title: Changes in BiP availability reveal hypersensitivity to acute endoplasmic reticulum stress in cells expressing mutant huntingtin.
abstract: Huntington's disease (HD) is caused by expanded glutamine repeats within the huntingtin (Htt) protein. Mutant Htt (mHtt) in the cytoplasm has been linked to induction of the luminal endoplasmic reticulum (ER) stress pathway, the unfolded protein response (UPR). How mHtt impacts the susceptibility of the ER lumen to stress remains poorly understood. To investigate molecular differences in the ER in cells expressing mHtt, we used live-cell imaging of a sensitive reporter of the misfolded secretory protein burden, GFP fused to the ER chaperone BiP (also known as GRP78), which decreases in mobility as it binds increasing amounts of misfolded proteins. Striatal neurons expressing full-length mHtt showed no differences in BiP-GFP mobility and no evidence of UPR activation compared with wild-type cells at steady state. However, mHtt-expressing cells were acutely sensitive to misfolded secretory proteins. Treatment with ER stressors, tunicamycin or DTT, rapidly decreased BiP-GFP mobility in mHtt striatal cells and accelerated UPR activation compared with wild-type cells. mHtt-expressing cells exhibited decreased misfolded protein flux as a result of ER associated degradation (ERAD) dysfunction. Furthermore, UPR-adapted mHtt cells succumbed to misfolded protein stresses that could be tolerated by adapted wild-type cells. Thus, mHtt expression impairs misfolded secretory protein turnover, decreases the ER stress threshold, and increases cell vulnerability to insults.
authors: Department Anatomy and Structural Biology, Albert Einstein College of Medicine of Yeshiva University, Bronx, NY 10461, USA.
authors: Patrick
authors: P
authors: Lajoie
authors: Erik L
authors: EL
authors: Snapp
mesh_terms: D000818:Animals; D017209:Apoptosis; D002460:Cell Line; D000091342:Endoplasmic Reticulum Chaperone BiP; D059865:Endoplasmic Reticulum Stress; D015852:Eukaryotic Initiation Factor-2 / Q000378:metabolism; D049452:Green Fluorescent Proteins / Q000378:metabolism; D006360:Heat-Shock Proteins / Q000378:metabolism*; D006801:Humans; D000071058:Huntingtin Protein; D006816:Huntington Disease / Q000235:genetics / Q000378:metabolism; D051379:Mice; D016254:Mutagenesis, Insertional; D050505:Mutant Proteins / Q000235:genetics / Q000378:metabolism*; D009419:Nerve Tissue Proteins / Q000235:genetics / Q000378:metabolism*; D009474:Neurons / Q000378:metabolism / Q000502:physiology; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism*; D010766:Phosphorylation; D017510:Protein Folding; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D017384:Sequence Deletion; D013312:Stress, Physiological; D056811:Unfolded Protein Response
chemical_list: D000091342:Endoplasmic Reticulum Chaperone BiP; D015852:Eukaryotic Initiation Factor-2; C000717247:HSPA5 protein, human; C086055:HTT protein, human; D006360:Heat-Shock Proteins; C000717248:Hspa5 protein, mouse; D000071058:Huntingtin Protein; D050505:Mutant Proteins; D009419:Nerve Tissue Proteins; D009687:Nuclear Proteins; D011993:Recombinant Fusion Proteins; D049452:Green Fluorescent Proteins