PF531 TRANSFORMING ACTIVITIES OF THE NUP98-KMT2A FUSION GENE ASSOCIATED WITH MYELODYSPLASIA AND ACUTE MYELOID LEUKEMIA

Abstract

Background: Inv (11)(p15q23) found in myelodysplastic syndromes (MDS) and acute myeloid leukemia (AML) was previously shown to lead to the expression of a fusion consisting of the N-terminal part of nucleoporin 98 (NUP98) and almost the entire open reading frame (ORF) of the lysine methyltransferase 2A (KMT2A, aka MLL1). Aims: To address the role of the NUP98-KMT2A fusion as a potential leukemogenic oncogene. Methods: To overcome the limitations related to the large size of the fusion ORF, we generated DOX-inducible transgenic iNUP98-KMT2A mice. We studied the effects of iNUP98-KMT2A expression in hematopoietic cells ex vivo in clonogenic assays; and in vivo by assessing blood counts, histology, and immunophenotyping as well as by competitive repopulation assays. In addition, we established primary mouse embryonic fibroblast (MEF) cultures to address the effects of iNUP98-KMT2A on cell cycle progression and cellular senescence. Results: In contrast to other KMT2A fusion such as MLL-AF9, induction of iNUP98-KMT2A did not alter differentiation but impaired growth of bone marrow (BM)-derived cells in vitro. Induction of iNUP98-KMT2A in vivo resulted in signs of disease after a highly variable latency of 13–106 weeks (median latency = 80 weeks, n = 22). Some symptomatic mice presented with increased white blood counts with morphological signs of dysplasia, reduced red blood cells, and increased apoptosis in the BM with signs of extramedullary hematopoiesis. In addition, we observed a 3-fold expansion of Lin−Sca-1+c-Kit+ (LSK) hematopoietic stem and progenitor cells (HSPC) in the BM of these mice. BM cells from symptomatic iNUP98-KMT2A mice had a competitive advantage in reconstitution assays. About 20% (5/22) of the mice on DOX presented with transplantable AML with elevated WBC counts and leukemic blasts in the peripheral blood with infiltration of multiple organs. Expression of iNUP98-KMT2A was associated with aberrant cell cycle progression in LSK cells from primary-induced mice. Similarly, iNUP98-KMT2A expression affected cell cycle progression and abrogated cellular senescence in MEF associated with aberrant expression of Sirt1, Tert, Rbl2, Twist1, Vim, and Prkcd that was also observed in BM cells. Notably, similar to patients with NUP98-KMT2A, and in contrast to other KMT2A fusions, primary AML cells from diseased iNUP98-KMT2A mice expressed very low levels of the Hox-A-B-C gene cluster. In addition, iNUP98-KMT2A leukemic blasts were resistant to the effects of pharmacological targeting of Menin/KMT2A interface or BET-family proteins. Summary/Conclusion: Our work shows that the NUP98-KMT2A fusion has oncogenic potential in mice leading to an MDS-like disease or AML. In contrast to other KMT2A fusions, NUP98-KMT2A does not primarily block differentiation and provide aberrant self-renewal potential, but alters cell cycle progression leading to dysplasia and impairs cellular senescence.