300 research outputs found

    SMAC Mimetic BV6 Induces Cell Death in Monocytes and Maturation of Monocyte-Derived Dendritic Cells

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    Background: Compounds mimicking the inhibitory effect of SMAC / DIABLO on X-linked inhibitor of apoptosis (XIAP) have been developed with the aim to achieve sensitization for apoptosis of tumor cells resistant due to deregulated XIAP expression. It turned out that SMAC mimetics also have complex effects on the NFkB system and TNF signaling. In view of the overwhelming importance of the NFkB transcription factors in the immune system, we analyzed here the effects of the SMAC mimetic BV6 on immune cells. Principal Findings: BV6 induced apoptotic and necrotic cell death in monocytes while T-cells, dendritic cells and macrophages were largely protected against BV6-induced cell death. In immature dendritic cells BV6 treatment resulted in moderate activation of the classical NFkB pathway, but it also diminished the stronger NFkB-inducing effect of TNF and CD40L. Despite its inhibitory effect on TNF- and CD40L signaling, BV6 was able to trigger maturation of immature DCs as indicated by upregulation of CD83, CD86 and IL12. Significance: The demonstrated effects of SMAC mimetics on immune cells may complicate the development of tumor therapeutic concepts based on these compounds but also arise the possibility to exploit them for the development of immune stimulatory therapies

    RAG-mediated DNA double-strand breaks activate a cell type-specific checkpoint to inhibit pre-B cell receptor signals

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    DNA double-strand breaks (DSBs) activate a canonical DNA damage response, including highly conserved cell cycle checkpoint pathways that prevent cells with DSBs from progressing through the cell cycle. In developing B cells, pre–B cell receptor (pre–BCR) signals initiate immunoglobulin light (Igl) chain gene assembly, leading to RAG-mediated DNA DSBs. The pre–BCR also promotes cell cycle entry, which could cause aberrant DSB repair and genome instability in pre–B cells. Here, we show that RAG DSBs inhibit pre–BCR signals through the ATM- and NF-κB2–dependent induction of SPIC, a hematopoietic-specific transcriptional repressor. SPIC inhibits expression of the SYK tyrosine kinase and BLNK adaptor, resulting in suppression of pre–BCR signaling. This regulatory circuit prevents the pre–BCR from inducing additional Igl chain gene rearrangements and driving pre–B cells with RAG DSBs into cycle. We propose that pre–B cells toggle between pre–BCR signals and a RAG DSB-dependent checkpoint to maintain genome stability while iteratively assembling Igl chain genes

    HGF/SF and its receptor c-MET play a minor role in the dissemination of human B-lymphoma cells in SCID mice

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    The MET protooncogene, c-MET, encodes a cell surface tyrosine kinase receptor. The ligand for c-MET is hepatocyte growth factor (HGF), also known as scatter factor (SF), which is known to affect proliferation and motility of primarily epithelial cells. Recently, HGF/SF was also shown to affect haemopoiesis. Studies with epithelial and transfected NIH3T3 cells indicated that the HGF/SF–c-MET interaction promotes invasion in vitro and in vivo. We previously demonstrated that HGF/SF induces adhesion of c-MET-positive B-lymphoma cells to extracellular matrix molecules, and promoted migration and invasion in in vitro assays. Here, the effect of HGF/SF on tumorigenicity of c-MET-positive and c-MET-negative human B-lymphoma cell lines was studied in C.B-17 scid/scid (severe combined immune deficient) mice. Intravenously (i.v.) injected c-MET-positive (BJAB) as well as c-MET-negative (Daudi and Ramos cells) B-lymphoma cells formed tumours in SCID mice. The B-lymphoma cells invaded different organs, such as liver, kidney, lymph nodes, lung, gonads and the central nervous system. We assessed the effect of human HGF/SF on the dissemination of the B-lymphoma cells and found that administration of 5 μg HGF/SF to mice, injected (i.v.) with c-MET-positive lymphoma cells, significantly (P = 0.018) increased the number of metastases in lung, liver and lymph nodes. In addition, HGF/SF did not significantly influence dissemination of c-MET-negative lymphoma cells (P = 0.350 with Daudi cells and P = 0.353 with Ramos cells). Thus the effect of administration of HGF/SF on invasion of lymphoma cells is not an indirect one, e.g. via an effect on endothelial cells. Finally, we investigated the effect of HGF/SF on dissemination of c-MET-transduced Ramos cells. In response to HGF/SF, c-MET-transduced Ramos cells showed an increased migration through Matrigel in Boyden chambers compared to wild-type and control-transduced Ramos cells. The dissemination pattern of c-MET-transduced cells did not differ from control cells in in vivo experiments using SCID mice. Also no effect of HGF/SF administration could be documented, in contrast to the in vitro experiments. From our experiments can be concluded that the HGF/SF–c-MET interaction only plays a minor role in the dissemination of human B-lymphoma cells. © 1999 Cancer Research Campaig

    Hepatocyte growth factor and invasion-stimulatory activity are induced in pleural fluid by surgery in lung cancer patients

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    Hepatocyte growth factor (HGF) is a stromal cell-derived cytokine that can stimulate matrix invasion by carcinoma cells. We analysed the concentrations of HGF and invasion-stimulatory activity in pleural fluid after lung surgery. The concentration of HGF in pleural fluids was measured by enzyme-linked immunosorbent assay in seven patients who underwent pulmonary resection for primary or metastatic lung cancer. The effect of the pleural fluid on cancer cell invasion across reconstituted basement membrane (Matrigel) was assessed with a Boyden chamber assay using a lung adenocarcinoma cell line, A549. HGF levels in the pleural fluid after lung surgery ranged from 6.0 to 23.0 ng ml−1 (average: 10.2 ± 4.3 ng ml−1). The matrix invasion of lung carcinoma cells in the presence of the pleural fluid was significantly higher than that in the presence of culture medium alone or sera from normal subjects (P < 0.01). The invasion-stimulatory activity of the pleural fluid was strongly inhibited by HGF-neutralizing antibody. Positive correlation was found between the HGF level and invasion-stimulatory activity in the pleural fluids and normal sera (P = 0.0073). This is the first report demonstrating that the lung surgery induces a considerable amount of HGF, which is closely correlated with the invasion-stimulatory activity of the pleural fluid. © 1999 Cancer Research Campaig

    NIK Stabilization in Osteoclasts Results in Osteoporosis and Enhanced Inflammatory Osteolysis

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    Maintenance of healthy bone requires the balanced activities of osteoclasts (OCs), which resorb bone, and osteoblasts, which build bone. Disproportionate action of OCs is responsible for the bone loss associated with postmenopausal osteoporosis and rheumatoid arthritis. NF-κB inducing kinase (NIK) controls activation of the alternative NF-κB pathway, a critical pathway for OC differentiation. Under basal conditions, TRAF3-mediated NIK degradation prevents downstream signaling, and disruption of the NIK:TRAF3 interaction stabilizes NIK leading to constitutive activation of the alternative NF-κB pathway.Using transgenic mice with OC-lineage expression of NIK lacking its TRAF3 binding domain (NT3), we now find that alternative NF-κB activation enhances not only OC differentiation but also OC function. Activating NT3 with either lysozyme M Cre or cathepsinK Cre causes high turnover osteoporosis with increased activity of OCs and osteoblasts. In vitro, NT3-expressing precursors form OCs more quickly and at lower doses of RANKL. When cultured on bone, they exhibit larger actin rings and increased resorptive activity. OC-specific NT3 transgenic mice also have an exaggerated osteolytic response to the serum transfer model of arthritis.Constitutive activation of NIK drives enhanced osteoclastogenesis and bone resorption, both in basal conditions and in response to inflammatory stimuli

    A novel role for RIP1 kinase in mediating TNFα production

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    Receptor-interacting protein 1 (RIP1) is a Ser/Thr kinase with both kinase-dependent and kinase-independent roles in death receptor signaling. The kinase activity of RIP1 is required for necroptosis, a caspase-independent pathway of programmed cell death. In some cell types, the inhibition of caspases leads to autocrine production of TNFα, which then activates necroptosis. Here, we describe a novel role for RIP1 kinase in regulating TNFα production after caspase inhibition. Caspase inhibitors activate RIP1 kinase and another protein, EDD, to mediate JNK signaling, which stimulates Sp1-dependent transcription of TNFα. This pathway is independent of nuclear factor κB and also occurs after Smac mimetic/IAP antagonist treatment or the loss of TNF receptor-associated factor 2 (Traf2). These findings implicate cIAP1/2 and Traf2 as negative regulators of this RIP1 kinase-dependent TNFα production pathway and suggest a novel role for RIP1 kinase in mediating TNFα production under certain conditions
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