title: VAV2, a guanine nucleotide exchange factor for Rac1, regulates glucose-stimulated insulin secretion in pancreatic beta cells.
abstract: OBJECTIVE
  Rho GTPases (Ras-related C3 botulinum toxin substrate 1 [Rac1] and cell division cycle 42 [Cdc42]) have been shown to regulate glucose-stimulated insulin secretion (GSIS) via cytoskeletal remodelling, trafficking and fusion of insulin-secretory granules with the plasma membrane. GTP loading of these G proteins, which is facilitated by GDP/GTP exchange factors, is a requisite step in the regulation of downstream effector proteins. Guanine nucleotide exchange factor VAV2 (VAV2), a member of the Dbl family of proteins, has been identified as one of the GDP/GTP exchange factors for Rac1. Despite recent evidence on the regulatory roles of VAV2 in different cell types, roles of this guanine nucleotide exchange factor in the signalling events leading to GSIS remain undefined. Using immunological, short interfering RNA (siRNA), pharmacological and microscopic approaches we investigated the role of VAV2 in GSIS from islet beta cells.
  
  
  METHODS
  Co-localisation of Rac1 and VAV2 was determined by Triton X-114 phase partition and confocal microscopy. Glucose-induced actin remodelling was quantified by live cell imaging using the LifeAct-GFP fluorescent biosensor. Rac1 activation was determined by G protein linked immunosorbent assay (G-LISA).
  
  
  RESULTS
  Western blotting indicated that VAV2 is expressed in INS-1 832/13 beta cells, normal rat islets and human islets. Vav2 siRNA markedly attenuated GSIS in INS-1 832/13 cells. Ehop-016, a newly discovered small molecule inhibitor of the VAV2-Rac1 interaction, or siRNA-mediated knockdown of VAV2 markedly attenuated glucose-induced Rac1 activation and GSIS in INS-1 832/13 cells. Pharmacological findings were recapitulated in primary rat islets. A high glucose concentration promoted co-localisation of Rac1 and VAV2. Real-time imaging in live cells indicated a significant inhibition of glucose-induced cortical actin remodelling by Ehop-016.
  
  
  CONCLUSIONS
  Our data provide the first evidence to implicate VAV2 in glucose-induced Rac1 activation, actin remodelling and GSIS in pancreatic beta cells.
authors.affiliation: Beta Cell Biochemistry Laboratory, John D. Dingell VA Medical Center, 4646 John R, Detroit, MI, 48201, USA.|Department of Pediatrics, Herman B Wells Center for Pediatric Research, Indiana University School of Medicine, Indianapolis, IN, USA.
authors.forename: Rajakrishnan
authors.initials: R
authors.lastname: Veluthakal
authors.affiliation: Department of Biochemistry and Molecular Biology, Indiana University School of Medicine, Indianapolis, IN, USA.
authors.forename: Ragadeepthi
authors.initials: R
authors.lastname: Tunduguru
authors.affiliation: Immunobiology and Cancer Research Program, Oklahoma Medical Research Foundation, Oklahoma City, OK, USA.
authors.forename: Daleep Kumar
authors.initials: DK
authors.lastname: Arora
authors.affiliation: Beta Cell Biochemistry Laboratory, John D. Dingell VA Medical Center, 4646 John R, Detroit, MI, 48201, USA.|Department of Pharmaceutical Sciences, Eugene Applebaum College of Pharmacy, Wayne State University, Detroit, MI, USA.
authors.forename: Vaibhav
authors.initials: V
authors.lastname: Sidarala
authors.affiliation: Beta Cell Biochemistry Laboratory, John D. Dingell VA Medical Center, 4646 John R, Detroit, MI, 48201, USA.|Department of Pharmaceutical Sciences, Eugene Applebaum College of Pharmacy, Wayne State University, Detroit, MI, USA.
authors.forename: Khadija
authors.initials: K
authors.lastname: Syeda
authors.affiliation: Department of Pharmaceutical Sciences, School of Pharmacy, University of Puerto Rico, Medical Sciences Campus, San Juan, Puerto Rico.
authors.forename: Cornelis P
authors.initials: CP
authors.lastname: Vlaar
authors.affiliation: Department of Pediatrics, Herman B Wells Center for Pediatric Research, Indiana University School of Medicine, Indianapolis, IN, USA.|Department of Biochemistry and Molecular Biology, Indiana University School of Medicine, Indianapolis, IN, USA.
authors.forename: Debbie C
authors.initials: DC
authors.lastname: Thurmond
authors.affiliation: Beta Cell Biochemistry Laboratory, John D. Dingell VA Medical Center, 4646 John R, Detroit, MI, 48201, USA. akowluru@med.wayne.edu.|Department of Pharmaceutical Sciences, Eugene Applebaum College of Pharmacy, Wayne State University, Detroit, MI, USA. akowluru@med.wayne.edu.|B-4237 Research Service, John D. Dingell VA Medical Center, 4646 John R, Detroit, MI, 48201, USA. akowluru@med.wayne.edu.
authors.forename: Anjaneyulu
authors.initials: A
authors.lastname: Kowluru
mesh_terms: D000199:Actins / Q000378:metabolism; D000818:Animals; D002460:Cell Line; D003599:Cytoskeleton / Q000378:metabolism; D005947:Glucose / Q000494:pharmacology*; D006801:Humans; D007328:Insulin / Q000378:metabolism*; D000078790:Insulin Secretion; D050417:Insulin-Secreting Cells / Q000187:drug effects / Q000378:metabolism*; D008297:Male; D051567:Proto-Oncogene Proteins c-vav / Q000235:genetics / Q000378:metabolism*; D034741:RNA, Small Interfering; D051381:Rats; D017207:Rats, Sprague-Dawley; D020830:rac1 GTP-Binding Protein / Q000235:genetics / Q000378:metabolism*
chemical_list: D000199:Actins; D007328:Insulin; D051567:Proto-Oncogene Proteins c-vav; D034741:RNA, Small Interfering; C093651:VAV2 protein, human; D020830:rac1 GTP-Binding Protein; D005947:Glucose
keywords: Cytoskeleton; Insulin secretion; Pancreatic islet; Rac1; VAV2