Processes of apoptosis and cell proliferation in uterine myomas originating from reproductive and perimenopausal women

We studied uterine myomas originating from females of reproductive age and from females of perimenopausal age. Uterine myomas represent benign tumors of the myometrium, and they develop frequently in women of reproductive age. The frequency of uterine myomas increases with age until women reach the menopause. The study included patients with a myomatous uterus, in the reproductive age or peri-menopausal age, independently evaluating small and large myomas. Myometrial alterations in their direct vicinity were evaluated independently of the myomas. The study included evaluation of immunolocalization of two index proteins which participate in myoma cells growth control: Ki-67 nuclear antigen and caspase 3. In women of reproductive age, both in small and large myomas, elevated immunostaining of Ki-67 was noted in parallel to low levels of caspase 3 staining, which indicated the ongoing process of proliferation. In women of peri-menopausal age with small or large myomas, no Ki-67 immunostaining was detected, while staining of caspase 3 manifested low levels. Proliferation in reproductive age women myomas is higher than in the peri-menopausal age.     

Proteomic identification of the TRAF6 regulation of vacuolar ATPase for osteoclast function

Osteoclasts are cells specialized for bone resorption. For osteoclast activation, tumor necrosis factor receptor-associated factor 6 (TRAF6) plays a pivotal role. To find new molecules that bind TRAF6 and have a function in osteoclast activation, we employed a proteomic approach. TRAF6-binding proteins were purified from osteoclast cell lysates by affinity chromatography and their identity was disclosed by MS. The identified proteins included several heat shock proteins, actin and actin-binding proteins, and vacuolar ATPase (V-ATPase). V-ATPase, documented for a great increase in expression during osteoclast differentiation, is an important enzyme for osteoclast function; it transports proton to resorption lacunae for hydroxyapatite dissolution. The binding of V-ATPase with TRAF6 was confirmed both in vitro by GST pull-down assays and in osteoclasts by co-immunoprecipitation and confocal microscopy experiments. In addition, the V-ATPase activity associated with TRAF6 increased in osteoclasts stimulated with receptor activator of nuclear factor kappaB ligand (RANKL). Furthermore, a dominant-negative form of TRAF6 abrogated the RANKL stimulation of V-ATPase activity. Our study identified V-ATPase as a TRAF6-binding protein using a proteomics strategy and proved a direct link between these two important molecules for osteoclast function.     

Cutting edge: requirement for TRAF6 in the induction of T cell anergy

TRAF6, TNFR-associated factor 6, is a key adaptor downstream from the TNF receptor and TLR superfamily members. T cell-specific deletion of TRAF6 (TRAF6-DeltaT) was recently shown to result in the development of multiorgan inflammatory disease and the resistance of responder T cells to suppression by CD4+CD25+ regulatory T cells. In this study we examined the role of TRAF6 in an additional mechanism of peripheral tolerance, anergy. We have determined that the loss of TRAF6 restores the ability of CD28-/- T cells to proliferate and produce IL-2. Consistent with this, TRAF6-DeltaT T cells were resistant to anergizing signals both in vitro and in vivo. Resistance to anergy was correlated with decreased expression of Cbl-b. These findings reveal that in addition to its role in rendering T cells susceptible to control by CD4+CD25+ regulatory T cells, TRAF6 is essential for the induction of T cell anergy, implicating TRAF6 as a critical mediator of peripheral tolerance.     

NUMBL interacts with TRAF6 and promotes the degradation of TRAF6

Tumor necrosis factor-associated factor 6 (TRAF6) is an essential adaptor protein for IL-1R or TLR-mediated NF-κB signaling pathway activation. In previous work we have found NUMBL interacts with TAB2 and negatively regulates NF-κB signaling pathway. Here, we report that NUMBL directly binds to TRAF6 in vivo and in vitro. NUMBL down-regulates TRAF6 protein level and shortens its half-life. Furthermore, knockdown of NUMBL significantly increases endogenous TRAF6 protein level in the cultured cortical neurons. In vivo ubiquitination assays indicate that NUMBL promotes the assembly of K48-linked polyubiquitination chains on TRAF6, but has no significant effect on its K63-linked polyubiquitination. Our results collectively reveal that NUMBL interacts with TRAF6 and promotes the degradation of TRAF6 in vivo, leading to the inhibition of NF-κB signaling pathway.     

TRAF6 is required for TRAF2-dependent CD40 signal transduction in nonhemopoietic cells

The emerging role of CD40, a tumor necrosis factor (TNF) receptor family member, in immune regulation, disease pathogenesis, and cancer therapy necessitates the analysis of CD40 signal transduction in a wide range of tissue types. In this study we present evidence that the CD40-interacting proteins TRAF2 and TRAF6 play an important physiological role in CD40 signaling in nonhemopoietic cells. Using mutational analysis of the CD40 cytoplasmic tail, we demonstrate that the specific binding of TRAF2 to CD40 is required for efficient signaling on the NF-kappaB, Jun N-terminal protein kinase (JNK), and p38 axis. In fibroblasts lacking TRAF2 or in carcinoma cells in which TRAF2 has been depleted by RNA interference, the CD40-mediated activation of NF-kappaB and JNK is significantly reduced, and the activation of p38 and Akt is severely impaired. Interestingly, whereas the TRAF6-interacting membrane-proximal domain of CD40 has a minor role in signal transduction, studies utilizing TRAF6 knockout fibroblasts and RNA interference in epithelial cells reveal that the CD40-induced activation of NF-kappaB, JNK, p38, and Akt requires the integrity of TRAF6. Furthermore, we provide evidence that TRAF6 regulates CD40 signal transduction not only through its direct binding to CD40 but also indirectly via its association with TRAF2. These observations provide novel insight into the mechanisms of CD40 signaling and the multiple roles played by TRAF6 in signal transduction.     

A functional interaction between the p75 neurotrophin receptor interacting factors, TRAF6 and NRIF

Neurotrophin signaling through the p75 receptor regulates apoptosis within the nervous system both during development and in response to injury. Whereas a number of p75 interacting factors have been identified, how these upstream factors function in a coordinated manner to mediate receptor signaling is still unclear. Here, we report a functional interaction between TRAF6 and the neurotrophin receptor interacting factor (NRIF), two proteins known to associate with the intracellular domain of the p75 neurotrophin receptor. The association between NRIF and TRAF6 was direct and occurred with both endogenous and ectopically expressed proteins. A KRAB repressor domain of NRIF and the carboxyl-terminal, receptor-binding region of TRAF6 were required for the interaction. Co-expression of TRAF6 increased the levels of NRIF protein and induced its nuclear translocation. Reciprocally, NRIF enhanced TRAF6-mediated activation of the c-Jun NH2-terminal kinase (JNK) by 3-fold, while only modestly increasing the stimulation of NF-kappaB. The expression of both NRIF and TRAF6 was required for reconstituting p75 activation of JNK in HEK293 cells, whereas NRIF mutants lacking the TRAF6 interaction domain were unable to substitute for the full-length protein in facilitating activation of the kinase. These results suggest that NRIF and TRAF6 functionally interact to facilitate neurotrophin signaling through the p75 receptor.     

Involvement of TRAF4 in oxidative activation of c-Jun N-terminal kinase

We previously found that the angiogenic factors TNFalpha and HIV-1 Tat activate an NAD(P)H oxidase in endothelial cells, which operates upstream of c-Jun N-terminal kinase (JNK), a MAPK involved in the determination of cell fate. To further understand oxidant-related signaling pathways, we screened lung and endothelial cell libraries for interaction partners of p47(phox) and recovered the orphan adapter TNF receptor-associated factor 4 (TRAF4). Domain analysis suggested a tail-to-tail interaction between the C terminus of p47(phox) and the conserved TRAF domain of TRAF4. In addition, TRAF4, like p47(phox), was recovered largely in the cytoskeleton/membrane fraction. Coexpression of p47(phox) and TRAF4 increased oxidant production and JNK activation, whereas each alone had minimal effect. In addition, a fusion between p47(phox) and the TRAF4 C terminus constitutively activated JNK, and this activation was decreased by the antioxidant N-acetyl cysteine. In contrast, overexpression of the p47(phox) binding domain of TRAF4 blocked endothelial cell JNK activation by TNFalpha and HIV-1 Tat, suggesting an uncoupling of p47(phox) from upstream signaling events. A secondary screen of endothelial cell proteins for TRAF4-interacting partners yielded a number of proteins known to control cell fate. We conclude that endothelial cell agonists such as TNFalpha and HIV-1 Tat initiate signals that enter basic signaling cassettes at the level of TRAF4 and an NAD(P)H oxidase. We speculate that endothelial cells may target endogenous oxidant production to specific sites critical to cytokine signaling as a mechanism for increasing signal specificity and decreasing toxicity of these reactive species.     

High-affinity interactions of tumor necrosis factor receptor-associated factors (TRAFs) and CD40 require TRAF trimerization and CD40 multimerization.

Signaling by some TNF receptor family members, including CD40, is mediated by TNF receptor-associated factors (TRAFs) that interact with receptor cytoplasmic domains following ligand-induced receptor oligomerization. Here we have defined the oligomeric structure of recombinant TRAF domains that directly interact with CD40 and quantitated the affinities of TRAF2 and TRAF3 for CD40. Biochemical and biophysical analyses demonstrated that TRAF domains of TRAF1, TRAF2, TRAF3, and TRAF6 formed homo-trimers in solution. N-terminal deletions of TRAF2 and TRAF3 defined minimal amino acid sequences necessary for trimer formation and indicated that the coiled coil TRAF-N region is required for trimerization. Consistent with the idea that TRAF trimerization is required for high-affinity interactions with CD40, monomeric TRAF-C domains bound to CD40 significantly weaker than trimeric TRAFs. In surface plasmon resonance studies, a hierarchy of affinity of trimeric TRAFs for trimeric CD40 was found to be TRAF2 > TRAF3 > TRAF1 and TRAF6. CD40 trimerization was demonstrated to be sufficient for optimal NF-kappaB and p38 mitogen activated protein kinase activation through wild-type CD40. In contrast, a higher degree of CD40 multimerization was necessary for maximal signaling in a cell line expressing a mutated CD40 (T254A) that signaled only through TRAF6. The affinities of TRAF proteins for oligomerized receptors as well as different requirements for degree of receptor multimerization appear to contribute to the selectivity of TRAF recruitment to receptor cytoplasmic domains.     

Identification of low-frequency TRAF3IP2 coding variants in psoriatic arthritis patients and functional characterization

Introduction

In recent genome-wide association studies for psoriatic arthritis (PsA) and psoriasis vulgaris, common coding variants in the TRAF3IP2 gene were identified to contribute to susceptibility to both disease entities. The risk allele of p.Asp10Asn (rs33980500) proved to be most significantly associated and to encode a mutant protein with an almost completely disrupted binding property to TRAF6, supporting its impact as a main disease-causing variant and modulator of IL-17 signaling.

Methods

To identify further variants, exons 2-4 encoding both known TNF-receptor-associated factor (TRAF) binding domains were sequenced in 871 PsA patients. Seven missense variants and one three-base-pair insertion were identified in 0.06% to 1.02% of alleles. Five of these variants were also present in 931 control individuals at comparable frequency. Constructs containing full-length wild-type or mutant TRAF3IP2 were generated and used to analyze functionally all variants for TRAF6-binding in a mammalian two-hybrid assay.

Results

None of the newly found alleles, though, encoded proteins with different binding properties to TRAF6, or to the cytoplasmic tail of the IL-17-receptor α-chain, suggesting that they do not contribute to susceptibility.

Conclusions

Thus, the TRAF3IP2-variant p.Asp10Asn is the only susceptibility allele with functional impact on TRAF6 binding, at least in the German population.     

过表达TRAF6对人急性髓系白血病细胞自噬活性的影响

该文旨在探讨过表达肿瘤坏死因子受体相关因子6(tumor necrosis factor receptorassociated factor 6,TRAF6)对人急性髓系白血病(acute myeloid leukemia,AML)细胞自噬活性的影响。利用基因表达数据库GEO分析TRAF6在AML患者白血病细胞中的mRNA表达水平。通过癌症基因组图谱TCGA分析TRAF6表达与AML患者临床预后的关系。将TRAF6重组质粒载体转染人AML细胞系(KG-1a和THP-1),采用自噬激活剂雷帕霉素(Rapamycin)和自噬相关抑制剂3-甲基腺嘌呤(3-methyladenine,3-MA)、巴弗洛霉素A1(bafilomycin A1,Baf-A1)分别处理AML细胞。荧光定量PCR、蛋白免疫印迹技术检测过表达TRAF6后白血病细胞自噬标志物(LC3和p62)mRNA和蛋白水平;免疫荧光方法检测LC3绿色荧光斑点结构(puncta);流式细胞术检测细胞凋亡率;CCK-8实验检测AML细胞的体外增殖能力。结果显示,AML患者白血病细胞高表达TRAF6(P<0.01);TRAF6高表达的白血病患者总体生存率和无事件生存率均较TRAF6低表达组显著降低(P=0.01)。TRAF6重组质粒转染能够显著增加两株AML细胞系中TRAF6的mRNA和蛋白水平(P<0.05)。Rapamycin处理能够激活AML细胞系自噬水平,过表达TRAF6后AML细胞LC3 mRNA和LC3II蛋白水平表达上调(P<0.05)、p62 mRNA和蛋白水平下调(P<0.05)以及LC3 puncta聚集增多。用Baf-A1处理以阻断过表达TRAF6的白血病细胞系中的自噬流后,LC3II蛋白表达水平显著提高(P<0.05)。3-MA处理过表达TRAF6的白血病细胞后,LC3II蛋白表达减少、p62蛋白表达增加(P<0.05)。此外,过表达TRAF6降低白血病细胞凋亡率和促进细胞的体外增殖(P<0.001),而过表达TRAF6后联合3-MA处理则可逆转TRAF6对白血病细胞的抗凋亡和促增殖作用(P<0.001)。以上研究结果提示,过表达TRAF6能够增强AML细胞的自噬活性,促进AML细胞的生长。     

TRAF6 regulates tumour metastasis through EMT and CSC phenotypes in head and neck squamous cell carcinoma

Epithelial–mesenchymal transition (EMT) is associated with metastasis formation, generation and maintenance of cancer stem cells (CSCs). However, the regulatory mechanisms of CSCs have not been clarified. This study aims to investigate the role of TNF receptor‐associated factor 6 (TRAF6) on EMT and CSC regulation in squamous cell carcinoma of head and neck (SCCHN). We found TRAF6 was overexpressed in human SCCHN tissues, and high TRAF6 expression was associated with lymphatic metastasis and resulted in poor prognosis in patients with SCCHN. In addition, elevated TRAF6 expression was observed in several HNSCC cell lines, and wound healing and transwell assay results showed that TRAF6 knockdown inhibited the migration and invasion ability of the SCCHN cells. Moreover, the expression of Vimentin, Slug and N‐cadherin was down‐regulated and that of E‐cadherin was elevated after TRAF6 knockdown but decreased by transforming growth factor beta 1 (TGF‐β1) and CAL27 similar to mesenchymal cells formed after TGF‐β1 induction. In addition, the expression levels of CD44, ALDH1, KLF4 and SOX2 were inhibited after TRAF6 knockdown, and the anchor‐dependent colony formation number and sphere number were remarkably reduced. Flow cytometry showed TRAF6 knockdown reduced ALDH1‐positive cancer stem cells. We also demonstrated that TRAF6 is closely associated with EMT process and cancer stem cells using a Tgfbr1/Pten 2cKO mice SCCHN model and human SCCHN tissue microarray. Our findings indicate that TRAF6 plays a role in EMT phenotypes, the generation and maintenance of CSCs in SCCHN, suggesting that TRAF6 is a potential therapeutic target for SCCHN.     

Relationship between TRAF6 and deterioration of HCC: an immunohistochemical and in vitro study

Objective

To explore the relationship between tumor necrosis factor receptor-associated factor 6 (TRAF6) and the clinicopathological features in HCC as well as its biological function.

Methods

Totally, 412 liver tissues were collected, including 171 hepatocellular carcinoma (HCC) and their corresponding non-tumor tissues, 37 cirrhosis and 33 normal liver tissues. The expression of TRAF6 was assessed by immunohistochemistry. Then, analysis of the correlations between TRAF6 expression and clinicopathological parameters in HCC was conducted. Furtherer, in vitro experiments on HepG2 and Hep3B cells were performed to validate the biological function of TRAF6 on HCC cells. TRAF6 siRNA was transfected into HepG2 and Hep3B cell lines and TRAF6 expression was evaluated with RT-qPCR and western blot. The assays of cell viability, proliferation, apoptosis and caspase-3/7 activity were carried out to investigate the effects of TRAF6 on HCC cells with RNA interference. Cell viability was assessed with Cell Titer-Blue kit. Cell proliferation was tested with MTS kit. Cell apoptosis was checked through morphologic detection with fluorescence microscope, as well as caspase-3/7 activity was measured with fluorogenic substrate detection.

Results

The positive expression rate of TRAF6 protein was 49.7 % in HCC, significantly higher than that of normal liver (12.1 %), cirrhosis (21.6 %) and adjacent non-cancerous tissues (36.3 %, all P < 0.05). Upregulated TRAF6 was detected in groups with metastasis (Z = ?2.058, P = 0.04) and with low micro-vessel density (MVD) expression (Z = ?2.813, P = 0.005). Spearman correlation analysis further showed that the expression of TRAF6 was positively correlated with distant metastasis (r = 0.158, P = 0.039) and negatively associated with MVD (r = ?0.249, P = 0.004). Besides, knock-down of TRAF6 mRNA in HCC cell lines HepG2 and Hep3B both resulted in cell viability and proliferation inhibition, also cell apoptosis induction and caspase-3/7 activity activation.

Conclusions

TRAF6 may contribute to metastasis and deterioration of the HCC via influencing cell growth and apoptosis. Thus, TRAF6 might become a predictive and therapeutic biomarker for HCC.

     

Roles of the Kinase TAK1 in TRAF6-Dependent Signaling by CD40 and Its Oncogenic Viral Mimic, LMP1

The Epstein-Barr virus (EBV)-encoded protein latent membrane protein 1 (LMP1) is essential for EBV-mediated B cell transformation and plays a critical role in the development of post-transplant B cell lymphomas. LMP1 also contributes to the exacerbation of autoimmune diseases such as systemic lupus erythematosus (SLE). LMP1 is a functional mimic of the tumor necrosis factor receptor (TNFR) superfamily member CD40, and relies on TNFR-associated factor (TRAF) adaptor proteins to mediate signaling. However, LMP1 activation signals to the B cell are amplified and sustained compared to CD40 signals. We previously demonstrated that LMP1 and CD40 use TRAF molecules differently. Although associating with CD40 and LMP1 via separate mechanisms, TRAF6 plays a significant role in signal transduction by both. It is unknown whether TRAF6 mediates CD40 versus LMP1 functions via distinct or shared pathways. In this study, we tested the hypothesis that TRAF6 uses the kinase TAK1 to trigger important signaling pathways following both CD40 and LMP1 stimulation. We determined that TAK1 was required for JNK activation and interleukin-6 (IL-6) production mediated by CD40 and LMP1, in both mouse and human B cells. Additionally, TRAF3 negatively regulated TRAF6-dependent, CD40-mediated TAK1 activation by limiting TRAF6 recruitment. This mode of regulation was not observed for LMP1 and may contribute to the dysregulation of LMP1 compared to CD40 signals.     

Activation of TRAF5 and TRAF6 signal cascades negatively regulates the latent replication origin of Epstein-Barr virus through p38 mitogen-activated protein kinase

Latent Epstein-Barr virus (EBV) is maintained by the virus replication origin oriP that initiates DNA replication with the viral oriP-binding factor EBNA1. However, it is not known whether oriP's replicator activity is regulated by virus proteins or extracellular signals. By using a transient replication assay, we found that a low level of expression of viral signal transduction activator latent membrane protein 1 (LMP1) suppressed oriP activity. The binding site of the tumor necrosis factor receptor-associated factor (TRAF) of LMP1 was essential for this suppressive effect. Activation of the TRAF signal cascade by overexpression of TRAF5 and/or TRAF6 also suppressed oriP activity. Conversely, blocking of TRAF signaling with dominant negative mutants of TRAF5 and TRAF6, as well as inhibition of a downstream signal mediator p38 MAPK, released the LMP1-induced oriP suppression. Furthermore, activation of TRAF6 signal cascade by lipopolysaccharides (LPS) resulted in loss of EBV from Burkitt's lymphoma cell line Akata, and inhibition of p38 MAPK abolished the suppressive effect of LPS. These results suggested that the level of oriP activity is regulated by LMP1 and extracellular signals through TRAF5- and TRAF6-mediated signal cascades.     

YopJ targets TRAF proteins to inhibit TLR-mediated NF-kappaB, MAPK and IRF3 signal transduction

The Yersinia pestis virulence factor YopJ is a potent inhibitor of the NF-kappaB and MAPK signalling pathways, however, its molecular mechanism and relevance to pathogenesis are the subject of much debate. In this report, we characterize the effects of this type III effector protein on bone fide signalling events downstream of Toll-like receptors (TLRs), critical sensors in innate immunity. YopJ inhibited TLR-mediated NF-kappaB and MAP kinase activation, as suggested by previous studies. In addition, induction of the TLR-mediated interferon response was blocked by YopJ, indicating that YopJ also inhibits IRF3 signalling. Examination of the NF-kappaB signalling pathway in detail suggested that YopJ acts at the level of TAK1 (MAP3K7) activation. Further studies revealed a YopJ-dependent decrease in the ubiquitination of TRAF3 and TRAF6. These data support the hypothesis that YopJ is a deubiquitinating protease that acts on TRAF proteins to prevent or remove the K63-polymerized ubiquitin conjugates required for signal transduction. Our data do not directly address the alternative hypothesis that YopJ is an acetyltransferase that acts on the activation loop of IKK and MKK proteins, but support the conclusion that the critical function of YopJ is to deubiquinate TRAF proteins.     

Critical roles of TRAF2 and TRAF5 in tumor necrosis factor-induced NF-kappa B activation and protection from cell death

Tumor necrosis factor (TNF) receptor-associated factors (TRAFs) were identified as signal transducers for the TNF receptor superfamily. However, the exact roles of TRAF2 and TRAF5 in TNF-induced NF-kappaB activation still remain controversial. To address this issue, we generated TRAF2 and TRAF5 double knockout (DKO) mice. TNF- but not interleukin-1-induced nuclear translocation of NF-kappaB was severely impaired in murine embryonic fibroblasts (MEFs) derived from DKO mice. Moreover, DKO MEFs were more susceptible to TNF-induced cytotoxicity than TRAF2 knockout MEFs. Collectively, these results indicate that both TRAF2 and TRAF5 are involved in TNF-induced NF-kappaB activation and protection from cell death.     

Protein kinase PKN1 associates with TRAF2 and is involved in TRAF2-NF-kappaB signaling pathway

PKN1 is a fatty acid and Rho-activated serine/threonine protein kinase whose catalytic domain is highly homologous to protein kinase C (PKC) family. In yeast two-hybrid screening for PKN1 binding proteins, we identified tumor necrosis factor alpha (TNFalpha) receptor-associated factor 2 (TRAF2). TRAF2 is one of the major mediators of TNF receptor superfamily transducing TNF signal to various functional targets, including activation of NF-kappaB, JNK, and apoptosis. FLAG-tagged PKN1 was co-immunoprecipitated with endogenous TRAF2 from HEK293 cell lysate, and in vitro binding assay using the deletion mutants of TRAF2 showed that PKN1 directly binds to the TRAF domain of TRAF2. PKN1 has the TRAF2-binding consensus sequences PXQX (S/T) at amino acid residues 580-584 (PIQES), and P580AQ582A mutant was not co-immunoprecipitated with TRAF2. Furthermore, the reduced expression of PKN1 by RNA interference (RNAi) down-regulated TRAF2-induced NF-kappaB activation in HEK293T cells. These results suggest that PKN1 is involved in TRAF2-NF-kappaB signaling pathway.     

TRAF family proteins interact with the common neurotrophin receptor and modulate apoptosis induction.

The common neurotrophin receptor, p75(NTR), has been shown to signal in the absence of Trk tyrosine kinase receptors, including induction of neural apoptosis and activation of NF-kappaB. However, the mechanisms by which p75(NTR) initiates these intracellular signal transduction pathways are unknown. Here we report interactions between p75(NTR) and the six members of TRAF (tumor necrosis factor receptor-associated factors) family proteins. The binding of different TRAF proteins to p75(NTR) was mapped to distinct regions in p75(NTR). Furthermore, TRAF4 interacted with dimeric p75(NTR), whereas TRAF2 interacted preferentially with monomeric p75(NTR). TRAF2-p75(NTR), TRAF4-p75(NTR), and TRAF6-p75(NTR) interactions modulated p75(NTR)-induced cell death and NF-kappaB activation with contrasting effects. Coexpression of TRAF2 with p75(NTR) enhanced cell death, whereas coexpression of TRAF6 was cytoprotective. Furthermore, overexpression of TRAF4 abrogated the ability of dimerization to prevent the induction of apoptosis normally mediated by monomeric p75(NTR). TRAF4 also inhibited the NF-kappaB response, whereas TRAF2 and TRAF6 enhanced p75(NTR)-induced NF-kappaB activation. These results demonstrate that TRAF family proteins interact with p75(NTR) and differentially modulate its NF-kappaB activation and cell death induction.