Transmembrane TNF (pro-TNF) is palmitoylated

Human transmembrane tumor necrosis factor (pro-TNF) was examined for protein acylation. The cDNA encoding pro-TNF was expressed in both COS-1 cells and Sf9 cells and metabolic labeling with [(3)H]myristic or [(3)H]palmitic acid was attempted. The 17 kDa mature TNF secreted from the transfected cells was not labeled, whereas the 26 kDa pro-TNF was specifically labeled with [(3)H]palmitic acid. The [(3)H]palmitic acid labeling of pro-TNF was eliminated by treatment with hydroxylamine, indicating that the labeling was due to palmitoylation of a cysteine residue via a thioester bond. Site-directed mutagenesis of the two cysteine residues residing in the leader sequence of pro-TNF demonstrated that palmitoylation of pro-TNF occurs solely at Cys-47, located at the boundary between the transmembrane and cytoplasmic domains of pro-TNF. Thus, pro-TNF interacts with the plasma membrane via both its proteinaceous transmembrane domain and a lipid anchor.