Department of Surgery, Kyushu University, Beppu, Japan.
Growth factor receptors transmit intracellular signals that may be important in carcinogenesis. The Grb7 protein was recently identified as a substrate of the epidermal growth factor receptor and related Her2/ erbB2 receptor-linked tyrosine kinase activity. The Grb7 gene has been found to be coamplified with Her2/erbB2 in breast carcinomas. In this study, Grb7 expression was studied in 32 human esophageal cancers. A human Grb7 cDNA encoding for N-terminal amino acids was isolated and found to be 90% homologous to the murine counterpart. Although there was no amplification of the Grb7 gene in esophageal cancers, Grb7 mRNA was found to be overexpressed in 14 cancers (43.8%) but not in adjacent normal esophageal mucosa. It is noteworthy that coexpression of Grb7 with epidermal growth factor receptor or Her2/erbB2 was detected in 10 esophageal carcinomas (31.3%) and was significantly related to extramucosal tumor invasion (P = 0.02), whereas such a relationship was not shown by each sole expression. These findings suggest a possible relationship of Grb7 signaling in association with expression of tyrosine kinase receptors in aggressive human esophageal cancer.