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Biomedical subjects

D S Straus

Publications and source records attributed to D S Straus.

At least 55 records · Page 3Linked to original sources
PubMed1984

Growth control variant cell line having increased serum requirement and decreased response to platelet-derived growth factor: reversion by 5-azacytidine.

Variants of the mouse embryo fibroblast X melanoma hybrid clone 100A have been isolated by a procedure that selects against cells that are able to grow in medium containing low concentrations of serum plus insulin. Three variant clones derived from this selection were found to have a much higher serum requirement than the parental clone 100A cells, as evidenced by a very low rate of DNA synthesis and growth in medium containing low concentrations of serum. Two of the variants had approximately double the number of chromosomes as the parental cell line, while one had approximately the same number of chromosomes as the parental cells. One of the variants was very strongly reverted by 5-azacytidine but not by ethyl methanesulfonate, suggesting that it reverted by a nonmutational mechanism such as a stable change in DNA methylation. Analysis of the growth requirements in hormone-supplemented serum-free media of the 100A parent, the INS 471 variant, and revertants of the variant indicated that the variant had a specific deficiency in its growth response to platelet-derived growth factor (PDGF). PDGF dose-response curves obtained with the variant cells were shifted approximately an order of magnitude toward higher PDGF concentrations relative to PDGF dose-response curves obtained with the parental 100A cells. This quantitative increase in PDGF requirement of the INS 471 variant appears to explain the increased serum requirement of this variant. Equilibrium binding experiments performed with 125I-PDGF suggest that the variant does not have a decreased number of PDGF receptors.

Animals↗
PubMed1984

Growth-stimulatory actions of insulin in vitro and in vivo.

Insulin stimulates the growth and proliferation of a variety of somatic cells in culture, and evidence suggests that insulin is also an important regulator of growth in vivo. In cell culture, insulin interacts synergistically with other hormones and growth factors such as platelet-derived growth factor (PDGF), fibroblast growth factor (FGF), epidermal growth factor (EGF), tumor-promoting phorbol esters, and thrombin, to stimulate progression through the cell cycle of cells that have been arrested in G1 by deprivation for serum. In addition, insulin is required by most cells for optimal long term growth in hormone-supplemented serum-free media. In some cells, such as human skin fibroblasts, the growth-promoting effects of insulin appear to be mediated primarily by its low affinity interaction with receptors for insulin-like growth factor I (IGF-I). In other cells, such as hepatocytes, hepatoma cells, adrenocortical tumor cells, mammary carcinoma cells, and F9 embryonal carcinoma cells, insulin appears to stimulate growth by binding to high affinity insulin receptors. The insulin and IGF-I receptor proteins, like the receptor proteins for other growth-promoting hormones such as EGF and PDGF, are closely associated with tyrosine-specific protein kinase activities. The mechanism by which the binding of insulin to its receptor and activation of the receptor-associated tyrosine protein kinase activity control intracellular protein phosphorylation and dephosphorylation reactions, such as the phosphorylation of ribosomal protein S6, is a subject of considerable current interest. The phosphorylation of ribosomal protein S6 may be related mechanistically to the activation by insulin of protein synthesis, and hence the passage of cells through the G1 phase of the cell cycle. Malignant transformation does not generally result in a total loss of the growth requirement of cells for insulin or insulin-like growth factors, although transformation is accompanied in some cases by a qualitative reduction in the insulin/IGF requirement. Abnormalities in insulin production or sensitivity in vivo are accompanied by abnormalities in growth; thus, insulin appears to be an important regulator of growth in vivo. Some of the growth-promoting effects of insulin in vivo may be attributable to direct action of insulin, while other effects may be caused by the regulatory effect of insulin on somatomedin production, and possibly on somatomedin action.

Animals↗
PubMed1983

Insulin-mediated phosphorylation of ribosomal protein S6 in mouse melanoma cells and melanoma x fibroblast hybrid cells in relation to cell proliferation.

The possible role of insulin-mediated phosphorylation of ribosomal protein S6 in the control of cell proliferation was examined in insulin-unresponsive mouse melanoma calls (PG19) and insulin-responsive melanoma x fibroblast clone 100A. In the hybrid cells, under conditions of growth arrest in medium with low serum, ribosomal protein S6 was rapidly phosphorylated in response to insulin or serum. The phosphorylation of the S6 protein increased over a wide range of insulin concentrations, suggesting that insulin stimulated the phosphorylation by interacting with both high- and low-affinity receptors. In contrast, in growth-arrested melanoma cells, an intermediate level of S6 phosphorylation was observed. Insulin caused only a marginal increase and serum caused a small but consistent increase in the level of S6 phosphorylation in the melanoma cells. Cell cycle analysis revealed that both cell lines arrested growth to a similar degree in the G1 phase of the cell cycle; thus, the higher baseline level of S6 phosphorylation observed in the melanoma cells was not attributable to less complete growth arrest of these cells in medium with low serum. The S6 phosphorylation results correlate well with previous results suggesting that the hybrid cells, but not the parental melanoma cells, can become growth-limited for processes regulated by insulin.

Animals↗
PubMed1982

Insulin receptors on cultured murine lymphoid tumor cell lines.

Eight murine lymphoid tumor cell lines have been examined for the presence of high-affinity insulin receptors. The eight cell lines included two Abelson murine leukemia virus-transformed pre-B cell lines, three plasmacytoma cell lines, and three spontaneous T-cell lymphomas from AKR mice. All of the cell lines in the B-cell series had high-affinity insulin binding sites. The apparent equilibrium association constant (Ka) for the high-affinity binding sites on these cells was 1.3-3.3 X 10(9) M-1. Two of the T-cell lymphomas had high-affinity receptor levels so low as to be undetectable in the whole cell binding assay under the conditions used for assaying the other cell lines, although in binding assays performed at very high cell densities, these two cell lines did appear to have a small number of high-affinity insulin binding sites. These results indicate that the growth stimulus provided by the tumor virus in neoplastic transformation of the AKR thymic lymphocytes differs from that provided by lectins in blast transformation of lymphocytes in that the neoplastic transforming event does not always result in the emergence of large numbers of high-affinity insulin receptors. In addition, the existence of cell lines such as the T-cell lymphomas that have nearly exclusively low-affinity binding sites suggests that the low-affinity sites may represent a distinct receptor that is not freely interconvertible with the high-affinity receptor.

Abelson murine leukemia virus↗
PubMed1981

Hitchhiking and linkage disequilibrium between hemoglobin S and nearby restriction sites.

The association of the hemoglobin S mutation with an unusual 13 kb Hpa I restriction fragment has been reexamined using new data and a stochastic model for linkage disequilibrium. In agreement with earlier analyses with deterministic models, the present-day association of the beta S allele with the 13 kb fragment is lower than would be expected if all beta S alleles carried by American blacks were derived from a unique mutation that occurred in the ancestral Bantu population. However, from the stochastic model, if the effective population size was small for an appreciable period during the time that selection has been operating on HbS, then the confidence limits on the allelic association are very large and a unique West African beta S mutation cannot be ruled out from the two locus data alone.

Base Sequence↗
PubMed1980

Growth response to insulin in mouse melanoma cells and fibroblast X melanoma hybrids.

PG19 mouse melanoma cells arrest growth when they become confluent in medium containing low concentrations of serum. Under these conditions, insulin does not stimulate DNA synthesis in the mouse melanoma cells, whereas it does in mouse embryo fibroblasts and fibroblast X melanoma hybrids. A detailed examination of the binding of insulin to the melanoma cells and fibroblast X melanoma hybrids in the presence of bacitracin has shown that they have approximately equal numbers of insulin receptors, and that these receptors have similar affinities for insulin. These results indicate that the unresponsiveness of the melanoma cells to the mitogenic action of insulin is not attributable to a lack of insulin receptors. Although insulin does not stimulate incorporation of 3H-thymidine into DNA in confluent cultures of the melanoma cells, it does stimulate uptake of alpha-aminoisobutyrate, indicating that the insulin receptors are functional and that insulin elicits an acute response in these cells. In hormone-supplemented serum-free medium, insulin does not stimulate growth of the melanoma cells, while it does stimulate growth of th fibroblast X melanoma hybrid. This suggests that an acute response to insulin is not sufficient for stimulation of growth either in confluent growth-arrested cells or in exponentially growing cells in serum-free medium.

Aminoisobutyric Acids↗
PubMed1978

Responsiveness to insulin is a dominant characteristic in somatic cell hybrids.

The mouse melanoma cell line PG19 has been found to be unresponsive to the growth-stimulatory action of insulin, although it responds well to other growth factors present in serum. Insulin stimulates DNA synthesis in mouse embryo fibroblasts, and responsiveness to insulin has been found to be a dominant characteristic in mouse fibroblast x PG19 hybrids. To examine the possibility that the unresponsiveness to insulin of the melanoma cells is attributable to a lack of insulin receptors, we have measured the binding of 125I-labeled insulin to the fibroblasts, melanoma cells, and fibroblast x melanoma hybrids. Insulin binds to the surface of the melanoma cells; however, the binding affinity appears to be lower than that observed for binding to diploid fibroblasts. In addition, the dissociation of insulin from the melanoma cells is not accelerated by excess unbound insulin, a kinetic effect observed in the dissociation of insulin from the fibroblasts and fibroblast x melanoma hybrids. This suggests that the class of insulin receptors characterized by this effect is absent on the PG19 cells, and present on the fibroblasts and fibroblast x PG19 hybrids.

Animals↗
PubMed1977

Growth in vitro of tumour cell x fibroblast hybrids in which malignancy is suppressed.

We have studied the growth in vitro of a lymphoma x fibroblast hybrid and several melanoma x fibroblast hybrids in which malignancy is suppressed. The parental cells, the hybrids, and malignant segregants derived from the hybrids were analysed for serum requirement, cloning efficiency in soft agarose, density-dependent inhibition of growth, and secretion of plasminogen-activating enzyme. One malignant segregant from the lymphoma x fibroblast cross was found by a number of criteria to have a more highly 'transformed' phenotype than the hybrid from which it was derived. However, in the case of the melanoma x fibroblast crosses, none of the parameters examined could be correlated in a direct way with malignancy.

Clone Cells↗
PubMed1975

Selection for a large genetic duplication in Salmonella typhimurium.

Salmonella typhimurium strains containing a duplication of nearly a third of the genome have been isolated by a simple procedure involving selection for improved utilization of L-malate as sole carbon source. The duplication occurs at a very high spontaneous frequency. Strains containing the duplication can be isolated selectively on malate medium, or by a non-selective procedure involving Hfr conjugation. When strains containing the duplication are maintained on non-selective medium, the duplication is readily lost. Genetic evidence suggests that the duplication is chromosomal and tandem. The fact that the recA gene is included in the duplication has been used to obtain evidence that the recA1 marker is recessive to its wild-type allele. Unlike tandem duplications previously described in I. coli, the duplication described in this report appears to have unique endpoints.

Acetates↗
PubMed1974

Induction by mutagens of tandem gene duplications in the glyS region of the Escherichia coli chromosome.

Four mutagens (ultraviolet light, nitrous acid, the acridine half mustard ICR 372, and niridazole) have been found to increase the frequency of tandem gene duplications in the glyS region of the Escherichia coli chromosome. This result was obtained by quantitating the spontaneous and mutagen-induced reversion frequency of a glycyl-tRNA synthetase (glyS) mutant. Following mutagenesis, as many as 0.2% of the survivors were observed to contain duplications in the glyS region. In addition, several classes of stable revertants of the glyS mutant have been identified.

Acridines↗
PubMed1974

Histidine regulation in Salmonella typhimurium. XV. Procedure for the selection of mutants unable to derepress the histidine operon.

A general search has been made for mutants defective in their ability to derepress the histidine operon. The procedure was to select for mutants with an increased sensitivity to the false feedback inhibitor, 2-thiazolealanine. Five mutant strains defective in derepression have been isolated. All five strains are unable to derepress normally because of mutations located in the operator-promoter region of the histidine operon.

Amino Acids, Sulfur↗
PubMed1973

Histidyl-transfer ribonucleic acid synthetase mutants requiring a high internal pool of histidine for growth.

Mutants that require histidine due to an altered structural gene for the histidyl-transfer ribonucleic acid synthetase (hisS) have been isolated by a general selection for histidine-requiring strains in which the mutation producing histidine auxotrophy is unlinked to the histidine operon. One of the mutants has been shown to require an abnormally high internal histidine pool for growth owing to an altered synthetase that is unstable at low histidine concentrations. It is difficult to determine accurately the K(m) for histidine of the synthetase enzyme from the mutant because of the instability of the enzyme at limiting histidine concentrations; however, a histidine K(m) value has been estimated that is approximately 100 times higher than the histidine K(m) of the wild-type enzyme. For the mutant strains to achieve the high internal pool of histidine required for growth, all the systems that transport histidine from the growth medium must be functioning to capacity. Amino acids that interfere with histidine transport strongly inhibit the growth of the mutants. The mutants have been useful in providing a selective genetic marker for transductional mapping in the hisS region. The mutants are discussed as representative of a general class of curable mutants that have an altered enzyme with poor affinity for a substrate or coenzyme.

Amino Acyl-tRNA Synthetases↗