CHARACTERIZATION OF A TELEOST INSULIN-LIKE-GROWTH-FACTOR-II (IGF-II) GENE - EVIDENCE FOR PROMOTER CCAAT ENHANCER-BINDING PROTEIN (C/EBP) SITES, AND THE PRESENCE OF HEPATIC C/EBP/

Insulin-like growth factor I (IGF-I) and IGF-II, acting under the regu latory control of growth hormone, are the principal mediators of verte brate growth. We have previously demonstrated that like humans, but un like rodents, rainbow trout maintain high hepatic IGF-II messenger RNA levels into adulthood. Here we describe a rainbow trout IGF-II gene w ith a proximal promoter that contains two CCAAT/enhancer-binding prote in (C/EBP) binding sites (TCBS1 and TCBS2). Nuclear proteins correspon ding in size to rat C/EBP alpha and C/EBP beta were detected on Wester n immunoblots of growth-hormone-treated and mock-treated trout liver e xtracts. Electrophoretic mobility shift assay of these nuclear extract s further suggests the presence of C/EBPs in trout liver and confirms the ability of TCBS1 to form a complex with trout liver nuclear protei ns that is identical in mobility and specificity to that formed by a m ammalian consensus CBS construct. In both Western blot and mobility as say results, the growth-hormone-treated trout livers appeared to have a greater accumulation of C/EBP, suggesting a molecular mechanism by w hich growth hormone can influence the level of serum IGF-II.