Glucocorticoid regulation of insulin-like growth factor-binding protein-3.
Short stature and decreased growth velocity are prominent features of endogenous and pharmacological glucocorticoid excess in children. Underlying processes may involve direct cellular effects or defective generation of insulin-like growth factors (IGFs) and/or IGF-binding proteins (IGFBPs), which modulate IGF-stimulated events and regulate growth. To evaluate potential mechanisms, we investigated the impact of dexamethasone (dex) on hepatic expression of IGFBP-3, the major carrier protein for IGFs. Using cocultured hepatic parenchymal and nonparenchymal cells, dex at 10(-8) and 10(-6) M decreased IGFBP-3 secretion by 67 +/- 9% and 73 +/- 9%, respectively (both P < 0.05 vs. no dex). In a separate experiment, IGFBP-3 messenger RNA (mRNA) expression was decreased by 84 +/- 2% and 75 +/- 2% (both P < 0.05 vs. no dex). In combined studies, levels of IGFBP-3 protein in conditioned medium were strongly correlated with the abundance of IGFBP-3 mRNA (r = 0.75; P < 0.01), consistent with regulation at a pretranslational level. After inhibition of transcription, levels of IGFBP-3 mRNA decreased 85% and 86% over 24 h in cells cultured in 10(-6) M and no dex, respectively; the t1/2 was 13.6 h at 10(-6) M and 12.6 h with no dex, indicating that dex had no effect on IGFBP-3 mRNA stability. To evaluate transcriptional effects, the rate of IGFBP-3 gene transcription was measured by incorporation of [alpha-32P]UTP into preinitiated message in isolated nuclei and fell 78% after the addition of 10(-6) M dex for 48 h (compared to cells cultured in 10(-9) M dex), an inhibition of a magnitude similar to the effects on protein release and mRNA abundance. We conclude that dex may reduce the production of IGFBP-3 by inhibiting IGFBP-3 gene transcription.
Villafuerte
B C
BC
Division of Endocrinology and Metabolism, Emory University School of Medicine, Atlanta, Georgia 30322, USA.
Koop
B L
BL
Pao
C I
CI
Phillips
L S
LS
D000818:Animals; D015152:Blotting, Northern; D002352:Carrier Proteins / Q000096:biosynthesis*; D002467:Cell Nucleus / Q000378:metabolism; D002478:Cells, Cultured; D002648:Child; D003907:Dexamethasone / Q000494:pharmacology*; D015870:Gene Expression / Q000187:drug effects; D006801:Humans; D018969:Insulin-Like Growth Factor Binding Proteins; D007700:Kinetics; D008099:Liver / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D013002:Somatomedins / Q000378:metabolism; D013997:Time Factors; D014158:Transcription, Genetic
D002352:Carrier Proteins; D018969:Insulin-Like Growth Factor Binding Proteins; D013002:Somatomedins; D003907:Dexamethasone