In human, loss of
Acid Sphingomeylinase (ASM/SMPD1) causes
Niemann-Pick Disease, type A. ASM hydrolyzes
sphingomyelins to produce
ceramides but
protein targets of ASM remain largely unclear. Our mass-spectrometry-based proteomic analyses have identified >100
proteins associated with the ASM-dependent,
detergent-resistant membrane microdomains (
lipid rafts), with >60% of these
proteins being palmitoylated, including SNAP23,
Src-family kinases Yes and Lyn, and Ras and Rab family
small GTPases. Inactivation of ASM abolished the presence of these
proteins in the plasma membrane, with many of them trapped in the Golgi. While palmitoylation inhibitors and palmitoylation mutants phenocopied the effects of ASM inactivation, we demonstrated that ASM is required for the transport of palmitoylated
proteins, such as SNAP23 and Lyn, from the Golgi to the plasma membrane without affecting palmitoylation directly. Importantly, ASM delivered extracellularly can regulate the trafficking of SNAP23 from the Golgi to the plasma membrane. Our studies suggest that ASM, acting at the plasma membrane to produce
ceramides, regulates the localization and trafficking of the palmitoylated
proteins.