PubMed Health⌕ Search

Biomedical subjects

A Strasser

Publications and source records attributed to A Strasser.

At least 37 records · Page 2Linked to original sources
PubMed1997

Expression of a bcl-2 transgene reduces proliferation and slows turnover of developing B lymphocytes in vivo.

B lymphocyte differentiation proceeds through a series of alternating stages of proliferative expansion interspersed with noncycling stationary phases during which cells undergo either positive selection or apoptotic cell death. The molecular control of cell cycle progression and that of apoptosis appear to be interconnected. Overexpression of Bcl-2 in lymphocytes or fibroblasts antagonizes apoptosis and delays their transition from the quiescent state into the cell cycle. We have undertaken a systematic analysis of the impact of bcl-2 transgene expression on cell cycle distribution and turnover rate of developing B lymphocytes in normal mice and in mutant animals in which B cell differentiation is arrested at the pro-B/pre-BI or the pre-BII stage. These experiments revealed that overexpression of Bcl-2 reduces proliferation and slows turnover of B cells at all stages of development. This demonstrates that Bcl-2 can retard transition of B cells between the quiescent and the cycling state regardless of the mitogenic stimulus and the differentiation stage. The implications of these results for the normal control of B lymphopoiesis and for lymphomagenesis are discussed.

Animals↗
PubMed1997

The anti-apoptosis function of Bcl-2 can be genetically separated from its inhibitory effect on cell cycle entry.

The Bcl-2 family of proteins regulate apoptosis, some antagonizing cell death and others facilitating it. It has recently been demonstrated that Bcl-2 not only inhibits apoptosis but also restrains cell cycle entry. We show here that these two functions can be genetically dissociated. Mutation of a tyrosine residue within the conserved N-terminal BH4 region had no effect on the ability of Bcl-2 or its closest homologs to enhance cell survival and did not prevent heterodimerization with death-enhancing family members Bax, Bak, Bad and Bik. Neither did this mutation override the growth-inhibitory effect of p53. However, on stimulation with cytokine or serum, starved quiescent cells expressing the mutant proteins re-entered the cell cycle much faster than those expressing comparable levels of wild-type proteins. When wild-type and Y28 mutant Bcl-2 were co-expressed, the mutant was dominant. Although R-Ras p23 has been reported to bind to Bcl-2, no interaction was detectable in transfected cells and R-Ras p23 did not interfere with the ability of Bcl-2 to inhibit apoptosis or cell cycle entry. These observations provide evidence that the anti-apoptotic function of Bcl-2 is mechanistically distinct from its inhibitory influence on cell cycle entry.

3T3 Cells↗
PubMed1997

Bcl-2 can rescue T lymphocyte development in interleukin-7 receptor-deficient mice but not in mutant rag-1-/- mice.

Signals from cytokine and antigen receptors play crucial roles during lymphocyte development. Mice lacking interleukin-7 receptor are lymphopenic, due to a defect in cell expansion at an early stage of differentiation, and the few mature T cells that develop in IL-7R-/- animals are functionally impaired. Both defects were rescued completely by overexpression of the anti-apoptosis protein Bcl-2. T cell progenitors lacking antigen receptor molecules are also blocked in differentiation and die, presumably because they fail to receive a positive signal via their pre-T cell receptor. Surprisingly, Bcl-2 did not promote survival or differentiation of T cells in rag-1-/- mice. These results provide evidence that blocking apoptosis is the essential function of IL-7R during differentiation and activation of T lymphocytes and that pre-TCR signaling blocks a pathway to apoptosis that is insensitive to Bcl-2.

Animals↗
PubMed1997

Transgenic expression of CD95 ligand on islet beta cells induces a granulocytic infiltration but does not confer immune privilege upon islet allografts.

Binding of CD95 (Fas/APO-1) by its ligand (CD95L) commonly induces apoptosis. Apoptosis of activated T cells, induced by CD95L expressed in the rodent testis, has been proposed to be the mechanism of immune privilege [Bellgrau, D., Gold, D., Selawry, H., Moore, J., Franzusoff, A. & Duke, R. C. (1995) Nature (London) 377, 630-632]. To test whether CD95L could protect pancreatic islet grafts from rejection, we made transgenic mice expressing murine CD95L on their islet beta cells and transplanted fetal pancreata under the kidney capsules of allogeneic animals. Expression of CD95L failed to protect the grafts from rejection. However, transgenic mice developed a granulocytic infiltration in their pancreata. These results demonstrate a pro-inflammatory function of CD95L and suggest that expression of CD95L may not be sufficient to protect organ allografts.

Animals↗
PubMed1997

Bcl-2, Bcl-XL and adenovirus protein E1B19kD are functionally equivalent in their ability to inhibit cell death.

Apoptosis is the physiological process by which unwanted cells in an organism are killed. Bcl-2, a membrane-bound cytoplasmic protein, is an effective inhibitor of apoptotic cell death induced by many cytotoxic agents. Survival-promoting homologues of Bcl-2 include its close relative, Bcl-xL and the 19 kD protein encoded by the E1B gene of adenoviruses. Whether these proteins are functionally equivalent and whether they can antagonise all or only some pathways to apoptosis is unresolved. We have carried out a systematic comparison of Bcl-2, Bcl-xL and adenovirus E1B19kD activity, using several cell lines and a range of cytotoxic conditions. High levels of expression of each of these proteins inhibited apoptosis induced by growth factor deprivation or treatment with gamma-radiation, glucocorticoid and various cytotoxic drugs. In contrast, none of them could effectively counter apoptosis induced via the TNF receptor or Fas/APO-1 (CD95). Biochemical analysis revealed that all three proteins can associate with Bax and Bak, members of the Bcl-2 protein subfamily that can facilitate apoptosis. The results provide evidence that Bcl-2, Bcl-xL and adenovirus protein E1B19kD are indistinguishable in their ability to regulate the cell death effector machinery.

Adenovirus E1B Proteins↗
PubMed1997

Hypoxia modulates free radical formation in brain microvascular endothelium.

Although free radical species (ROS; i.e., .O2-. .OH.H2O2) among other mediators, may be involved in altering the blood-brain barrier (BBB), little is known about the endogenous ability of cerebromicrovascular endothelium to generate ROS. This study examines the capacity of rat endothelial cells (RBEC) to produce ROS in normoxia and hypoxia/reoxygenation. Cultured RBEC were exposed to an oxygen-depleted atmosphere (containing 95% N2 and 5% CO2) for 4 hr at 37 degrees C and air (10 min) at room temperature to simulate "ischemia/reperfusion". Nitroblue tetrazolium (NBT) reduction [formation of nitroblue formazan (NBF)] served as a marker for the production of ROS. The release of lactate dehydrogenase (LDH) and [3H]arachidonic acid (AA) was used to assess cellular integrity. RBEC exposed to hypoxia/reoxygenation produced up to 59% greater NBF formation than controls without affecting the LDH or AA release. The production of ROS was calcium-dependent and not affected by AA or its metabolites. The findings indicate that the RBEC can produce superoxide dismutase (SOD)-inhibitable ROS which are augmented by hypoxia/reoxygenation. It is suggested that in vivo cerebromicrovascular endothelium may contribute to the formation of ROS and play a role in ischemic brain edema.

Animals↗
PubMed1997

The effect of nitric oxide inhibition on ischemic brain edema.

The involvement of nitric oxide (NO) in the development of ischemic cytotoxic edema was investigated by inhibiting nitric oxide synthase (NOS) activity with N omega-nitro-L-arginine (NLA). Bilateral carotid artery occlusion (15 min) alone or with release (15 and 60 min) served as a model for edema induction. NLA, N omega-nitro-D-arginine methyl ester (D-NAME) or Ringer's solution were administered 4 hr prior to ischemia or sham operation. Treatment with a stable nitroxide radical, 4-hydroxy-2,2, 6,6-tetramethylpiperidine-L-oxyl (TPL), was used to assess free radical involvement in edema. Accumulation of tissue water was evaluated by measuring specific gravity (SG) of brain cortex and histological examination. There was a greater reduction of cortical SG in early reperfusion (15 min) and a lesser decrease in SG (60 min later) in NLA-than in D-NAME- or Ringer's-treated gerbils. The NLA effect was confirmed by histological examination of the brain tissue. TPL treatment (pre- and postischemic) ameliorated the formation of edema to the same degree as NLA. The findings indicate a biphasic NLA modulation of cytotoxic edema most likely mediated through absence or presence of NO-derived free radicals.

Animals↗
PubMed1997

Establishment of multipotential and antigen presenting cell lines derived from myeloid leukemias in GM-CSF transgenic mice.

In this study neonatal mice expressing a GM-CSF transgene (GMT mice), and their normal littermate controls, were infected with Moloney murine leukemia virus (MoMLV) to examine in vivo tumorigenesis. By 200 days, all of the GMT mice had died whereas median survival had not been reached in the littermates (P < 0.0003). Thymomas developed in 32% of GMT mice and were more frequently CD4+CD8+ (83%) compared to the CD4+CD8- phenotype seen in 90% of thymomas developing in MoMLV-infected littermate mice. A primitive myeloid leukemia was induced in 21% of GMT mice, but none of the littermates. To characterize further the nature of the leukemic cells, a factor-dependent cell line (DGM36) was derived. DGM36 cells were tumorigenic, capable of differentiation to neutrophils, macrophages and eosinophils, and contained a partial deletion of chromosome 2. A subline arose spontaneously that was factor-independent and produced GM-CSF in an autocrine manner (IGM36 cells). Stimulation of the IGM36 cells with TNF alpha and IFNgamma resulted in increased expression of B7-1, class I MHC and class II MHC and consequent presentation of antigen in allogeneic MLRs. IGM36 cells thereby satisfy many of the criteria of dendritic cells and consequently may be used to examine antigen presentation by leukemic cells. This is the first report of primary myeloid leukemias arising in GMT mice and documents the derivation of a multipotential, autocrine leukemic cell line with dendritic cell characteristics.

Animals↗
PubMed1997

Continued differentiation during B lymphopoiesis requires signals in addition to cell survival.

During B lymphopoiesis, cells undergo successive rounds of division and growth arrest coupled to intermittent selection on the basis of Ig expression. It is unresolved whether differentiation requires specific signaling or is merely the consequence of sustained cell survival. Transgenic expression of the cell death antagonist, Bcl-2, promoted accumulation of B lymphoid cells in mice deficient in antigen receptor rearrangement (scid or rag-1-/-) and in mice lacking the IgM transmembrane domain (microMT). Continued differentiation occurred, however, only in the bcl-2/scid and bcl-2/microMT mice. The appearance of B lineage cells expressing CD21, CD22 and CD23 was associated with DHJH rearrangements which encode a truncated C mu-containing protein called D mu in bcl-2/scid mice and with expression of Ig heavy chain classes other than IgM in the bcl-2/ microMT mice. In neither case, however, were proliferating cells observed in the more mature B lineage compartments in the bone marrow. Thus, continued B cell development requires signaling via Ig heavy chain-containing receptors and is not simply a consequence of blocking apoptosis.

Animals↗
PubMed1997

bcl-2 transgene expression promotes survival and reduces proliferation of CD3-CD4-CD8- T cell progenitors.

Proliferative expansion and apoptotic cell death play prominent roles in T cell development. The molecular control of cell cycle progression and apoptosis appear to be inter-connected since the Bcl-2 protein can inhibit apoptosis and slow cell cycle progression in cortical thymocytes and mature T cells, particularly during the transition from the quiescent state into the cell cycle. Here the impact of bcl-2 transgene expression on CD3-CD4-CD8- T cell progenitors was assessed. Bcl-2 enhanced the survival of these progenitors at all of the four major differentiation stages, CD25- CD44+ (pro-T1), CD25 + CD44+ (pro-T2), CD25 + CD44- (pro-T3) and CD25-CD44- (pro-T4). However, it reduced cell cycling and slowed turnover only in the pro-T4 subset. From an analysis of bcl-2 transgenic mice expressing a TCR transgene or bearing a mutation in the scid or rag-1 gene we conclude that Bcl-2 inhibits proliferation only of T cell progenitors that are activated via the pre-TCR, not those stimulated via c-Kit and the IL-7 receptor.

Animals↗
PubMed1997

Age-dependent changes in cardiovascular and metabolic responses to exercise in beagle dogs.

There is little data available on age-dependent changes in cardiovascular and metabolic functional capacity in older dogs and their geriatric importance, although the frequency of cardiovascular diseases increases with age in the dog, too. Thus we investigated major cardiovascular and metabolic parameters during and after physical exercise by treadmill-running in 5-10 year-old Beagles. We analysed electrocardiograms, body temperature, haematology, blood chemistry and blood gases. There were hardly any significant differences in the baseline values at rest in the younger dogs as compared with the older ones. However, in many of these parameters, significant differences became manifest after exercise. In the younger animals we measured significantly higher values of haematocrit, red blood cell count and haemoglobin concentration after exercise by treadmill running. Furthermore, we also found a significantly lower venous oxygen tension and lower oxygen saturation in venous blood as well as a significant lower plasma glucose level in the older animals during the recovery period. Heart rate during and immediately after exercise, as well as body temperature after exercise, was significantly lower in the older animals. Almost all of our examined parameters that change significantly with age during and after exercise (e.g. heart rate, plasma glucose, body temperature and red blood cells) are modulated at least partly by catecholamines and the sympathetic system. We were able to demonstrate in our investigation that the ageing of the cardiovascular system also results in a progressive loss of organ reserve and adaptability, presumably due at least in part to functional changes in the catecholaminergic system. This age-related decline in the functional capability of the cardiovascular system probably creates a basis for cardiovascular diseases in older age.

Aging↗
PubMed1997

Deregulation of cell survival in lymphomagenesis.

Because normal lymphoid tissue homeostasis depends on a balance between cell proliferation and cell death, lymphomas can arise from mutations that interfere with the normal cell death process. We here discuss some circumstances in which lymphoid cell overexpression of a cell death antagonist, the Bcl2 protein, in E mu-bcl2 transgenic mice can contribute to the development of lymphomas and plasmacytomas.

Animals↗
PubMed1996

The cell death inhibitor Bcl-2 and its homologues influence control of cell cycle entry.

The effect of the cell death inhibitor Bcl-2 and its homologues on cell cycle regulation was explored in lymphocytes and cell lines. Expression of a bcl-2 transgene reduced proliferation of thymocytes and delayed cell cycle entry of mitogen-stimulated B and T lymphocytes. Overexpression of Bcl-2, Bcl-xL or adenovirus E1B19kD substantially delayed serum stimulation-induced S phase entry of quiescent NIH 3T3 fibroblasts. Bcl-2-mediated cell survival and growth inhibition are both antagonized by Bax. Bcl-2, Bcl-xL and E1B19kD, but not Bcl-2 mutants that are defective in blocking apoptosis, suppress growth of colon carcinoma cells. This evidence that regulation of cell survival is coupled to control of cell growth has implications for normal cell turnover and tumorigenesis.

3T3 Cells↗
PubMed1996

CrmA expression in T lymphocytes of transgenic mice inhibits CD95 (Fas/APO-1)-transduced apoptosis, but does not cause lymphadenopathy or autoimmune disease.

The cysteine protease interleukin-1beta converting enzyme (ICE) is implicated as an effector of apoptosis in mammalian cells. Proteolytic activity of ICE can be blocked in vitro by the cytokine response modifier A (crmA), a serpin-like protease inhibitor encoded by cowpox virus. Here we show that CD2 enhancer-driven expression of crmA in T lymphocytes of transgenic mice (CD2-crmA mice) reduces CD95 (Fas/APO-1)-transduced apoptosis in vitro to the level seen in CD95-deficient mutant lpr mice, but does not protect against gamma-radiation or corticosteroid-induced cell death. Unlike lpr mice, CD2-crmA transgenic mice developed neither T cell hyperplasia nor serum autoantibodies. These results provide evidence that the phenotype of lpr mice is not simply due to failure of CD95 to trigger T cell apoptosis mediated by ICE.

Animals↗
PubMed1996

Mutations in the p53 and SCID genes cooperate in tumorigenesis.

DNA damage can cause mutations that contribute to cellular transformation and tumorigenesis. The p53 tumor suppressor acts to protect the organism from DNA damage by inducing either G1 arrest to facilitate DNA repair or by activating physiological cell death (apoptosis). Consistent with this critical function of p53, mice lacking p53 are predisposed to developing tumors, particularly lymphoma. The severe combined immune deficiency (scid) focus encodes the catalytic subunit of DNA protein kinase (DNA-PKcs), a protein complex that has a role in the cellular response to DNA damage. Cells from scid mice are hypersensitive to radiation and scid lymphocytes fail to develop from precursors because they are unable to properly join DNA-coding ends during antigen receptor gene rearrangement. We examined the combined effect of loss of p53 and loss of DNA-PKcs on lymphocyte development and tumorigenesis by generating p53-/- scid mice. Our data demonstrate that loss of p53 promotes T-cell development in scid mice but does not noticeably affect B lymphopoiesis. Moreover, scid cells are able to induce p53 protein expression and activate G1 arrest or apoptosis in response to ionizing radiation, indicating that DNA-PKcs is not essential for these responses to DNA damage. Furthermore, p53-/- scid double mutant mice develop lymphoma earlier than p53-/- littermates, demonstrating that loss of these two genes can cooperate in tumorigenesis. Collectively, these results provide evidence for an unsuspected role of p53 as a checkpoint regulator in early T-cell development and demonstrate that loss of an additional component of the cellular response to DNA damage can cooperate with loss of p53 in lymphomagenesis.

Animals↗
PubMed1996

Progenitor tumours from Emu-bcl-2-myc transgenic mice have lymphomyeloid differentiation potential and reveal developmental differences in cell survival.

Mice expressing both a bcl-2 and a myc transgene within the B lymphoid cell compartment invariably develop novel immature haemopoietic tumours. The likely cell of origin of these tumours was identified by a common pattern of cell surface marker expression on a subset of cells comprising approximately 1% of normal mouse bone marrow. The bcl-2-myc tumour cells could be induced to differentiate into either B lymphocytes or macrophages in culture with certain cytokines and feeder cells. Analysis of their progression into the B lymphoid lineage revealed that Igk locus transcription can precede Igh as well as Igk rearrangement. Surprisingly, the undifferentiated tumour cells died rapidly in culture, even in the presence of multiple cytokines, but they proliferated on monolayers of stromal cells derived from haemopoietic tissues. Thus, even with Bcl-2 levels that protect more differentiated cells, these immature bi-potential progenitor cells require a stromal-induced signal for survival. These results provide insight into the process of lineage commitment and suggest new levels of control of cell survival during early steps in haemopoietic development.

Animals↗
PubMed1996

Cerebral postischemic hypoperfusion is mediated by ETA receptors.

Effect of ETA-receptor antagonist, BQ123, on postischemic hypoperfusion in the presence or absence of nitric oxide synthetase inhibitor, N omega-nitro-L-arginine (NLA), was investigated in Mongolian gerbils. BQ123 given prior to ischemia reversed the early incomplete recovery of cerebral blood flow observed with NLA without affecting the late postischemic hypoperfusion. Additional postischemic administration of BQ123 also reversed (P < 0.01) the late postischemic hypoperfusion seen in NLA-, N omega-nitro-D-arginine methyl ester- or Ringer's-treated animals.

Animals↗