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Biomedical subjects

E B Thompson

Publications and source records attributed to E B Thompson.

At least 19 recordsLinked to original sources
PubMed1992

Glucocorticoid, interleukin-2, and prostaglandin interactions in a clonal human leukemic T-cell line.

We have studied the growth effects of conditioned media, interleukin-2 and PGE prostaglandin analogs on the glucocorticoid-sensitive human leukemic T-cell clone, CEM-C7. After 4 days, the glucocorticoid dexamethasone at approximately 10 nM kills 50% of CEM-C7 cells. To test the hypothesis that glucocorticoid-mediated lymphocytolysis was due to suppression of lymphokine expression only, we attempted to protect CEM-C7 cells from lysis by provision of lymphokine(s). Conditioned media from interleukin-2 secreting Jurkat T-cells as well as the glucocorticoid-insensitive, but receptor positive clone, CEM-C1, failed to prevent lymphocytolysis; exogenous interleukin-2 also did not provide protection. There were complex, biphasic interactions between dexamethasone and the synthetic PGEs, enisoprost and enisoprost free acid. Low doses of enisoprost alone (0.01 to 1 microgram/ml) stimulated growth, and in combinations completely reversed the growth inhibitory effects of 10 nM dexamethasone. Higher concentrations of enisoprost were inherently lethal and were additive to the steroid effect. Thus the glucocorticoid-induced lymphocytolysis in this human leukemic T-cell line may be modified biphasically by PGE prostaglandins, depending on their concentration. However, interleukin-2 or components in the conditioned media assayed had no effect in ameliorating the lethal response to glucocorticoid.

Alprostadil↗
PubMed1992

Glucocorticoids in malignant lymphoid cells: gene regulation and the minimum receptor fragment for lysis.

We have examined clones of human malignant lymphoid cells for markers that correlate with glucocorticoid-mediated cell lysis. In glucocorticoid-sensitive clones of CEM, a human T-cell lymphoblastic leukemia line, two genes correlate with glucocorticoid-induced cell lysis. The glucocorticoid receptor (GR) itself is induced by standard glucocorticoids in sensitive clones and not in insensitive clones. The phenylpyrazolo-glucocorticoid cortivazol (CVZ) is capable of lysing several clones resistant to high concentrations of standard potent glucocorticoids. When these clones were tested for cortivazol responses, they were not only lysed by cortivazol but also showed induction of GR mRNA. Thus receptor induction appears to correlate with the lysis function of receptor in these cells. To determine what parts of the GR are required for lysis, we have mapped this function by transfecting and expressing GR and GR fragment genes in a GR-deficient CEM clone. Our results indicate that none of the known trans-activation regions of the GR are required. Removal of the steroid binding domain gives a fragment that is fully constitutive. Only one and one-half "Zn fingers" of the DNA binding region are required. We also find in CEM cells rapid suppression of the c-myc protooncogene, preceding growth arrest and cell lysis by glucocorticoids. This occurs only in clones possessing both intact receptors and lysis function. Thus the simple presence of GR alone is not sufficient to guarantee c-myc down-regulation. Introduction into the cells of c-myc driven by a promoter that does not permit suppression by glucocorticoids confers resistance to steroids. Furthermore, suppression of c-myc by antisense oligonucleotides also kills the cells. Therefore, c-myc appears to be a pivotal gene related both to ability of steroid to kill and to cell viability.

Cell Line↗
PubMed1992

Extinction of prolactin gene expression in somatic cell hybrids is correlated with the repression of the pituitary-specific trans-activator GHF-1/Pit-1.

The tissue-specific expression of the PRL and GH genes is dependent on the presence of a pituitary-specific trans-activator, GHF-1/Pit-1. Previous studies indicate that somatic cell hybridization of rat pituitary GH3 cells with LB82 mouse fibroblasts frequently results in the extinction of GH and PRL expression. The extinction of the GH gene occurs at the transcriptional level, and is accompanied by repression of GHF-1/Pit-1 synthesis. To elucidate the mechanism of PRL extinction we further characterized these same somatic cell hybrid lines as well as the parental GH3 and LB82 cells. The pattern of PRL extinction and reexpression paralleled that of GH in the three hybrid lines that were examined. Two of these lines extinguished both GH and PRL synthesis, while a third displayed reexpression of both genes, apparently due to the loss of mouse chromosomal material. These studies revealed that the extinction of PRL expression in these hybrid lines occurs at the level of mRNA accumulation and is strongly correlated with the loss of GHF-1/Pit-1 mRNA and protein synthesis. These data suggest that in pituitary x fibroblast hybrids repression of the trans-activator GHF-1/Pit-1 is a primary mechanism for the extinction of PRL and GH gene expression.

Animals↗
PubMed1979

Two different and compatible intraneuronal labels for ultrastructural study of synaptically related cells.

To examine the structural interactions between synaptically connected neurons in Aplysia, we have developed a method for simultaneously labeling two identified cell with different and compatible intraneuronal marking agents (horseradish peroxidase and [3H]N-acetyl-D-galactosamine) visible in both the light and electron microscopes. Combining these two agents within a single cell yields a third label.

Acetylgalactosamine↗
PubMed1979

Indented synapses in Aplysia.

A new type of synaptic contact has been found in Aplysia californica, in which a post-synaptic spine extensively invaginates the pre-synaptic element. The post-synaptic spine, usually less than 0.25 micrometer in diameter, may protrude up to 2 micrometer into the pre-synaptic element. In some instances a larger post-synaptic element indents and forms multiple thin projections into the pre-synaptic varicosity. Along or at the end of these projections a zone occurs at which the surface membranes of the two apposed synaptic elements are rigidly parallel, and the extracellular gap is approximately 60% greater than normal and contains a small amount of electron-dense material. Synaptic vesicles are concentrated against the pre-synaptic membrane in these regions. There are twice as many vesicles per unit area positioned against the membrane at these zones than at similar active zones occurring in the alternative type of synapse, which has a flat, rather than indented, geometry. Single pre-synaptic varicosities have been found to form both flat and indented synapses. These findings raise the possibility that these two forms of synapse may be dynamic transformations of each other, having differing synaptic effectiveness.

Animals↗
PubMed1979

Estrogen receptor values in patients with benign breast disease.

Tissue specimens from 55 female patients with benign breast disease were assayed for estrogen receptor. Twenty-one of 55 patients (38%) had tumors which contained significant amounts of estrogen receptor (greater than 10 femtomoles/mg protein). Fibroadenomas possessed estrogen receptor more frequently than fibrocystic disease or other benign breast tumors. Estrogen receptor positivity did not correlate with laterality of the tumor; location or size of the largest nodule. Patients with estrogen receptor positive tumors had a mean age of 26.9 years compared to 36.4 years for patients with estrogen receptor negative tumors (p less than 0.01). Twenty of 46 (43%) premenopausal patients had benign tumors which were estrogen receptor positive compared to zero of 8 postmenopausal patients (p less than 0.05).

Adenofibroma↗
PubMed1979

Dexamethasone induces irreversible G1 arrest and death of a human lymphoid cell line.

Growth of a human leukemic T-cell line (CEM C7) in 10(-6) M dexamethasone results in inhibition of growth and rapid loss of cell viability after a delay of approximately 18 to 24 hours. Analysis of dexamethasone-treated cells by flow-microfluorometry showed that they were arrested in the G1 phase of the cell cycle. Loss of cell viability began at the same time as G1 accumulation was first detectable, and 20% of all cells were found to be blocked in G1 at this time suggesting that loss of viability and G1 arrest were coincident events. Half-maximal and maximal effects on both viability and G1 arrest after 48 hours in steroid were nearly identical with respect to steroid concentration and corresponded to half-maximal and full occupancy of glucocorticoid specific receptor by hormone, consistent with a glucocorticoid receptor mediated mechanism for both phenomena. Most non-viable cells were arrested in G1, and accumulation of cells in G1 was irreversible; removal of steroid in the presence of colcemid did not result in a decreased fraction of G1 cells. Furthermore, dexamethasone treatment did not protect cells against the effects of 33258 Hoechst-amplified killing of bromodeoxyuridine substituted cells exposed to light. These results show that dexamethasone arrests these leukemic cells in G1 and strongly suggest that dexamethasone-treated cells are killed upon entry into G1.

Cell Cycle↗
PubMed1979

Fluorocarbon aerosol propellants XII: Correlation of blood level of trichloromonofluoromethane to cardiovascular and respiratory responses in anesthetized dogs.

Anesthetized mongrel dogs were exposed to various concentrations of trichloromonofluoromethane. Before, during, and after the inhalation, arterial and venous blood samples were obtained for fluorocarbon analysis. After the cessation of fluorocarbon inhalation, a multiexponential decline for the blood was observed. This finding was similar to that of previous study in which the fluorocarbon was administered intravenously to unanesthetized dogs. The half-life calculated from the terminal phase was about 280 min, and the pseudodistribution equilibrium was reached about 100 min after dosing. Study of the relationship between blood fluorocarbon levels and effects on the respiration rate and arterial blood pressure indicates that the sites of these pharmacological activities are located in the blood or central compartment rather than in the peripheral compartment. The effect on the heart rate appears to be quite instantaneous after inhalation. These results might shed some light on the fast effect of the fluorocarbon propellants, which caused sudden deaths after inhalation of a large quantity.

Aerosol Propellants↗
PubMed1979

Glucocorticoid induction of tyrosine aminotransferase in cultured cells.

For over a decade, tyrosine aminotransferase induction in tissue culture cells has been a useful model system in which to study glucocorticosteroid action. In the 1960s, the establishment in culture of rat hepatomas expressing the inducible enzyme, already known to be induced in liver in vivo, provoked a wide-ranging series of experiments. The data from these experiments have provided considerable information regarding the mechanism of action of steroids. These include the fundamental facts that the steroids act directly on the induced cell in unmetablized form, that removal of steroid results in deinduction, that induction does not require DNA synthesis or massive changes in RNA synthesis, and that cytoplasmic receptor occupancy by active steroids correlates closely with the steroids' ability to affect inductions. Studies in tissue culture cells have led to the analysis of transcriptional and posttranscriptional models attempting to explain enzyme induction. The effects on enzyme induction of nonsteroid hormones and other factors have been studied through the use of tissue culture cells. Finally, cells and clones of cell variants are being used to study enzyme induction, through biochemical analysis and cell genetic approaches, including somatic cell hybridization.

Animals↗
PubMed1979

Somatic cell fusion in the study of glucocorticoid action.

The basic phenomena of cell fusion and hybrid cell formation are briefly described and the potential of somatic cell hybridization in studies on the expression of differentiated cellular functions is discussed. The technique of cell hybridization has been applied to two types of cellular responses to glucocorticoids. The induction of specific proteins has been investigated in hybrids of inducible cells with uninducible cells. Most studies dealt with the liver-specific enzyme tyrosine aminotransferase, whose inducibility was extinguished in the majority of the hybrids between hepatoma and nonliver cells. However, upon chromosome segregation, inducibility reappeared in some of these hybrid cells. The current ideas about cellular control of inducibility are discussed. The other major glucocorticoid-responsive system investigated in cell hybridization studies consists of lymphoid cells which are killed when exposed to the steroid. Such sensitive cells were hybridized with several types of glucocorticoid-resistant lymphoid lines, and sensitivity was found to be dominant over resistence. Hybrids between sensitive and resistant lymphoid cells, however, showed an increase in the frequency at which resistance occurred as compared to the rate observed with the wild-type parental cells. No complementation to steroid sensitivity was found in hybrids between different types of resistant cells with defects in the glucocorticoid-specific receptor system.

Animals↗
PubMed1979

Glucocorticoids and lysosomes.

Steroids in general and glucocorticoids in particular affect lysosomes in various ways. The explanation of these effects remains in dispute, however. Theories include the view that steroids interact directly with lysosomal membranes, that steroids provoke induced changes in lysosomes, and that classical steroid receptors originate in lysosomes. Experiments pertaining to these views are discussed, particularly with respect to steroid specificity and tissue specificity of effects and to dose-response considerations.

Animals↗
PubMed1979

Ultrastructure of the synapses of sensory neurons that mediate the gill-withdrawal reflex in Aplysia.

We have identified the processes of mechanoreceptor sensory neurons by intracellular injection of horseradish peroxidase in order to study the structure of synapses which exhibit profound, behaviourally-relevant plasticity. These synapses are located at small, varicose expansions along or at the end of the fine, microtubule-containing neurites, and they are crowded with vesicles some of which are associated with the varicosity membrane at regions of membrane specialization morphologically equivalent to active zones described in other species. These active zones occur between pre- and postsynaptic processes at two varieties of apposition: a conventional flat one, and a more elaborate indented one. At indented appositions, the presynaptic varicosity is invaginated by a thin (less than 0.25 micrometer diameter) spine of variable length. The active zones of indented synapses have approximately twice the vesicle frequency of flat synapses, suggesting that indented synapses are more effective. Sensory neuron terminals are relatively uniform in their structure, having similar concentrations of vesicles and numbers of active zones, and the majority of the processes postsynaptic to them are less than 0.5 micrometer in diameter. These regularities, and the presence of two strikingly-different types of synaptic apposition, flat and indented, should facilitate structural comparisons of neurons from naive and behaviourally-modified animals. The possible dynamic interconversion of indented and flat appositions at the synaptic terminals of sensory neurons and its behavioural relevance are discussed.

Animals↗
PubMed1979

Unlinked control of multiple glucocorticoid-induced processes in HTC cells.

HTC cell variants chosen for their lack of tyrosine aminotransferase (EC 2.6.1.5) (TAT) induction by glucocorticoids were tested for interrelated effects on other glucocorticoid responses: TAT induction by dibutyryl cyclic AMP (dBcAMP) +/- dexamethasone, glutamine synthetase (GS) induction, cyclic nucleotide phosphodieterase (PDE) suppression, inhibition of alpha-aminoisobutyric acid (AIB) uptake, inhibition of plasminogen activator (PA), and induction of mouse mammary tumor virus (MTV). Loss of TAT induction by steroid was accompanied by loss of TAT induction by dBcAMP and of PDE suppression by steroid. In addition, subclones of MTV-infected cells were examined for the effect of the virus on glutamine synthetase (GS) and TAT induction. The virus had no effect on their induction in wild-type cells and no effect on GS induction in the variants. One MTV-infected subclone from a TAT variant, however, showed significant return of TAT induction.

3',5'-Cyclic-AMP Phosphodiesterases↗