Genome‐wide RNAi screen identifies degradation of protein damage as a novel and essential hypertonic stress response

Abstract

Hypertonic stress causes cellular and molecular damage in animal cells. Little is known about the mechanisms that detect and repair this damage. To begin addressing this problem, we used the genetic model organism C. elegans. These free‐living nematodes experience periods of desiccation in their native environments. Under laboratory conditions, C. elegans survives extreme hypertonic stress induced by raising environmental NaCl levels. To begin identifying genetic pathways required for survival under these conditions, we screened ~19,000 C. elegans genes by RNAi feeding. This screen identified 55 genes that are essential for survival during high NaCl hypertonic stress. Interestingly, 40% of these genes (22/55) encode proteins that function to transport and degrade damaged proteins, including components of the ubiquitin‐proteasome system and lysosomes. Western analysis demonstrated that hypertonic stress increases high molecular weight ubiquitin conjugates, suggesting increased ubiquitination of damaged proteins. In addition, protein aggregation detected with a fluorescent reporter dramatically increased under hypertonic conditions. Our data suggest that hypertonicity causes protein damage that is repaired by ubiquitin‐directed degradation and provide the foundation for a comprehensive genetic, biochemical, and molecular characterization of this novel osmotic stress response.