Regulation Of BRCA1 Expression Research Articles

BRCA1: An Endocrine and Metabolic Regulator.

The breast and ovarian cancer susceptibility gene (BRCA1) is a tumor suppressor whose mutation has been associated with the development of breast, ovarian and, probably, other malignancies at young ages. The BRCA1 gene product participates in multiple biological pathways including the DNA damage response, transcriptional control, cell growth and apoptosis. Inactivating germline mutations of the BRCA1 gene can be detected in a substantial portion of families with inherited breast and/or ovarian cancer. While the genomic and cancer-related actions of BRCA1 have been extensively investigated, not much information exists regarding the cellular and circulating factors involved in regulation of BRCA1 expression and action. The present review article dissects the emerging role of BRCA1 as an important regulator of various endocrine and metabolic axes. Experimental and clinical evidence links BRCA1 with a number of peptide and steroid hormones. Furthermore, comprehensive analyses identified complex interactions between the insulin/insulin-like growth factor-1 (IGF1) signaling axis and BRCA1. The correlation between metabolic disorders, including diabetes and the metabolic syndrome, and BRCA1 mutations, are discussed in this article.

BRCA1 Gene Expression is Down Regulated in Both Familial and Sporadic Breast Cancer Cases in Baghdad- Iraq

Breast cancer is the commonest cancer and the leading cause of malignancies-related mortality in women worldwide. Understanding the underlying biology of the disease could improve patients’ stratification and may offer novel therapeutic targets and strategies. This study was set to investigate the association between BRCA1 gene expression and some of the clinical features of breast cancer patients in Baghdad-Iraq. Eighty peripheral blood samples were collected from sixty patients diagnosed with breast cancer and twenty healthy age-matched controls for BRCA1 qPCR gene expression analysis.
 The results showed a significant reduction in BRCA1 gene expression in all of the breast cancer patients with the vast majority of them (75%) having BRCA1expression below 25%. The down regulation of BRCA1 expression also showed consistency in breast cancer patients of both sporadic (n=45) and family history (n=15) cases,with expression averages of 18% and 20.19%, respectively. Moreover, the redcuation in BRCA1 expression was negatively associated with the disease’s grades,asbreast cancer patients with the advanced stage III (n=19) showed the lowest expression average of BRCA1 (13.8%) as compared to those in stages II (n=29) and I (n=12) of the disease (17.7% and 19.8%, respectively). 
 Overall, the study highlights the key role of BRCA1gene expression in the development of breast cancer and suggests its potential utility in the diagnosis strategies and preventing the progression of the disease, especially the sporadic type.

BRCA1 as target for breast cancer prevention and therapy.

The Breast Cancer 1 protein (BRCA1) is a tumor suppressor involved in basic cellular functions necessary for cell replication and DNA synthesis, but reduced expression of BRCA1, due to mutations or epigenetic inactivation, leads to impaired mammary gland differentiation and increased risk of breast cancer development. Although BRCA1 acts as a tumor suppressor and is present in all cells, where it is essential for the maintenance of the genome integrity, it is still not clear why mutations in the BRCA1 gene predispose to breast and ovarian, but not to other types of cancer. In the first part of this review, we briefly discuss the function and regulation of the BRCA1 protein, including its role associated with familial and sporadic breast cancer. The second part is an overview of the therapeutic compounds used for breast cancer treatment targeting BRCA1, and the natural food components that hold potential preventive effect against those types of breast cancer in which BRCA1 expression is either reduced or lacking. Further studies elucidating the interactions between dietary compounds and cellular pathways, involved in regulation of BRCA1expression, are necessary for the development of strategies that may successfully prevent or treat breast cancer.

Abstract 3926: Chronic inflammatory levels of nitric oxide/reactive nitrogen species downregulate BRCA1 protein expression

Abstract The link between inflammation and cancer was proposed more than 150 years ago when Virchow suggested that malignancies tend to arise at sites of chronic inflammation. Recent studies have established that elevated levels of nitric oxide/reactive nitrogen species (NO/RNS) generated in the inflammatory microenvironment are associated with several conditions critical for initiation and promotion of cancer. The BRCA1 protein contributes to cell viability in multiple ways, including DNA repair, cell cycle checkpoint control, transcription, and regulation of chromosome segregation. Hundreds of mutations in the BRCA1 gene have been identified and associated with an increased risk of cancer. Sporadic breast carcinomas, on the other hand, rarely show mutations of this gene. Instead, BRCA1 protein expression is frequently reduced in sporadic cases. As sporadic tumors account for >90% of the breast cancer, considerable research is directed towards the identification of mechanisms that down-regulate the function of the wild type BRCA1 and lead to genetic instability. BRCA1 expression is negatively regulated at the transcriptional level by the repressive complex of retinoblastoma-like protein 2 (RBL2) and E2F4. Formation of the repression RBL2/E2F4 complex can be accelerated by, for example, RBL2 dephosphorylation. Recently, protein phosphatase 2A (PP2A), an enzyme responsible for RBL2 dephosphorylation, was shown to be nitrated and activated by NO/RNS (Ohama T., et al., JBC 285, 8711-18, 2010). In the present investigation I demonstrate that inflammatory levels of NO/RNS induce substantial dephosphorylation of RBL2. Normal human mammary epithelial cells (MCF-10A) were incubated with 0.1 mM of the NO-donor SNAP for 6 h. This concentration of NO-donor mimics the intracellular level of NO/RNS during chronic inflammation, hypoxia, and does not induce significant DNA damage and maintains the ATM/ATR-dependent pathways intact. After 6 h incubation with SNAP, significant decrease in total amount of BRCA1 protein was observed with no apparent changes in the levels of E2F1, E2F4, and the catalytic subunit of PP2A, all involved in the regulation of BRCA1. RBL2 dephosphorylation promotes a repressive RBL2/E2F4 complex formation, which inhibits expression of BRCA1. I hypothesize that NO/RNS generated by chronic inflammatory conditions posttranslationally modify proteins involved in the regulation of BRCA1 expression and downregulate BRCA1 expression, thereby constituting a critical role in genetic instability and ultimately carcinogenesis. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 3926. doi:10.1158/1538-7445.AM2011-3926

Involvement of MyoD and c-myb in regulation of basal and estrogen-induced transcription activity of the BRCA1 gene

BRCA1 is closely related to the pathogenesis of breast cancer, BRCA1 mRNA is reduced in sporadic breast cancer cells despite the lack of mutations. In the present report, we find that MyoD expression and BRCA1 expression is correlated in sporadic breast tumors, overexpression of MyoD and c-myb stimulates BRCA1 expression, knockdown of MyoD and c-myb attenuates BRCA1 expression and attenuates the ability of BRCA1 to protect cells against hydrogen peroxide. MyoD and c-myb interact with p300 and PCAF, forming activating transcriptional complexes which bind to E-box and c-myb sites on the BRCA1 promoter and activate its transcription by inducing histone acetylation. Regulation of BRCA1 expression by MyoD and c-myb complexes may be part of an integral signaling pathway that determines and explains breast cancer susceptibility. Detection expression status of the various proteins in these complexes may predispose to the onset of sporadic breast cancer.

Reduced BRCA1 expression due to promoter hypermethylation in therapy-related acute myeloid leukaemia

BRCA1 plays a pivotal role in the repair of DNA damage, especially following chemotherapy and ionising radiation. We were interested in the regulation of BRCA1 expression in acute myeloid leukaemia (AML), in particular in therapy-related forms (t-AML). Using real-time PCR and Western blot, we found that BRCA1 mRNA was expressed at barely detectable levels by normal peripheral blood granulocytes, monocytes and lymphocytes, whereas control BM-mononuclear cells and selected CD34+ progenitor cells displayed significantly higher BRCA1 expression (P=0.0003). Acute myeloid leukaemia samples showed heterogeneous BRCA1 mRNA levels, which were lower than those of normal bone marrows (P=0.0001). We found a high frequency of hypermethylation of the BRCA1 promoter region in AML (51/133 samples, 38%), in particular in patients with karyotypic aberrations (P=0.026), and in t-AML, as compared to de novo AML (76 vs 31%, P=0.0002). Examining eight primary tumour samples from hypermethylated t-AML patients, BRCA1 was hypermethylated in three of four breast cancer samples, whereas it was unmethylated in the other four tumours. BRCA1 hypermethylation correlated to reduced BRCA1 mRNA (P=0.0004), and to increased DNA methyltransferase DNMT3A (P=0.003) expression. Our data show that reduced BRCA1 expression owing to promoter hypermethylation is frequent in t-AML and that this could contribute to secondary leukaemogenesis.

Regulation of BRCA1 Expression by the Rb-E2F Pathway

Inheritance of a mutant allele of the breast cancer susceptibility gene BRCA1 confers increased risk of developing breast and ovarian cancers. Likewise, inheritance of a mutant allele of the retinoblastoma susceptibility gene (RB1) results in the development of retinoblastoma and/or osteosarcoma, and both alleles are often mutated or inactivated in sporadic forms of these and other cancers. We now demonstrate that the product of the RB1 gene, Rb, regulates the expression of the murine Brca1 and human BRCA1 genes through its ability to modulate E2F transcriptional activity. The Brca1 gene is identified as an in vivo target of E2F1 in a transgenic mouse model. The Brca1 promoter contains E2F DNA-binding sites that mediate transcriptional activation by E2F1 and repression by Rb. Moreover, ectopic expression of cyclin D1 and Cdk4 can stimulate the Brca1 promoter in an E2F-dependent manner, and this is inhibited by coexpression of the p16(INK4a) cyclin-dependent kinase inhibitor. The human BRCA1 promoter also contains a conserved E2F site and is similarly regulated by E2F1 and Rb. This functional link between the BRCA1 and Rb tumor suppressors may provide insight into the mechanism by which BRCA1 inactivation contributes to cancer development.