Amplification and expression of the TGF-α, EGF receptor and c-myc genes in four human oesophageal squamous cell carcinoma lines

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.