Cytoplasmic aggregation of TRAF2 and TRAF5 proteins in the Hodgkin-Reed-Sternberg cells

Bioinformatics Analysis of miRNAs Targeting TRAF5 in DLBCL Involving in NF-κB Signaling Pathway and Affecting the Apoptosis and Signal Transduction

Background

Diffuse large B-cell lymphoma (DLBCL) is an aggressive B-cell lymphoma with high heterogeneity. There is an unmet need to investigate valid indicators for the diagnosis and therapy of DLBCL.

Methods

GEO database was utilized to screen for differentially expressed genes (DEGs) and differential miRNAs in DLBCL tissues. The Gene Ontology (GO) and the Kyoto Encyclopedia of Genes and Genomes (KEGG) were applied to analyse DEGs. Then multiple databases were searched for related miRNAs within DLBCL, TNF receptor-associated factor 5 (TRAF5) and NF-kappa B (NF-κB) signaling pathways. The KOBAS database was used to assist in the screening of miRNAs of interest and construct the regulatory network of miRNA-mRNA. Finally, the expression level and diagnostic performance of miRNAs were analyzed with GEO datasets, and DEGs were identified from the GEPIA database.

Results

DEGs were significantly concentrated in the NF-κB signaling pathway and cytokine-cytokine receptor interaction, and involved in the process of immune response and protein binding. MiR-15a-5p, miR-147a, miR-192-5p, miR-197-3p, miR-532-5p, and miR-650 were revealed to be targeting TRAF5 and participating in NF-κB signaling pathway and might impact the apoptosis and signal transduction of DLBCL. In the GEPIA database, TRAF5 was significantly overexpressed in DLBCL. The expression of miR-197-3p was upregulated within GEO datasets, while the rest of the miRNAs were downregulated in DLBCL.

Conclusions

Subsets of miRNAs may participate in the NF-κB signaling pathway by co-targeting TRAF5 and could be prospective biomarkers exploring the pathogenesis of DLBCL.

MicroRNA-29b-3p promotes 5-fluorouracil resistance <em>via</em> suppressing TRAF5-mediated necroptosis in human colorectal cancer

Drug resistance in colorectal cancer is a great challenge in clinic. Elucidating the deep mechanism underlying drug resistance will bring much benefit to diagnosis, therapy and prognosis in patients with colorectal cancer. In this study, miR-29b-3p was shown to be involved in resistance to 5-fluorouracil (5-FU)-induced necroptosis of colorectal cancer. Further, miR-29b-3p was shown to target a regulatory subunit of necroptosis TRAF5. Rescue of TRAF5 could reverse the effect of miR-29b-3p on 5-FU-induced necroptosis, which was consistent with the role ofnecrostatin-1 (a specific necroptosis inhibitor). Then it was demonstrated that miR-29b-3p was positively correlated with chemo-resistance in colorectal cancer while TRAF5 negatively. In conclusion, it is deduced that miR-29b-3p/TRAF5 signaling axis plays critical role in drug resistance in chemotherapy for colorectal cancer patients by regulating necroptosis. The findings in this study provide us a new target for interfere therapy in colorectal cancer.

CD30 ligand deficiency accelerates glioma progression by promoting the formation of tumor immune microenvironment

CD30 ligand (CD30L, CD153), belonging to the tumor necrosis factor superfamily, has been reported to act as an immune regulator mainly in several autoimmune diseases and Hodgkin's lymphoma. However, little is known about its regulation in the glioma microenvironment. In this study, using a GL261 mouse glioma model, we showed that CD30L deficiency in the host accelerated glioma growth and reduced mouse survival, which might be associated with the accumulation of tumor-infiltrating immune cells, especially tumor-associated macrophages, myeloid-derived suppressor cells and CD8⁺ PD-1⁺ T cells. Moreover, CD30L deficiency resulted in distinct subsets of tumor-associated macrophages compared with those of wild-type mice. Furthermore, compared with those of wild-type mice, tumor-associated macrophages and microglia in CD30L-deficient mice adopted a more pro-tumorigenic phenotype within tumors. CD8⁺ T cells in CD30L-deficient mice decreased the expression of ki-67. Therefore, these results suggest that CD30L deficiency promotes the exhaustion of CD8⁺ T cells and the infiltration of tumor-associated macrophages and microglia. Our findings provide evidence for a new potential immunotherapy for glioma targeting CD30/CD30L signaling.

Molecular characteristics and function study of TNF receptor-associated factor 5 from grouper (Epinephelus coioides)

Tumor necrosis factor receptor-associated factor 5 (TRAF5) is a key adapter molecule that participates in numerous signaling pathways. The function of TRAF5 in fish is largely unknown. In the present study, a TRAF5 cDNA sequence (EcTRAF5) was identified in grouper (Epinephelus coioides). Similar to its mammalian counterpart, EcTRAF5 contained an N-terminal RING finger domain, a zinc finger domain, a C-terminal TRAF domain, including a coiled-coil domain and a MATH domain. The EcTRAF5 protein shared relatively low sequence identity with that of other species, but clustered with TRAF5 sequences from other fish. Real-time PCR analysis revealed that EcTRAF5 mRNA was broadly expressed in numerous tissues, with relatively high expression in skin, hindgut, and head kidney. Additionally, the expression of EcTRAF5 was up-regulated in gills and head kidney after infection with Cryptocaryon irritans. Intracellular localization analysis demonstrated that the full-length EcTRAF5 protein was uniformly distributed in the cytoplasm; while a deletion mutant of the coiled-coil domain of EcTRAF5 was observed uniformly distributed in the cytoplasm and the nucleus. After exogenous expression in HEK293T cells, TRAF5 significantly activated NF-κB. The deletion of the EcTRAF5 RING domain or of the zinc finger domain dramatically impaired its ability to activate NF-κB, implying that the RING domain and the zinc finger domain are required for EcTRAF5 signaling.

Genetic Alterations of TRAF Proteins in Human Cancers

The tumor necrosis factor receptor (TNF-R)-associated factor (TRAF) family of cytoplasmic adaptor proteins regulate the signal transduction pathways of a variety of receptors, including the TNF-R superfamily, Toll-like receptors (TLRs), NOD-like receptors (NLRs), RIG-I-like receptors (RLRs), and cytokine receptors. TRAF-dependent signaling pathways participate in a diverse array of important cellular processes, including the survival, proliferation, differentiation, and activation of different cell types. Many of these TRAF-dependent signaling pathways have been implicated in cancer pathogenesis. Here we analyze the current evidence of genetic alterations of TRAF molecules available from The Cancer Genome Atlas (TCGA) and the Catalog of Somatic Mutations in Cancer (COSMIC) as well as the published literature, including copy number variations and mutation landscape of TRAFs in various human cancers. Such analyses reveal that both gain- and loss-of-function genetic alterations of different TRAF proteins are commonly present in a number of human cancers. These include pancreatic cancer, meningioma, breast cancer, prostate cancer, lung cancer, liver cancer, head and neck cancer, stomach cancer, colon cancer, bladder cancer, uterine cancer, melanoma, sarcoma, and B cell malignancies, among others. Furthermore, we summarize the key in vivo and in vitro evidence that demonstrates the causal roles of genetic alterations of TRAF proteins in tumorigenesis within different cell types and organs. Taken together, the information presented in this review provides a rationale for the development of therapeutic strategies to manipulate TRAF proteins or TRAF-dependent signaling pathways in different human cancers by precision medicine.

Genetic Alterations of TRAF Proteins in Human Cancers

The tumor necrosis factor receptor (TNF-R)-associated factor (TRAF) family of cytoplasmic adaptor proteins regulate the signal transduction pathways of a variety of receptors, including the TNF-R superfamily, Toll-like receptors (TLRs), NOD-like receptors (NLRs), RIG-I-like receptors (RLRs), and cytokine receptors. TRAF-dependent signaling pathways participate in a diverse array of important cellular processes, including the survival, proliferation, differentiation, and activation of different cell types. Many of these TRAF-dependent signaling pathways have been implicated in cancer pathogenesis. Here we analyze the current evidence of genetic alterations of TRAF molecules available from The Cancer Genome Atlas (TCGA) and the Catalog of Somatic Mutations in Cancer (COSMIC) as well as the published literature, including copy number variations and mutation landscape of TRAFs in various human cancers. Such analyses reveal that both gain- and loss-of-function genetic alterations of different TRAF proteins are commonly present in a number of human cancers. These include pancreatic cancer, meningioma, breast cancer, prostate cancer, lung cancer, liver cancer, head and neck cancer, stomach cancer, colon cancer, bladder cancer, uterine cancer, melanoma, sarcoma, and B cell malignancies, among others. Furthermore, we summarize the key in vivo and in vitro evidence that demonstrates the causal roles of genetic alterations of TRAF proteins in tumorigenesis within different cell types and organs. Taken together, the information presented in this review provides a rationale for the development of therapeutic strategies to manipulate TRAF proteins or TRAF-dependent signaling pathways in different human cancers by precision medicine.

Brentuximab vedotin: clinical updates and practical guidance

Brentuximab vedotin (BV), a potent antibody-drug conjugate, targets the CD30 antigen. Owing to the remarkable efficacy shown in CD30-positive lymphomas, such as Hodgkin's lymphoma and systemic anaplastic large-cell lymphoma, BV was granted accelerated approval in 2011 by the US Food and Drug Administration. Thereafter, many large-scale trials in various situations have been performed, which led to extensions of the original indication. The aim of this review was to describe the latest updates on clinical trials of BV and the in-practice guidance for the use of BV.

Berberine prevents the apoptosis of mouse podocytes induced by TRAF5 overexpression by suppressing NF-κB activation

Berberine (BBR) has previously been found to exert beneficial effects on renal injury in experimental rats. However, the mechanisms underlying these effects are not yet fully understood. Tumor necrosis factor (TNF) receptor-associated factor 5 (TRAF5) has been demonstrated to mediate the activation of nuclear factor-κB (NF-κB), which has been implicated in the pathogenesis of chronic kidney disease (CKD). The aim of this study was to investigate the effects of BBR on kidney injury and the activation of the NF-κB signaling pathway in mouse podocytes. TRAF5 was found to be overexpressed in patients with CKD and chronic renal failure (CRF) (data obtained from the dataset GSE48944, as well as from patients at Shuguang Hospital). TRAF5 overexpression significantly inhibited cell viability and induced the apoptosis of mouse podocytes. However, BBR prevented the decrease in cell viability and the apoptosis induced by TRAF5 overexpression. The NF-κB inhibitor, caffeic acid phenethyl ester (CAPE), mimicked the protective effects of BBR, as evidenced by the increased expression of nephrin and podocin, and the decreased the expression of caspase-3 and the ratio of Bax/Bcl-2. Moreover, BBR prevented the decrease in cell viability decrease and the apoptosis induced by TNF-α, interleukin (IL)-6 and lipopolysaccharide (LPS). Taken together, our data indicate that BBR exerts protective effects against CRF partly through the TRAF5-mediated activation of the NF-κB signaling pathway in mouse podocytes.

NF-κB in Hematological Malignancies

NF-κB (Nuclear Factor Κ-light-chain-enhancer of activated B cells) transcription factors are critical regulators of immunity, stress response, apoptosis, and differentiation. Molecular defects promoting the constitutive activation of canonical and non-canonical NF-κB signaling pathways contribute to many diseases, including cancer, diabetes, chronic inflammation, and autoimmunity. In the present review, we focus our attention on the mechanisms of NF-κB deregulation in hematological malignancies. Key positive regulators of NF-κB signaling can act as oncogenes that are often prone to chromosomal translocation, amplifications, or activating mutations. Negative regulators of NF-κB have tumor suppressor functions, and are frequently inactivated either by genomic deletions or point mutations. NF-κB activation in tumoral cells is also driven by the microenvironment or chronic signaling that does not rely on genetic alterations.

NF-κB deregulation in Hodgkin lymphoma

Hodgkin and Reed/Sternberg (HRS) cells in classical Hodgkin lymphoma (HL) show constitutive activity of both the canonical and non-canonical NF-κB signaling pathways. The central pathogenetic role of this activity is indicated from studies with HL cell lines, which undergo apoptosis upon NF-κB inhibition. Multiple factors contribute to the strong NF-κB activity of HRS cells. This includes interaction with other cells in the lymphoma microenvironment through CD30, CD40, BCMA and other receptors, but also recurrent somatic genetic lesions in various factors of the NF-κB pathway, including destructive mutations in negative regulators of NF-κB signaling (e.g. TNFAIP3, NFKBIA), and copy number gains of genes encoding positive regulators (e.g. REL, MAP3K14). In Epstein-Barr virus-positive cases of classical HL, the virus-encoded latent membrane protein 1 causes NF-κB activation by mimicking an active CD40 receptor. NF-κB activity is also seen in the tumor cells of the rare nodular lymphocyte predominant form of HL, but the causes for this activity are largely unclear.

Induction of IκB-ζ by Epstein-Barr virus latent membrane protein-1 and CD30

Activation of nuclear factor-κB (NF-κB) in Burkitt's lymphoma (BL) and Hodgkin's lymphoma (HL) cells is important in the transformation and development process of these lymphomas. Epstein-Barr virus (EBV) latent membrane protein-1 (LMP-1) and ligand-independent signaling by overexpressed CD30 are known to cause permanent activation of NF-κB in lymphomas. However, hyperactivation of NF-κB triggers cellular senescence and apoptosis. Here, we show that IκB-ζ, an inducible regulator of NF-κB, is constitutively expressed in BL and HL cell lines. In addition, immunohistochemical staining identified nuclear IκB-ζ‑positive BL cells, and Hodgkin and Reed-Sternberg cells in lymph nodes. Expression of LMP-1 and CD30 increased IκB-ζ expression at the transcriptional level. IκB-ζ promoter was regulated by activation of the NF-κB‑inducing kinase (NIK)/IκB kinase/NF-κB pathway via the carboxyl‑terminal tumor necrosis factor (TNF) receptor‑associated factor (TRAF)-interacting regions of LMP-1 and CD30. Interestingly, IκB-ζ inhibited NF-κB activation by LMP-1 and CD30. The results suggest that NF-κB-induced IκB-ζ negatively modulates NF-κB hyperactivation, resulting in a fine balance that ultimately endows a net evolutionary benefit to the survival of BL and HL cells.

RIP1 Cleavage in the Kinase Domain Regulates TRAIL-Induced NF-κB Activation and Lymphoma Survival

Although TRAIL is considered a potential anticancer agent, it enhances tumor progression by activating NF-κB in apoptosis-resistant cells. Cellular FLICE-like inhibitory protein (cFLIP) overexpression and caspase-8 activation have been implicated in TRAIL-induced NF-κB activation; however, the underlying mechanisms are unknown. Here, we report that caspase-8-dependent cleavage of RIP1 in the kinase domain (KD) and intermediate domain (ID) determines the activation state of the NF-κB pathway in response to tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) treatment. In apoptosis-sensitive cells, caspase-8 cleaves RIP1 in the KD and ID immediately after the recruitment of RIP1 to the receptor complex, impairing IκB kinase (IKK) recruitment and NF-κB activation. In apoptosis-resistant cells, cFLIP restricts caspase-8 activity, resulting in limited RIP1 cleavage and generation of a KD-cleaved fragment capable of activating NF-κB but not apoptosis. Notably, depletion of the cytoplasmic pool of TRAF2 and cIAP1 in lymphomas by CD40 ligation inhibits basal RIP1 ubiquitination but does not prompt cell death, due to CD40L-induced cFLIP expression and limited RIP1 cleavage. Inhibition of RIP1 cleavage at the KD suppresses NF-κB activation and cell survival even in cFLIP-overexpressing lymphomas. Importantly, RIP1 is constitutively cleaved in human and mouse lymphomas, suggesting that cFLIP-mediated and caspase-8-dependent limited cleavage of RIP1 is a new layer of mechanism that promotes NF-κB activation and lymphoma survival.

The enteropathogenic E. coli (EPEC) Tir effector inhibits NF-κB activity by targeting TNFα receptor-associated factors

Enteropathogenic Escherichia coli (EPEC) disease depends on the transfer of effector proteins into epithelia lining the human small intestine. EPEC E2348/69 has at least 20 effector genes of which six are located with the effector-delivery system genes on the Locus of Enterocyte Effacement (LEE) Pathogenicity Island. Our previous work implied that non-LEE-encoded (Nle) effectors possess functions that inhibit epithelial anti-microbial and inflammation-inducing responses by blocking NF-κB transcription factor activity. Indeed, screens by us and others have identified novel inhibitory mechanisms for NleC and NleH, with key co-operative functions for NleB1 and NleE1. Here, we demonstrate that the LEE-encoded Translocated-intimin receptor (Tir) effector has a potent and specific ability to inhibit NF-κB activation. Indeed, biochemical, imaging and immunoprecipitation studies reveal a novel inhibitory mechanism whereby Tir interaction with cytoplasm-located TNFα receptor-associated factor (TRAF) adaptor proteins induces their proteasomal-independent degradation. Infection studies support this Tir-TRAF relationship but reveal that Tir, like NleC and NleH, has a non-essential contribution in EPEC's NF-κB inhibitory capacity linked to Tir's activity being suppressed by undefined EPEC factors. Infections in a disease-relevant intestinal model confirm key NF-κB inhibitory roles for the NleB1/NleE1 effectors, with other studies providing insights on host targets. The work not only reveals a second Intimin-independent property for Tir and a novel EPEC effector-mediated NF-κB inhibitory mechanism but also lends itself to speculations on the evolution of EPEC's capacity to inhibit NF-κB function.

Ascorbate promotes epigenetic activation of CD30 in human embryonic stem cells

Human embryonic stem cells (hESCs) and induced pluripotent stem cells have the ability to adapt to various culture conditions. Phenotypic and epigenetic changes brought about by the culture conditions can, however, have significant impacts on their use in research and in clinical applications. Here, we show that diploid hESCs start to express CD30, a biomarker for malignant cells in Hodgkin's disease and embryonal carcinoma cells, when cultured in knockout serum replacement (KOSR)-based medium, but not in fetal calf serum containing medium. We identify the commonly used medium additive, ascorbate, as the sole medium component in KOSR responsible for CD30 induction. Our data show that this epigenetic activation of CD30 expression in hESCs by ascorbate occurs through a dramatic loss of DNA methylation of a CpG island in the CD30 promoter. Analysis of the phenotype and transcriptome of hESCs that overexpress the CD30 signaling domain reveals that CD30 signaling leads to inhibition of apoptosis, enhanced single-cell growth, and transcriptome changes that are associated with cell signaling, lipid metabolism, and tissue development. Collectively, our data show that hESC culture media that contain ascorbate trigger CD30 expression through an epigenetic mechanism and that this provides a survival advantage and transcriptome changes that may help adapt hESCs to in vitro culture conditions.

TRAF5 Deficiency Accelerates Atherogenesis in Mice by Increasing Inflammatory Cell Recruitment and Foam Cell Formation

Rationale:

Tumor necrosis factor receptor–associated factors (TRAFs) are cytoplasmic adaptor proteins for the TNF/interleukin-1/Toll-like receptor superfamily. Ligands of this family comprise multiple important cytokines such as TNFα, CD40L, and interleukin-1β that promote chronic inflammatory diseases such as atherosclerosis. We recently reported overexpression of TRAF5 in murine and human atheromata and that TRAF5 promotes inflammatory functions of cultured endothelial cells and macrophages.

Objective:

This study tested the hypothesis that TRAF5 modulates atherogenesis in vivo.

Methods and Results:

Surprisingly, TRAF5 −/− /LDLR −/− mice consuming a high-cholesterol diet for 18 weeks developed significantly larger atherosclerotic lesions than did TRAF5 +/+ /LDLR −/− controls. Plaques of TRAF5-deficient animals contained more lipids and macrophages, whereas smooth muscle cells and collagen remained unchanged. Deficiency of TRAF5 in endothelial cells or in leukocytes enhanced adhesion of inflammatory cells to the endothelium in dynamic adhesion assays in vitro and in murine vessels imaged by intravital microscopy in vivo. TRAF5 deficiency also increased expression of adhesion molecules and chemokines and potentiated macrophage lipid uptake and foam cell formation. These findings coincided with increased activation of JNK and appeared to be independent of TRAF2. Finally, patients with stable or acute coronary heart disease had significantly lower amounts of TRAF5 mRNA in blood compared with healthy controls.

Conclusions:

Unexpectedly, TRAF5 deficiency accelerates atherogenesis in mice, an effect likely mediated by increased inflammatory cell recruitment to the vessel wall and enhanced foam cell formation.

Two distinct signalling cascades target the NF-kappaB regulatory factor c-IAP1 for degradation

c-IAP1 (cellular inhibitor of apoptosis 1) has recently emerged as a negative regulator of the non-canonical NF-κB (nuclear factor κB) signalling cascade. Whereas synthetic IAP inhibitors have been shown to trigger the autoubiquitination and degradation of c-IAP1, less is known about the physiological mechanisms by which c-IAP1 stability is regulated. In the present paper, we describe two distinct cellular processes that lead to the targeted loss of c-IAP1. Recruitment of a TRAF2 (tumour necrosis factor receptor-associated factor 2)–c-IAP1 complex to the cytoplasmic domain of the Hodgkin's/anaplastic large-cell lymphoma-associated receptor, CD30, leads to the targeting and degradation of the TRAF2–c-IAP1 heterodimer through a mechanism requiring the RING (really interesting new gene) domain of TRAF2, but not c-IAP1. In contrast, the induced autoubiquitination of c-IAP1 by IAP antagonists causes the selective loss of c-IAP1, but not TRAF2, thereby releasing TRAF2. Thus c-IAP1 can be targeted for degradation by two distinct processes, revealing the critical importance of this molecule as a regulator of numerous intracellular signalling cascades.

Phosphorylation of TRAF2 within its RING domain inhibits stress-induced cell death by promoting IKK and suppressing JNK activation

Tumor necrosis factor (TNF) receptor-associated factor 2 (TRAF2) is an adaptor protein that modulates the activation of the c-Jun NH(2) terminal kinase (JNK)/c-Jun and IkappaB kinase (IKK)/nuclear factor-kappaB (NF-kappaB) signaling cascades in response to TNFalpha stimulation. Although many serine/threonine kinases have been implicated in TNFalpha-induced IKK activation and NF-kappaB-dependent gene expression, most of them do not directly activate IKK. Here, we report that protein kinase Czeta phosphorylates TRAF2 at Ser(55), within the RING domain of the protein, after TNFalpha stimulation. Although this phosphorylation event has a minimal effect on induction of the immediate/transient phase of IKK and JNK activation by TNFalpha, it promotes the secondary/prolonged phase of IKK activation and inhibits that of JNK. Importantly, constitutive TRAF2 phosphorylation increased both basal and inducible NF-kappaB activation and rendered Ha-Ras-V12-transformed cells resistant to stress-induced apoptosis. Moreover, TRAF2 was found to be constitutively phosphorylated in some malignant cancer cell lines and Hodgkin's lymphoma. These results reveal a new level of complexity in TNFalpha-induced IKK activation modulated by TRAF2 phosphorylation and suggest that TRAF2 phosphorylation is one of the events that are responsible for elevated basal NF-kappaB activity in certain human cancers.

TRAF2 phosphorylation modulates tumor necrosis factor alpha-induced gene expression and cell resistance to apoptosis

TRAF2 is an adaptor protein that regulates the activation of the c-Jun N-terminal kinase (JNK) and IkappaB kinase (IKK) signaling cascades in response to tumor necrosis factor alpha (TNF-alpha) stimulation. Although the downstream events in TNF-alpha signaling are better understood, the membrane-proximal events are still elusive. Here, we demonstrate that TNF-alpha and cellular stresses induce TRAF2 phosphorylation at serine 11 and that this phosphorylation is required for the expression of a subset of NF-kappaB target genes. Although TRAF2 phosphorylation had a minimal effect on the TNF-alpha-induced rapid and transient IKK activation, it was essential for secondary and prolonged IKK activation. Consistent with this, TRAF2 phosphorylation is not required for its recruitment to the TNFR1 complex in response to TNF-alpha stimulation but is required for its association with a cytoplasmic complex containing RIP1 and IKK. In addition, TRAF2 phosphorylation was essential for the full TNF-alpha-induced activation of JNK. Notably, TRAF2 phosphorylation increased both basal and inducible c-Jun and NF-kappaB activities and rendered cells resistant to stress-induced apoptosis. Moreover, TRAF2 was found to be constitutively phosphorylated in some lymphomas. These results unveil a new, finely tuned mechanism for TNF-alpha-induced IKK activation modulated by TRAF2 phosphorylation and suggest that TRAF2 phosphorylation contributes to elevated levels of basal NF-kappaB activity in certain human cancers.

The role of NF-kappaB in lymphoid malignancies

Nuclear Factor kappaB (NF-kappaB) transcription factors are central regulators of lymphocyte proliferation, survival and development. Although normally subject to tight control, constitutive activation of NF-kappaB promotes inappropriate lymphocyte survival and proliferation, and is recognised as key pathological feature in various lymphoid malignancies. Inhibition of NF-kappaB may be an attractive therapeutic approach in these diseases. This review focuses on the mechanisms and functional consequences of NF-kappaB activation in lymphoid malignancies and potential therapeutic strategies for inhibition of NF-kappaB.

Hypomethylation of CD30 CpG islands with aberrant JunB expression drives CD30 induction in Hodgkin lymphoma and anaplastic large cell lymphoma

High expression of CD30 and JunB is the hallmark of malignant cells in Hodgkin lymphoma (HL) and anaplastic large cell lymphoma (ALCL). Ligand-independent signaling by CD30 induces JunB, which activates the CD30 promoter, stabilizing CD30 expression and supporting the survival of Hodgkin-Reed-Sternberg (H-RS) and ALCL cells. Here we show for the first time CpG islands encompassing 60 CpG dinucleotides, located in the core promoter, exon 1 and intron 1 of CD30 gene. Analysis of the methylation status of CD30 CpG islands in H-RS, ALCL and unrelated cell lines reveals an inverse relationship between the extent of CD30 CpG methylation and CD30 expression. CD30 CpG islands of H-RS and ALCL cell lines are rarely methylated. Methylation of the CD30 promoter decreases CD30 induction and JunB action on the demethylated CD30 promoter enhances CD30 induction. CD30 and JunB are strongly expressed in H-RS and ALCL cells, whereas they are not expressed in nonmalignant lymphocytes in which CD30 CpG islands are rarely methylated. We conclude that constitutive action of aberrantly expressed JunB on hypomethylated CD30 CpG islands of lymphocytes triggers CD30 induction and initiates activation of the JunB-CD30-JunB loop, essential to the pathogenesis of HL and ALCL.

Targeting TRAFs for Therapeutic Intervention

TNF-receptor associated factors (TRAFs) are the molecules that upon engagement of the TNF-receptor (TNFR) by a TNF-family ligand come first in contact with the activated TNFR, initially acting as docking molecules for kinases and other effector proteins that are recruited to the activated receptor. TRAFs later regulate the subcellular relocalization of the receptor-ligand complex and finally they modulate the extent of the response by controlling the degradation of key proteins in the pathway. In this chapter, we review the involvement of different TRAF family members in the etiology of a variety of pathologies and address the question of whether the use of TNFR-mimic-peptides or small molecule modulators targeting TRAFs might be suitable for therapeutic intervention, discussing the advantages and disadvantages of this strategy.

The Pathogenesis of Classical Hodgkin's Lymphoma: A Model for B-Cell Plasticity

It has been shown that differentiated lymphoid cells can display a broad developmental potential and might even differentiate into other cell types. Recent data implicate such processes in the pathogenesis of classical Hodgkin's lymphoma (HL). In the malignant, B cell-derived Hodgkin's and Reed-Sternberg (HRS) cells of HL the expression of B cell-specific genes is lost, and B lineage-inappropriate genes are up-regulated. Experimental evidence has been presented in recent years that functional disruption of the B lineage-specific transcription factor program contributes to this process. HRS cells might be reprogrammed into cells resembling undifferentiated progenitor cells, which might offer an explanation for the unique HL phenotype and demonstrate a high degree of plasticity of human lymphoid cells.

Epstein-Barr virus (EBV) latent membrane protein-1 down-regulates tumor necrosis factor-alpha (TNF-alpha) receptor-1 and confers resistance to TNF-alpha-induced apoptosis in T cells: implication for the progression to T-cell lymphoma in EBV-associated hemophagocytic syndrome

The infection of T cells by Epstein-Barr virus (EBV) may result in hemophagocytic syndrome (HPS) through enhanced cytokine secretion, particularly tumor necrosis factor-alpha (TNF-alpha), by EBV latent membrane protein-1 (LMP-1). One bewildering observation of HPS patients is relapsing disease or progression to T-cell lymphoma. This finding raises the question whether EBV LMP-1-expressing T cells may survive and proliferate in the cytokine milieu of HPS. To explore this possibility, we tested the sensitivity of LMP-1-expressing T cells to apoptosis in the presence of TNF-alpha. LMP-1 up-regulated TNF-alpha through TRAF2,5 and nuclear factor-kappaB pathway in T cells. The LMP-1-expressing T cells then became resistant to TNF-alpha-induced apoptosis. Interestingly, the expression of TNFR1 was remarkably down-regulated by LMP-1 in T cells. Furthermore, the TNF-alpha/TNFR1 downstream death signal TNFR1-associated death domain protein was constitutively recruited by LMP-1, and the activities of apoptotic caspases 3, 8, and 9 were suppressed. Reconstitution of TNFR1 successfully reversed the TNF-alpha-induced apoptotic cascades. Therefore, EBV LMP-1 not only activates T cells to proliferate but also confers resistance to TNF-alpha-mediated apoptosis via down-regulation of TNFR1 in the cytokine milieu of HPS. This finding provides a potential mechanism to explain the disease persistence or progression to T-cell lymphoma in HPS patients.

Aberrant NF-kappaB signaling in lymphoma: mechanisms, consequences, and therapeutic implications

The transcription factor NF-kappaB is a tightly regulated positive mediator of T- and B-cell development, proliferation, and survival. The controlled activity of NF-kappaB is required for the coordination of physiologic immune responses. However, constitutive NF-kappaB activation can promote continuous lymphocyte proliferation and survival and has recently been recognized as a critical pathogenetic factor in lymphoma. Various molecular events lead to deregulation of NF-kappaB signaling in Hodgkin disease and a variety of T- and B-cell non-Hodgkin lymphomas either up-stream or downstream of the central IkappaB kinase. These alterations are prerequisites for lymphoma cell cycling and blockage of apoptosis. This review provides an overview of the NF-kappaB pathway and discusses the mechanisms of NF-kappaB deregulation in distinct lymphoma entities with defined aberrant pathways: Hodgkin lymphoma (HL), diffuse large B-cell lymphoma (DLBCL), mucosa-associated lymphoid tissue (MALT) lymphoma, primary effusion lymphoma (PEL), and adult T-cell lymphoma/leukemia (ATL). In addition, we summarize recent data that validates the NF-kappaB signaling pathway as an attractive therapeutic target in T- and B-cell malignancies.

Molecular pathogenesis of Hodgkin's lymphoma

According to the WHO classification, Hodgkin's lymphoma (HL) is subdivided into a classical variant and a nodular lymphocyte predominant variant which are characterized by the presence of Hodgkin's and Reed-Sternberg (H-RS) cells or lymphocytic and histiocytic (L&H) cells, respectively. This article reviews genetic characteristics and transcriptional changes of H-RS and L&H cells, including recent knowledge about transforming mechanisms and signaling pathways that contribute to the antiapoptotic phenotype displayed by H-RS and L&H cells. We also discuss major cellular and molecular mediators contributing to the establishment and maintenance of a reactive background in HL-affected tissues. We believe that an in-depth understanding of the pathogenesis of HL will eventually lead to the development of novel biologically based therapeutic strategies in the near future.

JunB Induced by Constitutive CD30–Extracellular Signal-Regulated Kinase 1/2 Mitogen-Activated Protein Kinase Signaling Activates the CD30 Promoter in Anaplastic Large Cell Lymphoma and Reed-Sternberg Cells of Hodgkin Lymphoma

High expression of CD30 and JunB is characteristic of tumor cells in anaplastic large cell lymphoma (ALCL) and Hodgkin lymphoma (HL). Possible interactions of CD30 and JunB were examined in this study. We found that the CD30 promoter in tumor cells of both nucleophosmin (NPM)-anaplastic lymphoma kinase (ALK)-positive and NPM-ALK-negative ALCL and HL is regulated by a constitutively active CD30-extracellular signal-regulated kinase (ERK) 1/2 mitogen-activated protein kinase (MAPK). Phosphorylation of ERK1/2 MAPK was confirmed in nuclei of tumor cells in both ALCL and HL. CD30-ERK1/2 MAPK signals induce JunB expression, which maintains high activity of the CD30 promoter. JunB induction seems to be largely independent of nuclear factor kappaB in ALCL and HL. These results show a common mechanism of CD30 overexpression in ALCL and HL, although the outcome of CD30 signaling differs between NPM-ALK-positive ALCL and NPM-ALK-negative ALCL, cutaneous ALCL, and HL as we recently reported.

Signaling via the anti-CD30 mAb SGN-30 sensitizes Hodgkin's disease cells to conventional chemotherapeutics

SGN-30, a monoclonal antibody with activity against CD30+ malignancies, is currently in phase II clinical evaluation for treatment of Hodgkin's disease (HD) and anaplastic large cell lymphoma. The mechanisms underlying SGN-30's antitumor activity were investigated using cDNA array of L540 cells. SGN-30 treatment activated NF-kappaB and modulation of several messages including the growth regulator p21WAF1/CIP1 (p21) and cellular adhesion marker ICAM-1. p21 protein levels increased coincident with growth arrest and Annexin V/PI staining in treated HD cells. To determine if SGN-30-induced growth arrest would sensitize tumor cells to chemotherapeutics used against HD, L540cy and L428 cells were exposed to SGN-30 in combination with a panel of cytotoxic agents and resultant interactions quantified by the Combination Effects Method. Interactions between SGN-30 and all cytotoxic agents examined were additive or better. These in vitro data translated to increased efficacy of SGN-30 and bleomycin against L540cy tumor xenografts. In addition to direct cell killing, SGN-30 affects growth arrest and drug sensitization through growth regulating and proapoptotic machinery. Importantly, these data suggest that SGN-30 can enhance the efficacy of standard chemotherapies used to treat patients with CD30+ malignancies.

Epstein-Barr virus LMP1 inhibits the expression of SAP gene and upregulates Th1 cytokines in the pathogenesis of hemophagocytic syndrome

The primary infection of Epstein-Barr virus (EBV) may result in fatal infectious mononucleosis or hemophagocytic syndrome (HPS) in 2 diseases; that is, X-linked lymphoproliferative disorder (XLP) and hemophagocytic lymphohistiocytosis (HLH). XLP is linked to mutations of the SAP/SH2D1A gene with dysregulated T-cell activation in response to EBV infection. Patients with sporadic HLH, however, usually have no mutation of the SAP/SH2D1A gene, and EBV latent membrane protein-1 (LMP1) can up-regulate Th1 cytokines in EBV-infected T cells. Since both diseases share common manifestations of HPS, it is important to clarify whether a cross-talk exists between signaling lymphocyte activation molecule (SLAM)-associated protein (SAP) and LMP1-mediated pathways to explain the common pathogenesis of HPS. In this study, no mutation of the SAP/SH2D1A gene at exon 2/3 was detected in 7 HLH cases. Interestingly, EBV LMP1 could transcriptionally inhibit the expression of SAP/SH2D1A and activate downstream molecules ERK and interferon-gamma (IFN-gamma). LMP1-mediated SAP/ERK/IFN-gamma signals appear to act via the TNF receptor-associated factor (TRAF)2,5/nuclear factor kappaB (NF-kappaB) pathway, since dominant-negative TRAF2/5 and NF-kappaB inhibitor could rescue SAP expression and downregulate IFN-gamma. Although HLH is genetically distinct from XLP, our data suggest that both diseases share a common signal pathway, through either the mutation or LMP1-mediated suppression of the SAP gene, leading to overt T-cell activation and enhanced Th1 cytokine secretion in response to EBV infection.

A beginner's guide to NF-kappaB signaling pathways

Nuclear factor kappaB (NF-kappaB) belongs to a family of heterodimeric transcription factors that play a key role in inflammatory and stress responses as well as in tumor cell resistance to apoptosis. These effects are due to the NF-kappaB-dependent transcription of many proinflammatory and antiapoptotic genes, whose products ensure various cell responses to environmental conditions. The signal transduction pathways leading to NF-kappaB activation are well characterized, and the different steps implicated in these pathways involve proteins that could constitute targets for NF-kappaB inhibition. Several inhibitors aiming to prevent NF-kappaB activity and thus the transcription of target genes are studied, and a few compounds seem particularly promising. We try here to summarize the advantages that can issue from various studies on NF-kappaB.

From Hodgkin disease to Hodgkin lymphoma: biologic insights and therapeutic potential

Reclassification of Hodgkin disease as Hodgkin lymphoma (HL) represents a milestone in the lymphoma field, awarding recent insights in the molecular biology of Hodgkin and Reed-Sternberg (H-RS) cells and their environment. This review summarizes antiapoptotic and proproliferative pathways involved in the pathogenesis of this disease with the ultimate goal of translating laboratory knowledge into clinical decision making. The focus is on potential targets and novel drugs, which are discussed in the context of the complex biology of HL. Considering that HL patients are more likely to die from acute and late treatment-related toxicities than from HL itself, the introduction of targeted, biologically based therapies for HL patients with palliative and eventually curative intention might be justified. (Blood. 2005;105:4553-4560)

Elevated expression of CD30 in adult T-cell leukemia cell lines: possible role in constitutive NF-kappaB activation

Background

Human T-cell leukemia virus type 1 (HTLV-1) is associated with the development of adult T-cell leukemia (ATL). HTLV-1 encoded Tax1 oncoprotein activates the transcription of genes involved in cell growth and anti-apoptosis through the NF-κB pathway, and is thought to play a critical role in the pathogenesis of ATL. While Tax1 expression is usually lost or minimal in ATL cells, these cells still show high constitutive NF-κB activity, indicating that genetic or epigenetic changes in ATL cells induce activation independent of Tax1. The aim of this study was to identify the molecules responsible for the constitutive activation of NF-κB in ATL cells using a retroviral functional cloning strategy.

Results

Using enhanced green fluorescent protein (EGFP) expression and blasticidin-resistance as selection markers, several retroviral cDNA clones exhibiting constitutive NF-κB activity in Rat-1 cells, including full-length CD30, were obtained from an ATL cell line. Exogenous stable expression of CD30 in Rat-1 cells constitutively activated NF-κB. Elevated expression of CD30 was identified in all ATL lines examined, and primary ATL cells from a small number of patients (8 out of 66 cases).

Conclusion

Elevated CD30 expression is considered one of the causes of constitutive NF-κB activation in ATL cells, and may be involved in ATL development.

TRAF2 is essential for TNF-alpha-induced osteoclastogenesis

TRAF2-deficient mice show embryonic lethality, and we developed a new in vitro differentiation system to show the function of TRAF2 in osteoclastogenesis, in which osteoclast progenitors are derived from the fetal liver of TRAF2-deficient mice. Using this system, we showed that TRAF2 is required for TNF-alpha-induced osteoclastogenesis.

INTRODUCTION

TNF receptor-associated factor 2 (TRAF2) is a signal transducer for RANK and for two TNF receptor isotypes, TNFR1 and TNFR2. Because TRAF2-deficient mice show embryonic lethality, it has remained unclear whether TRAF2 is crucial in RANKL- or TNF-alpha-induced osteoclastogenesis.

MATERIALS AND METHODS

Osteoclast progenitors derived from fetal liver were cultured in the presence of monocyte macrophage colony-stimulating factor (M-CSF), and flow cytometry for characterization of surface markers on these cells was performed. To examine the involvement of TRAF2 in osteoclast differentiation, we cultured osteoclast progenitors from TRAF2-deficient and wildtype mice with soluble RANKL or TNF-alpha in the presence of M-CSF, and counted the number of TRACP(+) multinucleate cells formed. c-jun N-terminal kinase (JNK) and NF-kappaB activation in osteoclast progenitors was examined by Western blot analysis and electrophoretic mobility shift assay, respectively. Nuclear factor of activated T cells (NFATc1) expression and activation were analyzed by RT-PCR and immunofluorescence staining, respectively. To examine whether TRAF2 overexpression induced osteoclastogenesis, TRAF2 was overexpressed in osteoclast progenitors form wildtype bone marrow by retrovirus infection.

RESULTS AND CONCLUSIONS

Osteoclast progenitors from normal fetal liver, which were cultured with M-CSF, expressed surface molecules c-fms, Mac-1, and RANK, and could differentiate into TRACP(+) multinucleate cells in the presence of soluble RANKL or TNF-alpha. RANKL-induced osteoclastogenesis gave a reduction of 20% in the progenitors from TRAF2-deficient mice compared with that of the cells from littermate wildtype mice, whereas TNF-alpha-induced osteoclastogenesis was severely impaired in the cells from the TRAF2-deficient mice. Only a few TRACP(+) multinucleate cells were formed, and TNF-alpha-mediated activation of JNK, NF-kappaB, and NFATc1 was defective. TRAF2 overexpression induced differentiation of osteoclast progenitors from wildtype mice into TRACP(+) multinucleate cells. These results suggest that TRAF2 plays an important role in TNF-alpha-induced osteoclastogenesis.

Ubiquitin chains in the ladder of MAPK signaling

With a better understanding of the cellular stress response, it has become evident that catalytic modules consisting of kinases that mediate the activation of downstream effector components are subject to multiple layers of regulation. Such regulatory mechanisms are not limited to those involving scaffold proteins or protein phosphatases, and they appear to include a growing number of modifications by ubiquitin and ubiquitin-like proteins. The role of ubiquitin in the regulation of mitogen-activated protein kinase (MAPK) emerges as a paradigm for understanding the role of ubiquitination in regulating other signal transduction pathways. Ubiquitination influences signal diversification and limits the duration of the signal through its role in the assembly of protein kinase complexes, subcellular localization, and the actual degradation of the kinase or its substrate. This review summarizes our current understanding of the roles of ubiquitin in regulating MAPK signaling.

A novel NF-?B inhibitor DHMEQ selectively targets constitutive NF-?B activity and induces apoptosis of multiple myeloma cellsin vitro andin vivo

Multiple myeloma (MM) is a fatal lymphoid malignancy that is incurable with conventional modalities of chemotherapy. Strong and constitutive activation of nuclear factor kappa B (NF-kappaB) is a common characteristic of MM cells. In our study we successfully target NF-kappaB with a novel NF-kappaB inhibitor dehydroxymethylepoxyquinomycin (DHMEQ). DHMEQ completely abrogates constitutive NF-kappaB activity and induces apoptosis of MM cells, whereas control peripheral blood mononuclear cells (PBMC) are resistant to NF-kappaB inhibition and apoptosis by DHMEQ treatment. DHMEQ inhibition of NF-kappaB triggers activation of caspases 8 and 9, as well as G0/G1 cell cycle arrest accompanied by downregulation of antiapoptotic genes Bcl-XL and c-FLIP and cell cycle progression gene cyclins D1 and D2. DHMEQ-mediated inhibition of vascular endothelial growth factor (VEGF) production in MM cells raises the possibility that DHMEQ abrogates the autocrine VEGF loop and enhances its antitumor effects by inhibiting neovascularization in the bone marrow. Using an in vivo NOD/SCID/gammac(null) (NOG) mice model, we show that DHMEQ has a potent inhibitory effect on the growth of MM cells. Compared to other compounds having the potential to inhibit NF-kappaB, DHMEQ is a unique compound that blocks the translocation of NF-kappaB p65 into the nucleus and selectively targets NF-kappaB activated in tumor cells. Therefore, our study presents a new molecular target therapy in MM.

A novel dominant-negative mutant form of Epstein-Barr virus latent membrane protein-1 (LMP1) selectively and differentially impairs LMP1 and TNF signaling pathways

The latent membrane protein-1 (LMP1) is an integral membrane molecule expressed by Epstein-Barr virus (EBV) during viral latency and displays properties of a constitutively activated member of the TNF receptor family. LMP1 is required for B-cell or monocyte immortalization induced by EBV and is sufficient to transform rodent fibroblasts. Transforming potential of LMP1 is mediated by its cytoplasmic C-terminal domain, which activates various cellular signaling pathways including NFkappaB and JNK. In this report, we constructed mutants of LMP1 with preserved membrane spanning domain but mutated in the C-terminal domain and a second truncated C-terminal LMP1 fused to the enhanced green fluorescent protein. This latter mutant, termed LMP1-CT, impairs signaling by ectopic LMP1 as well as endogenous EBV-expressed wild-type (wt) LMP1. In contrast to dominant-negative mutants of LMP1 with preserved membrane spanning domains, LMP1-CT was unable to bind wt LMP1 to form an inactive complex. Its dominant-negative effects were due to binding and sequestration of LMP1 adapters TRAF2 and TRADD as assessed by coimmunoprecipitation experiments and confocal analysis. The effect was selective since LMP1-CT did not inhibit IL-1beta-induced signaling, whereas it impaired TNF-triggered NFkappaB and JNK signals without affecting TNF-induced apoptosis. In addition and in contrast to LMP1 constructs with membrane localization, LMP-CT did not display cytostatic properties in noninfected cells. Importantly, LMP1-CT inhibited survival induced by LMP1 in an EBV-transformed T-cell line expressing the type II viral latency commonly found in the majority of EBV-associated human tumors. These data demonstrate that LMP1-CT is a new tool to explore the differences between LMP1 and TNF signaling and may facilitate the design of molecules with potential therapeutic roles.

The NPM-ALK oncoprotein abrogates CD30 signaling and constitutive NF-kappaB activation in anaplastic large cell lymphoma

NPM-ALK characterizes anaplastic large cell lymphoma (ALCL), as does the high expression of CD30, a feature shared with H-RS cells of classic Hodgkin's lymphoma. In H-RS cells, ligand-independent signaling by overexpressed CD30 drives constitutive NF-kappaB activation, which is absent in ALCL cells. Here we show that NPM-ALK impedes CD30 signaling and NF-kappaB activation, dependent on both ALK kinase activity and the N-terminal NPM domain. NPM-ALK transduction into H-RS cell lines abrogates recruitment and aggregation of TRAF proteins, inducing an ALCL-like morphology and phenotype. TRAF2 associates with NPM-ALK at a consensus binding motif located in the kinase domain. Thus, NPM-ALK abrogates CD30-driven NF-kappaB activation and can also induce an ALCL phenotype, distinguishing ALCL cells from H-RS cells of T cell origin.

Ubiquitination and translocation of TRAF2 is required for activation of JNK but not of p38 or NF-kappaB

TRAF2 is a RING finger protein that regulates the cellular response to stress and cytokines by controlling JNK, p38 and NF-kappaB signaling cascades. Here, we demonstrate that TRAF2 ubiquitination is required for TNFalpha-induced activation of JNK but not of p38 or NF-kappaB. Intact RING and zinc finger domains are required for TNFalpha-induced TRAF2 ubiquitination, which is also dependent on Ubc13. TRAF2 ubiquitination coincides with its translocation to the insoluble cellular fraction, resulting in selective activation of JNK. Inhibition of Ubc13 expression by RNAi resulted in inhibition of TNFalpha-induced TRAF2 translocation and impaired activation of JNK but not of IKK or p38. TRAF2 aggregates in the cytoplasm, as seen in Hodgkin-Reed-Sternberg lymphoma cells, resulting in constitutive NF-kappaB activity but failure to activate JNK. These findings demonstrate that the TRAF2 RING is required for Ubc13-dependent ubiquitination, resulting in translocation of TRAF2 to an insoluble fraction and activation of JNK, but not of p38 or NF-kappaB. Altogether, our findings highlight a novel mechanism of TRAF2-dependent activation of diverse signaling cascades that is impaired in Hodgkin-Reed-Sternberg cells.

The human anti-CD30 antibody 5F11 shows in vitro and in vivo activity against malignant lymphoma

CD30 is a promising target for antibody-based immunotherapy of Hodgkin lymphoma (HL) and anaplastic large cell lymphoma. To overcome the limitations from currently available murine anti-CD30 monoclonal antibodies (mAbs), a new fully human anti-CD30 antibody was generated. Binding properties were evaluated by recombinant CD30 capture enzyme-linked immunosorbent assay (ELISA) and fluorescence-activated cell-sorter (FACS) flow cytometry. Activity of this new mAb was assessed in vitro using growth inhibition and antibody-dependent cellular cytotoxicity (ADCC) assays on several cell lines. In vivo activity was determined in a solid as well as in a disseminated xenografted model of HL in severe combined immunodeficiency (SCID) mice. The mAb 5F11 showed specific binding to CD30 (cluster A). The ADCC assays indicated dose-dependent lysis of L540 cells when 5F11 was combined with human effector cells. Upon cross-linking in vitro, 5F11 inhibited the growth of CD30-expressing cell lines. In vivo, treatment with 5F11 induced a marked growth delay or even a complete regression of established xenografted HL in SCID mice. In the disseminated HL model, a high proportion of 5F11-treated mice experienced long-term survival. The new human anti-CD30 monoclonal antibody 5F11 shows promise as a means of CD30-targeted immunotherapy of malignant lymphomas. Based on these results, a clinical phase 1 study in patients with refractory CD30+ lymphoma has been initiated.

NF-κB/Rel-mediated regulation of apoptosis in hematologic malignancies and normal hematopoietic progenitors

The activity of NF-kappaB/Rel transcription factors can downmodulate apoptosis in normal and neoplastic cells of the hematologic and other compartments, contributing in maintaining neoplastic clone survival and impairing response to therapy. Alterations in nfkappab or ikappaB genes are documented in some hematologic neoplasias, while in others dysfunction in NF-kappaB/Rel-activating signaling pathways can be recognized. The prosurvival properties of NF-kappaB/Rel appear to rely on the induced expression of molecules (caspase inhibitors, Bcl2 protein family members, etc.), which interfere with the apoptosis pathway. Constitutive NF-kappaB/Rel activity in some hematologic malignancies could be advantageous for neoplastic clone expansion by counteracting stress stimuli (consumption of growth factors and metabolites) and immune system-triggered apoptosis; it is furthermore likely to play a central role in determining resistance to therapy. Based on this evidence, NF-kappaB/Rel-blocking approaches have been introduced in antineoplastic strategies. The identification of NF-kappaB/Rel target genes relevant for survival in specific neoplasias is required in order to address tailored therapies and avoid possible detrimental effects due to widespread NF-kappaB/Rel inhibition. Moreover, comparative analyses of normal hematopoietic progenitors and neoplastic cell sensitivities to inhibitors of NF-kappaB/Rel and their target genes will allow to evaluate the impact of these tools on normal bone marrow.

A concept of essentially secondary factors central to definitive subtype characterization of Hodgkin's disease

Conceptually, Hodgkin's disease would appear to constitute a neoplasm that integrally incorporates responsive cellular elements in terms strictly of morphologic patterns of interaction resulting especially in a predictable scale of therapeutic and prognostic implications as related particularly to pathobiologic course and response to treatment. In this sense, Hodgkin's disease might in a real sense constitute a valid point of reference in terms of processes not only in the generation of the neoplastic process but particularly in terms of how such a neoplastic process interacts with host systems in specifically characterizing the very nature of the intrinsic neoplastic process itself. In this manner, therefore, it might be valid to consider the totality of manifestations of Hodgkin's disease as a fundamental series of processes that integrally determines the genesis and nature of the neoplastic process as a function especially of various host systems in response to that neoplasm. In terms strictly related to a viral or Epstein-Barr virus-related development of Hodgkin's disease, it might perhaps be true that transcription factor NF-kappaB might induce the signaling of a CD30 receptor pathway that is intrinsically linked with anti-apoptosis of germinal center lymphocytes. In overall terms, perhaps, the Epstein-Barr viral nuclear antigens such as Latent membrane protein 1 would activate NF-kappaB as a mechanism that induces anti-apoptotic effect by multiple pathways in the added context particularly of a concerted series of cytokines that secondarily regulate T lymphocyte response. Indeed, in simple terms, Hodgkin's disease would appear to involve a basic mechanism of induced transcription as an effective anti-apoptotic mechanism as exerted on Reed-Sternberg cells. The Epstein-Barr viral nuclear antigens might be pivotal in orchestrating a full series of cytokine and T lymphocyte responses that would perhaps contribute significantly to the effective perpetuation of such anti-apoptotic effect or effects as exerted on the Reed-Sternberg cells.

AP-1 mediated relief of repressive activity of the CD30 promoter microsatellite in Hodgkin and Reed-Sternberg cells

Overexpression of CD30 is the hallmark of Hodgkin and Reed-Sternberg (H-RS) cells and drives constitutive nuclear factor-kappaB activation that is the molecular basis for the pathophysiology of Hodgkin's lymphoma. Transcription of the CD30 gene is controlled by the core promoter that is driven by Sp-1 and the microsatellite sequences (MSs) that represses core promoter activity. To understand the mechanism(s) of CD30 overexpression in H-RS cells, we structurally and functionally characterized the CD30 MSs. Although the CD30 MS of H-RS cell lines was polymorphic, it was not truncated compared with that of control cells. A strong core promoter activity and constitutive Sp-1 binding were revealed in all cell lines examined irrespective of the levels of CD30 expression. In transient reporter gene assays, all MS clones derived from H-RS cell lines repressed the core promoter activity in unrelated cell lines, but not in the H-RS cell lines. An AP-1-binding site was found in the MS at nucleotide position of -377 to -371, the presence of which was found to relieve repression of the core promoter in H-RS cell lines but not in other tumor cell lines. H-RS cell lines showed constitutive and strong AP-1-binding activity, but other cell lines did not. The AP-1 complex contained JunB, whose overexpression activated reporter constructs driven by the CD30 promoter including the MSs, and was dependent on the AP-1 site. JunB expression was detected in H-RS cells in vitro and in vivo, but not in reactive cells or tumor cells of non-Hodgkin's lymphoma of diffuse large B-cell type. Transduction of JunB small interfering RNAs suppressed CD30 promoter activity in L428 cells but not in control cells. Taken together, overexpression and binding of JunB to the AP-1 site appear to relieve the repression of the core promoter by the CD30 MS in H-RS cells, which provide one basis for the constitutive overexpression of CD30 in Hodgkin's lymphoma.

Expression and a role of CD30 in regulation of T-cell activity

CD30 receptor has been known for almost 20 years, but its expression and activity are still the subject of many investigations. Its expression was found in different malignancies, and most of the studies regarding CD30 focus on its role in lymphomas. The progress that has already been made in this field is reflected in implementation of CD30 as a target for immunotoxin, which has been tested in phase I study in treating Hodgkin lymphoma. CD30 is present also on normal, activated T cells of all cytokine profiles. However, increased density of CD30 and CD30-mediated Th2 cytokine production provide evidence of its role in determining the activity of T cells toward synthesis of cytokines and involvement in reactions of Th2 characteristics. Pleiotropic signaling mediated by CD30 does not implicate this receptor just as a cytokine costimulator; it proves to be important in several different activities of T cells.

The molecular basis for the generation of Hodgkin and Reed-Sternberg cells in Hodgkin's lymphoma

Hodgkin's lymphoma (HL) is a lymphoid neoplasm with a low frequency of malignant tumor cells, known as Hodgkin and Reed-Sternberg (H-RS) cells, in a background of mixed cellular infiltrates. Despite extensive studies on H-RS cells, the molecular mechanisms of their growth and regulation have remained uncertain for a long period. Recently, constitutively activated nuclear factor-kappaB (NF-kappaB) was reported to be a unique and common characteristic of H-RS cells that prevents the cells from undergoing apoptosis. NF-kappaB triggers proliferation and provides a molecular basis for these cells' aberrant growth and cytokine gene expression. In HL pathogenesis associated with Epstein-Barr virus infection, the activation of NF-kappaB is induced by viral latent membrane protein 1 (LMP1). Coupled with recent insights into the molecular mechanisms of activation of NF-kappaB signaling in H-RS cells, this review discusses a linkage between LMP1 and HL via CD99, which has recently been reported to be down-regulated by LMP1 through the NF-kappaB signaling pathway. This down-regulation leads to the generation of cells with H-RS phenotypes related to the clinical and histologic characteristics of HL.

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.