PO-128 MicroRNA-449A enhances the radiosensitivity of prostate cancer cells

MicroRNAs (miRNAs) are evolutionarily conserved, endogenous, small noncoding RNAs that regulate the stability and translation of target mRNA by primarily binding to the 3′ -UTR18. MiRNAs have been reported to be involved in DNA damage response induced by ionising radiation (IR). c-Myc is reduced when cells treated with IR or other DNA damaging agents. However, it is unknown whether miRNAs participate in c-Myc downregulation in response to IR. MicroRNA-449a is deregulated in various types of cancers, including prostate cancer. Material and methods The human prostate cancer lines, LNCaP, PC-3 and DU-145 cells in exponential growth were irradiated by x-rays at room temperature. Overexpressing miR-499a and miR-con was generated by plasmid transduction using GV214. MiR-449a antagomir (anti-miR-449a) and non-targeting sequence were synthesised. Transfection was performed with Trans IT −2020 Transfection Reagent. The cell viability assay was carried out basis on thiazolyl blue tetrazolium blue (MTT). Cell proliferation was analysed using Cell Counting Kit-8(CCK-8). Cell cycle analysis was acquired using FACS Calibur flow cytometer. MiRNAs and mRNA expression were determined using quantitative RT-PCR analysis. Protein expression were analysed by western blotting. Results and discussions In the present study, we found that miR-449a was upregulated and c-Myc was downregulated in response to IR in LNCaP cells. Overexpression of miR-449a or knockdown of c-Myc promoted the sensitivity of LNCaP cells to IR. By establishing c-Myc as a direct target of miR-449a, we revealed that miR-449a enhanced radiosensitivity by repressing c-Myc expression in LNCaP cells. Moreover, we showed that miR-449a enhanced radiation-induced G2/M phase arrest by directly downregulating c-Myc, which controlled the Cdc2/CyclinB1 cell cycle signal by modulating Cdc25A. In summary, our study reported here demonstrated that miR-449a enhanced the sensitivity of LNCaP cells to IR by directly targeting c-Myc, which controlled the Cdc2/cyclinB1 cell cycle signal by modulating Cdc25A/Rb/E2F pathway. Furthermore, we found that both miR-449a and c-Myc responded to irradiation and either overexpression of miR-449a or knockdown of c-Myc sensitised LNCaP cells to irradiation. Conclusion These findings highlighted an unrecognised mechanism of miR-449a-mediated c-Myc regulation in response to IR, which provides a support for the combination of ionising radiation with miRNAs regulation as a therapeutic strategy for patients with prostate cancer.