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Intravesical Bacillus Calmette-Guerin (BCG) is the best treatment modality for progression of non-muscle invasive bladder cancer. We aimed to monitor changes at the proteome level to identify putative protein biomarkers associated with the response of urothelial precancerous lesions to intravesical BCG treatment. The rats were divided into three groups ( n = 10/group): control, non-treated, and BCG-treated groups. The non-treated and BCG-treated groups received N-methyl- N-nitrosourea intravesically. BCG Tice-strain was instilled into bladder in BCG-treated group. At the endpoint of experiment, all surviving rat bladders were collected and equally divided into two portions vertically from dome to neck. Half of each bladder was assessed immunohistopathologically and the other half was used for 2D-based comparative proteomic analysis. Differentially expressed proteins were validated by Western blot analysis. Precancerous lesions of bladder cancer were more common in non-treated group (77.8%) than in BCG-treated group (50%) and the control group (0%). Greater than twofold changes occurred in the expression of a number of proteins. Among them, Rab-GDIβ, aldehyde dehydrogenase 2 (ALDH2) and 14-3-3 zeta/delta were important since they were previously reported to be associated with cancer and their expression levels were found to be lower in BCG-treated group in comparison to the non-treated group. ALDH2 and 14-3-3 zeta/delta were also found to be highly expressed in the non-treated group compared to the control group. The down-regulation of these proteins and Rab-GDIβ was achieved with BCG; this result indicates that they may be used as putative biomarkers for monitoring changes in bladder carcinogenesis in response to BCG immunotherapy. [ABSTRACT FROM AUTHOR]