We have previously shown that four human oesophageal squamous cell carcinoma (SCC) cell lines secrete significant quantities of transforming growth factor alpha (TGF-α) in vitro. Three of these lines are known to produce supernumary low-affinity epidermal growth factor receptors (EGF-Rs). Using an125I-EGF compeitive binding assay and Scatchard analysis, we show that the fourth also overproduces low-affinity receptors. According to slot blot DNA analyses, the secretion of high levels of TGF-α is not associated with amplification of the TGF-α gene, and hyperproduction of the EGF-R is correlated with receptor gene amplification. Western blot analyses show that the c-Myc protein is overexpressed in two of the cell lines; and Southern and Northern blot analyses indicate that this overexpression occurs independently of c-myc gene amplification. Our results are consistent with an autocrine role for TGF-α and EGF-R in oesophageal carcinogenesis and support the possibility that c-myc overexpression may be required for the in vivo tumourigenicity of cells that produce high levels of TGF-α and the EGF-R.

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