Notch signaling: the core pathway and its posttranslational regulation

Treatment of allergic asthma: modulation of Th2 cells and their responses

Atopic asthma is a chronic inflammatory pulmonary disease characterised by recurrent episodes of wheezy, laboured breathing with an underlying Th2 cell-mediated inflammatory response in the airways. It is currently treated and, more or less, controlled depending on severity, with bronchodilators e.g. long-acting beta agonists and long-acting muscarinic antagonists or anti-inflammatory drugs such as corticosteroids (inhaled or oral), leukotriene modifiers, theophyline and anti-IgE therapy. Unfortunately, none of these treatments are curative and some asthmatic patients do not respond to intense anti-inflammatory therapies. Additionally, the use of long-term oral steroids has many undesired side effects. For this reason, novel and more effective drugs are needed. In this review, we focus on the CD4+ Th2 cells and their products as targets for the development of new drugs to add to the current armamentarium as adjuncts or as potential stand-alone treatments for allergic asthma. We argue that in early disease, the reduction or elimination of allergen-specific Th2 cells will reduce the consequences of repeated allergic inflammatory responses such as lung remodelling without causing generalised immunosuppression.

Notch in the kidney: development and disease

Notch signalling is a highly conserved cell-cell communication mechanism that regulates development, tissue homeostasis, and repair. Within the kidney, Notch has an important function in orchestrating kidney development. Recent studies indicate that Notch plays a key role in establishing proximal epithelial fate during nephron segmentation as well as the differentiation of principal cells in the renal collecting system. Notch signalling is markedly reduced in the adult kidney; however, increased Notch signalling has been noted in both acute and chronic kidney injury. Increased glomerular epithelial Notch signalling has been associated with albuminuria and glomerulosclerosis, while tubular epithelial Notch activation caused fibrosis development most likely inducing an improper epithelial repair pathway. Recent studies thereby indicate that Notch is a key regulator of kidney development, repair, and injury.

Ngn3(+) endocrine progenitor cells control the fate and morphogenesis of pancreatic ductal epithelium

During pancreas development, endocrine and exocrine cells arise from a common multipotent progenitor pool. How these cell fate decisions are coordinated with tissue morphogenesis is poorly understood. Here we have examined ductal morphology, endocrine progenitor cell fate and Notch signaling in Ngn3(-/-) mice, which do not produce islet cells. Ngn3 deficiency results in reduced branching and enlarged pancreatic duct-like structures, concomitant with Ngn3 promoter activation throughout the ductal epithelium and reduced Notch signaling. Conversely, forced generation of surplus endocrine progenitor cells causes reduced duct caliber and an excessive number of tip cells. Thus, endocrine progenitor cells normally provide a feedback signal to adjacent multipotent ductal progenitor cells that activates Notch signaling, inhibits further endocrine differentiation and promotes proper morphogenesis. These results uncover a novel layer of regulation coordinating pancreas morphogenesis and endocrine/exocrine differentiation, and suggest ways to enhance the yield of beta cells from stem cells.

Notch signaling and Notch signaling modifiers

Originally discovered nearly a century ago, the Notch signaling pathway is critical for virtually all developmental programs and modulates an astounding variety of pathogenic processes. The DSL (Delta, Serrate, LAG-2 family) proteins have long been considered canonical activators of the core Notch pathway. More recently, a wide and expanding network of non-canonical extracellular factors has also been shown to modulate Notch signaling, conferring newly appreciated complexity to this evolutionarily conserved signal transduction system. Here, I review current concepts in Notch signaling, with a focus on work from the last decade elucidating novel extracellular proteins that up- or down-regulate signal potency.

Influence of stochastic gene expression on the cell survival rheostat after traumatic brain injury

Experimental evidence suggests that random, spontaneous (stochastic) fluctuations in gene expression have important biological consequences, including determination of cell fate and phenotypic variation within isogenic populations. We propose that fluctuations in gene expression represent a valuable tool to explore therapeutic strategies for patients who have suffered traumatic brain injury (TBI), for which there is no effective drug therapy. We have studied the effects of TBI on the hippocampus because TBI survivors commonly suffer cognitive problems that are associated with hippocampal damage. In our previous studies we separated dying and surviving hippocampal neurons by laser capture microdissection and observed unexplainable variations in post-TBI gene expression, even though dying and surviving neurons were adjacent and morphologically identical. We hypothesized that, in hippocampal neurons that subsequently are subjected to TBI, randomly increased pre-TBI expression of genes that are associated with neuroprotection predisposes neurons to survival; conversely, randomly decreased expression of these genes predisposes neurons to death. Thus, to identify genes that are associated with endogenous neuroprotection, we performed a comparative, high-resolution transcriptome analysis of dying and surviving hippocampal neurons in rats subjected to TBI. We found that surviving hippocampal neurons express a distinct molecular signature — increased expression of networks of genes that are associated with regeneration, cellular reprogramming, development, and synaptic plasticity. In dying neurons we found decreased expression of genes in those networks. Based on these data, we propose a hypothetical model in which hippocampal neuronal survival is determined by a rheostat that adds injury-induced genomic signals to expression of pro-survival genes, which pre-TBI varies randomly and spontaneously from neuron to neuron. We suggest that pharmacotherapeutic strategies that co-activate multiple survival signals and enhance self-repair mechanisms have the potential to shift the cell survival rheostat to favor survival and therefore improve functional outcome after TBI.

Cellular and molecular effects of sirtuins in health and disease

Sirtuins are NAD+-dependent protein deacetylases that are broadly conserved from bacteria to humans. Because sirtuins extend the lifespan of yeast, worms and flies, much attention has been paid to their mammalian homologues. Recent studies have revealed diverse physiological functions of sirtuins that are essentially similar to those of their yeast homologue, Sir2 (silent information regulator 2). Sirtuins are implicated in the pathology of many diseases, for which sirtuin activators such as resveratrol have great promise as potential treatments. In the present review, we describe the functions of sirtuins in cell survival, inflammation, energy metabolism, cancer and differentiation, and their impact on diseases. We also discuss the organ-specific functions of sirtuins, focusing on the brain and blood vessels.

MRK003, a γ-secretase inhibitor exhibits promising in vitro pre-clinical activity in multiple myeloma and non-Hodgkin's lymphoma

Notch-stimulated signaling cascade results in transcriptional regulation of genes involved in cell fate decision, apoptosis and proliferation and has been implicated in various malignancies. Here, we investigated the impact of MRK003, an inhibitor of this pathway, on myeloma and lymphoma cells. We first studied the expression patterns of notch receptors and ligands on multiple myeloma (MM) and non-Hodgkin's lymphoma (NHL) cell lines. Next, we used a γ-secretase inhibitor, MRK003 to test the importance of notch-stimulated pathways in MM and NHL disease biology. We observed expression of notch receptors and ligands on MM and NHL cell lines. MRK003 treatment induced caspase-dependent apoptosis and inhibited proliferation of MM and NHL cell lines and patient cells. Examination of signaling events after treatment showed time-dependent decrease in levels of the notch intracellular domain, Hes1 and c-Myc. MRK003 downregulated cyclin D1, Bcl-Xl and Xiap levels in NHL cells and p21, Bcl-2 and Bcl-Xl in MM cells. In addition, MRK003 caused an upregulation of pAkt, indicating crosstalk with the PI3K/Akt pathway. We evaluated MRK003 in combination with Akt1/2 kinase inhibitor and observed synergy in killing MM and NHL cell lines examined.

Inhibition of Notch signaling prevents experimental fibrosis and induces regression of established fibrosis

OBJECTIVE

Tissue fibrosis caused by pathologic activation of fibroblasts with increased synthesis of extracellular matrix components is a major hallmark of systemic sclerosis (SSc). Notch signaling regulates tissue differentiation, and abnormal activation of Notch signaling has been implicated in the pathogenesis of various malignancies. The present study was undertaken to investigate the role of Notch signaling in SSc and to evaluate the therapeutic potential of Notch inhibition for the treatment of fibrosis.

METHODS

Activation of the Notch pathways was analyzed by staining for the Notch intracellular domain (NICD) and quantification of levels of HES-1 messenger RNA. In the mouse model of bleomycin-induced dermal fibrosis and in tight skin 1 mice, Notch signaling was inhibited by the γ-secretase inhibitor DAPT and by overexpression of a Notch-1 antisense construct.

RESULTS

Notch signaling was activated in SSc in vivo, with accumulation of the NICD and increased transcription of the target gene HES-1. Overexpression of a Notch antisense construct prevented bleomycin-induced fibrosis and hypodermal thickening in tight skin 1 mice. Potent antifibrotic effects were also obtained with DAPT treatment. In addition to prevention of fibrosis, targeting of Notch signaling resulted in almost complete regression of established experimental fibrosis.

CONCLUSION

The present results demonstrate that pharmacologic as well as genetic inhibition of Notch signaling exerts potent antifibrotic effects in different murine models of SSc. These findings might have direct translational implications because different inhibitors of the γ-secretase complex are available and have yielded promising results in cancer trials.

Inhibition of Notch signaling ameliorates insulin resistance in a FoxO1-dependent manner

Transcription factor FoxO1 promotes hepatic glucose production. Genetic inhibition of FoxO1 function prevents diabetes in experimental animal models, providing impetus to identify pharmacological approaches to modulate this function. Altered Notch signaling is evident in tumorigenesis, and Notch antagonists are in clinical testing for application in cancer. Here we report that FoxO1 and Notch coordinately regulate hepatic glucose metabolism. Combined haploinsufficiency of FoxO1 and Notch1 markedly raises insulin sensitivity in diet-induced insulin resistance, as does liver-specific knockout of the Notch transcriptional effector Rbp-Jκ. Conversely, Notch1 gain-of-function promotes insulin resistance in a FoxO1-dependent manner and induces glucose-6-phosphatase expression. Pharmacological blockade of Notch signaling with γ-secretase inhibitors raises insulin sensitivity after in vivo administration in lean mice and in obese, insulin-resistant mice. The data identify a heretofore unknown metabolic function of Notch and suggest that Notch inhibition is beneficial in diabetes treatment, in part by helping to offset excessive FoxO1-driven hepatic glucose production.

Notch signaling modulates MUC16 biosynthesis in an in vitro model of human corneal and conjunctival epithelial cell differentiation

PURPOSE

Notch proteins are a family of transmembrane receptors that coordinate binary cell fate decisions and differentiation in wet-surfaced epithelia. We sought to determine whether Notch signaling contributes to maintaining mucosal homeostasis by modulating the biosynthesis of cell surface-associated mucins in an in vitro model of human corneal (HCLE) and conjunctival (HCjE) epithelial cell differentiation.

METHODS

HCLE and HCjE cells were grown at different stages of differentiation, representing nondifferentiated (preconfluent and confluent) and differentiated (stratified) epithelial cultures. Notch signaling was blocked with the γ-secretase inhibitor dibenzazepine (DBZ). The presence of Notch intracellular domains (Notch1 to Notch3) and mucin protein (MUC1, -4, -16) was evaluated by electrophoresis and Western blot analysis. Mucin gene expression was determined by TaqMan real-time polymerase chain reaction.

RESULTS

Here we demonstrate that Notch3 is highly expressed in undifferentiated and differentiated HCLE and HCjE cells, and that Notch1 and Notch2 biosynthesis is enhanced by induction of differentiation with serum-containing media. Inhibition of Notch signaling with DBZ impaired MUC16 biosynthesis in a concentration-dependent manner in undifferentiated cells at both preconfluent and confluent stages, but not in postmitotic stratified cells. In contrast to protein levels, the amount of MUC16 transcripts were not significantly reduced after DBZ treatment, suggesting that Notch regulates MUC16 posttranscriptionally. Immunoblots of DBZ-treated epithelial cells grown at different stages of differentiation revealed no differences in the levels of MUC1 and MUC4.

CONCLUSIONS

These results indicate that MUC16 biosynthesis is posttranscriptionally regulated by Notch signaling at early stages of epithelial cell differentiation, and suggest that Notch activation contributes to maintaining a mucosal phenotype at the ocular surface.

Force-induced unfolding simulations of the human Notch1 negative regulatory region: possible roles of the heterodimerization domain in mechanosensing

Notch receptors are core components of the Notch signaling pathway and play a central role in cell fate decisions during development as well as tissue homeostasis. Upon ligand binding, Notch is sequentially cleaved at the S2 site by an ADAM protease and at the S3 site by the γ-secretase complex. Recent X-ray structures of the negative regulatory region (NRR) of the Notch receptor reveal an auto-inhibited fold where three protective Lin12/Notch repeats (LNR) of the NRR shield the S2 cleavage site housed in the heterodimerization (HD) domain. One of the models explaining how ligand binding drives the NRR conformation from a protease-resistant state to a protease-sensitive one invokes a mechanical force exerted on the NRR upon ligand endocytosis. Here, we combined physics-based atomistic simulations and topology-based coarse-grained modeling to investigate the intrinsic and force-induced folding and unfolding mechanisms of the human Notch1 NRR. The simulations support that external force applied to the termini of the NRR disengages the LNR modules from the heterodimerization (HD) domain in a well-defined, largely sequential manner. Importantly, the mechanical force can further drive local unfolding of the HD domain in a functionally relevant fashion that would provide full proteolytic access to the S2 site prior to heterodimer disassociation. We further analyzed local structural features, intrinsic folding free energy surfaces, and correlated motions of the HD domain. The results are consistent with a model in which the HD domain possesses inherent mechanosensing characteristics that could be utilized during Notch activation. This potential role of the HD domain in ligand-dependent Notch activation may have implications for understanding normal and aberrant Notch signaling.

Trp53 regulates Notch 4 signaling through Mdm2

Notch receptors and their ligands have crucial roles in development and tumorigenesis. We present evidence demonstrating the existence of an antagonistic relationship between Notch 4 and Trp53, which is controlled by the Mdm2-dependent ubiquitylation and degradation of the Notch receptor. We show that this signal-controlling mechanism is mediated by physical interactions between Mdm2 and Notch 4 and suggest the existence of a trimeric complex between Trp53, Notch 4 and Mdm2, which ultimately regulates Notch activity. Functional studies indicate that Trp53 can suppress NICD4-induced anchorage-independent growth in mammary epithelial cells and present evidence showing that Trp53 has a pivotal role in the suppression of Notch-associated tumorigenesis in the mammary gland.

Multiple O-glucosylation sites on Notch function as a buffer against temperature-dependent loss of signaling

Mutations in Drosophila rumi result in a temperature-sensitive loss of Notch signaling. Rumi is a protein O-glucosyltransferase that adds glucose to EGF repeats with a C-X-S-X-P-C consensus sequence. Eighteen of the 36 EGF repeats in the Drosophila Notch receptor contain the consensus O-glucosylation motif. However, the contribution of individual O-glucose residues on Notch to the regulation of Notch signaling is not known. To address this issue, we carried out a mutational analysis of these glucosylation sites and determined their effects on Notch activity in vivo. Our results indicate that even though no single O-glucose mutation causes a significant decrease in Notch activity, all of the glucose residues on Notch contribute in additive and/or redundant fashions to maintain robust signaling, especially at higher temperatures. O-glucose motifs in and around the ligand-binding EGF repeats play a more important role than those in other EGF repeats of Notch. However, a single O-glucose mutation in EGF12 can be compensated by other O-glucose residues in neighboring EGF repeats. Moreover, timecourse cell aggregation experiments using a rumi null cell line indicate that a complete lack of Rumi does not affect Notch-Delta binding at high temperature. In addition, rumi fully suppresses the gain-of-function phenotype of a ligand-independent mutant form of Notch. Our data suggest that, at physiological levels of Notch, the combined effects of multiple O-glucose residues on this receptor allow productive S2 cleavage at high temperatures and thereby serve as a buffer against temperature-dependent loss of Notch signaling.

Tarsal-less peptides control Notch signalling through the Shavenbaby transcription factor

The formation of signalling boundaries is one of the strategies employed by the Notch (N) pathway to give rise to two distinct signalling populations of cells. Unravelling the mechanisms involved in the regulation of these signalling boundaries is essential to understanding the role of N during development and diseases. The function of N in the segmentation of the Drosophila leg provides a good system to pursue these mechanisms at the molecular level. Transcriptional and post-transcriptional regulation of the N ligands, Serrate (Ser) and Delta (Dl) generates a signalling boundary that allows the directional activation of N in the distalmost part of the segment, the presumptive joint. A negative feedback loop between odd-skipped-related genes and the N pathway maintains this signalling boundary throughout development in the true joints. However, the mechanisms controlling N signalling boundaries in the tarsal joints are unknown. Here we show that the non-canonical tarsal-less (tal) gene (also known as pri), which encodes for four small related peptides, is expressed in the N-activated region and required for joint development in the tarsi during pupal development. This function of tal is both temporally and functionally separate from the tal-mediated tarsal intercalation during mid-third instar that we reported previously. In the pupal function described here, N signalling activates tal expression and reciprocally Tal peptides feedback on N by repressing the transcription of Dl in the tarsal joints. This Tal-induced repression of Dl is mediated by the post-transcriptional activation of the Shavenbaby transcription factor, in a similar manner as it has been recently described in the embryo. Thus, a negative feedback loop involving Tal regulates the formation and maintenance of a Dl+/Dl- boundary in the tarsal segments highlighting an ancient mechanism for the regulation of N signalling based on the action of small cell signalling peptides.

The single RBP-Jkappa site within the LANA promoter is crucial for establishing Kaposi's sarcoma-associated herpesvirus latency during primary infection

Kaposi's sarcoma-associated herpesvirus (KSHV; or human herpesvirus 8 [HHV8]) is implicated in the pathogenesis of many human malignancies including Kaposi's sarcoma (KS), multicentric Castleman's disease (MCD), and primary effusion lymphoma (PEL). KSHV infection displays two alternative life cycles, referred to as the latent and lytic or productive cycle. Previously, we have reported that the replication and transcription activator (RTA), a major lytic cycle transactivator, contributes to the development of KSHV latency by inducing latency-associated nuclear antigen (LANA) expression during early stages of infection by targeting RBP-Jκ, the master regulator of the Notch signaling pathway. Here, we generated a bacterial artificial chromosome (BAC) KSHV recombinant virus with a deletion of the RBP-Jκ site within the LANA promoter to evaluate the function of the RBP-Jκ cognate site in establishing primary latent infection. The results showed that genetic disruption of the RBP-Jκ binding site within the KSHV LANA promoter led to enhanced expression of the KSHV-encoded immediate early RTA, resulting in an increase in lytic replication during primary infection of human peripheral blood mononuclear cells (PBMCs). This system provides a powerful tool for use in indentifying additional cellular and viral molecules involved in LANA-mediated latency maintenance during the early stages of KSHV infection.

Notch signalling regulates fibroblast activation and collagen release in systemic sclerosis

BACKGROUND

Dermal fibroblasts from patients with systemic sclerosis (SSc) release excessive amounts of collagen resulting in tissue fibrosis. The molecular mechanisms underlying this pathological activation are incompletely understood.

OBJECTIVE

To investigate whether Notch signalling contributes to the uncontrolled activation of fibroblasts in SSc.

METHODS

Activation of the Notch pathway was assessed by immunohistochemistry or Western blot for the Notch intracellular domain and the Notch ligand Jagged-1 (Jag-1) and real-time PCR for the target gene hes-1. Differentiation of resting dermal fibroblasts into myofibroblasts was assessed by staining for α-smooth muscle actin. The synthesis of collagen was quantified by real-time PCR and Sircol assays.

RESULTS

Notch signalling was activated in lesional skin of patients with SSc. The activation persisted in cultured dermal SSc fibroblasts. Stimulation of healthy dermal fibroblasts with recombinant human Jag-1-Fc chimera resulted in an SSc-like phenotype with increased release of collagen and differentiation of resting fibroblasts into myofibroblasts. Consistent with the selective activation of the Notch pathway in dermal SSc fibroblasts, DAPT or siRNA against Notch strongly reduced the basal collagen expression in SSc fibroblasts, but not in fibroblasts from healthy volunteers.

CONCLUSION

It was shown that Notch signalling is activated in SSc and plays an important role in fibroblast activation and collagen release. Inhibition of Notch signalling might be an effective strategy to selectively prevent the aberrant activation of SSc fibroblasts.

UVRAG is required for organ rotation by regulating Notch endocytosis in Drosophila

Heterotaxy characterized by abnormal left-right body asymmetry causes diverse congenital anomalies. Organ rotation is a crucial developmental process to establish the left-right patterning during animal development. However, the molecular basis of how organ rotation is regulated is poorly understood. Here we report that Drosophila UV-resistance associated gene (UVRAG), a tumor suppressor that regulates autophagy and endocytosis, plays unexpected roles in controlling organ rotation. Loss-of-function mutants of UVRAG show seriously impaired organ rotation phenotypes, which are associated with defects in endocytic trafficking rather than autophagy. Blunted endocytic degradation by UVRAG deficiency causes endosomal accumulation of Notch, resulting in abnormally enhanced Notch activity. Knockdown of Notch itself or expression of a dominant negative form of Notch transcriptional co-activator Mastermind is sufficient to rescue the rotation defect in UVRAG mutants. Consistently, UVRAG-mutated heterotaxy patient cells also display highly increased Notch protein levels. These results suggest evolutionarily conserved roles of UVRAG in organ rotation by regulating Notch endocytic degradation.

Hierarchical phosphorylation within the ankyrin repeat domain defines a phosphoregulatory loop that regulates Notch transcriptional activity

The Notch signal transduction pathway mediates important cellular functions through direct cell-to-cell contact. Deregulation of Notch activity can lead to an altered cell proliferation and has been linked to many human cancers. Casein kinase 2 (CK2), a ubiquitous kinase, regulates several cellular processes by phosphorylating proteins involved in signal transduction, gene expression, and protein synthesis. In this report we identify Notch(ICD) as a novel target of phosphorylation by CK2. Using mapping and mutational studies, we identified serine 1901, located in the ankyrin domain of Notch, as the target amino acid. Interestingly, phosphorylation of serine 1901 by CK2 appears to generate a second phosphorylation site at threonine 1898. Furthermore, threonine 1898 phosphorylation only occurs when Notch forms a complex with Mastermind and CSL. Phosphorylation of both threonine 1898 and serine 1901 resulted in decreased binding of the Notch-Mastermind-CSL ternary complex to DNA and consequently lower transcriptional activity. These data indicate that the phosphorylation of serine 1901 and threonine 1898 negatively regulates Notch function by dissociating the complex from DNA. This study identifies a new component involved in regulation of Notch(ICD) transcriptional activity, reinforcing the notion that a precise and tight regulation is required for this essential signaling pathway.

Tumor Vessel Development and Expansion in Ewing's Sarcoma: A Review of the Vasculogenesis Process and Clinical Trials with Vascular-Targeting Agents

Ewing's sarcoma accounts for a disproportionately high portion of the overall pediatric mortality rate compared to its rare incidence in the pediatric population. Little progress has been made since the introduction of traditional chemotherapies, and understanding the biology of the tumor is critical for developing new therapies. Ewing's sarcomas rely on a functional vascular supply, which is formed by a combination of angiogenesis and vasculogenesis. Recent insights into the molecular regulation of bone marrow (BM) cell participation in vascular development have identified VEGF, SDF-1α, and DLL4 as critical players in the vasculogenesis process. Clinical trials using vascular targeting agents, specifically targeting VEGF or DLL4, are underway.

Dynamic expression of notch signaling genes in neural stem/progenitor cells

In neural stem/progenitor cells, expression of the Notch effector Hes1, a transcriptional repressor, oscillates with a period of 2–3 h by negative feedback, and Hes1 oscillations induce the oscillatory expression of the proneural gene Neurogenin2 (Ngn2) and the Notch ligand gene Delta-like1 (Dll1). Dll1 oscillation leads to the mutual activation of Notch signaling between neighboring cells, thereby maintaining a group of cells in the undifferentiated state. Not all cells express Hes1 in an oscillatory manner: cells in boundary regions such as the isthmus express Hes1 in a sustained manner, and these cells are rather dormant with regard to proliferation and differentiation. Thus, Hes1 allows cell proliferation and differentiation when its expression oscillates but induces dormancy when its expression is sustained. After Hes1 expression is repressed, Ngn2 is expressed in a sustained manner, promoting neuronal differentiation. Thus, Ngn2 leads to the maintenance of neural stem/progenitor cells by inducing Dll1 oscillation when its expression oscillates but to neuronal differentiation when its expression is sustained. These results indicate that the different dynamics of Hes1 and Ngn2 lead to different outcomes.

Minireview: the busy road to pheochromocytomas and paragangliomas has a new member, TMEM127

Characterization of the entire spectrum of cancer-associated genetic disruptions is an overarching goal of contemporary and future oncology and can inform on patient diagnosis, treatment, and surveillance. Hereditary endocrine tumors, by having the potential to reveal the cancer's primary molecular defect, have been especially informative in this realm. Within this group, pheochromocytomas and paragangliomas, neural crest-derived, catecholamine-secreting tumors have come to represent true conduits for gene discovery. About one-third of pheochromocytomas and paragangliomas are now known to result from germline mutations in one of at least eight genes that belong to a variety of functional classes. Greater understanding of the molecular signals transduced by these genes and their respective mutants has advanced our understanding of kinase signaling pathways, hypoxia regulation, and the link between metabolic disruptions and cell growth. A new susceptibility gene without homology to other functional classes has been recently identified and encodes for a three-spanner transmembrane protein, transmembrane protein 127 (TMEM127). Initial insights from in vitro and patient data suggest that this candidate tumor suppressor is linked to the endosomal system and the mechanistic target of rapamycin [formerly mammalian target of rapamycin (mTOR)] pathway, and that mutation carriers often have clinical features that are typically associated with sporadic forms of pheochromocytoma. Functional characterization of transmembrane protein 127 (TMEM127) and discovery of additional pheochromocytoma/paraganglioma susceptibility genes is likely to shed light on our understanding of these tumors and extend these insights to other cancers.

Ligation of Notch receptors in human conventional and plasmacytoid dendritic cells differentially regulates cytokine and chemokine secretion and modulates Th cell polarization

Notch signaling is involved in multiple cellular processes. Recent data also support the prominent role of Notch signaling in the regulation of the immune response. In this study, we analyzed the expression and function of Notch receptors and ligands on both human blood conventional dendritic cells (cDCs) and plasmacytoid DCs (pDCs). The expression and modulation upon TLR activation of Notch molecules partially differed between cDCs and pDCs, but functional involvement of the Notch pathway in both cell types was clearly revealed by specific inhibition using DAPT. Beyond the induction of Notch target genes and modulation of maturation markers, Notch pathway was also involved in a differential secretion of some specific cytokines/chemokines by DC subsets. Whereas Notch ligation induced IL-10 and CCL19 secretion in cDCs, Notch inhibition resulted in a diminished production of these proteins. With regard to pDCs, Notch activation induced TNF-α whereas Notch inhibition significantly abrogated the secretion of CCL19, CXCL9, CXCL10, and TNF-α. Additionally, Notch modulation of DC subsets differentially affected Th polarization of allostimulated T cells. Our results suggest that the Notch pathway may function as an additional mechanism controlling human DC responses, with differential activity on cDCs and pDCs. This control mechanism may ultimately contribute to define the local milieu promoted by these cells under the particular conditions of the immune response.

Mechanism and significance of cis-inhibition in Notch signalling

Notch receptors in a given cell are activated by cell surface ligands in neighbouring cells but can also be inhibited by the ligands present within the same cell. This process is known as cis-inhibition of Notch. Additionally, reciprocal cis-inhibition of the ligands by Notch has also been observed, albeit to a limited extent. Here, we review the mechanisms, functional relevance and potential implications of these cis-inhibitory interactions for Notch-mediated fate decisions.

p53 and Notch signaling in chronic lymphocytic leukemia: clues to identifying novel therapeutic strategies

The p53 tumor suppressor protein has a key role in the induction of apoptosis of chronic lymphocytic leukemia (CLL) cells. Abnormalities within the p53 pathway identify a subset of patients with a poor prognosis. This review describes recent advances in understanding the mechanisms that regulate p53 levels and the role of p53 in the control of the cell cycle and of apoptosis. The classical model of p53-mediated apoptosis emphasizes the transcriptional activation of proapoptotic genes. In contrast, a novel model emphasizes p53's non-transcriptional actions as the major route of apoptosis induction, whereas its transcriptional arm predominantly upregulates antiapoptotic genes, thus providing a negative feedback mechanism that limits apoptosis. Further studies have identified the Notch pathway as a candidate p53-induced antiapoptotic mechanism. In contrast to the classical model, the novel model predicts that pharmacological inhibition of p53's transcriptional function or of the Notch signaling pathway will augment apoptosis induction by cytotoxic agents. Therapeutic strategies based on the novel model, which we review here for the first time, may significantly augment the antitumor actions of cytotoxic agents in CLL and in other malignancies.

Notch in the vertebrate nervous system: an old dog with new tricks

The Notch pathway is prominent among those known to regulate neural development in vertebrates. Notch receptor activation can inhibit neurogenesis, maintain neural progenitor character, and in some contexts promote gliogenesis and drive binary fate choices. Recently, a wave of exciting studies has emerged, which has both solidified previously held assertions and expanded our understanding of Notch function during neurogenesis and in the adult brain. These studies have examined pathway regulators and interactions, as well as pathway dynamics, with respect to both gene expression and cell-cell signaling. Here, focusing primarily on vertebrates, we review the current literature on Notch signaling in the nervous system, and highlight numerous recent studies that have generated interesting and unexpected advances.

C. elegans Notch signaling regulates adult chemosensory response and larval molting quiescence

BACKGROUND

The conserved DOS-motif proteins OSM-7 and OSM-11 function as coligands with canonical DSL (Delta, Serrate, and LAG-2) ligands to activate C. elegans Notch receptors during development. We report here that Notch ligands, coligands, and the receptors LIN-12 and GLP-1 regulate two C. elegans behaviors: chemosensory avoidance of octanol and quiescence during molting lethargus.

RESULTS

C. elegans lacking osm-7 or osm-11 are defective in their response to octanol. We find that OSM-11 is secreted from hypodermal seam cells into the pseudocoelomic body cavity and acts non-cell autonomously as a diffusible factor. OSM-11 acts with the DSL ligand LAG-2 to activate LIN-12 and GLP-1 Notch receptors in the neurons of adult animals, thereby regulating octanol avoidance response. In adult animals, overexpression of osm-11 and consequent Notch receptor activation induces anachronistic sleep-like quiescence. Perturbation of Notch signaling alters basal activity in adults as well as arousal thresholds and quiescence during molting lethargus. Genetic epistasis studies reveal that Notch signaling regulates quiescence via previously identified circuits and genetic pathways including the egl-4 cGMP-dependent kinase.

CONCLUSIONS

Our findings indicate that the conserved Notch pathway modulates behavior in adult C. elegans in response to environmental stress. Additionally, Notch signaling regulates sleep-like quiescence in C. elegans, suggesting that Notch may regulate sleep in other species.

Notch signalling in solid tumours: a little bit of everything but not all the time

The discovery of Notch in Drosophila melanogaster nearly a century ago opened the door to an ever-widening understanding of cellular processes that are controlled or influenced by Notch signalling. As would be expected with such a pleiotropic pathway, the deregulation of Notch signalling leads to several pathological conditions, including cancer. A role for Notch is well established in haematological malignancies, and more recent studies have provided evidence for the importance of Notch activity in solid tumours. As it is thought to act as an oncogene in some cancers but as a tumour suppressor in others, the role of Notch in solid tumours seems to be highly context dependent.

Regulation of somatic myosin activity by protein phosphatase 1β controls Drosophila oocyte polarization

The Drosophila body axes are established in the oocyte during oogenesis. Oocyte polarization is initiated by Gurken, which signals from the germline through the epidermal growth factor receptor (Egfr) to the posterior follicle cells (PFCs). In response the PFCs generate an unidentified polarizing signal that regulates oocyte polarity. We have identified a loss-of-function mutation of flapwing, which encodes the catalytic subunit of protein phosphatase 1β (PP1β) that disrupts oocyte polarization. We show that PP1β, by regulating myosin activity, controls the generation of the polarizing signal. Excessive myosin activity in the PFCs causes oocyte mispolarization and defective Notch signaling and endocytosis in the PFCs. The integrated activation of JAK/STAT and Egfr signaling results in the sensitivity of PFCs to defective Notch. Interestingly, our results also demonstrate a role of PP1β in generating the polarizing signal independently of Notch, indicating a direct involvement of somatic myosin activity in axis formation.

Regulation of mammalian Notch signaling and embryonic development by the protein O-glucosyltransferase Rumi

Protein O-glucosylation is a conserved post-translational modification that occurs on epidermal growth factor-like (EGF) repeats harboring the C(1)-X-S-X-P-C(2) consensus sequence. The Drosophila protein O-glucosyltransferase (Poglut) Rumi regulates Notch signaling, but the contribution of protein O-glucosylation to mammalian Notch signaling and embryonic development is not known. Here, we show that mouse Rumi encodes a Poglut, and that Rumi(-/-) mouse embryos die before embryonic day 9.5 with posterior axis truncation and severe defects in neural tube development, somitogenesis, cardiogenesis and vascular remodeling. Rumi knockdown in mouse cell lines results in cellular and molecular phenotypes of loss of Notch signaling without affecting Notch ligand binding. Biochemical, cell culture and cross-species transgenic experiments indicate that a decrease in Rumi levels results in reduced O-glucosylation of Notch EGF repeats, and that the enzymatic activity of Rumi is key to its regulatory role in the Notch pathway. Genetic interaction studies show that removing one copy of Rumi in a Jag1(+/-) (jagged 1) background results in severe bile duct morphogenesis defects. Altogether, our data indicate that addition of O-glucose to EGF repeats is essential for mouse embryonic development and Notch signaling, and that Jag1-induced signaling is sensitive to the gene dosage of the protein O-glucosyltransferase Rumi. Given that Rumi(-/-) embryos show more severe phenotypes compared to those displayed by other global regulators of canonical Notch signaling, Rumi is likely to have additional important targets during mammalian development.

ETOILE regulates developmental patterning in the filamentous brown alga Ectocarpus siliculosus

Brown algae are multicellular marine organisms evolutionarily distant from both metazoans and land plants. The molecular or cellular mechanisms that govern the developmental patterning in brown algae are poorly characterized. Here, we report the first morphogenetic mutant, étoile (etl), produced in the brown algal model Ectocarpus siliculosus. Genetic, cellular, and morphometric analyses showed that a single recessive locus, ETL, regulates cell differentiation: etl cells display thickening of the extracellular matrix (ECM), and the elongated, apical, and actively dividing E cells are underrepresented. As a result of this defect, the overrepresentation of round, branch-initiating R cells in the etl mutant leads to the rapid induction of the branching process at the expense of the uniaxial growth in the primary filament. Computational modeling allowed the simulation of the etl mutant phenotype by including a modified response to the neighborhood information in the division rules used to specify wild-type development. Microarray experiments supported the hypothesis of a defect in cell-cell communication, as primarily Lin-Notch-domain transmembrane proteins, which share similarities with metazoan Notch proteins involved in binary cell differentiation were repressed in etl. Thus, our study highlights the role of the ECM and of novel transmembrane proteins in cell-cell communication during the establishment of the developmental pattern in this brown alga.

The functions of auxilin and Rab11 in Drosophila suggest that the fundamental role of ligand endocytosis in notch signaling cells is not recycling

Notch signaling requires ligand internalization by the signal sending cells. Two endocytic proteins, epsin and auxilin, are essential for ligand internalization and signaling. Epsin promotes clathrin-coated vesicle formation, and auxilin uncoats clathrin from newly internalized vesicles. Two hypotheses have been advanced to explain the requirement for ligand endocytosis. One idea is that after ligand/receptor binding, ligand endocytosis leads to receptor activation by pulling on the receptor, which either exposes a cleavage site on the extracellular domain, or dissociates two receptor subunits. Alternatively, ligand internalization prior to receptor binding, followed by trafficking through an endosomal pathway and recycling to the plasma membrane may enable ligand activation. Activation could mean ligand modification or ligand transcytosis to a membrane environment conducive to signaling. A key piece of evidence supporting the recycling model is the requirement in signaling cells for Rab11, which encodes a GTPase critical for endosomal recycling. Here, we use Drosophila Rab11 and auxilin mutants to test the ligand recycling hypothesis. First, we find that Rab11 is dispensable for several Notch signaling events in the eye disc. Second, we find that Drosophila female germline cells, the one cell type known to signal without clathrin, also do not require auxilin to signal. Third, we find that much of the requirement for auxilin in Notch signaling was bypassed by overexpression of both clathrin heavy chain and epsin. Thus, the main role of auxilin in Notch signaling is not to produce uncoated ligand-containing vesicles, but to maintain the pool of free clathrin. Taken together, these results argue strongly that at least in some cell types, the primary function of Notch ligand endocytosis is not for ligand recycling.

Non-canonical functions of the tuberous sclerosis complex-Rheb signalling axis

The protein products of the tuberous sclerosis complex (TSC) genes, TSC1 and TSC2, form a complex, which inhibits the small G-protein, Ras homolog enriched in brain (Rheb). The vast majority of research regarding these proteins has focused on mammalian Target of Rapamycin (mTOR), a target of Rheb. Here, we propose that there are clinically relevant functions and targets of TSC1, TSC2 and Rheb, which are independent of mTOR. We present evidence that such non-canonical functions of the TSC-Rheb signalling network exist, propose a standard of evidence for these non-canonical functions, and discuss their potential clinical and therapeutic implications for patients with TSC and lymphangioleiomyomatosis (LAM).

Jagged 1 regulates the restriction of Sox2 expression in the developing chicken inner ear: a mechanism for sensory organ specification

Hair cells of the inner ear sensory organs originate from progenitor cells located at specific domains of the otic vesicle: the prosensory patches. Notch signalling is necessary for sensory development and loss of function of the Notch ligand jagged 1 (Jag1, also known as serrate 1) results in impaired sensory organs. However, the underlying mechanism of Notch function is unknown. Our results show that in the chicken otic vesicle, the Sox2 expression domain initially contains the nascent patches of Jag1 expression but, later on, Sox2 is only maintained in the Jag1-positive domains. Ectopic human JAG1 (hJag1) is able to induce Sox2 expression and enlarged sensory organs. The competence to respond to hJag1, however, is confined to the regions that expressed Sox2 early in development, suggesting that hJag1 maintains Sox2 expression rather than inducing it de novo. The effect is non-cell-autonomous and requires Notch signalling. hJag1 activates Notch, induces Hes/Hey genes and endogenous Jag1 in a non-cell-autonomous manner, which is consistent with lateral induction. The effects of hJag1 are mimicked by Jag2 but not by Dl1. Sox2 is sufficient to activate the Atoh1 enhancer and to ectopically induce sensory cell fate outside neurosensory-competent domains. We suggest that the prosensory function of Jag1 resides in its ability to generate discrete domains of Notch activity that maintain Sox2 expression within restricted areas of an extended neurosensory-competent domain. This provides a mechanism to couple patterning and cell fate specification during the development of sensory organs.

Immunolocalization of notch signaling protein molecules in a maxillary chondrosarcoma and its recurrent tumor

Background

Notch receptors are critical determinants of cell fate in a variety of organisms. Notch signaling is involved in the chondrogenic specification of neural crest cells. Aberrant Notch activity has been implicated in numerous human diseases including cancers; however its role in chondrogenic tumors has not been clarified.

Method

Tissue samples from a case of primary chondrosarcoma of the maxilla and its recurrent tumor were examined immunohistochemically for Notch1-4 and their ligands (Jagged1, Jagged2 and Delta1) expression.

Results

Both primary and recurrent tumors were histopathologically diagnosed as conventional hyaline chondrosarcoma (WHO Grade I). Hypercellular tumor areas strongly expressed Notch3 and Jagged1 in spindle and pleomorphic cells suggesting up-regulation of these protein molecules at sites of tumor proliferation. Expression patterns were distinct with some overlap. Differentiated malignant and atypical chondrocytes demonstrated variable expression levels of Jagged1, and weak to absent staining for Notch1, 4 and Delta1. Protein immunolocalization was largely membranous and cytoplasmic, sometimes outlining the lacunae of malignant chondrocytes. Hyaline cartilage demonstrated a diffuse or granular precipitation of Jagged1 suggesting presence of soluble Jagged1 activity at sites of abnormal chondrogenesis. No immunoreactivity for the other Notch members was observed. Calcified cartilage was consistently Notch-negative indicating down-regulation of Notch with cartilage maturation. Stromal components namely endothelial cells and fibroblasts variably expressed Notch1, 3 and Jagged1 but were mildly or non-reactive for the other members.

Conclusions

Results indicate that Notch signaling pathway may participate in cellular differentiation and proliferation in chondrosarcoma. Findings implicate Notch3 and Jagged1 as key molecules that influence the differentiation and maturation of cells of chondrogenic lineage.

Notch signaling proteins: legitimate targets for cancer therapy

Proteins and small peptides (growth factors and hormones) are key molecules in maintaining cellular homeostasis. To that end, Notch signaling pathway proteins are known to play critical roles in maintaining the balance between cell proliferation, differentiation and apoptosis, and thus it has been suggested that Notch may be responsible for the development and progression of human malignancies. Therefore, the Notch signaling pathway proteins may present novel therapeutic targets, which could have promising therapeutic impact on eradicating human malignancies. This review describes the role of Notch signaling pathway proteins in cancer and how its deregulation is involved in tumor development and progression leading to metastasis and the ultimate demise of patients diagnosed with cancer. Further, we summarize the role of several Notch inhibitors especially "natural agents" that could represent novel therapeutic strategies targeting Notch signaling toward better treatment outcome of patients diagnosed with cancer.

Ral GTPase promotes asymmetric Notch activation in the Drosophila eye in response to Frizzled/PCP signaling by repressing ligand-independent receptor activation

Ral is a small Ras-like GTPase that regulates membrane trafficking and signaling. Here, we show that in response to planar cell polarity (PCP) signals, Ral modulates asymmetric Notch signaling in the Drosophila eye. Specification of the initially equivalent R3/R4 photoreceptor precursor cells in each developing ommatidium occurs in response to a gradient of Frizzled (Fz) signaling. The cell with the most Fz signal (R3) activates the Notch receptor in the adjacent cell (R4) via the ligand Delta, resulting in R3/R4 cell determination and their asymmetric positions within the ommatidium. Two mechanisms have been proposed for ensuring that the cell with the most Fz activation sends the Delta signal: Fz-dependent transcriptional upregulation in R3 of genes that promote Delta signaling, and direct blockage of Notch receptor activation in R3 by localization of an activated Fz/Disheveled protein complex to the side of the plasma membrane adjacent to R4. Here, we discover a distinct mechanism for biasing the direction of Notch signaling that depends on Ral. Using genetic experiments in vivo, we show that, in direct response to Fz signaling, Ral transcription is upregulated in R3, and Ral represses ligand-independent activation of Notch in R3. Thus, prevention of ligand-independent Notch activation is not simply a constitutive process, but is a target for regulation by Ral during cell fate specification and pattern formation.

Ductal plates in hepatic ductular reactions. Hypothesis and implications. III. Implications for liver pathology

This article discusses on the basis of the ductal plate hypothesis the implication of the concept for several liver abnormalities. The occurrence of ductal plates (DP) during liver growth in childhood would explain the paraportal and parenchymal localizations of von Meyenburg complexes in postnatally developed parts of the liver, and their higher incidence in adulthood versus childhood. It partly clarifies the lack of postnatal intrahepatic bile duct development in Alagille syndrome and the reduced number of portal tracts in this disease. Ductular reactions (DRs) in DP configuration are the predominant type of progenitor cell reaction in fulminant necro-inflammatory liver disease, when lack of sufficient parenchymal regeneration results in liver failure. The concept of dissecting DRs explains the micronodular pattern of advanced biliary and alcoholic cirrhosis. The concept explains the DP patterns of bile ducts in several cases of biliary atresia, with implications for diagnosis and prognosis. The hypothesis also has an impact on concepts about stem/progenitor cells and their niche.

Ductal plates in hepatic ductular reactions. Hypothesis and implications. III. Implications for liver pathology

This article discusses on the basis of the ductal plate hypothesis the implication of the concept for several liver abnormalities. The occurrence of ductal plates (DP) during liver growth in childhood would explain the paraportal and parenchymal localizations of von Meyenburg complexes in postnatally developed parts of the liver, and their higher incidence in adulthood versus childhood. It partly clarifies the lack of postnatal intrahepatic bile duct development in Alagille syndrome and the reduced number of portal tracts in this disease. Ductular reactions (DRs) in DP configuration are the predominant type of progenitor cell reaction in fulminant necro-inflammatory liver disease, when lack of sufficient parenchymal regeneration results in liver failure. The concept of dissecting DRs explains the micronodular pattern of advanced biliary and alcoholic cirrhosis. The concept explains the DP patterns of bile ducts in several cases of biliary atresia, with implications for diagnosis and prognosis. The hypothesis also has an impact on concepts about stem/progenitor cells and their niche.

Drosophila CtBP regulates proliferation and differentiation of eye precursors and complexes with Eyeless, Dachshund, Dan, and Danr during eye and antennal development

Specification factors regulate cell fate in part by interacting with transcriptional co-regulators like CtBP to regulate gene expression. Here, we demonstrate that CtBP forms a complex or complexes with the Drosophila melanogaster Pax6 homolog Eyeless (Ey), and with Distal antenna (Dan), Distal antenna related (Danr), and Dachshund to promote eye and antennal specification. Phenotypic analysis together with molecular data indicate that CtBP interacts with Ey to prevent overproliferation of eye precursors. In contrast, CtBP,dan,danr triple mutant adult eyes have significantly fewer ommatidia than CtBP single or dan,danr double mutants, suggesting that the CtBP/Dan/Danr complex functions to recruit ommatidia from the eye precursor pool. Furthermore, CtBP single and to a greater extent CtBP,dan,danr triple mutants affect the establishment and maintenance of the R8 precursor, which is the founding ommatidial cell. Thus, CtBP interacts with different eye specification factors to regulate gene expression appropriate for proliferative vs. differentiative stages of eye development.

A biological solution to a fundamental distributed computing problem

Computational and biological systems are often distributed so that processors (cells) jointly solve a task, without any of them receiving all inputs or observing all outputs. Maximal independent set (MIS) selection is a fundamental distributed computing procedure that seeks to elect a set of local leaders in a network. A variant of this problem is solved during the development of the fly's nervous system, when sensory organ precursor (SOP) cells are chosen. By studying SOP selection, we derived a fast algorithm for MIS selection that combines two attractive features. First, processors do not need to know their degree; second, it has an optimal message complexity while only using one-bit messages. Our findings suggest that simple and efficient algorithms can be developed on the basis of biologically derived insights.

CD46 plasticity and its inflammatory bias in multiple sclerosis

Known as a link to the adaptive immune system, a complement regulator, a "pathogen magnet" and more recently as an inducer of autophagy, CD46 is the human receptor that refuses to be put in a box. This review summarizes the current roles of CD46 during immune responses and highlights the role of CD46 as both a promoter and attenuator of the immune response. In patients with multiple sclerosis (MS), CD46 responses are overwhelmingly pro-inflammatory with notable defects in cytokine and chemokine production. Understanding the role of CD46 as an inflammatory regulator is a distant goal considering the darkness in which its regulatory mechanisms reside. Further research into the regulation of CD46 expression through its internalization and processing will undoubtedly extend our knowledge of how the balance is tipped in favor of inflammation in MS patients.

High tumor levels of IL6 and IL8 abrogate preclinical efficacy of the γ-secretase inhibitor, RO4929097

Interest continues to build around the early application of patient selection markers to prospectively identify patients likely to show clinical benefit from cancer therapies. Hypothesis generation and clinical strategies often begin at the preclinical stage where responder and nonresponder tumor cell lines are first identified and characterized. In the present study, we investigate the drivers of in vivo resistance to the γ-secretase inhibitor RO4929097. Beginning at the tissue culture level, we identified apparent IL6 and IL8 expression differences that characterized tumor cell line response to RO4929097. We validated this molecular signature at the preclinical efficacy level identifying additional xenograft models resistant to the in vivo effects of RO4929097. Our data suggest that for IL6 and IL8 overexpressing tumors, RO4929097 no longer impacts angiogenesis or the infiltration of tumor associated fibroblasts. These preclinical data provide a rationale for preselecting patients possessing low levels of IL6 and IL8 prior to RO4929097 dosing. Extending this hypothesis into the clinic, we monitored patient IL6 and IL8 serum levels prior to dosing with RO4929097 during Phase I. Interestingly, the small group of patients deriving some type of clinical benefit from RO4929097 presented with low baseline levels of IL6 and IL8. Our data support the continued investigation of this patient selection marker for RO4929097 and other types of Notch inhibitors undergoing early clinical evaluation.

Proprotein convertases process Pmel17 during secretion

Pmel17 is a melanocyte/melanoma-specific protein that traffics to melanosomes where it forms a fibrillar matrix on which melanin gets deposited. Before being cleaved into smaller fibrillogenic fragments the protein undergoes processing by proprotein convertases, a class of serine proteases that typically recognize the canonical motif RX(R/K)R↓. The current model of Pmel17 maturation states that this processing step occurs in melanosomes, but in light of recent reports this issue has become controversial. We therefore addressed this question by thoroughly assessing the processing kinetics of either wild-type Pmel17 or a secreted soluble Pmel17 derivative. Our results demonstrate clearly that processing of Pmel17 occurs during secretion and that it does not require entry of the protein into the endocytic system. Strikingly, processing proceeds even in the presence of the secretion inhibitor monensin, suggesting that Pmel17 is an exceptionally good substrate. In line with this, we find that newly synthesized surface Pmel17 is already quantitatively cleaved. Moreover, we demonstrate that Pmel17 function is independent of the sequence identity of its unconventional proprotein convertase-cleavage motif that lacks arginine in P4 position. The data alter the current view of Pmel17 maturation and suggest that the multistep processing of Pmel17 begins with an early cleavage during secretion that primes the protein for later functional processing.

The H(+) vacuolar ATPase maintains neural stem cells in the developing mouse cortex

The vacuolar H(+) ATPase (v-ATPase) is crucial for endosome acidification, endocytosis, and trafficking in essentially all eukaryotic cells. Recent studies have shown that inhibition of the v-ATPase also leads to downregulation of important signaling pathways, including Notch and Wnt, which are key regulators of cell differentiation and tissue homeostasis across the animal kingdom. However, the requirement of endosome acidification and endocytosis in the transduction of Notch signaling is still highly debated. Moreover, no study has yet investigated the role of the v-ATPase during mammalian development. Here we show that expression of a dominant-negative subunit of the v-ATPase in neural precursors of the developing mouse cortex depleted neural stem cells by promoting their differentiation and the generation of neurons. Moreover, inhibition of the v-ATPase reduced endogenous Notch signaling and prevented the proliferative effect of a transmembrane, γ-secretase-dependent, active Notch without blocking the effects of its cytoplasmic intracellular domain (NICD). Our data are consistent with recent reports in Drosophila in which the v-ATPase has been suggested to be important for the transduction of Notch signaling. By extending these reports to mammalian embryos, our data may contribute to a better understanding of the role of the v-ATPase, endosome acidification, and endocytosis in signal transduction during neural stem cell differentiation and brain development.

Fangjiomics: in search of effective and safe combination therapies

Millennia-old Chinese medicine treats disease with many combination therapies involving ingredients used in clinic practice. Fangjiomics is the science of identifying and designing effective mixtures of bioactive agents and elucidating their modes of action beyond those of Chinese patent medicines. Omics profiling and quantitative optimal modeling have been used to associate the various responses with biological pathways related to disease phenotype. Fangjiomics seeks to study myriad compatible combinations that may act through multiple targets, modes of action, and biological pathways balancing on off-target and on-target effects. This approach may lead to the discovery of controllable array-designed therapies to combine less potent elements that are more effective collectively but have fewer adverse side effects than does any element singly.