Constitutive JunB expression, associated with the JAK2 V617F mutation, stimulates proliferation of the erythroid lineage

Abstract

The JAK2 V617F mutation, present in the majority of polycythemia vera (PV) patients, causes constitutive activation of JAK2 and seems to be responsible for the PV phenotype. However, the transcriptional changes triggered by the mutation have not yet been totally characterized. In this study, we performed a large-scale gene expression study using serial analysis of gene expression in bone marrow cells of a newly diagnosed PV patient harboring the JAK2 V617F mutation and in normal bone marrow cells of healthy donors. JUNB was one of the genes upregulated in PV, and we confirmed, by quantitative real-time PCR, an overexpression of JUNB in hematopoietic cells of other JAK2 V617F PV patients. Using Ba/F3-EPOR cell lines and primary human erythroblast cultures, we found that JUNB was transcriptionally induced after erythropoietin addition and that JAK2 V617F constitutively induced JunB protein expression. Furthermore, JUNB knockdown reduced not only the growth of Ba/F3 cells by inducing apoptosis, but also the clonogenic and proliferative potential of human erythroid progenitors. These results establish a role for JunB in normal erythropoiesis and indicate that JunB may play a major role in the development of JAK2 V617F myeloproliferative disorders.

Novel mutations and their functional and clinical relevance in myeloproliferative neoplasms: JAK2, MPL, TET2, ASXL1, CBL, IDH and IKZF1

“…66 Such experimental data along with the fact that virtually all patients with PV carry a JAK2 mutation, 67 suggest a cause–effect relationship with erythrocytosis. 31, 68, 69, 70, 71 Somewhat consistent with this contention, JAK2 V617F homozygosity is infrequent in ET and its frequent occurrence in PV has been ascribed to mitotic recombination, possibly facilitated by JAK2 V617F-induced genetic instability. 72 However, both ET- and PMF-like disease are also induced in mice by experimental manipulation of the JAK2 V617F allele burden, 73, 74 and mutant allele burden in PMF is often as high as that seen in PV and its level increases further during fibrotic transformation.…”

Janus Kinase Deregulation in Leukemia and Lymphoma

“…MEK inhibitors suppress S phase entry but not prosurvival signals in mutant JAK-expressing cells (Funakoshi-Tago et al, 2010;Ugo et al, 2004). Consistent with this, elevated expression of ERK1 and ERK2 targets JUNB and FOSB is seen in JAK2-V617F-positive MPNs, and JUNB overexpression stimulates growth of erythroid cells in vitro (da Costa Reis Monte-Mó r et al, 2009;Puigdecanet et al, 2008). Additional insights into the hematological consequences of oncogenic RAS signaling have also been derived from studies of juvenile myelomoncytic leukemia (JMML) and chronic myelomonocytic leukemias (CMML).…”

Pathogenesis of Myeloproliferative Disorders

“…Inability to activate STAT5 through transcriptional inhibition by shRNA, or by Stat5 deletion, abrogates cytokine independent proliferation of JAK2 V617F expressing Ba/F3 cells (Basel F4 cell line), and erythrocytosis in JAK2 V617F expressing transgenic mice 35,36 . STAT5, in turn, has been reported to be involved in JAK2 V617F mediated deregulation of transcription of a wide variety of genes which include MYC, PIM, JUNB, ID1, BCL-xL and cell cycle regulators, resulting in increased myeloid lineage differentiation, inhibition of apoptosis, and proliferation [37][38][39][40][41] .…”