JAK2T875N is a novel activating mutation that results in myeloproliferative disease with features of megakaryoblastic leukemia in a murine bone marrow transplantation model

Abstract

Acute megakaryoblastic leukemia (AMKL) is a subtype of acute myeloid leukemia associated with a poor prognosis. However, there are relatively few insights into the genetic etiology of AMKL. We developed a screening assay for mutations that cause AMKL, based on the hypothesis that constitutive activation of STAT5 would be a biochemical indicator of mutation in an upstream effector tyrosine kinase. We screened human AMKL cell lines for constitutive STAT5 activation, and then used an approach combining mass spectrometry identification of tyrosine phosphorylated proteins and growth inhibition in the presence of selective small molecule tyrosine kinase inhibitors that would inform DNA sequence analysis of candidate tyrosine kinases. Using this strategy, we identified a new IntroductionAcute megakaryoblastic leukemia (AMKL) is a heterogeneous subtype of acute myeloid leukemia (AML) with diverse genetic and morphologic characteristics. The estimated frequency of AMKL varies between studies, perhaps due to a reliance on morphology for diagnostic criteria, but ranges from 3% to 14% of AML, and is more frequent in children than in adults. [1][2][3] In adults, AMKL is also frequently observed as secondary leukemia after chemotherapy or leukemic transformation of several chronic myeloproliferative syndromes including chronic myelogenous leukemia (CML), polycythemia vera (PV), essential thrombocytosis (ET), and idiopathic myelofibrosis (IMF). [4][5][6][7] Approximately 65% of AMKLs are associated with myelofibrosis. 2 Our understanding of the molecular basis of AMKL has progressed over the past several years. In adults, cytogenetic abnormalities are diverse and not restricted to AMKL, including abnormalities of 3p21-3p26; partial or total deletion of chromosomes 5 and 7; or gain of chromosome 19. 2,8,9 In childhood AMKL, 2 major subgroups have been described that include patients with constitutional trisomy 21 associated with GATA1 mutations, and those with the t(1;22)(p13;q13) translocation encoding the OTT-MAL (RBM15-MKL1) fusion protein. [10][11][12] Several observations suggest that these latter genetic mutations may not be sufficient to cause an AMKL phenotype. For example, although most Down syndrome patients with constitutional trisomy 21 and GATA1 mutations present with a transient myeloproliferative disorder (TMD) at or around birth, there is spontaneous remission of the TMD and absence of further malignant disease in most instances. However, in approximately 20% of cases, AMKL will develop in the first 4 years of life. 10,[13][14][15] In addition, expression of a mutant "GATA-1s" protein in a knock-in mouse model is able to induce a transient hyper-proliferation of yolk sac and fetal liver megakaryocyte progenitors, but is not sufficient to induce AMKL leukemogenesis per se. 16 Also, t(1;22)-positive AMKL has been found in monozygotic twins, indicating that the translocation can arise early in development, even though signs and symptoms of Constitutive tyrosine phosphorylation of STAT5 has been described in a si...

Deletions of the transcription factor Ikaros in myeloproliferative neoplasms

“…Mutations of Jak2 that lead to dramatic increase in its kinase activity (such as JAK2 fusions, JAK2-T875N and JAK2-R683) have been directly implicated in leukemogenesis. [37][38][39][40][41] The possible interaction of Ikaros with the JAK-STAT pathway in leukemic transformation is underlined by recent findings in childhood ALL, where JAK mutations (in particular JAK2 mutations) were significantly associated with IKZF1 defects. 42 We could induce cytokine hypersensitivity of mouse primary progenitors with shRNAmediated Ikzf1 deficiency, associated with elevated pStat5 levels ( Figure 4).…”

The role of Janus Kinase 2 V617F mutation in extramedullary hematopoiesis of the spleen in neoplastic myeloid disorders

“…19 It would be of great interest to further study our cohort of cases once assays using paraffin-embedded tissues become commercially available to detect other mutations associated with CMPD or acute leukemia, such as MPL-W515L, MPL-W515K, JAK2-L611S, JAK2-K607N and JAK2-T875N. [31][32][33][34][35][36] The finding of increased Bcl-xL expression in megakaryocytes of JAK2 V617F -positive spleen specimens suggests that the JAK2 V617F mutation may induce myeloproliferation via the STAT5/Bcl-xL pathway, at least partially, in splenic EMH. In support, sustained high levels of Bcl-xL were recently demonstrated to promote erythropoietin independent colony formation in vitro.…”

SOCS-mediated downregulation of mutant Jak2 (V617F, T875N and K539L) counteracts cytokine-independent signaling

“…The constitutively active Jak2 mutants have been shown to lead to cytokine receptor-dependent constitutive activation of various signaling proteins, such as STATs, mitogen-activated protein kinases and phosphatidylinositol-3-kinase/AKT (James et al, 2005;Lu et al, 2005;Mercher et al, 2006;Scott et al, 2007).…”