Restoration of miR-517a expression induces cell apoptosis in bladder cancer cell lines.

The aim of this study was to find novel tumor suppressor microRNAs through screening genes epigenetically silenced by methylation in bladder cancer (BC) cell lines using microRNA microarrays. Since miR-517a and miR-520g, both located on chromosome 19q13.42, were found to highly up-regulated genes after treatment with a demethylating agent, 5-aza-2'-deoxycytidine (5-Aza-dc), we hypothesized that they are tumor-suppressor microRNAs and performed a gain-of-function study using these mature microRNAs. The miR-517a restoration showed significant inhibition of cell proliferation in the transfectants compared to miR-control-transfected cells (p<0.0001 both in BOY and T24 cells). Furthermore, ectopic overexpression of miR-517a markedly induced apoptosis in the miR-517a-transfected BC cell lines. In addition, we carried out oligo microarray analysis using miR-517a transfectants and miR-control transfectants (BOY and T24), from which 35 down-regulated genes and 19 up-regulated genes were identified. These included amphiregulin (AREG) and BCL2-associated transcription factor 1, transcript variant 1 (BCLAF1), previously reported to be concerned with apoptosis, in both cell lines by miR-517a restoration. These data suggest that miR-517a functions as a tumor suppressor through inhibition of cell proliferation and induction of apoptosis under the regulation of AREG and/or BCLAF1 in BC cells. Anti-apoptotic effects may be maintained by down-regulation of miR-517a due to DNA hypermethylation in human BC cells, suggesting that restoration of miR-517a may be a novel therapeutic strategy for human BC.