Immunohistochemical analysis for cell regulatory proteins in bladder carcinogenesis induced by N-methyl-N-nitrosourea–terephthalic acid

To explore the cell cycle regulatory mechanism in bladder carcinogenesis promoted by terephthalic acid calculi (TPA-calculi), male Wistar rats were initiated with N-methyl-N-nitrosourea (MNU) (20 mg/kg b.w. i.p.) twice a week for 4 weeks, and then given basal diet containing 5% TPA, 5% TPA plus 4% Sodium bicarbonate (NaHCO3) or 1% TPA for the next 22 weeks. Major regulatory proteins in G1 cell cycle checkpoint including p16INK4a, cyclin-dependent kinase 4 (Cdk4), cyclin D1, retinoblastoma protein (pRb) were determined during various stages of urinary bladder carcinogenesis by using immunohistochemistry. In MNU–5% TPA treated group, the incidences of overexpression of Cdk4, cyclin D1 and pRb in papilloma were significantly higher than these in simple hyperplasia (p = 0.023, p < 0.001 and 0.001, respectively) and in PN hyperplasia (p = 0.042, 0.012 and 0.002, respectively). The incidence of absent expression of p16INK4a in papilloma was much higher than that in simple hyperplasia (p = 0.004) and in PN hyperplasia (p = 0.02). Our results clearly reveal that the deregulation of p16INK4a–cyclin D1/Cdk4–pRb pathway is associated with bladder carcinogenesis promoted by TPA-calculi.