U2AF1is a haplo-essential gene required for cancer cell survival

Somatic mutations in the spliceosome geneU2AF1are common in patients with myelodysplastic syndromes.U2AF1mutations that code for the most common amino acid substitutions are always heterozygous, and the retained wild-type allele is expressed, suggesting that mutant hematopoietic cells may require the residual wild-type allele to be viable and cause disease. We show that hematopoiesis and RNA splicing inU2af1heterozygous knock-out mice was similar to control mice, but that deletion of the wild-type allele in U2AF1(S34F) heterozygous mutant expressing hematopoietic cells (i.e., hemizygous mutant) was lethal. These results confirm that U2AF1 mutant hematopoietic cells are dependent on the expression of wild-type U2AF1 for survivalin vivoand thatU2AF1is a haplo-essential cancer gene. Mutant U2AF1 (S34F) expressing cells were also more sensitive to reduced, but not absent, expression of wild-type U2AF1 than non-mutant cells. Furthermore, mice transplanted with leukemia cells expressing mutant U2AF1 had significantly reduced tumor burden and improved survival after the wild-typeU2af1allele was deleted compared to when it was not deleted. These results suggest that selectively targeting the wild-typeU2AF1allele in heterozygous mutant cells could induce cancer cell death and be a therapeutic strategy for patients harboringU2AF1mutations.