Epigenetic targeted therapy of leukemia through a hyper-activated BAP1-ASXL1-mutant axis

The ASXL1 gene is the human homolog of the Drosophila Asx gene, a core subunit in the BAP1 histone H2A deubiquitinase complex. Mutations of ASXL1 occur in multiple myeloid neoplasms and are uniformly associated with poor prognosis. However, the molecular mechanism through which ASXL1 mutations alter BAP1 activity to drive leukemogenesis remains unclear. Here we demonstrate that cancer-associated frame-shift ASXL1 mutations, which were originally proposed to act as destabilizing loss-of-function mutations, in fact encode truncated stable gain-of-function proteins. Truncated ASXL1 protein stabilizes BAP1, enhances BAP1 complex recruitment to chromatin and promotes the expression of numerous leukemia associated genes. Chemical inhibition of BAP1 rescues these changes in gene expression in leukemic cells and inhibits tumor progression. This study represents a breakthrough advance in our understanding of the molecular mechanisms of ASXL1 mutations in leukemic pathogenesis and identifies small molecular inhibitors of BAP1 function as a potential targeted therapy for leukemia. Overall design: We will evaluate the function of mutant ASXL1 in human leukemia, and target the hyper-activated BAP1-ASXL1-mutant axis by small molecule inhibitors