Insulin-like growth factor-I is internalized after binding to the type I insulin-like growth factor receptor.
Receptor-mediated endocytosis may represent an important mechanism whereby peptide hormones exert their biological effects. The ability of recombinant insulin-like growth factor (IGF)-I to be internalized by cultured cells was evaluated in BRL-3A2 cells, a rat liver-derived cell line which lacks insulin receptors. Since recombinant IGF-I does not bind to the Type II IGF receptor, all specific binding of 125I-IGF-I in BRL-3A2 cells represents binding to the Type I receptor. Exposure of BRL-3A2 cells to IGF-I resulted in a rapid 50% downregulation of Type I IGF receptors. Only one-half of these binding sites were sensitive to treatment with trypsin, a phenomenon which indicates that the peptide and its receptor were internalized after the cells were exposed to IGF-I. In conclusion, these experiments demonstrate that IGF-I can be internalized by cultured cells via the Type I IGF receptor, and suggest that IGF hormone action may be exerted by receptor-mediated endocytosis.
Geary
E S
ES
Department of Medicine, Stanford University School of Medicine, California.
Rosenfeld
R G
RG
Hoffman
A R
AR
D000818:Animals; D002460:Cell Line; D004705:Endocytosis; D007334:Insulin-Like Growth Factor I / Q000378:metabolism*; D051381:Rats; D011956:Receptors, Cell Surface / Q000235:genetics / Q000378:metabolism*; D017451:Receptors, Somatomedin; D013002:Somatomedins / Q000378:metabolism*
D011956:Receptors, Cell Surface; D017451:Receptors, Somatomedin; D013002:Somatomedins; D007334:Insulin-Like Growth Factor I