Evidence for a dual function of EphB4 as tumor promoter and suppressor regulated by the absence or presence of the ephrin-B2 ligand

Eph receptors and ephrins in cancer progression

Evidence implicating Eph receptor tyrosine kinases and their ephrin ligands (that together make up the 'Eph system') in cancer development and progression has been accumulating since the discovery of the first Eph receptor approximately 35 years ago. Advances in the past decade and a half have considerably increased the understanding of Eph receptor-ephrin signalling mechanisms in cancer and have uncovered intriguing new roles in cancer progression and drug resistance. This Review focuses mainly on these more recent developments. I provide an update on the different mechanisms of Eph receptor-ephrin-mediated cell-cell communication and cell autonomous signalling, as well as on the interplay of the Eph system with other signalling systems. I further discuss recent advances in elucidating how the Eph system controls tumour expansion, invasiveness and metastasis, supports cancer stem cells, and drives therapy resistance. In addition to functioning within cancer cells, the Eph system also mediates the reciprocal communication between cancer cells and cells of the tumour microenvironment. The involvement of the Eph system in tumour angiogenesis is well established, but recent findings also demonstrate roles in immune cells, cancer-associated fibroblasts and the extracellular matrix. Lastly, I discuss strategies under evaluation for therapeutic targeting of Eph receptors-ephrins in cancer and conclude with an outlook on promising future research directions.

Over-expression by degradation rescue of RTKs via cancer-secreted autocrine growth factors: a Phospho-degron-driven actionable layer of post-translational regulation?

Recently published work provide the first known evidence of a malignancy-associated regulatory mechanism, functionally connecting a phospho-regulated degron domain embedded in a receptor tyrosine kinase (RTK), with its ectopic expression in cancer, conditional to a specific autocrine growth factor signal. Mechanistically, the growth factor-triggered phosphorylation inhibits the degron domain present in the regulated RTK, blocking access to a specific degradation complex. This ultimately rescues the RTK from rapid ubiquitin-proteasome-system-mediated degradation and, most importantly, causes its cellular overexpression. This mechanism, which has been here assigned the new functional name "Over-Expression by Degradation Rescue" (OEDR), provides an additional layer and potentially preferential tool for the control of RTKs expression in cancer, in addition to other mechanisms acting at the transcriptional and messenger transcript stabilization levels. We propose this newly defined phosphorylation/ubiquitination switch-dependent signal to bear wider unexploited relevance in cell biology and human pathophysiology. The recently identified mechanism underlying an OEDR-regulated RTK is discussed herein in the context of physiological endocrine circuits and cancer.

Ephrin B Activate Src Family Kinases in Fibroblasts Inducing Stromal Remodeling in Prostate Cancer

Simple Summary

Carcinoma associated fibroblasts (CAF) play a critical role in the tumor microenvironment (TME) of prostate cancer (PCa). Ephrin receptors (Eph) and ligands (EFN) have been implicated in distinct types of cancers. Alterations on EphB receptors are frequently found in PCa, but the role of ligands (EFNB1, EFNB2, EFNB3) activation in prostate fibroblasts and consequent effects on PCa is not known. We found increased EFNB ligands in fibroblasts isolated from PCa tissues. In this study, we assessed the effects of elevated stromal EFNB ligands on PCa tumor growth. Increased EFNB1 and EFNB3 expression transformed normal fibroblasts into CAF phenotypes through activation of Src family kinases. The secretome of EFNB-expressing CAF increased PCa cell proliferation and promoted TME remodeling. Overall, EFNB activation in CAF may participate in PCa progression via the release of soluble factors that modulate the surrounding tumor environment, which, in turn, promote prostate tumor growth and invasion.

Abstract

Through stromal-epithelial interactions, carcinoma associated fibroblasts (CAF) play a critical role in tumor growth and progression. Activation of erythrophoyetin-producing human hepatocellular (Eph) receptors has been implicated in cancer. Eph receptor interactions with Ephrin ligands lead to bidirectional signals in the recipient and effector cells. The consequences of continuous reverse Ephrin signaling activation in fibroblasts on prostate cancer (PCa) is unknown. When compared to benign prostate fibroblast, CAF displayed higher expression of Ephrin B1, B2, and B3 ligands (EFNB1, EFNB2, and EFNB3). In this study, we found that continuous activation of EFNB1 and EFNB3 in a benign human prostate stromal cell line (BHPrS1) increased the expression of CAF markers and induced a CAF phenotype. BHPrS1^EFNB1 and BHPrS1^EFNB3 displayed a pro-tumorigenic secretome with multiple effects on neovascularization, collagen deposition, and cancer cell proliferation, overall increasing tumorigenicity of a premalignant prostate epithelial cell line BPH1 and PCa cell line LNCaP, both in vitro and in vivo. Inhibition of Src family kinases (SFK) in BHPrS1^EFNB1 and BHPrS1^EFNB3 suppressed EFNB-induced ɑ-SMA (Alpha-smooth muscle actin) and TN-C (Tenascin-C) in vitro. Our study suggests that acquisition of CAF characteristics via SFK activation in response to increased EFNB ligands could promote carcinogenesis via modulation of TME in PCa.

Multilevel Mesoscale Complexities in Mesoregimes: Challenges in Chemical and Biochemical Engineering

This review discusses the complex behaviors in diverse chemical and biochemical systems to elucidate their commonalities and thus help develop a mesoscience methodology to address the complexities in even broader topics. This could possibly build a new scientific paradigm for different disciplines and could meanwhile provide effective tools to tackle the big challenges in various fields, thus paving a path toward combining the paradigm shift in science with the breakthrough in technique developments. Starting with our relatively fruitful understanding of chemical systems, the discussion focuses on the relatively pristine but very intriguing biochemical systems. It is recognized that diverse complexities are multilevel in nature, with each level being multiscale and the complexity emerging always at mesoscales in mesoregimes. Relevant advances in theoretical understandings and mathematical tools are summarized as well based on case studies, and the convergence between physics and mathematics is highlighted. Expected final online publication date for the Annual Review of Chemical and Biomolecular Engineering, Volume 13 is October 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

EphrinB2-EphB4 Signaling in Neurooncological Disease

EphrinB2-EphB4 signaling is critical during embryogenesis for cardiovascular formation and neuronal guidance. Intriguingly, critical expression patterns have been discovered in cancer pathologies over the last two decades. Multiple connections to tumor migration, growth, angiogenesis, apoptosis, and metastasis have been identified in vitro and in vivo. However, the molecular signaling pathways are manifold and signaling of the EphB4 receptor or the ephrinB2 ligand is cancer type specific. Here we explore the impact of these signaling pathways in neurooncological disease, including glioma, brain metastasis, and spinal bone metastasis. We identify potential downstream pathways that mediate cancer suppression or progression and seek to understand it´s role in antiangiogenic therapy resistance in glioma. Despite the Janus-faced functions of ephrinB2-EphB4 signaling in cancer Eph signaling remains a promising clinical target.

Low Expression of EphB2, EphB3, and EphB4 in Bladder Cancer: Novel Potential Indicators of Muscular Invasion

PURPOSE

Eph receptors are differentially expressed in numerous malignant tumors. This study intended to analyze the roles of EphB receptors (EphB2, B3, and B4) in urinary bladder cancer.

MATERIALS AND METHODS

Tissue microarray-based immunohistochemical analysis was used to investigate the expression patterns of EphB2, EphB3, and EphB4 in 154 bladder cancer specimens. Immunohistochemical staining was conducted examining the extent of stained cells and staining intensity. EphB was considered to be highly expressed when the intensity of staining was more than moderate in >25% of cells in the tissue section. Small interfering RNA (siRNA) was used to knock down EphB expression in bladder cancer cell lines (T24, 5637) to determine the effects of EphB on tumor cell invasion, proliferation, and migration.

RESULTS

EphB receptors (B2, B3, and B4) were detected in 40.9% (EphB2, 63/154), 71.4% (EphB3, 110/154), and 53.2% (EphB4, 82/154) of bladder cancer specimens. Low expression of EphB2, B3, and B4 receptors were significantly associated with higher tumor grade (EphB2, p<0.001; EphB3, p=0.032; EphB4, p<0.001) and muscular invasion (EphB2, p=0.002; EphB3, p=0.009; EphB4, p<0.001). No obvious correlation was observed with other clinicopathological variables, such as age, sex, recurrence, lymph node involvement, metastasis, and overall survival. Inactivation of EphB receptors by siRNA transfection increased cell viability, tumor cell invasion, proliferation, and migration in comparison with untransfected cancer cells.

CONCLUSION

Low expression of EphB receptors (B2, B3, and B4) can be a predictive marker for muscular invasion of bladder cancer.

The Value of EphB2 Receptor and Cognate Ephrin Ligands in Prognostic and Predictive Assessments of Human Breast Cancer

Cell–cell communication proteins Eph and ephrin constitute the largest family of receptor tyrosine kinases (RTKs). They are distinguished by the fact that both receptors and ligands are membrane-bound, and both can drive intracellular signaling in their respective cells. Ever since these RTKs have been found to be involved in cancer development, strategies to target them therapeutically have been actively pursued. However, before this goal can be rationally achieved, the contributions of either Eph receptors or their ephrin ligands to cancer development and progression should be scrutinized in depth. To assess the clinical pertinence of this concern, we performed a systematic review and meta-analysis of the prognostic/predictive value of EphB2 and its multiple cognate ephrin ligands in breast cancer. We found that EphB2 has prognostic value, as indicated by the association of higher EphB2 expression levels with lower distant metastasis-free survival (DMFS), and the association of lower EphB2 expression levels with poorer relapse-free survival (RFS). We also found that higher EphB2 expression could be a prognostic factor for distant metastasis, specifically in the luminal subtypes of breast cancer. EFNB2 showed a marked correlation between higher expression levels and shorter DMFS. EFNA5 or EFNB1 overexpression is correlated with longer RFS. Increased EFNB1 expression is correlated with longer OS in lymph node (LN)-negative patients and the luminal B subtype. Higher levels of EFNB2 or EFNA5 are significantly correlated with shorter RFS, regardless of LN status. However, while this correlation with shorter RFS is true for EFNB2 in all subtypes except basal, it is also true for EFNA5 in all subtypes except HER2+. The analysis also points to possible predictive value for EphB2. In systemically treated patients who have undergone either endocrine therapy or chemotherapy, we found that higher expression of EphB2 is correlated with better rates of RFS. Bearing in mind the limitations inherent to any mRNA-based profiling method, we complemented our analysis with an immunohistochemical assessment of expression levels of both the EphB2 receptor and cognate ephrin ligands. We found that the latter are significantly more expressed in cancers than in normal tissues, and even more so in invasive and metastatic samples than in ductal carcinoma in situ (DCIS). Finally, in an in vitro cellular model of breast cancer progression, based on H-Ras-transformation of the MCF10A benign mammary cell line, we observed dramatic increases in the mRNA expression of EphB2 receptor and EFNB1 and EFNB2 ligands in transformed and invasive cells in comparison with their benign counterparts. Taken together, these data show the clinical validity of a model whereby EphB2, along with its cognate ephrin ligands, have dual anti- and pro-tumor progression effects. In so doing, they reinforce the necessity of further biological investigations into Ephs and ephrins, prior to using them in targeted therapies.

Ligand-Dependent and Ligand-Independent Effects of Ephrin-B2-EphB4 Signaling in Melanoma Metastatic Spine Disease

Tumor–endothelial cell interactions represent an essential mechanism in spinal metastasis. Ephrin-B2–EphB4 communication induces tumor cell repulsion from the endothelium in metastatic melanoma, reducing spinal bone metastasis formation. To shed further light on the Ephrin-B2–EphB4 signaling mechanism, we researched the effects of pharmacological EphB4 receptor stimulation and inhibition in a ligand-dependent/independent context. We chose a preventative and a post-diagnostic therapeutic window. EphB4 stimulation during tumor cell seeding led to an increase in spinal metastatic loci and number of disseminated melanoma cells, as well as earlier locomotion deficits in the presence of endothelial Ephrin-B2. In the absence of endothelial Ephrin-B2, reduction of metastatic loci with a later manifestation of locomotion deficits occurred. Thus, EphB4 receptor stimulation affects metastatic dissemination depending on the presence/absence of endothelial Ephrin-B2. After the manifestation of solid metastasis, EphB4 kinase inhibition resulted in significantly earlier manifestation of locomotion deficits in the presence of the ligand. No post-diagnostic treatment effect was found in the absence of endothelial Ephrin-B2. For solid metastasis treatment, EphB4 kinase inhibition induced prometastatic effects in the presence of endothelial Ephrin-B2. In the absence of endothelial Ephrin-B2, both therapies showed no effect on the growth of solid metastasis.

Development of non-viral, ligand-dependent, EPHB4-specific chimeric antigen receptor T cells for treatment of rhabdomyosarcoma

Ephrin type-B receptor 4 (EPHB4), expressed in tumors including rhabdomyosarcoma, is a suitable target for chimeric antigen receptor (CAR)-T cells. Ligand-independent activation of EPHB4 causes cell proliferation and malignant transformation in rhabdomyosarcoma, whereas ligand-dependent stimulation of EPHB4 induces apoptosis in rhabdomyosarcoma. Therefore, we hypothesized that ligand-based, EPHB4-specific CAR-T cells may kill rhabdomyosarcoma cells without stimulating downstream cell proliferation mechanisms. We developed novel CAR-T cells by targeting EPHB4 via EPHRIN B2, a natural ligand of EPHB4. The generation of EPHB4-CAR-T cells via piggyBac (PB) transposon-based gene transfer resulted in sufficient T cell expansion and CAR positivity (78.5% ± 5.9%). PB-EPHB4-CAR-T cells displayed a dominant stem cell memory fraction (59.4% ± 7.2%) as well as low PD-1 expression (0.60% ± 0.21%) after 14 days of expansion. The PB-EPHB4-CAR-T cells inhibited EPHB4-positive tumor cells without activating cell proliferation downstream of EPHB4, even after multiple tumor re-challenges and suppressed tumor growth in xenograft-bearing mice. Therefore, PB-EPHB4-CAR-T cells possess a memory-rich fraction without early T cell exhaustion and show potential as promising therapeutic agents for treating rhabdomyosarcoma and other EPHB4-positive tumors.

The Role of the Eph Receptor Family in Tumorigenesis

Simple Summary

The Eph receptor family is implicated in both tumour promotion and suppression, depending on the tissue-specific context of available receptor interactions with ligands, adaptor proteins and triggered downstream signalling pathways. This complex interplay has not only consequences for tumorigenesis but also offers a basis from which new cancer-targeting strategies can be developed. This review comprehensively summarises the current knowledge of Eph receptor implications in oncogenesis in a tissue- and receptor-specific manner, with the aim to develop a better understanding of Eph signalling pathways for potential targeting in novel cancer therapies.

Abstract

The Eph receptor tyrosine kinase family, activated by binding to their cognate ephrin ligands, are important components of signalling pathways involved in animal development. More recently, they have received significant interest due to their involvement in oncogenesis. In most cases, their expression is altered, affecting the likes of cell proliferation and migration. Depending on the context, Eph receptors have the potential to act as both tumour promoters and suppressors in a number of cancers, such as breast cancer, colorectal cancer, lung cancer, prostate cancer, brain cancer and Kaposi’s sarcoma (KS), the latter being intrinsically linked to EphA2 as this is the receptor used for endothelial cell entry by the Kaposi’s sarcoma-associated herpesvirus (KSHV). In addition, EphA2 deregulation is associated with KS, indicating that it has a dual role in this case. Associations between EphA2 sequence variation and KSHV infection/KS progression have been detected, but further work is required to formally establish the links between EphA2 signalling and KS oncogenesis. This review consolidates the available literature of the role of the Eph receptor family, and particularly EphA2, in tumorigenesis, with the aim to develop a better understanding of Eph signalling pathways for potential targeting in novel cancer therapies.

Evaluation of EphB4 as Target for Image-Guided Surgery of Breast Cancer

Background: Targeted image-guided surgery is based on the detection of tumor cells after administration of a radio-active or fluorescent tracer. Hence, enhanced binding of a tracer to tumor tissue compared to healthy tissue is crucial. Various tumor antigens have been evaluated as possible targets for image-guided surgery of breast cancer, with mixed results. Methods: In this study we have evaluated tyrosine kinase receptor EphB4, a member from the Eph tyrosine kinase receptor family, as a possible target for image-guided surgery of breast cancers. Two independent tissue micro arrays, consisting of matched sets of tumor and normal breast tissue, were stained for EphB4 by immunohistochemistry. The intensity of staining and the percentage of stained cells were scored by two independent investigators. Results: Immunohistochemical staining for EphB4 shows that breast cancer cells display enhanced membranous expression compared to adjacent normal breast tissue. The enhanced tumor staining is not associated with clinical variables like age of the patient or stage or subtype of the tumor, including Her2-status. Conclusion: These data suggest that EphB4 is a promising candidate for targeted image-guided surgery of breast cancer, especially for Her2 negative cases.

The critical role of the interplays of EphrinB2/EphB4 and VEGF in the induction of angiogenesis

The significant role of VEGF (vascular endothelial growth factor) as an angiogenesis inducer is well recognized. Besides VEGF, EphrinB2/EphB4 also plays essential roles in vascular development and postnatal angiogenesis. Compared with classical proangiogenic factors, not only does EphrinB2/EphB4 promote sprouting of new vessels, it is also involved in the vessel maturation. Given their involvement in many physiologic and pathological conditions, EphB4 and EphrinB2 are increasingly recognized as attractive therapeutic targets for angiogenesis-related diseases through modulating their expression and function. Previous works mainly focused on the individual role of VEGF and EphrinB2/EphB4 in angiogenesis, respectively, but the correlation between EphrinB2/EphB4 and VEGF in angiogenesis has not been fully disclosed. Here, we summarize the structure and bidirectional signaling of EphrinB2/EphB4, provide an overview on the relationship between EphrinB2/EphB4 signaling and VEGF pathway in angiogenesis and highlight the associated potential usefulness in anti-angiogenetic therapy.

[Research progress on the expression and function of erythropoietin-producing hepatomocellular receptors and their receptor-interacting proteins in oral-related diseases]

Erythropoietin-producing hepatomocellular receptors and their receptor-interacting proteins (Eph/ephrin) can participate in the regulation of growth and development and promote the development of diseases through short-distance signal transduction between cells. To study the mechanism of Eph/ephrin and oral-related diseases, we provided a new theoretical basis and a strategy for the treatment of oral diseases. The Eph/ephrin pathway has been used to regulate oral diseases, especially in periodontal disease prevention, orthodontic bone reconstruction, and biological treatment of oral tumors. This paper reviews the research progress of Eph/ephrin pathway in oral-related diseases.

Targeting Forward and Reverse EphB4/EFNB2 Signaling by a Peptide with Dual Functions

The tyrosine kinase receptor EphB4 is frequently overexpressed in ovarian and other solid tumors and is involved in interactions between tumor cells and the tumor microenvironment, contributing to metastasis. Trans-interaction between EphB4 and its membrane-bound ligand ephrin B2 (EFNB2) mediates bi-directional signaling: forward EFNB2-to-EphB4 signaling suppresses tumor cell proliferation, while reverse EphB4-to-EFNB2 signaling stimulates the invasive and angiogenic properties of endothelial cells. Currently, no small molecule–based, dual-function, EphB4-binding peptides are available. Here, we report our discovery of a bi-directional ephrin agonist peptide, BIDEN-AP which, when selectively internalized via receptor-mediated endocytosis, suppressed invasion and epithelial-mesenchymal transition of ovarian cancer cells. BIDEN-AP also inhibited endothelial migration and tube formation. In vivo, BIDEN-AP and its nanoconjugate CCPM-BIDEN-AP significantly reduced growth of orthotopic ovarian tumors, with CCPM-BIDEN-AP displaying greater antitumor potency than BIDEN-AP. Both BIDEN-AP and CCPM-BIDEN-AP compromised angiogenesis by downregulating epithelial-mesenchymal transition and angiogenic pathways. Thus, we report a novel EphB4-based therapeutic approach against ovarian cancer.

Ephrin‑B2 inhibits cell proliferation and motility in vitro and predicts longer metastasis‑free survival in breast cancer

The tyrosine kinase receptor EphB4 and its ligand ephrin‑B2 interact through cell‑to‑cell contacts. Upon interaction, EphB4 transmits bidirectional signals. A forward signal inside EphB4‑expressing cells is believed to suppress tumor growth, while inside the ephrin‑expressing cells, an oncogenic reverse signal arises. In breast cancer cells with a high EphB4 receptor expression the forward signal is low, in part due to the low expression of the ligand ephrin‑B2. Therefore, we hypothesized that by re‑introducing the ligand in EphB4‑positive cells, tumor suppression could be induced by the stimulation of the forward signal. This question was addressed in vitro by the stable lentiviral infection of breast cancer cells with either wild‑type EFNB2 or with a mutant EFNB2‑5F, unable to transmit reverse signaling. Furthermore, we investigated ephrin‑B and EphB4 protein expression in 216 paraffin‑embedded tumors using immunohistochemistry. The in vitro results indicated that ephrin‑B2 expression was associated with a lower cell proliferation, migration and motility compared with the control cells. These effects were more pronounced when the cells lacked the ability to transmit the reverse signal (B2‑5F). In clinical material, ephrin‑B protein expression was associated with a positive estrogen receptor (ER) status, a low HER‑2 expression and was negatively associated with Nottingham histologic grade (NHG) III. Ephrin‑B expression indicated a good prognosis, whereas EphB4 expression was associated with a shorter metastasis‑free survival in univariate and multivariate analysis. Furthermore, the prognostic value of EFNB2 and EPHB4 was confirmed at the gene expression level in public datasets. Thus, on the whole, the findings of this study suggest that ephrin‑B2 expression is associated with less proliferation and lower motility of breast cancer cells and with a longer patient survival in breast cancer.

Identification of a novel EphB4 phosphodegron regulated by the autocrine IGFII/IRA axis in malignant mesothelioma

Malignant mesothelioma is a deadly disease with limited therapeutic options. EphB4 is an oncogenic tyrosine kinase receptor expressed in malignant mesothelioma as well as in a variety of cancers. It is involved in tumor microenvironment mediating angiogenesis and invasive cellular effects via both EphrinB2 ligand-dependent and independent mechanisms. The molecular network underlying EphB4 oncogenic effects is still unclear. Here we show that EphB4 expression in malignant mesothelioma cells is markedly decreased upon neutralization of cancer-secreted IGF-II. In particular, we demonstrate that EphB4 protein expression in malignant mesothelioma cells depend upon a degradation rescue mechanism controlled by the autocrine IGF-II-insulin receptor-A specific signaling axis. We show that the regulation of EphB4 expression is linked to a competing post-translational modification of its carboxy-terminal tail via phosphorylation of its tyrosine 987 by the Insulin receptor isoform-A kinase-associated activity in response to the autocrine IGF-II stimuli. Neutralization of this autocrine-induced EphB4-phosphorylation by IGF-II associates with the increased ubiquitination of EphB4 carboxy-terminal tail and with its rapid degradation. We also describe a novel Ubiquitin binding motif in the targeted region as part of the identified EphB4 phosphodegron and provide 3D modeling data supporting a possible model for the acute EphB4 PTM-driven regulation by IGF-II. Altogether, these findings disclose a novel molecular mechanism for the maintenance of EphB4-expression in malignant mesothelioma cells and other IGF-II-secreting cancers (IGF2omas).

Ephrin/Eph receptor interaction facilitates macrophage recognition of differentiating human erythroblasts

Erythropoiesis is one of the most efficient cellular processes in the human body producing approximately 2.5 million red blood cells every second. This process occurs in a bone marrow niche comprised of a central resident macrophage surrounded by differentiating erythroblasts, termed an erythroblastic island. It is not known what initially attracts the macrophage to erythroblasts to form these islands. The ephrin/Eph receptor family are known to regulate heterophilic cell-cell adhesion. We find that human VCAM1⁺ and VCAM1^- bone marrow macrophages and in vitro cultured macrophages are ephrin-B2 positive, whereas differentiating human erythroblasts express EPHB4, EPHB6 and EPHA4. Furthermore, we detect a rise in integrin activation on erythroblasts at the stage at which the cells bind which is independent of EPH receptor presence. Using a live cell imaging assay, we show that specific inhibitory peptides or shRNA depletion of EPHB4 cause a significant reduction in the ability of macrophages to interact with erythroblasts but do not affect integrin activation. This study demonstrates for the first time that EPHB4 expression is required on erythroblasts to facilitate the initial recognition and subsequent interaction with macrophages, alongside the presence of active integrins.

Prognostic value of ephrin B receptors in breast cancer: An online survival analysis using the microarray data of 3,554 patients

The roles of Ephrin B (EphB) receptors in cancer are relatively unknown as these receptors are associated with complex signaling pathways. A limited number of studies have investigated the association between EphB receptors and prognosis. Using the Kaplan-Meier plotter database, the present study investigated the associations between the mRNA expression levels of five EphB receptors and the outcomes of 3,554 patients with breast cancer who had been followed-up for 20 years. Hazard ratios (HR) and 95% confidence intervals (CI) were calculated to assess the relative risk of survival. The results demonstrated that high mRNA expression levels of EphB2 (HR, 0.74; 95% CI, 0.66-0.84; P=2.1×10-6), EphB4 (HR, 0.82; 95% CI, 0.72-0.93; P=0.0023) and EphB6 (HR, 0.69; 95% CI, 0.61-0.78; P=3×10-9) were significantly associated with improved survival, while a high mRNA expression level of EphB3 (HR, 1.14; 95% CI, 1.01-1.28; P=0.029) was associated with worse survival for patients with breast cancer. High expression levels of all EphB receptors, including EphB1 (HR, 1.4; 95% CI, 1.02-1.94; P=0.039), EphB2 (HR, 1.34; 95% CI, 1.07-1.67; P=0.011), EphB3 (HR, 1.39; 95% CI, 1.11-1.73, P=0.0038), EphB4 (HR, 1.33; 95% CI, 1.06-1.67; P=0.013) and EphB6 (HR, 1.32; 95% CI, 1.05-1.65; P=0.016), were associated with an increased risk of mortality in patients with lymph-node-positive breast cancer. High mRNA expression levels of EphB1 were not associated with survival for all patients with breast cancer (HR, 0.85; 95% CI, 0.72-1.01; P=0.058). The results of the present suggested that EphB receptors may be useful as prognostic biomarkers of breast cancer.

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.

Viewing the Eph receptors with a focus on breast cancer heterogeneity

Aberrant expression of different family members of the Eph/ephrin system, which comprises the Eph receptors (Ephs) and their ligands (ephrins), has been implicated in various malignancies including breast cancer. The latter presents as a heterogeneous disease with diverse molecular, morphologic and clinical behavior signatures. This review reflects the existing Eph/ephrin literature while focusing on breast cancer heterogeneity. Hormone positive, HER2 positive and triple negative breast cancer (TNBC) cell lines, xenografts/mutant animal models and patient samples are examined separately as, in humans, they represent entities with differences in prognosis and treatment. EphA2, EphB4 and EphB6 are the members most extensively studied in breast cancer. Existing research points to the potential use of various Eph/ephrin members as biomarkers for assessing prognosis and selecting the most suitable therapeutic strategies in variable clinical scenarios, also for overcoming drug resistance, in the era of breast cancer heterogeneity.

EphB4: A promising target for upper aerodigestive malignancies

The erythropoietin-producing hepatocellular carcinoma (Eph) receptors are the largest family of receptor tyrosine kinases (RTKs) that include two major subclasses, EphA and EphB. They form an important cell communication system with critical and diverse roles in a variety of biological processes during embryonic development. However, dysregulation of the Eph/ephrin interactions is implicated in cancer contributing to tumour growth, metastasis, and angiogenesis. Here, we focus on EphB4 and review recent developments in elucidating its role in upper aerodigestive malignancies to include lung cancer, head and neck cancer, and mesothelioma. In particular, we summarize information regarding EphB4 structure/function and role in disease pathobiology. We also review the data supporting EphB4 as a potential pharmacological and immunotherapy target and finally, progress in the development of new therapeutic strategies including small molecule inhibitors of its activity is discussed. The emerging picture suggests that EphB4 is a valuable and attractive therapeutic target for upper aerodigestive malignancies.

Prognostic Value of ACVRL1 Expression in Metastatic Colorectal Cancer Patients Receiving First-line Chemotherapy With Bevacizumab: Results From the Triplet Plus Bevacizumab (TRIBE) Study

BACKGROUND

No biomarkers exist to predict benefit from antiangiogenic therapy in metastatic colorectal cancer patients. ACVRL1 (activin receptor like-protein 1) encodes for ALK1, a member of the transforming growth factor-β receptor family, which directs pathologic angiogenesis. We examined the intratumoral expression of ACVRL1 and other angiogenesis pathway-related genes to identify molecular markers in the TRIBE study.

MATERIALS AND METHODS

Of 503 randomized patients, 228 had sufficient tissue for analysis. Formalin-fixed paraffin-embedded specimens were examined for expression of VEGF-A, VEGF-B, VEGF-C, VEGFR1, VEGFR2, ACVRL1, EphB4, and EGFL7 using reverse transcription polymerase chain reaction. A maximal χ² approach was used to determine the messenger RNA levels associated with progression-free survival (PFS), overall survival (OS), response rate, early tumor shrinkage, and depth of response. Recursive partitioning trees were constructed to identify composite prognostic biomarker profiles. External validation was conducted in silico using the Oncomine database.

RESULTS

High ACVRL1 expression was associated with superior OS in both treatment arms (FOLFOXIRI [5-fluorouracil, leucovorin, oxaliplatin, irinotecan]-bevacizumab, 32.7 vs. 13.5 months, hazard ratio [HR], 0.38, P = .023; FOLFIRI [5-fluorouracil, leucovorin, irinotecan]-bevacizumab, 35.1 vs. 22.0 months, HR, 0.36, P = .006) and prolonged PFS (11.7 vs. 5.9 months, multivariate HR, 0.17; P = .001) for patients receiving FOLFOXIRI-bevacizumab on univariate and multivariate analyses. In recursive partitioning analysis, ACVRL1 was the strongest discriminator of the response rate, PFS, and OS in patients receiving FOLFOXIRI-bevacizumab and of OS in patients receiving FOLFIRI-bevacizumab. In silico validation revealed significant associations between ACVRL1 expression, disease recurrence, and 1-year survival (P < .05) among all colorectal cancer stages.

CONCLUSION

ACVRL1 expression could serve as a prognostic biomarker in metastatic colorectal cancer patients receiving chemotherapy and bevacizumab and warrants further evaluation in prospective studies.

Differential Expression Patterns of Eph Receptors and Ephrin Ligands in Human Cancers

Eph receptors constitute the largest family of receptor tyrosine kinases, which are activated by ephrin ligands that either are anchored to the membrane or contain a transmembrane domain. These molecules play important roles in the development of multicellular organisms, and the physiological functions of these receptor-ligand pairs have been extensively documented in axon guidance, neuronal development, vascular patterning, and inflammation during tissue injury. The recognition that aberrant regulation and expression of these molecules lead to alterations in proliferative, migratory, and invasive potential of a variety of human cancers has made them potential targets for cancer therapeutics. We present here the involvement of Eph receptors and ephrin ligands in lung carcinoma, breast carcinoma, prostate carcinoma, colorectal carcinoma, glioblastoma, and medulloblastoma. The aberrations in their abundances are described in the context of multiple signaling pathways, and differential expression is suggested as the mechanism underlying tumorigenesis.

Overexpression of Receptor Tyrosine Kinase EphB4 Triggers Tumor Growth and Hypoxia in A375 Melanoma Xenografts: Insights from Multitracer Small Animal Imaging Experiments

Experimental evidence has associated receptor tyrosine kinase EphB4 with tumor angiogenesis also in malignant melanoma. Considering the limited in vivo data available, we have conducted a systematic multitracer and multimodal imaging investigation in EphB4-overexpressing and mock-transfected A375 melanoma xenografts. Tumor growth, perfusion, and hypoxia were investigated by positron emission tomography. Vascularization was investigated by fluorescence imaging in vivo and ex vivo. The approach was completed by magnetic resonance imaging, radioluminography ex vivo, and immunohistochemical staining for blood and lymph vessel markers. Results revealed EphB4 to be a positive regulator of A375 melanoma growth, but a negative regulator of tumor vascularization. Resulting in increased hypoxia, this physiological characteristic is considered as highly unfavorable for melanoma prognosis and therapy outcome. Lymphangiogenesis, by contrast, was not influenced by EphB4 overexpression. In order to distinguish between EphB4 forward and EphrinB2, the natural EphB4 ligand, reverse signaling a specific EphB4 kinase inhibitor was applied. Blocking experiments show EphrinB2 reverse signaling rather than EphB4 forward signaling to be responsible for the observed effects. In conclusion, functional expression of EphB4 is considered a promising differentiating characteristic, preferentially determined by non-invasive in vivo imaging, which may improve personalized theranostics of malignant melanoma.

Ephrin-B2 reverse signaling regulates progression and lymph node metastasis of oral squamous cell carcinoma

Oral squamous cell carcinoma (OSCC) is a common malignant tumor of the head and neck and frequently metastasizes to cervical lymph nodes. Aggressive local invasion and metastasis of OSCC are significant factors for poor prognosis. In this study, we investigated whether ephrin-B2 expressed in OSCC contributed to tumor progression and lymph node metastasis. Clinical specimens from patients with OSCC had robust ephrin-B2-positive tumor cells and ephrin-B2 protein level was associated with clinical stage, lymph node metastasis, and poor survival outcomes. We also determined that ephrin-B2 protein level was increased in OSCC cell lines compared to normal human oral keratinocytes and that its levels were associated with the migratory and invasive potential of OSCC cell lines. Transfection of an EFNB2-specific small interfering RNA (siRNA) into SAS-L1 cells significantly reduced proliferation, attachment, migration, and invasion through phosphorylation of the epidermal growth factor receptor, FAK, ERK1/2, p38, AKT, and JNK1/2 pathways. Furthermore, knockdown of EFNB2 significantly suppressed adhesion and transmigration of SAS-L1 cells toward human lymphatic endothelial cells. In addition, the growth rate of tumor xenografts and cervical lymph node metastases of OSCC were suppressed by local injection of EFNB2 siRNA. These results suggest that ephrin-B2 overexpression and activation of the ephrin-B2 reverse signaling pathway in tumor microenvironment in OSCC facilitates progression and lymph node metastasis via enhancement of malignant potential and interaction with surrounding cells.

Targeting receptor tyrosine kinase EphB4 in cancer therapy

Eph receptors and their Eph receptor-interacting (ephrin) ligands together form an important cell communication system with diverse roles. Experimental evidence demonstrated Eph receptor bidirectional signaling with both tumor-suppressing and tumor-promoting activities in cancer cells. The tyrosine kinase EphB4, a member of the Eph receptor family, has been associated with tumor angiogenesis, growth and metastasis, thus making it a valuable and attractive target for drug design for therapeutic applications. In the past decade, many studies have focused on elucidating the structure and function of EphB4 in complex with its ligand ephrinB2 for their role in carcinogenesis. Meanwhile, an array of compounds targeting EphB4 have been studied and several selective inhibitors have been tested in clinical studies. This review discusses the structure and function of the EphB4 receptor, analyzes its potential as a target for anticancer therapy, and summarizes the information about inhibitors of EphB4 kinase activity. Conclusively, EphB4 is a challenging but promising therapeutic target in cancer.

Aberrant EPHB4 gene methylation and childhood acute lymphoblastic leukemia

The present study aimed to investigate the association between aberrant DNA methylation of the promoter region of the ephrin type-B receptor 4 (EPHB4) gene and the development of childhood acute lymphoblastic leukemia (ALL). Bisulfite sequencing polymerase chain reaction (BSP) was performed to determine the methylation density of cytosine-guanine pair islands in the promoter region of EPHB4, in bone marrow samples from 40 children with ALL. The mRNA and protein expression levels of EPHB4 were detected using reverse transcription-quantitative polymerase chain reaction and western blot analysis. A total of 10 children with idiopathic thrombocytopenic purpura (ITP) were recruited as controls. The results revealed that the average methylation density of the bone marrow samples from the patients with ALL was significantly higher, compared with the patients with ITP (P=0.046). The relative mRNA expression levels of EPHB4 in the patients with ITP (25.08±4.03) and the patients with ALL without methylation (12.33±2.16) were significantly higher, compared with that observed in the patients with ALL with methylation (6.48±2.73; P<0.01). Pearson analysis revealed a significant negative linear correlation between EPHB4 gene methylation and its expression levels (r=−0.957; P<0.01). Western blot analysis indicated that EPHB4 protein expression levels were low in the methylated ALL samples. An evaluation of the two-year disease-free survival (DFS) of the patients with ALL was performed, which revealed that the patients with unmethylated ALL exhibited a significantly higher two-year DFS rate, as compared with patients with methylated ALL (P=0.036). These results suggest that the methylation of the EPHB4 gene is prevalent in childhood ALL and may result in expressional inactivation, which consequently promotes ALL pathogenesis and is associated with an unfavorable prognosis. Therefore, the EPHB4 gene may function as a potential tumor suppressor in childhood ALL.

EphB4 Regulates Self-Renewal, Proliferation and Neuronal Differentiation of Human Embryonic Neural Stem Cells in Vitro

Background/Aims: EphB4 belongs to the largest family of Eph receptor tyrosine kinases. It contributes to a variety of pathological progresses of cancer malignancy. However, little is known about its role in neural stem cells (NSCs). This study examined whether EphB4 is required for proliferation and differentiation of human embryonic neural stem cells (hNSCs) in vitro. Methods: We up- and down-regulated EphB4 expression in hNSCs using lentiviral over-expression and shRNA knockdown constructs and then investigated the influence of EphB4 on the properties of hNSCs. Results: Our results show that shRNA-mediated EphB4 reduction profoundly impaired hNSCs self-renewal and proliferation. Furthermore, detection of differentiation revealed that knockdown of EphB4 inhibited hNSCs differentiation towards a neuronal lineage and promoted hNSCs differentiation to glial cells. In contrast, EphB4 overexpression promoted hNSCs self-renewal and proliferation, further induced hNSCs differentiation towards a neuronal lineage and inhibited hNSCs differentiation to glial cells. Moreover, we found that EphB4 regulates cell proliferation mediated by the Abl-CyclinD1 pathway. Conclusion: These studies provide strong evidence that fine tuning of EphB4 expression is crucial for the proliferation and neuronal differentiation of hNSCs, suggesting that EphB4 might be an interesting target for overcoming some of the therapeutic limitations of neuronal loss in brain diseases.

Paradoxes of the EphB1 receptor in malignant brain tumors

Eph receptors are a subfamily of receptor tyrosine kinases. Eph receptor-mediated forward and ephrin ligand-mediated reverse signalings are termed bidirectional signaling. Increasing evidence shows that Eph/ephrin signaling regulates cell migration, adhesion, morphological changes, differentiation, proliferation and survival through cell–cell communication. Some recent studies have started to implicate Eph/ephrin signaling in tumorigenesis, metastasis, and angiogenesis. Previous studies have shown that EphB1 receptor and its ephrin ligands are expressed in the central nervous system. EphB1/ephrin signaling plays an important role in the regulation of synapse formation and maturation, migration of neural progenitors, establishment of tissue patterns, and the development of immune organs. Besides, various recent studies have detected the abnormal expression of EphB1 receptor in different brain tumors. However, the underlying molecular mechanisms of EphB1/ephrins signaling in the development of these tumors are not fully understood. This review focuses on EphB1 that has both tumor-suppressing and -promoting roles in some brain tumors. Understanding the intracellular mechanisms of EphB1 in tumorigenesis and metastasis of brain tumors might provide a foundation for the development of EphB1-targeted therapies.

Novel Nine-Exon AR Transcripts (Exon 1/Exon 1b/Exons 2-8) in Normal and Cancerous Breast and Prostate Cells

Nearly 20 different transcripts of the human androgen receptor (AR) are reported with two currently listed as Refseq isoforms in the NCBI database. Isoform 1 encodes wild-type AR (type 1 AR) and isoform 2 encodes the variant AR45 (type 2 AR). Both variants contain eight exons: they share common exons 2-8 but differ in exon 1 with the canonical exon 1 in isoform 1 and the variant exon 1b in isoform 2. Splicing of exon 1 or exon 1b is reported to be mutually exclusive. In this study, we identified a novel exon 1b (1b/TAG) that contains an additional TAG trinucleotide upstream of exon 1b. Moreover, we identified AR transcripts in both normal and cancerous breast and prostate cells that contained either exon 1b or 1b/TAG spliced between the canonical exon 1 and exon 2, generating nine-exon AR transcripts that we have named isoforms 3a and 3b. The proteins encoded by these new AR variants could regulate androgen-responsive reporters in breast and prostate cancer cells under androgen-depleted conditions. Analysis of type 3 AR-GFP fusion proteins showed partial nuclear localization in PC3 cells under androgen-depleted conditions, supporting androgen-independent activation of the AR. Type 3 AR proteins inhibited androgen-induced growth of LNCaP cells. Microarray analysis identified a small set of type 3a AR target genes in LNCaP cells, including genes known to modulate growth and proliferation of prostate cancer (PCGEM1, PEG3, EPHA3, and EFNB2) or other types of human cancers (TOX3, ST8SIA4, and SLITRK3), and genes that are diagnostic/prognostic biomarkers of prostate cancer (GRINA3, and BCHE).

ERK5 signalling rescues intestinal epithelial turnover and tumour cell proliferation upon ERK1/2 abrogation

The ERK1/2 MAPK signalling module integrates extracellular cues that induce proliferation and differentiation of epithelial lineages, and is an established oncogenic driver, particularly in the intestine. However, the interrelation of the ERK1/2 module relative to other signalling pathways in intestinal epithelial cells and colorectal cancer (CRC) is unclear. Here we show that loss of Erk1/2 in intestinal epithelial cells results in defects in nutrient absorption, epithelial cell migration and secretory cell differentiation. However, intestinal epithelial cell proliferation is not impeded, implying compensatory mechanisms. Genetic deletion of Erk1/2 or pharmacological targeting of MEK1/2 results in supraphysiological activity of the ERK5 pathway. Furthermore, targeting both pathways causes a more effective suppression of cell proliferation in murine intestinal organoids and human CRC lines. These results suggest that ERK5 provides a common bypass route in intestinal epithelial cells, which rescues cell proliferation upon abrogation of ERK1/2 signalling, with therapeutic implications in CRC.

It is unclear how the extracellular signal-regulated kinases 1 and 2 (ERK1/2) pathways interact with other signals in intestinal epithelial cells. Here, the authors show that upon loss of Erk1/2, or pharmacological inhibition of MEK1/2, the ERK5 pathway is upregulated to maintain epithelial cell proliferation.

Anti-tumour effects of antibodies targeting the extracellular cysteine-rich region of the receptor tyrosine kinase EphB4

EphB4 is a membrane-bound receptor tyrosine kinase (RTK) commonly over-produced by many epithelial cancers but with low to no expression in most normal adult tissues. EphB4 over-production promotes ligand-independent signaling pathways that increase cancer cell viability and stimulate migration and invasion. Several studies have shown that normal ligand-dependent signaling is tumour suppressive and therefore novel therapeutics which block the tumour promoting ligand-independent signaling and/or stimulate tumour suppressive ligand-dependent signaling will find application in the treatment of cancer. An EphB4-specific polyclonal antibody, targeting a region of 200 amino acids in the extracellular portion of EphB4, showed potent in vitro anti-cancer effects measured by an increase in apoptosis and a decrease in anchorage independent growth. Peptide exclusion was used to identify the epitope targeted by this antibody within the cysteine-rich region of the EphB4 protein, a sequence defined as a potential ligand interacting interface. Addition of antibody to cancer cells resulted in phosphorylation and subsequent degradation of the EphB4 protein, suggesting a mechanism that is ligand mimetic and tumour suppressive. A monoclonal antibody which specifically targets this identified extracellular epitope of EphB4 significantly reduced breast cancer xenograft growth in vivo confirming that EphB4 is a useful target for ligand-mimicking antibody-based anti-cancer therapies.

Membrane-mediated regulation of vascular identity

Vascular diseases span diverse pathology, but frequently arise from aberrant signaling attributed to specific membrane-associated molecules, particularly the Eph-ephrin family. Originally recognized as markers of embryonic vessel identity, Eph receptors and their membrane-associated ligands, ephrins, are now known to have a range of vital functions in vascular physiology. Interactions of Ephs with ephrins at cell-to-cell interfaces promote a variety of cellular responses such as repulsion, adhesion, attraction, and migration, and frequently occur during organ development, including vessel formation. Elaborate coordination of Eph- and ephrin-related signaling among different cell populations is required for proper formation of the embryonic vessel network. There is growing evidence supporting the idea that Eph and ephrin proteins also have postnatal interactions with a number of other membrane-associated signal transduction pathways, coordinating translation of environmental signals into cells. This article provides an overview of membrane-bound signaling mechanisms that define vascular identity in both the embryo and the adult, focusing on Eph- and ephrin-related signaling. We also discuss the role and clinical significance of this signaling system in normal organ development, neoplasms, and vascular pathologies.

Diagnostic and prognostic value of tissue and circulating levels of Ephrin-A2 in prostate cancer

Ephrin-A2, a member of the Eph/ephrin family, is associated with tumorigenesis and tumor progression. This study aimed to assess the diagnostic and prognostic value of both serum and tissue levels of Ephrin-A2 in prostate cancer (PCa) management. One hundred and forty-five frozen prostate tissues, 55 paraffin-embedded prostate tissues, 88 serum samples, and seven prostate cell lines (RWPE-1, LNCaP, LNCaP-LN3, PC-3, PC-3M, PC-3M-LN4, and DU145) were examined via quantitative reverse transcription-PCR (qRT-PCR), immunohistochemistry, enzyme-linked immunosorbent assay, and western blotting. Induced Ephrin-A2 messenger RNA (mRNA) or protein expression was detected in 8.6 % (5/58) benign prostatic hyperplasia (BPH), 59.8 % (52/87) PCa, and five prostate cancer cell lines. Ephrin-A2 immunostaining was present in 6.7 % (1/15) patients with BPHs and 62.5 % (25/40) clinically localized PCa. Accordingly, serum Ephrin-A2 was significantly higher in PCa patients compared to those in the BPH patients and controls (P < 0.001). The expression of Ephrin-A2 was higher in tumor patients with an elevated Gleason score or T3-T4 staging. Ephrin-A2 expression was correlated with Ki-67 expression in PCa patients, both at the gene scale and protein level. Our data indicate that Ephrin-A2 is a potential diagnostic and prognostic biomarker and a promising molecular therapeutic target to attenuate prostate cancer progression.

Eph receptor and ephrin function in breast, gut, and skin epithelia

Epithelial cells are tightly coupled together through specialized intercellular junctions, including adherens junctions, desmosomes, tight junctions, and gap junctions. A growing body of evidence suggests epithelial cells also directly exchange information at cell-cell contacts via the Eph family of receptor tyrosine kinases and their membrane-associated ephrin ligands. Ligand-dependent and -independent signaling via Eph receptors as well as reverse signaling through ephrins impact epithelial tissue homeostasis by organizing stem cell compartments and regulating cell proliferation, migration, adhesion, differentiation, and survival. This review focuses on breast, gut, and skin epithelia as representative examples for how Eph receptors and ephrins modulate diverse epithelial cell responses in a context-dependent manner. Abnormal Eph receptor and ephrin signaling is implicated in a variety of epithelial diseases raising the intriguing possibility that this cell-cell communication pathway can be therapeutically harnessed to normalize epithelial function in pathological settings like cancer or chronic inflammation.

The tumour-promoting receptor tyrosine kinase, EphB4, regulates expression of integrin-β8 in prostate cancer cells

Background

The EphB4 receptor tyrosine kinase is overexpressed in many cancers including prostate cancer. The molecular mechanisms by which this ephrin receptor influences cancer progression are complex as there are tumor-promoting ligand-independent mechanisms in place as well as ligand-dependent tumor suppressive pathways.

Methods

We employed transient knockdown of EPHB4 in prostate cancer cells, coupled with gene microarray analysis, to identify genes that were regulated by EPHB4 and may represent linked tumor-promoting factors. We validated target genes using qRT-PCR and employed functional assays to determine their role in prostate cancer migration and invasion.

Results

We discovered that over 500 genes were deregulated upon EPHB4 siRNA knockdown, with integrin β8 (ITGB8) being the top hit (29-fold down-regulated compared to negative non-silencing siRNA). Gene ontology analysis found that the process of cell adhesion was highly deregulated and two other integrin genes, ITGA3 and ITGA10, were also differentially expressed. In parallel, we also discovered that over-expression of EPHB4 led to a concomitant increase in ITGB8 expression. In silico analysis of a prostate cancer progression microarray publically available in the Oncomine database showed that both EPHB4 and ITGB8 are highly expressed in prostatic intraepithelial neoplasia, the precursor to prostate cancer. Knockdown of ITGB8 in PC-3 and 22Rv1 prostate cancer cells in vitro resulted in significant reduction of cell migration and invasion.

Conclusions

These results reveal that EphB4 regulates integrin β8 expression and that integrin β8 plays a hitherto unrecognized role in the motility of prostate cancer cells and thus targeting integrin β8 may be a new treatment strategy for prostate cancer.

Electronic supplementary material

The online version of this article (doi:10.1186/s12885-015-1164-6) contains supplementary material, which is available to authorized users.

Murine, but not human, ephrin-B2 can be efficiently cleaved by the serine protease kallikrein-4: implications for xenograft models of human prostate cancer

BACKGROUND

Ephrin-B2 is the sole physiologically-relevant ligand of the receptor tyrosine kinase EphB4, which is over-expressed in many epithelial cancers, including 66% of prostate cancers, and contributes to cancer cell survival, invasion and migration. Crucially, however, the cancer-promoting EphB4 signalling pathways are independent of interaction with its ligand ephrin-B2, as activation of ligand-dependent signalling causes tumour suppression. Ephrin-B2, however, is often found on the surface of endothelial cells of the tumour vasculature, where it can regulate angiogenesis to support tumour growth. Proteolytic cleavage of endothelial cell ephrin-B2 has previously been suggested as one mechanism whereby the interaction between tumour cell-expressed EphB4 and endothelial cell ephrin-B2 is regulated to support both cancer promotion and angiogenesis.

METHODS

An in silico approach was used to search accessible surfaces of 3D protein models for cleavage sites for the key prostate cancer serine protease, KLK4, and this identified murine ephrin-B2 as a potential KLK4 substrate. Mouse ephrin-B2 was then confirmed as a KLK4 substrate by in vitro incubation of recombinant mouse ephrin-B2 with active recombinant human KLK4. Cleavage products were visualised by SDS-PAGE, silver staining and Western blot and confirmed by N-terminal sequencing.

RESULTS

At low molar ratios, KLK4 cleaved murine ephrin-B2 but other prostate-specific KLK family members (KLK2 and KLK3/PSA) were less efficient, suggesting cleavage was KLK4-selective. The primary KLK4 cleavage site in murine ephrin-B2 was verified and shown to correspond to one of the in silico predicted sites between extracellular domain residues arginine 178 and asparagine 179. Surprisingly, the highly homologous human ephrin-B2 was poorly cleaved by KLK4 at these low molar ratios, likely due to the 3 amino acid differences at this primary cleavage site.

CONCLUSION

These data suggest that in in vivo mouse xenograft models, endogenous mouse ephrin-B2, but not human tumour ephrin-B2, may be a downstream target of cancer cell secreted human KLK4. This is a critical consideration when interpreting data from murine explants of human EphB4+/KLK4+ cancer cells, such as prostate cancer cells, where differential effects may be seen in mouse models as opposed to human clinical situations.

EphB4 localises to the nucleus of prostate cancer cells

The EphB4 receptor tyrosine kinase is over-expressed in a variety of different epithelial cancers including prostate where it has been shown to be involved in survival, migration and angiogenesis. We report here that EphB4 also resides in the nucleus of prostate cancer cell lines. We used in silico methods to identify a bipartite nuclear localisation signal (NLS) in the extracellular domain and a monopartite NLS sequence in the intracellular kinase domain of EphB4. To determine whether both putative NLS sequences were functional, fragments of the EphB4 sequence containing each NLS were cloned to create EphB4NLS-GFP fusion proteins. Localisation of both NLS-GFP proteins to the nuclei of transfected cells was observed, demonstrating that EphB4 contains two functional NLS sequences. Mutation of the key amino residues in both NLS sequences resulted in diminished nuclear accumulation. As nuclear translocation is often dependent on importins we confirmed that EphB4 and importin-α can interact. To assess if nuclear EphB4 could be implicated in gene regulatory functions potential EphB4-binding genomic loci were identified using chromatin immunoprecipitation and Lef1 was confirmed as a potential target of EphB4-mediated gene regulation. These novel findings add further complexity to the biology of this important cancer-associated receptor.

Downregulation of EphA5 by promoter methylation in human prostate cancer

Background

EphA5 is a member of the Eph/ephrin family and plays a critical role in the regulation of carcinogenesis. A significant reduction of EphA5 transcripts in high-grade prostate cancer tissue was shown using a transcriptomic analysis, compared to the low-grade prostate cancer tissue. As less is known about the mechanism of EphA5 downregulation and the function of EphA5, here we investigated the expression and an epigenetic change of EphA5 in prostate cancer and determined if these findings were correlated with clinicopathologic characteristics of prostate cancer.

Methods

Seven prostate cell lines (RWPE-1, LNCap, LNCap-LN3, CWR22rv-1, PC-3, PC-3M-LN4, and DU145), thirty-nine BPH, twenty-two primary prostate carcinomas, twenty-three paired noncancerous and cancerous prostate tissues were examined via qRT-PCR, methylation-specific PCR, bisulfite sequencing, immunohistochemistry and western blotting. The role of EphA5 in prostate cancer cell migration and invasion was examined by wound healing and transwell assay.

Results

Downregulation or loss of EphA5 mRNA or protein expression was detected in 28 of 45 (62.2%) prostate carcinomas, 2 of 39 (5.1%) hyperplasias, and all 6 prostate cancer cell lines. Methylation of the EphA5 promoter region was present in 32 of 45 (71.1%) carcinoma samples, 3 of 39 (7.7%) hyperplasias, and the 6 prostate cancer cell lines. Among 23 paired prostate carcinoma tissues, 16 tumor samples exhibited the hypermethylation of EphA5, and 15 of these 16 specimens (93.8%) shown the downregulation of EphA5 expression than that of their respectively matched noncancerous samples. Immunostaining analysis demonstrated that the EphA5 protein was absent or down-regulated in 10 of 13 (76.9%) available carcinoma samples, and 8 of these 10 samples (80.0%) exhibited hypermethylation. The frequency of EphA5 methylation was higher in cancer patients with an elevated Gleason score or T3-T4 staging. Following the treatment of 6 prostate cancer cell lines with 5-aza-2′-deoxycytidine, the levels of EphA5 mRNA were significantly increased. Prostate cancer cells invasion and migration were significantly suppressed by ectopic expression of EphA5 in vitro.

Conclusion

Our study provides evidence that EphA5 is a potential target for epigenetic silencing in primary prostate cancer and is a potentially valuable prognosis predictor and thereapeutic marker for prostate cancer.

Electronic supplementary material

The online version of this article (doi:10.1186/s12885-015-1025-3) contains supplementary material, which is available to authorized users.

Up-regulation of miR-582-5p regulates cellular proliferation of prostate cancer cells under androgen-deprived conditions

BACKGROUND

MicroRNAs are noncoding small RNA that negatively regulate target gene expression by binding to the 3'-UTR of mRNA. Previous studies have shown that several microRNAs play a pivotal role in prostate cancer by acting as oncogenes or tumor suppressors. This study was aimed at identifying microRNAs that contribute to the progression to castration resistant prostate cancer.

METHODS

MicroRNAs expression profiles of a xenograft model and cell lines were examined by microarray analysis and real-time PCR. Functional analysis of miR-582-5p in cellular proliferation was examined by cell counting. Furthermore, in order to investigate a candidate target of miR-582-5p, microarray analysis and analysis in silico were utilized.

RESULTS

MiR-582-5p was identified to be up-regulated at the castration resistant stage of a xenograft model, KUCaP2 and in castration resistant cell line, AILNCaP#1. Overexpression of miR-582-5p increased the number and the percentage of S phase of LNCaP cells under androgen deprived condition. Moreover, suppression of miR-582-5p decreased the number and the percentage of S phase of AILNCaP#1 cells. Furthermore, we identified that miR-582-5p down-regulates EFNB2 expression, which is down-regulated at the castration resistant stage of a xenograft model, KUCaP2 and in castration resistant cell line, AILNCaP#1.

CONCLUSIONS

Our results suggest that up-regulation of miR-582-5p contributes to an increase in the proliferation of prostate cancer cells under androgen deprived conditions.

Inhibiting Eph kinase activity may not be "Eph"ective for cancer treatment

Several Eph receptor tyrosine kinases (RTKs) are commonly over-expressed in epithelial and mesenchymal cancers and are recognized as promising therapeutic targets. Although normal interaction between Eph receptors and their ephrin ligands stimulates kinase activity and is generally tumor suppressive, significant Eph over-expression allows activation of ligand- and/or kinase-independent signaling pathways that promote oncogenesis. Single-agent kinase inhibitors are widely used to target RTK-driven tumors but acquired and de novo resistance to such agents is a major limitation to effective clinical use. Accumulating evidence suggests that Ephs can be inhibited by "leaky" or low-specificity kinase inhibitors targeted at other RTKs. Such off-target effects may therefore inadvertently promote ligand- and/or kinase-independent oncogenic Eph signaling, thereby providing a new mechanism by which resistance to the RTK inhibitors can emerge. We propose that combining specific, non-leaky kinase inhibitors with tumor-suppressive stimulators of Eph signaling may provide more effective treatment options for overcoming treatment-induced resistance and clinical failure.

Expression of EphB2/EphrinB2 in canceration of serrated polyps

AIM: To explore the role of EphB2 and its ligand EphrinB2 in colorectal tumorigenesis.

METHODS: The expression of EphB2 and EphrinB2 in 72 colorectal cancer, 64 serrated polyp and 33 normal colon tissues was detected by immunohistochemistry.

RESULTS: The area of EphB2 positive signal was located in the crypt base and the lower 2/3 region, while the positive area of EphrinB2 was mainly located throughout the crypt. EphB2 was expressed in the majority of normal colonic mucosa tissues, but showed a decreasing trend in serrated polyps and colorectal cancer. The positive rate of EphrinB2 in the normal mucosa was significantly lower than those in colorectal cancer and serrated polyps (P < 0.05). The expression rate of EphrinB2 in the normal colonic mucosa was significantly higher than those in serrated polyps and colorectal cancer (P < 0.05).

CONCLUSION: EphB2 may inhibit the occurrence of colorectal cancer. EphrinB2 may promote intestinal tumor growth.

EphB4 tyrosine kinase stimulation inhibits growth of MDA-MB-231 breast cancer cells in a dose and time dependent manner

BACKGROUND

EphB4 receptor tyrosine kinase is of diagnostic and therapeutic value due to its overexpression in breast tumors. Dual functions of tumor promotion and suppression have been reported for this receptor based on presence or absence of its ligand. To elucidate such discrepancy, we aimed to determine the effect of time- and dose-dependent stimulation of EphB4 on viability and invasion of breast cancer cells via recombinant ephrinB2-Fc.

METHODS

Cells were seeded into multiwell plates and were stimulated by various concentrations of preclustered ephrinB2-Fc. Cell viability was measured on days 3 and 6 following treatment using alamar-blue when cells were in different states of confluence.

RESULTS

Stimulation of cells with ephrinB2 did not pose any significant effect on cell viability before reaching confluence, while inhibition of cell growth was detected after 6 days when cells were in postconfluent state following a dose-dependent manner. EphrinB2 treatment did not affect tubular formation and invasion on matrigel.

CONCLUSION

This study showed that EphB4 can differentially inhibit cells at post confluent state and that presence of ligand manifests growth-inhibitory properties of EphB4 receptor. It is concluded that growth inhibition has occurred possibly due to long treatment with ligand, a process which leads to receptor downregulation.

The role of EPH receptors in cancer-related epithelial-mesenchymal transition

Erythropoietin-producing hepatoma (EPH) receptors are considered the largest family of receptor tyrosine kinases and play key roles in physiological and pathologic processes in development and disease. EPH receptors are often overexpressed in human malignancies and are associated with poor prognosis. However, the functions of EPH receptors in epithelial-mesenchymal transition (EMT) remain largely unknown. This review depicts the relationship between EPH receptors and the EMT marker E-cadherin as well as the crosstalk between EPH receptors and the signaling pathways involved EMT. Further discussion is focused on the clinical significance of EPH receptors as candidates for targeting in cancer therapeutics. Finally, we summarize how targeted inhibition of both EPH receptors and EMT-related signaling pathways represents a novel strategy for cancer treatment.

Cell mates: paracrine and stromal targets for prostate cancer therapy

After many years of limited treatment options for patients with metastatic castration-resistant prostate cancer (mCRPC), multiple systemic therapies are now available, providing patients with significant improvements in survival, symptom control and bone health. Most of the recent advances in this area have been based on better understanding of mCRPC biology, particularly with respect to the key role of androgen receptor signalling. However, most therapies are targeted towards the malignant epithelial cell component of the cancer and it should not be forgotten that cancer cells exist in close and symbiotic relationships with other components of the tumour. Paracrine and stromal signals are often critical to the growth of the cancer and represent new potential therapeutic targets that are separate from the malignant epithelial cells. The stroma produces numerous growth factors, including vascular endothelial growth factor family members, platelet-derived growth factors and fibroblast growth factors, which are all critical for tumour growth. Targeting prostate-cancer-associated fibroblasts in order to destroy the physical and functional scaffold of a cancer is also a logical approach. The interaction between prostate cancer and the immune system remains an active topic of basic and clinical research, with cytokines, chemokines and growth factors being potential targets for therapy. The biology of epithelial-mesenchymal transition and of circulating tumour cells might also provide insight into new therapeutic targets.

Gene expression profiling identifies EPHB4 as a potential predictive biomarker in colorectal cancer patients treated with bevacizumab

The anti-VEGF monoclonal antibody bevacizumab was approved in 2004 as a first-line treatment for metastatic colorectal cancer (CRC) in combination with chemotherapy and provided proof of principle for antiangiogenic therapy. However, there is no biomarker that can help to select patients who may benefit from bevacizumab in order to improve cost-effectiveness and therapeutic outcomes. The aim of this study was to compare gene expression profiles in CRC patients treated with bevacizumab who responded to the treatment with those that did not respond, in an effort to identify potential predictive biomarkers. RNA isolated from formalin-fixed paraffin-embedded tumor specimens of patients treated with bevacizumab was subjected to gene expression analysis with quantitative RT-PCR arrays profiling 84 genes implicated in the angiogenic process. Data were validated at the protein level using immunohistochemistry. We identified a gene, EPHB4, whose expression was significantly increased in nonresponders (p = 0.048, Mann-Whitney test). Furthermore, high EPHB4 tumor levels were associated with decreased median overall survival (16 months vs 48, Log-rank p = 0.012). This was not observed in a control group of CRC patients treated only with chemotherapy, suggesting that EPHB4 constitutes a potential predictive biomarker and not a mere prognostic one. These data support the notion of a potential synergy between EPHB4-EFNB2 and VEGF-VEGFR pathways, making patients with high EPHB4 expression more resistant to VEGF blocking. Therefore, determination of EPHB4 levels in CRC samples could be useful for the prediction of response to bevacizumab.