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PubMed2006

Cell-cell communication in the pituitary: orchestrator of pulsatile growth hormone secretion?

Hormone secretion is dependent on intracellular and extracellular regulation of hormone synthesis and release, including classical endocrine and paracrine mechanisms and transcription factors that determine cell differentiation and hormone gene transcription. Recent research has identified direct cell-cell communication in a three-dimensional network of pituitary growth hormone-secreting cells connected by adherens junctions. This challenges the conventional view of endocrine cells as collections of dispersed cells and suggests that physical connectivity mediates cellular responses to coordinate pulsatile secretion.

Animals↗
PubMed2003

Role of intracellular cyclic adenosine 3',5'-monophosphate concentration and oocyte-cumulus cells communications on the acquisition of the developmental competence during in vitro maturation of bovine oocyte.

The present study was designed to address the physiological role played by cAMP on gap junction (GJ) mediated communications between oocyte and cumulus cells during in vitro maturation. Cyclic AMP was stimulated by different collection and maturation media known to induce different rates of nuclear maturation and developmental competence as well as different levels of cumulus expansion. Cumulus-oocyte complexes (COCs) were matured for 0, 3, 7, 12, 18, and 24 h in the absence of stimulation or in the presence of serum and gonadotropins (fetal bovine serum+human menopausal gonadotropins [FCS+hMG]) or 0.01 microg/ml of invasive adenylate cyclase (iAC). For each time point, intracellular cAMP concentration ([cAMP]i) was determined either in the whole COC or oocyte after cumulus cell removal. GJ functional status was analyzed by microinjection of Lucifer yellow fluorescent dye in cumulus-enclosed oocytes and by immunohistochemical localization of connexin 43 (Cx43). In the absence of stimulation, [cAMP]i in COC and oocyte was lower than in other groups, and communications declined after 3 h of culture. In the FCS+hMG group, [cAMP]i increased significantly in COC, with a peak between 3 and 7 h that was temporally correlated with the beginning of the cumulus expansion process, which occurred only in this group and with the termination of the communications. COC matured in the presence of iAC showed a moderate increase of [cAMP]i during all of the maturation times as well as a prolongation of oocyte-cumulus cell communications. The immunohistochemical localization of Cx43 confirmed the delay in connexons protein turnover in iAC-treated COCs. Our results show that cumulus expansion and oocyte developmental competence are induced by different levels of cAMP and that its intracellular concentration may affect cell coupling between oocyte and cumulus cells. We hypothesize that the higher developmental competence of COCs matured in the presence of iAC could be achieved through a moderate increase of intracellular cAMP, which in turn determines a prolongation of communications between the two cell types.

Animals↗
PubMed1998

Cell-cell communication in carcinogenesis.

To explain the complex carcinogenic process by which a single normal cell in human beings can be converted to an invasive and metastatic cancer cell, a number of experimental findings, epidemiological observations and their associated hypothesis/theories have been integrated in this review. All cancers have been generally viewed as the result of a disruption of the homeostatic regulation of a cell's ability to respond appropriately to extra-cellular signals of the body which trigger intra-cellular signal transducting mechanisms which modulate gap junctional intercellular communication between the cells within a tissue. Normal homeostatic control of these three forms of cell communication determines whether: (a) the cell remains quiescent (Go); (b) enters into the cell proliferation phase; (c) is induced to differentiate; (d) is committed to apoptose; or (e) if it is already differentiated, it can adaptively respond. During the evolution from single cell organisms to multicellular organisms, new cellular/biological functions appeared, namely, the control of cell proliferation ("contact inhibition"), the appearance of the process of differentiation from committed stem cells of the various tissues and the need for programmed cell death or apoptosis. Interestingly, cancer cells have been characterized as cells: (a) having been derived from a stem-like cell; (b) without their ability to control cell growth or without the ability to contact inhibit; (c) which can not terminally differentiate under normal conditions; and (d) having altered ability to apoptosis under normal conditions. During that evolutionary transition from the single cell organism to the multicellular organism, many new genes appeared to accompany these new cellular functions. One of these new genes was the gene coding for a membrane associated protein channel (the gap junction) which between coupled cells, allowed the passive transfer on ions and small molecular weight molecules. A family of over a dozen of these highly evolutionarily-conserved genes (the connexin genes) coded for the connexin proteins. A hexameric unit of these connexins in one cell (a connexon) couples with a corresponding connexon in a contiguous cell to join the cytoplasms. This serves to synchronize either the metabolic or electrotonic functions of cells within a tissue. Most normal cells within solid tissues have functional gap junctional intercellular communication (GJIC) (exceptions are free-standing cells such as red blood cells, neutrophils, and several, if not all, the stem cells). On the other hand, the cancer cells of solid tissues appear to have either dysfunctional homologous or heterologous GJIC. Therefore, among the many differences between a cancer cell and its normal parental cell, the carcinogenic process involves the transition from a normal, GJIC-competent cell to one that is defective in GJIC. The review examines how GJIC can be either transiently or stably modulated by endogenous or exogenesis chemicals or by oncogenes and tumor suppressor genes at the transcriptional, translational, or posttranslational levels. It also uses the gap junction as the biological structure to facilitate cellular/tissue homeostasis to be the integrator for the "stem cell" theory, "disease of differentiation theory", "initiation/promotion/progression" concepts, nature and nurture concept of carcinogenesis, the mutation/ epigenetic theories of carcinogenesis, and the oncogene/ tumor suppressor gene theories of carcinogenesis. From this background, implications to cancer prevention and cancer therapy are generated.

Cell Communication↗
PubMed1991

Tissue factor expression in endothelial cell/monocyte cocultures stimulated by lipopolysaccharide and/or aggregated IgG. Mechanisms of cell:cell communication.

A human umbilical vein endothelial cell (EC)/monocyte (MC) coculture system was used to dissect cell:cell interactions associated with production of procoagulant activity (PCA) in response to two common stimuli of intravascular coagulation in vivo (LPS and immune complexes). We found that the presence of MC at a ratio of 1 MC:10 EC increased the sensitivity of EC to LPS by 4 logs and the maximal response approximately 20-fold. Aggregated IgG alone did not stimulate the system, but in the presence of small amounts of LPS (1 to 10 ng/ml) aggregated IgG was a powerful stimulus. More than 90% of the PCA was tissue factor as shown by clotting studies and mRNA analysis. PCA was not produced by either cell alone under the conditions of study, but was produced in large amounts when the EC and MC were cocultured. The supernatant from the coculture stimulated virgin EC, but not MC, to synthesize tissue factor. The major factor in the supernatant was IL-1 beta as shown by measuring IL-1 beta, IL-1 alpha, and TNF-alpha in supernatants and by blocking the production of PCA by preincubation of supernatants with anti-cytokine antibodies. Small amounts of TNF-alpha were present in the supernatant but anti-TNF-alpha did not inhibit PCA production. Studies using recombinant cytokines established that IL-1 beta was the most potent of the cytokines tested, that cytokines potentiated each other, and that the results could be explained in quantitative terms by the amounts of IL-1 beta measured. These data emphasize that cell:cell interactions are likely to modulate procoagulant events in vivo in the presence of both LPS and immune complexes, and that IL-1 beta may be an important cytokine in these events.

Antigen-Antibody Complex↗
PubMed1987

Regulation of pancreatic exocrine function: a role for cell-to-cell communication?

The effect of heptanol, an alkanol which decreases gap junctional permeability, was investigated in the perfused rat pancreas. Under basal conditions, heptanol (3.5 mM) caused a three- to fourfold increase of pancreatic juice, protein, and amylase outputs. The effect on enzyme secretion was fully reversible upon removal of the alkanol and was not secondary to the release of acetylcholine from nerve endings, since it was not prevented by addition of atropine (10(-6) M) to the perfusate. By contrast, another alkanol, hexanol (3 mM), which does not decrease coupling between acinar cells in spite of anesthetic properties analogous to those of heptanol, did not alter pancreatic secretion. The effect of heptanol was not mediated by a significant stimulation of cyclic AMP, nor did the alkanol increase the secretion of lactic dehydrogenase, a cytosolic marker. Analysis of the numerical density of freeze-fractured and immunolabeled gap junctions between acinar cells did not show differences between heptanol-perfused and control pancreases. In addition, heptanol did not alter carbachol (10(-6) M and 10(-5) M)-evoked amylase release. Since heptanol blocks cell coupling, apparently without interfering with the main intracellular pathways triggering enzyme release, we suggest that downregulation of direct cell-to-cell communications increases pancreatic exocrine secretion. Thus, cell coupling is probably involved in the regulation of the secretory activity of acinar cells.

Alcohols↗
PubMed2025

Alcohol-induced KDM5B activation in hepatocytes drives pathogenic cell-cell communication, leading to loss of liver function.

BACKGROUND: Alcohol-associated liver disease (ALD) is a major cause of alcohol-associated mortality. Previously, we identified KDM5B as a sex-specific mediator of ALD development; however, the mechanism behind KDM5B-induced pathological changes is not established. METHODS: Kdm5b flox/flox female mice were fed a western diet and 20% alcohol in the drinking water for 8-16 weeks (WDA). To induce KO, mice received 2×1011 genome copies of AAV8-CMV-Cre, AAV8-TBG-Cre, or AAV8-control. To test the role of myeloid C/EBPβ, Cebpbfl/fl, or Cebpbfl/fl Lyz2-Cre mice were fed WDA for 16 weeks. RESULTS: We found that Kdm5b KO prevented alcohol-induced liver fibrosis and liver inflammation in female mice. These changes were in part mediated by hepatocyte-to-non-parenchymal cell communication changes. KDM5B in hepatocytes promoted pro-inflammatory and pro-fibrotic changes in liver macrophages, endothelial cells, and stellate cells. Moreover, KDM5B promoted alcohol-induced early increase in EpCAM-positive liver progenitors and loss of liver function at later time points of alcohol feeding. We found that loss of liver function was dependent on a hepatocyte-to-macrophage communication feedback loop. KDM5B in hepatocytes inhibited macrophage C/EBPβ expression, which in turn resulted in loss of the mature KCs phenotype and prevented the ability of KCs to support hepatocyte differentiation, ultimately leading to loss of liver synthetic function. CONCLUSIONS: KDM5B activation in hepatocytes drives pathogenic cell-cell communication, leading to alcohol-induced loss of liver function in ALD.

Animals↗
PubMed2003

Cell behavior and cell-cell communication during fruiting body morphogenesis in Myxococcus xanthus.

Formation of spatial patterns of cells from a mass of initially identical cells is a recurring theme in developmental biology. The dynamics that direct pattern formation in biological systems often involve morphogenetic cell movements. An example is fruiting body formation in the gliding bacterium Myxococcus xanthus in which an unstructured population of identical cells rearranges into an asymmetric, stable pattern of multicellular fruiting bodies in response to starvation. Fruiting body formation depends on changes in organized cell movements from swarming to aggregation. The aggregation process is induced and orchestrated by the cell-surface associated 17 kDa C-signal protein. C-signal transmission depends on direct contact between cells. Evidence suggests that C-signal transmission is geometrically constrained to cell ends and that productive C-signal transmission only occurs when cells engage in end-to-end contacts. Here, we review recent progress in the understanding of the pattern formation process that leads to fruiting body formation. Gliding motility in M. xanthus involves two polarly localized gliding machines, the S-machine depends on type IV pili and the A-machine seems to involve a slime extrusion mechanism. Using time-lapse video microscopy the gliding motility parameters controlled by the C-signal have been identified. The C-signal induces cells to move with increased gliding speeds, in longer gliding intervals and with decreased stop and reversal frequencies. The combined effect of the C-signal dependent changes in gliding motility behaviour is an increase in the net-distance travelled by a cell per minute. The identification of the motility parameters controlled by the C-signal in combination with the contact-dependent C-signal transmission mechanism have allowed the generation of a qualitative model for C-signal induced aggregation. In this model, the directive properties of the C-signal are a direct consequence of the contact-dependent signal-transmission mechanism, which is a local event involving direct contact between cells that results in a global organization of cells. This pattern formation process does not depend on a diffusible substance. Rather it depends on a cell-surface associated signal to direct the cells appropriately.

Bacterial Proteins↗
PubMed2004

Synthesis of LuxS inhibitors targeting bacterial cell-cell communication.

[reaction: see text] Quorum sensing is a process by which bacteria sense cell density. This cell-cell communication process is mediated by autoinducers. A cross-species messenger, autoinducer-2 (AI-2) is produced from S-ribosyl-L-homocysteine by the LuxS enzyme. A proposed mechanism for LuxS is an aldose-ketose isomerization of S-ribosylhomocysteine followed by a beta-elimination. We report here the synthesis of two substrate analogues, S-anhydroribosyl-L-homocysteine and S-homoribosyl-L-cysteine, which prevent the initial and final step of the mechanism, respectively.

Bacteria↗
PubMed1994

Functions of the Golgi complex in cell division: formation of cell-matrix contacts and cell-cell communication channels in the terminal phase of cytokinesis.

The Golgi complex of mammalian cells is disorganized into dispersed vesicular and tubular elements during mitosis and is then reorganized into an interconnected system of cisternal stacks in each daughter cell during cytokinesis. Recent studies further indicate that the Golgi complex is typically relocated from the proximal to the distal side of the nucleus in the terminal phase of cytokinesis (as related to the intercellular bridge). Here, the functional role of this shift in position was approached using rat embryo fibroblasts synchronized with thymidine and nocodazole. Mitotic cells were collected by shaking and seeded in medium without or with brefeldin A (a fungal metabolite that inhibits protein secretion). They were fixed after one or two hours and stained for immunocytochemical demonstration of mannosidase II (a Golgi protein), fibronectin (an extracellular matrix protein), the fibronectin receptor (a member of the integrin family of proteins), and connexin 43 (a member of the connexin family of gap junction proteins). One hour after seeding, the cells had completed mitosis and progressed into cytokinesis. The Golgi complex was now usually located on the proximal side of the nucleus and overlapping fibrillar arrays of fibronectin and fibronectin receptors were observed in the contact zone between the daughter cells, while connexin 43 mainly occurred in fine dispersed spots. Two hours after seeding, the cells had spread out on the substrate and started to move apart. The Golgi complex was now usually located on the distal side of the nucleus. Moreover, fibronectin and fibronectin receptors were found to codistribute both in the contact zone between the daughter cells and in adhesive contacts beneath them, while connexin 43 was concentrated to plaques in the former zone. After treatment with brefeldin A, there was a diffuse cytoplasmic staining for mannosidase II and fibronectin and no distinct extracellular staining for fibronectin was noted. In addition, the connexin 43 positive plaques were reduced in size and number. Although the cells completed cytokinesis in the presence of the drug, they showed an increased tendency to detach from the substrate and locate on top of each other rather than to move apart normally. Taken together, the observations suggest that the change in position of the Golgi complex during cytokinesis serves the function to direct transport of secretory proteins as well as membrane constituents to different parts of the cell surface at different times.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1998

Endometrial connexin expression in the mare and pig: evidence for the suppression of cell-cell communication in uterine luminal epithelium.

This investigation examines the relationship between implantation strategy and gap junction protein expression in uterine endometrium. The pattern of gap junction and connexin protein expression was analyzed in porcine and equine endometrium from cycling and pregnant animals using electron microscopy and immunocytochemistry. Functional analysis of cell-cell communication was also monitored by laser cytometry in primary cultures of endometrial epithelial cells. Gap junctions were detected in endometrial stroma of cycling and pregnant animals, which was correlated with immunoreactive Cx43 within stromal fibroblasts and vascular elements. No Cx26, Cx32, or Cx43 immunostaining was detected in luminal endometrial epithelium in either the mare or the pig at any stage of the estrous cycle or pregnancy. In contrast, endometrial glands of the mare exhibited a spatiotemporal pattern of Cx43 expression in the apicolateral plasma membrane which, when present, colocalized with the tight junction-associated protein, ZO-1. Uterine glandular Cx43 expression in mares was present from day 3 postovulation through day 14 of diestrus and until day 23 of pregnancy, whereas Cx43 was absent within uterine glands during seasonal anestrus, estrus, and after day 30 of pregnancy. Primary cultures of equine endometrial epithelial cells expressed both immunoreactive Cx43 and significant gap junction-mediated intercellular communication (GJIC) which was rapidly upregulated by 1.0 mM 8-bromo-cAMP or blocked with 1.0 mM octanol. No GJIC or connexin protein was detected in cultured porcine epithelial cells despite incubation with a variety of agents, including 8-bromo-cAMP, steroid hormones, retinoic acid, and/or prolactin. Junctional communication in endometrial epithelium of domestic farm animals is different than that reported for species exhibiting invasive implantation. The absence of GJIC in uterine luminal epithelium of the gilt and mare may be involved in limiting trophoblast invasiveness.

Animals↗
PubMed2002

NBT-II carcinoma behaviour is not dependent on cell-cell communication through gap junctions.

To study the mechanism(s) underlying the proliferation of heterogeneous cell populations within a solid tumour, the NBT-II rat bladder carcinoma system was used. It has been first investigated whether the different cell populations are coupled through gap junctions (GJIC). Cells overexpressing the Cx43 were generated to test for any tumour suppressive activity in vivo. To determine whether GJIC is essential for tumour proliferation and the establishment of a cooperative community effect, NBT-II cells that are incompetent for cell coupling were generated. The data report that (i) carcinoma cells expressing or not FGF-1 are coupled through GJIC in vitro and in coculture and express the gap junction protein Cx43, (ii) overexpression of Cx43 in these cells does not affect their in vitro coupling capacities and in vivo tumourigenic growth properties, (iii) inhibition of GJIC through antisense strategy has no in vivo obvious consequence on the tumour growth properties of the carcinoma, and (iv) the community effect between two carcinoma cell populations does not critically involve cell coupling through gap junctions.

Animals↗
PubMed2003

Influence of nitric oxide on the secretory function of the bovine corpus luteum: dependence on cell composition and cell-to-cell communication.

The objective of the present study was to investigate the role of cell-to-cell contact in the influence of nitric oxide (NO) on the secretory function of the bovine corpus luteum (CL). In Experiment 1, separate small luteal cells (SLC) or large (LLC) luteal cells were perfused with 100 micro M spermineNONOate, a NO donor, or with 100 micro M Nomega-nitro-L-arginine methyl ester (L-NAME), a NO synthase (NOS) inhibitor; in Experiment 2, a mixture of LLC and SLC and endothelial cells was cultured and incubated with spermineNONOate or L-NAME; in Experiment 3, spermineNONOate was perfused into the CL (100 mg/4 hr) by a microdialysis system in vivo. Perfusion of isolated SLC and LLC with the NO donor or NOS inhibitor (Experiment 1) did not affect (P > 0.05) secretion of progesterone (P(4)) or oxytocin (OT). L-NAME perfusion increased (P < 0.05) leukotriene C(4) (LTC(4)) secretion by both SLC and LLC cells. Treatment of mixtures of luteal cells with an NO donor (Experiment 2) significantly decreased (P < 0.001) secretion of P(4) and OT and increased (P < 0.001) production of prostaglandin F(2alpha) (PGF(2alpha)) and LTC(4). L-NAME stimulated (P < 0.001) P(4) secretion, but did not influence (P > 0.05) OT, PGF(2alpha) or LTC(4) production. Intraluteal administration (Experiment 3) of spermineNONOate increased (P < 0.001) LTC(4) and PGF(2alpha), decreased OT, but did not change P(4) levels in perfusate samples. These data indicate that cell-to-cell contact and cell composition play important roles in the response of bovine CL to treatment with NO donors or NOS inhibitors, and that paracrine mechanisms are required for the full secretory response of the CL in NO action. Endothelial cells appear to be required for the full secretory response of the CL to NO.

Animals↗
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↗
PubMed1990

Selective silencing of cell communication influences anteroposterior pattern formation in C. elegans.

In C. elegans males, laterally located V cells generate a simple pattern of anterior alae (cuticular ridges) and posterior rays (mating sensilla). We have found that this pattern is generated, at least in part, by the selective interruption of cell-cell interactions. In anterior V cells, lineages leading to the production of alae are induced by cell interactions. These cell interactions are inhibited in specific posterior V cells by the activity of the gene pal-1, which allows these cells to generate rays instead of alae. The activities of cell signals and pal-1 appear to influence V cell fates by determining the state of a developmental switch that involves two homeotic genes, lin-22 and mab-5.

Alleles↗
PubMed2002

Bacterial cell-to-cell communication: sorry, can't talk now - gone to lunch!

The identification of novel bacterial cell-to-cell communication (quorum sensing) systems based on diffusible signal molecules, such as indole and the LuxS autoinducer-2, requires discrimination between true signalling molecules and metabolites present in culture supernatants. This depends on rigorous chemical characterisation and demonstration that the molecule controls cellular responses beyond those required to metabolise or detoxify the signal.

Bacterial Physiological Phenomena↗
PubMed1990

Promotion of altered hepatic foci development in rat liver, cytochrome P450 enzyme induction and inhibition of cell-cell communication by DDT and some structurally related organohalogen pesticides.

The organochlorine pesticide 1,1'-(2,2,2-trichloroethylidene) bis(4-chlorobenzene) (DDT) and four structural analogues (bromopropylate, chlorobenzilate, dicofol and fenarimol) were investigated for their ability to inhibit gap junctional intercellular communication both in the Chinese hamster V79 metabolic co-operation assay and in the scrape-loading/dye-transfer assay in WB-F344 rat liver epithelial cells. The pesticides were also studied for their ability to enhance the development of gamma-glutamyltranspeptidase-positive altered hepatic foci and induce cytochrome P450 monooxygenase isoenzymes in nitrosamine-initiated male Sprague-Dawley rats. The in vitro studies showed all organohalogens except fenarimol to be potent inhibitors of cell-cell communication in both test systems used. Concomitant results were recorded in the in vivo study. Thus, all potent inhibitors of intercellular communication were found to enhance significantly foci development and fenarimol was again without any significant effect. All pesticides studied were shown to be potent inducers of the phenobarbital-inducible cytochrome P450b isoenzyme and to cause hepatomegaly. Thus, no strict correlation between cytochrome P450b induction/liver growth and tumour promotion-related effects in vivo and in vitro was apparent for these organohalogen pesticides in the present study.

Animals↗