Exosomal circRNA HIPK3 knockdown inhibited cell proliferation and metastasis in prostate cancer by regulating miR-212/BMI-1 pathway.

Prostate cancer (PCa) is the second frequent malignancy among men in the world. Exosomal circular RNAs (circRNAs) have been reported to function in PCa progression. The current study aimed to investigate the role of exosomal circRNA homeodomain-interacting protein kinase 3 (circHIPK3) in PCa development. Exosomes were extracted from serum and cells utilizing commercial kit, and identified by transmission electron microscopy (TEM), Western blot assay and nanoparticle tracking analyzer. Relative expression of circHIPK3, microRNA (miR)-212 and B-cell specific MMLV insertion site-1 (BMI-1) was examined by quantitative realtime PCR or Western blot assay. Receiver Operating Characteristic (ROC) analysis was conducted to assess the diagnostic potential of exosomal miR-212. Cell viability, and metastasis including migration and invasion, were detected by Methyl thiazolyl tetrazolium (MTT) assay and Transwell assay, respectively. Cell apoptosis was monitored using flow cytometry. The interaction between miR-212 and circHIPK3 or BMI-1 was validated by dual-luciferase reporter assay. Xenograft tumor assay was employed to explore the role of exosomal circHIPK3 . Exosomal circHIPK3 was increased in serum of PCa patients, and could discriminate PCa patients from normal volunteers. Depletion of exosomal circHIPK3 or overexpression of exosomal miR-212 reduced viability, migration and invasion, but promoted cell apoptosis in PCa cells, which was attenuated by miR-212 inhibition or BMI-1, respectively. MiR-212 targeted BMI-1, and downregulated BMI-1 expression. Exosomal circHIPK3 knockdown also suppressed tumor growth . Exosomal circHIPK3 knockdown inhibited PCa progression by regulating miR-212/BMI-1 axis, at least in part, offering a new insight into the molecular mechanism of PCa.