MiR-133a induces apoptosis through direct regulation of GSTP1 in bladder cancer cell lines.

Objective: We previously demonstrated that miR-133a is a tumor-suppressive microRNA (miRNA) and is commonly down-regulated in human bladder cancer (BC). The aim of this study is to determine a novel oncogenic gene targeted by miR-133a in BC.

Methods: To identify genes targeted by miR-133a, an oligo-microarray analysis was performed using the miR-133a-transfected BC cell lines. For gain/loss-of-function studies, miR-133a/si-glutathione S-transferase π1 (GSTP1)-transfectants were subjected to XTT assay and flow cytometry to evaluate their cell viability and apoptosis status. The luciferase reporter assay was used to confirm the actual binding sites between miR-133a and GSTP1 mRNA. The mRNA and protein expression of GSTP1 in BC cell lines and clinical samples were evaluated by real-time RT-PCR and Western blot, respectively.

Results: MiR-133a transfection induced cell viability inhibition and apoptosis in BC cell lines. We focused on the GSTP1 gene that was the top 7 down-regulated one in the gene profile from the miR-133a-transfectants. MiR-133a transfection repressed expression levels of mRNA and protein levels of GSTP1. A luciferase reporter assay suggested that the actual binding may occur between miR-133a and GSTP1 mRNA. Cell viability inhibition and apoptosis were induced in the si-GSTP1 transfectants compared with the controls (P < 0.005). GSTP1 mRNA expression levels in 43 clinical BCs were significantly higher than those in eight normal bladder epitheliums (P = 0.0277).

Conclusion: Our data suggest that tumor suppressive miR-133a directly regulated oncogenic GSTP1 gene in BC, and that an anti-apoptotic effect mediated by GSTP1 is maintained by miR-133a down-regulation in human BC.