Transcriptional regulation of insulin-like growth factor-II gene expression by cortisol in fetal sheep during late gestation.
The objective of this study was to determine the mechanisms by which cortisol down-regulates hepatic insulin-like growth factor-II (IGF-II) gene expression in late gestation. Leader exons 6 and 7 of the ovine IGF-II gene, with their 5'-flanking regions, were first isolated. Characterization of transcription start sites revealed a unique site for exon 6 and three dispersed sites for exon 7. Nuclear run-on assays showed a 5-fold higher transcription rate of the IGF-II gene in liver of adrenalectomized fetuses compared with control animals, suggesting that regulation of IGF-II gene expression by cortisol is at the transcriptional level. RNase protection assays demonstrated hepatic leader exon 7 expression in adrenalectomized fetuses to be more than 2-fold higher than in controls, whereas it was reduced by 50% in cortisol-infused fetuses compared with controls. There was no effect on the expression of other leader exons. Functions of the upstream regulatory region of leader exon 7 (i.e. promoter P4) were investigated by luciferase transient expression. A region of -172 bases downstream relative to the first transcription site of leader exon 7 was shown to retain basal promoter activity and respond to cortisol. These results suggest that cortisol may induce the prenatal decline in ovine hepatic IGF-II expression by suppressing promoter P4 of the IGF-II gene.
Li
J
J
Department of Cellular Physiology, Babraham Institute, Babraham, Cambridge CB2 4AT, United Kingdom.
Saunders
J C
JC
Fowden
A L
AL
Dauncey
M J
MJ
Gilmour
R S
RS
D000818:Animals; D001483:Base Sequence; D003001:Cloning, Molecular; D018076:DNA, Complementary; D005333:Fetus / Q000378:metabolism*; D018507:Gene Expression Regulation, Developmental / Q000187:drug effects*; D006801:Humans; D006854:Hydrocortisone / Q000494:pharmacology*; D007335:Insulin-Like Growth Factor II / Q000235:genetics*; D008099:Liver / Q000196:embryology / Q000378:metabolism; D008969:Molecular Sequence Data; D011401:Promoter Regions, Genetic; D012045:Regulatory Sequences, Nucleic Acid; D012689:Sequence Homology, Nucleic Acid; D012756:Sheep / Q000196:embryology; D014158:Transcription, Genetic
D018076:DNA, Complementary; D007335:Insulin-Like Growth Factor II; D006854:Hydrocortisone