The chum salmon insulin-like growth factor II promoter requires Sp1 for its activation by C/EBP beta

The chum salmon insulin-like growth factor II (IGF-II) gene is highly expre ssed in liver tissue. In this study we demonstrate that two transcription f actors, Sp1 and C/EBP beta, are involved in the enhanced expression of the salmon IGF-II gene. The presence of the fish homolog for C/EBP beta in salm on liver RNA was confirmed by Northern blotting. The sIGF-II promoter was a ctivated up to 20-fold by co-transfection with C/EBP beta. The functional i mportance of four out of the five putative C/EBP beta binding sites was dem onstrated with mutational analysis in transient transfection assays. The tr anscription factor Sp1 binds to two sites within the salmon IGF-II promoter . Interestingly, mutation of the Sp1 binding sites decreases not only the b asal IGF-II promoter activity but also the C/EBP beta -induced transactivat ion. These results demonstrate that liver-enriched C/EBP beta and ubiquitou sly expressed Sp1 each activate the sIGF-II promoter and that Sp1 is requir ed for full transactivation of the sIGF-II gene by C/EBP beta. This suggest s that C/EBP beta and Spl act in synergy. (C) 2001 Elsevier Science Ireland Ltd. All rights reserved.