Alternative titles; symbols
HGNC Approved Gene Symbol: NLRX1
Cytogenetic location: 11q23.3 Genomic coordinates (GRCh38) : 11:119,168,334-119,184,016 (from NCBI)
Members of the nucleotide-binding domain (NBD), leucine-rich repeat (LRR)-containing protein family, or NOD-like receptors (NLRs), are innate immune receptors or regulators that are primarily associated with inflammasome function (see NLRP3, 606416). NLRs also modulate type I interferon (IFN; see 147660) production through various mechanisms. NLRX1 negatively regulates innate immune responses by inhibiting IFN and cytokine signaling (summary by Guo et al., 2016).
To study the potential role of NLR proteins in regulating mitochondrial antiviral signaling, Moore et al. (2008) used bioinformatics to identify NLRs localized in the mitochondria. They identified a putative mitochondrial NLR that they designated NLRX1, also known as CLR11.3 and NOD9 (Ting and Davis, 2005; Inohara et al., 2005). Consistent with the conserved motif structure of the NLR family, NLRX1 contains a central putative NBD and carboxy-terminal LRRs. The amino terminus contains a mitochondrial targeting sequence and 2 transmembrane regions. NLRX1 homologs were identified in all vertebrates examined, with a remarkably high (92.4%) degree of conservation between human and mouse.
The NLRX1 gene is ubiquitously expressed (Inohara et al., 2005).
Moore et al. (2008) determined that the NLRX1 gene contains 9 coding exons.
The NLRX1 gene maps to chromosome 11q23.3 (Ting and Davis, 2005; Inohara et al., 2005).
Moore et al. (2008) demonstrated that NLRX1 localizes to the mitochondrial outer membrane and interacts with MAVS (609676). Expression of NLRX1 results in the potent inhibition of RIG (609631)-like helicase (RLH) family and MAVS-mediated interferon-beta (IFNB1; 147640) promoter activity and in the disruption of virus-induced RLH-MAVS interactions. Depletion of NLRX1 with small interference RNA promoted virus-induced type I interferon (see 147570) production and decreased viral replication. Moore et al. (2008) concluded that their work identified NLRX1 as a check against mitochondrial antiviral responses and represented an intersection of 3 ancient cellular processes: NLR signaling, intracellular virus detection, and the use of mitochondria as a platform for antipathogen signaling. They also concluded that their work represented a conceptual advance, in that NLRX1 is a modulator of pathogen-associated molecular pattern receptors rather than a receptor, and identified a key therapeutic target for enhancing antiviral responses.
Using an NF-kappa-B (see 164011)-luciferase assay in human embryonic kidney cells, Xia et al. (2011) identified NLRX1 as a negative regulator of the NF-kappa-B pathway. NLRX1 inhibited NF-kappa-B activation mediated by MYD88 (602170), TRAF6 (602355), TAK1 (MAP3K7; 602614), IKKA (CHUK; 600664), and IKKB (IKBKB; 603258), but not p65 (RELA; 164014). Using wildtype and Mavs-deficient mouse embryonic fibroblasts, Xia et al. (2011) showed that Nlrx1 inhibited Il6 (147620) by a Mavs-independent pathway. In response to lipopolysaccharide (LPS) in mouse and human cells, NLRX1 appeared to inhibit NF-kappa-B signaling by dissociating from TRAF6 and interacting with TLR (see 603030)-activated IKK complex. Polyubiquitination of NLRX1 at lys63 was involved in binding of NEMO (IKBKG; 300248) to NLRX1, which facilitated the initial recruitment and stability of the NEMO/IKK complex after LPS stimulation. Coimmunoprecipitation analysis showed that the LRR domain of NLRX1 bound the kinase domain of activated IKKB. NLRX1 inhibition of IKKA and IKKB phosphorylation blocked NF-kappa-B activation in human cells, whereas knockdown of Nlrx1 in mouse cells enhanced IKK phosphorylation and NF-kappa-B-responsive genes. Xia et al. (2011) concluded that NLRX1 plays a significant role in negative regulation of NF-kappa-B signaling.
Guo et al. (2016) found that infection of a human monocyte cell line with attenuated NLRX1 expression with human immunodeficiency virus (HIV; see 609423)-vesicular stomatitis virus (VSV) pseudotype virus resulted in decreased nuclear import of HIV-1 DNA, increased IFNB mRNA and protein, and increased MX2 (147890) expression. Treatment with antibody to IFNAR1 (107450) abolished the difference in infection between wildtype and NLRX1-deficient cells. NLRX1-deficient cells generated an amplified STING (TMEM173; 612374)-dependent host response to cytosolic DNA, cyclic di-GMP, cGAMP, HIV-1, and DNA viruses. Guo et al. (2016) concluded that NLRX1 sequesters the DNA-sensing adaptor STING from interaction with TBK1 (604834) and negatively regulates host innate immune responses to HIV-1 and DNA viruses.
Xia et al. (2011) generated transgenic Nlrx1-knockdown mice constitutively expressing short hairpin RNA against mouse Nlrx1. Infection with vesicular stomatitis virus was strongly inhibited in fibroblasts from Nlrx1-knockdown mice or Nlrx1 -/- mice. However, in vivo survival was only slightly greater after viral challenge in Nlrx1-knockdown mice compared with wildtype mice. In contrast, LPS injection was rapidly lethal in Nlrx1-knockdown mice and correlated with markedly increased plasma Il6, but not Tnfa (191160) levels.
Soares et al. (2014) found that Nlrx1 -/- mice exposed to azoxymethane, a model of colorectal cancer, developed fewer tumors than wildtype mice exposed to the same chemical. In contrast, following exposure to both azoxymethane and the colitis-inducing agent dextran sulfate sodium, Nlrx1 -/- mice developed a more severe pathology than wildtype mice. Soares et al. (2014) concluded that NLRX1, a glucose-regulated molecule, is a critical mitochondrial protein involved in the regulation of apoptosis in cancer cells, but not in primary cells.
Guo et al. (2016) observed enhanced innate immune responses and reduced viral load in Nlrx1 -/- mice compared with wildtype mice infected with DNA viruses They concluded that NLRX1 is a negative regulator of the host innate immune response to HIV-1 and DNA viruses.
Using in vitro assays, Leber et al. (2017) found that mouse Nlrx1 -/- Cd4 (186940)-positive T cells had a higher rate of differentiation to inflammatory Th17-type cells (see 603149) compared with wildtype cells, whereas differentiation to inducible regulatory T (Treg) cells was similar to wildtype. Nlrx1 -/- cells also had a decreased response to immune checkpoint pathways and greater rates of lactate dehydrogenase (see LDHA, 150000) activity. Adoptive transfer of Nlrx1 -/- naive or effector cells to immunodeficient mice lacking Rag2 (179616) led to increased disease activity and effector T-cell numbers, whereas no difference was observed between mice receiving wildtype or Nlrx1 -/- Treg cells. Deletion of Nlrx1 specifically in Cd4-positive T cells resulted in increased inflammation in a bacteria-induced model of colitis. Leber et al. (2017) concluded that loss of NLRX1 in T cells promotes increased metabolic activity and a preference for lactate dehydrogenase activity, leading, along with decreased sensitivity to immunosuppressive checkpoint pathways, to greater lymphoproliferative capabilities and an inflammatory phenotype bias.
Guo, H., Konig, R., Deng, M., Riess, M., Mo, J., Zhang, L., Petrucelli, A., Yoh, S. M., Barefoot, B., Samo, M., Sempowski, G. D., Zhang, A., and 14 others. NLRX1 sequesters STING to negatively regulate the interferon response, thereby facilitating the replication of HIV-1 and DNA viruses. Cell Host Microbe 19: 515-528, 2016. [PubMed: 27078069] [Full Text: https://doi.org/10.1016/j.chom.2016.03.001]
Inohara, N., Chamaillard, M., McDonald, C., Nunez, G. NOD-LRR proteins: role in host-microbial interactions and inflammatory disease. Ann. Rev. Biochem. 74: 355-383, 2005. [PubMed: 15952891] [Full Text: https://doi.org/10.1146/annurev.biochem.74.082803.133347]
Leber, A., Hontecillas, R., Tubau-Juni, N., Zoccoli-Rodriguez, V., Hulver, M., McMillan, R., Eden, K., Allen, I. C., Bassaganya-Riera, J. NLRX1 regulates effector and metabolic functions of CD4+ T cells. J. Immun. 198: 2260-2268, 2017. [PubMed: 28159898] [Full Text: https://doi.org/10.4049/jimmunol.1601547]
Moore, C. B., Bergstralh, D. T., Duncan, J. A., Lei, Y., Morrison, T. E., Zimmermann, A. G., Accavitti-Loper, M. A., Madden, V. J., Sun, L., Ye, Z., Lich, J. D., Heise, M. T., Chen, Z., Ting, J. P.-Y. NLRX1 is a regulator of mitochondrial antiviral immunity. Nature 451: 573-577, 2008. [PubMed: 18200010] [Full Text: https://doi.org/10.1038/nature06501]
Soares, F., Tattoli, I., Rahman, M. A., Robertson, S. J., Belcheva, A., Liu, D., Streutker, C., Winer, S., Winer, D. A., Martin, A., Philpott, D. J., Arnoult, D., Girardin, S. E. The mitochondrial protein NLRX1 controls the balance between extrinsic and intrinsic apoptosis. J. Biol. Chem. 289: 19317-19330, 2014. [PubMed: 24867956] [Full Text: https://doi.org/10.1074/jbc.M114.550111]
Ting, J. P.-Y., Davis, B. K. CATERPILLER: a novel gene family important in immunity, cell death, and diseases. Annu. Rev. Immun. 23: 387-414, 2005. [PubMed: 15771576] [Full Text: https://doi.org/10.1146/annurev.immunol.23.021704.115616]
Xia, X., Cui, J., Wang, H. Y., Zhu, L., Matsueda, S., Wang, Q., Yang, X., Hong, J., Songyang, Z., Chen, Z. J., Wang, R.-F. NLRX1 negatively regulates TLR-induced NF-kappa-B signaling by targeting TRAF6 and IKK. Immunity 34: 843-853, 2011. [PubMed: 21703539] [Full Text: https://doi.org/10.1016/j.immuni.2011.02.022]