Peroxisome proliferator-binding protein: Identification and partial characterization of nafenopin-, clofibric acid-, and ciprofibrate-binding proteins from rat liver

Peroxisome proliferators (PP) induce a highly predictable pleiotropic response in rat and mouse liver that is characterized by hepatomegaly, increase in peroxisome number in hepatocytes, and induction of certain peroxisomal enzymes. The PP-binding protein (PPbP) was purified from rat liver cytosol by a two-step procedure involving affinity chromatography and ion-exchange chromatography. Three, PP, nafenopin and its structural analogs clofibric acid and ciprofibrate, were used as affinity ligands and eluting agents. This procedure yields a major protein with an apparent M(r) of 70,000 on NaDodSO₄/PAGE in the presence of reducing agent and M(r) 140,000 (M(r) 140,000-160,000) on gel filtration and polyacrylamide gradient gel electrophoresis under nondenaturing conditions, indicating that the active protein is a dimer. This protein has an acidic pI of 4.2 under nondenaturing conditions, which rises to 5.6 under denaturing conditions. The isolation of the same M(r) 70,000 protein with three different, but structurally related, agents as affinity ligands and the immunological identity of the isolated proteins constitute strong evidence that this protein is the PPbP capable of recognizing PP that are structurally related to clofibrate. The PPbP probably plays an important role in the regulation of PP-induced pleiotropic response.