title: Plasminogen activator regulation in osteoblasts: parathyroid hormone inhibition of type-1 plasminogen activator inhibitor and its mRNA.
abstract: In order to determine the mechanism by which parathyroid hormone (PTH) stimulates plasminogen activator (PA) activity in rat osteoblasts, we investigated the effect of human PTH(1-34) [hPTH(1-34)] on the synthesis of mRNAs for tissue-type PA (tPA), urokinase-type PA (uPA), and PA inhibitor-1 (PAI-1), and on release of PA activity and PAI-1 protein in both normal rat calvarial osteoblasts and UMR 106-01 osteogenic sarcoma cells. hPTH(1-34) (0.25-25 nM) decreased PAI-1 mRNA and protein, and increased PA activity in both cell types in a dose-dependent manner with ED50 of about 1 nM for both responses. Forskolin and isobutylmethylxanthine also stimulated PA activity and decreased PAI-1 protein and mRNA in both cell types. hPTH(1-34) did not show any consistent effect on tPA and uPA mRNA in calvarial osteoblasts, but a modest (two-fold) increase of both mRNAs was observed in UMR 106-01 cells treated with 25 nM hPTH(1-34). However, when protein synthesis was inhibited with 100 microM cycloheximide, the increase of tPA and uPA mRNA by hPTH(1-34) was enhanced in UMR 106-01 cells and became evident in calvarial osteoblasts. Fibrin autography also revealed that hPTH(1-34) increases tPA and uPA activity, especially after cycloheximide treatment in UMR 106-01 cells. These results strongly suggest that PTH increases PA activity predominantly by decreasing PAI-1 protein production through a cyclic adenosine monophosphate (cAMP)-dependent mechanism in rat osteoblasts. The reduction of PAI-1 protein by PTH results in enhanced action of both tPA and uPA, and would contribute to the specific roles of these PAs in bone.
authors.affiliation: Department of Medicine, St. Vincent's Institute of Medical Research, St. Vincent's Hospital, Melbourne, Victoria, Australia.
authors.forename: S
authors.initials: S
authors.lastname: Fukumoto
authors.forename: E H
authors.initials: EH
authors.lastname: Allan
authors.forename: J A
authors.initials: JA
authors.lastname: Yee
authors.forename: T D
authors.initials: TD
authors.lastname: Gelehrter
authors.forename: T J
authors.initials: TJ
authors.lastname: Martin
mesh_terms: D000818:Animals; D000242:Cyclic AMP / Q000502:physiology; D003513:Cycloheximide / Q000494:pharmacology; D003609:Dactinomycin / Q000494:pharmacology; D003907:Dexamethasone / Q000494:pharmacology; D010006:Osteoblasts / Q000378:metabolism*; D010281:Parathyroid Hormone / Q000494:pharmacology*; D010446:Peptide Fragments / Q000494:pharmacology*; D010960:Plasminogen Activators / Q000378:metabolism*; D015849:Plasminogen Inactivators / Q000378:metabolism*; D012333:RNA, Messenger / Q000037:antagonists & inhibitors*; D019379:Teriparatide; D010959:Tissue Plasminogen Activator / Q000235:genetics; D014407:Tumor Cells, Cultured; D014568:Urokinase-Type Plasminogen Activator / Q000235:genetics
chemical_list: D010281:Parathyroid Hormone; D010446:Peptide Fragments; D015849:Plasminogen Inactivators; D012333:RNA, Messenger; D019379:Teriparatide; D003609:Dactinomycin; D003907:Dexamethasone; D003513:Cycloheximide; D000242:Cyclic AMP; D010960:Plasminogen Activators; D010959:Tissue Plasminogen Activator; D014568:Urokinase-Type Plasminogen Activator