The I protein of the heterogeneous nuclear ribonucleoprotein complex is a novel dog nuclear autoantigen

In eukaryotic cells, heterogeneous nuclear RNA is associated with a set of abundant nuclear proteins to form complex ribonucleoprotein structures (hnRNP). Autoantibodies to hnRNP G protein have been previously reported in German shepherd dogs with lupus-like syndrome. In the present study, we describe the characterization of a novel antigen recognized by a serum from a schnauzer dog with a non-erosive polyarthritis. The autoantibodies give, by indirect immunofluorescence, a nuclear pattern with staining close to one of the nucleoli. Immunoblotting and immunoprecipitation data reveal that the autoantigens are in fact two closely related basic proteins (average pI 8.7) with apparent molecular weights of 56 kDa (p56) and 59 kDa (p59). The results of immunoprecipitation with anti-hnRNP antibodies and DNA affinity column chromatography strongly suggest that these autoantigens correspond to hnRNP I proteins. This point was confirmed by cloning and sequencing a cDNA clone encoding the complete sequence of the antigens. In addition, we found that anti-hnRNP I antibodies preferentially stain certain loops of the Pleurodeles waltl lampbruch chromosomes. These data, added to previous ones on anti-p43/hnRNP G protein in German shepherd dogs with lupus-like syndrome, confirm the interest of this category of antibodies to hnRNP proteins in autoimmune disorders.