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Mechanism of inhibitory action of angiostatin on plasminogen (PG) activation by tissue plasminogen activator (TPA) and urokinase (UPA)

Abstract number: PP-TH-227

Aisina¹ R.B., Mukhametova¹ L., Prisyazhnaya¹ N., Gulin¹ D., Gershkovich¹ K., Varfolomeyev¹ S.

¹¹Chemistry Faculty, Lomonosov Moscow State University, Moscow, Russian Federation

How-to-cite Aisina RB, Mukhametova L, Prisyazhnaya N, Gulin D, Gershkovich K, Varfolomeyev S. Mechanism of inhibitory action of angiostatin on plasminogen (PG) activation by tissue plasminogen activator (TPA) and urokinase (UPA). Journal of Thrombosis and Haemostasis 2009; Volume 7, Supplement 2: Abstract PP-TH-227

Earlier we showed an In Vitro inhibition of tPA and uPA activator activities by angiostatins - kringle-containing fragments of Pg. The aim was to elucidate a mechanism of inhibition of Pg activation by angiostatin K1-4,5.

Methods: K1-4,5 was prepared from human Pg. Kinetics of Glu-Pg activation by tPA in presence of soluble fibrin or by uPA coupled with S-2251 hydrolysis by Pm was studied at different Pg and K1-4,5 concentrations.

Results: K1-4,5 (≥ 2 μM) had no effect on own activities of Pm, tPA and uPA measured by S-2251, S-2288 and S-2444 hydrolysis, respectively. Kinetic parameters of Pg activation by tPA and uPA were determined from 1/Vact ÷ 1/[Pg] plots. The kPg and KPg values of Pg activation whithout K1-4,5 were found to be 0.02/s and 0,52 μM for uPA and 0,086/s and 0,023 μM for tPA. Angiostatin had not effect on kPg and increased in KPg at Pg activation by uPA, whereas it reduced in kPg and increased in KPg at fibrin-stimulated Pg activation by tPA. Inhibition constants (Ki) of the activation by angiostatin determined from 1/Vact ÷ 1/[K1-4,5] plots at different concentrations of Pg were found to be 0.59 and 0,12 μM, respectively for uPA and tPA.

Summary: Shapes of the plots and changes in kPg and KPg values indicate that K1-4,5 is competitive inhibitor of Pg activation by uPA and non-competitive inhibitor of fibrin-stimulated Pg activation by tPA. Suggested mechanism of the inhibition: K1-4,5 through its kringles binds to Pg binding sites, but it has no protease domain. K1-4,5 displaces directly Pg from uPA-Pg complex, whereas in case of tPA it more efficiently displaces Pg from fibrin. This leads to reduce in concentrations of uPA-Pg and tPA-Pg-fibrin complexes and Pm generation.

Disclosure of interest: none declared.

To cite this abstract use the following format:

Journal of Thrombosis and Haemostasis 2007; Volume 5, Supplement 2: abstract number

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