Attar Myriam A, Santy Lorraine C
Department of Biochemistry and Molecular Biology, The Pennsylvania State University, 208 Althouse Lab, University Park, PA 16802, USA.
BMC Cell Biol. 2013 Feb 26;14:9. doi: 10.1186/1471-2121-14-9.
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.
上皮细胞从正常的非运动状态转变为运动状态需要多种小GTP酶的协同作用。我们之前已经表明，Arf和Rac GTP酶的协同激活可刺激上皮细胞迁移。这种相互作用依赖于一种多蛋白复合物的组装，该复合物包含Arf激活蛋白细胞粘附分子2/ARNO和Rac激活蛋白Dock180。两种直接与细胞粘附分子2结合的支架蛋白组织了这个复合物。
我们现在发现，对肝细胞生长因子（HGF）作出反应的Rac激活需要细胞粘附分子2和Dock180。GRASP/Tamalin是构建包含细胞粘附分子2和Dock180的复合物的支架之一。我们在此确定，GRASP富含丙氨酸/脯氨酸的区域直接与Dock180的SH3结构域相互作用。通过与细胞粘附分子2/ARNO和Dock180两者结合，GRASP连接激活Arf和Rac的鸟嘌呤核苷酸交换因子（GEF），从而促进从Arf到Rac的信号传导。此外，我们发现敲低GRASP会损害肝细胞生长因子（HGF）刺激的Rac激活和HGF刺激的上皮迁移。
GRASP直接结合细胞粘附分子2和Dock180以协调它们的活性，从而促进Arf和Rac之间的相互作用。
