Protein palmitoylation and sphingolipid metabolism control regulated exocytosis in cytotoxic lymphocytes
Regulated exocytosis controls key cellular functions ranging from neurotransmitter release to the secretion of immune mediators and its disruption is associated with numerous pathologies. The cytotoxic activity of lymphocytes is particularly dependent on regulated and polarized lytic granule delivery towards infected or malignant cells. Although genetic and mechanistic studies have identified factors regulating exocytosis in cytotoxic lymphocytes, a systematic mapping of the relevant factors and their relationships is lacking. Through a genome-scale CRISPR knockout screen in a human natural killer cell line, we characterized a complex genetic network regulating cytotoxic granule exocytosis, with lipid metabolism and protein lipidation amongst the most prominent pathways. By combining global protein lipidation and membrane lipid composition studies, we found that ZDHHC17 drives palmitoylation of the core SNARE complex protein SNAP23 to target cytotoxic granules to GM1-rich lipid rafts whose assembly is controlled by serine palmitoyltransferase.