Oroxylin A alleviates immunoparalysis of CLP mice by degrading CHOP through interacting with FBXO15

Clinical reports have found that with the improvement of treatment, most septic patients are able to survive the severe systemic inflammatory response and to enter the immunoparalysis stage. Considering that immunoparalysis leads to numerous deaths of clinical sepsis patients, alleviation of the occurrence and development of immunoparalysis has become a top priority in the treatment of sepsis. In our study, we investigate the effects of oroxylin A on sepsis in cecal ligation and puncture (CLP) mice. We find that the 60 h + 84 h (30 mg/kg) injection scheme of oroxylin A induce the production of pro-inflammatory factors, and further significantly improves the survival of CLP mice during the middle or late stages of sepsis. Mechanistically, C/EBP-homologous protein (CHOP) is upregulated and plays anti-inflammatory roles to facilitate the development of immunoparalysis in CLP mice. Oroxylin A induces the transcription of E3 ligase F-box only protein 15 gene (fbxo15), and activated FBXO15 protein binds to CHOP and further mediates the degradation of CHOP through the proteasome pathway, which eventually relieves the immunoparalysis of CLP mice. Taken together, these findings suggest oroxylin A relieves the immunoparalysis of CLP mice by degrading CHOP through interacting with FBXO15.

A Coevolved EDS1-SAG101-NRG1 Module Mediates Cell Death Signaling by TIR-Domain Immune Receptors

Plant nucleotide binding/leucine-rich repeat (NLR) immune receptors are activated by pathogen effectors to trigger host defenses and cell death. Toll-interleukin 1 receptor domain NLRs (TNLs) converge on the ENHANCED DISEASE SUSCEPTIBILITY1 (EDS1) family of lipase-like proteins for all resistance outputs. In Arabidopsis (Arabidopsis thaliana) TNL-mediated immunity, AtEDS1 heterodimers with PHYTOALEXIN DEFICIENT4 (AtPAD4) transcriptionally induced basal defenses. AtEDS1 uses the same surface to interact with PAD4-related SENESCENCE-ASSOCIATED GENE101 (AtSAG101), but the role of AtEDS1-AtSAG101 heterodimers remains unclear. We show that AtEDS1-AtSAG101 functions together with N REQUIRED GENE1 (AtNRG1) coiled-coil domain helper NLRs as a coevolved TNL cell death-signaling module. AtEDS1-AtSAG101-AtNRG1 cell death activity is transferable to the Solanaceous species Nicotiana benthamiana and cannot be substituted by AtEDS1-AtPAD4 with AtNRG1 or AtEDS1-AtSAG101 with endogenous NbNRG1. Analysis of EDS1-family evolutionary rate variation and heterodimer structure-guided phenotyping of AtEDS1 variants and AtPAD4-AtSAG101 chimeras identify closely aligned ɑ-helical coil surfaces in the AtEDS1-AtSAG101 partner C-terminal domains that are necessary for reconstituted TNL cell death signaling. Our data suggest that TNL-triggered cell death and pathogen growth restriction are determined by distinctive features of EDS1-SAG101 and EDS1-PAD4 complexes and that these signaling machineries coevolved with other components within plant species or clades to regulate downstream pathways in TNL immunity.

Identification of novel genetic risk loci in Maltese dogs with necrotizing meningoencephalitis and evidence of a shared genetic risk across toy dog breeds

Necrotizing meningoencephalitis (NME) affects toy and small breed dogs causing progressive, often fatal, inflammation and necrosis in the brain. Genetic risk loci for NME previously were identified in pug dogs, particularly associated with the dog leukocyte antigen (DLA) class II complex on chromosome 12, but have not been investigated in other susceptible breeds. We sought to evaluate Maltese and Chihuahua dogs, in addition to pug dogs, to identify novel or shared genetic risk factors for NME development. Genome-wide association testing of single nucleotide polymorphisms (SNPs) in Maltese dogs with NME identified 2 regions of genome-wide significance on chromosomes 4 (chr4:74522353T>A, p = 8.1×10⁻⁷) and 15 (chr15:53338796A>G, p = 1.5×10⁻⁷). Haplotype analysis and fine-mapping suggests that ILR7 and FBXW7, respectively, both important for regulation of immune system function, could be the underlying associated genes. Further evaluation of these regions and the previously identified DLA II locus across all three breeds, revealed an enrichment of nominal significant SNPs associated with chromosome 15 in pug dogs and DLA II in Maltese and Chihuahua dogs. Meta-analysis confirmed effect sizes the same direction in all three breeds for both the chromosome 15 and DLA II loci (p = 8.6×10^–11 and p = 2.5×10⁻⁷, respectively). This suggests a shared genetic background exists between all breeds and confers susceptibility to NME, but effect sizes might be different among breeds. In conclusion, we identified the first genetic risk factors for NME development in the Maltese, chromosome 4 and chromosome 15, and provide evidence for a shared genetic risk between breeds associated with chromosome 15 and DLA II. Last, DLA II and IL7R both have been implicated in human inflammatory diseases of the central nervous system such as multiple sclerosis, suggesting that similar pharmacotherapeutic targets across species should be investigated.

Novel approach to identifying autoantibodies in rheumatoid synovitis with a biotinylated human autoantigen library and the enzyme-labeled antigen method

Synovial tissue in rheumatoid arthritis (RA) shows dense infiltration of plasmacytes. The purpose of the present study is to identify and localize autoantibodies produced in these immunocytes in RA synovitis. We developed a novel screening system for detecting specific autoantigens. Protein antigens recognized by antibodies in the serum and synovial tissue extract from five RA patients were screened with the AlphaScreen method. For screening, a biotinylated human autoantigen library was constructed by the wheat germ cell-free protein synthesis system. The AlphaScreen analysis of 2183 proteins detected a limited number of antigens reactive with the serum and synovial tissue extract. Eighteen biotinylated proteins, containing top five showing high signals in each synovitis tissue extract, were utilized as probes for the enzyme-labeled antigen method, in order to visualize the site of specific antibody production in synovial lesions. Specific antibodies against two proteins, tripartite motif-containing 21 (TRIM21, also known as SSA/Ro52) and F-box only protein 2 (FBXO2), were visualized in the cytoplasm of plasmacytes in two RA synovitis lesions, respectively. Absorption experiments using unlabeled proteins confirmed the specificity of staining. No positive signals against these two proteins were identified in the additionally evaluated RA and osteoarthritis synovial lesions. The present study indicated 1) the usefulness of screening the human autoantigen library with the AlphaScreen assay for detecting autoantibodies in RA synovitis, and 2) the applicability of biotinylated proteins to the enzyme-labeled antigen method for visualizing the site of autoantibody production within the lesion.

GogB is an anti-inflammatory effector that limits tissue damage during Salmonella infection through interaction with human FBXO22 and Skp1

Bacterial pathogens often manipulate host immune pathways to establish acute and chronic infection. Many Gram-negative bacteria do this by secreting effector proteins through a type III secretion system that alter the host response to the pathogen. In this study, we determined that the phage-encoded GogB effector protein in Salmonella targets the host SCF E3 type ubiquitin ligase through an interaction with Skp1 and the human F-box only 22 (FBXO22) protein. Domain mapping and functional knockdown studies indicated that GogB-containing bacteria inhibited IκB degradation and NFκB activation in macrophages, which required Skp1 and a eukaryotic-like F-box motif in the C-terminal domain of GogB. GogB-deficient Salmonella were unable to limit NFκB activation, which lead to increased proinflammatory responses in infected mice accompanied by extensive tissue damage and enhanced colonization in the gut during long-term chronic infections. We conclude that GogB is an anti-inflammatory effector that helps regulate inflammation-enhanced colonization by limiting tissue damage during infection.

Bacterial pathogens have evolved sophisticated ways to subvert the innate defenses of their host. One way in which pathogens do so is by blocking or dampening the inflammatory response that is triggered once a microorganism is detected by the innate immune system. In this way, the microorganism can limit the activation of innate defenses in the host to promote its own colonization and dissemination. In this work we found that the enteric human pathogen Salmonella enterica serovar Typhimurium limits the activation of innate immune defenses in the host by using a bacterial protein called GogB to interfere with NFκB activation. NFκB is a key human transcription factor involved in the expression of pro-inflammatory cytokines during infection. In this infection situation, Salmonella delivers GogB to the infected cell where it interferes with ubiquitination of the NFκB inhibitor protein called IκBα to prevent translocation of NFκB to the nucleus where it would normally activate pro-inflammatory gene expression. The anti-inflammatory property of GogB is important for the bacteria to reach optimal infection densities in host tissues and to actively limit the tissue damage associated with prolonged inflammatory responses.

A Competitive binding mechanism between Skp1 and exportin 1 (CRM1) controls the localization of a subset of F-box proteins

SCF-type E3 ubiquitin ligases are crucial regulators of cell cycle progression. As the F-box protein is the substrate-specifying subunit of this family of ligases, their availability dictates the timing and the location of the ubiquitination of substrates. We report here our investigation into the regulation of the localization of F-box proteins, in particular Fbxo7, whose mislocalization is associated with human disease. We identified a motif in Fbxo7 that we have characterized as a functional leucine-rich nuclear export sequence (NES), and which allowed binding to the nuclear export protein, exportin 1 (CRM1). Unusually, the NES was embedded within the F-box domain, which is bound by Skp1 and enables the F-box protein to form part of an E3 ubiquitin ligase. The NES of Fbxo7 controlled its localization and was conserved in Fbxo7 homologues in other species. Skp1 binding prevented Fbxo7 from contacting CRM1. We propose that this competitive binding allowed Fbxo7 to accumulate within the nucleus starting at the G1/S transition. More than ten other F-box proteins also contain an NES at the same location in their F-box domains, indicating that this competitive binding mechanism may contribute to the regulation of a sixth of the known F-box proteins.

A role for the anaphase-promoting complex inhibitor Emi2/XErp1, a homolog of early mitotic inhibitor 1, in cytostatic factor arrest of Xenopus eggs

Unfertilized vertebrate eggs are arrested in metaphase of meiosis II with high cyclin B/Cdc2 activity to prevent parthenogenesis. Until fertilization, exit from metaphase is blocked by an activity called cytostatic factor (CSF), which stabilizes cyclin B by inhibiting the anaphase-promoting complex (APC) ubiquitin ligase. The APC inhibitor early mitotic inhibitor 1 (Emi1) was recently found to be required for maintenance of CSF arrest. We show here that exogenous Emi1 is unstable in CSF-arrested Xenopus eggs and is destroyed by the SCF(betaTrCP) ubiquitin ligase, suggesting that endogenous Emi1, an apparent 44-kDa protein, requires a stabilizing factor. However, anti-Emi1 antibodies crossreact with native Emi2/Erp1/FBXO43, a homolog of Emi1 and conserved APC inhibitor. Emi2 is stable in CSF-arrested eggs, is sufficient to prevent CSF release, and is rapidly degraded in a Polo-like kinase 1-dependent manner in response to calcium-mediated egg activation. These results identify Emi2 as a candidate CSF maintenance protein.