1. The molecular basis for development of proinflammatory autoantibodies to progranulin.
- Author
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Thurner L, Fadle N, Regitz E, Kemele M, Klemm P, Zaks M, Stöger E, Bette B, Carbon G, Zimmer V, Assmann G, Murawski N, Kubuschok B, Held G, Preuss KD, and Pfreundschuh M
- Subjects
- Animals, Autoantibodies genetics, Autoantibodies metabolism, Binding Sites genetics, Blotting, Western, Cell Line, Cell Line, Tumor, Flow Cytometry, HEK293 Cells, Humans, Intercellular Signaling Peptides and Proteins genetics, Intercellular Signaling Peptides and Proteins metabolism, Mutagenesis, Site-Directed, Phosphorylation, Progranulins, Protein Isoforms genetics, Protein Isoforms immunology, Protein Isoforms metabolism, Protein Kinase C beta genetics, Protein Kinase C beta immunology, Protein Kinase C beta metabolism, Protein Precursors genetics, Protein Precursors metabolism, Receptors, Tumor Necrosis Factor, Member 25 immunology, Receptors, Tumor Necrosis Factor, Member 25 metabolism, Receptors, Tumor Necrosis Factor, Type I immunology, Receptors, Tumor Necrosis Factor, Type I metabolism, Receptors, Tumor Necrosis Factor, Type II immunology, Receptors, Tumor Necrosis Factor, Type II metabolism, Serine genetics, Serine metabolism, Autoantibodies immunology, Intercellular Signaling Peptides and Proteins immunology, Protein Precursors immunology, Serine immunology
- Abstract
Recently we identified in a wide spectrum of autoimmune diseases frequently occurring proinflammatory autoantibodies directed against progranulin, a direct inhibitor of TNFR1 & 2 and of DR3. In the present study we investigated the mechanisms for the breakdown of self-tolerance against progranulin. Isoelectric focusing identified a second, differentially electrically charged progranulin isoform exclusively present in progranulin-antibody-positive patients. Alkaline phosphatase treatment revealed this additional progranulin isoform to be hyperphosphorylated. Subsequently Ser81, which is located within the epitope region of progranulin-antibodies, was identified as hyperphosphorylated serine residue by site directed mutagenesis of candidate phosphorylation sites. Hyperphosphorylated progranulin was detected exclusively in progranulin-antibody-positive patients during the courses of their diseases. The occurrence of hyperphosphorylated progranulin preceded seroconversions of progranulin-antibodies, indicating adaptive immune response. Utilizing panels of kinase and phosphatase inhibitors, PKCβ1 was identified as the relevant kinase and PP1 as the relevant phosphatase for phosphorylation and dephosphorylation of Ser81. In contrast to normal progranulin, hyperphosphorylated progranulin interacted exclusively with inactivated (pThr320) PP1, suggesting inactivated PP1 to cause the detectable occurrence of phosphorylated Ser81 PGRN. Investigation of possible functional alterations of PGRN due to Ser81 phosphorylation revealed, that hyperphosphorylation prevents the interaction and thus direct inhibition of TNFR1, TNFR2 and DR3, representing an additional direct proinflammatory effect. Finally phosphorylation of Ser81 PGRN alters the conversion pattern of PGRN. In conclusion, inactivated PP1 induces hyperphosphorylation of progranulin in a wide spectrum of autoimmune diseases. This hyperphosphorylation prevents direct inhibition of TNFR1, TNFR2 and DR3 by PGRN, alters the conversion of PGRN, and is strongly associated with the occurrence of neutralizing, proinflammatory PGRN-antibodies, indicating immunogenicity of this alternative secondary modification., (Copyright © 2015 Elsevier Ltd. All rights reserved.)
- Published
- 2015
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