Protein S down-regulates factor Xase activity independent of activated protein C: specific binding of factor VIII(a) to protein S inhibits interactions with factor IXa

Analysis of PROS1 mutations and clinical characteristics in three Chinese families with hereditary protein S deficiency

We report three heterozygous PROS1 mutations that caused type I protein S deficiency in three unrelated Chinese families. We measured protein S activity and antigen levels for all participants, screened them for mutations in the PROS1 gene. And we employed the calibrated automated thrombin generation (CAT) method to investigate thrombin generation. Numerous bioinformatics tools were utilized to analyze the conservation, pathogenicity of mutation, and spatial structure of the protein S. Phenotyping analysis indicated that all three probands exhibited simultaneous reduced levels of PS:A, TPS:Ag, and FPS:Ag. Genetic testing revealed that proband A harbored a heterozygous c.458_458delA (p.Lys153Serfs*6) mutation in exon 5, proband B carried a heterozygous c.1687C>T (p.Gln563stop) mutation in exon 14, and proband C exhibited a heterozygous c.200A>C (p.Glu67Ala) mutation in exon 2. Bioinformatic analysis predicted that the p.Lys153Serfs*6 frameshift mutation and the p.Gln563stop nonsense mutation in the protein S were classified as "disease-causing." The identification of the novel mutation p.Lys153Serfs*6 in PROS1 enriches the Human Genome Database. Our research suggests that these three mutations (p.Lys153Serfs*6, p.Gln563stop, and p.Glu67Ala) are possibly responsible for the decreased level of protein S in the three families. Furthermore, the evidence also supports the notion that individuals who are asymptomatic but have a family history of PSD can benefit from genetic analysis of the PROS1 gene.

A Case of Type 2 Protein S Deficiency Presenting as Cerebral Venous Thrombosis (CVT) in an 18-Year-Old Female

Here, we report a case of cerebral venous thrombosis in an 18-year-old female. On evaluation, she was found to have type 2 protein S deficiency, which is the rarest form of protein S deficiency and is also known as a qualitative defect. Protein S is primarily synthesized by hepatocytes and undergoes vitamin K-dependent gamma-carboxylation. Mature protein S circulates in two states: free and bound to the complement component C4b-binding protein (C4b-BP). The free form of protein S acts as a cofactor for activated protein C. This case is unique as here, there is a qualitative effect that is responsible for the manifestations.

Antithrombotic potential of a single-domain antibody enhancing the activated protein C-cofactor activity of protein S

BACKGROUND

Protein S (PS) is a natural anticoagulant acting as a cofactor for activated protein C (APC) in the proteolytic inactivation of activated factors V (FVa) and VIII (FVIIIa), but also for tissue factor pathway inhibitor α (TFPIα) in the inhibition of activated factor X (FXa).

OBJECTIVE

For therapeutic purposes, we aimed at generating single-domain antibodies (sdAbs) that could specifically modulate the APC-cofactor activity of PS in vivo.

METHODS

A llama-derived immune library of sdAbs was generated and screened on recombinant human PS by phage display. PS binders were tested in a global activated partial thromboplastin time (APTT)-based APC-cofactor activity assay.

RESULTS

A PS-specific sdAb (PS003) was found to enhance the APC-cofactor activity of PS in our APTT-based assay, and this enhancing effect was greater for a bivalent form of PS003 (PS003biv). Further characterization of PS003biv demonstrated that PS003biv also enhanced the APC-cofactor activity of PS in a tissue factor (TF)-induced thrombin generation assay and stimulated APC in the inactivation of FVa, but not FVIIIa, in plasma-based assays. Furthermore, PS003biv was directed against the sex hormone-binding globulin (SHBG)-like domain but did not inhibit the binding of PS to C4b-binding protein (C4BP) and did not interfere with the TFPIα-cofactor activity of PS. In mice, PS003biv exerted an antithrombotic effect in a FeCl3 -induced thrombosis model, while not affecting physiological hemostasis in a tail-clip bleeding model.

DISCUSSION

Altogether, these results showed that pharmacological enhancement of the APC-cofactor activity of PS through an original anti-PS sdAb might constitute a promising and safe antithrombotic strategy.

Atypical presentation of pulmonary embolism and deep vein thrombosis due to protein S deficiency in a young female with chest pain

Venous thromboembolism has many risk factors including protein S deficiency, which poses a significant diagnostic challenge as it presents with atypical complaints. A treatable yet potentially fatal condition, acute pulmonary embolism, is currently third most common cause of cardiovascular death. Clinicians should include pulmonary embolism as differential diagnosis in young adults with atypical symptoms with 2 D ECHO findings of the dilated right atrium, right ventricle, and elevated pulmonary artery pressure, and diagnosis is confirmed by computed tomography pulmonary angiography (CTPA). Anticoagulants including NOACs should be initiated promptly to improve the outcome for patients.

Recommendations for clinical laboratory testing for protein S deficiency: Communication from the SSC committee plasma coagulation inhibitors of the ISTH

Hereditary deficiencies of protein S (PS) increase the risk of venous thrombosis; however, assessing the plasma levels of PS can be difficult because of its complex physiological interactions in plasma, sample-related preanalytical variables, and numerous acquired disease processes. Reliable laboratory assays are essential for accurate evaluation of PS when diagnosing a congenital deficiency based on the plasma phenotype alone. This report presents the current evidence-based recommendations for clinical PS assays as well as when to test for PS abnormalities.

Pleiotropic anticoagulant functions of protein S, consequences for the clinical laboratory. Communication from the SSC of the ISTH

Hereditary deficiencies of protein S (PS) increase the risk of thrombosis. However, assessing the plasma levels of PS is complicated by its manifold physiological interactions, while the large inter-individual variability makes it problematic to establish reliable cut-off values. PS has multiple physiological functions, with only two appearing to have significant anticoagulant properties: the activated protein C (APC) and tissue factor pathway inhibitor alpha (TFPIα) cofactor activities. Current clinical laboratory investigations for deficiency in PS function rely only on the APC-dependent activity. This communication presents an argument for reclassifying the qualitative PS deficiencies to differentiate the two major anticoagulant functions of PS. Reliable assays are necessary for accurate evaluation of PS function when making a specific diagnosis of PS deficiency based on the anticoagulant phenotype alone. This report emphasizes the pleiotropic anticoagulant functions of PS and presents evidence-based recommendations for their implementation in the clinical laboratory.

Anticoagulant protein S-New insights on interactions and functions

Protein S is a critical regulator of coagulation that functions as a cofactor for the activated protein C (APC) and tissue factor pathway inhibitor (TFPI) pathways. It also has direct anticoagulant functions, inhibiting the intrinsic tenase and prothrombinase complexes. Through these functions, protein S regulates coagulation during both its initiation and its propagation phases. The importance of protein S in hemostatic regulation is apparent from the strong association between protein S deficiencies and increased risk for venous thrombosis. This is most likely because both APC and TFPIα are inefficient anticoagulants in the absence of any cofactors. The detailed molecular mechanisms involved in protein S cofactor functions remain to be fully clarified. However, recent advances in the field have greatly improved our understanding of these functions. Evidence suggests that protein S anticoagulant properties often depend on the presence of synergistic cofactors and the formation of multicomponent complexes on negatively charged phospholipid surfaces. Their high affinity binding to negatively charged phospholipids helps bring the anticoagulant proteins to the membranes, resulting in efficient and targeted regulation of coagulation. In this review, we provide an update on protein S and how it functions as a critical hemostatic regulator.

Platelet-mediated proteolytic down regulation of the anticoagulant activity of protein S in individuals with haematological malignancies

The natural anticoagulant protein S contains a so-called thrombin-sensitive region (TSR), which is susceptible to proteolytic cleavage. We have previously shown that a platelet-associated protease is able to cleave protein S under physiological plasma conditions in vitro. The aim of the present study was to investigate the relation between platelet-associated protein S cleaving activity and in vivo protein S cleavage, and to evaluate the impact of in vivo protein S cleavage on its anticoagulant activity. Protein S cleavage in healthy subjects and in thrombocytopenic and thrombocythaemic patients was evaluated by immunological techniques. Concentration of cleaved and intact protein S was correlated to levels of activated protein C (APC)-dependent and APC-independent protein S anticoagulant activity. In plasma from healthy volunteers 25% of protein S is cleaved in the TSR. While in plasma there was a clear positive correlation between levels of intact protein S and both APC-dependent and APC-independent protein S anticoagulant activities, these correlations were absent for cleaved protein S. Protein S cleavage was significantly increased in patients with essential thrombocythaemia (ET) and significantly reduced in patients with chemotherapy-induced thrombocytopenia. In ET patients on cytoreductive therapy, both platelet count and protein S cleavage returned to normal values. Accordingly, platelet transfusion restored cleavage of protein S to normal values in patients with chemotherapy-induced thrombocytopenia. In conclusion, proteases from platelets seem to contribute to the presence of cleaved protein S in the circulation and may enhance the coagulation response in vivo by down regulating the anticoagulant activity of protein S.

Inhibition of Intrinsic Xase by Protein S

Objective—

Protein S is a vitamin K–dependent plasma protein that functions in the feedback regulation of thrombin generation. Our goal was to determine how protein S regulates the intrinsic pathway of blood coagulation.

Methods and Results—

We used plasma, including platelet-rich plasma, and in vitro methods to determine how the intrinsic pathway of blood coagulation is regulated by protein S. We obtained the following results: (1) activated partial thromboplastin time assays with protein S–supplemented plasma confirmed that protein S prolongs clotting time; (2) a modified activated partial thromboplastin time assay with factor IX (fIX)–deficient plasma confirmed that protein S affects fIX-initiated clotting; (3) a fIXa/factor VIIIa (fVIIIa)–mediated thrombin generation assay with either platelet-rich plasma or factor-deficient plasma, initiated with a limiting amount of tissue factor, was regulated by protein S; (4) in the presence of phosphatidylserine vesicles, protein S inhibited fIXa in the absence and presence of fVIIIa; and (5) protein S altered only the K M for factor X activation by fIXa in the absence of fVIIIa and both k cat and K M in the presence of fVIIIa.

Conclusion—

From our findings, it can be concluded that protein S inhibits fIXa in the presence or absence of fVIIIa in an activated protein C–independent way.

Grading the commercial optical biosensor literature-Class of 2008: 'The Mighty Binders'

Optical biosensor technology continues to be the method of choice for label-free, real-time interaction analysis. But when it comes to improving the quality of the biosensor literature, education should be fundamental. Of the 1413 articles published in 2008, less than 30% would pass the requirements for high-school chemistry. To teach by example, we spotlight 10 papers that illustrate how to implement the technology properly. Then we grade every paper published in 2008 on a scale from A to F and outline what features make a biosensor article fabulous, middling or abysmal. To help improve the quality of published data, we focus on a few experimental, analysis and presentation mistakes that are alarmingly common. With the literature as a guide, we want to ensure that no user is left behind.

Species-specific anticoagulant and mitogenic activities of murine protein S

BACKGROUND

The protein C pathway down-regulates thrombin generation and promotes cytoprotection during inflammation and stress. In preclinical studies using models of murine injury (e.g., sepsis and ischemic stroke), murine protein S may be required because of restrictive species specificity.

DESIGN AND METHODS

We prepared and characterized recombinant murine protein S using novel coagulation assays, immunoassays, and cell proliferation assays.

RESULTS

Purified murine protein S had good anticoagulant co-factor activity for murine activated protein C, but not for human activated protein C, in mouse or rat plasma. In human plasma, murine protein S was a poor co-factor for murine activated protein C and had no anticoagulant effect with human activated protein C, suggesting protein S species specificity for factor V in addition to activated protein C. We estimated that mouse plasma contains 22+/-1 microg/mL protein S and developed assays to measure activated protein C co-factor activity of the protein S in murine plasma. Activated protein C-independent anticoagulant activity of murine protein S was demonstrable and quantifiable in mouse plasma, and this activity was enhanced by exogenous murine protein S. Murine protein S promoted the proliferation of mouse and human smooth muscle cells. The potency of murine protein S was higher for mouse cells than for human cells and similarly, human protein S was more potent for human cells than for mouse cells.

CONCLUSIONS

The spectrum of bioactivities of recombinant murine protein S with mouse plasma and smooth muscle cells is similar to that of human protein S. However, in vitro and in vivo studies of the protein C pathway in murine disease models are more appropriately performed using murine protein S. This study extends previous observations regarding the remarkable species specificity of protein S to the mouse.