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Biomedical subjects

S Shall

Publications and source records attributed to S Shall.

At least 73 records · Page 4Linked to original sources
PubMed1983

A quantitative analysis of the aging of human glial cells in culture.

The kinetics of aging of normal human diploid brain cells in culture have been determined using the miniclone technique in which cells are cloned in the presence of a large number of other cells. The miniclone technique records the behaviour of every viable cell in the sample, not merely those cells capable of forming visible clones. This technique permits the direct measurement of the reproductive potential of individual cells growing in bulk culture and of the dispersion of the sizes of colonies generated by dividing cells. The fraction of cells that are able to divide declines smoothly and continuously from the beginning of in vitro cultures of human glial cells. There is a broad distribution of colony sizes; even at the earliest passages there are significant numbers of small colonies. With increasing age of the culture there is a shift in the distribution, so that fewer large colonies and more small colonies occur. The distribution of intermitotic times is almost identical in young and middle-aged cultures. Our data seem to exclude quite positively any description in terms of a catastrophe or any abrupt change in the population. On the contrary, the decline in reproductive potential may be described adequately either as a linear change with time, or as predicted by the mortality theory of Shall and Stein (1979), in which the single constant, gamma, describes the change in reproductive potential over the entire lifetime.

Adult↗
PubMed1983

Direct radioactive labelling of poly(ADP-ribose) in developing Xenopus laevis embryos.

It has not previously been possible to label the nuclear protein modification poly(ADP-ribose) directly from NAD because of the impermeability of the cell membrane. We have overcome this important problem by micro-injection of radioactively labelled NAD into Xenopus laevis early embryos. The polymer was identified and then quantified by its insensitivity to DNAase, RNAase, and spleen phosphodiesterase and by the chromatographic mobility of the products of digestion with snake-venom phosphodiesterase. The quantity of poly(ADP-ribose) present after 25 h of development (129 ng/mg DNA) is lower than that found in fully differentiated tissue.

Animals↗
PubMed1983

ADP-ribosylation, DNA repair, cell differentiation and cancer.

This review discusses the potential relationships between ADP-ribosylation reactions, DNA repair, cell differentiation, and cancer. ADP-ribosylation of chromatin proteins has been shown to participate in DNA excision repair in all nucleated cells. ADP-ribosylation of chromatin proteins is catalysed by nuclear ADP-ribosyl transferase (ADPRT). This enzyme is entirely dependent on DNA for its activity because it has an absolute requirement for ends or nicks in double-stranded DNA. Exposure of cells to small alkylating agents or to radiation causes a fall in cellular NAD+ levels due to a transient activation of ADPRT and a consequent ADP-ribosylation of chromatin proteins. Inhibitors of ADPRT retard DNA strand-rejoining induced by radiation or by small alkylating agents; such inhibition has at least two biological consequences; a synergistic potentiation of cytotoxicity and an enhancement of sister chromatid exchanges and chromosomal aberrations. No species differences have yet been reported; there are variations between cell types and between different damaging agents. The enzyme inhibitors do not block early steps in DNA repair, and repair synthesis does not require ADPRT activity. DNA damage increases the activity of both DNA polymerase beta and DNA ligase II. The activation of DNA ligase II can be blocked by ADPRT inhibitors; presumably ADPRT activity is required for the activation of DNA ligase II. A plausible molecular explanation for the function of ADPRT in DNA repair is that ADPRT regulates the activity of DNA ligase II, the "non-replicative" ligase. In addition to its function in DNA repair, ADPRT is an obligatory requirement in certain categories of cell differentiation. Inhibitors of ADPRT and nicotinamide starvation both reversibly block cell differentiation. We suggest that a similar mechanism to that of DNA repair may be involved because we observe 100 to 300 single-strand DNA breaks during the cytodifferentiation of primary chick myoblasts. These breaks are not due to a general deficiency in DNA repair. I suggest that in certain categories of cell differentiation there are rearrangements or transpositions within the mammalian genome, and that ADP-ribosylation reactions have a general function to be sensitive to DNA breaks and to regulate subsequent DNA ligation in DNA repair, in DNA recombination, in sister chromatid exchanges, in chromosome aberrations, in gene rearrangements, in transpositions and in certain categories of cell differentiation. The relevance of these observations and ideas to cancer is discussed.

Adenosine Diphosphate Ribose↗
PubMed1982

Evidence that poly(ADP-ribose) polymerase is involved in the loss of NAD from cultured rat liver cells.

Rat hepatocytes cultured from 24h lose 60% of their NAD content. By using the differential response to inhibitors of the two major enzymes that catabolize NAD in mammalian cells, it is shown that poly(ADP-ribose) polymerase is responsible for the loss of NAD. The relevance of this observation to the use of cultured hepatocytes for the study of DNA repair induced by carcinogens is discussed.

Animals↗
PubMed1982

Studies on autoantibodies to poly (adenosine diphosphate-ribose) in SLE and other autoimmune diseases.

Sera from 41 patients with systemic lupus erythematosus (SLE), 87 controls with various diseases, and 30 normal subjects were examined for poly (adenosine diphosphate-ribose) and ds DNA binding. Elevated levels of poly (ADP-ribose) binding were found in 73% of the SLE patients compared with 58% who had raised ds DNA binding. In a further study of 160 sera from 27 patients with SLE, levels of antipoly (ADP-ribose) antibodies were shown to correlate with clinical activity better than either anti-ds DNA or ss DNA antibodies.

Adult↗
PubMed1981

The effect of inhibition of (ADP-ribose)n biosynthesis on DNA repair assayed by the nucleoid technique.

DNA damage and repair was assayed by the loss and restoration of DNA supercoiling in nucleoids. This technique was used to assess the effects of inhibition of (ADP-ribose)n biosynthesis by 3-aminobenzamide on the capacity to repair DNA of mouse leukaemia L1210 cells following damage by gamma-irradiation and by the monofunctional alkylating agent, dimethyl sulphate. 3-Aminobenzamide partially inhibits restoration of supercoiling following gamma-irradiation and dimethyl sulphate treatment, but inhibits neither the enzymic incision events leading to breaks in the DNA nor the repair synthesis. This inhibition of repair can be observed at very low doses of damaging agents. These observations confirm and extend the evidence that (ADP-ribose)n biosynthesis is required for efficient cellular recovery from DNA damage. In particular, the nucleoid technique permits the demonstration that 3-aminobenzamide inhibits DNA repair after gamma-radiation; it is not possible to draw this unequivocal conclusion with the data from alkaline sucrose gradients because this technique is too insensitive. 1-beta-D-Arabinofuranosylcytosine, which inhibits semiconservative DNA replication, also retards repair, and this effect can be reversed by the addition of deoxycytidine. The inhibitors of DNA excision repair, arabinosylcytosine, hydroxyurea or 3-aminobenzoamide increase the steady-state number of DNA breaks. Thus, they can be used to enhance even further the sensitivity of the nucleoid assay of repair.

Adenosine Diphosphate Ribose↗
PubMed1980

Isolation of chromosomal origins of replication in yeast.

Origins of replication have been identified in the DNA of viruses, mitochondria, bacterial plasmids and the bacterial chromosome. However, origins of replication of eukaryote chromosomes have remained elusive because of the large size and sequence complexity of chromosomes and in particular for want of a suitable assay for their detection. Recent development of techniques for genetic transformation of yeast by autonomously replicating cytoplasmic plasmids now makes it possible to search for eukaryote origins in a manner analogous to that used for bacteria. Here we describe the construction and properties of a plasmid which contains no effective eukaryote replication origin and whose efficiency of replication in yeast is greatly enhanced by insertion of certain fragments of yeast chromosomal DNA. We believe these to contain replication origins, since yeast transformants are shown to contain copies of the transforming plasmids.

Base Sequence↗
PubMed1980

(ADP-ribose)n participates in DNA excision repair.

Chromatin proteins are covalently modified by at least five different processes; in no case has the precise physiological function been established. One of these post-synthetic, covalent modifications is effected by the enzyme poly(ADP-ribose) polymerase, which uses the coenzyme NAD+ to ADP-ribosylate chromatin proteins. The modification consists largely of mono(ADP-ribose), but long, homopolymer chains of (ADP-ribose) are also present. Various physiological functions have been suggested for (ADP-ribose)n. Here we demonstrate that one function of (ADP-ribose)n is to participate in the cellular recovery from DNA damage. Specific inhibitors of poly(ADP-ribose) polymerase prevent rejoining of DNA strand breaks caused by dimethyl sulphate and cytotoxicity is enhanced thereby. The rejoining of strand breaks is prevented also by nutritionally depleting the cells of NAD.

ADP Ribose Transferases↗
PubMed1980

The enhancement of cytotoxicity of N-methyl-N-nitrosourea and of gamma-radiation by inhibitors of poly(ADP-ribose) polymerase.

Inhibitors of poly(ADP-ribose) polymerase show a synergistic potentiation of cytotoxicity with certain DNA-damaging agents. Non-toxic concentrations of 5-methylnicotinamide dramatically potentiate the cytotoxicity of N-methyl-N-nitrosourea as tested by the cloning ability of mouse leukaemia (L1210) cells. A dose-enhancement factor of about 10 is observed. This potentiation is dependent on the concentration of 5-methylnicotinamide. The methylxanthines theobromine, theophylline and caffeine also increase the cytotoxicity of methylnitrosourea. Thymidine, in the presence of sufficient deoxycytidine to overcome the perturbation of deoxynucleotide metabolism, also potentiates the cytotoxicity of methylnitrosourea. Nicotinate, which is not an inhibitor of poly-(ADP-ribose) polymerase, has no effect on methylnitrosourea toxicity. A very small, but consistent, enhancement of the toxicity of gamma-radiation by the same inhibitors has been observed. We suggest that this potentiation of cytotoxicity is mediated by inhibition of (ADP-ribose)n biosynthesis; and that the biosynthesis is stimulated by DNA damage. We therefore propose that (ADP-ribose)n takes part in cellular repair mechanisms, either by modifying chromatin structure or by a specific participation in DNA repair.

Animals↗