Characterization of proliferating cell nuclear antigen recognized by autoantibodies in lupus sera.

Abstract

A nuclear antigen associated with cell proliferation (proliferating cell nuclear antigen [PCNA]) and blast transformation is recognized by autoantibodies in the sera of some patients with systemic lupus erythematosus. Using this autoantibody as a reagent, PCNA was purified 120-fold by (NH4)2SO4 fractionation, DEAE chromatography and Sephadex G200 gel filtration. The antigenicity of PCNA was sensitive to trypsin but resistant to RNase and DNase, suggesting that the antigenic determinant resided in protein and not nucleic acids. PCNA was inactivated at 56.degree.C for 30 min. Isoelectrophoretic focusing showed that the pI [isoelectric point] was 4.8. Analysis of immunoprecipitates on polyacrylamide gels showed the presence of IgG H and L chains and a single polypeptide band of 33,000 MW. This polypeptide band was the reactive antigen in immunoblotting (Western transfer) assays.