Regulation of expression of collagenase-3 in normal, differentiating rat osteoblasts.
We investigated the regulation of collagenase-3 expression in normal, differentiating rat osteoblasts. Fetal rat calvarial cell cultures showed an increase in alkaline phosphatase activity reaching maximal levels between 7-14 days post-confluence, then declining with the onset of mineralization. Collagenase-3 mRNA was just detectable after proliferation ceased at day 7, increased up to day 21, and declined at later ages. Postconfluent cells maintained in non-mineralizing medium expressed collagenase-3 but did not show the developmental increase exhibited by cells switched to mineralization medium. Cells maintained in non-mineralizing medium continued to proliferate; cells in mineralization medium ceased proliferation. In addition, collagenase-3 mRNA was not detected in subcultured cells allowed to remineralize. These results suggest that enhanced accumulation of collagenase-3 mRNA is triggered by cessation of proliferation or acquisition of a mineralized extracellular matrix and that other factors may also be required. After initiation of basal expression, parathyroid hormone (PTH) caused a dose-dependent increase in collagenase-3 mRNA. Both the cyclic adenosine monophosphate (cAMP) analogue, 8-bromo-cAMP (8-Br-cAMP), and the protein kinase C (PKC) activator, phorbol myristate acetate, increased collagenase-3 expression, while the calcium ionophore, ionomycin, did not, suggesting that PTH was acting through the protein kinase A (PKA) and PKC pathways. Inhibition of protein synthesis with cycloheximide caused an increase in basal collagenase-3 expression but blocked the effect of PTH, suggesting that an inhibitory factor prevents basal expression while an inductive factor is involved with PTH action. In summary, collagenase-3 is expressed in mineralized osteoblasts and cessation of proliferation and initiation of mineralization are triggers for collagenase-3 expression. PTH also stimulates expression of the enzyme through both PKA and PKC pathways in the mineralizing osteoblast.
Winchester
S K
SK
Department of Pharmacological and Physiological Science, Saint Louis University School of Medicine, St. Louis, Missouri 63104-1083, USA.
Bloch
S R
SR
Fiacco
G J
GJ
Partridge
N C
NC
D000469:Alkaline Phosphatase / Q000378:metabolism; D000818:Animals; D002454:Cell Differentiation; D002478:Cells, Cultured; D017364:Collagenases / Q000235:genetics*; D000242:Cyclic AMP / Q000378:metabolism; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism; D003513:Cycloheximide / Q000494:pharmacology; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects; D053509:Matrix Metalloproteinase 13; D020782:Matrix Metalloproteinases / Q000235:genetics*; D010006:Osteoblasts / Q000166:cytology* / Q000187:drug effects / Q000201:enzymology*; D010281:Parathyroid Hormone / Q000494:pharmacology; D011493:Protein Kinase C / Q000378:metabolism; D011500:Protein Synthesis Inhibitors / Q000494:pharmacology; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D051381:Rats
D010281:Parathyroid Hormone; D011500:Protein Synthesis Inhibitors; D012333:RNA, Messenger; D003513:Cycloheximide; D000242:Cyclic AMP; D017868:Cyclic AMP-Dependent Protein Kinases; D011493:Protein Kinase C; D000469:Alkaline Phosphatase; D017364:Collagenases; D053509:Matrix Metalloproteinase 13; D020782:Matrix Metalloproteinases; C507083:Mmp13 protein, rat