Role of the glycosaminoglycan component of thrombomodulin in its acceleration of the inactivation of single-chain urokinase-type plasminogen activator by thrombin.
Thrombomodulin (TM), a membrane proteoglycan on endothelial cells, binds thrombin in a 1:1 complex, accelerates the protein C activation by thrombin, promotes the thrombin inactivation by antithrombin III and inhibits the procoagulant properties of thrombin. The inactivation of single-chain urokinase-type plasminogen activator (scu-PA) by thrombin is accelerated about 70-fold by TM [De Munk, Groeneveld and Rijken (1991) J. Clin. Invest. 88, 1680-1684]. The present study investigates the role of the O-linked glycosaminoglycan moiety of TM in the latter reaction. In the presence of an excess of a fully-glycosylated soluble recombinant human TM mutant (high-Mr rec-TM), 0.11 nM thrombin inactivated 50% of 4.4 nM scu-PA in 45 min at 37 degrees C. In the presence of a soluble recombinant TM mutant lacking the glycosaminoglycans (low-Mr rec-TM), 1.9 nM thrombin was needed to inactivate 50% scu-PA, as compared with 4.7 nM thrombin in the absence of TM. Using the scu-PA inactivation assay the dissociation constant for the thrombin-TM interaction was found to be 0.4 nM for high-Mr rec-TM and 14 nM for low-Mr rec-TM. Treatment of high-Mr rec-TM with chondroitinase ABC to digest the glycosaminoglycans decreased the accelerating effect to the level of low-Mr rec-TM. A similar decrease was observed after treatment of solubilized rabbit TM with chondroitinase ABC. As expected, chondroitinase ABC had no influence on the accelerating effect of low-Mr rec-TM. The free glycosaminoglycans obtained by alkaline treatment of TM or chondroitin sulphate A also accelerated the inactivation of scu-PA by thrombin, but about 1000-fold higher concentrations than with TM were needed to obtain the same acceleration. It is concluded that the major glycosaminoglycan of TM plays a pivotal role in the inactivation of scu-PA by the TM-thrombin complex, both in the formation and in the activity of the complex.
de Munk
G A
GA
IVVO-TNO Gaubius Laboratory, Leiden, The Netherlands.
Parkinson
J F
JF
Groeneveld
E
E
Bang
N U
NU
Rijken
D C
DC
D002808:Chondroitin Lyases / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D006025:Glycosaminoglycans / Q000737:chemistry*; D006031:Glycosylation; D006801:Humans; D011956:Receptors, Cell Surface / Q000737:chemistry / Q000502:physiology*; D018179:Receptors, Thrombin; D011994:Recombinant Proteins / Q000737:chemistry / Q000494:pharmacology; D013329:Structure-Activity Relationship; D013917:Thrombin / Q000008:administration & dosage / Q000494:pharmacology*; D014568:Urokinase-Type Plasminogen Activator / Q000037:antagonists & inhibitors*
D006025:Glycosaminoglycans; D011956:Receptors, Cell Surface; D018179:Receptors, Thrombin; D011994:Recombinant Proteins; D013917:Thrombin; D014568:Urokinase-Type Plasminogen Activator; D002808:Chondroitin Lyases