@article{allio_donner_preston_2000, title={A comparison of the roles of p53 mutation and AraC inhibition in the enhancement of bleomycin-induced chromatid aberrations in mouse and human cells}, volume={447}, ISSN={["0027-5107"]}, DOI={10.1016/S0027-5107(99)00212-2}, abstractNote={Previous studies have shown that p53 is involved in the repair of bleomycin-induced DNA damage, and that the frequency of bleomycin-induced chromatid aberrations is elevated in G2-treated p53 null transgenic mouse embryo fibroblasts (MEF) as compared to isogenic controls. To further characterize p53-mediated DNA repair, we studied the effect of p53 status on the ability of the DNA repair inhibitor 1-ß-d-arabinofuranosylcytosine (AraC) to sensitize MEF to bleomycin-induced chromatid aberrations. Both p53+/+ and p53−/− MEF were treated in G2 with 0 to 7.5 μg/ml bleomycin in the presence or absence of AraC (5×10−5 M). The frequency of bleomycin-induced chromatid aberrations was significantly higher in p53−/− cells than wild-type cells in the absence of AraC. AraC treatment significantly increased the frequency of bleomycin-induced chromatid aberrations in p53+/+ MEF to the levels in p53−/− (no AraC) but had no effect in p53−/− MEF. These results suggest that an AraC-sensitive DNA repair component is altered or absent in p53−/− cells. Similar results were observed in p53-mutant WTK1 and wild-type TK6 human lymphoblast cells exposed to 0 to 3 μg/ml bleomycin in G2. However, AraC did cause a small increase in bleomycin sensitivity in WTK1 cells. This difference from the p53−/− MEF response may be due to differences in p53-mutant phenotype. To determine whether mutation of p53 alters DNA replication fidelity, p53+/+ and p53−/− MEF were exposed to 0 to 1 μg/ml mitomycin C (MMC). MMC did not induce chromosome aberrations in either cell line treated in G2 but did with the same effectiveness in both cell lines treated in S-phase. Thus, p53 deficiency does not affect DNA replication fidelity or the repair of MMC-induced DNA damage.}, number={2}, journal={MUTATION RESEARCH-FUNDAMENTAL AND MOLECULAR MECHANISMS OF MUTAGENESIS}, author={Allio, T and Donner, EM and Preston, RJ}, year={2000}, month={Feb}, pages={227–237} }
 @article{allio_preston_2000, title={Increased sensitivity to chromatid aberration induction by bleomycin and neocarzinostatin results from alterations in a DNA damage response pathway}, volume={453}, ISSN={["0027-5107"]}, DOI={10.1016/S0027-5107(00)00030-0}, abstractNote={DNA damage response pathways coordinate the cellular response to DNA damage. To investigate the roles of tumor suppressor genes in these pathways, human lymphoblastoid cells (wild-type, p53-/-, ATM-/-) were treated for 1 h with 0-3 microg/ml of the radiomimetic compound bleomycin (BLM), and cells treated in G(2) were analyzed for chromatid aberrations. BLM-induced aberration frequencies were significantly increased, to the greatest extent in the ATM-/- cells and, to a lesser extent, in the p53-/- cells compared to wild-type cells. These observations are consistent with p53 and ATM acting in a damage response pathway activated by DNA strand breaks. The consequences of disrupting this pathway were further investigated by studies using wortmannin, a PI-3 kinase and DNA repair inhibitor. Wortmannin significantly increased the BLM-induced aberration frequencies in all but the ATM-/- cells, elevating the sensitivity of p53-/- cells to ATM-/- levels and that of wild-type cells to intermediate levels. These differential sensitivities suggest that the ATM phenotype is the result of dual cellular defects, one involving p53 and the other a wortmannin-sensitive component. Similar studies in Brca1+/- and Brca2+/- human lymphoblasts showed no increased sensitization to BLM in the absence of inhibitor, and differential sensitization by wortmannin. To determine if there was any substrate specificity for p53- and ATM-mediated DNA damage responses, chromatid aberrations were assessed in wild-type, p53-/-, and ATM-/- cells exposed to 0-0.4 microg/ml neocarzinostatin (NCS) for 1 h. In contrast to results with BLM, the p53-/- cells exhibited a low sensitivity to NCS-induced aberrations, similar to wild-type, while ATM-/- cells remained highly sensitive. This suggests that the response to BLM- and NCS-induced lesions involves different mechanisms.}, number={1}, journal={MUTATION RESEARCH-FUNDAMENTAL AND MOLECULAR MECHANISMS OF MUTAGENESIS}, author={Allio, T and Preston, RJ}, year={2000}, month={Sep}, pages={5–15} }
 @article{gonzales_christensen_preston_goldsworthy_tlsty_fox_1998, title={Attenuation of G(1) checkpoint function by the non-genotoxic carcinogen phenobarbital}, volume={19}, ISSN={["0143-3334"]}, DOI={10.1093/carcin/19.7.1173}, abstractNote={Non-genotoxic chemical carcinogens are capable of inducing tumors in rodents without interacting with or directly altering the genetic material. Since a preponderance of evidence suggests that cancer results from the accumulation of genetic alterations, the mechanisms by which many non-genotoxic carcinogens induce genotoxic events remain unclear. The present study investigated whether the mitogenic, non-genotoxic carcinogen phenobarbital (PB) could alter cell-cycle checkpoint controls, thereby indirectly leading to the accumulation of genetic damage. Initial studies involved characterizing cell-cycle checkpoint responses to DNA damage in freshly isolated B6C3F1 mouse hepatocytes. These cells responded to bleomycin-induced DNA damage by arresting in G1 and G2. Cell-cycle arrest was coupled with p53 protein induction; however, p21WAF1 protein levels remained unchanged. Studies that utilized hepatocytes isolated from C57BL p53-/- mice showed that the DNA damage-induced G1 cell-cycle arrest was dependent on p53 function, but cell-cycle arrest in G2 was not affected by loss of p53. PB was able to delay and attenuate the G1 checkpoint response without altering G2 checkpoint function. A reduction in p53 protein, but not transcript levels, was observed in hepatocytes exposed to PB. Additionally, PB delayed and attenuated p53 protein induction during DNA damage, which suggests that changes in the p53 protein may be contributing to the attenuated G1 checkpoint response caused by PB. Altered G1 checkpoint function represents an epigenetic mechanism by which phenobarbital may prevent the detection and repair of DNA damage and indirectly increase the frequency of genotoxic events above that occurring spontaneously. Abrogation of checkpoint controls may, thus, play an important mechanistic role in mitogenic, non-genotoxic chemical carcinogenesis.}, number={7}, journal={CARCINOGENESIS}, author={Gonzales, AJ and Christensen, JG and Preston, RJ and Goldsworthy, TL and Tlsty, TD and Fox, TR}, year={1998}, month={Jul}, pages={1173–1183} }