title: Polyphosphate is a novel cofactor for regulation of complement by a serpin, C1 inhibitor.
abstract: The complement system plays a key role in innate immunity, inflammation, and coagulation. The system is delicately balanced by negative regulatory mechanisms that modulate the host response to pathogen invasion and injury. The serpin, C1-esterase inhibitor (C1-INH), is the only known plasma inhibitor of C1s, the initiating serine protease of the classical pathway of complement. Like other serpin-protease partners, C1-INH interaction with C1s is accelerated by polyanions such as heparin. Polyphosphate (polyP) is a naturally occurring polyanion with effects on coagulation and complement. We recently found that polyP binds to C1-INH, prompting us to consider whether polyP acts as a cofactor for C1-INH interactions with its target proteases. We show that polyP dampens C1s-mediated activation of the classical pathway in a polymer length- and concentration-dependent manner by accelerating C1-INH neutralization of C1s cleavage of C4 and C2. PolyP significantly increases the rate of interaction between C1s and C1-INH, to an extent comparable to heparin, with an exosite on the serine protease domain of the enzyme playing a major role in this interaction. In a serum-based cell culture system, polyP significantly suppressed C4d deposition on endothelial cells, generated via the classical and lectin pathways. Moreover, polyP and C1-INH colocalize in activated platelets, suggesting that their interactions are physiologically relevant. In summary, like heparin, polyP is a naturally occurring cofactor for the C1s:C1-INH interaction and thus an important regulator of complement activation. The findings may provide novel insights into mechanisms underlying inflammatory diseases and the development of new therapies.
authors.affiliation: Department of Biochemistry and Genetics and ARC Centre for Advanced Molecular Imaging, La Trobe Institute for Molecular Science, La Trobe University, Melbourne, VIC, Australia;
authors.forename: Lakshmi C
authors.initials: LC
authors.lastname: Wijeyewickrema
authors.affiliation: Centre for Blood Research, Department of Medicine, Faculty of Medicine, University of British Columbia, Vancouver, BC, Canada;
authors.forename: Emilie
authors.initials: E
authors.lastname: Lameignere
authors.affiliation: Department of Biochemistry and Genetics and ARC Centre for Advanced Molecular Imaging, La Trobe Institute for Molecular Science, La Trobe University, Melbourne, VIC, Australia;
authors.forename: Lilian
authors.initials: L
authors.lastname: Hor
authors.affiliation: Department of Biochemistry and Genetics and ARC Centre for Advanced Molecular Imaging, La Trobe Institute for Molecular Science, La Trobe University, Melbourne, VIC, Australia;
authors.forename: Renee C
authors.initials: RC
authors.lastname: Duncan
authors.affiliation: Regenetiss Inc., Tokyo, Japan;
authors.forename: Toshikazu
authors.initials: T
authors.lastname: Shiba
authors.affiliation: Department of Biochemistry, University of Illinois at Urbana-Champaign, Urbana, IL; and.
authors.forename: Richard J
authors.initials: RJ
authors.lastname: Travers
authors.affiliation: Centre for Blood Research, Department of Medicine, Faculty of Medicine, University of British Columbia, Vancouver, BC, Canada;
authors.forename: Piyushkumar R
authors.initials: PR
authors.lastname: Kapopara
authors.affiliation: Centre for Blood Research, Department of Medicine, Faculty of Medicine, University of British Columbia, Vancouver, BC, Canada;
authors.forename: Victor
authors.initials: V
authors.lastname: Lei
authors.affiliation: Department of Biochemistry, University of Illinois at Urbana-Champaign, Urbana, IL; and.
authors.forename: Stephanie A
authors.initials: SA
authors.lastname: Smith
authors.affiliation: Centre for Blood Research, Department of Medicine, Faculty of Medicine, University of British Columbia, Vancouver, BC, Canada; Faculty of Dentistry, University of British Columbia, Vancouver, BC, Canada.
authors.forename: Hugh
authors.initials: H
authors.lastname: Kim
authors.affiliation: Department of Biochemistry, University of Illinois at Urbana-Champaign, Urbana, IL; and.
authors.forename: James H
authors.initials: JH
authors.lastname: Morrissey
authors.affiliation: Department of Biochemistry and Genetics and ARC Centre for Advanced Molecular Imaging, La Trobe Institute for Molecular Science, La Trobe University, Melbourne, VIC, Australia;
authors.forename: Robert N
authors.initials: RN
authors.lastname: Pike
authors.affiliation: Centre for Blood Research, Department of Medicine, Faculty of Medicine, University of British Columbia, Vancouver, BC, Canada;
authors.forename: Edward M
authors.initials: EM
authors.lastname: Conway
mesh_terms: D001665:Binding Sites; D001792:Blood Platelets / Q000276:immunology / Q000378:metabolism; D002478:Cells, Cultured; D003174:Complement C1 Inactivator Proteins / Q000378:metabolism*; D050718:Complement C1 Inhibitor Protein; D003173:Complement C1s / Q000737:chemistry / Q000378:metabolism; D003175:Complement C2 / Q000378:metabolism; D003181:Complement C4 / Q000378:metabolism; D003171:Complement Pathway, Classical; D003165:Complement System Proteins / Q000378:metabolism*; D042783:Endothelial Cells / Q000276:immunology / Q000378:metabolism; D006493:Heparin / Q000378:metabolism; D006801:Humans; D066298:In Vitro Techniques; D011122:Polyphosphates / Q000737:chemistry / Q000378:metabolism*
chemical_list: D003174:Complement C1 Inactivator Proteins; D050718:Complement C1 Inhibitor Protein; D003175:Complement C2; D003181:Complement C4; D011122:Polyphosphates; C469952:SERPING1 protein, human; D006493:Heparin; D003165:Complement System Proteins; D003173:Complement C1s