Barbara Pardini

Genetic variants in selenoprotein genes increase risk of colorectal cancer

Low selenium (Se) status correlates with increased risk of colorectal cancer (CRC). Since Se exerts its biological roles through the selenoproteins, genetic variations in selenoprotein genes may influence susceptibility to CRC. This study analysed 12 single-nucleotide polymorphisms (SNPs) in selenoprotein genes [glutathione peroxidase 1 (GPX1), GPX4, 15 kDa selenoprotein (SEP15), selenoprotein S (SELS), selenoprotein P (SEPP1) and thioredoxin reductase 2 (TXNRD2)] and in genes that code for a key protein in Se incorporation [SECIS-binding protein 2 (SBP2)] and in antioxidant defence [superoxide dismutase 2 (SOD2)] in relation to sporadic CRC incidence. CRC patients (832) and controls (705) from the Czech Republic were genotyped using allele specific PCR. Logistic regression analysis showed that three SNPs were significantly associated with an altered risk of CRC: rs7579 (SEPP1), rs713041 (GPX4) and rs34713741 (SELS). The association of these SNPs with disease risk remained after data stratification for diagnosis and adjustments for lifestyle factors and sex. Significant two-loci interactions were observed between rs4880 (SOD2), rs713041 (GPX4) and rs960531 (TXNRD2) and between SEPP1 and either SEP15 or GPX4. The results indicate that SNPs in SEPP1, GPX4 and SELS influence risk of CRC. We hypothesize that the two-loci interactions reflect functional interactions between the gene products. We propose that these variants play a role in cancer development and represent potential biomarkers of CRC risk.

Association Between TAS2R38 Gene Polymorphisms and Colorectal Cancer Risk: A Case-Control Study in Two Independent Populations of Caucasian Origin

Molecular sensing in the lingual mucosa and in the gastro-intestinal tract play a role in the detection of ingested harmful drugs and toxins. Therefore, genetic polymorphisms affecting the capability of initiating these responses may be critical for the subsequent efficiency of avoiding and/or eliminating possible threats to the organism. By using a tagging approach in the region of Taste Receptor 2R38 (TAS2R38) gene, we investigated all the common genetic variation of this gene region in relation to colorectal cancer risk with a case-control study in a German population (709 controls and 602 cases) and in a Czech population (623 controls and 601 cases). We found that there were no significant associations between individual SNPs of the TAS2R38 gene and colorectal cancer in the Czech or in the German population, nor in the joint analysis. However, when we analyzed the diplotypes and the phenotypes we found that the non-taster group had an increased risk of colorectal cancer in comparison to the taster group. This association was borderline significant in the Czech population, (OR = 1.28, 95% CI 0.99–1.67; Pvalue = 0.058) and statistically significant in the German population (OR = 1.36, 95% CI 1.06–1.75; Pvalue = 0.016) and in the joint analysis (OR = 1.34, 95% CI 1.12–1.61; Pvalue = 0.001). In conclusion, we found a suggestive association between the human bitter tasting phenotype and the risk of CRC in two different populations of Caucasian origin.

Genetic variation in adipokine genes and risk of colorectal cancer

OBJECTIVE Obesity has been related to an increased risk of colorectal cancer (CRC). Adipokines produced by the adipose tissue are directly linked to obesity and may thus contribute to the pathogenesis of CRC. We hypothesized that potentially functional polymorphisms in the adipokine genes leptin (LEP), leptin receptor (LEPR), resistin (RETN), and adiponectin (ADIPOQ) may be associated with CRC. DESIGN AND METHODS We studied the association of four putatively functional single nucleotide polymorphisms (SNPs) with CRC risk using a hospital-based study design with 702 cases and 752 controls from the Czech Republic. We used likelihood ratio tests to select the best model to represent the relationship between genotypes and risk of CRC. Age-adjusted odds ratios (ORs) under the best model were calculated for each SNP. Previous genotyping data on insulin (INS)-related genes were used to explore interactions between genes in obesity- and diabetes-related pathways by using two independent methods, logistic regression, and multifactor-dimensionality reduction. RESULTS A trend to associate between the RETN SNP rs1862513 (C-420G) and CRC risk was observed (per allele OR 1.18, 95% confidence interval (0.99-1.40). Statistically, significant interactions were observed between the INS SNP rs3842754 (+1127INSPstI) genotypes and both the LEPR SNP rs1137101 (Q223R) and the ADIPOQ SNP rs266729 (C-11374G) genotypes. CONCLUSIONS Our results suggest that variants in the adipokine genes may affect CRC risk in combination with variants in diabetes-related genes.

Mutations and polymorphisms in TP53 gene-an overview on the role in colorectal cancer

A functionally normal TP53 is essential to protect organisms from developing cancer. Somatic mutations in the gene represent one of the highest recurring perturbations in human tumours, including colorectal cancer (CRC). However, the variegated phenotype of wide spectrum of somatic mutations in TP53 and the complexity of the disease prevent a straight interpretation of the mutational analysis in tumours. In addition to the presence of somatic mutations, polymorphic features of the gene may also contribute to alteration of the normal TP53 functioning and variants, mainly in the form of single nucleotide polymorphisms, can be expected to impact susceptibility to sporadic CRC. In the present study, we reviewed the potential role of alterations in the TP53 gene, both somatic mutations and inherited sequence variations, in predisposition to CRC and in the prognosis and response to therapy. The available data from association studies have mostly shown contradictory outcomes. The majority of the studies were based on limited sample sizes and focussed on a limited number of polymorphisms, with main being the rs1042522 (Arg72Pro). Thus far, there is no possible generalisation of the role of TP53 as also a predictor of therapeutic response and prognosis. The effects of TP53, and its abnormalities, on the response of tumours to cytotoxic drugs, radiation and chemoradiation are complex. However, from studies it is emerging that the inherited genetics of TP53 pathway components could be utilised to further define patient populations in their abilities to induce p53 activity in response to either DNA damaging or p53-targeted therapies.

Genome-wide association study for colorectal cancer identifies risk polymorphisms in German familial cases and implicates MAPK signalling pathways in disease susceptibility

Genetic susceptibility accounts for approximately 35% of all colorectal cancer (CRC). Ten common low-risk variants contributing to CRC risk have been identified through genome-wide association studies (GWASs). In our GWAS, 610 664 genotyped single-nucleotide polymorphisms (SNPs) passed the quality control filtering in 371 German familial CRC patients and 1263 controls, and replication studies were conducted in four additional case-control sets (4915 cases and 5607 controls). Known risk loci at 8q24.21 and 11q23 were confirmed, and a previously unreported association, rs12701937, located between the genes GLI3 (GLI family zinc finger 3) and INHBA (inhibin, beta A) [P = 1.1 x 10(-3), odds ratio (OR) 1.14, 95% confidence interval (CI) 1.05-1.23, dominant model in the combined cohort], was identified. The association was stronger in familial cases compared with unselected cases (P = 2.0 x 10(-4), OR 1.36, 95% CI 1.16-1.60, dominant model). Two other unreported SNPs, rs6038071, 40 kb upstream of CSNK2A1 (casein kinase 2, alpha 1 polypeptide) and an intronic marker in MYO3A (myosin IIIA), rs11014993, associated with CRC only in the familial CRC cases (P = 2.5 x 10(-3), recessive model, and P = 2.7 x 10(-4), dominant model). Three software tools successfully pointed to the overrepresentation of genes related to the mitogen-activated protein kinase (MAPK) signalling pathways among the 1340 most strongly associated markers from the GWAS (allelic P value < 10(-3)). The risk of CRC increased significantly with an increasing number of risk alleles in seven genes involved in MAPK signalling events (P(trend) = 2.2 x 10(-16), OR(per allele) = 1.34, 95% CI 1.11-1.61).

Circulating miRNAs miR-34a and miR-150 associated with colorectal cancer progression

BackgroundScreening for the early detection of colorectal cancer is important to improve patient survival. The aim of this study was to investigate the potential of circulating cell-free miRNAs as biomarkers of CRC, and their efficiency at delineating patients with polyps and benign adenomas from normal and cancer patient groups.MethodsThe expression of 667 miRNAs was assessed in a discovery set of 48 plasma samples comprising normal, polyp, adenoma, and early and advanced cancer samples. Three miRNAs (miR-34a, miR-150, and miR-923) were further examined in a validation cohort of 97 subjects divided into the same five groups, and in an independent public dataset of 40 CRC samples and paired normal tissues.ResultsHigh levels of circulating miR-34a and low miR-150 levels distinguished groups of patients with polyps from those with advanced cancer (AUC = 0.904), and low circulating miR-150 levels separated patients with adenomas from those with advanced cancer (AUC = 0.875). In addition, the altered expression of miR-34a and miR-150 in an independent public dataset of forty CRC samples and paired normal tissues was confirmed.ConclusionWe identified two circulating miRNAs capable of distinguishing patient groups with different diseases of the colon from each other, and patients with advanced cancer from benign disease groups.

MTHFR and MTRR genotype and haplotype analysis and colorectal cancer susceptibility in a case-control study from the Czech Republic

Polymorphic variants in genes involved in one-carbon metabolism, in particular of dietary folate, may modulate the risk for colorectal cancer through aberrant DNA-methylation and altered nucleotide synthesis and repair. In the present study, we have assessed the association of six polymorphisms and relative haplotypes in the MTHFR gene (rs1801133 and rs1801131) and in the MTRR gene (rs1801394, rs1532268, rs162036, and rs10380) with the risk for colorectal cancer in 666 patients and 1377 controls from the Czech Republic. We found that the 677 C>T polymorphism in the MTHFR gene significantly decreased the risk for colorectal cancer in homozygous carriers of the variant allele (OR, 0.58; 95% CI, 0.39-0.87). Also, we noted a significantly different distribution of genotypes between cases and controls for the 66A>G polymorphism in the MTRR gene. In particular, homozygous carriers of the G-containing allele of this polymorphism were at an increased risk for colorectal cancer (OR, 1.39; 95% CI, 1.04-1.85). Haplotype analysis of the two MTHFR polymorphisms showed a moderate difference in the distribution of the TA haplotype between cases and controls. In comparison to the most common haplotype (CA), the TA haplotype was associated with a decreased risk for colorectal cancer (OR, 0.84; 95% CI, 0.71-0.99). No difference in the distribution between cases and controls was observed for the haplotypes based on the four polymorphisms in the MTRR gene. The present study suggests that the 677TT genotype and the TA haplotype in the MTHFR gene may also have a role in colorectal cancer risk in the Czech population, indicating the importance of genes involved in folate metabolism with respect to cancer risk. For MTRR, additional studies on larger populations are needed to clarify the possible role of variation in this gene in colorectal carcinogenesis.

Association of serum bilirubin and promoter variations in HMOX1 and UGT1A1 genes with sporadic colorectal cancer

Heme oxygenase‐1 (HMOX1) and bilirubin UDP‐glucuronosyltransferase (UGT1A1) enzymes, both involved in bilirubin homeostasis, play an important role in the oxidative stress defense. The objective of our study was to assess the effect of promoter variations of HMOX1 and UGT1A1 genes and of serum bilirubin on the risk of sporadic colorectal cancer (CRC). This exploratory case‐control study was based on 777 CRC patients and 986 controls from the Czech Republic. The (GT)n and (TA)n dinucleotide variations in HMOX1 and UGT1A1 gene promoters, respectively, were determined by fragment analysis. In addition, the A(‐413)T variant in HMOX1 promoter was also analyzed using a polymerase chain reaction‐restriction fragment length polymorphism (PCR‐RFLP) method. Serum bilirubin levels were compared in a subset of 174 cases and 247 controls, for whom biochemical data were available. After adjustment for age, a significant association between CRC risk and UGT1A1*28 allele carrier status was detected [odds ratio (95% confidence intervals) = 0.80 (0.60–0.97), p = 0.022]. No association between CRC risk and individual HMOX1 gene variants was observed, although a diplotype analysis revealed an increased risk for a specific HMOX1 genotype combination. These effects were more pronounced in males. Substantially lower serum bilirubin levels were detected in CRC patients compared to the controls (p < 0.001); each 1 μmol/L decrease in serum bilirubin was associated with a 7% increase of CRC risk (p < 0.001). In conclusion, UGT1A1*28 allele carrier status might be a protective factor against the development of CRC in the male population, whereas low serum bilirubin levels are associated with an increased risk of CRC in both genders.

Insulin pathway related genes and risk of colorectal cancer: INSR promoter polymorphism shows a protective effect

Western lifestyle leading to obesity and type 2 diabetes has been associated with increased risk of colorectal cancer (CRC). Diet and related factors may affect the risk by modifying plasma insulin levels. Thus, the inter-individual variation in insulin signaling may play a plausible role in the development of CRC. We hypothesized that functional polymorphisms in the insulin pathway genes INS, INSR, IGFBPI, insulin receptor substrate 1 (IRS1), and IRS2 may be associated with CRC. We studied the association of five single nucleotide polymorphisms (SNPs) with the risk of CRC using a hospital-based case-control design with 712 cases and 748 controls from the Czech Republic. The INSR A-603G promoter SNP, which is located within a known Sp1-binding site, was associated with the risk of CRC, with carriers of the G allele having a decreased risk (odds ratios (OR) 0.71, 95% confidence interval (CI) 0.54-0.93). Carrying the variant allele of the IRS1 Gly972Arg SNP further decreased the risk among the INSR-603G allele carriers (OR 0.28, 95% CI 0.11-0.70). SNPs in the INS, IGFBPI, and IRS2 genes did not affect the risk of CRC. In conclusion, genetic variation in the insulin signaling pathway genes may affect the risk of CRC.

Polymorphisms in microRNA genes as predictors of clinical outcomes in colorectal cancer patients

Colorectal cancer (CRC) is one of the most frequently diagnosed malignancies worldwide. It is routinely cured by a 5-fluorouracil (5-FU)-based chemotherapy which improves outcomes in patients. We investigated the effect of single nucleotide polymorphisms (SNPs) in two microRNA (miRNA)-encoding genes that have been previously reported as important in prognosis in patients with stage III CRC and treated with 5-FU-based chemotherapy. Two SNPs (rs4919510 in miR-608 and rs213210 in miR-219-1) were genotyped in 1083 CRC patients recruited in the Czech Republic to evaluate their effect on clinical outcomes. Carriers of the variant T allele in rs213210 and receiving 5-FU chemotherapy were associated with a significantly worse survival [hazard ratio (HR) = 2.18; 95% confidence interval (CI): 1.20-3.98; adjusted P = 0.01] and an increased risk of relapse (HR = 1.94; 95% CI: 1.16-3.25; adjusted P = 0.01). After further stratification for tumor grading, stage III patients carrying the G allele of rs4919510 and undergoing adjuvant chemotherapy were at decreased risk of relapse (HR = 0.44; 95% CI: 0.20-0.94; adjusted P = 0.03). The present study confirms that variations in miRNA-encoding genes may be an important factor for modulating CRC prognosis and predicting therapy response.