Cortisol enhances the expression of mac25/insulin-like growth factor-binding protein-related protein-1 in cultured osteoblasts.
Glucocorticoids inhibit the synthesis of insulin-like growth factor I (IGF-I) and regulate the expression of IGF-binding proteins (IGFBPs) in osteoblast cultures. IGFBP-related protein-1 (IGFBP-rP1), the product of the mac25 gene, binds IGF-I, IGF-II, and insulin, and we postulated that glucocorticoids regulate IGFBP-rP1 synthesis in osteoblasts. We tested the expression of mac25/IGFBP-rP1 in cultures of osteoblast-enriched cells from 22-day-old fetal rat calvariae (Ob cells). Cortisol treatment at 10 nM to 1 microM for 24-48 h caused a time- and dose-dependent increase in mac25/IGFBP-rP1 messenger RNA (mRNA) levels in Ob cells. Cycloheximide at 3.6 microM did not alter mac25/IGFBP-rP1 transcripts in control or cortisol-treated cells. Cortisol did not modify the decay of mac25/IGFBP-rP1 mRNA in transcriptionally arrested Ob cells and increased the rate of IGFBP-rP1 transcription as determined by nuclear run-on assays. Retinoic acid also increased mac25/IGFBP-rP1 mRNA levels, but 17beta-estradiol, testosterone, 5alpha-dihydrotestosterone, progesterone, and 1,25-dihydroxyvitamin D3 did not. In conclusion, cortisol stimulates mac25/IGFBP-rP1 expression in Ob cells by transcriptional mechanisms. As IGFBP-rP1 binds and possibly modifies the effects of IGFs and insulin, its increased expression could be relevant to the inhibitory actions of cortisol in bone.
Pereira
R C
RC
Department of Research, Saint Francis Hospital and Medical Center, Hartford, Connecticut 06105, USA.
Blanquaert
F
F
Canalis
E
E
D000818:Animals; D015152:Blotting, Northern; D002352:Carrier Proteins / Q000096:biosynthesis* / Q000235:genetics*; D002478:Cells, Cultured; D004591:Electrophoresis, Polyacrylamide Gel; D005786:Gene Expression Regulation / Q000187:drug effects*; D006854:Hydrocortisone / Q000494:pharmacology*; D018969:Insulin-Like Growth Factor Binding Proteins / Q000096:biosynthesis*; D010006:Osteoblasts / Q000187:drug effects / Q000378:metabolism*; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats
D002352:Carrier Proteins; D018969:Insulin-Like Growth Factor Binding Proteins; D012333:RNA, Messenger; C102529:insulin-like growth factor binding protein-related protein 1; D006854:Hydrocortisone