Loss of BAP1 defines a unique subtype of TP53-mutated de novo AML and confers sensitivity to BCL-xL inhibitors Available to Purchase

• Compound loss of BAP1 and TP53 transforms a heterogeneous population of erythroid-primed multipotent progenitors.

• BAP1 deficient erythroleukemia is dependent on BCL2L1 expression and sensitive to BCL-xL inhibitors.

Mutations in TP53 are mutually exclusive with other known drivers of myeloid transformation and define a distinct molecular subtype within de novo Acute Myeloid Leukemia (AML) that is associated with a complex karyotype, resistance to chemotherapy, and poor prognosis. Although TP53 defects are rare in de novo AML, biallelic mutations are a defining molecular feature of erythroleukemia. The genetic alterations that cooperate with defective TP53 to transform erythroid progenitors remain unknown. We found that loss of BAP1 (BRCA1 Associated Protein-1) co-occurs in one-third of patients with TP53-mutated AML, is associated with an erythroid-primed gene expression signature, and confers an additional adverse effect on overall survival. BAP1 is a tumor suppressor involved in the DNA damage response as well as epigenetic regulation through histone H2AK119 de-ubiquitination. While Bap1KO mice develop myelodysplasia with prominent dyserythropoiesis, combined deletion of Bap1 and Trp53 caused transplantable erythroleukemia, and occasionally mixed AML, mirroring the heterogeneity of human disease. Bulk and single-cell RNA-seq coupled to ChIP-seq in hematopoietic progenitors revealed that Bap1 loss triggers a proinflammatory response and cooperates with Trp53 deficiency to transform erythroid-primed multipotent progenitors. Mechanistically, genomic instability led to the development of erythroleukemia, while epigenetic deregulation caused myelomonocytic skewing suggesting a dichotomous and context dependent role for BAP1. We also demonstrate that BAP1 deficient erythroleukemia is dependent on BCL2L1 expression and is sensitive to BCL-xL inhibitors in vivo.