Notum is required for neural and head induction via Wnt deacylation, oxidation, and inactivation

NOTUM promotes thermogenic capacity and protects against diet-induced obesity in male mice

We recently showed that NOTUM, a liver-secreted Wnt inhibitor, can acutely promote browning of white adipose. We now report studies of chronic overexpression of NOTUM in liver indicating that it protects against diet-induced obesity and improves glucose homeostasis in mice. Adeno-associated virus (AAV) vectors were used to overexpress GFP or mouse Notum in the livers of male C57BL/6J mice and the mice were fed an obesifying diet. After 14 weeks of high fat, high sucrose diet feeding, the AAV-Notum mice exhibited decreased obesity and improved glucose tolerance compared to the AAV-GFP mice. Gene expression and immunoblotting analysis of the inguinal fat and brown fat revealed increased expression of beige/brown adipocyte markers in the AAV-Notum group, suggesting enhanced thermogenic capacity by NOTUM. A β3 adrenergic receptor agonist-stimulated lipolysis test suggested increased lipolysis capacity by NOTUM. The levels of collagen and C–C motif chemokine ligand 2 (CCL2) in the epididymal white adipose tissue of the AAV-Notum mice were significantly reduced, suggesting decreased fibrosis and inflammation, respectively. RNA sequencing analysis of inguinal white adipose of 4-week chow diet-fed mice revealed a highly significant enrichment of extracellular matrix (ECM) functional cluster among the down-regulated genes in the AAV-Notum group, suggesting a potential mechanism contributing to improved glucose homeostasis. Our in vitro studies demonstrated that recombinant human NOTUM protein blocked the inhibitory effects of WNT3A on brown adipocyte differentiation. Furthermore, NOTUM attenuated WNT3A’s effects on upregulation of TGF-β signaling and its downstream targets. Overall, our data suggest that NOTUM modulates adipose tissue function by promoting thermogenic capacity and inhibiting fibrosis through inhibition of Wnt signaling.

Wnt signaling activation: targets and therapeutic opportunities for stem cell therapy and regenerative medicine

Wnt proteins are secreted morphogens that play critical roles in embryonic development, stem cell proliferation, self-renewal, tissue regeneration and remodeling in adults. While aberrant Wnt signaling contributes to diseases such as cancer, activation of Wnt/β-catenin signaling is a target of interest in stem cell therapy and regenerative medicine. Recent high throughput screenings from chemical and biological libraries, combined with improved gene expression reporter assays of Wnt/β-catenin activation together with rational drug design, led to the development of a myriad of Wnt activators, with different mechanisms of actions. Among them, Wnt mimics, antibodies targeting Wnt inhibitors, glycogen-synthase-3β inhibitors, and indirubins and other natural product derivatives are emerging modalities to treat bone, neurodegenerative, eye, and metabolic disorders, as well as prevent ageing. Nevertheless, the creation of Wnt-based therapies has been hampered by challenges in developing potent and selective Wnt activators without off-target effects, such as oncogenesis. On the other hand, to avoid these risks, their use to promote ex vivo expansion during tissue engineering is a promising application.

Ghrelin octanoylation by ghrelin O-acyltransferase: protein acylation impacting metabolic and neuroendocrine signalling

The acylated peptide hormone ghrelin impacts a wide range of physiological processes but is most well known for controlling hunger and metabolic regulation. Ghrelin requires a unique posttranslational modification, serine octanoylation, to bind and activate signalling through its cognate GHS-R1a receptor. Ghrelin acylation is catalysed by ghrelin O-acyltransferase (GOAT), a member of the membrane-bound O-acyltransferase (MBOAT) enzyme family. The ghrelin/GOAT/GHS-R1a system is defined by multiple unique aspects within both protein biochemistry and endocrinology. Ghrelin serves as the only substrate for GOAT within the human proteome and, among the multiple hormones involved in energy homeostasis and metabolism such as insulin and leptin, acts as the only known hormone in circulation that directly stimulates appetite and hunger signalling. Advances in GOAT enzymology, structural modelling and inhibitor development have revolutionized our understanding of this enzyme and offered new tools for investigating ghrelin signalling at the molecular and organismal levels. In this review, we briefly summarize the current state of knowledge regarding ghrelin signalling and ghrelin/GOAT enzymology, discuss the GOAT structural model in the context of recently reported MBOAT enzyme superfamily member structures, and highlight the growing complement of GOAT inhibitors that offer options for both ghrelin signalling studies and therapeutic applications.

Prednisolone induces osteocytes apoptosis by promoting Notum expression and inhibiting PI3K/AKT/GSK3β/β-catenin pathway

The apoptosis of mature osteocytes is the main factor causing damage to the microstructure of cortical bone in glucocorticoid-induced osteoporosis (GIOP). Our previous research found damaged areas and empty osteocytes lacunae in the tibial cortical bone of GIOP mice. However, the specific mechanism has not been clarified. Recently, a study showed that the quality of the cortical bone significantly increased by knocking out Notum, a gene encoding α/β hydrolase. However, it is not clear whether Notum affects cortical bone remodeling by participating in glucocorticoids (GCs)-induced apoptosis of osteocytes. The present study aimed to explore the correlation between Notum, osteocytes apoptosis, and cortical bone quality in GIOP. Prednisolone acetate was intragastrically administered to mice for two weeks. Histochemical staining was applied to evaluate changes in GIOP and Notum expression. Osteocytes were stimulated with prednisolone, and cell viability was assessed via CCK8. Hoechst 33342/PI staining, flow cytometry, RT-PCR, and western blot were used to detect osteocytes apoptosis, siRNA transfection efficiency, and expressions of pathway related factors. The results showed that the number of empty osteocytes lacunae increased in GIOP mice. TUNEL-stained apoptotic osteocytes and Notum immuno-positive osteocytes were also observed. Furthermore, prednisolone was found to promote Notum expression and osteocytes apoptosis in vitro. Knocking down Notum via siRNA partially restored osteocytes apoptosis and phosphoinositide 3-kinase (PI3K)/protein kinase B (AKT)/glycogen synthase kinase-3β (GSK3β)/β-catenin pathway. These findings showed GCs-induced osteocytes apoptosis by promoting Notum expression and inhibiting PI3K/AKT/GSK3β/β-catenin pathway. Thus, Notum might be a potential therapeutic target for the treatment of GIOP.

RNA m6A Methyltransferase Mettl3 Regulates Spatial Neural Patterning in Xenopus laevis

N⁶-Methyladenosine (m6A) is the most prevalent internal RNA modification and has a widespread impact on mRNA stability and translation. Methyltransferase-like 3 (Mettl3) is a methyltransferase responsible for RNA m6A modification, and it is essential for early embryogenesis before or during gastrulation in mice and zebrafish. However, due to the early embryonic lethality, loss-of-function phenotypes of Mettl3 beyond gastrulation, especially during neurulation stages when spatial neural patterning takes place, remain elusive. Here, we address multiple roles of Mettl3 during Xenopus neurulation in anteroposterior neural patterning, neural crest specification, and neuronal cell differentiation. Knockdown of Mettl3 causes anteriorization of neurulae and tailbud embryos along with the loss of neural crest and neuronal cells. Knockdown of the m6A reader Ythdf1 and mRNA degradation factors, such as 3' to 5' exonuclease complex component Lsm1 or mRNA uridylation enzyme Tut7, also show similar neural patterning defects, suggesting that m6A-dependent mRNA destabilization regulates spatial neural patterning in Xenopus. We also address that canonical WNT signaling is inhibited in Mettl3 morphants, which may underlie the neural patterning defects of the morphants. Altogether, this study reveals functions of Mettl3 during spatial neural patterning in Xenopus.

Notum suppresses the osteogenic differentiation of periodontal ligament stem cells through the Wnt/Beta catenin signaling pathway

OBJECTIVES

The aims of this study were to explore: (ⅰ) the effect of Notum on periodontitis in vivo; (ⅱ) the effect of Notum on the osteogenic differentiation of human periodontal ligament stem cells (hPDLSCs) in vitro; and (ⅲ) the potential mechanism of Notum in inhibiting the osteogenic differentiation of hPDLSCs.

DESIGN

C57BL/6J mice were randomly assigned into two groups: control group (n = 4) and periodontitis group (n = 4). Immunohistochemical staining was used to evaluate the expression of Notum. In in vitro experiments, Western blot, qRT- PCR and ELISA were used to examine the expression of Notum in a lipopolysaccharide-induced inflammation model. Alkaline phosphatase staining was used to evaluate alkaline phosphatase activity. Western blot and qRT - PCR were used to measure the expression of osteogenic-related markers after adding human recombinant Notum and Notum inhibitor ABC99. In addition, LiCl, an agonist of the Wnt/Beta-catenin signaling pathway, was added to explore using Western blot whether Notum was involved in regulating the osteogenic differentiation of human periodontal ligament stem cells through the Wnt/Beta-catenin signaling pathway.

RESULTS

Notum was highly expressed in periodontal tissues of mice and lipopolysaccharide-induced inflammation cell model. The protein and messenger ribonucleic acid levels of hPDLSCs osteogenic markers were reduced after adding human recombinant Notum. However, the inhibitory effect of Notum on the osteogenic differentiation of hPDLSCs could be significantly reversed by adding LiCl.

CONCLUSION

These results demonstrated that Notum inhibited the osteogenic differentiation of hPDLSCs probably via the Wnt/Beta-catenin the downstream signaling pathway.

Cell Biology of Canonical Wnt Signaling

Wnt signaling has multiple functions beyond the transcriptional effects of β-catenin stabilization. We review recent investigations that uncover new cell physiological effects through the regulation of Wnt receptor endocytosis, Wnt-induced stabilization of proteins (Wnt-STOP), macropinocytosis, increase in lysosomal activity, and metabolic changes. Many of these growth-promoting effects of canonical Wnt occur within minutes and are independent of new protein synthesis. A key element is the sequestration of glycogen synthase kinase 3 (GSK3) inside multivesicular bodies and lysosomes. Twenty percent of human proteins contain consecutive GSK3 phosphorylation motifs, which in the absence of Wnt can form phosphodegrons for polyubiquitination and proteasomal degradation. Wnt signaling by either the pharmacological inhibition of GSK3 or the loss of tumor-suppressor proteins, such as adenomatous polyposis coli (APC) and Axin1, increases lysosomal acidification, anabolic metabolites, and macropinocytosis, which is normally repressed by the GSK3-Axin1-APC destruction complex. The combination of these cell physiological effects drives cell growth. Expected final online publication date for the Annual Review of Cell and Developmental Biology, Volume 37 is October 2021. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Notum deacylates octanoylated ghrelin

OBJECTIVES

The only proteins known to be modified by O-linked lipidation are Wnts and ghrelin, and enzymatic removal of this post-translational modification inhibits ligand activity. Indeed, the Wnt-deacylase activity of Notum is the basis of its ability to act as a feedback inhibitor of Wnt signalling. Whether Notum also deacylates ghrelin has not been determined.

METHODS

We used mass spectrometry to assay ghrelin deacylation by Notum and co-crystallisation to reveal enzyme-substrate interactions at the atomic level. CRISPR/Cas technology was used to tag endogenous Notum and assess its localisation in mice while liver-specific Notum knock-out mice allowed us to investigate the physiological role of Notum in modulating the level of ghrelin deacylation.

RESULTS

Mass spectrometry detected the removal of octanoyl from ghrelin by purified active Notum but not by an inactive mutant. The 2.2 Å resolution crystal structure of the Notum-ghrelin complex showed that the octanoyl lipid was accommodated in the hydrophobic pocket of the Notum. The knock-in allele expressing HA-tagged Notum revealed that Notum was produced in the liver and present in the bloodstream, albeit at a low level. Liver-specific inactivation of Notum in animals fed a high-fat diet led to a small but significant increase in acylated ghrelin in the circulation, while no such increase was seen in wild-type animals on the same diet.

CONCLUSIONS

Overall, our data demonstrate that Notum can act as a ghrelin deacylase, and that this may be physiologically relevant under high-fat diet conditions. Our study therefore adds Notum to the list of enzymes, including butyrylcholinesterase and other carboxylesterases, that modulate the acylation state of ghrelin. The contribution of multiple enzymes could help tune the activity of this important hormone to a wide range of physiological conditions.

Small-molecule inhibitors of carboxylesterase Notum

Notum has recently been identified as a negative regulator of Wnt signaling through the removal of an essential palmitoleate group from Wnt proteins. There are emerging reports that Notum plays a role in human disease, with published data suggesting that targeting Notum could represent a new therapeutic approach for treating cancer, osteoporosis and neurodegenerative disorders. Complementary hit-finding strategies have been applied with successful approaches that include high-throughput screening, activity-based protein profiling, screening of fragment libraries and virtual screening campaigns. Structural studies are accelerating the discovery of new inhibitors of Notum. Three fit-for-purpose examples are LP-922056, ABC99 and ARUK3001185. The application of these small-molecule inhibitors is helping to further advance an understanding of the role Notum plays in human disease.

The Medicinal Chemistry of Caffeine

The purine alkaloid caffeine is the most widely consumed psychostimulant drug in the world and has multiple beneficial pharmacological activities, for example, in neurodegenerative diseases. However, despite being an extensively studied bioactive natural product, the mechanistic understanding of caffeine's pharmacological effects is incomplete. While several molecular targets of caffeine such as adenosine receptors and phosphodiesterases have been known for decades and inspired numerous medicinal chemistry programs, new protein interactions of the xanthine are continuously discovered providing potentially improved pharmacological understanding and a molecular basis for future medicinal chemistry. In this Perspective, we gather knowledge on the confirmed protein interactions, structure activity relationship, and chemical biology of caffeine on well-known and upcoming targets. The diversity of caffeine's molecular activities on receptors and enzymes, many of which are abundant in the CNS, indicates a complex interplay of several mechanisms contributing to neuroprotective effects and highlights new targets as attractive subjects for drug discovery.

Single-Cell Profiling and SCOPE-Seq Reveal Lineage Dynamics of Adult Ventricular-Subventricular Zone Neurogenesis and NOTUM as a Key Regulator

In the adult ventricular-subventricular zone (V-SVZ), neural stem cells (NSCs) generate new olfactory bulb (OB) neurons and glia throughout life. To map adult neuronal lineage progression, we profiled >56,000 V-SVZ and OB cells by single-cell RNA sequencing (scRNA-seq). Our analyses reveal the molecular diversity of OB neurons, including fate-mapped neurons, lineage progression dynamics, and an NSC intermediate enriched for Notum, which encodes a secreted WNT antagonist. SCOPE-seq technology, which links live-cell imaging with scRNA-seq, uncovers cell-size transitions during NSC differentiation and preferential NOTUM binding to proliferating neuronal precursors. Consistently, application of NOTUM protein in slice cultures and pharmacological inhibition of NOTUM in slice cultures and in vivo demonstrated that NOTUM negatively regulates V-SVZ proliferation. Timely, context-dependent neurogenesis demands adaptive signaling among neighboring progenitors. Our findings highlight a critical regulatory state during NSC activation marked by NOTUM, which attenuates WNT-stimulated proliferation in NSC progeny.

Multi-omics characterization of WNT pathway reactivation to ameliorate BET inhibitor resistance in liver cancer cells

The Bromodomain and Extra-terminal domain (BET) proteins are promising targets in treating cancers. Although BET inhibitors have been in clinical trials, they are limited by lacking of suitable biomarkers to indicate drug responses in different cancers. Here we identify DHRS2, ETV4 and NOTUM as potential biomarkers to indicate drug resistance in liver cancer cells of a recently discovered BET inhibitor, Hjp-6-171. Furthermore, we confirm that reactivation of WNT pathway, the target of NOTUM, contributes to the drug sensitivity restoration in Hjp-6-171 resistant cells. Specially, combinations of Hjp-6-171 and a GSK3β inhibitor CHIR-98014 show remarkable therapeutic effects in vitro and in vivo. Integrating RNA-seq and ChIP-seq data, we reveal the expression signature of β-catenin regulated genes is contrary in sensitive cells to that in resistant cells. We propose WNT signaling molecules such as β-catenin and ETV4 to be candidate biomarkers to indicate BET inhibitor responses in liver cancer patients.

Dysregulated Wnt Signalling in the Alzheimer's Brain

The Wnt signalling system is essential for both the developing and adult central nervous system. It regulates numerous cellular functions ranging from neurogenesis to blood brain barrier biology. Dysregulated Wnt signalling can thus have significant consequences for normal brain function, which is becoming increasingly clear in Alzheimer's disease (AD), an age-related neurodegenerative disorder that is the most prevalent form of dementia. AD exhibits a range of pathophysiological manifestations including aberrant amyloid precursor protein processing, tau pathology, synapse loss, neuroinflammation and blood brain barrier breakdown, which have been associated to a greater or lesser degree with abnormal Wnt signalling. Here we provide a comprehensive overview of the role of Wnt signalling in the CNS, and the research that implicates dysregulated Wnt signalling in the ageing brain and in AD pathogenesis. We also discuss the opportunities for therapeutic intervention in AD via modulation of the Wnt signalling pathway, and highlight some of the challenges and the gaps in our current understanding that need to be met to enable that goal.

Wnt signaling in breast cancer: biological mechanisms, challenges and opportunities

Wnt signaling is a highly conserved signaling pathway that plays a critical role in controlling embryonic and organ development, as well as cancer progression. Genome-wide sequencing and gene expression profile analyses have demonstrated that Wnt signaling is involved mainly in the processes of breast cancer proliferation and metastasis. The most recent studies have indicated that Wnt signaling is also crucial in breast cancer immune microenvironment regulation, stemness maintenance, therapeutic resistance, phenotype shaping, etc. Wnt/β-Catenin, Wnt-planar cell polarity (PCP), and Wnt-Ca2+ signaling are three well-established Wnt signaling pathways that share overlapping components and play different roles in breast cancer progression. In this review, we summarize the main findings concerning the relationship between Wnt signaling and breast cancer and provide an overview of existing mechanisms, challenges, and potential opportunities for advancing the therapy and diagnosis of breast cancer.

Runx2 Regulates Mouse Tooth Root Development Via Activation of WNT Inhibitor NOTUM

Progenitor cells are crucial in controlling organ morphogenesis. Tooth development is a well-established model for investigating the molecular and cellular mechanisms that regulate organogenesis. Despite advances in our understanding of how tooth crown formation is regulated, we have limited understanding of tooth root development. Runt-related transcription factor 2 (RUNX2) is a well-known transcription factor in osteogenic differentiation and early tooth development. However, the function of RUNX2 during tooth root formation remains unknown. We revealed in this study that RUNX2 is expressed in a subpopulation of GLI1+ root progenitor cells, and that loss of Runx2 in these GLI1+ progenitor cells and their progeny results in root developmental defects. Our results provide in vivo evidence that Runx2 plays a crucial role in tooth root development and in regulating the differentiation of root progenitor cells. Furthermore, we identified that Gli1, Pcp4, NOTUM, and Sfrp2 are downstream targets of Runx2 by integrating bulk and single-cell RNA sequencing analyses. Specifically, ablation of Runx2 results in downregulation of WNT inhibitor NOTUM and upregulation of canonical WNT signaling in the odontoblastic site, which disturbs normal odontoblastic differentiation. Significantly, exogenous NOTUM partially rescues the impaired root development in Runx2 mutant molars. Collectively, our studies elucidate how Runx2 achieves functional specificity in regulating the development of diverse organs and yields new insights into the network that regulates tooth root development. © 2020 The Authors. Journal of Bone and Mineral Research published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research (ASBMR).

Caffeine inhibits Notum activity by binding at the catalytic pocket

Notum inhibits Wnt signalling via enzymatic delipidation of Wnt ligands. Restoration of Wnt signalling by small molecule inhibition of Notum may be of therapeutic benefit in a number of pathologies including Alzheimer's disease. Here we report Notum activity can be inhibited by caffeine (IC50 19 µM), but not by demethylated caffeine metabolites: paraxanthine, theobromine and theophylline. Cellular luciferase assays show Notum-suppressed Wnt3a function can be restored by caffeine with an EC50 of 46 µM. The dissociation constant (Kd) between Notum and caffeine is 85 µM as measured by surface plasmon resonance. High-resolution crystal structures of Notum complexes with caffeine and its minor metabolite theophylline show both compounds bind at the centre of the enzymatic pocket, overlapping the position of the natural substrate palmitoleic lipid, but using different binding modes. The structural information reported here may be of relevance for the design of more potent brain-accessible Notum inhibitors.

TMEM79/MATTRIN defines a pathway for Frizzled regulation and is required for Xenopus embryogenesis

Wnt signaling through the Frizzled (FZD) family of serpentine receptors is essential for embryogenesis and homeostasis, and stringent control of the FZD protein level is critical for stem cell regulation. Through CRISPR/Cas9 genome-wide screening in human cells, we identified TMEM79/MATTRIN, an orphan multi-span transmembrane protein, as a specific inhibitor of Wnt/FZD signaling. TMEM79 interacts with FZD during biogenesis and promotes FZD degradation independent of ZNRF3/RNF43 ubiquitin ligases (R-spondin receptors). TMEM79 interacts with ubiquitin-specific protease 8 (USP8), whose activating mutations underlie human tumorigenesis. TMEM79 specifically inhibits USP8 deubiquitination of FZD, thereby governing USP8 substrate specificity and promoting FZD degradation. Tmem79 and Usp8 genes have a pre-bilaterian origin, and Tmem79 inhibition of Usp8 and Wnt signaling is required for anterior neural development and gastrulation in Xenopus embryos. TMEM79 is a predisposition gene for Atopic dermatitis, suggesting deregulation of Wnt/FZD signaling a possible cause for this most common yet enigmatic inflammatory skin disease.

Screening of a Custom-Designed Acid Fragment Library Identifies 1-Phenylpyrroles and 1-Phenylpyrrolidines as Inhibitors of Notum Carboxylesterase Activity

The Wnt family of proteins are secreted signaling proteins that play key roles in regulating cellular functions. Recently, carboxylesterase Notum was shown to act as a negative regulator of Wnt signaling by mediating the removal of an essential palmitoleate. Here we disclose two new chemical scaffolds that inhibit Notum enzymatic activity. Our approach was to create a fragment library of 250 acids for screening against Notum in a biochemical assay followed by structure determination by X-ray crystallography. Twenty fragments were identified as hits for Notum inhibition, and 14 of these fragments were shown to bind in the palmitoleate pocket of Notum. Optimization of 1-phenylpyrrole 20, guided by structure-based drug design, identified 20z as the most potent compound from this series. Similarly, the optimization of 1-phenylpyrrolidine 8 gave acid 26. This work demonstrates that inhibition of Notum activity can be achieved by small, drug-like molecules possessing favorable in vitro ADME profiles.

Roads to the Fountain of Youth? Rejuvenating Intestinal Stem Cells

The intestinal stem cells (ISCs) of old mice and humans exhibit a reduced capacity for regeneration and repair. Compromised intestinal function may play a key role in systemic aging-related changes: not only in the affected gut, but also in the nervous and cardiovascular systems. For example, progression of age-related neurodegenerative diseases such as Alzheimer's and Parkinson's has been linked to increased inflammation from gut microbiota in old mammals, which, in turn, may be linked bidirectionally with reduced ISC function. Intestinal organoid formation has been used to dissect the mechanisms of decline of ISC function. Alterations of the Wnt pathway, including downregulation of Wnt ligands in ISCs and upregulation of Wnt ligand inhibitor Notum in Paneth cells, and dysregulation of mTORC1 contribute to the observed age-related decline. Short-term fasting, caloric restriction, and peroxisome proliferator-activated receptor delta agonists have been reported to increase ISC function in adult mice. Moreover, the mTOR inhibitor rapamycin, NAD+ precursor nicotinamide riboside, and ABC99, a small molecule Notum inhibitor, have all been reported to rejuvenate ISC function in old mice and thus may have promise in humans. However, there is some controversy over the key mechanisms involved in loss of function of ISCs, which likely results, in part, from differences in how the in vitro organoid assays are performed. Moreover, how the microbiome modulates the function of ISCs and vice versa remains to be elucidated.

Structural characterization of melatonin as an inhibitor of the Wnt deacylase Notum

The hormone melatonin, secreted from the pineal gland, mediates multiple physiological effects including modulation of Wnt/β-catenin signalling. The Wnt palmitoleate lipid modification is essential for its signalling activity, while the carboxylesterase Notum can remove the lipid from Wnt and inactivate it. Notum enzyme inhibition can therefore upregulate Wnt signalling. While searching for Notum inhibitors by crystallographic fragment screening, a hit compound N-[2-(5-fluoro-1H-indol-3-yl)ethyl]acetamide that is structurally similar to melatonin came to our attention. We then soaked melatonin and its precursor N-acetylserotonin into Notum crystals and obtained high-resolution structures (≤1.5 Å) of their complexes. In each of the structures, two compound molecules bind with Notum: one at the enzyme's catalytic pocket, overlapping the space occupied by the acyl tail of the Wnt palmitoleate lipid, and the other at the edge of the pocket opposite the substrate entrance. Although the inhibitory activity of melatonin shown by in vitro enzyme assays is low (IC50 75 µmol/L), the structural information reported here provides a basis for the design of potent and brain accessible drugs for neurodegenerative diseases such as Alzheimer's disease, in which upregulation of Wnt signalling may be beneficial.

The physiological role of Wnt pathway in normal development and cancer

Over the decades, many studies have illustrated the critical roles of Wnt signaling pathways in both developmental processes as well as tumorigenesis. Due to the complexity of Wnt signaling regulation, there are still questions to be addressed about ways cells are able to manipulate different types of Wnt pathways in order to fulfill the requirements for normal or cancer development. In this review, we will describe different types of Wnt signaling pathways and their roles in both normal developmental processes and their role in cancer development and progression. Additionally, we will briefly introduce new strategies currently in clinical trials targeting Wnt signaling pathway components for cancer therapy.

Activity-based protein profiling: Recent advances in medicinal chemistry

Activity-based protein profiling (ABPP) has become an emerging chemical proteomic approach to illustrate the interaction mechanisms between compounds and proteins. This approach has combined organic synthesis, biochemistry, cell biology, biophysics and bioinformatics to accelerate the process of drug discovery in target identification and validation, as well as in the stage of lead discovery and optimization. This review will summarize new developments and applications of ABPP in medicinal chemistry. Here, we mainly described the design principles of activity-base probes (ABPs) and general workflows of ABPP approach. Moreover, we discussed various basic and advanced ABPP strategies and their applications in medicinal chemistry, including competitive and comparative ABPP, two-step ABPP, fluorescence polarization ABPP (FluoPol-ABPP) and ABPs for visualization. In conclusion, this review will give a general overview of the applications of ABPP as a powerful and efficient technique in medicinal chemistry.

Scaffold-hopping identifies furano[2,3-d]pyrimidine amides as potent Notum inhibitors

The carboxylesterase Notum is a key negative regulator of the Wnt signaling pathway by mediating the depalmitoleoylation of Wnt proteins. Our objective was to discover potent small molecule inhibitors of Notum suitable for exploring the regulation of Wnt signaling in the central nervous system. Scaffold-hopping from thienopyrimidine acids 1 and 2, supported by X-ray structure determination, identified 3-methylimidazolin-4-one amides 20-24 as potent inhibitors of Notum with activity across three orthogonal assay formats (biochemical, extra-cellular, occupancy). A preferred example 24 demonstrated good stability in mouse microsomes and plasma, and cell permeability in the MDCK-MDR1 assay albeit with modest P-gp mediated efflux. Pharmacokinetic studies with 24 were performed in vivo in mouse with single oral administration of 24 showing good plasma exposure and reasonable CNS penetration. We propose that 24 is a new chemical tool suitable for cellular studies to explore the fundamental biology of Notum.

The tumor suppressor PTPRK promotes ZNRF3 internalization and is required for Wnt inhibition in the Spemann organizer

A hallmark of Spemann organizer function is its expression of Wnt antagonists that regulate axial embryonic patterning. Here we identify the tumor suppressor Protein tyrosine phosphatase receptor-type kappa (PTPRK), as a Wnt inhibitor in human cancer cells and in the Spemann organizer of Xenopus embryos. We show that PTPRK acts via the transmembrane E3 ubiquitin ligase ZNRF3, a negative regulator of Wnt signaling promoting Wnt receptor degradation, which is also expressed in the organizer. Deficiency of Xenopus Ptprk increases Wnt signaling, leading to reduced expression of Spemann organizer effector genes and inducing head and axial defects. We identify a '4Y' endocytic signal in ZNRF3, which PTPRK maintains unphosphorylated to promote Wnt receptor depletion. Our discovery of PTPRK as a negative regulator of Wnt receptor turnover provides a rationale for its tumor suppressive function and reveals that in PTPRK-RSPO3 recurrent cancer fusions both fusion partners, in fact, encode ZNRF3 regulators.

How human and other animals form distinct head- and tail-ends as embryos is a fundamental question in biology. The fertilized eggs of the African clawed frog (also known as Xenopus) become embryos and grow into tadpoles within two days. This rapid growth makes Xenopus particularly suitable as a model to study how animals with backbones form their body plans.

In Xenopus embryos, a small group of cells known as the Spemann organizer plays a pivotal role in forming the body plan. It produces several enzymes known as Wnt inhibitors that repress a signal pathway known as Wnt signaling to determine the head- and tail-ends of the embryo.

Chang, Kim et al. searched for new Wnt inhibitors in the Spemann organizer of Xenopus embryos. The experiments revealed that the Spemann organizer produced an enzyme known as PTPRK that was essential to permit the head-to-tail patterning of the brain. PTPRK inhibited Wnt signaling by activating another enzyme known as ZNRF3.

Previous studies have shown that defects in Wnt signaling and in the activities of PTPRK and ZNRF3 are involved in colon cancer in mammals. Thus, these findings may help to develop new approaches for treating cancer in the future.

Cellular and Molecular Responses Unique to Major Injury Are Dispensable for Planarian Regeneration

The fundamental requirements for regeneration are poorly understood. Planarians can robustly regenerate all tissues after injury, involving stem cells, positional information, and a set of cellular and molecular responses collectively called the "missing tissue" or "regenerative" response. follistatin, which encodes an extracellular Activin inhibitor, is required for the missing tissue response after head amputation and for subsequent regeneration. We found that follistatin is required for the missing tissue response regardless of the wound context, but causes regeneration failure only after head amputation. This head regeneration failure involves follistatin-mediated regulation of Wnt signaling at wounds and is not a consequence of a diminished missing tissue response. All tested contexts of regeneration, including head regeneration, could occur with a defective missing tissue response, but at a slower pace. Our findings suggest that major cellular and molecular programs induced specifically by large injuries function to accelerate regeneration but are dispensable for regeneration itself.

Correlation of BRCA2 gene mutation and prognosis as well as variant genes in invasive urothelial carcinoma of the bladder

BACKGROUND

This study aimed to investigate the correlation of BRCA2 gene mutation and prognosis as well as variant genes in patients with invasive urothelial carcinoma of the bladder. It predicted and explored the possible mechanism and clinical value of BRCA2 in the occurrence and development of tumors.

METHODS

Data sets of patients with bladder cancer were collected from the Cancer Genome Atlas (TCGA) database. Also the gene expression profile data and clinical information of the BRCA2 mutation group and non-BRCA2 mutation group were downloaded.

RESULTS

The prognosis of the BRCA2 mutation group was better than that of the non-mutant group. Among the down-regulated genes, the following genes showed significant differences between the two groups: CCL22, CYP2B6, CYP2E1, CYP4F2, HTR1E, HTR1F, KLRC1, NAPSA, SELL, SFTPA1, SFTPA2, SFTPB, SFTPC and STRA8, while the following genes among the up-regulated genes showed significant differences between the two groups: ELAVL3, NOTUM, TRH and VIP. Meanwhile, the following gene sets were highly enriched in BRCA2: cell cycle, DNA replication, homologous recombination, oocyte meiosis, ubiquitin-mediated proteolysis, base excision repair, progestin mediated oocyte maturation, basal transcription factor, biosynthesis of N polysaccharide, mismatch repair, sliceosome, purine metabolism as well as P53 and neurotrophic factor signaling pathway, etc.CONCLUSION: These findings suggested that the BRCA2 gene mutation is a good prognostic factor and can be used as a gene to predict the prognosis in the bladder cancer patients.

An improved, scalable synthesis of Notum inhibitor LP-922056 using 1-chloro-1,2-benziodoxol-3-one as a superior electrophilic chlorinating agent

Background: The carboxylesterase Notum has been shown to act as a key negative regulator of the Wnt signalling pathway by mediating the depalmitoleoylation of Wnt proteins. LP-922056 (1) is an orally active inhibitor of Notum. We are investigating the role of Notum in modulating Wnt signalling in the central nervous system and wished to establish if 1 would serve as a peripherally restricted control. An accessible and improved synthetic route would allow 1 to become more readily available as a chemical tool to explore the fundamental biology of Notum and build target validation to underpin new drug discovery programs.

Results: An improved, scalable synthesis of 1 is reported. Key modifications include: (1) the introduction of the C7-cyclopropyl group was most effectively achieved with a Suzuki–Miyaura cross-coupling reaction with MIDA-boronate 11 (5 → 6), and (2) C6 chlorination was performed with 1-chloro-1,2-benziodoxol-3-one (12) (6 → 7) as a mild and selective electrophilic chlorination agent. This 7-step route from 16 has been reliably performed on large scale to produce multigram quantities of 1 in good efficiency and high purity. Pharmacokinetic studies in mouse showed CNS penetration of 1 is very low with a brain/plasma concentration ratio of just 0.01. A small library of amides 17 were prepared from acid 1 to explore if 1 could be modified to deliver a CNS penetrant tool by capping off the acid as an amide. Although significant Notum inhibition activity could be achieved, none of these amides demonstrated the required combination of metabolic stability along with cell permeability without evidence of P-gp mediated efflux.

Conclusion: Mouse pharmacokinetic studies demonstrate that 1 is unsuitable for use in models of disease where brain penetration is an essential requirement of the compound but would be an ideal peripherally restricted control. These data will contribute to the understanding of drug levels of 1 to overlay with appropriate in vivo efficacy endpoints, i.e., the PK-PD relationship. The identification of a suitable analogue of 1 (or 17) which combines Notum inhibition with CNS penetration would be a valuable chemical probe for investigating the role of Notum in disease models.

RNA-sequencing based bone marrow cell transcriptome analysis reveals the potential mechanisms of E'jiao against blood-deficiency in mice

As a health-care food and traditional Chinese medicine, E'jiao, from the skin of Equus animus L, has been used to nourish blood in China for more than 2000 years. In modern medicine, there are also evidences indicate it has a beneficial effect on chemotherapy-caused blood deficiency. However, its mechanism of action for blood invigoration remains unclear. In the present study, we investigated the hematopoietic effect of E'jiao in 5-Fluorouracil-treated mice. In addition to the counting of bone marrow nucleated cells (BMNCs), flow cytometry was used to detect the population of hematopoietic stem cells (HSCs), and colony-forming unit (CFU) was used to assay the differentiation ability of hematopoietic progenitor cells (HPCs). Gene expression profiles of bone marrow cells were obtained from RNA sequencing (RNA-seq) and differentially expressed genes (DEGs) were analyzed with an emphasis on hematopoiesis-related pathways. The results show that E'jiao promotes the proliferation of both BMNCs and HSCs, as well as the differentiation of HPCs. By providing a hematopoiesis-related molecular regulatory network of E'jiao, we point out that the mechanism of E'jiao is associated with pathways including ECM-receptor interaction, Wnt signaling pathway, PI3K-Akt signaling pathway, TGF-beta signaling pathway, Hematopoietic cell lineage and Osteoclast differentiation, in which Ibsp, Col1a1, Col1a2, Notum, Sost, Dkk1, Irx5, Irx3 and Dcn are the key regulatory molecules. These findings provide valuable molecular basis for the mechanism of action of E'jiao.

Discovery of 2-phenoxyacetamides as inhibitors of the Wnt-depalmitoleating enzyme NOTUM from an X-ray fragment screen

NOTUM is a carboxylesterase that has been shown to act by mediating the O-depalmitoleoylation of Wnt proteins resulting in suppression of Wnt signaling. Here, we describe the development of NOTUM inhibitors that restore Wnt signaling for use in in vitro disease models where NOTUM over activity is an underlying cause. A crystallographic fragment screen with NOTUM identified 2-phenoxyacetamide 3 as binding in the palmitoleate pocket with modest inhibition activity (IC50 33 μM). Optimization of hit 3 by SAR studies guided by SBDD identified indazole 38 (IC50 0.032 μM) and isoquinoline 45 (IC50 0.085 μM) as potent inhibitors of NOTUM. The binding of 45 to NOTUM was rationalized through an X-ray co-crystal structure determination which showed a flipped binding orientation compared to 3. However, it was not possible to combine NOTUM inhibition activity with metabolic stability as the majority of the compounds tested were rapidly metabolized in an NADPH-independent manner.

Essential long-range action of Wingless/Wnt in adult intestinal compartmentalization

Signal transduction activated by Wingless/Wnt ligands directs cell proliferation and fate specification in metazoans, and its overactivation underlies the development of the vast majority of colorectal cancers. In the conventional model, the secretion and movement of Wingless to cells distant from its source of synthesis are essential for long-range signaling in tissue patterning. However, this model was upended recently by an unanticipated finding: replacement of wild-type Drosophila Wingless with a membrane-tethered form produced viable adults with largely normal external morphology, which suggested that Wingless secretion and movement are dispensable for tissue patterning. Herein, we tested this foundational principle in the adult intestine, where Wingless signaling gradients coincide with all major boundaries between compartments. We find that the critical roles of Wingless during adult intestinal development, which include regulation of target gene activation, boundary formation, stem cell proliferation, epithelial cell fate specification, muscle differentiation, gut folding, and signaling crosstalk with the Decapentaplegic pathway, are all disrupted by Wingless tethering. These findings provide new evidence that supports the requirement for the direct, long-range action of Wingless in tissue patterning, with relevance for animal development, tissue homeostasis and Wnt-driven disease.

Mechanistic insights from the LHX1-driven molecular network in building the embryonic head

Development of an embryo is driven by a series of molecular instructions that control the differentiation of tissue precursor cells and shape the tissues into major body parts. LIM homeobox 1 (LHX1) is a transcription factor that plays a major role in the development of the embryonic head of the mouse. Loss of LHX1 function disrupts the morphogenetic movement of head tissue precursors and impacts on the function of molecular factors in modulating the activity of the WNT signaling pathway. LHX1 acts with a transcription factor complex to regulate the transcription of target genes in multiple phases of development and in a range of embryonic tissues of the mouse and Xenopus. Determining the interacting factors and transcriptional targets of LHX1 will be key to unraveling the ensemble of factors involved in head development and building a head gene regulatory network.

Neural control of body-plan axis in regenerating planaria

Control of axial polarity during regeneration is a crucial open question. We developed a quantitative model of regenerating planaria, which elucidates self-assembly mechanisms of morphogen gradients required for robust body-plan control. The computational model has been developed to predict the fraction of heteromorphoses expected in a population of regenerating planaria fragments subjected to different treatments, and for fragments originating from different regions along the anterior-posterior and medio-lateral axis. This allows for a direct comparison between computational and experimental regeneration outcomes. Vector transport of morphogens was identified as a fundamental requirement to account for virtually scale-free self-assembly of the morphogen gradients observed in planarian homeostasis and regeneration. The model correctly describes altered body-plans following many known experimental manipulations, and accurately predicts outcomes of novel cutting scenarios, which we tested. We show that the vector transport field coincides with the alignment of nerve axons distributed throughout the planarian tissue, and demonstrate that the head-tail axis is controlled by the net polarity of neurons in a regenerating fragment. This model provides a comprehensive framework for mechanistically understanding fundamental aspects of body-plan regulation, and sheds new light on the role of the nervous system in directing growth and form.

Notum attenuates HBV-related liver fibrosis through inhibiting Wnt 5a mediated non-canonical pathways

Background

Non-canonical Wnt pathways play important roles in liver fibrosis. Notum is a newly discovered inhibitor to Wnt proteins. This study was to investigate anti-fibrotic effects of Notum.

Methods

53 patients with hepatitis B virus (HBV) infection as well as a cell co-culture system of LX-2 and Hep AD38 cells were engaged in this study. Clinical, biological and virological data of each patient were analyzed. Cell viability was detected at different time points. mRNA and protein levels of NFATc1 (Nuclear factor of activated T-cells), Jnk, α-SMA, Col1A1 and TIMP-1 were detected both in LX-2 and liver tissue. Protein levels of NFATc1 and Jnk in liver tissue and their correlations with fibrosis score were analyzed.

Results

Hepatitis B virus replication up-regulated Wnt5a induced NFATc1 and Jnk activity in Hep AD38. Notum suppressed NFATc1, Jnk and fibrosis genes expression, reduced cell viability in co-cultured LX-2 cells induced by HBV. Interestingly, Patients with HBV DNA > 5log copies/ml had higher mRNA levels of NFATc1 and fibrosis genes than patients with HBV DNA < 5log copies/ml. Most importantly, protein expressions of NFATc1 and pJnk have positive correlations with liver fibrosis scores in HBV-infected patients.

Conclusions

Our data showed that Notum inhibited HBV-induced liver fibrosis through down-regulating Wnt 5a mediated non-canonical pathways. This study shed light on anti-fibrotic treatment.

Non-acylated Wnts Can Promote Signaling

Wnts are a family of 19 extracellular ligands that regulate cell fate, proliferation, and migration during metazoan embryogenesis and throughout adulthood. Wnts are acylated post-translationally at a conserved serine and bind the extracellular cysteine-rich domain (CRD) of Frizzled (FZD) seven-pass transmembrane receptors. Although crystal structures suggest that acylation is essential for Wnt binding to FZDs, we show here that several Wnts can promote signaling in Xenopus laevis and Danio rerio embryos, as well as in an in vitro cell culture model, without acylation. The non-acylated Wnts are expressed at levels similar to wild-type counterparts and retain CRD binding. By contrast, we find that certain other Wnts do require acylation for biological activity in Xenopus embryos, although not necessarily for FZD binding. Our data argue that acylation dependence of Wnt activity is context specific. They further suggest that acylation may underlie aspects of ligand-receptor selectivity and/or control other aspects of Wnt function.

NOTUM inhibition increases endocortical bone formation and bone strength

The disability, mortality and costs caused by non-vertebral osteoporotic fractures are enormous. Existing osteoporosis therapies are highly effective at reducing vertebral but not non-vertebral fractures. Cortical bone is a major determinant of non-vertebral bone strength. To identify novel osteoporosis drug targets, we phenotyped cortical bone of 3 366 viable mouse strains with global knockouts of druggable genes. Cortical bone thickness was substantially elevated in Notum^−/− mice. NOTUM is a secreted WNT lipase and we observed high NOTUM expression in cortical bone and osteoblasts but not osteoclasts. Three orally active small molecules and a neutralizing antibody inhibiting NOTUM lipase activity were developed. They increased cortical bone thickness and strength at multiple skeletal sites in both gonadal intact and ovariectomized rodents by stimulating endocortical bone formation. Thus, inhibition of NOTUM activity is a potential novel anabolic therapy for strengthening cortical bone and preventing non-vertebral fractures.

NOTUM is an enzyme that inactivates WNT proteins (which play a key role in early tissue development), and inhibiting NOTUM has been found to increase the formation of endocortical bone (within the cortex, the hard exterior of bone) and enhance bone strength. Existing therapies for osteoporosis (condition causing bone to become weak and brittle) are effective in reducing vertebral, but not non-vertebral, fractures. A team headed by Robert Brommage at Lexicon Pharmaceuticals, Texas aimed to identify novel osteoporosis drug targets in mice. Following inhibition of NOTUM activity, the authors observed increased cortical bone thickness and strength at multiple skeletal sites through stimulation of endocortical bone formation. The team concluded that inhibiting NOTUM activity has good potential as a new therapeutic strategy and could be beneficial in preventing non-vertebral osteoporotic fractures.

New Insights Into Monogenic Causes of Osteoporosis

Osteoporosis, characterized by deteriorated bone microarchitecture and low bone mineral density, is a chronic skeletal disease with high worldwide prevalence. Osteoporosis related to aging is the most common form and causes significant morbidity and mortality. Rare, monogenic forms of osteoporosis have their onset usually in childhood or young adulthood and have specific phenotypic features and clinical course depending on the underlying cause. The most common form is osteogenesis imperfecta linked to mutations in COL1A1 and COL1A2, the two genes encoding type I collagen. However, in the past years, remarkable advancements in bone research have expanded our understanding of the intricacies behind bone metabolism and identified novel molecular mechanisms contributing to skeletal health and disease. Especially high-throughput sequencing techniques have made family-based studies an efficient way to identify single genes causative of rare monogenic forms of osteoporosis and these have yielded several novel genes that encode proteins partaking in type I collagen modification or regulating bone cell function directly. New forms of monogenic osteoporosis, such as autosomal dominant osteoporosis caused by WNT1 mutations or X-linked osteoporosis due to PLS3 mutations, have revealed previously unidentified bone-regulating proteins and clarified specific roles of bone cells, expanded our understanding of possible inheritance mechanisms and paces of disease progression, and highlighted the potential of monogenic bone diseases to extend beyond the skeletal tissue. The novel gene discoveries have introduced new challenges to the classification and diagnosis of monogenic osteoporosis, but also provided promising new molecular targets for development of pharmacotherapies. In this article we give an overview of the recent discoveries in the area of monogenic forms of osteoporosis, describing the key cellular mechanisms leading to skeletal fragility, the major recent research findings and the essential challenges and avenues in future diagnostics and treatments.

NOTUM Is Involved in the Progression of Colorectal Cancer

BACKGROUND

There are limitations to current colorectal cancer (CRC)-specific diagnostic methods and therapies. Tumorigenesis proceeds because of interaction between cancer cells and various surrounding cells; discovering new molecular mediators through studies of the CRC secretome is a promising approach for the development of CRC diagnostics and therapies.

MATERIALS AND METHODS

A comparative secretomic analysis was performed using primary and metastatic human isogenic CRC cells. Proliferation was determined by MTT and thymidine incorporation assay, migration was determined by wound-healing assay (ELISA). The level of palmitoleoyl-protein carboxylesterase (NOTUM) in plasma from patients with CRC was determined by enzyme-linked immunosorbent assay.

RESULTS

NOTUM expression was increased in metastatic cells. Proliferation was suppressed by inhibiting expression of NOTUM. Knockdown of NOTUM genes inhibited proliferation as well as migration, with possible involvement of p38 and c-JUN N-terminal kinase in this process. The result was verified in patients with CRC.

CONCLUSION

NOTUM may be a new candidate for diagnostics and therapy of CRC.

Fatty acid recognition in the Frizzled receptor family

Wnt signaling regulates physiological processes ranging from cell differentiation to bone formation. Dysregulation of Wnt signaling is linked to several human ailments, including colorectal, pancreatic, and breast cancers. As such, modulation of this pathway has been an attractive strategy for therapeutic development of anticancer agents. Since the discovery of Wnt proteins more than 35 years ago, research efforts continue to focus on understanding the biochemistry of their molecular interactions and their biological functions. Wnt is a secreted glycoprotein covalently modified with a cis-unsaturated fatty acyl group at a conserved serine residue, and this modification is required for Wnt secretion and activity. To initiate signaling, Wnt proteins bind to cell-surface Frizzled (FZD) receptors, but the molecular basis for recognition of Wnt's fatty acyl moiety by the extracellular cysteine-rich domain of FZD has become clear only very recently. Here, we review the most recent developments in the field, focusing on structural and biochemical studies of the FZD receptor family and highlighting new insights into their molecular arrangement and mode of regulation by cis-unsaturated fatty acids. Additionally, we examine how other lipid-binding proteins recognize fatty acyl chains on Wnt proteins in the regulation of Wnt secretion and activities. Altogether, this perspective expands our understanding of fatty acid–protein interactions in the FZD system and provides a basis for guiding future research in the field.

Wnt lipidation: Roles in trafficking, modulation, and function

The Wnt signaling pathway consists of various downstream target proteins that have substantial roles in mammalian cell proliferation, differentiation, and development. Its aberrant activity can lead to uncontrolled proliferation and tumorigenesis. The posttranslational connection of fatty acyl chains to Wnt proteins provides the unique capacity for regulation of Wnt activity. In spite of the past belief that Wnt molecules are subject to dual acylation, it has been shown that these proteins have only one acylation site and undergo monounsaturated fatty acylation. The Wnt monounsaturated fatty acyl chain is more than just a hydrophobic coating and appears to be critical for Wnt signaling, transport, and receptor activation. Here, we provide an overview of recent findings in Wnt monounsaturated fatty acylation and the mechanism by which this lipid moiety regulates Wnt activity from the site of production to its receptor interactions.

Bighead is a Wnt antagonist secreted by the Xenopus Spemann organizer that promotes Lrp6 endocytosis

The Xenopus laevis embryo has been subjected to almost saturating screens for molecules specifically expressed in dorsal Spemann organizer tissue. In this study, we performed high-throughput RNA sequencing of ectodermal explants, called animal caps, which normally give rise to epidermis. We analyzed dissociated animal cap cells that, through sustained activation of MAPK, differentiate into neural tissue. We also microinjected mRNAs for Cerberus, Chordin, FGF8, BMP4, Wnt8, and Xnr2, which induce neural or other germ layer differentiations. The searchable database provided here represents a valuable resource for the early vertebrate cell differentiation. These analyses resulted in the identification of a gene present in frog and fish, which we call Bighead. Surprisingly, at gastrula, it was expressed in the Spemann organizer and endoderm, rather than in ectoderm as we expected. Despite the plethora of genes already mined from Spemann organizer tissue, Bighead encodes a secreted protein that proved to be a potent inhibitor of Wnt signaling in a number of embryological and cultured cell signaling assays. Overexpression of Bighead resulted in large head structures very similar to those of the well-known Wnt antagonists Dkk1 and Frzb-1. Knockdown of Bighead with specific antisense morpholinos resulted in embryos with reduced head structures, due to increased Wnt signaling. Bighead protein bound specifically to the Wnt coreceptor lipoprotein receptor-related protein 6 (Lrp6), leading to its removal from the cell surface. Bighead joins two other Wnt antagonists, Dkk1 and Angptl4, which function as Lrp6 endocytosis regulators. These results suggest that endocytosis plays a crucial role in Wnt signaling.

Mechanisms of Wnt signaling and control

The Wnt signaling pathway is a highly conserved system that regulates complex biological processes across all metazoan species. At the cellular level, secreted Wnt proteins serve to break symmetry and provide cells with positional information that is critical to the patterning of the entire body plan. At the organismal level, Wnt signals are employed to orchestrate fundamental developmental processes, including the specification of the anterior-posterior body axis, induction of the primitive streak and ensuing gastrulation movements, and the generation of cell and tissue diversity. Wnt functions extend into adulthood where they regulate stem cell behavior, tissue homeostasis, and damage repair. Disruption of Wnt signaling activity during embryonic development or in adults results in a spectrum of abnormalities and diseases, including cancer. The molecular mechanisms that underlie the myriad of Wnt-regulated biological effects have been the subject of intense research for over three decades. This review is intended to summarize our current understanding of how Wnt signals are generated and interpreted. This article is categorized under: Biological Mechanisms > Cell Signaling Developmental Biology > Stem Cell Biology and Regeneration.

Selective Irreversible Inhibitors of the Wnt-Deacylating Enzyme NOTUM Developed by Activity-Based Protein Profiling

Wnt proteins are secreted morphogens that play critical roles in embryonic development and tissue remodeling in adult organisms. Aberrant Wnt signaling contributes to diseases such as cancer. Wnts are modified by an unusual O-fatty acylation event (O-linked palmitoleoylation of a conserved serine) that is required for binding to Frizzled receptors. O-Palmitoleoylation of Wnts is introduced by the porcupine (PORCN) acyltransferase and removed by the serine hydrolase NOTUM. PORCN inhibitors are under development for oncology, while NOTUM inhibitors have potential for treating degenerative diseases. Here, we describe the use of activity-based protein profiling (ABPP) to discover and advance a class of N-hydroxyhydantoin (NHH) carbamates that potently and selectively inhibit NOTUM. An optimized NHH carbamate inhibitor, ABC99, preserves Wnt-mediated cell signaling in the presence of NOTUM and was also converted into an ABPP probe for visualizing NOTUM in native biological systems.

Wnt signaling in development and tissue homeostasis

The Wnt-β-catenin signaling pathway is an evolutionarily conserved cell-cell communication system that is important for stem cell renewal, cell proliferation and cell differentiation both during embryogenesis and during adult tissue homeostasis. Genetic or epigenetic events leading to hypo- or hyper-activation of the Wnt-β-catenin signaling cascade have also been associated with human diseases such as cancer. Understanding how this pathway functions is thus integral for developing therapies to treat diseases or for regenerative medicine approaches. Here, and in the accompanying poster, we provide an overview of Wnt-β-catenin signaling and briefly highlight its key functions during development and adult tissue homeostasis.

Peptide Lipidation - A Synthetic Strategy to Afford Peptide Based Therapeutics

Peptide and protein aberrant lipidation patterns are often involved in many diseases including cancer and neurological disorders. Peptide lipidation is also a promising strategy to improve pharmacokinetic and pharmacodynamic profiles of peptide-based drugs. Self-adjuvanting peptide-based vaccines commonly utilise the powerful TLR2 agonist Pam_nCys lipid to stimulate adjuvant activity. The chemical synthesis of lipidated peptides can be challenging hence efficient, flexible and straightforward synthetic routes to access homogeneous lipid-tagged peptides are in high demand. A new technique coined Cysteine Lipidation on a Peptide or Amino acid (CLipPA) uses a 'thiol-ene' reaction between a cysteine and a vinyl ester and offers great promise due to its simplicity, functional group compatibility and selectivity. Herein a brief review of various synthetic strategies to access lipidated peptides, focusing on synthetic methods to incorporate a Pam_nCys motif into peptides, is provided.

Positional information specifies the site of organ regeneration and not tissue maintenance in planarians

Most animals undergo homeostatic tissue maintenance, yet those capable of robust regeneration in adulthood use mechanisms significantly overlapping with homeostasis. Here we show in planarians that modulations to body-wide patterning systems shift the target site for eye regeneration while still enabling homeostasis of eyes outside this region. The uncoupling of homeostasis and regeneration, which can occur during normal positional rescaling after axis truncation, is not due to altered injury signaling or stem cell activity, nor specific to eye tissue. Rather, pre-existing tissues, which are misaligned with patterning factor expression domains, compete with properly located organs for incorporation of migratory progenitors. These observations suggest that patterning factors determine sites of organ regeneration but do not solely determine the location of tissue homeostasis. These properties provide candidate explanations for how regeneration integrates pre-existing tissues and how regenerative abilities could be lost in evolution or development without eliminating long-term tissue maintenance and repair.

Notum attenuates Wnt/β-catenin signaling to promote tracheal cartilage patterning

Tracheobronchomalacia (TBM) is a common congenital disorder in which the cartilaginous rings of the trachea are weakened or missing. Despite the high prevalence and clinical issues associated with TBM, the etiology is largely unknown. Our previous studies demonstrated that Wntless (Wls) and its associated Wnt pathways are critical for patterning of the upper airways. Deletion of Wls in respiratory endoderm caused TBM and ectopic trachealis muscle. To understand mechanisms by which Wls mediates tracheal patterning, we performed RNA sequencing in prechondrogenic tracheal tissue of Wls^f/f;Shh^Cre/wt embryos. Chondrogenic Bmp4, and Sox9 were decreased, while expression of myogenic genes was increased. We identified Notum, a deacylase that inactivates Wnt ligands, as a target of Wls induced Wnt signaling. Notum's mesenchymal ventral expression in prechondrogenic trachea overlaps with expression of Axin2, a Wnt/β-catenin target and inhibitor. Notum is induced by Wnt/β-catenin in developing trachea. Deletion of Notum activated mesenchymal Wnt/β-catenin and caused tracheal mispatterning of trachealis muscle and cartilage as well as tracheal stenosis. Notum is required for tracheal morphogenesis, influencing mesenchymal condensations critical for patterning of tracheal cartilage and muscle. We propose that Notum influences mesenchymal cell differentiation by generating a barrier for Wnt ligands produced and secreted by airway epithelial cells to attenuate Wnt signaling.

Methods for Studying Wnt Protein Modifications/Inactivations by Extracellular Enzymes, Tiki and Notum

Wnt proteins are modified and inactivated by two extracellular enzymatic antagonists, Tiki and Notum. Tiki proteins act as membrane-tethered metalloproteases to cleave a fragment from the amino terminus of Wnt proteins. Notum is a Wnt deacylase that removes the lipid modification that is essential for Wnt activities. Here, we provide detailed procedures for preparing enzymatic active Tiki and Notum proteins and the in vitro enzymatic reactions. We also describe a metabolic labeling and click chemistry method for detection of Wnt protein acylation.

Protein Lipidation: Occurrence, Mechanisms, Biological Functions, and Enabling Technologies

Protein lipidation, including cysteine prenylation, N-terminal glycine myristoylation, cysteine palmitoylation, and serine and lysine fatty acylation, occurs in many proteins in eukaryotic cells and regulates numerous biological pathways, such as membrane trafficking, protein secretion, signal transduction, and apoptosis. We provide a comprehensive review of protein lipidation, including descriptions of proteins known to be modified and the functions of the modifications, the enzymes that control them, and the tools and technologies developed to study them. We also highlight key questions about protein lipidation that remain to be answered, the challenges associated with answering such questions, and possible solutions to overcome these challenges.

Wnt Signaling in Hematological Malignancies

Leukemia and lymphoma are a wide encompassing term for a diverse set of blood malignancies that affect people of all ages and result in approximately 23,000 deaths in the United States per year (Siegel RL, Miller KD, Jemal A. Cancer statistics, 2016. CA Cancer J Clin. 2016;66(1):7-30.). Hematopoietic stem cells (HSCs) are tissue-specific stem cells at the apex of the hierarchy that gives rise to all of the terminally differentiated blood cells, through progressively restricted progenitor populations, a process that is known to be Wnt-responsive. In particular, the progenitor populations are subject to uncontrolled expansion during oncogenic processes, namely the common myeloid progenitor and common lymphoid progenitor, as well as the myeloblast and lymphoblast. Unregulated growth of these cell-types leads to mainly three types of blood cancers (i.e., leukemia, lymphoma, and myeloma), which frequently exhibit deregulation of the Wnt signaling pathway. Generally, leukemia is caused by the expansion of myeloid progenitors, leading to an overproduction of white blood cells; as such, patients are unable to make sufficient numbers of red blood cells and platelets. Likewise, an overproduction of lymphocytes leads to clogging of the lymph system and impairment of the immune system in lymphomas. Finally, cancer of the plasma cells in the blood is called myeloma, which also leads to immune system failure. Within each of these three types of blood cancers, there are multiple subtypes, usually characterized by their timeline of onset and their cell type of origin. Of these, 85% of leukemias are encompassed by the four most common diseases, that is, acute myeloid leukemia (AML), chronic myeloid leukemia (CML), acute lymphoblastic leukemia (ALL), and chronic lymphocytic leukemia (CLL); AML accounts for the majority of leukemia-related deaths (Siegel RL, Miller KD, Jemal A. Cancer statistics, 2016. CA Cancer J Clin. 2016;66(1):7-30.). Through understanding how HSCs are normally developed and maintained, we can understand how the normal functions of these pathways are disrupted during blood cancer progression; the Wnt pathway is important in regulation of both normal and malignant hematopoiesis. In this chapter, we will discuss the role of Wnt signaling in normal and aberrant hematopoiesis. Our understanding the relationship between Wnt and HSCs will provide novel insights into therapeutic targets.