Tumor Suppressor Gene BRCA1 Research Articles

Absence of 185delAG and 6174delT Mutations among Breast Cancer Patients of Eastern India.

The incidence of breast cancer in India is on the rise and is rapidly becoming the number one cancer in females, pushing the cervical cancer to the second position. Most of the predisposition to hereditary breast and ovarian cancer has been attributed to inherited defects in two tumor suppressor genes BRCA1 and BRCA2. Alterations in these genes have been reported in different populations, some of which are population- specific mutations showing founder effects. Two specific mutations in the BRCA1 (185delAG) and BRCA2 (6174delT) genes have been reported to be of high prevalence in different populations. The aim of this study was to estimate the carrier frequency of 185delAG and 6174delT mutations in eastern Indian breast cancer patients. We selected 231 histologically confirmed breast cancer patients from our tertiary cancer care center in eastern India. Family history was obtained by interview or a self-reported questionnaire. The presence of the mutation was investigated by allele specific duplex/multiplex-PCR on genomic DNA extracted from peripheral blood. A total of 231 patients (age range: 26-77 years), 130 with a family history and 101 without were screened. The two founder mutations 185delAG in BRCA1 and 6174delT in BRCA2 were not found in any of the subjects. This was confirmed by molecular analysis. Our findings suggest that these BRCA mutations may not have a strong recurrent effect on breast cancer among the eastern Indian population. The contribution of these founder mutations to breast cancer incidence is probably low and could be limited to specific subgroups. This may be particularly useful in establishing further pre-screening strategies.

Abstract 18789: BRCA2 is a Novel Regulator of Endothelial Cell Function and Apoptosis Following Hyperglycemia

Background: Germ-line mutations in the tumor suppressor gene BRCA2 (breast cancer 2, early onset) predispose carriers mostly to breast cancer, and BRCA2 mutation carriers also face a 2-fold increase in the risk of developing diabetes.Hyperglycemia, the hallmark of diabetes, is a major risk factor for endothelial dysfunction leading to vascular complications. The relationship linking role of BRCA2 in the development of diabetes and endothelial dysfunction remains mainly unexplored. Methods: To elucidate the role of BRCA2 in diabetes and endothelial apoptosis/dysfunction in vitro, we silenced BRCA2 in human umbilical vein endothelial cells (ECs) and evaluated the markers of EC function and apoptosis following hyperglycemia. Results: We first confirmed the basal expression of BRCA2 in ECs at transcript and protein levels by qPCR and immunoblotting, respectively. Interestingly, hyperglycemia significantly induced BRCA2 expression after 48 hours of treatment. We then silenced BRCA2 in ECs and confirmed successful silencing at transcript and protein levels. Hyperglycemia significantly increased the reactive oxygen species (ROS) production in the BRCA2-deficient ECs in comparison to control ECs. Increased ROS production was associated with exacerbated DNA-damage in BRCA2-silenced ECs as evidenced by increased expression and activation of DNA double-stranded breaks (DSBs) marker H2A.X and reduced RAD51-foci formation, an essential regulator of DSB repair. Increased DSBs were associated with significantly increased activation of p53. Elevated levels of DNA-damage and activated-p53 were further associated with significantly increased hyperglycemia-induced apoptosis in BRCA2-silenced ECs as measured by immunoblotting for cleaved-caspase-3, Bax and by TUNEL-staining.Key indices of endothelial function, including tube formation and NO production, were significantly reduced following hyperglycemia-treatment in BRCA2-deficient ECs. Conclusion: Our data for the first time, show an entirely novel role of BRCA2 as a regulator of endothelium in the setting of hyperglycemia, and provide important clues regarding the potential susceptibility of BRCA2 mutation carriers to hyperglycemia-induced cardiovascular complications.

Abstract 18705: BRCA2 is a Novel Regulator of Endothelial Cell Function and Apoptosis

Background: Germ-line mutations in the tumor suppressor gene BRCA2 (breast cancer 2, early onset) predispose carriers not only to breast cancer, but also to other cancers. BRCA2 plays crucial role in the genome integrity maintenance and is central to DNA-damage repair. BRCA2-associated DNA-damage responses are not only specific to cancer syndromes but also represent a common pathophysiological basis for diverse cardiovascular diseases (CVDs). These observations led us to hypothesize that BRCA2 is an essential regulator of endothelial function and apoptosis following genotoxic stress. Methods: To elucidate the role of BRCA2 in endothelial cells, we silenced BRCA2 in the human umbilical vein endothelial cells (ECs) and measured the indices of EC function; tube formation and proliferation, DNA-damage/repair and apoptosis by qPCR, immunoblotting and immunofluorescence following doxorubicin (Dox) treatment. Results: We confirmed the basal expression and successful silencing of BRCA2 in ECs at transcript and protein levels by qPCR and immunoblotting, respectively. Genotoxic stress in the form of Dox exacerbated DNA-damage in BRCA2-silenced ECs as evident by increased expression and activation of DNA double-stranded breaks (DSBs) marker H2A.X and reduced RAD51-foci formation, an essential regulator of DSB repair. Increased DSBs were associated with significantly increased expression and activation of p53, and increased expression of p53-upregulated modulator of apoptosis PUMA. Elevated levels of DNA-damage and p53 were further associated with significantly increased Dox-induced apoptosis in BRCA2-silenced ECs as measured by immunoblotting for cleaved-caspase-3 and TUNEL-staining.Key indices of endothelial function, including tube formation and proliferation, were significantly reduced following Dox-treatment in BRCA2-deficient ECs, which was accompanied with significantly increased expression of cell cycle inhibitor, p21 at transcript and protein levels. Conclusion: Our data for the first time, show an entirely novel role of BRCA2 as a regulator of endothelium, and provide important clues regarding a potential susceptibility of BRCA2 mutation carriers to anthracycline-induced CVDs, a cornerstone of chemotherapy for cancer.

Commentary: The unliganded glucocorticoid receptor positively regulates the tumor suppressor gene BRCA1 through GABP beta.

Commentary: The unliganded glucocorticoid receptor positively regulates the tumor suppressor gene BRCA1 through GABP beta.

Identification of miR-10b, miR-26a, miR-146a and miR-153 as potential triple-negative breast cancer biomarkers.

BackgroundFamilial triple-negative breast cancers are often linked to mutations in the BRCA1 tumor suppressor gene. In sporadic triple-negative breast cancers BRCA1 is frequently inactivated at the transcriptional level, and it has been reported that this inactivation may be brought about by promoter methylation. More recently, it was found that BRCA1 may also be regulated at the post-transcriptional level by miRNAs. Here, we explored the expression of putative BRCA1-regulating miRNAs in sporadic human triple-negative breast cancer cells.MethodsNine sporadic human breast cancer-derived cell lines and one benign breast epithelium-derived cell line were assessed for their hormone receptor, growth factor receptor and cytokeratin status by immunocytochemistry. The expression of 5 selected miRNAs predicted to target BRCA1 was assessed using qRT-PCR in the 10 cell lines. In addition, expression profiles of 84 known breast cancer-associated miRNAs were established in these 10 cell lines using PCR Array and qRT-PCR, respectively. The putative role of pre-selected candidate miRNAs in breast cancer development was assessed through exogenous expression of these miRNAs and their anti-miRNAs (‘antagomirs’) in MDA-MB-231 and MCF7 breast cancer-derived cells.ResultsBased on our expression profiling results, four candidate miRNAs (miR-10b, miR-26a, miR-146a and miR-153) were selected as being potentially involved in triple-negative breast cancer development. Exogenous expression assays revealed that miR-10b and miR-26a, but not miR-146a, can down-regulate the expression of BRCA1 in both triple-negative MDA-MB-231 and luminal epithelial MCF7 breast cancer-derived cells, whereas miR-153 could down-regulate BRCA1 expression only in MCF7 cells. In silico analysis of The Cancer Genome Atlas (TCGA) data confirmed that miR-146a is significantly higher expressed in triple-negative breast tumors compared to other (non triple-negative) breast tumors.ConclusionOur work provides evidence for the involvement of specific miRNAs in triple-negative breast cancer development through regulating BRCA1 expression.Electronic supplementary materialThe online version of this article (doi:10.1007/s13402-015-0239-3) contains supplementary material, which is available to authorized users.

The Oncogenic Properties Of The Redox Inflammatory Protein Inducible Nitric Oxide Synthase In ER(-) Breast Cancer

Inflammation generates reactive chemical species that induce conditions of oxidative nitrosative stress as emerged as factor in poor outcome of many cancers. Our recent findings show that in the inflammatory protein inducible nitric oxide synthase (iNOS) is a strong predictor of poor outcome in ER(-) patients (Glynn et al. JCI 2010). Furthermore 46 genes, of which 23 were associated with basal like breast cancer, were elevated when iNOS high. In vitro studies using ER(-) cell lines showed that fluxes of nitric oxide (NO) delivered by NO donors surprising mimic this relationship in the patient cohort. Using this model, we show that NO at different specific concentrations stimulate pro-oncogenic mechanisms such as AKT, ERK, NFkB, AP-1, and HIF-1α that lead to increase of metastatic and cancer stem cells proteins. In addition, we show that tumor suppressor gene BRCA1 and PP2A are inhibited by these NO levels. Similarly other studies show that these concentrations of NO increase immunosuppressive proteins TGF-β and IL-10 in leukocytes to decrease efficacy of some anticancer therapies further contributing to pro-tumorigenic environment. Using this model we have identified several new compounds that have efficacy in xenographic models. These finding have provided a model that shows how NO can affect numerous mechanism that leads to a more aggressive phenotype.

Abstract A33: γH2AX: A molecular marker of DNA damage response in smoking-induced pancreatic ductal adenocarcinoma

Abstract Introduction: Cigarette smoking is an important risk factor for the development pancreatic ductal adenocarcinoma (PDAC). Nicotine and nitrosamines cause pancreatic cell injury and contribute to a cascade of oncogenic events. Among multiple tobacco specific nitrosamines, 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) is considered to be the most carcinogenic and induces DNA double strand-breaks (DSBs). However, identification of potential prognostic biomarkers and experimental models of smoking-induced PDAC remain unknown. We have studied phosphorylated histone H2AX (γH2AX), a marker for double-stranded DNA breaks, as a new biomarker for detecting cigarette smoke-induced pathogenesis of PDAC. Experimental Procedure: We have characterized the expression of γH2AX protein in human pancreatic tissues, human pancreatic duct epithelial (HPDE)6, PDAC cell lines, and PanIn, primary PDAC (PDA) and liver metastasis (LMP) cell lines generated from a genetically engineered mice model of PDAC. Kaplan-Meier survival analysis was performed to determine the significance of γH2AX expression amongst smokers and non-smokers with PDAC. HPDE6 and PanIN cells were cultured for 4 days in the presence or absence of cigarette smoke (CS) (0-25μg/ml) or NNK (0-10μM). Cell cycle analysis and apoptosis were assessed through flow cytometry with the markers propidium iodide and annexin V respectively. HPDE6 and PanIN cells treated with CS or NNK for up to 50 days were analyzed for rapid activation of DNA damage response (DDR) pathway proteins γH2AX, RAD51, BRCA1, BRCA2, phospho-CHK2 and phospho-CHK1. Cells were treated with either CS or NNK along with a CHK2 inhibitor and analyzed for activation of γH2AX. To determine DNA integrity, accumulation of γH2AX was measured by ELISA in cells treated with CS or NNK. Immunofluorescence confocal microscopy was utilized to examine the role of γH2AX on nuclear foci formation with DNA repair complexes by quantifying the amount of co-localization. To replicate chronic smoke exposure, we treated HPDE6 and PanIn cells with 1 and 10 µg/ml CS or 10nM and 1µM NNK for 10 passages, and examined these cell lines for DSBs by comet assay, apoptosis markers by protein array and in vitro tumorigenicity by colony formation assay. Results: γH2AX expression was significantly higher (p<0.0001) in smokers when compared to non-smokers. Overall survival of patients with high γH2AX expression in their primary tumor was associated with significantly decreased median survival (11 months) when compared to low γH2AX expression (36 months, p=0.0007). HPDE6 cells exposed to CS or NNK, showed more than 80% survival. The surviving cells had altered morphology, acquired mesenchymal characteristics and displayed increased tumorigenicity suggesting that these cells acquire resistance to apoptosis after CS or NNK exposure. In addition, exposure of cells to CS or NNK resulted in generation of γH2AX and induction of phospho-CHK2 expression. RAD51 and phospho-CHK2 co-localize with γH2AX after DNA damage with CS or NNK exposure. Inhibition of CHK2 reduced expression of γH2AX. The product of the tumor suppressor gene BRCA2 co-localized with γH2AX indicating that γH2AX is necessary for the recruitment of DNA repair factors to the site of DNA damage. BRCA2 mutant cell line CAPAN1 exhibited a substantially reduced ability to form co-localization with RAD51 and γH2AX, consistent with a role of γH2AX in DNA damage repair. Conclusion: This work supports the role of γH2AX as a new molecular biomarker to assess the contribution of cigarette smoking-induced PDAC. γH2AX is necessary for DNA damage repair in PDAC and its activation is dependent on CHK2. Therapies that can block γH2AX expression by inhibiting upstream kinases may be a new potential therapeutic approach to treat and/or prevent PDAC. Citation Format: Kumaraswamy Honnenahally, Chanjuan Shi, Xi Chen, Jason Castellanos, Nipun Merchant, Timothy Blackwell, Nagaraj Nagathihalli. γH2AX: A molecular marker of DNA damage response in smoking-induced pancreatic ductal adenocarcinoma. [abstract]. In: Proceedings of the AACR Special Conference on Pancreatic Cancer: Innovations in Research and Treatment; May 18-21, 2014; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2015;75(13 Suppl):Abstract nr A33.

Repair versus Checkpoint Functions of BRCA1 Are Differentially Regulated by Site of Chromatin Binding.

The product of the Brca1 tumor-suppressor gene is involved in multiple aspects of the cellular DNA damage response (DDR), including activation of cell-cycle arrests and DNA double-stranded break (DSB) repair by homologous recombination. Prior reports demonstrated that BRCA1 recruitment to areas of DNA breakage depended on RAP80 and the RNF8/RNF168 E3 ubiquitin ligases. Here, we extend these findings by showing that RAP80 is only required for the binding of BRCA1 to regions flanking the DSB, whereas BRCA1 binding directly to DNA breaks requires Nijmegen breakage syndrome 1 (NBS1). These differential recruitment mechanisms differentially affect BRCA1 functions: (i) RAP80-dependent recruitment of BRCA1 to chromatin flanking DNA breaks is required for BRCA1 phosphorylation at serine 1387 and 1423 by ATM and, consequently, for the activation of S and G(2) checkpoints; and (ii) BRCA1 interaction with NBS1 upon DSB induction results in an NBS1-dependent recruitment of BRCA1 directly to the DNA break and is required for nonhomologous end-joining repair. Together, these findings illustrate that spatially distinct fractions of BRCA1 exist at the DSB site, which are recruited by different mechanisms and execute different functions in the DDR.

Multigene panel analysis identified germline mutations of DNA repair genes in breast and ovarian cancer

Approximately 5–10% of all breast and/or ovarian cancer cases are considered as inherited. BRCA1 and BRCA2 tumor suppressor genes account for a high penetrance of hereditary cases, but familial cases without mutations in these genes can also occur. Despite their low penetrance, other hereditary cancer-related genes are known to be associated with breast and ovarian cancer risk. However, the extent to which these genes prevail in breast and ovarian cancer remains to be elucidated. To estimate the frequency of mutations in these predisposition genes, we analyzed the germline mutations of 25 hereditary cancer-related genes in 155 patients using targeted next-generation sequencing. These subjects included 11 BRCA1/2 mutation-positive cases and 144 negative cases. Of these, three patients (1.9%) had pathogenic mutations in ATM, MRE11A, or MSH6, all of which have a central role in DNA repair and the mismatch repair pathway. The MSH6 splice-site mutation (IVS6+1G>T) was predicted to be pathogenic, as demonstrated by in vitro and immunohistochemical analyses. These results suggested deficiencies in cellular DNA repair functions result in the development of breast and ovarian cancer.

Functional variant analyses (FVAs) predict pathogenicity in the BRCA1 DNA double-strand break repair pathway.

Heritable mutations in the BRCA1 and BRCA2 and other genes in the DNA double-strand break (DSB) repair pathway disrupt binding of the encoded proteins, transport into the nucleus and initiation of homologous recombination, thereby increasing cancer risk [Scully, R., Chen, J., Plug, A., Xiao, Y., Weaver, D., Feunteun, J., Ashley, T. and Livingston, D.M. (1997) Association of BRCA1 with Rad51 in mitotic and meiotic cells. Cell, 88, 265-275, Chen, J., Silver, D.P., Walpita, D., Cantor, S.B., Gazdar, A.F., Tomlinson, G., Couch, F.J., Weber, B.L., Ashley, T., Livingston, D.M. et al. (1998) Stable interaction between the products of the BRCA1 and BRCA2 tumor suppressor genes in mitotic and meiotic cells. Mol. Cell, 2, 317-328]. To meet the challenge of correct classification, flow cytometry-based functional variant analyses (FVAs) were developed to determine whether variants in DSB repair genes disrupted the binding of BRCA1 to BARD1, PALB2, BRCA2 and FANCD2, phosphorylation of p53 or BRCA1 nuclear localization in response to DNA damage caused by diepoxybutane, mitomycin C and bleomycin. Lymphoblastoid cells from individuals with BRCA1 pathogenic mutations, benign variants, and variants of uncertain significance or with known BRCA2, FANCC or NBN mutations were tested. Mutations in BRCA1 decreased nuclear localization of BRCA1 in response to individual or combination drug treatment. Mutations in BRCA1 reduced binding to co-factors, PALB2 and FANCD2 and decreased phosphorylation of p53. Mutations in BRCA2, FANCC and NBN decreased nuclear localization of BRCA1 in response to drug treatment, cofactors binding and p53 phosphorylation. Unsupervised cluster analysis of all and as few as two assays demonstrated two apparent clusters, high-risk BRCA1 mutations and phenocopies and low-risk, fully sequenced controls and variants of uncertain significance (VUS). Thus, two FVA assays distinguish BRCA1 mutations and phenocopies from benign variants and categorize most VUS as benign. Mutations in other DSB repair pathway genes produce molecular phenocopies. FVA assays may represent an adjunct to sequencing for categorizing VUS or may represent a stand-alone measure for assessing breast cancer risk.

BRCA1 Circos: a visualisation resource for functional analysis of missense variants

BackgroundInactivating germline mutations in the tumour suppressor gene BRCA1 are associated with a significantly increased risk of developing breast and ovarian cancer. A large number (>1500) of unique BRCA1 variants...

Detection of BRCA1 and BRCA2 germline mutations in Japanese population using next-generation sequencing.

Tumor suppressor genes BRCA1 and BRCA2 are the two main breast and ovarian cancer susceptibility genes, and their genetic testing has been used to evaluate the risk of hereditary breast and ovarian cancer (HBOC). While several studies have reported the prevalence of BRCA1 and BRCA2 mutations in Japanese populations, there is insufficient information about deleterious mutations compared with western countries. Moreover, because many rare variants are found in BRCA1 and BRCA2, both of which encode large proteins, it is difficult to sequence all coding regions using the Sanger method for mutation detection. In this study, therefore, we performed next-generation sequencing (NGS) analysis of the entire coding regions of BRCA1 and BRCA2 in 135 breast and/or ovarian cancer patients. Deleterious BRCA1 and BRCA2 mutations were detected in 10 patients (7.4%) by NGS analysis. Of these, one mutation in BRCA1 and two in BRCA2 had not been reported previously. Furthermore, a BRCA2 mutation found in a proband was also identified in two unaffected relatives. These data suggest the utility of screening BRCA1 and BRCA2 mutations by NGS in clinical diagnosis.

Abstract 2822: A pan-cancer analysis of inferred homologous recombination deficiency identifies potential platinum benefit in novel subtypes

Abstract Personalized medicine in cancer aims to improve treatment outcome, by exploiting the molecular alterations of the individual tumor to inform therapeutic decisions. Ovarian and triple-negative breast cancers with defects in homologous recombination (HR) DNA repair are highly sensitive to treatment with platinum-based DNA-damaging agents. Reliable biomarkers to identify HR-deficient cancers prior to the initial treatment may be used to stratify patients for platinum chemotherapy. Extensive genome damage caused by deficient HR is readily observed as high frequencies of allelic imbalance and loss of heterozygosity in cancers with loss of either of the tumor suppressor genes BRCA1 or BRCA2, but is also common in ovarian and triple-negative breast cancers with no BRCA1/2 mutations, indicating HR loss due to alternative mechanisms. Recently, three independent methods were published that each quantitate the state of HR deficiency in a given cancer, by summarizing different types of DNA aberrations that are likely to be caused by improper DNA repair. Here we compare the three scores, named NtAI (1), LST (2), and HRD (3), utilizing a panel of 4400 patients representing 13 cancer types from The Cancer Genome Atlas. We found that the three scores are highly correlated with each other, suggesting they measure the effect of similar types of DNA damage. We found a strong association with overall survival only in ovarian cancer, which is consistent with frequent BRCA-related HR deficiency reported for this type of cancer. Next, we compared the distribution of the scores across cancer types, and found that those types ordinarily receiving platinum as standard of care have the highest median scores. Importantly, in most types not generally given platinum chemotherapy we also found small sub-populations of high scoring tumors, which may represent subtypes with a previously overlooked potential to respond to platinum agents. Lastly, we used RNAseq to identify genes whose expression is associated with high DNA aberration scores. We compared the 100 genes most highly correlated with each score and found a shared set of 53 genes; these were enriched for genes involved in cell cycle progression, mitosis and chromosome segregation. This suggests that replication stress, perhaps combined with or induced by HR deficiency, could play a role in the generation of the measured DNA aberrations. Overall, our results demonstrate that the three methods measure correlated aberration patterns possibly generated through replication stress, and that they show prognostic potential in patients who receive platinum chemotherapy. In addition, we identify subsets of patients suffering from cancers not presently receiving platinum chemotherapy, who may benefit from it. 1) Birkbak NJ, et al. (2012) Cancer Discov 2: 366-375 2) Popova T, et al. (2012) Cancer Res 72: 5454-5462 3) Abkevich V, et al. (2012) Br J Cancer 107: 1776-1782 Citation Format: Andrea M. Marquard, Aron C. Eklund, Zhigang C. Wang, Andrea L. Richardson, Zoltan Szallasi, Nicolai J. Birkbak. A pan-cancer analysis of inferred homologous recombination deficiency identifies potential platinum benefit in novel subtypes. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 2822. doi:10.1158/1538-7445.AM2014-2822

198: Inflammation and nitric oxide synthase 2 in driving poor prognosis in era(-) breast cancer

Inflammation generates reactive chemical species that induce conditions of oxidative nitrosative stress as emerged as factor in poor outcome of many cancers. Our recent finding show that in the inflammatory protein inducible nitric oxide synthase (iNOS) is a strong predictor of poor outcome in ER(-) patients (Glynn et al. JCI 2010). Furthermore 46 genes, of which 23 were associated with basal like breast cancer, were elevated when iNOS high. In vitro studies using ER(-) cell lines showed that fluxes of nitric oxide (NO) delivered by NO donors surprising mimic this relationship in the patient cohort. Using this model, we show that NO through nitrosation of key thiols and non heme metals at different specific concentration stimulate pro-oncogenic mechanisms such as AKT, ERK, NFkB, AP-1, and HIF-1a that lead to increase of metastatic and cancer stem cells proteins as well as pro-angiogenic and immunosuppressive factors. In addition, we show that tumor suppressor gene BRCA1 and PP2A are inhibited by these NO levels. In the induction of NOS2 was found to dependent inflammatory mediators IFNg, IL6, PGE2, TNFa, and TLR4 agonist (Heinecke et al., PNAS 2014). Since NOS2 and NO also induce these factors, a critical feed-forward autocrine loop is formed that drives poor outcome. These finding provide a novel model that shows how NO can drive numerous inflammatory mechanism that leads to a more aggressive landscape.

Expression microarray identifies the unliganded glucocorticoid receptor as a regulator of gene expression in mammary epithelial cells.

BackgroundWhile glucocorticoids and the liganded glucocorticoid receptor (GR) have a well-established role in the maintenance of differentiation and suppression of apoptosis in breast tissue, the involvement of unliganded GR in cellular processes is less clear. Our previous studies implicated unliganded GR as a positive regulator of the BRCA1 tumour suppressor gene in the absence of glucocorticoid hormone, which suggested it could play a similar role in the regulation of other genes.MethodsAn shRNA vector directed against GR was used to create mouse mammary cell lines with depleted endogenous levels of this receptor in order to further characterize the role of GR in breast cells. An expression microarray screen for targets of unliganded GR was performed using our GR-depleted cell lines maintained in the absence of glucocorticoids. Candidate genes positively regulated by unliganded GR were identified, classified by Gene Ontology and Ingenuity Pathway Analysis, and validated using quantitative real-time reverse transcriptase PCR. Chromatin immunoprecipitation and dual luciferase expression assays were conducted to further investigate the mechanism through which unliganded GR regulates these genes.ResultsExpression microarray analysis revealed 260 targets negatively regulated and 343 targets positively regulated by unliganded GR. A number of the positively regulated targets were involved in pro-apoptotic networks, possibly opposing the activity of liganded GR targets. Validation and further analysis of five candidates from the microarray indicated that two of these, Hsd11b1 and Ch25h, were regulated by unliganded GR in a manner similar to Brca1 during glucocorticoid treatment. Furthermore, GR was shown to interact directly with and upregulate the Ch25h promoter in the absence, but not the presence, of hydrocortisone (HC), confirming our previously described model of gene regulation by unliganded GR.ConclusionThis work presents the first identification of targets of unliganded GR. We propose that the balance between targets of liganded and unliganded GR signaling is responsible for controlling differentiation and apoptosis, respectively, and suggest that gene regulation by unliganded GR may represent a mechanism for reducing the risk of breast tumourigenesis by the elimination of abnormal cells.

Role of the breast cancer suppressor BRCA1 in the maintenance of genomic integrity (97.3)

Homology‐directed repair (HDR) is a critical pathway for the repair of DNA double‐strand breaks (DSBs) in mammalian cells. Most mammalian HDR studies have focused on transformed and immortalized cell lines. We now report the generation of a DR‐GFP reporter‐based mouse model to study HDR in primary cell types from diverse lineages. Embryonic and adult fibroblasts as well as cells derived from mammary epithelium, ovary and neonatal brain were observed to undergo HDR at I‐SceI endonuclease‐induced DSBs at similar frequencies. When the DR‐GFP reporter was crossed into mice carrying a hypomorphic mutation in the BRCA1 tumor suppressor gene, a significant reduction in HDR was detected, demonstrating that BRCA1 is critical for HDR in somatic cell types, as previously reported in embryonic and tumor cell lines. These results indicate that the DR‐GFP mouse provides a powerful tool for dissecting the genetic requirements of HDR in a diverse array of somatic cell types in a normal, non‐transformed cellular milieu. Further studies are underway to examine the role of BRCA1 specifically in mammary epithelial cells.We previously showed that BRCA1 works upstream of the other major breast tumor suppressor BRCA2 in HDR. Recent work from other labs is consistent with this result, and suggests that BRCA1 functions in an early step of HDR to control DSB repair pathway choice. We discuss our recent results in this regard.

Tissue-specific tumor suppression by BRCA1

Germ-line mutations in the tumor suppressor gene BRCA1 increase the lifetime risk for breast cancer and ovarian cancer by up to ∼80% and ∼50%, respectively. Population-based studies also support a sex- and tissue-specific tumor suppressor function of BRCA1, but the mechanisms of this specificity are not fully understood. Somatic loss of the normal functioning allele in BRCA1 carriers is common in cancer development and additional somatic events, including mutations of PTEN and TP53, occur at high frequencies (detailed below). Research over the last two decades has described the role of the ubiquitously expressed BRCA1 in maintaining genomic stability through its function in DNA repair and cell cycle checkpoint control, in addition to its activity as a transcriptional regulator. In PNAS, Gorrini et al. shed light on the specificity of BRCA1’s tumor suppressor function in breast tissue. The authors identify an estrogen-induced pathway that promotes the survival of BRCA1-deficient mammary epithelial cells (MECs), as well as Brca1-deficient mammary tumor cells from oxidative stress-induced cell death (1).

Sensitive and selective DNA probe based on “turn-on” photoluminescence of C-dots@RGO

In this study, highly hydrophilic and photoluminescent sheets of reduced graphene oxide decorated with carbon dots (C-dots@RGO), methylene blue (MB), and a probe DNA have been used for the detection of DNA. The photoluminescence of C-dots@RGO is quenched by MB, which is restored in the presence of a target DNA. The combination of the C-dots@RGO, MB, and a DNA probe is selective for perfectly matched DNA over mismatched DNA, mainly because relative to single-stranded DNA, double-stranded DNA intercalates more strongly with MB, but interacts more weakly with RGO. In the presence of a target DNA, MB intercalates with the as-formed double-stranded DNA and is released from the surface of C-dots@RGO, leading to "turn-on" photoluminescence. The practicality of this assay has been validated by the determination of tumor suppressor gene BRCA1, with linearity over the concentration range from 25 to 250 nM and a limit of detection (LOD, at a signal-to-noise ratio of 3) of 14.6 nM. The C-dots@RGO probe provides higher specificity towards target DNA than towards common salts, carbohydrates, amino acids, and proteins found in real samples. Having the advantages of simplicity, cost-effectiveness, selectivity, and sensitivity, the DNA-P/C-dots@RGO-MB probe on microwells has been successfully employed for the detection of DNA, suggesting its potential for multiple analyses of DNA targets when various DNA probes are employed.

Brca2 and tp53 Collaborate in Tumorigenesis in Zebrafish

Germline mutations in the tumor suppressor genes BRCA2 and TP53 significantly influence human cancer risk, and cancers from humans who inherit one mutant allele for BRCA2 or TP53 often display loss of the wildtype allele. In addition, BRCA2-associated cancers often exhibit mutations in TP53. To determine the relationship between germline heterozygous mutation (haploinsufficiency) and somatic loss of heterozygosity (LOH) for BRCA2 and TP53 in carcinogenesis, we analyzed zebrafish with heritable mutations in these two genes. Tumor-bearing zebrafish were examined by histology, and normal and neoplastic tissues were collected by laser-capture microdissection for LOH analyses. Zebrafish on a heterozygous tp53M214K background had a high incidence of malignant tumors. The brca2Q658X mutation status determined both the incidence of LOH and the malignant tumor phenotype. LOH for tp53 occurred in the majority of malignant tumors from brca2 wildtype and heterozygous mutant zebrafish, and most of these were malignant peripheral nerve sheath tumors. Malignant tumors in zebrafish with heterozygous mutations in both brca2 and tp53 frequently displayed LOH for both genes. In contrast, LOH for tp53 was uncommon in malignant tumors from brca2 homozygotes, and these tumors were primarily undifferentiated sarcomas. Thus, carcinogenesis in zebrafish with combined mutations in tp53 and brca2 typically requires biallelic mutation or loss of at least one of these genes, and the specific combination of inherited mutations influences the development of LOH and the tumor phenotype. These results provide insight into cancer development associated with heritable BRCA2 and TP53 mutations.

Screening for mutations in BRCA1 and BRCA2 genes by measuring the acoustic ratio with QCM

Screening for mutations in the tumor-suppressor genes BRCA1 and BRCA2 is of great importance for breast and ovarian cancer prevention. We describe a methodology for mutation screening and detection based on acoustic wave devices. In particular, we detect four mutations located in BRCA1 and BRCA2 genes using the quartz crystal microbalance technique. The detection is based on measurements of the acoustic ratio of dissipation versus frequency change (ΔD/ΔF) of double-stranded DNA molecules bound to the device surface that are produced after PCR amplification and restriction digestion; the acoustic ratio has been shown to be a measure of the intrinsic viscosity of the attached molecules, which, in turn, depends on the size of the dsDNAs. Novel features of this approach are the lack of a hybridization step, the label free sensing of the length, rather than mass, of the DNA molecules and the direct detection of the digested DNA products without prior purification. The method is generic, simple and capable of detecting single base mutations to long genomic rearrangements; it is also suitable and applicable to a Lab-on-a-chip concept.