title: Enhanced fibrinolysis by proteolysed coagulation factor Xa.
abstract: We previously showed that coagulation factor Xa (FXa) enhances activation of the fibrinolysis zymogen plasminogen to plasmin by tissue plasminogen activator (tPA). Implying that proteolytic modulation occurs in situ, intact FXa (FXaalpha) must be sequentially cleaved by plasmin or autoproteolysis, producing FXabeta and Xa33/13, which acquire necessary plasminogen binding sites. The implicit function of Xa33/13 in plasmin generation has not been demonstrated, nor has FXaalpha/beta or Xa33/13 been studied in clot lysis experiments. We now report that purified Xa33/13 increases tPA-dependent plasmin generation by at least 10-fold. Western blots confirmed that in situ conversion of FXaalpha/beta to Xa33/13 correlated to enhanced plasmin generation. Chemical modification of the FXaalpha active site resulted in the proteolytic generation of a product distinct from Xa33/13 and inhibited the enhancement of plasminogen activation. Identical modification of Xa33/13 had no effect on tPA cofactor function. Due to its overwhelming concentration in the clot, fibrin is the accepted tPA cofactor. Nevertheless, at the functional level of tPA that circulates in plasma, FXaalpha/beta or Xa33/13 greatly reduced purified fibrin lysis times by as much as 7-fold. This effect was attenuated at high levels of tPA, suggesting a role when intrinsic plasmin generation is relatively low. FXaalpha/beta or Xa33/13 did not alter the apparent size of fibrin degradation products, but accelerated the initial cleavage of fibrin to fragment X, which is known to optimize the tPA cofactor activity of fibrin. Thus, coagulation FXaalpha undergoes proteolytic modulation to enhance fibrinolysis, possibly by priming the tPA cofactor function of fibrin.
authors.affiliation: Canadian Blood Services, Research and Development Department, Vancouver, BC, Canada V6T 1Z3.
authors.forename: Kimberley
authors.initials: K
authors.lastname: Talbot
authors.forename: Scott C
authors.initials: SC
authors.lastname: Meixner
authors.forename: Edward L G
authors.initials: EL
authors.lastname: Pryzdial
mesh_terms: D000590:Amino Acid Chloromethyl Ketones / Q000494:pharmacology; D020134:Catalytic Domain; D003619:Dansyl Compounds / Q000494:pharmacology; D015951:Factor Xa / Q000737:chemistry* / Q000378:metabolism*; D065427:Factor Xa Inhibitors; D005337:Fibrin / Q000378:metabolism; D005338:Fibrin Fibrinogen Degradation Products / Q000378:metabolism; D005341:Fibrinolysin / Q000378:metabolism; D005342:Fibrinolysis / Q000502:physiology*; D006801:Humans; D066298:In Vitro Techniques; D008954:Models, Biological; D010446:Peptide Fragments / Q000737:chemistry / Q000378:metabolism; D010447:Peptide Hydrolases / Q000378:metabolism; D017434:Protein Structure, Tertiary; D010959:Tissue Plasminogen Activator / Q000378:metabolism
chemical_list: D000590:Amino Acid Chloromethyl Ketones; D003619:Dansyl Compounds; D065427:Factor Xa Inhibitors; D005338:Fibrin Fibrinogen Degradation Products; D010446:Peptide Fragments; C030824:dansylglutamyl-glycyl-arginine chloromethyl ketone; D005337:Fibrin; D010447:Peptide Hydrolases; D015951:Factor Xa; D010959:Tissue Plasminogen Activator; D005341:Fibrinolysin