Objective-To determine the prevalence of myositis specific autoantibodies (MSAs) and several myositis associated autoantibodies (MAAs) in a large group of patients with myositis. Methods-A total of 417 patients with myositis from 11 European countries (198 patients with polymyositis (PM), 181 with dermatomyositis (DM), and 38 with inclusion body myositis (IBM)) were serologically analysed by immunoblot, enzyme linked immunosorbent assay (ELISA) and/or immunoprecipitation. Results-Autoantibodies were found in 232 sera (56%), including 157 samples (38%) which contained MSAs. The most commonly detected MSA was anti-Jo-1 (18%). Other anti-synthetase, anti-Mi-2, and anti-SRP autoantibodies were found in 3%, 14%, and 5% of the sera, respectively. A relatively high number of anti-Mi-2 positive PM sera were found (9% of PM sera). The most commonly detected MAA was anti-Ro52 (25%). Anti-PM/Scl-100, anti-PM/Scl-75, anti-Mas, anti-Ro60, anti-La, and anti-U1 snRNP autoantibodies were present in 6%, 3%, 2%, 4%, 5%, and 6% of the sera, respectively. Remarkable associations were noticed between anti-Ro52 and anti-Jo-1 autoantibodies and, in a few sera, also between anti-Jo-1 and anti-SRP or anti-Mi-2 autoantibodies. Conclusions-The incidence of most of the tested autoantibody activities in this large group of European patients is in agreement with similar studies of Japanese and American patients. The relatively high number of PM sera with anti-Mi-2 reactivity may be explained by the use of multiple recombinant fragments spanning the complete antigen. Furthermore, our data show that some sera may contain more than one type of MSA and confirm the strong association of anti-Ro52 with anti-Jo-1 reactivity.

The yeast exosome is a complex of 3 3 5 exoribonucleases. Sequence analysis identified putative human homologues for exosome components, although several were found only as expressed sequence tags. Here we report the cloning of full-length cDNAs, which encode putative human homologues of the Rrp40p, Rrp41p, and Rrp46p components of the exosome. Recombinant proteins were expressed and used to raise rabbit antisera. In Western blotting experiments, these decorated HeLa cell proteins of the predicted sizes. All three human proteins were enriched in the HeLa cells nucleus and nucleolus, but were also clearly detected in the cytoplasm. Size exclusion chromatography revealed that hRrp40p, hRrp41p, and hRrp46p were present in a large complex. This cofractionated with the human homologues of other exosome components, hRrp4p and PM/ Scl-100. Anti-PM/Scl-positive patient sera coimmunoprecipitated hRrp40p, hRrp41p, and hRrp46p demonstrating their physical association. The immunoprecipitated complex exhibited 3 3 5 exoribonuclease activity in vitro. hRrp41p was expressed in yeast and shown to suppress the lethality of genetic depletion of yeast Rrp41p. We conclude that hRrp40p, hRrp41p, and hRrp46p represent novel components of the human exosome complex.In both bacteria and eukaryotes, the processing and degradation of many RNA species involves multiprotein complexes (reviewed in Refs. 1-4). The Escherichia coli degradosome includes the endoribonuclease E (RNase E), the 3Ј 3 5Ј exonuclease polynucleotide phosphorylase, the DEAD box RNA helicase RhlB, and several additional proteins whose role is unclear (5-7). Related complexes are implicated in RNA processing in chloroplasts and mitochondria (8 -10). The yeast exosome contains at least 11 components, which are known or predicted to be 3Ј 3 5Ј exoribonucleases (11,12). Ten of these (Rrp4p, Rrp40 -46p, Mtr3p, and Csl4p) have been demonstrated to be encoded by essential genes. These 10 components were found in both cytoplasmic and nuclear complexes, whereas the nonessential RRP6 gene product was detected only in the nucleus (11, 13).The 3Ј processing of many RNAs is affected by the absence or mutation of exosome components. The nuclear exosome is implicated in the processing of ribosomal RNA (rRNA), spliceosomal small nuclear RNAs, and small nucleolar RNAs, as well as the degradation of pre-rRNA spacers and unspliced pre-mRNAs (12-22). The cytoplasmic exosome complex is involved in the 3Ј 3 5Ј pathway of mRNA degradation (22). The activity of the exosome complex may be regulated by cofactors including, for example, the putative ATP-dependent DEVH box RNA helicases Dob1p and Ski2p (23,24).Human cells also contain a multiprotein complex that is related to the yeast exosome (11). This complex, initially designated as the polymyositis/scleroderma (PM/Scl) 1 overlap syndrome particle and herein referred to as the human exosome, was reported to contain 11 (25) to 16 (26) subunits ranging from 20 to 110 kDa. Two proteins of this complex were identified as autoantigens, which are tar...

Sera from patients suffering from systemic autoimmune diseases such as systemic lupus erythematosus (SLE) and systemic sclerosis (SSc) have been shown to contain reactivities to nuclear components. Autoantibodies specifically targeting nucleolar antigens are found most frequently in patients suffering from SSc or SSc overlap syndromes. We determined the prevalence and clinical significance of autoantibodies directed to nucleolar RNA-protein complexes, the so-called small nucleolar ribonucleoprotein complexes (snoRNPs). A total of 172 patient sera with antinucleolar antibodies were analysed by immunoprecipitation. From 100 of these patients clinical information was obtained by chart review. Autoantibodies directed to snoRNPs were detected not only in patients suffering from SSc and primary Raynaud's phenomenon (RP), but also in patients suffering from SLE, rheumatoid arthritis (RA) and myositis (PM/DM). Antibodies against box C/D small snoRNPs can be subdivided in antifibrillarin positive and antifibrillarin negative reactivity. Antifibrillarin-positive patient sera were associated with a poor prognosis in comparison with antifibrillarin negative (reactivity with U3 or U8 snoRNP only) patient sera. Anti-Th/To autoantibodies were associated with SSc, primary RP and SLE and were found predominantly in patients suffering from decreased co-diffusion and oesophagus motility and xerophthalmia. For the first time autoantibodies that recognize box H/ACA snoRNPs are described, identifying this class of snoRNPs as a novel autoantigenic activity. Taken together, our data show that antinucleolar patient sera directed to small nucleolar ribonucleoprotein complexes are found frequently in other diseases than SSc and that categorization of diagnoses and clinical manifestations based on autoantibody profiles seems particularly informative in patient sera recognizing box C/D snoRNPs.

IIM = idiopathic inflammatory myopathy; PM/Scl = polymyositis/scleroderma; pre-mRNA = precursor mRNA; Rrp = ribosomal RNA processing; snRNA = small nuclear RNA; snoRNA = small nucleolar RNA; U snRNP = U small nuclear ribonucleoprotein.Available online http://arthritis-research.com/content/3/2/102 IntroductionAutoantibodies are the hallmark of many autoimmune disorders, such as the connective-tissue diseases scleroderma, systemic lupus erythematosus, Sjögren's syndrome, idiopathic inflammatory myopathies (IIMs), rheumatoid arthritis, and mixed connective-tissue disease. Although their etiology and pathogenic role remain unclear, many different autoantibody specificities have been characterized. Some of these autoantibodies are very useful as diagnostic markers and may also have a prognostic value, as has been shown for anti-doublestranded-DNA antibodies in systemic lupus erythematosus and anti-cyclic-citrullinated-peptide antibodies in rheumatoid arthritis [1,2]. Other autoantibodies have proved to be valuable tools to study cellular processes in which the autoantigens are involved, such as the splicing of precursor messenger RNAs (pre-mRNAs) mediated by the autoantigenic U small nuclear ribonucleoprotein complexes (U snRNPs) [3]. Similarly, autoantibodies directed to a protein complex, known as the polymyositis-scleroderma (PM/Scl) complex, have contributed to the discovery of a large RNA-processing complex, which is now known as the human exosome.Here we present an overview of recent studies that have led to the current biochemical and functional understanding of the PM/Scl complex. Clinical characteristics of patients positive for anti-PM/Scl autoantibodiesThe anti-PM/Scl autoantibody, formerly known as anti-PM-1 [4], may be detected in sera of patients with myositis, scleroderma, and PM/Scl overlap syndrome, although some patients positive for anti-PM/Scl autoantibodies may not have either of these conditions [5,6] AbstractThe anti-PM/Scl autoantibodies are known to characterize a subset of autoimmune patients with myositis, scleroderma (Scl), and the PM/Scl overlap syndrome. The major autoantigens that are recognized by anti-PM/Scl autoantibodies are designated PM/Scl-100 and PM/Scl-75. These autoantigens have been reported to associate into a large complex consisting of 11 to 16 proteins and to play a role in ribosome synthesis. Recently, it was discovered that the PM/Scl complex is the human counterpart of the yeast (Saccharomyces cerevisiae) exosome, which is an RNA-processing complex consisting of 11 3′→5′ exoribonucleases. To date, 10 human exosome components have been identified, although only some of these were studied in more detail. In this review, we discuss some recent advances in the characterization of the PM/Scl complex.

Objective. To investigate the incidence of autoantibodies directed to deproteinized transfer RNAHi" (tRNAHiS) in anti-Jo-1 positive myositis patients and to determine the major B cell epitope.Methods. One hundred sixty-seven myositis sera were screened by immunoblotting and enzyme-linked immunosorbent assay for the presence of anti-Jo-l antibody. Autoantibodies directed to deproteinized RNA were detected by immunoprecipitation. Ribonuclease cleavage experiments were performed to determine the tRNAHi5-specific features important for recognition.Results. Approximately one-third of the antido-1 positive sera also contained autoantibodies recognizing tRNAHiS. This recognition was independent of modified bases, but the presence of stabilizing Mg2+ ions appeared to be essential for efficient immunoprecipitation. Transfer RNAHi'-specific features in the anticodon loop were not protected from ribonuclease cleavage by bound antibodies, while protection of bases located in the D and T loops was observed.Conclusion. A significant number of anti-Jo-1 positive myositis sera contain anti-tRNAHiS activity. Formation of the major autoepitope on tRNA"'" is strongly dependent on proper folding of this molecule mediated by an interaction between D and T loops which is stabilized by either modified residues or M g + ions.