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      Differential regulation of miR-21 and miR-146a by Epstein–Barr virus-encoded EBNA2

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          Abstract

          The discovery of microRNA (miR) represents a novel paradigm in RNA-based regulation of gene expression and their dysregulation has become a hallmark of many a tumor. In virally associated cancers, the host–pathogen interaction could involve alteration in miR expression. Epstein–Barr virus (EBV)-encoded EBNA2 is indispensable for the capacity of the virus to transform B cells in vitro. Here, we studied how it affects cellular miRs. Extensive miR profiling of the virus-infected and EBNA2-transfected B lymphoma cells revealed that oncomiR miR-21 is positively regulated by this viral protein. Conversely, Burkitt's lymphoma (BL) cell lines infected with EBNA2 lacking P3HR1 strain did not show any increase in miR-21. EBNA2 increased phosphorylation of AKT and this was directly correlated with increased miR-21. In contrast, miR-146a was downregulated by EBNA2 in B lymphoma cells. Low miR-146a expression correlates with an elevated level of IRAK1 and type I interferon in EBNA2 transfectants. Taken together, the present data suggest that EBNA2 might contribute to EBV-induced B-cell transformation by altering miR expression and in particular by increasing oncomiR-like miR-21 and by affecting the antiviral responses of the innate immune system through downregulation of its key regulator miR-146a.

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          Most cited references38

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          MicroRNA-21 is an antiapoptotic factor in human glioblastoma cells.

          MicroRNAs (miRNAs) are small noncoding RNA molecules that regulate protein expression by targeting the mRNA of protein-coding genes for either cleavage or repression of translation. The roles of miRNAs in lineage determination and proliferation as well as the location of several miRNA genes at sites of translocation breakpoints or deletions has led to the speculation that miRNAs could be important factors in the development or maintenance of the neoplastic state. Here we show that the highly malignant human brain tumor, glioblastoma, strongly over-expresses a specific miRNA, miR-21. Our studies show markedly elevated miR-21 levels in human glioblastoma tumor tissues, early-passage glioblastoma cultures, and in six established glioblastoma cell lines (A172, U87, U373, LN229, LN428, and LN308) compared with nonneoplastic fetal and adult brain tissues and compared with cultured nonneoplastic glial cells. Knockdown of miR-21 in cultured glioblastoma cells triggers activation of caspases and leads to increased apoptotic cell death. Our data suggest that aberrantly expressed miR-21 may contribute to the malignant phenotype by blocking expression of critical apoptosis-related genes.
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            miR-21-mediated tumor growth.

            MicroRNAs (miRNAs) are approximately 22 nucleotide non-coding RNA molecules that regulate gene expression post-transcriptionally. Although aberrant expression of miRNAs in various human cancers suggests a role for miRNAs in tumorigenesis, it remains largely unclear as to whether knockdown of a specific miRNA affects tumor growth. In this study, we profiled miRNA expression in matched normal breast tissue and breast tumor tissues by TaqMan real-time polymerase chain reaction miRNA array methods. Consistent with previous findings, we found that miR-21 was highly overexpressed in breast tumors compared to the matched normal breast tissues among 157 human miRNAs analysed. To better evaluate the role of miR-21 in tumorigenesis, we transfected breast cancer MCF-7 cells with anti-miR-21 oligonucleotides and found that anti-miR-21 suppressed both cell growth in vitro and tumor growth in the xenograft mouse model. Furthermore, this anti-miR-21-mediated cell growth inhibition was associated with increased apoptosis and decreased cell proliferation, which could be in part owing to downregulation of the antiapoptotic Bcl-2 in anti-miR-21-treated tumor cells. Together, these results suggest that miR-21 functions as an oncogene and modulates tumorigenesis through regulation of genes such as bcl-2 and thus, it may serve as a novel therapeutic target.
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              MicroRNA-21 targets tumor suppressor genes in invasion and metastasis.

              MicroRNAs (miRNAs) are a class of naturally occurring small non-coding RNAs that target protein-coding mRNAs at the post-transcriptional level. Our previous studies suggest that mir-21 functions as an oncogene and has a role in tumorigenesis, in part through regulation of the tumor suppressor gene tropomyosin 1 (TPM1). Given that TPM1 has been implicated in cell migration, in this study we further investigated the role of mir-21 in cell invasion and tumor metastasis. We found that suppression of mir-21 in metastatic breast cancer MDA-MB-231 cells significantly reduced invasion and lung metastasis. Consistent with this, ectopic expression of TPM1 remarkably reduced cell invasion. Furthermore, we identified two additional direct mir-21 targets, programmed cell death 4 (PDCD4) and maspin, both of which have been implicated in invasion and metastasis. Like TPM1, PDCD4 and maspin also reduced invasiveness of MDA-MB-231 cells. Finally, the expression of PDCD4 and maspin inversely correlated with mir-21 expression in human breast tumor specimens, indicating the potential regulation of PDCD4 and maspin by mir-21 in these tumors. Taken together, the results suggest that, as an oncogenic miRNA, mir-21 has a role not only in tumor growth but also in invasion and tumor metastasis by targeting multiple tumor/metastasis suppressor genes. Therefore, suppression of mir-21 may provide a novel approach for the treatment of advanced cancers.
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                Author and article information

                Journal
                Leukemia
                Leukemia
                Leukemia
                Nature Publishing Group
                0887-6924
                1476-5551
                November 2012
                19 April 2012
                22 May 2012
                : 26
                : 11
                : 2343-2352
                Affiliations
                [1 ]Department of Experimental Medicine, Istituto Pasteur-Fondazione Cenci-Bolognetti, La Sapienza University , Rome, Italy
                [2 ]Department of Molecular Medicine, Viale Regina Elena 324, La Sapienza University , Rome, Italy
                [3 ]Institute of Pathology Charité-Universitätsmedizin Berlin, Campus Benjamin Franklin , Berlin, Germany
                [4 ]Department of Genetics and Molecular Biology, La Sapienza University , Rome, Italy
                [5 ]Department of Infectious, parasitic and immunomediated diseases , Viale Regina Elena 299, Istituto Superiore di Sanità, Rome, Italy
                Author notes
                [* ]Department of Experimental Medicine, Istituto Pasteur-Fondazione Cenci-Bolognetti, La Sapienza University , Viale Regina Elena 324, Rome 00161, Italy. E-mail: alberto.faggioni@ 123456uniroma1.it (AF) or pankaj.trivedi@ 123456uniroma1.it (PT)
                [6]

                These authors contributed equally to this work.

                Article
                leu2012108
                10.1038/leu.2012.108
                3496086
                22614176
                7cbc3560-65b1-485d-a866-5dd3d8057c1a
                Copyright © 2012 Macmillan Publishers Limited

                This work is licensed under the Creative Commons Attribution-NonCommercial-No Derivative Works 3.0 Unported License. To view a copy of this license, visit http://creativecommons.org/licenses/by-nc-nd/3.0/

                History
                : 12 September 2011
                : 21 March 2012
                : 05 April 2012
                Categories
                Original Article

                Oncology & Radiotherapy
                dlbcl,ebna2,mir-146a,ebv,microrna,mir-21
                Oncology & Radiotherapy
                dlbcl, ebna2, mir-146a, ebv, microrna, mir-21

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