DNA Methylation And Functional Study Of The Downregulated Genes In Esophageal Squamous Cell Carcinoma

Esophageal squamous cell carcinoma (ESCC) is one of the most common tumors in human. Previous studies showed that multiple genetic and epigenetic alterations involved in carcinogenesis of esophagus, but its molecular mechanisms are poorly understood. So far, more and more ESCC-related genes have been found and retinoic acid receptor β₂ (RARβ₂) is such a gene. RARβ₂ has been recognized as a putative tumor suppressor gene. A growing evidence indicated that RARβ₂ was required for the growth inhibitory action of retinoic acid (RA). Moreover, loss of RARβ₂ expression has been reported in many types of tumors, including ESCC. It has been demonstrated that loss of RARp expression was an early event associated with esophageal carcinogenesis and the status of squamous differentiation. However, the molecular mechanism of its inactivation remained obscure in ESCC. We investigated the role of hypermethylation in RARβ₂ gene silencing in 12 ESCC cell lines by methylation-specific PCR (MSP) and compared its methylation status with RARβ₂ mRNA and protein expression. The MSP results were confirmed by bisulfite sequencing of RARβ₂ promoter region. The expression of RARβ₂ was restored in two RARβ₂-downregulated cell lines after 5-aza-2'-deoxycytidine (5-aza-dc) treatment. Therefore, methylation of the 5' region may play an important role in the downregulation of RARβ₂ in some ESCC cell lines suggesting that multiple mechanisms contribute to the loss of RARβ₂ expression in ESCC cell lines. Furthermore, the...