Genome-wide CRISPR-Cas9 screens reveal loss of redundancy between PKMYT1 and WEE1 in Glioblastoma stem-like cells

To identify new therapeutic targets for Glioblastoma (GBM), we performed genome-wide CRISPR-Cas9 "knockout" (KO) screens in patient-derived GBM stem-like cells (GSCs) and human neural stem/progenitors (NSCs), non-neoplastic stem cell controls, for genes required for their in vitro growth. Surprisingly, the vast majority GSC-lethal hits were found outside of molecular networks commonly altered in GBM and GSCs (e.g., oncogenic drivers). In vitro and in vivo validation of GSC-specific targets revealed several strong hits, including the wee1-like kinase, PKMYT1/Myt1. Mechanistic studies demonstrated that PKMYT1 acts redundantly with WEE1 to inhibit Cyclin B-CDK1 activity via CDK1-Tyr15 phosphorylation and to promote timely completion of mitosis in NSCs. However, in GSCs, this redundancy is lost, likely as a result of oncogenic signaling, causing GBM-specific lethality. A whole-genome CRISPR-Cas9 knockout screens targeting over 18,000 genes using the all-in-one LV-sgRNA:Cas9 platform system were performed using a “shot gun” approach by transducing 2 GBM patient-derived isolates and 2 human neural stem cell isolates with the pool library (2 biological replicates), and cultures were outgrown for ~3 weeks. The end time point of each screen was compared to day 0 in order to determine which sgRNAs were overrepresented or underrepresented in the population.