1
|
Werner LM, Criss AK. Diverse Functions of C4b-Binding Protein in Health and Disease. JOURNAL OF IMMUNOLOGY (BALTIMORE, MD. : 1950) 2023; 211:1443-1449. [PMID: 37931209 PMCID: PMC10629839 DOI: 10.4049/jimmunol.2300333] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/12/2023] [Accepted: 05/26/2023] [Indexed: 11/08/2023]
Abstract
C4b-binding protein (C4BP) is a fluid-phase complement inhibitor that prevents uncontrolled activation of the classical and lectin complement pathways. As a complement inhibitor, C4BP also promotes apoptotic cell death and is hijacked by microbes and tumors for complement evasion. Although initially characterized for its role in complement inhibition, there is an emerging recognition that C4BP functions in a complement-independent manner to promote cell survival, protect against autoimmune damage, and modulate the virulence of microbial pathogens. In this Brief Review, we summarize the structure and functions of human C4BP, with a special focus on activities that extend beyond the canonical role of C4BP in complement inhibition.
Collapse
Affiliation(s)
- Lacie M. Werner
- Department of Microbiology, Immunology, and Cancer Biology, University of Virginia School of Medicine, Charlottesville, VA, USA
| | - Alison K. Criss
- Department of Microbiology, Immunology, and Cancer Biology, University of Virginia School of Medicine, Charlottesville, VA, USA
| |
Collapse
|
2
|
Werner LM, Alcott A, Mohlin F, Ray JC, Belcher Dufrisne M, Smirnov A, Columbus L, Blom AM, Criss AK. Neisseria gonorrhoeae co-opts C4b-binding protein to enhance complement-independent survival from neutrophils. PLoS Pathog 2023; 19:e1011055. [PMID: 36862761 PMCID: PMC10013916 DOI: 10.1371/journal.ppat.1011055] [Citation(s) in RCA: 8] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/08/2022] [Revised: 03/14/2023] [Accepted: 02/07/2023] [Indexed: 03/03/2023] Open
Abstract
Neisseria gonorrhoeae (Gc) is a human-specific pathogen that causes the sexually transmitted infection gonorrhea. Gc survives in neutrophil-rich gonorrheal secretions, and recovered bacteria predominantly express phase-variable, surface-expressed opacity-associated (Opa) proteins (Opa+). However, expression of Opa proteins like OpaD decreases Gc survival when exposed to human neutrophils ex vivo. Here, we made the unexpected observation that incubation with normal human serum, which is found in inflamed mucosal secretions, enhances survival of Opa+ Gc from primary human neutrophils. We directly linked this phenomenon to a novel complement-independent function for C4b-binding protein (C4BP). When bound to the bacteria, C4BP was necessary and sufficient to suppress Gc-induced neutrophil reactive oxygen species production and prevent neutrophil phagocytosis of Opa+ Gc. This research identifies for the first time a complement-independent role for C4BP in enhancing the survival of a pathogenic bacterium from phagocytes, thereby revealing how Gc exploits inflammatory conditions to persist at human mucosal surfaces.
Collapse
Affiliation(s)
- Lacie M. Werner
- Department of Microbiology, Immunology, and Cancer Biology, University of Virginia, Charlottesville, Virginia, United States of America
| | - Allison Alcott
- Department of Microbiology, Immunology, and Cancer Biology, University of Virginia, Charlottesville, Virginia, United States of America
| | - Frida Mohlin
- Department of Translational Medicine, Lund University, Malmo, Sweden
| | - Jocelyn C. Ray
- Department of Microbiology, Immunology, and Cancer Biology, University of Virginia, Charlottesville, Virginia, United States of America
| | - Meagan Belcher Dufrisne
- Department of Chemistry, University of Virginia, Charlottesville, Virginia, United States of America
| | - Asya Smirnov
- Department of Microbiology, Immunology, and Cancer Biology, University of Virginia, Charlottesville, Virginia, United States of America
| | - Linda Columbus
- Department of Chemistry, University of Virginia, Charlottesville, Virginia, United States of America
| | - Anna M. Blom
- Department of Translational Medicine, Lund University, Malmo, Sweden
| | - Alison K. Criss
- Department of Microbiology, Immunology, and Cancer Biology, University of Virginia, Charlottesville, Virginia, United States of America
| |
Collapse
|
3
|
Gierula M, Ahnström J. Anticoagulant protein S-New insights on interactions and functions. J Thromb Haemost 2020; 18:2801-2811. [PMID: 32702208 DOI: 10.1111/jth.15025] [Citation(s) in RCA: 23] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/28/2020] [Revised: 06/25/2020] [Accepted: 07/10/2020] [Indexed: 01/21/2023]
Abstract
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.
Collapse
|
4
|
Schmidt CQ, Lambris JD, Ricklin D. Protection of host cells by complement regulators. Immunol Rev 2017; 274:152-171. [PMID: 27782321 DOI: 10.1111/imr.12475] [Citation(s) in RCA: 143] [Impact Index Per Article: 20.4] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
The complement cascade is an ancient immune-surveillance system that not only provides protection from pathogen invasion but has also evolved to participate in physiological processes to maintain tissue homeostasis. The alternative pathway (AP) of complement activation is the evolutionarily oldest part of this innate immune cascade. It is unique in that it is continuously activated at a low level and arbitrarily probes foreign, modified-self, and also unaltered self-structures. This indiscriminate activation necessitates the presence of preformed regulators on autologous surfaces to spare self-cells from the undirected nature of AP activation. Although the other two canonical complement activation routes, the classical and lectin pathways, initiate the cascade more specifically through pattern recognition, their activity still needs to be tightly controlled to avoid excessive reactivity. It is the perpetual duty of complement regulators to protect the self from damage inflicted by inadequate complement activation. Here, we review the role of complement regulators as preformed mediators of defense, explain their common and specialized functions, and discuss selected cases in which alterations in complement regulators lead to disease. Finally, rational engineering approaches using natural complement inhibitors as potential therapeutics are highlighted.
Collapse
Affiliation(s)
- Christoph Q Schmidt
- Institute of Pharmacology of Natural Products and Clinical Pharmacology, Ulm University, Ulm, Germany.
| | - John D Lambris
- Department of Pathology and Laboratory Medicine, University of Pennsylvania, Philadelphia, PA, USA
| | - Daniel Ricklin
- Department of Pathology and Laboratory Medicine, University of Pennsylvania, Philadelphia, PA, USA
| |
Collapse
|
5
|
Streptococcal pyrogenic exotoxin B inhibits apoptotic cell clearance by macrophages through protein S cleavage. Sci Rep 2016; 6:26026. [PMID: 27181595 PMCID: PMC4867609 DOI: 10.1038/srep26026] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/19/2015] [Accepted: 04/25/2016] [Indexed: 11/08/2022] Open
Abstract
Clearance of apoptotic cells by macrophages plays an important role in maintaining tissue homeostasis. Previous study indicated that streptococcal pyrogenic exotoxin B (SPE B) reduces phagocytic activity in group A streptococcus (GAS) infection. Here, we demonstrate that SPE B causes an inhibitory effect on protein S-mediated phagocytosis. In the presence of SPE B, serum- and purified protein S-mediated phagocytosis of apoptotic cells were significantly inhibited. The binding abilities of protein S to apoptotic cells were decreased by treatment with SPE B. Bacterial culture supernatants from GAS NZ131 strain also caused a reduction of protein S binding to apoptotic cells, but speB mutant strain did not. SPE B directly cleaved protein S in vitro and in vivo, whereas a lower level of cleavage occurred in mice infected with a speB isogenic mutant strain. SPE B-mediated initial cleavage of protein S caused a disruption of phagocytosis, and also resulted in a loss of binding ability of protein S-associated C4b-binding protein to apoptotic cells. Taken together, these results suggest a novel pathogenic role of SPE B that initiates protein S degradation followed by the inhibition of apoptotic cell clearance by macrophages.
Collapse
|
6
|
Microvesicles released constitutively from prostate cancer cells differ biochemically and functionally to stimulated microvesicles released through sublytic C5b-9. Biochem Biophys Res Commun 2015; 460:589-95. [PMID: 25817790 DOI: 10.1016/j.bbrc.2015.03.074] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/27/2015] [Accepted: 03/12/2015] [Indexed: 01/12/2023]
Abstract
We have classified microvesicles into two subtypes: larger MVs released upon stimulation of prostate cancer cells, sMVs, and smaller cMVs, released constitutively. cMVs are released as part of cell metabolism and sMVs, released at 10-fold higher levels, produced upon activation, including sublytic C5b-9. From electron microscopy, nanosight tracking analysis, dynamic light scattering and flow cytometry, cMVs (194-210 nm in diameter) are smaller than sMVs (333-385 nm). Furthermore, using a Quartz Crystal Microbalance measuring changes in resonant frequency (Δf) that equate to mass deposited on a sensor, an sMV and a cMV are estimated at 0.267 and 0.241 pg, respectively. sMVs carry more calcium and protein, express higher levels of lipid rafts, GPI-anchored CD55 and phosphatidylserine including deposited C5b-9 compared to cMVs. This may allude to biological differences such as increased bound C4BP on sMVs inhibiting complement more effectively.
Collapse
|
7
|
Min J, Ahn JY, Sekhon SS, Jin YM, Park CK, Um HJ, Jo I, Kim YH. Toxicoproteomic analysis of bovine aortic endothelial cell under exposure to cigarette smoking extracts. Mol Cell Toxicol 2013. [DOI: 10.1007/s13273-013-0043-y] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
|
8
|
Carlsson S, Dahlbäck B. Dependence on vitamin K-dependent protein S for eukaryotic cell secretion of the beta-chain of C4b-binding protein. J Biol Chem 2010; 285:32038-46. [PMID: 20693287 DOI: 10.1074/jbc.m110.148452] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The anticoagulant vitamin K-dependent protein S (PS) circulates in plasma in two forms, 30% free and 70% being bound to the complement regulatory protein C4b-binding protein (C4BP). The major C4BP isoform consists of 7 α-chains and 1 β-chain (C4BPβ(+)), the chains being linked by disulfide bridges. PS binds to the β-chain with high affinity. In plasma, PS is in molar excess over C4BPβ(+) and due to the high affinity, all C4BPβ(+) molecules contain a bound PS. Taken together with the observation that PS-deficient patients have decreased levels of C4BPβ(+), this raises the question of whether PS is important for secretion of the β-chain from the cell. To test this hypothesis, HEK293 cells were stably and transiently transfected with β-chain cDNA in combinations with cDNAs for PS and/or the α-chain. The concentration of β-chains in the medium increased after co-transfection with PS cDNA, but not by α-chain cDNA, suggesting secretion of the β-chains from the cells to be dependent on concomitant synthesis of PS, but not of the α-chains. Thus, β-chains that were not disulfide-linked to the α-chains were secreted in complex with PS, either as monomers or dimers. Pulse-chase demonstrated that the complexes between PS and β-chain were formed intracellularly, in the endoplasmic reticulum. In conclusion, our results demonstrate that successful secretion of β-chains depends on intracellular complex formation with PS, but not on the α-chains. This provides an explanation for the decreased β-chain levels observed in PS-deficient patients.
Collapse
Affiliation(s)
- Sofia Carlsson
- Department of Laboratory Medicine, Division of Clinical Chemistry, Lund University, Skåne University Hospital, SE-205 02 Malmö, Sweden
| | | |
Collapse
|
9
|
Trouw LA, Okroj M, Kupreishvili K, Landberg G, Johansson B, Niessen HWM, Blom AM. C4b-binding protein is present in affected areas of myocardial infarction during the acute inflammatory phase and covers a larger area than C3. PLoS One 2008; 3:e2886. [PMID: 18682851 PMCID: PMC2483938 DOI: 10.1371/journal.pone.0002886] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/23/2008] [Accepted: 07/16/2008] [Indexed: 11/18/2022] Open
Abstract
BACKGROUND During myocardial infarction reduced blood flow in the heart muscle results in cell death. These dying/dead cells have been reported to bind several plasma proteins such as IgM and C-reactive protein (CRP). In the present study we investigated whether fluid-phase complement inhibitor C4b-binding protein (C4BP) would also bind to the infarcted heart tissue. METHODS AND FINDINGS Initial studies using immunohistochemistry on tissue arrays for several cardiovascular disorders indicated that C4BP can be found in heart tissue in several cardiac diseases but that it is most abundantly found in acute myocardial infarction (AMI). This condition was studied in more detail by analyzing the time window and extent of C4BP positivity. The binding of C4BP correlates to the same locations as C3b, a marker known to correlate to the patterns of IgM and CRP staining. Based on criteria that describe the time after infarction we were able to pinpoint that C4BP binding is a relatively early marker of tissue damage in myocardial infarction with a peak of binding between 12 hours and 5 days subsequent to AMI, the phase in which infiltration of neutrophilic granulocytes in the heart is the most extensive. CONCLUSIONS C4BP, an important fluid-phase inhibitor of the classical and lectin pathway of complement activation binds to jeopardized cardiomyocytes early after AMI and co-localizes to other well known markers such as C3b.
Collapse
Affiliation(s)
- Leendert A. Trouw
- Department of Laboratory Medicine, Medical Protein Chemistry, Lund University, Malmö, Sweden
| | - Marcin Okroj
- Department of Laboratory Medicine, Medical Protein Chemistry, Lund University, Malmö, Sweden
| | - Koba Kupreishvili
- Institute for Cardiovascular Research, VU University Medical Center, Amsterdam, The Netherlands
| | | | - Bengt Johansson
- Department of Cardiology, Umeå University, Norrlands University Hospital, Umeå, Sweden
| | - Hans W. M. Niessen
- Institute for Cardiovascular Research, VU University Medical Center, Amsterdam, The Netherlands
- Department of Pathology and Cardiac Surgery, VU University Medial Center, Amsterdam, The Netherlands
| | - Anna M. Blom
- Department of Laboratory Medicine, Medical Protein Chemistry, Lund University, Malmö, Sweden
- * E-mail:
| |
Collapse
|
10
|
Trouw LA, Nielsen HM, Minthon L, Londos E, Landberg G, Veerhuis R, Janciauskiene S, Blom AM. C4b-binding protein in Alzheimer's disease: Binding to Aβ1–42 and to dead cells. Mol Immunol 2008; 45:3649-60. [DOI: 10.1016/j.molimm.2008.04.025] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/26/2008] [Revised: 04/23/2008] [Accepted: 04/24/2008] [Indexed: 11/16/2022]
|
11
|
Wenderfer SE, Soimo K, Wetsel RA, Braun MC. Analysis of C4 and the C4 binding protein in the MRL/lpr mouse. Arthritis Res Ther 2008; 9:R114. [PMID: 17971229 PMCID: PMC2212569 DOI: 10.1186/ar2320] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/15/2007] [Revised: 10/11/2007] [Accepted: 10/30/2007] [Indexed: 11/10/2022] Open
Abstract
Systemic lupus erythematosus is a complement-mediated autoimmune disease. While genetic deficiencies of classical pathway components lead to an increased risk of developing systemic lupus erythematosus, end organ damage is associated with complement activation and immune complex deposition. The role of classical pathway regulators in systemic lupus erythematosus is unknown. C4 binding protein (C4bp) is a major negative regulator of the classical pathway. In order to study the role of C4bp deficiency in an established murine model of lupus nephritis, mice with a targeted deletion in the gene encoding C4bp were backcrossed into the MRL/lpr genetic background. Compared with control MRL/lpr mice, C4bp knockout MLR/lpr mice had similar mortality and similar degrees of lymphoproliferation. There were no differences in the extent of proteinuria or renal inflammation. Staining for complement proteins and immunoglobulins in the kidneys of diseased mice revealed no significant strain differences. Moreover, there was no difference in autoantibody production or in levels of circulating immune complexes. In comparison with C57BL/6 mice, MRL/lpr mice had depressed C4 levels as early as 3 weeks of age. The absence of C4bp did not impact serum C4 levels or alter classical pathway hemolytic activity. Given that immune complex renal injury in the MRL/lpr mouse is independent of Fc receptors as well as the major negative regulator of the classical pathway, new mechanisms for immune-complex-mediated renal injury need to be considered.
Collapse
Affiliation(s)
- Scott E Wenderfer
- Center for Immunology and Autoimmune Diseases, Brown Foundation Institute of Molecular Medicine, 1825 Pressler Street, Houston, TX 77030, USA
| | | | | | | |
Collapse
|
12
|
Trouw L, Blom A, Gasque P. Role of complement and complement regulators in the removal of apoptotic cells. Mol Immunol 2008; 45:1199-207. [DOI: 10.1016/j.molimm.2007.09.008] [Citation(s) in RCA: 142] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/06/2007] [Accepted: 09/06/2007] [Indexed: 01/18/2023]
|
13
|
Xiong W, Chen Y, Wang H, Wang H, Wu H, Lu Q, Han D. Gas6 and the Tyro 3 receptor tyrosine kinase subfamily regulate the phagocytic function of Sertoli cells. Reproduction 2008; 135:77-87. [DOI: 10.1530/rep-07-0287] [Citation(s) in RCA: 70] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
The apoptotic spermatogenic cells and residual bodies are phagocytosed and degraded by Sertoli cells during spermatogenesis. The mechanisms of this process are largely unknown. Here, we demonstrate that Gas6 and its receptors, the Tyro 3 subfamily of receptor tyrosine kinases (RTKs; Tyro 3, Axl, and Mer), regulate the phagocytic function of Sertoli cells. The phagocytic ability of Sertoli cells increased by five times in the presence of Gas6 in serum-free medium when compared with controls. The Sertoli cells lacking Mer showed a 35% reduction in phagocytosis of apoptotic spermatogenic cells when compared with wild-type (WT) controls, whereas the Sertoli cells lacking Tyro 3 or Axl exhibited phagocytic activity comparable with the controls. Notably, the Sertoli cells lacking all three members of the Tyro 3 RTK subfamily showed a dramatic decrease in phagocytic ability of 7.6-fold when compared with WT Sertoli cells. The deficiency in phagocytosis by the triple-mutant Sertoli cells was due to the deficit in binding of the Sertoli cells to apoptotic germ cells. These findings suggest that Mer is responsible for triggering phagocytosis of apoptotic spermatogenic cells by Sertoli cells and that Tyro 3, Axl, and Mer participate in recognizing and binding apoptotic germ cells by Sertoli cells in a redundant manner. Gas6 is a functional ligand of the Tyro 3 RTK subfamily in mediating phagocytic ability of Sertoli cells.
Collapse
|
14
|
Trouw LA, Bengtsson AA, Gelderman KA, Dahlbäck B, Sturfelt G, Blom AM. C4b-binding Protein and Factor H Compensate for the Loss of Membrane-bound Complement Inhibitors to Protect Apoptotic Cells against Excessive Complement Attack. J Biol Chem 2007; 282:28540-28548. [PMID: 17699521 DOI: 10.1074/jbc.m704354200] [Citation(s) in RCA: 106] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022] Open
Abstract
Apoptotic cells have been reported to down-regulate membrane-bound complement regulatory proteins (m-C-Reg) and to activate complement. Nonetheless, most apoptotic cells do not undergo complement-mediated lysis. Therefore, we hypothesized that fluid phase complement inhibitors would bind to apoptotic cells and compensate functionally for the loss of m-C-Reg. We observed that m-C-Reg are down-regulated rapidly upon apoptosis but that complement activation follows only after a gap of several hours. Coinciding with, but independent from, complement activation, fluid phase complement inhibitors C4b-binding protein (C4BP) and factor H (fH) bind to the cells. C4BP and fH do not entirely prevent complement activation but strongly limit C3 and C9 deposition. Late apoptotic cells, present in blood of healthy controls and systemic lupus erythematosus patients, are also positive for C4BP and fH. Upon culture, the percentage of late apoptotic cells increases, paralleled by increased C4BP binding. C4BP binds to dead cells mainly via phosphatidylserine, whereas fH binds via multiple interactions with CRP playing no major role for binding of C4BP or fH. In conclusion, during late apoptosis, cells acquire fluid phase complement inhibitors that compensate for the down-regulation of m-C-Reg and protect against excessive complement activation and lysis.
Collapse
Affiliation(s)
- Leendert A Trouw
- Department of Laboratory Medicine, University Hospital Malmö, 5-20502 Malmö, Sweden
| | - Anders A Bengtsson
- Department of Clinical Science, Rheumatology, Lund University, 5-22184 Lund, Sweden
| | - Kyra A Gelderman
- Unit for Medical Inflammation Research, Lund University, 5-22184 Lund, Sweden
| | - Björn Dahlbäck
- Department of Laboratory Medicine, University Hospital Malmö, 5-20502 Malmö, Sweden
| | - Gunnar Sturfelt
- Department of Clinical Science, Rheumatology, Lund University, 5-22184 Lund, Sweden
| | - Anna M Blom
- Department of Laboratory Medicine, University Hospital Malmö, 5-20502 Malmö, Sweden.
| |
Collapse
|
15
|
Kulman JD, Harris JE, Xie L, Davie EW. Proline-rich Gla protein 2 is a cell-surface vitamin K-dependent protein that binds to the transcriptional coactivator Yes-associated protein. Proc Natl Acad Sci U S A 2007; 104:8767-72. [PMID: 17502622 PMCID: PMC1885577 DOI: 10.1073/pnas.0703195104] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Proline-rich Gla protein 2 (PRGP2) is one of four known vertebrate transmembrane gamma-carboxyglutamic acid (Gla) proteins. Members of this protein family are broadly expressed in fetal and adult human tissues and share a common architecture consisting of a predicted propeptide and Gla domain, a single-pass transmembrane segment, and tandem Pro/Leu-Pro-Xaa-Tyr (PY) motifs near their C termini. Using a methodology developed for the regulated expression of enzymatically biotinylated proteins in mammalian cells, we demonstrate that PRGP2 undergoes gamma-glutamyl carboxylation in a manner that is both dependent upon the presence of a proteolytically cleavable propeptide and sensitive to warfarin, a vitamin K antagonist that is widely used as an antithrombotic agent. When expressed at physiologically relevant levels, the majority of PRGP2 is present in the gamma-glutamyl carboxylated, propeptide-cleaved (mature) form. We additionally demonstrate, by Western blotting and flow cytometry, that mature PRGP2 is predominantly located on the cell surface with the Gla domain exposed extracellularly. In a yeast two-hybrid screen that used the C-terminal cytoplasmic region of PRGP2 as bait, we identified the WW domain-containing transcriptional coactivator Yes-associated protein (YAP) as a binding partner for PRGP2. In GST pull-down experiments, both PRGP2 PY motifs and both YAP WW domains were essential for complex formation, as were residues proximal to the core sequence of the first PY motif. These findings suggest that PRGP2 may be involved in a signal transduction pathway, the impairment of which may be an unintended consequence of warfarin therapy.
Collapse
Affiliation(s)
- John D. Kulman
- *Department of Biochemistry, University of Washington, Seattle, WA 98195; and
| | - Jeff E. Harris
- *Department of Biochemistry, University of Washington, Seattle, WA 98195; and
| | - Ling Xie
- National Institute of Arthritis and Musculoskeletal and Skin Diseases, Bethesda, MD 20892
| | - Earl W. Davie
- *Department of Biochemistry, University of Washington, Seattle, WA 98195; and
- To whom correspondence should be addressed. E-mail:
| |
Collapse
|
16
|
Kulman JD, Harris JE, Nakazawa N, Ogasawara M, Satake M, Davie EW. Vitamin K-dependent proteins in Ciona intestinalis, a basal chordate lacking a blood coagulation cascade. Proc Natl Acad Sci U S A 2006; 103:15794-9. [PMID: 17043233 PMCID: PMC1635082 DOI: 10.1073/pnas.0607543103] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
We have isolated and sequenced several cDNAs derived from the sea squirt Ciona intestinalis that encode vitamin K-dependent proteins. Four of these encode gamma-carboxyglutamic acid (Gla) domain-containing proteins, which we have named Ci-Gla1 through Ci-Gla4. Two additional cDNAs encode the apparent orthologs of gamma-glutamyl carboxylase and vitamin K epoxide reductase. Ci-Gla1 undergoes gamma-glutamyl carboxylation when expressed in CHO cells and is homologous to Gla-RTK, a putative receptor tyrosine kinase previously identified in a related ascidian. The remaining three Gla domain proteins are similar to proteins that participate in fundamental developmental processes, complement regulation, and blood coagulation. These proteins are generally expressed at low levels throughout development and exhibit either relatively constant expression (Ci-Gla1, gamma-glutamyl carboxylase, and vitamin K epoxide reductase) or spatiotemporal regulation (Ci-Gla2, -3, and -4). These results demonstrate the evolutionary emergence of the vitamin K-dependent Gla domain before the divergence of vertebrates and urochordates and suggest novel functions for Gla domain proteins distinct from their roles in vertebrate hemostasis. In addition, these findings highlight the usefulness of C. intestinalis as a model organism for investigating vitamin K-dependent physiological phenomena, which may be conserved among the chordate subphyla.
Collapse
Affiliation(s)
- John D. Kulman
- *Department of Biochemistry, University of Washington, Seattle, WA 98195
| | - Jeff E. Harris
- *Department of Biochemistry, University of Washington, Seattle, WA 98195
| | - Noriko Nakazawa
- Department of Biology, Faculty of Science, Chiba University, Chiba 263-8522, Japan; and
| | - Michio Ogasawara
- Department of Biology, Faculty of Science, Chiba University, Chiba 263-8522, Japan; and
| | - Masanobu Satake
- Institute of Development, Aging, and Cancer, Tohoku University, Sendai 980-8575, Japan
| | - Earl W. Davie
- *Department of Biochemistry, University of Washington, Seattle, WA 98195
- To whom correspondence should be addressed. E-mail:
| |
Collapse
|
17
|
de Wolf CJF, Cupers RMJ, Bertina RM, Vos HL. Interleukin-6 induction of protein s is regulated through signal transducer and activator of transcription 3. Arterioscler Thromb Vasc Biol 2006; 26:2168-74. [PMID: 16840717 DOI: 10.1161/01.atv.0000236202.39165.eb] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
OBJECTIVE The protein C anticoagulant pathway is an essential process for attenuating thrombin generation by the membrane-bound procoagulant complexes tenase and prothrombinase. In this pathway, protein S (PS) serves as a cofactor for activated protein C. PS circulates in plasma both in a free form and in complex with complement component 4b-binding protein (C4BP). C4BP is a known acute phase reactant, thereby suggesting a relation between PS and the acute phase response. Interleukin (IL)-6 has been shown to increase both PS and C4BP gene expression. Our objective was to study the regulation of PS gene expression by IL-6 in detail. METHODS AND RESULTS IL-6 upregulates both PS mRNA and protein levels in liver-derived HepG2 cells. The promoter of the PS gene (PROS1) was cloned upstream from a luciferase reporter gene. After transfection in HepG2 cells, the luciferase activity was shown to be stimulated by the addition of IL-6. IL-6 exerts its effect through Signal Transducer and Activator of Transcription 3 (STAT3) that interacts with the PROS1 promoter at a binding site in between nucleotides 229 to 207 upstream from the translational start. CONCLUSIONS IL-6 induces PS expression via STAT3. A possible function for IL-6-induced PS expression in cell survival is discussed.
Collapse
Affiliation(s)
- Cornelia J F de Wolf
- Hemostasis and Thrombosis Research Center, Department of Hematology, Leiden, The Netherlands
| | | | | | | |
Collapse
|
18
|
Sjöberg AP, Trouw LA, McGrath FDG, Hack CE, Blom AM. Regulation of Complement Activation by C-Reactive Protein: Targeting of the Inhibitory Activity of C4b-Binding Protein. THE JOURNAL OF IMMUNOLOGY 2006; 176:7612-20. [PMID: 16751408 DOI: 10.4049/jimmunol.176.12.7612] [Citation(s) in RCA: 75] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
Abstract
C-reactive protein (CRP) is the major acute phase protein in humans. It has been shown that CRP interacts with factor H, an inhibitor of the alternative pathway of complement, and now we demonstrate binding of CRP to the fluid-phase inhibitor of the classical pathway, C4b-binding protein (C4BP). C4BP bound to directly immobilized recombinant CRP as well as CRP attached to phosphorylcholine. The binding was sensitive to ionic strength and was enhanced in the presence of calcium. C4BP lacking beta-chain and protein S, which is a form of C4BP increasing upon inflammation, bound CRP with higher affinity than the C4BP-protein S complex. The binding could not be blocked with mAbs directed against peripheral parts of the alpha-chains of C4BP while the isolated central core of C4BP obtained by partial proteolytic digestion bound CRP, indicating that the binding site for CRP is localized in the central core of the C4BP molecule. Furthermore, we found complexes in serum from a patient with an elevated CRP level and trace amounts of CRP were also identified in a plasma-derived C4BP preparation. We were also able to detect C4BP-CRP complexes in solution and established that C4BP retains full complement regulatory activity in the presence of CRP. In addition, we found that C4BP can compete with C1q for binding to immobilized CRP and that it inhibits complement activation locally. We hypothesize that CRP limits excessive complement activation on targets via its interactions with both factor H and C4BP.
Collapse
Affiliation(s)
- Andreas P Sjöberg
- Department of Laboratory Medicine, Section of Clinical Chemistry, Wallenberg Laboratory, University Hospital Malmö, Lund University, Sweden
| | | | | | | | | |
Collapse
|
19
|
Trouw LA, Nilsson SC, Gonçalves I, Landberg G, Blom AM. C4b-binding protein binds to necrotic cells and DNA, limiting DNA release and inhibiting complement activation. ACTA ACUST UNITED AC 2005; 201:1937-48. [PMID: 15967823 PMCID: PMC2212022 DOI: 10.1084/jem.20050189] [Citation(s) in RCA: 80] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
After cell death, via apoptosis or necrosis, the uptake of dead cells by neighboring cells or phagocytes prevents the release of intracellular content. An array of molecules, including initiation molecules of the complement system, are involved in marking dead cells for uptake. After binding of these molecules, complement activation takes place, which when uncontrolled might result in a proinflammatory state. In the current study we demonstrate that complement inhibitor, C4b-binding protein (C4BP), binds strongly to necrotic cells, irrespective of the cell type used or the method of induction. After binding of the C4BP-protein S (PS) complex to necrotic cells via PS-phosphatidylserine and C4BP-DNA interactions, C4BP-PS inhibits complement activation on these cells. C4BP binds DNA via a patch of positively charged amino acids, mainly on the second complement control domain of the C4BP alpha-chain (affinity constant: 190 nM). Furthermore, C4BP limits DNA release from necrotic cells and inhibits DNA-mediated complement activation in solution. The C4BP-necrotic cell interaction also occurs in vivo as necrotic areas of arteriosclerotic plaques and of various cancers stain strongly positive for C4BP. This study describes a novel mechanism in which C4BP limits the inflammatory potential of necrotic cells.
Collapse
Affiliation(s)
- Leendert A Trouw
- Department of Laboratory Medicine, University Hospital Malmö, Lund University, S-205 02 Malmö, Sweden
| | | | | | | | | |
Collapse
|
20
|
Hall MO, Obin MS, Heeb MJ, Burgess BL, Abrams TA. Both protein S and Gas6 stimulate outer segment phagocytosis by cultured rat retinal pigment epithelial cells. Exp Eye Res 2005; 81:581-91. [PMID: 15949798 DOI: 10.1016/j.exer.2005.03.017] [Citation(s) in RCA: 99] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2004] [Revised: 03/08/2005] [Accepted: 03/29/2005] [Indexed: 01/12/2023]
Abstract
Survival of the retina requires the daily phagocytosis of photoreceptor outer segments (OS) by the overlying retinal pigment epithelium (RPE). OS phagocytosis by cultured RPE requires serum and we have recently shown that the vitamin K-dependent serum protein, Gas6, can completely replace serum in this process. Surprisingly, however, we show here that 4-month-old Gas6 knockout mice have normal appearing retinas, except for a reduced ratio of outer segment to inner segment length. We also show that removal of Gas6 from serum does not abrogate the ability of serum to support OS phagocytosis by rat RPE. Both of these findings suggest the presence of an additional serum ligand that is able to support OS phagocytosis by RPE cells. Protein S (PS) is a vitamin K-dependent serum protein with a high degree of structural similarity to Gas6, and a well characterized role in blood coagulation. We report here that recombinant rat PS is able to stimulate OS phagocytosis, and similar to Gas6, it does so through a Mer-dependent mechanism. This is the first demonstration of a common role for Gas6 and PS in any biological process. The existence of redundant ligands for Mer-dependent OS phagocytosis underscores the critical role of this process in the maintenance of retinal function.
Collapse
Affiliation(s)
- Michael O Hall
- Jules Stein Eye Institute, UCLA Medical Center, 100 Stein Plaza, Los Angeles, CA 90095-7008, USA.
| | | | | | | | | |
Collapse
|
21
|
Dahlbäck B. Blood coagulation and its regulation by anticoagulant pathways: genetic pathogenesis of bleeding and thrombotic diseases. J Intern Med 2005; 257:209-23. [PMID: 15715678 DOI: 10.1111/j.1365-2796.2004.01444.x] [Citation(s) in RCA: 112] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
Blood coagulation and its regulation by anticoagulant pathways: genetic pathogenesis Platelet-mediated primary haemostasis and blood coagulation have evolved as important defence mechanisms against bleeding. The formation of the platelet plug provides the initial occlusion of the vascular lesion. This is temporally co-ordinated with the activation of the coagulation system, which occurs in response to the rupture of endothelium and the exposure of blood to the extravascular tissue. The reactions of blood coagulation are carefully controlled by several anticoagulant mechanisms and under normal conditions they prevail over the procoagulant forces. Genetic or acquired disturbances of the natural balance between the pro- and anticoagulant systems may result in bleeding or thrombotic diseases.
Collapse
Affiliation(s)
- Björn Dahlbäck
- Department of Laboratory Medicine, Clinical Chemistry, Lund University, University Hospital, Malmö, Sweden.
| |
Collapse
|
22
|
Berkner KL, Runge KW. The physiology of vitamin K nutriture and vitamin K-dependent protein function in atherosclerosis. J Thromb Haemost 2004; 2:2118-32. [PMID: 15613016 DOI: 10.1111/j.1538-7836.2004.00968.x] [Citation(s) in RCA: 130] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
Recent advances in the discovery of new functions for vitamin K-dependent (VKD) proteins and in defining vitamin K nutriture have led to a substantial revision in our understanding of vitamin K physiology. The only unequivocal function for vitamin K is as a cofactor for the carboxylation of VKD proteins which renders them active. While vitamin K was originally associated only with hepatic VKD proteins that participate in hemostasis, VKD proteins are now known to be present in virtually every tissue and to be important to bone mineralization, arterial calcification, apoptosis, phagocytosis, growth control, chemotaxis, and signal transduction. The development of improved methods for analyzing vitamin K has shed considerable insight into the relative importance of different vitamin K forms in the diet and their contribution to hepatic vs. non-hepatic tissue. New assays that measure the extent of carboxylation in VKD proteins have revealed that while the current recommended daily allowance for vitamin K is sufficient for maintaining functional hemostasis, the undercarboxylation of at least one non-hemostatic protein is frequently observed in the general population. The advances in defining VKD protein function and vitamin K nutriture are described, as is the potential impact of VKD proteins on atherosclerosis. Many of the VKD proteins contribute to atherogenesis. Recent studies suggest involvement in arterial calcification, which may be influenced by dietary levels of vitamin K and by anticoagulant drugs such as warfarin that antagonize vitamin K action.
Collapse
Affiliation(s)
- K L Berkner
- Department of Molecular Cardiology, Lerner Research Institute, Cleveland Clinic Lerner College of Medicine at Case Western Reserve University, Cleveland, OH 44195, USA.
| | | |
Collapse
|
23
|
Attali G, Gancz D, Fishelson Z. Increased sensitivity of early apoptotic cells to complement-mediated lysis. Eur J Immunol 2004; 34:3236-45. [PMID: 15368275 DOI: 10.1002/eji.200425011] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Opsonization of apoptotic cells with complement proteins contributes to their clearance by phagocytes. Little is known about the lytic effects of complement on apoptotic cells. Sensitivity of cells treated with anti-Fas antibody (Jurkat cells), staurosporine or etoposide (Raji cells) to lysis by complement was examined. As shown here, early apoptotic cells are more sensitive to lysis by antibody and complement than control cells. More complement C3 and C9 bound to apoptotic than to control cells, even though antibody binding was similar. Enhanced killing and C3/C9 deposition were blocked by benzyloxy-Val-Ala-Asp-fluoromethylketone, a pan-caspase inhibitor. Complement-mediated lysis of early apoptotic cells was also prevented by inhibitors of caspases 6, 8, 9 or 10. In contrast, caspase inhibitors had no effect on the lysis of non-apoptotic Jurkat and Raji cells. Early apoptotic Jurkat cells were also more sensitive to lysis by the pore formers streptolysin O and melittin. Sensitivity of Jurkat Bcl-2 transfectants to lysis by complement was analyzed. Enhanced Bcl-2 expression was associated with reduced C3 deposition and lower sensitivity to complement-mediated lysis. These results demonstrate that at an early stage in apoptosis, following caspase activation, cells become sensitive to necrotic-type death by complement and other pore formers. Furthermore, they suggest that Bcl-2 is actively protecting Jurkat cells from complement-mediated lysis.
Collapse
Affiliation(s)
- Gitit Attali
- Department of Cell and Developmental Biology, Sackler School of Medicine, Tel Aviv University, Tel Aviv, Israel
| | | | | |
Collapse
|
24
|
Kask L, Trouw LA, Dahlbäck B, Blom AM. The C4b-binding Protein-Protein S Complex Inhibits the Phagocytosis of Apoptotic Cells. J Biol Chem 2004; 279:23869-73. [PMID: 15096498 DOI: 10.1074/jbc.c400159200] [Citation(s) in RCA: 64] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The phagocytosis of apoptotic cells is a complex process involving numerous interactions between the target cell and the macrophage. We have examined a role of the major soluble inhibitor of the classic and lectin complement pathways, C4b-binding protein (C4BP), in the clearance of apoptotic cells. The major form of C4BP present in blood is composed of seven alpha-chains and one beta-chain, which binds protein S (PS). Approximately 70% of all PS in human plasma is trapped in such a complex and is able to localize C4BP to the surface of apoptotic cells due to the high affinity to phosphatidylserine. Free PS has recently been shown to enhance phagocytosis of apoptotic cells by macrophages. We observed a stimulatory effect of free PS on the engulfment of apoptotic cells (BL-41 and Jurkat) by primary human macrophages or THP-1 cells and a decrease of activity in serum depleted of PS in agreement with previous results. However, we also show that the process is strongly inhibited in the presence of the C4BP-PS complex. Addition of the C4BP-PS complex to serum deficient in both molecules abolished the enhancing effect of serum on phagocytosis. The effect of both free PS and the C4BP-PS complex could be inhibited with monoclonal antibody directed against the Gla domain of PS. Although the presence of the C4BP-PS complex on apoptotic cells may lead to decreased phagocytosis, it may still be beneficial to the host, since it could prevent secondary necrosis because it inhibits further complement attack.
Collapse
Affiliation(s)
- Lena Kask
- Lund University, The Wallenberg Laboratory, Department of Clinical Chemistry, University Hospital Malmö; S-205 02 Malmö, Sweden
| | | | | | | |
Collapse
|
25
|
Blom AM, Villoutreix BO, Dahlbäck B. Complement inhibitor C4b-binding protein-friend or foe in the innate immune system? Mol Immunol 2004; 40:1333-46. [PMID: 15072852 DOI: 10.1016/j.molimm.2003.12.002] [Citation(s) in RCA: 135] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/09/2003] [Revised: 12/09/2003] [Accepted: 12/11/2003] [Indexed: 01/15/2023]
Abstract
The complement system constitutes an important component of the defence against foreign organisms, functioning both in innate and adaptive immune systems. It is potentially harmful also to the own organism and is therefore tightly regulated by a number of membrane-bound and soluble factors. C4b-binding protein (C4BP) is a potent circulating soluble inhibitor of the classical and lectin pathways of complement. In recent years, the relationships between the structure of C4BP and its functions have been elucidated using a combination of computer-based molecular analysis and recombinant DNA technologies. Moreover, two novel functions have recently been ascribed to C4BP. One is the ability of C4BP to localize complement regulatory activity to the surface of apoptotic cells via its interaction with the membrane-binding vitamin K-dependent protein S. The other is the ability of C4BP to act as a survival factor for B cells due to an interaction with CD40. The complement regulatory activity of C4BP is not only beneficial because it is also explored by pathogens such as Neisseria gonorrhoeae, Bordetella pertussis, Streptococcus pyogenes, Escherichia coli K1, and Candida albicans, that bind C4BP to their surfaces. This contributes to the serum resistance and the pathogenicity of these bacteria. In this review, the structural requirements and functional importance of the interactions between C4BP and its various ligands are discussed.
Collapse
Affiliation(s)
- Anna M Blom
- The Wallenberg Laboratory, Department of Clinical Chemistry, University Hospital Malmö, Lund University, S-205 02 Malmö, Sweden.
| | | | | |
Collapse
|
26
|
Rezende SM, Simmonds RE, Lane DA. Coagulation, inflammation, and apoptosis: different roles for protein S and the protein S-C4b binding protein complex. Blood 2004; 103:1192-201. [PMID: 12907438 DOI: 10.1182/blood-2003-05-1551] [Citation(s) in RCA: 139] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Protein S (PS) has an established role as an important cofactor to activated protein C (APC) in the degradation of coagulation cofactors Va and VIIIa. This anticoagulant role is evident from the consequences of its deficiency, when there is an increased risk of venous thromboembolism. In human plasma, PS circulates approximately 40% as free PS (FPS) and 60% in complex with C4b-binding protein (C4BP). Formation of this complex results in loss of PS cofactor function, and C4BP can then modulate the anticoagulant activity of APC. It had long been predicted that the complex could act as a bridge between coagulation and inflammation due to the involvement of C4BP in regulating complement activation. This prediction was recently supported by the demonstration of binding of the PS-C4BP complex to apoptotic cells. This review aims to summarize recent findings on the structure and functions of PS, the basis and importance of its deficiency, its interaction with C4BP, and the possible physiologic and pathologic importance of the PS-C4BP interaction.
Collapse
Affiliation(s)
- Suely Meireles Rezende
- Research Laboratory, Fundação HEMOMINAS, Alameda Ezequiel Dias, 321 Belo Horizonte-MG-Brazil, 30130-110.
| | | | | |
Collapse
|
27
|
Abstract
A natural anticoagulant pathway denoted the protein C system provides specific and efficient control of blood coagulation. Protein C is the key component of the system and circulates in the blood as a zymogen to an anticoagulant serine protease. Activation of protein C is achieved on the surface of endothelial cells by thrombin bound to the membrane protein thrombomodulin. The endothelial protein C receptor stimulates the activation of protein C on the endothelium. Activated protein C (APC) modulates blood coagulation by cleaving a limited number of peptide bonds in factor VIIIa (FVIIIa) and factor Va (FVa), cofactors in the activation of factor X and prothrombin, respectively. Vitamin K-dependent protein S stimulates the APC-mediated regulation of coagulation. Not only is protein S involved in the degradation of FVIIIa, but so is FV, which in recent years has been found to be a Janus-faced protein with both procoagulant and anticoagulant potentials. A number of genetic defects affecting the anticoagulant function of the protein C system, eg, APC resistance (Arg506Gln or FV Leiden) and deficiencies of protein C and protein S constitute major risk factors of venous thrombosis. The protein C system also has anti-inflammatory and antiapoptotic potentials, the molecular mechanisms of which are beginning to be unraveled. APC has emerged in recent years as a useful therapeutic compound in the treatment of severe septic shock. The beneficial effect of APC is believed be due to both its anticoagulant and its anti-inflammatory properties.
Collapse
Affiliation(s)
- Björn Dahlbäck
- Department of Laboratory Medicine, Division of Clinical Chemistry, Lund University, The Wallenberg Laboratory, University Hospital, Malmö, Malmö, Sweden.
| |
Collapse
|