Transduced CD34+ human hematopoietic progenitors as a model for myeloid neoplasms associated with PDGF receptor fusion genes

(eng) Myeloproliferative neoplasms (MPNs) are clonal hematopoietic diseases characterized by excess of one or more myeloid lineage. The pathogenesis of MPNs often involves the deregulation of a tyrosine kinase. Fusion genes involving the platelet derived growth factor receptor beta (PDGFRβ) or platelet derived growth factor alpha (PDGFRα), have been associated with a subgroup of these disorders associated with hypereosinophilia. In this thesis we setup a model based on the transduction of CD34+ human progenitors derived from umbilical cord blood. This model shed light on the possible mechanisms whereby the PDGFRs fusion genes exert their effects on cell differentiation and proliferation. We observed that either ETV6-PDGFRβ or FIP1L1-PDGFRα induce the activation of the transcription factors STATs and NF-κB. The latter pathway could be activated via PI3K and have a role in eosinophil differentiation. To gain insight into the mechanism of signal transduction by FIP1L1-PDGFRα, we performed systematic point mutations of tyrosine residues that are phosphorylated in this fusion protein. We observed that tyrosines 95 and 98 in FIP1L1 and tyrosine 720 in the PDGFRα could play a role in cell proliferation as well as in STAT5 and ERK signaling. We observed also that SHP2 binds to tyrosine 720 and SHP2 could form a complex with STAT5 in Ba/F3 cells expressing FIP1L1-PDGFRα. We also contributed to the study of the KANK1-PDGFRβ fusion gene. We observed that this fusion induces the STAT5 activation but does not require the JAK2 phosphorylation. In addition we observed that KANK1-PDGFRβ induces PLCγ and ERK1/2 phosphorylation and stimulate CD34+ progenitor growth. In conclusion, our model mimics the human disease induced by PDGF receptor fusions and allowed us to identify key signal transduction pathways downstream these oncogenes.