The JAK2 617V>F mutation triggers erythropoietin hypersensitivity and terminal erythroid amplification in primary cells from patients with polycythemia vera

Abstract

The JAK2 617V>F mutation is frequent in polycythemia vera (PV) and essential thrombocythemia (ET). Using quantitative polymerase chain reaction (PCR), we found that high levels of JAK2 617V>F in PV correlate with increased granulocytes and high levels of hemoglobin and endogenous erythroid colony formation. We detected normal progenitors and those that were heterozygous or homozygous for the mutation by genotyping ET and PV clonal immature and committed progenitors. In PV patients, we distinguished homozygous profiles with normal, heterozygous, and homozygous progenitors from heterozygous profiles with only heterozygous and normal progenitors. PV patients with a heterozygous profile had more mutated, committed progenitors than did other PV and ET patients, suggesting a selective amplification of mutated cells in the early phases of hematopoiesis. We demonstrated that mutated erythroid progenitors were more sensitive to erythropoietin than normal progenitors, and that most homozygous erythroid progenitors were erythropoietin independent. Moreover, we observed a greater in vitro erythroid amplification and a selective advantage in vivo for mutated cells in late stages of hematopoiesis. These results suggest that, for PV, erythrocytosis can occur through two mechanisms: terminal erythroid amplification triggered by JAK2 617V>F homozygosity, and a 2-step process including the upstream amplification of heterozygous cells that may involve additional molecular events. (Blood.

Phenotypic variations and new mutations in JAK2 V617F–negative polycythemia vera, erythrocytosis, and idiopathic myelofibrosis

“…The relationship of JAK2 V617F and erythrocytosis, the defining feature of PV, is supported by the observation of heightened erythropoietin sensitivity of homozygous V617F clones compared to heterozygous V617F clones (20), by higher hemoglobin concentrations in JAK2 V617F positive compared to JAK2 V617F-negative ET patients (21), by mouse gene transfection experiments (8) and more recently by the identification of JAK2 exon 12 lesions, which associate primarily with an erythrocytosis phenotype in both man and the mouse(10).…”

JAK2V617F monitoring in polycythemia vera and essential thrombocythemia: Clinical usefulness for predicting myelofibrotic transformation and thrombotic events

“…Accordingly, a stable mutational load over 50% or a progressive increase of granulocytic JAK2V617F would reflect the dominance of a JAK2V617F-positive clone over normal progenitors, while an unexplained decrease of granulocytic JAK2V6127F would mark the expansion of a JAK2V617F-negative clone. A major criticism to this hypothesis comes from the observation that the mutational load in granulocytes does not correlate with the mutational load in hematopoietic progenitors, since JAK2V617F-positive progenitors have a greater capacity for differentiation than normal progenitors [25,27]. This observation limits the value of a single determination of JAK2V617F as a prognostic factor or as a surrogate for clonal dominance.…”

Effects of the JAK2 mutation on the hematopoietic stem and progenitor compartment in human myeloproliferative neoplasms

“…18 Furthermore, the in vivo terminal expansion we demonstrate entirely corroborates the results in murine models [12][13][14] and human MPNs in vitro, where PV and ET patients demonstrated erythroid expansion compared with normal controls after long-term CD34 ϩ cell culture experiments. 19 We also demonstrate, using a novel PCR-based assay, that in individual patients the JAK2 V617F homozygous clone has a competitive advantage over the heterozygous clone and that the heterozygous clone does not significantly expand in vivo. Recent animal models have suggested that gene dosage of JAK2 V617F determines disease phenotype, with higher expression associated with PV and lower expression with an ET phenotype.…”