Sylvia Rabstein

One-Carbon Metabolism and Breast Cancer Risk: No Association of MTHFR, MTR, and TYMS Polymorphisms in the GENICA Study from Germany

Neoplastic development and growth are suspected to be influenced by availability and metabolism of folate due to effects on gene expression through DNA methylation and on genome integrity through DNA synthesis and repair ([1][1]-[3][2]). Key enzymatic regulators are methylene-tetrahydrofolate

Expression of xenobiotic and steroid hormone metabolizing enzymes in human breast carcinomas

The potential to metabolize endogenous and exogenous substances may influence breast cancer development and tumor growth. Therefore, the authors investigated the protein expression of Glutathione S‐transferase (GST) isoforms and cytochrome P450 (CYP) known to be involved in the metabolism of steroid hormones and endogenous as well as exogenous carcinogens in breast cancer tissue to obtain new information on their possible role in tumor progression. Expression of GST pi, mu, alpha and CYP1A1/2, 1A2, 3A4/5, 1B1, 2E1 was assessed by immunohistochemistry for primary breast carcinomas of 393 patients from the German GENICA breast cancer collection. The percentages of positive tumors were 50.1 and 44.5% for GST mu and CYP2E1, and ranged from 13 to 24.7% for CYP1A2, GST pi, CYP1A1/2, CYP3A4/5, CYP1B1. GST alpha was expressed in 1.8% of tumors. The authors observed the following associations between strong protein expression and histopathological characteristics: GST expression was associated with a better tumor differentiation (GST mu, p = 0.018) and with reduced lymph node metastasis (GST pi, p = 0.02). In addition, GST mu expression was associated with a positive estrogen receptor and progesterone receptor status (p < 0.001). CYP3A4/5 expression was associated with a positive nodal status (p = 0.018). Expression of CYP1B1 was associated with poor tumor differentiation (p = 0.049). Our results demonstrate that the majority of breast carcinomas expressed xenobiotic and drug metabolizing enzymes. They particularly suggest that GST mu and pi expression may indicate a better prognosis and that strong CYP3A4/5 and CYP1B1 expression may be key features of nonfavourable prognosis.

Investigation of Genetic Variants of Genes of the Hemochromatosis Pathway and Their Role in Breast Cancer

Iron overload has been noticed as a feature of human breast cancer. Cellular iron uptake is regulated by the hemochromatosis and transferrin receptor system, mutations of which cause the iron storage disease hereditary hemochromatosis. To understand the role of hemochromatosis and transferrin receptor system mutations in breast cancer, we analyzed 19 sequence variations at HFE, TFR1, TFR2, and FPN1 and compared genotype frequencies between cases and controls in a German population. There were 688 breast cancer patients and 724 population-based and age-matched controls. For genotyping, we applied the Hemochromatosis Strip Assay and TaqMan allelic discrimination analyses. In addition to genotype frequencies, we established frequencies of compound genotypes. The frequencies of HFE at His63Asp, Ser65Cys, and Cys282Tyr, and of TFR1 at Ser142Gly minor alleles in this German population were 15.9%, 1.8%, 5.6%, and 46.0%, respectively. No rare variants at 15 more loci at HFE, TFR2, and FPN1 were observed in breast cancer patients. There were no significant differences of allele and genotype frequencies between cases and controls. Triple and quadruple compound genotypes at HFE_His63_Cys282-TFR1_Ser142Gly and HFE_His63_Ser65_Cys282-TFR1_Ser142Gly showed a nonsignificant increase in cases. Although limited by low numbers, an increased prevalence of the HFE Tyr282 minor allele was observed in breast cancer cases with a high number of affected lymph nodes (P = 0.032). Our data suggest that variants of the hemochromatosis-transferrin receptor system have no direct effect on the incidence of breast cancer in Germany. Possible effects on tumor progression and prognosis remain elusive.

Common variants in the UBC9 gene encoding the SUMO-conjugating enzyme are associated with breast tumor grade

UBC9 encodes a protein that conjugates small ubiquitin‐related modifier (SUMO) to target proteins resulting in a change of their localization, activity or stability. Genetic variability may affect expression and activity of UBC9 and may have an impact on breast tumor progression. We investigated associations between UBC9 genotypes and histopathological parameters in 1,021 breast cancer cases of the GENICA collection using a single nucleotide polymorphism (SNP) tagging approach. Genotyping analyses were performed by TaqMan® allelic discrimination. Odds ratios (OR) and 95% confidence intervals (CI) were calculated by ordinal logistic regression. Multiple imputation based on HapMap data was applied to boost the power of the study. The study revealed significant associations of three UBC9 SNPs with histological grade (rs7187167, ptrend = 0.001; rs11248866, ptrend = 0.009; rs8052688, ptrend = 0.008). Model selection identified a recessive penetrance model for rs7187167 as the best representation of tumor grade (global p = 0.001). This model did not improve by inclusion of additional SNPs in linkage disequilibrium. Imputation of SNPs in a 300 kb region around the genotyped SNPs supported rs7187167 as a major contributor to tumor grade. Compared with common allele carriers, rare homozygotes presented less frequently with high grade tumors (G3 vs. G1: OR 0.26, 95% CI 0.11–0.62; G3 vs. G2: OR 0.45, 95% CI 0.23–0.86). In addition to tumor size, nodal status and estrogen receptor status, multivariate analyses confirmed an independent role of rs7187167 as predictor of tumor grade (p = 0.0003). The present results underline the value of genetic variation in UBC9 for breast cancer prognosis.

Dose-Response Modeling of Occupational Exposure to Polycyclic Aromatic Hydrocarbons with Biomarkers of Exposure and Effect

In regulatory toxicology, the dose-response relationship between occupational exposure and biomarkers is of importance in setting threshold values. We analyzed the relationships between occupational exposure to polycyclic aromatic hydrocarbons (PAH) and various biomarkers of internal exposure and DNA damage with data from 284 highly exposed male workers. Personal exposure to phenanthrene and other PAHs was measured during shift and correlated with the sum of 1−, 2+9−, 3−, and 4-hydroxyphenanthrenes in post-shift urine. PAHs and hydroxyphenanthrenes were associated with DNA damage assessed in WBC as 8-oxo-7,8-dihydro-2′-deoxyguanosine/106 dGuo and strand breaks by Comet assay as Olive tail moment. Hydroxyphenanthrenes correlated with phenanthrene (Spearman rs = 0.70; P < 0.0001). No correlations could be found between strand breaks and exposure (rs = 0.01, P < 0.0001 for PAHs; rs = −0.03, P = 0.68 for hydroxyphenanthrenes). Correlations with 8-oxo-7,8-dihydro-2′-deoxyguanosine/106 dGuo were weakly negative (rs = −0.22, P = 0.004 for PAHs) or flat (rs = −0.08, P = 0.31 for hydroxyphenanthrenes). Linear splines were applied to assess the relationships between the log-transformed variables. All regression models were adjusted for smoking and type of industry. For hydroxyphenanthrenes, 51.7% of the variance could be explained by phenanthrene and other predictors. Up to 0.77 μg/m3 phenanthrene, no association could be found with hydroxyphenanthrenes. Above that point, hydroxyphenanthrenes increased by a factor of 1.47 under a doubling of phenanthrene exposure (slope, 0.56; 95% confidence interval, 0.47-0.64). Hydroxyphenanthrenes may be recommended as biomarker of occupational PAH exposure, whereas biomarkers of DNA damage in blood did not show a dose-response relation to PAH exposure. (Cancer Epidemiol Biomarkers Prev 2007;16(9):1863–73)

N-acetyltransferase 2, exposure to aromatic and heterocyclic amines, and receptor-defined breast cancer.

The role of N-acetyltransferase 2 (NAT2) polymorphism in breast cancer is still unclear. We explored the associations between potential sources of exposure to aromatic and heterocyclic amines (AHA), acetylation status and receptor-defined breast cancer in 1020 incident cases and 1047 population controls of the German GENICA study. Acetylation status was assessed as slow or fast. Therefore, NAT2 haplotypes were estimated using genotype information from six NAT2 polymorphisms. Most probable haplotypes served as alleles for the deduction of NAT2 acetylation status. The risks of developing estrogen receptor &agr; (ER) and progesterone receptor (PR)-positive or negative tumors were estimated for tobacco smoking, consumption of red meat, grilled food, coffee, and tea, as well as expert-rated occupational exposure to AHA with logistic regression conditional on age and adjusted for potential confounders. Joint effects of these factors and NAT2 acetylation status were investigated. Frequent consumption of grilled food and coffee showed higher risks in slow acetylators for receptor-negative tumors [grilled food: ER−: odds ratio (OR) 2.57, 95% confidence interval (CI) 1.07–6.14 for regular vs. rare; coffee: ER−: OR 2.55, 95% CI 1.22–5.33 for ≥4 vs. 0 cups/day]. We observed slightly higher risks for never smokers that are fast acetylators for receptor-positive tumors compared with slow acetylators (ER−: OR 1.32, 95% CI 1.00–1.73). Our results support differing risk patterns for receptor-defined breast cancer. However, the modifying role of NAT2 for receptor-defined breast cancer is difficult to interpret in the light of complex mixtures of exposure to AHA.

Polymorphisms in the UBC9 and PIAS3 genes of the SUMO-conjugating system and breast cancer risk

SUMOylation consists in the covalent conjugation of small ubiquitin-related modifiers to target proteins. SUMOylation participates in processes that are tightly linked to tumorigenesis, and genetic variability in the SUMO-conjugating system may influence the development of breast cancer. We recently reported that variation in the UBC9 gene encoding the SUMO-conjugating enzyme may affect the grade of breast tumors. Following comprehensive in silico analyses for detection of putative functional polymorphisms in 14 genes of the SUMO system, we selected one coding SNP in PIAS3 and seven tag SNPs in UBC9 for association analyses. Results were based on 1,021 cases, and 1,015 matched controls from the population-based GENICA study. Odds ratios (OR) and 95% confidence intervals (CI) were estimated by conditional logistic regression. To explore the association with polymorphisms closely linked to the genotyped variants, multiple imputation based on HapMap data was applied. The study revealed associations of four UBC9 polymorphisms with risk of grade 1 tumors. Comparison of genotype and haplotype models indicated that the best representation of risk solely relied on rs7187167 under dominant penetrance. Women carrying the rare allele showed an increased risk of grade 1 tumors compared with common homozygotes (OR 1.87, 95% CI 1.18–2.95). This effect appeared to be stronger in women with a family history of breast or ovarian cancer. Imputation of polymorphisms in a 300-kb region around the genotyped polymorphisms identified no variants with stronger associations. Our findings suggest that genetic variation in UBC9 may affect the risk of grade 1 breast tumors.

N-acetyltransferase 2 phenotype, occupation, and bladder cancer risk: results from the EPIC cohort.

Background: An association between N-acetyltransferase 2 (NAT2) slow acetylation and bladder cancer has been consistently observed in epidemiologic studies. However, evidence has been mainly derived from case–control studies and was sparse from cohort studies. We evaluated the association between NAT2 slow acetylation and bladder cancer in a case–control study nested in the European Prospective Investigation into Cancer and Nutrition. Methods: Exposure to aromatic amines and polycyclic aromatic hydrocarbons (PAH) could be assessed for 754 cases and 833 controls for whom occupational information was documented. A semiquantitative job-exposure matrix was applied to at-risk occupations to estimate the exposure as low, medium, or high based on tertiles of the distribution of the exposure score in controls. Using a comprehensive genotyping, NAT2 acetylation status could be categorized from 6-single-nucleotide polymorphism genotypes as slow or fast in 607 cases and 695 controls with DNA from archived blood samples. Results: Occupational exposure to aromatic amines and PAH was associated with an increased bladder cancer risk [upper tertile of the distribution of the exposure score: OR = 1.37; 95% confidence interval (CI), 1.02–1.84, and OR = 1.50; 95% CI, 1.09–2.05, respectively]. NAT2 slow acetylation did not modify these risk estimates and was not itself associated with bladder cancer risk (OR = 1.02; 95% CI, 0.81–1.29). Conclusions: These findings confirm established or suspected occupational risk factors but not the anticipated role of NAT2 slow acetylation in bladder cancer. No interaction was detected between NAT2 and any exposure of interest, including smoking. Impact: Genetic testing for NAT2 would be inappropriate in occupational settings. Cancer Epidemiol Biomarkers Prev; 22(11); 2055–65. ©2013 AACR.

Polymorphic loci of E2F2, CCND1 and CCND3 are associated with HER2 status of breast tumors.

Overexpression of the human epidermal growth factor receptor 2 (HER2) in breast tumors is associated with bad prognosis. Therefore, it is highly relevant to further improve understanding of the regulatory mechanisms of HER2 expression. In addition to gene amplification, transcriptional regulation plays a crucial role in HER2 overexpression. In this study, we analyzed 3 polymorphisms E2F2_‐5368_A>G, CCND1_870_A>G and CCND3_‐677_C>T located in genes involved in cell cycle regulation in the GENICA population‐based and age‐matched breast cancer case‐control study from Germany. We genotyped 1,021 cases and 1,015 controls by matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry (MALDI‐TOF MS). Statistical analyses were performed by conditional logistic regression. We observed no differences in genotype frequencies between breast cancer cases and controls. Subgroup analysis showed associations between carriers of the E2F2_‐5368_G allele (OR: 0.60, 95% CI: 0.42–0.85), carriers of the CCND1_870_G allele (OR: 0.66, 95% CI: 0.45–0.96) and carriers of the CCND3_‐677_T allele (OR: 1.72, 95% CI: 1.20–2.49) and HER2 expression in breast tumors. This finding points to an association of an increased expression of these cell cycle regulators with lower expression of HER2. An explanation for this observation might be that low expression of E2F2, CCND1 and CCND3 decrease levels of factors down‐regulating HER2. We conclude that the analyzed polymorphisms located in E2F2, CCND1 and CCND3 are potential markers for HER2 status of breast tumors.

Variation of the N-Acetyltransferase 2 Gene in a Romanian and a Kyrgyz Population

As part of a project on environmental disasters in minority populations, this study aimed to evaluate differences in the sequence of N-acetyltransferase 2 (NAT2) as a metabolic susceptibility gene in yet unexplored ethnicities. Eight single nucleotide polymorphisms (SNP) in the NAT2 coding region and a variant in the 3′ flanking region were analyzed in 290 unrelated Kyrgyz and 140 unrelated Romanians by SNP-specific PCR analysis. The variants 341C, 481T, and 803G were less and 857A more prevalent in Kyrgyz (P < 0.0001). The variant at site 857 indicates Asian descent. 282C>T and 590G>A showed no significant variation by ethnicity. 364G>A and 411A>T turned out to be monomorphic. Database comparisons of the NAT2 minor allele frequencies support that Romanians belong to Caucasians and Kyrgyz are in between Caucasians and East Asians. The distributions of predicted haplotypes differed significantly between the two ethnicities where the Kyrgyz showed a higher genetic diversity. The haplotype without mutations was more common in Kyrgyz (40.1% in Kyrgyz, 29.3% in Romanians). Accordingly, the imputed slow acetylator phenotype was less prevalent in Kyrgyz (35.2% versus 51.4% in Romanians). We found pronounced ethnic differences in NAT2 genotypes with yet unknown effect on the health risks for environmental or occupational exposures in minority populations. (Cancer Epidemiol Biomarkers Prev 2006;(15)1:138–41)