A significant reduction of EphA7 expression in human colorectal cancers was shown using semi-quantitative reverse transcription-polymerase chain reaction analysis in 59 colorectal cancer tissues, compared to corresponding normal mucosas (P=0.008), and five colon cancer cell lines. To investigate the mechanism of EphA7 down-regulation in colorectal cancer, we examined the methylation status of the 5’CpG island around the translation start site in five colon cancer cell lines using restriction enzymes, methylation-specific PCR, and bisulfite sequencing and found evidence of aberrant methylation. The expression of EphA7 in colon cancer cell lines was restored after treatment with 5-aza-2’-deoxycytidine. Analysis of methylation status in totally 75 tumors compared to clinicopathological parameters revealed that hypermethylation of colorectal cancers was more frequent in male than in female (P=0.0078); and in moderately differentiated than in well differentiated adenocarcinomas (P=0.0361). There was a tendency that hypermethylation in rectal cancers was more frequent than in colon cancers (P=0.0816). Hypermethylation was also observed in colorectal adenomas. This is the first report describing the down-regulation of an Eph family gene in a solid tumor via aberrant 5’CpG island methylation. It provides the evidence that EphA7 gene is involved in human colorectal carcinogenesis. Together with the recent reports of EphB2 invovlvement in colorectal cancer porgression by downregulation, our observation would give an insight about unexpected and extensive roles of Eph family receptors in human cancer.
[Proc Amer Assoc Cancer Res, Volume 47, 2006]