Ionizing radiation-inducible microRNA miR-193a-3p induces apoptosis by directly targeting Mcl-1

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ORIGINAL PAPER

Ionizing radiation-inducible microRNA miR-193a-3p induces apoptosis by directly targeting Mcl-1 Jeong-Eun Kwon • Bu-Yeon Kim • Seo-Young Kwak In-Hwa Bae • Young-Hoon Han



Published online: 2 April 2013 Ó Springer Science+Business Media New York 2013

Abstract The functions of microRNAs (miRNAs) as either oncogenes or tumor suppressors in regulating cancerrelated events have been established. We analyzed the alterations in the miRNA expression profile of the glioma cell line U-251 caused by ionizing radiation (IR) by using an miRNA array and identified several miRNAs whose expression was significantly affected by IR. Among the IRresponsive miRNAs, we further examined the function of miR-193a-3p, which exhibited the most significant growthinhibiting effect. miR-193a-3p was observed to induce apoptosis in both U-251 and HeLa cells. We also demonstrated that miR-193a-3p induces the accumulation of intracellular reactive oxygen species (ROS) and DNA damage as determined by the level of cH2AX and by performing the comet assay. The induction of both apoptosis and DNA damage by miR-193a-3p was blocked by antioxidant treatment, indicating the crucial role of ROS in the action of miR-193a-3p. Among the putative target proteins, the expression of Mcl-1, an anti-apoptotic Bcl-2 family member, decreased because of miR-193a-3p transfection. A reporter assay using a luciferase construct containing the 30 -untranslated region of Mcl-1 confirmed that Mcl-1 is a direct target of miR-193a-3p. Down-regulation of Mcl-1 by siRNA transfection closely mimicked the outcome of miR-193a-3p transfection showing increased

J.-E. Kwon  B.-Y. Kim  S.-Y. Kwak  I.-H. Bae  Y.-H. Han (&) Division of Radiation Cancer Research, Korea Institute of Radiological and Medical Sciences, Nowon-gil 75, Nowon-gu, Seoul 139-706, South Korea e-mail: [email protected]

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ROS, DNA damage, cytochrome c release, and apoptosis. Ectopic expression of Mcl-1 suppressed the pro-apoptotic action of miR-193a-3p, suggesting that Mcl-1 depletion is critical for miR-193a-3p induced apoptosis. Collectively, our results suggest a novel function for miR-193a-3p and its potential application in cancer therapy. Keywords Mcl-1

microRNA  Apoptosis  ROS  miR-193a-3p 

Introduction In recent years, microRNAs (miRNAs) have received wide attention as important regulators of gene expression. miRNAs are a class of endogenous, small, non-coding RNAs *22 nucleotides in length. They negatively regulate gene expression at the post-transcriptional level by base pairing with the 30 -untranslated region (30 UTR) of the target mRNAs and subsequently induce mRNA degradation or translational repression [1, 2]. A single miRNA can regulate multiple target genes simultaneously partly due to imperfect base pairing, thereby making a global impact on gene expression. Many studies have shown that miRNAs play an important role in a wide range of biological processes such as proliferation, development, differentiation, and apoptosis [3, 4]. Growing evidence suggests that miRNAs

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