Characterization of Receptors for Insulin and Insulin-Like Growth Factor-1 on FRTL-5 Thyroid Cells
The development of the FRTL and FRTL-5 thyroid cells (Fig. 1A) by F.S. Ambesi-Impiombato and his colleagues (1,2) moved research in the thyroid area from a concern with the thyrotropin receptor to an examination of receptor interactions or cross-talk. These cells require TSH for their growth (Fig. 1B). However, the TSH action requires the presence of insulin and serum factors, one of which we now know to be IGF-I (Fig. 1B); no single factor, TSH, insulin, or IGF-I, can reproduce the mixture of all. Further it is evident that the insulin and IGF-I actions are not identical; thus when concentrations of insulin as high as 10 micrograms per ml are present, the addition of only 50 or 100 ng/ml of IGF-I is still significantly additive to TSH and insulin in stimulating an increase in cell number.
KeywordsInsulin Receptor Thyroid Cell Insulin Binding Scatchard Plot Normal Human Serum
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