Endothelial cell adhesion molecules expressed in distinct vascular branches of select organs are implicated in organ preference of metastasis. Two constitutively expressed adhesion molecules of the lung vasculature are described here. The first is the murine B 16 melanoma cell-binding endothelial cell adhesion molecule Lu-ECAM-1. The 90kDa Lu-ECAM-1 selectively promotes adhesion and lung metastasis of B 16 melanoma cells. Melanoma cell attachment to immobilized Lu-ECAM-1 is inhibited in a dose dependant manner by anti-Lu-ECAM-1 mAb 6D3, soluble Lu-ECAM-1, and lacto-N-fucopentose. In vivo blocking of Lu-ECAM-1 by its mAb 6D3 prevents lung colonization of B16-F10. However, Lu-ECAM-1 either binds nor affects metastasis of other lung colonizing tumor cells (e.g., KLN205 carcinoma cells), or tumor cell lines that metastasize to other organs than the lung (e.g., liver-metastatic B16-L8-F10, RAW117-H10), and does not bind lymphocytes and neutrophils. The second adhesion molecule is rat dipeptidyl peptidase IV(DPP IV). This sialoglycoprotein binds lung-metastatic rat prostate and breast carcinoma cells via fibronectin which is expressed in significantly higher amounts on the surface of metastatic than non-metastatic tumor cells. Increased fibronectin expression is associated with increases in tumor cell β1 and β3 integrins. DPP IV binding is mediated by a fibronectin sequence other than RGD and is independent of its peptidase domain. These constitutively expressed adhesion molecules are believed to be responsible for site-specific vascular arrest of blood-borne cancer cells and, through as yet unknown signaling events, may cause upregulation of other (transiently expressed) adhesion molecules to enhance tumor cell binding to endothelium and/or initiate gap junctional communication to promote extravasation and secondary tumor growth.
Although a large variety of carbohydrate-binding proteins are detected in brain tissue, a few number of them have been isolated and their role defined. They include β-galactoside binding lectins, mannose-binding lectins and glycosaminoglycan-binding proteins. These components play different roles during brain ontogenesis. Axonal tracing and/or neurite fasciculation, intracellular trafficking and nuclear function are suspected for the former. The role of mannose-binding lectins has been documented as molecules involved in cell-adhesion or recognition mechanism like contact guidance of migration of immature neurons, myelination and synaptogenesis. Both β-galactoside- and mannoside-binding lectins could be of interest for understanding demyelinating diseases like experimental allergic encephalomyelitis and multiple sclerosis, respectively. A special role of mannose-binding lectins could be postulated in loss of contact inhibition and specific homing of malignant cells. Several carbohydrate-binding proteins have been identified in brain tissue with variable carbohydrate specificities and function. Some of these compounds are involved in general phenomena like, intracellular trafficking and homing of circulating cells and other in specific cell adhesion processes. The cell adhesion concerned with, i) the role of a membrane-bound mannose binding lectin, R1, in neuronal recognition as a first step of synaptogenesis, ii) the role of a soluble mannose-binding protein, CSL, in adhesion processes like stabilization of myelin structure, formation of contact between axons and myelinating cells, contact guidance of neuron migration during development. These molecules are bearing on pathology, for example a β-galactoside-binding lectin is involved in experimental allergic encephalomyelitis and lectin CSL in multiple sclerosis. The glycobiological system of cell adhesion and cell recognition may be of importance in the process of loss of contact inhibition of malignant cells and in their homing mechanism.
In the differentiation of skeletal myoblasts, the cells, after aligning themselves in arrays, fuse to form myotubes. Although it has been suggested that high mannose type of glycoproteins may be invloved in differentiation, mutant myoblasts lacking high mannose type of chains are capable of myotube formation. There is evidence that some new glycoproteins are produced by myoblasts which participate in fusion. Before differentiation the cells bind to the extracellular matrix through integrin receptors. Cell-cell adhesion of myoblasts occurs through two types of mechanisms, one calcuim-dependent and another calcium-independent. The former type of interaction is homophilic and brought about by membranelocalized N- and M-cadherins. The calcium-independent mechanism involves participation of neural cell adhesion molecules (NCAMs), especially the forms linked to plasma membrane through glycosyl-phosphatidylinositol residues. The NCAMs are sialoglycoproteins which are capable of exsisting as isoforms. Transfection of phospholipid-linked form of human NCAM cDNA in myoblasts leads precocious differentiation.
A number of glycosidases have been detected in the seminal fluid of the male genital tract of mammals and in sperm and eggs of many invertebrate and vertebrate animals. Although some of these enzymes have been isolated and characterized, the elucidation of their presumed function in the fertilization process proved to be rather difficult. In relatively recent investigations evidence was presented that glycosidases are involved in binding of sperm to the acellular egg-coats of ascidian and mouse eggs, a step that is indispensable for successful fertilization. Furthermore, hyaluronidase and possibly β-N-acetylglucosaminidase from mammalian sperm are claimed to be involved in the penetration of the acellular egg coats, particularly through the cumulus oophorus. The precise mechanism of sperm penetration and whether it can be applied to fertilization in all mammals is still debated. Ascidians and mice are so far the only animals from which evidence exists that egg-bound glycosidases might be involved in the slow block to polyspermy. In summary, good evidence exists that glycosidases play an essential role in gamete interactions, particularly in the interaction of the sperm cell with the acellular egg matrix.
Extracellular matrices are formed as networks of stable and dynamic interactions between macromolecules. Such interactions provide connective tissues with specific biomechanical properties and may also regulate cellular activities. Fibromodulin, the matrix glycoprotein discussed in this article, is found in many connective tissues where it appears to be primarily associated with fibrillar collagen. The amino acid sequence of its 39kDa core protein shows extensive homology with the collagenbinding proteoglycans, decorin and lumican. Fibromodulin contains five N-linked glycosylation sites which are substituted in a developmentally regulated manner with polylactosamine chains of variable structure and sulfation pattern. These structural characteristics of fibromodulin are discussed, and it is suggested that this member of the group of small interstitial proteoglycans may serve additional functions beyond its proposed role in the modulation of collagen fibrillogenesis.
The cryoprotective mechanism of saccharides on the freeze-thawing and freeze-drying of liposome was studied by several methods, such as leakage of aqueous inner markar, Raman- and NMR-spectroscopy and DSC. The surface of frozen liposome was covered by a concentrated aqueous saccharide solution or glassy solid, which protects from the mechanical damage of ice crystal and the fusion of liposome. Mono-, di- and trisaccharides showed a similar protective effect per monosaccharide unit. In the course of drying, the water molecules hydrated to the polar phosphate group of lecithin were displaced by the saccharide molecules. In the liquid crystal state the lyophilized liposome was maintained and the lipid membrane was stable during the rehydration process. The liposome lyophilized with a disaccharide showed the strongest stability during the rehydration process, indicating the importance of hydrogen bonding between the phosphate group and a sugar molecule with suitable molecular size.