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At least 1,531 records · Page 85Linked to original sources
PubMed1987

Rescue of a wild-type MDCK cell by a ouabain-resistant mutant.

When wild-type MDCK cells (W-MDCK) were cocultured in mixed monolayers with a ouabain-resistant mutant (R-MDCK), the wild-type cells were protected from the effect of ouabain up to concentrations as high as 100 microM. Rescue depended on the dose of ouabain and on the proportion of each cell type in the coculture. The survival of R-MDCK cells at 1 microM ouabain was not endangered by varying from 1:9 to 9:1 the proportion of W-MDCK cells to be rescued. Ouabain binding revealed two kinds of binding sites in R-MDCK cells, one with high and the other with low affinity. Only the high affinity site was present in W-MDCK cells. Electron probe analysis of individual cells revealed that rescued cells kept a high K and a low Na intracellular contents, similar to control cells. Histograms of intracellular K/Na in cocultured cells treated with ouabain were unimodal. Using microinjection of Lucifer yellow or electrophysiological techniques we estimated that at most 13% of the R-MDCK and W-MDCK cells may be connected at a given time through cell-to-cell junctions. Therefore permanent cell-to-cell communication did not seem to play a central role in the rescue. W-MDCK cells cocultured with R-MDCK cells and subsequently separated, were not rescued. Thus rescue did not seem to depend on the transfer from R-MDCK to W-MDCK cells of either ouabain-resistant Na-K pumps or of information to synthesize them. It is speculated that intercellular communications were sporadic events, so that all cells may become intermittently connected and rescued.

Animals↗
PubMed2003

Gap junctional communication modulates gene transcription by altering the recruitment of Sp1 and Sp3 to connexin-response elements in osteoblast promoters.

Loss-of-function mutations of gap junction proteins, connexins, represent a mechanism of disease in a variety of tissues. We have shown that recessive (gene deletion) or dominant (connexin45 overexpression) disruption of connexin43 function results in osteoblast dysfunction and abnormal expression of osteoblast genes, including down-regulation of osteocalcin transcription. To elucidate the molecular mechanisms of gap junction-sensitive transcriptional regulation, we systematically analyzed the rat osteocalcin promoter for sensitivity to gap junctional intercellular communication. We identified an Sp1/Sp3 containing complex that assembles on a minimal element in the -70 to -57 region of the osteocalcin promoter in a gap junction-dependent manner. This CT-rich connexin-response element is necessary and sufficient to confer gap junction sensitivity to the osteocalcin proximal promoter. Repression of osteocalcin transcription occurs as a result of displacement of the stimulatory Sp1 by the inhibitory Sp3 on the promoter when gap junctional communication is perturbed. Modulation of Sp1/Sp3 recruitment also occurs on the collagen Ialpha1 promoter and translates into gap junction-sensitive transcriptional control of collagen Ialpha1 gene expression. Thus, regulation of Sp1/Sp3 recruitment to the promoter may represent a potential general mechanism for transcriptional control of target genes by signals passing through gap junctions.

Animals↗
PubMed1989

Intercellular contacts of astroglial cells in vitro in the presence of PGE2. SEM, TEM and immunocytochemical studies.

The investigations were performed on 32 tumors of the CNS of fibrillary and gemistocyte type of astrocytoma from which the cultures were derived. The dissociated culture was used and the cells were seeded direct on glass. The MEM was supplemented with calf serum and embryonal extract. The cells maintained in culture for 21 days. They developed multiple or single long and delicate processes which originated a network of relative high density. SEM observations indicate that the cell established intercellular connections through spikes and surfaces of the processes and cell bodies. TEM studies have shown that the cell to cell connections are very tight but the contacts between the cell processes are similar to those described by DUFFY as punctate connections. The addition of PGE2 does not disturb the reconstruction of intercellular communication. The estimation of GFAP antigenicity of the investigated cells proved their astrocytic origin and revealed that the intermediate fibres are in the cell processes, and in the location of the contacts between cells.

Astrocytoma↗
PubMed2007

Lipid-protein cargo transfer: a mode of direct cell-to-cell communication for lipids and their associated proteins.

Cells in tissues or in experimental cell colonies respond to stimuli in a co-ordinated manner when they are electrically and chemically coupled by gap junctions. These junctions permit the cell-to-cell passage of small molecules, such as inositol tris phosphate (IP(3)) within the colony and are important in co-ordinating tissue activity. This is the only recognised mechanism of direct chemical signalling that does not involve the release of an extracellular messenger between cells. However, the data in this article demonstrates a new mode of intercellular communication. Two potentially important signalling lipids, PIP(2) and ganglioside G-M1 were shown to move between cells in colonies by tracking (i) fluorescent lipids loaded into the plasma membranes of individual cells in a cell colony using a novel micropipette technique and (ii) movement of fluorescent lipids after localised photobleaching. Furthermore, a large protein molecule, cholera toxin B subunit bound to extracellularly facing ganglioside G-M1 was also shown to transfer between cells. The transfer was inhibited by pre-treatment with poly-L-lysine and polyethylenimine, suggesting a role for tight junctions, perhaps by permitting diffusion of lipids and their protein "cargo" across these cell-to-cell contact points. This is a hitherto unsuspected form of molecular signalling within cell colonies and tissues which may have implications for understanding co-ordinated cell colony behaviour.

Biological Transport↗
PubMed2000

Modulation of cell-cell communication in the cause and chemoprevention/chemotherapy of cancer.

Chemopreventive or chemotherapeutic agents have been those that either kill cancer cells to a differential degree over the non-cancer cells or those chemicals that either block the induction of tumors in carcinogen-treated animals or retard transplanted tumors in animals. Carcinogenesis is a multi-stage, multi-mechanism process, involving the irreversible alteration of a stem cell ("initiation"), followed by the clonal proliferation of the initiated cell ("promotion"). To develop a strategy for intervention with chemoprevention/chemotherapeutic chemicals, the basic mechanism(s) of carcinogenesis must be understood. Gap junction intercellular communication (GJIC) regulates cell growth, differentiation, apoptosis and adaptive functions of differentiated cells. Normal cells have functional GJIC while cancer cells do not. Tumor promoters and oncogenes inhibit GJIC, while anti-tumor promoter and anti-oncogene drugs can reverse the down-regulation of GJIC. Transfection of gap junction genes (connexins) has been shown to reverse the tumorigenic phenotype. If prevention/treatment of cancer is to occur, prevention of the chronic down regulation of GJIC by tumor promoters in non-tumorigenic but initiated cells or the up-regulation of GJIC in stably down-regulated GJIC in tumor cells must occur to prevent or to treat cancers.

Anticarcinogenic Agents↗
PubMed1996

Cytokine-mediated communication by keratinocytes and Langerhans cells with dendritic epidermal T cells.

Dendritic epidermal T cells (DETC) are skin-specific members of the epithelial gamma delta T-cell family that reside normally in murine epidermis. Recent studies indicate that certain cytokines (e.g. IL-2, IL-7 and IL-15) secreted by neighboring cells promote their residence and regulate their immune function. Conversely, DETC regulate the function of neighboring keratinocytes and Langerhans cells by elaborating other cytokines (e.g. interferon-gamma, keratinocyte growth factor and colony-stimulating factors). This reciprocal interaction represents a unique model of cytokine-mediated intercellular communication by tissue-specific gamma delta T cells with nearby epithelial and antigen presenting cells.

Animals↗
PubMed1996

Influence of the molecular structure of steroids on their ability to interrupt gap junctional communication.

17 beta-estradiol propionate was found to reduce the gap junctional communication in a concentration range similar to that of testosterone propionate, in primary cultures of rat Sertoli cells and cardiac myocytes. Uncoupling was reversible on washing out and occurred without concomitant rise in the intracellular calcium concentration. Esterification was prerequisite for the activity of extracellularly applied steroid compounds (for example, testosterone was ineffective even at external concentrations up to 100 microM, whereas its intracellular application at 1 microM totally interrupted intercellular communication), but their uncoupling efficiency did not depend on the nature of the ester chain nor on its position on the steroid nucleus. The derivatives of two other androgen hormones (derivatives of the androstane nucleus) were also efficient as junctional uncouplers. Among five steroid molecules belonging to the pregnane family, only one (pregnanediol diacetate) interrupted the junctional communication. Neither cholic acid nor cholesteryl acetate or ouabain showed this effect. Altogether, no correlation with the presence or position of double bonds nor with the trans- or cis-fusion of the A and B rings could be recognized. These results suggest that this reversible, nondeleterious uncoupling effect of steroids is independent of the shape of the molecules and is more probably related to their size and liposolubility, that condition their insertion into the lipid bilayer. Their incorporation into the membrane could disturb the activity of the membrane proteins by a physical mechanism.

Calcium↗
PubMed1990

Aberrant expression of gap junction gene in primary human hepatocellular carcinomas: increased expression of cardiac-type gap junction gene connexin 43.

The expression of connexin 32 (the major liver gap junction protein) and connexin 43 (the major cardiac gap junction protein) was examined in six surgically removed human hepatocellular carcinoma tissues and the surrounding nontumorous livers using specific rat connexin probes. No decrease in connexin 32 mRNA expression was found in carcinomas compared with the surrounding nontumorous tissue. Morphometrical analysis also showed that in most of the carcinomas the number of gap junction spots stained with connexin 32 antibody was not less than that in the surrounding livers. These results are in striking contrast to the significant reductions in connexin 32 mRNA and protein expression observed in rat primary liver tumors induced by chemicals. On the other hand, all of the six human hepatocellular carcinomas exhibited elevated levels of connexin 43 mRNA, which was expressed at a very low level in the surrounding nontumorous livers. These carcinomas exhibited no detectable amplification of the connexin 43 gene. The present study suggests that gap junctional intercellular communication is altered in human hepatocellular carcinomas by molecular mechanisms different from those in rat hepatocarcinogenesis.

Blotting, Northern↗
PubMed2003

ELF magnetic fields induce internalization of gap junction protein connexin 43 in Chinese hamster lung cells.

We have previously demonstrated that exposure of Chinese hamster lung (CHL) cells to 50 Hz magnetic fields (MFs) and/or 12-O-tetradecanoylphorbol-3-acetate (TPA)-inhibited gap junctional intercellular communication (GJIC). To explore and compare the mechanisms of GJIC inhibition induced by extremely low frequency (ELF) MF and TPA, the number and localization of connexin 43 (C x 43) were studied. The localization of C x 43 was determined with indirect immunofluorescence histochemical analysis and detected by confocal microscopy after exposing CHL cells to 50 Hz sinusoidal magnetic field at 0.8 mT for 24 h without or with TPA (5 ng/ml) for the last 1 h. The C x 43 levels in nuclei and in cytoplasm were examined by Western blotting analysis. The results showed that the cells exposed to MF and/or TPA displayed individual plaques at regions of intercellular contact, which were fewer than the normal cells in number, while the number of C x 43 in cytoplasm increased and congregated near the nuclei. Western blot analysis further demonstrated the quantity of changes in location of Cx43. These results suggest that reduction of C x 43 at regions of intercellular contact may be one of the mechanisms of GJIC inhibition induced by ELF MF.

Animals↗
PubMed2006

Selectivity of connexin 43 channels is regulated through protein kinase C-dependent phosphorylation.

Coordinated contractile activation of the heart and resistance to ischemic injury depend, in part, on the intercellular communication mediated by Cx43-composed gap junctions. The function of these junctions is regulated at multiple levels (assembly to degradation) through phosphorylation at specific sites in the carboxyl terminus (CT) of the Cx43 protein. We show here that the selective permeability of Cx43 junctions is regulated through protein kinase C (PKC)-dependent phosphorylation at serine 368 (S368). Selective permeability was measured in several Cx43-expressing cell lines as the rate constant for intercellular dye diffusion relative to junctional conductance. The selective permeability of Cx43 junctions under control conditions was quite variable, as was the open-state behavior of the comprising channels. Coexpression of the CT of Cx43 as a distinct protein, treatment with a PKC inhibitor, or mutation of S368 to alanine, all reduced (or eliminated) phosphorylation at S368, reduced the incidence of 55- to 70-pS channels, and reduced by 10-fold the selective permeability of the junctions for a small cationic dye. Because PKC activation during preischemic conditioning is cardioprotective during subsequent ischemic episodes, we examined no-flow, ischemic hearts for Cx43 phosphorylated at S368 (pS368). Consistent with early activation of PKC, pS368-Cx43 was increased in ischemic hearts; despite extensive lateralization of total Cx43, pS368-Cx43 remained predominantly at intercalated disks. Our data suggest that the selectivity of gap junction channels at intercalated disks is increased early in ischemia.

Animals↗
PubMed1986

Does Gonyaulax polyedra measure a week?

Cell communication was investigated in Gonyaulax polyedra by mixing two cultures grown on opposite lighting regimens, as reported in a companion paper. Herein, using the same data, 7-d (circaseptan) rhythms are also shown to characterize the luminescence of this cellular organism. A fraction of a culture of G. polyedra, grown in 12 h of light (L), alternating with 12 h of darkness (D), was exposed for 3 d to an LD-shift by 11 h. The circadian glow rhythm was compared under free-running conditions (LL) for cultures previously kept on the two differing LD regimens and for mixed cultures. A circaseptan modulation of the circadian amplitude is detected in cultures that had not undergone an LD shift and in some of the mixed cultures, but not in the shifted cultures. A statistically significantly lower circaseptan amplitude (less than 50%) and acrophase advance of over 120 degrees or 56 h (p less than 0.001) characterizes the mixed cultures, as compared to the original unshifted cultures, a finding that could mean that G. polyedra communicates along a circaseptan frequency. Whether a prior phase-shift known to affect circaseptan behavior in another unicell, Acetabularia mediterranea, led to an alteration of the time structure of G. polyedra remains an interesting subject for further study in this model, a model attractive to students of unicellular rhythms and underlying mechanisms that henceforth should be studied at multiple circadian and circaseptan frequencies. Circadian and circaseptan interrelations can both serve as markers for mechanisms of intercellular communication.

Animals↗
PubMed2006

Electrical properties and cell-to-cell communication of the salivary gland cells of the snail, Helix pomatia.

The aim of the present study was to assess the cellular mechanism of secretion in the salivary gland of the snail, Helix pomatia, using electrophysiological, electron microscopic and immunohistochemical techniques. A homogeneously distributed membrane potential (-56.6 +/- 9.8 mV) was determined mainly by a K+ -electrochemical gradient and partly by the contribution of the electrogenic Na+ -pump and Cl- conductance. Low resistance electrical coupling sites were identified physiologically. Transmission electron microscopy and innexin 2 antibody revealed the presence of gap-junction-like membrane structures between gland cells. It is suggested that gap-junctions are sites of electrotonic intercellular communication, which integrate the gland cells into a synchronized functional unit in the acinus. Stimulation of the salivary nerve elicited secretory potentials (depolarization) which could be mimicked by local application of acetylcholine, dopamine or serotonin. In voltage-clamp experiments four major conductances were identified: a delayed rectifier (IK), a transient (IA) and a Ca2+ -activated outward K+ current (IK(Ca)) and Ca2+ -inward currents (ICa). It is suggested that one or more of these conductances may give rise to a stimulus activated secretory potential leading to excitation-secretion coupling and subsequent the release of the mucus from the gland cells.

Acetylcholine↗
PubMed2001

[Ultrastructure of smooth myocytes of small extraorganic lymphatic vessels].

Leiomyocytes in musculature of small extraorganic human lymphatics were studied by means of electron microscopic method. Organization of the precollector wall muscular component indicates heterogeneity of smooth myocytes population and specific character of intercellular communications which is probably determined by peculiarities of these lymphatic bed link. In smooth myocytes population "light" and "dark" cells and "synthetic" type leiomyocytes were found. A problem on the role of endothelium and leiomyocytes interaction in mechanisms of regulation of precollector musculature contraction is under discussion. It was suggested that small extraorganic lymph vessels with muscular component in their wall provide lymph flow while the zones with random or single muscular elements are more often connected with intercellular fluid absorption.

Humans↗
PubMed2006

Up-regulation of connexin43 correlates with increased synthetic activity and enhanced contractile differentiation in TGF-beta-treated human aortic smooth muscle cells.

Up-regulation of the gap-junctional protein connexin43 (Cx43) in arterial smooth muscle cells (SMCs) features in response to injury and in atherosclerosis, in parallel with phenotypic transition to the synthetic state. TGF-beta1 is known to have a role in SMC differentiation and extracellular matrix (ECM) synthesis, key characteristics of phenotypic state. Here, we set out to examine the effects of TGF-beta1 on Cx43-gap junction expression in relation to SMC differentiation, ECM synthesis and growth. Cx43 expression was analysed by immunoconfocal microscopy and Western blotting in primary human aortic SMCs treated with TGF-beta1 over a 48-h period, with assessment of gap-junctional communication by cell-to-cell transfer of microinjected ethidium bromide. In parallel, synthetic activity was analysed by Northern blotting for ECM components alpha-1(I) and alpha1(III) procollagen transcripts, contractile differentiation was assessed by immunoconfocal microscopy and Western blotting of the markers smooth muscle alpha-actin, calponin and smooth muscle heavy chain isoform 1 (SM1), and growth was measured by BrdU incorporation. Our results demonstrate that TGF-beta1 significantly up-regulates Cx43 expression and intercellular communication, in concert with increased expression of alpha-actin, calponin and SM1. Concomitant with contractile protein expression, ECM synthesis was increased rather than decreased, TGF-beta1 inducing a significant up-regulation of both procollagen transcripts. These effects were independent of growth. We conclude that in human aortic SMCs, TGF-beta1 treatment leads to up-regulation of Cx43-mediated gap-junctional communication and increased synthetic activity yet, somewhat paradoxically, also enhanced contractile differentiation.

Actins↗
PubMed1998

Structure, function, regulation: experimental analysis in groups of non-excitable cells coupled via permeable junctions.

This presentation reviews the functional properties of different permeable junctions (microplasmodesmata of filamentous cyanobacteria, septal pores of fungi, and gap junctions of animals). Examples of the distribution of power by ionic fluxes and electric current through permeable cell-cell junctions are considered. Based on the analysis of intercellular communication occurring during apical growth of hyphae of wild-type and mutant lines of the mycelial fungus Neurospora crassa, approaches to studies of the molecular and genetic mechanisms of self-organization in systems of cells with permeable junctions are discussed.

Cell Membrane Permeability↗
PubMed1998

Gap junctional communication in the developing central nervous system.

The development of the central nervous system is a complex process involving multiple interactions between various cell types undergoing mitosis, migration, differentiation, axonal outgrowth, synaptogenesis and programmed cell death. For example, neocortical development is characterized by a series of transient events that ultimately leads to the formation of a discrete pattern of laminar and columnar organization. While neuron-glial cell-cell interactions have been shown to be involved in neuronal migration, recent observations that neurons are extensively coupled by gap junctions in the developing neocortex have implicated this phenomenon in the process of neocortical differentiation. The present review will examine the putative role of gap junctional intercellular communication in development of the central nervous system, with specific reference to recent studies in the development of the cerebral cortex.

Animals↗
PubMed2002

[Local immune tolerance mechanisms in kidney cancer].

Many arguments suggest that renal tumours are immunogenic. However, the immune cells present around or within the tumour are unable to induce tumour rejection and the results of immunotherapy in metastatic renal cancer remain disappointing regardless of the protocols used. The objective of this study was to review the main mechanisms by which a renal tumour can escape immune destruction. These mechanisms can concern: tumour antigens, antigen-presenting molecules on the cell surface or defects of the cell machinery leading to the preparation of these molecules. Defects may also concern intercellular communications, especially adhesion and co-stimulation molecules. The immune cells present may also be defective, presenting qualitative or quantitative deficits, abnormalities of the T receptor, defect of cytokine production and these defects may concern both effector cells and antigen-presenting cells. The capacity of tumour cells to release anergic substances, i.e. substances which paralyze the immune system, also constitutes another very powerful immunosuppressive mechanism. These substances are cytokines, especially TGF-b. This anergy can also be mediated by intercellular contacts between tumour cells and lymphocytes, especially via the Fas system. It is important to study these mechanisms for several reasons: 1/Understanding of anergy mechanisms in order to discover new therapeutic targets or to short-circuit these mechanisms in vitro; 2/Definition of an "immune phenotype" of the tumour which should be evaluated as a prognostic marker both for survival after radical surgery of localized tumours as a prognostic factor for response to immunotherapy in metastatic forms.

Antigen Presentation↗
PubMed1996

Transmission between the type I hair cell and its calyx ending.

The long, uninterrupted apposition between the type I hair cell and the calyx ending has implications for the intercellular communication between these structures. Conventional synaptic transmission will be compromised unless the impedance of the ending is made relatively high. The apposition also creates the possibility of ephaptic transmission between the hair cell and the ending. Ephaptic transmission from the hair cell to the outer face of the calyx ending is too weak to make more than a minor contribution to sensory coding. Basolateral currents associated with hair-cell transduction can result in a substantial accumulation of K+ ions in the intercellular space. The accumulation can alter conventional transmission by depolarizing the hair cell and can alter afferent firing by depolarizing the ending. Reasons were presented suggesting that K+ accumulation may play an essential role in transduction involving type I hair cells, including the linearization of input-output relations and an increase in the maximal rate of discharge.

Animals↗