Cooperation of germ line JAK2 mutations E846D and R1063H in hereditary erythrocytosis with megakaryocytic atypia

Abstract

• Cells expressing JAK2 E846D or R1063H exhibit pathologic STAT5 activation in the specific context of EPOR.• Cooperation of germ line JAK2 mutations E846D and R1063H defines a JAK2-signaling threshold for induction of erythrocytosis.The role of somatic JAK2 mutations in clonal myeloproliferative neoplasms (MPNs) is well established. Recently, germ line JAK2 mutations were associated with polyclonal hereditary thrombocytosis and triple-negative MPNs. We studied a patient who inherited 2 heterozygous JAK2 mutations, E846D from the mother and R1063H from the father, and exhibited erythrocytosis and megakaryocytic atypia but normal platelet number. Culture of erythroid progenitors from the patient and his parents revealed hypersensitivity to erythropoietin (EPO). Using cellular models, we show that both E846D and R1063H variants lead to constitutive signaling (albeit much weaker than JAK2 V617F), and both weakly hyperactivate JAK2/STAT5 signaling only in the specific context of the EPO receptor (EPOR). JAK2 E846D exhibited slightly stronger effects than JAK2 R1063H and caused prolonged EPO-induced phosphorylation of JAK2/STAT5 via EPOR. We propose that JAK2 E846D predominantly contributes to erythrocytosis, but is not sufficient for the full pathological phenotype to develop. JAK2 R1063H, with very weak effect on JAK2/ STAT5 signaling, is necessary to augment JAK2 activity caused by E846D above a threshold level leading to erythrocytosis with megakaryocyte abnormalities. Both mutations were detected in the germ line of rare polycythemia vera, as well as certain leukemia patients, suggesting that they might predispose to hematological malignancy.

The erythropoietin-derived peptide MK-X and erythropoietin have neuroprotective effects against ischemic brain damage

“…Activation of the EPO–EPO-receptors complex turns on the JAK2 signaling pathway, resulting in canonical activation of STAT5 by phosphorylation. 32 , 33 The JAK2 pathway also activates multiple secondary signaling pathways, including MAPKs and PI3K, in frequently studied cell types such as erythrocytes, neurons, astrocytes. 34 , 35 Thus, we examined the downstream signaling pathways that might contribute to the neuroprotective effect of MK-X.…”

Genetic Alterations in Essential Thrombocythemia Progression to Acute Myeloid Leukemia: A Case Series and Review of the Literature

“…We identified a novel JAK2 mutation at kinase domain that is predicted to result in STAT5 activation, as suggested by a previous study that showed a mutation in the same residue, JAK2 p.Arg1063His, associated with STAT5 phosphorylation and increase of CFU-E formation, in addition to in silico modeling, which predicted a facilitation of the active conformation of JH1 ( 38 ).…”

Coexistence of gain-of-function JAK2 germ line mutations with JAK2V617F in polycythemia vera

“…WT cell line ( Figure 2C ) and erythrocytosis (E846D and R1063H), 19 but our data also suggest that germ line mutations outside the core regulatory domain can alter the EPO-sensing properties of cells and therefore may provide proliferation advantage. Because the JAK2 FERM domain is required for EPOR association and consequent relief of inhibitory conformation of the kinase domain that leads to JAK2 activation, 20,21 the molecular basis of this activation remains to be elucidated.…”