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PubMed1998

[The correlation between gap junction-mediated communication and cell proliferation among retinal pigment epithelial cells].

I investigated gap junction-mediated intercellular communication during cell proliferation of retinal pigment epithelium (RPE) following experimental retinal tear formation in albino rabbit eyes. I used a dye-coupling method with lucifer yellow CH. I also evaluated the expression of proliferating cell nuclear antigen (PCNA) in the RPE cells. Immediately after tear formation, lucifer yellow CH introduced into a target RPE cell appeared in neighboring cells. The number of dye-recipient cells was 33.8 +/- 4.7 (mean +/- standard error of the mean). One week later, the number of fluorescent RPE cells decreased to 2.3 +/- 0.9. The extent of dye transfer between RPE cells increased (17.5 +/- 4.1). There was no expression of PCNA in RPE cells immediately after tear formation, but it became apparent as the nuclei of RPE cells became positive for PCNA. The immunoreactive cells and cell population decreased one mouth later. Because the duration of decreased dye-coupling coincides with that of cell proliferation, these finding suggest that an alteration of gap junctional intercellular communication is involved in RPE cell proliferation in the present experimental setup.

Animals↗
PubMed1994

Nongenotoxic effects of polycyclic aromatic hydrocarbons and their oxygenation by-products on the intercellular communication of rat liver epithelial cells.

Since polycyclic aromatic hydrocarbons (PAHs) are known to have epigenetic effects, we evaluated the effect of the parent chemical and the ozonated products on in vitro cell to cell communication bioassays which measures a nongenotoxic event. The scrape loading/dye transfer (SL/DT) technique was used to determine the effect of the following PAHs on gap-junction intercellular communication (GJIC): fluorene, 1-methyl-fluorene, fluoranthene, anthracene, 9-methyl-anthracene, phenanthrene, pyrene, benzo(a)pyrene, and benzo(e)pyrene. The methylated PAHs were more inhibitory to GJIC than the unmethylated counterparts. Fluoranthene, which has an additional ring added to fluorene, was more effective in inhibiting GJIC than fluorene. The three-ringed PAHs were also more inhibitory than the four- and five-ringed PAHs. A time-course study of fluoranthene and of pyrene resulted in maximal inhibition occurring within 30 min of incubation with the cells. The cells recovered from the inhibition within 1 hr after fluoranthene and pyrene were removed from the cell culture medium. Pyene, vbenzo(a)pyrene, fluorene, and fluoranthene were ozonated until the parent compound was completely eliminated as determined by reverse-phase high-pressure liquid chromatography (RP-HPLC). An increased level of inhibition of GJIC was observed for the ozonated mixtures of by-products of pyrene, fluoranthene, and benzo(a)pyrene, but not for fluorene, as monitored with the SL/DT technique. The products of the ozonated pyrene mixture were fractionated and collected by RP-HPLC. Each fraction was found to be inhibitory to GJIC as monitored by fluorescence recovery after photobleaching. In conclusion, current treatment technologies, such as ozonation or biologically based oxidations and methylations, do not necessarily eliminate toxicity.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed2003

Chemical communication among bacteria.

Cell-cell communication in bacteria is accomplished through the exchange of chemical signal molecules called autoinducers. This process, called quorum sensing, allows bacteria to monitor their environment for the presence of other bacteria and to respond to fluctuations in the number and/or species present by altering particular behaviors. Most quorum-sensing systems are species- or group-specific, which presumably prevents confusion in mixed-species environments. However, some quorum-sensing circuits control behaviors that involve interactions among bacterial species. These quorum-sensing circuits can involve both intra- and interspecies communication mechanisms. Finally, anti-quorumsensing strategies are present in both bacteria and eukaryotes, and these are apparently designed to combat bacteria that rely on cell-cell communication for the successful adaptation to particular niches.

Bacterial Physiological Phenomena↗
PubMed1996

Transforming growth factor-beta, osteogenin, and bone morphogenetic protein-2 inhibit intercellular communication and alter cell proliferation in MC3T3-E1 cells.

Intercellular communication by gap junctions has been implicated to function in the control of cell growth and differentiation in osseous tissues-processes which are regulated, in part, by peptide growth factors, including transforming growth factor-beta (TGF-beta) and the bone morphogenetic proteins (BMPs). Using the osteoblastic cell line MC3T3-E1, we tested the hypothesis that the effects of TGF-beta and BMPs on cell proliferation may be correlated to changes in intercellular communication. In a series of proliferation assays, MC3T3-E1 cells were cultured in the presence of bone morphogenetic protein-2 (BMP-2) or TGF-beta for up to 48 hr. Proliferation of cells during the linear log phase (days 2 to 4) was assessed by 3H-thymidine (3H-TdR) incorporation. After times ranging from 6 to 48 hr, BMP-2 significantly inhibited uptake of 3H-TdR at doses of 50-800 ng/ml. Similarly, TGF-beta inhibited uptake of 3H-TdR at doses of 2-32 ng/ml. In a separate group of experiments, intercellular communication through gap junctions was demonstrated by cell-cell transfer of the fluorescent tracer, lucifer yellow, after microinjection. One series of experiments showed that the gap junctional intercellular communication (GJIC) of cells, incubated for 48 hr in the presence of the higher dose of osteogenin (OG) (5.0 vs. 0.5 microgram/ml) or higher dose of TGF-beta (2.0 vs. 0.2 ng/ml), was significantly inhibited compared to control. In another series of experiments, time and dose dependent effects of BMP-2 and TGF-beta on GJIC were investigated. In the time course experiments (3, 6, 12, 24, and 48 hr), TGF-beta (2.0 ng/ml) demonstrated a statistically significant effect in inhibiting GJIC as early as 6 hr, while BMP-2 (50 ng/ml) inhibited GJIC after 24 and 48 hr of treatment. The dose-dependent effects of BMP-2 and TGF-beta on cell couplings, determined at 48 hr, showed significant inhibitory effects with BMP-2 at 25 and 50 ng/ml and with TGF-beta at 2 and 4 ng/ml. The cell count results and injection study performed at 12 hr, at a fixed cell density, confirmed that the inhibitory effect was not due to differences in cell density. The 50% effective inhibitory concentrations (EC50) calculated for BMP-2 and TGF-beta at 48 hr, showed no dose correlation between proliferation and GJIC, suggesting that these two events are independent occurrences. Additionally, marked morphological change was observed in the cells treated with TGF-beta. The observation may suggest that TGF-beta may have effects upon cytoskeletal elements in osseous tissues.

3T3 Cells↗
PubMed2003

Hypoxia and stretch regulate intercellular communication in vascular smooth muscle cells through reactive oxygen species formation.

OBJECTIVE: We hypothesized that the alterations in vasomotor tone and adaptive remodeling responses that occur in the circulation because of hypoxia were dependent on changes in cell to cell communication through regulation of gap junction protein expression and function. Consequently, we studied the amount, distribution, and permeability of the principal vascular smooth muscle cell (VSMC) gap junction protein, connexin43, in rat aortic cultures exposed to oxygen partial pressures of 150 or 15 mm Hg. METHODS AND RESULTS: Immunohistochemical staining, immunoblot assays, and Northern blot analyses demonstrated that connexin43 expression was reversibly increased in hypoxic cultures. As a result, hypoxic cells exhibited greater intercellular communication as determined by fluorescence recovery after photobleaching experiments. Using a fluorogenic substrate, hypoxic VSMCs showed increased reactive oxygen species generation, which could be prevented by the glutathione peroxidase mimic ebselen and the mitochondrial complex I inhibitor rotenone but not with the redox-sensitive thiol pyrrolidine dithiocarbamate. The rise in connexin43 expression attributable to hypoxia could be attenuated by ebselen and rotenone treatment. Interestingly, the previously reported induction of connexin43 expression by tensile stretch was also contingent on oxidative activity. CONCLUSIONS: Hypoxia and stretch increased gap junctional intercellular communication in VSMCs attributable to enhanced connexin43 expression initiated by reactive oxygen species formation.

Animals↗
PubMed1996

The role of matrix contact and of cell-cell interactions in choriocarcinoma cell differentiation.

Cell differentiation is supported much better by gels of extracellular matrix than by the same matrix provided as a rigid substrate. Many cell types including normal and malignant trophoblast cells, however, form multicellular multilayered aggregates on matrix gels with increased cell-to-cell contacts as compared to regular monolayers on rigid matrix substrates. In such cultures, it remained open, so far, whether stimulated expression of differentiation markers is caused by enhanced cell-to-cell communication or is displayed only by cells in direct contact to the gel. Therefore, choriocarcinoma cells (BeWo) were grown as aggregates: (a) on gels of the basement membrane-like Matrigel, (b) on plastic coated with poly-HEMA, or (c) as aggregates (spheroids) in suspension culture. Production of the differentiation marker chorionic gonadotropin was stimulated significantly in aggregates attached to gels of Matrigel or to the poly-HEMA substrate but not in suspended spheroids. With respect to cell-cell communications, however, expression of E-cadherin mRNA was not altered in any type of aggregates, as compared to control cultures on plastic. The expression of connexin43 mRNA (not of connexin26) was increased only in suspended spheroids, while microinjection of the fluorescent dye Lucifer Yellow suggested that cell communication via gap junctions was absent from cells grown as monolayers and was not induced in any type of aggregate. When cells were grown on gels of Matrigel, the relevance of direct cellular contact to the substrate for differentiation was analyzed by immunohistochemistry. Trophoblastic differentiation markers (chorionic gonadotropin, placental lactogen, placenta-type alkaline phosphatase, and pregnancy-specific glycoprotein beta 1) as well as the proliferation marker Ki-67 were not preferentially expressed in cells that were in contact with the gel. Similar random distributions of all these markers were also observed in spheroids cultured in suspension. The distributions of several matrix molecules and of different integrins were comparable between aggregates on matrix gels and those in suspension culture. According to these data, cell-cell communication appears to play a subordinate role for cytodifferentiation in cell aggregates on matrix gels, so that substrate anchorage and physical properties of the substrate may be the decisive factors. Interestingly, however, direct contact to the substrate does not seem to be essential for the stimulation of differentiation in cells on matrix gels. The results are discussed in the context of the "tensegrity"-model for cell-matrix interactions in which proper mechanical properties of the substrate are important for the regulation of cell differentiation by allowing a balanced integrity of external and cell-internal tensile forces.

Actins↗
PubMed1992

Roles of receptor tyrosine kinases in Drosophila development.

Communication between cells is a fundamental component of development and morphogenesis. Identification of the molecules mediating cell-cell communication is crucial for elucidation of the molecular basis of these processes. Receptor tyrosine kinases (RTKs) appear to play a central role in this context by transmitting into cells information dictating their fate. The functions of RTKs in Drosophila are extremely diverse, and include maternal determination of embryonic polarity (torso and torpedo), determination of neuroblast identity (faint little ball), and guidance of tracheal cell migration in the embryo (breathless). During compound eye development, RTKs affect the number of photoreceptor clusters (Ellipse) and the determination of photoreceptor R7 identity (sevenless). The phenotypes of mutations in RTK loci serve as a starting point for understanding processes dictating cell identity at the level of the whole organism. Recently, they have also begun to provide a basis for selection of second-site suppressor mutations, encoding additional elements in their signal transduction pathway. Common themes between the functions, regulation, and signal transduction pathways of Drosophila RTKs are drawn.

Animals↗
PubMed2006

Ochratoxin A alters cell adhesion and gap junction intercellular communication in MDCK cells.

Ochratoxin A (OTA) is one of the most potent renal carcinogens studied to date, but the mechanism of tumor formation by ochratoxin A remains largely unknown. Cell adhesion and cell-cell communication participate in the regulation of signaling pathways involved in cell proliferation and growth control and it is therefore not surprising that modulation of cell-cell signaling has been implicated in cancer development. Several nephrotoxicants and renal carcinogens have been shown to alter cell-cell signaling by interference with gap junction intercell communication (GJIC) and/or cell adhesion, and the aim of this study was to determine if disruption of cell-cell interactions occurs in kidney epithelial cells in response to OTA treatment. MDCK cells were treated with OTA (0-50 microM) for up to 24h and gap junction function was analyzed using the scrape-load/dye transfer assay. In addition, expression and intracellular localization of C x 43, E-cadherin and beta-catenin were determined by immunoblot and immunofluorescence analysis. A clear decrease in the distance of dye transfer was evident following treatment with OTA at concentrations/incubation times which did not affect cell viability. Consistent with the functional inhibition of GJIC, treatment with OTA resulted in a dose-dependent decrease in C x 43 expression. In contrast to C x 43, OTA did not alter total amount of the adherens junction proteins E-cadherin and beta-catenin. Moreover, Western blot analysis of Triton X-100 soluble and insoluble protein fractions did not indicate translocation of cell adhesion molecules from the membrane to the cytoplasm. However, a approximately 78 kDa fragment of beta-catenin was detected in the detergent soluble fraction, indicating proteolytic cleavage of beta-catenin. Immunofluorescence analysis also revealed changes in the pattern of both beta-catenin and E-cadherin labeling, suggesting that OTA may alter cell-adhesion. Taken together, these data support the hypothesis that disruption of cell-cell signaling may contribute to OTA toxicity and carcinogenicity.

Animals↗
PubMed2001

Polyamines regulate gap junction communication in connexin 43-expressing cells.

The control of cell-cell communication through gap junctions is thought to be crucial in normal tissue function and during various stages of tumorigenesis. However, few natural regulators of gap junctions have been found. We show here that increasing the activity of ornithine decarboxylase, or adding polyamines to the outside of cells, increases the level of gap junction communication between various epithelial cells. Conversely, reduction of ornithine decarboxylase activity decreases the level of gap junction communication. This regulation is dependent upon the expression of connexin 43 (Cx43 or Cxalpha1), which is a major connexin expressed in many different cell types, and involves an increase in Cx43 and its cellular re-distribution.

Animals↗
PubMed2005

Modulation of GJA1 turnover and intercellular communication by proinflammatory cytokines in the anterior pituitary folliculostellate cell line TtT/GF.

Our previous studies have advanced the idea that the folliculostellate cell GJA1 (gap junction membrane channel protein alpha1; previously known as connexin 43)-mediated gap junctions contribute to the establishment of an intercellular network that regulates the paracrine messages and the endocrine response within the anterior pituitary. The folliculostellate cells are targets for growth factors and cytokines that modulate hormone secretion. Proinflammatory cytokines modulate the cell-to-cell communication in many tissues of the body. The present study measured the effect of the proinflammatory cytokines tumor necrosis factor and interleukin-1 on the GJA1-mediated intercellular communication, specifically the expression, localization, degradation, and phosphorylation status of GJA1 in the folliculostellate cell line TtT/GF. The GJA1 localized to the plasma membrane and to minute cytoplasmic vesicles in the perinuclear area. Using different antibodies that recognize distinctly the nonphosphorylated from the phosphorylated forms of GJA1, we showed that nonphosphorylated GJA1 in Ser-368 (NP-GJA1) localized chiefly in the cytoplasm, whereas GJA1 phosphorylated in Ser-368 (P-GJA1) localized to the plasma membrane in controls. The cytokine treatment transiently increased 1) GJA1, NP-GJA1, and P-GJA1 levels; 2) NP-GJA1 and P-GJA1 degradation by both the lysosomal and proteasomal pathways; and 3) cell-to-cell communication in TtT/GF cells. The results suggest that the cytokine-evoked, transient enhancement of folliculostellate cell-mediated intercellular communication contributes to the coordination of the response among folliculostellate cells.

Animals↗
PubMed2003

Conformon-driven biopolymer shape changes in cell modeling.

Conceptual models of the atom preceded the mathematical model of the hydrogen atom in physics in the second decade of the 20th century. The computer modeling of the living cell in the 21st century may follow a similar course of development. A conceptual model of the cell called the Bhopalator was formulated in the mid-1980s, along with its twin theories known as the conformon theory of molecular machines and the cell language theory of biopolymer interactions [Ann. N.Y. Acad. Sci. 227 (1974) 211; BioSystems 44 (1997) 17; Ann. N.Y. Acad. Sci. 870 (1999a) 411; BioSystems 54 (2000) 107; Semiotica 138 (1-4) (2002a) 15; Fundamenta Informaticae 49 (2002b) 147]. The conformon theory accounts for the reversible actions of individual biopolymers coupled to irreversible chemical reactions, while the cell language theory provides a theoretical framework for understanding the complex networks of dynamic interactions among biopolymers in the cell. These two theories are reviewed and further elaborated for the benefit of both computational biologists and computer scientists who are interested in modeling the living cell and its functions. One of the critical components of the mechanisms of cell communication and cell computing has been postulated to be space- and time-organized teleonomic (i.e. goal-directed) shape changes of biopolymers that are driven by exergonic (free energy-releasing) chemical reactions. The generalized Franck-Condon principle is suggested to be essential in resolving the apparent paradox arising when one attempts to couple endergonic (free energy-requiring) biopolymer shape changes to the exergonic chemical reactions that are catalyzed by biopolymer shape changes themselves. Conformons, defined as sequence-specific mechanical strains of biopolymers first invoked three decades ago to account for energy coupling in mitochondria, have been identified as shape changers, the agents that cause shape changes in biopolymers. Given a set of space- and time-organized teleonomic shape changes of biopolymers driven by conformons, all of the functions of the cell can be accounted for in molecular terms-at least in principle. To convert a conceptual model of the cell into a computer model, it is necessary to represent the conceptual model in an algebraic language. To this end, we have begun to apply the process algebra of Milner [Communicating and Mobile Systems: The pi-calculus, Cambridge University Press, Cambridge, 1999] to develop what is here called the "shape algebra," capable of describing complex and mobile patterns of interactions among biomolecules leading to cell functions.

Algorithms↗
PubMed1987

Inhibition of intercellular communication by nickel(II): antagonistic effect of magnesium.

The level of gap-junctional (cell-cell) communication was studied by the radioisotope transfer technique in NIH 3T3 cells exposed to NiSO4, MgSO4, or both salts combined. Monolayered NIH 3T3 donor cells were labeled with [3H]-uridine for 3 h and then co-cultured with non-labeled recipient NIH 3T3 cells for 3 h in the presence of 0.5-20 mM NiSO4, 1.0-100 mM MgSO4, or 5 mM NiSO4 plus 1.0-100 mM MgSO4. 12-O-tetradecanoylphorbol-13-acetate (TPA), 16-160 pM, served as a positive control. The exposed cells were fixed with 2.5% glutaraldehyde and processed for autoradiography. The cell-cell communication rate was based on the number of radioactive recipient cells in relation to the total number of recipient cells for 100 donor cells. NiSO4 disrupted cell-cell communication in a dose-related manner from 98% of the base value at 0.5 mM NiSO4 to 2% at 5 mM NiSO4. Cell viability was not affected by 0.5-5 mM NiSO4. The inhibitory action of 5 mM NiSO4 could be partially prevented by 5.0-100 mM MgSO4. However, MgSO4 did not prevent the inhibition by TPA. The results indicate that NiSO4 is capable of inhibiting cell-cell communication at concentrations that do not cause cytotoxic effects in NIH 3T3 cells during a 3-h period. In this respect NiSO4 resembles such classical tumor promoters like TPA. The antagonism by magnesium of the nickel-induced inhibition of cell-cell communication may indicate a contributory mechanism by which magnesium counteracts the carcinogenicity of nickel in vivo.

Cell Communication↗
PubMed1996

Connexins, connexons, and intercellular communication.

Cells in tissues share ions, second messengers, and small metabolites through clusters of intercellular channels called gap junctions. This type of intercellular communication permits coordinated cellular activity. Intercellular channels are formed from two oligomeric integral membrane protein assemblies, called connexons, which span two adjacent cells' plasma membranes and join in a narrow, extracellular "gap." Connexons are formed from connexins, a highly related multigene family consisting of at least 13 members. Since the cloning of the first connexin in 1986, considerable progress has been made in our understanding of the complex molecular switches that control the formation and permeability of the intercellular channels. Analysis of the mechanisms of channel assembly has revealed the selectivity of inter-connexin interactions and uncovered novel characteristics of the channel permeability and gating behavior. Structure-function studies provide a molecular understanding of the significance of connexin diversity and demonstrate the unique regulation of connexins by tyrosine kinases and oncogenes.

Animals↗
PubMed1990

Cultured myometrial cells establish communicating gap junctions.

Myometrial cells were isolated and cultured from term rat uterus. The myometrial origin of the cultures was verified by antibody staining of cellular desmin and alpha-smooth muscle actin. The presence of functional gap junctions was indicated by transfer of radiolabeled nucleotide and microinjected Lucifer yellow dye. The cultured cells expressed mRNA recognized by a connexin43 gap junction cDNA probe. To our knowledge, this is the first report that isolated myometrial cells form gap junctions in culture.

Actins↗
PubMed1989

Intercellular communication between rat anterior pituitary cells.

Cell-to-cell communication within the rat anterior pituitary was investigated in 60-day-old male rats with immunohistochemistry, scanning electron microscopy, freeze-fracture electron microscopy, and conventional transmission electron microscopy. A dense cytoreticular network of cytoplasmic processes from the folliculostellate cells was found to contain immunoreactive S-100 protein and was observed throughout the anterior pituitary. Nonimmunoreactive cells, which were granular, were situated in the center of each network. Almost all of the granulated cells were situated in close proximity to the folliculostellate cells. Scanning electron microscopy revealed that the gland consisted of microlobules enclosed by a basal lamina. On the surface of the microlobules were blood vessels whose branches invaded its internal structures. Cytoplasmic processes from folliculostellate cells projected outside the microlobule. Freeze-fracture electron microscopy demonstrated the presence of numerous intramembranous particles on the P-face of the plasma membrane. Scattered on the cell surface were groups of particles forming gap junctions. Meshworks of ridges which were representations of tight junctions were also observed near clusters of microvillous fragments. Clusters of particles forming small gap junctions were located between the meshworks of tight junctions. Small gap junctions were clearly observed by conventional electron microscopy between junctional complexes in a manner similar to that seen by freeze-fracture electron microscopy. Slender cytoplasmic processes of folliculostellate cells came in contact near the basal lamina and were adjoined by small gap junctions. The ratio of nongranular cells which contained gap junctions to those in which the junctions were absent was about 1:1. The size of the gap junctions ranged from 50 nm to 3 microns. No gap junctions were observed along the plasma membranes of the granular cells. The significance of an intercellular communication system within the anterior pituitary gland of the rat is to establish a mechanism for rapid transmission of information in an organ which lacks direct innervation.

Animals↗
PubMed1990

Intercellular communication is cell cycle modulated during early Xenopus laevis development.

We investigated intercellular communication during the seventh and tenth cell cycles of Xenopus laevis development using microinjection of Lucifer yellow and FITC-dextran as well as freeze-fracture electron microscopy. We found that gap junction-mediated dye coupling visualized using Lucifer yellow was strongly cell cycle modulated in the tenth cell cycle. Cytoplasmic bridge-mediated dye coupling visualized via FITC-dextran was also, of course, cell cycle modulated. The basis of cell cycle-modulated gap junctional coupling was investigated by measuring the abundance of morphologically detectable gap junctions through the tenth cell cycle. These proved to be six times more abundant at the beginning than at the end of this cell cycle.

Animals↗