scholarly journals Inhibition of Ras activity coordinates cell fusion with cell–cell contact during yeast mating

2018 ◽  
Vol 217 (4) ◽  
pp. 1467-1483 ◽  
Author(s):  
Laura Merlini ◽  
Bita Khalili ◽  
Omaya Dudin ◽  
Laetitia Michon ◽  
Vincent Vincenzetti ◽  
...  
Keyword(s):  
Cell Fusion ◽  
Mitogen Activated Protein Kinase ◽  
Cell Contact ◽  
Pheromone Signaling ◽  
Mitogen Activated Protein ◽  
Fusion Cell ◽  
Local Cell ◽  
Guanosine Triphosphatase ◽  
Local Enrichment ◽  
Cell Cell

In the fission yeast Schizosaccharomyces pombe, pheromone signaling engages a signaling pathway composed of a G protein–coupled receptor, Ras, and a mitogen-activated protein kinase (MAPK) cascade that triggers sexual differentiation and gamete fusion. Cell–cell fusion requires local cell wall digestion, which relies on an initially dynamic actin fusion focus that becomes stabilized upon local enrichment of the signaling cascade on the structure. We constructed a live-reporter of active Ras1 (Ras1–guanosine triphosphate [GTP]) that shows Ras activity at polarity sites peaking on the fusion structure before fusion. Remarkably, constitutive Ras1 activation promoted fusion focus stabilization and fusion attempts irrespective of cell pairing, leading to cell lysis. Ras1 activity was restricted by the guanosine triphosphatase–activating protein Gap1, which was itself recruited to sites of Ras1-GTP and was essential to block untimely fusion attempts. We propose that negative feedback control of Ras activity restrains the MAPK signal and couples fusion with cell–cell engagement.

scholarly journals Feedback inhibition of Ras activity coordinates cell fusion with cell-cell contact

2017 ◽  
Author(s):  
Laura Merlini ◽  
Bita Khalili ◽  
Omaya Dudin ◽  
Laetitia Michon ◽  
Vincent Vincenzetti ◽  
...  
Keyword(s):  
Cell Fusion ◽  
Feedback Inhibition ◽  
Cell Contact ◽  
Fusion Cell ◽  
Negative Feedback Control ◽  
Local Cell ◽  
Local Enrichment ◽  
Pheromone Signalling ◽  
Signalling Cascade ◽  
Cell Cell

AbstractIn fission yeast Schizosaccharomyces pombe, pheromone signalling engages a GPCR-Ras-MAPK cascade to trigger sexual differentiation leading to gamete fusion. Cell-cell fusion necessitates local cell wall digestion, the location of which relies on an initially dynamic actin fusion focus that becomes stabilized upon local enrichment of the signalling cascade. We constructed a live-reporter of active Ras1 (Ras1-GTP), also functional in S. cerevisiae, which revealed Ras activity at polarity sites peaking on the fusion structure before fusion. Remarkably, constitutive Ras1 activation promoted fusion focus stabilization and fusion attempts irrespective of cell-cell pairing, leading to cell lysis. Ras1 activity is restricted by the GTPase activating protein (GAP) Gap1, itself recruited to sites of Ras1-GTP. While the GAP domain on its own does not suffice for this localization, its recruitment to Ras1-GTP sites is essential to block untimely fusion attempts. We conclude that negative feedback control of Ras activity restrains the MAPK signal and couples fusion with cell-cell engagement.

scholarly journals Loss of E-Cadherin–mediated Cell–Cell Contacts Activates a Novel Mechanism for Up-Regulation of the Proto-Oncogene c-Jun

2009 ◽  
Vol 20 (7) ◽  
pp. 2121-2129 ◽  
Author(s):  
Revital Knirsh ◽  
Iris Ben-Dror ◽  
Barbara Spangler ◽  
Gideon D. Matthews ◽  
Silke Kuphal ◽  
...  
Keyword(s):  
Cell Separation ◽  
Tumor Promotion ◽  
Mitogen Activated Protein Kinase ◽  
Cell Contact ◽  
Activator Protein 1 ◽  
Cell Contacts ◽  
Mitogen Activated Protein ◽  
Stimulation Of ◽  
E Cadherin ◽  
Cell Cell

Loss of E-cadherin–mediated cell–cell contacts can elicit a signaling pathway that leads to acquisition of an invasive phenotype. Here, we show that at the receiving end of this pathway is the proto-oncogene c-Jun, a member of the activator protein-1 family of transcription factors that play a key role in stimulation of cell proliferation and tumor promotion. Cell separation or abrogation of E-cadherin–mediated cell–cell contacts both cause a dramatic increase in accumulation of the c-Jun protein. Unlike growth factors that enhance the expression of c-Jun by activating the transcription of the c-jun gene, the cell contact-dependent increase in c-Jun accumulation is not accompanied by a corresponding increase in c-Jun mRNA or c-Jun protein stability but rather in the translatability of the c-Jun transcript. Consistently, the increase in c-Jun accumulation is not dependent on activation of the mitogen-activated protein kinase or β-catenin pathways but is mediated by signals triggered by the restructured cytoskeleton. Depolymerization of the cytoskeleton can mimic the effect of cell separation and cause a dramatic increase in c-Jun accumulation, whereas Taxol inhibits the cell contact-dependent increase. This novel mechanism of c-Jun regulation seems to underlie the robust overexpression of c-Jun in tumor cells of patients with colon carcinoma.

Studies of membrane fusion. I. Paramyxovirus-induced cell fusion, a scanning electron-microscope study

1977 ◽  
Vol 28 (1) ◽  
pp. 179-188
Author(s):  
S. Knutton ◽  
D. Jackson ◽  
M. Ford
Keyword(s):  
Cell Surface ◽  
Cell Fusion ◽  
Hela Cells ◽  
Cell Swelling ◽  
Cell Contact ◽  
Cell Agglutination ◽  
Scanning Electron Microscope Study ◽  
Virus Particles ◽  
Scanning Electron ◽  
Cell Cell

Fusion of erythrocytes and HeLa cells with Sendai and Newcastle disease viruses has been studied by scanning electron microscopy. Most virus particles are spherical but vary in diameter from approximately 200 to approximately 600 nm. At 4 degrees C virus particles bind randomly to the cell surface and at high cell densities cross-linking of adjacent cells by virus particles results in cell agglutination. Cell-cell fusion takes place when the agglutinated cell suspension is warmed to 37 degrees C. Fusion is initiated at sites of cell-cell contact and is accompanied in all cases by cell swelling. In the case of suspension HeLa cells, virally mediated cell swelling involves an ‘unfolding’ of cell surface microvilli and results in the formation of smooth-surfaced single or fused cells. With erythrocytes, swelling results in haemolysis. There is a dramatic reduction in the numbers of virus particles bound to cells following fusion.

scholarly journals Mechanical stress impairs pheromone signaling via Pkc1-mediated regulation of the MAPK scaffold Ste5

2019 ◽  
Vol 218 (9) ◽  
pp. 3117-3133 ◽  
Author(s):  
Frank van Drogen ◽  
Ranjan Mishra ◽  
Fabian Rudolf ◽  
Michal J. Walczak ◽  
Sung Sik Lee ◽  
...  
Keyword(s):  
Mechanical Stress ◽  
Cell Fusion ◽  
Polarized Growth ◽  
Conserved Residues ◽  
Cellular Processes ◽  
Pheromone Signaling ◽  
Stress Signals ◽  
Cell Cell

Cells continuously adapt cellular processes by integrating external and internal signals. In yeast, multiple stress signals regulate pheromone signaling to prevent mating under unfavorable conditions. However, the underlying crosstalk mechanisms remain poorly understood. Here, we show that mechanical stress activates Pkc1, which prevents lysis of pheromone-treated cells by inhibiting polarized growth. In vitro Pkc1 phosphorylates conserved residues within the RING-H2 domains of the scaffold proteins Far1 and Ste5, which are also phosphorylated in vivo. Interestingly, Pkc1 triggers dispersal of Ste5 from mating projections upon mechanically induced stress and during cell–cell fusion, leading to inhibition of the MAPK Fus3. Indeed, RING phosphorylation interferes with Ste5 membrane association by preventing binding to the receptor-linked Gβγ protein. Cells expressing nonphosphorylatable Ste5 undergo increased lysis upon mechanical stress and exhibit defects in cell–cell fusion during mating, which is exacerbated by simultaneous expression of nonphosphorylatable Far1. These results uncover a mechanical stress–triggered crosstalk mechanism modulating pheromone signaling, polarized growth, and cell–cell fusion during mating.

scholarly journals Streptococcus gordonii Modulates Candida albicans Biofilm Formation through Intergeneric Communication

2009 ◽  
Vol 77 (9) ◽  
pp. 3696-3704 ◽  
Author(s):  
Caroline V. Bamford ◽  
Anita d'Mello ◽  
Angela H. Nobbs ◽  
Lindsay C. Dutton ◽  
M. Margaret Vickerman ◽  
...  
Keyword(s):  
Candida Albicans ◽  
Oral Cavity ◽  
Mitogen Activated Protein Kinase ◽  
Cell Contact ◽  
Streptococcus Gordonii ◽  
Autoinducer 2 ◽  
Mitogen Activated Protein ◽  
Hyphal Formation ◽  
Coated Surfaces ◽  
Infection Processes

ABSTRACT The fungus Candida albicans colonizes human oral cavity surfaces in conjunction with a complex microflora. C. albicans SC5314 formed biofilms on saliva-coated surfaces that in early stages of development consisted of ∼30% hyphal forms. In mixed biofilms with the oral bacterium Streptococcus gordonii DL1, hyphal development by C. albicans was enhanced so that biofilms consisted of ∼60% hyphal forms. Cell-cell contact between S. gordonii and C. albicans involved Streptococcus cell wall-anchored proteins SspA and SspB (antigen I/II family polypeptides). Repression of C. albicans hyphal filament and biofilm production by the quorum-sensing molecule farnesol was relieved by S. gordonii. The ability of a luxS mutant of S. gordonii deficient in production of autoinducer 2 to induce C. albicans hyphal formation was reduced, and this mutant suppressed farnesol inhibition of hyphal formation less effectively. Coincubation of the two microbial species led to activation of C. albicans mitogen-activated protein kinase Cek1p, inhibition of Mkc1p activation by H2O2, and enhanced activation of Hog1p by farnesol, which were direct effects of streptococci on morphogenetic signaling. These results suggest that interactions between C. albicans and S. gordonii involve physical (adherence) and chemical (diffusible) signals that influence the development of biofilm communities. Thus, bacteria may play a significant role in modulating Candida carriage and infection processes in the oral cavity.

scholarly journals Zds1/Zds2–PP2ACdc55 complex specifies signaling output from Rho1 GTPase

2016 ◽  
Vol 212 (1) ◽  
pp. 51-61 ◽  
Author(s):  
Erin M. Jonasson ◽  
Valentina Rossio ◽  
Riko Hatakeyama ◽  
Mitsuhiro Abe ◽  
Yoshikazu Ohya ◽  
...  
Keyword(s):  
Cell Wall ◽  
Cell Growth ◽  
Mapk Pathway ◽  
Mitogen Activated Protein Kinase ◽  
Signaling Specificity ◽  
Actin Organization ◽  
Cell Wall Damage ◽  
Polarized Cell Growth ◽  
Mitogen Activated Protein ◽  
Guanosine Triphosphatase

Budding yeast Rho1 guanosine triphosphatase (GTPase) plays an essential role in polarized cell growth by regulating cell wall glucan synthesis and actin organization. Upon cell wall damage, Rho1 blocks polarized cell growth and repairs the wounds by activating the cell wall integrity (CWI) Pkc1–mitogen-activated protein kinase (MAPK) pathway. A fundamental question is how active Rho1 promotes distinct signaling outputs under different conditions. Here we identified the Zds1/Zds2–protein phosphatase 2ACdc55 (PP2ACdc55) complex as a novel Rho1 effector that regulates Rho1 signaling specificity. Zds1/Zds2–PP2ACdc55 promotes polarized growth and cell wall synthesis by inhibiting Rho1 GTPase-activating protein (GAP) Lrg1 but inhibits CWI pathway by stabilizing another Rho1 GAP, Sac7, suggesting that active Rho1 is biased toward cell growth over stress response. Conversely, upon cell wall damage, Pkc1–Mpk1 activity inhibits cortical PP2ACdc55, ensuring that Rho1 preferentially activates the CWI pathway for cell wall repair. We propose that PP2ACdc55 specifies Rho1 signaling output and that reciprocal antagonism between Rho1–PP2ACdc55 and Rho1–Pkc1 explains how only one signaling pathway is robustly activated at a time.

scholarly journals Restoration of Tight Junction Structure and Barrier Function by Down-Regulation of the Mitogen-activated Protein Kinase Pathway in Ras-transformed Madin-Darby Canine Kidney Cells

2000 ◽  
Vol 11 (3) ◽  
pp. 849-862 ◽  
Author(s):  
Yan-hua Chen ◽  
Qun Lu ◽  
Eveline E. Schneeberger ◽  
Daniel A. Goodenough
Keyword(s):  
Epithelial Cell ◽  
Tight Junction ◽  
Tight Junctions ◽  
Mitogen Activated Protein Kinase ◽  
Madin Darby Canine Kidney ◽  
Mitogen Activated Protein ◽  
Darby Canine Kidney ◽  
Canine Kidney ◽  
E Cadherin ◽  
Cell Cell

In the Madin-Darby canine kidney epithelial cell line, the proteins occludin and ZO-1 are structural components of the tight junctions that seal the paracellular spaces between the cells and contribute to the epithelial barrier function. In Ras-transformed Madin-Darby canine kidney cells, occludin, claudin-1, and ZO-1 were absent from cell–cell contacts but were present in the cytoplasm, and the adherens junction protein E-cadherin was weakly expressed. After treatment of the Ras-transformed cells with the mitogen-activated protein kinase kinase (MEK1) inhibitor PD98059, which blocks the activation of mitogen-activated protein kinase (MAPK), occludin, claudin-1, and ZO-1 were recruited to the cell membrane, tight junctions were assembled, and E-cadherin protein expression was induced. Although it is generally believed that E-cadherin–mediated cell–cell adhesion is required for tight junction assembly, the recruitment of occludin to the cell–cell contact area and the restoration of epithelial cell morphology preceded the appearance of E-cadherin at cell–cell contacts. Both electron microscopy and a fourfold increase in the transepithelial electrical resistance indicated the formation of functional tight junctions after MEK1 inhibition. Moreover, inhibition of MAPK activity stabilized occludin and ZO-1 by differentially increasing their half-lives. We also found that during the process of tight junction assembly after MEK1 inhibition, tyrosine phosphorylation of occludin and ZO-1, but not claudin-1, increased significantly. Our study demonstrates that down-regulation of the MAPK signaling pathway causes the restoration of epithelial cell morphology and the assembly of tight junctions in Ras-transformed epithelial cells and that tyrosine phosphorylation of occludin and ZO-1 may play a role in some aspects of tight junction formation.

scholarly journals A systematic screen for morphological abnormalities during fission yeast sexual reproduction identifies a mechanism of actin aster formation for cell fusion

2017 ◽  
Author(s):  
Omaya Dudin ◽  
Laura Merlini ◽  
Felipe Bendezú ◽  
Raphaël Groux ◽  
Vincent Vincenzetti ◽  
...  
Keyword(s):  
Sexual Reproduction ◽  
Fission Yeast ◽  
Cell Fusion ◽  
Coiled Coil ◽  
Actin Binding ◽  
Cell Contact ◽  
Myosin V ◽  
Morphological Abnormalities ◽  
Pheromone Signaling ◽  
Fusion Site

AbstractIn non-motile fungi, sexual reproduction relies on stron morphogenetic changes in response to pheromone signaling. We report here on asystematic screen for morphological abnormalities o the mating process in fission yeast Schizosaccharomyces pombe. We derived a homothallic (self-fertile) collection of viable deletions which, upon visual screening, revealed a plethora of phenotype affecting all stages of the mating process, including cell polarizati cell fusion and sporulation. Cell fusion relies onthe formation of the fusion focus, an aster-like F-actin structure that is marked by stron local accumulation of the myosin V Myo52, which concentrates secretion at the fusion site. A secondaryscreen for fusion-defective mutants identified the myosin V Myo51-associated coiled-coil proteins Rng8 and Rng9 as critical forthe coalescence of the fusion focus Indeed, rng8∆ and rng9∆ mutant cells exhibitmultiple stable dots a the cell-cell contact site, instead of the single cusfo observed in wildtype. Rng8 and Rng9 accumulate on the fusion focus, depende on Myo51 and tropomyosin Cdc8A. tropomyosin mutant allele, whic compromises Rng8/9 localization but not actin binding, similarly lea to multiple stable dots instead of a single focus.By contrast, myo51 deletion does not strongly affect fusion focus coalescenceWe. propose that focusing of the actinfilaments in the fusionaster primarily relies on Rng8/9-dependent cross-linking of tropomyosin-actin filaments.

scholarly journals Osmotic Balance Regulates Cell Fusion during Mating in Saccharomyces cerevisiae

1997 ◽  
Vol 138 (5) ◽  
pp. 961-974 ◽  
Author(s):  
Jennifer Philips ◽  
Ira Herskowitz
Keyword(s):  
Cell Wall ◽  
Cell Fusion ◽  
Cell Contact ◽  
Fusion Event ◽  
Glycerol Facilitator ◽  
Fusion Defect ◽  
Osmotic Balance ◽  
Glycerol 3 Phosphate Dehydrogenase ◽  
Gpd1 Gene ◽  
Cell Cell

Successful zygote formation during yeast mating requires cell fusion of the two haploid mating partners. To ensure that cells do not lyse as they remodel their cell wall, the fusion event is both temporally and spatially regulated: the cell wall is degraded only after cell–cell contact and only in the region of cell–cell contact. To understand how cell fusion is regulated, we identified mutants defective in cell fusion based upon their defect in mating to a fus1 fus2 strain (Chenevert, J., N. Valtz, and I. Herskowitz. 1994. Genetics 136:1287–1297). Two of these cell fusion mutants are defective in the FPS1 gene, which codes for a glycerol facilitator (Luyten, K., J. Albertyn, W.F. Skibbe, B.A. Prior, J. Ramos, J.M. Thevelein, and S. Hohmann. 1995. EMBO [Eur. Mol. Biol. Organ.] J. 14:1360–1371). To determine whether inability to maintain osmotic balance accounts for the defect in cell fusion in these mutants, we analyzed the behavior of an fps1Δ mutant with reduced intracellular glycerol levels because of a defect in the glycerol-3-phosphate dehydrogenase (GPD1) gene (Albertyn, J., S. Hohmann, J.M. Thevelein, and B.A. Prior. 1994. Mol. Cell. Biol. 14:4135– 4144): deletion of GPD1 partially suppressed the cell fusion defect of fps1 mutants. In contrast, overexpression of GPD1 exacerbated the defect. The fusion defect could also be partially suppressed by 1 M sorbitol. These observations indicate that the fusion defect of fps1 mutants results from inability to regulate osmotic balance and provide evidence that the osmotic state of the cell can regulate fusion. We have also observed that mutants expressing hyperactive protein kinase C exhibit a cell fusion defect similar to that of fps1 mutants. We propose that Pkc1p regulates cell fusion in response to osmotic disequilibrium. Unlike fps1 mutants, fus1 and fus2 mutants are not influenced by expression of GPD1 or by 1 M sorbitol. Their fusion defect is thus unlikely to result from altered osmotic balance.

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