EphA2 Receptor Signaling Mediates Inflammatory Responses in Lipopolysaccharide-Induced Lung Injury

Gene expression profiling of nasal inflammation induced by diesel particles using an in vivo system

Korean diesel particulate matter 20 (KDP20) is a pollutant comprising a complex mixture of carbon and chemical irritants. Although particulate matter and nasal inflammation are strongly associated, the underlying molecular mechanism based on systematic transcriptome analysis remains unknown. In this study, genome-wide gene expression profiles of mouse nasal tissues were determined following exposure to KDP20 for 5 and 10 days and compared with those of the control (n = 4/group). We identified 758 significant differentially expressed genes (DEGs) and classified them as 5-day-specific, 10-day-specific, and common among groups based on their expression patterns. The terms "regulation of alpha-beta T cell differentiation," "macrophage differentiation," and "cell adhesion mediated by integrin" were significantly enriched in each group. Receiver operating characteristic analysis revealed six genes as potential predictive biomarkers. The differential expression of these six genes was validated using quantitative RT-PCR (n = 3/group). Furthermore, a possible mechanism for nasal inflammation was suggested through the binding analysis between metal ions and genes. The genes identified in this study may play important roles in regulating the mechanism of nasal inflammation induced by diesel particles, especially immune cell regulation, and may function as markers for diesel particle-induced nasal inflammation.

NADPH oxidase 4 signaling in a ventilator-induced lung injury mouse model

Background

For patients with acute respiratory distress syndrome, a ventilator is essential to supply oxygen to tissues, but it may also cause lung damage. In this study, we investigated the role of NOX4 using NOX4 knockout (KO) mice and NOX4 inhibitors in a ventilator-induced lung injury (VILI) model.

Methods

Wild-type (WT) male C57BL/6J mice and NOX4 knockout (KO) male mice were divided into five groups: (1) control group; (2) high tidal ventilation (HTV) group: WT mice + HTV ± DMSO; (3) NOX4 KO group; (4) NOX4 KO with HTV group; (5) NOX4 inhibitor group: WT mice + HTV + NOX4 inhibitor. In the VILI model, the supine position was maintained at 24 mL/kg volume, 0 cm H₂O PEEP, 100/min respiratory rate, and 0.21 inspired oxygen fraction. In the NOX4 inhibitor group, 50 μL anti-GKT 137831 inhibitor was injected intraperitoneally, 2 h after ventilator use. After 5 h of HTV, mice in the ventilator group were euthanized, and their lung tissues were obtained for further analysis. In addition, the relationship between EphA2 (which is related to lung injury) and NOX4 was investigated using EphA2 KO mice, and NOX4 and EphA2 levels in the bronchoalveolar lavage fluid (BALF) of 38 patients with pneumonia were examined.

Results

Cell counts from BALFs were significantly lower in the NOX4 KO with HTV group (p < 0.01) and EphA2 KO with HTV group (p < 0.001) compared to that in the HTV group. In the NOX4 inhibitor group, cell counts and protein concentrations from BALF were significantly lower than those in the HTV group (both, p < 0.001). In the NOX4 KO group and the NOX4 inhibitor group, EphA2 levels were significantly lower than those in the HTV group (p < 0.001). In patients with respiratory disease, NOX4 and EphA2 levels were significantly higher in patients with pneumonia and patients who received ventilator treatment in the intensive care unit.

Conclusion

In the VILI model with high tidal volume, NOX4 KO, EphA2 KO or monoclonal antibodies attenuated the VILI. NOX4 and EphA2 levels were significantly higher in patients with pneumonia and especially in mechanical ventilated in the ICU. Inhibition of Nox4 is a potential therapeutic target for the prevention and reduction of VILI.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12931-022-01992-0.

A Putative Single-Photon Emission CT Imaging Tracer for Erythropoietin-Producing Hepatocellular A2 Receptor

Erythropoietin-producing hepatocellular (Eph) receptors are receptor tyrosine kinases involved in cell-cell contact. The EphA2 receptor is associated with cancer proliferation and migration. Therefore, EphA2 receptor imaging has the potential for cancer diagnosis. Here, we synthesized N-(5-((4-((4-ethylpiperazin-1-yl)methyl)-3-(trifluoromethyl)phenyl)carbamoyl)-2-methylphenyl)-5-[¹²³I]iodonicotinamide ([¹²³I]ETB) and evaluated it as an imaging tracer for single-photon emission computed tomography (SPECT) imaging of the EphA2 receptor. [¹²³I]ETB was designed on the basis of ALW-II-41-27, an inhibitor of EphA2 receptor kinase. Nonradioactive ETB was also synthesized and has been shown to efficiently inhibit EphA2 receptor kinase activity in vitro (IC₅₀: ETB, 90.2 ± 18.9 nM). A cell-binding assay demonstrated that [¹²⁵I]ETB binds specifically to the EphA2 receptor. The ex vivo biodistribution study of [¹²⁵I]ETB in U87MG tumor-bearing mice also revealed tumor uptake (2.2% ID/g at 240 min). In addition, [¹²³I]ETB uptake in tumors was visualized via SPECT/CT imaging. On the basis of the above, [¹²³I]ETB can be considered a potential SPECT imaging tracer for the EphA2 receptor.

Insights on the Functional Role of Beta-Glucans in Fungal Immunity Using Receptor-Deficient Mouse Models

Understanding the host anti-fungal immunity induced by beta-glucan has been one of the most challenging conundrums in the field of biomedical research. During the last couple of decades, insights on the role of beta-glucan in fungal disease progression, susceptibility, and resistance have been greatly augmented through the utility of various beta-glucan cognate receptor-deficient mouse models. Analysis of dectin-1 knockout mice has clarified the downstream signaling pathways and adaptive effector responses triggered by beta-glucan in anti-fungal immunity. On the other hand, assessment of CR3-deficient mice has elucidated the compelling action of beta-glucans in neutrophil-mediated fungal clearance, and the investigation of EphA2-deficient mice has highlighted its novel involvement in host sensing and defense to oral mucosal fungal infection. Based on these accounts, this review focuses on the recent discoveries made by these gene-targeted mice in beta-glucan research with particular emphasis on the multifaceted aspects of fungal immunity.

Homocysteine Impairs Endothelial Cell Barrier Function and Angiogenic Potential via the Progranulin/EphA2 Pathway

Hyperhomocysteinemia is a well-recognized independent risk factor for cardiovascular disease. To date, the mechanism of pathological plasma homocysteine (Hcy) level elevation remains to be elucidated. We aimed to investigate the levels of progranulin (PGRN), Eph-receptor tyrosine kinase-type A2 (EphA2), vascular cell adhesion molecule-1 (VCAM-1), and Hcy in patients with arteriosclerosis and investigate their functions in Hcy-injured human umbilical vein endothelial cells (HUVECs). EphA2 knockdown was induced in HUVECs by shRNA lentivirus infection with EphA2-RNAi, and bulk RNA-seq assay was performed. Then we investigated the mechanism underlying the effect of recombinant human PGRN (rhPGRN) combined with shRNA interference of EphA2 on cell proliferation, migration, and angiogenesis in Hcy-injured HUVECs. Results showed that serum EphA2, VCAM-1, and Hcy levels in acute coronary syndrome patients were significantly higher than those in chronic coronary syndrome patients (p = 0.000; p = 0.000; p = 0.033, respectively). In vitro, we demonstrated that knockdown of EphA2 significantly impaired cell adhesion and inhibited HUVECs migration and angiogenesis (p < 0.001), which was associated with reduction in VCAM1 and VE-cadherin (p < 0.05). Hcy modulated the expression of PGRN and EphA2 in a time-and dose-dependent manner. However, rhPGRN ameliorated the Hcy-induced reduction in cell viability and migration (p < 0.05). Mechanistically, we found that PGRN/EphA2 and its downstream AKT/NF-κB signaling might be the primary signal transduction pathways underlying Hcy-induced injury. The present study illustrated that PGRN plays a previously unrecognized role in Hcy-induced endothelial injury, which is achieved through its interaction with EphA2 signaling, implying a promising therapeutic target for cardiovascular disease.

EphA2 phosphorylates NLRP3 and inhibits inflammasomes in airway epithelial cells

Inflammasomes are intracellular complexes that form in the cytosol of inflammatory cells. NLRP3 is one of the sensor proteins in the complex that can recognize a wide variety of stimuli ranging from microbial components to environmental particulates. Here, we report that in mouse airway epithelial cells (AECs), inflammasome activation is inhibited by EphA2, a member of the transmembrane tyrosine kinase receptor family, via tyrosine phosphorylation of NLRP3 in a model of reovirus infection. We find that EphA2 depletion markedly enhances interleukin-1β (IL-1β) and interleukin-18 (IL-18) production in response to the virus. EphA2^-/- mice show stronger inflammatory infiltration and enhanced inflammasome activation upon viral infection, and aggravated asthma symptoms upon ovalbumin (ova) induction. Mechanistically, EphA2 binds to NLRP3 and induces its phosphorylation at Tyr132, thereby interfering with ASC speck formation and blocking the activation of the NLRP3-inflammasome. These data demonstrate that reovirus employs EphA2 to suppress inflammasome activation in AECs and that EphA2 deficiency causes a pathological exacerbation of asthma in an ova-induced asthma model.

Impact of Bacterial Toxins in the Lungs

Bacterial toxins play a key role in the pathogenesis of lung disease. Based on their structural and functional properties, they employ various strategies to modulate lung barrier function and to impair host defense in order to promote infection. Although in general, these toxins target common cellular signaling pathways and host compartments, toxin- and cell-specific effects have also been reported. Toxins can affect resident pulmonary cells involved in alveolar fluid clearance (AFC) and barrier function through impairing vectorial Na⁺ transport and through cytoskeletal collapse, as such, destroying cell-cell adhesions. The resulting loss of alveolar-capillary barrier integrity and fluid clearance capacity will induce capillary leak and foster edema formation, which will in turn impair gas exchange and endanger the survival of the host. Toxins modulate or neutralize protective host cell mechanisms of both the innate and adaptive immunity response during chronic infection. In particular, toxins can either recruit or kill central players of the lung's innate immune responses to pathogenic attacks, i.e., alveolar macrophages (AMs) and neutrophils. Pulmonary disorders resulting from these toxin actions include, e.g., acute lung injury (ALI), the acute respiratory syndrome (ARDS), and severe pneumonia. When acute infection converts to persistence, i.e., colonization and chronic infection, lung diseases, such as bronchitis, chronic obstructive pulmonary disease (COPD), and cystic fibrosis (CF) can arise. The aim of this review is to discuss the impact of bacterial toxins in the lungs and the resulting outcomes for pathogenesis, their roles in promoting bacterial dissemination, and bacterial survival in disease progression.

miR-200a-3p modulates gene expression in comorbid pain and depression: Molecular implication for central sensitization

Chronic pain and depression are often comorbid exhibiting common clinical presentations and biological connections related to central nervous system sensitization. Epigenetic regulation of gene expression in the brain plays a crucial role in response to long-lasting stress and chronic pain, and microRNA imbalance in the prefrontal cortex (PFC) might be involved in central sensitization. Male Sprague Dawley rats were subjected to unpredictable chronic mild stress (UCMS) and spared nerve injury (SNI) to initiate depressive-like behavior and chronic pain behavior, respectively. The next-generation sequencing technique was employed to analyze PFC microRNAs in both the UCMS and SNI models. Rats exposed to either UCMS or SNI exhibited both depressive-like and chronic pain behaviors. Five specific microRNAs (miR-10a-5p, miR-182, miR-200a-3p, miR-200b-3p, and miR-429) were simultaneously down-regulated in the depressive-like and chronic pain models after 4 weeks of short-term stress. Gene ontology revealed that the 4-week period of stress enhanced neurogenesis. Only the miR-200a-3p level was continuously elevated under prolonged stress, suggesting roles of reduced neurogenesis, inflammatory activation, disturbed circadian rhythm, lipid metabolism, and insulin secretion in the co-existence of pain and depression. Thus we conclude that miR-200a-3p might be a specific biomarker of central sensitization in chronic pain and depression.

Ephrins and Eph Receptor Signaling in Tissue Repair and Fibrosis

PURPOSE OF REVIEW

Fibrosis is a pathological feature of many human diseases that affect multiple organs. The development of anti-fibrotic therapies has been a difficult endeavor due to the complexity of signaling pathways associated with fibrogenic processes, complicating the identification and modulation of specific targets. Evidence suggests that ephrin ligands and Eph receptors are crucial signaling molecules that contribute to physiological wound repair and the development of tissue fibrosis. Here, we discuss recent advances in the understanding of ephrin and Eph signaling in tissue repair and fibrosis.

RECENT FINDINGS

Ephrin-B2 is implicated in fibrosis of multiple organs. Intercepting its signaling may help counteract fibrosis. Ephrins and Eph receptors are candidate mediators of fibrosis. Ephrin-B2, in particular, promotes fibrogenic processes in multiple organs. Thus, therapeutic strategies targeting Ephrin-B2 signaling could yield new ways to treat organ fibrosis.

EphA2 antagonism alleviates LPS-induced acute lung injury via Nrf2/HO-1, TLR4/MyD88 and RhoA/ROCK pathways

Eph receptor tyrosine kinases have a wide range of biological functions and have gradually been recognized increasingly as key regulators of inflammation and injury diseases. Although previous studies suggested that EphA2 receptor may be involved in the regulation of inflammation and vascular permeability in injured lung, the detailed effects of EphA2 on LPS-induced acute lung injury (ALI) are still inadequate and the underlying mechanism remains poorly understood. In this study, we detected the effects of EphA2 antagonism on inflammation, pulmonary vascular permeability and oxidative stress in LPS-induced ALI and investigate the potential mechanism. Our results showed that EphA2 antagonism markedly inhibited the cytokines release and inflammatory cells infiltration in BALF, prevented the LPS-induced elevations of MPO activity and MDA level in lung tissues. Our study also found that EphA2 antagonism significantly decreased the wet/dry ratios, reduced the Evans blue albumin extravasation in lung tissues and obviously alleviated the LPS-induced increment of pulmonary vascular permeability. Mechanistically, EphA2 antagonism significantly increased the activation of Nrf2 along with its target antioxidant enzyme HO-1 and inhibited the expressions of TLR4/MyD88 in lung tissues and A549 alveolar epithelial cells. Furthermore, EphA2 antagonism dramatically inhibited the LPS-evoked activations of RhoA/ROCK in lung tissues. In conclusion, our data indicate that EphA2 receptor plays an essential role in LPS-induced ALI and EphA2 antagonism has protective effects against LPS-induced ALI via Nrf2/HO-1, TLR4/MyD88 and RhoA/ROCK pathways. These results suggest that antagonism of EphA2 may be an effective therapeutic strategy for the treatment of ALI.

Targeted delivery of YSA-functionalized and non-functionalized polymeric nanoparticles to injured pulmonary vasculature

Ephrin type-A receptor 2 (EphA2) is a transmembrane receptor which is upregulated in injured lungs, including those treated with bleomycin. YSA peptide (YSAYPDSVPMMS), a mimic of ephrin ligands, binds to EphA2 receptors on cell surface with high affinity. In this study, we assessed the ability of YSA-functionalized and non-functionalized poly (dl-lactide-co-glycolide) (PLGA) nanoparticles to enhance delivery to bleomycin treated cultured vascular endothelial cells and, in a bleomycin induced lung injury mouse model. Nanoparticles were loaded with a lipophilic fluorescent dye. Human umbilical vein endothelial cells (HUVEC) with or without 2-day bleomycin pretreatment (25 µg/ml) and adult mice with or without intratracheal instillation of bleomycin (0.1 U) were dosed with nanoparticles. Mice received nanoparticles via tail vein injection 4 days after bleomycin treatment. Three days after nanoparticle injection, tissues (lung, heart, kidney, spleen, liver, brain, eyes and whole blood) were harvested and quantified for fluorescence using IVIS imaging. Mean particle uptake increased with time and concentration for both types of particles in HUVEC, with the uptake being higher for YSA-functionalized nanoparticles. Bleomycin treatment increased the 3-h uptake of both types of nanoparticles in HUVEC by about two-fold, with the YSA-functionalized nanoparticle uptake being 1.66-fold compared to non-functionalized nanoparticles (p < .05). In mice, bleomycin injury resulted in 2.3- and 4.7-fold increase in the lung levels of non-functionalized and YSA-functionalized nanoparticles (p < .05), respectively, although the differences between the two particle types were not significant. In conclusion, PLGA nanoparticle delivery to cultured vascular endothelial cells and mouse lungs in vivo is higher following bleomycin treatment, with the delivery tending to be higher for YSA functionalized nanoparticles.

MicroRNA-302b negatively regulates IL-1β production in response to MSU crystals by targeting IRAK4 and EphA2

Background

Interleukin-1β (IL-1β) is a pivotal proinflammatory cytokine that is strongly associated with the inflammation of gout. However, the underlying mechanism through which the production of IL-1β is regulated has not been fully elucidated. Our previous work identified that miR-302b had an important immune regulatory role in bacterial lung infections. This study was conducted to evaluate the function of miR-302b on monosodium urate (MSU) crystal-induced inflammation and its mechanism.

Methods

The expression pattern and the immune-regulatory role of miR-302b were evaluated both in vitro and in vivo. The functional targets of miR-302b were predicted by bioinformatics, and then validated by genetic approaches. In addition, the clinical feature of miR-302b was analyzed using serum samples of patients with gouty arthritis.

Results

The extremely high expression of miR-302b was observed in both macrophages and mouse air membranes treated with MSU. Intriguingly, overexpression of miR-302b regulated NF-κB and caspase-1 signaling, leading to significantly attenuate MSU-induced IL-1β. By genetic analysis, miR-302b exhibited inhibitory function on IRAK4 and EphA2 by binding to their 3′-UTR regions. Corporately silencing IRAK4 and EphA2 largely impaired MSU-induced IL-1β protein production. Moreover, it was also found that miR-302b and EphA2 suppressed the migration of macrophages. Finally, it was observed that high expression of miR-302b was a general feature in patients with gouty arthritis.

Conclusions

These results suggest that miR-302b can regulate IL-1β production in MSU-induced inflammation by targeting NF-κB and caspase-1 signaling, and may be a potential therapeutic target for gouty arthritis.

Electronic supplementary material

The online version of this article (10.1186/s13075-018-1528-9) contains supplementary material, which is available to authorized users.

All-trans retinoic acid attenuates bleomycin-induced pulmonary fibrosis via downregulating EphA2-EphrinA1 signaling

The role of all-trans retinoic acid (ATRA) in pulmonary fibrosis is relatively unknown, although this metabolite modulates cell differentiation, proliferation, and development. We aimed to evaluate the role of ATRA in bleomycin-induced pulmonary fibrosis, and whether the mechanism involves EphA2-EphrinA1 and PI3K-Akt signaling. We evaluated three groups of mice: a control group (intraperitoneal DMSO injection 3 times weekly after PBS instillation), bleomycin group (intraperitoneal DMSO injection 3 times weekly after bleomycin instillation), and bleomycin + ATRA group (intraperitoneal ATRA injection 3 times weekly after bleomycin instillation). The cell counts and protein concentration in the bronchoalveolar lavage fluid (BALF), changes in histopathology, Ashcroft score, hydroxyproline assay, expression of several signal pathway proteins including EphA2-EphrinA1, and PI3K-Akt, and cytokine levels were compared among the groups. We found that bleomycin significantly increased the protein concentration in the BALF, Ashcroft score in lung tissue, and hydroxyproline contents in lung lysates. Furthermore, bleomycin upregulated EphA2, EphrinA1, PI3K 110γ, Akt, IL-6 and TNF-α. However, administration of ATRA attenuated the upregulation of EphA2-EphrinA1 and PI3K-Akt after bleomycin instillation, and decreased pulmonary fibrosis. In addition, ATRA suppressed IL-6 and TNF-α production induced by bleomycin-induced injury. Collectively, these data suggest that ATRA attenuates bleomycin-induced pulmonary fibrosis by regulating EphA2-EphrinA1 and PI3K-Akt signaling.

Porphyromonas gingivalis lipopolysaccharide regulates ephrin/Eph signalling in human periodontal ligament fibroblasts

Objective

EphrinA2‐EphA2 and ephrinB2‐EphB4 critically engage in bidirectional signalling to modulate alveolar bone remodelling. The present study aimed to investigate the effects of lipopolysaccharides (LPS) derived from Porphyromonas gingivalis on ephrin/Eph signalling in periodontal ligament fibroblasts (PDLFs).

Material and Methods

The primary cultured PDLFs were incubated in the absence (as a control) or presence of P. gingivalisLPS at 0.001‐10 μg/mL for 24 hours. The PDLFs were then stimulated with P. gingivalisLPS at the optimal concentration (0.1 μg/mL) for different periods (6‐48 hours). The expression of ephrinA2, ephrinB2, EphA2 and EphB4 was assessed by quantitative reverse‐transcription real‐time polymerase chain reaction and western blotting. The osteoblastic markers alkaline phosphatase, osteocalcin and Runt‐related transcription factor 2 (Runx2), and the osteoclastogenesis‐related factors receptor activator of nuclear factor kappa‐B ligand (RANKL) and osteoprotegerin were also evaluated.

Results

The ephrinA2 and EphA2 expression was upregulated and EphB4 expression was downregulated by stimulation of P. gingivalisLPS. EphrinA2 mRNA expression in the PDLFs was significantly upregulated from 12 to 48 hours (P<.05), whereas EphA2 exhibited no change for the first 24 hours, after which there was a significant increase at 48 hours (P<.05). EphB4 exhibited lower mRNA expression at 12 and 24 hours than did the control (P<.05), but the change was insignificant at 48 hours. In contrast, the expression of ephrinB2 remained unchanged. The expressions of ephrinA2, EphA2, ephrinB2 and EphB4 at the protein level showed a similar pattern to that at the mRNA level. The expression of Runx2 and osteocalcin significantly decreased, whereas that of RANKL/osteoprotegerin increased.

Conclusion

The present study suggest that P. gingivalisLPS would contribute to a dysregulation of bone remodelling, whereby ephrinA2/EphA2 expression is stimulated and EphB4 expression is inhibited.

EphA2 Expression Regulates Inflammation and Fibroproliferative Remodeling in Atherosclerosis

BACKGROUND

Atherosclerotic plaque formation results from chronic inflammation and fibroproliferative remodeling in the vascular wall. We previously demonstrated that both human and mouse atherosclerotic plaques show elevated expression of EphA2, a guidance molecule involved in cell-cell interactions and tumorigenesis.

METHODS

Here, we assessed the role of EphA2 in atherosclerosis by deleting EphA2 in a mouse model of atherosclerosis (Apoe^-/-) and by assessing EphA2 function in multiple vascular cell culture models. After 8 to 16 weeks on a Western diet, male and female mice were assessed for atherosclerotic burden in the large vessels, and plasma lipid levels were analyzed.

RESULTS

Despite enhanced weight gain and plasma lipid levels compared with Apoe^-/- controls, EphA2^-/-Apoe^-/- knockout mice show diminished atherosclerotic plaque formation, characterized by reduced proinflammatory gene expression and plaque macrophage content. Although plaque macrophages express EphA2, EphA2 deletion does not affect macrophage phenotype, inflammatory responses, and lipid uptake, and bone marrow chimeras suggest that hematopoietic EphA2 deletion does not affect plaque formation. In contrast, endothelial EphA2 knockdown significantly reduces monocyte firm adhesion under flow. In addition, EphA2^-/-Apoe^-/- mice show reduced progression to advanced atherosclerotic plaques with diminished smooth muscle and collagen content. Consistent with this phenotype, EphA2 shows enhanced expression after smooth muscle transition to a synthetic phenotype, and EphA2 depletion reduces smooth muscle proliferation, mitogenic signaling, and extracellular matrix deposition both in atherosclerotic plaques and in vascular smooth muscle cells in culture.

CONCLUSIONS

Together, these data identify a novel role for EphA2 in atherosclerosis, regulating both plaque inflammation and progression to advanced atherosclerotic lesions. Cell culture studies suggest that endothelial EphA2 contributes to atherosclerotic inflammation by promoting monocyte firm adhesion, whereas smooth muscle EphA2 expression may regulate the progression to advanced atherosclerosis by regulating smooth muscle proliferation and extracellular matrix deposition.

Immunomodulatory Functions of Neuronal Guidance Proteins

Neuronal guidance proteins (NGPs) were originally identified for their role during the embryonic development of the nervous system. Recent years have seen the discovery of NGP functions during immune responses. In this context, NGPs were demonstrated to control leukocyte migration and the release of cytokines during conditions of acute inflammation, such as lung injury or sepsis. However, NGPs also display potent actions in the resolution of inflammation, chronic inflammatory conditions, the development of atherosclerosis, and during ischemia followed by reperfusion. Here, we provide an overview of the current state of knowledge about the role of NGPs in the immune system and describe their immunomodulatory function.

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

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

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