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At least 955 records · Page 53Linked to original sources
PubMed2004

A novel phosphatidylcholine-hydrolyzing phospholipase C induced by phosphate starvation in Arabidopsis.

During phosphate starvation, it is known that phospholipids are degraded, and conversely, a nonphosphorus galactolipid digalactosyldiacylglycerol accumulates in the root plasma membrane of plants. We report a novel phospholipase C that hydrolyzes phosphatidylcholine and is greatly induced in response to phosphate deprivation in Arabidopsis. Since phosphatidylcholine-hydrolyzing activity by phospholipase C was highly up-regulated in phosphate-deprived plants, gene expression of some phospholipase C was expected to be induced during phosphate starvation. Based on amino acid sequence similarity to a bacterial phosphatidylcholine-hydrolyzing phospholipase C, six putative phospholipase Cs were identified in the Arabidopsis genome, one of which, NPC4, showed significant transcriptional activation upon phosphate limitation. Molecular cloning and functional expression of NPC4 confirmed that the NPC4 gene encoded a functional phosphatidylcholine-hydrolyzing phospholipase C that did not require Ca(2+) for its activity. Subcellular localization analysis showed that NPC4 protein was highly enriched in the plasma membrane. Analyses of transferred DNA-tagged npc4 mutants revealed that disruption of NPC4 severely reduces the phosphatidylcholine-hydrolyzing phospholipase C activity in response to phosphate starvation. These results suggest that NPC4 plays an important role in the supply of both inorganic phosphate and diacylglycerol from membrane-localized phospholipids that would be used for phosphate supplementation and the replacement of polar lipids in the root plasma membrane during phosphate deprivation.

Amino Acid Sequence↗
PubMed2005

Role of mRNA stability during genome-wide adaptation of Lactococcus lactis to carbon starvation.

The stability of mRNA was investigated for the first time at the genomic scale during carbon starvation adaptation of Lactococcus lactis IL1403. In exponential phase, mRNA half-lives were correlated positively to open reading frame length. A polypurine sequence, AGGAG, was identified as a putative 5'-stabilizer and inverted repeated sequences as a 3'-destabilizer. These original findings suggested that multiple pathways of mRNA degradation should coexist: internal cleavage, endonuclease cleavage initiated at the 5'-end, and exonuclease attack at the 3'-end. During carbon starvation adaptation, mRNA stability globally increased, but specific mechanisms allowing a wide range of stabilization factors between genes and differential kinetic evolution were involved. A formal method allowing the quantification of the relative influences of transcription and degradation on the mRNA pool control was developed and applied in L. lactis. Gene expression was mostly controlled by altered transcription prior to carbon source exhaustion, while the influence of mRNA stability increased during the starvation phase. This study highlighted that stability modulation in response to adverse growth conditions can govern gene regulation to the same extent as transcription in bacteria.

Carbon↗
PubMed2005

Autophagy is required for maintenance of amino acid levels and protein synthesis under nitrogen starvation.

Autophagy is a transport system of cytoplasmic components to the lysosome/vacuole for degradation well conserved in eukaryotes. Autophagy is strongly induced by nutrient starvation. Several specific proteins, including amino acid synthesis enzymes and vacuolar enzymes, are increased during nitrogen starvation in wild-type cells but not in autophagy-defective delta atg7 cells despite similar mRNA levels. We further examined deficiencies in these cells. Bulk protein synthesis was substantially reduced in delta atg7 cells under nitrogen starvation compared with wild-type cells. The total intracellular amino acid pool was reduced in delta atg7 cells, and the levels of several amino acids fell below critical values. In contrast, wild-type cells maintained amino acid levels compatible with life. Autophagy-defective cells fail to maintain physiologic amino acid levels, and their inability to synthesize new proteins may explain most phenotypes associated with autophagy mutants at least partly.

Amino Acids↗
PubMed2003

Metabolic and ultrastructural responses of lupine embryo axes to sugar starvation.

Embryo axes isolated from germinating lupine seeds were cultivated in vitro for 24-96 h over media containing either 60 mmol/L sucrose or no sucrose. Ultrastructural studies showed that large vacuoles were accumulating in a central region of primary parenchyma cells in sucrose starved lupine embryo axes, whereas cytoplasm along with organelles were forced to a periphery of the cells. We suggest that the autolysis of cytoplasmic proteins contributes to the accumulation of the vacuoles and this suggestion is consistent with the results of the characterisation of protein content. The level of cytosolic proteins was reduced by 50% and the activity of cytosolic marker enzyme, PEP carboxylase, was reduced by 46% in starved embryos as compared to control. The mitochondria from starved tissues were not degraded. The level of mitochondrial proteins was reduced by only 10% and the activity of mitochondrial NAD-isocitrate dehydrogenase decreased by 8% as a result of starvation. As demonstrated by the results of Percoll density gradient centrifugation, sucrose starvation caused an increase of 49% in many of the higher density mitochondria fractions, whereas many of the lower density mitochondria fractions were decreased by 33%. The samples of mitochondria from starved embryo axes were determined to have higher respiration activity in the presence of glutamate and malate as compared to control samples. EPR-based analyses of free radicals showed the presence of free radicals with a signal at g = 2.0060 in embryo axes. The level of the radical was two times higher in sucrose-starved embryo axes than in control (the level of this radical increased in senescing plant tissues as well). The results of EPR-based quantitation of Mn2+ ions revealed that the level was a few times higher in starved material than in control. Starved embryo axes, however, do possess a number of adaptive mechanisms protecting them from oxidative damage. Densitometric analyses of gels revealed an increase in the activity of SOD in sugar-starved embryos, whereas CAT and POX activities were lower in axes grown without sucrose as compared to control. Superoxide dismutase, catalase and peroxidase zymogram analyses showed that synthesis of new isoforms was not induced by sugar starvation. An accumulation of phytoferritin was found in plastids of sucrose starved embryos. These results are discussed in relation to the metabolic changes observed in senescing plant tissues.

Antioxidants↗
PubMedDate not supplied

Starvation-induced autophagocytosis paradoxically decreases the susceptibility to oxidative stress of the extremely oxidative stress-sensitive NIT insulinoma cells.

Glucose and amino acid starvation of cells in culture generally enhances their sensitivity to oxidative stress. This is explained by compensatory autophagocytosis, which results in increased amounts of lysosomal low-molecular-weight, redox-active iron, due to the degradation of metallo-proteins, with a potential increase in iron-catalyzed, intralysosomal oxidative reactions. Such reactions diminish the stability of lysosomal membranes, with resultant leakage of hydrolytic enzymes into the cytosol and ensuing cellular degeneration, often of apoptotic type. However, starvation of NIT insulinoma cells, which are normally remarkably sensitive to oxidative stress, actually attenuated the sensitivity to such stress. We found that starved NIT cells rapidly synthesized ferritin. Moreover, ferritin was found to be autophagocytosed, and the lysosomes were stabilized, as assayed by the acridine orange relocation test. We hypothesize that compensatory autophagocytosis during starvation increases the cytosolic pool of redox-active iron, as a reflection of enhanced transportation of low-molecular-weight iron from autophagic lysosomes to the cytosol, resulting in ferritin induction. The newly formed ferritin would, in turn, become autophagocytosed and bind redox-active lysosomal iron in a non-redox-active form. We also suggest that the proposed mechanism may be a way for oxidative stress-sensitive cells to compensate partly for their failing capacity to degrade hydrogen peroxide before it leaks into the acidic vacuolar apparatus and induces intralysosomal oxidative stress. The insulin-producing beta cell may belong to this type of cells.

Animals↗
PubMed2001

The Candida albicans cell wall-associated glyceraldehyde-3-phosphate dehydrogenase activity increases in response to starvation and temperature upshift.

We have determined the effect of environmental factors (mild thermal upshift and starvation) on the Candida albicans cell wall-associated glyceraldehyde-3-phosphate dehydrogenase (cwGAPDH) activity. Temperature upshift (from 28 to 37 degrees C) and/ or starvation (at 28 or 37 degrees C in water) of exponentially growing yeast cells caused an increase in cwGAPDH activity (3 to 5-, and 7 to 8-fold, respectively). This increase in activity did not correlate with an increase in the amount of cwGAPDH protein present, as determined by flow cytometry, immunoelectron microscopy and Western-blotting. These results indicate that thermal upshift and starvation cause an activation of the cwGAPDH in C. albicans cells.

Candida albicans↗
PubMed2004

Dynamic behavior of compost biofilters during periods of starvation and fluctuating hydrogen sulfide loadings.

To understand transient-state performance of biofilters and the phenomena occurring during changes and interruptions in their operating conditions, dynamic behavior of biofilters exposed to shock loadings of contaminant (H2S) and periods of starvation has been investigated. The initial startup and the response of the biofilters to step changes in the H2S concentration and air-loading rate were also presented and discussed. Biofilters responded very effectively to H2S concentration spikes at H2S mass loading rates of 19.8-48.0 g/m3h by rapidly recovering their original removal rates within 1.2-20.2 min. The recovery time after each spike showed a positive correlation to the total amount of H2S loadings during the spike. Biofilters showed capabilities of withstanding 11-28 days of starvations and recovered their full performances after the starvations without any evident lag period.

Air Pollutants↗
PubMed1994

Cytoplasmic dynein undergoes intracellular redistribution concomitant with phosphorylation of the heavy chain in response to serum starvation and okadaic acid.

Cytoplasmic dynein is a microtubule-binding protein which is considered to serve as a motor for retrograde organelle movement. In cultured fibroblasts, cytoplasmic dynein localizes primarily to lysosomes, membranous organelles whose movement and distribution in the cytoplasm have been shown to be dependent on the integrity of the microtubule cytoskeleton. We have recently identified conditions which lead to an apparent dissociation of dynein from lysosomes in vivo, indicating that alterations in membrane binding may be involved in the regulation of retrograde organelle movement (Lin, S. X. H., and C. A. Collins. 1993. J. Cell Sci. 105:579-588). Both brief serum withdrawal and low extracellular calcium levels induced this alteration, and the effect was reversed upon addition of serum or additional calcium. Here we demonstrate that the phosphorylation state of the dynein molecule is correlated with changes in its intracellular distribution in normal rat kidney fibroblasts. Dynein heavy chain phosphorylation level increased during serum starvation, and decreased back to control levels upon subsequent addition of serum. We found that okadaic acid, a phosphoprotein phosphatase inhibitor, mimicked the effects of serum starvation on both phosphorylation and the intracellular redistribution of dynein from a membrane-associated pool to one that was more soluble, with similar dose dependence for both phenomena. Cell fractionation by differential detergent extraction revealed that a higher proportion of dynein was present in a soluble pool after serum starvation than was found in comparable fractions from control cells. Our data indicate that cytoplasmic dynein is phosphorylated in vivo, and changes in phosphorylation state may be involved in a regulatory mechanism affecting the distribution of this protein among intracellular compartments.

8-Bromo Cyclic Adenosine Monophosphate↗
PubMed1998

Protein, fat, and carbohydrate requirements during starvation: anaplerosis and cataplerosis.

The purpose of this work was to clarify the essentiality of glucose production from amino acids in obese subjects undergoing prolonged starvation and to provide an explanation for death after the depletion of lean body mass when some body fat is still available to meet body energy requirements. Five obese subjects fasted for 21 d. Nitrogen balance studies were combined with measurements of blood metabolite and hormone concentrations, indirect calorimetry, determination of body-composition changes, and catheterization techniques. Phenylacetate was administered from day 19 to day 21 to remove glutamine from the body and to assess this perturbation on energy requirements, ammoniagenesis, ureagenesis, gluconeogenesis, and ketogenesis. The obese subjects lost body fat and fat-free mass in parallel and resting metabolic energy requirements per mass remained constant during starvation. Urinary nitrogen excretion reflected continuous demands for amino acid oxidation. Phenylacetate administration decreased blood glutamine concentrations, increased plasma epinephrine concentrations, and increased urinary nitrogen loss through phenylacetylglutamine excretion; urinary excretion rates of urea, ammonium, urate, creatinine, and ketone bodies remained unchanged. The essentiality of amino acid oxidation was therefore shown. Late in prolonged starvation, aminogenic oxidation amounted to 7% and fat provided the remaining energy requirements. Hepatic and renal gluconeogenesis were not curtailed. Blood glutamate served as a vehicle for carbon and nitrogen transport; the contribution of glycerol to gluconeogenesis equaled that of all amino acids combined. The minimal quantities of amino acid (0.27 +/- 0.08 and 0.52 +/- 0.10 g) and fat (1.53 +/- 0.21 and 2.98 +/- 0.15 g) oxidized per kg body wt or fat-free mass/d, respectively, were determined. Included within amino acid and fat oxidation were the minimal amounts of precursors needed for synthesizing the essential quantity of glucose (0.34 +/- 0.14 and 0.66 +/- 0.20 g) oxidized per kg body wt or fat-free mass, respectively.

Adult↗
PubMed2002

Effects of a stay-green mutation on plant nitrogen relations in Lolium perenne during N starvation and after defoliation.

The stay-green mutation of the nuclear gene sid results in inhibition of chlorophyll degradation during leaf senescence in grasses, reducing N remobilization from senescing leaves. Effects on growth of Lolium perenne L. were investigated during N starvation (over 18 d) and after severe defoliation, when leaf growth depends on the remobilization of internal N. Rates of dry mater production, partitioning between shoots and roots, and re-partitioning of N from shoots to roots were very similar in stay-green and normal plants under N starvation. Km and Vmax for net uptake of NH4+ were also similar for both genotypes, and Vmax increased with the duration of N deprivation. The mutation had little effect on recovery of leaf growth following severe defoliation, but stay-green plants recommenced NO3- and K+ uptake 1 d later than normal plants. Import of remobilized N into new leaves was generally similar in both lines. However, stay-green plants remobilized less N from stubble compared with normal plants. It was concluded that the sid locus stay-green mutation has no significant adverse effect on the growth of L perenne during N starvation, or recovery from severe defoliation when plants are grown under an optimal regime of NO3- supply both before and after defoliation. The absence of any effect on leaf dry matter production implies that the difference in foliar N availability attributable to this mutation has little bearing on productivity, at least in the short to medium term.

Algorithms↗
PubMed1981

Starvation for arginine and glutamine sensitizes human diploid cells to the transforming effects of N-acetoxy-2-acetylaminofluorene.

We have examined the influence of the method of synchronization on the transformation of normal human diploid fibroblasts treated in mid-S phase with N-acetylaminofluorene (N-Ac-AAF), and on the subsequent kinetics of the removal of carcinogen damage. At early times post-treatment, the transformation frequency in cultures synchronized by a 24 h starvation for arginine and glutamine was enhanced over that of cultures synchronized by release from confluence. In cells synchronized by either method, transformation was enhanced at all times when the cells were incubated after treatment in medium containing high concentrations of nonessential amino acids, vitamins and serum. Synchronized cells treated with 3 microM [3H]N-Ac-AAF in mid-S removed significantly less DNA damage than cultures treated and held under confluent, noncycling conditions. Cells synchronized by amino acid starvation removed less damage than cells synchronized by release from confluence. S-phase treatment of synchronized cells resulted in a dose-dependent delay of DNA replication. The early, rapid phase of repair was temporally correlated with the delay in S-phase progression. We conclude from these data that synchrony achieved by amino acid starvation renders human cells more sensitive to N-Ac-AAF-induced transformation in vitro than does that achieved by release from density-inhibition of growth. The S-phase treated, cycling cells lost only about 10% of their initial carcinogen damage before reinitiation of treatment-delayed bulk DNA synthesis. These results support the hypothesis that the persistence of carcinogen damage in replicating DNA may be an important factor in cell transformation.

2-Acetylaminofluorene↗
PubMed2002

Gcn4 co-ordinates morphogenetic and metabolic responses to amino acid starvation in Candida albicans.

Candida albicans is a major fungal pathogen of humans. It regulates its morphology in response to various environmental signals, but many of these signals are poorly defined. We show that amino acid starvation induces filamentous growth in C.albicans. Also, starvation for a single amino acid (histidine) induces CaHIS4, CaHIS7, CaARO4, CaLYS1 and CaLYS2 gene expression in a manner reminiscent of the GCN response in Saccharomyces cerevisiae. These morphogenetic and GCN-like responses are both dependent upon CaGcn4, which is a functional homologue of S.cerevisiae Gcn4. Like ScGcn4, CaGcn4 activates the transcription of amino acid biosynthetic genes via the GCRE element, and CaGcn4 confers resistance to the histidine analogue, 3-aminotriazole. CaGcn4 interacts with the Ras-cAMP pathway to promote filamentous growth, but the GCN-like response is not dependent upon morphogenetic signalling. CaGcn4 acts as a global regulator in C.albicans, co-ordinating both metabolic and morphogenetic responses to amino acid starvation.

Amino Acid Sequence↗
PubMed1992

Sequence analysis of mutations arising during prolonged starvation of Salmonella typhimurium.

We have examined the effects of prolonged histidine deprivation on the reversion of Salmonella typhimurium histidine auxotrophs containing either hisG46, a missense mutation (CTC----CCC), or hisG428, an ochre mutation (CAA----TAA). Both of these mutants can revert to His+ via intragenic and extragenic mechanisms. Whereas the hisG46 mutant site consists of G/C base pairs, extragenic suppression of hisG46 requires mutation at an A/T site. Conversely, the hisG428 site itself contains only A/T base pairs, and extragenic suppression of hisG428 occurs principally at G/C sites. Thus, by examining the mutational spectrum of hisG46 and hisG428 revertants that occurred in the presence and in the absence of histidine, it was possible to determine the effects of histidine starvation on mutations at G/C vs. A/T sites as well as on intragenic sites vs. extragenic suppressor sites. Using DNA-colony hybridization, we determined the DNA sequences of over 1300 hisG46 and hisG428 revertants. Histidine-independent revertants that arose during growth in liquid medium that contained histidine included both intragenic and extragenic suppressor mutations. The relative frequency of such extragenic suppressors was greatly reduced among the His+ revertants that were isolated after 5-10 days of histidine starvation on agar medium. Moreover, DNA sequence analysis revealed striking differences in the distribution of particular transversions at the hisG428 locus in revertants arising after prolonged histidine starvation as compared to those arising after growth in the presence of histidine.

Base Sequence↗
PubMed1991

Influence of starvation and lighting on the movement behavior of the German cockroach (Blattodea: Blattellidae).

Computerized moving-image analysis measured the influence of starvation and lighting conditions on the locomotor activity of the German cockroach, Blattella germanica (L.). Starvation increased the distance traveled, velocity, and the proportion of time in motion of adult males and last instars but did not increase adult female movement. For females, males, and nymphs, starvation increased cockroach residence time around the source of water and harborage and decreased the distance traveled by females and nymphs around the observation arena's edge. Fluorescent light reduced the proportion of time in motion for males, but the velocity of males was greater in fluorescent light relative to infrared light. Adult males and females stopped more frequently in infrared light. Overall, males and nymphs were more mobile than females and they explored larger areas. The moving-image analysis technique is an efficient and accurate tool for observing movement of individual cockroaches and has applications in repellency, attractancy, and basic movement behavior studies.

Animals↗
PubMed2003

Physiological, biochemical and molecular analysis of sugar-starvation responses in tomato roots.

Two-month-old tomato plants were submitted to day/night cycles and to prolonged darkness in order to investigate the physiological and biochemical response to sugar starvation in sink organs. Roots appeared particularly sensitive to the cessation of photosynthesis, as revealed by the reduction of the growth rate and the decline of the carbohydrate and protein content. Therefore, excised tomato roots were used as a model to deepen the characterization of sugar starvation symptoms. In excised roots, the endogenous sugars were rapidly exhausted and significant degradation of protein was observed. Glutamine and asparagine accounted for most of the nitrogen released by protein breakdown. Respiration declined and proliferation- and growth-associated genes were repressed soon after the beginning of the sugar depletion. Among the genes studied, only the gene encoding asparagine synthetase was strongly induced. All the starvation symptoms were reversible when the roots were resupplied with sugar. When the culture conditions deteriorated, the metabolic and molecular changes led to the triggering of apoptosis of the root cells.

Amino Acids↗
PubMed1978

RNA synthesis in myeloma cells synchronized by isoleucine starvation.

Myeloma cells have been synchronized by isoleucine starvation. Changes in RNA synthetic rates as a result of starvation have been studied. The ability of isolated nuclei to synthesize RNA declines on starvation and increases subsequently on refeeding isoleucine. There is a coordinate drop in synthetic rate for all three polymerases both in vivo and in vitro. The chain elongation rate in vitro is the same in starved and normal cells, so the difference is in the number of active polymerases in vitro. However, the nuclei do not exactly parallel the state of the cell from which they were isolated, but the in vitro RNA synthesis increases more slowly than the in vivo RNA synthesis. There is no change in relative amounts of synthesis by the different RNA polymerases. The in vitro RNA product is similar in starved and growing cells.

Cell Division↗
PubMed1989

A protein that accumulates during starvation in Tetrahymena nuclei.

Tetrahymena pyriformis was starved in 50 mM Tris-HCl, pH 7.5, at 28 degrees C. The number of cells did not change appreciably under the starvation conditions. Nuclear proteins of unstarved cells and cells starved for 1, 2, 4, and 7 d were analyzed by SDS-polyacrylamide gel electrophoresis. Most of the large amount of nonhistone proteins present in the unstarved cell nucleus disappeared with the starvation time. However, the relative amounts of the high mobility group protein and histones did not change appreciably. On the other hand, a protein with a molecular weight of ca. 16,000 gradually accumulated in the nucleus on starvation. This protein was extracted with 0.25 M HCl, but was not soluble in 0.5 M perchloric acid. The amino acid composition and molecular weight of this protein were similar to those of HMG protein LG-2 of T. thermophila. Some lysyl endopeptidase peptides of this protein were found to have amino acid sequences present in LG-2, thus we tentatively named it an LG-2-like protein.

Amino Acid Sequence↗
PubMed1997

Development, glycolytic activity, and viability of preimplantation mouse embryos subjected to different periods of glucose starvation.

After compaction, the preimplantation mouse embryo switches to a glucose-based metabolism, whereas for the 2- to 4-cell stage embryo, glucose can be inhibitory. In this study, we investigated the adaptability of preimplantation embryos to different periods of glucose starvation by culturing in vitro fertilized (IVF) and in vivo-fertilized 1-cell OF1 mouse embryos. Blastocysts obtained from exposure to glucose starvation for different periods of time were examined for the number of cells in the trophectoderm and inner cell mass, and for glycolytic activity and viability. A high percentage of blastocysts was obtained when 1-cell embryos fertilized in vitro or in vivo were cultured in M16 until the 2-cell stage, were transferred to M16 without glucose (M16-G) until the 4- or 8-cell stage, and then were transferred to fresh M16-G. When in vivo-fertilized 1-cell embryos were cultured to the 2-cell stage and then left in M16, less than 5% formed blastocysts compared to 26% of those transferred into M16-G. Blastocysts obtained when in vivo-fertilized 1-cell embryos were left in M16-G after the 2-cell stage, however, showed a significantly elevated glycolytic activity compared to those transferred to fresh M16 or M16-G medium at the 4- or 8-cell stage. Interestingly, even though these embryos displayed elevated glycolytic activity, they did not exhibit differences in the numbers of inner cell mass and trophectoderm cells or in viability compared to embryos cultured according to other protocols. Blastocysts from all cultured protocols had a significantly lower total cell number and a lower trophectoderm, but not inner cell mass, cell number compared to blastocysts developed in vivo. This study documents the metabolic adaptability of the preimplantation embryo by highlighting its ability to proceed with development and retain viability when challenged with glucose starvation at different periods.

Animals↗