Evolutionarily conserved WNK and Ste20 kinases are essential for acute volume recovery and survival after hypertonic shrinkage in Caenorhabditis elegans.

Members of the germinal center kinase (GCK)-VI subfamily of Ste20 kinases regulate a Caenorhabditis elegans ClC anion channel and vertebrate SLC12 cation-Cl(-) cotransporters. With no lysine (K) (WNK) protein kinases interact with and activate the mammalian GCK-VI kinases proline-alanine-rich Ste20-related kinase (PASK) and oxidative stress-responsive 1 (OSR1). We demonstrate here for the first time that GCK-VI kinases play an essential role in whole animal osmoregulation. RNA interference (RNAi) knockdown of the single C. elegans GCK-VI kinase, GCK-3, dramatically inhibits systemic volume recovery and survival after hypertonic shrinkage. Tissue-specific RNAi suggests that GCK-3 functions primarily in the hypodermis and intestine to mediate volume recovery. The single C. elegans WNK kinase, WNK-1, binds to GCK-3, and wnk-1 knockdown gives rise to a phenotype qualitatively similar to that of gck-3(RNAi) worms. Knockdown of the two kinases together has no additive effect, suggesting that WNK-1 and GCK-3 function in a common pathway. We postulate that WNK-1 functions upstream of GCK-3 in a manner similar to that postulated for its mammalian homologs. Phylogenetic analysis of kinase functional domains suggests that the interaction between GCK-VI and WNK kinases first occurred in an early metazoan and therefore likely coincided with the need of multicellular animals to tightly regulate transepithelial transport processes that mediate systemic osmotic homeostasis.