Eph Receptor Tyrosine Kinases Research Articles

Cholesterol inhibits assembly and activation of the EphA2 receptor.

The receptor tyrosine kinase EphA2 drives cancer malignancy by facilitating metastasis. EphA2 can be found in different self-assembly states: as a monomer, dimer, and oligomer. However, our understanding remains limited regarding which EphA2 state is responsible for driving pro-metastatic signaling. To address this limitation, we have developed SiMPull-POP, a single-molecule method for accurate quantification of membrane protein self-assembly. Our experiments revealed that a reduction of plasma membrane cholesterol strongly promoted EphA2 self-assembly. Indeed, low cholesterol caused a similar effect to the EphA2 ligand ephrinA1-Fc. These results indicate that cholesterol inhibits EphA2 assembly. Phosphorylation studies in different cell lines revealed that low cholesterol increased phospho-serine levels, the signature of oncogenic signaling. Investigation of the mechanism that cholesterol uses to inhibit the assembly and activity of EphA2 indicate an in-trans effect, where EphA2 is phosphorylated by protein kinase A downstream of beta-adrenergic receptor activity, which cholesterol also inhibits. Our study not only provides new mechanistic insights on EphA2 oncogenic function, but also suggests that cholesterol acts as a molecular safeguard mechanism that prevents uncontrolled self-assembly and activation of EphA2.

The Receptor Tyrosine Kinase EphA2 and Integrin-linked Kinase Expression in Colorectal Cancer in Relation to the Severity of the Tumor

Abstract Background: Although colorectal carcinoma is still the second cancer-related death worldwide, the current knowledge of the prognostic profile of routine markers is still humble. This study aimed to study the receptor tyrosine kinase EphA2 and integrin-linked kinase expression in relation to the severity of the disease represented by the grade, extent of invasion, and lymph node involvement. Materials and Methods: This cross-sectional study included 87 colorectal cancer cases diagnosed between 2019 and 2022. The immunohistochemical expression and scoring of integrin-linked kinase and EphA2 was carried out and correlated to the histological variables of severity. Results: The mean age of the studied cases was 57.85 years, and approximately 56.3% of them were females. The majority of the cases were moderately differentiated carcinoma (81.61%). More than half of the patients presented in T3. No lymph-node involvement was detected in 65.52 cases. The majority of the studied cases showed negative integrin-linked kinase expression in tumor cells in the colon and lymph nodes. Even positive cases showed low scores. EphA2 marker showed higher positivity in tumor cells of the colon and lymph nodes with higher scores, but no significant correlation to the histopathological variables. Conclusion: The EphA2 marker is of higher benefit than the integrin-linked kinase and the last one is of limited prognostic role in colorectal cancer due to the very high negative and low score results.

Abstract 1680: Roles of EphA2 receptor signaling in prostate cancer development and progression

Abstract Aggressive forms of prostate cancer (PCa), while initially responsive to androgen deprivation therapy (ADT), inevitably become resistant to therapy and are considered castration resistant PCa (CRPC). A major goal of PCa research has been to broadly identify molecular and cellular mechanisms that aid this progression to identify potential therapeutic targets. Using a combination of human data and unique animal models, we found that the receptor tyrosine kinase (RTK) EphA2 is overexpressed specifically in castration resistant and advancing prostate cancers. Furthermore we show that in metastatic PCa the receptor undergoes ligand-independent oncogenic signaling mediated by phosphorylation of EphA2 at S897. Together our data indicate a potential mechanism in PCa progression in which EphA2 becomes overexpressed and aids acquisition of castration resistance via acting as a driver of cell migration, invasion, and proliferation. Citation Format: Ryan Lingerak, Aaron Petty, Hong Guo, Hebei Lin, Xiaojun Shi, Soyeon Kim, Bingcheng Wang. Roles of EphA2 receptor signaling in prostate cancer development and progression [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 1680.

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.

Receptor Tyrosine Kinase EPHA2 Drives Epidermal Differentiation through Regulation of EGFR Signaling

Intricate signaling systems are required to maintain homeostasis and promote differentiation in the epidermis. Receptor tyrosine kinases are central in orchestrating these systems in epidermal keratinocytes. In particular, EPHA2 and EGFR transduce distinct signals to dictate keratinocyte fate, yet how these cell communication networks are integrated has not been investigated. Our work shows that loss of EPHA2 impairs keratinocyte stratification, differentiation, and barrier function. To determine the mechanism of this dysfunction, we drew from our proteomics data of potential EPHA2 interacting proteins. We identified EGFR as a high-ranking EPHA2 interactor and subsequently validated this interaction. We found that when EPHA2 is reduced, EGFR activation and downstream signaling are intensified and sustained. Evidence indicates that prolonged SRC association contributes to the increase in EGFR signaling. We show that hyperactive EGFR signaling underlies the differentiation defect caused by EPHA2 knockdown because EGFR inhibition restores differentiation in EPHA2-deficient 3-dimensional skin organoids. Our data implicate a mechanism whereby EPHA2 restrains EGFR signaling, allowing for fine tuning in the processes of terminal differentiation and barrier formation. Taken together, we purport that crosstalk between receptor tyrosine kinases EPHA2 and EGFR is critical for epidermal differentiation.

Ubiquitin ligase and signalling hub MYCBP2 is required for efficient EPHB2 tyrosine kinase receptor function

Eph receptor tyrosine kinases participate in a variety of normal and pathogenic processes during development and throughout adulthood. This versatility is likely facilitated by the ability of Eph receptors to signal through diverse cellular signalling pathways: primarily by controlling cytoskeletal dynamics, but also by regulating cellular growth, proliferation, and survival. Despite many proteins linked to these signalling pathways interacting with Eph receptors, the specific mechanisms behind such links and their coordination remain to be elucidated. In a proteomics screen for novel EPHB2 multi-effector proteins, we identified human MYC binding protein 2 (MYCBP2 or PAM or Phr1). MYCBP2 is a large signalling hub involved in diverse processes such as neuronal connectivity, synaptic growth, cell division, neuronal survival, and protein ubiquitination. Our biochemical experiments demonstrate that the formation of a complex containing EPHB2 and MYCBP2 is facilitated by FBXO45, a protein known to select substrates for MYCBP2 ubiquitin ligase activity. Formation of the MYCBP2-EPHB2 complex does not require EPHB2 tyrosine kinase activity and is destabilised by binding of ephrin-B ligands, suggesting that the MYCBP2-EPHB2 association is a prelude to EPHB2 signalling. Paradoxically, the loss of MYCBP2 results in increased ubiquitination of EPHB2 and a decrease of its protein levels suggesting that MYCBP2 stabilises EPHB2. Commensurate with this effect, our cellular experiments reveal that MYCBP2 is essential for efficient EPHB2 signalling responses in cell lines and primary neurons. Finally, our genetic studies in Caenorhabditis elegans provide in vivo evidence that the ephrin receptor VAB-1 displays genetic interactions with known MYCBP2 binding proteins. Together, our results align with the similarity of neurodevelopmental phenotypes caused by MYCBP2 and EPHB2 loss of function, and couple EPHB2 to a signalling effector that controls diverse cellular functions.

Eph receptors and ephrins in cancer progression.

Evidence implicating Eph receptor tyrosine kinases and their ephrin ligands (thattogether 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 mainlyon 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.

The combination of tetracyclines effectively ameliorates liver fibrosis via inhibition of EphB1/2

Eph receptor tyrosine kinase EphB1/2 contributes to the development of liver fibrosis, suggesting the rationale that EphB1/2 inhibitors may be effective in liver fibrosis therapy. Since tetracycline antibiotics were recently demonstrated as EphB kinase inhibitors, in present study we investigated their therapeutic potential against liver fibrosis. Our results showed that the tetracycline combination of demeclocycline (D), chlortetracycline (C), and minocycline (M) inhibited the activation of hepatic stellate cells (HSCs) in vitro and alleviated CCl4-induced animal model of liver fibrosis in vivo. Mechanistically, DCM combination inhibited EphB1/2 phosphorylation and subsequent activation of the MAPK signaling. Moreover, we found that short-term and low-dose DCM combination treatment decreased tissue inflammation and improved liver fibrosis in mice. Thus, our study indicates that tetracyclines may be repurposed for the treatment of liver fibrosis.

Inhibition of EphA2 protects against atherosclerosis by synergizing with statins to mitigate macrophage inflammation

Statins are highly prevalent in patients with coronary artery disease. Statins exert their anti-inflammatory effects on the vascular wall and circulating levels of pro-inflammatory cytokines. However, increasing attention revealed the exacerbation of macrophage inflammation induced by statins, and a clear mechanistic explanation of whether the detrimental effects of statins on macrophage inflammatory phenotypes outweigh the beneficial effects is has not yet been established. Here, RNA-sequencing and RT-qPCR analyses demonstrated that statins significantly upregulated EphA2, Nlrp3, IL-1β and TNF-α expression in macrophages. Mechanistically, we found that atorvastatin reduced KLF4 binding to the EphA2 promoter using KLF4-chromatin immunoprecipitation, suppressed HDAC11-mediated deacetylation and subsequently led to enhanced EphA2 transcription. The 4D-label-free proteomics analysis further confirmed the upregulated EphA2 and inflammatory signals. Furthermore, the proinflammatory effect of atorvastatin was neutralized by an addition of recombinant Fc-ephrinA1, a selective Eph receptor tyrosine kinase inhibitor (ALW-II-41–27) or EphA2-silencing adenovirus (siEphA2). In vivo, EphA2 was identified a proatherogenic factor and apoE-/- mice placed on a high-fat diet following gastric gavage with atorvastatin exhibited a consistent elevation in EphA2 expression. We further observed that the transfection with siEphA2 in atorvastatin-treated mice significantly attenuated atherosclerotic plaque formation and abrogated statin-orchestrated macrophages proinflammatory genes expression as compared to that in atorvastatin alone. Increased plaque stability index was also observed following the addition of siEphA2, as evidenced by increased collagen and smooth muscle content and diminished lipid accumulation and macrophage infiltration. The data suggest that blockage of EphA2 provides an additional therapeutic benefit for further improving the anti-atherogenic effects of statins.

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

BackgroundEfferocytosis 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.MethodsWe 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.ResultsSingle-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.ConclusionsOur 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.

Lipidation and PEGylation strategies to prolong the in vivo half-life of a nanomolar EphA4 receptor antagonist

The EphA4 receptor tyrosine kinase plays a role in neurodegenerative diseases, inhibition of nerve regeneration, cancer progression and other diseases. Therefore, EphA4 inhibition has potential therapeutic value. Selective EphA4 kinase inhibitors are not available, but we identified peptide antagonists that inhibit ephrin ligand binding to EphA4 with high specificity. One of these peptides is the cyclic APY-d3 (βAPYCVYRβASWSC-NH2), which inhibits ephrin-A5 ligand binding to EphA4 with low nanomolar binding affinity and is highly protease resistant. Here we describe modifications of APY-d3 that yield two different key derivatives with greatly increased half-lives in the mouse circulation, the lipidated APY-d3-laur8 and the PEGylated APY-d3-PEG4. These two derivatives inhibit ligand induced EphA4 activation in cells with sub-micromolar potency. Since they retain high potency and specificity for EphA4, lipidated and PEGylated APY-d3 derivatives represent new tools for discriminating EphA4 activities in vivo and for preclinical testing of EphA4 inhibition in animal disease models.

Allosteric inhibition of the T cell receptor by a designed membrane ligand.

The T cell receptor (TCR) is a complex molecular machine that directs the activation of T cells, allowing the immune system to fight pathogens and cancer cells. Despite decades of investigation, the molecular mechanism of TCR activation is still controversial. One of the leading activation hypotheses is the allosteric model. This model posits that binding of pMHC at the extracellular domain triggers a dynamic change in the transmembrane (TM) domain of the TCR subunits, which leads to signaling at the cytoplasmic side. We sought to test this hypothesis by creating a TM ligand for TCR. Previously we described a method to create a soluble peptide capable of inserting into membranes and binding to the TM domain of the receptor tyrosine kinase EphA2 (Alves et al., eLife, 2018). Here, we show that the approach is generalizable to complex membrane receptors, by designing a TM ligand for TCR. We observed that the designed peptide caused a reduction of Lck phosphorylation of TCR at the CD3ζ subunit in T cells. As a result, in the presence of this peptide inhibitor of TCR (PITCR), the proximal signaling cascade downstream of TCR activation was significantly dampened. Co-localization and co-immunoprecipitation in diisobutylene maleic acid (DIBMA) native nanodiscs confirmed that PITCR was able to bind to the TCR. AlphaFold-Multimer predicted that PITCR binds to the TM region of TCR, where it interacts with the two CD3ζ subunits. Our results additionally indicate that PITCR disrupts the allosteric changes in the compactness of the TM bundle that occur upon TCR activation, lending support to the allosteric TCR activation model. The TCR inhibition achieved by PITCR might be useful to treat inflammatory and autoimmune diseases and to prevent organ transplant rejection, as in these conditions aberrant activation of TCR contributes to disease.

Inhibition of EphA3 Expression in Tumour Stromal Cells Suppresses Tumour Growth and Progression.

Tumour progression relies on interactions with untransformed cells in the tumour microenvironment (TME), including cancer-associated fibroblasts (CAFs), which promote blood supply, tumour progression, and immune evasion. Eph receptor tyrosine kinases are cell guidance receptors that are most active during development but re-emerge in cancer and are recognised drug targets. EphA3 is overexpressed in a wide range of tumour types, and we previously found expression particularly in stromal and vascular tissues of the TME. To investigate its role in the TME, we generated transgenic mice with inducible shRNA-mediated knockdown of EphA3 expression. EphA3 knockdown was confirmed in aortic mesenchymal stem cells (MSCs), which displayed reduced angiogenic capacity. In mice with syngeneic lung tumours, EphA3 knockdown reduced vasculature and CAF/MSC-like cells in tumours, and inhibited tumour growth, which was confirmed also in a melanoma model. Single cell RNA sequencing analysis of multiple human tumour types confirmed EphA3 expression in CAFs, including in breast cancer, where EphA3 was particularly prominent in perivascular- and myofibroblast-like CAFs. Our results thus indicate expression of the cell guidance receptor EphA3 in distinct CAF subpopulations is important in supporting tumour angiogenesis and tumour growth, highlighting its potential as a therapeutic target.

Colorectal cancer-associated mutations impair EphB1 kinase function

Erythropoietin-producing hepatoma (Eph) receptor tyrosine kinases regulate the migration and adhesion of cells that are required for many developmental processes and adult tissue homeostasis. In the intestinal epithelium, Eph signaling controls the positioning of cell types along the crypt-villus axis. Eph activity can suppress the progression of colorectal cancer (CRC). The most frequently mutated Eph receptor in metastatic CRC is EphB1. However, the functional effects of EphB1 mutations are mostly unknown. We expressed and purified the kinase domains of WT and five cancer-associated mutant EphB1 and developed assays to assess the functional effects of the mutations. Using purified proteins, we determined that CRC-associated mutations reduce the activity and stability of the folded structure of EphB1. By mammalian cell expression, we determined that CRC-associated mutant EphB1 receptors inhibit signal transducer and activator of transcription 3 and extracellular signal-regulated kinases 1 and 2 signaling. In contrast to the WT, the mutant EphB1 receptors are unable to suppress the migration of human CRC cells. The CRC-associated mutations also impair cell compartmentalization in an assay in which EphB1-expressing cells are cocultured with ligand (ephrin B1)-expressing cells. These results suggest that somatic mutations impair the kinase-dependent tumor suppressor function of EphB1 in CRC.

The Eph/Ephrin system in primary bone tumor and bone cancer pain.

The family of Eph receptor tyrosine kinases and their Ephrin ligands system constitutes a bidirectional signaling pathway. Eph/Ephrin system coordinate a wide spectrum of pathologic processes during development, metastasis, prognosis, drug resistance and angiogenesis in carcinogenesis. Chemotherapy, surgery and radiotherapy are the most commonly used clinical treatments for primary bone tumors. Therefore, surgical resection is often unable to completely eliminate the tumor, and this is the main cause of metastasis and postoperative recurrence. A growing body of literature has been published lately revitalizing our scientific interest towards the role of Eph/Ephrins in pathogenesis and the treatment of bone tumor and bone cancer pain. This study mainly reviewed the roles of Eph/Ephrin system that has both tumor-suppressing and -promoting roles in primary bone tumors and bone cancer pain. Understanding the intracellular mechanisms of Eph/Ephrin system in tumorigenesis and metastasis of bone tumors might provide a foundation for the development of Eph/Ephrin targeted anti-cancer therapy.

Combination of protein and cell internalization SELEX identifies a potential RNA therapeutic and delivery platform to treat EphA2-expressing tumors

The EphA2 receptor tyrosine kinase is overexpressed in most solid tumors and acts as the major driver of tumorigenesis. In this study, we developed a novel approach for targeting the EphA2 receptor using a 2'-fluoro-modified pyrimidine RNA aptamer termed ATOP. We identified the ATOP EphA2 aptamer using a novel bioinformatics strategy that compared aptamers enriched during a protein SELEX using recombinant human EphA2 and a cell-internalization SELEX using EphA2-expressing MDA231 tumor cells. When applied to EphA2-expressing tumor cell lines, the ATOP EphA2 aptamer attenuated tumor cell migration and clonogenicity. In a mouse model of spontaneous metastasis, the ATOP EphA2 aptamer slowed primary tumor growth and significantly reduced the number of lung metastases. The EphA2 ATOP aptamer represents a promising candidate for the development of next-generation targeted therapies that provide safer and more effective treatment of EphA2-overexpressing tumors.

Abstract 705: Epha2 Ligand-dependent And Ligand-independent Signaling In Vascular Smooth Muscle Cell Proliferation And Migration

During atherosclerotic plaque formation, vascular smooth muscle cells (VSMCs) undergo phenotypic modulation from a contractile, quiescent phenotype to a proliferative and synthetic phenotype, allowing VSMCs to deposit form a protective fibrous cap to stabilize the cap through extracellular matrix assembly. Our lab discovered a novel role for the receptor tyrosine kinase EphA2 in SMC phenotypic modulation and proliferation both in vitro and in vivo . In many cancer models, EphA2 can act as a tumor promoter in the absence of ligand and a tumor suppressor in the presence of its ephrinA1 ligand. Therefore, we sought to determine the role of ligand-dependent and ligand-independent signaling in VSMC function. While EphA2 expression is required for maximal VSMC proliferation and migration, EphA2 ligation with ephrinA1 inhibits VSMC proliferation (associated with diminished Erk1/2 and Akt activation) and migration. While ligand treatment induces EphA2 tyrosine phosphorylation, treating VSMCs with serum promotes robust S897 phosphorylation (marker for ligand-independent signaling) specifically through RSK2, whereas no role was found for other described S897 kinases (e.g. Akt, RSK1). EphA2 Ser897 phosphorylation specifically localizes to lamellipodia in VSMCs treated with serum, and blocking RSK2-dependent S897 phosphorylation significantly inhibited VSMC migration but did not affect VSMC proliferation. Taken together, these data suggest that VSMC EphA2 ligation suppresses proliferation and migration, whereas RSK2-dependent EphA2 Ser897 phosphorylation in the absence of ligand promotes VSMC migration, and EphA2 expression likely enhances VSMC proliferation through a ligand-independent response independent of S897 phosphorylation.

774 Receptor tyrosine kinase EPHA2 is required for epidermal barrier homeostasis

774 Receptor tyrosine kinase EPHA2 is required for epidermal barrier homeostasis

Cellular stress induces non-canonical activation of the receptor tyrosine kinase EphA2 through the p38-MK2-RSK signaling pathway

The receptor tyrosine kinase ephrin type-A receptor 2 (EphA2) is overexpressed in malignant tumors. We previously reported that non-canonical EphA2 phosphorylation at Ser-897 was catalyzed by p90 ribosomal S6 kinase (RSK) via the MEK-ERK pathway in ligand- and tyrosine kinase-independent manners. Non-canonical EphA2 activation plays a key role in tumor progression; however, its activation mechanism remains unclear. In the present study, we focused on cellular stress signaling as a novel inducer of non-canonical EphA2 activation. p38, instead of ERK in the case of epidermal growth factor signaling, activated RSK-EphA2 under cellular stress conditions, including anisomycin, cisplatin, and high osmotic stress. Notably, p38 activated the RSK-EphA2 axis via downstream MAPK-activated protein kinase 2 (MK2). Furthermore, MK2 directly phosphorylated both RSK1 Ser-380 and RSK2 Ser-386, critical residues for the activation of their N-terminal kinases, which is consistent with the result showing that the C-terminal kinase domain of RSK1 was dispensable for MK2-mediated EphA2 phosphorylation. Moreover, the p38-MK2-RSK-EphA2 axis promoted glioblastoma cell migration induced by temozolomide, a chemotherapeutic agent for the treatment of glioblastoma patients. Collectively, the present results reveal a novel molecular mechanism for non-canonical EphA2 activation under stress conditions in the tumor microenvironment.

Abstract 620: Regulation of anti-tumor immune response by EphA2 receptor tyrosine kinase

Abstract Eph receptors are the largest family of receptor tyrosine kinases. Overexpression of EphA2 is common across many types of human cancer, particularly in the late stage malignant diseases. We report here that EphA2 knock-out causes delayed tumor growth in several syngeneic mouse caner models, such as breast, colon, lung, and prostate cancer as well as melanoma. However, such effects are missing in immune deficient mice, which suggests the involvement of immune components. Immunophenotyping of the tumors shows elevated T cell infiltration and accompanied by reduced MDSC population in the EphA2 KO tumors. Single cell transcriptomic analysis and cytokine measurements support these results showing increased production of CCL5, CXCL9 and IFNg in the EphA2 KO tumors. Analysis on tumors at very early time points reveals elevated levels of CXCL1 and CXCL2 which recruits suppressive MDSCs. Consistently, larger population of MDSCs was found in PBMCs from the control tumor bearing mice than those bearing EphA2 KO tumors. These results suggest that EphA2 in cancer cells drive the production of CXCL1 and CXCL2 to recruit suppressive MDSCs to the tumor site, thus subvert the host anti-tumor immune surveillance. Targeting the overexpressed EphA2 in cancer can help reshape the tumor micro- environment towards type I anti-tumor immune response. Citation Format: Roger Xiaojun Shi, Ryan Lingerak, So-Yeon Kim, Wei Wang, Khalid Sossey-Alaoui, Bingcheng Wang. Regulation of anti-tumor immune response by EphA2 receptor tyrosine kinase [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 620.