hypermethylation and decreased expression in esophageal squamous cell carcinoma and histologically normal tumor surrounding esophageal cells.

BACKGROUND

Esophageal squamous cell carcinoma (ESCC) is one of the 10 most incident cancer types in the world, and it is mainly associated with tobacco and alcohol consumption. ESCC mortality rates stand very close to its incidence, which is a direct consequence of a late diagnosis and an inefficient treatment. Although this scenery is quite alarming, the major molecular alterations that drive this carcinogenesis process remain unclear. We have previously shown through the first ESCC methylome analysis that promoter is frequently hypermethylated in ESCC. Here, to evaluate methylation as a potential biomarker of early ESCC diagnosis, we investigated the status of promoter methylation and its expression in ESSC and histologically normal tumor surrounding tissue of ESCC patients in comparison to healthy esophagus of non-cancer individuals.

RESULTS

Analysis of promoter methylation, and gene and protein expression in 65 ESCC patients and 88 controls revealed that methylation levels were already increased in histologically normal tumor surrounding tissue of ESCC patients when compared to healthy esophagus of non-cancer individuals. This increase in DNA methylation was followed by the reduction of mRNA expression. Interestingly, expression was capable of distinguishing tumor surrounding normal tissue from normal mucosa of healthy individuals with 92% accuracy. In addition, TFF1 protein was undetectable both in tumor and surrounding mucosa by immunohistochemistry, while submucosa glands of the healthy esophagus showed positive staining. Furthermore, treatment of TE-1 and TE-13 ESCC cell lines with decitabine led to a reduction of promoter methylation and consequent upregulation of TFF1 gene and protein expression. Finally, using TCGA data we showed that loss is observed in ESCC, but not in esophageal adenocarcinoma, highlighting the different molecular mechanisms involved in the development of each histological subtype of esophageal cancer.

CONCLUSIONS

This study shows that expression is silenced in early phases of ESCC development, which seems to be mediated at least in part by promoter hypermethylation, and provides the basis for the use of expression as a potential biomarker for early ESCC detection.