The function of endocytosis in Wnt signaling

The origin and evolution of Wnt signalling

The Wnt signal transduction pathway has essential roles in the formation of the primary body axis during development, cellular differentiation and tissue homeostasis. This animal-specific pathway has been studied extensively in contexts ranging from developmental biology to medicine for more than 40 years. Despite its physiological importance, an understanding of the evolutionary origin and primary function of Wnt signalling has begun to emerge only recently. Recent studies on very basal metazoan species have shown high levels of conservation of components of both canonical and non-canonical Wnt signalling pathways. Furthermore, some pathway proteins have been described also in non-animal species, suggesting that recruitment and functional adaptation of these factors has occurred in metazoans. In this Review, we summarize the current state of research regarding the evolutionary origin of Wnt signalling, its ancestral function and the characteristics of the primal Wnt ligand, with emphasis on the importance of genomic studies in various pre-metazoan and basal metazoan species.

Transfer of polarity information via diffusion of Wnt ligands in C. elegans embryos

Different signaling mechanisms concur to ensure robust tissue patterning and cell fate instruction during animal development. Most of these mechanisms rely on signaling proteins that are produced, transported, and detected. The spatiotemporal dynamics of signaling molecules are largely unknown, yet they determine signal activity's spatial range and time frame. Here, we use the Caenorhabditis elegans embryo to study how Wnt ligands, an evolutionarily conserved family of signaling proteins, dynamically organize to establish cell polarity in a developing tissue. We identify how Wnt ligands, produced in the posterior half of the embryos, spread extracellularly to transmit information to distant target cells in the anterior half. With quantitative live imaging and fluorescence correlation spectroscopy, we show that Wnt ligands diffuse through the embryo over a timescale shorter than the cell cycle, in the intercellular space, and outside the tissue below the eggshell. We extracted diffusion coefficients of Wnt ligands and their receptor Frizzled and characterized their co-localization. Integrating our different measurements and observations in a simple computational framework, we show how fast diffusion in the embryo can polarize individual cells through a time integration of the arrival of the ligands at the target cells. The polarity established at the tissue level by a posterior Wnt source can be transferred to the cellular level. Our results support a diffusion-based long-range Wnt signaling, which is consistent with the dynamics of developing processes.

Dab2 (Disabled-2), an adaptor protein, regulates self-renewal of hair follicle stem cells

Disabled 2 (Dab2), an adaptor protein, is up regulated in the hair follicle stem cells (HFSCs); however, its role in any tissue stem cells has not been studied. In the present study, we have reported that Dab2 conditional knockout (Dab2-cKO) mice exhibited a delay in the HF cycle due to perturbed activation of HFSCs. Further, Dab2-cKO mice showed a reduction in the number of HFSCs and reduced colony forming ability of HFSCs. Dab2-cKO mice showed extended quiescence of HFSCs concomitant with an increased expression of Nfatc1. Dab2-cKO mice showed a decreased expression of anti-aging genes such as Col17a1, decorin, Sirt2 and Sirt7. Dab2-cKO mice did not show full hair coat recovery in aged mice thereby suggesting an accelerated aging process. Overall, we unveil for the first time, the role of Dab2 that regulate activation and self-renewal of HFSCs.

Nanoparticle and Nanotopography-Induced Activation of the Wnt Pathway in Bone Regeneration

Background and Aims: Recent research has focused on developing nanoparticle and nanotopography-based technologies for bone regeneration. The Wingless-related integration site (Wnt) signaling pathway has been shown to play a vital role in this process, in particular in osteogenic differentiation and proliferation. The exact mechanisms by which nanoparticles and nanotopographies activate the Wnt signaling pathway, however, are not fully understood. This review aimed to elucidate the mechanisms by which nanoscale technologies activate the Wnt signaling pathway during bone regeneration. Methods: The terms "Wnt," "bone," and "nano*" were searched on PubMed and Ovid with no date limit. Only original research articles related to Wnt signaling and bone regeneration in the context of nanotopographies, nanoparticles, or scaffolds with nanotopographies/nanoparticles were reviewed. Results: The primary mechanism by which nanoparticles activated the Wnt pathway was by internalization through the endocytic pathway or diffusion through the cell membrane, leading to accumulation of nonphosphorylated β-catenin in the cytoplasm and subsequently downstream osteogenic signaling (e.g., upregulation of runt-related transcription factor 2 [RUNX2]). The specific size of the nanoparticles and the process of endocytosis itself has been shown to modulate the Wnt-β-catenin pathway. Nanotopographies were shown to directly activate frizzled receptors, initiating Wnt/β-catenin signaling. Additional studies showed nanotopographies to activate the Wnt/calcium (Wnt/Ca2+)-dependent and Wnt/planar cell polarity pathways through nuclear factor of activated T cells, and α5β1 integrin stimulation. Finally, scaffolds containing nanotopographies/nanoparticles were found to induce Wnt signaling through a combination of ion release (e.g., lithium, boron, lanthanum, and icariin), which inhibited glycogen synthase kinase 3 beta (GSK-3β) activity, and through similar mechanisms to the nanotopographies. Conclusion: This review concludes that nanoparticles and nanotopographies cause Wnt activation through several different mechanisms, specific to the size, shape, and structure of the nanoparticles or nanotopographies. Endocytosis-related mechanisms, integrin signaling and ion release were the major mechanisms identified across nanoparticles, nanotopographies, and scaffolds, respectively. Knowledge of these mechanisms will help develop more effective targeted nanoscale technologies for bone regeneration. Impact statement Nanoparticles and nanotopographies can activate the Wingless-related integration site (Wnt) signaling pathway, which is essential for bone regeneration. This review has identified that activation is due to endocytosis, integrin signaling and ion release, depending on the size, shape, and structure of the nanoparticles or nanotopographies. By identifying and further understanding these mechanisms, more effective nanoscale technologies that target the Wnt signaling pathway can be developed. These technologies can be used for the treatment of nonunion bone fractures, a major clinical challenge, with the potential to improve the quality of life of millions of patients around the world.

Endocytosis and Alzheimer's disease

Alzheimer's disease (AD) is a progressive neurodegenerative disorder and is the most common cause of dementia. The pathogenesis of AD still remains unclear, including two main hypotheses: amyloid cascade and tau hyperphosphorylation. The hallmark neuropathological changes of AD are extracellular deposits of amyloid-β (Aβ) plaques and intracellular neurofibrillary tangles (NFTs). Endocytosis plays an important role in a number of cellular processes including communication with the extracellular environment, nutrient uptake, and signaling by the cell surface receptors. Based on the results of genetic and biochemical studies, there is a link between neuronal endosomal function and AD pathology. Taking this into account, we can state that in the results of previous research, endolysosomal abnormality is an important cause of neuronal lesions in the brain. Endocytosis is a central pathway involved in the regulation of the degradation of amyloidogenic components. The results of the studies suggest that a correlation between alteration in the endocytosis process and associated protein expression progresses AD. In this article, we discuss the current knowledge about endosomal abnormalities in AD.

SP4 Facilitates Esophageal Squamous Cell Carcinoma Progression by Activating PHF14 Transcription and Wnt/Β-Catenin Signaling

Specificity protein 4 transcription factor (SP4), a member of the Sp/Krüppel-like family (KLF), could bind to GT and GC box promoters, and plays an essential role in transcriptional activating. Despite SP4 having been detected to be highly expressed in a variety of human tumors, its biological effect and underlying molecular mechanism in esophageal squamous cell carcinoma (ESCC) remains unclear. Our research discovered that high SP4 expression is detected in primary ESCC specimens and cell lines and is strongly associated with the ESCC tumor grade and poor prognosis. In vitro, knockdown of SP4 suppressed cell proliferation and cell-cycle progression and promoted apoptosis, whereas overexpression of SP4 did the opposite. In vivo, inhibiting SP4 expression in ESCC cells suppresses tumor growth. Subsequently, we demonstrated that SP4 acts as the transcriptional upstream of PHF14, which binds to PHF14 promoter region, thus promoting PHF14 transcription. PHF14 was also significantly expressed in patient tissues and various ESCC cell lines and its expression promoted cell proliferation and inhibited apoptosis. Moreover, knockdown of SP4 inhibited the Wnt/β-catenin signaling pathway, whereas overexpression of PHF14 eliminated the effects of SP4 knockdown in ESCC cells. These results demonstrate that SP4 activates the Wnt/β-catenin signaling pathway by driving PHF14 transcription, thereby promoting ESCC progression, which indicates that SP4 might act as a prospective prognostic indicator or therapeutic target for patients with ESCC.

IMPLICATIONS

This study identified SP4/PH14 axis as a new mechanism to promote the progression of ESCC, which may serve as a novel therapeutic target for patients with ESCC.

Transport and gradient formation of Wnt and Fgf in the early zebrafish gastrula

Within embryonic development, the occurrence of gastrulation is critical in the formation of multiple germ layers with many differentiative abilities. These cells are instructed through exposure to signalling molecules called morphogens. The secretion of morphogens from a source tissue creates a concentration gradient that allows distinct pattern formation in the receiving tissue. This review focuses on the morphogens Wnt and Fgf in zebrafish development. Wnt has been shown to have critical roles throughout gastrulation, including in anteroposterior patterning and neural posterisation. Fgf is also a vital signal, contributing to involution and mesodermal specification. Both morphogens have also been found to work in finely balanced synergy for processes such as neural induction. Thus, the signalling range of Wnts and Fgfs must be strictly controlled to target the correct target cells. Fgf and Wnts signal to local cells as well as to cells in the distance in a highly regulated way, requiring specific dissemination mechanisms that allow efficient and precise signalling over short and long distances. Multiple transportation mechanisms have been discovered to aid in producing a stable morphogen gradient, including short-range diffusion, filopodia-like extensions called cytonemes and extracellular vesicles, mainly exosomes. These mechanisms are specific to the morphogen that they transport and the intended signalling range. This review article discusses how spreading mechanisms in these two morphogenetic systems differ and the consequences on paracrine signalling, hence tissue patterning.

Food-Derived Peptides: Beneficial CNS Effects and Cross-BBB Transmission Strategies

Food-derived peptides, as dietary supplements, have significant effects on promoting brain health and relieving central nervous system (CNS) diseases. However, the blood-brain barrier (BBB) greatly limits their in-brain bioavailability. Thus, overcoming the BBB to target the CNS is a major challenge for bioactive peptides in the prevention and treatment of CNS diseases. This review discusses improvement in the neuroprotective function of food-derived active peptides in CNS diseases, as well as the source of BBB penetrating peptides (BBB-shuttles) and the mechanism of transmembrane transport. Notably, this review also discusses various peptide modification methods to overcome the low permeability and stability of the BBB. Lipification, glycosylation, introduction of disulfide bonds, and cyclization are effective strategies for improving the penetration efficiency of peptides through the BBB. This review provides a new prospective for improving their neuroprotective function and developing treatments to delay or even prevent CNS diseases.

cRel and Wnt5a/Frizzled 5 Receptor-Mediated Inflammatory Regulation Reveal Novel Neuroprotectin D1 Targets for Neuroprotection

Wnt5a triggers inflammatory responses and damage via NFkB/p65 in retinal pigment epithelial (RPE) cells undergoing uncompensated oxidative stress (UOS) and in experimental ischemic stroke. We found that Wnt5a-Clathrin-mediated uptake leads to NFkB/p65 activation and that Wnt5a is secreted in an exosome-independent fashion. We uncovered that docosahexaenoic acid (DHA) and its derivative, Neuroprotectin D1 (NPD1), upregulate c-Rel expression that, as a result, blunts Wnt5a abundance by competing with NFkB/p65 on the Wnt5a promoter A. Wnt5a increases in ischemic stroke penumbra and blood, while DHA reduces Wnt5a abundance with concomitant neuroprotection. Peptide inhibitor of Wnt5a binding, Box5, is also neuroprotective. DHA-decreased Wnt5a expression is concurrent with a drop in NFkB-driven inflammatory cytokine expression, revealing mechanisms after stroke, as in RPE cells exposed to UOS. Limiting the Wnt5a activity via Box5 reduces stroke size, suggesting neuroprotection pertinent to onset and progression of retinal degenerations and stroke consequences. NPD1 disrupts Wnt5a feedback loop at two sites: (1) decreasing FZD5, thus Wnt5a internalization, and (2) by enhancing cREL activity, which competes with p65/NFkB downstream endocytosis. As a result, Wnt5a expression is reduced, and so is its inflammatory signaling in RPE cells and neurons in ischemic stroke.

Opposite changes in the expression of clathrin and caveolin-1 in normal and cancerous human prostate tissue: putative clathrin-mediated recycling of EGFR

Endocytosis, an important macromolecule uptake process in cells, is known to be dysregulated in cancer. Clathrin and caveolin-1 proteins play a major role in receptor-mediated endocytosis. We have used a quantitative, unbiased and semi-automated method to measure in situ protein expression of clathrin and caveolin-1 in cancerous and paired normal (cancer adjacent, non-cancerous) human prostate tissue. There was a significant (p < 0.0001) increase in the expression of clathrin in prostate cancer samples (N = 29, n = 91) compared to normal tissue (N = 29, n = 67) (N = number of patients, n = number of cores in tissue arrays). Conversely, there was a significant (p < 0.0001) decrease in expression of caveolin-1 in prostate cancer tissue compared to normal prostate tissue. The opposite change in expression of the two proteins was highly correlated to increasing cancer aggressiveness. There was also a concurrent increase in the expression of epidermal growth factor receptor (EGFR), a key receptor in carcinogenesis, with clathrin in prostate cancer tissue, indicating recycling of EGFR through clathrin-mediated endocytosis (CME). These results indicate that in prostate cancer, caveolin-1-mediated endocytosis (CavME) may be acting as a brake and increase in CME may facilitate tumorigenicity and aggressiveness of prostate cancer through recycling of EGFR. Changes in the expression of these proteins can also potentially be used as a biomarker for prostate cancer to aid in diagnosis and prognosis and clinical decision-making.

Local transplantation of GMSC-derived exosomes to promote vascularized diabetic wound healing by regulating the Wnt/β-catenin pathways

With the increasing number of diabetic patients, chronic wound healing remains a great challenge in clinical medicine. As one of the main components secreted by stem cells, the exosome is considered to be a promising candidate for promoting chronic wound healing. Here, gingival mesenchymal stem cell (GMSC)-derived exosomes (GMSC-Exo) were isolated and demonstrated to promote the proliferation, migration, and tube formation of human umbilical vein endothelial cells (HUVECs) by regulating the Wnt/β-catenin signaling pathway in a diabetic-mimicking high glucose environment. In order to deliver GMSCs-Exo to the target site and prolong their local retention, porous microspheres consisting of poly-lactic-co-glycolic acid (PLGA), amphiphilic block copolymer (PLLA-PEG-PLLA), nano-hydroxyapatite (nHAP), and poly-ε-l-lysine (EPL) coating were fabricated through a double emulsion method and following surface treatment, hereafter referred to as PHE microspheres. PHE microspheres loaded with GMSCs-Exo were implanted into the full-thickness skin wound of a diabetic mouse model, resulting in significant vascularized wound healing when compared to a control group only injected with GMSCs-Exo suspension or filled with PHE microspheres. These findings indicated that the GMSCs-Exo-loaded porous microspheres could efficiently treat diabetic wounds and have promising potential for future clinical translations.

Distinctive Roles of Wnt Signaling in Chondrogenic Differentiation of BMSCs under Coupling of Pressure and Platelet-Rich Fibrin

BACKGROUND

Although newly formed constructs of feasible pressure-preadjusted bone marrow mesenchymal stem cells (BMSCs) and platelet-rich fibrin (PRF) showed biomechanical flexibility and superior capacity for cartilage regeneration, it is still not very clear how BMSCs and seed cells feel mechanical stimuli and convert them into biological signals, and the difference in signal transduction underlying mechanical and chemical cues is also unclear.

METHODS

To determine whether mechanical stimulation (hydrostatic pressure) and chemical cues (platelet-rich fibrin, PRF) activate canonical or noncanonical Wnt signaling in BMSCs, BMSCs cocultured with PRF were subjected to hydrostatic pressure loading, and the activation of the Wnt signaling molecules and expression of cartilage-associated proteins and genes were determined by western blotting and polymerase chain reaction (PCR). Inhibitors of canonical or noncanonical Wnt signaling, XVX-939 or L690,330, were adopted to investigate the role of Wnt signaling molecules in mechanically promoted chondrogenic differentiation of BMSCs.

RESULTS

Hydrostatic pressure of 120 kPa activated both Wnt/β-catenin signaling and Wnt/Ca²⁺ signaling, with the the maximum promotion effect at 60 min. PRF exerted no synergistic effect on Wnt/β-catenin signaling activation. However, the growth factors released by PRF might reverse the promotion effects of pressure on Wnt/Ca²⁺ signaling. Real-time PCR and Western blotting results showed that pressure could activate the expression of Col-II, Sox9, and aggrecan in BMSCs cocultured with PRF. Blocking experiment found a positive role of Wnt/β-catenin signaling, and a negative role of Wnt/Ca²⁺ signaling in chondrogenic differentiation of the BMSCs. Mutual inhibition exists between canonical and noncanonical Wnt signaling in BMSCs under pressure.

CONCLUSION

Wnt signaling participates in the pressure-promoted chondrogenesis of the BMSCs co-cultured with PRF, with canonical and noncanonical pathways playing distinct roles during the process.

De Novo Design of A Membrane-Anchored Probe for Multidimensional Quantification of Endocytic Dynamics

As a process of cellular uptake, endocytosis, with gradient acidity in different endocytic vesicles, is vital for the homeostasis of intracellular nutrients and other functions. To study the dynamics of endocytic pathway, a membrane-anchored pH probe, ECGreen, is synthesized to visualize endocytic vesicles under structured illumination microscopy (SIM), a super-resolution technology. Being sensitive to acidity with increasing fluorescence at low pH, ECGreen can differentiate early and late endosomes as well as endolysosomes. Meanwhile, membrane anchoring not only improves the durability of ECGreen, but also provides an excellent anti-photobleaching property for long-time imaging with SIM. Moreover, by taking these advantages of ECGreen, a multidimensional analysis model containing spatial, temporal, and pH information is successfully developed for elucidating the dynamics of endocytic vesicles and their interactions with mitochondria during autophagy, and reveals a fast conversion of endosomes near the plasma membrane.

SIRT6 Promotes the Progression of Prostate Cancer via Regulating the Wnt/β-Catenin Signaling Pathway

Sirtuin 6 (SIRT6), a DNA repair-related gene, has undergone an extremely thorough study for its involvement in the development of many different cancers. The objective of our study was to explore the function and mechanism of SIRT6-induced regulation of prostate cancer (PCa). RT-PCR was performed to validate the levels of SIRT6 in PCa cell lines. Cell proliferation, migration, and invasion of cells with SIRT6 knockdown were assessed using CCK-8 assay, colony formation assay, wound-healing assay, and transwell assay. Western blot was applied to assess the related proteins. We found that SIRT6 expression was distinctly upregulated in PCa specimens and cells. Loss-of-functional assays revealed that SIRT6 silence suppressed the proliferation and metastasis of PCa cells. Mechanistic studies revealed that SIRT6 silence inhibited Wnt/β‐catenin signaling and EMT progress. Overall, the study confirmed the upregulation of SIRT6 in patients with PCa and its association with the progression. SIRT6 promoted PCa progression by regulating Wnt/β‐catenin signaling, providing a promising biomarker and treatment approach for preventing PCa.

The Effects of Crocin on Bone and Cartilage Diseases

Crocin, the main biologically active carotenoid of saffron, generally is derived from the dried trifid stigma of Crocus sativus L. Many studies have demonstrated that crocin has several therapeutic effects on biological systems through its anti-oxidant and anti-inflammatory properties. The wide range of crocin activities is believed to be because of its ability to anchor to many proteins, triggering some cellular pathways responsible for cell proliferation and differentiation. It also has therapeutic potentials in arthritis, osteoarthritis, rheumatoid arthritis, and articular pain probably due to its anti-inflammatory properties. Anti-apoptotic effects, as well as osteoclast inhibition effects of crocin, have suggested it as a natural substance to treat osteoporosis and degenerative disease of bone and cartilage. Different mechanisms underlying crocin effects on bone and cartilage repair have been investigated, but remain to be fully elucidated. The present review aims to undertake current knowledge on the effects of crocin on bone and cartilage degenerative diseases with an emphasis on its proliferative and differentiative properties in mesenchymal stem cells.

Polarized Dishevelled dissolution and reassembly drives embryonic axis specification in sea star oocytes

The organismal body axes that are formed during embryogenesis are intimately linked to intrinsic asymmetries established at the cellular scale in oocytes.1 However, the mechanisms that generate cellular asymmetries within the oocyte and then transduce that polarity to organismal scale body axes are poorly understood outside of select model organisms. Here, we report an axis-defining event in meiotic oocytes of the sea star Patiria miniata. Dishevelled (Dvl) is a cytoplasmic Wnt pathway effector required for axis development in diverse species,2-4 but the mechanisms governing its function and distribution remain poorly defined. Using time-lapse imaging, we find that Dvl localizes uniformly to puncta throughout the cell cortex in Prophase I-arrested oocytes but becomes enriched at the vegetal pole following meiotic resumption through a dissolution-reassembly mechanism. This process is driven by an initial disassembly phase of Dvl puncta, followed by selective reformation of Dvl assemblies at the vegetal pole. Rather than being driven by Wnt signaling, this localization behavior is coupled to meiotic cell cycle progression and influenced by Lamp1+ endosome association and Frizzled receptors pre-localized within the oocyte cortex. Our results reveal a cell cycle-linked mechanism by which maternal cellular polarity is transduced to the embryo through spatially regulated Dvl dynamics.

Integrated metabolomics coupled with pattern recognition and pathway analysis to reveal molecular mechanism of cadmium-induced diabetic nephropathy

Diabetic nephropathy (DN) is becoming a worldwide public health problem and its pathophysiological mechanism is not well understood. Emerging evidences indicated that cadmium (Cd), an industrial material but also an environmental toxin, may be involved in the development and progression of diabetes and diabetes-related kidney disease. However, the underlying mechanism is still unclear. Herein, a DN animal model was constructed by exposing to Cd, the metabolomic profiling of DN mice were obtained by using ultra performance liquid chromatography coupled with quadrupole time-of-flight mass spectrometry (UPLC-Q-TOF/MS), pattern recognition and pathway analysis were performed to screen potential biomarker. Moreover, western blotting was employed to verify the possible mechanism involved in the occurrence of Cd-induced DN. A total of 66 metabolites in serum have been screened out and identified as biomarkers, including free fatty acids, phospholipids, sphingomyelins, glycerides, and others. Significant differences were demonstrated between the metabolic profiles, including decreased levels of phospholipid and increased content of triglyceride, diacylglycerols, ceramide, lysophosphatidylcholine in Cd-induced DN mice compared with control. Protein expression level of p38 MAPK and Wnt/β-catenin were significantly increased. UPLC-Q-TOF/MS-based serum metabolomics coupled with pattern recognition methods and pathway analysis provide a powerful approach to identify potential biomarkers and is a new strategy to predict the underlying mechanism of disease caused by environmental toxicant.

Rab7 is required for mesoderm patterning and gastrulation in Xenopus

Early embryogenesis requires tightly controlled temporal and spatial coordination of cellular behavior and signaling. Modulations are achieved at multiple levels, from cellular transcription to tissue-scale behavior. Intracellularly, the endolysosomal system emerges as an important regulator at different levels, but in vivo studies are rare. In the frog Xenopus, little is known about the developmental roles of endosomal regulators, or their potential involvement in signaling, especially for late endosomes. Here, we analyzed a hypothesized role of Rab7 in this context, a small GTPase known for its role as a late endosomal regulator. First, rab7 showed strong maternal expression. Following localized zygotic transcript enrichment in the mesodermal ring and neural plate, it was found in tailbud-stage neural ectoderm, notochord, pronephros, eyes and neural crest tissues. Inhibition resulted in strong axis defects caused by a requirement of rab7 for mesodermal patterning and correct gastrulation movements. To test a potential involvement in growth factor signaling, we analyzed early Wnt-dependent processes in the mesoderm. Our results suggest a selective requirement for ligand-induced Wnt activation, implicating a context-dependent role of Rab7.

Summary: The late endosomal regulator Rab7 is required for gastrulation movements and axis elongation in Xenopus by regulating early mesoderm patterning.

Loss of zebrafish atp6v1e1b, encoding a subunit of vacuolar ATPase, recapitulates human ARCL type 2C syndrome and identifies multiple pathobiological signatures

The inability to maintain a strictly regulated endo(lyso)somal acidic pH through the proton-pumping action of the vacuolar-ATPases (v-ATPases) has been associated with various human diseases including heritable connective tissue disorders. Autosomal recessive (AR) cutis laxa (CL) type 2C syndrome is associated with genetic defects in the ATP6V1E1 gene and is characterized by skin wrinkles or loose redundant skin folds with pleiotropic systemic manifestations. The underlying pathological mechanisms leading to the clinical presentations remain largely unknown. Here, we show that loss of atp6v1e1b in zebrafish leads to early mortality, associated with craniofacial dysmorphisms, vascular anomalies, cardiac dysfunction, N-glycosylation defects, hypotonia, and epidermal structural defects. These features are reminiscent of the phenotypic manifestations in ARCL type 2C patients. Our data demonstrates that loss of atp6v1e1b alters endo(lyso)somal protein levels, and interferes with non-canonical v-ATPase pathways in vivo. In order to gain further insights into the processes affected by loss of atp6v1e1b, we performed an untargeted analysis of the transcriptome, metabolome, and lipidome in early atp6v1e1b-deficient larvae. We report multiple affected pathways including but not limited to oxidative phosphorylation, sphingolipid, fatty acid, and energy metabolism together with profound defects on mitochondrial respiration. Taken together, our results identify complex pathobiological effects due to loss of atp6v1e1b in vivo.

Cutis laxa syndromes are pleiotropic disorders of the connective tissue, characterized by skin redundancy and variable systemic manifestations. Cutis laxa syndromes are caused by pathogenic variants in genes encoding structural and regulatory components of the extracellular matrix or in genes encoding components of cellular trafficking, metabolism, and mitochondrial function. Pathogenic variants in genes coding for vacuolar-ATPases, a multisubunit complex responsible for the acidification of multiple intracellular vesicles, cause type 2 cutis laxa syndromes, a group of cutis laxa subtypes further characterized by neurological, skeletal, and rarely cardiopulmonary manifestations. To investigate the pathomechanisms of vacuolar-ATPase dysfunction, we generated zebrafish models that lack a crucial subunit of the vacuolar-ATPases. The mutant zebrafish models show morphological and functional features reminiscent of the phenotypic manifestations in cutis laxa patients carrying pathogenic variants in ATP6V1E1. In-depth analysis at multiple -omic levels identified biological signatures that indicate impairment of signaling pathways, lipid metabolism, and mitochondrial respiration. We anticipate that these data will contribute to a better understanding of the pathogenesis of cutis laxa syndromes and other disorders involving defective v-ATPase function, which may eventually improve patient treatment and management.

The BMP Pathway in Blood Vessel and Lymphatic Vessel Biology

Bone morphogenetic proteins (BMPs) were originally identified as the active components in bone extracts that can induce ectopic bone formation. In recent decades, their key role has broadly expanded beyond bone physiology and pathology. Nowadays, the BMP pathway is considered an important player in vascular signaling. Indeed, mutations in genes encoding different components of the BMP pathway cause various severe vascular diseases. Their signaling contributes to the morphological, functional and molecular heterogeneity among endothelial cells in different vessel types such as arteries, veins, lymphatic vessels and capillaries within different organs. The BMP pathway is a remarkably fine-tuned pathway. As a result, its signaling output in the vessel wall critically depends on the cellular context, which includes flow hemodynamics, interplay with other vascular signaling cascades and the interaction of endothelial cells with peri-endothelial cells and the surrounding matrix. In this review, the emerging role of BMP signaling in lymphatic vessel biology will be highlighted within the framework of BMP signaling in the circulatory vasculature.

A possible way to prevent the progression of bone lesions in multiple myeloma via Src-homology-region-2-domain-containing-phosphatase-1 activation

On the basis of our recent findings, in which multiple receptor-mediated mast cell functions are regulated via a common signaling cascade, we posit that the formation and functioning of osteoclasts are also controlled by a similar common mechanism. These cells are derived from the same granulocyte/monocyte progenitors and share multiple receptors except those that are cell-specific. In both types of cells, all known receptors reside in lipid rafts, form multiprotein complexes with recruited signaling molecules, and are internalized upon receptor engagement. Signal transduction proceeds in a chain of protein phosphorylations, where adaptor protein LAT (linker-for-activation-of-T-cells) plays a central role. The key kinase that associates LAT phosphorylation and lipid raft internalization is Syk (spleen-tyrosine-kinase) and/or an Src-family-kinase, most probably Lck (lymphocyte-specific-protein-tyrosine-kinase). Dephosphorylation of phosphorylated Syk and Lck by activated SHP-1 (Src-homology-region-2-domain-containing-phosphatase-1) terminates the signal transduction and endocytosis of receptors, resulting in inhibition of osteoclast differentiation and other functions. In malignant plasma cells (MM cells) too, SHP-1 plays a similar indispensable role in controlling signal transduction required for survival and proliferation, though BLNK (B-cell-linker-protein), a functional equivalent of LAT and SLP-76 (SH2-domain-containing-leukocyte-protein-of-76-kDa) in B cells, is used instead of LAT. In both osteoclasts and MM cells, therefore, activated SHP-1 acts negatively in receptor-mediated cellular functions. In osteoblasts, however, activated SHP-1 promotes differentiation, osteocalcin generation, and mineralization by preventing both downregulation of transcription factors, such as Ostrix and Runx2, and degradation of β-catenin required for activation of the transcription factors. SHP-1 is activated by tyrosine phosphorylation and micromolar doses (M-dose) of CCRI-ligand-induced SHP-1 activation. Small molecular compounds, such as A770041, Sorafenib, Nitedanib, and Dovitinib, relieve the autoinhibitory conformation. Activation of SHP-1 by M-dose CCRI ligands or the compounds described may prevent the progression of bone lesions in MM.

EHD3 positively regulated by NR5A1 participates in testosterone synthesis via endocytosis

AIMS

Increasing evidence has shown that hormone secretion is regulated by endocytosis. Eps15 homology domain-containing protein 3 (EHD3) is an endocytic-trafficking regulatory protein, but whether EHD3 is associated with testosterone secretion is not clear. This work aims to explore the role of EHD3 in testosterone synthesis.

MAIN METHODS

Testosterone concentration was determined by ELISA. The effects of EHD3 on endocytosis were assessed by exosomes tracing assay and Immunofluorescence. Targeting relationship between EHD3 and NR5A1 was verified by chromatin immunoprecipitation (ChIP) and dual luciferase reporter gene assay in Leydig cells. For in vivo assessments, conditional NR5A1 knockout mouse model was established with CRISPR/Cas9 gene targeting technology.

KEY FINDINGS

EHD3 overexpression significantly increased the concentration of testosterone. EHD3 knockdown markedly decreased testosterone synthesis by reducing endocytosis. The activity of the EHD3 promoter was positively regulated by NR5A1, which occupied the conserved sequence "AGGTCA" in the EHD3 promoter. Furthermore, mice with a Leydig cell-specific conditional NR5A1 knockout displayed the blunted levels of EHD3 and clathrin (a key factor for endocytosis), and serum testosterone concentration compared with NR5A1^f/f mice.

SIGNIFICANCE

This study suggests a potential molecular mechanism of testosterone synthesis to fully understand male reproductive health.

MicroRNA-665 facilitates cell proliferation and represses apoptosis through modulating Wnt5a/β-Catenin and Caspase-3 signaling pathways by targeting TRIM8 in LUSC

Background

MicroRNAs (miRNAs) are involved in the oncogenesis, development and transformation of lung squamous cell carcinoma (LUSC). miR-665 is clinically significant and acts as a pivotal function in some cancers. Nevertheless, the effects and the potential mechanisms of miR-665 in human LUSC are still unknown.

Methods

To analyse the clinical significant of miR-665 in human LUSC, quantitative real-time PCR (qRT-PCR) was use to measure miR-665 expression in LUSC specimen tissues and cell lines. Tripartite motif 8 (TRIM8) was verified a target of miR-665 by performing bioinformatic prediction and luciferase reporter assay. The expression levels of TRIM8 were examined through qRT-PCR and Western blotting in LUSC specimen tissues. CCK8 assay was fulfilled for analyzing the function in LUSC cell proliferation. Flow cytometry was used to detect cell and apoptosis. TRIM8 silencing and overexpression further verified the biological effects as those caused by miR-665.

Results

Here we reported that miR-665 expression was upregulated in LUSC specimen tissues and cell lines. High miR-665 levels were related to differentiation, tumor size and TNM stage. miR-665 mimics facilitated LUSC cell growth and cell cycle G1-S transition and repressed apoptosis. miR-665 inhibitor suppressed cell proliferation and G1-S transition and promoted apoptosis. miR-665 expression was negatively correlated with TRIM8 mRNA expression in LUSC. Luciferase reporter assay confirmed that TRIM8 was a direct target gene of miR-665. miR-665 mimics downregulated the TRIM8 levels, and miR-665 inhibitor upregulated the TRIM8 levels in LUSC cells. Particularly, silencing TRIM8 led to the similar effects of miR-665 mimics in LUSC cells. Overexpression of TRIM8 inhibited LUSC cell proliferation in vitro and in vivo. Furthermore, miR-665 promoted LUSC cell proliferation through facilitating the Wnt5a/β-catenin signaling pathway and restrained apoptosis via inhibiting Caspase-3 signaling pathway, whereas TRIM8 suppressed cell growth by repressing the Wnt5a/β-catenin signaling pathway and induced apoptosis through activating Caspase-3 signaling pathway.

Conclusions

The current study demonstrates that miR-665 facilitates LUSC cell proliferation and cell cycle transition by regulation of the Wnt5a/β-Catenin signaling pathway and represses cell apoptosis via modulation of Caspase-3 signaling pathway by directly targeting TRIM8. These findings suggest that miR-665 might be a potential new target for LUSC therapy.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12935-021-01913-z.

Neurodevelopmental defects and neurodegenerative phenotypes in human brain organoids carrying Parkinson's disease-linked DNAJC6 mutations

Loss-of-function mutations of DNAJC6, encoding HSP40 auxilin, have recently been identified in patients with early-onset Parkinson's disease (PD). To study the roles of DNAJC6 in PD pathogenesis, we used human embryonic stem cells with CRISPR-Cas9-mediated gene editing. Here, we show that DNAJC6 mutations cause key PD pathologic features, i.e., midbrain-type dopamine (mDA) neuron degeneration, pathologic α-synuclein aggregation, increase of intrinsic neuronal firing frequency, and mitochondrial and lysosomal dysfunctions in human midbrain-like organoids (hMLOs). In addition, neurodevelopmental defects were also manifested in hMLOs carrying the mutations. Transcriptomic analyses followed by experimental validation revealed that defects in DNAJC6-mediated endocytosis impair the WNT-LMX1A signal during the mDA neuron development. Furthermore, reduced LMX1A expression during development caused the generation of vulnerable mDA neurons with the pathologic manifestations. These results suggest that the human model of DNAJC6-PD recapitulates disease phenotypes and reveals mechanisms underlying disease pathology, providing a platform for assessing therapeutic interventions.

Regulation of Wnt Signaling Pathways at the Plasma Membrane and Their Misregulation in Cancer

Wnt signaling is one of the key signaling pathways that govern numerous physiological activities such as growth, differentiation and migration during development and homeostasis. As pathway misregulation has been extensively linked to pathological processes including malignant tumors, a thorough understanding of pathway regulation is essential for development of effective therapeutic approaches. A prominent feature of cancer cells is that they significantly differ from healthy cells with respect to their plasma membrane composition and lipid organization. Here, we review the key role of membrane composition and lipid order in activation of Wnt signaling pathway by tightly regulating formation and interactions of the Wnt-receptor complex. We also discuss in detail how plasma membrane components, in particular the ligands, (co)receptors and extracellular or membrane-bound modulators, of Wnt pathways are affected in lung, colorectal, liver and breast cancers that have been associated with abnormal activation of Wnt signaling. Wnt-receptor complex components and their modulators are frequently misexpressed in these cancers and this appears to correlate with metastasis and cancer progression. Thus, composition and organization of the plasma membrane can be exploited to develop new anticancer drugs that are targeted in a highly specific manner to the Wnt-receptor complex, rendering a more effective therapeutic outcome possible.

Regulation of Wnt receptor activity: Implications for therapeutic development in colon cancer

Hyperactivation of Wnt/β-catenin (canonical) signaling in colorectal cancers (CRCs) was identified in the 1990s. Most CRC patients have mutations in genes that encode components of the Wnt pathway. Inactivating mutations in the adenomatous polyposis coli (APC) gene, which encodes a protein necessary for β-catenin degradation, are by far the most prevalent. Other Wnt signaling components are mutated in a smaller proportion of CRCs; these include a FZD-specific ubiquitin E3 ligase known as ring finger protein 43 that removes FZDs from the cell membrane. Our understanding of the genetic and epigenetic landscape of CRC has grown exponentially because of contributions from high-throughput sequencing projects such as The Cancer Genome Atlas. Despite this, no Wnt modulators have been successfully developed for CRC-targeted therapies. In this review, we will focus on the Wnt receptor complex, and speculate on recent discoveries about ring finger protein 43regulating Wnt receptors in CRCs. We then review the current debate on a new APC-Wnt receptor interaction model with therapeutic implications.

Zooming in on the WNT/CTNNB1 Destruction Complex: Functional Mechanistic Details with Implications for Therapeutic Targeting

WNT/CTNNB1 signaling is crucial for balancing cell proliferation and differentiation in all multicellular animals. CTNNB1 accumulation is the hallmark of WNT/CTNNB1 pathway activation and the key downstream event in both a physiological and an oncogenic context. In the absence of WNT stimulation, the cytoplasmic and nuclear levels of CTNNB1 are kept low because of its sequestration and phosphorylation by the so-called destruction complex, which targets CTNNB1 for proteasomal degradation. In the presence of WNT proteins, or as a result of oncogenic mutations, this process is impaired and CTNNB1 levels become elevated.Here we discuss recent advances in our understanding of destruction complex activity and inactivation, focusing on the individual components and interactions that ultimately control CTNNB1 turnover (in the "WNT off" situation) and stabilization (in the "WNT on" situation). We especially highlight the insights gleaned from recent quantitative, image-based studies, which paint an unprecedentedly detailed picture of the dynamic events that control destruction protein complex composition and function. We argue that these mechanistic details may reveal new opportunities for therapeutic intervention and could result in the destruction complex re-emerging as a target for therapy in cancer.

Wnt signalling and endocytosis: Mechanisms, controversies and implications for stress responses

Wnt signalling is one of a few conserved pathways that control diverse aspects of development and morphogenesis in all metazoan species. Endocytosis is a key mechanism that regulates the secretion and graded extracellular distribution of Wnt glycoproteins from the source cells, as well as Wnt signal transduction in the receiving cells. However, controversies exist regarding the requirement of clathrin-dependent endocytosis in Wnt signalling. Various lines of evidence from recent studies suggest that Wnt-β-catenin signalling is also involved in the regulation of cellular stress responses in adulthood, a role that is beyond its canonical functions in animal development. In this review, we summarise recent advances in the molecular and cellular mechanisms by which endocytosis modulates Wnt signalling. We also discuss how Wnt signalling could be repurposed to regulate mitochondrial stress response in the nematode Caenorhabditis elegans.

Mucin-type O-glycosylation controls pluripotency in mouse embryonic stem cells via Wnt receptor endocytosis

Mouse embryonic stem cells (ESCs) can differentiate into a range of cell types during development, and this pluripotency is regulated by various extrinsic and intrinsic factors. Mucin-type O-glycosylation has been suggested to be a potential factor in the control of ESC pluripotency, and is characterized by the addition of N-acetylgalactosamine (GalNAc) to serine or threonine residues of membrane-anchored proteins and secreted proteins. To date, the relationship between mucin-type O-glycosylation and signaling in ESCs remains undefined. Here, we identify the elongation pathway via C1GalT1 that synthesizes T antigen (Galβ1-3GalNAc) as the most prominent among mucin-type O-glycosylation modifications in ESCs. Moreover, we show that mucin-type O-glycosylation on the Wnt signaling receptor frizzled-5 (Fzd5) regulates its endocytosis via galectin-3 binding to T antigen, and that reduction of T antigen results in the exit of the ESCs from pluripotency via canonical Wnt signaling activation. Our findings reveal a novel regulatory mechanism that modulates Wnt signaling and, consequently, ESC pluripotency.This article has an associated First Person interview with the first author of the paper.

Alleviation by Mahuang Fuzi and Shenzhuo Decoction in High Glucose-Induced Podocyte Injury by Inhibiting the Activation of Wnt/β-Catenin Signaling Pathway, Resulting in Activation of Podocyte Autophagy

Background

Organ fibrosis is a common endpoint of a variety of diseases. Many studies have shown that the pathogenesis of diabetic kidney disease (DKD) is related to the excessive activation of the Wnt/β-catenin signaling pathway on podocytes, so the treatment of DKD starts from this signaling pathway. At the same time, DKD, as a metabolic disease, has many connections related to podocyte autophagy.

Objectives

We experimented the effects of Mahuang Fuzi and Shenzhuo decoction (MFSD) which is the combination of Mahuang Fuzi decoction and Shenzhuo decoction in traditional Chinese medicine compounds used "The Golden Chamber" in high glucose-induced podocytes, determined whether this effect was related to Wnt/β-catenin signaling pathway, and further investigated the relationship between this effect and autophagy.

Methods

The mice podocytes were stimulated by using 30 mmol/L of high glucose and serum containing MFSD or Wnt/β-catenin signaling pathway inhibitor DKK1 (100 ng/ml) was used to intervene podocytes before high glucose stimulation. Podocyte injury-related proteins, Wnt/β-catenin signaling pathway-related proteins, and autophagy-related proteins were detected by using western blotting and immunofluorescence analysis.

Results

Our results showed that DKK1 and MFSD treatment significantly upregulated the protein expressions of nephrin, podocin, podocalyxin, and podoplanin in high glucose-induced podocytes and downregulated the β-catenin protein expression. Furthermore, the protein expressions of beclin1, LC3B, and P62 were also significantly increased in high glucose-induced podocytes.

Conclusion

Our experiments confirmed that the destruction of podocytes in DKD is related to the excessive activation of Wnt/β-catenin signaling pathway and the inhibition of autophagy after activation. MFSD treatment can inhibit the activation of Wnt/β-catenin signaling pathway in podocytes stimulated by high glucose and helpful in reducing the podocyte injury. This protective mechanism can be related to the enhancement of podocyte autophagy by MFSD treatment.

The Role of Proteoglycans in Cancer Metastasis and Circulating Tumor Cell Analysis

Circulating tumor cells (CTCs) are accessible by liquid biopsies via an easy blood draw. They represent not only the primary tumor site, but also potential metastatic lesions, and could thus be an attractive supplement for cancer diagnostics. However, the analysis of rare CTCs in billions of normal blood cells is still technically challenging and novel specific CTC markers are needed. The formation of metastasis is a complex process supported by numerous molecular alterations, and thus novel CTC markers might be found by focusing on this process. One example of this is specific changes in the cancer cell glycocalyx, which is a network on the cell surface composed of carbohydrate structures. Proteoglycans are important glycocalyx components and consist of a protein core and covalently attached long glycosaminoglycan chains. A few CTC assays have already utilized proteoglycans for both enrichment and analysis of CTCs. Nonetheless, the biological function of proteoglycans on clinical CTCs has not been studied in detail so far. Therefore, the present review describes proteoglycan functions during the metastatic cascade to highlight their importance to CTCs. We also outline current approaches for CTC assays based on targeting proteoglycans by their protein cores or their glycosaminoglycan chains. Lastly, we briefly discuss important technical aspects, which should be considered for studying proteoglycans.

Fgfbp1 promotes blood-brain barrier development by regulating collagen IV deposition and maintaining Wnt/β-catenin signaling

Central nervous system (CNS) blood vessels contain a functional blood-brain barrier (BBB) that is necessary for neuronal survival and activity. Although Wnt/β-catenin signaling is essential for BBB development, its downstream targets within the neurovasculature remain poorly understood. To identify targets of Wnt/β-catenin signaling underlying BBB maturation, we performed a microarray analysis that identified Fgfbp1 as a novel Wnt/β-catenin-regulated gene in mouse brain endothelial cells (mBECs). Fgfbp1 is expressed in the CNS endothelium and secreted into the vascular basement membrane during BBB formation. Endothelial genetic ablation of Fgfbp1 results in transient hypervascularization but delays BBB maturation in specific CNS regions, as evidenced by both upregulation of Plvap and increased tracer leakage across the neurovasculature due to reduced Wnt/β-catenin activity. In addition, collagen IV deposition in the vascular basement membrane is reduced in mutant mice, leading to defective endothelial cell-pericyte interactions. Fgfbp1 is required cell-autonomously in mBECs to concentrate Wnt ligands near cell junctions and promote maturation of their barrier properties in vitro Thus, Fgfbp1 is a crucial extracellular matrix protein during BBB maturation that regulates cell-cell interactions and Wnt/β-catenin activity.

Ykt6-dependent endosomal recycling is required for Wnt secretion in the Drosophila wing epithelium

Morphogens are important signalling molecules for tissue development and their secretion requires tight regulation. In the wing imaginal disc of flies, the morphogen Wnt/Wingless is apically presented by the secreting cell and re-internalized before final long-range secretion. Why Wnt molecules undergo these trafficking steps and the nature of the regulatory control within the endosomal compartment remain unclear. Here, we have investigated how Wnts are sorted at the level of endosomes by the versatile v-SNARE Ykt6. Using in vivo genetics, proximity-dependent proteomics and in vitro biochemical analyses, we show that most Ykt6 is present in the cytosol, but can be recruited to de-acidified compartments and recycle Wnts to the plasma membrane via Rab4-positive recycling endosomes. Thus, we propose a molecular mechanism by which producing cells integrate and leverage endocytosis and recycling via Ykt6 to coordinate extracellular Wnt levels.

Exploring the mechanistic and temporal regulation of LRP6 endocytosis in canonical WNT signaling

Endocytosis plays a pivotal regulatory role in canonical WNT signaling. Internalization of the low-density lipoprotein receptor-related protein 6 (LRP6) receptor complex can either promote or attenuate canonical WNT signaling, depending on the employed internalization pathway. Detailed analysis of the mechanism of LRP6 internalization and its temporal regulation is crucial for understanding the different cellular responses to WNT stimulation under varying conditions and in various cell types. Here, we elucidate the mechanisms involved in the internalization of LRP6 and re-evaluate existing, partly contradicting, theories on the regulation of LRP6 receptor internalization. We utilize a computational approach that aims at finding a set of mechanisms that accounts for the temporal dynamics of LRP6 receptor internalization upon WNT stimulation. Starting with a simple simulation model, we successively extend and probe the model's behavior based on quantitative measurements. The final model confirms that LRP6 internalization is clathrin independent in vertebrates, is not restricted to microdomains, and that signalosome formation delays LRP6 internalization within the microdomains. These findings partly revise the current understanding of LRP6 internalization in vertebrates.

Magnetic Mechanoactivation of Wnt Signaling Augments Dopaminergic Differentiation of Neuronal Cells

Wnt signaling is a key developmental pathway that regulates dopaminergic progenitor cell proliferation and differentiation during neuronal development. This makes Wnt signaling an important therapeutic target for neurodegenerative conditions such as Parkinson's disease. Wnt signaling can be modulated using peptides such as UM206, which bind to the Wnt receptor Frizzled. Previous work has demonstrated remote activation of the Wnt pathway through Frizzled using peptide-functionalized magnetic nanoparticles (MNPs) with magnetic field stimulation. Using this technology, Wnt signaling is remotely activated in the neuronal cell line SH-SY5Y, and the phenotypic response to stimulation is assessed. Results indicate β-catenin translocalization and activation of TCF/LEF responsive transcription in response to MNP and magnetic fields, which result in dopaminergic marker expression when synergistically combined with differentiation factors retinoic acid and the phorbol ester phorbol 12-myristate 13-acetate. This approach is translated into ex vivo postnatal rat brain slices modeling the developing nigrostriatal pathway. Dopaminergic marker expression is maintained in MNP-labeled SH-SY5Y cells after injection and magnetic stimulation. These results demonstrate the translational value of remote control of signal transduction for controlling neuronal precursor cell behavior and highlight the potential applications for controlled cell differentiation as part of cell therapies for neurodegenerative disease.

Clathrin regulates Wnt/β-catenin signaling by affecting Golgi to plasma membrane transport of transmembrane proteins

The canonical Wnt/β-catenin signaling pathway regulates cell proliferation in development and adult tissue homeostasis. Dysregulated signaling contributes to human diseases, in particular cancer. Growing evidence suggests a role for clathrin and/or endocytosis in the regulation of this pathway, but conflicting results exist and demand a deeper mechanistic understanding. We investigated the consequences of clathrin depletion on Wnt/β-catenin signaling in cell lines and found a pronounced reduction in β-catenin protein levels, which affects the amount of nuclear β-catenin and β-catenin target gene expression. Although we found no evidence that clathrin affects β-catenin levels via endocytosis or multivesicular endosome formation, an inhibition of protein transport through the biosynthetic pathway led to reduced levels of a Wnt co-receptor, low-density lipoprotein receptor-related protein 6 (LRP6), and cell adhesion molecules of the cadherin family, thereby affecting steady-state levels of β-catenin. We conclude that clathrin impacts on Wnt/β-catenin signaling by controlling exocytosis of transmembrane proteins, including cadherins and Wnt co-receptors that together control the membrane-bound and soluble pools of β-catenin.

LncRNA LINC00909 promotes cell proliferation and metastasis in pediatric acute myeloid leukemia via miR-625-mediated modulation of Wnt/β-catenin signaling

Long non-coding RNAs (lncRNAs) have been shown to involve in a variety of cancers. Our present study aimed to explore the exact roles of lncRNA LINC00909 (LINC00909) in the progression of pediatric acute myeloid leukemia (AML) and to study the potential molecular mechanism. In this study, the levels of LINC00909 were observed to be distinctly upregulated in AML patients and cell lines. Higher levels of LINC00909 were associated with FAB classification, cytogenetics and poorer prognosis. Functionally, knockdown of LINC00909 suppressed cell viabilities, migration and invasion, and promoted apoptosis of NB4 and HL-60 cells. Mechanistically, we demonstrated that LINC00909 functioned as a molecular sponge for miR-625. In addition, we observed that Wnt/β-catenin signaling pathway was suppressed by LINC00909 knockdown. Moreover, miR-625 levels were dramatically decreased in AML cells when Wnt/β-catenin signaling was activated. Overall, our findings identified a new AML-related lncRNA LINC00909 which may represent a novel biomarker and a potential therapeutic target of AML.

Endosomal Wnt signaling proteins control microtubule nucleation in dendrites

Dendrite microtubules are polarized with minus-end-out orientation in Drosophila neurons. Nucleation sites concentrate at dendrite branch points, but how they localize is not known. Using Drosophila, we found that canonical Wnt signaling proteins regulate localization of the core nucleation protein γTubulin (γTub). Reduction of frizzleds (fz), arrow (low-density lipoprotein receptor-related protein [LRP] 5/6), dishevelled (dsh), casein kinase Iγ, G proteins, and Axin reduced γTub-green fluorescent protein (GFP) at branch points, and two functional readouts of dendritic nucleation confirmed a role for Wnt signaling proteins. Both dsh and Axin localized to branch points, with dsh upstream of Axin. Moreover, tethering Axin to mitochondria was sufficient to recruit ectopic γTub-GFP and increase microtubule dynamics in dendrites. At dendrite branch points, Axin and dsh colocalized with early endosomal marker Rab5, and new microtubule growth initiated at puncta marked with fz, dsh, Axin, and Rab5. We propose that in dendrites, canonical Wnt signaling proteins are housed on early endosomes and recruit nucleation sites to branch points.

Astragalus polysaccharide inhibits breast cancer cell migration and invasion by regulating epithelial‑mesenchymal transition via the Wnt/β‑catenin signaling pathway

Epithelial-mesenchymal transition (EMT) serves an important role in tumor migration and invasion. Astragalus polysaccharide (APS), which is the main component of the traditional Chinese medicine Astragalus membranaceus, has been identified to display an antitumor effect. However, the effects and mechanisms of APS during breast cancer migration and invasion are not completely understood. The present study investigated whether APS inhibited breast cancer migration and invasion by modulating the EMT pathway. An MTT assay and a Ki67 immunofluorescence staining assay demonstrated that APS inhibited the proliferation of breast cancer cells. The results of the wound healing and Transwell Matrigel invasion assays suggested that APS decreased the migration and invasion of breast cancer cells. The western blotting and immunofluorescence analyses further demonstrated that APS had a regulatory effect on EMT-related molecules. APS decreased the expression levels of Snail and vimentin, but increased E-cadherin expression. APS also downregulated Wnt1, β-catenin and downstream target expression. Additionally, the present results suggested that APS decreased the proliferation, and EMT-mediated migration and invasion of cells by inhibiting the Wnt/β-catenin signaling pathway. The present study suggested that APS may serve as a promising therapeutic agent for breast cancer.

Crocin Alleviates Pain Hyperalgesia in AIA Rats by Inhibiting the Spinal Wnt5a/β-Catenin Signaling Pathway and Glial Activation

At present, most of the drugs have little effect on the pathological process of rheumatoid arthritis (RA). Analgesia is an important measure in the treatment of RA and is also one of the criteria to determine the therapeutic effects of the disease. Some studies have found that crocin, a kind of Chinese medicine, can effectively alleviate pain sensitization in pain model rats, but the mechanism is not clear. Emerging evidence indicates that crocin may inhibit the metastasis of lung and liver cancer cells from the breast by inhibiting Wnt/β-catenin and the Wnt signaling pathway is closely related to RA. Wnt5a belongs to the Wnt protein family and was previously thought to be involved only in nonclassical Wnt signaling pathways. Recent studies have shown that Wnt5a has both stimulatory and inhibitory effects on the classical Wnt signaling pathway, and so, Wnt5a has attracted increasing attention. This study demonstrated that crocin significantly increased the mechanical thresholds of adjuvant-induced arthritis (AIA) rats, suggesting that crocin can alleviate neuropathic pain. Crocin significantly decreased the levels of pain-related factors and glial activation. Foxy5, activator of Wnt5a, inhibited the above effects of crocin in AIA rats. In addition, intrathecal injection of a Wnt5a inhibitor significantly decreased hyperalgesia in AIA rats. This research shows that crocin may alleviate neuropathic pain in AIA rats by inhibiting the expression of pain-related molecules through the Wnt5a/β-catenin pathway, elucidating the mechanism by which crocin relieves neuropathic pain and provides a new way of thinking for the treatment of AIA pain.

RLIP controls receptor-ligand signaling by regulating clathrin-dependent endocytosis

RLIP (Ral-interacting protein) is a multifunctional protein that couples ATP hydrolysis with the movement of substances. Its primary function appears to be in the plasma membrane, where it catalyzes the ATP-dependent efflux of glutathione-conjugates (GS-Es), as well as un-metabolized drugs and toxins. In the plasma membrane, its interaction with the clathrin adaptor protein AP2 localizes it to endocytic vesicle, where its GS-E-stimulated ATPase and transport activity are required for clathrin-dependent endocytosis (CDE). CDE is an essential mechanism for internalizing ligand-receptor complexes that signal proliferation (EGF, insulin, IGF1), apoptosis (TNFα, TRAIL, Fas-L), and differentiation and morphogenesis (TGFβ, WNT, Notch, SHH). Aberrant functioning of these pathways appears crucial for most cancer cells to evade apoptosis, invade surrounding tissues, and metastasize. Internalization of receptor-ligand complexes by CDE begins a sequence of events that can terminate, initiate, or modulate downstream signaling; the consequences of signaling through these downstream pathways may be inherently different in cancer and normal cells, a view supported by numerous basic and clinical observations. In this review, we will discuss the GS-E transport activity of RLIP, which determines the rate of ligand endocytosis, and how the inhibition and/or depletion of RLIP globally disrupts in ligand-receptor signaling.

TMEM88 Inhibits Wnt Signaling by Promoting Wnt Signalosome Localization to Multivesicular Bodies

Wnt/β-catenin signaling is regulated in a bimodal fashion during cardiogenesis. Signaling is initially required to promote generation of precardiac mesoderm, but subsequently must be repressed for cardiac progenitor specification. TMEM88 was discovered recently as a negative regulator during the later phase of cardiac progenitor specification, but how TMEM88 functions was unknown. Based on a C-terminal PDZ-binding motif, TMEM88 was proposed to act by targeting the PDZ domain of Dishevelled, the positive Wnt signaling mediator. However, we discovered that TMEM88 acts downstream of the β-catenin destruction complex and can inhibit Wnt signaling independent of Dishevelled. TMEM88 requires the PDZ-binding motif for trafficking from Golgi to the plasma membrane and is also found in the multivesicular body (MVB) associated with the endocytosed Wnt signalosome. Expression of Tmem88 promotes association of the Wnt signalosome including β-catenin to the MVB, leading to reduced accumulation of nuclear β-catenin and repression of Wnt signaling.

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Human ESCs with a targeted TMEM88 knockout are impaired for cardiac specification

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TMEM88 does not require Dishevelled to inhibit Wnt signaling

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TMEM88 is trafficked from Golgi to plasma membrane and then to the MVB

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Expression of TMEM88 promotes association of the signalosome to the MVB

Mechanisms of intercellular Wnt transport

Wnt proteins are secreted glycoproteins that regulate multiple processes crucial to the development and tissue homeostasis of multicellular organisms, including tissue patterning, proliferation, cell fate specification, cell polarity and migration. To elicit these effects, Wnts act as autocrine as well as paracrine signalling molecules between Wnt-producing and Wnt-receiving cells. More than 40 years after the discovery of the Wg/Wnt pathway, it is still unclear how they are transported to fulfil their paracrine signalling functions. Several mechanisms have been proposed to mediate intercellular Wnt transport, including Wnt-binding proteins, lipoproteins, exosomes and cytonemes. In this Review, we describe the evidence for each proposed mechanism, and discuss how they may contribute to Wnt dispersal in tissue-specific and context-dependent manners, to regulate embryonic development precisely and maintain the internal steady state within a defined tissue.

Expression of transcriptional factor EB (TFEB) in differentiating spermatogonia potentially promotes cell migration in mouse seminiferous epithelium

BACKGROUND

Spermatogenesis is a complex process involving the self-renewal and differentiation of spermatogonia into mature spermatids in the seminiferous tubules. During spermatogenesis, germ cells migrate from the basement membrane to cross the blood-testis barrier (BTB) and finally reach the luminal side of the seminiferous epithelium. However, the mechanism for regulating the migration of germ cells remains unclear. In this study, we focused on the expression and function of transcriptional factor EB (TFEB), a master regulator of lysosomal biogenesis, autophagy and endocytosis, in spermatogenesis.

METHODS

The expression pattern of the TFEB in mouse testes were investigated by Western blotting and immunohistochemistry analyses. Either undifferentiated spermatogonia or differentiating spermatogonia were isolated from testes using magnetic-activated cell sorting based on specific cell surface markers. Differentiation of spermatogonia was induced with 100 nM retinoic acid (RA). shRNA was used to knock down TFEB in cells. TFEB expression was detected by immunofluorescence, qRT-PCR, and Western blotting. Cell migration was determined by both transwell migration assay and wound healing assay applied to a cell line of immortalized spermatogonia, GC-1 cells.

RESULTS

During testicular development, TFEB expression was rapidly increased in the testes at the period of 7 days post-partum (dpp) to 14 dpp, whereas in adult testis, it was predominantly localized in the nucleus of spermatogonia at stages VI to VIII of the seminiferous epithelial cycle. Accordingly, TFEB was observed to be mainly expressed in differentiating spermatogonia and was activated for nuclear translocation by RA treatment. Moreover, knockdown of TFEB expression by RNAi did not affect spermatogonial differentiation, but significantly reduced cell migration in GC-1 cells.

CONCLUSION

These findings imply that regionally distinct expression and activation of TFEB was strongly associated with RA signaling, and therefore may promote cell migration across the BTB and transport along the seminiferous epithelium.

Emerging role of contact-mediated cell communication in tissue development and diseases

Cells of multicellular organisms are in continuous conversation with the neighbouring cells. The sender cells signal the receiver cells to influence their behaviour in transport, metabolism, motility, division, and growth. How cells communicate with each other can be categorized by biochemical signalling processes, which can be characterised by the distance between the sender cell and the receiver cell. Existing classifications describe autocrine signals as those where the sender cell is identical to the receiver cell. Complementary to this scenario, paracrine signalling describes signalling between a sender cell and a different receiver cell. Finally, juxtacrine signalling describes the exchange of information between adjacent cells by direct cell contact, whereas endocrine signalling describes the exchange of information, e.g., by hormones between distant cells or even organs through the bloodstream. In the last two decades, however, an unexpected communication mechanism has been identified which uses cell protrusions to exchange chemical signals by direct contact over long distances. These signalling protrusions can deliver signals in both ways, from sender to receiver and vice versa. We are starting to understand the morphology and function of these signalling protrusions in many tissues and this accumulation of findings forces us to revise our view of contact-dependent cell communication. In this review, we will focus on the two main categories of signalling protrusions, cytonemes and tunnelling nanotubes. These signalling protrusions emerge as essential structural components of a vibrant communication network in the development and tissue homeostasis of any multicellular organism.

TMEM17 promotes malignant progression of breast cancer via AKT/GSK3β signaling

Purpose

Current knowledge of TMEM17, a recently identified protein of the transmembrane (TMEM) family, is limited, especially with respect to its expression and biological functions in malignant tumors. This study analyzed TMEM17 expression in invasive breast cancer tissue and breast cell lines and its relevance to clinicopathological factors, and investigated the mechanisms underlying the biological effects of TMEM17 on breast cancer cells.

Patients and methods

TMEM17 protein expression was determined in 20 freshly harvested specimens (tumor and paired normal tissues) by Western blotting. Immunohistochemical analysis was performed to determine the expression and subcellular localization of TMEM17 in samples from 167 patients (mean age, 49 years) diagnosed with invasive ductal carcinoma (38 with triple-negative breast cancer; 129 with non-triple-negative breast cancer) who underwent complete resection in the First Affiliated Hospital of China Medical University between 2011 and 2013. Furthermore, TMEM17 was knocked down by small interfering RNAs in breast cancer cell lines.

Results

TMEM17 was found to be significantly upregulated in breast cancer tissues compared to the corresponding normal breast tissues by Western blotting (p=0.015). Immunohistochemical analysis revealed that TMEM was significantly upregulated in invasive breast cancer cells compared to adjacent normal breast duct glandular epithelial cells (10.78% vs 76.05%, p<0.001), and its expression was closely related to the patient’s T-stage (p=0.022), advanced TNM stages (p=0.007), and lymph node metastasis (p=0.012). After TMEM17 knockdown or overexpression in breast cancer cell lines, TMEM17 upregulated p-AKT, p-GSK3β, active β-catenin, and Snail, and downstream target proteins c-myc and cyclin D1, and downregulated E-cadherin, resulting in increased cancer cell proliferation, invasion, and migration. These effects were reversed by the AKT inhibitor LY294002.

Conclusion

Our results indicate that TMEM17 is upregulated in breast cancer tissues and can promote malignant progression of breast cancer cells by activating the AKT/GSK3β signaling pathway.

From intra- to extracellular vesicles: extracellular vesicles in developmental signalling

Signalling from cell-to-cell is fundamental for determining differentiation and patterning. This communication can occur between adjacent and distant cells. Extracellular vesicles (EVs) are membrane-based structures thought to facilitate the long-distance movement of signalling molecules. EVs have recently been found to allow the transport of two major developmental signalling pathways: Hedgehog and Wnt. These signalling molecules undergo crucial post-translational lipid modifications, which anchor them to membranes and impede their free release into the extracellular space. Preparation of these ligands in EVs involves intracellular vesicle sorting in an endocytosis-dependent recycling process before secretion. In the present review, we discuss the most recent advances with regard to EV involvement in developmental signalling at a distance. We focus on the role of the protein complexes involved in EV genesis, and provide a comprehensive perspective of the contribution of these complexes to intracellular vesicle sorting of developmental signals for their extracellular secretion, reception and transduction.

Roles of two types of heparan sulfate clusters in Wnt distribution and signaling in Xenopus

Wnt proteins direct embryonic patterning, but the regulatory basis of their distribution and signal reception remain unclear. Here, we show that endogenous Wnt8 protein is distributed in a graded manner in Xenopus embryo and accumulated on the cell surface in a punctate manner in association with “N-sulfo-rich heparan sulfate (HS),” not with “N-acetyl-rich HS”. These two types of HS are differentially clustered by attaching to different glypicans as core proteins. N-sulfo-rich HS is frequently internalized and associated with the signaling vesicle, known as the Frizzled/Wnt/LRP6 signalosome, in the presence of Wnt8. Conversely, N-acetyl-rich HS is rarely internalized and accumulates Frzb, a secreted Wnt antagonist. Upon interaction with Frzb, Wnt8 associates with N-acetyl-rich HS, suggesting that N-acetyl-rich HS supports Frzb-mediated antagonism by sequestering Wnt8 from N-sulfo-rich HS. Thus, these two types of HS clusters may constitute a cellular platform for the distribution and signaling of Wnt8.

Wnt proteins mediate embryonic development but how protein localization and patterning is regulated is unclear. Here, the authors show that distinct structures with different heparan sulfate modifications (‘N-sulfo-rich’ and ‘N-acetyl-rich’) regulate cellular localization and signal transduction of Wnt8 in Xenopus.