The insulin receptor as a transmitter of a mitogenic signal in Chinese hamster ovary CHO-K1 cells.
Insulin is the only hormone required for continued growth of Chinese hamster ovary CHO-K1 cells in the defined medium M-F12. When CHO-K1 cells are incubated in M-F12 without insulin for 48-72 hr, the cells accumulate in G1. In response to physiological concentrations of insulin an 18-fold increase in rate of DNA synthesis occurs due to cells entering S phase after an 8- to 10-hr lag; cell division begins after 24 hr. The inhibitory effect of actinomycin D and 5,6-dichlorobenzimidazole riboside indicates that RNA synthesis is required for progression to S phase. CHO-K1 cells possess insulin receptors, and the insulin effect results from insulin binding to its own receptor: (i) Binding occurs at physiological insulin concentrations with a half-maximal stimulation at approximately 14 ng/ml. (ii) At insulin concentrations used, insulin-like growth factor I and II (IGF-I and IGF-II) have little or no effect. (iii) Scatchard analysis of 125I-labeled insulin binding shows the curvilinear response typical of insulin. (iv) The Kd for the so-called high-affinity binding site and the Ke are characteristic of the insulin receptor. (v) At the minimal insulin concentrations that stimulate growth, IGF-I and IGF-II compete poorly with insulin for insulin binding, insulin competes poorly with IGF-I for IGF-I binding, and affinity labeling with 125I-labeled insulin identifies a polypeptide (Mr = 125,000) typical of the alpha subunit of the insulin receptor.
Mamounas
M
M
Cell and Physiology Section, University of California, Santa Barbara 93106.
Gervin
D
D
Englesberg
E
E
D000818:Animals; D001667:Binding, Competitive; D002453:Cell Cycle / Q000187:drug effects*; D002455:Cell Division / Q000187:drug effects; D002460:Cell Line; D006224:Cricetinae; D003412:Cricetulus; D004261:DNA Replication / Q000187:drug effects*; D003609:Dactinomycin / Q000494:pharmacology; D005260:Female; D007328:Insulin / Q000378:metabolism / Q000494:pharmacology*; D007399:Interphase / Q000187:drug effects; D007700:Kinetics; D008934:Mitogens; D010053:Ovary; D011972:Receptor, Insulin / Q000502:physiology*; D013002:Somatomedins / Q000494:pharmacology
D007328:Insulin; D008934:Mitogens; D013002:Somatomedins; D003609:Dactinomycin; D011972:Receptor, Insulin