Negative regulator of the osmotic stress response. Acts via the transmembrane protein ptr-23. Expressed in the hypodermal syncitium but not in hypodermal seam cells. Expressed during larval development and strongly down-regulated in adults. Normal physiological responses to hypertonic stress, such as accumulation of organic osmolytes and activation of osmoresponsive genes, are constitutively activated with mutants exhibiting resistance to normally lethal levels of hypertonic stress.