Expression, biological activities and mechanisms of action of A20 (TNFAIP3)

Identifying and Characterizing Stress Pathways of Concern for Consumer Safety in Next-Generation Risk Assessment

Many substances for which consumer safety risk assessments need to be conducted are not associated with specific toxicity modes of action, but rather exhibit nonspecific toxicity leading to cell stress. In this work, a cellular stress panel is described, consisting of 36 biomarkers representing mitochondrial toxicity, cell stress, and cell health, measured predominantly using high content imaging. To evaluate the panel, data were generated for 13 substances at exposures consistent with typical use-case scenarios. These included some that have been shown to cause adverse effects in a proportion of exposed humans and have a toxicological mode-of-action associated with cellular stress (eg, doxorubicin, troglitazone, and diclofenac), and some that are not associated with adverse effects due to cellular stress at human-relevant exposures (eg, caffeine, niacinamide, and phenoxyethanol). For each substance, concentration response data were generated for each biomarker at 3 timepoints. A Bayesian model was then developed to quantify the evidence for a biological response, and if present, a credibility range for the estimated point of departure (PoD) was determined. PoDs were compared with the plasma Cmax associated with the typical substance exposures, and indicated a clear differentiation between "low" risk and "high" risk chemical exposure scenarios. Developing robust methods to characterize the in vitro bioactivity of xenobiotics is an important part of non-animal safety assessment. The results presented in this work show that the cellular stress panel can be used, together with other new approach methodologies, to identify chemical exposures that are protective of consumer health.

A20 of nucleus pulposus cells plays a self-protection role via the nuclear factor-kappa B pathway in the inflammatory microenvironment

Aims

Inflammatory response plays a pivotal role in the pathophysiological process of intervertebral disc degeneration (IDD). A20 (also known as tumour necrosis factor alpha-induced protein 3 (TNFAIP3)) is a ubiquitin-editing enzyme that restricts nuclear factor-kappa B (NF-κB) signalling. A20 prevents the occurrence of multiple inflammatory diseases. However, the role of A20 in the initiation of IDD has not been elucidated. The aim of the study was to investigate the effect of A20 in senescence of TNF alpha (TNF-α)-induced nucleus pulposus cells (NPCs).

Methods

Immunohistochemical staining was performed to observe the expression of A20 in normal and degenerated human intervertebral discs. The NPCs were dissected from the tail vertebrae of healthy male Sprague-Dawley rats and were cultured in the incubator. In the experiment, TNF-α was used to mimic the inflammatory environment of IDD. The cell viability and senescence were examined to investigate the effect of A20 on TNF-α-treated NPCs. The expression of messenger RNA (mRNA)-encoding proteins related to matrix macromolecules (collagen II, aggrecan) and senescence markers (p53, p16). Additionally, NF-κB/p65 activity of NPCs was detected within different test compounds.

Results

The expression of A20 was upregulated in degenerate human intervertebral discs. The A20 levels of NPCs in TNF-α inflammatory microenvironments were dramatically higher than those of the control group. TNF-α significantly decreased cell proliferation potency but increased senescence-associated beta-galactosidase (SA-β-Gal) activity, the expression of senescence-associated proteins, the synthesis of extracellular matrix, and G1 cycle arrest. The senescence indicators and NF-κB/p65 expression of A20 downregulated group treated with TNF-α were significantly upregulated compared to TNF-α-treated normal NPCs.

Conclusion

A20 has a self-protective effect on the senescence of NPCs induced by TNF-α. The downregulation of A20 in NPCs exacerbated the senescence of NPCs induced by TNF-α.

Cite this article:Bone Joint Res. 2020;9(5):225–235.

A20 Promotes Ripoptosome Formation and TNF-Induced Apoptosis via cIAPs Regulation and NIK Stabilization in Keratinocytes

The ubiquitin-editing protein A20 (TNFAIP3) is a known key player in the regulation of immune responses in many organs. Genome-wide associated studies (GWASs) have linked A20 with a number of inflammatory and autoimmune disorders, including psoriasis. Here, we identified a previously unrecognized role of A20 as a pro-apoptotic factor in TNF-induced cell death in keratinocytes. This function of A20 is mediated via the NF-κB-dependent alteration of cIAP1/2 expression. The changes in cIAP1/2 protein levels promote NIK stabilization and subsequent activation of noncanonical NF-κB signaling. Upregulation of TRAF1 expression triggered by the noncanonical NF-κB signaling further enhances the NIK stabilization in an autocrine manner. Finally, stabilized NIK promotes the formation of the ripoptosome and the execution of cell death. Thus, our data demonstrate that A20 controls the execution of TNF-induced cell death on multiple levels in keratinocytes. This signaling mechanism might have important implications for the development of new therapeutic strategies for the treatment of A20-associated skin diseases.

A20 at the Crossroads of Cell Death, Inflammation, and Autoimmunity

A20 is a potent anti-inflammatory protein, acting by inhibiting nuclear factor κB (NF-κB) signaling and inflammatory gene expression and/or by preventing cell death. Mutations in the A20/TNFAIP3 gene have been associated with a plethora of inflammatory and autoimmune pathologies in humans and in mice. Although the anti-inflammatory role of A20 is well accepted, fundamental mechanistic questions regarding its mode of action remain unclear. Here, we review new findings that further clarify the molecular and cellular mechanisms by which A20 controls inflammatory signaling and cell death, and discuss new evidence for its involvement in inflammatory and autoimmune disease development.

Computation capacities of a broad class of signaling networks are higher than their communication capacities

Due to structural and functional abnormalities or genetic variations and mutations, there may be dysfunctional molecules within an intracellular signaling network that do not allow the network to correctly regulate its output molecules, such as transcription factors. This disruption in signaling interrupts normal cellular functions and may eventually develop some pathological conditions. In this paper, computation capacity of signaling networks is introduced as a fundamental limit on signaling capability and performance of such networks. In simple terms, the computation capacity measures the maximum number of computable inputs, that is, the maximum number of input values for which the correct functional output values can be recovered from the erroneous network outputs, when the network contains some dysfunctional molecules. This contrasts with the conventional communication capacity that measures instead the maximum number of input values that can be correctly distinguished based on the erroneous network outputs. The computation capacity is higher than the communication capacity whenever the network response function is not a one-to-one function of the input signals, and, unlike the communication capacity, it takes into account the input-output functional relationships of the network. By explicitly incorporating the effect of signaling errors that result in the network dysfunction, the computation capacity provides more information about the network and its malfunction. Two examples of signaling networks are considered in the paper, one regulating caspase3 and another regulating NFκB, for which computation and communication capacities are investigated. Higher computation capacities are observed for both networks. One biological implication of this finding is that signaling networks may have more 'capacity' than that specified by the conventional communication capacity metric. The effect of feedback is studied as well. In summary, this paper reports findings on a new fundamental feature of the signaling capability of cell signaling networks.

The small GTPase RAB1B promotes antiviral innate immunity by interacting with TNF receptor-associated factor 3 (TRAF3)

Innate immune detection of viral nucleic acids during viral infection activates a signaling cascade that induces type I and type III IFNs as well as other cytokines, to generate an antiviral response. This signaling is initiated by pattern recognition receptors, such as the RNA helicase retinoic acid-inducible gene I (RIG-I), that sense viral RNA. These sensors then interact with the adaptor protein mitochondrial antiviral signaling protein (MAVS), which recruits additional signaling proteins, including TNF receptor-associated factor 3 (TRAF3) and TANK-binding kinase 1 (TBK1), to form a signaling complex that activates IFN regulatory factor 3 (IRF3) for transcriptional induction of type I IFNs. Here, using several immunological and biochemical approaches in multiple human cell types, we show that the GTPase-trafficking protein RAB1B up-regulates RIG-I pathway signaling and thereby promotes IFN-β induction and the antiviral response. We observed that RAB1B overexpression increases RIG-I-mediated signaling to IFN-β and that RAB1B deletion reduces signaling of this pathway. Additionally, loss of RAB1B dampened the antiviral response, indicated by enhanced Zika virus infection of cells depleted of RAB1B. Importantly, we identified the mechanism of RAB1B action in the antiviral response, finding that it forms a protein complex with TRAF3 to facilitate the interaction of TRAF3 with mitochondrial antiviral signaling protein. We conclude that RAB1B regulates TRAF3 and promotes the formation of innate immune signaling complexes in response to nucleic acid sensing during RNA virus infection.

Role of Zinc in Immune System and Anti-Cancer Defense Mechanisms

The human body cannot store zinc reserves, so a deficiency can arise relatively quickly, e.g., through an improper diet. Severe zinc deficiency is rare, but mild deficiencies are common around the world. Many epidemiological studies have shown a relationship between the zinc content in the diet and the risk of cancer. The anti-cancer effect of zinc is most often associated with its antioxidant properties. However, this is just one of many possibilities, including the influence of zinc on the immune system, transcription factors, cell differentiation and proliferation, DNA and RNA synthesis and repair, enzyme activation or inhibition, the regulation of cellular signaling, and the stabilization of the cell structure and membranes. This study presents selected issues regarding the current knowledge of anti-cancer mechanisms involving this element.

A20 protects cells from TNF-induced apoptosis through linear ubiquitin-dependent and -independent mechanisms

The cytokine TNF promotes inflammation either directly by activating the MAPK and NF-κB signaling pathways, or indirectly by triggering cell death. A20 is a potent anti-inflammatory molecule, and mutations in the gene encoding A20 are associated with a wide panel of inflammatory pathologies, both in human and in the mouse. Binding of TNF to TNFR1 triggers the NF-κB-dependent expression of A20 as part of a negative feedback mechanism preventing sustained NF-κB activation. Apart from acting as an NF-κB inhibitor, A20 is also well-known for its ability to counteract the cytotoxic potential of TNF. However, the mechanism by which A20 mediates this function and the exact cell death modality that it represses have remained incompletely understood. In the present study, we provide in vitro and in vivo evidences that deletion of A20 induces RIPK1 kinase-dependent and -independent apoptosis upon single TNF stimulation. We show that constitutively expressed A20 is recruited to TNFR1 signaling complex (Complex I) via its seventh zinc finger (ZF7) domain, in a cIAP1/2-dependent manner, within minutes after TNF sensing. We demonstrate that Complex I-recruited A20 protects cells from apoptosis by stabilizing the linear (M1) ubiquitin network associated to Complex I, a process independent of its E3 ubiquitin ligase and deubiquitylase (DUB) activities and which is counteracted by the DUB CYLD, both in vitro and in vivo. In absence of linear ubiquitylation, A20 is still recruited to Complex I via its ZF4 and ZF7 domains, but this time protects the cells from death by deploying its DUB activity. Together, our results therefore demonstrate two distinct molecular mechanisms by which constitutively expressed A20 protect cells from TNF-induced apoptosis.

A20 overexpression exerts protective effects on podocyte injury in lupus nephritis by downregulating UCH-L1

Lupus nephritis (LN), an autoimmune kidney disease caused by systemic lupus erythematosus (SLE), is the inflammation of the kidney. Although the treatment of LN is still a therapeutic challenge for many practitioners, the present study aims to provide a new insight for the treatment and management. The study aims to explore the effect of A20 on LN in relation to the nuclear factor-kappa B (NF-κB) signaling pathway. MRL/lpr mice were used as the LN mouse model. Next, A20, UCH-L1, and NF-κB expression in LN patients and MRL/lpr mice was determined. A20 was upregulated in podocytes to assess biological functions of A20 in LN. Furthermore, to further investigate the pivotal role of the NF-κB pathway in LN, the NF-κB pathway was blocked in podocytes. Next, UCH-L1 was downregulated in MRL/lpr mice to assess biological functions of UCH-L1 in LN. A20 was downregulated, whereas UCH-L1 was upregulated in LN. Overexpressed A20 declined NF-κB, UCH-L1 expression, and the extent of p65 phosphorylation. A20 overexpression or UCH-L1 inhibition increased expression of synaptoporin and nephrin but decreased desmin expression and ubiquitin accumulation level in podocytes. Moreover, A20 overexpression or UCH-L1 inhibition increased the podocyte number but decreased protein level of cleaved caspase-3, podocyte lesion improvement, decreased foot process width, glomerulus basement membrane, and foot process fusion rate. In addition, urine protein, blood urea nitrogen, serum creatinine, and ds-DNA antibody levels decreased with elevated A20 or depleted UCH-L1. Collectively, it could be concluded that A20 protects against podocyte injury in LN via UCH-L1 by inactivating the NF-κB signaling pathway.

Expanding the spectrum of A20 haploinsufficiency in two Chinese families: cases report

Background

The association between mutations in the TNFAIP3 gene and a new autoinflammatory disease (called A20 haploinsufficiency, HA20) has recently been recognized. Here, we describe four patients with HA20 from two unrelated Chinese families.

Case presentation

A total of four patients from two families were included. The average age at onset was 5.9 years. All patients had no signs of eye or skin problems, such as uveitis, rash, folliculitis and dermal abscess. Prior to the recognition of HA20, P1 was diagnosed with SLE, liver fibrosis and hypothyroidism. She also had no oral, genital or perineal ulcers. P2 was diagnosed with Crohn’s disease and inflammatory bowel disease-related arthritis (IBD-RA). He had a perianal abscess but no oral or genital ulcers. P3, the father of P1 and P2, only had mild oral ulcers, arthralgia, and archosyrinx. P4 was diagnosed with polyarticular juvenile idiopathic arthritis (JIA), macrophage activation syndrome (MAS) and interstitial lung disease (ILD). Whole exome sequencing (WES) was performed in two families. WES revealed heterozygous c.559C > T in the TNFAIP3 gene in P1, P2 and P3, while the c.259C > T mutation in the TNFAIP3 gene was identified in P4. The c.259C > T mutations is novel.

Conclusion

HA20 had a different phenotype between families and even between family members with the same mutation. Liver fibrosis, hypothyroidism, ILD and MAS in the patients with HA20 were first reported in this study. Our results expanded the phenotype and genotype spectrum of A20 haploinsufficiency.

Electronic supplementary material

The online version of this article (10.1186/s12881-019-0856-1) contains supplementary material, which is available to authorized users.

Activation of the NF-κB Pathway and Heterozygous Deletion of TNFAIP3 (A20) Confer Superior Survival in Extranodal Natural Killer/T-Cell Lymphoma, Nasal Type

OBJECTIVES

To investigate the role of TNFAIP3 deletions and NF-κB activation in extranodal natural killer/T-cell lymphoma (ENKTCL), nasal type.

METHODS

In total, 138 patients with ENKTCL were included. Activation of NF-κB pathway and expression of TNFAIP3 (A20) were examined by immunohistochemistry. TNFAIP3 was analyzed for deletions using FICTION (fluorescence immunophenotyping and interphase cytogenetics as a tool for investigating neoplasms), for mutations using Sanger sequencing, and for promoter methylation using methylation-specific sequencing.

RESULTS

NF-κB pathway activation was observed in 31.2% of cases (43/138), TNFAIP3 expression was negative in 15.2% of cases (21/138), and heterozygous TNFAIP3 deletion was observed in 35% of cases (35/100). TNFAIP3 exons 2 to 9 mutations and promoter methylation were not observed. Kaplan-Meier analysis showed patients with NF-κB pathway activation or TNFAIP3 heterozygous deletion to have a longer overall survival.

CONCLUSIONS

Our study demonstrated that NF-κB activation and TNFAIP3 heterozygous deletion confer superior survival in patients with ENKTCL.

Disturbed Transcription of TLRs' Negative Regulators and Cytokines Secretion among TLR4- and 9-Activated PBMCs of Agammaglobulinemic Patients

Toll-like receptors (TLRs) are inevitable elements for immunity development and antibody production. TLRs are in close interaction with Bruton's tyrosine kinase which has been found mutated and malfunctioned in the prototype antibody deficiency disease named X-linked agammaglobulinemia (XLA). TLRs' ability was evaluated to induce transcription of TLR-negative regulators, including suppressor of cytokine signaling 1 (SOCS1), interleukin-1 receptor-associated kinase 3 (IRAK-M), tumor necrosis factor alpha-induced protein 3 (TNFAIP3, A20), and Ring finger protein 216 (RNF216), and Tumor necrosis factor-α (TNF-α) and Interferon-α (IFN-α) production via Lipopolysaccharides (LPS) and CpG-A oligodeoxynucleotides (CpG-A ODN). Measured by TaqMan real-time polymerase chain reaction (PCR), meaningfully increased transcripts of SOCS1 and RNF216 were found in XLA peripheral blood mononuclear cells (PBMCs). Also, TLR inductions of XLA have led to similar downregulations in the regulator's transcription which was different from that in healthy donors. Cytokine measurement by enzyme-linked immunosorbent assay (ELISA) revealed a significant lower TNF-α production both before and after LPS. By selected molecules in this study, TLRs' potential defectiveness range expands TLRs expression, downstream signaling, and cytokine production. The results show new potential elements that could play a part in TLRs defect and pathogenesis of agammaglobulinemia as well.

Responsiveness of chronic lymphocytic leukemia cells to B-cell receptor stimulation is associated with low expression of regulatory molecules of the nuclear factor-κB pathway

Chronic lymphocytic leukemia (CLL) is a disease with heterogeneous clinical and biological characteristics. Differences in Ca²⁺ levels among cases, both basal and upon B-cell receptor (BCR) stimulation, may reflect heterogeneity in the pathogenesis due to cell-intrinsic factors. Our aim was to elucidate cell-intrinsic differences between BCR-responsive and -unresponsive cases. We therefore determined BCR responsiveness ex vivo based on Ca²⁺ influx upon α-IgM stimulation of purified CLL cell fractions from 52 patients. Phosphorylation levels of various BCR signaling molecules, and expression of activation markers were assessed by flow cytometry. Transcription profiling of responsive (n=6) and unresponsive cases (n=6) was performed by RNA sequencing. Real-time quantitative polymerase chain reaction analysis was used to validate transcript level differences in a larger cohort. In 24 cases an α-IgM response was visible by Ca²⁺ influx which was accompanied by higher phosphorylation of PLCγ2 and Akt after α-IgM stimulation in combination with higher surface expression of IgM, IgD, CD19, CD38 and CD43 compared to the unresponsive cases (n=28). Based on RNA sequencing analysis several components of the canonical nuclear factor (NF)-κB pathway, especially those related to NF-κB inhibition, were expressed more highly in unresponsive cases. Moreover, upon α-IgM stimulation, the expression of these NF-κB pathway genes (especially genes coding for NF-κB pathway inhibitors but also NF-κB subunit REL) was upregulated in BCR-responsive cases while the level did not change, compared to basal level, in the unresponsive cases. These findings suggest that cells from CLL cases with enhanced NF-κB signaling have a lesser capacity to respond to BCR stimulation.

Both knock-down and overexpression of Rap2a small GTPase in macrophages result in impairment of NF-κB activity and inflammatory gene expression

Small Ras GTPases are key molecules that regulate a variety of cellular responses in different cell types. Rap1 plays important functions in the regulation of macrophage biology during inflammation triggered by toll-like receptors (TLRs). However, despite sharing a relatively high degree of similarity with Rap1, no studies concerning Rap2 in macrophages and innate immunity have been reported yet. In this work, we show that either way alterations in the levels of Rap2a hampers proper macrophages response to TLR stimulation. Rap2a is activated by LPS in macrophages, and although putative activator TLR-inducible Ras guanine exchange factor RasGEF1b was sufficient to induce, it was not fully required for Rap2a activation. Silencing of Rap2a impaired LPS-induced production of IL-6 cytokine and KC/Cxcl1 chemokine, and also NF-κB activity as measured by reporter gene studies. Surprisingly, overexpression of Rap2a did also lead to marked inhibition of NF-κB activation induced by LPS, Pam3CSK4 and downstream TLR signaling molecules. We also found that Rap2a can inhibit the LPS-induced phosphorylation of the NF-κB subunit p65 at serine 536. Collectively, our data suggest that expression levels of Rap2a in macrophages might be tightly regulated to avoid unbalanced immune response. Our results implicate Rap2a in TLR-mediated responses by contributing to balanced NF-κB activity status in macrophages.

Regulators of A20 (TNFAIP3): new drug-able targets in inflammation

Persistent activation of the transcription factor Nuclear factor-κB (NF-κB) is central to the pathogenesis of many inflammatory disorders, including those of the lung such as cystic fibrosis (CF), asthma, and chronic obstructive pulmonary disease (COPD). Despite recent advances in treatment, management of the inflammatory component of these diseases still remains suboptimal. A20 is an endogenous negative regulator of NF-κB signaling, which has been widely described in several autoimmune and inflammatory disorders and more recently in terms of chronic lung disorders. However, the underlying mechanism for the apparent lack of A20 in CF, COPD, and asthma has not been investigated. Transcriptional regulation of A20 is complex and requires coordination of different transcription factors. In this review we examine the existing body of research evidence on the regulation of A20, concentrating on pulmonary inflammation. Special focus is given to the repressor downstream regulatory element antagonist modulator (DREAM) and its nuclear and cytosolic action to regulate inflammation. We provide evidence that would suggest the A20-DREAM axis to be an important player in (airway) inflammatory responses and point to DREAM as a potential future therapeutic target for the modification of phenotypic changes in airway inflammatory disorders. A schematic summary describing the role of DREAM in inflammation with a focus on chronic lung diseases as well as the possible consequences of altered DREAM expression on immune responses is provided.

Calcitriol Ameliorates AngiotensinII-Induced Renal Injury Partly via Upregulating A20

Inflammation and reactive oxygen species (ROS) play crucial roles in the progression of chronic kidney diseases. Vitamin D has been shown anti-inflammatory effects, but the underlying mechanism is not fully understood. Here, we investigated whether calcitriol exerts protective effects via upregulating A20 in angiotensinII (AngII)-induced renal injury. Male C57BL/6 mice were infused with vehicle or AngII for 10 days. Calcitriol reduced infiltration of T lymphocytes and macrophages. This reduction of inflammatory cells was accompanied by elevated A20 and decreased pro-inflammatory cytokines (PICs) and reactive oxygen species (ROS). Calcitriol could inhibit NF-κB activation and necroptotic pathway. Induction of A20 was located primarily to the tubular epithelial cells. In rat proximal tubular epithelial cells (NRK-52E), calcitriol stably upregulated A20 and reduced the PICs and ROS. Inhibitory effect of A20 on PICs and ROS depended on suppressing NF-κB pathway and necroptotic pathway, respectively. A20 knockdown diminished the effect of calcitriol on suppressing NF-κB and necroptotic pathways. However, A20 deficiency could not abrogate the inhibitory effect of calcitriol on NF-κB and necroptotic pathways. Our results established that A20 is involved in the renoprotective effect by calcitriol via negatively modulating the NF-κB pathway and necroptotic pathway in AngII-induced renal injury.

A20, an essential component of the ubiquitin-editing protein complex, is a negative regulator of inflammation in human myometrium and foetal membranes

STUDY QUESTION

Does A20 regulate mediators involved in the terminal processes of human labour in primary myometrial and amnion cells?

SUMMARY ANSWER

A20 is a nuclear factor-kappa B (NF-κB) responsive gene that acts as a negative regulator of NF-κB-induced expression of pro-labour mediators.

WHAT IS KNOWN ALREADY

Inflammation is commonly implicated in spontaneous preterm birth and the processes involved in rupture of foetal membranes and uterine contractions. In myometrium and foetal membranes, the pro-inflammatory transcription factor NF-κB regulates the transcription of pro-labour mediators in response to inflammatory stimuli. In non-gestational tissues, A20 is widely recognised as an anti-inflammatory protein that inhibits inflammation-induced NF-κB signalling.

STUDY DESIGN, SIZE, DURATION

Primary human amnion and myometrial cells were used to determine the effect of pro-inflammatory mediators on A20 expression and the effect of A20 siRNA on the expression and secretion of pro-labour mediators. The expression of A20 was assessed in myometrium and foetal membranes from non-labouring and labouring women at preterm and or term (n = 8 or nine samples per group).

PARTICIPANTS/MATERIALS, SETTING, METHODS

The effects of pro-inflammatory mediators and of A20 siRNA in cell cultures were determined by quantitative RT-PCR (qRT-PCR), western blots, immunoassays, gelatin zymography and luciferase assays. A20 expression in tissue samples was assessed by qRT-PCR. Statistical significance was ascribed to a P value < 0.05.

MAIN RESULTS AND THE ROLE OF CHANCE

In primary cells isolated from myometrium and or amnion, the pro-inflammatory cytokines IL1B and TNF, the bacterial products flagellin and fsl-1, and the viral double stranded RNA analogue poly(I:C) significantly increased A20 mRNA expression via NF-κB. A20 siRNA studies in primary myometrial and amnion cells demonstrated an augmentation of inflammation-induced expression and or secretion of pro-inflammatory cytokines (IL1A, IL6), chemokines (CXCL1, CXCL8, CCL2), adhesion molecules (ICAM1, VCAM1), contraction-associated proteins (PTGS2, PTGFR, PGF2α) and the extracellular matrix degrading enzyme MMP9, as well as NF-κB activation. Inhibition of NF-κB activity significant attenuated inflammation-induced expression of pro-labour mediators in A20 siRNA transfected cells. Finally, A20 mRNA expression was decreased in myometrium and foetal membranes with labour, and in foetal membranes with chorioamnionitis.

LARGE SCALE DATA

Not applicable.

LIMITATIONS, REASONS FOR CAUTION

The conclusions of this study are solely reliant on the data from in vitro experiments using cells isolated from myometrium and amnion.

WIDER IMPLICATIONS OF THE FINDINGS

The results of this study raise the possibility that targeting A20 may be a therapeutic approach to reduce inflammation associated with spontaneous preterm birth.

STUDY FUNDING AND COMPETING INTEREST(S)

Associate Professor Martha Lappas is supported by a Career Development Fellowship from the National Health and Medical Research Council (NHMRC; grant no. 1047025). Funding for this study was provided by the NHMRC (grant no. 1058786), Norman Beischer Medical Research Foundation and the Mercy Research Foundation. There are no competing interests.

IL-17RC is critically required to maintain baseline A20 production to repress JNK isoform-dependent tumor-specific proliferation

The IL-17/IL-17R axis has controversial roles in cancer, which may be explained by tumor-specific results. Here, we describe a novel molecular mechanism underlying IL-17RC-controlled tumor-specific proliferation. Triggered by IL-17RC knockdown (KD), B16 melanoma and 4T1 carcinoma cells inversely altered homeostatic tumor proliferation and tumor growth in vitro and in vivo. In contrast to the existing dogma that IL-17RC-dependent signaling activates the JNK pathway, IL-17RC KD in both tumor cell lines caused aberrant expression and activation of different JNK isoforms along with markedly diminished levels of the ubiquitin-editing enzyme A20. We demonstrated that differential up-regulation of JNK1 and JNK2 in the two tumor cell lines was responsible for the reciprocal regulation of c-Jun activity and tumor-specific proliferation. Furthermore, we showed that A20 reconstitution of IL-17RCKD clones with expression of full-length A20, but not a truncation-mutant, reversed aberrant JNK1/JNK2 activities and tumor-specific proliferation. Collectively, our study reveals a critical role of IL-17RC in maintaining baseline A20 production and a novel role of the IL-17RC-A20 axis in controlling JNK isoform-dependent tumor-specific homeostatic proliferation.

A20 regulates canonical wnt-signaling through an interaction with RIPK4

A20 is a ubiquitin-editing enzyme that is known to regulate inflammatory signaling and cell death. However, A20 mutations are also frequently found in multiple malignancies suggesting a potential role as a tumor suppressor as well. We recently described a novel role for A20 in regulating the wnt-beta-catenin signaling pathway and suppressing colonic tumor development in mice. The underlying mechanisms for this phenomenon are unclear. To study this, we first generated A20 knockout cell lines by genome-editing techniques. Using these cells, we show that loss of A20 causes dysregulation of wnt-dependent gene expression by RNAseq. Mechanistically, A20 interacts with a proximal signaling component of the wnt-signaling pathway, receptor interacting protein kinase 4 (RIPK4), and regulation of wnt-signaling by A20 occurs through RIPK4. Finally, similar to the mechanism by which A20 regulates other members of the receptor interacting protein kinase family, A20 modifies ubiquitin chains on RIPK4 suggesting a possible molecular mechanism for A20’s control over the wnt-signaling pathway.

A20 deubiquitinase controls PGC-1α expression in the adipose tissue

BACKGROUND

Peroxisome proliferator-activated receptor γ coactivator- 1alpha (PGC-1α) plays an important role in whole body metabolism and, particularly in glucose homeostasis. Its expression is highly regulated and, small variations in tissue levels can have a major impact in a number of physiological and pathological conditions. Recent studies have shown that the ubiquitin/proteasome system plays a role in the control of PGC-1α degradation.

METHODS

Here we evaluated the interaction of PGC-1α with the protein A20, which plays a dual-role in the control of the ubiquitin/proteasome system acting as a deubiquitinase and as an E3 ligase. We employed immunoprecipitation, quantitative real-time PCR and immunofluorescence staining to evaluate PGC-1α, A20, PPARγ and ubiquitin in the adipose tissue of humans and mice.

RESULTS

In distinct sites of the adipose tissue, A20 binds to PGC-1α. At least in the subcutaneous fat of humans and mice the levels of PGC-1α decrease during obesity, while its physical association with A20 increases. The inhibition of A20 leads to a reduction of PGC-1α and PPARγ expression, suggesting that A20 acts as a protective factor against PGC-1α disposal.

CONCLUSION

We provide evidence that mechanisms regulating PGC-1α ubiquitination are potentially involved in the control of the function of this transcriptional co-activator.

Zinc Inhibits Phosphate-Induced Vascular Calcification through TNFAIP3-Mediated Suppression of NF-κB

Background The high cardiovascular morbidity and mortality of patients with CKD may result in large part from medial vascular calcification, a process promoted by hyperphosphatemia and involving osteo-/chondrogenic transdifferentiation of vascular smooth muscle cells (VSMCs). Reduced serum zinc levels have frequently been observed in patients with CKD, but the functional relevance of this remains unclear.Methods We performed experiments in primary human aortic VSMCs; klotho-hypomorphic (kl/kl), subtotal nephrectomy, and cholecalciferol-overload mouse calcification models; and serum samples from patients with CKD.Results In cultured VSMCs, treatment with zinc sulfate (ZnSO₄) blunted phosphate-induced calcification, osteo-/chondrogenic signaling, and NF-κB activation. ZnSO₄ increased the abundance of zinc-finger protein TNF-α-induced protein 3 (TNFAIP3, also known as A20), a suppressor of the NF-κB pathway, by zinc-sensing receptor ZnR/GPR39-dependent upregulation of TNFAIP3 gene expression. Silencing of TNFAIP3 in VSMCs blunted the anticalcific effects of ZnSO₄ under high phosphate conditions. kl/kl mice showed reduced plasma zinc levels, and ZnSO₄ supplementation strongly blunted vascular calcification and aortic osteoinduction and upregulated aortic Tnfaip3 expression. ZnSO₄ ameliorated vascular calcification in mice with chronic renal failure and mice with cholecalciferol overload. In patients with CKD, serum zinc concentrations inversely correlated with serum calcification propensity. Finally, ZnSO₄ ameliorated the osteoinductive effects of uremic serum in VSMCs.Conclusions Zinc supplementation ameliorates phosphate-induced osteo-/chondrogenic transdifferentiation of VSMCs and vascular calcification through an active cellular mechanism resulting from GPR39-dependent induction of TNFAIP3 and subsequent suppression of the NF-κB pathway. Zinc supplementation may be a simple treatment to reduce the burden of vascular calcification in CKD.

O-Linked β-N-Acetylglucosamine Modification of A20 Enhances the Inhibition of NF-κB (Nuclear Factor-κB) Activation and Elicits Vascular Protection After Acute Endoluminal Arterial Injury

OBJECTIVE

Recently, we have demonstrated that acute glucosamine-induced augmentation of protein O-linked β-N-acetylglucosamine (O-GlcNAc) levels inhibits inflammation in isolated vascular smooth muscle cells and neointimal formation in a rat model of carotid injury by interfering with NF-κB (nuclear factor-κB) signaling. However, the specific molecular target for O-GlcNAcylation that is responsible for glucosamine-induced vascular protection remains unclear. In this study, we test the hypothesis that increased A20 (also known as TNFAIP3 [tumor necrosis factor α-induced protein 3]) O-GlcNAcylation is required for glucosamine-mediated inhibition of inflammation and vascular protection.

APPROACH AND RESULTS

In cultured rat vascular smooth muscle cells, both glucosamine and the selective O-linked N-acetylglucosaminidase inhibitor thiamet G significantly increased A20 O-GlcNAcylation. Thiamet G treatment did not increase A20 protein expression but did significantly enhance binding to TAX1BP1 (Tax1-binding protein 1), a key regulatory protein for A20 activity. Adenovirus-mediated A20 overexpression further enhanced the effects of thiamet G on prevention of TNF-α (tumor necrosis factor-α)-induced IκB (inhibitor of κB) degradation, p65 phosphorylation, and increases in DNA-binding activity. A20 overexpression enhanced the inhibitory effects of thiamet G on TNF-α-induced proinflammatory cytokine expression and vascular smooth muscle cell migration and proliferation, whereas silencing endogenous A20 by transfection of specific A20 shRNA significantly attenuated these inhibitory effects. In balloon-injured rat carotid arteries, glucosamine treatment markedly inhibited neointimal formation and p65 activation compared with vehicle treatment. Adenoviral delivery of A20 shRNA to the injured arteries dramatically reduced balloon injury-induced A20 expression and inflammatory response compared with scramble shRNA and completely abolished the vascular protection of glucosamine.

CONCLUSIONS

These results suggest that O-GlcNAcylation of A20 plays a key role in the negative regulation of NF-κB signaling cascades in TNF-α-treated vascular smooth muscle cells in culture and in acutely injured arteries, thus protecting against inflammation-induced vascular injury.

Evaluation of the TLR negative regulatory network in CVID patients

Common variable immunodeficiency (CVID), a clinically symptomatic primary immunodeficiency disease (PID), is characterized by hypogammaglobulinemia leading to recurrent infections and various complications. Recently, some defects in the signaling of TLRs have been identified in CVID patients which led us to investigate the expression of TLR4 and 9 negative regulatory molecules and their upregulation status following their activation. Using TaqMan real-time PCR, SOCS1, TNFAIP3, RFN216, and IRAK-M transcripts among peripheral blood mononuclear cells (PBMCs) were measured with/without TLR4 and 9 activations. TLR4 and 9 were activated by lipopolysaccharide (LPS) and unmethylated CpG-oligodeoxynucleotide (CpG-ODN), respectively. Production of IFN-α and TNF-α cytokines, as a part of the functional response of mentioned TLRs, was also measured using ELISA. Deficient transcripts of IRAK-M and TNFAIP3 in unstimulated PBMCs and lower production of TNF-α and IFN-α after treatments were observed. Upregulation of RFN216 and TNFAIP3 after TLR9 activation was abnormal compared to healthy individuals. Significant correlations were found between abnormal IRAK-M and TNFAIP3 transcripts, and lymphadenopathy and inflammatory scenarios in patients, respectively. It seems that the transcriptional status of some negative regulatory molecules is disturbed in CVID patients, and this could be caused by the underlying pathogenesis of CVID and could involve complications like autoimmunity and inflammatory responses.

Plasma proteins associated with circulating carotenoids in Nepalese school-aged children

Carotenoids are naturally occurring pigments that function as vitamin A precursors, antioxidants, anti-inflammatory agents or biomarkers of recent vegetable and fruit intake, and are thus important for population health and nutritional assessment. An assay approach that measures proteins could be more technologically feasible than chromatography, thus enabling more frequent carotenoid status assessment. We explored associations between proteomic biomarkers and concentrations of 6 common dietary carotenoids (α-carotene, β-carotene, lutein/zeaxanthin, β-cryptoxanthin, and lycopene) in plasma from 500 6-8 year old Nepalese children. Samples were depleted of 6 high-abundance proteins. Plasma proteins were quantified using tandem mass spectrometry and expressed as relative abundance. Linear mixed effects models were used to determine the carotenoid:protein associations, accepting a false discovery rate of q < 0.10. We quantified 982 plasma proteins in >10% of all child samples. Among these, relative abundance of 4 were associated with β-carotene, 11 with lutein/zeaxanthin and 51 with β-cryptoxanthin. Carotenoid-associated proteins are notably involved in lipid and vitamin A transport, antioxidant function and anti-inflammatory processes. No protein biomarkers met criteria for association with α-carotene or lycopene. Plasma proteomics may offer an approach to assess functional biomarkers of carotenoid status, intake and biological function for public health application. Original maternal micronutrient trial from which data were derived as a follow-up activity was registered at ClinicalTrials.gov: NCT00115271.

A20/Tumor Necrosis Factor α-Induced Protein 3 in Immune Cells Controls Development of Autoinflammation and Autoimmunity: Lessons from Mouse Models

Immune cell activation is a stringently regulated process, as exaggerated innate and adaptive immune responses can lead to autoinflammatory and autoimmune diseases. Perhaps the best-characterized molecular pathway promoting cell activation is the nuclear factor-κB (NF-κB) signaling pathway. Stimulation of this pathway leads to transcription of numerous pro-inflammatory and cell-survival genes. Several mechanisms tightly control NF-κB activity, including the key regulatory zinc finger (de)ubiquitinating enzyme A20/tumor necrosis factor α-induced protein 3 (TNFAIP3). Single nucleotide polymorphisms (SNPs) in the vicinity of the TNFAIP3 gene are associated with a spectrum of chronic systemic inflammatory diseases, indicative of its clinical relevance. Mice harboring targeted cell-specific deletions of the Tnfaip3 gene in innate immune cells such as macrophages spontaneously develop autoinflammatory disease. When immune cells involved in the adaptive immune response, such as dendritic cells or B-cells, are targeted for A20/TNFAIP3 deletion, mice develop spontaneous inflammation that resembles human autoimmune disease. Therefore, more knowledge on A20/TNFAIP3 function in cells of the immune system is beneficial in our understanding of autoinflammation and autoimmunity. Using the aforementioned mouse models, novel A20/TNFAIP3 functions have recently been described including control of necroptosis and inflammasome activity. In this review, we discuss the function of the A20/TNFAIP3 enzyme and its critical role in various innate and adaptive immune cells. Finally, we discuss the latest findings on TNFAIP3 SNPs in human autoinflammatory and autoimmune diseases and address that genotyping of TNFAIP3 SNPs may guide treatment decisions.

Dissection and function of autoimmunity-associated TNFAIP3 (A20) gene enhancers in humanized mouse models

Enhancers regulate gene expression and have been linked with disease pathogenesis. Little is known about enhancers that regulate human disease-associated genes in primary cells relevant for pathogenesis. Here we use BAC transgenics and genome editing to dissect, in vivo and in primary immune cells, enhancers that regulate human TNFAIP3, which encodes A20 and is linked with autoimmune diseases. A20 expression is dependent on a topologically associating subdomain (sub-TAD) that harbors four enhancers, while another >20 enhancers in the A20 locus are redundant. This sub-TAD contains cell- and activation-specific enhancers, including an enhancer (termed TT>A) harboring a proposed causal SLE-associated SNV. Deletion of the sub-TAD or the TT>A enhancer results in enhanced inflammatory responses, autoantibody production, and inflammatory arthritis, thus establishing functional importance in vivo and linking enhancers with a specific disease phenotype. These findings provide insights into enhancers that regulate human A20 expression to prevent inflammatory pathology and autoimmunity.

The human TNFAIP3 gene, which encodes for A20, is associated with autoimmune diseases. Here, the authors use BAC transgenics combined with CRISPR- and recombineering-mediated genome editing to dissect in vivo and in primary immune cells, the role of enhancers regulating TNFAIP3.

A20 inhibits the motility of HCC cells induced by TNF-α

Metastasis of hepatocellular carcinoma (HCC) can be facilitated by TNF-α, a prototypical inflammatory cytokine in the HCC microenvironment. A20 is a negative regulator of NF-κB signaling pathway. In the present study we ask whether A20 plays a role in HCC metastasis. We found that A20 expression was downregulated in the invasive cells of microvascular invasions (MVI) compared with the noninvasive cells in 89 tissue samples from patients with HCC by immunochemistry methods. Overexpression of A20 in HCC cell lines inhibited their motility induced by TNF-α. Furthermore, the overexpression of A20 inhibited epithelial-mesenchymal transition (EMT), FAK activation and RAC1 activity. By contrast, knockdown of A20 in one HCC cell line results in the converse. In addition, the overexpression of A20 restrained the formation of MVI in HCC xenograft in nude mice treated with TNF-α. All the results suggested that A20 functioned as a negative regulator in motility of HCC cells induced by TNF-α.

Deubiquitinases A20 and CYLD modulate costimulatory signaling via CD137 (4-1BB)

TRAF2 dependent K63-polyubiquitinations have been recently shown to connect CD137 (4-1BB) stimulation to NF-κB activation. In a search of deubiquitinase enzymes (DUBs) that could regulate such a signaling route, A20 and CYLD were found to coimmunoprecipitate with CD137 and TRAF2 complexes. Indeed, overexpression of A20 or CYLD downregulated CD137-elicited ubiquitination of TRAF2 and TAK1 upon stimulation with agonist monoclonal antibodies. Moreover, overexpression of A20 or CYLD downregulated CD137-induced NF-κB activation in cultured cells and in gene-transferred hepatocytes in vivo, while silencing these deubiquitinases enhanced CD137 costimulation of primary human CD8 T cells. Therefore A20 and CYLD directly downregulate the signaling from a T and NK-cell costimulatory receptor under exploitation for cancer immunotherapy in clinical trials.

Altered expression of Tumor Necrosis Factor Alpha -Induced Protein 3 correlates with disease severity in Ulcerative Colitis

Ulcerative colitis (UC), an inflammatory disorder of the colon arises from dysregulated immune response towards gut microbes. Transcription factor NFκB is a major regulatory component influencing mucosal inflammation. We evaluated expression of Tumor Necrosis Factor Alpha Induced Protein3 (TNFAIP3), the inhibitor of NFκB activation and its associated partners ITCH, RNF11 and Tax1BP1 in inflamed mucosa of UC patients. We found highly significant up-regulated mRNA expression of TNFAIP3 that negatively correlated with disease activity in UC. mRNA levels of ITCH, RNF11 and Tax1BP1 were significantly down-regulated. Significant positive correlation with disease activity was noted for Tax1BP1. All four genes showed significant down-regulation at protein level. mRNA levels of inducers of TNFAIP3 expression, NFκB p65 subunit and MAST3 was determined. There was significant increase in p65 mRNA expression and down-regulated MAST3 expression. This suggested that increase in NFκB expression regulates TNFAIP3 levels. Deficiency of TNFAIP3 expression resulted in significant up-regulation of NFκB p65 sub-unit as well as its downstream genes such as iNOS, an inflammatory marker, inhibitors of apoptosis like cIAP2 and XIAP and mediators of anti-apoptotic signals TRAF1 and TRAF2. Taken together, decreased expression of TNFAIP3 and its partners contribute to inflammation and up-regulation of apoptosis inhibitors that may create microenvironment for colorectal cancer.

Inflammation-Related Gene Polymorphisms Associated With Primary Immune Thrombocytopenia

Primary immune thrombocytopenia (ITP) is an acquired autoimmune disease characterized by a reduced platelet count and an increased risk of bleeding. Although immense research has improved our understanding of ITP, the pathogenesis remains unclear. Here, we investigated the involvement of 25 single-nucleotide polymorphisms (SNPs) of the inflammation-related genes, including CD24, CD226, FCRL3, IL2, IRF5, ITGAM, NLRP3, CARD8, PTPN22, SH2B2, STAT4, TNFAIP3, and TRAF1, in the pathogenesis and treatment response of ITP. We recruited 312 ITP inpatients and 154 healthy participants in this case–control study. Inflammation-related SNP genotyping was performed on the Sequenom MassARRAY iPLEX platform. The expression of TNFAIP3 mRNA was determined by quantitative real-time RT-PCR. All SNPs in healthy controls were consistent with Hardy–Weinberg equilibrium. Statistical analysis revealed that rs10499194 in TNFAIP3 was significantly associated with a decreased risk of ITP after Bonferroni multiple correction (codominant, CT vs. CC, OR = 0.431, 95% CI = 0.262–0.711, p = 0.001; dominant, TT/CT vs. CC, OR = 0.249, 95% CI = 0.141–0.440, p = 0.000). Besides, TNFAIP3 expression was significantly higher in patients with CT and pooled CT/TT genotypes compared with CC genotype (p = 0.001; p = 0.001). Interestingly, rs10499194 was also associated with corticosteroid-sensitivity (codominant, CT vs. CC, OR = 0.092, 95% CI = 0.021–0.398, p = 0.001; dominant, TT/CT vs. CC, OR = 0.086, 95% CI = 0.020–0.369, p = 0.001; allelic, T vs. C, OR = 0.088, 95% CI = 0.021–0.372, p = 0.001). Furthermore, no significant association was found between inflammation-related SNPs and the severity or refractoriness of ITP after Bonferroni multiple correction. Our findings suggest that rs10499194 may be a protective factor for susceptibility and corticosteroid sensitivity in ITP patients.

CYLD, A20 and OTULIN deubiquitinases in NF-κB signaling and cell death: so similar, yet so different

Polyubiquitination of proteins has a pivotal role in the regulation of numerous cellular functions such as protein degradation, DNA repair and cell signaling. As deregulation of these processes can result in pathological conditions such as inflammatory diseases, neurodegeneration or cancer, tight regulation of the ubiquitin system is of tremendous importance. Ubiquitination by E3 ubiquitin ligases can be counteracted by the activity of several deubiquitinating enzymes (DUBs). CYLD, A20 and OTULIN have been implicated as key DUBs in the negative regulation of NF-κB transcription factor-mediated gene expression upon stimulation of cytokine receptors, antigen receptors and pattern recognition receptors, by removing distinct types of polyubiquitin chains from specific NF-κB signaling proteins. In addition, they control TNF-induced cell death signaling leading to apoptosis and necroptosis via similar mechanisms. In the case of A20, also catalytic-independent mechanisms of action have been demonstrated to have an important role. CYLD, A20 and OTULIN have largely overlapping substrates, suggesting at least partially redundant functions. However, mice deficient in one of the three DUBs show significant phenotypic differences, indicating also non-redundant functions. Here we discuss the activity and polyubiquitin chain-type specificity of CYLD, A20 and OTULIN, their specific role in NF-κB signaling and cell death, the molecular mechanisms that regulate their activity, their role in immune homeostasis and the association of defects in their activity with inflammation, autoimmunity and cancer.

The NF-κB-dependent and -independent transcriptome and chromatin landscapes of human coronavirus 229E-infected cells

Coronavirus replication takes place in the host cell cytoplasm and triggers inflammatory gene expression by poorly characterized mechanisms. To obtain more insight into the signals and molecular events that coordinate global host responses in the nucleus of coronavirus-infected cells, first, transcriptome dynamics was studied in human coronavirus 229E (HCoV-229E)-infected A549 and HuH7 cells, respectively, revealing a core signature of upregulated genes in these cells. Compared to treatment with the prototypical inflammatory cytokine interleukin(IL)-1, HCoV-229E replication was found to attenuate the inducible activity of the transcription factor (TF) NF-κB and to restrict the nuclear concentration of NF-κB subunits by (i) an unusual mechanism involving partial degradation of IKKβ, NEMO and IκBα and (ii) upregulation of TNFAIP3 (A20), although constitutive IKK activity and basal TNFAIP3 expression levels were shown to be required for efficient virus replication. Second, we characterized actively transcribed genomic regions and enhancers in HCoV-229E-infected cells and systematically correlated the genome-wide gene expression changes with the recruitment of Ser5-phosphorylated RNA polymerase II and prototypical histone modifications (H3K9ac, H3K36ac, H4K5ac, H3K27ac, H3K4me1). The data revealed that, in HCoV-infected (but not IL-1-treated) cells, an extensive set of genes was activated without inducible p65 NF-κB being recruited. Furthermore, both HCoV-229E replication and IL-1 were shown to upregulate a small set of genes encoding immunomodulatory factors that bind p65 at promoters and require IKKβ activity and p65 for expression. Also, HCoV-229E and IL-1 activated a common set of 440 p65-bound enhancers that differed from another 992 HCoV-229E-specific enhancer regions by distinct TF-binding motif combinations. Taken together, the study shows that cytoplasmic RNA viruses fine-tune NF-κB signaling at multiple levels and profoundly reprogram the host cellular chromatin landscape, thereby orchestrating the timely coordinated expression of genes involved in multiple signaling, immunoregulatory and metabolic processes.

Coronaviruses are major human and animal pathogens. They belong to a family of plus-strand RNA viruses that have extremely large genomes and encode a variety of proteins involved in virus-host interactions. The four common coronaviruses (HCoV-229E, NL63, OC43, HKU1) cause mainly upper respiratory tract infections, while zoonotic coronaviruses (SARS-CoV and MERS-CoV) cause severe lung disease, including acute respiratory distress syndrome (ARDS). The molecular basis for this fundamentally different pathology is incompletely understood. Our study provides a genome-wide investigation of epigenetic changes occurring in response to HCoV-229E. We identify at high resolution a large number of regulatory regions in the genome of infected cells that coordinate de novo gene transcription. Many of these genes have immunomodulatory functions and, most likely, contribute to limiting viral replication, while other factors may promote viral replication. The study provides an intriguing example of a virus that completes its entire life cycle in the cytoplasm while sending multiple signals to the nuclear chromatin compartment to adjust the host cell repertoire of transcribed genes. The approach taken in this study is expected to provide a suitable framework for future studies aimed at dissecting and comparing host responses to representative coronaviruses with different pathogenic potential in humans.

Antioxidant and anti-inflammatory effects of zinc. Zinc-dependent NF-κB signaling

Zinc is a nutritionally fundamental trace element, essential to the structure and function of numerous macromolecules, including enzymes regulating cellular processes and cellular signaling pathways. The mineral modulates immune response and exhibits antioxidant and anti-inflammatory activity. Zinc retards oxidative processes on a long-term basis by inducing the expression of metallothioneins. These metal-binding cysteine-rich proteins are responsible for maintaining zinc-related cell homeostasis and act as potent electrophilic scavengers and cytoprotective agents. Furthermore, zinc increases the activation of antioxidant proteins and enzymes, such as glutathione and catalase. On the other hand, zinc exerts its antioxidant effect via two acute mechanisms, one of which is the stabilization of protein sulfhydryls against oxidation. The second mechanism consists in antagonizing transition metal-catalyzed reactions. Zinc can exchange redox active metals, such as copper and iron, in certain binding sites and attenuate cellular site-specific oxidative injury. Studies have demonstrated that physiological reconstitution of zinc restrains immune activation, whereas zinc deficiency, in the setting of severe infection, provokes a systemic increase in NF-κB activation. In vitro studies have shown that zinc decreases NF-κB activation and its target genes, such as TNF-α and IL-1β, and increases the gene expression of A20 and PPAR-α, the two zinc finger proteins with anti-inflammatory properties. Alternative NF-κB inhibitory mechanism is initiated by the inhibition of cyclic nucleotide phosphodiesterase, whereas another presumed mechanism consists in inhibition of IκB kinase in response to infection by zinc ions that have been imported into cells by ZIP8.

Mutation analysis of tumor necrosis factor alpha-induced protein 3 gene in Hodgkin lymphoma

AIMS

Survival and proliferation of Hodgkin and Reed-Sternberg (HRS) cells, the malignant cells of classical Hodgkin lymphoma (CHL), are dependent on constitutive activation of nuclear factor kB (NF-κB). A20, encoded by TNF alpha-induced protein 3 (TNFAIP₃₎, one of the inhibitors of NF-kB, was found to be inactivated by deletions and/or point mutations in CHL.

METHODS

TNFAIP₃ mutations were examined in 37 patients with CHL by using PCR and direct sequencing. In addition, protein expression of A20 was evaluated by immunohistochemistry. Epstein-Barr virus (EBV) status of HL samples was determined by EBV EBER chromogenic in situ hybridization (ISH).

RESULTS

We identified 8 mutation positive cases in a collective of 37 investigated cases (22%). Mutations were most frequent in the nodular sclerosis subtype. Our results revealed the tendency that cases harboring A20 mutations were negative for A20 staining. None of A20 mutation-positive CHL cases showed EBV infection.

CONCLUSIONS

Our study confirms the involvement of the TNFAIP₃ tumor suppressor gene in CHL. A20 may represent a suppressor of human lymphoma and provide a critical molecular link between chronic inflammation and cancer. None of A20 mutation-positive CHL cases showed EBV infection. This fact suggests complementing functions of TNFAIP₃ inactivation and EBV infection in CHL pathogenesis and may represent an interesting point of further investigations.

A20 inhibits lipopolysaccharide-induced inflammation in enterocytes

AIM

To examine the role of A20 in the regulation of intestinal epithelial cells (IECs) inflammation.

METHODS

Using gene transfection, both stable overexpression and knockdown A20-expressed HT-29 cell lines were established. Accordingly, the cells were divided into the following groups: The control group, the A20 overexpression group, the A20 knockdown group and the respective controls. A20 was stimulated with lipopolysaccharide (LPS) in a dose- and time-dependent manner and was detected using western blotting and real-time polymerase chain reaction (PCR) analyses. Immunofluorescence and western blotting analyses were performed to investigate the role of A20 in the regulation of nuclear factor (NF)-κB activation and translocation into the nucleus. ELISA and real-time PCR were performed to examine A20 in regulating the release of the following inflammatory cytokines: Tumor necrosis factor (TNF)-α, interleukin (IL)-1β, IL-6 and IL-8.

RESULTS

The expression of A20 in IECs was inducible. When intestinal epithelial cells were subjected to the stimulation of LPS, the expression of A20 was increased, and the expression of A20 was induced in a dose- and time-dependent manner. The expression of A20 was very low in HT-29 cells without LPS stimulation but rapidly increased and was maintained at a high level 2-4 h after stimulation with LPS. These levels gradually declined with a change in time-course, and the expression of A20 increased with increasing LPS stimulation. Western blotting and immunofluorescence revealed that overexpression of A20 can inhibit NF-κB activation and its translocation to the nucleus. The overexpression of A20 can reduce the levels of proinflammatory cytokines involved in the pathophysiology of inflammatory bowel disease. There was no significant difference in the expression of IL-8 mRNA in the control group, A20 overexpression group or A20 knockdown group without LPS stimulation (P > 0.05); however, while after 2 h, 4 h and 8 h stimulation with LPS, the expression of IL-8 in the A20 overexpression group was lower than the control group and the A20 knockdown group (P < 0.05 or P < 0.01). The expression of TNF-α was different at different time points after 8 h of LPS stimulation (F = 31.33, DF = 5, P < 0.001), and the expression of TNF-α increased as the LPS stimulation time increased. Upon LPS stimulation, lower levels of TNF-α were detected in the A20 overexpression cell lines (P < 0.05). There were no significant differences in the induction of IL-6 and IL-1β among the control group, A20 overexpression group and A20 knockdown group (P > 0.05).

CONCLUSION

A20 plays an important role in limiting inflammation by inhibiting LPS-induced NF-κB responses in the gut luminal. A20 may be a potential therapeutic tool for inflammatory diseases.

Upregulation of neuronal zinc finger protein A20 expression is required for electroacupuncture to attenuate the cerebral inflammatory injury mediated by the nuclear factor-kB signaling pathway in cerebral ischemia/reperfusion rats

Background

Zinc finger protein A20 (tumor necrosis factor alpha-induced protein 3) functions as a potent negative feedback inhibitor of the nuclear factor-kB (NF-kB) signaling. It exerts these effects by interrupting the activation of IkB kinase beta (IKKβ), the most critical kinase in upstream of NF-kB, and thereby controlling inflammatory homeostasis. We reported previously that electroacupuncture (EA) could effectively suppress IKKβ activation. However, the mechanism underlying these effects was unclear. Therefore, the current study further explored the effects of EA on A20 expression in rat brain and investigated the possible mechanism of A20 in anti-neuroinflammation mediated by EA using transient middle cerebral artery occlusion (MCAO) rats.

Methods

Rats were treated with EA at the “Baihui (GV20),” “Hegu (L14),” and “Taichong (Liv3)” acupoints once a day starting 2 h after focal cerebral ischemia. The spatiotemporal expression of A20, neurobehavioral scores, infarction volumes, cytokine levels, glial cell activation, and the NF-kB signaling were assessed at the indicated time points. A20 gene interference (overexpression and silencing) was used to investigate the role of A20 in mediating the neuroprotective effects of EA and in regulating the interaction between neuronal and glial cells by suppressing neuronal NF-kB signaling during cerebral ischemia/reperfusion-induced neuroinflammation.

Results

EA treatment increased A20 expression with an earlier peak and longer lasting upregulation. The upregulated A20 protein was predominantly located in neurons in the cortical zone of the ischemia/reperfusion. Furthermore, neuronal A20 cell counts were positively correlated with neurobehavioral scores but negatively correlated with infarct volume, the accumulation of pro-inflammatory cytokines, and glial cell activation. Moreover, the effects of EA on improving the neurological outcome and suppressing neuroinflammation in the brain were reversed by A20 silencing. Finally, A20 silencing also suppressed the ability of EA to inhibit neuronal NF-kB signaling pathway.

Conclusions

Ischemia/reperfusion cortical neurons in MCAO rats are the main cell types that express A20, and there is a correlation between A20 expression and the suppression of neuroinflammation and the resulting neuroprotective effects. EA upregulated neuronal A20 expression, which played an essential role in the anti-inflammatory effects of EA by suppressing the neuronal NF-kB signaling pathway in the brains of MCAO rats.

A20 reduces lipid storage and inflammation in hypertrophic adipocytes via p38 and Akt signaling

Adipose tissue plays a vital role in the development of obesity and related disorders. Our previous study showed that A20, an ubiquitin-editing enzyme with anti-inflammation function, attenuated free fatty acids (FFAs)-induced lipid accumulation in nonalcoholic steatohepatitis. Here, we investigated A20 expression in adipose tissue of obese individuals and its effects on 3T3-L1 lipogenesis as well as the likely mechanisms underlying this process. By re-annotation of raw microarray data downloaded from Gene Expression Omnibus, we found that obese individuals showed significantly higher A20 mRNA levels in adipocytes. In vitro, A20 inhibited MCP-1 and IL-6 secretion in adipocytes. Forced expression of A20 resulted in decreased expression of key markers of lipogenesis and adipogenesis, such as sterol regulatory element binding protein 1c (SREBP-1c) and adipogenesis (aP2), leading to less lipids accumulation in differentiated 3T3-L1 cells. This process was concomitant with attenuated activation of p38 and Akt signaling. Our results suggest that A20 may have therapeutic potential for obesity and related diseases. The mechanisms involved the suppression of lipid storage and inflammation in adipocytes.

TRAF3, ubiquitination, and B-lymphocyte regulation

The signaling adapter protein tumor necrosis factor receptor (TNFR)-associated factor 3 (TRAF3) is both modified by and contributes to several types of ubiquitination events. TRAF3 plays a variety of context-dependent regulatory roles in all types of immune cells. In B lymphocytes, TRAF3 contributes to regulation of signaling by members of both the TNFR superfamily and innate immune receptors. TRAF3 also plays a unique cell type-specific and critical role in the restraint of B-cell homeostatic survival, a role with important implications for both B-cell differentiation and the pathogenesis of B-cell malignancies. This review focuses upon the relationship between ubiquitin and TRAF3, and how this contributes to multiple functions of TRAF3 in the regulation of signal transduction, transcriptional activation, and effector functions of B lymphocytes.

Up-regulation of A20 gene expression in peripheral blood mononuclear cells is associated with acute-on-chronic hepatitis B liver failure

Aberrant immunity contributes to the pathogenesis of acute-on-chronic hepatitis B liver failure (ACHBLF), and A20 is a newly identified negative regulatory molecule of the immune response. However, no data have been reported for the role of A20 in ACHBLF. This study aimed to investigate A20 mRNA expression in ACHBLF and to determine the potential of A20 as a biomarker for the prognosis of ACHBLF. Quantitative real-time polymerase chain reaction (qPCR) was used to measure the mRNA expression of A20 in peripheral blood mononuclear cells (PBMCs) from 137 ACHBLF patients, 105 chronic hepatitis B (CHB) and 35 healthy controls (HCs). A secondary cohort with 37 ACHBLF patients was set up as validation data set. The plasma levels of interleukin (IL)-1β, IL-6 and IL-10 were determined using enzyme-linked immunosorbent assay (ELISA). Receiver-operating characteristic (ROC) curves were used to determine the predictive value of A20 for the prognosis of ACHBLF patients. A20 mRNA expression in ACHBLF was significantly higher compared with CHB and HCs. In ACHBLF patients, A20 mRNA was closely associated with total bilirubin, albumin, international normalized ratio, prothrombin time activity and model for end-stage liver disease. Furthermore, A20 mRNA was significantly correlated with IL-6 and IL-10. An optimal cut-off value of 12.32 for A20 mRNA had significant power in discriminating survival or death in ACHBLF patients. In conclusion, our results suggest that the up-regulation of the A20 gene might contribute to the severity of ACHBLF and A20 mRNA level might be a potential predictor for the prognosis of ACHBLF.

Zinc Prevents Abdominal Aortic Aneurysm Formation by Induction of A20-Mediated Suppression of NF-κB Pathway

Chronic inflammation and degradation of elastin are the main processes in the development of abdominal aortic aneurysm (AAA). Recent studies show that zinc has an anti-inflammatory effect. Based on these, zinc may render effective therapy for the treatment of the AAA. Currently, we want to investigate the effects of zinc on AAA progression and its related molecular mechanism. Rat AAA models were induced by periaortic application of CaCl₂. AAA rats were treated by daily intraperitoneal injection of ZnSO₄ or vehicle alone. The aorta segments were collected at 4 weeks after surgery. The primary rat aortic vascular smooth muscle cells (VSMCs) were stimulated with TNF-α alone or with ZnSO₄ for 3 weeks. The results showed that zinc supplementation significantly suppressed the CaCl₂-induced expansion of the abdominal aortic diameter, as well as a preservation of medial elastin fibers in the aortas. Zinc supplementation also obviously attenuated infiltration of the macrophages and lymphocytes in the aortas. In addition, zinc reduced MMP-2 and MMP-9 production in the aortas. Most importantly, zinc treatment significantly induced A20 expression, along with inhibition of the NF-κB canonical signaling pathway in vitro in VSMCs and in vivo in rat AAA. This study demonstrated, for the first time, that zinc supplementation could prevent the development of rat experimental AAA by induction of A20-mediated inhibition of the NF-κB canonical signaling pathway.