Hypomethylation of Alu repetitive elements in esophageal mucosa, and its potential contribution to the epigenetic field for cancerization.

BACKGROUND: Aberrant hypermethylation of specific genes is present in esophageal squamous cell carcinomas (ESCCs). Such hypermethylation is also present in normal-appearing esophageal mucosae of ESCC patients and is considered to contribute to the formation of a field for cancerization. On the other hand, the presence of global hypomethylation in ESCCs or in their background esophageal mucosae is unknown. METHOD: We collected 184 samples of esophageal mucosae (95 normal mucosae from healthy subjects, and 89 non-cancerous background mucosae from ESCC patients) and 93 samples of ESCCs. Methylation levels of repetitive elements (Alu, LINE1) and cancer/testis antigen genes (NY-ESO-1, MAGE-C1) were measured by bisulfite pyrosequencing and quantitative methylation-specific PCR, respectively. RESULTS: Methylation levels of Alu, LINE1, NY-ESO-1, and MAGE-C1 were significantly lower in ESCCs than in their background and normal mucosae. Also, in the background mucosae, a significant decrease of the Alu methylation level compared with the normal mucosae was present. In ESCCs, methylation levels of the two repetitive elements and the two cancer/testis antigen genes were correlated with each other. CONCLUSION: This is the first study to show the presence of global hypomethylation in ESCCs, and even in their non-cancerous background mucosae. Alu hypomethylation might reflect the severity of an epigenetic field for cancerization.