Direct regulation of microRNA biogenesis and expression by estrogen receptor beta in hormone-responsive breast cancer.

Estrogen effects on mammary epithelial and breast cancer (BC) cells are mediated by the nuclear receptors ERα and ERß, transcription factors that display functional antagonism with each other, with ERß acting as oncosuppressor and interfering with the effects of ERα on cell proliferation, tumor promotion and progression. Indeed, hormone-responsive, ERα+ BC cells often lack ERß, which when present associates with a less aggressive clinical phenotype of the disease. Recent evidences point to a significant role of microRNAs (miRNAs) in BC, where specific miRNA expression profiles associate with distinct clinical and biological phenotypes of the lesion. Considering the possibility that ERß might influence BC cell behavior via miRNAs, we compared miRNome expression in ERß+ vs ERß- hormone-responsive BC cells and found a widespread effect of this ER subtype on the expression pattern of these non-coding RNAs. More importantly, the expression pattern of 67 miRNAs, including 10 regulated by ERß in BC cells, clearly distinguishes ERß+, node-negative, from ERß-, metastatic, mammary tumors. Molecular dissection of miRNA biogenesis revealed multiple mechanisms for direct regulation of this process by ERß+ in BC cell nuclei. In particular, ERß downregulates miR-30a by binding to two specific sites proximal to the gene and thereby inhibiting pri-miR synthesis. On the other hand, the receptor promotes miR-23b, -27b and 24-1 accumulation in the cell by binding in close proximity of the corresponding gene cluster and preventing in situ the inhibitory effects of ERα on pri-miR maturation by the p68/DDX5-Drosha microprocessor complex. These results indicate that cell autonomous regulation of miRNA expression is part of the mechanism of action of ERß in BC cells and could contribute to establishment or maintenance of a less aggressive tumor phenotype mediated by this nuclear receptor.

Expression of epitopes of the tumour-associated glycoprotein 72 and clinicopathological correlations in mammary carcinomas.

We analysed the immunohistochemical expression pattern of the distinct carbohydrate epitopes of the TAG-72 molecule, defined by the monoclonal antibodies (MAbs) B72.3, CC-49 and CC-83, in 92 breast carcinomas of different histological type, and in other histological components identified in the mammary tissue samples studied. The results were correlated with the clinico-pathological characteristics of the tumours, and with their proliferative activity, assessed by thymidine labelling index (TLI). Expression of the TAG-72 epitopes was detected in all the tumour histotypes analysed, but patterns of immunoreactivity tended to vary in relation to type and level of differentiation. The comparative analysis of the reactivities of the three anti-TAG-72 MAbs revealed differences in their ability to recognise neoplastic lesions. MAb CC-49 reacted with the highest percentage of tumours (82%), and also tended to yield the highest percentages of immunoreactive cancer cells, while B72.3 and CC-83 reacted with lower percentages of tumours (respectively, 55 and 51%), and identified lower percentages of immunoreactive cells. High levels of expression of the three TAG-72 epitopes were detected in areas of in situ ductal carcinoma. Comparatively lower levels of immunohistochemical positivity were found in atypical epithelial hyperplasia, normal mammary epithelium and epithelium with cystic disease. TAG-72 epitope expression was correlated with prognostic parameters. The synchronous expression of the three epitopes significantly correlated with large tumour size (> 2 cm), and with high histological grade. No correlations could be demonstrated between TAG-72 phenotypes and nuclear grade, lymph node status and proliferative activity (high versus low).