ETHANOL-INDUCED RETENTION OF NASCENT PROTEINS IN RAT HEPATOCYTES IS ACCOMPANIED BY ALTERED DISTRIBUTION OF THE SMALL GTP-BINDING PROTEIN RAB2

Chronic ethanol consumption induces hepatocellular retention of nascen t proteins leading to hepatomegaly, While the molecular mechanisms beh ind this impairment are undefined, it has been predicted that protein retention results from a disruption of vesicle-mediated secretory proc esses. Small GTP-binding proteins (rab proteins) have recently been im plicated in the regulation of vesicular trafficking in eukaryotic cell s, Our objectives were to identify intracellular sites of ethanol-indu ced protein retention and to determine whether the distribution of sec retory rab proteins was altered by ethanol, Transport of hepatic prote ins along the secretory pathway in livers from control and ethanol-fed rats was analyzed using subcellular fractionation and immunoprecipita tion in the context of in vivo pulse-chase experiments. We show that p re-Golgi and Golgi compartments, as well as secretory vesicles, are si tes of ethanol-induced retention of nascent soluble and transmembrane secretory proteins, These results are supported by immunofluorescence localization of hepatic proteins on liver sections, Further, immunoblo t analyses of hepatic subcellular fractions from ethanol-damaged liver s indicate a dramatic reduction in the association of rab2 with a Golg i compartment as compared with controls, In contrast, rab6 and alpha-m annosidase II, Golgi marker proteins, appear unchanged, These studies provide a detailed analysis of the intracellular site of ethanol-induc ed protein retention in the hepatocyte and lend novel insight into a p otential mechanism behind this impairment. The effects of ethanol expo sure on rab proteins and Golgi function are discussed.