Systemic osmotic signaling pathways function upstream of WNK and GCK‐VI kinases to regulate hypertonic stress resistance in C. elegans

Abstract

The GCK‐VI subfamily of Ste20 kinases regulate volume‐sensitive ion channels and transporters. With no lysine (K) or WNK kinases interact with and activate the mammalian GCK‐VI kinases, PASK and OSR‐1. We recently reported that the C. elegans GCK‐VI kinase, GCK‐3, interacts and functions with the WNK kinase, WNK‐1, to regulate systemic volume and survival during hypertonic stress. The pathways that function upstream of WNK and GCK‐VI kinases are not defined. In C. elegans, cuticle collagens (e.g., DPY‐10) and novel proteins that are secreted from an epithelium near the cuticle (e.g., OSM‐11) have been postulated to be components of systemic mechanosensors that detect hypertonic shrinkage. Mutations in DPY or OSM proteins cause an osmotic stress resistant phenotype (Osr) characterized by elevated levels of the organic osmolyte glycerol and survival during exposure to hypertonic stress that is lethal to wild type worms. To determine if WNK‐1 or GCK‐3 function downstream from DPY or OSM proteins, we performed RNAi experiments. Knockdown of either kinase suppressed Osr in DPY and OSM mutants, but did not suppress glycerol accumulation or alter systemic volume. Our results demonstrate that WNK‐1 and GCK‐3 function downstream from systemic osmotic sensors to regulate hypertonic stress resistance by mechanisms that are independent from glycerol accumulation and volume regulation.