Critical Role Of Notch Signaling Research Articles

Expression analysis elucidates the roles of Nicastrin, Notch4, and Hes1 in prognosis and endocrine-therapy resistance in ER-positive breast cancer patients.

Although some proposed mechanisms responsible for tamoxifen resistance have already been present, further study is needed to determine the mechanisms underlying tamoxifen resistance more clearly. The critical role of Notch signaling has been described in promoting resistance in therapeutics, but there is little information about its role in tamoxifen resistance progression. In the present study, the expression of Notch pathway genes, including Notch4, nicastrin and the Notch downstream target Hes1 was evaluated using quantitative RT-PCR in 36 tamoxifen-resistant (TAM-R) and 36 tamoxifen-sensitive (TAM-S) patients. Expression data were correlated with the clinical outcome and survival of patients. mRNA levels of Notch4 (fold change = 2.7), nicastrin (fold change = 6.71), and Hes1 (fold change= 7.07) were significantly higher in TAM-R breast carcinoma patients compared to sensitive cases. We confirmed all these genes were co-expressed. Hence, it seems that Notch signaling is involved in tamoxifen resistance in our TAM-R patients. Obtained results showed that Hes1, nicastrin, and Notch4 mRNA upregulation was correlated with the N stage. The extracapsular nodal extension was associated with nicastrin and Notch4 overexpression. Moreover, nicastrin overexpression was correlated with perineural invasion. Hes1 upregulation was also associated with nipple involvement. Finally, the Cox regression proportional hazard test revealed that overexpression of nicastrin was an independent worse survival factor. Presumably, upregulation of the Notch pathway may be involved in tamoxifen resistance in breast cancer patients.

Notch1 signaling contributes to TLR4-triggered NF-κB activation in macrophages

Macrophages substantially influence the development, progression, and complications of inflammation-driven diseases. Although numerous studies support the critical role of Notch signaling in most inflammatory diseases, there is limited data on the role of Notch signaling in TLR4-induced macrophage activation and interaction of Notch signaling with other signaling pathways in macrophages during inflammation, such as the NF-κB pathway. This study confirmed that stimulation with lipopolysaccharide (LPS), a TLR4 ligand, upregulated Notch1 expression in monocyte/macrophage-like RAW264.7 cells and bone marrow-derived macrophages (BMDMs). LPS also induced increased mRNA expression of Notch target genes Notch1 and Hes1 in macrophages, suggesting that TLR4 signaling enhances activation of the Notch pathway. The upregulation of Notch1, Notch1 intracellular domain (NICD), and Hes1 proteins by LPS treatment was inhibited by DAPT, a Notch1 inhibitor. Additionally, the increased TNF-α, IL-6, and IL-1β expression induced by LPS was inhibited by DAPT and rescued by jagged1, a Notch1 ligand. Furthermore, suppression of Notch signaling by DAPT upregulated Cylindromatosis (CYLD) expression but downregulated TRAF6 expression, IκB kinase (IKK) α/β phosphorylation, and subsequently, phosphorylation and degradation of IκB-α, indicating that DAPT inhibited NF-κB activation triggered by TLR-4. Interestingly, DAPT did not inhibit the increased MyD88 expression induced by LPS. Our study findings demonstrate that macrophage stimulation via the TLR4 signaling cascade triggers activation of Notch1 signaling, which regulates the expression patterns of genes involved in pro-inflammatory responses by activating NF-κB. This effect may be dependent on the CYLD-TRAF6-IKK pathway. Thus, Notch1 signaling may provide a therapeutic target against infectious and inflammation-driven diseases.

Generation of cDC-like cells from human induced pluripotent stem cells via Notch signaling

BackgroundDendritic cells (DCs) play critical roles in regulating the innate and adaptive immune responses, and have long been a major focus of cancer immunotherapy. Accumulating evidence suggests that conventional type...

Targeting Notch and EGFR signaling in human mucoepidermoid carcinoma

Mucoepidermoid carcinoma (MEC) is the most common type of salivary gland cancers and patients with advanced, metastatic, and recurrent MECs have limited therapeutic options and poor treatment outcomes. MEC is commonly associated with a chromosomal translocation t(11;19) (q14-21;p12-13) that encodes the CRTC1-MAML2 oncogenic fusion. The CRTC1-MAML2 fusion is required for MEC growth in part through inducing autocrine AREG-EGFR signaling. Growing evidence suggests that MEC malignancy is maintained by cancer stem-like cells. In this study, we aimed to determine critical signaling for maintaining MEC stem-like cells and the effect of combined targeting of stem cell signaling and CRTC1-MAML2-induced EGFR signaling on blocking MEC growth. First, we evaluated the significance of Notch signaling in regulating MEC stem-like cells. Aberrantly activated Notch signaling was detected in human fusion-positive MEC cells. The inhibition of Notch signaling with genetic or pharmacological inhibitors reduced oncosphere formation and ALDH-bright population in vitro and blocked the growth of MEC xenografts in vivo. Next, we investigated the effect of co-targeting Notch signaling and EGFR signaling, and observed enhanced inhibition on MEC growth in vivo. Collectively, this study identified a critical role of Notch signaling in maintaining MEC stem-like cells and tumor growth, and revealed a novel approach of co-targeting Notch and EGFR signaling as a potential effective anti-MEC treatment.

Notch-1 Signaling Modulates Macrophage Polarization and Immune Defense against Mycobacterium avium paratuberculosis Infection in Inflammatory Diseases.

Despite the extensive research on Notch signaling involvement in inflammation, its specific role in macrophage response in autoimmune disease and defense mechanisms against bacterial infection, such as Mycobacterium avium paratuberculosis (MAP), remains unknown. In this study, we investigated the molecular role of Notch-1 signaling in the macrophage response during MAP infection. In particular, we measured the in vitro effect of MAP on Notch-1 signaling and downstream influence on interleukin (IL)-6 and myeloid cell leukemia sequence-1 (MCL-1) and consequent cellular apoptosis, MAP viability, and macrophage polarization. Overall, the data show significant upregulation in Notch-1, IL-6, and MCL-1 in MAP-infected macrophages, parallel with a decrease in apoptosis and elevated pro-inflammatory response in these infected cells. On the contrary, blocking Notch signaling with γ-secretase inhibitor (DAPT) decreased MAP survival and burden, increased apoptosis, and diminished the pro-inflammatory response. In particular, the treatment of infected macrophages with DAPT shifted macrophage polarization toward M2 anti-inflammatory phenotypic response. The outcome of this study clearly demonstrates the critical role of Notch signaling in macrophage response during infection. We conclude that MAP infection in macrophages activates Notch-1 signaling and downstream influence on IL-6 which hijack MCL-1 dependent inhibition of apoptosis leading to its chronic persistence, and further inflammation. This study supports Notch-1 signaling as a therapeutic target to combat infection in autoimmune diseases such as Crohn’s disease and Rheumatoid Arthritis.

The implications of hippocampal neurogenesis in adolescent rats after status epilepticus: a novel role of notch signaling pathway in regulating epileptogenesis.

Seizure-induced neurogenesis has a widely recognized pro-epileptogenic function. Given the critical role of Notch signaling during the maintenance and neurogenesis of neural stem cells, we hypothesized that Notch may affect epileptogenesis and its progression through its role in neurogenesis in the adolescent rat brain. We used the lithium-pilocarpine-induced epilepsy model in adolescent Sprague-Dawley rats in order to evaluate hippocampal neurogenesis and epileptogenesis following the onset of status epilepticus (SE). We used western blotting analyses and qPCR to measure levels of Notch signaling at different phases after seizures and immunofluorescence to detect the proliferation and differentiation of neural stem cells after seizure. Following the administration of DAPT, a Notch γ-secretase inhibitor, into the lateral ventricles, we observed a suppression of abnormal neurogenesis in the acute phase and a reduction of gliosis in the chronic phase after SE. Accordingly, the frequency and duration of spontaneous seizures in chronic phase were decreased. Our results clarify the basic concept regarding the involvement of Notch signaling in the regulation of hippocampal neurogenesis and epileptogenesis, thereby potentially offering a novel and alternative treatment for epilepsy.

Discrepancies of Notch 1 receptor during development of chronic seizures.

The critical role of Notch signaling has been shown in the pathogenesis of some neurological disorders including schizophrenia, epilepsy and Alzheimer's disease. This study was aimed to evaluate the role of Notch 1 receptor in epileptogenesis as well as seizure characteristics. The animals were divided into three groups of sham, early stage and end stage. In sham group: Normal saline was injected intraperitoneally (ip) in the same as protocol of pentylenetetrazol (PTZ) injection. PTZ was injected (ip) every 48 hr over a period of 1 week in the group of early stage and over a period of 4 weeks in the end stage. The gene expression as well as distribution of Notch 1 receptor was assessed in the parietal cortex and hippocampus. In addition, the effect of agonist or antagonist of Notch 1 receptor was assessed on the epileptic discharges induced by PTZ injection. The gene expression of Notch 1 decreased in the hippocampus significantly in the end-stage group compared with sham, and early groups. Furthermore, distribution of Notch 1 receptor increased in the somatosensory cortex and decreased in the CA1 hippocampal area in the end-stage group. Intraventricular microinjection of Notch 1 agonist significantly increased the amplitude as well as frequency of spikes and decreased the latency of first epileptic discharges. Our findings illustrate the critical role of Notch signalling as a potential pathway in the epileptogenesis during development of chronic seizures.

Large-Scale Human Dendritic Cell Differentiation Revealing Notch-Dependent Lineage Bifurcation and Heterogeneity

SummaryThe ability to generate large numbers of distinct types of human dendritic cells (DCs) in vitro is critical for accelerating our understanding of DC biology and harnessing them clinically. We developed a DC differentiation method from human CD34+ precursors leading to high yields of plasmacytoid DCs (pDCs) and both types of conventional DCs (cDC1s and cDC2s). The identity of the cells generated in vitro and their strong homology to their blood counterparts were demonstrated by phenotypic, functional, and single-cell RNA-sequencing analyses. This culture system revealed a critical role of Notch signaling and GM-CSF for promoting cDC1 generation. Moreover, we discovered a pre-terminal differentiation state for each DC type, characterized by high expression of cell-cycle genes and lack of XCR1 in the case of cDC1. Our culture system will greatly facilitate the simultaneous and comprehensive study of primary, otherwise rare human DC types, including their mutual interactions.

Notch signaling is protective in splenic T cells against apoptosis during endotoxemia via TLR4/Myd88/TRIF/iNOS/NO/TACE pathway.

Abstract Introduction Notch signaling regulates cell communication and fate decisions, though recently implicated in inflammatory responses, its regulation and roles in sepsis are unknown. We aim to study the biology of Notch signaling in endotoxemia. Methods WT (C57BL/6), Myd88−/− , TRIF−/−, TLR4−/−, iNOS−/−mice were injected saline or 5mg/kg LPS i.p, spleen and serum were harvested after 0, 4, 8, 12, 24h. The activation of Notch signaling was assessed as notch intracellular domain (NICD), and apoptosis was measured as cleaved-caspase 3 level by western blot. Results The NICD level in spleen peaked at 8h, decreasing to baseline level at 24 h after LPS injection. Cleaved-caspase 3 level in spleen was inversely correlated to the NICD level. Inhibition of Notch activation using DAPT (5 mg/kg) resulted in an increase of cleaved-caspase-3 at 8h after LPS stimulation, suggesting a critical role of Notch signaling for splenocyte survival after LPS stimulation. The sheddase, TNFα-converting enzyme (TACE/ADAM17) participates in activation of Notch and we have previously shown its activation via TLR4/iNOS/NO pathway in hepatocytes, thus we tested whether the pathway is conserved in spleen. LPS-induced Notch activation was significantly lower in TRIF−/−, Myd88−/− , TLR4−/− and iNOS−/− mice. In vitro treatment of SNAP (200 uM) and cGMP analog 8-pCPT-cGMP(400 uM) increased NICD level in primary splenocytes. Treatment with 1400W, an iNOS inhibitor or TAPI-II (800 nM), a TACE inhibitor, reduced LPS-induced Notch activation in splenocytes while increasing cleaved-caspase3. Conclusion Our data suggests that Notch signaling is activated during endotoxemia under the regulation of iNOS/NO/TACE and plays a critical role in regulating splenocytes survival.

Human Cytomegalovirus Infection Dysregulates the Localization and Stability of NICD1 and Jag1 in Neural Progenitor Cells

Human cytomegalovirus (HCMV) infection of the developing fetus frequently results in major neural developmental damage. In previous studies, HCMV was shown to downregulate neural progenitor/stem cell (NPC) markers and induce abnormal differentiation. As Notch signaling plays a vital role in the maintenance of stem cell status and is a switch that governs NPC differentiation, the effect of HCMV infection on the Notch signaling pathway in NPCs was investigated. HCMV downregulated mRNA levels of Notch1 and its ligand, Jag1, and reduced protein levels and altered the intracellular localization of Jag1 and the intracellular effector form of Notch1, NICD1. These effects required HCMV gene expression and appeared to be mediated through enhanced proteasomal degradation. Transient expression of the viral tegument proteins of pp71 and UL26 reduced NICD1 and Jag1 protein levels endogenously and exogenously. Given the critical role of Notch signaling in NPC growth and differentiation, these findings reveal important mechanisms by which HCMV disturbs neural cell development in vitro. Similar events in vivo may be associated with HCMV-mediated neuropathogenesis during congenital infection in the fetal brain. Congenital human cytomegalovirus (HCMV) infection is the leading cause of birth defects that primarily manifest as neurological disabilities. Neural progenitor cells (NPCs), key players in fetal brain development, are the most susceptible cell type for HCMV infection in the fetal brain. Studies have shown that NPCs are fully permissive for HCMV infection, which causes neural cell loss and premature differentiation, thereby perturbing NPC fate. Elucidation of virus-host interactions that govern NPC proliferation and differentiation is critical to understanding neuropathogenesis. The Notch signaling pathway is critical for maintaining stem cell status and functions as a switch for differentiation of NPCs. Our investigation into the impact of HCMV infection on this pathway revealed that HCMV dysregulates Notch signaling by altering expression of the Notch ligand Jag1, Notch1, and its active effector in NPCs. These results suggest a mechanism for the neuropathogenesis induced by HCMV infection that includes altered NPC differentiation and proliferation.

Retraction: Critical Role of Notch Signaling in Osteosarcoma Invasion and Metastasis

The authors wish to retract the article titled Critical Role of Notch Signaling in Osteosarcoma Invasion and Metastasis, which was published in the May 15, 2008, issue of Clinical Cancer Research (1). Many years after this article was published, we obtained new information showing that two of the cell lines used in this publication, OS 187 and COL, are not osteosarcoma cell lines. Both lines were first reported by us (2). Each of these cell lines has now been tested by DNA fingerprint analysis. OS 187testedidenticallytothecommonNCI60coloncancerlineHCT15,evenina vial from passage 2 in our laboratory that had been frozen in 2002. Injection of OS187intothececumofNOD/SCID/IL-2Rg / miceyieldedacolonicprimary with metastasis to the liver (data not shown). Therefore, all of our published results with OS 187 likely reflect the biology of colon cancer. Given the subsequent report by another group that Notch pathway signaling promotes invasionandmetastasisofcoloncancer(3),thedatawereportedforOS187are not surprising. The pattern observed for tumor growth after injection of COL cells into the tibia of NOD/SCID/IL-2Rg / mice (no bone primary, rapid growth of liver tumors, with additional masses arising in skin and retro-orbital spaces) suggested that this cell line likely represented neuroblastoma. We have recently reported the subsequent testing confirming that COL is a neuroblastoma (4). In this article, OS 187 and COL were included in Figs. 1 and 2. OS 187 was amongthecelllinesshowninFig.3andistheonlycelllineshowninFigs.4and 5. When these two cell lines are removed from the data presented, two findings reported should be interpreted with caution. First, the only real osteosarcoma cell lines in which Notch was directly manipulated genetically were SAOS2 (with low levels of Notch) and LM7 (a subline of SAOS2 with high levels of Notch).AlthoughtransductionofSAOS2withconstitutivelyactiveintracellular Notch1 (ICN1) or the Notch target gene Hes1 increased in vitro invasiveness, LM7 was not able to grow after transduction with these constructs, as indicated in the original publication. Thus, we have not proved that osteosarcoma invasiveness can be increased by further upregulating Notch activity in Notch-positive osteosarcoma. Second, because only OS 187 was used in vivo in this report, we can no longer say that our publication proves Notch’s role in metastasis in vivo for osteosarcoma. However, the subsequent confirmation of this function of Notch by other groups (5) renders it likely that this conclusion remains valid for osteosarcoma. Nonetheless, because the data provided from bonafideosteosarcomacelllinesarenolongeradequatetosupporttheassertions and conclusions of the article, the authors respectfully request its retraction.

The NOTCH signaling pathway: role in the pathogenesis of T-cell acute lymphoblastic leukemia and implication for therapy

T-cell acute lymphoblastic leukemia/lymphoma (T-ALL) is characterized by aberrant activation of NOTCH1 in over 60% of T-ALL cases. The high prevalence of activating NOTCH1 mutations highlights the critical role of NOTCH signaling in the pathogenesis of this disease and has prompted the development of therapeutic approaches targeting the NOTCH signaling pathway. Small molecule gamma secretase inhibitors (GSIs) can effectively inhibit oncogenic NOTCH1 and are in clinical testing for the treatment of T-ALL. Treatment with GSIs and glucocorticoids are strongly synergistic and may overcome the gastrointestinal toxicity associated with systemic inhibition of the NOTCH pathway. In addition, emerging new anti-NOTCH1 therapies include selective inhibition of NOTCH1 with anti-NOTCH1 antibodies and stapled peptides targeting the NOTCH transcriptional complex in the nucleus.

Blockage of Notch Signaling Inhibits the Migration and Proliferation of Retinal Pigment Epithelial Cells

The Notch signaling is an evolutionarily conserved cell-cell communication pathway that plays critical roles in the proliferation, survival, apoptosis, and fate determination of mammalian cells. Retinal pigment epithelial (RPE) cells are responsible for supporting the function of the neural retina and maintaining vision. This study investigated the function of Notch signaling in RPE cells. We found that the members of the Notch signaling pathway components were differentially expressed in RPE cells. Furthermore, blockage of Notch signaling inhibited the migration and proliferation of RPE cells and reduced the expression levels of certain Notch signaling target genes, including HES1, MYC, HEY2, and SOX9. Our data reveal a critical role of Notch signaling in RPE cells, suggesting that targeting Notch signaling may provide a novel approach for the treatment of ophthalmic diseases related to RPE cells.

Abstract 1022: Notch regulates the egression of angio-supportive bone marrow-derived cells after chemotherapy

Abstract Introduction Our understanding of angiogenesis has evolved from a simple endothelial-centric model into a multi-faceted process in which bone marrow-derived cells (BMDCs) are found to support the vasculature. BMDCs can act in an immediate “seek and repair” manner in response to various types of therapy, presumably to support tissue regeneration. This can induce an angiogenesis rebound after therapy and thereby impair therapy efficacy. Method By transplanting the bone marrow from the transgenic tamoxifen-inducible VE-cadherin Cre ERT2/EYFP (CIVE) mice into wild type, lethally irradiated, C57 Bl/6 mice, followed by tamoxifen treatment of the recipient mice, we created a mouse with YFP+ bone marrow-derived VE-Cadherin expressing cells (0.3% of the bone marrow). Allowing us to specifically track this lineage of BMDCs. In a second set of experiments, we used the CIVE-EYFP-notch-KO mice as bone marrow-donors. After tamoxifen induction, LLC cells were implanted subcutaneously and after eight days mice were either treated with vehicle control, cisplatin or paclitaxel. Tumor growth was measured and tumors were analyzed by FACS analysis and immunohistochemistry. Results Eight days after treatment with chemotherapy a significant increase in endothelial cells was seen in the tumor compared to the untreated tumors (p<0.01). This correlated with a rapid re-growth of the treated tumors six days after treatment initiation. This treatment-enhanced angiogenesis was accompanied by a clear increase in YFP+ cells as soon as 1 day after chemotherapy for 0.1 to 0.3% (p<0.05). The influx of YFP+ cells was specific for the tumor tissue, as no YFP+ cells were detected in control organs like lung, liver and spleen. Two populations of YFP+ cells were identified in the tumor, a macrophage-like population (Gr1/CD11b+) and an endothelial-like population (PECAM+). The YFP+ cells in the tumor were found in close association with the tumor vessels as per confocal microscopy. FACS analysis showed that in the untreated tumors housed 0.45% of all PECAM+ cells were YFP+, however, this value increased to 1-3% after chemotherapy. Transcriptional analysis of the YFP+ cells revealed high levels of Notch in this population. Using the notch KO mice as bone marrow donors resulted in a defective homing of the YFP+ cells to the tumor which completely prevented the therapy-enhanced angiogenesis and significantly enhanced anti-tumor effect of the chemotherapy. Conclusion In summary, our study identifies an important role for the BMD-VE-cadherin expressing cells in supporting angiogenesis, especially in response to chemotherapy. It reveals the critical role of notch signaling in the ability of these cells to egress the bone marrow and home to the tumor. Preventing the contribution of these angio-supportive cells significantly enhanced therapy efficacy and provides a new strategy to enhance anti-cancer therapy. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 1022. doi:1538-7445.AM2012-1022

Notch signaling mediates TGF-β1-induced epithelial–mesenchymal transition through the induction of Snai1

Epithelial–mesenchymal transition (EMT) is a process by which epithelial cells undergo phenotypic transition to mesenchymal cells and thus is involved in the pathogenesis of tumor metastasis and organ fibrosis. Notch signaling is a highly conserved pathway that regulates intercellular communication and directs cell fate decisions. Here, we show the critical role of Notch signaling in TGF-β1-induced EMT. Inhibition of Notch signaling either by γ-secretase inhibitor or by knocking down of Notch signaling molecules by small interfering RNA abrogated EMT in association with decreased expression of Snai1. Constitutive activation of Notch signaling was sufficient for the induction of Snai1 as well as Notch ligand Jagged1. Notch signaling induced Snai1 expression via direct transcriptional activation. Collectively, these data show that Notch signaling activation promote TGF-β1-induced EMT through the induction of Snai1. Further studies on Notch signaling may provide diagnostic and therapeutic targets for cancer and fibrotic disease.

Notch2 signaling is required for proper mast cell distribution and mucosal immunity in the intestine

AbstractNotch receptor-mediated signaling is involved in the developmental process and functional modulation of lymphocytes, as well as in mast cell differentiation. Here, we investigated whether Notch signaling is required for antipathogen host defense regulated by mast cells. Mast cells were rarely found in the small intestine of wild-type C57BL/6 mice but accumulated abnormally in the lamina propria of the small-intestinal mucosa of the Notch2-conditional knockout mice in naive status. When transplanted into mast cell–deficient Wsh/Wsh mice, Notch2-null bone marrow-derived mast cells were rarely found within the epithelial layer but abnormally localized to the lamina propria, whereas control bone marrow-derived mast cells were mainly found within the epithelial layer. After the infection of Notch2 knockout and control mice with L3 larvae of Strongyloides venezuelensis, the abundant number of mast cells was rapidly mobilized to the epithelial layer in the control mice. In contrast, mast cells were massively accumulated in the lamina propria of the small intestinal mucosa in Notch2-conditional knockout mice, accompanied by impaired eradication of Strongyloides venezuelensis. These findings indicate that cell-autonomous Notch2 signaling in mast cells is required for proper localization of intestinal mast cells and further imply a critical role of Notch signaling in the host-pathogen interface in the small intestine.

Notch Leads Lymphatics and Links Them to Blood Vessels

Lymphatic vessels sprout from the cardinal vein to form primary lymphatic sacs.1,2 However, molecular mechanisms that guide the formation of a mature functional lymphatic network are still shrouded in mystery. Several molecules that are considered markers of arterial endothelial cells (ECs), such as ephrin B2, Foxc2, and integrin α9, are involved in lymphangiogenesis.1 By using an elegant in vivo approach, Geudens et al3 added another arterial factor to this constellation of molecules. Specifically, they show that Notch (a regulator of cell fate decisions and blood vessel development) is also required for lymphatic network development. By systematically silencing zebra fish orthologues of the Notch family receptors (Notch 1a/b, Notch 5, and Notch 6) and their ligands (jagged 1a/b, jagged-2, delta A-D, and deltalike [Dll] 4) and then tracing blood and lymphatic ECs (LECs) during zebra fish embryogenesis, they reveal the critical role of Notch signaling in the guidance of lymphatics and the formation of a lymphatic network. See accompanying article on page 1695 Notch is known to control endothelial sprouting during angiogenesis.4 During embryogenesis, lymphangiogenesis occurs after angiogenesis, making it difficult to dissect whether and how Notch regulates lymphatic development in mouse models. To this end, Geudens et al3 took advantage of zebra fish as a model organism to study angiogenesis and lymphangiogenesis and …

Notch Promotes Radioresistance of Glioma Stem Cells

Radiotherapy represents the most effective nonsurgical treatments for gliomas. However, gliomas are highly radioresistant and recurrence is nearly universal. Results from our laboratory and other groups suggest that cancer stem cells contribute to radioresistance in gliomas and breast cancers. The Notch pathway is critically implicated in stem cell fate determination and cancer. In this study, we show that inhibition of Notch pathway with gamma-secretase inhibitors (GSIs) renders the glioma stem cells more sensitive to radiation at clinically relevant doses. GSIs enhance radiation-induced cell death and impair clonogenic survival of glioma stem cells but not non-stem glioma cells. Expression of the constitutively active intracellular domains of Notch1 or Notch2 protect glioma stem cells against radiation. Notch inhibition with GSIs does not alter the DNA damage response of glioma stem cells after radiation but rather reduces Akt activity and Mcl-1 levels. Finally, knockdown of Notch1 or Notch2 sensitizes glioma stem cells to radiation and impairs xenograft tumor formation. Taken together, our results suggest a critical role of Notch signaling to regulate radioresistance of glioma stem cells. Inhibition of Notch signaling holds promise to improve the efficiency of current radiotherapy in glioma treatment.

Critical Role of Notch Signaling in Osteosarcoma Invasion and Metastasis

Notch signaling is an important mediator of growth and survival in several cancer types, with Notch pathway genes functioning as oncogenes or tumor suppressors in different cancers. However, the role of Notch in osteosarcoma is unknown. We assessed the expression of Notch pathway genes in human osteosarcoma cell lines and patient samples. We then used pharmacologic and retroviral manipulation of the Notch pathway and studied the effect on osteosarcoma cell proliferation, survival, anchorage-independent growth, invasion, and metastasis in vitro and in vivo. Notch pathway genes, including Notch ligand DLL1, Notch1 and Notch2, and the Notch target gene HES1, were expressed in osteosarcoma cells, and expression of HES1 was associated with invasive and metastatic potential. Blockade of Notch pathway signaling with a small molecule inhibitor of gamma secretase eliminated invasion in Matrigel without affecting cell proliferation, survival, or anchorage-independent growth. Manipulation of Notch and HES1 signaling showed a crucial role for HES1 in osteosarcoma invasiveness and metastasis in vivo. These studies identify a new invasion and metastasis-regulating pathway in osteosarcoma and define a novel function for the Notch pathway: regulation of metastasis. Because the Notch pathway can be inhibited pharmacologically, these findings point toward possible new treatments to reduce invasion and metastasis in osteosarcoma.

A Temporal Switch from Notch to Wnt Signaling in Muscle Stem Cells Is Necessary for Normal Adult Myogenesis

The temporal switch from progenitor cell proliferation to differentiation is essential for effective adult tissue repair. We previously reported the critical role of Notch signaling in the proliferative expansion of myogenic progenitors in mammalian postnatal myogenesis. We now show that the onset of differentiation is due to a transition from Notch signaling to Wnt signaling in myogenic progenitors and is associated with an increased expression of Wnt in the tissue and an increased responsiveness of progenitors to Wnt. Crosstalk between these two pathways occurs via GSK3beta, which is maintained in an active form by Notch but is inhibited by Wnt in the canonical Wnt signaling cascade. These results demonstrate that the temporal balance between Notch and Wnt signaling orchestrates the precise progression of muscle precursor cells along the myogenic lineage pathway, through stages of proliferative expansion and then differentiation, during postnatal myogenesis.