Journal Article

Characterization of the Proteostasis Roles of Glycerol Accumulation, Protein Degradation and Protein Synthesis during Osmotic Stress in C. elegans

Choung-Hee Lee, Elaine, Choe, Keith P., Deonarine, Andrew, Burkewitz, Kristopher, Strange, Kevin

2012

Overview

Exposure of C. elegans to hypertonic stress-induced water loss causes rapid and widespread cellular protein damage. Survival in hypertonic environments depends critically on the ability of worm cells to detect and degrade misfolded and aggregated proteins. Acclimation of C. elegans to mild hypertonic stress suppresses protein damage and increases survival under more extreme hypertonic conditions. Suppression of protein damage in acclimated worms could be due to 1) accumulation of the chemical chaperone glycerol, 2) upregulation of protein degradation activity, and/or 3) increases in molecular chaperoning capacity of the cell. Glycerol and other chemical chaperones are widely thought to protect proteins from hypertonicity-induced damage. However, protein damage is unaffected by gene mutations that inhibit glycerol accumulation or that cause dramatic constitutive elevation of glycerol levels. Pharmacological or RNAi inhibition of proteasome and lyosome function and measurements of cellular protein degradation activity demonstrated that upregulation of protein degradation mechanisms plays no role in acclimation. Thus, changes in molecular chaperone capacity must be responsible for suppressing protein damage in acclimated worms. Transcriptional changes in chaperone expression have not been detected in C. elegans exposed to hypertonic stress. However, acclimation to mild hypertonicity inhibits protein synthesis 50-70%, which is expected to increase chaperone availability for coping with damage to existing proteins. Consistent with this idea, we found that RNAi silencing of essential translational components or acute exposure to cycloheximide results in a 50-80% suppression of hypertonicity-induced aggregation of polyglutamine-YFP (Q35::YFP). Dietary changes that increase protein production also increase Q35::YFP aggregation 70-180%. Our results demonstrate directly for the first time that inhibition of protein translation protects extant proteins from damage brought about by an environmental stressor, demonstrate important differences in aging- versus stress-induced protein damage, and challenge the widely held view that chemical chaperones are accumulated during hypertonic stress to protect protein structure/function.

• Publisher: Public Library of Science,Public Library of Science (PLoS)
• Subject: Acclimation / Acclimatization / Accumulation / Agglomeration / Aging / Animals / Autophagy / Bacterial Proteins - genetics / Bacterial Proteins - metabolism / Biodegradation / Biology / Caenorhabditis elegans / Caenorhabditis elegans - metabolism / Caenorhabditis elegans Proteins - antagonists & inhibitors / Caenorhabditis elegans Proteins - genetics / Caenorhabditis elegans Proteins - metabolism / Cell survival / Cellular proteins / Chaperones / Computer worms / Cycloheximide / Cycloheximide - pharmacology / Damage accumulation / Degradation / Diet / Environmental stress / Exposure / Gene expression / Gene mutation / Glycerol / Glycerol - metabolism / Homeostasis / Hypertonicity / Inhibition / Intracellular Signaling Peptides and Proteins - antagonists & inhibitors / Intracellular Signaling Peptides and Proteins - genetics / Intracellular Signaling Peptides and Proteins - metabolism / Laboratories / Luminescent Proteins - genetics / Luminescent Proteins - metabolism / Molecular Chaperones - metabolism / Mutation / Nematodes / Osmotic Pressure / Osmotic stress / Pathogens / Peptides - genetics / Peptides - metabolism / Pharmacology / Physiology / Polyglutamine / Proteasomes / Protein biosynthesis / Protein Biosynthesis - drug effects / Protein Folding / Protein structure / Protein synthesis / Proteins / Proteolysis / RNA Interference / RNA, Double-Stranded - metabolism / RNA-mediated interference / Stresses / Structure-function relationships / Survival / Transcription / Trinucleotide repeat diseases / Water loss / Worms