Vesicular transport of newly synthesized cytochromes P4501A to the outsideof rat hepatocyte plasma membranes

Anti-cytochrome P450 (CYP)1A2 autoantibodies are found in dihydralazine-ind uced hepatitis, and CYPs2B and 2C have been shown to follow vesicular flow to the plasma membrane (PM). However, it is unknown whether other CYPs foll ow this route, whether NADPH-CYP reductase is present on the hepatocyte sur face, and whether autoimmune hepatitis-inducing drugs increase PM CYPs. In this study, we determined the transmembrane topology and transport of CYPs1 A in rat hepatocytes. In cultured hepatocytes, colchicine and other vesicul ar transport inhibitors decreased PM CYPs1A assessed by flow cytometry. Col chicine administration also decreased PM CYPs1A in vivo. Pulse chase experi ments with [S-35]methionine showed that only the newly synthesized CYP mole cules are transferred to the PM, whereas microsomal CYP1A2 was stably radio labeled for several hours. In contrast, radiolabeled CYP1A2 reached the PM and disappeared from the PM with half-lives of less than 30 min. Confocal m icroscopy, biotinylation, and coimmunoprecipitation experiments showed that PM CYPs1A and CYP reductase are present on the cell surface, and that the reductase is closely associated with PM CYPs. Exposure of whole cells to an anti-CYP1A1/2 antibody at 4 degrees C, before five washes and PM preparati on, abolished PM CYPs1A-supported monooxygenase activity, indicating that P M CYPs are mostly located on the external surface. Dihydralazine and other CYPs1A inducers increased PM CYPs1A. In conclusion, newly synthesized CYPs1 A follow vesicular flow to the outside of the PM, and NADPH-CYP reductase a lso is located on the hepatocyte surface. Dihydralazine administration incr eases PM CYP1A2, its autoimmune target.