Aurora Kinase A is Required for Hematopoiesis and Myelofibrosis and Restricts Terminal Differentiation of Megakaryocytes Through Phosphorylation of NF-E2

Acute megakaryocytic leukemia (AMKL) is one of the most deadly and least treatable leukemias. In AMKL, the leukemia blasts possess megakaryocyte characteristics, but unlike normal megakaryocytes they fail to differentiate and exit the proliferative cycle (1). The prognosis for many patients with AMKL is poor, and new treatment approaches are needed. In 2012 the Crispino lab completed a high content screen to attempt to identify new AMKL therapeutics. The small molecule screen identified several promising compounds that induced proliferation arrest and polyploidization of malignant megakaryocytes. The most effective molecule, dimethylfasudil (diMF), selectively induced polyploidy, differentiation, and proliferation arrest of AMKL blasts in vitro and in vivo (2). To identify the relevant cellular targets of diMF, genetic and proteomic experiments were performed. These studies pointed to aurora kinase A (AURKA) as the critical target. Additional experiments with the highly selective and potent AURKA inhibitor MLN8237 confirmed that AURKA inhibition leads to polyploidization of malignant megakaryocytes and can effectively treat AMKL in several disease models.;To investigate the function of AURKA in normal hematopoiesis, megakaryocyte development and myelofibrosis, AURKA tissue specific knockout studies were completed. We found that loss of AURKA in hematopoietic cells causes profound, cell autonomous defects in the peripheral blood and bone marrow. In addition, we discovered that loss of just one allele of AURKA retards the development of myelofibrosis. AURKA inhibitors induced differentiation and cell death of MPN cells as well and with JAK2 inhibitors synergistically induced cell death. Surprisingly, in contrast to the survival defects of nearly all hematopoietic lineages, deletion of AURKA resulted in increased differentiation and polyploidization of megakaryocytes. With respect to the mechanism of megakaryocyte differentiation, we determined that AURKA phosphorylates the transcription factor NF-E2. AURKA phosphorylation of NF-E2 impaired its chromatin occupancy and transcriptional activity. Taken together, our data show that AURKA is required for adult hematopoiesis, development of myelofibrosis and that AURKA functions to suppress megakaryocyte maturation by maintaining phosphorylation of NF-E2. Thus, in addition to its cell cycle functions, AURKA controls the activity of an essential hematopoietic transcription factor to regulate differentiation.