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TASL is the SLC15A4-associated adaptor for IRF5 activation by TLR7–9

ABSTRACT: Toll-like receptors (TLRs) have a crucial role in the recognition of pathogens and initiation of immune responses. Here we show that a previously uncharacterized protein encoded by CXorf21—a gene that is associated with systemic lupus erythematosus—interacts with the endolysosomal transporter SLC15A4, an essential but poorly understood component of the endolysosomal TLR machinery also linked to autoimmune disease. Loss of this type-I-interferon-inducible protein, which we refer to as ‘TLR adaptor interacting with SLC15A4 on the lysosome’ (TASL), abrogated responses to endolysosomal TLR agonists in both primary and transformed human immune cells. Deletion of SLC15A4 or TASL specifically impaired the activation of the IRF pathway without affecting NF-κB and MAPK signalling, which indicates that ligand recognition and TLR engagement in the endolysosome occurred normally. Extensive mutagenesis of TASL demonstrated that its localization and function relies on the interaction with SLC15A4. TASL contains a conserved pLxIS motif (in which p denotes a hydrophilic residue and x denotes any residue) that mediates the recruitment and activation of IRF5. This finding shows that TASL is an innate immune adaptor for TLR7, TLR8 and TLR9 signalling, revealing a clear mechanistic analogy with the IRF3 adaptors STING, MAVS and TRIF. The identification of TASL as the component that links endolysosomal TLRs to the IRF5 transcription factor via SLC15A4 provides a mechanistic explanation for the involvement of these proteins in systemic lupus erythematosus.

ORGANISM(S): Homo sapiens

PROVIDER: GSE133317 | GEO | 2020/05/13

REPOSITORIES: GEO

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Project description:Polymorphisms in the transcription factor interferon regulatory factor 5 (IRF5) are strongly associated in human genetic studies with an increased risk of developing the autoimmune disease systemic lupus erythematosus. However, the biological role of IRF5 in lupus pathogenesis, if any, is not known. In this study we show that IRF5 is absolutely required for disease development in the FcgRIIB-/-Yaa and FcgRIIB-/- lupus models. In contrast to IRF5-sufficient FcgRIIB-/-Yaa mice, IRF5-deficient FcgRIIB-/-Yaa mice do not develop lupus manifestations and have a phenotype comparable to wildtype mice. Strikingly, full expression of IRF5 is required for the development of autoimmunity, as IRF5-heterozygotes had dramatically reduced disease. One effect of IRF5 is to induce the production of the type I interferon IFN-gamma, a cytokine implicated in lupus pathogenesis. To address the mechanism by which IRF5 promotes disease, we evaluated FcgRIIB-/-Yaa mice lacking the type I interferon receptor IFNAR1. Unlike the IRF5-deficient and IRF5-heterozygous FcgRIIB-/-Yaa mice, IFNAR1-deficient FcgRIIB-/-Yaa mice maintained a substantial level of residual disease. Furthermore, in FcgRIIB-/- mice lacking Yaa, IRF5-deficiency also markedly reduced disease manifestations, indicating that the beneficial effects of IRF5 deficiency in FcgRIIB-/-Yaa mice are not due only to inhibition of the enhanced TLR7 signaling associated with the Yaa mutation. Overall, we demonstrate that IRF5 plays an essential role in lupus pathogenesis in murine models and that this is mediated through pathways beyond that of type I interferon production. The fact that even IRF5 heterozygous mice developed minimal disease makes IRF5 a particularly attractive therapeutic target. Serum samples from a total of 70 mice were run on the Utz Lab Whole Protein Autoantigen Array V1.0 (a single-color platform) in order to profile their autoantibodies against a library of autoimmune antigens. All samples were run once with no replicates. The samples consisted of the following groups: For data appearing in Figure 3D, illustrating that mice lacking IRF5 have their autoantibody levels significantly affected: R2Yaa IRF5+/+: 12 R2Yaa IRF5+/-: 11 R2Yaa IRF5-/-: 14 C57BL/6 ("WT" control): 13 Total mice (arrays) for this group: 50 For data appearing in Figure 6D, illustrating that mice lacking Ifnar1 do not have their autoantibody levels significantly affected: R2Yaa Ifnar+/+: 10 R2Yaa Ifnar-/-: 10 Total mice (arrays) for this group: 20

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TASL is the SLC15A4-associated adaptor for IRF5 activation by TLR7–9

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