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C B Thompson

Publications and source records attributed to C B Thompson.

At least 91 records · Page 5Linked to original sources
PubMed1998

Bcl-2-family proteins: the role of the BH3 domain in apoptosis.

Bcl-2-related proteins have come to occupy a prominent position in the realm of programmed cell death. Members of this fast-growing family are highly related in one or more specific regions, commonly referred to as Bcl-2 homology (BH) domains. BH domains contribute at multiple levels to the function of these proteins in cell death and survival. Particularly intriguing is the emergence of the BH3 domain as a potent 'death domain' and of a growing subclass of pro-apoptotic proteins with no similarity to Bcl-2 beyond their BH3 homology. Here, the authors classify proteins of the Bcl-2 family on the basis of function and domain organization, discuss the importance of the BH3 domain in protein-protein interactions and in cell death and provide possible explanations for the perceived redundancy in the expression of this subclass of death promoters.

Amino Acid Sequence↗
PubMed1998

Effects of 1,2-naphthoquinones on human tumor cell growth and lack of cross-resistance with other anticancer agents.

The sensitivity of human tumor and rat prostate tumor cells to a series of naphthoquinones, including tricyclic compounds of the beta-lapachone and dunnione families as well as 4-alkoxy-1,2-naphthoquinones, was evaluated. To better understand the mechanism of cytotoxicity of 1,2-naphthoquinones, the roles of various resistance mechanisms including P-glycoprotein, multidrug resistant associated protein, glutathione (GSH) and related enzymes, altered topoisomerase activity, and overexpression of genes that control apoptosis (bcl-2 and bc-xL) were studied. MCF7 cells were most sensitive to the naphthoquinones with IC50 values ranging from 1.1 to 10.8 microM, as compared to 2.5 to >32 microM for HT29 human colon, A549 human lung, CEM leukemia and AT3.1 rat prostate cancer cells. MCF7 ADR cells, selected for resistance to adriamycin (ADR), displayed cross-resistance to the tricyclic 1,2-naphthoquinones. Drug efflux via a P-glycoprotein mechanism was ruled out as a mechanism of resistance to 1,2-naphthoquinones, since KB-V1 cells expressing high levels of P-glycoprotein and the KB-3.1 parent line were equally sensitive to these compounds. Any resistance of the tricyclic naphthoquinones noted in ADR-resistant cells appeared to relate to the GSH redox cycle and could be circumvented by exposure to buthionine sulfoximine or by changing the structure from a tricyclic derivative to a 4-alkoxy-1,2-naphthoquinone. The 1,2-naphthoquinones were found to be cytotoxic against CEM/VM-1 and CEM/M70-B1 cells that were selected for resistance to teniposide or merbarone, respectively. In addition, cells overexpressing bcl-2 or bcl-xL proteins were as sensitive to 1,2-naphthoquinones as were control cells. Because of their effectiveness in drug-resistant cells, these agents appear to hold promise as effective chemotherapeutic agents.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1998

4-1BB and Ox40 are members of a tumor necrosis factor (TNF)-nerve growth factor receptor subfamily that bind TNF receptor-associated factors and activate nuclear factor kappaB.

Members of the tumor necrosis factor (TNF)-nerve growth factor (NGF) receptor family have been shown to be important costimulatory molecules for cellular activation. 4-1BB and Ox40 are two recently described members of this protein family which are expressed primarily on activated T cells. To gain insight into the signaling pathways employed by these factors, yeast two-hybrid library screens were performed with the cytoplasmic domains of 4-1BB and Ox40 as baits. TNF receptor-associated factor 2 (TRAF2) was identified as an interacting protein in both screens. The ability of both 4-1BB and Ox40 to interact with TRAF2 was confirmed in mammalian cells by coimmunoprecipitation studies. When the binding of the receptors to other TRAF proteins was investigated, 4-1BB and Ox40 displayed distinct binding patterns. While 4-1BB bound TRAF2 and TRAF1, Ox40 interacted with TRAF3 and TRAF2. Using deletion and alanine scanning analysis, we defined the elements in the cytoplasmic domains of both receptors that mediate these interactions. The 4-1BB receptor was found to have two independent stretches of acidic residues that can mediate association of the TRAF molecules. In contrast, a single TRAF binding domain was identified in the cytoplasmic tail of Ox40. The cytoplasmic domains of both receptors were shown to activate nuclear factor kappaB in a TRAF-dependent manner. Taken together, our results indicate that 4-1BB and Ox40 bind TRAF proteins to initiate a signaling cascade leading to activation of nuclear factor kappaB.

Amino Acid Sequence↗
PubMed1998

Human IAP-like protein regulates programmed cell death downstream of Bcl-xL and cytochrome c.

The gene encoding human IAP-like protein (hILP) is one of several mammalian genes with sequence homology to the baculovirus inhibitor-of-apoptosis protein (iap) genes. Here we show that hILP can block apoptosis induced by a variety of extracellular stimuli, including UV light, chemotoxic drugs, and activation of the tumor necrosis factor and Fas receptors. hILP also protected against cell death induced by members of the caspase family, cysteine proteases which are thought to be the principal effectors of apoptosis. hILP and Bcl-xL were compared for their ability to affect several steps in the apoptotic pathway. Redistribution of cytochrome c from mitochondria, an early event in apoptosis, was not blocked by overexpression of hILP but was inhibited by Bcl-xL. In contrast, hILP, but not Bcl-xL, inhibited apoptosis induced by microinjection of cytochrome c. These data suggest that while Bcl-xL may control mitochondrial integrity, hILP can function downstream of mitochondrial events to inhibit apoptosis.

Apoptosis↗
PubMed1998

B-cell development and maturation.

Approximately 85% of all non-Hodgkin's lymphomas arise from cells of the B lineage. Sequential stages of B-cell development have been defined by molecular markers, and these markers can be used to reclassify lymphoid malignancies as representing maturational arrest and immortalization at specific points in B-cell ontogeny. Several of the factors controlling the ordered rearrangement and expression of the immunoglobulin (Ig) genes have been identified. Signals generated by intermediates in Ig gene rearrangement, as well as by the complete Ig molecule, have been found to be critical in guiding early B-cell development. The processes of peripheral B-cell activation, antigenic affinity maturation, and terminal B-cell differentiation are also highly regulated. The molecular mechanisms responsible for both promoting and attenuating B-cell (humoral) immune responses have been increasingly well defined. This review summarizes some aspects of the current understanding of normal B-cell development, maturation, activation, and death, focusing on the factors implicated in regulating progression through these stages.

Animals↗
PubMed1997

Effects of CD28 costimulation on long-term proliferation of CD4+ T cells in the absence of exogenous feeder cells.

In this report, conditions for prolonged in vitro proliferation of polyclonal adult CD4+ T cells via stimulation with immobilized anti-CD3 plus anti-CD28 have been established. CD4+ cells maintained exponential growth for more than 60 days during which a total 10(9)- to 10(11)-fold expansion occurred. Cell cultures exhibited cyclical changes in cell volume, indicating that, in terms of proliferative rate, cells do not have to rest before restimulation. Indeed, electronic cell size analysis was the most reliable method to determine when to restimulate with additional immobilized mAb. The initial approximately 10(5)-fold expansion was autocrine, occurring in the absence of exogenous cytokines or feeder cells. Addition of recombinant human IL-2 after the initial autocrine expansion resulted in continued exponential proliferation. Phorbol ester plus ionomycin also induced long-term growth when combined with anti-CD28 stimulation. Analysis of the T cell repertoire after prolonged expansion revealed a diverse repertoire as assessed by anti-TCR Vbeta Abs or a PCR-based assay. Cytokines produced were consistent with maintenance of both Th1 and Th2 phenotypes; however, the mode of CD3 and CD28 stimulation could influence the cytokine secretion pattern. When anti-CD3 and anti-CD28 were immobilized on the same surface, ELISAs on culture supernatants revealed a pattern consistent with Th1 secretion. Northern analysis revealed that cytokine gene expression remained inducible. Spontaneous growth or cell transformation was not observed in more than 100 experiments. Together, these observations may have implications for gene therapy and adoptive immunotherapy. Furthermore, these culture conditions establish a model to study the finite lifespan of mature T lymphocytes.

Antibodies, Monoclonal↗
PubMed1997

Bcl-xL regulates the membrane potential and volume homeostasis of mitochondria.

Mitochondrial physiology is disrupted in either apoptosis or necrosis. Here, we report that a wide variety of apoptotic and necrotic stimuli induce progressive mitochondrial swelling and outer mitochondrial membrane rupture. Discontinuity of the outer mitochondrial membrane results in cytochrome c redistribution from the intermembrane space to the cytosol followed by subsequent inner mitochondrial membrane depolarization. The mitochondrial membrane protein Bcl-xL can inhibit these changes in cells treated with apoptotic stimuli. In addition, Bcl-xL-expressing cells adapt to growth factor withdrawal or staurosporine treatment by maintaining a decreased mitochondrial membrane potential. Bcl-xL expression also prevents mitochondrial swelling in response to agents that inhibit oxidative phosphorylation. These data suggest that Bcl-xL promotes cell survival by regulating the electrical and osmotic homeostasis of mitochondria.

Anti-Bacterial Agents↗
PubMed1997

CD30-dependent degradation of TRAF2: implications for negative regulation of TRAF signaling and the control of cell survival.

CD30 is a cell-surface receptor that can augment lymphocyte activation and survival through its ability to induce the transcription factor NF-kappaB. CD30, however, has also been implicated in the induction of apoptotic cell death of lymphocytes. Here we show that one of the effects of CD30 signal transduction is to render cells sensitive to apoptosis induced by the type 1 tumor necrosis factor receptor (TNFR1). This sensitization is dependent on the TRAF-binding sites within the CD30 cytoplasmic domain. One of the proteins that binds to these sites is TRAF2, a signal transduction molecule that is also utilized by TNFR1 to mediate the activation of several downstream kinases and transcription factors. During CD30 signal transduction, we found that binding of TRAF2 to the cytoplasmic domain of CD30 results in the rapid depletion of TRAF2 and the associated protein TRAF1 by proteolysis. These data suggest a model in which CD30 limits its own ability to transduce cell survival signals through signal-coupled depletion of TRAF2. Depletion of intracellular TRAF2 and its coassociated proteins also increased the sensitivity of the cell to undergoing apoptosis during activation of death-inducing receptors such as TNFR1. Consistent with this hypothesis, expression of a dominant-negative form of TRAF2 was found to potentiate TNFR1-mediated death. These studies provide a potential mechanism through which CD30, as well as other TRAF-binding members of the TNFR superfamily, can negatively regulate cell survival.

Antigens, CD↗
PubMed1997

The avian chB6 (Bu-1) alloantigen can mediate rapid cell death.

The control of cell death is critical in the immune system. T and B lymphocytes must be censored during their development to remove nonfunctional or self-reactive lymphocytes. However, the molecules controlling cell deletion during lymphopoiesis have not been defined. B cells removed from the avian bursa of Fabricius rapidly undergo cell death in culture. We screened bursal B cells with a panel of Abs and lectins to identify molecules affecting their viability. Abs to the chB6 alloantigen caused a rapid loss of cell viability as measured by staining with propidium iodide. ChB6 Abs also cause adhesion between B cells. Transfection of cDNA encoding chB6 reconstituted the allele-specific cell death and adhesion effects in avian cell lines. These effects can be separated by binding cells onto Ab-coated plastic dishes. In these experiments, cells were killed in the absence of cell:cell contact. The ability of chB6 cross-linking to evoke cell aggregation and cell death is also observed when chB6 is expressed in growth factor-dependent mammalian cells. In these cells growth factor can almost completely prevent cell death but not cell aggregation. This suggests that known cell survival stimuli can suppress the cell death brought about by chB6 cross-linking. These results show that chB6 may have an important role in controlling cell survival and/or adhesion during avian B cell development.

Animals↗
PubMed1997

Interaction of CTLA-4 with the clathrin-associated protein AP50 results in ligand-independent endocytosis that limits cell surface expression.

CTLA-4 is a lymphocyte cell surface receptor expressed by activated T cells that functions to down-regulate T cell responses induced by TCR and CD28 stimulation. Since CTLA-4 competes with CD28 for binding to the common ligands B7-1 and B7-2, the level of CTLA-4 surface expression is likely to play an important role in its ability to inhibit CD28-dependent T cell activation. The factors that regulate these levels are poorly understood. Recent studies have revealed that following T cell activation, the majority of CTLA-4 is localized intracellularly rather than on the cell surface, and surface CTLA-4 is rapidly reinternalized. In this study, we investigate the molecular mechanism underlying the rapid clearance of CTLA-4 from the cell surface. The data demonstrate that cell surface CTLA-4 is endocytosed into clathrin-coated vesicles even in the absence of ligand. The targeting of CTLA-4 to clathrin-coated vesicles is mediated by the clathrin-associated adaptor complex AP-2. The cytoplasmic domain of CTLA-4 was found to specifically bind to AP50, the medium chain subunit of AP-2 in both yeast two-hybrid and coimmunoprecipitation assays. The interaction requires the peptide sequence 199-GVYVKM-204 in the cytoplasmic tail of CTLA-4. Mutation of the CTLA-4 amino acid residue Y201 abrogates the interaction with AP50, resulting in the accumulation of CTLA-4 at the cell surface. Together these data suggest that the interaction of CTLA-4 with AP50 plays an important role in regulating the cell surface expression of CTLA-4.

Abatacept↗
PubMed1997

CD28 engagement and proinflammatory cytokines contribute to T cell expansion and long-term survival in vivo.

To mount a productive response to Ag, CD4+ T cells in mice must divide, differentiate, and survive at least until the Ag has been eliminated. It has been suggested that to accomplish this, T cells must receive two signals, one through their TCRs and a second through CD28. The second signal through CD28 has been thought to fulfill two roles, to stimulate T cell proliferation and to promote T cell survival. In this paper we confirm that CD28 engagement can contribute to vigorous T cell expansion in mice injected with superantigens. However, CD28 engagement does not protect T cells produced during a superantigen-specific proliferative response from undergoing subsequent deletion. Even if CD28 is bound, 4 days after superantigen exposure, the majority of T cells produced in response to superantigen exposure are eliminated in vivo. In contrast, this loss of superantigen-stimulated T cells can be prevented by the inflammatory stimuli created by injection of bacterial LPS. This protection does not require engagement of CD28 by its ligands, B7-1 and B7-2. These data suggest that productive T cell responses in mice involve a number of signals, including those initiated through TCR and CD28, which are primarily involved in the activation and expansion of T cells, and others delivered by proinflammatory cytokines that protect an activated T cell from subsequent deletion.

Abatacept↗
PubMed1997

Bcl-x(L) can inhibit apoptosis in cells that have undergone Fas-induced protease activation.

Programmed cell death or apoptosis provides an irreversible mechanism for the elimination of excess or damaged cells. Several recent studies have implicated the activation of the interleukin 1beta-converting enzyme/Ced-3 (ICE/Ced-3) family of proteases as the "point of no return" in apoptotic cell death, while others have suggested that loss of mitochondrial membrane potential (delta psi(m)) is the ultimate determinant of cell death. The temporal relationship of these two events during apoptosis and the role of Bcl-2 proteins in inhibiting these steps has not been defined. To examine these issues, control and Bcl-x(L)-transfected Jurkat T cells were treated with Fas antibodies in the presence and absence of the ICE protease inhibitor zVAD-FMK. ICE/Ced-3 protease activity was monitored by following the cleavage of poly(ADP-ribose) polymerase (PARP) and delta psi(m) was followed by rhodamine 123 fluorescence. Although Bcl-x(L) expression did not block Fas-induced protease activation, it substantially inhibited the subsequent loss of delta psi(m) and cell death in Fas-treated cells. In contrast, zVAD-FMK blocked PARP cleavage as well as loss of delta psi(m) and cell death. Together these data demonstrate that Bcl-x(L) can maintain cell viability by preventing the loss of mitochondrial membrane potential that occurs as a consequence of ICE/Ced-3 protease activation.

Apoptosis↗
PubMed1997

Identification of a novel regulatory domain in Bcl-X(L) and Bcl-2.

Bcl-X(L), a member of the Bcl-2 family, can inhibit many forms of programed cell death. The three-dimensional structure of Bcl-X(L) identified a 60 amino acid loop lacking defined structure. Although amino acid sequence within this region is not conserved among Bcl-2 family members, structural modeling suggested that Bcl-2 also contains a large unstructured region. Compared with the full-length protein, loop deletion mutants of Bcl-X(L) and Bcl-2 displayed an enhanced ability to inhibit apoptosis. Despite enhanced function, the deletion mutants did not have significant alterations in the ability to bind pro-apoptotic proteins such as Bax. The loop deletion mutant of Bcl-2 also displayed a qualitative difference in its ability to inhibit apoptosis. Full-length Bcl-2 was unable to prevent anti-IgM-induced cell death of the immature B cell line WEHI-231. In contrast, the Bcl-2 deletion mutant protected WEHI-231 cells from death. Substantial differences were observed in the ability of WEHI-231 cells to phosphorylate the deletion mutant of Bcl-2 compared with full-length Bcl-2. Bcl-2 phosphorylation was found to be dependent on the presence of an intact loop domain. These results suggest that the loop domain in Bcl-X(L) and Bcl-2 can suppress the anti-apoptotic function of these genes and may be a target for regulatory post-translational modifications.

Amino Acid Sequence↗
PubMed1997

Structure of Bcl-xL-Bak peptide complex: recognition between regulators of apoptosis.

Heterodimerization between members of the Bcl-2 family of proteins is a key event in the regulation of programmed cell death. The molecular basis for heterodimer formation was investigated by determination of the solution structure of a complex between the survival protein Bcl-xL and the death-promoting region of the Bcl-2-related protein Bak. The structure and binding affinities of mutant Bak peptides indicate that the Bak peptide adopts an amphipathic alpha helix that interacts with Bcl-xL through hydrophobic and electrostatic interactions. Mutations in full-length Bak that disrupt either type of interaction inhibit the ability of Bak to heterodimerize with Bcl-xL.

Amino Acid Sequence↗
PubMed1997

Bcl-x(L) forms an ion channel in synthetic lipid membranes.

Bcl-2-related proteins are critical regulators of cell survival that are localized to the outer mitochondrial, outer nuclear and endoplasmic reticulum membranes. Despite their physiological importance, the biochemical function of Bcl-2-related proteins has remained elusive. The three-dimensional structure of Bcl-xL, an inhibitor of apoptosis, was recently shown to be similar to the structures of the pore-forming domains of bacterial toxins. A key feature of these pore-forming domains is the ability to form ion channels in biological membranes. Here we demonstrate that Bcl-xL shares this functional feature. Like the bacterial toxins, Bcl-xL can insert into either synthetic lipid vesicles or planar lipid bilayers and form an ion-conducting channel. This channel is pH-sensitive and becomes cation-selective at physiological pH. The ion-conducting channel(s) formed by Bcl-xL display multiple conductance states that have identical ion selectivity. Together, these data suggest that Bcl-xL may maintain cell survival by regulating the permeability of the intracellular membranes to which it is distributed.

Cations↗