ANTIBODIES TO DNA, DNA-BINDING PROTEINS, AND HISTONES

Phosphorylation of Ku70 subunit by cell cycle kinases modulates the replication related function of Ku heterodimer

The Ku protein, a heterodimer of Ku70 and Ku80, binds to chromosomal replication origins maximally at G1-phase and plays an essential role in assembly of origin recognition complex. However, the mechanism regulating such a critical periodic activity of Ku remained unknown. Here, we establish human Ku70 as a novel target of cyclin B1-Cdk1, which phosphorylates it in a Cy-motif dependent manner. Interestingly, cyclin E1- and A2-Cdk2 also phosphorylate Ku70, and as a result, the protein remains in a phosphorylated state during S-M phases of cell cycle. Intriguingly, the phosphorylation of Ku70 by cyclin-Cdks abolishes the interaction of Ku protein with replication origin due to disruption of the dimer. Furthermore, Ku70 is dephosphorylated in G1-phase, when Ku interacts with replication origin maximally. Strikingly, the over-expression of Ku70 with non-phosphorylable Cdk targets enhances the episomal replication of Ors8 origin and induces rereplication in HeLa cells, substantiating a preventive role of Ku phosphorylation in premature and untimely licensing of replication origin. Therefore, periodic phosphorylation of Ku70 by cyclin-Cdks prevents the interaction of Ku with replication origin after initiation events in S-phase and the dephosphorylation at the end of mitosis facilitates its participation in pre-replication complex formation.

Comparison of three anti-dsDNA assays: performance and correlation with systemic lupus erythematosus disease activity

OBJECTIVE

To investigate the BioPlex 2200 multiplex immunoassay and Farrzyme ELISA assays as alternatives to the established Farr radioimmunoassay for the correlation of anti-dsDNA antibodies in the assessment of disease activity in systemic lupus erythematosus (SLE).

DESIGN AND METHODS

Standard protocols were used to verify analytical performance claims. Anti-dsDNA antibody levels in SLE patient specimens (N=105) were measured and assessed for clinical performance using manufacturer cut-off limits along with the Systemic Lupus Erythematosus Disease Activity Index 2000 (SLEDAI-2K) score.

RESULTS

Assay precision, measurable range and normal reference interval met the manufacturers' stated claims. Agreement between Farr and BioPlex assays was moderate (positive agreement=62%; negative agreement=85%; kappa=0.48), as was agreement between Farr and Farrzyme assays (positive agreement=56%; negative agreement=91%; kappa=0.51). Mean SLEDAI-2K scores differed significantly between the anti-dsDNA positive and negative groups for BioPlex (p=0.0006), but not Farr (p=0.11) or Farrzyme (p=0.34). ROC curve analysis showed a similar area under the curve (AUC) for all three assays (0.76, 0.74, and 0.73 for Farr, BioPlex, and Farrzyme, respectively) in the discrimination of clinically active disease. Furthermore, increased anti-dsDNA levels from BioPlex showed significant correlation with active renal disease. However, results suggested a lower cut-off for the Farrzyme assay for assessment of global disease activity.

CONCLUSIONS

BioPlex and Farrzyme assays had similar overall agreement with the Farr assay, with BioPlex best reflecting disease activity in SLE patients.

Laboratory tests in pediatric rheumatology

Laboratory tests in rheumatology are important tools that help to support the diagnosis of autoimmune diseases, evaluate the disease activity, monitor the side effects of therapy, and also assist the physician to exclude rheumatologic mimics. Few relevant tests should be ordered after a detailed clinical review of the patient has been carried out and a provisional clinical diagnosis has been reached. There is no test that can rule in or rule out any rheumatologic disease and therefore, there is no role of a detailed "Rheumatology panel" of investigations. In this review, routine blood investigations, acute phase reactants, auto antibodies, HLA B27 and complements have been discussed.

Diagnosing systemic lupus erythematosus: new-generation immunoassays for measurement of anti-dsDNA antibodies are an effective alternative to the Farr technique and the Crithidia luciliae immunofluorescence test

The aim of this study was to evaluate the diagnostic performance of four new enzyme immunoassays (EIAs) for anti-double-stranded-DNA (anti-dsDNA) antibodies, in comparison with the Farr assay and the Crithidia luciliae immunofluorescence test (CLIFT). To this purpose, sera from four patient groups were collected: 52 sera from patients with systemic lupus erythematosus (SLE); 28 from patients with other connective tissue diseases (CTD); 36 from patients with hepatitis C virus (HCV) infection; and 24 from those with acute viral infection. All sera were tested for anti-dsDNA antibodies by four EIA methods using a different antigenic DNA source [synthetic oligonucleotide (Method A), circular plasmid (Method B), recombinant (Method C), and purified extracted (Method D)], and by CLIFT and Farr assays. The diagnostic sensitivity of the assays was as follows: 84.6% (Method A), 73% (B), 82.7% (C), 84.6% (D), 55.8% (CLIFT), and 78.8% (Farr). Specificity was 82.9% (A), 97.7% (B), 96.5% (C), 94.3% (D), 96.5% (CLIFT), and 90.9% (Farr). From these data, we can conclude that the new-generation EIA methods evaluated in this study have higher sensitivity than the CLIFT and Farr assays and, with the exception of Method A, have specificity similar to the CLIFT and slightly higher than the Farr assay. These findings suggest that EIA tests may replace CLIFT as a screening test and the Farr assay as a specific test, for anti-dsDNA antibody detection.

Parvovirus B19 infection and systemic lupus erythematosus: Activation of an aberrant pathway?

Parvovirus B19 infection has been associated with a variety of rheumatic manifestations/diseases, mainly rheumatoid arthritis, vasculitis and systemic lupus erythematosus (SLE). B19 infection may simulate both clinical and laboratory features of SLE, presenting either as a potential first time diagnosis of SLE or as an exacerbation of previously established disease. The similarities in both clinical and serological features of parvovirus infection and SLE at presentation may hinder the differential diagnosis between these two conditions. Hence, parvovirus B19 infection mimicking SLE usually fulfils <4 ACR criteria for SLE, rarely includes cardiac or renal involvement or presents with haemolytic anaemia, and is usually associated with short-lived, low titers of autoantibodies. Rarely, cases of multisystemic involvement solely attributed to a recent parvovirus B19 infection have been reported, rendering early accurate diagnosis of particular importance and justifying the screening for evidence of parvovirus B19 involvement in newly diagnosed cases of SLE, especially the ones with abrupt onset of symptoms along with cases of SLE flares. This review describes basic features of parvovirus B19 structure and pathogenicity and expands on the parvo-associated auto-immune manifestations particularly in relation to SLE-mimicking or SLE-triggering reported cases. The proposed mechanisms for viral-induced pathologic autoimmunity are discussed with emphasis on emerging data regarding the aberrant expression and localization of autoantigens and their potential implication in alternatively activated immunological cascades.

Identification of Histone H2B as a Regulated Plasminogen Receptor†

Tethering of plasminogen to cell surfaces controls plasmin formation and, thereby, influences pericellular proteolysis and cell migration. Modulation of cellular plasminogen binding sites provides a mechanism for regulation of these events. In this study, two distinct models, phorbol ester-stimulated adhesion of U937 monocytoid cells and culturing of peripheral blood neutrophils, treatments which modulate plasminogen binding sites, have been examined to determine the molecular basis for the upregulation of plasminogen receptors. Membranes were isolated from cell populations, with and without upregulated plasminogen binding capacities, and analyzed by [(125)I]plasminogen ligand blotting of gel transfers. Approximately 15 different [(125)I]plasminogen-binding proteins were discerned in the membrane fractions, and only relatively minor differences in the intensities of individual bands were noted in the different cell populations. The notable exception was the presence of a 17 kDa band, which was selectively and markedly enhanced in the membranes from cells with enhanced plasminogen binding capacities. The 17 kDa protein was isolated from both cell types, and amino acid sequencing of peptide fragments identified the same protein, histone H2B. Increased expression of histone H2B was observed on stimulated U937 cells and cultured neutrophils by confocal microscopy with an antibody raised to the carboxy-terminal octopeptide sequence of histone H2B. This antibody or its Fab fragments substantially decreased the level of binding of plasminogen to these cultured neutrophils and stimulated U937 cells that exhibited elevated levels of binding but not to nonstimulated cells. Thus, histone H2B represents a regulated plasminogen receptor, which contributes significantly to the plasminogen binding capacity of cells.

Interferon-?-inducible proteins are novel autoantigens in murine lupus

OBJECTIVE

To investigate the spectrum of B cell autoimmunity in the recently described anti-CD1-autoreactive T cell receptor (TCR)-transgenic murine lupus-like (CD1 lupus-like) model.

METHODS

Lethally irradiated BALB/c/nu/nu mice were injected intravenously with donor BALB/c bone marrow and spleen cells expressing TCRalpha and TCRbeta transgenes that recognize CD1d. Sera from adoptive host animals that developed lupus (i.e., CD1 lupus mice) were collected at serial time points and analyzed by Western blotting and immunoprecipitation, using protein extracts prepared from NIH3T3 mouse fibroblasts and EL-4 lymphocytes, respectively. Sera obtained from older animals in several models of spontaneous lupus (NZB/NZW, MRL++, and MRL/lpr mice), unmanipulated BALB/c/nu/nu mice, and normal BALB/c mice were used as controls.

RESULTS

Analyses demonstrated that the prominent targets of autoantibodies in the CD1 lupus-like model are interferon-alpha (IFNalpha)-inducible antigens. Biochemical and serologic characterizations identified one antigen as belonging to the interferon-inducible 202 (Ifi202) subfamily of proteins within the Ifi200 family, and a second antigen as a member of the 70-kd heat-shock protein family. Autoantibodies directed against these antigens were rapidly produced at an early stage of disease. Anti-p50 autoantibodies were present in sera from 7 (78%) of 9 CD1 lupus mice that developed severe kidney disease.

CONCLUSION

IFNalpha-inducible proteins represent a novel class of autoantigens in murine lupus, and the findings suggest additional roles for IFNalpha in this disease. Since Ifi202 autoantigens are encoded by the murine non-major histocompatibility complex lupus-susceptibility gene locus Ifi202, these data provide a link between recent advances in lupus genetics and the formation of autoantibodies.

Anti-dsDNA antibody avidity determination by a simple reliable ELISA method for SLE diagnosis and monitoring

High avidity anti-dsDNA antibodies are more specific for SLE diagnosis, and more closely associated with renal involvement than intermediate or low-affinity anti-dsDNA antibodies. ELISA methods are largely used to detect anti-dsDNA, but their high sensitivity is inversely related to specificity because they also detect low avidity antibodies. We developed an ELISA assay based on the law of mass action and the competitive binding of dsDNA in solution and coated to microwells with anti-dsDNA antibodies. A simplified Scatchard plot analysis system was used to measure anti-dsDNA antibody avidity which was expressed as apparent affinity constant (Kaa), and quantified in liters per unit (I/U). We prospectively studied 101 consecutive SLE patients, who were followed for 3 years; three serum samples were sequentially collected from each patient during follow-up for determination of IgG anti-dsDNA antibody concentration, and anti-dsDNA avidity. SLE disease activity was estimated using the European Consensus Lupus Activity Measure (ECLAM) index. Sera from 100 healthy subjects and 133 patients with other connective tissue diseases or infectious diseases were also assayed as controls. The mean Kaa in SLE patients was 65.2 +/- 47.3 l/U, with no variations over time. Anti-dsDNA-positive SLE patients had higher Kaa values (79.1 +/- 46.8) than anti-dsDNA negative patients (27.2 +/- 20.1; P < 0.001). No correlation emerged between anti-dsDNA avidity and the ECLAM activity index score. Avidity was significantly higher in patients with renal involvement vs patients without this complication (78.2 +/- 50 vs 59.9 +/- 45.6 l/U; P = 0.0013). This simple ELISA method could be very useful in the diagnostic phase to differentiate high avidity anti-dsDNA autoantibodies that are characteristically found in SLE patients from low avidity antibodies that can also be found in other inflammatory diseases. Moreover, our data confirm the predictive value of high avidity anti-dsDNA antibodies for the development of lupus nephritis.

Identification of human autoantibodies to the DNA ligase IV/XRCC4 complex and mapping of an autoimmune epitope to a potential regulatory region

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.

Deficiency in nuclear accumulation of G22p1 and Xrcc5 proteins in hyper-radiosensitive Long-Evans Cinnamon (LEC) rat cells after X irradiation

The DNA-dependent protein kinase (DNA-PK) complex has been implicated in the repair of DNA double-strand breaks (DSBs). DNA-PK is a heterotrimeric protein complex comprised of two components: a large catalytic subunit, Prkdc, with serine/threonine kinase activity and a DNA-targeting component, G22p1 and Xrcc5. In previous report, we showed that approximately 80% of the G22p1 and Xrcc5 proteins were observed in the cytoplasm of rat fibroblasts, and that nuclear translocation of the proteins from the cytoplasm is important for the repair of DNA DSBs. In the present study, we showed that nuclear accumulation of the G22p1 and Xrcc5 proteins was not observed in fibroblasts from a mutant strain of Long-Evans Cinnamon (LEC) rat that has an enhanced radiosensitivity and a reduced level of repair of DSBs after X irradiation. Nuclear translocation of the proteins was observed in both LEC rat cells and control rat cells with normal radiosensitivity at 5 min after X irradiation. Although high levels of G22p1 and Xrcc5 proteins were observed in the nuclei of control rat cells until 60 min postirradiation, the amounts of the proteins decreased rapidly in the nuclei of LEC rat cells in the first 10 min after X irradiation. These findings suggest that there are some defects in maintaining the levels of G22p1 and Xrcc5 proteins in the nuclei of LEC rat cells. An analysis of fibroblasts from backcross rats showed that the deficiency in nuclear accumulation of G22p1 and Xrcc5 proteins is genetically linked to enhanced radiosensitivity. Since the nucleotide sequences of the G22p1 and Xrcc5 genes of the LEC rats coincided with those of the control rats, the deficiency in nuclear accumulation may not be caused by mutations of the G22p1 and Xrcc5 proteins.

Hypoxia-activated ligand HAL-1/13 is lupus autoantigen Ku80 and mediates lymphoid cell adhesion in vitro

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.

Systemic lupus erythematosus in three ethnic groups: III. A comparison of characteristics early in the natural history of the LUMINA cohort. LUpus in MInority populations: NAture vs. Nurture

AIM

To determine and contrast the socioeconomic-demographic and clinical features of patients with recent onset (< or =5 y) systemic lupus erythematosus (SLE) from three ethnic groups, Hispanic, African-American and Caucasian (H, AA, C).

SUBJECTS AND METHODS

SLE cases (American College of Rheumatology criteria) (incident (n = 56), prevalent (n = 173)), were enrolled in a longitudinal study at The University of Alabama at Birmingham, The University of Texas-Houston Health Science Center and The University of Texas Medical Branch at Galveston. Socioeconomic-demographic, clinical, immunological, behavioral and psychological data were obtained using validated instruments and standard laboratory techniques, and compared.

RESULTS

70 H, 88 AA and 71 C SLE patients constitute this cohort. H and AA patients were younger and of lower socioeconomic-demographic status. They also had evidence of more frequent organ system involvement (renal, cardiovascular), more auto-antibodies, more active disease (after adjusting for discrepant socioeconomic-demographic features), lower levels of social support and more abnormal illness-related behaviors (more in H than in AA). H also were more likely to have an abrupt disease onset; C were more likely to be on antimalarials but less likely to be on corticosteroids. H, AA, and C used health care resources comparably. They had similar levels of pain and physical and mental functioning after adjusting for age, disease duration, income, education, social support, illness-related behaviors, and Systemic Lupus Activity Measure or SLAM scores.

CONCLUSIONS

H and AA patients have more active SLE, at an earlier age of onset, and a less favorable socioeconomic-demographic structure (worse among the H than AA) which predispose them to a less favorable natural history.

Hypertonic treatment inhibits radiation-induced nuclear translocation of the Ku proteins G22p1 (Ku70) and Xrcc5 (Ku80) in rat fibroblasts

The effects of X irradiation and hypertonic treatment with 0.5 M NaCl on the subcellular localization of the Ku proteins G22p1 (also known as Ku70) and Xrcc5 (also known as Ku80) in rat fibroblasts with normal radiosensitivity were examined using confocal laser microscopy and immunoblotting. Although these proteins were observed mainly in the nuclei of human fibroblasts, approximately 80% of the intensities of immunofluorescence from both G22p1 and Xrcc5 was observed in the cytoplasm of rat fibroblasts. When the rat cells were X-irradiated with 4 Gy, the intensities of the fluorescence derived from G22p1 and Xrcc5 in the nuclei increased from 20% to 50% of the total cellular fluorescence intensity at 20 min postirradiation. No significant differences were observed between the total intensities of the cellular fluorescence from the proteins in unirradiated and irradiated rat fibroblasts. The results showed that the proteins were translocated from the cytoplasm to the nucleus in the rat cells after X irradiation. The nuclear translocation of the proteins from the cytoplasm was inhibited by hypertonic treatment of the cells with 0.5 M NaCl for 20 min, which inhibits the fast repair process of potentially lethal damage (PLD). When the rat cells were treated with 0.5 M NaCl immediately after X irradiation, the repair of DNA DSBs was inhibited. The surviving fraction was approximately 60% of that of irradiated cells that were not treated with 0.5 M NaCl. The surviving fraction increased with incubation time in the growth medium before treatment with NaCl. The proportions of the intensities of fluorescence from G22p1 in the nuclei of X-irradiated cells also increased from 20% to 50% with increasing interval between X irradiation and treatment with NaCl. These results suggest that nuclear translocation of G22p1 and Xrcc5 is important for the fast repair process of PLD in rat cells.

Anti-subnucleosome reactivities in systemic lupus erythematosus (SLE) patients and their first-degree relatives

Antibodies specific for dsDNA appear to have different genetic origins and pathogenic consequences, compared with histone/dsDNA-specific antibodies, in a recently described murine model. The purpose of this study was to examine if this is also true in human lupus. Sera from 40 SLE families (comprising 40 probands and 153 first-degree relatives), and 45 normal adult controls were assayed for the levels of anti-dsDNA, anti-H1/dsDNA, anti-H2A/H2B/dsDNA, and anti-H3/H4/dsDNA autoantibodies by ELISA. Both the probands and the first-degree relatives exhibited significantly increased levels of antinuclear antibodies (ANA) targeting the different subnucleosomal epitopes. Importantly, probands with anti-dsDNA antibodies had a significantly higher incidence of renal disease compared with those with just anti-H2A/H2B/dsDNA antibodies, in resonance with murine studies. The frequency of anti-dsDNA and anti-H2A/H2B/DNA ANA among the first-degree relatives was 11.8% and 18.3%, respectively. Surprisingly, whereas probands with anti-dsDNA ANA had families with several seropositive members, first-degree relatives of patients with anti-H2A/H2B/DNA ANA (but not anti-dsDNA ANA) were uniformly ANA-free. These findings suggest that anti-dsDNA ANA in lupus may not only have worse disease associations, they may also have very different genetic origins, compared with anti-H2A/H2B/DNA (or anti-nucleosome) ANA.

Anti-dsDNA antibodies in sarcoidosis

BACKGROUND

Sarcoidosis is a chronic multisystem disorder characterized by an exaggerated cellular immune response to antigens with the production of various antibodies including rheumatoid factor and antinuclear antibodies (ANA). The prevalence and significance of antibodies to double-stranded DNA (anti-dsDNA) in sarcoid patients is unknown. The occurrence of anti-dsDNA antibodies is known to be a specific marker of systemic lupus erythematosus (SLE). Sarcoidosis can occur with SLE. It is unclear if anti-dsDNA antibodies in patients with sarcoidosis signify the eventual development of SLE.

OBJECTIVES

To determine the prevalence of anti-dsDNA antibodies in patients with sarcoidosis in a university hospital and their significance in predicting the diagnosis of associated SLE.

METHODS

In a retrospective study, 34 patient files with diagnosed sarcoidosis in a university hospital during a period of 15 years were reviewed for serological markers, including ANA, anti-dsDNA, and immunoglobulin and C3 levels. The occurrence of SLE in these patients also was evaluated.

RESULTS

ANA were positive in 10 of 34 of the patients screened. Two patients with sarcoidosis had antibodies to dsDNA. C3 levels in these 34 patients were an average of 87.7 +/- 25.3 mg/100 mL, which is within the normal range. IgG immunoglobulin levels were an average of 2,206 +/- 999 mg/100 mL, which was above normal limits. The 2 patients who were positive for anti-dsDNA had normal C3 levels and SLE did not develop during a follow-up period of 10 to 15 years.

CONCLUSIONS

Anti-dsDNA antibodies may occur in patients with sarcoidosis, but their presence does not predict the subsequent development of SLE.

Ku80 can translocate to the nucleus independent of the translocation of Ku70 using its own nuclear localization signal

Ku antigen is a complex of Ku70 and Ku80 subunits and plays an important role in not only DNA double-strand breaks (DSB) repair and V(D)J recombination, but also in growth regulation. Ku is generally believed to always form and function as heterodimers on the basis of in vitro observations. Here we demonstrate that the localization of Ku80 does not completely coincide with that of Ku70. Ku70 and Ku80 were colocalized in the nucleus in the interphase but not in the late telophase/early G1 phase of the cell cycle. Since the in vivo function of Ku might be partially regulated by the control of its transport, we attempted to investigate the molecular mechanisms underlying the nuclear translocation of Ku. The nuclear translocation of Ku80 started during the late telophase/early G1 phase after the nuclear envelope was formed and this was preceded by the nuclear translocation of Ku70. Furthermore, we found that the Ku80 protein was transported to the nucleus without heterodimerization with Ku70. To understand in detail the mechanism of transport of Ku80, we attempted to identify the nuclear localization signal (NLS) of Ku80 and defined to a region spanning nine amino acid residues (positions 561 - 569). The Ku80 NLS was demonstrated to be mediated to the nuclear rim by two components of PTAC58 and PTAC97. All these findings support the idea that Ku80 can translocate to the nucleus using its own NLS independent of the translocation of Ku70.

Autoantibodies define a family of proteins with conserved double-stranded RNA-binding domains as well as DNA binding activity

Cellular responses to viral infection are signaled by double-stranded (ds) RNA, which is not found in substantial amounts in uninfected cells. Although cellular dsRNA-binding proteins have been described, their characterization is incomplete. We show that dsRNA-binding proteins are prominent autoantigens. Sera from B6 and B10.S mice with pristane-induced lupus and human autoimmune sera immunoprecipitated a novel set of 130-, 110-, 90-, 80-, and 45-kDa proteins. The proteins were all major cellular poly(IC)-binding factors. N-terminal amino acid sequences of p110 and p90 were identical and matched nuclear factor (NF) 90 and M phase phosphoprotein 4. p45 and p90 were identified as the NF45.NF90 complex, which binds the interleukin-2 promoter as well as certain highly structured viral RNAs. NF90.NF45 and M phase phosphoprotein 4 belong to a large group of proteins with conserved dsRNA-binding motifs. Besides binding dsRNA, NF90.NF45, p110, and p130 had single-stranded and dsDNA binding activity. Some sera contained autoantibodies whose binding was inhibited by poly(IC) but not single-stranded DNA or vice versa, suggesting that the DNA- and RNA-binding sites are different. These autoantibodies will be useful probes of the function of dsRNA-binding proteins. Their interaction with dsRNA, an immunological adjuvant, also could promote autoimmunity.

The nuclear localization signal of the human Ku70 is a variant bipartite type recognized by the two components of nuclear pore-targeting complex

Ku protein is a complex of two subunits, Ku70 and Ku80. Ku is suspected to participate in both DNA double-strand break repair and transcription. Since both of these processes take place in the cell nucleus, we have been investigating the subcellular localization and nuclear transport of Ku proteins. In the present study, we analyzed the subcellular localization and nuclear localization signal (NLS) of Ku70. Fusion proteins of Ku70 and green fluorescent protein (GFP) transiently expressed in cells were clearly localized in the nuclei of interphase cells. Ku70 staining was distributed throughout both the nucleus and the cytoplasm in late telophase to early G1 phase cells. The NLS of Ku70 was located at the region composed of 18 amino acid residues (positions 539 to 556). This region overlapped with the Ku80-independent DNA-binding domain reported previously. The Ku70 NLS consisted of two basic subregions and a nonbasic intervening region. All the subregions were necessary for complete NLS activity. The amino acids in the nonbasic intervening region of Ku70 might be important for full NLS activity not only to provide sufficient length between the two separated clusters of basic amino acids but also to have an adequate amino acid sequence. All of the basic amino acid residues in the basic subregions were conserved among mammalian and avian homologues, confirming their importance in the nuclear translocation of Ku70. The structure of the Ku70 NLS resembled the consensus of a bipartite-type NLS. The Ku70 NLS was mediated to target to the nuclear rim by two components of the nuclear pore-targeting complex, PTAC58 and PTAC97.

Pulmonary manifestations of systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is an autoimmune disease that primarily affects young women. The respiratory system is more commonly involved in SLE than in any other collagen vascular disease. SLE may affect virtually all components of the respiratory system, including the upper airway, lung parenchyma, pulmonary vasculature, pleura, and respiratory muscles. Respiratory system involvement ranges from symptomatic to fulminant and life threatening. This article reviews the pulmonary manifestations of SLE, including drug-induced SLE.

Urine autoantibodies in interstitial cystitis

Interstitial cystitis is a chronic bladder disease with certain features that suggest autoimmunity may play a role in initiating or maintaining the disease process. We therefore determined whether immunoglobulin fractions from 14 IC patient and 19 control urine specimens bound in vitro to primary cultures of human bladder epithelial cells, as well as epithelial cells from a variety of other tissues. Urine autoantibodies that bound to normal human bladder epithelial cells were present in 8 of 14 IC specimens (from 6 of 9 IC patients) as compared to 3 of 23 control specimens (from 2 of 17 control patients). These antibodies, which were usually also present at low titers in sera from these persons, bound to at least four nuclear or cytoplasmic antigens, with the specificity of autoantibodies from a given individual varying over time. The autoantibodies were not specific for normal or malignant bladder epithelial cells, but bound to epithelial cells from a variety of tissues. These data show that anti-epithelial cell autoantibodies are present in the urine of IC patients, but suggest that these antibodies are not likely to be a primary cause of this disease.

Autoantibodies in black South Africans with systemic lupus erythematosus: spectrum and clinical associations

The clinical features and autoantibody profile of 111 black South Africans (103 females and 8 males) with systemic lupus erythematosus were retrospectively analysed. The mean age of the patients was 35.1 years and mean duration of disease 3.5 years. The commonest clinical and laboratory features noted were arthritis (62.2%), hypocomplementaemia (61.2%), haematological abnormalities (60.5%) and malar rash (55%). The serological abnormalities included antinuclear antibodies (98.2%), anti-dsDNA (66.2%), anti-Sm (44.2%), anti-RNP (65.5%), anti-Ro (60.5%), anti-La (28.4%) and rheumatoid factor (10.1%). Positive clinicoserological associations observed included: combination of anti-dsDNA antibodies and low C4 levels with renal disease; anti-dsDNA antibodies with cutaneous vasculitis; anti-Sm antibodies with psychosis; anti-RNP antibodies with Raynaud's phenomenon; anti-Ro antibodies with renal disease, psychosis and malar rash. Anti-La antibodies showed a weak negative association with serositis and Raynaud's phenomenon. Most of these clinical correlates are consistent with past studies. The high frequency of anti-Sm and anti-RNP antibodies is similar to the observations in African-Americans and Afro-Caribbeans.

Autoantibodies in black South Africans with systemic lupus erythematosus: spectrum and clinical associations

The clinical features and autoantibody profile of 111 black South Africans (103 females and 8 males) with systemic lupus erythematosus was retrospectively analysed. The mean age of the patients was 35.1 years and mean duration of disease 3.5 years. The commonest clinical and laboratory features noted were arthritis (62.2%), hypocomplementaemia (61.2%), haematological abnormalities (60.5%) and malar rash (55%). The serological abnormalities included antinuclear antibodies (98.2%), anti-dsDNA (66.2%), anti-Sm (44.2%), anti-RNP (65.5%), anti-Ro (60.5%), anti-La (28.4%) and rheumatoid factor (10.1%). Positive clinicoserological associations observed included: combination of anti-dsDNA antibodies and low C4 levels with renal disease; anti-dsDNA antibodies with cutaneous vasculitis; anti-Sm antibodies with psychosis; anti-RNP antibodies with Raynaud's phenomenon; anti-Ro antibodies with renal disease, psychosis and malar rash. Anti-La antibodies showed a weak negative association with serositis and Raynaud's phenomenon. Most of these clinical correlates are consistent with past studies. The high frequency of anti-Sm and anti-RNP antibodies is similar to the observations in African-Americans and Afro-Caribbeans.