Guanine Nucleotide Exchange Factors Dock7 And Ect2 Mediate Hgf/C-Met-Induced Glioblastoma Cell Invasion

Proceedings: AACR 104th Annual Meeting 2013; Apr 6-10, 2013; Washington, DC Glioblastoma multiforme (GBM) is the most common and lethal primary malignant brain tumor. It is an incurable disease with an average life expectancy of just 14 months following diagnosis. GBM morbidity is primarily due to its rapid growth, neovascularization and invasion throughout the brain. The angiogenesis inhibitor, bevacizumab, now approved for GBM treatment, has been shown to cause enhanced tumor cell invasion in part via c-MET (HGF-receptor) signaling. We have previously shown that several members of the Rho family of small GTPases, including Rac1, Rac3, RhoG and Cdc42, play central roles in GBM tumor cell invasion. Rho GTPases are activated by guanine nucleotide exchange factors (Rho GEFs). Herein we focus on identifying GEFs that act on Rac subfamily members and which are of functional importance in GBM. We found that Dock7 and Ect2, two GEFs that can activate Rac proteins, show elevated mRNA and protein expression in human GBM tissue in comparison with non-neoplastic brain. RNAi-mediated depletion of these GEFs in GBM cell lines resulted in decreased HGF- and serum-induced tumor cell invasion in 3-dimensional extracellular matrix in vitro and organotypic ex vivo brain slice invasion assays. GEF activity of Dock7 and Ect2 were shown to be increased by HGF using a pull-down with Rac1G15A, a nucleotide binding-deficient mutant of Rac1. Furthermore, Dock7 and Ect2 were shown to be required for HGF-induced Rac1 activation, lamellipodia formation and cell spreading. Dock7, but not Ect2, was shown to co-immunoprecipitate with c-MET and this interaction was HGF-dependent and required the c-MET adaptor protein GAB1. Dock7 and GAB1 were furthermore shown to co-immunoprecipitate in an HGF-dependent manner. GAB1 was shown to be required for HGF-induced Dock7 and Ect2 Rac1 GEF activities, Rac1 activation and HGF-induced GBM cell invasion. In summary, we have identified two GEFs that are of functional and clinical relevance in the development of the GBM pathologic phenotype. Dock7 and Ect 2 represent potential new drug targets for the management of GBM, especially in combination with an anti-angiogenic approach. Citation Format: David W. Murray, Sebastien Didier, Vincent M. Paulino, Amanda Chan, Nhan L. Tran, Annette T. Byrne, Marc H. Symons. Guanine nucleotide exchange factors Dock7 and Ect2 mediate HGF/c-MET-induced glioblastoma cell invasion. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr LB-40. doi:10.1158/1538-7445.AM2013-LB-40