Immune stimulation mediated by autoantigen binding sites within small nuclear RNAs involves Toll-like receptors 7 and 8

Systemic lupus erythematosus (SLE) is an autoimmune disease characterized by the production of autoantibodies to certain cellular macromolecules, such as the small nuclear ribonucleoprotein particles (snRNPs), which had been considered to be passive targets of the autoimmune response. SLE is also characterized by the increased expression of type I interferon (IFN), which appears to be associated with the development and severity of disease. Here, we show that specific, highly conserved RNA sequences within snRNPs can stimulate Toll-like receptors (TLRs) 7 and 8 as well as activate innate immune cells, such as plasmacytoid dendritic cells (pDCs), which respond by secreting high levels of type I IFN. SLE patient sera containing autoantibodies to snRNPs form immune complexes that are taken up through the Fc receptor γRII and efficiently stimulate pDCs to secrete type I IFNs. These results demonstrate that a prototype autoantigen, the snRNP, can directly stimulate innate immunity and suggest that autoantibodies against snRNP may initiate SLE by stimulating TLR7/8.

A 52-kD protein is a novel component of the SS-A/Ro antigenic particle

Anti-SS-A/Ro autoantibodies are found in the sera of patients with Sjogren's syndrome (SS) and SLE. In the course of analyzing 61 SS patients for their autoantibody profiles, we found that 42 were positive for anti-SS-A by double diffusion in agarose and demonstrated precipitin lines identical to that produced by a prototype anti-SS-A serum. Further analysis of these SS-A antibody-positive sera by Western blotting of cell extracts revealed that 21 sera reacted with two proteins of 60 and 52 kD, 13 sera reacted with 52-kD protein, two detected only 60 kD, while six were nonreactive. Affinity-purified anti-60-kD and anti-52-kD antibodies reacted exclusively with their corresponding antigens. Partial proteolysis of these proteins did not reveal common degradation fragments. Thus the 52- and 60-kD proteins were found to be antigenically and apparently structurally distinct from each other. They were also distinct from 48-kD SS-B/La protein. In immunoprecipitation using labeled cell extracts, affinity-purified anti-52-kD antibodies brought down the 52-kD protein as well as the 60-kD band. In [32P]orthophosphate-labeled HeLa cell extract both antibodies precipitated the same spectrum of small RNAs (hYl-5). In indirect immunofluorescence, anti-52-kD and anti-60-kD antibodies immunolocalized in similar subcellular structures and showed similar punctate nuclear staining patterns. Western blot analysis revealed that both proteins were present in lymphocytic as well as epithelial human cell lines tested. The data above define a new antigen of 52 kD which is another component of the SS-A particle and is associated in complex formation with the previously reported 60-kD protein.

Induction of interferon-alpha by immune complexes or liposomes containing systemic lupus erythematosus autoantigen- and Sjögren's syndrome autoantigen-associated RNA

OBJECTIVE

To investigate the ability of systemic lupus erythematosus (SLE) autoantigen- and Sjögren's syndrome (SS) autoantigen-associated U1 small nuclear RNA (U1 snRNA) and hY1RNA to induce interferon-alpha (IFNalpha) production.

METHODS

In vitro-transcribed U1 snRNA or hY1RNA and lipofectin were added to peripheral blood mononuclear cell (PBMC) cultures. Purified U1 snRNP particles and IgG from SLE patients (SLE-IgG) were added to cultures of PBMCs, enriched monocytes, or natural interferon-producing cells (NIPCs); the latter are also known as plasmacytoid dendritic cells (pDC). Cells were double-stained for IFNalpha and either blood dendritic cell antigen 2 (NIPCs/pDC) or CD14 (monocytes) and then analyzed by flow cytometry. In some experiments, RNase or inhibitors of Fc gamma receptor IIa (Fc gammaRIIa) (specific antibodies), endocytosis (chloroquine, bafilomycin A), or Toll-like receptors (TLRs; oligodeoxynucleotide 2088) were used. The produced IFNalpha was measured by immunoassay.

RESULTS

Lipofected U1 snRNA and hY1RNA both induced IFNalpha production in monocytes, but not in NIPC/pDC. In contrast, U1 snRNP combined with SLE-IgG induced IFNalpha production only in NIPCs/pDC, and this response was decreased by RNase treatment or inhibition of the Fc gammaRIIa, the endocytosis pathways, or the TLRs.

CONCLUSION

Our finding that U1 snRNA and hY1RNA have IFNalpha-inducing capacity indicates that immune complexes containing such RNA, for example U1 snRNP particles, can be at least partly responsible for the ongoing IFNalpha production seen in SLE and SS. These results may help to explain the molecular mechanisms behind the pathogenesis of these and other autoimmune diseases in which autoantibodies to RNA-binding proteins occur.

Small nuclear ribonucleoproteins and heterogeneous nuclear ribonucleoproteins in the amphibian germinal vesicle: loops, spheres, and snurposomes

We have examined the distribution of snRNPs in the germinal vesicle (GV) of frogs and salamanders by immunofluorescent staining and in situ nucleic acid hybridization. The major snRNAs involved in pre-mRNA splicing (U1, U2, U4, U5, and U6) occur together in nearly all loops of the lampbrush chromosomes, and in hundreds to thousands of small granules (1-4 microns diameter) suspended in the nucleoplasm. The loops and granules also contain several antigens that are regularly associated with snRNAs or spliceosomes (the Sm antigen, U1- and U2-specific antigens, and the splicing factor SC35). A second type of granule, often distinguishable by morphology, contains only U1 snRNA and associated antigens. We propose the term "snurposome" to describe the granules that contain snRNPs ("snurps"). Those that contain only U1 snRNA are A snurposomes, whereas those that contain all the splicing snRNAs are B snurposomes. GVs contain a third type of snRNP granule, which we call the C snurposome. C snurposomes range in size from less than 1 micron to giant structures greater than 20 microns in diameter. Usually, although not invariably, they have B snurposomes on their surface. They may also contain from one to hundreds of inclusions. Because of their remarkably spherical shape, C snurposomes with their associated B snurposomes have long been referred to as spheres or sphere organelles. Most spheres are free in the nucleoplasm, but a few are attached to chromosomes at specific chromosome loci, the sphere organizers (SOs). The relationship of sphere organelles to other snRNP-containing structures in the GV is obscure. We show by immunofluorescent staining that the lampbrush loops and B snurposomes also react with antibodies against heterogeneous nuclear ribonucleoproteins (hnRNPs). Transcription units on the loops are uniformly stained by anti-hnRNP and anti-snRNP antibodies, suggesting that nascent transcripts are associated with hnRNPs and snRNPs along their entire length, perhaps in the form of a unitary hnRNP/snRNP particle. That B snurposomes contain so many components involved in pre-mRNA packaging and processing suggests that they may serve as sites for assembly and storage of hnRNP/snRNP complexes destined for transport to the nascent transcripts on the lampbrush chromosome loops.

Disruption of pre-mRNA splicing in vivo results in reorganization of splicing factors

We have examined the functional significance of the organization of pre-mRNA splicing factors in a speckled distribution in the mammalian cell nucleus. Upon microinjection into living cells of oligonucleotides or antibodies that inhibit pre-mRNA splicing in vitro, we observed major changes in the organization of splicing factors in vivo. Interchromatin granule clusters became uniform in shape, decreased in number, and increased in both size and content of splicing factors, as measured by immunofluorescence. These changes were transient and the organization of splicing factors returned to their normal distribution by 24 h following microinjection. Microinjection of these oligonucleotides or antibodies also resulted in a reduction of transcription in vivo, but the oligonucleotides did not inhibit transcription in vitro. Control oligonucleotides did not disrupt splicing or transcription in vivo. We propose that the reorganization of splicing factors we observed is the result of the inhibition of splicing in vivo.

Small nuclear RNAs from Saccharomyces cerevisiae: unexpected diversity in abundance, size, and molecular complexity

Previous work showed that the simple eukaryote Saccharomyces cerevisiae contains a group of RNAs with the general structural properties predicted for small nuclear RNAs (snRNAs), including possession of the characteristic trimethylguanosine 5'-terminal cap. It was also demonstrated that, unlike their metazoan counterparts, the yeast snRNAs are present in low abundance (200-500 molecules per haploid cell). We have now used antibody directed against the 5' cap to investigate the total set size of snRNAs in this organism. We present evidence that the number of distinct yeast snRNAs is on the order of several dozen, that the length of the capped RNAs can exceed 1000 nucleotides, and that the relative abundance of a subset of these RNAs is 1/5th to 1/20th that of the class of snRNAs described previously. These findings suggest that the six highly abundant species of snRNAs (U1-U6) typically reported in metazoans may represent a serious underestimation of the total diversity of snRNAs in eukaryotes.

Association of phosphorylated serine/arginine (SR) splicing factors with the U1-small ribonucleoprotein (snRNP) autoantigen complex accompanies apoptotic cell death

Proteins subject to proteolysis or phosphorylation during apoptosis are commonly precipitated by autoantibodies found in the serum of patients with systemic lupus erythematosus (SLE). We screened a panel of murine monoclonal and human monospecific sera reactive with known autoantigens for their ability to selectively precipitate phosphoproteins from apoptotic Jurkat T cell lysates. Sera known to recognize the U1-small nuclear ribonucleoprotein (snRNP) complex (confirmed by their ability to precipitate U1-snRNA) selectively precipitated a phosphoprotein complex (pp54, pp42, pp34, and pp23) from apoptotic lysates. Monoclonal antibodies reactive with U1-snRNP proteins precipitated the same phosphoprotein complex from apoptotic lysates. The phosphorylation and/or recruitment of these proteins to the U1-snRNP complex is induced by multiple apoptotic stimuli (e.g., Fas ligation, gamma irradiation, or UV irradiation), and is blocked by overexpression of bcl-2. The U1-snRNP-associated phosphoprotein complex is immunoprecipitated by monoclonal antibodies reactive with serine/arginine (SR) proteins that comprise a structurally related family of splicing factors. The association of phosphorylated SR proteins with the U1-snRNP complex in cells undergoing apoptosis suggests a mechanism for regulation of alternative splicing of apoptotic effector molecules.

In vitro selection of an RNA epitope immunologically cross-reactive with a peptide

An antiserum raised against a peptide was used to select a unique RNA species from a degenerate pool of RNAs designed to resemble an autoantibody recognition site in U1 RNA. The peptide and the selected RNA epitope could compete for antibody binding, suggesting that both RNA and peptide epitopes occupy the same or overlapping antigen-combining sites. Thus, the RNA epitope functioned as a specific inhibitor of the antibody-antigen interaction. We demonstrate that the RNA epitope can be used to tag unrelated RNA molecules and also to detect the presence of the antibody. We propose that sequence-specific recognition of RNA by antibodies may involve protein-RNA contacts similar to those occurring in other nucleic acid-binding proteins. In addition, these findings are compatible with the suggestion that nucleic acid-binding autoantibodies may arise through immunological cross-reactivity between proteins and nucleic acids.

Anti-(U1) small nuclear RNA antibodies in anti-small nuclear ribonucleoprotein sera from patients with connective tissue diseases

Small nuclear ribonucleoprotein (snRNP) particles are a class of RNA-containing particles in the nucleus of eukaryotic cells. Sera from patients with connective tissue diseases often contain antibodies against the proteins present in these snRNPs. Antibodies against the RNA components of snRNPs, the U snRNAs, are thought to be rare. We tested 118 anti-snRNP sera for the presence of anti-snRNA antibodies and found them in 45 sera (38%). In all sera the antibodies (IgG and F(ab)2 fragments thereof) were exclusively directed against U1 snRNA. The anti-(U1) RNA antibodies were always accompanied by anti-(U1)RNP antibodies but were not found in sera which contain antibodies of the Sm serotype directed against all nucleoplasmic U snRNP particles. Like anti-RNP antibodies, anti-U1 RNA activity is confined to sera from patients with SLE or SLE overlap syndromes and is rarely found in patients with other connective tissue diseases. By analyzing binding to subfragments of U1 snRNA made in vitro, it was demonstrated that anti-(U1)RNA antibodies recognize epitopes distributed throughout the U1 RNA molecule. In most sera, however, either the second or the fourth hairpin loop is the main target of the antibody. The possible mechanisms that could lead to the production of this new type of autoantibody are discussed.

A sequence-specific conformational epitope on U1 RNA is recognized by a unique autoantibody

An autoantibody from a patient with lupus-overlap syndrome was found to bind a specific region of U1 RNA. By using RNA sequence analysis, immunoprecipitation, and competition experiments with in vitro synthesized fragments of U1 RNA, a region of 40 nucleotides representing a stem-loop secondary structure was found to be an immunoreactive domain. This antibody recognized a conformational epitope because neither the RNA stem nor the RNA loop alone was immunoprecipitable. Antisense U1 RNA, U1 DNA, and other small RNAs were not reactive with the antibody. While the origins of nucleic acid-binding antibodies are unknown, this RNA-specific autoantibody probably originated by direct presentation to the immune system or as an anti-idiotype against a more common U1 small nuclear ribonucleoprotein-specific autoantibody. Thus, these findings have implications for the mechanisms of autoimmune recognition and provide an immunological approach to probing RNA structure and protein-RNA interactions.

Isolation and sequence of four small nuclear U RNA genes of Trypanosoma brucei subsp. brucei: identification of the U2, U4, and U6 RNA analogs

Trypanosomes use trans splicing to place a common 39-nucleotide spliced-leader sequence on the 5' ends of all of their mRNAs. To identify likely participants in this reaction, we used antiserum directed against the characteristic U RNA 2,2,7-trimethylguanosine (TMG) cap to immunoprecipitate six candidate U RNAs from total trypanosome RNA. Genomic Southern analysis using oligonucleotide probes constructed from partial RNA sequence indicated that the four largest RNAs (A through D) are encoded by single-copy genes that are not closely linked to one another. We have cloned and sequenced these genes, mapped the 5' ends of the encoded RNAs, and identified three of the RNAs as the trypanosome U2, U4, and U6 analogs by virtue of their sequences and structural homologies with the corresponding metazoan U RNAs. The fourth RNA, RNA B (144 nucleotides), was not sufficiently similar to known U RNAs to allow us to propose an identify. Surprisingly, none of these U RNAs contained the consensus Sm antigen-binding site, a feature totally conserved among several classes of U RNAs, including U2 and U4. Similarly, the sequence of the U2 RNA region shown to be involved in pre-mRNA branchpoint recognition in yeast, and exactly conserved in metazoan U2 RNAs, was totally divergent in trypanosomes. Like all other U6 RNAs, trypanosome U6 did not contain a TMG cap and was immunoprecipitated from deproteinized RNA by anti-TMG antibody because of its association with the TMG-capped U4 RNA. These two RNAs contained extensive regions of sequence complementarity which phylogenetically support the secondary-structure model proposed by D. A. Brow and C. Guthrie (Nature [London] 334:213-218, 1988) for the organization of the analogous yeast U4-U6 complex.

U1 RNA induces innate immunity signaling

OBJECTIVE

The U1-70-kd RNP is a prominent target of autoimmunity in connective tissue diseases. In this study, we explored whether its endogenous ligand, U1 RNA, mediates a proimmune signal and may be immunogenic.

METHODS

We assayed the proliferation of control and MyD88-knockout splenocytes in response to in vitro-synthesized U1 RNA, and measured interleukin-6 (IL-6) and IL-8 secretion induced by U1 RNA in a human cell line competent for signaling through Toll-like receptor 3 (TLR-3) and TLR-5.

RESULTS

Treatment with U1 RNA or with poly(I-C), a known agonist of TLR-3, induced approximately twice as much control splenocyte proliferation as did treatment with RNase-digested U1 RNA. Proliferation in response to either poly(I-C) or U1 RNA by MyD88-knockout splenocytes was similarly attenuated. Similar to poly(I-C), U1 RNA induced significant secretion of both IL-6 and IL-8 from a TLR-3-expressing human cell line; in contrast, the TLR-5 agonist flagellin induced predominantly IL-8 secretion. Pretreatment of U1 RNA with RNase abolished IL-6 and IL-8 secretion.

CONCLUSION

U1 RNA is capable of inducing manifestations consistent with TLR-3 activation. The ability of U1 RNA (which has a substantial double-stranded secondary structure) to activate TLR-3 may contribute to the immunogenicity of the U1-70-kd autoantigen. Stimulation of innate immunity by native RNA molecules with a double-stranded secondary structure may help explain the high prevalence of autoimmunity to RNA binding proteins.

Molecular cloning of the cDNA for the human U2 snRNA-specific A' protein

The A' polypeptide is one of the protein constituents of the U2 snRNP particle. A potentially full-length cDNA clone containing the complete coding sequence for this U2 snRNP-specific protein was isolated by screening of a human lambda gt11 expression vector library with an autoimmune anti-(U1,U2)RNP serum. Monospecific antibodies, eluted from the 140-150 kD fusion protein of this cDNA recombinant, specifically recognized the A' protein on immunoblots and immunoprecipitated U2 snRNP particles from nuclear extracts. The identity of the clone was confirmed by in vitro translation of hybrid-selected mRNA or an RNA transcript synthesized from the cDNA insert. RNA blot analysis showed strong hybridization to a single polyadenylated transcript of 1.3 kb in human cells. The nucleotide sequence of the 1054 bp cDNA contains an open reading frame of 756 bp encoding a polypeptide of 255 amino acids with a predicted molecular weight of 28,444 D. The coding sequence is preceded by a 49 bp 5'-untranslated region and followed by a 226 bp 3'-untranslated region containing a single polyadenylation signal. Most striking feature of the deduced primary structure for the A' protein is a leucine-rich region in the amino-terminal half of the polypeptide. In contrast to the other U2 snRNP-specific protein B", the A' protein does not contain segments homologous to the RNP consensus sequences RNP1 and RNP2, common amino acid motifs found in several RNA-binding proteins. In the A' protein, however, the extremely hydrophilic carboxy terminus may constitute an RNA-binding moiety.

Pulmonary function in systemic lupus erythematosus is related to distinct clinical, serologic, and nailfold capillary patterns

PURPOSE

The purpose of this study was to investigate whether systemic lupus erythematosus (SLE) patients with interstitial lung disease represent a particular subset of patients characterized by the presence of clinical, serologic, and nailfold capillary patterns overlapping scleroderma.

PATIENTS AND METHODS

In 57 consecutive patients with SLE, a standardized detailed history was obtained and a physical examination performed, directed at signs and symptoms of connective tissue diseases, in particular scleroderma. Additionally, pulmonary function testing, chest radiography, radionuclide transit studies of the esophagus, nailfold capillary microscopy, and detailed serologic studies directed at the antigenic specificities of antinuclear antibodies were performed. Patients were divided into three groups based on the results of pulmonary function testing, i.e., normal lung function, restriction, or isolated impairment of diffusion. Clinical, serologic, and nailfold capillary microscopic findings were compared among these three groups.

RESULTS

Twenty patients had normal lung function, 19 had restrictive lung function loss, and 9 had an isolated impairment of the diffusing capacity (T1,CO). Patients with obstructive lung disease (n = 9) were excluded from analysis. Sclerodermatous changes of the hands were associated with a restrictive lung function pattern. Interstitial changes on chest radiograph were associated with isolated impairment of T1,CO. Nailfold capillary abnormalities correlated with decreased T1,CO and Dm, the component of T1,CO representing the diffusing capacity of the alveolocapillary membrane. Antibodies to U1-RNA were associated with restrictive lung function and decreased T1,CO.

CONCLUSION

We conclude that interstitial lung disease is present in a subset of SLE patients characterized by an increased prevalence of scleroderma traits and anti-(U1)RNA antibodies. Microvascular changes may contribute to the development of interstitial lung disease in SLE as well as in scleroderma.

Inflammatory myositis associated with anti-U1-small nuclear ribonucleoprotein antibodies: a subset of myositis associated with a favourable outcome

OBJECTIVES

Inflammatory myositides are rare chronic disorders which may be either isolated or associated with other conditions such as connective tissue diseases or neoplasia. A large variety of autoantibodies can be detected in patients with myositis, some of which have a diagnostic and/or a prognostic value. Myositis associated with anti-U1-small nuclear ribonucleoprotein antibodies (anti-U1-snRNP Abs) are usually considered as overlapping syndromes, mainly mixed connective tissue diseases (MCTD) in which muscle symptoms occur insidiously during the disease course and are characterized by a favourable outcome.

METHODS

The clinical, biological, immunological and pathological findings as well as the outcome of five patients with anti-U1-snRNP-associated myositis were retrospectively analysed.

RESULTS

Patients were mainly black females. In all five patients, myositis was the predominant manifestation at presentation. Associated conditions consisted of interstitial lung disease (ILD) (three), arthritis (three) and neurological symptoms (two). No patient presented Raynaud's phenomenon nor met criteria for MCTD. Biological inflammatory features, rheumatoid factor and polyclonal hypergammaglobulinaemia were present in all cases. Besides anti-U1-snRNP Abs, one patient had anti-Ro/SSA and anti-La/SSB Abs at presentation and one additional patient developed anti-double-stranded-DNA and anti-Sm Abs after a follow-up of more than 4 yr. No patient had anti-PM/sclerosis (Scl) nor anti-aminoacyl-tRNA synthetase Abs. All patients dramatically improved with steroids, and reached complete remission (CR) within 3 weeks. Two patients relapsed 18 months after CR. They both reached rapidly second CR using steroids associated or not with oral methotrexate.

CONCLUSION

Our data suggest that anti-U1-snRNP Abs may define a subset of myositis characterized by a favourable outcome, though often associated with ILD and/or neurological manifestations.

T cell immunity in connective tissue disease patients targets the RNA binding domain of the U1-70kDa small nuclear ribonucleoprotein

Although the T cell dependence of autoimmune responses in connective tissue diseases has been well established, limited information exists regarding the T cell targeting of self Ags in humans. To characterize the T cell response to a connective tissue disease-associated autoantigen, this study generated T cell clones from patients using a set of peptides encompassing the entire linear sequence of the 70-kDa subunit of U1 snRNP (U1-70kDa) small nuclear ribonucleoprotein. Despite the ability of U1-70kDa to undergo multiple forms of Ag modification that have been correlated with distinct clinical disease phenotypes, a remarkably limited and consistent pattern of T cell targeting of U1-70kDa was observed. All tested T cell clones generated against U1-70kDa were specific for epitopes within the RNA binding domain (RBD) of the protein. High avidity binding of the RBD with U1-RNA was preserved with the disease-associated modified forms of U1-70kDa tested. The high avidity interaction between the U1-RBD on the polypeptide and U1-RNA may be critical in immune targeting of this region in autoimmunity. The T cell autoimmune response to U1-70kDa appears to have less diversity than is seen in the humoral response; and therefore, may be a favorable target for therapeutic intervention.

Cyclin T1 but not cyclin T2a is induced by a post-transcriptional mechanism in PAMP-activated monocyte-derived macrophages

Positive transcription elongation factor b (P-TEFb) is an RNA polymerase II elongation factor which exists as multiple complexes in human cells. These complexes contain cyclin-dependent kinase 9 as the catalytic subunit and different cyclin subunits-cyclin T1, T2a, T2b, or K. Cyclin T1 is targeted by the human immunodeficiency virus (HIV) Tat protein to activate transcription of the HIV provirus. Expression of this P-TEFb subunit is highly regulated in monocyte-derived macrophages (MDMs). Cyclin T1 is induced early during differentiation and is shut off later by proteasome-mediated proteolysis. Cyclin T1 can be reinduced by pathogen-associated molecular patterns (PAMPs) or HIV infection. In this study, we analyzed regulation of P-TEFb in MDMs by examining 7SK small nuclear RNA and the HEXIM1 protein; these factors associate with P-TEFb and are thought to regulate its function. 7SK and HEXIM1 were induced early during differentiation, and this correlates with increased overall transcription. 7SK expression remained high, but HEXIM1 was shut off later during differentiation by proteasome-mediated proteolysis. Significantly, the cyclin T2a subunit of P-TEFb was not shut off during differentiation, and it was not induced by activation. Induction of cyclin T1 by PAMPs was found to be a slow process and did not involve an increase in cyclin T1 mRNA levels. Treatment of MDMs with PAMPs or a proteasome inhibitor induced cyclin T1 to a level equivalent to treatment with both agents together, suggesting that PAMPs and proteasome inhibitors act at a similar rate-limiting step. It is therefore likely that cyclin T1 induction by PAMPs is the result of a reduction in proteasome-mediated proteolysis.

The prevalence and clinical significance of anti-U1 RNA antibodies in patients with systemic sclerosis

We studied the prevalence and clinical significance of anti-U1 RNA antibodies in patients with systemic sclerosis. The presence of anti-U1 RNA antibodies was determined using immunoprecipitation in systemic sclerosis patients with anti-U1 RNP antibodies (n=36), antitopoisomerase I antibodies (n=20), or anticentromere antibodies (n=20), mixed connective tissue disease patients (n=23), systemic lupus erythematosus patients with anti-U1 RNP antibodies (n=26), and normal controls (n=20). Moreover, antigen specificities for anti-U1 RNP antibodies were examined in patients with systemic sclerosis by immunoblotting and enzyme-linked immunosorbent assay. Anti-U1 RNA antibodies was detected in 22 of 36 systemic sclerosis patients (61%) with anti-U1 RNP antibodies, 14 of 23 patients (61%) with mixed connective tissue disease, and eight of 26 systemic lupus erythematosus patients (31%) with anti-U1 RNP antibodies. Anti-U1 RNA antibodies were not detected in other groups. As for systemic sclerosis patients, the frequencies of pulmonary fibrosis and reduced percentage diffusion capacity for carbon monoxide were significantly greater in patients with anti-U1 RNA antibodies than in those without (76%vs 18%, p<0.005; 82%vs 27%, p<0.005, respectively). Moreover, patients with anti-U1 RNA antibodies had significantly lower percentage diffusion capacity for carbon monoxide and percentage vital capacity values than those without (51.9+/-16.8 vs 79.4+/-16.4, p<0.01; 83.8+/-21.4 vs 101.4+/-12.9, p<0.05, respectively). Regarding the antigen specificities of anti-U1 RNP antibodies in systemic sclerosis patients, the frequency of anti-70 kDa antibodies determined by immunoblotting was significantly higher in patients with anti-U1 RNA antibodies than in those without (77%vs 43%, p<0.05). This finding was also confirmed by enzyme-linked immunosorbent assay for anti-70 kDa antibodies (86%vs 43%, p<0.05). These results indicate that anti-U1 RNA antibodies may be a serologic indicator for pulmonary fibrosis in systemic sclerosis patients with anti-U1 RNP antibodies.

Increased association of 7SK snRNA with Tat cofactor P-TEFb following activation of peripheral blood lymphocytes

OBJECTIVE

This study was undertaken to determine whether 7SK small nuclear RNA (snRNA), which has been proposed to function as an inhibitor of Tat cofactor P-TEFb, plays a role in transcriptional latency in T cells.

DESIGN AND METHODS

The association of 7SK snRNA with P-TEFb was investigated in resting and activated peripheral blood lymphocytes (PBLs). Primary PBLs were isolated by standard methods and activated with phytohemagglutinin (PHA). Levels of 7SK snRNA were determined by Northern blotting and levels of the P-TEFb subunits cyclin-dependent kinase 9 and cyclin T1 were analyzed by immunoblotting.

RESULTS

The association of 7SK snRNA with P-TEFb complexes was specific. Following activation of PBLs, the levels of 7SK snRNA increased in a manner similar to U1 and U6 snRNA, sn RNAs involved in positive aspects of cellular gene expression. Unexpectedly, the association of 7SK snRNA with P-TEFb increased dramatically following lymphocyte activation.

CONCLUSION

Increased association of 7SK snRNA with P-TEFb in activated lymphocytes correlates with increased global transcription. This suggests that 7SK snRNA is unlikely to promote transcriptional latency in lymphocytes through an association with P-TEFb; it also suggests that the proposal that the association of 7SK snRNA with P-TEFb acts to inhibit transcriptional elongation needs to be re-evaluated.

(SWR x SJL)F1 mice: a new model of lupus-like disease

During the study of autoimmune models we found that (SWR x SJL)F1 mice (both parental strains with the V beta a phenotype) spontaneously produced immunoglobulin G (IgG) antibodies directed against Sm/U1 small nuclear ribonucleoproteins (snRNPs). In some of these females, the presence of these autoantibodies was found as early as 10 wk of age. Their frequency increased with age i.e., 70% at 40 wk. At that time, only 10% of males developed anti-Sm/U1snRNP antibodies. Anti-Sm/U1snRNP antibodies from positive mice generally recognized the peptides BB', D, 70 kD, and A from RNPs. These polypeptides are known to bear the autoantigenic epitopes that are recognized by human sera containing anti-Sm and anti-U1snRNP antibodies. Reactivity of IgG antibodies with the octapeptide sequence PPPGMRPP was also found in 30% of anti-Sm/U1snRNP positive (SWR x SJL)F1 mice that precipitated BB' peptides. This octapeptide has been described as the most immunoreactive linear epitope in systemic lupus erythematosus (SLE) patients with anti-Sm and anti-U1snRNP antibodies. Approximately 30% of anti-Sn/U1snRNP positive females, later produced anti-dsDNA antibodies. This fact was accompanied by the development of proteinuria due to glomerulonephritis mediated by immunocomplexes. In addition to the specific autoimmune response, (SWR x SJL)F1 females also showed other immunologic abnormalities such as hypergammaglobulinemia, and an approximately twofold increase in spleen cell number compared with control mice. These results indicate that (SWR x SJL)F1 females develop clinical and serological abnormalities similar to those observed in human SLE and constitute a novel model for the study of the genetic mechanisms that result in autoimmunity.

Generation of novel covalent RNA-protein complexes in cells by ultraviolet B irradiation: implications for autoimmunity

OBJECTIVE

To determine whether ultraviolet B (UVB) irradiation induces novel modifications in autoantigens targeted during experimental photoinduced epidermal damage.

METHODS

To search for novel UVB-induced autoantigen modifications, lysates made from UVB-irradiated human keratinocytes or HeLa cells were immunoblotted using human autoantibodies that recognize ribonucleoprotein autoantigens. Novel autoantigen structures identified were further characterized using nucleases and RNA hybridization.

RESULTS

Human sera that recognize U1-70 kd (U1-70K) and La by immunoblotting also recognized multiple novel species when they were used to immunoblot lysates of UVB-irradiated keratinocytes or HeLa cells. These species were not present in control cells and were not observed when apoptosis was induced by Fas ligation or cytotoxic lymphocyte granule contents. Biochemical analysis using multiple assays revealed that these novel UVB-induced molecular species result from the covalent crosslinking between the U1 RNA and the hYRNA molecules with their associated proteins, including U1-70K, La, and likely components of the Sm particle.

CONCLUSION

These data demonstrate that UVB irradiation of live cells can directly induce covalent RNA-protein complexes, which are recognized by human autoantibodies. As previously described for other autoantigens, these covalent complexes of RNA and proteins may have important consequences in terms of antigen capture and processing.

An immunoelectron study of karyosphere and nuclear bodies in oocytes of mealworm beetle, Tenebrio molitor (Coleoptera: polyphaga)

The karyosphere and nuclear bodies (NBs) were studied in Tenebrio molitor oocytes using immunoelectron cytochemistry. During early diplotene (previtellogenic stage), oocyte chromosomes begin to unite in a small nuclear volume forming the karyosphere. In vitellogenic oocyte nuclei, the chromatin undergoes condensation, and the karyosphere acquires a ring-shaped structure. The karyosphere is the only structure containing DNA in the oocyte nucleus. Pre-mRNA splicing factors [small nuclear ribonucleoproteins (snRNPs) and SC35] are not found in the karyosphere itself. In previtellogenic oocyte nuclei, these factors are present in NBs and in a fibrogranular substance surrounding the chromosomes in the early stages of karyosphere formation. At this stage, larger fibrillar NBs contain the non-snRNP splicing factor SC35. Smaller roundish NBs were shown to contain snRNPs. Some NBs with the same morphology contain neither snRNPs nor SC35. In the vitellogenic oocyte, there are fibrogranular NBs containing both snRNPs and SC35 splicing factors, fibrillar NBs containing snRNPs only, and complex NBs containing both. Complex NBs are often connected with the ring-shaped karyosphere. Based on the obtained immunoelectron data, we suggest that T. molitor oocyte NBs containing both snRNPs and the non-snRNP splicing factor SC35 are homologs of the well-characterized B-snurposomes in amphibian germinal vesicles and clusters of interchromatin granules in mammalian oocyte nuclei. Other NBs containing only snRNPs are suggested to represent a special class of insect oocyte snurposomes. The nuclear organelles mentioned seem to play a role as storage domains for pre-mRNA splicing factors during T. molitor oogenesis.

A new conformational epitope generated by the binding of recombinant 70-kd protein and U1 RNA to anti-U1 RNP autoantibodies in sera from patients with mixed connective tissue disease

OBJECTIVE

To establish an enzyme-linked immunosorbent assay (ELISA) using a complex of in vitro-transcribed U1 RNA and recombinant 70-kd, A, and C proteins (C-ELISA) to detect anti-U1 RNP antibodies reactive in double immunodiffusion (DID), but not in ELISA using the proteins alone (P-ELISA).

METHODS

Sera from 196 patients with mixed connective tissue disease were used to test reactivity in P- and C-ELISAs, and the specificity of the sera was also tested by DID and immunoprecipitation (IP).

RESULTS

In P-ELISA, 15 of 196 sera positive for anti-U1 RNP in DID did not react, while all sera reacted in C-ELISA. The reactivity of 15 sera to the U1 RNA was tested by IP and ELISA, and only 3 sera reacted with the U1 RNA. These results indicated that the increased reactivity in C-ELISA was not due to the U1 RNA itself. We confirmed that the 70-kd and A proteins were bound directly to the U1 RNA by IP using antibodies to His-tag, and we tested the reactivity of the sera to the U1 RNA-70-kd protein complex and the U1 RNA-A protein complex by IP. All sera reacted with the U1 RNA-70-kd protein complex, and 1 sample reacted with the U1 RNA-A protein complex.

CONCLUSION

These results suggest that some anti-U1 RNP-positive sera specifically recognize the conformational structure altered by the binding of U1 RNA to the proteins, and the ELISA using U1 RNA and recombinant proteins is as useful as the DID method for detecting anti-U1 RNP antibodies.

Epitope regions on U1 small nuclear RNA recognized by anti-U1RNA-specific autoantibodies

Autoantibodies specifically directed to U1RNA were found in patients suffering from systemic lupus erythematosus (SLE) overlap syndromes. To obtain more insight in the mechanism responsible for this U1RNA-specific antibody formation and to use the antibodies eventually as a tool to study U1RNA-protein (U1RNP) interactions, the B cell epitopes on U1RNA were mapped. Using in vitro synthesized domains of U1RNA, the main epitope regions were found in stemloops II and IV. Furthermore, 3'-end or 5'-end truncation of both stemloop II and stemloop IV showed that the conformation of the stemloops is critical for antibody recognition. Mutant studies on both stemloops indicated that in the case of stemloop II the stem is the main antigenic region, whereas in stemloop IV, the loop (E-loop) is a main target. The results of this study support the idea that the anti-U1RNA autoantibody could be the result of a process driven by the human U1RNP complex itself (antigen-driven process).