Identification of urine PLK2 as a marker of bladder tumors by proteomic analysis

To determine the patterns of urinary proteins in bladder cancer subjects using pooled urine from 27 bladder cancer patients. The urine matrix was removed by acetonitrile precipitation followed by molecular weight cutoff. High performance liquid chromatography coupled with electrospray ionization tandem mass spectrometry (HPLC-ESI-MS/MS) was used to analyze the urinary proteome. The candidate protein was validated by western blot. A total of 146 urinary proteins were identified. The protein list was screened using bioinformatic tools, and 11 cancer-related urinary proteins were found to be potential tumor markers for bladder cancer. However, only PLK2 was identified with high confidence. This candidate protein was validated by western blot using urine samples from 14 normal subjects and 10 bladder cancer patients. Statistically significant correlations were detected between PLK2 expression and bladder transitional cell carcinoma (TCC) (P < 0.05). Urinary PLK2 had a sensitivity of 80% at a specificity of 64% for bladder TCC in the samples tested. Our results demonstrate overexpression of PLK2 in bladder carcinomas, suggesting a possible role of PLK2 in the pathogenesis of bladder carcinomas. However, the small cohort, preliminary results, and lack of subgroup analysis (such as carcinoma in situ, high grade, and stage) in this study prevent us from drawing definitive conclusions about the diagnostic value of PLK2 in these patients. Further studies directed toward a multitude of possible carcinogenic mechanisms of PLK2 in bladder cancer are warranted.