The chum salmon insulin-like growth factor II promoter requires Sp1 for its activation by C/EBPbeta.
The chum salmon insulin-like growth factor II (IGF-II) gene is highly expressed in liver tissue. In this study we demonstrate that two transcription factors, Sp1 and C/EBPbeta, are involved in the enhanced expression of the salmon IGF-II gene. The presence of the fish homolog for C/EBPbeta in salmon liver RNA was confirmed by Northern blotting. The sIGF-II promoter was activated up to 20-fold by co-transfection with C/EBPbeta. The functional importance of four out of the five putative C/EBPbeta binding sites was demonstrated with mutational analysis in transient transfection assays. The transcription factor Sp1 binds to two sites within the salmon IGF-II promoter. Interestingly, mutation of the Sp1 binding sites decreases not only the basal IGF-II promoter activity but also the C/EBPbeta-induced transactivation. These results demonstrate that liver-enriched C/EBPbeta and ubiquitously expressed Sp1 each activate the sIGF-II promoter and that Sp1 is required for full transactivation of the sIGF-II gene by C/EBPbeta. This suggests that C/EBPbeta and Sp1 act in synergy.
Palamarchuk
A Y
AY
Laboratory for Physiological Chemistry, University Medical Center, Universiteitsweg 100, 3584 CG, Utrecht, The Netherlands.
Kavsan
V M
VM
Sussenbach
J S
JS
Holthuizen
P E
PE
D000818:Animals; D001483:Base Sequence; D001665:Binding Sites / Q000235:genetics; D015152:Blotting, Northern; D022782:CCAAT-Enhancer-Binding Protein-beta / Q000494:pharmacology*; D004357:Drug Synergism; D007334:Insulin-Like Growth Factor I / Q000235:genetics*; D008099:Liver / Q000378:metabolism; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D017685:Oncorhynchus keta / Q000235:genetics*; D011401:Promoter Regions, Genetic / Q000187:drug effects*; D012333:RNA, Messenger / Q000032:analysis; D016329:Sp1 Transcription Factor / Q000494:pharmacology*; D015533:Transcriptional Activation / Q000187:drug effects
D022782:CCAAT-Enhancer-Binding Protein-beta; D012333:RNA, Messenger; D016329:Sp1 Transcription Factor; D007334:Insulin-Like Growth Factor I