Hmga2 collaborates with V617F in the development of myeloproliferative neoplasms.

High-mobility group AT-hook 2 () is crucial for the self-renewal of fetal hematopoietic stem cells (HSCs) but is downregulated in adult HSCs via repression by and the polycomb-recessive complex 2 (PRC2) including EZH2. The messenger RNA (mRNA) level is often elevated in patients with myelofibrosis that exhibits an advanced myeloproliferative neoplasm (MPN) subtype, and deletion of promotes the progression of severe myelofibrosis in mice with upregulation of several oncogenes such as . However, the direct role of in the pathogenesis of MPNs remains unknown. To clarify the impact of on MPNs carrying the driver mutation, we generated Δ/ mice overexpressing Hmga2 due to deletion of the 3' untranslated region. Compared with mice, Δ/ mice exhibited more severe leukocytosis, anemia and splenomegaly, and shortened survival, whereas severity of myelofibrosis was comparable. Δ/ cells showed a greater repopulating ability that reproduced the severe MPN compared with cells in serial bone marrow transplants, indicating that Hmga2 promotes MPN progression at the HSC level. Hmga2 also enhanced apoptosis of erythroblasts that may worsen anemia. Relative to hematopoietic stem and progenitor cells (HSPCs), over 30% of genes upregulated in Δ/ HSPCs overlapped with those derepressed by loss in / HSPCs, suggesting that Hmga2 may facilitate upregulation of Ezh2 targets. Correspondingly, deletion of ameliorated anemia and splenomegaly in / mice, and suppression and PRC2 mutations correlated with the elevated mRNA levels in patients with MPNs, especially myelofibrosis. These findings suggest the crucial role of HMGA2 in MPN progression.