MARCH3 attenuates IL-1β-triggered inflammation by mediating K48-linked polyubiquitination and degradation of IL-1RI

YY1 induced USP13 transcriptional activation drives the malignant progression of hepatocellular carcinoma by deubiquitinating WWP1

BACKGROUND

Hepatocellular carcinoma (HCC) is the sixth most prevalent cancer globally and the third leading cause of cancer-related mortality. Protein ubiquitination and deubiquitination play vital roles in human cancers. Ubiquitin-specific protease 13 (USP13) is a deubiquitinating enzyme (DUB) that is involved in many cellular processes. However, the mechanism by which USP13 regulates deubiquitination remains largely unknown.

METHODS

Clinical data were analyzed via online databases. USP13 expression in HCC cell lines and tissues was analyzed via western blotting and immunohistochemistry. A lentivirus was used to established stable USP13-knockdown and USP13-overexpression cells. Cell Counting Kit-8, colony formation, wound healing, Transwell, and sphere formation assays were used to detect the malignant behaviors of HCC cells in vitro. A subcutaneous mouse model was used to investigate the function of USP13 in vivo. Co-immunoprecipitation, chromatin immunoprecipitation and dual-luciferase reporter assays were conducted to explore the molecular regulation.

RESULTS

USP13 was upregulated in HCC cell lines and tissues, which predicted a poor prognosis in patients with HCC. Functional experiments in which USP13 was overexpressed or depleted revealed the oncogenic role of USP13 in driving HCC progression both in vitro and in vivo. Mechanistically, WW domain-containing ubiquitin E3 ligase 1 (WWP1) was identified as a binding protein of USP13. Furthermore, USP13 can interact with WWP1 and then remove the K29- and K48-linked polyubiquitination chains from WWP1 to stabilize the WWP1 protein via the ubiquitin-proteasome pathway. Moreover, Yin Yang 1 (YY1) was explored as a new transcription factor of USP13, and YY1 could also upregulate WWP1 expression through USP13. Moreover, YY1 and WWP1 were shown to participate in the oncogenic role of USP13.

CONCLUSIONS

Our findings revealed the functional YY1/USP13/WWP1 signaling axis in HCC, identifying a promising therapeutic target for anti-HCC treatment.

Role of MARCH E3 ubiquitin ligases in cancer development

Membrane-associated RING-CH (MARCH) E3 ubiquitin ligases, a family of RING-type E3 ubiquitin ligases, have garnered increased attention for their indispensable roles in immune regulation, inflammation, mitochondrial dynamics, and lipid metabolism. The MARCH E3 ligase family consists of eleven distinct members, and the dysregulation of many of these members has been documented in several human malignancies. Over the past two decades, extensive research has revealed that MARCH E3 ligases play pivotal roles in cancer progression by ubiquitinating key oncogenes and tumor suppressors and orchestrating various signaling pathways. Some MARCH E3s act as oncogenes, while others act as tumor suppressors, and the majority of MARCH E3s play both oncogenic and tumor suppressive roles in a context-dependent manner. Notably, there is special emphasis on the sole mitochondrial MARCH E3 ligase MARCH5, which regulates mitochondrial homeostasis within cancer cells. In this review, we delve into the diverse functions of MARCH E3 ligases across different cancer types, shedding light on the underlying molecular mechanisms mediating their effects, their regulatory effects on cancer and their potential as therapeutic targets.

MARCH8 Mediates K27-Linked Polyubiquitination of IL-7 Receptor α to Negatively Regulate IL-7-Triggered T Cell Homeostasis

IL-7 is a cytokine produced by stromal cells, which binds to IL-7Rα and plays an important role for homeostasis of T lymphocytes. Excessive activities of IL-7-triggered signaling pathways causes autoimmune diseases. How IL-7-triggered signaling and immune effects are regulated is not fully understood. In this study, we show that the membrane-associated RING-CH (MARCH) E3 ligase family member MARCH8 mediates K27-linked polyubiquitination of IL-7Rα, leading to its lysosomal degradation. Site-directed mutagenesis suggests that MARCH8 meditates polyubiquitination of IL-7Rα at K265/K266, and mutation of these residues renders IL-7Rα resistance to MARCH8-mediated polyubiquitination and degradation. MARCH8 deficiency increases IL-7-triggered activation of the downstream transcription factor STAT5 and transcriptional induction of the effector genes in human T lymphoma cells. MARCH8 deficiency also promotes IL-7-triggered T cell proliferation and splenic memory CD8+ T cell differentiation in mice. Our findings suggest that MARCH8 negatively regulates IL-7-triggered signaling by mediating K27-linked polyubiquitination and lysosomal degradation of IL-7Rα, which reveals a negative regulatory mechanism of IL-7-triggered T cell homeostasis.

IL6 Derived from Macrophages under Intermittent Hypoxia Exacerbates NAFLD by Promoting Ferroptosis via MARCH3-Led Ubiquitylation of GPX4

Obstructive sleep apnea (OSA) is a common sleep disorder characterized by intermittent hypoxia (IH) and is associated with the occurrence and development of nonalcoholic fatty liver disease (NAFLD). However, the specific mechanism by which OSA induces NAFLD remains unclear. Therefore, effective interventions are lacking. This study aims to investigate the role and mechanism of ferroptosis in OSA-related NAFLD using clinical data analyses, cell-based molecular experiments, and animal experiments. Indicators of liver function, lipid accumulation, and ferroptosis are also examined. RNA-seq, qPCR, western blotting, gene intervention, and E3 ligase prediction using UbiBrowser and co-IP are used to explore the potential underlying mechanisms. The results show that ferroptosis increases in the liver tissues of patients with OSA. Chronic IH promotes NAFLD progression in mice and is alleviated by a ferroptosis inhibitor Fer-1. The increased secretion of IL6 by macrophages can promote the expression of MARCH3 in hepatocytes under intermittent conditions, and subsequently promote the ubiquitination and degradation of GPX4 to regulate ferroptosis and lipid accumulation in hepatocytes. Hence, targeted inhibition of MARCH3 may alleviate IH-induced ferroptosis and lipid accumulation in liver tissues and inhibit the progression of NAFLD.

Exosomes Derived From Cerulein-Stimulated Pancreatic Acinar Cells Mediate Peritoneal Macrophage M1 Polarization and Pyroptosis via an miR-24-3p/MARCH3/NLRP3 Axis in Acute Pancreatitis

OBJECTIVES

Acute pancreatitis (AP) has a high incidence of hospitalizations, morbidity, and mortality worldwide. A growing number of studies on AP pathogenesis are based on cerulein-induced experimental model, which simulates human AP in vivo. It has been demonstrated that both pancreatic acinar cells and peritoneal macrophages are involved in pancreatic inflammation and damage. However, their connection has not been well understood.

METHODS

A cerulein-induced AP model was established on the pancreatic acinar cell line AR42J. Rat macrophages were isolated from the peritoneal cavity. The effects of cerulein-induced pancreatic exosomes on the peritoneal macrophage and pancreas in vivo and in vitro were examined. The underlying molecular mechanism was investigated by exploring the regulatory role of downstream molecules.

RESULTS

We found that exosomes derived from cerulein-treated AR42J cells induced rat peritoneal macrophage M1 polarization and pyroptosis. miR-24-3p was upregulated in cerulein-stimulated exosomes, whereas the miR-24-3p inhibitor counteracted the effect of pancreatic exosomes on peritoneal macrophage M1 polarization and pyroptosis. Furthermore, miR-24-3p inhibited March3 expression, whereas MARCH3 mediated NLRP3 ubiquitination in rat peritoneal macrophages, which, in turn, contributed to the apoptosis, reactive oxygen species production, and inflammation in AR42J cells.

CONCLUSIONS

Exosomes derived from cerulein-stimulated pancreatic acinar cells mediate peritoneal macrophage M1 polarization and pyroptosis via an miR-24-3p/MARCH3/NLRP3 axis in AP.

LincR-PPP2R5C regulates IL-1β ubiquitination in macrophages and promotes airway inflammation and emphysema in a murine model of COPD

Chronic obstructive pulmonary disease (COPD) is a common disease with high global morbidity and mortality. Macrophages release IL-1β and orchestrate airway inflammation in COPD. Previously, we explored the role of a new lncRNA, LincR-PPP2R5C, in regulating Th2 cells in asthma. Here, we established a murine model of COPD and explored the roles and mechanisms by which LincR-PPP2R5C regulates IL-1β in macrophages. LincR-PPP2R5C was highly expressed in pulmonary macrophages from COPD-like mice. LincR-PPP2R5C deficiency ameliorated emphysema and pulmonary inflammation, as characterized by reduced IL-1β in macrophages. Unexpectedly, in both lung tissues and macrophages, LincR-PPP2R5C deficiency decreased the expression of the IL-1β protein but not the IL-1β mRNA. Furthermore, we found that LincR-PPP2R5C deficiency increased the level of ubiquitinated IL-1β in macrophages, which was mediated by PP2A activity. Targeting PP2A with FTY720 decreased IL-1β and improved COPD. In conclusion, LincR-PPP2R5C regulates IL-1β ubiquitination by affecting PP2A activity in macrophages, contributing to the airway inflammation and emphysema in a murine model of COPD. PP2A and IL-1β ubiquitination in macrophages might be new therapeutic avenues for COPD therapy.

Anaplastic Lymphoma Kinase signaling stabilizes SLC3A2 expression via MARCH11 to promote neuroblastoma cell growth

Solute Carrier Family 3, Member 2 (SLC3A2 or 4F2hc) is a multifunctional glycoprotein that mediates integrin-dependent signaling, acts as a trafficking chaperone for amino acid transporters, and is involved in polyamine transportation. We identified SLC3A2 as a potential Anaplastic Lymphoma Kinase (ALK) interacting partner in a BioID-proximity labeling screen in neuroblastoma (NB) cells. In this work we show that endogenous SLC3A2 and ALK interact in NB cells and that this SLC3A2:ALK interaction was abrogated upon treatment with the ALK inhibitor lorlatinib. We show here that loss of ALK activity leads to decreased SLC3A2 expression and reduced SLC3A2 protein stability in a panel of NB cell lines, while stimulation of ALK with ALKAL2 ligand resulted in increased SLC3A2 protein levels. We further identified MARCH11, an E3 ligase, as a regulator of SLC3A2 ubiquitination downstream of ALK. Further, knockdown of SLC3A2 resulted in inhibition of NB cell growth. To investigate the therapeutic potential of SLC3A2 targeting, we performed monotreatment of NB cells with AMXT-1501 (a polyamine transport inhibitor), which showed only moderate effects in NB cells. In contrast, a combination lorlatinib/AMXT-1501 treatment resulted in synergistic inhibition of cell growth in ALK-driven NB cell lines. Taken together, our results identify a novel role for the ALK receptor tyrosine kinase (RTK), working in concert with the MARCH11 E3 ligase, in regulating SLC3A2 protein stability and function in NB cells. The synergistic effect of combined ALK and polyamine transport inhibition shows that ALK/MARCH11/SLC3A2 regulation of amino acid transport is important for oncogenic growth and survival in NB cells.

IL-1β promotes esophageal squamous cell carcinoma growth and metastasis through FOXO3A by activating the PI3K/AKT pathway

Esophageal cancer is a common type of cancer that poses a significant threat to human health. While the pro-inflammatory cytokine IL-1β has been known to contribute to the development of various types of tumors, its role in regulating esophageal cancer progression has not been extensively studied. Our studies found that the expression of IL-1β and FOXO3A was increased in esophageal squamous cell carcinoma (ESCC). IL-1β not only increased the proliferation, migration, and invasion of two ESCC cell lines but also promoted tumor growth and metastasis in nude mice. We also observed that IL-1β and FOXO3A regulated the process of epithelial-mesenchymal transition (EMT) and autophagy. The PI3K/AKT pathway was found to be involved in the changes of FOXO3A with the expression level of IL-1β. The AKT agonist (SC79) reversed the reduction of FOXO3A expression caused by the knockdown of IL-1β, indicating that IL-1β plays a role through the PI3K/AKT/FOXO3A pathway. Furthermore, the knockdown of FOXO3A inhibited ESCC development and attenuated the pro-cancer effect of overexpressed IL-1β. Targeting IL-1β and FOXO3A may be potentially valuable for the diagnosis and treatment of ESCC.

Peptide-based allosteric inhibitor targets TNFR1 conformationally active region and disables receptor-ligand signaling complex

Tumor necrosis factor (TNF) receptor 1 (TNFR1) plays a pivotal role in mediating TNF induced downstream signaling and regulating inflammatory response. Recent studies have suggested that TNFR1 activation involves conformational rearrangements of preligand assembled receptor dimers and targeting receptor conformational dynamics is a viable strategy to modulate TNFR1 signaling. Here, we used a combination of biophysical, biochemical, and cellular assays, as well as molecular dynamics simulation to show that an anti-inflammatory peptide (FKCRRWQWRMKK), which we termed FKC, inhibits TNFR1 activation allosterically by altering the conformational states of the receptor dimer without blocking receptor-ligand interaction or disrupting receptor dimerization. We also demonstrated the efficacy of FKC by showing that the peptide inhibits TNFR1 signaling in HEK293 cells and attenuates inflammation in mice with intraperitoneal TNF injection. Mechanistically, we found that FKC binds to TNFR1 cysteine-rich domains (CRD2/3) and perturbs the conformational dynamics required for receptor activation. Importantly, FKC increases the frequency in the opening of both CRD2/3 and CRD4 in the receptor dimer, as well as induces a conformational opening in the cytosolic regions of the receptor. This results in an inhibitory conformational state that impedes the recruitment of downstream signaling molecules. Together, these data provide evidence on the feasibility of targeting TNFR1 conformationally active region and open new avenues for receptor-specific inhibition of TNFR1 signaling.

BLK positively regulates TLR/IL-1R signaling by catalyzing TOLLIP phosphorylation

TLR/IL-1R signaling plays a critical role in sensing various harmful foreign pathogens and mounting efficient innate and adaptive immune responses, and it is tightly controlled by intracellular regulators at multiple levels. In particular, TOLLIP forms a constitutive complex with IRAK1 and sequesters it in the cytosol to maintain the kinase in an inactive conformation under unstimulated conditions. However, the underlying mechanisms by which IRAK1 dissociates from TOLLIP to activate TLR/IL-1R signaling remain obscure. Herein, we show that BLK positively regulates TLR/IL-1R-mediated inflammatory response. BLK-deficient mice produce less inflammatory cytokines and are more resistant to death upon IL-1β challenge. Mechanistically, BLK is preassociated with IL1R1 and IL1RAcP in resting cells. IL-1β stimulation induces heterodimerization of IL1R1 and IL1RAcP, which further triggers BLK autophosphorylation at Y309. Activated BLK directly phosphorylates TOLLIP at Y76/86/152 and further promotes TOLLIP dissociation from IRAK1, thereby facilitating TLR/IL-1R-mediated signal transduction. Overall, these findings highlight the importance of BLK as an active regulatory component in TLR/IL-1R signaling.

Human MARCH1, 2, and 8 block Ebola virus envelope glycoprotein cleavage via targeting furin P domain

Membrane-associated RING-CH (MARCH) family proteins were recently reported to inhibit viral replication through multiple modes. Previous work showed that human MARCH8 blocked Ebola virus (EBOV) glycoprotein (GP) maturation. Our study here demonstrates that human MARCH1 and MARCH2 share a similar pattern to MARCH8 in restricting EBOV GP-pseudotyped viral infection. Human MARCH1 and MARCH2 retain EBOV GP at the trans-Golgi network, reduce its cell surface display, and impair EBOV GP-pseudotyped virions infectivity. Furthermore, we uncover that the host proprotein convertase furin could interact with human MARCH1/2 and EBOV GP intracellularly. Importantly, the furin P domain is verified to be recognized by MARCH1/2/8, which is critical for their blocking activities. Besides, bovine MARCH2 and murine MARCH1 also impair EBOV GP proteolytic processing. Altogether, our findings confirm that MARCH1/2 proteins of different mammalian origins showed a relatively conserved feature in blocking EBOV GP cleavage, which could provide clues for subsequent MARCHs antiviral studies and may facilitate the development of novel strategies to antagonize enveloped virus infection.

ANGPTL3 negatively regulates IL-1β-induced NF-κB activation by inhibiting the IL1R1-associated signaling complex assembly

Interleukin-1β (IL-1β)-induced signaling is one of the most important pathways in regulating inflammation and immunity. The assembly of the receptor complex, consisting of the ligand IL-1β, the IL-1 receptor (IL-1R) type 1 (IL1R1), and the IL-1R accessory protein (IL1RAP), initiates this signaling. However, how the IL1R1-associated complex is regulated remains elusive. Angiopoietin like 3 (ANGPTL3), a key inhibitor of plasma triglyceride clearance, is mainly expressed in the liver and exists in both intracellular and extracellular secreted forms. Currently, ANGPTL3 has emerged as a highly promising drug target for hypertriglyceridemia and associated cardiovascular diseases. However, most studies have focused on the secreted form of ANGPTL3, while its intracellular role is still largely unknown. Here, we report that intracellular ANGPTL3 acts as a negative regulator of IL-1β-triggered signaling. Overexpression of ANGPTL3 inhibited IL-1β-induced NF-κB activation and the transcription of inflammatory genes in HepG2, THP1, and HEK293T cells, while knockdown or knockout of ANGPTL3 resulted in opposite effects. Mechanistically, ANGPTL3 interacted with IL1R1 and IL1RAP through its intracellular C-terminal fibrinogen-like domain and disrupted the assembly of the IL1R1-associated complex. Taken together, our study reveals a novel role for ANGPTL3 in inflammation, whereby it inhibits the physiological interaction between IL1R1 and IL1RAP to maintain immune tolerance and homeostasis in the liver.

RNF173 suppresses RAF/MEK/ERK signaling to regulate invasion and metastasis via GRB2 ubiquitination in Hepatocellular Carcinoma

BACKGROUND

The role of the membrane-associated RING-CH (MARCH) family in carcinogenesis has been widely studied, but the member of this family, RNF173, has not yet been thoroughly explored in the context of hepatocellular carcinoma (HCC).

METHODS

With the use of an HCC tissue microarray and IHC staining, we aim to determine the differential expression of RNF173 in HCC patients and its clinical significance. The biological role of RNF173 is investigated through in vitro and in vivo experiments. RNA sequencing, mass spectrometry, and immunoprecipitation are performed to uncover the underlying mechanism of RNF173's impact on the development of HCC.

RESULTS

The mRNA and protein levels of RNF173 were significantly lower in HCC tissues than in normal tissues. HCC patients with low RNF173 expression had shorter overall survival and recurrence-free survival, and RNF173 was significantly correlated with tumor number, tumor capsule, tumor differentiation, and BCLC stage. In addition, in vitro and in vivo experiments showed that RNF173 downregulation exacerbated tumor progression, including migration, invasion, and proliferation. GRB2 is a key molecule in the RAF/MEK/ERK pathway. RNF173 inhibits the RAF/MEK/ERK signaling by ubiquitinating and degrading GRB2, thereby suppressing HCC cell proliferation, invasion and migration. Combining clinical samples, we found that HCC patients with high RNF173 and low GRB2 expression had the best prognosis.

CONCLUSION

RNF173 inhibits the invasion and metastasis of HCC by ubiquitinating and degrading GRB2, thereby suppressing the RAF/MEK/ERK signaling pathway. RNF173 is an independent risk factor for the survival and recurrence of HCC patients. RNF173 may serve as a novel prognostic molecule and potential therapeutic target for HCC. Video Abstract Graphical abstract Model of RNF173 on RAF/MEK/ERK signaling. RNF173 knockdown resulted in impaired ubiquitination and degradation of GRB2, leading to the activation of the RAF/MEK/ERK signaling pathway and promotion of invasion and metastasis in HCC cells.

Membrane compartmentalisation of the ubiquitin system

We now have a comprehensive inventory of ubiquitin system components. Understanding of any system also needs an appreciation of how components are organised together. Quantitative proteomics has provided us with a census of their relative populations in several model cell types. Here, by examining large scale unbiased data sets, we seek to identify and map those components, which principally reside on the major organelles of the endomembrane system. We present the consensus distribution of > 50 ubiquitin modifying enzymes, E2s, E3s and DUBs, that possess transmembrane domains. This analysis reveals that the ER and endosomal compartments have a diverse cast of resident E3s, whilst the Golgi and mitochondria operate with a more restricted palette. We describe key functions of ubiquitylation that are specific to each compartment and relate this to their signature complement of ubiquitin modifying components.

Analysis of long non-coding RNA expression profile of bovine monocyte-macrophage infected by Mycobacterium avium subsp. paratuberculosis

Mycobacterium avium subsp. paratuberculosis (MAP) is the causative agent of paratuberculosis. As a potential zoonotic pathogen, MAP also seriously threatens human health and social security. At present, long non-coding RNA (lncRNA) has attracted wide attention as an useful biomarker in various diseases. Therefore, our study analyzed the lncRNA expression profiles and lncRNA-mRNA regulatory network of MAP infected bovine monocytes-macrophages and uninfected bovine cells by high-throughput sequencing. A total of 4641 differentially expressed lncRNAs genes were identified, including 3111 up-regulated genes and 1530 down-regulated genes. In addition, lncRNA-mRNA interaction analysis was performed to predict the target genes of lncRNA. Among them, after MAP infection, 86 lncRNAs targeted to mRNA, of which only 6 genes were significantly different. The results of Gene Ontology (GO) enrichment analysis showed that the differentially expressed genes significantly enriched in functional groups were related to immune regulation. Multiple signal pathways including NF-κB, NOD-like receptor, Cytokine-cytokine receptor, Toll-like receptor signaling pathway, Chemokine signaling pathway, and other important biochemical, metabolic and signal transduction pathways were enriched in Kyoto Encyclopedia of Genes and Genomes (KEGG). In this study, analysis of macrophage transcriptomes in response to MAP infection is expected to provide key information to deeply understand role of the pathogen in initiating an inappropriate and persistent infection in susceptible hosts and molecular mechanisms that might underlie the early phases of paratuberculosis.

The membrane-associated ubiquitin ligases MARCH2 and MARCH3 target IL-5 receptor alpha to negatively regulate eosinophilic airway inflammation

Interleukin 5 (IL-5) plays crucial roles in type 2-high asthma by mediating eosinophil maturation, activation, chemotaxis and survival. Inhibition of IL-5 signaling is considered a strategy for asthma treatment. Here, we identified MARCH2 and MARCH3 as critical negative regulators of IL-5-triggered signaling. MARCH2 and MARCH3 associate with the IL-5 receptor α chain (IL-5Rα) and mediate its K27-linked polyubiquitination at K379 and K383, respectively, and its subsequent lysosomal degradation. Deficiency of MARCH2 or MARCH3 modestly increases the level of IL-5Rα and enhances IL-5-induced signaling, whereas double knockout of MARCH2/3 has a more dramatic effect. March2/3 double knockout markedly increases the proportions of eosinophils in the bone marrow and peripheral blood in mice. Double knockout of March2/3 aggravates ovalbumin (OVA)-induced eosinophilia and causes increased inflammatory cell infiltration, peribronchial mucus secretion and production of Th2 cytokines. Neutralization of Il-5 attenuates OVA-induced airway inflammation and the enhanced effects of March2/3 double deficiency. These findings suggest that MARCH2 and MARCH3 play redundant roles in targeting IL-5Rα for degradation and negatively regulating allergic airway inflammation.

Functional characterization of Vibrio alginolyticus T3SS regulator ExsA and evaluation of its mutant as a live attenuated vaccine candidate in zebrafish (Danio rerio) model

Vibrio alginolyticus, a Gram-negative bacterium, is an opportunistic pathogen of both marine animals and humans, resulting in significant losses in the aquaculture industry. Type III secretion system (T3SS) is a crucial virulence mechanism of V. alginolyticus. In this study, the T3SS regulatory gene exsA, which was cloned from V. alginolyticus wild-type strain HY9901, is 861 bp encoding a protein of 286 amino acids. The ΔexsA was constructed by homologous recombination and Overlap-PCR. Although there was no difference in growth between HY9901 and ΔexsA, the ΔexsA exhibited significantly decreased extracellular protease activity and biofilm formation. Besides, the ΔexsA showed a weakened swarming phenotype and an ~100-fold decrease in virulence to zebrafish. Antibiotic susceptibility testing showed the HY9901ΔexsA was more sensitive to kanamycin, minocycline, tetracycline, gentamicin, doxycycline and neomycin. Compared to HY9901 there were 541 up-regulated genes and 663 down-regulated genes in ΔexsA, screened by transcriptome sequencing. qRT-PCR and β-galactosidase reporter assays were used to analyze the transcription levels of hop gene revealing that exsA gene could facilitate the expression of hop gene. Finally, Danio rerio, vaccinated with ΔexsA through intramuscular injection, induced a relative percent survival (RPS) value of 66.7% after challenging with HY9901 wild type strain. qRT-PCR assays showed that vaccination with ΔexsA increased the expression of immune-related genes, including GATA-1, IL6, IgM, and TNF-α in zebrafish. In summary, these results demonstrate the importance of exsA in V. alginolyticus and provide a basis for further investigations into the virulence and infection mechanism.

Inosine Pretreatment Attenuates LPS-Induced Lung Injury through Regulating the TLR4/MyD88/NF-κB Signaling Pathway In Vivo

Inosine is a type of purine nucleoside, which is considered to a physiological energy source, and exerts a widely range of anti-inflammatory efficacy. The TLR4/MyD88/NF-κB signaling pathway is essential for preventing host oxidative stresses and inflammation, and represents a promising target for host-directed strategies to improve some forms of disease-related inflammation. In the present study, the results showed that inosine pre-intervention significantly suppressed the pulmonary elevation of pro-inflammatory cytokines (including tumor necrosis factor-α (TNF-α) and interleukin-1β (IL-1β)), malondialdehyde (MDA), nitric oxide (NO), and reactive oxygen species (ROS) levels, and restored the pulmonary catalase (CAT), glutathione peroxidase (GSH-Px), superoxide dismutase (SOD), and myeloperoxidase (MPO) activities (p < 0.05) in lipopolysaccharide (LPS)-treated mice. Simultaneously, inosine pre-intervention shifted the composition of the intestinal microbiota by decreasing the ratio of Firmicutes/Bacteroidetes, elevating the relative abundance of Tenericutes and Deferribacteres. Moreover, inosine pretreatment affected the TLR4/MyD88/NF-κB signaling pathway in the pulmonary inflammatory response, and then regulated the expression of pulmonary iNOS, COX2, Nrf2, HO-1, TNF-α, IL-1β, and IL-6 levels. These findings suggest that oral administration of inosine pretreatment attenuates LPS-induced pulmonary inflammatory response by regulating the TLR4/MyD88/NF-κB signaling pathway, and ameliorates intestinal microbiota disorder.

Notoginsenoside R1-loaded mesoporous silica nanoparticles targeting the site of injury through inflammatory cells improves heart repair after myocardial infarction

Notoginsenoside R1 (NGR1) is the main monomeric component extracted from the dried roots and rhizomes of Panax notoginseng, and exerts pharmacological action against myocardial infarction (MI). Owing to the differences in compound distribution, absorption, and metabolism in vivo, exploring a more effective drug delivery system with a high therapeutic targeting effect is crucial. In the early stages of MI, CD11b-expressing monocytes and neutrophils accumulate at infarct sites. Thus, we designed a mesoporous silica nanoparticle-conjugated CD11b antibody with loaded NGR1 (MSN-NGR1-CD11b antibody), which allowed NGR1 precise targeted delivery to the heart in a noninvasively manner. By increasing targeting to the injured myocardium, intravenous injection of MSN-NGR1-CD11b antibody nanoparticle in MI mice improved cardiac function and angiogenesis, reduced cell apoptosis, and regulate macrophage phenotype and inflammatory factors and chemokines. In order to further explore the mechanism of NGR1 protecting myocardium, cell oxidative stress model and oxygen-glucose deprivation (OGD) model were established. NGR1 protected H9C2 cells and primary cardiomyocytes against oxidative injury induced by H₂O₂ and OGD treatment. Further network pharmacology and molecular docking analyses suggested that the AKT, MAPK and Hippo signaling pathways were involved in the regulation of NGR1 in myocardial protection. Indeed, NGR1 could elevate the levels of p-Akt and p-ERK, and promote the nuclear translocation of YAP. Furthermore, LY294002 (AKT inhibitor), U0126 (ERK1/2 inhibitor) and Verteporfin (YAP inhibitor) administration in H9C2 cells indicated the involvement of AKT, MAPK and Hippo signaling pathways in NGR1 effects. Meanwhile, MSN-NGR1-CD11b antibody nanoparticles enhanced the activation of AKT and MAPK signaling pathways and the nuclear translocation of YAP at the infarcted site. Our research demonstrated that MSN-NGR1-CD11b antibody nanoparticle injection after MI enhanced the targeting of NGR1 to the infarcted myocardium and improved cardiac function. More importantly, our pioneering research provides a new strategy for targeting drug delivery systems to the ischemic niche.

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CD11b antibody modification enhanced the target of Mesoporous silica nanoparticles to injured myocardium.

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NGR1 promoted the survival of H9C2 against oxidative stress injury through PIK3/AKT, MAPK/ERK and YAP signaling pathways.

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NGR1 protected neonatal and adult cardiomyocytes from H₂O₂ and OGD induced oxidative stress damage.

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MSN-NGR1-CD11b antibody nanoparticles improved heart function by activating PIK3/AKT, MAPK/ERK and YAP signaling pathways.

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MSN-NGR1-CD11b antibody nanoparticles induced M2 polarization of macrophages and regulated the inflammatory factors.

Reciprocal regulation of IL-33 receptor-mediated inflammatory response and pulmonary fibrosis by TRAF6 and USP38

Significance IL-33R mediates local inflammatory responses and plays crucial roles in the pathogenesis of immune diseases. In this study, we identified USP38, which negatively regulates IL-33-triggered signaling by mediating K27-linked deubiquitination of IL-33R at K511 and its autophagic degradation. USP38 deficiency aggravates IL-33-induced lung inflammatory response and bleomycin-induced pulmonary fibrosis. We further show that the E3 ubiquitin ligase TRAF6 catalyzes K27-linked polyubiquitination of IL-33R at K511, and that deficiency of TRAF6 inhibits IL-33-mediated signaling. Our findings reveal an important mechanism regarding how IL-33R is precisely regulated to ensure its inactivation in rest cells and proper activation following IL-33 stimulation.

MARCH3 negatively regulates IL-3-triggered inflammatory response by mediating K48-linked polyubiquitination and degradation of IL-3Rα

Interleukin-3 (IL-3) is a hematopoietic growth factor and critical regulator of inflammatory response such as sepsis. IL-3 binds to IL-3 receptor α (IL-3Rα), which is then associated with IL-3Rβ to initiate signaling. How IL-3-triggered physiological and pathological effects are regulated at the receptor level is unclear. Here, we show that the plasma membrane-associated E3 ubiquitin ligase MARCH3 negatively regulates IL-3-triggered signaling. MARCH3 is associated with IL-3Rα, mediates its K48-linked polyubiquitination at K377 and promotes its proteasomal degradation. MARCH3-deficiency promotes IL-3-triggered transcription of downstream effector genes and IL-3-induced expansion of myeloid cells. In the cecal ligation and puncture (CLP) model of sepsis, MARCH3-deficiency aggravates IL-3-ampified expression of inflammatory cytokines, organ damage and inflammatory death. Our findings suggest that regulation of IL-3Rα by MARCH3 plays an important role in IL-3-triggered physiological functions and inflammatory diseases.

2'-Fucosyllactose Ameliorates Oxidative Stress Damage in d-Galactose-Induced Aging Mice by Regulating Gut Microbiota and AMPK/SIRT1/FOXO1 Pathway

The imbalance of reactive oxygen species is the main cause in aging, accompanied by oxidative stress. As the most abundant in human milk oligosaccharides (HMOs), 2′-Fucosyllactose (2′-FL) has been confirmed to have great properties in immunity regulation and anti-inflammatory. The research on 2′-FL is focused on infants currently, while there is no related report of 2′-FL for the elderly. A d-galactose-induced accelerated aging model was established to explore the protective effect of 2′-FL on the intestines and brain in mice. In this study, 2′-FL significantly reduced oxidative stress damage and inflammation in the intestines of aging mice, potentially by regulating the sirtuin1 (SIRT1)-related and nuclear factor E2-related factor 2 (Nrf2) pathways. In addition, 2′-FL significantly improved the gut mucosal barrier function and increased the content of short-chain fatty acids (SCFAs) in the intestine. The gut microbiota analysis indicated that 2′-FL mainly increased the abundance of probiotics like Akkermansia in aging mice. Moreover, 2′-FL significantly inhibited apoptosis in the brains of aging mice, also increasing the expression of SIRT1. These findings provided a basis for learning the benefits of 2′-FL in the aging process.

FAM177A1 Inhibits IL-1β-Induced Signaling by Impairing TRAF6-Ubc13 Association

The proinflammatory cytokine IL-1β is a crucial mediator of inflammatory responses. IL-1β-induced signaling is finely regulated by various mechanisms, and its imbalance is involved in a variety of diseases. In this study, we identified FAM177A1, a protein of unknown function, as a negative regulator of IL-1β-induced signaling in human cells. Overexpression of FAM177A1 inhibited IL-1β-triggered activation of NF-κB and transcription of inflammatory genes, whereas knockdown of FAM177A1 showed the opposite effects. Mechanistically, FAM177A1 competitively bound to the E3 ubiquitin ligase TRAF6 and impaired its interaction with the E2-conjugating enzyme Ubc13; therefore, it inhibited TRAF6-mediated polyubiquitination and recruitment of downstream signaling molecules. These findings reveal a function of FAM177A1 and promote our understanding of the regulatory mechanisms of IL-1β-induced inflammatory responses.

The membrane-associated E3 ubiquitin ligase MARCH3 downregulates the IL-6 receptor and suppresses colitis-associated carcinogenesis

The IL-6-STAT3 axis is critically involved in inflammation-associated carcinogenesis (IAC). How this axis is regulated to modulate IAC remains unknown. Here, we show that the plasma membrane-associated E3 ubiquitin ligase MARCH3 negatively regulates STAT3 activation triggered by IL-6, as well as another IL-6 subfamily member, Oncostatin M (OSM). MARCH3 is associated with the IL-6 receptor α-chain (IL-6Rα) and its coreceptor gp130. Biochemical experiments indicated that MARCH3 mediates the polyubiquitination of IL-6Rα at K401 and gp130 at K849 following IL-6 stimulation, leading to their translocation to and degradation in lysosomes. MARCH3 deficiency increases IL-6- and OSM-triggered activation of STAT3 and induction of downstream effector genes in various cell types. MARCH3 deficiency enhances dextran sulfate sodium (DSS)-induced STAT3 activation, increases the expression of inflammatory cytokines, and exacerbates colitis, as well as azoxymethane (AOM)/DSS-induced colitis-associated cancer in mice. In addition, MARCH3 is downregulated in human colorectal cancer tissues and associated with poor survival across different cancer types. Our findings suggest that MARCH3 is a pivotal negative regulator of IL-6-induced STAT3 activation, inflammation, and inflammation-associated carcinogenesis.

Evidence That the Etiology of Congenital Hypopituitarism Has a Major Genetic Component but Is Infrequently Monogenic

Purpose

Congenital hypopituitarism usually occurs sporadically. In most patients, the etiology remains unknown.

Methods

We studied 13 children with sporadic congenital hypopituitarism. Children with non-endocrine, non-familial idiopathic short stature (NFSS) (n = 19) served as a control group. Exome sequencing was performed in probands and both unaffected parents. A burden testing approach was used to compare the number of candidate variants in the two groups.

Results

First, we assessed the frequency of rare, predicted-pathogenic variants in 42 genes previously reported to be associated with pituitary gland development. The average number of variants per individual was greater in probands with congenital hypopituitarism than those with NFSS (1.1 vs. 0.21, mean variants/proband, P = 0.03). The number of probands with at least 1 variant in a pituitary-associated gene was greater in congenital hypopituitarism than in NFSS (62% vs. 21%, P = 0.03). Second, we assessed the frequency of rare, predicted-pathogenic variants in the exome (to capture undiscovered causes) that were inherited in a fashion that could explain the sporadic occurrence of the proband's condition with a monogenic etiology (de novo mutation, autosomal recessive, or X-linked recessive) with complete penetrance. There were fewer monogenic candidates in the probands with congenital hypopituitarism than those with NFSS (1.3 vs. 2.5 candidate variants/proband, P = 0.024). We did not find any candidate variants (0 of 13 probands) in genes previously reported to explain the phenotype in congenital hypopituitarism, unlike NFSS (8 of 19 probands, P = 0.01).

Conclusion

Our findings provide evidence that the etiology of sporadic congenital hypopituitarism has a major genetic component but may be infrequently monogenic with full penetrance, suggesting a more complex etiology.

MARCH8 inhibits influenza A virus infection by targeting viral M2 protein for ubiquitination-dependent degradation in lysosomes

The membrane-associated RING-CH (MARCH) proteins are E3 ligases that regulate the stability of various cellular membrane proteins. MARCH8 has been reported to inhibit the infection of HIV-1 and a few other viruses, thus plays an important role in host antiviral defense. However, the antiviral spectrum and the underlying mechanisms of MARCH8 are incompletely defined. Here, we demonstrate that MARCH8 profoundly inhibits influenza A virus (IAV) replication both in vitro and in mice. Mechanistically, MARCH8 suppresses IAV release through redirecting viral M2 protein from the plasma membrane to lysosomes for degradation. Specifically, MARCH8 catalyzes the K63-linked polyubiquitination of M2 at lysine residue 78 (K78). A recombinant A/Puerto Rico/8/34 virus carrying the K78R M2 protein shows greater replication and more severe pathogenicity in cells and mice. More importantly, we found that the M2 protein of the H1N1 IAV has evolved to acquire non-lysine amino acids at positions 78/79 to resist MARCH8-mediated ubiquitination and degradation. Together, our data support the important role of MARCH8 in host anti-IAV intrinsic immune defense by targeting M2, and suggest the inhibitory pressure of MARCH8 on H1N1 IAV transmission in the human population.

Human and viral membrane-associated E3 ubiquitin ligases MARCH1 and MIR2 recognize different features of CD86 to downregulate surface expression

Immune-stimulatory ligands, such as major histocompatibility complex molecules and the T-cell costimulatory ligand CD86, are central to productive immunity. Endogenous mammalian membrane-associated RING-CHs (MARCH) act on these and other targets to regulate antigen presentation and activation of adaptive immunity, whereas virus-encoded homologs target the same molecules to evade immune responses. Substrate specificity is encoded in or near the membrane-embedded domains of MARCHs and the proteins they regulate, but the exact sequences that distinguish substrates from nonsubstrates are poorly understood. Here, we examined the requirements for recognition of the costimulatory ligand CD86 by two different MARCH-family proteins, human MARCH1 and Kaposi's sarcoma herpesvirus modulator of immune recognition 2 (MIR2), using deep mutational scanning. We identified a highly specific recognition surface in the hydrophobic core of the CD86 transmembrane (TM) domain (TMD) that is required for recognition by MARCH1 and prominently features a proline at position 254. In contrast, MIR2 requires no specific sequences in the CD86 TMD but relies primarily on an aspartic acid at position 244 in the CD86 extracellular juxtamembrane region. Surprisingly, MIR2 recognized CD86 with a TMD composed entirely of valine, whereas many different single amino acid substitutions in the context of the native TM sequence conferred MIR2 resistance. These results show that the human and viral proteins evolved completely different recognition modes for the same substrate. That some TM sequences are incompatible with MIR2 activity, even when no specific recognition motif is required, suggests a more complicated mechanism of immune modulation via CD86 than was previously appreciated.

Proteomic analyses reveal that immune integrins are major targets for regulation by Membrane-Associated Ring-CH (MARCH) proteins MARCH2, 3, 4 and 9

MARCH proteins are membrane-associated Ring-CH E3 ubiquitin ligases that dampen immune responses by downregulating cell surface expression of major histocompatibility complexes I and II as well as immune co-stimulatory receptors. We recently showed that MARCH2,3,4 and 9 also downregulate cell surface expression of the inflammatory cytokine receptor for interleukin-6 (IL6Rα). Here we use over-expression of these MARCH proteins in the M1 myeloid leukaemia cell line and cell surface proteomic analyses to globally analyse other potential targets of these proteins. A large range of cell surface proteins regulated by more than one MARCH protein in addition to several MARCH protein-specific cell surface targets were identified most of which were downregulated by MARCH expression. Prominent among these were several integrin complexes associated with immune cell homing, adhesion and migration. Integrin α4β1 (VLA4 or VCAM-1 receptor) was downregulated only by MARCH2 and we showed that in MARCH2 knockout mice, Integrin α4 was upregulated specifically in mature B-lymphocytes and this was accompanied by decreased numbers of B-cells in the spleen.

An unconventional role of an ASB family protein in NF-κB activation and inflammatory response during microbial infection and colitis

Nuclear factor κB (NF-κB)-mediated signaling pathway plays a crucial role in the regulation of inflammatory process, innate and adaptive immune responses. The hyperactivation of inflammatory response causes host cell death, tissue damage, and autoinflammatory disorders, such as sepsis and inflammatory bowel disease. However, how these processes are precisely controlled is still poorly understood. In this study, we demonstrated that ankyrin repeat and suppressor of cytokine signaling box containing 1 (ASB1) is involved in the positive regulation of inflammatory responses by enhancing the stability of TAB2 and its downstream signaling pathways, including NF-κB and mitogen-activated protein kinase pathways. Mechanistically, unlike other members of the ASB family that induce ubiquitination-mediated degradation of their target proteins, ASB1 associates with TAB2 to inhibit K48-linked polyubiquitination and thereby promote the stability of TAB2 upon stimulation of cytokines and lipopolysaccharide (LPS), which indicates that ASB1 plays a noncanonical role to further stabilize the target protein rather than induce its degradation. The deficiency of Asb1 protects mice from Salmonella typhimurium- or LPS-induced septic shock and increases the survival of mice. Moreover, Asb1-deficient mice exhibited less severe colitis and intestinal inflammation induced by dextran sodium sulfate. Given the crucial role of ASB proteins in inflammatory signaling pathways, our study offers insights into the immune regulation in pathogen infection and inflammatory disorders with therapeutic implications.

Grass carp (Ctenopharyngodon idellus) Cdc25a down-regulates IFN 1 expression by reducing TBK1 phosphorylation

In vertebrates, TANK Binding Kinase 1 (TBK1) plays an important role in innate immunity, mainly because it can mediate production of interferon to resist the invasion of pathogens. In mammals, cell division cycle-25a (Cdc25a) is a member of the Cdc25 family of cell division cycle proteins. It is a phosphatase that plays an important role in cell cycle regulation by dephosphorylating its substrate proteins. Currently, many phosphatases are reported to play a role in innate immunity. This is because the phosphatases can shut down or reduce immune signaling pathways by down-regulating phosphorylation signals. However, there are no reports on fish Cdc25a in innate immunity. In this paper, we conducted a preliminary study on the involvement of grass carp Cdc25a in innate immunity. First, we cloned the full-length cDNA of grass carp Cdc25a (CiCdc25a), and found that it shares the highest genetic relationship with that of Anabarilius grahami through phylogenetic tree comparison. In grass carp tissues and CIK cells, the expression of CiCdc25a mRNA was up-regulated under poly (I:C) stimulation. Therefore, CiCdc25a can respond to poly (I:C). The subcellular localization results showed that CiCdc25a is distributed both in the cytoplasm and nucleus. We also found that CiCdc25a can down-regulate the expression of IFN 1 with or without poly (I:C) stimulation. In other words, the down-regulation of IFN1 by CiCdc25a is independent of poly (I:C) stimulation. Further functional studies have shown that the inhibition of IFN1 expression by CiCdc25a may be related to decrease of TBK1 activity. We also confirmed that the phosphorylation of TBK1 at Ser172 is essential for production of IFN 1. In short, CiCdc25a can interact with TBK1 and subsequently inhibits the phosphorylation of TBK1, thereby weakens TBK1 activity. These results indicated that grass carp Cdc25a down-regulates IFN 1 expression by reducing TBK1 phosphorylation.

Role of RING-Type E3 Ubiquitin Ligases in Inflammatory Signalling and Inflammatory Bowel Disease

Ubiquitination is a three-step enzymatic cascade for posttranslational protein modification. It includes the ubiquitin-activating enzyme (E1), ubiquitin-conjugating enzyme (E2), and ubiquitin ligase (E3). RING-type E3 ubiquitin ligases catalyse the posttranslational proteolytic and nonproteolytic functions in various physiological and pathological processes, such as inflammation-associated signal transduction. Resulting from the diversity of substrates and functional mechanisms, RING-type ligases regulate microbe recognition and inflammation by being involved in multiple inflammatory signalling pathways. These processes also occur in autoimmune diseases, especially inflammatory bowel disease (IBD). To understand the importance of RING-type ligases in inflammation, we have discussed their functional mechanisms in multiple inflammation-associated pathways and correlation between RING-type ligases and IBD. Owing to the limited data on the biology of RING-type ligases, there is an urgent need to analyse their potential as biomarkers and therapeutic targets in IBD in the future.

The Beneficial Effect of Eco-Friendly Green Nanoparticles Using Garcinia mangostana Peel Extract against Pathogenicity of Listeria monocytogenes in Female BALB/c Mice

Listeria monocytogenes is a psychrophilic bacterium, which causes widespread zoonosis in the natural environment, and mainly affects goat, sheep, and cattle herds. Recently, we predicted that it can be transmitted through food. It causes listeriosis, a severe infectious disease, which occurs with food contaminated with the pathogenic bacterium. Anti-inflammatory factors are important to treat the dangers of chronic inflammation associated with chronic diseases. Natural foodstuffs have made and are continuing to make vital contributions to the search for new antilisterial agents. The use of natural products in association with silver nanoparticles has drawn attention because of its easy, nonpathogenic, eco-friendly, and economical protocol. Hence, we aimed to biosynthesize silver nanoparticles (Ag-NPs) using Garcinia mangostana peel extract, which was found to be a good source for the synthesis of silver nanoparticles, their formation being confirmed by color change and stability in solution, and investigated the antilisterial activity of these nanoparticles in a murine model of L. monocytogenes infection. A total of 28 mice were divided into four groups-healthy control, infected, infected mice treated with green Ag-NPs biosynthesized with G. mangostana (5 mg/mL), and infected mice pretreated with Ag-NPs. From our results, oral treatment with Ag-NPs biosynthesized with G. mangostana peel extract resulted in a significant reduction in malondialdehyde (MDA), enhanced antioxidant enzyme activities, and increased the levels of the antiapoptotic protein, compared with the untreated mice. These results indicate that G. mangostana may provide therapeutic value against L. monocytogenes-induced oxidative stress and histopathological alterations, and that these effects may be related to antiapoptotic and antioxidant activities.

CircRNA104250 and lncRNAuc001.dgp.1 promote the PM2.5-induced inflammatory response by co-targeting miR-3607-5p in BEAS-2B cells

Long-term exposure to particulate matter 2.5 (PM_2.5) is closely related to the occurrence and development of airway inflammation. Exploration of the role of PM_2.5 in inflammation is the first step towards clarifying the harmful effects of particulate pollution. However, the molecular mechanisms underlying PM_2.5-induced airway inflammation are yet to be fully established. In this study, we focused on the specific roles of non-coding RNAs (ncRNAs) in PM_2.5-induced airway inflammation. In a human bronchial epithelial cell line, BEAS-2B, PM_2.5 at a concentration of 75 μg/mL induced the inflammatory response. Microarray and quantitative real-time polymerase chain reaction (qRT-PCR) analyses revealed significant upregulation of circRNA104250 and lncRNAuc001.dgp.1 during the PM_2.5-induced inflammatory response in this cell line. Data from functional analyses further showed that both molecules promote an inflammatory response. CircRNA104250 and lncRNAuc001.dgp.1 target miR-3607-5p and affect expression of interleukin 1 receptor 1 (IL1R1), which influences the nuclear factor κB (NF-κB) signaling pathway. In summary, we have uncovered an underlying mechanism of airway inflammation by PM_2.5 involving regulation of ncRNA for the first time, which provides further insights into the toxicological effects of PM_2.5.

RNF152 positively regulates TLR/IL-1R signaling by enhancing MyD88 oligomerization

Toll-like receptors (TLRs) are important pattern recognition receptors (PRRs) that are critical for the defense against invading pathogens. IL-1β is an important pro-inflammatory cytokine that also plays pivotal roles in shaping the adaptive immune response. TLRs and interleukin-1 receptor (IL-1R) share similar cytosolic domains and signaling processes. In this study, we identify the E3 ubiquitin ligase RNF152 as a positive regulator of TLR/IL-1R-mediated signaling. Overexpression of RNF152 potentiates IL-1β- and LPS-induced NF-κB activation in an ubiquitination-independent manner, whereas knockdown of RNF152 has the opposite effects. RNF152-deficient mice produce less inflammatory cytokines in response to LPS and are more resistant to LPS-induced lethal endotoxemia. Mechanistically, RNF152 interacts with the adaptor protein MyD88 and enhances oligomerization of MyD88, which is essential for the recruitment of downstream signaling components and activation of TLR/IL-1R-mediated signal transduction. Our findings suggest that RNF152-mediated oligomerization of MyD88 is important for TLR/IL-1R-mediated inflammatory response.

Deciphering the pathways to antiviral innate immunity and inflammation

The antiviral innate immune and inflammatory responses are critical for host defense against viral infection. How these antiviral responses are initiated and regulated has been intensively investigated. Viral nucleic acids are sensed by pattern-recognition receptors (PRRs), which trigger various signaling pathways by utilizing distinct adaptor proteins, kinases and regulatory proteins. These pathways lead to activation of the transcriptional factors NF-κB and IRF3 and ultimate induction of antiviral effector proteins including type I interferons (IFNs), TNF and IL-1β, which are critical mediators of antiviral innate immune and inflammatory responses. For the past 20 years, our groups at Peking University and Wuhan University have made restless efforts in deciphering the molecular mechanisms of antiviral innate immune and inflammatory responses. Here, we summarize the major discoveries from our groups, including the identifications of the critical adaptors VISA/MAVS and MITA/STING, regulatory mechanisms of these adapter-mediated signaling, and regulation of TNF- and IL1β-triggered inflammatory responses.

Membrane-associated RING-CH (MARCH) proteins down-regulate cell surface expression of the interleukin-6 receptor alpha chain (IL6Rα)

Interleukin 6 (IL6) is a cytokine that regulates a number of important immune and inflammatory pathways. We used the ability of IL6 to inhibit the clonal proliferation of the mouse M1 myeloid leukemia cell line in agar to positively screen a cDNA expression library for proteins that inhibited IL6 activity. We found three clones completely resistant to IL6 that contained the cDNA for the Membrane-Associated RING-CH E3 ubiquitin ligase MARCH2. MARCH2 is a member of a family of membrane-bound E3 ubiquitin ligases that target cell surface receptors for degradation. MARCH2 overexpressing M1 clones retained responsiveness to the related cytokines leukemia inhibitory factor and oncostatin M and we showed that its inhibitory effect was a result of selective down-regulation of the IL6 receptor alpha chain and not the shared receptor subunit, gp130 or other signalling molecules. This activity of MARCH2 was also shared with related proteins MARCH4, MARCH9 and an isoform of MARCH3. The transmembrane domains and C-terminal domains, as well as a functional RING domain, of MARCH proteins were all required for substrate recognition and down-regulation. Genetic deletion of individual MARCH proteins in mice had no or little effect on IL6Rα levels but combined deletions of MARCH2,3 and 4 displayed elevated steady-state levels of IL6Rα in selected haemopoietic cell subsets including CD8+ and CD4+ T cells. These studies extend the potential immunosuppressive roles of MARCH proteins to include down-regulation of IL6 inflammatory responses.

The zinc-finger protein ZFYVE1 modulates TLR3-mediated signaling by facilitating TLR3 ligand binding

Recognition of viral dsRNA by Toll-like receptor 3 (TLR3) leads to the induction of downstream antiviral effectors and the innate antiviral immune response. Here, we identified the zinc-finger FYVE domain-containing protein ZFYVE1, a guanylate-binding protein (GBP), as a positive regulator of TLR3-mediated signaling. Overexpression of ZFYVE1 promoted the transcription of downstream antiviral genes upon stimulation with the synthetic TLR3 ligand poly(I:C). Conversely, ZFYVE1 deficiency had the opposite effect. Zfyve1^-/- mice were less susceptible than wild-type mice to inflammatory death induced by poly(I:C) but not LPS. ZFYVE1 was associated with TLR3, and the FYVE domain of ZFYVE1 and the ectodomain of TLR3 were shown to be responsible for their interaction. ZFYVE1 was bound to poly(I:C) and increased the binding affinity of TLR3 to poly(I:C). These findings suggest that ZFYVE1 plays an important role in the TLR3-mediated innate immune and inflammatory responses by promoting the ligand binding of TLR3.

The Membrane-Associated MARCH E3 Ligase Family: Emerging Roles in Immune Regulation

The membrane-associated RING-CH-type finger (MARCH) proteins of E3 ubiquitin ligases have emerged as critical regulators of immune responses. MARCH proteins target immune receptors, viral proteins as well as components in innate immune response for polyubiquitination and degradations via distinct routes. This review summarizes the current progress about MARCH proteins and their regulation on immune responses.

MARCH ligases in immunity

Membrane associated RING-CH (MARCH) ubiquitin ligases control the stability, trafficking and function of important immunoreceptors, including MHC molecules and costimulatory molecule CD86. Regulation of the critical antigen presenting molecule MHC II by MARCH1 and the control of MARCH1 expression by inflammatory stimuli is a key step in the function of antigen presenting cells. MHC II ubiquitination by MARCH8 and CD83 plays a critical role in T cell thymic selection. Recent studies reveal new immune functions of MARCH ligases in innate immunity, regulation of FcγR expression and Treg development. In addition, we review the importance of MARCH in immunomodulation at the host-pathogen interface. Both bacterial and viral pathogens manipulate MARCH function, while MARCH ligases act as an important host anti-viral defence mechanism. Here, we review the role of membrane-bound MARCH ligases in immune function and provide an update on new substrates and concepts. Understanding the increasingly complex roles of MARCH E3 ligases will be vital to develop therapeutic strategies for their regulation.

USP19 Inhibits TNF-α- and IL-1β-Triggered NF-κB Activation by Deubiquitinating TAK1

The dynamic regulations of ubiquitination and deubiquitination play important roles in TGF-β-activated kinase 1 (TAK1)-mediated NF-κB activation, which regulates various physiological and pathological events. We identified ubiquitin-specific protease (USP)19 as a negative regulator of TNF-α- and IL-1β-triggered NF-κB activation by deubiquitinating TAK1. Overexpression of USP19 but not its enzymatic inactive mutant inhibited TNF-α- and IL-1β-triggered NF-κB activation and transcription of downstream genes, whereas USP19 deficiency had the opposite effects. Usp19^-/- mice produced higher levels of inflammatory cytokines and were more susceptible to TNF-α- and IL-1β-triggered septicemia death compared with their wild-type littermates. Mechanistically, USP19 interacted with TAK1 in a TNF-α- or IL-1β-dependent manner and specifically deconjugated K63- and K27-linked polyubiquitin chains from TAK1, leading to the impairment of TAK1 activity and the disruption of the TAK1-TAB2/3 complex. Our findings provide new insights to the complicated molecular mechanisms of the attenuation of the inflammatory response.