Localization changes of endogenous hydrogen peroxide during cell division cycle of Xanthomonas

Pharmacological relevance of CDK inhibitors in Alzheimer's disease

Evidence suggests that cell cycle activation plays a role in the pathophysiology of neurodegenerative diseases. Alzheimer's disease is a progressive, terminal neurodegenerative disease that affects memory and other important mental functions. Intracellular deposition of Tau protein, a hyperphosphorylated form of a microtubule-associated protein, and extracellular aggregation of Amyloid β protein, which manifests as neurofibrillary tangles (NFT) and senile plaques, respectively, characterize this condition. In recent years, however, several studies have concluded that cell cycle re-entry is one of the key causes of neuronal death in the pathogenesis of Alzheimer's disease. The eukaryotic cell cycle is well-coordinated machinery that performs critical functions in cell replenishment, such as DNA replication, cell creation, repair, and the birth of new daughter cells from the mother cell. The complex interplay between the levels of various cyclins and cyclin-dependent kinases (CDKs) at different checkpoints is needed for cell cycle synchronization. CDKIs (cyclin-dependent kinase inhibitors) prevent cyclin degradation and CDK inactivation. Different external and internal factors regulate them differently, and they have different tissue expression and developmental functions. The checkpoints ensure that the previous step is completed correctly before starting the new cell cycle phase, and they protect against the transfer of defects to the daughter cells. Due to the development of more selective and potent ATP-competitive CDK inhibitors, CDK inhibitors appear to be on the verge of having a clinical impact. This avenue is likely to yield new and effective medicines for the treatment of cancer and other neurodegenerative diseases. These new methods for recognizing CDK inhibitors may be used to create non-ATP-competitive agents that target CDK4, CDK5, and other CDKs that have been recognized as important therapeutic targets in Alzheimer's disease treatment.

Exogenously applied hydrogen peroxide modifies the course of the Chlamydomonas reinhardtii cell cycle

The interaction of NO and H₂O₂ in the regulation of plant development is well documented. We have recently shown that the content of NO and H₂O₂ changes in a characteristic way during the cell cycle of Chlamydomonas reinhardtii (Pokora et al., 2017), which implies participation of these molecules in the regulation of Chlamydomonas development. To verify this assumption, H₂O₂ was supplied at a concentration about 1.5 times higher than that determined in the control cells. Cells were synchronized by alternating the light/dark (10/14 h) regimen. H₂O₂ was added to zoospore suspensions, previously held in the dark, and cells growing for 3, 6, and 9 h in the light. The data indicate that, depending on the phase of the Chlamydomonas cell cycle, H₂O₂, via mild modification of redox homeostasis, may: a) accelerate or delay the duration of the cell cycle; b) increase the number of replication rounds occurring in one cell cycle; c) modify the biomass and cell volume of progeny cells and d) accelerate the liberation of daughter cells. This provides a tool to control the development of Chlamydomonas cell and thus offers the opportunity to obtain a population of cells with characteristics desired in biotechnology.

Changes in nitric oxide/hydrogen peroxide content and cell cycle progression: Study with synchronized cultures of green alga Chlamydomonas reinhardtii

The present study aimed to evaluate the possible relationship between the changes in hydrogen peroxide (H₂O₂) and nitric oxide (NO) content and the course of growth and reproductive processes of the cell cycle of Chlamydomonas reinhardtii. The peak of H₂O₂ observed at the beginning of the cell cycle was found to originate from Fe-SOD and Mn-SOD_chl. activity and result from the alternation in the photosynthetic processes caused by the dark-to-light transition of daughter cells. A rapid increase in NO concentration, observed before the light-to-dark cell transition, originated from NR and NIR activity and was followed by a photosynthesis-independent, Mn-SOD_chl.-mediated increases in H₂O₂ production. This H₂O₂ peak overlapped the beginning of Chlamydomonas cell division, which was indicated by a profile of CYCs and CDKs characteristic of cells' passage through the G1/S and S/M checkpoints. Taken together, our results show that there is a clear relationship between the course of the Chlamydomonas cell cycle and typical changes in the H₂O₂/NO ratio, as well as changes in expression and activity of enzymes involved in generation and scavenging of these signaling molecules.

Mutation of alkyl hydroperoxide reductase gene ahpC of Xanthomonas oryzae pv. oryzae affects hydrogen peroxide accumulation during the rice-pathogen interaction

Hydrogen peroxide (H2O2) is usually generated by normal aerobic respiration of pathogens and by the host defense response during plant-pathogen interactions. In this study, histochemical localization of H2O2 accumulation in rice inoculated with the wild-type strain (PXO99(A)) and the gene deletion mutant (ΔahpC) of alkyl hydroperoxide reductase subunit C (AhpC) of Xanthomonas oryzae pv. oryzae (Xoo), the bacterial blight pathogen of rice, was analyzed. The ΔahpC mutant displayed a significant decrease in endogenous H2O2 accumulation which was induced by the compensatory increase in H2O2 scavenging activity. The change in the bacterial endogenous H2O2 level affected the total amount of H2O2 accumulation during the interaction with rice plants. These results suggested that Xoo contributes to H2O2 accumulation in rice in a compatible interaction, and pathogen-driving H2O2 is in association with cell collapse of rice.

Revisiting the mesosome as a novel site of hydrogen peroxide accumulation in Escherichia coli

The major source of endogenous hydrogen peroxide is generally thought to be the respiratory chain of bacteria and mitochondria. In our previous works, mesosome structure was induced in cells during rifampicin effect, and the mesosome formation is always accompanied by excess hydrogen peroxide accumulation in bacterial cells. However, the underlying mechanisms of hydrogen peroxide production and the rationale behind it remain still unknown. Here we report that hydrogen peroxide can specifically accumulate in the mesosome in vitro. Mesosomes were interpreted earlier as artifacts of specific cells under stress through TEM preparation, while, in the current study, mesosomes were shown as intracellular compartments with specific roles and features by using quickly freezing preparation of TEM. Formation of hydrogen peroxide was observed in suspension of mesosomal vesicles by using either a fluorescence-based reporter assay or a histochemical method, respectively. Our investigation provides experimental evidence that mesosomes can be a novel site of hydrogen peroxide accumulation.

MRT letter: localization of endogenous hydrogen peroxide by modified processes of sample preparation for transmission electron microscope in Escherichia coli

The bacterial endogenous hydrogen peroxide (H(2)O(2)) was detected cytochemically by its reaction with cerium chloride (CeCl(3)) to produce electron-dense deposits of cerium perhydroxides. The sequence of fixation and CeCl(3) staining of H(2)O(2) in the processing of transmission electron microscope (TEM) sample preparation is crucial to the localization of endogenous H(2)O(2) in Escherichia coli. In this study, results confirmed that the process that fixation simultaneously with CeCl(3) staining provided optimum effects for H(2)O(2) localization in E. coli. The modified process of TEM provides very efficient protection for H(2)O(2) localization and more accurate quantization for the H(2)O(2) accumulation in bacterial cells.

The influence of reactive oxygen species on cell cycle progression in mammalian cells

Cell cycle regulation is performed by cyclins and cyclin dependent kinases (CDKs). Recently, it has become clear that reactive oxygen species (ROS) influence the presence and activity of these enzymes and thereby control cell cycle progression. In this review, we first describe the discovery of enzymes specialized in ROS production: the NADPH oxidase (NOX) complexes. This discovery led to the recognition of ROS as essential players in many cellular processes, including cell cycle progression. ROS influence cell cycle progression in a context-dependent manner via phosphorylation and ubiquitination of CDKs and cell cycle regulatory molecules. We show that ROS often regulate ubiquitination via intermediate phosphorylation and that phosphorylation is thus the major regulatory mechanism influenced by ROS. In addition, ROS have recently been shown to be able to activate growth factor receptors. We will illustrate the diverse roles of ROS as mediators in cell cycle regulation by incorporating phosphorylation, ubiquitination and receptor activation in a model of cell cycle regulation involving EGF-receptor activation. We conclude that ROS can no longer be ignored when studying cell cycle progression.

The expression, function and regulation of mitochondrial alternative oxidase under biotic stresses

To survive, plants possess elaborate defence mechanisms to protect themselves against virus or pathogen invasion. Recent studies have suggested that plant mitochondria may play an important role in host defence responses to biotic stresses. In contrast with animal mitochondria, plant mitochondria possess a unique respiratory pathway, the cyanide-insensitive alternative pathway, which is catalysed by the alternative oxidase (AOX). Much work has revealed that the genes encoding AOX, AOX protein and the alternative respiratory pathway are frequently induced during plant-pathogen (or virus) interaction. This raises the possibility that AOX is involved in host defence responses to biotic stresses. Thus, a key to the understanding of the role of mitochondrial respiration under biotic stresses is to learn the function and regulation of AOX. In this article, we focus on the theoretical and experimental progress made in the current understanding of the function and regulation of AOX under biotic stresses. We also address some speculative aspects to aid further research in this area.

Extracellular superoxide anion production contributes to the virulence ofXanthomonas oryzaepv.oryzae

Endogenous superoxide anion production was determined by electron spin resonance in wild-type strains and avrXa7 mutants of Xanthomonas oryzae pv. oryzae . The localization of superoxide anion was carried out in the intra- and extra-cellular fractions. Results showed the presence of superoxide anion in multi-locations of X. oryzae pv. oryzae cells. The extracellular fraction was the major location of superoxide anion production. Furthermore, a positive relationship was shown between the levels of endogenous superoxide anion and the virulence of strains. These indubitable results suggested that the superoxide anion contributes to the virulence of X. oryzae pv. oryzae.

Mesosome formation is accompanied by hydrogen peroxide accumulation in bacteria during the rifampicin effect

Ultrastructural alteration and hydrogen peroxide localization were examined in Xanthomonas campestris pv. phaseoli during rifampicin effect using transmission electron microscopy. Bacterial cells were treated with rifampicin and then were examined by electron microscopy to observe the changes of ultrastructure or hydrogen peroxide accumulation in living cells that took place before lysis. Intriguingly, rifampicin treatment led to presence of an additional location of hydrogen peroxide accumulation within the cells. There was an association between the frequency and size of the additional location of hydrogen peroxide accumulation and the concentration of rifampicin. Furthermore, an additional ultrastructure, mesosomes, was also present in cells during rifampicin effect. The frequency and size of mesosome increased with the increasing concentration of rifampicin. Result of multiple linear regression showed that the size of mesosome plays as a key factor in the quantity of excess hydrogen peroxide accumulation in cells during rifampicin effect. Linear correlation was confirmed between quantity of excess hydrogen peroxide accumulation and the size of mesosome in cells during rifampicin effect. This finding intensely indicated that mesosomes are just the additional location of hydrogen peroxide accumulation in cells under cellular injury caused by rifampicin treatment. The mesosome formation is always accompanied by excess hydrogen peroxide accumulation in X. campestris pv. phaseoli during rifampicin effect.