Autocrine down-regulation of collagenase-3 in rat bone cell cultures by insulin-like growth factors.
Insulin-like growth factors (IGF)-I and -II are presumed to act as autocrine regulators of bone formation. Recently, we demonstrated that IGF-I and -II inhibit bone collagen degradation and collagenase-3 synthesis in osteoblast cultures. Therefore, we tested the autocrine role of IGFs in the endogenous expression of collagenase-3 in cultures of osteoblast-enriched cells from 22-day fetal rat calvariae (Ob cells). Steady-state messenger RNA (mRNA) levels were determined by Northern blot analysis and collagenase concentrations in the culture medium were determined by Western immunoblot. Basal level collagenase-3 transcripts decreased in Ob cell cultures, coinciding with an increase in IGF-I and -II protein levels. Removal of the conditioned medium modestly increased collagenase-3 mRNA levels and restored the ability of exogenously added IGF-I to repress collagenase-3 transcripts. IGF neutralizing antibodies and IGF binding proteins-2 and -3 in excess increased and sustained collagenase mRNA, heterogeneous nuclear RNA, and protease levels in Ob cell cultures. In conclusion, IGF-I and -II are autocrine repressors of collagenase-3 synthesis, and this effect may contribute to their actions on the maintenance of a normal bone collagen matrix.
Department of Research, Saint Francis Hospital and Medical Center, Hartford, Connecticut 06105, USA.
A M
AM
Delany
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S
Rydziel
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E
Canalis
D000818:Animals; D000906:Antibodies / Q000494:pharmacology; D002478:Cells, Cultured; D017364:Collagenases / Q000096:biosynthesis*; D005333:Fetus; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects; D018971:Insulin-Like Growth Factor Binding Protein 2 / Q000494:pharmacology / Q000502:physiology; D007334:Insulin-Like Growth Factor I / Q000096:biosynthesis* / Q000276:immunology; D007335:Insulin-Like Growth Factor II / Q000096:biosynthesis* / Q000276:immunology; D053509:Matrix Metalloproteinase 13; D010006:Osteoblasts / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D012332:RNA, Heterogeneous Nuclear / Q000378:metabolism; D051381:Rats; D012886:Skull
D000906:Antibodies; D018971:Insulin-Like Growth Factor Binding Protein 2; D012332:RNA, Heterogeneous Nuclear; D007334:Insulin-Like Growth Factor I; D007335:Insulin-Like Growth Factor II; D017364:Collagenases; D053509:Matrix Metalloproteinase 13; C507083:Mmp13 protein, rat