Multiple liver-enriched trans-acting factors interact with the glucocorticoid- (GRU) and cAMP-(CRU) responsive units within the h-IGFBP-1 promoter.
In response to hormonal control, serum concentrations of insulin-like growth factor-binding protein-1 (IGFBP-1) may vary as much as 10-fold, owing to strict control of its gene's expression in hepatocytes. IGFBP-1 gene transcription is increased by glucocorticoids and cAMP and inhibited by insulin. The effect of insulin is dominant since it suppresses constitutive and both glucocorticoid- and cAMP-stimulated transcription. Close examination of the human (h)IGFBP-1 promoter sequences showed that the glucocorticoid (GRE, nt -88 to -102) and cAMP (CRE, nt -259 to -264) response elements are 5'-flanked by an A/T-rich imperfect palindrome (nt -102 to -117 and -265 to -285, respectively). These A/T-rich motifs are putative cis-elements for liver-enriched trans-acting factors. Competition experiments in electrophoretic mobility shift assay were carried out using rat liver nuclear extracts and a set of synthetic oligonucleotides designed from hIGFBP-1 Glucorticoid and cAMP Response Units (GRU and CRU), the rat transthyretin HNF3 cis-element and the "D-site' of the mouse albumin promoter. The nucleotide motifs located between nt -108 and -121 of the GRU, interacted with the HNF3 family of trans-acting factors (alpha, beta, gamma), whereas those encompassing nt -81 to -104 bound DBP and/or nuclear proteins sharing similar sequence specificity (i.e. from the C/EBP family of bZIP proteins). We have also shown that the hIGFBP-1-GRE binds glucocorticoid receptor homodimers. In the case of the CRU, the cis-elements located between nt -249 and -285 bound DBP and/or nuclear proteins sharing similar sequence specificities. In addition, the nucleotide stretch lying between nt -256 and -275 was able to interact with the HNF3 family of trans-acting factors. Our results support the view that the dominant inhibitory effect of insulin over glucocorticoid- and cAMP- enhanced transcription may be mediated by different target sequences located 5'- of the GRE and CRE. In both cases, the mechanism would involve the interplay of common trans-acting factor(s), some of which are liver-enriched [HNF3, DBP or C/EBP related bZIP proteins] with their cognate target sequence.
Neau
E
E
INSERM U.142, Hôpital Saint Antoine, Paris, France.
Chambéry
D
D
Schweizer-Groyer
G
G
Cadepond
F
F
Jibard
N
N
Groyer
A
A
D000818:Animals; D001667:Binding, Competitive; D022762:CCAAT-Enhancer-Binding Proteins; D016466:CHO Cells; D006224:Cricetinae; D000242:Cyclic AMP / Q000378:metabolism*; D017362:Cyclic AMP Response Element-Binding Protein / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000378:metabolism*; D005938:Glucocorticoids / Q000378:metabolism*; D006801:Humans; D018970:Insulin-Like Growth Factor Binding Protein 1 / Q000235:genetics*; D008099:Liver / Q000737:chemistry; D008297:Male; D051379:Mice; D009687:Nuclear Proteins / Q000378:metabolism*; D011401:Promoter Regions, Genetic; D051381:Rats; D017207:Rats, Sprague-Dawley; D011965:Receptors, Glucocorticoid / Q000378:metabolism; D014157:Transcription Factors / Q000378:metabolism*
D022762:CCAAT-Enhancer-Binding Proteins; D017362:Cyclic AMP Response Element-Binding Protein; D004268:DNA-Binding Proteins; D005938:Glucocorticoids; D018970:Insulin-Like Growth Factor Binding Protein 1; D009687:Nuclear Proteins; D011965:Receptors, Glucocorticoid; D014157:Transcription Factors; D000242:Cyclic AMP