Thromb Haemost 2001; 85(05): 761-765
DOI: 10.1055/s-0037-1615714
Rapid Communication
Schattauer GmbH

C4b-binding Protein Inhibits the Factor V-dependent but not the Factor V-independent Cofactor Activity of Protein S in the Activated Protein C-mediated Inactivation of Factor VIIIa

Authors

  • Robbert H. L. van de Poel

    1   Thrombosis and Haemostasis Laboratory, Department of Haematology, University Medical Center, Utrecht, Institute of Biomembranes, Utrecht University, Utrecht, The Netherlands
  • Joost C. M. Meijers

    1   Thrombosis and Haemostasis Laboratory, Department of Haematology, University Medical Center, Utrecht, Institute of Biomembranes, Utrecht University, Utrecht, The Netherlands
    2   Present address: Dr. J. C. M. Meijers, Department of Vascular Medicine, Academic Medical Center, 1100 DD Amsterdam, The Netherlands
  • Bonno N. Bouma

    1   Thrombosis and Haemostasis Laboratory, Department of Haematology, University Medical Center, Utrecht, Institute of Biomembranes, Utrecht University, Utrecht, The Netherlands
Further Information

Publication History

Received 14 July 2000

Accepted after resubmission 22 December 2000

Publication Date:
11 December 2017 (online)

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Summary

Activated protein C (APC) is an important inactivator of coagulation factors Va and VIIIa. In the inactivation of factors Va and VIIIa, protein S serves as a cofactor to APC. Protein S can bind to C4b-binding protein (C4BP), and thereby loses its cofactor activity to APC. By modulating free protein S levels, C4BP is an important regulator of protein S cofactor activity. In the factor VIIIa inactivation, protein S and factor V act as synergistic cofactors to APC. We investigated the effect of C4BP on both the factor V-independent and factor V-dependent cofactor activity of protein S in the factor VIIIa inactivation using a purified system. Protein S increased the APC-mediated inactivation of factor VIIIa to 60% and in synergy with protein S, factor V at equi-molar concentrations increased this effect further to 90%. The protein S/factor V synergistic effect was inhibited by preincubation of protein S and factor V with a four-fold molar excess of C4BP. However, C4BP did not inhibit the factor V-independent protein S cofactor activity in the purified system whereas it inhibited the cofactor activity in plasma. We conclude that C4BP-bound protein S retains its cofactor activity to APC in the factor VIIIa inactivation.