Human autoantibody-reactive epitopes of SS-B/La are highly conserved in comparison with epitopes recognized by murine monoclonal antibodies

The axis of complement C1 and nucleolus in antinuclear autoimmunity

Antinuclear autoantibodies (ANA) are heterogeneous self-reactive antibodies that target the chromatin network, the speckled, the nucleoli, and other nuclear regions. The immunological aberration for ANA production remains partially understood, but ANA are known to be pathogenic, especially, in systemic lupus erythematosus (SLE). Most SLE patients exhibit a highly polygenic disease involving multiple organs, but in rare complement C1q, C1r, or C1s deficiencies, the disease can become largely monogenic. Increasing evidence point to intrinsic autoimmunogenicity of the nuclei. Necrotic cells release fragmented chromatins as nucleosomes and the alarmin HMGB1 is associated with the nucleosomes to activate TLRs and confer anti-chromatin autoimmunogenecity. In speckled regions, the major ANA targets Sm/RNP and SSA/Ro contain snRNAs that confer autoimmunogenecity to Sm/RNP and SSA/Ro antigens. Recently, three GAR/RGG-containing alarmins have been identified in the nucleolus that helps explain its high autoimmunogenicity. Interestingly, C1q binds to the nucleoli exposed by necrotic cells to cause protease C1r and C1s activation. C1s cleaves HMGB1 to inactive its alarmin activity. C1 proteases also degrade many nucleolar autoantigens including nucleolin, a major GAR/RGG-containing autoantigen and alarmin. It appears that the different nuclear regions are intrinsically autoimmunogenic by containing autoantigens and alarmins. However, the extracellular complement C1 complex function to dampen nuclear autoimmunogenecity by degrading these nuclear proteins.

A Small Step, a Giant Leap: Somatic Hypermutation of a Single Amino Acid Leads to Anti-La Autoreactivity

The anti-La mab 312B, which was established by hybridoma technology from human-La transgenic mice after adoptive transfer of anti-human La T cells, immunoprecipitates both native eukaryotic human and murine La protein. Therefore, it represents a true anti-La autoantibody. During maturation, the anti-La mab 312B acquired somatic hypermutations (SHMs) which resulted in the replacement of four aa in the complementarity determining regions (CDR) and seven aa in the framework regions. The recombinant derivative of the anti-La mab 312B in which all the SHMs were corrected to the germline sequence failed to recognize the La antigen. We therefore wanted to learn which SHM(s) is (are) responsible for anti-La autoreactivity. Humanization of the 312B ab by grafting its CDR regions to a human Ig backbone confirms that the CDR sequences are mainly responsible for anti-La autoreactivity. Finally, we identified that a single amino acid replacement (D > Y) in the germline sequence of the CDR3 region of the heavy chain of the anti-La mab 312B is sufficient for anti-La autoreactivity.

Strong Association of the Myriad Discrete Speckled Nuclear Pattern With Anti-SS-A/Ro60 Antibodies: Consensus Experience of Four International Expert Centers

Introduction

The morphological patterns in indirect immunofluorescence assay on HEp-2 cells (HEp-2 IFA) reflect the autoantibodies in the sample. The International Consensus on ANA Patterns (ICAP) classifies 30 relevant patterns (AC-0 to AC-29). AC-4 (fine speckled nuclear pattern) is associated to anti-SS-A/Ro, anti-SS-B/La, and several autoantibodies. Anti-SS-A/Ro samples may contain antibodies to Ro60 and Ro52. A variation of AC-4 (herein designated AC-4a), characterized by myriad discrete nuclear speckles, was reported to be associated with anti-SS-A/Ro. The plain fine speckled pattern (herein designated AC-4b) seldom was associated with anti-SS-A/Ro. This study reports the experience of four expert laboratories on AC-4a and AC-4b.

Methods

Anti-Ro60 monoclonal antibody A7 was used to investigate the HEp-2 IFA pattern. Records containing concomitant HEp-2 IFA and SS-A/Ro tests from Durand Laboratory, Argentina (n = 383) and Fleury Laboratory, Brazil (n = 144,471) were analyzed for associations between HEp-2 IFA patterns and disease-associated autoantibodies (DAA): double-stranded DNA, Scl-70, nucleosome, SS-B/La, Sm, and U1-RNP. A total of 381 samples from Dresden Technical University (TU-Dresden), Germany, were assayed for HEp-2 IFA and DAA.

Results

Monoclonal A7 recognized Ro60 in Western blot and immunoprecipitation, and yielded the AC-4a pattern on HEp-2 IFA. Analyses from Durand Laboratory and Fleury Laboratory yielded compatible results: AC-4a was less frequent (8.9% and 2.7%, respectively) than AC-4b (26.1% and 24.2%) in HEp-2 IFA-positive samples. Reactivity to SS-A/Ro occurred in 67.6% and 96.3% of AC-4a-pattern samples against 23% and 6.8% of AC-4b pattern samples. Reciprocally, AC-4a occurred in 24% and 47.1% of anti-SS-A/Ro-positive samples, and in 3.8% and 0.1% of anti-SS-A/Ro-negative samples. Data from TU-Dresden show that the AC-4a pattern occurred in 69% of 169 anti-SS-A/Ro-monospecific samples (62% of all anti-SS-A/Ro-positive samples) and in 4% of anti-SS-A/Ro-negative samples, whereas anti-SS-A/Ro occurred in 98.3% of AC-4a samples and in 47.9% of AC-4b samples. In all laboratories, coexistence of anti-SS-B/La, but not other DAA, in anti-SS-A/Ro-positive samples did not disturb the AC-4a pattern. AC-4a was predominantly associated with anti-Ro60 antibodies.

Conclusions

This study confirms the association of AC-4a pattern and anti-SS-A/Ro in opposition to the AC-4b pattern. The results of four international expert laboratories support the worldwide applicability of these AC-4 pattern variants and their incorporation into ICAP classification under codes AC-4a and AC-4b, respectively. The AC-4 pattern should be maintained as an umbrella pattern for cases in which one cannot discriminate AC-4a and AC-4b patterns. The acknowledgment of the AC-4a pattern should add value to HEp-2 IFA interpretation.

T Cell Mediated Conversion of a Non-Anti-La Reactive B Cell to an Autoreactive Anti-La B Cell by Somatic Hypermutation

Since the first description of nuclear autoantigens in the late 1960s and early 1970s, researchers, including ourselves, have found it difficult to establish monoclonal antibodies (mabs) against nuclear antigens, including the La/SS-B (Sjögrens' syndrome associated antigen B) autoantigen. To date, only a few anti-La mabs have been derived by conventional hybridoma technology; however, those anti-La mabs were not bona fide autoantibodies as they recognize either human La specific, cryptic, or post-translationally modified epitopes which are not accessible on native mouse La protein. Herein, we present a series of novel murine anti-La mabs including truly autoreactive ones. These mabs were elicited from a human La transgenic animal through adoptive transfer of T cells from non-transgenic mice immunized with human La antigen. Detailed epitope and paratope analyses experimentally confirm the hypothesis that somatic hypermutations that occur during T cell dependent maturation can lead to autoreactivity to the nuclear La/SS-B autoantigen.

Antibody fingerprints in lyme disease deciphered with high density peptide arrays

Lyme disease is the most common tick-borne infectious disease in Europe and North America. Previous studies discovered the immunogenic role of a surface-exposed lipoprotein (VlsE) of Borreliella burgdorferi. We employed high density peptide arrays to investigate the antibody response to the VlsE protein in VlsE-positive patients by mapping the protein as overlapping peptides and subsequent in-depth epitope substitution analyses. These investigations led to the identification of antibody fingerprints represented by a number of key residues that are indispensable for the binding of the respective antibody. This approach allows us to compare the antibody specificities of different patients to the resolution of single amino acids. Our study revealed that the sera of VlsE-positive patients recognize different epitopes on the protein. Remarkably, in those cases where the same epitope is targeted, the antibody fingerprint is almost identical. Furthermore, we could correlate two fingerprints with human autoantigens and an Epstein-Barr virus epitope; yet, the link to autoimmune disorders seems unlikely and must be investigated in further studies. The other three fingerprints are much more specific for B. burgdorferi. Since antibody fingerprints of longer sequences have proven to be highly disease specific, our findings suggest that the fingerprints could function as diagnostic markers that can reduce false positive test results.

Dr Eng M. Tan: a tribute to an enduring legacy in autoimmunity

At the age of ninety years, Dr Eng Meng Tan has had a remarkable impact on the accumulated knowledge of autoimmune diseases, including seminal findings in systemic lupus erythematosus (SLE) and a wide range of other autoimmune diseases. Dating to the first description of the Sm (Smith) autoantibody in SLE, his focus has been the use of autoantibodies as probes to identify and elucidate novel cellular molecules and then translating these discoveries into biomarkers and immunoassays for a wide range of these diseases and, later, cancer. He led efforts to standardize autoantibody nomenclature and testing protocols. Through his mentorship a great number of trainees and collaborators have had remarkably successful careers, and by that virtue he has garnered a remarkable continuing legacy.

Neurotrophic effects of fibroblast growth factor-like autoantibodies in serum from three patients with breast cancer

Basic fibroblast growth factor (FGF) promotes branching neuritogenesis and survival in rat hippocampal neurons in vitro. Basic FGF is a broad spectrum mitogen which does not normally circulate, but increases in serum from a variety of cancers. In prior work, we described spontaneously-occurring fibroblast growth factor-like autoantibodies in serum from a subset of breast cancer patients with neurological complications. The FGF-like autoantibodies mimicked the potent endothelial cell growth-promoting activity of bFGF yet had remarkably increased stability (activity survived storage at 0-4 degrees C for up to 5 years). In the present study we tested whether FGF-like autoantibodies from breast cancer sera is neurotrophic or neuroprotective. We now report that FGF-like autoantibodies (2-3 microg/mL) from breast cancer sera promoted neuritogenesis in DIV 12 embryonic day 18 rat hippocampal neurons and neurite extension in undifferentiated rat pheochromocytoma PC12 cells. The FGF-like autoantibodies from a breast cancer patient with lupus were unique in protecting rat hippocampal neurons from glutamate-induced cell loss and promoting long-lasting neurite extension and survival in PC-12 cells (up to 25 days in vitro). Breast cancer sera FGF-like autoantibodies induced large sustained increases in inward cationic current associated with depolarization in hippocampal neurons that exceeded the electrophysiological effects of substantial concentrations of basic FGF. These results suggest that differences in potency or other unknown factors contribute to whether subsets of FGF-like autoantibodies from breast cancer sera exhibit long-lasting neurotrophic and neuroprotective effects or an early neurotrophic effect followed by accelerated late neuron death.

Rck/p54 interacts with APP mRNA as part of a multi-protein complex and enhances APP mRNA and protein expression in neuronal cell lines

Overproduction of amyloid precursor protein (APP) and beta-amyloid likely contribute to neurodegeneration seen in Alzheimer's disease (AD). APP mRNA contains several, 3'-untranslated region (UTR), cis-acting regulatory elements. A 52 base element (52sce), immediately downstream from the stop codon, has been previously shown to complex with uncharacterized cytoplasmic proteins. In this study, we purify and identify six proteins that specifically bind to the 52sce, and show that these proteins interact with each other and with APP mRNA in intact human neuroblastoma cells. We also present evidence that at least one of these proteins, the DEAD-box helicase rck/p54, is involved in post-transcriptional regulation, as its overexpression in cultured cells results in elevated levels of APP mRNA and protein. These findings suggest a novel mechanism for post-transcriptional regulation of APP mRNA.

Autoantibodies to tumor-associated antigens: reporters from the immune system

Although autoantibodies have been recognized as participants in pathogenesis of tissue injury, the collateral role of autoantibodies as reporters from the immune system identifying cellular participants in tumorigenesis has not been fully appreciated. The immune system appears to be capable of sensing aberrant structure, distribution, and function of certain cellular components involved in tumorigenesis and making autoantibody responses to the tumor-associated antigens (TAAs). Autoantibodies to TAAs can report malignant transformation before standard clinical studies and may be useful as early detection biomarkers. The autoantibody response also provides insights into factors related to how cellular components may be rendered immunogenic. As diagnostic biomarkers, specific TAA miniarrays for identifying autoantibody profiles could have sufficient sensitivity in differentiating between types of tumors. Such anti-TAA profiles could also be used to monitor response to therapy. The immune system of cancer patients reveals the immune interactive sites or the autoepitopes of participants in tumorigenesis, and this information should be used in the design of immunotherapy.

Neuron-specific enolase antibodies in patients with sudden acquired retinal degeneration syndrome

Sudden acquired retinal degeneration syndrome (SARDS) is a disease characterised by sudden and bilateral vision loss of dogs. Previous studies failed to identify the underlying cause [Mattson, A., Roberts, S.M., Isherwood, J.M.E., 1992. Clinical features suggesting hyperadrenocorticism associated with sudden acquired retinal degeneration syndrome in a dog. J. Am. Anim. Hosp. Assoc. 28, 199-202; Van der Woerdt, A., Nasisse, M.P., Davidson, M.G., 1991. Sudden acquired retinal degeneration in the dog: clinical and laboratory findings in 36 cases. Prog. Vet. Comp. Ophthamol. 1, 11-18] and earlier investigations about the occurrence of anti-retinal antibodies in SARDS patients showed inconsistent results. To provide a novel approach to those findings we designed a more detailed study. Autoantibodies of SARDS patients and normal controls were tested against the purified autoantigens S-antigen and cellular retinaldehyde binding protein (CRALBP) that play a role in human autoimmune uveitis. Next we tested the autoantibody binding pattern to whole retinal lysate. No difference in the incidence of autoantibodies could be found between SARDS patients and healthy controls while testing the well-known autoantigens S-antigen and CRALBP. Potential novel, yet unknown autoantigens were identified by a screening test using the retinal proteome as an autoantigenic source. In SARDS patients and normal controls, several retinal proteins were bound by IgG antibodies, but one band was strongly marked by SARDS patients. That band was excised, subjected to mass spectrometry (matrix-assisted laser desorption/ionisation-time of flight (MALDI-TOF/TOF)) and identified as neuron-specific enolase. Binding of the IgG autoantibodies of SARDS-affected dogs to this protein was verified using purified NSE, revealing 25% of NSE autoantibody-positive SARDS patients and 0% of negative controls. Our findings indicate that at least some dogs with SARDS have autoantibodies against NSE, although it is unclear whether these play a causative role in SARDS or whether they are the result of retinal destruction by another mechanism.

A search for structurally similar cellular internal ribosome entry sites

Internal ribosome entry sites (IRES) allow ribosomes to be recruited to mRNA in a cap-independent manner. Some viruses that impair cap-dependent translation initiation utilize IRES to ensure that the viral RNA will efficiently compete for the translation machinery. IRES are also employed for the translation of a subset of cellular messages during conditions that inhibit cap-dependent translation initiation. IRES from viruses like Hepatitis C and Classical Swine Fever virus share a similar structure/function without sharing primary sequence similarity. Of the cellular IRES structures derived so far, none were shown to share an overall structural similarity. Therefore, we undertook a genome-wide search of human 5'UTRs (untranslated regions) with an empirically derived structure of the IRES from the key inhibitor of apoptosis, X-linked inhibitor of apoptosis protein (XIAP), to identify novel IRES that share structure/function similarity. Three of the top matches identified by this search that exhibit IRES activity are the 5'UTRs of Aquaporin 4, ELG1 and NF-kappaB repressing factor (NRF). The structures of AQP4 and ELG1 IRES have limited similarity to the XIAP IRES; however, they share trans-acting factors that bind the XIAP IRES. We therefore propose that cellular IRES are not defined by overall structure, as viral IRES, but are instead dependent upon short motifs and trans-acting factors for their function.

Subcellular relocalization of a trans-acting factor regulates XIAP IRES-dependent translation

Translation of the X-linked inhibitor of apoptosis (XIAP) proceeds by internal ribosome entry site (IRES)-mediated initiation, a process that is physiologically important because XIAP expression is essential for cell survival under conditions of compromised cap-dependent translation, such as cellular stress. The regulation of internal initiation requires the interaction of IRES trans-acting factors (ITAFs) with the IRES element. We used RNA-affinity chromatography to identify XIAP ITAFs and isolated the heterogeneous nuclear ribonucleoprotein A1 (hnRNP A1). We find that hnRNP A1 interacts with XIAP IRES RNA both in vitro and in vivo and that hnRNP A1 negatively regulates XIAP IRES activity. Moreover, XIAP IRES-dependent translation is significantly reduced when hnRNP A1 accumulates in the cytoplasm. Osmotic shock, a cellular stress that causes cytoplasmic accumulation of hnRNP A1, also leads to a decrease in XIAP levels that is abrogated by knockdown of hnRNP A1 expression. These results suggest that the subcellular localization of hnRNP A1 is an important determinant of its ability to negatively regulate XIAP IRES activity, suggesting that the subcellular distribution of ITAFs plays a critical role in regulating IRES-dependent translation. Our findings demonstrate that cytoplasmic hnRNP A1 is a negative regulator of XIAP IRES-dependent translation, indicating a novel function for the cytoplasmic form of this protein.

Tolerance through indifference: autoreactive B cells to the nuclear antigen La show no evidence of tolerance in a transgenic model

Systemic autoimmune diseases are characterized by the production of high titer autoantibodies specific for ubiquitous nuclear self-Ags such as DNA, Sm, and La (SS-B), so the normal mechanisms of B cell tolerance to disease-associated nuclear Ags have been of great interest. Mechanisms of B cell tolerance include deletion, anergy, developmental arrest, receptor editing, and B cell differentiation to the B-1 subtype. However, recent studies in our laboratory have suggested that B cell tolerance to the nuclear autoantigen La is limited in normal mice, and tolerance may reside primarily in the T cell compartment. To test this hypothesis, we created Ig transgenic mice expressing the IgM H chain from an mAb specific for a xenogeneic epitope within human La (hLa). These mice were bred with hLa-transgenic mice that constitutively express hLa in a manner comparable to endogenous mouse La. Between 5-15% of transgenic B cells developing in the absence of hLa were specific for hLa, and these cells were neither depleted nor developmentally arrested in the presence of endogenous hLa expression. Instead, these autoreactive B cells matured normally and differentiated into Ab-forming cells, capable of secreting high titer autoantibody. Additionally, the life span of autoreactive hLa-specific B cells was not reduced, and they were phenotypically and functionally indistinguishable from naive nonautoreactive hLa-specific B cells developing in the absence of hLa. Together these data suggest a lack of intrinsic B cell tolerance involving any known mechanisms indicating that these autoreactive B cells are indifferent to their autoantigen.

The internal ribosome entry site-mediated translation of antiapoptotic protein XIAP is modulated by the heterogeneous nuclear ribonucleoproteins C1 and C2

The X-chromosome-linked inhibitor of apoptosis, XIAP, is the most powerful and ubiquitous intrinsic inhibitor of apoptosis. We have shown previously that the translation of XIAP is controlled by a potent internal ribosome entry site (IRES) element. IRES-mediated translation of XIAP is increased in response to cellular stress, suggesting the critical role for IRES translation during cellular stress. Here, we demonstrate that heterogeneous nuclear ribonucleoproteins C1 and C2 (hnRNPC1 and -C2) are part of the RNP complex that forms on XIAP IRES. Furthermore, the cellular levels of hnRNPC1 and -C2 parallel the activity of XIAP IRES and the overexpression of hnRNPC1 and -C2 specifically enhanced translation of XIAP IRES, suggesting that hnRNPC1 and -C2 may modulate XIAP expression. Given the central role of XIAP in the regulation of apoptosis these results are important for our understanding of the control of apoptosis.

The La RNA-binding protein interacts with the vault RNA and is a vault-associated protein

Vaults are highly conserved ubiquitous ribonucleoprotein particles with an undefined function. Three protein species (p240/TEP1, p193/VPARP, and p100/MVP) and a small RNA comprise the 13-MDa vault particle. The expression of the unique 100-kDa major vault protein is sufficient to form the basic vault structure. Previously, we have shown that stable association of the vault RNA with the vault particle is dependent on its interaction with the p240/TEP1 protein. To identify other proteins that interact with the vault RNA, we used a UV-cross-linking assay. We find that a portion of the vault RNA is complexed with the La autoantigen in a separate smaller ribonucleoprotein particle. La interacts with the vault RNA (both in vivo and in vitro) presumably through binding to 3'-uridylates. Moreover, we also demonstrate that the La autoantigen is the 50-kDa protein that we have previously reported as a protein that co-purifies with vaults.

A phosphorylated cytoplasmic autoantigen, GW182, associates with a unique population of human mRNAs within novel cytoplasmic speckles

A novel human cellular structure has been identified that contains a unique autoimmune antigen and multiple messenger RNAs. This complex was discovered using an autoimmune serum from a patient with motor and sensory neuropathy and contains a protein of 182 kDa. The gene and cDNA encoding the protein indicated an open reading frame with glycine-tryptophan (GW) repeats and a single RNA recognition motif. Both the patient's serum and a rabbit serum raised against the recombinant GW protein costained discrete cytoplasmic speckles designated as GW bodies (GWBs) that do not overlap with the Golgi complex, endosomes, lysosomes, or peroxisomes. The mRNAs associated with GW182 represent a clustered set of transcripts that are presumed to reside within the GW complexes. We propose that the GW ribonucleoprotein complex is involved in the posttranscriptional regulation of gene expression by sequestering a specific subset of gene transcripts involved in cell growth and homeostasis.

Autoantibody to hLSm4 and the heptameric LSm complex in anti-Sm sera

OBJECTIVE

To characterize the 15-kd human SmD-like autoantigen and its associated proteins previously shown to be recognized by IgM antibodies in patients with Epstein-Barr virus (EBV)-induced infectious mononucleosis.

METHODS

The full-length complementary DNA for the 15-kd protein was expressed as recombinant protein and analyzed for reactivity using biochemical analysis and immunoprecipitation (IP).

RESULTS

The 15-kd protein was determined to be the human like-Sm protein LSm4 (hLSm4). Rabbit antibody raised against the C-terminal polypeptide immunoprecipitated a 68-kd complex composed of LSm4 together with a group of smaller proteins ranging in size from 6.5 to 14 kd, consistent with the reported heptameric LSm complexes involved in U4/U6 duplex formation and messenger RNA (mRNA) decapping/degradation. About 80% of all anti-Sm sera from patients with systemic lupus erythematosus (SLE) recognized the hLSm4 in vitro translated product, while 6.7% (29 of 434) immunoprecipitated from cell extracts hLSm4 together with the other members of the hLSm complex. Four sera (0.92%) showed apparently exclusive reactivity to the hLSm complex in the absence of reactivity to Sm core proteins in the IP assay.

CONCLUSION

These findings document that while IgM, but not IgG, autoantibodies to LSm4 were found in sera from patients with EBV infection, IgG autoantibodies to hLSm4 are detected in a large number of anti-Sm-positive sera from patients with SLE. Importantly, in a small number of anti-Sm sera the LSm complex can be recognized independently of the Sm core protein antigens. Our data introduce the concept that "Sm" autoantigens include Sm as well as LSm complexes involved in the maturation and degradation of mRNA.

Binding of the La autoantigen to the 5' untranslated region of a chimeric human translation elongation factor 1A reporter mRNA inhibits translation in vitro

Human translation elongation factor 1A (EF1A) is a member of a large class of mRNAs, including ribosomal proteins and other translation elongation factors, which are coordinately translationally regulated under various conditions. Each of these mRNAs contains a terminal oligopyrimidine tract (TOP) that is required for translational control. A human growth hormone (hGH) expression construct containing the promoter region and 5' untranslated region (UTR) of EF1A linked to the hGH coding region (EF1A/hGH) was translationally repressed following rapamycin treatment in similar fashion to endogenous EF1A in human B lymphocytes. Mutation of two nucleotides in the TOP motif abolished the translational regulation. Gel mobility shift assays showed that both La protein from human B lymphocyte cytoplasmic extracts as well as purified recombinant La protein specifically bind to an in vitro-synthesized RNA containing the 5' UTR of EF1A mRNA. Moreover, extracts prepared from rapamycin-treated cells showed increased binding activity to the EF1A 5' UTR RNA, which correlates with TOP mRNA translational repression. In an in vitro translation system, recombinant La dramatically decreased the expression of EF1A/hGH construct mRNA, but not mRNAs lacking an intact TOP element. These results indicate that TOP mRNA translation may be modulated through La binding to the TOP element.

The La antigen associates with the human telomerase ribonucleoprotein and influences telomere length in vivo

La is an important component of ribonucleoprotein complexes and telomerase is a ribonucleoprotein that compensates for the shortening of the ends of linear DNA by adding telomeric repeats onto the ends of chromosomes by using an integral RNA as the template. We have identified a direct and specific interaction between La and the RNA component of human telomerase. Antibodies specific to La precipitate the human telomerase ribonucleoprotein complex derived from tumor cells, telomerase immortalized normal cells, and in vitro transformed cells. Overexpression of La in both experimentally immortalized human cells and prostate cancer cells results in gradual telomere shortening. Our results demonstrate that La can associate with telomerase and its expression level can influence telomere homeostasis in vivo.

Cognate T cell help is sufficient to trigger anti-nuclear autoantibodies in naive mice

The mechanisms involved in the initiation of anti-nuclear autoantibodies are unknown. In this study, we show that one factor allowing anti-nuclear autoantibodies to develop is the incomplete nature of immune tolerance to many of these proteins. Immune responses in mice toward the ubiquitous nuclear autoantigen La/SS-B are much weaker than responses to the xenoantigen, human La (hLa; 74% identical). However, in transgenic (Tg) mice expressing hLa, the Ab response to this neo-autoantigen was reduced to a level resembling the weak autoimmune response to mouse LA: Partial tolerance to endogenous La autoantigen was restricted to the T compartment because transfer of CD4(+) T cells specific for one or more hLa determinants into mice bearing the hLa transgene was sufficient to elicit production of anti-hLa autoantibodies. Notably, only hLa- specific T cells from non-Tg mice, and not T cells from hLa Tg mice, induced autoantibody production in hLa Tg mice. These findings confirm partial Th tolerance to endogenous La and indicate the existence in normal animals of autoreactive B cells continuously presenting La nuclear AG: Therefore, the B cell compartment is constitutively set to respond to particular nuclear autoantigens, implicating limiting Th responses as a critical checkpoint in the development of anti-nuclear autoantibodies in normal individuals.

Use of the NADH-quinone oxidoreductase (NDI1) gene of Saccharomyces cerevisiae as a possible cure for complex I defects in human cells

The Ndi1 enzyme of Saccharomyces cerevisiae is a single subunit rotenone-insensitive NADH-quinone oxidoreductase that is located on the matrix side of the inner mitochondrial membrane. We have shown previously that the NDI1 gene can be functionally expressed in Chinese hamster cells (Seo, B. B., Kitajima-Ihara, T., Chan, E. K., Scheffler, I. E., Matsuno-Yagi, A., and Yagi, T. (1998) Proc. Natl. Acad. Sci. U. S. A. 95, 9167-9171) and human embryonal kidney 293 (HEK 293) cells (Seo, B. B., Matsuno-Yagi, A., and Yagi, T. (1999) Biochim. Biochem. Acta 1412, 56-65) and that the Ndi1 protein is capable of compensating respiratory deficiencies caused by defects in the host NADH-quinone oxidoreductase (complex I). To extend the potential use of this enzyme to repair complex I deficiencies in vivo, we constructed a recombinant adeno-associated virus vector carrying the NDI1 gene (rAAV-NDI1). With rAAV-NDI1 as the gene delivery method, we were able to achieve high transduction efficiencies (nearly 100%) even in 143B cells that are difficult to transfect by lipofection or calcium phosphate precipitation methods. The NDI1 gene was successfully introduced into non-proliferating human cells using rAAV-NDI1. The expressed Ndi1 protein was shown to be functionally active just as seen for proliferating cells. Furthermore, when cells were cultured under the conditions where energy has to be provided by respiration, the NDI1-transduced cells were able to grow even in the presence of added complex I inhibitor such as rotenone and 1-methyl-4-phenylpyridinium ion. In contrast, control cells that did not receive the NDI1 gene failed to survive as anticipated. The Ndi1 protein has a great potential as a molecular remedy for complex I defects, and it is highly likely that the same strategy can be extended to correction of other mitochondrial disorders.

Functional characterization of the X-linked inhibitor of apoptosis (XIAP) internal ribosome entry site element: role of La autoantigen in XIAP translation

X-linked inhibitor of apoptosis protein (XIAP) is a key regulator of programmed cell death triggered by various apoptotic triggers. Translation of XIAP is controlled by a 162-nucleotide (nt) internal ribosome entry site (IRES) element located in the 5' untranslated region of XIAP mRNA. XIAP IRES mediates efficient translation of XIAP under physiological stress and enhances cell protection against serum deprivation and radiation-induced apoptosis. In the present report we describe the assembly of a sequence-specific RNA-protein complex consisting of at least four cytosolic proteins on the XIAP IRES element. We determine that the core binding sequence is approximately 28 nt long and is located 34 nt upstream of the initiation site. Moreover, we identify the La autoantigen as a protein that specifically binds XIAP IRES in vivo and in vitro. The biological relevance of this interaction is further demonstrated by the inhibition of XIAP IRES-mediated translation in the absence of functional La protein. The results suggest an important role for the La protein in the regulation of XIAP expression, possibly by facilitating ribosome recruitment to the XIAP IRES.

Human autoantibodies to a novel Golgi protein golgin-67: high similarity with golgin-95/gm 130 autoantigen

Autoantibodies to subcellular organelles have been described in patients with various systemic rheumatic diseases and our laboratories have been focused on studies of the Golgi complex as the autoimmune target. We have previously isolated and described four of the five known Golgi autoantigens reported to date. During the characterization of Golgi autoantigen golgin-95/gm130, another human cDNA that shared a significant degree of similarity in both nucleotide and amino acid sequences was identified. Analysis of cDNAs from different libraries suggested that this is a distinct gene encoding a protein of 67 kDa which has four regions with sequence identity to gm130, ranging between 42 and 60%. In this report, we describe the complete cDNA encoding a closely related Golgi protein provisionally named golgin-67. Among a group of 84 human anti-Golgi sera, five (6%) were shown to recognize golgin-67. Anti-golgin-67 human sera and affinity purified rabbit antibody to the recombinant protein gave predominant Golgi staining. Golgin-67 is thus the smallest member of a growing family of Golgi autoantigens rich in alpha-helical coiled-coil domain. The current hypothesis for the generation of autoimmune antibody to the Golgi complex is discussed.

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.

Modulation of oxidative phosphorylation of human kidney 293 cells by transfection with the internal rotenone-insensitive NADH-quinone oxidoreductase (NDI1) gene of Saccharomyces cerevisiae

In contrast to the mitochondrial proton-translocating NADH-quinone oxidoreductase (complex I), which consists of at least 43 different subunits, the internal rotenone-insensitive NADH-quinone oxidoreductase (Ndi1) of Saccharomyces cerevisiae is a single polypeptide enzyme. The NDI1 gene was stably transfected into the human embryonal kidney 293 (HEK 293) cells. The transfected NDI1 gene was then transcribed and translated in the HEK 293 cells to produce the functional enzyme. The immunochemical and immunofluorescence analyses indicated that the expressed Ndi1 polypeptide was located to the inner mitochondrial membranes. The expression of Ndi1 did not alter the content of existing complex I in the HEK 293 mitochondria, suggesting that the expressed Ndi1 enzyme does not displace the endogenous complex I. The NADH oxidase activity of the NDI1-transfected HEK 293 cells was not affected by rotenone but was inhibited by flavone. The ADP/O ratios coupled to NADH oxidation were lowered from 2.4 to 1.8 by NDI1-transfection while the ADP/O ratios coupled to succinate oxidation (1.6) were not changed. The NDI1-transfected HEK 293 cells were able to grow in media containing a complex I inhibitor such as rotenone and 1-methyl-4-phenylpyridinium ion. The potential usefulness of incorporating the Ndi1 protein into mitochondria of human cells is discussed.

Accessibility of SSA/Ro and SSB/La Antigens to Maternal Autoantibodies in Apoptotic Human Fetal Cardiac Myocytes

Access of intracellular Ags SSA/Ro and SSB/La to cognate maternal autoantibodies is unexplained despite their strong association with congenital heart block. To investigate the hypothesis that apoptosis facilitates surface accessibility of these Ags, human fetal cardiac myocytes from 16- to 22-wk abortuses were established in culture using a novel technique in which cells were isolated after perfusing the aorta with collagenase. Confirmation of cardiac myocytes included positive staining with antisarcomeric α-actinin and contractility induced by 1.8 mM calcium. Incubation with 0.5 μM staurosporine or 0.3 mM 2,3-dimethoxy-1,4-naphthoquinone induced the characteristic morphologic and biochemical changes of apoptosis. The cellular topology of Ro and La was evaluated with confocal microscopy and determined in nonapoptotic and apoptotic cardiocytes by indirect immunofluorescence. In permeabilized nonapoptotic cardiocytes, Ro and La were predominantly nuclear, and propidium iodide (PI) stained the nucleus. In early apoptotic cardiocytes, condensation of the PI- and Ro- or La-stained nucleus was observed, accompanied by Ro/La fluorescence around the cell periphery. In later stages of apoptosis, nuclear Ro and La staining became weaker, and PI demonstrated nuclear fragmentation. Ro/La-stained blebs emerged from the cell membrane, a finding observed in nonpermeabilized cells, supporting an Ab-Ag interaction at the cell surface. In summary, induction of apoptosis in cultured cardiocytes results in surface translocation of Ro/La and recognition by Abs. Although apoptotic cells are programmed to die and do not characteristically evoke inflammation, binding of maternal Abs and subsequent influx of leukocytes could damage surrounding healthy fetal cardiocytes.

Molecular remedy of complex I defects: rotenone-insensitive internal NADH-quinone oxidoreductase of Saccharomyces cerevisiae mitochondria restores the NADH oxidase activity of complex I-deficient mammalian cells

The NDI1 gene encoding rotenone-insensitive internal NADH-quinone oxidoreductase of Saccharomyces cerevisiae mitochondria was cotransfected into the complex I-deficient Chinese hamster CCL16-B2 cells. Stable NDI1-transfected cells were obtained by screening with antibiotic G418. The NDI1 gene was shown to be expressed in the transfected cells. The expressed Ndi1 enzyme was recognized to be localized to mitochondria by immunoblotting and confocal immunofluorescence microscopic analyses. Using digitonin-permeabilized cells, it was shown that the transfected cells, but not nontransfected control cells, exhibited the electron transfer activities with glutamate/malate as the respiratory substrate. The activities were inhibited by flavone, antimycin A, and KCN but not by rotenone. Added NADH did not serve as the substrate, suggesting that the expressed Ndi1 enzyme was located on the matrix side of the inner mitochondrial membranes. Furthermore, although nontransfected cells could not survive in a medium low in glucose (0.6 mM), which is a substrate of glycolysis, the NDI1-transfected cells were able to grow in the absence of added glucose. When glycolysis is slow, either at low glucose concentrations or in the presence of galactose, respiration is required for cells to survive. The mutant cells do not survive at low glucose or in galactose, but they can be rescued by Ndi1. These results indicated that the S. cerevisiae Ndi1 was expressed functionally in CCL16-B2 cells and catalyzed electron transfer from NADH in the matrix to ubiquinone-10 in the inner mitochondrial membranes. It is concluded that the NDI1 gene provides a potentially useful tool for gene therapy of mitochondrial diseases caused by complex I deficiency.

Diversity of antinuclear antibody responses in hepatocellular carcinoma

BACKGROUND/AIMS

The development of antinuclear antibodies (ANA) in malignancies has been described but its mechanism is still not understood. The aim of this study was to examine ANA specificities in hepatocellular carcinoma to further understand autoimmunity in cancer.

METHODS

Two hundred and four hepatocellular carcinoma patients were compared with 68 chronic hepatitis C, with 126 chronic hepatitis B and with 30 alcoholic liver cirrhosis patients, as well as with 87 healthy donors. Indirect immunofluorescence, immunoblotting, and immunoprecipitation were used to study ANA reactivities.

RESULTS

Hepatocellular carcinoma had a significantly higher frequency of ANA using HEp-2 cells as substrate (31%) than chronic hepatitis C (10%), chronic hepatitis B (9.5%), alcoholic liver cirrhosis (10%) or healthy donors (4.5%). A great diversity of ANA specificities was found in hepatocellular carcinoma. Three hepatoma sera had antibodies that co-localized with non-snRNP splicing factor SC35, suggesting that the antigenic targets might be involved in mRNA splicing. We identified antibodies to two known nuclear autoantigens: fibrillarin and p330d/CENP-F. These autoantigens are involved in the 5' processing of precursor ribosomal RNA transcripts and in mitotic functions, respectively.

CONCLUSIONS

Diversity was found in the autoantibody specificity, in contrast to the specific subsets of autoantibodies seen in several systemic rheumatic autoimmune diseases. Our data suggest that immune response in hepatocellular carcinoma targets important proteins involved in cellular biosynthetic or proliferative functions.

What happens inside lentivirus or influenza virus infected cells: insights into regulation of cellular and viral protein synthesis

Efficient manipulation of the regulatory mechanisms controlling host cell gene expression provides the means for productive infection by animal viruses. Upon infecting the host cell, viruses must: (i) bypass the cellular antiviral defense mechanisms to prevent the translational blocks imposed by the interferon pathway; and (ii) effectively "hijack" the host protein synthetic machinery into mass production of virion protein components. The multicomponent regulatory nature of cellular gene expression has provided the means of selecting for a diverse range of mechanisms utilized by animal viruses to ensure that replication efficiency is maintained throughout the virus life cycle. One important research component of the careful examination of gene regulation is those studies that focus on elucidating the mechanisms by which viruses control mRNA translation during host cell infection. Much of the work in our laboratory has focused on elucidating the strategies by which human immunodeficiency virus type 1 and influenza virus regulate protein synthesis during infection. Here we describe the ways in which these two distinctly different RNA viruses ensure the selective and efficient translation of their viral mRNAs in infected cells. These strategies include circumvention of the deleterious effects associated with activation of the interferon-induced protein kinase, PKR. Herein we describe our methodologies designed to elucidate the translational regulation in cells infected by these viruses. We conclude with a brief summary of new directions, utilizing these methods, taken toward understanding the translational control mechanisms imposed by these viral systems, and how our studies of virally infected cells have allowed us to identify growth-regulating components of normal, uninfected cells.

Production of anti-Ro/SS-A and anti-La/SS-B autoantibodies is closely coordinated in systemic lupus erythematosus and independent of anti-dsDNA production

Autoimmune diseases such as Sjögren's Syndrome and systemic lupus erythematosus (SLE) are characterized by serum autoantibodies against protein components of small cytoplasmic ribonucleoproteins (scRNPs). The origin and regulation of these anti-Ro/SS-A and anti-La/SS-B antibodies is not well understood. Regular co-occurrence of these two autoantibodies in humans together with murine studies on antibody responses against scRNPs after immunization suggest a role for scRNPs as common antigen. We sought additional evidence for this hypothesis in a longitudinal serological study of patients with SLE. Quantitative measurement of the antibody responses against Ro/SS-A and La/SS-B proteins and for comparison to dsDNA in 852 serum samples was performed. These samples were collected from nine patients during an average observation period of more than 10 years. A significant and strong correlation between the two anti-scRNP responses emerged during 90% of follow-up. In contrast, correlation of anti-scRNP with anti-dsDNA responses was remarkably absent in the same patients. Our results confirm the unique relationship between anti-Ro/SS-A and anti-La/ SS-B responses and could thus be interpreted as support for a model wherein induction and perpetuation of autoantibody production is dependent on scRNPs containing both proteins as antigen.

The HuD paraneoplastic protein shares immunogenic regions between PEM/PSN patients and several strains and species of experimental animals

Patients with small-cell carcinoma of the lung and paraneoplastic encephalomyelitis develop antibodies (anti-Hu) against HuD, a member of a family of neuronal specific RNA-binding proteins, which are also expressed by the tumor. In order to determine if the human HuD paraneoplastic antigen shares immunogenic regions between patients and several strains and species of animals, we immunized animals with HuD and several deletion constructs of this protein. All immunized animals developed high titers of anti-HuD antibodies, comparable to the antibody titers found in paraneoplastic patients. Using immunohistochemistry and Western blot analysis of human and mouse cerebral cortex, the pattern of reactivity of these antibodies could not be differentiated from the human paraneoplastic anti-Hu antibodies. None of the immunized animals developed neurologic symptoms. Western blot analysis of HuD deletion constructs demonstrated that the first and second RNA binding domains were the main immunodominant regions, and that the animal immune response was both strain and species dependent.

Two major autoantigen-antibody systems of the mitotic spindle apparatus

OBJECTIVE

To characterize human autoantigen-antibody systems related to the mitotic poles and spindles.

METHODS

Thirty-seven human sera with autoantibodies staining mitotic poles and spindles in indirect immunofluorescence (IIF) studies were further characterized by immunofluorescence on mitotic cells and by immunoblotting and immunoprecipitation. Clinical diagnoses meeting the American College of Rheumatology criteria were based on chart review and interview with the corresponding physicians.

RESULTS

Two autoantibody systems reactive with mitotic poles and spindles were defined. Type 1 nuclear mitotic apparatus (NuMA-1) antibodies were identified in the serum of 30 patients. Interphase cells showed a fine, speckled, nuclear staining, while mitotic cells had bright staining of the rim of the centrosomes and light staining of the spindles proximal to the centrosomes. In telophase, the staining shifted from the centrosomes to the reforming nuclei. On immunoblotting, anti-NuMA-1 sera reacted with a 210-kd protein. The reactivity of these sera was identified (with the aid of reference antibodies) as the previously described NuMA antigen-antibody system. Clinical information was available for only 17 of the 30 patients with anti-NuMA-1; of these, 17 (53%) had clinical and lip biopsy findings that met the criteria for Sjögren's syndrome. NuMA-2 antibodies were found in the sera of 7 patients. Interphase cells showed no nuclear or cytoplasmic staining, but mitotic cells had brightly stained poles and spindles. At anaphase/telophase, staining shifted to the midbody and the intercellular bridge. Anti-NuMA-2 sera immunoprecipitated a protein of 116 kd. This group of patients was more heterogeneous and had both systemic and organ-specific autoimmune diseases.

CONCLUSIONS

NuMA protein (here called NuMA-1) and a 116-kd protein (here called NuMA-2) are the major targets of the autoimmune response in the mitotic apparatus, since most of the selected sera (based on IIF staining of the mitotic spindles and poles) recognized 1 of these 2 antigens.

Features of autoantigens

The major cellular antigens recognized by autoantibodies in SLE and other systemic autoimmune diseases have been identified and characterized over the past 25 years. The pioneering studies of Eng Tan demonstrate the importance of autoantibodies as diagnostic markers. However, why certain autoantibodies, such as anti-Sm, are pathognomonic of SLE, while others are markers of other autoimmune disease subsets, remains unanswered. This central question continues to drive much current research into the pathogenesis of SLE. Features of the autoantigens recognized by autoantibodies may provide important clues to the causes of lupus. Most autoantigens in systemic autoimmunity are multicomponent nucleoprotein complexes. These particles are encountered by the immune system as units, resulting in the tandem production of autoantibodies recognizing several components of the same complex. However, the intermolecular-intrastructural spreading of autoimmunity is regulated by mechanisms that at present are defined poorly. Also unexplained is the observation that the antigenic determinants recognized by autoantibodies are restricted and frequently correspond to active sites or functional domains. Analysis of experimental models of autoimmunity suggests that altering the structure of autoantigens, due to abnormal protein-protein interactions, hapten binding, altered degradation, or other mechanisms, could help to explain both the restricted patterns of autoantibody spreading and the selective targeting of antigenic sites. This may be a worthwhile area for further investigation of the pathogenesis of systemic autoimmune diseases.

Translational control by influenza virus. Identification of cis-acting sequences and trans-acting factors which may regulate selective viral mRNA translation

We have shown that sequences contained within the viral mRNA 5'-untranslated region (UTR) played a critical role in directing selective influenza viral mRNA translation. We therefore attempted to identify transacting factors that may regulate viral mRNA translation through interactions with the 5'-UTR and at the same time map the precise sequences to which these factors bind. We can now demonstrate that multiple cellular proteins interact with influenza viral but not cellular 5'-UTRs using gel mobility shift and UV cross-linking analyses. Gel supershift studies revealed that the La autoantigen was one of the cellular proteins that interacted with the viral 5'-UTR. Utilizing mutants of the viral mRNA 5' UTR, we have determined that sequences within the very 5'-conserved region and nucleotides immediately 3' are necessary but not always sufficient for binding certain cellular proteins. Northwestern analysis showed the binding of a distinct subset of cellular proteins to the viral 5'-UTR, but also demonstrated interactions of the viral nonstructural protein NS1. Gel shift analysis with purified recombinant NS1 confirmed the binding of the viral protein to a specific region of the viral 5'-UTRs. A model describing the possible role of these cellular and viral RNA-binding proteins in regulating influenza virus mRNA translation will be discussed.

Anti-La monoclonal antibodies recognizing epitopes within the RNA-binding domain of the La protein show differential capacities to immunoprecipitate RNA-associated La protein

The La (SS-B) autoimmune antigen is an RNA-binding protein that is present in both the nucleus and cytoplasm of eukaryotic cells, where it is found associated with RNA polymerase III transcripts. We have investigated the capacity of anti-La monoclonal antibodies SW1, SW3, and SW5 to immunoprecipitate human La ribonucleoprotein particles. Distinct differences were observed for SW3 in comparison with SW1 and SW5. While SW1 and SW5 precipitated ribonucleoproteins containing pre-tRNA, pre-5S rRNA, hY RNAs, pre-U6 snRNA or the viral EBER1 and VA RNAs, SW3 precipitated only ribonucleoproteins containing VA RNAs or (the precursor of) 7-2 RNA. Mapping of the epitopes recognized by SW1, SW3, and SW5 revealed that all three monoclonal antibodies recognize an epitope within the domain of the protein formed by the ribonucleoprotein motif. Cross-competition studies suggested that the epitope recognized by SW1 and SW5 are identical but distinct from the epitope recognized by SW3. Further analyses of the recognition of La from other species by these monoclonal antibodies revealed that they all reacted with bovine La and were not reactive with La from rodents and Xenopus laevis. Replacement of a single amino acid in the human protein by its murine counterpart abolished recognition by SW1 and SW5, but had no effect on recognition by SW3. Taken together, our results indicate that SW1 and SW5 recognize the same epitope and that SW3 recognizes a distinct epitope, both of which are located in the RNA-binding domain of La, and that the accessibility of these epitopes is differentially influenced by the association of La with various RNA polymerase III transcripts.

Characterization of murine monoclonal antibodies against 60-kD Ro/SS-A and La/SS-B autoantigens

Small cytoplasmic ribonucleoproteins (scRNPs) are important autoantigens in patients with systemic lupus erythematosus and Sjögren's syndrome. MoAbs against these proteins were made by immunization of BALB/c mice with purified human recombinant 60-kD Ro/SS-A or 50-kD La/SS-B proteins. Five stable hybridoma cell lines were obtained, of which four secreted anti-Ro/SS-A antibodies (clones 1D8, 1D11, 2G10 and 6G8) and one produced anti-La/SS-B antibodies (clone 7F6). The MoAbs were further characterized using four different immunoassays: immunofluorescence, immunoblotting, RNA precipitation combined with Northern blotting, and recombinant protein precipitation. All four MoAbs against Ro/SS-A recognized the native protein and one of them (2G10) recognized also intact scRNP particles. Interestingly, hY3-RNA was reproducibly not efficiently precipitated by MoAb 2G10. Epitope mapping using deletion mutants of the 60-kD Ro/SS-A antigen showed that MoAb 1D8 recognized the C-terminal part of this protein, while 1D11 and 2G10 recognized distinct epitopes in the region between the RNP motif and the putative zinc finger domain. The epitopes recognized by these MoAbs are highly conserved among species, and the epitope recognized by MoAb 2G10 may be identical to an autoepitope recognized by sera of patients. This is the first report describing the isolation and characterization of MoAbs of the IgG class against the 60-kD Ro/SS-A and La/SS-B autoantigens obtained by immunization with purified human recombinant proteins. These MoAbs can be of great use in studying the cellular processes in which scRNPs are involved, and may help to determine why these scRNPs become autoantigenic in autoimmune diseases.

A perinucleolar compartment contains several RNA polymerase III transcripts as well as the polypyrimidine tract-binding protein, hnRNP I

We have investigated the subcellular organization of the four human Y RNAs. These RNAs, which are transcribed by RNA polymerase III, are usually found complexed with the Ro autoantigen, a 60-kD protein. We designed 2'-OMe oligoribonucleotides that were complementary to accessible single-stranded regions of Y RNAs within Ro RNPs and used them in fluorescence in situ hybridization. Although all four Y RNAs were primarily cytoplasmic, oligonucleotides directed against three of the RNAs hybridized to discrete structures near the nucleolar rim. We have termed these structures "perinucleolar compartments" (PNCs). Double labeling experiments with appropriate antisera revealed that PNCs are distinct from coiled bodies and fibrillar centers. Co-hybridization with a genomic DNA clone spanning the human Y1 and Y3 genes showed that PNCs are not stably associated with the transcription site for these Y RNAs. Although 5S rDNA was often located near the nucleolar periphery, PNCs are not associated with 5S gene loci. Two additional pol III transcripts, the RNA components of RNase P and RNase MRP, did colocalize within PNCs. Most interestingly, the polypyrimidine tract-binding protein hnRNP I/PTB was also concentrated in this compartment. Possible roles for this novel nuclear subdomain in macromolecular assembly and/or nucleocytoplasmic shuttling of these five pol III transcripts, along with hnRNP I/PTB, are discussed.

Autoepitope mapping of the centrosome autoantigen PCM-1 using scleroderma sera with anticentrosome autoantibodies

We previously characterized a scleroderma serum (serum 1) containing autoantibodies against centrosome autoantigens that have been named PCM-1, PCM-2 and PCM-3. In this study, we analyzed another scleroderma serum (serum 2) reactive with centrosome autoantigens of identical molecular weights to those recognized by serum 1. To further analyze the autoepitope domains in PCM-1 recognized by the autoantibodies present in scleroderma sera, cDNAs encoding different portions of the PCM-1 autoantigen were expressed in bacteria as fusion proteins. The immunoreactivity of the fusion proteins to the scleroderma sera was assayed by immunoblot analysis. Two regions containing autoepitope domains reactive with both sera were identified in the PCM-1 molecule. One is between amino acids 312-706 of the PCM-1 autoantigen, and the other is localized between amino acids 1,433-1,787, indicating that the immune response is oligoclonal. The results are important to clarify the mechanism of induction of anticentrosome autoantibodies. The potential diagnostic and prognostic significance of the autoantibodies for subgroups of scleroderma is discussed.

Autoantibodies to RNA polymerase II are common in systemic lupus erythematosus and overlap syndrome. Specific recognition of the phosphorylated (IIO) form by a subset of human sera

Autoantibodies to RNA polymerases (RNAP) I, II, and III are reported to be highly specific for the diagnosis of scleroderma (systemic sclerosis, SSc). In the present study, the specificity of autoantibodies to RNAP I and III for SSc was confirmed by immunoprecipitation of 35S-labeled proteins. However, we report here the previously unrecognized production of anti-RNAP II autoantibodies by 9-14% of patients with SLE and mixed connective tissue disease/overlap syndrome. 12 out of 32 anti-RNAP II positive sera (group 1) immunoprecipitated a diffuse 220-240-kD band identified as the largest subunit of RNAP II whereas the remaining 20 (group 2) immunoprecipitated preferentially the 240-kD phosphorylated (IIo) form of the large subunit. After pulse labeling, group 1 sera immunoprecipitated only the 220-kD (IIa) RNAP II subunit, whereas the diffuse IIa/IIo band plus the 145-kD second largest RNAP II subunit (IIc) were immunoprecipitated after several hours of cold chase, suggesting that these sera recognized primarily the largest subunit of RNAP II. Group 2 sera recognized the IIc subunit after pulse labeling, and immunoprecipitated the IIc and IIo, but not the IIa, subunits after cold chase. Although it has been suggested that autoantibodies to RNAP II are usually accompanied by anti-RNAP I/III in SSc, all but one of the anti-RNAP II positive sera from SLE or mixed connective tissue disease/overlap syndrome patients, as well as most of the SSc sera, were negative for anti-RNAP I/III. Moreover, in contrast to previous reports suggesting that anti-RNAP antibodies rarely coexist with other SSc subset marker antibodies, anti-RNAP II antibodies were often accompanied by anti-Ku, anti-nRNP, or anti-topoisomerase I autoantibodies in the present study. We conclude that autoantibodies to RNAP II are not a specific marker for SSc, whereas autoantibodies to RNAP I/III are associated primarily with SSc. In addition, we have identified two distinctive patterns of RNAP II antigen recognition by autoantibodies, one of them characterized by specific recognition of the transcriptionally active (phosphorylated) form of RNAP II. The clinical significance of these different patterns remains to be determined.

Immunocytochemical characterization of human NOR-90 (upstream binding factor) and associated antigens reactive with autoimmune sera. Two MR forms of NOR-90/hUBF autoantigens

The 90-kDa nucleolus organizer region autoantigen (NOR-90) was previously shown to be identical to the human upstream binding factor (hUBF) and composed of two Mr forms. In this study, thirteen human anti-NOR-90/hUBF autoimmune sera were used to further characterize NOR-90/hUBF and its associated autoantigens. Nucleolar and nucleoplasmic staining of interphase cells and NOR staining in mitosis were observed with all sera by immunofluorescence. All sera showed equal reactivity with both high and low Mr forms in Western blotting and immunoprecipitation, suggesting that the cellular content and distribution for both Mr forms were approximately equal. Using extracts of [35S]methionine- and [32P]orthophosphate-labeled cells, phosphorylated and nonphosphorylated NOR-90/hUBF were identified for both Mr forms and these two populations were recognized by human autoantibodies. In immunoprecipitation analyses, the nonphosphorylated population was readily extracted while the phosphorylated population was tightly bound. Clinical data were available for 8 patients in whom anti-NOR-90/hUBF autoantibodies were present. They had diverse diagnoses including SLE, rheumatoid arthritis and malignancies. Although only one patient was diagnosed as scleroderma, Raynaud's phenomenon was observed in 4 of the 8 patients. Interestingly, one NOR-90/hUBF serum was shown to contain additional antibodies to RNA polymerases I and II.

Is primary biliary cirrhosis an autoimmune disease?

This review summarizes the experimental and clinical support for an autoimmune origin of primary biliary cirrhosis (PBC). Direct proof is lacking, but indications in favour of an immunologic destructive mechanism include the demonstration of antibodies and T cell clones with specificity for mitochondrial autoantigens, and the lymphocytic infiltration/destruction of small bile ducts similar to that of graft-vs-host disease and rejection. There is a weak association with other autoimmune diseases, but no clear HLA linkage. Spontaneous animal models for PBC are lacking, and immunization of animals with purified autoantigen does not result in typical disease. Anti-mitochondrial antibodies (AMAs) of M2 type are diagnostic of PBC, and are mainly directed against a functional, restricted epitope on the E2 subunit of the pyruvate dehydrogenase complex (PDC). PDC-E2 shows several similarities to other classical autoantigens. The pathogenic role of AMA remains elusive. Recent studies have shown that AMAs detect an antigenic epitope expressed on the luminal surface of biliary epithelium in PBC liver. The initial triggering event might represent a microbial infection (molecular mimicry), or an aberrant surface expression of a true autoepitope.

Identification of a human-specific epitope in a conserved region of the La/SS-B autoantigen

Human anti-La/SS-B autoantibodies are known to react with highly conserved epitopes suggested to be functional or active sites on the La/SS-B polypeptide. This study was designed to determine whether the autoantibodies also react with poorly conserved regions of La/SS-B as predicted by an antigen-driven autoimmune response. Binding of human autoantibodies to purified human, mouse, and bovine recombinant fragments representing immunodominant regions of the La/SS-B polypeptide was compared using Western blotting and ELISA. A cross-reactive epitope was located in the highly conserved NH2-terminal region of La/SS-B. Significantly, human-specific epitopes were identified in both the conserved RNA-recognition motif and a poorly conserved COOH-terminal fragment, providing direct evidence for an autoantigen-driven response. The lack of autoantibody cross-reactivity with a conserved domain of mouse and bovine La/SS-B implies that a small number of residues in human autoepitopes may be critical for autoimmunogenicity.

An autoimmune disease with multiple molecular targets abrogated by the transgenic expression of a single autoantigen in the thymus

Many autoimmune diseases are characterized by autoantibody reactivities to multiple cellular antigens. Autoantigens are commonly defined as targets of the autoimmune B cell response, but the role, if any, of these autoantigens in T cell-mediated autoimmune diseases is generally unknown. Murine experimental autoimmune gastritis is a CD4+ T cell-mediated organ-specific autoimmune disease induced by neonatal thymectomy of BALB/c mice. The murine disease is similar to human autoimmune gastritis and pernicious anemia, and is characterized by parietal and chief cell loss, submucosal mononuclear cell infiltrates, and autoantibodies to the alpha and beta subunits of the gastric H/K ATPase. However, the specificity of T cells that cause the disease is not known. To examine the role of the H/K ATPase in this T cell-mediated disease, transgenic mice were generated that express the beta subunit of the H/K ATPase under the control of the major histocompatibility complex class II I-Ek alpha promoter. We show that transgenic expression of the gastric H/K ATPase beta subunit specifically prevents the onset of autoimmune gastritis after neonatal thymectomy. In addition, thymocyte transfer experiments suggest that tolerance of pathogenic autoreactive T cells is induced within the thymus of the transgenic mice. We conclude that the beta subunit of the gastric H/K ATPase is a major T cell target in autoimmune gastritis and that thymic expression of a single autoantigen can abrogate an autoimmune response to multiple autoantigens.

Molecular characterization of two human autoantigens: unique cDNAs encoding 95- and 160-kD proteins of a putative family in the Golgi complex

Serum autoantibodies from a patient with autoantibodies directed against the Golgi complex were used to screen clones from a HepG2 lambda Zap cDNA library. Three related clones, designated SY2, SY10, and SY11, encoding two distinct polypeptides were purified for further analysis. Antibodies affinity purified by adsorption to the lambda Zap-cloned recombinant proteins and antibodies from NZW rabbits immunized with purified recombinant proteins reproduced Golgi staining and bound two different proteins, 95 and 160 kD, from whole cell extracts. The SY11 protein was provisionally named golgin-95 and the SY2/SY10 protein was named golgin-160. The deduced amino acid sequence of the cDNA clone of SY2 and SY11 represented 58.7- and 70-kD proteins of 568 and 620 amino acids. The in vitro translation products of SY2 and SY11 cDNAs migrated in SDS-PAGE at 65 and 95 kD, respectively. The in vitro translated proteins were immunoprecipitated by human anti-Golgi serum or immune rabbit serum, but not by normal human serum or preimmune rabbit serum. Features of the cDNA suggested that SY11 was a full-length clone encoding golgin-95 but SY2 and SY10 together encoded a partial sequence of golgin-160. Analysis of the SY11 recombinant protein identified a leucine zipper spanning positions 419-455, a glutamic acid-rich tract spanning positions 322-333, and a proline-rich tract spanning positions 67-73. A search of the SwissProt data bank indicated sequence similarity of SY11 to human restin, the heavy chain of kinesin, and the heavy chain of myosin. SY2 shared sequence similarity with the heavy chain of myosin, the USO1 transport protein from yeast, and the 150-kD cytoplasmic dynein-associated polypeptide. Sequence analysis demonstrated that golgin-95 and golgin-160 share 43% sequence similarity and, therefore, may be functionally related proteins.

La autoantigen enhances and corrects aberrant translation of poliovirus RNA in reticulocyte lysate

Translation initiation on poliovirus RNA occurs by internal binding of ribosomes to a sequence within the 5' untranslated region. We have previously characterized a HeLa cell protein, p52, that binds to a fragment of the poliovirus 5' untranslated region (K. Meerovitch, J. Pelletier, and N. Sonenberg, Genes Dev. 3:1026-1034, 1989). Here we report the purification of the HeLa p52. Protein microsequencing identified p52 as La autoantigen. The La protein is a human antigen that is recognized by antibodies from patients with autoimmune disorders such as systemic lupus erythematosus and Sjögren's syndrome. We show that the La protein stimulates translation of poliovirus RNA, but not brome mosaic virus, tobacco mosaic virus, and alfalfa mosaic virus 4 RNA, translation in a reticulocyte lysate. In addition, La corrects aberrant translation of poliovirus RNA in a reticulocyte lysate. Subcellular immunolocalization showed that La protein is mainly nuclear, but after poliovirus infection, La is redistributed to the cytoplasm. Our results suggest that La protein is involved in poliovirus internal initiation of translation and might function through a similar mechanism in the translation of cellular mRNAs.