Searching for new biomarkers of bladder cancer based on proteomic analysis

Urine cytology is the gold standard for detection of bladder cancer. However, it has poor sensitivity, and currently several diagnostic markers have high false-positive rates. One of the problems with bladder cancer is high locoregional recurrence after surgery. Therefore new diagnostic markers of bladder cancer are needed. We have conducted a comprehensive study of high molecular mass (HMM) protein expression in bladder cancer tissue by means of agarose two-dimensional gel electrophoresis (agarose 2-DE) followed by the analysis of liquid chromatography tandem mass spectroscopy. We successfully identified 53 proteins from cancer tissue and 33 proteins from normal mucosa in the HMM area of the 2DE gel, and they were classified as proteins of transcription, translation or the cytoskeleton. Among them, eight differentially regulated proteins were selected as new marker candidates, and we performed experiments to validate their use as diagnostic markers. The results of Western blotting showed that these proteins except for α spectrin were significantly upregulated in bladder cancer tissue, and one of them, structural maintenance of chromosomes protein 3 (SMC3), was specifically detected in urine samples from bladder cancer patients. On the other hand, the results of Immunohistochemistry showed that expression of neuroblast differentiation-associated protein AHNAK (AHNAK) was significantly increased and that of plectin-1 was significantly decreased in the bladder cancer specimens compared with normal bladder mucosa specimens. However, no significant difference was observed in other proteins. These results suggest that AHNAK and Plectin-1 would be the potential markers for urine cytology and SMC3 is possible to be that for diagnosis marker for urinalysis.