Abstract 4321: EGFR signaling in glioblastoma regulates the expression of a brain specific isoform of alphaPIX/Arhgef6 to promote invasion

Abstract

Abstract The gene Arhgef6 encodes the protein alphaPIX/Cool-2, a guanine nucleotide exchange factor specific for the Rho GTPases Rac1 and Cdc42. AlphaPIX is a protein of 90 kDa predominantly expressed in haemopoietic cells where it has been shown to have a role in cytoskeletal reorganization. However, Arhgef6 is also expressed in the brain and mutations in Arhgef6 have been linked to intellectual disability (ID) in humans. AlphaPIX mRNA was reported to be upregulated in glioblastoma multiforme (GBM), the most lethal form of brain cancer. We examined alphaPIX expression in several glioma cell lines and observed a smaller isoform migrating at 72 kDa. To characterize this isoform we performed 5′RACE from several glioma cell lines and show the smaller isoform is an amino-terminal truncated form of alphaPIX lacking the calponin homology (CH) domain. We demonstrate this isoform is expressed during post-natal brain development and its expression coincides with activation of mTOR. Examination of glioblastoma from both autopsy and biopsy clinical samples shows alphaPIX expression correlates with EGFR/PI3K/Akt/mTOR activation. EGF stimulation is shown to upregulate alphaPIX, and pharmacological inhibition of Akt inhibits alphaPIX expression. To examine the function of alphaPIX in glioblastoma we performed siRNA-mediated knockdown and demonstrate increased cell adhesion upon alphaPIX loss. In addition, knockdown of alphaPIX in glioma cells decreases invasive capacity and decreases the formation of invadopodia. These data demonstrate a previously uncharacterized isoform of alphaPIX is expressed during post-natal brain development, and is highly upregulated in GBM with activated EGFR signaling. A functional consequence of EGFR-mediated alphaPIX expression in glioma is increased invasion as a result of dysregulated cytoskeletal organization. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 4321. doi:1538-7445.AM2012-4321