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PubMed1996

Gap junction involvement in secretion: the pancreas experience.

1. Gap junctions and junction-mediated cell-to-cell communications are obligatory features of gland cells, whatever their secretory product is. 2. Studies on pancreatic islets and acinar cells indicate that cell-to-cell communication via gap junction channels is required for proper biosynthesis, storage and release of both insulin and amylase. 3. However, the endocrine and exocrine portions of the pancreas show opposite connexin (Cx) and coupling changes in relation to the activation and inhibition of their secretory functions. 4. These differences may be accounted for by the expression of Cx43 in pancreatic islets and of Cx26 and Cx32 in pancreatic acini. This alternative expression of connexin isoforms is also found in several other endocrine and exocrine glands. 5. These observations indicate that connexin-made channels play a central role in the control of secretory events.

Animals↗

PubMed2001

Bimodal inhibition of connexin 43 gap junctions decreases ACTH-induced steroidogenesis and increases bovine adrenal cell population growth.

In order to elucidate the role of gap junctions in adrenal cell responses, we measured the effect of inhibiting gap junctions with 18-alpha glycerrhetinic acid (GA; a potent inhibitor of cell-cell communication) and connexin antisense transfection on cell proliferation and adrenocorticotropin (ACTH)-stimulated steroidogenesis. In these experiments we utilized a bovine adrenocortical cell (SBAC) population, which responds to ACTH treatment with a dose-dependent increase in steroid production, an increase in connexin 43 (alpha(1)-Cx43) gap junction protein concentrations, and a decrease in cell population growth. SBAC cell populations treated with GA had increased growth rates, decreased ACTH-stimulated steroidogenesis, but no reduction in alpha(1)-Cx43 gap junction protein contents. In contrast, when SBAC cells were transfected with alpha(1)-Cx43 antisense cDNA, gap junction protein concentration was dramatically reduced as expected, unlike the GA-treated cell populations. Cell populations transfected with alpha(1)-Cx43-antisense also exhibited increased growth rates and a decreased steroidogenic response to ACTH treatment as compared with control or vector-only transfected cell populations. The decreased responsiveness and increased number of cells in the population after gap junction function was decreased by either GA treatment or antisense transfection, suggests that gap junctions may be necessary factors in ACTH-stimulated responsiveness and growth control in the adrenal gland.

Adrenal Glands↗

PubMed1985

Cultured intestinal smooth muscle cells: its morphology and physiology.

The electrical properties and morphological characteristics of cultured smooth muscle cells were studied. During the culture, the cells proliferated, lined up in linear parallel arrays and exhibited a typical formation of hills and valleys. Injection of depolarizing or hyperpolarizing current pulses evoked action potentials in the cells, and the cells often displayed spontaneous action potential activity. These action potentials were found to be calcium dependent. ACh produced membrane depolarization, noradrenaline membrane hyperpolarization. The cells were coupled by low-resistance junctions that permit the cell-to-cell-passage of electrical current and fluorescein dye. The permeability of junction was blocked by the increased concentration of cytoplasmic calcium ions. These results indicate that the cell-to-cell communication properties of cultured smooth muscle cells are modelated by the cytoplasmic calcium ions concentration.

Acetylcholine↗

PubMed1997

The polymorphonuclear leukocyte: a cell tuned for transcellular biosynthesis of cys-leukotrienes.

Sulfidopeptide leukotrienes (cysLT) are potent vasoactive mediators that can constrict coronary vessels and alter caliber of the microcirculation. They can be formed "in situ" via a peculiar type of cell communication termed "transcellular biosynthesis" whereby donor cells (polymorphonuclear leukocytes, PMNL) feed acceptor cells (endothelial cells, EC) the unstable epoxide intermediate leukotriene A4 for further metabolism to cysLT. We have investigated the relative amount of leukotriene A4 that is synthesized by PMNL and made available for transcellular biosynthesis. This has been accomplished by measuring the relative amounts of enzymatic vs non-enzymatic leukotriene A4-derived metabolites after challenge with the Ca(2+)-ionophore A23187, using PMNL suspensions at different concentrations. Non-enzymatic leukotriene A4-derived metabolites were used as a quantitative index of the amount of leukotriene A4 released into the extracellular milieu. In human, as well as in bovine PMNL, the relative amounts of non-enzymatic vs enzymatic leukotriene A4-derived metabolites increased with decreasing cell concentrations. By diminishing possible cell-cell interactions via increased dilution, it is calculated that approx. 60% of leukotriene A4 synthesized is released from the PMNL. These data provide evidence that, in PMNL, transfer of leukotriene A4 to neighbouring acceptor cells is taking place as a predominant mechanisms of cell communication.

Animals↗

PubMed1987

Is a mosaic embryo also a mosaic of communication compartments?

We have studied the pathways of cell communication in embryos of the mollusc Lymnaea stagnalis in which the developmental fate of a cell or a group of cells is known from cell lineage studies. We iontophoretically injected Lucifer Yellow CH and followed the spread of fluorescence between cells interconnected via gap junctions. In early stages all blastomeres appear to be dye-coupled, but later on communication is restricted within compartments. The pattern of cell communication corresponds with the development of compartments with specific cell fates. Dye-spread is limited by communication boundaries which completely or mostly prevent the passage of dye to adjacent compartments with different developmental fates. These boundaries appear progressively during development. Our results suggest that, during the development of Lymnaea, the progressive changes in the pattern of dye spread correspond with the progressive restrictions of the developmental fates of individual cells or groups of cells. We conclude that changes in the pattern of cell communication and in the appearance of communication compartments are not exclusive features of regulative embryos.

Animals↗

PubMed1989

Mechanistic studies on the DDT-induced inhibition of intercellular communication.

Two structurally unrelated compounds, 1,1'-(2,2,2-trichloroethylidene) bis(4-chlorobenzene) (DDT) and 12-O-tetradecanoylphorbol-13-acetate (TPA), are both potent inhibitors of cell-cell communication in vitro as well as tumour promoters in vivo. There is evidence that TPA acts via a specific receptor mechanism involving activation of protein kinase C (pkC). The mechanism of action of DDT has been discussed in terms of membrane perturbation, increased intracellular calcium, interaction with calmodulin and decreased cAMP levels. In the present study the objective was to examine the potential role of pkC activation in DDT-induced inhibition of intercellular communication in cultured cells. The V79 metabolic cooperation assay was used for measuring intercellular communication. Furthermore, the effects of DDT on the activity of partially purified pkC from V79 cells was measured, as was the interaction of DDT with the phorbol ester/DAG-binding site on the pkC enzyme. Results from the biochemical studies showed that DDT neither activates pkC nor binds to the phorbol ester/DAG-binding site, as measured by displacement of PDBU binding. Using the metabolic cooperation assay it was demonstrated that pretreatment with TPA made cells refractory, i.e. a second application of TPA did not inhibit cell-cell communication. DDT added to cells down-regulated with TPA inhibited cell-cell communication, even though these cells were refractive to TPA. This result further supports the hypothesis that DDT and TPA inhibit intercellular communication primarily by different pathways. At non-cytotoxic concentrations, pkC inhibitors (H7, W7 and palmitoyl carnitine) did not affect the TPA- or DDT-induced inhibition of cell-cell communication in the V79 metabolic cooperation assay. Quercetin, a pkC inhibitor which has been reported to eliminate DDT- or TPA-induced inhibition of intercellular communication, was investigated in an in vivo study that measured promotion of enzyme-altered foci in DEN-treated rat liver. Quercetin co-administered with DDT did not act as an antipromoter.

Animals↗

PubMed1998

Cell-cell signaling during neurogenesis: some answers and many questions.

Development of a multicellular organism requires that cells communicate with each other in order to regulate their growth, organize into tissues and coordinate their function. This cell-cell communication is mediated by signals cells receive (or send) between each other and from the environment. The signaling can be a short range remote signaling (through secreted signaling molecules), contact signaling (via plasma membrane bound molecules, gap junctions) or a long range signaling (through hormones). In this article, I have reviewed the recent advances on the role of cell-cell signaling in the development of the embryonic nervous system of the fruitfly Drosophila melanogaster and discussed some of the open questions raised by these studies. It discusses the contributions of the neurogenic genes Notch and Delta and the signaling pathways controlled by wingless, patched and hedgehog in neuroblast formation, neuroblast identity specification and neuroblast lineage elaboration.

Animals↗

PubMed1993

Endoplasmic Reticulum Forms a Dynamic Continuum for Lipid Diffusion between Contiguous Soybean Root Cells.

Intercellular communication between plant cells for low molecular weight hydrophilic molecules occurs through plasmodesmata. These tubular structures are embedded in the plant cell wall in association with the plasmalemma and endoplasmic reticulum (ER). Transmission electron microscopy has provided strong evidence to support the view that both the ER and plasmalemma are structurally continuous across the wall at these sites. In experiments to be described, the technique of fluorescence redistribution after photobleaching was used to examine the lateral mobility and intercellular transport capability of a number of fluorescent lipid and phospholipid analogs. These probes were shown by confocal fluorescence microscopy to partition in either the ER or plasmalemma. Results from these measurements provide evidence for cell communication between contiguous cells for probes localized predominantly in the ER. In contrast, no detectable intercellular communication was observed for probes residing exclusively in the plasmalemma. It was of particular interest to note that when 1-acyl-2-(N-4-nitrobenzo-2-oxa-l,3-diazole)aminoacylphosphatidylcholine was utilized as a potential reporter molecule for phospholipids in the plasmalemma, it was quickly degraded to 1-acyl-2-(N-4-nitrobenzo-2-oxa-1,3-diazole)aminoacyldiglyceride (NBD-DAG), which then appeared predominantly localized to the ER and nuclear envelope. This endogenously synthesized NBD-DAG was found to be capable of transfer between cells, as was exogenously incorporated NBD-DAG. Results from these investigations provide support for the following conclusions: (1) ER, but apparently not the plasmalemma, can form dynamic communication pathways for lipids across the cell wall between connecting plant cells; (2) the plasmodesmata appear to form a barrier for lipid diffusion through the plasmalemma; and (3) lipid signaling molecules such as diacylglycerol are capable of transfer between contiguous plant cells through the ER. These observations speak to issues of plant cell autonomy for lipid synthesis and mechanisms of intercellular signaling and communication.

Journal Article↗

PubMed1998

Hormonal regulation of connexin-43 in baboon corpora lutea.

The synthesis and secretion of progesterone in the corpus luteum are regulated by both endocrine and paracrine/ autocrine factors which affect the steroidogenic cells. Evidence suggests that these cells communicate via cell-cell junctional proteins, the connexins. Previously we have shown that connexin-43 is expressed in both human and baboon (Papio hamadryus anubis) corpora lutea, with differential expression throughout luteal development, but is not detectable in corpora albicantia. We have examined the effect of human chorionic gonadotropin (hCG), oxytocin, clomiphene citrate and the anti-progesterone onapristone on expression of connexin-43 protein in the early luteal phase 1-5 days after the mid-cycle luteinizing hormone (LH) surge (LH+ 1-5 days), the mid-luteal phase 6-10 days after the LH surge (LH+ 6-10 days), and the late luteal phase 11-15 days after the LH surge (LH+ 11-15 days) in corpora lutea obtained from normal adult cycling females. Connexin-43 was localized by immunohistochemistry in cultured cells from all the three stages. Western blot analysis of the treated cells indicated the presence of two bands at 43 and 45 kDa. The band at 45 kDa was found to be phosphorylated connexin-43, indicating the presence of functional gap junctions. hCG (10 IU/ml) stimulated the expression of connexin-43 throughout luteal development; however, maximum expression occurred in the early luteal phase with a significantly greater expression of the non-phosphorylated protein. In contrast, in the mid-luteal phase, the expression of the phosphorylated protein was predominant. Oxytocin (200 mU/ml) also stimulated connexin-43 expression throughout luteal development with similar effects on the phosphorylated and non-phosphorylated protein in the early and mid-luteal phase; however, compared with hCG, oxytocin had a greater effect on mid-luteal phase connexin-43 expression. In the presence of both hCG and oxytocin, the expression of connexin-43 was significantly higher than the control only in the late luteal phase. Both clomiphene citrate and onapristone suppressed connexin-43 expression, and concomitant addition of hCG did not counteract their effect. In the context of our previous studies, it is concluded that, together with LH/hCG and the steroid hormones, oxytocin is involved in cell-cell contact-dependent communication in the corpus luteum.

Animals↗

PubMedDate not supplied

A synaptic basis for T-lymphocyte activation.

T lymphocytes respond to foreign antigen by forming specialized junctions with antigen-presenting cells (APC) or target cells. A hypothesis is presented, illustrating the similarity between the T-cell recognition-activation process and the cell communication processes found in other organ systems, especially the nervous system. Based on data showing that a major neuronal protein, Thy-1, is also a mitogenic site on T cells, and based on predictions for the structures of the T-cell receptor (TcR) and Ia proteins, an activation model is presented as follows. 1) The T-cell receptor initiates cell-cell contact with the APC by interacting with Ia and antigen, forming an antigen-binding site. 2) Sets of adhesion molecules then bind, focusing the interacting proteins to the junctional site. One binding protein, L3/T4, binds Ia and concentrates the Ia molecules to the contact site. 3) The two-chain TcR then links together the TcR-Ia-antigen complexes, forming a linear chain of receptors which will self-associate once reaching a critical length, forming a cluster. This cluster juxtaposes associated channel subunits, the T3 membrane molecules, creating an ion channel, stimulating the T cell. 4) The MHC molecule is structurally a part of this activation complex, and therefore also forms a cluster on the APC surface, possibly activating the presenting cell. 5) Secretory products are then released into the synaptic site allowing for efficient and directed cell-cell communication. Cytolytic class-I-restricted cells use a similar pathway to focus the effect of cytolytic proteins. This analogy views neuronal communication and lymphoid recognition as evolutionary descendents of a primordial lymphocytic type of cell interaction.

Animals↗

PubMed1998

Primary role of Kupffer cell-hepatocyte communication in the expression of oxidative stress in the post-ischaemic liver.

It has been reported that hepatocyte metabolism and function can be modulated by the activated Kupffer cell through the release of different biomolecules like cytokines, eicosanoids, oxygen free radicals and enzymes. In relation to these paracrine factors involved in circuits of intercellular communication, the existence of a hepatic oxygen sensor located in the Kupffer cell has been postulated. According to this postulate the oxygen metabolism of the liver parenchymal cells could be under the control of the Kupffer cells. In order to study the role of the Kupffer cell in the reperfusion syndrome of the liver, a lobular ischaemia-reperfusion model was performed in rats with or without previous treatment with gadolinium chloride to block Kupffer cell function. Spontaneous chemiluminescence of the liver surface, oxygen uptake by tissue slices and tertbutyl hydroperoxide-initiated chemiluminescence determinations were performed to evaluate the oxygen metabolism and the oxy-radical generation by the liver. The lower basal photoemission, in parallel with a lower basal oxygen uptake registered in the hepatic lobes from the animals pretreated with gadolinium chloride clearly indicates that the gadolinium chloride-dependent functional inhibition of Kupffer cell leads to a downregulation of oxygen metabolism by the liver. Moreover, the intensity of oxidative stress exhibited by the postischaemic lobes appears to be closely linked with the Kupffer cell activity. On the basis of the data obtained we propose that a paracrine circuit between activated Kupffer cell and hepatocytes is an early key event in the induction of postischaemic oxidative stress in the liver. Furthermore the interference with the mitochondrial electron flow by some biomolecules released from the activated Kupffer cell, such as tumour necrosis factor, interleukins, eicosanoids, etc., would increase the rate of generation of reactive oxygen species by the inhibited mitochondrial respiratory chain.

Animals↗

PubMed1992

Effects of ethanol on intercellular communications and polarization of hepatocytes in short-term culture.

The formation of intracellular lumina with apical differentiation is observed in several cancerous epithelial cell lines including human hepatocarcinoma. This disorder of cell polarization can be induced by the inhibition of cell-cell communication, a known factor of carcinogenesis. This work was designed to study the effects of ethanol on the differentiation of hepatocytes in short-term culture. Isolated hepatocytes were plated on plastic culture dishes that were 35 mm in diameter (10(6) cells/dish). Three hours after plating, the hepatocytes were incubated in the presence of 20 mmol/L ethanol for 1 hr. Treated cells were compared with controls using morphometric methods after conventional treatment for ultramicroscopy and by measuring cellular dye coupling by the fluorescent Lucifer Yellow CH transfer method. Bile canaliculi formation decreased in alcohol-treated cells (6.5% vs. 9.9%, 2p less than 0.05), whereas intracellular lumina incidence increased (3.1% vs. 0.5%, 2p less than 0.01). In parallel, the dye-coupling capacity decreased significantly when hepatocytes were treated with alcohol (2p less than 0.01). This work shows that short-term ethanol treatment induces significant disturbances of cell polarization and inhibits the reestablishment of cell-cell communication in cultured hepatocytes. These disorders could, at least in part, explain the carcinogenic effects of ethanol.

Animals↗

PubMed2005

Development of a quantitative tool for measuring changes in the coefficient of conductivity of plasmodesmata induced by developmental, biotic, and abiotic signals.

The regulation of intercellular and interorgan communication is pivotal for cell fate decisions in plant development and probably plays a significant role in the systemic regulation of gene expression and in defense reactions against pathogens or other biotic and abiotic environmental factors. In plants, symplasmic cell-to-cell communication is provided by plasmodesmata (Pd), coaxial membranous tunnels that span cell walls interconnecting adjacent cytoplasms. Macromolecules, proteins, and RNA may be transported through Pd by passive diffusion or by a facilitated mechanism. A quantitative tool was developed to measure the coefficient of conductivity, C(Pd), for diffusion-driven transport via Pd and to assess changes in the coefficient induced by developmental, biotic and abiotic signals. (GFP)C(Pd), the coefficient of conductivity for cell-to-cell spread of green-fluorescent protein (GFP), a protein with a Stokes radius of 2.82 nm, was determined in epidermal cells of sink and source leaves of wild-type and transgenic Nicotiana benthamiana plants expressing the movement protein of tobacco mosaic virus (MP(TMV)) incubated both in dark and light and at 16 and 25 degrees C. Under all conditions, Pd in source leaves conducted macromolecules, with (GFP)C(Pd)sink>(GFP)C(Pd)source. Light down-regulated (GFP)C(Pd) (all conditions); down-regulation was stronger for sink cells. The effect of MP(TMV) on (GFP)C(Pd) between epidermal cells was dependent on temperature and leaf development; at 16 degrees C, MP(TMV) down-regulated (GFP)C(Pd) only in source leaves, while at 25 degrees C, MP(TMV) had no significant effect. This quantitative tool should be useful for investigating differences in Pd conductivity that are induced by mutations or silencing.

Biological Transport, Active↗

PubMed1994

Paracrine interactions among parathyroid cells: effect of cell density on cell secretion.

Cell-cell interactions are important in the regulation of endocrine cell secretion. To investigate the possibility that cell communication may alter the regulation of parathyroid cell secretion, we utilized the reverse hemolytic plaque assay (RHPA) to measure parathyroid hormone (PTH) release from individual cells. Bovine parathyroid cells were dispersed and plated with protein A-conjugated erythrocytes at cell densities ranging from 0.9 to 36 x 10(2) cells/cm2 in 0.2 mM calcium. Cell populations were greater than 98% homogenous as determined by immunocytochemistry and in situ hybridization for PTH mRNA. Plaques were developed and data analyzed for the amount of PTH per cell released (plaque area in microns 2 x 10(4)) and the determination of cell recruitment (% plaques formed). A positive correlation existed between parathyroid cell density and the amount of PTH released. As the distance between cells increased, the plaque area (amount of PTH released per cell) decreased (ranging from 1.0 x 10(4) microns 2 at 0.9 x 10(2) cells/cm2 versus 1.6 x 10(4) microns 2 at 36 x 10(2) cells/cm2). The percentage of cells releasing PTH (recruitment) also decreased (16% at 0.9 x 10(2) cells/cm2 versus 47% at 36 x 10(2) cells/cm2). These data suggest that parathyroid cells in close proximity are stimulated to secrete more hormone than those at lesser densities. In addition, parathyroid cells are recruited to secrete PTH when plated at high density. Factor(s) released by the parathyroid cell may increase cell responsiveness and stimulate secretion in a paracrine fashion.

Animals↗

PubMed2003

Effects of 18beta-glycyrrhetinic acid on the junctional complex and steroidogenesis in rat adrenocortical cells.

Cellular junctions play important roles in cell differentiation, signal transduction, and cell function. This study investigated their function in steroid secretion by adrenal cells. Immunofluorescence staining revealed the presence of gap junctions and adherens junctions between adrenal cells. The major gap junction protein, connexin43, was seen as a linear dotted pattern of the typical gap junction plaques, in contrast to alpha-, beta-, and gamma-catenin, which were seen as continuous, linear staining of cell-cell adherens junction. Treatment with 18beta-glycyrrhetinic acid, a gap junction inhibitor, reduced the immunoreactivity of these proteins in a time- and dose-dependent manner, and caused the gap junction and adherens junction to separate longitudinally from the cell-cell contact sites, indicating the structural interdependency of these two junctions. Interestingly, 18beta-glycyrrhetinic acid stimulated a two- to three-fold increase in steroid production in these adrenal cells lacking intact cell junctions. These data raise the question of the necessity for cell communication for the endocrine function of adrenal cells. Pharmacological analyses indicated that the steroidogenic effect of 18beta-glycyrrhetinic acid was partially mediated by extracellular signal-related kinase and calcium/calmodulin-dependent kinase, a pathway distinct from the protein kinase A signaling pathway already known to mediate steroidogenesis in adrenal cells.

Adrenal Cortex↗

PubMed1996

Regulation of connexin31 gene expression upon retinoic acid treatment in rat choriocarcinoma cells.

The controlled invasiveness of the trophoblast is based on the balance between invasive properties at implantation and the differentiation program of the developing placenta. During placental development in rats a switch of connexin gene expression has been observed in parallel to the switch from the invasive to the differentiated phenotype of trophoblast cells. To investigate the role of connexin expression for trophoblast invasion, proliferation, and differentiation, we studied one rat trophoblast (HRP-1) and one rat choriocarcinoma cell line (Rcho-1). The choriocarcinoma cells were characterized by expression of cx31 and a lack of E-cadherin, corresponding to the invasive trophoblast in vivo, whereas HRP-1 cells expressed cx43, normally found in the spongiotrophoblast and in late giant cells, and E-cadherin. Upon retinoic acid treatment, Rcho-1 cells irreversibly lost cx31 expression, accompanied by a loss of functional coupling. No changes in regard to connexin expression and cell-cell communication could be observed in HRP-1 cells. In addition, treatment of Rcho-1 cells with retinoic acid for 7 days upregulated expression of cx43 transcript, but no protein could be found. Proliferation was clearly reduced and the mean volume of cells doubled from Day 4 to Day 7 of retinoic acid treatment in Rcho-1 cells, while both parameters were not affected in HRP-1 cells. Both cell lines showed a similar invasion rate using a Matrigel invasion assay, and invasion was equally suppressed upon retinoic acid treatment. Thus the different connexin expression appears more likely to play a role in regulating proliferation and differentiation along the multilineage pathway than invasiveness of rat trophoblast cells.

Animals↗

PubMed2006

A dedicated Wnt secretion factor.

The Wnt family of signaling proteins mediates cell-cell communication during development. In this issue of Cell, Bänziger et al. (2006) and Bartscherer et al. (2006) identify Wntless/Evi, a multipass transmembrane protein in the secretory pathway of Wnt-producing cells that promotes Wnt secretion.

Animals↗

PubMed1998

Cell density modulates protein-tyrosine phosphorylation.

The growth of normal cells is arrested at saturating cell density in a process termed contact inhibition. An understanding of how cells communicate their contact with one another is critical for determining how cancers develop and spread. Because the molecular details of how fibroblasts communicate density changes are unclear, we examined cell density itself as a source of signaling events rather than examine specific receptors. A technique was developed to measure tyrosine phosphorylation acutely as a function of cell density. The tyrosine phosphorylation of a number of proteins was found to be modified in response to cell density. Three of these proteins were identified as Src, paxillin, and focal adhesion kinase (FAK), all of which show an increase in their tyrosine phosphate levels with increasing density. All of these proteins are found in focal adhesions, and both FAK and paxillin are believed to be localized exclusively in focal adhesions. Thus, changing cell density alters tyrosine phosphorylation of focal adhesion components.

3T3 Cells↗