Up-Regulation of Anti-Inflammatory, STAT3-Activating Hepatocyte Growth Factor and Interleukin-11 In Polycythemia Vera Is Independent of JAK2V617F and Contributes to the Growth of Clonal Erythroblasts

The V617F activating mutation of JAK2, JAK2V617F, characterizes Polycythemia vera (PV). However, expression of JAK2V617F does not always result in clone expansion, implying that additional events are required for the growth of JAK2-mutated progenitors and development of the PV phenotype. In the present study, we provide evidence that anti-inflammatory cytokines are required for the growth of JAK2V617F-mutated erythroid progenitors.

We searched for cytokines over-expressed in PV using cytokine antibody arrays and ELISAs for analyses of serum and bone marrow (BM) plasma, and quantitative RT-PCRs for analyses of cells purified from PV patients and controls. Transient transfection of JAK2V617F and invalidation of JAK2V617F with siRNA were used to study the effect of JAK2V617F on cytokine expression.

We found that PV patients over-expressed anti-inflammatory hepatocyte growth factor (HGF) and interleukin-11 (IL-11), BM stromal cells (BMSC) and erythroblasts being the main producers. HGF induced the production of IL-11 and both cytokines activate the STAT3 pathway. We used neutralizing antibodies specific for IL-11 or c-MET, the HGF receptor, to block autocrine/paracrine cytokine stimulation of erythroblasts in in vitro cultures. The growth of JAK2V617F-mutated PV erythroblasts and HEL cells was inhibited by at least 40%, indicating that JAK2V617F-mutated cells depend on HGF and IL-11 for their growth. Consistent with activation of HGF/IL-11 pathways, mRNA levels of gp130 (the receptor chain responsible for signalling common to cytokines of the IL-11/IL-6 family) and STAT3 were significantly elevated in PV erythroblasts. Moreover, mRNA levels of c-MET, HGF and IL-11 were correlated, a logical finding as c-MET, HGF and IL-11 act in cascade. No correlation was found with JAK2V617F mRNA levels. To the opposite, we provide evidence that the up-regulation of HGF and IL-11 in PV is not a consequence of JAK2V617F: transient expression of JAK2V617F in BaF-3/Epo-R cells and invalidation of JAK2V617F in HEL cells using anti-JAK2 siRNA had no effect on HGF and IL-11 expression.

Anti-inflammatory, STAT3-activating HGF and IL-11 are up-regulated in PV independently of JAK2V617F. Both cytokines contribute to the proliferation of JAK2V617F-mutated erythroblasts, suggesting that drugs blocking the HGF/IL-11 pathways, such as c-MET antagonists, could be of interest as an additional therapeutic option in PV.

Marjorie Boissinot and Cedric Cleyrat contibuted equally.

No relevant conflicts of interest to declare.