Mechanisms associated with abnormal E-cadherin immunoreactivity in human bladder tumors

The involvement of E-cadherin in the progression of carcinoma is supported by a large number of studies showing an inverse relationship between E-cadherin immunoreactivity and tumor aggressiveness. However, the mechanisms leading to decreased E-cadherin immunoreactivity are soil unclear. Comparison of Northern blotting and immunohistochemistry in a series of 49 frozen bladder tumors revealed that, in 16 of 23 tumors with abnormal staining, clear mRNA down-regulation occurred. In the 7 cases without mRNA down-regulation, no structural anomalies of E-cadherin could be detected by Southern blotting, Western blotting or PCR-SSCP. Western blotting confirmed that, in 6 of these tumors, E-cadherin was down-regulated at the protein level. This down-regulation was accompanied by down-regulation of α-catenin and, to a lesser extent, of β- or γ-catenin. However, Northern-blot analysis indicated that expression of the 3 catenins is maintained at the mRNA level. Thus our data show that, in bladder tumors, mRNA down-regulation accounts for about two thirds (16/23) of tumors with abnormal staining and that post-transcriptional down-regulation of E-cadherin occurs in 6/23 of these tumors.