Ionizing Radiation Resistance Research Articles

A cell line selected for resistance to ionizing radiation exhibits cross resistance to other genotoxic agents and a mutator phenotype for loss of heterozygosity events.

An ionizing radiation resistant derivative was obtained from the mouse P19H22 (aprt hemizygote) embryonal carcinoma cell line by repeated exposure to 137Cs gamma radiation. Ionizing radiation resistance in the 6Gy-R cell line was not correlated with a failure to undergo cell cycle arrest or a loss of the p53 response after exposure to 137Cs gamma radiation. Moreover, the cells did not display increased resistance to bleomycin, a double strand break inducing agent. However, the cells did display increased resistance to ultraviolet radiation, ethyl methanesulfonate, and 95% oxygen. A mutational analysis demonstrated a > 700 fold-fold increase in the frequency of aprt mutants for the 6Gy-R cells, but no change in the frequency of hprt or dhfr mutants. A molecular analysis suggested that the aprt mutations in the 6Gy-R cells arose by recombinational events. A possible association between radiation resistance, DNA repair, and a mutator phenotype for large-scale mutational events is discussed.

Radioresistance of Deinococcus radiodurans: functions necessary to survive ionizing radiation are also necessary to survive prolonged desiccation.

Forty-one ionizing radiation-sensitive strains of Deinococcus radiodurans were evaluated for their ability to survive 6 weeks of desiccation. All exhibited a substantial loss of viability upon rehydration compared with wild-type D. radiodurans. Examination of chromosomal DNA from desiccated cultures revealed a time-dependent increase in DNA damage, as measured by an increase in DNA double-strand breaks. The evidence presented suggests that D. radiodurans' ionizing radiation resistance is incidental, a consequence of this organism's adaptation to a common physiological stress, dehydration.

ONCOGENES AND CELLULAR-SENSITIVITY TO RADIOTHERAPY - A STUDY ON MURINE KERATINOCYTES TRANSFORMED BY V-H-RAS, V-MYC, V-NEU, ADENOVIRUS E1A AND MUTANT P53

Mechanisms involved in cellular radioresistance are mostly unknown and may be related to specific genetic alterations. In order to correlate the most frequent oncogenic alterations detected in tumors and ionizing radiation resistance, we studied the effect of irradiation on murine keratinocytes transformed by different oncogenes. Mouse PAM 212 keratinocytes were transformed by transfection or retroviral mediated infection with the oncogenes v-H-ras, v-myc, adenovirus Ela, neu and a mutant p53 (mp53). Cells were gamma irradiated with a Co-60 source. Cell viability was evaluated by the crystal violet method and thymidine uptake and data adjusted to the linear-quadratic model. Surviving fraction 2Gy (SF2) and DO was calculated. Cell cycle study was assessed by incorporation of bromodeoxyridine (BrdUrd) and flow cytometry. p53 protein was studied by Western-blot and apoptosis in DNA agarose gels. The surviving fraction for the different keratinocytes, PAM 212, 212 neo, 212 Ela, 212 v-H-ras, 212 myc, 212 neu and 212 mp53 was 0.79, 0.78, 0.34, 0.82, 0.68, 0.74, and 0.72, respectively. Ela oncogene induced a great sensitivity to irradiation and v-H-ras a mild radioresistance. In flow cytometry, 212 Ela keratinocytes displayed a pronounced and prolonged arrest in G2/M phase. Apoptosis was observed after irradiation only in the 212 Ela keratinocytes. With these results, we conclude that some oncogene products may modulate radiosensitivity in keratinocytes. Mechanisms involved in radiosensitivity mediated by the Ela oncogene seem to be related to p53 protein level, induction of apoptosis and to an irreversible premitotic arrest in G2/M phase, ineffective for repair of DNA damage.

Regulation of Heat and Radiation Stress Responses in Yeast by hsp-104

We have investigated the role of heat-shock protein 104 (hsp-104) in the induction of ionizing radiation resistance in yeast. Yeast defective in the production of hsp-104 are constitutively sensitive to killing by heat and are known to be compromised for the induction of thermotolerance. We confirmed that hsp104 yeast mutants are altered in their ability to become thermotolerant by a heat stress. However, we found that the mutant strain did respond to heat shock and increased its resistance to a second lethal heat stress, although the magnitude of the increase was much lower than for the parental wild-type strain. Here we report that the constitutive level of ionizing radiation resistance was higher in the hsp104 mutant compared to wild-type cells and that heat shock induced increased radioresistance in both strains. When radiation was used as the stressing agent, thermal resistance was fully induced in wild-type cells and only slightly induced in the hsp104 mutant. In comparison, radioresistance was induced in both cell strains by a radiation stress. The increased radiation resistance was always slightly higher in the hsp104 mutant but developed with similar kinetics in both cell strains. Entry into stationary growth phase is another event known to induce both thermal tolerance and radiation resistance in yeast. In these experiments, entry into stationary phase induced similar levels of thermal tolerance in the two strains but higher levels of radioresistance in hsp104 mutants. The activation of both resistance mechanisms occurred earlier in the hsp104 mutants compared to wild-type cells. These results show that hsp-104 is not essential for either the process by which the cell recognizes and responds to any of these stresses, or the mechanisms by which the cell actually elevates its resistance to heat and radiation. We conclude, however, that hsp-104 is important in regulating the development and magnitude of induced radiation resistance as well as induced thermal tolerance in yeast.

Bacterial sensitivity to UV light as a model for ionizing radiation resistance

Six bacterial isolates from the U.S. DOE Subsurface Science Program and three references bacteria were tested for resistance to UV light and gamma radiation. The subsurface isolates included three aerobic, pigmented, Gram positive bacteria and three microaerophilic, non-pigmented, Gram negative bacteria. Deinococcus radiodurans was the most resistant bacterium to both types of radiation, with a D 37 value of 4.0 × 10 4 μWs cm −2 to UV light and 300 krads to gamma radiation. The aerobic subsurface bacteria were found to be significantly more resistant ( p < 0.05) than the microaerophilic subsurface bacteria to UV light and gamma radiation. Due to the similarities of bacterial survival between UV and gamma radiation; it is proposed that UV light could be utilized to model the fate of microorganisms exposed to ionizing radiation.

Sensitivity of Hyperthermia-Treated Human Cells to Killing by Ultraviolet or γ Radiation

Human xeroderma pigmentosum (XP) or Fanconi anemia (FA) fibroblasts displayed shouldered 45 degrees C heat survival curves not significantly different from normal fibroblasts, a result similar to that previously found for ataxia telangiectasia (AT) cells, indicating heat resistance is not linked to either uv or low-LET ionizing radiation resistance. Hyperthermia (45 degrees C) sensitized normal and XP fibroblasts to killing by gamma radiation but failed to sensitize the cells to the lethal effects of 254 nm uv radiation. Thermal inhibition of repair of ionizing radiation lesions but not uv-induced lesions appears to contribute synergistically to cell death. The thermal enhancement ratio (TER) for the synergistic interaction of hyperthermia (45 degrees C, 30 min) and gamma radiation was significantly lower in one FA and two strains (TER = 1.7-1.8) than that reported previously for three normal strains (TER = 2.5-3.0). These XP and FA strains may be more gamma sensitive than normal human fibroblasts. Since hyperthermia treatment only slightly increases the gamma-radiation sensitivity of ataxia telangiectasia (AT) fibroblasts compared to normal strains, it is possible that the degree of thermal enhancement attainable reflects the genetically inherent ionizing radiation repair capacity of the cells. The data indicate that both repair inhibition and particular lesion types are required for lethal synergism between heat and radiation. We therefore postulate that the transient thermal inhibition of repair results in the conversion of gamma-induced lesions to irrepairable lethal damage, while uv-type damage can remain unaltered during this period.

Heat-Shock Induction of Ultraviolet Light Resistance in Saccharomyces cerevisiae

When exponentially growing diploid wild type Saccharomyces cerevisiae cells were subjected to a sudden rise in temperature (heat shock) they responded by increasing their resistance to the lethal effects of ultraviolet light. We have previously reported heat shock-induced increases in heat and ionizing radiation resistance. The shock-induced rise in resistance to uv light reported here was examined in terms of DNA repair capacity, and we find that the increase is due to induction of the recombinational repair system with no significant response from the uv-excision repair process.

Heat-Shock Induction of Ionizing Radiation Resistance in Saccharomyces cerevisiae. Transient Changes in Growth Cycle Distribution and Recombinational Ability

MITCHEL, R. E. J., AND MORRISON, D. P., Heat-Shock Induction of Ionizing Radiation Resistance in Saccharomyces cerevisiae. Transient Changes in Growth Cycle Distribution and Recombinational Ability. Radiat. Res. 92, 182-187 (1982). We have shown previously that a heat shock induces a transient increase in the resistance of wild-type Saccharomyces cerevisiae to the lethal effects of ionizing radiation. This increase was similar to the increase in resistance to thermal killing induced by the same heat shock, but appeared at a slightly earlier time after the temperature increase. We now show that while excision-defective mutants respond like the wild type, recombination-deficient mutants do not display this heat-shock induction of radiation resistance, but still show induction of thermal resistance. The maximum ability for recombinational repair after a heat shock was measured directly (by gene conversion) in wild-type diploids and was found to increase transiently with kinetics very similar to the increase in resistance to the lethal effects of a single dose of radiation. Radiation survival curves of wild-type cells exposed to the elevated temperature were able to resolve two populations of cells on the basis of their sensitivity to ionizing radiation. Following a heat shock, the proportion of resistant cells increased temporarily in parallel with the increase in radiation resistance. We conclude that heat-shock induction of radiation resistance in wild-type diploid yeast results from at least two changes, an increase in recombinational repair capacity, possibly associated with G1 cells, and a shift in population distribution to a higher fraction of resistant cells. We further conclude that heat-shock induction of thermal resistance proceeds by an independent mechanism.

Heat-Shock Induction of Ionizing Radiation Resistance in Saccharomyces cerevisiae, and Correlation with Stationary Growth Phase

Radiation resistance and thermal resistance vary as a function of culture temperature in logarithmically growing Saccharomyces cerevisiae and are related to the optimum temperature for growth. Radiation resistance and thermal resistance were also induced when cells grown at low temperatures were subjected to a heat shock at or above the optimum growth temperature. Exposure to ionizing radiation followed by a short incubation at low temperature also induced resistance to killing by heat. Heat-shocked cells are induced to a level of thermal and radioresistance much greater than the characteristic resistance level of cells grown continuously at the shock temperature. This high level of resistance, which resembles that of stationary-phase cells, decays to the characteristic log-phase level within one doubling of cell number after the heat shock. Both induction of resistance and decay of that induction require protein synthesis. It is postulated that induction of resistance by heat shock or ionizing radiation is a response of the cells to stress and represents a preparation to enter stationary phase.

Iron-Induced Pigment Formation and Ionizing Radiation Resistance in Three Strains of Micrococcus violagabriellae

Three strains of Micrococcus violagabriellae-Littlepig, Pig (Parental), and Superpig--were studied. The pulcherrimin pigment (which imparts a violet-red color to the colonies of the Parental and Superpig strains) is produced only when the cells are grown in the presence of excess iron and provides a unique system for the study of the radioprotection conferred by a pigment. Cell suspensions of each of the three strains (initially grown in the presence and in the absence of excess iron) were exposed to gamma rays and plated on media containing an excess of iron and on media without iron. The survival curves of the treated strains indicate a correlation between the color intensity of the pigment (pulcherrimin), and the ability of the organisms to survive moderate doses of ionizing radiation. Studies using radioactive iron (59Fe) showed that a correlation also exists between the intensity of the pigment and the amount of iron that the cells of each strain can remove from the medium. The effect of gamma irradiation on postirradiation cell growth is discussed for each strain irradiated during logarithmic growth and during a stationary state.