TRAIP suppressed apoptosis and cell cycle to promote prostate cancer proliferation via TRAF2-PI3K-AKT pathway activation

BACKGROUND

TRAF-interacting protein (TRAIP) is a RING-type E3 ubiquitin ligase, which has been implicated in various cellular processes and participated in various cancers as an oncogene. However, the function and potential mechanism of TRAIP in prostate cancer (PCa) have not been investigated so far.

METHODS

Public TGCA data were used to evaluate the expression profile of TRAIP in prostatic tumors. The relative expression of TRAIP and TRAF2 in PCa tissues and tumor cell lines was detected by qPCR, western blot, and IHC staining. Next, TRAIP knockdown and overexpression plasmids were constructed and transfected into PCa cell lines. Moreover, cell proliferation, invasion, migration, and apoptosis were measured by colony formation, Transwell, wound healing, and flow cytometry assays. Subsequently, cell cycle and signaling pathway-related proteins were tested by western blot. Finally, the effect of TRAIP on PCa was measured based on the nude mouse xenograft model.

RESULTS

TRAIP was significantly upregulated in PCa tissues and tumor cell lines. In addition, TRAIP promoted cell proliferation, invasion, and migration of PCa cell lines. Such an oncogenic property was mediated by the cell cycle arrest and the inhibition of apoptosis, as indicated by different functional assays and the expression of cell cycle and apoptosis regulatory proteins in cultured cells. Moreover, TRAIP combined with TRAF2 to activate PI3K/AKT pathway. Finally, TRAIP depletion suppressed the growth of tumors and cell proliferation in vivo.

CONCLUSIONS

Our study first revealed that TRAIP promoted tumor progression and identified it as a potential therapeutic target for PCa patients in the future.

B(a)P induces ovarian granulosa cell apoptosis via TRAF2-NFκB-Caspase1 axis during early pregnancy

Benzo(a)pyrene [B(a)P] is an environmental endocrine disruptor with reproductive toxicity. The corpus luteum (CL) of the ovary plays an important role in embryo implantation and pregnancy maintenance. Our previous studies have shown that B(a)P exposure affects embryo implantation and endometrial decidualization in mouse, but its effects and mechanisms on CL function remain unclear. In this study, we explore the mechanism of ovarian toxicity of B(a)P using a pregnant mouse model and an in vitro model of human ovarian granulosa cells (GCs) KGN. Pregnant mice were gavaged with corn oil or 0.2 mg/kg.bw B(a)P from pregnant day 1 (D1) to D7, while KGN cells were treated with DMSO, 1.0IU/mL hCG, or 1.0IU/mL hCG plus benzo(a)pyrene-7,8-dihydrodiol-9,10-epoxide (BPDE), a B(a)P metabolite. Our findings revealed that B(a)P exposure damaged embryo implantation and reduced estrogen and progesterone levels in early pregnant mice. Additionally, in vitro, BPDE impaired luteinization in KGN cells. We observed that B(a)P/BPDE promoted oxidative stress (OS) and inflammation, leading to apoptosis rather than pyroptosis in ovaries and luteinized KGN cells. This apoptotic response was mediated by the activation of inflammatory Caspase1 through the cleavage of BID. Furthermore, B(a)P/BPDE inhibited TRAF2 expression and suppressed NFκB signaling pathway activation. The administration of VX-765 to inhibit the Caspase1 activation, over-expression of TRAF2 using TRAF2-pcDNA3.1 (+) plasmid, and BetA-induced activation of NFκB signaling pathway successfully alleviated BPDE-induced apoptosis and cellular dysfunction in luteinized KGN cells. These findings were further confirmed in the KGN cell treated with H2O2 and NAC. In conclusion, this study elucidated that B(a)P/BPDE induces apoptosis rather than pyroptosis in GCs via TRAF2-NFκB-Caspase1 during early pregnancy, and highlighting OS as the primary contributor to B(a)P/BPDE-induced ovarian toxicity. Our results unveil a novel role of TRAF2-NFκB-Caspase1 in B(a)P-induced apoptosis and broaden the understanding of mechanisms underlying unexplained luteal phase deficiency.

TRAF2 decrease promotes the TGF-β-mTORC1 signal in MAFLD-HCC through enhancing AXIN1-mediated Smad7 degradation

According to recent research, metabolic-associated fatty liver disease (MAFLD) has emerged as an important underlying etiology of hepatocellular carcinoma (HCC). However, the molecular mechanism of MAFLD-HCC is still unclear. Tumor necrosis factor receptor-associated factor 2 (TRAF2) is the key molecule to mediate the signal of inflammatory NF-κB pathway. This study aims to investigate the potential dysregulation of TRAF2 and its biological function in MAFLD-HCC. Huh7 TRAF2-/- demonstrated increased tumor formation ability compared to huh7 TRAF2+/+ when stimulated with transforming growth factor-β (TGF-β). The decisive role of TGF-β in the development of MAFLD-HCC was confirmed through the specific depletion of TGF-β receptor II gene in the hepatocytes (Tgfbr2ΔHep) of mice. In TRAF2-/- cells treated with TGF-β, both the glycolysis rate and lipid synthesis were enhanced. We proved the signal of the mechanistic target of rapamycin complex 1 (mTORC1) could be activated in the presence of TGF-β, and was enhanced in TRAF2-/- cells. The coimmunoprecipitation (co-IP) experiments revealed that TRAF2 fortified the Smurf2-mediated ubiquitination degradation of AXIN1. Hence, TRAF2 depletion resulted in increased Smad7 degradation induced by AXIN1, thus promoting the TGF-β signal. We also discovered that PLX-4720 could bind with AXIN1 and restrained the tumor proliferation of TRAF2-/- in mice fed with high-fat diet (HFD). Our findings indicate that TRAF2 plays a significant role in the pathogenesis of MAFLD-HCC. The reduction of TRAF2 expression leads to the enhancement of the TGF-β-mTORC1 pathway by facilitating AXIN1-mediated Smad7 degradation.

TRAF2 inhibits senescence in hepatocellular carcinoma cells via regulating the ROMO1/ NAD+/SIRT3/SOD2 axis

The suppression of tumor proliferation via cellular senescence has emerged as a promising approach for anti-tumor therapy. Tumor necrosis factor receptor-associated factor 2 (TRAF2), an adaptor protein involved in the NF-κB signaling pathway and reactive oxygen species (ROS) production, has been implicated in hepatocellular carcinoma (HCC) proliferation. However, little is currently known about whether TRAF2 promotes HCC development by inhibiting cellular senescence. Replicative senescence model and IR-induced mouse model demonstrated that TRAF2 expression was decrease in senescence cells or liver tissues. Depletion of TRAF2 could inhibit proliferation and arrest the cell cycle via activating p53/p21WAF1 and p16INK4a/pRb signaling pathways in HCC cells and eventually lead to cellular senescence. Mechanistically, TRAF2 deficiency increased the expression of mitochondrial protein reactive oxygen species modulator 1 (ROMO1) and subsequently activated the NAD+/SIRT3/SOD2 pathway to promote the production of ROS and cause mitochondrial dysfunction, which eventually contributed to DNA damage response (DDR). Our findings demonstrate that TRAF2 deficiency inhibits the proliferation of HCC by promoting senescence. Therefore, targeting TRAF2 through various approaches holds therapeutic potential for treating HCC.

Molecular and cellular evidence of a direct interaction between the TRAF2 C-terminal domain and ganglioside GM1

TNF receptor-associated factor 2 (TRAF2) is involved in different cellular processes including signal transduction and transcription regulation. We here provide evidence of a direct interaction between the TRAF domain of TRAF2 and the monosialotetrahexosylganglioside (GM1). Previously, we showed that the TRAF domain occurs mainly in a trimeric form in solution, but it can also exist as a stable monomer when in the nanomolar concentration range. Here, we report that the quaternary structure of the TRAF domain is also affected by pH changes, since a weakly acidic pH (5.5) favors the dissociation of the trimeric TRAF domain into stable monomers, as previously observed at neutral pH (7.6) with the diluted protein. The TRAF domain-GM1 binding was similar at pH 5.5 and 7.6, suggesting that GM1 interacts with both the trimeric and monomeric forms of the protein. However, only the monomeric protein appeared to cause membrane deformation and inward vesiculation in GM1-containing giant unilamellar vesicles (GUVs). The formation of complexes between GM1 and TRAF2, or its TRAF domain, was also observed in cultured human leukemic HAP1 cells expressing either the truncated TRAF domain or the endogenous full length TRAF2. The GM1-protein complexes were observed after treatment with tunicamycin and were more concentrated in cells undergoing apoptosis, a condition which is known to cause cytoplasm acidification. These findings open the avenue for future studies aimed at deciphering the physiopathological relevance of the TRAF domain-GM1 interaction.

Oncogenic KEAP1 mutations activate TRAF2-NFκB signaling to prevent apoptosis in lung cancer cells

The Kelch-like ECH-associated protein 1 (KEAP1) - Nuclear factor erythroid 2 -related factor 2 (NRF2) pathway is the major transcriptional stress response system in cells against oxidative and electrophilic stress. NRF2 is frequently constitutively active in many cancers, rendering the cells resistant to chemo- and radiotherapy. Loss-of-function (LOF) mutations in the repressor protein KEAP1 are common in non-small cell lung cancer, particularly adenocarcinoma. While the mutations can occur throughout the gene, they are enriched in certain areas, indicating that these may have unique functional importance. In this study, we show that in the GSEA analysis of TCGA lung adenocarcinoma RNA-seq data, the KEAP1 mutations in R320 and R470 were associated with enhanced Tumor Necrosis Factor alpha (TNFα) - Nuclear Factor kappa subunit B (NFκB) signaling as well as MYC and MTORC1 pathways. To address the functional role of these hotspot mutations, affinity purification and mass spectrometry (AP-MS) analysis of wild type (wt) KEAP1 and its mutation forms, R320Q and R470C were employed to interrogate differences in the protein interactome. We identified TNF receptor associated factor 2 (TRAF2) as a putative protein interaction partner. Both mutant KEAP1 forms showed increased interaction with TRAF2 and other anti-apoptotic proteins, suggesting that apoptosis signalling could be affected by the protein interactions. A549 lung adenocarcinoma cells overexpressing mutant KEAP1 showed high TRAF2-mediated NFκB activity and increased protection against apoptosis, XIAP being one of the key proteins involved in anti-apoptotic signalling. To conclude, KEAP1 R320Q and R470C and its interaction with TRAF2 leads to activation of NFκB pathway, thereby protecting against apoptosis.

The natural compound Sanggenon C inhibits PRRSV infection by regulating the TRAF2/NF-κB signalling pathway

Porcine reproductive and respiratory syndrome (PRRS) is a serious infectious disease and one of the major causes of death in the global pig industry. PRRS virus (PRRSV) strains have complex and diverse genetic characteristics and cross-protection between strains is low, which complicates vaccine selection; thus, the current vaccination strategy has been greatly compromised. Therefore, it is necessary to identify effective natural compounds for the clinical treatment of PRRS. A small molecule library composed of 720 natural compounds was screened in vitro, and we found that Sanggenon C (SC) was amongst the most effective natural compound inhibitors of PRRSV infection. Compared with ribavirin, SC more significantly inhibited PRRSV infection at both the gene and protein levels and reduced the viral titres and levels of protein expression and inflammatory cytokine secretion to more effectively protect cells from PRRSV infection and damage. Mechanistically, SC inhibits activation of the NF-κB signalling pathway by promoting TRAF2 expression, thereby reducing PRRSV replication. In conclusion, by screening natural compounds, we found that SC suppresses PRRSV infection by regulating the TRAF2/NF-κB signalling pathway. This study contributes to a deeper understanding of the therapeutic targets and pathogenesis of PRRSV infection. More importantly, our results demonstrate that SC has potential as a candidate for the treatment of PRRS.

Silencing of CPNE1-TRAF2 Axis Restrains the Development of Pancreatic Cancer

BACKGROUND

Copine 1 (CPNE1) acts as a promoter in the progression of many kinds of cancers with the exception of pancreatic cancer (PC). This research is designed to probe the function of the CPNE1-tumor necrosis factor receptor-associated factor 2 (TRAF2) axis in PC.

METHODS

In vivo and in vitro models of PC were constructed, and a series of biological function tests, including MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide], colony formation, flow cytometry, and immunohistochemistry, were performed.

RESULTS

The level of CPNE1 elevated dramatically in PC cells. Downregulation of CPNE1in PC cells resulted in the inhibition of colony formation and proliferation. In addition, the silencing of CPNE1 induced the G1/S arrest and apoptosis in PC cells. Additionally, TRAF2 positively interacted with CPNE1 in PANC cells. CPNE1 silencing also inhibited the growth of tumors in in vivo mouse models. Functional experiments revealed that the anti-tumor effect of CPNE1 silencing was counteracted by TRAF2 overexpression, and the tumor-promoting effect of TRAF2 overexpression was reversed by CPNE1 silencing.

CONCLUSIONS

In summary, our findings indicate that the silencing of the CPNE1-TRAF2 axis restrains PC development.

Fn14 and TNFR2 as regulators of cytotoxic TNFR1 signaling

Tumor necrosis factor (TNF) receptor 1 (TNFR1), TNFR2 and fibroblast growth factor-inducible 14 (Fn14) belong to the TNF receptor superfamily (TNFRSF). From a structural point of view, TNFR1 is a prototypic death domain (DD)-containing receptor. In contrast to other prominent death receptors, such as CD95/Fas and the two TRAIL death receptors DR4 and DR5, however, liganded TNFR1 does not instruct the formation of a plasma membrane-associated death inducing signaling complex converting procaspase-8 into highly active mature heterotetrameric caspase-8 molecules. Instead, liganded TNFR1 recruits the DD-containing cytoplasmic signaling proteins TRADD and RIPK1 and empowers these proteins to trigger cell death signaling by cytosolic complexes after their release from the TNFR1 signaling complex. The activity and quality (apoptosis versus necroptosis) of TNF-induced cell death signaling is controlled by caspase-8, the caspase-8 regulatory FLIP proteins, TRAF2, RIPK1 and the RIPK1-ubiquitinating E3 ligases cIAP1 and cIAP2. TNFR2 and Fn14 efficiently recruit TRAF2 along with the TRAF2 binding partners cIAP1 and cIAP2 and can thereby limit the availability of these molecules for other TRAF2/cIAP1/2-utilizing proteins including TNFR1. Accordingly, at the cellular level engagement of TNFR2 or Fn14 inhibits TNFR1-induced RIPK1-mediated effects reaching from activation of the classical NFκB pathway to induction of apoptosis and necroptosis. In this review, we summarize the effects of TNFR2- and Fn14-mediated depletion of TRAF2 and the cIAP1/2 on TNFR1 signaling at the molecular level and discuss the consequences this has in vivo.

Neurorescuing effect of Cinacalcet against hypercalcemia-induced nerve injury in chronic kidney disease via TRAF2/cIAP1/KLF2/SERPINA3 signal axis

Hypercalcemia is a common complication in chronic kidney disease (CKD) and unfortunately contributes to nerve injury. This study aims to investigate the potential role and underlying mechanisms of Cinacalcet (CIN) in hypercalcemia-driven nerve injury in CKD. A CKD mouse model was first established by adenine feeding to identify the therapeutic effects of CIN. Molecules related to CIN and CKD were predicted by bioinformatics analysis and their expression in the kidney tissues of CKD mice was measured by immunochemistry. Gain- and loss-of-functions assays were performed both in vitro and in vivo to evaluate their effects on nerve injury in CKD, as reflected by Scr and BUN, and brain calcium content as well as behavior tests. CIN ameliorated hypercalcemia-driven nerve injury in CKD mice. Interactions among TRAF2, an E3-ubiquitin ligase, KLF2, and SERPINA3 were bioinformatically predicted on CIN effect. CIN restricted the ubiquitin-mediated degradation of KLF2 by downregulating TRAF2. KLF2 targeted and inversely regulated SERPINA3 to repress hypercalcemia-driven nerve injury in CKD. CIN was substantiated in vivo to ameliorate hypercalcemia-driven nerve injury in CKD mice through the TRAF2/KLF2/SERPINA3 regulatory axis. Together, CIN suppresses SERPINA3 expression via TRAF2-mediated inhibition of the ubiquitin-dependent degradation of KLF2, thus repressing hypercalcemia-induced nerve injury in CKD mice.

Sublethal necroptosis signaling promotes inflammation and liver cancer

It is currently not well known how necroptosis and necroptosis responses manifest in vivo. Here, we uncovered a molecular switch facilitating reprogramming between two alternative modes of necroptosis signaling in hepatocytes, fundamentally affecting immune responses and hepatocarcinogenesis. Concomitant necrosome and NF-κB activation in hepatocytes, which physiologically express low concentrations of receptor-interacting kinase 3 (RIPK3), did not lead to immediate cell death but forced them into a prolonged "sublethal" state with leaky membranes, functioning as secretory cells that released specific chemokines including CCL20 and MCP-1. This triggered hepatic cell proliferation as well as activation of procarcinogenic monocyte-derived macrophage cell clusters, contributing to hepatocarcinogenesis. In contrast, necrosome activation in hepatocytes with inactive NF-κB-signaling caused an accelerated execution of necroptosis, limiting alarmin release, and thereby preventing inflammation and hepatocarcinogenesis. Consistently, intratumoral NF-κB-necroptosis signatures were associated with poor prognosis in human hepatocarcinogenesis. Therefore, pharmacological reprogramming between these distinct forms of necroptosis may represent a promising strategy against hepatocellular carcinoma.

TRAF2 promotes M2-polarized tumor-associated macrophage infiltration, angiogenesis and cancer progression by inhibiting autophagy in clear cell renal cell carcinoma

BACKGROUND

The management of advanced clear cell renal cell carcinoma (ccRCC) remains a major challenge in clinical practice, and the construction of more reliable prognostic prediction models and the further elucidation of key molecular mechanisms of tumor progression are topics in urgent need of in-depth investigation.

METHODS

We used CIBERSORT to estimate the proportion of 22 tumor-infiltrating immune cell types in the TCGA-KIRC cohort. Weighted gene co-expression network analysis, least absolute shrinkage and selection operator regression analysis were used to build risk prediction models. Expression patterns and clinical significance of TRAF2 were determined through bioinformatics analysis, real-time qPCR, Western Blot, immunohistochemistry. GSEA analysis, transmission electron microscopy, 2D/3D colony formation assay, cell migration and invasion assay, and tube-formation assay were used to investigate the underlying function and mechanism of the TRAF2/M2 macrophage/autophagy axis.

RESULTS

We constructed a novel prognostic prediction model based on M2 macrophage-related genes, which was identified as an accurate, independent and specific prognostic risk model for ccRCC patients. A reliable nomogram was constructed to predict 1-, 3-, and 5-year overall survival for patients with ccRCC. As one of the constituent genes of the risk model, TRAF2 was determined to be upregulated in ccRCC and associated with poor clinical prognosis. We found that TRAF2 promotes malignant progression of ccRCC by regulating macrophage polarization, migration and angiogenesis. Mechanistically, we found that TRAF2 promotes the polarization of M2 macrophages, and this chemotaxis is achieved in an autophagy-dependent pathway. Orthotopic tumor growth assay results revealed that TRAF2 plays a key role as a promotor of ccRCC growth and metastasis.

CONCLUSIONS

In conclusion, this risk model is highly predictive of prognostic in ccRCC patients, which is expected to promote improved treatment evaluation and comprehensive management of ccRCC. Moreover, our findings reveal that the TRAF2/M2 macrophage/autophagy axis plays a key regulatory role in the malignant progression of ccRCC, and suggest that TRAF2 is a potential novel therapeutic target for advanced ccRCC.

Scoparone inhibits breast cancer cell viability through the NF‑κB signaling pathway

Scoparone (SCO) is a compound found in the stems and leaves of Artemisia capillaris. The pharmacological uses of SCO include significant hypotensive, cholagogic, anti-inflammatory, analgesic, lipid-lowering, anti-asthmatic and anti-coagulant effects. The present study aimed to verify the anticancer potential of SCO in breast cancer (BC) cells and its underlying molecular mechanism. Cell Counting Kit-8 and flow cytometry were used to analyze the effects of SCO on cell viability and apoptosis. Nucleocytoplasmic separation was used to analyze the location of the long non-coding RNA (lncRNA) small nucleolar RNA host gene 12 (SNHG12) in BC cells. Reverse transcription-quantitative PCR was used to analyze the effect of SCO on the expression levels of SNHG12, microRNA (miRNA/miR)-140-3p and tumor necrosis factor receptor associated factor 2 (TRAF2). Western blotting was used to analyze the protein expression levels of TRAF2 and downstream nuclear factor κB (NF-κB) signaling pathways. The results demonstrated that SCO had a time- and dose-dependent inhibitory effect on the viability of BC cells, and that the upregulated lncRNA SNHG12 in BC cells was inhibited by SCO. SNHG12, which was primarily expressed in the cytoplasm, acted as a competing endogenous RNA, sponged miR-140-3p and inhibited the expression of miR-140-3p. The transcriptional activity and translational level of TRAF2, a downstream target of miR-140-3p, decreased following the SCO-mediated suppression of SNHG12 expression. As an upstream effector, TRAF2 activity reduction mediated the inhibition of NF-κB signaling, decreased the viability and migration of BC cells, and promoted BC cell apoptosis. In conclusion, SCO-induced inhibition of viability and promotion of apoptosis in BC cells are achieved through the inhibition of NF-κB signaling, which is associated with regulation of the SNHG12/miR-140-3p/TRAF2 axis. This understanding provides new drug candidates for the treatment of BC and a theoretical basis for biology.

The CD40 agonist HERA-CD40L results in enhanced activation of antigen presenting cells, promoting an anti-tumor effect alone and in combination with radiotherapy

Introduction

The ability to modulate and enhance the anti-tumor immune responses is critical in developing novel therapies in cancer. The Tumor Necrosis Factor (TNF) Receptor Super Family (TNFRSF) are potentially excellent targets for modulation which result in specific anti-tumor immune responses. CD40 is a member of the TNFRSF and several clinical therapies are under development. CD40 signaling plays a pivotal role in regulating the immune system from B cell responses to myeloid cell driven activation of T cells. The CD40 signaling axis is well characterized and here we compare next generation HERA-Ligands to conventional monoclonal antibody based immune modulation for the treatment of cancer.

Methods & results

HERA-CD40L is a novel molecule that targets CD40 mediated signal transduction and demonstrates a clear mode of action in generating an activated receptor complex via recruitment of TRAFs, cIAP1, and HOIP, leading to TRAF2 phosphorylation and ultimately resulting in the enhanced activation of key inflammatory/survival pathway and transcription factors such asNFkB, AKT, p38, ERK1/2, JNK, and STAT1 in dendritic cells. Furthermore, HERA-CD40L demonstrated a strong modulation of the tumor microenvironment (TME) via the increase in intratumoral CD8+ T cells and the functional switch from pro-tumor macrophages (TAMs) to anti-tumor macrophages that together results in a significant reduction of tumor growth in a CT26 mouse model. Furthermore, radiotherapy which may have an immunosuppressive modulation of the TME, was shown to have an immunostimulatory effect in combination with HERA-CD40L. Radiotherapy in combination with HERA-CD40L treatment resulted in an increase in detected intratumoral CD4+/8+ T cells compared to RT alone and, additionally, the repolarization of TAMs was also observed, resulting in an inhibition of tumor growth in a TRAMP-C1 mouse model.

Discussion

Taken together, HERA-CD40L resulted in activating signal transduction mechanisms in dendritic cells, resulting in an increase in intratumoral T cells and manipulation of the TME to be pro-inflammatory, repolarizing M2 macrophages to M1, enhancing tumor control.

Deciphering the molecular mechanism of the THBS1 gene in the TNF signaling axis in glioma stem cells

Glioma stem cells (GSCs) are thought to be responsible for the initiation and progression of glioblastoma (GBM). GBM presents highly invasive growth with a very high recurrence rate, so it has become a clinical problem to be solved urgently. RNAseq demonstrates that thrombospondin 1 (THBS1) acts not only in the angiogenic core of glioma but also with a high degree of invasiveness and infiltration. Nevertheless, defects in the signaling pathway research lead to a poor prognosis in glioma patients. To investigate the relevant molecular mechanism and signal pathway of glioma stem cell behavior mediated by THBS1, U251 astroglioma cells and GSCs were taken as model cells for in vitro experiments. The biological effects of THBS1 on glioma proliferation, migration, and adhesion were evaluated using Cell Counting Kit-8(CCK8) assays, EdU incorporation assays, migration assays, Transwell assays, Western blotting, and RNAseq. We found that the knockout of the THBS1 gene by CRISPR/Cas9 promoted proliferation and migration in U251 cells and GSCs, as well as influencing cell cycle progression by regulating the TNF/MAPK/NF-κB and TGF-β/Smad signaling pathways. Moreover, U251 cells and GSCs showed different responses to THBS1 knockout, suggesting specific and potential targets for GSCs in signaling pathways mediated by THBS1.

Anti-apoptotic Splicing Variant of AIMP2 Recover Mutant SOD1-Induced Neuronal Cell Death

Although a couple of studies have reported that mutant superoxide dismutase 1 (SOD1), one of the causative genes of familial amyotrophic lateral, interacts physically with lysyl-tRNA synthetase (KARS1) by a gain of function, there is limited evidence regarding the detailed mechanism about how the interaction leads to neuronal cell death. Our results indicated that the aminoacyl-tRNA synthetase-interacting multi-functional protein 2 (AIMP2) mediated cell death upon the interplay between mutant SOD1 and KARS1 in ALS. Binding of mutant SOD1 with KARS1 led to the release of AIMP2 from its original binding partner KARS1, and the free form of AIMP2 induced TRAF2 degradation followed by TNF-α-induced cell death. We also suggest a therapeutic application that overexpression of DX2, the exon 2-deleted antagonistic splicing variant of AIMP2 (AIMP2-DX2), reduced neuronal cell death in the ALS mouse model. Expression of DX2 suppressed TRAF2 degradation and TNF-α-induced cell death by competing mode of action against full-length AIMP2. Motor neuron differentiated form iPSC showed a resistance in neuronal cell death after DX2 administration. Further, intrathecal administration of DX2-coding adeno-associated virus (AAV) improved locomotive activity and survival in a mutant SOD1-induced ALS mouse model. Taken together, these results indicated that DX2 could prolong life span and delay the ALS symptoms through compensation in neuronal inflammation.

TRAF2 as a key candidate gene in clinical hepatitis B-associated liver fibrosis

Objectives: Approximately 240 million individuals are infected with chronic hepatitis B virus (HBV) worldwide. HBV infection can develop into liver fibrosis. The mechanism of HBV-related liver fibrosis has not been fully understood, and there are few effective treatment options. The goal of this study was to use transcriptomics in conjunction with experimental validation to identify new targets to treat HBV-related liver fibrosis. Methods: To identify differentially expressed genes (DEGs), five liver tissues were collected from both healthy individuals and patients with chronic hepatitis B. NovoMagic and Java GSEA were used to screen DEGs and key genes, respectively. Immunocell infiltration analysis of RNA-seq data was, and the results were confirmed by Western blotting (WB), real-time quantitative polymerase chain reaction (RT-qPCR), and immunohistochemistry. Results: We evaluated 1,105 genes with differential expression, and 462 and 643 genes showed down- and upregulation, respectively. The essential genes, such as tumor necrosis factor (TNF) receptor-associated factor-2 (TRAF2), were screened out of DEGs. TRAF2 expression was abnormally high in hepatic fibrosis in patients with hepatitis B compared with healthy controls. The degree of hepatic fibrosis and serum levels of glutamate transaminase (ALT), aspartate aminotransferase (AST), and total bilirubin (TBIL) were positively linked with TRAF2 expression. TRAF2 may be crucial in controlling T lymphocyte-mediated liver fibrosis. Conclusion: Our findings imply that TRAF2 is essential for HBV-induced liver fibrosis progression, and it may potentially be a promising target for the treatment of hepatic fibrosis in hepatitis B.

TRAF2 regulates the protein stability of HIPK2

A nuclear serine/threonine kinase homeodomain-interacting protein kinase 2 (HIPK2) is a critical regulator of development and DNA damage response. HIPK2 can induce apoptosis under cellular stress conditions and thus its protein level is maintained low by constant proteasomal degradation. In the present study, we present evidence that TNF receptor-associated factor 2 (TRAF2) regulates the protein stability of HIPK2. Overexpression of TRAF2 decreased while its knockdown increased the HIPK2 protein level. The TRAF2-mediated decrease in HIPK2 protein expression was blocked by proteasomal inhibitor. In addition, TRAF2 decreased the protein half-life of HIPK2. We found that HIPK2 and TRAF2 co-immunoprecipitated. Interestingly, the co-immunoprecipitation was reduced while HIPK2 protein level increased following TNFα treatment, suggesting TNFα induced dissociation of TRAF2 from HIPK2 to accumulate HIPK2. Inhibition of HIPK2 partially suppressed TNFα-induced cell death, indicating that the accumulated HIPK2 may contribute to the TNFα-induced cell death. Our results suggest that TRAF2 can regulate proapoptotic function of HIPK2 by promoting proteasomal degradation.

Revisited role of TRAF2 and TRAF2 C-terminal domain in endoplasmic reticulum stress-induced autophagy in HAP1 leukemia cells

The scaffold protein Tumor Necrosis Factor Receptor-Associated Factor 2 (TRAF2) has been reported to play a key role in the endoplasmic reticulum (ER) stress-induced activation of c-Jun N-terminal Kinase (JNK) and hence autophagy. Autophagy is a highly conserved catabolic process, whose dysregulation is involved in the pathogenesis of various human diseases, including cancer. We investigated the involvement of TRAF2 in autophagy regulation in the human leukemic HAP1 cell line, under both basal and ER stress conditions. In TRAF2-knockout HAP1 cell line (KO), the basal autophagic flux was higher than in the parental cell line (WT). Moreover, tunicamycin-induced ER stress stimulated JNK activation and autophagy both in WT and KO HAP1. On the other hand, re-expression of a TRAF2 C-terminal fragment (residues ,310-501), in a TRAF2-KO cellular background, rendered HAP1 cells unable to activate both JNK and autophagy upon ER stress induction. Of note, this apparent dominant negative effect of the C-terminal fragment was observed even in the absence of the endogenous, full-length TRAF2 molecule. Furthermore, the expression of the C-terminal fragment resulted in both protein kinase B (AKT) pathway activation and increased resistance to the toxic effects induced by prolonged ER stress conditions. These findings indicate that TRAF2 is dispensable for the activation of both JNK and autophagy in HAP1 cells, while the TRAF2 C-terminal domain may play an autonomous role in regulating the cellular response to ER stress.

Characterization of TRAF2 in Nile tilapia: Expression profiles and the role in decreasing NF-κB pathway

Mammals TRAF2 played a dual role in several immune signaling transduction processes. In this study, TRAF2 was cloned from Nile tilapia, Oreochromis niloticus, which named OnTRAF2. The open reading frame was 1797 bp, encoding 598 amino acids. Amino acid alignment and phylogenetic analysis indicated that OnTRAF2 showed relatively low identify with other teleost TRAF2 proteins, with the exception of TRAF2s from Epinephelus coioides. In healthy tilapia, OnTRAF2 was expressed widely in all the examined tissues, which had highest expression level in the brain. After Streptococcus agalactiae infection, the expression level of OnTRAF2 was increased significantly at different times in several organs, implying that OnTRAF2 may be involved in host defense against S. agalactiae infection. The result of subcellular localization showed that OnTRAF2 presented in cytoplasm and nucleus of HEK293T cells. Additionally, overexpression of OnTRAF2 significantly decreased the transcriptional activity of the NF-κB reporter in HEK293T cells, yeast two-hybrid results revealed that OnTRAF2 had no interaction with E3 ubiquitin ligase OnNEDD4. These results indicated that OnTRAF2 played important function during bacterial infection, and negatively mediated the immune signaling transduction in Nile tilapia, while the mechanism need further study.

TRAF2, an Innate Immune Sensor, Reciprocally Regulates Mitophagy and Inflammation to Maintain Cardiac Myocyte Homeostasis

Mitochondria are essential for cardiac myocyte function, but damaged mitochondria trigger cardiac myocyte death. Although mitophagy, a lysosomal degradative pathway to remove damaged mitochondria, is robustly active in cardiac myocytes in the unstressed heart, its mechanisms and physiological role remain poorly defined. We discovered a critical role for TRAF2, an innate immunity effector protein with E3 ubiquitin ligase activity, in facilitating physiological cardiac myocyte mitophagy in the adult heart, to prevent inflammation and cell death, and maintain myocardial homeostasis.

Liquidambaric acid inhibits Wnt/β-catenin signaling and colon cancer via targeting TNF receptor-associated factor 2

Wnt/β-catenin signaling is a well-established driver of colon cancer; however, a targeted therapeutic agent has not reached clinics yet. In the present study, we report that the natural compound liquidambaric acid (LDA) inhibits oncogenic Wnt/β-catenin signaling in vitro and in vivo through its direct target tumor necrosis factor receptor-associated factor 2 (TRAF2). Mechanistically, TRAF2 positively regulates Wnt signaling by interacting with the N-terminal of β-catenin via its TRAF-C domain; this interaction is disrupted in presence of LDA. Particularly, a TRAF2/β-catenin/TCF4/TNIK complex is present in colon cancer cells, where TRAF2 is indispensable for the complex formation, and TRAF2/β-catenin and β-catenin/TCF4 interactions are disrupted upon LDA treatment. Our findings not only highlight that TRAF2 is an oncogenic regulator of Wnt/β-catenin signaling and colon cancer but also provide a lead compound targeting TRAF2 for cancer therapy.

Engagement of gcFKBP5/TRAF2 by spring viremia of carp virus to promote host cell apoptosis for supporting viral replication in grass carp

Spring viremia of carp virus (SVCV) causes severe morbidity and mortality in grass carp (Ctenopharyngodon idellus) in Europe, America and several Asian countries. We found that FKBP5 (FK506-binding protein 5) is an SVCV infection response factor; however, its role in the innate immune mechanism caused by SVCV infection remains unknown. This study cloned gcFKBP5 (grass carp FKBP5) and made its mimic protein structure for function discussion. We found that gcFKBP5 expression in the primary innate immune organs of grass carp, including intestine, liver and spleen, was highly upregulated by SVCV in 24 h, with a similar result in fish cells by poly(I:C) treatment. gcFKBP overexpression aggravates viral damage to cells and increases viral replication. Furthermore, SVCV engages gcFKBP5 interacting with TRAF2 (tumour necrosis factor receptor-associated factor 2) to promote host cell apoptosis for supporting viral replication. The enhanced viral replication seems not to be due to the repression of IFN and other antiviral factors as expected. For the first time, these data show the pivotal role of gcFKBP5 in the innate immune response of grass carp to SVCV infection.

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.

Fish TRAF2 promotes innate immune response to RGNNV infection

Tumour necrosis factor receptor-associated factors (TRAFs) are key regulatory proteins in the NF-κB signaling pathways. TRAF2 participates in the activation of both canonical and non-canonical NF-κB pathways, which are crucial for cell inflammation and cell survival. To elucidate its function in teleost fish, TRAF2 homologues of yellow grouper (Epinephelus awoara) and golden pompano (Trachinotus ovatus) have been cloned and characterized in this study. The open reading frame (ORF) of grouper TRAF2 (EaTRAF2) consists of 1563 nucleotides encoding a 521 amino acid protein with a predicted molecular mass of 58.70 kDa. The ORF of golden pompano TRAF2 (ToTRAF2) consists of 1563 nucleotides encoding a 521 amino acid protein with a predicted molecular mass of 58.66 kDa EaTRAF2 and ToTRAF2 share 99.23% and 99.42% identity with orange-spotted grouper (Epinephelus coioides) TRAF2 (EcTRAF2), respectively. Quantitative real-time PCR analysis indicated that the expression of EaTRAF2 was increased in grouper spleen (GS) cells after Red-spotted grouper nervous necrosis virus (RGNNV) infection; while the expression of ToTRAF2 was decreased in golden pompano brain (TOGB) cells after RGNNV infection. Both EaTRAF2 and ToTRAF2 were identified as a cytosolic protein and suggested to be associated with vesicles scattering in the cytoplasm. Both EaTRAF2 and ToTRAF2 enhanced RGNNV replication during viral infection in vitro. Further studies showed that EaTRAF2 and ToTRAF2 overexpression decreased the expression levels of interferon associated cytokines and pro-inflammatory factors. Taken together, these results are important for better understanding of the function of TRAF2 in fish and reveal its involvement in host response to immune challenges in RGNNV.