Tumor necrosis factor alpha (TNFalpha) triggers necroptotic cell death through an intracellular signaling complex containing receptor-interacting protein kinase (RIPK) 1 and RIPK3, called the necrosome. RIPK1 phosphorylates RIPK3, which phosphorylates the pseudokinase mixed lineage kinase-domain-lik
e (MLKL)-driving its oligomerization and membrane-disrupting necroptotic activity. Here, we show that TNF receptor-associated factor 2 (TRAF2)-previously implicated in apoptosis suppression-also inhibits necroptotic signaling by TNFalpha. TRAF2 disruption in mouse fibroblasts augmented TNFalpha-driven necrosome formation and RIPK3-MLKL association, promoting necroptosis. TRAF2 constitutively associated with MLKL, whereas TNFalpha reversed this via cylindromatosis-dependent TRAF2 deubiquitination. Ectopic interaction of TRAF2 and MLKL required the C-terminal portion but not the N-terminal, RING, or CIM region of TRAF2. Induced TRAF2 knockout (KO) in adult mice caused rapid lethality, in conjunction with increased hepatic necrosome assembly. By contrast, TRAF2 KO on a RIPK3 KO background caused delayed mortality, in concert with elevated intestinal caspase-8 protein and activity. Combined injection of TNFR1-Fc, Fas-Fc and DR5-Fc decoys prevented death upon TRAF2 KO. However, Fas-Fc and DR5-Fc were ineffective, whereas TNFR1-Fc and interferon alpha receptor (IFNAR1)-Fc were partially protective against lethality upon combined TRAF2 and RIPK3 KO. These results identify TRAF2 as an important biological suppressor of necroptosis in vitro and in vivo.
OBJECTIVES: Tumor necrosis factor a (TNF-a) is implicated in the pathophysiology of renal obstruction through its interactions with two TNF-a receptors: TNFR1 and TNFR2. Activation of TNFR1 leads to the recruitment of the adaptor TNFR-associated death domain protein (TRADD), which binds t
he Ser/Thr kinase receptor-interacting protein (RIP) and TNFR-associated factors 2 (TRAF2). This TRADD-RIP-TRAF complex causes activation of the antiapoptotic pathway and inhibits caspase 8 activation. Meanwhile, activation of TNFR2 leads to depletion of TRAF2 and enhancement of the apoptotic pathway. Curcumin, the major component found in turmeric spice, has been reported to possess a protective role against renal injury elicited by unilateral ureteral obstruction (UUO). The present study aimed mainly to address the cytoprotective role of curcumin-rich diet (5% w/w) on the apoptotic pathway induced by UUO in rats after 30 d of ligation. METHODS: The levels of mRNA for TNFR1, TNFR2, RIP, TRAF2, and caspase 8 were measured by reverse transcription-polymerase chain reaction. The levels of TNF-a was determined by ELISA. Kidney sections were exposed to histologic and morphometric studies. RESULTS: Administration of curcumin decreased TNF-a, TNFR2, and caspase 8 without affecting TNFR1 levels. The gene expression levels of the antiapoptotic molecules RIP and TRAF2 were increased. CONCLUSIONS: The cytoprotective role of curcumin relies on its ability to decrease the TNFR2 mRNA and enhance the antiapoptotic molecules RIP and TRAF2 to decrease the apoptotic pathway via decreasing the caspase 8.
Takahashi H, etal., BMC Cancer. 2015 Oct 24;15:794. doi: 10.1186/s12885-015-1783-y.
BACKGROUND: The potential of expression profiling using microarray analysis as a tool to predict the prognosis for different types of cancer has been realized. This study aimed to identify a novel biomarker for colorectal cancer (CRC). METHODS: The expression profiles of cancer cells in 152 patient
s with stage I-III CRC were examined using microarray analysis. High expression in CRC cells, especially in patients with distant recurrences, was a prerequisite to select candidate genes. Thus, we identified seventeen candidate genes, and selected Traf2- and Nck-interacting kinase (TNIK), which was known to be associated with progression in CRC through Wnt signaling pathways. We analyzed the protein expression of TNIK using immunohistochemistry (IHC) and investigated the relationship between protein expression and patient characteristics in 220 stage I-III CRC patients. RESULTS: Relapse-free survival was significantly worse in the TNIK high expression group than in the TNIK low expression group in stage II (p = 0.028) and stage III (p = 0.006) patients. In multivariate analysis, high TNIK expression was identified as a significant independent risk factor of distant recurrence in stage III patients. CONCLUSION: This study is the first to demonstrate the prognostic significance of intratumoral TNIK protein expression in clinical tissue samples of CRC, in that high expression of TNIK protein in primary tumors was associated with distant recurrence in stage II and III CRC patients. This TNIK IHC study might contribute to practical decision-making in the treatment of these patients.
Zhang J, etal., Int J Clin Exp Pathol. 2015 Nov 1;8(11):14228-34. eCollection 2015.
The purpose was to investigate whether the expression level of TRAF2 gene was regulated by DNA methylation and explore the role of TRAF2 methylation in the diagnosis and prognosis of gastric cancer (GC). Firstly, we detected
the expression of TRAF2 both at mRNA level and protein level. And the up-regulated of TRAF2 expression at two different levels were both found (P<0.001). Then we measured the methylated status of TRAF2 by MSP and got a result of that TRAF2 was hypomethylated in GC patients compared with healthy controls (P<0.001). Meanwhile, the relationship between TRAF2 methylation and clinicopathologic characteristics was estimated through chi-square. The outcome proved that TRAF2 methylation was impacted by age (P=0.024), lymph node metastasis (P=0.046), TNM stage (P=0.021), distant metastasis (P=0.002) and depth of invasion (P=0.002). The AUC of 0.795 accompanying a sensitivity of 66.7% and a specificity of 94.7% were obtained from Receiver Operating Characteristic (ROC) curve which indicated the diagnostic value of TRAF2 methylation was high. At last, we researched the prognostic value of TRAF2 methylation. Kaplan-Meier showed that patients with TRAF2 hypomethylation had lived much shorter than those with TRAF2 hypermethylation (log rank test, P<0.001). Cox regression analysis revealed TRAF2 hypomethylation (HR=18.827, 95% CI=3.103-114.222, P=0.001), lymph node metastasis (HR=0.154, 95% CI=0.047-0.512, P=0.002), distant metastasis (HR=3.032, 95% CI=1.116-8.237, P=0.030), as well as differentiation (HR=0.287, 95% CI=0.113-0.731, P=0.009) were all vital prognostic factors in GC. Taken together, TRAF2 expression was increased in GC patients by DNA hypomethylation and this methylation could be an independent diagnostic and prognostic indicator in GC.
Yuan F, etal., Biomed Res Int. 2019 Nov 20;2019:9276831. doi: 10.1155/2019/9276831. eCollection 2019.
Background: Liver transplantation (LT) is currently an effective treatment for end-stage liver disease, but the occurrence of acute rejection (AR) is still the main problem to be solved. The present study aimed to evaluate the effect of gastrodin (GAS) on LT. Methods: Rat transp
lant models were established and divided into SHAM, LT, GAS-L (50 mg/kg GAS), and GAS-H (100 mg/kg GAS) groups. The liver function, inflammatory factors, liver histopathology, survival of rats, number of M2-type macrophages, liver cell apoptosis, and pathway proteins were assayed at 7 days and 14 days after the operations. Results: With increasing GAS concentrations, liver function, expression of proinflammatory factors in the liver, and expression of M2-type molecules in macrophages were significantly improved, and the survival time of rats was significantly prolonged (P < 0.05). All rats treated with low or high doses of GAS were judged to have nondeterministic acute rejection. Flow cytometry showed that liver cell apoptosis was decreased significantly in the GAS-L and GAS-H groups after GAS administration compared with apoptosis and differentiation in the LT group (P < 0.05). Expression levels of Caspase-3, Bad, and Bax proteins were decreased, and the expression of the antiapoptotic protein Bcl-2 was increased in the GAS-L and GAS-H groups (P < 0.05). Mechanistically, the ERS-related IRE1α/TRAF2/NF-κB pathway was suppressed by GAS, and GAS acted mainly on intrahepatic macrophages to affect AR and reduce ROS production (P < 0.05). Conclusion: GAS ameliorated AR by inhibiting the IRE1α/TRAF2/NF-κB pathway in LT.
Roh KH and Choi EJ, Free Radic Biol Med. 2016 Feb;91:105-13. doi: 10.1016/j.freeradbiomed.2015.12.010. Epub 2015 Dec 15.
Reactive oxygen species (ROS) have many physiological and pathological effects on diverse cellular events. In particular, excessive ROS causes oxidative stress that leads to cell death. The mammalian STE20-like kinase-1 (MST1), a multifunctional serine-threonine kinase, plays a pivotal role in oxida
tive stress-induced cellular signaling events. Tumor necrosis factor receptor (TNFR)-associated factor 2 (TRAF2) is also known to be essential for oxidative stress-induced cell death. Here, we showed that H2O2 induced the physical interaction between TRAF2 and MST1, and that this interaction promoted the homodimerization as well as the activation of MST1. Furthermore, TRAF2 was required for MST1 to mediate the H2O2-induced stimulation of c-Jun N-terminal kinase and p38 kinase as well as apoptosis. Taken together, our results suggest that TRAF2 functions as a key activator of MST1 in oxidative stress-induced intracellular signaling processes.
Choudhury S, etal., Cell Death Dis. 2013 Mar 7;4:e528. doi: 10.1038/cddis.2013.34.
The UPR is activated in the mouse retina expressing misfolded T17M rhodopsin (RHO) during autosomal dominant retinitis pigmentosa (ADRP) progression. Therefore, the goal of this study is to validate the UPR-induced caspase-7 as a new therapeutic target that modulates the UPR, reduces the level of ap
optosis and protects the ADRP retina from retinal degeneration and light-induced damage. Mice were analyzed using ERG, SD-OCT and histology to determine the role of caspase-7 ablation. The results of these experiments demonstrate the significant preservation of photoreceptors and their function in T17M RHO CASP-7 retinas from P30 to P90 compared with control mice. These mice were also protected from the light-induced decline in the ERG responses and apoptosis. The RNA and protein analyses of T17M RHO+Csp7-siRNA, Tn+Csp7-siRNA 661W cells and T17M RHO CASP-7 retinas revealed that caspase-7 ablation reprograms the UPR and reduces JNK-induced apoptosis. This reduction is believed to occur through the downregulation of the mTOR and Hif1a proteins. In addition, decline in activated PARP1 was detected in T17M RHO CASP-7 retina. Altogether, our findings indicate that the targeting of caspase-7 in T17M RHO mice could be a feasible therapeutic strategy for advanced stages of ADRP.
3K MEK kinase 1 (MEKK1) interact in vivo and in vitro with the STE20 protein homologue germinal center kinase (GCK), and both GCK and MEKK1 associate in vivo with the adapter protein tumor necrosis factor (TNF) receptor-associated factor 2 (TRAF2). These interactions may couple TNF receptors to the SAPK/JNK family of MAPKs; however, a molecular mechanism by which these proteins might collaborate to recruit the SAPKs/JNKs has remained elusive. Here we show that endogenous GCK and MEKK1 associate in vivo. In addition, we have developed an in vitro assay system with which we demonstrate that purified, active GCK and TRAF2 activate MEKK1. The RING domain of TRAF2 is necessary for optimal in vitro activation of MEKK1, but the kinase domain of GCK is not. Autophosphorylation within the MEKK1 kinase domain activation loop is required for activation. Forced oligomerization also activates MEKK1, and GCK elicits enhanced oligomerization of coexpressed MEKK1 in vivo. These results represent the first activation of MEKK1 in vitro using purified proteins and suggest a mechanism for MEKK1 activation involving induced oligomerization and consequent autophosphorylation mediated by upstream proteins.
BACKGROUND: TRAF2 and TRAF4, members of the tumor necrosis factor receptor- associated factor family of intracellular signal transduction proteins, are associated with breast cancer progression and metastasis. METHODS: We collected malignant serous effusion cell
s from the patients with breast cancer (n = 46). Cell blocks prepared from plural effusions (n = 46) and primary breast cancer (n = 50), lymph node metastases (n = 50), and normal breast tissue specimens (n = 30). The immunohistochemistry was performed for the detection of TRAF2 and TRAF4 expression with the correlation of their expression with clinicopathological parameters and survival rate analyzed. RESULTS: Compared with normal breast tissues, TRAF2 expression was upregulated, and nuclear TRAF4 expression was downregulated in malignant pleural effusion cells, primary tumors, and lymph node metastases (P < 0.05). Multivariate analysis revealed TRAF2 expression in pleural effusions was associated with the molecular/pathological type, venous invasion, and lymph node metastasis, while nuclear TRAF4 expression was associated with age, tumor size, venous invasion, and lymph node metastasis, clinical staging, molecular/pathological subtype and p53 status (P < 0.05). There was a significant positive correlation between TRAF2 and TRAF4 expression levels in malignant pleural effusion cells (r = 0.937; P < 0.01). Kaplan-Meire analysis demonstrated a close correlation of TRAF2 and TRAF4 expression in malignant pleural effusion cells with cumulative overall survival (P < 0.05). CONCLUSION: TRAF2 and nuclear TRAF4 expression in malignant pleural effusion cells may represent potential prognostic factors and biomarkers of invasion and metastasis in breast cancer.
Lin TB, etal., J Neurosci. 2015 Dec 16;35(50):16545-60. doi: 10.1523/JNEUROSCI.2301-15.2015.
Emerging evidence has indicated that the pathogenesis of neuropathic pain is mediated by spinal neural plasticity in the dorsal horn, which provides insight for analgesic therapy. Here, we report that the abundance of tumor necrosis factor receptor-associated factor 2 and NcK-interacting kinase (TNI
K), a kinase that is presumed to regulate neural plasticity, was specifically enhanced in ipsilateral dorsal horn neurons after spinal nerve ligation (SNL; left L5 and L6). Spinal TNIK-associated allodynia is mediated by downstream TNIK-GluR1 coupling and the subsequent phosphorylation-dependent trafficking of GluR1 toward the plasma membrane in dorsal horn neurons. Tumor necrosis factor receptor-associated factor 2 (TRAF2), which is regulated by spinal F-box protein 3 (Fbxo3)-dependent F-box and leucine-rich repeat protein 2 (Fbxl2) ubiquitination, contributes to SNL-induced allodynia by modifying TNIK/GluR1 phosphorylation-associated GluR1 trafficking. Although exhibiting no effect on Fbxo3/Fbxl2/TRAF2 signaling, focal knockdown of spinal TNIK expression prevented SNL-induced allodynia by attenuating TNIK/GluR1 phosphorylation-dependent subcellular GluR1 redistribution. In contrast, intrathecal administration of BC-1215 (N1,N2-Bis[[4-(2-pyridinyl)phenyl]methyl]-1,2-ethanediamine) (a novel Fbxo3 inhibitor) prevented SNL-induced Fbxl2 ubiquitination and subsequent TFAF2 de-ubiquitination to ameliorate behavioral allodynia via antagonizing TRAF2/TNIK/GluR1 signaling. By targeting spinal Fbxo3-dependent Fbxl2 ubiquitination and the subsequent TRAF2/TNIK/GluR1 cascade, spinal application of a TNF-alpha-neutralizing antibody ameliorated SNL-induced allodynia, and, conversely, intrathecal TNF-alpha injection into naive rats induced allodynia via a spinal Fbxo3/Fbxl2-dependent modification of the TRAF2/TNIK/GluR1 cascade. Together, our results suggest that spinal TNF-alpha contributes to the development of neuropathic pain by upregulating TRAF2/TNIK/GluR1 signaling via Fbxo3-dependent Fbxl2 ubiquitination and degradation. Thus, we propose a potential medical treatment strategy for neuropathic pain by targeting the F-box protein or TNIK. SIGNIFICANCE STATEMENT: TNF-alpha participates in neuropathic pain development by facilitating the spinal TRAF2-dependent TNIK-GluR1 association, which drives GluR1-containing AMPA receptor trafficking toward the plasma membrane. In addition, F-box protein 3 modifies this pathway by inhibiting F-box and leucine-rich repeat protein 2-mediated TRAF2 ubiquitination, suggesting that protein ubiquitination contributes crucially to the development of neuropathic pain. These results provide a novel therapeutic strategy for pain relief.
Post-operative pulmonary complications are the most common morbidity associated with lung resection in non-small cell lung cancer (NSCLC) patients. The TNF/TRAF2/ASK1/p38 kinase pathway is activated by stress stimuli and inflammatory signals. We hypothesized tha
t genetic polymorphisms within this pathway may contribute to risk of complications. In this case-only study, we genotyped 173 germline genetic variants in a discovery population of 264 NSCLC patients who underwent a lobectomy followed by genotyping of the top variants in a replication population of 264 patients. Complications data was obtained from a prospective database at MD Anderson. MAP2K4:rs12452497 was significantly associated with a decreased risk in both phases, resulting in a 40% reduction in the pooled population (95% CI:0.43-0.83, P = 0.0018). In total, seven variants were significant for risk in the pooled analysis. Gene-based analysis supported the involvement of TRAF2, MAP2K4, and MAP3K5 as mediating complications risk and a highly significant trend was identified between the number of risk genotypes and complications risk (P = 1.63 x 10(-8)). An inverse relationship was observed between association with clinical outcomes and complications for two variants. These results implicate the TNF/TRAF2/ASK1/p38 kinase pathway in modulating risk of pulmonary complications following lobectomy and may be useful biomarkers to identify patients at high risk.
Armstrong MJ, etal., Cancer Biol Ther. 2015;16(7):1029-41. doi: 10.1080/15384047.2015.1046646.
Interferon Regulatory Factor (IRF)-1, originally identified as a transcription factor of the human interferon (IFN)-beta gene, mediates tumor suppression and may inhibit oncogenesis. We have shown that IRF-1 in human breast cancer cells results in the down-regulation of survivin, tumor cell death, a
nd the inhibition of tumor growth in vivo in xenogeneic mouse models. In this current report, we initiate studies comparing the effect of IRF-1 in human nonmalignant breast cell and breast cancer cell lines. While IRF-1 in breast cancer cells results in growth inhibition and cell death, profound growth inhibition and cell death are not observed in nonmalignant human breast cells. We show that TNF-alpha or IFN-gamma induces IRF-1 in breast cancer cells and results in enhanced cell death. Abrogation of IRF-1 diminishes TNF-alpha and IFN-gamma-induced apoptosis. We test the hypothesis that IRF-1 augments TNF-alpha-induced apoptosis in breast cancer cells. Potential signaling networks elicited by IRF-1 are investigated by evaluating the NF-kappaB pathway. TNF-alpha and/or IFN-gamma results in decreased presence of NF-kappaB p65 in the nucleus of breast cancer cells. While TNF-alpha and/or IFN-gamma can induce IRF-1 in nonmalignant breast cells, a marked change in NF-kappaB p65 is not observed. Moreover, the ectopic expression of IRF-1 in breast cancer cells results in caspase-3, -7, -8 cleavage, inhibits NF-kappaB activity, and suppresses the expression of molecules involved in the NF-kappaB pathway. These data show that IRF-1 in human breast cancer cells elicits multiple signaling networks including intrinsic and extrinsic cell death and down-regulates molecules involved in the NF-kappaB pathway.
Jin J, etal., Pathol Res Pract. 2014 Oct;210(10):621-7. doi: 10.1016/j.prp.2013.10.007. Epub 2014 Feb 24.
BACKGROUND AND AIMS: TRAF2- and NCK-interacting kinase (TNIK) is a member of the germinal center kinase family and a transcription factor 4 (TCF4) interactor is recruited to promoters of Wnt target genes via phosphorylation of the TCF/β-catenin comple
x. The aim of this study was to evaluate the TNIK, the active form of TNIK (p-TNIK), and β-catenin expression in hepatocellular carcinoma (HCC), and to identify the prognostic significance of p-TNIK. METHODS: We assessed the expression status of TNIK, p-TNIK, and β-catenin by using immunohistochemical analysis of 302 HCCs in 8 tissue microarray blocks, and we evaluated their clinicopathologic features and survival rates based on their p-TNIK expression. RESULTS: Of 302 HCCs, 92.7% stained positive for TNIK in the cytoplasm. Nuclear expression of p-TNIK was identified in 7.9% HCCs. Aberrant cytoplasmic expression of β-catenin was identified in 77.2% and nuclear expression in 3.3%. p-TNIK nuclear staining was positively correlated to β-catenin nuclear expression (P=0.036). Cytoplasmic and nuclear expression of p-TNIK was more frequently observed in high Edmondson-Steiner (ES) nuclear grade groups (P=0.030). Nuclear p-TNIK expression was also associated with pathological M1 stage (pM1 stage) patients (P<0.0001). Aberrant cytoplasmic expression of β-catenin was more frequently identified in larger tumors (P=0.014). Univariate (DFS, P=0.049; OS, 0.037) and multivariate analysis (DFS, P=0.006; OS, P=0.003) confirmed the independent prognostic significance of nuclear p-TNIK expression. CONCLUSION: This is the first time that nuclear p-TNIK expression was studied in HCC, and p-TNIK nuclear expression was associated with poor prognosis and is a candidate prognostic marker for HCC.
Portillo JA, etal., Invest Ophthalmol Vis Sci. 2014 Dec 4;55(12):8590-7. doi: 10.1167/iovs.14-15340.
PURPOSE: The cell surface receptor CD40 is required for the development of retinopathies induced by diabetes and ischemia/reperfusion. The purpose of this study was to identify signaling pathways by which CD40 triggers proinflammatory responses in retinal cells, since this may lead to pharmacologic
targeting of these pathways as novel therapy against retinopathies. METHODS: Retinal endothelial and Muller cells were transduced with vectors that encode wild-type CD40 or CD40 with mutations in sites that recruit TNF receptor associated factors (TRAF): TRAF2,3 (DeltaT2,3), TRAF6 (DeltaT6), or TRAF2,3 plus TRAF6 (DeltaT2,3,6). Cells also were incubated with CD40-TRAF2,3 or CD40-TRAF6 blocking peptides. We assessed intercellular adhesion molecule-1 (ICAM-1), CD40, monocyte chemoattractant protein-1 (MCP-1), VEGF, and prostaglandin E(2) (PGE(2)) by fluorescence-activated cell sorting (FACS), ELISA, or mass spectrometry. Mice (B6 and CD40(-/-)) were made diabetic using streptozotocin. The MCP-1 mRNA was assessed by real-time PCR. RESULTS: The CD40-mediated ICAM-1 upregulation in endothelial and Muller cells was markedly inhibited by expression of CD40 DeltaT2,3 or CD40 DeltaT6. The CD40 was required for MCP-1 mRNA upregulation in the retina of diabetic mice. The CD40 stimulation of endothelial and Muller cells enhanced MCP-1 production that was markedly diminished by CD40 DeltaT2,3 or CD40 DeltaT6. Similar results were obtained in cells incubated with CD40-TRAF2,3 or CD40-TRAF6 blocking peptides. The CD40 ligation upregulated PGE(2) and VEGF production by Muller cells, that was inhibited by CD40 DeltaT2,3 or CD40 DeltaT6. All cellular responses tested were obliterated by expression of CD40 DeltaT2,3,6. CONCLUSIONS: Blockade of a single CD40-TRAF pathway was sufficient to impair ICAM-1, MCP-1, PGE(2), and VEGF upregulation in retinal endothelial and/or Muller cells. Blockade of CD40-TRAF signaling may control retinopathies.
Jin J, etal., Nat Commun. 2015 Jan 7;6:5930. doi: 10.1038/ncomms6930.
Signal transduction from toll-like receptors (TLRs) is important for innate immunity against infections, but deregulated TLR signalling contributes to inflammatory disorders. Here we show that myeloid cell-specific ablation of TRAF2 greatly promotes TLR-stimulat
ed proinflammatory cytokine expression in macrophages and exacerbates colitis in an animal model of inflammatory bowel disease. TRAF2 deficiency does not enhance upstream signalling events, but it causes accumulation of two transcription factors, c-Rel and IRF5, known to mediate proinflammatory cytokine induction. Interestingly, TRAF2 controls the fate of c-Rel and IRF5 via a proteasome-dependent mechanism that also requires TRAF3 and the E3 ubiquitin ligase cIAP. We further show that TRAF2 also regulates inflammatory cytokine production in tumour-associated macrophages and facilitates tumour growth. These findings demonstrate an unexpected anti-inflammatory function of TRAF2 and suggest a proteasome-dependent mechanism that limits the proinflammatory TLR signalling.
Gao L, etal., Mol Med. 2015 Feb 18;21:154-66. doi: 10.2119/molmed.2014.00235.
Double-stranded RNA-dependent protein kinase (PKR), an intracellular pathogen recognition receptor, is involved both in insulin resistance in peripheral tissues and in downregulation of pancreatic beta-cell function in a kinase-dependent manner, indicating PKR as a core component in the progression
of type 2 diabetes. PKR also acts as an adaptor protein via its protein-binding domain. Here, the PKR protein-binding function promoted beta-cell proliferation without its kinase activity, which is associated with enhanced physical interaction with tumor necrosis factor receptor-associated factor 2 (TRAF2) and TRAF6. In addition, the transcription of the nuclear factor kappa-light-chain-enhancer of activated B cell (NF-kappaB)-dependent survival gene c-Myc was upregulated significantly and is necessary for proliferation. Upregulation of the PKR protein-binding function induced the NF-kappaB pathway, as observed by dose-dependent degradation of IkappaBalpha, induced nuclear translocation of p65 and elevated NF-kappaB-dependent reporter gene expression. NF-kappaB-dependent reporter activity and beta-cell proliferation both were suppressed by TRAF2-siRNA, but not by TRAF6-siRNA. TRAF2-siRNA blocked the ubiquitination of receptor-interacting serine/threonine-protein kinase 1 (RIP1) induced by PKR protein binding. Furthermore, RIP1-siRNA inhibited beta-cell proliferation. Proinflammatory cytokines (TNFalpha) and glucolipitoxicity also promoted the physical interaction of PKR with TRAF2. Collectively, these data indicate a pivotal role for PKR's protein-binding function on the proliferation of pancreatic beta cells through TRAF2/RIP1/NF-kappaB/c-Myc pathways. Therapeutic opportunities for type 2 diabetes may arise when its kinase catalytic function, but not its protein-binding function, is downregulated.
To elucidate the function of Bcl10, recently cloned as an apoptosis-associated gene mutated in MALT lymphoma, we identified its binding partner TRAF2, which mediates signaling via tumor necrosis factor receptors. In mammalian cells, low levels of Bcl10 expressio
n promoted the binding of TRAF2 and c-IAPs. Conversely, excessive expression inhibited complex formation. Overexpressed Bcl10 reduced c-Jun N-terminal kinase activation and induced nuclear factor kappaB activation downstream of TRAF2. To determine whether overexpression of Bcl10 could perturb the regulation of apoptosis in vivo, we generated Bcl10 transgenic mice. In these transgenic mice, atrophy of the thymus and spleen was observed at postnatal stages. The morphological changes in these tissues were caused by acceleration of apoptosis in T cells and B cells. The phenotype of Bcl10 transgenic mice was similar to that of TRAF2-deficient mice reported previously, indicating that excessive expression of Bcl10 might deplete the TRAF2 function. In contrast, in the other organs such as the brain, where Bcl10 was expressed at high levels, no apoptosis was detected. The altered sensitivities to overexpressed Bcl10 may have been due to differences in signal responses to Bcl10 among cell types. Thus, Bcl10 was suggested to play crucial roles in the modulation of apoptosis associated with TRAF2.
Su D, etal., J Neuroimmunol. 2017 Apr 15;305:35-41. doi: 10.1016/j.jneuroim.2017.01.015. Epub 2017 Jan 26.
Sphingosine kinase 1 (Sphk1), a key enzyme responsible for phosphorylating sphingosine into sphingosine1-phosphate (S1P), plays an important role in mediating post-stroke neuroinflammation. However, the pathway and mechanism of the Sphk1-mediated inflammatory response remains unknown. In this study,
we found that suppression of Sphk1 decreased IL17 production and relieved neuronal damage induced by microglia in cerebral ischemia reperfusion (IR) or in an in vitro oxygen-glucose deprivation reperfusion (OGDR) system. Inhibition of Sphk1 with an inhibitor or siRNA decreased tumor necrosis factor receptor-associated factor 2 (TRAF2) and nuclear factor-kappa B (NF-κB) sequentially in microglia in response to IR or OGDR. Moreover, we also found that after suppression of TRAF2 or NF-κB by siRNA in microglia, reductions in the downstream molecules NF-κB and IL-17 and in neuronal apoptosis were observed in response to OGDR. Taken together, we hypothesize that Sphk1, TRAF2 and NF-κB form an axis that leads to increased IL-17 and neuronal apoptosis. This axis may be a potential therapeutic target to control neuroinflammation in brain IR.
Oh YT, etal., Oncotarget. 2015 Dec 1;6(38):41324-38. doi: 10.18632/oncotarget.5847.
The role of death receptor 5 (DR5), a well-known cell surface pro-apoptotic protein, in the negative regulation of invasion and metastasis of human cancer cells and the underlying mechanisms are largely unknown and were hence the focus of this study. In this report, we have demonstrated that DR5 fu
nctions to suppress invasion and metastasis of human cancer cells, as evidenced by enhanced cancer cell invasion and metastasis upon genetic suppression of DR5 either by gene knockdown or knockout. When DR5 is suppressed, FADD and caspase-8 may recruit and stabilize TRAF2 to form a metastasis and invasion signaling complex, resulting in activation of ERK and JNK/AP-1 signaling that mediate the elevation and activation of matrix metalloproteinase-1 (MMP1) and eventual promotion of cancer invasion and metastasis. Our findings thus highlight a novel non-apoptotic function of DR5 as a suppressor of human cancer cell invasion and metastasis and suggest a basic working model elucidating the underlying biology.
Prause M, etal., Mol Cell Endocrinol. 2016 Jan 15;420:24-36. doi: 10.1016/j.mce.2015.11.021. Epub 2015 Nov 22.
Interleukin-1beta (IL-1beta) and interferon-gamma (IFNgamma) contribute to type 1 diabetes (T1D) by inducing beta-cell death. Tumor necrosis factor (TNF) receptor-associated factor (TRAF) proteins are adaptors that transduce signaling from a variety of membrane receptors including cytokine receptor
s. We show here that IL-1beta and IFNgamma upregulate the expression of TRAF2 in insulin-producing INS-1E cells and isolated rat pancreatic islets. siRNA-mediated knockdown (KD) of TRAF2 in INS-1E cells reduced IL-1beta-induced phosphorylation of JNK1/2, but not of p38 or ERK1/2 mitogen-activated protein kinases. TRAF2 KD did not modulate NFkappaB activation by cytokines, but reduced cytokine-induced inducible nitric oxide synthase (iNOS) promotor activity and expression. We further observed that IFNgamma-stimulated phosphorylation of STAT3 required TRAF2. KD of TRAF2 or STAT3 reduced cytokine-induced caspase 3/7 activation, but, intriguingly, potentiated cytokine-mediated loss of plasma membrane integrity and augmented the number of propidium iodide-positive cells. Finally, we found that TRAF2 KD increased cytokine-induced production of reactive oxygen species (ROS). In summary, our data suggest that TRAF2 is an important mediator of IL-1beta and IFNgamma signaling in pancreatic beta-cells.
Villanueva JE, etal., Eur J Immunol. 2015 Jun;45(6):1820-31. doi: 10.1002/eji.201445416. Epub 2015 May 26.
In this study, a critical and novel role for TNF receptor (TNFR) associated factor 2 (TRAF2) is elucidated for peripheral CD8(+) T-cell and NKT-cell homeostasis. Mice deficient in TRAF2 only in their T cells (TRAF2
nt-weight:700;'>TRAF2TKO) show approximately 40% reduction in effector memory and approximately 50% reduction in naive CD8(+) T-cell subsets. IL-15-dependent populations were reduced further, as TRAF2TKO mice displayed a marked approximately 70% reduction in central memory CD8(+) CD44(hi) CD122(+) T cells and approximately 80% decrease in NKT cells. TRAF2TKO CD8(+) CD44(hi) T cells exhibited impaired dose-dependent proliferation to exogenous IL-15. In contrast, TRAF2TKO CD8(+) T cells proliferated normally to anti-CD3 and TRAF2TKO CD8(+) CD44(hi) T cells exhibited normal proliferation to exogenous IL-2. TRAF2TKO CD8(+) T cells expressed normal levels of IL-15-associated receptors and possessed functional IL-15-mediated STAT5 phosphorylation, however TRAF2 deletion caused increased AKT activation. Loss of CD8(+) CD44(hi) CD122(+) and NKT cells was mechanistically linked to an inability to respond to IL-15. The reduced CD8(+) CD44(hi) CD122(+) T-cell and NKT-cell populations in TRAF2TKO mice were rescued in the presence of high dose IL-15 by IL-15/IL-15Ralpha complex administration. These studies demonstrate a critical role for TRAF2 in the maintenance of peripheral CD8(+) CD44(hi) CD122(+) T-cell and NKT-cell homeostasis by modulating sensitivity to T-cell intrinsic growth factors such as IL-15.
Yang CY, etal., Cell Signal. 2016 Jan;28(1):145-51. doi: 10.1016/j.cellsig.2015.10.017. Epub 2015 Oct 28.
Dual-specificity phosphatase 14 (DUSP14, also known as MKP6) is a MAP kinase phosphatase that dephosphorylates JNK, ERK, and p38 in vitro. We recently reported that DUSP14 negatively regulates T-cell activation and immune responses by interfering activation of TAB1-TAK1 complex. However, the molecu
lar mechanism that regulates the phosphatase activity of DUSP14 remains unclear. Here, we report the post-translational modification of DUSP14 by ubiquitination. Mass spectrometry and mutational analyses identified that DUSP14 was Lys63-linked ubiquitinated at lysine 103 residue. Furthermore, DUSP14 inducibly interacted with the E3 ligase TRAF2 during T-cell receptor (TCR) signaling; TRAF2 shRNA knockdown reduced the DUSP14 ubiquitination. We also show that ubiquitination of DUSP14 was required for its phosphatase activity during TCR signaling. Together, these findings reveal a novel mechanism by which TRAF2 mediates Lys63-linked ubiquitination of DUSP14, leading to DUSP14 activation in T cells.
