Activation of EphA receptor tyrosine kinase inhibits the Ras/MAPK pathway

Eph receptor signaling complexes in the plasma membrane

Eph receptor tyrosine kinases, together with their cell surface-anchored ephrin ligands, constitute an important cell-cell communication system that regulates physiological and pathological processes in most cell types. This review focuses on the multiple mechanisms by which Eph receptors initiate signaling via the formation of protein complexes in the plasma membrane. Upon ephrin binding, Eph receptors assemble into oligomers that can further aggregate into large complexes. Eph receptors also mediate ephrin-independent signaling through interplay with intracellular kinases or other cell-surface receptors. The distinct characteristics of Eph receptor family members, as well as their conserved domain structure, provide a framework for understanding their functional differences and redundancies. Possible areas of interest for future investigations of Eph receptor signaling complexes are also highlighted.

DDR1 promotes metastasis of cervical cancer and downstream phosphorylation signal via binding GRB2

Cervical cancer is a leading cause of cancer-related death among women and its recurrence and metastasis poses challenges to treatment. Discoidin domain receptor 1 (DDR1) was associated with cellular migration and invasion in several types of cancers. However, its function in cervical cancer is still unclear. In this study, we found that DDR1 was significantly more expressed in cervical cancer samples than in normal tissues. SRY-Box transcription factor 2 (SOX2), a known oncogene in cervical cancer, showed a positive correlation with DDR1 and regulated DDR1 transcription, contributing to the elevated expression of DDR1 in cervical cancer. Regarding the function of DDR1 in cervical cancer, the overexpression of DDR1 caused an increase in the migration, invasion, and epithelial-mesenchymal transition (EMT) of cervical cancer cells. In contrast, cervical cancer cells with reduced DDR1 expression exhibited a lower migration rate, fewer invasive cells, and decreased levels of EMT markers. In vivo, mice injected with cervical cancer cells with overexpressed DDR1 showed more pulmonary metastasis and nodule number. Opposite results were found in mice injected with DDR1 silenced cervical cancer cells. Since DDR1 can cause phosphorylation of downstream targets, a phosphorylation omics was employed to reveal the downstream targets of DDR1, including eukaryotic translation initiation factor 4E binding protein 1 and EPH receptor A2. Furthermore, DDR1 bound directly with Src homology 2 domain of growth factor receptor bound protein 2 (GRB2) which mediated the function of DDR1 in the malignant behaviors of cervical cancer and the phosphorylation of downstream targets. In conclusion, DDR1 binds directly to GRB2 and then affects downstream phosphorylation signals, ultimately exacerbating the metastasis of cervical cancer cells. This work sheds light on the mechanism by which DDR1 functions in cervical cancer cells, providing therapeutic strategy for the treatment of cervical cancer.

EphA2 regulates vascular permeability and prostate cancer metastasis via modulation of cell junction protein phosphorylation

Prostate cancer morbidity and mortality demonstrate a need for more effective targeted therapies. One potential target is EphA2, although paradoxically, pro- and anti-oncogenic effects have been shown to be mediated by EphA2. We demonstrate that unique activating and blocking EphA2-targeting monoclonal antibodies display opposing tumor-suppressive and oncogenic properties in vivo. To further explore this complexity, we performed detailed phosphoproteomic analysis following ligand-induced EphA2 activation. Our analysis identified altered phosphorylation of 73 downstream proteins related to the PI3K/AKT/mTOR and ERK/MAPK pathways, with the majority implicated in cell junction and cytoskeletal organization, cell motility, and tumor metastasis. We demonstrate that the adapter protein SHB is an essential component in mediating the inhibition of the ERK/MAPK pathway in response to EphA2 receptor activation. Furthermore, we identify the adherence junction protein afadin as an EphA2-regulated phosphoprotein which is involved in prostate cancer migration and invasion.

Canonical ligand-dependent and non-canonical ligand-independent EphA2 signaling in the eye lens of wild-type, knockout, and aging mice

Disruption of Eph-ephrin bidirectional signaling leads to human congenital and age-related cataracts, but the mechanisms for these opacities in the eye lens remain unclear. Eph receptors bind to ephrin ligands on neighboring cells to induce canonical ligand-mediated signaling. The EphA2 receptor also signals non-canonically without ligand binding in cancerous cells, leading to epithelial-to-mesenchymal transition (EMT). We have previously shown that the receptor EphA2 and the ligand ephrin-A5 have diverse functions in maintaining lens transparency in mice. Loss of ephrin-A5 leads to anterior cataracts due to EMT. Surprisingly, both canonical and non-canonical EphA2 activation are present in normal wild-type lenses and in the ephrin-A5 knockout lenses. Canonical EphA2 signaling is localized exclusively to lens epithelial cells and does not change with age. Non-canonical EphA2 signaling is in both epithelial and fiber cells and increases significantly with age. We hypothesize that canonical ligand-dependent EphA2 signaling is required for the morphogenesis and organization of hexagonal equatorial epithelial cells while non-canonical ligand-independent EphA2 signaling is needed for complex membrane interdigitations that change during fiber cell differentiation and maturation. This is the first demonstration of non-canonical EphA2 activation in a non-cancerous tissue or cell and suggests a possible physiological function for ligand-independent EphA2 signaling.

EphA-Mediated Regulation of Stomatin Expression in Prostate Cancer Cells

BACKGROUND AND AIMS

Tumor growth and progression are affected by interactions between tumor cells and stromal cells within the tumor microenvironment. We previously showed that the expression of an integral membrane protein, called stomatin, was increased in cancer cells following their association with stromal cells. Additionally, stomatin impaired the Akt signaling pathway to suppress tumor growth. However, it remains unclear how stomatin expression is regulated. To explore this, we examined the cell surface molecules that can transduce the intercellular communication signals between cancer cells and stromal cells.

RESULTS

Among these molecules, EphA3 and EphA7 receptors and their ligand ephrin-A5 were found to be expressed in prostate cancer cells, but not in prostate stromal cells. Cell-to-cell contact of prostate cancer cells through the EphA-ephrin-A interaction suppressed stomatin expression, while knockdown of EphA3/7 or ephrin-A5 increased stomatin expression. This increase contributed to an inhibition of prostate cancer cell proliferation. Intracellularly, the binding of ephrin-A to EphA attenuated extracellular signaling-regulated kinase (ERK) activation that promoted stomatin expression. Furthermore, ELK1 and ELK4, which are Ets family transcription factors phosphorylated by ERK, were involved in the induction of stomatin expression. We also found that higher Gleason score prostate cancer tissue samples had increased activation of EphA, while the stomatin expression and activated ERK and ELK levels were all low. In the mouse xenograft tumor samples generated by implantation of prostate cancer cells, EphA3 phosphorylation was attenuated and the ERK-ELK signaling and stomatin expression were enhanced in the area where stromal cells infiltrated the tumor.

CONCLUSION

The EphA-mediated signaling suppresses the ERK-ELK pathway, leading to the reduction of stomatin expression that affects prostate cancer malignancy.

EPHA2 is a novel cell surface marker of OCT4-positive undifferentiated cells during the differentiation of mouse and human pluripotent stem cells

Embryonic stem cells (ESCs) and induced pluripotent stem cells (iPSCs) possess the intrinsic ability to differentiate into diverse cellular lineages, marking them as potent instruments in regenerative medicine. Nonetheless, the proclivity of these stem cells to generate teratomas post-transplantation presents a formidable obstacle to their therapeutic utility. In previous studies, we identified an array of cell surface proteins specifically expressed in the pluripotent state, as revealed through proteomic analysis. Here we focused on EPHA2, a protein found to be abundantly present on the surface of undifferentiated mouse ESCs and is diminished upon differentiation. Knock-down of Epha2 led to the spontaneous differentiation of mouse ESCs, underscoring a pivotal role of EPHA2 in maintaining an undifferentiated cell state. Further investigations revealed a strong correlation between EPHA2 and OCT4 expression during the differentiation of both mouse and human PSCs. Notably, removing EPHA2+ cells from mouse ESC-derived hepatic lineage reduced tumor formation after transplanting them into immune-deficient mice. Similarly, in human iPSCs, a larger proportion of EPHA2+ cells correlated with higher OCT4 expression, reflecting the pattern observed in mouse ESCs. Conclusively, EPHA2 emerges as a potential marker for selecting undifferentiated stem cells, providing a valuable method to decrease tumorigenesis risks after stem-cell transplantation in regenerative treatments.

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.

Spatial-temporal comparison of Eph/Ephrin gene expression in ocular lenses from aging and knockout mice

Cataracts, defined as any opacity in the transparent ocular lens, remain the leading cause of blindness and visual impairment in the world; however, the etiology of this pathology is not fully understood. Studies in mice and humans have found that the EphA2 receptor and the ephrin-A5 ligand play important roles in maintaining lens homeostasis and transparency. However, due to the diversity of the family of Eph receptors and ephrin ligands and their promiscuous binding, identifying functional interacting partners remains a challenge. Previously, 12 of the 14 Ephs and 8 of 8 ephrins in mice were characterized to be expressed in the mouse lens. To further narrow down possible genes of interest in life-long lens homeostasis, we collected and separated the lens epithelium from the fiber cell mass and isolated RNA from each compartment in samples from young adult and middle-aged mice that were either wild-type, EphA2-/- (knockout), or ephrin-A5 -/- . Reverse transcription quantitative polymerase chain reaction (RT-qPCR) was implemented to compare transcript levels of 33 Eph and ephrin gene variants in each tissue compartment. Our results show that, of the Eph and ephrin variants screened, 5 of 33 showed age-related changes, and 2 of 33 showed genotype-related changes in lens epithelium. In the isolated fibers, more dynamic gene expression changes were observed, in which 12 of 33 variants showed age-related changes, and 6 of 33 showed genotype-related changes. These data allow for a more informed decision in determining mechanistic leads in Eph-ephrin-mediated signaling in the lens.

Ephs in cancer progression: complexity and context-dependent nature in signaling, angiogenesis and immunity

Eph receptors constitute the largest family of receptor tyrosine kinases, comprising 14 distinct members classified into two subgroups: EphAs and EphBs.. Despite their essential functions in normal physiological processes, accumulating evidence suggests that the involvement of the Eph family in cancer is characterized by a dual and often contradictory nature. Research indicates that Eph/ephrin bidirectional signaling influences cell-cell communication, subsequently regulating cell migration, adhesion, differentiation and proliferation. The contradictory functionalities may arise from the diversity of Eph signaling pathways and the heterogeneity of different cancer microenvironment. In this review, we aim to discuss the dual role of the Eph receptors in tumor development, attempting to elucidate the paradoxical functionality through an exploration of Eph receptor signaling pathways, angiogenesis, immune responses, and more. Our objective is to provide a comprehensive understanding of the molecular mechanisms underlying tumor development. Additionally, we will explore the evolving landscape of utilizing Eph receptors as potential targets for tumor therapy and diagnostic tools.

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.

Targeting EphA2: a promising strategy to overcome chemoresistance and drug resistance in cancer

Erythropoietin-producing hepatocellular A2 (EphA2) is a vital member of the Eph tyrosine kinase receptor family and has been associated with developmental processes. However, it is often overexpressed in tumors and correlates with cancer progression and worse prognosis due to the activation of its noncanonical signaling pathway. Throughout cancer treatment, the emergence of drug-resistant tumor cells is relatively common. Since the early 2000s, researchers have focused on understanding the role of EphA2 in promoting drug resistance in different types of cancer, as well as finding efficient and secure EphA2 inhibitors. In this review, the current knowledge regarding induced resistance by EphA2 in cancer treatment is summarized, and the types of cancer that lead to the most cancer-related deaths are highlighted. Some EphA2 inhibitors were also investigated. Regardless of whether the cancer treatment has reached a drug-resistance stage in EphA2-overexpressing tumors, once EphA2 is involved in cancer progression and aggressiveness, targeting EphA2 is a promising therapeutic strategy, especially in combination with other target-drugs for synergistic effect. For that reason, monoclonal antibodies against EphA2 and inhibitors of this receptor should be investigated for efficacy and drug toxicity.

Optogenetic Regulation of EphA1 RTK Activation and Signaling

Eph receptors are ubiquitous class of transmembrane receptors that mediate cell-cell communication, proliferation, differentiation, and migration. EphA1 receptors specifically play an important role in angiogenesis, fetal development, and cancer progression; however, studies of this receptor can be challenging as its ligand, ephrinA1, binds and activates several EphA receptors simultaneously. Optogenetic strategies could be applied to circumvent this requirement for ligand activation and enable selective activation of the EphA1 subtype. In this work, we designed and tested several iterations of an optogenetic EphA1 - Cryptochrome 2 (Cry2) fusion, investigating their capacity to mimic EphA1-dependent signaling in response to light activation. We then characterized the key cell signaling target of MAPK phosphorylation activated in response to light stimulation. The optogenetic regulation of Eph receptor RTK signaling without the need for external stimulus promises to be an effective means of controlling individual Eph receptor-mediated activities and creates a path forward for the identification of new Eph-dependent functions.

Contrasting Effects of Cancer-Associated Mutations in EphA3 and EphB2 Kinases

Erythropoietin-producing hepatoma (Eph) receptors are a family of tyrosine kinases that can act as tumor promoters or tumor suppressors, depending on the receptor and cancer cell type. Cancer-associated somatic mutations have been identified in all Eph receptors, but in most cases, the functional effects of the mutations are unknown. In this study, we expressed and purified the kinase domains of wild-type (WT) EphA3 and EphB2 along with 16 cancer-associated mutants. We identified mutations that decrease EphA3 activity and both activating and inhibitory mutations in EphB2. To shed light on the mechanisms by which the mutations altered kinase activity, we measured the thermal stabilities of the enzymes and performed steady-state kinetic experiments. We also expressed the full-length receptors in HEK293T cells to determine the cellular effects. WT EphB2 promoted downstream ERK signaling, while a kinase-inactive mutant (S706F) was similar to the control cells. In contrast, WT EphA3 (but not loss-of-function mutants) inhibited ERK signaling. The reciprocal effects of EphB2 and EphA3 on ERK phosphorylation in HEK293T cells were also evident in Ras-GTP loading. Thus, consistent with the dual roles of Eph receptors as tumor promoters and tumor suppressors, somatic mutations have the potential to increase or decrease Eph function, resulting in changes in the downstream signaling transduction.

Eph receptors and ephrins in cancer progression

Evidence implicating Eph receptor tyrosine kinases and their ephrin ligands (that together make up the 'Eph system') in cancer development and progression has been accumulating since the discovery of the first Eph receptor approximately 35 years ago. Advances in the past decade and a half have considerably increased the understanding of Eph receptor-ephrin signalling mechanisms in cancer and have uncovered intriguing new roles in cancer progression and drug resistance. This Review focuses mainly on these more recent developments. I provide an update on the different mechanisms of Eph receptor-ephrin-mediated cell-cell communication and cell autonomous signalling, as well as on the interplay of the Eph system with other signalling systems. I further discuss recent advances in elucidating how the Eph system controls tumour expansion, invasiveness and metastasis, supports cancer stem cells, and drives therapy resistance. In addition to functioning within cancer cells, the Eph system also mediates the reciprocal communication between cancer cells and cells of the tumour microenvironment. The involvement of the Eph system in tumour angiogenesis is well established, but recent findings also demonstrate roles in immune cells, cancer-associated fibroblasts and the extracellular matrix. Lastly, I discuss strategies under evaluation for therapeutic targeting of Eph receptors-ephrins in cancer and conclude with an outlook on promising future research directions.

Time-resolved live-cell spectroscopy reveals EphA2 multimeric assembly

Ephrin type-A receptor 2 (EphA2) is a receptor tyrosine kinase that initiates both ligand-dependent tumor-suppressive and ligand-independent oncogenic signaling. We used time-resolved, live-cell fluorescence spectroscopy to show that the ligand-free EphA2 assembles into multimers driven by two types of intermolecular interactions in the ectodomain. The first type entails extended symmetric interactions required for ligand-induced receptor clustering and tumor-suppressive signaling that inhibits activity of the oncogenic extracellular signal-regulated kinase (ERK) and protein kinase B (AKT) protein kinases and suppresses cell migration. The second type is an asymmetric interaction between the amino terminus and the membrane proximal domain of the neighboring receptors, which supports oncogenic signaling and promotes migration in vitro and tumor invasiveness in vivo. Our results identify the molecular interactions that drive the formation of the EphA2 multimeric signaling clusters and reveal the pivotal role of EphA2 assembly in dictating its opposing functions in oncogenesis.

Targeting EPHA2 with Kinase Inhibitors in Colorectal Cancer

The ephrin type-A 2 receptor tyrosine kinase (EPHA2) is involved in the development and progression of various cancer types, including colorectal cancer (CRC). There is also evidence that EPHA2 plays a key role in the development of resistance to the endothelial growth factor receptor (EGFR) monoclonal antibody Cetuximab used clinically in CRC. Despite the promising pharmacological potential of EPHA2, only a handful of specific inhibitors are currently available. In this concept paper, general strategies for EPHA2 inhibition with molecules of low molecular weight (small molecules) are described. Furthermore, available examples of inhibiting EPHA2 in CRC using small molecules are summarized, highlighting the potential of this approach.

Efferocytosis is restricted by axon guidance molecule EphA4 via ERK/Stat6/MERTK signaling following brain injury

BACKGROUND

Efferocytosis is a process that removes apoptotic cells and cellular debris. Clearance of these cells alleviates neuroinflammation, prevents the release of inflammatory molecules, and promotes the production of anti-inflammatory cytokines to help maintain tissue homeostasis. The underlying mechanisms by which this occurs in the brain after injury remain ill-defined.

METHODS

We used GFP bone marrow chimeric knockout (KO) mice to demonstrate that the axon guidance molecule EphA4 receptor tyrosine kinase is involved in suppressing MERTK in the brain to restrict efferocytosis of resident microglia and peripheral-derived monocyte/macrophages.

RESULTS

Single-cell RNAseq identified MERTK expression, the primary receptor involved in efferocytosis, on monocytes, microglia, and a subset of astrocytes in the damaged cortex following brain injury. Loss of EphA4 on infiltrating GFP-expressing immune cells improved functional outcome concomitant with enhanced efferocytosis and overall protein expression of p-MERTK, p-ERK, and p-Stat6. The percentage of GFP+ monocyte/macrophages and resident microglia engulfing NeuN+ or TUNEL+ cells was significantly higher in KO chimeric mice. Importantly, mRNA expression of Mertk and its cognate ligand Gas6 was significantly elevated in these mice compared to the wild-type. Analysis of cell-specific expression showed that p-ERK and p-Stat6 co-localized with MERTK-expressing GFP + cells in the peri-lesional area of the cortex following brain injury. Using an in vitro efferocytosis assay, co-culturing pHrodo-labeled apoptotic Jurkat cells and bone marrow (BM)-derived macrophages, we demonstrate that efferocytosis efficiency and mRNA expression of Mertk and Gas6 was enhanced in the absence of EphA4. Selective inhibitors of ERK and Stat6 attenuated this effect, confirming that EphA4 suppresses monocyte/macrophage efferocytosis via inhibition of the ERK/Stat6 pathway.

CONCLUSIONS

Our findings implicate the ERK/Stat6/MERTK axis as a novel regulator of apoptotic debris clearance in brain injury that is restricted by peripheral myeloid-derived EphA4 to prevent the resolution of inflammation.

A novel signature of the ligand and receptor genes associated with disulfidoptosis for prediction of prognosis, immunologic therapy responses in hepatocellular carcinoma

Backgroud

We aimed to explore the prognostic features of ligand and receptor genes associated with disulfidoptosis in hepatocellular carcinoma (HCC) and establish a risk signature utilizing these genes to predict the prognosis of HCC patients.

Methods

We used scRNA-seq data from GSE166635 to differentiate malignant cells from normal cells using "copykat".The study thoroughly examined the disparities in disulfidoptosis scores and the associated gene expressions between malignant and normal cells.We identified key ligand and receptor genes that are specific to HCC cells.Subsequently, Correlation analysis was conducted to ascertain the ligand and receptor genes associated with disulfidoptosis.We performed univariate Cox regression analysis to identify prognostic ligand and receptor genes associated with disulfidoptosis.We employed LASSO to construct a risk signature using prognostic ligand and receptor genes associated with disulfidoptosis.Lastly, we developed a nomogram model that integrates the risk signature with clinicopathological characteristics.

Results

Malignant cells displayed a marked increase in disulfidoptosis scores and the expression of associated genes compared to normal cells.We identified 110 receptor and ligand genes significantly associated with disulfidoptosis, and narrowed them down to create a risk signature comprising eight genes.Multivariate analysis confirmed the risk signature as an independent prognostic factor for HCC and validated its predictive value for immunotherapy outcomes.A novel nomogram was developed, incorporating stage information and the risk signature derived from disulfidoptosis-related receptor and ligand genes, demonstrating excellent predictive accuracy and reliability in HCC prognosis prediction.

Conclusion

Risk signatures based on disulfidoptosis-associated ligand and receptor genes can effectively predict HCC prognosis and may inform immunotherapy strategies.

Efferocytosis is restricted by axon guidance molecule EphA4 via ERK/Stat6/Mertk signaling following brain injury

Background

Efferocytosis is a process that removes apoptotic cells and cellular debris. Clearance of these cells alleviates neuroinflammation and prevents the release of inflammatory molecules and promotes the production of anti-inflammatory cytokines to help maintain tissue homeostasis. The underlying mechanisms by which this occurs in the brain after injury remains ill-defined.

Methods

We demonstrate using GFP bone marrow chimeric knockout (KO) mice, that the axon guidance molecule EphA4 receptor tyrosine kinase is involved in suppressing Mertk signaling in the brain to restrict the function of efferocytosis on resident microglia and peripheral-derived monocyte/macrophages.

Results

Single-cell RNAseq identified Mertk expression, the primary receptor involved in efferocytosis, on monocytes, microglia, and a subset of astrocytes in the damaged cortex following brain injury. Loss of EphA4 on infiltrating GFP-expressing immune cells improved functional outcome concomitant with enhanced efferocytosis, and overall protein expression of p-Mertk, p-ERK, and p-Stat6. The percentage of GFP+ monocyte/macrophages and resident microglia engulfing NeuN+ or TUNEL+ cells was significantly higher in KO chimeric mice. Importantly, mRNA expression of Mertk and its cognate ligand Gas6 was significantly elevated in these mice compared to wild-type. Analysis of cell-specific expression showed that p-ERK and p-Stat6 co-localized with Mertk-expressing GFP + cells in the peri-lesional area of the cortex following brain injury. Using an in vitro efferocytosis assay, co-culturing pHrodo-labeled apoptotic Jurkat cells and bone marrow (BM)-derived macrophages, we demonstrate that efferocytosis efficiency and mRNA expression of Mertk and Gas6 was enhanced in the absence of EphA4. Select inhibitors of ERK and Stat6 attenuated this effect confirming that EphA4 suppresses monocyte/macrophage efferocytosis via inhibition of the ERK/Stat6 pathway.

Conclusions

Our findings implicate the Mertk/ERK/Stat6 axis as a novel regulator of apoptotic debris clearance in brain injury that is restricted by peripheral myeloid-derived EphA4 to prevent the resolution of inflammation.

Targeting CDK1 in cancer: mechanisms and implications

Cyclin dependent kinases (CDKs) are serine/threonine kinases that are proposed as promising candidate targets for cancer treatment. These proteins complexed with cyclins play a critical role in cell cycle progression. Most CDKs demonstrate substantially higher expression in cancer tissues compared with normal tissues and, according to the TCGA database, correlate with survival rate in multiple cancer types. Deregulation of CDK1 has been shown to be closely associated with tumorigenesis. CDK1 activation plays a critical role in a wide range of cancer types; and CDK1 phosphorylation of its many substrates greatly influences their function in tumorigenesis. Enrichment of CDK1 interacting proteins with Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis was conducted to demonstrate that the associated proteins participate in multiple oncogenic pathways. This abundance of evidence clearly supports CDK1 as a promising target for cancer therapy. A number of small molecules targeting CDK1 or multiple CDKs have been developed and evaluated in preclinical studies. Notably, some of these small molecules have also been subjected to human clinical trials. This review evaluates the mechanisms and implications of targeting CDK1 in tumorigenesis and cancer therapy.

A computational and laboratory approach for the investigation of interactions of peptide conjugated natural terpenes with EpHA2 receptor

CONTEXT

Ephrin type A receptor 2 (EphA2) is a well-known drug target for cancer treatment due to its overexpression in numerous types of cancers. Thus, it is crucial to determine the binding interactions of this receptor with both the ligand-binding domain (LBD) and the kinase-binding domain (KBD) through a targeted approach in order to modulate its activity. In this work, natural terpenes with inherent anticancer properties were conjugated with short peptides YSAYP and SWLAY that are known to bind to the LBD of EphA2 receptor. We examined the binding interactions of six terpenes (maslinic acid, levopimaric acid, quinopimaric acid, oleanolic, polyalthic, and hydroxybetulinic acid) conjugated to the above peptides with the ligand-binding domain (LBD) of EphA2 receptor computationally. Additionally, following the "target-hopping approach," we also examined the interactions of the conjugates with the KBD. Our results indicated that most of the conjugates showed higher binding interactions with the EphA2 kinase domain compared to LBD. Furthermore, the binding affinities of the terpenes increased upon conjugating the peptides with the terpenes. In order to further investigate the specificity toward EphA2 kinase domain, we also examined the binding interactions of the terpenes conjugated to VPWXE (x = norleucine), as VPWXE has been shown to bind to other RTKs. Our results indicated that the terpenes conjugated to SWLAY in particular showed high efficacy toward binding to the KBD. We also designed conjugates where in the peptide portion and the terpenes were separated by a butyl (C4) group linker to examine if the binding interactions could be enhanced. Docking studies showed that the conjugates with linkers had enhanced binding with the LBD compared to those without linkers, though binding remained slightly higher without linkers toward the KBD. As a proof of concept, maslinate and oleanolate conjugates of each of the peptides were then tested with F98 tumor cells which are known to overexpress EphA2 receptor. Results indicated that the oleanolate-amido-SWLAY conjugates were efficacious in reducing the cell proliferation of the tumor cells and may be potentially developed and further studied for targeting tumor cells overexpressing the EphA2 receptor. To test if these conjugates could bind to the receptor and potentially function as kinase inhibitors, we conducted SPR analysis and ADP-Glo assay. Our results indicated that OA conjugate with SWLAY showed the highest inhibition.

METHODS

Docking studies were carried out using AutoDock Vina, v.1.2.0; Molecular Dynamics and MMGBSA calculations were carried out through Schrodinger Software DESMOND.

The role of EphA2 in ADAM17- and ionizing radiation-enhanced lung cancer cell migration

Purpose

Ionizing radiation (IR) enhances the migratory capacity of cancer cells. Here we investigate in non-small-cell-lung-cancer (NSCLC) cells a novel link between IR-enhanced ADAM17 activity and the non-canonical pathway of EphA2 in the cellular stress response to irradiation.

Methods

Cancer cell migration in dependence of IR, EphA2, and paracrine signaling mediated by ADAM17 was determined using transwell migration assays. Changes of EphA2 pS897 and mRNA expression levels upon different ADAM17-directed treatment strategies, including the small molecular inhibitor TMI-005, the monoclonal antibody MEDI3622, and shRNAs, were mechanistically investigated. ADAM17-mediated release and cleavage of the EphA2 ligand ephrin-A1 was measured using ELISA and an acellular cleavage assay.

Results

Irradiation with 5 Gy enhanced tumor cell migration of NSCLC NCI-H358 cells in dependence of EphA2. At the same time, IR increased growth factor-induced EphA2 S897 phosphorylation via auto- and paracrine signaling. Genetic and pharmaceutical downregulation of ADAM17 activity abrogated growth factor (e.g. amphiregulin) release, which reduced MAPK pathway-mediated EphA2 S897 phosphorylation in an auto- and paracrine way (non-canonical EphA2-pathway) in NCI-H358 and A549 cells. These signaling processes were associated with reduced cell migration towards conditioned media derived from ADAM17-deficient cells. Interestingly, ADAM17 inhibition with the small molecular inhibitor TMI-005 led to the internalization and proteasomal degradation of EphA2, which was rescued by amphiregulin or MG-132 treatment. In addition, ADAM17 inhibition also abrogated ephrin-A1 cleavage and thereby interfered with the canonical EphA2-pathway.

Conclusion

We identified ADAM17 and the receptor tyrosine kinase EphA2 as two important drivers for (IR-) induced NSCLC cell migration and described a unique interrelation between ADAM17 and EphA2. We demonstrated that ADAM17 influences both, EphA2 (pS897) and its GPI-anchored ligand ephrin-A1. Using different cellular and molecular readouts, we generated a comprehensive picture of how ADAM17 and IR influence the EphA2 canonical and non-canonical pathway in NSCLC cells.

EPHB4-RASA1-Mediated Negative Regulation of Ras-MAPK Signaling in the Vasculature: Implications for the Treatment of EPHB4- and RASA1-Related Vascular Anomalies in Humans

Ephrin receptors constitute a large family of receptor tyrosine kinases in mammals that through interaction with cell surface-anchored ephrin ligands regulate multiple different cellular responses in numerous cell types and tissues. In the cardiovascular system, studies performed in vitro and in vivo have pointed to a critical role for Ephrin receptor B4 (EPHB4) as a regulator of blood and lymphatic vascular development and function. However, in this role, EPHB4 appears to act not as a classical growth factor receptor but instead functions to dampen the activation of the Ras-mitogen activated protein signaling (MAPK) pathway induced by other growth factor receptors in endothelial cells (EC). To inhibit the Ras-MAPK pathway, EPHB4 interacts functionally with Ras p21 protein activator 1 (RASA1) also known as p120 Ras GTPase-activating protein. Here, we review the evidence for an inhibitory role for an EPHB4-RASA1 interface in EC. We further discuss the mechanisms by which loss of EPHB4-RASA1 signaling in EC leads to blood and lymphatic vascular abnormalities in mice and the implications of these findings for an understanding of the pathogenesis of vascular anomalies in humans caused by mutations in EPHB4 and RASA1 genes. Last, we provide insights into possible means of drug therapy for EPHB4- and RASA1-related vascular anomalies.

Chronic Inhalation Exposure to Antimony Trioxide Exacerbates the MAPK Signaling in Alveolar Bronchiolar Carcinomas in B6C3F1/N Mice

Antimony trioxide (AT) is used as a flame retardant in fabrics and plastics. Occupational exposure in miners and smelters is mainly through inhalation and dermal contact. Chronic inhalation exposure to AT particulates in B6C3F1/N mice and Wistar Han rats resulted in increased incidences and tumor multiplicities of alveolar/bronchiolar carcinomas (ABCs). In this study, we demonstrated Kras (43%) and Egfr (46%) hotspot mutations in mouse lung tumors (n = 80) and only Egfr (50%) mutations in rat lung tumors (n = 26). Interestingly, there were no differences in the incidences of these mutations in ABCs from rats and mice at exposure concentrations that did and did not exceed the pulmonary overload threshold. There was increased expression of p44/42 mitogen-activated protein kinase (MAPK) (Erk1/2) protein in ABCs harboring mutations in Kras and/or Egfr, confirming the activation of MAPK signaling. Transcriptomic analysis indicated significant alterations in MAPK signaling such as ephrin receptor signaling and signaling by Rho-family GTPases in AT-exposed ABCs. In addition, there was significant overlap between transcriptomic data from mouse ABCs due to AT exposure and human pulmonary adenocarcinoma data. Collectively, these data suggest chronic AT exposure exacerbates MAPK signaling in ABCs and, thus, may be translationally relevant to human lung cancers.

Proteomics uncover EPHA2 as a potential novel therapeutic target in colorectal cancer cell lines with acquired cetuximab resistance

BACKGROUND

In metastatic colorectal cancer (mCRC), acquired resistance against anti-EGFR targeted monoclonal antibodies, such as cetuximab (CET), was shown to be frequently caused by activating alterations in the RAS genes KRAS or NRAS. To this day, no efficient follow-up treatment option has emerged to treat mCRC in such a setting of resistance.

METHODS

To uncover potential targets for second-line targeted therapies, we used mass-spectrometric proteomics to shed light on kinome reprogramming in an established cellular model of acquired, KRAS-associated CET resistance.

RESULTS

This CET resistance was reflected by significant changes in the kinome, most of them individual to each cell line. Interestingly, all investigated resistant cell lines displayed upregulation of the Ephrin type-A receptor 2 (EPHA2), a well-known driver of traits of progression. Expectedly resistant cell lines displayed increased migration (p < 0.01) that was significantly reduced by targeting the EPHA2 signalling axis using RNA interference (RNAi) (p < 0.001), ephrin-A1 stimulation (p < 0.001), dasatinib (p < 0.01), or anti-EPHA2 antibody treatment (p < 0.001), identifying it as an actionable target in mCRC with acquired CET resistance.

CONCLUSION

These results highlight EPHA2 and its role in mCRC with KRAS-gene mutated acquired CET resistance and support its use as a potential actionable target for the development of future precision medicine therapies.

Proteolytic cleavage of membrane proteins by membrane type-1 MMP regulates cancer malignant progression

Strategies to develop cancer therapies using inhibitors that target matrix metalloproteinases (MMPs), particularly membrane type-1 MMP (MT1-MMP), have failed. This is predominantly attributed to the specificity of MMP inhibitors and numerous functions of MMPs; therefore, targeting substrates with such broad specificity can lead to off-target effects. Thus, new drug development for cancer therapeutics should focus on the ability of MT1-MMP to break down substrates, such as functional cell membrane proteins, to regulate the functions of these proteins that promote tumor malignancy. In this review, we discuss the mechanism by which proteolysis of cell surface proteins by MT1-MMP promotes progression of malignant tumor cells. In addition, we discuss the two protein fragments generated by limited cleavage of erythropoietin-producing hepatoma receptor tyrosine kinase A2 (EphA2-NF, -CF), which represent a promising basis for developing new cancer therapies and diagnostic techniques.

Cytomegalovirus US28 regulates cellular EphA2 to maintain viral latency

Cytomegalovirus (CMV) reactivation from latency following immune dysregulation remains a serious risk for patients, often causing substantial morbidity and mortality. Here, we demonstrate the CMV-encoded G protein-coupled receptor, US28, in coordination with cellular Ephrin receptor A2, attenuates mitogen-activated protein kinase signaling, thereby limiting viral replication in latently infected primary monocytes. Furthermore, treatment of latently infected primary monocytes with dasatinib, a Food and Drug Association-approved kinase inhibitor used to treat a subset of leukemias, results in CMV reactivation. These ex vivo data correlate with our retrospective analyses of the Explorys electronic health record database, where we find dasatinib treatment is associated with a significant risk of CMV-associated disease (odds ratio 1.58, P = 0.0004). Collectively, our findings elucidate a signaling pathway that plays a central role in the balance between CMV latency and reactivation and identifies a common therapeutic cancer treatment that elevates the risk of CMV-associated disease.

Cellular loci involved in the development of brain arteriovenous malformations

Brain arteriovenous malformations (bAVMs) are abnormal vessels that are prone to rupture, causing life-threatening intracranial bleeding. The mechanism of bAVM formation is poorly understood. Nevertheless, animal studies revealed that gene mutation in endothelial cells (ECs) and angiogenic stimulation are necessary for bAVM initiation. Evidence collected through analyzing bAVM specimens of human and mouse models indicate that cells other than ECs also are involved in bAVM pathogenesis. Both human and mouse bAVMs vessels showed lower mural cell-coverage, suggesting a role of pericytes and vascular smooth muscle cells (vSMCs) in bAVM pathogenesis. Perivascular astrocytes also are important in maintaining cerebral vascular function and take part in bAVM development. Furthermore, higher inflammatory cytokines in bAVM tissue and blood demonstrate the contribution of inflammatory cells in bAVM progression, and rupture. The goal of this paper is to provide our current understanding of the roles of different cellular loci in bAVM pathogenesis.

Non-canonical EphA2 activation underpins PTEN-mediated metastatic migration and poor clinical outcome in prostate cancer

Background

The key process of mesenchymal to amoeboid transition (MAT), which enables prostate cancer (PCa) transendothelial migration and subsequent development of metastases in red bone marrow stroma, is driven by phosphorylation of EphA2^S897 by pAkt, which is induced by the omega-6 polyunsaturated fatty acid arachidonic acid. Here we investigate the influence of EphA2 signalling in PCa progression and long-term survival.

Methods

The mechanisms underpinning metastatic biopotential of altered EphA2 signalling in relation to PTEN status were assessed in vitro using canonical (EphA2^D739N) and non-canonical (EphA2^S897G) PC3-M mutants, interrogation of publicly available PTEN-stratified databases and clinical validation using a PCa TMA (n = 177) with long-term follow-up data. Spatial heterogeneity of EphA2 was assessed using a radical prostatectomy cohort (n = 67).

Results

Non-canonical EphA2 signalling via pEphA2^S897 is required for PCa transendothelial invasion of bone marrow endothelium. High expression of EphA2 or pEphA2^S897 in a PTEN^low background is associated with poor overall survival. Expression of EphA2, pEphA2^S897 and the associated MAT marker pMLC2 are spatially regulated with the highest levels found within lesion areas within 500 µm of the prostate margin.

Conclusion

EphA2 MAT-related signalling confers transendothelial invasion. This is associated with a substantially worse prognosis in PTEN-deficient PCa.

EFNA1 in gastrointestinal cancer: Expression, regulation and clinical significance

Ephrin-A1 is a protein that in humans is encoded by the EFNA1 gene. The ephrins and EPH-related receptors comprise the largest subfamily of receptor protein-tyrosine kinases which play an indispensable role in normal growth and development or in the pathophysiology of various tumors. The role of EFNA1 in tumorigenesis and development is complex and depends on the cell type and microenvironment which in turn affect the expression of EFNA1. This article reviews the expression, prognostic value, regulation and clinical significance of EFNA1 in gastrointestinal tumors.

Ligands with different dimeric configurations potently activate the EphA2 receptor and reveal its potential for biased signaling

The EphA2 receptor tyrosine kinase activates signaling pathways with different, and sometimes opposite, effects in cancer and other pathologies. Thus, highly specific and potent biased ligands that differentially control EphA2 signaling responses could be therapeutically valuable. Here, we use EphA2-specific monomeric peptides to engineer dimeric ligands with three different geometric configurations to combine a potential ability to differentially modulate EphA2 signaling responses with the high potency and prolonged receptor residence time characteristic of dimeric ligands. The different dimeric peptides readily induce EphA2 clustering, autophosphorylation and signaling, the best with sub-nanomolar potency. Yet, there are differences in two EphA2 signaling responses induced by peptides with different configurations, which exhibit distinct potency and efficacy. The peptides bias signaling when compared with the ephrinA1-Fc ligand and do so via different mechanisms. These findings provide insights into Eph receptor signaling, and proof-of-principle that different Eph signaling responses can be distinctly modulated.

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.

Cellular and molecular mechanisms of EPH/EPHRIN signaling in evolution and development

The EPH receptor tyrosine kinases and their signaling partners, the EPHRINS, comprise a large class of cell signaling molecules that plays diverse roles in development. As cell membrane-anchored signaling molecules, they regulate cellular organization by modulating the strength of cellular contacts, usually by impacting the actin cytoskeleton or cell adhesion programs. Through these cellular functions, EPH/EPHRIN signaling often regulates tissue shape. Indeed, recent evidence indicates that this signaling family is ancient and associated with the origin of multicellularity. Though extensively studied, our understanding of the signaling mechanisms employed by this large family of signaling proteins remains patchwork, and a truly "canonical" EPH/EPHRIN signal transduction pathway is not known and may not exist. Instead, several foundational evolutionarily conserved mechanisms are overlaid by a myriad of tissue -specific functions, though common themes emerge from these as well. Here, I review recent advances and the related contexts that have provided new understanding of the conserved and varied molecular and cellular mechanisms employed by EPH/EPHRIN signaling during development.

The Pathologic and Genetic Characteristics of Extranodal NK/T-Cell Lymphoma

Extranodal NK/T-cell lymphoma is a neoplasm of NK cells or cytotoxic T cells presenting in extranodal sites, most often in the nasal cavity. The typical immunophenotypes are cCD3+, sCD3-, CD4-, CD5-, CD8-, CD16-, and CD56+ with the expression of cytotoxic molecules. Tumor subsets express NK cell receptors, CD95/CD95L, CD30, MYC, and PDL1. Virtually all the tumor cells harbor the EBV genome, which plays a key role in lymphomagenesis as an epigenetic driver. EBV-encoded oncoproteins modulate the host-cell epigenetic machinery, reprogramming the viral and host epigenomes using host epigenetic modifiers. NGS analysis revealed the mutational landscape of ENKTL, predominantly involving the JAK-STAT pathway, epigenetic modifications, the RNA helicase family, the RAS/MAP kinase pathway, and tumor suppressors, which indicate an important role of these pathways and this group of genes in the lymphomagenesis of ENKTL. Recently, three molecular subtypes were proposed, the tumor-suppressor/immune-modulator (TSIM), MGA-BRDT (MB), and HDAC9-EP300-ARID1A (HEA) subtypes, and they are well-correlated with the cell of origin, EBV pattern, genomic alterations, and clinical outcomes. A future investigation into the function and interaction of discovered genes would be very helpful for better understanding the molecular pathogenesis of ENKTL and establishing better treatment strategies.

Regulation of the EphA2 receptor intracellular region by phosphomimetic negative charges in the kinase-SAM linker

Eph receptor tyrosine kinases play a key role in cell-cell communication. Lack of structural information on the entire multi-domain intracellular region of any Eph receptor has hindered understanding of their signaling mechanisms. Here, we use integrative structural biology to investigate the structure and dynamics of the EphA2 intracellular region. EphA2 promotes cancer malignancy through a poorly understood non-canonical form of signaling involving serine/threonine phosphorylation of the linker connecting its kinase and SAM domains. We show that accumulation of multiple linker negative charges, mimicking phosphorylation, induces cooperative changes in the EphA2 intracellular region from more closed to more extended conformations and perturbs the EphA2 juxtamembrane segment and kinase domain. In cells, linker negative charges promote EphA2 oligomerization. We also identify multiple kinases catalyzing linker phosphorylation. Our findings suggest multiple effects of linker phosphorylation on EphA2 signaling and imply that coordination of different kinases is necessary to promote EphA2 non-canonical signaling.

Eph receptor tyrosine kinases and their ephrin ligands mediate cell-cell communication. Here, the authors assess the structure and dynamics of the EphA2 intracellular region and uncover complex effects of phosphorylation within the linker region between EphA2 kinase and SAM domains.

DNA nanotechnology-facilitated ligand manipulation for targeted therapeutics and diagnostics

Ligands, mostly binding to proteins to form complexes and catalyze chemical reactions, can serve as drug and probe molecules, as well as sensing elements. DNA nanotechnology can integrate the high editability of DNA nanostructures and the biological activity of ligands into functionalized DNA nanostructures in a manner of controlled ligand stoichiometry, type, and arrangement, which provides significant advantages for targeted therapeutics and diagnostics. As therapeutic agents, multiple- and multivalent-ligands functionalized DNA nanostructures increase ligand-receptor affinity and activate multivalent ligand-receptor interactions, enabling improved regulation of cell signaling and enhanced control of cell behavior. As diagnostic agents, multiple ligands interaction via DNA nanostructures endows DNA nanosensors with high sensitivity and excellent signal transduction capability. Herein, we review the principles and advantages of using DNA nanostructures to manipulate ligands for targeted therapeutics and diagnostics and provide future perspectives.

MEK inhibition overcomes resistance to EphA2-targeted therapy in uterine cancer

BACKGROUND

Our pilot clinical study of EphA2 inhibitor (dasatinib) plus paclitaxel and carboplatin showed interesting clinical activity in endometrial cancer with manageable toxicity. However, the underlying mechanisms of dasatinib resistance in uterine cancer are unknown. Here, we investigated potential mechanisms underlying resistance to EphA2 inhibitors in uterine cancer and examined the anti-tumor activity of EphA2 inhibitors alone and in combination with a MEK inhibitor.

METHODS

We evaluated the antitumor activity of EphA2 inhibitors plus a MEK inhibitor using in vitro and in vivo orthotopic models of uterine cancer.

RESULTS

EphA2 inhibitor induced MAPK in dasatinib-resistant uterine cancer cells (HEC-1A and Ishikawa) and BRAF/CRAF heterodimerization in HEC-1A cells. EphA2 inhibitor and trametinib significantly increased apoptosis in cancer cells resistant to EphA2 inhibitors compared with controls (p < 0.01). An in vivo study with the orthotopic HEC-1A model showed significantly greater antitumor response to combination treatment compared with dasatinib alone (p < 0.01). Combination treatment increased EphrinA1 and BIM along with decreased pMAPK, Jagged 1, and c-MYC expression in dasatinib-resistant cells. In addition, Spearman analysis using the TCGA data revealed that upregulation of EphA2 was significantly correlated with JAG1, MYC, NOTCH1, NOTCH3 and HES1 expression (p < 0.001, r = 0.25-0.43). Specifically, MAP3K15 and the NOTCH family genes were significantly related to poor clinical outcome in patients with uterine cancer.

CONCLUSIONS

These findings indicate that the MAPK pathway is activated in dasatinib-resistant uterine cancer cells and that EphrinA1-mediated MEK inhibition overcomes dasatinib resistance. Dual targeting of both EphA2 and MEK, combined with chemotherapy, should be considered for future clinical development.

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.

Nogo-A-Δ20/EphA4 interaction antagonizes apoptosis of neural stem cells by integrating p38 and JNK MAPK signaling

Nogo-A protein consists of two main extracellular domains: Nogo-66 (rat amino acid [aa] 1019-1083) and Nogo-A-Δ20 (extracellular, active 180 amino acid Nogo-A region), which serve as strong inhibitors of axon regeneration in the adult CNS (Central Nervous System). Although receptors S1PR2 and HSPGs have been identified as Nogo-A-Δ20 binding proteins, it remains at present elusive whether other receptors directly interacting with Nogo-A-Δ20 exist, and decrease cell death. On the other hand, the key roles of EphA4 in the regulation of glioblastoma, axon regeneration and NSCs (Neural Stem Cells) proliferation or differentiation are well understood, but little is known the relationship between EphA4 and Nogo-A-Δ20 in NSCs apoptosis. Thus, we aim to determine whether Nogo-A-Δ20 can bind to EphA4 and affect survival of NSCs. Here, we discover that EphA4, belonging to a member of erythropoietin-producing hepatocellular (Eph) receptors family, could be acting as a high affinity ligand for Nogo-A-Δ20. Trans-membrane protein of EphA4 is needed for Nogo-A-Δ20-triggered inhibition of NSCs apoptosis, which are mediated by balancing p38 inactivation and JNK MAPK pathway activation. Finally, we predict at the atomic level that essential residues Lys-205, Ile-190, Pro-194 in Nogo-A-Δ20 and EphA4 residues Gln-390, Asn-425, Pro-426 might play critical roles in Nogo-A-Δ20/EphA4 binding via molecular docking.

Effects and mechanisms of Eps8 on the biological behaviour of malignant tumours (Review)

Epidermal growth factor receptor pathway substrate 8 (Eps8) was initially identified as the substrate for the kinase activity of EGFR, improving the responsiveness of EGF, which is involved in cell mitosis, differentiation and other physiological functions. Numerous studies over the last decade have demonstrated that Eps8 is overexpressed in most ubiquitous malignant tumours and subsequently binds with its receptor to activate multiple signalling pathways. Eps8 not only participates in the regulation of malignant phenotypes, such as tumour proliferation, invasion, metastasis and drug resistance, but is also related to the clinicopathological characteristics and prognosis of patients. Therefore, Eps8 is a potential tumour diagnosis and prognostic biomarker and even a therapeutic target. This review aimed to describe the structural characteristics, role and related molecular mechanism of Eps8 in malignant tumours. In addition, the prospect of Eps8 as a target for cancer therapy is examined.

EPHA5 mutations predict survival after immunotherapy in lung adenocarcinoma

Eph receptors constitute the largest family of RTKs, and their associations with antitumor immunity and immunotherapy are largely unknown. By integrating genomic, transcriptomic and clinical data from cohorts in public databases, we identified EPHA5 as the most common mutated gene of Eph receptors in lung adenocarcinoma (LUAD). Moreover, compared with EPHA5 wild-type (WT) patients, EPHA5-mutant (Mut) patients exhibited significantly enhanced infiltration of CD8⁺ T cells and M1 macrophages, reduced recruitment of immunosuppressive regulatory T cells (Tregs) into the tumor site, as well as the increased level of chemokine, interferon-gamma, inhibitory immune checkpoint signatures, tumor mutation burden (TMB) and tumor neoantigen burden (TNB). Additionally, EPHA5 mutation cooccurred with homologous recombination (HR) or mismatch repair (MMR) gene mutations. These data were validated in the LUAD cell line H1299 and a Chinese LUAD cohort. Most importantly, clinical analysis of a Memorial Sloan Kettering Cancer Center (MSKCC) immunotherapy cohort indicated that LUAD patients with EPHA5 mutations who were treated with immunotherapy had markedly prolonged survival times.

Our results revealed the correlation of EPHA5 mutations with tumor immune microenvironment and predictive factors for immunotherapy, implying the potential of EPHA5 mutations as a prognostic marker for the prognosis of LUAD patients to immune checkpoint blockade therapy.

Exploring Dysregulated Signaling Pathways in Cancer

Cancer cell biology takes advantage of identifying diverse cellular signaling pathways that are disrupted in cancer. Signaling pathways are an important means of communication from the exterior of cell to intracellular mediators, as well as intracellular interactions that govern diverse cellular processes. Oncogenic mutations or abnormal expression of signaling components disrupt the regulatory networks that govern cell function, thus enabling tumor cells to undergo dysregulated mitogenesis, to resist apoptosis, and to promote invasion to neighboring tissues. Unraveling of dysregulated signaling pathways may advance the understanding of tumor pathophysiology and lead to the improvement of targeted tumor therapy. In this review article, different signaling pathways and how their dysregulation contributes to the development of tumors have been discussed.

Kinase activity-independent role of EphA2 in the regulation of M-phase progression

Cell division is a tightly regulated, essential process for cell proliferation. Very recently, we reported that EphA2 is phosphorylated at Ser897, via the Cdk1/MEK/ERK/RSK pathway, during M phase and contributes to proper M-phase progression by maintaining cortical rigidity via the EphA2pSer897/ephexin4/RhoG pathway. Here, we show that EphA2 kinase activity is dispensable for M-phase progression. Although EphA2 knockdown delayed this progression, the delay was rescued by an EphA2 mutant expression with an Asp739 to Asn substitution, as well as by wild-type EphA2. Western blotting analysis confirmed that the Asp739Asn mutant lost its EphA2 kinase activity. Like wild-type EphA2, the Asp739Asn mutant was localized to the plasma membrane irrespective of cell cycle. While RhoG localization to the plasma membrane was decreased in EphA2 knockdown cells, it was rescued by re-expression of wild-type EphA2 but not via the mutant containing the Ser897 to Ala substitution. This confirmed our recent report that phosphorylation at Ser897 is responsible for RhoG localization to the plasma membrane. In agreement with the M-phase progression's rescue effect, the Asp739Asn mutant rescued RhoG localization in EphA2 knockdown cells. These results suggest that EphA2 regulates M-phase progression in a manner independent of its kinase activity.

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.

DNA methylation maintains the CLDN1-EPHB6-SLUG axis to enhance chemotherapeutic efficacy and inhibit lung cancer progression

The loss of cancer-cell junctions and escape from the primary-tumor microenvironment are hallmarks of metastasis. A tight-junction protein, Claudin 1 (CLDN1), is a metastasis suppressor in lung adenocarcinoma. However, as a metastasis suppressor, the underlying molecular mechanisms of CLDN1 has not been well studied. Methods: The signaling pathway regulated by CLDN1 was analyzed by Metacore software and validated by immunoblots. The effect of the CLDN1-EPHB6-ERK-SLUG axis on the formation of cancer stem-like cells, drug resistance and metastasis were evaluated by sphere assay, aldefluor assay, flow cytometry, migration assay, cytotoxicity, soft agar assay, immunoprecipitation assay and xenograft experiments. Furthermore, the methylation-specific PCR, pyrosequencing assay, chromatin immunoprecipitation and reporter assay were used to study the epigenetic and RUNX3-mediated CLDN1 transcription. Finally, the molecular signatures of RUNX3/CLDN1/SLUG were used to evaluate the correlation with overall survival by using gene expression omnibus (GEO) data. Results: We demonstrated that CLDN1 repressed cancer progression via a feedback loop of the CLDN1-EPHB6-ERK1/2-SLUG axis, which repressed metastasis, drug resistance, and cancer stemness, indicating that CLDN1 acts as a metastasis suppressor. CLDN1 upregulated the cellular level of EPHB6 and enhanced its activation, resulting in suppression of ERK1/2 signaling. Interestingly, DNA hypermethylation of the CLDN1 promoter abrogated SLUG-mediated suppression of CLDN1 in low-metastatic cancer cells. In contrast, the histone deacetylase inhibitor trichostatin A or vorinostat facilitated CLDN1 expression in high-metastatic cancer cells and thus increased the efficacy of chemotherapy. Combined treatment with cisplatin and trichostatin A or vorinostat had a synergistic effect on cancer-cell death. Conclusions: This study revealed that DNA methylation maintains CLDN1 expression and then represses lung cancer progression via the CLDN1-EPHB6-ERK1/2-SLUG axis. Because CLDN1 enhances the efficacy of chemotherapy, CLDN1 is not only a prognostic marker but a predictive marker for lung adenocarcinoma patients who are good candidates for chemotherapy. Forced CLDN1 expression in low CLDN1-expressing lung adenocarcinoma will increase the chemotherapy response, providing a novel therapeutic strategy.

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.

Ephrin or not? Six tough questions on Eph targeting

Introduction: The Eph-ephrin is a cell-cell communication system generating a forward signal in cell expressing Eph receptors and a reverse signal in ephrin-ligand expressing cells. While clearly involved in the insurgence and progression of cancer, the understanding of the molecular mechanisms regulated by this system needs development; this is a hurdle to the development of therapeutic strategies that can target the Eph receptors and/or their ephrin ligands.Areas covered: We have taken the opportunity to share some key questions on the most effective strategies to target the Eph-ephrin system. This article is based on our experience of the field and therefore is a Perspective and not comprehensive examination of the literature.Expert opinion: Targeting of the Eph-ephrin system has emerged as a potentially valuable approach for cancer therapy. Pharmacological tools have been reported in the last 15 years and these include forward signaling blockers such as kinases inhibitors and antagonists of forward and reverse signaling. Also, biologics including antibodies and recombinant proteins have been developed and some have reached early clinical stages. Data deem the Eph-ephrin system as a signaling axis that is an elusive target. A better understanding of the basic pharmacology behind the activity of available agents and a comprehensive knowledge of the ephrin biology are necessary. We are looking forward to knowing the opinion of the readers.

Phosphoproteomics identifies a bimodal EPHA2 receptor switch that promotes embryonic stem cell differentiation

Embryonic Stem Cell (ESC) differentiation requires complex cell signalling network dynamics, although the key molecular events remain poorly understood. Here, we use phosphoproteomics to identify an FGF4-mediated phosphorylation switch centred upon the key Ephrin receptor EPHA2 in differentiating ESCs. We show that EPHA2 maintains pluripotency and restrains commitment by antagonising ERK1/2 signalling. Upon ESC differentiation, FGF4 utilises a bimodal strategy to disable EPHA2, which is accompanied by transcriptional induction of EFN ligands. Mechanistically, FGF4-ERK1/2-RSK signalling inhibits EPHA2 via Ser/Thr phosphorylation, whilst FGF4-ERK1/2 disrupts a core pluripotency transcriptional circuit required for Epha2 gene expression. This system also operates in mouse and human embryos, where EPHA receptors are enriched in pluripotent cells whilst surrounding lineage-specified trophectoderm expresses EFNA ligands. Our data provide insight into function and regulation of EPH-EFN signalling in ESCs, and suggest that segregated EPH-EFN expression coordinates cell fate with compartmentalisation during early embryonic development.

"Amyloid-beta accumulation cycle" as a prevention and/or therapy target for Alzheimer's disease

The cell cycle and its regulators are validated targets for cancer drugs. Reagents that target cells in a specific cell cycle phase (e.g., antimitotics or DNA synthesis inhibitors/replication stress inducers) have demonstrated success as broad-spectrum anticancer drugs. Cyclin-dependent kinases (CDKs) are drivers of cell cycle transitions. A CDK inhibitor, flavopiridol/alvocidib, is an FDA-approved drug for acute myeloid leukemia. Alzheimer's disease (AD) is another serious issue in contemporary medicine. The cause of AD remains elusive, although a critical role of latent amyloid-beta accumulation has emerged. Existing AD drug research and development targets include amyloid, amyloid metabolism/catabolism, tau, inflammation, cholesterol, the cholinergic system, and other neurotransmitters. However, none have been validated as therapeutically effective targets. Recent reports from AD-omics and preclinical animal models provided data supporting the long-standing notion that cell cycle progression and/or mitosis may be a valid target for AD prevention and/or therapy. This review will summarize the recent developments in AD research: (a) Mitotic re-entry, leading to the "amyloid-beta accumulation cycle," may be a prerequisite for amyloid-beta accumulation and AD pathology development; (b) AD-associated pathogens can cause cell cycle errors; (c) thirteen among 37 human AD genetic risk genes may be functionally involved in the cell cycle and/or mitosis; and (d) preclinical AD mouse models treated with CDK inhibitor showed improvements in cognitive/behavioral symptoms. If the "amyloid-beta accumulation cycle is an AD drug target" concept is proven, repurposing of cancer drugs may emerge as a new, fast-track approach for AD management in the clinic setting.

Membrane receptor activation mechanisms and transmembrane peptide tools to elucidate them

Single-pass membrane receptors contain extracellular domains that respond to external stimuli and transmit information to intracellular domains through a single transmembrane (TM) α-helix. Because membrane receptors have various roles in homeostasis, signaling malfunctions of these receptors can cause disease. Despite their importance, there is still much to be understood mechanistically about how single-pass receptors are activated. In general, single-pass receptors respond to extracellular stimuli via alterations in their oligomeric state. The details of this process are still the focus of intense study, and several lines of evidence indicate that the TM domain (TMD) of the receptor plays a central role. We discuss three major mechanistic hypotheses for receptor activation: ligand-induced dimerization, ligand-induced rotation, and receptor clustering. Recent observations suggest that receptors can use a combination of these activation mechanisms and that technical limitations can bias interpretation. Short peptides derived from receptor TMDs, which can be identified by screening or rationally developed on the basis of the structure or sequence of their targets, have provided critical insights into receptor function. Here, we explore recent evidence that, depending on the target receptor, TMD peptides cannot only inhibit but also activate target receptors and can accommodate novel, bifunctional designs. Furthermore, we call for more sharing of negative results to inform the TMD peptide field, which is rapidly transforming into a suite of unique tools with the potential for future therapeutics.