Project description:Janus kinases (Jak) mediate cytokine, hormone and growth factor responses in hematopoietic cells. Jak2 is one of the most frequently mutated genes in the aging hematopoietic system and in hematopoietic cancers. Mutations in Jak constitutively activate downstream signaling and are drivers of myeloproliferative neoplasms (MPN). In clinical use, Jak-inhibitors have incomplete effects on overall disease burden of Jak2 mutated clones prompting us to investigate the mechanism underlying disease persistence. By in-depth phospho-proteome profiling we here identify proteins involved in mRNA processing as targets of mutant Jak2. Inactivation of the post-translationally modified Jak2-target Ybx1 sensitizes Jak-inhibitor persistent cells to apoptosis and results in RNA mis-splicing, retained intron enrichment and disruption of the transcriptional control of extracellular signal-regulated kinase (ERK) signaling. In combination with pharmacological Jak-inhibition it induces apoptosis in Jak2-dependent murine and primary human cells, leading to in vivo regression of the malignant clones and inducing remission. This identifies and validates a novel cell-intrinsic mechanism how differential protein phosphorylation results in splicing-dependent alterations of Jak2-ERK-signaling and the maintenance of Jak2V617F malignant clones. Therapeutic targeting of Ybx1 dependent ERK-signaling in combination with Jak2-inhibition may eradicate Jak2-mutated cells.
Project description:Janus kinases (Jak) mediate cytokine, hormone and growth factor responses in hematopoietic cells. Jak2 is one of the most frequently mutated genes in the aging hematopoietic system and in hematopoietic cancers. Mutations in Jak constitutively activate downstream signaling and are drivers of myeloproliferative neoplasms (MPN). In clinical use, Jak-inhibitors have incomplete effects on overall disease burden of Jak2 mutated clones, prompting us to investigate the mechanism underlying disease persistence. By in-depth phospho-proteome profiling we here identify proteins involved in mRNA processing as targets of mutant Jak2. Inactivation of the post-translationally modified Jak2-target Ybx1 sensitizes Jak-inhibitor persistent cells to apoptosis and results in RNA mis-splicing, retained intron enrichment and disruption of the transcriptional control of extracellular signal-regulated kinase (ERK) signaling. In combination with pharmacological Jak-inhibition it induces apoptosis in Jak2-dependent murine and primary human cells, leading to in vivo regression of the malignant clones and inducing remission. This identifies and validates a novel cell-intrinsic mechanism how differential protein phosphorylation results in splicing-dependent alterations of Jak2-ERK-signaling and the maintenance of Jak2V617F malignant clones. Therapeutic targeting of Ybx1 dependent ERK-signaling in combination with Jak2-inhibition may eradicate Jak2-mutated cells.
Project description:Inactivation of Ybx1 results in RNA mis-splicing, retained intron enrichment and disruption of the transcriptional and post-translational control of extracellular signal-regulated kinase (ERK) signaling
Project description:Persistence of malignant clones following cytotoxic or targeted therapy is a major determinant of adverse outcome in patients with hematologic malignancies. Despite the fact that the majority of patients with acute myeloid leukemia (AML) achieve complete remission after chemotherapy, a large proportion of them relapse as a result of residual malignant cells. After discontinuation of treatment, these persistent clones have a competitive advantage and re-establish disease. Therefore, targeting strategies that specifically reduce competitive advantage of malignant cells while leaving normal cells unaffected are clearly warranted. Recently, our group identified cold-shock protein and splicing factor YBX1 as a mediator of disease persistence in JAK2-mutated myeloproliferative neoplasia. The role of cold-shock proteins in AML, however, remained so far elusive. Using genetic screening, we identified YBX1 as a relevant functional dependency in AML. Inactivation of YBX1 in vitro and in vivo confirmed its role as an essential driver of leukemia development and maintenance. Here, we identified its ability to bind specific mRNAs, including MYC, and amplify their translation at the ribosomes by recruitment to polysomal chains. Genetic inactivation of YBX1 disrupted this regulatory circuit and displaced a number of oncogenic drivers from polysomes, with subsequent depletion of protein abundance. As a consequence, leukemia cells showed reduced proliferation and were out-competed in vitro and in vivo, while normal cells remained largely unaffected. Collectively, this data establishes YBX1 as a specific dependency and therapeutic target in AML that is essentially required for oncogenic protein expression.
Project description:Model describing how HOXA9 may control the evolution of myeloproliferative neoplasms by integrating the orders of JAK2 and TET2 mutation
Project description:The genetics of classical Hodgkin lymphoma (cHL) is poorly understood. The finding of a JAK2-involving t(4;9)(q21;p24) in one case of cHL prompted us to characterize this translocation on a molecular level and to determine the prevalence of JAK2 rearrangements in cHL. We showed that the t(4;9)(q21;p24) leads to a novel SEC31A-JAK2 fusion. Screening of 131 cHL cases identified one additional case with SEC31A-JAK2 and two additional cases with rearrangements involving JAK2. We demonstrated that SEC31A-JAK2 is oncogenic in vitro and acts as a constitutively activated tyrosine kinase that is sensitive to JAK inhibitors. In vivo, SEC31A-JAK2 was found to induce a T-lymphoblastic lymphoma or myeloid hyperplasia in a murine bone marrow transplant model. Altogether, we identified SEC31A-JAK2 as a first aberration characteristic for cHL and provide evidence that JAK2 rearrangements occur in a minority of cHL cases. Given the proven oncogenic potential of this novel fusion, our studies provide new insights into the pathogenesis of cHL and indicate that in at least some cases, constitutive activation of the JAK-STAT pathway is caused by JAK2 rearrangements. The finding that SEC31A-JAK2 responds to JAK inhibitors indicates that patients with cHL and JAK2 rearrangements may benefit from targeted therapies. Genomic profiling of primary and secondary transplanted mice expressing SEC31A-JAK2 with myeloid hyperplasia and T-lymphoblastic lymphoma Individual sample against a normal control