Identification of a primary biliary cirrhosis associated protein as lysosome-associated membrane protein-2.

Primary biliary cirrhosis (PBC) is a chronic cholestatic liver disease of unknown etiology and abnormality of hepatobiliary transport might contribute to its pathogenesis. In this study, we aimed to isolate and identify new molecules associated with PBC. With hepatocyte canalicular membrane vesicles (CMVs) of PBC patients as immunogens, we screened the monoclonal antibody 1F9 (mAb1F9), whose antigen dominantly recognized the subapical domains in hepatocytes in normal livers. Immunohistochemistry revealed that the expression of mAb1F9 antigen (mAb1F9-Ag) significantly increased in PBC livers compared with control groups including normal livers, cirrhosis or cholestasis other than PBC. Interestingly, the augmented expression of mAb1F9-Ag was correlated with the severity of PBC, and ursodeoxycholic acid treatment may significantly improve the recovery of mAb1F9-Ag. In addition, redistribution of mAb1F9-Ag was found in 46% of PBC. mAb1F9-Ag was isolated and analyzed with mass spectrometry, which indicated lysosome-associated membrane protein 2 (LAMP-2) as the candidate. Further studies showed that mAb1F9 recognized LAMP-2 immunoprecipitates and vice verse, mAb1F9 reacted with recombinant LAMP-2. mAb1F9 and LAMP-2 antibody exhibited similar staining pattern and displayed similar subcellular localization. Together, the identity of mAb1F9-Ag is LAMP-2, suggesting that LAMP-2 may assist in the differentiation of PBC and predict a poor outcome in patients with PBC. BIOLOGICAL SIGNIFICANCE: This manuscript describes the expression of a specific antibody, named mAb1F9. The antigen recognized by mAb1F9 may assist in the differentiation of primary biliary cirrhosis (PBC) and predict a poor outcome in patients with PBC. Through antigen identification, we confirm the identity of mAb1F9-Ag as lysosome-associated membrane protein 2 (LAMP-2). The clinical relevance of the manuscript is well regarded since markers are rare and usually not successful for PBC diagnosis and treatment.