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E A Thompson

Publications and source records attributed to E A Thompson.

At least 127 records · Page 7Linked to original sources
PubMed1988

Biochemical and molecular characterization of the glucocorticoid receptor of lymphosarcoma P1798 variants.

Three phenotypically distinct isolates from lymphosarcoma P1798 have been compared with respect to properties of the glucocorticoid receptor. Wild type P1798 cells express functional receptors and glucocorticoid treatment of such cells causes cytolysis in vivo. Wild type cells do not undergo cytolysis in culture. Rather, such cells exhibit reversible inhibition of proliferation in the presence of dexamethasone. Two variant populations were selected from this background. One was selected for the ability to form tumors in mice receiving pharmacological doses of glucocorticoids. Cells from such tumors are resistant to the cytolytic effects of glucocorticoids in vivo, but are sensitive to the antiproliferative effects of the hormone in culture. Variants were also selected based upon their ability to proliferate in the presence of dexamethasone in culture. These variants were resistant to glucocorticoid-mediated cytolysis in vivo. Wild type P1798 cells express approximately 20,000 high affinity dexamethasone-binding sites per cell. Dexamethasone-mesylate labeling and immunoblotting experiments indicate that hormone binding is due to a polypeptide of Mr 90-100 K. This polypeptide is encoded in an mRNA species that resolved as a single entity of approximately 7000 nucleotides. Variants selected for resistance to cytolysis in vivo are indistinguishable in any of these respects from wild type cells. The receptors are fully functional, as evidenced by their ability to precipitate growth arrest of dexamethasone-treated cultures. Variants selected for resistance in culture harbor a receptor mutation. They express fewer than 500 dexamethasone-binding sites per cell. Such variants contain neither detectable dexamethasone-mesylate-binding protein nor any protein that is recognized by a receptor antibody.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1988

The detection of linkage disequilibrium between closely linked markers: RFLPs at the AI-CIII apolipoprotein genes.

Study of very closely linked DNA variants at various loci has frequently shown linkage disequilibrium. We studied three closely linked RFLPs at the apolipoprotein AI-CIII locus. Two variants detected by MspI and SstI were in strong linkage disequilibrium; but when conventional statistical tests were used, a third variant (PstI), located between the MspI and SstI markers, appeared to be in linkage equilibrium with these two "outside" markers. Similar discrepancies from the expected monotone relationship between physical distance and linkage disequilibrium have been reported by others. To investigate these discrepancies, the power to detect linkage disequilibrium was calculated. It could be shown that, for the gene frequencies encountered, very large sample sizes would be required to demonstrate negative (i.e., repulsion-phase) linkage disequilibrium. Such numbers are usually very difficult to attain in human studies. Failure to demonstrate linkage disequilibrium by conventional methods therefore does not imply its absence. Appropriate nomograms and tables are provided.

Apolipoprotein A-I↗
PubMed1988

Bayesian interval estimation of genetic relationships: application to paternity testing.

Using genetic marker data, we have developed a general methodology for estimating genetic relationships between a set of individuals. The purpose of this paper is to illustrate the practical utility of these methods as applied to the problem of paternity testing. Bayesian methods are used to compute the posterior probability distribution of the genetic relationship parameters. Use of an interval-estimation approach rather than a hypothesis-testing one avoids the problem of the specification of an appropriate null hypothesis in calculating the probability of paternity. Monte Carlo methods are used to evaluate the utility of two sets of genetic markers in obtaining suitably precise estimates of genetic relationship as well as the effect of the prior distribution chosen. Results indicate that with currently available markers a "true" father may be reliably distinguished from any other genetic relationship to the child and that with a reasonable number of markers one can often discriminate between an unrelated individual and one with a second-degree relationship to the child.

Bayes Theorem↗
PubMed1987

Cyclosporin A inhibits rDNA transcription in lymphosarcoma P1798 cells.

Effects of cyclosporin A (CsA) on rRNA synthesis in vivo and in vitro were studied using lymphosarcoma P1798 in culture. Pulse labeling with [3H]uridine indicated that treatment of P1798 cells with 1 microgram/ml of CsA for 24-h reduced rRNA levels by 50-60%, whereas rRNA levels of cells rescued from CsA and grown for 24 h were similar to those of controls. Transcription experiments using nuclei from control, treated, and rescued cells indicated that the reduction in rRNA synthesis in treated cells was due to reversible inhibition of transcription of rDNA. Transcription studies in vitro indicated that S100 extracts from CsA-treated cells were unable to carry out faithful transcription of cloned mouse rDNA, even though RNA polymerase I levels of control and treated cell extracts were similar. Mixing experiments indicated that the inability of the CsA-treated cell extract to transcribe cloned rDNA in vitro was not due to the presence of inhibitor(s) or nuclease(s) in such extracts. Supplementation of CsA-treated cell extract with partially or highly purified preparations of a transcription initiation factor for RNA polymerase I, obtained from control cell extracts, conferred transcriptional ability on the CsA-treated cell extract. Extracts from cells treated with cyclosporin H, an inactive analogue of CsA, faithfully transcribed rDNA, indicating the specificity of CsA action. These data indicate that CsA-treated cells lack the ability to initiate rDNA transcription in vivo and in vitro, due to specific, reversible reduction in the amount or activity of transcription factor IC. Significance of these results in understanding the mechanisms of the lymphostatic activity of CsA is discussed.

Animals↗
PubMed1987

The effects of human thrombomodulin on the inactivation of thrombin by its serum inhibitors.

Thrombomodulin is an endothelial cell protein which accelerates thrombin-dependent protein C activation by over 1000 fold. In this study, the effect of thrombomodulin on the inactivation of thrombin by its serum inhibitors was evaluated. 125I-thrombin was incubated at 37 degrees C with serum and the resulting complexes separated by SDS-PAGE. Antithrombin III was the major complex formed with some 125I-thrombin bound to heparin cofactor II and higher molecular weight fractions. Inclusion of thrombomodulin at increasing concentrations inhibited 125I-thrombin binding to antithrombin III and the higher molecular weight fractions but had little effect on thrombin-heparin cofactor II complex formation. Similar results were obtained using a purified antithrombin III/heparin cofactor II system. Kinetic studies, using purified antithrombin III, revealed that thrombomodulin acts as a weak competitive inhibitor towards antithrombin III (Ki = 39 nM). We postulate that in the microcirculation, where the ratio of thrombomodulin to antithrombin III is relatively high, thrombin bound to thrombomodulin may be protected from inactivation by antithrombin III and can thus promote efficient activation of protein C.

Antithrombin III↗
PubMed1987

Crossover counts and likelihood in multipoint linkage analysis.

For large numbers of genetic loci, jointly tested to determine their order along a chromosome, likelihood methods become unfeasible owing to the very large numbers of discrete alternative hypotheses (locus orderings) whose likelihoods must be separately evaluated. A method to order loci according to the criterion of minimizing the obligatory crossover count is therefore proposed. A branch-and-bound algorithm implementing this proposal has been programmed; the properties of this algorithm are investigated. The statistical properties of the proposed method are also considered. It is shown to be consistent under wide conditions, including arbitrary locus spacings, variable amounts of information per locus, and some patterns of interference. The relationship between the minimum crossover order and the maximum likelihood order is discussed. For fully informative gametes, and tight linkage, there is a virtual equivalence of the two criteria. For looser linkage, there remains a close relationship.

Algorithms↗
PubMed1987

Glucocorticoids selectively inhibit translation of ribosomal protein mRNAs in P1798 lymphosarcoma cells.

When P1798 murine lymphosarcoma cells are exposed to 10(-7) M dexamethasone, there is a dramatic inhibition of rRNA synthesis, which is completely reversible when the hormone is withdrawn. In the present experiments we examined whether dexamethasone treatment causes any alteration in the accumulation or utilization of mRNAs that encode ribosomal proteins (rp mRNAs). No effect on the accumulation of six different rp mRNAs was detected. However, the translation of five of six rp mRNAs was selectively inhibited in the presence of the hormone, as judged by a substantial decrease in ribosomal loading. Normal translation of rp mRNA was resumed within a few hours after hormone withdrawal. In untreated or fully recovered cells, the distribution of rp mRNAs between polyribosomes and free ribonucleoprotein is distinctly bimodal, suggesting that rp mRNAs are subject to a particular form of translational control in which they are either translationally inactive or fully loaded with ribosomes. A possible relationship between this mode of translational control and the selective suppression of rp mRNA translation by glucocorticoids is discussed.

Animals↗
PubMed1987

Glucocorticoid regulation of transcription of the c-myc cellular protooncogene in P1798 cells.

Glucocorticoids regulate proliferation of lymphosarcoma P1798 in culture. Treatment with dexamethasone caused a redistribution of cells with respect to the cell cycle. A decrease in cells in S and G2 + M phases was observed. This was accompanied by a corresponding increase in G1 cells. Growth arrest was preceded by a rapid and precipitous decrease in the expression of the cellular c-myc gene. Restriction analysis of the c-myc gene indicated that this locus was neither amplified nor grossly rearranged in P1798 cells. Glucocorticoids caused a decrease in the abundance of c-myc mRNA. After 24 h in 0.1 microM dexamethasone, c-myc mRNA levels declined to less than 5% of control. Fifty percent inhibition occurred within 90 min. The effects of dexamethasone were completely reversible. The amount of c-myc mRNA returned to control levels within 4 h after withdrawal of the hormone. Nuclear run-on transcription analysis indicated that glucocorticoids regulate transcription of the c-myc gene in P1798 cells. Transcription of exons I and II was inhibited to the same extent, suggesting that glucocorticoids inhibit initiation of transcription. Inhibition of transcription may account for decreased expression of c-myc which may, in turn, account for the antiproliferative effects of the hormone.

Animals↗
PubMed1987

Intractable complex partial seizures: the "initial motionless stare" and surgical outcome following temporal lobectomy.

Complex partial seizures (CPSs) beginning with an initial motionless stare (IMS) have been reported to respond well to temporal lobectomy. CPSs without the IMS or with early lateralizing motor phenomena often persisted after temporal lobectomy. We have studied video-EEG-recorded seizures of 18 patients with depth electrodes who then underwent temporal lobectomy. The IMS did not correlate with success or failure of surgery. However, initial head and/or eye deviation was correlated with poor surgical outcome.

Adolescent↗
PubMed1987

The role of heparin cofactor II in the modulation of hemostasis.

Human plasma contains two distinct heparin dependent thrombin inhibitors; antithrombin III (ATIII) and Heparin cofactor II (HCII). The latter is also known as antithrombin BM, because of its moderate binding affinity to heparin. The protein is distinct from ATIII by immunological and functional criteria as well as by its amino acid sequence. HCII selectively inhibits thrombin by forming a 1:1 molar complex with the protease and has no activity towards other coagulation serine proteases. Dermatan sulphate, a glycosaminoglycan, specifically activates HCII and increases its thrombin neutralizing activity by over a thousand fold. Dermatan sulphate does not catalyze the activity of ATIII. Human fibroblasts have been shown to accelerate the neutralization of thrombin by HCII. These cells can synthesize proteoglycans containing dermatan sulphate. Current evidence would thus suggest that extravascular tissues are the major sites of action of HCII. The specificity of dermatan sulphate for HCII has allowed the development of functional assays for this protein. Reduced levels have been observed in patients with significant hepatocellular dysfunction and in association with disseminated intravascular coagulation. Two families have been reported with hereditary HCII deficiency and recurrent thrombosis (both venous and arterial). Although these observations suggest a role for HCII in the modulation of hemostatic system, further studies are required to define the importance of HCII deficiency as a marker of thrombosis.

Antithrombin III↗
PubMed1987

Parental and sib likelihoods in genealogy reconstruction.

Estimation of genealogical relationships from genetic data provides an approach to answering many questions of population biology. In this estimation problem, previous work has shown that bilateral relatives such as full sibs may be more likely parents than the true parent individuals. This paper investigates the source of this paradox, and the circumstances under which it may arise. Alternative approaches to inferring parentage are proposed; these involve analysis of the distributions of log-likelihood statistics and of the bivariate distribution of sib and parent log-likelihoods. A Bayesian approach may also be superposed on the likelihood analysis, enabling any prior knowledge of the population to be incorporated.

Alleles↗
PubMed1986

Hormonal regulation of transcription of rDNA. Initiation of transcription by RNA polymerase I in vitro.

Transcription of mouse rDNA in vitro proceeds by an ordered mechanism of at least three steps. The first reaction involves formation of stable preinitiation complexes (Wandelt, C., and Grummt, I., (1983) Nucleic Acids Res. 11, 3795-3809; Cizewski, V., and Sollner-Webb, B. (1983) Nucleic Acids Res. 11, 7043-7056). Such complexes form at reduced temperature and in the absence of nucleoside triphosphates. The data presented here identify a second intermediate in the process of initiatio. This intermediate, called the convertible complex, forms slowly or not at all at 10 degrees C. Formation of the convertible complex requires the presence of ATP plus CTP or the dinucleotide ApC. ATP may be replaced with 5'-adenylyl imidotriphosphate. It is concluded that formation of the convertible complex is associated with formation of the first phosphodiester bond of nascent pre-rRNA. In the presence of all four nucleoside triphosphates, the convertible complex undergoes conversion to an elongation complex. This represents the third discernible step in the transcription process. The elongation complex is distinguished from the convertible complex by virtue of the observation that formation of the latter is inhibited by heparin, Sarkosyl, and 150 mM KCl. The elongation complex is not significantly affected by any of these substances. Moreover, formation of the convertible complex requires the glucocorticoid-regulated initiation factor designated TFIC.

Adenosine Triphosphate↗
PubMed1986

Maximum likelihood alignment of DNA sequences.

The optimal alignment problem for pairs of molecular sequences under a probabilistic model of evolutionary change is equivalent to the problem of estimating the maximum likelihood time required to transform one sequence to the other. When this time has been estimated, various alignments of high posterior probability may be written down. A simple model with two parameters is presented and a method is described by which the likelihood may be computed. Maximum likelihood estimates for some pairs of tRNA genes illustrate the method and allow us to obtain the best alignments under the model.

Animals↗
PubMed1986

Neutralization of heparin-related saccharides by histidine-rich glycoprotein and platelet factor 4.

Heparin and heparin oligosaccharides prepared by nitrous acid depolymerization were fractionated by affinity chromatography on immobilized antithrombin and by gel chromatography. The anticoagulant activities of high affinity heparin of Mr greater than or equal to 7,800 could be readily neutralized by the plasma protein histidine-rich glycoprotein (see also Lijnen, H.R., Hoylaerts, M., and Collen, D. (1983) J. Biol. Chem. 258, 3803-3808), whereas oligosaccharides falling below 18 saccharide units (Mr 5,400) became increasingly resistant to neutralization. An octasaccharide with characteristic marked ability to accelerate the inactivation of Factor Xa by antithrombin retained greater than 50% of its activity even at a histidine-rich glycoprotein/oligosaccharide molar ratio of 500:1. Histidine-rich glycoprotein, like the platelet-derived heparin neutralizing protein platelet factor 4 (Lane, D.A., Denton, J., Flynn, A.M., Thunberg, L. and Lindahl, U. (1984) Biochem J. 218, 725-732), therefore requires interaction with saccharide sequences in addition to the antithrombin-binding pentasaccharide of heparin in order to efficiently express its antiheparin activity. Heparan sulfate isolated from pig intestinal mucosa (HS I, Mr approximately 20,000) and from human aorta (HS II, Mr approximately 40,000) exhibited anti-Factor Xa activities of 180 and 20 units/micromol [corrected], respectively. A fraction corresponding to about 5% of HS I bound with high affinity to immobilized antithrombin and contained all of the anticoagulant activity of the starting material. While these heparan sulfates were readily neutralized by platelet factor 4, they were relatively resistant to neutralization by histidine-rich glycoprotein, although complete neutralization could be attained in the presence of molar excess of this protein. These findings may be of importance in relation (a) to the functional role of endogenous anticoagulant polysaccharides at the vascular wall and (b) to clinical situations in which heparin or heparin-related compounds are administered as exogenous anticoagulants.

Heparin↗
PubMed1986

The effects of cycloheximide upon transcription of rRNA, 5 S RNA, and tRNA genes.

The effects of inhibitors of protein synthesis upon transcription have been re-examined. Cycloheximide (1 microgram/ml) inhibits incorporation of uridine into RNA of P1798.S20 lymphosarcoma cells. Filter hybridization studies indicate that labeling of pre-rRNA is inhibited 60-80% after 1 h and quantitative S1 nuclease mapping reveals a corresponding decrease in the amount of cellular pre-rRNA. Cycloheximide also inhibits labeling of 5 S RNA and tRNA, but incorporation of uridine into poly(A+) RNA is unaffected. Transcription experiments carried out in nuclei from cycloheximide-treated cells indicate that the inhibitor causes a selective decrease in the activity of RNA polymerases I and III. Cell-free extracts from P1798.S20 were used to transcribe the cloned mouse rRNA gene, Syrian hamster 5 S RNA gene, and the Drosophila tRNAArg gene. Extracts from cycloheximide-treated cells were inhibited in this respect. Transcription of rRNA and 5 S RNA genes was inhibited by 90% after 2 h and 50% inhibition occurred within 20-30 min. Transcription of the tRNA gene was inhibited 75% after 2 h with a half-time of approximately 1 h. Inhibition was due neither to a direct effect of cycloheximide nor to the presence of nucleases or diffusible inhibitors of transcription. Moreover, transcription of rDNA in extracts from cycloheximide-treated cells could be restored by the addition of a partially purified initiation factor preparation. The data indicate that inhibition of protein synthesis results in rapid depletion of transcription factors that are required for initiation by RNA polymerases I and III. Among these is the glucocorticoid-regulated rDNA initiation factor designated TFIC.

Animals↗
PubMed1986

Inhibition by human thrombomodulin of factor Xa-mediated cleavage of prothrombin.

Human thrombomodulin significantly inhibited the rate of prothrombin conversion to thrombin by Factor Xa in the presence of phospholipid or platelets, calcium, and Factor Va. Sodium dodecyl sulfate polyacrylamide gel electrophoresis of 125I-prothrombin activation revealed that thrombomodulin reduced the rate of prothrombin activation but did not alter the cleavage pattern. The inhibition was reversed by the inclusion of a highly specific rabbit antithrombomodulin antibody. If thrombomodulin was replaced by hirudin, the rate of thrombin generation was not decreased excluding the possibility that the inhibition by thrombomodulin was secondary to the binding of small amounts of thrombin formed early in the reaction and the prevention of feedback breakdown of prothrombin by thrombin. The inhibitory activity of thrombomodulin was overcome by increasing the concentration of Factor Xa and specific, saturable binding of thrombomodulin to Factor Xa was demonstrated. These results indicate that thrombomodulin binds to Factor Xa and thereby inhibits the activity of the prothrombinase complex.

Animals↗