Rat pituitary GC cell insulin-like growth factor-I receptor regulation.
Exposure of rat GC pituitary cells to insulin-like growth factor-I (IGF-I) resulted in a time- and concentration-dependent reduction in cell surface IGF-I receptor binding. Preincubation of cells with 6.5 nM IGF-I for 24 h caused an approximately 50% reduction of the number of cell surface receptors. Scatchard analysis revealed that the number of IGF-I cell surface receptors decreased from 18,500 to 9,100 sites/cell, with no apparent alteration in the affinity of IGF-I receptor for its ligand. The level of IGF-I receptor mRNA, however, was not altered by preincubating cells for up to 24 h with 6.5 nM IGF-I. The sequestered IGF-I receptors reappeared on the cell membrane and return to their preincubation surface distribution within 3 h after removal of IGF-I. These results support the notion that down-regulation of somatotroph IGF-I receptors involves translocation of cell surface receptors to the intracellular pool, and this effect is reversed by removal of IGF-I ligand.
Yamamoto
H
H
Department of Medicine, Cedars-Sinai Medical Center, University of California School of Medicine, Los Angeles 90048.
Prager
D
D
Yamasaki
H
H
Melmed
S
S
D000818:Animals; D001667:Binding, Competitive; D002352:Carrier Proteins / Q000378:metabolism; D002478:Cells, Cultured; D004305:Dose-Response Relationship, Drug; D015536:Down-Regulation; D004591:Electrophoresis, Polyacrylamide Gel; D018969:Insulin-Like Growth Factor Binding Proteins; D007334:Insulin-Like Growth Factor I / Q000008:administration & dosage / Q000378:metabolism / Q000494:pharmacology; D007335:Insulin-Like Growth Factor II / Q000494:pharmacology; D007700:Kinetics; D010902:Pituitary Gland / Q000378:metabolism*; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D017526:Receptor, IGF Type 1 / Q000235:genetics / Q000378:metabolism*
D002352:Carrier Proteins; D018969:Insulin-Like Growth Factor Binding Proteins; D012333:RNA, Messenger; D007334:Insulin-Like Growth Factor I; D007335:Insulin-Like Growth Factor II; D017526:Receptor, IGF Type 1