Variation in EGF-induced EGF receptor downregulation in human hepatoma-derived cell lines expressing different amounts of EGF receptor.
The effect of epidermal growth factor (EGF) receptor overexpression on ligand-induced EGF receptor downregulation was examined using a hepatoma-derived cell line, PLC/PRF/5, which expresses normal amounts of the EGF receptor, and a subline, NPLC/PRF/5, which expresses 10-fold more receptors at its cell surface. PLC/PRF/5 cells efficiently downregulated surface receptor levels upon exposure to saturating and subsaturating concentrations of EGF; the rate of receptor downregulation corresponded to that of ligand-receptor internalization. Upon internalization, EGF receptors were degraded and receptor biosynthesis remained at basal levels. EGF surface receptor remained downregulated for as long as cells were exposed to EGF. By contrast, surface EGF receptor abundance in NPLC/PRF/5 cells decreased by only 5-15% after 1-4 h incubation with subsaturating doses of EGF and actually increased by 67% within 20 h. Exposure of these cells to saturating concentrations of EGF induced modest decreases in surface receptor abundance during the initial 12 h incubation, followed by a progressive decline to 30% of initial values by 24 h. Relative ligand-receptor internalization rates in NPLC/PRF/5 cells were lower than those in PLC/PRF/5, although their surface receptor population was even higher than that predicted by the decreased internalization rates. EGF receptor degradation in NPLC/PRF/5 cells was also inhibited; exposure to saturating levels of EGF for more than 16 h was necessary before significant degradation occurred. Receptor protein and mRNA biosynthesis in NPLC/PRF/5 were stimulated by 8 h exposure to EGF but when saturating concentrations of EGF were present for 16 h, receptor biosynthesis was inhibited. EGF receptor overexpression circumvents the downregulatory effect of EGF by decreasing the rate of receptor internalization, inhibiting degradation of the internalized receptor pool, and stimulating EGF receptor biosynthesis. Conversely, receptor downregulation becomes pronounced at late times when receptor degradation is high and biosynthesis is inhibited.
Gilligan
A
A
Wistar Institute of Anatomy and Biology, Philadelphia, Pennsylvania 19104.
Bushmeyer
S
S
Knowles
B B
BB
D006528:Carcinoma, Hepatocellular; D015536:Down-Regulation; D004705:Endocytosis; D004815:Epidermal Growth Factor / Q000378:metabolism; D066246:ErbB Receptors / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism*; D015870:Gene Expression; D006801:Humans; D066298:In Vitro Techniques; D007295:Inositol Phosphates / Q000378:metabolism; D008113:Liver Neoplasms; D012333:RNA, Messenger / Q000235:genetics; D015398:Signal Transduction; D014407:Tumor Cells, Cultured
D007295:Inositol Phosphates; D012333:RNA, Messenger; D004815:Epidermal Growth Factor; D066246:ErbB Receptors