Showing papers by "Andreas Strasser published in 2008"
TL;DR: New insights into interactions among BCL-2 family proteins reveal how these proteins are regulated, but a unifying hypothesis for the mechanisms they use to activate caspases remains elusive.
Abstract: BCL-2 family proteins, which have either pro- or anti-apoptotic activities, have been studied intensively for the past decade owing to their importance in the regulation of apoptosis, tumorigenesis and cellular responses to anti-cancer therapy. They control the point of no return for clonogenic cell survival and thereby affect tumorigenesis and host-pathogen interactions and regulate animal development. Recent structural, phylogenetic and biological analyses, however, suggest the need for some reconsideration of the accepted organizational principles of the family and how the family members interact with one another during programmed cell death. Although these insights into interactions among BCL-2 family proteins reveal how these proteins are regulated, a unifying hypothesis for the mechanisms they use to activate caspases remains elusive.
4,246 citations
TL;DR: These results identify critical overlapping roles for Fas and Bim in T cell death in immune response shutdown and prevention of immunopathology and thereby resolve a long-standing controversy.
261 citations
TL;DR: The therapeutic efficacy of MEK inhibition requires concurrent unleashing of apoptosis by a BH3 mimetic and represents a potent combination treatment for tumors harboring B-RAF mutations.
Abstract: B-RAF is frequently mutated in solid tumors, resulting in activation of the MEK/ERK signaling pathway and ultimately tumor cell growth and survival. MEK inhibition in these cells results in cell cycle arrest and cytostasis. Here, we have shown that MEK inhibition also triggers limited apoptosis of human tumor cell lines with B-RAF mutations and that this effect was dependent on upregulation and dephosphorylation of the proapoptotic, Bcl-2 homology 3-only (BH3-only) Bcl-2 family member Bim. However, upregulation of Bim was insufficient for extensive apoptosis and was countered by overexpression of Bcl-2. To overcome apoptotic resistance, we treated the B-RAF mutant cells both with MEK inhibitors and with the BH3 mimetic ABT-737, resulting in profound synergism and extensive tumor cell death. This treatment was successful because of both efficient antagonism of the prosurvival Bcl-2 family member Mcl-1 by Bim and inhibition of Bcl-2 and Bcl-x(L) by ABT-737. Critically, addition of ABT-737 converted the predominantly cytostatic effect of MEK inhibition to a cytotoxic effect, causing long-term tumor regression in mice xenografted with human tumor cell lines. Thus, the therapeutic efficacy of MEK inhibition requires concurrent unleashing of apoptosis by a BH3 mimetic and represents a potent combination treatment for tumors harboring B-RAF mutations.
208 citations
TL;DR: If tumor growth can indeed be sustained either by rare cancer stem cells or dominant clones or both, as current evidence suggests, curative therapy for many types of tumors will most likely require targeting all the tumor cell populations.
Abstract: A key issue for cancer biology and therapy is whether the relentless growth of a tumor is driven by a substantial proportion of its cells or exclusively by a rare subpopulation, commonly termed "cancer stem cells." Support for the cancer stem cell model has been stimulated by experiments in which human tumor cells were transplanted into immunodeficient mice. Most notably, in human acute myeloid leukemia, only a minute proportion of the cells, displaying a defined phenotype, could seed leukemia in mice. Xenotransplantation, however, may fail to reveal many tumor growth-sustaining cells because the foreign microenvironment precludes essential interactions with support cells. In studies that instead have transplanted mouse leukemias and lymphomas into syngeneic animals, most of the tumors seem to be maintained by the dominant cell population, and only a few types of mouse leukemia seem to be sustained by a minor tumor growth-sustaining subpopulation. The collective evidence suggests that various tumors may span the spectrum between the extremes represented by the two models. If tumor growth can indeed be sustained either by rare cancer stem cells or dominant clones or both, as current evidence suggests, curative therapy for many types of tumors will most likely require targeting all the tumor cell populations.
207 citations
TL;DR: Results indicate that, at least in fibroblasts and thymocytes, p53-induced apoptosis proceeds principally via Noxa and Puma, with Puma having the predominant role in diverse cell types.
Abstract: The ability of p53 to induce apoptosis in cells with damaged DNA is thought to contribute greatly to its tumour suppressor function. P53 has been proposed to induce apoptosis via numerous transcriptional targets or even by direct cytoplasmic action. Two transcriptional targets shown to mediate its apoptotic role in several cell types encode Noxa and Puma, BH3-only members of the Bcl-2 family. To test if their functions in p53-dependent apoptosis overlap, we generated mice lacking both. These mice develop normally and no tumours have yet arisen. In embryonic fibroblasts, the absence of both Noxa and Puma prevented induction of apoptosis by etoposide. Moreover, following whole body γ-irradiation, the loss of both proteins protected thymocytes better than loss of Puma alone. Indeed, their combined deficiency protected thymocytes as strongly as loss of p53 itself. These results indicate that, at least in fibroblasts and thymocytes, p53-induced apoptosis proceeds principally via Noxa and Puma, with Puma having the predominant role in diverse cell types. The absence of tumours in the mice suggests that tumour suppression by p53 requires functions in addition to induction of apoptosis.
187 citations
TL;DR: It is shown that Bmf is dispensable for embryonic development and certain forms of stress-induced apoptosis, including loss of cell attachment (anoikis) or UV irradiation, and can function as a tumor suppressor.
Abstract: Members of the Bcl-2 protein family play crucial roles in the maintenance of tissue homeostasis by regulating apoptosis in response to developmental cues or exogenous stress. Proapoptotic BH3-only members of the Bcl-2 family are essential for initiation of cell death, and they function by activating the proapoptotic Bcl-2 family members Bax and/or Bak, either directly or indirectly through binding to prosurvival Bcl-2 family members. Bax and Bak then elicit the downstream events in apoptosis signaling. Mammals have at least eight BH3-only proteins and they are activated in a stimulus-specific, as well as a cell type-specific, manner. We have generated mice lacking the BH3-only protein Bcl-2-modifying factor (Bmf) to investigate its role in cell death signaling. Our studies reveal that Bmf is dispensable for embryonic development and certain forms of stress-induced apoptosis, including loss of cell attachment (anoikis) or UV irradiation. Remarkably, loss of Bmf protected lymphocytes against apoptosis induced by glucocorticoids or histone deacetylase inhibition. Moreover, bmf(-/-) mice develop a B cell-restricted lymphadenopathy caused by the abnormal resistance of these cells to a range of apoptotic stimuli. Finally, Bmf-deficiency accelerated the development of gamma irradiation-induced thymic lymphomas. Our results demonstrate that Bmf plays a critical role in apoptosis signaling and can function as a tumor suppressor.
130 citations
TL;DR: This study identifies Bim for the first time as a critical initiator of T-cell death in the liver, and strategies inhibiting the up-regulation of this molecule could potentially be used to rescue CD8 T cells, clear the virus, and reverse the outcome of viral chronic infections affecting the liver.
118 citations
TL;DR: Results demonstrate that Bid is essential for death receptor–induced apoptosis of islets, similar to its demonstrated role in hepatocytes, and indicates that blocking Bid activity may be useful for protection of islet from immune-mediated attack and possibly also in other pathological states in which β-cells are destroyed.
Abstract: OBJECTIVE: Apoptosis of pancreatic beta-cells is critical in both diabetes development and failure of islet transplantation. The role in these processes of pro- and antiapoptotic Bcl-2 family proteins, which regulate apoptosis by controlling mitochondrial integrity, remains poorly understood. We investigated the role of the BH3-only protein Bid and the multi-BH domain proapoptotic Bax and Bak, as well as prosurvival Bcl-2, in beta-cell apoptosis. RESEARCH DESIGN AND METHODS: We isolated islets from mice lacking Bid, Bax, or Bak and those overexpressing Bcl-2 and exposed them to Fas ligand, tumor necrosis factor (TNF)-alpha, and proinflammatory cytokines or cytotoxic stimuli that activate the mitochondrial apoptotic pathway (staurosporine, etoposide, gamma-radiation, tunicamycin, and thapsigargin). Nuclear fragmentation was measured by flow cytometry. RESULTS: Development and function of islets were not affected by loss of Bid, and Bid-deficient islets were as susceptible as wild-type islets to cytotoxic stimuli that cause apoptosis via the mitochondrial pathway. In contrast, Bid-deficient islets and those overexpressing antiapoptotic Bcl-2 were protected from Fas ligand-induced apoptosis. Bid-deficient islets were also resistant to apoptosis induced by TNF-alpha plus cycloheximide and were partially resistant to proinflammatory cytokine-induced death. Loss of the multi-BH domain proapoptotic Bax or Bak protected islets partially from death receptor-induced apoptosis. CONCLUSIONS: These results demonstrate that Bid is essential for death receptor-induced apoptosis of islets, similar to its demonstrated role in hepatocytes. This indicates that blocking Bid activity may be useful for protection of islets from immune-mediated attack and possibly also in other pathological states in which beta-cells are destroyed.
95 citations
TL;DR: The roles of the proapoptotic Bcl‐2 family member Bim and the small family of Nur77‐related transcriptional regulators in lymphocyte negative selection are discussed and the processes that may lead to the activation of Bim are speculated on.
Abstract: Tolerance to self-antigens within the adaptive immune system is safeguarded, at least in part, through deletion of autoreactive T and B lymphocytes. This deletion can occur during the development of these cells in primary lymphoid organs, the thymus or bone marrow, respectively, or at the mature stage in peripheral lymphoid tissues. Deletion of autoreactive lymphocytes is achieved to a large extent through apoptotic cell death. This review describes current understanding of the mechanisms that mediate apoptosis of autoreactive lymphocytes during their development in primary lymphoid organs and during their activation in the periphery. In particular, we discuss the roles of the proapoptotic Bcl-2 family member Bim and the small family of Nur77-related transcriptional regulators in lymphocyte negative selection. Finally, we speculate on the processes that may lead to the activation of Bim when antigen receptors are activated on autoreactive T or B cells.
70 citations
TL;DR: Findings show that Puma contributes to the death of antigen-specific T cells during shutdown of an immune response, and also shows that other proapoptotic factors must contribute to T cell killing.
Abstract: During acute T cell immune responses to viral infection, antigen-specific T cells first proliferate and differentiate into effector cells, but after pathogen clearance most are deleted by apoptosis. The developmentally programmed death of antigen-specific T cells during shutdown of a T cell response is mediated by the Bcl-2-regulated apoptotic pathway and partly depends on the proapoptotic BH3-only protein Bim. However, loss of Bim enhanced survival of antigen-activated T cells to a lesser extent than Bcl-2 overexpression, indicating that other proapoptotic factors must contribute to T cell killing. In this study, we investigated the contributions of several BH3-only proteins to the shutdown of an acute T cell immune response in vivo. After infection with human herpes simplex virus (HSV-1), mice lacking Noxa, Bid, or Bad had a normal increase and subsequent decline in the numbers of antigen-specific CD8+ T cells. In contrast, Puma-deficient mice showed an abnormally prolonged persistence of antigen-specific CD8+ T cells in the spleen, associated with enhanced in vitro survival of these cells in the absence of cytokines. Puma was dispensable for viral clearance and also did not play a role in proliferation or activation of HSV-1-specific CD8+ T cells in vivo. Collectively, these findings show that Puma contributes to the death of antigen-specific T cells during shutdown of an immune response.
59 citations
TL;DR: The data suggest a selective crosstalk between extracellular matrix and Fas‐mediated signaling that favors mitochondria‐independent type I apoptosis induction.
TL;DR: It is established that optimal survival of TLR4-activated B cells depends on the NF-kappaB pathway neutralizing Bim through a combination of Bcl-2 prosurvival protein induction and Tpl2/ERK-dependent Bim phosphorylation and degradation.
TL;DR: It is demonstrated that, in FcepsilonRI stimulated mast cells, A1 is transcriptionally regulated by NFAT1 but not by NF-kappaB, and that NFAT plays a crucial role.
TL;DR: A cell-autonomous role for Abl in T cell function and survival is demonstrated in mice lacking Abl, demonstrating impaired ability to reject syngeneic tumor, to induce T-mediated tumor cell killing, and to generate anti-tumor antibodies.
Abstract: C-Abl (Abl) regulates multiple cellular processes, including proliferation, survival, shape determination and motility, and participates in cellular responses to genotoxic and oxidative stress stimuli. Mice lacking Abl exhibit retarded growth, osteoporosis and defects in the immune system resulting in lymphopoenia and susceptibility to infections, leading to early death. To define the role of Abl in the regulation of adult T cells we ablated Abl exclusively in T cells by generating mice with floxed abl alleles and expressing an Lck-Cre transgene (Abl-T(-/-)). These mice exhibited thymic atrophy and abnormally reduced T cell numbers in the periphery. The thymic atrophy was caused by increased susceptibility of thymocytes to cell death. Importantly, Abl deficient T cells displayed abnormally reduced response to mitogenic stimulation in vitro. Consequently, Abl-T(-/-) mice exhibited impaired ability to reject syngeneic tumor, to induce T-mediated tumor cell killing, and to generate anti-tumor antibodies. These results demonstrate a cell-autonomous role for Abl in T cell function and survival.
TL;DR: Investigation of the role for Bim, a BH3 domain only protein, in the embryonic lethality and increased developmental cell death in bcl-x-deficient animals and the perturbed testicular function in bCl-x +/- adults finds that testicular degeneration of adult bcl -x +/- males was rescued by concomitant Bim deficiency.
Abstract: Members of the Bcl-2 family include pro- and antiapoptotic proteins that regulate programmed cell death of developing tissues and death in response to cellular damage. In developing mice, the antiapoptotic Bcl-xL is necessary for survival of neural and hematopoietic cells, and consequently, bcl-x–deficient mice die around Day 13.5 of embryogenesis. Furthermore, adult bcl-x+/− heterozygous male mice have reduced fertility because of testicular degeneration. Bax, a multi-BH (Bcl-2 homology) domain proapoptotic member of the Bcl-2 family, is regulated by Bcl-xL and is required for the neuropathological abnormalities seen in bcl-x–deficient embryos. The BH3 domain only subgroup of the Bcl-2 family includes proapoptotic members that are essential for the initiation of apoptotic signaling. In this study, we investigated the role for Bim, a BH3 domain only protein, in the embryonic lethality and increased developmental cell death in bcl-x–deficient animals and the perturbed testicular function in bcl-x+/− adults. Our studies show that bim deficiency attenuates hematopoietic cell death in the fetal liver of bcl-x–deficient animals, indicating that Bim contributes to programmed cell death in this cell population. In addition, we found that testicular degeneration of adult bcl-x+/− males was rescued by concomitant Bim deficiency. However, concomitant Bim deficiency had no effect on the embryonic lethality and widespread nervous system abnormalities caused by bcl-x deficiency. Our work identifies Bim as an important regulator of bcl-x deficiency–induced cell death during hematopoiesis and testicular development. (J Histochem Cytochem 56:921–927, 2008)
TL;DR: The absence of endogenous Bcl-2 in mice expressing an Emu-myc transgene reduced mature B-cell numbers and enhanced their apoptosis, but unexpectedly, lymphoma development was undiminished or even delayed, which suggests that these tumors originate in an earlier cell type, such as the pro-B or pre-B cell, and that the nascent neoplastic clones do not require BCl-2 but may instead be protected by a B cl-2 relative.
Abstract: One critical issue for cancer biology is the nature of the cells that drive the inexorable growth of malignant tumors. Reports that only rare cell populations within human leukemias seeded leukemia in mice stimulated the now widely embraced hypothesis that only such "cancer stem cells" maintain all tumor growth. However, the mouse microenvironment might instead fail to support the dominant human tumor cell populations. Indeed, on syngeneic transplantation of mouse lymphomas and leukemias, we and other investigators have found that a substantial proportion (>10%) of their cells drive tumor growth. Thus, dominant clones rather than rare cancer stem cells appear to sustain many tumors. Another issue is the role of cell survival in tumorigenesis. Because tumor development can be promoted by the overexpression of prosurvival genes such as bcl-2, we are exploring the role of endogenous Bcl-2-like proteins in lymphomagenesis. The absence of endogenous Bcl-2 in mice expressing an Emu-myc transgene reduced mature B-cell numbers and enhanced their apoptosis, but unexpectedly, lymphoma development was undiminished or even delayed. This suggests that these tumors originate in an earlier cell type, such as the pro-B or pre-B cell, and that the nascent neoplastic clones do not require Bcl-2 but may instead be protected by a Bcl-2 relative.
TL;DR: The unfolded protein response is a pro-survival response to reduce the accumulation of unfolded proteins and restore normal ER function and plays a critical role in certain developmental processes that are associated with increased demand for protein synthesis and/or export, such as differentiation of immunoglobulin-secreting plasma cells and myoblast formation.
Abstract: The acquisition of the endoplasmic reticulum (ER) during evolution of eukaryotes represents one of the fundamental shifts in biochemical reactions, from the relics of prokaryotes in which biochemical processes occur in the cytosol, requiring the primordial, anaerobic reducing conditions, to the far more sophisticated metabolic pathways in which oxygen is an absolute necessity. In eukaryotes, the ER is recognised as the site of synthesis and folding of secreted, membrane-bound and some organelle-targeted proteins. Several factors are required for disulphide-bond formation, which is needed for optimal protein folding, including ATP, Ca2þ and an oxidising environment. As a consequence of these special requirements, the ER is highly sensitive to stresses that perturb cellular energy levels, the redox state or Ca2þ concentration. Such stresses reduce the protein-folding capacity of the ER, which can result in the accumulation and aggregation of unfolded proteins and/or an imbalance between the load of resident and transit proteins in the ER and the organelle’s ability to process that load. This condition is referred to as ER stress. The ER stress response can promote cellular repair and sustained survival by reducing the load of unfolded proteins through global attenuation of protein synthesis and/or upregulation of chaperones, enzymes and structural components of the ER, which enhance protein folding. This response is collectively termed as the unfolded protein response (UPR) and it is mediated through three ER transmembrane receptors: pancreatic ER kinase (PERK), activating transcription factor 6 (ATF6) and inositol-requiring enzyme 1 (IRE1). In resting cells, all of these ER stress receptors are maintained in an inactive state through their association with the ER chaperone, GRP78 (also called BiP). Accumulation of unfolded proteins causes dissociation of GRP78 from PERK, ATF6 and IRE1, thereby initiating the UPR. Thus, the UPR is a pro-survival response to reduce the accumulation of unfolded proteins and restore normal ER function. In addition, the UPR plays a critical role in certain developmental processes that are associated with increased demand for protein synthesis and/or export, such as differentiation of immunoglobulin (Ig)-secreting plasma cells and myoblast formation. However, when misfolded-protein aggregation persists and the ER stress cannot be resolved, signalling switches from a pro-survival to a pro-apoptotic response. Thus lack of a UPR could be a mortal danger but an excessive response could be an absolute disaster!
TL;DR: It is reported that T cells from these mice show massive cell death and severely reduced proliferation in response to T‐cell receptor (TCR) stimulation in vitro, suggesting that FADD and Bcl‐3 regulate separate pathways that both contribute to survival and proliferation in mouse T cells.
Abstract: Fas-associated protein with death domain/mediator of receptor induced toxicity (FADD/MORT1) was first described as a transducer of death receptor signalling but was later recognized also to be important for proliferation of T cells. B-cell lymphoma 3 (Bcl-3) is a relatively little understood member of the nuclear factor (NF)-kappaB family of transcription factors. We recently found that Bcl-3 is up-regulated in T cells from mice where FADD function is blocked by a dominant negative transgene (FADD-DN). To understand the importance of this, we generated FADD-DN/bcl-3(-/-) mice. Here, we report that T cells from these mice show massive cell death and severely reduced proliferation in response to T-cell receptor (TCR) stimulation in vitro. Transgenic co-expression of Bcl-2 (FADD-DN/bcl-3(-/-)/vav-bcl-2 mice) rescued the survival but not the proliferation of T cells. FADD-DN/bcl-3(-/-) mice had normal thymocyte numbers but reduced numbers of peripheral T cells despite an increase in cycling T cells in vivo. However, activation of the classical NF-kappaB and extracellular regulated kinase (ERK) pathways and expression of interleukin (IL)-2 mRNA upon stimulation were normal in T cells from FADD-DN/bcl-3(-/-) mice. These data suggest that FADD and Bcl-3 regulate separate pathways that both contribute to survival and proliferation in mouse T cells.
Patent•
24 Jun 2008
TL;DR: In this article, a plug-in connection device with a temperature measuring core is proposed to be used as a ring-gap reactor in laboratory catalysts or micro-catalyst apparatuses for receiving pulverulent catalysts.
Abstract: The present invention relates to a plug-in connection device with a temperature measuring core, which is preferably used as a ring-gap reactor in laboratory catalyst apparatuses or microcatalyst apparatuses for receiving pulverulent catalysts. According to the invention, the plug-in connection device can easily be filled with catalyst material, in particular with pulverulent catalyst material. Due to its modular structure and reproducible geometry, it is possible to obtain catalyst data of higher data quality and to scale up the installation in an advantageous manner.