Abstract

Abstract MicroRNAs (miRNAs) are small noncoding RNAs that negatively regulate protein‐coding genes. To identify miRNAs that have a tumor suppressive function in bladder cancer (BC), 156 miRNAs were screened in 14 BCs, 5 normal bladder epithelium (NBE) samples and 3 BC cell lines. We identified a subset of 7 miRNAs ( miR‐145 , miR‐30a‐3p , miR‐133a , miR‐133b , miR‐195 , miR‐125b and miR‐199a* ) that were significantly downregulated in BCs. To confirm these results, 104 BCs and 31 NBEs were subjected to real‐time RT‐PCR‐based experiments, and the expression levels of each miRNA were significantly downregulated in BCs ( p < 0.0001 in all). Receiver‐operating characteristic curve analysis revealed that the expression levels of these miRNAs had good sensitivity (>70%) and specificity (>75%) to distinguish BC from NBE. Our target search algorithm and gene‐expression profiling in BCs (Kawakami et al ., Oncol Rep 2006;16:521–31) revealed that Keratin7 ( KRT7 ) mRNA was a common target of the downregulated miRNAs, and the mRNA expression levels of KRT7 were significantly higher in BCs than in NBEs ( p = 0.0004). Spearman rank correlation analysis revealed significant inverse correlations between KRT7 mRNA expression and each downregulated miRNA ( p < 0.0001 in all). Gain‐of‐function analysis revealed that KRT7 mRNA was significantly reduced by transfection of 3 miRNAs ( miR‐30‐3p , miR‐133a and miR‐199a* ) in the BC cell line (KK47). In addition, significant decreases in cell growth were observed after transfection of 3 miRNAs and si‐KRT7 in KK47, suggesting that miR‐30‐3p , miR‐133a and miR‐199a* may have a tumor suppressive function through the mechanism underlying transcriptional repression of KRT7 . © 2009 UICC