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 JAK2T875N mutation in the AMKL cell line CHRF-288-11. JAK2T875N is a constitutively activated tyrosine kinase that activates downstream effectors including STAT5 in hematopoietic cells in vitro. In a murine transplant model, JAK2T875N induced a myeloproliferative disease characterized by features of AMKL, including megakaryocytic hyperplasia in the spleen; impaired megakaryocyte polyploidization; and increased reticulin fibrosis of the bone marrow and spleen. These findings provide new insights into pathways and therapeutic targets that contribute to the pathogenesis of AMKL.
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ABSTRACT: The redox regulation of Janus kinases (JAKs) is a complex subject. Due to other redox-sensitive kinases in the kinome, redox-sensitive phosphatases, and cellular antioxidant systems and reactive oxygen species (ROS) production systems, the net biological outcomes of oxidative stress on JAK-dependent signal transduction vary according to the specific biological system examined. This review begins with a discussion of the biochemical evidence for a cysteine-based redox switch in the catalytic domain of JAKs, proceeds to consider direct and indirect regulatory mechanisms involved in biological experiments, and ends with a discussion of the role(s) of redox regulation of JAKs in various diseases.JAK-STAT. 10/2013; 2(4):e26141.
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ABSTRACT: The proto-oncogene SKI is highly expressed in human myeloid leukemia and also in murine hematopoietic stem cells. However, its operative relevance in these cells remains elusive. We have over-expressed SKI to define its intrinsic role in hematopoiesis and myeloid neoplasms, which resulted in a robust competitive advantage upon transplantation, a complete dominance of the stem and progenitor compartments, and a marked enhancement of myeloid differentiation at the expense of other lineages. Accordingly, enforced expression of SKI induced a gene signature associated with hematopoietic stem cells and myeloid differentiation, as well as hepatocyte growth factor signaling. Here we demonstrate that, in contrast to what has generally been assumed, the significant impact of SKI on hematopoiesis is independent of its ability to inhibit TGF-beta signaling. Instead, myeloid progenitors expressing SKI are partially dependent on functional hepatocyte growth factor signaling. Collectively our results demonstrate that SKI is an important regulator of hematopoietic stem cell activity and its over-expression leads to myeloproliferative disease.Haematologica 01/2014; · 5.94 Impact Factor
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ABSTRACT: Janus kinases (JAK) are the mediators of a variety of cytokine signals via their cognate receptors that result in activation of intracellular signaling pathways. Alterations in JAK1, JAK2, JAK3 and TYK2 signaling contribute to different disease states, and dysregulated JAK-STAT signaling is associated with hematological malignancies, autoimmune disorders and immune-deficient conditions. Genetic alterations of JAK2 occur in the majority of patients with myeloproliferative neoplasms (MPN) and occur in a subset of patients with acute leukemias. JAK-mediated signaling critically relies on STAT transcription factors, and on activation of the MAPK and PI3K/Akt signaling axes. Hyperactive JAK at the apex of these potent oncogenic signaling pathways therefore represents an important target for small molecule kinase inhibitors in different disease states. The JAK1/2 inhibitor ruxolitinib and the JAK3 inhibitor tofacitinib were recently approved for the treatment of myelofibrosis and rheumatoid arthritis, respectively and additional ATP-competitive JAK inhibitors are in clinical development. Although these agents show clinical activity, the ability of these JAK inhibitors to induce clinical/molecular remissions in hematological malignancies appears limited and resistance upon chronic drug exposure is seen. Alternative modes of targeting JAK2 such as allosteric kinase inhibition or HSP-90 inhibition are under evaluation as is the use of histone deacetylase inhibitors. Combination therapy approaches integrating inhibition of STAT, PI3K/Akt and MAPK pathways with JAK kinase inhibitors might be critical to overcome malignancies characterized by dysregulated JAK signaling.Clinical Cancer Research 02/2014; · 8.19 Impact Factor