Review
Regulation of blood coagulation

https://doi.org/10.1016/S0167-4838(99)00266-6Get rights and content

Abstract

The protein C anticoagulant pathway converts the coagulation signal generated by thrombin into an anticoagulant response through the activation of protein C by the thrombin-thrombomodulin (TM) complex. The activated protein C (APC) thus formed interacts with protein S to inactivate two critical coagulation cofactors, factors Va and VIIIa, thereby dampening further thrombin generation. The proposed mechanisms by which TM switches the specificity of thrombin include conformational changes in thrombin, blocking access of normal substrates to thrombin and providing a binding site for protein C. The function of protein S appears to be to alter the cleavage site preferences of APC in factor Va, probably by changing the distance of the active site of APC relative to the membrane surface. The clinical relevance of this pathway is now established through the identification of deficient individuals with severe thrombotic complications and through the analysis of families with partial deficiencies in these components and an increased thrombotic tendency. One possible reason that even partial deficiencies are a thrombotic risk is that the function of the pathway can be down-regulated by inflammatory mediators. For instance, clinical studies have shown that the extent to which protein C levels decrease in patients with septic shock is predictive of a negative outcome. Initial clinical studies suggest that supplementation with protein C may be useful in the treatment of acute inflammatory diseases such as sepsis.

Section snippets

Regulation of the coagulation cascade by the protein C anticoagulant pathway

Blood coagulation proceeds through a series of zymogen activations that culminate in the generation of thrombin (Fig. 1). Thrombin then cleaves fibrinogen generating fibrin and activates platelets by cleaving thrombin receptors on the platelet surface. Generation of too much thrombin leads to thrombosis (i.e. blood clots that occlude blood vessels). Because thrombosis causes heart attacks, strokes, pulmonary emboli and venous thrombosis, it is the major cause of morbidity and mortality in

Properties of the protein C activation complex

Several lines of evidence suggest that TM binding to thrombin alters thrombin conformation. The fluorescence yield of dyes placed near the active center of thrombin exhibits altered quantum yields following TM binding [119]. These dyes can distinguish between conformational changes induced by the active and inactive forms of TM that bind to the anion binding exosite 1 of thrombin (Fig. 2). Furthermore, TM binding to thrombin alters chromogenic substrate specificity and this change in

Calcium influences on protein C activation

One of the most unusual features of protein C activation is the dominant role played by Ca2+ in this process. For the discussion in this paragraph, all of the experimental results relate to studies of protein C and its activation in the absence of membrane surfaces. In the absence of TM, calcium inhibits protein C activation by thrombin 1 resulting in a very large increase in Km (more than 20-fold) [30]. In the presence of TM, calcium has the opposite effect, strongly stimulating the rate of

Protein C activation on the membrane surface

Although protein C can be activated relatively well by the thrombin-TM complex in solution, membrane surfaces accelerate the activation considerably. Two distinct mechanisms are involved. One involves direct interaction of the Gla domain of protein C with the phospholipid. In this case, binding is augmented by calcium and negatively charged phospholipids are the most active [117] (Fig. 2). Analysis of the membrane binding properties of protein C indicates that this interaction with negatively

APC anticoagulant activity

A major function of APC is to inhibit clot formation. It does so through limited proteolytic inactivation of the two cofactors, factors Va and VIIIa. Interest in the inactivation of factor Va has increased since the initial description of a clinical condition referred to as APC resistance [17]. Subsequently, it was shown that APC resistance is caused most commonly by a mutation in the gene, a substitution of Arg-506 with Gln in factor V [7], giving rise to an alternative designation of the

Clinical aspects of the protein C anticoagulant pathway

In recent years, an explosion of clinical reports has emerged linking defects in the protein C system with human thrombotic disease. In the following section, I will try to highlight some of the examples that illustrate key clinical aspects of the system.

Hereditary defects

Heterozygous protein C deficiency is relatively common, about 0.15–0.3% [67], [103]. Clinical studies demonstrate that the deficiency at the heterozygous level increases the risk of venous thrombosis [105], particularly in patients that carry a second defect, for instance the relatively common APC resistance trait [51], [55], [56], [63], [71]. Homozygous deficiency is associated with life threatening thrombotic complications [11], [92] that can be effectively treated by protein C

Gene deletion in mice

The thrombotic risk observed in patients with defects in the protein C pathway is supported by studies on gene deletion in mice. Deletion of the TM gene leads to early embryonic lethality [44] whereas replacing the TM gene with a mutant gene leads to mice with an increased propensity to thrombosis, particularly in the heart [115]. Deletion of the protein C gene also leads to thrombotic death in mice shortly after birth [47].

Protein C pathway components as a potential therapy for acute inflammatory thrombotic complications

One reason for the apparently strong penetrance of deficiencies in the protein C pathway may involve its link with inflammatory mediators. Tumor necrosis factor α [15], [72] and endotoxin [69] can down-regulate TM and EPCR expression [32] on cultured endothelial cells. Protein S levels are also reduced in acute inflammatory conditions [61] and the extent of protein C consumption has been linked to a negative outcome in patients with septic shock, particularly meningococcemia, and the

Concluding remarks

It has become quite clear in the last 20 years that the protein C system plays a major role in the regulation of coagulation. Through the unusual mechanism by which the pathway is initiated, it provides a unique method for sensing the need for an anticoagulant response and adjusting the response appropriately. Defects in the pathway are clearly linked to an increase in in thrombotic risk and are the most common risk factors for venous thrombosis. Finally, both preclinical pharmacological

References (123)

  • P. Ascenzi et al.

    Biochim. Biophys. Acta

    (1988)
  • L. Bajzar et al.

    J. Biol. Chem.

    (1996)
  • L. Bajzar et al.

    J. Biol. Chem.

    (1998)
  • M.C. Bourin et al.

    J. Biol. Chem.

    (1990)
  • H. Branson et al.

    Lancet

    (1983)
  • F.J. Castellino

    Trends Cardiovasc. Med.

    (1995)
  • P.C. Comp et al.

    Blood

    (1986)
  • M.C.H. deVisser et al.

    Blood

    (1999)
  • C.T. Esmon

    J. Biol. Chem.

    (1989)
  • N.L. Esmon et al.

    J. Biol. Chem.

    (1983)
  • F. España et al.

    Blood

    (1991)
  • K. Fukudome et al.

    J. Biol. Chem.

    (1994)
  • K. Fukudome et al.

    J. Biol. Chem.

    (1996)
  • M. Galli et al.

    Blood

    (1998)
  • B. Gerlitz et al.

    J. Biol. Chem.

    (1996)
  • J.H. Griffin et al.

    Blood

    (1993)
  • E.R. Guinto et al.

    J. Biol. Chem.

    (1994)
  • M.J. Heeb et al.

    Blood

    (1995)
  • M. Kalafatis et al.

    J. Biol. Chem.

    (1994)
  • B.P.C. Koeleman et al.

    Blood

    (1994)
  • S. Kurosawa et al.

    J. Biol. Chem.

    (1987)
  • B.F. Le Bonniec et al.

    J. Biol. Chem.

    (1991)
  • R. Lu et al.

    J. Biol. Chem.

    (1989)
  • M.J. Manco-Johnson et al.

    J. Pediatr.

    (1996)
  • K.G. Mann et al.

    J. Biol. Chem.

    (1997)
  • G.A.F. Nicolaes et al.

    J. Biol. Chem.

    (1995)
  • A.-K. Öhlin et al.

    Blood

    (1995)
  • J.E. Phillips et al.

    J. Biol. Chem.

    (1994)
  • L.M. Regan et al.

    J. Biol. Chem.

    (1997)
  • L.M. Regan et al.

    J. Biol. Chem.

    (1996)
  • A.R. Rezaie et al.

    J. Biol. Chem.

    (1995)
  • A.R. Rezaie et al.

    J. Biol. Chem.

    (1992)
  • F.R. Rosendaal et al.

    Blood

    (1997)
  • J. Rosing et al.

    J. Biol. Chem.

    (1995)
  • L. Shen et al.

    J. Biol. Chem.

    (1994)
  • M.D. Smirnov et al.

    J. Biol. Chem.

    (1998)
  • O.P. Smith et al.

    Lancet

    (1997)
  • D.J. Stearns et al.

    J. Biol. Chem.

    (1988)
  • M.T. Stubbs et al.

    Thromb. Res.

    (1993)
  • G.W. Amphlett et al.

    Biochemistry

    (1981)
  • D.T. Berg et al.

    Science

    (1996)
  • R.M. Bertina

    Clin. Chem.

    (1997)
  • R.M. Bertina et al.

    Nature

    (1994)
  • W. Bode et al.

    EMBO J.

    (1989)
  • W. Bode et al.

    Protein Sci.

    (1992)
  • W.T. Christiansen et al.

    Biochemistry

    (1995)
  • E.M. Conway et al.

    Mol. Cell. Biol.

    (1988)
  • B. Dahlbäck

    J. Clin. Invest.

    (1994)
  • B. Dahlbäck et al.

    Proc. Natl. Acad. Sci. USA

    (1993)
  • Q.D. Dang et al.

    Nat. Biotechnol.

    (1997)

    • Cited by (0)

    View full text
    Copyright © 2000 Elsevier Science B.V. All rights reserved.