SKIP, a CBF1-associated protein, interacts with the ankyrin repeat domain of NotchIC To facilitate NotchIC function

Notch signaling pathway in osteogenesis, bone development, metabolism, and diseases

The skeletal system provides vital importance to support organ development and functions. The Notch signaling pathway possesses well-established functions in organ development and cellular homeostasis. The Notch signaling pathway comprises five typical ligands (JAG1, JAG2, DLL1, DLL3, and DLL4), four receptors (Notch1-4), and four intracellular domains (NICD1-4). Each component of the Notch signaling pathway has been demonstrated to be fundamental in osteoblast differentiation and bone formation. The dysregulation in the Notch signaling pathway is highly linked with skeletal disorders or diseases at the developmental and postnatal stages. Recent studies have highlighted the importance of the elements of the Notch signaling pathway in the skeletal system, as well as its interaction with signaling, such as Wnt/β-catenin, BMP, TGF-β, FGF, autophagy, and hedgehog (Hh) to construct a potential gene regulatory network to orchestrate osteogenesis and ossification. Our review has provided a comprehensive summary of the Notch signaling pathway in the skeletal system, as well as the insights targeting Notch signaling for innovative potential drug discovery targets or therapeutic interventions to treat bone disorders, such as osteoporosis and osteoarthritis. An in-depth molecular mechanistic strategy to modulate the Notch signaling pathway and its associated signaling pathway will be encouraged for consideration to trigger enhanced therapeutic approaches for bone disorders by defining Notch-regulating drugs for clinical use.

Phosphorylation of SNW1 protein associated with equine melanocytic neoplasm identified in serum and feces

Equine melanocytic neoplasm (EMN) represents a form of skin tumor observed predominantly in grey horses aged over 15 years. Despite its prevalence, current therapeutic and preventive strategies for EMN have been subject to limited investigation. This study endeavors to shed light on potential phosphoproteins present in equine serum and fecal samples, potentially linked to EMN, with a specific focus on functional interactions in EMN pathogenesis. We examined 50 samples (25 serum, 25 feces), divided into three groups based on EMN severity: normal (n = 16), mild (n = 18), and severe EMN (n = 16). Equine phosphoproteome analysis identified 2,359 annotated serum phosphoproteins and 2002 annotated fecal phosphoproteins through differentially expressed proteins (DEPs). KEGG analysis emphasized the role of environmental information processing. Notably, the integrin NF-kappaB binding P-TEFb to stimulate transcriptional elongation signaling pathway, involving SNW1 protein, was implicated in early stage of EMN development in both serum and fecal samples. This highlights SNW1's potential role in mediating transcriptional processes, offering a novel marker within environmental information processing. This study enhances understanding of EMN mechanisms in horses, suggesting early detection through non-invasive methods and identifying a functional pathway involving SNW1, which could inform future treatment and prevention strategies.

Notch-Dependent Expression of the Drosophila Hey Gene Is Supported by a Pair of Enhancers with Overlapping Activities

Drosophila Hey is a basic helix-loop-helix-orange (bHLH-O) protein with an important role in the establishment of distinct identities of postmitotic cells. We have previously identified Hey as a transcriptional target and effector of Notch signalling during the asymmetric division of neuronal progenitors, generating neurons of two types, and we have shown that Notch-dependent expression of Hey also marks a subpopulation of the newborn enteroendocrine (EE) cells in the midgut primordium of the embryo. Here, we investigate the transcriptional regulation of Hey in neuronal and intestinal tissues. We isolated two genomic regions upstream of the promoter (HeyUP) and in the second intron (HeyIN2) of the Hey gene, based on the presence of binding motifs for Su(H), the transcription factor that mediates Notch activity. We found that both regions can direct the overlapping expression patterns of reporter transgenes recapitulating endogenous Hey expression. Moreover, we showed that while HeyIN2 represents a Notch-dependent enhancer, HeyUP confers both Notch-dependent and independent transcriptional regulation. We induced mutations that removed the Su(H) binding motifs in either region and then studied the enhancer functionality in the respective Hey mutant lines. Our results provide direct evidence that although both enhancers support Notch-dependent regulation of the Hey gene, their role is redundant, as a Hey loss-of-function lethal phenotype is observed only after deletion of all their Su(H) binding motifs by CRISPR/Cas9.

NOTCH localizes to mitochondria through the TBC1D15-FIS1 interaction and is stabilized via blockade of E3 ligase and CDK8 recruitment to reprogram tumor-initiating cells

The P53-destabilizing TBC1D15-NOTCH protein interaction promotes self-renewal of tumor-initiating stem-like cells (TICs); however, the mechanisms governing the regulation of this pathway have not been fully elucidated. Here, we show that TBC1D15 stabilizes NOTCH and c-JUN through blockade of E3 ligase and CDK8 recruitment to phosphodegron sequences. Chromatin immunoprecipitation (ChIP-seq) analysis was performed to determine whether TBC1D15-dependent NOTCH1 binding occurs in TICs or non-TICs. The TIC population was isolated to evaluate TBC1D15-dependent NOTCH1 stabilization mechanisms. The tumor incidence in hepatocyte-specific triple knockout (Alb::CreERT2;Tbc1d15Flox/Flox;Notch1Flox/Flox;Notch2Flox/Flox;HCV-NS5A) Transgenic (Tg) mice and wild-type mice was compared after being fed an alcohol-containing Western diet (WD) for 12 months. The NOTCH1-TBC1D15-FIS1 interaction resulted in recruitment of mitochondria to the perinuclear region. TBC1D15 bound to full-length NUMB and to NUMB isoform 5, which lacks three Ser phosphorylation sites, and relocalized NUMB5 to mitochondria. TBC1D15 binding to NOTCH1 blocked CDK8- and CDK19-mediated phosphorylation of the NOTCH1 PEST phosphodegron to block FBW7 recruitment to Thr-2512 of NOTCH1. ChIP-seq analysis revealed that TBC1D15 and NOTCH1 regulated the expression of genes involved in mitochondrial metabolism-related pathways required for the maintenance of TICs. TBC1D15 inhibited CDK8-mediated phosphorylation to stabilize NOTCH1 and protect it from degradation The NUMB-binding oncoprotein TBC1D15 rescued NOTCH1 from NUMB-mediated ubiquitin-dependent degradation and recruited NOTCH1 to the mitochondrial outer membrane for the generation and expansion of liver TICs. A NOTCH-TBC1D15 inhibitor was found to inhibit NOTCH-dependent pathways and exhibited potent therapeutic effects in PDX mouse models. This unique targeting of the NOTCH-TBC1D15 interaction not only normalized the perinuclear localization of mitochondria but also promoted potent cytotoxic effects against TICs to eradicate patient-derived xenografts through NOTCH-dependent pathways.

HDAC6 and ERK/ADAM17 Regulate VEGF-Induced NOTCH Signaling in Lung Endothelial Cells

Angiogenesis plays a critical role in various physiological and pathological processes and is regulated by VEGF. Histone Deacetylase 6 (HDAC6) is a class IIB HDAC that regulates cytoplasmic signaling through deacetylation and is emerging as a target for modulating angiogenesis. We investigated the hypothesis that VEGF-induced endothelial cell (EC) NOTCH signaling is regulated by HDAC6 through acetylation of NOTCH intracellular cytoplasmic domain (NICD). In pulmonary endothelial cells (EC), VEGF-induced activation of the NICD transcriptional response was regulated by ERK1/2 and ADAM 17 and required DLL4. While HDAC6 inhibition induced the acetylation of NICD and stabilized NICD, it repressed NICD-SNW1 binding required for the NOTCH transcriptional responses. In vitro experiments showed that HDAC6 inhibition inhibited lung EC angiogenesis, and neonatal mice treated with a systemic HDAC6 inhibitor had significantly altered angiogenesis and alveolarization. These findings shed light on the role of HDAC6 in modulating VEGF-induced angiogenesis through acetylation and repression of the transcriptional regulators, NICD and SNW1.

A spatially defined human Notch receptor interaction network reveals Notch intracellular storage and Ataxin-2-mediated fast recycling

The Notch signaling pathway controls cell growth, differentiation, and fate decisions. Dysregulation of Notch signaling has been linked to various human diseases. Notch receptor resides in multiple cellular compartments, and its translocation plays a central role in pathway activation. However, the spatial regulation of Notch receptor functions remains largely elusive. Using TurboID-based proximity labeling followed by affinity purification and mass spectrometry, we establish a spatially defined human Notch receptor interaction network. Notch receptors interact with different proteins in distinct subcellular compartments to perform specific cellular functions. This spatially defined interaction network also reveals that a large fraction of NOTCH is stored at the endoplasmic reticulum (ER)-Golgi intermediate compartment and recruits Ataxin-2-dependent recycling machinery for rapid recycling, Notch signaling activation, and leukemogenesis. Our work provides insights into dynamic Notch receptor complexes with exquisite spatial resolution, which will help in elucidating the detailed regulation of Notch receptors and highlight potential therapeutic targets for Notch-related pathogenesis.

Proteome balance in ciliopathies: the OFD1 protein example

The balance of protein synthesis and degradation is finely regulated and influences cellular homeostasis and biological processes (e.g., embryonic development and neuronal plasticity). Recent data demonstrated that centrosomal/ciliary proteins enable proteome control in response to spatial or microenvironmental stimuli. Here, we discuss recent discoveries regarding the role in the balance of the proteome of centrosomal/ciliary proteins associated with genetic disorders known as ciliopathies. In particular, OFD1 was the first example of a ciliopathy protein controlling both protein expression and autophagic/proteasomal degradation. Understanding the role of proteome balance in the pathogenesis of the clinical manifestations of ciliopathies may pave the way to the identification of a wide range of putative novel therapeutic targets for these conditions.

Genetic and Molecular Interactions between HΔCT, a Novel Allele of the Notch Antagonist Hairless, and the Histone Chaperone Asf1 in Drosophila melanogaster

Cellular differentiation relies on the highly conserved Notch signaling pathway. Notch activity induces gene expression changes that are highly sensitive to chromatin landscape. We address Notch gene regulation using Drosophila as a model, focusing on the genetic and molecular interactions between the Notch antagonist Hairless and the histone chaperone Asf1. Earlier work implied that Asf1 promotes the silencing of Notch target genes via Hairless (H). Here, we generate a novel HΔCT allele by genome engineering. Phenotypically, HΔCT behaves as a Hairless gain of function allele in several developmental contexts, indicating that the conserved CT domain of H has an attenuator role under native biological contexts. Using several independent methods to assay protein-protein interactions, we define the sequences of the CT domain that are involved in Hairless-Asf1 binding. Based on previous models, where Asf1 promotes Notch repression via Hairless, a loss of Asf1 binding should reduce Hairless repressive activity. However, tissue-specific Asf1 overexpression phenotypes are increased, not rescued, in the HΔCT background. Counterintuitively, Hairless protein binding mitigates the repressive activity of Asf1 in the context of eye development. These findings highlight the complex connections of Notch repressors and chromatin modulators during Notch target-gene regulation and open the avenue for further investigations.

The developmental origins of Notch-driven intrahepatic bile duct disorders

The Notch signaling pathway is an evolutionarily conserved mechanism of cell-cell communication that mediates cellular proliferation, cell fate specification, and maintenance of stem and progenitor cell populations. In the vertebrate liver, an absence of Notch signaling results in failure to form bile ducts, a complex tubular network that radiates throughout the liver, which, in healthy individuals, transports bile from the liver into the bowel. Loss of a functional biliary network through congenital malformations during development results in cholestasis and necessitates liver transplantation. Here, we examine to what extent Notch signaling is necessary throughout embryonic life to initiate the proliferation and specification of biliary cells and concentrate on the animal and human models that have been used to define how perturbations in this signaling pathway result in developmental liver disorders.

Chromatin Regulator SPEN/SHARP in X Inactivation and Disease

Simple Summary

Carcinogenesis is a multistep process involving not only the activation of oncogenes and disabling tumor suppressor genes, but also epigenetic modulation of gene expression. X chromosome inactivation (XCI) is a paradigm to study heterochromatin formation and maintenance. The double dosage of X chromosomal genes in female mammals is incompatible with early development. XCI is an excellent model system for understanding the establishment of facultative heterochromatin initiated by the expression of a 17,000 nt long non-coding RNA, known as Xinactivespecifictranscript (Xist), on the X chromosome. This review focuses on the molecular mechanisms of how epigenetic modulators act in a step-wise manner to establish facultative heterochromatin, and we put these in the context of cancer biology and disease. An in depth understanding of XCI will allow a better characterization of particular types of cancer and hopefully facilitate the development of novel epigenetic therapies.

Abstract

Enzymes, such as histone methyltransferases and demethylases, histone acetyltransferases and deacetylases, and DNA methyltransferases are known as epigenetic modifiers that are often implicated in tumorigenesis and disease. One of the best-studied chromatin-based mechanism is X chromosome inactivation (XCI), a process that establishes facultative heterochromatin on only one X chromosome in females and establishes the right dosage of gene expression. The specificity factor for this process is the long non-coding RNA Xinactivespecifictranscript (Xist), which is upregulated from one X chromosome in female cells. Subsequently, Xist is bound by the corepressor SHARP/SPEN, recruiting and/or activating histone deacetylases (HDACs), leading to the loss of active chromatin marks such as H3K27ac. In addition, polycomb complexes PRC1 and PRC2 establish wide-spread accumulation of H3K27me3 and H2AK119ub1 chromatin marks. The lack of active marks and establishment of repressive marks set the stage for DNA methyltransferases (DNMTs) to stably silence the X chromosome. Here, we will review the recent advances in understanding the molecular mechanisms of how heterochromatin formation is established and put this into the context of carcinogenesis and disease.

SKIP Silencing Decreased Disease Resistance Against Botrytis cinerea and Pseudomonas syringae pv. tomato DC3000 in Tomato

SKIP, a component of the spliceosome, is involved in numerous signaling pathways. However, there is no direct genetic evidence supporting the function of SKIP in defense responses. In this paper, two SKIPs, namely, SlSKIP1a and SlSKIP1b, were analyzed in tomato. qRT-PCR analysis showed that the SlSKIP1b expression was triggered via Pseudomonas syringae pv. tomato (Pst) DC3000 and Botrytis cinerea (B. cinerea), together with the defense-associated signals. In addition, the functions of SlSKIP1a and SlSKIP1b in disease resistance were analyzed in tomato through the virus-induced gene silencing (VIGS) technique. VIGS-mediated SlSKIP1b silencing led to increased accumulation of reactive oxygen species (ROS), along with the decreased expression of defense-related genes (DRGs) after pathogen infection, suggesting that it reduced B. cinerea and Pst DC3000 resistance. There was no significant difference in B. cinerea and Pst DC3000 resistance in TRV-SlSKIP1a-infiltrated plants compared with the TRV-GUS-silencing counterparts. As suggested by the above findings, SlSKIP1b plays a vital role in disease resistance against pathogens possibly by regulating the accumulation of ROS as well as the expression of DRGs.

A novel SNW/SKIP domain-containing protein, Bx42, is involved in the antibacterial responses of Macrobrachium nipponense

Bx42, the homologue of SNW1 in mammals, is involved in pre-mRNA splicing and transcriptional regulation. However, the presence and function of Bx42 have remained poorly understood in invertebrates until now. In the current study, a novel SNW domain-containing protein (MnBx42) from Macrobrachium nipponense was identified, and its potential role in the immune response was investigated. The full-length MnBx42 was 7467 bp with an open reading frame of 1653 bp, encoding 550 amino acids. Real-time PCR analysis suggested that MnBx42 was predominantly expressed in the intestine, gills and hepatopancreas, and immunofluorescence assays indicated that it was located in the nucleus. Its expression level was significantly decreased in M. nipponense post-challenge with white spot syndrome virus (WSSV) as well as Aeromonas hydrophila and Staphylococcus aureus, implying its participation in the innate immune response. The knockdown of MnBx42 in vivo notably increased the susceptibility of the prawns to bacterial infection, markedly increased the bacterial load in the gills, and significantly attenuated the phagocytic activity of haemocytes. Dual-luciferase reporter assays illustrated that MnBx42 could activate the NF-κB pathway. Consistent with this, when MnBx42 was silenced in vivo, the expression levels of antimicrobial peptides (AMPs), including ALF2, ALF3, ALF4, ALF5, Cru1 and Cru2, and NF-κB signalling genes, including dorsal, relish, TAK1, TAB1, Ikkβ, and Ikkε, were significantly reduced. Taken together, these findings may provide new insights about Bx42 in crustaceans and pave the way for a better understanding of the crustacean innate immune system.

Binding Nemo

Article highlight based on "SNW1 interacts with IKKγ to positively regulate antiviral innate immune responses against influenza A virus infection" by Qiao et al.

Skip is essential for Notch signaling to induce Sox2 in cerebral arteriovenous malformations

Notch signaling and Sry-box (Sox) family transcriptional factors both play critical roles in endothelial cell (EC) differentiation in vascularization. Recent studies have shown that excessive Notch signaling induces Sox2 to cause cerebral arteriovenous malformations (AVMs). Here, we examine human pulmonary AVMs and find no induction of Sox2. Results of epigenetic studies also show less alteration of Sox2-DNA binding in pulmonary AVMs than in cerebral AVMs. We identify high expression of ski-interacting protein (Skip) in brain ECs, a Notch-associated chromatin-modifying protein that is lacking in lung ECs. Knockdown of Skip abolished Notch-induction of Sox2 in brain ECs, while restoration of Skip in lung ECs enabled Notch-mediated Sox2 induction. The results suggest that Skip is a key factor for induction of Sox2 in cerebral AVMs.

Novel tumor-suppressor FOXN3 is downregulated in adult acute myeloid leukemia

Forkhead box protein N3 (FOXN3) is a transcriptional repressor involved in cell cycle regulation and tumorigenesis. Abnormalities in gene structure and epigenetics of FOXN3 are closely associated with the occurrence of hematological malignancies; however, its involvement in the pathogenesis of acute myeloid leukemia (AML) remains unknown. The present study aimed to examine the potential significance of FOXN3 in AML. FOXN3 expression levels were examined in patients with AML and AML cell lines, and its clinical significance in AML was evaluated. FOXN3-overexpressing AML cell lines were established, and the biological function of FOXN3 was detected by flow cytometry and a Cell Counting Kit-8 assay. A significant decrease in FOXN3 expression levels was observed in patients with AML and in the AML cell lines in vitro. FOXN3 expression levels were associated with the number of leukocytes in patients. FOXN3 overexpression may inhibit cell proliferation in AML cell lines, induce cell cycle S-phase arrest and promote apoptosis in OCI-AML3 and THP-AML cells. The present study provided insight into how FOXN3 may serve as a novel tumor suppressor in AML.

Histone variant H2A.Z deposition and acetylation directs the canonical Notch signaling response

A fundamental as yet incompletely understood feature of Notch signal transduction is a transcriptional shift from repression to activation that depends on chromatin regulation mediated by transcription factor RBP-J and associated cofactors. Incorporation of histone variants alter the functional properties of chromatin and are implicated in the regulation of gene expression. Here, we show that depletion of histone variant H2A.Z leads to upregulation of canonical Notch target genes and that the H2A.Z-chaperone TRRAP/p400/Tip60 complex physically associates with RBP-J at Notch-dependent enhancers. When targeted to RBP-J-bound enhancers, the acetyltransferase Tip60 acetylates H2A.Z and upregulates Notch target gene expression. Importantly, the Drosophila homologs of Tip60, p400 and H2A.Z modulate Notch signaling response and growth in vivo. Together, our data reveal that loading and acetylation of H2A.Z are required to assure tight control of canonical Notch activation.

An in vitro attempt at precision toxicology reveals the involvement of DNA methylation alteration in ochratoxin A-induced G0/G1 phase arrest

Precision toxicology evaluates the toxicity of certain substances by isolating a small group of cells with a typical phenotype of interest followed by a single cell sequencing-based analysis. In this in vitro attempt, ochratoxin A (OTA), a typical mycotoxin and food contaminant, is found to induce G0/G1 phase cell cycle arrest in human renal proximal tubular HKC cells at a concentration of 20 μM after a 24h-treatment. A small number of G0/G1 phase HKC cells are evaluated in both the presence and absence of OTA. These cells are sorted with a flow cytometer and subjected to mRNA and DNA methylation sequencing using Smart-Seq2 and single-cell reduced-representation bisulfite sequencing (scRRBS) technology, respectively. Integrated analysis of the transcriptome and methylome profiles reveals that OTA causes abnormal expression of the essential genes that regulate G1/S phase transition, act as signal transductors in G1 DNA damage checkpoints, and associate with the anaphase-promoting complex/cyclosome. The alteration of their DNA methylation status is a significant underlying epigenetic mechanism. Furthermore, Notch signaling and Ras/MAPK/CREB pathways are found to be suppressed by OTA. This attempt at precision toxicology paves the way for a deeper understanding of OTA toxicity and provides an innovative strategy to researchers in the toxicology and pharmacology field.

Regulation of notch signaling by a chromatin modeling protein Hat-trick

Notch signaling plays pleiotropic role in astounding variety of cellular processes including cell fate determination, differentiation, proliferation and apoptosis. The increasingly complex regulatory mechanisms of Notch signaling account for the multitude of functions exhibited by Notch during development. We identified Hat-trick (Htk), a DNA binding protein, as an interacting partner of Notch-ICD in a yeast two-hybrid screen and their physical interaction was further validated by co-immunoprecipitation experiments. htk genetically interacts with Notch pathway components in trans-heterozygous combinations. Loss of htk function in htk mutant somatic clones showed down-regulation of Notch targets, whereas over-expression of htk caused ectopic expression of Notch target, without affecting the level of Notch protein. Immunocytochemical analysis has demonstrated that Htk co-localizes with over-expressed Notch-ICD in the same nuclear compartment. We have shown here that Htk cooperates with Notch-ICD and Suppressor of Hairless to form activation complex and binds to the regulatory sequences of Notch downstream targets, Enhancer of Split complex genes to direct their expression. Taken together, our results suggest a novel mode of regulation of Notch signaling by a chromatin modeling protein Htk.

HiPLA: High-throughput imaging proximity ligation assay

Protein-protein interactions are essential for cellular structure and function. To delineate how the intricate assembly of protein interactions contribute to cellular processes in health and disease, new methodologies that are both highly sensitive and can be applied at large scale are needed. Here, we develop HiPLA (high-throughput imaging proximity ligation assay), a method that employs the well-established antibody-based proximity ligation assay in a high-throughput imaging screening format as a novel means to systematically visualize protein interactomes. Using HiPLA with a library of antibodies targeting nuclear proteins, we probe the interaction of 60 proteins and associated post-translational modifications (PTMs) with the nuclear lamina in a model of the premature aging disorder Hutchinson-Gilford progeria syndrome (HGPS). We identify a subset of proteins that differentially interact with the nuclear lamina in HGPS. Using HiPLA in combination with quantitative indirect immunofluorescence, we find that the majority of differential interactions are accompanied by corresponding changes in expression of the interacting protein. Taken together, HiPLA offers a novel approach to probe cellular protein-protein interaction at a large scale and reveals mechanistic insights into the assembly of protein complexes.

The role of Cancer/Testis Antigens in Multiple Myeloma pathogenesis and their application in disease monitoring and therapy

A unique group of genes, encoding tumour associated antigens, known as the Cancer/Testis Antigens (CTAs), have been explored as novel markers of disease progression and as targets of immunotherapy in several cancers, including the haematological malignancy Multiple Myeloma (MM). This review aims to update the knowledge of CTA involvement in MM pathogenesis and how their potential as biomarkers for disease monitoring and targets of immunotherapy has been explored in the MM disease arena. Despite the initial promise of these antigens, their use as immunotherapy targets has not been successful, yet with a greater understanding of their role in disease pathogenesis they may still have a significant role to play as biomarkers of disease and therapeutic targets.

Identification and functional analysis of the aspergillic acid gene cluster in Aspergillus flavus

Aspergillus flavus can colonize important food staples and produce aflatoxins, a group of toxic and carcinogenic secondary metabolites. Previous in silico analysis of the A. flavus genome revealed 56 gene clusters predicted to be involved in the biosynthesis of secondary metabolites. A. flavus secondary metabolites produced during infection of maize seed are of particular interest, especially with respect to their roles in the biology of the fungus. A predicted nonribosomal peptide synthetase-like (NRPS-like) gene, designated asaC (AFLA_023020), present in the uncharacterized A. flavus secondary metabolite gene cluster 11 was previously shown to be expressed during the earliest stages of maize kernel infection. Cluster 11 is composed of six additional genes encoding a number of putative decorating enzymes as well as a transporter and transcription factor. We generated knock-out mutants of the seven predicted cluster 11 genes. LC-MS analysis of extracts from knockout mutants of these genes showed that they were responsible for the synthesis of the previously characterized antimicrobial mycotoxin aspergillic acid. Extracts of the asaC mutant showed no production of aspergillic acid or its precursors. Knockout of the cluster 11 P450 oxidoreductase afforded a pyrazinone metabolite, the aspergillic acid precursor deoxyaspergillic acid. The formation of hydroxyaspergillic acid was abolished in a desaturase/hydroxylase mutant. The hydroxamic acid functional group in aspergillic acid allows the molecule to bind to iron resulting in the production of a red pigment in A. flavus identified previously as ferriaspergillin. A reduction of aflatoxin B₁ and cyclopiazonic acid that correlated with reduced fungal growth was observed in maize kernel infection assays when aspergillic acid biosynthesis in A. flavus is halted.

CSL-Associated Corepressor and Coactivator Complexes

The highly conserved Notch signal transduction pathway orchestrates fundamental cellular processes including, differentiation, proliferation, and apoptosis during embryonic development and in the adult organism. Dysregulated Notch signaling underlies the etiology of a variety of human diseases, such as certain types of cancers, developmental disorders and cardiovascular disease. Ligand binding induces proteolytic cleavage of the Notch receptor and nuclear translocation of the Notch intracellular domain (NICD), which forms a ternary complex with the transcription factor CSL and the coactivator MAML to upregulate transcription of Notch target genes. The DNA-binding protein CSL is the centrepiece of transcriptional regulation in the Notch pathway, acting as a molecular hub for interactions with either corepressors or coactivators to repress or activate, respectively, transcription. Here we review previous structure-function studies of CSL-associated coregulator complexes and discuss the molecular insights gleaned from this research. We discuss the functional consequences of both activating and repressing binding partners using the same interaction platforms on CSL. We also emphasize that although there has been a significant uptick in structural information over the past decade, it is still under debate how the molecular switch from repression to activation mediated by CSL occurs at Notch target genes and whether it will be possible to manipulate these transcription complexes therapeutically in the future.

Regulation of NOTCH signaling by RAB7 and RAB8 requires carboxyl methylation by ICMT

Isoprenylcysteine carboxyl methyltransferase (ICMT) methylesterifies C-terminal prenylcysteine residues of CaaX proteins and some RAB GTPases. Deficiency of either ICMT or NOTCH1 accelerates pancreatic neoplasia in Pdx1-Cre;LSL-KrasG12D mice, suggesting that ICMT is required for NOTCH signaling. We used Drosophila melanogaster wing vein and scutellar bristle development to screen Rab proteins predicted to be substrates for ICMT (ste14 in flies). We identified Rab7 and Rab8 as ICMT substrates that when silenced phenocopy ste14 deficiency. ICMT, RAB7, and RAB8 were all required for efficient NOTCH1 signaling in mammalian cells. Overexpression of RAB8 rescued NOTCH activation after ICMT knockdown both in U2OS cells expressing NOTCH1 and in fly wing vein development. ICMT deficiency induced mislocalization of GFP-RAB7 and GFP-RAB8 from endomembrane to cytosol, enhanced binding to RABGDI, and decreased GTP loading of RAB7 and RAB8. Deficiency of ICMT, RAB7, or RAB8 led to mislocalization and diminished processing of NOTCH1-GFP. Thus, NOTCH signaling requires ICMT in part because it requires methylated RAB7 and RAB8.

Notch Signaling: Linking Embryonic Lung Development and Asthmatic Airway Remodeling

Lung development is mediated by assorted signaling proteins and orchestrated by complex mesenchymal-epithelial interactions. Notch signaling is an evolutionarily conserved cell-cell communication mechanism that exhibits a pivotal role in lung development. Notably, both aberrant expression and loss of regulation of Notch signaling are critically linked to the pathogenesis of various lung diseases, in particular, pulmonary fibrosis, lung cancer, pulmonary arterial hypertension, and asthmatic airway remodeling; implying that precise regulation of intensity and duration of Notch signaling is imperative for appropriate lung development. Moreover, evidence suggests that Notch signaling links embryonic lung development and asthmatic airway remodeling. Herein, we summarized all-recent advances associated with the mechanistic role of Notch signaling in lung development, consequences of aberrant expression or deletion of Notch signaling in linking early-impaired lung development and asthmatic airway remodeling, and all recently investigated potential therapeutic strategies to treat asthmatic airway remodeling.

Protein sequestration at the nuclear periphery as a potential regulatory mechanism in premature aging

Serebryannyy and Misteli provide a perspective on how protein sequestration at the inner nuclear membrane and nuclear lamina might influence aging.

Despite the extensive description of numerous molecular changes associated with aging, insights into the driver mechanisms of this fundamental biological process are limited. Based on observations in the premature aging syndrome Hutchinson–Gilford progeria, we explore the possibility that protein regulation at the inner nuclear membrane and the nuclear lamina contributes to the aging process. In support, sequestration of nucleoplasmic proteins to the periphery impacts cell stemness, the response to cytotoxicity, proliferation, changes in chromatin state, and telomere stability. These observations point to the nuclear periphery as a central regulator of the aging phenotype.

Notch Signaling in Development, Tissue Homeostasis, and Disease

Notch signaling is an evolutionarily highly conserved signaling mechanism, but in contrast to signaling pathways such as Wnt, Sonic Hedgehog, and BMP/TGF-β, Notch signaling occurs via cell-cell communication, where transmembrane ligands on one cell activate transmembrane receptors on a juxtaposed cell. Originally discovered through mutations in Drosophila more than 100 yr ago, and with the first Notch gene cloned more than 30 yr ago, we are still gaining new insights into the broad effects of Notch signaling in organisms across the metazoan spectrum and its requirement for normal development of most organs in the body. In this review, we provide an overview of the Notch signaling mechanism at the molecular level and discuss how the pathway, which is architecturally quite simple, is able to engage in the control of cell fates in a broad variety of cell types. We discuss the current understanding of how Notch signaling can become derailed, either by direct mutations or by aberrant regulation, and the expanding spectrum of diseases and cancers that is a consequence of Notch dysregulation. Finally, we explore the emerging field of Notch in the control of tissue homeostasis, with examples from skin, liver, lung, intestine, and the vasculature.

Leptin signaling and cancer chemoresistance: Perspectives

Obesity is a major health problem and currently is endemic around the world. Obesity is a risk factor for several different types of cancer, significantly promoting cancer incidence, progression, poor prognosis and resistance to anti-cancer therapies. The study of this resistance is critical as development of chemoresistance is a serious drawback for the successful and effective drug-based treatments of cancer. There is increasing evidence that augmented adiposity can impact on chemotherapeutic treatment of cancer and the development of resistance to these treatments, particularly through one of its signature mediators, the adipokine leptin. Leptin is a pro-inflammatory, pro-angiogenic and pro-tumorigenic adipokine that has been implicated in many cancers promoting processes such as angiogenesis, metastasis, tumorigenesis and survival/resistance to apoptosis. Several possible mechanisms that could potentially be developed by cancer cells to elicit drug resistance have been suggested in the literature. Here, we summarize and discuss the current state of the literature on the role of obesity and leptin on chemoresistance, particularly as it relates to breast and pancreatic cancers. We focus on the role of leptin and its significance in possibly driving these proposed chemoresistance mechanisms, and examine its effects on cancer cell survival signals and expansion of the cancer stem cell sub-populations.

Atrophin protein RERE positively regulates Notch targets in the developing vertebrate spinal cord

The Notch signaling pathway controls cell fate decision, proliferation, and other biological functions in both vertebrates and invertebrates. Precise regulation of the canonical Notch pathway ensures robustness of the signal throughout development and adult tissue homeostasis. Aberrant Notch signaling results in profound developmental defects and is linked to many human diseases. In this study, we identified the Atrophin family protein RERE (also called Atro2) as a positive regulator of Notch target Hes genes in the developing vertebrate spinal cord. Prior studies have shown that during early embryogenesis in mouse and zebrafish, deficit of RERE causes various patterning defects in multiple organs including the neural tube. Here, we detected the expression of RERE in the developing chick spinal cord, and found that normal RERE activity is needed for proper neural progenitor proliferation and neuronal differentiation possibly by affecting Notch-mediated Hes expression. In mammalian cells, RERE co-immunoprecipitates with CBF1 and Notch intracellular domain (NICD), and is recruited to nuclear foci formed by over-expressed NICD1. RERE is also necessary for NICD to activate the expression of Notch target genes. Our findings suggest that RERE stimulates Notch target gene expression by preventing degradation of NICD protein, thereby facilitating the assembly of a transcriptional activating complex containing NICD, CBF1/RBPjκ in vertebrate, Su(H) in Drosophila melanogaster, Lag1 in C. elegans, and other coactivators.

Turn It Down a Notch

In the developing vertebrate embryo, segmentation initiates through the formation of repeated segments, or somites, on either side of the posterior neural tube along the anterior to posterior axis. The periodicity of somitogenesis is regulated by a molecular oscillator, the segmentation clock, driving cyclic gene expression in the unsegmented paraxial mesoderm, from which somites derive. Three signaling pathways underlie the molecular mechanism of the oscillator: Wnt, FGF, and Notch. In particular, Notch has been demonstrated to be an essential piece in the intricate somitogenesis regulation puzzle. Notch is required to synchronize oscillations between neighboring cells, and is moreover necessary for somite formation and clock gene oscillations. Following ligand activation, the Notch receptor is cleaved to liberate the active intracellular domain (NICD) and during somitogenesis NICD itself is produced and degraded in a cyclical manner, requiring tightly regulated, and coordinated turnover. It was recently shown that the pace of the segmentation clock is exquisitely sensitive to levels/stability of NICD. In this review, we focus on what is known about the mechanisms regulating NICD turnover, crucial to the activity of the pathway in all developmental contexts. To date, the regulation of NICD stability has been attributed to phosphorylation of the PEST domain which serves to recruit the SCF/Sel10/FBXW7 E3 ubiquitin ligase complex involved in NICD turnover. We will describe the pathophysiological relevance of NICD-FBXW7 interaction, whose defects have been linked to leukemia and a variety of solid cancers.

Global phosphoproteomic profiling reveals perturbed signaling in a mouse model of dilated cardiomyopathy

Phospholamban (PLN) plays a central role in Ca²⁺ homeostasis in cardiac myocytes through regulation of the sarco(endo)plasmic reticulum Ca²⁺-ATPase 2A (SERCA2A) Ca²⁺ pump. An inherited mutation converting arginine residue 9 in PLN to cysteine (R9C) results in dilated cardiomyopathy (DCM) in humans and transgenic mice, but the downstream signaling defects leading to decompensation and heart failure are poorly understood. Here we used precision mass spectrometry to study the global phosphorylation dynamics of 1,887 cardiac phosphoproteins in early affected heart tissue in a transgenic R9C mouse model of DCM compared with wild-type littermates. Dysregulated phosphorylation sites were quantified after affinity capture and identification of 3,908 phosphopeptides from fractionated whole-heart homogenates. Global statistical enrichment analysis of the differential phosphoprotein patterns revealed selective perturbation of signaling pathways regulating cardiovascular activity in early stages of DCM. Strikingly, dysregulated signaling through the Notch-1 receptor, recently linked to cardiomyogenesis and embryonic cardiac stem cell development and differentiation but never directly implicated in DCM before, was a prominently perturbed pathway. We verified alterations in Notch-1 downstream components in early symptomatic R9C transgenic mouse cardiomyocytes compared with wild type by immunoblot analysis and confocal immunofluorescence microscopy. These data reveal unexpected connections between stress-regulated cell signaling networks, specific protein kinases, and downstream effectors essential for proper cardiac function.

The CSL proteins, versatile transcription factors and context dependent corepressors of the notch signaling pathway

The Notch signaling pathway is a reiteratively used cell to cell communication pathway that triggers pleiotropic effects. The correct regulation of the pathway permits the efficient regulation of genes involved in cell fate decision throughout development. This activity relies notably on the CSL proteins, (an acronym for CBF-1/RBPJ-κ in Homo sapiens/Mus musculus respectively, Suppressor of Hairless in Drosophila melanogaster, Lag-1 in Caenorhabditis elegans) which is the unique transcription factor and DNA binding protein involved in this pathway. The CSL proteins have the capacity to recruit activation or repression complexes according to the cellular context. The aim of this review is to describe the different co-repressor proteins that interact directly with CSL proteins to form repression complexes thereby regulating the Notch signaling pathway in animal cells to give insights into the paralogous evolution of these co-repressors in higher eumetazoans and their subsequent effects at developmental processes.

Phosphorylation-dependent regulation of Notch1 signaling: the fulcrum of Notch1 signaling

Notch signaling plays a pivotal role in cell fate determination, cellular development, cellular self-renewal, tumor progression, and has been linked to developmental disorders and carcinogenesis. Notch1 is activated through interactions with the ligands of neighboring cells, and acts as a transcriptional activator in the nucleus. The Notch1 intracellular domain (Notch1-IC) regulates the expression of target genes related to tumor development and progression. The Notch1 protein undergoes modification after translation by posttranslational modification enzymes. Phosphorylation modification is critical for enzymatic activation, complex formation, degradation, and subcellular localization. According to the nuclear cycle, Notch1-IC is degraded by E3 ligase, FBW7 in the nucleus via phosphorylation-dependent degradation. Here, we summarize the Notch signaling pathway, and resolve to understand the role of phosphorylation in the regulation of Notch signaling as well as to understand its relation to cancer.

Notch1 Autoactivation via Transcriptional Regulation of Furin, Which Sustains Notch1 Signaling by Processing Notch1-Activating Proteases ADAM10 and Membrane Type 1 Matrix Metalloproteinase

Notch1 is an evolutionarily conserved transmembrane receptor involved in melanoma growth. Notch1 is first cleaved by furin in the Golgi apparatus to produce the biologically active heterodimer. Following ligand binding, Notch1 is cleaved at the cell membrane by proteases such as ADAM10 and -17 and membrane type 1 matrix metalloproteinase (MT1-MMP), the latter of which we recently identified as a novel protease involved in Notch1 processing. The final cleavage is γ-secretase dependent and releases the active Notch intracellular domain (NIC). We now demonstrate that Notch1 directly regulates furin expression. Aside from activating Notch1, furin cleaves and activates several proteases, including MT1-MMP, ADAM10, and ADAM17. By chromatin immunoprecipitation and a reporter assay, we demonstrate that Notch1 binds at position -1236 of the furin promoter and drives furin expression. The Notch1-dependent enhancement of furin expression increases the activities of MT1-MMP and ADAM10 but not that of ADAM17, as demonstrated by short hairpin RNA (shRNA) knockdown of furin, and promotes the cleavage of Notch1 itself. These data highlight a novel positive-feedback loop whereby Notch1-dependent furin expression can induce Notch1 signaling by increasing Notch1 processing and by potentiating the activity of the proteases responsible for Notch1 activation. This leads to Notch1 signal amplification, which can promote melanoma tumor growth and progression, as demonstrated by the inhibition of cell migration and invasion upon furin inhibition downstream of Notch1. Disruption of such feedback signaling might represent an avenue for the treatment of melanoma.

Changes in Communication between Muscle Stem Cells and their Environment with Aging

Aging is associated with both muscle weakness and a loss of muscle mass, contributing towards overall frailty in the elderly. Aging skeletal muscle is also characterised by a decreasing efficiency in repair and regeneration, together with a decline in the number of adult stem cells. Commensurate with this are general changes in whole body endocrine signalling, in local muscle secretory environment, as well as in intrinsic properties of the stem cells themselves. The present review discusses the various mechanisms that may be implicated in these age-associated changes, focusing on aspects of cell-cell communication and long-distance signalling factors, such as levels of circulating growth hormone, IL-6, IGF1, sex hormones, and inflammatory cytokines. Changes in the local environment are also discussed, implicating IL-6, IL-4, FGF-2, as well as other myokines, and processes that lead to thickening of the extra-cellular matrix. These factors, involved primarily in communication, can also modulate the intrinsic properties of muscle stem cells, including reduced DNA accessibility and repression of specific genes by methylation. Finally we discuss the decrease in the stem cell pool, particularly the failure of elderly myoblasts to re-quiesce after activation, and the consequences of all these changes on general muscle homeostasis.

Non-small-cell lung carcinoma: role of the Notch signaling pathway

Notch signaling plays a pivotal role during embryogenesis. It regulates three fundamental processes: lateral inhibition, boundary formation, and lineage specification. During post-natal life, Notch receptors and ligands control critical cell fate decisions both in compartments that are undergoing differentiation and in pluripotent progenitor cells. First recognized as a potent oncogene in certain lymphoblastic leukemias and mesothelium-derived tissue, the role of Notch signaling in epithelial, solid tumors has been far more controversial. The overall consequence of Notch signaling and which form of the Notch receptor drives malignancy in humans is deeply debated. Most likely, this is due to the high degree of context-dependent effects of Notch signaling. More recently, it has been discovered that Notch (especially Notch-1) can exert different, even opposite effects in the same tissue under differing microenvironmental conditions. Further complicating the understanding of Notch receptors is the recently discovered role for non-canonical Notch signaling. Additionally, the most frequent Notch signaling antagonists used in biological systems have been inhibitors of the transmembrane protease complex γ-secretase, which itself processes a plethora of class one transmembrane proteins and thus cannot be considered a Notch-specific upstream regulator. Here we review the available empirical evidence gathered in recent years concerning Notch receptors and ligands in non-small-cell lung carcinoma (NSCLC). Although an overview of the field reveals seemingly contradicting results, we propose that Notch signaling can be exploited as a therapeutic target in NSCLC and represents a promising complement to the current arsenal utilized to combat this malignancy, particularly in targeting NSCLC tissues under specific environmental conditions, such as hypoxia.

UXT potentiates angiogenesis by attenuating Notch signaling

Angiogenesis is spatially and temporally orchestrated by a myriad of signaling pathways, including the Notch signaling pathway. Here, we identified UXT as an evolutionarily conserved and developmentally expressed protein, indispensable for intersegmental vessel (ISV) formation in zebrafish. Deficiency of UXT in zebrafish embryos results in shorter ISVs, loss of tip cell behavior, and impairment of endothelial cell migration and division. Significantly, UXT attenuates the expression of the Notch-responsive genes in vitro and in vivo. Mechanistically, UXT binds to the promoters of the Notch signaling target genes and specifically interacts with the transactivation region domain of the Notch intracellular domain (NICD), impairing the interaction between NICD and the transcription factor RBP-Jκ endogenously. This prevents RBP-Jκ/CSL from activation and thus inhibits the consequent gene inductions. Furthermore, blockade of Notch signaling rescues the angiogenesis defect caused by UXT knockdown both in vitro and in vivo. Taken together, the data presented in this study characterize UXT as a novel repressor of Notch signaling, shedding new light on the molecular regulation of angiogenesis.

Summary: UXT/ART27 is a novel repressor of Notch signaling that impairs the interaction between NICD and RBP-Jκ/CSL and is indispensable for zebrafish intersegmental vessel formation.

Inhibition of SNW1 association with spliceosomal proteins promotes apoptosis in breast cancer cells

RNA splicing is a fundamental process for protein synthesis. Recent studies have reported that drugs that inhibit splicing have cytotoxic effects on various tumor cell lines. In this report, we demonstrate that depletion of SNW1, a component of the spliceosome, induces apoptosis in breast cancer cells. Proteomics and biochemical analyses revealed that SNW1 directly associates with other spliceosome components, including EFTUD2 (Snu114) and SNRNP200 (Brr2). The SKIP region of SNW1 interacted with the N-terminus of EFTUD2 as well as two independent regions in the C-terminus of SNRNP200. Similar to SNW1 depletion, knockdown of EFTUD2 increased the numbers of apoptotic cells. Furthermore, we demonstrate that exogenous expression of either the SKIP region of SNW1 or the N-terminus region of EFTUD2 significantly promoted cellular apoptosis. Our results suggest that the inhibition of SNW1 or its associating proteins may be a novel therapeutic strategy for cancer treatment.

Signaling pathways in breast cancer: therapeutic targeting of the microenvironment

Breast cancer is the most common cancer in women worldwide. Understanding the biology of this malignant disease is a prerequisite for selecting an appropriate treatment. Cell cycle alterations are seen in many cancers, including breast cancer. Newly popular targeted agents in breast cancer include cyclin dependent kinase inhibitors (CDKIs) which are agents inhibiting the function of cyclin dependent kinases (CDKs) and agents targeting proto-oncogenic signaling pathways like Notch, Wnt, and SHH (Sonic hedgehog). CDKIs are categorized as selective and non-selective inhibitors of CDK. CDKIs have been tried as monotherapy and combination therapy. The CDKI Palbocyclib is now a promising therapeutic in breast cancer. This drug recently entered phase III trial for estrogen receptor (ER) positive breast cancer after showing encouraging results in progression free survival in a phase II trials. The tumor microenvironment is now recognized as a significant factor in cancer treatment response. The tumor microenvironment is increasingly considered as a target for combination therapy of breast cancer. Recent findings in the signaling pathways in breast cancer are herein summarized and discussed. Furthermore, the therapeutic targeting of the microenvironment in breast cancer is also considered.

SKIP and BIR-1/Survivin have potential to integrate proteome status with gene expression

SKIP and BIR are evolutionarily conserved proteins; SKIP (SKP-1) is a known transcription and splicing cofactor while BIR-1/Survivin regulates cell division, gene expression and development. Their loss of function induces overlapping developmental phenotypes. We searched for SKP-1 and BIR-1 interaction on protein level using yeast two-hybrid screens and identified partially overlapping categories of proteins as SKIP-1 and BIR-1 interactors. The interacting proteins included ribosomal proteins, transcription factors, translation factors and cytoskeletal and motor proteins suggesting involvement in multiple protein complexes. To visualize the effect of BIR-1 on the proteome in Caenorhabditis elegans we induced a short time pulse BIR-1 overexpression in synchronized L1 larvae. This led to a dramatic alteration of the whole proteome pattern indicating that BIR-1 alone has the capacity to alter the chromatographic profile of many target proteins including proteins found to be interactors in yeast two hybrid screens. The results were validated for ribosomal proteins RPS3 and RPL5, non-muscle myosin and TAC-1, a transcription cofactor and a centrosome associated protein. Together, these results suggest that SKP-1 and BIR-1 are multifunctional proteins that form multiple protein complexes in both shared and distinct pathways and have the potential to connect proteome signals with the regulation of gene expression.

BIOLOGICAL SIGNIFICANCE

The genomic organization of the genes encoding BIR-1 and SKIP (SKP-1) in C. elegans have suggested that these two factors, each evolutionarily conserved, have related functions. However, these functional connections have remained elusive and underappreciated in light of limited information from C. elegans and other biological systems. Our results provide further evidence for a functional link between these two factors and suggest they may transmit proteome signals towards the regulation of gene expression.

Simplet/Fam53b is required for Wnt signal transduction by regulating β-catenin nuclear localization

Canonical β-catenin-dependent Wnt signal transduction is important for several biological phenomena, such as cell fate determination, cell proliferation, stem cell maintenance and anterior-posterior axis formation. The hallmark of canonical Wnt signaling is the translocation of β-catenin into the nucleus where it activates gene transcription. However, the mechanisms regulating β-catenin nuclear localization are poorly understood. We show that Simplet/Fam53B (Smp) is required for Wnt signaling by positively regulating β-catenin nuclear localization. In the zebrafish embryo, the loss of smp blocks the activity of two β-catenin-dependent reporters and the expression of Wnt target genes, and prevents nuclear accumulation of β-catenin. Conversely, overexpression of smp increases β-catenin nuclear localization and transcriptional activity in vitro and in vivo. Expression of mutant Smp proteins lacking either the nuclear localization signal or the β-catenin interaction domain reveal that the translocation of Smp into the nucleus is essential for β-catenin nuclear localization and Wnt signaling in vivo. We also provide evidence that mammalian Smp is involved in regulating β-catenin nuclear localization: the protein colocalizes with β-catenin-dependent gene expression in mouse intestinal crypts; siRNA knockdown of Smp reduces β-catenin nuclear localization and transcriptional activity; human SMP mediates β-catenin transcriptional activity in a dose-dependent manner; and the human SMP protein interacts with human β-catenin primarily in the nucleus. Thus, our findings identify the evolutionary conserved SMP protein as a regulator of β-catenin-dependent Wnt signal transduction.

Stochastic simulation of notch signaling reveals novel factors that mediate the differentiation of neural stem cells

Notch signaling controls cell fate decisions and regulates multiple biological processes, such as cell proliferation, differentiation, and apoptosis. Computational modeling of the deterministic simulation of Notch signaling has provided important insight into the possible molecular mechanisms that underlie the switch from the undifferentiated stem cell to the differentiated cell. Here, we constructed a stochastic model of a Notch signaling model containing Hes1, Notch1, RBP-Jk, Mash1, Hes6, and Delta. mRNA and protein were represented as a discrete state, and 334 reactions were employed for each biochemical reaction using a graphics processing unit-accelerated Gillespie scheme. We employed the tuning of 40 molecular mechanisms and revealed several potential mediators capable of enabling the switch from cell stemness to differentiation. These effective mediators encompass different aspects of cellular regulations, including the nuclear transport of Hes1, the degradation of mRNA (Hes1 and Notch1) and protein (Notch1), the association between RBP-Jk and Notch intracellular domain (NICD), and the cleavage efficiency of the NICD. These mechanisms overlap with many modifiers that have only recently been discovered to modulate the Notch signaling output, including microRNA action, ubiquitin-mediated proteolysis, and the competitive binding of the RBP-Jk-DNA complex. Moreover, we identified the degradation of Hes1 mRNA and nuclear transport of Hes1 as the dominant mechanisms that were capable of abolishing the cell state transition induced by other molecular mechanisms.

Prostate tumor OVerexpressed-1 (PTOV1) down-regulates HES1 and HEY1 notch targets genes and promotes prostate cancer progression

BACKGROUND

PTOV1 is an adaptor protein with functions in diverse processes, including gene transcription and protein translation, whose overexpression is associated with a higher proliferation index and tumor grade in prostate cancer (PC) and other neoplasms. Here we report its interaction with the Notch pathway and its involvement in PC progression.

METHODS

Stable PTOV1 knockdown or overexpression were performed by lentiviral transduction. Protein interactions were analyzed by co-immunoprecipitation, pull-down and/or immunofluorescence. Endogenous gene expression was analyzed by real time RT-PCR and/or Western blotting. Exogenous promoter activities were studied by luciferase assays. Gene promoter interactions were analyzed by chromatin immunoprecipitation assays (ChIP). In vivo studies were performed in the Drosophila melanogaster wing, the SCID-Beige mouse model, and human prostate cancer tissues and metastasis. The Excel package was used for statistical analysis.

RESULTS

Knockdown of PTOV1 in prostate epithelial cells and HaCaT skin keratinocytes caused the upregulation, and overexpression of PTOV1 the downregulation, of the Notch target genes HEY1 and HES1, suggesting that PTOV1 counteracts Notch signaling. Under conditions of inactive Notch signaling, endogenous PTOV1 associated with the HEY1 and HES1 promoters, together with components of the Notch repressor complex. Conversely, expression of active Notch1 provoked the dismissal of PTOV1 from these promoters. The antagonist role of PTOV1 on Notch activity was corroborated in the Drosophila melanogaster wing, where human PTOV1 exacerbated Notch deletion mutant phenotypes and suppressed the effects of constitutively active Notch. PTOV1 was required for optimal in vitro invasiveness and anchorage-independent growth of PC-3 cells, activities counteracted by Notch, and for their efficient growth and metastatic spread in vivo. In prostate tumors, the overexpression of PTOV1 was associated with decreased expression of HEY1 and HES1, and this correlation was significant in metastatic lesions.

CONCLUSIONS

High levels of the adaptor protein PTOV1 counteract the transcriptional activity of Notch. Our evidences link the pro-oncogenic and pro-metastatic effects of PTOV1 in prostate cancer to its inhibitory activity on Notch signaling and are supportive of a tumor suppressor role of Notch in prostate cancer progression.

SKIP expression is correlated with clinical prognosis in patients with bladder cancer

The Ski-interacting protein (SKIP) is a transcriptional cofactor distinct from other cofactors and is involved in regulation of many cancer-related proteins. However, its distribution and clinical significances in bladder cancer remains poorly understood. In this study, Quantitative real-time PCR and immunohistochemistry were performed to detect the expression of SKIP in clinical bladder cancer samples. In addition, the correlation of SKIP expression and clinicopathological features and clinical outcomes were analyzed. The expression levels of SKIP in clinical bladder cancer were much higher than that in paired adjacent noncancerous tissues. High expression of SKIP was closely related with histological grades and the poor prognosis of bladder cancer. Based on our data, we speculated that SKIP may be a potential prognostic marker in bladder cancer.

BEND6 is a nuclear antagonist of Notch signaling during self-renewal of neural stem cells

The activity of the Notch pathway revolves around a CSL-class transcription factor, which recruits distinct complexes that activate or repress target gene expression. The co-activator complex is deeply conserved and includes the cleaved Notch intracellular domain (NICD) and Mastermind. By contrast, numerous CSL co-repressor proteins have been identified, and these are mostly different between invertebrate and vertebrate systems. In this study, we demonstrate that mammalian BEND6 is a neural BEN-solo factor that shares many functional attributes with Drosophila Insensitive, a co-repressor for the Drosophila CSL factor. BEND6 binds the mammalian CSL protein CBF1 and antagonizes Notch-dependent target activation. In addition, its association with Notch- and CBF1-regulated enhancers is promoted by CBF1 and antagonized by activated Notch. In utero electroporation experiments showed that ectopic BEND6 inhibited Notch-mediated self-renewal of neocortical neural stem cells and promoted neurogenesis. Conversely, knockdown of BEND6 increased NSC self-renewal in wild-type neocortex, and exhibited genetic interactions with gain and loss of Notch pathway activity. We recapitulated all of these findings in cultured neurospheres, in which overexpression and depletion of BEND6 caused reciprocal effects on neural stem cell renewal and neurogenesis. These data reveal a novel mammalian CSL co-repressor in the nervous system, and show that the Notch-inhibitory activity of certain BEN-solo proteins is conserved between flies and mammals.

Notch signaling at a glance

Cell-cell interactions define a quintessential aspect of multicellular development. Metazoan morphogenesis depends on a handful of fundamental, conserved cellular interaction mechanisms, one of which is defined by the Notch signaling pathway. Signals transmitted through the Notch surface receptor have a unique developmental role: Notch signaling links the fate of one cell with that of a cellular neighbor through physical interactions between the Notch receptor and the membrane-bound ligands that are expressed in an apposing cell. The developmental outcome of Notch signals is strictly dependent on the cellular context and can influence differentiation, proliferation and apoptotic cell fates. The Notch pathway is conserved across species (Artavanis-Tsakonas et al., 1999; Bray, 2006; Kopan and Ilagan, 2009). In humans, Notch malfunction has been associated with a diverse range of diseases linked to changes in cell fate and cell proliferation including cancer (Louvi and Artavanis-Tsakonas, 2012). In this Cell Science at a Glance article and the accompanying poster we summarize the molecular biology of Notch signaling, its role in development and its relevance to disease.

Morphogen pathways as molecular targets for the treatment of fibrosis in systemic sclerosis

Wnt-, Hedgehog- and Notch-signaling cascades are morphogen pathways that play crucial roles in development and tissue homeostasis. While morphogen pathways are tightly regulated at multiple levels, inappropriate activation of Wnt, Hedgehog and Notch signaling has been implicated into the pathogenesis of various diseases. In particular, Wnt, Hedgehog and Notch signaling have emerged as central players in the pathogenesis of fibrotic diseases. Here, we will review the pro-fibrotic effects of Wnt, Hedgehog and Notch signaling in systemic sclerosis (SSc), prototypical systemic fibrotic disease. Wnt, Hedgehog and Notch pathways are activated in SSc. They potently stimulate fibroblasts to differentiate into myofibroblasts and to release collagen and other extracellular matrix components. Genetic or pharmacological inhibition of morphogen pathways effectively prevents experimental fibrosis in different preclinical models and induces regression of pre-established fibrosis. As several inhibitors of Wnt, Hedgehog and Notch have recently been developed with first ones being already approved for clinical trials, morphogen pathways maybe a novel approach for the treatment of fibrosis.

Jagged-1-mediated activation of notch signalling induces adipogenesis of adipose-derived stem cells

OBJECTIVES

Notch signalling plays an important role in many cell activities, involving proliferation, migration, differentiation and cell death. The aim of this study was to investigate effects of such signalling on adipogenesis of mouse adipose-derived stem cells (mASCs).

MATERIALS AND METHODS

Jagged1 (50 and 100 ng/ml) was added to mASCs to activate Notch signalling, 2 days before adipogenic induction. At 5 and 7 days after induction, oil red-O staining was performed to evaluate lipid accumulation. Then real-time PCR was performed to examine expression of Notch downstream genes (Notch-1, -2, Hes-1 and Hey-1) and adipogenic transcription factor (PPAR-γ). Expressions of Hes-1 and PPAR-γ at protein level were confirmed by immunofluorescence staining.

RESULTS

Our data indicated that Jagged1 promoted adipogenic differentiation of mASCs. Moreover, Jagged1 also increased expression of Notch downstream genes and PPAR-γ. Expressions of Hes-1 and PPAR-γ were found to be enhanced in Jagged1 pre-treated mASCs when compared to controls.

DISCUSSION

The results led to the conclusion that activation of Notch signalling had stimulated adipogenesis of mASCs in the presence of adipogenic medium by promoting expression of PPAR-γ.