Project description:FDCP cells were stably transfected with JAK2V617F or WT JAK2 vectors and then examined for genome wide methylation with the HELP assay
Project description:Even though the Ten-eleven translocation (TET) enzymes catalyze the generation of 5-hydroxymethylcytosines required for lineage commitment and subsequent differentiation of stem cells into erythroid cells, the mechanisms that link extracellular signals to TET activation and DNA hydroxymethylation are unknown. We demonstrate that hematopoietic cytokines phosphorylate TET2, leading to its activation in erythroid progenitors. Specifically, cytokine receptor-associated JAK2 phosphorylates TET2 at tyrosines 1939 and 1964. Phosphorylated TET2 interacts with the erythroid transcription factor KLF1, and this interaction with TET2 is increased upon exposure to erythropoietin. The activating JAK2V617F mutation seen in myeloproliferative disease patient samples and in mouse models is associated with increased TET activity and cytosine hydroxymethylation as well as genome-wide loss of cytosine methylation. These epigenetic and functional changes are also associated with increased expression of several oncogenic transcripts. Thus, we demonstrate that JAK2-mediated TET2 phosphorylation provides a mechanistic link between extracellular signals and epigenetic changes during hematopoiesis. SIGNIFICANCE: Identification of TET2 phosphorylation and activation by cytokine-stimulated JAK2 links extracellular signals to chromatin remodeling during hematopoietic differentiation. This provides potential avenues to regulate TET2 function in the context of myeloproliferative disorders and myelodysplastic syndromes associated with the JAK2V617F-activating mutation.This article is highlighted in the In This Issue feature, p. 681.
Project description:Hyperactivation of JAK2 kinase is a unifying feature of human Ph- myeloproliferative neoplasms (MPNs), most commonly due to the JAK2 V617F mutation. Mice harboring a homologous mutation in the Jak2 locus exhibit a phenotype resembling polycythemia vera. NFκB pathway hyperactivation is present in myeloid neoplasms, including MPNs, despite scarcity of mutations in NFκB pathway genes. To determine the impact of NFκB pathway hyperactivation in conjunction with Jak2 V617F, we utilized Ikk2 (Ikk2-CA) mice. Pan-hematopoietic Ikk2-CA alone produced depletion of hematopoietic stem cells and B cells. When combined with the Jak2 V617F mutation, Ikk2-CA rescued the polycythemia vera phenotype of Jak2 V617F. Likewise, Jak2 V617F ameliorated defects in hematopoiesis produced by Ikk2-CA. Single-cell RNA sequencing of hematopoietic stem and progenitor cells revealed multiple genes antagonistically regulated by Jak2 and Ikk2, including subsets whose expression was altered by Jak2 V617F and/or Ikk2-CA but partly or fully rectified in the double mutant. We hypothesize that Jak2 promotes hematopoietic stem cell population self-renewal, whereas Ikk2 promotes myeloid lineage differentiation, and biases cell fates at several branch points in hematopoiesis. Jak2 and Ikk2 both regulate multiple genes affecting myeloid maturation and cell death. Therefore, the presence of dual Jak2 and NFκB hyperactivation may present neomorphic therapeutic vulnerabilities in myeloid neoplasms.
Project description:Model describing how HOXA9 may control the evolution of myeloproliferative neoplasms by integrating the orders of JAK2 and TET2 mutation
Project description:Clonal hematopoiesis of indeterminate potential is prevalent in elderly individuals and associated with increased risks of all-cause mortality and cardiovascular disease. However, mouse models to study the dynamics of clonal hematopoiesis and its consequences on the cardiovascular system under homeostatic conditions are lacking. We used a model of clonal hematopoiesis using adoptive transfer of unfractionated ten-eleven translocation 2-mutant (Tet2-mutant) bone marrow cells into nonirradiated mice. Consistent with age-related clonal hematopoiesis observed in humans, these mice displayed a progressive expansion of Tet2-deficient cells in multiple hematopoietic stem and progenitor cell fractions and blood cell lineages. The expansion of the Tet2-mutant fraction was also observed in bone marrow-derived CCR+ myeloid cell populations within the heart, but there was a negligible impact on the yolk sac-derived CCR2- cardiac resident macrophage population. Transcriptome profiling revealed an enhanced inflammatory signature in the donor-derived macrophages isolated from the heart. Mice receiving Tet2-deficient bone marrow cells spontaneously developed age-related cardiac dysfunction characterized by greater hypertrophy and fibrosis. Altogether, we show that Tet2- mediated hematopoiesis contributes to cardiac dysfunction in a nonconditioned setting that faithfully models the human clonal hematopoiesis in unperturbed bone marrow. Our data support clinical findings that clonal hematopoiesis per se may contribute to diminished health span.
Project description:To investigate the signaling pathway required for the Tet2 mutant associated clonal hematopoiesis, we identified the activated signaling pathway in Tet2-deficient hematopoietic stem/progenitor cells compared to WT cells and using transgentic mouse model to validate our findings. In short, the cGAS-STING pathway is activated in Tet2-deficient HSPCs and promotes the development of CH associated with Tet2 deficiency.
Project description:TET2 is among the most commonly mutated genes in both clonal hematopoiesis and myeloid malignancies, thus, the ability to identify selective dependencies in TET2 deficient cells has broad translational significance. Here, we identify regulators of Tet2 knockout (KO) hematopoietic stem and progenitor cell (HSPC) expansion using an in vivo CRISPR-Cas9 KO screen, in which nucleotide barcoding enabled large-scale clonal tracing of Tet2 deficient HSPCs in a physiological setting. Our screen identified candidate genes, including Ncoa4, that are selectively required for Tet2 KO clonal outgrowth compared to wild-type (WT). Ncoa4 targets ferritin for lysosomal degradation (ferritinophagy), maintaining intracellular iron homeostasis by releasing labile iron (Fe2+) in response to cellular demands. In Tet2-deficient HSPCs, increased mitochondrial ATP production correlates with increased cellular iron requirements, and in turn, promotes Ncoa4-dependent ferritinophagy. Restricting iron availability reduces Tet2 KO stem cell numbers, revealing a dependency in TET2-mutated myeloid neoplasms.
Project description:Ruxolinitib was approved by the FDA for the treatment of JAK2-V617F positive myelofibrosis. Unexpectedly, treatment of JAK2-V617F expressing cells with ruxolitinib causes paradoxical hyperphosphorylation of JAK2 at Tyr1007/1008 sites. The mechanism of ruxolitinib-induced JAK2 hyperphosphorylation is not well understood. A ruxolitinib-resistant JAK2 variant (V617F+L983F) and a JAK2-V617F kinase dead mutant (JAK2-V617F+K882R) did not show paradox hyperphosphorylation after ruxolitinib treatment indicating that ruxolitinib-mediated JAK2 hyperphosphorylation is mediated by a JAK2 intrinsic mechanism. Native immunocomplexes of JAK2-V617F with an antibody against pTyr1007/1008 could be blocked by the presence of ruxolitinib, although JAK2-V617F was hyperphosphorylated at these sites, suggesting that in the presence of ruxolitinib the JAK2 activation loop is buried within the kinase domain. This stabilization of the activation loop conformation results in the protection of pTyr1007/1008 sites from phosphatases. When JAK2 is in an inhibited conformationally restricted state, the phosphate group of Tyr1007 and Tyr1008 forms an intermolecular interaction with Arg975 and Lys999, respectively. Mutation of Arg975 and Lys999 to Ala reduced the phosphorylation at both Tyr1007/1008 residues, and importantly, ruxolitinib treatment did not lead to JAK2 hyperphosphorylation in these variants. Hyperphosphorylated JAK2 is hyperactive after ruxolitinib dissociation and activates STAT5 target genes PIM2, ID1, and MPL. Our results suggest a novel mode of kinase regulation by modulating kinase activity through conformational changes induced by ruxolitinib.
Project description:Gene expression profile of purified peripheral CD14+CD163+ macrophages was analyzed via RNA-Seq in the presence or absence of inflammatory stress to assess the impact of TET2 disruption on gene expression in macaque hematopoiesis.