Transforming growth factor beta inhibits plasminogen activator (PA) activity and stimulates production of urokinase-type PA, PA inhibitor-1 mRNA, and protein in rat osteoblast-like cells

• Published in: Journal of cellular physiology Vol. 149; no. 1; p. 34
• Main Authors: Allan, E H, Zeheb, R, Gelehrter, T D, Heaton, J H, Fukumoto, S, Yee, J A, Martin, T J
• Format: Journal Article
• Language: English
• Published: United States 01.10.1991
• Subjects: Animals; Cycloheximide - pharmacology; Dactinomycin - pharmacology; Fibrinolysin - pharmacology; Osteoblasts - drug effects; Osteoblasts - metabolism; Osteosarcoma; Plasminogen Activators - metabolism; Plasminogen Inactivators - metabolism; Protein Biosynthesis; Rats; RNA, Messenger - genetics; RNA, Messenger - metabolism; Tissue Plasminogen Activator - metabolism; Transforming Growth Factor beta - pharmacology; Tumor Cells, Cultured; Urokinase-Type Plasminogen Activator - biosynthesis; Urokinase-Type Plasminogen Activator - metabolism
• ISSN: 0021-9541
• DOI: 10.1002/jcp.1041490106

Transforming growth factor beta (TGF beta) treatment of rat osteoblast-rich calvarial cells or of the clonal osteogenic sarcoma cells, UMR 106-01, resulted in dose-dependent inhibition of plasminogen activator (PA) activity, and increased production of 3.2 kb mRNA and protein for PA inhibitor -1 (PAI-1). Although tissue-type PA (tPA) protein was not measured, TGF beta did not influence production of mRNA for tPA. Production of 2.3 kb mRNA for urokinase-type PA (uPA) was also increased by TGF beta in a dose-dependent manner. The effects of TGF beta on synthesis of mRNA for PAI-1 and uPA were maintained when protein synthesis was inhibited, and were abolished by inhibition of RNA synthesis. Although uPA had not been detected previously as a product of rat osteoblasts, treatment of lysates of osteoblast-like cells with plasmin yielded a band of PA activity on reverse fibrin autography, corresponding to a low Mr form of uPA. Untreated conditioned media from normal osteoblasts or UMR 106-01 cells contained no significant TGF beta activity, but activity could be detected in acidified medium. Treatment of conditioned media with plasmin resulted in activation of approximately 50% of the TGF beta detectable in acidified media. The results identify several effects of TGF beta on the PA-PA inhibitor system in osteoblasts. Net regulation of tPA activity through the stimulatory actions of several calciotropic hormones and the promotion of PAI-1 formation by TGF beta could determine the amount of osteoblast-derived TGF beta activated locally in bone. Stimulation of osteoblast production of mRNA for uPA could reflect effects on the synthesis of sc-uPA, a precursor for the active form of the enzyme.