Platelet-derived growth factor and transforming growth factor-beta regulate plasminogen activator inhibitor-1 synthesis in vascular smooth muscle cells.
Bovine vascular smooth muscle cells (SMC) were examined for production of plasminogen activator inhibitor-1 (PAI-1) which may play a key role in regulating the fibrinolytic system. Growth-arrested SMC released active PAI (101 arbitrary units (AU)/10(6) cells/24 h) and a latent form of PAI (880 AU/10(6) cells/24 h) into the conditioned medium (CM). The levels of PAI were significant since 880 AU of PAI could inhibit approximately 1 microgram of tissue plasminogen activator. The extracellular matrix of SMC also contained PAI activity; however, the level was 17-fold less than that observed in the CM. SMC-PAI was a rapid inhibitor of tissue plasminogen activator (kass greater than 10(7) M-1 S-1) and was identified as a 45-kDa protein immunologically related to endothelial cell PAI-1. PAI-1 comprised 20 and 30%, respectively, of the newly synthesized protein detected in the CM and extracellular matrix of SMC. The SMC growth modulators, platelet-derived growth factor and transforming growth factor-beta, induced PAI-1 activity and protein synthesis by 2- and 3-fold, respectively, in a dose- and time-dependent manner. The increases in PAI-1 activity and protein synthesis were ascribed to elevated levels of PAI-1 mRNA as judged by Northern blot analysis of total RNA prepared from control and platelet-derived growth factor- and transforming growth factor-beta-treated cells. Increases in PAI-1 mRNA levels were evident 1 h after growth factor treatment and were maximal after 4 h. PAI-1 mRNA levels were unaffected by cycloheximide treatment. The results indicate that SMC synthesize and release PAI-1 which could regulate the normal fibrinolytic environment of the arterial wall. During atherosclerosis or after vascular injury increases in platelet-derived or locally produced mitogens may stimulate further PAI-1 synthesis and generate a prothrombotic state.
Reilly
C F
CF
Department of Pharmacology, Merck Sharp and Dohme Research Laboratories, West Point, Pennsylvania 19486.
McFall
R C
RC
D000818:Animals; D015152:Blotting, Northern; D002417:Cattle; D003513:Cycloheximide / Q000494:pharmacology; D004591:Electrophoresis, Polyacrylamide Gel; D005342:Fibrinolysis; D007700:Kinetics; D009131:Muscle, Smooth, Vascular / Q000166:cytology / Q000378:metabolism*; D015849:Plasminogen Inactivators / Q000378:metabolism*; D010974:Platelet Aggregation / Q000187:drug effects; D010982:Platelet-Derived Growth Factor / Q000494:pharmacology*; D012333:RNA, Messenger / Q000378:metabolism; D016212:Transforming Growth Factor beta / Q000494:pharmacology*
D015849:Plasminogen Inactivators; D010982:Platelet-Derived Growth Factor; D012333:RNA, Messenger; D016212:Transforming Growth Factor beta; D003513:Cycloheximide