Shigella and autophagy

Bacterial invasion of eukaryotic cells, and host recognition and elimination of the invading bacteria, determines the fate of bacterial infection. Once inside mammalian cells, many pathogenic bacteria enter the host cytosol to escape from the lytic compartment and gain a replicative niche. Recent studies indicate that autophagy also recognizes intracellular bacteria. Although autophagy is a conserved membrane trafficking pathway in eukaryotic cells that sequesters undesirable or recyclable cytoplasmic components or organelles and delivers them to lysosomes, autophagy has recently been described as playing a pivotal role as an intracellular surveillance system for recognition and eradication of the pathogens that have invaded the cytoplasm. Indeed, unless they are able to circumvent entrapping by autophagosomes, bacteria ultimately undergo degradation by delivery into autolysosomes. In this review we discuss recent discoveries regarding Shigella strategies for infecting mammalian cells, and then focus on recent studies of an elegant bacterial survival strategy against autophagic degradation.     

Seed Germination and Radicle Growth of a Halophyte, Kalidium caspicum(Chenopodiaceae)

Effects of temperature, light, NaCl and polyethylene glycol(PEG)-6000 on seed germination and radicle growth in a halophyticshrub, Kalidium caspicum(L.) Ung.-Sternb. were investigated.When seeds were incubated in deionized water at constant temperaturesbetween 10 and 30°C, the percentage germination in the darkexceeded 75%; light suppressed seed germination at alternatingtemperatures. Incubating seeds with a hypersaline solution ofNaCl for 30 d had no adverse effect on their germinability.The percentage germination of seeds incubated with a –0.8MPa NaCl solution was 73, 80 and 54% at 10, 20 and 30°C,respectively, but all radicles died before their length exceeded5 mm. In contrast, when seeds were incubated with a –0.8MPa PEG solution at 20°C, 68% of seeds germinated, and 95%of the emerging radicles survived beyond 5 mm. The high sensitivityof small radicles of this species to salinity indicated thatsalt must be removed from the soil surface for seedling establishment.Copyright2000 Annals of Botany Company Chinese desert, radicle growth, germination, halophyte, Kalidium caspicum, salinity     

Purification and characterization of a novel enzyme, arylalkyl acylamidase, from Pseudomonas putida Sc2.

A novel enzyme, arylalkyl acylamidase, which shows a strict specificity for N-acetyl arylalkylamines, but not acetanilide derivatives, was purified from the culture broth of Pseudomonas putida Sc2. The purified enzyme appeared to be homogeneous, as judged by native and SDS/PAGE. The enzyme has a molecular mass of approximately 150 kDa and consists of four identical subunits. The purified enzyme catalyzed the hydrolysis of N-acetyl-2-phenylethylamine to 2-phenylethylamine and acetic acid at the rate of 6.25 mumol.min-1.mg-1 at 30 degrees C. It also catalyzed the hydrolysis of various N-acetyl arylalkylamines containing a benzene or indole ring, and acetic acid arylalkyl esters. The enzyme did not hydrolyze acetanilide, N-acetyl aliphatic amines, N-acetyl amino acids, N-acetyl amino sugars or acylthiocholine. The apparent Km for N-acetylbenzylamine, N-acetyl-2-phenylethylamine and N-acetyl-3-phenylpropylamine are 41 mM, 0.31 mM and 1.6 mM, respectively. The purified enzyme was sensitive to thiol reagents such as Ag2SO4, HgCl2 and p-chloromercuribenzoic acid, and its activity was enhanced by divalent metal ions such as Zn2+, Mg2+ and Mn2+.     

Immunocytochemical studies on the pancreatic endocrine cells in the Japanese newt (Cynopus pyrrhogaster)]

Pancreatic endocrine cells were examined by light and electron microscopic immunocytochemistry to discuss the co-localization of peptides in one cell type. A cells were irregular in shape with an occasional long cytoplasmic process, and contained glucagon-immunoreactive granules with various contours. These granules were 160-300nm in diameter with various density, and also immunoreactive to anti-human pancreatic polypeptide (PP) serum. A part of them were further immunoreactive to anti-somatostatin serum. B cells were round to elliptical in shape, and often aggregated around the capillaries. Granules of B cells were round to irregular in shape, 270-410 nm in diameter, and immunoreactive to anti-insulin serum. D cells were irregular in shape with meager cytoplasm, and contained somatostatin-immunoreactive granules. These granules were ovoid or teardrop in shape, 140-250nm in longitudinal diameter, and immunoreactive to both anti-somatostatin and anti-human PP sera. PP cells were round to spindle-shaped, and contained human PP-immunoreactive round granules 150-35nm in diameter. These findings reveal the existence of at least 4 types of endocrine cells secreting glucagon, insulin, somatostatin, and PP, respectively, in the newt pancreas, and suggest the co-localization of some of these peptides in one cell type.     

Enhanced plasma ghrelin levels in rats with streptozotocin-induced diabetes

Human saliva, which contains nitrite, is normally mixed with gastric juice, which contains ascorbic acid (AA). When saliva was mixed with an acidic buffer in the presence of 0.1 mM AA, rapid nitric oxide formation and oxygen uptake were observed. The oxygen uptake was due to the oxidation of nitric oxide, which was formed by AA-dependent reduction of nitrite under acidic conditions, by molecular oxygen. A salivary component SCN⁻ enhanced the nitric oxide formation and oxygen uptake by the AA/nitrite system. The oxygen uptake by the AA/nitrite/SCN⁻ system was also observed in an acidic buffer solution. These results suggest that oxygen is normally taken up in the stomach when saliva and gastric juice are mixed.     

Pigment-dispersing factor affects nocturnal activity rhythms, photic entrainment, and the free-running period of the circadian clock in the cricket gryllus bimaculatus

Pigment-dispersing factor (PDF) is a neuropeptide widely distributed in insect brains and plays important roles in the circadian system. In this study, we used RNA interference to study the role of the pigment-dispersing factor (pdf) gene in regulating circadian locomotor rhythms in the cricket, Gryllus bimaculatus. Injections of pdf double-stranded RNA (dspdf) effectively knocked down the pdf mRNA and PDF peptide levels. The treated crickets maintained the rhythm both under light-dark cycles (LD) and constant darkness (DD). However, they showed rhythms with reduced nocturnal activity with prominent peaks at lights-on and lights-off. Entrainability of dspdf-injected crickets was higher than control crickets as they required fewer cycles to resynchronize to the LD cycles shifted by 6 h. The free-running periods of the dspdf-injected crickets were shorter than those of control crickets in DD. These results suggest that PDF is not essential for the rhythm generation but involved in control of the nocturnality, photic entrainment, and fine tuning of the free-running period of the circadian clock.     

Dietary resveratrol prevents the development of food allergy in mice

Background

Resveratrol is a bioactive polyphenol enriched in red wine that exhibits many beneficial health effects via multiple mechanisms. However, it is unclear whether resveratrol is beneficial for the prevention of food allergy. This study investigated whether resveratrol inhibited the development of food allergy by using a mouse model of the disease.

Methodology/Principal Findings

Mice fed standard diet or standard diet plus resveratrol were sensitized by intragastric administration of ovalbumin (OVA) and mucosal adjuvant cholera toxin (CT). Several manifestations of food allergy were then compared between the mice. The effects of resveratrol on T cells or dendritic cells were also examined by using splenocytes from OVA-specific T cell-receptor (TCR) transgenic DO11.10 mice or mouse bone marrow-derived dendritic cells (BMDCs) in vitro. We found that mice fed resveratrol showed reduced OVA-specific serum IgE production, anaphylactic reaction, and OVA-induced IL-13 and IFN-ã production from the mesenteric lymph nodes (MLNs) and spleens in comparison to the control mice, following oral sensitization with OVA plus CT. In addition, resveratrol inhibited OVA plus CT-induced IL-4, IL-13, and IFN-ã production in splenocytes from DO11.10 mice associated with inhibition of GATA-3 and T-bet expression. Furthermore, resveratrol suppressed the OVA plus CT-induced CD25 expression and IL-2 production in DO11.10 mice-splenocytes in association with decreases in CD80 and CD86 expression levels. Finally, resveratrol suppressed CT-induced cAMP elevation in association with decreases in CD80 and CD86 expression levels in BMDCs.

Conclusions/Significance

Ingestion of resveratrol prevented the development of a food allergy model in mice. Given the in vitro findings, resveratrol might do so by inhibiting DC maturation and subsequent early T cell activation and differentiation via downregulation of CT-induced cAMP activation in mice. These results suggest that resveratrol may have potential for prophylaxis against food allergy.     

Interaction of alpha-and beta-oligoarginine-acids and amides with anionic lipid vesicles: a mechanistic and thermodynamic study

The interaction of alpha- and beta-oligoarginine amides and acids and of alpha-polyarginine with anionic lipid vesicles was studied. The beta-oligoarginines used were beta3-homologues of the alpha-oligoarginines. Lipid bilayers were composed of POPC (1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine) and POPG (1-palmitoyl-2-oleoyl-sn-glycero-3-[phospho-rac-(1-glycerol)]) containing 5 mol % pyrene-PG (1-hexadecanoyl-2-(1-pyrenedecanoyl)-sn-glycero-3-[phospho-rac-1-glycerol]). Kinetic analysis of the binding process onto large unilamellar POPC/POPG (3:7, molar ratio) vesicles (100 nm diameter) shows biphasic time courses for all tested peptides. The first binding step is fast and takes place within approximately 10 s with no disruption of the membrane as indicated by corresponding calcein release measurements. The second binding phase is slow and occurs within the next 30-300 s with substantial membrane disruption. In this context, beta-hexa- and octaarginine amides possess higher second half-times than the beta-hexa- and octaarginine acids of the same chain length. Furthermore beta-octaarginine amide induces a calcein release approximately twice as large as that of the beta-octaarginine acid. Thermodynamic analysis of the binding process, using the complex formation model that assumes that each peptide binds independently to n POPG lipids, reveals apparent binding constants (K(app1)) of approximately 5 x 10(6)-10(8) M(-1) and n-values from 3.7 for beta-hexaarginine acid up to 24.8 for alpha-polyarginine. Although the K(app1)-values are similar, the number of binding sites clearly depends on the chemical nature of the oligoarginine: beta-oligoarginine amides and alpha-oligoarginine acids interact with more lipids than beta-oligoarginine acids of the same length. Calculation of the electrostatic contribution to the total free energy of binding reveals that for all oligoarginines only 25-30% has electrostatic origin. The remaining approximately 70-75% is nonelectrostatic, corresponding to hydrogen bonding and/or hydrophobic interactions. From the obtained data, a mechanism is suggested by which oligoarginines interact with anionic vesicles: (1) initial electrostatic interaction that is fast, nonspecific, and relatively weak; (2) nonelectrostatic interaction that is rate-limiting, stronger, and induces bilayer rigidification as well as release of aqueous contents from the vesicles.