Project description:The Wnt-signalling pathway is one of the core de-regulated pathways in chronic lymphocytic leukemia (CLL), activated in a subset of patients by somatic coding mutations. Here we describe an alternative mechanism of Wnt-activation in malignant B cells, mediated by Notch2 activity in mesenchymal stromal cells (MSC) in the tumor microenvironment. We identified that tumor cells specifically induce and activate Notch2 in MSCs. Notch2 orchestrates the expression of target genes essential for the activation of canonical Wnt-signaling in CLL cells. Mechanistically, stromal Notch2 mediates the stabilization of â-catenin by inhibiting the activation of Gsk3-â in malignant B cells. Pharmacological inhibition of the Wnt-pathway mitigates microenvironment-mediated survival of malignant B cells in vitro. Similarly, inhibition of Notch-signaling impaired survival of CLL cells and disease engraftment in a PDX mouse model. Notch2 activation in the tumour microenvironment is a pre-requisite for the GSK3-â dependent activation of the canonical Wnt-signaling in tumor cells.
Project description:We used microarrays to investigate differential gene expression in mouse bone marrow derived mesenchymal stromal cells, proficient or deficient for Notch2, cultured for 5 days in the presence or absence with primary CLL cells from 6 patients
Project description:Mesenchymal stromal cells (MSCs) are located in bone marrow where they help to maintain bone homeostasis and repair through the ability to expand in response to mitotic stimuli and differentiate into skeletal linages. The signalling mechanisms that enable precise control of MSC function remain unclear. Here, we have identified a non-canonical epidermal growth factor (EGF) signalling pathway in MSCs, which acts via integrin-linked kinase (ILK) to activate β-catenin, a key component of Wnt signalling. EGF induces nuclear translocation of β-catenin in MSCs but does not drive T cell factor (TCF)-mediated transactivation of Wnt target genes, and we demonstrate by Design of Experiments statistical analysis that the EGF/β-catenin and Wnt/β-catenin pathways do not cross-talk following co-stimulation with multiple concentrations of both ligands. By examining EGF-regulated genes in MSCs by RNA-Sequencing, we identified gene sets that were exclusively regulated by the EGF/b-catenin pathway, which were distinct from canonical EGF-regulated genes. In contrast, the expression of subsets of canonical EGF signalling gene targets were significantly influenced by b-catenin activation. These newly-identified EGF signalling pathways cooperate to enable EGF-mediated proliferation of MSCs by alleviating the suppression of cell cycle pathways induced by canonical EGF signalling.
Project description:Notch signaling is essential for proper lens development, however the specific requirements of individual Notch receptors has not been previously investigated. Here we report the lens phenotypes of Notch2 conditionally mutant mice, which exhibited severe microphthalmia, reduced pupillary openings, disrupted fiber cell morphology, eventual loss of the anterior epithelium, fiber cell dysgenesis, and cataracts. Notch2 mutants also had a persistent lens stalk phenotype at E11.5, and aberrant DNA synthesis in the fiber cell compartment by E14.5. Gene expression analyses showed elevated levels of the cell cycle regulators Cdkn1a (p21Cip1), Ccnd2 (CyclinD2) and Trp63 (p63) that negatively regulates Wnt signaling. Although removal of Notch2 phenocopied the increased proportion of fiber cells of Rbpj and Jag1 conditional mutant lenses, Notch2 is not required for AEL proliferation, suggesting that a different receptor regulates this process. Instead, we found that the Notch2 normally blocks progenitor cell death. Overall, we conclude that Notch2-mediated signaling regulates lens morphogenesis, apoptosis, cell cycle withdrawal, and secondary fiber cell differentiation. We have compared gene expression of ocular lenses of mice that are lens specific conditional mutants of Notch2 gene to that of littermate controls that had no ablation of Notch2 gene in the lens. Two lenses of each of the three conditional mutants and controls were pooled together and total RNA was harvested from embryonic day 19.5 (E19.5) lenses. Gene expression changes caused by absence of Notch2 gene in the lens were analyzed.
Project description:Canonical Wnt signalling regulates the self-renewal of most if not all stem cell systems. In the blood system, the role of Wnt signalling has been subject of much debate, with positive and negative roles of Wnt signalling proposed for hematopoietic stem cells (HSC). As we have shown previously, this controversy can be largely explained by the effects of different dosages of Wnt signalling. What remained unclear however, was why high Wnt signals would lead to loss of reconstituting capacity. To better understand this phenomenon, we have taken advantage of a series of hypomorphic mutant Apc alleles resulting in a broad range of Wnt dosages in HSCs, purified those HSCs and performed whole genome gene expression analyses. Gene expression profiling and functional studies show that HSCs with APC mutations lead to high Wnt levels , enhanced differentiation and diminished proliferation, but have no effect on apoptosis, collectively leading to loss of stemness. Thus, we provide mechanistic insight into the role of APC mutations and Wnt signalling in HSC biology. As Wnt signals are explored in various in vivo and ex vivo expansion protocols for HSCs, our findings also have clinical ramifications. To investigate the effects of Wnt signals in hematopoietic cells, mice carrying floxed Apc or hypomorphic Apc mutants were crossed, LSK cells were isolated and treated with Cre IRES GFP gamma-retrovirus ex vivo, GFP+ cells were sorted and RNA expression was determined.
Project description:Notch signaling is essential for proper lens development, however the specific requirements of individual Notch receptors has not been previously investigated. Here we report the lens phenotypes of Notch2 conditionally mutant mice, which exhibited severe microphthalmia, reduced pupillary openings, disrupted fiber cell morphology, eventual loss of the anterior epithelium, fiber cell dysgenesis, and cataracts. Notch2 mutants also had a persistent lens stalk phenotype at E11.5, and aberrant DNA synthesis in the fiber cell compartment by E14.5. Gene expression analyses showed elevated levels of the cell cycle regulators Cdkn1a (p21Cip1), Ccnd2 (CyclinD2) and Trp63 (p63) that negatively regulates Wnt signaling. Although removal of Notch2 phenocopied the increased proportion of fiber cells of Rbpj and Jag1 conditional mutant lenses, Notch2 is not required for AEL proliferation, suggesting that a different receptor regulates this process. Instead, we found that the Notch2 normally blocks progenitor cell death. Overall, we conclude that Notch2-mediated signaling regulates lens morphogenesis, apoptosis, cell cycle withdrawal, and secondary fiber cell differentiation.
Project description:RNA-seq profiles of Wild Type or Prkcb-/- mouse bone marrow derived mesenchymal stromal cells (BMSCs), either monocultured or co-cultured with primary CLL cells.