Human Insulin-Like Growth Factor I (IGF-I) Produced in the Mammary Glands of Transgenic Rabbits: Yield, Receptor Binding, Mitogenic Activity, and Effects on IGF-Binding Proteins

Insulin-like growth factor I (IGF-I) has acute insulin-like metabolic effects and long-term anabolic actions offering a range of important therapeutic applications. To evaluate a system for large-scale production of this peptide in the mammary glands of transgenic livestock, we generated transgenic rabbits carrying fusion genes in which a synthetic DNA coding for human IGF-I (hIGF-I) was placed under the transcriptional control of regulatory elements isolated from the bovine αS1-casein (αS1-cas) gene. Western blot analysis of milk from αS1-cas-hIGF-I transgenic rabbits demonstrated production of high amounts of mature hIGF-I peptide (7.6 kDa). Quantitative analysis by RIA revealed hIGF-I levels between 50 and 300 μg/ml milk. Recombinant hIGF-I purified from the milk of αS1-cas-hIGF-I transgenic rabbits bound to IGF-I receptors on human IM-9 lymphoblasts and stimulated DNA synthesis by growth-arrested MG-63 human osteosarcoma cells as efficiently as hIGF-I produced in Escherichia coli. Ligand blot analysis...