γ-Catenin-Dependent Signals Maintain BCR-ABL1+ B Cell Acute Lymphoblastic Leukemia

The BCR-ABL1 fusion protein is the cause of chronic myeloid leukemia (CML) and of a significant fraction of adult-onset B cell acute lymphoblastic leukemia (B-ALL) cases. Using mouse models and patient-derived samples, we identified an essential role for γ-catenin in the initiation and maintenance of BCR-ABL1 + B-ALL but not CML. The selectivity was explained by a partial γ-catenin dependence of MYC expression together with the susceptibility of B-ALL, but not CML, to reduced MYC levels. MYC and γ-catenin enabled B-ALL maintenance by augmenting BIRC5 and enforced BIRC5 expression overcame γ-catenin loss. Since γ-catenin was dispensable for normal hematopoiesis, these lineage- and disease-specific features of canonical Wnt signaling identified a potential therapeutic target for the treatment of BCR-ABL1 + B-ALL.

Notch signaling in the immune system

Nicolas Fasnacht, Freddy Radtke

The Notch signaling pathway regulates many aspects of embryonic development, as well as differentiation processes and tissue homeostasis in multiple adult organ systems. Disregulation of Notch signaling is associated with several human disorders, including cancer. In the last decade, it became evident that Notch signaling plays important roles within the hematopoietic and immune systems. Notch plays an essential role in the development of embryonic hematopoietic stem cells and influences multiple lineage decisions of developing lymphoid and myeloid cells. Moreover, recent evidence suggests that Notch is an important modulator of T cell-mediated immune responses. In this review, we discuss Notch signaling in hematopoiesis, lymphocyte development, and function as well as in T cell acute lymphoblastic leukemia.

2010

The chromatin remodeller Chd7 and the calcium ATPase Serca2 - adding new facets to the role of Notch in Hematopoiesis and T-ALL

Monique Coersmeyer

Project I: Chd7 Deficiency does not affect N1-driven T-ALL Induction and Maintenance nor impair Hematopoiesis Notch1 has been shown to be a key driver in pediatric T-cell acute lymphobastic leukemia (T-ALL). Previous work in the lab identified the chromatin-remodeling enzyme Chd7 to be highly over-expressed in aggressive versus pre-malignant disease. The aim of this project was to study if Chd7 is required during T-ALL initiation and disease maintenance as well as to characterize its role in the hematopoietic system under physiological and stress conditions. Therefore, Chd7 cKO animals were crossed with the MxCre deleter to ablate Chd7 specifically in BM progenitors. Chd7 deficiency did not induce any overt phenotype in the hematopoietic system, when studied under âsteadyâ state or stress conditions. In addition, Chd7 proved to be dispensable in the initiation and maintenance of murine and human Notch1-driven T-ALL. Therefore, we can rule out a role of Chd7 during late-stage leukemogenesis in Notch1-induced murine and human T-ALL. Project II: Serca2, a putative drug target to fight Notch1-driven T cell acute lymphoblastic leukemia, and its role in Hematopoiesis The Notch signalling pathway represents a bona fide drug target. We and Roti et al. performed a chemical compound screen and identified Cyclopiazonic acid (CPA) as potent Notch inhibitor. Biological target of this compound is the Sarco/Endoplasmic Reticulum ATPase2 (Serca2) that is involved in calcium homeostasis within the cell. Recently, it was shown that Serca2 regulates Notch1 (N1) receptor maturation and inhibition of Serca ATPases, using thapsigargin, blocks T-ALL progression in xenografts (Roti et al., 2013). The putative global effects of Serca2 inhibition on hematopoiesis have, however, not been addressed in this study. Aim of this study was to characterize the function of Serca2 in the hematopoietic system. Therefore, we crossed Serca2 cKO with MxCre to ablate Serca2 function in BM progenitors. Serca2 haploinsufficiency did not lead to any overt phenotype under physiological or competitive conditions. In contrast, Serca2ÎMxCre chimeras showed (i) impaired long-term reconstitution capacity upon transplantation, (ii) a severe reduction of total BM, splenic and thymic cellularity and (iii) an enrichment of KLS cells, the cell pool that contains HSCs. Mature lineages were highly apoptotic, while KLS were not majorly affected by apoptosis, resided predominantly in G0 phase of the cell cycle, exhibited slower cycling kinetics and were functionally impaired as they formed less and smaller colony forming units in vitro. Deregulated calcium levels can lead to an accumulation of unfolded proteins in the ER. In order to resolve ER stress, the cell activates the unfolded protein response (UPR). In case of unresolved ER stress, however, the cell undergoes apoptosis. We demonstrate that mature hematopoietic lineages up-regulate UPR-associated and pro-apoptotic genes, while KLS cells, in contrast, show unperturbed expression of these genes. In addition, we performed in vitro experiments, inhibiting Serca function in Lin- BM cells via thapsigargin (TH) treatment. TH induced severe apoptosis in the overall cell population, while KLS accumulated and were blocked in the G0 phase, closely mimicking Serca2 LOF in vivo. We therefore question the therapeutic approach of targeting Serca2 in N1-driven T-ALL due to severe side effects induced by Serca2 inactivation in the BM.

EPFL2015

Notch1-driven T-ALL chromatin landscape is regulated by Tcf1 in hematopoietic progenitors

Mateusz Waldemar Antoszewski

Notch1 receptor signaling is essential for T cell fate specification and physiological thymic T lymphocyte development. Its dysregulation and oncogenic activation are detected in almost 80% of pediatric patients suffering from T cell acute lymphoblastic leukemia (T-ALL). T-ALL is a hematological neoplasm arising from immature thymocytes. T cell factor 1 (Tcf1) is a crucial well-known transcription factor regulating the early stages of thymocyte maturation and Notch1 directly drives the expression of Tcf1 during normal T cell development. Here we assessed the role of Tcf1 in modulating chromatin topology which enables the initiation of T-ALL at the level of early hematopoietic progenitors. This allows for the discovery of stage-setting epigenetic regulators establishing a leukemia-prone chromatin landscape during Notch1-driven disease initiation. We found Tcf1 to be an essential mediator of Notch1 signaling during T-ALL induction. Inactivation of Tcf1 prevented leukemogenesis despite oncogenic Notch1 activation. Genomic analysis of hematopoietic progenitors revealed T cell lineage specification to be essential in T-ALL initiation prior to the appearance of phenotypic features of T cells. The expression of genes associated with the T cell lineage was dependent on Notch1 and Tcf1. Chromatin accessibility, chromosome conformation capture and ChIP-seq analysis revealed the co-regulatory epigenetic function of Notch1 and Tcf1 in imprinting a leukemic chromatin landscape. Epigenetic modulation of distal enhancers which regulate leukemic oncogenes has been well described in patient-derived T-ALL cells. The Notch1-Myc enhancer region was shown to be indispensable in the process of leukemogenesis. We have identified a novel regulatory locus, dependent on Tcf1 and Notch1, essential for the expression of Myc in pre-T-ALL cells. This genomic region termed Tcf1-regulated Myc enhancer (TMe) was highly conserved across species. TMe was essential for the transition of pre-leukemic cells to a transplantable full-blown T-ALL but was dispensable for the physiological development of T cells. After activation of the enhancer in hematopoietic progenitors, this regulatory site remained accessible and bound by Tcf1 in murine and human T-ALL cells. Tcf1 is therefore required for shaping the epigenetic landscape of hematopoietic progenitors overexpressing oncogenic Notch1, and thus regulates the expression of genes involved in leukemogenesis.