Autoantibodies from patients with primary biliary cirrhosis recognize a region within the nucleoplasmic domain of inner nuclear membrane protein LBR

Autoantibodies from rare patients with primary biliary cirrhosis (PBC) recognize LBR, or lamin B receptor, an integral membrane protein of the inner nuclear membrane. Human LBR has a nucleoplasmic, amino-terminal domain of 208 amino acids followed by a carboxyl-terminal domain with eight putative transmembrane segments. Autoantibodies against LBR from four patients with PBC recognized the nucleoplasmic, amino terminal domain but not the carboxyl-terminal domain. Immunoblotting of smaller fusion proteins demonstrated that these autoantibodies recognized a conformational epitope(s) contained within the stretch of amino acids hom 1 to 60, These results, combined with those of previous studies, show that autoepitopes of nuclear membrane proteins are located within their nucleocytoplasmic domains and that autoantibodies hom patients with PBC predominantly react with one domain of a protein antigen, This work also provides further characterization of anti-LBR antibodies that have found utility as reagents in cell biology research.