Notch1 augments NF-kappaB activity by facilitating its nuclear retention

How are T(H)1 and T(H)2 effector cells made?

Differentiation of T(H)1 and T(H)2 effector cells proceeds through several phases: First, naïve CD4(+) precursor cells are instructed to differentiate as appropriate to optimally fight the infectious threat encountered. This process is governed by the IL12 and IL4 cytokines, as well as by signaling through the Notch receptor. In response to these signals, transcription is initiated of lineage specific cytokine genes including the Ifngamma and Il4 genes as well as of genes encoding transcriptional regulators, such as T-bet and Gata3. The respective differentiation programs are reinforced by both positive and negative feedback mechanisms. Furthermore, epigenetic modifications of the lineage specific genes result in the emergence of regulatory elements, which control high level lineage restricted expression by both intrachromosomal and interchromosomal associations. Together, these mechanisms ensure stable inheritance of the differentiated fate in the numerous progeny of the original naïve CD4(+) T cells.

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.

Gamma-secretase inhibitor reduces allergic pulmonary inflammation by modulating Th1 and Th2 responses

RATIONALE

Gamma-secretase inhibitor (GSI) has been used to effectively block Notch signaling, which is implicated in the differentiation and functional regulation of T helper (Th) effector cells. In asthma, a subset of CD4(+) T cells is believed to initiate and perpetuate the disease.

OBJECTIVES

The aim of this study was to evaluate the therapeutic potential of GSI against allergic asthma.

METHODS

GSI was administered to an ovalbumin-sensitized mouse via an intranasal route at the time of ovalbumin challenge.

MEASUREMENTS AND MAIN RESULTS

The administration of GSI inhibits asthma phenotypes, including eosinophilic airway inflammation, goblet cell metaplasia, methacholine-induced airway hyperresponsiveness, and serum IgE production. GSI treatment of bronchoalveolar lavage cells stimulated via TCR or non-TCR pathways led to a decrease in Th2 cytokine production with a concomitant increase in Th1 cytokine secretion. Expression of Hes-1, a target of Notch signaling, was down-regulated in conjunction with a reduction of Notch intracellular domain and GATA-3 levels after GSI treatment of bronchoalveolar lavage cells. GSI treatment resulted in an inhibition of NF-kappaB activation, and combined treatment with GSI and an NF-kappaB inhibitor augmented IFN-gamma production in a synergistic manner.

CONCLUSIONS

These data suggest that GSI directly regulates Th1 and Th2 responses in allergic pulmonary inflammation through a Notch signaling-dependent pathway and that GSI is of high therapeutic value for treating asthma by inhibiting airway inflammatory responses.

The role of NOTCH1 signaling in T-ALL

The identification of activating mutations in NOTCH1 in over 50% of T-cell acute lymphoblastic leukemias (T-ALL) has generated major interest in the elucidation of the mechanisms of transformation downstream of oncogenic NOTCH and in the targeting of the NOTCH signaling pathway in this disease. Small molecule gamma-secretase inhibitors (GSIs) block NOTCH1 signaling in T-ALL lymphoblasts, yet the clinical development of GSIs has been held back by the development of gastrointestinal toxicity and their weak antileukemic effects against human T-ALL. However, new therapeutic strategies aiming to optimize the use of anti-NOTCH1 therapies for T-ALL, including combination therapies with molecularly targeted drugs and glucocorticoids, have started to emerge as a result of improved understanding of the molecular mechanisms that mediate the effects of GSIs in leukemic cells and the intestinal epithelium. This review focuses on the molecular basis of NOTCH1-induced transformation, the mechanisms of action of oncogenic NOTCH1 and clinical significance of NOTCH1 mutations in T-ALL.

Downregulation of Notch signaling by gamma-secretase inhibition can abrogate chemotherapy-induced apoptosis in T-ALL cell lines

Activation of Notch1 signaling plays an important role in the pathogenesis of precursor T-cell lymphoblastic leukemia (T-ALL). The Notch1 receptor is cleaved and activated via the gamma-secretase complex. Downregulation of Notch1 signaling by gamma-secretase inhibitors (GSIs) thus represents a potential novel therapeutic approach. In this study, we analyzed the response of four T-ALL cell lines to compound E, a potent gamma-secretase inhibitor, and to the combination of compound E with vincristine, daunorubicin, L-asparaginase (L-ASP), and dexamethasone (DEX). We identified two distinct types of responses: In type 1 cell lines, represented by TALL1 and HSB2, GSI-induced apoptosis followed cell cycle arrest and enhanced the induction of apoptosis caused by DEX and L-ASP. In type 2 cell lines, represented by CEM and Jurkat J6, GSI caused neither cell cycle block nor cell death. Notably, the combination of GSI with chemotherapy-induced resistance by decreasing apoptosis. In type 2 cells, GSI induced the upregulation of Bcl-xl mRNA and protein, which was thus identified as a candidate mechanism for the inhibition of apoptosis. In conclusion, the data presented here caution against clinical use of a combination treatment of GSI and chemotherapy in T-ALL.

Notch and Vascular Smooth Muscle Cell Phenotype

The Notch signaling pathway is critical for cell fate determination during embryonic development, including many aspects of vascular development. An emerging paradigm suggests that the Notch gene regulatory network is often recapitulated in the context of phenotypic modulation of vascular smooth muscle cells (VSMC), vascular remodeling, and repair in adult vascular disease following injury. Notch ligand receptor interactions lead to cleavage of receptor, translocation of the intracellular receptor (Notch IC), activation of transcriptional CBF-1/RBP-Jκ–dependent and –independent pathways, and transduction of downstream Notch target gene expression. Hereditary mutations of Notch components are associated with congenital defects of the cardiovascular system in humans such as Alagille syndrome and cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL). Recent loss- or gain-of-function studies have provided insight into novel Notch-mediated CBF-1/RBP-Jκ–dependent and –independent signaling and cross-regulation to other molecules that may play a critical role in VSMC phenotypic switching. Notch receptors are critical for controlling VSMC differentiation and dictating the phenotypic response following vascular injury through interaction with a triad of transcription factors that act synergistically to regulate VSMC differentiation. This review focuses on the role of Notch receptor ligand interactions in dictating VSMC behavior and phenotype and presents recent findings on the molecular interactions between the Notch components and VSMC-specific genes to further understand the function of Notch signaling in vascular tissue and disease.

Gamma-secretase limits the inflammatory response through the processing of LRP1

Inflammation is a potentially self-destructive process that needs tight control. We have identified a nuclear signaling mechanism through which the low-density lipoprotein receptor-related protein 1 (LRP1) limits transcription of lipopolysaccharide (LPS)-inducible genes. LPS increases the proteolytic processing of the ectodomain of LRP1, which results in the gamma-secretase-dependent release of the LRP1 intracellular domain (ICD) from the plasma membrane and its translocation to the nucleus, where it binds to and represses the interferon-gamma promoter. Basal transcription of LPS target genes and LPS-induced secretion of proinflammatory cytokines are increased in the absence of LRP1. The interaction between LRP1-ICD and interferon regulatory factor 3 (IRF-3) promotes the nuclear export and proteasomal degradation of IRF-3. Feedback inhibition of the inflammatory response through intramembranous processing of LRP1 thus defines a physiological role for gamma-secretase.

Notch signaling mediates G1/S cell-cycle progression in T cells via cyclin D3 and its dependent kinases

Notch signaling plays a role in normal lymphocyte development and function. Activating Notch1-mutations, leading to aberrant downstream signaling, have been identified in human T-cell acute lymphoblastic leukemia (T-ALL). While this highlights the contribution of Notch signaling to T-ALL pathogenesis, the mechanisms by which Notch regulates proliferation and survival in normal and leukemic T cells are not fully understood. Our findings identify a role for Notch signaling in G(1)-S progression of cell cycle in T cells. Here we show that expression of the G(1) proteins, cyclin D3, CDK4, and CDK6, is Notch-dependent both in vitro and in vivo, and we outline a possible mechanism for the regulated expression of cyclin D3 in activated T cells via CSL (CBF-1, mammals; suppressor of hairless, Drosophila melanogaster; Lag-1, Caenorhabditis elegans), as well as a noncanonical Notch signaling pathway. While cyclin D3 expression contributes to cell-cycle progression in Notch-dependent human T-ALL cell lines, ectopic expression of CDK4 or CDK6 together with cyclin D3 shows partial rescue from gamma-secretase inhibitor (GSI)-induced G(1) arrest in these cell lines. Importantly, cyclin D3 and CDK4 are highly overexpressed in Notch-dependent T-cell lymphomas, justifying the combined use of cell-cycle inhibitors and GSI in treating human T-cell malignancies.

Rbpj conditional knockout reveals distinct functions of Notch4/Int3 in mammary gland development and tumorigenesis

Transgenic mice expressing the Notch 4 intracellular domain (ICD) (Int3) in the mammary gland have two phenotypes: arrest of mammary alveolar/lobular development and mammary tumorigenesis. Notch4 signaling is mediated primarily through the interaction of Int3 with the transcription repressor/activator Rbpj. We have conditionally ablated the Rbpj gene in the mammary glands of mice expressing whey acidic protein (Wap)-Int3. Interestingly, Rbpj knockout mice (Wap-Cre(+)/Rbpj(-/-)/Wap-Int3) have normal mammary gland development, suggesting that the effect of endogenous Notch signaling on mammary gland development is complete by day 15 of pregnancy. RBP-J heterozygous (Wap-Cre(+)/Rbpj(-/+)/Wap-Int3) and Rbpj control (Rbpj(flox/flox)/Wap-Int3) mice are phenotypically the same as Wap-Int3 mice with respect to mammary gland development and tumorigenesis. In addition, the Wap-Cre(+)/Rbpj(-/-)/Wap-Int3-knockout mice also developed mammary tumors at a frequency similar to Rbpj heterozygous and Wap-Int3 control mice but with a slightly longer latency. Thus, the effect on mammary gland development is dependent on the interaction of the Notch ICD with the transcription repressor/activator Rbpj, and Notch-induced mammary tumor development is independent of this interaction.

Notch-1 associates with IKKalpha and regulates IKK activity in cervical cancer cells

Notch-1 inhibits apoptosis in some transformed cells through incompletely understood mechanisms. Notch-1 can increase nuclear factor-kappa B (NF-kappaB) activity through a variety of mechanisms. Overexpression of cleaved Notch-1 in T-cell acute lymphoblastic leukemia cells activates NF-kappaB via interaction with the I kappa B kinase (IKK) signalosome. Concomitant activation of the Notch and NF-kappaB pathways has been described in a large series of cervical cancer specimens. Here, we show that wild-type, spontaneously expressed Notch-1 stimulates NF-kappaB activity in CaSki cervical cancer cells by associating with the IKK signalosome through IKKalpha. A significant fraction of tumor necrosis factor (TNF)-alpha-stimulated IkappaB kinase activity in CaSki cells is Notch-1-dependent. In addition, Notch-1 is found in the nucleus in association with IKKalpha at IKKalpha-stimulated promoters and is required for association of IKKalpha with these promoters under basal and TNF-alpha-stimulated conditions. Notch-1-IKKalpha complexes are found in normal human keratinocytes as well, suggesting that IKK regulation is a physiological function of Notch-1. Both Notch-1 and IKKalpha knockdown sensitize CaSki cells to cisplatin-induced apoptosis to equivalent extents. Our data indicate that Notch-1 regulates NF-kappaB in cervical cancer cells at least in part via cytoplasmic and nuclear IKK-mediated pathways.

Notch tumor suppressor function

Cancer development results from deregulated control of stem cell populations and alterations in their surrounding environment. Notch signaling is an important form of direct cell-cell communication involved in cell fate determination, stem cell potential and lineage commitment. The biological function of this pathway is critically context dependent. Here we review the pro-differentiation role and tumor suppressing function of this pathway, as revealed by loss-of-function in keratinocytes and skin, downstream of p53 and in cross-connection with other determinants of stem cell potential and/or tumor formation, such as p63 and Rho/CDC42 effectors. The possibility that Notch signaling elicits a duality of signals, involved in growth/differentiation control and cell survival will be discussed, in the context of novel approaches for cancer therapy.

Constitutively activated Notch signaling is involved in survival and apoptosis resistance of B-CLL cells

Notch signaling is involved in tumorigenesis, but its role in B-chronic lymphocytic leukemia (B-CLL) pathogenesis is not completely defined. This study examined the expression and activation of Notch receptors in B-CLL cells and the role of Notch signaling in sustaining the survival of these cells. Our results show that B-CLL cells but not normal B cells constitutively express Notch1 and Notch2 proteins as well as their ligands Jagged1 and Jagged2. Notch signaling is constitutively activated in B-CLL cells, and its activation is further increased in B-CLL cells, which resist spontaneous apoptosis after 24-hour ex vivo culture. Notch stimulation by a soluble Jagged1 ligand increases B-CLL cell survival and is accompanied by increased nuclear factor-kappa B (NF-kappaB) activity and cellular inhibitor of apoptosis protein 2 (c-IAP2) and X-linked inhibitor of apoptosis protein (XIAP) expression. In contrast, Notch-signaling inhibition by the gamma-secretase inhibitor I (GSI; z-Leu-Leu-Nle-CHO) and the specific Notch2 down-regulation by small-interfering RNA accelerate spontaneous B-CLL cell apoptosis. Apoptotic activity of GSI is accompanied by reduction of NF-kappaB activity and c-IAP2 and XIAP expression. Overall, our findings show that Notch signaling plays a critical role in B-CLL cell survival and apoptosis resistance and suggest that it could be a novel potential therapeutic target.

Inhibition of gamma-secretase affects proliferation of leukemia and hepatoma cell lines through Notch signaling

Notch signaling is a well-conserved pathway playing crucial roles in regulating cell fate decision, proliferation, and apoptosis during the development of multiple cell lineages. Aberration in Notch signaling is associated with tumorigenesis of tissues from various origins. To investigate the role Notch signaling plays in the proliferation of cancer cell lines, the expression profiles of Notch1 in six human cancer cell lines (Jurkat, HepG2, SW620, KATOIII, A375, BT474) were examined. All cell lines differentially expressed Notch1, and only Jurkat and SW620 expressed cleaved Notch1 (Val1744). Among the six cell lines tested, only Jurkat and HepG2 showed a decrease in cell proliferation during 4 days of treatment with a gamma-secretase inhibitor (GSI). This is the first report on the anti-proliferative effects of GSI on a human hepatoma cell line. These two cell lines expressed Notch1-3, Jagged1, Jagged2, Dlk1 and Hes1. GSI treatment led to a decrease in Hes1 expression in both cell lines. Surprisingly, GSI treatment resulted in the accumulation of Notch1 protein upon treatment. During this period, GSI treatment did not induce apoptosis, but caused cell cycle arrest in both cell lines. This was also correlated with decreased c-myc expression. Forced expression of activated intracellular Notch1 completely abrogated GSI sensitivity in both cell lines. These results clearly demonstrate that Notch signaling positively regulates cell proliferation in Jurkat and HepG2 cell lines and that GSI treatment inhibits tumor cell proliferation through the suppression of Notch signaling.

IkappaBalpha is required for marginal zone B cell lineage development

Inactivation of members of the nuclear factor-kappaB (NF-kappaB) family results in the decrease or defect of marginal zone B (MZB) cells. It is not known which inhibitors of the NF-kappaB family (IkappaB) are required for MZB cell development. Here, we show that mice with B cell-specific inactivation of the main NF-kappaB inhibitor IkappaBalpha have a marked decrease of MZB cells and their presumed precursors. They exhibited increased mortality rates after blood-borne bacterial infection, indicating the importance of MZB cells for bacterial clearance. In contrast, response to T cell-dependent and -independent antigens resulted only in minor changes in immunoglobulin production. Our data demonstrate the importance of the intact NF-kappaB/IkappaBalpha pathway for proper MZB cell development.

The association of Notch2 and NF-kappaB accelerates RANKL-induced osteoclastogenesis

Notch signaling plays a key role in various cell differentiation processes including bone homeostasis. However, the specific involvement of Notch in regulating osteoclastogenesis is still controversial. In the present study, we show that RANKL induces expression of Jagged1 and Notch2 in bone marrow macrophages during osteoclast differentiation. Suppression of Notch signaling by a selective gamma-secretase inhibitor or Notch2 short hairpin RNA suppresses RANKL-induced osteoclastogenesis. In contrast, induction of Notch signaling by Jagged1 or by ectopic expression of intracellular Notch2 enhances NFATc1 promoter activity and expression and promotes osteoclastogenesis. Finally, we found that Notch2 and p65 interact in the nuclei of RANKL-stimulated cells and that both proteins are recruited to the NFATc1 promoter, driving its expression. Taken together, our results show a new molecular cross talk between Notch and NF-kappaB pathways that is relevant in osteoclastogenesis.

Defects in Notch1 upregulation upon activation of T Cells from patients with systemic lupus erythematosus are related to lupus disease activity

Systemic lupus erythematosus (SLE) is an autoimmune disorder characterized by the production of autoantibodies and deposition of immune complexes in various organs. T cells play a central role in driving disease progression, and multiple defects in T cells from patients with SLE have been uncovered. Notch signalling is an evolutionarily well-conserved signalling cascade involved in the proliferation, differentiation and apoptosis of T lymphocytes during development and peripheral effector functions. In this study, we investigated the correlation between expression of Notch receptor and the severity of SLE disease. On the contrary to T lymphocytes from healthy controls ( n = 11), Tlymphocytes from patients with active SLE ( n = 12) failed to upregulate Notch1 upon in-vitro stimulation as quantified by quantitative real time RT-PCR ( P ≤ 0.025). Among patients with inactive SLE ( n = 10), those with late onset of flare exhibited significantly less Notch1 upregulation compared with SLE patients with remission. Expression of the Notch target genes, Hes1 and deltex, was also lower in patients with active SLE. The decrease in Notch1 mRNA expression was consistent with less Notch1 protein expression in patients with active SLE. The defects in Notch1 upregulation correlated with decreased proliferation, CD25 and Foxp3 expression upon stimulation in vitro. Taken together, the failure of T cells to upregulate Notch1 upon activation may be a key feature of active SLE and a potential therapeutic target.

Initiation and maintenance of Th2 cell identity

T helper type 2 (Th2) cells produce IL-4, IL-5, and IL-13 and play an important role in humoral immunity and allergic reactions. During Th2 cell differentiation, naïve CD4 T cells acquire 'Th2 cell identity', that is, the capability to produce selectively a large amount of Th2 cytokines. Th2 cell identity is maintained in memory Th2 cells. Significant advances in understanding of the molecular requirement for these processes have been made. The expression of GATA3, a master transcription factor for Th2 cell differentiation, is uniquely regulated by several distinct mechanisms. Molecular analyses of memory Th2 cells revealed that cell survival and the maintenance of Th2 cell function are epigenetically regulated by various nuclear factors, including Polycomb and Trithorax molecules.

Notch signaling in leukemia

Recent discoveries indicate that gain-of-function mutations in the Notch1 receptor are very common in human T cell acute lymphoblastic leukemia/lymphoma. This review discusses what these mutations have taught us about normal and pathophysiologic Notch1 signaling, and how these insights may lead to new targeted therapies for patients with this aggressive form of cancer.

Peripheral B cell subsets

Our understanding of the origins and the biological functions of different peripheral B cell subsets continues to evolve. Some understanding has been obtained regarding the synergy between BCR-derived signals and other receptors and signaling pathways that drive the development of follicular, marginal zone, and B-1 B cells, but this remains a complex and poorly understood issue. More recent information regarding the origins of B-1 and B-2 B cells, the ability of follicular B cells to mature both in the bone marrow and the spleen, the existence of a definable precursor for MZ B cells, and the ability of follicular B cells to occupy two distinct niches are all highlighted in this review.

Notch signaling in CD4 and CD8 T cell development

Because Notch often acts in concert with other signaling pathways, it is able to regulate a diverse set of biological processes in a cell-context dependent manner. In lymphocytes, Notch is essential for specifying the T cell fate and for promoting early stages of T cell differentiation. At later stages of development, Notch signaling is proposed to direct CD4 versus CD8 T lineage commitment. This hypothesis has been challenged by recent studies of conditional Presenilin-deficient mice showing that Notch promotes the selection and maturation of CD4 and CD8 T cells by potentiating TCR signal transduction in immature thymocytes. While similar conclusions have not been reported with conditional mutation of other downstream mediators of Notch activation, it appears that functional inhibition may not have been achieved at a comparable stage of development and/or analogous issues have not been addressed. The differences also question whether in thymocytes Notch signals only through the canonical pathway. Further study of conditional mutants, signaling intermediates, and transcriptional regulators are needed to elucidate how Notch facilitates TCR signaling in generating mature T cells.

Notch3 and IL-1beta exert opposing effects on a vascular smooth muscle cell inflammatory pathway in which NF-kappaB drives crosstalk

Atherogenesis begins with the transfer of monocytes from the lumen to the intimal layer of arteries. The paracrine activity acquired by these monocytes shifts vascular smooth muscle cells from a contractile-quiescent to a secretory-proliferative phenotype, allowing them to survive and migrate in the intima. Transformed and relocated, they also start to produce and/or secrete inflammatory enzymes, converting them into inflammatory cells. Activation of the Notch pathway, a crucial determinant of cell fate, regulates some of the new features acquired by these cells as it triggers vascular smooth muscle cells to grow and inhibits their death and migration. Here, we evaluate whether and how the Notch pathway regulates the cell transition towards an inflammatory or de-differentiated state. Activation of the Notch pathway by the notch ligand Delta1, as well as overexpression of the active form of Notch3, prevents this phenomenon [initiated by interleukin 1beta (IL-1beta)], whereas inhibiting the Notch pathway enhances the transition. IL-1beta decreases the expression of Notch3 and Notch target genes. As shown by using an IkappaBalpha-mutated form, the decrease of Notch3 signaling elements occurs subsequent to dissociation of the NF-kappaB complex. These results demonstrate that the Notch3 pathway is attenuated through NF-kappaB activation, allowing vascular smooth muscle cells to switch into an inflammatory state.

Downregulation by lipopolysaccharide of Notch signaling, via nitric oxide

The Notch signaling pathway appears to perform an important function in inflammation. Here, we present evidence to suggest that lipopolysaccharide (LPS) suppresses Notch signaling via the direct modification of Notch by the nitration of tyrosine residues in macrophages. In the RAW264.7 macrophage cell line and in rat primary alveolar macrophages, LPS was found to inhibit Notch1 intracellular domain (Notch1-IC) transcription activity, which could then be rescued by treatment with N(G)-nitro-l-arginine, a nitric oxide synthase (NOS) inhibitor. Nitric oxide (NO), which was produced in cells that stably express endothelial NOS (eNOS) and brain NOS (bNOS), also induced the inhibition of Notch1 signaling. The NO-induced inhibition of Notch1 signaling remained unchanged after treatment with 1H-[1,2,4]oxadiazolo[4,3-alpha]quinoxalin-1-one (ODQ), a guanylyl-cyclase inhibitor, and was not found to be mimicked by 8-bromo-cyclic GMP in the primary alveolar macrophages. With regards to the control of Notch signaling, NO appears to have a significant negative influence, via the nitration of Notch1-IC, on the binding that occurs between Notch1-IC and RBP-Jk, both in vitro and in vivo. By intrinsic fluorescence, we also determined that nitration could mediate conformational changes of Notch1-IC. The substitution of phenylalanine for tyrosine at residue 1905 in Notch1-IC abolished the nitration of Notch1-IC by LPS. Overall, our data suggest that an important relationship exists between LPS-mediated inflammation and the Notch1 signaling pathway, and that this relationship intimately involves the nitration of Notch1-IC tyrosine residues.

The FoxO3a gene is a key negative target of canonical Notch signalling in the keratinocyte UVB response

Notch signalling has an important role in skin homeostasis, promoting keratinocyte differentiation and suppressing tumorigenesis. Here we show that this pathway also has an essential anti-apoptotic function in the keratinocyte UVB response. Notch1 expression and activity are significantly induced, in a p53-dependent manner, by UVB exposure of primary keratinocytes as well as intact epidermis of both mouse and human origin. The apoptotic response to UVB is increased by deletion of the Notch1 gene or down-modulation of Notch signalling by pharmacological inhibition or genetic suppression of 'canonical' Notch/CSL/MAML1-dependent transcription. Conversely, Notch activation protects keratinocytes against apoptosis through a mechanism that is not linked to Notch-induced cell cycle withdrawal or NF-kappaB activation. Rather, transcription of FoxO3a, a key pro-apoptotic gene, is under direct negative control of Notch/HERP transcription in keratinocytes, and upregulation of this gene accounts for the increased susceptibility to UVB of cells with suppressed Notch signalling. Thus, the canonical Notch/HERP pathway functions as a protective anti-apoptotic mechanism in keratinocytes through negative control of FoxO3a expression.

NOTCH1 up-regulation and signaling involved in Mycobacterium bovis BCG-induced SOCS3 expression in macrophages

Suppressor of cytokine signaling (SOCS) 3 is a critical negative regulator of cytokine signaling and is induced by Mycobacterium bovis Bacille Calmette-Guérin (M. bovis BCG) in mouse macrophages. However, little is known about the early receptor proximal signaling mechanisms underlying mycobacteria-mediated induction of SOCS3. We demonstrate here for the first time that M. bovis BCG up-regulates NOTCH1 and activates the NOTCH1 signaling pathway, leading to the expression of SOCS3. We show that perturbing Notch signaling in infected macrophages results in the marked reduction in the expression of SOCS3. Furthermore, enforced expression of the Notch1 intracellular domain in RAW 264.7 macrophages induces the expression of SOCS3, which can be further potentiated by M. bovis BCG. The perturbation of Toll-like receptor (TLR) 2 signaling resulted in marked reduction in SOCS3 levels and expression of the NOTCH1 target gene, Hes1. The down-regulation of MyD88 resulted in a significant decrease in SOCS3 expression, implicating the role of the TLR2-MyD88 axis in M. bovis BCG-triggered signaling. However, the SOCS3 inducing ability of M. bovis BCG remains unaltered also upon infection of macrophages from TLR4-defective C3H/HeJ mice. More importantly, signaling perturbation data suggest the involvement of cross-talk among members of the phosphoinositide 3-kinase and mitogen-activated protein kinase cascades with NOTCH1 signaling in SOCS3 expression. Furthermore, SOCS3 expression requires the NOTCH1-mediated recruitment of Suppressor of Hairless (CSL) and nuclear factor-kappaB to the Socs3 promoter. Overall, these results implicate NOTCH1 signaling during inducible expression of SOCS3 following infection of macrophages with an intracellular bacillus-like M. bovis BCG.

NUMBL interacts with TAB2 and inhibits TNFalpha and IL-1beta-induced NF-kappaB activation

The cytokines TNFalpha and IL-1beta induce inflammation through activation of transcription factors NF-kappaB. TAB2 is an adapter protein that facilitates TNFalpha and IL-1beta-mediated NF-kappaB activation. In this work, using yeast two-hybrid system TAB2 was identified to interact with NUMBL. The interaction was further confirmed in vitro and in vivo. PTB domain of NUMBL and C-terminal region are required for their interaction. Overexpression of NUMBL inhibited TNFalpha, IL-1beta-induced activation of NF-kappaB signaling pathway. NUMBL also inhibited TAB2, TAK1, TRAF6 and RIP-induced activation of NF-kappaB in a dose-dependent manner. We found that NUMBL can impair TAB2 binding to TRAF6 or RIP and inhibit ubiquitination of TRAF6 enhanced by TAB2. Taken together, our data suggest that NUMBL is involved in negative regulation of NF-kappaB signaling through its interaction with TAB2. These findings also reveal the new functions of NUMBL and implicate that NUMBL potentially links Notch pathway to NF-kappaB pathway.

Down-regulation of platelet-derived growth factor-D inhibits cell growth and angiogenesis through inactivation of Notch-1 and nuclear factor-kappaB signaling

Platelet-derived growth factor-D (PDGF-D) signaling plays critical roles in the pathogenesis and progression of human malignancies; however, the precise mechanism by which PDGF-D causes tumor cell invasion and angiogenesis remain unclear. Because Notch-1, nuclear factor-kappaB (NF-kappaB), vascular endothelial growth factor (VEGF), and matrix metalloproteinases (MMP) are critically involved in the processes of tumor cell invasion and metastasis, we investigated whether PDGF-D down-regulation could be mechanistically associated with the down-regulation of Notch-1, NF-kappaB, VEGF, and MMP-9, resulting in the inhibition of tumor cell invasion and angiogenesis. Our data showed that down-regulation of PDGF-D leads to the inactivation of Notch-1 and NF-kappaB DNA-binding activity and, in turn, down regulates the expression of its target genes, such as VEGF and MMP-9. We also found that the down-regulation of PDGF-D by small interfering RNA (siRNA) decreased tumor cell invasion, whereas PDGF-D overexpression by cDNA transfection led to increased cell invasion. Consistent with these results, we also found that the down-regulation of PDGF-D not only decreased MMP-9 mRNA and its protein expression but also inhibited the processing of pro-MMP-9 protein to its active form. Moreover, conditioned medium from PDGF-D siRNA-transfected cells showed reduced levels of VEGF and, in turn, inhibited the tube formation of human umbilical vascular endothelial cells, suggesting that down-regulation of PDGF-D leads to the inhibition of angiogenesis. Taken together, we conclude that the down-regulation of PDGF-D by novel approaches could lead to the down-regulation of Notch-1 and, in turn, inactivate NF-kappaB and its target genes (i.e., MMP-9 and VEGF), resulting in the inhibition of invasion and angiogenesis.

Cell-cell signaling through NOTCH regulates human embryonic stem cell proliferation

Unlike pluripotent mouse embryonic stem (ES) cells, human ES cells and their malignant equivalents, embryonal carcinoma (EC) cells, require close cell-cell contact for efficient growth. Signaling through the NOTCH receptor, initiated by interaction with ligands of the DELTA/JAGGED family expressed on neighboring cells, plays a role in regulating the self-renewal of several stem cell systems. Members of the NOTCH and DELTA/JAGGED families are expressed by human EC and ES cells, and we have therefore investigated the possible role of NOTCH in the maintenance of these cells. Cleavage of both NOTCH1 and NOTCH2 to yield the intracellular domain responsible for the canonical signaling pathway of NOTCH was detected in several human EC and ES cell lines, suggesting that NOTCH signaling is active. Furthermore, the proliferation of human EC cells, as well as the expression of several downstream NOTCH target genes, was markedly reduced after small interfering RNA knockdown of NOTCH1, NOTCH2, and the canonical effector CBF-1 or after blocking NOTCH signaling with the gamma-secretase inhibitor L-685,458. The inhibitor also caused a reduction in the growth of human ES cells, although without evidence of differentiation. The results indicate that cell-cell signaling through the NOTCH system provides a critical cue for the proliferation of human EC and ES cell in vitro.

Curcumin, both histone deacetylase and p300/CBP-specific inhibitor, represses the activity of nuclear factor kappa B and Notch 1 in Raji cells

Curcumin, the active chemical of the Asian spice turmeric, exhibits anticancer activity in several human cancer cell lines. We previously have proved that curcumin was a new member of the histone deacetylases (HDAC) inhibitors, while constitutive nuclear factor kappa B (NF-kappaB) is believed to be a crucial event for enhanced proliferation and survival of malignant cells. Here, we investigate the effect of curcumin on the activation of NF-kappaB signal molecule in Raji cells to explore its relationship with HDACs or p300/CREB binding protein (CBP). Curcumin presented striking proliferation inhibition potency on Raji cells in vitro, with the IC(50) value for 24 hr being 25 micromol/l. Significant decreases in the amounts of p300, HDAC1 and HDAC3 were detected after treatment with curcumin. These suppressing effects were more pronounced when the administered dose increased. The protection degradation of HDAC1 and p300 by MG-132 could be partially reversed by curcumin. Furthermore, curcumin could also prevent degradation of I kappaB alpha and inhibit nuclear translocation of the NF-kappaB/p65 subunit, as well as expression of Notch 1, induced by tumour necrosis factor-alpha. The results suggest that the depressive effect of curcumin on NF-kappaB signal transduction pathway may be mediated via the various components of the HDACs and p300/Notch 1 signal molecules, and may represent a new remedy for acute leukaemia.

Presenilins regulate alphabeta T cell development by modulating TCR signaling

TCRαβ signaling is crucial for the maturation of CD4 and CD8 T cells, but the role of the Notch signaling pathway in this process is poorly understood. Genes encoding Presenilin (PS) 1/2 were deleted to prevent activation of the multiple Notch receptors expressed by developing thymocytes. PS1/2 knockout thymocyte precursors inefficiently generate CD4 T cells, a phenotype that is most pronounced when thymocytes bear a single major histocompatibility complex (MHC) class II–restricted T cell receptor (TCR). Diminished T cell production correlated with evidence of impaired TCR signaling, and could be rescued by manipulations that enhance MHC recognition. Although Notch appears to directly regulate binary fate decisions in many systems, these findings suggest a model in which PS-dependent Notch signaling influences positive selection and the development of αβ T cells by modifying TCR signal transduction.

The SCFFBW7 ubiquitin ligase complex as a tumor suppressor in T cell leukemia

Recent studies have shown that activating mutations of NOTCH1 are responsible for the majority of T cell acute lymphoblastic leukemia (T-ALL) cases. Most of these mutations truncate its C-terminal domain, a region that is important for the NOTCH1 proteasome-mediated degradation. We report that the E3 ligase FBW7 targets NOTCH1 for ubiquitination and degradation. Our studies map in detail the amino acid degron sequence required for NOTCH1–FBW7 interaction. Furthermore, we identify inactivating FBW7 mutations in a large fraction of human T-ALL lines and primary leukemias. These mutations abrogate the binding of FBW7 not only to NOTCH1 but also to the two other characterized targets, c-Myc and cyclin E. The majority of the FBW7 mutations were present during relapse, and they were associated with NOTCH1 HD mutations. Interestingly, most of the T-ALL lines harboring FBW7 mutations were resistant to γ-secretase inhibitor treatment and this resistance appeared to be related to the stabilization of the c-Myc protein. Our data suggest that FBW7 is a novel tumor suppressor in T cell leukemia, and implicate the loss of FBW7 function as a potential mechanism of drug resistance in T-ALL.

Direct regulation of Gata3 expression determines the T helper differentiation potential of Notch

CD4(+) T helper cells differentiate into T helper 1 (Th1) or Th2 effector lineages, which orchestrate immunity to different types of microbes. Both Th1 and Th2 differentiation can be induced by Notch, but what dictates which of these programs is activated in response to Notch is not known. By using T cell-specific gene ablation of the Notch effector RBP-J or the Notch1 and 2 receptors, we showed here that Notch was required on CD4(+) T cells for physiological Th2 responses to parasite antigens. GATA-3 was necessary for Notch-induced Th2 differentiation, and we identified an upstream Gata3 promoter as a direct target for Notch signaling. Moreover, absence of GATA-3 turned Notch from a Th2 inducer into a powerful inducer of Th1 differentiation. Therefore, Gata3 is a critical element determining inductive Th2 differentiation and limiting Th1 differentiation by Notch.

Notch inhibition in Kaposi's sarcoma tumor cells leads to mitotic catastrophe through nuclear factor-κB signaling

Kaposi's sarcoma (KS) is the most common neoplasm in untreated AIDS patients and accounts for significant morbidity and mortality worldwide. We have recently reported that Notch signaling (which plays an important role in cell proliferation, apoptosis, and oncogenesis) is constitutively activated in KS tumor cells. Blockade of this activity using γ-secretase inhibitors resulted in apoptosis of SLK cells, a KS tumor cell line; however, this apoptosis was preceded by a prolonged G2-M cell cycle arrest. This result led us to hypothesize that the cells were undergoing mitotic catastrophe, an abnormal mitosis that leads to eventual cell death. Here, we show that Notch inhibition in KS tumor cells using γ-secretase inhibitors or Notch-1 small interfering RNA resulted in G2-M cell cycle arrest and mitotic catastrophe characterized by the presence of micronucleated cells and an increased mitotic index. Interestingly, Notch inhibition led to a sustained increase in nuclear cyclin B1, a novel observation suggesting that Notch signaling can modulate expression of this critical cell cycle protein. Further analysis showed the induction of cyclin B1 was due, at least in part, to increased nuclear factor-κB (NF-κB) activity, which was also required for the G2-M growth arrest after Notch inhibition. Taken together, these studies suggest that Notch inhibition can initiate aberrant mitosis by inducing NF-κB activity that inappropriately increases cyclin B1 resulting in cell death via mitotic catastrophe. [Mol Cancer Ther 2007;6(7):1983–92]

Regulation of functional phenotypes of cord blood derived eosinophils by gamma-secretase inhibitor

Eosinophils develop from stem cells in the bone marrow under the influence of hematopoietic cytokines, particularly IL-5. Previously, we have demonstrated that blockage of Notch signaling by a gamma-secretase inhibitor (GSI) promotes the differentiation of umbilical cord blood (UCB)-derived eosinophils. These highly major basic protein (MBP)-positive eosinophils cultured in the presence of the inhibitor lack the migratory response to eotaxin, although their CCR3 levels are similar to those of eosinophils cultured without the inhibitor. We investigated the mechanism underlying the differential responses of differentiating eosinophils and their functionalities in response to eosinophil-active cytokines in the presence and absence of GSI. UCB cells cultured for 4 weeks with hematopoietic cytokines in the presence or absence of GSI were monitored for extracellular signal-regulated kinase (ERK) phosphorylation, MBP expression, and functionality. Eosinophil differentiation from UCB cells was accompanied by activation of the ERK1/2 pathway during the 4-week culture period. In particular, strong ERK1/2 phosphorylation was observed in eosinophils during the final stage of culture when GSI was present. Consistent with this finding, ERK inhibition nullified the effect of GSI on eosinophil differentiation. Eosinophils cultured with GSI resembled airway eosinophils rather than peripheral blood eosinophils based on reduced IL-5Ralpha expression, blunted eosinophil cationic protein (ECP) degranulation, and decreased IL-13 and granulocyte macrophage-colony-stimulating factor production. These results suggest that Notch signaling regulates the terminal differentiation and subsequent effector phenotypes of eosinophils, partly through modulation of the ERK pathway. GSI has therapeutic potential for eosinophilic inflammatory diseases, such as asthma.

Notch1 is a p53 target gene involved in human keratinocyte tumor suppression through negative regulation of ROCK1/2 and MRCKalpha kinases

Little is known about the regulation and function of the Notch1 gene in negative control of human tumors. Here we show that Notch1 gene expression and activity are substantially down-modulated in keratinocyte cancer cell lines and tumors, with expression of this gene being under p53 control in these cells. Genetic suppression of Notch signaling in primary human keratinocytes is sufficient, together with activated ras, to cause aggressive squamous cell carcinoma formation. Similar tumor-promoting effects are also caused by in vivo treatment of mice, grafted with keratinocytes expressing oncogenic ras alone, with a pharmacological inhibitor of endogenous Notch signaling. These effects are linked with a lesser commitment of keratinocytes to differentiation, an expansion of stem cell populations, and a mechanism involving up-regulation of ROCK1/2 and MRCKalpha kinases, two key effectors of small Rho GTPases previously implicated in neoplastic progression. Thus, the Notch1 gene is a p53 target with a role in human tumor suppression through negative regulation of Rho effectors.

Notch1 induces cell cycle arrest and apoptosis in human cervical cancer cells: involvement of nuclear factor kappa B inhibition

Notch signaling can serve as a tumor suppressor or tumor promoter in the same kind of cancer, such as human papillomavirus-positive cervical cancer cells. However, the exact mechanisms remain poorly characterized. Our studies demonstrated that constitutively overexpressed active Notch1 via stable transfection with exogenous intracellular domain of Notch1 (ICN) resulted in growth inhibition of the human cervical cancer cell line HeLa by inducing G(2)-M arrest and apoptosis. Moreover, the growth inhibition was correlated with inhibition of nuclear factor kappa B (NF-kappaB) p50 activation, accompanied by a decrease in the nuclear expression of NF-kappaB p50 and an increase in the cytosolic expression of IkappaBalpha. Consistent with these results, downregulation of cyclin D1 and Bcl-2, which are both the downstream genes of NF-kappaB, were observed in ICN-overexpressed cells. Overall, our results suggest that NF-kappaB inhibition may contribute partially to cell cycle arrest and apoptosis induced by Notch1 activation in human cervical cancer cells.

Notch inhibits apoptosis by direct interference with XIAP ubiquitination and degradation

The physiological activity of Notch is a function of its ability to increase survival in many cell types. Several pathways have been shown to contribute to the survival effect of Notch, but the exact mechanism of Notch action is not completely understood. Here we identified that the regulation of cell survival by Notch intracellular domain could partly be attributed to a selective increase of X-linked inhibitor of apoptosis protein (XIAP). We further found that Notch intracellular domain inhibited the degradation of XIAP during apoptosis. The transactivation domain of Notch interacted directly with the RING region of XIAP to block the binding of E2 and prevent the in vivo and in vitro ubiquitination of XIAP. This antiapoptotic activity of Notch was abolished when XIAP was knocked down. Our results reveal a novel mechanism for Notch-selective suppression of apoptosis through an increase in the stability of a key antiapoptotic protein, XIAP.

Kaposi's sarcoma-associated herpesvirus induces sustained NF-kappaB activation during de novo infection of primary human dermal microvascular endothelial cells that is essential for viral gene expression

In vitro Kaposi's sarcoma-associated herpesvirus (KSHV) infection of primary human dermal microvascular endothelial (HMVEC-d) cells and human foreskin fibroblast (HFF) cells is characterized by the induction of preexisting host signal cascades, sustained expression of latency-associated genes, transient expression of a limited number of lytic genes, and induction of several cytokines, growth factors, and angiogenic factors. Since NF-kappaB is a key molecule involved in the regulation of several of these factors, here, we examined NF-kappaB induction during de novo infection of HMVEC-d and HFF cells. Activation of NF-kappaB was observed as early as 5 to 15 min postinfection by KSHV, and translocation of p65-NF-kappaB into nuclei was detected by immunofluorescence assay, electrophoretic mobility shift assay, and p65 enzyme-linked immunosorbent assay. IkappaB phosphorylation inhibitor (Bay11-7082) reduced this activation significantly. A sustained moderate level of NF-kappaB induction was seen during the observed 72 h of in vitro KSHV latency. In contrast, high levels of ERK1/2 activation at earlier time points and a moderate level of activation at later times were observed. p38 mitogen-activated protein kinase was activated only at later time points, and AKT was activated in a cyclic manner. Studies with UV-inactivated KSHV suggested a role for virus entry stages in NF-kappaB induction and a requirement for KSHV viral gene expression in sustained induction. Inhibition of NF-kappaB did not affect target cell entry by KSHV but significantly reduced the expression of viral latent open reading frame 73 and lytic genes. KSHV infection induced the activation of several host transcription factors, including AP-1 family members, as well as several cytokines, growth factors, and angiogenic factors, which were significantly affected by NF-kappaB inhibition. These results suggest that during de novo infection, KSHV induces sustained levels of NF-kappaB to regulate viral and host cell genes and thus possibly regulates the establishment of latent infection.

Coexpression of Notch1 and NF-κB signaling pathway components in human cervical cancer progression

OBJECTIVES

Features of deregulated Notch1 signaling and NF-kappaB activation have independently been reported in cervical cancers. Here, we have extended these observations and examined both these pathways simultaneously in human cervical cancer tissue. Further, we have investigated the potential cross-talk between these pathways in a human cervical cancer derived cell line CaSki, which mirrors features of Notch activation as in the majority of human cervical cancers.

METHODS

Cervical tissue samples were analyzed for the expression of Notch1, Jagged 1, Hes1, pAKT, NF-kappaB p50, NF-kappaB p65, IkappaB-alpha, Bcl-2, CyclinD1, Cdk9, c-Fos, and p53 by immunohistochemistry. A total of 352 samples were analyzed which included 69 normal cervical tissue, 132 preinvasive lesions and 151 squamous cell carcinomas of the uterine cervix. Dual immunofluorescent analysis was performed to evaluate the coexpression of Notch1 and NF-kappaB. Transcriptional reporter assays and xenografts were undertaken with CaSki cells.

RESULTS

Features of Notch1 activation as measured by intracellular Notch1, high levels of Jagged1, Hes1 and Cdk9 were paralleled by nuclear translocation of both NF-kappaB p50 and p65 with target gene expression (IkappaB-alpha, Bcl-2, and CyclinD1) in human cervical cancer sections. Reporter assays in CaSki cells are consistent with Notch being an upstream regulator of NF-kappaB. Further, the xenografts recreate key aspects of human cancer tissue.

CONCLUSIONS

Results from this study suggest that there is a co-activation of Notch1 and NF-kappaB signaling pathways at the cellular level in the majority of human cervical cancers, with Notch as an upstream regulator.

Targeting the NF-kappaB signaling pathway in Notch1-induced T-cell leukemia

T-cell acute lymphoblastic leukemia (T-ALL), unlike other ALL types, is only infrequently associated with chromosomal aberrations, but it was recently shown that most individuals with T-ALL carry activating mutations in the NOTCH1 gene. However, the signaling pathways and target genes responsible for Notch1-induced neoplastic transformation remain undefined. We report here that constitutively active Notch1 activates the NF-kappaB pathway transcriptionally and via the IkappaB kinase (IKK) complex, thereby causing increased expression of several well characterized target genes of NF-kappaB in bone marrow hematopoietic stem cells and progenitors. Our observations demonstrate that the NF-kappaB pathway is highly active in established human T-ALL and that inhibition of the pathway can efficiently restrict tumor growth both in vitro and in vivo. These findings identify NF-kappaB as one of the major mediators of Notch1-induced transformation and suggest that the NF-kappaB pathway is a potential target of future therapies of T-ALL.

Notch signalling during peripheral T-cell activation and differentiation

For many years, researchers have focused on the contribution of Notch signalling to lymphoid development. Only recently have investigators begun to ask what role, if any, Notch has during the activation and differentiation of naive CD4(+) T cells in the periphery. As interest in this issue grows, it is becoming increasingly clear that the main role of Notch signalling, to regulate cell-fate decisions, might also be influential in peripheral T cells.

Current insights into the regulation of programmed cell death by NF-kappaB

The nuclear factor-kappaB (NF-kappaB) transcription factors have emerged as major regulators of programmed cell death (PCD) whether via apoptosis or necrosis. In this context, NF-kappaB's activity has important ramifications for normal tissue development, homoeostasis and the physiological functions of various cell systems including the immune, hepatic, epidermal and nervous systems. However, improper regulation of PCD by NF-kappaB can have severe pathologic consequences, ranging from neurodegeneration to cancer, where its activity often precludes effective therapy. Although NF-kappaB generally protects cells by inducing the expression genes encoding antiapoptotic and antioxidizing proteins, its role in apoptosis and necrosis can vary markedly in different cell contexts, and NF-kappaB can sensitize cells to death-inducing stimuli in some instances. This article describes our current knowledge of the role of NF-kappaB in apoptosis and necrosis, and focuses on the many advances since we last reviewed this rapidly evolving topic in Oncogene 3 years ago. There has been substantial progress in understanding NF-kappaB's mode of action in apoptosis and necrosis and the mechanisms that regulate its anti- vs proapoptotic activities. These recent developments shed new light on the role of NF-kappaB in many disease conditions including tumor development, tumor progression and anticancer treatment.

Quantitative dissection of the Notch:CSL interaction: insights into the Notch-mediated transcriptional switch

Complex formation between the intracellular domain of the Notch receptor (NICD) and the transcription factor CSL is indispensable for transcriptional activation. To understand how NICD displaces CSL-associated co-repressors, we have quantified the binding of different Notch1 ICD regions to a key interaction domain (the beta trefoil domain, or BTD) of human CSL. Electrophoresis, scattering, and titration calorimetry indicate that NICD and BTD combine to form a 1:1 heterodimer. Neither the Notch1 ankyrin domain (ANK) nor C-terminal region contributes binding energy towards BTD. In contrast, binding energy is attributed largely to a short segment including the conserved WFP sequence motif within the RAM region (the approximately 140 residue polypeptide segment N-terminal to the ANK domain); substitution of this motif substantially reduces affinity. Short (< or =25 residues) WFP-containing peptides encoded by the four mammalian Notch genes have similar affinities to BTD; thus, activity differences between paralogues either result from other regions of NICD and CSL or from differences in interaction with downstream components. The importance of RAM was demonstrated by the ability of a short RAM peptides to dissociate NICD:CSL interaction in cellular lysates. These results support an emerging molecular mechanism for the displacement of co-repressors from DNA-bound CSL by NICD.

Keeping up NF-κB appearances: Epigenetic control of immunity or inflammation-triggered epigenetics

Controlled expression of cytokine genes is an essential component of an immune response and is crucial for homeostasis. In order to generate an appropriate response to an infectious condition, the type of cytokine, as well as the cell type, dose range and the kinetics of its expression are of critical importance. The nuclear factor-kappaB (NF-kappaB) family of transcription factors has a crucial role in rapid responses to stress and pathogens (innate immunity), as well as in development and differentiation of immune cells (acquired immunity). Although quite a number of genes contain NF-kappaB-responsive elements in their regulatory regions, their expression pattern can significantly vary from both a kinetic and quantitative point of view, reflecting the impact of environmental and differentiative cues. At the transcription level, selectivity is conferred by the expression of specific NF-kappaB subunits and their respective posttranslational modifications, and by combinatorial interactions between NF-kappaB and other transcription factors and coactivators, that form specific enhanceosome complexes in association with particular promoters. These enhanceosome complexes represent another level of signaling integration, whereby the activities of multiple upstream pathways converge to impress a distinct pattern of gene expression upon the NF-kappaB-dependent transcriptional network. Today, several pieces of evidence suggest that the chromatin structure and epigenetic settings are the ultimate integration sites of both environmental and differentiative inputs, determining proper expression of each NF-kappaB-dependent gene. We will therefore discuss in this review the multilayered interplay of NF-kappaB signaling and epigenome dynamics, in achieving appropriate gene expression responses and transcriptional activity.

Higher expression of transcription targets and components of the nuclear factor-kappaB pathway is a distinctive feature of umbilical cord blood CD34+ precursors

Delayed engraftment, better reconstitution of progenitors, higher thymic function, and a lower incidence of the graft-versus-host disease are characteristics associated with umbilical cord blood (UCB) transplants, compared with bone marrow (BM). To understand the molecular mechanisms causing these intrinsic differences, we analyzed the differentially expressed genes between BM and UCB hematopoietic stem and progenitor cells (HSPCs). The expressions of approximately 10,000 genes were compared by serial analysis of gene expression of magnetically sorted CD34(+) cells from BM and UCB. Differential expression of selected genes was evaluated by real-time polymerase chain reaction on additional CD34(+) samples from BM (n = 22), UCB (n = 9), and granulocyte colony stimulating factor-mobilized peripheral blood (n = 6). The overrepresentation of nuclear factor-kappaB (NF-kappaB) pathway components and targets was found to be a major characteristic of UCB HSPCs. Additional promoter analysis of 41 UCB-overrepresented genes revealed a significantly higher number of NF-kappaB cis-regulatory elements (present in 22 genes) than would be expected by chance. Our results point to an important role of the NF-kappaB pathway on the molecular and functional differences observed between BM and UCB HSPCs. Our study forms the basis for future studies and potentially for new strategies to stem cell graft manipulation, by specific NF-kappaB pathway modulation on stem cells, prior to transplant.

Cross-regulation between Notch and p63 in keratinocyte commitment to differentiation

Notch signaling promotes commitment of keratinocytes to differentiation and suppresses tumorigenesis. p63, a p53 family member, has been implicated in establishment of the keratinocyte cell fate and/or maintenance of epithelial self-renewal. Here we show that p63 expression is suppressed by Notch1 activation in both mouse and human keratinocytes through a mechanism independent of cell cycle withdrawal and requiring down-modulation of selected interferon-responsive genes, including IRF7 and/or IRF3. In turn, elevated p63 expression counteracts the ability of Notch1 to restrict growth and promote differentiation. p63 functions as a selective modulator of Notch1-dependent transcription and function, with the Hes-1 gene as one of its direct negative targets. Thus, a complex cross-talk between Notch and p63 is involved in the balance between keratinocyte self-renewal and differentiation.

Down-regulation of notch-1 inhibits invasion by inactivation of nuclear factor-kappaB, vascular endothelial growth factor, and matrix metalloproteinase-9 in pancreatic cancer cells

Notch signaling plays a critical role in the pathogenesis and progression of human malignancies but the precise role and mechanism of Notch-1 for tumor invasion remains unclear. In our earlier report, we showed that down-regulation of Notch-1 reduced nuclear factor-kappaB (NF-kappaB) DNA-binding activity and matrix metalloproteinase-9 (MMP-9) expression. Because NF-kappaB, VEGF, and MMPs are critically involved in the processes of tumor cell invasion and metastasis, we investigated the role and mechanism(s) by which Notch-1 down-regulation (using molecular approaches) may lead to the down-regulation of NF-kappaB, vascular endothelial growth factor (VEGF), and MMP-9, thereby inhibiting invasion of pancreatic cancer cells through Matrigel. We found that the down-regulation of Notch-1 by small interfering RNA decreased cell invasion, whereas Notch-1 overexpression by cDNA transfection led to increased tumor cell invasion. Consistent with these results, we found that the down-regulation of Notch-1 reduced NF-kappaB DNA-binding activity and VEGF expression. Down-regulation of Notch-1 also decreased not only MMP-9 mRNA and its protein expression but also inactivated the pro-MMP-9 protein to its active form. Taken together, we conclude that the down-regulation of Notch-1 could be an effective approach for the down-regulation and inactivation of NF-kappaB and its target genes, such as MMP-9 and VEGF expression, resulting in the inhibition of invasion and metastasis.