Ephexin4-mediated promotion of cell migration and anoikis resistance is regulated by serine 897 phosphorylation of EphA2

Anoikis in cell fate, physiopathology, and therapeutic interventions

The extracellular matrix (ECM) governs a wide spectrum of cellular fate processes, with a particular emphasis on anoikis, an integrin-dependent form of cell death. Currently, anoikis is defined as an intrinsic apoptosis. In contrast to traditional apoptosis and necroptosis, integrin correlates ECM signaling with intracellular signaling cascades, describing the full process of anoikis. However, anoikis is frequently overlooked in physiological and pathological processes as well as traditional in vitro research models. In this review, we summarized the role of anoikis in physiological and pathological processes, spanning embryonic development, organ development, tissue repair, inflammatory responses, cardiovascular diseases, tumor metastasis, and so on. Similarly, in the realm of stem cell research focused on the functional evolution of cells, anoikis offers a potential solution to various challenges, including in vitro cell culture models, stem cell therapy, cell transplantation, and engineering applications, which are largely based on the regulation of cell fate by anoikis. More importantly, the regulatory mechanisms of anoikis based on molecular processes and ECM signaling will provide new strategies for therapeutic interventions (drug therapy and cell-based therapy) in disease. In summary, this review provides a systematic elaboration of anoikis, thus shedding light on its future research.

Unveiling the therapeutic promise of EphA2 in glioblastoma: a comprehensive review

Glioblastoma (GBM), a primary brain tumor, exhibits remarkable invasiveness and is characterized by its intricate location, infiltrative behavior, the presence of both the blood-brain barrier (BBB) and the blood-brain tumor barrier (BBTB), phenotypic diversity, an immunosuppressive microenvironment with limited development yet rich vascularity, as well as the resistant nature of glioblastoma stem cells (GSCs) towards traditional chemotherapy and radiotherapy. These formidable factors present substantial obstacles in the quest for effective GBM treatments. Following extensive research spanning three decades, the hepatocellular receptor A2 (EphA2) receptor tyrosine kinase has emerged as a promising molecular target with translational potential in the realm of cancer therapy. Numerous compounds aimed at targeting EphA2 have undergone rigorous evaluation and clinical investigation. This article provides a comprehensive account of the distinctive roles played by canonical and non-canonical EphA2 signaling in various contexts, while also exploring the involvement of the EphA2-ephrin A1 signaling axis in GBM pathogenesis. Additionally, the review offers an overview of completed clinical trials targeting EphA2 for GBM treatment, shedding light on both the prospects and challenges associated with EphA2-directed interventions in the domain of cancer therapeutics.

Targeting the EphA2 pathway: could it be the way for bone sarcomas?

Bone sarcomas are malignant tumors of mesenchymal origin. Complete surgical resection is the cornerstone of multidisciplinary treatment. However, advanced, unresectable forms remain incurable. A crucial step towards addressing this challenge involves comprehending the molecular mechanisms underpinning tumor progression and metastasis, laying the groundwork for innovative precision medicine-based interventions. We previously showed that tyrosine kinase receptor Ephrin Type-A Receptor 2 (EphA2) is overexpressed in bone sarcomas. EphA2 is a key oncofetal protein implicated in metastasis, self-renewal, and chemoresistance. Molecular, genetic, biochemical, and pharmacological approaches have been developed to target EphA2 and its signaling pathway aiming to interfere with its tumor-promoting effects or as a carrier for drug delivery. This review synthesizes the main functions of EphA2 and their relevance in bone sarcomas, providing strategies devised to leverage this receptor for diagnostic and therapeutic purposes, with a focus on its applicability in the three most common bone sarcoma histotypes: osteosarcoma, chondrosarcoma, and Ewing sarcoma.

The EphA2 Receptor Regulates Invasiveness and Drug Sensitivity in Canine and Human Osteosarcoma Cells

Osteosarcoma is an aggressive bone cancer affecting both humans and dogs, often leading to pulmonary metastasis. Despite surgery and chemotherapy being the primary treatment modalities, survival rates remain low in both species, underscoring the urgent need for more efficacious therapeutic options. Accumulating evidence indicates numerous biological and clinical similarities between human and canine osteosarcoma, making it an ideal choice for comparative oncological research that should benefit both species. The EphA2 receptor has been implicated in controlling invasive responses across different human malignancies, and its expression is associated with poor prognosis. In this study, we utilized a comparative approach to match EphA2 functions in human and canine osteosarcoma models. Our objectives were to assess EphA2 levels and its pro-malignant action in osteosarcoma cells of both species. We found that EphA2 is overexpressed in most of both canine and human osteosarcoma cell lines, while its silencing significantly reduced cell viability, migration, and invasion. Moreover, EphA2 silencing enhanced the sensitivity of osteosarcoma cells to cisplatin, a drug commonly used for treating this cancer. Furthermore, inhibition of EphA2 expression led to a significant reduction in tumor development capability of canine osteosarcoma cells. Our data suggest that these EphA2 effects are likely mediated through various signaling mechanisms, including the SRC, AKT, and ERK-MAPK pathways. Collectively, our findings indicate that EphA2 promotes malignant behaviors in both human and canine osteosarcoma and that targeting EphA2, either alone or in combination with chemotherapy, could offer potential benefits to osteosarcoma patients.

Targeting anoikis resistance as a strategy for cancer therapy

Anoikis, known as matrix detachment-induced apoptosis or detachment-induced cell death, is crucial for tissue development and homeostasis. Cancer cells develop means to evade anoikis, e.g. anoikis resistance, thereby allowing for cells to survive under anchorage-independent conditions. Uncovering the mechanisms of anoikis resistance will provide details about cancer metastasis, and potential strategies against cancer cell dissemination and metastasis. Here, we summarize the principal elements and core molecular mechanisms of anoikis and anoikis resistance. We discuss the latest progress of how anoikis and anoikis resistance are regulated in cancers. Furthermore, we summarize emerging data on selective compounds and nanomedicines, explaining how inhibiting anoikis resistance can serve as a meaningful treatment modality against cancers. Finally, we discuss the key limitations of this therapeutic paradigm and possible strategies to overcome them. In this review, we suggest that pharmacological modulation of anoikis and anoikis resistance by bioactive compounds could surmount anoikis resistance, highlighting a promising therapeutic regimen that could be used to overcome anoikis resistance in cancers.

A narrative review of the role of Eph receptors in head and neck squamous cell carcinoma

Tyrosine kinase receptors (TKR) coordinate a variety of pathological processes in head and neck squamous cell carcinoma (HNSCC), and eventually play a role in patient outcomes. In this review, the role of Eph receptors in HNSCC progression and the possibility of targeting these receptors are illustrated. All relevant studies were identified through a comprehensive search of four electronic databases, including PubMed, Scopus, web of science, and Embase till August 2022. EphA2 and EphB4, along with ephrin-B2, were the most extensively studied proteins in this family. However, overexpression of EphB4 and its ligand ephrin-B2 were the only proteins that consistently showed association with a poor outcome, indicating that these proteins might serve as valuable prognostic markers in HNSCC. High expression of EphA3 and EphB4 was found to play a crucial role in radioresistance of HNSCC. EphB4 loss, in particular, was observed to induce an immunosuppression phenotypic HNSCC. Currently, ongoing clinical trials are investigating the benefits of EphB4-ephrin-B2 blockade in combination with standard of care treatment in HNSCC. Further efforts are needed to explore the biological role and behavioral complexity of this family of TKR in HNSCC with great attention to avoid heterogeneity of HNSCC subsites.

Development of adaptive anoikis resistance promotes metastasis that can be overcome by CDK8/19 Mediator kinase inhibition

Anoikis resistance or evasion of cell death triggered by cell detachment into suspension is a hallmark of cancer that is concurrent with cell survival and metastasis. The effects of frequent matrix detachment encounters on the development of anoikis resistance in cancer remains poorly defined. Here we show using a panel of ovarian cancer models, that repeated exposure to suspension stress in vitro followed by attached recovery growth leads to the development of anoikis resistance paralleling in vivo development of anoikis resistance in ovarian cancer ascites. This resistance is concurrent with enhanced invasion, chemoresistance and the ability of anoikis adapted cells to metastasize to distant sites. Adapted anoikis resistant cells show a heightened dependency on oxidative phosphorylation and can also evade immune surveillance. We find that such acquired anoikis resistance is not genetic, as acquired resistance persists for a finite duration in the absence of suspension stress. Transcriptional reprogramming is however essential to this process, as acquisition of adaptive anoikis resistance in vitro and in vivo is exquisitely sensitive to inhibition of CDK8/19 Mediator kinase, a pleiotropic regulator of transcriptional reprogramming. Our data demonstrate that growth after recovery from repeated exposure to suspension stress is a direct contributor to metastasis and that inhibition of CDK8/19 Mediator kinase during such adaptation provides a therapeutic opportunity to prevent both local and distant metastasis in cancer.

Role of Akt/Protein Kinase B in Cancer Metastasis

Metastasis is a critical step in the process of carcinogenesis and a vast majority of cancer-related mortalities result from metastatic disease that is resistant to current therapies. Cell migration and invasion are the first steps of the metastasis process, which mainly occurs by two important biological mechanisms, i.e., cytoskeletal remodelling and epithelial to mesenchymal transition (EMT). Akt (also known as protein kinase B) is a central signalling molecule of the PI3K-Akt signalling pathway. Aberrant activation of this pathway has been identified in a wide range of cancers. Several studies have revealed that Akt actively engages with the migratory process in motile cells, including metastatic cancer cells. The downstream signalling mechanism of Akt in cell migration depends upon the tumour type, sites, and intracellular localisation of activated Akt. In this review, we focus on the role of Akt in the regulation of two events that control cell migration and invasion in various cancers including head and neck squamous cell carcinoma (HNSCC) and the status of PI3K-Akt pathway inhibitors in clinical trials in metastatic cancers.

EphA2 Proteolytic Fragment as a Sensitive Diagnostic Biomarker for Very Early-stage Pancreatic Ductal Carcinoma

Cleavage of erythropoietin-producing hepatocellular ephrin receptor A2 (EphA2) triggers malignant progression and yields an N-terminal fragment (EphA2-NF) detectable in sera from patients with pancreatic ductal carcinoma. We established a quantitative automated chemiluminescence immunoassay for EphA2-NF and evaluated serum EphA2-NF levels as a biomarker to diagnose pancreatic ductal carcinoma in the test and validation cohorts. The EphA2-NF value was elevated (above the cutoff: mean ± SD) in more than half of the patients with stage I/II pancreatic ductal carcinoma. Among patients receiving standard chemotherapy for pancreatic ductal carcinoma [gemcitabine plus nab-paclitaxel (GnP)], the median survival time of patients with elevated serum EphA2-NF was half that of patients with values below the cutoff. Patients with intraductal papillary mucinous neoplasm (IPMN), a precancerous pancreatic ductal carcinoma lesion, also show high serum EphA2 levels, which are associated with an increase in pancreatic duct size and the development of pancreatic ductal carcinoma in some cases. IHC showed loss of EphA2-NF staining in IPMN with pancreatic ductal carcinoma, but not in the normal epithelium or IPMN without pancreatic ductal carcinoma, regardless of the histologic grade. These results suggest that EphA2 cleavage is an essential event that occurs very early in pancreatic ductal carcinoma development, and that the consequent release of EphA2-NF can be detected in the serum. Thus, serum EphA2-NF could be a diagnostic biomarker for very early-stage pancreatic ductal carcinoma and pancreatic ductal carcinoma development from high-risk IPMN and as a prognostic biomarker after chemotherapy with GnP.

SIGNIFICANCE

EphA2 N-terminus deletion is involved in pancreatic ductal carcinoma development from high-risk IPMN and EphA2-NF produced by cleavage can be used as a serum biomarker to diagnose pancreatic ductal carcinoma and predict pancreatic ductal carcinoma development from high-risk IPMN.

Identification of biomarkers for immunotherapy response in prostate cancer and potential drugs to alleviate immunosuppression

Background: Immunotherapy has a significant effect on the treatment of many tumor types. However, prostate cancers generally fail to show significant responses to immunotherapy owing to their immunosuppressive microenvironments. To sustain progress towards more effective immunotherapy for prostate cancer, comprehensive analyses of the genetic characteristics of the immune microenvironment and novel therapeutic strategies are required.

Methods: The transcriptome profiles of patients with prostate cancer were obtained from GEO and processed with the TIDE algorithm to predict their responses to immunotherapy. Next, the significant differentially expressed genes (DEGs) between the responder and non-responder groups were identified and used to compute the co-expression modules by WGCNA. Then, co-expression networks were constructed and survival analysis was applied to hub genes. Finally, drug candidates to alleviate immunosuppression were filtered in prostate cancer using GSEA based on hub genes.

Results: In total, we identified 2758 significant DEGs and constructed 16 co-expression modules, seven of which were significantly correlated with the immune response score. In total, 133 hub genes were identified, of which 13 were significantly associated with prostate cancer prognosis. Co-expression networks of hub genes were constructed with KMT2B at the center. Finally, six candidate drugs for prostate cancer immunotherapy were identified in PC3 and LNCaP cell lines.

Conclusions: We obtained datasets from multiple platforms, performed integrated bioinformatic analysis to identify 133 hub genes and 13 biomarkers of an immunotherapy response, and six candidate drugs were filtered to inhibit the immunosuppressive tumor microenvironment, to ultimately improve patient responses to immunotherapy in prostate cancer.

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.

Double inhibition and activation mechanisms of Ephexin family RhoGEFs

Ephexin family guanine nucleotide exchange factors (GEFs) transfer signals from Eph tyrosine kinase receptors to Rho GTPases, which play critical roles in diverse cellular processes, as well as cancers and brain disorders. Here, we elucidate the molecular basis underlying inhibition and activation of Ephexin family RhoGEFs. The crystal structures of partially and fully autoinhibited Ephexin4 reveal that the complete autoinhibition requires both N- and C-terminal inhibitory modes, which can operate independently to impede Ras homolog family member G (RhoG) access. This double inhibition mechanism is commonly employed by other Ephexins and SGEF, another RhoGEF for RhoG. Structural, enzymatic, and cell biological analyses show that phosphorylation of a conserved tyrosine residue in its N-terminal inhibitory domain and association of PDZ proteins with its C-terminal PDZ-binding motif may respectively relieve the two autoinhibitory modes in Ephexin4. Our study provides a mechanistic framework for understanding the fine-tuning regulation of Ephexin4 GEF activity and offers possible clues for its pathological dysfunction.

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.

Serine 897 Phosphorylation of EPHA2 Is Involved in Signaling of Oncogenic ERK1/2 Drivers in Thyroid Cancer Cells

Background: Phosphorylation of the intracellular domain of the EPHA2 receptor tyrosine kinase (RTK) on serine 897 (S897) has been demonstrated to mediate EPHA2 oncogenic activity. Here, we show that in thyroid cancer cells harboring driver oncogenes that signal through the extracellular regulated kinase (ERK1/2) signaling pathway [rearranged RET RTK (RET/PTC), KRAS(G12R), or BRAFV600E oncogenes], EPHA2 is robustly phosphorylated on S897. EPHA2 S897 is embedded in a consensus sequence for phosphorylation by the AGC family kinases, including p90RSK (ribosomal protein S6 kinase), a direct ERK1/2 target. Methods: We show that recombinant p90RSK phosphorylates in vitro EPHA2 S897 and that treatment with chemical inhibitors targeting p90RSK or other components of the ERK1/2 pathway blunts S897 phosphorylation. Results: RNA interference-mediated knockdown combined with rescue experiments demonstrated that EPHA2 S897 phosphorylation mediates thyroid cancer cell proliferation and motility. Conclusions: These findings point to EPHA2 S897 as a crucial mediator of the oncogenic activity of the ERK1/2 signaling cascade in thyroid cancer.

Y772 phosphorylation of EphA2 is responsible for EphA2-dependent NPC nasopharyngeal carcinoma growth by Shp2/Erk-1/2 signaling pathway

EphA2 is an important oncogenic protein and emerging drug target, but the oncogenic role and mechanism of ligand-independent phosphorylation of EphA2 at tyrosine 772 (pY772-EphA2) is unclear. In this study, we established nasopharyngeal carcinoma (NPC) cell lines with stable expression of exogenous EphA2 and EphA2-Y772A (phosphorylation inactivation) using endogenous EphA2-knockdown cells, and observed that pY772A EphA2 was responsible for EphA2-promoting NPC cell proliferation and anchorage-independent and in vivo growth in mice. Mechanistically, EphA2-Y772A mediated EphA2-activating Shp2/Erk-1/2 signaling pathway in the NPC cells, and Gab1 (Grb2-associated binder 1) and Grb2 (growth factor receptor-bound protein 2) were involved in pY772-EphA2 activating this signaling pathway. Our results further showed that Shp2/Erk-1/2 signaling mediated pY772-EphA2-promoting NPC cell proliferation and anchorage-independent growth. Moreover, we observed that EphA2 tyrosine kinase inhibitor ALW-II-41-27 inhibited pY772-EphA2 and EphA2-Y772A decreased the inhibitory effect of ALW-II-41-27 on NPC cell proliferation. Collectively, our results demonstrate that pY772-EphA2 is responsible for EphA2-dependent NPC cell growth in vitro and in vivo by activating Shp2/Erk-1/2 signaling pathway, and is a pharmacologic target of ALW-II-41-27, suggesting that pY772-EphA2 can serve as a therapeutic target in NPC and perhaps in other cancers.

FYN is required for ARHGEF16 to promote proliferation and migration in colon cancer cells

ARHGEF16 is a recently identified Rho-family guanine nucleotide exchange factor (GEF) that has been implicated in the activation of Rho-family GTPases such as Rho G, Rac, and Cdc42. However, its functions in colon cancer cell proliferation and migration are not well understood. In this study, we showed that ARHGEF16 was highly expressed in clinical specimens of colon cancer. In colon cancer cells, ARHGEF16-stimulated proliferation and migration in vitro and in vivo. Furthermore, we identified a nonreceptor tyrosine kinase, FYN, as a novel partner of ARHGEF16. Knocking down FYN expression decreased ARHGEF16 protein level in colon cancer cells. We further demonstrated that ARHGEF16-induced colon cancer cell proliferation and migration were dependent on FYN since knockdown FYN abolished the ARHGEF16-induced proliferation and migration of colon cancer cells. The FYN-ARHGEF16 axis mediates colon cancer progression and is a potential therapeutic target for colon cancer treatment.

Protein kinase C phosphorylates the EphA2 receptor on serine 892 in the regulatory linker connecting the kinase and SAM domains

The EphA2 receptor tyrosine kinase signals through two distinct mechanisms, one regulated by tyrosine phosphorylation and the other by serine/threonine phosphorylation. Serine 892 (S892) is one of the major serine/threonine phosphorylation sites in EphA2, but little is known about its regulation and function. S892 is located in the linker connecting the EphA2 kinase and SAM domains, and is part of a cluster of five phosphorylated residues that includes the well characterized S897. EphA2 can be phosphorylated on S897 by the RSK, AKT and PKA kinases to promote a non-canonical form of signaling that plays an important role in cancer malignancy. Here we show that the Protein Kinase C (PKC) family phosphorylates the EphA2 S892 motif in vitro and in cells. By using a newly developed phosphospecific antibody, we detected EphA2 S892 phosphorylation in a variety of cell lines. As expected for a PKC target site, the PKC activator 12-O-tetradecanoylphorbol-13-acetate (TPA) increases S892 phosphorylation whereas the broad-spectrum PKC inhibitor Go 6983 inhibits both basal and TPA-induced S892 phosphorylation. Besides phosphorylating S892, PKC can also increase EphA2 phosphorylation on S897 through the MEK kinase, which regulates the ERK-RSK signaling axis. We also found that S892 and S897 phosphorylation induced by PKC activation can be downregulated by ephrin ligand-induced EphA2 canonical signaling. Our data reveal that the PKC family contributes to the phosphorylation cluster in the EphA2 kinase-SAM linker, which regulates EphA2 non-canonical signaling and cancer malignancy.

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.

Emerging Roles of Ephexins in Physiology and Disease

Dbl (B-cell lymphoma)-related guanine nucleotide exchange factors (GEFs), the largest family of GEFs, are directly responsible for the activation of Rho family GTPases and essential for a number of cellular events such as proliferation, differentiation and movement. The members of the Ephexin (Eph-interacting exchange protein) family, a subgroup of Dbl GEFs, initially were named for their interaction with Eph receptors and sequence homology with Ephexin1. Although the first Ephexin was identified about two decades ago, their functions in physiological and pathological contexts and regulatory mechanisms remained elusive until recently. Ephexins are now considered as GEFs that can activate Rho GTPases such as RhoA, Rac, Cdc42, and RhoG. Moreover, Ephexins have been shown to have pivotal roles in neural development, tumorigenesis, and efferocytosis. In this review, we discuss the known and proposed functions of Ephexins in physiological and pathological contexts, as well as their regulatory mechanisms.

EphA2 phosphorylation at Ser897 by the Cdk1/MEK/ERK/RSK pathway regulates M-phase progression via maintenance of cortical rigidity

Successful cell division is accomplished by the proper formation of the mitotic spindle. Here, we show that EphA2 knockdown causes mitotic errors, including a delay in M-phase progression, asymmetric spindle positioning, multipolar spindles, and cell blebs. It has been known that EphA2 is phosphorylated at Tyr588, which is triggered by the ligand binding, and at Ser897 downstream of growth factor signaling. Upon mitotic entry, EphA2 is phosphorylated at Ser897, accompanied by a reduction in Tyr588 phosphorylation. This EphA2 phosphorylation at Ser897 is inhibited by MEK/ERK and 90 kDa ribosomal S6 kinase (RSK) inhibitors and is induced by the introduction of active cyclin-dependent kinase 1 (Cdk1) and cyclin B1. EphA2 knockdown-induced M-phase delay and cell blebs are rescued by wild type EphA2 expression but not by Ser897Ala mutant. The Ras homolog gene family member G (RhoG) guanine nucleotide exchange factor Ephexin4 interacts with EphA2 in a Ser897 phosphorylation-dependent manner, and its knockdown delays M-phase progression and causes RhoG delocalization. RhoG knockdown delays M-phase progression, and EphA2 knockdown-induced M-phase delay is partially rescued by the constitutively active RhoG mutant. These results suggest that, in EphA2-expressing cells, EphA2 phosphorylation at Ser897 participates in proper M-phase progression downstream of the Cdk1/MEK/ERK/RSK pathway because of its role in maintaining cortical rigidity via Ephexin4 and RhoG and thereby regulating mitotic spindle formation.-Kaibori, Y. Saito, Y., Nakayama, Y. EphA2 phosphorylation at Ser897 by the Cdk1/MEK/ERK/RSK pathway regulates M-phase progression via maintenance of cortical rigidity.

S897 phosphorylation of EphA2 is indispensable for EphA2-dependent nasopharyngeal carcinoma cell invasion, metastasis and stem properties

Our phosphoproteomics identified that phosphorylation of EphA2 at serine 897 (pS897-EphA2) was significantly upregulated in the high metastatic nasopharyngeal carcinoma (NPC) cells relative to non-metastatic NPC cells. However, the role and underlying mechanism of pS897-EphA2 in cancer metastasis and stem properties maintenance remain poorly understood. In this study, we established NPC cell lines with stable expression of exogenous EphA2 and EphA2-S897A using endogenous EphA2 knockdown cells, and observed that pS897-EphA2 maintained EphA2-dependent NPC cell in vitro migration and invasion, in vivo metastasis and cancer stem properties. Using phospho-kinase antibody array to identify signaling downstream of pS897-EphA2, we found that AKT/Stat3 signaling mediated pS897-EphA2-promoting NPC cell invasion, metastasis and stem properties, and Sox-2 and c-Myc were the effectors of pS897-EphA2. Immunohistochemistry showed that pS897-EphA2 was positively correlated with NPC metastasis and negatively correlated with patient overall survival. Moreover, ERK/RSK signaling controlled serum-induced pS897-EphA2 in NPC cells. Collectively, our results demonstrate that pS897-EphA2 is indispensable for EphA2-dependent NPC cell invasion, metastasis and stem properties by activating AKT/Stat3/Sox-2 and c-Myc signaling pathway, suggesting that pS897-EphA2 can serve as a therapeutic target in NPC and perhaps in other cancers.

GLI2 promotes cell proliferation and migration through transcriptional activation of ARHGEF16 in human glioma cells

BACKGROUND

The Hedgehog (Hh) signaling pathway plays critical roles in modulating embryogenesis and maintaining tissue homeostasis, with glioma-associated oncogene (GLI) transcription factors being the main mediators. Aberrant activation of this pathway is associated with various human malignancies including glioblastoma, although the mechanistic details are not well understood.

METHODS

We performed a microarray analysis of genes that are differentially expressed in glioblastoma U87 cells overexpressing GLI2A, the active form of GLI2, relative to the control cells. Chromatin immunoprecipitation and dual-luciferase assays were used to determine whether Rho guanine nucleotide exchange factor 16 (ARHGEF16) is a downstream target of GLI2. Then, transwell migration, EdU and soft-agar colony formation assays were employed to test effects of ARHGEF16 on glioma cancer cell migration and proliferation, and the effects of GLI2/ARHGEF16 signaling on tumor growth were examined in vivo. Finally, we performed yeast two-hybrid assay, Co-IP and GST-pull down to identify factors that mediate effects of ARHGEF16.

RESULTS

We found that ARHGEF16 mRNA level was upregulated in U87 cells overexpressing GLI2A relative to control cells. GLI2 binds to the ARHGEF16 promoter and activates gene transcription. Glioma cells U87 and U118 overexpressing ARHGEF16 showed enhanced migration and proliferation relative to the control cells, while knockdown of ARHGEF16 in H4 cells led to decreased cell proliferation compared to the control H4 cells. In contrast to the promoting effect of GLI2A overexpression on glioma xenograft growth, both GLI2 inhibition and ARHGEF16 knockdown retarded tumor growth. Cytoskeleton-associated protein 5 (CKAP5) was identified as an interaction protein of ARHGEF16, which is important for the stimulatory effects of ARHGEF16 on glioma cell migration and proliferation.

CONCLUSIONS

These results suggest that therapeutic strategies targeting the GLI2/ARHGEF16/CKAP5 signaling axis could inhibit glioma progression and recurrence.

Emerging and Diverse Functions of the EphA2 Noncanonical Pathway in Cancer Progression

Erythropoietin-producing hepatocellular receptor A2 (EphA2) receptor tyrosine kinase controls multiple physiological processes to maintain homeostasis in normal cells. In many types of solid tumors, it has been reported that EphA2 is overexpressed and plays a critical role in oncogenic signaling. However, in recent years, the opposing functions of EphA2 have been explained by the canonical and noncanonical signaling pathways. Ligand- and tyrosine kinase-dependent EphA2 activation (the canonical pathway) inhibits cancer cell proliferation and motility. In contrast, ligand- and tyrosine kinase-independent EphA2 signaling (the noncanonical pathway) promotes tumor survival and metastasis and controls acquired drug resistance and maintenance of cancer stem cell-like properties. Evidence has accumulated showing that the EphA2 noncanonical pathway is mainly regulated by inflammatory cytokines and growth factors via phosphorylation at Ser-897 in the intracellular C-tail region via some serine/threonine kinases, including p90 ribosomal S6 kinase. In this review, we focus on the regulation of Ser-897 phosphorylation and its functional importance in tumor malignancy and discuss future therapeutic targeting.

Ionizing radiation induces EphA2 S897 phosphorylation in a MEK/ERK/RSK-dependent manner

PURPOSE

The EphA2 tyrosine kinase is frequently overexpressed in human tumors that are also treated with radiation. However, few studies have examined the effect of radiation on the EphA2 receptor itself. The purpose of this project was to investigate the impact of radiation on EphA2 to better understand mechanisms of radioresistance.

MATERIALS AND METHODS

Cell lines were exposed to X-rays and assayed for changes in EphA2 protein levels and phosphorylation over time by Western blotting. HEK293 cells stably expressing wild-type EphA2 or the S897A mutant were analyzed for cell survival from X-rays.

RESULTS

Treatment of different cancer cell lines with 2 Gy of X-rays induced the phosphorylation of EphA2 on S897 but no changes were found in EphA2 total levels or its tyrosine phosphorylation. Radiation-induced S897 phosphorylation was unaffected by an AKT inhibitor but blocked by a MEK or RSK inhibitor. HEK293 cells expressing the EphA2 S897A mutant had a nearly 2-fold lower level of cell survival from X-rays than cells expressing wild-type EphA2.

CONCLUSIONS

These findings show that radiation induces S897 EphA2 phosphorylation, an event associated with increased cell survival. Therefore, targeting pathways that mediate EphA2 S897 phosphorylation may be a beneficial strategy to reduce radioresistance.

Intermolecular steric inhibition of Ephexin4 is relieved by Elmo1

Ephexin4, a guanine nucleotide-exchange factor for RhoG, promotes engulfment of apoptotic cells and cancer cell migration in a RhoG-dependent manner, which is synergistically augmented by Elmo1, an Ephexin4-interacting protein. However, the underlying molecular mechanism remains elusive. Here, we report a mechanism by which Elmo1 cooperates with Ephexin4 to activate RhoG. We found that Ephexin4 activity was increased by elimination of its SH3 domain which intermolecularly interacts with the N20 region of Ephexin4. This interaction prevented RhoG from binding to Ephexin4 and thus inhibited RhoG activation. Moreover, we also found that Elmo1 associated with the SH3 domain as well as the N20 region and competed with the SH3 domain for binding to the N20 region, interrupting the interaction of the SH3 domain with the N20 region and thereby promoting RhoG binding to Ephexin4. In addition, the activity of Ephexin4 lacking the SH3 domain was comparable to that of Ephexin4 with Elmo1. Taken together, the data suggest that Elmo1 relieves the steric hindrance of Ephexin4 generated by the intermolecular interaction of the SH3 domain and makes Ephexin4 more accessible to RhoG.

Design of novel lead molecules against RhoG protein as cancer target - a computational study

Cancer is a class of diseases characterized by uncontrolled cell growth. Every year more than 2 million people are affected by the disease. Rho family proteins are actively involved in cytoskeleton regulation. Over-expression of Rho family proteins show oncogenic activity and promote cancer progression. In the present work RhoG protein is considered as novel target of cancer. It is a member of Rho family and Rac subfamily protein, which plays pivotal role in regulation of microtubule formation, cell migration and contributes in cancer progression. In order to understand the binding interaction between RhoG protein and the DH domain of Ephexin-4 protein, the 3D structure of RhoG was evaluated and Molecular Dynamic Simulations was performed to stabilize the structure. The 3D structure of RhoG protein was validated and active site identified using standard computational protocols. Protein-protein docking of RhoG with Ephexin-4 was done to understand binding interactions and the active site structure. Virtual screening was carried out with ligand databases against the active site of RhoG protein. The efficiency of virtual screening is analysed with enrichment factor and area under curve values. The binding free energy of docked complexes was calculated using prime MM-GBSA module. The SASA, FOSA, FISA, PISA and PSA values of ligands were carried out. New ligands with high docking score, glide energy and acceptable ADME properties were prioritized as potential inhibitors of RhoG protein.

Tyrosine Phosphorylation of SGEF Regulates RhoG Activity and Cell Migration

SGEF and Ephexin4 are members of the Ephexin subfamily of RhoGEFs that specifically activate the small GTPase RhoG. It is reported that Ephexin1 and Ephexin5, two well-characterized Ephexin subfamily RhoGEFs, are tyrosine-phosphorylated by Src, and that their phosphorylation affect their activities and functions. In this study, we show that SGEF, but not Ephexin4, is tyrosine-phosphorylated by Src. Tyrosine phosphorylation of SGEF suppresses its interaction with RhoG, the elevation of RhoG activity, and SGEF-mediated promotion of cell migration. We identified tyrosine 530 (Y530), which is located within the Dbl homology domain, as a major phosphorylation site of SGEF by Src, and Y530F mutation blocked the inhibitory effect of Src on SGEF. Taken together, these results suggest that the activity of SGEF is negatively regulated by tyrosine phosphorylation of the DH domain.

Protein kinase A can block EphA2 receptor-mediated cell repulsion by increasing EphA2 S897 phosphorylation

The EphA2 receptor plays multiple roles in cancer through two distinct signaling mechanisms. In a novel cross-talk, the β2-adrenoceptor/cAMP/PKA axis can promote EphA2 pro-oncogenic, ligand-independent signaling, blocking cell repulsion induced by ligand-dependent signaling. PKA emerges as a third kinase, besides AKT and RSK, that can regulate EphA2.

The EphA2 receptor tyrosine kinase plays key roles in tissue homeostasis and disease processes such as cancer, pathological angiogenesis, and inflammation through two distinct signaling mechanisms. EphA2 “canonical” signaling involves ephrin-A ligand binding, tyrosine autophosphorylation, and kinase activity; EphA2 “noncanonical” signaling involves phosphorylation of serine 897 (S897) by AKT and RSK kinases. To identify small molecules counteracting EphA2 canonical signaling, we developed a high-content screening platform measuring inhibition of ephrin-A1–induced PC3 prostate cancer cell retraction. Surprisingly, most hits from a screened collection of pharmacologically active compounds are agents that elevate intracellular cAMP by activating G protein–coupled receptors such as the β2-adrenoceptor. We found that cAMP promotes phosphorylation of S897 by protein kinase A (PKA) as well as increases the phosphorylation of several nearby serine/threonine residues, which constitute a phosphorylation hotspot. Whereas EphA2 canonical and noncanonical signaling have been viewed as mutually exclusive, we show that S897 phosphorylation by PKA can coexist with EphA2 tyrosine phosphorylation and block cell retraction induced by EphA2 kinase activity. Our findings reveal a novel paradigm in EphA2 function involving the interplay of canonical and noncanonical signaling and highlight the ability of the β2-adrenoceptor/cAMP/PKA axis to rewire EphA2 signaling in a subset of cancer cells.

EphA2 is a key effector of the MEK/ERK/RSK pathway regulating glioblastoma cell proliferation

EphA2, a member of the Eph receptor tyrosine kinases, is frequently overexpressed in a variety of malignancies, including glioblastoma, and its expression is correlated with poor prognosis. EphA2 acts as a tumor promoter through a ligand ephrin-independent mechanism, which requires phosphorylation of EphA2 on serine 897 (S897), leading to increased cell migration and invasion. In this study, we show that ligand-independent EphA2 signaling occurs downstream of the MEK/ERK/RSK pathway and mediates epidermal growth factor (EGF)-induced cell proliferation in glioblastoma cells. Suppression of EphA2 expression by long-term exposure to ligand ephrinA1 or EphA2-targeted shRNA inhibited EGF-induced cell proliferation. Stimulation of the cells with EGF induced EphA2 S897 phosphorylation, which was suppressed by MEK and RSK inhibitors, but not by phosphatidylinositol 3-kinase (PI3K) and Akt inhibitors. The RSK inhibitor or RSK2-targeted shRNA also suppressed EGF-induced cell proliferation. Furthermore, overexpression of wild-type EphA2 promoted cell proliferation without EGF stimulation, whereas overexpression of EphA2-S897A mutant suppressed EGF- or RSK2-induced proliferation. Taken together, these results suggest that EphA2 is a key downstream target of the MEK/ERK/RSK signaling pathway in the regulation of glioblastoma cell proliferation.

Genome-Wide Association Study of Staphylococcus aureus Carriage in a Community-Based Sample of Mexican-Americans in Starr County, Texas

Staphylococcus aureus is the number one cause of hospital-acquired infections. Understanding host pathogen interactions is paramount to the development of more effective treatment and prevention strategies. Therefore, whole exome sequence and chip-based genotype data were used to conduct rare variant and genome-wide association analyses in a Mexican-American cohort from Starr County, Texas to identify genes and variants associated with S. aureus nasal carriage. Unlike most studies of S. aureus that are based on hospitalized populations, this study used a representative community sample. Two nasal swabs were collected from participants (n = 858) 11–17 days apart between October 2009 and December 2013, screened for the presence of S. aureus, and then classified as either persistent, intermittent, or non-carriers. The chip-based and exome sequence-based single variant association analyses identified 1 genome-wide significant region (KAT2B) for intermittent and 11 regions suggestively associated with persistent or intermittent S. aureus carriage. We also report top findings from gene-based burden analyses of rare functional variation. Notably, we observed marked differences between signals associated with persistent and intermittent carriage. In single variant analyses of persistent carriage, 7 of 9 genes in suggestively associated regions and all 5 top gene-based findings are associated with cell growth or tight junction integrity or are structural constituents of the cytoskeleton, suggesting that variation in genes associated with persistent carriage impact cellular integrity and morphology.

Screening for tumor suppressors: Loss of ephrin receptor A2 cooperates with oncogenic KRas in promoting lung adenocarcinoma

Lung adenocarcinoma, a major form of non-small cell lung cancer, is the leading cause of cancer deaths. The Cancer Genome Atlas analysis of lung adenocarcinoma has identified a large number of previously unknown copy number alterations and mutations, requiring experimental validation before use in therapeutics. Here, we describe an shRNA-mediated high-throughput approach to test a set of genes for their ability to function as tumor suppressors in the background of mutant KRas and WT Tp53. We identified several candidate genes from tumors originated from lentiviral delivery of shRNAs along with Cre recombinase into lungs of Loxp-stop-Loxp-KRas mice. Ephrin receptorA2 (EphA2) is among the top candidate genes and was reconfirmed by two distinct shRNAs. By generating knockdown, inducible knockdown and knockout cell lines for loss of EphA2, we showed that negating its expression activates a transcriptional program for cell proliferation. Loss of EPHA2 releases feedback inhibition of KRAS, resulting in activation of ERK1/2 MAP kinase signaling, leading to enhanced cell proliferation. Intriguingly, loss of EPHA2 induces activation of GLI1 transcription factor and hedgehog signaling that further contributes to cell proliferation. Small molecules targeting MEK1/2 and Smoothened hamper proliferation in EphA2-deficient cells. Additionally, in EphA2 WT cells, activation of EPHA2 by its ligand, EFNA1, affects KRAS-RAF interaction, leading to inhibition of the RAS-RAF-MEK-ERK pathway and cell proliferation. Together, our studies have identified that (i) EphA2 acts as a KRas cooperative tumor suppressor by in vivo screen and (ii) reactivation of the EphA2 signal may serve as a potential therapeutic for KRas-induced human lung cancers.

Eph receptor and ephrin function in breast, gut, and skin epithelia

Epithelial cells are tightly coupled together through specialized intercellular junctions, including adherens junctions, desmosomes, tight junctions, and gap junctions. A growing body of evidence suggests epithelial cells also directly exchange information at cell-cell contacts via the Eph family of receptor tyrosine kinases and their membrane-associated ephrin ligands. Ligand-dependent and -independent signaling via Eph receptors as well as reverse signaling through ephrins impact epithelial tissue homeostasis by organizing stem cell compartments and regulating cell proliferation, migration, adhesion, differentiation, and survival. This review focuses on breast, gut, and skin epithelia as representative examples for how Eph receptors and ephrins modulate diverse epithelial cell responses in a context-dependent manner. Abnormal Eph receptor and ephrin signaling is implicated in a variety of epithelial diseases raising the intriguing possibility that this cell-cell communication pathway can be therapeutically harnessed to normalize epithelial function in pathological settings like cancer or chronic inflammation.

Crucial roles of RSK in cell motility by catalysing serine phosphorylation of EphA2

Crosstalk between inflammatory signalling pathways and receptor tyrosine kinases has been revealed as an indicator of cancer malignant progression. In the present study, we focus on EphA2 receptor tyrosine kinase, which is overexpressed in many human cancers. It has been reported that ligand-independent phosphorylation of EphA2 at Ser-897 is induced by Akt. We show that inflammatory cytokines promote RSK-, not Akt-, dependent phosphorylation of EphA2 at Ser-897. In addition, the RSK-EphA2 signalling pathway controls cell migration and invasion of metastatic breast cancer cells. Moreover, Ser-897-phosphorylated EphA2 co-localizes with phosphorylated active form of RSK in various human tumour specimens, and this double positivity is related to poor survival in lung cancer patients, especially those with a smoking history. Taken together, these results indicate that the phosphorylation of EphA2 at Ser-897 is controlled by RSK and the RSK-EphA2 axis might contribute to cell motility and promote tumour malignant progression.

HGF-induced serine 897 phosphorylation of EphA2 regulates epithelial morphogenesis of MDCK cells in 3D culture

Expression of EphA2 is upregulated in various cancers that are derived from epithelial cells and correlates with the ability of a cancer cell to undergo migration and invasion. Here we have investigated the role of EphA2 in the epithelial morphogenesis of Madin-Darby canine kidney (MDCK) cells in three-dimensional culture. We show that EphA2 is phosphorylated on serine residue 897 through hepatocyte growth factor (HGF) stimulation using a phosphatidylinositol 3-kinase (PI3K)-Akt-dependent mechanism and that this phosphorylation is required for the formation of extensions, the first step of tubulogenesis, in MDCK cysts. By contrast, stimulation using the ligand ephrinA1 dephosphorylates EphA2 on serine residue 897 and suppresses the HGF-induced morphological change. Furthermore, activation of the small GTPase RhoG is involved in the HGF-induced formation of extensions downstream of EphA2. These observations suggest that a ligand-independent activity of EphA2 contributes to epithelial morphogenesis.

Eph family co-expression patterns define unique clusters predictive of cancer phenotype

The Eph genes are the largest sub-family of receptor tyrosine kinases; however, it is most likely the least understood and the arena for many conflicting reports. In this tribute to Prof. Martin Lackmann and Prof. Tony Pawson, we utilized The Cancer Genome Atlas resources to shed new light on the understanding of this family. We found that mutation and expression analysis define two clusters of co-expressed Eph family genes that relate to aggressive phenotypes across multiple cancer types. Analysis of signal transduction pathways using reverse-phase protein arrays revealed a network of interactions, which associates cluster-specific Eph genes with epithelial-mesenchymal transition, metabolism, DNA-damage repair and apoptosis. Our findings support the role of the Eph family in modulating cancer progression and reveal distinct patterns of Eph expression, which correlate with disease outcome. These observations provide further rationale for seeking cancer therapies, which target the Eph/ephrin system.

Eph- and ephrin-dependent mechanisms in tumor and stem cell dynamics

The erythropoietin-producing hepatocellular (Eph) receptors comprise the largest family of receptor tyrosine kinases (RTKs). Initially regarded as axon-guidance and tissue-patterning molecules, Eph receptors have now been attributed with various functions during development, tissue homeostasis, and disease pathogenesis. Their ligands, ephrins, are synthesized as membrane-associated molecules. At least two properties make this signaling system unique: (1) the signal can be simultaneously transduced in the receptor- and the ligand-expressing cell, (2) the signaling outcome through the same molecules can be opposite depending on cellular context. Moreover, shedding of Eph and ephrin ectodomains as well as ligand-dependent and -independent receptor crosstalk with other RTKs, proteases, and adhesion molecules broadens the repertoire of Eph/ephrin functions. These integrated pathways provide plasticity to cell-microenvironment communication in varying tissue contexts. The complex molecular networks and dynamic cellular outcomes connected to the Eph/ephrin signaling in tumor-host communication and stem cell niche are the main focus of this review.

EphB6 promotes anoikis by modulating EphA2 signaling

Anoikis is a specific type of apoptosis induced by detachment of epithelial cells from extracellular matrix, and acquiring resistance to anoikis is an important step that enables cancer cells to metastasize. EphA2, which is overexpressed in a variety of human cancers, is phosphorylated by Akt on serine 897 and mediates ligand ephrin-independent promotion of anoikis resistance through the RhoG activator Ephexin4. EphB6 is frequently silenced in invasive and metastatic cancers; however, its role in cancer progression is poorly understood. Here we show that EphB6 interacts with EphA2 and suppresses EphA2-mediated promotion of anoikis resistance in MCF7 breast cancer cells. On the other hand, knockdown of EphB6 promotes anoikis resistance. We further show that expression of EphB6 decreases serine 897 phosphorylation of EphA2 and suppresses EphA2-Ephexin4 interaction and the RhoG activation. These findings implicate EphB6 as a negative regulator of EphA2 oncogenic signaling.