Insulin and glucocorticoids regulate IGFBP-1 expression via a common promoter region

Hepatic expression of insulin-like growth factor binding protein-1 is regulated by insulin and glucocorticoids. To study underlying mechanisms, rat hepatocytes in primary culture were transfected with deletion mutants and heterologous promoter constructs, identifying a 41 bp region of the rat insulin-like growth factor binding protein-1 promoter which is sufficient to mediate regulation by both insulin and glucocorticoids. Half maximal suppression of promoter activity by insulin occurred at a physiologic concentration, 5 x 10(-10) M, and regulation by insulin was dominant in that insulin suppressed promoter activity at all dexamethasone concentrations. Transfection of rat hepatocytes in primary culture should be a useful approach for exploring the regulation of gene expression by insulin.