SPARC induces the expression of type 1 plasminogen activator inhibitor in cultured bovine aortic endothelial cells.
SPARC, a Ca(2+)-binding glycoprotein that is expressed during tissue morphogenesis and functions as an inhibitor of cell spreading in vitro, was found to induce the secretion of an Mr = 45,000 protein in bovine aortic endothelial (BAE) cells. This protein was identified as type 1 plasminogen activator inhibitor (PAI-1) on Western blots with anti-PAI-1 antiserum. SPARC stimulated the secretion of PAI-1 protein into the medium of subconfluent BAE cells, but not confluent BAE cells, in a dose- and time-dependent manner. Secretion of PAI-1 into the culture medium was progressive and exhibited an increase of 3- to 7-fold over control values within 24 h after the addition of SPARC. Levels of PAI-1 mRNA were elevated 2-fold within 4 to 24 h after the addition of SPARC and did not increase with higher concentrations of SPARC. Since the induction of PAI-1 mRNA by SPARC was not blocked by cycloheximide, de novo protein synthesis was apparently not required for this stimulation. Control experiments showed that the induction of PAI-1 was not due to contamination of the SPARC preparations with endotoxin. These data demonstrate that SPARC induces the biosynthesis of PAI-1 in BAE cells and suggest a role for SPARC in the regulation of fibrinolysis and in the control of proteolytic events in remodeling tissues.
Hasselaar
P
P
Department of Biological Structure, University of Washington, Seattle 98195.
Loskutoff
D J
DJ
Sawdey
M
M
Sage
E H
EH
D000818:Animals; D001011:Aorta; D015152:Blotting, Northern; D002417:Cattle; D002460:Cell Line; D002478:Cells, Cultured; D004305:Dose-Response Relationship, Drug; D004730:Endothelium, Vascular / Q000187:drug effects / Q000502:physiology*; D007700:Kinetics; D008070:Lipopolysaccharides / Q000494:pharmacology; D009693:Nucleic Acid Hybridization; D015676:Osteonectin / Q000302:isolation & purification / Q000494:pharmacology*; D015849:Plasminogen Inactivators / Q000378:metabolism*; D012313:RNA / Q000235:genetics / Q000302:isolation & purification; D012333:RNA, Messenger / Q000187:drug effects / Q000235:genetics
D008070:Lipopolysaccharides; D015676:Osteonectin; D015849:Plasminogen Inactivators; D012333:RNA, Messenger; D012313:RNA