Mutations of factor H impair regulation of surface-bound C3b by three mechanisms in atypical hemolytic uremic syndrome

Markus J Lehtinen, Angelique L Rops, David E Isenman, Johan van der Vlag, T. Sakari Jokiranta

    Research output: Contribution to journalArticleScientificpeer-review

    Abstract

    Atypical hemolytic uremic syndrome (aHUS) is a thrombotic microangiopathy associated with mutations in complement proteins, most frequently in the main plasma alternative pathway regulator factorH(FH). The hotspot for the FH mutations is in domains 19-20 (FH19-20) that are indispensable for FH activity on C3b bound covalently to host cells. In aHUS, down-regulation of cell-bound C3b by FH is impaired, but it is not clear whether this is due to an altered FH binding to surface-bound C3b or to cell surface structures. To explore the molecular pathogenesis of aHUS we tested binding of 14 FH19-20 point mutants to C3b and its C3d fragment, mouse glomerular endothelial cells (mGEnC-1), and heparin. The cell binding correlated well, but not fully, with heparin binding and the cell binding site was overlapping but distinct from the C3b/C3d binding site that was shown to extend to domain 19. Our results show that aHUS-associated FH19-20 mutants have different combinations of three primary defects: impaired binding to C3b/C3d, impaired binding to the mGEnC-1 cells/heparin, and, as a novel observation, an enhanced mGEnC-1 cell or heparin binding. We propose a model of the molecular pathogenesis of aHUS where all three mechanisms lead eventually to impaired control of C3b on the endothelial cell surfaces. Based on the results with the aHUS patient mutants and the overlap in FH19-20 binding sites for mGEnC-1/heparin and C3b/C3d we conclude that binding of FH19-20 to C3b/C3d is essential for target discrimination by the alternative pathway.
    Original languageEnglish
    JournalJournal of Biological Chemistry
    Volume284
    Issue number23
    Pages (from-to)15650-15658
    Number of pages9
    ISSN0021-9258
    DOIs
    Publication statusPublished - 2009
    MoE publication typeA1 Journal article-refereed

    Cite this

    @article{5474dc5a0d524d5f9452f60d0a6ddc71,
    title = "Mutations of factor H impair regulation of surface-bound C3b by three mechanisms in atypical hemolytic uremic syndrome",
    abstract = "Atypical hemolytic uremic syndrome (aHUS) is a thrombotic microangiopathy associated with mutations in complement proteins, most frequently in the main plasma alternative pathway regulator factorH(FH). The hotspot for the FH mutations is in domains 19-20 (FH19-20) that are indispensable for FH activity on C3b bound covalently to host cells. In aHUS, down-regulation of cell-bound C3b by FH is impaired, but it is not clear whether this is due to an altered FH binding to surface-bound C3b or to cell surface structures. To explore the molecular pathogenesis of aHUS we tested binding of 14 FH19-20 point mutants to C3b and its C3d fragment, mouse glomerular endothelial cells (mGEnC-1), and heparin. The cell binding correlated well, but not fully, with heparin binding and the cell binding site was overlapping but distinct from the C3b/C3d binding site that was shown to extend to domain 19. Our results show that aHUS-associated FH19-20 mutants have different combinations of three primary defects: impaired binding to C3b/C3d, impaired binding to the mGEnC-1 cells/heparin, and, as a novel observation, an enhanced mGEnC-1 cell or heparin binding. We propose a model of the molecular pathogenesis of aHUS where all three mechanisms lead eventually to impaired control of C3b on the endothelial cell surfaces. Based on the results with the aHUS patient mutants and the overlap in FH19-20 binding sites for mGEnC-1/heparin and C3b/C3d we conclude that binding of FH19-20 to C3b/C3d is essential for target discrimination by the alternative pathway.",
    author = "Lehtinen, {Markus J} and Rops, {Angelique L} and Isenman, {David E} and {van der Vlag}, Johan and Jokiranta, {T. Sakari}",
    year = "2009",
    doi = "10.1074/jbc.M900814200",
    language = "English",
    volume = "284",
    pages = "15650--15658",
    journal = "Journal of Biological Chemistry",
    issn = "0021-9258",
    publisher = "American Society for Biochemistry and Molecular Biology",
    number = "23",

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    Mutations of factor H impair regulation of surface-bound C3b by three mechanisms in atypical hemolytic uremic syndrome. / Lehtinen, Markus J; Rops, Angelique L; Isenman, David E; van der Vlag, Johan; Jokiranta, T. Sakari.

    In: Journal of Biological Chemistry, Vol. 284, No. 23, 2009, p. 15650-15658.

    Research output: Contribution to journalArticleScientificpeer-review

    TY - JOUR

    T1 - Mutations of factor H impair regulation of surface-bound C3b by three mechanisms in atypical hemolytic uremic syndrome

    AU - Lehtinen, Markus J

    AU - Rops, Angelique L

    AU - Isenman, David E

    AU - van der Vlag, Johan

    AU - Jokiranta, T. Sakari

    PY - 2009

    Y1 - 2009

    N2 - Atypical hemolytic uremic syndrome (aHUS) is a thrombotic microangiopathy associated with mutations in complement proteins, most frequently in the main plasma alternative pathway regulator factorH(FH). The hotspot for the FH mutations is in domains 19-20 (FH19-20) that are indispensable for FH activity on C3b bound covalently to host cells. In aHUS, down-regulation of cell-bound C3b by FH is impaired, but it is not clear whether this is due to an altered FH binding to surface-bound C3b or to cell surface structures. To explore the molecular pathogenesis of aHUS we tested binding of 14 FH19-20 point mutants to C3b and its C3d fragment, mouse glomerular endothelial cells (mGEnC-1), and heparin. The cell binding correlated well, but not fully, with heparin binding and the cell binding site was overlapping but distinct from the C3b/C3d binding site that was shown to extend to domain 19. Our results show that aHUS-associated FH19-20 mutants have different combinations of three primary defects: impaired binding to C3b/C3d, impaired binding to the mGEnC-1 cells/heparin, and, as a novel observation, an enhanced mGEnC-1 cell or heparin binding. We propose a model of the molecular pathogenesis of aHUS where all three mechanisms lead eventually to impaired control of C3b on the endothelial cell surfaces. Based on the results with the aHUS patient mutants and the overlap in FH19-20 binding sites for mGEnC-1/heparin and C3b/C3d we conclude that binding of FH19-20 to C3b/C3d is essential for target discrimination by the alternative pathway.

    AB - Atypical hemolytic uremic syndrome (aHUS) is a thrombotic microangiopathy associated with mutations in complement proteins, most frequently in the main plasma alternative pathway regulator factorH(FH). The hotspot for the FH mutations is in domains 19-20 (FH19-20) that are indispensable for FH activity on C3b bound covalently to host cells. In aHUS, down-regulation of cell-bound C3b by FH is impaired, but it is not clear whether this is due to an altered FH binding to surface-bound C3b or to cell surface structures. To explore the molecular pathogenesis of aHUS we tested binding of 14 FH19-20 point mutants to C3b and its C3d fragment, mouse glomerular endothelial cells (mGEnC-1), and heparin. The cell binding correlated well, but not fully, with heparin binding and the cell binding site was overlapping but distinct from the C3b/C3d binding site that was shown to extend to domain 19. Our results show that aHUS-associated FH19-20 mutants have different combinations of three primary defects: impaired binding to C3b/C3d, impaired binding to the mGEnC-1 cells/heparin, and, as a novel observation, an enhanced mGEnC-1 cell or heparin binding. We propose a model of the molecular pathogenesis of aHUS where all three mechanisms lead eventually to impaired control of C3b on the endothelial cell surfaces. Based on the results with the aHUS patient mutants and the overlap in FH19-20 binding sites for mGEnC-1/heparin and C3b/C3d we conclude that binding of FH19-20 to C3b/C3d is essential for target discrimination by the alternative pathway.

    U2 - 10.1074/jbc.M900814200

    DO - 10.1074/jbc.M900814200

    M3 - Article

    VL - 284

    SP - 15650

    EP - 15658

    JO - Journal of Biological Chemistry

    JF - Journal of Biological Chemistry

    SN - 0021-9258

    IS - 23

    ER -