Chronic ethanol exposure in rats affects rabs-dependent hepatic trafficking of apolipoprotein E and transferrin

Abstract 

Because of the important roles of rabs in protein trafficking, we tested whether chronic ethanol exposure affected the trafficking of newly synthesized apolipoprotein E (apoE) or transferrin (O-glycosylated and N-glycosylated proteins, respectively) attached to acylated or prenylated rabs. The in vivo 30-min incorporation ratios of [³H]palmitate:[³⁵S]methionine or [³H]mevalonate:[³⁵S]methionine (relative ratios of rabs acylation or prenylation to total protein or to immunoisolated apoE or transferrin) were measured in various hepatic subcellular organelles of 8 week-ethanol-fed (E) and pair-fed control (C) Wistar–Furth rats. With respect to total protein trafficking, ethanol increased rabs acylation ratio by 136% (P < .01), 69% (P < .05), and 64% (P < .01) in the endoplasmic reticulum (ER), Golgi light fraction (GLF), and Golgi heavy fraction (GHF), respectively, and decreased this ratio by 76% (P < .01) in carrier vesicle fraction 2 (CV2). With respect to apoE trafficking, ethanol increased rabs acylation ratio by 121% in GHF and decreased this ratio by 27% in CV2. Rabs prenylation ratio increased by 21% and 53% in GHF and CV2, respectively, and decreased by 42% in GLF. With respect to transferrin trafficking, ethanol increased rabs acylation ratio by 53% (P < .01) in GHF, with no significant effect in ER, whereas rabs prenylation ratio increased by 26% (P < .05) in ER, with no significant effect in GHF. Therefore, we conclude that ethanol-induced impaired trafficking of newly synthesized O- and N-glycosylated proteins occurs primarily in ER and Golgi and is due to altered lipidation of rabs, possibly rabs 1, 2, or 6 or combinations of these three rabs.

Keywords: ApoE, Transferrin, Rabs, Alcoholism, Protein trafficking