title: Glucosamine-induced endoplasmic reticulum stress attenuates apolipoprotein B100 synthesis via PERK signaling.
abstract: Glucosamine impairs hepatic apolipoprotein B100 (apoB100) production by inducing endoplasmic reticulum (ER) stress and enhancing cotranslational and posttranslational apoB100 degradation (Qiu, W., R. K. Avramoglu, A. C. Rutledge, J. Tsai, and K. Adeli. Mechanisms of glucosamine-induced suppression of the hepatic assembly and secretion of apolipoprotein B-100-containing lipoproteins. J. Lipid Res. 2006. 47: 1749-1761). Here, we report that glucosamine also regulates apoB100 protein synthesis via ER-stress-induced PERK activation. Short-term (4 h) glucosamine treatment of HepG2 cells reduced both cellular (by 62%) and secreted apoB100 (by 43%) without altering apoB100 mRNA. Treatment with proteasomal inhibitors only partially prevented the suppressive effects of glucosamine, suggesting that mechanisms other than proteasomal degradation may also be involved. Glucosamine-induced ER stress was associated with a significantly reduced apoB100 synthesis with no significant change in posttranslational decay rates, suggesting that glucosamine exerted its effect early during apoB biosynthesis. The role of PERK and its substrate, alpha-subunit of eukaryotic initiation factor 2 (eIF2alpha), in the suppressive effects of glucosamine on apoB synthesis was then investigated. Coexpression of apoB15 (normally resistant to intracellular degradation) with wild-type double stranded (ds) RNA activated protein kinase (PKR)-like endoplasmic reticulum kinase (PERK) in COS-7 cells resulted in a dramatic reduction in the levels of newly synthesized apoB15. Interestingly, cotransfection with apoB15 and a kinase inactive PERK mutant (K618A) increased apoB15 expression. In addition, short-term glucosamine treatment stimulated an increase in phosphorylation of PERK and eIF2alpha. Taken together, these data suggest that in addition to the induction of ER-associated degradation and other degradative pathways, ER stress is associated with suppression of apoB synthesis via a PERK-dependent mechanism.
authors.affiliation: Molecular Structure and Function, Research Institute, The Hospital for Sick Children, University of Toronto, Ontario, M5G 1X8, Canada.
authors.forename: Wei
authors.initials: W
authors.lastname: Qiu
authors.forename: Qiaozhu
authors.initials: Q
authors.lastname: Su
authors.forename: Angela C
authors.initials: AC
authors.lastname: Rutledge
authors.forename: Jing
authors.initials: J
authors.lastname: Zhang
authors.forename: Khosrow
authors.initials: K
authors.lastname: Adeli
mesh_terms: D000111:Acetylcysteine / Q000031:analogs & derivatives / Q000494:pharmacology; D051702:Activating Transcription Factor 6 / Q000378:metabolism; D000818:Animals; D053299:Apolipoprotein B-100 / Q000096:biosynthesis* / Q000378:metabolism; D002460:Cell Line; D004721:Endoplasmic Reticulum / Q000187:drug effects* / Q000378:metabolism*; D000091342:Endoplasmic Reticulum Chaperone BiP; D004722:Endoribonucleases / Q000378:metabolism; D015852:Eukaryotic Initiation Factor-2 / Q000378:metabolism; D005786:Gene Expression Regulation / Q000187:drug effects; D005944:Glucosamine / Q000494:pharmacology*; D006360:Heat-Shock Proteins / Q000235:genetics; D006801:Humans; D007976:Leupeptins / Q000494:pharmacology; D008565:Membrane Proteins / Q000378:metabolism; D010766:Phosphorylation / Q000187:drug effects; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D012313:RNA / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects*; D013997:Time Factors; D019892:eIF-2 Kinase / Q000378:metabolism*
chemical_list: D000111:Acetylcysteine; D051702:Activating Transcription Factor 6; D053299:Apolipoprotein B-100; D000091342:Endoplasmic Reticulum Chaperone BiP; D004722:Endoribonucleases; D015852:Eukaryotic Initiation Factor-2; D005944:Glucosamine; D006360:Heat-Shock Proteins; D007976:Leupeptins; D008565:Membrane Proteins; D017346:Protein Serine-Threonine Kinases; D012313:RNA; D019892:eIF-2 Kinase; C497111:ATF6 protein, human; C063261:acetylleucyl-leucyl-norleucinal; C067713:lactacystin; C403982:ERN2 protein, human