Postnatal liver-specific expression of human insulin-like growth factor-II is highly stimulated by the transcriptional activators liver-enriched activating protein and CCAAT/enhancer binding protein-alpha.
Transcription of the human gene encoding insulin-like growth factor II (IGF-II) is directed by four promoters (P1-P4), which are active in a tissue- and development-dependent manner. High levels of IGF-II in postnatal serum are due to activation of P1 in the liver. Since liver tissue contains high levels of the bZIP factors, liver-enriched activating protein (LAP), the CCAAT/enhancer binding protein-alpha (C/EBP alpha), and the D-element binding protein (DBP), and since P1 contains a functional C/EBP alpha binding site (P1 CBS), we have examined the role of these transcription factors in the activation of IGF-II P1. Transient transfection experiments reveal that P1 can be activated up to 15-fold by LAP and up to 6-fold by C/EBP alpha but can not be activated by DBP. Electrophoretic mobility shift assays with liver nuclear extract show that P1 CBS is predominantly bound by LAP and C/EBP alpha. Mutational analysis of P1 CBS indicates that DBP binding is prevented by one distinct G-C base pair in the P1 CBS element. The P1 CBS element is a high affinity binding site, which was demonstrated by comparing P1 CBS with other LAP-C/EBP alpha binding sites employing quantitative electrophoretic mobility shift assay. These results indicate that LAP and C/EBP alpha are major contributors to the postnatal liver-specific activation of the human IGF-II promoter P1.
Rodenburg
R J
RJ
Laboratory for Physiological Chemistry, Graduate School of Developmental Biology, Utrecht University, The Netherlands.
Teertstra
W
W
Holthuizen
P E
PE
Sussenbach
J S
JS
D001483:Base Sequence; D001665:Binding Sites; D022782:CCAAT-Enhancer-Binding Protein-beta; D022762:CCAAT-Enhancer-Binding Proteins; D006528:Carcinoma, Hepatocellular / Q000473:pathology; D004268:DNA-Binding Proteins / Q000494:pharmacology*; D018507:Gene Expression Regulation, Developmental / Q000187:drug effects*; D006367:HeLa Cells / Q000187:drug effects; D006801:Humans; D007335:Insulin-Like Growth Factor II / Q000096:biosynthesis* / Q000235:genetics; D008099:Liver / Q000254:growth & development / Q000378:metabolism*; D008113:Liver Neoplasms / Q000473:pathology; D008969:Molecular Sequence Data; D009687:Nuclear Proteins / Q000494:pharmacology*; D011401:Promoter Regions, Genetic / Q000187:drug effects; D011485:Protein Binding; D011993:Recombinant Fusion Proteins / Q000096:biosynthesis; D012045:Regulatory Sequences, Nucleic Acid; D012097:Repressor Proteins / Q000494:pharmacology; D014157:Transcription Factors / Q000494:pharmacology; D014158:Transcription, Genetic / Q000187:drug effects*; D014407:Tumor Cells, Cultured / Q000187:drug effects
D022782:CCAAT-Enhancer-Binding Protein-beta; D022762:CCAAT-Enhancer-Binding Proteins; C063898:DBP protein, human; D004268:DNA-Binding Proteins; D009687:Nuclear Proteins; D011993:Recombinant Fusion Proteins; D012097:Repressor Proteins; D014157:Transcription Factors; D007335:Insulin-Like Growth Factor II