Activation of the small GTPase Rac1 by a specific guanine-nucleotide-exchange factor suffices to induce glucose uptake into skeletal-muscle cells

2008 ◽  
Vol 100 (11) ◽  
pp. 645-661 ◽  
Author(s):  
Shuji Ueda ◽  
Tohru Kataoka ◽  
Takaya Satoh
Keyword(s):  
Skeletal Muscle ◽  
Glucose Uptake ◽  
Guanine Nucleotide Exchange Factor ◽  
Muscle Cells ◽  
Small Gtpase ◽  
Skeletal Muscle Cells ◽  
Guanine Nucleotide ◽  
Nucleotide Exchange ◽  
Guanine Nucleotide Exchange ◽  
Nucleotide Exchange Factor

scholarly journals The Rho/Rac guanine nucleotide exchange factor Vav1 regulates HIF-1α and GLUT-1 expression and glucose uptake in the brain

2019 ◽  
Author(s):  
Jaewoo Hong ◽  
Yurim Kim ◽  
Sudhirkumar Yanpallewar ◽  
P. Charles Lin
Keyword(s):  
Endothelial Cells ◽  
Glucose Uptake ◽  
Guanine Nucleotide Exchange Factor ◽  
Guanine Nucleotide ◽  
Nucleotide Exchange ◽  
Glut 1 ◽  
Exchange Factor ◽  
Guanine Nucleotide Exchange ◽  
Nucleotide Exchange Factor ◽  
The Brain

AbstractVav1 is a Rho/Rac guanine nucleotide exchange factor expressed in hematopoietic and endothelial cells that are involved in a wide range of cellular functions. It is also stabilized under hypoxic conditions when it regulates the accumulation of the transcription factor HIF-1α, which activates the transcription of target genes to orchestrate a cellular response to low oxygen. One of the genes induced by HIF-1α is GLUT-1, which is the major glucose transporter expressed in vessels that supply energy to the brain. Here, we identify a role for Vav1 in providing glucose to the brain. We found that Vav1 deficiency downregulates HIF-1α and GLUT-1 levels in endothelial cells, including blood-brain barrier cells. This downregulation of GLUT-1, in turn, reduced glucose uptake to endothelial cells both in vitro and in vivo, and reduced glucose levels in the brain.Furthermore, endothelial cell-specific Vav1 knock-out in mice, which caused glucose uptake deficiency, also led to a learning delay in fear conditioning experiments. Our results suggest that Vav1 promotes learning by activating HIF-1α and GLUT-1 and thereby distributing glucose to the brain. They further demonstrate the importance of glucose transport by endothelial cells in brain functioning and reveal a potential new axis for targeting GLUT-1 deficiency syndromes and other related brain diseases.

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.

scholarly journals Substrate Trapping Proteomics Reveals Targets of the βTrCP2/FBXW11 Ubiquitin Ligase

2014 ◽  
Vol 35 (1) ◽  
pp. 167-181 ◽  
Author(s):  
Tai Young Kim ◽  
Priscila F. Siesser ◽  
Kent L. Rossman ◽  
Dennis Goldfarb ◽  
Kathryn Mackinnon ◽  
...  
Keyword(s):  
Mass Spectrometry ◽  
Ubiquitin Ligase ◽  
Guanine Nucleotide Exchange Factor ◽  
Small Gtpase ◽  
Mass Spectrometry Analysis ◽  
Guanine Nucleotide ◽  
Nucleotide Exchange ◽  
Exchange Factor ◽  
Guanine Nucleotide Exchange ◽  
Nucleotide Exchange Factor

Defining the full complement of substrates for each ubiquitin ligase remains an important challenge. Improvements in mass spectrometry instrumentation and computation and in protein biochemistry methods have resulted in several new methods for ubiquitin ligase substrate identification. Here we used the parallel adapter capture (PAC) proteomics approach to study βTrCP2/FBXW11, a substrate adaptor for the SKP1–CUL1–F-box (SCF) E3 ubiquitin ligase complex. The processivity of the ubiquitylation reaction necessitates transient physical interactions between FBXW11 and its substrates, thus making biochemical purification of FBXW11-bound substrates difficult. Using the PAC-based approach, we inhibited the proteasome to “trap” ubiquitylated substrates on the SCFFBXW11E3 complex. Comparative mass spectrometry analysis of immunopurified FBXW11 protein complexes before and after proteasome inhibition revealed 21 known and 23 putatively novel substrates. In focused studies, we found that SCFFBXW11bound, polyubiquitylated, and destabilized RAPGEF2, a guanine nucleotide exchange factor that activates the small GTPase RAP1. High RAPGEF2 protein levels promoted cell-cell fusion and, consequently, multinucleation. Surprisingly, this occurred independently of the guanine nucleotide exchange factor (GEF) catalytic activity and of the presence of RAP1. Our data establish new functions for RAPGEF2 that may contribute to aneuploidy in cancer. More broadly, this report supports the continued use of substrate trapping proteomics to comprehensively define targets for E3 ubiquitin ligases. All proteomic data are available via ProteomeXchange with identifier PXD001062.

scholarly journals The Guanine Nucleotide Exchange Factor GBF1 Participates in Rotavirus Replication

2019 ◽  
Vol 93 (19) ◽  
Author(s):  
José L. Martínez ◽  
Francesca Arnoldi ◽  
Elisabeth M. Schraner ◽  
Catherine Eichwald ◽  
Daniela Silva-Ayala ◽  
...  
Keyword(s):  
Guanine Nucleotide Exchange Factor ◽  
Small Gtpase ◽  
Transport Processes ◽  
Replication Cycle ◽  
Guanine Nucleotide ◽  
Nucleotide Exchange ◽  
Virus Surface ◽  
Exchange Factor ◽  
Guanine Nucleotide Exchange ◽  
Nucleotide Exchange Factor

ABSTRACTCellular and viral factors participate in the replication cycle of rotavirus. We report that the guanine nucleotide exchange factor GBF1, which activates the small GTPase Arf1 to induce COPI transport processes, is required for rotavirus replication since knocking down GBF1 expression by RNA interference or inhibiting its activity by treatment with brefeldin A (BFA) or Golgicide A (GCA) significantly reduces the yield of infectious viral progeny. This reduction in virus yield was related to a block in virus assembly, since in the presence of either BFA or GCA, the assembly of infectious mature triple-layered virions was significantly prevented and only double-layered particles were detected. We report that the catalytic activity of GBF1, but not the activation of Arf1, is essential for the assembly of the outer capsid of rotavirus. We show that both BFA and GCA, as well as interfering with the synthesis of GBF1, alter the electrophoretic mobility of glycoproteins VP7 and NSP4 and block the trimerization of the virus surface protein VP7, a step required for its incorporation into virus particles. Although a posttranslational modification of VP7 (other than glycosylation) could be related to the lack of trimerization, we found that NSP4 might also be involved in this process, since knocking down its expression reduces VP7 trimerization. In support, recombinant VP7 protein overexpressed in transfected cells formed trimers only when cotransfected with NSP4.IMPORTANCERotavirus, a member of the familyReoviridae, is the major cause of severe diarrhea in children and young animals worldwide. Despite significant advances in the characterization of the biology of this virus, the mechanisms involved in morphogenesis of the virus particle are still poorly understood. In this work, we show that the guanine nucleotide exchange factor GBF1, relevant for COPI/Arf1-mediated cellular vesicular transport, participates in the replication cycle of the virus, influencing the correct processing of viral glycoproteins VP7 and NSP4 and the assembly of the virus surface proteins VP7 and VP4.

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