Decreased expression of RASSF1A and up-regulation of RASSF1C is associated with esophageal squamous cell carcinoma.

The Ras-Association Domain Family 1 (RASSF1) gene, which is located on the small arm of chromosome 3, contains two CpG islands and generates seven transcripts (RASSF1A-RASSF1G) by differential promoter usage and alternative splicing. As the main transcript, RASSF1A, B and C may play different roles in tumorigenesis. The present study was to detect the role of RASSF1A, B and C in esophageal squamous cell carcinoma (ESCC) and clarify the critical CpG sites of RASSF1A, in order to clarify more information on the role of RASSF1 with regard to the pathogenesis of ESCC. Frequent silencing of RASSF1A but not RASSF1B and RASSF1C were found in esophageal cancer cell lines and the silencing of RASSF1A may be reversed by 5-Aza-dC treatment. The aberrant promoter and exon 1 especially exon 1 methylation of RASSF1A induces silencing of its expression in TE13 cell line. Decreased mRNA and protein expression of RASSF1A was observed in ESCC tumor tissues and was associated with RASSF1A promoter and exon 1 methylation status. Unlike RASSF1A, methylation and expression variation of RASSF1B was not found in ESCC tissues. However, RASSF1C is highly expressed in ESCC tissues. RASSF1A methylation and protein expression were independently associated with ESCC patients' survival. These data indicated that the inactivation of RASSF1A through promoter and exon 1 methylation may play an important role in ESCC carcinogenesis and reactivation of RASSF1A gene may has therapeutic potential and may be used as a prognostic marker for ESCC patients.