Histone chaperone HIRA dictate proliferation vs differentiation of chronic myeloid leukemia cells

Abnormal proliferation and disrupted differentiation of hematopoietic progenitors mark leukemia. Histone cell cycle regulator A (HIRA), a histone chaperone, regulates hemogenic to hematopoietic transition involved in normal hematopoiesis. But, its role remains unexplored in leukemia, a case of dysregulated hematopoiesis. Here, the Cancer Cell Line Encyclopedia database analysis showed enhanced HIRA mRNA expression in cells of hematopoietic and lymphoid origin with maximal expression in the chronic myeloid leukemia (CML) cell line, K562. This observation was further endorsed by the induced expression of HIRA in CML patient samples compared to healthy individuals and Acute Myeloid Leukemia patients. Downregulation of HIRA in K562 cells displayed cell cycle arrest, loss in proliferation, presence of polyploidy with significant increase in CD41⁺ population thereby limiting proliferation but inducing differentiation of leukemia cells to megakaryocyte fate. Induced megakaryocyte differentiation of mouse Hira-knockout hematopoietic progenitors in vivo further confirmed the in vitro findings in leukemia cells. Molecular analysis showed the involvement of MKL1/GATA2/H3.3 axis in dictating differentiation of CML cells to megakaryocytes. Thus, HIRA could be exploited for differentiation induction therapy in CML and in chronic pathological conditions involving low platelet counts.