STEM-25. IN VIVO FUNCTIONAL GENOMICS IDENTIFIES ESSENTIALITY OF POTASSIUM HOMEOSTASIS IN MEDULLOBLASTOMA Free

Distinguishing cancer maintenance genes—i.e. genes essential and specific to tumor survival—from initiation, progression, and passenger genes is critical for developing effective cancer therapeutics. We engineered the Lazy Piggy genetic screening system, which uses a Sleeping Beauty / piggyBac hybrid transposon to dysregulate and later restore gene expression. In vivo spatiotemporal control of Lazy Piggy transposon insertion and remobilization depletes insertions that are non-essential for tumor survival while enriching for maintenance driver insertions. Using this functional genomic approach, we identify potassium channels as a regulator for medulloblastoma, the most common pediatric brain malignancy. Loss of potassium channel Kcnb2 diminishes the pool of medulloblastoma-propagating cells by hampering their replication potential, thereby prolonging the survival of tumor-bearing mice. Mechanistically, Kcnb2 governs potassium homeostasis to regulate plasma membrane tension-gated EGFR signaling, which drives the proliferative expansion of medulloblastoma-propagating cells. Our in vivo functional genomics reveals potassium homeostasis as a tumor maintenance essentiality, establishes a link between potassium channel activity and plasma membrane tension, and defines a mechanism by which ion homeostasis integrates biomechanical and biochemical signaling to promote medulloblastoma aggression.