Cadherin-6B undergoes macropinocytosis and clathrin-mediated endocytosis during cranial neural crest cell EMT

Inhibition of epithelial-to-mesenchymal transition augments antitumor efficacy of nanotherapeutics in pancreatic ductal adenocarcinoma

Intrinsic drug resistance mechanisms of tumor cells often reduce intracellular drug concentration to suboptimal levels. Epithelial-to-mesenchymal transition (EMT) is a pivotal process in tumor progression and metastasis that confers an aggressive phenotype as well as resistance to chemotherapeutics. Therefore, it is imperative to develop novel strategies and identify new targets to improve the overall efficacy of cancer treatment. We developed SN38 (active metabolite of irinotecan)-assembled glycol chitosan nanoparticles (cSN38) for the treatment of pancreatic ductal adenocarcinoma (PDAC). Furthermore, cSN38 and the TGF-β1 inhibitor LY364947 formed composite nanoparticles upon self-assembly (cSN38 + LY), which obviated the poor aqueous solubility of LY364947 and enhanced drug sensitivity. The therapeutic efficacy of cSN38 + LY nanotherapeutics was studied in vitro and in vivo using suitable models. The cSN38 nanoparticles exhibited an antitumor effect that was significantly attenuated by TGF-β-induced EMT. The cellular uptake of SN38 was impeded during EMT, which affected the therapeutic efficacy. The combination of LY364947 and cSN38 markedly enhanced the cellular uptake of SN38, increased cytotoxic effects, and inhibited EMT in PDAC cells in vitro. Furthermore, cSN38 + LY significantly inhibited PDAC xenograft growth in vivo. The cSN38 + LY nanoparticles increased the therapeutic efficacy of cSN38 via repressing the EMT of PDAC cells. Our findings provide a rationale for designing nanoscale therapeutics to combat PDAC.

Temporal changes in plasma membrane lipid content induce endocytosis to regulate developmental epithelial-to-mesenchymal transition

Epithelial-to-mesenchymal transition (EMT) is a dramatic change in cellular physiology during development and metastasis, which requires coordination between cell signaling, adhesion, and membrane protrusions. These processes all involve dynamic changes in the plasma membrane; yet, how membrane lipid content regulates membrane function during EMT remains incompletely understood. By screening for differential expression of lipid-modifying genes over the course of EMT in the avian neural crest, we have identified the ceramide-producing enzyme neutral sphingomyelinase 2 (nSMase2) as a critical regulator of a developmental EMT. nSMase2 expression begins at the onset of EMT, and in vivo knockdown experiments demonstrate that nSMase2 is necessary for neural crest migration. We find that nSMase2 promotes Wnt and BMP signaling and is required to activate the mesenchymal gene expression program. Mechanistically, we show that nSMase2-dependent ceramide production is necessary for and sufficient to up-regulate endocytosis and is required for Wnt co-receptor internalization. Finally, inhibition of endocytosis in the neural crest mimics the loss of migration and Wnt signaling observed following nSMase2 knockdown. Our results support a model in which nSMase2 is expressed at the onset of neural crest EMT to produce ceramide and facilitate receptor-mediated endocytosis of Wnt and BMP signaling complexes, thereby activating promigratory gene expression. These results highlight the critical role of plasma membrane lipid metabolism in regulating transcriptional changes during developmental EMT programs.

Chick cranial neural crest cells release extracellular vesicles that are critical for their migration

The content and activity of extracellular vesicles purified from cell culture media or bodily fluids have been studied extensively; however, the physiological relevance of exosomes within normal biological systems is poorly characterized, particularly during development. Although exosomes released by invasive metastatic cells alter migration of neighboring cells in culture, it is unclear whether cancer cells misappropriate exosomes released by healthy differentiated cells or reactivate dormant developmental programs that include exosome cell-cell communication. Using chick cranial neural fold cultures, we show that migratory neural crest cells, a developmentally critical cell type and model for metastasis, release and deposit CD63-positive 30-100 nm particles into the extracellular environment. Neural crest cells contain ceramide-rich multivesicular bodies and produce larger vesicles positive for migrasome markers as well. We conclude that neural crest cells produce extracellular vesicles including exosomes and migrasomes. When Rab27a plasma membrane docking is inhibited, neural crest cells become less polarized and rounded, leading to a loss of directional migration and reduced speed. These results indicate that neural crest cell exosome release is critical for migration.

Cadherin Signaling in Cancer and Autoimmune Diseases

Cadherins mediate cell–cell adhesion through a dynamic process that is strongly dependent on the cellular context and signaling. Cadherin regulation reflects the interplay between fundamental cellular processes, including morphogenesis, proliferation, programmed cell death, surface organization of receptors, cytoskeletal organization, and cell trafficking. The variety of molecular mechanisms and cellular functions regulated by cadherins suggests that we have only scratched the surface in terms of clarifying the functions mediated by these versatile proteins. Altered cadherins expression is closely connected with tumorigenesis, epithelial–mesenchymal transition (EMT)-dependent fibrosis, and autoimmunity. We review the current understanding of how cadherins contribute to human health and disease, considering the mechanisms of cadherin involvement in diseases progression, as well as the clinical significance of cadherins as therapeutic targets.

Mechanisms involved in selecting and maintaining neuroblastoma cancer stem cell populations, and perspectives for therapeutic targeting

Pediatric neuroblastomas (NBs) are heterogeneous, aggressive, therapy-resistant embryonal tumours that originate from cells of neural crest (NC) origin and in particular neuroblasts committed to the sympathoadrenal progenitor cell lineage. Therapeutic resistance, post-therapeutic relapse and subsequent metastatic NB progression are driven primarily by cancer stem cell (CSC)-like subpopulations, which through their self-renewing capacity, intermittent and slow cell cycles, drug-resistant and reversibly adaptive plastic phenotypes, represent the most important obstacle to improving therapeutic outcomes in unfavourable NBs. In this review, dedicated to NB CSCs and the prospects for their therapeutic eradication, we initiate with brief descriptions of the unique transient vertebrate embryonic NC structure and salient molecular protagonists involved NC induction, specification, epithelial to mesenchymal transition and migratory behaviour, in order to familiarise the reader with the embryonic cellular and molecular origins and background to NB. We follow this by introducing NB and the potential NC-derived stem/progenitor cell origins of NBs, before providing a comprehensive review of the salient molecules, signalling pathways, mechanisms, tumour microenvironmental and therapeutic conditions involved in promoting, selecting and maintaining NB CSC subpopulations, and that underpin their therapy-resistant, self-renewing metastatic behaviour. Finally, we review potential therapeutic strategies and future prospects for targeting and eradication of these bastions of NB therapeutic resistance, post-therapeutic relapse and metastatic progression.

Cellular organization and boundary formation in craniofacial development

Craniofacial morphogenesis is a highly dynamic process that requires changes in the behaviors and physical properties of cells in order to achieve the proper organization of different craniofacial structures. Boundary formation is a critical process in cellular organization, patterning, and ultimately tissue separation. There are several recurring cellular mechanisms through which boundary formation and cellular organization occur including, transcriptional patterning, cell segregation, cell adhesion and migratory guidance. Disruption of normal boundary formation has dramatic morphological consequences, and can result in human craniofacial congenital anomalies. In this review we discuss boundary formation during craniofacial development, specifically focusing on the cellular behaviors and mechanisms underlying the self-organizing properties that are critical for craniofacial morphogenesis.

Nutrient scavenging in cancer

While cancer cell proliferation depends on access to extracellular nutrients, inadequate tumour perfusion means that glucose, amino acids and lipids are often in short supply. To overcome this obstacle to growth, cancer cells utilize multiple scavenging strategies, obtaining macromolecules from the microenvironment and breaking them down in the lysosome to produce substrates for ATP generation and anabolism. Recent studies have revealed four scavenging pathways that support cancer cell proliferation in low-nutrient environments: scavenging of extracellular matrix proteins via integrins, receptor-mediated albumin uptake and catabolism, macropinocytic consumption of multiple components of the tumour microenvironment and the engulfment and degradation of entire live cells via entosis. New evidence suggests that blocking these pathways alone or in combination could provide substantial benefits to patients with incurable solid tumours. Both US Food and Drug Administration (FDA)-approved drugs and several agents in preclinical or clinical development shut down individual or multiple scavenging pathways. These therapies may increase the extent and durability of tumour growth inhibition and/or prevent the development of resistance when used in combination with existing treatments. This Review summarizes the evidence suggesting that scavenging pathways drive tumour growth, highlights recent advances that define the oncogenic signal transduction pathways that regulate scavenging and considers the benefits and detriments of therapeutic strategies targeting scavenging that are currently under development.

Cadherin-6B proteolytic N-terminal fragments promote chick cranial neural crest cell delamination by regulating extracellular matrix degradation

During epithelial-to-mesenchymal transitions (EMTs), chick cranial neural crest cells simultaneously delaminate from the basement membrane and segregate from the epithelia, in part, via multiple protease-mediated mechanisms. Proteolytic processing of Cadherin-6B (Cad6B) in premigratory cranial neural crest cells by metalloproteinases not only disassembles cadherin-based junctions but also generates shed Cad6B ectodomains or N-terminal fragments (NTFs) that may possess additional roles. Here we report that Cad6B NTFs promote delamination by enhancing local extracellular proteolytic activity around neural crest cells undergoing EMT en masse. During EMT, Cad6B NTFs of varying molecular weights are observed, indicating that Cad6B may be cleaved at different sites by A Disintegrin and Metalloproteinases (ADAMs) 10 and 19 as well as by other matrix metalloproteinases (MMPs). To investigate Cad6B NTF function, we first generated NTF constructs that express recombinant NTFs with similar relative mobilities to those NTFs shed in vivo. Overexpression of either long or short Cad6B NTFs in premigratory neural crest cells reduces laminin and fibronectin levels within the basement membrane, which then facilitates precocious neural crest cell delamination. Zymography assays performed with supernatants of neural crest cell explants overexpressing Cad6B long NTFs demonstrate increased MMP2 activity versus controls, suggesting that Cad6B NTFs promote delamination through a mechanism involving MMP2. Interestingly, this increase in MMP2 does not involve up-regulation of MMP2 or its regulators at the transcriptional level but instead may be attributed to a physical interaction between shed Cad6B NTFs and MMP2. Taken together, these results highlight a new function for Cad6B NTFs and provide insight into how cadherins regulate cellular delamination during normal developmental EMTs as well as aberrant EMTs that underlie human disease.

Alcohol exposure induces chick craniofacial bone defects by negatively affecting cranial neural crest development

Excess alcohol consumption during pregnancy could lead to fetal alcohol syndrome (FAS). However, the molecular mechanism leading to craniofacial abnormality, a feature of FAS, is still poorly understood. The cranial neural crest cells (NCCs) contribute to the formation of the craniofacial bones. Therefore, NCCs exposed to ethanol was investigated - using chick embryos and in vitro explant culture as experimental models. We demonstrated that exposure to 2% ethanol induced craniofacial defects, which includes parietal defect, in the developing chick fetus. Immunofluorescent staining revealed that ethanol treatment downregulated Ap-2ɑ, Pax7 and HNK-1 expressions by cranial NCCs. Using double-immunofluorescent stainings for Ap-2ɑ/pHIS3 and Ap-2ɑ/c-Caspase3, we showed that ethanol treatment inhibited cranial NCC proliferation and increased NCC apoptosis, respectively. Moreover, ethanol treatment of the dorsal neuroepithelium increased Laminin, N-Cadherin and Cadherin 6B expressions while Cadherin 7 expression was repressed. In situ hybridization also revealed that ethanol treatment up-regulated Cadherin 6B expression but down-regulated slug, Msx1, FoxD3 and BMP4 expressions. In summary, our experimental results demonstrated that ethanol treatment interferes with the production of cranial NCCs by affecting the proliferation and apoptosis of these cells. In addition, ethanol affected the delamination, epithelial-mesenchymal transition (EMT) and cell migration of cranial NCCs, which may have contributed to the etiology of the craniofacial defects.

Should I stay or should I go? Cadherin function and regulation in the neural crest

Our increasing comprehension of neural crest cell development has reciprocally advanced our understanding of cadherin expression, regulation, and function. As a transient population of multipotent stem cells that significantly contribute to the vertebrate body plan, neural crest cells undergo a variety of transformative processes and exhibit many cellular behaviors, including epithelial-to-mesenchymal transition (EMT), motility, collective cell migration, and differentiation. Multiple studies have elucidated regulatory and mechanistic details of specific cadherins during neural crest cell development in a highly contextual manner. Collectively, these results reveal that gradual changes within neural crest cells are accompanied by often times subtle, yet important, alterations in cadherin expression and function. The primary focus of this review is to coalesce recent data on cadherins in neural crest cells, from their specification to their emergence as motile cells soon after EMT, and to highlight the complexities of cadherin expression beyond our current perceptions, including the hypothesis that the neural crest EMT is a transition involving a predominantly singular cadherin switch. Further advancements in genetic approaches and molecular techniques will provide greater opportunities to integrate data from various model systems in order to distinguish unique or overlapping functions of cadherins expressed at any point throughout the ontogeny of the neural crest.

Cadherin-6B proteolysis promotes the neural crest cell epithelial-to-mesenchymal transition through transcriptional regulation

Cadherin proteolysis reduces cell–cell adhesion and generates cleavage products that could possess independent functions. Here, Schiffmacher et al. reveal that the intracellular C-terminal fragment generated by Cadherin-6B proteolysis promotes chick cranial neural crest cell EMT through positive transcriptional feedback into the neural crest gene regulatory network.

During epithelial-to-mesenchymal transitions (EMTs), cells disassemble cadherin-based junctions to segregate from the epithelia. Chick premigratory cranial neural crest cells reduce Cadherin-6B (Cad6B) levels through several mechanisms, including proteolysis, to permit their EMT and migration. Serial processing of Cad6B by a disintegrin and metalloproteinase (ADAM) proteins and γ-secretase generates intracellular C-terminal fragments (CTF2s) that could acquire additional functions. Here we report that Cad6B CTF2 possesses a novel pro-EMT role by up-regulating EMT effector genes in vivo. After proteolysis, CTF2 remains associated with β-catenin, which stabilizes and redistributes both proteins to the cytosol and nucleus, leading to up-regulation of β-catenin, CyclinD1, Snail2, and Snail2 promoter-based GFP expression in vivo. A CTF2 β-catenin–binding mutant, however, fails to alter gene expression, indicating that CTF2 modulates β-catenin–responsive EMT effector genes. Notably, CTF2 association with the endogenous Snail2 promoter in the neural crest is β-catenin dependent. Collectively, our data reveal how Cad6B proteolysis orchestrates multiple pro-EMT regulatory inputs, including CTF2-mediated up-regulation of the Cad6B repressor Snail2, to ensure proper cranial neural crest EMT.

Cadherin tales: Regulation of cadherin function by endocytic membrane trafficking

Cadherins are the primary adhesion molecules in adherens junctions and desmosomes and play essential roles in embryonic development. Although significant progress has been made in understanding cadherin structure and function, we lack a clear vision of how cells confer plasticity upon adhesive junctions to allow for cellular rearrangements during development, wound healing and metastasis. Endocytic membrane trafficking has emerged as a fundamental mechanism by which cells confer a dynamic state to adhesive junctions. Recent studies indicate that the juxtamembrane domain of classical cadherins contains multiple endocytic motifs, or "switches," that can be used by cellular membrane trafficking machinery to regulate adhesion. The cadherin-binding protein p120-catenin (p120) appears to be the master regulator of access to these switches, thereby controlling cadherin endocytosis and turnover. This review focuses on p120 and other cadherin-binding proteins, ubiquitin ligases, and growth factors as key modulators of cadherin membrane trafficking.

Ankfy1 is dispensable for neural stem/precursor cell development

There are few studies on the membrane protein Ankfy1. We have found Ankfy1 is specifically expressed in neural stem/precursor cells during early development in mice (murine). To further explore Ankfy1 function in neural development, we developed a gene knockout mouse with a mixed Balb/C and C57/BL6 genetic background. Using immunofluorescence and in situ hybridization, neural defects were absent in mixed genetic Ankfy1 null mice during development and in adults up to 2 months old. However, Ankfy1 gene knockout mice with a pure genetic background were found to be lethal in the C57/BL6 inbred mice embryos, even after seven generations of backcrossing. Polymerase chain reaction confirmed homozygotes were unattainable as early as embryonic day 11.5. We conclude that Ankfy1 protein is dispensable in neural stem/precursor cells, but could be critical for early embryonic murine development, depending on the genetic background.

Cadherin-11 endocytosis through binding to clathrin promotes cadherin-11-mediated migration in prostate cancer cells

Cadherin-11 (Cad11) cell adhesion molecule plays a role in prostate cancer cell migration. Because disassembly of adhesion complexes through endocytosis of adhesion proteins has been shown to play a role in cell migration, we examined whether Cad11 endocytosis plays a role in Cad11-mediated migration. The mechanism by which Cad11 is internalized is unknown. Using a GST pulldown assay, we found that clathrin binds to the Cad11 cytoplasmic domain but not to that of E-cadherin. Using deletion analysis, we identified a unique sequence motif, VFEEE, in the Cad11 membrane proximal region (amino acid residues 11-15) that binds to clathrin. Endocytosis assays using K(+)-depletion buffer showed that Cad11 internalization is clathrin dependent. Proximity ligation assays showed that Cad11 colocalizes with clathrin, and immunofluorescence assays showed that Cad11 localizes in vesicles that stain for the early endosomal marker Rab5. Deletion of the VFEEE sequence from the Cad11 cytoplasmic domain (Cad11-cla-Δ5) leads to inhibition of Cad11 internalization and reduces Cad11-mediated cell migration in C4-2B and PC3-mm2 prostate cancer cells. These observations suggest that clathrin-mediated internalization of Cad11 regulates surface trafficking of Cad11 and that dynamic turnover of Cad11 regulates the migratory function of Cad11 in prostate cancer cells.