The solute carrier SLC15A4 is required for optimal trafficking of nucleic acid–sensing TLRs and ligands to endolysosomes

Abstract

Significance A large body of evidence has indicated that recognition of self-nucleic acids by endosomal toll-like receptors (TLRs) is central to the pathogenesis of lupus-like systemic autoimmunity in spontaneous mouse models, and the solute carrier SLC15A4 is required for this recognition. Here we describe a mechanism in which SLC15A4 is a major contributor to the proper trafficking of TLRs and their ligands to endolysosomes, wherein recognition and signaling is initiated. This finding supports ongoing efforts to identify pharmacologic inhibitors for this carrier as a means to treat lupus and other inflammatory disorders.

Chemoproteomics-guided development of SLC15A4 inhibitors with anti-inflammatory activity

“…Here, we report the development of, to our knowledge, the first SLC15A4 inhibitors. We demonstrate that our lead compound, AJ2-30, engages SLC15A4 directly in primary immune cells, inhibits TLR7-9 signaling pathways and cytokine production as well as SLC15A4-mediated NOD 1/2 activation in primary human and mouse immune cells, key functions regulated by SLC15A4 ( 1, 4, 5, 8-10 ). Our findings suggest that pharmacological inhibition of SLC15A4 results in disruption of an mTOR-IRF circuit essential for IFN-I and other inflammatory cytokine production, however the molecular details of how SLC15A4 modulates this pathway are not yet elucidated.…”

“…Mouse cells were isolated from a single cell suspension of mouse splenocytes, coming from either Wild-type C57BL/6J or feeble mice (PMID: 21045126)( 5 ) which had been back-crossed onto the C57BL/6J line. Mouse immune cells were isolated using corresponding isolation kits from StemCell Technologies.…”

“…Mice were subsequently challenged with 2 μg of CpG-A complexed with 12 μL DOTAP Liposomal transfection reagent (Roche), administered by intravenous tail vein injection as described previously. ( 5 ) 6 hours following CpG-A/DOTAP administration, blood was drawn by a retinal orbital bleed, and serum was isolated using centrifugation. Serum cytokine levels were quantitated by either Mouse IFN-Alpha ELISA Kit (pbl Assay Science) or the Bio-Plex Pro Mouse Cytokine 23-plex assay (Bio-Rad).…”

Nucleic Acid Sensing by Toll-Like Receptors in the Endosomal Compartment

“…SLC15A4 is required for TLR7 and TLR9 responses in pDCs ( 52 ). It also mediates AP3-dependent endosomal trafficking required for TLR7 and TLR9 responses ( 53 ). Moreover, SLC15A4 serves as a scaffold protein by associating with TLR adaptor interacting with SLC15A4 on the lysosome (TASL) ( 54 ), which recruits IRFs to transmit signals from TLR7, TLR8, and TLR9.…”

Methotrexate inhibition of muropeptide transporter SLC46A2 controls psoriatic skin inflammation

“…Several reports have linked the solute carrier 15 (SLC15) family of peptide transporters to cytosolic muropeptide delivery (16)(17)(18)(19)(20)(21). However, these solute carriers have not been directly demonstrated to transport muropeptides and are not specifically required for NOD signaling, but instead have recently been linked to IRF5 activation following stimulation of TLRs as well as NODs (22,23). On the other hand, we recently identified the SLC46 family as candidate muropeptide transporters in Drosophila and mammalian cells (24).…”