Up-regulation of Frizzled-7 (FZD7) in human gastric cancer

Human Frizzled-7 (FZD7) and human FzE3, showing 98.8% nucleotide identity, encode almost identical WNT receptors with nine amino-acid substitutions. FzE3 is claimed to be expressed specifically in esophageal cancer. We determined the structure of the FZD7 gene and the FZD7 cDNA expressed in esophageal cancer. The FZD7 gene without intron and the FZD7 cDNAs isolated from esophageal cancer cell lines TE4 and TE5 were found to encode WNT receptor identical to FZD7, but not to FzE3. Nucleotide sequence of FzE3 was not identified on the human genome draft sequence. Thus, we could not obtain any data suggesting the existence of FzE3. Expression profile of FZD7 was also investigated. FZD7 was expressed throughout normal gastrointestinal tract, from esophagus to rectum. Among human esophageal and gastric cancer cell lines, expression level of FZD7 was relatively lower in esophageal cancer cell lines, and was highest in the gastric cancer cell line MKN7. FZD7 was up-regulated in one out of six cases of human primary gastric cancer. As over-expression of Frizzled-7 leads to activation of the WNT-β-catenin-TCF pathway, up-regulation of FZD7 in human gastric cancer might play key roles in carcinogenesis through activation of the WNT-β-catenin-TCF pathway.