommon cancer with higher incidence in certain areas including Japan. Because of the difficulty in diagnosis, prognosis of GC is very poor. To identify genetic determinants of GC, we conducted a genome-wide association study (GWAS) in 41 GC patients and 866 controls. Association between each single-nucleotide polymorphism (SNP) with GC susceptibility was evaluated by multivariate logistic regression analysis conditioned on age and gender of subjects. SNPs that showed suggestive association (P<1 × 10(-4)) with GC were further examined in 30 cases and 898 controls. SNP rs7504990 in the DCC (deleted in colorectal cancer, 18q21.3) that encodes a netrin 1 receptor achieved a combined P-value of 7.46 × 10(-8) (OR=6.95; 95% CI=3.43-14.08). Subsequent imputation analysis identified multiple SNPs with similarly strong associations in an adjacent genomic region, where loss of heterozygosity was reported in GC and other cancers. Reduced expression of DCC was indicated to be associated with the poorly differentiated histological type, increased proliferation and metastasis through loss of adhesiveness. However, due to the limited sample size investigated here, further replication study and functional analysis would be necessary to further confirm the result of the association.

DNA repair gene polymorphisms and tobacco smoking in the risk for colorectal adenomas

DNA damage is thought to play a critical role in the development of colorectal adenoma. Variation in DNA repair genes may alter their capacity to correct endogenous and exogenous DNA damage. We explored the association between common single-nucleotide polymorphisms (SNPs) in DNA repair genes and adenoma risk with a case-control study nested in the Prostate, Lung, Colorectal and Ovarian Cancer Screening Trial. A total of 1338 left sided, advanced colorectal adenoma cases and 1503 matched controls free of left-sided polyps were included in the study. Using DNA extracted from blood, 3144 tag SNPs in 149 DNA repair genes were successfully genotyped. Among Caucasians, 30 SNPs were associated with adenoma risk at P < 0.01, with four SNPs remaining significant after gene-based adjustment for multiple testing. The most significant finding was for a non-synonymous SNP (rs9350) in Exonuclease-1 (EXO1) [odds ratio (OR) = 1.30, 95% confidence interval (CI) = 1.11-1.51, P = 0.001)], which was predicted to be damaging using bioinformatics methods. However, the association was limited to smokers with a strong risk for current smokers (OR = 2.15, 95% CI = 1.27-3.65) and an intermediate risk for former smokers (OR = 1.45, 95% CI = 1.14-1.82) and no association for never smokers (OR = 0.98, 95% CI = 0.76-1.25) (P(interaction) = 0.002). Among the top findings, an SNP (rs17503908) in ataxia telangiectasia mutated (ATM) was inversely related to adenoma risk (OR = 0.75, 95% CI = 0.63-0.91). The association was restricted to never smokers (OR = 0.55, 95% CI = 0.40-0.76) with no increased risk observed among smokers (OR = 0.89, 95% CI = 0.70-1.13) (P(interaction) = 0.006). This large comprehensive study, which evaluated all presently known DNA repair genes, suggests that polymorphisms in EXO1 and ATM may be associated with risk for advanced colorectal adenoma with the associations modified by tobacco-smoking status.

Methylenetetrahydrofolate reductase polymorphism (677 C>T) predicts long time to progression in metastatic colon cancer treated with 5-fluorouracil and folinic acid

BACKGROUND AND AIMS

Fluoropyrimidine-based chemotherapy is the most common treatment for unresectable metastatic colorectal cancer (m-CRC). Therapy with 5-FU/folinic acid (FA) continues to be a standard treatment in developing countries. Pharmacogenomics allows the tailoring of cancer therapy to the patient. The polymorphism 677C>T of the methylenetetrahydrofolate reductase (MTHFR) gene seems to influence the effectiveness of treatment with 5-FU. We undertook this study to evaluate the frequency of MTHFR 677C>T polymorphism and its relationship to the time to progression (TTP) and overall survival (OS) in m-CRC treated with 5-FU/FA.

METHODS

The MTHFR 677C>T polymorphism was determined using PCR and allele-specific digestion. The clinical variables, TTP and OS, were analyzed in each case and compared between wild-type and variant polymorphic groups.

RESULTS

Among 34 patients (12 males and 22 females), we detected eight wild-type homozygous patients (CC; 24%), nine variant homozygous (TT; 26%), and 17 heterozygous (CT; 50%) individuals. The median TTP in patients with the MTHFR 677 CC, CT, and TT genotypes was 3.43, 4.77, and 4.80 months, respectively (p = 0.047, log rank). A longer TTP was observed in patients with polymorphic variant (CT and TT) compared with the wild-type homozygous patients (4.80 vs. 3.43 months; p = 0.031, log rank).

CONCLUSIONS

In this study, the frequency of the MTHFR 677C>T polymorphism is 50% among m-CRC Mexican patients. The results of this study appear to show that the presence of the MTHFR 677C>T polymorphism is associated with longer TTP and OS in m-CRC treated with 5-FU/FA.

Potentially functional polymorphisms in cell cycle genes and the survival of non-small cell lung cancer in a Chinese population

The cell cycle governs the proliferation and growth of cells and is strictly controlled by some regulators including cyclins, CDKs and CKIs. Germ-line and somatic mutations in cell cycle genes were frequently observed in a subset of cancers including non-small cell lung cancer (NSCLC). In this study, we hypothesized that potentially functional single nucleotide polymorphisms (SNPs) in cell cycle genes may contribute to the prognosis of NSCLC in China. 54 potentially functional polymorphisms in key cell cycle genes (CDK1, CDK2, CDK4, CDK6, CDK7, CCND1, CCND2, CCND3, CCNE1, CCNA1, CCNA2, CCNB1, CCNH, p15, p16, p18, p19, p21, p27, Cdc25A and Cdc25B) were genotyped by using Illumina SNP genotyping platform to evaluate their associations with survival of NSCLC in a clinical cohort of 568 patients. We found that p18 rs3176447 variant genotypes were significantly associated with the decreased risk of death of NSCLC patients (adjusted HR=0.74, 95% CI=0.57-0.97 in an additive model; adjusted HR=0.76, 95% CI=0.55-0.97 in a dominant model); however, p21 rs2395655 variant genotypes were significantly associated with the increased risk of death (adjusted HR=1.21, 95% CI=1.02-1.42 in an additive model; adjusted HR=1.38, 95% CI=1.07-1.78 in a recessive model). Furthermore, the combined effect of unfavorable genotypes for these two SNPs was more prominent in patients with squamous cell carcinoma, late stage and without chemo- or radio-therapy. Although the exact biological function remains to be explored, our findings suggest possible association of polymorphisms of p18 and p21 with the prognosis of NSCLC in a Chinese population. Further large and functional studies are needed to confirm our findings.

SNP-RFLPing 2: an updated and integrated PCR-RFLP tool for SNP genotyping

Background

PCR-restriction fragment length polymorphism (RFLP) assay is a cost-effective method for SNP genotyping and mutation detection, but the manual mining for restriction enzyme sites is challenging and cumbersome. Three years after we constructed SNP-RFLPing, a freely accessible database and analysis tool for restriction enzyme mining of SNPs, significant improvements over the 2006 version have been made and incorporated into the latest version, SNP-RFLPing 2.

Results

The primary aim of SNP-RFLPing 2 is to provide comprehensive PCR-RFLP information with multiple functionality about SNPs, such as SNP retrieval to multiple species, different polymorphism types (bi-allelic, tri-allelic, tetra-allelic or indels), gene-centric searching, HapMap tagSNPs, gene ontology-based searching, miRNAs, and SNP500Cancer. The RFLP restriction enzymes and the corresponding PCR primers for the natural and mutagenic types of each SNP are simultaneously analyzed. All the RFLP restriction enzyme prices are also provided to aid selection. Furthermore, the previously encountered updating problems for most SNP related databases are resolved by an on-line retrieval system.

Conclusions

The user interfaces for functional SNP analyses have been substantially improved and integrated. SNP-RFLPing 2 offers a new and user-friendly interface for RFLP genotyping that can be used in association studies and is freely available at http://bio.kuas.edu.tw/snp-rflping2.

Surface-enhanced Raman scattering based ligase detection reaction

Genomics provides a comprehensive view of the complete genetic makeup of an organism. Individual sequence variations, as manifested by single nucleotide polymorphisms (SNPs), can provide insight into the basis for a large number of phenotypes and diseases including cancer. The ability rapidly screen for SNPs will have a profound impact on a number of applications, most notably personalized medicine. Here we demonstrate a new approach to SNP detection through the application of surface-enhanced Raman scattering (SERS) to the ligase detection reaction (LDR). The reaction uses two LDR primers, one of which contains a Raman enhancer and the other a reporter dye. In LDR, one of the primers is designed to interrogate the SNP. When the SNP being interrogated matches the discriminating primer sequence, the primers are ligated and the enhancer and dye are brought into close proximity enabling the dye's Raman signature to be detected. By detecting the Raman signature of the dye rather than its fluorescence emission, our technique avoids the problem of spectral overlap which limits number of reactions which can be carried out in parallel by existing systems. We demonstrate the LDR-SERS reaction for the detection of point mutations in the human K-ras oncogene. The reaction is implemented in an electrokinetically active microfluidic device that enables physical concentration of the reaction products for enhanced detection sensitivity and quantization. We report a limit of detection of 20 pM of target DNA with the anticipated specificity engendered by the LDR platform.