Biomedical subjects

C B Thompson

Publications and source records attributed to C B Thompson.

At least 145 records · Page 8Linked to original sources

PubMed1996

Role of skeletal muscle sodium pumps in the adaptation to potassium deprivation.

Skeletal muscle is specialized to lose K+ to the extracellular fluid during potassium deprivation which buffers the fall in plasma K+ concentration. While it remains to be determined whether K+ efflux from muscle is altered during K+ deprivation, active K+ uptake driven by sodium pumps is significantly depressed. The activity of sodium pumps in skeletal muscle does not increase during K+ depletion despite elevated intracellular Na+, a strong stimulus to increase activity in other cells. There is a decrease in the total pool size of sodium pump alpha beta heterodimers during potassium deprivation. The alpha 2 (not the alpha 1) sodium pump isoform is specifically decreased and beta 1 and/or beta 2 decreases in a muscle-fibre-dependent manner. The specific loss of K+ from skeletal muscle is probably a consequence of the fact that the alpha 2 isoform predominates in this tissue. In tissues such as heart, where alpha 2-type pumps are only a minor fraction of the sodium pumps, the activity of the ubiquitous alpha 1 isoform maintains intracellular Na+ and K+ at control levels, despite the fact that alpha 2 levels decrease by 50%. Analysis of the time course of change in alpha 2 mRNA vs. protein during K+ deprivation indicates that there is both a decrease in alpha 2 synthesis and an increase in alpha 2 degradation. The apparent time-lag during potassium deprivation between the early decreases in both surface alpha 2-type sodium pump number (assessed by 3H-ouabain binding) and intracellular K+, and the later decrease in total pool size of alpha 2, suggests the hypothesis that there may be an early internalization of alpha 2 sodium pumps to endosomal pools, followed by a degradation of these internalized pumps, contributing to the decrease in total alpha 2 pool size. The signals mediating this specific response to hypokalemia, and those mediating the restoration of muscle K+ stores remain to be determined.

Animals↗

PubMed1996

Apoptosis induced by differentiation or serum deprivation in an immortalized central nervous system neuronal cell line.

To characterize the nature of programmed cell death (PCD) induced in neuronal cells during development, three regulators of apoptosis were investigated: one, the bcl-2-related genes, modulate cell survival, and the other two, the interleukin-1 beta converting enzyme (ICE)-related enzymes and the tumor suppressor protein p53, have been implicated as mediators of apoptosis. These regulators were studied in H19-7 cells, an SV40 Tts-immortalized rat hippocampal neuronal cell line that can be differentiated with basic fibroblast growth factor at the nonpermissive temperature, resulting in a rapid attrition of cells by apoptosis. PCD occurred by two mechanisms in H19-7 cells: The first was initiated by removal of serum from undifferentiated cells, and the second was a consequence of neuronal differentiation. In differentiated H19-7 cells, the survival time was increased by both human bcl-2 and bcl-xL, and this could be reversed by bcl-xs. Addition of a peptide inhibitor of the ICE enzyme family to H19-7 cells resulted in a transient protection against differentiation-associated apoptosis, whereas no further protection was observed in the BCL-2- or BCL-XL-expressing cells. Shifting the differentiated cells to 33 degrees C to inactivate p53 did not significantly affect the apoptotic process, indicating that apoptosis induced by neuronal differentiation is not dependent on the continued presence of p53. By contrast, in undifferentiated cells, cell loss induced by transfer to serum-free media occurred more rapidly on inactivation of large T, consistent with p53 involvement. This medium-induced decrease in cell survival could not be rescued by the ICE inhibitor but was partially rescued by BCL-2 or BCL-XL. Furthermore, studies involving expression of BCL-2 and BCL-XL alone or together revealed differences in the survival dependent on the cellular environment. These results suggest that apoptosis of neuronal cells occurs by at least two processes: one in undifferentiated cells initiated by removal of serum and one linked to differentiation. The data implicate the ICE enzyme family but not p53 in apoptosis induced by differentiation and demonstrate that either BCL-2 or BCL-XL can prolong the survival of differentiated neuronal cells.

Amino Acid Chloromethyl Ketones↗

PubMed1996

Challenges in developing estimates of exposure rate near the Nevada Test Site.

As one of several dose reconstruction projects, the Off-site Radiation Exposure Review Project needed to develop models that reflect processes and lifestyles of the past and obtain accurate and adequate historical data to drive the models. One of the critical pieces, ultimately used to estimate the potential dose to people in the area surrounding the Nevada Test Site, was the development of exposure rate estimates used as input to the external and internal dose models. The historical data available for making these estimates were collected in manners and for purposes not necessarily consistent with the needs of this task. The Town Data Base is the culmination of the effort to develop those estimates for the Project's Phase I region (or for locations near the Nevada Test Site that were primarily covered by ground monitoring at the time of the nuclear tests). It includes estimates of discernible exposure rate at 353 populated locations in Arizona, California, Nevada, and Utah and for 74 nuclear tests at the Nevada Test Site. Each dose reconstruction effort has similarities with, and variations from, others. This paper describes some of the challenges encountered in creating the Town Data Base and the approaches used to address them. These challenges included collecting historical data, incorporating net exposure rate values of zero into the estimates, defining a discernible fallout level, handling the lack of measurements at some locations and creating dispersion estimates. The approaches were developed to create "best" estimates and to use actual data (as opposed to assumed values) as the primary source where such data were available. A summary of the spatial distribution of these estimates and a comparison of relative levels of fallout by location are also included.

Environmental Exposure↗

PubMed1996

Research to support holistic nursing taxonomies.

A philosophy of holism and the development of nursing taxonomies may appear to have goals that are inconsistent. Taxonomies are typically hierarchic in structure, and their content often consists of atomic level elements rather than holistic concepts. The article explores the development of taxonomies and how they can be enriched by a holistic perspective.

Holistic Nursing↗

PubMed1996

Apoptotic signaling in lymphocytes.

Two families of cell surface receptors are integral to the control of lymphocyte survival and programmed cell death (apoptosis): the tumor necrosis factor receptor family and the CD28/CTLA4 family. Tumor necrosis factor receptor family members bind a related collection of ligands (the tumor necrosis factor family) that can either induce or inhibit cell death. Two of the tumor necrosis factor receptor family members, tumor necrosis factor receptor 1 and Fas, have been implicated in the termination of immune responses through their ability to induce apoptosis. A number of cytoplasmic proteins implicated in signal generation by these receptors recently have been identified. These proteins fall into several related classes sharing intriguing structural motifs. The CD28 and CTLA4 molecules share at least two extracellular ligands and signaling through the two receptors appears to determine the apoptotic sensitivity of activated T cells. The effects of CD28 and CTLA4 on cell survival are dependent on T-cell antigen receptor engagement, providing a potent mechanism for clonally specific T-cell expansion or deletion. The study of the apoptotic pathways in lymphocytes has led to a better understanding of the mechanisms of autoimmune disease and serves as a model system for the study of the regulation of cell survival and tissue homeostasis.

Abatacept↗

PubMed1996

The ability of Bcl-x(L) and Bcl-2 to prevent apoptosis can be differentially regulated.

Although expression of Bcl-2 has been shown to prevent apoptosis under many circumstances, there are several systems in which Bcl-2 fails to promote cell survival. We have previously reported that Bcl-2 and Bcl-x(L) display differential ability to protect WEHI-231 cells from multiple inducers of apoptosis. A possible explanation for this paradox was provided by the discovery of Bax. Bax is a Bcl-2-related protein which can inhibit the ability of Bcl-2 to enhance the survival of growth factor-dependent cell lines in the absence of growth factor. Consistent with the possibility that Bcl-2 function in WEHI-231 cells is inhibited by Bax, WEHI-231 cells were found to express a high level of Bax. To directly test the effects of Bax expression on Bcl-x(L) function, FL5.12 cells were transfected with both genes. Although Bax overexpression can inhibit Bcl-2 from prolonging cell survival upon growth factor withdrawal, Bax overexpression did not inhibit Bcl-x(L) from preventing apoptosis in this cell line. Although Bcl-2 and Bcl-x(L) were both found to be able to form heterodimers with Bax, the majority of Bax in both cases was not complexed to a partner. Our data suggest that Bcl-x(L) does not function by simply preventing the formation of Bax homodimers which promote cell death. Instead Bax appears to display selectivity in its ability to inhibit Bcl-2 but not Bcl-x(L) from prolonging survival. Furthermore, our data suggest that the abilities of Bcl-2 and Bcl-x(L) to promote cell survival are not identical and can be independently regulated within a cell. Regulation of a cell's apoptotic threshold is likely to result from a complex set of interactions among Bcl-2 family members and other, as yet uncharacterised, regulators of apoptosis.

Journal Article↗

PubMed1996

Protective effect of transforming growth factor-beta 1 on beta-amyloid neurotoxicity in rat hippocampal neurons.

Neurodegeneration associated with Alzheimer's disease is believed to involve toxicity to beta-amyloid (A beta) and related peptides. Treatment of cultured rat hippocampal neurons with A beta 1-40 (1 microM) or the active fragment A beta 25-35 (1 microM) for 5 days led to a approximately 40-50% decrease in neuronal viability. The hydrophilic antioxidant ascorbic acid (300 microM) and the lipophilic antioxidant 2-mercaptoethanol (10 microM) both protected significantly against A beta neurotoxicity. Despite the protective effects of these antioxidants, both acute and chronic treatments with A beta 25-35 did not increase production of superoxide anions, as monitored with the fluorescent probe hydroethidine. Similarly, overexpression of Cu/Zn-superoxide dismutase using adenovirus-mediated gene transfer did not protect against A beta neurotoxicity. A beta neurotoxicity, however, was prevented in cultures infected with a recombinant, replication-defective adenovirus overexpressing the Ca2+ binding protein calbindin D28k. Transforming growth factor-beta 1 (TGF-beta 1) has been shown to protect neurons against both Ca(2+)- and free radical-mediated neuronal degeneration. We found that A beta neurotoxicity was significantly attenuated by single treatments with TGF-beta 1 (0.1-10 ng/ml) and prevented by repetitive treatments (10 ng/ml/day). The protective effects of TGF-beta 1 were associated with a preservation of mitochondrial potential and function, as determined with rhodamine-123-based microfluorimetry. Because both increased oxidative stress and pathophysiological Ca2+ fluxes can impair mitochondrial function, preservation of mitochondrial potential by TGF-beta 1 could be directly associated with its protection against A beta neurotoxicity. The ability of TGF-beta 1 to increase the expression of the anti-apoptotic proteins Bcl-2 and Bcl-XL is discussed in this context.

6-Cyano-7-nitroquinoxaline-2,3-dione↗

PubMed1996

Kaposi's sarcoma tumor cells preferentially express Bcl-xL.

Several recently identified proteins such as Bcl-2 and Bcl-x have been found to regulate programmed cell death (i.e., apoptosis). In this report, we examined the levels of expression of proteins that can either prevent apoptosis (i.e., Bcl-2 or the long form of Bcl-x, designated Bcl-x1) or promote apoptosis (i.e., Bax or the short form of Bcl-x, designated Bcl-xs) in proliferating benign and malignant endothelial cells (ECs). In normal skin with quiescent ECs, no detection by immunohistochemical staining was observed for Bcl-xL, Bcl-xs, or Bcl-2. However, in diseased skin samples that feature a prominent angiogenic response such as in psoriasis or pyogenic granulomas, the proliferating ECs markedly overexpressed Bcl-xL, with little to no Bcl-2. In an acquired-immune-deficiency-syndrome-related neoplasm, Kaposi's sarcoma, the spindle-shaped tumor cells also overexpressed Bcl-xL compared with Bcl-2. These in vivo studies were extended in vitro using cultured ECs and Kaposi's sarcoma tumor cells that were examined by flow cytometry and immunoblot analysis. Both cultured ECs and Kaposi's sarcoma tumor cells express significantly higher levels of Bcl-xL than Bcl-2. Such overexpression of cell survival gene products may contribute to prolonging the longevity of EC-derived cells in several different benign and neoplastic skin disorders that are characterized by a prominent angiogenic tissue response.

Blotting, Western↗

PubMed1996

Overexpression of HER2 modulates bcl-2, bcl-XL, and tamoxifen-induced apoptosis in human MCF-7 breast cancer cells.

Overexpression of HER2 in estrogen receptor (ER)-positive human breast tumors has been associated with resistance to endocrine therapy. Here we investigated the effects of HER2 on expression of apoptotic pathways and modulation of tamoxifen-induced apoptosis in ER-positive MCF-7 breast cancer cells. We report that HER2 overexpression in MCF-7 cells is accompanied by up-regulation of antiapoptotic Bcl-2 and Bcl-XL proteins and suppression of tamoxifen-induced apoptosis. In addition, human tumor cell lines that are both ER positive and overexpress HER2 also express enhanced levels of Bcl-2 compared to cells that are either ER positive or overexpress HER2 alone. Our findings suggest that possible deregulation of antiapoptotic Bcl-2 and Bcl-XL may be associated with the enhanced survival of HER2-overexpressing and ER-positive breast cancer cells treated with antiestrogens.

Apoptosis↗

PubMed1995

Expression of sialyl Lewis(x) and Lewis(x) defines distinct stages of chicken B cell maturation.

Commitment of cells to the B lineage in chickens occurs only during a brief period of embryogenesis. B cell progenitors then progress through discrete developmental stages resulting in the production of mature B cells that are competent to form a functioning humoral immune system in the adult bird. During embryogenesis, chicken B cell precursors undergo tissue and developmental stage-specific changes in cell-surface glycosylation. Immature B cell progenitors that migrate to the bursa of Fabricius express the carbohydrate epitope sialyl Lewis(x). Such cells undergo initial clonal expansion within the bursa without undergoing gene conversion. Beginning between days 15 and 17 of embryogenesis, B cells in the bursa undergo a tissue specific change in surface glycosylation that results in the loss of sialyl Lewis(x) expression and the acquisition of the related carbohydrate structure Lewis(x). Expression of Lewis(x) identifies B lymphocytes that have begun to undergo gene conversion. Before emigration from the bursa, bursal lymphocytes undergo another phenotypic switch in glycosylation and down-regulate Lewis(x) expression. Therefore, developmental switches in glycosylation allow us to distinguish three populations of B cells in the bursa of Fabricius at defined stages of development and suggest that regulation of cell-surface glycosylation plays a role in B cell development in the chicken.

Animals↗

PubMed1995

B7/CD28-dependent and -independent induction of CD40 ligand expression.

The induction of a T cell-dependent Ab response is mediated by the interaction of the T cell activation Ag, CD40 ligand (CD40L), with CD40. Since this interaction is independent of Ag, coreceptors such as CD4, and MHC molecules, the expression of the CD40L must be strictly regulated or B cell-mediated autoimmunity may be produced. In this study, we examined the requirements for costimulatory signals for induction of CD40L expression in vitro and in vivo on CD4+ T cells from normal and CD28-deficient mice following stimulation with anti-CD3, Con A, or specific peptide Ag. Expression of B7-1 was both necessary and sufficient for induction of the CD40L on normal CD4+ T cells when L cell transfectants were used as APCs. When normal accessory cell populations were used, only partial inhibition of induction of the CD40L was observed with reagents that inhibit B7/CD28 interactions. Furthermore, the CD40L could be induced on CD4+ T cells from CD28-deficient mice. Thus, non-B7/CD28 cellular interactions can also mediate the costimulatory signals needed for induction of CD40L expression.

Animals↗

PubMed1995

A recombinant bcl-x s adenovirus selectively induces apoptosis in cancer cells but not in normal bone marrow cells.

Many cancers overexpress a member of the bcl-2 family of inhibitors of apoptosis. To determine the role of these proteins in maintaining cancer cell viability, an adenovirus vector that expresses bcl-xs, a functional inhibitor of these proteins, was constructed. Even in the absence of an exogenous apoptotic signal such as x-irradiation, this virus specifically and efficiently kills carcinoma cells arising from multiple organs including breast, colon, stomach, and neuroblasts. In contrast, normal hematopoietic progenitor cells and primitive cells capable of repopulating severe combined immunodeficient mice were refractory to killing by the bcl-xs adenovirus. These results suggest that Bcl-2 family members are required for survival of cancer cells derived from solid tissues. The bcl-xs adenovirus vector may prove useful in killing cancer cells contaminating the bone marrow of patients undergoing autologous bone marrow transplantation.

Adenoviruses, Human↗

PubMed1995

Lymphoproliferative disorders with early lethality in mice deficient in Ctla-4.

The role of the cell-surface molecule CTLA-4 in the regulation of T cell activation has been controversial. Here, lymph nodes and spleens of CTLA-4-deficient mice accumulated T cell blasts with up-regulated activation markers. These blast cells also infiltrated liver, heart, lung, and pancreas tissue, and amounts of serum immunoglobulin were elevated. The mice invariably became moribund by 3 to 4 weeks of age. Although CTLA-4-deficient T cells proliferated spontaneously and strongly when stimulated through the T cell receptor, they were sensitive to cell death induced by cross-linking of the Fas receptor and by gamma irradiation. Thus, CTLA-4 acts as a negative regulator of T cell activation and is vital for the control of lymphocyte homeostasis.

Abatacept↗

PubMed1995

IgM receptor-mediated transactivation of the IgH 3' enhancer couples a novel Elf-1-AP-1 protein complex to the developmental control of enhancer function.

The function of the temporally regulated B lymphocyte-specific immunoglobulin heavy chain (IgH) 3' enhancer has been linked to the IgH class switch machinery, but the physiological mechanism(s) of activation has not been discerned. Following crosslinking of the IgM receptor, we demonstrate that the enhancer is transactivated in the B lymphoma cell line BAL-17. In both induced primary B lymphocytes and BAL-17 cells, the enhancer activation is concomitant with the recruitment of a novel DNA binding complex, nuclear factor of activated B cells (NFAB). NFAB contains the tissue-restricted Ets protein Elf-1 and the AP-1 factors Jun-B and c-Fos, which bind to a novel 3' enhancer ETS-AP-1 motif. IgM receptor-mediated activation or stimulation by phorbol-ester in BAL-17 cells demonstrates that the ETS-AP-1 motif, when linked to a heterologous gene, can confer a ligand/receptor-dependent response. In NIH 3T3 cells, Elf-1 expression is required for efficient ETS-AP-1 promoter activity in response to stimulation by 12-O-tetradecanylphorbol 13-acetate. Our results suggest a biological role for Elf-1 in the regulation of IgH gene expression, attribute a functional role for receptor-induced AP-1 proteins in B lymphocytes and provide evidence for a direct link between IgM receptor-mediated signalling and 3' enhancer activation.

Animals↗

PubMed1995

Receptors that regulate T-cell susceptibility to apoptotic cell death.

The immune system provides a useful model system in which to study the signal transduction events involved in the regulation of programmed cell death. Mature lymphocytes have the capacity to survive in the body for prolonged periods of time. During an immune response, cells of the appropriate antigenic specificity must undergo clonal amplification to mount a protective response, and cells participating in inflammatory immune responses need to have the capacity to survive at sites of inflammation. However, upon completion of a successful inflammatory response, the majority of cells produced must die off in order to maintain the homeostasis of the organism. Over the last several years we have learned a great deal about how mature lymphocytes regulated their susceptibility to undergo programmed cell death. Three types of information appear to be used by the lymphocyte to control its susceptibility to undergo programmed cell death. The intrinsic susceptibility of a cell to undergo programmed cell death is determined by members of the Bcl-2 gene family. In addition, extrinsic survival factors, such as IL-2, can initiate signal transduction events that can prevent a cell from initiating apoptosis. Finally, lymphocytes appear to have specific receptors, such as Fas, that can directly induce programmed cell death upon ligand binding. The integration of these three systems is discussed.

Animals↗

PubMed1995

Bcl-XL and Bcl-2 repress a common pathway of cell death.

The effect of Bcl-xL upon the developmental death of T cells was assessed by generating transgenic mice that expressed Bcl-xL within all thymocyte subsets. Bcl-xL protected thymocytes from a variety of apoptotic stimuli, including gamma irradiation, glucocorticoids, and anti-CD3 treatment. Bcl-xL altered thymocyte maturation, resulting in increased numbers of CD3int/hi and CD4-8+ thymocytes. Overall, the phenotype of Bcl-xL transgenics was essentially indistinguishable from a Bcl-2 transgenic model. Overexpression of Bcl-xL or Bcl-2 resulted in the down-regulation of the other molecule, providing further evidence of their reciprocal regulation. In a genetic test of redundancy, the Bcl-xL transgene rescued mature T cells in Bcl-2 null mice. Immunoprecipitation indicated that Bcl-xL, like Bcl-2, heterodimerized with the death-promoting molecule Bax in thymocytes. This in vivo model argues that Bcl-xL, like Bcl-2, functions in a common pathway to repress cell death.

Animals↗

PubMed1995

Expression of bcl-xL can confer a multidrug resistance phenotype.

It has been suggested that genes that regulate apoptotic cell death may play an important role in determining the sensitivity of tumor cells to chemotherapy. We have recently cloned a member of the bcl-2 family, bcl-x. To test whether bcl-XL expression affects the sensitivity of tumor cells to chemotherapy, we have created stable cell lines overexpressing bcl-XL and have tested these cells for resistance to cell death induced by metabolic inhibitors and chemotherapeutic agents. Bcl-XL expression dramatically reduces the cytotoxicity of bleomycin, cisplatin, etoposide, vincristine, hygromycin B, and mycophenolic acid for up to 4 days in culture. Bcl-XL does not prevent cells from undergoing cell cycle arrest in response to these drugs, but rather prevents treated cells from undergoing apoptosis. Cell-cycle analysis on cells treated with the chemotherapeutic agents bleomycin, cisplatin, etoposide, and vincristine, show that the drugs cause growth arrest in different positions within the cell cycle. Bcl-XL expressing cells treated with chemotherapeutic drugs retain their proliferative ability after the drugs are removed. Interestingly, vincristine-treated cells expressing bcl-XL become polyploid after drug removal. These data show that bcl-XL protects cells from a wide variety of apoptotic stimuli, acts in multiple positions within the cell cycle, and confers a multidrug resistance phenotype. The ability of bcl-XL to prevent apoptotic cell death in response to chemotherapy-induced DNA damage and cell-cycle arrest may contribute to the accumulation of chromosomal aberrations within tumors. The expression of bcl-XL in tumor cells is likely to be an important indicator of chemotherapeutic efficacy.

Animals↗

PubMed1995

Multiple Bcl-2 family members demonstrate selective dimerizations with Bax.

A family of Bcl-2-related proteins regulates cell death and shares highly conserved BH1 and BH2 domains. BH1 and BH2 domains of Bcl-2 were required for it to heterodimerize with Bax and to repress apoptosis. A yeast two-hybrid assay accurately reproduced this interaction and defined a selectivity and hierarchy of further dimerizations. Bax also heterodimerizes with Bcl-xL, Mcl-1, and A1. A Gly-159-->Ala substitution in BH1 of Bcl-xL disrupted its heterodimerization with Bax and abrogated its inhibition of apoptosis in mammalian cells. This suggests that the susceptibility to apoptosis is determined by multiple competing dimerizations in which Bax may be a common partner.

Amino Acid Sequence↗