Progesterone stimulation of human insulin-like growth factor-binding protein-5 gene transcription in human osteoblasts is mediated by a CACCC sequence in the proximal promoter.

Abstract

Insulin-like growth factor-binding protein-5 (IGFBP-5) is produced by osteoblasts and potentiates insulin-like growth factor mitogenic stimulation in osteoblast cell cultures. Progesterone (PG) increased IGFBP-5 expression in normal human osteoblasts and increased IGFBP-5 transcription in U2 human osteosarcoma cells. We developed a chloramphenicol acetyltransferase reporter construct containing the human IGFBP-5 proximal promoter sequence, which includes TATA and CAAT boxes, and five putative PG response element half-sites. 10(-8) M PG increased promoter activity of this construct in U2 cells co-transfected with a PG receptor isoform A (PR(A)) expression vector. Analysis of 5' deletion constructs indicates that PG transactivation of IGFBP-5 promoter activity does not require the PG response element half-sites but does require the region -162 to -124 containing two tandem CACCC box sequences. Mutation of the proximal CACCC box at -139 eliminated PG transactivation. Gel shift assays using a -162 to -124 DNA fragment, U2 cell nuclear extracts, and purified PR(A) protein indicate that nuclear factors bind to a CACCC sequence at -139 and that PR(A) alters the pattern of transcription factor interaction with the CACCC sequence. Using a luciferase reporter construct containing base pairs -252 to +24 of the IGFBP-5 promoter, we found that both PR(A) and PR(B) isoforms mediated PG stimulation of promoter activity. These results suggest that PG may stimulate IGFBP-5 gene transcription via a novel mechanism involving PR and CACCC-binding factors.

• Authors: V Boonyaratanakornkit, D D Strong, S Mohan, D J Baylink, C A Beck, T A Linkhart
• Journal: The Journal of biological chemistry (J Biol Chem) Vol. 274 Issue 37 Pg. 26431-8 (Sep 10 1999) ISSN: 0021-9258 [Print] United States
• PMID: 10473602 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't, Research Support, U.S. Gov't, Non-P.H.S., Research Support, U.S. Gov't, P.H.S.)

Chemical References

• DNA Primers
• Hormone Antagonists
• Insulin-Like Growth Factor Binding Protein 5
• Nuclear Proteins
• Mifepristone
• Progesterone

Topics

• Base Sequence
• DNA Primers
• Hormone Antagonists (pharmacology)
• Humans
• Insulin-Like Growth Factor Binding Protein 5 (genetics)
• Mifepristone (pharmacology)
• Nuclear Proteins (metabolism)
• Osteoblasts (drug effects, metabolism)
• Progesterone (pharmacology)
• Promoter Regions, Genetic
• Transcription, Genetic (drug effects)
• Tumor Cells, Cultured