Downregulation of miR-221, -30d, and -15a contributes to pathogenesis of prostate cancer by targeting Bmi-1.

Prostate cancer is the second leading cause of cancer-related deaths of men. Bmi-1, a member of PcG family of proteins, has been implicated in the pathogenesis of prostate cancer, and disturbed profile of microRNAs (miRNAs) has been found in prostate cancer tissues. How Bmi-1 is regulated by miRNAs is unclear. In this study, we screened 18 miRNAs that potentially repress the expression of Bmi-1 using a dual luciferase system and found that 12 miRNAs could bind with the 3'-untranslated region of Bmi-1 mRNA. Using qRT-PCR, we found that expression of miR-221, -15a, and -30d was significantly reduced in prostate cancer tissues. Subsequent functional study indicated that miR-221 and miR-30d can repress prostate cancer cell proliferation, and this effect can be partially rescued by Bmi-1 overexpression. Our study constructs the relation between downregulated miR-221 and miR-30d and prostate cancer pathogenesis. These results indicate that miR-221 and miR-30d are candidate tumor suppressor miRNAs in prostate cancer and therefore serve as potential clinical classification markers and therapeutic targets for human prostate cancer.