Evidence for a role for notch signaling in the cytokine-dependent survival of activated T cells

NOTCH1 Signalling: A key pathway for the development of high-risk chronic lymphocytic leukaemia

NOTCH1 is a cell surface receptor that releases its intracellular domain as transcription factor upon activation. With the advent of next-generation sequencing, the NOTCH1 gene was found recurrently mutated in chronic lymphocytic leukaemia (CLL). Here, virtually all NOTCH1 mutations affect the protein’s PEST-domain and impair inactivation and degradation of the released transcription factor, thus increasing NOTCH1 signalling strength. Besides sequence alterations directly affecting the NOTCH1 gene, multiple other genomic and non-genomic alterations have by now been identified in CLL cells that could promote an abnormally strong NOTCH1 signalling strength. This renders NOTCH1 one of the key signalling pathways in CLL pathophysiology. The frequency of genomic alterations affecting NOTCH1 signalling is rising over the CLL disease course culminating in the observation that besides TP53 loss, 8q gain and CDKN2A/B loss, NOTCH1 mutation is a hallmark genomic alteration associated with transformation of CLL into an aggressive lymphoma (Richter transformation). Both findings associate de-regulated NOTCH1 signalling with the development of high-risk CLL. This narrative review provides data on the role of NOTCH1 mutation for CLL development and progression, discusses the impact of NOTCH1 mutation on treatment response, gives insight into potential modes of NOTCH1 pathway activation and regulation, summarises alterations that have been discussed to contribute to a de-regulation of NOTCH1 signalling in CLL cells and provides a perspective on how to assess NOTCH1 signalling in CLL samples.

Molecular Genetic Features of Cerebral Cavernous Malformations (CCM) Patients: An Overall View from Genes to Endothelial Cells

Cerebral cavernous malformations (CCMs) are vascular lesions that affect predominantly microvasculature in the brain and spinal cord. CCM can occur either in sporadic or familial form, characterized by autosomal dominant inheritance and development of multiple lesions throughout the patient's life. Three genes associated with CCM are known: CCM1/KRIT1 (krev interaction trapped 1), CCM2/MGC4607 (encoding a protein named malcavernin), and CCM3/PDCD10 (programmed cell death 10). All the mutations identified in these genes cause a loss of function and compromise the protein functions needed for maintaining the vascular barrier integrity. Loss of function of CCM proteins causes molecular disorganization and dysfunction of endothelial adherens junctions. In this review, we provide an overall vision of the CCM pathology, starting with the genetic bases of the disease, describing the role of the proteins, until we reach the cellular level. Thus, we summarize the genetics of CCM, providing a description of CCM genes and mutation features, provided an updated knowledge of the CCM protein structure and function, and discuss the molecular mechanisms through which CCM proteins may act within endothelial cells, particularly in endothelial barrier maintenance/regulation and in cellular signaling.

Febrile temperature change modulates CD4 T cell differentiation via a TRPV channel-regulated Notch-dependent pathway

Fever is a conserved and prominent response to infection. Yet, the issue of how CD4 T cell responses are modulated if they occur at fever temperatures remains poorly addressed. We have examined the priming of naive CD4 T cells in vitro at fever temperatures, and we report notable fever-mediated modulation of their cytokine commitment. When naive CD4 T cells were primed by plate-bound anti-CD3 and anti-CD28 monoclonal antibodies at moderate fever temperature (39 °C), they enhanced commitment to IL4/5/13 (Th2) and away from IFNg (Th1). This was accompanied by up-regulation of the Th2-relevant transcription factor GATA3 and reduction in the Th1-relevant transcription factor Tbet. Fever sensing by CD4 T cells involved transient receptor potential vanilloid cation channels (TRPVs) since TRPV1/TRPV4 antagonism blocked the febrile Th2 switch, while TRPV1 agonists mediated a Th2 switch at 37 °C. The febrile Th2 switch was IL4 independent, but a γ-secretase inhibitor abrogated it, and it was not found in Notch1-null CD4 T cells, identifying the Notch pathway as a major mediator. However, when naive CD4 T cells were primed via antigen and dendritic cells (DCs) at fever temperatures, the Th2 switch was abrogated via increased production of IL12 from DCs at fever temperatures. Thus, immune cells directly sense fever temperatures with likely complex physiological consequences.

CD28 Signaling Drives Notch Ligand Expression on CD4 T Cells

Notch signaling provides an important cue in the mammalian developmental process. It is a key player in T cell development and function. Notch ligands such as Delta-like ligands (DLL) 1, 3, 4, and JAG1, 2 can impact Notch signaling positively or negatively, by trans-activation or cis-inhibition. Trans and cis interactions are receptor-ligand interaction on two adjacent cells and interaction on the same cell, respectively. The former sends an activation signal and the later, a signal for inhibition of Notch. However, earlier reports suggested that Notch is activated in the absence of Notch ligand-expressing APCs in a purified population of CD4 T cells. Thus, the role of ligands in Notch activation, in a purified population of CD4 T cells, remains obscure. In this study, we demonstrate that mature CD4 T cells are capable of expressing Notch ligands on their surface very early upon activation with soluble antibodies against CD3 and CD28. Moreover, signaling solely through CD28 induces Notch ligand expression and CD3 signaling inhibits ligand expression, in contrast to Notch which is induced by CD3 signaling. Additionally, by using decoys, mimicking the Notch extracellular domain, we demonstrated that DLL1, DLL4, and JAG1, expressed on the T cells, can cis-interact with the Notch receptor and inhibit activation of Notch. Thus, our data indicate a novel mechanism of the regulation of Notch ligand expression on CD4 T cells and its impact on activated Notch.

Recent advances in cerebral cavernous malformation research

Cerebral cavernous malformations (CCM) are manifested by microvascular lesions characterized by leaky endothelial cells with minimal intervening parenchyma predominantly in the central nervous system predisposed to hemorrhagic stroke, resulting in focal neurological defects. Till date, three proteins are implicated in this condition: CCM1 (KRIT1), CCM2 (MGC4607), and CCM3 (PDCD10). These multi-domain proteins form a protein complex via CCM2 that function as a docking site for the CCM signaling complex, which modulates many signaling pathways. Defects in the formation of this signaling complex have been shown to affect a wide range of cellular processes including cell-cell contact stability, vascular angiogenesis, oxidative damage protection and multiple biogenic events. In this review we provide an update on recent advances in structure and function of these CCM proteins, especially focusing on the signaling cascades involved in CCM pathogenesis and the resultant CCM cellular phenotypes in the past decade.

A Review of Notch Processing With New Insights Into Ligand-Independent Notch Signaling in T-Cells

The Notch receptor is an evolutionarily highly conserved transmembrane protein essential to a wide spectrum of cellular systems, and its deregulation has been linked to a vast number of developmental disorders and malignancies. Regulated Notch function is critical for the generation of T-cells, in which abnormal Notch signaling results in leukemia. Notch activation through trans-activation of the receptor by one of its ligands expressed on adjacent cells has been well defined. In this canonical ligand-dependent pathway, Notch receptor undergoes conformational changes upon ligand engagement, stimulated by a pulling-force on the extracellular fragment of Notch that results from endocytosis of the receptor-bound ligand into the ligand-expressing cell. These conformational changes in the receptor allow for two consecutive proteolytic cleavage events to occur, which release the intracellular region of the receptor into the cytoplasm. It can then travel to the nucleus, where it induces gene transcription. However, there is accumulating evidence that other pathways may induce Notch signaling. A ligand-independent mechanism of Notch activation has been described in which receptor processing is initiated via cell-internal signals. These signals result in the internalization of Notch into endosomal compartments, where chemical changes existing in this microenvironment result in the conformational modifications required for receptor processing. This review will present mechanisms underlying both canonical ligand-dependent and non-canonical ligand-independent Notch activation pathways and discuss the latter in the context of Notch signaling in T-cells.

Notch signalling pathway as an oncogenic factor involved in cancer development

Notch signalling is an evolutionarily conserved signalling pathway, which plays a significant role in a wide array of cellular processes including proliferation, differentiation, and apoptosis. Nevertheless, it must be noted that Notch is a binary cell fate determinant, and its overexpression has been described as oncogenic in a broad range of human malignancies. This finding led to interest in therapeutically targeting this pathway especially by the use of GSIs, which block the cleavage of Notch at the cell membrane and inhibit release of the transcriptionally active NotchIC subunit. Preclinical cancer models have clearly demonstrated that GSIs suppress the growth of such malignancies as pancreatic, breast, and lung cancer; however, GSI treatment in vivo is associated with side effects, especially those within the gastrointestinal tract. Although intensive studies are associated with the role of γ-secretase in pathological states, it should be pointed out that this complex impacts on proteolytic cleavages of around 55 membrane proteins. Therefore, it is clear that GSIs are highly non-specific and additional drugs must be designed, which will more specifically target components of the Notch signalling.

MUC4 is negatively regulated through the Wnt/β-catenin pathway via the Notch effector Hath1 in colorectal cancer

MUC4 is a transmembrane mucin lining the normal colonic epithelium. The aberrant/de novo over-expression of MUC4 is well documented in malignancies of the pancreas, ovary and breast. However, studies have reported the loss of MUC4 expression in the majority of colorectal cancers (CRCs). A MUC4 promoter analysis showed the presence of three putative TCF/LEF sites, implying a possible regulation by the Wnt/β-catenin pathway, which has been shown to drive CRC progression. Thus, the objective of our study was to determine whether MUC4 is regulated by β-catenin in CRC. We first knocked down (KD) β-catenin in three CRC cell lines; LS180, HCT-8 and HCT116, which resulted in increased MUC4 transcript and MUC4 protein. Additionally, the overexpression of stabilized mutant β-catenin in LS180 and HCT-8 resulted in a decrease in MUC4 expression. Immunohistochemistry (IHC) of mouse colon tissue harboring tubular adenomas and high grade dysplasia showed dramatically reduced Muc4 in lesions relative to adjacent normal tissue, with increased cytosolic/nuclear β-catenin. Luciferase assays with the complete MUC4 promoter construct p3778 showed increased MUC4 promoter luciferase activity in the absence of β-catenin (KD). Mutation of all three putative TCF/LEF sites showed that MUC4 promoter luciferase activity was increased relative to the un-mutated promoter. Interestingly, it was observed that MUC4 expressing CRC cell lines also expressed high levels of Hath1, a transcription factor repressed by both active Wnt/β-catenin and Notch signaling. The KD of β-catenin and/or treatment with a Notch γ-secretase inhibitor, Dibenzazepine (DBZ) resulted in increased Hath1 and MUC4 in LS180, HCT-8 and HCT116. Furthermore, overexpression of Hath1 in HCT-8 and LS180 caused increased MUC4 transcript and MUC4 protein. Taken together, our results indicate that the Wnt/β-catenin pathway suppresses the Notch pathway effector Hath1, resulting in reduced MUC4 in CRC.

Notch signaling in cerebrovascular diseases (Review)

The Notch signaling pathway is a crucial regulator of numerous fundamental cellular processes. Increasing evidence suggests that Notch signaling is involved in inflammation and oxidative stress, and thus in the progress of cerebrovascular diseases. In addition, Notch signaling in cerebrovascular diseases is associated with apoptosis, angiogenesis and the function of blood-brain barrier. Despite the contradictory results obtained to date as to whether Notch signaling is harmful or beneficial, the regulation of Notch signaling may provide a novel strategy for the treatment of cerebrovascular diseases.

Notch1 regulated autophagy controls survival and suppressor activity of activated murine T-regulatory cells

Cell survival is one of several processes regulated by the Notch pathway in mammalian cells. Here we report functional outcomes of non-nuclear Notch signaling to activate autophagy, a conserved cellular response to nutrient stress, regulating survival in murine natural T-regulatory cells (Tregs), an immune subset controlling tolerance and inflammation. Induction of autophagy required ligand-dependent, Notch intracellular domain (NIC) activity, which controlled mitochondrial organization and survival of activated Tregs. Consistently, NIC immune-precipitated Beclin and Atg14, constituents of the autophagy initiation complex. Further, ectopic expression of an effector of autophagy (Atg3) or recombinant NIC tagged to a nuclear export signal (NIC-NES), restored autophagy and suppressor function in Notch1(-/-) Tregs. Furthermore, Notch1 deficiency in the Treg lineage resulted in immune hyperactivity, implicating Notch activity in Treg homeostasis. Notch1 integration with autophagy, revealed in these experiments, holds implications for Notch regulated cell-fate decisions governing differentiation.

Rescue of notch-1 signaling in antigen-specific CD8+ T cells overcomes tumor-induced T-cell suppression and enhances immunotherapy in cancer

An impaired antitumor immunity is found in patients with cancer and represents a major obstacle in the successful development of different forms of immunotherapy. Signaling through Notch receptors regulates the differentiation and function of many cell types, including immune cells. However, the effect of Notch in CD8(+) T-cell responses in tumors remains unclear. Thus, we aimed to determine the role of Notch signaling in CD8(+) T cells in the induction of tumor-induced suppression. Our results using conditional knockout mice show that Notch-1 and Notch-2 were critical for the proliferation and IFNγ production of activated CD8(+) T cells and were significantly decreased in tumor-infiltrating T cells. Conditional transgenic expression of Notch-1 intracellular domain (N1IC) in antigen-specific CD8(+) T cells did not affect activation or proliferation of CD8(+) T cells, but induced a central memory phenotype and increased cytotoxicity effects and granzyme B levels. Consequently, a higher antitumor response and resistance to tumor-induced tolerance were found after adoptive transfer of N1IC-transgenic CD8(+) T cells into tumor-bearing mice. Additional results showed that myeloid-derived suppressor cells (MDSC) blocked the expression of Notch-1 and Notch-2 in T cells through nitric oxide-dependent mechanisms. Interestingly, N1IC overexpression rendered CD8(+) T cells resistant to the tolerogenic effect induced by MDSC in vivo. Together, the results suggest the key role of Notch in the suppression of CD8(+) T-cell responses in tumors and the therapeutic potential of N1IC in antigen-specific CD8(+) T cells to reverse T-cell suppression and increase the efficacy of T cell-based immunotherapies in cancer.

Involvement of Notch in activation and effector functions of γδ T cells

Notch signaling plays a pivotal role in cell fate decision and lineage commitment of lymphocytes. Although the role of Notch in CD4(+) and CD8(+) αβ T cells is well documented, there are no reports on how Notch signaling regulates effector functions of γδ T cells. γδ T cells are a minor fraction in the peripheral blood but are known to play a major role in defense against pathogens and tumors. In this study, we show that Notch receptors (mRNA and protein) are expressed in peripheral γδ T cells. Inhibition of Notch signaling by γ-secretase inhibitor inhibited the proliferation and IFN-γ secretion of γδ T cells in response to stimulation with phosphoantigens and anti-CD3 mAb. In the presence of γ-secretase inhibitor, the antitumor cytolytic ability of γδ T cells was inhibited with a decreased CD107a expression. Knockdown of Notch1 and Notch2 genes in γδ T cells using small interfering RNA inhibited their antitumor cytotoxic potential. Our study describes for the first time, to our knowledge, the role of Notch as an additional signal contributing to Ag-specific effector functions of γδ T cells.

Loss of CCM3 impairs DLL4-Notch signalling: implication in endothelial angiogenesis and in inherited cerebral cavernous malformations

CCM3, a product of the cerebral cavernous malformation 3 or programmed cell death 10 gene (CCM3/PDCD10), is broadly expressed throughout development in both vertebrates and invertebrates. Increasing evidence indicates a crucial role of CCM3 in vascular development and in regulation of angiogenesis and apoptosis. Furthermore, loss of CCM3 causes inherited (familial) cerebral cavernous malformation (CCM), a common brain vascular anomaly involving aberrant angiogenesis. This study focused on signalling pathways underlying the angiogenic functions of CCM3. Silencing CCM3 by siRNA stimulated endothelial proliferation, migration and sprouting accompanied by significant downregulation of the core components of Notch signalling including DLL4, Notch4, HEY2 and HES1 and by activation of VEGF and Erk pathways. Treatment with recombinant DLL4 (rhDLL4) restored DLL4 expression and reversed CCM3-silence-mediated impairment of Notch signalling and reduced the ratio of VEGF-R2 to VEGF-R1 expression. Importantly, restoration of DLL4-Notch signalling entirely rescued the hyper-angiogenic phenotype induced by CCM3 silence. A concomitant loss of CCM3 and the core components of DLL4-Notch signalling were also demonstrated in CCM3-deficient endothelial cells derived from human CCM lesions (CCMEC) and in a CCM3 germline mutation carrier. This study defined DLL4 as a key downstream target of CCM3 in endothelial cells. CCM3/DLL4-Notch pathway serves as an important signalling for endothelial angiogenesis and is potentially implicated in the pathomechanism of human CCMs.

Distinct spatial and molecular features of notch pathway assembly in regulatory T cells

Variations in the spatial localization of signaling components and crosstalk among signaling cascades are mechanisms through which diversity in signaling networks is generated. The receptor Notch provides an example of regulation by spatial localization: In the canonical Notch signaling pathway, Notch is cleaved to produce the Notch intracellular domain (NICD, also known as NIC), which translocates to the nucleus to regulate gene expression. We describe a T cell receptor-dependent, non-nuclear distribution and function of the processed receptor Notch, which was associated with the improved survival of regulatory T cells (T(regs)) in vitro and in vivo and was compromised by T cell-specific deletion of Notch1. Unlike a nuclear-restricted mutant of NICD, mutant NICD that underwent nuclear export or was targeted to the plasma membrane protected Notch1(-/-) T(regs) from apoptosis induced by nutrient deprivation and oxidative stress. Notch signaling integrated with phosphatidylinositol 3-kinase signaling and mammalian target of rapamycin complex 2 (mTORC2) for this cell survival function. Biochemical and imaging approaches revealed a membrane-proximal complex containing NICD and the mTORC2 component Rictor, and this complex was stabilized by specific interactions with the Notch ligand Delta-like-1 and mediated the survival of T(regs). Together, our evidence for the spatial control of Notch and the crosstalk of Notch signaling with other pathways reveals coupling between the localization of Notch and diverse intracellular signaling pathways.

Notch controls the magnitude of T helper cell responses by promoting cellular longevity

Generation of effective immune responses requires expansion of rare antigen-specific CD4(+) T cells. The magnitude of the responding population is ultimately determined by proliferation and survival. Both processes are tightly controlled to limit responses to innocuous antigens. Sustained expansion occurs only when innate immune sensors are activated by microbial stimuli or by adjuvants, which has important implications for vaccination. The molecular identity of the signals controlling sustained T-cell responses is not fully clear. Here, we describe a prominent role for the Notch pathway in this process. Coactivation of Notch allows accumulation of far greater numbers of activated CD4(+) T cells than stimulation via T-cell receptor and classic costimulation alone. Notch does not overtly affect cell cycle entry or progression of CD4(+) T cells. Instead, Notch protects activated CD4(+) T cells against apoptosis after an initial phase of clonal expansion. Notch induces a broad antiapoptotic gene expression program that protects against intrinsic, as well as extrinsic, apoptosis pathways. Both Notch1 and Notch2 receptors and the canonical effector RBPJ (recombination signal binding protein for immunoglobulin kappa J region) are involved in this process. Correspondingly, CD4(+) T-cell responses to immunization with protein antigen are strongly reduced in mice lacking these components of the Notch pathway. Our findings, therefore, show that Notch controls the magnitude of CD4(+) T-cell responses by promoting cellular longevity.

Notch, apoptosis and cancer

Proper embryonic development and normal tissue homeostasis require a series of molecular processes, regulating cell growth, differentiation and apoptosis. Perturbation in any of these processes invariably contributes to the development of cancer. In particular, defects in apoptosis are seen in virtually all types of human cancers. The Notch pathway plays an important role in cell fate determination in both embryonic development and organ homeostasis. Not surprisingly, Notch also plays a role in cancer when it is dysregulated. In this chapter, we will explore how Notch signaling interacts with key pathways that regulate apoptosis in cancer. Particularly, we will focus on the relationship between Notch and proteins responsible for activation of the caspase pathway. Notch regulates apoptosis through extensive networks, involving cell cycle, growth and survival pathways. Thus, we will also examine how apoptosis is modulated by the crosstalk between Notch and other signaling pathways such as p53, NF-κB and PI3K-Akt pathways.

Canonical notch pathway protects hepatocytes from ischemia/reperfusion injury in mice by repressing reactive oxygen species production through JAK2/STAT3 signaling

Hepatic ischemia/reperfusion (I/R) injury is initiated by reactive oxygen species (ROS) accumulated during the early reperfusion phase after ischemia, but cellular mechanisms controlling ROS production and scavenging have not been fully understood. In this study, we show that blocking Notch signal by knockout of the transcription factor RBP-J or a pharmacological inhibitor led to aggravated hepatic I/R injury, as manifested by deteriorated liver function and increased apoptosis, necrosis, and inflammation, both in vitro and in vivo. Interruption of Notch signaling resulted in increased intracellular ROS in hepatocytes, and a ROS scavenger cured exacerbated hepatic I/R injury after Notch signaling blockade, suggesting that Notch signal deficiency aggravated I/R injury through increased ROS levels. Notch signal blockade resulted in down-regulation of Hes5, leading to reduced formation of the Hes5-STAT3 complex and hypophosphorylation of STAT3, which further attenuated manganese superoxide dismutase (MnSOD) expression and increased ROS and apoptosis. Indeed, overexpression of a constitutively active STAT3 rescued MnSOD expression and I/R injury-induced apoptosis in the absence of Notch signaling. Finally, forced Notch activation by ligand stimulation or Hes5 overexpression reduced intracellular ROS and protected hepatocytes from apoptosis after I/R injury through the activation of STAT3 and MnSOD expression.

CONCLUSION

Notch signal protects hepatocytes from I/R injury by Hes5-dependent activation of STAT3, which activates the expression of MnSOD, leading to the scavenging of ROS.

GSI-I (Z-LLNle-CHO) inhibits γ-secretase and the proteosome to trigger cell death in precursor-B acute lymphoblastic leukemia

Gamma secretase inhibitors (GSIs) comprise a growing class of compounds that interfere with the membrane-bound Notch signaling protein and its downstream intra-nuclear transcriptional targets. As GSI-I (Z-LLNle-CHO) is also a derivative of a widely used proteosome inhibitor MG-132, we hypothesized that this compound might be active in precursor-B acute lymphoblastic leukemia (ALL) cell lines and patient samples. We found that GSI-I treatment of precursor-B ALL blasts induced apoptotic cell death within 18-24 h. With confirmation using RNA and protein analyses, GSI-I blocked nuclear accumulation of cleaved Notch1 and Notch2, and inhibited Notch targets Hey2 and Myc. Microarray analyses of 207 children with high-risk precursor-B ALL demonstrate that Notch pathway expression is a common feature of these neoplasms. However, microarray studies also implicated additional transcriptional targets in GSI-I-dependent cell death, including genes in the unfolded protein response, nuclear factor-κB and p53 pathways. Z-LLNle-CHO blocks both γ-secretase and proteosome activity, inducing more robust cell death in precursor-B ALL cells than either proteosome-selective or γ-secretase-selective inhibitors alone. Using Z-LLNle-CHO in a nonobese diabetes/severe combined immunodeficiency (NOD/SCID) precursor-B ALL xenograft model, we found that GSI-I alone delayed or prevented engraftment of B-lymphoblasts in 50% of the animals comprising the experimental group, suggesting that this compound is worthy of additional testing.

TLR-activated dendritic cells enhance the response of aged naive CD4 T cells via an IL-6-dependent mechanism

The most effective immunological adjuvants contain microbial products, such as TLR agonists, which bind to conserved pathogen recognition receptors. These activate dendritic cells (DCs) to become highly effective APCs. We assessed whether TLR ligand-treated DCs can enhance the otherwise defective response of aged naive CD4 T cells. In vivo administration of CpG, polyinosinic-polycytidylic acid, and Pam(3)CSK(4) in combination with Ag resulted in the increased expression of costimulatory molecules and MHC class II by DCs, increased serum levels of the inflammatory cytokines IL-6 and RANTES, and increased cognate CD4 T cell responses in young and aged mice. We show that, in vitro, preactivation of DCs by TLR ligands makes them more efficient APCs for aged naive CD4 T cells. After T-DC interaction, there are enhanced production of inflammatory cytokines, particularly IL-6, and greater expansion of the aged T cells, resulting from increased proliferation and greater effector survival with increased levels of Bcl-2. TLR preactivation of both bone marrow-derived and ex vivo DCs improved responses. IL-6 produced by the activated DCs during cognate T cell interaction was necessary for enhanced aged CD4 T cell expansion and survival. These studies suggest that some age-associated immune defects may be overcome by targeted activation of APCs by TLR ligands.

Notch1 as a potential therapeutic target in cutaneous T-cell lymphoma

Deregulation of Notch signaling has been linked to the development of T-cell leukemias and several solid malignancies. Yet, it is unknown whether Notch signaling is involved in the pathogenesis of mycosis fungoides and Sézary syndrome, the most common subtypes of cutaneous T-cell lymphoma. By immunohistochemistry of 40 biopsies taken from skin lesions of mycosis fungoides and Sézary syndrome, we demonstrated prominent expression of Notch1 on tumor cells, especially in the more advanced stages. The γ-secretase inhibitor I blocked Notch signaling and potently induced apoptosis in cell lines derived from mycosis fungoides (MyLa) and Sézary syndrome (SeAx, HuT-78) and in primary leukemic Sézary cells. Specific down-regulation of Notch1 (but not Notch2 and Notch3) by siRNA induced apoptosis in SeAx. The mechanism of apoptosis involved the inhibition of nuclear factor-κB, which is the most important prosurvival pathway in cutaneous T-cell lymphoma. Our data show that Notch is present in cutaneous T-cell lymphoma and that its inhibition may provide a new way to treat cutaneous T-cell lymphoma.

Notch-activated signaling cascade interacts with mitochondrial remodeling proteins to regulate cell survival

Survival of differentiated cells is one of several processes regulated by Notch activity, although the general principles underlying this function remain to be characterized. Here, we probe the mechanism underlying Notch-mediated survival, building on emerging evidence that apoptotic responses coordinated by specialized intermediates converge on mitochondria, identifying a core event in death pathways. The Bcl-2 family protein Bax is one such intermediate, which in a unifying response to diverse apoptotic stimuli nucleates multiprotein assemblies on mitochondria, committing cells to irrevocable damage. Using Bax as the prototype stimulus, we analyze Notch signaling for potential interactions with mitochondria, probe intrinsic properties of the Notch receptor, and describe key intermediates in the Notch-activated signaling cascade. Ligand-dependent processing was necessary to generate the Notch intracellular domain (NIC) although signaling was independent of canonical interactions with nuclear factors. Notably, antiapoptotic activity was recapitulated by NIC recombinants, localized outside the nucleus, and compromised by enforced nuclear sequestration. NIC signaled via the kinase Akt to prevent the loss of mitochondrial function, contiguity, and consequent nuclear damage, outcomes critically depend on mitochondrial remodeling proteins Mitofusins-(Mfn)-1 and 2. Thus, the NIC-Akt-Mfn signaling cascade identifies a pathway regulating cell-survival, independent of canonical functions associated with NIC activity.

Notch-regulation upon Dll4-stimulation of TGFb-induced apoptosis and gene expression in human B-cell non-Hodgkin lymphomas

Notch-signalling has been implicated as a pathogenetic factor and a therapeutical target in T-cell leukaemias and in some lymphomas of B-cell origin. Our aim was to investigate the role of Notch-signalling in apoptosis regulation in human non-Hodgkin B-cell lymphoma (B-NHL) cell lines and in primary chronic lymhocytic leukaemia (CLL) cells using Delta-like 4 (Dll4) ligand mediated Notch activation and gamma-secretase inhibitor (GSI) mediated Notch inhibition in vitro. The potential cross-talk of Notch with the transforming growth factor-beta (TGFb) pathway in apoptosis induction was also explored, and the effect of GSI on drug-induced apoptosis was assessed. Modulation of Notch-signalling by itself did not change the rate of apoptosis in B-NHL cell lines and in CLL cells. TGFb-induced apoptosis was decreased - but not completely abolished - by GSI in TGFb-sensitive cell lines, but resistance to the apoptotic effects of TGFb were not reversed by Notch activation or inhibition. Drug-induced apoptosis was not modified by GSI. We identified Hairy/Enhancer of Split (HES)-1 as a TGFb target gene in selected - TGFb-sensitive - B-NHL cell lines. TGFb-induced HES-1 was only partially Notch-dependent in later phases. Apoptosis regulation by TGFb and GSI was not dependent on the transcriptional regulation of c-myc. In conclusion, our data does not support a unifying role of Notch in regulating apoptosis in B-NHL, but warns that gamma-secretase inhibitors may actually counteract apoptosis in some cases.

Altered ex vivo expression of caspase 8, caspase 9, and Bcl-2 is associated with T-cell hyporeactivity in patients with paracoccidioidomycosis

To better understand the T-cell hyporesponsiveness of patients with paracoccidioidomycosis, we tested the hypothesis that the T cells were committed to apoptosis. We show here that T cells of patients with paracoccidioidomycosis overexpress caspase 9 and caspase 8 but express low Bcl-2 levels and that interleukin-2 was unable to revert the hyporesponsiveness. These data suggest that the T cells would in vivo be driven to a tolerant state and apoptosis.

A hierarchical cascade activated by non-canonical Notch signaling and the mTOR-Rictor complex regulates neglect-induced death in mammalian cells

The regulation of cellular metabolism and survival by trophic factors is not completely understood. Here, we describe a signaling cascade activated by the developmental regulator Notch, which inhibits apoptosis triggered by neglect in mammalian cells. In this pathway, the Notch intracellular domain (NIC), which is released after interaction with ligand, converges on the kinase mammalian target of rapamycin (mTOR) and the substrate-defining protein rapamycin independent companion of mTOR (Rictor), culminating in the activation of the kinase Akt/PKB. Biochemical and molecular approaches using site-directed mutants identified AktS473 as a key downstream target in the antiapoptotic pathway activated by NIC. Despite the demonstrated requirement for Notch processing and its predominant nuclear localization, NIC function was independent of CBF1/RBP-J, an essential DNA-binding component required for canonical signaling. In experiments that placed spatial constraints on NIC, enforced nuclear retention abrogated antiapoptotic activity and a membrane-anchored form of NIC-blocked apoptosis through mTOR, Rictor and Akt-dependent signaling. We show that the NIC-mTORC2-Akt cascade blocks the apoptotic response triggered by removal of medium or serum deprivation. Consistently, membrane-tethered NIC, and AktS473 inhibited apoptosis triggered by cytokine deprivation in activated T cells. Thus, this study identifies a non-canonical signaling cascade wherein NIC integrates with multiple pathways to regulate cell survival.

Redox regulation of multidrug resistance in cancer chemotherapy: molecular mechanisms and therapeutic opportunities

The development of multidrug resistance to cancer chemotherapy is a major obstacle to the effective treatment of human malignancies. It has been established that membrane proteins, notably multidrug resistance (MDR), multidrug resistance protein (MRP), and breast cancer resistance protein (BCRP) of the ATP binding cassette (ABC) transporter family encoding efflux pumps, play important roles in the development of multidrug resistance. Overexpression of these transporters has been observed frequently in many types of human malignancies and correlated with poor responses to chemotherapeutic agents. Evidence has accumulated showing that redox signals are activated in response to drug treatments that affect the expression and activity of these transporters by multiple mechanisms, including (a) conformational changes in the transporters, (b) regulation of the biosynthesis cofactors required for the transporter's function, (c) regulation of the expression of transporters at transcriptional, posttranscriptional, and epigenetic levels, and (d) amplification of the copy number of genes encoding these transporters. This review describes various specific factors and their relevant signaling pathways that are involved in the regulation. Finally, the roles of redox signaling in the maintenance and evolution of cancer stem cells and their implications in the development of intrinsic and acquired multidrug resistance in cancer chemotherapy are discussed.

Notch1 is an effector of Akt and hypoxia in melanoma development

Melanomas are highly aggressive neoplasms resistant to most conventional therapies. These tumors result from the interaction of altered intracellular tumor suppressors and oncogenes with the microenvironment in which these changes occur. We previously demonstrated that physiologic skin hypoxia contributes to melanomagenesis in conjunction with Akt activation. Here we show that Notch1 signaling is elevated in human melanoma samples and cell lines and is required for Akt and hypoxia to transform melanocytes in vitro. Notch1 facilitated melanoma development in a xenograft model by maintaining cell proliferation and by protecting cells from stress-induced cell death. Hyperactivated PI3K/Akt signaling led to upregulation of Notch1 through NF-kappaB activity, while the low oxygen content normally found in skin increased mRNA and protein levels of Notch1 via stabilization of HIF-1alpha. Taken together, these findings demonstrate that Notch1 is a key effector of both Akt and hypoxia in melanoma development and identify the Notch signaling pathway as a potential therapeutic target in melanoma treatment.

Defining a modular signalling network from the fly interactome

Background

Signalling pathways relay information by transmitting signals from cell surface receptors to intracellular effectors that eventually activate the transcription of target genes. Since signalling pathways involve several types of molecular interactions including protein-protein interactions, we postulated that investigating their organization in the context of the global protein-protein interaction network could provide a new integrated view of signalling mechanisms.

Results

Using a graph-theory based method to analyse the fly protein-protein interaction network, we found that each signalling pathway is organized in two to three different signalling modules. These modules contain canonical proteins of the signalling pathways, known regulators as well as other proteins thereby predicted to participate to the signalling mechanisms. Connections between the signalling modules are prominent as compared to the other network's modules and interactions within and between signalling modules are among the more central routes of the interaction network.

Conclusion

Altogether, these modules form an interactome sub-network devoted to signalling with particular topological properties: modularity, density and centrality. This finding reflects the integration of the signalling system into cell functioning and its important role connecting and coordinating different biological processes at the level of the interactome.

Essential role of Notch signaling in effector memory CD8+ T cell-mediated airway hyperresponsiveness and inflammation

Adoptive transfer of in vivo-primed CD8(+) T cells or in vitro-generated effector memory CD8(+) T (T(EFF)) cells restores airway hyperresponsiveness (AHR) and airway inflammation in CD8-deficient (CD8(-/-)) mice. Examining transcription levels, there was a strong induction of Notch1 in T(EFF) cells compared with central memory CD8(+) T cells. Treatment of T(EFF) cells with a gamma-secretase inhibitor (GSI) strongly inhibited Notch signaling in these cells, and after adoptive transfer, GSI-treated T(EFF) cells failed to restore AHR and airway inflammation in sensitized and challenged recipient CD8(-/-) mice, or to enhance these responses in recipient wild-type (WT) mice. These effects of GSI were also associated with increased expression of the Notch ligand Delta1 in T(EFF) cells. Treatment of sensitized and challenged WT mice with Delta1-Fc resulted in decreased AHR and airway inflammation accompanied by higher levels of interferon gamma in bronchoalveolar lavage fluid. These results demonstrate a role for Notch in skewing the T cell response from a T helper (Th)2 to a Th1 phenotype as a consequence of the inhibition of Notch receptor activation and the up-regulation of the Notch ligand Delta1. These data are the first to show a functional role for Notch in the challenge phase of CD8(+) T cell-mediated development of AHR and airway inflammation, and identify Delta1 as an important regulator of allergic airway inflammation.

Notch ligand Delta-like 4 regulates disease pathogenesis during respiratory viral infections by modulating Th2 cytokines

Recent data have indicated that an important instructive class of signals regulating the immune response is Notch ligand–mediated activation. Using quantitative polymerase chain reaction, we observed that only Delta-like 4 (dll4) was up-regulated on bone marrow–derived dendritic cells after respiratory syncytial virus (RSV) infection, and that it was dependent on MyD88-mediated pathways. Using a polyclonal antibody specific for dll4, the development of RSV-induced disease was examined. Animals treated with anti-dll4 had substantially increased airway hyperresponsiveness compared with control antibody-treated animals. When the lymphocytic lung infiltrate was examined, a significant increase in total CD4⁺ T cells and activated (perforin⁺) CD8⁺ T cells was observed. Isolated lung CD4⁺ T cells demonstrated significant increases in Th2-type cytokines and a decrease in interferon γ, demonstrating an association with increased disease pathogenesis. Parellel in vitro studies examining the integrated role of dll4 with interleukin-12 demonstrated that, together, both of these instructive signals direct the immune response toward a more competent, less pathogenic antiviral response. These data demonstrate that dll4-mediated Notch activation is one regulator of antiviral immunity.

A low level of reactive oxygen species selects for primitive hematopoietic stem cells that may reside in the low-oxygenic niche

A low-oxygenic niche in bone marrow limits reactive oxygen species (ROS) production, thus providing long-term protection for hematopoietic stem cells (HSCs) from ROS stress. Although many approaches have been used to enrich HSCs, none has been designed to isolate primitive HSCs located within the low-oxygenic niche due to difficulties of direct physical access. Here we show that an early HSC population that might reside in the niche can be functionally isolated by taking advantage of the relative intracellular ROS activity. Many attributes of primitive HSCs in the low-oxygenic osteoblastic niche, such as quiescence, and calcium receptor, N-cadherin, Notch1, and p21 are higher in the ROS(low) population. Intriguingly, the ROS(low) population has a higher self-renewal potential. In contrast, significant HSC exhaustion in the ROS(high) population was observed following serial transplantation, and expression of activated p38 mitogen-activated protein kinase (MAPK) and mammalian target of rapamycin (mTOR) was higher in this population. Importantly, treatment with an antioxidant, a p38 inhibitor, or rapamycin was able to restore HSC function in the ROS(high) population. Thus, more potent HSCs associated with the low-oxygenic niche can be isolated by selecting for the low level of ROS expression. The ROS-related signaling pathways together with specific characteristics of niche HSCs may serve as targets for beneficial therapies.