Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C0024141 (systemic lupus erythematosus)
 44,322 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The Ku autoantigen is a heterodimer of 70- and 80-kD proteins recognized by autoantibodies from patients with systemic lupus erythematosus and related diseases that is the DNA-binding component of a DNA-dependent protein kinase. The catalytic activity of DNA-dependent protein kinase is carried by a 350-kD subunit (p350). In light of the recently described role of Ku in repairing double-strand DNA breaks, we investigated the regulation of Ku and p350 levels in neutrophils, a terminally differentiated cell type destined to undergo apoptosis. Since the appearance of double-strand DNA breaks is characteristic of apoptosis, we were interested in the possibility that Ku might oppose programmed cell death. Analysis of peripheral blood cells by flow cytometry using anti-Ku and anti-p350 monoclonal antibodies revealed that neutrophils were unstained, whereas resting (G0) lymphocytes were positive. The absence of Ku in mature neutrophils was confirmed by Western blotting and enzyme-linked immunosorbent assay for Ku antigen. In contrast, the human promyelocytic leukemia line, HL-60, which undergoes differentiation toward neutrophils after dimethylsulfoxide treatment, was positive for Ku and p350. In view of the short lifespan of neutrophils and the prolonged half-life of Ku and p350 (> 5 d), these data suggested that Ku was actively degraded during myeloid differentiation. Analysis of HL-60 cells by flow cytometry revealed that Ku staining was bimodal. Cells in G1/G0, S, or G2/M were all stained positively, whereas cells with a subdiploid DNA content characteristic of apoptosis were Ku negative. Similar results were obtained with phytohemagglutin-stimulated human lymphocytes. These data suggest that the Ku antigen is actively degraded in both myeloid cells destined to undergo apoptosis and apoptotic lymphocytes, raising the possibility that degradation of Ku may help to prevent the inappropriate repair of fragmented nuclear DNA during apoptosis.
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PMID:Absence of autoantigen Ku in mature human neutrophils and human promyelocytic leukemia line (HL-60) cells and lymphocytes undergoing apoptosis. 775 97

The interleukin-1 beta-converting enzyme (ICE) family of proteases is an important component of the mechanism of the apoptotic process, but the physiologic roles of the different homologs during apoptosis remain unclear. Significant information about the roles of proteolysis in apoptosis will be gained through identification of the distal substrates through which these proteases achieve their pro-apoptotic effects. Identification of these substrates therefore remains an important challenge. A subset of autoantibodies from patients with systemic lupus erythematosus (SLE) recognize molecules that are specifically cleaved early during apoptosis. Several of the identified autoantigens are nuclear proteins (PARP, U1-70 kDa, and DNA-PKcs) that are substrates for CPP32 in vitro and in apoptotic cells. Of note, these substrates are catalytic proteins involved in homeostatic pathways, suggesting that abolition of homeostasis is one fundamental feature ensuring the rapid irreversibility of the apoptotic process. Identification of the other substrates for this protease family will provide the tools to assess the roles of the different proteases in apoptotic death.
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PMID:Macromolecular substrates for the ICE-like proteases during apoptosis. 901 54

Hypoxia is known to induce extravasation of lymphocytes and leukocytes during ischemic injury and increase the metastatic potential of malignant lymphoid cells. We have recently identified a new adhesion molecule, hypoxia-activated ligand-1/13 (HAL-1/13), that mediates the hypoxia-induced increases in lymphocyte and neutrophil adhesion to endothelium and hypoxia-mediated invasion of endothelial cell monolayers by tumor cells. In this report, we used expression cloning to identify this molecule as the lupus antigen and DNA-dependent protein kinase-associated nuclear protein, Ku80. The HAL-1/13-Ku80 antigen is present on the surface of leukemic and solid tumor cell lines, including T and B lymphomas, myeloid leukemias, neuroblastoma, rhabdomyosarcoma, and breast carcinoma cells. Transfection and ectopic expression of HAL-1/13-Ku80 on (murine) NIH/3T3 fibroblasts confers the ability of these normally nonadhesive cells to bind to a variety of human lymphoid cell lines. This adhesion can be specifically blocked by HAL-1/13 or Ku80-neutralizing antibodies. Loss of expression variants of these transfectants simultaneously lost their adhesive properties toward human lymphoid cells. Hypoxic exposure of tumor cell lines resulted in upregulation of HAL-1/13-Ku80 expression at the cell surface, mediated by redistribution of the antigen from the nucleus. These studies indicate that the HAL-1/13-Ku80 molecule may mediate, in part, the hypoxia-induced adhesion of lymphocytes, leukocytes, and tumor cells.
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PMID:Hypoxia-activated ligand HAL-1/13 is lupus autoantigen Ku80 and mediates lymphoid cell adhesion in vitro. 1124 7

Sera from patients with systemic lupus erythematosus, polymyositis, scleroderma, and mixed connective tissue disease are frequently characterized by the presence of high levels of autoantibodies directed against linked sets of nuclear proteins. One of these autoantigen systems is made up of Ku and the DNA-dependent protein kinase catalytic subunit (DNA-PKcs), proteins that are essential for double-strand DNA break repair and for the related process of V(D)J recombination. Ku and DNA-PKcs bind avidly to DNA ends in vivo and in vitro and form an active protein kinase complex. One hypothesis is that this assembled nucleoprotein particle, rather than its component proteins, is a primary trigger for the autoimmune response and thus a major target for the resulting autoantibodies. To screen for particle-specific antibodies, we developed an assay in which the fully native nucleoprotein particle is reconstituted in vitro and is tethered to the surface of an ELISA plate via a streptavidin-biotin linkage. These particles are recognized efficiently by monoclonal antibodies and by autoantibodies present in patient sera. The assay may detect a broader spectrum of epitopes than a conventional ELISA in which Ku and DNA-PKcs are adsorbed directly to a plastic surface. The method will be advantageous for high-throughput screening for antibodies and other ligands that bind the assembled DNA-dependent protein kinase complex.
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PMID:A method to detect particle-specific antibodies against Ku and the DNA-dependent protein kinase catalytic subunit in autoimmune sera. 1129 81

Autoantibodies against cellular components are commonly present in sera from patients with systemic rheumatic diseases and may play an important role in pathogenesis. The Ku protein was recognized 20 years ago as a major target of autoantibodies in a subset of Japanese patients with scleroderma-polymyositis overlap syndrome, and anti-Ku antibodies have since been shown to occur in 10-20% of patients with these and other systemic rheumatic diseases, including systemic lupus erythematosus. Ku functions physiologically in the repair of DNA double-strand breaks, where it carries out the initial recognition of damaged DNA ends. The three dimensional structure of the Ku-DNA complex has recently been solved, and helps illuminate the relationship between the autoimmune epitopes and other features of the protein. In addition to Ku, three other polypeptides in the same DNA repair pathway have more recently been identified as autoantigens: the DNA-dependent protein kinase catalytic subunit, DNA ligase IV, and XRCC4. Two hypotheses have been invoked to explain the ability of these proteins to elicit an autoimmune response in susceptible individuals. One is that DNA damage induces formation of nucleoprotein complexes that present novel composite or conformational epitopes. The other is that cleavage of these proteins by caspases or Granzyme B leads to presentation of immunocryptic peptides capable of stimulating autoreactive T lymphocytes. In the case of DNA double-strand break repair proteins, there is evidence that both of these mechanisms may be at work. Because of their role in the maintenance of genome stability, DNA double-strand break repair proteins have been the subject of intense study, and a wealth of new structural, biochemical and functional information makes them excellent models for investigation of the humoral autoimmune response.
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PMID:Autoantibodies against DNA double-strand break repair proteins. 1168 55

The nonhomologous end-joining pathway is the principal mechanism for repair of ionizing radiation-induced, double-strand breaks in mammalian cells. Three polypeptides in this pathway, including the two subunits of Ku protein and the catalytic subunit of the DNA-dependent protein kinase, are known targets of autoantibodies in systemic rheumatic diseases. Here we show that two additional polypeptides in the pathway, DNA ligase IV and XRCC4, are also targets of autoantibodies. These Abs were present in 20% of patients with systemic lupus erythematosus and overlap syndrome. Previous work has shown that XRCC4 is subject to radiation-induced post-translational modification, including phosphorylation by DNA-dependent protein kinase and cleavage by caspase 3. We mapped a major autoimmune epitope in XRCC4 and found that it encompassed a DNA-dependent protein kinase phosphorylation site, which is located at serine 260; that it was adjacent to a site for caspase 3, which cleaves after residue 265; and that it also spanned a site for the inflammatory protease, granzyme B, which cleaves after residue 254. The finding that five different polypeptides in the nonhomologous end-joining pathway are potential targets of autoantibodies together with the observation that one of the autoimmune epitopes in XRCC4 coincides with a sequence that is a nexus for radiation-induced regulatory events suggest that exposure to agents that introduce DNA double-strand breaks may be one of the factors that influences the development of an autoimmune response in susceptible individuals.
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PMID:Identification of human autoantibodies to the DNA ligase IV/XRCC4 complex and mapping of an autoimmune epitope to a potential regulatory region. 1221 64

In eukaryotes the non-homologous end-joining repair of double strand breaks in DNA is executed by a series of proteins that bring about the synapsis, preparation and ligation of the broken DNA ends. The mechanism of this process appears to be initiated by the obligate heterodimer (Ku70/Ku86) protein complex Ku that has affinity for DNA ends. Ku then recruits the DNA-dependent protein kinase catalytic subunit (DNA-PKcs). The three-dimensional structures of the major part of the Ku heterodimer, representing the DNA-binding core, both free and bound to DNA are known from X-ray crystallography. However, these structures lack a region of ca 190 residues from the C-terminal region (CTR) of the Ku86 subunit (also known as Lupus Ku autoantigen p86, Ku80, or XRCC5) that includes the extreme C-terminal tail that is reported to be sufficient for DNA-PKcs-binding. We have examined the structural characteristics of the Ku86CTR protein expressed in bacteria. By deletion mutagenesis and heteronuclear NMR spectroscopy we localised a globular domain consisting of residues 592-709. Constructs comprising additional residues either to the N-terminal side (residues 543-709), or the C-terminal side (residues 592-732), which includes the putative DNA-PKcs-binding motif, yielded NMR spectra consistent with these extra regions lacking ordered structure. The three-dimensional solution structure of the core globular domain of the C-terminal region of Ku86 (Ku86CTR(592-709)) has been determined using heteronuclear NMR spectroscopy and dynamical simulated annealing using structural restraints from nuclear Overhauser effect spectroscopy, and scalar and residual dipolar couplings. The polypeptide fold comprises six regions of alpha-helical secondary structure that has an overall superhelical topology remotely homologous to the MIF4G homology domain of the human nuclear cap binding protein 80 kDa subunit and the VHS domain of the Drosophila protein Hrs, though strict analysis of the structures suggests that these domains are not functionally related. Two prominent hydrophobic pockets in the gap between helices alpha2 and alpha4 suggest a potential ligand-binding characteristic for this globular domain.
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PMID:The 3D solution structure of the C-terminal region of Ku86 (Ku86CTR). 1467 64

DNA-dependent protein kinase (DNA-PK) is a serine/threonine kinase that has critical roles in DNA double-strand break repair, as well as B- and T-cell antigen receptor rearrangement. The DNA-PK enzyme consists of the Ku regulatory subunit and a 450-kDa catalytic subunit termed DNA-PK(CS). Both of these subunits are autoantigens associated with connective tissue diseases such as systemic lupus erythematosus (SLE) and scleroderma. In this report, we show that DNA-PK(CS) is cleaved during poliovirus infection of HeLa cells. Cleavage was visible as early as 1.5 h postinfection (hpi) and resulted in an approximately 40% reduction in the levels of native protein by 5.5 hpi. Consistent with this observation, the activity of the DNA-PK(CS) enzyme was also reduced during viral infection, as determined by immunoprecipitation kinase assays. Although it has previously been shown that DNA-PK(CS) is a substrate of caspase-3 in vitro, the protein was still cleaved during poliovirus infection of the caspase-3-deficient MCF-7 cell line. Cleavage was not prevented by infection in the presence of a soluble caspase inhibitor, suggesting that cleavage in vivo was independent of host caspase activation. DNA-PK(CS) is directly cleaved by a picornaviral 2A protease in vitro, producing a fragment similar in size to the cleavage product observed in vivo. Taken together, our results indicate that DNA-PK(CS) is cleaved by the 2A protease during poliovirus infection. Proteolytic cleavage of DNA-PK(CS) during poliovirus infection may contribute to inhibition of host immune responses. Furthermore, cleavage of autoantigens by viral proteases may target these proteins for the autoimmune response by generating novel, or "immunocryptic," protein fragments.
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PMID:Proteolytic cleavage of the catalytic subunit of DNA-dependent protein kinase during poliovirus infection. 1516 25

DNA repair is reduced in patients suffering from systemic lupus erythematosus (SLE), and it can induce the production of autoreactive antibodies due to the accumulation of DNA damage and nucleoprotein that produce immunogenic antigens. The accumulations of anti-Ku and DNA-PKcs antibodies, which are involved in nonhomologous DNA end joining pathway, have been detected in SLE patients. The present study was designed to evaluate the association of XRCC5, XRCC6, and XRCC7 polymorphisms with SLE susceptibility. Polymerase chain reaction (PCR) was performed to genotype 163 SLE patients and 180 healthy controls for the XRCC5 variable number of tandem repeat (VNTR) polymorphism. The genotype analysis of XRCC6-61C>G and XRCC7 6721G>T polymorphisms was performed using the polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) technique. There was a significant association between XRCC5 VNTR, XRCC7 6721G>T polymorphisms and risk of SLE development. Notably, the frequency of XRCC5 VNTR 0R allele and genotypes with 2R allele was greatly enhanced in SLE patients with Malar rash (p=0.032 and p=0.024, respectively). Moreover, a higher frequency of genotypes with the XRCC5 VNTR 2R allele was observed in SLE patients with a positive antinuclear antibody (ANA) test (p=0.03). The present study shows an association between the XRCC5 VNTR, XRCC7 6721G>T polymorphisms and SLE. These polymorphisms might be genetic risk factors for SLE susceptibility and some SLE manifestations in the population southeast of Iran.
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PMID:Association Between Functional Polymorphisms of DNA Double-Strand Breaks in Repair Genes XRCC5, XRCC6 and XRCC7 with the Risk of Systemic Lupus Erythematosus in South East Iran. 2575 10