Identification of autoantibodies to the I protein of the heterogeneous nuclear ribonucleoprotein complex in patients with systemic sclerosis

Abstract

Objective. To assess the presence of autoantibodies to the I protein (polypyrimidine‐tract binding protein) of the heterogeneous nuclear RNPs (hnRNP) in different connective tissue diseases. Antibodies to other hnRNP proteins (A1, A2, and B) have been previously found in patients with rheumatoid arthritis (RA), systemic lupus erythematosus (SLE), and mixed connective tissue disease (MCTD).Methods. Sera from 101 patients with various connective tissue diseases and 25 normal controls were investigated by enzyme‐linked immunosorbent assay and immunoblotting, for their reactivity to highly purified recombinant hnRNP I. Moreover, reactivity to cellular hnRNP I protein was investigated by immunoblotting using a partially purified preparation of hnRNP proteins (including A1, A2, B, and I), and by indirect immunofluorescence. For the analysis of the fluorescence pattern, affinity‐purified antibodies to hnRNP I, obtained from a selected patient, were tested on HEp‐2 cells.Results. By immunoblotting, antibodies reacting to recombinant hnRNP I were found in 22 of 40 patients with systemic sclerosis (SSc), 3 of 32 with RA, 0 of 23 with SLE, and 0 of 6 with MCTD. Antibodies to recombinant hnRNP I were more frequently found in patients with pre‐SSc or limited SSc (15 of 24) than in those with intermediate or diffuse SSc (7 of 16). In indirect immunofluorescence studies, affinity‐purified anti—hnRNP I autoantibodies gave a diffuse nucleoplasmic staining. Using an hnRNP preparation from nuclear extracts, anti—hnRNP I reactivity was detectable in SSc sera, while it was not detectable in RA, SLE, and MCTD sera reacting with hnRNP A/B proteins.Conclusion. Human autoimmune sera show distinct patterns of anti‐hnRNP reactivity, i.e., anti‐A/B in SLE and RA sera, and anti‐I in SSc sera. This suggests that A/B proteins and the I protein may be involved in different dynamic hnRNP complexes that elicit different autoimmune responses. From a clinical perspective, anti—hnRNP I antibodies are frequently associated with pre‐SSc features, suggesting an early appearance of these antibodies during the course of the disease.

Heterogeneous Nuclear Ribonucleoprotein H1, a Novel Nuclear Autoantigen

“…Antibodies to hnRNP A1 as well as antibodies to hnRNP A2, and its alternatively spliced variants B1 and B2, (the RA33 complex) have been described in RA, SLE, and MCTD (27,31,32 ). Anti-hnRNP I antibodies seem to be associated with (pre)-systemic sclerosis (33 ). Antibodies to hnRNP C1/C2 have been reported, but it is not known whether they are related to a specific disease (34 ).…”

Proteomics-based Identification of Human Acute Leukemia Antigens That Induce Humoral Immune Response

“…For two other identified proteins, hnRNP L and ENO1, autoantibodies against them have already been described in various pathological situations, mainly in nonorgan-specific autoimmune diseases (33)(34)(35). hnRNP L belongs to the large superfamily of hnRNPs, which are frequently recognized by autoantibodies present in patients with nonorgan-specific autoimmune diseases: antibodies to hnRNP A1, A2, and B have been previously found in patients with rheumatoid arthritis, systemic lupus erythematosus, and mixed connective tissue diseases, and antibodies directed against hnRNP I (polypyrimidine tract-binding protein) were detected in the sera of systemic sclerosis patients (36,37). Notably the amino acid sequence of hnRNP L is highly homologous to that of hnRNP I; together they constitute a new family of hnRNP proteins within the ribonucleoprotein consensus RNA-binding proteins.…”

Orderly Pattern of Development of the Autoantibody Response in (New Zealand White × BXSB)F1 Lupus Mice: Characterization of Target Antigens and Antigen Spreading by Two-Dimensional Gel Electrophoresis and Mass Spectrometry

“…UV excision-repair protein RAD23 is a highly conserved 58-kDa protein, located in the nucleus and involved in nucleotide excision-repair and possibly in DNA-damage recognition and/or in altering chromatin structure to allow access by damage-processing enzymes (28). hnRNP L belongs to the large superfamily of hnRNP, which are frequently recognized by autoantibodies present in patients with nonorgan-specific autoimmune diseases: Abs to hnRNP A1, A2, and B have been previously found in patients with rheumatoid arthritis, SLE, and mixed connective tissue diseases (29) and Abs directed to hnRNP I (polypyrimidine tract-binding protein) were detected in the sera of systemic sclerosis patients (30). Notably, the amino acid sequence of hnRNP L is highly homologous to that of hnRNP I which together constitute a new family of hnRNP proteins within the RNP consensus RNA-binding proteins (31).…”