TNF-α impairs EP4 signaling through the association of TRAF2-GRK2 in primary fibroblast-like synoviocytes

Our previous study showed that chronic treatment with tumor necrosis factor-α (TNF-α) decreased cAMP concentration in fibroblast-like synoviocytes (FLSs) of collagen-induced arthritis (CIA) rats. In this study we investigated how TNF-α impairs cAMP homeostasis, particularly clarifying the potential downstream molecules of TNF-α and prostaglandin receptor 4 (EP4) signaling that would interact with each other. Using a cAMP FRET biosensor PM-ICUE3, we demonstrated that TNF-α (20 ng/mL) blocked ONO-4819-triggered EP4 signaling, but not Butaprost-triggered EP2 signaling in normal rat FLSs. We showed that TNF-α (0.02-20 ng/mL) dose-dependently reduced EP4 membrane distribution in normal rat FLS. TNF-α significantly increased TNF receptor 2 (TNFR2) expression and stimulated proliferation in human FLS (hFLS) via ecruiting TNF receptor-associated factor 2 (TRAF2) to cell membrane. More interestingly, we revealed that TRAF2 interacted with G protein-coupled receptor kinase (GRK2) in the cytoplasm of primary hFLS and helped to bring GRK2 to cell membrane in response of TNF-α stimulation, the complex of TRAF2 and GRK2 then separated on the membrane, and translocated GRK2 induced the desensitization and internalization of EP4, leading to reduced production of intracellular cAMP. Silencing of TRAF2 by siRNA substantially diminished TRAF2-GRK2 interaction, blocked the translocation of GRK2, and resulted in upregulated expression of membrane EP4 and intracellular cAMP. In CIA rats, administration of paroxetine to inhibit GRK2 effectively improved the symptoms and clinic parameters with significantly reduced joint synovium inflammation and bone destruction. These results elucidate a novel form of cross-talk between TNFR (a cytokine receptor) and EP4 (a typical G protein-coupled receptor) signaling pathways. The interaction between TRAF2 and GRK2 may become a potential new drug target for the treatment of inflammatory diseases.

Scutellarein protects against cardiac hypertrophy via suppressing TRAF2/NF-κB signaling pathway

BACKGROUND

Scutellarein, a widely studied ingredient of scutellaria herbs, has higher bioavailability and solubility than that of scutellarin. Although the scutellarein had been reported to modulate numerous biological functions, its ability in suppressing cardiac hypertrophy remains unclear. Hence, the present study attempted to investigate whether scutellarein played critical roles in preventing phenylephrine (PE)-induced cardiac hypertrophy.

METHODS AND RESULTS

Immunocytochemistry (ICC) was employed for evaluating the morphology of the treated cardiomyocytes. Real-time PCR and western blot were respectively applied to assess the mRNA levels and protein expression of the relevant molecules. Bioinformatics analyses were carried out to investigate the potential mechanisms by which scutellarein modulated the PE-induced cardiac hypertrophy. The results showed that Scutellarein treatment significantly inhibited PE-induced increase in H9c2 and AC16 cardiomyocyte size. Besides, scutellarein treatment also dramatically suppressed the expression of the cardiac hypertrophic markers: ANP, BNP and β-MHC. Furthermore, the effects of scutellarein on attenuating the cardiac hypertrophy might be mediated by suppressing the activity of TRAF2/NF-κB signaling pathway.

CONCLUSIONS

Collectively, our data indicated that scutellarein could protect against PE-induced cardiac hypertrophy via regulating TRAF2/NF-κB signaling pathway using in vitro experiments.

SNHG15 is a negative regulator of inflammation by mediating TRAF2 ubiquitination in stroke-induced immunosuppression

BACKGROUND

Abnormal expression of long noncoding RNAs (lncRNAs) has been reported in the acute stage of acute ischemic stroke (AIS). This study aimed to explore differential lncRNA expression in the subpopulations of peripheral blood mononuclear cells (PBMCs) from AIS patients and further evaluate its underlying mechanisms in stroke-induced immunosuppression.

METHODS

We reanalyzed lncRNA microarray data and investigated abnormally expressed lncRNAs in the subpopulations of PBMCs by magnetic cell sorting and real-time quantitative PCR. The potential mechanism of small nucleolar RNA host gene 15 (SNHG15) was explored through in vitro and in vivo approaches.

RESULTS

The stroke-induced SNHG15 acted as a checkpoint to inhibit peripheral inflammatory responses. Functional studies showed that SNHG15 promoted M2 macrophage polarization. Mechanistically, SNHG15 expression was dysregulated through the Janus kinase (JAK)-signal transducer and activator of transcription 6 (STAT6) signaling pathway. SNHG15, localized in the cytoplasm, interfered with K63-linked ubiquitination of tumor necrosis factor receptor-associated factor 2 and thereby repressed the activation of mitogen-activated protein kinase and nuclear factor kappa-B signaling pathways and prevented the production of proinflammatory cytokines. Administration of an adenovirus targeting SNHG15 improved stroke-induced immunosuppression in mice.

CONCLUSIONS

This study identified SNHG15 as a negative regulator of inflammation in stroke-induced immunosuppression, suggesting it as a novel biomarker and therapeutic target in stroke-associated infection. Trial registration ClinicalTrials.gov NCT04175691. Registered November 25, 2019, https://www.clinicaltrials.gov/ct2/show/NCT04175691 .

Variation in Plasma Levels of TRAF2 Protein During Development of Squamous Cell Carcinoma of the Oral Tongue

As early detection is crucial for improvement of cancer prognosis, we searched for biomarkers in plasma from individuals who later developed squamous cell carcinoma of the oral tongue (SCCOT) as well as in patients with an already established SCCOT. Levels of 261 proteins related to inflammation and/or tumor processes were measured using the proximity extension assay (PEA) in 179 plasma samples (42 collected before diagnosis of SCCOT with 81 matched controls; 28 collected at diagnosis of SCCOT with 28 matched controls). Statistical modeling tools principal component analysis (PCA) and orthogonal partial least square - discriminant analysis (OPLS-DA) were applied to provide insights into separations between groups. PCA models failed to achieve group separation of SCCOT patients from controls based on protein levels in samples taken prior to diagnosis or at the time of diagnosis. For pre-diagnostic samples and their controls, no significant OPLS-DA model was identified. Potentials for separating pre-diagnostic samples collected up to five years before diagnosis (n = 15) from matched controls (n = 28) were seen in four proteins. For diagnostic samples and controls, the OPLS-DA model indicated that 21 proteins were important for group separation. TNF receptor associated factor 2 (TRAF2), decreased in pre-diagnostic plasma (< 5 years) but increased at diagnosis, was the only protein showing altered levels before and at diagnosis of SCCOT (p-value < 0.05). Taken together, changes in plasma protein profiles at diagnosis were evident, but not reliably detectable in pre-diagnostic samples taken before clinical signs of tumor development. Variation in protein levels during cancer development poses a challenge for the identification of biomarkers that could predict SCCOT development.

N4BP3 Regulates RIG-I-Like Receptor Antiviral Signaling Positively by Targeting Mitochondrial Antiviral Signaling Protein

Mitochondrial antiviral signaling protein (MAVS), an adaptor protein, is activated by RIG-I, which is critical for an effective innate immune response to infection by various RNA viruses. Viral infection causes the RIG-I-like receptor (RLR) to recognize pathogen-derived dsRNA and then becomes activated to promote prion-like aggregation and activation of MAVS. Subsequently, through the recruitment of TRAF proteins, MAVS activates two signaling pathways mediated by TBK1-IRF3 and IKK- NF-κb, respectively, and turns on type I interferon and proinflammatory cytokines. This study discovered that NEDD4 binding protein 3 (N4BP3) is a positive regulator of the RLR signaling pathway by targeting MAVS. Overexpression of N4BP3 promoted virus-induced activation of the interferon-β (IFN-β) promoter and interferon-stimulated response element (ISRE). Further experiments showed that knockdown or knockout N4BP3 impaired RIG-I-like receptor (RLR)-mediated innate immune response, induction of downstream antiviral genes, and cellular antiviral responses. We also detected that N4BP3 could accelerate the interaction between MAVS and TRAF2. Related experiments revealed that N4BP3 could facilitate the ubiquitination modification of MAVS. These findings suggest that N4BP3 is a critical component of the RIG-I-like receptor (RLR)-mediated innate immune response by targeting MAVS, which also provided insight into the mechanisms of innate antiviral responses.

microRNA-26a shuttled by extracellular vesicles secreted from adipose-derived mesenchymal stem cells reduce neuronal damage through KLF9-mediated regulation of TRAF2/KLF2 axis

Extracellular vesicles (EVs) are nano-sized vesicles secreted actively by numeorus cells and have fundamental roles in intercellular communication through shuttling functional RNAs. This study sets out to elucidate the role of microRNA-26a (miR-26a) shuttled by EVs derived from adipose-derived mesenchymal stem cells (ASCs) in neuronal damage. After extraction and identification of ASC-derived EVs (ASC-EVs), mouse cortical neuronal cells were selected to establish an in vivo cerebral ischemia/reperfusion mouse model and an in vitro oxygen glucose deprivation/reperfusion (OGD/RP) cell model. The downstream genes of miR-26a were analyzed. The gain- and loss-of function of miR-26a and KLF9 was performed in mouse and cell models. Neuronal cells were subjected to co-culture with ASC-EVs and biological behaviors were detected by flow cytometry, Motic Images Plus, TTC, TUNEL staining, qRT-PCR and western blot analysis. ASC-EVs protected neuronal cells against neuronal damage following cerebral ischemia/reperfusion, which was related to transfer of miR-26a into neuronal cells. In neuronal cells, miR-26a targeted KLF9. KLF9 could suppress the expression of TRAF2 and KLF2 to facilitate neuronal damage. In vitro and in vivo results showed that miR-26a delivered by ASC-EVs inhibited neuronal damage. In summary, ASC-EVs-derived miR-26a can arrest neuronal damage by disrupting the KLF9-meidated suppression on TRAF2/KLF2 axis.

SMYD2-mediated TRAF2 methylation promotes the NF-κB signaling pathways in inflammatory diseases

BACKGROUND

The methylation of lysine residues has been involved in the multiple biological and diseases processes. Recently, some particular non-histone proteins have been elucidated to be methylated by SMYD2, a SET and MYND domain protein with lysine methyltransferase activity.

METHODS

SMYD2 was evaluated in synovial tissue and cells derived from rheumatoid arthritis patients. We confirmed TRAF2 could be methylated by SMYD2 using Mass spectrometry, pull-down, immunoprecipitation, methyltransferase assay, ubiquitination assay, luciferase reporter assays, and western blot analyses. Using loss- and gain-of function studies, we explored the biological functions of SMYD2 in vitro and in vivo. Using acute and chronic inflammation with different mice models to determine the impact of SMYD2.

RESULTS

Here, we first time confirmed that the cytoplasmic protein TRAF2 as the kernel node for NF-κB signaling pathway could be methylated by SMYD2. SMYD2-mediated TRAF2 methylation contributed to the durative sensitization of NF-κB signaling transduction through restraining its own proteolysis and enhancing the activity. In addition, we found knocking down of SMYD2 has different degrees of mitigation in acute and chronic inflammation mice models. Furthermore, as the lysine-specific demethylase, LSD1 could resist methylation on TRAF2 induced by SMYD2.

CONCLUSIONS

Our data uncovered an unprecedented cytoplasmic protein network that employed methylation of TRAF2 for the maintenance of NF-κB activation during inflammatory diseases.

Molecular docking analysis of flupenthixol and desmethylastemizole with the apoptotic regulator proteins CFLAR and TRAF2 linked to lung carcinoma

It is known that molecular changes in apoptotic genes due to mutation may cause disruption of apoptotic pathway resulting in an abrupt increase in cell proliferation. Therefore, it is of interest to identify compounds that could potentially replenish the changes in the apoptotic pathway, resulted from mutation. The gene network analysis using the Network Analyzer Plugin of Cytoscape (3.5.1) shows CFLAR and TRAF2 as influential genes in the apoptotic pathway. Mutation in these genes brings loss in apoptotic property of a cell and thus increases the cell proliferating activity. Thus, data on the molecular docking analysis of four natural compounds from Ottelia alismoides (L.) Pers with the two target proteins were reported. Flupenthixol and desmethylastemizole was found to be two efficient ligand molecules based on ligand-target interaction. In stereochemical quality assessment, the Ramachandran plot analysis of receptors indicates the better stereochemical characteristics for receptor-ligand interaction.

BRCC3 Promotes Tumorigenesis of Bladder Cancer by Activating the NF-κB Signaling Pathway Through Targeting TRAF2

NF-κB signaling is very important in cancers. However, the role of BRCC3-associated NF-κB signaling activation in bladder cancer remains to be characterized. Western blotting and IHC of tissue microarray were used to confirm the abnormal expression of BRCC3 in bladder cancer. Growth curve, colony formation, soft agar assay and Xenograft model were performed to identify the role of BRCC3 over-expression or knock-out in bladder cancer. Further, RNA-Seq and luciferase reporter assays were used to identify the down-stream signaling pathway. Finally, co-immunoprecipitation and fluorescence confocal assay were performed to verify the precise target of BRCC3. Here, we found that high expression of BRCC3 promoted tumorigenesis through targeting the TRAF2 protein. BRCC3 expression is up-regulated in bladder cancer patients which indicates a negative prognosis. By in vitro and in vivo assays, we found genetic BRCC3 ablation markedly blocks proliferation, viability and migration of bladder cancer cells. Mechanistically, RNA-Seq analysis shows that NF-κB signaling is down-regulated in BRCC3-deficient cells. BRCC3 binds to and synergizes with TRAF2 to activate NF-κB signaling. Our results indicate that high BRCC3 expression activates NF-κB signaling by targeting TRAF2 for activation, which in turn facilitates tumorigenesis in bladder cancer. This finding points to BRCC3 as a potential target in bladder cancer patients.

TRAF2 regulates T cell immunity by maintaining a Tpl2-ERK survival signaling axis in effector and memory CD8 T cells

Generation and maintenance of antigen-specific effector and memory T cells are central events in immune responses against infections. We show that TNF receptor-associated factor 2 (TRAF2) maintains a survival signaling axis in effector and memory CD8 T cells required for immune responses against infections. This signaling axis involves activation of Tpl2 and its downstream kinase ERK by NF-κB-inducing kinase (NIK) and degradation of the proapoptotic factor Bim. NIK mediates Tpl2 activation by stimulating the phosphorylation and degradation of the Tpl2 inhibitor p105. Interestingly, while NIK is required for Tpl2-ERK signaling under normal conditions, uncontrolled NIK activation due to loss of its negative regulator, TRAF2, causes constitutive degradation of p105 and Tpl2, leading to severe defects in ERK activation and effector/memory CD8 T cell survival. Thus, TRAF2 controls a previously unappreciated signaling axis mediating effector/memory CD8 T cell survival and protective immunity.

RETRACTED: TRAF2 gene silencing induces proliferation and represses apoptosis of nucleus pulposus cells in rats with intervertebral disc degeneration

This article has been retracted: please see Elsevier Policy on Article Withdrawal (http://www.elsevier.com/locate/withdrawalpolicy). This article has been retracted at the request of the Editor-in-Chief. Concern was raised about the reliability of the Western blot results in Figs. 1E, 2G and 6C, which appear to have the same eyebrow shaped phenotype as many other publications tabulated here (https://docs.google.com/spreadsheets/d/149EjFXVxpwkBXYJOnOHb6RhAqT4a2llhj9LM60MBffM/edit#gid=0). Concerns were also raised over the provenance of the flow cytometry plots in Fig. 8A. The journal requested the corresponding author comment on these concerns and provide the raw data. However the authors were not able to satisfactorily fulfil this request and therefore the Editor-in-Chief decided to retract the article.

TRIF-mediated antiviral signaling is differentially regulated by TRAF2 and TRAF6 in black carp

TRIF is an antiviral adaptor downstream of Toll-like receptors, the roles of teleost TRIF and their regulation remain largely unknown. In this study, a TRIF homologue (bcTRIF) of black carp (Mylopharyngodon piceus) has been cloned, and the transcription of bcTRIF in vivo and ex vivo increased in response to different stimuli. Overexpressed bcTRIF induced the transcription of interferon promoter in the EPC cells and enhanced protection of cells against infection of spring viremia of carp virus (SVCV). The previous study has identified that black carp TRAF2 (bcTRAF2) and TRAF6 (bcTRAF6) functioned positively in RIG-I/MAVS signaling. When co-expressed with bcTRAF2, bcTRIF-induced the transcription of interferon promoter in EPC cells was decreased, and the antiviral activity of bcTRIF was dampened accordingly. On the contrary, co-expressed bcTRAF6 enhanced both bcTRIF-mediated interferon promoter transcription and antiviral activity. The subsequent co-immunoprecipitation identified the interaction between bcTRAF2/6 and bcTRIF. Thus, bcTRIF-mediated antiviral signaling is up-regulated by bcTRAF6 and down-regulated by bcTRAF2.

TRAF2 Is a Novel Ubiquitin E3 Ligase for the Na,K-ATPase β-Subunit That Drives Alveolar Epithelial Dysfunction in Hypercapnia

Several acute and chronic lung diseases are associated with alveolar hypoventilation leading to accumulation of CO2 (hypercapnia). The β-subunit of the Na,K-ATPase plays a pivotal role in maintaining epithelial integrity by functioning as a cell adhesion molecule and regulating cell surface stability of the catalytic α-subunit of the transporter, thereby, maintaining optimal alveolar fluid balance. Here, we identified the E3 ubiquitin ligase for the Na,K-ATPase β-subunit, which promoted polyubiquitination, subsequent endocytosis and proteasomal degradation of the protein upon exposure of alveolar epithelial cells to elevated CO2 levels, thus impairing alveolar integrity. Ubiquitination of the Na,K-ATPase β-subunit required lysine 5 and 7 and mutating these residues (but not other lysines) prevented trafficking of Na,K-ATPase from the plasma membrane and stabilized the protein upon hypercapnia. Furthermore, ubiquitination of the Na,K-ATPase β-subunit was dependent on prior phosphorylation at serine 11 by protein kinase C (PKC)-ζ. Using a protein microarray, we identified the tumor necrosis factor receptor-associated factor 2 (TRAF2) as the E3 ligase driving ubiquitination of the Na,K-ATPase β-subunit upon hypercapnia. Of note, prevention of Na,K-ATPase β-subunit ubiquitination was necessary and sufficient to restore the formation of cell-cell junctions under hypercapnic conditions. These results suggest that a hypercapnic environment in the lung may lead to persistent epithelial dysfunction in affected patients. As such, the identification of the E3 ligase for the Na,K-ATPase may provide a novel therapeutic target, to be employed in patients with acute or chronic hypercapnic respiratory failure, aiming to restore alveolar epithelial integrity.

Single nucleotide polymorphisms of TRAF2 and TRAF5 gene in ankylosing spondylitis: a case-control study

Objective To investigate the role of eight locus polymorphisms of tumor necrosis factor receptor-associated factor 2 (TRAF2) and TRAF5 gene and their interaction in the susceptibility to ankylosing spondylitis (AS) in Chinese Han population. Methods Eight single nucleotide polymorphisms (SNPs) of TRAF2 (rs3750511, rs10781522, rs17250673, rs59471504) and TRAF5 (rs6540679, rs12569232, rs4951523, rs7514863) gene were genotyped in 673 AS patients and 687 controls. Results The SNPs of TRAF2 and TRAF5 do not indicate a correlation with the susceptibility of AS in Chinese Han population. Genotype frequencies of rs3750511 were statistically significant in females between patients and controls. The allele frequencies of rs10781522 and genotype frequencies of rs3750511 were statistically significant between groups of different diseases activity. One three-locus model, TRAF2 (rs10781522, rs17250673) and TRAF5 (rs12569232), had a maximum testing accuracy of 52.67% and a maximum cross-validation consistency (10/10) that was significant at the level of P = 0.0001, after determined empirically by permutation testing. As to environmental variables, only marginal association was found between sleep quality and AS susceptibility. Conclusion TRAF2 rs3750511 polymorphism may be associated with the susceptibility and severity of AS. Besides, the interaction of TRAF2 and TRAF5 genes may be associated with AS susceptibility, but many open questions remain.

Novel TNIP2 and TRAF2 Variants Are Implicated in the Pathogenesis of Pulmonary Arterial Hypertension

Background: Pulmonary arterial hypertension (PAH) is a rare disease characterized by pulmonary vascular remodeling and right heart failure. Specific genetic variants increase the incidence of PAH in carriers with a family history of PAH, those who suffer from certain medical conditions, and even those with no apparent risk factors. Inflammation and immune dysregulation are related to vascular remodeling in PAH, but whether genetic susceptibility modifies the PAH immune response is unclear. TNIP2 and TRAF2 encode for immunomodulatory proteins that regulate NF-κB activation, a transcription factor complex associated with inflammation and vascular remodeling in PAH. Methods: Two unrelated families with PAH cases underwent whole-exome sequencing (WES). A custom pipeline for variant prioritization was carried out to obtain candidate variants. To determine the impact of TNIP2 and TRAF2 in cell proliferation, we performed an MTS [3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium] assay on healthy lung pericytes transfected with siRNA specific for each gene. To measure the effect of loss of TNIP2 and TRAF2 on NF-kappa-beta (NF-κB) activity, we measured levels of Phospho-p65-NF-κB in siRNA-transfected pericytes using western immunoblotting. Results: We discovered a novel missense variant in the TNIP2 gene in two affected individuals from the same family. The two patients had a complex form of PAH with interatrial communication and scleroderma. In the second family, WES of the proband with PAH and primary biliary cirrhosis revealed a de novo protein-truncating variant in the TRAF2. The knockdown of TNIP2 and TRAF2 increased NF-κB activity in healthy lung pericytes, which correlated with a significant increase in proliferation over 24 h. Conclusions: We have identified two rare novel variants in TNIP2 and TRAF2 using WES. We speculate that loss of function in these genes promotes pulmonary vascular remodeling by allowing overactivation of the NF-κB signaling activity. Our findings support a role for WES in helping identify novel genetic variants associated with dysfunctional immune response in PAH.

Brief Research Report Regional Difference in TRAF2 and TRAF3 Gene Mutations in Colon Cancers

TRAF2 and TRAF3 genes of tumor necrosis factor receptor (TNF-R)-associated factor (TRAF) family are involved in diverse cell signaling, and function as both tumor suppressor gene and oncogene. Alterations of TRAF2 and TRAF3 in colon cancer (CC) along with their regional difference and microsatellite instability (MSI) are largely unknown. In the present study, we analyzed TRAF2 and TRAF3 frameshift mutations in 168 sporadic CCs (100 high MSI (MSI-H) and 68 microsatellite-stable (MSS) CCs). We identified TRAF2 and TRAF3 frameshift mutations in 4 (4%) and 3 CCs (3%) with MSI-H, respectively, but none in 68 cases of MSS CCs. Of the 168 CCs, we analyzed the mutations in multi-regions for 39 CCs (16 MSI-H and 23 MSS CCs), and discovered that 12.5% (2/16) and 6.3% (1/16) of MSI-H CCs exhibited regional difference in TRAF2 and TRAF3 mutations, respectively. In the multi-region samples of 23 MSS CCs, neither TRAF2 nor TRAF3 frameshift mutation was found. In 40% of CCs, both TRAF2 and TRAF3 expressions were increased compared to normal colon cells. Our data indicate that TRAF2 and TRAF3 frameshift mutations and their regional difference as well as altered expressions are present in MSI-H CCs, which could contribute to MSI-H cancer development.

The Traf2DNxBCL2-tg Mouse Model of Chronic Lymphocytic Leukemia/Small Lymphocytic Lymphoma Recapitulates the Biased IGHV Gene Usage, Stereotypy, and Antigen-Specific HCDR3 Selection of Its Human Counterpart

Chronic lymphocytic leukemia (CLL)/Small lymphocytic lymphoma (SLL) is a heterogeneous disease consisting of at least two separate subtypes, based on the mutation status of the immunoglobulin heavy chain variable gene (IGHV) sequence. Exposure to antigens seems to play a role in malignant transformation and in the selection and expansion of more aggressive CLL clones. Furthermore, a biased usage of particular IGHV gene subgroups and the existence of stereotyped B-cell receptors (BCRs) are distinctive characteristics of human CLL. We have previously described that Traf2DN/BCL2 double-transgenic (tg, ^+/+) mice develop CLL/SLL with high incidence with aging. In this model, TNF-Receptor Associated Factor (TRAF)-2 deficiency cooperates with B cell lymphoma (BCL)-2 in promoting CLL/SLL in mice by specifically enforcing marginal zone (MZ) B cell differentiation and rendering B cells independent of BAFF for survival. In this report, we have performed the sequencing of the IGHV-D-J rearrangements of B cell clones from the Traf2DN/BCL2-tg^+/+ mice with CLL/SLL. The results indicate that these mice develop oligoclonal and monoclonal B cell expansions. Allotransplantation of the oligoclonal populations into immunodeficient mice resulted in the preferential expansion of one of the parental clones. The analysis of the IGHV sequences indicated that 15% were mutated (M) and 85% unmutated (UM). Furthermore, while the Traf2DN/BCL2-tg^-/- (wild-type), ^-/+ (BCL2 single-tg) and ^+/- (Traf2DNDN single-tg) littermates showed the expression of various IGHV gene subgroups, the CLL/SLL expanded clones from the Traf2DN/BCL2-tg^+/+ (double-transgenic) mice showed a more restricted IGHV gene subgroup usage and an overrepresentation of particular IGHV genes. In addition, the HCDR3-encoded protein sequence indicates the existence of stereotyped immunoglobulin (Ig) in the BCRs and strong similarities with BCR recognizing autoantigens and pathogen-associated antigens. Altogether, these results highlight the remarkable similarities between the CLL/SLL developed by the Traf2DN/BCL2-tg^+/+ mice and its human counterpart.

Mitochondrial DUT-M potentiates RLR-mediated antiviral signaling by enhancing VISA and TRAF2 association

Upon recognition of intracytoplasmic viral RNA, activated RIG-I is recruited to the mitochondrion-located adaptor protein VISA (also known as MAVS, CARDIF, and IPS-1). VISA then acts as a central signaling platform for linking RIG-I and downstream signaling components, such as TRAF2, 5, and 6, TBK1, and IKK, leading to activation of the kinases TBK1 and IKK. These activated kinases further phosphorylate the transcription factors IRF3/7 and NF-κB, leading to the induction of downstream antiviral genes. Here, we report a mitochondrial isoform, deoxyuridine triphosphate nucleotidohydrolase (dUTPase), DUT-M, as a positive regulator in RLR-VISA-mediated antiviral signaling. DUT-M interacts with VISA and RIG-I to facilitate the assembly of the VISA-TRAF2 complex and to augment the polyubiquitination of TRAF2, leading to potentiated activation of IRF3 dimerization and phosphorylation of P65, and enhanced VISA-mediated innate immune response. RLR-VISA-mediated IRF3 dimerization and P65 phosphorylation, were inhibited in DUT-knockdown and DUT-deficient 293 cells. Thus, DUT-M is a positive regulator of the RIG-I-VISA-mediated innate immune response to RNA viruses.

Allium macrostemon Saponin Inhibits Activation of Platelet via the CD40 Signaling Pathway

Allium macrostemon saponin is a traditional Chinese medicine that exhibits anti-atherosclerosis effects. However, the mechanism of its action has not been fully clarified. Platelet activation induced by CD40L plays an important role in the process of atherosis. In the present study, we demonstrate for the first time that A. macrostemon saponin inhibits platelet activation induced by CD40L. Moreover, the effects of saponin on platelet activation were achieved by activation of the classical CD40L-associated pathway, including the PI3K/Akt, MAPK and NF-κB proteins. In addition, the present study further demonstrated that saponin exhibited an effect on the TRAF2-mediated ubiquitination degradation, which contributed to the inhibition of the CD40 pathway and its downstream members. The findings determine that A. macrostemon saponin inhibits activation of platelets via activation of downstream proteins of the CD40 pathway. This in turn affected TRAF2-associated ubiquitination degradation and caused an anti-thrombotic effect.

Circ_0114876 promoted IL-1β-induced chondrocyte injury by targeting miR-671/TRAF2 axis

Osteoarthritis (OA) is a chronic joint disease, which occurs in the elderly. The regulatory mechanisms of circRNAs were involved in the occurrence and development of various diseases. However, the potential regulatory network of circRNA in OA remains further research and clarification. The expression of circ_0114876 was increased in OA tissues and inhibition of circ_0114876 could induce cell viability and suppress inflammation as well as inhibit cell apoptosis in IL-1β induced CHON-001 cells. Circ_0114876 regulated TRAF2 expression via sponging miR-671 in CHON-001 cells. Down-regulated miR-671 expression could reverse the effects of low circ_0114876 expression on cell progression and inflammation in IL-1β induced CHON-001 cells. Overexpression of TRAF2 could weaken the promotion effects of high miR-671 expression on cell progression and inflammation in IL-1β induced CHON-001 cells. Circ_0114876 targeted miR-671 to regulate cell progression and inflammation via modulating TRAF2 expression in IL-1β induced CHON-001 cells, and played an important regulatory mechanism in IL-1β-induced chondrocyte injury, providing a novel diagnostics and therapeutics in OA.

Immunoblot Analysis of the Regulation of TNF Receptor Family-Induced NF-κB Signaling by c-IAP Proteins

Proper maintenance of organismal homeostasis, development, and immune defense requires precise regulation of survival and signaling pathways. Inhibitor of apoptosis (IAP) proteins are evolutionarily conserved regulators of cell death and immune signaling that impact numerous cellular processes. Although initially characterized as inhibitors of apoptosis, the ubiquitin ligase activity of IAP proteins is critical for modulating various signaling pathways (e.g., NF-κB, MAPK) and cell survival. Cellular IAP1 and 2 regulate the pro-survival canonical NF-κB pathway by ubiquitinating RIP1 and themselves thus enabling recruitment of kinase (IKK) and E3 ligase (LUBAC) complexes. On the other hand, c-IAP1 and c-IAP2 are negative regulators of noncanonical NF-κB signaling by promoting ubiquitination and consequent proteasomal degradation of the NF-κB-inducing kinase NIK. Here we describe the involvement of c-IAP1 and c-IAP2 in NF-κB signaling and provide detailed methodology for examining functional roles of c-IAPs in these pathways.

TNFAIP8 Promotes Cisplatin Chemoresistance in Triple-Negative Breast Cancer by Repressing p53-Mediated miR-205-5p Expression

Tumor necrosis factor alpha-induced protein 8 (TNFAIP8) is implicated in the tumor progression and prognosis of triple-negative breast cancer (TNBC), but the detailed regulatory mechanism of TNFAIP8 in cisplatin tolerance in TNBC has not yet been investigated. TNFAIP8 was evidently upregulated in TNBC tumor tissues and cell lines. Knocking down TNFAIP8 led to impaired proliferation and elevated apoptosis of TNBC cells upon cisplatin (DDP) treatment. Mechanistic studies revealed that TNFAIP8 repressed the expression of p53 and p53-promoted microRNA (miR)-205-5p; moreover, miR-205-5p targeted multiple genes required for the cell cycle and repressed Akt phosphorylation, which thus inhibited the proliferation of TNBC cells. In addition, silencing of TNFAIP8 led to the upregulation of miR-205-5p and the restraint of the TRAF2-NF-κB pathway, which thus enhanced the suppressive effects of DDP on tumor growth in nude mice. This study revealed that TNFAIP8 was essential in the DDP tolerance formation of TNBC cells by reducing p53-promoted miR-205-5p expression. Thus, targeting TNFAIP8 might become a promising strategy to suppress TNBC progression.

HtrA2 is required for inflammatory responses in BMDMs via controlling TRAF2 stability in collagen-induced arthritis

Rheumatoid arthritis (RA) is an autoimmune inflammatory disease characterized by the destruction of cartilage and bone. The present study aims to investigate the role of HtrA serine peptidase 2 (HtrA2) in the collagen-induced arthritis. The expressions of HtrA2 were determined in the database BioGPS and bone marrow-derived macrophages (BMDMs). The populations of myeloid and lymphoid cells were determined in wild type and HtrA2 knockout (HtrA2^MKO) mice using flow cytometry. In addition, the expressions of pro-inflammatory cytokines (Il6, Tnf, and Il1β) were determined in the activated BMDMs from wild type (WT) and HtrA2^MKO mice. STRING database was used to predict the interactive proteins of HtrA2 and Co-Immunoprecipitation was used to confirm these interactions. A collagen-induced arthritis model was established to investigate the effects of HtrA2 on the arthritis symptoms. It was found that HtrA2 reduction was associated with the activation of myeloid cells. Interestingly, HtrA2 deficiency did not affect the development of myeloid and lymphoid cells. Further studies demonstrated that HtrA2 deficiency suppressed the production of pro-inflammatory cytokines in BMDMs induced by lipopolysaccharide or CpG. Co-Immunoprecipitation results demonstrated that HtrA2 enhanced the stability of TNF receptor-associated factor 2 (TRAF2). HtrA2 participated in the activation of the inflammatory response in a collagen-induced arthritis model. In summary, HtrA2 modulates inflammatory responses in BMDMs by controlling TRAF2 stability in a collagen-induced arthritis mouse model.

Pro-apoptotic functions of TRAF2 in p53-mediated apoptosis induced by cisplatin

Tumor necrosis factor receptor-associated factor 2 (TRAF2) is an essential component of tumor necrosis factor-α (TNF-α) signaling that regulates nuclear factor-κB (NF-κB) and c-Jun N-terminal kinase (JNK) pathways, and compelling evidence has demonstrated that TRAF2 suppresses TNF-α-induced cytotoxicity. On the other hand, it has been reported that oxidative stress-induced cytotoxicity is potentiated by TRAF2, indicating that TRAF2 both positively and negatively regulates stress-induced cytotoxicity in a context-specific manner. However, the causal role of TRAF2 in DNA damage response (DDR) remains to be explored. In this study, we assessed the function of TRAF2 in DDR induced by cisplatin, a representative DNA-damaging agent, and found that TRAF2 exerts pro-apoptotic activity through p53-dependent mechanisms at least in human fibrosarcoma cell line HT1080. TRAF2 deficient cells exhibit significant resistance to cell death induced by cisplatin, accompanied by the reduction of both p53 protein level and caspase-3 activation. Moreover, cisplatin-induced JNK activation was attenuated in TRAF2-deficient cells, and pharmacological inhibition of JNK signaling suppressed p53 stabilization. These results suggest that TRAF2 promotes p53-dependent apoptosis by activating the JNK signaling cascade in HT1080 cells. Thus, our data demonstrate a novel function of TRAF2 in cisplatin-induced DDR as a pro-apoptotic protein.

TRIM52 positively mediates NF-κB to promote the growth of human benign prostatic hyperplasia cells through affecting TRAF2 ubiquitination

AIMS

Benign prostatic hyperplasia (BPH) is a progressive disease, which severely affects men's health. Here, we sought to analyze the functions and mechanism of action of the tripartite motif protein 52 (TRIM52), a novel prostate basal cell biomarker in BPH.

MATERIALS AND METHODS

Immunohistochemistry assay was performed in sectioned human BPH tissues, BPH-1 cells, and prostate RWPE-1 cells, to detect the expressions of TRIM52 and NF-κB. Western blotting and qRT-PCR analyses were conducted to measure the relative protein and mRNA expression levels, respectively. Further, lentiviral transfection was performed in BPH-1 and RWPE-1 cells to study the overexpression and siRNA knockdown of TRIM52. Dual-luciferase reporter assay was applied to evaluate the relationship between NF-κB and TRIM52. Furthermore, CCK-8 assay and flow cytometry were employed to analyze cell proliferation and apoptosis.

KEY FINDINGS

TRIM52 and NF-κB levels were elevated in BPH tissues, and TRIM52 expression positively correlated with NF-κB expression. TRIM52 silencing suppressed the growth of BPH-1 cells and decreased the promoter activity of NF-κB. Moreover, the NF-κB inhibitor, pyrrolidine dithiocarbamate (PDTC), suppressed TRIM52-induced proliferation of RWPE-1 cells and inhibited NF-κB promoter activity in oeTRIM52 transfected RWPE-1 cells. Silencing TRIM52 also inhibited TRAF2 ubiquitination in BPH-1 cells. Further, NF-κB promoter activity in siNC transfected cells was enhanced by the recombinant protein TNF-α and inhibited by siTRIM52.

SIGNIFICANCE

TRIM52 accelerated the growth of BPH-1 cells by upregulating NF-κB, and TRIM52 could promote TRAF2 ubiquitination. These findings might contribute to the understanding of the biological functions and action mechanisms of TRIM52 in BPH.