Up-regulation of microRNA in bladder tumor tissue is not common.

MicroRNAs (miRNAs) have recently been shown to down-regulate gene expression by targeting mRNA translation and to play a critical role in tumorigenesis; how they regulate bladder tumor development, particularly in patients, is, however, poorly understood. The difference in miRNA expression in a bladder tumor compared with healthy tissue from the same patients was examined using microRNA arrays in seven patients. Here, we showed that up-regulation of miRNA was not commonly found in this limited number of patients, and four miRNAs (miR-26a, miR-29c, miR-30c, miR-30e-5p) were down-regulated as a common marker in patients with a 1-3 grade of disease. Our data suggest that instead of up-regulation of carcinogenic miRNAs, loss of regulation of these miRNA may be critical for bladder tumor development in patients.