Heat shock does not induce γH2AX foci formation but protects cells from N-methyl-N′-nitro-N-nitrosoguanidine-induced genotoxicity

DNA damage response and apoptosis induced by hyperthermia in human umbilical cord blood lymphocytes

While hyperthermia (HT) is a promising modality for cancer treatment, the knowledge on mechanisms of its effect on cells is still limited. We have investigated DNA double-strand break (DSB) and apoptosis induced by HT. Umbilical cord blood lymphocytes (UCBL) were subjected to HT at 43 °C. We have treated cells for 1 h (1 h HT), 2 h (2 h HT) and by combined HT and ice treatment (both lasting 1 h). Enumeration of DSB by 53BP1/γH2AX DNA repair focus formation and early apoptosis by γH2AX pan-staining was conducted by automated fluorescent microscopy. Apoptotic stages and viability were assessed by the annexin/propidium iodide (PI) assay using flow cytometry 0, 18, and 42 h post-treatment. HT induced either immediate (2 h HT) or postponed (1 h HT) DNA damage. The levels of 53BP1 and γH2AX foci differed under the same treatment conditions, suggesting that the ratio of co-localized γH2AX/53BP1 foci to all γH2AX and also to all 53BP1 foci could be a valuable marker. The ratio of co-localized foci increased immediately after 2 h HT regardless the way of assessment. For the first time we show, by both annexin/PI and γH2AX pan-staining assay that apoptosis can be induced during or immediately after the 2 h HT treatment. Our results suggest that HT may induce DSB in dependence on treatment duration and post-treatment time due to inhibition of DNA repair pathways and that HT-induced apoptosis might be dependent or associated with DSB formation in human lymphocytes. Assessment of γH2AX pan-staining in lymphocytes affected by HT may represent a valuable marker of HT treatment side effects.

Micronuclei formation in rainbow trout cells exposed to multiple stressors: Morpholine, heat shock, and ionizing radiation

Discharges from industrial cooling water systems can include low levels of morpholine (a chemical pH regulator and corrosion inhibitor), as well as transiently higher temperature effluent water which present a potential source of environmental impact to aquatic biota. The effects of environmental levels of morpholine or heat shock (HS) treatment alone and in combination with a challenge high-dose of ¹³⁷Cs ionizing radiation were studied using the cytokinesis block micronucleus assay in a rainbow trout cell line (RTG-2). Morpholine treatment of 10 or 100mgL^-1 alone produced no significant effects, and no interaction was observed in combination with 7.75Gy radiation. A 9°C magnitude HS treatment alone significantly increased micronuclei formation. A synergistic response was observed when 9°C HS was combined with 7.75Gy radiation, with 15% more cells containing 3 or more micronuclei than the sum of each individual stressor. A synergistic increase in the average number of micronuclei was observed when morpholine and a 9°C HS were co-treated. These results indicate that morpholine at environmentally-relevant levels does not impact micronuclei formation or cell cycle progression however 9°C HS may be of potential concern both alone and in combination with other stressor treatments.

Nuclear proteome analysis of cisplatin-treated HeLa cells

Cisplatin has been widely accepted as one of the most efficient anticancer drugs for decades. However, the mechanisms for the cytotoxic effects of cisplatin are still not fully understood. Cisplatin primarily targets DNA, resulting in the formation of DNA double strand breaks and eventually causing cell death. In this study, we applied two-dimensional electrophoresis coupled with LC-MS/MS to analyze the nuclear proteome of HeLa cells treated with cisplatin, in an effort to uncover new mechanistic clues regarding the cellular response to cisplatin. A total of 19 proteins were successfully identified, and these proteins are involved in a variety of basal metabolic and biological processes in cells, including biosynthesis, cell cycle, glycolysis and apoptosis. Six were related to the regulation of mRNA splicing, and we therefore asked whether the Fas gene might undergo alternative splicing following cisplatin treatment. This proved to be the case, as the splicing forms of Fas were modified in cisplatin-treated HeLa cells. This work provides novel information, from the perspective of the nuclear response, for understanding the cytotoxicity caused by cisplatin-induced DNA damage.

Heat induces gammaH2AX foci formation in mammalian cells

H2AX is a histone variant which is present and ubiquitously distributed throughout the genome. An immunocytochemical assay using antibodies capable of recognizing histone H2AX phosphorylated at serine 139 (gammaH2AX) is very sensitive and is a specific indicator for the existence of a DNA double strand break. Although heat stress has been reported to induce the formation of gammaH2AX foci, no gammaH2AX foci formation was observed in several mammalian cell lines after heat shock. Since this was in contrast to earlier reports, the work described here was intended to verify that heat-induced gammaH2AX foci do form in mammalian cell lines other than the cell lines used in earlier reports concerning gammaH2AX foci formation. The cell lines used in this work includes cell lines with differing p53-gene status (H1299, H1299/neo, H1299/mp53 and H1299/wtp53 cells), various cancer cell lines (HeLa, HepG2, U2-OS cells), normal human cells (HEK-293 and AG1522), and cell lines established from other species (MEF normal mouse cells and CHL normal Chinese hamster cells). Exponentially growing cells were exposed to heat shock (42 degrees C for 6 h or 45.5 degrees C for 20 min) or to X-rays (3Gy). The presence of gammaH2AX was examined with immunocytochemistry and flow cytometry. Induction of gammaH2AX foci formation was observed in all of the mammalian cell lines used here after heat-treatment as well as after X-irradiation. However, the intensity of gammaH2AX was different in the different cell lines used. These results confirm that heat can induce gammaH2AX foci formation in many mammalian cell lines.

Mycoplasma pneumoniae infection induces reactive oxygen species and DNA damage in A549 human lung carcinoma cells

Mycoplasma pneumoniae is a frequent cause of community-acquired bacterial respiratory infections in children and adults. In the present study, using a proteomic approach, we studied the effects of M. pneumoniae infection on the protein expression profile of A549 human lung carcinoma cells. M. pneumoniae infection induced changes in the expression of cellular proteins, in particular a group of proteins involved in the oxidative stress response, such as glucose-6-phosphate 1-dehydrogenase, NADH dehydrogenase (ubiquinone) Fe-S protein 2, and ubiquinol-cytochrome c reductase complex core protein I mitochondrial precursor. The oxidative status of M. pneumoniae-infected cells was evaluated, and the results revealed that M. pneumoniae infection indeed caused generation of reactive oxygen species (ROS). It was further shown that M. pneumoniae infection also induced DNA double-strand breaks, as demonstrated by the formation of gammaH2AX foci. On the other hand, an ROS scavenger, N-acetylcysteine, could inhibit the ROS generation, as well as decrease gammaH2AX focus formation. This is the first report showing that M. pneumoniae infection can directly induce DNA damage, at least partially, through the generation of ROS, and thus this report strengthens the powerful application of proteomics in the study of the pathogenesis of M. pneumoniae.