The DEK Nuclear Autoantigen Is a Secreted Chemotactic Factor

Abstract

The nuclear DNA-binding protein DEK is an autoantigen that has been implicated in the regulation of transcription, chromatin architecture, and mRNA processing. We demonstrate here that DEK is actively secreted by macrophages and is also found in synovial fluid samples from patients with juvenile arthritis. Secretion of DEK is modulated by casein kinase 2, stimulated by interleukin-8, and inhibited by dexamethasone and cyclosporine A, consistent with a role as a proinflammatory molecule. DEK is secreted in both a free form and in exosomes, vesicular structures in which transcription-modulating factors such as DEK have not previously been found. Furthermore, DEK functions as a chemotactic factor, attracting neutrophils, CD8؉ T lymphocytes, and natural killer cells. Therefore, the DEK autoantigen, previously described as a strictly nuclear protein, is secreted and can act as an extracellular chemoattractant, suggesting a direct role for DEK in inflammation.DEK is a mammalian oncoprotein and putative autoantigen whose primary biological function has not been previously elucidated, despite literature linking it to the regulation of transcription, chromatin architecture, and mRNA processing (1,2,11,15,16,24,35,51,65). The DEK protein is widely conserved among species and is transcribed at high levels, especially in hematopoietically derived cells (14,(62)(63)(64). DEK was first characterized as part of the protein product of the DEK-CAN fusion oncogene, resulting from a t(6;9) translocation found in a subset of patients with acute myelogenous leukemia (64). DEK is overexpressed in several different malignancies, including melanoma, hepatocellular carcinoma, glioblastoma, retinoblastoma, bladder cancer, T-cell large granular lymphocyte leukemia, and acute myelogenous leukemia independent of the t(6;9) translocation (7,10,19,20,29,30,32,39,64). Although DEK has previously been described as a strictly nuclear protein, DEK autoreactivity has been identified as a major component of the autoantibody profile in patients with juvenile idiopathic arthritis (JIA) and is also seen in patients with other autoimmune diseases (8,21,38,49,54,55). In the studies presented in this paper, we show that the nuclear protein DEK can be actively secreted by inflammatory cells, is found in synovial fluid samples from JIA patients, and can function as a chemoattractant for inflammatory cells, suggesting a potential role for DEK in immunity and/or autoimmunity. MATERIALS AND METHODSCell preparation. Monocyte-derived macrophages (MDM) were prepared as previously described (31). Briefly, heparinized venous blood samples were collected from healthy volunteers following a protocol approved by the institutional review board, and peripheral blood mononuclear cells were separated by FicollHypaque (Amersham Pharmacia Biotech AB, Uppsala, Sweden) density gradient centrifugation. MDM were purified by adherence to plastic for 2 h at 37°C at a concentration of 5 ϫ 10 5 /ml. Adherent cells were consistently Ͼ90% monocytes (31). Adherence-purified human mon...

The human oncoprotein and chromatin architectural factor DEK counteracts DNA replication stress

“…In cells that have undergone malignant changes that result in accelerated proliferation, such as oncogene activation, the properties of DEK unveiled by our study may favor genomic restabilization and contribute to overcome the DNA damage barrier of oncogenesis (Figure 4f). Furthermore, extracellular DEK-either actively secreted or released by dying cells 11,12,39 -once taken up by neighboring cells may render them more resistant to replication stress-induced DNA damage and less sensitive towards chemotherapeutic agents interfering with DNA replication thereby negatively influencing tumor prognosis.…”

Exosomes in the ascites of ovarian cancer patients: origin and effects on anti-tumor immunity

“…But recent research has shown that exosomes also have certain nuclear proteins. Mor-Vaknin et al (25) found in the patients of juvenile arthritis, that the synovial fluid had exosomes derived from macrophage expressing DNA binding protein DEK. In the ascites of the ovarian cancer patients, Taylor et al (11) found exosomes expressing nucleolin B23 that related to the mature of ribosome and cell proliferation.…”

Stacking the DEK: From chromatin topology to cancer stem cells

“…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.…”

“…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.…”

“…Furthermore, the fact that a secreted form of DEK can function as an extracellular chemo-attractant factor, and that fragments of the DEK protein can freely enter cells may have interesting implications for direct communication between progenitor cells producing DEK and neighboring cells receiving and responding to DEK in the stem cell niche. 114,115 In addition, DEK is likely to support the maintenance of the cancer stem cell population and, at least when present as a fusion protein with CAN, can induce the transformation of normal stem cells. DEK expression appears to be absent in fully differentiated, non-proliferative cells, such as the suprabasal layers of the epidermis.…”