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B C Armstrong

Publications and source records attributed to B C Armstrong.

9 recordsLinked to original sources
PubMed1992

Isolation and characterization of complementary DNA for N-cym, a gene encoded by the DNA strand opposite to N-myc.

The N-myc oncogene has been implicated in the pathogenesis of a number of human tumors, including childhood neuroblastoma and adult small cell lung cancer. We have isolated and characterized complementary DNA clones derived from a transcription unit, N-cym, located on the opposite DNA strand to N-myc, with extensive overlap existing between the 5' ends of the two transcription units. The N-cym gene, which can encode a 109-amino acid protein, is expressed during fetal development, as well as in tumor cell lines containing amplified N-myc loci, where it is expressed at very high levels. Although other examples of overlapping, opposite-strand eukaryotic genes exist, N-myc and N-cym are unique in that they appear to be coregulated in tumor cell lines under basal growth conditions and in response to the differentiating agent retinoic acid. This coregulation suggests that their protein products may be functionally interrelated during normal development and oncogenesis.

Amino Acid Sequence↗
PubMed1991

Actin polymerization in cellular oxidant injury.

Microfilaments undergo an ATP-dependent disruption into shortened bundles following cellular exposure to oxidants. This phenomenon does not require a net change in the amount of polymerized actin. However, increased amounts of polymerized actin have been detected in oxidant-injured cells and it was the purpose of this study to determine the conditions under which the actin polymerization may occur. Utilizing the formation of oxidized glutathione (GSSG) as an indicator of cellular sulfhydryl oxidation, conditions were chosen to accentuate sulfhydryl oxidation within the target P388D1 cell line following exposure to the oxidants, H2O2 and diamide. Using the DNase I and flow cytometric assays of actin polymerization, significant polymerization of actin was detected only under conditions in which sulfhydryl oxidation occurred after exposure to the two oxidizing agents. Greater sulfhydryl oxidation early in the course of injury was associated with a greater rate and extent of actin polymerization in the injured cells. Experiments with cells depleted of glutathione (GSH) demonstrated that neither loss of GSH nor absolute levels of GSSG formed during oxidant exposure were responsible for the polymerization of actin. The data presented are consistent with the hypothesis that oxidizing conditions which induce significant sulfhydryl oxidation in target cells are correlated with assembly of polymerized actin and that this represents a process which is distinct and separate from the ATP-dependent gross disruption of microfilaments.

Actins↗
PubMed1990

N-myc mRNA forms an RNA-RNA duplex with endogenous antisense transcripts.

Nuclear runoff transcription studies revealed nearly equivalent sense and antisense transcription across exon 1 of the N-myc locus. Antisense primary transcription initiates at multiple sites in intron 1 and gives rise to stable polyadenylated and nonpolyadenylated transcripts. This pattern of antisense transcription, which is directed by RNA polymerase II, is independent of gene amplification and cell type. The nonpolyadenylated antisense transcripts have 5' ends which are complementary to the 5' ends of the N-myc sense mRNA. We determined, by using an RNase protection technique designed to detect in vivo duplexes, that most of the cytoplasmic nonpolyadenylated antisense RNA exists in an RNA-RNA duplex with approximately 5% of the sense N-myc mRNA. Duplex formation appeared to occur with only a subset of the multiple forms of the N-myc mRNA, with the precise transcriptional initiation site of the RNA playing a role in determining this selectivity. Cloning of each strand of the RNA-RNA duplex revealed that most duplexes included both exon 1 and intron 1 sequences, suggesting that duplex formation could modulate RNA processing by preserving a population of N-myc mRNA which retains intron 1.

Base Sequence↗
PubMed1989

Mechanism of endothelial cell shape change in oxidant injury.

Changes in endothelial cell morphology induced by neutrophil-generated hydrogen peroxide (H2O2) may account for the capillary leak of the adult respiratory distress syndrome (ARDS). The relationship of H2O2 effects on the concentration of intracellular Ca2+ [( Ca2+]i) and ATP to changes in microfilaments and microtubules, important determinants of cell shape, was examined. Bovine pulmonary artery endothelial cells were injured over a 2-hr time course with a range of H2O2 doses (0-20 mM). The higher concentrations of H2O2 consistently produced contraction and rounding of greater than 50-75% of cells by 1-2 hr. The range of 1-20 mM H2O2 produced rapid, significant reductions in endothelial ATP levels over the time course of injury. Although there were significant increases in mean endothelial [Ca2+]i in response to 5, 10, and 20 mM H2O2, 1 mM H2O2 did not affect the [Ca2+]i. Fluorescence microscopy revealed that microfilament disruption occurred as ATP levels fell and preceded depolymerization of microtubules which developed after [Ca2+]i approached 1 X 10(-6) M. H2O2 at 1 mM injury caused microfilament disruption but did not depolymerize microtubules. Microfilament disruption occurred without oxidant exposure, when ATP levels were reduced by glucose depletion and mitochondrial inhibition with oligomycin (650 nM). If a Ca2+ ionophore, ionomycin (5 microM), was then added, [Ca2+]i rose to greater than 1 X 10(-6) M, microtubules fragmented and depolymerized, and cell contraction and rounding very similar to that induced by H2O2 occurred. These results suggest that endothelial cell dysfunction and capillary leak in ARDS may be due to H2O2-mediated changes in cellular ATP and [Ca2+]i.

Actin Cytoskeleton↗
PubMed1988

A cellular model of endothelial cell ischemia.

Endothelial cell dysfunction in ischemia may cause increased capillary permeability. We examined the effect of failing ATP synthesis, a major consequence of ischemia, on microfilaments--important structural determinants of the endothelial cell. Glycolytic and mitochondrial ATP synthesis in bovine pulmonary artery endothelial cells was inhibited by glucose depletion and 650 picomole (pmole) oligomycin/micrograms DNA, respectively. ATP levels were monitored with the luciferase-luciferin assay over a 2-hr time course followed by recovery for 1 hr after removal of the oligomycin and addition of 5.5 mM glucose. ATP levels fell to 83.6 +/- 63.8 pmole/micrograms DNA (n = 11) by 30 min, 26.9 +/- 13.8 pmole/micrograms DNA (n = 11) by 60 min, and 17.2 +/- 3.8 pmole/micrograms DNA (n = 6) by 120 min, whereas control uninjured cells had 541.3 +/- 196.8 pmole/micrograms DNA (n = 6) at 120 min. Fluorescence microscopy of microfilaments stained with rhodamine-phalloidin revealed progressive disassembly and shortening of the microfilaments in greater than 90% of cells over 60 min which correlated with the fall in ATP. Ultrastructural examination revealed that side to side aggregation of microfilaments had occurred over the 120-min time course. Two hours of glucose depletion (305.5 +/- 130.8 pmole ATP/micrograms DNA, n = 6) or oligomycin alone (480.0 +/- 90.1 pmole ATP/micrograms DNA, n = 6) failed to produce the dramatic fall in ATP or the microfilament changes. During cell recovery, there was a rapid reassembly of microfilaments, detected by fluorescence microscopy, which was nearly complete in 85-90% of cells by 45-60 min. ATP levels increased significantly (P = 0.002) to 96.1 +/- 36.8 pmole/micrograms DNA (n = 6) by 30 min. This model should provide insight into the pathogenesis and treatment of the capillary leak seen with ischemia.

Actin Cytoskeleton↗
PubMed1988

ATP and microfilaments in cellular oxidant injury.

Oxidant injury produces dramatic changes in cytoskeletal organization and cell shape. ATP synthetic pathways are major targets of oxidant injury resulting in rapid depletion of cellular ATP following oxidant exposure. The relation of ATP depletion to the changes in microfilament organization seen following H2O2 exposure were examined in the P388D1 cell line. Three hours of glucose depletion alone resulted in a decline in cellular ATP levels to less than 10% of controls, which was comparable to ATP levels in cells 30 to 60 minutes after exposure to 5 mM H2O2 in the presence of glucose. Adherent cells stained with rhodamine phalloidin, a probe specific for polymerized (F) actin, revealed a progressive shortening of microfilaments into globular aggregates within cells depleted of glucose over 3 hours, a pattern similar to earlier observations of H2O2-injured cells after 1 hour. The changes in cellular ATP associated with glucose depletion or H2O2 exposure were then correlated with G actin content measured by the DNAse 1 inhibition assay. No real differences in G actin content as a percentage of total actin were seen in P388D1 cells following 3 hours of glucose depletion or 30 to 60 minutes after exposure to 5 mM H2O2. But 2 to 3 hours after exposure to H2O2 there was a progressive decrease in G actin as a percentage of total actin within the cells. Transmission electron microscopy of cells depleted of glucose for 3 h or 1 hour after exposure to H2O2 revealed the presence of side-to-side aggregates or bundles of microfilaments within the cells. These observations suggest that declining levels of ATP either from metabolic inhibition or H2O2 injury are correlated with the fragmentation and shortening of microfilaments into aggregates. No net change in monomeric or polymeric actin was necessary for this to occur. However, at later time points after H2O2 exposure some actin assembly did occur.

Actin Cytoskeleton↗
PubMed1983

Alteration of staphylococcal flora in cardiac surgery patients receiving antibiotic prophylaxis.

The changes in staphylococcal flora induced by antibiotic prophylaxis with rifampin and nafcillin in combination among patients undergoing cardiac valve surgery were compared to those in patients undergoing coronary artery bypass surgery concurrently, who received only cefazolin. Rifampin-nafcillin prophylaxis eradicated carriage of Staphylococcus aureus at a significantly higher rate than did cefazolin (eradicated carriage of 89% vs. 48%, respectively; P less than 0.01); however, by the seventh postoperative day, 75% of the patients receiving rifampin and nafcillin had rifampin-resistant, coagulase-negative staphylococcal perianal floras, compared to 19% of those who received cefazolin (P less than 0.001). Patients receiving rifampin-nafcillin were colonized as frequently (66%) with coagulase-negative staphylococci resistant to gentamicin and methicillin as were those receiving cefazolin (68%). Patients in the coronary intensive care unit who received no antibiotics were infrequently colonized with either rifampin-resistant (none) or gentamicin- and methicillin-resistant (11%) staphylococci. Antibiotic prophylaxis may, therefore, be an important factor in perpetuating the hospital reservoir for antibiotic-resistant, coagulase-negative staphylococci.

Anti-Bacterial Agents↗
PubMed1982

Rifampin blood and tissue levels in patients undergoing cardiac valve surgery.

Single 600-mg capsules of rifampin were given orally to 26 patients as prophylaxis during cardiac valve replacement. Antibiotic concentrations were measured in blood (serum or plasma) and tissue (excised cardiac valve). The serum or plasma levels of rifampin in 18 patients who ingested this drug 2 h before they received preoperative opiates and anticholinergics intramuscularly were not significantly different from the levels in four normal volunteers who received the drug. These levels were 15.9 +/- 6.5 micrograms/ml (mean +/- standard deviation) 2 h after drug administration, 7.1 +/- 4.3 micrograms/ml 8 h after drug administration and 2 h after a mean of 1.4 h on cardiopulmonary bypass, and 1.6 +/- 1.6 micrograms/ml 24 h after drug ingestion. The valve tissue level was 3.8 +/- 2.7 micrograms/g (mean +/- standard deviation; n = 10). This value was 65% of the simultaneous serum and plasma levels and 31% of the peak serum and plasma levels. Eight patients who were given rifampin at the same time that they received other preoperative medications had significantly lower blood levels than the 18 patients who received rifampin 2 h earlier (P less than 0.001). No rifampin was detected in valves from seven of these patients. Decreased rifampin absorption due to simultaneous administration with opiates and anticholinergics was the probable reason for the low plasma and serum levels observed. These data suggest that, if properly dosed, rifampin administered orally gives high blood and valve tissue levels, which are affected minimally by cardiopulmonary bypass in patients undergoing cardiac valve surgery.

Female↗