Notch signaling is a potent inducer of growth arrest and apoptosis in a wide range of B-cell malignancies

Abstract

[3][4][5] Many potential targets of Notch signaling have been identified in various cell contexts, and several members of the Hairy/Enhancer of Split (Hes) family of basic helix-loophelix (bHLH) proteins are direct Notch/CSL targets, including Hes1. 6,7 Notch signaling has multiple functions during normal hematolymphoid development. These include regulation of T-cell commitment from a multipotential precursor, regulation of ␣␤ T-cell development, and marginal zone B-cell development. 8 Notch signaling is tightly controlled, and failure to maintain this regulation can lead to transformation. 9 Within the hematolymphoid compartment, constitutive Notch signaling causes T-cell malignancy in multiple species, and recent data identified Notchactivating mutations as the most frequent event in human T-cell leukemia. 10 In malignant T cells, Notch signaling influences proliferation, differentiation, and survival.Although Notch receptor expression is widespread throughout the hematolymphoid compartment, its transforming potential seems to be restricted to developing T cells. For personal use only. on March 27, 2019. by guest www.bloodjournal.org From with less dramatic effects on the cell cycle. In a second study, Romer et al 12 showed that Notch signaling enhanced apoptosis in a murine B-cell lymphoma line after B-cell antigen receptor (BCR) crosslinking. In the third study, Nefedova et al 13 found that Notch activation induced growth arrest in 4 human myeloma-derived cell lines.In contrast, 3 studies suggest that Notch signaling promotes proliferation of malignant B cells. Hubmann et al 14 reported that Notch2 induced CD23a expression in a pre-B acute lymphoblastic leukemia (ALL) cell line, and both Notch2 and CD23a are expressed at high levels in chronic lymphocytic leukemia (CLL) samples, suggesting a potential role for Notch2 in CD23a-mediated proliferation. In 2 publications that used Jagged1-expressing cells to induce Notch signaling, Jundt et al 15,16 demonstrated that 5 Hodgkin and 3 myeloma-derived cell lines increased thymidine incorporation after 48 hours of ligand signaling, suggesting a proliferative effect on these cell lines. This result is in contrast to that of Nefedova et al 13 who observed decreased thymidine incorporation in 2 of the same cell lines tested.These conflicting results reveal the need to reevaluate the effects of Notch signaling in B-cell malignancies. Given the variety of effects in a range of different B-cell malignancies, we sought to address 3 topics: (1) whether Notch signaling had a consistent effect on different types of B-cell malignancies, (2) whether different Notch receptors differentially affected the B-cell response, and (3) to determine the transcriptional targets of Notch signaling that mediate the B-cell effect. To establish the effects of Notch signaling in B cells, we investigated the effects of constitutive Notch signaling in transformed murine B cells. We found that, in contrast to T cells, murine B-cell lines underwent caspasedependent apoptosis and growth inhibition...

The notch pathway positively regulates programmed cell death during erythroid differentiation

“…Conversely, Notch activation can induce apoptosis during the development of the retina 46 and the serotonin lineage 47 in Drosophila. Notch also induces apoptosis in B-cell lymphomas, 16 normal monocytes 48 or hepatocellular carcinoma cells. 49 Based on this and our results, it is likely that apoptosis is another mechanism used by Notch to control specific tissue homeostasis.…”

“…14 Notch pathway has previously been shown to induce apoptosis in cell lines from different hematopoietic lineages most likely through the activation of its target gene hes1. [15][16][17] However, the overall data linking Notch and erythroid apoptosis is controversial. 18,19 In this work, we demonstrate that the Notch signaling pathway is a positive regulator of apoptosis in primitive erythropoiesis in the yolk sac but also in erythroid cells from adult bone marrow (BM).…”

A ubiquitin ligase, skeletrophin, is a negative regulator of melanoma invasion

“…In order to examine the expression status of members of the Notch pathway, RT-PCR was first performed according to the methods of Zweidler-McKay et al (2005) and Nijjar et al (2002). The primers set used in this assay are shown in Table 1.…”

Expression of a non‐DNA‐binding Ikaros isoform exclusively in B cells leads to autoimmunity but not leukemogenesis

“…It is possible that T cells with diminished levels of Ikaros activity are likely to develop mutations leading to constitutive Notch activation, making them vulnerable to transformation. However, constitutive activation of Notch appears to have the opposite effect in proliferating B cells, leading to growth arrest and apoptosis [26]. Therefore, within the B cell lineage, decreased levels of Ikaros may predispose B cells to apoptosis rather than transformation.…”

“…The following antibodies were used: anti-CD4 (GK1.5), anti-CD8 (53-6.7), anti-TCRb (H57-597), anti-CD69 (H1-2F3), anti-CD45R/B220 (RA3-6B2), anti-CD62L (MEL-14), anti-CD44 (IM7), anti-IgD (11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22)(23)(24)(25)(26), anti-IgM (II/41), anti-MHC class II (M5/114.15.2), anti-CD138,anti-CD22.2 (Cy34.1, BD Pharmingen), anti-CD21 (7G6, BD Pharmingen) and anti-CD23 (B3B4, BD Pharmingen). All antibodies were purchased from eBioscience unless otherwise stated.…”