BRCA1 gene in breast cancer

BRCA1 localization to the telomere and its loss from the telomere in response to DNA damage

BRCA1, a tumor suppressor, participates in DNA damage signaling and repair. Previously, we showed that BRCA1 overexpression caused inhibition of telomerase activity and telomere shortening in breast and prostate cancer cells. We now report that BRCA1 knockdown causes increased telomerase reverse transcriptase expression, telomerase activity, and telomere length; but studies utilizing a combination of BRCA1 and telomerase reverse transcriptase small interfering RNAs suggest that BRCA1 also regulates telomere length independently of telomerase. Using telomeric chromatin immunoprecipitation assays, we detected BRCA1 at the telomere and demonstrated time-dependent loss of BRCA1 from the telomere following DNA damage. Further studies suggest that BRCA1 interacts with TRF1 and TRF2 in a DNA-dependent manner and that some of the nuclear BRCA1 colocalizes with TRF1/2. Our findings further suggest that Rad50 is required to localize BRCA1 at the telomere and that the association of BRCA1 with Rad50 does not require DNA. Finally, we found that BRCA1 regulates the length of the 3' G-rich overhang in a manner that is dependent upon Rad50. Our findings suggest that BRCA1 is recruited to the telomere in a Rad50-dependent manner and that BRCA1 may regulate telomere length and stability, in part through its presence at the telomere.

Gene promoter methylation is associated with increased mortality among women with breast cancer

To better understand breast cancer etiology and progression, we explored the association between promoter methylation status of three breast cancer-related genes (BRCA1, APC, and p16) and survival in a large cohort of women with breast cancer. About 800 archived tumor tissues were collected from women diagnosed with a first primary invasive or in situ breast cancer in 1996-1997. The vital status of the participants was followed through the end of year 2005 with a mean follow-up time of 8.0 years. Promoter methylation was assessed by methylation-specific PCR (for BRCA1) and MethyLight (for APC and p16). The association of promoter methylation and breast cancer mortality was evaluated by Cox-proportional hazards models. Methylated promoters were found in 59.0, 48.4, and 3.6% of the tumor samples for BRCA1, APC, and p16, respectively. Breast cancer-specific mortality was strongly associated with promoter methylation of p16 [HR and 95% CI: 3.53 (1.83-6.78)], whereas the associations with of BRCA1 and APC were less pronounced [HR and 95% CI: 1.81 (1.18-2.78) and 1.46 (0.98-2.17), respectively]. Similar associations were observed with all-cause mortality. As the number of methylated genes increased, the risk of breast cancer-specific mortality also increased in a dose-dependent manner (P, trend = 0.01). Importantly, even with our results stratified by hormone receptor status, promoter methylation of the three genes remained predictive of mortality. Our results suggest that promoter methylation could be promising epigenetic markers to be considered for breast cancer survival.

Modulatory effects of alpha- and gamma-tocopherols on 4-hydroxyestradiol induced oxidative stresses in MCF-10A breast epithelial cells

The elevated level of circulating estradiol increases the risk of breast tumor development. To gain further insight into mechanisms involved in their actions, we investigated the molecular mechanisms of 4-hydroxyestradiol (4-OHE₂) to initiate and/or promote abnormal cell growth, and of α- or γ-tocopherol to inhibit this process. MCF-10A, human breast epithelial cells were incubated with 0.1 µM 4-OHE₂, either with or without 30 µM tocopherols for 96 h. 4-OHE₂ caused the accumulation of intracellular ROS, while cellular GSH/GSSG ratio and MnSOD protein levels were decreased, indicating that there was an oxidative burden. 4-OHE₂ treatment also changed the levels of DNA repair proteins, BRCA1 and PARP-1. γ-Tocopherol suppressed the 4-OHE₂-induced increases in ROS, GSH/GSSG ratio, and MnSOD protein expression, while α-tocopherol up-regulated BRCA1 and PARP-1 protein expression. In conclusion, 4-OHE₂ increases oxidative stress reducing the level of proteins related to DNA repair. Tocopherols suppressed oxidative stress by scavenging ROS or up-regulating DNA repair elements.

BRCA1 interacts with Smad3 and regulates Smad3-mediated TGF-beta signaling during oxidative stress responses

Background

BRCA1 is a key regulatory protein participating in cell cycle checkpoint and DNA damage repair networks. BRCA1 plays important roles in protecting numerous cellular processes in response to cell damaging signals. Transforming growth factor-beta (TGF-β) is a potent regulator of growth, apoptosis and invasiveness of tumor cells. TFG-β activates Smad signaling via its two cell surface receptors, the TbetaRII and ALK5/TbetaRI, leading to Smad-mediated transcriptional regulation.

Methodology/Principal Findings

Here, we report an important role of BRCA1 in modulating TGF-β signaling during oxidative stress responses. Wild-type (WT) BRCA1, but not mutated BRCA1 failed to activate TGF-β mediated transactivation of the TGF-β responsive reporter, p3TP-Lux. Further, WT-BRCA1, but not mutated BRCA1 increased the expression of Smad3 protein in a dose-dependent manner, while silencing of WT-BRCA1 by siRNA decreased Smad3 and Smad4 interaction induced by TGF-β in MCF-7 breast cancer cells. BRCA1 interacted with Smad3 upon TGF-β1 stimulation in MCF-7 cells and this interaction was mediated via the domain of 298–436aa of BRCA1 and Smad3 domain of 207–426aa. In addition, H₂O₂ increased the colocalization and the interaction of Smad3 with WT-BRCA1. Interestingly, TGF-β1 induced Smad3 and Smad4 interaction was increased in the presence of H₂O₂ in cells expressing WT-BRCA1, while the TGF-β1 induced interaction between Smad3 and Smad4 was decreased upon H₂O₂ treatment in a dose-dependent manner in HCC1937 breast cancer cells, deficient for endogenous BRCA1. This interaction between Smad3 and Smad4 was increased in reconstituted HCC1937 cells expressing WT-BRCA1 (HCC1937/BRCA1). Further, loss of BRCA1 resulted in H₂O₂ induced nuclear export of phosphor-Smad3 protein to the cytoplasm, resulting decreased of Smad3 and Smad4 interaction induced by TGF-β and in significant decrease in Smad3 and Smad4 transcriptional activities.

Conclusions/Significance

These results strongly suggest that loss or reduction of BRCA1 alters TGF-β growth inhibiting activity via Smad3 during oxidative stress responses.

A polymorphic variant in human MDM4 associates with accelerated age of onset of estrogen receptor negative breast cancer

Murine double minute 4 (MDM4) shares significant structural homology with murine double minute 2 (MDM2) and interacts and regulates transcriptional activity of the tumor suppressor p53. In tumors with wild-type p53, there is often overexpression of MDM2 or MDM4 leading to functional inactivation of p53. A single-nucleotide polymorphism (SNP) in the promoter of human MDM2 (SNP309) was shown to associate with increased MDM2 expression and increased risk of cancer. This study evaluated the association of a SNP in human MDM4 (C>T) with age of onset of breast cancer in two independent cohorts. In cohort 1 of 675 patients, the average age of diagnosis for women with estrogen receptor (ER)-positive and ER-negative breast cancers was 53.2 and 48 years, respectively. In this cohort, homozygous variant (TT) carriers developed ER-negative carcinomas at an earlier age than homozygous wild-type (CC) or heterozygous (TC) such that the age at diagnosis was accelerated by 5.0 years (P = 0.018). This association was validated in a second cohort of breast cancer patients (n = 148), where TT carriers with ER-negative cancer developed the disease 3.8 years earlier than CC carriers (P = 0.006). The effect was more pronounced in Caucasians with ER-negative ductal carcinomas with TT homozygotes developing disease 7.5 years (P = 0.031) and 6.2 years (P = 7 x 10(-5)) earlier than CC carriers in cohorts 1 and 2, respectively. No association was seen in ER-positive ductal cancers suggesting that the SNP in MDM4 only has a functional association in ER-negative breast cancer.

The ordering of expression among a few genes can provide simple cancer biomarkers and signal BRCA1 mutations

Background

A major challenge in computational biology is to extract knowledge about the genetic nature of disease from high-throughput data. However, an important obstacle to both biological understanding and clinical applications is the "black box" nature of the decision rules provided by most machine learning approaches, which usually involve many genes combined in a highly complex fashion. Achieving biologically relevant results argues for a different strategy. A promising alternative is to base prediction entirely upon the relative expression ordering of a small number of genes.

Results

We present a three-gene version of "relative expression analysis" (RXA), a rigorous and systematic comparison with earlier approaches in a variety of cancer studies, a clinically relevant application to predicting germline BRCA1 mutations in breast cancer and a cross-study validation for predicting ER status. In the BRCA1 study, RXA yields high accuracy with a simple decision rule: in tumors carrying mutations, the expression of a "reference gene" falls between the expression of two differentially expressed genes, PPP1CB and RNF14. An analysis of the protein-protein interactions among the triplet of genes and BRCA1 suggests that the classifier has a biological foundation.

Conclusion

RXA has the potential to identify genomic "marker interactions" with plausible biological interpretation and direct clinical applicability. It provides a general framework for understanding the roles of the genes involved in decision rules, as illustrated for the difficult and clinically relevant problem of identifying BRCA1 mutation carriers.

Is chromosome radiosensitivity and apoptotic response to irradiation correlated with cancer susceptibility?

PURPOSE

Individuals who have been treated for breast cancer have been reported to have increased lymphocyte chromosomal sensitivity to ionizing radiation and a significantly lower apoptotic response to irradiation compared to controls. We set out to test these findings using a substantial number of cases sampled before treatment (which could alter the parameters measured), compared to age-matched controls with normal mammograms.

MATERIAL AND METHODS

We used the G2 chromosome breakage, and apoptotic response assays of peripheral blood lymphocytes to ionizing radiation to compare 211 unselected newly diagnosed and untreated breast cancer patients, with 170 age, sex and ethnically matched controls.

RESULTS

We found no significant differences between breast cancer patients and their matched controls in the G2 assay or apoptotic response. However, there was some evidence that both cases and controls with a strong family history of breast cancer had higher radiosensitivity than those without.

CONCLUSIONS

This is the largest and best controlled study of its kind, but it has not replicated previous reports of differences between chromosome breakage or apoptotic response in breast cancer cases vs. controls. However there was a suggestion of increased radiosensitivity in patients with a strong family history, which may indicate a heritable cancer susceptibility trait, warranting further study.

Oncogenic pathways in hereditary and sporadic breast cancer

Cancer is a genetic disease. Breast cancer tumorigenesis can be described as a multi-step process in which each step is thought to correlate with one or more distinct mutations in major regulatory genes. The question addressed is how far a multi-step progression model for sporadic breast cancer would differ from that for hereditary breast cancer. Hereditary breast cancer is characterized by an inherited susceptibility to breast cancer on basis of an identified germline mutation in one allele of a high penetrance susceptibility gene (such as BRCA1, BRCA2, CHEK 2, TP53 or PTEN). Inactivation of the second allele of these tumour suppressor genes would be an early event in this oncogenic pathway (Knudson's "two-hit" model). Sporadic breast cancers result from a serial stepwise accumulation of acquired and uncorrected mutations in somatic genes, without any germline mutation playing a role. Mutational activation of oncogenes, often coupled with non-mutational inactivation of tumour suppressor genes, is probably an early event in sporadic tumours, followed by more, independent mutations in at least four or five other genes, the chronological order of which is likely less important. Oncogenes that have been reported to play an early role in sporadic breast cancer are MYC, CCND1 (Cyclin D1) and ERBB2 (HER2/neu). In sporadic breast cancer, mutational inactivation of BRCA1/2 is rare, as inactivation requires both gene copies to be mutated or totally deleted. However, non-mutational functional suppression could result from various mechanisms, such as hypermethylation of the BRCA1 promoter or binding of BRCA2 by EMSY. In sporadic breast tumorigenesis, at least three different pathway-specific mechanisms of tumour progression are recognizable, with breast carcinogenesis being different in ductal versus lobular carcinoma, and in well differentiated versus poorly differentiated ductal cancers. Thus, different breast cancer pathways emerge early in the process of carcinogenesis, ultimately leading to clinically different tumour types. As mutations acquired early during tumorigenesis will be present in all later stages, large-scale gene expression profiling using DNA microarray analysis techniques can help to classify breast cancers into clinically relevant subtypes.

Gene signaling pathways mediating the opposite effects of prepubertal low-fat and high-fat n-3 polyunsaturated fatty acid diets on mammary cancer risk

In rats, prepubertal exposure to low-fat diet containing n-3 polyunsaturated fatty acids (PUFA) reduces mammary cell proliferation, increases apoptosis, and lowers risk of mammary tumors in adulthood, whereas prepubertal high-fat n-3 PUFA exposure has opposite effects. To identify signaling pathways mediating these effects, we performed gene microarray analyses and determined protein levels of genes related to mammary epithelial cell proliferation. Nursing female rats and rat pups were fed low-fat (16% energy from fat) or high-fat (39% energy from fat) n-3 or n-6 PUFA diets between postnatal days 5 and 24. cDNA gene expression microarrays were used to identify global changes in the mammary glands of 50-day-old rats. Differences in gene expression were confirmed by real-time quantitative PCR, and immunohistochemistry was used to assess changes in the peroxisome proliferator-activated receptor gamma and cyclin D1 levels. DNA damage was determined by 8-hydroxy-2'-deoxyguanosine assay. Expressions of the antioxidant genes thioredoxin, heme oxygenase, NADP-dependent isocitrate dehydrogenase, and metallothionein III, as well as peroxisome proliferator-activated receptor gamma protein, were increased in the mammary glands of 50-day-old rats prepubertally fed the low-fat n-3 PUFA diet. Prepubertal exposure to the high-fat n-3 PUFA diet increased DNA damage and cyclin D1 protein and reduced expression of BRCA1 and cardiotrophin-1. Reduction in mammary tumorigenesis among rats prepubertally fed a low-fat n-3 PUFA diet was associated with an up-regulation of antioxidant genes, whereas the increase in mammary tumorigenesis in the high-fat n-3 PUFA fed rats was linked to up-regulation of genes that induce cell proliferation and down-regulation of genes that repair DNA damage and induce apoptosis.

MYC in breast tumor progression

Breast cancer is the second leading cause of cancer deaths and is the most frequently diagnosed cancer in women of industrialized nations. Breast cancer progression is a multistep process involving genetic and epigenetic alterations that drive normal breast cells into highly malignant derivatives with metastatic potential. MYC is a proto-oncogene whose protein product contains a basic helix-loop-helix domain. MYC functions as a transcription factor regulating up to 15% of all human genes. MYC is regulated at multiple levels, and the protein is a downstream effector of several signaling pathways. In breast cancer cells, MYC target genes are involved in cell growth, transformation, angiogenesis and cell-cycle control. BRCA1 is linked to transcriptional regulation through interaction with MYC. Although the relationship between amplification and overexpression is not clearly delineated, MYC amplification is significantly correlated with aggressive tumor phenotypes and poor clinical outcomes. MYC amplification is emerging as an important predictor of response to HER2-targeted therapies and its role in BRCA1-associated breast cancer makes it an important target in basal-like/triple-negative breast cancers.

Methionine-dependence phenotype in the de novo pathway in BRCA1 and BRCA2 mutation carriers with and without breast cancer

Methionine-dependence phenotype (MDP) refers to the reduced ability of cells to proliferate when methionine is restricted and/or replaced by its immediate precursor homocysteine. MDP is a characteristic of human tumors in vivo, human tumor cell lines, and normal somatic tissue in some individuals. It was hypothesized that MDP is a risk factor for developing breast cancer in BRCA (BRCA1 and BRCA2) germline mutation carriers. To test the hypothesis, human peripheral blood lymphocytes of BRCA carriers with and without breast cancer and healthy non-carrier relatives (controls) were cultured for 9 days in medium containing either 0.1 mmol/L L-methionine or 0.2 mmol/L D,L-homocysteine, with the ratio of viable cell growth in both types of medium after 9 days used to calculate the methionine-dependence index (MDI), a measure of MDP. We also tested whether MDP was associated with common polymorphisms in methionine metabolism. Viable cell growth, MDI, and polymorphism frequency in MTRR (A66G and C524T) and MTHFR (A1298C and A1793G) did not differ among the study groups; however, MDI tended to be higher in BRCA carriers with breast cancer than those without and was significantly increased in MTHFR 677T allele carriers relative to wild-type carriers (P=0.017). The presence of MTR A2756G mutant allele and MTHFR C677T mutant allele in carriers was associated with increased breast cancer risk [odds ration, 3.2 (P=0.16; 95% confidence interval, 0.76-13.9) and 3.9 (P=0.09; 95% confidence interval, 0.93-16.3), respectively]. The results of this study support the hypothesis that defects in methionine metabolism may be associated with breast cancer risk in BRCA carriers.

Identification and functional analysis of novel BRCA1 transcripts, including mouse Brca1-Iris and human pseudo-BRCA1

Recent characterization of the mammalian transcriptome has confirmed its predicted complexity, with many loci encoding multiple splice variants and pseudogenes. The breast cancer susceptibility gene BRCA1 is a tumour suppressor gene that produces multiple functional transcripts. For example, BRCA1-IRIS is a splice variant of BRCA1, which encodes a protein that is functionally distinct from BRCA1. Here we describe the identification of ten novel Brca1 splice variants including Brca1-Iris, the mouse orthologue of human BRCA1-IRIS. We show that Brca1-Iris is differentially expressed during mammary epithelial differentiation and regulates survival of mammary epithelial cells. Another transcript, Brca1-Delta22, expressed in both mouse and human cells, was found to be defective in transcriptional activation capacity. Finally, we show that the human BRCA1 pseudogene produces a spliced pseudoBRCA1 transcript. The identification of these transcripts has implications for the understanding of the role of BRCA1 in biology and disease and for the interpretation of mouse knockout models.

Identification of proteins binding to E-Box/Ku86 sites and function of the tumor suppressor SAFB1 in transcriptional regulation of the human xanthine oxidoreductase gene

The xanthine oxidoreductase gene (XOR) encodes an important source of reactive oxygen species and uric acid, and its expression is associated with various human diseases including several forms of cancer. We previously reported that basal human XOR (hXOR) expression is restricted or repressed by E-box and TATA-like elements and a cluster of transcriptional proteins, including AREB6-like proteins and DNA-dependent protein kinase (DNA-PK). We now demonstrate that the cluster contains the tumor suppressors SAFB1, BRG1, and SAF-A. We further demonstrate that SAFB1 silencing increases hXOR expression and that SAFB1 directly binds to the E-box. Multiple studies in vitro and in vivo including pulldown, immunoprecipitation and chromatin immunoprecipitation analyses indicate that SAFB1, Ku86, and BRG1 associate with each other. The results suggest that the SAFB1 complex binds to the hXOR promoter in a chromatin environment and plays a critical role in restricting hXOR expression via its direct interaction with the E-box, DNA-PK, and tumor suppressors. Moreover, we demonstrate that the cytokine, oncostatin M (OSM), induces the phosphorylation of SAFB1 and that the OSM-induced hXOR mRNA expression is significantly inhibited by silencing the DNA-PK catalytic subunit or SAFB1 expression. The present studies for the first time demonstrate that hXOR is a tumor suppressor-targeted gene and that the phosphorylation of SAFB1 is regulated by OSM, providing a molecular basis for understanding the role of SAFB1-regulated hXOR transcription in cytokine stimulation and tumorigenesis.

Cell-type-specific level of DNA nucleotide excision repair in primary human mammary and ovarian epithelial cell cultures

DNA repair, a fundamental function of cellular metabolism, has long been presumed to be constitutive and equivalent in all cells. However, we have previously shown that normal levels of nucleotide excision repair (NER) can vary by 20-fold in a tissue-specific pattern. We have now successfully established primary cultures of normal ovarian tissue from seven women by using a novel culture system originally developed for breast epithelial cells. Epithelial cells in these cultures aggregated to form three-dimensional structures called "attached ovarian epispheres". The availability of these actively proliferating cell cultures allowed us to measure NER functionally and quantitatively by the unscheduled DNA synthesis (UDS) assay, a clinical test used to diagnose constitutive deficiencies in NER capacity. We determined that ovarian epithelial cells manifested an intermediate level of NER capacity in humans, viz., only 25% of that of foreskin fibroblasts, but still 2.5-fold higher than that of peripheral blood lymphocytes. This level of DNA repair capacity was indistinguishable from that of normal breast epithelial cells, suggesting that it might be characteristic of the epithelial cell type. Similar levels of NER activity were observed in cultures established from a disease-free known carrier of a BRCA1 truncation mutation, consistent with previous normal results shown in breast epithelium and blood lymphocytes. These results establish that at least three "normal" levels of such DNA repair occur in human tissues, and that NER capacity is epigenetically regulated during cell differentiation and development.

BRCA1 promoter methylation is associated with increased mortality among women with breast cancer

Promoter-CpG island hypermethylation has been proposed as an alternative mechanism to inactivate BRCA1 in the breast where somatic mutations of BRCA1 are rare. To better understand breast cancer etiology and progression, we explored the association between BRCA1 promoter methylation status and prognostic factors as well as survival among women with breast cancer. Promoter methylation of BRCA1 was assessed in 851 archived tumor tissues collected from a population-based study of women diagnosed with invasive or in situ breast cancer in 1996-1997, and who were followed for vital status through the end of 2002. About 59% of the tumors were methylated at the promoter of BRCA1. The BRCA1 promoter methylation was more frequent in invasive cancers (P = 0.02) and among premenopausal cases (P = 0.05). BRCA1 promoter methylation was associated with increased risk of breast cancer-specific mortality (age-adjusted HR 1.71; 95% CI: 1.05-2.78) and all-cause mortality (age-adjusted HR 1.49; 95% CI: 1.02-2.18). Neither dietary methyl intakes in the year prior to the baseline interview nor the functional polymorphisms in one-carbon metabolism were associated with BRCA1 methylation status. Our study is the first epidemiological investigation on the prognostic value of BRCA1 promoter methylation in a large population-based cohort of breast cancer patients. Our results indicate that BRCA1 promoter methylation is an important factor to consider in predicting breast cancer survival.

Hydrocortisone down-regulates the tumor suppressor gene BRCA1 in mammary cells: a possible molecular link between stress and breast cancer

Psychological stress has been correlated with breast cancer development in numerous epidemiological studies. However, physiological and molecular models which may account for this association are not readily available. We have found that the stress hormone hydrocortisone (cortisol) down-regulates the expression of the breast cancer susceptibility gene BRCA1 in the nonmalignant mouse mammary cell line EPH4. This effect is concentration-dependent, is reliant on the continuous presence of hydrocortisone, and is not affected by the addition of lactogenic hormones, or growth conditions. Hydrocortisone was also found to negate a known positive effect of estrogen on BRCA1 expression and, therefore, may interfere with estrogen-related signaling in mammary epithelial cells. The repressive effect of hydrocortisone is diminished or lost in the mouse mammary lines HC-11 and SP1, respectively, suggesting regulation of the BRCA1 may differ between lines. We have uncovered two promoter regulatory sites, which are involved in BRCA1 regulation by hydrocortisone, namely the RIBS and UP regulatory elements. Binding of the transcription factor GABP to both sites is lost upon hydrocortisone addition, though the levels of these factors are not altered by hydrocortisone treatment. Because BRCA1 activity is important for a number of intracellular pathways involved in prevention of tumorigenesis, its observed down-regulation may represent a novel molecular mechanism for cortisol's involvement in breast cancer development.

BCoR-L1 variation and breast cancer

Introduction

BRCA1 is involved in numerous essential processes in the cell, and the effects of BRCA1 dysfunction in breast cancer carcinogenesis are well described. Many of the breast cancer susceptibility genes such as BRCA2, p53, ATM, CHEK2, and BRIP1 encode proteins that interact with BRCA1. BCL6 corepressor-like 1 (BCoR-L1) is a newly described BRCA1-interacting protein that displays high homology to several proteins known to be involved in the fundamental processes of DNA damage repair and transcription regulation. BCoR-L1 has been shown to play a role in transcription corepression, and expression of the X-linked BCoR-L1 gene has been reported to be dysregulated in breast cancer subjects. BCoR-L1 is located on the X chromosome and is subject to X inactivation.

Methods

We performed mutation analysis of 38 BRCA1/2 mutation-negative breast cancer families with male breast cancer, prostate cancer, and/or haplotype sharing around BCoR-L1 to determine whether there is a role for BCoR-L1 as a high-risk breast cancer predisposition gene. In addition, we conducted quantitative real-time PCR (qRT-PCR) on lymphoblastoid cell lines (LCLs) from the index cases from these families and a number of cancer cell lines to assess the role of BCoR-L1 dysregulation in cancer and cancer families.

Results

Very little variation was detected in the coding region, and qRT-PCR analysis revealed that BCoR-L1 expression is highly variable in cancer-free subjects, high-risk breast cancer patients, and cancer cell lines. We also report the investigation of a new expression control, DIDO1 (death inducer-obliterator 1), that is superior to GAPDH (glyceraldehyde-3-phosphate dehydrogenase) and UBC (ubiquitin C) for analysis of expression in LCLs.

Conclusion

Our results suggest that BCoR-L1 expression does not play a large role in predisposition to familial breast cancer.

Early Events in the Pathogenesis of Epithelial Ovarian Cancer

Ovarian carcinogenesis, as in most cancers, involves multiple genetic alterations. A great deal has been learned about proteins and pathways important in the early stages of malignant transformation and metastasis, as derived from studies of individual tumors, microarray data, animal models, and inherited disorders that confer susceptibility. However, a full understanding of the earliest recognizable events in epithelial ovarian carcinogenesis is limited by the lack of a well-defined premalignant state common to all ovarian subtypes and by the paucity of data from early-stage cancers. Evidence suggests that ovarian cancers can progress both through a stepwise mutation process (low-grade pathway) and through greater genetic instability that leads to rapid metastasis without an identifiable precursor lesion (high-grade pathway). In this review, we discuss many of the genetic and molecular disorders in each key process that is altered in cancer cells, and we present a model of ovarian pathogenesis that incorporates the role of tumor cell mutations and factors in the host microenvironment important to tumor initiation and progression.

BRCA1 modulates sensitivity to 5F-203 by regulating xenobiotic stress-inducible protein levels and EROD activity

PURPOSE

We have investigated the effects of BRCA1 over-expression and knockdown on 5F-203-induced gene expression and cytotoxicity in human breast cancer cells. 5F-203 is a chemotherapeutic prodrug that both induces a p450 enzyme, CYP1A1, and is metabolically activated by CYP1A1.

METHODS

We used several molecular biological techniques to confirm our findings. BRCA1 regulates sensitivity to 5F-203 by regulating the expression of CYP1A1 mRNA and its EROD activity. XRE-Luc reporter assays, semi-quantitative RT-PCR, Western blot analysis, EROD activity measurements, gene knockdown and MTT cell survival assays were used for this study.

RESULTS

Our results show that the ability of 5F-203 treatments to increase CYP1A1 mRNA level and CYP1A1 enzymatic activity (EROD activity) are affected by BRCA1 protein levels. In addition, the ability of 5F-203 treatments to induce proteins, P53 and P53 target genes such as P21, is significantly decreased in BRCA1 knockdown cells, suggesting that BRCA1-related effects could at least partially explain why BRCA1 knockdown increases resistance to 5F-203-mediated cytotoxicity. We also observed altered expression of the two major transcription factors (AhR and ARNT) that affect CYP1A1 expression when BRCA1 protein levels are altered.

CONCLUSION

BRCA1 is an important protein, which affects 5F-203-mediated cytotoxicity. Our findings are potentially clinically significant; they suggest that those patients most likely to respond to this new prodrug will have tumors containing normal amounts of BRCA1.

Mammalian evolution and biomedicine: new views from phylogeny

Recent progress resolving the phylogenetic relationships of the major lineages of mammals has had a broad impact in evolutionary biology, comparative genomics and the biomedical sciences. Novel insights into the timing and historical biogeography of early mammalian diversification have resulted from a new molecular tree for placental mammals coupled with dating approaches that relax the assumption of the molecular clock. We highlight the numerous applications to come from a well-resolved phylogeny and genomic prospecting in multiple lineages of mammals, from identifying regulatory elements in mammalian genomes to assessing the functional consequences of mutations in human disease loci and those driving adaptive evolution.

Genetic variants in the H2AFX promoter region are associated with risk of sporadic breast cancer in non-Hispanic white women aged <or=55 years

The histone protein family member X (H2AFX) is important in maintaining chromatin structure and genetic stability. Genetic variants in H2AFX may alter protein functions and thus cancer risk. In this case-control study, we genotyped four common single nucleotide polymorphisms (i.e., -1654A > G [rs643788], -1420G > A [rs8551], and -1187T > C [rs7759] in the H2AFX promoter region and 1057C > T [rs7350] in the 3' untranslated region (UTR)) in 467 patients with sporadic breast cancer and 488 cancer-free controls. All female subjects were non-Hispanic whites aged <or=55 years. We found that significantly increased risk of breast cancer was associated with variant genotypes in the H2AFX promoter: adjusted odds ratio [OR] = 1.80, 95% confidence interval [CI] = 1.38-2.34 for -1654AG/GG; OR = 1.40, 95% CI = 1.07-1.83 for -1420GA/AA; and OR = 1.65, 95% CI = 1.26-2.16 for -1187TC/CC. Furthermore, the number of variant alleles in the promoter haplotypes was associated with increased risks of breast cancer in a dose-response manner (OR = 6.08, 95% CI = 3.25-11.38; OR = 6.83, 95% CI = 3.83-12.18; and OR = 23.61, 95% CI = 3.95-140.99 for one, two, and three variant alleles, respectively) (P (trend) \ < 0.0001). Age at onset of breast cancer significantly decreased as the number of variant alleles increased (P (trend) = 0.024). However, these effects were not observed in the 3'UTR 1057C > T polymorphism. Therefore, we believe that H2AFX promoter polymorphisms may contribute to the etiology of sporadic breast cancer in young non-Hispanic white women. Larger association studies and related functional studies are warranted to confirm these findings.

Regulation ofBRCA1messenger RNA stability in human epithelial cell lines and during cell cycle progression

The mechanisms regulating expression of breast cancer 1 (BRCA1) are not fully characterised. By studying regulation of endogenous BRCA1 in human epithelial cell lines and during cell cycle progression, we provide evidence to suggest BRCA1 is regulated post-transcriptionally at the level of messenger RNA stability. We also show that RNA-binding proteins associate with an AU-rich, cis-active sequence of the BRCA1 3' untranslated region in a cell cycle-dependent manner. Our data identify a new post-transcriptional regulatory axis and a novel mechanism for modulating the levels of BRCA1 protein, with possible implications for understanding the mechanisms underlying BRCA1 repression in breast cancer.

Aberrant expression of TopBP1 in breast cancer

AIMS

The TopBP1 protein includes eight BRCT domains (originally identified in BRCA1) and has homology with BRCA1 over the carboxyl terminal half of the protein. The aim of this study was to determine whether TopBP1 is aberrantly expressed in breast cancer.

METHODS AND RESULTS

Sixty-one breast carcinomas from an unselected consecutive patient cohort were studied along with 12 samples of breast tissue from cosmetic breast reduction surgery; these were analysed immunohistochemically for TopBP1 expression using a rabbit polyclonal antibody. This antibody was validated in immunoprecipitation and immunofluorescence experiments. Immunohistochemical analysis demonstrated that TopBP1 was expressed almost exclusively in the nuclei of the normal breast epithelium. However, in a significant number of breast carcinomas TopBP1 was aberrantly expressed, as it was detected in the cytoplasm and nucleus of some tumours and exclusively in the cytoplasm of others. In two out of 61 carcinomas investigated, no TopBP1 expression was detected.

CONCLUSIONS

For the first time this report demonstrates aberrant expression of the TopBP1 protein in breast carcinoma. We propose TOPBP1 as a breast cancer susceptibility gene.

Information recovery in cancer families: value for risk estimations

BACKGROUND

Drawing an informative pedigree is fundamental in genetic counselling. It is very common for some parts of pedigrees to remain ambiguous because of the proband's inability to recall the past history of her/his family. Current age, date of birth, date of death and age of diagnosis are the commonest missing information in pedigrees.

METHODS

The Scottish Social Statistics website, National Statistics website and English language literature were used to model extrapolations. About 172 Grampian families and three high-risk Grampian families with complete information were chosen to evaluate the influence of extrapolations on models' performance. Differences between original data and extrapolated data were assessed by independent samples t-test.

RESULTS

Changes made by extrapolations in age- and cancer-related information were not statistically significant (P > 0.05) in comparison with original data, except for average age of diagnosis of breast cancer (P = 0.03). The differences made by extrapolations in estimated probabilities generated by probability assessment models were small and ignorable except that for Tyrer-Cuzick model for Grampian family 3.

CONCLUSION

Extrapolations based on National Health Statistics can scientifically cover missing information in a defined population with minimum effect on performance of probability assessment models.

Potential roles of 3'-5' exonuclease activity of NM23-H1 in DNA repair and malignant progression

NM23-H1 is a metastasis suppressor protein that exhibits 3'-5' exonuclease activity in vitro. As 3'-5' exonucleases are generally required for maintenance of genome integrity, this activity represents a plausible candidate mediator of the metastasis suppressor properties of the NM23-H1 molecule. Consistent with an antimutator function, ablation of the yeast NM23 homolog, YNK1, results in increased mutation rates following exposure to UV irradiation and exposure to the DNA damaging agents etoposide, cisplatin, and MMS. In human cells, a DNA repair function is further suggested by increased NM23-H1 expression and nuclear translocation following DNA damage. Also, forced expression of NM23-H1 in NM23-deficient and metastatic cell lines results in coordinate downregulation of multiple DNA repair genes, possibly reflecting genomic instability associated with the NM23-deficient state. To assess the relevance of the 3'-5' exonuclease activity of NM23-H1 to its antimutator and metastasis suppressor functions, a panel of mutants harboring defects in the 3'-5' exonuclease and other enzymatic activities of the molecule (NDPK, histidine kinase) have been expressed by stable transfection in the melanoma cell line, 1205Lu. Pilot in vivo metastasis assays indicate 1205Lu cells are highly responsive to the metastasis suppressor effects of NM23-H1, thus providing a valuable model for measuring the extent to which the nuclease function opposes metastasis and metastatic progression.

BRCA1a has antitumor activity in TN breast, ovarian and prostate cancers

Breast cancer gene 1 (BRCA1) mutations predispose women to breast and ovarian cancers and men to increased risks for prostate cancer. We have previously showed BRCA1 splice variant BRCA1a/p110 to induce apoptosis of human breast cancer cells. In the current study, stable expression of BRCA1a/p110 resulted in inhibition of growth of estrogen receptor (ER)-positive and triple-negative (TN) human breast, ovarian, prostate and colon cancer cells and mouse fibroblast cells. Similar to wild-type BRCA1, only those cells with wild-type Rb were sensitive to BRCA1a-induced growth suppression and the status of p53 did not affect the ability of BRCA1a to suppress growth of tumor cells. BRCA1a also significantly inhibited tumor mass in nude mice bearing human CAL-51 TN breast cancer, ES-2 ovarian cancer and PC-3 prostate cancer xenografts. These results suggest that the majority of exon 11 sequences (residues 263-1365) are not required for the tumor suppressor function of BRCA1 proteins. This is the first report demonstrating antitumor activity of BRCA1a in human ER-positive and TN breast, hormone-independent ovarian and prostate cancer cells. Currently, there are no effective treatments against TN breast cancers and results from these studies will provide new treatments for one of the biggest needs in breast cancer research.

Functional consequences of cyclin D1/BRCA1 interaction in breast cancer cells

The inheritance of one defective BRCA1 or BRCA2 allele predisposes an individual to developing breast and ovarian cancers. BRCA1 is a multifunctional tumor suppressor protein, which through interaction with a vast array of proteins has implications in processes such as cell cycle, transcription, DNA damage response and chromatin remodeling. Conversely, the oncogene, cyclin D1 is overexpressed in about 35% of all breast cancer cases. In this study, we provide detailed analyses on the phosphorylation state of BRCA1 by cyclin D1/cdk4 complexes. In particular, we have identified Ser 632 of BRCA1 as a cyclin D1/cdk4 phosphorylation site in vitro. Using chromatin immunoprecipitation assays, we observed that the inhibition of cyclin D1/cdk4 activity resulted in increased BRCA1 DNA binding at particular promoters in vivo. In addition, we identified multiple novel genes that are bound by BRCA1 in vivo. Collectively, these results indicate that cyclin D1/cdk4-mediated phosphorylation of BRCA1 inhibits the ability of BRCA1 to be recruited to particular promoters in vivo. Therefore, cyclin D1/Cdk4 phosphorylation of BRCA1 could provide a mechanism to interfere with the DNA-dependent activities of BRCA1.

Lymphoblasts of women with BRCA1 mutations are deficient in cellular repair of 8,5'-Cyclopurine-2'-deoxynucleosides and 8-hydroxy-2'-deoxyguanosine

Mutations in breast and ovarian cancer susceptibility genes BRCA1 and BRCA2 predispose women to a high risk of these cancers. Here, we show that lymphoblasts of women with BRCA1 mutations who had been diagnosed with breast cancer are deficient in the repair of some products of oxidative DNA damage, namely, 8-hydroxy-2'-deoxyguanosine and 8,5'-cyclopurine-2'-deoxynucleosides. Cultured lymphoblasts from 10 individuals with BRCA1 mutations and those from 5 control individuals were exposed to 5 Gy of ionizing radiation to induce oxidative DNA damage and then allowed to repair this damage. DNA samples isolated from these cells were analyzed by liquid chromatography/mass spectrometry and gas chromatography/mass spectrometry to measure 8-hydroxy-2'-deoxyguanosine, (5'-S)-8,5'-cyclo-2'-deoxyadenosine, (5'-R)-8,5'-cyclo-2'-deoxyguanosine, and (5'-S)-8,5'-cyclo-2'-deoxyguanosine. After irradiation and a subsequent period of repair, no significant accumulation of these lesions was observed in the DNA from control cells. In contrast, cells with BRCA1 mutations accumulated statistically significant levels of these lesions in their DNA, providing evidence of a deficiency in DNA repair. In addition, a commonly used breast tumor cell line exhibited the same effect when compared to a relevant control cell line. The data suggest that BRCA1 plays a role in cellular repair of oxidatively induced DNA lesions. The failure of cells with BRCA1 mutations to repair 8,5'-cyclopurine-2'-deoxynucleosides indicates the involvement of BRCA1 in nucleotide-excision repair of oxidative DNA damage. This work suggest that accumulation of these lesions may lead to a high rate of mutations and to deleterious changes in gene expression, increasing breast cancer risk and contributing to breast carcinogenesis.

Tumor-protective and tumor-promoting actions of dietary whey proteins in an N-methyl-N-nitrosourea model of rat mammary carcinogenesis

The mammary tumor-protective effects of dietary factors are considered to be mediated by multiple signaling pathways, consistent with the heterogeneous nature of the disease and the distinct genetic profiles of tumors arising from diverse mammary cell populations. In a 7,12-dimethylbenz(a)anthracene-induced model of carcinogenesis, we showed previously that female Sprague-Dawley rats exposed to AIN-93G diet containing whey protein hydrolysate (WPH) beginning at gestation Day 4 had reduced tumor incidence than those exposed to diet containing casein (CAS), due partly to increased mammary differentiation and reduced activity of phase I metabolic enzymes. Here, we evaluated the tumor-protective effects of these same dietary proteins to the direct-acting carcinogen N-methyl-N-nitrosourea (NMU). We found that lifetime exposure to WPH, relative to CAS, decreased mammary tumor incidence and prolonged the appearance of tumors in NMU-treated female rats, with no corresponding effects on tumor multiplicity. At 115 days post-NMU, histologically normal mammary glands from WPH-fed tumor-bearing rats had increased gene expression for the tumor suppressor BRCA1 and the differentiation marker kappa-casein than those of CAS-fed tumor-bearing rats. Tumor-bearing rats from the WPH group had more advanced tumors, with a greater incidence of invasive ductal carcinoma than ductal carcinoma in situ and higher serum C-peptide levels than corresponding rats fed CAS. WPH-fed tumor-bearing rats were also heavier after NMU administration than CAS tumor-bearing rats, although no correlation was noted between body weight and C-peptide levels for either diet group. Results demonstrate the context-dependent tumor-protective and tumor-promoting effects of WPH; provide support for distinct signaling pathways underlying dietary effects on development of mammary carcinoma; and raise provocative questions on the role of diet in altering the prognosis of existing breast tumors.

A list of candidate cancer biomarkers for targeted proteomics

We have compiled from literature and other sources a list of 1261 proteins believed to be differentially expressed in human cancer. These proteins, only some of which have been detected in plasma to date, represent a population of candidate plasma biomarkers that could be useful in early cancer detection and monitoring given sufficiently sensitive specific assays. We have begun to prioritize these markers for future validation by frequency of literature citations, both total and as a function of time. The candidates include proteins involved in oncogenesis, angiogenesis, development, differentiation, proliferation, apoptosis, hematopoiesis, immune and hormonal responses, cell signaling, nucleotide function, hydrolysis, cellular homing, cell cycle and structure, the acute phase response and hormonal control. Many have been detected in studies of tissue or nuclear components; nevertheless we hypothesize that most if not all should be present in plasma at some level. Of the 1261 candidates only 9 have been approved as "tumor associated antigens" by the FDA. We propose that systematic collection and large-scale validation of candidate biomarkers would fill the gap currently existing between basic research and clinical use of advanced diagnostics.

The functional significance of nuclear receptor acetylation

The endocrine signaling governing nuclear receptor (NR) function has been known for several decades to play a crucial role in the onset and progression of several tumor types. Notably among these are the estrogen receptor (ER) in breast cancer and androgen receptor (AR) in prostate cancer. Other nuclear receptors may be involved in cancer progression including the peroxisome-proliferator activating receptor gamma (PPARgamma), which has been implicated in breast, thyroid, and colon cancers. These NR are phylogenetically conserved modular transcriptional regulators, which like histones, undergo post-translational modification by acetylation, phosphorylation and ubiquitination. Importantly, the transcriptional activity of the receptors is governed by the coactivator p300, the activity of which is thought to be rate-limiting in the activity of these receptors. Histone acetyltransferases (HATs) and histone deacetylases (HDACs), modify histones by adding or removing an acetyl group from the epsilon amino group of lysines within an evolutionarily conserved lysine motif. Histone acetylation results in changes in chromatin structure in response to specific signals. These enzymes can also directly catalyze the NRs themselves, thus modifying signals at the receptor level. The post-translational modification of NR which is regulated by hormones, alters the NR function toward a growth promoting receptor. The deacetylation of NR is mediated by TSA-sensitive and NAD-dependent deacetylases. The regulation of NR by NAD-dependent enzymes provides a direct link between intracellular metabolism and hormone signaling.

Acceptance for preventive genetic testing and prophylactic surgery in women with a family history of breast and gynaecological cancers

The fear of family members of patients with breast or gynaecologic cancer of developing a similar disease is often high. We investigated the acceptance for genetic testing of untested women with a positive family history and their attitude for prophylactic surgery. A total of 659 women with a familial history of breast or gynaecologic cancer were asked to answer a questionnaire regarding their interest in genetic testing for breast cancer as well as for gynaecologic carcinoma and their interest in prophylactic surgery. Genetic testing is seen to be accepted by the majority of participants: 85.0 and 77.8% chose a genetic test for breast and gynaecologic cancer, respectively. Prophylactic surgery was much less chosen; prophylactic mastectomy as well as prophylactic hysterectomy or bilateral prophylactic oophorectomy was an option only for a minority of women. Genetic testing for risk assessment of healthy women with a positive family history was observed to be accepted by a majority of participants. Prophylactic surgery was an option only for a minority and was not acceptable for most of the women.

Is the association between cigarette smoking and breast cancer modified by genotype? A review of epidemiologic studies and meta-analysis

Epidemiologic studies have examined the association between cigarette smoking and breast cancer risk according to genotype with increasing frequency, commensurate with the growing awareness of the roles genes play in detoxifying or activating chemicals found in cigarette smoke and in preventing or repairing the damage caused by those compounds. To date, approximately 50 epidemiologic studies have examined the association between smoking and breast cancer risk according to variation in genes related to carcinogen metabolism, modulation of oxidative damage, and DNA repair. Some of the findings presented here suggest possible effect modification by genotype. In particular, 14 epidemiologic studies have tended to show positive associations with long-term smoking among NAT2 slow acetylators, especially among postmenopausal women. Summary analyses produced overall meta-relative risk (RR) estimates for smoking of 1.2 [95% confidence interval (95% CI), 1.0-1.5] for rapid acetylators and 1.5 (95% CI, 1.2-1.8) for slow acetylators. After stratification by menopausal status, the meta-RR for postmenopausal slow acetylators was 2.4 (95% CI, 1.7-3.3), whereas similar analyses for the other categories showed no association. In addition, summary analyses produced meta-RRs for smoking of 1.1 (95% CI, 0.8-1.4) when GSTM1 was present and 1.5 (95% CI, 1.1-2.1) when the gene was deleted. Overall, however, interpretation of the available literature is complicated by methodologic limitations, including small sample sizes, varying definitions of smoking, and difficulties involving single nucleotide polymorphism selection, which likely have contributed to the inconsistent findings. These methodologic issues should be addressed in future studies to help clarify the association between smoking and breast cancer.

MMTV-like sequences in human breast cancer: a fluorescent PCR/laser microdissection approach

The hypothesis that a retrovirus homologous to the mouse mammary tumour virus (MMTV) is involved in human breast cancer aetiology has fascinated scientists from many years, but it has never been convincingly demonstrated. Renewed interest in this hypothesis developed when an MMTV env gene-like sequence was found in 38% of human breast cancer tissues. Whereas some subsequent studies confirmed these findings, others did not. The main reasons for this discrepancy, among others, are the different sensitivities and technical details of current molecular approaches to the detection of these sequences. This study is an attempt to find sensitive and reproducible conditions capable of detecting MMTV env-like sequence in human samples. To this end, we first developed a fluorescence nested-PCR (FN-PCR) method that was able to detect very low copies of the viral genome, and then screened a panel of 45 frozen breast cancer samples obtained by laser microdissection. The MMTV env gene-like sequence was found in 15 (33%) of the human breast cancers analysed, whereas the same sequence was detectable neither in normal tissues nor in other types of tumour. Sequence analysis revealed 96% homology with the MMTV genome, but no other significant similarities with the human genome. The combined use of frozen material, microdissected cell populations and FN-PCR provides a novel, sensitive, robust, non-radioactive and fast methodology for the molecular detection of human-MTV. This approach might be successfully used in large molecular studies that aim to investigate the hypothesis of a retroviral aetiology of human breast cancer.

Gene signature of breast cancer cell lines treated with lycopene

Among the micronutrients studied in relation between nutrition and cancer, lycopene appears to be a breast cancer preventive phytochemical candidate found in raw tomatoes and tomato-derived products. In order to investigate the responsiveness of breast cancer genes to lycopene and to better understand the molecular mechanisms underlying the effects of lycopene, we used an oligonucleotide microarray approach. Human breast cancer cell lines (MCF-7 and MDA-MB-231) and a fibrocystic breast cell line (MCF-10a) were either exposed or not exposed to 10 microM lycopene for 48 h. Microarrays comprising 202 genes were used to identify genes responsive to lycopene supplementation. Hierarchical clustering revealed a cell line-specific lycopene modulation of breast cells. Based on the observed results, lycopene seems to exert regulation on apoptosis, cell cycle and DNA repair mechanisms according to estrogen and retinoic acid receptor cell status.

Genética molecular aplicada ao câncer cutâneo não melanoma

Os cânceres cutâneos não melanoma são as neoplasias malignas mais comuns em humanos. O carcinoma basocelular e o carcinoma espinocelular representam cerca de 95% dos cânceres cutâneos não melanoma, o que os torna um crescente problema para a saúde pública mundial devido a suas prevalências cada vez maiores. As alterações genéticas que ocorrem no desenvolvimento dessas malignidades cutâneas são apenas parcialmente compreendidas, havendo muito interesse no conhecimento e determinação das bases genéticas dos cânceres cutâneos não melanoma que expliquem seus fenótipos, comportamentos biológicos e potenciais metastáticos distintos. Apresenta-se uma revisão atualizada da genética molecular aplicada aos cânceres cutâneos não melanoma, em especial ao carcinoma basocelular e carcinoma espinocelular, enfatizando os mais freqüentes genes e os principais mecanismos de instabilidade genômica envolvidos no desenvolvimento dessas malignidades cutâneas.

Genome-wide scan for genes involved in bipolar affective disorder in 70 European families ascertained through a bipolar type I early-onset proband: supportive evidence for linkage at 3p14

Preliminary studies suggested that age at onset (AAO) may help to define homogeneous bipolar affective disorder (BPAD) subtypes. This candidate symptom approach might be useful to identify vulnerability genes. Thus, the probability of detecting major disease-causing genes might be increased by focusing on families with early-onset BPAD type I probands. This study was conducted as part of the European Collaborative Study of Early Onset BPAD (France, Germany, Ireland, Scotland, Switzerland, England, Slovenia). We performed a genome-wide search with 384 microsatellite markers using non-parametric linkage analysis in 87 sib-pairs ascertained through an early-onset BPAD type I proband (AAO of 21 years or below). Non-parametric multipoint analysis suggested eight regions of linkage with P-values<0.01 (2p21, 2q14.3, 3p14, 5q33, 7q36, 10q23, 16q23 and 20p12). The 3p14 region showed the most significant linkage (genome-wide P-value estimated over 10 000 simulated replicates of 0.015 [0.01-0.02]). After genome-wide search analysis, we performed additional linkage analyses with increased marker density using markers in four regions suggestive for linkage and having an information contents lower than 75% (3p14, 10q23, 16q23 and 20p12). For these regions, the information content improved by about 10%. In chromosome 3, the non-parametric linkage score increased from 3.51 to 3.83. This study is the first to use early-onset bipolar type I probands in an attempt to increase sample homogeneity. These preliminary findings require confirmation in independent panels of families.

Prospective screening study of 0.5 Tesla dedicated magnetic resonance imaging for the detection of breast cancer in young, high-risk women

Background

Evidence-based screening guidelines are needed for women under 40 with a family history of breast cancer, a BRCA1 or BRCA2 mutation, or other risk factors. An accurate assessment of breast cancer risk is required to balance the benefits and risks of surveillance, yet published studies have used narrow risk assessment schemata for enrollment. Breast density limits the sensitivity of film-screen mammography but is not thought to pose a limitation to MRI, however the utility of MRI surveillance has not been specifically examined before in women with dense breasts. Also, all MRI surveillance studies yet reported have used high strength magnets that may not be practical for dedicated imaging in many breast centers. Medium strength 0.5 Tesla MRI may provide an alternative economic option for surveillance.

Methods

We conducted a prospective, nonrandomized pilot study of 30 women age 25–49 years with dense breasts evaluating the addition of 0.5 Tesla MRI to conventional screening. All participants had a high quantitative breast cancer risk, defined as ≥ 3.5% over the next 5 years per the Gail or BRCAPRO models, and/or a known BRCA1 or BRCA2 germline mutation.

Results

The average age at enrollment was 41.4 years and the average 5-year risk was 4.8%. Twenty-two subjects had BIRADS category 1 or 2 breast MRIs (negative or probably benign), whereas no category 4 or 5 MRIs (possibly or probably malignant) were observed. Eight subjects had BIRADS 3 results, identifying lesions that were "probably benign", yet prompting further evaluation. One of these subjects was diagnosed with a stage T1aN0M0 invasive ductal carcinoma, and later determined to be a BRCA1 mutation carrier.

Conclusion

Using medium-strength MRI we were able to detect 1 early breast tumor that was mammographically undetectable among 30 young high-risk women with dense breasts. These results support the concept that breast MRI can enhance surveillance for young high-risk women with dense breasts, and further suggest that a medium-strength instrument is sufficient for this application. For the first time, we demonstrate the use of quantitative breast cancer risk assessment via a combination of the Gail and BRCAPRO models for enrollment in a screening trial.

BRCA1 Modulates Xenobiotic Stress-inducible Gene Expression by Interacting with ARNT in Human Breast Cancer Cells

Previously, we have reported that BRCA1 regulates the expression of various classes of genes, including genes involved in xenobiotic stress responses (Bae, I., Fan, S., Meng, Q., Rih, J. K., Kim, H. J., Kang, H. J., Xu, J., Goldberg, I. D., Jaiswal, A. K., and Rosen, E. M. (2004) Cancer Res. 64, 7893-7909). In the present study, we have investigated the effects of BRCA1 on xenobiotic stress-inducible gene expression. In response to aryl hydrocarbon receptor (AhR) ligands, cytoplasmic AhR becomes activated and then translocates to the nucleus where it forms a complex with the aryl hydrocarbon receptor nuclear translocator (ARNT). Subsequently, the AhR.ARNT complex binds to the enhancer or promoter of genes containing a xenobiotic stress-responsive element and regulates the expression of multiple target genes including cytochrome P450 subfamily polypeptide 1 (CYP1A1). In this study, we have found that endogenous and overexpressed exogenous wild-type BRCA1 affect xenobiotic stress-induced CYP1A1 gene expression. Using a standard chromatin immunoprecipitation assay, we have demonstrated that BRCA1 is recruited to the promoter regions of CYP1A1 and CYP1B1 along with ARNT and/or AhR following xenobiotic exposure. Our findings suggest that BRCA1 may be physiologically important for mounting a normal response to xenobiotic insults and that it may function as a coactivator for ARNT activity. Using immunoprecipitation, Western blotting, and glutathione S-transferase capture assays, a xenobiotic-independent interaction between BRCA1 and ARNT has been identified, although it is not yet known whether this is a direct or indirect interaction. We have also found that the inducibility of CYP1A1 and CYP1B1 transcripts following xenobiotic stress was significantly attenuated in BRCA1 knockdown cells. This reduced inducibility is associated with an altered stability of ARNT and was almost completely reversed in cells transfected with an ARNT expression vector. Finally, we have found that xenobiotic (TCDD) treatments of breast cancer cells containing reduced levels of BRCA1 cause the transcription factor ARNT to become unstable.

Regulation of progesterone receptor signaling by BRCA1 in mammary cancer

Inherited mutations of the BRCA1 gene (chromosome 17q21), a tumor suppressor, lead to an increased risk of breast cancer, ovarian cancer, and several other hormone-responsive tumor types. Over the last ten years, BRCA1 has been found to play major roles in DNA damage signaling, repair, and cell cycle checkpoints. In addition, unfolding evidence suggests that BRCA1 functions as a co-regulator for steroid hormone receptors and modulates steroid hormone action. In this paper, we will briefly review this evidence and present a model to address the role of the progesterone and estrogen receptors in BRCA1 mutant mammary carcinogenesis. Finally, we will consider some of the clinical implications of this model.

ACCA phosphopeptide recognition by the BRCT repeats of BRCA1

The tumour suppressor gene BRCA1 encodes a 220 kDa protein that participates in multiple cellular processes. The BRCA1 protein contains a tandem of two BRCT repeats at its carboxy-terminal region. The majority of disease-associated BRCA1 mutations affect this region and provide to the BRCT repeats a central role in the BRCA1 tumour suppressor function. The BRCT repeats have been shown to mediate phospho-dependant protein-protein interactions. They recognize phosphorylated peptides using a recognition groove that spans both BRCT repeats. We previously identified an interaction between the tandem of BRCA1 BRCT repeats and ACCA, which was disrupted by germ line BRCA1 mutations that affect the BRCT repeats. We recently showed that BRCA1 modulates ACCA activity through its phospho-dependent binding to ACCA. To delineate the region of ACCA that is crucial for the regulation of its activity by BRCA1, we searched for potential phosphorylation sites in the ACCA sequence that might be recognized by the BRCA1 BRCT repeats. Using sequence analysis and structure modelling, we proposed the Ser1263 residue as the most favourable candidate among six residues, for recognition by the BRCA1 BRCT repeats. Using experimental approaches, such as GST pull-down assay with Bosc cells, we clearly showed that phosphorylation of only Ser1263 was essential for the interaction of ACCA with the BRCT repeats. We finally demonstrated by immunoprecipitation of ACCA in cells, that the whole BRCA1 protein interacts with ACCA when phosphorylated on Ser1263.

Primary structure-based function characterization of BRCT domain replicates in BRCA1

BRCA1 is a large protein that exhibits a multiplicity of functions in its apparent role in DNA repair. Certain mutations of BRCA1 are known to have exceptionally high penetrance with respect to familial breast and ovarian cancers. The structures of the N-terminus and C-terminus of the protein have been determined. The C-terminus unit consists of two alpha-beta-alpha domains designated BRCT. We predicated two homologous BRCT regions in the BRCA1 internal region, and subsequently produced and purified these protein domains. Both recombinant domains show significant self-association capabilities as well as a preferential tendency to interact with each other. These results suggest a possible regulatory mechanism for BRCA1 function. We have demonstrated p53-binding activity by an additional region, and confirmed previous results showing that two regions of BRCA1 protein bind p53 in vitro. Based on sequence analysis, we predict five p53-binding sites. Our comparison of binding by wild-type and mutant domains indicates the sequence specificity of BRCA1-p53 interaction.

BRCA1 plays a role in the hypoxic response by regulating HIF-1alpha stability and by modulating vascular endothelial growth factor expression

A recent study of breast cancer patients with and without BRCA1 gene mutations found significantly lower levels of VEGF in serum from patients with BRCA1 mutations (Tarnowski, B., Chudecka-Glaz, A., Gorski, B., and Rzepka-Gorska, I. (2004) Breast Cancer Res. Treat. 88, 287-288). Here, we describe a possible mechanistic explanation for this correlation. Because hypoxia in tumors stimulates VEGF expression and secretion we hypothesized that altered BRCA1 protein levels in breast tumors could affect hypoxia-stimulated VEGF promoter activity. This possibility was tested in cells transfected with various combinations of expression plasmids for BRCA1, BRCA1 specific inhibitory RNAs (BRCA1-siRNAs), HIF-1alpha, and a VEGF promoter-reporter and then incubated in normoxia (21%, O2) or hypoxia (0.1%, O2). As predicted, increased BRCA1 levels enhanced both hypoxia-stimulated VEGF promoter activity and the amounts of VEGF mRNA, as determined by semiquantitative RT-PCR and quantitative real time PCR. Using the ChIP assay, we discovered that BRCA1 could be recruited to the endogenous human VEGF promoter along with HIF-1alpha following hypoxia. An interaction between BRCA1 and HIF-1alpha was found in human breast cancer cells. We also found that hypoxia-stimulated VEGF promoter activity and secretion was reduced in cells containing reduced amounts of endogenous BRCA1 protein (obtained by transfecting with BRCA1 siRNAs). A mechanistic explanation for these effects is provided by our finding a reduced half-life and reduced accumulation of HIF-1alpha in hypoxic cells transfected with BRCA1-siRNAs and that proteasome inhibitors blocked these effects of BRCA1-siRNAs. Thus, our results suggest that normal amounts of BRCA1 function in hypoxia to regulate HIF-1alpha stability, probably by interacting with HIF-1alpha.

Natural selection and mammalian BRCA1 sequences: elucidating functionally important sites relevant to breast cancer susceptibility in humans

Comparison of orthologous gene sequences is emerging as a powerful approach to elucidating functionally important positions in human disease genes. Using a diverse array of 132 mammalian BRCA1 (exon 11) sequences, we evaluated the functional significance of specific sites in the context of selection information (purifying, neutral, or diversifying) as well as the ability to extract such information from alignments that index varying degrees of mammalian diversity. Small data sets of either closely related taxa (Primates) or divergent placental taxa were unable to distinguish sites conserved due to purifying selection from sites conserved due to chance (false-positive rate = 65%-99%). Increasing the number of placental taxa to 57 greatly reduced the potential false-positive rate (0%-1.5%). Using the larger data set, we ranked the oncogenic risk of human missense mutations using a novel method that incorporates site-specific selection level and severity of the amino acid change evaluated against the amino acids present in other mammalian taxa. In addition to sites undergoing positive selection in Marsupialia, Laurasiatheria, Euarchontoglires, and Primates, we identified sites most likely to be undergoing divergent selection pressure in different lineages and six pairs of potentially interacting sites. Our results demonstrate the necessity of including large numbers of sequences to elucidate functionally important sites of a protein when using a comparative evolutionary approach.

BRCA1: a locus-specific "liaison" in gene expression and genetic integrity

Mutations in BRCA1 predominantly lead to elevated risks of breast and ovarian cancers. In contrast to the tissue-specific nature of BRCA1tumors, the normal BRCA1 gene product functions in diverse nuclear events including transcription, DNA repair, and DNA damage checkpoint. Recent findings of physical and functional associations between BRCA1 and the RNA polymerase II (RNAPII)-dependent transcription machinery may shed some light on this longstanding paradox of BRCA1 biology. Eukaryotic gene expression is now known to be a continuous process, whereby each step is physically and functionally connected to the next. In particular, RNAPII plays a pivotal role in coordinating transcription with various pre-mRNA processing events and stress response. Interestingly, BRCA1 preferentially interacts with the processive form of RNAPII and proteins that regulate RNAPII activity and movement during transcription elongation. In response to DNA damage, BRCA1 dissociates from RNAPII and localizes to DNA damage sites. We propose that BRCA1 may coordinate multiple steps in gene expression, including transcription initiation, elongation, and pre-mRNA processing via its interactions with the transcription machinery at selected gene loci. The same BRCA1-associated transcription apparatus may serve as a sensor for stress signals and facilitate the transition from a transcription state to checkpoint/DNA repair state. Such a coordinating role of BRCA1 in gene expression may ensure the appropriate quantity and quality of the mature transcripts for certain breast and ovarian cancer-related genes, as well as the genetic integrity of the breast and ovary tissues.

Towards a dietary prevention of hereditary breast cancer

Inheritance of a deleterious mutation in BRCA1 or BRCA2 confers a high lifetime risk of developing breast cancer. Variation in penetrance between individuals suggests that factors other than the gene mutation itself may influence the risk of cancer in susceptible women. Several risk factors have been identified which implicate estrogen-induced growth stimulation as a probable contributor to breast cancer pre-disposition. The protein products of both of these genes appear to help preserve genomic integrity via their participation in the DNA damage response and repair pathways. To date, the evidence for a cancer-protective role of dietary nutrients, for the most part those with antioxidant properties, has been based on women without any known genetic pre-disposition and it is important to identify and evaluate dietary factors which may modify the risk of cancer in BRCA carriers. Here we propose that diet modification may modulate the risk of hereditary breast cancer by decreasing DNA damage (possibly linked to estrogen exposure) or by enhancing DNA repair. The prevention of hereditary breast cancer through diet is an attractive complement to current management strategies and deserves exploration.