Pharmacological characterization of second generation FXR agonists as effective EphA2 antagonists: A successful application of target hopping approach

It is well demonstrated the key role of Eph-ephrin system, specifically of EphA2 receptor, in supporting tumor growth, invasion, metastasis and neovascularization. We previously identified FXR agonists as eligible antagonists of Eph-ephrin system. Herein we characterize new commercially available FXR (Farnesoid X Receptor) agonists as potential Eph ligands including Cilofexor, Nidufexor, Tropifexor, Turofexorate isopropyl and Vonafexor. Our exploration based on molecular modelling investigations and binding assays shows that Cilofexor binds specifically and reversibly to EphA2 receptor with a Ki value in the low micromolar range. Furthermore, Cilofexor interferes with the phosphorylation of EphA2 and the cell retraction and rounding in PC3 prostate cancer cells, both events depending on EphA2 activation. In conclusion, we can confirm that target hopping can be a successful approach to discover new moiety of protein-protein inhibitors.

May EPH/Ephrin Targeting Revolutionize Lung Cancer Treatment?

Lung cancer (LC) is the leading cause of cancer death in the United States. Erythropoietin-producing hepatocellular receptors (EPHs) comprise the largest receptor tyrosine kinases (RTKs) family in mammals. EPHs along with their ligands, EPH-family receptor-interacting proteins (ephrins), have been found to be either up- or downregulated in LC cells, hence exhibiting a defining role in LC carcinogenesis and tumor progression. In their capacity as membrane-bound molecules, EPHs/ephrins may represent feasible targets in the context of precision cancer treatment. In order to investigate available therapeutics targeting the EPH/ephrin system in LC, a literature review was conducted, using the MEDLINE, LIVIVO, and Google Scholar databases. EPHA2 is the most well-studied EPH/ephrin target in LC treatment. The targeting of EPHA2, EPHA3, EPHA5, EPHA7, EPHB4, EPHB6, ephrin-A1, ephrin-A2, ephrin-B2, and ephrin-B3 in LC cells or xenograft models not only directly correlates with a profound LC suppression but also enriches the effects of well-established therapeutic regimens. However, the sole clinical trial incorporating a NSCLC patient could not describe objective anti-cancer effects after anti-EPHA2 antibody administration. Collectively, EPHs/ephrins seem to represent promising treatment targets in LC. However, large clinical trials still need to be performed, with a view to examining the effects of EPH/ephrin targeting in the clinical setting.

Single-Cell Transcriptomics of Endothelial Cells in Upper and Lower Human Esophageal Squamous Cell Carcinoma

Esophageal squamous cell carcinoma (ESCC) is a type of progressive and distant metastatic tumor. Targeting anti-angiogenic genes could effectively hinder ESCC development and metastasis, whereas ESCC locating on the upper or the lower esophagus showed different response to the same clinical treatment, suggesting ESCC location should be taken into account when exploring new therapeutic targets. In the current study, to find novel anti-angiogenic therapeutic targets, we identified endothelial cell subsets in upper and lower human ESCC using single-cell RNA sequencing (scRNA-seq), screened differentially expressed genes (DEGs), and performed gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis. The results showed that common DEGs shared in the upper and the lower endothelial cells mainly are involved in vessel development, angiogenesis, and cell motility of endothelial cells by regulating PI3K-AKT, Rap1, Ras, TGF-beta, and Apelin signaling pathways. The critical regulatory genes were identified as ITGB1, Col4A1, Col4A2, ITGA6, LAMA4, LAMB1, LAMC1, VWF, ITGA5, THBS1, PDGFB, PGF, RHOC, and CTNNB1. Cell metabolism-relevant genes, e.g., MGST3, PNP, UPP1, and HYAL2 might be the prospective therapeutic targets. Furthermore, we found that DEGs only in the upper endothelial cells, such as MAPK3, STAT3, RHOA, MAPK11, HIF1A, FGFR1, GNG5, GNB1, and ARHGEF12, mainly regulated cell adhesion, structure morphogenesis, and motility through Phospholipase D, Apelin, and VEGF signaling pathways. Moreover, DEGs only in the lower endothelial cells, for instance PLCG2, EFNA1, CALM1, and RALA, mainly regulated cell apoptosis and survival by targeting calcium ion transport through Rap1, Ras, cAMP, Phospholipase D, and Phosphatidylinositol signaling pathways. In addition, the upper endothelial cells showed significant functional diversity such as cytokine-responsive, migratory, and proliferative capacity, presenting a better angiogenic capacity and making it more sensitive to anti-angiogenic therapy compared with the lower endothelial cells. Our study has identified the potential targeted genes for anti-angiogenic therapy for both upper and lower ESCC, and further indicated that anti-angiogenic therapy might be more effective for upper ESCC, which still need to be further examined in the future.

H4 acetylation by the NuA4 complex is required for plastid transcription and chloroplast biogenesis

Chloroplast biogenesis is crucial in plant development, as it is essential for the transition to autotrophic growth. This process is light-induced and relies on the orchestrated transcription of nuclear and plastid genes, enabling the effective assembly and regulation of the photosynthetic machinery. Here we reveal a new regulation level for this process by showing the involvement of chromatin remodelling in the nuclear control of plastid gene expression for proper chloroplast biogenesis and function. The two Arabidopsis homologues of yeast EPL1 protein, components of the NuA4 histone acetyltransferase complex, are essential for plastid transcription and correct chloroplast development and performance. We show that EPL1 proteins are light-regulated and necessary for concerted expression of nuclear genes encoding most components of chloroplast transcriptional machinery, directly mediating H4K5ac deposition at these loci and promoting the expression of plastid genes required for chloroplast biogenesis. These data unveil a NuA4-mediated mechanism regulating chloroplast biogenesis that links the transcription of nuclear and plastid genomes during chloroplast development.

The Expression of ephrinA1/ephA2 Receptor Increases in Chronic Rhinosinusitis and ephrinA1/ephA2 Signaling Affects Rhinovirus-Induced Innate Immunity in Human Sinonasal Epithelial Cells

EphA2 receptor and its ephrin ligands are involved in virus infection, epithelial permeability, and chemokine secretion. We hypothesized that ephrinA1/ephA2 signaling participates in rhinovirus (RV)-induced antiviral immune response in sinonasal mucosa of patients with chronic rhinosinusitis (CRS). Therefore, we investigated the expression of ephrinA1/ephA2 in normal and inflamed sinonasal mucosa and evaluated whether they regulate chemokine secretion and the production of antiviral immune mediators including interferons (IFNs) in RV-infected human primary sinonasal epithelial cells. For this purpose, the expression and distribution of ephrinA1/ephA2 in sinonasal mucosa were evaluated with RT-qPCR, immunofluorescence, and western blot. Their roles in chemokine secretion and the production of antiviral immune mediators such as type I and III IFNs, and interferon stimulated genes were evaluated by stimulating ephA2 with ephrinA1 and inactivating ephA2 with ephA2 siRNA or inhibitor in cells exposed to RV and poly(I:C). We found that ephrinA1/ephA2 were expressed in normal mucosa and their levels increased in inflamed sinonasal mucosa of CRS patients. RV infection or poly(I:C) treatment induced chemokine secretion which were attenuated by blocking the action of ephA2 with ephA2 siRNA or inhibitor. The production of antiviral immune mediators enhanced by rhinovirus or poly (I:C) is increased by blocking ephA2 compared with that of cells stimulated by either rhinovirus or poly(I:C) alone. In addition, blocking ephA2 attenuated RV replication in cultured cells. Taken together, these results describe a novel role of ephrinA1/ephA2 signaling in antiviral innate immune response in sinonasal epithelium, suggesting their participation in RV-induced development and exacerbations of CRS.

Drug-resistant cancer cell-derived exosomal EphA2 promotes breast cancer metastasis via the EphA2-Ephrin A1 reverse signaling

Tumor metastasis induced by drug resistance is a major challenge in successful cancer treatment. Nevertheless, the mechanisms underlying the pro-invasive and metastatic ability of drug resistance remain elusive. Exosome-mediated intercellular communications between cancer cells and stromal cells in tumor microenvironment are required for cancer initiation and progression. Recent reports have shown that communications between cancer cells also promote tumor aggression. However, little attention has been regarded on this aspect. Herein, we demonstrated that drug-resistant cell-derived exosomes promoted the invasion of sensitive breast cancer cells. Quantitative proteomic analysis showed that EphA2 was rich in exosomes from drug-resistant cells. Exosomal EphA2 conferred the invasive/metastatic phenotype transfer from drug-resistant cells to sensitive cells. Moreover, exosomal EphA2 activated ERK1/2 signaling through the ligand Ephrin A1-dependent reverse pathway rather than the forward pathway, thereby promoting breast cancer progression. Our findings indicate the key functional role of exosomal EphA2 in the transmission of aggressive phenotype between cancer cells that do not rely on direct cell-cell contact. Our study also suggests that the increase of EphA2 in drug-resistant cell-derived exosomes may be an important mechanism of chemotherapy/drug resistance-induced breast cancer progression.

Inhibition of EphA2 by Dasatinib Suppresses Radiation-Induced Intestinal Injury

Radiation-induced multiorgan dysfunction is thought to result primarily from damage to the endothelial system, leading to a systemic inflammatory response that is mediated by the recruitment of leukocytes. The Eph–ephrin signaling pathway in the vascular system participates in various disease developmental processes, including cancer and inflammation. In this study, we demonstrate that radiation exposure increased intestinal inflammation via endothelial dysfunction, caused by the radiation-induced activation of EphA2, an Eph receptor tyrosine kinase, and its ligand ephrinA1. Barrier dysfunction in endothelial and epithelial cells was aggravated by vascular endothelial–cadherin disruption and leukocyte adhesion in radiation-induced inflammation both in vitro and in vivo. Among all Eph receptors and their ligands, EphA2 and ephrinA1 were required for barrier destabilization and leukocyte adhesion. Knockdown of EphA2 in endothelial cells reduced radiation-induced endothelial dysfunction. Furthermore, pharmacological inhibition of EphA2–ephrinA1 by the tyrosine kinase inhibitor dasatinib attenuated the loss of vascular integrity and leukocyte adhesion in vitro. Mice administered dasatinib exhibited resistance to radiation injury characterized by reduced barrier leakage and decreased leukocyte infiltration into the intestine. Taken together, these data suggest that dasatinib therapy represents a potential approach for the protection of radiation-mediated intestinal damage by targeting the EphA2–ephrinA1 complex.

Role of Nuclear Claudin-4 in Renal Cell Carcinoma

Claudin-4 (CLDN4) is a tight junction protein to maintain the cancer microenvironment. We recently reported the role of the CLDN4 not forming tight junction in the induction of epithelial-mesenchymal transition (EMT). Herein, we investigated the role of CLDN4 in renal cell carcinoma (RCC), focusing on CLDN4. CLDN4 expression in 202 RCCs was examined by immunostaining. CLDN4 phosphorylation and subcellular localization were examined using high metastatic human RCC SN12L1 and low metastatic SN12C cell lines. In 202 RCC cases, the CLDN4 expression decreased in the cell membrane and had no correlation with clinicopathological factors. However, CLDN4 was localized in the nucleus in 5 cases (2%), all of which were pT3. Contrastingly, only 6 of 198 nuclear CLDN4-negative cases were pT3. CLDN4 was found in the nuclear fraction of a highly metastatic human RCC cell line, SN12L1, but not in the low metastatic SN12C cells. In SN12L1 cells, phosphorylation of tyrosine and serine residues was observed in cytoplasmic CLDN4, but not in membranous CLDN4. In contrast, phosphorylation of serine residues was observed in nuclear CLDN4. In SN12L1 cells, CLDN4 tyrosine phosphorylation by EphA2/Ephrin A1 resulted in the release of CLDN4 from tight junction and cytoplasmic translocation. Furthermore, protein kinase C (PKC)-ε phosphorylated the CLDN4 serine residue, resulting in nuclear import. Contrarily, in SN12C cells that showed decreased expression of EphA2/Ephrin A1 and PKCε, the activation of EphA2/EphrinA1 and PKCε induced cytoplasmic and nuclear translocation of CLDN4, respectively. Furthermore, the nuclear translocation of CLDN4 promoted the nuclear translocation of Yes-associated protein (YAP) bound to CLDN4, which induced the EMT phenotype. These findings suggest that the release of CLDN4 by impaired tight junction might be a mechanism underlying the malignant properties of RCC. These findings suggest that the release of CLDN4 by impaired tight junction might be one of the mechanisms of malignant properties of RCC.

Use of Multifactorial Treatments to Address the Challenge of Translating Experimental Myocardial Infarct Reduction Strategies

Myocardial tissue damage that occurs during an ischemic event leads to a spiraling deterioration of cardiac muscle structural and functional integrity. Reperfusion is the only known efficacious strategy and is the most commonly used treatment to reduce injury and prevent remodeling. However, timing is critical, and the procedure is not always feasible for a variety of reasons. The complex molecular basis for cardioprotection has been studied for decades but formulation of a viable therapeutic that can significantly attenuate myocardial injury remains elusive. In this review, we address barriers to the development of a fruitful approach that will substantially improve the prognosis of those suffering from this widespread and largely unmitigated disease. Furthermore, we proffer that ephrinA1, a candidate molecule that satisfies many of the important criteria discussed, possesses robust potential to overcome these hurdles and thus offers protection that surpasses the limitations currently observed.

Theoretical Model of EphA2-Ephrin A1 Inhibition

This work aims at the theoretical description of EphA2-ephrin A1 inhibition by small molecules. Recently proposed ab initio-based scoring models, comprising long-range components of interaction energy, is tested on lithocholic acid class inhibitors of this protein–protein interaction (PPI) against common empirical descriptors. We show that, although limited to compounds with similar solvation energy, the ab initio model is able to rank the set of selected inhibitors more effectively than empirical scoring functions, aiding the design of novel compounds.

EphA2 Transmembrane Domain Is Uniquely Required for Keratinocyte Migration by Regulating Ephrin-A1 Levels

EphA2 receptor tyrosine kinase is activated by ephrin-A1 ligand, which harbors a glycosylphosphatidylinositol anchor that enhances lipid raft localization. Although EphA2 and ephrin-A1 modulate keratinocyte migration and differentiation, the ability of this cell-cell communication complex to localize to different membrane regions in keratinocytes remains unknown. Using a combination of biochemical and imaging approaches, we provide evidence that ephrin-A1 and a ligand-activated form of EphA2 partition outside of lipid raft domains in response to calcium-mediated cell-cell contact stabilization in normal human epidermal keratinocytes. EphA2 transmembrane domain swapping with a shorter and molecularly distinct transmembrane domain of EphA1 resulted in decreased localization of this receptor tyrosine kinase at cell-cell junctions and increased expression of ephrin-A1, which is a negative regulator of keratinocyte migration. Accordingly, altered EphA2 membrane distribution at cell-cell contacts limited the ability of keratinocytes to seal linear scratch wounds in vitro in an ephrin-A1-dependent manner. Collectively, these studies highlight a key role for the EphA2 transmembrane domain in receptor-ligand membrane distribution at cell-cell contacts that modulates ephrin-A1 levels to allow for efficient keratinocyte migration with relevance for cutaneous wound healing.

HIC1 and miR-23~27~24 clusters form a double-negative feedback loop in breast cancer

MicroRNAs (miRNAs) have emerged as a major regulator of the initiation and progression of human cancers, including breast cancer. However, the cooperative effects and transcriptional regulation of multiple miRNAs, especially miRNAs that are present in clusters, remain largely undiscovered. Here we showed that all members of the miR-23~27~24 clusters are upregulated and function as oncogenes in breast cancer and simultaneously target HIC1. Furthermore, we found that HIC1 functions as a transcriptional repressor to negatively control the expression of miR-23~27~24 clusters and forms a double-negative (overall positive) feedback loop. This feedback regulatory pathway is important because overexpression of miR-23~27~24 clusters can remarkably accelerate tumor growth, whereas restoration of HIC1 significantly blocks tumor growth in vivo. A mathematical model was created to quantitatively illustrate the regulatory circuit. Our finding highlights the cooperative effects of miRNAs in a cluster and adds another layer of complexity to the miRNA regulatory network. This study may also provide insight into the molecular mechanisms of breast cancer progression.

The SAM domain inhibits EphA2 interactions in the plasma membrane

All members of the Eph receptor family of tyrosine kinases contain a SAM domain near the C terminus, which has been proposed to play a role in receptor homotypic interactions and/or interactions with binding partners. The SAM domain of EphA2 is known to be important for receptor function, but its contribution to EphA2 lateral interactions in the plasma membrane has not been determined. Here we use a FRET-based approach to directly measure the effect of the SAM domain on the stability of EphA2 dimers on the cell surface in the absence of ligand binding. We also investigate the functional consequences of EphA2 SAM domain deletion. Surprisingly, we find that the EphA2 SAM domain inhibits receptor dimerization and decreases EphA2 tyrosine phosphorylation. This role is dramatically different from the role of the SAM domain of the related EphA3 receptor, which we previously found to stabilize EphA3 dimers and increase EphA3 tyrosine phosphorylation in cells in the absence of ligand. Thus, the EphA2 SAM domain likely contributes to a unique mode of EphA2 interaction that leads to distinct signaling outputs.

Lack of ephrin receptor A1 is a favorable independent prognostic factor in clear cell renal cell carcinoma

The EPH receptor tyrosine kinases and their cell-bound ligands, the ephrins, have been shown to be associated with cancer development and progression. In this study, mRNA and protein expression of the receptors EPHA1 and EPHA2 as well as of their ligand EFNA1 and their prognostic relevance in clear cell renal cell carcinoma was evaluated. Gene expression was measured in 75 cryo-preserved primary tumors and matched non-malignant renal specimens by quantitative PCR. Protein expression was analyzed by immunohistochemistry on tissue microarrays comprising non-malignant, primary tumors and metastatic renal tissues of 241 patients. Gene and protein expression of all three factors was altered in tumor specimens with EPHA1 and EPHA2 being generally diminished in tumors compared to normal renal tissue, whereas EFNA1 was commonly elevated. A positive EPHA1 and EPHA2 protein staining as well as a low EFNA1 protein level were significantly linked to more aggressive tumor features, but only a positive EPHA1 immunoreactivity was significantly associated with poor survival. In subgroup analyses, EPHA1 and EPHA2 protein levels were significantly higher in metastatic than in primary lesions. Patients with EPHA1/EPHA2-positive tumors or with tumors with positive EPHA1 and low EFNA1 immunoreactivity had the shortest survival rates compared to the respective other combinations. In a multivariate model, EPHA1 was an independent prognostic marker for different survival endpoints. In conclusion, an impaired EPH-ephrin signaling could contribute to the pathogenesis and progression of clear cell renal cell carcinoma.

Spatial organization of EphA2 at the cell-cell interface modulates trans-endocytosis of ephrinA1

EphA2 is a receptor tyrosine kinase (RTK) that is sensitive to spatial and mechanical aspects of the cell's microenvironment. Misregulation of EphA2 occurs in many aggressive cancers. Although its juxtacrine signaling geometry (EphA2's cognate ligand ephrinA1 is expressed on the surface of an apposing cell) provides a mechanism by which the receptor may experience extracellular forces, this also renders the system challenging to decode. By depositing living cells on synthetic supported lipid membranes displaying ephrinA1, we have reconstituted key features of the juxtacrine EphA2-ephrinA1 signaling system while maintaining the ability to perturb the spatial and mechanical properties of the membrane-cell interface with precision. In addition, we developed a trans-endocytosis assay to monitor internalization of ephrinA1 from a supported membrane into the apposing cell using a quantitative three-dimensional fluorescence microscopy assay. Using this experimental platform to mimic a cell-cell junction, we found that the signaling complex is not efficiently internalized when lateral reorganization at the membrane-cell contact sites is physically hindered. This suggests that EphA2-ephrinA1 trans-endocytosis is sensitive to the mechanical properties of a cell's microenvironment and may have implications in physical aspects of tumor biology.

Ephrin-A1 is up-regulated by hypoxia in cancer cells and promotes angiogenesis of HUVECs through a coordinated cross-talk with eNOS

Hypoxia, ephrin-A1 and endothelial nitric oxide synthase (eNOS) have been proved to play critical roles in tumor angiogenesis. However, how ephrin-A1 is regulated by hypoxia and whether ephrin-A1 cooperates with eNOS in modulation of angiogenesis remain to be addressed in details. Here we demonstrated that both ephrin-A1 in squamous cell carcinoma cells (SCC-9) and especially soluble ephrin-A1 in the supernatants were up-regulated under hypoxic condition. An increased nitric oxide (NO) production in human umbilical vein endothelial cells (HUVECs) was observed in ephrin-A1-induced angiogenesis which was reversed after co-culture with eNOS specific inhibitor, N-nitro-L-arginine methyl ester hydrochloride (L-NAME). Western blot analysis confirmed that both phosphorylation of Akt_Ser473 and eNOS_Ser1177 were up-regulated in ephrin-A1-stimulated HUVECs, with the total eNOS expression unchanged. The specific inhibitor of phosphatidylinositol 3-kinase (PI3K), LY294002, significantly down-regulated ephrin-A1-induced expression of phosphorylated Akt_Ser473 as well as phosphorylation of eNOS_Ser1177. These results revealed a possible novel mechanism whereby ephrin-A1 is regulated in tumor microenvironment and promotes angiogenesis through a coordinated cross-talk with PI3K/Akt-dependent eNOS activation which may relate to normal vascular development and tumor neovascularization.

Metabolite profiling of polyphenols in a Terminalia chebula Retzius ayurvedic decoction and evaluation of its chemopreventive activity

ETHNOPHARMACOLOGICAL RELEVANCE

The decoction of Terminalia chebula fruit is an ayurvedic remedy whose prolonged oral administration is prized as a generic intestinal and hepatic detoxifying agent. Its administration is suggested also under the perspective of a reduced risk of cancer, metabolic and cardiovascular diseases.

AIM OF THE STUDY

To evaluate the phytochemical profile and the chemopreventive potential of Terminalia chebula fruit decoction prepared according to the ayurvedic decoction recipe.

MATERIALS AND METHODS

The quali- and quantitative metabolite profiling of polyphenols was obtained using HPLC-UV/DAD and HPLC-ESI-MS. The crude decoction and purified compounds were tested for their capability to interact with the EphA2-ephrin-A1 system and for their antimutagenic properties against dietary and environmental mutagens (AA, 2-NF, NaN3, and heterocyclic amines IQ, MeIQ, MeIQx, Glu-P1, Glu-P2,) in the Ames-Salmonella/microsome assay, with and without enzymatic induction.

RESULTS

The decoction was found to contain 3,4,6-tri-O-galloyl-d-glucose (55.87 mg/g), chebulic acid (54.03 mg/g), β-punicalagin (41.25mg/g), corilagin (40.31 mg/g), α-punicalagin (35.55 mg/g), chebulagic acid (29.09 mg/g), gallic acid (27.96 mg/g) 1,3,4,6-tri-O-galloyl-β-d-glucose (24.25mg/g) chebulinic acid (20.23 mg/g), 1,2,3,4,6-penta-O-galloyl-d-glucose (13.53 mg/g), ellagic acid (8.00 mg/g), 1,6-di-O-galloyl-d-glucose (4.16 mg/g). An inhibitory effect was recorded in both Salmonella typhimurium TA98 and TA100 strains against the mutagenic activity of heterocyclic amines (22-61%), promutagen AA (91-97%) and directly acting mutagen 2-NF (52%) with but not against NaN3 (7%). Galloyl derivatives allowed an inhibition of mutagenicity induced by MeIQ above 80% at 0.01 mol/plate. Both decoction and purified compounds were able to modulate the EphA2-ephrinA1 system, suggesting a potential multiple chemopreventive mechanism.

CONCLUSIONS

The traditional ayurvedic decoction of Terminalia chebula may harbour a potential as a safe and low-cost chemopreventive agent at the intestinal level, if administered according to the ayurvedic specifications. Moreover, its recourse may enhance the presence of some polyphenolic constituents.

The EphA2 receptor drives self-renewal and tumorigenicity in stem-like tumor-propagating cells from human glioblastomas

In human glioblastomas (hGBMs), tumor-propagating cells with stem-like characteristics (TPCs) represent a key therapeutic target. We found that the EphA2 receptor tyrosine kinase is overexpressed in hGBM TPCs. Cytofluorimetric sorting into EphA2(High) and EphA2(Low) populations demonstrated that EphA2 expression correlates with the size and tumor-propagating ability of the TPC pool in hGBMs. Both ephrinA1-Fc, which caused EphA2 downregulation in TPCs, and siRNA-mediated knockdown of EPHA2 expression suppressed TPCs self-renewal ex vivo and intracranial tumorigenicity, pointing to EphA2 downregulation as a causal event in the loss of TPCs tumorigenicity. Infusion of ephrinA1-Fc into intracranial xenografts elicited strong tumor-suppressing effects, suggestive of therapeutic applications.

G-A variant in miR-200c binding site of EFNA1 alters susceptibility to gastric cancer

MicroRNAs (miRNAs) post-transcriptionally modulate gene expression by binding to complementary sites at 3'-untranslated regions (3'UTRs) of their target messenger RNAs (mRNAs). Genetic variations in miRNA binding sites may alter individual susceptibilities to many cancers. However, whether miRNA binding site single nucleotide polymorphisms (SNPs) interfere with gastric cancer (GC) susceptibility has not been reported. In this case-control study including 525 GC patients and 501 controls, we selected three miRNA binding site SNPs located in 3'UTRs of genes involved in GC to investigated their associations with GC susceptibility. We identified that rs12904 in ephrin-A1 (EFNA1) gene was significantly associated with risk of GC, with the OR for carrying AG or GG genotype being 0.65 (P = 0.002, OR 0.65; 95% CI, 0.50-0.85) compared with AA genotype. Specifically, we found that rs12904 is in strong linkage disequilibrium (LD) with rs4072037, a susceptibility variant reported by previous genome-wide association study (GWAS). No significant associations were observed for the other two SNPs (rs699517 in TYMS and rs1042542 in BIRC5). Furthermore, luciferase assays indicated EFNA1 as the target of hsa-miR-200c and rs12904 G > A change resulted in altered regulation of luciferase expression. In addition, rs12904 AA genotype was associated with increased expression of EFNA1 mRNA compared with AG or GG genotype in the cancer tissues from 48 patients. Taken together, these findings indicate that the miR-200c binding site SNP (rs12904 G > A) in the 3'UTR of EFNA1 can modulate EFNA1 expression and is associated with GC susceptibility. Larger replication studies are needed to confirm our findings.

Perturbation of the EphA2-EphrinA1 system in human prostate cancer cells by colonic (poly)phenol catabolites

The Eph tyrosine kinase receptors and their ephrin ligands play a central role in human cancer as their deregulated expression induces tumorigenesis with aggressive phenotypes. To evaluate their potential contribution to EphA2-ephrinA1 modulation, several colonic catabolites of dietary (poly)phenolics, known to be generated in vivo, were screened using an ELISA-based binding assay. Some of the catabolites inhibited the binding in a dose-dependent manner (IC(50) values from 0.26 to 43 μM). Functional studies on prostate adenocarcinoma cells revealed that pyrogallol and protocatechuic acid specifically antagonized ephrinA1-Fc-induced EphA2 phosphorylation at concentrations that were not cytotoxic. The active concentrations of pyrogallol appear to be close to what can be reached in vivo under physiological conditions. Finally, because of the roles played by the Eph-ephrin system not only in cancer development but also in neurodegeneration and diabetes, pyrogallol and protocatechuic acid are candidates for more detailed functional studies to elucidate their role in these pathophysiological processes.

Structure-activity relationships and mechanism of action of Eph-ephrin antagonists: interaction of cholanic acid with the EphA2 receptor

The Eph-ephrin system, including the EphA2 receptor and the ephrinA1 ligand, plays a critical role in tumor and vascular functions during carcinogenesis. We previously identified (3α,5β)-3-hydroxycholan-24-oic acid (lithocholic acid) as an Eph-ephrin antagonist that is able to inhibit EphA2 receptor activation; it is therefore potentially useful as a novel EphA2 receptor-targeting agent. Herein we explore the structure-activity relationships of a focused set of lithocholic acid derivatives based on molecular modeling investigations and displacement binding assays. Our exploration shows that while the 3-α-hydroxy group of lithocholic acid has a negligible role in recognition of the EphA2 receptor, its carboxylate group is critical for disrupting the binding of ephrinA1 to EphA2. As a result of our investigation, we identified (5β)-cholan-24-oic acid (cholanic acid) as a novel compound that competitively inhibits the EphA2-ephrinA1 interaction with higher potency than lithocholic acid. Surface plasmon resonance analysis indicates that cholanic acid binds specifically and reversibly to the ligand binding domain of EphA2, with a steady-state dissociation constant (K(D) ) in the low micromolar range. Furthermore, cholanic acid blocks the phosphorylation of EphA2 as well as cell retraction and rounding in PC3 prostate cancer cells, two effects that depend on EphA2 activation by the ephrinA1 ligand. These findings suggest that cholanic acid can be used as a template structure for the design of effective EphA2 antagonists, and may have potential impact in the elucidation of the role played by this receptor in pathological conditions.

[Expression of EphA2 and EphrinA1 in human renal cell carcinoma and its relationship with angiogenesis]

OBJECTIVE

To investigate the expression of EphA2 and EphrinA1 and its relationship with angiogenesis in renal cell carcinoma and its relevance to clinicopathologic features.

METHODS

The expression of the EphA2 and EphrinA1 was detected by immunohistochemistry (IHC) in the tissues samples from 68 renal cell carcinomas and 24 normal kidneys, and quantitatively analyzed. The microvessel density (MVD) was determined by CD34 immunostaining of microvascular endothelial cells. Statistical analysis was performed using the software SPSS (version 13.0).

RESULTS

The expression of EphA2, EphrinA1 and MND in the cancerous tissues were significantly higher (P<0.01) than that in the normal ones. Significantly increased expression of EphA2, EphrinA1 and MVD (P<0.01) was detected in cancer tissues with higher grade differentiation, more advanced stage and more lymph node metastasis, respectively (P<0.05 for each group). Expression of the EphA2 and EphrinA1 protein was shown to be positively associated with the MVD assessed by Spearman's correlation and factor analysis (r=0.555, r=0.485, P<0.01). The MVD was also significantly correlated with the diameter of the tumor (P<0.01).

CONCLUSION

EphA2 and EphrinA1 are highly expressed in renal cell carcinoma, and positively correlated with histological differentiation, clinical stage and angiogenesis in the cancer.

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.

Identification and functional analysis of phosphorylated tyrosine residues within EphA2 receptor tyrosine kinase

EphA2 is a member of the Eph family of receptor tyrosine kinases. EphA2 mediates cell-cell communication and plays critical roles in a number of physiological and pathologic responses. We have previously shown that EphA2 is a key regulator of tumor angiogenesis and that tyrosine phosphorylation regulates EphA2 signaling. To understand the role of EphA2 phosphorylation, we have mapped phosphorylated tyrosines within the intracellular region of EphA2 by a combination of mass spectrometry analysis and phosphopeptide mapping using two-dimensional chromatography in conjunction with site-directed mutagenesis. The function of these phosphorylated tyrosine residues was assessed by mutational analysis using EphA2-null endothelial cells reconstituted with EphA2 tyrosine-to-phenylalanine or tyrosine-to-glutamic acid substitution mutants. Phosphorylated Tyr(587) and Tyr(593) bind to Vav2 and Vav3 guanine nucleotide exchange factors, whereas Tyr(P)(734) binds to the p85 regulatory subunit of phosphatidylinositol 3-kinase. Mutations that uncouple EphA2 with Vav guanine nucleotide exchange factors or p85 are defective in Rac1 activation and cell migration. Finally, EphA2 mutations in the juxtamembrane region (Y587F, Y593F, Y587E/Y593E), kinase domain (Y734F), or SAM domain (Y929F) inhibited ephrin-A1-induced vascular assembly. In addition, EphA2-null endothelial cells reconstituted with these mutants were unable to incorporate into tumor vasculature, suggesting a critical role of these phosphorylation tyrosine residues in transducing EphA2 signaling in vascular endothelial cells during tumor angiogenesis.

Expression and prognostic significance of a panel of tissue hypoxia markers in head-and-neck squamous cell carcinomas

PURPOSE

To investigate the expression pattern of hypoxia-induced proteins identified as being involved in malignant progression of head-and-neck squamous cell carcinoma (HNSCC) and to determine their relationship to tumor pO(2) and prognosis.

METHODS AND MATERIALS

We performed immunohistochemical staining of hypoxia-induced proteins (carbonic anhydrase IX [CA IX], BNIP3L, connective tissue growth factor, osteopontin, ephrin A1, hypoxia inducible gene-2, dihydrofolate reductase, galectin-1, IkappaB kinase beta, and lysyl oxidase) on tumor tissue arrays of 101 HNSCC patients with pretreatment pO(2) measurements. Analysis of variance and Fisher's exact tests were used to evaluate the relationship between marker expression, tumor pO(2), and CA IX staining. Cox proportional hazard model and log-rank tests were used to determine the relationship between markers and prognosis.

RESULTS

Osteopontin expression correlated with tumor pO(2) (Eppendorf measurements) (p = 0.04). However, there was a strong correlation between lysyl oxidase, ephrin A1, and galectin-1 and CA IX staining. These markers also predicted for cancer-specific survival and overall survival on univariate analysis. A hypoxia score of 0-5 was assigned to each patient, on the basis of the presence of strong staining for these markers, whereby a higher score signifies increased marker expression. On multivariate analysis, increasing hypoxia score was an independent prognostic factor for cancer-specific survival (p = 0.015) and was borderline significant for overall survival (p = 0.057) when adjusted for other independent predictors of outcomes (hemoglobin and age).

CONCLUSIONS

We identified a panel of hypoxia-related tissue markers that correlates with treatment outcomes in HNSCC. Validation of these markers will be needed to determine their utility in identifying patients for hypoxia-targeted therapy.

Ephrin-A1 stimulates migration of CD8+CCR7+ T lymphocytes

We have previously demonstrated that binding of ephrin-A1 to Eph receptors on human CD4+ T cells stimulates migration. Here, we show that a distinct population of CD8+ T lymphocytes, expressing the chemokine receptor CCR7, also binds ephrin-A1 and is stimulated to migrate after binding. The Eph receptor signaling pathway taking part in the migration event was here investigated. Induced tyrosine phosphorylation of several proteins was seen after ephrin-A1 binding. In particular, induced phosphorylation and kinase activity of the Src kinase family member Lck was observed. An Lck inhibitor inhibited ephrin-A1-induced migration, indicating the involvement of Lck in the migration event. In addition, we observed an induced association of the focal adhesion-like kinase proline-rich tyrosine kinase 2 (Pyk2) and the guanidine exchange factor Vav1 with Lck. PI3K inhibitors also inhibited migration, and studies in transfectants indicate an association of PI3K with EphA1. Further, ephrin-A1-induced migration could be related to the activation of Rho GTPases. This was also observed by using an inhibitor of the Rho-associated kinase ROCK, a downstream effector of Rho. Our results suggest that stimulation of Eph receptors on CD8+CCR7+ T cells leads to migration involving activation of Lck, Pyk2, PI3K, Vav1 and Rho GTPase.

Increased expression of ephrin A1 in brain arteriovenous malformation: DNA microarray analysis

A number of previous studies have revealed the abnormal expression of various angiogenesis-related genes or products in brain arteriovenous malformation (AVM). To understand the molecular process of this disease, we analyzed gene expression profiles in brain AVM. Using a DNA microarray consisting of 17,086 genes, we identified differentially expressed genes in 5 brain AVMs from their draining veins, vessels retaining basic venous architecture. Not many genes were differentially expressed between the AVM nidus and the draining vein. When we applied an absolute cut-off value for normalized log2 (cy5/cy3 ratio) of 0.4, 19 genes were selected. Genes such as SOX8, TRIM2, FENA1 (ephrin A1), and AQP4 were upregulated, and genes such as I_1000105, KRT18, IGFBP7, EMILIN-2, and KRT14 were downregulated. Genes relating to angiogenesis, such as vascular endothelial growth factor and angiopoietin and other members of the ephrin family, were not differentiated. Among differentially expressed genes detected in this analysis, we focused on ephrin A1, a gene related to embryogenesis and angiogenesis. The expression of ephrin A1 was two and three to nine times higher than that of the draining vein and normal brain, respectively, using real-time reverse transcription-polymerase chain reaction. For the first time, here we report the increased expression of ephrin A1 in brain AVM, which may play an important role in the pathogenesis of AVM.

EphrinA1 activates a Src/focal adhesion kinase-mediated motility response leading to rho-dependent actino/myosin contractility

Eph receptors and ephrin ligands are widely expressed in epithelial cells and mediate cell repulsive motility through heterotypic cell-cell interactions. Several Ephs, including EphA2, are greatly overexpressed in certain tumors, in correlation with poor prognosis and high vascularity in cancer tissues. The ability of several Eph receptors to regulate cell migration and invasion likely contribute to tumor progression and metastasis. We report here that in prostatic carcinoma cells ephrinA1 elicits a repulsive response that is executed through a Rho-dependent actino/myosin contractility activation, ultimately leading to retraction of the cell body. This appears to occur through assembly of an EphA2-associated complex involving the two kinases Src and focal adhesion kinase (FAK). EphrinA1-mediated repulsion leads to the selective phosphorylation of Tyr-576/577 of FAK, enhancing FAK kinase activity. The repulsive response elicited by ephrinA1 in prostatic carcinoma cells is mainly driven by a Rho-mediated phosphorylation of myosin light chain II, in which Src and FAK activation are required steps. Consequently, Src and FAK are upstream regulators of the overall response induced by ephrinA1/EphA2, instructing cells to retract the cell body and to move away, probably facilitating dissemination and tissue invasion of ephrin-sensitive carcinomas.

[Expression and clinical significance of Ephrin-A1 in primary hepatocellular carcinoma]

OBJECTIVE

To investigate the expression and clinical significance of Ephrin-A1 mRNA and protein expression level in hepatocellular carcinoma.

METHODS

Reverse transcription polymerase chain reaction (RT-PCR) and immunohistochemistry technique were used to detect the expression of the Ephrin-A1 mRNA and protein of 40 cases of hepatocellular carcinoma and their corresponding para-cancerous tissues and 10 cases of normal liver tissues. The relationships with its clinical pathology characters were analyzed.

RESULTS

The mRNA of Ephrin-A1 was expressed in all of the 40 cases of hepatocellular carcinoma and their corresponding para-cancerous tissues and 10 cases of normal liver tissues. Semiquantitative analysis showed that the mRNA expression level of Ephrin-A1 in hepatocellular carcinoma (0.5413 +/- 0.1527) was greater than that in corresponding para-cancerous tissues (0.3895 +/- 0.0549, P < 0.05) and normal liver tissues (0.3770 +/- 0.1055, P < 0.05); but between corresponding para-cancerous tissues (0.3895 +/- 0.0549) and normal liver tissues (0.3770 +/- 0.1055), the mRNA expression level had no significant difference (P > 0.05). The positive rates of Ephrin-A1 protein were 20% (2/10) in normal tissues, 35% (14/40) in para-cancerous tissues and 62% (25/40) in hepatocellular carcinoma tissues, respectively; the protein expression level of Ephrin-A1 was gradually rising (chi(2) = 14.762, P < 0.05). The overexpression of Ephrin-A1 protein was correlated with histological differentiation, tumor thrombi in portal vein and lymph node metastasis (P < 0.05).

CONCLUSIONS

The overexpression of Ephrin-A1 protein is correlated with histological differentiation, the lymph node metastasis and tumor thrombi in portal vein. It indicates that Ephrin-A1 may play an important role in the malignancy transformation, invasion progression and metastasis of hepatocellular carcinoma.

Nucleosome recognition by the Piccolo NuA4 histone acetyltransferase complex

The mechanisms by which multisubunit histone acetyltransferase (HAT) complexes recognize and perform efficient acetylation on nucleosome substrates are largely unknown. Here, we use a variety of biochemical approaches and compare histone-based substrates of increasing complexity to determine the critical components of nucleosome recognition by the MOZ, Ybf2/Sas3, Sas2, Tip60 family HAT complex, Piccolo NuA4 (picNuA4). We find the histone tails to be dispensable for binding to both nucleosomes and free histones and that the H2A, H3, and H2B tails do not influence the ability of picNuA4 to tetra-acetylate the H4 tail within the nucleosome. Most notably, we discovered that the histone-fold domain (HFD) regions of histones, particularly residues 21-52 of H4, are critical for tight binding and efficient tail acetylation. Presented evidence suggests that picNuA4 recognizes the open surface of the nucleosome on which the HFD of H4 is located. This binding mechanism serves to direct substrate access to the tails of H4 and H2A and allows the enzyme to be "tethered", thereby increasing the effective concentration of the histone tail and permitting successive cycles of H4 tail acetylation.

Profiling the Sulfation Specificities of Glycosaminoglycan Interactions with Growth Factors and Chemotactic Proteins Using Microarrays

We report a carbohydrate microarray-based approach for the rapid, facile analysis of glycosaminoglycan-protein interactions. The key structural determinants responsible for protein binding, such as sulfate groups that participate in the interactions, were elucidated. Specificities were also readily compared across protein families or functional classes, and comparisons among glycosaminoglycan subclasses provided a more comprehensive understanding of protein specificity. To validate the approach, we showed that fibroblast growth factor family members have distinct sulfation preferences. We also demonstrated that heparan sulfate and chondroitin sulfate interact in a sulfation-dependent manner with various axon guidance proteins, including slit2, netrin1, ephrinA1, ephrinA5, and semaphorin5B. We anticipate that these microarrays will accelerate the discovery of glycosaminoglycan-binding proteins and provide a deeper understanding of their roles in regulating diverse biological processes.

Redox regulation of ephrin/integrin cross-talk

Interactions linking the Eph receptor tyrosine kinase and ephrin ligands transduce short-range repulsive signals regulating several motile biological processes including axon path-finding, angiogenesis and tumor growth. These ephrin-induced effects are believed to be mediated by alterations in actin dynamics and cytoskeleton reorganization. The members of the small Rho GTPase family elicit various effects on actin structures and are probably involved in Eph receptor-induced actin modulation. In particular, some ephrin ligands lead to a decrease in integrin-mediated cell adhesion and spread. Here we show that the ability of ephrinA1 to inhibit cell adhesion and spreading in prostatic carcinoma cells is strictly dependent on the decrease in the activity of the small GTPase Rac1. Given the recognized role of Rac-driven redox signaling for integrin function, reported to play an essential role in focal adhesion formation and in the overall organization of actin cytoskeleton, we investigated the possible involvement of oxidants in ephrinA1/EphA2 signaling. We now provide evidence that Reactive Oxygen Species are an integration point of the ephrinA1/integrin interplay. We identify redox circuitry in which the ephrinA1-mediated inhibition of Rac1 leads to a negative regulation of integrin redox signaling affecting the activity of the tyrosine phosphatase LMW-PTP. The enzyme in turn actively dephosphorylates its substrate p190RhoGAP, finally leading to RhoA activation. Altogether our data suggest a redox-based Rac-dependent upregulation of Rho activity, concurring with the inhibitory effect elicited by ephrinA1 on integrin-mediated adhesion strength.

Expression of EphA2 and EphrinA-1 in vulvar carcinomas and its relation to prognosis

AIMS

To examine the expression of EphA2 and EphrinA-1 in vulvar squamous cell carcinomas and investigate their prognostic relevance.

METHODS

Tumours from 224 patients with vulvar squamous cell carcinomas were investigated for expression of EphA2 and EphrinA-1 using single and double immunostaining methods.

RESULTS

High expression (strong/moderate staining intensity) of EphA2 and EphrinA-1 was observed in 114 (51%) and 126 (56%) vulvar carcinomas, respectively. In the three cases tested using the double immunostaining method, colocalisation of EphA2 and EphrinA-1 proteins was identified in the same neoplastic cells. High EphA2 expression was significantly correlated to high expression of EphrinA-1 (p<0.01) and cyclin A (p<0.01), large tumour size (p = 0.03), deep invasion (p<0.01) and higher FIGO stage (p = 0.05). A correlation between high EphrinA-1 expression and high levels of cyclin A (p<0.01) and p21 (p<0.01), deep invasion (p<0.01) and higher FIGO stage (p = 0.01) was also seen. In univariate analysis, high expression of EphrinA-1 was associated with poor survival (p = 0.03). However, in the multivariate analysis neither EphrinA-1 nor EphA2 were significantly correlated to survival.

CONCLUSIONS

EphA2 and EphrinA-1 were overexpressed in 51% and 56% of the vulvar squamous cell carcinomas, respectively, and high levels of EphA2 and EphrinA-1 proteins were associated with deep tumour invasion and high FIGO stage. However, EphA2 and EphrinA-1 were not independently associated with clinical outcome in vulvar carcinomas.

Expression analysis of the Epha1 receptor tyrosine kinase and its high-affinity ligands Efna1 and Efna3 during early mouse development

Interaction of Eph receptor tyrosine kinases with their membrane bound ephrin ligands initiates bidirectional signaling events that regulate cell migratory and adhesive behavior. Whole-mount in situ hybridization revealed overlapping expression of the Epha1 receptor and its high-affinity ligands ephrin A1 (Efna1) and ephrin A3 (Efna3) in the primitive streak and the posterior paraxial mesoderm during early mouse development. These results show complex and dynamic expression for all three genes with expression domains that are successively complementary, overlapping, and divergent.

EphrinA1 inhibits vascular endothelial growth factor-induced intracellular signaling and suppresses retinal neovascularization and blood-retinal barrier breakdown

The Eph receptor/ephrin system is a recently discovered regulator of vascular development during embryogenesis. Activation of EphA2, one of the Eph receptors, reportedly suppresses cell proliferation and adhesion in a wide range of cell types, including vascular endothelial cells. Vascular endothelial growth factor (VEGF) plays a primary role in both pathological angiogenesis and abnormal vascular leakage in diabetic retinopathy. In the study described herein, we demonstrated that EphA2 stimulation by ephrinA1 in cultured bovine retinal endothelial cells inhibits VEGF-induced VEGFR2 receptor phosphorylation and its downstream signaling cascades, including PKC (protein kinase C)-ERK (extracellular signal-regulated kinase) 1/2 and Akt. This inhibition resulted in the reduction of VEGF-induced angiogenic cell activity, including migration, tube formation, and cellular proliferation. These inhibitory effects were further confirmed in animal models. Intraocular injection of ephrinA1 suppressed ischemic retinal neovascularization in a dose-dependent manner in a mouse model. At a dose of 125 ng/eye, the inhibition was 36.0 +/- 14.9% (P < 0.001). EphrinA1 also inhibited VEGF-induced retinal vascular permeability in a rat model by 46.0 +/- 10.0% (P < 0.05). These findings suggest a novel therapeutic potential for EphA2/ephrinA1 in the treatment of neovascularization and vasopermeability abnormalities in diabetic retinopathy.

Ischemic preconditioning modulates the expression of several genes, leading to the overproduction of IL-1Ra, iNOS, and Bcl-2 in a human model of liver ischemia-reperfusion

Ischemia triggers an inflammatory response that precipitates cell death during reperfusion. Several studies have shown that tissues are protected by ischemic preconditioning (IP) consisting of 10 min of ischemia followed by 10 min of reperfusion just before ischemia. The molecular basis of this protective effect is poorly understood. We used cDNA arrays (20K) to compare global gene expression in liver biopsies from living human liver donors who underwent IP (n=7) or not (n=7) just before liver devascularization. Microarray data were analyzed using pairedt test with a type I error rate fixed at alpha = 2.5 10(6) (Bonferroni correction). We found that 60 genes were differentially expressed (36 over- and 24 underexpressed in preconditioning group). After IP, the most significantly overexpressed gene was IL-1Ra. This was confirmed by immunoblotting. Differentially expressed were genes involved in apoptosis (NOD2, ephrin-A1, and calpain) and in the carbohydrate metabolism. A significant increase in the amount of the anti-apoptotic protein Bcl-2 in preconditioned livers but no change in the cleavage of procaspase-3, -8, and -9 was observed. We also observed an increase in the amount in the inducible nitric oxide synthase. Therefore, the benefits of IP may be associated with the overproduction of IL-1Ra, Bcl-2, and NO countering the proinflammatory and proapoptotic effects generated during ischemia-reperfusion.

Expression of EphA2 and Ephrin A-1 in carcinoma of the urinary bladder

PURPOSE

The EphA2 receptor tyrosine kinase is believed to play a role in tumor growth and metastasis. The clinical significance of the expression of EphA2 was observed in breast, prostate, colon, skin, cervical, ovarian, and lung cancers. The purpose of this work was to determine the expression of EphA2 and its ligand, Ephrin A-1, and E-cadherin in carcinoma of the urinary bladder, and determine EphA2 as a new target for therapy in bladder cancer.

EXPERIMENTAL DESIGN

EphA2 mRNA and protein expression was investigated by reverse transcription-PCR and Western blot, respectively, in bladder cancer cell lines. In addition, the expression of EphA2, Ephrin A-1, and E-cadherin in tissues from patients with different stages of urinary bladder cancer was determined by immunohistochemistry. Furthermore, the ability of Ephrin A-1 to inhibit growth of bladder cancer cells was also investigated using an adenoviral delivery system.

RESULTS

Western blot analysis showed high EphA2 expression in TCCSUP, T24, and UMUC-3 cell lines. In tissues, the staining intensity of EphA2 was less in normal urothelium but increased greatly in advancing stages of urothelial carcinoma (P < 0.05). Similarly, the staining intensity of Ephrin A-1 was low in normal tissues and high in cancerous tissues, but it was similar across the various stages of urothelial carcinoma (T(a)-T(4)). E-cadherin immunoreactivity decreased in urothelial cancer. Association of EphA2 and Ephrin A-1 expression was found to be significant between T(a) stage and T(1)-T(2) (P < 0.04) and T(a) and T(3)-T(4) stages (P < 0.0001). Adenovirus delivery of Ephrin A-1 inhibited proliferation of TCCSUP cells.

CONCLUSION

EphA2 may serve as a novel target for bladder cancer therapy.

VE-cadherin regulates EphA2 in aggressive melanoma cells through a novel signaling pathway: implications for vasculogenic mimicry

The formation of matrix-rich, vasculogenic-like networks, termed vasculogenic mimicry (VM), is a unique process characteristic of highly aggressive melanoma cells found to express genes previously thought to be exclusively associated with endothelial and epithelial cells. This study contributes new observations demonstrating that VE-cadherin can regulate the expression of EphA2 at the cell membrane by mediating its ability to become phosphorylated through interactions with its membrane bound ligand, ephrin-A1. VE-cadherin and EphA2 were also found to be colocalized in cell-cell adhesion junctions, both in vitro and in vivo. Immunoprecipitation studies revealed that EphA2 and VE-cadherin could interact, directly and/or indirectly, during VM. Furthermore, there was no change in the colocalization of EphA2 and VE-cadherin at cell-cell adhesion sites when EphA2 was phosphorylated on tyrosine residues. Although transient knockout of EphA2 expression did not alter VE-cadherin localization, transient knockout of VE-cadherin expression resulted in the reorganization of EphA2 on the cells' surface, an accumulation of EphA2 in the cytoplasm, and subsequent dephosphorylation of EphA2. Collectively, these results suggest that VE-cadherin and EphA2 act in a coordinated manner as a key regulatory element in the process of melanoma VM and illuminate a novel signaling pathway that could be potentially exploited for therapeutic intervention.

EphA2 as a novel molecular marker and target in glioblastoma multiforme

We investigated the presence of EphA2, and its ligand, ephrinA1, in glioblastoma multiforme (GBM), a malignant neoplasm of glial cells, and normal brain. We also initially examined the functional importance of the interaction between EphA2 and ephrinA1 in glioma cells. Expression and localization of EphA2 and ephrinA1 in human GBM and normal brain were examined using Western blotting, immunofluorescence, and immunohistochemistry. A functional role for EphA2 was investigated by assessing the activation status of the receptor and the effect of ephrinA1 on the anchorage-independent growth and invasiveness of GBM cells. We found EphA2 to be elevated in approximately 90% of GBM specimens and cell lines but not in normal brain, whereas ephrinA1 was present at consistently low levels in both GBM and normal brain. EphA2 was activated and phosphorylated by ephrinA1 in GBM cells. Furthermore, ephrinA1 induced a prominent, dose-dependent inhibitory effect on the anchorage-independent growth and invasiveness of GBM cells highly overexpressing EphA2, which was not seen in cells expressing low levels of the receptor. Thus, EphA2 is both specifically overexpressed in GBM and expressed differentially with respect to its ligand, ephrinA1, which may reflect on the oncogenic processes of malignant glioma cells. EphA2 seems to be functionally important in GBM cells and thus may play an important role in GBM pathogenesis. Hence, EphA2 represents a new marker and novel target for the development of molecular therapeutics against GBM.

Impaired tumor microenvironment in EphA2-deficient mice inhibits tumor angiogenesis and metastatic progression

EphA2 belongs to a unique family of receptor tyrosine kinases that play critical roles in development and disease. Since EphA2 is required for ephrin-A1 ligand-induced vascular remodeling and is overexpressed in a variety of vascularized human adenocarcinomas, we assessed tumor angiogenesis and metastatic progression in EphA2-deficient host animals. 4T1 metastatic mammary adenocarcinoma cells transplanted subcutaneously and orthotopically into EphA2-deficient female mice displayed decreased tumor volume, tumor cell survival, microvascular density, and lung metastasis relative to tumor-bearing littermate controls. To determine if the phenotype in EphA2-deficient mice was endothelial cell intrinsic, we also analyzed endothelial cells isolated from EphA2-deficient animals for their ability to incorporate into tumor vessels in vivo, as well as to migrate in response to tumor-derived signals in vitro. EphA2-deficient endothelial cells displayed impaired survival and failed to incorporate into tumor microvessels in vivo, and displayed impaired tumor-mediated migration in vitro relative to controls. These data suggest that host EphA2 receptor tyrosine kinase function is required in the tumor microenvironment for tumor angiogenesis and metastatic progression.

A conditional feedback loop regulates Ras activity through EphA2

The EphA2 receptor tyrosine kinase is frequently overexpressed in many cancers, including 40% of breast cancers. Here, we show that EphA2 is a direct transcriptional target of the Ras-Raf-MAPK pathway and that ligand-stimulated EphA2 attenuates the growth factor-induced activation of Ras. Thus, a negative feedback loop is created that regulates Ras activity. Interestingly, the expression of EphA2 and ephrin-A1 is mutually exclusive in a panel of 28 breast cancer cell lines. We show that the MAPK pathway inhibits ephrin-A1 expression, and the ligand expression inhibits EphA2 levels contributing to the receptor-ligand reciprocal expression pattern in these cell lines. Our results suggest that an escape from the negative effects of this interaction may be important in the development of cancer.

Ephrin-A1 expression contributes to the malignant characteristics of {alpha}-fetoprotein producing hepatocellular carcinoma

BACKGROUND AND AIMS

alpha-Fetoprotein (AFP), a tumour marker for hepatocellular carcinoma (HCC), is associated with poor prognosis. Using cDNA microarray analysis, we previously found that ephrin-A1, an angiogenic factor, is the most differentially overexpressed gene in AFP producing hepatoma cell lines. In the present study, we investigated the significance of ephrin-A1 expression in HCC.

METHODS

We examined ephrin-A1 expression and its effect on cell proliferation and gene expression in five AFP producing hepatoma cell lines, three AFP negative hepatoma cell lines, and 20 human HCC specimens.

RESULTS

Ephrin-A1 expression levels were lowest in normal liver tissue, elevated in cirrhotic tissue, and further elevated in HCC specimens. Ephrin-A1 expression was strongly correlated with AFP expression (r = 0.866). We showed that ephrin-A1 induced expression of AFP. This finding implicates ephrin-A1 in the mechanism of AFP induction in HCC. Ephrin-A1 promoted the proliferation of ephrin-A1 underexpressing HLE cells, and an ephrin-A1 antisense oligonucleotide inhibited the proliferation of ephrin-A1 overexpressing Huh7 cells. Thus ephrin-A1 affects hepatoma cell growth. cDNA microarray analysis showed that ephrin-A1 induced expression of genes related to the cell cycle (p21), angiogenesis (angiopoietin 1 and thrombospondin 1), and cell-cell interactions (Rho, integrin, and matrix metalloproteinases) in cultured hepatoma cells. These ephrin-A1 induced genes are also activated in HCC tissues that overexpress AFP.

CONCLUSION

These findings suggest that the poor prognosis of patients with AFP producing HCC is partially caused by ephrin-A1 expression, which induces expression of genes related to tumour cell growth, angiogenesis, invasion, and metastasis.

Ephrin-A1 binding to CD4+ T lymphocytes stimulates migration and induces tyrosine phosphorylation of PYK2

Eph receptors, the largest subfamily of receptor tyrosine kinases, and their ephrin ligands are important mediators of cell-cell communication regulating cell attachment, shape, and mobility. Here we demonstrate that CD4+ T lymphocytes express the EphA1 and EphA4 receptors and that these cells bind the ligand ephrin-A1. Further we show ephrin-A1 expression in vivo on high endothelial venule (HEV) endothelial cells. Ephrin-A1 binding to CD4+ T cells stimulates both stromal cell-derived factor 1α (SDF-1α)- and macrophage inflammatory protein 3β (MIP3β)-mediated chemotaxis. In line with the increased chemotactic response, increased actin polymerization is observed in particular with the combination of ephrin-A1 and SDF-1α. Signaling through EphA receptors induces intracellular tyrosine phosphorylation. In particular, proline-rich tyrosine kinase 2 (PYK2) is phosphorylated on tyrosine residues 402 and 580. Ephrin-A1-induced chemotaxis and intracellular tyrosine phosphorylation, including EphA1 and Pyk2, was inhibited by Tyrphostin-A9. In conclusion, ligand engagement of EphA receptors on CD4+ T cells stimulates chemotaxis, induces intracellular tyrosine phosphorylation, and affects actin polymerization. This, together with our finding that ephrin-A1 is expressed by HEV endothelial cells, suggests a role for Eph receptors in transendothelial migration.

Expression of Eph receptors and their ligands, ephrins, during lipopolysaccharide fever in rats

Erythropoietin-producing hepatocellular (Eph) receptor tyrosine kinases and their ligands, ephrins, are involved in embryogenesis and oncogenesis by mediating cell adhesion and migration. Although ephrins can be induced by bacterial LPS in vitro, whether they are involved in inflammation in vivo is unknown. Using differential mRNA display, we found that a febrigenic dose of LPS (50 microg/kg iv) induces a strong transcriptional upregulation of ephrin-A1 in rat liver. We confirmed this finding by real-time RT-PCR. We then quantified the mRNA expression of different ephrins and Eph receptors at phases 1-3 of LPS fever in different organs. Febrile phases 2 (90 min post-LPS) and 3 (300 min) were characterized by robust upregulation (up to 16-fold) and downregulation (up to 21-fold) of several ephrins and Eph receptors. With the exception of EphA2, which showed upregulation in the brain at phase 2, expressional changes of Eph receptors and ephrins were limited to the LPS-processing organs: liver and lung. Characteristic, counter-directed changes in expressional regulation of Eph receptors and their corresponding ligands were found: upregulation of EphA2, downregulation of ephrin-A1 in the liver and lung at phase 2; downregulation of EphB3, upregulation of ephrin-B2 in the liver at phase 2; downregulation of EphA1 and EphA3, upregulation of ephrins-A1 and -A3 in liver at phase 3. In the liver, transcriptional changes of EphA2 and EphB3 at phase 2 were confirmed at protein level. These coordinated, phase-specific responses suggest that different sets of ephrins and Eph receptors may be involved in cellular events (such as disruption of tissue barriers and leukocyte transmigration) underlying different stages of systemic inflammatory response to LPS.

Ephrin-A1 suppresses Th2 cell activation and provides a regulatory link to lung epithelial cells

Gene expression screening showed decreased ephrin-A1 expression in CD4+ T cells of asthma patients. Ephrin-A1 is the ligand of the Eph receptor family of tyrosine kinases, forming the largest family of receptor tyrosine kinases. Their immune regulatory properties are largely unknown. This study demonstrates significantly reduced ephrin-A1 expression in T cells of asthma patients using real time-PCR. Immunohistological analyses revealed strong ephrin-A1 expression in lung tissue and low expression in cortical areas of lymph nodes. It is absent in T cell/B cell areas of the spleen. Colocalization of ephrin-A1 and its receptors was found only in the lung, but not in lymphoid tissues. In vitro activation of T cells reduced ephrin-A1 at mRNA and protein levels. T cell proliferation, activation-induced, and IL-2-dependent cell death were inhibited by cross-linking ephrin-A1, and not by engagement of Eph receptors. However, anti-EphA1 receptor slightly enhances Ag-specific and polyclonal proliferation of PBMC cultures. Furthermore, activation-induced CD25 up-regulation was diminished by ephrin-A1 engagement. Ephrin-A1 engagement reduced IL-2 expression by 82% and IL-4 reduced it by 69%; the IFN-gamma expression remained unaffected. These results demonstrate that ephrin-A1 suppresses T cell activation and Th2 cytokine expression, while preventing activation-induced cell death. The reduced ephrin-A1 expression in asthma patients may reflect the increased frequency of activated T cells in peripheral blood. That the natural ligands of ephrin-A1 are most abundantly expressed in the lung may be relevant for Th2 cell regulation in asthma and Th2 cell generation by mucosal allergens.

Identification of the Jak/Stat Proteins as Novel Downstream Targets of EphA4 Signaling in Muscle

Eph receptors and their cognate ligands ephrins are important players in axon guidance and neural patterning during development of the nervous system. Much of our knowledge about the signal transduction pathways triggered by Eph receptors has been related to the modulation of actin cytoskeleton, which is fundamental in mediating the cellular responses in growth cone navigation, cell adhesion, and cell migration. In contrast, little was known about whether long term activation of Eph receptor would regulate gene expression. Here we report a novel signaling pathway of EphA4, which involves activation of the tyrosine kinase Jak2 and the transcriptional activator Stat3. Transfection of COS7 cells with EphA4, but not the kinase-dead mutant, induced tyrosine phosphorylation of Jak2, Stat1, and Stat3. Treatment of cultured C2C12 myotubes with ephrin-A1 also induced tyrosine phosphorylation of Stat3, which was abolished by the Jak2 inhibitor AG490. Moreover, Jak2 was co-immunoprecipitated with EphA4 in muscle, and both proteins were concentrated at the neuromuscular junction (NMJ) of adult muscle. By using microarray analysis, we have identified acetylcholinesterase, the critical enzyme that hydrolyzed the neurotransmitter acetylcholine at the NMJ, as a downstream target gene of the Jak/Stat pathway in muscle. More importantly, ephrin-A1 increased the expression of acetylcholinesterase protein in C2C12 myotubes, which was abolished by AG490. In contrast, ephrin-A1 reduced the expression of fibronectin mRNA in C2C12 myotubes independently of Jak2. Finally, the expression level of acetylcholinesterase in limb muscle of EphA4 null mice was significantly reduced compared with the wild-type control. Taken together, these results have identified Jak/Stat proteins as the novel downstream targets of EphA4 signaling. In addition, the present study provides the first demonstration of a potential function of Eph receptors and Jak/Stat proteins at the NMJ.

EphA2 receptor tyrosine kinase regulates endothelial cell migration and vascular assembly through phosphoinositide 3-kinase-mediated Rac1 GTPase activation

Angiogenesis is critical for vascular remodeling during development and contributes to the pathogenesis of diseases such as cancer. Targeted disruption of several EphB class receptor tyrosine kinases results in vascular remodeling defects during embryogenesis. The role of EphA class receptors in vascular remodeling, however, is not well-characterized. We recently demonstrated that global inhibition of EphA receptors disrupts endothelial migration induced by ephrin, VEGF or tumor-derived signals, though the specific target remained undefined. Here, we report that EphA2 regulates endothelial cell assembly and migration through phosphoinositide (PI) 3-kinase-mediated activation of Rac1 GTPase in two model systems: primary bovine and murine pulmonary microvascular endothelial cells. EphA2-deficient endothelial cells fail to undergo vascular assembly and migration in response to ephrin-A1 in vitro. Ephrin-A1 stimulation induces PI3-kinase-dependent activation of Rac1 in wild-type endothelial cells, whereas EphA2-deficient cells fail to activate Rac1 upon stimulation. Expression of dominant negative PI3-kinase or Rac1 inhibits ephrin-A1-induced endothelial cell migration. Consistent with in vitro data, EphA2-deficient mice show a diminished angiogenic response to ephrin-A1 in vivo. Moreover, EphA2-deficient endothelial cells fail to assemble in vivo when transplanted into recipient mice. These data suggest that EphA2 is an essential regulator of post-natal angiogenesis.

EphA kinase activation regulates HGF-induced epithelial branching morphogenesis

Eph kinases and their ephrin ligands are widely expressed in epithelial cells in vitro and in vivo. Our results show that activation of endogenous EphA kinases in Madin-Darby canine kidney (MDCK) cells negatively regulates hepatocyte growth factor/scatter factor (HGF)–induced branching morphogenesis in collagen gel. Cotreatment with HGF and ephrin-A1 reduced sprouting of cell protrusions, an early step in branching morphogenesis. Moreover, addition of ephrin-A1 after HGF stimulation resulted in collapse and retraction of preexisting cell protrusions. In a newly developed assay that simulates the localized interactions between Ephs and ephrins in vivo, immobilized ephrin-A1 suppressed HGF-induced MDCK cell scattering. Ephrin-A1 inhibited basal ERK1/2 mitogen-activated protein kinase activity; however, the ephrin-A1 effect on cell protrusion was independent of the mitogen-activated protein kinase pathway. Ephrin-A1 suppressed HGF-induced activation of Rac1 and p21-activated kinase, whereas RhoA activation was retained, leading to the preservation of stress fibers. Moreover, dominant-negative RhoA or inhibitor of Rho-associated kinase (Y27632) substantially negated the inhibitory effects of ephrin-A1. These data suggest that interfering with c-Met signaling to Rho GTPases represents a major mechanism by which EphA kinase activation inhibits HGF-induced MDCK branching morphogenesis.

Ephrin-A1 induces c-Cbl phosphorylation and EphA receptor down-regulation in T cells

Eph receptor tyrosine kinases are expressed by T lineage cells, and stimulation with their ligands, the ephrins, has recently been shown to modulate T cell behavior. We show that ephrin-A1 stimulation of Jurkat T cells induces tyrosine phosphorylation of EphA3 receptors and cytoplasmic proteins, including the c-cbl proto-oncogene. Cbl phosphorylation was also observed in peripheral blood T cells. In contrast, stimulation of Jurkat cells with the EphB receptor ligand ephrin-B1 does not cause Cbl phosphorylation. EphA activation also induced Cbl association with Crk-L and Crk-II adapters, but not the related Grb2 protein. Induction of Cbl phosphorylation upon EphA activation appeared to be dependent upon Src family kinase activity, as Cbl phosphorylation was selectively abrogated by the Src family inhibitor 4-amino-5(4-chlorophenyl-7-(tert-butyl)pyrazolo[3,4-d]pyrimidine, while EphA phosphorylation was unimpaired. Ephrin-A1 stimulation of Jurkat cells was also found to cause down-regulation of endogenous EphA3 receptors from the cell surface and their degradation. In accordance with the role of Cbl as a negative regulator of receptor tyrosine kinases, overexpression of wild-type Cbl, but not its 70-Z mutant, was found to down-regulate EphA receptor expression. Receptor down-regulation could also be inhibited by blockage of Src family kinase activity. Our findings show that EphA receptors can actively signal in T cells, and that Cbl performs multiple roles in this signaling pathway, functioning to transduce signals from the receptors as well as regulating activated EphA receptor expression.

EphrinA1 inactivates integrin-mediated vascular smooth muscle cell spreading via the Rac/PAK pathway

Interactions between the Eph receptor tyrosine kinase and ephrin ligands transduce short-range signals regulating axon pathfinding, development of the cardiovascular system, as well as migration and spreading of neuronal and non-neuronal cells. Some of these effects are believed to be mediated by alterations in actin dynamics. The members of the small Rho GTPase family elicit various effects on actin structures and are probably involved in Eph receptor-induced actin modulation. EphrinA1 is proposed to contribute to angiogenesis as it is strongly expressed at sites of neovascularization. Moreover, angiogenic factors induce the expression of ephrinA1 in endothelial cells. In this study, using rat vascular smooth muscle cells (VSMCs), we investigated the contribution of the small Rho GTPases in ephrinA1-induced integrin inactivation. EphrinA1 did not significantly affect early adhesion of VSMCs on purified laminin or fibronectin, but strongly impaired cell spreading. The Rho kinase inhibitor Y-27632 partly reversed the ephrinA1 effect, suggesting involvement of Rho in this model. However, inhibition of RhoA synthesis with short interfering (si)RNA had a modest effect, suggesting that RhoA plays a limited role in ephrinA1-mediated inhibition of spreading in VSMCs. The ephrinA1-mediated morphological alterations correlated with inhibition of Rac1 and p21-activated kinase 1 (PAK1) activity, and were antagonized by the expression of a constitutively active Rac mutant. Moreover, repression of Rac1 synthesis with siRNA amplifies the ephrinA1-induced inhibition of spreading. Finally, sphingosine-1-phosphate (S1P), a lipid mediator known to inhibit Rac activation in VSMCs amplifies the ephrinA1 effect. In conclusion, our results emphasize the role of the Rac/PAK pathway in ephrinA1-mediated inhibition of spreading. In this way, ephrinA1, alone or in synergy with S1P, can participate in blood vessel destabilization, a prerequisite for angiogenesis.