CYTOCHROME P4502B FOLLOWS A VESICULAR ROUTE TO THE PLASMA-MEMBRANE INCULTURED RAT HEPATOCYTES

Background/Aims: Autoantibodies against cytochrome P450 are found in s ome forms of autoimmune hepatitis. Cytochrome P450 is synthesized and mainly located in the endoplasmic reticulum but may also be expressed on the plasma membrane of hepatocytes. Vesicles migrate from the endop lasmic reticulum to the Golgi apparatus and then to the plasma membran e along microtubules. We determined the route followed by cytochrome P 4502B to reach the plasma membrane. Methods: Rat hepatocytes were cult ured for 2 hours after plating with: various inhibitors of cellular tr afficking. Detached, uncut, nonpermeabilized hepatocytes were then exp osed to a monoclonal antibody specific for cytochrome P4502B and studi ed by flow cytometry and confocal microscopy. Results: The plasma memb rane expression of cytochrome P4502B was markedly decreased after 2 ho urs of culture with cycloheximide (an inhibitor of protein synthesis), caffeine at 20 degrees C (conditions that decrease vesicular transpor t from the endoplasmic reticulum to the Golgi apparatus), brefeldin A (which redistributes Golgi components back to the endoplasmic reticulu m), monensin (an inhibitor of Golgi functions), and colchicine, vinbla stine or nocodazole (three microtubule inhibitors). Conclusions: Part of cytochrome P4502B follows a microtubule-dependent vesicular route f rom the endoplasmic reticulum to the plasma membrane in cultured rat h epatocytes.