Extracellular functions of galectin-3

Galectin-3 has been suspected of modulating cell to extracellular matrix interactions in a novel fashion ever since it was first described. However, the rapid accumulation of research data in just the last 8 years alone has completely changed our perspective of this multifunctional protein. Its chimeric nature (consists of carbohydrate recognition and collagen like domains) somehow makes it suited to interact with a plethora of interesting extracellular matrix proteins some of which might enable it to cross the plasma membrane despite its lack of appropriate signal peptides. It is now becoming established as a mediator of signal transduction events on the cell surface as well as a mediator of a variety of extra-cellular processes such as kidney development, angiogenesis, neuronal functions, tumor metastasis, autoimmune disorders, endocytosis and possibly exocytosis. Nevertheless, it still retains its unique position as a mediator/modulator of cell to extracellular matrix adhesive interactions. Cells, particularly epithelial cells which lack galectin-3 expression, interact poorly with their extracellular matrices. In some of these processes, it functions as a matricellular protein, displaying both pro- and anti-adhesive properties. Published in 2004.     

Focal adhesion kinase: protein interactions and cellular functions

Integrin-mediated cell adhesion to extracellular matrix (ECM) plays important roles in a variety of biological processes. Recent studies suggested that integrins mediate signal transduction across the plasma membrane via activating several intracellular signaling pathways. Focal adhesion kinase (FAK) is a non-receptor tyrosine kinase that has been shown to be a major mediator of integrin signal transduction pathways. Upon activation by integrins, FAK undergoes autophosphorylation as well as associations with several other intracellular signaling molecules. These interactions in the signaling pathways have been shown to regulation a variety of cellular functions such as cell spreading, migration, cell proliferation, apoptosis and cell survival. Recent progress in the understanding of FAK interactions with other proteins in the regulation of these cellular functions will be discussed in this review.     

PTEN:抑制肿瘤侵袭及转移的新靶点

侵袭与转移是恶性肿瘤的主要生物学特征之一,并影响肿瘤的疗效及预后.其主要通过肿瘤细胞与血管内皮细胞以及细胞基质之间的相互作用,穿透血管内皮细胞、降解细胞外基质,从而向局部及远处转移.多种信号转导分子参与了肿瘤的侵袭、转移过程.PTEN基因表达的蛋白具有蛋白磷酸酶及脂质磷酸酶双重活性,其作为抑癌基因通过对细胞内多种信号转导通路的调控,参与维持细胞的正常生理活动;负调控肿瘤细胞的生长、细胞周期;诱导肿瘤细胞凋亡;抑制肿瘤细胞的侵袭、浸润及转移.本文就PTEN如何参与抑制肿瘤细胞侵袭及转移做一综述.     

Extracellular matrix remodelling and cellular differentiation.

The extracellular matrix is not merely a passive structure. In the past few years, it has emerged that the matrix is a dynamic action zone that functions to instruct cellular phenotype. Extracellular matrix proteins interact directly with cell surface receptors to initiate signal transduction pathways and to modulate those triggered by differentiation and growth factors. The extracellular matrix also controls the activity and presentation of a wide range of growth factors. Thus modulation of the extracellular matrix, by remodelling its structure and activity, has profound effects on its function and the consequent behaviour of cells residing on or within it.     

MicroRNAs in melanocyte and melanoma biology

The importance of microRNAs as key molecular components of cellular processes is now being recognized. Recent reports have shown that microRNAs regulate processes as diverse as protein expression and nuclear functions inside cells and are able to signal extracellularly, delivered via exosomes, to influence cell fate at a distance. The versatility of microRNAs as molecular tools inspires the design of novel strategies to control gene expression, protein stability, DNA repair and chromatin accessibility that may prove very useful for therapeutic approaches due to the extensive manageability of these small molecules. However, we still lack a comprehensive understanding of the microRNA network and its interactions with the other layers of regulatory elements in cellular and extracellular functions. This knowledge may be necessary before we exploit microRNA versatility in therapeutic settings. To identify rules of interactions between microRNAs and other regulatory systems, we begin by reviewing microRNA activities in a single cell type: the melanocyte, from development to disease.     

细胞表面半乳糖基转移酶及其生物学功能

根据mRNA转录子的大小,β-1,4-半乳糖基转移酶分为短型和长型两类半乳糖基转移酶.短型的位于高尔基体的成熟面.长型的主要表达在细胞表面,通过与相邻细胞表面或细胞外基质上的适当的糖苷底物的结合介导细胞-细胞和细胞-基质间的相互作用,如精子发生、精卵结合、早期胚胎细胞间粘附、次生滋养层巨细胞迁移和神经轴突向外生长等,或作为胞外寡糖链配基的信号传递受体影响G蛋白信号途径.另外,表面半乳糖基转移酶通过调节表皮生长因子受体信号传导能力向胞内传递生长抑制信号,在细胞增殖控制中起重要作用.     

Matrilin-3 switches from anti- to pro-anabolic upon integration to the extracellular matrix

The extracellular matrix (ECM) has long been viewed primarily as an organized network of solid-phase ligands for integrin receptors. During degenerative processes, such as osteoarthritis, the ECM undergoes deterioration, resulting in its remodeling and in the release of some of its components. Matrilin-3 (MATN3) is an almost cartilage specific, pericellular protein acting in the assembly of the ECM of chondrocytes. In the past, MATN3 was found required for cartilage homeostasis, but also involved in osteoarthritis-related pro-catabolic functions. Here, to better understand the pathological and physiological functions of MATN3, its concentration as a circulating protein in articular fluids of human osteoarthritic patients was determined and its functions as a recombinant protein produced in human cells were investigated with particular emphasis on the physical state under which it is presented to chondrocytes. MATN3 down-regulated cartilage extracellular matrix (ECM) synthesis and up-regulated catabolism when administered as a soluble protein. When artificially immobilized, however, MATN3 induced chondrocyte adhesion via a α5β1 integrin-dependent mechanism, AKT activation and favored survival and ECM synthesis. Furthermore, MATN3 bound directly to isolated α5β1 integrin in vitro. TGFβ1 stimulation of chondrocytes allowed integration of exogenous MATN3 into their ECM and ECM-integrated MATN3 induced AKT phosphorylation and improved ECM synthesis and accumulation. In conclusion, the integration of MATN3 to the pericellular matrix of chondrocytes critically determines the direction toward which MATN3 regulates cartilage metabolism. These data explain how MATN3 plays either beneficial or detrimental functions in cartilage and highlight the important role played by the physical state of ECM molecules.     

Glycosaminoglycan–Protein Interactions: The First Draft of the Glycosaminoglycan Interactome

The six mammalian glycosaminoglycans (GAGs), chondroitin sulfate, dermatan sulfate, heparin, heparan sulfate, hyaluronan, and keratan sulfate, are linear polysaccharides. Except for hyaluronan, they are sulfated to various extent, and covalently attached to proteins to form proteoglycans. GAGs interact with growth factors, morphogens, chemokines, extracellular matrix proteins and their bioactive fragments, receptors, lipoproteins, and pathogens. These interactions mediate their functions, from embryonic development to extracellular matrix assembly and regulation of cell signaling in various physiological and pathological contexts such as angiogenesis, cancer, neurodegenerative diseases, and infections. We give an overview of GAG–protein interactions (i.e., specificity and chemical features of GAG- and protein-binding sequences), and review the available GAG–protein interaction networks. We also provide the first comprehensive draft of the GAG interactome composed of 832 biomolecules (827 proteins and five GAGs) and 932 protein–GAG interactions. This network is a scaffold, which in the future should integrate structures of GAG–protein complexes, quantitative data of the abundance of GAGs in tissues to build tissue-specific interactomes, and GAG interactions with metal ions such as calcium, which plays a major role in the assembly of the extracellular matrix and its interactions with cells. This contextualized interactome will be useful to identify druggable GAG–protein interactions for therapeutic purpose:     

Cytosolic GAPDH: a key mediator in redox signal transduction in plants

Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) serves not only as a key enzyme in glycolysis, but also as a multifunctional protein in other biological processes, especially in response to abiotic stresses in plants. Cytosolic GAPDH (GAPC) is a typical redox protein with selected catalytic cysteine, which undergoes reversible redox post-translational modifications (RPTMs) on its thiol group by reacting with hydrogen peroxide and nitric oxide related species. Moreover, the modified GAPC may interact with certain signal transmitters such as phosphatidic acid, phospholipase D, and osmotic stress-activated protein kinase. All these observations suggest that GAPC serve as a key mediator in redox signal transduction in plants. In this review, we provide an up-to-date insight into molecular mechanisms after H₂O₂- and NO-dependent oxidation of GAPC. We also discuss GAPC catalytic functions and potential functions as a modified protein by RPTMs.     

Modulation of heart fibroblast migration and collagen gel contraction by IGF-I

Dynamic interactions between cells and the extracellular matrix are essential in the regulation of a number of cellular processes including migration, adhesion, proliferation and differentiation. A variety of factors have been identified which modulate these interactions including transforming growth factor-beta, platelet-derived growth factor and others. Insulin-like growth factors have been shown to regulate collagen production by heart fibroblasts; however, the effects of this growth factor on the interactions of heart fibroblasts with the extracellular matrix have not been examined. The present studies were carried out to determine the effects of IGF-I on the ability of fibroblasts to interact with the extracellular matrix and to begin to determine the mechanisms of this response. These experiments illustrate that IGF-I treatment results in increased migration, collagen reorganization and gel contraction by heart fibroblasts. IGF-I has been shown to activate both the mitogen-activated protein kinase and phophatidylinositol-3 kinase pathways in isolated cells. Experiments with pharmacological antagonists of these pathways indicate that the mitogen-activated protein kinase pathway is essential for IGF-I stimulated collagen gel contraction by fibroblasts. These studies illustrate that IGF-I modulates the ability of fibroblasts to interact with the collagen matrix and that activation of multiple signaling pathways by IGF-I may produce distinct downstream responses in these cells.     

Modulation of Heart Fibroblast Migration and Collagen Gel Contraction by IGF-I

Dynamic interactions between cells and the extracellular matrix are essential in the regulation of a number of cellular processes including migration, adhesion, proliferation and differentiation. A variety of factors have been identified which modulate these interactions including transforming growth factor+, platelet-derived growth factor and others. Insulin-like growth factors have been shown to regulate collagen production by heart fibroblasts; however, the effects of this growth factor on the interactions of heart fibroblasts with the extracellular matrix have not been examined. The present studies were carried out to determine the effects of IGF-I on the ability of fibroblasts to interact with the extracellular matrix and to begin to determine the mechanisms of this response. These experiments illustrate that IGF-I treatment results in increased migration, collagen reorganization and gel contraction by heart fibroblasts. IGF-I has been shown to activate both the mitogen-activated protein kinase and phophatidylinositol-3 kinase pathways in isolated cells. Experiments with pharmacological antagonists of these pathways indicate that the mitogen-activated protein kinase pathway is essential for IGF-I stimulated collagen gel contraction by fibroblasts. These studies illustrate that IGF-I modulates the ability of fibroblasts to interact with the collagen matrix and that activation of multiple signaling pathways by IGF-I may produce distinct downstream responses in these cells.     

The extracellular matrix in development and morphogenesis: A dynamic view

The extracellular matrix (ECM) is synthesized and secreted by embryonic cells beginning at the earliest stages of development. Our understanding of ECM composition, structure and function has grown considerably in the last several decades and this knowledge has revealed that the extracellular microenvironment is critically important for cell growth, survival, differentiation and morphogenesis. ECM and the cellular receptors that interact with it mediate both physical linkages with the cytoskeleton and the bidirectional flow of information between the extracellular and intracellular compartments. This review considers the range of cell and tissue functions attributed to ECM molecules and summarizes recent findings specific to key developmental processes. The importance of ECM as a dynamic repository for growth factors is highlighted along with more recent studies implicating the 3-dimensional organization and physical properties of the ECM as it relates to cell signaling and the regulation of morphogenetic cell behaviors. Embryonic cell and tissue generated forces and mechanical signals arising from ECM adhesion represent emerging areas of interest in this field.     

Bi-directional signal transduction by integrin receptors

The integrin family of cell surface glycoproteins functions primarily as receptors for extracellular matrix ligands. There are now many well characterized integrin-ligand interactions which are known to influence many aspects of cell behaviour including cell morphology, cell adhesion, cell migration as well as cellular proliferation and differentiation. However, in fulfilling these functions, integrins are not simple adhesion receptors that physically mediate connections across the plasma membrane. Rather, integrin function itself is highly regulated, largely through the formation of specific associations with both structural and regulatory components within cells. It is these intracellular interactions which allow integrin function to effect many biochemical signalling pathways and therefore to impinge upon complex cellular activities. Recently, much research has focused on elucidating the molecular mechanisms which control integrin function and the molecular processes which transduce integrin-mediated signalling events. In this review, we discuss progress in the field of integrin signal transduction including, where applicable, potential therapeutic applications arising from the research.     

Myelin glycosphingolipids, galactosylceramide and sulfatide, participate in carbohydrate-carbohydrate interactions between apposed membranes and may form glycosynapses between oligodendrocyte and/or myelin membranes

Glycosphingolipids (GSLs) can interact with each other by homotypic or heterotypic trans carbohydrate-carbohydrate interactions across apposed membranes, resulting in cell-cell adhesion. This interaction can also provide an extracellular signal which is transmitted to the cytosolic side, thus forming a glycosynapse between two cells. The two major GSLs of myelin, galactosylceramide (GalC) and its sulfated form, galactosylceramide I(3)-sulfate (SGC), are an example of a pair of GSLs which can participate in these trans carbohydrate-carbohydrate interactions and trigger transmembrane signaling. These GSLs could interact across apposed oligodendrocyte membranes at high cell density or when a membranous process of a cell contacts itself as it wraps around the axon. GalC and SGC also face each other in the apposed extracellular surfaces of the multilayered myelin sheath. Communication between the myelin sheath and the axon regulates both axonal and myelin function and is necessary to prevent neurodegeneration. Participation of transient GalC and SGC interactions in glycosynapses between the apposed extracellular surfaces of mature myelin might allow transmission of signals throughout the myelin sheath and thus facilitate myelin-axonal communication.     

Glycosylphosphatidylinositol-anchored proteins: structure, function, and cleavage by phosphatidylinositol-specific phospholipase C.

A wide variety of proteins are tethered by a glycosylphosphatidylinositol (GPI) anchor to the extracellular face of eukaryotic plasma membranes, where they are involved in a number of functions ranging from enzymatic catalysis to adhesion. The exact function of the GPI anchor has been the subject of much speculation. It appears to act as an intracellular signal targeting proteins to the apical surface in polarized cells. GPI-anchored proteins are sorted into sphingolipid- and cholesterol-rich microdomains, known as lipid rafts, before transport to the membrane surface. Their localization in raft microdomains may explain the involvement of this class of proteins in signal transduction processes. Substantial evidence suggests that GPI-anchored proteins may interact closely with the bilayer surface, so that their functions may be modulated by the biophysical properties of the membrane. The presence of the anchor appears to impose conformational restraints, and its removal may alter the catalytic properties and structure of a GPI-anchored protein. Release of GPI-anchored proteins from the cell surface by specific phospholipases may play a key role in regulation of their surface expression and functional properties. Reconstitution of GPI-anchored proteins into bilayers of defined phospholipids provides a powerful tool with which to explore the interactions of these proteins with the membrane and investigate how bilayer properties modulate their structure, function, and cleavage by phospholipases.     

Landscape of the hnRNP K protein-protein interactome

The heterogeneous nuclear ribonucleoprotein K is an ancient RNA/DNA-binding protein that is involved in multiple processes that compose gene expression. The pleiotropic action of K protein reflects its ability to interact with different classes of factors, interactions that are regulated by extracellular signals. We used affinity purification and MS to better define the repertoire of K protein partners. We identified a large number of new K protein partners, some typically found in subcellular compartments, such as plasma membrane, where K protein has not previously been seen. Electron microscopy showed K protein in the nucleus, cytoplasm, mitochondria, and in vicinity of plasma membrane. These observations greatly expanded the view of the landscape of K protein-protein interaction and provide new opportunities to explore signal transduction and gene expression in several subcellular compartments.     

Molecular mechanisms of tumor invasion and metastasis: an integrated view

As tumors progress to increased malignancy, cells within them develop the ability to invade into surrounding normal tissues and through tissue boundaries to form new growths (metastases) at sites distinct from the primary tumor. The molecular mechanisms involved in this process are incompletely understood but those associated with cell-cell and cell-matrix adhesion, with the degradation of extracellular matrix, and with the initiation and maintenance of early growth at the new site are generally accepted to be critical. This article discusses current knowledge of molecular events involved in these various processes. The potential role of adhesion molecules (eg. integrins and cadherins) has undergone a major transition over the last ten years, as it has become apparent that such molecules play a major role in signaling from outside to inside a cell, thereby controlling how a cell is able (or not) to sense and interact with its local environment. Similarly the roles of proteolytic enzymes and their inhibitors (eg. matrix metalloproteinases and TIMPs) have also expanded as it has become apparent that they not only have the abilities to break down the components of the extracellular matrix but also are involved in the release of factors which can affect the growth of the tumor cells positively or negatively. Recent work has highlighted the importance of the later, post-extravasational stages of metastasis, where adhesion and proteolysis are now known to play a role along with other processes such as apoptosis, dormancy, growth factor-receptor interactions and signal transduction. Recent work has also demonstrated that not only the immediate cellular microenvironment, in terms of specific cell-cell and cell-matrix interactions, but also the extended cellular microenvironment, in terms of vascular insufficiency and hypoxia in the primary tumor, can modify cellular gene expression and enhance metastasis. Mechanisms of metastasis appear to involve a complex array of genetic and epigenetic changes many of which appear to be specific both for different types of tumors and for different sites of metastasis. Our improved understanding of the expanded roles of the individual molecules involved has resulted in a mechanistic blurring of the previously described discrete stages of the metastatic process.     

Activation-enhanced alpha(IIb)beta(3)-integrin-cytoskeleton interactions outside of focal contacts require the alpha-subunit

Integrins link the cell's cytoskeleton to the extracellular matrix, as well as to receptors on other cells. These links occur not only at focal contacts but also at smaller integrin-containing protein complexes outside of focal contacts. We previously demonstrated the importance of focal contact-independent integrin-cytoskeleton interactions of beta(2) integrins: activation of adhesion resulted from a release of integrins from cytoskeletal constraints. To determine whether changes in integrin-cytoskeleton interactions were related to activation of the integrin, we used single particle tracking to examine focal contact-independent cytoskeletal associations of alpha(IIb)beta(3)-integrin, in which activation results in a large conformational change. Direct activation of alpha(IIb)beta(3) by mutation did not mimic activation of lymphocytes with phorbol ester, because it enhanced integrin-cytoskeleton interactions, whereas activation of lymphocytes decreased them. Using additional integrin mutants, we found that both alpha- and beta-cytoplasmic domains were required for these links. This suggests that 1) both beta(2)- and beta(3)-integrins interact with the cytoskeleton outside of focal contacts; 2) activation of a cell and activation of an integrin are distinct processes, and both can affect integrin-cytoskeleton interactions; and 3) the role of the alpha-subunit in integrin-cytoskeleton interactions in at least some circumstances is more direct than generally supposed.