A review on the role of different ephrins in glioma

EphB3 receptor suppressor invasion, migration and proliferation in glioma by inhibiting EGFR-PI3K/AKT signaling pathway

Eph receptors are the largest subfamily of receptor tyrosine kinases, and they have been shown to play a crucial role in glioma. The EphB3 receptor is a member of this family, and its effect on the invasion, migration and proliferation of glioma cells was examined in this study. It was found that the expression of EphB3 was decreased in glioma specimens with increasing tumor grade. Additionally, the U87MG and U251 cell lines showed low levels of EphB3 expression. This finding was consistent with the negative correlation between EphB3 expression in glioma tissues and tumor grade. Depletion of EphB3 gene in U87MG and U251 cell lines resulted in a substantial enhancement of their invasion, migration, and proliferation capacities in vitro. Furthermore, the knockdown of EphB3 led to an upregulation of EGFR, p-PI3K, and p-AKT protein levels. On the other hand, EphB3 overexpression reduced the invasiveness, proliferative capacity and migration rate of U87MG and U251 cells, and downregulated EGFR, p-PI3K and p-AKT. These findings indicate that EphB3 functions as a tumor suppressor in glioma, and its downregulation enhances the malignant potential of glioma cells by activating the EGFR-PI3K/AKT pathway. Thus, EphB3 is a promising diagnostic marker for glioma, and the EphB3-EGFR-PI3K / AKT axis deserves further investigation as a potential therapeutic target.

Eph signal inhibition potentiates the growth-inhibitory effects of PLK1 inhibition toward cancer cells

Anti-mitotic drugs are clinically used as anti-cancer treatments. Polo-like kinase 1 (PLK1) is a promising target against cancer cell division due to its importance in the whole process of mitosis, and thus PLK1-targeting agents have been developed in the last few decades. Clinical trial studies show that several PLK1 inhibitors are generally well-tolerated. However, the response rates are limited; therefore, it is needed to improve the efficacy of those drugs. Here, we show that NVP-BHG712, an erythropoietin-producing human hepatocellular (Eph) signaling inhibitor, potentiates the growth-inhibitory effects of the PLK1 inhibitors BI2536 and BI6727 in cancer cells. This combination treatment strongly suppresses cancer spheroid formation. Moreover, the combination drastically arrests cells at mitosis by continuous activation of the spindle assembly checkpoint (SAC), thereby inducing apoptosis. SAC activation caused by the combination of NVP-BHG712 and BI2536 is due to the inhibition of centrosome maturation and separation. Although the inactivation level of the PLK1 kinase is comparable between BI2536 treatment alone and combination treatment, the combination treatment strongly inactivates MAPK signaling in mitosis. Since inhibition of MAPK signaling potentiates the efficacy of BI2536 treatment, inactivation of PLK1 kinase and MAPK signaling contributes to the strong inhibition of centrosome separation. These results suggest that Eph signal inhibition potentiates the effect of PLK1 inhibition, leading to strong mitotic arrest via SAC activation and the subsequent reduction of cancer cell survival. The combination of PLK1 inhibition and Eph signal inhibition will provide a new effective strategy for targeting cancer cell division.

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.

Molecular Determinants of EphA2 and EphB2 Antagonism Enable the Design of Ligands with Improved Selectivity

With the aim of identifying novel antagonists selective for the EphA receptor family, a combined experimental and computational approach was taken to investigate the molecular basis of the recognition between a prototypical Eph-ephrin antagonist (UniPR1447) and two representative receptors of the EphA and EphB subfamilies, namely, EphA2 and EphB2 receptors. The conformational free-energy surface (FES) of the binding state of UniPR1447 within the ligand binding domain of EphA2 and EphB2, reconstructed from molecular dynamics (MD) simulations performed on the microsecond time scale, was exploited to drive the design and synthesis of a novel antagonist selective for EphA2 over the EphB2 receptor. The availability of compounds with this pharmacological profile will help discriminate the importance of these two receptors in the insurgence and progression of cancer.

Association between EPHA5 methylation status in peripheral blood leukocytes and the risk and prognosis of gastric cancer

Purpose

Altered DNA methylation, genetic alterations, and environmental factors are involved in tumorigenesis. As a tumor suppressor gene, abnormal EPHA5 methylation was found in gastric cancer (GC) tissues and was linked to the initiation, progression and prognosis of GC. In this study, the EPHA5 methylation level in peripheral blood leukocytes (PBLs) was detected to explore its relationship with GC risk and prognosis.

Methods

A total of 366 GC cases and 374 controls were selected as the subjects of this study to collect their environmental factors, and the EPHA5 methylation status was detected through the methylation-sensitive high-resolution melting method. Logistic regression analysis was utilized to evaluate the associations among EPHA5 methylation, environmental factors and GC risk. Meanwhile, the propensity score (PS) was used to adjust the imbalance of some independent variables.

Results

After PS adjustment, EPHA5 Pm (positive methylation) was more likely to increase the GC risk than EPHA5 Nm (negative methylation) (OR^b = 1.827, 95% CI [1.202-2.777], P = 0.005). EPHA5 Pm had a more significant association with GC risk in the elderly (OR^a = 2.785, 95% CI [1.563-4.961], P = 0.001) and H. pylori-negative groups (OR^a = 2.758, 95% CI [1.369-5.555], P = 0.005). Moreover, the combined effects of EPHA5 Pm and H. pylori infection (OR_c ^a = 3.543, 95% CI [2.233-5.621], P < 0.001), consumption of alcohol (OR_c ^a = 2.893, 95% CI [1.844-4.539], P < 0.001), and salty food intake (OR_c ^a = 4.018, 95% CI [2.538-6.362], P < 0.001) on increasing the GC risk were observed. In addition, no convincing association was found between EPHA5 Pm and the GC prognosis.

Conclusions

EPHA5 methylation in PBLs and its combined effects with environmental risk factors are related to the GC risk.

Tumor Microenvironment in Glioma Invasion

A major malignant trait of gliomas is their remarkable infiltration capacity. When glioma develops, the tumor cells have already reached the distant part. Therefore, complete removal of the glioma is impossible. Recently, research on the involvement of the tumor microenvironment in glioma invasion has advanced. Local hypoxia triggers cell migration as an environmental factor. The transcription factor hypoxia-inducible factor (HIF) -1α, produced in tumor cells under hypoxia, promotes the transcription of various invasion related molecules. The extracellular matrix surrounding tumors is degraded by proteases secreted by tumor cells and simultaneously replaced by an extracellular matrix that promotes infiltration. Astrocytes and microglia become tumor-associated astrocytes and glioma-associated macrophages/microglia, respectively, in relation to tumor cells. These cells also promote glioma invasion. Interactions between glioma cells actively promote infiltration of each other. Surgery, chemotherapy, and radiation therapy transform the microenvironment, allowing glioma cells to invade. These findings indicate that the tumor microenvironment may be a target for glioma invasion. On the other hand, because the living body actively promotes tumor infiltration in response to the tumor, it is necessary to reconsider whether the invasion itself is friend or foe to the brain.

EPHA2 mediates PDGFA activity and functions together with PDGFRA as prognostic marker and therapeutic target in glioblastoma

Platelet-derived growth subunit A (PDGFA) plays critical roles in development of glioblastoma (GBM) with substantial evidence from TCGA database analyses and in vivo mouse models. So far, only platelet-derived growth receptor α (PDGFRA) has been identified as receptor for PDGFA. However, PDGFA and PDGFRA are categorized into different molecular subtypes of GBM in TCGA_GBM database. Our data herein further showed that activity or expression deficiency of PDGFRA did not effectively block PDGFA activity. Therefore, PDGFRA might be not necessary for PDGFA function.To profile proteins involved in PDGFA function, we performed co-immunoprecipitation (Co-IP) and Mass Spectrum (MS) and delineated the network of PDGFA-associated proteins for the first time. Unexpectedly, the data showed that EPHA2 could be temporally activated by PDGFA even without activation of PDGFRA and AKT. Furthermore, MS, Co-IP, in vitro binding thermodynamics, and proximity ligation assay consistently proved the interaction of EPHA2 and PDGFA. In addition, we observed that high expression of EPHA2 leaded to upregulation of PDGF signaling targets in TCGA_GBM database and clinical GBM samples. Co-upregulation of PDGFRA and EPHA2 leaded to worse patient prognosis and poorer therapeutic effects than other contexts, which might arise from expression elevation of genes related with malignant molecular subtypes and invasive growth. Due to PDGFA-induced EPHA2 activation, blocking PDGFRA by inhibitor could not effectively suppress proliferation of GBM cells, but simultaneous inhibition of both EPHA2 and PDGFRA showed synergetic inhibitory effects on GBM cells in vitro and in vivo. Taken together, our study provided new insights on PDGFA function and revealed EPHA2 as a potential receptor of PDGFA. EPHA2 might contribute to PDGFA signaling transduction in combination with PDGFRA and mediate the resistance of GBM cells to PDGFRA inhibitor. Therefore, combination of inhibitors targeting PDGFRA and EHA2 represented a promising therapeutic strategy for GBM treatment.