Identification of asparagine-linked oligosaccharides involved in tumor cell adhesion to laminin and type IV collagen

MDW4, a wheat germ agglutinin-resistant nonmetastatic mutant of the highly metastatic murine tumor cell line called MDAY-D2 has previously been shown to attach to fibronectin and type IV collagen, whereas MDAY- D2 and phenotypic revertants of MDW4 attached poorly to these substrates. The increased adhesiveness of the mutant cells appeared to be closely related to a lesion in cell surface carbohydrate structures. In an effort to identify the carbohydrates involved in cell attachment, glycopeptides isolated from mutant and wild-type cells as well as from purified glycoproteins were tested for their ability to inhibit the attachment of MDW4 cells to plastic surfaces coated with fibronectin, laminin, or type IV collagen. The addition of mannose-terminating glycopeptide to the adhesion assay inhibited MDW4 cell attachment to type IV collagen. In contrast, a sialylated poly N-acetyllactosamine- containing glycopeptide, isolated from wheat germ agglutinin-sensitive MDAY-D2 cells but absent in MDW4 cells, inhibited MDW4 attachment to laminin. None of the glycopeptides used in this study inhibited attachment of MDW4 cells to fibronectin-coated plastic. Peptide N- glycosidase treatment of the cells to remove surface asparagine-linked oligosaccharides inhibited MDW4 adhesion to type IV collagen, but not to laminin, and the same treatment of the wheat germ agglutinin- sensitive cells enhanced attachment to laminin. Tumor cell attachment to, and detachment from, the sublaminal matrix protein laminin and type IV collagen are thought to be important events in the metastatic process. Our results indicate that tumor cell attachment to these proteins may be partially modulated by the expression of specific oligosaccharide structures associated with the cell surface.     

Effects of laminin, fibronectin and type IV collagen on liver cell cultures

The effects on mouse liver cells of laminin, fibronectin and type IV collagen, all of which are the main matrix of the basement membrane, were studied. Laminin, a glycoprotein isolated from cultures of rat yolk sac carcinoma cells, promoted the attachment of mouse fetal liver cells to laminin-coated dishes, but did not have a strong influence upon the attachment of normal adult liver cells. On the other hand, fibronectin which was purified from mouse plasma promoted the attachment of adult liver cells but not that of fetal liver cells. The number of neonatal liver cells attached to the surfaces coated was intermediate between those of fetal and adult liver cells in each matrix. DNA synthesis and cell proliferation during the culture of full-term fetal liver cells in laminin-coated dishes were higher than those in fibronectin- or type IV collagen-coated dishes. The amount of alpha-fetoprotein secreted in the laminin-coated dishes was more than in other groups. No differences in secretion of albumin into media, however, were observed in either group. These results suggest that laminin may be necessary for cell growth, tissue organization and cell differentiation during the normal development of liver in vivo.     

Binding domain for laminin on type IV collagen

Binding of type IV collagen to laminin was studied by attaching one member of the ligand pair to a solid phase. When laminin was bound to a solid phase, type IV collagen exhibited saturable binding. Digestion of type IV collagen with high concentrations of pepsin destroyed the laminin binding activity. Type IV collagen was also found to bind to fibronectin but the binding activity was not destroyed by pepsin treatment. Rotary shadowing electron microscopy of the pepsin digested type IV collagen indicated that the carboxy terminal end region of about 100 nm is cleaved. Rotary shadowing electron microscopy studies demonstrate that the carboxy terminal end of type IV collagen has a major laminin binding site.     

Altered cellular interactions between endothelial cells and nonenzymatically glucosylated laminin/type IV collagen.

Laminin and type IV collagen are two major basement membrane glycoproteins. In previous studies it has been shown that nonenzymatic glucosylation induces structural alterations of these macromolecules and also reduces their ability to self-associate. In the present study, endothelial cells were tested for their ability to adhere and spread on nonenzymatically glucosylated laminin and type IV collagen. Adhesion and spreading were reduced when glucosylated macromolecules were used as substrates. Glucosylation-induced changes in adhesion and spreading may be an important initial event signaling other phenotypic modifications of cells in the microvasculature and may be a crucial factor in order to understand the pathogenesis of diabetic microangiopathy at the molecular level.     

Recombinant nidogen consists of three globular domains and mediates binding of laminin to collagen type IV.

Recombinant mouse nidogen and two fragments were produced in mammalian cells and purified from culture medium without resorting to denaturing conditions. The truncated products were fragments Nd-I (positions 1-905) comprising the N-terminal globule and rod-like domain and Nd-II corresponding mainly to the C-terminal globule (position 906-1217). Recombinant nidogen was indistinguishable from authentic nidogen obtained by guanidine dissociation from tumor tissue with respect to size, N-terminal sequence, CD spectra and immunochemical properties. They differed in protease stability and shape indicating that the N-terminal domain of the more native, recombinant protein consists of two globules connected by a flexible segment. This established a new model for the shape of nidogen consisting of three globes of variable mass (31-56 kDa) connected by either a rod-like or a thin segment. Recombinant nidogen formed stable complexes (Kd less than or equal to 1 nM) with laminin and collagen IV in binding assays with soluble and immobilized ligands and as shown by electron microscopy. Inhibition assays demonstrated different binding sites on nidogen for both ligands with different specificities. This was confirmed in studies with fragment Nd-I binding to collagen IV and fragment Nd-II binding to laminin fragment P1. In addition, recombinant nidogen but not Nd-I was able to bridge between laminin or P1 and collagen IV. Formation of such ternary complexes implicates a similar role for nidogen in the supramolecular organization of basement membranes.     

Distribution of extracellular matrix proteins type I collagen, type IV collagen, fibronectin, and laminin in mouse folliculogenesis

The extracellular matrix (ECM) plays a prominent role in ovarian function by participating in processes such as cell migration, proliferation, growth, and development. Although some of these signaling processes have been characterized in the mouse, the relative quantity and distribution of ECM proteins within developing follicles of the ovary have not been characterized. This study uses immunohistochemistry and real-time PCR to characterize the ECM components type I collagen, type IV collagen, fibronectin, and laminin in the mouse ovary according to follicle stage and cellular compartment. Collagen I was present throughout the ovary, with higher concentrations in the ovarian surface epithelium and follicular compartments. Collagen IV was abundant in the theca cell compartment with low-level expression in the stroma and granulosa cells. The distribution of collagen was consistent throughout follicle maturation. Fibronectin staining in the stroma and theca cell compartment increased throughout follicle development, while staining in the granulosa cell compartment decreased. Heavy staining was also observed in the follicular fluid of antral follicles. Laminin was localized primarily to the theca cell compartment, with a defined ring at the exterior of the follicular granulosa cells marking the basement membrane. Low levels of laminin were also apparent in the stroma and granulosa cell compartment. Taken together, the ECM content of the mouse ovary changes during follicular development and reveals a distinct spatial and temporal pattern. This understanding of ECM composition and distribution can be used in the basic studies of ECM function during follicle development, and could aid in the development of in vitro systems for follicle growth.     

Functional differences in the interactions of glycosylation-deficient cell lines with fibronectin, laminin, and type IV collagen

Fibronectin isolated from the conditioned medium of monolayer cultures of baby hamster kidney (BHK) cells and several ricin-resistant (Ric) mutants derived from them express differences in N-glycosylation. The asparagine-linked oligosaccharides of BHK cell-derived fibronectin consist largely of complex chains, whereas hybrid and/or high-mannose chains are present in the fibronectins of mutant cell lines. The fibronectins exhibiting different glycosylation patterns are incorporated to similar extents into the cell-layer of human skin fibroblasts. In contrast, mutant cells retain significantly less endogenously produced fibronectin than BHK cells and also incorporate less human cellular fibronectin into a pericellular matrix. In vitro adhesion assays show that mutant cells attach to and spread relatively poorly on fibronectin-or type IV collagen-coated substrata but interact as well as do BHK cells with a laminin substratum. These results indicate that asparagine-linked oligosaccharides of fibronectin are not required for the binding and incorporation of the molecule into cell layers, but, as constituents of other cellular glycoproteins, they do modulate the ability of BHK cells to interact with some matrix components.     

TEM8 expression stimulates endothelial cell adhesion and migration by regulating cell-matrix interactions on collagen

The TEM8 gene is selectively expressed in tumor versus normal blood vessels, though its function in endothelial cell biology is not known. Towards the goal of clarifying this function, we tested whether TEM8 overexpression, or blocking TEM8's function with a dominant negative protein, would modulate endothelial cell activities. We found that TEM8-expressing endothelial cells migrated at a rate 3-fold greater than control cells in a monolayer denudation assay. Also, the addition of recombinant TEM8 extracellular domain (TEM8-ED) specifically inhibited both chemokinetic and chemotactic migration on collagen in the denudation and Boyden chamber assays, respectively. The TEM8-ED binds preferentially to collagen, and TEM8 expression enhanced endothelial adhesion to collagen 3-fold; the latter response was antagonized by the TEM8-ED. Consistent with the TEM8-ED acting as a dominant negative inhibitor of endogenously expressed protein were data showing that the TEM8-ED had no effect on the activation of beta1 integrin. TEM8 protein is present in human umbilical vein in situ and is expressed in low passage HUVEC in vitro. TEM8 protein expression in HUVEC was increased 5-fold by the initiation of tube formation, correlating expression of TEM8 with the angiogenic response. Taken together, these results indicate that TEM8 plays a positive role in endothelial cell activities related to angiogenesis.     

Expression and localization of laminin 5, laminin 10, type IV collagen,and amelotin in adult murine gingiva

The biochemical composition of the internal and external basal laminae in the junctional epithelium differs significantly, and the precise cellular origin of their respective molecules remains to be determined. In the present study, the expression and localization of three basement membrane-specific molecules—laminin 5 (γ2 chain), type IV collagen (α1 chain), and laminin 10 (α5 chain)—and one tooth-specific molecule, amelotin, was analyzed in adult murine gingiva by using in situ hybridization and immunohistochemistry. The results showed that the outermost cells in junctional epithelium facing the tooth enamel strongly expressed laminin 5 mRNA, supporting the immunohistochemical staining data. This suggests that laminin 5 is actively synthesized in junctional epithelial cells and that the products are incorporated into the internal basal lamina to maintain firm epithelial adhesion to the tooth enamel throughout life. Conversely, no amelotin mRNA signals were detected in the junctional epithelial cells, suggesting that the molecules localized on the internal basal lamina are mainly derived from maturation-stage ameloblasts. Weak and sporadic expression of type IV collagen in addition to laminin 10 in the gingiva indicates that these molecules undergo turnover less frequently in adult animals.     

Differential expression of type IV collagen isoforms in rat glomerular endothelial and mesangial cells

Type IV collagen, which is encoded by six genetically distinct alpha-chains (alpha 1-alpha 6), is a major component of the kidney glomerulus. The alpha 1(IV) and alpha 2(IV) chains are present predominantly in the mesangial matrix, whereas the alpha 3(IV), alpha 4(IV), and alpha 5(IV) chains are localized almost exclusively to the glomerular basement membrane (GBM). Thickening of the GBM and expansion of the mesangial matrix are believed to contribute to the pathogenesis of diabetic nephropathy. In the present study, we evaluated the expression of alpha 1(IV), alpha 3(IV), and alpha 5(IV) chains in rat glomerular endothelial (GEndC) and mesangial cells (GMC). Under physiological concentrations of glucose (5 mM), alpha 1(IV) and alpha 5(IV) chains were detectable in GMCs, with an obvious absence of alpha 3(IV) chain. All three isoforms tested were present in GEndCs. At diabetic concentrations of glucose (25 mM), alpha 1(IV) was up-regulated in GMCs, whereas expression level of alpha 1(IV) remained unaltered in GEndCs. The alpha 3(IV) and alpha 5(IV) chains were up-regulated in GEndCs, but remained unchanged in GMCs under diabetic glucose concentrations (25 mM). Collectively, our results demonstrate that GMC might contribute to mesangial matrix expansion, mediated by alpha 1(IV) collagen, while GEndC might contribute to thickening of GBM, mediated by alpha 3(IV) collagen, in patients with diabetic nephropathy.     

Binding of laminin to type IV collagen: a morphological study

A mixture of laminin and type IV collagen was analyzed by rotary shadowing using carbon/platinum and electron microscopy. Laminin was found to form distinct complexes with type IV collagen: one site of interaction is located 140 nm from the COOH-terminal, noncollagenous (NC1) domain and the other is located within the NH2-terminal region. The isolated NC1 fragment of type IV collagen does not appear to interact with laminin, while pepsin-treated type IV collagen, which lacks the NC1 domain, retains its ability to form complexes with laminin. Analysis of the laminin-type IV complexes indicates that laminin binds to type IV collagen via the globular regions of either of its four arms. This finding is supported by experiments using fragment P1 of laminin which lacks the globular regions and which does not bind to type IV collagen in a specific way. In addition, after heat-denaturation of laminin no specific binding is observed.     

Distribution of laminin,type IV collagen,and fibronectin in the cell columns and trophoblastic shell of early macaque placentas

Summary The cytotrophoblastic cell columns and trophoblastic shell of macaque placentas accumulate progressively greater amounts of intercellular material during early gestation. We studied the composition of this material in placentas collected from 22–34 days of gestation by using immunoperoxidase techniques directed to the extracellular matrix molecules fibronectin, type IV collagen, and laminin. These antigens co-localized within the intercellular deposits at all stages studied. At day 22 the proximal cell columns were composed of cells with narrow interstices and which lacked immunoreactivity for the 3 antigens. Distally the cells were vacuolated and the intercellular spaces increased in size and contained dense matrix deposits. The trophoblastic shell consisted of closely packed, non-vacuolated cytotrophoblast cells with only a delicate meshwork of matrix. By day 27 the matrix deposits of the distal cell columns increased markedly in size. The trophoblastic shell contained larger numbers of vacuolated cells and was occupied by accumulations of matrix. By 34 days the matrix deposits of the cell columns expanded substantially along the longitudinal axes of the columns. These deposits were often continuous with a matrix-dense, cell-deficient layer in the trophoblastic shell. This matrix-rich zone lay between a cellular layer adjacent to the intervilous space and a similar, but discontinuous, cell layer that formed the junctional zone with the endometrium.     

Differential effects of cellular fibronectin and plasma fibronectin on ovarian cancer cell adhesion, migration, and invasion

Summary The main form of fibronectin (FN) encountered by tumor cells in vivo is cellular FN (cFN), which differs structurally and functionally from the commonly used plasma FN (pFN). We compared the effects of cFN and pFN on the ovarian carcinoma lines OVCAR-3 and SKOV-3 and on cultures of normal ovarian surface epithelium, which is the precursor of the epithelial ovarian carcinomas. Ovarian surface epithelial cells and SKOV-3 cells attached and spread faster on cFN than on pFN. On cFN, SKOV-3 migration was enhanced compared with pFN or plastic. In a matrigel transfilter assay, cFN strongly inhibited SKOV-3 invasion, whereas pFN did not. In contrast to SKOV-3, OVCAR-3 cells adhered faster on FN than on plastic but did not discriminate between cFN and pFN, and they did not migrate or invade matrigel either with or without FN. In both carcinoma lines, proliferation was unaffected by either FN. The results show profound differences in the responses to cFN and pFN by two invasive ovarian carcinoma lines. Because cFN is the main type that cancer cells encounter in vivo, extrapolations from culture data to in vivo events should preferably be based on studies using this form of FN.     

Reversible effects of dibutyryl cAMP on laminin and type IV collagen secretion from retinoic acid treated F9 cells

The effects of dibutyryl cAMP on the differentiation of embryonal carcinoma F9 cells were studied mainly using the secretion of laminin and type IV collagen as the marker. For this purpose, F9 cells were labeled with 35S-methionine and radioactive proteins in the medium were analyzed by SDS-polyacrylamide gel electrophoresis. Treatment of F9 cells with retinoic acid alone induced differentiation into cells secreting type IV collagen. The combination of retinoic acid and dibutyryl cAMP stimulated laminin secretion in addition to type IV collagen secretion. This effect of dibutyryl cAMP was observed only 16 h after adding dibutyryl cAMP. Immunofluorescence staining demonstrated that the majority of the cells in culture were converted into cells secreting laminin under these conditions. In contrast to the irreversible effect of retinoic acid, the effect of dibutyryl cAMP on laminin and type IV collagen secretion was reversible at least during the first 5 days of maintaining cells in the medium containing retinoic acid plus dibutyryl cAMP. Removal of dibutyryl cAMP from the culture medium decreased the protein secretion to the basal levels within 2 days. This reversibility was not due to a change in cell number. An in vitro translation assay also suggested the reversible effect of dibutyryl cAMP on the levels of laminin mRNA. Coinciding with variations of the protein secretion, a reversible and homogeneous change in the morphology of retinoic acid generated F9 cells was observed by dibutyryl cAMP.     

Characterization of a synthetic peptide from type IV collagen that promotes melanoma cell adhesion, spreading, and motility

The adhesion and motility of tumor cells on basement membranes is a central consideration in tumor cell invasion and metastasis. Basement membrane type IV collagen directly promotes the adhesion and migration of various tumor cell types in vitro. Our previous studies demonstrated that tumor cells adhered and spread on surfaces coated with intact type IV collagen or either of the two major enzymatically purified domains of this protein. Only one of these major domains, the pepsin-generated major triple helical fragment, also supported tumor cell motility in vitro, implicating the involvement of the major triple helical region in type IV collagen-mediated tumor cell invasion in vivo. The present studies extend our previous observations using a synthetic peptide approach. A peptide, designated IV-H1, was derived from a continuous collagenous region of the major triple helical domain of the human alpha 1(IV) chain. This peptide, which has the sequence GVKGDKGNPGWPGAP, directly supported the adhesion, spreading, and motility of the highly metastatic K1735 M4 murine melanoma cell line, as well as the adhesion and spreading of other cell types, in a concentration-dependent manner in vitro. Furthermore, excess soluble peptide IV-H1, or polyclonal antibodies directed against peptide IV-H1, inhibited type IV collagen-mediated melanoma cell adhesion, spreading, and motility, but had no effect on these cellular responses to type I collagen. The full complement of cell adhesion, spreading, and motility promoting activities was dependent upon the preservation of the three prolyl residues in the peptide IV-H1 sequence. These studies indicate that peptide IV-H1 represents a cell-specific adhesion, spreading, and motility promoting domain that is active within the type IV collagen molecule.     

Doxazosin inhibits human vascular endothelial cell adhesion, migration, and invasion

The quinazoline-derived alpha1-adrenoceptor antagonists, doxazosin and terazosin have been recently shown to induce an anoikis effect in human prostate cancer cells and to suppress prostate tumor vascularity in clinical specimens [Keledjian and Kyprianou, 2003]. This study sought to examine the ability of doxazosin to affect the growth of human vascular endothelial cells and to modulate vascular endothelial growth factor (VEGF)-mediated angiogenesis. Human umbilical vein endothelial cells (HUVECs) were used as an in vitro model to determine the effect of doxazosin on cell growth, apoptosis, adhesion, migration, and angiogenic response of endothelial cells. The effect of doxazosin on cell viability and apoptosis induction of human endothelial cells, was evaluated on the basis of trypan blue and Hoechst 33342 staining, respectively. Doxazosin antagonized the VEGF-mediated angiogenic response of HUVEC cells, by abrogating cell adhesion to fibronectin and collagen-coated surfaces and inhibiting cell migration, via a potential downregulation of VEGF expression. Furthermore there was a significant suppression of in vitro angiogenesis by doxazosin on the basis of VEGF-mediated endothelial tube formation (P < 0.01). Fibroblast growth factor-2 (FGF-2) significantly enhanced HUVEC cell tube formation (P < 0.01) and this effect was suppressed by doxazosin. These findings provide new insight into the ability of doxazosin to suppress the growth and angiogenic response of human endothelial cells by interfering with VEGF and FGF-2 action. This evidence may have potential therapeutic significance in using this quinazoline-based compound as an antiangiogenic agent for the treatment of advanced prostate cancer.     

Distribution of type IV collagen, laminin, nidogen and fibronectin in the haemodynamically stressed vascular wall

Changes in the extracellular matrix of haemodynamically stressed blood vessel walls were studied by immunofluorescence histochemistry in venous-pouch aneurysms fashioned on the site of the common carotid artery of nine sheep. Tissues from the thickened walls of the experimental aneurysms were examined from 11 to 98 months post-operatively for changes in the distribution of the basement membrane components type IV collagen, laminin, nidogen and fibronectin. In the younger aneurysms, there was an increase of the basement membrane components in the thickened area. Very little basement membrane was detected in older aneurysms. Diffuse staining for fibronectin was noted in aneurysms of all ages. Thick deposits of basement membrane material were observed in calcified tissues. The changes in the matrix proteins were similar to alterations occurring during the development of atherosclerosis in human vascular tissue.     

Platelet endothelial cell adhesion molecule, PECAM-1, modulates cell migration.

Cell migration is an important process in such phenomena as growth, development, and wound healing. The control of cell migration is orchestrated in part by cell surface adhesion molecules. These molecules fall into two major categories: those that bind to extracellular matrix and those that bind to adjacent cells. Here, we report on the role of a cell-cell adhesion molecule, platelet-endothelial cell adhesion molecule-1, (PECAM-1), a member of the lg superfamily, in the modulation of cell migration and cell-cell adhesion. PECAM-1 is a 120-130 kDa integral membrane protein that resides on endothelial cells and localizes at sites of cell-cell contact. Since endothelial cells express PECAM-1 constitutively, we studied the effects of PECAM-1 on cell-cell adhesion and migration in a null-cell population. Specifically, we transfected NIH/3T3 cells with the full length PECAM-1 molecule (two independent clones). Transfected cells containing only the neomycin resistance gene, cells expressing a construct coding for the extracellular domain of the molecule, and cells expressing the neu oncogene were used as controls. The PECAM-1 transfectants appeared smaller and more polygonal and tended to grow in clusters. Indirect immunofluorescence of PECAM-1 transfectants showed peripheral staining at sites of cell-cell contact, while the extracellular domain transfectants and the control cells did not. In two quantitative migration assays, the full-length PECAM-1 transfectants migrated more slowly than control cells. Thus, PECAM-1 transfected into a null cell appears to localize to sites of cell-cell contact, promote cell-cell adhesion, and diminish the rate of migration. These findings suggest a role for this cell-cell adhesion molecule in the process of endothelial cell migration.     

Interaction between endothelial cells and basement membrane components. In vitro studies on endothelial cell adhesion to collagen types I, III, IV and high molecular weight fragments of IV

Understanding the mechanisms involved in maintaining the integrity of the vascular endothelium is fundamental to studies on atherosclerosis, thrombosis, inflammation and tumor invasion. One of the essential aspects is the relationship between the endothelial cell (EC) layer and the underlying components of the basement membrane (BM). The importance of the biological role of the individual components of the BM in the promotion of EC adhesion is investigated. In this study suspensions of bovine corneal ECs (BCECs; 5 x 10(4)/ml) were used to investigate the adhesion of EC to collagen type IV and a mixture of fragments of the tetrameric molecule (IV-F, consisting of 75, 120 and 140 kD fragments), as well as collagen types I and III, coated at a 10-micrograms/ml concentration onto glass coverslips in vitro. Adhesion was quantified after 2 h of interaction by direct counting in the light microscope following fixation of the adherent cells. Collagens type IV and IV-F markedly promoted BCEC adhesion both in the presence or absence of 10 or 50% fetal calf serum, indicating that the integrity of the tetrameric molecule is not required for EC adhesion to collagen type IV, but can be replaced by high molecular weight fragments. Collagens type I and III increased EC adhesion in the absence of serum, although not in the presence of serum. Indirect evidence for a possible role of fibronectin in EC adhesion to type-IV collagen is given by the ability of the tetrapeptide (Arg-Gly-Asp-Ser (10 micrograms) to temporarily block (15-30 min) the adhesion-promoting effect of type-IV collagen. The nature of the adhesion sequences on the fragments of type-IV collagen remains to be elucidated.     

Collagen-bound LDL modifies endothelial cell adhesion to type V collagen: Implications for atherosclerosis

Low density lipoprotein (LDL) is retained in the extracellular matrix of the arterial wall where it is considered to be atherogenic, but little is known about how cell adhesion to the matrix is affected by collagen-bound LDL. We tested the effect of native, oxidized and acetylated LDL reacted with adsorbed monomeric type I, III and V collagen on endothelial cell adhesion to collagen using a colorimetric adhesion assay. We found that none of the LDL species affected adhesion to type I and III collagen, but that collagen-bound native and acetylated LDL enhanced attachment to type V collagen, whereas bound oxidized LDL inhibited adhesion to this collagen. We therefore suggest that oxidized LDL associated with type V collagen in the arterial wall would favor de-endothelialization and contribute to atherogenesis and thrombosis.