A forward genetic screen identifies potassium channel essentiality in SHH medulloblastoma maintenance [RNA-seq]

Sequencing cancer genomes is predicted to uncover therapeutic tumor vulnerabilities. This has been complicated by the abundance of genetic alterations which are either non-functional, or only important in tumor initiation or progression. Distinguishing tumor maintenance genes from initiation, progression, and passenger genes is critical for developing effective cancer therapy. We employed a functional genomic approach using the Lazy Piggy transposon to identify tumor maintenance genes in vivo, and apply this to SHH medulloblastoma (MB). Combining Lazy Piggy screening in mice and transcriptomic profiling of human MB, we discovered candidate maintenance genes including the voltage-gated potassium channel Kcnb2. Genetic knockout of Kcnb2 impairs MB growth. Kcnb2 mediates potassium efflux in MB-propagating cells to govern cell volume. Loss of Kcnb2 leads to chronic osmotic swelling and decreased plasma membrane tension, which elevates endocytosis to dampen Egfr signaling, thereby mitigating proliferation of MB-propagating cells. Kcnb2 is largely dispensable for mouse development and synergizes with anti-SHH therapy in treating MB. These results demonstrate the utility of the Lazy Piggy functional genomic approach in identifying cancer maintenance genes, and elucidate a mechanism by which a potassium channel integrates biomechanical and biochemical signaling to promote MB aggression. To identify transcriptional changes following tamoxifen-induced remobilization of Lazy Piggy transposons, we sequenced cDNA libraries reverse transcribed from bulk RNA from mouse Lazy Piggy-induced Shh tumours. Additionally, to identify transcriptional changes following Kcnb2 knockout in an established model for Shh medulloblastoma, we sequenced cDNA libraries reverse transcribed from bulk RNA from mouse Math1-Cre; SmoM2 tumours that were Kcnb2 wild-type or knockout.