Activation of the AP-1 transcription factor by inflammatory cytokines of the TNF family

Inflammatory cytokines of the tumor necrosis factor (TNF) family mediate a large variety of cellular and organismal inflammatory responses and are important to the pathogenesis of a number of important disease states including arthritis, septic shock, inflammatory bowel disease, and, possibly, type II diabetes. Many of the responses to these cytokines require de novo gene expression mediated by the activator protein-1 (AP-1) heterodimeric transcription factor. This review will discuss what is known of how cytokines of the TNF family, acting at the cell surface, recruit two mitogen-activated protein kinase (MAPK) subfamilies, the stress-activated protein kinases (SAPKs, also called JNKs) and the p38s, to transduce signals to AP-1.

Overnight changes of immune parameters and catecholamines are associated with mood and stress

OBJECTIVES

To test the hypothesis that a nocturnal decrease of secretion of inflammation markers and catecholamines would be associated with mood and stress variables even after controlling for objective sleep variables.

METHODS

A total of 130 healthy volunteers participated in this study, spending 2 nights in the Gillin Laboratory of Sleep and Chronobiology at the University of California, San Diego, General Clinical Research Center. Blood samples were obtained before sleep (10:30 PM) and after awakening (6:30 AM) on the first day, and these samples were assayed for inflammatory biomarkers and catecholamines. On the second night, polysomnographic records were scored for objective sleep variables, e.g., total sleep time and wake after sleep onset. Self-rating scales for mood, stress, depression, and daily hassles were administered the second day.

RESULTS

The nocturnal decrease in interleukin-6 was smaller in people who reported more negative mood or fatigue and greater in those who reported more uplift events (e.g., with Profile of Mood States fatigue r(p) = -.25 to -.30). People with high stress or high depression levels had smaller nocturnal decreases of epinephrine. That relationship was even stronger when partial correlations were used to control for morning level and sleep variables. The associations between nocturnal changes of C-reactive protein, soluble tumor necrosis factor-receptor I, and norepinephrine with psychological states were nonremarkable.

CONCLUSIONS

The analyses of nocturnal change scores (difference scores) add substantial information compared with the traditional analyses of morning levels of immune variables and catecholamines alone. Subjective well-being is significantly associated with a greater nocturnal decrease of interleukin-6 and epinephrine. More research on nocturnal adaptation processes is warranted.

[Expression and function of TRAF1 in Hodgkin's lymphoma cells.]

OBJECTIVE

To investigate the function of tumor necrosis factor receptor-associated factor 1 (TRAF1) and CD30-TRAF1 signaling in Hodgkin's lymphoma.

METHODS

Endogenous and CD30 ligand-induced TRAF1 expression at mRNA and protein levels were examined by quantitative RT-PCR and Western blot analyses, respectively. RNA interference was performed to silence the expression of TRAF1 in L428 cells and examine its effect on cell survival. ELISA-based NF-kappaB family transcription factor activity assay was performed to quantify the kappaB DNA-binding activity in nuclear extracts. The expression of JunB was measured by Western blot.

RESULTS

TRAF1 expression was detected at both mRNA and protein levels in B cell-derived lymphoma cell lines (L428 and KM-H2). CD30 activation via binding to CD30 ligand induced the TRAF1 expression, the relative mRNA expression was increased to 7.26 +/- 0.23 from 3.50 +/- 0.20, the relative protein expression was increased to 4.53 +/- 0.55 from 2.31 +/- 0.35. The apoptosis rate was increased to (27.7 +/- 5.8)% in TRAF1-silenced L428 cells compared to (5.7 +/- 1.2)% in control cells. The p50 and RelA DNA-binding activity were decreased in TRAF1-silenced L428 cells. The expression of JunB upon CD30 ligand stimulation was not changed in TRAF1-silenced L428 cells.

CONCLUSIONS

TRAF1 is overexpressed in B cell-derived Hodgkin's lymphoma cells, which is regulated by CD30 signaling pathway. TRAF1 is a crucial molecule mediating the activation of the classical NF-kappaB activity, which further facilitates the anti-apoptosis.

Constitutive NF-κB/Rel Activation in Philadelphia Chromosome Positive (Ph+) Acute Lymphoblastic Leukemia (ALL)

The Bcr-Abl translocation t(9;22)(q34;q11 ) defines a subgroup of ALL patients with a dismal prognosis despite the introduction of intensified induction and consolidation regimen. Although Bcr-Abl induced NF-kappaB/Rel activation has previously been shown, the role of NF-kappaB/Rel in Ph+ leukemia is unclear. Using DNA binding assays, we demonstrate constitutive NF-kappaB/Rel activity in nuclear extracts from Ph+ ALL blasts, whereas Ph- primary blast cells and B-precursor cell lines lack NF-kappaB/Rel activity. NF-kappaB/Rel activity was shown in the ela2 and the b2a2 subtypes. Constitutive NF-kappaB/Rel activity in Ph+ blasts is not due to elevated endogenous IkappaB kinase (IKK) activity as shown by immune complex kinase assays. Since NF-kappaB/Rel is a transcriptional regulator of inhibitors of apoptosis we examined the expression of anti-apoptotic genes known to be induced by NF-kappaB/Rel by real time PCR analysis. We found no induction of TRAFI, TRAF2, cIAPI, cIAP2, XIAP, A20 or Bfl/Al in Ph+ ALL samples as compared to Ph-negative ALL controls. In summary, constitutive NF-kappaB/Rel activation independent of endogenous IKK activation may be a common finding in Ph+ ALL. However, targets of NF-kappaB/Rel mediated transcriptional regulation in this disease remain to be identified.

Resistance to CD95-mediated apoptosis of CD40-activated chronic lymphocytic leukemia B cells is not related to lack of DISC molecules expression

In B-cell chronic lymphocytic leukemia (CLL), accumulation of neoplastic B cells may be the result of dysregulated apoptosis. One of the major molecules triggering apoptosis, CD95 (FAS), is not expressed on CLL B cells at resting conditions. However, CD40 triggering of CLL B cells upregulates receptors belonging to the tumor necrosis factor (TNF) superfamily, like CD95. In the present study, we analyzed in B cells from 20 CLL patients the effect of CD40/CD40L interaction on: (i) CD95 modulation; (ii) CD95-mediated apoptosis and (iii) mRNA and protein expression of the death-inducing signaling complex (DISC) molecules.CD40 activation of CLL B cells was carried out by coculture with CD40L-transfected cells and cytofluorimetric analyses were performed to study CD95 modulation and apoptosis induction by an anti-CD95 moAb. Despite strong CD95 upregulation on the membrane of all the cases studied, only a minority of cases analyzed (3/20) proved weakly responsive to CD95-mediated apoptosis. Multiplex RT-PCR was used to analyze FLICE, FAS, FADD and TRADD mRNAs before and after CD40 triggering. In agreement with the cytofluorimetric data, FAS mRNA appeared significantly increased after CD40 triggering; the other molecules involved in DISC formation and in CD95-mediated apoptosis were also expressed without relevant differences between resting and activated conditions. Western blot analyses further confirmed FLICE and FADD protein expression by resting and activated CLL cells. Our findings demonstrate that, following CD40 triggering, CLL B cells are resistant to CD95-mediated apoptosis despite a strong CD95 upregulation on the membrane and a normal mRNA or protein expression of the DISC components.

Cyclooxygenase (COX)-2 inhibitor celecoxib abrogates TNF-induced NF-kappa B activation through inhibition of activation of I kappa B alpha kinase and Akt in human non-small cell lung carcinoma: correlation with suppression of COX-2 synthesis

The cyclooxygenase 2 (COX-2) inhibitor celecoxib (also called celebrex), approved for the treatment of colon carcinogenesis, rheumatoid arthritis, and other inflammatory diseases, has been shown to induce apoptosis and inhibit angiogenesis. Because NF-kappa B plays a major role in regulation of apoptosis, angiogenesis, carcinogenesis, and inflammation, we postulated that celecoxib modulates NF-kappa B. In the present study, we investigated the effect of this drug on the activation of NF-kappa B by a wide variety of agents. We found that celecoxib suppressed NF-kappa B activation induced by various carcinogens, including TNF, phorbol ester, okadaic acid, LPS, and IL-1 beta. Celecoxib inhibited TNF-induced I kappa B alpha kinase activation, leading to suppression of I kappa B alpha phosphorylation and degradation. Celecoxib suppressed both inducible and constitutive NF-kappa B without cell type specificity. Celecoxib also suppressed p65 phosphorylation and nuclear translocation. Akt activation, which is required for TNF-induced NF-kappa B activation, was also suppressed by this drug. Celecoxib also inhibited the TNF-induced interaction of Akt with I kappa B alpha kinase (IKK). Celecoxib abrogated the NF-kappa B-dependent reporter gene expression activated by TNF, TNF receptor, TNF receptor-associated death domain, TNF receptor-associated factor 2, NF-kappa B-inducing kinase, and IKK, but not that activated by p65. The COX-2 promoter, which is regulated by NF-kappa B, was also inhibited by celecoxib, and this inhibition correlated with suppression of TNF-induced COX-2 expression. Besides NF-kappa B, celecoxib also suppressed TNF-induced JNK, p38 MAPK, and ERK activation. Thus, overall, our results indicate that celecoxib inhibits NF-kappa B activation through inhibition of IKK and Akt activation, leading to down-regulation of synthesis of COX-2 and other genes needed for inflammation, proliferation, and carcinogenesis.

Compartmentalization of TNF receptor 1 signaling: internalized TNF receptosomes as death signaling vesicles

The molecular regulation of the recruitment of initial signaling complexes at the TNF-R1 is poorly defined. We demonstrate here that within minutes internalized TNF-R1 (TNF receptosomes) recruits TRADD, FADD, and caspase-8 to establish the "death-inducing signaling complex" (DISC). In addition, we identified the TNF-R1 internalization domain (TRID) required for receptor endocytosis and provide evidence that TNF-R1 internalization, DISC formation, and apoptosis are inseparable events. Analyzing cell lines expressing an internalization-deficient receptor (TNF-R1 DeltaTRID) revealed that recruitment of RIP-1 and TRAF-2 to TNF-R1 occurred at the level of the plasma membrane. In contrast, aggregation of TRADD, FADD, and caspase-8 to establish the TNF-R1-associated DISC is critically dependent on receptor endocytosis. Furthermore, fusion of TNF receptosomes with trans-Golgi vesicles results in activation of acid sphingomyelinase and cathepsin D. Thus, TNF receptosomes establish the different TNF signaling pathways by compartmentalization of plasma membrane-derived endocytic vesicles harboring the TNF-R1-associated DISC.

Expression of tumor necrosis factor receptor-associated factor 1 in nasopharyngeal carcinoma: possible upregulation by Epstein-Barr virus latent membrane protein 1

EBV infection is associated with virtually all cases of undifferentiated NPC, and the EBV-encoded LMP1 is expressed in a proportion of cases. LMP1 has transforming functions similar to members of the TNF receptor family and activates intracellular signaling cascades through interaction with TRAFs. In B cells, expression of TRAF1 is in turn upregulated by LMP1. LMP1 signaling in epithelial cells may be affected by the presence or absence of TRAF1. By immunohistochemistry, we detected TRAF1 expression in 17 of 42 (40%) EBV+ undifferentiated NPCs. All 7 LMP1+ NPC biopsies were also TRAF1+. Using an RNAse protection assay, high-level TRAF1 expression was detected in an LMP1-expressing NPC-derived cell line (C15) and expression was weaker in 2 LMP1- cell lines (C17, C19). Finally, LMP1 upregulated TRAF1 expression in an EBV- keratinocyte cell line. Our results demonstrate that TRAF1 is expressed in NPC tumor cells in vivo and suggest that TRAF1 expression may be upregulated by LMP1 in NPC. An antiapoptotic function has been proposed for TRAF1, and this may be relevant for the pathogenesis of NPC.

A novel assay to quantify cell death after transient expression of apoptotic genes in B- and T-lymphocytes

We developed an assay allowing the detection and quantification of cell death after transient expression of apoptotic genes in B- and T-lymphocytes. For efficient gene transfer, B- and T-cells were electroporated under optimized conditions. To blind out the high background of non-transfected cells and cell death caused by the electroporation procedure itself, the green fluorescent protein (GFP) was co-transfected with the gene of interest. However, if the gene of interest was a potent apoptosis inducer, most successfully transfected cells were killed before GFP was expressed to levels sufficient for standard flow cytometry analysis or apoptosis assays. After staining of the transfected cells with propidium iodide (PI), very few GFP+/PI+ cells were detectable. To overcome this problem, the cell death rate induced by the transiently expressed gene was determined as the reduction of living green cells in the apoptotic versus a reference sample. This was achieved by an advanced flow cytometrical analysis quantifying the number of surviving green cells in normalised sample volumes directly relating to the number of initially transfected cells. Functioning of the assay was demonstrated by transient transfection of the potent apoptosis inducers TNF-receptor-associated death domain protein (TRADD) and a fusion protein of the transmembrane domain of the latent membrane protein 1 (LMP1) of Epstein-Barr virus and the signaling domain of TNF-receptor 1. We successfully applied the assay to the Burkitt lymphoma cell line BJAB and the T-leukemia cell line Jurkat.

Epstein-Barr Virus Latent Membrane Protein 1 Activates Nuclear Factor-κB in Human Endothelial Cells and Inhibits Apoptosis

BACKGROUND

Although vascular changes and transplant vasculopathy have been described with cytomegalovirus, the impact of Epstein-Barr virus (EBV) on the vascular endothelium of the transplanted allograft is largely unknown. We recently reported that EBV (+) patients taken off immunosuppressive medications for periods of time had a low incidence of chronic rejection. In another report, we noted that there was expression of the "protective" antiapoptotic factor Bcl-2 in the vascular endothelium of transplant allografts from EBV (+) patients. In this report, we determined the effect of latent EBV infection on endothelial cell activation and apoptosis.

METHODS

Cultured human umbilical vein endothelial cells (HUVEC) were either infected with EBV or transduced with EBV latent membrane protein 1 and examined for apoptosis, nuclear factor (NF)-kappaB activation, and expression of chemokines, cytokines, and adhesion molecules.

RESULTS

EBV infection and latent membrane protein 1 expression in HUVEC resulted in NF-kappaB activation and increased expression of the cytokines interleukin (IL)-1alpha, IL-1beta, and IL-6; the chemokines IL-8, monocyte chemotactic protein-1, and RANTES; and the adhesion molecules intercellular adhesion molecule-1, vascular cell adhesion molecule-1, and E-selectin. There was increased expression of the antiapoptotic genes A1, c-IAP2, and TRAF1; inhibition of caspase 3; and protection from apoptosis.

CONCLUSIONS

Latent EBV in HUVEC results in constitutive NF-kappaB activation, protection from apoptosis, and increased basal expression of inflammatory factors. The in vivo effect of latent EBV in the vascular endothelium of the transplanted allograft and its resultant impact on transplant vasculopathy are the subject of further investigations in our laboratory.

Hydroid TNF-receptor-associated factor (TRAF) and its splice variant: a role in development

TNF-receptor-associated factors (TRAFs) mediate signaling via tumor necrosis factor receptor (TNFR)/TLR molecules, playing a role in cellular processes such as growth, differentiation and apoptosis. They have been most studied in the immunological context. Within the animal kingdom, TRAFs have been characterized from vertebrates, flies and worms. We have cloned and characterized the first TRAF homologue from a member of the most basal eumetazoan phylum, the Cnidaria. The cnidarian TRAF, HyTRAF1, is a typical member of its family, containing one RING finger and five zinc finger domains in its N-terminal region, followed by a TRAF domain located at the C terminus. In addition to the full-length mRNA, the gene is alternatively spliced to create a shorter isoform, HyTRAF1a, with a deletion of 35 amino acids, resulting in a protein with only four zinc fingers. This is the first described TRAF alternative splicing in invertebrates. Whereas the full-length protein is expressed in most life stages of the animal, the short isoform is exclusively found at the larval and early metamorphic stages. This stage is characterized by extensive apoptosis, suggesting that HyTRAF1a mediates a proapoptotic c-jun N-terminal kinase (JNK) signaling, similar to the murine TRAF2A isoform. Based on neighbor joining analysis of TRAF molecules across the animal kingdom, we propose that the cnidarian TRAF interacts with TNFR, rather than with TLR. Our findings suggest that TNF signaling has evolved in the common ancestor to cnidarians and bilaterians and that it has been conserved in the entire animal kingdom.

Selective regulation by delta-PKC and PI 3-kinase in the assembly of the antiapoptotic TNFR-1 signaling complex in neutrophils

TNF is implicated in the attenuation of neutrophil constitutive apoptosis during sepsis. Antiapoptotic signaling is mediated principally through the TNF receptor-1 (TNFR-1). In adherent neutrophils, when beta-integrin signaling is activated, TNF phosphorylates TNFR-1 and activates prosurvival and antiapoptotic signaling. Previously, we identified the delta-PKC isotype and phosphatidylinositol (PI) 3-kinase as critical regulators of TNF signaling in adherent neutrophils. Both kinases associate with TNFR-1 in response to TNF and are required for TNFR-1 serine phosphorylation, NF-kappaB activation, and inhibition of apoptosis. The purpose of this study was to examine the role of delta-PKC and PI 3-kinase in the assembly of TNFR-1 signaling complex that regulates NF-kappaB activation and antiapoptotic signaling. Coimmunoprecipitation studies established that PI 3-kinase, delta-PKC, and TNFR-1 formed a signal complex in response to TNF. delta-PKC recruitment required both delta-PKC and PI 3-kinase activity, whereas PI 3-kinase recruitment was delta-PKC independent, suggesting that PI 3-kinase acts upstream of delta-PKC. An important regulatory step in control of antiapoptotic signaling is the assembly of the TNFR-1-TNFR-1-associated death domain protein (TRADD)-TNFR-associated factor 2 (TRAF2)-receptor interacting protein (RIP) complex that controls NF-kappaB activation. Inhibition of either delta-PKC or PI 3-kinase decreased TNF-mediated recruitment of RIP and TRAF2 to TNFR-1. In contrast, TRADD recruitment was enhanced. Thus delta-PKC and PI 3-kinase are positive regulators of TNF-mediated association of TRAF2 and RIP with TNFR-1. Conversely, these kinases are negative regulators of TRADD association. These results suggest that delta-PKC and PI 3-kinase regulate TNF antiapoptotic signaling at the level of the TNFR-1 through control of assembly of a TNFR-1-TRADD-RIP-TRAF2 complex.

Mutation analysis of the apoptotic "death-receptors" and the adaptors TRADD and FADD/MORT-1 in osteosarcoma tumor samples and osteosarcoma cell lines

Apoptosis is a key mechanism of the organism that regulates embryogenesis and development, maintains homeostasis of the immune system and removes potentially hazardous cells. A dysregulation of apoptosis signaling may thus disturb the balance of cell survival and cell death, leading to the development of several diseases including cancer. In order to determine whether osteosarcomas display an increased frequency of genetic alterations that affect apoptosis signaling, we analyzed the death domains of the death receptor genes CD95/Fas/Apo1, TNFR1, DR3/Apo3/WSL-1/LARD/TRAMP, DR5/TRAIL-R2/TRICK2/KILLER, DR6 and the complete coding sequences of the death receptor gene DR4/TRAIL-R1 and the genes of the adaptors TRADD and FADD/MORT-1. The investigation included 15 osteosarcoma tumor samples, 3 osteosarcoma cell lines (SAOS-2, HOS and MG63) and peripheral blood from 20 donors as controls. We were able to identify 4 different sequence variations within the DR4 gene located on exons 3, 4, 5 and 10 (death-domain). No alterations have been detected in the other genes or exons investigated. Except the sequence variant affecting exon 4, the alterations were homozygous in 15% of the tumor samples and cell lines, whereas the same alterations found in the control group were heterozygous or even not detectable. Three out of 4 alterations are located in the receptor's extracellular cysteine rich domain, which contains the ligand binding area and 1 on exon 10 coding for the death-domain. They may thus exert influence on ligand-receptor interactions and subsequent apoptosis induction. Our findings suggest that homozygous genetic alterations within the DR4 gene may be implicated in the formation of osteosarcoma.

Regulation of phorbol ester-mediated TRAF1 induction in human colon cancer cells through a PKC/RAF/ERK/NF-κB-dependent pathway

Tumor necrosis factor (TNF) receptor-associated factors (TRAFs) are cytoplasmic adapter proteins that link a wide variety of cell surface receptors to the apoptotic signaling cascade. The purpose of this study was to delineate the signaling pathways and TRAF1 promoter elements responsible for phorbol ester-mediated TRAF1 induction in human colon cancers. Here, we found that the PKC activators, phorbol 12-myristate 13-acetate (PMA) and bryostatin I, induced TRAF1 mRNA expression; pretreatment with actinomycin D blocked PMA-mediated TRAF1 expression suggesting induction at the transcriptional level. In contrast, expression of other TRAFs (TRAF2, 3 and 4) was minimally altered by PMA. Various PKC isoform-selective inhibitors blocked PMA-mediated TRAF1 mRNA and promoter stimulation; rottlerin, a selective PKCdelta inhibitor, had no effect suggesting that Ca(2+)-dependent PKC isoforms (e.g., PKCalpha and betaI) play a role in TRAF1 regulation. In addition, the MEK/ERK inhibitors, PD98059 and UO126, suppressed PMA-stimulated TRAF1 promoter activity indicating a role for ERK in TRAF1 induction. Moreover, cotransfection of a dominant-negative Raf-1 (Raf-C4) significantly reduced PMA-stimulated TRAF1 promoter activity whereas transfection of dominant-negative Ras or treatment with Ras inhibitors had minimal to no effect on TRAF1 induction suggesting dependence on Raf, but not Ras, activation. Finally, site-specific mutagenesis of functional NF-kappaB sites (particularly the most proximal site) in the TRAF1 promoter significantly decreased PMA-mediated promoter activity. In conclusion, our results demonstrate selective induction of TRAF1 in human colon cancer cells through a Ca(2+)-dependent PKC/Raf-1/ERK/NF-kappaB-dependent pathway.

Increased serum concentrations of soluble CD95/Fas and caspase 1/ICE in patients with acute angina

OBJECTIVES

To investigate the expression of death inducing receptors in the sera of patients with stable and unstable angina.

DESIGN

80 consecutive patients with stable (n = 40) or unstable (n = 40) angina pectoris were studied. Serum concentrations of soluble CD95 (sCD95), soluble CD95 ligand (sCD95L; CD178), tumour necrosis factor (TNF) alpha, soluble TNFalpha receptor type 1 (sTNFR1), and interleukin 1beta converting enzyme (ICE; caspase 1) were measured by enzyme linked immunosorbent assay (ELISA).

RESULTS

Significant increases in the concentrations of sCD95 and ICE (p < 0.001 and p < 0.023, respectively) were found in the serum from patients with unstable angina relative to those with stable angina. There were no significant differences in the concentrations of sCD95L, TNF alpha, and sTNFR1 between the groups.

CONCLUSIONS

These data provide the first evidence that sCD95 and ICE are important serological markers that may help to discriminate between stable and unstable angina. This observation may warrant further clinical study to elucidate the clinical impact of sCD95 and ICE in acute coronary syndromes.

A novel interaction between protein kinase D and TNF receptor-associated factor molecules regulates B cell receptor-CD40 synergy

Signaling by Ag to the B cell Ag receptor (BCR) is enhanced by several cooperating signals, including several provided by B-T cell interactions. One of these, CD40, provides critical signals for B cell differentiation, isotype switching, and B cell memory. The molecular mechanisms by which BCR and CD40 signals synergize are not well understood. Although the BCR and CD40 share certain signaling pathways, we hypothesized that unique signals provided by each could provide mutual enhancement of their signaling pathways. The BCR, but not CD40, activates protein kinase D (PKD), while CD40, but not the BCR, employs the TNFR-associated factor (TRAF) adapter proteins in signaling. In this study, we show that genetic or pharmacologic inhibition of BCR-mediated PKD activation in B lymphocytes abrogated the synergy between the CD40 and the BCR, as measured by activation of Ig and cytokine secretion. Interestingly, the role of PKD was dependent upon the association of CD40 with TRAF2, and was inhibited by the binding of TRAF3, revealing a novel functional link between these two classes of signaling molecules.

Epstein-Barr virus latent infection membrane protein 1 TRAF-binding site induces NIK/IKK alpha-dependent noncanonical NF-kappaB activation

Epstein-Barr virus (EBV) latent infection membrane protein 1 (LMP1)-induced NF-kappaB activation is important for infected cell survival. LMP1 activates NF-kappaB, in part, by engaging tumor necrosis factor (TNF) receptor-associated factors (TRAFs), which also mediate NF-kappaB activation from LTbetaR and CD40. LTbetaR and CD40 activation of p100/NF-kappaB2 is now known to be NIK/IKKalpha-dependent and IKKbeta/IKKgamma independent. In the experiments described here, we found that EBV LMP1 induced p100/NF-kappaB2 processing in human lymphoblasts and HEK293 cells. LMP1-induced p100 processing was NIK/IKKalpha dependent and IKKbeta/IKKgamma independent. Furthermore, the LMP1 TRAF-binding site was required for p100 processing and p52 nuclear localization, whereas the LMP1 death domain-binding site was not. Moreover, the LMP1 TRAF-binding site preferentially caused RelB nuclear accumulation. In murine embryo fibroblasts (MEFs), IKKbeta was essential for LMP1 up-regulation of macrophage inflammatory protein (MIP)-2, TNFalpha, I-TAC, ELC, MIG, and CXCR4 RNAs. Interestingly, in IKKalpha knockout MEFs, LMP1 hyperinduced MIP-2, TNFalpha, and I-TAC expression, consistent with a role for IKKalpha in down-modulating canonical IKKbeta activation or its effects. In contrast, LMP1 failed to up-regulate CXCR4 and MIG RNA in IKKalpha knockout MEFs, indicating a dependence on noncanonical IKKalpha activation. Furthermore, LMP1 up-regulation of MIP-2 RNA in MEFs was both IKKbeta- and IKKgamma-dependent, whereas LMP1 upregulation of MIG and I-TAC RNA was fully IKKgamma independent. Thus, LMP1 induces typical canonical IKKbeta/IKKgamma-dependent, atypical canonical IKKbeta-dependent/IKKgamma-independent, and noncanonical NIK/IKKalpha-dependent NF-kappaB activations; NIK/IKKalpha-dependent NF-kappaB activation is principally mediated by the LMP1 TRAF-binding site.

Tumor Necrosis Factor Receptor-associated Factor (TRAF) 1 Regulates CD40-induced TRAF2-mediated NF-κB Activation

To investigate CD40 signaling complex formation in living cells, we used green fluorescent protein (GFP)-tagged CD40 signaling intermediates and confocal life imaging. The majority of cytoplasmic TRAF2-GFP and, to a lesser extent, TRAF3-GFP, but not TRAF1-GFP or TRAF4-GFP, translocated into CD40 signaling complexes within a few minutes after CD40 triggering with the CD40 ligand. The inhibitor of apoptosis proteins cIAP1 and cIAP2 were also recruited by TRAF2 to sites of CD40 signaling. An excess of TRAF2 allowed recruitment of TRAF1-GFP to sites of CD40 signaling, whereas an excess of TRAF1 abrogated the interaction of TRAF2 and CD40. Overexpression of TRAF1, however, had no effect on the interaction of TRADD and TRAF2, known to be important for tumor necrosis factor receptor 1 (TNF-R1)-mediated NF-kappaB activation. Accordingly, TRAF1 inhibited CD40-dependent but not TNF-R1-dependent NF-kappaB activation. Moreover, down-regulation of TRAF1 with small interfering RNAs enhanced CD40/CD40 ligand-induced NF-kappaB activation but showed no effect on TNF signaling. Because of the trimeric organization of TRAF proteins, we propose that the stoichiometry of TRAF1-TRAF2 heteromeric complexes ((TRAF2)2-TRAF1 versus TRAF2-(TRAF1)2) determines their capability to mediate CD40 signaling but has no major effect on TNF signaling.

Discrete functions of TRAF1 and TRAF2 in Drosophila melanogaster mediated by c-Jun N-terminal kinase and NF-kappaB-dependent signaling pathways

Two Drosophila tumor necrosis factor receptor-associated factors (TRAF), DTRAF1 and DTRAF2, are proposed to have similar functions with their mammalian counterparts as a signal mediator of cell surface receptors. However, their in vivo functions and related signaling pathways are not fully understood yet. Here, we show that DTRAF1 is an in vivo regulator of c-Jun N-terminal kinase (JNK) pathway in Drosophila melanogaster. Ectopic expression of DTRAF1 in the developing eye induced apoptosis, thereby causing a rough-eye phenotype. Further genetic interaction analyses revealed that the apoptosis in the eye imaginal disc and the abnormal eye morphogenesis induced by DTRAF1 are dependent on JNK and its upstream kinases, Hep and DTAK1. In support of these results, DTRAF1-null mutant showed a remarkable reduction in JNK activity with an impaired development of imaginal discs and a defective formation of photosensory neuron arrays. In contrast, DTRAF2 was demonstrated as an upstream activator of nuclear factor-kappaB (NF-kappaB). Ectopic expression of DTRAF2 induced nuclear translocation of two Drosophila NF-kappaBs, DIF and Relish, consequently activating the transcription of the antimicrobial peptide genes diptericin, diptericin-like protein, and drosomycin. Consistently, the null mutant of DTRAF2 showed immune deficiencies in which NF-kappaB nuclear translocation and antimicrobial gene transcription against microbial infection were severely impaired. Collectively, our findings demonstrate that DTRAF1 and DTRAF2 play pivotal roles in Drosophila development and innate immunity by differentially regulating the JNK- and the NF-kappaB-dependent signaling pathway, respectively.

An autocrine/paracrine loop linking keratin 14 aggregates to tumor necrosis factor alpha-mediated cytotoxicity in a keratinocyte model of epidermolysis bullosa simplex

Epidermolysis bullosa simplex (EBS) is a blistering cutaneous disease featuring protein aggregates. Here we investigate the molecular mechanisms linking protein aggregates to cell death in a cellular model of EBS in which HaCaT keratinocytes are transfected with plasmids expressing various mutant forms of keratin 14 (K14). In HaCaT cells, mutant K14 was found to form ubiquitinated protein aggregates that suppressed 20 S proteasome function instead of being degraded by 20 S proteasome. Keratinocytes with mutant K14-induced phosphorylation of the stress-activated kinase c-Jun, as well as up-regulation of unfolding protein Bip, indicates induction of endoplasmic reticulum stress. HaCaT cells were susceptible to apoptosis by activation of caspases-3, and -8, but not caspase-9 or -12. Tumor necrosis factor-alpha (TNFalpha) in the culture medium was increased in keratinocytes with mutant K14 compared with wild K14, and the addition of neutralizing anti-TNFalpha antibody to the culture medium rescued keratinocytes from cell death. Thus, TNFalpha release and the subsequent activation of the TNFalpha receptor by an autocrine/paracrine pathway links protein aggregates to cell death in this keratinocyte EBS cellular model. Furthermore, mutation in K14 reduced its affinity to TNFalpha receptor-associated death domain (TRADD), suggesting that the susceptibility of keratinocytes to caspase-8-mediated apoptosis is increased in mutated K14 because of impairment of the cytoprotective mechanism mediated by K14-TRADD interaction.

The molecular signature of mediastinal large B-cell lymphoma differs from that of other diffuse large B-cell lymphomas and shares features with classical Hodgkin lymphoma

Mediastinal large B-cell lymphoma (MLBCL) is a recently identified subtype of diffuse large B-cell lymphoma (DLBCL) that characteristically presents as localized tumors in young female patients. Although MLBCL has distinctive pathologic features, it clinically resembles the nodular sclerosis subtype of classical Hodgkin lymphoma (cHL). To elucidate the molecular features of MLBCL, we compared the gene expression profiles of newly diagnosed MLBCL and DLBCL and developed a classifier of these diseases. MLBCLs had low levels of expression of multiple components of the B-cell receptor signaling cascade, a profile resembling that of Reed-Sternberg cells of cHL. Like cHLs, MLBCLs also had high levels of expression of the interleukin-13 (IL-13) receptor and downstream effectors of IL-13 signaling (Janus kinase-2 [JAK2] and signal transducer and activator of transcription-1 [STAT1]), tumor necrosis factor (TNF) family members, and TNF receptor-associated factor-1 (TRAF1). Increased expression of STAT1 and TRAF1 in MLBCL was confirmed by immunohistochemistry. Given the TRAF1 expression and known link to nuclear factor-kappa B (NF- kappa B), MLBCLs were also evaluated for nuclear translocation of c-REL protein. In almost all cases, c-REL was localized to the nucleus, consistent with activation of the NF-kappa B pathway. These studies identify a molecular link between MLBCL and cHL and a shared survival pathway.

Enhanced expression of interleukin-1alpha and tumor necrosis factor receptor-associated protein 1 in ileal tissues of cattle infected with Mycobacterium avium subsp. paratuberculosis

Infection with Mycobacterium avium subsp. paratuberculosis is associated with high levels of morbidity, decreased production, and early culling in dairy cattle. Clinical symptoms of Johne's disease include persistent diarrhea, inappetence, and resultant weight loss due to chronic inflammation of the small intestine. Although the presence or absence of intestinal lesions cannot be used as a definitive indicator of M. avium subsp. paratuberculosis infection, most infected cattle exhibit significant changes to intestinal mucosa, with the focus of pathology surrounding the ileal cecal junction. Typical pathology of M. avium subsp. paratuberculosis infection includes inflammation, thickening of the lumenal wall, and hyperplasia in draining lymph nodes. To further understand the pathology of Johne's disease, we compared the gene expression profiles of ileal tissues from Johne's disease-positive (n = 6), and Johne's disease-negative (n = 5) Holstein cattle. Gene expression profiles were compared with a bovine total leukocyte (BOTL-3) cDNA microarray. Genes that were expressed at significantly higher levels (>1.5-fold; P < 0.05) in tissues from Johne's disease-infected animals relative to noninfected animals included those encoding tumor necrosis factor receptor-associated protein 1 (TRAF1), interleukin-1alpha (IL-1alpha), MCP-2, N-cadherin, and beta1 integrin (CD29). Dramatic upregulation of IL-1alpha (21.5-fold) and TRAF1 (27.5-fold) gene expression in tissues of Johne's disease-positive cows relative to tissues from control cows was confirmed by quantitative real-time PCR. Western blot analysis confirmed that IL-1alpha and TRAF1 mRNA levels resulted in increased protein expression in tissues of Johne's disease-positive cattle relative to tissues from control cattle. High levels of IL-1alpha can produce symptoms similar to those found in clinical Johne's disease. Taken together, the data presented in this report suggest that many outward symptoms of Johne's disease may be due to IL-1alpha toxicity. In addition, enhanced levels of TRAF1 could result in cells within the lesions of Johne's disease-positive cattle that are highly resistant to TNF-alpha-induced signaling.

Hydrogen peroxide signaling through tumor necrosis factor receptor 1 leads to selective activation of c-Jun N-terminal kinase

Binding of tumor necrosis factor-alpha (TNFalpha) to its receptor, TNF-R1, results in the activation of inhibitor of kappaB kinase (IKK) and c-Jun N-terminal kinase (JNK) pathways that are coordinately regulated and important in survival and death. We demonstrated previously that in response to hydrogen peroxide (H2O2), the ability of TNFalpha to activate IKK in mouse lung epithelial cells (C10) was inhibited and that H2O2 alone was sufficient to activate JNK and induce cell death. In the current study, we investigated the involvement of TNF-R1 in H2O2-induced JNK activation. In lung fibroblasts from TNF-R1-deficient mice the ability of H2O2 to activate JNK was inhibited compared with fibroblasts from control mice. Additionally, in C10 cells expressing a mutant form of TNF-R1, H2O2-induced JNK activation was also inhibited. Immunoprecipitation of TNF-R1 revealed that in response to H2O2, the adapter proteins, TRADD and TRAF2, and JNK were recruited to the receptor. However, expression of the adaptor protein RIP, which is essential for IKK activation by TNFalpha, was decreased in cells exposed to H2O2, and its chaperone Hsp90 was cleaved. Furthermore, data demonstrating that expression of TRAF2 was not affected by H2O2 and that overexpression of TRAF2 was sufficient to activate JNK provide an explanation for the inability of H2O2 to activate IKK and for the selective activation of JNK by H2O2. Our data demonstrate that oxidative stress interferes with IKK activation while promoting JNK signaling, creating a signaling imbalance that may favor apoptosis.

TRUSS, a novel tumor necrosis factor receptor 1 scaffolding protein that mediates activation of the transcription factor NF-kappaB

We describe the cloning and characterization of tumor necrosis factor receptor (TNF-R)-associated ubiquitous scaffolding and signaling protein (TRUSS), a novel TNF-R1-interacting protein of 90.7 kDa. TRUSS mRNA was ubiquitously expressed in mouse tissues but was enriched in heart, liver, and testis. Co-immunoprecipitation experiments showed that TRUSS was constitutively associated with unligated TNF-R1 and that the complex was relatively insensitive to stimulation with TNF-alpha. Deletion mutagenesis of TNF-R1 indicated that TRUSS interacts with both the membrane-proximal region and the death domain of TNF-R1. In addition, the N-terminal region of TRUSS (residues 1 to 440) contains sequences that permit association with the cytoplasmic domain of TNF-R1. Transient overexpression of TRUSS activated NF-kappaB and increased NF-kappaB activation in response to ligation of TNF-R1. In contrast, a COOH-terminal-deletion mutant of TRUSS (TRUSS(1-723)) was found to inhibit NF-kappaB activation by TNF-alpha. Co-precipitation and co-immunoprecipitation assays revealed that TRUSS can interact with TRADD, TRAF2, and components of the IKK complex. These findings suggest that TRUSS may serve as a scaffolding protein that interacts with TNF-R1 signaling proteins and may link TNF-R1 to the activation of IKK.

Death receptor activation complexes: it takes two to activate TNF receptor 1

The extrinsic pathway of apoptosis originates at the membrane and engages membrane death receptors. Tumor necrosis factor receptor 1 (TNF-R1) is a death receptor that transduces both the death and survival signals but the molecular mechanisms via which TNF-R1 mediates these signals remain poorly understood. Recently, it has been reported that the TNF-R1 transduces these signals via two signaling complexes. The first complex (complex I) is formed at the membrane by TNF-R1, TRADD, RIP, TRAF2 and c-IAP1, while the second complex (complex II), formed in the cytosol, predominantly contains FADD and pro-caspases 8/10 but lacks TNF-R1. Complex I is responsible for activating NF-kappaB and thus, the transduction of survival signals. Complex II, on the other hand, is reported to transduce the apoptotic signals and it does so only if NF-kappaB is unable to promote upregulation of the anti-apoptotic FLIPL. These findings highlighting the complexities of TNF-R1-mediated signaling events are likely to further the progress in the constantly evolving area of death receptor-dependent signaling pathways.

Death receptor-induced activation of initiator caspase 8 is antagonized by serine/threonine kinase PAK4

Normal cell growth requires a precisely controlled balance between cell death and survival. This involves activation of different types of intracellular signaling cascades within the cell. While some types of signaling proteins regulate apoptosis, or programmed cell death, other proteins within the cell can promote survival. The serine/threonine kinase PAK4 can protect cells from apoptosis in response to several different types of stimuli. As is the case for other members of the p21-activated kinase (PAK) family, one way that PAK4 may promote cell survival is by phosphorylating and thereby inhibiting the proapoptotic protein Bad. This leads in turn to the inhibition of effector caspases such as caspase 3. Here we show that in response to cytokines which activate death domain-containing receptors, such as the tumor necrosis factor and Fas receptors, PAK4 can inhibit the death signal by a different mechanism. Under these conditions, PAK4 inhibits apoptosis early in the caspase cascade, antagonizing the activation of initiator caspase 8. This inhibition, which does not require PAK4's kinase activity, may involve inhibition of caspase 8 recruitment to the death domain receptors. This role in regulating initiator caspases is an entirely novel role for the PAK proteins and suggests a new mechanism by which these proteins promote cell survival.

Inositol 1,3,4-trisphosphate 5/6-kinase inhibits tumor necrosis factor-induced apoptosis

Tumor necrosis factor receptor 1 (TNF-R1) signaling elicits a wide range of biological responses, including inflammation, proliferation, differentiation, and apoptosis. TNF-R1 activates both caspase-mediated apoptosis and NF-kappaB transcription of anti-apoptotic factors. We now report a link between the TNF-R1 and inositol phosphate signaling pathways. We observed that overexpression of inositol 1,3,4-trisphosphate 5/6-kinase (5/6-kinase) inhibited apoptosis induced by TNFalpha. The anti-apoptotic effect by 5/6-kinase is not attributable to NF-kappaB activation, as no changes were detected in the levels of NF-kappaB DNA binding, IkappaBalpha degradation, or anti-apoptotic factors, such as x-linked inhibitor of apoptosis protein. Decreased expression of 5/6-kinase by RNA interference rendered HeLa cells more susceptible to TNFalpha-induced apoptosis. Overexpression of 5/6-kinase in human embryonic kidney 293 cells inhibited TNFalpha-induced activation of caspases-8, -3, and -9, BID, and poly(ADP-ribose) polymerase. However, 5/6-kinase did not protect against Fas-, etoposide-, or cycloheximide-induced apoptosis. Further, 5/6-kinase protected against apoptosis induced by the overexpression of TNF-R1-associated death domain but not Fas-associated death domain. Therefore, we suggest that 5/6-kinase modifies TNFalpha-induced apoptosis by interfering with the activation of TNF-R1-associated death domain.

Phosphorylation of tumor necrosis factor receptor 1 (p55) protects macrophages from silica-induced apoptosis

Macrophages play a fundamental role in silicosis in part by removing silica particles and producing inflammatory mediators in response to silica. Tumor necrosis factor alpha (TNFalpha) is a prominent mediator in silicosis. Silica induction of apoptosis in macrophages might be mediated by TNFalpha. However, TNFalpha also activates signal transduction pathways (NF-kappaB and AP-1) that rescue cells from apoptosis. Therefore, we studied the TNFalpha-mediated mechanisms that confer macrophage protection against the pro-apoptotic effects of silica. We will show that exposure to silica induced TNFalpha production by RAW 264.7 cells, but not by IC-21. Silica-induced activation of NF-kappaB and AP-1 was only observed in RAW 264.7 macrophages. ERK activation in response to silica exposure was only observed in RAW 264.7 macrophages, whereas activation of p38 phosphorylation was predominantly observed in IC-21 macrophages. No changes in JNK activity were observed in either cell line in response to silica exposure. Silica induced apoptosis in both macrophage cell lines, but the induction of apoptosis was significantly larger in IC-21 cells. Protection against apoptosis in RAW 264.7 cells in response to silica was mediated by enhanced NF-kappaB activation and ERK-mediated phosphorylation of the p55 TNFalpha receptor. Inhibition of these two protective mechanisms by specific pharmacological inhibitors or transfection of dominant negative mutants that inhibit IkappaBalpha or ERK phosphorylation significantly increased silica-induced apoptosis in RAW 264.7 macrophages. These data suggest that NF-kappaB activation and ERK-mediated phosphorylation of the p55 TNF receptor are important cell survival mechanisms in the macrophage response to silica exposure.

Latent Membrane Protein 1, Tumor Necrosis Factor Receptor–Associated Factor (TRAF) 1, TRAF-2, TRAF-3, and Nuclear Factor Kappa B Expression in Posttransplantation Lymphoproliferative Disorders

Context.—Most posttransplantation lymphoproliferative disorders (PTLDs) are associated with Epstein-Barr virus (EBV) infection. The EBV latent membrane protein 1 (LMP-1) is important in the transformation of B lymphocytes through its interaction with intracellular tumor necrosis factor receptor–associated factors (TRAFs) that, in turn, can activate transcription factors such as nuclear factor kappa B (NFκB) and Jun-N-kinase. Of the 6 members of the TRAF family, TRAF-1, TRAF-2, and TRAF-3 are most commonly associated with LMP-1. Recently, it has been suggested that LMP-1–induced TRAF activation is important in the pathogenesis of PTLDs.

Objective.—To characterize the expression patterns of these proteins in PTLDs, we studied a series of well-characterized cases for expression of LMP-1, TRAF-1, TRAF-2, TRAF-3, and NFκB by immunohistochemical analysis.

Methods.—A total of 27 specimens from 25 patients were analyzed for LMP-1, TRAF-1, TRAF-2, TRAF-3, and NFκB (active form) by immunohistochemical analysis. Expression of EBV-encoded RNA (EBER) was evaluated by in situ hybridization. Correlation between the expression of the different markers was performed using the Mantel-Haenszel χ2 test. Cox proportional hazards analysis and Kaplan-Meier analysis with log-rank testing were used to analyze antigen expression and clinical outcome.

Results.—Ninety-six percent of PTLDs expressed NFκB, 74% to 84% expressed TRAFs, 78% expressed EBER, and 77% expressed LMP-1. TRAF-1, TRAF-2, and TRAF-3 expression did not correlate with either EBER or LMP-1 expression. TRAF-2, but not TRAF-1 or TRAF-3, expression correlated with NFκB expression (P = .02).

Conclusions.—These results suggest that TRAF molecules and active NFκB are expressed in PTLDs regardless of EBV positivity. Given the association of TRAF-2 and active NFκB expression, TRAF-2 may play an important role in regulating this transcription factor in PTLD.

Murine cytomegalovirus infection inhibits tumor necrosis factor alpha responses in primary macrophages

Despite robust host immune responses the betaherpesvirus murine cytomegalovirus (MCMV) is able to establish lifelong infection. This capacity is due at least in part to the virus utilizing multiple immune evasion mechanisms to blunt host responses. Macrophages are an important cell for MCMV infection, dissemination, and latency despite expression in the host of multiple cytokines, including tumor necrosis factor alpha (TNF-alpha), that can induce an antiviral state in macrophages or other cells. In this study, we found that MCMV infection of bone marrow-derived macrophages inhibited TNF-alpha-induced ICAM-1 surface expression and mRNA expression in infected cells via expression of immediate early and/or early viral genes. MCMV infection blocked TNF-alpha-induced nuclear translocation of NF-kappaB. This inhibition of TNF-alpha signaling was explained by a decrease in TNF receptor 1 (TNFR1) and TNFR2 that was due to decreased mRNA for the latter. These findings provide a mechanism by which MCMV can evade the effects of an important host cytokine in macrophages.

1Hepatitis C virus NS5A protein modulates c-Jun N-terminal kinase through interaction with tumor necrosis factor receptor-associated factor 2

The nonstructural 5A (NS5A) protein of hepatitis C virus (HCV) is a phosphoprotein possessing various functions. We have previously reported that the HCV NS5A protein interacts with tumor necrosis factor (TNF) receptor-associated factor (TRAF) domain of TRAF2 (Park, K.-J., Choi, S.-H., Lee, S. Y., Hwang, S. B., and Lai, M. M. C. (2002) J. Biol. Chem. 277, 13122-13128). Both TNF-alpha- and TRAF2-mediated nuclear factor-kappaB (NF-kappaB) activations were inhibited by NS5A-TRAF2 interaction. Because TRAF2 is required for the activation of both NF-kappaB and c-Jun N-terminal kinase (JNK), we investigated HCV NS5A protein for its potential capacity to modulate TRAF2-mediated JNK activity. Using in vitro kinase assay, we have found that NS5A protein synergistically activated both TNF-alpha- and TRAF2-mediated JNK in human embryonic kidney 293T cells. Furthermore, synergism of NS5A-mediated JNK activation was inhibited by dominant-negative form of MEK kinase 1. Our in vivo binding data show that NS5A does not inhibit interaction between TNF receptor-associated death domain and TRAF2 protein, indicating that NS5A and TRAF2 may form a ternary complex with TNF receptor-associated death domain. These results indicate that HCV NS5A protein modulates TNF signaling of the host cells and may play a role in HCV pathogenesis.

Caspase-mediated cleavage converts the tumor necrosis factor (TNF) receptor-associated factor (TRAF)-1 from a selective modulator of TNF receptor signaling to a general inhibitor of NF-kappaB activation

The role of tumor necrosis factor (TNF) receptor-associated factor (TRAF)-1 in NF-kappaB activation by various members of the TNF receptor family is not well understood, and conflicting data have been published. Here, we show that TRAF1 differentially affects TRAF2 recruitment and activation of NF-kappaB by members of the TNF receptor family. Interestingly, a naturally occurring caspase-derived cleavage product of TRAF1 solely comprising its TRAF domain (TRAF1-(164-416)) acted as a general inhibitor of NF-kappaB activation. In contrast, a corresponding fragment generated by cleavage of TRAF3 showed no effect in this regard. In accordance with these functional data, TRAF1, but not TRAF3, interacted with the IKK complex via its N-TRAF domain. Endogenous TRAF1 and the overexpressed TRAF domain of TRAF1 were found to be constitutively associated with the IKK complex, whereas endogenous receptor interacting protein was only transiently associated with the IKK complex upon TNF stimulation. Importantly, the caspase-generated TRAF1-fragment, but not TRAF1 itself inhibited IKK activation. Our results suggest that TRAF1 and TRAF1-(164-416) exert their regulatory effects on receptor-induced NF-kappaB activation not only by modulation of TRAF2 receptor interaction but especially TRAF1-(164-416) also by directly targeting the IKK complex.

Induction of TNF receptor I-mediated apoptosis via two sequential signaling complexes

Apoptosis induced by TNF-receptor I (TNFR1) is thought to proceed via recruitment of the adaptor FADD and caspase-8 to the receptor complex. TNFR1 signaling is also known to activate the transcription factor NF-kappa B and promote survival. The mechanism by which this decision between cell death and survival is arbitrated is not clear. We report that TNFR1-induced apoptosis involves two sequential signaling complexes. The initial plasma membrane bound complex (complex I) consists of TNFR1, the adaptor TRADD, the kinase RIP1, and TRAF2 and rapidly signals activation of NF-kappa B. In a second step, TRADD and RIP1 associate with FADD and caspase-8, forming a cytoplasmic complex (complex II). When NF-kappa B is activated by complex I, complex II harbors the caspase-8 inhibitor FLIP(L) and the cell survives. Thus, TNFR1-mediated-signal transduction includes a checkpoint, resulting in cell death (via complex II) in instances where the initial signal (via complex I, NF-kappa B) fails to be activated.

The TNF receptor 1: a split personality complex

The tumor necrosis factor receptor 1 (TNFR1), a prototypic member of the death receptor family signals both cell survival and apoptosis. In this issue of Cell, report that apoptotic TNFR1 signaling proceeds via the sequential formation of two distinct complexes. Since the first complex can activate survival signals and influence the activity of the second complex, this mechanism provides a checkpoint to control the execution of apoptosis.

Fas-associated death domain protein and caspase-8 are not recruited to the tumor necrosis factor receptor 1 signaling complex during tumor necrosis factor-induced apoptosis

Death receptors are a subfamily of the tumor necrosis factor (TNF) receptor subfamily. They are characterized by a death domain (DD) motif within their intracellular domain, which is required for the induction of apoptosis. Fas-associated death domain protein (FADD) is reported to be the universal adaptor used by death receptors to recruit and activate the initiator caspase-8. CD95, TNF-related apoptosis-inducing ligand (TRAIL-R1), and TRAIL-R2 bind FADD directly, whereas recruitment to TNF-R1 is indirect through another adaptor TNF receptor-associated death domain protein (TRADD). TRADD also binds two other adaptors receptor-interacting protein (RIP) and TNF-receptor-associated factor 2 (TRAF2), which are required for TNF-induced NF-kappaB and c-Jun N-terminal kinase activation, respectively. Analysis of the native TNF signaling complex revealed the recruitment of RIP, TRADD, and TRAF2 but not FADD or caspase-8. TNF failed to induce apoptosis in FADD- and caspase-8-deficient Jurkat cells, indicating that these apoptotic mediators were required for TNF-induced apoptosis. In an in vitro binding assay, the intracellular domain of TNF-R1 bound TRADD, RIP, and TRAF2 but did not bind FADD or caspase-8. Under the same conditions, the intracellular domain of both CD95 and TRAIL-R2 bound both FADD and caspase-8. Taken together these results suggest that apoptosis signaling by TNF is distinct from that induced by CD95 and TRAIL. Although caspase-8 and FADD are obligatory for TNF-mediated apoptosis, they are not recruited to a TNF-induced membrane-bound receptor signaling complex as occurs during CD95 or TRAIL signaling, but instead must be activated elsewhere within the cell.

Epstein-Barr virus encoded latent membrane protein 1 induces TRAF1 expression to promote anti-apoptosis activity via NF-kappaB signaling pathway in nasopharyngeal carcinoma

OBJECTIVES

To identify whether Epstein-Barr virus (EBV) encoded latent membrane protein 1 (LMP1) can induce tumor necrosis factor receptor-associated factor 1 (TRAF1) expression and promote its anti-apoptosis activity via the NF-kappaB signaling pathway, and assess that LMP1 suppresses apoptosis in nasopharyngeal carcinoma (NPC).

METHODS

A stable transfected cell line HNE2-LMP1 was established by introducing LMP1 cDNA into HNE2 cells. Transactivation of TRAF1 was determined by luciferase reporter assay, while expression of TRAF1 mRNA was detected by RT-PCR and expression of TRAF1 protein and caspase 3 by Western blot analysis. Apoptosis activity was observed through fluorescence staining.

RESULTS

LMP1 induced TRAF1 expression in NPC cells and caused a decrease in apoptosis. This induction could be blocked by antisense LMP1. Moreover, LMP1-mediated induction of a TRAF1 promoter-driven reporter gene was significantly impaired when the kappaB site kappaB1 or kappaB5 was disrupted, whereas mutation of kappaB3 had only a minor effect on LMP1 dependent up-regulation of the reporter gene.

CONCLUSION

LMP1 induces TRAF1 expression and promotes its anti-apoptosis activity via the NF-kappaB signaling pathway, which may be one of the mechanisms that LMP1 uses to suppress apoptosis in NPC cells.

Angiotensin-converting enzyme inhibition induces death receptor apoptotic pathways in erythroid precursors following renal transplantation

BACKGROUND

Posttransplant erythrocytosis (PTE) is a condition that occurs in kidney transplant patients and is characterized by increase in hematocrit above 51%. While its pathogenesis remains unclear, angiotensin-converting enzyme inhibitors (ACEI) have been used successfully in the treatment of PTE. We have previously shown that ACEI induce apoptosis in the peripheral erythroid precursors from patients with PTE. In the current study we elucidate the molecular mechanisms of ACEI-induced apoptosis.

METHODS

Peripheral CD34+ cells were obtained from four normal controls, five normal kidney transplants, and six kidney transplants with PTE, before and after treatment with ACEI. We evaluated the expression of a variety of apoptotic factors by quantitative reverse transcription-multiplex polymerase chain reaction, Western blot and immunocytochemistry.

RESULTS

ACEI resulted in a significant induction of Fas, FADD, and TRADD mRNAs in renal transplant patients with or without PTE. No changes were noted in the expression of mRNAs encoding Bcl-2, Bcl-xL, Bax, caspase 8, caspase 3, or GAPDH. ACEI also resulted in a significant upregulation of Fas, FADD and TRADD protein expression, and their localization predominantly at the plasma membrane.

CONCLUSIONS

Our results suggest that ACEI therapy induces apoptosis in erythrocyte progenitor cells of renal transplant patients at least in part via induction of death receptor apoptotic cascades.

Expression of TNF receptors and related signaling molecules in the bone marrow from patients with myelodysplastic syndromes

Myelodysplastic syndromes (MDS) are characterized by peripheral blood cytopenias despite hypercellularity of the bone marrow regarded as the result of ineffective hematopoiesis mainly caused by apoptosis. In this study, we examined the role of tumor necrosis factor (TNF)-induced apoptosis in the bone marrow cells of MDS patients. The constitutive expression of mRNA for TNF receptors (TNFR), including TNFRI and TNFRII, and the adapter molecules, such as the TNF receptor-associated death domain protein (TRADD), Fas-associated death domain protein (FADD), receptor interacting protein (RIP) and TNF receptor-associated factor 2 (TRAF-2) were analyzed by reverse transcriptase (RT)-PCR in bone marrow samples from control, MDS and AML cases. In bone marrow cells from refractory anemia (RA) patients, there was a significant increase in TNFRI expression as compared with control subjects. The expression of TNFRII was also up-regulated in RA cases. In contrast, RA with excess of blasts (RAEB), RAEB in transformation (RAEB-T) and AML cases revealed increased expression of TNFRII, whereas the expression of TNFRI was comparable to control subjects. Immunohistochemical staining revealed that the TNFRI, as well as TNFRII of MDS bone marrow was expressed mainly in hematopoietic cells, but not in macrophage-lineage stromal cells at the protein level. An increased constitutive expression of mRNA for TRADD, FADD and RIP and decreased expression of mRNA for TRAF-2 were observed in bone marrow cells from MDS patients, especially from RA patients, as compared with controls, although the differences were not significant. In many of the AML bone marrow samples, strong expression of TRAF-2 mRNA was marked, while expression levels of other proteins were similar to those in control subjects. These data suggested enhanced signaling by the TNFRI-TRADD-FADD pathway and suppressed signaling by the TRAF-2 pathway in RA. Thus, TNF-alpha-induced apoptosis may play a role in ineffective hematopoiesis in "early stage MDS" bone marrow, although the regulatory mechanisms for TNF-alpha-induced signaling would be complicated and not be simply explained only by these pathways.

Differential expression and function of A20 and TRAF1 in Hodgkin lymphoma and anaplastic large cell lymphoma and their induction by CD30 stimulation

A20 and TRAF1 are two anti-apoptotic components of the intracellular signalling pathway of the tumour necrosis factor receptor (TNFR) family. Induction of apoptosis seems to be a main function of these receptors. It is astonishing that a member of this family, CD30, is overexpressed by highly proliferating tumours such as Hodgkin lymphoma (HL) and anaplastic large cell lymphoma (ALCL). It is known that CD30 stimulation leads to the apoptosis of ALCL tumour cells but not of Hodgkin-Reed-Sternberg (HRS) cells. We have already established the overexpression of TRAF1 in HRS cells. In this study we demonstrate that A20 is highly expressed in the HRS cells in 20/22 of cases of classical HL, in 4/4 cases of nodular lymphocyte-predominant HL (NLPHL), and in 2/2 cases of the anaplastic variant of diffuse large B cell lymphoma. In contrast, all other non-Hodgkin lymphomas, including ALCL, revealed either no A20 reactivity, or reactivity in less than 1% of all tumour cells. CD30 stimulation induced A20 and TRAF1 expression. This effect was most prominent in HL and ALCL cell lines with low basal expression levels of these molecules. Immunohistological studies of reactive lymphoid blasts in tonsillar tissue demonstrated that co-expression of CD30, A20, and TRAF1 also occurs in vivo. Cell lines with high basal A20 and TRAF1 expression were resistant to CD30-mediated apoptosis. The sensitivity to CD30-induced apoptosis was increased by inhibition of protein synthesis. TRAF1 transfection decreased CD30-induced apoptosis. Our data suggest that A20 and TRAF1 contribute to apoptosis resistance and, therefore, play an important role in the pathogenesis of classical HL.

Epstein-Barr virus encoded latent membrane protein 1 (LMP1) and TNF receptor associated factors (TRAF): colocalisation of LMP1 and TRAF1 in primary EBV infection and in EBV associated Hodgkin lymphoma

AIMS

Epstein-Barr virus (EBV) immortalises B cells in vitro and is associated with several malignancies. Most phenotypic effects of EBV are mediated by latent membrane protein 1 (LMP1), which interacts with tumour necrosis factor receptor associated factors (TRAFs) to activate NF-kappaB. This study examines TRAF1 and LMP1 expression in EBV associated lymphoproliferations.

METHODS

TRAF1 expression was investigated in 26 Hodgkin lymphomas (HL; 18 EBV+, eight EBV-), seven EBV+ Burkitt lymphomas (BL), two infectious mononucleosis (IM) tonsils, and lymphoreticular tissue from eight chronic virus carriers. Seven anaplastic large cell lymphomas and 10 follicular B cell lymphomas were also studied. Colocalisation of TRAF1 and LMP1 was studied by immunofluorescent double labelling and confocal laser microscopy.

RESULTS

TRAF1 colocalises with LMP1 in EBV infected cells in IM. EBV positive lymphocytes from chronic virus carriers were negative for TRAF1 and LMP1. In HL biopsies, TRAF1 was strongly expressed independently of EBV status, whereas all BL cases were TRAF1-. In EBV+ HL cases, TRAF1 colocalised with LMP1. Eight of 10 follicular lymphomas expressed TRAF1 in centroblast-like cells. Four of seven anaplastic large cell lymphomas weakly expressed TRAF1.

CONCLUSIONS

These results suggest that in non-neoplastic lymphocytes, TRAF1 expression is dependent on the presence of LMP1, and that in IM B cells in vivo, LMP1 associated signalling pathways are active. In HL, TRAF1 is expressed independently of EBV status, probably because of constitutive NF-kappaB activation. The function of TRAF1 in HL remains to be determined.

The signaling adaptors and pathways activated by TNF superfamily

Members of the TNF receptor superfamily play pivotal roles in numerous biological events in metazoan organisms. Ligand-mediated trimerization by corresponding homo- or heterotrimeric ligands, the TNF family ligands, causes recruitment of several intracellular adaptors, which activate multiple signal transduction pathways. While recruitment of death domain (DD) containing adaptors such as Fas associated death domain (FADD) and TNFR associated DD (TRADD) can lead to the activation of a signal transduction pathway that induces apoptosis, recruitment of TRAF family proteins can lead to the activation of transcription factors such as, NF-kappaB and JNK thereby promoting cell survival and differentiation as well as immune and inflammatory responses. Individual TNF receptors are expressed in different cell types and have a range of affinities for various intracellular adaptors, which provide tremendous signaling and biological specificities. In addition, numerous signaling modulators are involved in regulating activities of signal transduction pathways downstream of receptors in this superfamily. Most of the TNF receptor superfamily members as well as many of their signaling mediators, have been uncovered in the last two decades. However, much remains unknown about how individual signal transduction pathways are regulated upon activation by any particular TNF receptor, under physiological conditions.

Tumor necrosis factor receptor-associated death domain protein is involved in the neurotrophin receptor-mediated antiapoptotic activity of nerve growth factor in breast cancer cells

The common neurotrophin receptor p75(NTR) has been shown to initiate intracellular signaling that leads either to cell survival or to apoptosis depending on the cell type examined; however, the mechanism by which p75(NTR) initiates its intracellular transduction remains unclear. We show here that the tumor necrosis factor receptor-associated death domain protein (TRADD) interacts with p75(NTR) upon nerve growth factor (NGF) stimulation. TRADD could be immunodetected after p75(NTR) immunoprecipitation from MCF-7 breast cancer cells stimulated by nerve growth factor. In addition, confocal microscopy indicated that NGF stimulation induced the plasma membrane localization of TRADD. Using a dominant negative form of TRADD, we also show that interactions between p75(NTR) and TRADD are dependent on the death domain of TRADD, thus demonstrating its requirement for binding. Furthermore, the p75(NTR)-mediated activation of NF-kappaB was inhibited by transfection with a dominant negative TRADD, resulting in an inhibition of NGF antiapoptotic activity. These results thus demonstrate that TRADD is involved in the p75(NTR)-mediated antiapoptotic activity of NGF in breast cancer cells.

Expression of TNF-receptor-associated factor genes in murine tooth development

Tumor necrosis factor receptor-associated factors (TRAFs) belong to a family of intracellular adaptor proteins that mediate signaling downstream of various cell surface receptors. We carried out comparative in situ hybridization analysis of five Traf genes Traf1, Traf2, Traf3, Traf4 and Traf6 during murine odontogenesis from the formation of the epithelial thickening to the early bell stage. Traf2, Traf3 and Traf6 showed weak expression in the thickened epithelium. Expression of Traf1, Traf2 and Traf6 were observed in the outer edges of the bud epithelium whereas Traf3 was strongly expressed at the tip of the bud epithelium. Expression of Traf1, Traf4 and Traf6 were detected in the dental papilla mesenchyme. Traf2 showed restricted expression in the internal enamel epithelium of the bell stage while expression of Traf1, Traf3, Traf4 and Traf6 were observed in both the internal and the external enamel epithelium. During early odontogenesis, all five genes show dynamic spatiotemporal expression patterns.

Cloning and characterization of cDNAs for two distinct tumor necrosis factor receptor superfamily genes from Japanese flounder Paralichthys olivaceus

Tumor necrosis factor receptor (TNFR) superfamily regulates diverse biologic functions, including cell proliferation, differentiation, and survival, in addition to providing costimulatory signals for programmed cell death or apoptosis. In this study, cDNA fragments for two distinct TNFR homologues were obtained from a Japanese flounder, Paralichthys olivaceus, cDNA library. Full-length cDNAs of TNFR-1 and TNFR-2 homologues were obtained by using these cDNA fragments as probes. The cDNA for the Japanese flounder TNFR-1 homologue predicts a peptide of 395 amino acids that is 35% identical to the extracellular region of mouse TNFR-1, whereas the cDNA of the Japanese flounder TNFR-2 homologue predicts a peptide of 483 amino acids that is 40% identical to the extracellular region of human TNFR-2. The cytoplasmic domain contains a sequence that has the consensus motif of the death domain of the Japanese flounder TNFR-1 homologue. In a healthy fish, the mRNAs of both TNFR homologues were predominantly expressed in leukocytes, kidney, gill, and spleen. Expression of the Japanese flounder TNFR-1 homologue was induced in peripheral blood lymphocytes (PBLs) after stimulation with LPS (500 microg/ml) for 1 h, and TNFR-2 homologue was strongly induced in PBLs after stimulation with Con A (50 microg/ml) and PMA (0.35 microg/ml) for 3 h. The different expression patterns of the two distinct TNFR homologues may be critical in determining whether binding with TNF-alpha or TNF-beta have activating, proliferative, or apoptotic effects on target cells.

The Fn14 cytoplasmic tail binds tumour-necrosis-factor-receptor-associated factors 1, 2, 3 and 5 and mediates nuclear factor-kappaB activation

Fn14 is a growth-factor-inducible immediate-early-response gene encoding a 102-amino-acid type I transmembrane protein. The human Fn14 protein was recently identified as a cell-surface receptor for the tumour necrosis factor (TNF) superfamily member named TWEAK (TNF-like weak inducer of apoptosis). In the present paper, we report that the human TWEAK extracellular domain can also bind the murine Fn14 protein. Furthermore, site-specific mutagenesis and directed yeast two-hybrid interaction assays revealed that the TNFR-associated factor (TRAF) 1, 2, 3 and 5 adaptor molecules bind the murine Fn14 cytoplasmic tail at an overlapping, but non-identical, amino acid sequence motif. We also found that TWEAK treatment of quiescent NIH 3T3 cells stimulates inhibitory kappaBalpha phosphorylation and transcriptional activation of a nuclear factor-kappaB (NF-kappaB) enhancer/luciferase reporter construct. Fn14 overexpression in transiently transfected NIH 3T3 cells also promotes NF-kappaB activation, and this cellular response requires an intact TRAF binding site. These results indicate that Fn14 is a functional TWEAK receptor that can associate with four distinct TRAF family members and stimulate the NF-kappaB transcription factor signalling pathway.

IL-12 plays a significant role in the apoptosis of human T cells in the absence of antigenic stimulation

Interleukin-12 (IL-12) is an immunoregulatory cytokine that plays an essential role in cell-mediated immunity. It is known to induce T cell apoptosis in in vivo systems such as graft-versus-host disease (GVHD) and experimental autoimmune uveitis (EAU). However, the role of IL-12 in T cell apoptosis in the absence of antigenic stimulation has not been clearly defined. This study was conducted to investigate whether IL-12, in the absence of an antigen, is able to induce T cell apoptosis, and also, which signalling pathways utilized by IL-12 are involved in this process. Our data clearly showed that IL-12 in the absence of an antigen induces apoptosis in T cells. Flow cytometry and ELISA showed FasL up-regulation and increased IFN-gamma synthesis in IL-12 treated T cells, while Fas and TNF-R1 showed little change. Semi-quantitative RT-PCR demonstrated that IL-12 was able to up-regulate TNF-alpha and FasL mRNA expression. Furthermore, IL-12 induced apoptosis was associated with caspase-3, caspase-2, caspase-7, DNA fragmentation factor 45 (DFF45) and Fas associated death domain (FADD) whereas TNF receptor associated death domain (TRADD) and receptor interacting protein (RIP) were not. Inhibition of Janus tyrosine kinase (JAK) was able to suppress IL-12 induced T cell apoptosis. Anti-FasL antibody was able to block IL-12 induced T cell apoptosis. In conclusion, our findings suggest that IL-12 is able to induce T cell apoptosis in the absence of an antigen. In addition, the present data suggest that this process is FasL mediated and caspase-3 dependent. Furthermore, JAK was shown to be involved in this process. These results may have significant implications in the understanding of IL-12 mediated T cell apoptosis.

The induction of the TNFalpha death domain signaling pathway in Alzheimer's disease brain

The tumor necrosis factor-alpha death domain pathway contributes to cellular degeneration in a variety of conditions. This study investigates the hypothesis that this death domain pathway is progressively induced in the brain during the progression of Alzheimer's disease (AD). AD cases had increased levels of proapoptotic markers including tumor necrosis factor-alpha (TNFalpha), TNF receptor type 1 (TNF-R1), TNF receptor-associated death domain (TRADD), and caspase-3, 2- to 10-fold higher (P < .01) than age-matched controls and 1 to 3 times higher than transitional cases. In striking contrast, potentially neuroprotective TNF receptor type 2 (TNF-R2), and Fas-associated death domain-like interleukin-1beta-converting enzyme (FLICE) inhibitor protein (FLIP) were decreased in AD as compared with age-matched control cases (P < .01). Overall, there was an elevation in proapoptotic elements, including a 5-fold increase in TNF-R1 and a 12-fold decrease in FLIP in AD brains. These changes may translate to increased degenerative potential because the downstream effector caspase-3 and product of the TNF pathway was also increased in parallel with enhanced TNF proapoptotic conditions. Our findings suggest that the TNF death receptor pathway and caspases are activated in the early stages of neuronal degeneration in AD.

Apoptosis and TRAF-1 cleavage in Epstein-Barr virus-positive nasopharyngeal carcinoma cells treated with doxorubicin combined with a farnesyl-transferase inhibitor

Epstein-Barr virus (EBV)-associated nasopharyngeal carcinomas (NPC) are much more sensitive to chemotherapy than other head and neck carcinomas. Spectacular regressions are frequently observed after induction chemotherapy. However, these favorable responses are difficult to predict and often of short duration. So far there have been only few experiments to investigate the mechanisms which underline the cytotoxic effects of anti-neoplastic drugs against NPC cells. In addition, these studies were performed almost entirely on EBV-negative cell lines therefore not truly representative of NPC cells. For the first time, we have used two EBV-positive NPC tumor lines derived from a North African (C15) and a Chinese (C666-1) patient as in vitro targets for a panel of anti-neoplastic agents. Doxorubicin, taxol and in a lesser extent cis-platinum efficiently inhibited NPC cell proliferation at clinically relevant concentrations, but all three agents failed to induce apoptosis. However, massive apoptosis of C15 cells was achieved when doxorubicin (1 microM) was combined with a farnesyl-transferase inhibitor, BIM 2001 (5 microM). Moreover, this apoptotic process was associated with a caspase-dependent early cleavage of the TNF-receptor associated factor 1 (TRAF-1) molecule, a signaling adaptor which is specifically expressed in latently EBV-infected cells. TRAF-1 cleavage might become a useful indicator of chemo-induced apoptosis in EBV-associated NPCs.

Functional relevance of soluble TNF-alpha, transmembrane TNF-alpha and TNF-signal transduction in gastrointestinal diseases with special reference to inflammatory bowel diseases

As a result of extensive clinical and basic research, the pivotal role of tumour necrosis factor (TNF) in the pathogenesis of chronic inflammatory diseases such as inflammatory bowel disease (IBD) has now generally been acknowledged. This has led to promising clinically effective anti-TNF-strategies. Of note, there is more and more evidence that TNF seems to play a key role in other gastrointestinal diseases including Helicobacter pylori infection, pancreatitis, viral hepatitis and toxic liver damage, too. The action of TNF at the cellular level is mediated by two cell surface receptors, TNF-R1 (p60) and TNF-R2 (p80). The function of these receptors and the downstream intracellular signal transduction pathway have been extensively studied in vitro and it can be expected, that there are critically important steps in TNF-signal transduction that might be dysregulated in these disease states. Their elucidation could lead to a better understanding of the pathogenesis of these diseases, in particular IBD and potentially reveal new, more specific therapeutic targets. Objective of this review is to give an overview about the current knowledge on TNF signal transduction in relationship to selected examples of important gastrointestinal disorders with special focus on IBD. Finally, the implications for future research efforts will be discussed.