Edited by Tamas DalmayKeywords: MiR-199a-5p DRAM1 Beclin1 Autophagy Irradiation a b s t r a c t Autophagy is a self-degrading process that is triggered by diverse stimuli including ionizing radiation. In this study we show novel phenomena in which transfection of miR-199a-5p mimic significantly suppresses IR-induced autophagy in MCF7 cells, and up-regulates basal and IR-induced autophagy in MDA-MB-231 breast cancer cells. We also identify DRAM1 and Beclin1 as novel target genes for miR-199a-5p. Overexpression of miR-199a-5p inhibits DRAM1 and Beclin1 expression in MCF7 cells, while it enhances expression of these genes in MDA-MB-231 cells. Furthermore, we show that miR-199a-5p sensitizes MDA-MB-231 cells to irradiation. Therefore, our data identify miR-199a-5p as a novel and unique regulator of autophagy, which plays an important role in cancer biology and cancer therapy.

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Autophagy is an evolutionarily conserved, multi-step lysosomal degradation process in which a cell degrades its own long-lived proteins and damaged organelles. Ataxia telangiectasia mutated (ATM) has recently been shown to upregulate the process of autophagy. Previous studies showed that certain microRNAs, including miR-18a, potentially regulate ATM in cancer cells. However, the mechanisms behind the modulation of ATM by miR-18a remain to be elucidated in colon cancer cells. In the present study, we explored the impact of miR-18a on the autophagy process and ATM expression in HCT116 colon cancer cells. To determine whether a preliminary link exists between autophagy and miR-18a, HCT116 cells were irradiated and quantitative (q) PCR was performed to measure miR-18a expression. HCT116 cells were transfected with an miR-18a mimic to study its impact on indicators of autophagy. Western blotting and luciferase assays were implemented to explore the impact of miR-18a on ATM gene expression in HCT116 cells. The results showed that miR-18a expression was strongly stimulated by radiation. Ectopic overexpression of miR-18a in HCT116 cell lines potently enhanced autophagy and ionizing radiation-induced autophagy. Moreover, miR-18a overexpression led to the upregulation of ATM expression and suppression of mTORC1 activity. Results of the present study pertaining to the role of miR-18a in regulating autophagy and ATM gene expression in colon cancer cells revealed a novel function for miR-18a in a critical cellular event and on a crucial gene with significant impacts in cancer development, progression, treatment and in other diseases.

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