High EPHB2 mutation rate in gastric but not endometrial tumors with microsatellite instability

Recurring EPHB1 mutations in human cancers alter receptor signalling and compartmentalisation of colorectal cancer cells

BACKGROUND

Ephrin (EPH) receptors have been implicated in tumorigenesis and metastasis, but the functional understanding of mutations observed in human cancers is limited. We previously demonstrated reduced cell compartmentalisation for somatic EPHB1 mutations found in metastatic colorectal cancer cases. We therefore integrated pan-cancer and pan-EPH mutational data to prioritise recurrent EPHB1 mutations for functional studies to understand their contribution to cancer development and metastasis.

METHODS

Here, 79,151 somatic mutations in 9,898 samples of 33 different tumour types were analysed with a bioinformatic pipeline to find 3D-mutated cluster pairs and hotspot mutations in EPH receptors. From these, 15 recurring EPHB1 mutations were stably expressed in colorectal cancer followed by confocal microscopy based in vitro compartmentalisation assays and phospho-proteome analysis.

RESULTS

The 3D-protein structure-based bioinformatics analysis resulted in 63% EPHB1 mutants with compartmentalisation phenotypes vs 43% for hotspot mutations. Whereas the ligand-binding domain mutations C61Y, R90C, and R170W, the fibronectin domain mutation R351L, and the kinase domain mutation D762N displayed reduced to strongly compromised cell compartmentalisation, the kinase domain mutations R743W and G821R enhanced this phenotype. While mutants with reduced compartmentalisation also had reduced ligand induced receptor phosphorylation, the enhanced compartmentalisation was not linked to receptor phosphorylation level. Phosphoproteome mapping pinpointed the PI3K pathway and PIK3C2B phosphorylation in cells harbouring mutants with reduced compartmentalisation.

CONCLUSIONS

This is the first integrative study of pan-cancer EPH receptor mutations followed by in vitro validation, a robust way to identify cancer-causing mutations, uncovering EPHB1 mutation phenotypes and demonstrating the utility of protein structure-based mutation analysis in characterization of novel cancer genes. Video Abstract.

Gene Expression Profile Reveals a Prognostic Signature of Non–MSI-H/pMMR Colorectal Cancer

Studies have demonstrated that non–MSI-H/pMMR colorectal cancer (CRC) has a worse prognosis and relapse rate than microsatellite instability-high (MSI-H)/mismatch repair deficient (dMMR) CRC. Hence, searching for a novel tool to advance the prognostic management of non–MSI-H/pMMR CRC is vital. In this study, using three independent public cohorts and a clinical in-house cohort, we developed and validated a microsatellite stable–associated signature (MSSAS). The initial signature establishment was performed in GSE39582 (n = 454). This was followed by independent validation of this signature in The Cancer Genome Atlas–CRC (n = 312), GSE39084 (n = 54), and in-house cohort (n = 146). As a result, MSSAS was proven to be an independent risk factor for overall survival and relapse-free survival in non–MSI-H/pMMR CRC. Receiver operating characteristic analysis showed that MSSAS had a stable and accurate performance in all cohorts for 1, 3, and 5 years, respectively. Further analysis suggested that MSSAS performed better than age, gender, and the T, N, M, and AJCC stages, adjuvant chemotherapy, tumor mutation burden, neoantigen, and TP53, KRAS, BRAF, and PIK3CA mutations. The clinical validation was executed to further ensure the robustness and clinical feasibility of this signature. In conclusion, MSSAS might be a robust and promising biomarker for advancing clinical management of non–MSI-H/pMMR CRC.

The Roles of EphB2 in Cancer

The erythropoietin-producing hepatocellular carcinoma (Eph) receptors and their Eph receptor-interacting (ephrin) ligands together constitute a vital cell communication system with diverse roles. Experimental evidence revealed Eph receptor bidirectional signaling with both tumor-promoting and tumor-suppressing activities in different cancer types and surrounding environment. Eph receptor B2 (EphB2), an important member of the Eph receptor family, has been proved to be aberrantly expressed in many cancer types, such as colorectal cancer, gastric cancer and hepatocellular carcinoma, resulting in tumor occurrence and progression. However, there are no reviews focusing on the dual roles of EphB2 in cancer. Thus, in this paper we systematically summarize and discuss the roles of EphB2 in cancer. Firstly, we review the main biological features and the related signaling regulatory mechanisms of EphB2, and then we summarize the roles of EphB2 in cancer through current studies. Finally, we put forward our viewpoint on the future prospects of cancer research focusing on EphB2, especially with regard to the effects of EphB2 on tumor immunity.

Gynecological Cancers Caused by Deficient Mismatch Repair and Microsatellite Instability

Mutations in mismatch repair genes leading to mismatch repair (MMR) deficiency (dMMR) and microsatellite instability (MSI) have been implicated in multiple types of gynecologic malignancies. Endometrial carcinoma represents the largest group, with approximately 30% of these cancers caused by dMMR/MSI. Thus, testing for dMMR is now routine for endometrial cancer. Somatic mutations leading to dMMR account for approximately 90% of these cancers. However, in 5-10% of cases, MMR protein deficiency is due to a germline mutation in the mismatch repair genes MLH1, MSH2, MSH6, PMS2, or EPCAM. These germline mutations, known as Lynch syndrome, are associated with an increased risk of both endometrial and ovarian cancer, in addition to colorectal, gastric, urinary tract, and brain malignancies. So far, gynecological cancers with dMMR/MSI are not well characterized and markers for detection of MSI in gynecological cancers are not well defined. In addition, currently advanced endometrial cancers have a poor prognosis and are treated without regard to MSI status. Elucidation of the mechanism causing dMMR/MSI gynecological cancers would aid in diagnosis and therapeutic intervention. Recently, a new immunotherapy was approved for the treatment of solid tumors with MSI that have recurred or progressed after failing traditional treatment strategies. In this review, we summarize the MMR defects and MSI observed in gynecological cancers, their prognostic value, and advances in therapeutic strategies to treat these cancers.

Eph receptors: the bridge linking host and virus

Eph (erythropoietin-producing hepatoma) receptors and Ephrin ligands constitute the largest subfamily of receptor tyrosine kinase (RTK), which were first discovered in tumors. Heretofore, Eph protein has been shown to be involved in various tumor biological behaviors including proliferation and progression. The occurrence of specific types of tumor is closely related to the virus infection. Virus entry is a complex process characterized by a series of events. The entry into target cells is an essential step for virus to cause diseases, which requires the fusion of the viral envelope and host cellular membrane mediated by viral glycoproteins and cellular receptors. Integrin molecules are well known as entry receptors for most herpes viruses. However, in recent years, Eph receptors and their Ephrin ligands have been reported to be involved in virus infections. The main mechanism may be the interaction between Eph receptors and conserved viral surface glycoprotein, such as the gH/gL or gB protein of the herpesviridae. This review focuses on the relationship between Eph receptor family and virus infection that summarize the processes of viruses such as EBV, KSHV, HCV, RRV, etc., infecting target cells through Eph receptors and activating its downstream signaling pathways resulting in malignancies. Finally, we discussed the perspectives to block virus infection, prevention, and treatment of viral-related tumors via Eph receptor family.

EphB2 represents an independent prognostic marker in patients with gastric cancer and promotes tumour cell aggressiveness

Dysregulated expression of ephrin type-B receptor 2 (EphB2) has been linked with the development and progression of solid tumours. In the current study, we attempted to investigate the clinical relevance in GC and the effect of EphB2 expression on gastric cancer (GC) cells. EphB2 protein levels in GC and benign gastric tissues were determined using immunohistochemistry. EphB2 transcript expression in a GC cohort with GC tissue samples (n=171) and paired adjacent normal gastric tissues (n=97) was determined using qPCR. The EphB2 expression was over-activated using a CRISPR activator for the investigation of its cellular function. The expression levels of the EphB2 protein in the tumour tissues of tissue arrays were higher than the benign non-cancerous gastric tissues (P<0.05). EphB2 mRNA expression in GC tissues was also significantly elevated when compared with adjacent non-cancerous tissues (P<0.01). EphB2 activation promoted the migration and invasion abilities of the GC cell lines (P<0.01, respectively). In contrast, EphB2 activation significantly decreased the adhesion in GC cells (P<0.0001, respectively). The enrichment analysis of the correlated genes in a GC cohort indicates that EphB2 may function through mediating the cytokine-cytokine interaction, JAK-STAT and TP53 signaling pathways. In conclusion, EphB2 represents as a novel independent prognostic marker in GC. And activation of the EphB2 gene expression elevated the levels of migration and invasion, but suppressed adhesion of GC cells, indicating that EphB2 may act as a tumour promotor in GC. Our findings thus provide fundamental evidence for the consideration of the therapeutic potential of targeting EphB2 in GC.

Viewing the Eph receptors with a focus on breast cancer heterogeneity

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

Loss of the EPH receptor B6 contributes to colorectal cancer metastasis

Although deregulation of EPHB signaling has been shown to be an important step in colorectal tumorigenesis, the role of EPHB6 in this process has not been investigated. We found here that manipulation of EPHB6 levels in colon cancer cell lines has no effect on their motility and growth on a solid substrate, soft agar or in a xenograft mouse model. We then used an EphB6 knockout mouse model to show that EphB6 inactivation does not efficiently initiate tumorigenesis in the intestinal tract. In addition, when intestinal tumors are initiated genetically or pharmacologically in EphB6^+/+ and EphB6^−/− mice, no differences were observed in animal survival, tumor multiplicity, size or histology, and proliferation of intestinal epithelial cells or tumor cells. However, reintroduction of EPHB6 into colon cancer cells significantly reduced the number of lung metastasis after tail-vein injection in immunodeficient mice, while EPHB6 knockdown in EPHB6-expressing cells increased their metastatic spread. Consistently, although EPHB6 protein expression in a series of 130 primary colorectal tumors was not associated with patient survival, EPHB6 expression was significantly lower in lymph node metastases compared to primary tumors. Our results indicate that the loss of EPHB6 contributes to the metastatic process of colorectal cancer.

EphB2 Promotes Progression of Cutaneous Squamous Cell Carcinoma

Keratinocyte-derived skin cancer, cutaneous squamous cell carcinoma (cSCC), is the most common metastatic skin cancer. We have examined the role of Eph/ephrin signaling in the progression of cSCC. Analysis of the expression of EPH and EFN families in cSCC cells and normal epidermal keratinocytes revealed overexpression of EPHB2 mRNA in cSCC cells and cSCC tumors in vivo. Tumor cell-specific overexpression of EphB2 was detected in human cSCCs and in chemically induced mouse cSCCs with immunohistochemistry, whereas the expression of EphB2 was low in premalignant lesions and normal skin. Knockdown of EphB2 expression in cSCC cells suppressed growth and vascularization of cSCC xenografts in vivo and inhibited proliferation, migration, and invasion of cSCC cells in culture. EphB2 knockdown downregulated expression of genes associated with biofunctions cell viability, migration of tumor cells, and invasion of tumor cells. Among the genes most downregulated by EphB2 knockdown were MMP1 and MMP13. Moreover, activation of EphB2 signaling by ephrin-B2-Fc enhanced production of invasion proteinases matrix metalloproteinase-13 (MMP13) and MMP1, and invasion of cSCC cells. These findings provide mechanistic evidence for the role of EphB2 in the early progression of cSCC to the invasive stage and identify EphB2 as a putative therapeutic target in this invasive skin cancer.

Microsatellite instability: an update

Deficient DNA mismatch repair (MMR) results in a strong mutator phenotype known as microsatellite instability (MSI), which is a hallmark of Lynch syndrome-associated cancers. MSI is characterized by length alterations within simple repeated sequences that are called microsatellites. Lynch syndrome is primarily caused by mutations in the MMR genes, mainly MLH1 and MSH2, and less frequently in MSH6, and rarely PMS2, and large genomic rearrangements account for 5-20 % of all mutations. Germ line hemiallelic methylations of MLH1 or MSH2 are termed as epimutations and have been identified as causative of Lynch syndrome. Moreover, germ line 3' deletions of EPCAM gene is involved in MSH2 methylation. MSI is also observed in about 15 % of sporadic colorectal cancer (CRC), gastric cancer (GC), and endometrial cancer (EC), and at lower frequencies in other cancers, often in association with hypermethylation of the MLH1 gene. Trimethylation of histone H3 on Lys36 (H3K36 me3) is an epigenetic histone mark that was required for DNA MMR in vivo. Thus, mutations in the H3K36 trimethyltransferase SETD2 have been reported as a potential cause of MSI. Genetic, epigenetic, and transcriptomic differences have been identified between cancers with and without MSI. Recent comprehensive molecular characterizations of CRC, EC, and GC by The Cancer Genome Atlas indicate that MSI+ cancers are distinct biological entities. The BRAF V600E mutation is specifically associated with sporadic MSI+ CRCs with methylated MLH1, but is not associated with Lynch syndrome-related CRCs. Accumulating evidence indicates a role of interactions between MSI and microRNA (miRNA) in the pathogenesis of MSI-positive (MSI+) cancer. As another new mechanism underlying MSI, overexpression of miR-155 or miR-21 has been shown to downregulate the expression of the MMR genes. Gene targets of frameshift mutations caused by MSI are involved in various cellular functions, including DNA repair (MSH3 and MSH6), cell signaling (TGFBR2 and ACVR2A), apoptosis (BAX), epigenetic regulation (HDAC2 and ARID1A), and miRNA processing (TARBP2 and XPO5), and a subset of MSI+ CRCs reportedly shows the mutated miRNA machinery phenotype. Moreover, microsatellite repeats in miRNA genes, such as hsa-miR-1273c, may be novel MSI targets for CRC, and mutations in noncoding regulatory regions of MRE11, BAX (BaxΔ2), and HSP110 (HSP110ΔE9) may affect the efficiency of chemotherapy. Thus, analyses of MSI and its related molecular alterations in cancers are increasingly relevant in clinical settings, and MSI is a useful screening marker for identifying patients with Lynch syndrome and a prognostic factor for chemotherapeutic interventions. In this review, we summarize recent advances in the pathogenesis of MSI and focus on genome-wide analyses that indicate the potential use of MSI and related alterations as biomarkers and novel therapeutic targets.

Aberrant EphB/ephrin-B expression in experimental gastric lesions and tumor cells

AIM: To determine whether the expression profiles of EphB receptor and ephrin-B ligand can be used as markers for dysplastic/oncogenic transformation in gastric mucosa.

METHODS: The protein expression and localization of EphB and ephrin-B in normal, ulcerated regenerating, and dysplastic gastric mucosa were examined in a rat experimental model by immunolabeling, and mRNA expression was assessed in four human gastric carcinoma cell lines by reverse transcription-polymerase chain reaction.

RESULTS: Ephrin-B- and EphB-expressing regions were divided along the pit-gland axis in normal gastric units. EphB2 was transiently upregulated in the experimental ulcer, and its expression domain extended to gastric pits and/or the luminal surface where ephrin-B-expressing pit cells reside. EphB2, B3, and B4 and ephrin-B1 were coexpressed in the experimental gastric dysplasia, and more than one ligand-receptor pair was highly expressed in each of the gastric carcinoma cell lines.

CONCLUSION: Robust and stable coexpression of EphB and ephrin-B is a feature common to experimentally induced gastric dysplasia and human gastric carcinoma cell lines as compared to normal gastric and ulcerated regenerating epithelia. Thus, EphB/ephrin-B may be a useful marker combination for dysplastic/oncogenic transformation in gastric cancer.

Expression of Eph A4, Eph B2 and Eph B4 receptors in AML

Eph receptors represent the largest subfamily of receptor tyrosine kinases (RTKs). The up- regulation of Eph receptors has been documented in various solid tumors, where it often correlates with poor prognosis. Their significance in hematologic malignancies is still unclear. This study aimed to investigate the expression of Eph A4, Eph B2, and Eph B4 mRNA in non - M3 AML patients and determine their prognostic significance. Bone marrow samples from 101 newly diagnosed non - M3 AML patients and 26 healthy controls for comparison were quantified by real time reverse transcriptase polymerase chain reaction (RT-PCR), and the comparative cycle threshold (Ct) method was used to determine their relative expression levels to GUS control gene. The results showed that expression of all selected Eph receptors was significantly lower in AML patients comparing to controls. It also differed according to FAB subtypes. The decreased expression levels of Eph A4 were associated with higher leukocytes (p = 0.022) and blast cell counts (p = 0.001), and unfavorable FLT3-ITD mutation. Our study revealed significant correlation between lower EphB2 expression levels, and higher complete remission rate (p = 0.009724) and longer overall survival. Additionally, we found that patients with shorter RFS had decreased EphB4 expression (p = 0.00). In conclusion, the results suggest the prognostic impact of decreased expression levels of some Eph receptors in AML patients.

Eph receptors and ephrins as targets for cancer therapy

Eph receptor tyrosine kinases and their ephrin ligands are involved in various signalling pathways and mediate critical steps of a wide variety of physiological and pathological processes. Increasing experimental evidence demonstrates that both Eph receptor and ephrin ligands are overexpressed in a number of human tumours, and are associated with tumour growth, invasiveness and metastasis. In this regard, the Eph/ephrin system provides the foundation for potentially exciting new targets for anticancer therapies for Eph-expressing tumours. The purpose of this review is to outline current advances in the role of Eph receptors and ephrin ligands in cancer, and to discuss novel therapeutic approaches of anticancer therapies.

An efficient bioorthogonal strategy using CuAAC click chemistry for radiofluorinations of SNEW peptides and the role of copper depletion

The EphB2 receptor is known to be overexpressed in various types of cancer and is therefore a promising target for tumor cell imaging by positron emission tomography (PET). In this regard, imaging could facilitate the early detection of EphB2-overexpressing tumors, monitoring responses to therapy directed toward EphB2, and thus improvement in patient outcomes. We report the synthesis and evaluation of several fluorine-18-labeled peptides containing the SNEW amino acid motif, with high affinity for the EphB2 receptor, for their potential as radiotracers in the non-invasive imaging of cancer using PET. For the purposes of radiofluorination, EphB2-antagonistic SNEW peptides were varied at the C terminus by the introduction of L-cysteine, and further by alkyne- or azide-modified amino acids. In addition, two novel bifunctional and bioorthogonal labeling building blocks [(18)F]AFP and [(18)F]BFP were applied, and their capacity to introduce fluorine-18 was compared with that of the established building block [(18)F]FBAM. Copper-assisted Huisgen 1,3-dipolar cycloaddition, which belongs to the set of bioorthogonal click chemistry reactions, was used to introduce both novel building blocks into azide- or alkyne-modified SNEW peptides under mild conditions. Finally, the depletion of copper immediately after radiolabeling is a highly important step of this novel methodology.

Brush border myosin Ia inactivation in gastric but not endometrial tumors

Brush border Myosin Ia (MYO1A) has been shown to be frequently mutated in colorectal tumors with microsatellite instability (MSI) and to have tumor suppressor activity in intestinal tumors. Here, we investigated the frequency of frameshift mutations in the A8 microsatellite in exon 28 of MYO1A in MSI gastric and endometrial tumors and found a high mutation rate in gastric (22/47; 46.8%) but not endometrial (3/48; 6.2%) tumors. Using a regression model, we show that MYO1A mutations are likely to confer a growth advantage to gastric, but not endometrial tumors. The mutant MYO1A(7A) protein was shown to lose its membrane localization in gastric cancer cells and a cycloheximide-chase assay demonstrated that the mutant MYO1A(7A) protein has reduced stability compared to the wild type MYO1A. Frequent MYO1A promoter hypermethylation was also found in gastric tumors. Promoter methylation negatively correlates with MYO1A mRNA expression in a series of 58 non-MSI gastric primary tumors (Pearson's r = -0.46; p = 0.0003) but not in a cohort of 54 non-MSI endometrial tumors and treatment of gastric cancer cells showing high MYO1A promoter methylation with the demethylating agent 5-aza-2'-deoxycytidine, resulted in a significant increase of MYO1A mRNA levels. We found that normal gastric epithelial cells, but not normal endometrial cells, express high levels of MYO1A. Therefore, when considered together, our findings suggest that MYO1A has tumor suppressor activity in the normal gastric epithelium but not in the normal endometrium and inactivation of MYO1A either genetically or epigenetically may confer gastric epithelial cells a growth advantage.

Eph-dependent cell-cell adhesion and segregation in development and cancer

Numerous studies attest to essential roles for Eph receptors and their ephrin ligands in controlling cell positioning and tissue patterning during normal and oncogenic development. These studies suggest multiple, sometimes contradictory, functions of Eph-ephrin signalling, which under different conditions can promote either spreading and cell-cell adhesion or cytoskeletal collapse, cell rounding, de-adhesion and cell-cell segregation. A principle determinant of the balance between these two opposing responses is the degree of receptor/ligand clustering and activation. This equilibrium is likely altered in cancers and modulated by somatic mutations of key Eph family members that have emerged as candidate cancer markers in recent profiling studies. In addition, cross-talk amongst Ephs and with other signalling pathways significantly modulates cell-cell adhesion, both between and within Eph- and ephrin-expressing cell populations. This review summarises our current understanding of how Eph receptors control cell adhesion and morphology, and presents examples demonstrating the importance of these events in normal development and cancer.

Complementary expression and repulsive signaling suggest that EphB receptors and ephrin-B ligands control cell positioning in the gastric epithelium

Eph receptors and ephrin ligands are membrane-bound cell-cell communication molecules with well-defined roles in development. However, their expression and functions in the gastric epithelium are virtually unknown. We detected several EphB receptors and ephrin-Bs in the gastric corpus mucosa of the adult rodent stomach by RT-PCR amplification. Immunostaining showed complementary expression patterns, with EphB receptors preferentially expressed in the deeper regions and ephrin-Bs in the superficial regions of the gastric units. EphB1, EphB2 and EphB3 are expressed in mucous neck, chief and parietal cells, respectively. In contrast, ephrin-B1 is in pit cells and proliferating cells of the isthmus. In a mouse ulcer model, EphB2 expression was upregulated in the regenerating epithelium and expanded into the isthmus. Thus, EphB/ephrin-B signaling likely occurs preferentially in the isthmus, where receptor-ligand overlap is highest. We show that EphB signaling in primary gastric epithelial cells promotes cell retraction and repulsion at least in part through RhoA activation. Based on these findings, we propose that the EphB-positive progeny of gastric stem cells migrates from the isthmus toward the bottom of the gastric glands due to repulsive signals arising from contact with ephrin-Bs, which are preferentially expressed in the more superficial regions of the isthmus and gastric pits.

KRAS signaling pathway alterations in microsatellite unstable gastrointestinal cancers

Microsatellite instability (MSI) occurs in about 15% of gastrointestinal cancers and it is associated with specific clinic, pathologic, and molecular features of the tumors. MSI-high (MSI-H) carcinomas also follow specific tumor development pathways. This review is focused on the molecular profile of alterations in members of the KRAS signaling pathway (EGFR, KRAS, BRAF, PIK3CA, RASSF1A, and MLK3 genes) in MSI gastrointestinal carcinomas. Alterations in these genes characterize more than half of gastrointestinal cancers and frequently occur simultaneously in the same tumor, pinpointing the KRAS signaling pathway as one of the most frequently altered pathways in this subset of cancers. Nowadays, many and novel inhibitors targeting molecules of this signaling pathway are being described; therefore, it is worthwhile to test their efficacy in MSI gastrointestinal cancers in order to develop new and more directed targeted therapies for patients affected by this disease.

Influence of A9 region mutation in EphB2 gene in the prognosis of patients with colorectal adenocarcinoma

BACKGROUND

EphB2 is a transmembrane glycoprotein implicated in the regulation of cell growth, differentiation, and motility. It has been proposed as a tumor suppressor gene, and the role of EphB2 protein in tumorogenesis has been demonstrated. The aim of this study was to test the influence of mutation of A9 region in EphB2 gene in the prognosis of patients with sporadic CCR.

MATERIALS AND METHODS

A total of 473 patients with colorectal cancer were included. A9 region in exon 17 of EphB2 was amplified using specific primer and analyzed using Genescan. All mutations were confirmed by direct sequencing.

RESULTS

EphB2 mutation was detected in 13 of the 473 patients (2.7%). Mutation of EphB2 showed association with tumor site, 12 of 13 mutations were proximal tumors (P < 0.001). EphB2 mutation confers better prognosis in the adenocarcinoma group; 100% of patients carrying the mutation survived and were disease free after 72 months (P = 0.02 and 0.03, respectively).

CONCLUSIONS

Despite the low frequency of EphB2 gene, we got promising results. It would be very interesting to increase the population size to verify our results. If these findings are confirmed, EphB2 could help discriminate patients with adenocarcinoma with different prognosis and to improve the election of the most suitable treatment in each case.

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.

Reduced expression of EphB2 is significantly associated with nodal metastasis in Chinese patients with gastric cancer

AIMS

EphB2 is a member of the Eph receptor tyrosine kinase family that has been involved in the regulation of cytoskeleton organization and cell migration in various cell types. Its role and regulation in carcinogenesis is controversial, especially in gastric cancer. We detected EphB2 expression and determined its clinical significance and explored its underlying molecular mechanism in gastric cancers.

METHODS

Tissue microarray blocks containing primary gastric cancer, lymph node metastases, and adjacent normal mucosa specimens obtained from 337 Chinese patients were constructed. Expression of EphB2 in these specimens was analyzed using immunohistochemistry. Mutation analysis at the A9 tract in exon 17 and loss of heterozygosity analysis at the EphB2 gene locus were carried out in 13 sporadic EphB2-negative gastric cancers.

RESULTS

Complete loss of EphB2 expression was observed in 177 (52.5%) of the 337 primary tumor and 41 (82%) of the 50 nodal metastases. Loss of EphB2 expression was significantly associated with advanced T stage, nodal metastasis, advanced disease stage, and poor histological differentiation. Loss of EphB2 expression correlated significantly with poor survival rates in both univariate and multivariate analysis. No frameshift mutation, but a higher frequency of allelic loss, was found in EphB2-negative primary and metastatic tumor samples.

CONCLUSIONS

Frequent deletion and decreased expression of EphB2 protein suggested it as a negative biomarker for gastric carcinogenesis and a potential predictor of the outcome of patients with gastric cancer.

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.

Molecular targets and biological modifiers in gastric cancer

The overall survival of gastric cancer patients remains poor despite efforts and advances in its prevention, diagnosis, and treatment. The development of new therapies is crucial for the effective control of this disease. An increasing number of genetic and epigenetic alterations have been associated with distinct histological types of gastric cancer. In this review, we will discuss the involvement of E-cadherin, EGFR, ERBB2, MMR genes, KRAS, and PIK3CA in the development and progression of gastric cancer and their role as biomarkers or as novel putative targets for therapy.

Overexpression of the receptor tyrosine kinase EphA4 in human gastric cancers

AIM: To clarify the expression and role of Ephrin receptor A4 (EphA4) in gastric cancer in relation to clinicopathological characteristics and the expression of fibroblast growth factor receptor 1 (FGFR1) and ephrin ligands.

METHODS: Eleven gastric carcinoma cell lines, 24 paired surgical fresh specimens of gastric adenocarcinoma and adjacent nontumor tissue, 74 conventional formalin-fixed, paraffin-embedded tumor specimens, and 55 specimens spotted on tissue microarray (TMA) were analyzed. Reverse transcription-PCR (RT-PCR), real-time RT-PCR, immunohistochemistry, and cell growth assays were performed.

RESULTS: Overexpression of EphA4 mRNA expression was observed in 8 (73%) of 11 gastric cancer cell lines and 10 (42%) of 24 gastric cancer tissues. Overexpression of EphA4, analyzed by immunohistochemistry, was observed in 62 (48%) of 129 gastric cancer tissues. EphA4 overexpression, at the protein level, was significantly associated with depth of invasion and recurrence. EphA4 overexpression was also correlated with FGFR1 overexpression. Patients with EphA4-positive cancer had significantly shorter overall survival periods than did those with EphA4-negative cancer (P = 0.0008). The mRNAs for ephrin ligands were coexpressed in various combinations in gastric cancer cell lines and cancer tissues. Downregulation of EphA4 expression by siRNA in EphA4-overexpressing gastric cancer cell lines resulted in a significant decrease in cell growth.

CONCLUSION: Our results suggest that overexpression of EphA4 plays a role in gastric cancer.

Carcinogenesis and microsatellite instability: the interrelationship between genetics and epigenetics

DNA mismatch repair (MMR) deficiency results in a strong mutator phenotype and high-frequency microsatellite instability (MSI-H), which are the hallmarks of tumors arising within Lynch syndrome. MSI-H is characterized by length alterations within simple repeated sequences, microsatellites. Lynch syndrome is primarily due to germline mutations in one of the DNA MMR genes; mainly hMLH1 or hMSH2 and less frequently hMSH6 and rarely hPMS2. Germline hemiallelic methylation of MLH1, termed epimutation, has been reported to be a new cause of Lynch syndrome. MSI-H is also observed in approximately 15% of colorectal, gastric and endometrial cancers and in lower frequencies in a minority of other tumors, where it is associated with the hypermethylation of the promoter region of hMLH1. MSI-H underlies a distinctive tumorigenic pathway because cancers with MSI-H exhibit many differences in genotype and phenotype relative to cancers without MSI-H, irrespective of their hereditary or sporadic origins. Genetic, epigenetic and transcriptomic differences exist between cancers with and those without the MSI-H. The BRAF V600E mutation is associated with sporadic MSI-H colorectal cancers (CRCs) harboring hMLH1 methylation but not Lynch syndrome-related CRCs. The differences in genotype and phenotype between cancers with and those without MSI-H are likely to be causally linked to their differences in biological and clinical features. Therefore, the diagnosis of MSI-H in cancers is thus considered to be of increasing relevance, because MSI-H is a useful screening marker for identifying patients with Lynch syndrome, a better prognostic factor and could affect the efficacy of chemotherapy. This review addresses recent advances in the field of microsatellite instability research.

Eph-ephrin signalling in adult tissues and cancer

Eph receptor tyrosine kinases and their ligands, the ephrins, play key roles in the regulation of migration and cell adhesion during development, thereby influencing cell fate, morphogenesis and organogenesis. Recent findings suggest that Eph signalling also controls the architecture and physiology of different tissues in the adult body under normal and pathological conditions such as cancer. A prime example is the intestinal epithelium where EphB-ephrinB interactions regulate both cell positioning and tumor progression. Here, we will review recent advances on the role of Eph-ephrin signalling in the intestine and other organs.

Three-dimensional structure of the EphB2 receptor in complex with an antagonistic peptide reveals a novel mode of inhibition

The Eph family of receptor tyrosine kinases has been implicated in tumorigenesis as well as pathological forms of angiogenesis. Understanding how to modulate the interaction of Eph receptors with their ephrin ligands is therefore of critical interest for the development of therapeutics to treat cancer. Previous work identified a set of 12-mer peptides that displayed moderate binding affinity but high selectivity for the EphB2 receptor. The SNEW antagonistic peptide inhibited the interaction of EphB2 with ephrinB2, with an IC50 of approximately 15 microm. To gain a better molecular understanding of how to inhibit Eph/ephrin binding, we determined the crystal structure of the EphB2 receptor in complex with the SNEW peptide to 2.3-A resolution. The peptide binds in the hydrophobic ligand-binding cleft of the EphB2 receptor, thus competing with the ephrin ligand for receptor binding. However, the binding interactions of the SNEW peptide are markedly different from those described for the TNYL-RAW peptide, which binds to the ligand-binding cleft of EphB4, indicating a novel mode of antagonism. Nevertheless, we identified a conserved structural motif present in all known receptor/ligand interfaces, which may serve as a scaffold for the development of therapeutic leads. The EphB2-SNEW complex crystallized as a homodimer, and the residues involved in the dimerization interface are similar to those implicated in mediating tetramerization of EphB2-ephrinB2 complexes. The structure of EphB2 in complex with the SNEW peptide reveals novel binding determinants that could serve as starting points in the development of compounds that modulate Eph receptor/ephrin interactions and biological activities.

Microsatellite instability markers for identifying early-onset colorectal cancers caused by germ-line mutations in DNA mismatch repair genes

PURPOSE

Microsatellite instability (MSI) testing of colorectal cancer tumors is used as a screening tool to identify patients most likely to be mismatch repair (MMR) gene mutation carriers. We wanted to examine which microsatellite markers currently used to detect MSI best predict early-onset colorectal cancer caused by germ-line mutations in MMR genes.

EXPERIMENTAL DESIGN

Invasive primary tumors from a population-based sample of 107 cases of colorectal cancer diagnosed before age 45 years and tested for germ-line mutations in MLH1, MSH2, MSH6, and PMS2 and MMR protein expression were screened for MSI using the National Cancer Institute panel and an expanded 10-microsatellite marker panel.

RESULTS

The National Cancer Institute five-marker panel system scored 31 (29%) as (NCI)MSI-High, 13 (12%) as (NCI)MSI-Low, and 63 (59%) as (NCI)MS-Stable. The 10-marker panel classified 18 (17%) as (10)MSI-High, 17 (16%) as (10)MSI-Low, and 72 (67%) as (10)MS-Stable. Of the 26 cancers that lacked the expression of at least one MMR gene, 24 (92%) were positive for some level of MSI (using either microsatellite panel). The mononucleotide repeats Bat26, Bat40, and Myb were unstable in all (10)MSI-High cancers and all MLH1 and MSH2 mutation carriers (100% sensitive). Bat40 and Bat25 were unstable in all tumors of MSH6 mutation carriers (100% sensitive). Bat40 was unstable in all MMR gene mutation carriers (100% sensitive). By incorporating seven mononucleotide repeats markers into the 10-marker panel, we were able to distinguish the carriers of MSH6 mutations (all scored (10)MSI-Low) from the MLH1 and MSH2 mutation carriers (all scored (10)MSI-High).

CONCLUSIONS

In early-onset colorectal cancer, a microsatellite panel containing a high proportion of mononuclear repeats can distinguish between tumors caused by MLH1 and MSH2 mutations from those caused by MSH6 mutations.