An inhibitory effect of A20 on NF-kappaB activation in airway epithelium upon influenza virus infection

Establishment of a porcine bronchial epithelial cell line and its application to study innate immunity in the respiratory epithelium

In vitro culture models that precisely mirror the porcine respiratory epithelium are needed to gain insight into how pathogens and host interact. In this study, a new porcine bronchial epithelial cell line, designated as PBE cells, was established from the respiratory tract of a neonatal pig. PBE cells assumed a cobblestone-epithelial like morphology with close contacts between the cells when they reached confluence. The PBE cell line was characterized in terms of its expression of pattern recognition receptors (PRRs) and its ability to respond to the activation of the Toll-like receptor 3 (TLR3) and TLR4 signaling pathways, which are key PRRs involved in the defense of the respiratory epithelium against pathogens. PBE cells stimulated with poly(I:C) were able to up-regulate the expression of IFN-β, IFN-λ1 (IL-29), IFN-λ3 (IL-28B), the antiviral factors Mx1, OAS1, and PKR, as well as the viral PRRs RIG-1 and MDA5. The expression kinetics studies of immune factors in PBE cells allow us to speculate that this cell line can be a useful in vitro tool to investigate treatments that help to potentiate antiviral immunity in the respiratory epithelium of the porcine host. In addition, poly(I:C) and LPS treatments increased the expression of the inflammatory cytokines TNF-α, IL-6, IL-8, and MCP-1/CCL2 and differentially modulated the expression of negative regulators of the TLR signaling pathways. Then, PBE cells may also allow the evaluation of treatments that can regulate TLR3- and TLR4-mediated inflammatory injury in the porcine airway, thereby protecting the host against harmful overresponses.

Protein Kinase C δ (PKCδ) Attenuates Bleomycin Induced Pulmonary Fibrosis via Inhibiting NF-κB Signaling Pathway

Idiopathic pulmonary fibrosis (IPF) is a chronic, progressive and lethal interstitial lung disease characterized by consistent pulmonary inflammation. Although protein kinase C delta (PKCδ) is involved in broad scope cellular response, the role of PKCδ in IPF is complicated and has not been fully defined yet. Here, we reported that PKCδ deficiency (PKCδ^-/-) aggravated bleomycin (BLM)-induced pulmonary fibrosis and inflammation. Upon challenge with BLM, the pulmonary capillary permeability, immune cell infiltration, inflammatory cytokine production, and collagen deposition were enhanced in PKCδ^-/- mice compared to that in PKCδ^+/+ mice. In response to poly(I:C) stimulation, PKCδ deficient macrophages displayed an increased production of IL-1β, IL-6, TNF-α, and IL-33, which were associated with an enhanced NF-κB activation. Furthermore, we found that PKCδ could directly bind to and phosphorylate A20, an inhibitory protein of NF-κB signal. These results suggested that PKCδ may inhibit the NF-κB signaling pathway via enhancing the stability and activity of A20, which in turn attenuates pulmonary fibrosis, suggesting that PKCδ is a promising target for treating pulmonary fibrosis.

Host microRNAs and exosomes that modulate influenza virus infection

MicroRNAs (miRNAs) are small non-coding RNAs that post-transcriptionally regulate over half of human protein-coding genes and play a vital role in cellular development, proliferation, metabolism, and homeostasis. Exosomes are rounded or cup-like extracellular vesicles that carry proteins, mRNAs, miRNAs, and lipids for release and exchange messages between cells involved in various cellular processes. Influenza virus is a substantial public health challenge. The expression of host miRNAs is altered in response to stimulation by influenza virus. These dysregulated miRNAs directly or indirectly target viral genes to regulate viral replication and stimulate or suppress innate immune responses and cell apoptosis during viral infection. Exosomes released by infected cells are associated with the transfer of antigens and key molecules that activate and modulate immune function. Dysregulation of miRNAs and secretion of exosomes are associated with pathogenicity and immune regulation during influenza infection. This review provides a comprehensive summary of the information available regarding host miRNAs and exosomes that are involved in the modulation of influenza virus infection and will facilitate the development of preventative or therapeutic strategies against influenza virus.

Selenium Treatment Enhanced Clearance of Salmonella in Chicken Macrophages (HD11)

As an important micronutrient, selenium (Se) plays many essential roles in immune response and protection against pathogens in humans and animals, but underlying mechanisms of Se-based control of salmonella growth within macrophages remain poorly elucidated. In this study, using RNA-seq analyses, we demonstrate that Se treatment (at an appropriate concentration) can modulate the global transcriptome of chicken macrophages HD11. The bioinformatic analyses (KEGG pathway analysis) revealed that the differentially expressed genes (DEGs) were mainly enriched in retinol and glutathione metabolism, revealing that Se may be associated with retinol and glutathione metabolism. Meanwhile, Se treatment increased the number of salmonella invading the HD11 cells, but reduced the number of salmonella within HD11 cells, suggesting that enhanced clearance of salmonella within HD11 cells was potentially modulated by Se treatment. Furthermore, RNA-seq analyses also revealed that nine genes including SIVA1, FAS, and HMOX1 were differentially expressed in HD11 cells infected with salmonella following Se treatment, and GO enrichment analysis showed that these DEGs were mainly enriched in an extrinsic apoptotic signaling pathway. In summary, these results indicate that Se treatment may not only affect retinol and glutathione metabolism in macrophages, but could also inhibit salmonella-induced macrophage apoptosis via an extrinsic apoptotic signaling pathway involving SIVA1.

Transcriptomic analysis of Baltic cod (Gadus morhua) liver infected with Contracaecum osculatum third stage larvae indicates parasitic effects on growth and immune response

High infection levels due to third-stage larvae of the anisakid nematode Contracaecum osculatum have been documented in cod from the eastern part of the Baltic sea during the latest decades. The nematode larvae mainly infect the liver of Baltic cod and prevalence of infection has reached 100% with a mean intensity up to 80 parasites per host in certain areas and size classes. Low condition factors of the cod have been observed concomitant with the rise in parasite abundance suggesting a parasitic effect on growth parameters. To investigate any association between parasite infection and physiological status of the host we performed a comparative transcriptomic analysis of liver obtained from C. osculatum infected and non-infected cod. A total of 47,025 predicted gene models showed expression in cod liver and sequences corresponding to 2084 (4.43%) unigenes were differentially expressed in infected liver when compared to non-infected liver. Of the differentially expressed unigenes (DEGs) 1240 unigenes were up-regulated while 844 unigenes were down-regulated. The Gene Ontology (GO) enrichment analysis showed that 1304 DEGs were represented in cellular process and single-organism process, cell and cell part, binding and catalytic activity. As determined by the Kyoto Encyclopedia of Gene and Genomes (KEGG) Pathways analysis, 454 DEGs were involved in 138 pathways. Ninety-seven genes were related to metabolic pathways including carbohydrate, lipid, and amino acid metabolism. Thirteen regulated genes were playing a role in immune response such as Toll-like receptor signaling, NOD-like receptor signaling, RIG-I-like receptor signalling and thirty-six genes were associated with growth processes. This indicates that the nematode infection in Baltic cod may affect on molecular mechanisms involving metabolism, immune function and growth.

A20 as a novel target for the anti-neuroinflammatory effect of chrysin via inhibition of NF-κB signaling pathway

Neuroinflammation is now recognized to be a feature of many neurological disorders. More accumulated evidences suggested chrysin which was contained in honey, propolis, vegetables, fruits and plants can exert biological activities including anti-neuroinflammatory effects. However, the precise molecular mechanisms of anti-neuroinflammatory effects remain unclear. In the present study, we explored a novel molecular mechanism involved in the anti-neuroinflammatory effect of chrysin. Firstly, we investigated the anti-neuroinflammatory effects of chrysin in LPS-induced BV2, primary microglial cells and mice. Next, we found chrysin can inhibit NF-κB pathway and TRAF6 expression, but upregulate the expression of zinc-finger protein A20. Further studies have revealed upregulation of A20 can regulate the inhibitory effects of chrysin on NF-κB pathways via regulation of TRAF6 polyubiquitination. This present study demonstrates that chrysin exerts an anti-neuroinflammatory effect via a novel mechanism, the upregulation of A20 expression, also validates A20 is a novel effective pharmacological target for developing agents in the treatment of neuroinflammation-related diseases.

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.

Association of TNFAIP3 and TNIP1 polymorphisms with systemic lupus erythematosus risk: A meta-analysis

OBJECT

With the development of GWAS, both TNFAIP3 and TNIP1 were revealed to be susceptibility genes of SLE. However, some other studies revealed no association between TNFAIP3, TNIP1 and SLE susceptibility. In order to estimate such association more precisely and systemically, a meta-analysis was conducted.

METHOD

Studies on the association between TNFAIP3 rs2230926, TNIP1 rs7708392 and SLE risk were carefully selected via searching 3 databases (Pubmed, Embase, and Web of Science). A fixed- or random-effect model was used according to the heterogeneity, and a subgroup analysis by ethnicity was also performed.

RESULTS

26 studies from 18 articles involving a total of 21,372 patients and 30,165 controls were analyzed for TNFAIP3 rs2230926. A significant association between the minor G allele of TNFAIP3 rs2230926 and SLE risk was found via a random-effect model (OR = 1.643, 95% CI = (1.462, 1.847), p < 0.01). In the subgroup analysis by ethnicity, significant correlations were also found in all Caucasians, Asians, and Africans (OR = 1.675, 95% CI = (1.353, 2.074), p < 0.01; OR = 1.738, 95% CI = (1.557, 1.940), p < 0.01; OR = 1.324, 95% CI = (1.029, 1.704), p < 0.05). As for TNIP1 rs7708392, 21 studies from 12 articles involving 24,716 cases and 32,200 controls were analyzed. A significant association of the minor C allele of TNIP1 rs7708392 and SLE risk was found via a random-effect model (OR = 1.247, 95% CI = (1.175, 1.323), p < 0.01). In the subgroup analysis by ethnicity, significant correlations were found in Caucasians, and Africans (OR = 1.317, 95% CI = (1.239, 1.401), p < 0.01; OR = 1.210, 95% CI = (1.108, 1.322), p < 0.01). However, there was no significant association in Asians (OR = 1.122, 95% CI = (0.953, 1.321), p > 0.05).

CONCLUSION

The minor G allele of TNFAIP3 rs2230926 was associated with increased risk of SLE in all Caucasians, Asians, and Africans. The minor C allele of TNIP1 rs7708392 was associated with the increased risk of SLE in Caucasians and Africans, while it was not associated with SLE susceptibility in Asians.

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.

Overexpression of A20 inhibits the inflammatory response during dengue fever infection

Aim: Dengue hemorrhagic fever is a devastating disease. This study aimed to investigate the role of A20 in dengue fever infection. Materials & methods: DENV2-infected human umbilical vein endothelial cells were transfected with shRNA-A20/CD14 and A20/CD14-mimics, respectively. The expressions of inflammatory and anti-inflammatory factors, A20 and downstream proteins of the NF-κB signaling pathway were detected. Results: A20 knockdown increased the expression of IL-6, IL-10, IL-8 and CD14 during dengue virus infection, whereas overexpression of A20 had the opposite effect. FACS revealed that A20 negatively regulated the expression of CD14. Conclusion: In DENV2-infected human umbilical vein endothelial cells overexpressing A20, TNF-α stimulation inhibited NF-κB-mediated inflammatory response by negative feedback. Furthermore, A20 could affect the release of inflammatory factors via negative regulation of CD14, thus affecting the entire inflammatory response.

Influenza a virus NS1 protein induced A20 contributes to viral replication by suppressing interferon-induced antiviral response

The innate immune response provides the first line of defense against viruses and other pathogens by responding to specific microbial molecules. A20 is a cytoplasmic ubiquitin-editing protein that negatively regulates the retinoic acid-inducible gene I (RIG-I)-mediated activation of interferon regulatory factors (IRF) 3. Here, we found that influenza A virus (IAV) non-structural protein (NS) 1 dramatically induced the protein level of A20 in A549 cells whose expression levels were positively associated with the viral virulence. A20 overexpression in A549 cells significantly suppressed IAV-induced the activation of IRF3 and interferon (IFN) promoter, resulted in downregulation of IFNβ and IFN-stimulated genes (ISGs) mRNA. Conversely, silencing A20 expression markedly enhanced IRF3-mediated innate antiviral responses. Furthermore, we demonstrated that A20 overexpression in A549 cells obviously promoted IAV replication, and conversely, knockdown of A20 inhibited the viral replication. Overall, the findings described in this study support and extend previous results on interferon-antagonistic strategies of IAV NS1 by showing an induced host target A20, which restricts IAV-induced host innate immune antiviral responses and thereby facilitates viral replication.

Connectivity mapping (ssCMap) to predict A20-inducing drugs and their antiinflammatory action in cystic fibrosis

Cystic fibrosis (CF) lung disease is characterized by chronic and exaggerated inflammation in the airways. Despite recent developments to therapeutically overcome the underlying functional defect in the cystic fibrosis transmembrane conductance regulator, there is still an unmet need to also normalize the inflammatory response. The prolonged and heightened inflammatory response in CF is, in part, mediated by a lack of intrinsic down-regulation of the proinflammatory NF-κB pathway. We have previously identified reduced expression of the NF-κB down-regulator A20 in CF as a key target to normalize the inflammatory response. Here, we have used publicly available gene array expression data together with a statistically significant connections' map (sscMap) to successfully predict drugs already licensed for the use in humans to induce A20 mRNA and protein expression and thereby reduce inflammation. The effect of the predicted drugs on A20 and NF-κB(p65) expression (mRNA) as well as proinflammatory cytokine release (IL-8) in the presence and absence of bacterial LPS was shown in bronchial epithelial cells lines (16HBE14o-, CFBE41o-) and in primary nasal epithelial cells from patients with CF (Phe508del homozygous) and non-CF controls. Additionally, the specificity of the drug action on A20 was confirmed using cell lines with tnfαip3 (A20) knockdown (siRNA). We also show that the A20-inducing effect of ikarugamycin and quercetin is lower in CF-derived airway epithelial cells than in non-CF cells.

Increased A20 mRNA Level in Peripheral Blood Mononuclear Cells is Associated With Immune Phases of Patients With Chronic Hepatitis B

The zinc finger protein A20 is a newly identified negative regulator of immune response and mediates signal pathway of NF-κB in liver inflammation. However, the role of A20 in the natural history of patients with chronic hepatitis B (CHB) has not been demonstrated. In this present study, we aimed to investigate the dynamic expression of A20 and determine the potential association of A20 in the progression of chronic hepatitis B virus infection.This retrospective study contained 136 patients with chronic hepatitis B and 30 healthy controls (HCs). The mRNA level of A20, TNF-α, NF-κB p65 and toll-like receptor (TLR) 4 in peripheral blood mononuclear cells (PBMCs) was determined using a relative quantitative real-time polymerase chain reaction. The hepatic A20 protein expression was determined by immunohistochemistry. Clinical and laboratory parameters were obtained.In the present study, the relative expression of A20 mRNA was significantly increased in CHB patients compared with HCs and was positively associated with alanine aminotransferase, aspartate aminotransferase, and total bilirubin. In CHB patients, the levels of A20 mRNA in the immune clearance (IC) phase and hepatitis B negative (ENH) phase were significantly higher than that in immune tolerance (IT) phase and low-replicative (LR) phase (P < 0.001). Furthermore, the A20 mRNA level was significantly correlated with TNF-α/ NF-κB p65/TLR4 mRNA levels in CHB patients. Of note, we reported that cutoff values of 4.19 and 3.97 for the level of A20 mRNA have significant power in discriminating IC from IT, and ENH from LR in CHB patients respectively.In conclusion, our results suggested that increased levels of A20 mRNA and protein contribute to disease progression of chronic hepatitis B virus infection.

MicroRNA let-7 modulates the immune response to Mycobacterium tuberculosis infection via control of A20, an inhibitor of the NF-κB pathway

The outcome of the interaction between Mycobacterium tuberculosis (Mtb) and a macrophage depends on the interplay between host defense and bacterial immune subversion mechanisms. MicroRNAs critically regulate several host defense mechanisms, but their role in the Mtb-macrophage interplay remains unclear. MicroRNA profiling of Mtb-infected macrophages revealed the downregulation of miR-let-7f in a manner dependent on the Mtb secreted effector ESAT-6. We establish that let-7f targets A20, a feedback inhibitor of the NF-κB pathway. Expression of let-7f decreases and A20 increases with progression of Mtb infection in mice. Mtb survival is attenuated in A20-deficient macrophages, and the production of TNF, IL-1β, and nitrite, which are mediators of immunity to Mtb, is correspondingly increased. Further, let-7f overexpression diminishes Mtb survival and augments the production of cytokines including TNF and IL-1β. These results uncover a role for let-7f and its target A20 in regulating immune responses to Mtb and controlling bacterial burden.

Cystic Fibrosis from Laboratory to Bedside: The Role of A20 in NF-κB-Mediated Inflammation

Cystic fibrosis (CF) is a lifelong, inflammatory multi-organ disease and the most common lethal, genetic condition in Caucasian populations, with a median survival rate of 41.5 years. Pulmonary disease, characterized by infective exacerbations, bronchiectasis and increasing airway insufficiency is the most serious manifestation of this disease process, currently responsible for over 80% of CF deaths. Chronic dysregulation of the innate immune and host inflammatory response has been proposed as a mechanism central to this genetic condition, primarily driven by the nuclear factor κB (NF-κB) pathway. Chronic activation of this transcription factor complex leads to the production of pro-inflammatory cytokines and mediators such as IL-6, IL-8 and TNF-α. A20 has been described as a central and inducible negative regulator of NF-κB. This intracellular molecule negatively regulates NF-κB-driven pro-inflammatory signalling upon toll-like receptor activation at the level of TRAF6 activation. Silencing of A20 increases cellular levels of p65 and induces a pro-inflammatory state. We have previously shown that A20 expression positively correlates with lung function (FEV1%) in CF. Despite improvement in survival rates in recent years, advancements in available therapies have been incremental. We demonstrate that the experimental use of naturally occurring plant diterpenes such as gibberellin on lipopolysaccharide-stimulated cell lines reduces IL-8 release in an A20-dependent manner. We discuss how the use of a novel bio-informatics gene expression connectivity-mapping technique to identify small molecule compounds that similarly mimic the action of A20 may lead to the development of new therapeutic approaches capable of reducing chronic airway inflammation in CF.

Anti-inflammatory and protective properties of daphnetin in endotoxin-induced lung injury

Uncontrolled inflammatory responses cause tissue injury and severe immunopathology. Pharmacological interference of intracellular pro-inflammatory signaling may confer a therapeutic benefit under these conditions. Daphnetin, a natural coumarin derivative, has been used to treat inflammatory diseases including bronchitis. However, the protective effect of daphnetin in inflammatory airway disorders has yet to be determined, and the molecular basis for its anti-inflammatory properties is unknown. This paper shows that daphnetin treatment conferred substantial protection from endotoxin-induced acute lung injury (ALI), in parallel with reductions in the production of inflammatory mediators, symptoms of airway response, and infiltration of inflammatory cells. Further studies indicate that activation of macrophage and human alveolar epithelial cells in response to lipopolysaccharide (LPS) was remarkably suppressed by daphnetin, which was related to the down-regulation of NF-κB-dependent signaling events. Importantly, this study demonstrates that TNF-α-induced protein 3 (TNFAIP3), also known as A20, was significantly induced by daphnetin, which appeared to be largely responsible for the down-regulation of NF-κB activity through modulation of nondegradative TRAF6 ubiquitination. Accordingly, the deletion of TNFAIP3 in primary macrophages reversed daphnetin-elicited inhibition of immune response, and the beneficial effect of daphnetin in the pathogenesis of ALI was, partially at least, abrogated by TNFAIP3 knockdown. These findings demonstrate the anti-inflammatory and protective functions of daphnetin in endotoxin-induced lung inflammation and injury and also reveal the key mechanism underlying its action in vitro as well as in vivo.

Induction of the cellular miR-29c by influenza virus inhibits the innate immune response through protection of A20 mRNA

Influenza A viruses (IAVs) are negative-sense, single-stranded, segmented RNA viruses, which primarily targets respiratory epithelial cells and produces clinical outcomes ranging from mild upper respiratory infection to severe pneumonia. MicroRNAs (miRNAs) represent a family of small noncoding RNAs controlling translation and transcription of many genes. The human miR-29 family of miRNAs has three mature members, miR-29a, miR-29b, and miR-29c. Recent studies have revealed that miR-29 is involved in regulation of the innate and adaptive immune responses. However, the function of miR-29 in the immune response to IAV infection remains to be further explored. Our previous study has shown that miR-29 family members are up-regulated during IAV infection, especially miR-29c. Here we report that miR-29c is involved in inhibition of IAV-induced innate immune responses. We found that posttranscriptional regulation was involved in IAV-induced A20 expression in A549 cells. Consistent with a previous report, miR-29c functionally protected A20 transcripts in A549 cells. Overexpression of miR-29c with miR-29c mimic enhanced IAV-induced A20 protein expression and conversely that miR-29c inhibitor significantly blocked IAV-induced A20 protein expression in A549 cells. Furthermore, functional results showed that IAV-induced miR-29c expression correlated with decreased NF-κB activity and expression of several antiviral and proinflammatory cytokines via up-regulation of A20. Together, the findings indicate a new role of miR-29c in IAV infection and suggest its induction may contribute to counteract the innate immune response.

Regulatory effect of zinc finger protein A20 on inflammation and apoptosis: Implications for inflammatory bowel disease

Zinc finger protein A20, also known as tumor necrosis factor alpha-induced protein 3 (TNFAIP3), is a protein with dual enzyme activities: ubiquitination and deubiquitination. It can negatively regulate inflammation and apoptosis mediated by a variety of signal transduction pathway, playing an important role in the occurrence, development and prognosis of inflammatory diseases, especially inflammatory bowel diseases. In recent years, the role of zinc finger protein A20 in inflammation and apoptosis has gained growing concern. This paper gives a brief overview of the biological effects of zinc finger protein A20 on inflammation and apoptosis mediated by tumor necrosis factor alpha/tumor necrosis factor receptor 1, nuclear factor kappa B, lipopolysaccharide/lipopolysaccharide - nuclear factor kappa B, oxidized low density lipoprotein and other pathways as well as the negative regulatory effect of zinc finger protein A20 on intestinal inflammation and epithelial apoptosis in inflammatory bowel disease.

Elevated A20 contributes to age-dependent macrophage dysfunction in the lungs

Advanced age is associated with chronic low-grade inflammation (i.e. inflamm-aging) and poor macrophage function that includes a weak pro-inflammatory cytokine response to bacteria and diminished phagocytosis (i.e. age-dependent macrophage dysfunction [ADMD]). One reason for this is that ADMD is associated with poor NFκB and MAPK activation following Toll-like receptor stimulation. Herein, we tested the hypothesis that inflamm-aging induces production of A20, a cytosolic and homeostatic suppressor of the NFκB and MAPK signaling cascades that deubiquitinates (i.e. inactivates) the common upstream signaling molecule TRAF6, and this is responsible for ADMD. Western blots and immunohistochemistry comparing tissues from young, mature, and aged C57BL/6 mice indicated that A20 was strongly elevated in the lungs of aged mice but not in other tissues. Elevated A20 was also detected in alveolar macrophages (AM) from aged mice. In contrast CYLD, a second deubiquitinase that also negatively regulates the NFκB pathway was decreased with aging. Following co-incubation of AM with the bacteria Streptococcus pneumoniae, TRAF6 polyubiquitination was diminished in AM isolated from aged versus young mice. A20 production was inducible in the J774A.1 macrophage cell line and C57BL/6AM by overnight incubation with TNFα but not IL-6. Retrovirus-induced expression of A20 in J774A.1 cells resulted in their diminished production of IL-6 following exposure to S. pneumoniae but had no effect on levels of phagocytosis. Overnight incubation of AM from young mice with TNFα also resulted in a dampened IL-6 response to S. pneumoniae. Finally, dietary supplementation of aged mice with anti-inflammatory n-3 polyunsaturated fatty acids in the form of fish oil lowered lung A20 levels and enhanced resistance, including a 100-fold reduction in bacterial titers in the lungs, to experimental challenge with S. pneumoniae. We conclude that elevated A20 due to TNFα partially explains the ADMD phenotype and that ADMD is potentially reversible.

Anti-viral tetris: modulation of the innate anti-viral immune response by A20

The A20 protein has emerged as an important negative regulator of Toll like receptor (TLR) and retinoic acid-inducible gene 1 (RIG-I)-mediated anti-viral signaling. A20 functions both as a RING-type E3 ubiquitin ligase and as a de-ubiquitinating enzyme. Nuclear factor kappa B (NF-kappaB) and interferon regulatory factor (IRF) pathways are targeted by A20 through mechanisms that appear to be both overlapping and distinct, resulting in the downregulation of interferon alpha/beta (IFNalpha/beta) production. This review specifically details the impact of A20 on the cytosolic RIG-I/MDA5 pathway, a process that is less understood than that of NF-kappaB but is essential for the regulation of the innate immune response to viral infection.

A20 (TNFAIP3) alleviates CVB3-induced myocarditis via inhibiting NF-κB signaling

Background

Viral myocarditis, which is most prevalently caused by Coxsackievirus B3 (CVB3) infection, is a serious clinical condition characterized by cardiac inflammation. However, efficient therapies targeting inflammation are still lacking and much needed. A20, also known as tumor necrosis factor alpha induced protein 3 (TNFAIP3) is a key negative regulator of inflammation. But whether A20 may affect cardiac inflammation during acute viral myocarditis remains to be elucidated. The aim of this study was to investigate the potential protective effect of A20 on CVB3-induced myocarditis.

Methodology/Principal Findings

Mice were intraperitoneally inoculated with CVB3 to establish acute viral myocarditis model. We found that the expression of pro-inflammatory cytokines, including tumor necrosis factor-α (TNF-α), interleukin (IL)-1β, IL-6 and monocyte chemotactic protein-1 (MCP-1) were markedly and persistently increased during the progression of CVB3-induced myocarditis, and positively correlated with the disease severity. Notably, intravenous injection in vivo with adenovirus expressed A20 (Ad-A20) remarkably reduced CVB3-induced pro-inflammatory cytokines production and alleviated the severity of myocarditis. Further, we observed that nuclear factor-kappaB (NF-κB) signaling which mediates inflammatory response was significantly inhibited in CVB3-infected mice with Ad-A20 treatment. Finally, we revealed that A20 was required to inhibit CVB3-induced NF-κB signaling by restricting TNF receptor associated factor 6 (TRAF6) ubiquitylation.

Conclusion/Significance

This study demonstrates the protective role of A20 against CVB3-induced myocarditis, which may provide a new therapeutic strategy for the treatment of viral myocarditis.

Leishmania donovani exploits host deubiquitinating enzyme A20, a negative regulator of TLR signaling, to subvert host immune response

TLRs, which form an interface between mammalian host and microbe, play a key role in pathogen recognition and initiation of proinflammatory response thus stimulating antimicrobial activity and host survival. However, certain intracellular pathogens such as Leishmania can successfully manipulate the TLR signaling, thus hijacking the defensive strategies of the host. Despite the presence of lipophosphoglycan, a TLR2 ligand capable of eliciting host-defensive cytokine response, on the surface of Leishmania, the strategies adopted by the parasite to silence the TLR2-mediated proinflammatory response is not understood. In this study, we showed that Leishmania donovani modulates the TLR2-mediated pathway in macrophages through inhibition of the IKK-NF-κB cascade and suppression of IL-12 and TNF-α production. This may be due to impairment of the association of TRAF6 with the TAK-TAB complex, thus inhibiting the recruitment of TRAF6 in TLR2 signaling. L. donovani infection drastically reduced Lys 63-linked ubiquitination of TRAF6, and the deubiquitinating enzyme A20 was found to be significantly upregulated in infected macrophages. Small interfering RNA-mediated silencing of A20 restored the Lys 63-linked ubiquitination of TRAF6 as well as IL-12 and TNF-α levels with a concomitant decrease in IL-10 and TGF-β synthesis in infected macrophages. Knockdown of A20 led to lower parasite survival within macrophages. Moreover, in vivo silencing of A20 by short hairpin RNA in BALB/c mice led to increased NF-κB DNA binding and host-protective proinflammatory cytokine response resulting in effective parasite clearance. These results suggest that L. donovani might exploit host A20 to inhibit the TLR2-mediated proinflammatory gene expression, thus escaping the immune responses of the host.

Emerging role of ubiquitination in antiviral RIG-I signaling

Detection of viruses by the innate immune system involves the action of specialized pattern recognition receptors. Intracellular RIG-I receptors sense the presence of viral nucleic acids in infected cells and trigger signaling pathways that lead to the production of proinflammatory and antiviral proteins. Over the past few years, posttranslational modification of RIG-I and downstream signaling proteins by different types of ubiquitination has been found to be a key event in the regulation of RIG-I-induced NF-κB and interferon regulatory factor 3 (IRF3) activation. Multiple ubiquitin ligases, deubiquitinases, and ubiquitin binding scaffold proteins contribute to both positive and negative regulation of the RIG-I-induced antiviral immune response. A better understanding of the function and activity of these proteins might eventually lead to the development of novel therapeutic approaches for management of viral diseases.

A20 (Tnfaip3) deficiency in myeloid cells protects against influenza A virus infection

The innate immune response provides the first line of defense against viruses and other pathogens by responding to specific microbial molecules. Influenza A virus (IAV) produces double-stranded RNA as an intermediate during the replication life cycle, which activates the intracellular pathogen recognition receptor RIG-I and induces the production of proinflammatory cytokines and antiviral interferon. Understanding the mechanisms that regulate innate immune responses to IAV and other viruses is of key importance to develop novel therapeutic strategies. Here we used myeloid cell specific A20 knockout mice to examine the role of the ubiquitin-editing protein A20 in the response of myeloid cells to IAV infection. A20 deficient macrophages were hyperresponsive to double stranded RNA and IAV infection, as illustrated by enhanced NF-κB and IRF3 activation, concomitant with increased production of proinflammatory cytokines, chemokines and type I interferon. In vivo this was associated with an increased number of alveolar macrophages and neutrophils in the lungs of IAV infected mice. Surprisingly, myeloid cell specific A20 knockout mice are protected against lethal IAV infection. These results challenge the general belief that an excessive host proinflammatory response is associated with IAV-induced lethality, and suggest that under certain conditions inhibition of A20 might be of interest in the management of IAV infections.

Influenza virus or flu epidemics represent a recurrent threat to the public health, especially for individuals which are part of a high-risk group such as children, elderly or immune-compromised people. Sporadic pandemic flu outbreaks, such as the Spanish flu of 1918, may cause high grades of mortality among healthy persons. A better understanding of how the immune system deals with these pathogens is of key importance. The protein A20 is an important negative regulator of both innate and adaptive immune responses. We show that the specific deletion of A20 in myeloid cells, such as macrophages and neutrophils, improves the resistance against otherwise lethal influenza infections. This protective effect is mediated by an enhanced innate immune response following respiratory challenge with influenza virus. Although exaggerated pulmonary immune responses are believed to be the primary cause of often life threatening influenza virus induced pneumonia, we demonstrate that boosting the innate immune response by selectively targeting the functionality of A20 in myeloid cells is beneficial for the host survival. This finding provides us with a novel valuable approach for treating influenza and potentially other respiratory viral infections.

A monoclonal antibody against RAGE alters gene expression and is protective in experimental models of sepsis and pneumococcal pneumonia

The RAGE (receptor for advanced glycation end products) is believed to play a role in sepsis by perpetuating inflammation. The interaction of RAGE with a variety of host-derived ligands that accumulate during stress and inflammation further induces the expression of RAGE. It was previously shown that a rat anti-RAGE monoclonal antibody protected mice from lethality in a cecal ligation and puncture model. We studied the effects of a humanized anti-RAGE monoclonal antibody in the murine pneumococcal pneumonia model of sepsis. Moreover, a gene expression analysis was performed in lung tissue of animals that underwent cecal ligation and puncture and treated with the rat anti-RAGE monoclonal antibody, compared with controls. Administration of humanized anti-RAGE mAb 6 h after intratracheal infection with Streptococcus pneumoniae improved mortality in BALB/c mice whether a 7.5 mg/kg (P < 0.01) or a 15 mg/kg dose (P < 0.01) was administered in combination with antibiotics. Gene expression analysis showed that many of the genes modulated by treatment with the anti-RAGE antibody were those that play an important role in regulating inflammation. Anti-RAGE monoclonal antibody offered a survival advantage to septic mice. This protective role in treated animals is supported by the observed gene expression profile changes of genes involved in sepsis and inflammation.

Viral takeover of the host ubiquitin system

Like the other more well-characterized post-translational modifications (phosphorylation, methylation, acetylation, acylation, etc.), the attachment of the 76 amino acid ubiquitin (Ub) protein to substrates has been shown to govern countless cellular processes. As obligate intracellular parasites, viruses have evolved the capability to commandeer many host processes in order to maximize their own survival, whether it be to increase viral production or to ensure the long-term survival of latently infected host cells. The first evidence that viruses could usurp the Ub system came from the DNA tumor viruses and Adenoviruses, each of which use Ub to dysregulate the host cell cycle (Scheffner et al., 1990; Querido et al., 2001). Today, the list of viruses that utilize Ub includes members from almost every viral class, encompassing both RNA and DNA viruses. Among these, there are examples of Ub usage at every stage of the viral life cycle, involving both ubiquitination and de-ubiquitination. In addition to viruses that merely modify the host Ub system, many of the large DNA viruses encode their own Ub modifying machinery. In this review, we highlight the latest discoveries regarding the myriad ways that viruses utilize Ub to their advantage.

Genome-wide expression profiling identifies an impairment of negative feedback signals in the Crohn's disease-associated NOD2 variant L1007fsinsC

NOD2 is an intracellular receptor for the bacterial cell wall component muramyl dipeptide (MDP), and variants of NOD2 are associated with chronic inflammatory diseases of barrier organs (e.g., Crohn's disease, asthma, and atopic eczema). It is known that activation of NOD2 induces a variety of inflammatory and antibacterial factors. The exact transcriptomal signatures that define the cellular programs downstream of NOD2 activation and the influence of the Crohn-associated variant L1007fsinsC are yet to be defined. To describe the MDP-induced activation program, we analyzed the transcriptomal reactions of isogenic HEK293 cells expressing NOD2(wt) or NOD2(L1007fsinsC) to stimulation with MDP. Importantly, a clear loss of function could be observed in the cells carrying the Crohn-associated variant L1007fsinsC, whereas the NOD2(wt) cells showed differential regulation of growth factors, chemokines, and several antagonists of NF-κB (e.g., TNFAIP3 [A20] and IER3). This genotype-dependent regulation pattern was confirmed in primary human myelomonocytic cells. The influence of TNFAIP3 and IER3 in the context of NOD2 signaling was characterized, and we could validate the predicted role as inhibitors of NOD2-induced NF-κB activation. We show that IER3 impairs the protective effect of NOD2(wt) against bacterial cytoinvasion. These results further our understanding of NOD2 as a first-line defense molecule and emphasize the importance of simultaneous upregulation of counterregulatory anti-inflammatory factors as an integral part of the NOD2-induced cellular program. Lack of these regulatory events due to the L1007fsinsC variant may pivotally contribute to the induction and perpetuation of chronic inflammation.

A20 regulation of nuclear factor-κB: perspectives for inflammatory lung disease

Persistent activation of NF-κB is central to the pathogenesis of many inflammatory lung disorders, including cystic fibrosis, asthma, and chronic obstructive pulmonary disease. A20 is an endogenous negative regulator of NF-κB signaling, which has been widely described in autoimmune and inflammatory disorders, including diabetes and Crohn's disease, but which has received little attention in terms of chronic lung disorders. This review examines the existing body of research on A20 regulation of NF-κB signaling and details the mechanism and regulation of A20 action focusing, where possible, on pulmonary inflammation. A20 and its associated signaling molecules are highlighted as being of potential therapeutic interest for the treatment of inflammatory disorders, and a proposed model of A20 activity in inflammatory lung disease is provided.

Herpes simplex virus immediate-early ICP0 protein inhibits Toll-like receptor 2-dependent inflammatory responses and NF-kappaB signaling

The discovery of the Toll-like receptors (TLRs) and their importance in the regulation of host responses to infection raised attention to the complex interplay between viral gene products and the host innate immune responses in determining the outcome of virus infection. Robust inflammatory cytokine responses are observed in herpes simplex virus (HSV)-infected animals and cells. Our studies have demonstrated that Toll-like receptor 2 (TLR2) activation by HSV results in NF-κB activation with concomitant inflammatory cytokine production and that TLR2 activation plays a critical role in HSV-induced pathology and mortality. Here we demonstrate that the HSV-1 immediate-early ICP0 protein reduces the TLR2-mediated inflammatory response to HSV 1 (HSV-1) infection. Expression of ICP0 alone is sufficient to block TLR2-driven responses to both viral and nonviral ligands at or downstream of the MyD88 adaptor and upstream of p65. ICP0 alone can also reduce the levels of MyD88 and Mal (TIRAP). In HSV-infected cells, the E3 ligase function of ICP0 and cellular proteasomal activity are required for the inhibitory activity. Our results argue for a model in which ICP0 promotes the degradation of TLR adaptor molecules and inhibition of the inflammatory response, much as it inhibits the interferon response by sequestration and degradation of interferon regulatory factor 3 (IRF-3).

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

A20 (also known as TNFAIP3) is a cytoplasmic protein that plays a key role in the negative regulation of inflammation and immunity. Polymorphisms in the A20 gene locus have been identified as risk alleles for multiple human autoimmune diseases, and A20 has also been proposed to function as a tumor suppressor in several human B-cell lymphomas. A20 expression is strongly induced by multiple stimuli, including the proinflammatory cytokines TNF and IL-1, and microbial products that trigger pathogen recognition receptors, such as Toll-like receptors. A20 functions in a negative feedback loop, which mediates its inhibitory functions by downregulating key proinflammatory signaling pathways, including those controlling NF-κB- and IRF3-dependent gene expression. Activation of these transcription factors is controlled by both K48- and K63- polyubiquitination of upstream signaling proteins, respectively triggering proteasome-mediated degradation or interaction with other signaling proteins. A20 turns off NF-κB and IRF3 activation by modulating both types of ubiquitination. Induction of K48-polyubiquitination by A20 involves its C-terminal zinc-finger ubiquitin-binding domain, which may promote interaction with E3 ligases, such as Itch and RNF11 that are involved in mediating A20 inhibitory functions. A20 is thought to promote de-ubiquitination of K63-polyubiquitin chains either directly, due to its N-terminal deubiquitinase domain, or by disrupting the interaction between E3 and E2 enzymes that catalyze K63-polyubiquitination. A20 is subject to different mechanisms of regulation, including phosphorylation, proteolytic processing, and association with ubiquitin binding proteins. Here we review the expression and biological activities of A20, as well as the underlying molecular mechanisms.

A20 is overexpressed in glioma cells and may serve as a potential therapeutic target

OBJECTIVE

A20 is a TNF-inducible primary response gene, which has been found to have antiapoptotic function in several cancer cells. This study investigates A20 expression in human glioma tissues and four glioma cell lines, and its effect on tumorigenesis of glioma cells and a mouse tumor model.

METHODS

Human glioma tissue samples and cells were subject to reverse transcription-PCR (RT-PCR), western blotting and immunohistochemistry. Glioma cells was tested by flow cytometry. A xenograft tumor model in mice was utilized to examine the knock-down effect of specific A20 siRNAs on tumorigenesis.

RESULTS

A20 was overexpressed in clinical glioma tissue samples (63.9%) and correlated with clinical staging. All four human glioma cell lines expressed A20, among which U87 displayed the strongest expression signals. Inhibiting A20 expression by siRNAs in vitro reduced the growth rates of glioma cells and resulted in G1/S arrest and increased apoptosis. In a mouse tumor model, local administration of siRNA significantly suppressed solid tumor growth.

CONCLUSIONS

A20 was overexpressed both in human glioma tissues and cell lines, and inhibiting A20 expression greatly slowed tumor cell growth in culture and in mice. These findings indicated that A20 is involved in tumorigenesis of human glioma, and may serve as a future therapeutic target.

The ubiquitin-editing enzyme A20 (TNFAIP3) is a central regulator of immunopathology

Nuclear factor (NF)-kappaB has an important role in immunity and inappropriate NF-kappaB activity has been linked with many autoimmune and inflammatory diseases. Multiple mechanisms normally ensure the proper termination of NF-kappaB activation. In this context, the intracellular ubiquitin-editing protein A20 (also known as Tumor Necrosis Factor Alpha-Induced Protein 3 or TNFAIP3) is a key player in the negative feedback regulation of NF-kappaB signaling in response to multiple stimuli. Moreover, A20 also regulates tumor necrosis factor (TNF)-induced apoptosis. Recent genetic studies demonstrate a clear association between several mutations in the human A20 locus and immunopathologies such as Crohn's disease, rheumatoid arthritis, systemic lupus erythematosus, psoriasis and type 1 diabetes. These findings further illustrate the importance of A20 in the resolution of inflammation and the prevention of human disease.

Genome-wide transcriptional response of primary alveolar macrophages following infection with porcine reproductive and respiratory syndrome virus

Porcine reproductive and respiratory syndrome is a major cause of economic loss for the swine industry worldwide. Porcine reproductive and respiratory syndrome virus (PRRSV) triggers weak and atypical innate immune responses, but key genes and mechanisms by which the virus interferes with the host innate immunity have not yet been elucidated. In this study, genes that control the response of the main target of PRRSV, porcine alveolar macrophages (PAMs), were profiled in vitro with a time-course experiment spanning the first round of virus replication. PAMs were obtained from six piglets and challenged with the Lelystad PRRSV strain, and gene expression was investigated using Affymetrix microarrays and real-time PCR. Of the 1409 differentially expressed transcripts identified by analysis of variance, two, five, 25, 16 and 100 differed from controls by a minimum of 1.5-fold at 1, 3, 6, 9 and 12 h post-infection (p.i.), respectively. A PRRSV infection effect was detectable between 3 and 6 h p.i., and was characterized by a consistent downregulation of gene expression, followed by the start of the host innate immune response at 9 h p.i. The expression of beta interferon 1 (IFN-β), but not of IFN-α, was strongly upregulated, whilst few genes commonly expressed in response to viral infections and/or induced by interferons were found to be differentially expressed. A predominance of anti-apoptotic transcripts (e.g. interleukin-10), a shift towards a T-helper cell type 2 response and a weak upregulation of tumour necrosis factor-α expression were observed within 12 h p.i., reinforcing the hypotheses that PRRSV has developed sophisticated mechanisms to escape the host defence.

Viral infection in asthma

In bronchial asthma, respiratory virus infection involves several issues: 1) respiratory virus infection in infancy is a risk factor for, and may predispose to, the development of asthma later in life; 2) respiratory virus infection is associated with the acute exacerbation of bronchial asthma; and, 3) glucocorticosteroids (GC) are not adequate for controlling asthma-related symptoms upon respiratory virus infection. Various cells, inflammatory mediators and cytokines participate in the production of airway inflammation upon respiratory virus infection. Bronchial epithelial cells are a site of infection and replication of respiratory virus. They actively participate in the production of airway inflammation: 1) they produce various proinflammatory cytokines, chemokines and mediators; and, 2) they undergo apoptosis, thereby impairing the repair process. It is therefore important to understand the role of bronchial epithelial cells in the pathophysiology of bronchial asthma. In this review, the interaction between viral infection and asthma is discussed to elucidate the role of bronchial epithelial cells in viral infection.

Measles virus P protein suppresses Toll-like receptor signal through up-regulation of ubiquitin-modifying enzyme A20

We recently reported that the activation of NF-kappaB and AP-1 was suppressed in monocytes infected with measles virus, but not in infected epithelial cells. This cell-type-specific suppression of the inflammatory response represents a potential for measles virus to evade host immune system. In the current study, we examined the suppression mechanism of lipopolysaccharide (LPS)-induced, namely Toll-like receptor 4 (TLR4)-mediated, activation of NF-kappaB and AP-1 in measles virus-infected monocytic cells. In the infected cells, LPS treatment failed to induce the formation of active protein kinase complex containing TAK1, TAB2 and tumor necrosis factor receptor-associated factor 6 (TRAF6), dissociate from TLR complexes containing Interleukin-1 receptor-associated kinase 1 (IRAK1). Ubiquitin-modifying enzyme A20, which is a host negative feedback regulator of NF-kappaB, was dramatically up-regulated in infected monocytic cells, but not in infected epithelial cells. Suppression of A20 expression by siRNA restored LPS-induced signaling in infected cells. Measles virus phosphoprotein (P protein) expression was necessary and sufficient for the induction of A20. P protein interacted indirectly with a negative regulatory motif in the A20 gene promoter, and released the suppression of A20 transcription, independent of the activation of NF-kappaB.

A20/TNFAIP3, a new estrogen-regulated gene that confers tamoxifen resistance in breast cancer cells

The zinc-finger protein A20/TNFAIP3, an inhibitor of nuclear factor-kappaB (NF-kappaB) activation, has been shown to protect MCF-7 breast carcinoma cells from TNFalpha-induced apoptosis. As estrogen receptor (ER) status is an important parameter in the development and progression of breast cancer, we analysed the effect of 17beta-estradiol (E2) treatment on the expression of A20. We found that A20 is a new E2-regulated gene, whose expression correlates with ER expression in both cell lines and tumor samples. With the aim of investigating the impact of A20 expression on MCF-7 cells in response to ER ligands, we established stably transfected-MCF-7 cells overexpressing A20 (MCF-7-A20). These cells exhibited a phenotype of resistance to the 4-hydroxy-tamoxifen cytostatic and pro-apoptotic actions and of hyper-response to E2. Dysregulations in bax, bcl2, bak, phospho-bad, cyclin D1, cyclin E2, cyclin D2 and cyclin A2 proteins expression were shown to be related to the resistant phenotype developed by the MCF-7-A20 cells. Interestingly, we found that A20 was also overexpressed in MVLN and VP tamoxifen-resistant cell lines. Furthermore, high A20 expression levels were observed in more aggressive breast tumors (ER-negative, progesterone receptor-negative and high histological grade). These overall findings strongly suggest that A20 is a key protein involved in tamoxifen resistance, and thus represents both a new breast cancer marker and a promising target for developing new strategies to prevent the emergence of acquired mechanisms of drug resistance in breast cancer.