IDENTIFICATION OF NOVEL PROMOTER AND REPRESSOR ELEMENTS IN THE 5'-FLANKING REGIONS OF THE RAT INSULIN-LIKE GROWTH-FACTOR-I GENE

Although the major endocrine source of insulin-like growth factor-I (I GF-I) is the liver, little is known about IGF-I transcriptional mechan isms in this tissue. To evaluate the role of cis-regulatory elements, rat hepatocytes in primary culture were transfected with DNA construct s containing IGF-I 5' flanking sequences, fused to a luciferase report er. We demonstrate the presence of a novel promoter similar to 0.5 kb upstream from exon 1 transcription initiation sites, together with a r epressor element in this region, and a downstream repressor element wh ich can modulate the activity of both endogenous and heterologous prom oters. (C) 1995 Academic Press, Inc.