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Arthritis Rheumatol. 2019 Mar 12. doi: 10.1002/art.40886. [Epub ahead of print]

Citrullinated Inhibitor of DNA Binding 1 is a Novel Autoantigen in Rheumatoid Arthritis.

Author information

1
Division of Rheumatology, Clinical Autoimmunity Center of Excellence, Department of Internal Medicine, University of Michigan Medical School, Ann Arbor, MI, USA.
2
Division of Rheumatology, Department of Medicine, Showa University School of Medicine, Tokyo, Japan.
3
Department of Biological Chemistry, University of Michigan Medical School, Ann Arbor, MI, USA.
4
Department of Orthopaedic Surgery, University of Michigan Health System, A. Alfred Taubman Health Care Center, Ann Arbor, MI, USA.

Abstract

OBJECTIVE:

We explored the intrinsic role of inhibitor of DNA binding 1 (ID1) in rheumatoid arthritis (RA) fibroblast-like synoviocytes (FLS) and investigated whether ID1 is citrullinated and autoantigenic in RA.

METHODS:

RA patient serum ID1 levels were measured before and after infliximab treatment. RA FLS were transfected with a CRISPR/Cas9 construct targeting ID1 to examine the effects of ID1 deletion. RA synovial fluids (SFs) and homogenized synovial tissues (STs) were immunoprecipitated for ID1 and measured for citrullinated residues using ELISA and Western blot. Liquid chromatography-tandem mass spectrometry (LC-MS/MS) was performed on in vitro citrullinated recombinant human ID1 (citID1) to localize the sites of citrullination. Normal (NL) and RA sera and SFs were analyzed by immunodot blot (IDB) for anti-citrullinated protein antibodies (ACPAs) to citID1.

RESULTS:

RA patient serum ID1 levels positively correlated with several disease parameters and were reduced after infliximab treatment. RA FLS displayed reduced growth and robust increase in interleukin-6 (IL-6) and IL-8 production upon deletion of ID1. ID1 immunodepletion significantly reduced the levels of citrullinated residues in RA SFs, and citrullinated ID1 was detected in homogenized RA STs. IDB analyses revealed ACPAs to citID1, but not to native ID1, in RA PB sera and SFs, but not in NL PB sera. Following analyses of LC-MS/MS for citrullination sites and corresponding reactivity in IDB assays, we determined the critical arginines in ID1 for autoantigenicity: R33, R52 and R121.

CONCLUSIONS:

Novel roles of ID1 in RA include regulation of FLS proliferation and cytokine secretion and autoantigenicity following citrullination. This article is protected by copyright. All rights reserved.

KEYWORDS:

ACPA ; citrullination; rheumatoid arthritis; transcription factors

PMID:
30861322
DOI:
10.1002/art.40886

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