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C J Myers

Publications and source records attributed to C J Myers.

10 recordsLinked to original sources
PubMed2000

Efficient induction of cell death by adenoviruses requires binding of E1B55k and p53.

The use of an Elb55k-deficient adenovirus, ONYX-015, to selectively target tumor cells containing a mutated p53 gene has produced promising results. However, recent reports have questioned the selectivity of this virus, showing that ONYX-015 can replicate in cells containing a wild-type p53 and that p53 may actually be required for cell death. To address these apparent contradictions in the literature, we infected a number of mutant and wild-type p53-containing cell lines with ONYX-015 and wild-type adenovirus and observed their death profiles up to 10 days postinfection. We demonstrate that two distinct cell death phenotypes exist, one of which is rapid and dependent on the presence of p53 and one of which is p53 independent. Using adenoviruses expressing E1b55k proteins deficient in their ability to bind p53, we show that formation of a complex between p53 and the adenoviral Elb55k protein is necessary for the activation of the rapid cell death pathway. In the absence of p53 or the absence of complex formation between p53 and Elb55k, cell death is delayed considerably. These data suggest three things: that the selectivity of killing appears to be dependent on the presence of the E1b55k/p53 complex; that viruses lacking Elb55k (such as ONYX-015) kill cells in a delayed manner independent of p53; and that binding of E1b55k to p53 does not merely serve to inactivate p53, but rather is required for the induction of rapid cell death. The components of this complex that lead to rapid cell death remain to be determined.

Adenoviridae↗
PubMed1997

p53/E1b58kDa complex regulates adenovirus replication.

We have explored a role for the adenovirus (Ad5) E1b58kDa/p53 protein complex in adenovirus replication. This was done by using virus mutants containing different defects in the E1b58kDa gene and cell lines that express either a wild-type p53 protein or a mutant p53 protein. We find that infection of wild-type p53-containing cells with wild-type Ad5 causes a shutoff of p53 and alpha-actin protein synthesis by distinct mechanisms, but neither occurs in mutant p53 cells. Our data also indicate that the shutoff is dependent on formation of the p53/E1b complex and may also involve another virus protein, E4ORF6. Following from these observations we asked whether failure to form the complex resulted in impaired adenovirus replication. Our experiments showed that neither wild-type Ad5 nor the E1b mutant dl338 could replicate in cells expressing a mutant p53 protein, but that wild-type adenovirus replicated well in wild-type p53-expressing cells. Collectively, our data suggest that the interaction between p53 and the E1b58kDa protein is necessary for efficient adenovirus replication. This is the first time such a direct link between the complex and virus replication has been demonstrated. These data raise serious questions about the usefulness of E1b-defective viruses in tumor therapy.

Adenoviridae↗
PubMed1992

Biological and chemical interactions of pesticides with soil organic matter.

There is little doubt that organic matter plays a major role in the binding of pesticides in soil, and that this phenomenon is usually the most important cause for interaction of pesticides in the soil environment. Fulvic or humic acids are the chemicals most commonly involved in the binding interactions. Binding can occur with the original pesticide or a transformation product, the reaction being caused by abiotic agents or biotic agents (microbial or plant enzymes). The reactions or processes involved appear to be the same as those responsible for the formation of humic substances, i.e. for the humification process. Binding of pesticides to organic matter can occur by sorption (Van der Waal's forces, hydrogen bonding, hydrophobic bonding), electrostatic interactions (charge transfer, ion exchange or ligand exchange), covalent bonding or combinations of these reactions. Our investigation focused primarily on the binding of substituted phenols and aromatic amines to humus monomers and humic substances. In model reactions, we demonstrated the formation of covalent linkages between pesticides and humus constituents and fulvic or humic acids in the presence of phenol oxidases or clay minerals. With chlorinated phenols and carboxylic acids, it was possible to isolate and identify cross-coupling products and to elucidate the site and type of binding. The binding of chlorinated phenols to humic substances was determined by using 14C-labelled chemicals and by measuring the uptake of radioactivity by the humic material. These experiments provide a base for explaining the formation of bound residues in certain cases and for assuming the toxic potential of the immobilized pollutants.

Adsorption↗
PubMed1991

The phenotype in placental trisomy 7.

Trisomy 7, in mosaic state, was identified at chorionic villus sampling. The pregnancy was closely followed, and proceeded uneventfully. Mosaic trisomy 7 was confirmed in the term placenta, the organ having no structural abnormalities; the karyotype of the phenotypically normal baby was 46,XY. Trisomy 7, mosaic or nonmosaic, detected at chorionic villus sampling in an ultrasonographically normal pregnancy, appears typically to be associated with a normal fetal karyotype, and placental growth, structure, and function are not discernibly compromised.

Adult↗
PubMed1989

Linear kalilo DNA is a Neurospora mitochondrial plasmid that integrates into the mitochondrial DNA.

The linear autonomous form of kalilo DNA (previously called AR-kalDNA) is shown to be resident within mitochondria rather than nuclei, as had been suggested by previous experiments. This form has been renamed mtAR-kalDNA, to signify its mitochondrial location. Experiments are described that illustrate the inheritance and somatic transmission patterns of the mitochondrial kalilo plasmid and the mitochondrial inserted form of kalilo DNA (mtIS-kalDNA). Progeny of a cross with a pre-senescent subculture as the female parent inherited mtAR-kalDNA only; mtIS-kalDNA was not transmitted sexually. During somatic propagation of the ascospore cultures, novel kalilo DNA inserts appeared and most of them persisted until death. We propose that these inserts originated from de novo integration of mtAR-kalDNA into the mitochondrial DNA. In two of the ascopore-derived series analyzed, the first inserts detected were seen only transiently and inserts appearing subsequent to the transient inserts were retained until death. We propose that these enduring inserts originated either from rearrangements of the transient inserts or from novel integration events, either from mtAR-kalDNA or from transposition of the transient inserts.

Blotting, Southern↗
PubMed1988

Double stranded RNA in natural isolates of Neurospora.

Thirty-six wild type isolates of Neurospora were surveyed for the presence of dsRNA. The survey identified seven strains which contain dsRNA molecules. These seven strains are all from different geographic locations. The sizes of the dsRNAs range from 500 bp to 18 kb and a total of seven distinct dsRNA species was identified. Cross homologies of some of the dsRNAs were apparent. There was homology between the 9.0 kb dsRNA and genomic DNA prepared from all strains in the survey, indicating a possible cellular rather than viral origin for this dsRNA species. None of the other dsRNAs hybridized with genomic DNA suggesting a viral origin for these dsRNAs.

DNA, Fungal↗
PubMed1987

Human platelet factor 4 and protamine sulphate interaction with glycosaminoglycans in the rabbit.

We studied the action of protamine sulphate on human platelet factor 4 (PF4) kinetics in rabbits in the presence of various glycosaminoglycans (CAGs). The animals pretreated with heparin showed high initial PF4 levels with a subsequent slow monoexponential clearance. The PF4 kinetics, in the presence of heparan and dermatan sulphate, reflected the different affinities that PF4 has for these GAGs. Protamine, at dosages that totally neutralized 1000 USP units of heparin pretreatment, caused an immediate disappearance in the circulating PF4. However, a second heparin injection 10 min after protamine, induced a PF4 peak release. It is possible that protamine displaced the PF4 from the binding sites of heparin, releasing it for storage in the body 'pool', from where it can be harvested again. The action of protamine on PF4 kinetics in the rabbits pretreated with 30 mg heparan sulphate was similar to that obtained with heparin pretreatment; however, a higher dose of protamine was required to obtain the optimal effect. After a 20 mg dose of protamine, unexpectedly, a bolus of heparin did not produce any peak release of PF4 in the rabbits pretreated with 30 mg of dermatan sulphate. Although part of the protamine will displace PF4 from the binding sites of the dermatan sulphate molecule, the remaining part of protamine could probably be bound to this GAG without losing its activity so that, upon subsequent heparin injection, it is immediately neutralized, rendering it unavailable for further PF4 harvesting.

Animals↗
PubMed1975

Osmotically induced electrical changes in isolated bullfrog small intestine.

1. Steady state values of cell water, intracellular Na+ and K+ concentrations, and the electrical parameters ETr, Em, and Isc in the mucosa of isolated bullfrog small intestine were determined following immersion in sodium sulfate Ringer solutions with identical ionic composition but different osmolalities. 2. Cell water and intracellular K+ concentration were inversely related to the osmolality of the bathing medium. During 1 h immersion, intracellular Na+ concentration was not significantly affected by an increase or decrease in external osmolality. 3. Replacement of a hypotonic or an approximately isotonic (normal) medium by a medium of greater osmolality caused statistically significant decreases in ETr, Isc and the (inside negative) magnitude of Em. Conversely, when a hypertonic or a normal medium was replaced by one of lower osmolality, significant increases in the magnitude of these parameters were observed. 4. An equivalent circuit model for the epithelial cell layer, in which the resistance of a relatively highly conducting extracellular shunt pathway is assumed to be the major determinant of the electrical responses of the small intestine to external osmolality, has been shown to account satisfactorily for the observed changes in ETr and Em. In terms of this model, the experimentally observed dependence of Isc on external osmolality requires that, even when both the mucosal and the serosal sides of the tissue are bathed by identical media, isolated bullfrog small intestine maintains a finite diffusion potential across the shunt pathway. This is consistent with current views concerning transepithelial ionic transfer mechanisms.

Animals↗
PubMedDate not supplied

Structure-activity relationship for the intrinsic hepatotoxicity of dinitrotoluenes.

The relation of various structural parameters to hepatotoxic potential was investigated by using six dinitrotoluene (DNT) isomers and isolated rat hepatocyte suspensions as the biological test system. DNT-induced hepatotoxicity was found to correlate with an inhibition of protein synthesis and an increase in lactate dehydrogenase (LDH) release but not with lipid peroxidation. With each isomer, protein synthesis inhibition was the most sensitive indicator of cytotoxicity. Regardless of the indicator, ortho- and para-substituted isomers were more hepatotoxic at the same concentration than meta-substituted isomers. High-performance liquid chromatograms (HPLC) on samples at 4 h revealed significant quantities of reduced metabolites in the medium. However, increased lipid peroxidation (formation of thiobarbituric acid reactants or evolution of ethane) in the cells was not consistently demonstrated. log EC50 for protein synthesis inhibition and log EC20 for LDH release were linearly correlated with the C atomic charge on the ring carbons bearing the nitro substituents by using molecular orbital (MNDO calculations) theory. The relation was used to predict the hepatotoxic potentials of untested nitrotoluenes, and the predictions were verified to a first approximation by using three trinitrotoluene isomers.

Animals↗