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

Anti-NOR90 antibodies and their clinical significance: a multicenter experience in southern Spain

INTRODUCTION

Anti-NOR90 antibodies were initially described in patients with autoimmune diseases based on staining of a nucleolar region known as the nucleolar organizer region (NOR). This study aims to explore the clinical aspects of anti-NOR90 antibodies in patients with systemic autoimmune diseases.

METHODS

Observational study of patients with positive anti-NOR90 antibodies using the EUROLINE Systemic Sclerosis profile (IgG) kit (Euroimmun, Germany). Data on demographics, comorbidities, autoimmune diseases, treatment, and clinical manifestations were collected.

RESULTS

Fifteen Patients with positive anti-NOR90 antibodies were included. Majority were female (86.7%), with median age of 54 years. Most common clinical manifestations were Raynaud's phenomenon, dryness, and interstitial lung disease (ILD). Some patients had hematological or solid organ neoplasms. EPID was prevalent, with one case showing rapid progression requiring aggressive treatment.

DISCUSSION AND CONCLUSION

This study highlights the association between anti-NOR90 antibodies and systemic autoimmune diseases, particularly SS and ES. EPID was a notable feature, suggesting its consideration in IPAF diagnosis for anti-NOR90 positive patients. Further multicenter studies are needed for better understanding and detection methods optimization.

Clinical significance of the anti-Nucleolar Organizer Region 90 antibodies (NOR90) in systemic sclerosis: Analysis of the European Scleroderma Trials and Research (EUSTAR) cohort and a systematic literature review

BACKGROUND

The anti-Nucleolar Organizer Region 90 antibodies (NOR90) are rare antinuclear antibodies (ANA) reported in systemic sclerosis (SSc). Especially due to low prevalence, the clinical relevance of NOR90 in SSc remains uncertain.

OBJECTIVES

To analyze the clinical associations of NOR90 in patients with SSc in a multicentric cohort.

METHODS

Post-hoc, cross-sectional study of prospectively collected data from the European Scleroderma Trials and Research (EUSTAR) database, with additional information on NOR90. Further, we performed a systematic literature search, using the terms "systemic sclerosis" and "NOR90" across three databases: Medline via PubMed, Scopus, and Thomson Reuters' Web of Science Core Collection, from inception to November 1st, 2023.

RESULTS

Overall, 1318 patients with SSc were included (mean age 58.3 ± 13.7 years, 81.3 % female), of whom 44 (3.3 %) were positive for NOR90. Of these, 32 were also positive for one of the SSc-criteria antibodies: 9/44 (20.5 %) for anti-topoisomerase I, 18/42 (42.9 %) for anti-centromere, and 5/40 (12.5 %) for anti-RNA polymerase III. NOR90-positive patients were more frequently female, had lower modified Rodnan skin score (mRSS), and lower prevalence of upper and lower gastrointestinal (GI) symptoms compared to NOR90-negative patients. In multivariable analysis, NOR90 remained significantly associated with lower mRSS and less frequent GI symptoms. The literature search identified 17 articles, including a total number of 87 NOR90-positive out of 3357 SSc patients, corresponding to an overall prevalence of 2.6 %.

CONCLUSION

To our best knowledge, this is the largest SSc cohort tested for NOR90 to date, confirming the NOR90 prevalence in SSc patients is around 3 %.

Clinical features of patients with connective tissue disease with anti-human upstream binding factor antibodies: A single-center retrospective study

Anti-human upstream-binding factor (anti-hUBF) antibodies have been reported predominantly in patients with connective tissue diseases (CTDs); these have also been reported in patients without CTDs such as hepatocellular carcinoma. Because of the low frequency of expression and few case reports, there is no consensus on the clinical significance of these antibodies. Thus, we aimed to examine the clinical features of patients with anti-hUBF antibodies and analyzed 1042 patients with clinically suspected CTDs. The presence of anti-hUBF antibodies was screened using immunoprecipitation assays. Of the 1042 patients, 19 (1.82%) tested positive for anti-hUBF antibodies; among them, 10 (56%) were diagnosed with undifferentiated CTD (UCTD), six with systemic sclerosis (SSc) and three with other diseases. Five of the 10 patients with UCTD were referred to our hospital with suspected SSc. None of the five patients fulfilled the 2013 American College of Rheumatology/European League Against Rheumatism classification criteria, but three scored seven points, a relatively high score. Six anti-hUBF-positive patients with SSc had a significantly lower modified Rodnan skin score (mRSS) than that of anti-hUBF-negative patients with SSc (2 [0-2] vs 7 [0-49], p < 0.01). Compared with anti-topoisomerase I-positive patients, anti-hUBF-positive patients had a significantly lower mRSS (2 [0-2] vs 13 [0-42], p < 0.01) and lower incidence of scleroderma renal crisis (0 of 6 vs 8 of 184, p < 0.01). Compared with anti-centromere-positive patients, anti-hUBF-positive patients had a higher incidence of interstitial lung disease (ILD), but the difference was not statistically significant (4 of 6 vs 19 of 239). In conclusion, anti-hUBF antibodies were predominantly detected in patients with CTDs and UCTD. In patients with CTDs, SSc exhibited a high ratio, displaying a lower mRSS and higher incidence of ILD. In patients with UCTD, careful follow-up is recommended as they may develop CTDs in the future.

Clinical Significance of Antinucleolar Antibodies: Biomarkers for Autoimmune Diseases, Malignancies, and others

Nucleolar staining is one of the standard patterns in immunofluorescence antinuclear antibodies (ANA), seen in 5-9% of ANA in various conditions. Antinucleolar antibodies (ANoA) are classified into 3 patterns in the International Consensus on ANA Patterns (ICAP) classification; AC-8 homogeneous pattern, AC-9 clumpy pattern, and AC-10 punctate pattern. Specificities known to show AC-8 include anti-Th/To, -PM-Scl, -nucleophosmin/B23, -nucleolin/C23, -No55, and others. AC-9 is seen by anti-fibrillarin/U3RNP and AC-10 by anti-RNA polymerase I and hUBF/NOR-90. ANoA has been classically known to be associated with scleroderma (SSc) and the characterization of nucleolar antigens identified several autoantigens recognized by SSc autoantibodies. The clinical association of anti-Th/To, PM-Scl, fibrillarin/U3RNP, and RNA polymerase I with SSc or SSc-overlap syndrome is well established, and commercial assays are developed. Anti-hUBF/NOR90, nucleophosmin/B23, and nucleolin/C23 are known for decades and reported in systemic autoimmune rheumatic diseases (SARDs), malignancies, graft versus host disease (GVHD), and others; however, their clinical significance remains to be established.

Clinical significance of anti-NOR90 antibodies in systemic sclerosis and idiopathic interstitial pneumonia

OBJECTIVE

Anti-NOR90 antibodies are usually found in patients with systemic sclerosis (SSc); however, their clinical relevance remains obscure. We developed an enzyme-linked immunosorbent assay (ELISA) for measuring them to investigate the clinical features of patients with anti-NOR90 antibodies.

METHODS

Serum samples from 1,252 patients with various conditions from Nagoya University Hospital and 244 patients with idiopathic interstitial pneumonia (IIP) from Tosei General Hospital were included. Anti-NOR90 antibodies were assayed by an ELISA using the recombinant protein produced by in vitro transcription/translation.

RESULTS

Five (0.4%) patients in the Nagoya University Hospital cohort had anti-NOR90 antibodies. One patient with diffuse cutaneous SSc, 3 with limited cutaneous SSc, and 1 with Raynaud's disease were positive for anti-NOR90 antibodies. Anti-NOR90 antibodies were found more frequently in patients with systemic scleroderma-spectrum disorders (SSDs) than without SSDs (5/316 vs. 0/936, P<0.00101) and were found more frequently in patients with SSc than without SSc (4/249 vs. 0/528, P<0.0104) in the systemic autoimmune rheumatic diseases cohort. Three of the 4 anti-NOR90-positive SSc patients had interstitial lung disease (ILD), and 2 of those 4 had cancer. Three (1.2%) patients in the Tosei General Hospital cohort had anti-NOR90 antibodies. All 3 of the anti-NOR90-positive IIP patients had gastrointestinal tract involvement, and 2 of those 3 had cancer or skin lesions observed in SSc.

CONCLUSIONS

Although anti-NOR90 antibodies are rarely found in clinics, our ELISA is useful for their detection. Further studies are needed to confirm the association of anti-NOR90 antibodies with ILD and cancer in SSc and IIP patients.

Antinuclear Antibodies in Systemic Sclerosis: an Update

Systemic sclerosis is an autoimmune disease characterized by fibrosis of skin and internal organs, vasculopathy, and dysregulation of immune system. A diagnostically important feature of immunological abnormalities in systemic sclerosis is the presence of circulating antinuclear antibodies, which may be detected in 90-95% of patients with either of the four main laboratory methods: immunofluorescence, enzyme-linked immunosorbent assay, immunodiffusion, and immunoblotting. There are several antinuclear antibodies specific for systemic sclerosis. These include antibodies against topoisomerase (anti-TOPO I), kinetochore proteins (ACA), RNA polymerase enzyme (anti-RNAP III), ribonuclear proteins (anti-U11/U12 RNP, anti-U1 RNP, anti-U3 RNP) and nucleolar antigens (anti-Th/To, anti-NOR 90, anti-Ku, antiRuvBL1/2, and anti-PM/Scl). Autoantibodies specific for systemic sclerosis have been linked to distinct clinical features. Therefore, detecting a particular antibody type is important in predicting a possible organ involvement and prognosis and may have an impact on monitoring and treatment.

Antinuclear Antibodies: Marker of Diagnosis and Evolution in Autoimmune Diseases

Antinuclear antibodies (ANAs) are autoantibodies that attack self-proteins within cell nucleus structures; their presence in serum may indicate an autoimmune disease. Also, positive ANA test results have been obtained in chronic infectious diseases, cancers, medication-related adverse events, and even healthy individuals. As a result, a correct interpretation of the presence of ANAs is needed.Identification of ANAs subtypes is an important part of clinical immunology. The presence of ANAs in patient blood specimens is detected using a cell-line substrate from human laryngeal carcinoma (HEp-2 cells). On this substrate, ANAs will bind specific antigens, which will lead to a suggestive fluorescent emission. The fluorescence patterns visualized under the fluorescence microscope can be correlated with certain subtypes of ANA and certain autoimmune diseases.Depending on the subtype of ANA present in the serum and the targeted antigen, several staining patterns are reported, namely, nuclear patterns, nucleolar patterns, cell cycle patterns, or cytoplasmatic patterns. Identification of a certain pattern can lead to diagnosis of a certain autoimmune disease.

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.

A re-evaluation of anti-NA-14 antibodies in patients with primary Sjögren's syndrome: Significant role of interferon-γ in the production of autoantibodies against NA-14

Novel autoantibodies against nuclear antigen of 14 kDa (NA-14)/Sjögren's syndrome nuclear antigen-1 (SSNA-1) are predominantly recognized in sera of patients with primary Sjögren's syndrome (pSS). However, the detailed characteristics of the anti-NA-14 antibody remain unknown. Here, we sought to clarify the characteristics of anti-SSNA-1/NA-14 antibodies and the mechanisms of autoantibody production using sera from patients with connective tissue diseases (including pSS), autoimmune sera reacting with standard autoantigens (SS-A/Ro and/or SS-B/La, ds DNA, Scl-70 and Jo-1), and normal healthy controls (NHCs). Anti-NA-14 antibodies were predominantly recognized in sera from patients with pSS and in autoimmune sera reacting with thSS-A/Ro and/or -SS-B/Lo. Indirect immunofluorescence analysis showed that NA-14 was strongly expressed in mitotic-phase cells. Patients with pSS having anti-NA-14 antibodies exhibited significant elevation of serum IP-10 and BAFF compared to that in patients with pSS without anti-NA-14 antibodies and NHCs. Thus, our data demonstrated that anti-NA-14 antibodies could be classified as novel autoantibodies reacting with mitosis-related autoantigens predominantly recognized in pSS. Moreover, interferon-γ played an important role in the production of anti-NA-14 autoantibodies as patients with pSS having anti-NA-14 antibodies exhibited increased serum levels of IP-10 and BAFF.

Pol I transcription and pre-rRNA processing are coordinated in a transcription-dependent manner in mammalian cells

Pre-rRNA synthesis and processing are key steps in ribosome biogenesis. Although recent evidence in yeast suggests that these two processes are coupled, the nature of their association is unclear. In this report, we analyze the coordination between rDNA transcription and pre-rRNA processing in mammalian cells. We found that pol I transcription factor UBF interacts with pre-rRNA processing factors as analyzed by immunoprecipitations, and the association depends on active rRNA synthesis. In addition, injections of plasmids containing the human rDNA promoter and varying lengths of 18S rDNA into HeLa nuclei show that pol I transcription machinery can be recruited to rDNA promoters regardless of the product that is transcribed, whereas subgroups of pre-rRNA processing factors are recruited to plasmids only when specific pre-rRNA fragments are produced. Our observations suggest a model for sequential recruitment of pol I transcription factors and pre-rRNA processing factors to elongating pre-rRNA on an as-needed basis rather than corecruitment to sites of active transcription.

Colocalization of coilin and nucleolar proteins in Cajal body-like structures of micronucleated PtK2 cells

Cajal bodies (CB) are ubiquitous nuclear structures involved in the biogenesis of small nuclear ribonucleoproteins and show narrow association with the nucleolus. To identify possible relationships between CB and the nucleolus, the localization of coilin, a marker of CB, and of a set of nucleolar proteins was investigated in cultured PtK2 cells undergoing micronucleation. Nocodazol-induced micronucleated cells were examined by double indirect immunofluorescence with antibodies against coilin, fibrillarin, NOR-90/hUBF, RNA polymerase I, PM/Scl, and To/Th. Cells were imaged on a BioRad 1024-UV confocal system attached to a Zeiss Axiovert 100 microscope. Since PtK2 cells possess only one nucleolus organizer region, micronucleated cells presented only one or two micronuclei containing nucleolus. By confocal microscopy we showed that in most micronuclei lacking a typical nucleolus a variable number of round structures were stained by antibodies against fibrillarin, NOR-90/hUBF protein, and coilin. These bodies were regarded as CB-like structures and were not stained by anti-PM/Scl and anti-To/Th antibodies. Anti-RNA polymerase I antibodies also reacted with CB-like structures in some micronuclei lacking nucleolus. The demonstration that a set of proteins involved in RNA/RNP biogenesis, namely coilin, fibrillarin, NOR-90/hUBF, and RNA polymerase I gather in CB-like structures present in nucleoli-devoid micronuclei may contribute to shed some light into the understanding of CB function.

A functional screen in human cells identifies UBF2 as an RNA polymerase II transcription factor that enhances the beta-catenin signaling pathway

beta-Catenin signaling plays an important role in the development of many organisms and has a key part in driving the malignant transformation of epithelial cells comprising a variety of cancers. beta-Catenin can activate gene expression through its association with transcription factors of the lymphoid enhancer factor 1 (LEF-1)/T-cell factor (TCF) family. We designed a screen in human cells to identify novel genes that activate a beta-catenin-LEF/TCF-responsive promoter and isolated the high-mobility group box transcription factor, UBF2. UBF1 and UBF2 are splice variants of a common precursor RNA. Although UBF1 has been shown to activate RNA polymerase I-regulated genes, the function of UBF2 has remained obscure. Here, we show for the first time that both UBF1 and UBF2 activate RNA polymerase II-regulated promoters. UBF2 associates with LEF-1, as shown by coimmunoprecipitation experiments, and potentiates transcriptional activation stimulated by LEF-1/beta-catenin from a synthetic promoter with multimerized LEF/TCF binding sites and a natural cyclin D1 promoter with consensus LEF/TCF binding sites. Downregulation of endogenous UBF expression using an RNA interference approach reduces transcriptional activation of a beta-catenin-LEF/TCF-responsive promoter by means of overexpressed beta-catenin, further implicating UBF as a transcriptional enhancer of the beta-catenin pathway.

[Immunological diagnosis of scleroderma]

Systemic sclerosis is characterized by a fibrosis and a microvascular injury. These vascular lesions can affect internal organs causing severe visceral damages. The pathogenesis of this disease is complex but some immunological disorders with a production of antinuclear auto-antibodies can be useful to the clinicians, especially for an early diagnosis and to distinguish the scleroderma/myositis overlap syndromes. This review presents the target antigens and the methods of detection of the different antinuclear auto-antibodies. Sensitivity, specificity and clinical association between the antinuclear auto-antibodies and the different subclasses of scleroderma are also presented in detail.

Cancer and autoimmunity: autoimmune and rheumatic features in patients with malignancies

OBJECTIVES

To review the autoimmune and rheumatic manifestations of patients with malignancy.

METHODS

A Medline search of all published papers using keywords related to malignancies, autoimmunity, rheumatic diseases, and paraneoplastic syndromes.

RESULTS

Patients with malignant diseases may develop autoimmune phenomena and rheumatic diseases as a result of (a) generation of autoantibodies against various autoantigens, including oncoproteins (P185, 1-myc, c-myc, c-myb), tumour suppression genes (P53), proliferation associated antigens (cyclin A, B1, D1, E; CENP-F; CDK, U3-RNP), onconeural antigens (Hu, Yo, Ri, Tr), cancer/testis antigens (MAGE, GAGE, BAGE, SSX, ESO, SCP, CT7), and rheumatic disease associated antigens (RNP, Sm). The clinical significance of the various autoantibodies is not clear. Anti-oncoprotein and anti-tumour suppression gene antigens are detected before the diagnosis of the cancer or in the early stages of the malignant disease, suggesting a potential diagnostic or prognostic role. Anti-onconeural antibodies are pathogenic and are associated with specific clinical neurological syndromes (anti-Hu syndrome and others). (b) Paraneoplastic syndromes, a wide range of clinical syndromes, including classic autoimmune rheumatic diseases that develop among patients with cancer. (c) Rheumatism after chemotherapy, a clinical entity characterised by the development of musculoskeletal symptoms after combination chemotherapy for malignancy.

CONCLUSION

Autoimmune and rheumatic features are not rare among patients with malignancies. They are the result of various diverse mechanisms and occasionally they may be associated with serious clinical entities.

The mitotically phosphorylated form of the transcription termination factor TTF-1 is associated with the repressed rDNA transcription machinery

The transcription termination factor TTF-1 exerts two functions in ribosomal gene (rDNA) transcription: facilitating initiation and mediating termination of transcription. Using HeLa cells, we show that TTF-1 protein is colocalized with the active transcription machinery in the nucleolus and also with the inactive machinery present in certain mitotic nucleolar organizer regions (NORs) when rDNA transcription is repressed. We also show that TTF-1 is specifically phosphorylated during mitosis in a manner dependent on the cdc2-cyclin B kinase pathway and on an okadaic acid-sensitive phosphatase. Interestingly, the mitotically phosphorylated form of TTF-1 appearing at the G(2)/M transition phase was more easily solubilized than was the interphase form. This indicates that the chromatin-binding affinity of TTF-1 appears to be different in mitotic chromosomes compared to the interphase nucleolus. Correlated with this, the other DNA-binding factor, UBF, which interferes with chromatin conformation in the rDNA promoter, was more strongly bound to rDNA during mitosis than at interphase. The reorganization of the mitotic rDNA promoter might be induced by phosphorylation of certain components of the rDNA transcription machinery and participate in silencing of rDNA during mitosis.

Expression of the transcriptional repressor protein Kid-1 leads to the disintegration of the nucleolus

The rat Kid-1 gene codes for a 66-kDa protein with KRAB domains at the NH2 terminus and two Cys2His2-zinc finger clusters of four and nine zinc fingers at the COOH terminus. It was the first KRAB-zinc finger protein for which a transcriptional repressor activity was demonstrated. Subsequently, the KRAB-A domain was identified as a widespread transcriptional repressor motif. We now present a biochemical and functional analysis of the Kid-1 protein in transfected cells. The full-length Kid-1 protein is targeted to the nucleolus and adheres tightly to as yet undefined nucleolar structures, leading eventually to the disintegration of the nucleolus. The tight adherence and nucleolar distribution can be attributed to the larger zinc finger cluster, whereas the KRAB-A domain is responsible for the nucleolar fragmentation. Upon disintegration of the nucleolus, the nucleolar transcription factor upstream binding factor disappears from the nucleolar fragments. In the absence of Kid-1, the KRIP-1 protein, which represents the natural interacting partner of zinc finger proteins with a KRAB-A domain, is homogeneously distributed in the nucleus, whereas coexpression of Kid-1 leads to a shift of KRIP-1 into the nucleolus. Nucleolar run-ons demonstrate that rDNA transcription is shut off in the nucleolar fragments. Our data demonstrate the functional diversity of the KRAB and zinc finger domains of Kid-1 and provide new functional insights into the regulation of the nucleolar structure.

Autoantibodies to components of the mitotic apparatus

Autoantibodies directed to a variety of cellular antigens and organelles are a feature of autoimmune diseases. They have proven useful in a clinical setting to establish diagnosis, estimate prognosis, follow disease progression, alter therapy, and initiate new investigations. Cellular and molecular biologists have used autoantibodies as probes to identify molecules involved in key cellular processes. One of the most interesting sets of autoantibodies are those that target antigens within the mitotic apparatus (MA). The MA includes chromosomes, spindle microtubules and centrosomes. The identification, localization, function, and clinical relevance of MA autoantigens is the focus of this review.

The transcriptional activator Sp1, a novel autoantigen

OBJECTIVE

To identify one nuclear autoantigenic protein within a complex of DNA binding proteins that bind to GC-rich sequences in Epstein-Barr virus and cellular DNA, and to describe the clinical characteristics of patients whose sera contained autoantibodies to this novel autoantigen.

METHODS

Antibodies to autoantigen Sp1 were initially measured by an electrophoretic mobility shift assay to detect DNA binding proteins. Nuclear extracts and purified Sp1 protein were used in these assays. Recognition of the autoantigen by autoimmune sera was confirmed by immunoprecipitation and immunoblotting.

RESULTS

The autoantigen was identified as Sp1. Anti-Sp1 was detected in sera from 8 (3%) of 230 patients. These sera contained antinuclear antibodies, but lacked antibodies to double-stranded DNA or to several extractable nuclear antigens. The patients whose sera contained antibodies to Sp1 were white women with fatigue, arthritis, Raynaud's phenomenon, malar rash, and photosensitivity.

CONCLUSION

Sp1 is the first described example of an RNA polymerase II transcription activator as an autoantigen. The presence of Sp1 autoantibodies is associated with undifferentiated connective tissue disease.

Immunopathogenesis of systemic sclerosis

The information outlined above can be used to generate a model of the immunopathogenesis of SSc (Fig. 3). This model includes a susceptible host, with age greater than 25 and female gender being risk factors. The model also includes exposure to exogenous agents, which could be different in different individuals and may include inhaled or ingested chemicals or infectious agents. An early event is T-cell activation, with infiltration in the skin and internal organs. Activation of the T cells is a selective process that appears to be influenced by antigen in SSc patients. The importance of a particular T-cell subpopulation may depend upon the organ involved and the stage of the disease. CD4+ T cells predominate in the skin. In contrast, CD8+ T cells are increased in the lungs of patients with alveolitis, where they are oligoclonal, showing evidence of antigen-driven selection. V delta 1+ gamma/delta T cells are increased in both the blood and lungs of SSc patients and also show evidence of selection by antigen. B cells are activated early, with polyclonal activation leading to hypergammaglobulinemia. SSc-specific autoantibodies target DNA topoisomerase I, centromeric proteins, and RNA polymerases I and III. Characteristics of autoantibodies in SSc suggest that the target antigens are presented to the immune system as native molecules or even part of a multiunit complex. There is some homology between viruses and autoantibody targets in SSc, which suggests that molecular mimicry may play a role in initiating the antibody response. Many nonspecific inflammatory cells infiltrate the tissues and show evidence of activation. These include macrophages and monocytes, mast cells, eosinophils, basophils, and natural killer cells. Soluble mediators made by these T cells, B cells, and nonspecific inflammatory cells can activate and damage fibroblasts, endothelial cells, and other vascular cells. The relative importance of the various candidate cytokines, the temporal sequence of their production, and their cellular sources remain largely to be defined. There may be some contribution of direct T-cell cytotoxicity or antibody-dependent cellular cytoxicity to the tissue damage that occurs.

Detection of autoantibodies to nucleolar transcription factor NOR 90/hUBF in sera of patients with rheumatic diseases, by recombinant autoantigen-based assays

OBJECTIVE

We attempted to clarify the clinical characteristics of Japanese patients with autoantibodies to nucleolar transcription factor NOR 90/hUBF (anti-NOR 90) and to analyze the autoantigenic epitopes recognized by anti-NOR 90.

METHODS

Ninety-one patient sera containing anti-nucleolar antibodies (ANoA) by indirect immunofluorescence were collected. Immunoblottings were performed using recombinant fusion proteins expressed from several cloned complementary DNA (cDNA) encoding the NOR 90/hUBF autoantigen.

RESULTS

Anti-NOR 90 were detected in sera from 9 (9.9%) of 91 patients with ANoA. Seven of these patients were diagnosed as having Sjögren's syndrome, 4 had concomitant rheumatoid arthritis, 1 had concomitant systemic sclerosis (SSc), and 2 had SSc alone. All 9 sera were reactive with more than 2 recombinant fusion proteins from cDNA encoding separate regions on the hUBF polypeptide.

CONCLUSION

The results suggest that while anti-NOR 90 antibodies are rare, they are associated with Sjögren's syndrome in Japanese patients, and that autoimmunity is targeted toward at least 2 separate regions (amino acids 89-310 and 310-633) of the hUBF polypeptide.

The rDNA transcription machinery is assembled during mitosis in active NORs and absent in inactive NORs

In cycling cells, the rDNAs are expressed from telophase to the end of G2 phase. The early resumption of rDNA transcription at telophase raises the question of the fate of the rDNA transcription machinery during mitosis. At the beginning of mitosis, rDNA transcription is arrested, and the rDNAs are clustered in specific chromosomal sites, the nucleolar organizer regions (NOR). In human cells, we demonstrate that the rDNA transcription machinery, as defined in vitro, is colocalized in some NORs and absent from others whatever the mitotic phase: RNA polymerase I and the RNA polymerase I transcription factors, upstream binding factor and promoter selectivity factor (as verified for TATA-binding protein and TATA-binding protein-associated factor for RNA polymerase I [110]), were colocalized in the same NORs. The RNA polymerase I complex was localized using two different antibodies recognizing the two largest subunits or only the third largest subunit, respectively. These two antibodies immunoprecipitated the RNA polymerase I complex in interphase cells as well as in mitotic cells. These results clearly indicated that the RNA polymerase I complex remained assembled during mitosis. In addition, RNA polymerase I and the transcription factors varied in the same proportions in the positive NORs, suggesting stoichiometric association of these components. The fact that the rDNA transcription machinery is not equally distributed among NORs most likely reflects the implication of the different NORs during the subsequent interphase. Indeed, we demonstrate that only positive NORs exhibit transcription activity at telophase and that the level of transcription activity is related to the amount of rDNA transcription machinery present in the NOR. We propose that assembly of rDNA transcription machinery preceding mitosis determines expression of the rDNAs at the beginning of the next cell cycle. Consequently, the association of rDNAs with the rDNA transcription machinery defines the "active" NORs and the level of activity at the transition telophase/interphase.

Identification of human autoantibodies to transcription factor IIB

We have characterized the ability of various human autoimmune sera to react with RNA polymerase II transcription factors. One serum, which strongly inhibited transcription in a cell-free system, was shown to contain antibodies directed against human TFIIB. The serum did not show reactivity against the other general transcription factors, including human TBP, TFIIE and TFIIF. The inhibition of transcription was directly attributable to depletion of TFIIB activity, as demonstrated by reconstitution of activity with recombinant TFIIB. It has long been recognized that components of the RNA processing machinery are major human autoantigens. The present results show that at least one general transcription factor required for messenger RNA synthesis is an autoantigen as well.

Autoantibodies in the diagnosis of systemic rheumatic diseases

Distinct profiles of autoantibodies directed to intracellular antigens can be detected in the systemic connective tissue diseases. They aid in establishing the correct diagnosis and are included in many sets of diagnostic criteria, such as the ones developed for systemic lupus erythematosus (anti-Smith antigen and anti-double-strand DNA antibodies), mixed connective tissue disease (anti-U1-nuclear ribonucleoprotein antibodies), and Sjögren's syndrome (SS) (anti-SS-A/Ro and anti-SS-B/La antibodies). They are useful prognostic markers in some situations and facilitate clinical and treatment follow-up. Autoantibodies have also been used as probes to gain insights into cell biology, helping to isolate and purify intracellular proteins involved in key cellular functions. We give detailed information on two of the most useful techniques for the detection of autoantibodies in the clinical and research laboratory settings, indirect immunofluorescence and immunoblotting. We also discuss several of the antigen-autoantibody systems found in systemic lupus erythematosus (Smith antigen, U1-nuclear ribonucleoprotein, SS-A/Ro, SS-B/La, proliferating cell nuclear antigen ribosomal ribonucleoprotein, double-strand DNA, histones, antiphospholipids, Ku, Ki/SL), systemic sclerosis (centromere, topo I, RNA polymerases, fibrillarin, polymyositis-Scl, Th/To), polymyositis/dermatomyositis (transferRNA synthetases, signal recognition particle, and others), and SS (SS-A/Ro, SS-B/La, nucleolar organizing region-90, p80-coilin), addressing their clinical significance, common detection methods, immunogenetic associations, and the molecular and cellular biology of the cognate antigens.