C-cadherin ectodomain structure and implications for cell adhesion mechanisms

Cadherins are transmembrane proteins that mediate adhesion between cells in the solid tissues of animals. Here we present the 3.1 angstrom resolution crystal structure of the whole, functional extracellular domain from C-cadherin, a representative "classical" cadherin. The structure suggests a molecular mechanism for adhesion between cells by classical cadherins, and it provides a new framework for understanding both cis (same cell) and trans (juxtaposed cell) cadherin interactions. The trans adhesive interface is a twofold symmetric interaction defined by a conserved tryptophan side chain at the membrane-distal end of a cadherin molecule from one cell, which inserts into a hydrophobic pocket at the membrane-distal end of a cadherin molecule from the opposing cell.     

Neural cadherin: role in selective cell-cell adhesion

Cadherins are a family of Ca2+-dependent intercellular adhesion molecules. Complementary DNAs encoding mouse neural cadherin (N-cadherin) were cloned, and the cell binding specificity of this molecule was examined. Mouse N-cadherin shows 92 percent similarity in amino acid sequence to the chicken homolog, while it shows 49 percent and 43 percent similarity to epithelial cadherin and to placental cadherin of the same species, respectively. In cell binding assays, mouse N-cadherin did not cross-react with other mouse cadherins, but it did cross-react with chicken N-cadherin. The results indicate that each cadherin type confers distinct adhesive specificities on different cells, and also that the specificity of N-cadherin is conserved between mammalian and avian cells.     

The premetazoan ancestry of cadherins

Cadherin-mediated cell adhesion and signaling is essential for metazoan development and yet is absent from all other multicellular organisms. We found cadherin genes at numbers similar to those observed in complex metazoans in one of the closest single-celled relatives of metazoans, the choanoflagellate Monosiga brevicollis. Because the evolution of metazoans from a single-celled ancestor required novel cell adhesion and signaling mechanisms, the discovery of diverse cadherins in choanoflagellates suggests that cadherins may have contributed to metazoan origins.     

Evolution of key cell signaling and adhesion protein families predates animal origins

The evolution of animals from a unicellular ancestor involved many innovations. Choanoflagellates, unicellular and colonial protozoa closely related to Metazoa, provide a potential window into early animal evolution. We have found that choanoflagellates express representatives of a surprising number of cell signaling and adhesion protein families that have not previously been isolated from nonmetazoans, including cadherins, C-type lectins, several tyrosine kinases, and tyrosine kinase signaling pathway components. Choanoflagellates have a complex and dynamic tyrosine phosphoprotein profile, and cell proliferation is selectively affected by tyrosine kinase inhibitors. The expression in choanoflagellates of proteins involved in cell interactions in Metazoa demonstrates that these proteins evolved before the origin of animals and were later co-opted for development.     

An inducible endothelial cell surface glycoprotein mediates melanoma adhesion

Hematogenous metastasis requires the arrest and extravasation of blood-borne tumor cells, possibly involving direct adhesive interactions with vascular endothelium. Cytokine activation of cultured human endothelium increases adhesion of melanoma and carcinoma cell lines. An inducible 110-kD endothelial cell surface glycoprotein, designated INCAM-110, appears to mediate adhesion of melanoma cells. In addition, an inducible endothelial receptor for neutrophils, ELAM-1, supports the adhesion of a human colon carcinoma cell line. Thus, activation of vascular endothelium in vivo that results in increased expression of INCAM-110 and ELAM-1 may promote tumor cell adhesion and affect the incidence and distribution of metastases.     

A polarized epithelium organized by beta- and alpha-catenin predates cadherin and metazoan origins

A fundamental characteristic of metazoans is the formation of a simple, polarized epithelium. In higher animals, the structural integrity and functional polarization of simple epithelia require a cell-cell adhesion complex that contains a classical cadherin, the Wnt-signaling protein β-catenin and the actin-binding protein α-catenin. We show that the non-metazoan Dictyostelium discoideum forms a polarized epithelium that is essential for multicellular development. Although D. discoideum lacks a cadherin homolog, we identify an α-catenin ortholog that binds a β-catenin-related protein. Both proteins are essential for formation of the epithelium, polarized protein secretion, and proper multicellular morphogenesis. Thus, the organizational principles of metazoan multicellularity may be more ancient than previously recognized, and the role of the catenins in cell polarity predates the evolution of Wnt signaling and classical cadherins.     

SynCAM,a synaptic adhesion molecule that drives synapse assembly

Synapses, the junctions between nerve cells through which they communicate, are formed by the coordinated assembly and tight attachment of pre- and postsynaptic specializations. We now show that SynCAM is a brain-specific, immunoglobulin domain-containing protein that binds to intracellular PDZ-domain proteins and functions as a homophilic cell adhesion molecule at the synapse. Expression of the isolated cytoplasmic tail of SynCAM in neurons inhibited synapse assembly. Conversely, expression of full-length SynCAM in nonneuronal cells induced synapse formation by cocultured hippocampal neurons with normal release properties. Glutamatergic synaptic transmission was reconstituted in these nonneuronal cells by coexpressing glutamate receptors with SynCAM, which suggests that a single type of adhesion molecule and glutamate receptor are sufficient for a functional postsynaptic response.     

滋阴活血解毒方对AGEs诱导VEC损伤黏附分子及凝血相关因子表达的影响

目的 观察滋阴活血解毒方对糖基化终末产物（advanced glycation end-producs,AGEs）诱导血管内皮细胞（vascular endothelial cell,VEC）损伤的影响及其黏附分子、凝血相关因子表达的变化,进一步探讨该方对AGEs诱导VEC损伤的保护作用。方法 以人脐静脉内皮细胞（human umbilical vein endothelial cells,HUVEC）作为实验对象,以终浓度（100 mg/L）的AGEs诱导HUVEC损伤。各模型组及给药组细胞分别继续培养12、24、48 h。在显微镜下观察各组细胞形态变化,并以Western-blot法检测各组黏附分子VCAM-1、ICAM-1的表达;以RT-PCR方法检测TF、TM mRNA表达。结果 相对于空白组细胞,模型组细胞出现异常增殖,细胞数量明显增多,多数细胞变形皱缩,胞膜轮廓模糊,细胞内出现粗糙样颗粒变化,VCAM-1、ICAM-1、TF表达明显上调,TM表达下调,且在作用24 h后差异有显著性意义（P<0.01）;相同时间点,给药组较模型组圆缩形细胞减少,能下调VCAM-1、ICAM-1、TF表达,上调TM表达,且随着作用时间的延长更明显（P<0.01）。结论 滋阴活血解毒方能抑制AGEs对VEC的损伤,降低黏附分子的表达,下调表达组织因子mRNA转录,上调血栓调节素mRNA转录。     

Convergence of Wnt, beta-catenin, and cadherin pathways

The specification and proper arrangements of new cell types during tissue differentiation require the coordinated regulation of gene expression and precise interactions between neighboring cells. Of the many growth factors involved in these events, Wnts are particularly interesting regulators, because a key component of their signaling pathway, beta-catenin, also functions as a component of the cadherin complex, which controls cell-cell adhesion and influences cell migration. Here, we assemble evidence of possible interrelations between Wnt and other growth factor signaling, beta-catenin functions, and cadherin-mediated adhesion.     

羊口疮病毒F1L蛋白对山羊痘病毒黏附BHK21细胞的影响

以提取羊口疮痂皮中病毒的DNA为模板,用PCR扩增羊口疮病毒(ORFV)的059基因序列,并进行基因克隆、测序鉴定和生物信息学分析;优化合成059基因编码序列,连接载体pET42a(+),转化Escherichia coli BL21(DE3);用异丙基硫代半乳糖苷(IPTG)诱导阳性克隆菌,采用免疫印迹检测表达的F1...     

层连蛋白受体67LR在胶质瘤细胞增殖中作用的研究

脑胶质瘤是颅内常见恶性肿瘤,常规的治疗手段很难将其完全治愈.67 kD层连蛋白受体(67 kDlaminin receptor,67LR)属于高亲和,非整联蛋白家族成员,试验表明,该蛋白在许多癌细胞表面过量表达,并且其表达水平与肿瘤细胞的粘附、增殖、分化、迁移、信号转导及转移能力密切相关.本试验利用shRNA干扰、RT-PCR、免疫细胞化学和MTT等技术通过下调67LR基因的表达来探讨其在胶质瘤细胞中的表达情况,及其对胶质瘤细胞增殖能力的影响.结果发现,相对于正常脑组织,67LR在脑胶质瘤细胞表面大量表达.采用shRNA下调其表达后发现胶质瘤细胞的增殖能力明显降低.结果表明,67LR在胶质瘤细胞表面的过表达与此细胞的增殖能力呈明显相关.     

选择素及其配体在哺乳动物胚胎着床过程中的作用

选择素是一种非免疫来源的多价糖类结合蛋白,为细胞粘附分子(celladhesionmolecules,cAMs)超家族的一员,选择素家族有3个结构类似的成员:E-选择素、L-选择素、P-选择素,它们在炎症发生时可介导白细胞与血管内皮细胞之间、白细胞与白细胞及白细胞与血小板之间的粘附。近年来研究发现,选择素及其配体还在精卵识别、滋养层细胞和子宫内膜的相互识别、滋养层细胞侵入、胎盘形成等过程中发挥重要作用。在此,主要对E-选择素、L-选择素及它们的配体在哺乳动物胚胎着床过程中发挥的作用及其表达调节作一综述。     

微囊藻毒素MC-LR对凡纳滨对虾细胞免疫相关基因表达水平的影响

对凡纳滨对虾进行血窦注射微囊藻毒素MC-LR染毒,取染毒前后肝胰腺及血细胞,采用Illumina Hiseq 2500测序平台进行基因表达谱分析,并对差异基因的基因本体(gene ontology,GO)注释和京都基因与基因组百科全书(kyoto encyclopedia of genes and genomes,KEGG)通路进行显著性富集分析。结果发现,酚氧化酶原、胰蛋白酶及C型凝集素等基因有显著的差异性表达。在GO富集性分析中发现细胞粘附显著性差异表达,细胞杀伤及细胞粘附分子结合物差异表达。KEGG富集性分析发现血细胞中吞噬体显著性差异表达,细胞凋亡、内吞作用和细胞粘附分子等通路呈表达差异。结果表明,凡纳滨对虾在被MC-LR染毒后,细胞免疫是抵御毒素的重要部分,其中细胞粘附和吞噬作用在抵御MC-LR对虾体的毒害过程中发挥了重要作用。     

Germline stem cells anchored by adherens junctions in the Drosophila ovary niches

How stem cells are recruited to and maintained in their niches is crucial to understanding their regulation and use in regenerative medicine. Here, we demonstrate that DE-cadherin-mediated cell adhesion is required for anchoring germline stem cells (GSCs) in their niches in the Drosophila ovary. Two major components of this adhesion process, DE-cadherin and Armadillo/beta-catenin, accumulate at high levels in the junctions between GSCs and cap cells, one of the niche components. Removal of these proteins from GSCs results in stem cell loss. Furthermore, DE-cadherin is required for recruiting GSCs to their niche. Our study demonstrates that anchorage of GSCs in their niche by DE-cadherin-mediated adhesion is important for stem cell maintenance and function.     

Forces and bond dynamics in cell adhesion

Adhesion of a biological cell to another cell or the extracellular matrix involves complex couplings between cell biochemistry, structural mechanics, and surface bonding. The interactions are dynamic and act through association and dissociation of bonds between very large molecules at rates that change considerably under stress. Combining molecular cell biology with single-molecule force spectroscopy provides a powerful tool for exploring the complexity of cell adhesion, that is, how cell signaling processes strengthen adhesion bonds and how forces applied to cell-surface bonds act on intracellular sites to catalyze chemical processes or switch molecular interactions on and off. Probing adhesion receptors on strategically engineered cells with force during functional stimulation can reveal key nodes of communication between the mechanical and chemical circuitry of a cell.     

Isolation of single human hematopoietic stem cells capable of long-term multilineage engraftment

Lifelong blood cell production is dependent on rare hematopoietic stem cells (HSCs) to perpetually replenish mature cells via a series of lineage-restricted intermediates. Investigating the molecular state of HSCs is contingent on the ability to purify HSCs away from transiently engrafting cells. We demonstrated that human HSCs remain infrequent, using current purification strategies based on Thy1 (CD90) expression. By tracking the expression of several adhesion molecules in HSC-enriched subsets, we revealed CD49f as a specific HSC marker. Single CD49f(+) cells were highly efficient in generating long-term multilineage grafts, and the loss of CD49f expression identified transiently engrafting multipotent progenitors (MPPs). The demarcation of human HSCs and MPPs will enable the investigation of the molecular determinants of HSCs, with a goal of developing stem cell-based therapeutics.     

Correction of CD18-deficient lymphocytes by retrovirus-mediated gene transfer

Leukocyte adhesion deficiency (LAD) is an inherited disorder of leukocyte function caused by derangements in CD18 expression. The genetic and functional abnormalities in a lymphocyte cell line from a patient with LAD have been corrected by retrovirus-mediated transduction of a functional CD18 gene. Lymphocytes from patients with LAD were exposed to CD18-expressing retrovirus and enriched for cells that express CD11a and CD18 (LFA-1) on the cell surface. Molecular and functional analyses of these cells revealed (i) one copy of proviral sequence per cell, (ii) viral-directed CD18 RNA that exceeded normal endogenous levels, (iii) normal quantities of CD11a and CD18 protein on the cell surface, and (iv) reconstitution of LFA-1-dependent adhesive function.     

N-Cadherin, a cell adhesion molecule involved in establishment of embryonic left-right asymmetry

Within the bilaterally symmetric vertebrate body plan, many organs develop asymmetrically. Here, it is demonstrated that a cell adhesion molecule, N-cadherin, is one of the earliest proteins to be asymmetrically expressed in the chicken embryo and that its activity is required during gastrulation for proper establishment of the left-right axis. Blocking N-cadherin function randomizes heart looping and alters the expression of Snail and Pitx2, later components of the molecular cascade that regulate left-right asymmetry. However, the expression of other components of this cascade (Nodal and Lefty) was unchanged after blocking N-cadherin function, suggesting the existence of parallel pathways in the establishment of left-right morphogenesis. Here, the results suggest that N-cadherin-mediated cell adhesion events are required for establishment of left-right asymmetry.