Growth factors regulate the synthesis of insulin-like growth factor-I in bone cell cultures.
Insulin-like growth factor-I (IGF-I), a prevalent growth factor secreted by bone cells, has important effects on bone remodeling. Hormones are known to regulate the synthesis of skeletal IGF-I, but there is limited information about the actions of growth factors on IGF-I synthesis. We tested the effects of basic fibroblast growth factor (bFGF), transforming growth factor-beta 1 (TGF beta 1), and platelet-derived growth factors (PDGF) AA and BB on IGF-I mRNA expression and polypeptide concentrations in cultures of osteoblast-enriched (Ob) cells from 22-day-old fetal rat calvariae. Steady state IGF-I mRNA levels were determined by Northern blot analysis, and IGF-I concentrations were determined in acidified and fractionated culture medium by a specific RIA. Treatment of Ob cells with bFGF at 0.06-6 nM, TGF beta 1 at 0.04-4 nM, and PDGF BB at 0.3-3.3 nM caused a dose-dependent decrease in steady state IGF-I mRNA. A smaller effect was observed with PDGF AA. The effect was initially observed after 6-8 h of treatment and was maximal after 16 h. Treatment with bFGF at 0.6-6 nM, TGF beta 1 at 0.4-4 nM, and PDGF BB at 0.3-3.3 nM for 24 h decreased IGF-I polypeptide concentrations by 40-80%. The effects of bFGF, TGF beta 1, and PDGF BB and AA on IGF-I mRNA were independent of protein synthesis and cell division, as they were observed in the presence and absence of cycloheximide at 3.6 microM or hydroxyurea at 1 mM. Similarly, their inhibitory actions on immunoreactive IGF-I were not prevented by hydroxyurea. In conclusion, bFGF, TGF beta 1, PDGF BB, and, to a lesser extent, PDGF AA decrease skeletal IGF-I synthesis by reducing IGF-I transcript levels, and this effect may contribute to their actions on selected aspects of Ob cell function.
Canalis
E
E
Department of Research, Saint Francis Hospital and Medical Center, Hartford, Connecticut 06105.
Pash
J
J
Gabbitas
B
B
Rydziel
S
S
Varghese
S
S
D000818:Animals; D000077214:Becaplermin; D015152:Blotting, Northern; D001842:Bone and Bones / Q000187:drug effects / Q000378:metabolism*; D002478:Cells, Cultured; D003513:Cycloheximide / Q000494:pharmacology; D004622:Embryo, Mammalian; D016222:Fibroblast Growth Factor 2 / Q000494:pharmacology; D006133:Growth Substances / Q000494:pharmacology*; D006918:Hydroxyurea / Q000494:pharmacology; D007334:Insulin-Like Growth Factor I / Q000096:biosynthesis* / Q000235:genetics; D010006:Osteoblasts / Q000378:metabolism; D010982:Platelet-Derived Growth Factor / Q000494:pharmacology; D020574:Proto-Oncogene Proteins c-sis; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D011994:Recombinant Proteins; D016212:Transforming Growth Factor beta / Q000494:pharmacology
D006133:Growth Substances; D010982:Platelet-Derived Growth Factor; D020574:Proto-Oncogene Proteins c-sis; D012333:RNA, Messenger; D011994:Recombinant Proteins; D016212:Transforming Growth Factor beta; C075278:platelet-derived growth factor A; D016222:Fibroblast Growth Factor 2; D000077214:Becaplermin; D007334:Insulin-Like Growth Factor I; D003513:Cycloheximide; D006918:Hydroxyurea