Breast cancer-associated Abraxas mutation disrupts nuclear localization and DNA damage response functions

Breast cancer is the most common cancer in women in developed countries and has a well-established genetic component. Germline mutations in a network of genes encoding BRCA1, BRCA2, and their interacting partners confer hereditary susceptibility to breast cancer. Abraxas directly interacts with the BRCA1 BRCT (BRCA1 carboxyl-terminal) repeats and contributes to BRCA1-dependent DNA damage responses, making Abraxas a candidate for yet unexplained disease susceptibility. Here, we have screened 125 Northern Finnish breast cancer families for coding region and splice-site Abraxas mutations and genotyped three tagging single-nucleotide polymorphisms within the gene from 991 unselected breast cancer cases and 868 female controls for common cancer-associated variants. A novel heterozygous alteration, c.1082G>A (Arg361Gln), that results in abrogated nuclear localization and DNA response activities was identified in three breast cancer families and in one additional familial case from an unselected breast cancer cohort, but not in healthy controls (P = 0.002). On the basis of its exclusive occurrence in familial cancers, disease cosegregation, evolutionary conservation, and disruption of critical BRCA1 functions, the recurrent Abraxas c.1082G>A mutation connects to cancer predisposition. These findings contribute to the concept of a BRCA-centered tumor suppressor network and provide the identity of Abraxas as a new breast cancer susceptibility gene.     

VARS2基因单核苷酸多态性和广东汉族女性散发性乳腺癌相关性研究

目的探讨VARS2(valyl-tRNA synthetase 2)基因中单核苷酸多态性位点(single nucleotide polymorphisms,SNP)rs2249464与广东省汉族女性散发性乳腺癌的相关性。方法采用MassARRAY-IPLEX SNP分型技术,以南方医科大学南方医院的216例广东汉族乳腺癌患者及216例同期健康体检者为研究对象,对rs2249464多态性位点进行基因分型,利用χ2检验统计分析病例组和对照组的基因型频率有无差异,利用非条件Logistic回归计算比数比(odds ratio,OR)和95%可信区间(confidence interval,CI)来评价此位点多态性与乳腺癌的相关性。然后进一步将病例组按雌激素受体(estrogen receptor,ER)和孕激素受体(progesterone receptor,PR)免疫组化结果行分层分析。结果 rs2249464位点C/C,C/T,T/T 3种基因型分布在对照组和病例组之间有统计学差异。根据免疫组化情况进一步分层分析结果表明rs2249464的基因型分布在ER阳性/阴性组之间的差异无统计学意义(P>0.05);但在PR阳性/阴性组之间的差异有统计学意义(P<0.05)。结论 VARS2基因rs2249464位点单核苷酸多态性与广东汉族散发性乳腺癌的易感性具有相关性,且携带T/T基因型的患者更容易罹患PR阴性乳腺癌。     

Sex differences and genomics in autoimmune diseases

Autoimmune diseases (AIDs) are believed to be multifactorial diseases that commonly involve multiple organ systems. About three fourth of the patients afflicted with AIDs are women suggesting that sex differences impact the incidence of AID. However, the proportion of females to males suffering from AID varies depending on the disease. The response to some AID therapeutics also differs in females versus males, suggesting that enrollment of adequate numbers of women and men is important in clinical trials for development of AID drugs. It is known for a long time that genetic factors are important contributors to AID susceptibility. Currently available information suggests that multiple genes with modest association to AID contribute to susceptibility to AID. Also, the associations may differ for the various ethnicities. The major histocompatibility (MHC) locus appears to be a major genetic factor that confers susceptibility to multiple AIDs, even though the locus is complex and has the highest density of genes in the human genome. Thus, the association of different AIDs could be with different genes in the MHC locus. Among the non-MHC genes, some of the risk alleles are shared between different AIDs, but may not be common to all AIDs. For example, genetic polymorphisms in the Protein Tyrosine Phosphatase-22 (PTPN22) gene have reproducibly shown to have association with systemic lupus erythematosus (SLE), Graves' disease (GD), rheumatoid arthritis (RA) and multiple sclerosis (MS), but not with psoriasis. Identification of factors responsible for risk for developing AID and the of the pathways underlying these diseases are likely to help understand subsets of disease, identify responders to a specific treatment and develop better therapeutics for AID.     

High incidence of oestrogen receptor negative progesterone receptor positive phenotype in Indian breast cancer: fact or fiction?

The incidence of oestrogen receptor negative and progesterone receptor positive (ER-/PR+) invasive breast carcinoma is reported to be as high as 21% in India, as compared to 3-5% in the western literature. We used automated immunohistochemistry with Biogenex antibodies to re-evaluate the ER status in 37 Indian patients with invasive breast carcinomas previously reported as ER-/PR+ by a different manual staining protocol in two city hospitals. The automated technique utilized different reagents (all US FDA approved for in vitro diagnostic use) and staining protocols from those used in the manual assays. Of the 37 previously ER-tumours, only 9 (24.3%) tumours remained ER-. Twenty-eight (75.6%) tumours were found to be ER+. Our results indicate that the high incidence of ER-/PR+ breast cancer reported from India is most likely due to the use of suboptimal manual assays, rather than true genetic differences. ER expression in breast cancer among Indian women may be much higher than previously believed. These results have important implications for the use of oestrogen modulators such as tamoxifen in developing countries such as India.     

Association of three single nucleotide polymorphisms of ESR1 with breast cancer susceptibility: a meta-analysis

Expression of estrogen receptors is correlated with breast cancer risk, but inconsistent results have been reported. To clarify potential estrogen receptor (ESR)-related breast cancer risk, we analyzed genetic variants of ESR1 in association with breast cancer susceptibility. We performed a meta-analysis to investigate the association between rs2234693, rs1801132, and rs2046210 (single nucleotide polymorphisms of ESR1), and breast cancer risk. Our analysis included 44 case-control studies. For rs2234693, the CC genotype had a higher risk of breast cancer compared to the TT or CT genotype. For rs2046210, the AA, GA, or GA + GG genotype had a much higher risk compared to the GG genotype. No significant association was found for the rs1801132 polymorphism with breast cancer risk. This meta-analysis demonstrates association between the rs2234693 and rs2046210 polymorphisms of ESR1 and breast cancer risk. The correlation strength between rs2234693 and breast cancer susceptibility differs in subgroup assessment by ethnicity.     

Allelic association of the human homologue of the mouse modifier Ptprj with breast cancer

Human homologues of mouse cancer modifier genes may play a role in cancer risk and prognosis. A proportion of the familial risk of common cancers may be attributable to variants in such genes, each contributing to a small effect. The protein tyrosine phosphatase receptor type J (PTPRJ) has been recently identified as being the protein encoded by the Scc1 mouse gene (susceptibility to colon cancer-1). In addition, the PTPRJ gene has been shown to be somatically altered in several human cancer types such as colon, lung and breast cancers and to have the characteristics of a tumour-suppressor gene. The purpose of this study was to determine whether common variants in the PTPRJ gene represent low penetrance breast cancer susceptibility alleles. To test this hypothesis, we assessed single nucleotide polymorphisms (SNPs) tagging the common SNPs and haplotypes of the gene in 4512 cases and 4554 controls from the East Anglian population. We observed a difference in the haplotype frequency distributions between cases and controls (P = 0.0023, OR = 0.81 [0.72-0.92]). Thus, carrying a specific PTPRJ haplotype confers a protective effect on the risk of breast cancer. This result establishes the principle that mouse cancer modifier genes are candidates for low penetrance human breast cancer susceptibility genes.     

Genes other than BRCA1 and BRCA2 involved in breast cancer susceptibility

This review focuses on genes other than the high penetrance genes BRCA1 and BRCA2 that are involved in breast cancer susceptibility. The goal of this review is the discovery of polymorphisms that are either associated with breast cancer or that are in strong linkage disequilibrium with breast cancer causing variants. An association with breast cancer at a 5% significance level was found for 13 polymorphisms in 10 genes described in more than one breast cancer study. Our data will help focus on the further analysis of genetic polymorphisms in populations of appropriate size, and especially on the combinations of such polymorphisms. This will facilitate determination of population attributable risks, understanding of gene-gene interactions, and improving estimates of genetic cancer risks.     

Novel BRCA1/2 mutations in Serbian breast and breast-ovarian cancer patients with hereditary predisposition

Mutations in breast cancer susceptibility (BRCA) genes lead to defects in DNA repair processes resulting in elevated genome instability and predisposing to breast and ovarian cancer. The study was designed to detect mutational spectra of BRCA1/2 genes in a Serbian population. Using automated DNA sequencing, we tested individuals for BRCA mutations, based on positive family history of either breast or ovarian cancer or both. Two novel mutations (c.4765_4784del in BRCA1 exon 15 and c.4367_4368dupTT in BRCA2 exon 11) were detected, in three probands from two different families. These mutations have not been reported previously in the BIC or LOVD databases. Protein products of these mutated alleles lack domains necessary for their DNA repair functions, an indicator that these are deleterious mutations. Neither mutation was found in any proband from 50 other families with hereditary predisposition, so the two mutations are likely family-specific rather than population-specific. Although BRCA1-associated tumors are typically negative for estrogen receptor (ER), progesterone receptor (PR), and ERBB2, the novel BRCA1 mutation identified in this study was detected in a proband with ER- and PR-positive breast cancer. Steroid receptor-positive BRCA-related breast cancer in this proband supports the idea of characteristic pathological features and older age of onset among BRCA1-mutated ER-positive breast cancers.     

Assessment of TP53 Polymorphisms and MDM2 SNP309 in Premenopausal Breast Cancer Risk

Germline polymorphic variants in cancer predisposition genes such as TP53 have been shown to impact the risk of premenopausal cancer. Accordingly, the aim of this study was to assess the spectrum of polymorphisms in TP53 and its negative regulatory gene, MDM2 (SNP309:T>G) in patients with premenopausal breast cancer. Our findings in a cohort of 40 female patients demonstrate no significant correlation between the studied polymorphisms and risk of premenopausal breast cancer. Although one polymorphism is found in high frequency in this cohort (rs1800372:A>G, 9.0%), it was not associated with the risk of developing cancer before the age of 35 years in an extended cohort of 1,420 breast cancer cases. Functional studies of the rs1800372:A>G polymorphic allele reveal that it does not affect p53 transactivation function. Further study of variants or mutations in other cancer susceptibility genes is warranted to refine our understanding of the germline contribution to premenopausal breast cancer susceptibility.     

Breast cancer susceptibility: current knowledge and implications for genetic counselling

Breast cancer is the most common malignancy in women in the Western world. Except for the high breast cancer risk in BRCA1 and BRCA2 mutation carriers as well as the risk for breast cancer in certain rare syndromes caused by mutations in TP53, STK11, PTEN, CDH1, NF1 or NBN, familial clustering of breast cancer remains largely unexplained. Despite significant efforts, BRCA3 could not be identified, but several reports have recently been published on genes involved in DNA repair and single nucleotide polymorphisms (SNPs) associated with an increased breast cancer risk. Although candidate gene approaches demonstrated moderately increased breast cancer risks for rare mutations in genes involved in DNA repair (ATM, CHEK2, BRIP1, PALB2 and RAD50), genome-wide association studies identified several SNPs as low-penetrance breast cancer susceptibility polymorphisms within genes as well as in chromosomal loci with no known genes (FGFR2, TOX3, LSP1, MAP3K1, TGFB1, 2q35 and 8q). Some of these low-penetrance breast cancer susceptibility polymorphisms also act as modifier genes in BRCA1/BRCA2 mutation carriers. This review not only outlines the recent key developments and potential clinical benefit for preventive management and therapy but also discusses the current limitations of genetic testing of variants associated with intermediate and low breast cancer risk.     

A protein-truncating mutation in CYP17A1 in three sisters with early-onset breast cancer

The hormonal etiology of breast cancer is well-established. Many studies have assessed whether polymorphisms in steroid hormone metabolism genes are associated with breast cancer risk. We measured the CYP17A1 -34T>C (c.-34T>C) promoter polymorphism in a population-based study of 1,404 Australian women with breast cancer diagnosed before age 60 years (case probands), 1,903 relatives, and 788 controls. Within-family analyses suggested the CC genotype was associated with, on average, a small increased risk. This finding appeared to be influenced by the families of three early-onset case probands with multiple affected sisters. CYP17A1 mutation screening revealed a case proband diagnosed at age 38 years who had a germline protein-truncating mutation (c.775C>T, p.Arg239X), which results in a nonfunctional enzyme and has been reported in a male compound heterozygote with 17 alpha-hydroxylase deficiency. This mutation was carried by both sisters diagnosed with breast cancer at ages 34 and 42 years, but not by a 57-year-old unaffected sister. It was not found in any of the other tested case probands (48 with multiple-affected relatives and 241 randomly selected) or controls. This study suggests there may be rare mutations in steroid hormone metabolism genes associated with a high dominantly-inherited breast cancer risk, and demonstrates how "high-risk susceptibility genes" might be discovered using population-based case-control-family studies.     

Insulin-like growth factor-2 (IGF-2) activates estrogen receptor-α and -β via the IGF-1 and the insulin receptors in breast cancer cells

The estrogen receptor (ER) is a primary target for breast cancer (BC) treatment. As BC progresses to estrogen-independent growth, the insulin-like growth factor-1 receptor (IGF-1R) and the ER interact in synergistic cross-talk mechanisms, which result in enhanced activation of both receptors' signaling cascades. Insulin-like growth factor-2 (IGF-2) is critical in BC progression and its actions are mediated by the IGF-1R. Our previous studies showed that IGF-2 regulates survival genes that protect the mitochondria and promote chemoresistance. In this study, we analyzed BC cells by subcellular fractionation, Western-Blot, qRT-PCR, and siRNA analysis. Our results demonstrate that IGF-2 activates ER-α and ER-β, and modulates their translocation to the nucleus, membrane organelles, and the mitochondria. IGF-2 actions are mediated by the IGF-1R and the insulin receptor. This novel mechanism of IGF-2 synergistic cross-talk signaling with ER-α and ER-β can promote estrogen-independent BC progression and provide new therapeutic targets for the treatment of BC patients.     

Germ-line mutations in BRCA1 or BRCA2 in the normal breast are associated with altered expression of estrogen-responsive proteins and the predominance of progesterone receptor A

The breast cancer susceptibility genes BRCA1 and BRCA2 are responsible for a large proportion of familial breast and ovarian cancer, yet little is known of how disruptions in the functions of the proteins these genes encode increased cancer risk preferentially in hormone-dependent tissue. There is no information on whether a germ-line mutation in BRCA1 or BRCA2 causes disruptions in hormone-signaling pathways in the normal breast. In this study markers of hormone responsiveness were measured in prophylactically removed normal breast tissue (n = 31) in women bearing a germ-line pathogenic mutation in one of the BRCA genes. The estrogen receptor (ER) and proteins associated with ER action in hormone-sensitive tissues, namely, PS2 and the progesterone receptor (PR), were detected immunohistochemically. ER expression was not different in BRCA mutation carriers than in noncarriers, but there was a reduction in PS2 expression. PR expression was also reduced, and there was a striking lack of expression of the PRB isoform, which resulted in cases with PRA-only expression in BRCA1 and BRCA2 mutation carriers. The alterations in PS2 and PR expression were similar in the BRCA1 and BRCA2 carriers, demonstrating that although these proteins are structurally and functionally distinct, there is overlap in their interaction with hormone-signaling pathways. This study provides evidence for altered cell function arising from loss of function of one BRCA allele in the normal breast, leading to PS2 loss, preferential PRB loss, and expression of PRA alone. In breast cancer development, PRA overexpression becomes evident in premalignant lesions and is associated with features of poor prognosis in invasive disease and altered cell function in vitro. The results of this study suggest that heterozygosity for a germ-line mutation in BRCA1 or BRCA2 results in development of PRA predominance. This is likely to lead to changes in progesterone signaling in hormone-dependent tissues, which may be a factor in the increased risk of cancer in these tissues in women with germ-line BRCA1 or BRCA2 mutations.     

Insulin-like growth factor-2 (IGF-2) activates estrogen receptor-α and -β via the IGF-1 and the insulin receptors in breast cancer cells

The estrogen receptor (ER) is a primary target for breast cancer (BC) treatment. As BC progresses to estrogen-independent growth, the insulin-like growth factor-1 receptor (IGF-1R) and the ER interact in synergistic cross-talk mechanisms, which result in enhanced activation of both receptors' signaling cascades. Insulin-like growth factor-2 (IGF-2) is critical in BC progression and its actions are mediated by the IGF-1R. Our previous studies showed that IGF-2 regulates survival genes that protect the mitochondria and promote chemoresistance. In this study, we analyzed BC cells by subcellular fractionation, Western-Blot, qRT-PCR, and siRNA analysis. Our results demonstrate that IGF-2 activates ER-α and ER-β, and modulates their translocation to the nucleus, membrane organelles, and the mitochondria. IGF-2 actions are mediated by the IGF-1R and the insulin receptor. This novel mechanism of IGF-2 synergistic cross-talk signaling with ER-α and ER-β can promote estrogen-independent BC progression and provide new therapeutic targets for the treatment of BC patients.     

"Other" breast cancer susceptibility genes: searching for more holy grail

While germline mutations in BRCA1 and BRCA2 account for most, if not all families with autosomal dominant transmission of susceptibility to both breast and ovarian cancer, it has become clear that together these genes only account for a small proportion of hereditary site-specific breast cancer susceptibility. However, difficulties due to genetic heterogeneity, reduced penetrance and perhaps gene mutation frequency complicate ongoing efforts to identify additional susceptibility genes. Therefore, multiple approaches are being used to identify additional high and low penetrance genes. Families with three or more breast cancer cases are being used in traditional linkage studies, which are expected to yield only moderate or high penetrance susceptibility genes. Breast cancer case-control studies are being used to look for genetic variants or polymorphisms that confer an increased risk of breast cancer in a wide variety of cellular pathways, ranging from the detoxification of environmental carcinogens to steroid hormone metabolism, DNA damage repair and immune surveillance, an approach useful primarily to identify low penetrance susceptibililty genes. However, neither approach has yielded convincing results to date. A third approach, using BRCA1 and BRCA2 mutation carriers to identify genes that are associated with modification of breast cancer risk has met with some limited success, perhaps because effects on breast cancer risk in BRCA1 and BRCA2 mutation carriers are more readily detected in smaller studies, given the much higher number of events in these cohorts at very high risk of breast cancer. Clearly, hereditary breast cancer susceptibility is a complex phenomenon, in which multiple genes may play a role. It will be necessary to use all of these approaches, as well as more comprehensive genomic studies, to identify additional breast cancer-related genes.     

New single nucleotide polymorphisms (SNPs) in homologous recombination repair genes detected by microarray analysis in Polish breast cancer patients

Breast cancer is the most common cause of malignancy and mortality in women worldwide. This study aimed at localising homologous recombination repair (HR) genes and their chromosomal loci and correlating their nucleotide variants with susceptibility to breast cancer. In this study, authors analysed the association between single nucleotide polymorphisms (SNPs) in homologous recombination repair genes and the incidence of breast cancer in the population of Polish women. Blood samples from 94 breast cancer patients were analysed as test group. Individuals were recruited into the study at the Department of Oncological Surgery and Breast Diseases of the Institute of the Polish Mother’s Memorial Hospital in Lodz, Poland. Healthy controls (n = 500) were obtained from the Biobank Laboratory, Department of Molecular Biophysics, University of Lodz. Then, DNA of breast cancer patients was compared with one of the disease-free women. The test was supported by microarray analysis. Statistically significant correlations were identified between breast cancer and 3 not described previously SNPs of homologous recombination repair genes BRCA1 and BRCA2: rs59004709, rs4986852 and rs1799950. Further studies on larger groups are warranted to support the hypothesis of correlation between the abovementioned genetic variants and breast cancer risk.     

Breast cancer: hormones and other risk factors

In North America and Northern Europe, breast cancer incidence rates begin increasing in the early reproductive years and continue climbing into the late seventies, whereas rates plateau after menopause in japan and less developed countries. Female gender, age and country of birth are the strongest determinants of disease risk. Family history and mutations in the BRCA1 and BRCA2 genes are important correlates of lifetime risk. Genetic polymorphisms associated with estrogen synthesis and metabolism are currently under study. Atypical hyperplasia and molecular alterations in benign breast lesions appear to be involved in the pathogenesis of invasive carcinoma. In postmenopausal women, increased breast density on mammograms increases risk. Bone density and breast cancer are associated, presumably through the mechanism of endogenous estrogen levels. Serum estrogen levels are higher in breast cancer cases than controls. Many established risk factors for breast cancer may function through and endocrine mechanism. Current use of oral contraceptives and prolonged, current or recent use of hormone replacement therapy moderately increase risk. Tamoxifen and possibly other selective estrogen receptor modulators reduce breast cancer risk in high risk women. Relationships between various dietary micro and macronutrients and breast cancer have been suggested but require evaluation in clinical trials. Whereas alcohol consumption is associated with increased risk, most environmental factors, including polychlorinated compounds and electromagnetic fields, are not. Conclusion: Breast cancer etiology is becoming clearer through the study of molecular alterations in germline and somatic cell genes, and the interaction of these genes with steroid hormones and relevant growth factors. This knowledge should be useful for breast cancer prevention.     

Role of ERRF, a novel ER-related nuclear factor, in the growth control of ER-positive human breast cancer cells

Whereas estrogen-estrogen receptor α (ER) signaling plays an important role in breast cancer growth, it is also necessary for the differentiation of normal breast epithelial cells. How this functional conversion occurs, however, remains unknown. Based on a genome-wide sequencing study that identified mutations in several breast cancer genes, we examined some of the genes for mutations, expression levels, and functional effects on cell proliferation and tumorigenesis. We present the data for C1orf64 or ER-related factor (ERRF) from 31 cell lines and 367 primary breast cancer tumors. Whereas mutation of ERRF was infrequent (1 of 79 or 1.3%), its expression was up-regulated in breast cancer, and the up-regulation was more common in lower-stage tumors. In addition, increased ERRF expression was significantly associated with ER and/or progesterone receptor (PR) positivity, which was still valid in human epidermal growth factor receptor 2 (HER2)-negative tumors. In ER-positive tumors, ERRF expression was inversely correlated with HER2 status. Furthermore, higher ERRF protein expression was significantly associated with better disease-free survival and overall survival, particularly in ER- and/or PR-positive and HER2-negative tumors (luminal A subtype). Functionally, knockdown of ERRF in two ER-positive breast cancer cell lines, T-47D and MDA-MB-361, suppressed cell growth in vitro and tumorigenesis in xenograft models. These results suggest that ERRF plays a role in estrogen-ER-mediated growth of breast cancer cells and could, thus, be a potential therapeutic target.     

The breast cancer information core: database design, structure, and scope

The Breast Cancer Information Core (BIC) is an open access, on-line mutation database for breast cancer susceptibility genes. In addition to creating a catalogue of all mutations and polymorphisms in breast cancer susceptibility genes, a principle aim of the BIC is to facilitate the detection and characterization of these genes by providing technical support in the form of mutation detection protocols, primer sequences, and reagent access. Additional information at the site includes a literature review compiled from published studies, links to other internet-based, breast cancer information and research resources, and an interactive discussion forum which enables investigators to post or respond to questions and/or comments on a bulletin board. Hum Mutat 16:123-131, 2000. Published 2000 Wiley-Liss, Inc.