Interleukin-6 and its soluble receptor regulate the expression of insulin-like growth factor binding protein-5 in osteoblast cultures.
Interleukin-6 (IL-6), a cytokine produced by bone cells, is known to influence bone resorption by stimulating the development of osteoclasts from precursor cells and to have mitogenic actions on osteoblastic cells. Insulin-like growth factors (IGFs) are important local regulators of bone formation, and IGF binding protein (IGFBP)-5 stimulates bone cell growth and enhances the effects of IGF-I. We tested the effects of IL-6 in the presence and absence of its soluble receptor (sIL-6R) on IGFBP-5 expression in cultures of osteoblast-enriched cells from 22-day-old fetal rat calvariae (Ob cells). When tested individually, IL-6 and sIL-6R had a modest stimulatory effect on IGFBP-5 messenger RNA (mRNA) levels. In contrast, when IL-6 and sIL-6R were tested in combination, they caused a considerable increase in IGFBP-5 mRNA levels, and IL-6 at 100 ng/ml and sIL-6R at 125 ng/ml increased IGFBP-5 transcripts by 5- to 7-fold after 24 h. The effect of IL-6 and sIL-6R on IGFBP-5 transcripts was not blocked by indomethacin, but cycloheximide markedly inhibited IGFBP-5 mRNA levels in control and treated cultures. IL-6 and sIL-6R did not modify the decay of IGFBP-5 mRNA in transcriptionally arrested Ob cells, and stimulated the rate of IGFBP-5 transcription as demonstrated by a nuclear run-on assay. IL-6 and sIL-6R did not increase intact IGFBP-5 levels in the extracellular matrix and increased IGFBP-5 fragments in the culture medium. Conditioned medium from Ob cells induced the proteolytic fragmentation of an IGFBP-5 standard, an effect that was accelerated and enhanced by conditioned medium from IL-6/sIL-6R-treated cultures and prevented by metalloprotease inhibitors. In conclusion, IL-6, in the presence of sIL-6R, stimulates IGFBP-5 mRNA expression in Ob cells by transcriptional mechanisms, and accelerates the fragmentation of the protein.
Franchimont
N
N
Department of Research, Saint Francis Hospital and Medical Center, Hartford, Connecticut 06105, USA.
Durant
D
D
Canalis
E
E
D000818:Animals; D015703:Antigens, CD / Q000502:physiology*; D015152:Blotting, Northern; D015153:Blotting, Western; D002478:Cells, Cultured; D003513:Cycloheximide / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D005260:Female; D018507:Gene Expression Regulation, Developmental / Q000187:drug effects / Q000502:physiology; D007213:Indomethacin / Q000494:pharmacology; D018975:Insulin-Like Growth Factor Binding Protein 5 / Q000096:biosynthesis* / Q000235:genetics / Q000378:metabolism; D015850:Interleukin-6 / Q000494:pharmacology / Q000502:physiology*; D010006:Osteoblasts / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D010294:Parietal Bone / Q000166:cytology / Q000196:embryology; D011247:Pregnancy; D011500:Protein Synthesis Inhibitors / Q000494:pharmacology; D012333:RNA, Messenger / Q000032:analysis / Q000235:genetics / Q000378:metabolism; D051381:Rats; D018123:Receptors, Interleukin / Q000502:physiology*; D019947:Receptors, Interleukin-6; D013997:Time Factors
D015703:Antigens, CD; D018975:Insulin-Like Growth Factor Binding Protein 5; D015850:Interleukin-6; D011500:Protein Synthesis Inhibitors; D012333:RNA, Messenger; D018123:Receptors, Interleukin; D019947:Receptors, Interleukin-6; D003513:Cycloheximide; D007213:Indomethacin