Reduced expression of E-cadherin in oral squamous cell carcinoma: relationship with DNA methylation of 5' CpG island.

E-cadherin, a Ca2+-dependent cell-cell adhesion molecule, is involved in the maintenance of the epithelial phenotype. The reduction of its expression is considered to be important in the invasive and metastatic potential of carcinomas. A series of 52 primary oral squamous-cell carcinomas (SCCs) were studied immunohistochemically for E-cadherin expression in microwave-treated paraffin-embedded sections using a monoclonal antibody (HECD-1). Significant correlation was found between reduced E-cadherin expression and tumor dedifferentiation, grade of invasiveness, and lymph node metastasis. The possibility of E-cadherin gene mutation was also investigated by polymerase chain reaction-single strand conformation polymorphism (PCR-SSCP), but none was found. In addition, to clarify the CpG methylation state around E-cadherin gene promoter in oral SCC, we examined DNA samples by PCR assay after restriction digestion with methylation-sensitive enzyme HpaII. CpG methylation was found in 9 (17%) of 52 primary oral SCCs, but not in the corresponding normal tissues. In particular, 8 of the 9 methylated cases showed reduced expression of E-cadherin and histologically diffuse invasion type of tumor. These results suggest that reduction of E-cadherin expression is associated with the progression of human oral SCCs, and CpG methylation of E-cadherin gene promoter causes reduction of E-cadherin expression in the tumor, resulting in acquisition of the invasive phenotype.