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J Borsa

Publications and source records attributed to J Borsa.

At least 37 records · Page 2Linked to original sources
PubMed1984

Effects of Ca2+ and Mg2+ on the switch-on of transcriptase function in reovirus in vitro.

Effects of Ca2+ and Mg2+ on the "switch-on" of transcriptase function in reovirus intermediate subviral particles were examined. Switch-on in this system is triggered by K+ ions, whereas Na+ ions antagonize the effects of K+ ions. Once effected, switch-on is irreversible. In the absence of Ca2+ and Mg2+ ions, switch-on of transcriptase is effected by incubation at 37 degrees C in the presence of a particular ratio of K+/Na+ (total K+ plus Na+ being kept constant). Inclusion of Ca2+ in the activation step lowers the ratio that triggers the switch-on event. This indicates that Ca2+ destabilizes the switched-off state of the transcriptase. Inclusions of Mg2+ ions in the activation step raises the K+/Na+ ratio necessary to trigger switch-on. Thus Mg2+ tends to stabilize the switched-off state of the transcriptase to the triggering action of K+ ions. Inclusion of both Ca2+ and Mg2+ together during the activation step results in mutual inhibition of the effects expected from each divalent cation alone. These results indicate that switch-on of transcriptase function, which is triggered by K+ ions, can be modulated by interactions involving the major physiological cations (Na+, K+, Mg2+, Ca2+).

Calcium↗
PubMed1984

Inhibition of DMSO-induced differentiation by hyperthermia in a murine erythroleukemia cell system.

Friend erythroleukemia cells were induced by dimethyl sulfoxide (DMSO) into erythroid differentiation, as characterized by the production of hemoglobin. Induction increased with DMSO concentrations up to 1.5% v/v, at which point about 90% of the cell population produced hemoglobin as measured by a benzidine-staining technique. Heat treatment at 39.0-40.5 degrees C during a 7-day-incubation period, for differentiation in the presence of DMSO, resulted in the inhibition of hemoglobin induction. Also, acute heat treatments at 41.5-46.0 degrees C before or after the addition of DMSO resulted in the inhibition of DMSO induction. This effect was greatest when DMSO was present during heating. The results support the conclusion that hyperthermia inhibits the differentiation process which is induced by DMSO treatment.

Animals↗
PubMed1984

Effects of oxygen and misonidazole on cell transformation and cell killing in C3H 10T1/2 cells by X rays in vitro.

The effects of oxygen (air) and misonidazole on the transformation and killing of 10T1/2 cells by X rays were examined. The oxygen effect for the cell transformation end point was very similar to that for cell killing. Misonidazole enhanced both cell killing and cell transformation to a similar extent. The enhancement of both end points by misonidazole occurred only in the absence of oxygen during irradiation and was of lesser magnitude than that observed for oxygen. These results demonstrate that the radiation chemical processes leading to cell killing and cell transformation, respectively, are affected similarly by these two enhancers of radiation action.

Aerobiosis↗
PubMed1984

Variation of radiation sensitivity of Friend erythroleukemia cells cultured in the presence of the differentiation inducer DMSO.

Differentiation of Friend erythroleukemia cells (FELC) was induced with 1.5% dimethyl sulfoxide (DMSO) in the culture medium. Cell growth, erythroid differentiation, and radiosensitivity of the proliferative capacity of the cells were measured and compared to a noninduced control culture of identical age. Induced cells first appeared on Day 2 after DMSO addition, and increased to a maximum of 80 to 90% of the cell population on Day 5, whereas in the control culture, induction was less than 2% of the cells. Radiosensitivity of the cells in the induced culture, relative to that of cells in the control culture, showed an age-dependent variation. On Days 1 and 2 after DMSO addition, the cells in the induced culture were more radiosensitive than those in the control culture. At later times this relationship was reversed, and between Days 3 and 5 the clonable cells in the induced culture were less radiosensitive than those in the control culture. These results suggest that the metabolic events associated with commitment of FELC to differentiate affect their ability to cope with the radiation-induced lesions underlying the loss of division capacity.

Animals↗
PubMed1984

Modification by anisotonic treatment of repair and fixation of radiation damage in cell killing and transformation.

Anisotonic treatment of V79 cells after irradiation resulted in extensive fixation of potentially lethal damage (PLD). Fixation of PLD occurred more rapidly when treated with 1.5 mol l-1 NaCl than with 0.05 mol l-1 NaCl. These effects were further enhanced when cells were held at 0 degree C instead of 37 degrees C during irradiation. When the X-ray (10.0 Gy) and salt treatments were separated by incubation at 37 degrees C, survival increased rapidly by a factor of 2000, while repair of PLD in cells held in a plateau phase after X-rays (10.0 Gy) caused survival to increase four-fold. The data indicate that these mammalian cells sustain and repair a much larger amount of PLD than is measured by the conventional method of holding cells in a non-progressing state after irradiation. Radiation sensitivity in cells was modified by BrdUrd incorporation into cellular DNA or exposure to DMSO during irradiation. For these cells, fixation of damage by post-irradiation anisotonic treatment proceeded at the same rate for BrdUrd-treated cells, and at a diminished rate for DMSO-treated cells, compared with cells irradiated in the absence of these compounds. In C3H-10T 1/2 cells, post-irradiation anisotonic treatment (with 0.05 or 1.5 mol l-1 NaCl) also resulted in fixation of PLD and a rapid recovery when the X-ray and salt treatments were separated by incubation at 37 degrees C. Treatment with 0.05 or 1.5 mol l-1 NaCl solutions immediately after irradiation also resulted in elevated transformation frequencies, which increased with exposure time to anisotonic solutions.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1983

Hyperthermia in a differentiating murine erythroleukemia cell line: cell killing by heat and radiation.

The survival response of Friend erythroleukemia cells (a differentiating cell system) to heat and radiation has been examined. The Friend erythroleukemia cells (FELC) were more heat and radiation sensitive than V79 cells, and the heat and radiation survival curves possessed shoulders, showing the ability of the cells to accumulate sublethal damage. Thermal tolerance was expressed after prolonged heating at 41.0-42.0 degrees C. Thermal radiosensitization by heating at 42.0 or 45.0 degrees C was greatest for simultaneous heat and radiation treatments, and recovery occurred when the cells were incubated at 37 degrees C between the heat and radiation or radiation and heat treatments. Arrhenius analysis of the FELC heat survival data showed that the curve for thermal inactivation possessed a break at about 43.0 degrees C and that the thermal inactivation energies above and below the break point were comparable to those for V79 cells and other cell lines reported in the literature.

Animals↗
PubMed1983

Hyperthermia in a differentiating murine erythroleukaemia cell line: II. Effect of heat on haem induction by radiation.

Friend erythroleukaemia cells (FELC) were induced to a haem-producing state by X-rays. The percentage of haem positive cells was maximum for doses between 10 and 15 Gy. Heat treatment at 42.0 degrees C or 45.0 degrees C during or after irradiation inhibited haem induction whereas heating before irradiation enhanced it. Incubation at 37 degrees C between heating and irradiation resulted in a decline in induction levels, indicating repair of heat damage that interacts with X-ray damage. Incubation at 37 degrees C between irradiation and heating did not result in changed haem induction levels, indicating a lack of repair of radiation damage that could interact with subsequent damage produced by heating.

Animals↗
PubMed1982

Perturbation of the switch-on of transcriptase activity in intermediate subviral particles from reovirus.

Intermediate subviral particles (ISVP) derived from reovirus represent a simple model system for the switch-on of transcriptase function. In such particles the endogenous transcriptase is present in a switched-off form, one step removed from the switched-on state. Switch-on of transcriptase function is an active process in this system and can be triggered by K+ions. A variety of agents which affect gene expression in cells were tested for an effect on switch-on in ISVP. Marked effects on switch-on in ISVP were observed with a diverse group of test agents, including DMSO and other solvents, BUdR, TdR, caffeine, theophylline, and temperature. The correlation in response between ISVP and cells suggests that the ISVP system may be useful as a model for studying the biochemical mechanisms underlying the perturbative effects of such agents on gene expression in cells.

Animals↗
PubMed1982

Radiobiology of a differentiating cell system in vitro.

Friend erythroleukaemia cells (FELC) in vitro were used to examine the effects of ionizing radiation on differentiation and proliferation of mammalian cells. Results suggest that X-rays can affect differentiation in two different ways. First, X-rays inactivate the ability of these cells to respond to an external trigger of differentiation, e.g., dimethyl sulphoxide. Second, X-rays themselves trigger a partial differentiation response, in the absence of any other external trigger. The radiation-induced lesions leading to these two end-points are not repaired in split-dose experiments, unlike those lesions which lead to loss of cell proliferative capacity. The profile of soluble FELC proteins, as analysed by isoelectric focusing, was also affected by irradiation. These effects of ionizing radiation on the expression of genetic information in mammalian cells have important implications for radiobiology, particularly at low doses where acute lethal effects are minimal.

Animals↗
PubMed1979

Two modes of entry of reovirus particles into L cells.

Evidence is presented supporting the hypothesis that reovirus intermediate subviral particles (ISVP), which show increased infectivity relative to intact virions, can gain entry into host L cells by two alternative pathways. One pathway is by the process of viropexis, involving phagocytic vacuoles. A second entry pathway is via direct penetration of the plasma membrane of the cell, without involvement of a phagocytic vacuole. Using electron microscopy, a kinetic analysis of the uptake process was carried out. Results indicate that at 37 degrees C ISVP gain entry into host cells primarily by direct entry, although viropexis also occurs, while intact virions gain entry by viropexis almost exclusively. A second line of experimental evidence consistent with the idea that ISVP can 'melt' their way through the plasma membrane is provided by studies on the release of pre-loaded radioactive 51Cr from host cells following infection. 51Cr release data demonstrate that infection with ISVP leads to an immediate increased leakiness of the cell plasma membrane, whereas no such increase takes place following infection with an equivalent number of intact virions. This demonstrates that ISVP can interact with the plasma membrane of the cell in a manner which is qualitatively different from the interaction between intact virions and the plasma membrane. The ability of ISVP to directly penetrate the plasma membrane of the host cell, which intact virions apparently cannot do, could explain the decreased duration of the eclipse phase, as well as the increased infectivity of ISVP, relative to that observed for infection with intact virions.

Adsorption↗
PubMed1979

Ionizing radiation perturbs the switch-on of transcriptase in a model transcription complex in vitro.

Ionizing radiation markedly alters the response of the reovirus transcriptase unblocking mechanism to stimulation by K+ ions, which normally trigger the switch-on of transcription in this system. In irradiated subviral particles the concentration of K+ ions needed to trigger switch-on is reduced in a dose-dependent way. The observed alteration of switch-on characteristics appears to correlate with alteration of the electrophoretic behaviour of a single major polypeptide species. These observations have important implications for understanding some of the effects of ionizing radiation on cells, most notably the induction of both latent virus and cell differentiation.

DNA-Directed RNA Polymerases↗
PubMed1976

Circular dichroism of intermediate subviral particles of reovirus. Elucidation of the mechanism underlying the specific monovalent cation effects on uncoating.

1. Circular dichroic (CD) spectra of purified intermediate subviral particles of reovirus were determined in the presence of different monovalent cations. 2. The CD spectra reveal that reo intermediate subviral particles can exist in two conformationally different forms. The two forms are readily distinguished by comparison of their ellipticities in the wavelength regions 210 nm and 220 nm, with a Na+-induced form exhibiting a reduced negative ellipticity relative to a Cs+-induced form. 3. The transition between the Na+- and Cs+-induced forms is reversible by manipulation of the species of monovalent cation present and appears to be temperature independent. 4. Temperature variation studies on dilute suspensions of particles indicate that the Na+-induced form is stable, whereas the Cs+-induced from undergoes a second transition, temperature dependent and irreversible, to become a viral core. 5. A model is presented relating these observations to the known properties of reovirus uncoating and transcriptase activation.

Cesium↗