UMLS:C0038187 - FACTA Search

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Query: UMLS:C0038187 (starvation)
24,951 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Microtubule-associated protein 1 light chain 3 (LC3) is a unique modifier protein. LC3-I, the cytosolic form, is modified to LC3-II, the membrane-bound form, by a mechanism similar to ubiquitylation by E1- and E2-like enzymes, Apg7p and Apg3p, respectively. In the present study, we found that LC3-I is processed to LC3-II during the differentiation and recovery from puromycin aminonucleoside-induced nephrosis of podocytes. LC3 is especially expressed in the podocytes of rat kidney as the membrane-bound form LC3-II. Biochemical analysis using a conditionally immortalized mouse podocyte clone (MPC) revealed that LC3-I is processed to LC3-II during the differentiation of cells into mature podocytes and accumulates in the membrane-rich fraction of the cell lysate. LC3-II-localized vesicles, which differ from lysosomes and endosomes, in differentiated MPC cells are morphologically similar to autophagic vacuoles during starvation-induced autophagy. During starvation-induced autophagy, autophagosomes fuses with lysosome and LC3-II on autophagosomes is finally degraded by lysosomal proteases. However, in differentiated MPC cells, little LC3-II on the vesicles is degraded by lysosomal proteases, suggesting that little LC3-II-localized vesicles in differentiated MPC cells fuse with lysosome. Furthermore, the LC3-II level in differentiated MPC cells increases with recovery from damage caused by experimental puromycin aminonucleoside-induced nephrosis. These results suggest that LC3-II-localized vesicles play an important role in the physiological function of podocytes.
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PMID:MAP-LC3, a promising autophagosomal marker, is processed during the differentiation and recovery of podocytes from PAN nephrosis. 1270 12

Autophagy in plant cells is induced by nutrient starvation. Initially, double membrane-bound organelles, termed autophagosomes, enclose a portion of cytoplasm, and then fuse with a vacuole or lysosome to give an autolysosome. Autolysosomes can be visualized by incubating cells in the presence of a membrane-permeable cysteine protease inhibitor. The inhibitor presumably decreases proteolytic degradation of the autolysosome contents that are composed of portions of cytoplasm enclosed by the membrane originating from the inner membrane of autophagosomes, and allows them to accumulate. The origin of membranes that give rise to autophagosomes and autolysosomes is unknown. Here we use an acidotropic fluorescent dye, LysoTracker Red, to label autolysosomes specifically. We demonstrate that autolysosome membranes are marked by the presence of alpha-tonoplast intrinsic protein (alpha-TIP) but not by gamma-TIP or delta-TIP. The identification of a TIP specifically associated with membranes derived from an autophagic process may help our understanding of how plant cells generate and maintain functionally distinct types of vacuoles.
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PMID:Alpha tonoplast intrinsic protein is specifically associated with vacuole membrane involved in an autophagic process. 1294 71

The roles of two adjacent genes in the Staphylococcus aureus chromosome with functions in starvation survival and the response to stressful conditions have been characterized. One of these, hprT, encoding a hypoxanthine-guanine phosphoribosyltransferase homologue, was initially identified in a transposon mutagenesis screen. Mutation of hprT affects starvation survival in amino-acid-limiting conditions and the ability of S. aureus to grow in high-salt concentrations. Downstream of hprT is ftsH, which encodes a membrane-bound, ATP- and Zn(2+)-dependent 'AAA'-type protease. Mutation of ftsH in S. aureus leads to pleiotropic defects including slower growth, sensitivity to salt, acid, methyl viologen and potassium tellurite stresses, and reduced survival in amino-acid- or phosphate-limiting conditions. Both hprT-lacZ and ftsH-lacZ gene fusions are expressed maximally in the post-exponential phase of growth. Although secretion of exoproteins is not affected, an ftsH mutant is attenuated in a murine skin lesion model of pathogenicity.
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PMID:Role of the hprT-ftsH locus in Staphylococcus aureus. 1476 15

Starvation induces Bacillus subtilis to initiate a developmental process (sporulation) that includes asymmetric cell division to form the prespore and the mother cell. The integral membrane protein SpoIIE is essential for the prespore-specific activation of the transcription factor sigmaF, and it also has a morphogenic activity required for asymmetric division. An increase in the local concentration of SpoIIE at the polar septum of B. subtilis precedes dephosphorylation of the anti-anti-sigma factor SpoIIAA in the prespore. After closure and invagination of the asymmetric septum, phosphatase activity of SpoIIE increases severalfold, but the reason for this dramatic change in activity has not been determined. The central domain of SpoIIE has been seen to self-associate (I. Lucet et al., EMBO J. 19:1467-1475, 2000), suggesting that activation of the C-terminal PP2C-like phosphatase domain might be due to conformational changes brought about by the increased local concentration of SpoIIE in the sporulating septum. Here we report the inclusion of purified SpoIIE protein into a model membrane as a method for studying the effect of local concentration in a lipid bilayer on activity. In vitro assays indicate that the membrane-bound enzyme maintains dephosphorylation rates similar to the highly active micellar state at all molar ratios of protein to lipid. Atomic force microscopy images indicate that increased local concentration does not lead to self-association.
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PMID:Evaluation of the kinetic properties of the sporulation protein SpoIIE of Bacillus subtilis by inclusion in a model membrane. 1512 82

Bacterial extra cytoplasmic function (ECF) sigma factors control a wide range of cell envelope activities including iron and haem uptake systems. Sigma activity is usually inhibited by membrane-bound antisigma. An extra cytoplasmic signal modulates sigma-antisigma interactions and thereby leads to the transcription of the target operon. Sigma and antisigma genes generally belong to one autoregulated operon. However, ECF sigma and antisigma genes involved in iron acquisition, also called iron starvation ECF, are non-autoregulated exceptions to this rule. We fully reconstituted the has signalling cascade of Serratia marcescens in Escherichia coli. Binding of the haem-loaded haemophore to the outer membrane receptor, HasR, inactivates the antisigma HasS, turning on HasI and thereby allowing has operon transcription. Deletion of the HasR N-terminal extension, present in all characterized outer membrane receptors endowed with signal transduction capacity, abolished the inducing activity but not the transport activity. Induction required the TonB-ExbB-ExbD complex. HasI, like the other iron starvation sigma, is iron repressed but not autoregulated. We found an entirely new regulation for the antisigma hasS gene, the transcription of which is HasI dependent. We suggest that the has system is both activated and repressed by the availability of external haem. When there is enough haem, the HasS antisigma activity is turned off and HasI induces the transcription of hasS. This leads to the storage of inactive HasS molecules which become active when HasR is not occupied by holo-haemophore ligand molecules: as soon as there is a haem shortage transcription is turned off. Positive autoregulation of ECF sigma and antisigma genes is usually considered as a mechanism for amplifying a perceived signal. However, our findings suggest, on the contrary, that antisigma regulation allows fine-tuning to the external signal. The biological significance of ECF sigma and antisigma autoregulation may need to be reconsidered.
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PMID:Haemophore-mediated signalling in Serratia marcescens: a new mode of regulation for an extra cytoplasmic function (ECF) sigma factor involved in haem acquisition. 1530 27

P(II)-type signal transduction proteins play a central role in nitrogen regulation in many bacteria. In response to the intracellular nitrogen status, these proteins are rendered in their function and interaction with other proteins by modification/demodification events, e.g. by phosphorylation or uridylylation. In this study, we show that GlnK, the only P(II)-type protein in Corynebacterium glutamicum, is adenylylated in response to nitrogen starvation and deadenylylated when the nitrogen supply improves again. Both processes depend on the GlnD protein. As shown by mutant analyses, the modifying activity of this enzyme is located in the N-terminal part of the enzyme, while demodification depends on its C-terminal domain. Besides its modification status, the GlnK protein changes its intracellular localization in response to changes of the cellular nitrogen supply. While it is present in the cytoplasm during nitrogen starvation, the GlnK protein is sequestered to the cytoplasmic membrane in response to an ammonium pulse following a nitrogen starvation period. About 2-5% of the GlnK pool is located at the cytoplasmic membrane after ammonium addition. GlnK binding to the cytoplasmic membrane depends on the ammonium transporter AmtB, which is encoded in the same transcriptional unit as GlnK and GlnD, the amtB-glnK-glnD operon. In contrast, the structurally related methylammonium/ammonium permease AmtA does not bind GlnK. The membrane-bound GlnK protein is stable, most likely to inactivate AmtB-dependent ammonium transport in order to prevent a detrimental futile cycle under post-starvation ammonium-rich conditions, while the majority of GlnK is degraded within 2-4 min. Proteolysis in the transition period from nitrogen starvation to nitrogen-rich growth seems to be specific for GlnK; other proteins of the nitrogen metabolism, such as glutamine synthetase, or proteins unrelated to ammonium assimilation, such as enolase and ATP synthase subunit F(1)beta, are stable under these conditions. Our analyses of different mutant strains have shown that at least three different proteases influence the degradation of GlnK, namely FtsH, the ClpCP and the ClpXP protease complex.
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PMID:Regulation of GlnK activity: modification, membrane sequestration and proteolysis as regulatory principles in the network of nitrogen control in Corynebacterium glutamicum. 1545 11

In the haloarchaea Haloferax volcanii, ribosomes are found in the cytoplasm and membrane-bound at similar levels. Transformation of H. volcanii to express chimeras of the translocon components SecY and SecE fused to a cellulose-binding domain substantially decreased ribosomal membrane binding, relative to non-transformed cells, likely due to steric hindrance by the cellulose-binding domain. Treatment of cells with the polypeptide synthesis terminator puromycin, with or without low salt washes previously shown to prevent in vitro ribosomal membrane binding in halophilic archaea, did not lead to release of translocon-bound ribosomes, indicating that ribosome release is not directly related to the translation status of a given ribosome. Release was, however, achieved during cell starvation or stationary growth, pointing at a regulated manner of ribosomal release in H. volcanii. Decreased ribosomal binding selectively affected membrane protein levels, suggesting that membrane insertion occurs co-translationally in Archaea. In the presence of chimera-incorporating sterically hindered translocons, the reduced ability of ribosomes to bind in the transformed cells modulated protein synthesis rates over time, suggesting that these cells manage to compensate for the reduction in ribosome binding. Possible strategies for this compensation, such as a shift to a post-translational mode of membrane protein insertion or maintained ribosomal membrane-binding, are discussed.
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PMID:In the Archaea Haloferax volcanii, membrane protein biogenesis and protein synthesis rates are affected by decreased ribosomal binding to the translocon. 1547 49

Cold ischemia-warm reperfusion injury of liver grafts has been investigated thoroughly, but its underlying mechanism remains poorly understood. Here we show that autophagy is involved not only during cold preservation but also during warm reperfusion following transplantation. Immunohistochemistry using an antibody against LC3, a microtubule associated protein 1 light chain 3 and a marker of autophagosomes, showed dot-like weak staining in hepatocytes of rat liver grafts during cold preservation. Since University of Wisconsin solution for graft preservation lacks amino acids, the induction of autophagy in hepatocytes was similar to that under starvation conditions. Intense immunopositive punctate structures were detected abundantly in the hepatocytes 30 min after the beginning of reperfusion. LC3-positive granules were often co-localized in ED2-positive Kupffer cells at 60 min of the reperfusion phase. The molecular form of LC3 was mainly LC3-II, a membrane-bound form, during reperfusion, especially at 30 min of the phase. Electron microscopic examination demonstrated numerous vacuolar structures in hepatocytes at 30 min of the reperfusion period, while some hepatocytes with such vacuolar structures were present in the sinusoidal lumen. At the late stage of the reperfusion period, Kupffer cells contained phagocytosed cells that possessed numerous autophagic vacuoles/autolysosomes and nuclei with condensed chromatin. Our results showing the presence of autophagic vacuoles/autolysosomes in hepatocytes of liver grafts after the start of reperfusion suggest that warm reperfusion acted as a stress stimulus to hepatocytes. Moreover, the stress response of hepatocytes may be involved in their degeneration process.
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PMID:Participation of autophagy in the degeneration process of rat hepatocytes after transplantation following prolonged cold preservation. 1582 80

Autophagy is a process that is thought to occur in all eukaryotes in which cells recycle cytoplasmic contents when subjected to environmental stress conditions or during certain stages of development. Upon induction of autophagy, double membrane-bound structures called autophagosomes engulf portions of the cytoplasm and transfer them to the vacuole or lysosome for degradation. In this study, we have characterized two potential markers for autophagy in plants, the fluorescent dye monodansylcadaverine (MDC) and a green fluorescent protein (GFP)-AtATG8e fusion protein, and propose that they both label autophagosomes in Arabidopsis. Both markers label the same small, apparently membrane-bound structures found in cells under conditions that are known to induce autophagy such as starvation and senescence. They are usually seen in the cytoplasm, but occasionally can be observed within the vacuole, consistent with a function in the transfer of cytoplasmic material into the vacuole for degradation. MDC-staining and the GFP-AtATG8e fusion protein can now be used as very effective tools to complement biochemical and genetic approaches to the study of autophagy in plant systems.
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PMID:Visualization of autophagy in Arabidopsis using the fluorescent dye monodansylcadaverine and a GFP-AtATG8e fusion protein. 1586 17

Several different cellular processes determine the size of the metabolically available nitrate pool in the cytoplasm. These processes include not only ion fluxes across the plasma membrane and tonoplast but also assimilation by the activity of nitrate reductase (NR). In roots, the maintenance of cytosolic nitrate activity during periods of nitrate starvation and resupply (M. van der Leij, S.J. Smith, A.J. Miller [1998] Planta 205: 64-72; R.-G. Zhen, H.-W. Koyro, R.A. Leigh, A.D. Tomos, A.J. Miller [1991] Planta 185: 356-361) suggests that this pool is regulated. Under nitrate-replete conditions vacuolar nitrate is a membrane-bound store that can release nitrate to the cytoplasm; after depletion of cytosolic nitrate, tonoplast transporters would serve to restore this pool. To study the role of assimilation, specifically the activity of NR in regulating the size of the cytosolic nitrate pool, we have compared wild-type and mutant plants. In leaf mesophyll cells, light-to-dark transitions increase cytosolic nitrate activity (1.5-2.8 mm), and these changes were reversed by dark-to-light transitions. Such changes were not observed in nia1nia2 NR-deficient plants indicating that this change in cytosolic nitrate activity was dependent on the presence of functional NR. Furthermore, in the dark, the steady-state cytosolic nitrate activities were not statistically different between the two types of plant, indicating that NR has little role in determining resting levels of nitrate. Epidermal cells of both wild type and NR mutants had cytosolic nitrate activities that were not significantly different from mesophyll cells in the dark and were unaltered by dark-to-light transitions. We propose that the NR-dependent changes in cytosolic nitrate provide a cellular mechanism for the diurnal changes in vacuolar nitrate storage, and the results are discussed in terms of the possible signaling role of cytosolic nitrate.
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PMID:Light-dark changes in cytosolic nitrate pools depend on nitrate reductase activity in Arabidopsis leaf cells. 1590 93

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