scholarly journals Epidermal growth factor disrupts gap-junctional communication and induces phosphorylation of connexin43 on serine.

1992 ◽  
Vol 3 (8) ◽  
pp. 865-874 ◽  
Author(s):  
A F Lau ◽  
M Y Kanemitsu ◽  
W E Kurata ◽  
S Danesh ◽  
A L Boynton
Keyword(s):  
Growth Factor ◽  
Epidermal Growth Factor ◽  
Tyrosine Kinase ◽  
Gap Junction ◽  
Intracellular Signaling ◽  
Gap Junctional Communication ◽  
Junctional Communication ◽  
Junction Protein ◽  
Epidermal Growth ◽  
Gap Junctional

Growth factors regulate cellular proliferation and differentiation by activating plasma membrane tyrosine kinase receptors and triggering a cascade of events mediated by intracellular signaling proteins. The mechanism underlying growth factor modification of cellular functions, such as gap-junctional communication (gjc), has not been established clearly. Addition of epidermal growth factor (EGF) to T51B rat liver epithelial cells resulted in the rapid activation of EGF receptor tyrosine kinase activity followed by a transient dose-dependent disruption of gjc. This change did not result from the gross disturbance of membrane gap junction plaques as measured by immunofluorescence microscopy, but instead correlated with markedly elevated phosphorylation of the connexin43 (cx43) gap junction protein, a profound shift to predominantly phosphorylated forms of cx43, and the appearance of a novel phosphorylated cx43 protein. These changes in cx43 phosphorylation involved only serine residues. On restoration of gjc, these alterations in cx43 phosphorylation reverted to the pre-EGF treatment state. Both events were inhibited by the serine/threonine protein phosphatase inhibitor, okadaic acid. Therefore, unlike the case for pp60v-src, EGF-induced disruption of gjc is not associated with tyrosine phosphorylation of cx43, but instead may result from phosphorylation of cx43 by activated intracellular signaling serine protein kinase(s).

Phosphorylation of connexin43 gap junction protein in uninfected and Rous sarcoma virus-transformed mammalian fibroblasts

1990 ◽  
Vol 10 (4) ◽  
pp. 1754-1763
Author(s):  
D S Crow ◽  
E C Beyer ◽  
D L Paul ◽  
S S Kobe ◽  
A F Lau
Keyword(s):  
Gap Junctions ◽  
Gap Junction ◽  
Rous Sarcoma Virus ◽  
Gap Junctional Communication ◽  
Rous Sarcoma ◽  
Junctional Communication ◽  
Junction Protein ◽  
Sarcoma Virus ◽  
Gap Junction Protein ◽  
Gap Junctional

Gap junctions are membrane channels that permit the interchange of ions and other low-molecular-weight molecules between adjacent cells. Rous sarcoma virus (RSV)-induced transformation is marked by an early and profound disruption of gap-junctional communication, suggesting that these membrane structures may serve as sites of pp60v-src action. We have begun an investigation of this possibility by identifying and characterizing putative proteins involved in junctional communication in fibroblasts, the major cell type currently used to study RSV-induced transformation. We found that uninfected mammalian fibroblasts do not appear to contain RNA or protein related to connexin32, the major rat liver gap junction protein. In contrast, vole and mouse fibroblasts contained a homologous 3.0-kilobase RNA similar in size to the heart tissue RNA encoding the gap junction protein, connexin43. Anti-connexin43 peptide antisera specifically reacted with three proteins of approximately 43, 45 and 47 kilodaltons (kDa) from communicating fibroblasts. Gap junctions of heart cells contained predominantly 45- and 47-kDa species similar to those found in fibroblasts. Uninfected fibroblast 45- and 47-kDa proteins were phosphorylated on serine residues. Phosphatase digestions of 45- and 47-kDa proteins and pulse-chase labeling studies indicated that these proteins represented phosphorylated forms of the 43-kDa protein. Phosphorylation of connexin protein appeared to occur shortly after synthesis, followed by an equally rapid dephosphorylation. In comparison with these results, connexin43 protein in RSV-transformed fibroblasts contained both phosphotyrosine and phosphoserine. Thus, the presence of phosphotyrosine in connexin43 correlates with the loss of gap-junctional communication observed in RSV-transformed fibroblasts.

Mechanisms for the coordination of intercellular calcium signaling in insulin-secreting cells

1997 ◽  
Vol 110 (4) ◽  
pp. 497-504 ◽  
Author(s):  
D. Cao ◽  
G. Lin ◽  
E.M. Westphale ◽  
E.C. Beyer ◽  
T.H. Steinberg
Keyword(s):  
Gap Junction ◽  
Islet Cells ◽  
Cytosolic Calcium ◽  
Calcium Waves ◽  
Gap Junctional Communication ◽  
Junctional Communication ◽  
Junction Protein ◽  
Insulin Secreting Cells ◽  
Gap Junction Protein ◽  
Gap Junctional

Insulin-mediated increases in cytosolic calcium are synchronized among the cells in a pancreatic islet, and result in pulsatile secretion of insulin. Pancreatic beta cells express the gap junction protein connexin43 and are functionally coupled, making gap junctional communication a likely mechanism for the synchronization of calcium transients among islet cells. To define the mechanism by which pancreatic islet cells coordinate calcium responses, we studied mechanically-induced intercellular calcium waves in the communication-deficient rat insulinoma cell line RINm5f, and in RINm5f cells transfected with the gap junction protein connexin43. Both RINm5f and RINm5f cells transfected with connexin43 propagated calcium waves that required release of calcium from intracellular stores, did not involve gap junctional communication, and appeared to be mediated by autocrine activity of secreted ATP acting on P2U purinergic receptors. Connexin43 transfectants also propagated calcium waves that required gap junctional communication and influx of extracellular calcium through voltage-gated calcium channels. Gap junction-dependent intercellular calcium waves were inhibited by preventing plasma membrane depolarization. These studies demonstrate two distinct pathways by which insulin-secreting cells can coordinate cytosolic calcium rises, and show that it is by ionic traffic that gap junctions synchronize calcium-dependent events in these cells.

VEGF transiently disrupts gap junctional communication in endothelial cells

2001 ◽  
Vol 114 (6) ◽  
pp. 1229-1235
Author(s):  
S. Suarez ◽  
K. Ballmer-Hofer
Keyword(s):  
Endothelial Cells ◽  
Growth Factor ◽  
Tyrosine Kinase ◽  
Map Kinases ◽  
Cell Junctions ◽  
Early Effect ◽  
Gap Junctional Communication ◽  
Junctional Communication ◽  
Gap Junctional ◽  
Cell Cell

Vascular endothelial growth factor, VEGF, stimulates angiogenesis by directly acting on endothelial cells. The effects of VEGF are mediated by two tyrosine kinase receptors, VEGFR-1 (Flt-1) and VEGFR-2 (Flk-1/KDR) that are highly related to receptors of the platelet derived growth factor (PDGF) receptor family. We are interested in early signalling events downstream from VEGF receptors that affect blood vessel homeostasis. Endothelial cells form multiple types of cell-cell junctions that are required for cellular organization into complex networks. These junctions also regulate communication among adjacent cells. Stimulation by various growth factors such as epidermal growth factor (EGF) or PDGF has been shown to disrupt cell-cell junctions, consequently affecting cell-to-cell communication. We investigated gap junctional communication (GJC) by monitoring the transfer of a low molecular mass fluorescent tracer molecule between adjacent cells using immunofluorescence microscopy. VEGF maximally blocked GJC 15 minutes after growth factor administration. The cells resumed communication via gap junctions within 1–2 hours after treatment. This early effect of VEGF on communication correlated with changes in the phosphorylation state of one of the proteins involved in gap junction formation, connexin 43 (Cx43). The signalling mechanisms involved in this phenomenon depend on activation of VEGFR-2, impinge on a tyrosine kinase of the Src family and activate the Erk family of MAP kinases. The function of VEGF-mediated disruption of GJC might be to restrict an increase in endothelium permeability to the environment affected by local injury to blood vessels.

scholarly journals Transforming Growth Factor-β3 Increases Gap-Junctional Communication among Folliculostellate Cells to Release Basic Fibroblast Growth Factor

Endocrinology ◽  
2005 ◽  
Vol 146 (9) ◽  
pp. 4054-4060 ◽  
Author(s):  
Nurul Kabir ◽  
Kirti Chaturvedi ◽  
Lian Sheng Liu ◽  
Dipak K. Sarkar
Keyword(s):  
Growth Factor ◽  
Gap Junction ◽  
Fibroblast Growth Factor ◽  
Basic Fibroblast Growth Factor ◽  
Connexin 43 ◽  
Fibroblast Growth ◽  
Gap Junctional Communication ◽  
Junctional Communication ◽  
Gap Junctional ◽  
Gap Junction Inhibitor

Abstract Folliculostellate (FS) cells are known to communicate with each other and with endocrine cells via gap junctions in the anterior pituitary. We investigated whether TGFβ3 and estradiol, known to regulate FS cell production and secretion of basic fibroblast growth factor (bFGF), increases gap junctional communication to alter bFGF secretion from FS cells. FS cells in monolayer cultures were treated with TGFβ3 or vehicle alone for 24 h and then microinjected with Lucifer Yellow and high-molecular-weight Texas Red dextran. Ten minutes later the transfer of dye among adjacent cells was recorded with a digital microscope. TGFβ3 increased the transfer of dye. The TGFβ3-neutralizing antibody and the gap junction inhibitor octanol reduced the effect of TGFβ3 on the transfer of dye. The TGFβ3-induced transfer of dye was unaltered by simultaneous treatment with estradiol. The steroid alone also had no effect. TGFβ3 increased total and phosphorylated levels of connexin 43. Estradiol treatment did not produce any significant changes on basal or TGFβ3-induced increases in connexin 43 levels. The gap-junction inhibitor octanol reduced TGFβ3-increased levels of bFGF in FS cells. Taken together, these results suggest that TGFβ3 may act on FS cells to increase gap-junctional communication to maximize its effect on bFGF secretion.

Shapes of astrocyte networks in the juvenile brain

2006 ◽  
Vol 2 (1) ◽  
pp. 3-14 ◽  
Author(s):  
VANESSA HOUADES ◽  
NATHALIE ROUACH ◽  
PASCAL EZAN ◽  
FRANK KIRCHHOFF ◽  
ANNETTE KOULAKOFF ◽  
...  
Keyword(s):  
Gap Junction ◽  
Brain Function ◽  
Connexin 43 ◽  
Gap Junctional Communication ◽  
Junctional Communication ◽  
Junction Protein ◽  
Gap Junction Protein ◽  
High Level ◽  
Gap Junctional ◽  
Neuronal Compartments

The high level of intercellular communication mediated by gap junctions between astrocytes indicates that, besides individual astrocytic domains, a second level of organization might exist for these glial cells as they form communicating networks. Therefore, the contribution of astrocytes to brain function should also be considered to result from coordinated groups of cells. To evaluate the shape and extent of these networks we have studied the expression of connexin 43, a major gap junction protein in astrocytes, and the intercellular diffusion of gap junction tracers in two structures of the developing brain, the hippocampus and the cerebral cortex. We report that the shape of astrocytic networks depends on their location within neuronal compartments in a defined brain structure. Interestingly, not all astrocytes are coupled, which indicates that connections within these networks are restricted. As gap junctional communication in astrocytes is reported to contribute to several glial functions, differences in the shape of astrocytic networks might have consequences on neuronal activity and survival.

scholarly journals Phosphorylation of connexin43 gap junction protein in uninfected and Rous sarcoma virus-transformed mammalian fibroblasts.

1990 ◽  
Vol 10 (4) ◽  
pp. 1754-1763 ◽  
Author(s):  
D S Crow ◽  
E C Beyer ◽  
D L Paul ◽  
S S Kobe ◽  
A F Lau
Keyword(s):  
Gap Junctions ◽  
Gap Junction ◽  
Rous Sarcoma Virus ◽  
Gap Junctional Communication ◽  
Rous Sarcoma ◽  
Junctional Communication ◽  
Junction Protein ◽  
Sarcoma Virus ◽  
Gap Junction Protein ◽  
Gap Junctional

Gap junctions are membrane channels that permit the interchange of ions and other low-molecular-weight molecules between adjacent cells. Rous sarcoma virus (RSV)-induced transformation is marked by an early and profound disruption of gap-junctional communication, suggesting that these membrane structures may serve as sites of pp60v-src action. We have begun an investigation of this possibility by identifying and characterizing putative proteins involved in junctional communication in fibroblasts, the major cell type currently used to study RSV-induced transformation. We found that uninfected mammalian fibroblasts do not appear to contain RNA or protein related to connexin32, the major rat liver gap junction protein. In contrast, vole and mouse fibroblasts contained a homologous 3.0-kilobase RNA similar in size to the heart tissue RNA encoding the gap junction protein, connexin43. Anti-connexin43 peptide antisera specifically reacted with three proteins of approximately 43, 45 and 47 kilodaltons (kDa) from communicating fibroblasts. Gap junctions of heart cells contained predominantly 45- and 47-kDa species similar to those found in fibroblasts. Uninfected fibroblast 45- and 47-kDa proteins were phosphorylated on serine residues. Phosphatase digestions of 45- and 47-kDa proteins and pulse-chase labeling studies indicated that these proteins represented phosphorylated forms of the 43-kDa protein. Phosphorylation of connexin protein appeared to occur shortly after synthesis, followed by an equally rapid dephosphorylation. In comparison with these results, connexin43 protein in RSV-transformed fibroblasts contained both phosphotyrosine and phosphoserine. Thus, the presence of phosphotyrosine in connexin43 correlates with the loss of gap-junctional communication observed in RSV-transformed fibroblasts.

scholarly journals Epidermal Growth Factor Activates Store-Operated Calcium Channels in Human Glomerular Mesangial Cells

2001 ◽  
Vol 12 (1) ◽  
pp. 47-53
Author(s):  
RONG MA ◽  
STEVEN C. SANSOM
Keyword(s):  
Growth Factor ◽  
Epidermal Growth Factor ◽  
Tyrosine Kinase ◽  
Intracellular Signaling ◽  
Mesangial Cells ◽  
Cell Types ◽  
Glomerular Mesangial Cells ◽  
Signaling Mechanism ◽  
Baseline Activity ◽  
Epidermal Growth

Abstract. A cellular influx of Ca2+ is critical for initiating and maintaining growth in a variety of cell types. Experiments were performed to determine whether epidermal growth factor (EGF), which is known to initiate a proliferative response in mesangial cells, could regulate by intracellular signal transduction the store-operated Ca2+ channels (SOC) of human mesangial cells (HMC) in culture. The cell-attached patch configuration was used to monitor the activity of SOC, with 90 mM Ba2+ in the pipette and physiologic saline solution in the bath. Under control conditions, the mean NPo value was 1.06 at a holding potential of -80 mV. When 100 nM EGF was added to the bath, SOC were activated by 53%. The EGF-evoked response was dose-dependent, with a half-maximal activation concentration of 4.8 nM. An inhibitor of tyrosine kinase, i.e., tyrphostin A23 (100 μM), completely abolished EGF-evoked channel activation. EGF combined with the inactive control compound tyrphostin A1 (100 μM) elicited significant (85%) activation of SOC. Calphostin C, an inhibitor of protein kinase C (PKC), did not affect the baseline activity of SOC but abolished the EGF-evoked enhancement of SOC activity. The PKC activator phorbol-12-myristate-13-acetate (PMA) significantly activated SOC. However, the effects of PMA were duplicative rather than additive or potentiating with maximal concentrations (100 nM) of EGF, suggesting that PMA and EGF activate SOC through a common PKC pathway. In addition, downregulation of PKC via incubation of HMC with PMA for 1 to 20 h depressed both basal activity and EGF-induced activation of SOC. It is concluded that EGF stimulates SOC in HMC through an intracellular signaling mechanism involving tyrosine kinase and PKC.

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