Multiple proteins bind the insulin response element in the human IGFBP-1 promoter

An insulin response element (IRE) has been identified ∼100 base pairs (bp) 5′ to the transcription start site of the human insulin-like growth factor binding protein-1 (hIGFBP-1) gene. This cis element appears crucial to the multihormonal regulation of hIGFBP-1 expression in liver, since (i) an intact IRE is required for maximal stimulation of hIGFBP-1 promoter activity by dexamethasone, and (ii) the IRE confers activity. Further progress in understanding how the IRE confers insulin and glucocorticoid effects requires identification of transcription factors confering effects of these hormones. D-site binding protein (DBP), and members of the hepatic nuclear factor 3 (HNF 3) and high mobility group I/Y (HMG I/Y) protein families, each known to bind DNA elements similar in sequence to the IRE, were tested for IRE binding. DBP, HMGI and HNF 3β each protected the hIGFBP-1 IRE from DN AseI digestion. Additional studies are required to establish whether binding of any of these proteins to the IRE is important to the regulation of hIGFBP-1 expression by insulin and/or glucocorticoids.