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 (IGF-I) is the liver, little is known about IGF-I transcriptional mechanisms in this tissue. To evaluate the role of cis-regulatory elements, rat hepatocytes in primary culture were transfected with DNA constructs containing IGF-I 5'flanking sequences, fused to a luciferase reporter. We demonstrate the presence of a novel promoter approximately 0.5 kb upstream from exon 1 transcription initiation sites, together with a repressor element in this region, and a downstream repressor element which can modulate the activity of both endogenous and heterologous promoters.