EphB Receptors Coordinate Migration and Proliferation in the Intestinal Stem Cell Niche

Potential role of the Eph/ephrin system in colorectal cancer: emerging druggable molecular targets

The Eph/ephrin system regulates many developmental processes and adult tissue homeostasis. In colorectal cancer (CRC), it is involved in different processes including tumorigenesis, tumor angiogenesis, metastasis development, and cancer stem cell regeneration. However, conflicting data regarding Eph receptors in CRC, especially in its putative role as an oncogene or a suppressor gene, make the precise role of Eph-ephrin interaction confusing in CRC development. In this review, we provide an overview of the literature and highlight evidence that collaborates with these ambiguous roles of the Eph/ephrin system in CRC, as well as the molecular findings that represent promising therapeutic targets.

Diversity of Intercellular Communication Modes: A Cancer Biology Perspective

From the moment a cell is on the path to malignant transformation, its interaction with other cells from the microenvironment becomes altered. The flow of molecular information is at the heart of the cellular and systemic fate in tumors, and various processes participate in conveying key molecular information from or to certain cancer cells. For instance, the loss of tight junction molecules is part of the signal sent to cancer cells so that they are no longer bound to the primary tumors and are thus free to travel and metastasize. Upon the targeting of a single cell by a therapeutic drug, gap junctions are able to communicate death information to by-standing cells. The discovery of the importance of novel modes of cell-cell communication such as different types of extracellular vesicles or tunneling nanotubes is changing the way scientists look at these processes. However, are they all actively involved in different contexts at the same time or are they recruited to fulfill specific tasks? What does the multiplicity of modes mean for the overall progression of the disease? Here, we extend an open invitation to think about the overall significance of these questions, rather than engage in an elusive attempt at a systematic repertory of the mechanisms at play.

Cell Death, by Any Other Name…

Studies trying to understand cell death, this ultimate biological process, can be traced back to a century ago. Yet, unlike many other fashionable research interests, research on cell death is more alive than ever. New modes of cell death are discovered in specific contexts, as are new molecular pathways. But what is "cell death", really? This question has not found a definitive answer yet. Nevertheless, part of the answer is irreversibility, whereby cells can no longer recover from stress or injury. Here, we identify the most distinctive features of different modes of cell death, focusing on the executive final stages. In addition to the final stages, these modes can differ in their triggering stimulus, thus referring to the initial stages. Within this framework, we use a few illustrative examples to examine how intercellular communication factors in the demise of cells. First, we discuss the interplay between cell-cell communication and cell death during a few steps in the early development of multicellular organisms. Next, we will discuss this interplay in a fully developed and functional tissue, the gut, which is among the most rapidly renewing tissues in the body and, therefore, makes extensive use of cell death. Furthermore, we will discuss how the balance between cell death and communication is modified during a pathological condition, i.e., colon tumorigenesis, and how it could shed light on resistance to cancer therapy. Finally, we briefly review data on the role of cell-cell communication modes in the propagation of cell death signals and how this has been considered as a potential therapeutic approach. Far from vainly trying to provide a comprehensive review, we launch an invitation to ponder over the significance of cell death diversity and how it provides multiple opportunities for the contribution of various modes of intercellular communication.

Listen to Your Gut: Key Concepts for Bioengineering Advanced Models of the Intestine

The intestine performs functions central to human health by breaking down food and absorbing nutrients while maintaining a selective barrier against the intestinal microbiome. Key to this barrier function are the combined efforts of lumen-lining specialized intestinal epithelial cells, and the supportive underlying immune cell-rich stromal tissue. The discovery that the intestinal epithelium can be reproduced in vitro as intestinal organoids introduced a new way to understand intestinal development, homeostasis, and disease. However, organoids reflect the intestinal epithelium in isolation whereas the underlying tissue also contains myriad cell types and impressive chemical and structural complexity. This review dissects the cellular and matrix components of the intestine and discusses strategies to replicate them in vitro using principles drawing from bottom-up biological self-organization and top-down bioengineering. It also covers the cellular, biochemical and biophysical features of the intestinal microenvironment and how these can be replicated in vitro by combining strategies from organoid biology with materials science. Particularly accessible chemistries that mimic the native extracellular matrix are discussed, and bioengineering approaches that aim to overcome limitations in modelling the intestine are critically evaluated. Finally, the review considers how further advances may extend the applications of intestinal models and their suitability for clinical therapies.

HOXA3 functions as the on-off switch to regulate the development of hESC-derived third pharyngeal pouch endoderm through EPHB2-mediated Wnt pathway

Objectives

Normal commitment of the endoderm of the third pharyngeal pouch (3PP) is essential for the development and differentiation of the thymus. The aim of this study was to investigate the role of transcription factor HOXA3 in the development and differentiation of 3PP endoderm (3PPE) from human embryonic stem cells (hESCs).

Methods

The 3PPE was differentiated from hESC-derived definitive endoderm (DE) by mimicking developmental queues with Activin A, WNT3A, retinoic acid and BMP4. The function of 3PPE was assessed by further differentiating into functional thymic epithelial cells (TECs). The effect of HOXA3 inhibition on cells of 3PPE was subsequently investigated.

Results

A highly efficient approach for differentiating 3PPE cells was developed and these cells expressed 3PPE related genes HOXA3, SIX1, PAX9 as well as EpCAM. 3PPE cells had a strong potential to develop into TECs which expressed both cortical TEC markers K8 and CD205, and medullary TEC markers K5 and AIRE, and also promoted the development and maturation of T cells. More importantly, transcription factor HOXA3 not only regulated the differentiation of 3PPE, but also had a crucial role for the proliferation and migration of 3PPE cells. Our further investigation revealed that HOXA3 controlled the commitment and function of 3PPE through the regulation of Wnt signaling pathway by activating EPHB2.

Conclusion

Our results demonstrated that HOXA3 functioned as the on-off switch to regulate the development of hESC-derived 3PPE through EPHB2-mediated Wnt pathway, and our findings will provide new insights into studying the development of 3PP and thymic organ in vitro and in vivo.

Recurring EPHB1 mutations in human cancers alter receptor signalling and compartmentalisation of colorectal cancer cells

BACKGROUND

Ephrin (EPH) receptors have been implicated in tumorigenesis and metastasis, but the functional understanding of mutations observed in human cancers is limited. We previously demonstrated reduced cell compartmentalisation for somatic EPHB1 mutations found in metastatic colorectal cancer cases. We therefore integrated pan-cancer and pan-EPH mutational data to prioritise recurrent EPHB1 mutations for functional studies to understand their contribution to cancer development and metastasis.

METHODS

Here, 79,151 somatic mutations in 9,898 samples of 33 different tumour types were analysed with a bioinformatic pipeline to find 3D-mutated cluster pairs and hotspot mutations in EPH receptors. From these, 15 recurring EPHB1 mutations were stably expressed in colorectal cancer followed by confocal microscopy based in vitro compartmentalisation assays and phospho-proteome analysis.

RESULTS

The 3D-protein structure-based bioinformatics analysis resulted in 63% EPHB1 mutants with compartmentalisation phenotypes vs 43% for hotspot mutations. Whereas the ligand-binding domain mutations C61Y, R90C, and R170W, the fibronectin domain mutation R351L, and the kinase domain mutation D762N displayed reduced to strongly compromised cell compartmentalisation, the kinase domain mutations R743W and G821R enhanced this phenotype. While mutants with reduced compartmentalisation also had reduced ligand induced receptor phosphorylation, the enhanced compartmentalisation was not linked to receptor phosphorylation level. Phosphoproteome mapping pinpointed the PI3K pathway and PIK3C2B phosphorylation in cells harbouring mutants with reduced compartmentalisation.

CONCLUSIONS

This is the first integrative study of pan-cancer EPH receptor mutations followed by in vitro validation, a robust way to identify cancer-causing mutations, uncovering EPHB1 mutation phenotypes and demonstrating the utility of protein structure-based mutation analysis in characterization of novel cancer genes. Video Abstract.

IL-38 regulates intestinal stem cell homeostasis by inducing WNT signaling and beneficial IL-1β secretion

The IL-1 Family member IL-38 has been characterized primarily as an antiinflammatory cytokine in human and mouse models of systemic diseases. Here, we examined the role of IL-38 in the murine small intestine (SI). Immunostaining of SI revealed that IL-38 expression partially confines to intestinal stem cells. Cultures of intestinal organoids reveal IL-38 functions as a growth factor by increasing organoid size via inducing WNT3a. In contrast, organoids from IL-38-deficient mice develop more slowly. This reduction in size is likely due to the downregulation of intestinal stemness markers (i.e., Fzd5, Ephb2, and Olfm4) expression compared with wild-type organoids. The IL-38 binding to IL-1R6 and IL-1R9 is still a matter of debate. Therefore, to analyze the molecular mechanisms of IL-38 signaling, we also examined organoids from IL-1R9-deficient mice. Unexpectedly, these organoids, although significantly smaller than wild type, respond to IL-38, suggesting that IL-1R9 is not involved in IL-38 signaling in the stem cell crypt. Nevertheless, silencing of IL-1R6 disabled the organoid response to the growth property of IL-38, thus suggesting IL-1R6 as the main receptor used by IL-38 in the crypt compartment. In organoids from wild-type mice, IL-38 stimulation induced low concentrations of IL-1β which contribute to organoid growth. However, high concentrations of IL-1β have detrimental effects on the cultures that were prevented by treatment with recombinant IL-38. Overall, our data demonstrate an important regulatory function of IL-38 as a growth factor, and as an antiinflammatory molecule in the SI, maintaining homeostasis.

Oat beta-glucan reduces colitis by promoting autophagy flux in intestinal epithelial cells via EPHB6-TFEB axis

Inflammatory bowel disease (IBD) is a group of chronic inflammatory disorders of the gastrointestinal tract, mainly including Crohn's disease and ulcerative colitis. Epidemiological findings suggest that inadequate dietary fibers intake may be a risk factor for IBD. Oat beta-glucan is a type of fermentable dietary fiber and has been proved to reduce experimental colitis. However, the mechanism remains unclear. The aim of this study was to explore the role and possible mechanism of oat beta-glucan in reducing experimental colitis. We used a dextran sulfate sodium (DSS)-induced mice acute colitis model to explore the potential mechanism of oat beta-glucan in reducing experimental colitis. As a result, oat beta-glucan upregulated the expressions of Erythropoietin-producing hepatocyte receptor B6 (EPHB6) and transcription factor EB (TFEB), promoted autophagy flux and downregulated the expressions of interleukin 1 beta (IL-1β), interleukin 6 (IL-6) and tumor necrosis factor alpha (TNF-α) in intestinal epithelial cells (IECs). The role of the EPHB6-TFEB axis was explored using a lipopolysaccharide-induced HT-29 cells inflammation model. The results revealed that EPHB6 regulated the expression of TFEB, and knockdown of EPHB6 decreased the protein level of TFEB. When EPHB6 or TFEB was knocked down, autophagy flux was inhibited, and the anti-inflammatory effect of sodium butyrate, a main metabolite of oat beta-glucan in the gut, was blocked. In summary, our findings demonstrated that oat beta-glucan reduced DSS-induced acute colitis in mice, promoted autophagy flux via EPHB6-TFEB axis and downregulated the expressions of IL-1β, IL-6 and TNF-α in IECs, and this effect may be mediated by butyrate.

Intracellular pH dynamics regulates intestinal stem cell lineage specification

Intracellular pH dynamics is increasingly recognized to regulate myriad cell behaviors. We report a finding that intracellular pH dynamics also regulates adult stem cell lineage specification. We identify an intracellular pH gradient in mouse small intestinal crypts, lowest in crypt stem cells and increasing along the crypt column. Disrupting this gradient by inhibiting H+ efflux by Na+/H+ exchanger 1 abolishes crypt budding and blocks differentiation of Paneth cells, which are rescued with exogenous WNT. Using single-cell RNA sequencing and lineage tracing we demonstrate that intracellular pH dynamics acts downstream of ATOH1, with increased pH promoting differentiation toward the secretory lineage. Our findings indicate that an increase in pH is required for the lineage specification that contributes to crypt maintenance, establishing a role for intracellular pH dynamics in cell fate decisions within an adult stem cell lineage.

Cbl and Cbl-b Ubiquitin Ligases are Essential for Intestinal Epithelial Stem Cell Maintenance

Among the signaling pathways that control the stem cell self-renewal and maintenance vs. acquisition of differentiated cell fates, those mediated by receptor tyrosine kinase (RTK) activation are well established as key players. CBL family ubiquitin ligases are negative regulators of RTKs but their physiological roles in regulating stem cell behaviors are unclear. While hematopoietic Cbl/Cblb knockout (KO) leads to a myeloproliferative disease due to expansion and reduced quiescence of hematopoietic stem cells, mammary epithelial KO led to stunted mammary gland development due to mammary stem cell depletion. Here, we examined the impact of inducible Cbl/Cblb double-KO (iDKO) selectively in the Lgr5-defined intestinal stem cell (ISC) compartment. Cbl/Cblb iDKO led to rapid loss of the Lgr5 ^Hi ISC pool with a concomitant transient expansion of the Lgr5 ^Lo transit amplifying population. LacZ reporter-based lineage tracing showed increased ISC commitment to differentiation, with propensity towards enterocyte and goblet cell fate at the expense of Paneth cells. Functionally, Cbl/Cblb iDKO impaired the recovery from radiation-induced intestinal epithelial injury. In vitro , Cbl/Cblb iDKO led to inability to maintain intestinal organoids. Single cell RNAseq analysis of organoids revealed Akt-mTOR pathway hyperactivation in iDKO ISCs and progeny cells, and pharmacological inhibition of the Akt-mTOR axis rescued the organoid maintenance and propagation defects. Our results demonstrate a requirement for Cbl/Cblb in the maintenance of ISCs by fine tuning the Akt-mTOR axis to balance stem cell maintenance vs. commitment to differentiation.

Effects of hormones on intestinal stem cells

The maintenance of intestinal renewal and repair mainly depends on intestinal stem cells (ISCs), which can also contribute to the growth of intestinal tumours. Hormones, which are vital signalling agents in the body, have various effects on the growth and replacement of intestinal stem cells. This review summarises recent progress in the identification of hormones associated with intestinal stem cells. Several hormones, including thyroid hormone, glucagon-like peptide-2, androgens, insulin, leptin, growth hormone, corticotropin-releasing hormone and progastrin, promote the development of intestinal stem cells. However, somatostatin and melatonin are two hormones that prevent the proliferation of intestinal stem cells. Therefore, new therapeutic targets for the diagnosis and treatment of intestinal illnesses can be identified by examining the impact of hormones on intestinal stem cells.

Impact of enteric bacterial infections at and beyond the epithelial barrier

The mucosal lining of the gut has co-evolved with a diverse microbiota over millions of years, leading to the development of specialized mechanisms to actively limit the invasion of pathogens. However, some enteric microorganisms have adapted against these measures, developing ways to hijack or overcome epithelial micro-integrity mechanisms. This breach of the gut barrier not only enables the leakage of host factors out of circulation but can also initiate a cascade of detrimental systemic events as microbiota, pathogens and their affiliated secretions passively leak into extra-intestinal sites. Under normal circumstances, gut damage is rapidly repaired by intestinal stem cells. However, with substantial and deep perturbation to the gut lining and the systemic dissemination of gut contents, we now know that some enteric infections can cause the impairment of host regenerative processes. Although these local and systemic aspects of enteric disease are often studied in isolation, they heavily impact one another. In this Review, by examining the journey of enteric infections from initial establishment to systemic sequelae and how, or if, the host can successfully repair damage, we will tie together these complex interactions to provide a holistic overview of the impact of enteric infections at and beyond the epithelial barrier.

1'-O-methyl-averantin isolated from the endolichenic fungus Jackrogersella sp. EL001672 suppresses colorectal cancer stemness via sonic Hedgehog and Notch signaling

Endolichenic fungi are host organisms that live on lichens and produce a wide variety of secondary metabolites. Colorectal cancer stem cells are capable of self-renewal and differentiation into cancer cells, which makes cancers difficult to eradicate. New alternative therapeutics are needed to inhibit the growth of tumor stem cells. This study examined the ability of an extract of Jackrogersella sp. EL001672 (derived from the lichen Cetraria sp.) and the isolated compound 1'-O-methyl-averantin to inhibit development of cancer stemness. The endolichenic fungus Jackrogersella sp. EL001672 (KACC 83021BP), derived from Cetraria sp., was grown in culture medium. The culture broth was extracted with acetone to obtain a crude extract. Column chromatography and reverse-phase HPLC were used to isolate an active compound. The anticancer activity of the extract and the isolated compound was evaluated by qRT-PCR and western blotting, and in cell viability, spheroid formation, and reporter assays. The acetone extract of EL001672 did not affect cell viability. However, 1'-O-methyl-averantin showed cytotoxic effects against cancer cell lines at 50 μg/mL and 25 μg/mL. Both the crude extract and 1'-O-methyl-averantin suppressed spheroid formation in CRC cell lines, and downregulated expression of stemness markers ALDH1, CD44, CD133, Lgr-5, Msi-1, and EphB1. To further characterize the mechanism underlying anti-stemness activity, we examined sonic Hedgehog and Notch signaling. The results showed that the crude extract and the 1'-O-methyl-averantin inhibited Gli1, Gli2, SMO, Bmi-1, Notch-1, Hes-1, and the CSL complex. Consequently, an acetone extract and 1'-O-methyl-averantin isolated from EL001672 suppresses colorectal cancer stemness by regulating the sonic Hedgehog and Notch signaling pathways.

Eph Receptors in Cancer

Eph receptor tyrosine kinases play critical functions during development, in the formation of tissue and organ borders, and the vascular and neural systems. Uniquely among tyrosine kinases, their activities are controlled by binding to membrane-bound ligands, called ephrins. Ephs and ephrins generally have a low expression in adults, functioning mainly in tissue homeostasis and plasticity, but are often overexpressed in cancers, where they are especially associated with undifferentiated or progenitor cells, and with tumour development, vasculature, and invasion. Mutations in Eph receptors also occur in various tumour types and are suspected to promote tumourigenesis. Ephs and ephrins have the capacity to operate as both tumour promoters and tumour suppressors, depending on the circumstances. They have been demonstrated to impact tumour cell proliferation, migration, and invasion in vitro, as well as tumour development, angiogenesis, and metastases in vivo, making them potential therapeutic targets. However, successful development of therapies will require detailed understanding of the opposing roles of Ephs in various cancers. In this review, we discuss the variations in Eph expression and functions in a variety of malignancies. We also describe the multiple strategies that are currently available to target them in tumours, including preclinical and clinical development.

RNF186/EPHB2 Axis Is Essential in Regulating TNF Signaling for Colorectal Tumorigenesis in Colorectal Epithelial Cells

The receptor tyrosine kinase EPHB2 (EPH receptor B2) is highly expressed in many human cancer types, especially in gastrointestinal cancers, such as colorectal cancer. Several coding mutations of the EPHB2 gene have been identified in many cancer types, suggesting that EPHB2 plays a critical role in carcinogenesis. However, the exact functional mechanism of EPHB2 in carcinogenesis remains unknown. In this study, we find that EPHB2 is required for TNF-induced signaling activation and proinflammatory cytokine production in colorectal epithelial cells. Mechanistically, after TNF stimulation, EPHB2 is ubiquitinated by its E3 ligase RNF186. Then, ubiquitinated EPHB2 recruits and further phosphorylates TAB2 at nine tyrosine sites, which is a critical step for the binding between TAB2 and TAK1. Due to defects in TNF signaling in RNF186-knockout colorectal epithelial cells, the phenotype of colitis-propelled colorectal cancer model in RNF186-knockout mice is significantly reduced compared with that in wild-type control mice. Moreover, we find that a genetic mutation in EPHB2 identified in a family with colorectal cancer is a gain-of-function mutation that promoted TNF signaling activation compared with wild-type EPHB2. We provide evidence that the EPHB2-RNF186-TAB2-TAK1 signaling cascade plays an essential role in TNF-mediated signal transduction in colorectal epithelial cells and the carcinogenesis of colorectal cancer, which may provide potential targets for the treatment of colorectal cancer.

Diverse roles for axon guidance pathways in adult tissue architecture and function

Classical axon guidance ligands and their neuronal receptors were first identified due to their fundamental roles in regulating connectivity in the developing nervous system. Since their initial discovery, it has become clear that these signaling molecules play important roles in the development of a broad array of tissue and organ systems across phylogeny. In addition to these diverse developmental roles, there is a growing appreciation that guidance signaling pathways have important functions in adult organisms, including the regulation of tissue integrity and homeostasis. These roles in adult organisms include both tissue-intrinsic activities of guidance molecules, as well as systemic effects on tissue maintenance and function mediated by the nervous and vascular systems. While many of these adult functions depend on mechanisms that mirror developmental activities, such as regulating adhesion and cell motility, there are also examples of adult roles that may reflect signaling activities that are distinct from known developmental mechanisms, including the contributions of guidance signaling pathways to lineage commitment in the intestinal epithelium and bone remodeling in vertebrates. In this review, we highlight studies of guidance receptors and their ligands in adult tissues outside of the nervous system, focusing on in vivo experimental contexts. Together, these studies lay the groundwork for future investigation into the conserved and tissue-specific mechanisms of guidance receptor signaling in adult tissues.

Scaffold Protein Lnx1 Stabilizes EphB Receptor Kinases for Synaptogenesis

Postsynaptic structure assembly and remodeling are crucial for functional synapse formation during the establishment of neural circuits. However, how the specific scaffold proteins regulate this process during the development of the postnatal period is poorly understood. In this study, we find that the deficiency of ligand of Numb protein X 1 (Lnx1) leads to abnormal development of dendritic spines to impair functional synaptic formation. We further demonstrate that loss of Lnx1 promotes the internalization of EphB receptors from the cell surface. Constitutively active EphB2 intracellular signaling rescues synaptogenesis in Lnx1 mutant mice. Our data thus reveal a molecular mechanism whereby the Lnx1-EphB complex controls postsynaptic structure for synapse maturation during the adolescent period.

The EPH/Ephrin System in Colorectal Cancer

The EPH/ephrin system constitutes a bidirectional signaling pathway comprised of a family of tyrosine kinase receptors in tandem with their plasma membrane-bound ligand (ephrins). Its significance in a wide variety of physiologic and pathologic processes has been recognized during the past decades. In carcinogenesis, EPH/ephrins coordinate a wide spectrum of pathologic processes, such as angiogenesis, vessel infiltration, and metastasis. Despite the recent advances in colorectal cancer (CRC) diagnosis and treatment, it remains a leading cause of death globally, accounting for 9.2% of all cancer deaths. A growing body of literature has been published lately revitalizing our scientific interest towards the role of EPH/ephrins in pathogenesis and the treatment of CRC. The aim of the present review is to present the recent CRC data which might lead to clinical practice changes in the future.

Tissue geometry drives deterministic organoid patterning

Epithelial organoids are stem cell–derived tissues that approximate aspects of real organs, and thus they have potential as powerful tools in basic and translational research. By definition, they self-organize, but the structures formed are often heterogeneous and irreproducible, which limits their use in the lab and clinic. We describe methodologies for spatially and temporally controlling organoid formation, thereby rendering a stochastic process more deterministic. Bioengineered stem cell microenvironments are used to specify the initial geometry of intestinal organoids, which in turn controls their patterning and crypt formation. We leveraged the reproducibility and predictability of the culture to identify the underlying mechanisms of epithelial patterning, which may contribute to reinforcing intestinal regionalization in vivo. By controlling organoid culture, we demonstrate how these structures can be used to answer questions not readily addressable with the standard, more variable, organoid models.

Digesting the mechanobiology of the intestinal epithelium

The dizzying life of the homeostatic intestinal epithelium is governed by a complex interplay between fate, form, force and function. This interplay is beginning to be elucidated thanks to advances in intravital and ex vivo imaging, organoid culture, and biomechanical measurements. Recent discoveries have untangled the intricate organization of the forces that fold the monolayer into crypts and villi, compartmentalize cell types, direct cell migration, and regulate cell identity, proliferation and death. These findings revealed that the dynamic equilibrium of the healthy intestinal epithelium relies on its ability to precisely coordinate tractions and tensions in space and time. In this review, we discuss recent findings in intestinal mechanobiology, and highlight some of the many fascinating questions that remain to be addressed in this emerging field.

Lef1 restricts ectopic crypt formation and tumor cell growth in intestinal adenomas

Somatic mutations in APC or CTNNB1 genes lead to aberrant Wnt signaling and colorectal cancer (CRC) initiation and progression via-catenin–T cell factor/lymphoid enhancer binding factor TCF/LEF transcription factors. We found that Lef1 was expressed exclusively in Apc-mutant, Wnt ligand–independent tumors, but not in ligand-dependent, serrated tumors. To analyze Lef1 function in tumor development, we conditionally deleted Lef1 in intestinal stem cells of Apcfl/fl mice or broadly from the entire intestinal epithelium of Apcfl/fl or ApcMin/+ mice. Loss of Lef1 markedly increased tumor initiation and tumor cell proliferation, reduced the expression of several Wnt antagonists, and increased Myc proto-oncogene expression and formation of ectopic crypts in Apc-mutant adenomas. Our results uncover a previously unknown negative feedback mechanism in CRC, in which ectopic Lef1 expression suppresses intestinal tumorigenesis by restricting adenoma cell dedifferentiation to a crypt-progenitor phenotype and by reducing the formation of cancer stem cell niches.

The ephrin receptor EphB2 regulates the connectivity and activity of enteric neurons

Highly organized circuits of enteric neurons are required for the regulation of gastrointestinal functions, such as peristaltism or migrating motor complex. However, the factors and molecular mechanisms that regulate the connectivity of enteric neurons and their assembly into functional neuronal networks are largely unknown. A better understanding of the mechanisms by which neurotrophic factors regulate this enteric neuron circuitry is paramount to understanding enteric nervous system (ENS) physiology. EphB2, a receptor tyrosine kinase, is essential for neuronal connectivity and plasticity in the brain, but so far its presence and function in the ENS remain largely unexplored. Here we report that EphB2 is expressed preferentially by enteric neurons relative to glial cells throughout the gut in rats. We show that in primary enteric neurons, activation of EphB2 by its natural ligand ephrinB2 engages ERK signaling pathways. Long-term activation with ephrinB2 decreases EphB2 expression and reduces molecular and functional connectivity in enteric neurons without affecting neuronal density, ganglionic fiber bundles, or overall neuronal morphology. This is highlighted by a loss of neuronal plasticity markers such as synapsin I, PSD95, and synaptophysin, and a decrease of spontaneous miniature synaptic currents. Together, these data identify a critical role for EphB2 in the ENS and reveal a unique EphB2-mediated molecular program of synapse regulation in enteric neurons.

Muscarinic receptor M3 contributes to intestinal stem cell maintenance via EphB/ephrin-B signaling

Acetylcholine (ACh) signaling through activation of nicotinic and muscarinic ACh receptors regulates expression of specific genes that mediate and sustain proliferation, differentiation, and homeostasis in the intestinal crypts. This signaling plays a pivotal role in the regulation of intestinal stem cell function, but the details have not been clarified. Here, we performed experiments using type 3 muscarinic acetylcholine receptor (M3) knockout mice and their intestinal organoids and report that endogenous ACh affects the size of the intestinal stem niche via M3 signaling. RNA sequencing of crypts identified up-regulation of the EphB/ephrin-B signaling pathway. Furthermore, using an MEK inhibitor (U0126), we found that mitogen-activated protein kinase/extracellular signal-regulated kinase (MAPK/ERK) signaling, which is downstream of EphB/ephrin-B signaling, is activated in M3-deficient crypts. Collectively, M3, EphB/ephrin-B, and the MAPK/ERK signaling cascade work together to maintain the homeostasis of intestinal epithelial cell growth and differentiation following modifications of the cholinergic intestinal niche.

Stem-like Cells from Invasive Breast Carcinoma Cell Line MDA-MB-231 Express a Distinct Set of Eph Receptors and Ephrin Ligands

BACKGROUND/AIM

Breast cancer cell lines consist of bulk tumor cells and a small proportion of stem-like cells. While the bulk cells are known to express a distinct combination of Eph receptors and ephrin ligands, the transcript profiles of stem-like cells in these cell lines have not been adequately characterized. The aim of this study was to determine Eph receptor/ephrin ligand profiles of cancer stem cells specific to a triple negative breast carcinoma cell line.

MATERIALS AND METHODS

The normal breast cell line MCF10A and the invasive breast carcinoma cell line MDA-MB-231 were used to isolate CD24⁺/CD24^- cell populations. The profiles of Eph receptors and ephrin ligands were determined by real-time PCR and the relative abundance in bulk and stem cells were compared.

RESULTS

Based on the mean ΔCT values, the descending order of abundance was as follows. Ephrin-A5 > EPHA2 > (EPHA8, EPHB2) > ephrin-B2 > (EPHA7, EPHB4, ephrin-A4) > ephrin-A3 > ephrin-A1 > (EPHB3, ephrin-B1) > EPHA4 > EPHA1 > EPHA10. EPHA6 and ephrin-A2 transcripts were not detectable in stem cells from either cell line. The expression of EPHA4, EPHA7, EPHA8, and ephrin-A5 in MDA-MB-231 stem cells was up-regulated by 12, 20, ~500, and 6.5-fold respectively.

CONCLUSION

The up-regulation of transcripts for EPHA8 and its cognate ligand, ephrin-A5, in the stem cells isolated from MDA-MB-231, suggest their involvement in the invasiveness of this cell line. Based on literature reports, we propose the role of EPHA8 and ephrin-A5 in MDA-MB-231 stem cells via the PI3K-AKT-mTOR pathway.

Cutting Edge: EPHB2 Is a Coreceptor for Fungal Recognition and Phosphorylation of Syk in the Dectin-1 Signaling Pathway

Invasive fungal infections have become a leading cause of death among immunocompromised patients, leading to around 1.5 million deaths per year globally. The molecular mechanisms by which hosts defend themselves against fungal infection remain largely unclear, which impedes the development of antifungal drugs and other treatment options. In this article, we show that the tyrosine kinase receptor EPH receptor B2 (EPHB2), together with dectin-1, recognizes β-glucan and activates downstream signaling pathways. Mechanistically, we found that EPHB2 is a kinase for Syk and is required for Syk phosphorylation and activation after dectin-1 ligand stimulation, whereas dectin-1 is critical for the recruitment of Syk. Ephb2-deficient mice are susceptible to Candida albicans-induced fungemia model, which also supports the role of EPHB2 in antifungal immunity. Overall, we provide evidence that EPHB2 is a coreceptor for the recognition of dectin-1 ligands and plays an essential role in antifungal immunity by phosphorylating Syk.

Emerging Role and Therapeutic Potential of lncRNAs in Colorectal Cancer

Maintenance of the intestinal epithelium is dependent on the control of stem cell (SC) proliferation and differentiation. The fine regulation of these cellular processes requires a complex dynamic interplay between several signaling pathways, including Wnt, Notch, Hippo, EGF, Ephrin, and BMP/TGF-β. During the initiation and progression of colorectal cancer (CRC), key events, such as oncogenic mutations, influence these signaling pathways, and tilt the homeostatic balance towards proliferation and dedifferentiation. Therapeutic strategies to specifically target these deregulated signaling pathways are of particular interest. However, systemic blocking or activation of these pathways poses major risks for normal stem cell function and tissue homeostasis. Interestingly, long non-coding RNAs (lncRNAs) have recently emerged as potent regulators of key cellular processes often deregulated in cancer. Because of their exceptional tissue and tumor specificity, these regulatory RNAs represent attractive targets for cancer therapy. Here, we discuss how lncRNAs participate in the maintenance of intestinal homeostasis and how they can contribute to the deregulation of each signaling pathway in CRC. Finally, we describe currently available molecular tools to develop lncRNA-targeted cancer therapies.

RNF186 regulates EFNB1 (ephrin B1)-EPHB2-induced autophagy in the colonic epithelial cells for the maintenance of intestinal homeostasis

Although genome-wide association studies have identified the gene RNF186 encoding an E3 ubiquitin-protein ligase as conferring susceptibility to ulcerative colitis, the exact function of this protein remains unclear. In the present study, we demonstrate an important role for RNF186 in macroautophagy/autophagy activation in colonic epithelial cells and intestinal homeostasis. Mechanistically, RNF186 acts as an E3 ubiquitin-protein ligase for EPHB2 and regulates the ubiquitination of EPHB2. Upon stimulation by ligand EFNB1 (ephrin B1), EPHB2 is ubiquitinated by RNF186 at Lys892, and further recruits MAP1LC3B for autophagy. Compared to control mice, rnf186^-/- and ephb2^-/- mice have a more severe phenotype in the DSS-induced colitis model, which is due to a defect in autophagy in colon epithelial cells. More importantly, treatment with ephrin-B1-Fc recombinant protein effectively relieves DSS-induced mouse colitis, which suggests that ephrin-B1-Fc may be a potential therapy for human inflammatory bowel diseases.Abbreviations: ACTB: actin beta; ATG5: autophagy related 5; ATG16L1: autophagy related 16 like 1; ATP: adenosine triphosphate; Cas9: CRISPR associated protein 9; CD: Crohn disease; CQ: chloroquine; Csf2: colony stimulating factor 2; Cxcl1: c-x-c motif chemokine ligand 1; DMSO: dimethyl sulfoxide; DSS: dextran sodium sulfate; EFNB1: ephrin B1; EPHB2: EPH receptor B2; EPHB3: EPH receptor B3; EPHB2^K788R: lysine 788 mutated to arginine in EPHB2; EPHB2^K892R: lysine 892 mutated to arginine in EPHB2; ER: endoplasmic reticulum; FITC: fluorescein isothiocyanate; GFP: green fluorescent protein; GWAS: genome-wide association studies; HRP: horseradish peroxidase; HSPA5/BiP: heat shock protein family A (Hsp70) member 5; IBD: inflammatory bowel diseases; Il1b: interleukin 1 beta; Il6: interleukin 6; IRGM:immunity related GTPase M; i.p.: intraperitoneally; IPP: inorganic pyrophosphatase; KD: knockdown; KO: knockout; MAP1LC3B: microtubule associated protein 1 light chain 3 beta; MTOR: mechanistic target of rapamycin kinase; NOD2: nucleotide binding oligomerization domain containing 2; PI3K: phosphoinositide 3-kinase; PtdIns3K: class III phosphatidylinositol 3-kinase; RNF186: ring finger protein 186; RNF186^A64T: alanine 64 mutated to threonine in RNF186; RNF186^R179X: arginine 179 mutated to X in RNF186; RPS6: ribosomal protein S6; Tnf: tumor necrosis factor; SQSTM1: sequestosome 1; Ub: ubiquitin; UBE2D2: ubiquitin conjugating enzyme E2 D2; UBE2H: ubiquitin conjugating enzyme E2 H; UBE2K: ubiquitin conjugating enzyme E2 K; UBE2N: ubiquitin conjugating enzyme E2 N; UC: ulcerative colitis; ULK1:unc-51 like autophagy activating kinase 1; WT: wild type.

Ephrin-B2-EphB4 communication mediates tumor-endothelial cell interactions during hematogenous spread to spinal bone in a melanoma metastasis model

Metastases account for the majority of cancer deaths. Bone represents one of the most common sites of distant metastases, and spinal bone metastasis is the most common source of neurological morbidity in cancer patients. During metastatic seeding of cancer cells, endothelial-tumor cell interactions govern extravasation to the bone and potentially represent one of the first points of action for antimetastatic treatment. The ephrin-B2-EphB4 pathway controls cellular interactions by inducing repulsive or adhesive properties, depending on forward or reverse signaling. Here, we report that in an in vivo metastatic melanoma model, ephrin-B2-mediated activation of EphB4 induces tumor cell repulsion from bone endothelium, translating in reduced spinal bone metastatic loci and improved neurological function. Selective ephrin-B2 depletion in endothelial cells or EphB4 inhibition increases bone metastasis and shortens the time window to hind-limb locomotion deficit from spinal cord compression. EphB4 overexpression in melanoma cells ameliorates the metastatic phenotype and improves neurological outcome. Timely harvesting of bone tissue after tumor cell injection and intravital bone microscopy revealed less tumor cells attached to ephrin-B2-positive endothelial cells. These results suggest that ephrin-B2-EphB4 communication influences bone metastasis formation by altering melanoma cell repulsion/adhesion to bone endothelial cells, and represents a molecular target for therapeutic intervention.

Neurogenesis From Neural Crest Cells: Molecular Mechanisms in the Formation of Cranial Nerves and Ganglia

The neural crest (NC) is a transient multipotent cell population that originates in the dorsal neural tube. Cells of the NC are highly migratory, as they travel considerable distances through the body to reach their final sites. Derivatives of the NC are neurons and glia of the peripheral nervous system (PNS) and the enteric nervous system as well as non-neural cells. Different signaling pathways triggered by Bone Morphogenetic Proteins (BMPs), Fibroblast Growth Factors (FGFs), Wnt proteins, Notch ligands, retinoic acid (RA), and Receptor Tyrosine Kinases (RTKs) participate in the processes of induction, specification, cell migration and neural differentiation of the NC. A specific set of signaling pathways and transcription factors are initially expressed in the neural plate border and then in the NC cell precursors to the formation of cranial nerves. The molecular mechanisms of control during embryonic development have been gradually elucidated, pointing to an important role of transcriptional regulators when neural differentiation occurs. However, some of these proteins have an important participation in malformations of the cranial portion and their mutation results in aberrant neurogenesis. This review aims to give an overview of the role of cell signaling and of the function of transcription factors involved in the specification of ganglia precursors and neurogenesis to form the NC-derived cranial nerves during organogenesis.

Single-cell analysis of EphA clustering phenotypes to probe cancer cell heterogeneity

The Eph family of receptor tyrosine kinases is crucial for assembly and maintenance of healthy tissues. Dysfunction in Eph signaling is causally associated with cancer progression. In breast cancer cells, dysregulated Eph signaling has been linked to alterations in receptor clustering abilities. Here, we implemented a single-cell assay and a scoring scheme to systematically probe the spatial organization of activated EphA receptors in multiple carcinoma cells. We show that cancer cells retain EphA clustering phenotype over several generations, and the degree of clustering reported for migration potential both at population and single-cell levels. Finally, using patient-derived cancer lines, we probed the evolution of EphA signalling in cell populations that underwent metastatic transformation and acquisition of drug resistance. Taken together, our scalable approach provides a reliable scoring scheme for EphA clustering that is consistent over multiple carcinomas and can assay heterogeneity of cancer cell populations in a cost- and time-effective manner.

Ravasio et al. develop an assay to quantify the clustering of Eph receptor EphA2 upon ligand binding, based on the scoring of single cells. They discover that clustering phenotype predicts cell and population migration potential in cancer cells and reflects Eph associated gene expression profiles in cancer cell lines.

DNA methylation maintains the CLDN1-EPHB6-SLUG axis to enhance chemotherapeutic efficacy and inhibit lung cancer progression

The loss of cancer-cell junctions and escape from the primary-tumor microenvironment are hallmarks of metastasis. A tight-junction protein, Claudin 1 (CLDN1), is a metastasis suppressor in lung adenocarcinoma. However, as a metastasis suppressor, the underlying molecular mechanisms of CLDN1 has not been well studied. Methods: The signaling pathway regulated by CLDN1 was analyzed by Metacore software and validated by immunoblots. The effect of the CLDN1-EPHB6-ERK-SLUG axis on the formation of cancer stem-like cells, drug resistance and metastasis were evaluated by sphere assay, aldefluor assay, flow cytometry, migration assay, cytotoxicity, soft agar assay, immunoprecipitation assay and xenograft experiments. Furthermore, the methylation-specific PCR, pyrosequencing assay, chromatin immunoprecipitation and reporter assay were used to study the epigenetic and RUNX3-mediated CLDN1 transcription. Finally, the molecular signatures of RUNX3/CLDN1/SLUG were used to evaluate the correlation with overall survival by using gene expression omnibus (GEO) data. Results: We demonstrated that CLDN1 repressed cancer progression via a feedback loop of the CLDN1-EPHB6-ERK1/2-SLUG axis, which repressed metastasis, drug resistance, and cancer stemness, indicating that CLDN1 acts as a metastasis suppressor. CLDN1 upregulated the cellular level of EPHB6 and enhanced its activation, resulting in suppression of ERK1/2 signaling. Interestingly, DNA hypermethylation of the CLDN1 promoter abrogated SLUG-mediated suppression of CLDN1 in low-metastatic cancer cells. In contrast, the histone deacetylase inhibitor trichostatin A or vorinostat facilitated CLDN1 expression in high-metastatic cancer cells and thus increased the efficacy of chemotherapy. Combined treatment with cisplatin and trichostatin A or vorinostat had a synergistic effect on cancer-cell death. Conclusions: This study revealed that DNA methylation maintains CLDN1 expression and then represses lung cancer progression via the CLDN1-EPHB6-ERK1/2-SLUG axis. Because CLDN1 enhances the efficacy of chemotherapy, CLDN1 is not only a prognostic marker but a predictive marker for lung adenocarcinoma patients who are good candidates for chemotherapy. Forced CLDN1 expression in low CLDN1-expressing lung adenocarcinoma will increase the chemotherapy response, providing a novel therapeutic strategy.

Loss of the nuclear Wnt pathway effector TCF7L2 promotes migration and invasion of human colorectal cancer cells

The transcription factor TCF7L2 is indispensable for intestinal tissue homeostasis where it transmits mitogenic Wnt/β-Catenin signals in stem and progenitor cells, from which intestinal tumors arise. Yet, TCF7L2 belongs to the most frequently mutated genes in colorectal cancer (CRC), and tumor-suppressive functions of TCF7L2 were proposed. This apparent paradox warrants to clarify the role of TCF7L2 in colorectal carcinogenesis. Here, we investigated TCF7L2 dependence/independence of CRC cells and the cellular and molecular consequences of TCF7L2 loss-of-function. By genome editing we achieved complete TCF7L2 inactivation in several CRC cell lines without loss of viability, showing that CRC cells have widely lost the strict requirement for TCF7L2. TCF7L2 deficiency impaired G1/S progression, reminiscent of the physiological role of TCF7L2. In addition, TCF7L2-negative cells exhibited morphological changes, enhanced migration, invasion, and collagen adhesion, albeit the severity of the phenotypic alterations manifested in a cell-line-specific fashion. To provide a molecular framework for the observed cellular changes, we performed global transcriptome profiling and identified gene-regulatory networks in which TCF7L2 positively regulates the proto-oncogene MYC, while repressing the cell cycle inhibitors CDKN2C/CDKN2D. Consistent with its function in curbing cell motility and invasion, TCF7L2 directly suppresses the pro-metastatic transcription factor RUNX2 and impinges on the expression of cell adhesion molecules. Altogether, we conclude that the proliferation-stimulating activity of TCF7L2 persists in CRC cells. In addition, TCF7L2 acts as invasion suppressor. Despite its negative impact on cell cycle progression, TCF7L2 loss-of-function may thereby increase malignancy, which could explain why TCF7L2 is mutated in a sizeable fraction of colorectal tumors.

The receptor tyrosine kinase EPHB6 regulates catecholamine exocytosis in adrenal gland chromaffin cells

The erythropoietin-producing human hepatocellular receptor EPH receptor B6 (EPHB6) is a receptor tyrosine kinase that has been shown previously to control catecholamine synthesis in the adrenal gland chromaffin cells (AGCCs) in a testosterone-dependent fashion. EPHB6 also has a role in regulating blood pressure, but several facets of this regulation remain unclear. Using amperometry recordings, we now found that catecholamine secretion by AGCCs is compromised in the absence of EPHB6. AGCCs from male knockout (KO) mice displayed reduced cortical F-actin disassembly, accompanied by decreased catecholamine secretion through exocytosis. This phenotype was not observed in AGCCs from female KO mice, suggesting that testosterone, but not estrogen, contributes to this phenotype. Of note, reverse signaling from EPHB6 to ephrin B1 (EFNB1) and a 7-amino acid-long segment in the EFNB1 intracellular tail were essential for the regulation of catecholamine secretion. Further downstream, the Ras homolog family member A (RHOA) and FYN proto-oncogene Src family tyrosine kinase (FYN)-proto-oncogene c-ABL-microtubule-associated monooxygenase calponin and LIM domain containing 1 (MICAL-1) pathways mediated the signaling from EFNB1 to the defective F-actin disassembly. We discuss the implications of EPHB6's effect on catecholamine exocytosis and secretion for blood pressure regulation.

TAGAP instructs Th17 differentiation by bridging Dectin activation to EPHB2 signaling in innate antifungal response

The TAGAP gene locus has been linked to several infectious diseases or autoimmune diseases, including candidemia and multiple sclerosis. While previous studies have described a role of TAGAP in T cells, much less is known about its function in other cell types. Here we report that TAGAP is required for Dectin-induced anti-fungal signaling and proinflammatory cytokine production in myeloid cells. Following stimulation with Dectin ligands, TAGAP is phosphorylated by EPHB2 at tyrosine 310, which bridges proximal Dectin-induced EPHB2 activity to downstream CARD9-mediated signaling pathways. During Candida albicans infection, mice lacking TAGAP mount defective immune responses, impaired Th17 cell differentiation, and higher fungal burden. Similarly, in experimental autoimmune encephalomyelitis model of multiple sclerosis, TAGAP deficient mice develop significantly attenuated disease. In summary, we report that TAGAP plays an important role in linking Dectin-induced signaling to the promotion of effective T helper cell immune responses, during both anti-fungal host defense and autoimmunity.

TAGAP gene variants are linked to human autoimmunity. Here the authors identify TAGAP as a Dectin-1 and EphB2-binding protein mediating antifungal innate immune signaling and cytokine production, and demonstrate TAGAP in non-T cells promotes Th17 response in mouse models of infection and autoimmunity.

Ephrin or not? Six tough questions on Eph targeting

Introduction: The Eph-ephrin is a cell-cell communication system generating a forward signal in cell expressing Eph receptors and a reverse signal in ephrin-ligand expressing cells. While clearly involved in the insurgence and progression of cancer, the understanding of the molecular mechanisms regulated by this system needs development; this is a hurdle to the development of therapeutic strategies that can target the Eph receptors and/or their ephrin ligands.Areas covered: We have taken the opportunity to share some key questions on the most effective strategies to target the Eph-ephrin system. This article is based on our experience of the field and therefore is a Perspective and not comprehensive examination of the literature.Expert opinion: Targeting of the Eph-ephrin system has emerged as a potentially valuable approach for cancer therapy. Pharmacological tools have been reported in the last 15 years and these include forward signaling blockers such as kinases inhibitors and antagonists of forward and reverse signaling. Also, biologics including antibodies and recombinant proteins have been developed and some have reached early clinical stages. Data deem the Eph-ephrin system as a signaling axis that is an elusive target. A better understanding of the basic pharmacology behind the activity of available agents and a comprehensive knowledge of the ephrin biology are necessary. We are looking forward to knowing the opinion of the readers.

Stem Cell Signaling Pathways in the Small Intestine

The ability of stem cells to divide and differentiate is necessary for tissue repair and homeostasis. Appropriate spatial and temporal mechanisms are needed. Local intercellular signaling increases expression of specific genes that mediate and maintain differentiation. Diffusible signaling molecules provide concentration-dependent induction of specific patterns of cell types or regions. Differentiation of adjacent cells, on the other hand, requires cell–cell contact and subsequent signaling. These two types of signals work together to allow stem cells to provide what organisms require. The ability to grow organoids has increased our understanding of the cellular and molecular features of small “niches” that modulate stem cell function in various organs, including the small intestine.

Recapitulating complex biological signaling environments using a multiplexed, DNA-patterning approach

Elucidating how the spatial organization of extrinsic signals modulates cell behavior and drives biological processes remains largely unexplored because of challenges in controlling spatial patterning of multiple microenvironmental cues in vitro. Here, we describe a high-throughput method that directs simultaneous assembly of multiple cell types and solid-phase ligands across length scales within minutes. Our method involves lithographically defining hierarchical patterns of unique DNA oligonucleotides to which complementary strands, attached to cells and ligands-of-interest, hybridize. Highlighting our method's power, we investigated how the spatial presentation of self-renewal ligand fibroblast growth factor-2 (FGF-2) and differentiation signal ephrin-B2 instruct single adult neural stem cell (NSC) fate. We found that NSCs have a strong spatial bias toward FGF-2 and identified an unexpected subpopulation exhibiting high neuronal differentiation despite spatially occupying patterned FGF-2 regions. Overall, our broadly applicable, DNA-directed approach enables mechanistic insight into how tissues encode regulatory information through the spatial presentation of heterogeneous signals.

CD74 Signaling Links Inflammation to Intestinal Epithelial Cell Regeneration and Promotes Mucosal Healing

BACKGROUND & AIMS

The inflammatory response to intestinal damage promotes healing through mechanisms that are incompletely understood. Gene expression of cluster of differentiation 74 (CD74), the receptor for cytokine macrophage migration inhibitory factor, is increased in patients with inflammatory bowel disease (IBD), however, the role of CD74 signaling in intestinal inflammation remains poorly understood. The aim of this study was to determine the functional role of CD74 signaling in intestinal inflammation.

METHODS

We studied the characteristics of CD74 protein expression in human IBD and experimental colitis. The functional role of CD74 signaling in the intestine was investigated using cellular models; wild-type, CD74^-/-, and bone marrow chimera mice; neutralizing anti-CD74 antibodies; flow cytometry; immunohistochemistry; immunofluorescence; immunoblotting; and clustered regularly interspaced short palindromic repeats and associated protein 9 technology.

RESULTS

In IBD patients and experimental colitis, CD74-receptor protein expression was increased in inflamed intestinal tissue, prominently in the crypt epithelial cells. By using distinct but complementary chemical and non-chemically induced mouse models of colitis with genetic and antibody neutralization approaches, we found that CD74 signaling was necessary for gut repair. Mechanistically, we found that the macrophage migration inhibitory factor cytokine, which also is increased in colitis, stimulated the CD74 receptor, enhancing intestinal epithelial cell proliferation through activation of the protein kinase B and the extracellular signal-regulated kinase pathways. Our data also suggest that CD74 signaling in immune cells was not essential for mucosal healing.

CONCLUSIONS

CD74 signaling is strongly activated during intestinal inflammation and protects the host by promoting epithelial cell regeneration, healing, and maintaining mucosal barrier integrity. Enhancing the CD74 pathway may represent a unique therapeutic strategy for promoting healing in IBD.

Identification of Eph receptor signaling as a regulator of autophagy and a therapeutic target in colorectal carcinoma

Advanced colorectal carcinoma is currently incurable, and new therapies are urgently needed. We report that phosphotyrosine‐dependent Eph receptor signaling sustains colorectal carcinoma cell survival, thereby uncovering a survival pathway active in colorectal carcinoma cells. We find that genetic and biochemical inhibition of Eph tyrosine kinase activity or depletion of the Eph ligand EphrinB2 reproducibly induces colorectal carcinoma cell death by autophagy. Spautin and 3‐methyladenine, inhibitors of early steps in the autophagic pathway, significantly reduce autophagy‐mediated cell death that follows inhibition of phosphotyrosine‐dependent Eph signaling in colorectal cancer cells. A small‐molecule inhibitor of the Eph kinase, NVP‐BHG712 or its regioisomer NVP‐Iso, reduces human colorectal cancer cell growth in vitro and tumor growth in mice. Colorectal cancers express the EphrinB ligand and its Eph receptors at significantly higher levels than numerous other cancer types, supporting Eph signaling inhibition as a potential new strategy for the broad treatment of colorectal carcinoma.

EphB2 receptor cell-autonomous forward signaling mediates auditory memory recall and learning-driven spinogenesis

While ephrin-B ligands and EphB receptors are expressed to high levels in the learning centers of the brain, it remains largely unknown how their trans-synaptic interactions contribute to memory. We find that EphB2 forward signaling is needed for contextual and sound-evoked memory recall and that constitutive over-activation of the receptor's intracellular tyrosine kinase domain results in enhanced memory. Loss of EphB2 expression does not affect the number of neurons activated following encoding, although a reduction of neurons activated after the sound-cued retrieval test was detected in the auditory cortex and hippocampal CA1. Further, spine density and maturation was reduced in the auditory cortex of mutants especially in the neurons that were dual-activated during both encoding and retrieval. Our data demonstrates that trans-synaptic ephrin-B-EphB2 interactions and forward signaling facilitate neural activation and structural plasticity in learning-associated neurons involved in the generation of memories.

Long-term mucosal injury and repair in a murine model of pelvic radiotherapy

Chronic intestinal injury after pelvic radiotherapy affects countless cancer survivors worldwide. A comprehensive understanding of the long-term injury dynamics is prevented in available animal models. With linear accelerators that are used to treat cancer in patients, we irradiated a small volume encompassing the colorectum in mice with four fractions of 8 Gy per fraction. We then determined the long-term dynamics of mucosal injury, repair, and the duration of inflammation. We show that crypt fission, not cell proliferation, is the main long-term mechanism for rescuing crypt density after irradiation, and provides a potentially wide window for clinical interventions. Persisting macrophage aggregations indicate a chronic mucosal inflammation. A better understanding as to how crypt fission is triggered and why it fails to repair fully the mucosa may help restore bowel health after pelvic radiotherapy. Moreover, anti-inflammatory interventions, even if implemented long after completed radiotherapy, could promote bowel health in pelvic cancer survivors.

The RTK Interactome: Overview and Perspective on RTK Heterointeractions

Receptor tyrosine kinases (RTKs) play important roles in cell growth, motility, differentiation, and survival. These single-pass membrane proteins are grouped into subfamilies based on the similarity of their extracellular domains. They are generally thought to be activated by ligand binding, which promotes homodimerization and then autophosphorylation in trans. However, RTK interactions are more complicated, as RTKs can interact in the absence of ligand and heterodimerize within and across subfamilies. Here, we review the known cross-subfamily RTK heterointeractions and their possible biological implications, as well as the methodologies which have been used to study them. Moreover, we demonstrate how thermodynamic models can be used to study RTKs and to explain many of the complicated biological effects which have been described in the literature. Finally, we discuss the concept of the RTK interactome: a putative, extensive network of interactions between the RTKs. This RTK interactome can produce unique signaling outputs; can amplify, inhibit, and modify signaling; and can allow for signaling backups. The existence of the RTK interactome could provide an explanation for the irreproducibility of experimental data from different studies and for the failure of some RTK inhibitors to produce the desired therapeutic effects. We argue that a deeper knowledge of RTK interactome thermodynamics can lead to a better understanding of fundamental RTK signaling processes in health and disease. We further argue that there is a need for quantitative, thermodynamic studies that probe the strengths of the interactions between RTKs and their ligands and between different RTKs.

Sonic hedgehog pathway activation is associated with cetuximab resistance and EPHB3 receptor induction in colorectal cancer

A major problem of colorectal cancer (CRC) targeted therapies is relapse caused by drug resistance. In most cases of CRC, patients develop resistance to anticancer drugs. Cetuximab does not show many of the side effects of other anticancer drugs and improves the survival of patients with metastatic CRC. However, the molecular mechanism of cetuximab resistance is not fully understood.

Methods: EPHB3-mediated cetuximab resistance was confirmed by in vitro western blotting, colony-forming assays, WST-1 colorimetric assay, and in vivo xenograft models (n = 7 per group). RNA-seq analysis and receptor tyrosine kinase assays were performed to identify the cetuximab resistance mechanism of EPHB3. All statistical tests were two-sided.

Results: The expression of EFNB3, which upregulates the EPHB3 receptor, was shown to be increased via microarray analysis. When resistance to cetuximab was acquired, EPHB3 protein levels increased. Hedgehog signaling, cancer stemness, and epithelial-mesenchymal transition signaling proteins were also increased in the cetuximab-resistant human colon cancer cell line SW48R. Despite cells acquiring resistance to cetuximab, STAT3 was still responsive to EGF and cetuximab treatment. Moreover, inhibition of EPHB3 was associated with decreased STAT3 activity. Co-immunoprecipitation confirmed that EGFR and EPHB3 bind to each other and this binding increases upon resistance acquisition, suggesting that STAT3 is activated by the binding between EGFR and EPHB3. Protein levels of GLI-1, SOX2, and Vimentin, which are affected by STAT3, also increased. Similar results were obtained in samples from patients with CRC.

Conclusion: EPHB3 expression is associated with anticancer drug resistance.

A neuronal molecular switch through cell-cell contact that regulates quiescent neural stem cells

The quiescence of radial neural stem cells (rNSCs) in adult brain is regulated by environmental stimuli. However, little is known about how the neurogenic niche couples the external signal to regulate activation and transition of quiescent rNSCs. Here, we reveal that long-term excitation of hippocampal dentate granule cells (GCs) upon voluntary running leads to activation of adult rNSCs in the subgranular zone and thereby generation of newborn neurons. Unexpectedly, the role of these excited GC neurons in NSCs depends on direct GC-rNSC interaction in the local niche, which is through down-regulated ephrin-B3, a GC membrane-bound ligand, and attenuated transcellular EphB2 kinase-dependent signaling in the adjacent rNSCs. Furthermore, constitutively active EphB2 kinase sustains the quiescence of rNSCs during running. These findings thus elucidate the physiological significance of GC excitability on adult rNSCs under external environments and indicate a key-lock switch regulation via cell-cell contact for functional transition of rNSCs.

Depletion of MOB1A/B causes intestinal epithelial degeneration by suppressing Wnt activity and activating BMP/TGF-β signaling

The Hippo pathway is involved in intestinal epithelial homeostasis with Wnt, BMP, Notch, and EGF signaling. We investigated the relationship between Hippo and other signaling pathways and the role of MOB kinase activator 1A/1B (MOB1A/B) in intestinal homeostasis. Mice with intestinal epithelial cell (IEC)-specific depletion of MOB1A/B showed hyperproliferation in IECs, defects in secretory lineage differentiation and loss of intestinal stem cells and eventually died at 10–12 days after tamoxifen treatment. In MOB1A/B-depleted IECs, expression of Wnt target genes were downregulated but Bmp2 and Tgfbr2 were transcriptionally activated with enhanced YAP activity. In in vivo and in vitro experiments with several signaling inhibitors, it has been shown that the BMP inhibitor LDN193189 or TGF-β inhibitor SB431542 had effects on partial restoration of the intestinal degenerative phenotype. Treatment with these inhibitors restored differentiation of secretory lineage cells in MOB1A/B-deficient mice, but not ISC pools in the crypt region. These studies reveal that IEC-specific depletion of MOB1A/B induced overexpression of Bmp2 and Tgfbr2 and inhibited Wnt activity, finally leading to loss of ISCs and functional epithelia in the mouse intestine. These results suggest that MOB1A/B has an essential function for intestinal epithelial homeostasis by regulating YAP, Wnt activity, and BMP/TGF-β signaling.

Loss of EfnB1 in the osteogenic lineage compromises their capacity to support hematopoietic stem/progenitor cell maintenance

The bone marrow stromal microenvironment contributes to the maintenance and function of hematopoietic stem/progenitor cells (HSPCs). The Eph receptor tyrosine kinase family members have been implicated in bone homeostasis and stromal support of HSPCs. The present study examined the influence of EfnB1-expressing osteogenic lineage on HSPC function. Mice with conditional deletion of EfnB1 in the osteogenic lineage (EfnB1_OB^-/-), driven by the Osterix promoter, exhibited a reduced prevalence of osteogenic progenitors and osteoblasts, correlating to lower numbers of HSPCs compared with Osx:Cre mice. Long-term culture-initiating cell (LTC-IC) assays confirmed that the loss of EfnB1 within bone cells hindered HSPC function, with a significant reduction in colony formation in EfnB1_OB^-/- mice compared with Osx:Cre mice. Human studies confirmed that activation of EPHB2 on CD34⁺ HSPCs via EFNB1-Fc stimulation enhanced myeloid/erythroid colony formation, whereas functional blocking of either EPHB1 or EPHB2 inhibited the maintenance of LTC-ICs. Moreover, EFNB1 reverse signaling in human and mouse stromal cells was found to be required for the activation of the HSPC-promoting factor CXCL12. Collectively, the results of this study confirm that EfnB1 contributes to the stromal support of HSPC function and maintenance and may be an important factor in regulating the HSPC niche.

Retrograde regulation of mossy fiber axon targeting and terminal maturation via postsynaptic Lnx1

Synapse formation relies on the coordination of dynamic pre- and postsynaptic structures during brain development. Liu et al. reveal that presynaptic terminal maturation of mossy fiber axons is retrogradely regulated by postsynaptic scaffold protein Lnx1 via stabilizing EphB receptor kinases.

Neuronal connections are initiated by axon targeting to form synapses. However, how the maturation of axon terminals is modulated through interacting with postsynaptic elements remains elusive. In this study, we find that ligand of Numb protein X 1 (Lnx1), a postsynaptic PDZ protein expressed in hippocampal CA3 pyramidal neurons, is essential for mossy fiber (MF) axon targeting during the postnatal period. Lnx1 deletion causes defective synaptic arrangement that leads to aberrant presynaptic terminals. We further identify EphB receptors as novel Lnx1-binding proteins to form a multiprotein complex that is stabilized on the CA3 neuron membrane through preventing proteasome activity. EphB1 and EphB2 are independently required to transduce distinct signals controlling MF pruning and targeting for precise DG-CA3 synapse formation. Furthermore, constitutively active EphB2 kinase rescues structure of the wired MF terminals in Lnx1 mutant mice. Our data thus define a retrograde trans-synaptic regulation required for integration of post- and presynaptic structure that participates in building hippocampal neural circuits during the adolescence period.

Effects of EphB4 receptor expression on colorectal cancer cells, tumor growth, vascularization and composition

BACKGROUND

Colorectal cancer (CRC) is one of the most common causes of cancer-related deaths worldwide. Increased expression of the molecular target, EphB4 receptor, has been observed in several cancer types. However, studies on the role of EphB4 receptor in CRC have yielded contradictory results. The aim of this study was to investigate the influence of EphB4 expression levels on CRC cell behavior and its contribution to tumor growth and vascularization.

METHODS

SW480, LIM2405 and CT26 CRC cell lines were transfected with EphB4 expression vector. High EphB4 expressing cells were compared to low EphB4 expressing empty vector controls. Proliferation and migration assays as well as EphrinB2-Fc cell stimulations were conducted in vitro and subcutaneous xenografts of CRC were analyzed in vivo.

RESULTS

High EphB4 expression enhanced migratory ability of these CRC cell lines in vitro and contributed to a significant increase in tumor growth and vascularization in vivo. Tumours induced with high EphB4 expressing SW480 and LIM2405 cells yielded homogenous masses densely packed with cancer cells. EphrinB2-Fc cell stimulations induced cell clustering of high EphB4 expressing SW480 and LIM2405 in vitro.

CONCLUSION

These results suggest that with enhanced vascularization and an increase in migratory abilities, the high EphB4 expressing cells may be able to metastasize more readily.