Differential gene expression of Eph receptors and ephrins in benign human tissues and cancers

Peritumoral small ephrinA5 isoform level predicts the postoperative survival in hepatocellular carcinoma

Background

EphrinA5, a member of Eph/Ephrin family, possesses two alternative isoforms, large ephrinA5 isoform (ephrinA5L) and small ephrinA5 isoform (ephrinA5S). EphrinA5L is a putative tumor suppressor in several types of human cancers. However, the role of ephrinA5S in hepato-carcinogenesis remains unclear. In this study, we evaluate the role of ephrinA5 isoforms in human hepatocellular carcinomas (HCC).

Methodology/Principal Findings

A total of 142 paired HCCs and peritumoral liver tissue was examined for relative expression of ephrinA5L and ephrinA5S by using quantitative real-time polymerase chain reaction. We analyzed their expression in relation to clinical parameters, disease-free survival and overall survival. Functional assays were performed to dissect the possible underlying mechanisms. Both ephrinA5L and ephrinA5S were significantly downregulated in HCCs, as compared to those in peritumoral tissue (p = 0.013 and 0.001). Univariate analysis demonstrated that ephrinA5S was positively correlated with old age and histological grade. In multivariate analysis, high ephrinA5S expression in peritumoral tissue had better disease-free survival (p = 0.002) and overall survival (p = 0.045) in patients with HCC after surgical resection. Functional analysis in HCC cell lines revealed that ephrinA5S had a more potent suppressive effect than ephrinA5L on cell proliferation (p<0.05) and migration (p<0.01). Furthermore, forced expression of both ephrinA5 isoforms in HCC cell lines significantly down-regulated epidermal growth factor receptor (EGFR) expression by promoting c-Cbl-mediated EGFR degradation.

Conclusions/Significance

EphrinA5S might be a useful prognostic biomarker for HCCs after surgical resection. EphrinA5, especially ephrinA5S, acts as a tumor suppressor in hepatocarcinogenesis. Peritumoral small ephrinA5 isoform level could determine the postoperative survival in hepatocellular carcinoma.

Aberrant expression of EphA3 in gastric carcinoma: correlation with tumor angiogenesis and survival

BACKGROUND

EphA3, a member of the Eph receptor tyrosine kinases, plays important roles in tumor angiogenesis and progression. However, the function of EphA3 in solid tumors has not been widely studied. We aimed to explore EphA3 expression in gastric carcinoma and analyze its role as a potential prognostic factor.

METHODS

Quantitative reverse transcription polymerase chain reaction (qRT-PCR) was used to assess EphA3 mRNA in a normal gastric mucosa cell line and carcinoma cell lines. Immunohistochemistry for EphA3 and vascular endothelial growth factor (VEGF) was performed in 318 cases of gastric carcinoma. CD34 immunohistochemical staining was used for microvessel density (MVD) counting. Western blotting was used to analyze EphA3 expression in the cell lines and to determine the expression of EphA3 and VEGF in 75 cases of gastric carcinoma and matched normal mucosa.

RESULTS

EphA3 mRNA and protein expression was significantly higher in gastric cancer than that in normal mucosa (all P < 0.001). EphA3 was significantly correlated with TNM stage and poor prognosis (all P < 0.001). Multivariate analysis showed that EphA3 had an independent effect on survival (P = 0.037). EphA3 was positively correlated with VEGF (P < 0.001), and MVD (P < 0.001). According to Western blot analysis, both EphA3 and VEGF expression were significantly higher in carcinoma than that in normal mucosa (all P < 0.001). A positive correlation was observed between EphA3 and VEGF expression in cancer (P < 0.001, r = 0.513).

CONCLUSIONS

EphA3 may play important roles in the angiogenesis and prognosis of gastric carcinoma, and thus may become a useful target for therapeutic intervention and a potential indicator for clinical assessment of tumor prognosis.

Profiling Eph receptor expression in cells and tissues: a targeted mass spectrometry approach

The Eph receptor tyrosine kinase family includes many members, which are often expressed together in various combinations and can promiscuously interact with multiple ephrin ligands, generating intricate networks of intracellular signals that control physiological and pathological processes. Knowing the entire repertoire of Eph receptors and ephrins expressed in a biological sample is important when studying their biological roles. Moreover, given the correlation between Eph receptor/ephrin expression and cancer pathogenesis, their expression patterns could serve important diagnostic and prognostic purposes. However, profiling Eph receptor and ephrin expression has been challenging. Here we describe a novel and straightforward approach to catalog the Eph receptors present in cultured cells and tissues. By measuring the binding of ephrin Fc fusion proteins to Eph receptors in ELISA and pull-down assays, we determined that a mixture of four ephrins is suitable for isolating both EphA and EphB receptors in a single pull-down. We then used mass spectrometry to identify the Eph receptors present in the pull-downs and estimate their relative levels. This approach was validated in cultured human cancer cell lines, human tumor xenograft tissue grown in mice, and mouse brain tissue. The new mass spectrometry approach we have developed represents a useful tool for the identification of the spectrum of Eph receptors present in a biological sample and could also be extended to profiling ephrin expression.

Cancer somatic mutations disrupt functions of the EphA3 receptor tyrosine kinase through multiple mechanisms

The Eph receptor tyrosine kinases make up an important family of signal transduction molecules that control many cellular processes, including cell adhesion and movement, cell shape, and cell growth. All of these are important aspects of cancer progression, but the relationship between Eph receptors and cancer is complex and not fully understood. Genetic screens of tumor specimens from cancer patients have revealed somatic mutations in many Eph receptors. The most highly mutated Eph receptor is EphA3, but its functional role in cancer is currently not well established. Here we show that many EphA3 mutations identified in lung, colorectal, and hepatocellular cancers, melanoma, and glioblastoma impair kinase activity or ephrin ligand binding and/or decrease the level of receptor cell surface localization. These results suggest that EphA3 has ephrin- and kinase-dependent tumor suppressing activities, which are disrupted by somatic cancer mutations.

EPHA7, a new target gene for 6q deletion in T-cell lymphoblastic lymphomas

Cryptic deletions at chromosome 6q are common cytogenetic abnormalities in T-cell lymphoblastic leukemia/lymphoma (T-LBL), but the target genes have not been formally identified. Our results build on detection of specific chromosomal losses in a mouse model of γ-radiation-induced T-LBLs and provide interesting clues for new putative susceptibility genes in a region orthologous to human 6q15-6q16.3. Among these, Epha7 emerges as a bona fide candidate tumor suppressor gene because it is inactivated in practically all the T-LBLs analyzed (100% in mouse and 95.23% in human). We provide evidence showing that Epha7 downregulation may occur, at least in part, by loss of heterozygosity (19.35% in mouse and 12.5% in human) or promoter hypermethylation (51.61% in mouse and 43.75% in human) or a combination of both mechanisms (12.90% in mouse and 6.25% in human). These results indicate that EPHA7 might be considered a new tumor suppressor gene for 6q deletions in T-LBLs. Notably, this gene is located in 6q16.1 proximal to GRIK2 and CASP8AP2, other candidate genes identified in this region. Thus, del6q seems to be a complex region where inactivation of multiple genes may cooperatively contribute to the onset of T-cell lymphomas.

Roles of EphB3/ephrin-B1 in feather morphogenesis

The ephrin receptor (Eph) tyrosine kinases and their ephrin ligands are involved in morphogenesis during organ formation. We studied their role in feather morphogenesis, focusing on ephrin-B1 and its receptor EphB3. Early in feather development, ephrin-B1 mRNA and protein were found to be expressed in the dermal condensation, but not in the inter-bud mesenchyme. Later, in feather buds, expression was found in both the epithelium and mesenchyme. In the feather follicle, ephrin-B1 protein expression was found to be enriched in the feather filament epithelium and in the marginal plate which sets the boundary between the barb ridges. EphB3 mRNA was also expressed in epithelia. In the feather bud, its expression was restricted to the posterior bud. In the follicle, its expression formed a circle at the bud base which may set the boundary between bud and inter-bud domains. Perturbation with ephrin-B1/Fc altered feather primordia segregation and feather bud elongation. Analyses revealed that ephrin-B1/Fc caused three types of changes: blurred placode boundaries with loose dermal condensations, incomplete follicle invagination with less compact dermal papillae, and aberrant barb ridge patterning in feather filament morphogenesis. Thus, while ephrin-B1 suppression does not inhibit the initial emergence of a new epithelial domain, Eph/ephrin-B1 interaction is required for its proper completion. Consequently, we propose that interaction between ephrin-B1 and its receptor is involved in boundary stabilization during feather morphogenesis.

Eph-A2 and Eph-A4 expression in human benign and malignant thyroid lesions: an immunohistochemical study

Background

Ephrin receptors (Ephs) are frequently overexpressed in a wide variety of human malignant tumors, being associated with tumor growth, invasion, metastasis and angiogenesis. The aim of the present study was to evaluate the clinical significance of Eph-A2 and Eph-A4 expression in human benign and malignant thyroid lesions.

Material/Methods

Eph-A2 and Eph-A4 protein expression was assessed immunohistochemically on paraffin-embedded thyroid tissues from 131 patients with benign and malignant lesions.

Results

Eph-A2 was significantly overexpressed in malignant compared to benign thyroid lesions (p<0.001). Papillary carcinoma cases presented significantly increased Eph-A2 expression compared to those with hyperplasia nodules (p<0.001). Eph-A4 expression was not differentiated between cases with malignant or benign thyroid lesions. Papillary carcinoma cases presented significantly increased Eph-A4 expression compared to those with hyperplasia nodules (p=0.006). In the subgroup of malignant thyroid lesions, Eph-A2 and Eph-A4 expression was not associated with TNM stage, capsular, lymphatic or vascular invasion.

Conclusions

The present data suggest that Eph-A2, but not Eph-A4, overexpression may be associated with the malignant transformation of thyroid neoplasia. Further studies conducted on cohorts including a higher proportion of patients with advanced nodal and metastatic disease are recommended to draw definite conclusions on the clinical significance of Eph proteins in thyroid neoplasia.

Eph receptor function is modulated by heterooligomerization of A and B type Eph receptors

Beyond homotypic receptor interactions that are required for Eph signaling, ligand-independent association and crosstalk between members of the EphA and -B subclasses determine cell signaling outcomes.

Eph receptors interact with ephrin ligands on adjacent cells to facilitate tissue patterning during normal and oncogenic development, in which unscheduled expression and somatic mutations contribute to tumor progression. EphA and B subtypes preferentially bind A- and B-type ephrins, respectively, resulting in receptor complexes that propagate via homotypic Eph–Eph interactions. We now show that EphA and B receptors cocluster, such that specific ligation of one receptor promotes recruitment and cross-activation of the other. Remarkably, coexpression of a kinase-inactive mutant EphA3 with wild-type EphB2 can cause either cross-activation or cross-inhibition, depending on relative expression. Our findings indicate that cellular responses to ephrin contact are determined by the EphA/EphB receptor profile on a given cell rather than the individual Eph subclass. Importantly, they imply that in tumor cells coexpressing different Ephs, functional mutations in one subtype may cause phenotypes that are a result of altered signaling from heterotypic rather from homotypic Eph clusters.

EphrinA5 suppresses colon cancer development by negatively regulating epidermal growth factor receptor stability

Colon cancer is one of the most common human cancers worldwide. Owing to its aggressiveness and lethality, it is necessary to determine the mechanisms regulating the carcinogenesis of colon cancer. EphrinA5 has been reported to act as a putative tumor suppressor in glioma; however, little is known concerning the role of this protein in the context of colon cancer. To elucidate the biological significance of ephrinA5 in colon cancer, we examined ephrinA5 and epidermal growth factor receptor (EGFR) expression profiles in both colon cancer and normal tissues, using immunohistochemistry on a 96-spot tissue microarray. Gain-of-function and loss-of-function experiments were performed on the human colon cancer cell lines SW480 and WiDr to determine the biological effects of ephrinA5 in relation to cell proliferation, survival, and migration. It was found that ephrinA5 mRNA and protein levels were significantly reduced in colon cancer as compared with normal colon tissue specimens. EphrinA5 expression was also negatively associated with tumor differentiation and clinical stage. In colon cancer cell line models, ephrinA5 exerted an inhibitory effect on EGFR by promoting c-Cbl-mediated EGFR ubiquitination and degradation. EphrinA5 did not affect the transcriptional regulation of EGFR mRNA expression in colon cancer cells. Expression of ephrinA5 suppressed colon cancer cell proliferation, migration, and chemotherapeutic resistance. In conclusion, ephrinA5 inhibited colon cancer progression by promoting c-Cbl-mediated EGFR degradation. Our findings identify a novel mechanism that could be utilized to improve the therapeutic efficiency of EGFR-targeting strategies.

Ectodomain structures of Eph receptors

Eph receptors, the largest subfamily of receptor tyrosine kinases (RTKs), and their ephrin ligands are important mediators of cell-cell communication that regulate axon guidance, long-term potentiation, and stem cell development, among others. By now, many Eph receptors and ephrins have also been found to play important roles in the progression of cancer. Since both the receptor and the ligand are membrane-bound, their interaction leads to the multimerization of both molecules to distinct clusters within their respective plasma membranes, resulting in the formation of discrete signaling centers. In addition, and unique to Eph receptors and ephrins, their interaction initiates bi-directional signaling cascades where information is transduced in the direction of both the receptor- and the ligand-bearing cells. The Ephs and the ephrins are divided into two subclasses, A and B, based on their affinities for each other and on sequence conservation. Crystal structures and other biophysical studies have indicated that isolated extracellular Eph and ephrin domains initially form high-affinity heterodimers around a hydrophobic loop of the ligand that is buried in a hydrophobic pocket on the surface of the receptor. The dimers can then further arrange by weaker interactions into higher-order Eph/ephrin clusters observed in vivo at the sites of cell-cell contact. Although the hetero-dimerization is a universal way to initiate signaling, other extracellular domains of Ephs are involved in the formation of higher-order clusters. The structures also show important differences defining the unique partner preferences of the two ligand and receptor subclasses, namely, how subclass specificity is determined both by individual interacting residues and by the precise architectural arrangement of ligands and receptors within the complexes.

EphA receptor signaling--complexity and emerging themes

The impact of Eph and ephrin signaling on cell behavior is complex and highly context dependent. Forward signaling initiated by Eph receptor activation and reverse signaling initiated by ephrin activation often mediate opposite effects. The apparent ligand-independent functions of Eph receptors recognized recently add another layer of complexity. This review will attempt to sort out the information generated recently on signaling by the A subfamily of Eph receptors and ephrin ligands. We will focus on EphA/ephrin-A signaling in the context of several physiological and disease processes, where new progresses have been made lately and unifying themes are emerging amid previous confusions. For more comprehensive survey of literature on Eph/ephrin signaling pathways and networks, readers are referred to outstanding reviews both in this volume and in other recent publications.

Clinical relevance of Ephs and ephrins in cancer: lessons from breast, colorectal, and lung cancer profiling

Pre-clinical studies provide compelling evidence that members of the Eph family of receptor tyrosine kinases and their ephrin ligands promote tumor growth, invasion and metastasis, and neovascularization. Tumor suppressive roles have also been reported for the receptors, and ligand-dependent versus ligand-independent signaling has emerged as one key mechanism underlying tumor suppressive function as opposed to oncogenic effects. Determining how these observations relate to clinical outcome is a crucial step for translating the biological and mechanistic data into new molecularly targeted therapies. Expression profiling in human patient samples bridges this gap and provides valuable clinical relevance to laboratory observations. In addition to analyses performed using privately assembled patient tumor samples, publically available microarray datasets and tissue microarrays linked to clinical data have emerged as tractable tools for addressing the clinical relevance of specific molecules and families of related molecules. This review summarizes the clinical relevance of specific Eph and ephrin molecules in human breast, colorectal, and lung cancers.

Complex expression patterns of Eph receptor tyrosine kinases and their ephrin ligands in colorectal carcinogenesis

Aberrant expression of Eph and ephrin proteins in human cancers is extensively documented. However, data are frequently limited to one gene and therefore incomplete and in some instances conflicting. We analysed expression of all Eph and ephrin genes in colorectal cancer (CRC) cell lines and 153 clinical specimens, providing for the first time a comprehensive analysis of this system in CRC. Eph/ephrin mRNA expression was assessed by quantitative real-time PCR and correlated with protein expression (flow cytometry, Western blotting and immunocytochemistry). These data show that EphA1, EphA2, EphB2 and EphB4 were significantly over expressed in CRC. In all cases, at least one Eph gene was found in normal colon (EphA1, EphA2, EphB2, EphB4), where expression was observed at high levels in most CRCs. However, other Eph gene expression was lost in individual CRCs compared to the corresponding normal, EphA7 being a striking example. Loss of expression was more common in advanced disease and thus correlated with poor survival. This is consistent with the redundant functionality of Eph receptors, such that expression of a single Eph gene is sufficient for effector function. Overall, the data suggest a progressive loss of expression of individual Eph genes suggesting that individual CRCs need to be phenotyped to determine which Eph genes are highly expressed. Targeted therapies could then be selected from a group of specific antibodies, such as those developed for EphA1.

Dancing with the dead: Eph receptors and their kinase-null partners

Eph receptor tyrosine kinases and their ligands, ephrins, are membrane proteins coordinating a wide range of biological functions both in developing embryos and in adult multicellular organisms. Numerous studies have implicated Eph receptors in the induction of opposing responses, including cell adhesion or repulsion, support or inhibition of cell proliferation and cell migration, and progression or suppression of multiple malignancies. Similar to other receptor tyrosine kinases, Eph receptors rely on their ability to catalyze tyrosine phosphorylation for signal transduction. Interestingly, however, Eph receptors also actively utilize three kinase-deficient receptor tyrosine kinases, EphB6, EphA10, and Ryk, in their signaling network. The accumulating evidence suggests that the unusual flexibility of the Eph family, allowing it to initiate antagonistic responses, might be partially explained by the influence of the kinase-dead participants and that the exact outcome of an Eph-mediated action is likely to be defined by the balance between the signaling of catalytically potent and catalytically null receptors. We discuss in this minireview the emerging functions of the kinase-dead EphB6, EphA10, and Ryk receptors both in normal biological responses and in malignancy, and analyze currently available information related to the molecular mechanisms of their action in the context of the Eph family.

Polyphenol rich botanicals used as food supplements interfere with EphA2-ephrinA1 system

The Eph tyrosine kinase receptors and their ephrin ligands play a central role in several human cancers and their deregulated expression or function promotes tumorigenesis, inducing aggressive tumor phenotypes. Green tea extracts (GTE) have been recently found to inhibit Eph-kinase phosphorylation. In order to evaluate the potential contribution of edible and medicinal plants on EphA2-ephrinA1 modulation, 133 commercially available plant extracts used as food supplements, essential and fixed oils were screened with an ELISA-based binding assay. Nine plant extracts, rich of polyphenols, reversibly inhibited binding in a dose-dependent manner (IC₅₀ 0.83-24 μg/ml). Functional studies on PC3 prostate adenocarcinoma cells revealed that active extracts antagonized ephrinA1-Fc-induced EphA2-phosphorylation at non-cytotoxic concentrations (IC₅₀ 0.31-11.3 μg/ml) without interfering with EGF-induced EGFR activation, suggesting a specific effect. These findings could furnish an interesting starting point regarding the potential relationship between diet, edible plant secondary metabolites and Eph-ephrin system, suggesting their possible involvement in cancer development modulation.

Phosphoproteomic profiling of NSCLC cells reveals that ephrin B3 regulates pro-survival signaling through Akt1-mediated phosphorylation of the EphA2 receptor

The ephrin and Eph signaling circuit has been reported as deregulated in a number of tumor types including nonsmall cell lung cancer (NSCLC). Here we show that suppression of the ephrin-familly member ephrin B3 decreases NSCLC cell proliferation and has profound effects on cell morphology. To reveal which signaling networks ephrin B3 utilize to regulate such effects on growth and morphology, differential regulation of phosphorylated proteins was analyzed in the NSCLC cell line U-1810. Using strong cat ion exchange (SCX) and TiO(2)-based fractionation followed by nano-LC and mass spectrometry analysis, we identified 1083 unique phosphorylated proteins. Out of these, 150 proteins were found only when ephrin B3 is expressed, whereas 66 proteins were found exclusively in U-1810 cells with silenced ephrin B3. Network analysis of changes in the phosphoproteome with regard to the presence or absence of ephrin B3 expression generated a hypothesis that the site specific phosphorylation on Ser-897 detected on the erythropoietin-producing hepatocellular receptor tyrosine kinase class A2 (EphA2) is critical for the survival of NSCLC cells. Upstream of the EphA2 phosphorylation, activation of Akt1 on Ser 129 was also revealed as part of the ephrin B3-mediated signaling pathway. Phosphorylation of these sites was further confirmed by immune-based strategies in combination with mass spectrometry. Moreover, by further stepwise pathway walking, annotating the phosphorylated sites and their corresponding kinases upstream, our data support the process in which a Heat shock protein 90 isoform (HSP90AA1) acts as a protector of EphA2, thereby saving it from degradation. In addition, protein kinase CK2 (CK2) is suggested as a dominant kinase, activating downstream substrates to generate the effects on NSCLC proliferation and morphology.

Cells under siege: viral glycoprotein interactions at the cell surface

As obligate parasites, viruses are required to enter and replicate within their host, a process which employs many of their proteins to hijack natural cellular processes. High resolution X-ray crystallographic analysis has proven to be an ideal method to visualize the mechanisms by which such virus-host interactions occur and has revealed the innovative capacity of viruses to adapt efficiently to their hosts. In this review, we draw upon recently elucidated paramyxovirus-, arenavirus-, and poxvirus-host protein complex crystal structures to reveal both the capacity of viruses to appropriate one component of a physiological protein–protein binding event (often modifying it to out-compete the host-protein), and the ability to utilize novel binding sites on host cell surface receptors. The structures discussed shed light on a number of biological processes ranging from viral entry to virulence and host antagonism. Drawn together they reveal the common strategies which viruses have evolved to interact with their natural host. The structures also support molecular level rationales for how viruses can be transmitted to unrelated organisms and thus pose severe health risks.

Upregulation of EphA4 on astrocytes potentially mediates astrocytic gliosis after cortical lesion in the marmoset monkey

Glial scar formation occurs in response to brain injury in mammalian models and inhibits axonal growth. Identification of molecules that may mediate reactivity of astrocytes has become a leading therapeutic goal in the field of neurotrauma. In adult rodent brain and spinal cord, many of the Eph receptors and their ephrin ligands have been demonstrated to be upregulated on reactive astrocytes at the injury site; however, little is known about the expression of these molecules in nonhuman primate injury models. This study examines the role of the tyrosine kinase EphA4 receptor, which predominantly binds most ephrin ligands, after injury in marmoset monkey brain. Following lesioning of the primary visual cortex (V1) in the adult marmoset, EphA4 is strongly upregulated on reactive astrocytes around the lesion site, which secrete extracellular matrix molecules such as chondroitin sulfate proteoglycans, which are known for their inhibitory effect on axonal growth and regeneration. This astrocyte reactivity was also associated with neuronal death in the area adjacent to the lesion site. EphA4 activation induced by clustered ephrin A5-Fc-mediated astrocyte proliferation and glial fibrillary acidic protein expression in vitro, as demonstrated by closure of scratched wound and MTT assays, occurs via two potential signaling pathways, the mitogen-activated protein kinase and Rho pathways. These results in a nonhuman primate model highlight the importance of developing pharmacotherapeutic approaches to block these molecules following brain injury.

EPH-EPHRIN in human gastrointestinal cancers

Ever since its discovery two decades ago, the erythropoietin-producing hepatoma (EPH)-EPHRIN system has been shown to play multifaceted roles in human gastroenterological cancer as well as neurodevelopment. Over-expression, amplification and point mutations have been found in many human cancers and many investigators have shown correlations between these up-regulations and tumor angiogenesis. Thus, the genes in this family are considered to be potential targets of cancer therapy. On the other hand, the down-regulation of some members as a result of epigenetic changes has also been reported in some cancers. Furthermore, the correlation between altered expressions and clinical prognosis seems to be inconclusive. A huge amount of protein-protein interaction studies on the EPH-EPHRIN system have provided a basic scheme for signal transductions, especially bi-directional signaling involving EPH-ERPHRIN molecules at the cell membrane. This information also provides a manipulative strategy for harnessing the actions of these molecules. In this review, we summarize the known alterations of EPH-EPHRIN genes in human tumors of the esophagus, stomach, colorectum, liver and pancreas and present the perspective that the EPH-EPHRIN system could be a potential target of cancer therapy.

Developmental expression of Eph and ephrin family genes in mammalian small intestine

BACKGROUND

Eph receptor tyrosine kinases EphB2 and EphB3, and ephrin-B1 ligand play a critical role in regulating small intestinal epithelial cell migration. Although well studied in developing brain, the expression pattern of Ephs/ephrins has not been delineated in the developing small intestine.

AIMS

To examine the gene expression of all known members of Ephs/ephrins during development of mouse small intestine.

METHODS

We examined the expression of 21 A- and B-Ephs/ephrins in mouse small intestine or the Caco-2 cell line using reverse-transcription polymerase chain reaction (RT-PCR), quantitative (q)RT-PCR, and immunohistochemical analyses. EphB2-expressing cells from isolated crypts were detected by immunofluorescence and fluorescence-activated cell sorting (FACS) analyses.

RESULTS

With the exception of EphA5, all family members were expressed throughout the intestine at all ages examined. Most were uniformly expressed. In contrast, levels of EphA4, EphA8, EphB4, and ephrin-B2 messenger RNA (mRNA) were highest during early fetal development and declined with age. At E15, EphB2 and EphB4 proteins were diffusely expressed in proliferating stratified intestinal epithelial cells. By E18, the proteins had become localized to cell membranes of columnar epithelial cells within intervillus regions, and later were expressed on epithelial cell membranes in adult crypts. EphB2-expressing cells can be specifically isolated from crypt cell fractions.

CONCLUSIONS

The current study represents the first analysis of Ephs/ephrins during intestinal development. The elevated expression of EphA4, EphA8, EphB4, and ephrin-B2 during the fetal period of intestinal morphogenesis suggests an important role in development. Continued intestinal expression of other family members implicates a role in differentiation.

Henipavirus: A Review of Laboratory Animal Pathology

The genus Henipavirus contains two members—Hendra virus (HeV) and Nipah virus (NiV)—and each can cause fatal disease in humans and animals. HeV and Niv are currently classified as biosafety level 4, and NiV is classified as a category C priority pathogen. The aim of this article is to discuss the pathology of laboratory animal models of henipavirus infection and to assess their suitability as animal models for the development and testing of human therapeutics and vaccines. There has been considerable progress in the development of animal models for henipavirus disease. Suitable animal models include the golden hamster, ferrets, cats, and pigs, which develop disease resembling that observed in humans. Guinea pigs are a less reliable model for henipavirus disease, but they do develop henipavirus-induced encephalitis. Because human efficacy studies with henipaviruses are not permitted, animal studies are critical for the development of antiviral therapeutics and vaccines. Current research indicates that passive immunotherapy using monoclonal antibodies is protective of ferrets against NiV infection and that passive immunotherapy using NiV antibodies protects hamsters from HeV. Recombinant vaccines have been used to protect cats and pigs against NiV infection. Ribavirin and 6-aza-uridine were able to delay but not prevent NiV-induced mortality in hamsters. Further research is needed to develop a model and therapy for late-onset henipavirus encephalitis.

Constitutional inv(3) in myelodysplastic syndromes

The constitutional pericentric inversion on chromosome 3, inv(3), is rarely found in a normal population. The aim of our study was to investigate its possible link to hematologic malignancy. Chromosomes from bone marrow cells in 890 patients with hematologic disorders were analyzed with the Q-banding technique. Thirty-four patients had inv(3) (3.8%). In 241 patients with myelodysplastic syndromes the frequency was 6.2% as opposed to 2.9% in the remaining 649 patients (p=0.02). The increased frequency of inv(3) in patients with myelodysplastic syndromes indicates that inv(3) could be a risk factor for the development of the disease.

FGFR3 mutation affects cell growth, apoptosis and attachment in keratinocytes

FGFR3 mutations have recently been identified in several benign epidermal skin lesions such as seborrheic keratosis, epidermal nevus and solar lentigo. The functional consequences of these mutations in human skin are as yet unknown. In this study we analyzed the functional effects of the most common FGFR3 mutation in benign skin tumors, the R248C FGFR3 hotspot mutation, in human HaCaT keratinocytes. The cells were stably transduced with either the R248C or wildtype FGFR3 IIIb cDNA using a retroviral vector system. FGFR3 mutant and wildtype cells showed similar growth rates at subconfluence. However, at confluence FGFR3 mutant keratinocytes revealed a significantly higher cell number than wildtype cells. Furthermore, FGFR3 mutant cells showed significantly lower levels of apoptosis and decreased attachment to fibronectin compared with FGFR3 wildtype cells. Expression of mutant FGFR3 did not alter migration and senescence. Microarray analysis revealed only a few differentially expressed genes between FGFR3 mutant and wildtype keratinocytes. Enhanced phosphorylation of ERK1/2 was observed in confluent R248C mutant HaCaT cells compared with wildtype keratinocytes. Our results suggest that an increased cell number at confluence along with a decreased apoptosis may contribute to the development of acanthotic tumors in FGFR3 mutant skin in vivo.

The EPHB6 receptor tyrosine kinase is a metastasis suppressor that is frequently silenced by promoter DNA hypermethylation in non-small cell lung cancer

PURPOSE

Loss of EPHB6 receptor tyrosine kinase expression in early-stage non-small cell lung carcinoma (NSCLC) is associated with the subsequent development of distant metastasis. Here, we analyzed the regulation and function of EPHB6 in lung cancer metastasis.

EXPERIMENTAL DESIGN

The expression levels of EPHB6 were compared among normal lung tissue (n = 9), NSCLC without metastasis (n = 39), and NSCLC with metastasis (n = 39) according to the history of the patients. In addition, EPHB6 expression levels of matched tumor-normal pairs from 24 NSCLC patients were analyzed. The promoter DNA methylation status and its association with the expression levels of EPHB6 were determined among 14 pairs of tumor-normal samples. Metastatic potential of EPHB6 was assessed in vitro and in vivo in a metastasis mouse model. Overexpression and RNA interference (RNAi) approaches were used for analysis of the biological functions of EPHB6.

RESULTS

EPHB6 mRNA and protein levels were significantly reduced in NSCLC tumors compared with matched normal lung tissue. Decreased EPHB6 expression levels were associated with an increased risk for metastasis development in NSCLC patients. Loss of expression correlated with EPHB6 hypermethylation. EPHB6 expression was induced by 5-aza-2'-deoxycytidine treatment in an NSCLC cell line. Restoration of EPHB6 expression in lung adenocarcinoma cells increased adhesion and decreased migration. Reexpression of EPHB6 in lung cancer cells almost entirely abolished metastasis formation in non obese diabetic (NOD)/severe combined immunodeficient mice.

CONCLUSIONS

Taken together, these analyses show that EPHB6 is a metastasis inhibitory gene that is frequently silenced by hypermethylation of its promoter in NSCLC.

Aberrant DNA methylation and epigenetic inactivation of Eph receptor tyrosine kinases and ephrin ligands in acute lymphoblastic leukemia

Eph receptors and their ephrin ligands are involved in normal hematopoietic development and tumorigenesis. Using methylated CpG island amplification/DNA promoter microarray, we identified several EPH receptor and EPHRIN genes as potential hypermethylation targets in acute lymphoblastic leukemia (ALL). We subsequently studied the DNA methylation status of the Eph/ephrin family by bisulfite pyrosequencing. Hypermethylation of EPHA2, -A4, -A5, -A6, -A7, -A10, EPHB1, -B2, -B3, -B4, EFNA1, -A3, -A5, and EFNB1 and -B2 genes was detected in leukemia cell lines and primary ALL bone marrow samples. Expression analysis of EPHB4, EFNB2, and EFNA5 genes demonstrated that DNA methylation was associated with gene silencing. We cloned the promoter region of EPHB4 and demonstrated that promoter hypermethylation can result in EPHB4 transcriptional silencing. Restoration of EPHB4 expression by lentiviral transduction resulted in reduced proliferation and apoptotic cell death in Raji cells in which EPHB4 is methylated and silenced. Finally, we demonstrated that phosphorylated Akt is down-regulated in Raji cells transduced with EPHB4. These results suggest that epigenetic silencing by hypermethylation of EPH/EPHRIN family genes contributes to ALL pathogenesis and that EPHB4 can function as a tumor suppressor in ALL.

Ephrin-B2 regulates endothelial cell morphology and motility independently of Eph-receptor binding

The transmembrane protein ephrin-B2 regulates angiogenesis, i.e. the formation of new blood vessels through endothelial sprouting, proliferation and remodeling processes. In addition to essential roles in the embryonic vasculature, ephrin-B2 expression is upregulated in the adult at sites of neovascularization, such as tumors and wounds. Ephrins are known to bind Eph receptor family tyrosine kinases on neighboring cells and trigger bidirectional signal transduction downstream of both interacting molecules. Here we show that ephrin-B2 dynamically modulates the motility and cellular morphology of isolated endothelial cells. Even in the absence of Eph-receptor binding, ephrin-B2 stimulates repeated cycling between actomyosin-dependent cell contraction and spreading episodes, which requires the presence of the C-terminal PDZ motif. Our results show that ephrin-B2 is a potent regulator of endothelial cell behavior, and indicate that the control of cell migration and angiogenesis by ephrins might involve both receptor-dependent and receptor-independent activities.

Eph receptors and ephrins in cancer: bidirectional signalling and beyond

The Eph receptor tyrosine kinases and their ephrin ligands have intriguing expression patterns in cancer cells and tumour blood vessels, which suggest important roles for their bidirectional signals in many aspects of cancer development and progression. Eph gene mutations probably also contribute to cancer pathogenesis. Eph receptors and ephrins have been shown to affect the growth, migration and invasion of cancer cells in culture as well as tumour growth, invasiveness, angiogenesis and metastasis in vivo. However, Eph signalling activities in cancer seem to be complex, and are characterized by puzzling dichotomies. Nevertheless, the Eph receptors are promising new therapeutic targets in cancer.

Liver cancer: EphrinA2 promotes tumorigenicity through Rac1/Akt/NF-kappaB signaling pathway

Eph/Ephrin family, one of the largest receptor tyrosine kinase families, has been extensively studied in morphogenesis and neural development. Recently, growing attention has been paid to its role in the initiation and progression of various cancers. However, the role of Eph/Ephrins in hepatocellular carcinoma (HCC) has been rarely investigated. In this study, we found that the expression of EphrinA2 was significantly up-regulated in both established cell lines and clinical tissue samples of HCC, and the most significant increase was observed in the tumors invading the portal veins. Forced expression of EphrinA2 in HCC cells significantly promoted in vivo tumorigenicity, whereas knockdown of this gene inhibited this oncogenic effect. We further found that suppression of apoptosis, rather than accelerating proliferation, was responsible for EphrinA2-enhanced tumorigenicity. In addition, EphrinA2 endowed cancer cells with resistance to tumor necrosis factor alpha (TNF-alpha)-induced apoptosis, thus facilitating their survival. Furthermore, we disclosed a novel EphrinA2/ras-related c3 botulinum toxin substrate 1 (Rac1)/V-akt murine thymoma viral oncogene homolog (Akt)/nuclear factor-kappa B (NF-kappaB) pathway contributing to the inhibitory effect on apoptosis in HCC cells.

CONCLUSION

This study revealed that EphrinA2 played an important role in the development and progression of HCC by promoting the survival of cancer cells, indicating its role as a potential therapeutic target in HCC.

Guidance molecules in lung cancer

Guidance molecules were first described in the nervous system to control axon outgrowth direction. They are also widely expressed outside the nervous system where they control cell migration, tissue development and establishment of the vascular network. In addition, they are involved in cancer development, tumor angiogenesis and metastasis. This review is primarily focused on their functions in lung cancer and their involvement in lung development is also presented. Five guidance molecule families and their corresponding receptors are described, including the semaphorins/neuropilins/plexins, ephrins and Eph receptors, netrin/DCC/UNC5, Slit/Robo and Notch/Delta. In addition, the possibility to target these molecules as a therapeutic approach in cancer is discussed.

Selective removal of ovarian cancer cells from human ascites fluid using magnetic nanoparticles

A majority of ovarian cancer metastases result from the shedding of malignant cells from the primary tumor into the abdominal cavity. Free-floating cancer cells in serous effusions of late-stage ovarian cancer patients may spread to internal organs, making effective treatment extremely difficult. Selective removal of ovarian cancer cells from serous fluids may abate metastasis and improve long-term prognoses. We have already shown that superparamagnetic nanoparticles conjugated to an ephrin-A1 mimetic peptide with a high affinity for the EphA2 receptor can be used to capture and remove cultured human ovarian cancer cells from the peritoneal of experimental mice. Here we demonstrate the potential clinical utility of the methodology by in vitro capture and isolation of cancer cells from the ascites fluid of ovarian cancer patients.

FROM THE CLINICAL EDITOR

Ovarian cancer metastases usually are the result of shedding of malignant cells from the primary tumor into the abdominal cavity. In this paper, a novel nanotechnology-based method is demonstrated for the in vitro capture and isolation of cancer cells from the ascites fluid of ovarian cancer patients.

EphA2 in the early pathogenesis and progression of non-small cell lung cancer

Overexpression of the receptor tyrosine kinase EphA2 occurs in non-small cell lung cancer (NSCLC) and a number of other human cancers. This overexpression correlates with a poor prognosis, smoking, and the presence of Kirsten rat sarcoma (K-Ras) mutations in NSCLC. In other cancers, EphA2 has been implicated in migration and metastasis. To determine if EphA2 can promote NSCLC progression, we examined the relationship of EphA2 with proliferation and migration in cell lines and with metastases in patient tumors. We also examined potential mechanisms involving AKT, Src, focal adhesion kinase, Rho guanosine triphosphatases (GTPase), and extracellular signal-regulated kinase (ERK)-1/2. Knockdown of EphA2 in NSCLC cell lines decreased proliferation (colony size) by 20% to 70% in four of five cell lines (P < 0. 04) and cell migration by 7% to 75% in five of six cell lines (P < 0. 03). ERK1/2 activation correlated with effects on proliferation, and inhibition of ERK1/2 activation also suppressed proliferation. In accordance with the in vitro data, high tumor expression of EphA2 was an independent prognostic factor in time to recurrence (P = 0.057) and time to metastases (P = 0.046) of NSCLC patients. We also examined EphA2 expression in the putative premalignant lung lesion, atypical adenomatous hyperplasia, and the noninvasive bronchioloalveolar component of adenocarcinoma because K-Ras mutations occur in atypical adenomatous hyperplasia and are common in lung adenocarcinomas. Both preinvasive lesion types expressed EphA2, showing its expression in the early pathogenesis of lung adenocarcinoma. Our data suggest that EphA2 may be a promising target for treating and preventing NSCLC.

Structural plasticity of eph receptor A4 facilitates cross-class ephrin signaling

The EphA4 tyrosine kinase cell surface receptor regulates an array of physiological processes and is the only currently known class A Eph receptor that binds both A and B class ephrins with high affinity. We have solved the crystal structure of the EphA4 ligand binding domain alone and in complex with (1) ephrinB2 and (2) ephrinA2. This set of structures shows that EphA4 has significant conformational plasticity in its ligand binding face. In vitro binding data demonstrate that it has a higher affinity for class A than class B ligands. Structural analyses, drawing on previously reported Eph receptor structures, show that EphA4 in isolation and in complex with ephrinA2 resembles other class A Eph receptors but on binding ephrinB2 assumes structural hallmarks of the class B Eph receptors. This interactive plasticity reveals EphA4 as a structural chameleon, able to adopt both A and B class Eph receptor conformations, and thus provides a molecular basis for EphA-type cross-class reactivity.

c-Rel is a transcriptional repressor of EPHB2 in colorectal cancer

The receptor tyrosine kinase EPHB2 has recently been identified as a TCF4 transcriptional target that controls the intestinal epithelial architecture through repulsive interactions with Ephrin-B ligands. Many reports have demonstrated that most human colorectal cancers lose EPHB2 expression despite constitutive Wnt activation. Therefore, we investigated the mechanisms that cause EPHB2 down-regulation in colorectal cancer. In this study, we demonstrate that DNA hypermethylation was not responsible for the frequent loss of EPHB2 expression in colorectal cancer. Cloning and functional characterization of the EPHB2 gene 5'-flanking region revealed a potential negative regulatory element in the distal regulatory region. In vitro electrophoretic gel mobility shift and in vivo chromatin immunoprecipitation assays demonstrated that c-Rel directly binds to the putative element. Inhibiting c-Rel activity or knocking down c-Rel expression by RNA interference in colon cancer cells was sufficient to induce EPHB2 expression. Furthermore, transient transfection assays demonstrated that c-Rel over-expression repressed endogenous EPHB2 expression in colon cancer cells. We demonstrate for the first time that c-Rel acts as a transcriptional repressor of EPHB2 and plays an active role in EPHB2 down-regulation in colorectal cancers.

Generation and characterization of EphA1 receptor tyrosine kinase reporter knockout mice

Eph receptor tyrosine kinases (RTKs) are a highly conserved family of signaling proteins with functions in cellular migration, adhesion, apoptosis, and proliferation during both adult and embryonic life. Here, we describe a knock-in mouse in which EphA1 expression is disrupted via the insertion of an internal ribosome entry site (IRES)-human placental alkaline phosphatase (ALPP) reporter cassette into exon II of the EphA1 gene. This was shown to successfully knockout expression of endogenous EphA1 and enforce expression of the ALPP reporter by the EphA1 promoter. Staining for the ALPP reporter protein demonstrated an epithelially restricted expression pattern in mouse tissues. In EphA1 null mice, two separate phenotypes were identified: abnormal tail development manifesting as a kinky tail was found in approximately 80% of homozygous adults. A second, distinct abnormality present in approximately 18% of females was characterized by imperforate uterovaginal development with hydrometrocolpos and caused by a resistance of cells to apoptosis during reproductive tract canalization. These results indicate a possible role for EphA1 in tissue patterning and hormone-induced apoptotic processes.

Overexpression of beta3/gamma2 chains of laminin-5 and MMP7 in biliary cancer

AIM

To clarify the clinicopathological significance of laminin-5 gamma2 (LNgamma2) and beta3 (LNbeta3) chains and MMP7 expression in biliary tract cancer.

METHODS

We analyzed the association between immunohistochemically detected LNgamma2, LNbeta3, and MMP7 expression in biliary tract cancer and clinicopathological characteristics. Activity of MMP7 was analyzed by casein zymography. An in vitro invasion assay after treatment with MMP7-specific siRNA was performed.

RESULTS

LNgamma2 expression was predominantly observed in carcinoma cells at the invasive front. LNgamma2 expression was seen in 57% of patients with biliary tract cancer, and was associated with depth of invasion, histologic type, and advanced stage. The expression pattern of LNbeta3 was classified into two types: invasive front dominant type (38%) and diffuse type (28%). The invasive front dominant type was associated with histologic type and advanced stage. MMP7 positivity was correlated with LNgamma2 or LNbeta3 expression but not with clinicopathological characteristics. Active MMP7 detected by casein zymography was correlated with depth of invasion and advanced stage. Downregulation of MMP7 expression by siRNA resulted in a significant decrease in biliary tract cancer cell invasion in vitro.

CONCLUSION

Our results suggest that LNgamma2 and LNbeta3, in conjunction with MMP7, play a key role in the progression of biliary tract cancer.

EphA2 immunoconjugate as molecularly targeted chemotherapy for ovarian carcinoma

BACKGROUND

EphA2 is overexpressed in many types of human cancer but is absent or expressed at low levels in normal epithelial tissues. We investigated whether a novel immunoconjugate containing an anti-EphA2 monoclonal antibody (1C1) linked to a chemotherapeutic agent (monomethyl auristatin phenylalanine [MMAF]) through a noncleavable linker maleimidocaproyl (mc) had antitumor activity against ovarian cancer cell lines and tumor models.

METHODS

Specificity of 1C1-mcMMAF was examined in EphA2-positive HeyA8 and EphA2-negative SKMel28 ovarian cancer cells by antibody binding and internalization assays. Controls were phosphate-buffered saline (PBS), 1C1, or control IgG-mcMMAF. Viability and apoptosis were investigated in ovarian cancer cell lines and tumor models (10 mice per group). Antitumor activities were tested in the HeyA8-luc and SKOV3ip1 orthotopic mouse models of ovarian cancer. Endothelial cells were identified by use of immunohistochemistry and anti-CD31 antibodies. All statistical tests were two-sided.

RESULTS

The 1C1-mcMMAF immunoconjugate specifically bound to EphA2-positive HeyA8 cells but not to EphA2-negative cells and was internalized by HeyA8 cells. Treatment with 1C1-mcMMAF decreased the viability of HeyA8-luc cells in an EphA2-specific manner. In orthotopic mouse models, treatment with 1C1-mcMMAF inhibited tumor growth by 85%-98% compared with that in control mice (eg, for weight of HeyA8 tumors, 1C1-mcMMAF = 0.05 g and control = 1.03 g; difference = 0.98 g, 95% confidence interval [CI] = 0.40 to 1.58 g; P = .001). Even in bulkier disease models with HeyA8-luc cells, 1C1-mcMMAF treatment, compared with control treatment, caused regression of established tumors and increased survival of the mice (eg, 1C1-mcMMAF vs control, mean = 60.6 days vs 29.4 days; difference = 31.2 days, 95% CI = 27.6 to 31.2 days; P = .001). The antitumor effects of 1C1-mcMMAF therapy, in SKOV3ip1 tumors, for example, were statistically significantly related to decreased proliferation (eg, 1C1-mcMMAF vs control, mean = 44.1% vs 55.8% proliferating cells; difference = 11.7%, 95% CI = 2.45% to 20.9%; P = .01) and increased apoptosis of tumor cells (eg, 1C1-mcMMAF vs control, mean = 8.6% vs 0.9% apoptotic cells; difference = 7.7%, 95% CI = 3.8% to 11.7%; P < .001) and of mouse endothelial cells (eg, 1C1-mcMMAF vs control, mean 2.8% vs 0.4% apoptotic endothelial cells; difference = 2.4%, 95% CI = 1.4% to 4.6%; P = .034).

CONCLUSION

The 1C1-mcMMAF immunoconjugate had antitumor activity in preclinical models of ovarian carcinoma.

EphA2 mediates ligand-dependent inhibition and ligand-independent promotion of cell migration and invasion via a reciprocal regulatory loop with Akt

Both pro- and antioncogenic properties have been attributed to EphA2 kinase. We report that a possible cause for this apparent paradox is diametrically opposite roles of EphA2 in regulating cell migration and invasion. While activation of EphA2 with its ligand ephrin-A1 inhibited chemotactic migration of glioma and prostate cancer cells, EphA2 overexpression promoted migration in a ligand-independent manner. Surprisingly, the latter effects required phosphorylation of EphA2 on serine 897 by Akt, and S897A mutation abolished ligand-independent promotion of cell motility. Ephrin-A1 stimulation of EphA2 negated Akt activation by growth factors and caused EphA2 dephosphorylation on S897. In human astrocytoma, S897 phosphorylation was correlated with tumor grades and Akt activation, suggesting that the Akt-EphA2 crosstalk may contribute to brain tumor progression.

Expression of the receptor tyrosine kinase EphA2 is increased in smokers and predicts poor survival in non-small cell lung cancer

PURPOSE

Up-regulation of the receptor tyrosine kinase EphA2 has been shown in several epithelial cancers. Epidermal growth factor receptor (EGFR) and K-Ras have been reported to regulate EphA2 in several in vitro models, but this regulation has never been examined in tumors from patients. Because of the established importance of EGFR and K-Ras mutations in non-small cell lung cancer (NSCLC), we investigated the relationship between these mutations and EphA2 in this cancer type. The significance of EphA2 expression was further examined by testing for correlation with other clinical parameters.

EXPERIMENTAL DESIGN

EphA2 expression was analyzed by immunohistochemistry in tissue microarray format using surgically resected NSCLC specimens (n = 279). EGFR and K-Ras mutation status was determined for most specimens. The correlation between EphA2 expression and EGFR or K-Ras mutation status was examined, along with several clinicopathologic variables of the tumors. The effects of increasing EGFR and K-Ras activity on EphA2 expression and activity were examined in two cell lines.

RESULTS

EphA2 expression was detected in >90% of tumor samples. Expression of EphA2 was positively correlated with activated EGFR but not with EGFR mutations. EphA2 expression was increased in patients harboring K-Ras mutations. EphA2 expression was positively correlated with a history of smoking, and high EphA2 scores predicted poorer progression-free and overall survivals.

CONCLUSIONS

EphA2 expression in NSCLC is associated with K-Ras mutations, EGFR activation, smoking history, and poor prognosis. EphA2 expression is up-regulated in the context of EGFR or K-Ras activation. The potential of EphA2 as a therapeutic target for NSCLC should be further investigated.

Synthetic lethal RNAi screening identifies sensitizing targets for gemcitabine therapy in pancreatic cancer

Background

Pancreatic cancer retains a poor prognosis among the gastrointestinal cancers. It affects 230,000 individuals worldwide, has a very high mortality rate, and remains one of the most challenging malignancies to treat successfully. Treatment with gemcitabine, the most widely used chemotherapeutic against pancreatic cancer, is not curative and resistance may occur. Combinations of gemcitabine with other chemotherapeutic drugs or biological agents have resulted in limited improvement.

Methods

In order to improve gemcitabine response in pancreatic cancer cells, we utilized a synthetic lethal RNAi screen targeting 572 known kinases to identify genes that when silenced would sensitize pancreatic cancer cells to gemcitabine.

Results

Results from the RNAi screens identified several genes that, when silenced, potentiated the growth inhibitory effects of gemcitabine in pancreatic cancer cells. The greatest potentiation was shown by siRNA targeting checkpoint kinase 1 (CHK1). Validation of the screening results was performed in MIA PaCa-2 and BxPC3 pancreatic cancer cells by examining the dose response of gemcitabine treatment in the presence of either CHK1 or CHK2 siRNA. These results showed a three to ten-fold decrease in the EC₅₀ for CHK1 siRNA-treated cells versus control siRNA-treated cells while treatment with CHK2 siRNA resulted in no change compared to controls. CHK1 was further targeted with specific small molecule inhibitors SB 218078 and PD 407824 in combination with gemcitabine. Results showed that treatment of MIA PaCa-2 cells with either of the CHK1 inhibitors SB 218078 or PD 407824 led to sensitization of the pancreatic cancer cells to gemcitabine.

Conclusion

These findings demonstrate the effectiveness of synthetic lethal RNAi screening as a tool for identifying sensitizing targets to chemotherapeutic agents. These results also indicate that CHK1 could serve as a putative therapeutic target for sensitizing pancreatic cancer cells to gemcitabine.

Epigenetic silencing of EphA1 expression in colorectal cancer is correlated with poor survival

Aberrant expression of Eph and ephrin proteins has well-established functions in oncogenesis and tumour progression. We describe EphA1 expression in 6 colorectal cancer (CRC) cell lines, 18 controls and 125 CRC specimens. In addition, a well-characterised cohort of 53 paired normal colon and CRCs was also assessed. Expression of EphA1 mRNA was assessed by quantitative real-time PCR and correlated with protein expression by flow cytometry, immunoprecipitation, western blotting and immunohistochemistry. Significant upregulation (2- to 10-fold) of EphA1 was seen in over 50% of cases (P=0.005) whereas many of the remainder showed downregulation of EphA1. Intriguingly, EphA1 over-expression was more prevalent in stage II compared to stage III CRCs (P=0.02). Low EphA1 expression significantly correlated with poor survival (P=0.02). Epigenetic silencing appeared to explain the loss of EphA1 expression as methylation of the EphA1 CpG island strongly correlated with low EphA1 expression (P<0.01). Furthermore, EphA1 re-expression could be induced by treatment with demethylating agents. Our findings identify EphA1 as a potential prognostic marker in CRC. Although therapies targeting high EphA1 expression seem plausible in CRC, the loss of expression in advanced disease suggests a potential risk that targeted therapy, by selecting for loss of expression, might contribute to disease progression.

Acute Hendra virus infection: Analysis of the pathogenesis and passive antibody protection in the hamster model

Hendra virus (HeV) and Nipah virus (NiV) are recently-emerged, closely related and highly pathogenic paramyxoviruses. We have analysed here the pathogenesis of the acute HeV infection using the new animal model, golden hamster (Mesocricetus auratus), which is highly susceptible to HeV infection. HeV-specific RNA and viral antigens were found in multiple organs and virus was isolated from different tissues. Dual pathogenic mechanism was observed: parenchymal infection in various organs, including the brain, with vasculitis and multinucleated syncytia in many blood vessels. Furthermore, monoclonal antibodies specific for the NiV fusion protein neutralized HeV in vitro and efficiently protected hamsters from HeV if given before infection. These results reveal the similarities between HeV and NiV pathogenesis, particularly in affecting both respiratory and neuronal system. They demonstrate that hamster presents a convenient novel animal model to study HeV infection, opening new perspectives to evaluate vaccine and therapeutic approaches against this emergent infectious disease.

Inhibition of Src family kinases with dasatinib blocks migration and invasion of human melanoma cells

Src family kinases (SFK) are involved in regulating a multitude of biological processes, including cell adhesion, migration, proliferation, and survival, depending on the cellular context. Therefore, although SFKs are currently being investigated as potential targets for treatment strategies in various cancers, the biological responses to inhibition of SFK signaling in any given tumor type are not predictable. Dasatinib (BMS-354825) is a dual Src/Abl kinase inhibitor with potent antiproliferative activity against hematologic malignancies harboring activated BCR-ABL. In this study, we show that dasatinib blocks migration and invasion of human melanoma cells without affecting proliferation and survival. Moreover, dasatinib completely inhibits SFK kinase activity at low nanomolar concentrations in all eight human melanoma cell lines investigated. In addition, two known downstream targets of SFKs, focal adhesion kinase and Crk-associated substrate (p130(CAS)), are inhibited with similar concentrations and kinetics. Consistent with inhibition of these signaling pathways and invasion, dasatinib down-regulates expression of matrix metalloproteinase-9. We also provide evidence that dasatinib directly inhibits kinase activity of the EphA2 receptor tyrosine kinase, which is overexpressed and/or overactive in many solid tumors, including melanoma. Thus, SFKs and downstream signaling are implicated as having key roles in migration and invasion of melanoma cells.

EphA1 interacts with integrin-linked kinase and regulates cell morphology and motility

The Eph-ephrin receptor-ligand system is implicated in cell behavior and morphology. EphA1 is the founding member of the Eph receptors, but little is known about its function. Here, we show that activation of EphA1 kinase inhibits cell spreading and migration in a RhoA-ROCK-dependent manner. We also describe a novel interaction between EphA1 and integrin-linked kinase (ILK), a mediator of interactions between integrin and the actin cytoskeleton. The C-terminal sterile alpha motif (SAM) domain of EphA1 is required and the ankyrin region of ILK is sufficient for the interaction between EphA1 and ILK. The interaction is independent of EphA1 kinase activity but dependent on stimulation of the EphA1 ligand ephrin-A1. Activation of EphA1 kinase resulted in a decrease of ILK activity. Finally, we demonstrated that expression of a kinase-active form of ILK (S343D) rescued the EphA1-mediated spreading defect, and attenuated RhoA activation. These results suggest that EphA1 regulates cell morphology and motility through the ILK-RhoA-ROCK pathway.

Expression of EphB2 in the development of anorectal malformations in fetal rats

PURPOSE

The receptor tyrosine kinase of the Eph family is a large group of highly conserved molecules that function in diverse intercellular recognition events. It has been reported that EphB2 is related to caudal remodeling events. The aim of this study is to investigate EphB2 expression in anorectal development in normal and rat embryos with anorectal malformations (ARMs) and attempt to define its role in anorectal morphogenesis.

METHODS

The ethylenethiourea (ETU) rat model of the ARMs was used in this study. Immunohistochemical analyses and real time quantitative polymerase chain reaction (PCR) were carried out to investigate EphB2 protein localizations and messenger RNA (mRNA) expression levels. (1) Rat embryos with ARMs were obtained by treating pregnant rats (n = 24) with administration of ETU on gestation day (Gd) 10. Normal rat embryos (n = 111) and embryos treated by ETU without ARMs (n = 90) were the control groups, and embryos with ARMs (n = 108) from Gd13 to Gd16 were divided according to the sections taken from specimens. (2) Embryos were sequentially sectioned in the sagittal and transversal planes before staining with a specific antibody to EphB2. Spatiotemporal study was carried out on EphB2 expression. (3) Individual frozen sections were used to manually microdissect the cloaca and anorectal specimens for total RNA extraction. EphB2 expression was evaluated by real time quantitative PCR.

RESULTS

On the immunologic labeling study, EphB2 expression was confined to the cloaca in control groups, whereas EphB2 expression was mainly located at the urorectal septum (URS) and cloacal membrane on Gd13 and Gd14. The increased positive expression was observed in the fused tissue of the URS and cloacal membrane on Gd15. On Gd16, the anal membrane broke down, and the rectum was able to be in contact with the anus, and EphB2 expression was then noted in mucous membrane of rectum. EphB2 expression was seen in the cloacal and anorectal tissues of embryos with ARMs. By integrated optical density (IOD) measurement, IOD value of EphB2 protein was significantly lower in the ARM group than that in the control groups on Gd13 to Gd16 (P < .05), respectively. As shown by real time quantitative PCR, EphB2 expression was detected in 3 groups. EphB2 mRNA level increased on Gd13 to Gd16 but gradually decreased after Gd16. The expression level of EphB2 mRNA in the ARM embryos was lower on Gd13 to Gd16 than that in control groups (P < .05).

CONCLUSIONS

EphB2 expression decreased in the ARM embryos and was confined to URS and cloaca, whereas it was higher in control group. Our data thus indicated that EphB2 molecules possibly contributed to the anorectal morphogenesis and the decreased expression of EphB2 might be related to the development of ARMs.

Loss of EphA2 receptor tyrosine kinase reduces ApcMin/+ tumorigenesis

The Eph receptor A2 (EphA2) is overexpressed in a range of human epithelial cancers, a phenotype that is associated with cancer cell proliferation, progression and angiogenesis. Mouse models of mammary neoplasia have confirmed the role of EphA2 as mice carrying a knockout allele of EphA2 were resistant to breast cancer, a phenotype that was associated with interactions between EphA2 and ErbB2. We investigated in vivo the role of EphA2 in GI cancer. To determine whether EphA2 influences intestinal tumorigenesis, we used qRT-PCR to examine the mRNA expression levels of EphA2 in tumors from the small intestine and colon of Apc(Min/+) mice. We found that EphA2 was significantly up-regulated in tumors from both regions when compared with normal control tissues. We then evaluated the spatial expression patterns of EphA2 protein using immunohistochemistry in both the small intestine and colon and found that in normal tissues EphA2 was robustly expressed in highly differentiated cells, such as cells of the villi, but that EphA2 expression was largely absent from the stem cell niche and proliferative zones of intestinal crypts. In contrast, in tumors EphA2 was broadly expressed. Finally, we created a strain of Apc(Min/+) mice carrying a genetic knockout of the EphA2 gene. These mice developed significantly fewer and smaller tumors in both the small and large intestine. Overall, our results indicate that EphA2 plays an oncogenic role in the mammalian intestine suggesting that strategies to target EphA2 activity may offer new therapeutic modalities for colorectal cancer.