The MLLT10 gene, located at 10p13, is a known partner of MLL and PICALM in specific leukemic fusions generated from recurrent 11q23 and 11q14 chromosome translocations. Deep sequencing recently identified NAP1L1/12q21 as another MLLT10 partner in T-cell acute lymphoblastic leukemia (T-ALL). In pediatric T-ALL, we have identified 2 RNA processing genes, that is, HNRNPH1/5q35 and DDX3X/Xp11.3 as new MLLT10 fusion partners. Gene expression profile signatures of the HNRNPH1- and DDX3X-MLLT10 fusions placed them in the HOXA subgroup. Remarkably, they were highly similar only to PICALM-MLLT10-positive cases. The present study showed MLLT10 promiscuity in pediatric T-ALL and identified a specific MLLT10 signature within the HOXA subgroup.

Deregulated Notch signaling has been extensively linked to T-cell acute lymphoblastic leukemia (T-ALL). Here, we show a direct relationship between Notch3 receptor and Jagged1 ligand in human cell lines and in a mouse model of T-ALL. We provide evidence that Notch-specific ligand Jagged1 is a new Notch3 signaling target gene. This essential event justifies an aberrant Notch3/Jagged1 cis-expression inside the same cell. Moreover, we demonstrate in Notch3-IC–overexpressing T lymphoma cells that Jagged1 undergoes a raft-associated constitutive processing. The proteolytic cleavage allows the Jagged1 intracellular domain to empower Notch signaling activity and to increase the transcriptional activation of Jagged1 itself (autocrine effect). On the other hand, the release of the soluble Jagged1 extracellular domain has a positive impact on activating Notch signaling in adjacent cells (paracrine effect), finally giving rise to a Notch3/Jagged1 auto-sustaining loop that supports the survival, proliferation, and invasion of lymphoma cells and contributes to the development and progression of Notch-dependent T-ALL. These observations are also supported by a study conducted on a cohort of patients in which Jagged1 expression is associated to adverse prognosis.

Infiltration of the central nervous system is a severe trait of T cell acute lymphoblastic leukemia. Inhibition of CXC chemokine receptor 4 significantly ameliorates T cell acute lymphoblastic leukemia in murine models of the disease; however, signaling by CXC chemokine receptor 4 is important in limiting the divagation of peripheral blood mononuclear cells out of the perivascular space into the central nervous system parenchyma. Therefore, Inhibition of CXC chemokine receptor 4 potentially may untangle T cell acute lymphoblastic leukemia cells from retention outside the brain. Here, we show that leukemic lymphoblasts massively infiltrate cranial bone marrow, with diffusion to the meninges without invasion of the brain parenchyma, in mice that underwent xenotransplantation with human T cell acute lymphoblastic leukemia cells or that developed leukemia from transformed hematopoietic progenitors. We tested the hypothesis that T cell acute lymphoblastic leukemia neuropathology results from meningeal infiltration through CXC chemokine receptor 4-mediated bone marrow colonization. Inhibition of leukemia engraftment in the bone marrow by pharmacologic CXC chemokine receptor 4 antagonism significantly ameliorated neuropathologic aspects of the disease. Genetic deletion of CXCR4 in murine hematopoietic progenitors abrogated leukemogenesis induced by constitutively active Notch1, whereas lack of CCR6 and CCR7, which have been shown to be involved in T cell and leukemia extravasation into the central nervous system, respectively, did not influence T cell acute lymphoblastic leukemia development. We hypothesize that lymphoblastic meningeal infiltration as a result of bone marrow colonization is responsible for the degenerative alterations of the neuroparenchyma as well as the alteration of cerebrospinal fluid drainage in T cell acute lymphoblastic leukemia xenografts. Therefore, CXC chemokine receptor 4 may constitute a pharmacologic target for T cell acute lymphoblastic leukemia neuropathology.

Precursor-B cell acute lymphoblastic leukemia (pre-B ALL) is the most common pediatric cancer, but there are no useful zebrafish pre-B ALL models. We describe the first highly-penetrant zebrafish pre-B ALL, driven by human MYC. Leukemias express B lymphoblast-specific genes and are distinct from T cell ALL (T-ALL)-which these fish also develop. Zebrafish pre-B ALL shares in vivo features and expression profiles with human pre-B ALL, and these profiles differ from zebrafish T-ALL or normal B and T cells. These animals also exhibit aberrant lymphocyte development. As the only robust zebrafish pre-B ALL model and only example where T-ALL also develops, this model can reveal differences between MYCdriven pre-B vs. T-ALL and be exploited to discover novel pre-B ALL therapies.

Key Points• MYC translocations represent a genetic subgroup of NOTCH1-independent T-ALL clustered within the TAL/LMO category.• MYC translocations are secondary abnormalities, which appear to be associated with induction failure and relapse.MYC translocations represent a genetic subtype of T-lineage acute lymphoblastic leukemia (T-ALL), which occurs at an incidence of ∼6%, assessed within a cohort of 196 T-ALL patients (64 adults and 132 children). The translocations were of 2 types; those rearranged with the T-cell receptor loci and those with other partners. MYC translocations were significantly associated with the TAL/LMO subtype of T-ALL (P 5 .018) and trisomies 6 (P < .001) and 7 (P < .001). Within the TAL/LMO subtype, gene expression profiling identified 148 differentially expressed genes between patients with and without MYC translocations; specifically, 77 were upregulated and 71 downregulated in those with MYC translocations. The poor prognostic marker, CD44, was among the upregulated genes. MYC translocations occurred as secondary abnormalities, present in subclones in one-half of the cases. Longitudinal studies indicated an association with induction failure and relapse. (Blood. 2014;124(24):3577-3582)

T-cell acute lymphoblastic leukemia (T-ALL) is an aggressive hematological cancer characterized by skewed epigenetic patterns, raising the possibility of therapeutically targeting epigenetic factors in this disease. Here we report that among different cancer types, epigenetic factor TET1 is highly expressed in TALL and is crucial for human TALL cell growth in vivo. Tet1 knockout mice and knockdown in human T-cells did not perturb normal T-cell proliferation, indicating that TET1 expression is dispensable for normal T-cell growth. The promotion of leukemic growth by TET1 was depending on its catalytic property to maintain global 5hydroxymethylcytosine (5hmC) marks, thereby regulating cell cycle, DNA repair genes and TALL associated oncogenes. Furthermore, overexpression of the Tet1 catalytic domain was sufficient to augment global 5hmC levels and leukemic growth of TALL cells in vivo. We demonstrate that PARP enzymes, which are highly expressed in TALL patients, participate in establishing H3K4me3 marks at the TET1 promoter and that PARP1 interacts with the TET1 protein. Importantly, the growth related role of TET1 in TALL could be antagonized by the clinically approved PARP inhibitor Olaparib, which abrogated TET1 expression, induced loss of 5hmC marks and antagonized leukemic growth of TALL cells, opening a therapeutic avenue for this disease. 10 transplantation (Fig. S2H). Moreover, in a published microarray analysis of TALL cell lines transplanted into xenografts, a similar increase in TET1 expression was observed (Fig. S2I), suggesting that high TET1 expression is associated with leukemic growth in vivo. Indeed, forced expression of Tet1-CD in TALL cell lines significantly augmented leukemic growth in vitro and in vivo (Fig. 3D-E). These data clearly suggest that the growth-promoting role of TET1 in TALL is at least partly dependent on its enzymatic activity. TET1 depletion induces loss of 5hmC marks at promoters and gene bodies of genes involved in cell cycle, DNA repair and NOTCH pathway Next we analyzed 5hmC levels in TALL cells via Intracellular fluorescence (IF) in our knockdown, rescue and overexpression experiments. IF-flow cytometry for 5hmC marks in TET1 depleted JURKAT cells, primary TALL patients and TET1 knockout bulk TALL cell lines revealed a significant decrease in global 5hmC levels (Fig. 4A-B and Fig. S3A-B) and increase in 5mC levels (Fig. S3C). Conversely, overexpression of Tet1-CD in TET1 depleted cells or wild type TALL cells induced a global increase in 5hmC levels (Fig. 4C-D). Furthermore, we performed hydroxymethylated DNA immunoprecipitation (hMeDIP)-seq in TET1 depleted JURKAT cells. In hMeDIP-seq, TET1 depletion resulted in more than a 59% reduction of global 5hmC enrichment at the promoter (-5kbTSS), gene body (GB) and intergenic regions compared to scrambled control (referred to as TET1 dependent 5hmC or T1-5hmC regions from here) (Fig. 4E-F). In detail, a total of 2,404 and 6,115 5hmC enriched promoters and GB were observed in the scrambled arm, respectively, out of which more th...

cAMP response element binding protein (CREB) is frequently overexpressed in acute myeloid leukemia (AML) and acts as a proto-oncogene; however, it is still debated whether such overactivation alone is able to induce leukemia as its pathogenetic downstream signaling is still unclear. We generated a zebrafish model overexpressing CREB in the myeloid lineage, which showed an aberrant regulation of primitive hematopoiesis, and in 79% of adult CREB-zebrafish a block of myeloid differentiation, triggering to a monocytic leukemia akin the human counterpart. Gene expression analysis of CREB-zebrafish revealed a signature of 20 differentially expressed human homologous CREB targets in common with pediatric AML. Among them, we demonstrated that CREB overexpression increased CCAAT-enhancer-binding protein-δ (C/EBPδ) levels to cause myeloid differentiation arrest, and the silencing of CREB-C/EBPδ axis restored myeloid terminal differentiation. Then, C/EBPδ overexpression was found to identify a subset of pediatric AML affected by a block of myeloid differentiation at monocytic stage who presented a significant higher relapse risk and the enrichment of aggressive signatures. Finally, this study unveils the aberrant activation of CREB-C/EBPδ axis concurring to AML onset by disrupting the myeloid cell differentiation process. We provide a novel in vivo model to perform high-throughput drug screening for AML cure improvement.

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