Inhibits endoplasmic reticulum (ER) stress response (By similarity). Retained in the ER under normal conditions and is up-regulated and secreted by the ER in response to ER stress and hypoxia (By similarity). Following secretion by the ER, directly binds to 3-O-sulfogalactosylceramide, a lipid sulfatide in the outer cell membrane of target cells (PubMed:29497057). Sulfatide binding promotes its cellular uptake by endocytosis, and is required for its role in alleviating ER stress under ER stress conditions (By similarity). Has a neuroprotective role, ensuring survival of dopaminergic neurons during normal growth (PubMed:30147641). Retained in the endoplasmic reticulum (ER) under normal conditions. Up-regulated and secreted by the ER in response to ER stress. Expressed in the intestine, spermatheca and nervous system (PubMed:30147641, PubMed:29497057). Expressed in the hypoderm (PubMed:29497057). Expressed in structures of the excretory system (PubMed:30147641). Not expressed in the male gonad (PubMed:30147641). Expressed throughout development, but expression declines with age (PubMed:30147641). Expressed in regions corresponding to intestinal cells and the body wall muscle quadrant in gastrulating embryos, and this continues throughout all larval stages and into adulthood in most tissues except gonadal cells (PubMed:30147641). In L4 stage larva, expressed in pharyngeal and vulval muscles (PubMed:30147641). By endoplasmic reticulum stress. Animals are viable, and despite a delay in growth rate, appear healthy and have a normal lifespan (PubMed:30147641). No defects in the axon formation or guidance of dopaminergic, GABAergic or serotinergic neurons (PubMed:30147641). However, there is an age-dependent decline in the number of viable dopaminergic neurons under normal growth conditions (PubMed:30147641). Up-regulation of ER stress response protein hsp-4 in the intestine, hypodermis and spermatheca (PubMed:30147641). RNAi-mediated knockdown results in up-regulation of hsp-4 in the intestine and pharyngeal epithelium (PubMed:29497057). Belongs to the ARMET family.