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      Role of MicroRNA in Response to Ionizing Radiations: Evidences and Potential Impact on Clinical Practice for Radiotherapy

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          Abstract

          MicroRNAs (miRNA) are small, non-coding, RNAs with gene expression regulator roles. As an important class of regulators of many cellular pathways, miRNAs are involved in many signaling pathways and DNA damage repair processes, affecting cellular radiosensitivity. Their role has led to interest in oncological implications to improve treatment results. MiRNAs represent a great opportunity to enhance the efficacy of radiotherapy treatments—they can be used to profile the radioresistance of tumors before radiotherapy, monitor their response throughout the treatment, thus helping to select intensification strategies, and also to define the final response to therapy along with risks of recurrence or metastatization. Even though many interesting studies support such potential, nowadays most studies on patient data are limited to experiments profiling tumor aggressiveness and response to radiotherapy. Moreover many studies report different although not conflicting results on the miRNAs evaluated for each tumor type. Without doubt, the clinical potential of such molecules for radiotherapy is striking and of high interest.

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          Most cited references80

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          A novel response of cancer cells to radiation involves autophagy and formation of acidic vesicles.

          The mechanisms underlying neoplastic epithelial cell killing by ionizing radiation are largely unknown. We discovered a novel response to radiation manifested by autophagy and the development of acidic vesicular organelles (AVO). Acidification of AVO was mediated by the vacuolar H+-ATPase. Staining with the lysosomotropic agent acridine orange enabled us to quantify AVO accumulation and to demonstrate their time- and dose-dependent appearance. The appearance of AVO occurred in the presence of the pan-caspase inhibitor z-Val-Ala-Asp(Ome)-fluoromethyl ketone, but was inhibited by 3-methyladenine, an inhibitor of autophagy. The accretion of AVO in surviving progenies of irradiated cells, and the increased incidence of clonogenic death after inhibition of vacuolar H+-ATPase suggest that formation of acidic organelles represents a novel defense mechanism against radiation damage.
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            MicroRNA-125b is a novel negative regulator of p53.

            The p53 transcription factor is a key tumor suppressor and a central regulator of the stress response. To ensure a robust and precise response to cellular signals, p53 gene expression must be tightly regulated from the transcriptional to the post-translational levels. Computational predictions suggest that several microRNAs are involved in the post-transcriptional regulation of p53. Here we demonstrate that miR-125b, a brain-enriched microRNA, is a bona fide negative regulator of p53 in both zebrafish and humans. miR-125b-mediated down-regulation of p53 is strictly dependent on the binding of miR-125b to a microRNA response element in the 3' untranslated region of p53 mRNA. Overexpression of miR-125b represses the endogenous level of p53 protein and suppresses apoptosis in human neuroblastoma cells and human lung fibroblast cells. In contrast, knockdown of miR-125b elevates the level of p53 protein and induces apoptosis in human lung fibroblasts and in the zebrafish brain. This phenotype can be rescued significantly by either an ablation of endogenous p53 function or ectopic expression of miR-125b in zebrafish. Interestingly, miR-125b is down-regulated when zebrafish embryos are treated with gamma-irradiation or camptothecin, corresponding to the rapid increase in p53 protein in response to DNA damage. Ectopic expression of miR-125b suppresses the increase of p53 and stress-induced apoptosis. Together, our study demonstrates that miR-125b is an important negative regulator of p53 and p53-induced apoptosis during development and during the stress response.
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              MicroRNA miR-34 Inhibits Human Pancreatic Cancer Tumor-Initiating Cells

              Background MicroRNAs (miRNAs) have been implicated in cancer initiation and progression via their ability to affect expression of genes and proteins that regulate cell proliferation and/or cell death. Transcription of the three miRNA miR-34 family members was recently found to be directly regulated by p53. Among the target proteins regulated by miR-34 are Notch pathway proteins and Bcl-2, suggesting the possibility of a role for miR-34 in the maintenance and survival of cancer stem cells. Methodology/Principal Findings We examined the roles of miR-34 in p53-mutant human pancreatic cancer cell lines MiaPaCa2 and BxPC3, and the potential link to pancreatic cancer stem cells. Restoration of miR-34 expression in the pancreatic cancer cells by either transfection of miR-34 mimics or infection with lentiviral miR-34-MIF downregulated Bcl-2 and Notch1/2. miR-34 restoration significantly inhibited clonogenic cell growth and invasion, induced apoptosis and G1 and G2/M arrest in cell cycle, and sensitized the cells to chemotherapy and radiation. We identified that CD44+/CD133+ MiaPaCa2 cells are enriched with tumorsphere-forming and tumor-initiating cells or cancer stem/progenitor cells with high levels of Notch/Bcl-2 and loss of miR-34. More significantly, miR-34 restoration led to an 87% reduction of the tumor-initiating cell population, accompanied by significant inhibition of tumorsphere growth in vitro and tumor formation in vivo. Conclusions/Significance Our results demonstrate that miR-34 may restore, at least in part, the tumor suppressing function of the p53 in p53-deficient human pancreatic cancer cells. Our data support the view that miR-34 may be involved in pancreatic cancer stem cell self-renewal, potentially via the direct modulation of downstream targets Bcl-2 and Notch, implying that miR-34 may play an important role in pancreatic cancer stem cell self-renewal and/or cell fate determination. Restoration of miR-34 may hold significant promise as a novel molecular therapy for human pancreatic cancer with loss of p53–miR34, potentially via inhibiting pancreatic cancer stem cells.
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                Author and article information

                Journal
                Molecules
                Molecules
                molecules
                Molecules
                MDPI
                1420-3049
                24 April 2014
                April 2014
                : 19
                : 4
                : 5379-5401
                Affiliations
                [1 ]Radiation Oncology Department, Policlinico Universitario Campus Bio-Medico; Via Álvaro del Portillo 200, 00144 Rome, Italy
                [2 ]Radiotherapy Department, Università Cattolica del Sacro Cuore; Fondazione di Ricerca e Cura “Giovanni Paolo II”, Largo Agostino Gemelli 1, 86100 Campobasso, Italy; E-Mail: amorganti@ 123456rm.unicatt.it
                [3 ]Radiation Oncology Department, Università Cattolica del Sacro Cuore; L.go Francesco Vito 1, 00168 Roma, Italy; E-Mail: vvalentini@ 123456rm.unicatt.it
                [4 ]Radiation Oncology Department, Università “G. D'Annunzio”; Via dei Vestini 31, 66100 Chieti, Italy; E-Mail: d.genovesi@ 123456unich.it
                [5 ]Medical Oncology Unit - Cancer Institute “Giovanni Paolo II”; Viale Orazio Flacco, 65, 70124 Bari, Italy; E-Mail: n.silvestris@ 123456oncologico.bari.it
                Author notes
                [* ]Author to whom correspondence should be addressed; E-Mail: f.cellini@ 123456unicampus.it ; Tel.: +30-06-22541-420; Fax: +30-06-22541-433.
                Article
                molecules-19-05379
                10.3390/molecules19045379
                6271831
                24879584
                c43036fa-078e-4b1e-a4d8-25781051b0f2
                © 2014 by the authors.

                Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution license ( http://creativecommons.org/licenses/by/3.0/).

                History
                : 10 February 2014
                : 17 April 2014
                : 23 April 2014
                Categories
                Review

                mirna,mirnas,microrna,radiation,radiotherapy,resistance,review,tumor,dna damage repair,radiosensibilization

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