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      Down-regulation of BRCA1 expression by miR-146a and miR-146b-5p in triple negative sporadic breast cancers

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          Abstract

          Germ-line mutations in the BRCA1 gene strongly predispose women to breast cancer (lifetime risk up to 80%). Furthermore, the BRCA1 protein is absent or present at very low levels in about one third of sporadic breast cancers. However, the mechanisms underlying BRCA1 somatic inactivation appear multiple and are still not fully understood. We report here the involvement of miR-146a and miR-146b-5p that bind to the same site in the 3′UTR of BRCA1 and down-regulate its expression as demonstrated using reporter assays. This was further confirmed with the endogenous BRCA1 gene by transfecting microRNA (miRNA) precursors or inhibitors in mammary cell lines. This down-regulation was accompanied by an increased proliferation and a reduced homologous recombination rate, two processes controlled by BRCA1. Furthermore, we showed that the highest levels of miR-146a and/or miR-146b-5p are found in basal-like mammary tumour epithelial cell lines and in triple negative breast tumours, which are the closest to tumours arising in carriers of BRCA1 mutations. This work provides further evidence for the involvement of miRNAs in sporadic breast cancer through down-regulation of BRCA1.

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          Most cited references 33

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          XRCC3 promotes homology-directed repair of DNA damage in mammalian cells.

          Homology-directed repair of DNA damage has recently emerged as a major mechanism for the maintenance of genomic integrity in mammalian cells. The highly conserved strand transferase, Rad51, is expected to be critical for this process. XRCC3 possesses a limited sequence similarity to Rad51 and interacts with it. Using a novel fluorescence-based assay, we demonstrate here that error-free homology-directed repair of DNA double-strand breaks is decreased 25-fold in an XRCC3-deficient hamster cell line and can be restored to wild-type levels through XRCC3 expression. These results establish that XRCC3-mediated homologous recombination can reverse DNA damage that would otherwise be mutagenic or lethal.
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            The role of microRNA genes in papillary thyroid carcinoma.

            Apart from alterations in the RET/PTC-RAS-BRAF pathway, comparatively little is known about the genetics of papillary thyroid carcinoma (PTC). We show that numerous microRNAs (miRNAs) are transcriptionally up-regulated in PTC tumors compared with unaffected thyroid tissue. A set of five miRNAs, including the three most up-regulated ones (miR-221, -222, and -146), distinguished unequivocally between PTC and normal thyroid. Additionally, miR-221 was up-regulated in unaffected thyroid tissue in several PTC patients, presumably an early event in carcinogenesis. Tumors in which the up-regulation (11- to 19-fold) of miR-221, -222, and -146 was strongest showed dramatic loss of KIT transcript and Kit protein. In 5 of 10 such cases, this down expression was associated with germline single-nucleotide changes in the two recognition sequences in KIT for these miRNAs. We conclude that up-regulation of several miRs and regulation of KIT are involved in PTC pathogenesis, and that sequence changes in genes targeted by miRNAs can contribute to their regulation.
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              Aberrant Expression of Oncogenic and Tumor-Suppressive MicroRNAs in Cervical Cancer Is Required for Cancer Cell Growth

              MicroRNAs (miRNAs) play important roles in cancer development. By cloning and sequencing of a HPV16+ CaSki cell small RNA library, we isolated 174 miRNAs (including the novel miR-193c) which could be grouped into 46 different miRNA species, with miR-21, miR-24, miR-27a, and miR-205 being most abundant. We chose for further study 10 miRNAs according to their cloning frequency and associated their levels in 10 cervical cancer- or cervical intraepithelial neoplasia-derived cell lines. No correlation was observed between their expression with the presence or absence of an integrated or episomal HPV genome. All cell lines examined contained no detectable miR-143 and miR-145. HPV-infected cell lines expressed a different set of miRNAs when grown in organotypic raft cultured as compared to monolayer cell culture, including expression of miR-143 and miR-145. This suggests a correlation between miRNA expression and tissue differentiation. Using miRNA array analyses for age-matched normal cervix and cervical cancer tissues, in combination with northern blot verification, we identified significantly deregulated miRNAs in cervical cancer tissues, with miR-126, miR-143, and miR-145 downregulation and miR-15b, miR-16, miR-146a, and miR-155 upregulation. Functional studies showed that both miR-143 and miR-145 are suppressive to cell growth. When introduced into cell lines, miR-146a was found to promote cell proliferation. Collectively, our data indicate that downregulation of miR-143 and miR-145 and upregulation of miR-146a play a role in cervical carcinogenesis.
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                Author and article information

                Journal
                EMBO Mol Med
                EMBO Mol Med
                emmm
                EMBO Molecular Medicine
                WILEY-VCH Verlag (Weinheim )
                1757-4676
                1757-4684
                May 2011
                : 3
                : 5
                : 279-290
                Affiliations
                [1 ]CNRS UMR5286 Inserm U1052, “Equipe Labellisée LIGUE 2008”, University Lyon 1, Cancer Research Center of Lyon, Centre Léon Bérard Lyon, France
                [2 ]CNRS-CEA UMR 217, “Equipe Labellisée LIGUE 2008”, Institut de Radiobiologie Cellulaire et Moléculaire Fontenay-aux-Roses, France
                [3 ]CNRS UMR5286 Inserm U1052, University Lyon 1, Cancer Research Center of Lyon, Centre Léon Bérard Lyon, France
                [4 ]Laboratoire d'Oncogénétique, Inserm U735, Institut Curie, Hôpital René Huguenin Saint-Cloud, France
                Author notes
                * Corresponding author: Tel: +33 469 16 66 79; Fax: +33 469 16 66 60; E-mail: mazoyer@ 123456lyon.fnclcc.fr
                Article
                10.1002/emmm.201100136
                3377076
                21472990
                Copyright © 2011 EMBO Molecular Medicine
                Categories
                Research Articles

                Molecular medicine

                brca1, microrna, post-transcriptional regulation, breast cancer

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