Involvement of CRAF1, a relative of TRAF, in CD40 signaling

Epstein-Barr virus (EBV)-related oral squamous cell carcinoma in Okinawa, a subtropical island, in southern Japan--simultaneously infected with human papillomavirus (HPV)

Up to now, many authors have reported on the EBV infection and its carcinogenic importance in undifferentiated nasopharyngeal carcinoma (WHO classification, type III), but the infection of the virus in well differentiated oral squamous cell carcinoma has not been well described. We introduce the EBV-related well differentiated oral squamous cell carcinomas in Okinawa, a subtropical island in the southernmost part of Japan. This study aimed to clarify the pathogenesis of this malignancy in this area by carrying out analysis of the histology and the Epstein-Barr (EBV) and human papillomavirus (HPV) infection. In the Department of Oral Surgery, Ryukyu University Hospital Okinawa, 188 cases of oral malignant tumours were encountered from 1996 to 2000. The histopathological examination and the sequence analysis of LMP-1 carboxy terminal region and EBNA2 region of EBV were carried out, as were the analysis of virus subtypes, A and B, BamHI-F and f, and C and D. Additionally, HPV infection in the squamous cell carcinomas were demonstrated using E6 and E7 region primer sets by PCR method. In Okinawa, 94% (177/188) of the cases were squamous cell carcinomas. A surprisingly large number of EBV (72%) and HPV (78%) infections in the oral squamous cell carcinomas were demonstrated. EBV type B virus infection was found in 36% of EBV-related oral squamous cell carcinoma in Okinawa, but in only 2-5% of the mainland cases. In both regions the incidence of the BamHI- f variant infection was very low. The infected virus in 79 out of 80 (39 Okinawan and 41 mainland) cases was BamHI- F type. In Okinawa, the numbers of C and D variants were almost equal, whereas in the mainland the D variant was rare. Further, a 30 bp deletion in LMP-1 gene was frequently demonstrated in Okinawan and mainland cases of type A virus, but not in type B virus. Lastly, single nucleotide mutations in EBNA2 region of type A virus when compared with B95-8 strain were demonstrated in Okinawan cases. The prognosis for (mostly EBV/HPV infected) squamous cell carcinomas in Okinawa was better than that in the mainland where most cases were negative for EBV and/or HPV.

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.

CD40-dependent activation of phosphatidylinositol 3-kinase/Akt pathway mediates endothelial cell survival and in vitro angiogenesis

CD40 has been involved in tumor and inflammatory neoangiogenesis. In this study we determined that stimulation of endothelial CD40 with sCD154 induced resistance to apoptosis and in vitro vessel-like formation by human microvascular endothelial cells (HMEC). These effects were determined to be mediated by CD40-dependent signaling because they were inhibited by a soluble CD40-muIg fusion protein. Moreover, apoptosis of HMEC was associated with an impairment of Akt phosphorylation, which was restored by stimulation with sCD154. The anti-apoptotic effect as well as in vitro vessel-like formation and Akt phosphorylation were inhibited by treatment of HMEC with two unrelated pharmacological inhibitors of phosphatidylinositol 3-kinase (PI3K), wortmannin and LY294002. CD40 stimulation induced a rapid increase in Akt enzymatic activity that was not prevented by cycloheximide, an inhibitor of protein synthesis. The enhanced Akt activity induced by stimulation of endothelial CD40 was temporarily correlated with the association of CD40 with TRAF6, c-Cbl, and the p85 subunit of PI3K. Expression of negative-dominant Akt inhibited the activation of endogenous Akt through CD40 stimulation, despite the observation that association of CD40 with TRAF6, c-Cbl, and PI3K was intact. The defective activation of Akt abrogated not only the anti-apoptotic effect of CD40 stimulation but also the proliferative response, the enhanced motility, and the in vitro formation of vessel-like tubular structures by CD40-stimulated HMEC. In conclusion, these results suggest that endothelial CD40, through activation of the PI3K/Akt signaling pathway, regulates cell survival, proliferation, migration, and vessel-like structure formation, all steps considered critical for angiogenesis.

Enhancement of B-MYB transcriptional activity by ZPR9, a novel zinc finger protein

By using the yeast two-hybrid system, the zinc finger protein ZPR9 was identified as one of the B-MYB interacting proteins that associates with the carboxyl-terminal conserved region of B-MYB. ZPR9 was found to form in vivo complexes with B-MYB, as demonstrated by in vivo binding assay and coimmunoprecipitation experiments of the endogenously and exogenously expressed proteins. Deletion analysis revealed that this binding was mediated by all three functional domains, an amino-terminal DNA-binding domain, a transactivation domain, and a carboxyl-terminal conserved region of B-MYB. We show that the interaction of ZPR9 with B-MYB is functional because cotransfection of ZPR9 significantly up-regulates B-MYB transcriptional activity in a dose-dependent manner. In addition, coexpression of ZPR9 with B-MYB caused the accumulation of B-MYB, as well as ZPR9, in the nucleus. Furthermore, constitutive expression of ZPR9 in human neuroblastoma cells induces apoptosis in the presence of retinoic acid. These results strongly suggest that ZPR9 plays an important role in modulation of the transactivation by B-MYB and cellular growth of neuroblastoma cells.

Hodgkin's lymphoma and CD30 signal transduction

Advances in molecular biology have shed light on the biological basis of Hodgkin's lymphoma (HL). Knowledge of the biological basis has enabled us to understand that most Hodgkin and Reed-Sternberg (H-RS) cells are derived from germinal center B-cells and constitutive nuclear factor kappaB (NF-kappaB) activation is a common molecular feature. Molecular mechanisms responsible for constitutive NF-kappaB activation, Epstein Barr virus latent membrane protein 1, and defective IkappaBalpha and IkappaB kinase activation have been clarified in the past several years. A recent study revealed the biological link between 2 characteristic features of H-RS cells: CD30 overexpression and constitutive NF-kappaB activation. Ligand-independent signaling by overexpressed CD3O was shown to be a common mechanism that induced constitutive NF-kappaB activation in these cells. These results suggest the self-growth-promoting potential of H-RS cells and redefine the biology of HL composed of H-RS cells and lymphocytes.

CD40 and its viral mimic, LMP1: similar means to different ends

CD40 is an important regulator of diverse aspects of the immune response including the T-cell-dependent humoral immune response, the development of antigen-presenting cells (APCs) and inflammation. Latent membrane protein 1 (LMP1), a protein encoded by Epstein-Barr Virus (EBV), appears to mimic CD40 in multiple ways. CD40 and LMP1 bind similar sets of cellular signalling proteins and activate overlapping signalling pathways. Despite many similarities shared between CD40 and LMP1, they also differ substantively. In this review, we will compare and contrast the signalling mediated by CD40 and LMP1.

TNFR-associated factor-3 is associated with BAFF-R and negatively regulates BAFF-R-mediated NF-kappa B activation and IL-10 production

TALL-1 is a member of the TNF family that is critically involved in B cell survival, maturation, and progression of lupus-like autoimmune diseases. TALL-1 has three receptors, including BCMA, TACI, and BAFF-R, which are mostly expressed by B lymphocytes. Gene knockout studies have indicated that BAFF-R is the major stimulatory receptor for TALL-1 signaling and is required for normal B cell development. The intracellular signaling mechanisms of BAFF-R are not known. In this report, we attempted to identify BAFF-R-associated downstream proteins by yeast two-hybrid screening. This effort identified TNFR-associated factor (TRAF)3 as a protein specifically interacting with BAFF-R in yeast two-hybrid assays. Coimmunoprecipitation experiments indicated that BAFF-R interacts with TRAF3 in B lymphoma cells and this interaction is stimulated by TALL-1 treatment. Domain mapping experiments indicated that both a 6-aa membrane proximal region and the C-terminal 35 aa of BAFF-R are required for its interaction with TRAF3. Moreover, overexpression of TRAF3 inhibits BAFF-R-mediated NF-kappaB activation and IL-10 production. Taken together, our findings suggest that TRAF3 is a negative regulator of BAFF-R-mediated NF-kappaB activation and IL-10 production.

Influence of omega-3 fatty acids on the growth of human colon carcinoma in nude mice

The present study investigated the influence of dietary omega-3 fatty acid supplementation on the growth of human colon carcinoma xenograft in athymic nude mice. Four diets were fed to evaluate the effect of levels and types of fat on colon tumor growth. Animals were maintained on a standard diet modified by addition of fats containing omega-3 and omega-6 fatty acids to represent high and low fat intakes for 53 days. The final mean estimated tumor weight for the high fat corn oil (24%) fed group was 2,302 mg, whereas the low fat (8% corn oil) group was 1,681 mg. The final mean tumor weight of the high fat menhaden oil fed group was 782 mg representing a 66% decrease in growth compared to the high fat corn oil group and a decrease of 54% compared to the low corn oil fed group. The high fat golden algae oil fed group resulted in a mean final tumor weight of 223 mg representing a 90% inhibition of tumor growth relative to the high fat corn oil fed group and 87% inhibition of growth compared to the low fat corn oil fed group. These findings indicate that dietary omega-3 fatty acids possess significant tumor suppressing properties and that the primary tumor suppressing fatty acid is docosahexaenoic acid. Histopathologic examination of control and treated tumors and expression array analyses (human cytokine and apoptosis arrays) support the tumor growth inhibition data and provide evidence for discussion of possible mechanisms for the observed growth inhibition.

The binding site for TRAF2 and TRAF3 but not for TRAF6 is essential for CD40-mediated immunoglobulin class switching

To define the role of TRAF proteins in CD40-dependent isotype switching in B cells, we introduced wild-type (WT) and mutant CD40 transgenes that lacked the binding motifs for TRAF6 (CD40deltaTRAF6), TRAF2 and TRAF3 (CD40deltaTRAF2/3), or both (CD40deltaTRAFs) into B cells of CD40(-/-) mice. The in vivo isotype switch defect in CD40(-/-) mice was fully corrected by WT and CD40deltaTRAF6, partially by CD40deltaTRAF2/3, and not at all by CD40deltaTRAFs transgenes. CD40-mediated isotype switching, proliferation, and activation of p38, JNK, and NFkappaB in B cells were normal in WT and CD40deltaTRAF6 mice, severely impaired in CD40deltaTRAF2/3, and absent in CD40deltaTRAFs mice. These results suggest that binding to TRAF2 and/or TRAF3 but not TRAF6 is essential for CD40 isotype switching and activation in B cells.

Infection of simian B lymphoblastoid cells with simian immunodeficiency virus is associated with upregulation of CD23 and CD40 cell surface markers

Simian immunodeficiency virus (SIV) as well as human immunodeficiency virus (HIV) induce polyclonal B-cell activation and are associated with the appearance of lymphomas in their respective hosts in either the presence or the absence of other co-infecting viruses such as Epstein-Barr virus (EBV). However, the pathogenic role of these retroviruses in the development of lymphoproliferative disorders remains poorly understood. To explore the virus-B-cell interactions, two immortalized lymphoblastoid B-cell lines (SL-P1 and SL-691) were established from cynomolgus monkeys that were naturally co-infected with a simian type D retrovirus-2 (SRV-2) and with the herpes virus Macaca fascicularis (HVMF-1). We addressed their susceptibility to SIV infection and the phenotypic modifications associated with SIV infection. In response, both cell lines (1) were co-infected with HVMF-1 (latent infection) and with SRV-2 (productive infection), (2) had a transformed phenotype because they did not require exogenous growth factors, and (3) when injected into mice with severe combined immunodeficiency (SCID), generated serially transplantable tumors. The B-cell origin of SL cells was demonstrated by the presence of rearrangements of the IgH gene and by the expression of typical B-cell lineage markers, such as CD20. SL-P1 and SL-691 could be discriminated on the basis of different expressions of CD23 and CD40 and of kappa- and lambda-chains. Most importantly, SL-691 cells, but not SL-P1 cells, were susceptible to chronic noncytolytic SIV infection. This infection occurred in a CD4/CCR5/CXCR4-independent manner and was associated with the upregulated expression of CD23 and CD40 cell surface markers. In addition, CD20 expression, which progressively disappeared in SL-691 noninfected cells, was maintained in the SIV-infected counterpart. These findings support the hypothesis that SIV induce phenotypic perturbations in B cells that might eventually contribute to the development of lymphoproliferative disease.

Structurally adaptive hot spots at a protein interaction interface on TRAF3

Tumor necrosis factor (TNF) signaling is controlled by receptors and intracellular signaling pathways that activate the NF-kappaB transcription factor. The resulting signals elicit immune responses and have important implications for disorders such as autoimmunity or allergic reactions. TNF-receptor-associated factors (TRAFs) bind to the cytoplasmic portion of TNFRs as well as downstream regulators and thus are co-inducers of the signal transduction. TRAF3 binds to diverse receptors and regulators by accomodating a conserved motif that is embedded in completely different structural frameworks. Thus, the protein-protein contact region on TRAF3 represents a binding interface that is structurally and functionally adaptive. In this report, three 'hot spots' at the TRAF3 protein-interaction interface are defined that provide the principal contact regions for different binding partners. The side-chains of residues at these 'hot spots' are flexible and undergo movements on binding the different partners. These side chain rearrangements provide a structural adaptability that promotes interaction with a variety of distinct proteins. It is proposed that similar adaptive 'hot spots' are also present on the binding surfaces of TRAF1, TRAF2 and TRAF5.

Adenovirus transduction to effect CD40 signalling improves the immune stimulatory activity of myeloma cells

Neoplastic plasma cells from patients with myeloma fail to stimulate an effective anti-myeloma immune response, which may be in part due to their deficient expression of immune accessory molecules. Attempting to alter this, we infected myeloma cell lines and patient-derived primary myeloma cells with an adenovirus encoding CD154 (Ad-CD154). Myeloma cells were made to express the CD154 transgene at multiplicity of infection (MOI) between 10 and 1000. Furthermore, infection of CD40(positive) myeloma cells with Ad-CD154, but not an adenovirus encoding an irrelevant transgene, beta-galactosidase (Ad-LacZ), induced enhanced expression of immune accessory molecules, such as CD54, HLA-DR and CD70. In addition, Ad-CD154-infected myeloma cells could activate bystander CD40(positive) antigen-presenting cells to express immune accessory molecules. Consequently, Ad-CD154 infected myeloma cells stimulated proliferation in allogeneic mixed lymphocyte reactions (MLR). Finally, co-infection of CD40(negative) myeloma cells with Ad-CD154 and an adenovirus encoding CD40 (Ad-CD40) induced expression of immune accessory molecules and enhanced the MLR stimulatory capacity of transduced myeloma cells. Collectively, these results indicate that infection of myeloma cells with Ad-CD154 or Ad-CD154/Ad-CD40 can induce changes in myeloma cells that enhance their ability to induce cellular immune activation. As such, this approach may have potential application for immune therapy of patients with this disease.

CD40:CD40L interactions in X-linked and non-X-linked hyper-IgM syndromes

Hyper-IgM (HIM) syndrome is a rare immunodeficiency characterized by low or absent IgG, IgA, and IgE with normal or elevated levels of IgM. This disorder can be acquired or familial with either X-linked or autosomal patterns of inheritance. The X-linked form of the disease is a consequence of mutations in the CD40 ligand (CD40L) gene that encodes a protein expressed primarily on activated CD4+ T cells. The cognate interaction between CD40L on T cells and CD40 on antigen-stimulated B cells, macrophage, and dendritic cells is critical for the development of a comprehensive immune response. The non-X-linked form of HIM syndrome is heterogeneous and appears in some cases to be a consequence of mutations in the AlD gene which encodes a B cell specific protein required for class switch recombination, somatic mutation, and germinal center formation. However, mutations in other unidentified genes are clearly the basis of the disease in a subset of patients. In this article, we review the essential features of the X-linked and non-X-linked forms of HIM syndrome and discuss the critical role the CD40:CD40L receptor-ligand pair plays in the pathogenesis of these immune deficiencies.

Nonstructural 5A protein of hepatitis C virus modulates tumor necrosis factor alpha-stimulated nuclear factor kappa B activation

The hepatitis C virus nonstructural protein 5A (NS5A) is a multifunctional phosphoprotein that leads to pleiotropic responses, in part by regulating cell growth and cellular signaling pathways. Here we show that overexpression of NS5A inhibits tumor necrosis factor (TNF)-alpha-induced nuclear factor kappaB (NF-kappaB) activation in HEK293 cells, as determined by luciferase reporter gene expression and by electrophoretic mobility shift assay. When overexpressed, NS5A cannot inhibit the recruitment of TNF receptor-associated factor 2 (TRAF2) and IkappaB kinase (IKK)beta into the TNF receptor 1-TNF receptor-associated death domain complex. In contrast, NS5A is a part of the TNF receptor 1 signaling complex. NF-kappaB activation by TNF receptor-associated death domain and TRAF2 was inhibited by NS5A, whereas MEKK1 and IKKbeta-dependent NF-kappaB activation was not affected, suggesting that NS5A may inhibit NF-kappaB activation signaled by TRAF2. Coimmunoprecipitation and colocalization of NS5A and TRAF2 expressed in vivo provide compelling evidence that NS5A directly interacts with TRAF2. This interaction was mapped to the middle one-third (amino acids 148-301) of NS5A and the TRAF domain of TRAF2. Our findings suggest a possible molecular mechanism that could explain the ability of NS5A to negatively regulate TNF-alpha-induced NF-kappaB activation.

CD40 activation in epithelial ovarian carcinoma cells modulates growth, apoptosis, and cytokine secretion

BACKGROUND/AIMS

CD40, a member of the tumour necrosis factor (TNF) receptor family, is expressed on a variety of haematopoietic cells and is crucial in orchestrating both humoral and cellular immune responses. CD40 is also expressed on some carcinoma cells, where its function remains largely unknown. This study investigated the effects of CD40 ligation on ovarian carcinoma cell growth and apoptosis and on cytokine production, in addition to the role of the NF-kappa B and JNK signalling pathways.

METHODS

CD40 expression was measured in epithelial ovarian carcinoma (EOC) biopsies by immunohistochemistry and in EOC cell lines by flow cytometry. To examine the effects of CD40 ligation on cell growth recombinant soluble CD40 ligand was used to stimulate EOC cell lines and growth was measured by MMT assays. Cytokine production was measured by enzyme linked immunosorbent assays interleukin 8 (IL-8) gene transcription was estimated by means of reverse transcription polymerase chain reaction. The integrity of the CD40 signalling pathway in those cell lines that did not produce cytokines in response to CD40 ligation was assessed by the detection of the transcription factor NF-kappa B by an electrophoretic mobility shift assay. To investigate the defect in the NF-kappa B pathway the phosphorylation status of I kappa B alpha was determined by an antibody specific to phosphorylated I kappa B alpha and dissociation of the I kappa B alpha-p65 complex was assessed by co-immunoprecipitation.

RESULTS

CD40 is expressed in primary ovarian carcinoma biopsies and EOC cell lines. CD40 ligation resulted in growth inhibition in most of these carcinoma cell lines and was also found to promote apoptosis, with this last effect only being evident in early passage EOC cells. CD40 ligation also induced significant IL-6 and IL-8 production in most of the EOC cell lines examined and it was confirmed for IL-8 that this effect was regulated at the transcriptional level. NF-kappa B activation in response to CD40 ligation was found in three of the EOC cell lines and specific defects in the CD40 induced NF-kappa B pathway were identified in two cell lines. However, CD40 engagement induced JNK activation in all the EOC cell lines.

CONCLUSIONS

These data suggest that the CD40 pathway is functional in ovarian carcinoma cells and highlight the need for further studies to provide insight into the role of CD40 in the carcinogenic process and the possible exploitation of this pathway for novel therapeutic approaches.

A double RING-H2 domain in RNF32, a gene expressed during sperm formation

The RING domain is a cysteine-rich zinc-binding motif, which is found in a wide variety of proteins, among which are several proto-oncogenes and the gene implicated in autosomal recessive juvenile parkinsonism, Parkin. The domain mediates binding to other proteins, either via their RING domains or other motifs. In several proteins, RING domains are found in combination with other cysteine-rich binding motifs and some proteins contain two RING domains. Recent evidence suggests that RING finger proteins function in the ubiquitin pathway as E3 ligases. A variant of the RING domain is the RING-H2 domain, in which one of the cysteines is replaced by a histidine. We have cloned and characterized a novel gene, RNF32, located on chromosome 7q36. RNF32 is contained in 37 kb of genomic DNA and consists of 9 constitutive and 8 alternatively spliced exons, most of which are alternative first exons. A long and a short transcript of the gene are expressed; the short transcript containing exons 1-4 only. This gene encodes two RING-H2 domains separated by an IQ domain of unknown function. This is the first reported gene with a double RING-H2 domain. In humans, RNF32 overlaps with a processed retroposon located on the opposite strand, C7orf13. RNF32 is specifically expressed in testis and ovary, whereas C7orf13 is testis-specific, suggesting that its expression may be regulated by elements in the RNF32 promoter region. RNF32 is expressed during spermatogenesis, most likely in spermatocytes and/or in spermatids, suggesting a possible role in sperm formation.

Downstream regulator TANK binds to the CD40 recognition site on TRAF3

TRAFs (tumor necrosis factor receptor [TNFR]-associated factors) bind to the cytoplasmic portion of liganded TNFRs and stimulate activation of NF-kappaB or JNK pathways. A modulator of TRAF signaling, TANK, serves as either an enhancer or an inhibitor of TRAF-mediated signaling pathways. The crystal structure of a region of TANK bound to TRAF3 has been determined and compared to a similar CD40/TRAF3 complex. TANK and CD40 bind to the same crevice on TRAF3. The recognition motif PxQxT is presented in a boomerang-like structure in TANK that is markedly different from the hairpin loop that forms in CD40 upon binding to TRAF3. Critical TANK contact residues were confirmed by mutagenesis to be required for binding to TRAF3 or TRAF2. Binding affinity, measured by isothermal titration calorimetry and competition assays, demonstrated that TANK competes with CD40 for the TRAF binding site.

Dissection of B cell differentiation during primary immune responses in mice with altered CD40 signals

CD40 is essential for efficient humoral immune responses. CD40 has two cytoplasmic domains required for binding of tumor necrosis factor receptor-associated factors (TRAF). The TRAF6-binding site is within the membrane proximal cytoplasmic (Cmp) region, while a PXQXT motif in the membrane distal cytoplasmic (Cmd) region needs to engage TRAF2/3/5. To dissect CD40 signals necessary for B cell differentiation, we generated transgenic mice expressing wild-type and mutant human CD40 (hCD40) molecules in a mouse CD40-deficient (mCD40(-/-)) background. The B cell-specific expression of hCD40 in mCD40(-/-) mice resulted in T-dependent antibody responses including germinal center (GC) formation. Mutant hCD40 molecules that carry either a point mutation of the TRAF2/3/5-binding site or a deletion of the Cmd region rescued extrafollicular B cell differentiation but not GC formation. A mutant hCD40 that comprises of only the TRAF2/3/5-binding site in the cytoplasmic region also rescued low but significant titers of antigen-specific IgG1 without GC formation. These results demonstrated that two distinct signals either from the Cmp or from the Cmd region induced the extrafollicular B cell differentiation and Ig class switching; however, GC formation required both. We conclude that combinations of these two signals determine which of the extrafollicular or the follicular (GC) differentiation pathway B cells enter.

All TRAFs are not created equal: common and distinct molecular mechanisms of TRAF-mediated signal transduction

The tumor necrosis factor (TNF) receptor associated factors (TRAFs) have emerged as the major signal transducers for the TNF receptor superfamily and the interleukin-1 receptor/Toll-like receptor (IL-1R/TLR) superfamily. TRAFs collectively play important functions in both adaptive and innate immunity. Recent functional and structural studies have revealed the individuality of each of the mammalian TRAFs and advanced our understanding of the underlying molecular mechanisms. Here, we examine this functional divergence among TRAFs from a perspective of both upstream and downstream TRAF signal transduction pathways and of signaling-dependent regulation of TRAF trafficking. We raise additional questions and propose hypotheses regarding the molecular basis of TRAF signaling specificity.

Phosphorylation of a novel zinc-finger-like protein, ZPR9, by murine protein serine/threonine kinase 38 (MPK38)

We have identified previously a new murine protein serine/threonine kinase, MPK38, closely related to the sucrose-non-fermenting protein kinase family [Gil, Yang, Lee, Choi and Ha (1997) Gene 195, 295-301]. Using the C-terminal half of the putative human counterpart of MPK38, HPK38, as a bait in a yeast two-hybrid screen of a human HeLa cDNA library, it was discovered that the zinc-finger-motif-containing protein, termed zinc-finger-like protein 9 (ZPR9), bound both HPK38 and MPK38. In a co-expression assay, ZPR9 associated with MPK38 in vivo, and we showed that the ZPR9 is also phosphorylated by MPK38. In addition, ZPR9 physically interacts with itself in mammalian cells. The ZPR9 cDNA hybridized with a mRNA species of approx. 1.7 kb in Northern-blot analysis. The ZPR9 transcript was detected in all tissues examined, including lung, kidney, spleen,liver and brain. Co-expression of ZPR9 with MPK38 caused the accumulation of ZPR9 in the nucleus. These findings suggest a potentially important role for ZPR9 in MPK38-mediated signal transduction, and that ZPR9 is a physiological substrate of MPK38 in vivo.

T2BP, a novel TRAF2 binding protein, can activate NF-kappaB and AP-1 without TNF stimulation

TRAF2 is a key molecule involved in TNF signaling, which is crucial for the regulation of inflammatory processes. We have identified a novel TRAF2 binding protein, designated as T2BP (TRAF2 binding protein), by a mammalian two-hybrid screening approach. T2BP is a relatively small protein of 184 amino acids, which includes a forkhead-associated domain, the phosphopeptide binding motif. The interaction domain search showed that the TRAF domain in TRAF2 is required for the binding to T2BP whereas almost the entire protein in T2BP binds to TRAF2. The interaction was further confirmed by co-immunoprecipitation. Expression profiling for T2BP and TRAF2 revealed an ubiquitous expression in adult mouse tissues. Overexpression of T2BP in HEK293 cells activated NF-kappaB and AP-1 in a dose dependent manner as well as seen in the TNF-treated control cells. Our results suggest that T2BP is involved in the TNF-mediated signaling by its interaction with TRAF2.

Identification of protein substrates of Ca(2+)/calmodulin-dependent protein kinase II in the postsynaptic density by protein sequencing and mass spectrometry

Previously we detected more than 28 PSD proteins to be phosphorylated by CaM kinase II, and identified 14 protein substrates (Yoshimura, Y., Aoi, T., Yamauchi, T., Mol. Brain Res. 81, 118-128, 2000). In the present study, the remaining substrates were analyzed by protein sequencing and mass spectrometry. We found 6 proteins not previously known to be substrates of CaM kinase II, namely PSD95-associated protein, SAP97, TOAD-64, TNF receptor-associated protein, insulin-receptor tyrosine kinase 58/53 kDa substrate, and homer 1b.

Ceramide-rich membrane rafts mediate CD40 clustering

Many receptor systems use receptor clustering for transmembrane signaling. In this study, we show that acid sphingomyelinase (ASM) is essential for the clustering of CD40. Stimulation of lymphocytes via CD40 ligation results in ASM translocation from intracellular stores, most likely vesicles, into distinct membrane domains on the extracellular surface of the plasma membrane. Surface ASM initiates a release of extracellularly oriented ceramide, which in turn mediates CD40 clustering in sphingolipid-rich membrane domains. ASM, ceramide, and CD40 colocalize in the cap-like structure of stimulated cells. Deficiency of ASM, destruction of sphingolipid-rich rafts, or neutralization of surface ceramide prevents CD40 clustering and CD40-initiated cell signaling. These findings indicate that the ASM-mediated release of ceramide and/or metabolites of ceramide regulate clustering of CD40, which seems to be a prerequisite for cellular activation via CD40.

Characterization of a CD40-dominant inhibitory receptor mutant

CD40 is an important mediator of immune and inflammatory responses. It is a costimulatory molecule for B cell proliferation and survival. Blockade of CD40 has been shown to induce tolerance and its role in other pathogenic conditions has led to the proposal that CD40 inhibition could be valuable therapeutically. As a first step to this end, we have characterized a CD40-dominant negative receptor. This inhibitory mutant lacks the identified CD40 signaling domains. It inhibits both cotransfected and endogenous CD40 activation of NF-kappaB. This mutant is specific, as it does not affect TNF or latent membrane protein 1 signaling. Its potential usefulness is illustrated by its ability to inhibit the CD40 ligand-stimulated increases of HLA and CD54 expression, molecules involved in Ag recognition and lymphocyte recruitment leading to organ rejection. The inhibitory mutant has no TNFR-associated factor 2-binding capabilities and inhibits the recruitment of TNFR-associated factor 2 to the CD40 signaling complex after stimulation. These studies show that the CD40 inhibitory receptor molecule is effective, specific, and useful both for research and potentially as a clinical tool. And furthermore, it is likely that similar dominant inhibitory receptors can be generated for all of the members of the TNFR superfamily.

Molecular characterization of CD40 signaling intermediates

Signal transduction through the CD40 receptor is initiated by binding of its trimeric ligand and propagated by interactions of tumor necrosis factor receptor-associated factor (TRAF) proteins with the multimerized CD40 cytoplasmic domain. Using defined multimeric constructs of the CD40 cytoplasmic domain expressed as either soluble or myristoylated proteins, we have addressed the extent of receptor multimerization needed to initiate signal transduction and identified components of CD40 signaling complexes. Signal transduction in human embryonic kidney 293 cells, measured by nuclear factor kappaB activation, was observed in cells expressing soluble trimeric CD40 cytoplasmic domain and to a lesser extent in cells expressing dimeric CD40 cytoplasmic domain. Nuclear factor kappaB activation was strongest in cells expressing myristoylated trimeric CD40 cytoplasmic domain. Signal transduction through trimeric CD40 cytoplasmic domains with various point mutations in the TRAF binding sites was similar to signal transduction through analogous full-length receptors. Transiently expressed soluble trimeric CD40 cytoplasmic domain was isolated as complexes that contained TRAF2, TRAF3, TRAF5, TRAF6, and the inhibitor of apoptosis protein (c-IAP1). Association of c-IAP1 with the CD40 cytoplasmic domain complex was indirect and dependent on the presence of an intact TRAF1/2/3 binding site. These results suggest that extracellular ligation of CD40 can be bypassed and that soluble trimerized CD40 complexes can be isolated and used to identify components that link CD40 with signaling pathways.

Upregulation of TRAF-3 by shear stress blocks CD40-mediated endothelial activation

Atherosclerosis is an inflammatory disease of large arteries that is initiated through the activation of endothelium by proinflammatory mediators. CD40 receptor stimulation has been implicated in the pathogenesis of atherosclerosis. One of the most important atheroprotective stimuli is the viscous drag (shear stress) generated by the streaming blood acting on the endothelial monolayer. Here, we demonstrate that shear stress prevents CD40 ligand-induced endothelial cell activation, and we identify upregulation of TNF receptor-associated factor-3 (TRAF-3) as a potent CD40-inhibitory mechanism. Shear stress specifically upregulates TRAF-3 in cultured endothelial cells. Moreover, in the endothelial cells overlying human atherosclerotic plaques, TRAF-3 expression is upregulated in areas with high shear stress. Overexpression of TRAF-3 inhibits endothelial expression of proinflammatory cytokines and tissue factor and blocks DNA-binding activity of the transcription factor AP-1; it thereby prevents CD40-induced endothelial activation. Thus, upregulation of TRAF-3 represents a novel mechanism for preserving the functional integrity of the endothelial monolayer.

Tumor necrosis factor receptor-associated factors (TRAFs)

Tumor necrosis factor receptor-associated factors (TRAFS) were initially discovered as adaptor proteins that couple the tumor necrosis factor receptor family to signaling pathways. More recently they have also been shown to be signal transducers of Toll/interleukin-1 family members. Six members of the TRAF family have been identified. All TRAF proteins share a C-terminal homology region termed the TRAF domain that is capable of binding to the cytoplasmic domain of receptors, and to other TRAF proteins. In addition, TRAFs 2-6 have RING and zinc finger motifs that are important for signaling downstream events. TRAF proteins are thought to be important regulators of cell death and cellular responses to stress, and TRAF2, TRAF5 and TRAF6 have been demonstrated to mediate activation of NF-kappaB and JNK. TRAF proteins are expressed in normal and diseased tissue in a regulated fashion, suggesting that they play an important role in physiological and pathological processes.

Expression and function of TRAF-3 splice-variant isoforms in human lymphoma cell lines

TRAF-3 gene products are signaling adaptor molecules required for lymphocytes to mediate T-dependent antibody responses in vivo. Previous work identified 8 splice-variant TRAF-3 mRNA species by RT-PCR that have the potential to encode novel isoforms, seven of which induce NF-kappaB activation when over-expressed in 293 cells. Here, their expression was characterized by RNAse protection assay, which showed the T cell line Jurkat D1.1 and the B cell lines BJAB, Daudi, and Raji each expressed mRNA encoding TRAF-3 splice-variants in approximately the same rank order (from highest to lowest); TRAF-3 Delta103aa, Delta83aa, full-length, Delta25aa, Delta52aa, Delta56aa, Delta27aa, and Delta221aa mRNA. The TRAF-3 Delta130aa mRNA was not detectable in any of the cell lines examined. The functional effect of over-expressing each TRAF-3 splice-variant on NF-kappaB activation was studied in the TRAF-5-responsive B cell line, BJAB. Of the seven TRAF-3 splice-variant isoforms that induce NF-kappaB activation in 293 cells, only TRAF-3 Delta27aa, Delta103aa, or Delta130aa induce NF-kappaB activation in BJAB cells. Together, these data indicate that a number of TRAF-3 splice-variant mRNAs are expressed and function in B and T lymphoma lines, which suggests that certain TRAF-3 splice-variant isoforms may participate in mediating the known functions of the TRAF-3 gene in lymphocytes.

Expression profiling of cancer-related genes in human keratinocytes following non-lethal ultraviolet B irradiation

Ultraviolet B irradiation initiates and promotes skin cancers, photo-aging, and immune suppression. In order to elucidate the effect of these processes at the level of gene expression, we used cDNA microarray technology to examine the effect of ultraviolet B irradiation on 588 cancer-related genes in human keratinocytes at 1, 6, and 24 h post-irradiation with a mildly cytotoxic dose of ultraviolet B (170 mJ/cm(2)). The viability of the irradiated keratinocytes was 75% at 24 h post-irradiation. Various cytokeratins and transcription factors were up-regulated within 1 h post-irradiation. After 6 h, expression of a variety of genes related to growth regulation (e.g. p21(WAF1), notch 4, and smoothened), apoptosis (e.g. caspase 10, hTRIP, and CRAF1), DNA repair (ERCC1, XRCC1), cytokines (e.g. IL-6, IL-13, TGF-beta, and endothelin 2), and cell adhesion (e.g. RhoE, and RhoGDI) were altered in human keratinocytes. These data suggest the changes in a cascade of gene expression in human keratinocytes occurring within 24 h after UVB exposure. Although the roles of these cellular genes after UVB-irradiation remain to be elucidated, microarray analysis may provide a new view of gene expression in epidermal keratinocytes following UVB exposure.

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.

Differential signaling and tumor necrosis factor receptor-associated factor (TRAF) degradation mediated by CD40 and the Epstein-Barr virus oncoprotein latent membrane protein 1 (LMP1)

Latent membrane protein 1 (LMP1) plays a critical role in B cell transformation by Epstein-Barr virus (EBV) and appears to mimic a constitutively active CD40 receptor. Intracellular tumor necrosis factor (TNF) receptor-associated factor (TRAF) adapter proteins, shown to contribute to signaling by both CD40 and LMP1, were recruited by both molecules to lipid-enriched membrane rafts. However, we found that TRAFs 2 and 3 were subsequently degraded after CD40- but not LMP1-induced signaling. This degradation was proteasome-dependent and required direct TRAF binding by CD40. Using a model system designed to directly compare the signaling potency of the cytoplasmic domains of LMP1 and CD40 in B lymphocytes, we found that LMP1 more potently activates c-Jun kinase and nuclear factor kappaB and induces higher levels of several B cell effector functions than does CD40. This suggests that LMP1 utilizes a modified CD40 signaling pathway. Failure to regulate TRAFs may contribute to the enhanced capacity of LMP1 to activate B cells as well as promote B cell transformation.

Activation of c-Jun N-terminal kinase in the absence of NFkappaB function prior to induction of NK cell death triggered by a combination of anti-class I and anti-CD16 antibodies

Addition of antibodies to major histocompatibility complex class I (MHC class I) and F(c) gamma RIII (CD16) antigens resulted in the synergistic augmentation of natural killer (NK) cell death, and the loss of NK cell cytotoxic function. The binding of anti-CD16 and anti-class I antibodies to the same population of NK cells is required for the synergistic augmentation of NK cell death. Moreover, the addition of antibodies to leukocyte function antigen-1 (LFA-1), which significantly inhibited the phorbol 12-myristate 13-acetate (PMA) and ionomycin mediated NK cell death, had no effect on NK cell death mediated by anti-CD16 and anti-class I antibodies. The increase in NK cell death was associated with an increase in tumor necrosis factor-alpha (TNF-alpha) secretion, and concomitant inhibition of nuclear factor kappa B (NFkappaB) activation and the induction of c-jun N-terminal kinase (JNK) activity in NK cells treated with the combination of anti-class I and anti-CD16 antibodies. Furthermore, the inhibition of NFkappaB activation in anti-CD16 and anti-class I antibody treated NK cells was paralleled with a significant increase in inhibitor of kappa B (IkappaB) protein expression. Overexpression of IkappaB super-repressor in YT, a NK cell line, caused significant up-regulation of TNF-alpha, PMA and ionomycin and Fusobacterium nucleatum mediated NK cell death. Overall, our studies suggest an important regulatory role for NFkappaB and JNK activities in MHC class I mediated NK cell death.

Caveolin-1 associates with TRAF2 to form a complex that is recruited to tumor necrosis factor receptors

Tumor necrosis factor (TNF) receptor-associated factor (TRAF) 2 is an intracellular adapter protein, which, upon TNF stimulation, is directly recruited to the intracellular region of TNF receptor 2 (TNFR2) or indirectly, via TRADD, to the intracellular region of TNF receptor 1 (TNFR1). In cultured human umbilical vein endothelial cells, endogenous TRAF2 colocalizes with the membrane-organizing protein caveolin-1 at regions of enrichment subjacent to the plasma membrane as detected by confocal fluorescence microscopy. Both endogenous and transfected TRAF2 protein coimmunoprecipitate with caveolin-1 in the absence of ligand. Upon TNF treatment, the TRAF2-caveolin-1 complex transiently associates with TRADD, and upon overexpression of TNFR2, the TRAF2-caveolin-1 complex stably associates with and causes redistribution of this receptor as detected by confocal fluorescence microscopy. In human embryonic kidney 293 cells, which have minimal endogenous expression of caveolin-1, cotransfection of TRAF2 and caveolin-1 results in spontaneous association of these proteins which can further associate with and redistribute transfected TNFR2 molecules. The association of caveolin-1 with TNFR2 depends upon TRAF2. Cotransfection of caveolin-1 protein increases TRAF2 protein expression levels in HEK 293 cells, which correlates with enhancement of TNF and TRAF2 signaling, measured as transcription of a NF-kappaB promoter-reporter gene, although the caveolin-enhanced response to TNF is attenuated at higher caveolin levels. These findings suggest that intracellular distribution of activated TNF receptors may be regulated by caveolin-1 via its interaction with TRAF2.

TRAF1 is a substrate of caspases activated during tumor necrosis factor receptor-alpha-induced apoptosis

TRAF family proteins are signal-transducing adapter proteins that interact with the cytosolic domains of tumor necrosis factor (TNF) family receptors. Here we show that TRAF1 (but not TRAF2-6) is cleaved by certain caspases in vitro and during TNF-alpha- and Fas-induced apoptosis in vivo. (160)LEVD(163) was identified as the caspase cleavage site within TRAF1, generating two distinct fragments. Significant enhancement of TNF receptor-1 (CD120a)- and, to a lesser extent, Fas (CD95)-mediated apoptosis was observed when overexpressing the C-terminal TRAF1 fragment in HEK293T and HT1080 cells. The same fragment was capable of potently suppressing TNF receptor-1- and TRAF2-mediated nuclear factor-kappaB activation in reporter gene assays, providing a potential mechanism for the enhancement of TNF-mediated apoptosis. Cell death induced by other death receptor-independent stimuli such as cisplatin, staurosporine, and UV irradiation did not result in cleavage of TRAF1, and overexpression of the C-terminal TRAF1 fragment did not enhance cell death in these cases. TRAF1 cleavage was markedly reduced in cells that contain little procaspase-8 protein, suggesting that this apical protease in the TNF/Fas death receptor pathway is largely responsible. These data identify TRAF1 as a specific target of caspases activated during TNF- and Fas-induced apoptosis and illustrate differences in the repertoire of protease substrates cleaved during activation of different apoptotic pathways.

Segregation of TRAF6-mediated signaling pathways clarifies its role in osteoclastogenesis

Signals emanating from the receptor for interleukin-1 (IL-1), lipopolysaccharide (LPS) or osteoclast differentiation factor/receptor activator of NF kappa B ligand (ODF/RANKL) stimulate transcription factors AP-1 through mitogen-activated protein kinase (MAPK) activation and NF kappa B through I kappa B kinase (IKK) activation. These kinases are thought to be activated by tumor necrosis factor receptor-associated factor 6 (TRAF6). However, molecular mechanisms by which TRAF6 activates various downstream kinases remain to be elucidated. We identified functional domains of TRAF6 under physiological conditions established by appropriate expression of TRAF6 mutants in TRAF6-deficient cells. In IL-1 and LPS signaling pathways, the RING finger and first zinc finger domains are not required for NF kappa B activation but are required for full activation of MAPK. However, IL-1 and LPS signals utilize distinct regions within the zinc finger domains of TRAF6 to activate NF kappa B. Furthermore, the RING finger domain is not required for differentiation of splenocytes to multinuclear osteoclasts, but is essential for osteoclast maturation. Thus, TRAF6 plays essential roles in both the differentiation and maturation of osteoclasts by activating various kinases via its multiple domains.

CD40-mediated signaling in monocytic cells: up-regulation of tumor necrosis factor receptor-associated factor mRNAs and activation of mitogen-activated protein kinase signaling pathways

The biochemical pathways involved in CD40 signaling have been extensively studied in B cells and B cell lines, and appear to be primarily initiated by recruitment of the tumor necrosis factor (TNF) receptor-associated factor (TRAF) signaling proteins to the CD40 cytoplasmic domain. Signaling pathways activated through CD40 in monocytes/macrophages have not been characterized as well as in B cells. Using human monocytes and the human monocytic cell line THP1, we examined signal transduction events induced by CD40 engagement with its ligand, CD154. In human monocytes, all TRAF mRNAs were expressed constitutively and CD40 ligation resulted in a strong up-regulation of TRAF1 mRNA. In THP1 cells, CD40 ligation induced expression of TRAF1 and TRAF5 mRNAs. Engagement of CD40 in both monocytes and THP1 cells led to the rapid and transient activation of the extracellular signal-regulated kinases (ERK) 1 and 2, and to low levels of JNK activation. No CD40-dependent activation of p38 mitogen-activated protein kinase (MAPK) was found. In CD154-stimulated monocytes and THP1 cells the upstream ERK1/2 activator, MAPK kinase (MEK) 1/2, and downstream substrate, c-Myc, were activated. By blocking activation of ERK1/2 with a MEK-specific inhibitor, PD98059, CD40-dependent secretion of the pro-inflammatory cytokines, TNF-alpha, IL-6 and IL-8, was demonstrated to be linked to the ERK1/2 pathway. The ERK1/2 pathway did not appear to be involved in up-regulating TRAF1 and TRAF5 mRNAs in THP1 cells. Collectively, these results suggest distinct differences between B cells and monocytic cells in CD40-dependent activation of MAPK pathways.

IgE regulation and roles in asthma pathogenesis

Asthma and the predisposition to produce IgE are inherited as linked traits in families. In patients IgE levels correlate with asthma severity and bronchial hyperresponsiveness. The concept that IgE plays a critical role in asthma pathogenesis has driven the development of IgE blockers, which are currently being introduced into clinical use. This review focuses on the mechanisms whereby IgE participates both in immediate hypersensitivity responses in the airways and in the induction of chronic allergic bronchial inflammation. The molecular genetic events that give rise to IgE production by B cells and the cellular and cytokine factors that support IgE production in the bronchial mucosal microenvironment are discussed. It is clear that much remains to be learned regarding the roles of IgE in asthma and the genetic and environmental influences that lead to its production. Over the next few years, the emerging experience with anti-IgE in patients will provide a more complete understanding of the mechanisms whereby IgE contributes to disease, as well as the therapeutic potential of its inhibition.

Rewiring of CD40 is necessary for delivery of rescue signals to B cells in germinal centres and subsequent entry into the memory pool

Memory B-cell development is impaired by in vivo blockade of the CD40-CD40 ligand (CD40L) interaction using human Fc immunoglobulin G1 (IgG1)-mouse CD40 fusion protein (CD40-Ig); however, germinal centre (GC) formation is not. We show here that the block in B-cell differentiation in these mice is at the stage of rescue from apoptosis and exit from the GC. Thus, GC from CD40-Ig-treated mice contain a three- to fourfold higher level of apoptotic cells than found in control mice injected with human IgG1 alone. This increase in apoptosis is not caused by a blockade of the CD40L-mediated rescue signal but is the result of an intrinsic defect of GC B cells in CD40-Ig-treated mice to receive rescue signals via CD40. While anti-CD40 stimulation maintained the viability in culture of GC B cells from control mice, it did not rescue GC B cells from CD40-Ig-treated mice. This data is consistent with the notion that a 'rewiring' of the CD40 molecule is induced by CD40 ligation early in the response and is necessary to allow B-cell rescue from apoptosis when they subsequently enter the GC.

Expression of the tumor necrosis factor receptor-associated factors (TRAFs) 1 and 2 is a characteristic feature of Hodgkin and Reed-Sternberg cells

Tumor necrosis factor receptor-associated factors (TRAFs) are a recently established group of proteins involved in the intracellular signal transduction of several members of the tumor necrosis factor receptor (TNFR) superfamily. Recently, specific members of the TRAF family have been implicated in promoting cell survival as well as activation of the transcription factor NF-kappaB. We investigated the constitutive expression of TRAF1 and TRAF2 in Hodgkin and Reed-Sternberg (HRS) cells from archived paraffin-embedded tissues obtained from 21 patients diagnosed with classical Hodgkin's disease (HD). In a selective portion of cases, examination of HRS cells for Epstein-Barr virus (EBV)-encoded RNA was performed by in situ hybridization, and the results were compared with the magnitude of TRAF1 and TRAF2 staining. We also determined the TRAF profile in the classical HD cell lines L428, KMH2, and HS445 by Western blotting using a series of antibodies that specifically recognize the six individual TRAF family proteins (TRAF1-TRAF6). Moderate to high constitutive expression of TRAF1 and TRAF2 were found in 19 of 21 and 20 of 21 cases of classical HD, respectively. Of the remaining cases, one case showed weak expression of TRAF1, and another case showed weak expression of both proteins. No relationship was found between the staining intensity of the TRAF proteins and EBV expression in HRS cells. Strong constitutive expression of TRAF1 was also identified in the HD cell line L428, compared with the relatively weak expression observed in KMH2 and HS445. All three HD cell lines showed strong expression of TRAF2 protein and moderate, comparatively equal expression of TRAF4 and TRAF6. In contrast, TRAF3 was not expressed in the HD cell lines. Although KMH2 showed weak expression, the remaining HD cell lines also lacked TRAF5 protein. These data demonstrate that constitutive expression of TRAF1 and TRAF2 is a characteristic feature of HRS cells from both patient and cell line specimens. Furthermore, with the exception of TRAF1 expression, HRS cells from the three HD cell lines showed similar TRAF protein expression patterns. Overall, these findings demonstrate the expression of several TRAF proteins in HD. Significantly, the altered regulation of selective TRAF proteins may reflect HRS cell response to stimulation from the microenvironment and potentially contribute both to apoptosis resistance and cell maintenance of HRS cells.

Gene expression in chronic lymphocytic leukemia B cells and changes during induction of apoptosis

Our studies in chronic lymphocytic leukemia (CLL) are directed at understanding which signals maintain viability in vivo and become lost upon removal of leukemic cells from the body, such that they immediately begin to undergo apoptosis ex vivo. In this report, we examine changes in gene expression observed between freshly isolated CLL B cells and after maintenance in vitro with and without Fludara. We compare these effects with an Epstein-Barr virus (EBV)-transformed cell line treated similarly. Kinetic effects of drug treatment on apoptosis and cell division were examined with DNA laddering, radioisotopic labeling, and flow cytometry using the fluorescent dye carboxyfluorescein diacetate succinimidyl ester. Reverse transcriptase polymerase chain reaction and hybridization blots of microarray cDNA analyses were performed to examine gene expression. We demonstrate that many genes, especially cyclin D1, were downregulated after culture of CLL cells. Anti-apoptotic genes BAG-1 and Akt2 were upregulated. The greatest positive effect with Fludara was the upregulation of JNK1. The EBV-transformed cell line was resistant to classic DNA laddering induced with Fludara. Although DNA synthesis was blocked, the EBV-transformed cell line had some ability to recover from treatment following drug washout. CLL cells express cell cycle regulatory genes that are specific for activated cells in the G(1)-S phase of the cell cycle. Growth regulatory signals are lost when the leukemic cells are isolated from the body. Fludara enhances kinetics of apoptosis and induces expression of a gene responsive to stress that regulates expression of a kinase involved in initiation of the apoptotic pathway.

Identification and characterization of two CD40-inducible enhancers in the mouse TRAF1 gene locus

We have shown that CD40 engagement induces TRAF1 gene expression in B lymphocytes. Here we report that CD40-dependent TRAF1 gene transcription in murine B cells is controlled by two enhancer regions. One region is located approximately 2 kb upstream of the transcription start site and the other lies in the intron between exons 5 and 6. The upstream enhancer contains a single NF-kappaB site in addition to sites that bind constitutive transcription factors. Mutation of this NF-kappaB site completely abrogates CD40-driven TRAFl transcription. The intronic enhancer contains two sites that strongly bind the CD40-inducible factors NF-kappaB and AP-1. Simultaneous mutation of the AP-1 site and of the NF-kappaB site abolishes transcription driven by this enhancer. When cloned together into reporter constructs, the two TRAF1 enhancers do not synergize, suggesting that each enhancer may separately participate in the induction of TRAF1 transcription in B cells following CD40 activation.

A human gene coding for a membrane-associated nucleic acid-binding protein

Studies to clone a cell-surface DNA-binding protein involved in the binding and internalization of extracellular DNA have led to the isolation of a gene for a membrane-associated nucleic acid-binding protein (MNAB). The full-length cDNA is 4.3 kilobases with an open reading frame of 3576 base pairs encoding a protein of approximately 130 kDa (GenBank accession numbers and ). The MNAB gene is on human chromosome 9 with wide expression in normal tissues and tumor cells. A C3HC4 RING finger and a CCCH zinc finger have been identified in the amino-terminal half of the protein. MNAB bound DNA (K(D) approximately 4 nm) and mutagenesis of a single conserved amino acid in the zinc finger reduced DNA binding by 50%. A potential transmembrane domain exists near the carboxyl terminus. Antibodies against the amino-terminal half of the protein immunoprecipitated a protein of molecular mass approximately 150 kDa and reacted with cell surfaces. The MNAB protein is membrane-associated and primarily localized to the perinuclear space, probably to the endoplasmic reticulum or trans-Golgi network. Characterization of the MNAB protein as a cell-surface DNA-binding protein, critical in binding and internalization of extracellular DNA, awaits confirmation of its localization to cell surfaces.

Hodgkin disease: pharmacologic intervention of the CD40-NFκB pathway by a protease inhibitor

The malignant Reed-Sternberg cell of Hodgkin disease is an aberrant B cell that persists in an immunolgically mediated inflammatory infiltrate. Despite its nonproductive immunoglobulin genes, the Reed-Sternberg cell avoids the usual apoptotic fate of defective immune cells through an unknown mechanism. A likely candidate is the surface receptor, CD40, consistently expressed by Reed-Sternberg cells, and the first link in the pathway to NF-κB activation, the central regulator of cytokine production and apoptosis. CD40 signaling in B lymphocytes coordinates the immune response, including immunoglobulin isotype switch and Fas-mediated apoptosis. CD40-induced NF-κB activation is mediated by adapter proteins, the TNF receptor (TNFR)-associated factors (TRAFs), especially TRAFs 2, 3, and 5. Using a Hodgkin cell line, this study demonstrates that CD40 activation of NF-κB is mediated by proteolysis of TRAF3. Results further demonstrate that the pathway can be blocked by treatment with pharmacologic doses of a specific protease inhibitor, pepstatin-A, even in the presence of a mutated NF-κB inhibitor, I-κBα. The stability of TRAF3 regulates CD40/NF-κB–mediated control of the immune response, which is central to the biologic activity of the Reed-Sternberg cell. Prevention of TRAF3 proteolysis may be an entry point for design of novel pharmaceuticals to treat Hodgkin disease and immune system disorders.

Hodgkin disease: pharmacologic intervention of the CD40-NFκB pathway by a protease inhibitor

The malignant Reed-Sternberg cell of Hodgkin disease is an aberrant B cell that persists in an immunolgically mediated inflammatory infiltrate. Despite its nonproductive immunoglobulin genes, the Reed-Sternberg cell avoids the usual apoptotic fate of defective immune cells through an unknown mechanism. A likely candidate is the surface receptor, CD40, consistently expressed by Reed-Sternberg cells, and the first link in the pathway to NF-κB activation, the central regulator of cytokine production and apoptosis. CD40 signaling in B lymphocytes coordinates the immune response, including immunoglobulin isotype switch and Fas-mediated apoptosis. CD40-induced NF-κB activation is mediated by adapter proteins, the TNF receptor (TNFR)-associated factors (TRAFs), especially TRAFs 2, 3, and 5. Using a Hodgkin cell line, this study demonstrates that CD40 activation of NF-κB is mediated by proteolysis of TRAF3. Results further demonstrate that the pathway can be blocked by treatment with pharmacologic doses of a specific protease inhibitor, pepstatin-A, even in the presence of a mutated NF-κB inhibitor, I-κBα. The stability of TRAF3 regulates CD40/NF-κB–mediated control of the immune response, which is central to the biologic activity of the Reed-Sternberg cell. Prevention of TRAF3 proteolysis may be an entry point for design of novel pharmaceuticals to treat Hodgkin disease and immune system disorders.