Ephrin Signaling Research Articles

Expression alterations of genes on both neuronal and glial development in rats after developmental exposure to 6-propyl-2-thiouracil

The present study was performed to determine target gene profiles associated with pathological mechanisms of developmental neurotoxicity. For this purpose, we selected a rat developmental hypothyroidism model because thyroid hormones play an essential role in both neuronal and glial development. Region-specific global gene expression analysis was performed at postnatal day (PND) 21 on four brain regions representing different structures and functions, i.e., the cerebral cortex, corpus callosum, dentate gyrus and cerebellar vermis of rats exposed to 6-propyl-2-thiouracil in the drinking water at 3 and 10ppm from gestational day 6 to PND 21. Expression changes of gene clusters of neuron differentiation and development, cell migration, synaptic function, and axonogenesis were detected in all four regions. Characteristically, gene expression profiles suggestive of affection of ephrin signaling and glutamate transmission were obtained in multiple brain regions. Gene clusters suggestive of suppression of myelination and glial development were specifically detected in the corpus callosum and cerebral cortex. Immunohistochemically, immature astrocytes immunoreactive for vimentin and glial fibrillary acidic protein were increased, and oligodendrocytes immunoreactive for oligodendrocyte lineage transcription factor 2 were decreased in the corpus callosum. Immunoreactive intensity of myelin basic protein was also decreased in the corpus callosum and cerebral cortex. The hippocampal dentate gyrus showed downregulation of Ptgs2, which is related to synaptic activity and neurogenesis, as well as a decrease of cyclooxygenase-2-immunoreactive granule cells, suggesting an impaired synaptic function related to neurogenesis. These results suggest that multifocal brain region-specific microarray analysis can determine the affection of neuronal or glial development.

Exploring the Spatio-Mechanosensitivity of Eph Receptor in Stem Cells

The Eph receptors constitute the largest family of receptor tyrosine kinases (RTK), and their ligands, ephrins, are glycophophatidylinositol-linked (ephrinA1-10) or transmembrane (ephrinB1-3) proteins which bind to the Eph receptors on the opposing cell membrane to initiate bidirectional juxtacrine signalling [1]. Our collaborators in the Schaffer group have uncovered a previously unknown role of EphB4 signalling in regulating neural stem cell fate commitment. In particular, antibody-clustered ephrinB2 in solution induces neuronal differentiation in vivo and in vitro [2]. Experiments in solution [2], however, cannot reflect the microenvironment of cell-cell junction. Because ephrin ligands and Eph receptors are membrane bound, Eph:ephrin signalling is cell-cell contact dependent. The Groves group has developed a unique platform which is ideally suited for investigating the role of the physical microenvironment on cell-cell signalling. This hybrid system simulates the cell-cell contact geometry by combining live cells with a supported lipid bilayer_a synthetic cell membrane formed on a glass substrate which can be functionalised with cell surface ligands. By fabricating microstructures on the glass substrate, one can induce a spatial mutation, which is the orchestrated mechanical disruption of the spatial patterning of proteins on the lipid bilayer. Spatial mutations have been shown to have a demonstrably significant impact on EphA2-ephrinA1 signalling in cancer cells which alters the downstream molecule recruitment [3]. Altogether, these results motivate us to explore the effect of spatial-reorganisation of EphB receptor in stem cell functions by reconstituting the cell-cell contact geometry on a supported lipid bilayer. [1] Pasquale, E.B. Nat. Rev. Mol. Cell Biol. 6, 462-475 (2005). [2] Ashton, R.S. et al. Nat. Neurosci. 15, 1399-1406 (2012). [3] Khalid S. et al. Science. 327, 1380 (2012).

Glia and the Synapse: Plasticity and Disease

Glia and the Synapse: Plasticity and Disease

Therapeutic targeting of EPH receptors and their ligands

Critical roles for EPH receptor (EPH)-ephrin signalling in a range of chronic and regenerative diseases are increasingly being recognized. In particular, the complex roles of EPHs and ephrins in tumour growth and progression, and in nerve injury and regeneration have been studied extensively. This has led to considerable progress in developing strategies for their therapeutic targeting, with some anticancer agents already in clinical trials. Promising leads for non-malignant diseases are also emerging, with compelling preclinical data encouraging clinical development. We discuss this rapidly developing area of drug discovery, highlighting the associated challenges and limitations.

Target Hopping as a Useful Tool for the Identification of Novel EphA2 Protein–Protein Antagonists

Lithocholic acid (LCA), a physiological ligand for the nuclear receptor FXR and the G-protein-coupled receptor TGR5, has been recently described as an antagonist of the EphA2 receptor, a key member of the ephrin signalling system involved in tumour growth. Given the ability of LCA to recognize FXR, TGR5, and EphA2 receptors, we hypothesized that the structural requirements for a small molecule to bind each of these receptors might be similar. We therefore selected a set of commercially available FXR or TGR5 ligands and tested them for their ability to inhibit EphA2 by targeting the EphA2-ephrin-A1 interface. Among the selected compounds, the stilbene carboxylic acid GW4064 was identified as an effective antagonist of EphA2, being able to block EphA2 activation in prostate carcinoma cells, in the micromolar range. This finding proposes the "target hopping" approach as a new effective strategy to discover new protein-protein interaction inhibitors.

Eph:ephrin-B1 forward signaling controls fasciculation of sensory and motor axons

Axon fasciculation is one of the processes controlling topographic innervation during embryonic development. While axon guidance steers extending axons in the accurate direction, axon fasciculation allows sets of co-extending axons to grow in tight bundles. The Eph:ephrin family has been involved both in axon guidance and fasciculation, yet it remains unclear how these two distinct types of responses are elicited. Herein we have characterized the role of ephrin-B1, a member of the ephrinB family in sensory and motor innervation of the limb. We show that ephrin-B1 is expressed in sensory axons and in the limb bud mesenchyme while EphB2 is expressed in motor and sensory axons. Loss of ephrin-B1 had no impact on the accurate dorso-ventral innervation of the limb by motor axons, yet EfnB1 mutants exhibited decreased fasciculation of peripheral motor and sensory nerves. Using tissue-specific excision of EfnB1 and in vitro experiments, we demonstrate that ephrin-B1 controls fasciculation of axons via a surround repulsion mechanism involving growth cone collapse of EphB2-expressing axons. Altogether, our results highlight the complex role of Eph:ephrin signaling in the development of the sensory-motor circuit innervating the limb.

Comprehensive Analysis of MicroRNA (miRNA) Targets in Breast Cancer Cells

MicroRNAs (miRNAs) regulate mRNA stability and translation through the action of the RNAi-induced silencing complex. In this study, we systematically identified endogenous miRNA target genes by using AGO2 immunoprecipitation (AGO2-IP) and microarray analyses in two breast cancer cell lines, MCF7 and MDA-MB-231, representing luminal and basal-like breast cancer, respectively. The expression levels of ∼70% of the AGO2-IP mRNAs were increased by DROSHA or DICER1 knockdown. In addition, integrated analysis of miRNA expression profiles, mRNA-AGO2 interaction, and the 3'-UTR of mRNAs revealed that >60% of the AGO2-IP mRNAs were putative targets of the 50 most abundantly expressed miRNAs. Together, these results suggested that the majority of the AGO2-associated mRNAs were bona fide miRNA targets. Functional enrichment analysis uncovered that the AGO2-IP mRNAs were involved in regulation of cell cycle, apoptosis, adhesion/migration/invasion, stress responses (e.g. DNA damage and endoplasmic reticulum stress and hypoxia), and cell-cell communication (e.g. Notch and Ephrin signaling pathways). A role of miRNAs in regulating cell migration/invasion and stress response was further defined by examining the impact of DROSHA knockdown on cell behaviors. We demonstrated that DROSHA knockdown enhanced cell migration and invasion, whereas it sensitized cells to cell death induced by suspension culture, glucose depletion, and unfolding protein stress. Data from an orthotopic xenograft model showed that DROSHA knockdown resulted in reduced growth of primary tumors but enhanced lung metastasis. Taken together, these results suggest that miRNAs collectively function to promote survival of tumor cells under stress but suppress cell migration/invasion in breast cancer cells.

Early Insights into the Function of KIAA1199, a Markedly Overexpressed Protein in Human Colorectal Tumors

We previously reported that the expression of KIAA1199 in human colorectal tumors (benign and malignant) is markedly higher than that in the normal colonic mucosa. In this study, we investigated the functions of the protein encoded by this gene, which are thus far unknown. Immunostaining studies were used to reveal its subcellular localization, and proteomic and gene expression experiments were conducted to identify proteins that might interact with KIAA1199 and molecular pathways in which it might play roles. Using colon cancer cell lines, we showed that both endogenous and ectopically expressed KIAA1199 is secreted into the extracellular environment. In the cells, it was found mainly in the perinuclear space (probably the ER) and cell membrane. Both cellular compartments were also over-represented in lists of proteins identified by mass spectrometry as putative KIAA1199 interactors and/or proteins encoded by genes whose transcription was significantly changed by KIAA1199 expression. These proteomic and transcriptomic datasets concordantly link KIAA1199 to several genes/proteins and molecular pathways, including ER processes like protein binding, transport, and folding; and Ca2+, G-protein, ephrin, and Wnt signaling. Immunoprecipitation experiments confirmed KIAA1199’s interaction with the cell-membrane receptor ephrin A2 and with the ER receptor ITPR3, a key player in Ca2+ signaling. By modulating Ca2+ signaling, KIAA1199 could affect different branches of the Wnt network. Our findings suggest it may negatively regulate the Wnt/CTNNB1 signaling, and its expression is associated with decreased cell proliferation and invasiveness.

Retinocollicular mapping explained?

We review and comment on the recent model of Grimbert and Cang of the development of topographically ordered maps from the retina to the superior colliculus. This model posits a phase in which arbors are created in zones permitted by Eph and ephrin signaling, followed by a phase in which activity-dependent synaptic plasticity refines the map. We show that it is not possible to generate the arborization probability functions used in the simulations of Grimbert and Cang using gradients of Ephs and ephrins and the interaction mechanism that Grimbert and Cang propose in their results. Furthermore, the arborization probabilities we do generate are far less sharp than we imagine truly “permissive” ones would be. It remains to be seen if maps can be generated from the nonpermissive arborization probabilities generated from gradients.

Regulation of contact inhibition of locomotion by Eph–ephrin signalling

Contact inhibition of locomotion (CIL) occurs when a cell stops migrating in a particular direction upon contact with another cell. Many cancer cells show Contact inhibition of locomotion when contacting one another but display contact-unimpeded migration following collision with noncancer cells. Here we review current understanding of Contact inhibition of locomotion, from Abercrombie's historical studies of cells in tissue culture to more recent analyses of Contact inhibition of locomotion in vivo. We discuss the cellular machinery required for CIL and the molecular signals that regulate it. We focus on our recent finding that in prostate cancer cells, Contact inhibition of locomotion is regulated by a balance between EphA and EphB receptor signalling. We show that, as recently described for chick heart fibroblasts, microtubule dynamics are required for Contact inhibition of locomotion in prostate cancer cells and we propose that stabilization of microtubules could account for defective Contact inhibition of locomotion between cancer cells and noncancer cells.

Getting the “Inside” Scoop on EphrinB2 Signaling in Pericytes and the Effect on Peritubular Capillary Stability

Progressive CKD develops from a lack of fidelity in tissue remodeling after acute injury. A lack of successful repair following even subtle injuries, regardless of their cause, suggests that complete resolution of function may be difficult to achieve, even if initiating deficits are corrected. This

Pharmacological inhibition of Eph receptors enhances glucose-stimulated insulin secretion from mouse and human pancreatic islets

Type 2 diabetes is characterised by impaired glucose-stimulated insulin secretion (GSIS) from pancreatic islets. Since erythropoietin-producing hepatoma (Eph)-ephrin bidirectional signalling fine-tunes GSIS from pancreatic beta cells, we investigated Eph receptor tyrosine kinases (RTK) as potential drug targets for selectively increasing GSIS. Insulin secretion assays were carried out using mouse and human pancreatic islets as well as mouse insulinoma (MIN6) cells in the presence or absence of two Eph RTK inhibitors. Furthermore, the most potent inhibitor was injected into mice to evaluate its effects on glucose tolerance and plasma insulin levels. We showed that the Eph RTK inhibitors selectively increased GSIS from MIN6 cells as well as mouse and human islets. Our results also showed that the insulin secretory effects of these compounds required Eph-ephrin signalling. Finally, pharmacological inhibition of Eph receptor signalling improved glucose tolerance in mice. We showed for the first time that Eph RTKs represent targets for small molecules to selectively increase GSIS and improve glucose tolerance.

Eph–ephrin bidirectional signalling: A promising approach for osteoporosis treatment

Abstract Osteoporosis is a common disease characterised by low bone density and brittle bone due to osteoblast–osteoclast uncoupling. The cellular and molecular mechanisms responsible for osteoblast–osteoclast coupling lead to the identification of novel therapeutic targets. The increasing evidence for a role for Eph–ephrin signalling in biological processes, including cell–cell interactions, cell morphology, cell migration, angiogenesis, cancer and bone homeostasis, identifies new molecular pathways and potentially novel therapeutic targets for the treatment of diseases. Recent studies suggest that the interactions between Eph and ephrin play critical roles in bone cell differentiation and patterning by exerting dimorphic effects on osteoblast and osteoclast differentiation, resulting in the intriguing coupling of bone resorption and bone formation. These findings suggest that interventions targeting osteoblast–osteoclast coupling by the regulation of the Eph–ephrin bidirectional signalling according to its biological effects, which results in inhibiting osteoclastic resorption and promoting osteoblastic formation, may be a promising approach for osteoporosis prevention and treatment in the near future.

Boundary formation in the development of the vertebrate hindbrain

The formation of a sharp interface of adjacent subdivisions is important for establishing the precision of tissue organization, and at specific borders it serves to organize key signaling centers. We discuss studies of vertebrate hindbrain development that have given important insights into mechanisms that underlie the formation and maintenance of sharp borders. The hindbrain is subdivided into a series of segments with distinct anteroposterior identity that underlies the specification of distinct neuronal cell types. During early stages of segmentation, cell identity switching contributes to the refinement of borders and enables homogenous territories to be maintained despite intermingling of cells between segments. At later stages, there is a specific restriction to cell intermingling between segments that is mediated by Eph receptor and ephrin signaling. Eph-ephrin signaling can restrict cell intermingling and sharpen borders through multiple mechanisms, including the regulation of cell adhesion and contact inhibition of cell migration.

Evidence That the EphA2 Receptor Exacerbates Ischemic Brain Injury

Ephrin (Eph) signaling within the central nervous system is known to modulate axon guidance, synaptic plasticity, and to promote long-term potentiation. We investigated the potential involvement of EphA2 receptors in ischemic stroke-induced brain inflammation in a mouse model of focal stroke. Cerebral ischemia was induced in male C57Bl6/J wild-type (WT) and EphA2-deficient (EphA2−/−) mice by middle cerebral artery occlusion (MCAO; 60 min), followed by reperfusion (24 or 72 h). Brain infarction was measured using triphenyltetrazolium chloride staining. Neurological deficit scores and brain infarct volumes were significantly less in EphA2−/− mice compared with WT controls. This protection by EphA2 deletion was associated with a comparative decrease in brain edema, blood-brain barrier damage, MMP-9 expression and leukocyte infiltration, and higher expression levels of the tight junction protein, zona occludens-1. Moreover, EphA2−/− brains had significantly lower levels of the pro-apoptotic proteins, cleaved caspase-3 and BAX, and higher levels of the anti-apoptotic protein, Bcl-2 as compared to WT group. We confirmed that isolated WT cortical neurons express the EphA2 receptor and its ligands (ephrin-A1–A3). Furthermore, expression of all four proteins was increased in WT primary cortical neurons following 24 h of glucose deprivation, and in the brains of WT mice following stroke. Glucose deprivation induced less cell death in primary neurons from EphA2−/− compared with WT mice. In conclusion, our data provide the first evidence that the EphA2 receptor directly contributes to blood-brain barrier damage and neuronal death following ischemic stroke.

The Ephrin Signaling Pathway Regulates Morphology and Adhesion of Mouse Granulosa Cells In Vitro1

Follicle-stimulating hormone (FSH)-mediated changes in granulosa cell adhesion and morphology are essential for preovulatory follicle development, given the dramatic changes in follicle size and granulosa cell number that occur during this transition. Members of the Eph-ephrin family of cell-positioning and adhesion molecules, a family that consists of ephrin ligands and their Ephrin (Eph) receptors, regulate cell location, adhesion, and migration during embryonic development and tumor growth. However, very little is known about ephrin signaling during folliculogenesis. We have found that FSH increases the expression of several members of the Eph-ephrin family and that this signaling regulates granulosa cell morphology and adhesion. FSH induced increased mRNA levels of the ephrin ligand, ephrin-A5 (Efna5), and its receptors, Eph receptors A3, A5, and A8 (Epha3, Epha5, and Epha8, respectively), in granulosa cells. Immunofluorescence studies indicated that EFNA5 and EPHA5 are located in the membrane of granulosa cells of developing mouse follicles. Eph-ephrin signaling directly affected granulosa cell morphology and adhesion. Recombinant EFNA5 reduced cell spreading and increased cell rounding in mouse primary granulosa cells and in a rat granulosa cell line, whereas EPHA5 reduced granulosa cell adhesion in both model systems. Both FSH and forskolin also increased Efna5 and Epha5 mRNA levels in rat and human granulosa cell lines, indicating that FSH regulates these genes via the cAMP-dependent protein kinase A pathway and that this regulation is conserved across different species. The present study identifies Eph-ephrin signaling as a novel FSH-mediated pathway regulating granulosa cell morphology and adhesion.

Eph receptors and ephrin class B ligands are expressed at tissue boundaries in Hydra vulgaris

Eph receptors and ephrins are important players in axon guidance, cell sorting and boundary formation. Both the receptors and the ligands are integrated transmembrane proteins and signalling is bidirectional. The prevalent outcome of signal transduction is repulsion of adjacent cells or cell populations. Eph/ephrins have been identified in all multicellular animals from human to sponge, their functions however appear to have been altered during evolution. Here we have identified four Eph receptors and three class B ligands in the cnidarian Hydra vulgaris, indicating that those are the evolutionary older ones. In situ hybridisation experiments revealed a striking complementarity of expression of receptors and ligands in tentacles and in developing buds. This suggests that the original function of ephrin signalling may have been in epithelial cell adhesion and the formation of tissue boundaries.

Neural tube patterning by Ephrin, FGF and Notch signaling relays

There was an error published in Development138, 5429-5439.On p. 5431, PIPES-sucrose-FA buffer was incorrectly described. The correct composition of this buffer is: 400 mM sucrose, 50 mM EGTA, 100 mM PIPES pH 7, 4% formaldehyde.The authors apologise to readers for this mistake.

Gdnf Activates Midline Repulsion by Semaphorin3B via NCAM during Commissural Axon Guidance

The Neurotrophic factor gdnf plays diverse developmental roles, supporting survival and also acting asachemoattractant for axon and cell migration. We report that in the developing spinal cord, a focal source of gdnf is present in the floor plate (FP) where commissural axons cross the midline. Gdnf has nodirect guidance properties but switches on the responsiveness of crossing commissural growth cones to the midline repellent Semaphorin3B by suppressing calpain-mediated processing of the Sema3B signaling coreceptor Plexin-A1. Analysis of single and double mutant mouse models indicates that although gdnf is the principal trigger of Sema3B midline repulsion, it acts with another FP cue, NrCAM. Finally, genetic and invitro experiments provide evidence that this gdnf effect is RET independent and mediated by NCAM/GFRα1 signaling. This study identifies a regulator of midline crossing and reveals interplays between Semaphorin and gdnf signaling during axon guidance.

Abstract LB-404: Genomic analysis reveals roles for chromatin modification and axon guidance in pancreatic cancer

Abstract Pancreatic cancer (PC) is the fourth leading cause of cancer death with an overall 5-year survival rate of < 5%, a statistic that has not changed in almost 50 years. A deeper understanding of the underlying molecular pathophysiology is expected to advance the urgent need to develop effective therapeutic and early detection strategies for this disease. Genomic characterisation of Pancreatic Ductal Adenocarcinoma (PDAC), which accounts for over 90% of PC has to date relied on targeted PCR based exome sequencing of primary and metastatic lesions propagated as xenografts or cell lines. Here we use exome sequencing and copy number analysis to define genomic aberrations in a prospectively accrued clinical cohort (n = 142) of early (Stage I and II) PDAC. Detailed analysis of 99 informative tumours identified 1984 non-silent mutations and 1628 significant CNV events, and defined 439 significantly mutated genes based on stringent Significant Mutated Gene and GISTIC analysis. Integration with functional data from in vitro shRNA and in vivo Sleeping Beauty-mediated somatic mutagenesis screens provided supportive evidence for 182 of these as candidate driver mutations. Pathway based analysis recapitulated clustering of mutations in core signalling pathways in PDAC, and identified multiple new components in each, particularly in DNA damage repair mechanisms (ATM, TOP2A, RPA1, BRCC3). We also identified frequent and diverse somatic aberrations in genes involved in chromatin modification (SWI/SNF complex members, SETD2, EPC1), and novel mechanisms such as axon guidance (Semaphorin, Slit, Netrin and Ephrin signalling), extending the number of core perturbed pathways in PDAC. Aberrant expression of axon guidance genes co-segregated with poor patient survival, and in animal models was associated with disease development and progression, further implicating perturbation of the axon guidance pathway as a novel mechanism important in PDAC. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr LB-404. doi:1538-7445.AM2012-LB-404