Cadherin switches during epithelial-mesenchymal transition: CDH4 / RCAD downregulation reduces bladder cancer progression

Purpose Non-muscle invasive bladder cancer (NMIBC) is a highly recurrent disease that progresses to muscle-invasive bladder cancer (MIBC) in 5–25% of the cases. Epithelial-mesenchymal transition (EMT) has been associated with features of disease progression. Thus, we aimed to characterize the cadherin switch (CS), an EMT hallmark, and its regulatory mechanisms in bladder cancer (BlCa) progression, as well as the biological role of RCAD, a lesser-known cadherin, in bladder carcinogenesis. Methods Cadherin mRNA and promoter methylation levels were retrieved from The Cancer Genome Atlas (TCGA). Validation was performed in an independent set of 121 primary BlCa (NMIBC and MIBC) and 40 normal bladder samples from IPO Porto, using RT-qPCR and qMSP. Immunohistochemistry was performed in these samples and in 14 additional sarcomatoid BlCa. CRISPR-Cas9 was performed to explore the potential in vitro impact of RCAD on BlCa cell migration and invasion. Results In both the TCGA and IPO Porto BlCa cohorts, cadherin gene deregulation was observed compared to normal tissue samples, independent of promoter methylation. At the protein level, decreased E-cadherin and increased P- and R-cadherin expression was noted in BlCa tissues. In sarcomatoid BlCa the same trend was observed, with a more intense staining compared to that in conventional MIBCs. RCAD knockout considerably reduced the malignant properties of BlCa cells. Conclusions Our data indicate that E-, P- and R-cadherin switches occur in BlCa, being associated with tumor progression. Promoter methylation is not the likely mechanism underlying cadherin expression deregulation. Our findings suggest an oncogenic role of RCAD in BlCa progression.