SHEDDING LIGHT ON GLIOBLASTOMA AND DERIVED EXTRACELLULAR VESICLES IN ONE CLIC

ABSTRACT The treatment of glioblastoma (GBM) still represents a tremendous clinical challenge, with the average survival that is not exceeding 14 months. Given the lack of reliable prognostic markers and druggable targets in GBM, several years ago our lab’s interest focused on Chloride intracellular channel-1 (CLIC1), a protein belonging to a class of chloride channels that does not fit the classical paradigm of ion channels proteins. CLIC1 proteins can exist as both soluble globular protein and integral membrane protein with ion channel function. Upon oxidative stress, CLIC1 translocates from the cytoplasm to the plasma membrane where it exerts its function as a chloride (Cl-) channel. CLIC1 is overexpressed in several human solid tumors, including gliomas. In this study we demonstrated that CLIC1 silencing in cancer stem cells (CSCs) isolated from human GBM patients negatively influences both proliferative capacity and self-renewal properties in vitro and impairs the in vivo tumorigenic potential. Moreover, CLIC1 expression inversely associates with GBM patient survival, thus suggesting a potential exploitation of CLIC1 as a new molecular therapeutic target and a possible outcome predictor. CLIC1 has been identified as a secreted protein and detected in exosomes released from different cell types, including primary tumors. Extracellular vesicles (40-1000 nm) (EVs) are secreted by virtually all cell types that arise from the invagination and the budding of the limiting membrane of late endosomes (hence called multivesicular bodies, MVB). We showed that CLIC1 is a protein localized within EVs isolated by GBM cell lines and GBM-derived CSCs and by tuning CLIC1 expression within EVs it is possible to modulate cellular response to EVs both in vitro and in vivo. Taken together, our data suggest that CLIC1 plays an important role in regulating GBM proliferation and tumorigenic status, experimental evidences hint the possible transmission of these features to recipient cells by EV secretion.