Expression of a synthetic gene encoding human insulin-like growth factor I in cultured mouse fibroblasts

A synthetic gene encoding human insulin-like growth factor I (hIGF-I) was assembled and inserted into an expression vector containing the cytomegalovirus immediate early (CMV-IE) transcriptional regulatory region and portions of the bovine growth hormone gene. The recombinant plasmid encodes a 97 amino acid fusion protein containing the first 27 amino acids of the bovine growth hormone precursor and the 70 amino acids of hIGF-I. This plasmid, when transiently introduced into cultured mouse fibroblasts, directs synthesis of the fusion protein, subsequent proteolytic removal of the bovine growth hormone signal peptide, and secretion of hIGF-I into the culture medium. Conditioned medium from transfected cells inhibits binding of 125I-labeled IGF-I to type I IGF receptors on human placental membranes and to acid-stable human serum carrier proteins. The recombinant hIGF-I produced is biologically active, as monitored by the stimulation of DNA synthesis in vascular smooth muscle cells.