Interplay among epigenetic alterations and crosstalk between genetic and epigenetic alterations in esophageal squamous cell carcinoma

Epigenetic alterations that do not involve a change in the DNA sequence have been increasingly recognized to be important key events in the regulation of the gene expression and carcinogenesis. Major epigenetic mechanisms include the methylation of cytosine in DNA, changes in the histone and chromatin structure due to covalent posttranslational modification of histone proteins and the RNA-mediated regulation of the gene expression. Esophageal squamous cell carcinoma (ESCC) continues to be associated with a very poor prognosis, indicating that obtaining a clear understanding of the pathogenesis of ESCC is desired for improving clinical outcomes. In this review, we discuss the recent progress in research on epigenetic alterations in ESCC, with respect to the following points: (1) DNA methylation, including global hypomethylation and DNA hypermethylation at CpG islands in the promoters of tumor suppressor genes, (2) histone acetylation/deacetylation and histone methylation with the alteration of histone-modifying enzymes and (3) alterations in the expression of microRNA and the recently emerging long non-coding RNA. We then discuss the interplay among these epigenetic events and the crosstalk between epigenetic and genetic changes in ESCC. It is therefore important to understand the molecular mechanisms underlying the development and progression of ESCC to improve the treatment outcome of this devastating disease, although this information is quite complicated and confusing.