Attenuating ABHD17 enhances S-palmitoylation, membrane localization and signal transduction of NOD2 and Crohn's disease-associated variants.

Abstract

BACKGROUND AND AIMSNOD2 is an intracellular innate immune receptor that detects bacterial peptidoglycan fragments. Although nominally soluble, some NOD2 is associated with the plasma membrane and endosomal compartments for microbial surveillance. This membrane targeting is achieved through post-translational S- acylation of NOD2 by the protein acyltransferase ZDHHC5. Membrane attachment is necessary to initiate a signaling cascade in response to cytosolic peptidoglycan fragments. Ultimately, this signaling results in the production of antimicrobial peptides and proinflammatory cytokines. In most cases, S-acylation is a reversible post- translational modification with removal of the fatty acyl chain catalyzed by one of several acyl protein thioesterases. Deacylation of NOD2 by such an enzyme will displace it from the plasma membrane and endosomes, thus preventing signaling. METHODSTo identify the enzymes responsible for NOD2 deacylation, we used engineered cell lines with RNA interference and small-molecule inhibitors. These approaches were combined with confocal microscopy, acyl-resin-assisted capture, immunoblotting, and cytokine multiplex assays. RESULTSWe identified /{beta}-hydrolase domain-containing protein 17 isoforms (ABHD17A, ABHD17B, and ABHD17C) as the acyl protein thioesterases responsible for NOD2 deacylation. Inhibiting ABHD17 increased the plasma membrane localization of wild-type NOD2 and a subset of poorly acylated Crohns disease-associated variants. This enhanced NOD2 activity, increasing NF-{kappa}B activation and pro-inflammatory cytokine production in epithelial cells. CONCLUSIONSThese findings demonstrate that ABHD17 isoforms are negative regulators of NOD2. The results also suggest that targeting ABHD17 isoforms could restore functionality to specific Crohns disease-associated NOD2 variants, offering a potential therapeutic strategy. Grant SupportThis work was supported by a Project Grant from the Canadian Institutes of Health Research (grant no.: PJT166010; to G.D.F.), an Innovator Award from the Kenneth Rainin Foundation, and a grant from the National Institutes of Health, (R01CA193994 to B.F.C). A Tier 1 Canada Research Chair supports G.D.F. in Multiomics of Lipids and Innate Immunity. C.L.D. was supported by a Breakthrough Accelerator Fellowship from the Dalhousie Medical Research Foundation/Medical Research Development Office. N.M is a recipient of a graduate scholarship from the I3V Wave and the Dalhousie Medical Research Development Office. DisclosuresThe authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest. SYNOPSISThe peptidoglycan sensor NOD2 requires post-translational S-acylation to associate with cellular membranes and transduce signals. This study identified the ABHD17 family of thioesterases as responsible for NOD2 deacylation and inactivation. Inhibiting or silencing ABHD17 isoforms increases S-acylation and functionality of NOD2 and a subset of Crohns disease-associated variants.