Identification of cyclin A as a molecular target of antinuclear antibodies (ANA) in hepatic and non-hepatic autoimmune diseases

Background/Aims: Antinuclear antibodies (ANA) are a diagnostic hallmark of various autoimmune diseases and also of autoimmune hepatitis type 1, The designation ANA describes a heterogeneous group of autoantibodies, In liver diseases, only a few nuclear target antigens have been molecularly identified and characterized, Cyclins play a central role in cell cycle regulation, DNA transcription, and cell proliferation, Cyclin A was also identified as an integration site of the hepatitis B virus in a patient with hepatocellular carcinoma, In this study we identify cyclin A as a novel nuclear target protein of ANA, Methods: Sera of patients with autoimmune hepatitis (AIH) type 1 (n=61), type 2 (n=21), and type 3 (n=39), primary biliary cirrhosis (PBC) (n=107), rheumatic diseases (systemic lupus erythematosus (SLE), rheumatoid arthritis (RA), mixed connective tissue disease (MCTD)) (n=42) and normal controls (n=100) were evaluated for ANA by indirect immunofluorescence. Baculovirus-generated recombinant human cyclin A protein was used for immunoblotting to study the prevalence of anti-cyclin A autoantibodies in these sera, Results: Sera of patients with AIH type 1 and rheumatic diseases had ANA detected by indirect immunofluorescence, In AIH type 1 12/61 (20%) and in rheumatic diseases 6/42 (14%) were immunoblot positive for autoantibodies against human cyclin A, In PBC, AIH type 3 and normal control sera negative for ANA by immunofluorescence, anti-cyclin A autoantibodies were present in 7-9%; in AIH type 2 and SLE they were undetectable by immunoblot, In some sera a typical cyclin A immunofluorescence was observed, Anti-cyclin A antibodies recognize a 45 and 50 kDa recombinant protein species, providing evidence for the recognition of at least two molecular epitopes, Conclusions: This study has identified cyclin A as a human autoantigen in hepatic and non-hepatic autoimmune diseases, More studies are required to evaluate the clinical and pathophysiological significance of anti-cyclin A autoantibodies. The identification of human anti-cyclin A autoantibodies may additionally become a valuable tool for studying the function and regulation of cyclin A in mammalian and human cells.