Osmosensitive gene expression in C. elegans is regulated by conserved signaling mechanisms that control protein translation initiation

Abstract

Osmotic homeostasis is fundamental for life. To cope with hypertonic stress (HS), C. elegans accumulates the organic osmolyte glycerol via increased expression of the glycerol synthesis enzyme GPDH‐1. We previously identified 122 rgpd (regulators of gpdh‐1) genes that when silenced constitutively activate gpdh‐1 expression and glycerol accumulation in the absence of HS. Fifty‐five rgpd genes play highly conserved roles in protein translation. Both HS and RNAi silencing of rgpd genes that encode aminoacyl‐tRNA synthetases and eukaryotic translation initiation factors (eIFs) dramatically reduce protein synthesis. Pharmacological inhibition of protein synthesis with cycloheximide or kasugamycin induces constitutive gpdh‐1 expression. eIF‐2α phosphorylation is a highly conserved signal for translation inhibition. Phospho‐eIF‐2α levels increase 2‐fold within 1 h of HS. Loss‐of‐function mutations in GCN kinases, which mediate eIF‐2α phosphorylation, inhibit HS induced gpdh‐1 expression. We suggest that components of the protein synthesis network function as part of an osmosensing and signaling circuit that detects cellular HS and activates downstream effector mechanisms including gpdh‐1 gene expression.