The viable but nonculturable state of Kanagawa positive and negative strains of Vibrio parahaemolyticus

Ingestion of shellfish-associated Vibrio parahaemolyticus is the primary cause of potentially severe gastroenteritis in many countries. However, only Kanagawa phenomenon (hemolysin) positive (KP+) strains of V. parahaemolyticus are isolated from patients, whereas >99% of strains isolated from the environment do not produce this hemolysin (i.e. are KP-). The reasons for these differences are not known. Following a temperature downshift, Vibrio parahaemolyticus enters the viable but nonculturable (VBNC) state wherein cells maintain viability but cannot be cultured on routine microbiological media We speculated that KP+ and KP- strains may respond differently to the temperature and salinity conditions of seawater by entering into this state which might account for the low numbers of culturable KP+ strains isolated from estuarine waters. The response of eleven KP+ and KP- strains of V. parahaemolyticus following exposure to a nutrient and temperature downshift in different salinities, similar to conditions encountered in their environment, was examined. The strains included those from which the KP+ genes had been selectively removed or added. Our results indicated that the ability to produce hemolysin did not affect entrance into the VBNC state. Further, VBNC cells of both biotypes could be restored to the culturable state following an overnight temperature upshift.     

Flt-1-dependent survival characterizes the epithelial-mesenchymal transition of colonic organoids

Aberrant cell survival and resistance to apoptosis are hallmarks of tumor invasion and progression to metastatic disease, but the mechanisms involved are poorly understood. The epithelial-mesenchymal transition (EMT), a process that facilitates progression to invasive cancer, provides a superb model for studying such survival mechanisms. Here, we used a unique spheroid culture system that recapitulates the structure of the colonic epithelium and undergoes an EMT in response to cytokine stimulation to study this problem. Our data reveal that the EMT results in the increased expression of both VEGF and Flt-1, a tyrosine kinase VEGF receptor, and that the survival of these cells depends on a VEGF/Flt-1 autocrine pathway. Perturbation of Flt-1 function by either a blocking antibody or adenoviral expression of soluble Flt-1, which acts in a dominant-negative fashion, caused massive apoptosis only in cells that underwent EMT. This pathway was critical for the survival of other invasive colon carcinoma cell lines, and we observed a correlative upregulation of Flt-1 expression linked to in vivo human cancer progression. A role for Flt-1 in cell survival is unprecedented and has significant implications for Flt-1 function in tumor progression, as well as in other biological processes, including angiogenesis and development.     

Changes in GAD67 mRNA expression evidenced by in situ hybridization in the brain of R6/2 transgenic mice

Huntington's disease is an autosomal dominant disorder with degeneration of medium size striatal neurones. As the disease evolves, other neuronal populations are also progressively affected. A transgenic mouse model of the disease (R6/2) that expresses exon 1 of the human Huntington gene with approximately 150 CAG repeats has been developed, but GABA concentrations are reported to be normal in the striatum of these animals. In the present study, we analysed the status of GABAergic systems by means of glutamic acid decarboxylase (GAD)67 mRNA in situ hybridization in the brain of R6/2 transgenic mice and wild-type littermates. We show that GAD67 expression is normal in the striatum, cerebellum and septum but decreased in the frontal cortex, parietal cortex, globus pallidus, entopeduncular nucleus and substantia nigra pars reticulata of R6/2 mice. These data, which may, in part, account for the behavioural changes seen in these animals, indicate that at 12.5 weeks of age the pathological features seen in the mice differ from those seen in humans with Huntington's disease.     

Membrane-anchoring and charge effects in the interaction of myelin basic protein with lipid bilayers studied by site-directed spin labeling

Myelin basic protein (MBP) maintains the compaction of the myelin sheath in the central nervous system by anchoring the cytoplasmic face of the two apposing bilayers and may also play a role in signal transduction. Site-directed spin labeling was done at eight matching sites in each of two recombinant murine MBPs, qC1 (charge +19) and qC8 charge (+13), which, respectively, emulate the native form of the protein (C1) and a post-translationally modified form (C8) that is increased in multiple sclerosis. When interacting with large unilamellar vesicles, most spin-labeled sites in qC8 were more mobile than those in qC1. Depth measurement via continuous wave power saturation indicated that the N-terminal and C-terminal sites in qC1 were located below the plane of the phospholipid headgroups. In qC8, the C-terminal domain dissociated from the membrane, suggesting a means by which the exposure of natural C8 to cytosolic enzymes and ligands might increase in vivo in multiple sclerosis. The importance of two Phe-Phe pairs in MBP to its interactions with lipids was investigated by separately mutating each pair to Ala-Ala. The mobility at F42A/F43A and especially F86A/F87A increased significantly. Depth measurements and helical wheel analysis indicated that the Phe-86/Phe-87 region could form a surface-seeking amphipathic alpha-helix.     

The effects of deimination of myelin basic protein on structures formed by its interaction with phosphoinositide-containing lipid monolayers

The recombinant 18.5-kDa charge isoform of murine myelin basic protein (rmMBP) is unmodified posttranslationally and was used to study the effects of deimination, i.e., the conversion of arginyl to citrullinyl residues, on the protein's interactions with itself and with lipids. The unmodified species rmMBP-Cit(0) (i.e., containing no citrullinyl residues) interacted with binary monolayers containing acidic (phosphatidylinositol) and nickel-chelating lipids to form paracrystalline arrays with 4.8-nm spacing. A sample of protein was deiminated to an average of 9 citrullinyl residues per molecule of protein, yielding rmMBP-Cit(9). Under both low- and high-salt conditions, this species formed better-ordered domains than rmMBP-Cit(0), viz., planar crystalline assemblies. Thus, deimination of MBP resulted in a significant alteration of its lipid-organizing and self-interaction properties that might be operative in myelin in vivo, especially in progression of the autoimmune disease multiple sclerosis. Comparisons of amino acid sequences indicated significant similarities of MBP with filaggrin, a protein that is deiminated in another autoimmune disease, rheumatoid arthritis, suggesting that comparable epitopes could be targeted in both pathologies. In contrast, binary lipid monolayers consisting of phosphatidylinositol-4-phosphate (or phosphatidylinositol-4,5-bisphosphate) and a nickel-chelating lipid formed helical tubular vesicular structures, which appeared to be induced and/or stabilized by rmMBP, especially in its deiminated form. Sequence comparisons with other actin- and phosphoinositide-binding proteins (vinculin, ActA, MARCKS) suggested that the carboxyl-terminal segment of MBP could form an amphipathic alpha helix and was the phosphoinositide binding site.     

Biosensor detection of triplex formation by modified oligonucleotides

Due to the instability of DNA oligonucleotides in biological solutions, antisense or antigene therapies aimed at modulation of specific gene expression will most likely require the use of oligonucleotides with modified backbones. Here, we examine the use of a surface plasmon resonance biosensor (BIAcore) to compare triplex-directed binding of modified oligonucleotides targeted to a region of the murine c-myc promoter. We describe optimization of experimental conditions to minimize nonspecific interactions between the oligonucleotides and the sensor chip surface, and the limitations imposed by certain backbones and sequence types. The abilities of pyrimidine oligonucleotides with various modified backbones to form specific triple helices with an immobilized hairpin duplex were readily determined using the biosensor. Modification of the third-strand oligonucleotide with RNA or 2(')-O-methyl RNA was found to enhance triplex formation, whereas phosphorothioate or phosphotriester substitutions abrogated it. A comparison of these results to DNase I footprinting experiments using the same oligonucleotides showed complete agreement between the two sets of data.     

INK4a-deficient human diploid fibroblasts are resistant to RAS-induced senescence

The CDKN2A tumour suppressor locus encodes two distinct proteins, p16(INK4a) and p14(ARF), both of which have been implicated in replicative senescence, the state of permanent growth arrest provoked in somatic cells by aberrant proliferative signals or by cumulative population doublings in culture. Here we describe primary fibroblasts from a member of a melanoma-prone family who is homozygous for an intragenic deletion in CDKN2A. Analyses of the resultant gene products imply that the cells are p16(INK4a) deficient but express physiologically relevant levels of a frameshift protein that retains the known functions of p14(ARF). Although they have a finite lifespan, the cells are resistant to arrest by oncogenic RAS. Indeed, ectopic expression of RAS and telomerase (hTERT) results in outgrowth of anchorage-independent colonies that have essentially diploid karyotypes and functional p53. We find that in human fibroblasts, ARF is not induced demonstrably by RAS, pointing to significant differences between the proliferative barriers implemented by the CDKN2A locus in different cell types or species.     

Decreased expression of membrane IL-5 receptor alpha on human eosinophils: I. Loss of membrane IL-5 receptor alpha on airway eosinophils and increased soluble IL-5 receptor alpha in the airway after allergen challenge

IL-5 is a key cytokine for eosinophil maturation, recruitment, activation, and possibly the development of inflammation in asthma. High concentrations of IL-5 are present in the airway after Ag challenge, but the responsiveness of airway eosinophils to IL-5 is not well characterized. The objectives of this study were to establish, following airway Ag challenge: 1) the expression of membrane (m)IL-5Ralpha on bronchoalveolar lavage (BAL) eosinophils; 2) the responsiveness of these cells to exogenous IL-5; and 3) the presence of soluble (s)IL-5Ralpha in BAL fluid. To accomplish these goals, blood and BAL eosinophils were obtained from atopic subjects 48 h after segmental bronchoprovocation with Ag. There was a striking reduction in mIL-5Ralpha on airway eosinophils compared with circulating cells. Furthermore, sIL-5Ralpha concentrations were elevated in BAL fluid, but steady state levels of sIL-5Ralpha mRNA were not increased in BAL compared with blood eosinophils. Finally, BAL eosinophils were refractory to IL-5 for ex vivo degranulation, suggesting that the reduction in mIL-5Ralpha on BAL eosinophils may regulate IL-5-mediated eosinophil functions. Together, the loss of mIL-5Ralpha, the presence of sIL-5Ralpha, and the blunted functional response (degranulation) of eosinophils to IL-5 suggest that when eosinophils are recruited to the airway, regulation of their functions becomes IL-5 independent. These observations provide a potential explanation for the inability of anti-IL-5 therapy to suppress airway hyperresponsiveness to inhaled Ag, despite a reduction in eosinophil recruitment.     

Arfaptin 2 regulates the aggregation of mutant huntingtin protein

Huntington's disease (HD) is an inherited neurodegenerative disorder. Here we demonstrate that expression of arfaptin 2/POR1 (partner of Rac1) in cultured cells induces the formation of pericentriolar and nuclear aggregates, which morphologically resemble mutant huntingtin aggregates characteristic of HD. Endogenous arfaptin 2 localizes to aggregates induced by expression of an abnormal amino-terminal fragment of huntingtin that contains polyglutamine (polyQ) expansions. A dominant inhibitory mutant of arfaptin 2 inhibits aggregation of mutant huntingtin, but not in the presence of proteasome inhibitors. Using cell-free biochemical assays, we show that arfaptin 2 inhibits proteasome activity. Finally, we show that expression of arfaptin 2 is increased at sites of neurodegeneration and the protein localizes to huntingtin aggregates in HD transgenic mouse brains. Our data suggest that arfaptin 2 is involved in regulating huntingtin protein aggregation, possibly by impairing proteasome function.     

An Arg/Lys-->Gln mutant of recombinant murine myelin basic protein as a mimic of the deiminated form implicated in multiple sclerosis

The degree of post-translational enzymatic deimination (conversion of arginyl to citrullinyl residues) of myelin basic protein (MBP) is correlated with the severity of the human autoimmune disease multiple sclerosis (MS). It is difficult to obtain large quantities of deiminated MBP from natural sources (autopsy material), and in vitro deimination using peptidylarginine deiminase (EC 3.5.3.15) is both non-specific and irreproducible. Since there is no known codon for citrulline, we have constructed a mutant form of recombinant murine MBP (rmMBP) in which 5 Arg and 1 Lys residues have been replaced by Gln as the most reasonable analogue of Cit. The residues were chosen to correspond to the 6 Arg residues in human MBP which are most commonly deiminated in chronic MS. The mutant species, rmMBP-qCit(6) where the "q" represents "quasi-," was probed by numerous biochemical and biophysical techniques. Highly homogeneous protein preparations were obtained using a modified expression system which minimised spurious misincorporation of Lys for Arg, as ascertained by electrospray ionisation mass spectrometry. The mutant form rmMBP-qCit(6) had a reduced ability to aggregate lipid vesicles, a slightly greater susceptibility to digestion by cathepsin D, a greater proportion of random secondary structure, and different conformational responses to lipids, compared with the unmodified rmMBP. Overall, the mutant protein's properties were consistent with the effects of deimination and support its use as a model for evaluating the effects of this modification.