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
|
Serrano I, Luque A, Mitjavila F, Blom AM, Rodríguez de Córdoba S, Vega MC, Torras J, Aran JM. The Hidden Side of Complement Regulator C4BP: Dissection and Evaluation of Its Immunomodulatory Activity. Front Immunol 2022; 13:883743. [PMID: 35547734 PMCID: PMC9084231 DOI: 10.3389/fimmu.2022.883743] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/25/2022] [Accepted: 03/28/2022] [Indexed: 11/18/2022] Open
Abstract
C4b-binding protein (C4BP) is a well-known regulator of the complement system that holds additional and important activities unrelated to complement inhibition. Recently, we have described a novel immunomodulatory activity in the minor C4BP(β-) isoform directly acting over inflammatory phagocytes. Here we show that incorporation of the β-chain to the C4BP α-chain oligomer interferes with this immunomodulatory activity of C4BP. Moreover, an oligomeric form including only the complement control protein 6 (CCP6) domain of the C4BP α-chain (PRP6-HO7) is sufficient to “reprogram” monocyte-derived DCs (Mo-DCs) from a pro-inflammatory and immunogenic phenotype to an anti-inflammatory and tolerogenic state. PRP6-HO7 lacks complement regulatory activity but retains full immunomodulatory activity over inflammatory Mo-DCs induced by TLRs, characterized by downregulation of relevant surface markers such as CD83, HLA-DR, co-stimulatory molecules such as CD86, CD80 and CD40, and pro-inflammatory cytokines such as IL-12 and TNF-α. Furthermore, PRP6-HO7-treated Mo-DCs shows increased endocytosis, significantly reduced CCR7 expression and CCL21-mediated chemotaxis, and prevents T cell alloproliferation. Finally, PRP6-HO7 shows also full immunomodulatory activity over Mo-DCs isolated from lupus nephritis patients with active disease, even without further pro-inflammatory stimulation. Therefore PRP6-HO7, retaining the immunomodulatory activity of C4BP(β-) and lacking its complement regulatory activity, might represent a promising and novel alternative to treat autoimmune diseases.
Collapse
Affiliation(s)
- Inmaculada Serrano
- Immune-inflammatory Processes and Gene Therapeutics Group, Institut d'Investigació Biomèdica de Bellvitge (IDIBELL), L'Hospitalet de Llobregat, Barcelona, Spain
| | - Ana Luque
- Immune-inflammatory Processes and Gene Therapeutics Group, Institut d'Investigació Biomèdica de Bellvitge (IDIBELL), L'Hospitalet de Llobregat, Barcelona, Spain
| | - Francesca Mitjavila
- Internal Medicine Service, Bellvitge University Hospital, University of Barcelona and Institut d'Investigació Biomèdica de Bellvitge (IDIBELL), L'Hospitalet de Llobregat, Barcelona, Spain
| | - Anna M Blom
- Department of Translational Medicine, Section of Medical Protein Chemistry, Lund University, Malmö, Sweden
| | - Santiago Rodríguez de Córdoba
- Molecular Pathology/Genetics of Complement Group, Centro de Investigaciones Biológicas Margarita Salas (CSIC) and Ciber de Enfermedades Raras (CIBERER), Madrid, Spain
| | - M Cristina Vega
- Structural Biology of Host-Pathogen Interactions Group, Centro de Investigaciones Biológicas Margarita Salas (CSIC), Madrid, Spain
| | - Joan Torras
- Nephrology Department, Bellvitge University Hospital, Experimental Nephrology Lab., University of Barcelona and Institut d'Investigació Biomèdica de Bellvitge (IDIBELL), L'Hospitalet de Llobregat, Barcelona, Spain
| | - Josep M Aran
- Immune-inflammatory Processes and Gene Therapeutics Group, Institut d'Investigació Biomèdica de Bellvitge (IDIBELL), L'Hospitalet de Llobregat, Barcelona, Spain
| |
Collapse
|
3
|
Ermert D, Blom AM. C4b-binding protein: The good, the bad and the deadly. Novel functions of an old friend. Immunol Lett 2015; 169:82-92. [PMID: 26658464 DOI: 10.1016/j.imlet.2015.11.014] [Citation(s) in RCA: 94] [Impact Index Per Article: 10.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/08/2015] [Revised: 11/26/2015] [Accepted: 11/27/2015] [Indexed: 01/29/2023]
Abstract
C4b-binding protein (C4BP) is best known as a potent soluble inhibitor of the classical and lectin pathways of the complement system. This large 500 kDa multimeric plasma glycoprotein is expressed mainly in the liver but also in lung and pancreas. It consists of several identical 75 kDa α-chains and often also one 40 kDa β-chain, both of which are mainly composed of complement control protein (CCP) domains. Structure-function studies revealed that one crucial binding site responsible for inhibition of complement is located to CCP1-3 of the α-chain. Binding of anticoagulant protein S to the CCP1 of the β-chain provides C4BP with the ability to strongly bind apoptotic and necrotic cells in order to prevent inflammation arising from activation of complement by these cells. Further, C4BP interacts strongly with various types of amyloid and enhances fibrillation of islet amyloid polypeptide secreted from pancreatic beta cells, which may attenuate pro-inflammatory and cytotoxic effects of this amyloid. Full deficiency of C4BP has not been identified but non-synonymous alterations in its sequence have been found in haemolytic uremic syndrome and recurrent pregnancy loss. Furthermore, C4BP is bound by several bacterial pathogens, notably Streptococcus pyogenes, which due to inhibition of complement and enhancement of bacterial adhesion to endothelial cells provides these bacteria with a survival advantage in the host. Thus, depending on the context, C4BP has a protective or detrimental role in the organism.
Collapse
Affiliation(s)
- David Ermert
- Lund University, Department of Translational Medicine, Division of Medical Protein Chemistry, Inga Marie Nilssons Street 53, Malmö, 20502, Sweden.
| | - Anna M Blom
- Lund University, Department of Translational Medicine, Division of Medical Protein Chemistry, Inga Marie Nilssons Street 53, Malmö, 20502, Sweden.
| |
Collapse
|
4
|
Okroj M, Jenkins HT, Herbert AP, Barlow PN, Blom AM. Structural basis and functional effects of the interaction between complement inhibitor C4b-binding protein and DNA. Mol Immunol 2008; 46:62-9. [DOI: 10.1016/j.molimm.2008.07.008] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/29/2008] [Accepted: 07/06/2008] [Indexed: 10/21/2022]
|
5
|
Oksjoki R, Kovanen PT, Mäyränpää MI, Laine P, Blom AM, Meri S, Pentikäinen MO. Complement regulation in human atherosclerotic coronary lesions. Atherosclerosis 2007; 192:40-8. [PMID: 16846604 DOI: 10.1016/j.atherosclerosis.2006.06.013] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/10/2006] [Revised: 06/02/2006] [Accepted: 06/02/2006] [Indexed: 10/24/2022]
Abstract
OBJECTIVE The complement system is activated in human atherosclerotic lesions and may hence aggravate local inflammation. We studied the presence and localization of C4b-binding protein (C4bp), the major inhibitor of the classical complement pathway, in human atherosclerotic lesions in relation to complement activation products and protein S, which circulates in complex with C4bp. METHODS AND RESULTS Immunohistochemistry of human coronary arteries showed C4bp to be virtually absent in normal arteries but present in early and advanced atherosclerotic lesions. In the lesions, C4bp is associated with proteoglycans, and affinity chromatography showed that C4bp interacts with human arterial proteoglycans. Areas containing C4bp also contained IgM and C4 suggesting that C4bp is involved in the regulation of the classical complement pathway. However, C5b-9 was virtually absent in these areas but, instead, colocalized with properdin deeper in the intima, suggesting that C5b-9 is formed by the alternative complement pathway. A fraction of C4bp was associated with protein S and apoptotic cells. CONCLUSIONS The results indicate that C4bp regulates the classical complement pathway in human atherosclerotic lesions. Thus, unlike the alternative pathway, the classical complement pathway does not generate C5b-9, but is likely to be involved in the clean-up of apoptotic cells and cell debris in the arterial intima.
Collapse
Affiliation(s)
- Riina Oksjoki
- Wihuri Research Institute, Kalliolinnantie 4, FIN-00140 Helsinki, Finland
| | | | | | | | | | | | | |
Collapse
|
6
|
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: 130] [Impact Index Per Article: 6.5] [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
|
7
|
Abstract
OBJECTIVE To review the multifaceted roles of the anticoagulant protein S, facilitating a better comprehension of this protein's role in anticoagulation and inflammation pathways and the crosstalk between these pathologic states. DATA SOURCES AND STUDY SELECTION Original research and review articles published in English pertaining to protein S, sourced from PubMed, during the last 30 yrs. DATA EXTRACTION AND SYNTHESIS The protein C anticoagulant pathway is an essential mechanism for attenuating thrombin generation by the membrane-bound procoagulant complexes, tenase and prothrombinase. Protein S is a nonenzymatic protein. In the absence of activated protein C, it demonstrates anticoagulant activity; in the presence of activated protein C, it functions as a cofactor for activated protein C-dependent proteolytic inactivation of the coagulation cofactors factor Va and factor VIIIa. However, in plasma, these anticoagulant activities are limited by the concentration of free protein S (approximately 40% of the total protein S plasma concentration). The remaining protein S (approximately 60%) is found in a high-affinity, calcium-stabilized complex with C4b-binding protein, which renders this fraction devoid of anticoagulant function. Several recent investigations have attributed novel activated protein C-independent functions of protein S to the association of protein S with C4b-binding protein, thus establishing the importance of this fraction of plasma protein S. CONCLUSIONS Together, these data support a role for protein S in both anticoagulation and inflammation, facilitating a better understanding of the need for both free and C4b-binding protein-bound protein S. Although these physiologic roles are truly dichotomous in terms of functional end point, mechanistically, both involve high-affinity membrane binding to phosphatidylserine-bearing surfaces. This binding is mediated by the n-terminal gamma-carboxyglutamic acid-rich domain of this protein.
Collapse
Affiliation(s)
- Alan C Rigby
- Center for Hemostasis, Thrombosis, and Vascular Biology, Beth Israel Deaconess Medical Center, and the Department of Medicine, Harvard Medical School, Boston, MA 02115, USA.
| | | |
Collapse
|
8
|
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
|
9
|
Abstract
The protein C (PC) anticoagulant system provides specific and efficient control of blood coagulation. The system comprises circulating or membrane-bound protein components that take part in complicated multimolecular protein complexes being assembled on specific cellular phospholipid membranes. Each of the participating proteins is composed of multiple domains, many of which are known at the level of their three-dimensional structures. The key component of the PC system, the vitamin K-dependent PC, circulates in blood as zymogen to an anticoagulant serine protease. Activation is achieved on the surface of endothelial cells by thrombin bound to the membrane protein thrombomodulin. The endothelial PC receptor binds the Gla domain of PC and stimulates the activation. Activated PC (APC) modulates the activity of blood coagulation by specific proteolytic cleavages of a limited number of peptide bonds in factor (F)VIIIa and FVa, cofactors in the activation of FX and prothrombin, respectively. These reactions occur on the surface of negatively charged phospholipid membranes and are stimulated by the vitamin K-dependent protein S. Regulation of FVIIIa activity by APC is stimulated not only by protein S but also by FV, which, like thrombin, is a Janus-faced protein with both pro- and anticoagulant potential. However, whereas the properties of thrombin are modulated by protein-protein interactions, the specificity of FV function is governed by proteolysis by pro- or anti-coagulant enzymes. The molecular recognition of the PC system is beginning to be unravelled and provides insights into a fascinating and intricate molecular scenario.
Collapse
Affiliation(s)
- B Dahlbäck
- Department of Laboratory Medicine, Division of Clinical Chemistry, Lund University, The Wallenberg Laboratory, University Hospital Malmö, Malmö, Sweden.
| | | |
Collapse
|
10
|
|
11
|
Blom AM, Webb J, Villoutreix BO, Dahlbäck B. A cluster of positively charged amino acids in the C4BP alpha-chain is crucial for C4b binding and factor I cofactor function. J Biol Chem 1999; 274:19237-45. [PMID: 10383431 DOI: 10.1074/jbc.274.27.19237] [Citation(s) in RCA: 84] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
C4b-binding protein (C4BP) is a regulator of the classical complement pathway, acting as a cofactor to factor I in the degradation of C4b. Computer modeling and structural analysis predicted a cluster of positively charged amino acids at the interface between complement control protein modules 1 and 2 of the C4BP alpha-chain to be involved in C4b binding. Three C4BP mutants, R39Q, R64Q/R66Q, and R39Q/R64Q/R66Q, were expressed and assayed for their ability to bind C4b and to function as factor I cofactors. The apparent affinities of R39Q, R64Q/R66Q, and R39Q/R64Q/R66Q for immobilized C4b were 15-, 50-, and 140-fold lower, respectively, than that of recombinant wild type C4BP. The C4b binding site demonstrated herein was also found to be a specific heparin binding site. In C4b degradation, the mutants demonstrated decreased ability to serve as factor I cofactors. In particular, the R39Q/R64Q/R66Q mutant was inefficient as cofactor for cleavage of the Arg937-Thr938 peptide bond in C4b. In contrast, the factor I mediated cleavage of Arg1317-Asn1318 bond was less affected by the C4BP mutations. In conclusion, we identify a cluster of amino acids that is part of a C4b binding site involved in the regulation of the complement system.
Collapse
Affiliation(s)
- A M Blom
- The Wallenberg Laboratory, Department of Clinical Chemistry, Lund University, University Hospital Malmö, S-205 02 Malmö, Sweden
| | | | | | | |
Collapse
|