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 mechanis ms, rat hepatocytes in primary culture were transfected with deletion mutants and heterologous promoter constructs, identifying a 41 bp regi on of the rat insulin-like growth factor binding protein-1 promoter wh ich is sufficient to mediate regulation by both insulin and glucocorti coids. Half maximal suppression of promoter activity by insulin occurr ed at a physiologic concentration, 5 x 10(-10) M, and regulation by in sulin was dominant in that insulin suppressed promoter activity at all dexamethasone concentrations. Transfection of rat hepatocytes in prim ary culture should be a useful approach for exploring the regulation o f gene expression by insulin. (C) 1994 Academic Press, Inc.