Molecular and functional studies of ABL1 and FGFR1 fusion oncogenes in myeloproliferative neoplasms

Abstract: The tyrosine kinase encoding genes ABL1 and FGFR1 are involved in fusion genes underlying the myeloproliferative neoplasms chronic myeloid leukemia (CML) and the 8p11-myeloproliferative syndrome (EMS). CML and EMS are both myeloproliferative disorders with an initiating, relatively indolent, chronic phase that after some time progresses into acute myeloid or lymphoid leukemia. The mechanisms underlying disease progression are currently unknown, but additional genetic aberrations are commonly found in the progressed phase. The general aim of this thesis was to study BCR/ABL1 and FGFR1 fusion oncogenes in a relevant cellular context, that of primary human hematopoietic cells, in order to increase our understanding of disease mechanisms underlying the development of CML and EMS. In Article I, a secondary translocation between chromosomes 9 and 21, identified in the leukemic cells from a patient in the progressed phase of EMS, was investigated. The translocation was found to result in a truncated RUNX1 gene, suggesting that haploinsufficiency for RUNX1 could be a mechanism behind disease progression in EMS. It was also found that trisomy 21 is a common secondary change in EMS. In Article II, two variants of BCR/ABL1, P190 and P210, were retrovirally expressed in cord-blood derived human CD34-positive cells. Both variants induced erythroid expansion, increased proliferation, and similar gene expression profiles, indicating that P190 and P210 BCR/ABL1 have a similar mode of action. These results indirectly support the theory that the difference in disease manifestation between P190 and P210 BCR/ABL1 depends on separate cellular origins rather than intrinsic differences of the two fusion proteins. In Article III, retroviral expression of BCR/FGFR1 or ZMYM2/FGFR1 in human CD34-positive cells resulted in increased cellular proliferation and erythroid expansion, in similar to the effects caused by BCR/ABL1. Transplantation of BCR/FGFR1- and ZMYM2/FGFR1-expressing cells into immunodeficient mice resulted in engraftment of human cells in the mouse bone marrow. The human cells differentiated into a myeloid and erythroid direction. Both fusion genes induced similar EMS-like disorders in transplanted mice, with eosinophilia, splenomegaly, and accumulation of blasts. The established in-vivo model of EMS should constitute a valuable tool for obtaining further insights into FGFR1 fusion gene mediated leukemogenesis and for the development and evaluation of new treatment strategies in EMS.