HUWE1 mediates inflammasome activation and promotes host defense against bacterial infection

NCF4 attenuates colorectal cancer progression by modulating inflammasome activation and immune surveillance

The spatiotemporal regulation of inflammasome activation remains unclear. To examine the mechanism underlying the assembly and regulation of the inflammasome response, here we perform an immunoprecipitation-mass spectrometry analysis of apoptosis-associated speck-like protein containing a CARD (ASC) and identify NCF4/1/2 as ASC-binding proteins. Reduced NCF4 expression is associated with colorectal cancer development and decreased five-year survival rate in patients with colorectal cancer. NCF4 cooperates with NCF1 and NCF2 to promote NLRP3 and AIM2 inflammasome activation. Mechanistically, NCF4 phosphorylation and puncta distribution switches from the NADPH complex to the perinuclear region, mediating ASC oligomerization, speck formation and inflammasome activation. NCF4 functions as a sensor of ROS levels, to establish a balance between ROS production and inflammasome activation. NCF4 deficiency causes severe colorectal cancer in mice, increases transit-amplifying and precancerous cells, reduces the frequency and activation of CD8+ T and NK cells, and impairs the inflammasome-IL-18-IFN-γ axis during the early phase of colorectal tumorigenesis. Our study implicates NCF4 in determining the spatial positioning of inflammasome assembly and contributing to inflammasome-mediated anti-tumor responses.

Monosodium Urate Crystal-Induced Pyroptotic Cell Death in Neutrophil and Macrophage Facilitates the Pathological Progress of Gout

Monosodium urate (MSU) crystal deposition in joints can lead to the infiltration of neutrophils and macrophages, and their activation plays a critical role in the pathological progress of gout. However, the role of MSU crystal physicochemical properties in inducing cell death in neutrophil and macrophage is still unclear. In this study, MSU crystals of different sizes are synthesized to explore the role of pyroptosis in gout. It is demonstrated that MSU crystals induce size-dependent pyroptotic cell death in bone marrow-derived neutrophils (BMNs) and bone marrow-derived macrophages (BMDMs) by triggering NLRP3 inflammasome-dependent caspase-1 activation and subsequent formation of N-GSDMD. Furthermore, it is demonstrated that the size of MSU crystal also determines the formation of neutrophil extracellular traps (NETs) and aggregated neutrophil extracellular traps (aggNETs), which are promoted by the addition of interleukin-1β (IL-1β). Based on these mechanistic understandings, it is shown that N-GSDMD oligomerization inhibitor, dimethyl fumarate (DMF), inhibits MSU crystal-induced pyroptosis in BMNs and J774A.1 cells, and it further alleviates the acute inflammatory response in MSU crystals-induced gout mice model. This study elucidates that MSU crystal-induced pyroptosis in neutrophil and macrophage is critical for the pathological progress of gout, and provides a new therapeutic approach for the treatment of gout.

The cytoplasmic sensor, the AIM2 inflammasome: A precise therapeutic target in vascular and metabolic diseases

Cardio-cerebrovascular diseases encompass pathological changes in the heart, brain and vascular system, which pose a great threat to health and well-being worldwide. Moreover, metabolic diseases contribute to and exacerbate the impact of vascular diseases. Inflammation is a complex process that protects against noxious stimuli but is also dysregulated in numerous so-called inflammatory diseases, one of which is atherosclerosis. Inflammation involves multiple organ systems and a complex cascade of molecular and cellular events. Numerous studies have shown that inflammation plays a vital role in cardio-cerebrovascular diseases and metabolic diseases. The absent in melanoma 2 (AIM2) inflammasome detects and is subsequently activated by double-stranded DNA in damaged cells and pathogens. With the assistance of the mature effector molecule caspase-1, the AIM2 inflammasome performs crucial biological functions that underpin its involvement in cardio-cerebrovascular diseases and related metabolic diseases: The production of interleukin-1 beta (IL-1β), interleukin-18 (IL-18) and N-terminal pore-forming Gasdermin D fragment (GSDMD-N) mediates a series of inflammatory responses and programmed cell death (pyroptosis and PANoptosis). Currently, several agents have been reported to inhibit the activity of the AIM2 inflammasome and have the potential to be evaluated for use in clinical settings. In this review, we systemically elucidate the assembly, biological functions, regulation and mechanisms of the AIM2 inflammasome in cardio-cerebrovascular diseases and related metabolic diseases and outline the inhibitory agents of the AIM2 inflammasome as potential therapeutic drugs.

Post-translational control of NLRP3 inflammasome signaling

Inflammasomes serve as critical sensors for disruptions to cellular homeostasis, with inflammasome assembly leading to inflammatory caspase activation, gasdermin cleavage, and cytokine release. While the canonical pathways leading to priming, assembly, and pyroptosis are well characterized, recent work has begun to focus on the role of post-translational modifications (PTMs) in regulating inflammasome activity. A diverse array of PTMs, including phosphorylation, ubiquitination, SUMOylation, acetylation, and glycosylation, exert both activating and inhibitory influences on members of the inflammasome cascade through effects on protein-protein interactions, stability, and localization. Dysregulation of inflammasome activation is associated with a number of inflammatory diseases, and evidence is emerging that aberrant modification of inflammasome components contributes to this dysregulation. This review provides insight into PTMs within the NLRP3 inflammasome pathway and their functional consequences on the signaling cascade and highlights outstanding questions that remain regarding the complex web of signals at play.

Cardiolipin oxidized by ROS from complex II acts as a target of gasdermin D to drive mitochondrial pore and heart dysfunction in endotoxemia

Cardiac dysfunction, an early complication of endotoxemia, is the major cause of death in intensive care units. No specific therapy is available at present for this cardiac dysfunction. Here, we show that the N-terminal gasdermin D (GSDMD-N) initiates mitochondrial apoptotic pore and cardiac dysfunction by directly interacting with cardiolipin oxidized by complex II-generated reactive oxygen species (ROS) during endotoxemia. Caspase-4/11 initiates GSDMD-N pores that are subsequently amplified by the upregulation and activation of NLRP3 inflammation through further generation of ROS. GSDMD-N pores form prior to BAX and VDAC1 apoptotic pores and further incorporate into BAX and VDAC1 oligomers within mitochondria membranes to exacerbate the apoptotic process. Our findings identify oxidized cardiolipin as the definitive target of GSDMD-N in mitochondria of cardiomyocytes during endotoxin-induced myocardial dysfunction (EIMD), and modulation of cardiolipin oxidation could be a therapeutic target early in the disease process to prevent EIMD.

Proximity proteomics reveals UCH-L1 as an essential regulator of NLRP3-mediated IL-1β production in human macrophages and microglia

Activation of the NACHT, LRR, and PYD domains-containing protein 3 (NLRP3) inflammasome complex is an essential innate immune signaling mechanism. To reveal how human NLRP3 inflammasome assembly and activation are controlled, in particular by components of the ubiquitin system, proximity labeling, affinity purification, and RNAi screening approaches were performed. Our study provides an intricate time-resolved molecular map of different phases of NLRP3 inflammasome activation. Also, we show that ubiquitin C-terminal hydrolase 1 (UCH-L1) interacts with the NACHT domain of NLRP3. Downregulation of UCH-L1 decreases pro-interleukin-1β (IL-1β) levels. UCH-L1 chemical inhibition with small molecules interfered with NLRP3 puncta formation and ASC oligomerization, leading to altered IL-1β cleavage and secretion, particularly in microglia cells, which exhibited elevated UCH-L1 expression as compared to monocytes/macrophages. Altogether, we profiled NLRP3 inflammasome activation dynamics and highlight UCH-L1 as an important modulator of NLRP3-mediated IL-1β production, suggesting that a pharmacological inhibitor of UCH-L1 may decrease inflammation-associated pathologies.

Targeting epigenetic and post-translational modifications regulating pyroptosis for the treatment of inflammatory diseases

Inflammatory diseases, including infectious diseases, diabetes-related diseases, arthritis-related diseases, neurological diseases, digestive diseases, and tumor, continue to threaten human health and impose a significant financial burden despite advancements in clinical treatment. Pyroptosis, a pro-inflammatory programmed cell death pathway, plays an important role in the regulation of inflammation. Moderate pyroptosis contributes to the activation of native immunity, whereas excessive pyroptosis is associated with the occurrence and progression of inflammation. Pyroptosis is complicated and tightly controlled by various factors. Accumulating evidence has confirmed that epigenetic modifications and post-translational modifications (PTMs) play vital roles in the regulation of pyroptosis. Epigenetic modifications, which include DNA methylation and histone modifications (such as methylation and acetylation), and post-translational modifications (such as ubiquitination, phosphorylation, and acetylation) precisely manipulate gene expression and protein functions at the transcriptional and post-translational levels, respectively. In this review, we summarize the major pathways of pyroptosis and focus on the regulatory roles and mechanisms of epigenetic and post-translational modifications of pyroptotic components. We also illustrate these within pyroptosis-associated inflammatory diseases. In addition, we discuss the effects of novel therapeutic strategies targeting epigenetic and post-translational modifications on pyroptosis, and provide prospective insight into the regulation of pyroptosis for the treatment of inflammatory diseases.

Marine bromophenols suppressed choroidal neovascularization by targeting HUWE1 through NF-κb signaling pathway

Inflammation plays a key role in the progression of choroidal neovascularization (CNV). Regular intravitreal injection of anti-VEGF medication is required for many patients to sustain eye condition as CNV always recurs due to persistent chronic inflammation in the retina and choroid. Marine bromophenols (BDB) have been widely studied due to their diverse bioactivities, including anti-inflammatory effect, though the mechanism of which remained unclear. Our study demonstrated that BDB could restricted endothelial cells' function and suppressed choroidal explants both in vitro and in vivo without out affecting the cells viability. BDB also significantly reduced numerous inflammatory cytokines in both raw cells and choroidal tissue, including IL-1β, IL-6, TNF-α, IL-4 and MMP-9. Moreover, we demonstrated that BDB down regulated phosphorylation of NF-κB p65 in the raw cells. By Co-IP assay, HUWE1 was found to be bound with BDB and the binding location was at sequences position 4214. When overexpressed HUWE1 in HUVECs, the suppression of endothelial cells' function by BDB became more significant. Taken together, the findings in this study showed that BDB suppressed endothelial cells' function and choroidal neovascularization by targeting HUWE1 through NF-κB pathway, which suggested that BDB could be a potential therapeutic candidate in treating chronic inflammation in choroidal neovascularization.

Demethyleneberberine alleviates Pseudomonas aeruginosa-induced acute pneumonia by inhibiting the AIM2 inflammasome and oxidative stress

BACKGROUND

Acute pneumonia induced by Pseudomonas aeruginosa is characterized by massive infiltration of inflammatory cell and the production of reactive oxygen species (ROS), which lead to severe and transient pulmonary inflammation and acute lung injury. However, P.aeruginosa infection is resistant to multiple antibiotics and causes high mortality in clinic, the search for alternative prophylactic and therapeutic strategies is imperative.

PURPOSE

This study was aimed to investigate the anti-inflammatory and antioxidant effects of DMB, a novel derivative of berberine, and explore the role of AIM2 inflammasome in P. aeruginosa-induced acute pneumonia.

METHODS

Acute pneumonia mice were established by tracheal injection of P. aeruginosa suspension. Pathological changes of lung tissue were observed by its appearance and H&E staining. The lung coefficient ratio was measured to evaluate pulmonary edema. Inflammatory factors were detected by qRT-PCR, western blotting and immunohistochemistry. ROS and other indicators of oxidative damage were analyzed by flow cytometry and specific kit. Proteins related to AIM2 inflammasome were detected by western blotting.

RESULTS

Compared with the P. aeruginosa-induced group, DMB ameliorated pulmonary edema, hyperemia, and pathological damage based on its appearance and H&E staining in DMB groups. First, DMB attenuated the inflammatory response induced by P.aeruginosa. Compared with the P. aeruginosa-induced group, the lung coefficient ratio was decreased by 31.5%, the MPO activity of lung tissue was decreased by 44.0%, the mRNA expression levels of TNF-α, IL-1β and IL-6 were decreased by 64.8%, 51.2% and 64.0% respectively, and those protein expression levels were decreased by 40.1%, 42.8% and 47.8% respectively, and the number of white blood cells, neutrophils and monocytes were decreased by 53.5%, 29.4% and 13.7% in high dose (200 mg/kg) DMB group. Second, DMB alleviates oxidative stress in the lung tissue during P. aeruginosa-induced acute pneumonia. Compared with the P. aeruginosa-induced group, the level of GSH was increased by 42.5% and MDA was decreased by 49.5% in high dose DMB group. Moreover, the western blotting results showed that DMB markedly suppressed the expression of AIM2, ASC, Cleaved caspase1 and decreased the secretion of IL-1β. Additionally, these results were also confirmed by in vitro experiments using MH-S and BEAS-2B cell lines.

CONCLUSIONS

Taken together, these results indicated that DMB ameliorates P. aeruginosa-induced acute pneumonia through anti-inflammatory, antioxidant effects, and inhibition of AIM2 inflammasome activation.

New Potentiality of Bioactive Substances: Regulating the NLRP3 Inflammasome in Autoimmune Diseases

The NOD-like receptor family pyrin domain-containing 3 (NLRP3) inflammasome is an essential component of the human innate immune system, and is closely associated with adaptive immunity. In most cases, the activation of the NLRP3 inflammasome requires priming and activating, which are influenced by various ion flux signals and regulated by various enzymes. Aberrant functions of intracellular NLRP3 inflammasomes promote the occurrence and development of autoimmune diseases, with the majority of studies currently focused on rheumatoid arthritis, systemic lupus erythematosus and systemic sclerosis. In recent years, a number of bioactive substances have shown new potentiality for regulating the NLRP3 inflammasome in autoimmune diseases. This review provides a concise overview of the composition, functions, and regulation of the NLRP3 inflammasome. Additionally, we focus on the newly discovered bioactive substances for regulating the NLRP3 inflammasome in autoimmune diseases in the past three years.

Dysregulation of inflammasome activation in glioma

Gliomas are the most common brain tumors characterized by complicated heterogeneity. The genetic, molecular, and histological pathology of gliomas is characterized by high neuro-inflammation. The inflammatory microenvironment in the central nervous system (CNS) has been closely linked with inflammasomes that control the inflammatory response and coordinate innate host defenses. Dysregulation of the inflammasome causes an abnormal inflammatory response, leading to carcinogenesis in glioma. Because of the clinical importance of the various physiological properties of the inflammasome in glioma, the inflammasome has been suggested as a promising treatment target for glioma management. Here, we summarize the current knowledge on the contribution of the inflammasomes in glioma and therapeutic insights. Video Abstract.

The therapeutic potential of targeting regulated non-apoptotic cell death

Cell death is critical for the development and homeostasis of almost all multicellular organisms. Moreover, its dysregulation leads to diverse disease states. Historically, apoptosis was thought to be the major regulated cell death pathway, whereas necrosis was considered to be an unregulated form of cell death. However, research in recent decades has uncovered several forms of regulated necrosis that are implicated in degenerative diseases, inflammatory conditions and cancer. The growing insight into these regulated, non-apoptotic cell death pathways has opened new avenues for therapeutic targeting. Here, we describe the regulatory pathways of necroptosis, pyroptosis, parthanatos, ferroptosis, cuproptosis, lysozincrosis and disulfidptosis. We discuss small-molecule inhibitors of the pathways and prospects for future drug discovery. Together, the complex mechanisms governing these pathways offer strategies to develop therapeutics that control non-apoptotic cell death.

Ubiquitination is a major modulator for the activation of inflammasomes and pyroptosis

Inflammasomes are a central node of the innate immune defense system against the threat of homeostatic perturbance caused by pathogenic organisms or host-derived molecules. Inflammasomes are generally composed of multimeric protein complexes that assemble in the cytosol after sensing danger signals. Activated inflammasomes promote downstream proteolytic activation, which triggers the release of pro-inflammatory cytokines therefore inducing pyroptotic cell death. The inflammasome pathway is finely tuned by various mechanisms. Recent studies found that protein post-translational modifications such as ubiquitination also modulate inflammasome activation. Targeting the ubiquitination modification of the inflammasome pathway might be a promising strategy for related diseases. In this review, we extensively discuss the advances in inflammasome activation and pyroptosis modulated by ubiquitination which help in-depth understanding and controlling the inflammasome and pyroptosis in various diseases.

The NLRP3 inflammasome in viral infection (Review)

The interplay between pathogen and host determines the immune response during viral infection. The Nod‑like receptor (NLR) protein 3 inflammasome is a multiprotein complex that induces the activation of inflammatory caspases and the release of IL‑1β, which play an important role in the innate immune responses. In the present review, the mechanisms of the NLR family pyrin domain containing 3 inflammasome activation and its dysregulation in viral infection were addressed.

The role of ubiquitination in microbial infection induced endothelial dysfunction: potential therapeutic targets for sepsis

INTRODUCTION

The ubiquitin system is an evolutionarily conserved and universal means of protein modification that regulates many essential cellular processes. Endothelial dysfunction plays a critical role in the pathophysiology of sepsis and organ failure. However, the mechanisms underlying the ubiquitination-mediated regulation on endothelial dysfunction are not fully understood.

AREAS COVERED

Here we review the advances in basic and clinical research for relevant papers in PubMed database. We attempt to provide an updated overview of diverse ubiquitination events in endothelial cells, discussing the fundamental role of ubiquitination mediated regulations involving in endothelial dysfunction to provide potential therapeutic targets for sepsis.

EXPERT OPINION

The central event underlying sepsis syndrome is the overwhelming host inflammatory response to the pathogen infection, leading to endothelial dysfunction. As the key components of the ubiquitin system, E3 ligases are at the center stage of the battle between host and microbial pathogens. Such a variety of ubiquitination regulates a multitude of cellular regulatory processes, including signal transduction, autophagy, inflammasome activation, redox reaction and immune response and so forth. In this review, we discuss the many mechanisms of ubiquitination-mediated regulation with a focus on those that modulate endothelial function to provide potential therapeutic targets for the management of sepsis.

HECT, UBA and WWE domain containing 1 represses cholesterol efflux during CD4+ T cell activation in Sjögren's syndrome

Introduction: Sjögren's syndrome (SS) is a chronic autoimmune disorder characterized by exocrine gland dysfunction, leading to loss of salivary function. Histological analysis of salivary glands from SS patients reveals a high infiltration of immune cells, particularly activated CD4⁺ T cells. Thus, interventions targeting abnormal activation of CD4⁺ T cells may provide promising therapeutic strategies for SS. Here, we demonstrate that Hect, uba, and wwe domain containing 1 (HUWE1), a member of the eukaryotic Hect E3 ubiquitin ligase family, plays a critical role in CD4⁺ T-cell activation and SS pathophysiology. Methods: In the context of HUWE1 inhibition, we investigated the impact of the HUWE1 inhibitor BI8626 and sh-Huwe1 on CD4⁺ T cells in mice, focusing on the assessment of activation levels, proliferation capacity, and cholesterol abundance. Furthermore, we examined the therapeutic potential of BI8626 in NOD/ShiLtj mice and evaluated its efficacy as a treatment strategy. Results: Inhibition of HUWE1 reduces ABCA1 ubiquitination and promotes cholesterol efflux, decreasing intracellular cholesterol and reducing the expression of phosphorylated ZAP-70, CD25, and other activation markers, culminating in the suppressed proliferation of CD4⁺ T cells. Moreover, pharmacological inhibition of HUWE1 significantly reduces CD4⁺ T-cell infiltration in the submandibular glands and improves salivary flow rate in NOD/ShiLtj mice. Conclusion: These findings suggest that HUWE1 may regulate CD4⁺ T-cell activation and SS development by modulating ABCA1-mediated cholesterol efflux and presents a promising target for SS treatment.

The Role of Post-Translational Modifications in Regulation of NLRP3 Inflammasome Activation

Pathogen-associated molecular patterns (PAMPs) and danger-associated molecular patterns (DAMPs) induce NLRP3 inflammasome activation, and subsequent formation of active caspase-1 as well as the maturation of interleukin-1β (IL-1β) and gasdermin D (GSDMD), mediating the occurrence of pyroptosis and inflammation. Aberrant NLRP3 inflammasome activation causes a variety of diseases. Therefore, the NLRP3 inflammasome pathway is a target for prevention and treatment of relative diseases. Recent studies have suggested that NLRP3 inflammasome activity is closely associated with its post-translational modifications (PTMs). This review focuses on PTMs of the components of the NLRP3 inflammasome and the resultant effects on regulation of its activity to provide references for the exploration of the mechanisms by which the NLRP3 inflammasome is activated and controlled.

E3-ubiquitin ligases and recent progress in osteoimmunology

Ubiquitin-mediated proteasomal degradation is a post-transcriptional protein modification that is comprised of various components including the 76-amino acid protein ubiquitin (Ub), Ub-activating enzyme (E1), Ub-conjugating enzyme (E2), ubiquitin ligase (E3), deubiquitinating enzyme (DUB) and proteasome. We and others have recently provided genetic evidence showing that E3-ubiquitin ligases are associated with bone metabolism, the immune system and inflammation through ubiquitylation and subsequent degradation of their substrates. Dysregulation of the E3-ubiquitin ligase RNF146-mediated degradation of the adaptor protein 3BP2 (SH3 domain-binding protein 2) causes cherubism, an autosomal dominant disorder associated with severe inflammatory craniofacial dysmorphia syndrome in children. In this review, on the basis of our discoveries in cherubism, we summarize new insights into the roles of E3-ubiquitin ligases in the development of human disorders caused by an abnormal osteoimmune system by highlighting recent genetic evidence obtained in both human and animal model studies.

Absent in melanoma 2 (AIM2) in rheumatoid arthritis: novel molecular insights and implications

Absent in melanoma 2 (AIM2), a member of the Pyrin and HIN domain protein family, is a cytoplasmic receptor that recognizes double-stranded DNA. AIM2 exhibits limited expression under physiological conditions but is widely expressed in many human diseases, including autoimmune diseases, and plays an essential role in the immune response. Rheumatoid arthritis (RA) is an autoimmune disease that poses a severe threat to physical and mental health, and is caused by several genetic and metabolic factors. Multiple immune cells interact to form a complex inflammatory network that mediates inflammatory responses and bone destruction. Abnormal AIM2 expression in multiple immune cell populations (T cells, B cells, fibroblast-like synoviocytes, monocytes, and macrophages) may regulate multiple functional responses in RA through mechanisms such as pyroptosis, PANoptosis, and regulation of other molecules. In this review, we describe and summarize the functional regulation and impact of AIM2 expression in immune cells to improve our understanding of the complex pathological mechanisms. These insights may provide potential directions for the development of new clinical diagnostic strategies for RA.

Ubiquitin proteasome system in immune regulation and therapeutics

The ubiquitin proteasome system (UPS) is a proteolytic machinery for the degradation of protein substrates that are post-translationally conjugated with ubiquitin polymers through the enzymatic action of ubiquitin ligases, in a process termed ubiquitylation. Ubiquitylation of substrates precedes their proteolysis via proteasomes, a hierarchical feature of UPS. E3-ubiquitin ligases recruit protein substrates providing specificity for ubiquitylation. Innate and adaptive immune system networks are regulated by ubiquitylation and substrate degradation via E3-ligases/UPS. Deregulation of E3-ligases/UPS components in immune cells is involved in the development of lymphomas, neurodevelopmental abnormalities, and cancers. Targeting E3-ligases for therapeutic intervention provides opportunities to mitigate the unintended broad effects of 26S proteasome inhibition. Recently, bifunctional moieties such as PROTACs and molecular glues have been developed to re-purpose E3-ligases for targeted degradation of unwanted aberrant proteins, with a potential for clinical use. Here, we summarize the involvement of E3-ligases/UPS components in immune-related diseases with perspectives.

IL-1β/NF-κB signaling inhibits IGF-1 production via let-7f-5p in dendritic epidermal T cells

Dendritic epidermal T cells (DETCs) are the main source of insulin-like growth factor-1 (IGF-1) in epidermal tissue, which promote re-epithelialization and wound healing. In refractory wounds, IL-1β has been shown to activate NF-κB and suppress IGF-1 expression in DETCs. Nevertheless, the underlying mechanisms remain unclear. In this study, chromatin immunoprecipitation analysis revealed that IL-1β did not inhibit NF-κB binding to IGF-1 promoter, indicating that IL-1β/NF-κB may suppress IGF-1 expression by alternative mechanisms. MiRNAs negatively regulate gene expression predominantly by base pairing to the 3' untranslation region (UTR) of target mRNAs. Let-7f-5p, miR-1a-3p, and miR-98-5p have been identified as IGF-1-specific miRNAs that can bind directly to the 3'UTR of IGF-1 mRNA and dysregulate IGF-1 mRNA and protein levels. In IL-1β-treated epidermis around wounds or DETCs in vitro, NF-κB promoted the expression of let-7f-5p, and IGF-1 expression was impeded via NF-κB/let-7f-5p pathway. As pre-let-7f-5p, let-7f-1 is located in the 3'UTR of LOC118568094, and let-7f-2 is located in the intron of HUWE1. We discovered that NF-κB p65 bound to the promoters of LOC118568094 and HUWE1 to accelerate let-7f-5p expression, but NF-κB p65 did not affect the methylation levels of LOC118568094 and HUWE1 CpG islands. Injections of Let-7f-5p antagomir into IL-1β-treated and ischemic wound margins restored IGF-1 secretion in DETCs and promoted wound healing. In conclusion, we demonstrated that NF-κB signaling pathway activated by IL-1β could increase let-7f-5p expression to inhibit IGF-1 production in DETCs and delay wound healing. And let-7f-5p antagomir utilized in wound margin could effectively promote refractory wound healing.

USP3 deubiquitinates and stabilizes the adapter protein ASC to regulate inflammasome activation

Inflammasomes are essential components of the innate immune system and its defense against infections, whereas the dysregulation of inflammasome activation has a detrimental effect on human health. The activation of inflammasomes is subjected to tight regulation to maintain immune homeostasis, yet the underlying mechanism remains elusive. Here, we identify USP3 as a direct deubiquitinating enzyme (DUB) for ASC, the central adapter mediating the assembly and activation of most inflammasomes. USP3 removes the K48-linked ubiquitination on ASC and strengthens its stability by blocking proteasomal degradation. Additionally, USP3 promotes inflammasome activation, and this function was confirmed in mouse models of aluminum (Alum)-induced peritonitis, F. novicida infection and flagellin-induced pneumonia in vivo. Our work unveils that USP3 functions as a key regulator of ASC ubiquitination and maintains the physiological role of ASC in mediating inflammasome activation, and we propose a new mechanism by which the ubiquitination of ASC regulates inflammasome activation.

The giant E3 ligase HUWE1 is linked to tumorigenesis, spermatogenesis, intellectual disability, and inflammatory diseases

E3 ubiquitin ligases determine the substrate specificity and catalyze the ubiquitination of lysine residues. HUWE1 is a catalytic HECT domain-containing giant E3 ligase that contains a substrate-binding ring structure, and mediates the ubiquitination of more than 40 diverse substrates. HUWE1 serves as a central node in cellular stress responses, cell growth and death, signal transduction, etc. The expanding atlas of HUWE1 substrates presents a major challenge for the potential therapeutic application of HUWE1 in a particular disease. In addition, HUWE1 has been demonstrated to play contradictory roles in certain aspects of tumor progression in either an oncogenic or a tumor-suppressive manner. We recently defined novel roles of HUWE1 in promoting the activation of multiple inflammasomes. Inflammasome activation-mediated immune responses might lead to multifunctional effects on tumor therapy, inflammation, and autoimmune diseases. In this review, we summarize the known substrates and pleiotropic functions of HUWE1 in different types of cells and models, including its involvement in development, cancer, neuronal disorder and infectious disease. We also discuss the advances in cryo-EM-structural analysis for a functional-mechanistic understanding of HUWE1 in modulating the multitudinous diverse substrates, and introduce the possibility of revisiting the comprehensive roles of HUWE1 in multiple aspects within one microenvironment, which will shed light on the potential therapeutic application of targeting giant E3 ligases like HUWE1.

Activation and Pharmacological Regulation of Inflammasomes

Inflammasomes are intracellular signaling complexes of the innate immune system, which is part of the response to exogenous pathogens or physiological aberration. The multiprotein complexes mainly consist of sensor proteins, adaptors, and pro-caspase-1. The assembly of the inflammasome upon extracellular and intracellular cues drives the activation of caspase-1, which processes pro-inflammatory cytokines IL-1β and IL-18 to maturation and gasdermin-D for pore formation, leading to pyroptosis and cytokine release. Inflammasome signaling functions in numerous infectious or sterile inflammatory diseases, including inherited autoinflammatory diseases, metabolic disorders, cardiovascular diseases, cancers, neurodegenerative disorders, and COVID-19. In this review, we summarized current ideas on the organization and activation of inflammasomes, with details on the molecular mechanisms, regulations, and interventions. The recent developments of pharmacological strategies targeting inflammasomes as disease therapeutics were also covered.

Posttranslational Regulation of Inflammasomes, Its Potential as Biomarkers and in the Identification of Novel Drugs Targets

In this review, we have summarized classical post-translational modifications (PTMs) such as phosphorylation, ubiquitylation, and SUMOylation of the different components of one of the most studied NLRP3, and other emerging inflammasomes. We will highlight how the discovery of these modifications have provided mechanistic insight into the biology, function, and regulation of these multiprotein complexes not only in the context of the innate immune system but also in adaptive immunity, hematopoiesis, bone marrow transplantation, as well and their role in human diseases. We have also collected available information concerning less-studied modifications such as acetylation, ADP-ribosylation, nitrosylation, prenylation, citrullination, and emphasized their relevance in the regulation of inflammasome complex formation. We have described disease-associated mutations affecting PTMs of inflammasome components. Finally, we have discussed how a deeper understanding of different PTMs can help the development of biomarkers and identification of novel drug targets to treat diseases caused by the malfunctioning of inflammasomes.

Pyroptosis and Its Role in Autoimmune Disease: A Potential Therapeutic Target

Autoimmune diseases are a group of heterogeneous diseases with diverse clinical manifestations that can be divided into systemic and organ-specific. The common etiology of autoimmune diseases is the destruction of immune tolerance and the production of autoantibodies, which attack specific tissues and/or organs in the body. The pathogenesis of autoimmune diseases is complicated, and genetic, environmental, infectious, and even psychological factors work together to cause aberrant innate and adaptive immune responses. Although the exact mechanisms are unclear, recently, excessive exacerbation of pyroptosis, as a bond between innate and adaptive immunity, has been proven to play a crucial role in the development of autoimmune disease. Pyroptosis is characterized by pore formation on cell membranes, as well as cell rupture and the excretion of intracellular contents and pro-inflammatory cytokines, such as IL-1β and IL-18. This overactive inflammatory programmed cell death disrupts immune system homeostasis and promotes autoimmunity. This review examines the molecular structure of classical inflammasomes, including NLRP3, AIM2, and P2X7-NLRP3, as the switches of pyroptosis, and their molecular regulation mechanisms. The sophisticated pyroptosis pathways, including the canonical caspase-1-mediated pathway, the noncanonical caspase-4/5/11-mediated pathway, the emerging caspase-3-mediated pathway, and the caspase-independent pathway, are also described. We highlight the recent advances in pyroptosis in autoimmune diseases, such as systemic lupus erythematosus, rheumatoid arthritis, inflammatory bowel disease, Sjögren's syndrome and dermatomyositis, and attempt to identify its potential advantages as a therapeutic target or prognostic marker in these diseases.

Toxoplasma gondii Rhoptry Protein 7 (ROP7) Interacts with NLRP3 and Promotes Inflammasome Hyperactivation in THP-1-Derived Macrophages

Toxoplasma gondii is a common opportunistic protozoan pathogen that can parasitize the karyocytes of humans and virtually all other warm-blooded animals. In the host’s innate immune response to T. gondii infection, inflammasomes can mediate the maturation of pro-IL-1β and pro-IL-18, which further enhances the immune response. However, how intercellular parasites specifically provoke inflammasome activation remains unclear. In this study, we found that the T. gondii secretory protein, rhoptry protein 7 (ROP7), could interact with the NACHT domain of NLRP3 through liquid chromatography-mass spectrometry analysis and co-immunoprecipitation assays. When expressing ROP7 in differentiated THP-1 cells, there was significant up-regulation in NF-κB and continuous release of IL-1β. This process is pyroptosis-independent and leads to inflammasome hyperactivation through the IL-1β/NF-κB/NLRP3 feedback loop. The loss of ROP7 in tachyzoites did not affect parasite proliferation in host cells but did attenuate parasite-induced inflammatory activity. In conclusion, these findings unveil that a T. gondii-derived protein is able to promote inflammasome activation, and further study of ROP7 will deepen our understanding of host innate immunity to parasites.

K48- and K27-mutant ubiquitin regulates adaptive immune response by affecting cross-presentation in bone marrow precursor cells

K48-linked ubiquitination determines antigen degradation and plays vital roles in the process of cross-presentation of bone marrow precursor cell (BMPC)-derived dendritic cells (DCs). Although previous studies revealed that K48 and K27-linked ubiquitination regulates innate immunity, the exact roles of K48 and K27-linked ubiquitination in cross-presentation and BMPC-based adaptive immunity are still uncertain. In this study, we investigated the effects of K48- and K27-mutant ubiquitin (Ub) on BMPC-based adaptive immune response by observing the effects of MG132, Ub deficiency, and K48/K27-mutant Ub on cross-presentation, T cell proliferation, IFN-γ secretion, BMPC-based CTL priming, and thereby the efficiency of cytolytic capacity of BMPC-activate T cells. We demonstrated that MG132, Ub deficiency, and K48-mutant Ub impair cross-presentation, T cell proliferation, IFN-γ secretion, BMPC-based CTL priming, and the cytolytic capacity of BMPC-activated T cells. Moreover, although K27-only Ub decreases cross-presentation, the replenishment of K27-mutant Ub restores Ub deficiency impaireds the abilities of T cell proliferation, IFN-γ secretion, CTL priming, and the cytolytic capacity of BMPC-activated T cells. Thus, these data suggest that K48- and K27-linked ubiquitination contributes to BMPC-mediated adaptive immune response by affecting BMPC cross-presentation and the cytolytic capacity by up-regulating both perforin and granzyme B in BMPC-activated T cells. K48- and K27-mutant Ub might have potential clinical therapeutic function in adaptive immune response-associated diseases.

Gut microbiota dysbiosis-derived macrophage pyroptosis causes polycystic ovary syndrome via steroidogenesis disturbance and apoptosis of granulosa cells

Gut microbiota dysbiosis is critical in the etiology of polycystic ovary syndrome (PCOS). However, the mechanisms of gut microbiota in PCOS pathogenesis have not been fully elucidated. We aimed to explore the role of gut microbiota-derived macrophage pyroptosis in PCOS. This study conducted dehydroepiandrosterone (DHEA) induced PCOS mice model, 16S rDNA sequencing, western blot, genetic knocking out, transcriptome and translatome profiling, et al. to evaluate the underlying mechanisms. 16S rDNA sequencing showed reduced gut Akkermansia and elevated gram-negative bacteria (Desulfovibrio and Burkholderia) abundances in DHEA induced PCOS mice, which was accompanied by increased serum lipopolysaccharide (LPS). LPS could induce macrophage pyroptosis in mice ovaries, also activated in PCOS. Gasdermin D (GSDMD) is the final executor of macrophage pyroptosis. We demonstrated that Gsdmd knockout in mice could dramatically ameliorate PCOS. Mechanistically, transcriptome and translatome profiling revealed that macrophage pyroptosis disrupted estrogen production and promoted apoptosis of granulosa cells. Interferon (IFN)-γ, which was elevated in PCOS mice serum and ovaries, enhanced macrophage pyroptosis and exacerbated its effect on estrogen receptor in granulosa cells. Inspiringly, we identified that disulfiram and metformin could augment gut Akkermansia abundance, reduce serum IFN-γ level, inhibit macrophage pyroptosis in ovaries, therefore ameliorating PCOS. Collectively, this study emphasizes that macrophage pyroptosis, which was induced by gut microbiota dysbiosis and enhanced by IFN-γ, plays a key role in PCOS pathogenesis through estrogen synthesis dysfunction and apoptosis of granulosa cells. Disulfiram and metformin, which enhanced gut Akkermansia abundance and suppressed macrophage pyroptosis, may be considered as potential therapeutic strategies for PCOS.

E3 ubiquitin ligase SYVN1 is a key positive regulator for GSDMD-mediated pyroptosis

Gasdermin D (GSDMD) participates in the activation of inflammasomes and pyroptosis. Meanwhile, ubiquitination strictly regulates inflammatory responses. However, how ubiquitination regulates Gasdermin D activity is not well understood. In this study, we show that pyroptosis triggered by Gasdermin D is regulated through ubiquitination. Specifically, SYVN1, an E3 ubiquitin ligase of gasdermin D, promotes GSDMD-mediated pyroptosis. SYVN1 deficiency inhibits pyroptosis and subsequent LDH release and PI uptake. SYVN1 directly interacts with GSDMD, and mediates K27-linked polyubiquitination of GSDMD on K203 and K204 residues, promoting GSDMD-induced pyroptotic cell death. Thus, our findings revealed the essential role of SYVN1 in GSDMD-mediated pyroptosis. Overall, GSDMD ubiquitination is a potential therapeutic module for inflammatory diseases.

Ubiquitination of NLRP3 by gp78/Insig-1 restrains NLRP3 inflammasome activation

The NLRP3 (NOD-, LRR- and pyrin domain-containing protein 3) inflammasome plays a pivotal role in defending the host against infection as well as sterile inflammation. Activation of the NLRP3 inflammasome is critically regulated by a de-ubiquitination mechanism, but little is known about how ubiquitination restrains NLRP3 activity. Here, we showed that the membrane-bound E3 ubiquitin ligase gp78 mediated mixed ubiquitination of NLRP3, which inhibited NLRP3 inflammasome activation by suppressing the oligomerization and subcellular translocation of NLRP3. In addition, the endoplasmic reticulum membrane protein insulin-induced gene 1 (Insig-1) was required for this gp78-NLRP3 interaction and gp78-mediated NLRP3 ubiquitination. gp78 or Insig-1 deficiency in myeloid cells led to exacerbated NLRP3 inflammasome-dependent inflammation in vivo, including lipopolysaccharide-induced systemic inflammation and alum-induced peritonitis. Taken together, our study identifies gp78-mediated NLRP3 ubiquitination as a regulatory mechanism that restrains inflammasome activation and highlights NLRP3 ubiquitination as a potential therapeutic target for inflammatory diseases.

Host E3 ligase HUWE1 attenuates the proapoptotic activity of the MERS-CoV accessory protein ORF3 by promoting its ubiquitin-dependent degradation

With the outbreak of severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2), coronaviruses have begun to attract great attention across the world. Of the known human coronaviruses, however, Middle East respiratory syndrome coronavirus (MERS-CoV) is the most lethal. Coronavirus proteins can be divided into three groups: nonstructural proteins, structural proteins, and accessory proteins. While the number of each of these proteins varies greatly among different coronaviruses, accessory proteins are most closely related to the pathogenicity of the virus. We found for the first time that the ORF3 accessory protein of MERS-CoV, which closely resembles the ORF3a proteins of severe acute respiratory syndrome coronavirus and SARS-CoV-2, has the ability to induce apoptosis in cells in a dose-dependent manner. Through bioinformatics analysis and validation, we revealed that ORF3 is an unstable protein and has a shorter half-life in cells compared to that of severe acute respiratory syndrome coronavirus and SARS-CoV-2 ORF3a proteins. After screening, we identified a host E3 ligase, HUWE1, that specifically induces MERS-CoV ORF3 protein ubiquitination and degradation through the ubiquitin-proteasome system. This results in the diminished ability of ORF3 to induce apoptosis, which might partially explain the lower spread of MERS-CoV compared to other coronaviruses. In summary, this study reveals a pathological function of MERS-CoV ORF3 protein and identifies a potential host antiviral protein, HUWE1, with an ability to antagonize MERS-CoV pathogenesis by inducing ORF3 degradation, thus enriching our knowledge of the pathogenesis of MERS-CoV and suggesting new targets and strategies for clinical development of drugs for MERS-CoV treatment.

Francisella novicida Mutant XWK4 Triggers Robust Inflammasome Activation Favoring Infection

Bacterial infection tendentiously triggers inflammasome activation, whereas the roles of inflammasome activation in host defense against diverse infections remain unclear. Here, we identified that an ASC-dependent inflammasome activation played opposite roles in host defense against Francisella novicida wild-type (WT) U112 and mutant strain XWK4. Comparing with U112, XWK4 infection induced robust cytokine production, ASC-dependent inflammasome activation, and pyroptosis. Both AIM2 and NLRP3 were involved and played independent roles in XWK4-induced inflammasome activation. Type II interferon was partially required for XWK4-triggered inflammasome activation, which was different from type I interferon dependency in U112-induced inflammasome activation. Distinct from F. novicida U112 and Acinetobacter baumannii infection, Asc^-/- mice were more resistant than WT mice response to XWK4 infection by limiting bacterial burden in vivo. The excessive inflammasome activation triggered by XWK4 infection caused dramatical cell death and pathological damage. Our study offers novel insights into mechanisms of inflammasome activation in host defense and provides potential therapeutic approach against bacterial infections and inflammatory diseases.

Nod-like Receptors: Critical Intracellular Sensors for Host Protection and Cell Death in Microbial and Parasitic Infections

Cell death is an essential immunological apparatus of host defense, but dysregulation of mutually inclusive cell deaths poses severe threats during microbial and parasitic infections leading to deleterious consequences in the pathological progression of infectious diseases. Nucleotide-binding oligomerization domain (NOD)-Leucine-rich repeats (LRR)-containing receptors (NLRs), also called nucleotide-binding oligomerization (NOD)-like receptors (NLRs), are major cytosolic pattern recognition receptors (PRRs), their involvement in the orchestration of innate immunity and host defense against bacteria, viruses, fungi and parasites, often results in the cleavage of gasdermin and the release of IL-1β and IL-18, should be tightly regulated. NLRs are functionally diverse and tissue-specific PRRs expressed by both immune and non-immune cells. Beyond the inflammasome activation, NLRs are also involved in NF-κB and MAPK activation signaling, the regulation of type I IFN (IFN-I) production and the inflammatory cell death during microbial infections. Recent advancements of NLRs biology revealed its possible interplay with pyroptotic cell death and inflammatory mediators, such as caspase 1, caspase 11, IFN-I and GSDMD. This review provides the most updated information that caspase 8 skews the NLRP3 inflammasome activation in PANoptosis during pathogen infection. We also update multidimensional roles of NLRP12 in regulating innate immunity in a content-dependent manner: novel interference of NLRP12 on TLRs and NOD derived-signaling cascade, and the recently unveiled regulatory property of NLRP12 in production of type I IFN. Future prospects of exploring NLRs in controlling cell death during parasitic and microbial infection were highlighted.

USP21 Deubiquitinase Regulates AIM2 Inflammasome Activation

Innate immune sensing of cytosolic DNA via absent in melanoma 2 (AIM2) is a key mechanism leading to inflammatory responses. As aberrant immune responses by dysregulated AIM2 are associated with autoinflammatory diseases, activation of the AIM2 inflammasome should be tightly controlled. In this study, we discovered that ubiquitination and deubiquitination of AIM2 are critical events that regulate AIM2 inflammasome activation. In resting human macrophage cells, AIM2 is constitutively ubiquitinated and undergoes proteasomal degradation to avoid autoinflammation. Upon DNA stimulation, USP21 binds to AIM2 and deubiquitinates it, thereby increasing its protein stability. In addition to the role of USP21 in regulating AIM2 turnover, we uncovered that USP21-mediated deubiquitination of AIM2 is required for the assembly of the AIM2 inflammasome. Depletion of USP21 does not affect the DNA-binding ability of AIM2 but inhibits the formation of the AIM2-ASC complex. Our findings establish that fine-tuning of AIM2 by the ubiquitin system is important for regulating AIM2 inflammasome activation.

Neurodevelopmental Disorders (NDD) Caused by Genomic Alterations of the Ubiquitin-Proteasome System (UPS): the Possible Contribution of Immune Dysregulation to Disease Pathogenesis

Over thirty years have passed since the first description of ubiquitin-positive structures in the brain of patients suffering from Alzheimer’s disease. Meanwhile, the intracellular accumulation of ubiquitin-modified insoluble protein aggregates has become an indisputable hallmark of neurodegeneration. However, the role of ubiquitin and a fortiori the ubiquitin-proteasome system (UPS) in the pathogenesis of neurodevelopmental disorders (NDD) is much less described. In this article, we review all reported monogenic forms of NDD caused by lesions in genes coding for any component of the UPS including ubiquitin-activating (E1), -conjugating (E2) enzymes, ubiquitin ligases (E3), ubiquitin hydrolases, and ubiquitin-like modifiers as well as proteasome subunits. Strikingly, our analysis revealed that a vast majority of these proteins have a described function in the negative regulation of the innate immune response. In this work, we hypothesize a possible involvement of autoinflammation in NDD pathogenesis. Herein, we discuss the parallels between immune dysregulation and neurodevelopment with the aim at improving our understanding the biology of NDD and providing knowledge required for the design of novel therapeutic strategies.

Microscopic Detection of ASC Inflammasomes in Bone Marrow Derived Macrophages Post Stimulation

An inflammasome is an intracellular multiprotein complex that plays important roles in host defense and inflammatory responses. Inflammasomes are typically composed of the adaptor protein apoptosis-associated speck-like protein containing a CARD (ASC), cytoplasmic sensor protein, and the effector protein pro-caspase-1. ASC assembly into a protein complex termed ASC speck is a readout for inflammasome activation. Here, we provide a step-by-step protocol for the detection of ASC speck by confocal microscopy in Bone marrow derived macrophages (BMBDs) triggered by chemical stimuli and bacterial pathogens. We also describe the detailed procedure for the generation of BMDMs, stimulating conditions for inflammasome activation, immunofluorescence cell staining of ASC protein, and microscopic examination. Thus far, this method is a simple and reliable manner to visualize and quantify the intracellular localization of ASC speck. Graphic abstract: Figure 1. Confocal microscopy detection of ASC speck formation in untreated WT BMDMs and WT BMDMs stimulated with LPS and ATP, transfected with dsDNA, and infected with F. novicida or Salmonella as indicated. Arrow indicates the ASC speck. Scale bars: 10 μm.

NLRP3 Ubiquitination-A New Approach to Target NLRP3 Inflammasome Activation

In response to diverse pathogenic and danger signals, the cytosolic activation of the NLRP3 (NOD-, LRR-, and pyrin domain-containing (3)) inflammasome complex is a critical event in the maturation and release of some inflammatory cytokines in the state of an inflammatory response. After activation of the NLRP3 inflammasome, a series of cellular events occurs, including caspase 1-mediated proteolytic cleavage and maturation of the IL-1β and IL-18, followed by pyroptotic cell death. Therefore, the NLRP3 inflammasome has become a prime target for the resolution of many inflammatory disorders. Since NLRP3 inflammasome activation can be triggered by a wide range of stimuli and the activation process occurs in a complex, it is difficult to target the NLRP3 inflammasome. During the activation process, various post-translational modifications (PTM) of the NLRP3 protein are required to form a complex with other components. The regulation of ubiquitination and deubiquitination of NLRP3 has emerged as a potential therapeutic target for NLRP3 inflammasome-associated inflammatory disorders. In this review, we discuss the ubiquitination and deubiquitination system for NLRP3 inflammasome activation and the inhibitors that can be used as potential therapeutic agents to modulate the activation of the NLRP3 inflammasome.

K27-linked noncanonic ubiquitination in immune regulation

Ubiquitination is a common form of posttranslational modification that has been implicated in regulating considerable immune signaling pathways. The functions of canonic K48- and K63-linked ubiquitination have been well studied. However, the roles of noncanonic ubiquitination remain largely unexplored and require further investigations. There is increasing evidence suggesting that K27-linked noncanonic ubiquitination turns out to be indispensable to both innate immune signaling and T cell signaling. In this review, we provide an overview of the latest findings related to K27-linked ubiquitination, and highlight the crucial roles of K27-linked ubiquitination in regulating antimicrobial response, cytokine signaling and response, as well as T cell activation and differentiation. We also propose interesting areas for better understanding how K27-linked ubiquitination regulates immunity.

The Ubiquitination System within Bacterial Host-Pathogen Interactions

Ubiquitination of proteins, like phosphorylation and acetylation, is an important regulatory aspect influencing numerous and various cell processes, such as immune response signaling and autophagy. The study of ubiquitination has become essential to learning about host-pathogen interactions, and a better understanding of the detailed mechanisms through which pathogens affect ubiquitination processes in host cell will contribute to vaccine development and effective treatment of diseases. Pathogenic bacteria (e.g., Salmonella enterica, Legionella pneumophila and Shigella flexneri) encode many effector proteins, such as deubiquitinating enzymes (DUBs), targeting the host ubiquitin machinery and thus disrupting pertinent ubiquitin-dependent anti-bacterial response. We focus here upon the host ubiquitination system as an integral unit, its interconnection with the regulation of inflammation and autophagy, and primarily while examining pathogens manipulating the host ubiquitination system. Many bacterial effector proteins have already been described as being translocated into the host cell, where they directly regulate host defense processes. Due to their importance in pathogenic bacteria progression within the host, they are regarded as virulence factors essential for bacterial evasion. However, in some cases (e.g., Francisella tularensis) the host ubiquitination system is influenced by bacterial infection, although the responsible bacterial effectors are still unknown.