Inhibition of USP7 Destabilizes the Noncanonical PRC1.1 Complex and Induces Neuroblastoma Differentiation.

UNLABELLED: Pediatric cancers are frequently driven by genomic alterations that result in impaired differentiation during development. To identify complex-level dependencies required for differentiation in neuroblastoma, a pediatric cancer of the developing peripheral nervous system, we curated a list of protein complexes using the CORUM database and mined the Dependency Map using gene set enrichment analysis. This analysis identified the noncanonical polycomb repressive complex 1.1 (PRC1.1) complex, which represses transcriptional activity through ubiquitination of histone 2A, lysine 119 (H2AK119Ub), as a selectively enriched dependency in neuroblastoma. Knockout of PRC1.1 subunits reduced neuroblastoma growth by inducing a neuronal differentiation program. Although no known direct inhibitors of PRC1.1 exist, codependency analysis identified that the deubiquitinase USP7 strongly correlated with PRC1.1 dependency. Treatment with XL177A, a small molecule inhibitor of USP7, significantly reduced neuroblastoma growth in both cellular and animal models. Integrated RNA and chromatin immunoprecipitation sequencing showed that both PRC1.1 knockout and USP7 inhibition resulted in highly correlated transcriptional alterations and reduced H2AK119Ub deposition on chromatin, suggesting that USP7 inhibition reduced neuroblastoma growth through a PRC1.1-dependent mechanism. Mechanistically, global proteomics and ubiquitinomics revealed that USP7 inhibition disrupted noncanonical PRC1 complex assembly, resulting in the destabilization of PRC1.1 and subsequent proteolysis. Our findings expand our understanding of the chromatin complexes required to maintain a dedifferentiated state in neuroblastoma and suggest the therapeutic potential for USP7 inhibitors in the treatment of this disease.

IMPLICATIONS: Our study reveals the potential for utilizing USP7 inhibitors to target epigenetic repression of differentiation programs in neuroblastoma by reducing PRC1 activity.