EGF and TGF‐α, the ligands of hyperproduced EGFR in human esophageal carcinoma cells, act as autocrine growth factors

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Abstract
In order to ascertain autocrine growth factors in esophageal carcinomas, we analysed expression of mRNAs and proteins for epidermal growth factor (EGF), transforming growth factor‐α (TGF‐α) and epidermal growth factor receptor (EGFR) in 6 esophageal carcinoma cell lines. Gene alterations were also examined. All of the esophageal carcinoma cell lines expressed mRNA for EGFR and TGF‐α genes. Interestingly, EGF mRNA of about 5.0 kb was also detected in TE‐1, TE‐2, and TE‐8 cells. Production of protein was also confirmed by binding assay and ELISA on 3 of the 6 cell lines. The cells had a relatively high number of EGFRs and produced TGF‐α and EGF protein at the same time. Furthermore, anti‐EGF (KEM‐10) and anti‐TGF‐α (WA‐3) monoclonal antibodies (MAbs) inhibited spontaneous uptake of tritiated thymidine (3H‐TdR) by TE‐1 cells which expressed EGF, TGF‐α and EGFR mRNA and protein. These results strongly suggest that EGF and/or TGF‐α produced by carcinoma cells function as autocrine growth factors for human esophageal carcinomas.