title: The scaffolding protein GRASP/Tamalin directly binds to Dock180 as well as to cytohesins facilitating GTPase crosstalk in epithelial cell migration.
abstract: BACKGROUND
  The transition of epithelial cells from their normal non-motile state to a motile one requires the coordinated action of a number of small GTPases. We have previously shown that epithelial cell migration is stimulated by the coordinated activation of Arf and Rac GTPases. This crosstalk depends upon the assembly of a multi-protein complex that contains the Arf-activating protein cytohesin 2/ARNO and the Rac activating protein Dock180. Two scaffolding proteins that bind directly to cytohesin 2 organize this complex.
  
  
  RESULTS
  We now have found that Rac activation in response to hepatocyte growth factor (HGF) requires cytohesin 2 and Dock180. GRASP/Tamalin is one of the scaffolds that builds the complex containing cytohesin 2 and Dock180. We determine here that the Ala/Pro rich region of GRASP directly interacts with the SH3 domain of Dock180. By binding to both cytohesin 2/ARNO and Dock180, GRASP bridges the guanine nucleotide exchange factors (GEFs) that activate Arf and Rac, thereby promoting Arf-to-Rac signaling. Furthermore, we find that knockdown of GRASP impairs hepatocyte growth factor (HGF)-stimulated Rac activation and HGF-stimulated epithelial migration.
  
  
  CONCLUSIONS
  GRASP binds directly both cytohesin 2 and Dock180 to coordinate their activities, and by doing so promotes crosstalk between Arf and Rac.
authors: Department of Biochemistry and Molecular Biology, The Pennsylvania State University, 208 Althouse Lab, University Park, PA 16802, USA.
authors: Myriam A
authors: MA
authors: Attar
authors: Lorraine C
authors: LC
authors: Santy
mesh_terms: D000089982:ADP-Ribosylation Factor 6; D020727:ADP-Ribosylation Factors / Q000378:metabolism; D000818:Animals; D002352:Carrier Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D002465:Cell Movement / Q000187:drug effects; D004285:Dogs; D004789:Enzyme Activation / Q000187:drug effects; D020558:GTP Phosphohydrolases / Q000378:metabolism*; D020690:GTPase-Activating Proteins / Q000378:metabolism*; D057809:HEK293 Cells; D017228:Hepatocyte Growth Factor / Q000494:pharmacology; D006801:Humans; D061985:Madin Darby Canine Kidney Cells; D008565:Membrane Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D011485:Protein Binding; D034622:RNA Interference; D034741:RNA, Small Interfering / Q000378:metabolism; D015398:Signal Transduction; D020744:rac GTP-Binding Proteins / Q000378:metabolism*; D020830:rac1 GTP-Binding Protein / Q000378:metabolism; D018909:src Homology Domains
chemical_list: D000089982:ADP-Ribosylation Factor 6; D002352:Carrier Proteins; C099818:DOCK1 protein, human; D020690:GTPase-Activating Proteins; D008565:Membrane Proteins; D034741:RNA, Small Interfering; C102474:cytohesin-2; C410230:tamalin protein, human; D017228:Hepatocyte Growth Factor; D020558:GTP Phosphohydrolases; D020727:ADP-Ribosylation Factors; D020744:rac GTP-Binding Proteins; D020830:rac1 GTP-Binding Protein