microRNA-32 induces radioresistance by targeting DAB2IP and regulating autophagy in prostate cancer cells.

The aberrant expression of microRNAs (miRNAs/miRs) has been found in numerous cancer types. miR-32 is an oncomiR in prostate cancer (PCa), however, the mechanisms by which miR-32 functions as a regulator of radiotherapy response and resistance in PCa are largely unknown. In the present study, it was found that DAB2 interacting protein (DAB2IP), the miR-32-dependent tumor-suppressor gene, was downregulated and induced autophagy and inhibited radiotherapy-induced apoptosis in PCa cells. miR-32 expression was upregulated or overexpressed in PCa, and miR-32 inhibited DAB2IP expression through a direct binding site within the DAB2IP 3' untranslated region. miR-32 mimics enhanced tumor cell survival and decreased radiosensitivity in the PCa cells, which were reversed by miR-32 inhibitor. Flow cytometric analysis revealed that overexpressed miR-32, consistent with the DAB2IP-knockdown results, reduced ionizing radiation (IR)-induced cell apoptosis, which was restored by 4 nM brefeldin A treatment. More significantly, the overexpression of miR-32 and the knockdown of DAB2IP enhanced autophagy in the IR-treated PCa cells. miR-32 regulated the expression of autophagy-related proteins, such as DAB2IP, Beclin 1 and Light chain 3β I/II, as well as phosphorylation of S6 kinase and mammalian target of rapamycin. In conclusion, these data provide novel insights into the mechanisms governing the regulation of DAB2IP expression by miR-32 and their possible contribution to autophagy and radioresistance in PCa.