Methylation of the 5' CpG island of the FHIT gene is closely associated with transcriptional inactivation in esophageal squamous cell carcinomas.

Previous studies suggested that the FHIT (fragile histidine triad) gene on 3p14.2 might be involved in the development of esophageal squamous cell carcinomas, but the mechanisms for inactivating the gene have not been fully revealed. In the present study, we examined aberrations of the FHIT gene in 23 esophageal squamous cell carcinoma cell lines and 35 primary tumors. We detected aberrant expression in seven cell lines (30%), including a shorter transcript in two cell lines and loss of apparent transcript in five cell lines. Genomic PCR or cDNA sequencing analysis revealed a single exon deletion in two cell lines with a shorter transcript and one cell line without expression, but no structural alterations were found in the other 20 cell lines, including transcriptionally repressed four cell lines. Next we examined methylation of the 5' CpG island of the FHIT gene by bisulfite genomic sequencing. Hypermethylation of the 5' CpG island of the FHIT gene was observed in three of four structurally unaltered but transcriptionally repressed cell lines. The remaining cell line harbored a point mutation upstream of exon 1. All methylated cell lines exhibit re-expression of the FHIT gene and demethylation in the CpG island after treatment with demethylating agent 5-aza-2'-deoxycytidine. Hypermethylation was also found in 5 of 35 (14%) primary tumors, whereas corresponding normal tissue shows no methylation. These findings suggest that methylation of the 5' CpG island of the FHIT gene is closely associated with transcriptional inactivation and might be involved in tumor development of the esophagus.