Anti-inflammatory cytokines hepatocyte growth factor and interleukin-11 are over-expressed in Polycythemia vera and contribute to the growth of clonal erythroblasts independently of JAK2V617F

The V617F activating mutation of janus kinase 2 (JAK2), a kinase essential for cytokine signalling, characterizes Polycythemia vera (PV), one of the myeloproliferative neoplasms (MPN). However, not all MPNs carry mutations of JAK2, and in JAK2-mutated patients, expression of JAK2V617F does not always result in clone expansion. In the present study, we provide evidence that inflammation-linked cytokines are required for the growth of JAK2V617F-mutated erythroid progenitors. In a first series of experiments, we searched for cytokines over-expressed in PV using cytokine antibody (Ab) arrays, and enzyme-linked immunosorbent assays for analyses of serum and bone marrow (BM) plasma, and quantitative reverse transcription–PCRs for analyses of cells purified from PV patients and controls. We found that PV patients over-expressed anti-inflammatory hepatocyte growth factor (HGF) and interleukin-11 (IL-11), BM mesenchymal stromal cells (BMMSCs) and erythroblasts being the main producers. In a second series of experiments, autocrine/paracrine cytokine stimulation of erythroblasts was blocked using neutralizing Abs specific for IL-11 or c-MET, the HGF receptor. The growth of JAK2V617F-mutated HEL cells and PV erythroblasts was inhibited, indicating that JAK2-mutated cells depend on HGF and IL-11 for their growth. Additional experiments showed that transient expression of JAK2V617F in BaF-3/erythropoietin receptor cells, and invalidation of JAK2V617F in HEL cells using anti-JAK2 small interfering RNA, did not affect HGF and IL-11 expression. Thus, anti-inflammatory HGF and IL-11 are upregulated in PV and their overproduction is not a consequence of JAK2V617F. As both cytokines contribute to the proliferation of PV erythroblasts, blocking the c-MET/HGF/IL-11 pathways could be of interest as an additional therapeutic option in PV.