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Biomedical subjects

A Strasser

Publications and source records attributed to A Strasser.

At least 73 records · Page 4Linked to original sources
PubMed1999

Insights from Bcl-2 and Myc: malignancy involves abrogation of apoptosis as well as sustained proliferation.

The chromosome translocations typifying Burkitt's lymphoma and follicular lymphoma deregulate very different oncogenes, myc and bcl-2. Transgenic mouse models have illuminated how each contributes to lymphomagenesis. Constitutive myc expression provokes sustained cell proliferation and retards differentiation. However, the resulting expansion in cell number is self-limiting, because the cells remain dependent on cytokines and undergo apoptosis when these become limiting. In contrast, bcl-2 is the prototype of a new class of oncogene that enhances cell survival but does not promote proliferation. Coexpression of these genes leads to the rapid transformation of lymphocytes, probably because each can counter an antioncogenic aspect of the other. Several close homologues of Bcl-2 also enhance cell survival and are thus potential oncogenes; each is essential for maintenance of particular major organs. More distant Bcl-2 relatives instead promote apoptosis and can be regarded as tumor suppressors. For many but not all apoptic signals, the balance between these competing activities determines cell survival. Learning how to adjust the apoptotic threshold in cancer cells should promote development of more effective therapeutic strategies.

Animals↗
PubMed1999

The transcriptional regulator Rel is essential for antigen receptor-mediated stimulation of mature T cells but dispensable for positive and negative selection of thymocytes and T cell apoptosis.

The family of Rel/NF-kappaB transcription factors is a crucial regulator of various cellular responses. Using Rel-deficient (c-rel-/-) mice crossed with T cell receptor (TCR)-transgenic mice we show that Rel is neither required for positive selection of major histocompatibility complex (MHC)-restricted T cells nor for deletion of thymocytes bearing autoreactive antigen receptors. Our studies also demonstrate that Rel is dispensable for T lymphocyte apoptosis. Rel is, however, essential for antigen-induced activation of mature T cells and its absence exacerbates the anergic state. These results indicate that thymocytes and mature T cells differ in their requirement for Rel in mediating TCR-induced responses.

Animals↗
PubMed1999

Apoptosis and autoimmune disease.

The process of programmed cell death or apoptosis was already noted in 1842 by Vogt [1], but it was not until the more recent studies of Kerr et al. 1972 [2] that an explosion of interest in apoptosis research occurred. Genetic, biochemical and cellular analysis in certain mammals, in the nematode Caenorhabditis elegans and in the fruitfly Drosophila melanogaster have identified several apoptosis regulating genes. This indicates that programmed cell death is an active, genetically controlled process. Many of the known cell death regulators are homologous in mammals, nematodes and insects, indicating that apoptosis is an evolutionarily conserved process. Apoptosis can be induced via multiple independent signalling pathways which converge upon a common final effector machinery. This stimulates activation of latent cysteine proteases (caspases), which cleave vital cellular substrates and thereby lead to the death of cells. The regulatory pathways of apoptosis are becoming clear with the discovery of specific signalling molecules. It has become evident that many disease processes including autoimmunity and cancer can be caused by deregulation of the apoptotic process. With the discovery of novel cell surface-bound death receptors, their ligands and further insight into the apoptotic machinery within the cell, research may ultimately lead to the design of therapies that allow intervention in the apoptotic process. The aims of such strategies would be to turn on apoptosis in neoplastic cells or in lymphocytes that are causing autoimmune disease or to prevent cell death in degenerative disorders. This review describes current understanding of the molecular regulation of apoptosis, and focuses on issues relating to possible roles of defective cell death control in autoimmunity.

Animals↗
PubMed1999

[Pathophysiologic effects of nitric oxide (NO) and endothelin-1 in global cerebral ischemia in an animal model--an overview].

These studies were performed in an attempt to clarify some of the pathophysiologic mechanisms which occur during and after global ischemia. Both nitric oxide and endothelin were demonstrated in gerbils to participate in responses to ischemia. It was shown that endogenous nitric oxide influences early postischemic reperfusion, systemic blood pressure and postischemic dopamine metabolism. Furthermore, the results indicated that nitric oxide played a role in dopamine release and that preischemic intracerebral nitric oxide formation significantly decreased ischemic dopamine release. In addition, ischemic release of endothelin-1 was detected; participation of nitric oxide in this release was observed. Further indication of functional interactions between nitric oxide and endothelin-1 in postischemic reperfusion were indicated by observations that endothelin-1 antagonists inhibited early hypoperfusion caused by Nitro-L-arginin and late hypoperfusion caused by endogenous endothelin-1. Nitric oxide was shown to decrease edema formation during the early postischemic period but contribute to edema formation during the late postischemic period. The findings indicate the importance of nitric oxide in stroke and ischemia.

Animals↗
PubMed1999

The proapoptotic activity of the Bcl-2 family member Bim is regulated by interaction with the dynein motor complex.

Bcl-2 family members that have only a single Bcl-2 homology domain, BH3, are potent inducers of apoptosis, and some appear to play a critical role in developmentally programmed cell death. We examined the regulation of the proapoptotic activity of the BH3-only protein Bim. In healthy cells, most Bim molecules were bound to LC8 cytoplasmic dynein light chain and thereby sequestered to the microtubule-associated dynein motor complex. Certain apoptotic stimuli disrupted the interaction between LC8 and the dynein motor complex. This freed Bim to translocate together with LC8 to Bcl-2 and to neutralize its antiapoptotic activity. This process did not require caspase activity and therefore constitutes an initiating event in apoptosis signaling.

Amino Acid Sequence↗
PubMed1999

FADD/MORT1, a signal transducer that can promote cell death or cell growth.

FADD/MORT1 is a cytosolic adaptor protein which is critical for signalling from CD95 (Fas/APO-1) and certain other members of the tumour necrosis factor receptor (TNF-R) family (called 'death receptors'). Two protein interaction domains have been identified in FADD/MORT1. The C-terminal 'death domain' is needed for recruitment of FADD/MORT1 to ligated 'death receptors' and the N-terminal 'death effector domain' mediates oligomerisation and activation of caspase-8 zymogens. Caspase-8 activates other cysteine proteases by cleavage and this starts a proteolytic cascade which constitutes the 'point of no return' in apoptosis signalling. Experiments in mice lacking FADD/MORT1 function proved that this adaptor is required for CD95- and TNF-RI-transduced cell death but is dispensable for other pathways to apoptosis. Surprisingly, FADD/MORT1 is also essential for mitogen-induced proliferation of T-lymphocytes. Therapeutic activation of FADD/MORT1 function may be used to kill unwanted cells in cancer or autoimmunity and its suppression may help prevent cell death in certain degenerative disorders.

Animals↗
PubMed1999

A portrait of the Bcl-2 protein family: life, death, and the whole picture.

The Bcl-2 family of proteins are important regulators of cell death. They are comprised of two opposing factions, the proapoptotic versus the antiapoptotic members. Both are required for normal development and cellular homeostasis of the immune system and other tissues. However, in certain circumstances they may participate in the development of disease.

Animals↗
PubMed1998

Mechanisms of beta cell death in diabetes: a minor role for CD95.

Insulin-dependent diabetes mellitus is an autoimmune disease, under polygenic control, manifested only when >90% of the insulin-producing beta cells are destroyed. Although the disease is T cell mediated, the demise of the beta cell results from a number of different insults from the immune system. It has been proposed that foremost amongst these effector mechanisms is CD95 ligand-induced beta cell death. Using the nonobese diabetic lpr mouse as a model system, we have found, to the contrary, that CD95 plays only a minor role in the death of beta cells. Islet grafts from nonobese diabetic mice that carry the lpr mutation and therefore lack CD95 were protected only marginally from immune attack when grafted into diabetic mice. An explanation to reconcile these differing results is provided.

Animals↗
PubMed1998

A simple method for the simultaneous separation of peripheral blood mononuclear and polymorphonuclear cells in the dog.

A simple method for the simultaneous separation and purification of peripheral blood mononuclear cells (PBMC) and polymorphonuclear neutrophil cells (PMNC) was developed for comparative and functional studies in the immune system of the dog. Purity and cell viability were > 95%, yields were similar to those obtained by other techniques but without red blood cell contamination. Differential blood cell count studies of the isolated cells in blood samples of beagle dogs and German shepherd dogs demonstrated that the 1.077/1.119 double density centrifugation is an effective method of acquiring both highly purified blood mononuclear cells and polymorphonuclear cells as separate entities from the same sample. The interface between plasma and 1.077 contained an average 97% blood mononuclear cells vs. 3% polymorphonuclear cells, and the interface between 1.077 and 1.119 an average 96% polymorphonuclear cells vs. 4% blood mononuclear cells. These data indicate that Histopaque 1.077/1.119 double density gradient allows the purification and physical separation of lymphocytes and phagocytes from a blood sample in the dog, enabling the investigator to examine both cell types from the same sample simultaneously.

Animals↗
PubMed1998

B lymphocytes differentially use the Rel and nuclear factor kappaB1 (NF-kappaB1) transcription factors to regulate cell cycle progression and apoptosis in quiescent and mitogen-activated cells.

Rel and nuclear factor (NF)-kappaB1, two members of the Rel/NF-kappaB transcription factor family, are essential for mitogen-induced B cell proliferation. Using mice with inactivated Rel or NF-kappaB1 genes, we show that these transcription factors differentially regulate cell cycle progression and apoptosis in B lymphocytes. Consistent with an increased rate of mature B cell turnover in naive nfkb1-/- mice, the level of apoptosis in cultures of quiescent nfkb1-/-, but not c-rel-/-, B cells is higher. The failure of c-rel-/- or nfkb1-/- B cells to proliferate in response to particular mitogens coincides with a cell cycle block early in G1 and elevated cell death. Expression of a bcl-2 transgene prevents apoptosis in resting and activated c-rel-/- and nfkb1-/- B cells, but does not overcome the block in cell cycle progression, suggesting that the impaired proliferation is not simply a consequence of apoptosis and that Rel/NF-kappaB proteins regulate cell survival and cell cycle control through independent mechanisms. In contrast to certain B lymphoma cell lines in which mitogen-induced cell death can result from Rel/NF-kappaB-dependent downregulation of c-myc, expression of c-myc is normal in resting and stimulated c-rel-/- B cells, indicating that target gene(s) regulated by Rel that are important for preventing apoptosis may differ in normal and immortalized B cells. Collectively, these results are the first to demonstrate that in normal B cells, NF-kappaB1 regulates survival of cells in G0, whereas mitogenic activation induced by distinct stimuli requires different Rel/NF-kappaB factors to control cell cycle progression and prevent apoptosis.

Animals↗
PubMed1998

A dominant interfering mutant of FADD/MORT1 enhances deletion of autoreactive thymocytes and inhibits proliferation of mature T lymphocytes.

Members of the tumour necrosis factor receptor family that contain a death domain have pleiotropic activities. They induce apoptosis via interaction with intracellular FADD/MORT1 and trigger cell growth or differentiation via TRADD and TRAF molecules. The impact of FADD/MORT1-transduced signals on T lymphocyte development was investigated in transgenic mice expressing a dominant negative mutant protein, FADD-DN. Unexpectedly, FADD-DN enhanced negative selection of self-reactive thymic lymphocytes and inhibited T cell activation by increasing apoptosis. Thus signalling through FADD/MORT1 does not lead exclusively to cell death, but under certain circumstances can promote cell survival and proliferation.

Adaptor Proteins, Signal Transducing↗
PubMed1998

BCR-ABL activates pathways mediating cytokine independence and protection against apoptosis in murine hematopoietic cells in a dose-dependent manner.

The hallmark of chronic myeloid leukemia (CML) is the chimeric tyrosine kinase oncogene bcr-abl. Since expression of bcr-abl mRNA frequently increases with disease progression and a duplication of the Philadelphia chromosome (harbouring the bcr-abl hybrid locus) represents the most frequent karyotypic abnormality in acute phase CML, we hypothesized that the level of BCR-ABL protein may affect the disease phenotype. Therefore, the biological effects of high and low levels of BCR-ABL expression were compared in growth factor-dependent and -independent myeloid and lymphoid cell lines. Our results demonstrated that low levels of BCR - ABL were sufficient to render these cell lines growth factor independent and tumorigenic, but higher levels were mandatory for additional protection against apoptotic stimuli. The provision of growth factor or an activated ras oncogene did not afford the same degree of protection as high levels of BCR-ABL and there were qualitative differences between the survival signals mediated by BCR-ABL and Bcl-2. These results have enabled us to establish a dose-dependent hierarchy of BCR-ABL induced biological effects, thus distinguishing the activation of pathways mediating protection from cytokine withdrawal from those protecting against other apoptotic stimuli.

Animals↗
PubMed1998

Bim: a novel member of the Bcl-2 family that promotes apoptosis.

Certain members of the Bcl-2 family inhibit apoptosis while others facilitate this physiological process of cell death. An expression screen for proteins that bind to Bcl-2 yielded a small novel protein, denoted Bim, whose only similarity to any known protein is the short (nine amino acid) BH3 motif shared by most Bcl-2 homologues. Bim provokes apoptosis, and the BH3 region is required for Bcl-2 binding and for most of its cytotoxicity. Like Bcl-2, Bim possesses a hydrophobic C-terminus and localizes to intracytoplasmic membranes. Three Bim isoforms, probably generated by alternative splicing, all induce apoptosis, the shortest being the most potent. Wild-type Bcl-2 associates with Bim in vivo and modulates its death function, whereas Bcl-2 mutants that lack survival function do neither. Significantly, Bcl-xL and Bcl-w, the two closest homologues of Bcl-2, also bind to Bim and inhibit its activity, but more distant viral homologues, adenovirus E1B19K and Epstein-Barr virus BHRF-1, can do neither. Hence, Bim appears to act as a 'death ligand' which can only neutralize certain members of the pro-survival Bcl-2 sub-family.

Amino Acid Sequence↗
PubMed1998

Constitutive expression of Bcl-xL or Bcl-2 prevents peptide antigen-induced T cell deletion but does not influence T cell homeostasis after a viral infection.

We examined the CD8+ T cell response to lymphocytic choriomeningitis virus (LCMV) in mice doubly transgenic for an LCMV-specific TCR and for either bcl-xL or bcl-2. Clonal down-sizing of the anti-viral CD8+ T cell response and the generation of T cell memory was not influenced by constitutive expression of these anti-apoptotic proteins in T cells. Expression of Bcl-xL or Bcl-2 did, however, prevent LCMV peptide-induced peripheral deletion of mature CD8+ T cells in vivo and apoptosis of activated LCMV-specific effector T cells in vitro. The CD8+ T cells "rescued" by Bcl-xL or Bcl-2 from peptide antigen-induced cell death were anergic and this could not be reversed by addition of IL-2 in vitro or by adoptive transfer into antigen-free recipient mice followed by LCMV infection in vivo. Taken together, we show here that 1) Bcl-xL or Bcl-2 are functionally equivalent in their ability to modulate CD8+ T cell survival in vivo, 2) distinct apoptosis signaling pathways exist in CD8+ T cells, one that can be inhibited by Bcl-2 or Bcl-xL and one that cannot be blocked, and 3) apoptosis of CD8+ effector T cells during the declining phase of an immune response is not prevented by constitutive expression of the anti-apoptotic proteins Bcl-xL and Bcl-2.

Animals↗
PubMed1998

The Bcl-2 family and cell death regulation.

Members of the Bcl-2 protein family fall into two categories on the basis of their ability to either promote or suppress apoptosis. Recent findings have linked these proteins to caspases, the cysteine proteases that effect the collapse of the cell via binding to CED-4. It seems that Bcl-2 proteins influence cell survival by regulating the activation of key caspases.

Animals↗