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At least 379 records · Page 21Linked to original sources
PubMed2003

'Small' talk: Opa proteins as mediators of Neisseria-host-cell communication.

Opa proteins are variable outer membrane proteins of Neisseria gonorrhoeae and Neisseria meningitidis that mediate tight interaction of these pathogens with human cells. They have emerged as a paradigm of a bacterial toolbox allowing recognition of different host receptors and orchestrating the cell type tropism displayed by pathogenic Neisseriae. Recent work has highlighted the molecular basis of Opa-protein-host-receptor interaction and has shed new light on the functional consequences of this interaction with regard to bacterial attachment, invasion, and responses elicited in particular host cells.

Antigens, Bacterial↗
PubMed1999

Quinolone signaling in the cell-to-cell communication system of Pseudomonas aeruginosa.

Numerous species of bacteria use an elegant regulatory mechanism known as quorum sensing to control the expression of specific genes in a cell-density dependent manner. In Gram-negative bacteria, quorum sensing systems function through a cell-to-cell signal molecule (autoinducer) that consists of a homoserine lactone with a fatty acid side chain. Such is the case in the opportunistic human pathogen Pseudomonas aeruginosa, which contains two quorum sensing systems (las and rhl) that operate via the autoinducers, N-(3-oxododecanoyl)-L-homoserine lactone and N-butyryl-L-homoserine lactone. The study of these signal molecules has shown that they bind to and activate transcriptional activator proteins that specifically induce numerous P. aeruginosa virulence genes. We report here that P. aeruginosa produces another signal molecule, 2-heptyl-3-hydroxy-4-quinolone, which has been designated as the Pseudomonas quinolone signal. It was found that this unique cell-to-cell signal controlled the expression of lasB, which encodes for the major virulence factor, LasB elastase. We also show that the synthesis and bioactivity of Pseudomonas quinolone signal were mediated by the P. aeruginosa las and rhl quorum sensing systems, respectively. The demonstration that 2-heptyl-3-hydroxy-4-quinolone can function as an intercellular signal sheds light on the role of secondary metabolites and shows that P. aeruginosa cell-to-cell signaling is not restricted to acyl-homoserine lactones.

Bacterial Proteins↗
PubMed2006

Mesenchymal progenitor cells communicate via alpha and beta integrins with a three-dimensional collagen type I matrix.

BACKGROUND/AIMS: The aim of our study was to investigate interactions of mesenchymal progenitor cells (MPCs) with collagen matrices. METHODS: Human bone-marrow-derived MPCs were cultivated in collagen type I gels with and without inhibition of beta(1)-integrin by a specific antibody. Collagen gel contraction, cell morphology, expression of integrin subunits and several genes related to matrix synthesis and turnover as well as MPC differentiation were analyzed over 14 days. RESULTS: Human MPCs markedly contracted free-floating collagen gels. Contraction was nearly completely inhibited by blocking beta(1)-integrin. Cellular morphology was elongated in the absence and mostly round in the presence of the antibody. Expression of integrin alpha(1), alpha(2) and beta(1) subunits showed several changes partly dependent on beta(1)-integrin blocking. Expression of matrix metalloproteinase-1 was elevated irrespective of beta(1)-integrin blocking and tenascin-C was subsequently induced during gel contraction. Spontaneous induction of chondrogenic, osteogenic or adipogenic differentiation was observed neither in the presence nor in the absence of the beta(1)-integrin antibody. CONCLUSION: Our results indicate that the interaction of human MPCs with fibrillar collagen type I involves beta(1)- and alpha-integrin subunits and induces changes in gene expression related to extracellular matrix synthesis and turnover but not differentiation to the chondrogenic, osteogenic or adipogenic phenotype.

Antibodies, Monoclonal↗
PubMed2005

DNA binding-uptake system: a link between cell-to-cell communication and biofilm formation.

DNA has recently been described as a major structural component of the extracellular matrix in biofilms. In streptococci, the competence-stimulating peptide (CSP) cell-to-cell signal is involved in competence for genetic transformation, biofilm formation, and autolysis. Among the genes regulated in response to the CSP are those involved in binding and uptake of extracellular DNA. We show in this study that a functional DNA binding-uptake system is involved in biofilm formation. A comGB mutant of Streptococcus mutans deficient in DNA binding and uptake, but unaffected in signaling, showed reduced biofilm formation. During growth in the presence of DNase I, biofilm was reduced in the wild type to levels similar to those found with the comGB mutant, suggesting that DNA plays an important role in the wild-type biofilm formation. We also showed that growth in the presence of synthetic CSP promoted significant release of DNA, with similar levels in the wild type and in the comGB mutant. The importance of the DNA binding-uptake system in biofilm formation points to possible novel targets to fight infections.

Bacterial Proteins↗
PubMed2002

Cell to cell communication by autoinducing peptides in gram-positive bacteria.

While intercellular communication systems in Gram-negative bacteria are often based on homoserine lactones as signalling molecules, it has been shown that autoinducing peptides are involved in intercellular communication in Gram-positive bacteria. Many of these peptides are exported by dedicated systems, posttranslationally modified in various ways, and finally sensed by other cells via membrane-located receptors that are part of two-component regulatory systems. In this way the expression of a variety of functions including virulence, genetic competence and the production of antimicrobial compounds can be modulated in a co-ordinated and cell density- and growth phase-dependent manner. Occasionally the autoinducing peptide has a dual function, such as in the case of nisin that is both a signalling pheromone involved in quorum sensing and an antimicrobial peptide. Moreover, biochemical, genetic and genomic studies have shown that bacteria may contain multiple quorum sensing systems, underlining the importance of intercellular communication. Finally, in some cases different peptides may be recognised by the same receptor, while also hybrid receptors have been constructed that respond to new peptides or show novel responses. This paper provides an overview of the characteristics of autoinducing peptide-based quorum sensing systems, their application in various gram-positive bacteria, and the discovery of new systems in natural and engineered ecosystems.

Amino Acid Sequence↗
PubMed2006

Pathway-specific differences between tumor cell lines and normal and tumor tissue cells.

BACKGROUND: Cell lines are used in experimental investigation of cancer but their capacity to represent tumor cells has yet to be quantified. The aim of the study was to identify significant alterations in pathway usage in cell lines in comparison with normal and tumor tissue. METHODS: This study utilized a pathway-specific enrichment analysis of publicly accessible microarray data and quantified the gene expression differences between cell lines, tumor, and normal tissue cells for six different tissue types. KEGG pathways that are significantly different between cell lines and tumors, cell lines and normal tissues and tumor and normal tissue were identified through enrichment tests on gene lists obtained using Significance Analysis of Microarrays (SAM). RESULTS: Cellular pathways that were significantly upregulated in cell lines compared to tumor cells and normal cells of the same tissue type included ATP synthesis, cell communication, cell cycle, oxidative phosphorylation, purine, pyrimidine and pyruvate metabolism, and proteasome. Results on metabolic pathways suggested an increase in the velocity nucleotide metabolism and RNA production. Pathways that were downregulated in cell lines compared to tumor and normal tissue included cell communication, cell adhesion molecules (CAMs), and ECM-receptor interaction. Only a fraction of the significantly altered genes in tumor-to-normal comparison had similar expressions in cancer cell lines and tumor cells. These genes were tissue-specific and were distributed sparsely among multiple pathways. CONCLUSION: Significantly altered genes in tumors compared to normal tissue were largely tissue specific. Among these genes downregulation was a major trend. In contrast, cell lines contained large sets of significantly upregulated genes that were common to multiple tissue types. Pathway upregulation in cell lines was most pronounced over metabolic pathways including cell nucleotide metabolism and oxidative phosphorylation. Signaling pathways involved in adhesion and communication of cultured cancer cells were downregulated. The three way pathways comparison presented in this study brings light into the differences in the use of cellular pathways by tumor cells and cancer cell lines.

Biosynthetic Pathways↗
PubMed2005

Interference with AI-2-mediated bacterial cell-cell communication.

Bacteria communicate by means of chemical signal molecules called autoinducers. This process, called quorum sensing, allows bacteria to count the members in the community and to alter gene expression synchronously across the population. Quorum-sensing-controlled processes are often crucial for successful bacterial--host relationships--both symbiotic and pathogenic. Most quorum-sensing autoinducers promote intraspecies communication, but one autoinducer, called AI-2, is produced and detected by a wide variety of bacteria and is proposed to allow interspecies communication. Here we show that some species of bacteria can manipulate AI-2 signalling and interfere with other species' ability to assess and respond correctly to changes in cell population density. AI-2 signalling, and the interference with it, could have important ramifications for eukaryotes in the maintenance of normal microflora and in protection from pathogenic bacteria.

Bacteria↗
PubMed1970

Cell communication, calcium ion, and cyclic adenosine monophosphate.

The hypothesis advanced in this article requires further validation. Undoubtedly it will require modification as our knowledge of biochemical control increases. Nevertheless, it should prove useful in focusing attention on the apparent similarity in the response of a large number of specific cell types to particular stimuli. Emphasis has been placed on a few common and apparently key elements in these responses. It is recognized that other factors are undoubtedly involved. Specifically, the changes in membrane potentials indicate the likelihood of widespread changes in the properties of the cell membrane, for example, changes in Na(+) and K(+) transport and distribution. These aspects of cellular responses may eventually prove to be of equal or greater importance than those common aspects of the system already identified.

Action Potentials↗
PubMed1975

Formation of the enzymatic apparatus of respiration in growing cells. Communication II. Reorganization of the respiratory cycle of mitochondria in the corn root tip.

The content of cytochromes a,b and c, the activity of marker enzymes of the matrix and inner membrane of the mitochondria: glutamate dehydrogenase and cytochrome oxidase, as well as the rate of absorption of O2 by root segments in the presence of respiratory substrates, oxygen, inhibitors of respiration, and dinitrophenol, were determined. The intensification of cell respiration in the phase of elongation is determined not so much by new formation of cytochrome components of the respiratory cycle (during this period there is an accumulation only of cytochrome c) as by reorganization of the respiratory cycle (primarily its portion NADH - cytochrome b) and synthesis of enzymes of the matrix.

Cytochromes↗
PubMed1983

Effect of several uncouplers of cell-to-cell communication on gap junction morphology in mammalian heart.

Electrical conduction in sheep Purkinje fibers has been blocked by three different procedures: (I) 1 mM 2-4-dinitrophenol, (II) 3.5 mM n-Heptan-1-ol (heptanol), and (III) treatment by a hypotonic (120 mOsmoles) Ca2+-free solution for half an hour, followed by return to normal conditions. The gap junction morphology was analyzed quantitatively in freeze-fracture replicas and compared in electrically conducting and nonconducting fibers. It is found that the three uncouplers of cell-to-cell conduction induce consistent and statistically significant alterations of the gap junction structure. The investigated morphological criteria: (a) P-face junctional particle diameter, control value 8.18 +/- 0.70 nm (mean +/- SD), (b) P-face junctional particles center-to-center spacing, control value 10.23 +/- 1.57 nm, and (c) E-face pits spacing, control value 9.45 +/- 0.98 nm, are, respectively, decreased to 7.46 +/- 0.62 nm, 9.25 +/- 1.34 nm and 8.67 +/- 1.13 nm in Purkinje fibers with complete conduction blocks. All three gap junctional dimensions are seen to decline progressively with time from the onset of an uncoupling treatment towards stable minima reached in half an hour. The observed morphological transitions appear related to the electrical uncoupling for the following reasons: partial electrical uncoupling results in values of the gap junctional dimensions that are intermediate between those measured in electrically coupled and uncoupled preparations, and the three morphological indices are seen to increase again towards control values very soon after electrical conduction has been re-established. It is concluded that the junctional channels closure on electrical uncoupling correlates with a measurable (-0.72 +/- 0.01 nm, difference of the means +/- SE) decrease of the junctional particle diameters.

Animals↗
PubMed1995

The bacterial 'enigma': cracking the code of cell-cell communication.

In recent years it has become clear that the production of N-acyl homoserine lactones (N-AHLs) is widespread in Gram-negative bacteria. These molecules act as diffusible chemical communication signals (bacterial pheromones) which regulate diverse physiological processes including bioluminescence, antibiotic production, plasmid conjugal transfer and synthesis of exoenzyme virulence factors in plant and animal pathogens. The paradigm for N-AHL production is in the bioluminescence (lux) phenotype of Photobacterium fischeri (formerly classified as Vibrio fischeri) where the signalling molecule N-(3-oxohexanoyl)-L-homoserine lactone (OHHL) is synthesized by the action of the LuxI protein. OHHL is thought to bind to the LuxR protein, allowing it to act as a positive transcriptional activator in an autoinduction process that physiologically couples cell density (and growth phase) to the expression of the bioluminescence genes. Based on the growing information on LuxI and LuxR homologues in other N-AHL-producing bacterial species such as Erwinia carotovora, Pseudomonas aeruginosa, Yersinia enterocolitica, Agrobacterium tumefaciens and Rhizobium leguminosarum, it seems that analogues of the P. fischeri lux autoinducer sensing system are widely distributed in bacteria. The general physiological function of these simple chemical signalling systems appears to be the modulation of discrete and diverse metabolic processes in concert with cell density. In an evolutionary sense, the elaboration and action of these bacterial pheromones can be viewed as an example of multicellularity in prokaryotic populations.

4-Butyrolactone↗
PubMed2006

Novel explant model to study mechanotransduction and cell-cell communication.

To understand in situ behavior of osteocytes, we characterized a model of osteocytes in their native bone matrix and demonstrated real-time biologic activity of osteocytes while bending the bone matrix. Using 43 male Sprague-Dawley rats, dumbbell-shaped explants were harvested from stainless steel femoral implants after 6-12 weeks and incubated in culture medium or fixed. Sixteen specimens were used to determine bone volume density (BV/TV), volumetric bone mineral density (BMD) and histology for different implantation periods. Osteocyte viability was evaluated by L-lactate dehydrogenase (LDH) activity in 12 cultured explants. Confocal microscopy was used to assess tracer diffusion in three explants and changes in osteocyte pH of a mechanically loaded explant. From 6 to 12 weeks, explant BV/TV and volumetric BMD trended up 92.5% and 101%, respectively. They were significantly and highly correlated. Tissues were uniformly intramembranous and all bone cell types were present. Explants maintained LDH activity through culture day 8. Diffusion at 200 microM was limited to 1,209 Da. Explants appeared capable of reproducing complex bone biology. This model may be useful in understanding osteocyte mechanotransduction in the context of a physiologically relevant bone matrix.

Animals↗
PubMed1992

Interleukin-1, platelet derived growth factor, free radicals and monocyte aryl hydrocarbon hydroxylase activity in liver disease. Role of cell communication.

Monocytes were isolated from blood of human origin and cultured in supplemented Leibovitz (L-15) medium for 24 hr. The medium was then decanted and filtered, and all subsequent tests were done on monocyte conditioned medium (MCM). The monocytes of patients with liver disease spontaneously secrete temperature-sensitive arylhydrocarbon hydroxylase (AHH) inhibitory factors detectable in the MCM. Anti-interleukin-1 antibody (IL-1Ab) reduced the AHH inhibitory activity of the MCM, suggesting that part of the AHH inhibitory activity was due to interleukin-1 (IL-1). Platelet derived growth factor did not affect AHH activity. Interleukin-1 beta was detectable in MCM but did not differ significantly between patients and normal volunteers. A time course experiment indicated that interleukin-1 beta inhibited hepatocyte AHH activity after only 2 hr of incubation. Catalase partially blocked the AHH inhibitory activity of MCM suggesting that activated oxygen intermediates are partially involved in the AHH inhibitory activity of the MCM. Simultaneous incubation of interleukin-1 beta and catalase did not prevent or augment the inhibitory action of IL-1 on AHH activity. IL-1 stimulates collagen synthesis and elevates serum procollagen type 3 peptide (P-III-P). Results indicated that serum P-III-P was elevated in blood sources producing temperature-sensitive AHH inhibitory factor.

Antibodies↗