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At least 235 records · Page 13Linked to original sources
PubMed1999

Shiga toxin-producing Escherichia coli can impair T84 cell structure and function without inducing attaching/effacing lesions.

Enteropathogenic Escherichia coli (EPEC) intimately adhere to epithelial cells producing cytoskeletal rearrangement with typical attaching and effacing lesions and altered epithelial barrier and transport function. Since EPEC and Shiga toxin-producing E. coli (STEC) share similar genes in the "locus for enterocyte effacement" (LEE) thought to cause these changes, it has been assumed that STEC shares similar pathogenic mechanisms with EPEC. The aims of this study were to compare the effects of EPEC and STEC on bacterial-epithelial interactions and to examine changes in epithelial function. T84 monolayers were infected with STEC O157:H7 (wild strain EDL 933 or non-toxin-producing strain 85/170), EPEC (strain E2348/69), or HB101 (nonpathogenic) and studied at various times after infection. EPEC bound more avidly than EDL 933, but both strains exhibited greater binding than HB101. Attaching and effacing lesions and severe disruption to the actin cytoskeleton were observed in EPEC by 3 h postinfection but not in EDL 933 or HB101 at any time point. EPEC and EDL 933 increased monolayer permeability to [(3)H]mannitol 5- to 10-fold. In contrast to EPEC, EDL 933 completely abolished secretagogue-stimulated anion secretion as assessed under voltage clamp conditions in Ussing chambers. Several other STEC strains induced changes similar to those of EDL 933. In conclusion, STEC impairs epithelial barrier function and ion transport without causing major disruption to the actin cytoskeleton. Pathogenic factors other than products of LEE may be operant in STEC.

Bacterial Adhesion↗
PubMedDate not supplied

[Characteristics of Debye potentials in cell structures].

The activity of the cellular system is accompanied by the changes of substrate concentrations and excreted substances in the medium. This event brings about essential changes of the medium electrical properties. For the accomplishment of stationary metabolism the following condition should be fulfilled B=--2nsquare rootA, where n=1,2...., A and B are some functions depending on the diffusion coefficient of the substrate and excrement, their molecular weights, dissociation coefficients, membrane permeabilities and other parameters of the cellular structure.

Cell Physiological Phenomena↗
PubMed1987

Biochemical and ultrastructural characterization of a novel cell structure associated with immunoglobulin secretion in B-lymphocytes.

In the companion paper, it was established that a secretory form of immunoglobulin, sIg, is present at or near the cell surface. This unexpected occurrence of sIg was postulated to be due to the labelling of sIg which remains temporarily associated with the cell packaged in a vesicle which appears to bud from the plasma membrane at a single pole of the cell. The question that is addressed in this report is whether or not this polar accumulation of sIg represents a common pathway for the exit of this protein which is used by antibody-producing cells. This question is important since, in spite of the fact that the intracellular events associated with immunoglobulin synthesis (processing and movement between subcellular compartments) have been defined, very little data exists on how or where immunoglobulin finally leaves the plasma cell. This question was approached here by first demonstrating that the polar immunoglobulin secretory vesicles (ISV) are associated with several sIg-producing cells including other hybridomas, B-cell lines, and mitogen-activated spleen cells. The second approach was to characterize the ISV on the cell ultrastructurally and to establish that these vesicles are released from the cell carrying with them sIg. Isolated vesicles released from biosynthetically labeled Ig-producing cells were analyzed by SDS-PAGE in order to confirm the presence of sIg and to determine the number of other proteins associated with the ISV, their molecular weights, and the degree of disulfide crosslinking of the molecules comprising this structure. Finally, the kinetics of sIg release was established by a pulse chase protocol for biosynthetically labeled cells, and by monitoring the release of radioactive Ig from surface iodinated cells. As was predicted from our biochemical studies of the ISV, we observed a very slow phase of sIg release as well as a rapid release phase. Our studies have established that at least one of the pathways for the release of Ig from hybridomas, B-cell lines, and normal splenic B-cells is via a polar multivesiculated structure that we have termed ISV, and that the sIg can be released either as a free form of the protein or packaged within a satellite vesicle which may release the sIg later and perhaps at considerable distance from the cell that produced it.

Animals↗
PubMed2003

Growth phase-coupled alterations in cell structure and function of Escherichia coli.

Escherichia coli cultures can be fractionated into more than 20 cell populations, each having a different bouyant density and apparently representing a specific stage of cell differentiation from exponential growth to stationary phase (H. Makinoshima, A. Nishimura, and A. Ishihama, Mol. Microbiol. 43:269-279, 2002). The density increase was found to be impaired at an early step for a mutant E. coli with the disrupted rpoS gene, which encodes the RNA polymerase RpoS (sigma-S) for stationary-phase gene transcription. This finding suggests that RpoS is need for the entire process of cell density increase. In the absence of RpoF sigma factor, the flagella are not formed as observed by electron microscopy, but the growth phase-coupled density increase takes place as in wild-type E. coli, confirming that the alteration in cell density is not directly correlated with the presence or absence of flagella. In the stationary-phase cells, accumulation of electron-dense areas was observed by electron microscopic observation of bacterial thin sections. By chemical determination, the increase in glycogen (or polysaccharides) was suggested to be one component, which contributes to the increase in weight-to-volume ratio of stationary-phase E. coli cells.

Bacterial Proteins↗
PubMed1997

Receptors that induce erythroid differentiation of Ba/F3 cells: structural requirements and effect on STAT5 binding.

Ectopic expression of the erythropoietin receptor (EpoR) in the interleukin-3 (IL-3)-dependent cell line Ba/F3 results in growth and partial erythroid differentiation in Epo. In contrast, introduction and activation of the interleukin-5 receptor (IL-5R) or of the granulocyte-macrophage colony-stimulating factor receptor (GM-CSFR) results in proliferation only. As this effect is specific to the EpoR, the role of its extracellular or cytoplasmic domain in differentiation was tested after construction of two chimeric receptors. One receptor contained the extracellular domain of EpoR fused to the endodomain of IL-3R beta-chain (E/beta), while the other contained the EpoR cytoplasmic region fused to the extracellular domain of GM-CSFR alpha-chain (GMER). Surprisingly, both receptors induced differentiation ruling out a strict specificity of the extracellular or cytoplasmic region of EpoR in this process. Instead the ability to signal differentiation correlated with structural features shared by the EpoR, GMER, and E/beta receptors. Dimerization of all three receptors results in the pairing of two signal transducing chains in the cytoplasm, in contrast to the mitogenic receptors IL-3R, IL-5R, GM-CSFR, which assemble as alphabeta heterodimers. Two new chimeric receptors that fulfilled the structural requirement exemplified by EpoR, but lacked any part of EpoR, were designed to consolidate this model. They consisted of the ectodomains of the GMR-alpha and IL-5R alpha, respectively, fused to the endodomain of IL-3R beta-chain. Both receptors were as effective as EpoR in signaling differentiation in response to their cognate ligand. Another property of receptors fulfilling these structural requirements is that they cause a marked delay in signal transducers and activators of transcription 5 (STAT5) activation on ligand stimulation. Taken together our studies show that structural assembly of receptors dictates their potential to signal erythroid differentiation in Ba/F3 cells, that differentiation can take place in the absence of Epo and that a delay in STAT5 activation is highly predictive of this process.

Base Sequence↗
PubMed1995

Intersegmental fusion in vertebrate rod photoreceptors. Rod cell structure revisited.

PURPOSE: To determine the cause of intersegmental fusion--a fusion between the plasma membranes of the inner and outer segments--in vertebrate rod cells. METHODS: Rod cells from adult salamander, frog, and rat retinas were examined with electron microscopy. The fine structure of fusion and the frequency of occurrence were assessed in three types of preparations (intact eyeballs, eyecup preparations, and neural retinas detached from the retinal pigmented epithelium). The effects of temperature, depolarization, and calcium were examined in isolated neural retinas by maintaining retinas in culture under defined conditions. Retinas from anesthetized animals also were examined. RESULTS: Intersegmental fusion in rod cells was consistently observed in all species after retinal detachment and maintenance in a standard Ringer's solution for 20 to 30 minutes. The amount of fusion seen in isolated amphibian retinas was sensitive to a number of factors: Elevated temperature increased the number of fused rod cells, whereas high KCl, low CaCl2, and Tricaine, which has calcium-related effects, reduced or prevented fusion. In attached retinas, fusion was seen infrequently; the incidence of fused cells in amphibian eyecup preparations, however, could be increased by incubation in the cold. The extensive continuity between the inner and outer segments created by their fusion did not disrupt intracellular structure. Moreover, the fusion seemed to be reversible with time. CONCLUSIONS: Intersegmental fusion is a feature of vertebrate rod cells. Although seen predominantly after retinal detachment, it is influenced by factors that affect other well-known exoplasmic membrane fusions. Thus, it may be one of the many regulated membrane fusion-fission events within the rod photoreceptor.

Ambystoma↗
PubMed2001

Podosomes in osteoclast-like cells: structural analysis and cooperative roles of paxillin, proline-rich tyrosine kinase 2 (Pyk2) and integrin alphaVbeta3.

Macrophages and osteoclasts develop unique contact sites with the extracellular matrix called podosomes. Podosomes have been associated with migratory and invasive cell characteristics, but a basic mechanism outlining their function is lacking. We have used chicken and human monocytes differentiating in vitro into osteoclast-like cells in the presence of RANKL-ODF to study these cytoskeletal structures. During the differentiation process, podosomes are redistributed from the cell body in early macrophages to the cell periphery in increasingly spread and multinucleated cells expressing high levels of integrin alphaVbeta3. Immunofluorescence with anti-phosphotyrosine antibodies revealed increased tyrosine-phosphorylation at the basal tips of these podosomes. RANKL-ODF treatment reinforced the peripheral location of podosomes and initiated their partial fusion to larger F-actin-containing structures that displayed reduced levels of tyrosine phosphorylation. Paxillin and the FAK-related kinase Pyk2 colocalized with integrin alphaVbeta3 in the juxtamembrane region surrounding individual podosomes. In lysates of macrophages and differentiated osteoclasts both paxillin and Pyk2 associated with synthetic and recombinant polypeptides containing the C-terminal region of the integrin beta3 cytoplasmic domain. These in vitro interactions were direct and they were abolished by substitutions in the beta3 integrin peptides known to disrupt integrin function in vivo. The marked adhesion-dependent tyrosinephosphorylation of Pyk2 and paxillin however did not detectably alter their interaction with beta3 tail peptides in cell lysates. Our results provide novel insight into the molecular architecture and the phosphorylation dynamics in podosomes. Moreover, they outline a novel potential mechanism for the recruitment of paxillin and Pyk2 to beta3 integrin-dependent cell contacts.

Actins↗
PubMed2000

Changes in cell structure during the formation of root aerenchyma inSAGITTARIA LANCIFOLIA (Alismataceae).

In many wetland species, root aerenchyma is produced by the predictable collapse of root cortex cells, indicating a programmed cell death (PCD). The objective of this study was to characterize the cellular changes that accompany this PCD in the marsh species Sagittaria lancifolia. Structural changes in membranes and organelles were examined during development of root cortex cells to compare with previous examples of PCD. The organization of cortical microtubule (CMT) arrays in root cells from S. lancifolia was also evaluated as a possible predictor of cell lysis. Nuclear fragmentation and condensation were the earliest changes observed in cells undergoing lysis. Breakdown of the tonoplast and other organelles and disruption of the plasma membrane followed. After loss of cytoplasm, cells collapsed to form gas spaces. These results were compared to collapse of root cortical cells of Zea mays and Oryza sativa during aerenchyma development. Changes in the appearance of the cytoplasm of all three species were similar at later stages of aerenchyma development. The relative timing of disintegration of the tonoplast and middle lamella appeared to differ among the three species. Changes in the organization of CMT arrays did not appear to be a predictor of PCD in S. lancifolia. Aerenchyma production in plants involves a type of PCD that is morphologically distinct from PCD described from many animals.

Journal Article↗
PubMed2000

F-actin fiber distribution in glomerular cells: structural and functional implications.

BACKGROUND: Glomerular distention is associated with cellular mechanical strain. In addition, glomerular distention/contraction is assumed to influence the filtration rate through changes in filtration surface area. A contractile cytoskeleton in podocytes and mesangial cells, formed by F-actin-containing stress fibers, maintains structural integrity and modulates glomerular expansion. In this study, the glomerular cell distribution of F-actin and vimentin filaments was studied in normal control and nine-month streptozotocin-diabetic rats. Results in situ were compared with observations in tissue culture. METHODS: Microdissected rat glomeruli were perfused to obtain a physiological 25% glomerular expansion over the basal value. Fixation was done without change in glomerular volume. Dual fluorescent labeling of F-actin and vimentin was carried out, and samples were examined by confocal laser scanning microscopy. RESULTS: The podocyte cell bodies and their cytoplasmic projections, including the foot processes, contained bundles of vimentin-containing fibers. Except for a thin layer at the base of foot processes, they did not demonstrate F-actin. While mesangial cells in culture had F-actin as long stress fibers resembling tense cables, mesangial cells stretched in situ contained a maze of short tortuous F-actin fibers organized in bundles that often encircled vascular spaces. This fibrillar organization was disrupted in diabetic glomeruli. CONCLUSION: Mesangial cells, but not podocytes, contain a cytoskeleton capable of contraction that is disorganized in long-term diabetes. Together with previous observations, the distribution of this cytoskeleton suggests that mesangial cell contraction may be involved in the redistribution of glomerular capillary blood flow, but not substantially in the modulation of glomerular distention. Disorganization of stress fibers may be a cause of hyperfiltration in diabetes.

Actins↗
PubMed2002

Mössbauer study of reduced rubredoxin as purified and in whole cells. Structural correlation analysis of spin Hamiltonian parameters.

The [Fe(II)(Cys)(4)](2-) site of rubredoxin from Clostridium pasteurianum (Rd(red)) has been studied by Mössbauer spectroscopy in both purified protein and whole cells of Escherichia coli overproducing it. Excellent fits were obtained to an S = 2 spin Hamiltonian for D = 5.7(3) cm(-1), E/D = 0.25(2), delta = 0.70(3) mm/s, DeltaE(Q) = -3.25(2) mm/s, eta = 0.75(5), A(x) = -20.1(7) MHz, A(y) = -11.3(2) MHz, and A(z) = -33.4(14) MHz. These parameters were analyzed with crystal-field theory for the (5)D manifold of iron(II), revealing a d(z(2)) orbital ground state that is admixed by approximately 0.21 d(x(2) - y(2)). The spin-Hamiltonian parameters are consistent within the (5)D theory, apart from the zero-field splitting parameter, D. This problem was solved by extending the crystal-field treatment with spin-orbit coupling to spin-triplet d-d excited states of the iron. Theoretical estimates are given for the spin-triplet (D(T)) and spin-quintet contributions (D(Q)) to D based on excitation energies derived from time-dependent density functional theory, TD-DFT. The computational results were interpreted in terms of crystal-field theory, yielding the Racah parameters B = 682 cm(-1) and C = 2583 cm(-1). The theoretical analysis gives the relative magnitudes D(Q):D(T):D(ss) = 51%: 42%:7% (D(ss) originates from spin-spin interaction). The DFT analysis corroborates the pivotal role of the torsion angles (omega(i)) of the C-S(i) bonds in shaping the electronic structure of the iron(II) site. Rd(red) in overexpressing whole cells accounts for 60% of the Mössbauer absorption. The Rd(red) spectra from whole cells are virtually identical to those of the purified protein. By using the theoretical omega dependence of the spin Hamiltonian parameters, the torsions for Rd(red) in whole cells and purified protein samples are estimated to be the same within 2 degrees. These findings establish Mössbauer spectroscopy as a structural tool for investigating iron sites in whole cells.

Algorithms↗
PubMed2003

The effect of drugs on cell structure of Tritrichomonas foetus.

The effects of the microtubule affecting drugs taxol, nocodazole and colchicine on the cell cycle and ultrastructure of Tritrichomonas foetus, a protist parasite of cattle, were studied. Alterations in the cytoskeleton, motility and organellar ultrastructure were followed using anti-tubulin antibodies and fluorescence microscopy, scanning- and transmission-electron microscopy. Flow cytometry was also used to analyze the effect of the drugs on the cell cycle. T. foetus was treated with 10 microM taxol, 15 microM nocodazole or 1.5 mM colchicine for 12 h. The first effect observed was pseudocyst formation and alterations in cell motility. The cell cycle was affected and the cells have blocked cytokinesis, but not karyokinesis. The behavior of Golgi, hydrogenosomes and vacuoles was analyzed. The following effects were seen following drug treatments: (1) cell motility was altered and flagella internalized; (2) microtubules of the pelta-axostyle complex were not depolymerized and the axostyle assumed a curved form; (3) hydrogenosomes were of abnormal size and shape; (4) cells became multinucleate; (5) the division process was blocked in cytokinesis; (6) autophagic vacuoles containing a large amount of microtubules were seen; (7) axoneme organization was altered; (8) zoids were formed; (9) signs of cell death, such as membrane blebbing, were observed.

Animals↗