The oxidative stress responsive transcription factor Pap1 confers DNA damage resistance on checkpoint-deficient fission yeast cells

A strategy for the investigation of toxic mechanisms and protection by efflux pumps using Schizosaccharomyces pombe strains: Application to rotenone

Effects not related with the inhibition of complex I of the mitochondrial electron transport chain are studied in S. pombe, which lacks it. This study aims: First, the use of a strategy with S. pombe strains to investigate the toxicity, mechanisms of action, interactions and detoxication by efflux pumps. Second, to investigate the mechanisms of toxic action of rotenone. In the dose-response assessment, the yeast presented a good correlation with the toxicity in Daphnia magna for 15 chemicals. In the mechanistic study, the mph1Δ strain presented marked specificity to the interaction with microtubules by carbendazim. DNA damage caused by hydroxyurea, an inhibitor of deoxynucleotide synthesis, was identified with marked specificity with the rad3Δ strain. The sty1Δ strain was very sensitive to the oxidative and osmotic stress induced by hydrogen peroxide and potassium chloride, respectively, being more sensitive to oxidative stress than the pap1Δ strain. The protection by exclusion pumps was also evaluated. Rotenone presented low toxicity in S. pombe due to the lack of its main target, and the marked protection by the exclusion transporters Bfr1, Pmd1, Caf5 and Mfs1. Marked cellular stress was detected. Finally, the toxicity of rotenone could be potentiated by the fungicide carbendazim and the antimetabolite hydroxyurea. In conclusion, the use of S. pombe strains is a valid strategy to: a) assess global toxicity; b) investigate the main mechanisms of toxic action, particularly spindle and DNA interferences, and osmotic and oxidative stress not related to complex I inhibition; c) explore the detoxication by efflux pumps; and d) evaluate possible chemical interactions. Therefore, it should be useful for the investigation of adverse outcome pathways.

Schizosaccharomyces pombe MAP kinase Sty1 promotes survival of Δppr10 cells with defective mitochondrial protein synthesis

Deletion of the Schizosaccharomyces pombe pentatricopeptide repeat gene ppr10 severely impairs mitochondrial translation, resulting in defective oxidative phosphorylation (OXPHOS). ppr10 deletion also induces iron starvation response, resulting in increased reactive oxygen species (ROS) production and reduced viability under fermentative conditions. S. pombe has two principal stress-response pathways, which are mediated by the mitogen-activated protein kinase Sty1 and the basic leucine zipper transcription factor Pap1, respectively. In this study, we examined the roles of Sty1 and Pap1 in the cellular response to the mitochondrial translation defect caused by ppr10 deletion. We found that ppr10 deletion resulted in two waves of stress protein activation. The early response occurred in exponential phase and resulted in the expression of a subset of stress proteins including Gst2 and Obr1. The upregulation of some of these stress proteins in Δppr10 cells in early response is dependent on the basal nuclear levels of Sty1 or Pap1. The late response occurred in early stationary phase and coincided with the stable localization of Sty1 and Pap1 in the nucleus, presumably resulting in persistent activation of a large set of stress proteins. Deletion of sty1 in Δppr10 cells caused severe defects in cell division and growth, and further impaired cell viability. Deletion of the mitochondrial superoxide dismutase gene sod2 whose expression is controlled by Sty1 severely inhibited the growth of Δppr10 cells. Overexpression of sod2 improves the viability of Δppr10 cells. Our results support an important role for Sty1 in counteracting stress induced by ppr10 deletion under fermentative growth conditions.

Induction of oxidative stress, apoptosis and DNA damage by koumine in Tetrahymena thermophila

Koumine is a component of the Chinese medicinal herb Gelsemium elegans and is toxic to vertebrates. We used the ciliate Tetrahymena thermophila as a model to evaluate the toxic effects of this indole alkaloid in eukaryotic microorganisms. Koumine inhibited T. thermophila growth and viability in a dose-dependent manner. Moreover, this drug produced oxidative stress in T. thermophila cells and expressions of antioxidant enzymes were significantly elevated at high koumine levels (p < 0.05). Koumine also caused significant levels of apoptosis (p < 0.05) and induced DNA damage in a dose-dependent manner. Mitophagic vacuoles were present in cells indicating induction of autophagy by this drug. Expression of ATG7, MTT2/4, CYP1 and HSP70 as well as the MAP kinase pathway gene MPK1 and MPK3 were significantly altered after exposed to koumine. This study represents a preliminary toxicological evaluation of koumine in the single celled eukaryote T. thermophila.

Effects of gelsemine on oxidative stress and DNA damage responses of Tetrahymena thermophila

Gelsemine is an important toxic substance extracted from Gelsemium elegans, which has a lot of biological functions in cells and organisms, but its toxicity has been rarely reported in Tetrahymena thermophila. In this study, we used the protozoan T. thermophila as an experimental model to investigate the potential toxicity-induced mechanism of gelsemine in the unicellular eukaryote. Our results clearly showed gelsemine inhibited T. thermophila growth in a dose-dependent manner. This exposure also resulted in oxidative stress on T. thermophila cells and antioxidant enzyme levels were significantly altered at high gelsemine levels (p < 0.05). Gelsemine produced a slight apoptotic effect at the highest (0.8 mg/mL) gelsemine level used here (p < 0.05). Furthermore, the toxin-induced DNA damage in a dose-dependent manner. The ultrastructural analysis also revealed mitophagic vacuoles at 0.4 and 0.8 mg/mL levels of gelsemine exposure. Moreover, expressions of oxidative stress-related and MAP kinase genes were significantly changed after exposure to 0.8 mg/mL level of gelsemine (p < 0.05). Altogether, our results clearly show that gelsemine from G. elegans can inhibit the growth via inducing oxidative stress and DNA damage in T. thermophila cells.

Pap1 + confers microtubule damage resistance to mut2a, an extragenic suppressor of the rad26:4A allele in S. pombe

The DNA structure checkpoint protein Rad26^ATRIP is also required for an interphase microtubule damage response. This checkpoint delays spindle pole body separation and entry into mitosis following treatment of cells with microtubule poisons. This checkpoint requires cytoplasmic Rad26^ATRIP, which is compromised by the rad26:4A allele that inhibits cytoplasmic accumulation of Rad26^ATRIP following microtubule damage. The rad26::4a allele also disrupts minichromosome stability and cellular morphology, suggesting that the interphase microtubule damage checkpoint pathway operates in an effort to maintain chromosome stability and proper cell shape. To identify other proteins of the Rad26-dependent interphase microtubule damage response, we used ultra violet (UV) radiation to identify extragenic interaction suppressors of the rad26::4A growth defect on microtubule poisons. One suppressor mutation, which we named mut2a, permitted growth of rad26:4A cells on MBC media and conferred sensitivity to a microtubulin poison upon genetic outcross. In an attempt to clone this interaction suppressor using a genomic library complementation strategy, we instead isolated pap1 ⁺ as an extracopy suppressor of the mut2a growth defect. We discuss the mechanism by which pap1 ⁺ overexpression may allow growth of mut2a cells in conditions that destabilize microtubules.

Multimodal control of transcription factor Pap1 in Schizosaccharomyces pombe under nitrosative stress

Schizosaccharomyces pombe Pap1, a bZIP transcription factor, is highly homologous to the mammalian c-Jun protein that belongs to the AP1 family of transcriptional regulators. The role of transcription factor Pap1 has been extensively studied under oxidative stress. Two cysteine residues in Pap1p namely, C278 and C501 form disulfide linkage under oxidative stress resulting in nuclear accumulation. We first time showed the involvement of Pap1 in the protection against nitrosative stress. In the present study we show that pap1 deletion makes growth of S. pombe sensitive to nitrosative stress. pap1 deletion also causes delayed recovery in terms of mitotic index under nitrosative stress. Our flow cytometry data shows that pap1 deletion causes slower recovery from the slowdown of DNA replication under nitrosative stress. This is the first report where we show that Pap1 transcription factor is localized in the nucleus under nitrosative stress. From our study it is evident that nuclear localization of Pap1 under nitrosative stress was not due to reactive oxygen species formation.

Latrunculin A-Induced Perturbation of the Actin Cytoskeleton Mediates Pap1p-Dependent Induction of the Caf5p Efflux Pump in Schizosaccharomyces pombe

As part of an earlier study aimed at uncovering gene products with roles in defending against latrunculin A (LatA)-induced cytoskeletal perturbations, we identified three members of the oxidative stress response pathway: the Pap1p AP-1-like transcription factor, the Imp1p α-importin, and the Caf5p efflux pump. In this report, we characterize the pathway further and show that Pap1p translocates from the cytoplasm to the nucleus in an Imp1p-dependent manner upon LatA treatment. Moreover, preventing this translocation, through the addition of a nuclear export signal (NES), confers the same characteristic LatA-sensitive phenotype exhibited by pap1Δ cells. Lastly, we show that the caf5 gene is induced upon exposure to LatA and that Pap1p is required for this transcriptional upregulation. Importantly, the expression of trr1, a Pap1p target specifically induced in response to oxidative stress, is not significantly altered by LatA treatment. Taken together, these results suggest a model in which LatA-mediated cytoskeletal perturbations are sensed, triggering the Imp1p-dependent translocation of Pap1p to the nucleus and the induction of the caf5 gene (independently of oxidative stress).

The Cell Killing Mechanisms of Hydroxyurea

Hydroxyurea is a well-established inhibitor of ribonucleotide reductase that has a long history of scientific interest and clinical use for the treatment of neoplastic and non-neoplastic diseases. It is currently the staple drug for the management of sickle cell anemia and chronic myeloproliferative disorders. Due to its reversible inhibitory effect on DNA replication in various organisms, hydroxyurea is also commonly used in laboratories for cell cycle synchronization or generating replication stress. However, incubation with high concentrations or prolonged treatment with low doses of hydroxyurea can result in cell death and the DNA damage generated at arrested replication forks is generally believed to be the direct cause. Recent studies in multiple model organisms have shown that oxidative stress and several other mechanisms may contribute to the majority of the cytotoxic effect of hydroxyurea. This review aims to summarize the progress in our understanding of the cell-killing mechanisms of hydroxyurea, which may provide new insights towards the improvement of chemotherapies that employ this agent.

Probiotics Lactobacillus plantarum and bifidobacterium B94: cognitive function in demyelinated model

BACKGROUND

Multiple Sclerosis (MS) is a disease of the immune system that creates damage of Learning and memory in that. Using probiotic supplements is recommended for preventing MS disease and improving memory. This study aimed to investigate the effect of Lactobacillus plantarum (LP) and bifidobacterium B94 (BB94), on acquisition phase of spatial memory in the local demyelination of rats` hippocampus.

METHODS

In this study, 32 male Wistar rats were divided into control, damage group and treatment groups. Treatment groups were including (LP) and (BB94). After the induction of demyelination by 3 μl of EB into the right dentate gyrus of the hippocampus in treatment groups, 1.5×10(8) probiotic bacteria were administered by gavage for 28 days. Data was analyzed using one-way ANOVA and Tukey post-hoc tests (p≤0.05).

RESULTS

Findings demonstrated that injection of EB caused a significant increase in traveled distance (p<0.01) and also escape latency (p<0.05) compared with control group. Also, effect administrations of (LP) and (BB94) on traveled distance and escape latency were reviewed, and it was determined that administration of them do not cause significant reduction in the traveled distance compared with the lesion group. Also mentioned probiotics has no significant effect on swimming speed compared with lesion and saline groups.

CONCLUSION

According to some studies, probiotics have a positive impact on improving the performance of spatial memory and learning, although the results of the current study could not indicate finality of this assumption. It seems that more researches is needed on this subject.