Protein S stimulates inhibition of the tissue factor pathway by tissue factor pathway inhibitor

Abstract

Tissue factor (TF) plays an important role in hemostasis, inflammation, angiogenesis, and the pathophysiology of atherosclerosis and cancer. In this article we uncover a mechanism in which protein S, which is well known as the cofactor of activated protein C, specifically inhibits TF activity by promoting the interaction between full-length TF pathway inhibitor (TFPI) and factor Xa (FXa). The stimulatory effect of protein S on FXa inhibition by TFPI is caused by a 10-fold reduction of the Ki of the FXa͞TFPI complex, which decreased from 4.4 nM in the absence of protein S to 0.5 nM in the presence of protein S. This decrease in Ki not only results in an acceleration of the feedback inhibition of the TF-mediated coagulation pathway, but it also brings the TFPI concentration necessary for effective FXa inhibition well within range of the concentration of TFPI in plasma. This mechanism changes the concept of regulation of TF-induced thrombin formation in plasma and demonstrates that protein S and TFPI act in concert in the inhibition of TF activity. Our data suggest that protein S deficiency not only increases the risk of thrombosis by impairing the protein C system but also by reducing the ability of TFPI to down-regulate the extrinsic coagulation pathway.anticoagulant ͉ venous thrombosis ͉ extrinsic coagulation

Factor V‐short and protein S as synergistic tissue factor pathway inhibitor (TFPIα) cofactors

“…Protein S is a cofactor to TFPIα in the inactivation of FXa on the surface of negatively charged phospholipid vesicles and as TFPIα/FXa efficiently inhibits TF/FVIIa, protein S indirectly stimulates inhibition of TF/FVIIa 15, 18, 20, 34, 35. There is no consensus regarding the question whether protein S directly stimulates inhibition of TF/FVIIa.…”

“…The first Kunitz domain of full length TFPIα inhibits FVIIa, the second inhibits FXa, whereas the third Kunitz domain interacts with protein S 13, 14, 15, 16. The interaction between TFPIα and protein S is associated with stimulation of the inhibition of FXa by TFPIα 17, 18. Full length FV has also been reported to potentiate the activity of TFPIα 19, 20.…”

TFPI cofactor function of protein S: essential role of the protein S SHBG-like domain

“…It has previously been hypothesized that protein S, through its high affinity for negatively charged phospholipids, brings TFPI in close proximity to FXa on an activated membrane and thereby increases the TFPI/FXa association rate. [15][16][17]35 We propose that protein S and TFPI can associate in plasma through a direct interaction between the protein S SHBG-like domain and the TFPI Kunitz 3 domain, particularly with Glu226. Upon initiation of coagulation on phospholipid surfaces, protein S brings TFPI Kunitz domain 2 into proximity of the active site of the protease domain of FXa, thereby decreasing the concentration of TFPI needed for efficient inhibition of FXa ( Figure 6).…”

“…[37][38][39] Hackeng et al have previously shown that the addition of a molar excess of C4BP to free protein S in normal plasma resulted in a 40% decrease of the TFPI enhancement by protein S in thrombin-generation assays. 15 In addition, immunodepletion experiments showed that protein S Figure 5. Binding of WT protein S and protein S/Gas6 chimeras I to III to TFPI studied with SPR.…”

“…on April 11, 2019. by guest www.bloodjournal.org From effect on the thrombin generation, whereas it efficiently enhanced TFPI-mediated inhibition of thrombin generation, as reported previously. 15,17,34 Inhibitory antibodies against TFPI and protein S were used to verify that inhibitory effects were a direct consequence of TFPI and TFPI cofactor function of protein S ( Figure 1B).The functional interaction site of protein S for TFPI was investigated using the library of 44 protein S variants. The screening of WT protein S and the protein S variants for their TFPI cofactor function was performed at 1 nM TFPI and 50 nM protein S ( Figure 1C).…”