Strong Correlation of Basement Membrane Degradation With P53 Inactivation and/or MDM2 Overexpression in Superficial Urothelial Carcinomas

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Abstract
We investigated the relationships between the degradation of basement membrane underlying superficial urothelial carcinomas, including carcinoma in situ and the functional p53 loss caused by inactivation of p53 and the overexpression of mdm2 oncoprotein. Nuclear accumulations of p53 and mdm2 were examined immunohistochemically for 60 transitional cell carcinomas (primary lesions) and 13 accompanying (concomitant) carcinoma in situ lesions. Degradation of the basement membrane was defined as the reduction or total loss of type IV collagen expression. Whether there was up-regulation of MMP-1, MMP-2, and MMP-9 was analyzed immunohistochemically. The frequency of the degradation of basement membrane underlying grade 1 pTa tumors was 0%, grade 2-3 pTa tumors 57.1%, and primary CIS lesions 83.3%. Nuclear over-accumulation of p53 was found in 48.3% and of mdm2 in 23.3% of the primary tumors. In pTa-pT1 carcinomas, nuclear staining of p53, mdm2, or both was highly correlated with degradation of the basement membrane underlying carcinomas (p = 0.00002). In the CIS lesions, the association of p53 nuclear staining with the destruction of type IV collagen expression was of borderline significance (p = 0.03). When mdm2 overexpression was considered as a molecular abnormality together with p53 inactivation, the correlation with the degradation of the basement membrane was highly significant (p = 0.00006). Moreover, the functional p53 loss was strongly associated with the up-regulation of matrix metalloproteinases (MMPs) (p = 0.0005). This finding was well correlated with the strong association of basement membrane degradation with up-regulation of MMPs (p = 0.000004). Degradation of basement membranes underlying superficial carcinomas or CIS of the urothelium was significantly related to p53 inactivation, mdm2 overexpression, or both. The expression status of mdm2 should provide better information about the progression of superficial urothelial carcinomas than the status of p53 alone.