Abstract A011: Stopping brain tumors in their tracks: the role of RhoGTPase activating proteins (ARHGAPs) in glioma cell migration and invasion
Authors: Vaughn-Beaucaire Philippa C. , Lawler Sean , Bruning-Richardson Anke , Hawkins William , Jimenez-Macias Jorge , Srinivasan Praveen 
Published: March 2024

Abstract
Despite efforts to improve outcomes, patients diagnosed with glioblastoma (GBM) have a median survival of only 12-15 months. Tumors are characterized by rapid growth and invasion. We previously have shown that the broadly selective kinase inhibitor (2'Z,3'E)-6-Bromoindirubin-3'-oxime (BIO) has potent anti-migratory properties in GBM cells. To investigate the mechanisms involved we performed transcriptomic analysis which showed a wide range of alterations in GBM cell lines associated with BIO treatment. This included multiple members of the RhoGTPase activating protein (ARHGAP) family. ARHGAPs are a family of proteins that have been associated with various diseases including cancers but have not been studied in GBM. Using 2D and 3D migration/invasion assays with established and patient derived cell lines as well as in vivo models and human GBM tissue, the role of ARHGAPs 4, 22 and 25 in cell migration and dissemination was investigated. Migration studies after gene knockdown in the patient derived cell line G9 revealed that the three ARHGAPs had pro-or-anti-migratory activity. Preliminary in vivo studies in mice indicated that silencing ARHGAP25 in GBM cells enhances invasiveness. ARHGAP25 negatively regulates RhoA, a key player in cell migration. By decreasing ARHGAP25 activity, RhoA becomes more active, leading to actin polymerization, stress fiber formation, and enhanced invasive behavior in G9-ARHGAP25 knockdown cells. These cells exhibit a rounder, amoeboid phenotype, with reduced protrusions, enabling them to navigate tight spaces and invade surrounding tissue more easily. Conversely, G9 and G9-ARHGAP 22 knockdown cells display a protrusive, elongated phenotype, suggesting a slower form of cell migration, influenced by Rac1 signaling. Knocking down ARHGAP22 promotes RhoA-driven migration, while Rac1 promotes mesenchymal migration through membrane protrusions like lamellipodia. Clinical relevance of the ARHGAPs was determined by an association of ARHGAP expression and survival after treatment in a GBM tissue microarray (TMA) donated by Professor Michel Mittelbronn, which revealed a significant association between high ARHGAP22 expression and longer disease-free survival. Distinct protein localizations were observed for each ARHGAP. ARHGAP22 showed a potential correlation with necrotic regions and blood vessels in GBM tumors. The study's findings enhance our understanding of GBM cell migration, providing potential targets for therapeutic intervention. Overall, the discoveries made represent an important step forward in the identification of new targets for this devastating disease.
Citation Format: Philippa C. Vaughn-Beaucaire, Sean Lawler, Anke Bruning-Richardson, William Hawkins, Jorge Jimenez-Macias, Praveen Srinivasan. Stopping brain tumors in their tracks: the role of RhoGTPase activating proteins (ARHGAPs) in glioma cell migration and invasion [abstract]. In: Proceedings of the AACR Special Conference on Brain Cancer; 2023 Oct 19-22; Minneapolis, Minnesota. Philadelphia (PA): AACR; Cancer Res 2024;84(5 Suppl_1):Abstract nr A011.