en Molecular Genetics & Genomics Molecular Genetics & Genomics مقاله کامل Full Length/Original Article <strong>Background:</strong> A growing body of literature has revealed&nbsp;the effective role of miR-34a, as a tumor suppressor and regulator of expression of multiple targets in tumorigenesis and cancer progression. This study aimed at evaluating the potential effects of miR-34a alone or in combination with paclitaxel on breast cancer cells. <strong>Methods:</strong> After miR-34a transduction by lentiviral vectors in two MCF-7 and MDA-MB-231 cell lines of breast cancer, effects of the elevated expression of miR-34a in the cell viability and the cell proliferation were determined using MTT assay &nbsp;in treated and untreated cells with paclitaxel. The mRNA level of the <em>CCND1 </em>(Cyclin D1)gene was then measured in the two cell lines using the qRT-PCR assay. Finally, the influence of miR-34a and paclitaxel on apoptosis and cell cycle progression were examined by flow cytometry. <strong>Results:</strong> The <em>CCND1</em> mRNA expression levels were significantly down-regulated by overexpressed lentiviral miR-34a in MCF-7 and MDA-MB-231 cells. Combined treatment by miR-34a and paclitaxel reduced the cell viability and proliferation compared to single-drug treatment. In addition, the cell cycle arrest appeared at two phases by the combination of miR-34a and paclitaxel in MDA-MB-231 cells. <strong>Conclusion:</strong> Our results suggest that miR34a, in combination with paclitaxel, has a potential for decreasing the cell viability and proliferation. Moreover, it can reduce the expression of <em>CCND1</em> mRNA independent of the paclitaxel effect. Breast cancer, Cyclin D1, Drug resistance, Paclitaxel, miR-34a 361 369 http://ibj.pasteur.ac.ir/browse.php?a_code=A-10-1-830&slc_lang=en&sid=1 Shiva Irani 0000-0002-4202-9931 Yes Department of Biology, Science and Research Branch, Islamic Azad University, Tehran, Iran Mahsa Paknejad 0000-0001-7114-0228 No Department of Biology, Science and Research Branch, Islamic Azad University, Tehran, Iran Masoud Soleimani 0000-0003-1972-7771 No Department of Hematology, Faculty of Medical Sciences, Tarbiat Modares University, Tehran, Iran Azam Soleimani 0000-0002-3100-1706 No Legal Medicine Research Center, Legal Medicine Organization, Tehran, Iran