Ephrin Expression Research Articles

Knockdown of ephrin-A5 expression by 40% does not affect motor axon growth or migration into the chick hindlimb.

Bidirectional signaling between Eph receptor tyrosine kinases and their cell-surface protein signals, the ephrins, comprises one mechanism for guiding motor axons to their proper targets. During projection of motor axons from the lateral motor column (LMC) motor neurons of the spinal cord to the hindlimb muscles in chick embryos, ephrin-A5 has been shown to be expressed in the LMC motor axons until they reach the base of the limb bud and initiate sorting into their presumptive dorsal and ventral nerve trunks, at which point expression is extinguished. We tested the hypothesis that this dynamic pattern of ephrin-A5 expression in LMC motor axons is important for the growth and guidance of the axons to, and into, the hindlimb by knocking down endogenous ephrin-A5 expression in the motor neurons and their axons. No perturbation of LMC motor axon projections was observed in response to this treatment, suggesting that ephrin-A5 is not needed for LMC motor axon growth or guidance.

Eph/Ephrin Profiling in Human Breast Cancer Reveals Significant Associations between Expression Level and Clinical Outcome

Pre-clinical studies provide compelling evidence that Eph family receptor tyrosine kinases (RTKs) and ligands promote cancer growth, neovascularization, invasion, and metastasis. Tumor suppressive roles have also been reported for the receptors, however, creating a potential barrier for clinical application. Determining how these observations relate to clinical outcome is a crucial step for translating the biological and mechanistic data into new molecularly targeted therapies. We investigated eph and ephrin expression in human breast cancer relative to endpoints of overall and/or recurrence-free survival in large microarray datasets. We also investigated protein expression in commercial human breast tissue microarrays (TMA) and Stage I prognostic TMAs linked to recurrence outcome data. We found significant correlations between ephA2, ephA4, ephA7, ephB4, and ephB6 and overall and/or recurrence-free survival in large microarray datasets. Protein expression in TMAs supported these trends. While observed no correlation between ephrin ligand expression and clinical outcome in microarray datasets, ephrin-A1 and EphA2 protein co-expression was significantly associated with recurrence in Stage I prognostic breast cancer TMAs. Our data suggest that several Eph family members are clinically relevant and tractable targets for intervention in human breast cancer. Moreover, profiling Eph receptor expression patterns in the context of relevant ligands and in the context of stage may be valuable in terms of diagnostics and treatment.

Ephrin-Mediated cis-Attenuation of Eph Receptor Signaling Is Essential for Spinal Motor Axon Guidance

Axon guidance receptors guide neuronal growth cones by binding in trans to axon guidance ligands in the developing nervous system. Some ligands are coexpressed in cis with their receptors, raising the question of the relative contribution of cis and trans interactions to axon guidance. Spinal motor axons use Eph receptors to select a limb trajectory in response to trans ephrins, while expressing ephrins in cis. We show that changes in motor neuron ephrin expression result in trajectory selection defects mirrored by changes in growth cone sensitivity to ephrins in vitro, arguing for ephrin cis-attenuation of Eph function. Furthermore, the relative contribution of trans-signaling and cis-attenuation is influenced by the subcellular distribution of ephrins to membrane patches containing Eph receptors. Thus, growth cone ephrins are essential for axon guidance in vivo and the balance between cis and trans modes of axon guidance ligand-receptor interaction contributes to the diversity of axon guidance signaling responses.

Enhanced expression of ephrins and thrombospondins in the dermis of patients with early diffuse systemic sclerosis: potential contribution to perturbed angiogenesis and fibrosis

To determine the skin and fibroblast expression of ephrins (EphB4 and EphrinB2) and thrombospondins (TSPs: TSP1 and TSP2) in patients with SSc. All experiments were performed in skin sections and dermal fibroblasts issued from control and clinically involved/non-involved SSc skin biopsies. Dermal fibroblasts were stimulated with hypoxia or TGF-β, or treated with TGF-β-neutralizing antibodies. Ephrin and TSP mRNA levels were assessed in skin tissue and dermal fibroblasts by in situ hybridization and quantitative RT-PCR, respectively, and protein levels were assessed by immunohistochemistry and western blots, respectively. Enhanced ephrin and TSP mRNA and protein levels were observed in clinically involved SSc skin. EphrinB2, TSP1 and TSP2 mRNA and protein levels were also up-regulated in non-involved SSc skin. Similar mRNA and protein levels of ephrinB2 and EphB4 were detected in unstimulated and stimulated control and SSc dermal fibroblasts. TSP1 and TSP2 mRNA and protein levels were significantly increased in fibroblasts issued from involved and non-involved SSc skin. This up-regulation was not modified by hypoxic exposure, but was markedly reduced by the addition of TGF-β-neutralizing antibodies. Stimulation of healthy fibroblasts with TGF-β significantly increased TSP1 and TSP2 mRNA and protein levels. EphB4 and EphrinB2 are up-regulated in clinically involved skin of SSc patients, suggesting their participation in SSc-perturbed angiogenesis. TSP1 and TSP2 are up-regulated in both clinically involved and non-involved SSc skin and are constitutively overexpressed in a TGF-β-dependent and hypoxia-independent manner in SSc dermal fibroblasts, suggesting their potential early contribution in SSc pathogenesis.

De novo expression of EphA2 in osteosarcoma modulates activation of the mitogenic signalling pathway

In osteosarcoma patients the development of metastases, often to the lungs, is the most frequent cause of death. The aim of this study was to elucidate the molecular mechanisms governing osteosarcoma development and dissemination and, thereby, to identify possible novel drug targets for improved treatment. Osteosarcoma samples were characterized using genome-wide microarrays: increased expression of the EphA2 receptor and its ligand EFNA1 was detected. In addition, increased expression of EFNB1, EFNB3 and EphA3 was suggested. Immunohistochemistry revealed an absence of EphA2 in normal bone, and de novo expression in osteosarcomas. EFNA1 was expressed in normal bone, but was significantly elevated in tumours. Further in vitro investigations on the functional role of EphA2 and EFNA1 showed that EFNA1 ligand binding induced increased tyrosine phosphorylation, receptor degradation and downstream mitogen-activated protein kinase (MAPK) activation. Interference with the MAPK pathway unravelled a potential autoregulatory loop governing mainly EFNA1 expression via the same pathway. Upregulation and de novo expression of ephrins in osteosarcomas are involved in oncogenic signalling and thus might stimulate osteosarcoma metastasis.

Ephrin-B1 forward signaling regulates craniofacial morphogenesis by controlling cell proliferation across Eph–ephrin boundaries

Mutations in the X-linked human EPHRIN-B1 gene result in cleft palate and other craniofacial anomalies as part of craniofrontonasal syndrome (CFNS), but the molecular and developmental mechanisms by which ephrin-B1 controls the underlying developmental processes are not clear. Here we demonstrate that ephrin-B1 plays an intrinsic role in palatal shelf outgrowth in the mouse by regulating cell proliferation in the anterior palatal shelf mesenchyme. In ephrin-B1 heterozygous mutants, X inactivation generates ephrin-B1-expressing and -nonexpressing cells that sort out, resulting in mosaic ephrin-B1 expression. We now show that this process leads to mosaic disruption of cell proliferation and post-transcriptional up-regulation of EphB receptor expression through relief of endocytosis and degradation. The alteration in proliferation rates resulting from ectopic Eph-ephrin expression boundaries correlates with the more severe dysmorphogenesis of ephrin-B1(+/-) heterozygotes that is a hallmark of CFNS. Finally, by integrating phosphoproteomic and transcriptomic approaches, we show that ephrin-B1 controls proliferation in the palate by regulating the extracellular signal-regulated kinase/mitogen-activated protein kinase (ERK/MAPK) signal transduction pathway.

Ectopic Expression of Ephrin-A5 Under the EphA8 Promoter at the Anterior Region of the Superior Colliculus

EphA/ephrin-A mediated signaling has emerged as a key mechanism regulating axon guidance and topographic mapping, particularly in the well-characterized visual system from the retina to the superior colliculus (SC). In this study, EphA8 bacterial artificial chromosome (BAC) was manipulated to contain a floxed eGFP and human ephrin-A5 expression cassette using homologous recombination method. In the mice containing the recombinant BAC, it was shown that GFP is expressed in an anterior>posterior gradient in the SC. Furthermore, when these mice were crossed with the transgenic mice expressing Cre under the EphA8 promoter, it was evident that a GFP expression cassette was eliminated, and that human ephrin-A5 was ectopically expressed in the anterior region of the SC. This transgenic model would be useful to analyze the role of ephrin-A5 in the SC during the retinocollicular topography formation.

Expression of ephrin A family genes in mice with oxygen-induced retinal neovascularization

Objective To investigate the role of ephrin A genes in the development of oxygen-induced retinal neovascularization (OIR) in mice. Methods The OIR model was established by oxygen induction in new born C57BL/6J mice. Reversed transcript - polymerase chain reaction (RT-PCR) was used to measure the expression levels of ephrin A1-A5 in retinas of mice in experimental and normal control group. Results All of the ephrin A family genes expressed in normal retinas. Ephrin A1 mRNA was significantly higher in OIR group (t= 3.19, P = 0. 019); ephrin A2 mRN A was higher in the 15-day-old OIR retinas (t= 3. 71,P=0. 033) ; ephrin A3-A5 mRNA decreased or disappeared in 12- and 13-day-old RNV mice, and increased in 15-day-old OIR mice. Conclusion Ephrin A genes are involved in the development of retina and OIR. Key words: Retinal neovaseularization/pathophysiology; Protein-Tyrosine kinases/physiology; Animal experimentation

Enhanced expression of ephrins and thrombospondins in the dermis of patients with early diffuse systemic sclerosis

Ephrins have emerged as essential regulators of angiogenesis and thrombospondins are inhibitors of angiogenesis and strong promoters of fibrosis that are both involved in systemic sclerosis (SSc). Our aim was...

Role of the tyrosine kinase receptor EphA5 in recovery from perinatal brain injury

Event Abstract Back to Event Role of the tyrosine kinase receptor EphA5 in recovery from perinatal brain injury Qi Cheng1, Mark D. Graves1* and Sarah L. Pallas1 1 Georgia State University, Neuroscience Institute and Biology Department, United States Traumatic brain injury (TBI) is a serious public health problem and one of the major causes of death and disability in young people. The topographically ordered projection between the retina and midbrain superior colliculus (SC) in rodents is an excellent model system in which to approach this difficult problem. The retina makes a map of visual space on the midbrain superior colliculus. This retinotopic map is established during development in part by a family of graded molecular guidance cues in the SC called ephrin-As, recognized by their EphA tyrosine kinase receptors in the retina. Damage to the caudal part of SC at birth, instead of deleting part of the map, causes it to compress in toto onto the remaining SC. This process of recovery from injury preserves visual function, but the compensatory mechanism underlying map compression is unknown. Our previous results showed that in compressed maps the rostrocaudal gradient of ephrinA expression is steeper than normal. We proposed that the change in the slope of the gradient plays an instructive role in map compression. Here we test the hypothesis that TBI to SC leads to changes in retinal EphA5 receptor expression that are complementary to the changes in collicular ephrinA expression. We measured EphA5 mRNA and protein levels after SC damage, and found that the nasotemporal gradient of EphA5 expression steepens in the retina and overall expression levels change dynamically. Importantly, the alterations in retinal EphA5 expression occur after the change in collicular ephrinA5 expression. Taken together, these findings, suggest that neonatal TBI triggers changes in the ephrinA gradient and then in the retinal EphA gradient. Map compression could be instructed directly by the change in ligand expression or by the subsequent change in receptor expression, guiding the recovery of this visual pathway from early injury. Understanding what molecular signals direct for the response to TBI is important for developing clinical approaches to rehabilitation and for maximizing the potential for recovery. Conference: 2010 South East Nerve Net (SENN) and Georgia/South Carolina Neuroscience Consortium (GASCNC) conferences, Atlanta , United States, 5 Mar - 7 Mar, 2010. Presentation Type: Poster Presentation Topic: Posters Citation: Cheng Q, Graves MD and Pallas SL (2010). Role of the tyrosine kinase receptor EphA5 in recovery from perinatal brain injury. Front. Neurosci. Conference Abstract: 2010 South East Nerve Net (SENN) and Georgia/South Carolina Neuroscience Consortium (GASCNC) conferences. doi: 10.3389/conf.fnins.2010.04.00045 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 16 Mar 2010; Published Online: 16 Mar 2010. * Correspondence: Mark D Graves, Georgia State University, Neuroscience Institute and Biology Department, Atlanta, GA, United States, biomdg@langate.gsu.edu Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Qi Cheng Mark D Graves Sarah L Pallas Google Qi Cheng Mark D Graves Sarah L Pallas Google Scholar Qi Cheng Mark D Graves Sarah L Pallas PubMed Qi Cheng Mark D Graves Sarah L Pallas Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

Ephrin Expression and Function in Cancer

Ephrins are cell membrane-associated signaling proteins bound by transmembrane Eph receptors on juxtaposed cells. Eph-ephrin interactions result in bidirectional signaling within both receptor- and ligand-bearing cells, with diverse consequences for cell morphology and behavior. Such interactions are especially important during early vertebrate development, and growing evidence has revealed equally important roles in adult-tissue homeostasis. As for the Eph receptors, abnormal expression of ephrins is associated with disease, especially cancer. The ephrins have received less attention than the Ephs in the literature, owing, in part, to their later discovery and that they are fewer in number. Here, we attempt to redress this imbalance and provide an 'ephrin-centric' discussion of the expression and function of ephrins in cancer.

Suppression of gastric cancer dissemination by ephrin‐B1‐derived peptide

Interaction of the Eph family of receptor protein tyrosine kinases and their ligands, ephrin family members, induces bidirectional signaling through cell-cell contacts. High expression of B-type ephrin is associated with high invasion potential of tumors, and we previously observed that signaling through the C-terminus of ephrin-B1 mediates the migration and invasion of cells, and is involved in the promotion of carcinomatous peritonitis in vivo. Here we show that the intracellular introduction of a synthetic peptide derived from ephrin-B1 C-terminus blocks ephrin-B1 mediated signaling in scirrhous gastric cancer cells. Treatment of cancer cells with a fusion peptide consisting of HIV-TAT and amino acids 331-346 of ephrin-B1 (PTD-EFNB1-C) suppressed the activation of RhoA, mediated by the association of ephrin-B1 with an adaptor protein Dishevelled, and also inhibited extracellular secretion of metalloproteinase. Moreover, injection of PTD-EFNB1-C peptide into the peritoneal cavity of nude mice suppressed carcinomatous peritonitis of intraperitoneally transplanted scirrhous gastric cancer cells. These results indicate the possible application of ephrin-B1 C-terminal peptide to develop novel protein therapy for scirrhous gastric carcinoma, especially in the stage of tumor progression, including peritoneal dissemination.

Down-regulation of ephrin-A5, a gene product of normal cartilage, in chondrosarcoma

As ephrins have been associated with tumorigenesis and tumor progression, we investigated ephrin-A5 (EFNA5) expression in specimens of normal cartilage and chondrosarcomas of different grade by conventional and quantitative reverse transcription polymerase chain reaction (RT-PCR), Western blot, and immunohistochemistry. We detected a significant EFNA5 down-regulation in chondrosarcomas compared with normal cartilage using quantitative RT-PCR (P < .05). The results were confirmed by Western blot and immunohistochemistry. We did not detect any causative genetic or epigenetic alterations in EFNA5 promoter methylation, loss of heterozygosity, or mutation analyses. Apart from slight differences in EFNA5 transcript amounts, we detected no significant influence of hypoxia on EFNA5 expression in C3842 and SW1353 chondrosarcoma cells. As EFNA5 down-regulation is a consistent finding in chondrosarcomas, we presume that it represents another essential alteration in tumorigenesis and tumor progression associated with cell adhesion, in addition to a multitude of other partially unknown biologic functions mediated by bidirectional ephrin/Eph receptor signaling and cross talk.

Expression of ephrinA5 during development and potential involvement in the guidance of the mesostriatal pathway

Identifying guidance cues that direct axon growth to their final connections during development is of crucial interest if we aim to repair circuits damaged in adulthood following neurodegenerative disorders or common traumatic injuries. In this work, we set out to determine the ephrinA5 guidance molecule involvement in the establishment of the mouse mesostriatal pathway during development. We showed, in vitro and in vivo, that a proportion of mesencephalic dopaminergic cells express the ephrinA5 receptor, EphA5. Moreover, we observed, using stripe assays, that ephrinA5 purified protein has a repulsive effect on most of the mesencephalic dopaminergic projections. In vivo, we detected rostro-caudal and ventro-dorsal ephrinA5 protein expression gradients in the vicinity of the dopaminergic axons in the ventral telencephalon and in the striatum, during the embryonic and early postnatal development. In addition, other EphA5 ligands were also detected in the mesostriatal pathway. Together, these expression patterns suggest that, ephrinAs and more specifically ephrinA5, may be actors in the guidance of dopaminergic projections. Further studies will focus on identifying the molecular specificity of these guidance cues, taking into account the mesencephalic dopaminergic heterogeneous neuronal population. This may help increase the integration of neuronal transplants in the mature lesioned brain or provide tools to re-establish mesostriatal circuits in vivo.

Bidirectional Signaling through EphrinA2-EphA2 Enhances Osteoclastogenesis and Suppresses Osteoblastogenesis

Bone is remodeled constantly throughout life by bone-resorbing osteoclasts and bone-forming osteoblasts. To maintain bone volume and quality, differentiation of osteoclasts and osteoblasts is tightly regulated through communication between and within these two cell lineages. Previously we reported that cell-cell interaction mediated by ephrinB2 ligand on osteoclasts and EphB4 receptor on osteoblasts generates bidirectional anti-osteoclastogenic and pro-osteoblastogenic signals into respective cells and presumably facilitates transition from bone resorption to bone formation. Here we show that bidirectional ephrinA2-EphA2 signaling regulates bone remodeling at the initiation phase. EphrinA2 expression was rapidly induced by receptor activator of NF-kappaB ligand in osteoclast precursors; this was dependent on the transcription factor c-Fos but independent of the c-Fos target gene product NFATc1. Receptor EphA2 was expressed in osteoclast precursors and osteoblasts. Overexpression experiments revealed that both ephrinA2 and EphA2 in osteoclast precursors enhanced differentiation of multinucleated osteoclasts and that phospholipase Cgamma2 may mediate ephrinA2 reverse signaling. Moreover, ephrinA2 on osteoclasts was cleaved by metalloproteinases, and ephrinA2 released in the culture medium enhanced osteoclastogenesis. Interestingly, differentiation of osteoblasts lacking EphA2 was enhanced along with alkaline phosphatase, Runx2, and Osterix expression, indicating that EphA2 on osteoblasts generates anti-osteoblastogenic signals presumably by up-regulating RhoA activity. Therefore, ephrinA2-EphA2 interaction facilitates the initiation phase of bone remodeling by enhancing osteoclast differentiation and suppressing osteoblast differentiation.

EphrinA5 acts as a tumor suppressor in glioma by negative regulation of epidermal growth factor receptor

Eph receptors, the largest subfamily of receptor tyrosine kinases, and their ephrin ligands play important roles in nervous system development. Recently, they have been implicated in tumorigenesis of different cancers. In this study, we showed that the expression of ephrinA5 was dramatically downregulated in primary gliomas compared with normal tissues. Forced expression of ephrinA5 reduced tumorigenicity of human glioma U373 cells. Epidermal growth factor receptor (EGFR), which frequently acts as an oncoprotein in glioma, was greatly decreased in ephrinA5-transfected glioma cells, and the two molecules exhibited a mutually exclusive expression pattern in primary glioma samples. We found that ephrinA5 enhanced c-Cbl binding to EGFR, thus promoted ubiquitylation and degradation of the receptor. Either ephrinA5-Fc or EphA2-Fc treatment simulating bidirectional signaling of Eph/ephrin system resulted in EGFR decrease. This study discovered that ephrinA5 acted as a tumor suppressor in glioma, and its negative regulation of EGFR contributed to the suppressive effects. In addition to identifying a novel mechanism underlying tumor suppressor activity of ephrinA5, we also showed cross-talk between different receptor tyrosine kinase families in glioma. These findings may improve therapeutic strategies for glioma.

Environmental modulation of dendritic spine dynamics in mouse hippocampus

Event Abstract Back to Event Environmental modulation of dendritic spine dynamics in mouse hippocampus Antonio Trabalza1*, Carmelo Alessio-Sgobio2, Martine Ammassari-Teule3 and Arturo Bevilacqua1 1 University of Rome “Sapienza”, Department of Psychology, Italy 2 IRCCS “Santa Lucia”, Laboratory of Neurophysiology, Italy 3 C.N.R., Rome and IRCCS “Santa Lucia”, Institute of Psychopharmacology, Italy Ephrins and their tyrosine kinase receptors are involved in patterning of axonal connections during development in the nervous system of vertebrates [1]. They also play a role in neuronal plasticity in the adult brain, with particular reference to the hippocampus [2], in which they also modulate LTP induction [3]. We have raised C57/BL6 mice in an enriched environment, which increases adult hippocampal activity and alters hippocampal-dependent behaviors in rodents [4], to examine whether experience-dependent stimulation induces behavioral ameliorations, modifications in neuronal morphology and variations in the expression of ephrins, such as ephrin-B2 and eph-B2 receptor, in such structure. After an eight-week enrichment training, mice were challenged by the context-dependent fear conditioning test and Morris Water Maze, which are behavioral paradigms sensitive to hippocampal modifications [5], and by the cue-dependent fear conditioning test, which mainly relies on amygdala functions. Enriched mice (EM) performed better than non-enriched ones (CM) in the context-dependent fear conditioning and Morris Water Maze tests, but not in the cue-dependent fear conditioning test. After the enrichment period, dendritic arborization and spine density of Golgi-Cox stained CA1 hippocampal neurons were increased with respect to CM. After the fear conditioning testing however, spine density of EM hippocampal neurons decreased below the level of CM. Immunohistochemical analysis revealed a specific higher abundance of ephrin-B2 and eph-B2 receptor in the pyramidal layer of the CA1 area and in cortical layers, but not the amygdala, of EM. We suggest that: hippocampal neuron complexity is enhanced by enrichment along with spatial learning, but is rapidly decreased by an aversive experience; ephrin-B2 and eph-B2 receptor are involved in dendritic spine dinamycs during learning.

The influence of electro-acupuncture on neural plasticity in acute cerebral infarction

Objective: To observe the effect of electro-acupuncture (EA) on dendritic spine and ephrin-A5 and to investigate the action of EA on neural plasticity after acute cerebral ischemic infarction.Methods: Focal acute cerebral ischemia model was established by middle cerebral artery occlusion (MCAO) with electrocoagulation contralateral method. Ninety male Sprague–Dawley rats were randomly divided into sham operation (SO) group, MCAO group and EA treatment (ET) group. Golgi dying, double immunofluorescence method and RT-PCR were used to detect dendritic spine density, expression patterns of ephrin-A5 and the effect of EA on them at the end of the first, second and fourth week after ischemia.Results: The dendritic spine density in MCAO group significantly decreased after ischemia (p<0.01). The dendritic spine density was raised in ET group in the corresponding time period (p<0.01) and among the ET groups. It was higher at the end of the fourth week than before (p<0.05). The signal of ephrin-A5 was detected mainly in neuron cytoplasm, and the mRNA expression in MCAO group and ET group increased compared to that in SO group (p<0.01). The mRNA expression in ET group at the first week was much higher than that in MCAO group (p<0.01). In ET groups, the mRNA expression of ephrin-A5 was down-regulated along with the time going (p<0.01).Conclusion: It is possibly the regulation of the ephrin-A5 expression by which EA treatment improves the neural plasticity at the peri-infarct cerebral cortex in acute cerebral ischemia rat. There may be a time window in EA treatment for acute cerebral ischemia.

Comparative 3'UTR Analysis Allows Identification of Regulatory Clusters that Drive Eph/ephrin Expression in Cancer Cell Lines

Eph receptors are the largest family of receptor tyrosine kinases. Together with their ligands, the ephrins, they fulfill multiple biological functions. Aberrant expression of Ephs/ephrins leading to increased Eph receptor to ephrin ligand ratios is a critical factor in tumorigenesis, indicating that tight regulation of Eph and ephrin expression is essential for normal cell behavior. The 3'-untranslated regions (3'UTRs) of transcripts play an important yet widely underappreciated role in the control of protein expression. Based on the assumption that paralogues of large gene families might exhibit a conserved organization of regulatory elements in their 3'UTRs we applied a novel bioinformatics/molecular biology approach to the 3'UTR sequences of Eph/ephrin transcripts. We identified clusters of motifs consisting of cytoplasmic polyadenylation elements (CPEs), AU-rich elements (AREs) and HuR binding sites. These clusters bind multiple RNA-stabilizing and destabilizing factors, including HuR. Surprisingly, despite its widely accepted role as an mRNA-stabilizing protein, we further show that binding of HuR to these clusters actually destabilizes Eph/ephrin transcripts in tumor cell lines. Consequently, knockdown of HuR greatly modulates expression of multiple Ephs/ephrins at both the mRNA and protein levels. Together our studies suggest that overexpression of HuR as found in many progressive tumors could be causative for disarranged Eph receptor to ephrin ligand ratios leading to a higher degree of tissue invasiveness.

The Eph Receptor/Ephrin System: An Emerging Player in the Invasion Game

Eph receptor tyrosine kinases (Ephs) and their membrane-anchored ligands (ephrins) form a vital cell communication system capable of bi-directional signaling. This Eph receptor/ephrin system has classically been demonstrated to play a role in development. However, emerging evidence has revealed differential expression of Ephs and ephrins in numerous cancers. Recent studies suggest that this system influences invasive behaviour, promoting a more aggressive and metastatic phenotype. Hence, this minireview summarizes the current understanding of the contribution of both Eph receptors and their ephrin ligands to invasiveness in cancer, as well as their use as potential therapeutic targets.