T淋巴瘤侵袭转移诱导因子1的结构与功能

T淋巴瘤侵袭转移诱导因子1(T-lymphoma invasion and metastasis inducing factor 1，Tiam1)是Ras相关的C3肉毒素底物1(Ras-Related C3 botulinum toxin substrate 1，Rac1)的特异性鸟苷酸交换因子(guanine nucleotide ex-change factor，GEF)。在细胞外信号刺激下Tiam1可以促进Rac1从无活性的GDP结合状态向有活性的GTP结合状态转换，有活性的Rac1-GTP与不同的下游效应分子相互作用，从而影响多种细胞事件。     

Endocytosis of EphA receptors is essential for the proper development of the retinocollicular topographic map

Endocytosis of Eph-ephrin complexes may be an important mechanism for converting cell-cell adhesion to a repulsive interaction. Here, we show that an endocytosis-defective EphA8 mutant forms a complex with EphAs and blocks their endocytosis in cultured cells. Further, we used bacterial artificial chromosome transgenic (Tg) mice to recapitulate the anterior>posterior gradient of EphA in the superior colliculus (SC). In mice expressing the endocytosis-defective EphA8 mutant, the nasal axons were aberrantly shifted to the anterior SC. In contrast, in Tg mice expressing wild-type EphA8, the nasal axons were shifted to the posterior SC, as predicted for the enhanced repellent effect of ephrinA reverse signalling. Importantly, Rac signalling was shown to be essential for EphA-ephrinA internalization and the subsequent nasal axonal repulsion in the SC. These results indicate that endocytosis of the Eph-ephrin complex is a key mechanism by which axonal repulsion is generated for proper guidance and topographic mapping.     

Endocytosis and cancer: an 'insider' network with dangerous liaisons

From the signaling point of view, endocytosis has long been regarded as a major mechanism of attenuation, through the degradation of signaling receptors and, in some cases, of their ligands. This outlook has changed, over the past decade, as it has become clear that signaling persists in the endocytic route, and that intracellular endocytic stations (the 'signaling endosomes') actually contribute to the sorting of signals in space and time. Endocytosis-mediated recycling of receptors and of signaling molecules to specific regions of the plasma membrane is also coming into focus as a major mechanism in the execution of spatially restricted functions, such as cell motility. In addition, emerging evidence connects endocytosis as a whole, or individual endocytic proteins, to complex cellular programs, such as the control of the cell cycle, mitosis, apoptosis and cell fate determination. Thus, endocytosis seems to be deeply ingrained into the cell regulation blueprint and its subversion is predicted to play an important role in human diseases: first and foremost, cancer.     

Proteomic analysis of Tiam1-mediated metastasis in colorectal cancer

Tiam1 (T lymphoma invasion and metastasis 1), a guanine nucleotide exchange factor that activates Rac, was recently identified as a novel colorectal cancer metastasis-related gene. To better understand the mechanism underlying Tiam1-mediated metastasis, we applied two-dimensional polyacrylamide gel electrophoresis (2-DE) and matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS) analysis to identify differentially expressed proteins between Tiam1 transfected and mock transfected colorectal cancer HT29 cells. Eleven differentially expressed proteins were identified and further validated by Western blot and/or real-time PCR. The results revealed that Tiam1 transfection in colorectal cancer cells could upregulate the expression of Fascin-1, heat shock protein 27 (HSP27), high-mobility group box 1 (HMGB1), glutathione S-transferase omega 1 (GSTO1) and downregulate the expression of annexin IV. These differentially expressed proteins may be directly or indirectly regulated by Tiam1 and be helpful in studying mechanisms that lead to the function of Tiam1. These results give some clues to elucidate the mechanism of Tiam1-mediated metastasis for colorectal cancer.     

EphA2: A promising therapeutic target in breast cancer

Ephrin type-A receptor 2(EphA2), a receptor tyrosine kinase, is overexpressed in human breast cancers often linked to poor patient prognosis. Accumulating evidence demonstrates that EphA2 plays important roles in several critical processes associated with malignant breast progression, such as proliferation,survival, migration, invasion, drug resistance, metastasis, and angiogenesis. As its inhibition through multiple approaches can inhibit the growth of breast cancer and restore drug sensitivity, EphA2 has become a promising therapeutic target for breast cancer treatment. Here, we summarize the expression,functions, mechanisms of action, and regulation of EphA2 in breast cancer. We also list the potential therapeutic strategies targeting EphA2. Furthermore, we discuss the future directions of studying EphA2 in breast cancer.     

Regulation of Tiam1-Rac signalling

The GTPases of the Rho family are molecular switches that play an important role in a wide range of cellular processes and are increasingly implicated in tumourigenesis. Unlike what was found for the Ras oncogenes in tumours, hardly any activating mutations have been found in the genes encoding Rho proteins. In the past, we have identified Tiam1 (T-lymphoma invasion and metastasis) as a specific activator for the Rho-like GTPase Rac. In vivo, Tiam1 deficiency protects against Ras-induced skin carcinogenesis, underscoring the consequences of deregulated signalling for the onset and progression of tumours. Thus, an important level of regulation of signalling via the Rho-like GTPases comes from the specific control of their activators. In this paper, we review what is known on the specific regulation of Tiam1 signalling towards Rac.     

EphA2、E-钙黏素在肿瘤中的研究

Eph受体激酶是受体酪氨酸激酶(RTKs)家族中最大的一个亚族.EphA2是Eph受体中的一员,可以调节细胞生长、迁移和血管生成.EphA2受体广泛过表达于上皮来源的肿瘤细胞,导致正常细胞恶性转化,增强肿瘤细胞的侵袭性、浸润性和转移性.E-cadherin是一种常见的上皮黏附分子,可以介导细胞之间的黏附,细胞向正常及肿瘤组织的移动并定位,同时可以影响其它蛋白的定位和转化,进一步促进肿瘤的恶型性.研究证明:许多上皮性肿瘤中,包括食管癌、宫颈癌、乳腺癌、结肠癌等都发现EphA2和E-cadherin均有异常表达,且与肿瘤的恶性程度和疾病的预后有密切的关系.本文从EphA2、E-cadherin的结构、功能、相互关系以及在肿瘤中的研究加以综述.     

Biochemical characterization of APPL endosomes: the role of annexin A2 in APPL membrane recruitment

APPL endosomes are a recently identified subpopulation of early endosomes characterized by the presence of two homologous Rab5 effector proteins APPL1 and APPL2. They exhibit only limited colocalization with EEA1, another Rab5 effector and a marker of the canonical early endosomes. Although APPL endosomes appear to play important roles in cargo trafficking and signal transduction, their protein composition and biochemical properties remain largely unknown. Here we employed membrane fractionation methods to characterize APPL endosomes biochemically. We demonstrate that they represent heterogeneous membrane structures which can be discriminated from the canonical EEA1-positive early endosomes by their partly different physical properties and a distinct migration pattern in the continuous density gradients. In search for other potential markers of APPL endosomes we identified Annexin A2 as an interacting partner of both APPL1 and APPL2. Annexin A2 is a Ca(2+) and phosphatidylinositol 4,5-bisphosphate binding protein, previously implicated in several endocytic steps. We show that Annexin A2 co-fractionates and colocalizes with APPL endosomes. Moreover, silencing of its expression causes solubilization of APPL2 from endosomes. Although Annexin A2 is not an exclusive marker of APPL endosomes, our data suggest that it has an important function in membrane recruitment of APPL proteins, acting in parallel to Rab5.     

Endocytosis of Peptidase Inhibitor SerpinE2 promotes Myocardial Fibrosis through activating ERK1/2 and β-catenin Signaling Pathways

Cardiac fibrosis is one of the common pathological processes in many cardiovascular diseases characterized by excessive extracellular matrix deposition. SerpinE2 is a kind of protein that inhibits peptidase in extracellular matrix and up-regulated tremendously in mouse model of cardiac fibrosis induced by pressure-overloaded via transverse aortic constriction (TAC) surgery. However, its effect on cardiac fibroblasts (CFs), collagen secretion and the underlying mechanism remains unclear. In this study, DyLight® 488 green fluorescent dye or His-tagged proteins were used to label the exogenous serpinE2 protein. It was showed that extracellular serpinE2 translocated into CFs by low-density lipoprotein receptor-related protein 1 (LRP1) and urokinase plasminogen activator receptor (uPAR) of cell membrane through endocytosis. Knockdown of LRP1 or uPAR reduced the level of serpinE2 in CFs and down-regulated the collagen expression. Inhibition of the endocytosis of serpinE2 could inhibit ERK1/2 and β-catenin signaling pathways and subsequently attenuated collagen secretion. Knockdown of serpinE2 attenuates cardiac fibrosis in TAC mouse. We conclude that serpinE2 could be translocated into cardiac fibroblasts due to endocytosis through directly interact with the membrane protein LRP1 and uPAR, and this process activated the ERK1/2, β-catenin signaling pathways, consequently promoting collagen production.     

Tom1L1在细胞信号转导及受体内吞中的研究进展

Tom1L1（Tom1 like 1）参与并调节细胞信号转导及受体运输通路。在不同细胞中Tom1L1对信号转导具有不同的调节作用。Tom1L1-CHC（clathrinheavychain）复合物减少Src蛋白在小窝（caveolae）处富集,从而阻碍Src蛋白与血小板衍生因子（platelet derived growth factor,PDGF）受体的结合。抑制PDGF受体介导的有丝分裂和转化信号传导。活化的表皮生长因子受体（epidermal growth factor receptor,EGFR）通过Src家族蛋白激酶（src family kinase,SFK）磷酸化T0m1L1,磷酸化的Tom1L1通过Grb2和Shc的桥梁作用与EGFR结合,介导EGFR的内吞进程。Tom1L1和Hrs（hepatocyte growth factor regulated tyrosine kinase substrate）、TSG101（tumor susceptibility gene 101）的相互作用表明,它也可能参与了泛素化蛋白分选入多泡体的过程。该文就其在细胞信号转导通路及受体内吞／分选过程的作用作一综述。     

EphA2对神经胶质瘤细胞系U251的凋亡﹑增殖﹑迁移和侵袭的研究

为了研究EphA2对神经胶质瘤细胞系U251在增殖、凋亡、迁移和侵袭方面所起的作用,用RT-PCR方法检测正常脑组织标本与两种恶性胶质瘤细胞系中EphA2 mRNA表达水平,然后用化学合成的针对EphA2基因的小干扰RNA(siRNA)下调该基因的表达,以检测其在U251中的生物学功能．证实了EphA2基因在正常脑组织标本中的表达水平远低于两种恶性胶质瘤细胞系．把体外化学合成针对EphA2基因的小干扰RNA(siRNA- EphA2)转染入U251细胞后,Western blot, 实时定量 RT-PCR检测到U251细胞中EphA2蛋白及mRNA表达水平都明显降低,并且细胞增殖受到显著抑制,同时出现了明显的细胞凋亡．伤口愈合实验(检测细胞迁移能力),Transwell小室实验(检测细胞侵袭能力)均表明,下调EphA2的表达后,细胞的迁移和侵袭能力较阴性对照组显著减弱．上述结果表明,在神经胶质瘤U251细胞中,EphA2与其恶性增殖及高度侵染性相关,可作为分子治疗的有效靶点．     

Targeting EphA2 suppresses hepatocellular carcinoma initiation and progression by dual inhibition of JAK1/STAT3 and AKT signaling

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芸苔属植物自交不亲和性S-受体激酶的内吞作用及信号传递网络

文章就芸苔属植物自交不亲和性反应中S-受体激酶的内吞作用以及下游信号传递网络的研究进展作一综述。     

Specificity of HCPTP variants toward EphA2 tyrosines by quantitative selected reaction monitoring

EphA2 receptor tyrosine kinase and the human cytoplasmic protein tyrosine phosphatase (HCPTP) are overexpressed in a number of epithelial cancers. Overexpressed EphA2 in these cancers shows a significant decrease in phosphotyrosine content which results in suppression of receptor signaling and endocytosis and an increase in metastatic potential. The decreased phosphotyrosine content of EphA2 has been associated with decreased contact with its ligand, ephrin A1 and dephosphorylation by HCPTP. Potential specificity of the two HCPTP variants for tyrosines on EphA2 has not been investigated. We have used a mass spectrometry assay to measure relative rates of dephosphorylation for the two HCPTP variants at phosphotyrosine sites associated with control of the EphA2 kinase activity or interaction with downstream targets. Our results suggest that although both variants dephosphorylate the EphA2 receptor, the rate and specificity of dephosphorylation for specific tyrosines are different for HCPTP-A and HCPTP-B. The SAM domain tyrosine Y960 which has been implicated in downstream PI3K signaling is dephosphorylated exclusively by HCPTP-B. The activation loop tyrosine (Y772) which directly controls kinase activity is dephosphorylated about six times faster by HCPTP-A. In contrast, the juxtamembrane tyrosines (Y575, Y588 and Y594) which are implicated in both control of kinase activity and downstream signaling are dephosphorylated by both variants with similar rates. This difference in preference for dephosphorylation sites on EphA2 not only illuminates the different roles of the two variants of the phosphatase in EphA2 signaling, but also explains why both HCPTP variants are highly conserved in most mammals.     

Antisense Tiam1 Down-Regulates the Invasiveness of 95D Cells in Vitro

Invasion and metastasis are the main death causes oftumor patients, and aberrant expression of some genescontributes to tumor cell invasion and metastasis [1]. Tiam1was firstly identified as a gene amplified by insertedretrovirus which can confer metastat…     

EphA kinase activation regulates HGF-induced epithelial branching morphogenesis

Eph kinases and their ephrin ligands are widely expressed in epithelial cells in vitro and in vivo. Our results show that activation of endogenous EphA kinases in Madin-Darby canine kidney (MDCK) cells negatively regulates hepatocyte growth factor/scatter factor (HGF)-induced branching morphogenesis in collagen gel. Cotreatment with HGF and ephrin-A1 reduced sprouting of cell protrusions, an early step in branching morphogenesis. Moreover, addition of ephrin-A1 after HGF stimulation resulted in collapse and retraction of preexisting cell protrusions. In a newly developed assay that simulates the localized interactions between Ephs and ephrins in vivo, immobilized ephrin-A1 suppressed HGF-induced MDCK cell scattering. Ephrin-A1 inhibited basal ERK1/2 mitogen-activated protein kinase activity; however, the ephrin-A1 effect on cell protrusion was independent of the mitogen-activated protein kinase pathway. Ephrin-A1 suppressed HGF-induced activation of Rac1 and p21-activated kinase, whereas RhoA activation was retained, leading to the preservation of stress fibers. Moreover, dominant-negative RhoA or inhibitor of Rho-associated kinase (Y27632) substantially negated the inhibitory effects of ephrin-A1. These data suggest that interfering with c-Met signaling to Rho GTPases represents a major mechanism by which EphA kinase activation inhibits HGF-induced MDCK branching morphogenesis.     

The LIS1/NDE1 Complex Is Essential for FGF Signaling by Regulating FGF Receptor Intracellular Trafficking

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Identification of potential genes/proteins regulated by Tiam1 in colorectal cancer by microarray analysis and proteome analysis

Tiam1 (T-cell lymphoma invasion and metastasis-inducing protein 1), a guanine nucleotide exchange factor that activates Rac, is a colorectal cancer metastasis-related gene. In this study, we aimed to better understand the mechanism underlying Tiam1-mediated metastasis. We applied gene microarray and proteome analysis and compared expression of genes and proteins in a stable Tiam1-silencing colorectal cancer cell line and in a control cell line. Our analysis identified three genes, high-mobility group box1 (HMGB1), annexin IV (ANXA4) and phosphoglycerate mutase 1 (PGAM1) that were associated with Tiam1. Analysis of these proteins, which may be directly or indirectly regulated by Tiam1, may provide insight into the role and mechanism of Tiam1 in colorectal cancer metastasis.     

原癌蛋白c-Cbl促进受体酪氨酸激酶EphA2的降解

c Cbl最近被证明是泛素 蛋白酶体 (ubiquitin proteasome)通路中的一个新的RINGFinger型泛素连接酶 (ubiquitinligase ,E3) .c Cbl可以介导受体酪氨酸激酶和非受体酪氨酸受体激酶的降解 .利用内源性表达较高EphA2的大肠癌细胞株HCT1 1 6 ,通过转染野生型c Cbl和显性负变异体(dominantnegativemutant)c Cbl 70Z ,探讨c Cbl在EphA2降解中的作用 .结果显示 ,c Cbl可促进磷酸化EphA2的降解 ,EphA2的降解必须依赖其配体ephrin A1的刺激 ;利用蛋白酶体 (proteasome)抑制剂MG1 32可抑制磷酸化的EphA2降解 ,提示EphA2的最终降解部位是在蛋白酶体 .研究的结果提示 ,c Cbl作为泛素连接酶诱导磷酸化后的EphA2在蛋白酶体中降解