Int J Biol Sci 2015; 11(1):109-121. doi:10.7150/ijbs.10276

Research Paper

MiR-467a is Upregulated in Radiation-Induced Mouse Thymic Lymphomas and Regulates Apoptosis by Targeting Fas and Bax

Fu Gao1*, Song Chen2*, Mingjuan Sun3*, Ronald E.J. Mitchel4, Bailong Li1, Zhiyong Chu2, Jianming Cai1✉, Cong Liu1✉

1. Department of Radiation Medicine, Faculty of Naval Medicine, Second Military Medical University, Shanghai 200433, PR China;
2. Department of Radiological Protection, Naval Medical Research Institute, Shanghai 200433, PR China;
3. Department of Biochemistry and Molecular Biology, Second Military Medical University, Shanghai 200433, PR China;
4. Radiological Protection Research and Instrumentation Branch, Atomic Energy of Canada Limited, Chalk River Laboratories, Chalk River, ON, K0J1J0, Canada.
* These authors contributed equally to this work.

Abstract

It has been reported dysregulation of certain microRNAs (miRNAs / miRs) is involved in tumorigenesis. However, the miRNAs associated with radiocarcinogenesis remain undefined. In this study, we validated the upregulation of miR-467a in radiation-induced mouse thymic lymphoma tissues. Then, we investigated whether miR-467a functions as an oncogenic miRNA in thymic lymphoma cells. For this purpose, we assessed the biological effect of miR-467a on thymic lymphoma cells. Using miRNA microarray, we found four miRNAs (miR-467a, miR-762, miR-455 and miR-714) were among the most upregulated (>4-fold) miRNAs in tumor tissues. Bioinformatics prediction suggests miR-467a may potentially regulate apoptosis pathway via targeting Fas and Bax. Consistently, in miR-467a-transfected cells, both proliferation and colony formation ability were significantly increased with decrease of apoptosis rate, while, in miR-467a-knockdown cells, proliferation was suppressed with increase of apoptosis rate, indicating that miR-467a may be involved in the regulation of apoptosis. Furthermore, miR-467a-knockdown resulted in smaller tumors and better prognosis in an in vivo tumor-transplanted model. To explain the mechanism of apoptosis suppression by miR-467a, we explore the expression of candidate target genes (Fas and Bax) in miR-467a-transfected relative to negative control transfected cells using flow cytometry and immunoblotting. Fas and Bax were commonly downregulated in miR-467a-transfected EL4 and NIH3T3 cells, and all of the genes harbored miR-467a target sequences in the 3'UTR of their mRNA. Fas and Bax were actually downregulated in radiation-induced thymic lymphoma tissues, and therefore both were identified as possible targets of miR-467a in thymic lymphoma. To ascertain whether downregulation of Fas and / or Bax is involved in apoptosis suppression by miR-467a, we transfected vectors expressing Fas and Bax into miR-467a-upregulated EL4 cells. Then we found that both Fas- and Bax-overexpression decreased cell viability with increase of apoptosis rate, indicating that downregulation of Fas and Bax may be at least partly responsible for apoptosis suppression by miR-467a. These data suggest that miR-467a may have oncogenic functions in radiation-induced thymic lymphoma cells and that its increased expression may confer a growth advantage on tumor cells via aberrant expression of Fas and Bax.

Keywords: radiocarcinogenesis, thymic lymphoma, miR-467a, Fas, Bax, apoptosis.

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How to cite this article:
Gao F, Chen S, Sun M, Mitchel REJ, Li B, Chu Z, Cai J, Liu C. MiR-467a is Upregulated in Radiation-Induced Mouse Thymic Lymphomas and Regulates Apoptosis by Targeting Fas and Bax. Int J Biol Sci 2015; 11(1):109-121. doi:10.7150/ijbs.10276. Available from http://www.ijbs.com/v11p0109.htm