Autoantigens of the nuclear pore complex

Genetic Associations and Differential mRNA Expression Levels of Host Genes Suggest a Viral Trigger for Endemic Pemphigus Foliaceus

The long search for the environmental trigger of the endemic pemphigus foliaceus (EPF, fogo selvagem) has not yet resulted in any tangible findings. Here, we searched for genetic associations and the differential expression of host genes involved in early viral infections and innate antiviral defense. Genetic variants could alter the structure, expression sites, or levels of the gene products, impacting their functions. By analyzing 3063 variants of 166 candidate genes in 227 EPF patients and 194 controls, we found 12 variants within 11 genes associated with differential susceptibility (p < 0.005) to EPF. The products of genes TRIM5, TPCN2, EIF4E, EIF4E3, NUP37, NUP50, NUP88, TPR, USP15, IRF8, and JAK1 are involved in different mechanisms of viral control, for example, the regulation of viral entry into the host cell or recognition of viral nucleic acids and proteins. Only two of nine variants were also associated in an independent German cohort of sporadic PF (75 patients, 150 controls), aligning with our hypothesis that antiviral host genes play a major role in EPF due to a specific virus−human interaction in the endemic region. Moreover, CCL5, P4HB, and APOBEC3G mRNA levels were increased (p < 0.001) in CD4+ T lymphocytes of EPF patients. Because there is limited or no evidence that these genes are involved in autoimmunity, their crucial role in antiviral responses and the associations that we observed support the hypothesis of a viral trigger for EPF, presumably a still unnoticed flavivirus. This work opens new frontiers in searching for the trigger of EPF, with the potential to advance translational research that aims for disease prevention and treatment.

An Autoantigen Atlas From Human Lung HFL1 Cells Offers Clues to Neurological and Diverse Autoimmune Manifestations of COVID-19

COVID-19 is accompanied by a myriad of both transient and long-lasting autoimmune responses. Dermatan sulfate (DS), a glycosaminoglycan crucial for wound healing, has unique affinity for autoantigens (autoAgs) from apoptotic cells. DS-autoAg complexes are capable of stimulating autoreactive B cells and autoantibody production. We used DS-affinity proteomics to define the autoantigen-ome of lung fibroblasts and bioinformatics analyses to study the relationship between autoantigenic proteins and COVID-induced alterations. Using DS-affinity, we identified an autoantigen-ome of 408 proteins from human HFL1 cells, at least 231 of which are known autoAgs. Comparing with available COVID data, 352 proteins of the autoantigen-ome have thus far been found to be altered at protein or RNA levels in SARS-CoV-2 infection, 210 of which are known autoAgs. The COVID-altered proteins are significantly associated with RNA metabolism, translation, vesicles and vesicle transport, cell death, supramolecular fibrils, cytoskeleton, extracellular matrix, and interleukin signaling. They offer clues to neurological problems, fibrosis, smooth muscle dysfunction, and thrombosis. In particular, 150 altered proteins are related to the nervous system, including axon, myelin sheath, neuron projection, neuronal cell body, and olfactory bulb. An association with the melanosome is also identified. The findings from our study illustrate a connection between COVID infection and autoimmunity. The vast number of COVID-altered proteins with high intrinsic propensity to become autoAgs offers an explanation for the diverse autoimmune complications in COVID patients. The variety of autoAgs related to mRNA metabolism, translation, and vesicles suggests a need for long-term monitoring of autoimmunity in COVID. The COVID autoantigen atlas we are establishing provides a detailed molecular map for further investigation of autoimmune sequelae of the pandemic, such as “long COVID” syndrome.

A Master Autoantigen-ome Links Alternative Splicing, Female Predilection, and COVID-19 to Autoimmune Diseases

Chronic and debilitating autoimmune sequelae pose a grave concern for the post-COVID-19 pandemic era. Based on our discovery that the glycosaminoglycan dermatan sulfate (DS) displays peculiar affinity to apoptotic cells and autoantigens (autoAgs) and that DS-autoAg complexes cooperatively stimulate autoreactive B1 cell responses, we compiled a database of 751 candidate autoAgs from six human cell types. At least 657 of these have been found to be affected by SARS-CoV-2 infection based on currently available multi-omic COVID data, and at least 400 are confirmed targets of autoantibodies in a wide array of autoimmune diseases and cancer. The autoantigen-ome is significantly associated with various processes in viral infections, such as translation, protein processing, and vesicle transport. Interestingly, the coding genes of autoAgs predominantly contain multiple exons with many possible alternative splicing variants, short transcripts, and short UTR lengths. These observations and the finding that numerous autoAgs involved in RNA-splicing showed altered expression in viral infections suggest that viruses exploit alternative splicing to reprogram host cell machinery to ensure viral replication and survival. While each cell type gives rise to a unique pool of autoAgs, 39 common autoAgs associated with cell stress and apoptosis were identified from all six cell types, with several being known markers of systemic autoimmune diseases. In particular, the common autoAg UBA1 that catalyzes the first step in ubiquitination is encoded by an X-chromosome escape gene. Given its essential function in apoptotic cell clearance and that X-inactivation escape tends to increase with aging, UBA1 dysfunction can therefore predispose aging women to autoimmune disorders. In summary, we propose a model of how viral infections lead to extensive molecular alterations and host cell death, autoimmune responses facilitated by autoAg-DS complexes, and ultimately autoimmune diseases. Overall, this master autoantigen-ome provides a molecular guide for investigating the myriad of autoimmune sequalae to COVID-19 and clues to the rare but reported adverse effects of the currently available COVID vaccines.

Trigeminal neuralgia in systemic sclerosis

OBJECTIVES

Although trigeminal neuralgia (TN) has been associated with systemic sclerosis (SSc), there is a paucity of evidence and pathophysiological processes remain unknown. We undertook a nested case-control study to identify associations between TN and SSc in a large multi-centered cohort and identify possible pathophysiological links.

METHODS

Data were derived from a longitudinal cohort of 1652 SSc subjects. Cases with a physician-reported diagnosis of TN were identified at baseline visit (prevalent) and during follow-up (incident). Each case was matched on study visit to four SSc patients without TN. Sociodemographic, clinical and serological characteristics of cases and controls were compared.

RESULTS

At enrolment, 43/1652 (2.6%) subjects had a history of TN. During follow-up, an additional 36 subjects developed TN over 6193 person-years of observation (incidence rate 5.8 per 1000 person-years). Cases were identified and matched to 172 and 144 controls, respectively. Compared to controls, prevalent cases had more inflammatory myositis (24.4% versus 5.2%, p<0.001) and inflammatory arthritis (46.5% versus 30.2%, p = 0.043). Incident cases also had more inflammatory myositis (19.4% versus. 6.3%, p = 0.033) and inflammatory arthritis (50.0% versus. 16.2%, p<0.001) compared to controls. There was a trend towards more interstitial lung disease in prevalent (32.6% versus 23.8%, p = 0.241) and incident (55.6% versus 40.6%, p = 0.105) cases compared to controls.

CONCLUSION

This study provides novel evidence for a clinical association linking TN, inflammatory myositis, inflammatory arthritis and possibly interstitial lung disease. In addition to ischemia, we propose that TN in SSc could also be a consequence of inflammatory and possibly fibrotic processes.

Bench to bedside review of myositis autoantibodies

Idiopathic inflammatory myopathies represent a heterogeneous group of autoimmune diseases with systemic involvement. Even though numerous specific autoantibodies have been recognized, they have not been included, with the only exception of anti-Jo-1, into the 2017 Classification Criteria, thus perpetuating a clinical-serologic gap. The lack of homogeneous grouping based on the antibody profile deeply impacts the diagnostic approach, therapeutic choices and prognostic stratification of these patients. This review is intended to highlight the comprehensive scenario regarding myositis-related autoantibodies, from the molecular characterization and biological significance to target antigens, from the detection tools, with a special focus on immunofluorescence patterns on HEp-2 cells, to their relative prevalence and ethnic diversity, from the clinical presentation to prognosis. If, on the one hand, a notable body of literature is present, on the other data are fragmented, retrospectively based and collected from small case series, so that they do not sufficiently support the decision-making process (i.e. therapeutic approach) into the clinics.

Nucleoporin genes in human diseases

Nuclear pore complexes (NPCs) are large channels spanning the nuclear envelope that mediate nucleocytoplasmic transport. They are composed of multiple copies of ~30 proteins termed nucleoporins (NUPs). Alterations in NUP genes are linked to several human neoplastic and non-neoplastic diseases. This review focuses on NUPs, their genes, localization, function in the NPC and involvement in human diseases.

An autoimmune myositis-overlap syndrome associated with autoantibodies to nuclear pore complexes: description and long-term follow-up of the anti-Nup syndrome

Autoimmune myositis encompasses various myositis-overlap syndromes, each being identified by the presence of serum marker autoantibodies. We describe a novel myositis-overlap syndrome in 4 patients characterized by the presence of a unique immunologic marker, autoantibodies to nuclear pore complexes. The clinical phenotype was characterized by prominent myositis in association with erosive, anti-CCP, and rheumatoid factor-positive arthritis, trigeminal neuralgia, mild interstitial lung disease, Raynaud phenomenon, and weight loss. The myositis was typically chronic, relapsing, and refractory to corticosteroids alone, but remitted with the addition of a second immunomodulating drug. There was no clinical or laboratory evidence for liver disease. The prognosis was good with 100% long-term survival (mean follow-up 19.5 yr).By indirect immunofluorescence on HEp-2 cells, sera from all 4 patients displayed a high titer of antinuclear autoantibodies (ANA) with a distinct punctate peripheral (rim) fluorescent pattern of the nuclear envelope characteristic of nuclear pore complexes. Reactivity with nuclear pore complexes was confirmed by immunoelectron microscopy. In a cohort of 100 French Canadian patients with autoimmune myositis, the nuclear pore complex fluorescent ANA pattern was restricted to these 4 patients (4%). It was not observed in sera from 393 adult patients with systemic sclerosis (n = 112), mixed connective tissue disease (n = 35), systemic lupus (n = 94), rheumatoid arthritis (n = 45), or other rheumatic diseases (n = 107), nor was it observed in 62 normal adults.Autoantibodies to nuclear pore complexes were predominantly of IgG isotype. No other IgG autoantibody markers for defined connective tissue diseases or overlap syndromes were present, indicating a selective and highly focused immune response. In 3 patients, anti-nuclear pore complex autoantibody titers varied in parallel with myositis activity, suggesting a pathogenic link to pathophysiology. The nuclear pore complex proteins, that is, nucleoporins (nup), recognized by these sera were heterogeneous and included Nup358/RanBP2 (n = 2 patients), Nup90 (n = 1), Nup62 (n = 1), and gp210 (n = 1). Taken together the data suggest that nup autoantigens themselves drive the anti-nup autoimmune response. Immunogenetically, the 4 patients shared the DQA1*0501 allele associated with an increased risk for autoimmune myositis.In conclusion, we report an apparent novel subset of autoimmune myositis in our population of French Canadian patients with connective tissue diseases. This syndrome is recognized by the presence of a unique immunologic marker, autoantibodies to nuclear pore complexes that react with nups, consistent with an "anti-nup syndrome."

Microbead-based technologies in diagnostic autoantibody detection

BACKGROUND

There is a rapid proliferation of new technologies to identify a spectrum of autoantibodies in medical conditions that range from organ-specific autoimmune diseases to systemic rheumatic diseases. Although many laboratories have adopted high-throughput diagnostic platforms such as enzyme linked immunoassays (ELISA), other technologies such as microbead-based assays are emerging as an alternative diagnostic platform.

OBJECTIVE

To understand the performance and importance of bead based immunoassays in clinical diagnostics and therapeutics.

METHOD

Current literature was reviewed using the PubMed search engine combining keywords of immunoassay and Luminex, as well as a personal literature database. Included in the evaluation and commentary are bead-based assays such as addressable laser bead immunoassays and related magnetic bead assays.

CONCLUSIONS

Comparison with other conventional technologies has indicated that laser microbead immunoassays are reliable, accurate, cost-effective, highly sensitive and have rapid turn around time for results. While there are advantages to this diagnostic platform, there are challenges that must be addressed before wider acceptance or long-term use of this technology platform in the routine clinical diagnostic laboratory.

The role of Nup98 in transcription regulation in healthy and diseased cells

Nuclear pore complex (NPC) proteins are known for their critical roles in regulating nucleocytoplasmic traffic of macromolecules across the nuclear envelope. However, recent findings suggest that some nucleoporins (Nups), including Nup98, have additional functions in developmental gene regulation. Nup98, which exhibits transcription-dependent mobility at the NPC but can also bind chromatin away from the nuclear envelope, is frequently involved in chromosomal translocations in a subset of patients suffering from acute myeloid leukemia (AML). A common paradigm suggests that Nup98 translocations cause aberrant transcription when they are recuited to aberrant genomic loci. Importantly, this model fails to account for the potential loss of wild type (WT) Nup98 function in the presence of Nup98 translocation mutants. Here we examine how the cell might regulate Nup98 nucleoplasmic protein levels to control transcription in healthy cells. In addition, we discuss the possibility that dominant negative Nup98 fusion proteins disrupt the transcriptional activity of WT Nup98 in the nucleoplasm to drive AML.

Lab-on-a-chip: emerging analytical platforms for immune-mediated diseases

Miniaturization of analytical procedures has a significant impact on diagnostic testing since it provides several advantages such as: reduced sample and reagent consumption, shorter analysis time and less sample handling. Lab-on-a-chip (LoC), usually silicon, glass, or silicon-glass, or polymer disposable cartridges, which are produced using techniques inherited from the microelectronics industry, could perform and integrate the operations needed to carry out biochemical analysis through the mechanical realization of a dedicated instrument. Analytical devices based on miniaturized platforms like LoC may provide an important contribution to the diagnosis of high prevalence and rare diseases. In this paper we review some of the uses of Lab-on-a-chip in the clinical diagnostics of immune-mediated diseases and we provide an overview of how specific applications of these technologies could improve and simplify several complex diagnostic procedures.

Toward a new autoantibody diagnostic orthodoxy: understanding the bad, good and indifferent

Rapid advances in diagnostic technologies used to detect autoantibodies have made it difficult for even the most modern laboratory to keep abreast of the changing approaches and platforms, not to mention the clinicians who are hard pressed to keep abreast of evolving diagnostic paradigms attended by these newer techniques. While autoantibody testing is traditionally considered to be primarily serving the realm of diagnostic medicine, there is little doubt that autoantibodies are also being recognized as an approach to providing prognostic and therapeutic information. Accordingly, along with related proteomics, genomics and metabolomics, it is taking on increasing importance in the realm of personalized medicine. In today's world of autoantibody diagnostics, overarching concerns about false-negative and false-positive autoantibodies tests cannot be summarily dismissed by citing pros or cons of any one technology or diagnostic platform, but often point to persisting gaps in our knowledge about, and understanding of, the origin and roles of autoantibodies. Before we can hope to completely understand the enigmas that attend the results of autoantibody diagnostic tests, perhaps it is time to step back and re-examine long-accepted paradigms and beliefs. This review will address some of the issues that impact on autoantibody detection technologies and some of the considerations and issues that will attend a new orthodoxy of autoantibody diagnostics. These issues will be addressed in the context of "bad" (pathogenic), "good" (protective) or "indifferent" (no apparent role in disease) autoantibodies.

Autoantibodies to GW bodies and other autoantigens in primary biliary cirrhosis

Autoantibodies to intracellular targets in mitochondria and nuclei are serological hallmarks of primary biliary cirrhosis (PBC). One of the most recently identified cellular targets of PBC autoantibodies is a novel cytoplasmic structure referred to as GW bodies [GWB, G (glycine) W (tryptophan)-containing bodies (GWB)]. GWB are indentified as discrete cytoplasmic domains that are involved in mRNA processing via the RNA interference (RNAi) pathway. Key components of GWB include the proteins GW182, Ago2, RNA-associated protein 55 (RAP55) and Ge-1/Hedls. The primary objective was to study the frequency and clinical association of antibodies directed to GWB components, in 109 PBC patients. Autoantibodies to mitochondrial antigen-pyruvate dehydrogenase complex (M2), branched-chain 2-oxo-acid dehydrogenase complex and 2-oxo glutarate dehydrogenase complex (3E-BPO), gp210, sp100, promyelocytic leukaemia cell antigen (PML) and liver kidney microsomal-1 antigen (LKM-1) were detected by a line immunoassay and antibodies to GWB (GW182, RAP55, Ge-1, GW2, GW3) and glutamate receptor interacting protein (GRIP)-associated protein-1 (GRASP-1), by an addressable laser bead immunoassay (ALBIA). The most common GWB autoantigen targets were: RAP55-28%, GW182-12%, GW2-2% and antibodies to GRASP-1-17%. By comparison, the frequency of reactivity to established PBC autoantigens was: gp210, 27%; sp100, 27% and PML, 17%. None of the autoantibodies were associated with differences in Mayo risk score or liver decompensation. This study is the first study to show that antibodies to RAP55, GW182 and GRASP-1 are the most common GWB targets in PBC.

Nuclear Pore Protein p62 Autoantibodies in Systemic Lupus Erythematosus

Systemic lupus erythematosus (SLE) is a systemic autoimmune disease which is classically characterised by a variety of autoantibodies to deoxyribonucleic acid (DNA), ribonucleic acid (RNA), other nuclear and cytoplasmic antigens. Recently several novel autoantibodies against a variety of specific nuclear pore proteins have been described, including the nucleoporin p62. In this paper we evaluate anti-nucleoporin p62 antibodies by western blot analysis in 25 systemic lupus erythematosus patients. Six patients showed antibodies directed against nucleoporin p62. Our data indicate that p62 antibodies could be a useful additional marker in SLE.

Gene regulation by nucleoporins and links to cancer

Nuclear pore complexes (NPCs) composed of approximately 30 individual nucleoporins form huge macromolecular assemblies in the nuclear envelope, through which bidirectional cargo movement between the nucleus and cytoplasm occurs. Beyond their transport function, NPCs can serve as docking sites for chromatin and thereby contribute to the organization of the overall topology of chromosomes in conjunction with other factors of the nuclear envelope. Recent studies suggest that gene-NPC interactions may promote both transcription and the definition of heterochromatin-euchromatin boundaries. Intriguingly, several nucleoporins were linked to cancer, mostly in the context of chromosomal translocations, which encode nucleoporin chimeras. An emerging concept is that tumor cells exploit specific properties of nucleoporins to deregulate transcription, chromatin boundaries, and essential transport-dependent regulatory circuits. This review outlines new mechanistic links between nucleoporin function and cancer pathogenesis.

Differential detection of nuclear envelope autoantibodies in primary biliary cirrhosis using routine and alternative methods

Background

Detection of autoantibodies giving nuclear rim pattern by immunofluorescence (anti-nuclear envelope antibodies - ANEA) in sera from patients with primary biliary cirrhosis (PBC) is a useful tool for the diagnosis and prognosis of the disease. Differences in the prevalence of ANEA in PBC sera so far reported have been attributed to the methodology used for the detection as well as to ethnic/geographical variations. Therefore, we evaluated the prevalence of ANEA in sera of Greek patients with PBC by using methods widely used by clinical laboratories and a combination of techniques and materials.

Methods

We screened 103 sera by immunoblotting on nuclear envelopes and indirect immunofluorescence (IIF) using cells and purified nuclei. Reactivities against specific autoantigens were assessed using purified proteins, ELISA, immunoprecipitation and mass spectrometry.

Results

We found higher prevalence of ANEA when sera were assayed by IIF on purified nuclei or cultured cells (50%) compared to Hep2 commercially available slides (15%). Anti-gp210 antibodies were identified in 22.3% and 33% of sera using ELISA for the C-terminal of gp210 or both ELISA and immunoprecipitation, respectively. Immunoblotting on nuclear envelopes revealed that immunoreactivity for the 210 kDa zone is related to anti-gp210 antibodies (p < 0.0001). Moreover, we found that sera had antibodies for lamins A (6.8%), B (1%) and C (1%) and LBR (8.7%), whereas none at all had detectable anti-p62 antibodies.

Conclusions

The prevalence of ANEA or anti-gp210 antibodies is under-estimated in PBC sera which are analyzed by conventional commercially available IIF or ELISA, respectively. Therefore, new substrates for IIF and ELISA should be included by clinical laboratories in the analysis of ANEA in autoimmune sera.

CPR5: A Jack of all trades in plants

In our recent paper in Journal of Experimental Botany, we examined the effects of cpr5/old1 mutations and CPR5 overexpression on Arabidopsis growth and development.1 We found that CPR5 is important for early plant growth but promotes senescence at late development and hence proposed it as a senescence-regulatory gene as predicted by the Evolutionary Theory of Senescence derived from studies on animal ageing. One of the key unsolved issues is how CPR5 contributes to the early plant growth and development. Here we discuss the possible cellular functions of CPR5.

Characterization of the antibodies to p62 nucleoporin in primary biliary cirrhosis using human recombinant antigen

Reactivity of sera from patients with primary biliary cirrhosis (PBC) with a 60 kDa component of nuclear pore complexes (NPCs), purified by affinity chromatography on wheat-germ agglutinin (WGA)-Sepharose, was previously detected. Recently, clinical significance of the anti-NPC antibodies in PBC became evident. In the light of recent reports, indicating the correlation of the anti-NPC antibodies with severity and progression of the disease, the characterization of the reactive antigens is becoming essential in the clinical management of patients with PBC. Since accurate autoantibody detection represents one of the fundamental requirements for a reliable testing, we have generated a human recombinant p62 protein and validated an immunoprecipitation assay for the detection of anti-p62. We also demonstrated that the generated human recombinant p62 nucleoporin was modified by N-acetylglucosamine residues. More than 50% of tested PBC sera precipitated (35)S-radioactively labeled p62 recombinant nucleoporin and 40% recognized this recombinant antigen by immunoblotting. We compared the reactivity of PBC sera with rat and human nucleoporin. The incidence of anti-p62 nucleoporin positive PBC sera increased by 15% when human recombinant antigen was used. The titer of autoantibodies in p62-positive PBC samples strongly varied. Preadsorption of the PBC sera with p62 recombinant protein completely abolished their reactivity with the antigen. In conclusion, this study unequivocally proves that autoantibodies reacting with the 60 kDa component of NPCs target p62 nucleoporin and, more importantly, provide a better antigen source for future evaluations of the clinical role of anti-p62 in PBC.

Tracking Differential Gene Expression in MRL/MpJ Versus C57BL/6 Anergic B Cells: Molecular Markers of Autoimmunity

Background

Anergy is a key mechanism controlling expression of autoreactive B cells and a major site for failed regulation in autoimmune diseases. Yet the molecular basis for this differentiated cell state remains poorly understood. The current lack of well-characterized surface or molecular markers hinders the isolation of anergic cells for further study. Global gene profiling recently identified transcripts whose expression differentiates anergic from naïve B cells in model mouse systems. The objective of the current study was to evaluate the molecular and cellular processes that differentiate anergic cells that develop in the healthy C57BL/6 (B6) milieu from those that develop in the autoimmune-prone MRL/MpJ (MRL) background. This approach takes advantage of B6 and MRL mice bearing an anti-laminin Ig transgene with a well characterized anergic B cell phenotype.

Results

Global gene expression was evaluated in purified transgenic B cells using Operon version 3.0 oligonucleotide microarray assaying >31,000 oligoprobes. Genes with a 2-fold expression difference in B6 as compared to MRL anergic B cells were identified. Expression of selected genes was confirmed using quantitative RT-PCR. This approach identified 43 probes corresponding to 37 characterized genes, including Ptpn22, CD74, Birc1f/Naip, and Ctla4, as differentially expressed in anergic B cells in the two strains. Gene Ontology classification identified differentiation, cell cycle, proliferation, development, apoptosis, and cell death as prominently represented ontology groups. Ingenuity Pathway Analysis identified two major networks incorporating 27 qualifying genes. Network 1 centers on beta-estradiol and TP53, and Network 2 encompasses RB1, p38 MAPK, and NFkB cell growth, proliferation, and cell cycle signaling pathways.

Conclusion

Using microarray analysis we identified 37 characterized genes and two functional pathways engaged in maintenance of B cell anergy for which expression is distorted by underlying autoimmune genetic susceptibility. This approach identifes a new biological role for multiple genes and potential new therapeutic targets in autoimmunity.

Topology of yeast Ndc1p: predictions for the human NDC1/NET3 homologue

The nuclear pore complex is the predominant structure in the nuclear envelope that spans the double nuclear membranes of all eukaryotes. Yeasts have one additional organelle that is also embedded in the nuclear envelope: the spindle pole body, which functions as the microtubule organizing center. The only protein known to localize to and be important in the assembly of both of these yeast structures is the integral membrane protein, Ndc1p. However, no homologues of Ndc1p had been characterized in metazoa. Here, we identify and analyze NDC1 homologues that are conserved throughout evolution. We show that the overall topology of these homologues is conserved. Each contains six transmembrane segments in its N-terminal half and has a large soluble C-terminal half of approximately 300 amino acids. Charge distribution analysis infers that the N- and C-termini are exposed to the cytoplasm. Limited proteolysis of yeast Ndc1p in cellular membranes confirms the orientation of its C-terminus. Although it is not known whether vertebrate NDC1 protein localizes to nuclear pores like its yeast counterpart, the human homologue contains three FG repeats in the C-terminus, a feature of many nuclear pore proteins. Moreover, a small region containing mutations that affect assembly of the nuclear pore in yeast is highly conserved throughout evolution. Lastly, we bring together data from another study to demonstrate that the human homologue of NDC1 is the known inner nuclear membrane protein, NET3.

Gene cloning and fusion expression of human autoantigen Sp100 in yeasts

AIM: To clone and construct the plasmid cont-aining human autoantigene Sp100 gene, and then to identify the immunoreactivity of the purified recombinant protein.

METHODS: The Sp100 gene was amplified from human liver cDNA library, and then was cloned into PEGH vector to induce the Sp100 expression. The obtained products were identified and analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and Western blot.

RESULTS: The sequence of Sp100 autoantigene gene was confirmed to be the same as the sequence reported in GenBank. The fusion pro-teins were found at 53-, 55-, 52-, 37-, 42-, and 47-ku strip on SDS-PAGE gel. Western blot analysis showed that the fusion protein with 55, 52, 42 and 47 ku had the same immunoreactivity as human Sp100 autoantigene.

CONCLUSION: Human plasmid containing Sp100 gene is successfully cloned and expressed in yeast Y258.

Versatility at the nuclear pore complex: lessons learned from the nucleoporin Nup153

The vertebrate pore protein Nup153 plays pivotal roles in nuclear pore function. In addition to being important to pore architecture, Nup153 is a key participant in both import and export. The scope of Nup153 function also extends beyond the canonical view of the pore as a trafficking gateway. During the transition into mitosis, Nup153 directs proteins involved in membrane remodeling to the nuclear envelope. As cells exit mitosis, Nup153 is recruited to the chromosomal surface, where nuclear pores are formed anew in a complicated process still under much experimental scrutiny. In addition, Nup153 is targeted for protease cleavage during apoptosis and in response to certain viral infections, providing molecular insight into pore reconfiguration during cell response. Overall, the versatile nature of Nup153 underscores an emerging view of the nuclear pore at the nexus of many key cellular processes.

Small ubiquitin-related modifiers: A novel and independent class of autoantigens in primary biliary cirrhosis

Serum autoantibodies against components of nuclear dots (anti-NDs), namely PML and Sp100, are specifically detected in 20% to 30% of patients with primary biliary cirrhosis (PBC). Although anti-ND antibodies are nonpathogenic, the mechanisms that lead to this unique reactivity are critical to understanding the loss of immune tolerance in PBC. Importantly, Sp100 and PML are both covalently linked to small ubiquitin-related modifiers (SUMOs). Therefore, we investigated whether SUMO proteins are independent autoantigens in PBC and studied 99 PBC sera samples for reactivity against NDs, PML, and Sp100, as well as against SUMO-2 and SUMO-1 recombinant proteins. Autoantibodies against SUMO-2 and SUMO-1 were found in 42% and 15% of anti-ND-positive PBC sera, respectively. Anti-SUMO reactivity was not observed in anti-ND-negative sera. Anti-SUMO-2 autoantibodies were found in 58% of sera containing autoantibodies against both PML and Sp100 and were detected exclusively in sera containing anti-Sp100 autoantibodies. In conclusion, SUMO proteins constitute a novel and independent class of autoantigens in PBC. Furthermore, we believe our data emphasize the post-translational modification of lysine by either lipoylation in the case of AMA or SUMOylation in the case of specific anti-ND autoantibodies as the pivotal site for autoantibody generation in PBC.