Conversion of epidermal growth factor (EGF) into a stimulatory ligand for A431-cell growth by herbimycin A by decreasing the level of expression of EGF receptor.
We examined effect of the tyrosine kinase inhibitor herbimycin A on A431 human epidermoid carcinoma cells which over-express epidermal growth factor (EGF) receptor. Herbimycin A inhibited the autophosphorylation of EGF-stimulated receptors in intact cells both time- and dose-dependently. The inhibition was found to be due to a decrease in the level of expression of the receptor amount, because herbimycin A equally decreased the receptor quantity and EGF-stimulated receptor kinase activity in intact cells, but did not exhibit a direct inhibitory effect on EGF receptor kinase activity in vitro. The decrease of the level of EGF receptor was also confirmed by 125I-EGF binding to herbimycin A-treated cells, and Scatchard analysis showed that the decrease in the receptor number occurred in the major population of the low-affinity binding ones, whereas the number with high-affinity binding was unaffected. Interestingly, although the proliferation of A431 cells was inhibited by EGF, herbimycin A converted EGF into a stimulatory ligand for cell growth, as determined by both cell number and DNA synthesis. These findings indicated that herbimycin A decreased the level of expression of EGF receptor by a mechanism other than inactivation of the receptor kinase and reversed the transformed phenotype of A431 cells to a normal one in the proliferative response to EGF.
Murakami
Y
Y
Department of Bioactive Molecules, National Institute of Health, Tokyo, Japan.
Fukazawa
H
H
Mizuno
S
S
Uehara
Y
Y
D016227:Benzoquinones; D002294:Carcinoma, Squamous Cell / Q000378:metabolism / Q000473:pathology; D002455:Cell Division / Q000187:drug effects; D004815:Epidermal Growth Factor / Q000378:metabolism*; D066246:ErbB Receptors / Q000187:drug effects* / Q000378:metabolism; D006801:Humans; D047029:Lactams, Macrocyclic; D008024:Ligands; D010766:Phosphorylation; D011505:Protein-Tyrosine Kinases / Q000037:antagonists & inhibitors; D011809:Quinones / Q000494:pharmacology*; D017828:Rifabutin / Q000031:analogs & derivatives; D014407:Tumor Cells, Cultured / Q000166:cytology / Q000187:drug effects / Q000378:metabolism
D016227:Benzoquinones; D047029:Lactams, Macrocyclic; D008024:Ligands; D011809:Quinones; D017828:Rifabutin; D004815:Epidermal Growth Factor; C020754:herbimycin; D066246:ErbB Receptors; D011505:Protein-Tyrosine Kinases