Eph/ephrin profiling in human breast cancer reveals significant associations between expression level and clinical outcome

EphA2 cleavage by MT1-MMP triggers single cancer cell invasion via homotypic cell repulsion

Metalloproteinase-mediated cleavage of EphA2 induces breast tumor cells to shift from collective invasion to single-cell invasion.

Changes in EphA2 signaling can affect cancer cell–cell communication and motility through effects on actomyosin contractility. However, the underlying cell–surface interactions and molecular mechanisms of how EphA2 mediates these effects have remained unclear. We demonstrate here that EphA2 and membrane-anchored membrane type-1 matrix metalloproteinase (MT1-MMP) were selectively up-regulated and coexpressed in invasive breast carcinoma cells, where, upon physical interaction in same cell–surface complexes, MT1-MMP cleaved EphA2 at its Fibronectin type-III domain 1. This cleavage, coupled with EphA2-dependent Src activation, triggered intracellular EphA2 translocation, as well as an increase in RhoA activity and cell junction disassembly, which suggests an overall repulsive effect between cells. Consistent with this, cleavage-prone EphA2-D359I mutant shifted breast carcinoma cell invasion from collective to rounded single-cell invasion within collagen and in vivo. Up-regulated MT1-MMP also codistributed with intracellular EphA2 in invasive cells within human breast carcinomas. These results reveal a new proteolytic regulatory mechanism of cell–cell signaling in cancer invasion.

EphA4 is a prognostic factor in gastric cancer

BACKGROUND

Erythropoietin-producing hepatocellular (Eph) receptor, consisting of a family of receptor tyrosine kinases, plays critical roles in tumour development and is considered an attractive target for cancer therapy.

METHODS

Tumour samples were obtained from 222 patients with gastric adenocarcinoma who underwent gastrectomy. The expressions of EphA2, EphA4, and ephrinA1 were evaluated immunohistochemically.

RESULTS

High expressions of EphA2, EphA4, and ephrinA1 significantly correlated with variables related to tumour progression, including the depth of invasion, metastatic lymph nodes, pathological stage, and distant metastasis or recurrent disease. High expressions of EphA2, EphA4, and ephrinA1 were significantly associated with poorer disease-specific survival (DSS; p < 0.001, p < 0.001, p = 0.026). On multivariate analysis, EphA4 was an independent prognostic factor of DSS (hazard ratio [HR], 2.3; 95% confidence interval [CI], 1.1-4.8; p = 0.028), and EphA2 tended to be a prognostic factor (HR, 2.4; 95% CI, 1.0-5.8; p = 0.050). In stage II and III cancer, EphA4 and EphA2 were both significantly associated with shorter survival (p = 0.007 and 0.019), but only EphA2 was an independent prognostic factor (HR, 2.6; 95% CI, 1.1-6.3; p = 0.039).

CONCLUSION

EphA4 may play important roles in tumor progression and outcomes in patients with gastric cancer.

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

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

Deciphering HIC1 control pathways to reveal new avenues in cancer therapeutics

INTRODUCTION

The tumor suppressor gene HIC1 (Hypermethylated in Cancer 1), which encodes a transcriptional repressor with multiple partners and multiple targets, is epigenetically silenced but not mutated in tumors. HIC1 has broad biological roles during normal development and is implicated in many canonical processes of cancer such as control of cell growth, cell survival upon genotoxic stress, cell migration, and motility.

AREAS COVERED

The HIC1 literature herein discussed includes its discovery as a candidate tumor suppressor gene hypermethylated or deleted in many human tumors, animal models establishing it as tumor suppressor gene, its role as a sequence-specific transcriptional repressor recruiting several chromatin regulatory complexes, its cognate target genes, and its functional roles in normal tissues. Finally, this review discusses how its loss of function contributes to the early steps in tumorigenesis.

EXPERT OPINION

Given HIC1's ability to direct repressive complexes to sequence-specific binding sites associated with its target genes, its loss results in specific changes in the transcriptional program of the cell. An understanding of this program through identification of HIC1's target genes and their involvement in feedback loops and cell process regulation will yield the ability to leverage this knowledge for therapeutic translation.

Regulation of tumor initiation and metastatic progression by Eph receptor tyrosine kinases

In recent years, a growing body of evidence has indicated that signaling molecules previously implicated in axon guidance are important regulators of multistep tumorigenesis and progression. Eph receptors and ephrins belong to this special class of molecules that play important roles in both axon guidance and cancer. Tremendous progress has been made in the past few years in both understanding the role of Eph receptors and ephrins in cancer and designing therapeutic strategies for cancer therapy. This review will focus on new advances in elucidating the contribution of Eph/ephrin molecules to key processes in tumor initiation and metastatic progression, including cancer cell proliferation, invasion and metastasis, and tumor angiogenesis.

Distinctive binding of three antagonistic peptides to the ephrin-binding pocket of the EphA4 receptor

The EphA4 receptor tyrosine kinase interacts with ephrin ligands to regulate many processes, ranging from axon guidance and nerve regeneration to cancer malignancy. Thus antagonists that inhibit ephrin binding to EphA4 could be useful for a variety of research and therapeutic applications. In the present study we characterize the binding features of three antagonistic peptides (KYL, APY and VTM) that selectively target EphA4 among the Eph receptors. Isothermal titration calorimetry analysis demonstrated that all three peptides bind to the ephrin-binding domain of EphA4 with low micromolar affinity. Furthermore, the effects of a series of EphA4 mutations suggest that the peptides interact in different ways with the ephrin-binding pocket of EphA4. Chemical-shift changes observed by NMR spectroscopy upon binding of the KYL peptide involve many EphA4 residues, consistent with extensive interactions and possibly receptor conformational changes. Additionally, systematic replacement of each of the 12 amino acids of KYL and VTM identify the residues critical for EphA4, binding. The peptides exhibit a long half-life in cell culture medium which, with their substantial binding affinity and selectivity for EphA4, makes them excellent research tools to modulate EphA4 function.

EphrinA1-EphA2 interaction-mediated apoptosis and FMS-like tyrosine kinase 3 receptor ligand-induced immunotherapy inhibit tumor growth in a breast cancer mouse model

BACKGROUND

The receptor tyrosine kinase EphA2 is overexpressed in several types of cancers and is currently being pursued as a target for breast cancer therapeutics. The EphA2 ligand EphrinA1 induces EphA2 phosphorylation and intracellular internalization and degradation, thus inhibiting tumor progression. The hematopoietic growth factor, FMS-like tyrosine kinase 3 receptor ligand (Flt3L), promotes expansion and mobilization of functional dendritic cells.

METHODS

We tested the EphrinA1-EphA2 interaction in MDA-MB-231 breast cancer cells focusing on the receptor-ligand-mediated apoptosis of breast cancer cells. To determine whether EphrinA1-EphA2 interaction-associated apoptosis and Flt3L-mediated immunotherapy would have an additive effect in inhibiting tumor growth, we used an immunocompetent mouse model of breast cancer to evaluate intratumoral (i.t.) inoculation strategies with human adenovirus (HAd) vectors expressing either EphrinA1 (HAd-EphrinA1-Fc), Flt3L (HAd-Flt3L) or a combination of EphrinA1-Fc + Flt3L (HAd-EphrinA1-Fc + HAd-Flt3L).

RESULTS

In vitro analysis demonstrated that an EphrinA1-EphA2 interaction led to apoptosis-related changes in breast cancer cells. In vivo, three i.t. inoculations of HAd-EphrinA1-Fc showed potent inhibition of tumor growth. Furthermore, increased inhibition in tumor growth was observed with the combination of HAd-EphrinA1-Fc and HAd-Flt3L accompanied by the generation of an anti-tumor adaptive immune response.

CONCLUSIONS

The results obtained in the present study, indicating the induction of apoptosis and inhibition of mammary tumor growth, show the potential therapeutic benefits of HAd-EphrinA1-Fc. In combination with HAd-Flt3L, this represents a promising strategy for effectively inducing mammary tumor regression by HAd vector-based therapy.

The role of pseudokinases in cancer

Kinases play a critical role in regulating many cellular functions including development, differentiation and proliferation. To date, over 518 proteins with kinase activity, comprising ~2-3% of total cellular proteins, have been identified from within the human kinome. Interestingly, approximately 10% of kinases are categorised as pseudokinases since they lack one or more conserved catalytic residues within their kinase domain and were originally thought to have no enzymatic activity. Recently, there has been strong evidence to suggest that some pseudokinsases can not only function as scaffold proteins, but may also possess kinase activity leading to modulation of cell signalling pathways. Altered activity of these pseudokinases can result in impaired cellular function, particularly in malignancies. In this review we are discussing recent evidence that apart from a scaffolding role, pseudokinases also orchestrate cellular processes as active kinases per se in signalling pathways of malignant cells.

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.

The multifaceted roles of Eph/ephrin signaling in breast cancer

Eph receptors and their membrane-bound ligands are intimately involved in the control of morphogenic processes during embryonic development and adult tissue homeostasis. By their ability to orchestrate cell migration, pattern formation and tissue integrity they are also prone to be involved in carcinogenic growth. In this review we concentrate on their involvement in the normal and carcinogenic development of the breast. In this context we summarize their multi-faceted functions as tumor suppressors, tumor promoters, angiogenic inducers and regulators of stem cell homeostasis.

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.