Tyrosine kinase activity of EphA2 promotes its S897 phosphorylation and glioblastoma cell proliferation

Comprehensive analysis of EphA2 in pan-cancer: A prognostic biomarker associated with cancer immunity

BACKGROUND

Several studies have reported a significant relationship between Ephrin receptor A2 (EphA2) and malignant progression in numerous cancers. However, there is a lack of comprehensive pan-cancer analysis on the prognostic value, mutation status, methylation landscape, and potential immunological function of EphA2.

METHOD

Using The Cancer Genome Atlas, Genotype Tissue Expression Database and GEO data, we analysed the differences in EphA2 expression between normal and tumour tissues and the effects of EphA2 on the prognosis of different tumours. Furthermore, using GSCALite, cBioPortal, TISDB, ULCLAN and TIMER 2.0 databases or platforms, we comprehensively analysed the potential oncogenic mechanisms or manifestations of EphA2 in 33 different tumour types, including tumour mutation status, DNA methylation status and immune cell infiltration. The correlation of EphA2 with immune checkpoints, tumour mutational burden, DNA microsatellite instability and DNA repair genes was also calculated. Finally, the effects of EphA2 inhibitors on the proliferation of human glioma and lung cancer cells were verified in cellular experiments.

RESULTS

EphA2 is differentially expressed in different tumours, and patients with overexpression have poorer overall survival. In addition, gene mutations, gene copy number variation and DNA/RNA methylation of EphA2 have been identified in various tumours. Moreover, EphA2 is positively associated with immune infiltration involving macrophages and CD8+ T cells. Further, EphA2 mRNA expression is significantly associated with immune checkpoint in various cancers, especially programmed death-ligand 1. Finally, the EphA2 inhibitor ALW-II-41-27 shows potent anti-tumour activity.

CONCLUSION

Our first pan-cancer study of EphA2 provides insight into the prognostic and immunological roles of EphA2 in different tumours, suggesting that EphA2 might be a potential biomarker for poor prognosis and immune infiltration in cancer.

Downregulation of EphA2 stability by RNF5 limits its tumor-suppressive function in HER2-negative breast cancers

Ephrin receptor A2 (EphA2) plays dual functions in tumorigenesis through ligand-independent tumor promotion or ligand-dependent tumor suppression. However, the regulation of EphA2 tumor-suppressive function remains unclear. Here, we showed that RNF5 interacts with EphA2 and induces its ubiquitination and degradation, decreases the stability and cell surface distribution of EphA2 and alters the balance of its phosphorylation at S897 and Y772. In turn, RNF5 inhibition decreases ERK phosphorylation and increases p53 expression through an increase in the EphA2 level in HER2-negative breast cancer cells. Consequently, RNF5 inhibition increases the adhesion and decreases the migration of HER2-negative breast cancer cells, and RNF5 silencing suppresses the growth of xenograft tumors derived from ER-positive, HER2-negative breast cancer cells with increased EphA2 expression and altered phosphorylation. RNF5 expression is inversely correlated with EphA2 expression in breast cancers, and a high EphA2 level accompanied by a low RNF5 level is related to better survival in patients with ER-positive, HER2-negative breast cancers. These studies revealed that RNF5 negatively regulates EphA2 properties and suppresses its tumor-suppressive function in HER2-negative breast cancers.

Filamin A forms a complex with EphA2 and regulates EphA2 serine 897 phosphorylation and glioblastoma cell proliferation

EphA2 is phosphorylated on serine 897 (S897) in response to growth factors such as epidermal growth factor (EGF) and on tyrosine 588 (Y588) in response to its ligand ephrinA1, causing different cellular responses. In this study, we show that the actin-binding protein Filamin A forms a complex with EphA2 and promotes its S897 phosphorylation and glioblastoma cell proliferation. Suppression of Filamin A expression by siRNAs inhibited glioblastoma cell proliferation induced by EGF stimulation or overexpression of EphA2. Knockdown of Filamin A inhibited EGF-induced S897 phosphorylation of EphA2, whereas it had little effect on ephrinA1-induced Y588 phosphorylation of EphA2. Furthermore, Filamin A expression affected the subcellular localization of EphA2. This study suggests that Filamin A selectively promotes EphA2 S897 phosphorylation and plays an important role in glioblastoma cell proliferation.

Cholenic acid derivative UniPR1331 impairs tumor angiogenesis via blockade of VEGF/VEGFR2 in addition to Eph/ephrin

Angiogenesis, the formation of new blood vessels from preexisting ones, is crucial for tumor growth and metastatization, and is considered a promising therapeutic target. Unfortunately, drugs directed against a specific proangiogenic growth factor or receptor turned out to be of limited benefit for oncology patients, likely due to the high biochemical redundancy of the neovascularization process. In this scenario, multitarget compounds that are able to simultaneously tackle different proangiogenic pathways are eagerly awaited. UniPR1331 is a 3β-hydroxy-Δ⁵-cholenic acid derivative, which is already known to inhibit Eph-ephrin interaction. Here, we employed an analysis pipeline consisting of molecular modeling and simulation, surface plasmon resonance spectrometry, biochemical assays, and endothelial cell models to demonstrate that UniPR1331 directly interacts with the vascular endothelial growth factor receptor 2 (VEGFR2) too. The binding of UniPR1331 to VEGFR2 prevents its interaction with the natural ligand vascular endothelial growth factor and subsequent autophosphorylation, signal transduction, and in vitro proangiogenic activation of endothelial cells. In vivo, UniPR1331 inhibits tumor cell-driven angiogenesis in zebrafish. Taken together, these data shed light on the pleiotropic pharmacological effect of UniPR1331, and point to Δ⁵-cholenic acid as a promising molecular scaffold for the development of multitarget antiangiogenic compounds.

FLOT2 upregulation promotes growth and invasion by interacting and stabilizing EphA2 in gliomas

The expression and roles of FLOT2, especially for its underlying mechanism, in gliomas have been rarely revealed. In this study, upregulations of both FLOT2 and EphA2 in gliomas tissues were validated by immunohistochemistry (IHC) staining and Western blot. FLOT2 silencing notably inhibited the growth and invasion of gliomas cells. Simultaneously, FLOT2 depletion suppressed Akt and NF-κB activities, induced apoptosis, cell cycle arrest, and epithelial-mesenchymal transition (EMT) inhibition, demonstrated by expression alterations of key proteins of the above processes. Mechanistically, FLOT2 could maintain EphA2 stability viainteraction, and restoration of EphA2 could remarkably release the suppressive effects on gliomas cells induced by FLOT2 knockdown. Lastly, FLOT2 and EphA2, whose protein and mRNA levels are both positively correlated in gliomas, shows significant association with clinical characteristics like Ki67 intensity, p53 expression, and tumor stage in patients with gliomas. In conclusion, our results reveal the upregulation, oncogenic roles of FLOT2, and the corresponding underlying mechanism in gliomas, highlighting that the FLOT2-EphA2 axis is served as a promising therapeutic target for gliomas.

EphA2 and EGFR: Friends in Life, Partners in Crime. Can EphA2 Be a Predictive Biomarker of Response to Anti-EGFR Agents?

The Eph receptors represent the largest group among Receptor Tyrosine kinase (RTK) families. The Eph/ephrin signaling axis plays center stage during development, and the deep perturbation of signaling consequent to its dysregulation in cancer reveals the multiplicity and complexity underlying its function. In the last decades, they have emerged as key players in solid tumors, including colorectal cancer (CRC); however, what causes EphA2 to switch between tumor-suppressive and tumor-promoting function is still an active theater of investigation. This review summarizes the recent advances in understanding EphA2 function in cancer, with detail on the molecular determinants of the oncogene-tumor suppressor switch function of EphA2. We describe tumor context-specific examples of EphA2 signaling and the emerging role EphA2 plays in supporting cancer-stem-cell-like populations and overcoming therapy-induced stress. In such a frame, we detail the interaction of the EphA2 and EGFR pathway in solid tumors, including colorectal cancer. We discuss the contribution of the EphA2 oncogenic signaling to the resistance to EGFR blocking agents, including cetuximab and TKIs.

Genomic and transcriptomic characterization of the human glioblastoma cell line AHOL1

Cancer cell lines are widely used as in vitro models of tumorigenesis, facilitating fundamental discoveries in cancer biology and translational medicine. Currently, there are few options for glioblastoma (GBM) treatment and limited in vitro models with accurate genomic and transcriptomic characterization. Here, a detailed characterization of a new GBM cell line, namely AHOL1, was conducted in order to fully characterize its molecular composition based on its karyotype, copy number alteration (CNA), and transcriptome profiling, followed by the validation of key elements associated with GBM tumorigenesis. Large numbers of CNAs and differentially expressed genes (DEGs) were identified. CNAs were distributed throughout the genome, including gains at Xq11.1-q28, Xp22.33-p11.1, Xq21.1-q21.33, 4p15.1-p14, 8q23.2-q23.3 and losses at Yq11.21-q12, Yp11.31-p11.2, and 15q11.1-q11.2 positions. Nine druggable genes were identified, including HCRTR2, ETV1, PTPRD, PRKX, STS, RPS6KA6, ZFY, USP9Y, and KDM5D. By integrating DEGs and CNAs, we identified 57 overlapping genes enriched in fourteen pathways. Altered expression of several cancer-related candidates found in the DEGs-CNA dataset was confirmed by RT-qPCR. Taken together, this first comprehensive genomic and transcriptomic landscape of AHOL1 provides unique resources for further studies and identifies several druggable targets that may be useful for therapeutics and biologic and molecular investigation of GBM.

Kinome Array Profiling of Patient-Derived Pancreatic Ductal Adenocarcinoma Identifies Differentially Active Protein Tyrosine Kinases

Pancreatic cancer remains one of the most difficult malignancies to treat. Minimal improvements in patient outcomes and persistently abysmal patient survival rates underscore the great need for new treatment strategies. Currently, there is intense interest in therapeutic strategies that target tyrosine protein kinases. Here, we employed kinome arrays and bioinformatic pipelines capable of identifying differentially active protein tyrosine kinases in different patient-derived pancreatic ductal adenocarcinoma (PDAC) cell lines and wild-type pancreatic tissue to investigate the unique kinomic networks of PDAC samples and posit novel target kinases for pancreatic cancer therapy. Consistent with previously described reports, the resultant peptide-based kinome array profiles identified increased protein tyrosine kinase activity in pancreatic cancer for the following kinases: epidermal growth factor receptor (EGFR), fms related receptor tyrosine kinase 4/vascular endothelial growth factor receptor 3 (FLT4/VEGFR-3), insulin receptor (INSR), ephrin receptor A2 (EPHA2), platelet derived growth factor receptor alpha (PDGFRA), SRC proto-oncogene kinase (SRC), and tyrosine kinase non receptor 2 (TNK2). Furthermore, this study identified increased activity for protein tyrosine kinases with limited prior evidence of differential activity in pancreatic cancer. These protein tyrosine kinases include B lymphoid kinase (BLK), Fyn-related kinase (FRK), Lck/Yes-related novel kinase (LYN), FYN proto-oncogene kinase (FYN), lymphocyte cell-specific kinase (LCK), tec protein kinase (TEC), hemopoietic cell kinase (HCK), ABL proto-oncogene 2 kinase (ABL2), discoidin domain receptor 1 kinase (DDR1), and ephrin receptor A8 kinase (EPHA8). Together, these results support the utility of peptide array kinomic analyses in the generation of potential candidate kinases for future pancreatic cancer therapeutic development.

Targeting EphA2 in cancer

Eph receptors and the corresponding Eph receptor-interacting (ephrin) ligands jointly constitute a critical cell signaling network that has multiple functions. The tyrosine kinase EphA2, which belongs to the family of Eph receptors, is highly produced in tumor tissues, while found at relatively low levels in most normal adult tissues, indicating its potential application in cancer treatment. After 30 years of investigation, a large amount of data regarding EphA2 functions have been compiled. Meanwhile, several compounds targeting EphA2 have been evaluated and tested in clinical studies, albeit with limited clinical success. The present review briefly describes the contribution of EphA2-ephrin A1 signaling axis to carcinogenesis. In addition, the roles of EphA2 in resistance to molecular-targeted agents were examined. In particular, we focused on EphA2's potential as a target for cancer treatment to provide insights into the application of EphA2 targeting in anticancer strategies. Overall, EphA2 represents a potential target for treating malignant tumors.

Spatial organization-dependent EphA2 transcriptional responses revealed by ligand nanocalipers

Ligand binding induces extensive spatial reorganization and clustering of the EphA2 receptor at the cell membrane. It has previously been shown that the nanoscale spatial distribution of ligands modulates EphA2 receptor reorganization, activation and the invasive properties of cancer cells. However, intracellular signaling downstream of EphA2 receptor activation by nanoscale spatially distributed ligands has not been elucidated. Here, we used DNA origami nanostructures to control the positions of ephrin-A5 ligands at the nanoscale and investigated EphA2 activation and transcriptional responses following ligand binding. Using RNA-seq, we determined the transcriptional profiles of human glioblastoma cells treated with DNA nanocalipers presenting a single ephrin-A5 dimer or two dimers spaced 14, 40 or 100 nm apart. These cells displayed divergent transcriptional responses to the differing ephrin-A5 nano-organization. Specifically, ephrin-A5 dimers spaced 40 or 100 nm apart showed the highest levels of differential expressed genes compared to treatment with nanocalipers that do not present ephrin-A5. These findings show that the nanoscale organization of ephrin-A5 modulates transcriptional responses to EphA2 activation.

The role of Eph receptors in cancer and how to target them: novel approaches in cancer treatment

INTRODUCTION

Erythropoietin-producing human hepatocellular (Eph) receptors are among the largest family of tyrosine kinases that are divided into two classes: EphA and EphB receptors. Over the past two decades, their role in cancer has become more evident.

AREAS COVERED

There is a need for new anticancer treatments and more insight in the emerging role of Eph receptors in cancer. Molecular mechanisms underlying the pro-tumorigenic effects of Eph receptors could be exploited for future therapeutic strategies. This review describes the variability in expression levels and different effects on oncogenic and tumor suppressive downstream signaling of Eph receptors in various cancer types, and the small molecules, antibodies and peptides that target these receptors.

EXPERT OPINION

The complexity of Eph signaling is a challenge for the definition of clear targets for cancer treatment. Nevertheless, numerous drugs that target EphA2 and EphB4 are currently in clinical trials. However, some Eph targeted drugs also inhibit other tyrosine kinases, so it is unclear to what extent the targeting of Eph receptors contributes to their efficacy. Future research is warranted for an improved understanding of the full network in which Eph receptors function. This will be critical for the improvement of the anticancer effects of drugs that target the Eph receptors.

Adaptive RSK-EphA2-GPRC5A signaling switch triggers chemotherapy resistance in ovarian cancer

Metastatic cancers commonly activate adaptive chemotherapy resistance, attributed to both microenvironment‐dependent phenotypic plasticity and genetic characteristics of cancer cells. However, the contribution of chemotherapy itself to the non‐genetic resistance mechanisms was long neglected. Using high‐grade serous ovarian cancer (HGSC) patient material and cell lines, we describe here an unexpectedly robust cisplatin and carboplatin chemotherapy‐induced ERK1/2‐RSK1/2‐EphA2‐GPRC5A signaling switch associated with cancer cell intrinsic and acquired chemoresistance. Mechanistically, pharmacological inhibition or knockdown of RSK1/2 prevented oncogenic EphA2‐S897 phosphorylation and EphA2‐GPRC5A co‐regulation, thereby facilitating a signaling shift to the canonical tumor‐suppressive tyrosine phosphorylation and consequent downregulation of EphA2. In combination with platinum, RSK inhibitors effectively sensitized even the most platinum‐resistant EphA2^high, GPRC5A^high cells to the therapy‐induced apoptosis. In HGSC patient tumors, this orphan receptor GPRC5A was expressed exclusively in cancer cells and associated with chemotherapy resistance and poor survival. Our results reveal a kinase signaling pathway uniquely activated by platinum to elicit adaptive resistance. They further identify GPRC5A as a marker for abysmal HGSC outcome and putative vulnerability of the chemo‐resistant cells to RSK1/2‐EphA2‐pS897 pathway inhibition.

The cystine/glutamate antiporter xCT is a key regulator of EphA2 S897 phosphorylation under glucose-limited conditions

EphA2, which belongs to the Eph family of receptor tyrosine kinases, is overexpressed in a variety of human cancers. Serine 897 (S897) phosphorylation of EphA2 is known to promote cancer cell migration and proliferation in a ligand-independent manner. In this study, we show that glucose deprivation induces S897 phosphorylation of EphA2 in glioblastoma cells. The phosphorylation requires the activity of the cystine/glutamate antiporter xCT and reactive oxygen species (ROS)-dependent ERK and RSK activation. Furthermore, depletion of EphA2 in glioblastoma cells leads to decreased cell viability under glucose starvation. Our results suggest a role of EphA2 in glioblastoma cell viability under glucose-limited conditions.

The Small Molecule Ephrin Receptor Inhibitor, GLPG1790, Reduces Renewal Capabilities of Cancer Stem Cells, Showing Anti-Tumour Efficacy on Preclinical Glioblastoma Models

Therapies against glioblastoma (GBM) show a high percentage of failure associated with the survival of glioma stem cells (GSCs) that repopulate treated tumours. Forced differentiation of GSCs is a promising new approach in cancer treatment. Erythropoietin-producing hepatocellular (Eph) receptors drive tumourigenicity and stemness in GBM. We tested GLPG1790, a first small molecule with inhibition activity versus inhibitor of various Eph receptor kinases, in preclinical GBM models using in vitro and in vivo assays. GLPG1790 rapidly and persistently inhibited Ephrin-A1-mediated phosphorylation of Tyr⁵⁸⁸ and Ser⁸⁹⁷, completely blocking EphA2 receptor signalling. Similarly, this compound blocks the ephrin B2-mediated EphA3 and EphB4 tyrosine phosphorylation. This resulted in anti-glioma effects. GLPG1790 down-modulated the expression of mesenchymal markers CD44, Sox2, nestin, octamer-binding transcription factor 3/4 (Oct3/4), Nanog, CD90, and CD105, and up-regulated that of glial fibrillary acidic protein (GFAP) and pro-neural/neuronal markers, βIII tubulin, and neurofilaments. GLPG1790 reduced tumour growth in vivo. These effects were larger compared to radiation therapy (RT; U251 and T98G xenografts) and smaller than those of temozolomide (TMZ; U251 and U87MG cell models). By contrast, GLPG1790 showed effects that were higher than Radiotherapy (RT) and similar to Temozolomide (TMZ) in orthotopic U87MG and CSCs-5 models in terms of disease-free survival (DFS) and overall survival (OS). Further experiments were necessary to study possible interactions with radio- and chemotherapy. GLPG1790 demonstrated anti-tumor effects regulating both the differentiative status of Glioma Initiating Cells (GICs) and the quality of tumor microenvironment, translating into efficacy in aggressive GBM mouse models. Significant common molecular targets to radio and chemo therapy supported the combination use of GLPG1790 in ameliorative antiglioma therapy.

EphA3 is up-regulated by epidermal growth factor and promotes formation of glioblastoma cell aggregates

EphA3, a member of the Eph family of receptor tyrosine kinases, has been reported to be overexpressed in some human cancers including glioblastoma. Here, we found that expression of EphA3 is up-regulated in response to epidermal growth factor (EGF) stimulation and promotes formation of cell aggregates in suspension culture of glioblastoma cells. Suppression of EphA3 expression by short hairpin RNA-mediated knockdown or CRISPR/Cas9-mediated gene deletion inhibited EGF-induced promotion of cell aggregate formation, whereas overexpression of EphA3 promoted formation of cell aggregates in suspension culture. EGF-induced EphA3 expression and promotion of cell aggregate formation required Akt activity. Furthermore, N-cadherin, whose expression was regulated by EGF and EphA3, contributed to the formation of cell aggregates in suspension culture. These results suggest that the regulation of EphA3 expression plays a critical role in glioblastoma cell growth in non-adherent conditions.