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Biomedical subjects

E F Howard

Publications and source records attributed to E F Howard.

31 records · Page 2Linked to original sources
PubMed1986

Functional, developmentally expressed genes for mouse U1a and U1b snRNAs contain both conserved and non-conserved transcription signals.

Four genes that encode mouse U1a1, U1b2 and U1b6 snRNAs have been isolated from a mouse genomic DNA library. They all appear to be functional U1 genes since they are accurately transcribed into full length, capped snRNAs upon injection into Xenopus oocytes. A mouse pseudogene that is not transcribed in Xenopus oocytes was also isolated from the mouse genomic library. DNA sequence analysis of the 5' and 3' flanking regions of the functional genes revealed the presence of three highly conserved sequence elements that have been shown to be required for transcription initiation or 3' end formation in other U1 genes. Each of these U1 RNA genes also contains non-conserved sequences in the 5' flanking region that could function in their controlled expression during development.

Animals↗
PubMed1986

Characterization and mapping of DNA sequence homologous to mouse U1a1 snRNA: localization on chromosome 11 near the Dlb-1 and Re loci.

A phage clone which contained a functional U1a1 snRNA gene was isolated from a mouse genomic library. A single copy fragment was isolated from the 3' flanking region of the U1a1 gene and used as a hybridization probe for Southern blotted DNAs from recombinant inbred strains of mice, mouse-hamster hybrid cells, and the offspring from backcrosses between BALB/c mice and mice which were heterozygous for the Rex (Re) marker. The results of these experiments prove that the U1a1 gene is located on chromosome 11 near the Delb-1 and Re loci.

Animals↗
PubMed1981

Phosphorylation of chromosomal proteins from mammary cell lines.

Phosphorylation of histone and none-histone chromosomal proteins in two clonal mouse mammary cell lines having low (V-14) and high (T-19) tumorigenicity was investigated. Logarithmic phase cells were incubated in medium containing 125 muCi/ml[32P]-orthophosphate. Cell nuclei were isolated, chromosomal proteins (histones and non-histones) extracted and their amino acid composition, protein/DNA mass ratios, 32P-uptake and gel electrophoretic patterns examined. Significant differences in the histone and NHC-protein phosphorylation of these two cell lines were found. Comparison of radioactivity profiles of electrophoretically separated T-19 and V-14 NHC-proteins showed that 60% of the T-19 bands in the mol. wt range of 160,000 to 15,000 daltons had increased [32P]-orthophosphate uptake. Differences in histone radiolabelling between V-14 and T-19 were confined to the H1, H3 and H4 classes. [32P]-ATP-pool measurements of V-14 and T-19 at 30, 60 and 120 min of incubation were similar, hence the difference in 32P-uptake was not due to ATP-pool fluctuations. Results of studies on growth rate, growth potential and the possibility that comparisons were made between cells at different stages of the growth cycle indicated that these variables did not account for the higher phosphorylation of T-19 chromosomal proteins. The increased [32P]-phosphate uptake into T-19 cell protein was correlated with an elevated content of NHC and histone proteins and pointed towards a correlation between the degree of phosphorylation and the high tumorigenicity of this cell line.

Adenosine Triphosphate↗
PubMed1980

Mitogenic activity and plasminogen activator in harvest fluid concentrates from mammary cells in culture.

Harvest fluid concentrates (HFC's) from three human mammary tumor cell lines (T47D), HSO578T, and MDA-MB-157), one nontumorigenic human mammary cell line (HBL-100), and one mouse mammary tumor cell line (MCG-T14) stimulated thymidine incorporation in confluent quiescent BALB/c 3T3 cells in a dose-dependent manner. HFC's from all of the cell lines also exhibited plasminogen activator activity. Levels of mitogenic activity and plasminogen activator in the HFC preparations were not correlated with cell growth potential or with the amount of protein which was recovered in the HFC's. High levels of mitogenic activity and plasminogen activator in the HFC's from HBL-100 cells suggested that the production of these biological activities is not a unique feature of tumorigenic mammary cells. The HFC's from three human cell lines (T47D), HS0578T, MDA-MB-157) exhibited high levels of mitogenic activity but low levels of plasminogen activator. This suggested that plasminogen activator is not the source of the mitogenic activity in the HFC's from these cells. The HFC's from a human mammary carcinoma line, BT-20, contained very low levels of mitogenic activity and plasminogen activator. In addition, BT-20 HFC's inhibited the mitogenic activity of fetal bovine serum in a dose-dependent manner. It is proposed that BT-20 cells are the source of a macromolecular inhibitor of serum mitogens.

Animals↗
PubMed1977

Aryl hydrocarbon hydroxylase in mouse mammary gland: in vitro study using mammary cell lines.

The effects of 3-methylcholanthrene (MCA), 5,6-benzoflavone (betaNF), 7,8-benzoflavone (alphaNF) and pregnenolone 16alpha-carbonitrile (PCN) upon aryl hydrocarbon hydroxylase (AHH) were determined in primary mammary gland epithelial cell cultures prepared from the C3Hf-/Ki mouse. MCA elevated AHH activity by 3--4 fold after 24 h of treatment; alphaNF produced a 50% inhibition. The specific activity of AHH in these cells was elevated by 6 h after exposure to MCA; enzyme activity was still maximally elevated after 48 h. The effects of MCA were also investigated in a group of mammary cell lines, one of which was derived from a control virgin mouse, the MCG V14; 3 of which arose from mammary tumors, MCG T10, MCG T14 and MCG T19; and 2 of which were sublines developed from hyperplastic alveolar nodules, HAN-1 and HAN-2. Induction was seen in all lines at 24 h, with the MCG T14 being the most responsive and the HAN-2, the least. Although the MCG T19 tumor cells did respond in culture, when implanted in the mouse, the AHH of the subsequent tumor was not elevated upon administration of MCA in vivo.

Animals↗
PubMed1977

Cyclic nucleotide levels in mouse mammary epithelial cells during growth arrest and growth initiation in culture.

Intracellular levels of cyclic AMP (cAMP) and cyclic GMP (cGMP) were measured in high and low tumorigenic mouse mammary epithelial cells during growth arrest in 1% fetal bovine serum and during the first 60 minutes after serum stimulation of cell proliferation in arrested cultures. Stationary MCG-T14 cells, which are highly tumorigenic and grow to high densities in 1% serum, exhibited lower levels of cAMP, higher levels of cGMP, and a lower ratio of cAMP to cGMP than quiescent MCG-V14 cells, which have low tumorigenicity and achieve low cell densities in 1% serum. Within 5-10 minutes after cell growth was initiated in arrested cultures by the addition of serum, both cell lines responded with a fourfold to fivefold increase in cGMP and a concomitant 50% decrease in cAMP. MCG-T14 cells exhibited the highest intracellular levels of cGMP and the lowest cAMP to cGMP ratio within 10 minutes after serum addition.

Animals↗
PubMed1976

Stimulation of thymidine uptake and cell proliferation in mouse embryo fibroblasts by conditioned medium from mammary cells in culture.

Undialyzed conditioned medium from several cell culture sources did not stimulate thymidine incorporation or cell overgrowth in quiescent, density-inhibited mouse embryo fibroblast cells. However, dialyzed conditioned medium (DCM) from clonal mouse mammary cell lines MCG-V14, MCG-T14, MCG-T10; HeLa cells; primary mouse adenocarcinoma cells; and BALB/c normal mouse mammary epithelial cells promoted growth in quiescent fibroblasts. The amount of growth-promoting activity produced per cell varied from 24% (HeLa) to 213% (MCG-V14) of the activity produced by primary tumor cells. The production of growth-promoting activity was not unique to tumor-derived cells or cells of high tumorigenicity. The amount of growth-promoting activity produced per cell in the active cultures was not correlated with any of the following: tumorigenicity, growth rat, cell density achieved at saturation, cell type, or species of cell origin. It is concluded that transformed and non-transformed cells of diverse origin, cell type, and tumorigenicity can produce growth factors in culture. The growth-promoting potential of the active media from primary tumor cultures accumulated with time of contact with cells and was too great to be accounted for entirely by the removal of low-molecular-weight inhibitors by dialysis. The results are consistent with the hypothesis that conditioned medium from the active cultures contained a dialyzable, growth-promoting activity. Different cell lines exhibited differential sensitivity to tumor cell DCM and fetal bovine serum. Furthermore, quiescent fibroblasts were stimulated by primary tumor cell DCM in the presence of saturating concentrations of fetal bovine serum. These observations support the notion that the active growth-promoting principle in primary tumor cell DCM may not be a serum factor(s).

Adenocarcinoma↗
PubMed1976

Breakage of human cell DNA after exposure to 3-methylcholanthrene-11,12-oxide.

Damage to and repair of DNA isolated from human neonatal and fetal skin cells were measured by alkaline sucrose gradient analysis. 3-Methylcholanthrene did not induce single-strand breaks in DNA of the cells in culture, whereas the 11,12-oxide of 3-methylcholanthrene was very effective in this regard. The cis-1,2-dihydroxy, trans-11,12-dihydroxy, and cis-11,12-dihydroxy derivatives of 3-methylcholanthrene exerted little effect. The breaks in DNA caused by 3-methylcholanthrene oxide occurred during a 60-min incubation period and were repaired during the following 60 min. Methylmethane sulfonate also induced breaks in the DNA within 60 min.

Cells, Cultured↗
PubMed1968

Chromosomal DNA synthesis in Drosophila melanogaster.

Analysis of labeling patterns in three chromosome segments of Drosophila melanogaster has shown that the replicative activity within chromosomes is temporally ordered. Moreover, specific labeling patterns on one chromosome occur with specific patterns on another chromosome with a very high degree of correlation. This circumstance leads to the conclusion that DNA synthesis among all the regions in the three chromosome segments studied is coordinated. The various labeling patterns observed in any one chromosome and the combinations of labeling patterns observed in all three chromosome segments can be arranged in ordered arrays, if one assumes that the DNA synthesis in each chromosome region will go to completion without stopping once it has started. Such arrays can serve as models for the temporal order of DNA synthesis among chromosome regions. They predict that in any one chromosome DNA replication begins and ends at very few loci and that synthesis at a larger number of points occurs at an intermediate time.

Autoradiography↗