The death receptor Fas undergoes a variety of post-translational modifications including S-palmitoylation. This protein acylation has been reported essential for an optimal cell death signaling by allowing both a proper Fas localization in cholesterol and sphingolipid-enriched membrane nanodomains, as well as Fas high-molecular weight complexes. In human, S-palmitoylation is controlled by 23 members of the DHHC family through their palmitoyl acyltransferase activity. In order to better understand the role of this post-translational modification in the regulation of the Fas-mediated apoptosis pathway, we performed a screen that allowed the identification of DHHC7 as a Fas-palmitoylating enzyme. Indeed, modifying DHHC7 expression by specific silencing or overexpression, respectively, reduces or enhances Fas palmitoylation and DHHC7 co-immunoprecipitates with Fas. At a functional level, DHHC7-mediated palmitoylation of Fas allows a proper Fas expression level by preventing its degradation through the lysosomes. Indeed, the decrease of Fas expression obtained upon loss of Fas palmitoylation can be restored by inhibiting the lysosomal degradation pathway. We describe the modification of Fas by palmitoylation as a novel mechanism for the regulation of Fas expression through its ability to circumvent its degradation by lysosomal proteolysis. Cell Death and Differentiation (2015) We demonstrated that Fas and FasL are constitutively modified by S-palmitoylation, a reversible post-translational modification that consists in the addition of a palmitic acid on the cysteine residue through a thiol linkage. [8][9][10] The palmitoylation of a protein can affect its interactions with its surrounding membrane lipids and proteins, therefore impacting certain properties such as association with specific membrane domains, trafficking between cell compartments or stability. [11][12][13] The palmitoylation reaction is catalyzed by the conserved DHHC (aspartate-histidine-histidine-cysteine) family of enzymes, which are characterized by the specific DHHC motif required for the palmitoyl acyltransferase (PAT) activity. 14 In human, the 23 members of the DHHC family described are localized to the distinct intracellular membrane compartments, mainly the Golgi apparatus and the endoplasmic reticulum where palmitoylation likely occurs. 14,15 Since their discovery in 2002, increasing numbers of DHHC-substrate pairs have been identified allowing a deeper comprehension of palmitoylation regulation. 16 Fas palmitoylation occurs on an intracellular cysteine adjacent to the transmembrane domain (cysteine 199 in human) and is critical for its ability to trigger cell death. 8,9 At the molecular level, we and others already reported that the pro-death role of Fas palmitoylation relies on (i) the formation of supramolecular Fas aggregates 9 and (ii) Fas targeting in nanodomains enriched in cholesterol and glycosphingolipids, which is a prerequisite for proper activation of Fas-induced cell death. 8,[17][18][19][20][21] In these domains and upon FasL...