The scaffolding protein GRASP/Tamalin directly binds to Dock180 as well as to cytohesins facilitating GTPase crosstalk in epithelial cell migration
Department of Biochemistry and Molecular Biology, The Pennsylvania State University, 208 Althouse Lab, University Park, PA 16802, USA
BMC Cell Biology 2013, 14:9 doi:10.1186/1471-2121-14-9Published: 26 February 2013
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.
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.
GRASP binds directly both cytohesin 2 and Dock180 to coordinate their activities, and by doing so promotes crosstalk between Arf and Rac.