Abstract
The thrombopoietin receptor (MPL) has been shown to be mutated (MPL W515L) in myelofibrosis and thrombocytosis yet new approaches to treat this disorder are still required. We have previously shown that transcriptome and proteomic effects do not correlate well in oncogene-mediated leukemogenesis. We therefore investigated the effects of MPL W515L using proteomics. The consequences of MPL W515L expression on over 3300 nuclear and 3500 cytoplasmic proteins were assessed using relative quantification mass spectrometry. We demonstrate that MPL W515L expression markedly modulates the CXCL12/CXCR4/CD45 pathway associated with stem and progenitor cell chemotactic movement. We also demonstrated that MPL W515L expressing cells displayed increased chemokinesis which required the MPL W515L-mediated dysregulation of MYC expression via phosphorylation of the RNA transport protein THOC5 on tyrosine 225. In addition MPL W515L expression induced TGFβ secretion which is linked to sphingosine 1-phosphate production and the increased chemokinesis. These studies identify several pathways which offer potential targets for therapeutic intervention in the treatment of MPL W515L-driven malignancy. We validate our approach by showing that CD34+ cells from MPL W515L positive patients display increased chemokinesis and that treatment with a combination of MYC and sphingosine kinase inhibitors leads to the preferential killing of MPL W515L expressing cells.
Highlights
Myeloproliferative neoplasms (MPNs) are clonal disorders of hematopoietic stem cells (HSCs) characterized by aberrant proliferation of one or several myeloid lineages
We demonstrate that MPL W515L expression leads to an increase in proteins associated with motility and that chemokinesis is increased in these cells
The MPL W515L transfected cell line was shown to be independent of Interleukin-3 and to have the same growth rate as control cells cultured in Interleukin-3 (Supplementary Figure 2A2B)
Summary
Myeloproliferative neoplasms (MPNs) are clonal disorders of hematopoietic stem cells (HSCs) characterized by aberrant proliferation of one or several myeloid lineages. MPNs include essential thrombocythemia (ET), polycythemia vera (PV), and primary myelofibrosis (PMF). Whilst these disorders have overlapping clinical features it is only in recent years that the molecular basis of these diseases have been defined [1]. [2] as PV progresses bone marrow scarring can occur leading to myelofibrosis (MF) in 5- 15% of cases [3]. [7] a consideration of the effects of MPL W515L will inform our understanding of MF and leukemic progression. This could lead to effective management of the disease
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