UC San Diego

Glioblastoma is the most common primary malignant tumor of the central nervous system, and is usually treated with maximal surgical resection followed by radiotherapy and concurrent and adjuvant temozolomide. Despite treatment, the tumor almost always recurs, carrying significant mortality, but the specific biological mechanisms by which it recurs are poorly characterized, though it has been suggested that radiotherapy may play a role. microRNA-34c has been shown to be increased by DNA damage in a nuclear ABL-specific manner, and has increased abundance in bystander effect-inducing extracellular vesicles from irradiated cells. We sought to understand whether ionizing radiation could induce expression and secretion of miR-34c in glioblastoma, and if not, whether exogenous miR-34c could induce bystander effects. We exposed validated p53-wildtype and p53-null glioblastoma cell lines to ionizing radiation and found that miR-34c induction did not occur in glioblastoma and that exposing radiation-naïve glioblastoma responder cells to conditioned media from irradiated glioblastoma producer cells did not induce expression of miR-34c in bystander cells. Using HEK-293T cells as extracellular vesicle-producing cells following transfection with miR-34c minigenes generated conditioned media that was capable of inducing ROS and γH2AX in glioblastoma responder cells. MicroRNA mimics were also used to directly transfect glioblastoma cells, and increased the level of nuclear foci of a 53BP1-mCherry fusion protein in a stable glioma line.