BMI1 and prostate cancer: MiR-708-5p has a tumor-suppressive role by targeting zinc-finger E-box-binding homeobox 2 as well as polycomb ring-finger oncogene (BMI1) to induce apoptosis and inhibit tumorigenesis in renal cancer.22 Furthermore, miR-708-5p also inhibits prostate cancer-initiating cells by targeting CD44 as well as thymoma viral proto-oncogene 2 (AKT2).23 Our finding of metformin's regulatory role on miR-708-5p supports the reports that metformin can suppress cancer stem cell's self-renewal.24 In this study, we found that NNAT was inhibited by miR-708-5p in prostate cancer cells.