Promoter methylation as a common mechanism for inactivating E-cadherin in human salivary gland adenoid cystic carcinoma.

BACKGROUND

The role of promoter methylation in the inactivation of E-cadherin (E-cad) in salivary gland adenoid cystic carcinoma (ACC) is unknown. The objective of this study was to determine the role and potential clinical implications of promoter methylation of E-cad in salivary gland ACC.

METHODS

The promoter methylation status of E-cad was determined by using methylation-specific polymerase chain reaction (PCR) analysis in 60 primary salivary gland ACC tissues and 3 ACC cell lines. The level of E-cad protein expression was determined by immunohistochemical analysis of each tumor. E-cad protein and messenger RNA (mRNA) expression levels were examined by immunohistochemical analysis and reverse transcriptase-PCR in 3 ACC cell lines. Associations between molecular alterations and patients' clinicopathologic characteristics were analyzed statistically. E-cad mRNA expression was examined in a 5-azacytidine-treated ACC-2 cell line.

RESULTS

Promoter methylation of E-cad was detected in 34 of 60 tumors (57%). Of those 34 tumors, 18 tumors (53%) showed no E-cad protein expression, whereas only 5 of the remaining 26 tumors (19%) without E-cad promoter methylation showed no E-cad protein expression (P = .01). Tumors that had E-cad promoter methylation had a significantly higher histologic grade (P = .01) and more perineural invasion (P = .02) compared with tumors that did not have methylation. All 3 ACC cell lines exhibited E-cad promoter methylation and a lack of E-cad mRNA and protein expression, whereas 5-azacytidine restoredE-cad mRNA expression in the ACC-2 cell line.

CONCLUSIONS

E-cad frequently is inactivated in salivary gland ACC through promoter methylation, and E-cad promoter methylation may play a role in tumor cell differentiation and perineural invasion.