Biomedical subjects

E A Thompson

Publications and source records attributed to E A Thompson.

At least 91 records · Page 5Linked to original sources

PubMed1992

Effect of dexamethasone on nucleolar casein kinase II activity and phosphorylation of nucleolin in lymphosarcoma P1798 cells.

Ribosomal RNA (rRNA) synthesis in murine P1798 lymphosarcoma cells is reversibly inhibited by glucocorticoids. The effects of dexamethasone upon nucleolin phosphorylation and upon the amount and activity of casein kinase II have been examined. P1798 cells were exposed to 0.1 microM dexamethasone for 36 h. Cells were labeled in vivo with [32P]orthophosphate followed by immunoprecipitation with anti-nucleolin antibody. Nucleolin phosphorylation was reduced by 60% in dexamethasone-treated cells. Nucleoli were isolated and labeled with [gamma-32P]ATP in vitro. Nucleolin protein was reduced to 40% of control in nuclei from dexamethasone-treated cells. Nucleolin phosphorylation was reduced to 20% of control. Nucleolar casein kinase II activity and protein were also reduced (30-55% and 35-50% of control, respectively) by treatment with dexamethasone. Cycloheximide (10 micrograms/ml for 3 h) reduced the amount and activity of casein kinase II, but did not cause a decrease in nucleolin protein. These observations are discussed relative to the hypothesis that glucocorticoids regulate the amount or activity of proteins of short biological half-life that are involved in the regulation of rRNA synthesis.

Animals↗

PubMed1992

Copurification of RNA polymerase I and the glucocorticoid-regulated transcription factor IC.

A simple and rapid method to copurify RNA polymerase I and the glucocorticoid-regulated transcription factor, TFIC, is described. This protocol results in 1262-fold purification and 15% total recovery of the enzyme and factors needed to support faithful transcription in vitro from cloned mouse rRNA gene (rDNA). Using this method, proteins involved in rDNA transcription were purified from exponentially growing lymphosarcoma P1798 cells as well as cells treated with 0.1 microM dexamethasone. A combination of transcription and reconstitution assays using G-free cassette-containing constructs and polyacrylamide gel electrophoretic analysis upon silver staining were used to detect TFIC activity as well as the characteristic TFIC polypeptides in control and dexamethasone-treated cell extracts. Treatment of P1798 cells with 0.1 microM dexamethasone for 24 h results in an over 95% reduction of TFIC activity, but no significant differences in the amount of TFIC polypeptides in the final product purified from control and glucocorticoid-treated cells could be detected. Our data indicate that glucocorticoid regulation of transcription of rDNA is mediated via post-translational modulation of the activity of TFIC.

Animals↗

PubMed1992

Estimating polygenic models for multivariate data on large pedigrees.

We have developed algorithms for the likelihood estimation of additive genetic models for quantitative traits on large pedigrees. The approach uses the expectation L-maximization (EM) algorithm, but avoids intensive computation. In this paper, we focus on extensions of previous work to the case of multivariate data. We exemplify the approach by analyses of bivariate data on a four-generation, 949-member pedigree of the snail Lymnaea elodes, and on a three-generation pedigree of the guppy Poecilia reticulata containing about 400 individuals.

Algorithms↗

PubMed1992

Glucocorticoid regulation of c-myc promoter utilization in P1798 T-lymphoma cells.

Glucocorticoids rapidly inhibit the expression of c-myc mRNA in P1798 lymphoma cells. Statistically significant decreases can be observed within 5-10 min after the addition of glucocorticoids. Although transcription of c-myc decreases within a few hours after dexamethasone is added to P1798 cell cultures, nuclear run-on transcription cannot be used to demonstrate that the very early changes in mRNA abundance reflect corresponding changes in transcriptional activity. An RNase protection assay has been used to measure the abundance and rates of turnover of the two major c-myc transcripts arising from the P1 and P2 initiation sites. The relative rates of synthesis of the c-myc mRNAs (i.e. transcription) can be calculated from such data. The abundance of the P2 transcript exceeds that of P1 mRNA by 3- to 4-fold in midlog phase cells. The turnover rates of the two c-myc mRNAs are essentially identical (0.02 min-1), indicating that the P2 promoter is 3-4 times stronger than P1. This was confirmed by measuring the relative transcriptional activities of templates containing the individual c-myc promoters in P1798 extracts in vitro. The expression of P1 and P2 mRNAs decreases at different rates in glucocorticoid-treated cells. A 50% decrease in the abundance of P1 mRNA occurs within 1 h after the addition of dexamethasone. Expression of P2 mRNA is reduced by 50% within 4 h. However, the turnover rates of the major c-myc transcripts do not change in glucocorticoid-treated cells. The t1/2 values of P1 and P2 mRNAs are about 25-30 min and not different from the turnover rates measured in control cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1992

A Monte Carlo method for combined segregation and linkage analysis.

We introduce a Monte Carlo approach to combined segregation and linkage analysis of a quantitative trait observed in an extended pedigree. In conjunction with the Monte Carlo method of likelihood-ratio evaluation proposed by Thompson and Guo, the method provides for estimation and hypothesis testing. The greatest attraction of this approach is its ability to handle complex genetic models and large pedigrees. Two examples illustrate the practicality of the method. One is of simulated data on a large pedigree; the other is a reanalysis of published data previously analyzed by other methods.

Algorithms↗

PubMed1992

Microevolution of the Chibcha-speaking peoples of lower Central America: rare genes in an Amerindian complex.

Models are developed for the survival, history, and spread of variant alleles, in order to consider what can, and what cannot, be inferred from this type of data. The high variances of the processes involved, and questions of sampling, place severe limitations on inferences. Nonetheless, by combining information on a number of rare variants observed in a group of interrelated populations, reliable qualitative inferences are possible. These ideas and models are developed in the context of data on five rare variants and six private polymorphisms observed in eight Chibcha-speaking tribes of Costa Rica and Panama. The decline and fragmentation of the Amerindian populations of Central America over the last 300 years create considerable difficulties in attempting inference of past genetic events. However, these tribes have been well studied genetically, anthropologically, and linguistically and thus provide an excellent framework for the study of rare-variant spread.

Biological Evolution↗

PubMed1992

Performing the exact test of Hardy-Weinberg proportion for multiple alleles.

The Hardy-Weinberg law plays an important role in the field of population genetics and often serves as a basis for genetic inference. Because of its importance, much attention has been devoted to tests of Hardy-Weinberg proportions (HWP) over the decades. It has long been recognized that large-sample goodness-of-fit tests can sometimes lead to spurious results when the sample size and/or some genotypic frequencies are small. Although a complete enumeration algorithm for the exact test has been proposed, it is not of practical use for loci with more than a few alleles due to the amount of computation required. We propose two algorithms to estimate the significance level for a test of HWP. The algorithms are easily applicable to loci with multiple alleles. Both are remarkably simple and computationally fast. Relative efficiency and merits of the two algorithms are compared. Guidelines regarding their usage are given. Numerical examples are given to illustrate the practicality of the algorithms.

Alleles↗

PubMed1991

Effect of retinoic acid on the synthesis of tissue-type plasminogen activator and plasminogen activator inhibitor-1 in human endothelial cells.

The synthesis of plasminogen activators and inhibitors in endothelial cells is highly regulated by hormones, drugs and growth factors. The present study evaluates the effect of retinoic acid on the synthesis of tissue-type plasminogen activator (t-PA) and of plasminogen activator inhibitor-1 (PAI-1) by cultured human umbilical vein endothelial cells (HUVEC). Retinoic acid produced a time- and concentration-dependent increase in the secretion of t-PA-related antigen but not of PAI-1 related antigen into the culture medium. A maximal sevenfold increase of t-PA antigen after 24 h was observed with 10 microM and a half-maximal increase with 0.1 microM retinoic acid. Retinoic acid induced a time-dependent increase of the t-PA mRNA, with a maximum at 8 h and returning to normal at 24 h. The protein kinase inhibitor H7 decreased the t-PA antigen induced by both retinoic acid and phorbol 12-myristate 13-acetate. These results suggest that treatment of HUVEC with retinoic acid increases t-PA production by a pathway which, at some level, involves protein kinases. Thus, retinoic acid induces t-PA synthesis in the absence of altered PAI-1 synthesis, which may enhance the fibrinolytic potential of the endothelium.

1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine↗

PubMed1991

Insensitivity to the cytolytic effects of glucocorticoids in vivo is associated with a novel "slow death" phenotype.

Tumors formed from wild type P1798 mouse lymphoma cells undergo regression when treated with pharmacological doses of natural and synthetic glucocorticoids in vivo. Variants have been selected that are insensitive to the cytolytic effects of glucocorticoids in vivo. Although the response of wild type and insensitive tumors is markedly different in vivo, the manner in which cells from such tumors respond to glucocorticoids is indistinguishable in culture under routine conditions. Glucocorticoids inhibit proliferation of wild type cells as well as those that are insensitive to glucocorticoids in vivo. Although neither cell line dies when exposed to dexamethasone in culture in the presence of fetal bovine serum, both sensitive and insensitive cell lines undergo cytolysis when exposed to dexamethasone in serum-free medium. Sensitive cells die more quickly, with 50% cell death observed within 6 h. Insensitive cells exhibit less than 10% cell death within 6 h. Sensitive cells continue to die after transitory exposure to dexamethasone, whereas insensitive cells do not. Thus, growth in serum-free medium mimics the response that prevails in vivo. Cell death is associated with rapid, internucleosomal chromatin degradation. The rate of DNA fragmentation is comparable to that of cell death. About 30% of the DNA in sensitive cells is degraded to fragments of less than 10 kilobases within 2 h after addition of dexamethasone, and 70-80% of the DNA is degraded within 6 h. There is no significant degradation observed when insensitive cells are treated for 6 h. P1798 cell lines express an endonuclease that is capable of degrading chromatin in vitro. Basal expression of this activity does not correlate with glucocorticoid sensitivity, and insensitivity does not appear to be attributable to a decrease in expression of the enzyme(s) thought to be responsible for glucocorticoid-mediated chromatin degradation. The data suggest that glucocorticoid insensitivity is associated with delayed activation and/or induction of some lytic principle. Alternatively, resistance may be due to enhanced ability to repair the damage induced by transitory exposure to glucocorticoids in vivo.

Animals↗

PubMed1991

Glucocorticoid insensitivity of P1798 lymphoma cells is associated with production of a factor that attenuates the lytic response.

P1798 murine lymphoma cells die when exposed to glucocorticoids in vivo. Such cells are sensitive to glucocorticoids in culture in serum-free medium, and 80-90% of wild type cells will die within 24 h after addition of 0.1 microM dexamethasone. However, addition of fetal bovine serum prevents cell death in culture. Variants that were selected for resistance to the cytolytic effects of glucocorticoids in vivo are relatively insensitive to dexamethasone in culture. Insensitive variants die more slowly than wild type cells, with 10-20% cell death observed within 24 h after addition of dexamethasone. Conditioned medium from insensitive cultures protects wild type P1798 cells from dexamethasone in serum-free medium. Such medium contains one or more factors that attenuate the lytic response. This lysis resistance factor(s) has the properties of a protein and may be a growth factor. Expression of the lysis resistance factor(s) appears to be regulated by glucocorticoids. These studies define an heretofore uncharacterized mechanism whereby the ability of malignant lymphoid cells to elaborate and/or respond to an autocrine factor(s) influences the extent to which such cells die when exposed to glucocorticoids in culture and probably in vivo.

Cell Death↗

PubMed1991

Confirmation of oxytetracycline, tetracycline and chlortetracycline residues in milk by particle beam liquid chromatography/mass spectrometry.

A method using particle beam liquid chromatography/mass spectrometry was developed for the confirmation of oxytetracycline, tetracycline and chlortetracycline residues in bovine milk. This method is one of the first to apply particle beam technology to the confirmation of animal drug residues in food products for regulatory purposes. The milk is centrifuged, using molecular weight cut-off filters to remove components of 25,000 daltons and above from the milk. The filtrate is passed through a C-18 sample preparation cartridge which retains the tetracyclines. After the columns are washed with water, the tetracyclines are eluted with 0.1 M oxalic acid in methanol and concentrated. The compounds are separated on a Novapak C-18 column with a methanol-oxalic acid-acetonitrile mobile phase. Negative chemical ionization with selective ion monitoring is used to identify the tetracyclines. The procedure was used to confirm the presence of each tetracycline at 100 ng ml-1 in fortified and incurred milk samples.

Animals↗

PubMed1991

Evaluation of likelihood ratios for complex genetic models.

Although methods for computing likelihoods for simple genetic models on large and complex pedigrees have been known for some time, and although methods for evaluating likelihoods for complex genetic models on small pedigrees have likewise been well known, likelihood evaluation for complex models given data on extended pedigrees has remained an intractable problem. The Gibbs sampler provides a method of Monte Carlo evaluation of likelihood ratios for complex models on extended and/or complex pedigrees. With increasing computer speeds, this approach provides a tractable and efficient approach to many such likelihood evaluation problems in linkage and segregation analysis. In this paper, however, the authors restrict attention to two basic building-blocks of the overall process. The first is the sequential computation of Gaussian likelihoods for multiple random-effects models on extended pedigrees. The second is the use of this in the Monte Carlo evaluation of likelihoods for the classical mixed model of segregation analysis. The implementation of the Gibbs sampler on pedigrees that permits this Monte Carlo evaluation is detailed. An example is then presented, and finally, in the context of this same example, it is also shown how linkage analysis for a quantitative trait falls within this same framework.

Female↗

PubMed1991

Monte Carlo estimation of variance component models for large complex pedigrees.

Variance component models are widely used in animal and plant breeding. In human genetics, they can be used to identify, among other traits associated with the definition of disease, those that have a significant genetic component in their aetiology. In addition, they can be used in genetic counselling. Most of the methods currently proposed for estimating variance component models often involve repeated inversion of large matrices, resulting in intensive computations, large storage requirements, and numerical instability. Consequently, these methods are restricted to data on nuclear families, to small pedigrees, or to designed pedigrees of simple form. In this paper, the authors propose a method for estimating variance component models for large complex pedigrees using jointly the EM algorithm and the Gibbs sampler. The method can handle variance component models with multiple variance components, without the need for repeated inversion of large matrices even on large complex pedigrees. The method is conceptually simple, numerically stable, and easy to implement.

Algorithms↗

PubMed1991

Antithrombin Vicenza, Ala 384 to Pro (GCA to CCA) mutation, transforming the inhibitor into a substrate.

Antithrombin (AT) Vicenza has been previously identified as a functionally abnormal antithrombin associated with familial thrombosis (Finazzi et al, 1985). It binds normally to heparin, but loses its affinity following interaction with thrombin: it is a poor inhibitor of thrombin. AT Vicenza was isolated from plasma by heparin-Sepharose and thrombin-Sepharose chromatography, fragmented with cyanogen bromide (CNBr) and its tryptic peptides were analysed by fast atom bombardment mass spectrometry mapping. An abnormal peptide mass 1112 was identified. Edman degradation confirmed a substitution of Ala to Pro in the sequence Ala 383-Arg 393. Polymerase chain reaction amplification of exon 6 of the gene followed by genomic sequencing, localized the mutation to codon 384, GCA to CCA. The same mutation has recently been reported in AT Charleville (Mohlo-Sabatier et al, 1989). Sodium dodecyl-sulphate polyacrylamide gel electrophoresis of AT Vicenza (/Charleville) under non-reducing conditions revealed an apparent increase in mol. wt following interaction with thrombin: under reducing conditions the mol. wt was less than that of normal AT. This indicated cleavage and unfolding of the molecule. The site of cleavage was determined by incubation of AT Vicenza (/Charleville) with thrombin-Sepharose, reduction and S-carboxymethylation and reverse phase FPLC. A peptide was identified with the NH2-terminal sequence beginning Ser-Leu-Asn, demonstrating the cleavage had occurred at the reactive site of the variant. It is concluded that the Ala 384 to Pro substitution transforms AT Vicenza (/Charleville) from an inhibitor into a substrate.

Amino Acid Sequence↗

PubMed1990

Oxygen radicals generated during anoxia followed by reoxygenation reduce the synthesis of tissue-type plasminogen activator and plasminogen activator inhibitor-1 in human endothelial cell culture.

The effect of anoxia and reoxygenation on the synthesis and secretion of tissue-type plasminogen activator (t-PA) and plasminogen activator inhibitor-1 (PAI-1) was studied in primary cultures of human umbilical vein endothelial cells. Sublethal anoxia, determined by trypan blue dye exclusion and lactate dehydrogenase release, was produced by cell culture under a 95% N2, 5% CO2 atmosphere for 2-24 h and was followed by reoxygenation with 95% air, 5% CO2 for 24 or 48 h. Anoxia did not alter the levels of mRNA for t-PA or PAI-1 in the cells or the secretion of t-PA or PAI-1 into the medium. At 24 h, t-PA secreted into conditioned medium was 7.0 +/- 1.4 ng/2 x 10(6) cells (n = 9) and PAI-1 was 300 +/- 13 IU/2 x 10(6) cells (n = 9), whereas the content of t-PA mRNA was 2.2 pg/micrograms of RNA and PAI-1 mRNA was 180 pg/micrograms of RNA. During reoxygenation, however, t-PA antigen and PAI-1 activity as well as mRNA for PAI-1 decreased proportionally to the duration of anoxia, to reach 27 +/- 1.0, 49 +/- 2.0, and 47 +/- 14% of control values, respectively, within 24 h of anoxia. t-PA mRNA also decreased significantly during reoxygenation following anoxia, but the extent could not be accurately quantitated. Addition, during anoxia, of a 200 micrograms/ml concentration of the superoxide anion radical scavenger superoxide dismutase or of a 5 mM concentration of the iron chelator deferoxamine mesylate prevented the subsequent decrease of t-PA antigen during reoxygenation; addition of these compounds during reoxygenation had no effect. Superoxide dismutase, but not deferoxamine mesylate, when added during anoxia prevented the subsequent decrease in PAI-1 activity. These studies suggest that the marked alteration of endothelial cell fibrinolysis during anoxia followed by reoxygenation is most likely mediated by a mechanism dependent on oxygen radicals. Impaired endothelial cell fibrinolysis may contribute to the pathophysiology of ischemia/reperfusion injury.

Aerobiosis↗

PubMed1990

Hormonal regulation of transcription of rDNA. Purification and characterization of the hormone-regulated transcription factor IC.

Glucocorticoids reversibly inhibit transcription of ribosomal RNA genes in murine lymphosarcoma P1798 cells in culture. Inhibition of rDNA transcription is due to reduction in the amount or activity of an RNA polymerase I transcription factor called transcription factor IC (TFIC). TFIC has been purified over 100,000-fold. The highly purified preparation contains neither RNA polymerase I activity nor any of the conventional RNA polymerase I subunits. TFIC activity co-purifies with three polypeptides of approximately 55, 50, and 42 kDa molecular mass. These polypeptides are present in a stoichiometric ration of 1:1:1.

Animals↗

PubMed1990

Hormonal regulation of transcription of rDNA. Formation of initiated complexes by RNA polymerase I in vitro.

This paper describes studies of initiation of transcription by RNA polymerase I in vitro. The protocols take advantage of the observation that active transcription complexes precipitate when incubated with S100 extracts. The pellets contain less than 5% of the protein present in unfractionated extracts and are stable to centrifugal washing. This permits rapid manipulation of the reaction conditions and facilitates kinetic studies of aspects of the initiation reaction. An initiated complex has been defined which forms rapidly at 30 degrees C and is associated with formation of the first phosphodiester bond of nascent rRNA. Once formed, initiated complexes are capable of elongation in the presence of heparin or KCl in concentrations sufficient to preclude subsequent initiation. One can therefore estimate the number of initiated complexes formed in a given reaction by measuring the number of full length transcripts recovered in a KCl or heparin-start reaction. The number of such complexes formed correlates well with the formation of a presumptive initiator trinucleotide ApCpU.

Animals↗

PubMed1990

Hormonal regulation of transcription of rDNA. The role of TFIC in formation of initiation complexes.

Glucocorticoids inhibit transcription of rDNA in P1798 lymphoma cells. This observation can be recapitulated in vitro in that extracts from hormone-treated cells are virtually incapable of transcribing from the cloned mouse rRNA promoter. However, such extracts can be reconstituted by addition of a RNA polymerase I transcription factor, called TFIC. TFIC has been purified to homogeneity. Assays have been developed which facilitate analysis of various aspects of initiation of transcription by RNA polymerase I in vitro. This paper describes a series of experiments designed to test two related hypotheses. It is proposed that TFIC is a bona fide initiation factor and that the inability of hormone-treated cells to synthesize rRNA is due to failure to form initiation complexes on rDNA. The data indicate that extracts from hormone-treated cells cannot form KCl or heparin-resistant initiated complexes upon the rRNA promoter. The ability to form such complexes is dependent upon the addition of TFIC. The lack of TFIC precludes formation of the first phosphodiester bond. At low concentrations of TFIC there is a more or less direct relationship between the amount of the factor and the number of initiated complexes formed. At higher concentrations, the system saturates and addition of TFIC beyond 80 pg/microliters (approximately 0.5 nM) has no effect upon initiation. Addition of TFIC to control extracts does not influence the formation of initiated complexes. This is consistent with the conclusion that control extracts contain excess TFIC, whereas hormone-treated extracts are depleted in this respect. The kinetics of reconstitution have been examined, and the results suggest that association of highly purified TFIC with the transcriptional apparatus is a relatively slow process, with a t1/2 of about 2 min. The data are consistent with the hypothesis that TFIC is an initiation factor and suggest that the active form of RNA polymerase I is associated with TFIC. It is proposed that in the absence of this association, initiation of transcription of rDNA does not occur.

Animals↗