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J M Weber

Publications and source records attributed to J M Weber.

At least 127 records · Page 7Linked to original sources
PubMed1990

Tumor necrosis factor mediated cytolysis requires the adenovirus E1a protein but not the transformed phenotype.

Adenovirus transformed cells are susceptible to lysis by human recombinant tumor necrosis factor (TNF). This susceptibility correlates with the presence of E1a in these cells. A flat revertant cell line which expresses a biologically functional E1a but not the transformed phenotype was nevertheless susceptible to TNF. However, flat revertants retransformed by 5-azacytidine, without concomitant reactivation of E1a, were resistant to TNF-alpha. This result suggests TNF susceptibility is not transformation but E1a dependent. To study the mechanism of cytolysis in these cell lines, we examined the possibility that changes in the transcription of E1a were brought about by TNF, as it was reported in the case of a c-myc transformed cell line. The results showed that TNF did not affect either E1a or c-myc transcription in our cells during the development of the cytotoxic response.

Adenoviridae↗
PubMed1990

Drug-induced revertants of adenovirus-transformed cells: retransformation by 5-azacytidine without reactivation of E1a.

We have isolated drug-resistant variants from adenovirus-transformed rat cells that had concomitantly lost their transformed phenotype. Our aim was to determine the reason for reversion, to attempt retransformation with 5-azacytidine (5-AzaC) and to study the mechanism of retransformation. Of the three cell lines studied, one (G4F) had lost the integrated E1a genes, whereas the other two (G2a and G5) failed to synthesize E1a RNA or proteins. Incubation of these cell lines with 3 microM-5-AzaC for 2 days, followed by passaging in the absence of drug, gave rise to transformed foci in all of the cell lines. The efficiency of transformation was typical of each cell line. Surprisingly, retransformation was not accompanied by the reappearance of detectable levels of E1a gene activity in the G2aAza and G5Aza cell lines. In search of a mechanistic explanation for the loss of gene activity in the revertants and its reappearance in the retransformants, we examined the state of methylation of the E1a gene region in these cells. Neither the E1a promoter nor its upstream region was methylated in the revertants or the 5-AzaC retransformants. These results suggest that E1a transcription was suppressed by mechanisms other than DNA methylation and that 5-AzaC could retransform these cells without lifting the E1a-suppressed state.

Adenovirus Early Proteins↗
PubMed1990

Organization of a cluster of erythromycin genes in Saccharopolyspora erythraea.

We used a series of gene disruptions and gene replacements to mutagenically characterize 30 kilobases of DNA in the erythromycin resistance gene (ermE) region of the Saccharopolyspora erythraea chromosome. Five previously undiscovered loci involved in the biosynthesis of erythromycin were found, eryBI, eryBII, eryCI, eryCII, and eryH; and three known loci, eryAI, eryG, and ermE, were further characterized. The new Ery phenotype, EryH, was marked by (i) the accumulation of the intermediate 6-deoxyerythronolide B (DEB), suggesting a defect in the operation of the C-6 hydroxylase system, and (ii) a block in the synthesis or addition reactions for the first sugar group. Analyses of ermE mutants indicated that ermE is the only gene required for resistance to erythromycin, and that it is not required for production of the intermediate erythronolide B (EB) or for conversion of the intermediate 3-alpha-mycarosyl erythronolide B (MEB) to erythromycin. Mutations in the eryB and eryC loci were similar to previously reported chemically induced eryB and eryC mutations blocking synthesis or attachment of the two erythromycin sugar groups. Insertion mutations in eryAI, the macrolactone synthetase, defined the largest (at least 9-kilobase) transcription unit of the cluster. These mutants help to define the physical organization of the erythromycin gene cluster, and the eryH mutants provide a source for the production of the intermediate DEB.

Chromosomes, Bacterial↗
PubMed1990

Role of triglyceride-fatty acid cycle in controlling fat metabolism in humans during and after exercise.

We have investigated the role of triglyceride-fatty acid cycling in amplifying control of the net flux of fatty acids in response to exercise and in recovery from exercise. Five normal volunteers were infused with [1-13C]palmitate and D-5-glycerol throughout rest, 4 h of treadmill exercise at 40% maximum O2 consumption, and 2 h of recovery. Total fat oxidation was quantified by indirect calorimetry. Lipolysis (rate of appearance of glycerol) increased from 2.1 +/- 0.3 to 6.0 +/- 1.2 mumol.kg-1.min-1 after 30 min of exercise and progressively increased thereafter to a value of 10.5 +/- 0.8 mumol.kg-1.min-1 after 4 h. Lipolysis decreased rapidly during the first 20 min of recovery, but it was still significantly elevated after 2 h of recovery. The rate of appearance of free fatty acids followed the same pattern of response. Seventy percent of released fatty acids were reesterified at rest, and this value decreased to 25% within the first 30 min of exercise. Reesterification remained less than 35% of lipolysis until the start of recovery, at which time the value rose to 90%. In exercise, more than one-half the increase in fat oxidation could be attributed to the reduction in the percent reesterification. Most of the change in percent reesterification during exercise and recovery was caused by changes in extracellular cycling of fatty acids released into plasma. We conclude that triglyceride-fatty acid cycling plays an important role in enabling a rapid response of fatty acid metabolism to major changes in energy metabolism.

Adult↗
PubMed1990

Role of the glucose cycle in control of net glucose flux in exercising humans.

The hepatic glucose cycle involves the production of plasma glucose from glucose 6-phosphate and the simultaneous conversion of glucose back to glucose 6-phosphate. We have evaluated the role of the glucose cycle in the regulation of plasma glucose concentration during exercise at 70% of maximal O2 uptake and during recovery in five normal volunteers. Total glucose flux was measured by use of [2-2H]glucose (Ra2), net glucose flux through the glucose cycle was determined with [6,6-2H2]glucose (Ra6), and the rate of glucose cycling was determined by Ra2 - Ra6. Gas chromatography-mass spectrometry was used for analysis of isotopic enrichment. At rest, 33% of total glucose flux was recycled. In exercise, total flux increased 300%, but so did glucose cycling, which means that there was no change in the percentage of flux recycled. In recovery, both total flux and the rate of recycling returned rapidly to the resting value. We therefore conclude that whereas total glucose production can respond extremely quickly to large changes in energy requirements caused by exercise, thereby enabling maintenance of a constant blood glucose concentration, glucose cycling does not have an important role in amplifying the control of net hepatic glucose flux through the glucose cycle.

Adult↗
PubMed1989

Non-p-glycoprotein-mediated multidrug resistance in detransformed rat cells selected for resistance to methylglyoxal bis(guanylhydrazone).

Three independent variants (G2, G4, G5), resistant to methylglyoxal bis(guanylhydrazone), an anticancer drug, have been isolated by single step selection from an adenovirus-transformed rat brain cell line (1). These variants display selective cross-resistance to several natural product drugs of dissimilar structure and action. Multidrug resistance has recently been shown to be caused by overexpression of the membrane-associated p-glycoprotein, most often caused by amplification of the mdr gene. Several types of experiments were conducted to determine whether the observed drug resistance in our cell lines could be due to changes at the mdr locus. The following results were obtained: (a) the mdr locus was not amplified; (b) transcription of the mdr gene and p-glycoprotein synthesis were not increased; (c) multidrug resistance cell lines, which carry an amplified mdr locus, were not cross-resistant to methylglyoxal bis(guanylhydrazone); (d) verapamil did not reverse the resistance of G cells or mdr cells to methylglyoxal bis(guanylhydrazone), nor that of G cells to vincristine; and (e) methylglyoxal bis(guanylhydrazone) resistance was recessive and depended on a block to drug uptake, as opposed to mdr cells which are dominant and express increased drug efflux. The results obtained suggest that the drug resistance in the G2, G4, and G5 cells was atypical and may be due to a mechanism distinct from that mediated by the mdr locus.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1989

Identification of a gene required for the terminal step in erythromycin A biosynthesis in Saccharopolyspora erythraea (Streptomyces erythreus).

We have identified a transcription unit in the ermE region of the chromosome of the erythromycin (Er)-producing bacterium Saccharopolyspora erythraea (Streptomyces erythreus) that is briefly switched on at about the time that macrolide production commences. Disruption of the transcription unit, herein designated eryG, by insertion of an integrational plasmid vector, caused a block at the terminal step in the biosynthesis of erythromycin, the conversion of erythromycin C to A by O-methylation.

Blotting, Northern↗
PubMed1989

The orientation of the adenovirus fiber and its anchor domain identified through molecular mimicry.

An antibody prepared against a synthetic peptide derived from the sequence of the adenovirus protease cross-reacted with the viral fiber protein of adenovirus types 2, 3, 4, and 9. Four residues in a conserved hexamer sequence near the N-terminus of the Ad2 and Ad3 fibers were homologous to the peptide. The epitope was masked by attachment of the penton base and thus lies within an anchoring domain 30 residues from the N-terminus of the fiber polypeptide.

Adenoviridae↗
PubMed1988

The use of a chromosome integration vector to map erythromycin resistance and production genes in Saccharopolyspora erythraea (Streptomyces erythraeus).

The thiostrepton-resistance-conferring plasmid pIJ702 was integrated into the ermE region of the chromosome of erythromycin (Er)-producing bacterium Saccharopolyspora erythraea (Streptomyces erythraeus) by single, reciprocal (Campbell) recombination between DNA cloned in the vector and homologous nucleotide sequences in the chromosome. Genetic mapping experiments by conjugational transfer were used to establish that the ErR gene, ermE, was located close to the Er-production loci eryA34 and eryB25.

Blotting, Southern↗
PubMed1988

Normalization of epidermal growth factor receptor and transforming growth factor production in drug resistant variants derived from adenovirus transformed cells.

Variants (G2, G5) resistant to the cancer chemotherapeutic drug methylglyoxal bis (guanylhydrazone) (MGBG) were isolated from adenovirus type 2 transformed rat brain cells (F4; Sircar et al., 1987). Although at least one of these variants continued to express the adenovirus Ela and Elb transforming proteins, they both exhibited a detransformed phenotype as witnessed by flat morphology, loss of anchorage independent growth, and tumor forming capacity. Reverse transformation suggested the possibility of changes in growth factor receptors and the production of transforming growth factors. To test this possibility, we investigated the status of epidermal growth factor receptors (EGF-r) and transforming growth factor alpha (TGF-alpha) production in F4, G2 and G5 cells. The level of 125I-labeled EGF binding to intact drug resistant cells increased by 2- to 3-fold compared to the transformed parental cell. Scatchard analysis suggests that increased binding was the result of increased receptor levels rather than altered affinity of receptor for ligand. The production of growth factors which compete with 125I-labeled EGF binding declined in the detransformed G2 and G5 cells to a level intermediate between transformed (F4) and normal cells (FR3T3). EGF-receptor increase and the complementary decrease in growth factor production in the drug resistant variants may be associated with detransformation.

Adenoviridae↗
PubMed1988

Dietary restraint and obesity: their effects on dietary intake.

The current investigation evaluated the effects of levels of restraint, dietary intake, and obesity on both immediate (i.e., in the laboratory) and subsequent (i.e., outside the laboratory) self-reported dietary intake. Subjects were 102 college females, half of whom were given a high-caloric snack of a chocolate milkshake. Subjects were classified according to their level of chronic dieting status and relative weight. Chronic dieting status was measured by utilizing both the Concern for Dieting (CD) and the Weight Fluctuation (WF) factors of the revised restraint scale (Polivy, 1980). When using the WF factor, results indicated that obesity interacted with dieting status on total food consumption (i.e., calories for the entire day). That is, nondieting obese subjects reportedly ate significantly more calories than nondieting normal-weight subjects. Further, nondieting overweight subjects reported eating significantly more than low-restrained normal-weight subjects. On the CD factor, restrained eaters who received a preload reported eating significantly more calories than nondieters at lunch. For those subjects not receiving a milkshake, restrained eaters ate fewer calories at lunch than nondieters. The significance of these results for understanding possible energy imbalances in obese individuals as well as understanding pathological overeating and its consequences is discussed.

Body Weight↗
PubMed1988

Activation of the major late promoter in adenovirus transformed cells by 5-azacytidine.

The adenovirus major late promoter (MLP) is normally not active in transformed cells. We investigated if it could be activated with 5-azacytidine. Three days of treatment with 10 microM 5-azacytidine induced transient activation of the MLP as shown by hybridization with an L1 r-strand-specific probe. The po/III-transcribed VA-RNAs were not activated. L1 activation was not accompanied by detectable changes in methylation of HpaII sites at the promoter or in the body of the transcript. Stably activated cell clones could be obtained at 20% frequency after long-term drug treatment.

Adenoviridae↗