Induction of Cytosolic Acetyl-Coenzyme A Carboxylase in Pea Leaves by Ultraviolet-B Irradiation

Levels of subunits of two acetyl-coenzyme A carboxylases werehigh in small leaves of Pisum sativum, decreased with growth,and remained constant in fully expanded leaves. Irradiationof fully expanded leaves induced the cytosolic isozyme only.This result suggests a key role for the cytosolic enzyme inprotection against UV-B. ¹Present address: Laboratory of Molecular Genetics, BiotechnologyInstitute, Akita Prefectural College of Agriculture, 2-2 Minami,Ohgata, Akita, 010-04 Japan ²Present address: Laboratory of Plant Molecular Biology, Schoolof Agricultural Sciences Nagoya University, Nagoya, 464-01 Japan     

Nucleocytosolic Depletion of the Energy Metabolite Acetyl-Coenzyme A Stimulates Autophagy and Prolongs Lifespan

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Characterization of Maize Acetyl-Coenzyme A Carboxylase

Maize (Zea mays L.) leaf acetyl-CoA carboxylase (ACCase) was purified about 500-fold by ammonium sulfate fractionation and gel filtration and blue Sepharose affinity and anion-exchange chromatography. Most ACCase activity (85%) recovered from the anion-exchange column was found in a highly purified fraction (specific activity 5.5 [mu]mol acid-stable product min-1 mg-1) that consisted primarily of a single 227-kD biotinylated polypeptide. The fraction represented 29% of the original activity and was designated ACCase I. A second partially purified ACCase activity (ACCase II) eluted earlier during anion-exchange chromatography, contained a single biotinylated polypeptide of 219 kD, was poorly recognized by antiserum raised against the ACCase I polypeptide, and was less inhibited by the herbicides haloxyfop or sethoxydim than was ACCase I. ACCase I and II both utilized propionyl-CoA as substrate about 50% as effectively as acetyl-CoA, and neither utilized methylcrotonyl-CoA. Immunoprecipitation with antiserum and protein blotting of crude extracts of leaf, embryo, and endosperm tissue and suspension cells indicated that most ACCase activity in these tissues was immunologically similar and consisted of ACCase I. Only leaves contained significant amounts of the ACCase II polypeptide; however, no ACCase II polypeptide was found in isolated mesophyll chloroplasts. The ACCase I and II polypeptides appear to be subunits of distinct ACCase isoforms.     

Regulation of Autophagy by the p300 Acetyltransferase

Autophagy is a regulated process of intracellular catabolism required for normal cellular maintenance, as well as serving as an adaptive response under various stress conditions, including starvation. The molecular regulation of autophagy in mammalian cells remains incompletely understood. Here we demonstrate a role for protein acetylation in the execution and regulation of autophagy. In particular, we demonstrate that the p300 acetyltransferase can regulate the acetylation of various known components of the autophagy machinery. Knockdown of p300 reduces acetylation of Atg5, Atg7, Atg8, and Atg12, although overexpressed p300 increases the acetylation of these same proteins. Furthermore, p300 and Atg7 colocalize within cells, and the two proteins physically interact. The interaction between p300 and Atg7 is dependent on nutrient availability. Finally, we demonstrate that knockdown of p300 can stimulate autophagy, whereas overexpression of p300 inhibits starvation-induced autophagy. These results demonstrate a role for protein acetylation and particularly p300 in the regulation of autophagy under conditions of limited nutrient availability.Macro-autophagy, herein referred to as autophagy, is an evolutionary conserved process first characterized in lower organisms (1). In yeast, over 20 separate genes (designated ATG1, ATG2, etc.) have been demonstrated to be essential to carry out the autophagy program. This process is thought to provide a mechanism for the efficient removal of both long lived proteins and damaged cellular organelles. This regulated degradation provides several essential functions for the cell. First, it allows for the removal of damaged and potentially harmful cellular contents. In addition, in breaking down various intracellular components, the autophagy process provides essential building blocks for the cell to use in the re-synthesis of necessary macromolecules. To accomplish this recycling effort, the coordinated actions of various Atg gene products are required. In particular, the Atg gene products together orchestrate the formation of a double membrane structure known as the autophagosome that engulfs the intended cellular cargo targeted for degradation. The autophagosome eventually fuses with the vacuole in yeast or the lysosome in mammals.In both yeast and mammalian cells, autophagy can be stimulated by the withdrawal of nutrients. Under these conditions, autophagic degradation of nonessential components may be essential to meet ongoing energetic needs in the presence of limited extracellular nutrients. This point was underscored by the analysis of mice containing a targeted deletion of Atg5 (2). In the absence of Atg5, there is a lack of both basal and starvation-induced autophagy. Mice lacking Atg5 are born normally but succumb within the 1st day of life. This post-natal lethality is thought to be due in large part for the requirement of autophagy to supply the energetic needs of neonates. These needs are particularly critical during the small window of time where the animal no longer has a placental circulation and before the pup can begin to nurse and thus obtain external nutrients.Relatively little is known regarding how signals such as nutrient availability are able to be transduced to ultimately regulate the level of cellular autophagy. One important pathway that impinges on the process is signaling thorough the target of rapamycin (TOR)2 network (3). Evidence suggests that TOR signaling inhibits autophagy, and indeed agents such as rapamycin that can inhibit TOR are known to result in increased autophagy. We recently have observed that in addition to this mode of regulation, the NAD-dependent deacetylase Sirt1 is also a regulator of autophagy in mammalian cells and tissues (4). In particular, we demonstrated that in the absence of Sirt1 levels of acetylation for various components of the autophagy machinery are increased and that starvation-induced autophagy is impaired. Interestingly, like the Atg5 knock-out animals, Sirt1^-/- mice are also born normally but die within the few hours to days after birth. Consistent with a defect in autophagy, electron micrographs of hearts from Sirt1^-/- mice demonstrated an accumulation of abnormal appearing organelles, including mitochondria, a phenotype previously observed in Atg-deficient animals (5). Here we have further characterized the role of acetylation in the regulation of autophagy, and in particular, we demonstrate a role for the p300 acetyltransferase in this process.     

The Salmonella Deubiquitinase SseL Inhibits Selective Autophagy of Cytosolic Aggregates

Cell stress and infection promote the formation of ubiquitinated aggregates in both non-immune and immune cells. These structures are recognised by the autophagy receptor p62/sequestosome 1 and are substrates for selective autophagy. The intracellular growth of Salmonella enterica occurs in a membranous compartment, the Salmonella-containing vacuole (SCV), and is dependent on effectors translocated to the host cytoplasm by the Salmonella pathogenicity island-2 (SPI-2) encoded type III secretion system (T3SS). Here, we show that bacterial replication is accompanied by the formation of ubiquitinated structures in infected cells. Analysis of bacterial strains carrying mutations in genes encoding SPI-2 T3SS effectors revealed that in epithelial cells, formation of these ubiquitinated structures is dependent on SPI-2 T3SS effector translocation, but is counteracted by the SPI-2 T3SS deubiquitinase SseL. In macrophages, both SPI-2 T3SS-dependent aggregates and aggresome-like induced structures (ALIS) are deubiquitinated by SseL. In the absence of SseL activity, ubiquitinated structures are recognized by the autophagy receptor p62, which recruits LC3 and targets them for autophagic degradation. We found that SseL activity lowers autophagic flux and favours intracellular Salmonella replication. Our data therefore show that there is a host selective autophagy response to intracellular Salmonella infection, which is counteracted by the deubiquitinase SseL.     

Mechanism of α-Glycerophosphate Regulation of Acetyl-Coenzyme A Carboxylase of Saccharomyces cerevisiae

The mechanism proposed for the activation of animal acetyl-coenzyme A (CoA) carboxylase by alpha-glycerophosphate, namely, the removal of inhibitory palmityl-CoA via glyceride synthesis, is not the only possible one in the yeast system because extracts exhibiting marked stimulation of acetyl-CoA carboxylase activity by alpha-glyerophosphate show a lack of acyl-CoA compounds.     

细胞自噬在病毒感染与免疫调节中的作用机制

细胞自噬(autophagy)是一种主要由溶酶体介导的降解通路,作为细胞维持内环境稳态的一种保护性机制,不仅通过将长寿命蛋白和衰老细胞器降解为小肽或氨基酸为细胞提供再生资源,而且也可作为防御机制抵抗病原微生物感染和寄生. 自噬缺失与许多疾病如癌症、心血管疾病等的发生关系密切,在机体生理、病理过程中发挥重要作用. 本文拟就细胞自噬与病毒感染、机体免疫的关系加以综述,以期为研究细胞自噬的发生、参与机体免疫、发挥抗病毒感染作用及其分子机制提供参考,也为进一步研究抗病毒治疗的靶标提供新思路.     

Regulation of Histone Acetylation by Autophagy in Parkinson Disease

Parkinson disease (PD) is the most common age-dependent neurodegenerative movement disorder. Accumulated evidence indicates both environmental and genetic factors play important roles in PD pathogenesis, but the potential interaction between environment and genetics in PD etiology remains largely elusive. Here, we report that PD-related neurotoxins induce both expression and acetylation of multiple sites of histones in cultured human cells and mouse midbrain dopaminergic (DA) neurons. Consistently, levels of histone acetylation are markedly higher in midbrain DA neurons of PD patients compared to those of their matched control individuals. Further analysis reveals that multiple histone deacetylases (HDACs) are concurrently decreased in 1-methyl-4-phenylpyridinium (MPP⁺)-treated cells and 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-treated mouse brains, as well as midbrain tissues of human PD patients. Finally, inhibition of histone acetyltransferase (HAT) protects, whereas inhibition of HDAC1 and HDAC2 potentiates, MPP⁺-induced cell death. Pharmacological and genetic inhibition of autophagy suppresses MPP⁺-induced HDACs degradation. The study reveals that PD environmental factors induce HDACs degradation and histone acetylation increase in DA neurons via autophagy and identifies an epigenetic mechanism in PD pathogenesis.     

Regulation of the Fast Vacuolar Channel by Cytosolic and Vacuolar Potassium

At resting cytosolic Ca²⁺, passive K⁺ conductance of a higher plant tonoplast is likely dominated by fast vacuolar (FV) channels. This patch-clamp study describes K⁺-sensing behavior of FV channels in Beta vulgaris taproot vacuoles. Variation of K⁺ between 10 and 400 mM had little effect on the FV channel conductance, but a pronounced one on the open probability. Shift of the voltage dependence by cytosolic K⁺ could be explained by screening of the negative surface charge with a density σ = 0.25 e⁻/nm². Vacuolar K⁺ had a specific effect on the FV channel gating at negative potentials without significant effect on closed-open transitions at positive ones. Due to K⁺ effects at either membrane side, the potential at which the FV channel has minimal activity was always situated at ~50 mV below the potassium equilibrium potential, E_K⁺. At tonoplast potentials below or equal to E_K⁺, the FV channel open probability was almost independent on the cytosolic K⁺ but varied in a proportion to the vacuolar K⁺. Therefore, the release of K⁺ from the vacuole via FV channels could be controlled by the vacuolar K⁺ in a feedback manner; the more K⁺ is lost the lower will be the transport rate.     

Cellular Localization of Acetyl-Coenzyme A Synthetase in Yeast

In cells of Saccharomyces cerevisiae grown with glucose in standing cultures, the microsomal fraction had the highest specific activity for acetyl-coenzyme A synthetase and contained the greatest fraction of the total activity regardless of when the cells were harvested during growth. The addition of acetate did not affect the distribution of the enzyme, nor did subsequent aeration of such cells in phosphate buffer even in the presence of glucose, acetate, or succinate. In cells grown aerobically, however, the microsomal fraction had the highest specific activity and the greatest fraction of the total activity only until the cells reached the stationary phase. After this time, most of the activity was associated with the mitochondrial fraction. Finally, 3 or 4 days after inoculation, this fraction appeared to lose most of the enzyme to the microsomal and soluble fractions. Chloramphenicol, at concentrations that interfered with respiration but not with fermentation, prevented the association of acetyl-coenzyme A synthetase with the mitochondrial fraction in aerated cells, but it did not appreciably affect the large increases in enzyme activity observed during aerobic incubation. Cells grown with glucose under strict anaerobic conditions contained barely detectable amounts of acetyl-coenzyme A synthetase.     

Repression of Acetyl-Coenzyme A Carboxylase by Unsaturated Fatty Acids: Relationship to Coenzyme Repression

It has been reported that the level of d-biotin in the growth medium of Lactobacillus plantarum regulates the synthesis of apoacetyl-coenzyme A (CoA) carboxylase; high levels cause repression, and deficient levels effect derepression. In this study, evidence has been obtained which suggests that coenzyme repression by biotin is an indirect effect; i.e., biotin regulates the synthesis of unsaturated fatty acids which are the true repressors of the acetyl-CoA carboxylase. This was observed in an experiment in which long-chain unsaturated fatty acids were added to media containing deficient, sufficient, or excess levels of d-biotin. In every case, independently of the biotin concentration for growth, the unsaturated fatty acids caused a severe repression of the carboxylase. Saturated fatty acids were without effect. The level of oleic acid required to give maximal repression was 50 mug/ml. The free fatty acids had no adverse effect on the activity of the cell-free extracts nor on the permeation of d-biotin into the cell. Saturated and unsaturated fatty acids decreased the rate of holocarboxylase formation from d-biotin and the apoacetyl-CoA carboxylase in the extracts. It is concluded that there are at least three mechanisms that control the acetyl-CoA carboxylase in this organism: (i) indirect coenzyme repression by d-biotin, (ii) repression by unsaturated fatty acids, and (iii) regulation of the activity of the holocarboxylase synthetase by both saturated and unsaturated fatty acids.     

Studies on Acetyl-Coenzyme A Synthetase of Yeast: Inhibition by Long-Chain Acyl-Coenzyme A Esters

Long-chain acyl-coenzyme A (CoA) compounds (palmityl, stearyl, and oleyl) were found to be potent inhibitors of acetyl-CoA synthetase (ACS) of Saccharomyces cerevisiae strain LK2G12 from aerobic, but not from nonaerobic, cells. The effectiveness of the inhibitors of the aerobic enzyme was in the following order: palmityl-CoA < stearyl-CoA < oleyl-CoA. Short-chain acyl-CoA compounds (propionyl, butyryl, and valeryl) and long-chain fatty acids had no effect on ACS from either source. The inhibition by oleyl-CoA was found to be dependent on enzyme concentration, whereas the inhibition by palmityl- and stearyl-CoA was independent of ACS concentration. Inhibition by palmityl-CoA was noncompetitive with respect to both acetate and CoA, and with increasing concentration of inhibitor the pattern was sigmoidal, with a Hill value of 3.24. At maximally inhibitory concentrations of palmityl-CoA, a small amount of enzyme activity remained. This noninhibitable enzyme in aerobic cells was shown not to be of nonaerobic origin.     

Cytosolic HMGB1 Mediates Autophagy Activation in an Emulsified Isoflurane Anesthesia Cell Model

Neurochemical Research - Inhalation anesthetic isoflurane may cause an increased risk of cognitive impairment. Previous studies have indicated that this cognitive decline is associated with...