Objective: Urinary bladder hyperplasia associated with terephthalic acid (TPA) treatment was examined with concomitant use of sodium bicarbonate (NaHCO3) or hydrochlorothiazide to allow assessment of the relationship among bladder stones,epithelial hyperplasia,and corresponding cell cycle checkpoint gene expression in Sprague–Dawley (SD)rat. Methods:A total of 112 weanling male SD rats that divided between six groups were given basal diet (control), diets containing 5% TPA or in combination with either 4% sodium NaHCO3 or 0.02% hydrochlorothiazide.After 90-day feeding,bladder samples were collected for histopathological diagnoses,and immunohistochemical method was used to characterize the expression of p16Ink4a,cyclin D1, CDK4, EGFr and cyclin E in relation to that of proliferating cell nuclear antigen (PCNA). Results:In TPA treatment groups, bladder stone incidence was 40% (21/52) with 14 cases of proliferative bladder.In control and other groups,neither stone nor epithelial cell proliferation was diagnosed.PCNA-positive focal hyperplasic lesions involved all epithelial layers.Overexpressions of cyclin D1, CDK4, EGFr are found in the corresponding lesion. p16Ink4a nuclear staining reduced in proliferative bladders especially with a great quantity of stone.In addition,no positive expression was detected on cyclin E. Conclusion: The present study provides a strong evidence of a link between induction of bladder hyperplasia, deregulation of the p16Ink4a-cyclin D1/CDK4 pathway,and abnormal EGFr mediated signal transduction pathway.