PROJECT 2 ABSTRACT PIs: John Crispino, PhD; Anna Rita Migliaccio, PhD Myelofibrosis (MF), caused by mutations in JAK2, MPL, and CALR, progress from a pre-fibrotic stage where patients have minimal symptoms to a more advanced fibrotic state which is associated with an increasing symptom burden, progressive splenomegaly, cytopenias and marrow fibrosis. MF disease progression is characterized by the accumulation of atypical megakaryocytes that express low levels of the critical transcription factor GATA1 and elevated levels of TGF-β. MF evolves to acute myeloid leukemia (MPN blast phase, MPN- BP) in nearly 20% of patients. The goal of project 2 is to understand the events that contribute to disease progression by focusing on megakaryocytes and the factors that they secrete, such as TGF-β and IL-13. Based on our prior research, we hypothesize that changes in the megakaryocytic lineage substantially contribute to key features of MF progression, including bone marrow fibrosis, the predominance of MF hematopoietic stem cells and the impaired function of wild-type hematopoietic stem cells. We further hypothesize that alterations in p53 activity contribute to both the inhibition of normal hematopoiesis and the progression of MF to MPN-BP. In this project, we will: 1) Investigate the changes in the megakaryocyte lineage that contribute to the MF progression; 2) Identify the contributions of IL-13 and TGF-β to MF progression; and 3) Evaluate and target the contributions of HIF-1 alpha pathway activation and p53 inhibition driving MF leukemia progression. Our research interacts with Projects 1 and 3 through our work on cytokines and the role of p53 in MF progression, and with Project 4 through both bench to beside and bedside to bench exchanges of information, with the ultimate goal of bringing new treatments to MF patients. Our work will also require integration with each of the MPN-RC cores. Drs. Crispino and Migliaccio have a longstanding history of collaboration, particularly dealing with the role of GATA1 in megakaryopoiesis, and will leverage their complementary expertise to achieve the goals of this project.