Some Aspects of the Cell Biology of the Bacterial Stationary Phase: Programmed Cell Death and Its Regulation by Guanosine Tetraphosphate

This paper discusses (1) programmed cell death, a phenomenon typical of the stationary phase of bacteria occurring under unfavorable conditions, (2) its pleiotropic regulation by guanosine tetraphosphate, and (3) the conception of addiction module, a specific genetic system responsible for the cell choice between survival and death under unfavorable conditions. The shortcomings of the proposed interpretation of the problem at hand are considered and the necessity of their further investigation is substantiated.     

Correlation of death modes of photosensitized cells with intracellular ATP concentration

The impact of intensity of glycolysis and oxidative phosphorylation on death of photosensitized murine hepatoma MH22 cells in vitro has been investigated. Cells photosensitized with meso-tetra(4-sulfonatophenyl)-porphine localized to lysosomes died mostly by necrosis, and the mode of cell death did not depend on the energy metabolism. Photosensitization with 5-aminolevulinic acid-stimulated endogenous porphyrins localized mainly in mitochondria or 5,10,15,20-tetrakis(m-hydroxyphenyl)-chlorine localized to cell membranes, including mitochondria, led to cell death mostly by apoptosis. In this case, the mode of cell death depended on the medium: under conditions unfavorable to glycolysis the ratio apoptosis/necrosis decreased significantly.     

Autophagy induced by ionizing radiation promotes cell death over survival in human colorectal cancer cells

Autophagy is commonly described as a cell survival mechanism and has been implicated in chemo- and radioresistance of cancer cells. Whether ionizing radiation induced autophagy triggers tumor cell survival or cell death still remains unclear. In this study the autophagy related proteins Beclin1 and ATG7 were tested as potential targets to sensitize colorectal carcinoma cells to ionizing radiation under normoxic, hypoxic and starvation conditions. Colony formation, apoptosis and cell cycle analysis revealed that knockdown of Beclin1 or ATG7 does not enhance radiosensitivity in HCT-116 cells. Furthermore, ATG7 knockdown led to an increased survival fraction under oxygen and glutamine starvation, indicating that ionizing radiation indeed induces autophagy which, however, leads to cell death finally. These results highlight that inhibition of autophagic pathways does not generally increase therapy success but may also lead to an unfavorable outcome especially under amino acid and oxygen restriction.     

Small heat shock proteins HSP27 (HspB1), αB-crystallin (HspB5) and HSP22 (HspB8) as regulators of cell death

Hsp27, αB-crystallin and HSP22 are ubiquitous small heat shock proteins (sHsp) whose expression is induced in response to a wide variety of unfavorable physiological and environmental conditions. These sHsp protect cells from otherwise lethal conditions mainly by their involvement in cell death pathways such as necrosis, apoptosis or autophagy. At a molecular level, the mechanisms accounting for sHsp functions in cell death are (1) prevention of denatured proteins aggregation, (2) regulation of caspase activity, (3) regulation of the intracellular redox state, (4) function in actin polymerization and cytoskeleton integrity and (5) proteasome-mediated degradation of selected proteins. In cancer cells, these sHsp are often overexpressed and associated with increased tumorigenicity, cancer cells metastatic potential and resistance to chemotherapy. Altogether, these properties suggest that Hsp27, αB-crystallin and Hsp22 are appropriate targets for modulating cell death pathways. In the present, we briefly review recent reports showing molecular evidence of cell death regulation by these sHsp and co-chaperones. This article is part of a Directed Issue entitled: Small HSPs in physiology and pathology.     

Hyperphagia by self- and xeno-cannibalism: cell death by indigestion?: a reminiscence of the Phedrus Fabula "Rana Rupta et Bos"?

The occurrence of self- and xeno-cannibalism could be considered as two different aspects of the same well-regulated process. The formation of autophagosomes can represent a survival option for a cell in unfavorable conditions but it can also lead to cell demise. In fact, autophagy has been considered as an additional and clear-cut cell death pathway. We herein speculate that selfeating by autophagy could be paralleled by a cannibalistic behavior, e.g., by cell feeding of siblings, that can also become detrimental. This behavior in fact, once exacerbated, can also lead to cell death, probably bolstering intracellular oxidative imbalance. In this case, a survival option, such as self- and xeno-cannibalism, can be turned into a peculiar death option: cell death by feeding excess. Under this point of view, over-feeding cells are reminiscent of the frog in the Phedrus Fabula "Rana Rupta et Bos".     

Adaptive reactions of mycoplasmas in vitro: "viable but unculturable forms" and nanocells of Acholeplasma laidlawii

The adaptation of Acholeplasma laidlawii to conditions unfavorable for growth has been found to be accompanied by cell transformation into special morphological structures known as ultramicroforms (nanocells). The ratio of the cells of the two morphological types in the population depended on the growth conditions. Nanocells retained viability for a long time under conditions unfavorable for growth and showed resistance to stressors. Reduction in the cell size occurred due to unequal division, which involved the loss of cytoplasmic material. A. laidlawii ultramicroforms (nanocells) were able to restore proliferative activity and to revert to their initial vegetative form; they measured less than 0.2 microm and are the smallest cells known at present. Nanocells formed in vitro under exposure to abiogenic stressors may correspond to the A. laidlawii minibodies observed in infected plants upon exposure to biogenic stressors. The transformation of A. laidlawii cells into ultramicroforms was accompanied by condensation of the nucleoid, a change in the polypeptide spectrum, and a change in the availability of rRNA operons for in vitro amplification. All these changes are indicative of reorganization of the genetic and metabolic systems of mycoplasmas.     

Hyperphagia by self- and xeno-cannibalism: Cell death by indigestion? A reminiscence of the Phedrus Fabula “Rana Rupta et Bos”?

The occurrence of self- and xeno-cannibalism could be considered as two different aspects of the same well-regulated process. The formation of autophagosomes can represent a survival option for a cell in unfavorable conditions but it can also lead to cell demise. In fact, autophagy has been considered as an additional and clear-cut cell death pathway. We herein speculate that self-eating by autophagy could be paralleled by a cannibalistic behavior, e.g., by cell feeding of siblings, that can also become detrimental. This behavior in fact, once exacerbated, can also lead to cell death, probably bolstering intracellular oxidative imbalance. In this case, a survival option, such as self- and xeno-cannibalism, can be turned into a peculiar death option: cell death by feeding excess. Under this point of view, over-feeding cells are reminiscent of the frog in the Phedrus Fabula “Rana Rupta et Bos”.     

Infant mortality and intra‐household competition in the Northern Islands of Orkney,Scotland, 1855–2001

This study applies principles from the theory of household life cycles to the study of early childhood mortality in the population of the Northern Orkney Islands, Scotland. The primary hypothesis is that unfavorable household economic conditions resulting from changes in household demographic composition increase the risk of death for children under the age of 5 years because of limited resources and intra‐household competition. We apply Cox proportional hazards models to nearly 5,000 linked birth and death records from the Northern Orkney Islands, Scotland, from the period 1855 to 2001. The dependent variable is the child's risk of death before age 5. Findings suggest that children in households with unfavorable age compositions face higher risk of death. This elevated risk of death continues once heterogeneity among children, islands, and households is controlled. Results also show differential risk of death for male children, children of higher birth orders, and twin births. The analyses present evidence for intra‐household competition in this historic setting. The most convincing evidence of competition is found in the effects of household consumer/producer ratios and twinning on child mortality risks. Am J Phys Anthropol 151:191–201, 2013. © 2013 Wiley Periodicals, Inc.     

Heat shock protein 60 modified with O-linked N-acetylglucosamine is involved in pancreatic beta-cell death under hyperglycemic conditions

The objective of this study was to identify proteins modified with O-linked N-acetylglucosamine (O-GlcNAc) in pancreatic beta-cells and to understand their roles in cell death under hyperglycemic conditions. Here we report that heat shock protein 60 (HSP60) is modified with O-GlcNAc. Levels of O-GlcNAcylated HSP60 increased twofold in response to hyperglycemic conditions. HSP60 is a chaperonin known to bind to Bax in the cytoplasm under normoglycemic conditions. Under hyperglycemic conditions, Bax detached from O-GlcNAcylated HSP60 and translocated to mitochondria. Hyperglycemic conditions were also associated with cytochrome c release, caspase-3 activation, and cell death, suggesting that elevated O-GlcNAcylation of HSP60 interferes with HSP60-Bax interactions, leading to pancreatic beta-cell death.     

Human PRP19 interacts with prolyl-hydroxylase PHD3 and inhibits cell death in hypoxia

Prolyl-hydroxylase PHDs are the key regulators of hypoxia-inducible factor (HIF) stability. PHD3 has been shown to form a large complex under hypoxic conditions. While attempting to characterize the complex by determining its components, we identified human PRP19. hPRP19 is a multi-functional protein that plays a role in splicing, ubiquitination, and cell growth. Here, we report that PHD3 efficiently forms a complex with hPRP19 under hypoxic conditions and prevents cell death under prolonged hypoxic conditions. hPRP19 interacts with PHD3 via its C-terminal WD40 region, and the interaction is enhanced under hypoxic conditions through the utilization of the N-terminal coiled-coil domain. Cell death observed under prolonged hypoxic conditions is suppressed by the forced expression of hPRP19 in PC12 and HEK293T cells. In contrast, hPRP19 silencing by siRNA increased the caspase activity and enhanced cell death under hypoxic conditions in HeLa cells. Further, silencing of both PHD3 and hPRP19 recovers the cell death induced by hPRP19 single siRNA. Taken together, the results of our study indicate that hPRP19 interacts with PHD3 to suppress the cell death under hypoxic conditions by limiting the function of PHD3 which leads to caspase activation.     

Sedimentation in the seasonal cycle of unicellular algae. Model analysis]

The efficiency of quick sedimentation (quicker then at normal condition) of unicellular algae at the end of seasonal cycle was studied in Okhotsk Sea. Model researches were based on the effect of competition of two algae populations. Analytical investigations of simplified variant of mathematical model and computing experiments showed that cell sedimentation and falling into the unfavorable (dark and cold) environment could be compensated by the increase in survival under these "negative" conditions. Vertical mixing of water has effect. Generally, mechanism of convective mixing is one of the factors that helps competing populations of unicellular algae to exist under conditions of changing environment.     

Expression of Animal Anti-Apoptotic Gene Ced-9 Enhances Tolerance during Glycine max L.–Bradyrhizobium japonicum Interaction under Saline Stress but Reduces Nodule Formation

The mechanisms by which the expression of animal cell death suppressors in economically important plants conferred enhanced stress tolerance are not fully understood. In the present work, the effect of expression of animal antiapoptotic gene Ced-9 in soybean hairy roots was evaluated under root hairs and hairy roots death-inducing stress conditions given by i) Bradyrhizobium japonicum inoculation in presence of 50 mM NaCl, and ii) severe salt stress (150 mM NaCl), for 30 min and 3 h, respectively. We have determined that root hairs death induced by inoculation in presence of 50 mM NaCl showed characteristics of ordered process, with increased ROS generation, MDA and ATP levels, whereas the cell death induced by 150 mM NaCl treatment showed non-ordered or necrotic-like characteristics. The expression of Ced-9 inhibited or at least delayed root hairs death under these treatments. Hairy roots expressing Ced-9 had better homeostasis maintenance, preventing potassium release; increasing the ATP levels and controlling the oxidative damage avoiding the increase of reactive oxygen species production. Even when our results demonstrate a positive effect of animal cell death suppressors in plant cell ionic and redox homeostasis under cell death-inducing conditions, its expression, contrary to expectations, drastically inhibited nodule formation even under control conditions.     

Influence of water limitation on endogenous oxidative stress and cell death within unsaturated Pseudomonas putida biofilms

Here we examined how water limitation (matric stress) and high osmolarity (solute stress) influence the extent of endogenous oxidative stress and cell death patterns within Pseudomonas putida biofilms. The temporal dynamics and spatial organization of reactive oxygen species (ROS) accumulation and dead cells in biofilms developed under water‐replete and solute stress conditions were similar to each other. Arrays of dead cells, typically one cell width in diameter, were distributed throughout the biofilm and occasionally they spanned the entire depth of the biofilm. These arrays of dead cells were not observed under water‐limiting conditions, although the extent of ROS accumulation and cell death was substantially greater. Despite the greater death rate under water‐limiting conditions, culturable population sizes were transiently maintained at levels comparable to those under water‐replete and solute stress conditions. There was greater spatial stratification of dead cells under water‐limiting than water‐replete conditions with viable cells primarily located at the air interface, which could facilitate cell dispersal following a wetting event. Under water‐limiting conditions, ROS accumulation is greater in an ΔalgD mutant compared with the wild type, suggesting that the exopolysaccharide alginate attenuates the extent of dehydration‐mediated oxidative stress. We conclude that endogenous ROS accumulation is correlated with cell death within P. putida biofilms, although mechanisms contributing to their accumulation may differ under water‐replete and water‐limiting conditions.     

Autophagy inhibition enhances daunorubicin-induced apoptosis in K562 cells

Anthracycline daunorubicin (DNR) is one of the major antitumor agents widely used in the treatment of myeloid leukemia. Unfortunately, the clinical efficacy of DNR was limited because of its cytotoxity at high dosage. As a novel cytoprotective mechanism for tumor cell to survive under unfavorable conditions, autophagy has been proposed to play a role in drug resistance of tumor cells. Whether DNR can activate to impair the sensitivity of cancer cells remains unknown. Here, we first report that DNR can induce a high level of autophagy, which was associated with the activation of extracellular signal-regulated kinase 1/2 (ERK1/2). Moreover, cell death induced by DNR was greatly enhanced after autophagy inhibition by the pharmacological inhibitor chloroquine (CQ) and siRNAs targeting Atg5 and Atg7, the most important components for the formation of autophagosome. In conclusion, we found that DNR can induce cytoprotective autophagy by activation of ERK in myeloid leukemia cells. Autophagy inhibition thus represents a promising approach to improve the efficacy of DNR in the treatment of patients with myeloid leukemia.     

A novel Mtd splice isoform is responsible for trophoblast cell death in pre-eclampsia

Pre-eclampsia is a serious disorder of human pregnancy, characterized by decreased utero-placental perfusion and increased trophoblast cell death. Presently, the mechanisms regulating trophoblast cell death in pre-eclampsia are not fully elucidated. Herein, we have identified a novel Mtd/Bok splice isoform (Mtd-P) resulting from exon-II skipping. Mtd-P expression was unique to early-onset severe pre-eclamptic placentae as assessed by quantitative real-time-PCR and immunoblotting. Mtd-P overexpression in cell lines (BeWo: cytotrophoblast-derived; and CHO: ovary-derived) resulted in increased apoptotic cell death as assessed by caspase-3 cleavage, internucleosomal DNA laddering and mitochondrial depolarization. Moreover, Mtd-P expression increased under conditions of low oxygenation/oxidative stress in human villous explants. Antisense knockdown of Mtd under conditions of oxidative stress resulted in decreased caspase-3 cleavage. We conclude that under conditions of reduced oxygenation/oxidative stress, Mtd-P causes trophoblast cell death in pre-eclampsia and hence may contribute to the molecular events leading to the clinical manifestations of this disease.     

Effect of culture conditions on growth and adhesion of Bacillus licheniformis

Adhesion to glass of actively growing cells of the thermophilic Bacillus licheniformis, isolated from the Medyaginskaya test borehole (Yaroslavl' oblast), was studied. The reversible adhesion (RA) manifests itself in a decline of cell density (short of cell lysis) in the liquid culture over the first 20-40 min of growth followed by normal exponential growth. The RA is minimal under favorable growth conditions but increases when cells are transferred to a new medium, especially one with a pH, temperature, salinity, or concentration of Ca2+ ions nonoptimal for the given species. Under unfavorable growth conditions, the adhesion becomes irreversible. The obtained data suggest that RA represents an adaptation mechanism important for population survival.     

Inhibition of macroautophagy triggers apoptosis

Mammalian cells were observed to die under conditions in which nutrients were depleted and, simultaneously, macroautophagy was inhibited either genetically (by a small interfering RNA targeting Atg5, Atg6/Beclin 1-1, Atg10, or Atg12) or pharmacologically (by 3-methyladenine, hydroxychloroquine, bafilomycin A1, or monensin). Cell death occurred through apoptosis (type 1 cell death), since it was reduced by stabilization of mitochondrial membranes (with Bcl-2 or vMIA, a cytomegalovirus-derived gene) or by caspase inhibition. Under conditions in which the fusion between lysosomes and autophagosomes was inhibited, the formation of autophagic vacuoles was enhanced at a preapoptotic stage, as indicated by accumulation of LC3-II protein, ultrastructural studies, and an increase in the acidic vacuolar compartment. Cells exhibiting a morphology reminiscent of (autophagic) type 2 cell death, however, recovered, and only cells with a disrupted mitochondrial transmembrane potential were beyond the point of no return and inexorably died even under optimal culture conditions. All together, these data indicate that autophagy may be cytoprotective, at least under conditions of nutrient depletion, and point to an important cross talk between type 1 and type 2 cell death pathways.     

Cell death by autophagy: facts and apparent artefacts

Autophagy (the process of self-digestion by a cell through the action of enzymes originating within the lysosome of the same cell) is a catabolic process that is generally used by the cell as a mechanism for quality control and survival under nutrient stress conditions. As autophagy is often induced under conditions of stress that could also lead to cell death, there has been a propagation of the idea that autophagy can act as a cell death mechanism. Although there is growing evidence of cell death by autophagy, this type of cell death, often called autophagic cell death, remains poorly defined and somewhat controversial. Merely the presence of autophagic markers in a cell undergoing death does not necessarily equate to autophagic cell death. Nevertheless, studies involving genetic manipulation of autophagy in physiological settings provide evidence for a direct role of autophagy in specific scenarios. This article endeavours to summarise these physiological studies where autophagy has a clear role in mediating the death process and discusses the potential significance of cell death by autophagy.