Isolation of a revertant clone from a variant embryonal carcinoma cell line deficient in metabolic co-operation

A revertant clone with restored capacity for metabolic cooperation has been isolated from the cooperation-defective variant embryonal carcinoma cell line R5/3. The properties of the revertant clone provide evidence that deficiencies shown by R5/3 in intercellular transfer of nucleotides and sodium ions are the result of a common genetic lesion which can be dissociated from a secondary lesion causing increased thioguanine resistance and from an increase in ploidy.     

Intercellular communication and tissue growth

Summary Three cancer cell strains that fail to make permeable membrane junctions were tested for ability to transfer an endogenous hypoxanthine derivative from cell to cell. The cells of these strains, loaded with³H-hypoxanthine, were grown in contact with cells from a mutant line incapable of incorporating exogenous hypoxanthine. The transfer of the³H-hypoxanthine derivative to the mutant cells was determined by radio-autography and, in the same preparations, the presence of permeable membrane junctions was determined by intercellular fluorescein tracer diffusion and electrical measurement. The cells of the three strains showed no transfer of hypoxanthine derivative to contiguous mutant cells; the cells that make permeable junctions did show such transfer, under the same conditions.In contrast to this contact-requiring mode of transfer, a contact-independent transfer phenomenon was observed with these three cancer cell strains.     

Interaction of HIV-1 with dendritic cell-specific intercellular adhesion molecule-3-grabbing nonintegrin-expressing cells is influenced by gp120 envelope modifications associated with disease progression

Dendritic cells can enhance the replication of HIV-1 in CD4(+) lymphocytes through the interaction of the gp120 envelope protein with such molecules as dendritic cell-specific intercellular adhesion molecule-3-grabbing nonintegrin. The variable loops of gp120 have previously been shown to modulate the interaction of HIV-1 with its principal receptor CD4 and its various coreceptors, namely CCR5 and CXCR4. Here, we utilized a panel of molecular cloned viruses to identify whether gp120 modifications can influence the virus interaction with immature dendritic cells or a cell line expressing dendritic cell-specific intercellular adhesion molecule-3-grabbing nonintegrin (Raji-DC-SIGN). The viruses encompass the R5, R5X4 and X4 phenotypes, and are based upon V1V2 and V3 sequences from a patient with disease progression. We found that dendritic cell-specific intercellular adhesion molecule-3-grabbing nonintegrin enhancement of virus replication can be modulated by the V1V2 length, the overall V3 charge and N-linked glycosylation patterns; similar results were observed with immature dendritic cells. Viruses with higher V3 charges are more readily transferred to CD4(+) lymphocytes when the V1V2 region is longer and contains an additional N-linked glycosylation site, whereas transfer of viruses with lower V3 charges is greater when the V1V2 region is shorter. Viruses differing in the V1V2 and V3 regions also demonstrated differential capture by Raji-DC-SIGN cells in the presence of mannan. These results indicate that the interaction between HIV-1 and immature dendritic cells via such molecules as dendritic cell-specific intercellular adhesion molecule-3-grabbing nonintegrin may have a role in selecting viruses undergoing transmission and evolution during disease progression.     

Gap junction channels exhibit connexin-specific permeability to cyclic nucleotides

Gap junction channels exhibit connexin dependent biophysical properties, including selective intercellular passage of larger solutes, such as second messengers and siRNA. Here, we report the determination of cyclic nucleotide (cAMP) permeability through gap junction channels composed of Cx43, Cx40, or Cx26 using simultaneous measurements of junctional conductance and intercellular transfer of cAMP. For cAMP detection the recipient cells were transfected with a reporter gene, the cyclic nucleotide-modulated channel from sea urchin sperm (SpIH). cAMP was introduced via patch pipette into the cell of the pair that did not express SpIH. SpIH-derived currents (I(h)) were recorded from the other cell of a pair that expressed SpIH. cAMP diffusion through gap junction channels to the neighboring SpIH-transfected cell resulted in a five to sixfold increase in I(h) current over time. Cyclic AMP transfer was observed for homotypic Cx43 channels over a wide range of conductances. However, homotypic Cx40 and homotypic Cx26 exhibited reduced cAMP permeability in comparison to Cx43. The cAMP/K(+) permeability ratios were 0.18, 0.027, and 0.018 for Cx43, Cx26, and Cx40, respectively. Cx43 channels were approximately 10 to 7 times more permeable to cAMP than Cx40 or Cx26 (Cx43 > Cx26 > or = Cx40), suggesting that these channels have distinctly different selectivity for negatively charged larger solutes involved in metabolic/biochemical coupling. These data suggest that Cx43 permeability to cAMP results in a rapid delivery of cAMP from cell to cell in sufficient quantity before degradation by phosphodiesterase to trigger relevant intracellular responses. The data also suggest that the reduced permeability of Cx26 and Cx40 might compromise their ability to deliver cAMP rapidly enough to cause functional changes in a recipient cell.     

Effects of gap junction to Ca(2+) and to IP(3) on the synchronization of intercellular calcium oscillations in hepatocytes

The frequency of free cytosolic calcium concentration ([Ca(2+)]) oscillations elicited by a given agonist concentration differs between individual hepatocytes. However, in multicellular systems of rat hepatocytes and even in the intact liver, [Ca(2+)] oscillations are synchronized and highly coordinated. In this paper, we have investigated theoretically the gap junction permeable to calcium and to IP(3) on intercellular synchronization by means of a mathematical model, respectively. It is shown that gap junction permeable to calcium and to IP(3) are effective on synchronizing calcium oscillations in coupled hepatocytes. Our theoretical results are similar either for the case of Ca(2+) acting as coordinating messenger or for the case of IP(3) as coordinating messenger. There exists an optimal coupling strength for a pair of connected hepatocytes. Appropriate coupling strength and IP(3) level can induce various harmonic locking of intercellular [Ca(2+)] oscillations. Furthermore, a phase diagram in two-dimensional parameter space of the coupling strength and IP(3) level (or the velocity of IP(3) synthesis) has been predicted, in which the synchronization region is similar to Arnol'd tongue.     

A paraxial exclusion zone creates patterned cranial neural crest cell outgrowth adjacent to rhombomeres 3 and 5.

Cranial neural crest cell migration is patterned, with neural crest cell-free zones adjacent to rhombomere (R) 3 and R5. These zones have been suggested to result from death of premigratory neural crest cells via upregulation of BMP-4 and Msx-2 in R3 and R5, consequent to R2-, R4-, and R6-derived signals. We reinvestigated this model and found that cell death detected by acridine orange staining in avian embryos varied widely numerically and in pattern, but with a tendency for an elevated zone centered at the R2/3 boundary. In situ hybridization of BMP-4 mRNA resolved to centers at R3 and R5 but Msx-2 resolved to the R2/3 border with only a faint smear from R5 to R6. Outgrowth of neural crest cells was less in isolated R3 cultures than in R1+2, R2, and R4 cultures, but R3 showed neither a decrease in outgrowth of neural crest cells nor an increase in cell death when cocultured with R1+2, R2, or R4. In addition, in serum-free culture, exogenous BMP-4 strikingly reduced neural crest cell outgrowth from R1+2 and R4 as well as R3. Thus we cannot confirm the role of intraneural cell death in patterning rhombomeric neural crest outgrowth. However, grafting quail R2 or R4 adjacent to the chick hindbrain demonstrated a neural crest cell exclusion zone next to R3 and R5. We suggest that one important pattern determinant for rhombomeric neural crest cell migration involves the microenvironment next to the neural tube.     

Mutations in the second extracellular region of connexin 43 prevent localization to the plasma membrane,but do not affect its ability to suppress cell growth

Connexin 43 (Cx43), the most widely expressed gap junction protein, has a role in regulation of cell growth. In this study, we demonstrate that the point mutations F199L, R202E, and E205R in the second extracellular region of Cx43 prevent localization of the mutant proteins to the plasma membrane. The mutants were aberrantly localized in the cytoplasm if expressed in HeLa cells, which lack Cx43. Coexpression with wild-type Cx43 promoted localization of the F199L and R202E mutant proteins to the plasma membrane. By dye transfer assay, we showed that gap junctional intercellular communication (GJC) is decreased in cells expressing the mutants, compared to Cx43 wild-type-expressing cells. However, the F199L mutant does not appear to have a dominant-negative effect on GJC. Despite the loss of GJC, the ability of the F199L Cx43 mutant to inhibit growth of either Cx43-/- cells or two cancer cell lines, HeLa and C6 glioma cells, was similar to that of the wild-type Cx43. In addition, we showed that both R202E and E205R Cx43 mutant expressions cause growth retardation of HeLa cells. Therefore, the point mutations in the second extracellular region of Cx43 do not affect the ability of the mutant proteins in vitro to suppress cell growth, although they prevent localization to the plasma membrane. The results support the concept that regulation of cell growth by Cx43 does not necessarily require GJC and suggest that the growth-suppressive properties of Cx43 may be independent of the second extracellular loop.     

Exosomes: vesicular carriers for intercellular communication in neurodegenerative disorders

The intercellular transfer of misfolded proteins has received increasing attention in various neurodegenerative diseases characterized by the aggregation of specific proteins, as observed in Alzheimer’s, Parkinson’s and Huntington’s disease. One hypothesis holds that intercellular dissemination of these aggregates within the central nervous system results in the seeded assembly of the cognate soluble protein in target cells, similar to that proposed for transmissible prion diseases. The molecular mechanisms underlying the intercellular transfer of these proteinaceous aggregates are poorly understood. Various transfer modes of misfolded proteins including continuous cell-cell contacts such as nanotubes, unconventional secretion or microvesicle/exosome-associated dissemination have been suggested. Cells can release proteins, lipids and nucleic acids by vesicular exocytosis pathways destined for horizontal transfer. Encapsulation into microvesicular/exosomal vehicles not only protects these molecules from degradation and dilution in the extracellular space but also facilitates delivery over large distances, e.g. within the blood flow or interstitial fluid. Specific surface ligands might allow the highly efficient and targeted uptake of these vesicles by recipient cells. In this review, we focus on the cell biology and function of neuronal microvesicles/exosomes and discuss the evidence for pathogenic intercellular protein transfer mediated by vesicular carriers.     

Quantitative determination of gap junction intercellular communication using flow cytometric measurement of fluorescent dye transfer

Gap junction intercellular communication (GJIC) is involved in several aspects of normal cell behaviour, and disturbances in this type of communication have been associated with many pathological conditions. Reliable and accurate methods for the determination of GJIC are therefore important in studies of cell biology. (Tomasetto, C., Neveu, M.J., Daley, J., Horan, P.K. and Sager, R. (1993) Journal of Cell Biology, 122, 157-167) reported some years ago the use of flow cytometer to determine transfer between cells of a mobile dye, calcein, as a measure of cell communication through gap junctions. In spite of this being a method with potential for quantitative and reliable determination of GJIC, it has been modestly used, possibly due to technical difficulties. In the present work we have illustrated several ways to use flow cytometric data to express cell communication through gap junctions. The recipient cells were pre-stained with the permanent lipophilic dye PKH26, and the donor cell population were loaded with the gap junction permeable dye, calcein. We show that the method may be used to measure the effect of chemicals on GJIC, and that the information is reliable, objective and reproducible due to the large number of cells studied. The data may give additional information to that obtained with other methods, since the effect observed will be on the establishment of cell communication as compared to what is observed for microinjection or scrape loading, where the effect is on already established communication. This is probably the reason for the more potent effects of DMSO on GJIC measured by the present method than on already existing GJIC measured by microinjection or quantitative scrape loading. We also show that the problem related to the mobile dye calcein not being fixable with aldehydes will not affect the results as long as the cells are kept on ice in the dark and analysed by flow cytometer within the first hours after formalin cell fixation.     

Dynamic gap junctional communication: a delimiting model for tissue responses.

Gap junctions are aqueous intercellular channels formed by a diverse class of membrane-spanning proteins, known as connexins. These aqueous pores provide partial cytoplasmic continuity between cells in most tissues, and are freely permeable to a host of physiologically relevant second messenger molecules/ionic species (e.g., Ca2+, IP3, cAMP, cGMP). Despite the fact that these second messenger molecules/ionic species have been shown to alter junctional patency, there is no clear basis for understanding how dynamic and transient changes in the intracellular concentration of second messenger molecules might modulate the extent of intercellular communication among coupled cells. Thus, we have modified the tissue monolayer model of Ramanan and Brink (1990) to account for both the up-regulatory and down-regulatory effects on junctions by second messenger molecules that diffuse through gap junctions. We have chosen the vascular wall as our morphological correlate because of its anisotropy and large investment of gap junctions. The model allows us to illustrate the putative behavior of gap junctions under a variety of physiologically relevant conditions. The modeling studies demonstrated that transient alterations in intracellular second messenger concentrations are capable of producing 50-125% changes in the number of cells recruited into a functional syncytial unit, after activation of a single cell. Moreover, the model conditions required to demonstrate such physiologically relevant changes in intercellular diffusion among coupled cells are commonly observed in intact tissues and cultured cells.     

Response to myocardial ischemia/reperfusion injury involves Bnip3 and autophagy

Ischemia and reperfusion (I/R) injury is associated with extensive loss of cardiac myocytes. Bnip3 is a mitochondrial pro-apoptotic Bcl-2 protein which is expressed in the adult myocardium. To investigate if Bnip3 plays a role in I/R injury, we generated a TAT-fusion protein encoding the carboxyl terminal transmembrane deletion mutant of Bnip3 (TAT-Bnip3DeltaTM) which has been shown to act as a dominant negative to block Bnip3-induced cell death. Perfusion with TAT-Bnip3DeltaTM conferred protection against I/R injury, improved cardiac function, and protected mitochondrial integrity. Moreover, Bnip3 induced extensive fragmentation of the mitochondrial network and increased autophagy in HL-1 myocytes. 3D rendering of confocal images revealed fragmented mitochondria inside autophagosomes. Enhancement of autophagy by ATG5 protected against Bnip3-mediated cell death, whereas inhibition of autophagy by ATG5K130R enhanced cell death. These results suggest that Bnip3 contributes to I/R injury which triggers a protective stress response with upregulation of autophagy and removal of damaged mitochondria.     

Cytokine signaling through Stat3 activates integrins, promotes adhesion, and induces growth arrest in the myeloid cell line 32D

Hematopoietic cell development and function is dependent on cytokines and on intercellular interactions with the microenvironment. Although the intracellular signaling pathways stimulated by cytokine receptors are well described, little is known about the mechanisms through which these pathways modulate hematopoietic cell adhesion events in the microenvironment. Here we show that cytokine-activated Stat3 stimulates the expression and function of cell surface adhesion molecules in the myeloid progenitor cell line 32D. We generated an erythropoietin receptor (EpoR) isoform (ER343/401-S3) that activates Stat3 rather than Stat5 by substituting the Stat3 binding/activation sequence motif from gp130 for the sequences surrounding tyrosines 343 and 401 in the receptor cytoplasmic region. Activation of Stat3 leads to homotypic cell aggregation, increased expression of intercellular adhesion molecule 1 (ICAM-1), CD18, and CD11b, and activation of signaling through CD18-containing integrins. Unlike the wild type EpoR, ER343/401-S3 is unable to support long term Epo-dependent proliferation in 32D cells. Instead, Epo-treated ER343/401-S3 cells undergo G(1) arrest and express elevated levels of the cyclin-dependent kinase inhibitor p27(Kip1). Sustained activation of Stat3 in these cells is required for their altered morphology and growth properties since constitutive SOCS3 expression abrogates homotypic cell aggregation, signaling through CD18-containing integrins, G(1) arrest, and accumulation of p27(Kip1). Collectively, our results demonstrate that cytokine-activated Stat3 stimulates the expression and function of cell surface adhesion molecules, indicating that a role for Stat3 is to regulate intercellular contacts in myeloid cells.     

Growth-Inhibitory Functions of a Mutated Gelsolin (His321) in NIH/3T3 Mouse Fibroblasts

We have previously established a murine flat revertant cell line R1 from an activated H-ras transformant EJ-NIH/3T3 by subjecting it to ethyl methanesulfonate. From the R1 cells, we cloned a mutated gelsolin gene His321 and have shown the inhibitory activity of His321 against EJ-NIH/3T3 tumors. Our present experiments were conducted to find out whether the His321 gene has any effects on untransformed NIH/3T3 fibroblasts. Rhodamine-phalloidin staining revealed that two NIH/3T3 clones expressing His321 (NIH/λ2S-3 and NIH/λ2S-6) form organized actin stress fibers as two clones transfected with the vector alone (NIH/neo-3 and NIH/neo-5). We also found that in a liquid medium, NIH/λ2S-3 and NIH/λ2S-6 grew more slowly than NIH/neo-3 and NIH/neo-5 and that the doubling times of the former were about 10 h slower than those of the latter. To investigate the effects of His321 on the signal transduction pathway necessary for cell growth, we stimulated the cell lines by prostaglandin E1 (PGE1), a platelet-derived growth factor (PDGF), or the epidermal growth factor (EGF). Although stimulation by PGE1 increased intercellular cyclic AMP in R1 cells, it did not do so in NIH/λ2S-3 and NIH/λ2S-6 cells. On the other hand, stimulation by PDGF or EGF induced far less DNA synthesis in NIH/λ2S-3 and NIH/λ2S-6 than in NIH/neo-3 and NIH/neo5. These results suggest that through the effects on the signal transduction pathway of PDGF and/or EGF His321-mutated gelsolin inhibits the growth of NIH/3T3.     

Cation and ATP content of ferret red cells

Ferret red cells were shown to have the following properties: 1. They have a high sodium (96 mmol/l cell) and low potassium (3.9 mmol/l cell) content. 2. The majority do not appear to have an active sodium pump in their membranes. 3. Their membranes are highly permeable to rubidium indicating that they are probably also highly permeable to potassium. 4. Their magnesium (3.01 mmol/l cell) and calcium (0.01 mmol/l cell) contents are similar to those of red cells from other species. 5. Their ATP content (0.6 mmol/l cell) is similar to that of cat and dog red cells and is sufficiently high to activate known ion transport systems.     

Connexin37 forms high conductance gap junction channels with subconductance state activity and selective dye and ionic permeabilities.

Gap junctions are thought to mediate the direct intercellular coupling of adjacent cells by the open-closed gating of an aqueous pore permeable to ions and molecules of up to 1 kDa or 10-14 A in diameter. We symmetrically altered the ionic composition or asymmetrically added 6-carboxyfluorescein (6-CF, M(r) = 376), a fluorescent tracer, to pairs of connexin37-transfected mouse neuro2A cells to examine the ionic and dye permeability of human connexin37 channels. We demonstrate that the 300-pS channel formed by connexin37 has an effective relative anion/cation permeability ratio of 0.43, directly converts to at least one intermediate (63 pS) subconductance state, and that 6-CF dye transfer is accompanied by a 24% decrease in unitary channel conductance. These observations favor a new interpretation of the gap junction pore consistent with direct ion-channel interactions or electrostatic charge effects common to more conventional multistate ion channels. These results have distinct implications about the different forms of intercellular signaling (cationic, ionic, and/or biochemical) that can occur depending on the expression and conformation of the connexin channel proteins.     

Highly permeable contacts between epithelial cells in culture]

Cultured epithelial cells producing monolayered sheets were used to study intercellular contacts permeable to sodium fluorescein. Cells in dense cultures were more capable of forming permeable junctions than cells of sparse cultures. In addition, the standard microelectrode technique revealed some differences in cellular membrane potentials in dense and sparse cultures. A possible correlation is discussed between intercellular contact formation and other features of cells depending on cell culture density.     

Quantitative determination of gap junction intercellular communication by scrape loading and image analysis

Gap junction intercellular communication (GJIC) consists of intercellular exchange of low molecular weight molecules. Chemically induced alterations of this communication have been suggested to result in abnormal cell growth and tumour promotion. Several in vitro assays have been developed to determine the effect of chemicals on gap junction communication in cultured cells. The scrape loading dye transfer technique is based on studying the transfer of the fluorescent dye Lucifer Yellow in cells where the dye is loaded through a cut in the cell monolayer. This technique is rapid and relatively uncomplicated, but has only been used to qualitatively demonstrate communication, due to lack of an appropriate method for quantification of the dye spreading. We show here that analysis of digital fluorescence images of cells scrape loaded with Lucifer Yellow can be used for quantitative determination of GJIC. We have analysed the images both by means of distance of diffusion of the dye in the cell monolayer, as well as by area of dye-coupled cells. The results are consistent with that obtained using microinjection of Lucifer Yellow and the method offers a simple way for quantitative determination of GJIC.     

Quantitative Determination of Gap Junction Intercellular Communication Using Flow Cytometric Measurement of Fluorescent Dye Transfer

Gap junction intercellular communication (GJIC) is involved in several aspects of normal cell behaviour, and disturbances in this type of communication have been associated with many pathological conditions. Reliable and accurate methods for the determination of GJIC are therefore important in studies of cell biology. (Tomasetto, C., Neveu, M.J., Daley, J., Horan, P.K. and Sager, R.(1993) Journal of Cell Biology, 122, 157–167) reported some years ago the use of flow cytometer to determine transfer between cells of a mobile dye, calcein, as a measure of cell communication through gap junctions. In spite of this being a method with potential for quantitative and reliable determination of GJIC, it has been modestly used, possibly due to technical difficulties. In the present work we have illustrated several ways to use flow cytometric data to express cell communication through gap junctions. The recipient cells were pre-stained with the permanent lipophilic dye PKH26, and the donor cell population were loaded with the gap junction permeable dye, calcein. We show that the method may be used to measure the effect of chemicals on GJIC, and that the information is reliable, objective and reproducible due to the large number of cells studied. The data may give additional information to that obtained with other methods, since the effect observed will be on the establishment of cell communication as compared to what is observed for microinjection or scrape loading, where the effect is on already established communication. This is probably the reason for the more potent effects of DMSO on GJIC measured by the present method than on already existing GJIC measured by microinjection or quantitative scrape loading. We also show that the problem related to the mobile dye calcein not being fixable with aldehydes will not affect the results as long as the cells are kept on ice in the dark and analysed by flow cytometer within the first hours after formalin cell fixation.