en 23408179 MicroRNAs (miRNAs) are a class of small non coding regulatory RNAs that have key functions in multiple cell processes. Deregulation of these tiny miRNAs are involved in various human diseases. MiR-155 is one of the multifunctional miRNA that its over-expression has been found to be associated with different kinds of cancer such as leukemia, breast and colon cancers. It is thought that deregulation and over-expression of this microRNA may be associated with PC12 cell proliferation. So, the aim of this study was to investigate the role of miR-155 expression on PC12 cell growth. For this reason, PC12 cells were cultured and transfected by 3 different concentration (25, 50 and 75 nmol) of either LNA anti-miR-155 or scramble antisense in 24-well plate. Then, total RNA was extracted from transfected cells. miRNA cDNAs were synthesized from isolated total RNA. In the second step, miR-155 expression level was analyzed using the quantitative real-time polymerase chain reaction (QRT-PCR). MTT test was performed to evaluate cell viability. In the next step, apoptosis assay was assessed to investigate anti miR-155 effect on PC12 cells death. Obtained results were analyzed with t-test. MTT test revealed that cell viability of transfected cells with 75 nM of anti-miR- 155 to be reduced by half of the control and scramble groups (0.5 vs. 0.97 and 0.94). Our data suggest that miR-155 over-expression is associated with PC12 cell growth. So, miR-155 down regulation by anti-miR-155 could open up new ways to restrain brain tumor growth, as anti-miR-155 causes PC12 cells to repress. Apoptosis, miR-155, MTT test, PC12 cells 61 66 https://www.ajmb.org/En/Article.aspx?id=61 https://www.ajmb.org/PDF/En/FullText/61.pdf FatemehKouhkanDepartment of Genetics, Faculty of Basic Sciences, Tarbiat Modares University, Tehran, Iran218ShabanAlizadehDepartment of Hematology, Allied Medical School, Tehran University of Medical Sciences, Tehran, Iran219SaeidKavianiDepartment of Hematology, School of Medicine, Tarbiat Modares University, Tehran, Iran220MasoudSoleimaniDepartment of Hematology, School of Medicine, Tarbiat Modares University, Tehran, Iran221Ali AkbarPourfathollahImmunology Department, School of Medicine, Tarbiat Modares University, Tehran, Iran222NaserAmirizadehResearch Center of Iranian Blood Transfusion Organization (IBTO), Tehran, Iran223SaeidAbrounDepartment of Hematology, School of Medicine, Tarbiat Modares University, Tehran, Iran224MehrdadNoruziniaDepartment of Hematology, School of Medicine, Tarbiat Modares University, Tehran, Iran225ShahinMohamadiDepartment of Hematology, Allied Medical School, Tehran University of Medical Sciences, Tehran, Iran226