Different responses to EGF in two human carcinoma cell lines, A431 and UCVA-1, possessing high numbers of EGF receptors

Abstract EGF binding capacity was examined in 9 different human cell lines which were derived from colon, rectum and pancreas tumors. Among these cell lines, a pancreatic carcinoma cell line, UCVA-1, was found to possess a high number (0.9 × 10 6 /cell) of EGF receptors. This number is comparable to that of EGF receptors in human vulva epidermoid carcinoma A431 cells (2 × 10 6 /cell). However, it was found that, unlike A431 cells, the growth of UCVA-1 cells, in serum-containing and serum-free conditions, was not inhibited by EGF. The UCVA-1 cells have EGF receptor of M r = 170 K and of two affinity types: K d1 = 2 × 10 −9 M and K d2 = 2 × 10 −8 M. The EGF receptors in UCVA-1 cells are less susceptible to proteolytic cleavage than those in A431 cells. In UCVA-1 cells, EGF is apparently processed via a receptor-mediated endocytosis. The UCVA-1 cell membrane contained EGF-stimulated protein kinase as was found in A431 cells. The stimulation of phosphorylation by EGF was only ∼ 20% in UCVA-1 while it was over 100% in A431. When angiotensin II was used as a substrate, the relative activity of EGF-dependent tyrosine-specific protein phosphorylation was ∼ 8 times less in UCVA-1 cell membrane. The EGF-stimulated phosphorylation was mostly on EGF receptors for both cell lines. However, several other components ( M r = 100 K, 80 K, 72 K and 65 K) were readily detected in A431 cells. These observations indicate that the EGF receptor/protein kinase relation differs in these two cell lines and suggests that it may be related to the growth-inhibitory effect of EGF seen in A431.