The Regulation of Lipid Binding and Kinase Activities of EphA2 Kinase Domain by Its Adjacent SAM Domain / 中国生物化学与分子生物学报

The erythropoietin-producing hepatocellular receptor (Eph receptor) family is the largest subfamily in the receptor tyrosine kinase (RTK) families which mediates cell morphology, adhesion, movement, proliferation, survival, and differentiation by its bidirectional signals coupled with Ephrin ligands. EphA2 receptor is an important isoform which is involved in the pathological changes in cataract, breast cancer, etc. Previous studies found that the kinase domain of the EphA2 receptor binds to the plasma membrane, and its kinase activity is regulated by the plasma membrane. However, it is still unclear that the impact of the adjacent SAM domain on the membrane binding and kinase activities of kinase domain. In this study we purified the cytoplasmic kinase-SAM tandem of the EphA2 receptor by co-expression with the phosphatase PTP1B 1-301 fragment. Our results showed that the SAM domain of EphA2 receptor can further enhance the interaction between the kinase domain and liposomes (4 mg/mL) by 6 folds (P<0. 001). And the phosphorylation of kinase-SAM tandem can enhance its lipid (4 mg/mL) binding ability by 2. 5 folds (P < 0. 05). In addition, the lipid binding ability and tyrosine phosphorylation activities of kinase domain are mutual promoted, which creating a positive feedback loop in the two biological processes. In conclusion, our studies indicate that the kinase domain and the adjacent SAM domain can function as an intact unit, whose lipid binding ability and kinase activity are quite different from the individual kinase domain. Therefore, our results provide a biochemical basis for better understanding of the regulation mechanism of other Eph receptors in its kinase domain.

Role of EphA2 in pathogenesis of nasopharyngeal carcinoma and its potential as a therapeutic target / 中国肿瘤临床

The erythropoietin-producing hepatocellular receptor (Eph) and its ligand ephrin are the largest of the receptor tyrosine kinases (RTKs) family in humans. Since ephrin ligands and Eph receptors are membrane-bound proteins, binding and activation of Eph/ephrin intracellular signaling pathways can only occur via direct cell-cell interaction. Eph-ephrin complexes emanate bidirectional signals that affect cells expressing Eph and ephrin, respectively. Its repulsive signaling effects include retraction, which plays an important role in many physiological and pathological processes. EphA2 has been found to have a strong association with tumors and is most widely studied. EphA2 signal transduction in tumor cells may promote or inhibit tumor, depending on the tumor microenvironment. EphA2 "canonical" signaling involves ligand binding and kinase activity; thus EphA2 "noncanonical" signaling is ligand independent and lacks kinase activity. This review summarizes the pathogenesis of EphA2 in nasopharyngeal carcinoma (NPC), including ligand independent signal and EBV infection receptor, furthermore evaluates the prospect of its potential utilization as a target for cancer therapeutics. This may provide a new method for the prevention and treatment of NPC.

Preliminary exploration for effect of EphA2 on drug resistance of colorec-tal carcinoma cells / 中国病理生理杂志

AIM:To investigate the effect of Eph receptor A2 (EphA2) on drug resistance of colorectal carci-noma cells and its possible mechanisms .METHODS:Real-time PCR and Western blot were used to detect the expression of EphA2 at mRNA and protein levels in LoVo and LoVo/5-FU cells.EphA2 siRNA was transfected to down-regulate the EphA2 expression in LoVo/5-FU cells, and the drug sensitivity was calculated by CCK-8 assay.Meanwhile, cell migration and invasion were measured by wound healing assay and Transwell assay , and the protein levels of E-cadherin,β-catenin, N-cadherin, vimentin, Notch and Snail were determined by Western blot .RESULTS: The expression of EphA2 at both mRNA and protein levels was significantly up-regulated in LoVo/5-FU cells (P<0.05).Knockdown of EphA2 suppressed the cell viability, and migration and invasion abilities , but promoted drug sensitivity of LoVo/5-FU cells.Up-regulation of E-cadherin and β-catenin, and down-regulation of N-cadherin and vimentin were observed , indicating that the epithelial-mesenchymal transition ( EMT) process was suppressed .Knockdown of EphA2 decreased the expression levels of Notch and Snail.CONCLUSION:Down-regulation of EphA2 partly reverses drug resistance of LoVo/5-FU cells.The mechanism may be related to suppressing cell growth , migration, invasion and EMT process via Notch/Snail signaling pathway .

Erythropoietin-producing Human Hepatocellular Carcinoma Receptor B1 Polymorphisms are Associated with HBV-infected Chronic Liver Disease and Hepatocellular Carcinoma in a Korean Population

Erythropoietin-producing human hepatocellular carcinoma receptor B1 (EPHB1) is a member of the Eph family of receptor tyrosine kinases that mediate vascular system development. Eph receptor overexpression has been observed in various cancers and is related to the malignant transformation, metastasis, and differentiation of cancers, including hepatocellular carcinoma (HCC). Eph receptors regulate cell migration and attachment to the extracellular matrix by modulating integrin activity. EphrinB1, the ligand of EPHB1, has been shown to regulate HCC carcinogenesis. Here, we sought to determine whether EPHB1 polymorphisms are associated with hepatitis B virus (HBV)-infected liver diseases, including chronic liver disease (CLD) and HCC. We genotyped 26 EPHB1 single nucleotide polymorphisms (SNPs) in 399 Korean CLD, HCC, and LD (CLD+HCC) cases and seroconverted controls (HBV clearance, CLE) using the GoldenGate assay. Two SNPs (rs6793828 and rs11717042) and 1 haplotype that were composed of these SNPs were associated with an increased risk for CLD, HCC, and LD (CLD+HCC) compared with CLE. Haplotypes that could be associated with HBV-infected liver diseases by affecting downstream signaling were located in the Eph tyrosine kinase domain of EPHB1. Therefore, we suggest that EPHB1 SNPs, haplotypes, and diplotypes may be genetic markers for the progression of HBV-associated acute hepatitis to CLD and HCC.

Relationship between tyrosine protein kinase and synapse plasticity, learning and memory / 中国药理学通报

In recent years, the importance of tyrosine phosphorylation in the nervous system of mammalian is gaining recognition. Tyros ine protein kinases exert important modulatory effect on the proliferation, diff erentiation, migration and metabolism-related singal transduction pathways in c ells. In this paper we reviewed the signal cascade process of three different ty rosine protein kinase families, including Trk, Src and Eph tyrosine protein kina se families. Furthermore, we discussed important role and possible mechanisms of these tyrosine protein kinases on the neuron synapse plasticity and learning an d memory process.