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PubMed1995

Melatonin enhances junctional transfer in normal C3H/10T1/2 cells.

Gap junctional intercellular communication is known to be involved in controlling cell proliferation and differentiation, and seems to play a crucial role in suppression of tumor promotion. The pineal gland and its hormone, melatonin, are believed to intervene in the control of neoplastic processes. Several possible mechanisms have been suggested to be potentially responsible for melatonin's oncostatic action; however, the actual mechanisms involved in melatonin's effects at the cellular level remain unidentified. In the present study low-density cultures of C3H/10T1/2 mouse embryo fibroblasts were incubated until relatively quiescent monolayers were established (17-18 days). Gap junctional intercellular communication in control samples and in cells treated with 10(-12) to 10(-8) M melatonin was determined by the scrape-loading assay using the fluorescent dye Lucifer yellow. The results showed that concentrations of melatonin considered physiological (10(-11) and 10(-10) M) induced a significant increase in the transfer of the dye to adjacent cells through gap junctions; both higher and lower concentrations were ineffective. These results suggest that melatonin could exert its putative oncostatic action, in part, by modulating the levels of gap junctional intercellular communication.

Animals↗
PubMed2003

Novel genes regulated by gonadotropins in granulosa cells: new perspectives on their physiological functions.

Follicular stimulating hormone (FSH) is a key hormone secreted from the pituitary, which controls the development of the follicle-enclosed oocytes in the mammalian ovary by interacting with specific receptors located exclusively on granulosa cells. Its biological activity involves stimulation of intercellular communication and upregulation of steroidogenesis, yet the entire spectrum of genes which are regulated by FSH are not fully characterized. We have established rat and human FSH responsive granulosa cell lines, which express FSH receptors at 20-times higher rates compared to primary cells. Since the lines are monoclonal, they are expected to have a homogeneous composition of RNA among the entire cell population, which increases the probability of yielding a distinct view of genes modulated by FSH eliminating the possibility of other cell types contamination. Using Affymetrix DNA microarrays to uncover novel FSH-regulated genes, we discovered genes not reported earlier to be regulated by FSH. These include genes coding for (1) proteases; (2) growth factors and cytokines; (3) proteins involved in intercellular communication and connection with the nervous system; (4) protein phosphatases and kinases; (5) anti oxidants and anti-toxicants; (6) G-coupled proteins. These findings can deepen our understanding in the mechanism of FSH action in stimulation of the development of the ovarian follicular cells, in the modulation of ovarian intracellular and intercellular communication and in the process of selection of the dominant follicle. When human granulosa cells, obtained from in vitro fertilization patients were exposed to either hLH- or hFSH stimulation and mRNAs of these cells were analyzed by DNA microarrays, novel genes, similar to those found modulated by FSH in FSH responsive cell lines, were discovered in the human primary cells. This suggests that the immortalized cell systems established in our laboratory could serve as a useful system expanding the spectrum of authentic genes modulated by gonadotropin stimulation in normal ovarian function and in ovarian malfunction.

Animals↗
PubMedDate not supplied

Inhibitory effects of organochlorine pesticides on intercellular transfer of Lucifer Yellow in cultured bovine oviductal cells.

The present study investigated the effects of dichlorodiphenyltrichloroethane (DDT), methoxychlor (MXC), and gamma-hexachlorocyclohexane (gammaHCH, lindane) on gap junctional intercellular communication (GJIC) in cultured bovine oviductal cells. GJIC was evaluated by microinjecting fluorescent dye Lucifer Yellow and observing the inhibition of the spreading of dye into adjacent cells. After incubation for 1 h at 37 degrees C, a dose-dependent inhibition of GJIC was observed over a concentration range of 16 to 128 microM DDT, MXC, or gammaHCH compared with nonexposed controls. A significant inhibition began at 32 microM DDT, MXC, or gammaHCH. After incubation for 5 h, a dose-dependent inhibition of GJIC was obtained in the concentration range from 8 to 64 microM of the pesticides. The first significant inhibitory effect on GJIC was caused by 8 microM DDT, 16 microM MXC, and 32 microM gammaHCH. The 128 microM concentration of the pesticides was toxic. At pesticide concentration of 64 microM, the decrease in dye-coupling observed was not due to lethal cell injury, as is indicated by the use of trypan blue dye exclusion. After removal of 64 microM DDT from the culture medium, intercellular communication was reestablished within 3 h. Measurement of cytosolic free Ca2+ concentration [Ca2+]i in fura-2/AM-loaded oviductal cells showed that the inhibition of GJIC by addition of DDT, MXC, or gammaHCH was not associated with a detectable increase in [Ca2+]i. Coincubation of the DDT with dibutyryl-cAMP prevented the 64 microM DDT-induced inhibition of intercellular communication in adherent oviduct cells. It is suggested that organochlorine pesticides can influence cells responsible for reproduction.

Animals↗
PubMed2001

Reduced expression of connexin-43 and functional gap junction coupling in human gliomas.

Gap junctions are an important means for intercellular communication during development, processes of tissue differentiation, and in maintenance of adult tissue homeostasis. We investigated the expression levels and distribution of connexin-43 (Cx-43), the most abundant astrocytic gap junction protein, in acutely isolated astrocytes and glioma cells from biopsy tissue obtained from patients diagnosed with glioblastoma multiforme (GBM), low-grade astrocytomas (LGAs), or mesial temporal lobe epilepsy. Western blot and immunohistochemical analyses indicated an inverse correlation between the amount of Cx-43 protein and tumor malignancy grade, as assessed by calculating tissue mitotic indexes (MI) obtained using anti-Ki-67 nuclear antigen staining. Samples from epilepsy patients had a low MI and were intensely positive for Cx-43 staining, while LGA tissue samples exhibited moderate staining for Cx-43 and average MI, and GBM biopsies showed significantly lower levels of Cx-43 and high MI. Functional coupling was assayed using fluorescence recovery after photobleach (FRAP). We found that cells from glioma cell lines and primary cultures of human astrocytes from GBM tissues displayed significantly lower degrees of gap junction intercellular communication (GJIC) as indicated by longer and less complete recovery from photobleaching. Mean recovery values were GBM 23.8% +/- 11.4%, LGA 49.4% +/- 47%, and nontumor astrocytes 67.2% +/- 8.4%. Western blot analysis of several human glioma cell lines and tissue biopsies showed variable expression levels of Cx-43, which correlated negatively with the extent of recovery in the same samples. Taken together, our findings suggest that high-grade brain tumors show reduced intercellular communication and a decrease in connexin-43 protein levels.

Astrocytes↗
PubMed2002

Expression and regulation of gap junctions in rat cholangiocytes.

Hepatocytes and other digestive epithelia exchange second messengers and coordinate their functions by communicating through gap junctions. However, little is known about intercellular communication in cholangiocytes. The aim of this study was to examine expression and regulation of gap junctions in cholangiocytes. Connexin expression was determined by confocal immunofluorescence in rat bile ducts and in normal rat cholangiocyte (NRC) cells, a polarized cholangiocyte cell line. Intercellular Ca(2+) signaling was monitored by fluorescent microscopy. Microinjection studies assessed regulation of gap junction permeability in NRC cells and in SKHep1 cells, a liver-derived cell line engineered to express connexin 43. Immunochemistry showed that cholangiocytes from normal rat liver as well as the NRC cells express connexin 43. Localization of apical, basolateral, and tight junction proteins confirmed that NRC cells are well polarized. Apical exposure to ATP induced Ca(2+) oscillations that were coordinated among neighboring NRC cells, and inhibition of gap junction conductance desynchronized the Ca(2+) oscillations. NRC cells transfected with a connexin 43 antisense were significantly less coupled. Transcellular dye spreading was inhibited by activation of protein kinase A or protein kinase C. The same was observed in transfected SKHep1 cells, which expressed only connexin 43. Rat cholangiocytes and NRC cells express connexin 43, which permits synchronization of Ca(2+) signals among cells. Permeability of connexin 43-gap junctions is negatively regulated by protein kinases A and C. In conclusion, cholangiocytes have the capacity for intercellular communication of second messenger signals via gap junctions in a fashion that is under hormonal control.

Adenosine Triphosphate↗
PubMed2004

The gap junction protein connexin32 is a mouse lung tumor suppressor.

Although loss of connexin expression and/or gap junction intercellular communication correlates with decreased growth control and increased neoplastic potential, there is limited evidence directly linking gap junction intercellular communication function with tumor suppression in situ. Here, we show for the first time that a gap junction protein, connexin32 (Cx32), acts as a lung tumor suppressor in a mouse model. Cx32-deficient nontumorous lung tissue exhibited an increased proliferative index (P < 0.001), and, after exposure to the carcinogen diethylnitrosamine, Cx32-deficient mice exhibited a highly statistically significant (P < 0.001) increase in bronchioloalveolar lung tumor incidence (28 of 45, 62%) and a 45% increase in average multiplicity compared with wild-type mice (7 of 29, 24%). Tumors from Cx32-deficient mice also showed increased activation of mitogen-activated protein kinase (P < 0.001) compared with wild-type tumors, implicating this signaling pathway in Cx32/gap junction intercellular communication-associated lung tumorigenesis.

Animals↗
PubMed1988

Selective gap-junctional communication capacity of transformed and non-transformed rat liver epithelial cell lines.

To investigate whether a selective intercellular communication exists between transformed epithelial cells and their counterparts, the homologous and heterologous communication capacities of four rat liver epithelial cell lines were compared with their expression of transformed phenotypes. All four cell lines showed reasonably good homologous junctional communication capacity, as measured by the dye-transfer assay. In heterologous co-cultures, the non-transformed cell line IAR 20 did not communicate with the transformed cell lines IAR 6-1 or IAR 27 F. These two cell lines showed a high degree of transformed phenotypes such as cell morphology, growth in soft agar and expression of gamma-glutamyltranspeptidase activity. Another cell line IAR 27 E, showed the least degree of transformation and it communicated with IAR 20 cells. Thus, it appears that there is an inverse correlation between the extent of expression of transformed phenotypes by rat liver epithelial cells and their ability to communicate with non-transformed counterparts. There was no heterologous intercellular communication between any combination of IAR 27 E, IAR 27 F and IAR 6-1 cell lines.

Animals↗
PubMed1993

Inhibition of chemically induced neoplastic transformation by carotenoids. Mechanistic studies.

In 10T1/2 cells several dietary carotenoids have been shown to be capable of inhibiting carcinogen-induced neoplastic transformation. Their action appears qualitatively similar to the previously documented action of retinoids in this cell system. However, higher concentrations (10-1000-fold) are required. Both types of compound were found to strongly upregulate gap junctional intercellular communication at concentrations which inhibit transformation. Upregulation of gap junctional intercellular communication was caused by the increased expression of connexin 43, a junctional protein. This activity of carotenoids and retinoids is highly correlated with, and has been proposed to be mechanistically linked to, inhibition of transformation in 10T1/2 cells. In this model the gap junction serves as a conduit for growth regulatory signals from normal to initiated cells. These putative signals act to suppress transformation of the initiated cell.

Animals↗
PubMed1993

Cancer prevention by carotenoids. Mechanistic studies in cultured cells.

In 10T1/2 cells several dietary carotenoids have been shown to be capable of inhibiting carcinogen-induced neoplastic transformation. Their action appears qualitatively similar to the previously documented action of retinoids in this cell system; however, higher concentrations (10-1000-fold) are required. Both types of compound were found to strongly upregulate gap junctional intercellular communication, and these activities were statistically correlated. Upregulation of gap junctional intercellular communication was caused by the increased expression of connexin 43, a structural protein of the gap junction. Increased junctional communication has been proposed to be mechanistically linked to inhibition of transformation in 10T1/2 cells. In this model the gap junction serves as a conduit for growth regulatory signals from normal to initiated cells. These putative signals act to suppress transformation of the carcinogen-initiated cell.

Animals↗
PubMed2002

Molecular mechanisms of neutrophil recruitment elicited by bacteria in the lungs.

The recruitment of leukocytes to an extravascular destination requires intercellular communication between tissue cells and leukocytes. The molecules mediating this intercellular communication play differing roles in recruiting different types of leukocytes, in response to different stimuli, in different tissues, and in different hosts. The present communication reviews the adhesion molecules, chemokines, other cytokines, and NF- kappa B proteins which regulate the recruitment of neutrophils elicited by bacteria in the lungs.

Animals↗
PubMed2001

Prevention of organochlorine-induced inhibition of gap junctional communication by chaetoglobosin K in astrocytes.

Innumerable toxic substances present in the environment inhibit gap junctions, intercellular membrane channels that play fundamental roles in coordinated function of cells and tissues. Included are persistent organochlorine compounds, which pose health risks to humans and animals owing to their widespread use, bioaccumulation, and ability to inhibit gap junction channel-mediated intercellular communication in liver, lung, skin, heart, and brain cells. In this study, the organochlorine xenobiotics dieldrin and endosulfan, at micromolar concentrations, were found to inhibit gap junction-mediated intercellular communication and induce hypophosphorylation of connexin 43 in cultured rat astrocytes, the predominant cell type in the brain coupled through gap junctions. This inhibition of gap junctional communication was substantially reduced by preincubation with chaetoglobosin K (ChK), a bioactive natural produce previously shown to have ras tumor suppressor activity. Chaetoglobosin K also prevented dieldrin and endosulfan-induced hypophosphorylation of connexin 43 and prevented dieldrin-induced connexin 43 plaque dissolution in both astrocytes and cultured liver epithelial cells. The results suggest that stabilization of the native, phosphorylated form of connexin 43 by ChK may contribute to its ability to prevent organochlorine-induced inhibition of gap junction-mediated communication and dissolution of gap junction plaques within the plasma membrane.

Animals↗
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↗
PubMed2000

Gap junctions in human synovial cells and tissue.

Our objective was to establish the existence of intercellular communication through gap junctions in synovial lining cells and in primary and passaged cultures of human synovial cells. Communication between cells was assessed using the nystatin perforated-patch method, fluorescent dye transfer, immunochemistry, transmission electron microscopy, and immunoblotting. Functional gap junctions were observed in primary and passaged cultures and were based on measurements of the transient current response to a step voltage. The average resistance between cells in small aggregates was 300 +/- 150 MOmega. Gap junctions were also observed between synovial lining cells in tissue explants; the size of the cell network in synovial tissue was estimated to be greater than 40 cells. Intercellular communication between cultured cells and between synovial lining cells was confirmed by dye injection. Punctate fluorescent regions were seen along intercellular contacts between cultured cells and in synovial membranes in cells and tissue immunostained for connexin43. The presence of the protein was verified in immunoblots. Regular 2-nm intermembrane gap separations characteristic of gap junctions were seen in transmission electron micrographs of synovial biopsies. The results showed that formation of gap-junction channels capable of mediating ionic and molecular communication was a regular feature of synovial cells, both in tissue and in cultured cells. The gap junctions contained connexin43 protein and perhaps other proteins. The physiological purpose of gap junctions in synovial cells is unknown, but it is reasonable to anticipate that intercellular communication serves some presently unrecognized function.

Arthritis, Rheumatoid↗
PubMed2005

[Correlation of expression of connexin to growth and progression of cervical carcinoma in situ].

BACKGROUND & OBJECTIVE: Gap junction intercellular communication (GJIC), mediated by connexin (CX), is the unique type of intercellular communication in carcinoma in situ (CIS). Changes in expression of CXs and function of GJIC may play roles in carcinogenesis of cervical cancer and progression of CIS. This study was to investigate the expression of CXs in normal epithelium (NE), hyperplasia, CIS, and invasive carcinoma (IC) of cervix, to explore correlation of expression of CXs to pathogenesis and progression of cervical CIS. METHODS: Expression of CX43 (mRNA, protein), CX26 (mRNA), and Ki-67 (protein) in 30 specimens of cervical NE, 22 specimens of cervical hyperplasia, 30 specimens of cervical CIS, and 26 specimens of cervical IC were detected by immunohistochemistry and in situ hybridization. RESULTS: In cervical NE, hyperplasia, CIS, and IC, positive rates of CX43 protein were 83%, 55%, 50%, and 30%, respectively, and positive rates of CX43 mRNA were 97%, 64%, 58%, and 46%, respectively; positive rates of CX26 mRNA was 93%, 68%, 55%, and 42%, respectively. Positive rates of CX43 (mRNA, protein) and CX26 (mRNA) were gradually decreased. Positive rate of CX was significantly lower in CIS group than in NE group (P < 0.05). The expressions of CX26 and CX43 were weaker in CIS group than in NE groupu their expressions were obviously decreased, or even vanished in the area of CIS adjacent to NE. Proliferating index (PI), indicated by expression of Ki-67 protein, was increased gradually in NE (5%), hyperplasia (12%), CIS (30%), and IC (62%)u the differences were significant (P < 0.05) between CIS group and other groups. CONCLUSIONS: CX26 and CX43 may play important roles in carcinogenesis of cervical cancer. CXs may inhibit tumorigenesis and cell proliferation; it might be key factors in earlier stages when cellular malignant phenotypes have been established, or NE has been transformed into CIS.

Carcinoma in Situ↗
PubMed2003

Developmental regulation and significance of KNOX protein trafficking in Arabidopsis.

Intercellular communication delivers critical information for position-dependent specification of cell fate. In plants, a novel mechanism for cell-to-cell communication involves the intercellular trafficking of regulatory proteins and mRNAs. The maize KNOTTED1 (KN1) gene acts non cell-autonomously in the maize leaf, and KN1 was the first plant protein shown to traffic cell-to-cell, presumably through plasmodesmata. We have compared the intercellular trafficking of green fluorescent protein (GFP) fusions of KN1 and Arabidopsis KN1-related homeobox proteins to that of the viral movement protein from turnip vein clearing tobamovirus. We show that there is specific developmental regulation of GFP approximately KN1 trafficking. GFP -- KN1 was able to traffic from the inner layers of the leaf to the epidermis, but not in the opposite direction, from epidermis to mesophyll. However, GFP or the GFP -- movement protein fusion moved readily out of the epidermis. GFP -- KN1 was however able to traffic out of the epidermal (L1) layer in the shoot apical meristem, indicating that KN1 movement out of the L1 was developmentally regulated. GFP -- KNAT1/BREVIPEDICELLUS and GFP -- SHOOTMERISTEMLESS fusions could also traffic from the L1 to the L2/L3 layers of the meristem. In a test for the functional significance of trafficking, we showed that L1-specific expression of KN1 or of KNAT1 was able to partially complement the strong shootmeristemless-11 (stm-11) mutant. However, a cell-autonomous GUS fusion to KN1 showed neither trafficking ability nor complementation of stm-11 when expressed in the L1. These results suggest that the activity of KN1 and related homeobox proteins is maintained following intercellular trafficking, and that trafficking may be required for their normal developmental function.

Arabidopsis↗
PubMed1999

Inhibition of gap junction communication in alveolar epithelial cells by 18alpha-glycyrrhetinic acid.

Cultured alveolar epithelial cells exhibit gap junction intercellular communication (GJIC) and express regulated levels of connexin (Cx) 43 mRNA and protein. Newly synthesized radiolabeled Cx43 protein equilibrates with phosphorylated Cx43 isoforms; these species assemble to form both connexons and functional gap junction plaques. The saponin 18alpha-glycyrrhetinic acid (GA) rapidly and reversibly blocks GJIC at low concentrations (5 microM). Extended exposure to 18alpha-GA at higher concentrations causes inhibition of GJIC and time- and dose-dependent reductions in both Cx43 protein and mRNA expression. The latter toxic effects are paralleled by disassembly of gap junction plaques and are reversed less readily than acute effects on GJIC. These observations demonstrate 18alpha-GA-sensitive regulation of intercellular communication in epithelial cells from the mammalian lung and suggest a role for Cx43 expression and phosphorylation in acute and chronic regulation of GJIC between alveolar epithelial cells.

Animals↗
PubMed1988

Metastatic spermatocytic seminoma. A case report with light microscopic, ultrastructural, and immunohistochemical findings.

A case of metastatic spermatocytic seminoma with metastases to homolateral retroperitoneal paraaortic lymph nodes in a 50-year-old man is described. The metastases were detected 18 months after orchiectomy. A retroperitoneal biopsy with cytoreductive lymphadenectomy was performed followed by radiotherapy and consecutively by combination chemotherapy. The patient died 25 months after orchiectomy of complications arising after a second course of chemotherapy. No signs of further tumor spread were observed. Autopsy was not performed. The tissue of the metastases fulfilled the light microscopic criteria for spermatocytic seminoma and ultrastructurally showed intercellular communications with typical intercellular bridges. The absence of placental alkaline phosphatase in tumor cells is also consistent with this diagnosis. The metastases differed from the primary tumor in the presence of focal lymphocytic infiltration and granulomatous reaction. This patient represents the first fully documented case of a metastasizing spermatocytic seminoma.

Dysgerminoma↗