THE MAJOR DERMATOMYOSITIS-SPECIFIC MI-2 AUTOANTIGEN IS A PRESUMED HELICASE INVOLVED IN TRANSCRIPTIONAL ACTIVATION

Objective, To characterize the complementary DNA (cDNA) and protein se quences of autoantigens recognized by anti-Mi-2 antibodies, using reco mbinant Mi-2 proteins for improved autoantibody detection, Methods, A cDNA expression library was immunoscreened, and cDNA isolation, alignm ent, and sequence analysis were performed, Northern blotting and in si tu hybridization techniques were used, A recombinant protein (rMi-2) w as synthesized. Immunoprecipitation of S-35-methionine-labeled HEp-2 c ell proteins and immunoblotting of rMi-2 and natural nuclear proteins were performed, Immunofluorescence studies were done with anti-Mi-2 po sitive sera of dermatomyositis (DM) patients, and with human or rabbit antibodies specific for rMi-2, Antibody screening of systemic lupus e rythematosus, rheumatoid arthritis, DM, and antinuclear antibody-posit ive human sera was performed using an rMi-2 protein enzyme-linked immu nosorbent assay (ELISA), Results, A major antigen recognized by antiMi -2 positive sera of DM patients was found to constitute a 218-kd nucle ar protein (218-kd Mi-2) encoded on chromosome 12 and to belong to the SNF2/RAD 54 helicase family. Human and rabbit antibodies that were af finity purified using the recombinant protein reacted with and precipi tated a nuclear protein of similar size, which was also recognized by anti-Mi-2 sera, Anti-218-kd Mi-2 antibodies detected by rMi-2 protein ELISA seemed to be mainly restricted to sera from patients with DM, Co nclusion, The molecular characterization of the 218-kd Mi-2 antigen ma y contribute to our understanding of autoimmune phenomena in DM, The u se of immunoreactive recombinant proteins allows structural and functi onal studies of the helicase and the development of sensitive and accu rate antibody screening tests.