scholarly journals Rufy3 is an adapter protein for small GTPases that activates a Rac guanine nucleotide exchange factor to control neuronal polarity

2017 ◽  
Vol 292 (51) ◽  
pp. 20936-20946 ◽  
Author(s):  
Atsuko Honda ◽  
Hiroshi Usui ◽  
Kenji Sakimura ◽  
Michihiro Igarashi
Keyword(s):  
Guanine Nucleotide Exchange Factor ◽  
Small Gtpases ◽  
Neuronal Polarity ◽  
Guanine Nucleotide ◽  
Adapter Protein ◽  
Nucleotide Exchange ◽  
Exchange Factor ◽  
Guanine Nucleotide Exchange ◽  
Nucleotide Exchange Factor

scholarly journals The DHR1 Domain of DOCK180 Binds to SNX5 and Regulates Cation-independent Mannose 6-phosphate Receptor Transport

2008 ◽  
Vol 19 (9) ◽  
pp. 3823-3835 ◽  
Author(s):  
Shigeo Hara ◽  
Etsuko Kiyokawa ◽  
Shun-ichiro Iemura ◽  
Tohru Natsume ◽  
Thomas Wassmer ◽  
...  
Keyword(s):  
Guanine Nucleotide Exchange Factor ◽  
Retrograde Transport ◽  
Small Gtpases ◽  
Guanine Nucleotide ◽  
Nucleotide Exchange ◽  
Sorting Nexins ◽  
Exchange Factor ◽  
Guanine Nucleotide Exchange ◽  
Nucleotide Exchange Factor ◽  
Mannose 6 Phosphate

DOCK180 is the archetype of the DOCK180-family guanine nucleotide exchange factor for small GTPases Rac1 and Cdc42. DOCK180-family proteins share two conserved domains, called DOCK homology region (DHR)-1 and -2. Although the function of DHR2 is to activate Rac1, DHR1 is required for binding to phosphoinositides. To better understand the function of DHR1, we searched for its binding partners by direct nanoflow liquid chromatography/tandem mass spectrometry, and we identified sorting nexins (SNX) 1, 2, 5, and 6, which make up a multimeric protein complex mediating endosome-to-trans-Golgi-network (TGN) retrograde transport of the cation-independent mannose 6-phosphate receptor (CI-MPR). Among these SNX proteins, SNX5 was coimmunoprecipitated with DOCK180 most efficiently. In agreement with this observation, DOCK180 colocalized with SNX5 at endosomes. The RNA interference-mediated knockdowns of SNX5 and DOCK180, but not Rac1, resulted in the redistribution of CI-MPR from TGN to endosomes. Furthermore, expression of the DOCK180 DHR1 domain was sufficient to restore the perturbed CI-MPR distribution in DOCK180 knockdown cells. These data suggest that DOCK180 regulates CI-MPR trafficking via SNX5 and that this function is independent of its guanine nucleotide exchange factor activity toward Rac1.

scholarly journals The Guanine Nucleotide Exchange Factor Tiam1 Affects Neuronal Morphology; Opposing Roles for the Small GTPases Rac and Rho

1997 ◽  
Vol 139 (3) ◽  
pp. 797-807 ◽  
Author(s):  
Frank N. van Leeuwen ◽  
Hendrie E.T. Kain ◽  
Rob A. van der Kammen ◽  
Frits Michiels ◽  
Onno W. Kranenburg ◽  
...  
Keyword(s):  
Guanine Nucleotide Exchange Factor ◽  
Small Gtpases ◽  
Neuronal Morphology ◽  
Laminin Receptor ◽  
Guanine Nucleotide ◽  
Nucleotide Exchange ◽  
Exchange Factor ◽  
Guanine Nucleotide Exchange ◽  
Nucleotide Exchange Factor ◽  
Neurite Formation

The invasion-inducing T-lymphoma invasion and metastasis 1 (Tiam1) protein functions as a guanine nucleotide exchange factor (GEF) for the small GTPase Rac1. Differentiation-dependent expression of Tiam1 in the developing brain suggests a role for this GEF and its effector Rac1 in the control of neuronal morphology. Here we show that overexpression of Tiam1 induces cell spreading and affects neurite outgrowth in N1E-115 neuroblastoma cells. These effects are Rac-dependent and strongly promoted by laminin. Overexpression of Tiam1 recruits the α6β1 integrin, a laminin receptor, to specific adhesive contacts at the cell periphery, which are different from focal contacts. Cells overexpressing Tiam1 no longer respond to lysophosphatidic acid– induced neurite retraction and cell rounding, processes mediated by Rho, suggesting that Tiam1-induced activation of Rac antagonizes Rho signaling. This inhibition can be overcome by coexpression of constitutively active RhoA, which may indicate that regulation occurs at the level of Rho or upstream. Conversely, neurite formation induced by Tiam1 or Rac1 is further promoted by inactivating Rho. These results demonstrate that Rac- and Rho-mediated pathways oppose each other during neurite formation and that a balance between these pathways determines neuronal morphology. Furthermore, our data underscore the potential role of Tiam1 as a specific regulator of Rac during neurite formation and illustrate the importance of reciprocal interactions between the cytoskeleton and the extracellular matrix during this process.

Human p63RhoGEF, a novel RhoA-specific guanine nucleotide exchange factor, is localized in cardiac sarcomere

2002 ◽  
Vol 115 (3) ◽  
pp. 629-640 ◽  
Author(s):  
Michel Souchet ◽  
Elodie Portales-Casamar ◽  
David Mazurais ◽  
Susanne Schmidt ◽  
Isabelle Léger ◽  
...  
Keyword(s):  
Guanine Nucleotide Exchange Factor ◽  
Small Gtpases ◽  
Fiber Formation ◽  
Pleckstrin Homology Domain ◽  
Guanine Nucleotide ◽  
Nucleotide Exchange ◽  
Intact Cells ◽  
Exchange Factor ◽  
Guanine Nucleotide Exchange ◽  
Nucleotide Exchange Factor

The Rho small GTPases are crucial proteins involved in regulation of signal transduction cascades from extracellular stimuli to cell nucleus and cytoskeleton. It has been reported that these GTPases are directly associated with cardiovascular disorders. In this context, we have searched for novel modulators of Rho GTPases, and here we describe p63RhoGEF a new Db1-like guanine nucleotide exchange factor (GEF). P63RhoGEF encodes a 63 kDa protein containing a Db1 homology domain in tandem with a pleckstrin homology domain and is most closely related to the second Rho GEF domain of Trio. Northern blot and in situ analysis have shown that p63RhoGEF is mainly expressed in heart and brain. In vitro guanine nucleotide exchange assays have shown that p63RhoGEF specifically acts on RhoA. Accordingly, p63RhoGEF expression induces RhoA-dependent stress fiber formation in fibroblasts and in H9C2 cardiac myoblasts. Moreover, we show that p63RhoGEF activation of RhoA in intact cells is dependent on the presence of the PH domain. Using a specific anti-p63RhoGEF antibody, we have detected the p63RhoGEF protein by immunocytochemistry in human heart and brain tissue sections. Confocal microscopy shows that p63RhoGEF is located in the sarcomeric I-band mainly constituted of cardiac sarcomeric actin. Together, these results show that p63RhoGEF is a RhoA-specific GEF that may play a key role in actin cytoskeleton reorganization in different tissues, especially in heart cellular morphology.

scholarly journals ARHGEF7 (β-PIX) Is Required for the Maintenance of Podocyte Architecture and Glomerular Function

2020 ◽  
Vol 31 (5) ◽  
pp. 996-1008 ◽  
Author(s):  
Jun Matsuda ◽  
Mirela Maier ◽  
Lamine Aoudjit ◽  
Cindy Baldwin ◽  
Tomoko Takano
Keyword(s):  
Knockout Mice ◽  
Critical Role ◽  
Guanine Nucleotide Exchange Factor ◽  
Small Gtpases ◽  
Guanine Nucleotide ◽  
Nucleotide Exchange ◽  
Glomerular Function ◽  
Exchange Factor ◽  
Guanine Nucleotide Exchange ◽  
Nucleotide Exchange Factor

BackgroundPrevious studies showed that Cdc42, a member of the prototypical Rho family of small GTPases and a regulator of the actin cytoskeleton, is critical for the normal development and health of podocytes. However, upstream regulatory mechanisms for Cdc42 activity in podocytes are largely unknown.MethodsWe used a proximity-based ligation assay, BioID, to identify guanine nucleotide exchange factors that activate Cdc42 in immortalized human podocytes. We generated podocyte-specific ARHGEF7 (commonly known as β-PIX) knockout mice by crossing β-PIX floxed mice with Podocin-Cre mice. Using shRNA, we established cultured mouse podocytes with β-PIX knockdown and their controls.ResultsWe identified β-PIX as a predominant guanine nucleotide exchange factor that interacts with Cdc42 in human podocytes. Podocyte-specific β-PIX knockout mice developed progressive proteinuria and kidney failure with global or segmental glomerulosclerosis in adulthood. Glomerular podocyte density gradually decreased in podocyte-specific β-PIX knockout mice, indicating podocyte loss. Compared with controls, glomeruli from podocyte-specific β-PIX knockout mice and cultured mouse podocytes with β-PIX knockdown exhibited significant reduction in Cdc42 activity. Loss of β-PIX promoted podocyte apoptosis, which was mediated by the reduced activity of the prosurvival transcriptional regulator Yes-associated protein.ConclusionsThese findings indicate that β-PIX is required for the maintenance of podocyte architecture and glomerular function via Cdc42 and its downstream Yes-associated protein activities. This appears to be the first evidence that a Rho–guanine nucleotide exchange factor plays a critical role in podocytes.

scholarly journals Plekhg4 Is a Novel Dbl Family Guanine Nucleotide Exchange Factor Protein for Rho Family GTPases

2013 ◽  
Vol 288 (20) ◽  
pp. 14522-14530 ◽  
Author(s):  
Meghana Gupta ◽  
Elena Kamynina ◽  
Samantha Morley ◽  
Stacey Chung ◽  
Nora Muakkassa ◽  
...  
Keyword(s):  
Guanine Nucleotide Exchange Factor ◽  
Small Gtpases ◽  
Guanine Nucleotide ◽  
Nucleotide Exchange ◽  
Developmentally Regulated ◽  
Nih3t3 Cells ◽  
Exchange Factor ◽  
Guanine Nucleotide Exchange ◽  
Nucleotide Exchange Factor ◽  
Bona Fide

Mutations in the PLEKHG4 (puratrophin-1) gene are associated with the heritable neurological disorder autosomal dominant spinocerebellar ataxia. However, the biochemical functions of this gene product have not been described. We report here that expression of Plekhg4 in the murine brain is developmentally regulated, with pronounced expression in the newborn midbrain and brainstem that wanes with age and maximal expression in the cerebellar Purkinje neurons in adulthood. We show that Plekhg4 is subject to ubiquitination and proteasomal degradation, and its steady-state expression levels are regulated by the chaperones Hsc70 and Hsp90 and by the ubiquitin ligase CHIP. On the functional level, we demonstrate that Plekhg4 functions as a bona fide guanine nucleotide exchange factor (GEF) that facilitates activation of the small GTPases Rac1, Cdc42, and RhoA. Overexpression of Plekhg4 in NIH3T3 cells induces rearrangements of the actin cytoskeleton, specifically enhanced formation of lamellopodia and fillopodia. These findings indicate that Plekhg4 is an aggregation-prone member of the Dbl family GEFs and that regulation of GTPase signaling is critical for proper cerebellar function.

scholarly journals Protein Kinase A-Dependent Phosphorylation Modulates β1Pix Guanine Nucleotide Exchange Factor Activity through 14-3-3β Binding

2007 ◽  
Vol 28 (5) ◽  
pp. 1679-1687 ◽  
Author(s):  
Ahmed Chahdi ◽  
Andrey Sorokin
Keyword(s):  
Protein Kinase ◽  
Protein Kinase A ◽  
Guanine Nucleotide Exchange Factor ◽  
Small Gtpases ◽  
Guanine Nucleotide ◽  
Nucleotide Exchange ◽  
Exchange Factor ◽  
Guanine Nucleotide Exchange ◽  
Nucleotide Exchange Factor ◽  
Kinase A

ABSTRACT β1Pix is a guanine nucleotide exchange factor (GEF) for the small GTPases Rac and Cdc42 which has been shown to mediate signaling pathways leading to cytoskeletal reorganization. In the present study, we show that the basal association between endogenous βPix and endogenous 14-3-3β was increased after forskolin stimulation and significantly inhibited by protein kinase A inhibitor. However, forskolin stimulation failed to increase the interaction between 14-3-3β and a β1Pix mutant that is insensitive to protein kinase A phosphorylation, β1Pix(S516A, T526A). We present evidence indicating that forskolin-induced binding of 14-3-3β to β1Pix results in inhibition of Rac1 GTP loading in 293 cells and in vitro. Furthermore, we show that deletion of 10 amino acid residues within the leucine zipper domain is sufficient to block β1Pix homodimerization and 14-3-3β binding and modulates β1Pix-GEF activity. These residues also play a crucial role in β1Pix intracellular localization. These results indicate that 14-3-3β negatively affects the GEF activity of dimeric β1Pix only. Altogether, these results provide a mechanistic insight into the role of 14-3-3β in modulating β1Pix-GEF activity.

scholarly journals The Rho-Guanine Nucleotide Exchange Factor Domain of Obscurin Activates RhoA Signaling in Skeletal Muscle

2009 ◽  
Vol 20 (17) ◽  
pp. 3905-3917 ◽  
Author(s):  
Diana L. Ford-Speelman ◽  
Joseph A. Roche ◽  
Amber L. Bowman ◽  
Robert J. Bloch
Keyword(s):  
Skeletal Muscle ◽  
Guanine Nucleotide Exchange Factor ◽  
Small Gtpases ◽  
Guanine Nucleotide ◽  
Nucleotide Exchange ◽  
Exchange Factor ◽  
Guanine Nucleotide Exchange ◽  
Nucleotide Exchange Factor

Obscurin is a large (∼800-kDa), modular protein of striated muscle that concentrates around the M-bands and Z-disks of each sarcomere, where it is well positioned to sense contractile activity. Obscurin contains several signaling domains, including a rho-guanine nucleotide exchange factor (rhoGEF) domain and tandem pleckstrin homology domain, consistent with a role in rho signaling in muscle. We investigated the ability of obscurin's rhoGEF domain to interact with and activate small GTPases. Using a combination of in vitro and in vivo approaches, we found that the rhoGEF domain of obscurin binds selectively to rhoA, and that rhoA colocalizes with obscurin at the M-band in skeletal muscle. Other small GTPases, including rac1 and cdc42, neither associate with the rhoGEF domain of obscurin nor concentrate at the level of the M-bands. Furthermore, overexpression of the rhoGEF domain of obscurin in adult skeletal muscle selectively increases rhoA expression and activity in this tissue. Overexpression of obscurin's rhoGEF domain and its effects on rhoA alter the expression of rho kinase and citron kinase, both of which can be activated by rhoA in other tissues. Injuries to rodent hindlimb muscles caused by large-strain lengthening contractions increases rhoA activity and displaces it from the M-bands to Z-disks, similar to the effects of overexpression of obscurin's rhoGEF domain. Our results suggest that obscurin's rhoGEF domain signals at least in part by inducing rhoA expression and activation, and altering the expression of downstream kinases in vitro and in vivo.

Signalling to actin: role of C3G, a multitasking guanine-nucleotide-exchange factor

2011 ◽  
Vol 31 (4) ◽  
pp. 231-244 ◽  
Author(s):  
Vegesna Radha ◽  
Aninda Mitra ◽  
Kunal Dayma ◽  
Kotagiri Sasikumar
Keyword(s):  
Current Knowledge ◽  
Neurite Growth ◽  
Guanine Nucleotide Exchange Factor ◽  
Small Gtpases ◽  
Cell Junctions ◽  
Guanine Nucleotide ◽  
Nucleotide Exchange ◽  
Exchange Factor ◽  
Guanine Nucleotide Exchange ◽  
Nucleotide Exchange Factor

C3G (Crk SH3-domain-binding guanine-nucleotide-releasing factor) is a ubiquitously expressed member of a class of molecules called GEFs (guanine-nucleotide-exchange factor) that activate small GTPases and is involved in pathways triggered by a variety of signals. It is essential for mammalian embryonic development and many cellular functions in adult tissues. C3G participates in regulating functions that require cytoskeletal remodelling such as adhesion, migration, maintenance of cell junctions, neurite growth and vesicle traffic. C3G is spatially and temporally regulated to act on Ras family GTPases Rap1, Rap2, R-Ras, TC21 and Rho family member TC10. Increased C3G protein levels are associated with differentiation of various cell types, indicating an important role for C3G in cellular differentiation. In signalling pathways, C3G serves functions dependent on catalytic activity as well as protein interaction and can therefore integrate signals necessary for the execution of more than one cellular function. This review summarizes our current knowledge of the biology of C3G with emphasis on its role as a transducer of signals to the actin cytoskeleton. Deregulated C3G may also contribute to pathogenesis of human disorders and therefore could be a potential therapeutic target.

scholarly journals Activation of Rab8 guanine nucleotide exchange factor Rabin8 by ERK1/2 in response to EGF signaling

2014 ◽  
Vol 112 (1) ◽  
pp. 148-153 ◽  
Author(s):  
Juanfei Wang ◽  
Jinqi Ren ◽  
Bin Wu ◽  
Shanshan Feng ◽  
Guoping Cai ◽  
...  
Keyword(s):  
Plasma Membrane ◽  
Membrane Trafficking ◽  
Guanine Nucleotide Exchange Factor ◽  
Small Gtpases ◽  
Guanine Nucleotide ◽  
Nucleotide Exchange ◽  
Exchange Factor ◽  
Guanine Nucleotide Exchange ◽  
Nucleotide Exchange Factor ◽  
Egf Signaling

Exocytosis is tightly regulated in many cellular processes, from neurite expansion to tumor proliferation. Rab8, a member of the Rab family of small GTPases, plays an important role in membrane trafficking from the trans-Golgi network and recycling endosomes to the plasma membrane. Rabin8 is a guanine nucleotide exchange factor (GEF) and major activator of Rab8. Investigating how Rabin8 is activated in cells is thus pivotal to the understanding of the regulation of exocytosis. Here we show that phosphorylation serves as an important mechanism for Rabin8 activation. We identified Rabin8 as a direct phospho-substrate of ERK1/2 in response to EGF signaling. At the molecular level, ERK phosphorylation relieves the autoinhibition of Rabin8, thus promoting its GEF activity. We further demonstrate that blocking ERK1/2-mediated phosphorylation of Rabin8 inhibits transferrin recycling to the plasma membrane. Together, our results suggest that ERK1/2 activate Rabin8 to regulate vesicular trafficking to the plasma membrane in response to extracellular signaling.

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