Ryouichi Horie

Ligand-independent signaling by overexpressed CD30 drives NF-κB activation in Hodgkin–Reed-Sternberg cells

Overexpression of CD30 and constitutive NF-κB activation characterizes tumor cells of Hodgkins disease (HD), Hodgkin and Reed-Sternberg (H–RS) cells. We report that in H–RS cells overexpression of CD30 leads to self-aggregation, recruitment of TRAF2 and TRAF5, and NF-κB activation, independent of CD30 ligand. CD30 and TRAF proteins co-localized in H–RS cell lines and in lymph nodes of HD. An adenovirus-vector carrying a decoy CD30 lacking the cytoplasmic region or a dominant negative IκBα mutant blocks NF-κB activation, down regulates IL-13 expression and induces apoptosis. Thus, in H–RS cells, ligand-independent activation of CD30 signaling drives NF-κB activation and this leads to constitutive cytokine expression, which provides a molecular basis for HD. Inhibition of NF-κB activation by adenovirus vector-mediated gene transfer may provide a novel strategy of cell- and target molecule-specific therapy for patients with HD.

Tumor Necrosis Factor Receptor-associated Factor (TRAF) 5 and TRAF2 Are Involved in CD30-mediated NFκB Activation

Signals emanated from CD30 can activate the nuclear factor κB (NFκB). The two conserved subdomains, D1 and D2, in the C-terminal cytoplasmic region of CD30 were tested for interaction with two tumor necrosis factor receptor-associated factor (TRAF) proteins with NFκB activating capacity, TRAF2 and TRAF5. TRAF5 is the newest member of the TRAF family that binds to lymphotoxin β receptor and CD40. TRAF5, as well as TRAF2, interacted with the D2 subdomain of CD30 in vitro and in vivo. Deletion analysis by the yeast two-hybrid system revealed that the C-terminal 22 and 30 amino acid residues are dispensable for interaction of TRAF5 and TRAF2 with CD30, respectively. Substitution of alanine for threonine at 463 abolished the interaction with TRAF2. Overexpression of the TRAF domain of TRAF2 or TRAF5 showed a dominant negative effect on CD30-mediated NFκB activation. Simultaneous expression of these TRAF domains further suppressed the NFκB activation, suggesting an interplay of these TRAF proteins. Expression of TRAF2 and TRAF5 mRNA was demonstrated in T- and B-cell lines that express CD30. Taken together, our results indicate that TRAF2 and TRAF5 directly interact with CD30 and are involved in NFκB activation by CD30 signaling.

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.

Inactivation of NF-κB Components by Covalent Binding of (−)-Dehydroxymethylepoxyquinomicin to Specific Cysteine Residues

Previously, we designed and synthesized a potent NF-kappaB inhibitor, DHMEQ. Although DHMEQ showed potent anti-inflammatory and anticancer activities in animals, its molecular target has not been elucidated. In the present study, its target protein was found to be p65 and other Rel homology proteins. We found that (-)-DHMEQ bound to p65 covalently with a 1:1 stoichiometry by conducting SPR and MALDI-TOF MS analyses. MS analysis of the chymotrypsin-digested peptide suggested the binding of (-)-DHMEQ to a Cys residue. Formation of Cys/(-)-DHMEQ adduct in the protein was supported by chemical synthesis of the adduct. Substitution of specific Cys in p65 and other Rel homology proteins resulted in the loss of (-)-DHMEQ binding. (-)-DHMEQ is the first NF-kappaB inhibitor that was proven to bind to the specific Cys by chemical methodology. These findings may explain the highly selective inhibition of NF-kappaB and the low toxic effect of (-)-DHMEQ in cells and animals.

The NPM-ALK oncoprotein abrogates CD30 signaling and constitutive NF-κB 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 Hodgkins 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.

A novel NF‐κB inhibitor DHMEQ selectively targets constitutive NF‐κB activity and induces apoptosis of multiple myeloma cells in vitro and in 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‐κB) is a common characteristic of MM cells. In our study we successfully target NF‐κB with a novel NF‐κB inhibitor dehydroxymethylepoxyquinomycin (DHMEQ). DHMEQ completely abrogates constitutive NF‐κB activity and induces apoptosis of MM cells, whereas control peripheral blood mononuclear cells (PBMC) are resistant to NF‐κB inhibition and apoptosis by DHMEQ treatment. DHMEQ inhibition of NF‐κB 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/γcnull (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‐κB, DHMEQ is a unique compound that blocks the translocation of NF‐κB p65 into the nucleus and selectively targets NF‐κB activated in tumor cells. Therefore, our study presents a new molecular target therapy in MM.

Cytoplasmic Aggregation of TRAF2 and TRAF5 Proteins in the Hodgkin-Reed-Sternberg Cells

We previously reported that ligand-independent signaling by highly expressed CD30 in Hodgkin-Reed-Sternberg (H-RS) cells is responsible for constitutive activation of NF-kappa B. In the present study, we characterize the intracellular localization of tumor necrosis factor (TNF) receptor associated factor (TRAF) proteins in H-RS cells. Confocal immunofluorescence microscopy of cell lines derived from H-RS cells and HEK293 transformants highly expressing CD30 revealed aggregation of TRAF2 and TRAF5 in the cytoplasm as well as clustering near the cell membrane. In contrast, TRAF proteins were diffusely distributed in the cytoplasm in cell lines unrelated to Hodgkins disease (HD) and control HEK293 cells. Furthermore, the same intracellular distribution of TRAF proteins was demonstrated in H-RS cells of lymph nodes of HD, but not in lymphoma cells in lymph nodes of non-Hodgkins lymphoma. Dominant-negative TRAF2 and TRAF5 suppressed cytoplasmic aggregation along with constitutive NF-kappa B activation in H-RS cell lines. Confocal immunofluorescence microscopy also revealed co-localization of IKK alpha, NIK, and I kappa B alpha with aggregated TRAF proteins in H-RS cell lines. These results suggest involvement of TRAF protein aggregation in the signaling process of highly expressed CD30 and suggest they function as scaffolding proteins. Thus, cytoplasmic aggregation of TRAF proteins appears to reflect constitutive CD30 signaling which is characteristic of H-RS 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 Hodgkins 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-Hodgkins 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 Hodgkins lymphoma.

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 κB (NF-κ) activation is a common molecular feature. Molecular mechanisms responsible for constitutive NF-κB activation, Epstein Barr virus latent membrane protein 1, and defective IκBα and IκB 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-κB activation. Ligand-independent signaling by over-expressed CD30 was shown to be a common mechanism that induced constitutive NF-κB 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.

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

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