出版社：American Society for Biochemistry and Molecular Biology
摘要：Glucosamine-induced endoplasmic reticulum (ER) stress was recentlyshown to specifically reduce apolipoprotein B-100 (apoB-100)secretion by enhancing the proteasomal degradation of apoB-100.Here, we examined the mechanisms linking glucosamine-inducedER stress and apoB-lipoprotein biogenesis. Trypsin sensitivitystudies suggested glucosamine-induced changes in apoB-100 conformation.Endoglycosidase H studies of newly synthesized apoB-100 revealedglucosamine induced N-linked glycosylation defects resultingin reduced apoB-100 secretion. We also examined glucosamine-inducedchanges in VLDL assembly and secretion. A dose-dependent (1–10mM glucosamine) reduction was observed in VLDL-apoB-100 secretionin primary hepatocytes (24.2–67.3%) and rat McA-RH7777cells (23.2–89.5%). Glucosamine also inhibited the assemblyof larger VLDL-, LDL-, and intermediate density lipoprotein-apoB-100but did not affect smaller HDL-sized apoB-100 particles. Glucosaminetreatment during the chase period (posttranslational) led toa 24% reduction in apoB-100 secretion (P < 0.01; n = 4) andpromoted post-ER apoB degradation. However, the contributionof post-ER apoB-100 degradation appeared to be quantitativelyminor. Interestingly, the glucosamine-induced posttranslationalreduction in apoB-100 secretion could be partially preventedby treatment with desferrioxamine or vitamin E. Together, thesedata suggest that cotranslational glucosamine treatment maycause defects in apoB-100 N-linked glycosylation and folding,resulting in enhanced proteasomal degradation. Posttranslationally,glucosamine may interfere with the assembly process of apoBlipoproteins, leading to post-ER degradation via nonproteasomalpathways.Supplementary key words very low density lipoprotein • hepatocytes • apolipoprotein B degredation • proteasome • glycosylation
Abbreviations: ALLN, N-acetyl-leucinyl-leucinyl-nor-leucinal; apoB-100, apolipoprotein B-100; BFA, brefeldin A; DFX, desferrioxamine; ER, endoplasmic reticulum; IDL, intermediate density lipoprotein; MTP, microsomal triglyceride transfer protein; PERPP, postendoplasmic reticulum presecretory proteolysis; TBARS, thiobarbituric acid-reactive substances
