scholarly journals Positive feedback between Cdc42 activity and H+ efflux by the Na-H exchanger NHE1 for polarity of migrating cells

2007 ◽  
Vol 179 (3) ◽  
pp. 403-410 ◽  
Author(s):  
Christian Frantz ◽  
Anastasios Karydis ◽  
Perihan Nalbant ◽  
Klaus M. Hahn ◽  
Diane L. Barber
Keyword(s):  
Cell Polarity ◽  
Positive Feedback ◽  
Eukaryotic Cell ◽  
Feedback Signal ◽  
Nucleotide Exchange ◽  
Spatial Cues ◽  
Membrane Recruitment ◽  
Nucleotide Exchange Factor ◽  
Guanosine Triphosphatase ◽  
Migrating Cells

A fundamental feature of cell polarity in response to spatial cues is asymmetric amplification of molecules generated by positive feedback signaling. We report a positive feedback loop between the guanosine triphosphatase Cdc42, a central determinant in eukaryotic cell polarity, and H+ efflux by Na-H+ exchanger 1 (NHE1), which is necessary at the front of migrating cells for polarity and directional motility. In response to migratory cues, Cdc42 is not activated in fibroblasts expressing a mutant NHE1 that lacks H+ efflux, and wild-type NHE1 is not activated in fibroblasts expressing mutationally inactive Cdc42-N17. H+ efflux by NHE1 is not necessary for release of Cdc42–guanosine diphosphate (GDP) from Rho GDP dissociation inhibitor or for the membrane recruitment of Cdc42 but is required for GTP binding by Cdc42 catalyzed by a guanine nucleotide exchange factor (GEF). Data indicate that GEF binding to phosphotidylinositol 4,5–bisphosphate is pH dependent, suggesting a mechanism for how H+ efflux by NHE1 promotes Cdc42 activity to generate a positive feedback signal necessary for polarity in migrating cells.

scholarly journals Activation of Cdc42 GTPase upon CRY2-Induced Cortical Recruitment Is Antagonized by GAPs in Fission Yeast

Cells ◽  
2020 ◽  
Vol 9 (9) ◽  
pp. 2089 ◽  
Author(s):  
Iker Lamas ◽  
Nathalie Weber ◽  
Sophie G. Martin
Keyword(s):  
Fission Yeast ◽  
Positive Feedback ◽  
Antagonistic Activity ◽  
Cell Polarization ◽  
Small Gtpase ◽  
Nucleotide Exchange ◽  
Gtpase Activating Protein ◽  
Guanine Nucleotide Exchange ◽  
Nucleotide Exchange Factor ◽  
Cell Architecture

The small GTPase Cdc42 is critical for cell polarization in eukaryotic cells. In rod-shaped fission yeast Schizosaccharomyces pombe cells, active GTP-bound Cdc42 promotes polarized growth at cell poles, while inactive Cdc42-GDP localizes ubiquitously also along cell sides. Zones of Cdc42 activity are maintained by positive feedback amplification involving the formation of a complex between Cdc42-GTP, the scaffold Scd2, and the guanine nucleotide exchange factor (GEF) Scd1, which promotes the activation of more Cdc42. Here, we use the CRY2-CIB1 optogenetic system to recruit and cluster a cytosolic Cdc42 variant at the plasma membrane and show that this leads to its moderate activation also on cell sides. Surprisingly, Scd2, which binds Cdc42-GTP, is still recruited to CRY2-Cdc42 clusters at cell sides in individual deletion of the GEFs Scd1 or Gef1. We show that activated Cdc42 clusters at cell sides are able to recruit Scd1, dependent on the scaffold Scd2. However, Cdc42 activity is not amplified by positive feedback and does not lead to morphogenetic changes, due to antagonistic activity of the GTPase activating protein Rga4. Thus, the cell architecture is robust to moderate activation of Cdc42 at cell sides.

scholarly journals Concentration of Sec12 at ER exit sites via interaction with cTAGE5 is required for collagen export

2014 ◽  
Vol 206 (6) ◽  
pp. 751-762 ◽  
Author(s):  
Kota Saito ◽  
Koh Yamashiro ◽  
Noriko Shimazu ◽  
Tomoya Tanabe ◽  
Kenji Kontani ◽  
...  
Keyword(s):  
Direct Interaction ◽  
Secretory Proteins ◽  
Nucleotide Exchange ◽  
Guanine Nucleotide Exchange ◽  
Transport Vesicles ◽  
Nucleotide Exchange Factor ◽  
Receptor Component ◽  
Er Exit Sites ◽  
Guanosine Triphosphatase ◽  
Trimeric Structure

Mechanisms for exporting variably sized cargo from the endoplasmic reticulum (ER) using the same machinery remain poorly understood. COPII-coated vesicles, which transport secretory proteins from the ER to the Golgi apparatus, are typically 60–90 nm in diameter. However, collagen, which forms a trimeric structure that is too large to be accommodated by conventional transport vesicles, is also known to be secreted via a COPII-dependent process. In this paper, we show that Sec12, a guanine-nucleotide exchange factor for Sar1 guanosine triphosphatase, is concentrated at ER exit sites and that this concentration of Sec12 is specifically required for the secretion of collagen VII but not other proteins. Furthermore, Sec12 recruitment to ER exit sites is organized by its direct interaction with cTAGE5, a previously characterized collagen cargo receptor component, which functions together with TANGO1 at ER exit sites. These findings suggest that the export of large cargo requires high levels of guanosine triphosphate–bound Sar1 generated by Sec12 localized at ER exit sites.

scholarly journals Linking Ras to myosin function: RasGEF Q, a Dictyostelium exchange factor for RasB, affects myosin II functions

2008 ◽  
Vol 181 (5) ◽  
pp. 747-760 ◽  
Author(s):  
Subhanjan Mondal ◽  
Deenadayalan Bakthavatsalam ◽  
Paul Steimle ◽  
Berthold Gassen ◽  
Francisco Rivero ◽  
...  
Keyword(s):  
Cell Polarity ◽  
Cell Sorting ◽  
Myosin Ii ◽  
Guanine Nucleotide ◽  
Nucleotide Exchange ◽  
Exchange Factor ◽  
Guanine Nucleotide Exchange ◽  
Nucleotide Exchange Factor ◽  
Myosin Heavy Chain Kinase ◽  
Null Mutants

Ras guanine nucleotide exchange factor (GEF) Q, a nucleotide exchange factor from Dictyostelium discoideum, is a 143-kD protein containing RasGEF domains and a DEP domain. We show that RasGEF Q can bind to F-actin, has the potential to form complexes with myosin heavy chain kinase (MHCK) A that contain active RasB, and is the predominant exchange factor for RasB. Overexpression of the RasGEF Q GEF domain activates RasB, causes enhanced recruitment of MHCK A to the cortex, and leads to cytokinesis defects in suspension, phenocopying cells expressing constitutively active RasB, and myosin-null mutants. RasGEF Q− mutants have defects in cell sorting and slug migration during later stages of development, in addition to cell polarity defects. Furthermore, RasGEF Q− mutants have increased levels of unphosphorylated myosin II, resulting in myosin II overassembly. Collectively, our results suggest that starvation signals through RasGEF Q to activate RasB, which then regulates processes requiring myosin II.

scholarly journals Induction of cell retraction by the combined actions of Abl–CrkII and Rho–ROCK1 signaling

2008 ◽  
Vol 183 (4) ◽  
pp. 711-723 ◽  
Author(s):  
XiaoDong Huang ◽  
Diana Wu ◽  
Hua Jin ◽  
Dwayne Stupack ◽  
Jean Y.J. Wang
Keyword(s):  
Nucleotide Exchange ◽  
Downstream Target ◽  
Abl Tyrosine Kinase ◽  
Guanine Nucleotide Exchange ◽  
Cell Matrix ◽  
Nucleotide Exchange Factor ◽  
Wide Range ◽  
Important Regulator ◽  
Guanosine Triphosphatase ◽  
Cell Retraction

Dynamic modulation of cell adhesion is integral to a wide range of biological processes. The small guanosine triphosphatase (GTPase) Rap1 is an important regulator of cell–cell and cell–matrix adhesions. We show here that induced expression of activated Abl tyrosine kinase reduces Rap1-GTP levels through phosphorylation of Tyr221 of CrkII, which disrupts interaction of CrkII with C3G, a guanine nucleotide exchange factor for Rap1. Abl-dependent down-regulation of Rap1-GTP causes cell rounding and detachment only when the Rho–ROCK1 pathway is also activated, for example, by lysophosphatidic acid (LPA). During ephrin-A1–induced retraction of PC3 prostate cancer cells, we show that endogenous Abl is activated and disrupts the CrkII–C3G complex to reduce Rap1-GTP. Interestingly, ephrin-A1–induced PC3 cell retraction also requires LPA, which stimulates Rho to a much higher level than that is activated by ephrin-A1. Our results establish Rap1 as another downstream target of the Abl–CrkII signaling module and show that Abl–CrkII collaborates with Rho–ROCK1 to stimulate cell retraction.

scholarly journals Lte1 contributes to Bfa1 localization rather than stimulating nucleotide exchange by Tem1

2009 ◽  
Vol 187 (4) ◽  
pp. 497-511 ◽  
Author(s):  
Marco Geymonat ◽  
Adonis Spanos ◽  
Geoffroy de Bettignies ◽  
Steven G. Sedgwick
Keyword(s):  
Mutational Analysis ◽  
Spindle Pole ◽  
Cell Polarization ◽  
Nucleotide Exchange ◽  
Nucleotide Exchange Factor ◽  
Spindle Pole Bodies ◽  
Guanosine Triphosphatase ◽  
Spindle Position ◽  
Mitotic Regulation

Lte1 is a mitotic regulator long envisaged as a guanosine nucleotide exchange factor (GEF) for Tem1, the small guanosine triphosphatase governing activity of the Saccharomyces cerevisiae mitotic exit network. We demonstrate that this model requires reevaluation. No GEF activity was detectable in vitro, and mutational analysis of Lte1’s putative GEF domain indicated that Lte1 activity relies on interaction with Ras for localization at the bud cortex rather than providing nucleotide exchange. Instead, we found that Lte1 can determine the subcellular localization of Bfa1 at spindle pole bodies (SPBs). Under conditions in which Lte1 is essential, Lte1 promoted the loss of Bfa1 from the maternal SPB. Moreover, in cells with a misaligned spindle, mislocalization of Lte1 in the mother cell promoted loss of Bfa1 from one SPB and allowed bypass of the spindle position checkpoint. We observed that lte1 mutants display aberrant localization of the polarity cap, which is the organizer of the actin cytoskeleton. We propose that Lte1’s role in cell polarization underlies its contribution to mitotic regulation.

scholarly journals Oxidized LDL/CD36 interaction induces loss of cell polarity and inhibits macrophage locomotion

2012 ◽  
Vol 23 (16) ◽  
pp. 3057-3068 ◽  
Author(s):  
Young Mi Park ◽  
Judith A. Drazba ◽  
Amit Vasanji ◽  
Thomas Egelhoff ◽  
Maria Febbraio ◽  
...  
Keyword(s):  
Cell Polarity ◽  
Oxidized Ldl ◽  
Oxidant Stress ◽  
Low Density Lipoprotein ◽  
Myosin Ii ◽  
Density Lipoprotein ◽  
Cell Polarization ◽  
Nucleotide Exchange ◽  
Intracellular Signals ◽  
Nucleotide Exchange Factor

Cell polarization is essential for migration and the exploratory function of leukocytes. However, the mechanism by which cells maintain polarity or how cells revert to the immobilized state by gaining cellular symmetry is not clear. Previously we showed that interaction between oxidized low-density lipoprotein (oxLDL) and CD36 inhibits macrophage migration; in the current study we tested the hypothesis that oxLDL/CD36-induced inhibition of migration is the result of intracellular signals that regulate cell polarity. Live cell imaging of macrophages showed that oxLDL actuated retraction of macrophage front end lamellipodia and induced loss of cell polarity. Cd36 null and macrophages null for Vav, a guanine nucleotide exchange factor (GEF), did not show this effect. These findings were caused by Rac-mediated inhibition of nonmuscle myosin II, a cell polarity determinant. OxLDL induced dephosphorylation of myosin regulatory light chain (MRLC) by increasing the activity of Rac. Six-thioguanine triphosphate (6-thio-GTP), which inhibits Vav-mediated activation of Rac, abrogated the effect of oxLDL. Activation of the Vav-Rac-myosin II pathway by oxidant stress may induce trapping of macrophages at sites of chronic inflammation such as atherosclerotic plaque.

The cAMP Sensor Epac2 Is a Direct Target of Antidiabetic Sulfonylurea Drugs

Science ◽  
2009 ◽  
Vol 325 (5940) ◽  
pp. 607-610 ◽  
Author(s):  
Chang-Liang Zhang ◽  
Megumi Katoh ◽  
Tadao Shibasaki ◽  
Kohtaro Minami ◽  
Yasuhiro Sunaga ◽  
...  
Keyword(s):  
Insulin Secretion ◽  
Resonance Energy Transfer ◽  
Resonance Energy ◽  
Gut Hormones ◽  
Nucleotide Exchange ◽  
Nucleotide Exchange Factor ◽  
Promising Target ◽  
Guanosine Triphosphatase

Epac2, a guanine nucleotide exchange factor for the small guanosine triphosphatase Rap1, is activated by adenosine 3′,5′-monophosphate. Fluorescence resonance energy transfer and binding experiments revealed that sulfonylureas, widely used antidiabetic drugs, interact directly with Epac2. Sulfonylureas activated Rap1 specifically through Epac2. Sulfonylurea-stimulated insulin secretion was reduced both in vitro and in vivo in mice lacking Epac2, and the glucose-lowering effect of the sulfonylurea tolbutamide was decreased in these mice. Epac2 thus contributes to the effect of sulfonylureas to promote insulin secretion. Because Epac2 is also required for the action of incretins, gut hormones crucial for potentiating insulin secretion, it may be a promising target for antidiabetic drug development.

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