Autoantibody to RNA polymerase I in scleroderma sera

Area of Science:

• Immunology
• Molecular Biology
• Cell Biology

Background:

• Autoantibodies targeting nucleolar components are characteristic of scleroderma.
• Specific autoantibodies can cause a speckled nucleolar staining pattern in immunofluorescence.
• Previous studies indicated heterogeneity in autoantibody specificities within scleroderma.

Purpose of the Study:

• To identify the specific nucleolar target of certain scleroderma autoantibodies.
• To investigate the functional consequences of these autoantibodies on cellular processes.
• To determine the diagnostic specificity of these autoantibodies for scleroderma.

Main Methods:

• Immunofluorescence microscopy using drug-treated Vero cells to localize autoantibody targets.
• Double immunofluorescence with specific rabbit anti-RNA polymerase I antibodies.
• Immunoprecipitation of [35S]methionine-labeled HeLa cell extracts using scleroderma sera.
• Immunoabsorption experiments to confirm antibody specificities.
• Microinjection of patient-derived IgG to assess effects on ribosomal RNA transcription.

Main Results:

• Scleroderma autoantibodies with speckled nucleolar staining localized to fibrillar regions, distinct from granular regions, in drug-treated cells.
• These autoantibodies recognized the same fibrillar structures as specific rabbit anti-RNA polymerase I antibodies.
• Scleroderma sera immunoprecipitated multiple polypeptides, consistent with RNA polymerase I subunits.
• Patient-derived IgG microinjection inhibited ribosomal RNA transcription.
• Autoantibodies to RNA polymerase I were exclusively found in scleroderma patients, not in other autoimmune diseases.

Conclusions:

• Autoantibodies to RNA polymerase I are a specific serological marker for a subset of scleroderma patients.
• These autoantibodies interfere with ribosomal RNA transcription, suggesting a pathogenic role in scleroderma.
• The findings highlight RNA polymerase I as a key autoantigen in scleroderma.