Analysis of Loss of heterozygosity and immunohistochemistry in BRCA1 gene in sporadic breast cancers

BRCA1 Promoter Methylation and Expression - Associations with ER+, PR+ and HER2+ Subtypes of Breast Carcinoma

Introduction: Considering the increasing trend in incidence rates, morbidity and mortality of breast cancer, there is an urgent need to identify and validate new biomarkers for early detection and better management. The purpose of the study was to investigate BRCA1 protein expression and promoter methylation of the BRCA1 gene and their association with molecular subtypes based on estrogen receptor (ER), progesterone receptor (PR) and human epidermal growth factor receptor 2 (HER2) positivity. Materials and Methods: A total of 114 breast cancer tissue biopsies were collected for methylation specific PCR (MSP) and immunohistochemical (IHC) analysis. Results: Seven tissue microarrays were constructed. BRCA1 protein expression was reduced in 55/114 (48.2%) and in the majority of ER-negative tumors (73.3%) (p<0.001). Similarly BRCA1 expression was reduced in the majority of PR-negative tumors (69.2%) but without statistical significance (p value=0.083). BRCA1 methylation was positive in 59.6% cases. A subset regarding ER+, PR+ and HER2+ was identified which consisted of 31.6% in which an inverse relationship between BRCA1 methylation and protein expression was noted. Conclusion: Reduced expression was associated with ER and PR negative status which is linked with a poor prognosis. BRCA1 protein expression might thus be used as a prognostic indicator to predict treatment response to hormone therapy.

Targeting the Akt/mTOR pathway in Brca1-deficient cancers

The breast cancer susceptibility gene 1 (Brca1) has a key role in both hereditary and sporadic mammary tumorigenesis. However, the reasons why Brca1-deficiency leads to the development of cancer are not clearly understood. Activation of Akt kinase is one of the most common molecular alterations associated with human malignancy. Increased Akt kinase activity has been reported in most breast cancers. We previously found that downregulation of Brca1 expression or mutations of the Brca1 gene activate the Akt oncogenic pathway. To further investigate the role of Brca1/Akt in tumorigenesis, we analyzed Brca1/Akt expression in human breast cancer samples and found that reduced expression of Brca1 was highly correlated with increased phosphorylation of Akt. Consistent with the clinical data, knockdown of Akt1 by short-hairpin RNA inhibited cellular proliferation of Brca1 mutant cells. Importantly, depletion of Akt1 significantly reduced tumor formation induced by Brca1-deficiency in mice. The third generation inhibitor of mammalian target of rapamycin (mTOR), Palomid 529, significantly suppressed Brca1-deficient tumor growth in mice through inhibition of both Akt and mTOR signaling. Our results indicate that activation of Akt is involved in Brca1-deficiency mediated tumorigenesis and that the mTOR pathway can be used as a novel target for treatment of Brca1-deficient cancers.

Epigenetic inactivation of BRCA1 is associated with aberrant expression of CTCF and DNA methyltransferase (DNMT3B) in some sporadic breast tumours

We assessed expression of the BRCA1, CTCF and DNMT3b methyltransferase genes along with BRCA1 promoter methylation to better define the epigenetic events involved in BRCA1 inactivation in sporadic breast cancer. These gene expression patterns were determined in 54 sporadic breast tumours by immunohistochemistry and the methylation status of the BRCA1 promoter was evaluated using methylation-specific PCR. We observed significant DNMT3b expression in 80% of the tumours and that 43% of tumours exhibited novel cytoplasmic CTCF expression. Pairwise analyses of gene expression patterns showed that 28/32 tumours lacked BRCA1 expression and also exhibited cytoplasmic CTCF staining, while 24/32 of these tumours also overexpressed DNMT3b. Furthermore, 86% of the BRCA1 low-expressing tumours were methylated at the BRCA1 promoter and a subset of these tumours displayed both cytoplasmic CTCF and increased DNMT3b expression. Thus, tumour subsets exist that display concurrent decreased BRCA1 expression, BRCA1 promoter methylation, cytoplasmic CTCF expression and with DNMT3b over-expression. We suggest that these altered CTCF and DNMT3b expression patterns represent (a) critical events responsible for the epigenetic inactivation of BRCA1 and (b) a diagnostic signature for epigenetic inactivation of other tumour suppressor genes in sporadic breast tumours.