DEK in the synovium of patients with juvenile idiopathic arthritis: Characterization of DEK antibodies and posttranslational modification of the DEK autoantigen

Abstract

Objective. DEK is a nuclear phosphoprotein and autoantigen in a subset of children with juvenile idiopathic arthritis (JIA). Autoantibodies to DEK are also found in a broad spectrum of disorders associated with abnormal immune activation. We previously demonstrated that DEK is secreted by macrophages, is released by apoptotic T cells, and attracts leukocytes.Since DEK has been identified in the synovial fluid (SF) of patients with JIA, this study was undertaken to investigate how DEK protein and/or autoantibodies may contribute to the pathogenesis of JIA.Methods. DEK autoantibodies, immune complexes (ICs), and synovial macrophages were purified from the SF of patients with JIA. DEK autoantibodies and ICs were purified by affinity-column chromatography and analyzed by 2-dimensional gel electrophoresis, immunoblotting, and enzyme-linked immunosorbent assay. DEK in supernatants and exosomes was purified by serial centrifugation and immunoprecipitation with magnetic beads, and posttranslational modifications of DEK were identified by nano-liquid chromatography tandem mass spectrometry (nano-LC-MS/MS).Results. DEK autoantibodies and protein were found in the SF of patients with JIA. Secretion of DEK by synovial macrophages was observed both in a free form and via exosomes. DEK autoantibodies (IgG2) may activate the complement cascade, primarily recognize the C-terminal portion of DEK protein, and exhibit higher affinity for acetylated DEK. Consistent with these observations, DEK underwent acetylation on an unprecedented number of lysine residues, as demonstrated by nano-LC-MS/MS.Conclusion. These results indicate that DEK can contribute directly to joint inflammation in JIA by generating ICs through high-affinity interaction between DEK and DEK autoantibodies, a process enhanced by acetylation of DEK in the inflamed joint.Juvenile idiopathic arthritis (JIA), a polymorphic chronic inflammatory disease of unknown etiology, is

Disease Association and Arthritogenic Potential of Circulating Antibodies against the α1,4-Polygalacturonic Acid Moiety

“…It is evident that complement activation occurs locally in inflamed joints in RA (30). IgG and complement C3 are found together on the cartilage surface, in the synovium and within phagocytes (15,31).…”

Stacking the DEK: From chromatin topology to cancer stem cells

“…Additionally, functions for acetylation and non-covalent as well as covalent attachment of poly(ADP-ribose) moieties to DEK, mostly under stress conditions, have been identified as critical regulators of its DNA/chromatin binding, localization and biological activity. [108][109][110] Even though formally only shown for a few scenarios, these modifications are believed to be pivotal in integrating and regulating its various functions, controlling its subcellular localization and directing its interaction with other partners or structures. They may additionally play a central part in human disease phenotypes.…”

“…Cytoplasmic activities for DEK are currently uncharacterized, but secreted forms of DEK that have been found in synovial fluid were implicated in triggering autoimmune events associated with juvenile idiopathic arthritis and found in the urine of over 80% of bladder cancer patients. 108,115,124 The nuclear fraction of DEK carries out numerous activities associated with DNA binding and chromatin organization. However, recent reports might have uncovered principal biological modes of action for DEK that could account for its diverse, cellular functions.…”

“…Through cis-and trans-acting mechanisms, perturbed DEK expression levels could thus dramatically alter nucleic acid structures and globally impact processes such as transcription, arthritis, and phosphorylation and poly(ADP-ribosyl)ation have been linked to increased programmed cell death. 108,111,112 However, DEK is highly phosphorylated in normally cycling cells and still remains tightly bound to chromatin; only in vitro did phosphorylation decrease DNA affinity. 106 Perhaps phosphorylation weakens the affinity of individual DEK molecules to DNA, but its subsequent oligomerization increases the collective affinity.…”

“…114 This has many biological implications, as reports have shown DEK is not solely nuclear but also can be secreted into the extracellular space, where it functions as a chemotactic factor and autoantigen in the pathogenesis of juvenile arthritis. 108,115 Perhaps in addition to being a chromatin-binding protein, DEK is also an intercellular signaling molecule, secreted by a certain population of cells and subsequently taken up by neighboring cells. It is becoming increasingly clear that there are many varied DEK activities, and continued structure-function studies are needed to explore these in different cell types and disease models.…”