scholarly journals Checkpoint control of mitotic exit—do budding yeast mind the GAP?

2006 ◽  
Vol 172 (3) ◽  
pp. 331-333 ◽  
Author(s):  
John A. Cooper ◽  
Scott A. Nelson
Keyword(s):  
Budding Yeast ◽  
Spindle Pole ◽  
Small Gtpase ◽  
Mitotic Exit ◽  
Cell Cycle Checkpoints ◽  
Nucleotide Exchange ◽  
Checkpoint Control ◽  
Guanine Nucleotide Exchange ◽  
Nucleotide Exchange Factor ◽  
Spindle Pole Bodies

Cell cycle checkpoints can delay mitotic exit in budding yeast. The master controller is the small GTPase Tem1, with inputs from a proposed guanine nucleotide exchange factor (GEF), Lte1, and a GTPase-activating protein (GAP), Bub2/Bfa1. In this issue, Fraschini et al. (p. 335) show that GAP activity of Bub2/Bfa1 appears to be dispensable for inactivation of Tem1 in cells. Their results call into question the GTP/GDP switch model for Tem1 activity, as have other results in the past. The paper also focuses attention on the two spindle pole bodies as potential sites for regulation of Tem1.

scholarly journals Different Levels of Bfa1/Bub2 GAP Activity Are Required to Prevent Mitotic Exit of Budding Yeast Depending on the Type of Perturbations

2008 ◽  
Vol 19 (10) ◽  
pp. 4328-4340 ◽  
Author(s):  
Junwon Kim ◽  
Selma Sun Jang ◽  
Kiwon Song
Keyword(s):  
Budding Yeast ◽  
Mitotic Exit ◽  
Nucleotide Exchange ◽  
Guanine Nucleotide Exchange ◽  
Nucleotide Exchange Factor ◽  
Surveillance Mechanism ◽  
Spindle Position ◽  
First Time ◽  
Different Levels

In budding yeast, Tem1 is a key regulator of mitotic exit. Bfa1/Bub2 stimulates Tem1 GTPase activity as a GTPase-activating protein (GAP). Lte1 possesses a guanine-nucleotide exchange factor (GEF) domain likely for Tem1. However, recent observations showed that cells may control mitotic exit without either Lte1 or Bfa1/Bub2 GAP activity, obscuring how Tem1 is regulated. Here, we assayed BFA1 mutants with varying GAP activities for Tem1, showing for the first time that Bfa1/Bub2 GAP activity inhibits Tem1 in vivo. A decrease in GAP activity allowed cells to bypass mitotic exit defects. Interestingly, different levels of GAP activity were required to prevent mitotic exit depending on the type of perturbation. Although essential, more Bfa1/Bub2 GAP activity was needed for spindle damage than for DNA damage to fully activate the checkpoint. Conversely, Bfa1/Bub2 GAP activity was insufficient to delay mitotic exit in cells with misoriented spindles. Instead, decreased interaction of Bfa1 with Kin4 was observed in BFA1 mutant cells with a defective spindle position checkpoint. These findings demonstrate that there is a GAP-independent surveillance mechanism of Bfa1/Bub2, which, together with the GTP/GDP switch of Tem1, may be required for the genomic stability of cells with misaligned spindles.

scholarly journals Ras recruits mitotic exit regulator Lte1 to the bud cortex in budding yeast

2003 ◽  
Vol 161 (5) ◽  
pp. 889-897 ◽  
Author(s):  
Satoshi Yoshida ◽  
Ryuji Ichihashi ◽  
Akio Toh-e
Keyword(s):  
Small Gtpase ◽  
Mitotic Exit ◽  
Effector Protein ◽  
Nucleotide Exchange ◽  
Guanine Nucleotide Exchange ◽  
Downstream Effector ◽  
Nucleotide Exchange Factor ◽  
Family Protein

ACdc25 family protein Lte1 (low temperature essential) is essential for mitotic exit at a lowered temperature and has been presumed to be a guanine nucleotide exchange factor (GEF) for a small GTPase Tem1, which is a key regulator of mitotic exit. We found that Lte1 physically associates with Ras2-GTP both in vivo and in vitro and that the Cdc25 homology domain (CHD) of Lte1 is essential for the interaction with Ras2. Furthermore, we found that the proper localization of Lte1 to the bud cortex is dependent on active Ras and that the overexpression of a derivative of Lte1 without the CHD suppresses defects in mitotic exit of a Δlte1 mutant and a Δras1 Δras2 mutant. These results suggest that Lte1 is a downstream effector protein of Ras in mitotic exit and that the Ras GEF domain of Lte1 is not essential for mitotic exit but required for its localization.

scholarly journals Fission Yeast Ras1 Effector Scd1 Interacts With the Spindle and Affects Its Proper Formation

Genetics ◽  
2000 ◽  
Vol 156 (3) ◽  
pp. 995-1004
Author(s):  
Ying-chun Li ◽  
Chang-rung Chen ◽  
Eric C Chang
Keyword(s):  
Chromosome Segregation ◽  
Spindle Pole ◽  
Nucleotide Exchange ◽  
Spindle Formation ◽  
Guanine Nucleotide Exchange ◽  
Nucleotide Exchange Factor ◽  
Spindle Pole Bodies ◽  
Synthetically Lethal ◽  
Tubulin Mutations ◽  
Localization Data

Abstract Ras1 GTPase is the Schizosaccharomyces pombe homolog of the mammalian Ha-Ras proto-oncoprotein. Ras1 interacts with Scd1 (aka Ral1), a presumptive guanine nucleotide exchange factor for Cdc42sp, to control organization of the cytoskeleton. In this study, we demonstrated that the scd1 deletion (scd1Δ) induced hypersensitivity to microtubule destabilizing drugs and instability of the minichromosome. Overexpression of scd1 induced formation of abnormal spindles and chromosome missegregation. The scd1 deletion worsened the defects of spindle formation in tubulin mutants; by contrast, it did not induce lethality in mutants defective in the spindle pole bodies. These genetic data suggest that Scd1 can interact with tubulin with substantial specificity to affect proper spindle formation and chromosome segregation. Subcellular localization data further illustrated that a GFP-Scd1 fusion protein can associate with the spindle. Finally, we showed that unlike ras1Δ and scd1Δ, byr2Δ (affecting the Ras1 effector for mating) is not synthetically lethal with the tubulin mutations. These data collectively suggest that the Ras1 pathway can impinge upon microtubules through Scd1, but not Byr2, to affect proper spindle formation and chromosome segregation.

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 Myoblast Migration and Directional Persistence Affected by Syndecan-4-Mediated Tiam-1 Expression and Distribution

2020 ◽  
Vol 21 (3) ◽  
pp. 823 ◽  
Author(s):  
Daniel Becsky ◽  
Szuzina Gyulai-Nagy ◽  
Arpad Balind ◽  
Peter Horvath ◽  
Laszlo Dux ◽  
...  
Keyword(s):  
Skeletal Muscle ◽  
Underlying Mechanism ◽  
Small Gtpase ◽  
Asymmetric Distribution ◽  
Nucleotide Exchange ◽  
Muscle Stem Cells ◽  
Guanine Nucleotide Exchange ◽  
Nucleotide Exchange Factor ◽  
T Lymphoma ◽  
Migration Capacity

Skeletal muscle is constantly renewed in response to injury, exercise, or muscle diseases. Muscle stem cells, also known as satellite cells, are stimulated by local damage to proliferate extensively and form myoblasts that then migrate, differentiate, and fuse to form muscle fibers. The transmembrane heparan sulfate proteoglycan syndecan-4 plays multiple roles in signal transduction processes, such as regulating the activity of the small GTPase Rac1 (Ras-related C3 botulinum toxin substrate 1) by binding and inhibiting the activity of Tiam1 (T-lymphoma invasion and metastasis-1), a guanine nucleotide exchange factor for Rac1. The Rac1-mediated actin remodeling is required for cell migration. Syndecan-4 knockout mice cannot regenerate injured muscle; however, the detailed underlying mechanism is unknown. Here, we demonstrate that shRNA-mediated knockdown of syndecan-4 decreases the random migration of mouse myoblasts during live-cell microscopy. Treatment with the Rac1 inhibitor NSC23766 did not restore the migration capacity of syndecan-4 silenced cells; in fact, it was further reduced. Syndecan-4 knockdown decreased the directional persistence of migration, abrogated the polarized, asymmetric distribution of Tiam1, and reduced the total Tiam1 level of the cells. Syndecan-4 affects myoblast migration via its role in expression and localization of Tiam1; this finding may facilitate greater understanding of the essential role of syndecan-4 in the development and regeneration of skeletal muscle.

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 A GAP that Divides

F1000Research ◽  
2017 ◽  
Vol 6 ◽  
pp. 1788 ◽  
Author(s):  
Angika Basant ◽  
Michael Glotzer
Keyword(s):  
Small Gtpase ◽  
Nucleotide Exchange ◽  
Contractile Ring ◽  
C Elegans ◽  
Rhoa Activation ◽  
Guanine Nucleotide Exchange ◽  
Nucleotide Exchange Factor ◽  
Parallel Pathway ◽  
Mutant Phenotypes

Cytokinesis in metazoan cells is mediated by an actomyosin-based contractile ring that assembles in response to activation of the small GTPase RhoA. The guanine nucleotide exchange factor that activates RhoA during cytokinesis, ECT-2, is highly regulated. In most metazoan cells, with the notable exception of the early Caenorhabditis elegans embryo, RhoA activation and furrow ingression require the centralspindlin complex. This exception is due to the existence of a parallel pathway for RhoA activation in C. elegans. Centralspindlin contains CYK-4 which contains a predicted Rho family GTPase-activating protein (GAP) domain. The function of this domain has been the subject of considerable debate. Some publications suggest that the GAP domain promotes RhoA activation (for example, Zhang and Glotzer, 2015; Loria, Longhini and Glotzer, 2012), whereas others suggest that it functions to inactivate the GTPase Rac1 (for example, Zhuravlev et al., 2017). Here, we review the mechanisms underlying RhoA activation during cytokinesis, primarily focusing on data in C. elegans. We highlight the importance of considering the parallel pathway for RhoA activation and detailed analyses of cyk-4 mutant phenotypes when evaluating the role of the GAP domain of CYK-4.

scholarly journals cTAGE5 acts as a Sar1 GTPase regulator for collagen export

2018 ◽  
Author(s):  
Norito Sasaki ◽  
Masano Shiraiwa ◽  
Miharu Maeda ◽  
Tomohiro Yorimitsu ◽  
Ken Sato ◽  
...  
Keyword(s):  
Small Gtpase ◽  
Coated Vesicles ◽  
Secretory Proteins ◽  
Efficient Production ◽  
Nucleotide Exchange ◽  
Gtpase Activating Protein ◽  
Guanine Nucleotide Exchange ◽  
Collagen Secretion ◽  
Nucleotide Exchange Factor ◽  
Er Exit Sites

AbstractSecretory proteins synthesized within the endoplasmic reticulum (ER) are exported via coat protein complex II (COPII)-coated vesicles. The formation of the COPII-coated vesicles is initiated by activation of the small GTPase, Sar1. cTAGE5 directly interacts with a guanine-nucleotide exchange factor (GEF), Sec12, and a GTPase-activating protein (GAP) of Sar1, Sec23. We have previously shown that cTAGE5 recruits Sec12 to the ER exit sites for efficient production of activated Sar1 for collagen secretion. However, the functional significance of the interaction between cTAGE5 and Sec23 has not been fully elucidated. In this study, we showed that cTAGE5 enhances the GAP activity of Sec23 toward Sar1. In addition, the interaction of cTAGE5 with Sec23 is necessary for collagen exit from the ER. Our data suggests that cTAGE5 acts as a Sar1 GTPase regulator for collagen secretion.

scholarly journals Amino acids stimulate the endosome-to-Golgi trafficking through Ragulator and small GTPase Arl5

2018 ◽  
Author(s):  
Meng Shi ◽  
Bing Chen ◽  
Boon Kim Boh ◽  
Yan Zhou ◽  
Divyanshu Mahajan ◽  
...  
Keyword(s):  
Amino Acids ◽  
Small Gtpase ◽  
Guanine Nucleotide ◽  
Nucleotide Exchange ◽  
Retrograde Trafficking ◽  
Guanine Nucleotide Exchange ◽  
Trafficking Pathway ◽  
Nucleotide Exchange Factor ◽  
Mtorc1 Signaling ◽  
Nutrient Signaling

AbstractThe endosome-to-Golgi or endocytic retrograde trafficking pathway is an important post-Golgi recycling route. We made a novel discovery that the retrograde trafficking of cargos is inhibited and stimulated by the absence and presence, respectively, of amino acids (AAs), especially glutamine. By testing components of the AA-stimulated mTORC1 signaling pathway, we demonstrated that SLC38A9, v-ATPase and Ragulator, but not Rag GTPases and mTORC1, are essential for the AA-stimulated trafficking. Arl5, an ARF-like family small GTPase, interacts with Ragulator in an AA-regulated manner and both Arl5 and its effector, the Golgi-associated retrograde protein complex (GARP), are required for the AA-stimulated trafficking. We have therefore identified a mechanistic connection between the nutrient signaling and the retrograde trafficking pathway, whereby SLC38A9 and v-ATPase sense AA-sufficiency and Ragulator functions as a guanine nucleotide exchange factor to activate Arl5, which, together with GARP, a tethering factor, probably facilitates the endosome-to-Golgi trafficking.

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