References of "Dejardin, Emmanuel"
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See detailContext-dependent roles for lymphotoxin-beta receptor signaling in cancer development.
Fernandes, Monica T.; Dejardin, Emmanuel ULg; Santos, Nuno R. Dos

in Biochimica et biophysica acta (2016)

The LTalpha1beta2 and LIGHT TNF superfamily cytokines exert pleiotropic physiological functions through the activation of their cognate lymphotoxin-beta receptor (LTbetaR). Interestingly, since the ... [more ▼]

The LTalpha1beta2 and LIGHT TNF superfamily cytokines exert pleiotropic physiological functions through the activation of their cognate lymphotoxin-beta receptor (LTbetaR). Interestingly, since the discovery of these proteins, accumulating evidence has pinpointed a role for LTbetaR signaling in carcinogenesis. Early studies have shown a potential anti-tumoral role in a subset of solid cancers either by triggering apoptosis in malignant cells or by eliciting an anti-tumor immune response. However, more recent studies provided robust evidence that LTbetaR signaling is also involved in diverse cell-intrinsic and microenvironment-dependent pro-oncogenic mechanisms, affecting several solid and hematological malignancies. Consequently, the usefulness of LTbetaR signaling axis blockade has been investigated as a potential therapeutic approach for cancer. Considering the seemingly opposite roles of LTbetaR signaling in diverse cancer types and their key implications for therapy, we here extensively review the different mechanisms by which LTbetaR activation affects carcinogenesis, focusing on the diverse contexts and different models assessed. [less ▲]

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See detailNIK promotes tissue destruction independently of the alternative NF-kappaB pathway through TNFR1/RIP1-induced apoptosis.
Boutaffala, L.; Bertrand, M. J. M.; Remouchamps, Caroline ULg et al

in Cell death and differentiation (2015), 10.1038/cdd.2015.69

NF-kappaB-inducing kinase (NIK) is well-known for its role in promoting p100/NF-kappaB2 processing into p52, a process defined as the alternative, or non-canonical, NF-kappaB pathway. Here we reveal an ... [more ▼]

NF-kappaB-inducing kinase (NIK) is well-known for its role in promoting p100/NF-kappaB2 processing into p52, a process defined as the alternative, or non-canonical, NF-kappaB pathway. Here we reveal an unexpected new role of NIK in TNFR1-mediated RIP1-dependent apoptosis, a consequence of TNFR1 activation observed in c-IAP1/2-depleted conditions. We show that NIK stabilization, obtained by activation of the non-death TNFRs Fn14 or LTbetaR, is required for TNFalpha-mediated apoptosis. These apoptotic stimuli trigger the depletion of c-IAP1/2, the phosphorylation of RIP1 and the RIP1 kinase-dependent assembly of the RIP1/FADD/caspase-8 complex. In the absence of NIK, the phosphorylation of RIP1 and the formation of RIP1/FADD/caspase-8 complex are compromised while c-IAP1/2 depletion is unaffected. In vitro kinase assays revealed that recombinant RIP1 is a bona fide substrate of NIK. In vivo, we demonstrated the requirement of NIK pro-death function, but not the processing of its substrate p100 into p52, in a mouse model of TNFR1/LTbetaR-induced thymus involution. In addition, we also highlight a role for NIK in hepatocyte apoptosis in a mouse model of virus-induced TNFR1/RIP1-dependent liver damage. We conclude that NIK not only contributes to lymphoid organogenesis, inflammation and cell survival but also to TNFR1/RIP1-dependent cell death independently of the alternative NF-kappaB pathway.Cell Death and Differentiation advance online publication, 5 June 2015; doi:10.1038/cdd.2015.69. [less ▲]

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See detailLymphotoxin-beta receptor in microenvironmental cells promotes the development of T-cell acute lymphoblastic leukaemia with cortical/mature immunophenotype.
Fernandes, Monica T.; Ghezzo, Marinella N.; Silveira, Andre B. et al

in British journal of haematology (2015)

Lymphotoxin-mediated activation of the lymphotoxin-beta receptor (LTbetaR; LTBR) has been implicated in cancer, but its role in T-cell acute lymphoblastic leukaemia (T-ALL) has remained elusive. Here we ... [more ▼]

Lymphotoxin-mediated activation of the lymphotoxin-beta receptor (LTbetaR; LTBR) has been implicated in cancer, but its role in T-cell acute lymphoblastic leukaemia (T-ALL) has remained elusive. Here we show that the genes encoding lymphotoxin (LT)-alpha and LTbeta (LTA, LTB) are expressed in T-ALL patient samples, mostly of the TAL/LMO molecular subtype, and in the TEL-JAK2 transgenic mouse model of cortical/mature T-ALL (Lta, Ltb). In these mice, expression of Lta and Ltb is elevated in early stage T-ALL. Surface LTalpha1 beta2 protein is expressed in primary mouse T-ALL cells, but only in the absence of microenvironmental LTbetaR interaction. Indeed, surface LT expression is suppressed in leukaemic cells contacting Ltbr-expressing but not Ltbr-deficient stromal cells, both in vitro and in vivo, thus indicating that dynamic surface LT expression in leukaemic cells depends on interaction with its receptor. Supporting the notion that LT signalling plays a role in T-ALL, inactivation of Ltbr results in a significant delay in TEL-JAK2-induced leukaemia onset. Moreover, young asymptomatic TEL-JAK2;Ltbr-/- mice present markedly less leukaemic thymocytes than age-matched TEL-JAK2;Ltbr+/+ mice and interference with LTbetaR function at this early stage delayed T-ALL development. We conclude that LT expression by T-ALL cells activates LTbetaR signalling in thymic stromal cells, thus promoting leukaemogenesis. [less ▲]

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See detailDUSP3 genetic deletion confers M2-like−macrophage-dependent tolerance to septic shock
Singh, Pratibha; Dejager, Lien; Amand, Mathieu ULg et al

in Journal of Immunology (2015), 194(10), 4951-62

DUSP3 is a small dual-specificity protein phosphatase with an unknown physiological function. We report that DUSP3 is strongly expressed in human and mouse monocytes and macrophages and that its ... [more ▼]

DUSP3 is a small dual-specificity protein phosphatase with an unknown physiological function. We report that DUSP3 is strongly expressed in human and mouse monocytes and macrophages and that its deficiency in mice promotes tolerance to lipopolysaccharide (LPS)-induced endotoxin shock and to polymicrobial septic shock following cecal ligation and puncture. By using adoptive transfer experiments, we demonstrate that resistance to endotoxin is macrophage-dependent and transferable and that this protection is associated with a striking increase of M2-like macrophages in DUSP3-/- mice in both the LPS and cecal ligation and puncture models. We show that the altered response of DUSP3-/- mice to sepsis is reflected in decreased TNF production and impaired ERK1/2 activation. Our results demonstrate that DUSP3 plays a key and non-redundant role as a regulator of innate immune responses by mechanisms involving the control of ERK1/2 activation, TNF secretion and macrophage polarization. [less ▲]

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See detailMethods to Assess the Activation of the Alternative (Noncanonical) NF-kappaB Pathway by Non-death TNF Receptors.
Remouchamps, Caroline ULg; Dejardin, Emmanuel ULg

in NF-kappa B: Methods and Protocols (2015)

The alternative or noncanonical NF-kappaB pathway regulates the generation of p52-containing NF-kappaB dimers (e.g., p52/RelB) through a partial degradation (called processing) of the precursor p100 into ... [more ▼]

The alternative or noncanonical NF-kappaB pathway regulates the generation of p52-containing NF-kappaB dimers (e.g., p52/RelB) through a partial degradation (called processing) of the precursor p100 into p52. This pathway is activated by a subset of non-death TNF receptor members, which ultimately activate two kinases: NIK (NF-kappaB-Inducing Kinase) and IKKalpha (Inhibitor of kappaB Kinase alpha). These kinases create a phosphodegron for the E3 ligase SCF-beta-TrCP that covalently binds K48-linked polyubiquitin chain onto p100 prior to its proteasomal processing. The resulting p52-containing complexes translocate into the nucleus to activate target genes involved in secondary lymphoid organ development, B cell survival or in osteoclastogenesis.We describe in this chapter straightforward methods to monitor the activation of the alternative NF-kappaB pathway. These methods uncover cytosolic and nuclear biochemical modifications of key proteins of the alternative NF-kappaB pathway required prior to the transcription of NF-kappaB target genes. [less ▲]

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See detailNF-kappaB-Independent Role of IKKalpha/IKKbeta in Preventing RIPK1 Kinase-Dependent Apoptotic and Necroptotic Cell Death during TNF Signaling.
Dondelinger, Yves; Jouan-Lanhouet, Sandrine; Divert, Tatyana et al

in Molecular cell (2015)

TNF is a master pro-inflammatory cytokine. Activation of TNFR1 by TNF can result in both RIPK1-independent apoptosis and RIPK1 kinase-dependent apoptosis or necroptosis. These cell death outcomes are ... [more ▼]

TNF is a master pro-inflammatory cytokine. Activation of TNFR1 by TNF can result in both RIPK1-independent apoptosis and RIPK1 kinase-dependent apoptosis or necroptosis. These cell death outcomes are regulated by two distinct checkpoints during TNFR1 signaling. TNF-mediated NF-kappaB-dependent induction of pro-survival or anti-apoptotic molecules is a well-known late checkpoint in the pathway, protecting cells from RIPK1-independent death. On the other hand, the molecular mechanism regulating the contribution of RIPK1 to cell death is far less understood. We demonstrate here that the IKK complex phosphorylates RIPK1 at TNFR1 complex I and protects cells from RIPK1 kinase-dependent death, independent of its function in NF-kappaB activation. We provide in vitro and in vivo evidence that inhibition of IKKalpha/IKKbeta or its upstream activators sensitizes cells to death by inducing RIPK1 kinase-dependent apoptosis or necroptosis. We therefore report on an unexpected, NF-kappaB-independent role for the IKK complex in protecting cells from RIPK1-dependent death downstream of TNFR1. [less ▲]

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See detailA Role for APPL1 in TLR3/4-dependent TBK1 and IKKe activation in macrophages
Chau, Tieu-Lan ULg; Göktuna, Serkan ULg; Rammal, Ayman et al

in Journal of Immunology (2015)

Endosomes have important roles in intracellular signal transduction as a sorting platform. Signaling cascades from TLR engagement to IRF3-dependent gene transcription rely on endosomes, yet the proteins ... [more ▼]

Endosomes have important roles in intracellular signal transduction as a sorting platform. Signaling cascades from TLR engagement to IRF3-dependent gene transcription rely on endosomes, yet the proteins that specifically recruit IRF3-activating molécules to them are poorly defined. We show that adaptor protein containing a pleckstrin-homology domain, a phosphotyrosine-binding domain, and a leucine zipper motif (APPL)1, an early endosomal protein, is required for both TRIF- and retinoic acid–inducible gene 1–dependent signaling cascades to induce IRF3 activation. APPL1, but not early endosome Ag 1, deficiency impairs IRF3 target gene expression upon engagement of both TLR3 and TLR4 pathways, as well as in H1N1-infected macrophages. The IRF3-phosphorylating kinases TBK1 and IKK« are recruited to APPL1 endosomes in LPS-stimulated macrophages. Interestingly, APPL1 undergoes proteasome-mediated degradation through ERK1/2 to turn off signaling. APPL1 degradation is blocked when signaling through the endosome is inhibited by chloroquine or dynasore. Therefore, APPL1 endosomes are critical for IRF3-dependent gene expression in response to some viral and bacterial infections in macrophages. Those signaling pathways involve the signal-induced degradation of APPL1 to prevent aberrant IRF3-dependent gene expression linked to immune diseases. [less ▲]

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See detailSpecific and Nonhepatotoxic Degradation of Nuclear Hepatitis B Virus cccDNA.
Lucifora, Julie; Xia, Yuchen; Reisinger, Florian et al

in Science (New York, N.Y.) (2014), 343

Current antivirals can control but not eliminate hepatitis-B-virus (HBV), because HBV establishes a stable nuclear cccDNA. Interferon-alpha treatment can clear HBV but is limited by systemic side effects ... [more ▼]

Current antivirals can control but not eliminate hepatitis-B-virus (HBV), because HBV establishes a stable nuclear cccDNA. Interferon-alpha treatment can clear HBV but is limited by systemic side effects. Here, we describe how interferon-alpha can induce specific degradation of the nuclear viral DNA without hepatotoxicity and propose lymphotoxin-beta-receptor activation as a therapeutic alternative. Interferon-alpha and lymphotoxin-beta-receptor activation up-regulated APOBEC3A and 3B cytidine-deaminases, respectively, in HBV-infected cells, primary hepatocytes and human liver-needle biopsies. HBV-core protein mediated the interaction with nuclear cccDNA resulting in cytidine-deamination, apurinic/apyrimidinic site formation and finally cccDNA degradation that prevented HBV-reactivation. Genomic DNA was not affected. Thus, inducing nuclear deaminases - e.g., by lymphotoxin-beta-receptor activation - allows development of new therapeutics that combined with existing antivirals may cure hepatitis B. [less ▲]

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See detailNoncanonical NF-kappaB Signaling Is Limited by Classical NF-kappaB Activity.
Gray, Carolyn M.; Remouchamps, Caroline ULg; McCorkell, Kelly A. et al

in Science signaling (2014), 7(311), 13

Precise regulation of nuclear factor kappaB (NF-kappaB) signaling is crucial for normal immune responses, and defective NF-kappaB activity underlies a range of immunodeficiencies. NF-kappaB is activated ... [more ▼]

Precise regulation of nuclear factor kappaB (NF-kappaB) signaling is crucial for normal immune responses, and defective NF-kappaB activity underlies a range of immunodeficiencies. NF-kappaB is activated through two signaling cascades: the classical and noncanonical pathways. The classical pathway requires inhibitor of kappaB kinase beta (IKKbeta) and NF-kappaB essential modulator (NEMO), and hypomorphic mutations in the gene encoding NEMO (ikbkg) lead to inherited immunodeficiencies, collectively termed NEMO-ID. Noncanonical NF-kappaB activation requires NF-kappaB-inducing kinase (NIK) and IKKalpha, but not NEMO. We found that noncanonical NF-kappaB was basally active in peripheral blood mononuclear cells from NEMO-ID patients and that noncanonical NF-kappaB signaling was similarly enhanced in cell lines lacking functional NEMO. NIK, which normally undergoes constitutive degradation, was aberrantly present in resting NEMO-deficient cells, and regulation of its abundance was rescued by reconstitution with full-length NEMO, but not a mutant NEMO protein unable to physically associate with IKKalpha or IKKbeta. Binding of NEMO to IKKalpha was not required for ligand-dependent stabilization of NIK or noncanonical NF-kappaB signaling. Rather, an intact and functional IKK complex was essential to suppress basal NIK activity in unstimulated cells. Despite interacting with IKKalpha and IKKbeta to form an IKK complex, NEMO mutants associated with immunodeficiency failed to rescue classical NF-kappaB signaling or reverse the accumulation of NIK. Together, these findings identify a crucial role for classical NF-kappaB activity in the suppression of basal noncanonical NF-kappaB signaling. [less ▲]

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See detailRIPK3 contributes to TNFR1-mediated RIPK1 kinase-dependent apoptosis in conditions of cIAP1/2 depletion or TAK1 kinase inhibition
Dondelinger, Yves; Aguileta, M; Goosens, V et al

in Cell Death & Differentiation (2013), 10

Receptor-interacting protein kinase (RIPK) 1 and RIPK3 have emerged as essential kinases mediating a regulated form of necrosis, known as necroptosis, that can be induced by tumor necrosis factor (TNF ... [more ▼]

Receptor-interacting protein kinase (RIPK) 1 and RIPK3 have emerged as essential kinases mediating a regulated form of necrosis, known as necroptosis, that can be induced by tumor necrosis factor (TNF) signaling. As a consequence, inhibiting RIPK1 kinase activity and repressing RIPK3 expression levels have become commonly used approaches to estimate the contribution of necroptosis to specific phenotypes. Here, we report that RIPK1 kinase activity and RIPK3 also contribute to TNF-induced apoptosis in conditions of cellular inhibitor of apoptosis 1 and 2 (cIAP1/2) depletion or TGF-β-activated kinase 1 (TAK1) kinase inhibition, implying that inhibition of RIPK1 kinase activity or depletion of RIPK3 under cell death conditions is not always a prerequisite to conclude on the involvement of necroptosis. Moreover, we found that, contrary to cIAP1/2 depletion, TAK1 kinase inhibition induces assembly of the cytosolic RIPK1/Fas-associated protein with death domain/caspase-8 apoptotic TNF receptor 1 (TNFR1) complex IIb without affecting the RIPK1 ubiquitylation status at the level of TNFR1 complex I. These results indicate that the recruitment of TAK1 to the ubiquitin (Ub) chains, and not the Ub chains per se, regulates the contribution of RIPK1 to the apoptotic death trigger. In line with this, we found that cylindromatosis repression only provided protection to TNF-mediated RIPK1-dependent apoptosis in condition of reduced RIPK1 ubiquitylation obtained by cIAP1/2 depletion but not upon TAK1 kinase inhibition, again arguing for a role of TAK1 in preventing RIPK1-dependent apoptosis downstream of RIPK1 ubiquitylation. Importantly, we found that this function of TAK1 was independent of its known role in canonical nuclear factor-κB (NF-κB) activation. Our study therefore reports a new function of TAK1 in regulating an early NF-κB-independent cell death checkpoint in the TNFR1 apoptotic pathway. In both TNF-induced RIPK1 kinase-dependent apoptotic models, we found that RIPK3 contributes to full caspase-8 activation independently of its kinase activity or intact RHIM domain. In contrast, RIPK3 participates in caspase-8 activation by acting downstream of the cytosolic death complex assembly, possibly via reactive oxygen species generation. [less ▲]

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See detailInduction of the Alternative NF-{kappa}B Pathway by Lymphotoxin {alpha}{beta} (LT{alpha}{beta}) Relies on Internalization of LT{beta} Receptor
Ganeff, Corine; Remouchamps, Caroline ULg; Boutaffala, Layla et al

in Molecular & Cellular Biology (2011), 21

Several tumor necrosis factor receptor (TNFR) family members activate both the classical and the alternative NF-κB pathways. However, how a single receptor engages these two distinct pathways is still ... [more ▼]

Several tumor necrosis factor receptor (TNFR) family members activate both the classical and the alternative NF-κB pathways. However, how a single receptor engages these two distinct pathways is still poorly understood. Using lymphotoxin β receptor (LTβR) as a prototype, we showed that activation of the alternative, but not the classical, NF-κB pathway relied on internalization of the receptor. Further molecular analyses revealed a specific cytosolic region of LTβR essential for its internalization, TRAF3 recruitment, and p100 processing. Interestingly, we found that dynamin-dependent, but clathrin-independent, internalization of LTβR appeared to be required for the activation of the alternative, but not the classical, NF-κB pathway. In vivo, ligand-induced internalization of LTβR in mesenteric lymph node stromal cells correlated with induction of alternative NF-κB target genes. Thus, our data shed light on LTβR cellular trafficking as a process required for specific biological functions of NF-κB. [less ▲]

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See detailBiology and Signal Transduction pathways of the Lymphotoxin-αβ/LTβR system
Remouchamps, Caroline ULg; Boutaffala, Layla; Ganeff, Corinne et al

in Cytokine & Growth Factor Reviews (2011), 22

This review focuses on the biological functions and signalling pathways activated by Lymphotoxin α (LTα)/Lymphotoxin β (LTβ) and their receptor LTβR. Genetic mouse models shed light on crucial roles for ... [more ▼]

This review focuses on the biological functions and signalling pathways activated by Lymphotoxin α (LTα)/Lymphotoxin β (LTβ) and their receptor LTβR. Genetic mouse models shed light on crucial roles for LT/LTβR to build and to maintain the architecture of lymphoid organs and to ensure an adapted immune response against invading pathogens. However, chronic inflammation, autoimmunity, cell death or cancer development are disorders that occur when the LT/LTβR system is twisted. Biological inhibitors, such as antagonist antibodies or decoy receptors, have been developed and used in clinical trials for diseases associated to the LT/LTβR system. Recent progress in the understanding of cellular trafficking and NF-κB signaling pathways downstream of LTα/LTβ may bring new opportunities to develop therapeutics that target the pathological functions of these cytokines. [less ▲]

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See detailThe hidden function of NIK (NF-κB-Inducing Kinase) in cell death
Boutaffala, Layla; Bertrand, Mathieu; Remouchamps, Caroline ULg et al

Conference (2011)

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See detailTNFL–Induced p100 processing (TIPP) relies on the internalization of the cognate TNFR
Ganeff, Corinne; Galopin, Géraldine; Remouchamps, Caroline ULg et al

Conference (2010, January)

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See detailPyrazolo[4,3-c]isoquinolines as potential inhibitors of NF-kappaB activation.
Mortier, Jeremie; Frederick, Raphael; Ganeff, Corinne et al

in Biochemical Pharmacology (2010), 79(10), 1462-72

In this work, we aimed to build a 3D-model of NIK and to study the binding of pyrazolo[4,3-c]isoquinolines with a view to highlight the structural elements responsible for their inhibitory potency ... [more ▼]

In this work, we aimed to build a 3D-model of NIK and to study the binding of pyrazolo[4,3-c]isoquinolines with a view to highlight the structural elements responsible for their inhibitory potency. However, in the course of this work, we unexpectedly found that the pyrazolo[4,3-c]isoquinolines initially reported as NIK inhibitors were neither inhibitors of this enzyme nor of the alternative NF-kappaB pathway, but were in fact inhibitors of another kinase, the TGF-beta activated kinase 1 (TAK1) which is involved in the classical NF-kappaB pathway. [less ▲]

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See detailTNFR-induced activation of MAP3K14/NIK enhances TNFR1-induced cell death
Boutafalla, Layla; Bertrand, Mathieu; Remouchamps, Caroline ULg et al

Conference (2010)

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See detailInterplay between non-death and death TNFR in inflammation.
Dejardin, Emmanuel ULg

Conference (2010)

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See detailThe lymphotoxin-β receptor induces different patterns of gene expression via two NF-κB pathways
Dejardin, Emmanuel ULg; Droin, Nathalie; Delhase, Mireille et al

Conference (2009, October 30)

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See detailMatrix Metalloproteinase-9 gene induction by a truncated oncogenic NF-κB2 protein involves the recruitment of MLL1 and MLL2 H3K4 histone methyltransferase complexes.
Robert, Isabelle ULg; Aussems, Marie ULg; Keutgens, Aurore ULg et al

in Oncogene (2009), 28(13), 1626-1638

Constitutive nuclear factor (NF)-kappaB activation in haematological malignancies is caused in several cases by loss of function mutations within the coding sequence of NF-kappaB inhibitory molecules such ... [more ▼]

Constitutive nuclear factor (NF)-kappaB activation in haematological malignancies is caused in several cases by loss of function mutations within the coding sequence of NF-kappaB inhibitory molecules such as IkappaBalpha or p100. Hut-78, a truncated form of p100, constitutively generates p52 and contributes to the development of T-cell lymphomas but the molecular mechanism underlying this oncogenic potential remains unclear. We show here that MMP9 gene expression is induced through the alternative NF-kappaB-activating pathway in fibroblasts and also on Hut-78 or p52 overexpression in fibroblasts as well as in lymphoma cells. p52 is critical for Hut-78-mediated MMP9 gene induction as a Hut-78 mutant as well as other truncated NF-kappaB2 proteins that are not processed into p52 failed to induce the expression of this metalloproteinase. Conversely, MMP9 gene expression is impaired in p52-depleted HUT-78 cells. Interestingly, MLL1 and MLL2 H3K4 methyltransferase complexes are tethered by p52 on the MMP9 but not on the IkappaBalpha promoter, and the H3K4 trimethyltransferase activity recruited on the MMP9 promoter is impaired in p52-depleted HUT-78 cells. Moreover, MLL1 and MLL2 are associated with Hut-78 in a native chromatin-enriched extract. Thus, we identified a molecular mechanism by which the recruitment of a H3K4 histone methyltransferase complex on the promoter of a NF-kappaB-dependent gene induces its expression and potentially the invasive potential of lymphoma cells harbouring constitutive activity of the alternative NF-kappaB-activating pathway. [less ▲]

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See detailThe prevention of spontaneous apoptosis of follicular lymphoma B cells by a follicular dendritic cell line: involvement of caspase-3, caspase-8 and c-FLIP.
Goval, Jean-Jacques; Thielen, Caroline ULg; Bourguignon, Caroline et al

in Haematologica (2008), 93(8), 1169-77

BACKGROUND: Follicular lymphoma, the neoplastic counterpart of germinal center B cells, typically recapitulates a follicular architecture. Several observations point to the crucial role of the cellular ... [more ▼]

BACKGROUND: Follicular lymphoma, the neoplastic counterpart of germinal center B cells, typically recapitulates a follicular architecture. Several observations point to the crucial role of the cellular microenvironment in the development and/or progression of follicular lymphoma cells in vivo. The aim of our study was to characterize the spontaneous apoptosis of follicular lymphoma cells in vitro, and the modulation of this apoptosis by follicular dendritic cells. DESIGN AND METHODS: We used a cell line derived from follicular dendritic cells to model the functional interactions of these cells and lymphoma cells in co-culture. Follicular lymphoma cells were isolated from tissue biopsies. Apoptosis was quantified by flow cytometry and apoptotic pathways were investigated by western blotting. RESULTS: The spontaneous apoptosis of follicular lymphoma cells in vitro involves the activation of caspases-3 and -8 but not of caspase-9, occurs despite persistent high levels of BCL-2 and MCL-1, and is associated with down-regulation of c-FLIP(L). Spontaneous apoptosis of follicular lymphoma cells is partially prevented by co-culture with the follicular dendritic cells, which prevents activation of caspase-8, caspase-3 and induces an upregulation of c-FLIP(L). Using neutralizing antibodies, we demonstrated that interactions involving CD54 (ICAM-1), CD106 (VCAM-1) and CD40 are implicated in this biological process. CONCLUSIONS: Follicular dendritic cells constitute a useful tool to study the functional interactions between follicular lymphoma cells and follicular dendritic cells in vitro. Understanding the molecular mechanisms involved in these protective interactions may lead to the identification of therapeutic agents that might suppress the survival and growth of follicular lymphoma cells. [less ▲]

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