STEM-01. PLEXIN-B2 DRIVES CONFINED MIGRATION OF GLIOBLASTOMA STEM CELLS THROUGH MEMBRANE TENSION, ENDOCYTOSIS, AND MECHANO-ELECTRO REGULATION

Glioblastoma is a malignant brain tumor of uncontrolled proliferation and infiltration. GBM stem cells (GSCs) are constantly challenged by confined spaces during their migration through the brain parenchyma. Understanding the factors that drive GSC confined migration (CM) is thus critical for effective drug development. Using microchannel devices, we showed that GSCs are adept at squeezing through narrow constrictions at faster speed than through non-constricted spaces. During CM, cytoskeletal components and plasma membrane self-organize to establish polarity and propel the cell through the constrictions. Among the mechanical plasticity observed for meeting the challenges of CM the cells remodel their shape and plasma membrane through increased endocytosis. Rapid endocytosis of inner leaflet anionic phospholipids-such as PI(4,5)P2 and phosphatidylserine at the front of the cell collectively contribute to drive positive-charged actin filaments and calcium to the rear end of cells, abruptly leading to localized changes in membrane potential and propelling the cell. Correspondingly, inhibiting endocytosis abrogates polarity and results in failure to CM. These effects were recapitulated by deletion of the cell surface receptor Plexin-B2. Plexin-B2-CRISPR knockout (KO) GSCs displayed reduced capability to squeeze through constrictions in microchannel devices. Mechanistically, Plexin-B2 KO in GSCs compromised membrane dynamics and reduced endocytosis as consequence of low cell stiffness and membrane tension. Computational simulations demonstrated that membrane tension couples with cell stiffness in feedback loops and support the model that Plexin-B2 controls membrane tension through actomyosin contractility. On a molecular level, the locked extracellular ring domain of Plexin-B2 prevents GSCs to migrate through constrictions and recapitulates the defects associated with Plexin-B2 KO phenotype, indicating that ring bending is required for membrane tension. Thus, our results describe critical mechano-electro events necessary to establish polarity and prompt GSCs migration under confinement and provide a mechanism by which a single mechanosensor exert regulation at the cytoskeletal and membrane levels.