SNX8 mediates IFNγ-triggered noncanonical signaling pathway and host defense against Listeria monocytogenes

SNX8 enables lysosome reformation and reverses lysosomal storage disorder

Lysosomal Storage Disorders (LSDs), which share common phenotypes, including enlarged lysosomes and defective lysosomal storage, are caused by mutations in lysosome-related genes. Although gene therapies and enzyme replacement therapies have been explored, there are currently no effective routine therapies against LSDs. During lysosome reformation, which occurs when the functional lysosome pool is reduced, lysosomal lipids and proteins are recycled to restore lysosome functions. Here we report that the sorting nexin protein SNX8 promotes lysosome tubulation, a process that is required for lysosome reformation, and that loss of SNX8 leads to phenotypes characteristic of LSDs in human cells. SNX8 overexpression rescued features of LSDs in cells, and AAV-based delivery of SNX8 to the brain rescued LSD phenotypes in mice. Importantly, by screening a natural compound library, we identified three small molecules that enhanced SNX8-lysosome binding and reversed LSD phenotypes in human cells and in mice. Altogether, our results provide a potential solution for the treatment of LSDs.

Estrogen receptor α-mediated signaling inhibits type I interferon response to promote breast carcinogenesis

Estrogen receptor α (ERα) is an important driver and therapeutic target in ∼70% of breast cancers. How ERα drives breast carcinogenesis is not fully understood. In this study, we show that ERα is a negative regulator of type I interferon (IFN) response. Activation of ERα by its natural ligand estradiol inhibits IFN-β-induced transcription of downstream IFN-stimulated genes (ISGs), whereas ERα deficiency or the stimulation with its antagonist fulvestrant has opposite effects. Mechanistically, ERα induces the expression of the histone 2A variant H2A.Z to restrict the engagement of the IFN-stimulated gene factor 3 (ISGF3) complex to the promoters of ISGs and also interacts with STAT2 to disrupt the assembly of the ISGF3 complex. These two events mutually lead to the inhibition of ISG transcription induced by type I IFNs. In a xenograft mouse model, fulvestrant enhances the ability of IFN-β to suppress ERα+ breast tumor growth. Consistently, clinical data analysis reveals that ERα+ breast cancer patients with higher levels of ISGs exhibit higher long-term survival rates. Taken together, our findings suggest that ERα inhibits type I IFN response via two distinct mechanisms to promote breast carcinogenesis.

Out of the ESCPE room: Emerging roles of endosomal SNX-BARs in receptor transport and host-pathogen interaction

Several functions of the human cell, such as sensing nutrients, cell movement and interaction with the surrounding environment, depend on a myriad of transmembrane proteins and their associated proteins and lipids (collectively termed "cargoes"). To successfully perform their tasks, cargo must be sorted and delivered to the right place, at the right time, and in the right amount. To achieve this, eukaryotic cells have evolved a highly organized sorting platform, the endosomal network. Here, a variety of specialized multiprotein complexes sort cargo into itineraries leading to either their degradation or their recycling to various organelles for further rounds of reuse. A key sorting complex is the Endosomal SNX-BAR Sorting Complex for Promoting Exit (ESCPE-1) that promotes the recycling of an array of cargos to the plasma membrane and/or the trans-Golgi network. ESCPE-1 recognizes a hydrophobic-based sorting motif in numerous cargoes and orchestrates their packaging into tubular carriers that pinch off from the endosome and travel to the target organelle. A wide range of pathogens mimic this sorting motif to hijack ESCPE-1 transport to promote their invasion and survival within infected cells. In other instances, ESCPE-1 exerts restrictive functions against pathogens by limiting their replication and infection. In this review, we discuss ESCPE-1 assembly and functions, with a particular focus on recent advances in the understanding of its role in membrane trafficking, cellular homeostasis and host-pathogen interaction.

Modulation of Host Antiviral Innate Immunity by African Swine Fever Virus: A Review

African swine fever (ASF), caused by African swine fever virus (ASFV), is a highly contagious and fatal disease found in swine. However, the viral proteins and mechanisms responsible for immune evasion are poorly understood, which has severely hindered the development of vaccines. This review mainly focuses on studies involving the innate antiviral immune response of the host and summarizes the latest studies on ASFV genes involved in interferon (IFN) signaling and inflammatory responses. We analyzed the effects of candidate viral proteins on ASFV infection, replication and pathogenicity and identified potential molecular targets for novel ASFV vaccines. These efforts will contribute to the construction of novel vaccines and wonder therapeutics for ASF.

IKKβ mediates homeostatic function in inflammation via competitively phosphorylating AMPK and IκBα

Inhibitor of nuclear factor kappa-B kinase subunit beta (IKKβ) is one of important kinases in inflammation to phosphorylate inhibitor of nuclear factor kappa-B (IκBα) and then activate nuclear factor kappa-B (NF-κB). Inhibition of IKKβ has been a therapeutic strategy for inflammatory and autoimmune diseases. Here we report that IKKβ is constitutively activated in healthy donors and healthy Ikkβ^C46A (cysteine 46 mutated to alanine) knock-in mice although they possess intensive IKKβ–IκBα–NF-κB signaling activation. These indicate that IKKβ activation probably plays homeostatic role instead of causing inflammation. Compared to Ikkβ^WT littermates, lipopolysaccharides (LPS) could induce high mortality rate in Ikkβ^C46A mice which is correlated to breaking the homeostasis by intensively activating p-IκBα–NF-κB signaling and inhibiting phosphorylation of 5ʹ adenosine monophosphate-activated protein kinase (p-AMPK) expression. We then demonstrated that IKKβ kinase domain (KD) phosphorylates AMPKα1 via interacting with residues Thr183, Ser184, and Thr388, while IKKβ helix–loop–helix motifs is essential to phosphorylate IκBα according to the previous reports. Kinase assay further demonstrated that IKKβ simultaneously catalyzes phosphorylation of AMPK and IκBα to mediate homeostasis. Accordingly, activation of AMPK rather than inhibition of IKKβ could substantially rescue LPS-induced mortality in Ikkβ^C46A mice by rebuilding the homeostasis. We conclude that IKKβ activates AMPK to restrict inflammation and IKKβ mediates homeostatic function in inflammation via competitively phosphorylating AMPK and IκBα.

Cloning and functional analysis of SNX8 from grass carp (Ctenopharyngodon idellus)

Sorting nexin 8 (SNX8), a member of sorting nexin protein family, plays important roles in endocytosis, endosomal sorting, and innate immune response. To date, a few homologs of SNX8 have been found in fish except in mammals. In this study, a teleost SNX8 cDNA was identified from grass carp (Ctenopharyngodon idellus). CiSNX8 was up-regulated significantly after infection with poly I:C or GCRV. We found that SNX8 was mainly distributed in the endoplasmic reticulum (ER) in CIK cells. Further analysis indicated that CiSNX8 might negatively regulate RLR signaling pathway that is quite distinct from mammalian SNX8. In addition, CiSNX8 could interact with MAVS, STING, TBK1, IRF3 and IRF7. Either wild type CiSNX8 or mutants of N-terminal PX domain (aa 1-245) and C-terminal BAR domain (aa 256-519) could associate with STING. These results suggested that fish SNX8 participated in innate immune response through different molecular mechanisms.

Fatty Acid Synthase-Suppressor Screening Identifies Sorting Nexin 8 as a Therapeutic Target for NAFLD

BACKGROUND AND AIMS

NAFLD is the most prevalent chronic liver disease without any Food and Drug Administration-approved pharmacological intervention in clinic. Fatty acid synthase (FASN) is one of the most attractive targets for NAFLD treatment because of its robust rate-limiting capacity to control hepatic de novo lipogenesis. However, the regulatory mechanisms of FASN in NAFLD and potential therapeutic strategies targeting FASN remain largely unknown.

METHODS AND RESULTS

Through a systematic interactomics analysis of FASN-complex proteins, we screened and identified sorting nexin 8 (SNX8) as a binding partner of FASN. SNX8 directly bound to FASN and promoted FASN ubiquitination and subsequent proteasomal degradation. We further demonstrated that SNX8 mediated FASN protein degradation by recruiting the E3 ligase tripartite motif containing 28 (TRIM28) and enhancing the TRIM28-FASN interaction. Notably, Snx8 interference in hepatocytes significantly deteriorated lipid accumulation in vitro, whereas SNX8 overexpression markedly blocked hepatocyte lipid deposition. Furthermore, the aggravating effect of Snx8 deletion on NAFLD was validated in vivo as hepatic steatosis and lipogenic pathways in the liver were significantly exacerbated in Snx8-knockout mice compared to wild-type controls. Consistently, hepatocyte-specific overexpression of Snx8 in vivo markedly suppressed high-fat, high-cholesterol diet (HFHC)-induced hepatic steatosis. Notably, the protective effect of SNX8 against NAFLD was largely dependent on FASN suppression.

CONCLUSIONS

These data indicate that SNX8 is a key suppressor of NAFLD that promotes FASN proteasomal degradation. Targeting the SNX8-FASN axis is a promising strategy for NAFLD prevention and treatment.

SNP prioritization in targeted sequencing data associated with humoral immune responses in chicken

Our study aimed to identify single nucleotide polymorphisms (SNPs) with a significant impact on the innate immunity represented by antibody response against lipopolysaccharide (LPS) and lipoteichoid acid (LTA) and the adaptive immune response represented toward keyhole limpet hemocyanin (KLH) using the SNP prioritization method. Data set consisted of 288 F2 experimental individuals, created by crossing Green-legged Partridgelike and White Leghorn. The analyzed SNPs were located within 24 short genomic regions of GGA1, GGA2, GGA3, GGA4, GGA9, GGA10, GGA14, GGA18, and GGZ, pre-targeted based on literature references and database information. For the specific antibody response toward KLH at d 0 the most highly prioritized SNP for additive and dominance effects were located on GGA2 in the 3’UTR of MYD88. For the response at d 7, the most highly prioritized SNP pointed at the 3’UTR of MYD88, but potential causal additive variants were located within ADIPOQ and one in PROCR. The highest priority for additive and dominance effects in the antibody response toward lipoteichoic acid at d 0 was attributed to the same SNP, located on GGA2 in the 3’UTR region of MYD88. Two SNPs among the top-10 for additive effect were located in the exon of NOCT. SNPs selected for their additive effect on antibody response toward lipopolysaccharide at d 0 marked 3 genes – NOCT, MYD88, and SNX8, while SNPs selected for their dominance effect marked – NOCT, ADIPOQ, and MYD88. The top-10 variants identified in our study were located in different functional parts of the genome. In the context of causality three groups can be distinguished: variants located in exons of protein coding genes (ADIPOQ, NOCT, PROCR, SNX8), variants within exons of non-coding transcripts, and variants located in genes’ UTR regions. Variants from the first group influence protein structure and variants from both latter groups’ exhibit regulatory roles on DNA (UTR) or RNA (lncRNA).

African swine fever virus protein MGF-505-7R promotes virulence and pathogenesis by inhibiting JAK1- and JAK2-mediated signaling

African swine fever virus (ASFV) is a large DNA virus that is highly contagious and pathogenic in domestic pigs with a mortality rate up to 100%. However, how ASFV suppresses JAK-STAT1 signaling to evade the immune response remains unclear. In this study, we found that the ASFV-encoded protein MGF-505-7R inhibited proinflammatory IFN-γ-mediated JAK-STAT1 signaling. Mechanistically, MGF-505-7R was found to interact with JAK1 and JAK2 and mediate their degradation. Further study indicated that MGF-505-7R promoted degradation of JAK1 and JAK2 by upregulating the E3 ubiquitin ligase RNF125 expression and inhibiting expression of Hes5, respectively. Consistently, MGF-505-7R-deficient ASFV induced high levels of IRF1 expression and displayed compromised replication both in primary porcine alveolar macrophages and pigs compared with wild-type ASFV. Furthermore, MGF-505-7R deficiency attenuated the virulence of the ASFV and pathogenesis of ASF in pigs. These findings suggest that the JAK-STAT1 axis mediates the innate immune response to the ASFV and that MGF-505-7R plays a critical role in the virulence of the ASFV and pathogenesis of ASF by antagonizing this axis. Thus, we conclude that deletion of MGF-505-7R may serve as a strategy to develop attenuated vaccines against the ASFV.

ZCCHC3 modulates TLR3-mediated signaling by promoting recruitment of TRIF to TLR3

Toll-like receptor 3 (TLR3)-mediated signaling is important for host defense against RNA virus. Upon viral RNA stimulation, toll and interleukin-1 receptor domain-containing adaptor inducing IFN-β (TRIF) is recruited to TLR3 and then undergoes oligomerization, which is required for the recruitment of downstream molecules to transmit signals. Here, we identified zinc finger CCHC-type containing 3 (ZCCHC3) as a positive regulator of TLR3-mediated signaling. Overexpression of ZCCHC3 promoted transcription of downstream antiviral genes stimulated by the synthetic TLR3 ligand poly(I:C). ZCCHC3-deficiency markedly inhibited TLR3- but not TLR4-mediated induction of type I interferons (IFNs) and proinflammatory cytokines. Zcchc3^−/− mice were more resistant to poly(I:C)- but not lipopolysaccharide-induced inflammatory death. Mechanistically, ZCCHC3 promoted recruitment of TRIF to TLR3 after poly(I:C) stimulation. Our findings reveal that ZCCHC3 plays an important role in TLR3-mediated innate immune response by promoting the recruitment of TRIF to TLR3 after ligand stimulation.

Temporal multiomic modeling reveals a B-cell receptor proliferative program in chronic lymphocytic leukemia

B-cell receptor (BCR) signaling is crucial for the pathophysiology of most mature B-cell lymphomas/leukemias and has emerged as a therapeutic target whose effectiveness remains limited by the occurrence of mutations. Therefore, deciphering the cellular program activated downstream this pathway has become of paramount importance for the development of innovative therapies. Using an original ex vivo model of BCR-induced proliferation of chronic lymphocytic leukemia cells, we generated 108 temporal transcriptional and proteomic profiles from 1 h up to 4 days after BCR activation. This dataset revealed a structured temporal response composed of 13,065 transcripts and 4027 proteins, comprising a leukemic proliferative signature consisting of 430 genes and 374 proteins. Mathematical modeling of this complex cellular response further highlighted a transcriptional network driven by 14 early genes linked to proteins involved in cell proliferation. This group includes expected genes (EGR1/2, NF-kB) and genes involved in NF-kB signaling modulation (TANK, ROHF) and immune evasion (KMO, IL4I1) that have not yet been associated with leukemic cells proliferation. Our study unveils the BCR-activated proliferative genetic program in primary leukemic cells. This approach combining temporal measurements with modeling allows identifying new putative targets for innovative therapy of lymphoid malignancies and also cancers dependent on ligand-receptor interactions.

Immunopathobiology and therapeutic targets related to cytokines in liver diseases

Chronic liver injury with any etiology can progress to fibrosis and the end-stage diseases cirrhosis and hepatocellular carcinoma. The progression of liver disease is controlled by a variety of factors, including liver injury, inflammatory cells, inflammatory mediators, cytokines, and the gut microbiome. In the current review, we discuss recent data on a large number of cytokines that play important roles in regulating liver injury, inflammation, fibrosis, and regeneration, with a focus on interferons and T helper (Th) 1, Th2, Th9, Th17, interleukin (IL)-1 family, IL-6 family, and IL-20 family cytokines. Hepatocytes can also produce certain cytokines (such as IL-7, IL-11, and IL-33), and the functions of these cytokines in the liver are briefly summarized. Several cytokines have great therapeutic potential, and some are currently being tested as therapeutic targets in clinical trials for the treatment of liver diseases, which are also described.

When STING Meets Viruses: Sensing, Trafficking and Response

To effectively defend against microbial pathogens, the host cells mount antiviral innate immune responses by producing interferons (IFNs), and hundreds of IFN-stimulated genes (ISGs). Upon recognition of cytoplasmic viral or bacterial DNAs and abnormal endogenous DNAs, the DNA sensor cGAS synthesizes 2',3'-cGAMP that induces STING (stimulator of interferon genes) undergoing conformational changes, cellular trafficking, and the activation of downstream factors. Therefore, STING plays a pivotal role in preventing microbial pathogen infection by sensing DNAs during pathogen invasion. This review is dedicated to the recent advances in the dynamic regulations of STING activation, intracellular trafficking, and post-translational modifications (PTMs) by the host and microbial proteins.

Thioredoxin 2 Negatively Regulates Innate Immunity to RNA Viruses by Disrupting the Assembly of the Virus-Induced Signaling Adaptor Complex

The virus-induced signaling adaptor (VISA) complex plays a critical role in the innate immune response to RNA viruses. However, the mechanism of VISA complex formation remains unclear. Here, we demonstrate that thioredoxin 2 (TRX2) interacts with VISA at mitochondria both in vivo and in vitro Knockdown and knockout of TRX2 enhanced the formation of the VISA-associated complex, as well as virus-triggered activation of interferon regulatory factor 3 (IRF3) and transcription of the interferon beta 1 (IFNB1) gene. TRX2 inhibits the formation of VISA aggregates by repressing reactive oxygen species (ROS) production, thereby disrupting the assembly of the VISA complex. Furthermore, our data suggest that the C93 residue of TRX2 is essential for inhibition of VISA aggregation, whereas the C283 residue of VISA is required for VISA aggregation. Collectively, these findings uncover a novel mechanism of TRX2 that negatively regulates VISA complex formation.IMPORTANCE The VISA-associated complex plays pivotal roles in inducing type I interferons (IFNs) and eliciting the innate antiviral response. Many host proteins are identified as VISA-associated-complex proteins, but how VISA complex formation is regulated by host proteins remains enigmatic. We identified the TRX2 protein as an important regulator of VISA complex formation. Knockout of TRX2 increases virus- or poly(I·C)-triggered induction of type I IFNs at the VISA level. Mechanistically, TRX2 inhibits the production of ROS at its C93 site, which impairs VISA aggregates at its C283 site, and subsequently impedes the assembly of the VISA complex. Our findings suggest that TRX2 plays an important role in the regulation of VISA complex assembly.

SNX8 modulates the innate immune response to RNA viruses by regulating the aggregation of VISA

The mitochondrial virus-induced signaling adaptor (VISA, also called mitochondrial antiviral signaling, MAVS) protein is a central adaptor in the innate immune response to cytosolic viral RNA. Viral infection causes the aggregation of VISA, which is important for its recruitment of downstream signaling components. How VISA aggregation is regulated remains unknown. Here, we found that sorting nexin 8 (SNX8) is a positive regulator of the RNA virus-triggered induction of downstream effector genes and innate immune response. The brains and lungs of Snx8^-/- mice infected with RNA viruses exhibited lower serum cytokine levels and higher viral titers than those of wild-type mice, resulting in higher lethality. Mechanistically, viral infection induced the translocation of SNX8 from the cytosol to mitochondria and its increased association with VISA, leading to VISA aggregation, its recruitment of downstream signaling components and the induction of downstream antiviral genes. Our findings suggest that SNX8 is a critical component of the RIG-I-like receptor (RLR)-mediated innate immune response by modulating VISA aggregation and activation.

Human Cytomegalovirus DNA Polymerase Subunit UL44 Antagonizes Antiviral Immune Responses by Suppressing IRF3- and NF-κB-Mediated Transcription

Innate immunity is the first line of host defense against viral invasion. The induction of type I interferons (IFNs) and inflammatory cytokines is essential to host antiviral immune responses, which are also key targets of viral immune evasion. Human cytomegalovirus (HCMV) can establish long-term latent infections, in which immune evasion is a pivotal step. In this study, we identified HCMV protein UL44, a DNA polymerase processivity factor, as an inhibitor of the interferon regulatory factor 3 (IRF3)- and NF-κB-dependent antiviral response. Ectopic expression of UL44 inhibited HCMV-triggered induction of downstream effector genes and enhanced viral replication. Conversely, knockdown of UL44 potentiated HCMV-triggered induction of downstream antiviral genes. UL44 interacted with IRF3 and p65, and it inhibited the binding of IRF3 and NF-κB to the promoters of their downstream antiviral genes. These findings reveal an important mechanism of immune evasion by HCMV at the transcriptional level.IMPORTANCE Induction of type I IFNs and inflammatory cytokines plays pivotal roles in host antiviral innate immune responses. Viruses have evolved various mechanisms to interfere with these processes. HCMV causes severe ailments in immunodeficient populations and is a major cause of birth defects. It has been shown that HCMV antagonizes host innate immune defenses, which is important for establishing immune evasion and latent infection. In this study, we identified the HCMV DNA polymerase subunit UL44 as a suppressor of antiviral innate immune responses. Overexpression of UL44 impaired HCMV-triggered induction of type I IFNs and other antiviral genes and thus potentiated viral replication, whereas UL44 deficiency showed opposite effects. Mechanistic studies indicated that UL44 acts by inhibiting the binding of IRF3 and NF-κB to the promoters of downstream antiviral genes. These findings defined an important mechanism of HCMV immune evasion at the transcriptional level, which may provide a therapeutic target for the treatment of HCMV infection.

SNX8 modulates innate immune response to DNA virus by mediating trafficking and activation of MITA

MITA (also called STING) is a central adaptor protein in innate immune response to cytosolic DNA. Cellular trafficking of MITA from the ER to perinuclear microsomes after DNA virus infection is critical for MITA activation and onset of innate antiviral response. Here we found that SNX8 is a component of DNA-triggered induction of downstream effector genes and innate immune response. Snx8^-/- mice infected with the DNA virus HSV-1 exhibited lower serum cytokine levels and higher viral titers in the brains, resulting in higher lethality. Mechanistically, SNX8 recruited the class III phosphatylinositol 3-kinase VPS34 to MITA, which is required for trafficking of MITA from the ER to perinuclear microsomes. Our findings suggest that SNX8 is a critical component in innate immune response to cytosolic DNA and DNA virus.

Infection by virus, such as the DNA virus herpes simplex virus 1, induces the host cells to express proteins that mediate antiviral immune response. The protein called MITA plays an essential role in the process of antiviral immune response. After viral infection, MITA traffics from the endoplasmic reticulum (ER) to perinuclear punctuate structures, a process required for its activation and induction of downstream antiviral genes. How the trafficking of MITA is regulated remains enigmatic. In this study, we found that a protein called SNX8 plays a critical role in regulation of MITA trafficking from the ER to perinuclear punctuate structures. SNX8 does this by recruiting the VPS34-containing translocon machinery to MITA. Deficiency of SNX8 impaired antiviral immune response and rendered the mice more sensitive to DNA virus-induced death. Our results suggest that SNX8 is a critical component in antiviral immune response to DNA virus.

ZCCHC3 is a co-sensor of cGAS for dsDNA recognition in innate immune response

Cyclic GMP-AMP synthase (cGAS) senses double-strand (ds) DNA in the cytosol and then catalyzes synthesis of the second messenger cGAMP, which activates the adaptor MITA/STING to initiate innate antiviral response. How cGAS activity is regulated remains enigmatic. Here, we identify ZCCHC3, a CCHC-type zinc-finger protein, as a positive regulator of cytosolic dsDNA- and DNA virus-triggered signaling. We show that ZCCHC3-deficiency inhibits dsDNA- and DNA virus-triggered induction of downstream effector genes, and that ZCCHC3-deficient mice are more susceptible to lethal herpes simplex virus type 1 or vaccinia virus infection. ZCCHC3 directly binds to dsDNA, enhances the binding of cGAS to dsDNA, and is important for cGAS activation following viral infection. Our results suggest that ZCCHC3 is a co-sensor for recognition of dsDNA by cGAS, which is important for efficient innate immune response to cytosolic dsDNA and DNA virus.

cGAS is an important mediator of antiviral immune responses, but the regulation of its activity is unknown. Here, the authors identify a zinc finger protein, ZCCHC3, that enhances the binding of cGAS to dsDNA and is important for its activation following viral infection.

Crosstalk between type I and II interferons in regulation of myeloid cell responses during bacterial infection

Type I and type II interferons (IFNα/β and IFNγ) are cytokines that play indispensable roles in directing myeloid cell activity during inflammatory and immune responses. Each IFN type binds a distinct receptor (IFNAR or IFNGR) to transduce signals that reshape gene expression and function of myeloid and other cell types. In the context of murine models and human bacterial infections, production of IFNγ generally promotes resistance while production of IFNα/β is associated with increased host susceptibility. Here, we review mechanisms of crosstalk between type I and II IFNs in myeloid cells and their impact on myeloid cell activation and anti-microbial function.