Evidence for a novel enzymatic mechanism of neural crest cell migration on extracellular glycoconjugate matrices

Method comparison for analyzing wound healing rates

Wound healing scratch assay is a frequently used method to characterize cell migration, which is an important biological process in the course of development, tissue repair, and immune response for example. The measurement of wound healing rate, however, varies among different studies. Here we summarized these measurements into three types: (I) direct rate average; (II) regression rate average; and (III) average distance regression rate. Using Chinese hamster ovary (CHO) cells as a model, we compared the three types of analyses on quantifying the wound closing rate, and discovered that type I & III measurements are more resistant to outliers, and type II analysis is more sensitive to outliers. We hope this study can help researchers to better use this simple yet effective assay.

Mouse fibroblasts null for the long isoform of β1,4-galactosyltransferase-I show defective cell-matrix interactions

β1,4 Galactosyltransferase-I (GalT-I) is expressed as two nearly identical polypeptides that differ only in the length of their cytoplasmic domains. The longer isoform has been implicated as a cell surface receptor for extracellular glycoside ligands, such as laminin. To more stringently test the function of the long GalT-I isoform during cell interactions with laminin, we created multiple independent fibroblastic cell lines that fail to express the long isoform, but which express the short GalT-I isoform normally and appear to have normal intracellular galactosylation. Cells devoid of the long GalT-I isoform are unable to adhere and spread on laminin substrates as well as control cells, but retain near normal interactions with fibronectin, which do not rely upon surface GalT-I function. The loss of the long GalT-I isoform also leads to a loss of actin stress fibers, focal adhesions and rac GTPase activation.

Adrenal Medulla Autografts in Parkinson's Disease: A Proposed Mechanism of Action

Concepts emerging from experimental manipulations of neurobiological systems in vivo and in vitro may provide explanations for some clinical observations following adrenal medulla autografting in patients with Parkinson's disease. These concepts are reviewed, and a proposed mechanism of action of adrenal autografts in Parkinson's disease is advanced.

Cloning and characterization of a novel member of human beta-1,4-galactosyltransferase gene family

By using the EST strategy for identifying novel members belonging to homologous gene families, a novel fulklength cDNA encoding a protein significantly homologous to UDP-Gal: N-acetylglucosamine beta-1, 4-galactosyltransferase (GalT) was isolated from a human testis cDNA library. A nucleotide sequence of 2 173 bp long was determined to contain an open reading frame of 1 032 nucleotides (344 amino acids). In view of the homology to memben of the galactosyltransferase gene family and especially the closest relationship toGallus gallus GalT type I (CK I), the predicted product of the novel cDNA was designated as human beta-1,4-galactosyltransferase homolog I (HumGT-H1). Its mRNA is present in different degrees in 16 tissues examined. Southern analysis of human genomic DNA revealed its locus on chromosome 3.

Cell surface beta 1, 4-galactosyltransferase 1 promotes apoptosis by inhibiting epidermal growth factor receptor pathway

Our previous studies have shown that overexpression of beta1,4-galactosyltransferase1 (beta1,4GT1) leads to increased apoptosis induced by cycloheximide (CHX) in SMMC-7721 human hepatocarcinoma cells. However, the role of beta1,4GT1 in apoptosis remains unclear. Here we demonstrated that cell surface beta1,4GT1 inhibited the autophosphorylation of epidermal growth factor receptor (EGFR) especially at Try 1068. The phosphorylation of protein kinase B (PKB/Akt) and extracellular signal-regulated protein kinase1/2 (ERK1/2), which are downstream molecules of EGFR, were also reduced in cell surface beta1,4GT1-overexpressing cells. Furthermore, the translocations of Bad and Bax that are regulated by PKB/Akt and ERK1/2 were also increased in these cells. As a result, the release of cytochrome c from mitochondria to cytosol was increased and caspase-3 was activated. In contrast, RNAi-mediated knockdown of beta1,4GT1 increased the autophosphorylation of EGFR. These results demonstrated that cell surface beta1,4GT1 may negatively regulate cell survival possibly through inhibiting and modulating EGFR signaling pathway.

Primordial germ cell migration in the rat: preliminary evidence for a role of galactosyltransferase

The precise cellular mechanism of primordial germ cell (PGC) migration remains unknown. Cell surface galactosyltransferase (GalTase) is known to play unique roles in the process of locomotion of many migratory cells. With an objective to seek evidence for possible involvement of GalTase in the migratory process of PGC, we evaluated germ cell migration in the rat following experimental modulation of embryonic GalTase activity. Pregnant rats were laparotomized under anesthesia on Day 10 of pregnancy. While embryos of one uterine horn received lysozyme (100 microg/fetus), those of the other received alpha-lactalbumin (LA; 100 microg/fetus), N-acetylglucosamine (GlcNAc; 250 nmole/fetus), uridine 5'-monophosphate (UMP; 2.5 micromole/fetus), uridine diphosphate-galactose (UDP-gal; 250 nmole/fetus), or a combination of 250 nmole of UDP-gal and 2.5 micromole of UMP/fetus. Between gestation Days 12 and 14, embryos were dissected out and processed for histochemical localization of PGC on the basis of binding of Dolichos biflorus agglutinin on the surface glycoconjugate of the germ cells. The number of PGC in each embryo was counted. There was a daywise increase in the number of PGC in all groups. As compared with lysozyme-exposed controls, the numbers of PGCs at the day-specific sites on all days of examination were significantly lower in the LA- as well as GlcNAc-exposed groups. UMP or UDP-gal individually exerted little or no influence, while the total PGC count rose significantly over the respective control values under simultaneous exposure to UMP and UDP-gal. The present findings suggest a likely catalytic role of GalTase in the process of germ cell migration.

Regulation of the expression and activity of beta1,4-galactosyltransferase I by focal adhesion kinase

beta1,4-Galactosyltransferase I (GalT) participates in both glycoconjugates and cellular interactions. GalT's role in lamellipodia formation and cell migration on laminin is associated with a transient phosphorylation of focal adhesion kinase (FAK) and a consequent reorganization of the actin cytoskeleton and focal adhesions. We transfected wild type FAK and different FAK mutants into NIH3T3 cell line, measured GalT gene expression by Northern blot hybridization, and evaluated its activity. It was found that wtFAK and FAKY576F up-regulated GalT gene expression and its surface activity, while FAKY397F down-regulated them. At the same time, we used ricinus communis agglutinin (RCA)-I lectin staining to demonstrate its binding reactions. We found that wtFAK and FAKY576F bound stronger, while FAKY397F bound weaker than the control. By flow cytometry analysis, it was found that FAK promoted G1/S transition and enhanced the expression of cyclin D1 while FAKY397F inhibited these steps compared with the control NIH3T3 cells. G1/S checkpoint regulation proteins control GalT mRNA transcription. The results indicate that FAK regulated the expression of GalT and its activity in NIH3T3 cells may contribute to the effect of FAK on the cell-cycle.

Cell surface beta1,4-galactosyltransferase function in mammary gland morphogenesis: insights from transgenic and knockout mouse models

Development and morphogenesis are profoundly influenced by cell-cell and cell-extracellular matrix (ECM) interactions that are governed by cell surface receptor association with specific ligands. One such receptor is the long isoform of beta1,4-galactosyltransferase I (GalT I), a small proportion of which is targeted to the plasma membrane. Surface-expressed GalT I binds to specific glycoside residues on multiple extracellular ligands, and GalT I binding to specific ligands mediates cell-cell as well as cell-matrix interactions for a variety of cells, including mammary epithelia. Significant insight into surface GalT I function in mammary gland development and morphogenesis has been gained through the analysis of mouse transgenic and knockout models of surface GalT I misexpression. Overexpression of cell surface GalT I leads to impaired lactation as a result of reduced branching and differentiation and elevated apoptosis, while deleting surface GalT I enhances branching and differentiation and reduces apoptosis. These phenotypes can be attributed in large part to altered cell-ECM interactions. The current and future challenges are to use these mouse models to dissect the molecular mechanisms that govern surface GalT I function as a receptor in the normal mammary gland, as well as to assess the potential for surface GalT I misexpression to contribute to disease.

Enhanced branching morphogenesis in mammary glands of mice lacking cell surface beta1,4-galactosyltransferase

Development of the mammary gland is influenced both by the systemic hormonal environment and locally through cell-cell and cell-extracellular matrix (ECM) interactions. We have previously demonstrated aberrant mammary gland morphogenesis in transgenic mice with elevated levels of the long isoform of beta1,4-galactosyltransferase 1 (GalT), a proportion of which is targeted to the plasma membrane, where it plays a role in cell-ECM interactions. Here, we show that mammary glands of mice lacking the long GalT isoform exhibit a complementary phenotype. Cell-surface GalT activity was reduced by over 60%, but because the short GalT isoform is intact, total GalT activity was reduced only slightly relative to wild type. Mammary glands from long GalT-null mice were characterized by excess branching, and this phenotype was accompanied by altered expression of laminin chains. Laminin alpha1 and alpha3 were reduced 2.4- and 3.0-fold, respectively, while expression of laminin gamma2 was elevated 2.3-fold. The expression and cleavage of laminin gamma2 have been correlated with branching and cell migration, and Western blotting revealed an altered pattern in gamma2 cleavage products in long GalT-null mammary glands. We then examined the expression of metalloproteases that cleave laminins or that have been shown to play a role in mammary gland morphogenesis. Expression of MT1-MMP, a membrane-bound protease that can cleave laminin gamma2, was elevated 5.5-fold in the long GalT-nulls. MMP 7 was also elevated 5.1-fold. Our results suggest that expression of surface GalT is important for the proper regulation of matrix expression and deposition, which in turn regulates the proper branching morphogenesis of the mammary epithelial ductal system.

Synthesis of extracellular matrix and adhesion through beta(1) integrins are critical for fetal ventricular myocyte proliferation

Extracellular matrix (ECM) regulates vascular smooth muscle cell proliferation. The role of ECM in myocardial growth is unexplored. We sought to determine whether human fetal ventricular myocytes (HFVMs) produce ECM and whether synthesis and attachment to ECM are necessary for their epidermal growth factor (EGF)-dependent and -independent proliferation. Cultured HFVMs proliferate in the presence but not absence of serum and EGF, as determined by increase in cell number and [(3)H]thymidine and [(14)C]leucine incorporation (measures of DNA and protein synthesis, respectively). Using a cyanogen bromide digestion technique to measure collagen and elastin and using affinity chromatography for fibronectin, we found that HFVMs synthesized collagen and fibronectin but not elastin. HFVMs grown on exogenous ECM (including fibronectin and type I collagen and laminin) demonstrated no change in proliferation or DNA and protein synthesis with or without EGF. However, inhibition of collagen synthesis using cis-4-hydroxyproline resulted in a decrease in EGF-related HFVM proliferation and DNA and protein synthesis, which was reversed by exposure to L-proline but not by growth on type I collagen. Use of beta(1) but not beta(3) integrin antibody to inhibit cell interaction with ECM resulted in a decrease in HFVM proliferation and DNA and protein synthesis in response to EGF. Furthermore, EGF-dependent proliferation was enhanced by alpha(1)beta(1) and alpha(5)beta(1) antibodies that act as functional ligands, but not alpha(3)beta(1), the only beta(1) subtype expressed in adult myocytes. In conclusion, proliferating HFVMs synthesize collagen and fibronectin. The proliferative response of HFVMs to EGF requires the synthesis of collagen as well as attachment to specific alpha/beta(1) integrin heterodimers.

Form and function: the laminin family of heterotrimers

The laminins are a family of glycoproteins that provide an integral part of the structural scaffolding of basement membranes in almost every animal tissue. Each laminin is a heterotrimer assembled from alpha, beta, and gamma chain subunits, secreted and incorporated into cell-associated extracellular matrices. The laminins can self-assemble, bind to other matrix macromolecules, and have unique and shared cell interactions mediated by integrins, dystroglycan, and other receptors. Through these interactions, laminins critically contribute to cell differentiation, cell shape and movement, maintenance of tissue phenotypes, and promotion of tissue survival. Recent advances in the characterization of genetic disruptions in humans, mice, nematodes and flies have revealed developmental roles for the different laminin subunits in diverse cell types, affecting differentiation from blastocyst formation to the post-natal period. These genetic defects have challenged some of the previous concepts about basement membranes and have shed new light on the diversity and complexity of laminin functions as well as established the molecular basis of several human diseases.

The level of cell surface beta1,4-galactosyltransferase I influences the invasive potential of murine melanoma cells

Beta1,4-Galactosyltransferase I (GalT I) is localized on the leading lamellipodia of migrating cells, where it associates with the cytoskeleton and facilitates cell spreading and migration on basal lamina matrices. It has previously been reported that a variety of highly metastatic murine and human cell lines are characterized by elevated levels of cell surface GalT I, although the intracellular biosynthetic pool is similar between cells of high and low metastatic potential. In this study, we examined whether the elevated expression of surface GalT I characteristic of metastatic cells is instructive or incidental to their metastatic behavior by altering the expression of surface GalT I and by the use of GalT I-specific perturbants. Surface GalT I levels were positively and negatively altered on murine melanoma cells by either overexpressing full-length GalT I or by homologous recombination, respectively. The consequences of altered surface GalT I expression on cell invasion in vitro and lung colonization in vivo were determined. Increasing surface GalT I expression on cells of low metastatic potential to levels characteristic of highly metastatic cells recapitulated the highly invasive phenotype in vitro. Alternatively, decreasing surface GalT I expression on highly metastatic cells to levels characteristic of low metastatic cells reduced their invasive behavior in vitro and metastatic activity in vivo. Within the physiological range of surface GalT I expression, the invasive potential of each clonal cell line correlated strongly with the level of surface GalT I expressed. As an independent means to assess the involvement of surface GalT I in metastatic behavior, cells were pretreated with two different classes of surface GalT I perturbants, a competitive oligosaccharide substrate and a substrate modifier protein. Both perturbants inhibited metastatic colonization of the lung, whereas control reagents did not. Finally, as reported by others, surface GalT I on metastatic cells selectively interacted with one glycoprotein substrate, or ligand, of approximately 100 kDa, the identity of which remains obscure. These results show that the elevated expression of surface GalT I characteristic of highly metastatic cells contributes to their invasive phenotype in vitro and to their metastatic phenotype in vivo.

Lectins inhibit periodontal ligament fibroblast attachment, spreading and migration on laminin substrates

The ways in which carbohydrate signals from the extracellular matrix influence the responses of periodontal ligament (PDL) fibroblasts are essentially unknown. The purpose of this study, using video digital image analysis, was to examine the effects of lectins on the attachment, spreading and migrational responses of rat periodontal ligament fibroblasts on the highly glycosylated glycoprotein laminin (LN) in vitro. PDL fibroblasts were isolated from rat molar teeth and grown in culture. Bound LN and control substrates (bovine serum albumin and untreated plastic) were incubated with solutions of either wheatgerm agglutinin (WGA), specific for N-acetylglucosamine, or concanavalin A (ConA), specific for mannose, in 96-well plates. Unbound lectin was rinsed away and 10.0 x 10(3) cells were seeded per well and allowed to attach for 1.5 h. Incubation of LN substrates with WGA, prior to the addition of any cells, inhibited PDL fibroblast binding more than 5-fold. ConA, however, had no effect on cell binding but inhibited mean individual cell spreading nearly 3-fold under similar assay conditions. The effects could be prevented by adding each lectin's respective specific sugar. The lectins had no effects on the control substrates. In a 24-h cell migration assay WGA and ConA both significantly inhibited migration of PDL fibroblasts. It is likely that WGA inhibited cell attachment and cell migration, by binding to oligosaccharides and blocking access to adjacent polypeptide cell recognition sequences on LN. The results from the ConA experiments, where binding was allowed but spreading was severely inhibited, suggest a possible informational role for the carbohydrates present on LN.

Growth retardation and early death of beta-1,4-galactosyltransferase knockout mice with augmented proliferation and abnormal differentiation of epithelial cells

Carbohydrate chains on a glycoprotein are important not only for protein conformation, transport and stability, but also for cell-cell and cell-matrix interactions. UDP-Gal:N-acetylglucosamine beta-1,4-galactosyltransferase (GalT) (EC 2.4.1.38) is the enzyme which transfers galactose (Gal) to the terminal N-acetylglucosamine (GlcNAc) of complex-type N-glycans in the Golgi apparatus. In addition, it has also been suggested that this enzyme is involved directly in cell-cell interactions during fertilization and early embryogenesis through a subpopulation of this enzyme distributed on the cell surface. In this study, GalT-deficient mice were produced by gene targeting in order to examine the pathological effects of the deficiency. GalT-deficient mice were born normally and were fertile, but they exhibited growth retardation and semi-lethality. Epithelial cell proliferation of the skin and small intestine was enhanced, and cell differentiation in intestinal villi was abnormal. These observations suggest that GalT plays critical roles in the regulation of proliferation and differentiation of epithelial cells after birth, although this enzyme is dispensable during embryonic development.

Mammary gland morphogenesis is inhibited in transgenic mice that overexpress cell surface beta1,4-galactosyltransferase

Mammary gland morphogenesis is facilitated by a precise sequence of cell-cell and cell-matrix interactions, which are mediated in part through a variety of cell surface receptors and their ligands (Boudreau, N., Myers, C. and Bissell, M. J. (1995). Trends in Cell Biology 5, 1–4). Cell surface beta1,4-galactosyltransferase (GalTase) is one receptor that participates in a variety of cell-cell and cell-matrix interactions during fertilization and development, including mammary epithelial cell-matrix interactions (Barcellos-Hoff, M. H. (1992). Exp. Cell Res. 201, 225–234). To analyze GalTase function during mammary gland morphogenesis in vivo, we created transgenic animals that overexpress the long isoform of GalTase under the control of a heterologous promoter. As expected, mammary epithelial cells from transgenic animals had 2.3 times more GalTase activity on their cell surface than did wild-type cells. Homozygous transgenic females from multiple independent lines failed to lactate, whereas transgenic mice overexpressing the Golgi-localized short isoform of GalTase lactated normally. Glands from transgenic females overexpressing surface GalTase were characterized by abnormal and reduced ductal development with a concomitant reduction in alveolar expansion during pregnancy. The phenotype was not due to a defect in proliferation, since the mitotic index for transgenic and wild-type glands was similar. Morphological changes were accompanied by a dramatic reduction in the expression of milk-specific proteins. Immunohistochemical markers for epithelia and myoepithelia demonstrated that both cell types were present. To better understand how overexpression of surface GalTase impairs ductal morphogenesis, primary mammary epithelial cultures were established on basement membranes. Cultures derived from transgenic mammary glands were unable to form anastomosing networks of epithelial cells and failed to express milk-specific proteins, unlike wild-type mammary cultures that formed epithelial tubules and expressed milk proteins. Our results suggest that cell surface GalTase is an important mediator of mammary cell interaction with the extracellular matrix. Furthermore, perturbing surface GalTase levels inhibits the expression of mammary-specific gene products, implicating GalTase as a component of a receptor-mediated signal transduction pathway required for normal mammary gland differentiation.

IL-4 and TNF-alpha induce changes in integrin expression and adhesive properties and decrease the lung-colonizing potential of HT-29 colon carcinoma cells

The colon carcinoma cell line HT-29 was used to explore the potential of interleukin-4 (IL-4) and tumor necrosis factor alpha (TNF-alpha) to modify integrin expression and adhesive functions of tumor cells in vitro and to examine corresponding metastatic effects in vivo. Preincubation of HT-29 cells with 100 U/ml of IL-4 for 48 h downregulated the surface expression of the integrin subunits alpha 2, alpha 3, beta 1 and beta 4 after 48 h, whereas the alpha 1 subunit was upregulated. In contrast, 100 U/ml to TNF-alpha selectively upmodulated the expression of alpha v. Attachment to fibronectin of cells treated with IL-4 increased twofold (63.5% vs 32.4%). Adhesion to fibronectin (54.0% vs 32.4%) and vitronectin (37.9% vs 16.4%) was elevated in the case of TNF-alpha stimulation. Using an experimental metastasis model, HT-29 cells showed a significant reduction of their lung-colonizing potential in nude mice when preincubated with IL-4 for 48 h before intravenous injection. The decrease also observed for TNF-alpha-treated cells was less pronounced. The data indicate that the cytokines IL-4 and TNF-alpha can act as direct regulators of adhesive mechanisms of tumor cells bearing adequate receptors, thus influencing lung-colony formation.

Rodent myoblast interactions with laminin require cell surface glycoconjugates but not laminin glycosyl groups

Laminin glycosyl groups are necessary for the spreading of murine melanoma cells which become attached to this glycoprotein. Laminin has been implicated in myogenesis but the potential role of its glycosyl groups in this process has not been examined. In this study we report the effects of the carbohydrate moieties of laminin on myoblast adhesion, spreading, and differentiation. Unglycosylated laminin from tunicamycin-treated cultures of a mouse cell line, M1536 B3, was used in the experiments. Glycosylated laminin from a murine tumor and from cultures of M1563 B3 cells served as controls. Cell binding experiments with C2C12 mouse myoblasts showed that the cells preferred a laminin-coated surface, compared to the uncoated plastic surface (nontissue culture wells). Myoblasts did not distinguish between glycosylated and unglycosylated laminin substrates. Both glycosylated and unglycosylated forms of laminin promoted myoblast growth and differentiation. In contrast, cells on uncoated plastic surfaces grew very slowly and did not further differentiate. The L6 rat myoblast response to glycosylated and unglycosylated laminin was the same. These results indicate that although rodent myoblasts in culture require a laminin substratum for spreading, growth, and differentiation on a proprietary plastic surface, laminin carbohydrates are not implicated in those cellular responses. In contrast, parallel studies using the lectin, Con A, indicate that cell surface glycoconjugates of myoblasts are implicated in the response of these cells to a laminin substratum.

Control of stable lamellipodia formation by expression of cell surface beta 1,4-galactosyltransferase cytoplasmic domains

Mesenchymal cell migration on basal lamina is mediated, in part, by the binding of cell surface beta 1,4-galactosyltransferase (GalTase) to specific N-linked oligosaccharides in the E8 domain of laminin. On migrating cells, surface GalTase is anchored to the cytoskeleton; when GalTase is prevented from associating with the cytoskeleton, lamellipodia formation and subsequent migration are inhibited. To define better the involvement of GalTase-cytoskeleton interactions in cell motility, we examined the lamellipodia formation, polarity and migratory behavior of stably transfected 3T3 fibroblasts expressing increased or decreased levels of GalTase capable of interacting with the cytoskeleton. Initially, the motile behavior of individual cells was quantified in the absence of exogenous stimuli. Cells that overexpress GalTase binding sites for the cytoskeleton changed their polarity more frequently and translocated more erratically than did control cells when assayed on laminin substrata. These differences were not observed, however, when cells were plated on fibronectin, which does not contain binding sites for surface GalTase. GalTase-transfected cells were also assayed for their ability to polarize in response to a specific stimulus. In this case, the ability of a cell to reorient towards a gradient of platelet-derived growth factor was found to be directly proportional to the amount of GalTase associated with the cytoskeleton. Differences in response to platelet-derived growth factor were not due to differences in growth factor binding. Indirect immunofluorescence showed that altering the level of GalTase did not affect the ventrally distributed pool of GalTase stably associated with the cytoskeleton; however, stress fiber formation was inhibited. Thus, increasing surface GalTase binding sites for the cytoskeleton leads to erratic, multipolar behavior in the absence of any vectorial stimulus, but the ability to form a functional lamellipodium in response to a stimulus is dependent upon the amount of surface GalTase associated with the cytoskeleton. Apparently, cells are able to regulate cytoskeletal assembly and lamellipodial stability by altering the expression and/or affinity of appropriate matrix receptors, such as GalTase, and their corresponding binding sites in the cytoskeleton.

Rat olfactory neurons can utilize the endogenous lectin, L-14, in a novel adhesion mechanism

L-14 is a divalent, lactosamine-binding lectin expressed in many vertebrate tissues. In the rat nervous system, L-14 expression has been observed previously in restricted neuronal subsets within the dorsal root ganglia and spinal cord. In this study we report that L-14 is expressed by nonneuronal cells in the rat olfactory nerve. We demonstrate that L-14 binds and co-localizes with two ligands in the rat olfactory system: a beta-lactosamine-containing glycolipid, and a putative member of the laminin family. The former is expressed on the surfaces of nascent olfactory axons originating from neuron cell bodies in the olfactory epithelium. The latter is present in the extracellular matrix of the axonal path leading to synaptic targets in the olfactory bulb. In vitro, we find that recombinant L-14 promotes primary olfactory neuron adhesion to two laminin family members, and promotes intercellular adhesion. Both activities are dose-dependent, and are independent of integrin-mediated mechanisms. We have thus found that L-14 can serve two distinct adhesive functions in vitro, and propose that L-14 in vivo can promote olfactory axon fasciculation by crosslinking adjacent axons and promote axonal adhesion to the extracellular matrix.

Carbohydrates play a role in neurite outgrowth in vivo during development and regeneration

We have used the alpha-glucosidase inhibitor, castanospermine, to investigate the possible involvement of N-linked glycosylation in the process of neurite outgrowth both during the development and regeneration of sympathetic nerve fibres into the iris of the rat. The effects on nerve growth were assessed qualitatively using catecholamine histochemistry and quantitatively by measuring the uptake of [3H]noradrenaline. Castanospermine was injected during the first, second or third postnatal week or during the second to fourth week after degeneration of adrenergic nerve terminals with the neurotoxin, 6-hydroxydopamine. Results showed that both the initial growth of sympathetic nerve fibres, as well as the regeneration of these fibres, was inhibited by castanospermine treatment. The inhibitory effects were restricted to injection of castanospermine at particular time periods during postnatal development and regeneration. These results suggest that N-linked carbohydrates may be important in particular stages of the processes of initial nerve growth and regeneration of sympathetic nerve fibres in the iris.

Movement of embryonic chick sympathetic neurons on laminin in vitro is preceded by neurite extension

Chick sympathetic neurons (E-9) are capable of moving on a laminin substrate but not on more adhesive substrates in vitro. The effect of laminin is dose-dependent and reduced by the addition of anti-laminin antibodies, whereas soluble laminin does not stimulate movement. The onset of neuronal movement is preceded by, and highly correlated with, the onset of neurite formation. The addition of 1,2 dioctanoyl-sn-glycerol (DAG), a stimulator or protein kinase C that has been shown to inhibit neurite outgrowth, was found to delay both process formation and neuronal movement but did not affect the correlation between these two measures. These results support the conclusion that laminin stimulates primary neuronal movement in vitro and suggest that the mechanism underlying movement involves process formation followed by "towing" of the cell body by the advancing process. The similarities of this in vitro behavior to that observed in vivo suggest that similar mechanisms may underlie neuronal movement in the developing nervous system as suggested by Morest (Z Anat Entwicklungsgesch 130:265-305, 1970) and Liesi (EMBO J 4:1163-1170, 1985; Exp Neurol 117:103-113, 1992).

Adhesion molecules in neural crest development

Peripheral nerve cells, various endocrine and pigment cells and cranial connective tissue cells of vertebrates stem mainly from the embryonic neural crest. This originates with the central nervous system, but the crest cells detach from this tissue, via a decrease of cell-cell adhesion involving, particularly, a reduction of the adherens junction cell adhesive molecule A-CAM. This epithelio-mesenchymal transformation allows crest cells to migrate along pathways that are defined partly by the distribution of substrate adhesion molecules, the archetype being fibronectin, an extracellular matrix molecule recognized by integrin receptors on crest cells. Many other molecules, however, may act in the same way. In contrast, some molecules may define migration pathways by reducing adhesion; chondroitin sulfate proteoglycan is a candidate for this role. Pathway selection is most likely achieved by balanced combinations of molecules that promote and reduce adhesion. Cessation of migration, in the case of the nervous ganglia, correlated with re-expression of cell-cell adhesion molecules like A-CAM and others, consistent with an adhesive basis, although functional tests have not yet been performed. The development of the neural crest system provides a useful model that emphasizes the role of adhesion in morphogenesis.

Eosinophil adhesion and maturation is modulated by laminin

Eosinophils (Eo) participate in the inflammatory response to parasites, allergins, toxins, and epitopes recognized by autoimmune antibodies. Nonetheless, little attention has heretofore been paid to the interactions of Eo with extracellular matrix (ECM) proteins during their migration through the subendothelial basement membrane and into the surrounding tissue. Therefore, we have studied the adhesion of Eo to specific ECM proteins and the effect of this adhesion on Eo viability and maturation. Control Eo (from normal donors) adhere no better to substrates coated with laminin (LM), fibronectin (FN), cytotactin (CT), or collagen types I or IV (Col IV) than they do to human serum albumin coated substrates. In contrast, Eo activated in vitro with IL-5 or in vivo in patients with eosinophilia bind well to LM, FN and Col IV. LM is by far the most avid ligand among these molecules. For example, 43% of input cells bind to a substrate bearing 200 fmol/cm2 of LM; a similar level of adhesion to FN requires 30 times as much absorbed protein. Antibody inhibition experiments suggest that the alpha 6 beta 1 integrin heterodimer is the predominant LM receptor on these cells. Flow cytometry showed similar levels of these subunits on control and activated Eo, suggesting that Eo adhesion to LM is not regulated simply by cell surface integrin concentration. The effects of ECM proteins on Eo behavior were also examined. A LM-coated substrate (with no added cytokine) was found to be almost as effective as IL-5 in maintaining Eo viability while an equally adhesive FN-coated substrate had much less effect. Normally, even in the presence of 10% serum, no Eo survive a 5-day incubation in vitro unless IL-3, IL-5, or GM-CSF is added to the medium. Conditions that inhibit adhesion to LM (anti-integrin antibodies in the medium or CT on the substrate) and certain anti-cytokine antibodies inhibited the promotion of Eo viability by LM. During incubation on LM, Eo become hypodense, as they do in the presence of IL-5, indicating that they have become activated. These observations suggest that the interactions of Eo and ECM proteins may be important both for their potential to direct Eo migration and for their ability to regulate Eo viability, cytokine production, and maturation.

Expression and accumulation of interstitial collagen in the neonatal rat heart

Significant physiological changes occur in the heart following birth including increased arterial blood pressure and heart rate. Concurrently, biochemical and structural alterations are evident in the neonatal heart in response to these dynamic physiological properties. Prominent among these is the elaborate development of the cardiac extracellular matrix, composed primarily of interstitial collagen. The collagenous fibers, together with other matrix components, form an elastic, stress-tolerant network which functions in the dissipation of force throughout the heart wall. The present studies have used biochemical and molecular techniques to show the temporal and spatial patterns of interstitial collagen accumulation and expression during late fetal and neonatal development of the rat heart. The use of biochemical and particularly molecular methodologies allows the analysis of the expression of matrix components at a resolution previously not attained by structural studies alone. These data show relative increases in interstitial collagen immediately following birth as well as spatial differences in collagen mRNAs within the heart. The data presented provide further evidence for a role of mechanical stimulation in the regulation of collagen gene expression during this period of heart development.

Immunocytochemical analysis of a novel carbohydrate differentiation antigen (CDA-3C2) associated with olfactory and otic systems during embryogenesis in the rat

Carbohydrate differentiation antigens are known to display specific patterns of expression during mammalian development and are thought to participate in significant morphogenetic events. In the present study, two monoclonal antibodies that react with a novel carbohydrate differentiation antigen (CDA-3C2) were used to analyze, by light microscopy, the spatiotemporal distribution of this unique high molecular weight antigen during embryogenesis in the rat. Correlative analysis of the development of peripheral neural structures, in which CDA-3C2 was expressed, was carried out with an anti-neurofilament antibody. Enzymatic digestion, combined with Western blots, reveal that the CDA-3C2 epitope is a carbohydrate which is carried on a high molecular weight glycoprotein with a mass of greater than 1 million Daltons. Characteristic of carbohydrate antigens, immunoreactivity was found in several distinct cellular patterns: only along the apical border of cells, along lateral and basal membranes of cells, and extracellular-like staining in the mesenchyme. During neurulation, CDA-3C2 showed differential staining in the ectoderm, distinguishing lateral from neural regions. Following closure of the neural tube, there was a striking specificity of expression of CDA-3C2 in the periphery, found almost exclusively in olfactory and otic epithelial structures. While CDA-3C2 is found in placode-derived tissues that subserve sensory transduction, it appears to be primarily associated with the supportive cells (and their secretions) in both otic and olfactory regions and less so with the sensory cells. The data suggest that a unique carbohydrate antigen on a large macromolecule may play a role in neurulation and/or morphogenesis of the placode-derived otic and olfactory structures.

Immunoelectron microscopic analysis of a novel carbohydrate differentiation antigen (CDA-3C2) in the developing rat olfactory and otic systems

A carbohydrate differentiation antigen (CDA-3C2) exhibits a highly specific and restricted pattern of expression during rat embryogenesis. In the periphery of the embryo, this antigen is associated transiently with the lateral ectoderm but is retained only in the olfactory and otic epithelium throughout morphogenesis. At the light microscopic level, CDA-3C2 immunoreactivity appears mostly along cell periphery and in the extracellular matrix. The aim of the present study was to determine the specific cellular and subcellular distribution of CDA-3C2 in vivo in order to identify potential sites of cellular and tissue function of the antigen during embryogenesis. There was a strikingly similar subcellular distribution of CDA-3C2 in the developing otic and olfactory systems, found mostly along cell membranes, microvillar projections and acellular secretions of the epithelium. Mature sensory components of the epithelia were not immunoreactive, whereas supportive cells and their secreted structures were densely stained. The highly coincident nature of CDA-3C2 in both sensory epithelia suggests that this carbohydrate epitope, and possibly its carrier macromolecule, participate in a morphogenetic function common to these two sensory epithelia.

Mechanisms of neural crest cell migration

Neural crest cells are remarkable in their extensive and stereotypic patterns of migration. The pathways of neural crest migration have been documented by cell marking techniques, including interspecific neural tube grafts, immunocytochemistry and DiI-labelling. In the trunk, neural crest cells migrate dorsally under the skin or ventrally through the somites, where they move in a segmental fashion through the rostral half of each sclerotome. The segmental migration of neural crest cells appears to be prescribed by the somites, perhaps by an inhibitory cue from the caudal half. Within the rostral sclerotome, neural crest cells fill the available space except for a region around the notochord, suggesting the notochord may inhibit neural crest cells in its vicinity. In the cranial region, antibody perturbation experiments suggest that multiple cell-matrix interactions are required for proper in vivo migration of neural crest cells. Neural crest cells utilize integrin receptors to bind to a number of extracellular matrix molecules. Substrate selective inhibition of neural crest cell attachment in vitro by integrin antibodies and antisense oligonucleotides has demonstrated that they possess at least three integrins, one being an alpha 1 beta 1 integrin which functions in the absence of divalent cations. Thus, neural crest cells utilize complex sets of interactions which may differ at different axial levels.

Environmental influences on neural crest cell migration

Neural crest cells migrate extensively and interact with numerous tissues and extracellular matrix components during their movement. Cell marking techniques have shown that neural crest cells in the trunk of the avian embryo migrate through the anterior, but not posterior, half of each sclerotome and avoid the region around the notochord. A possible mechanism to account for this migratory pattern is that neural crest cells may be inhibited from entering the posterior sclerotome and the perinotochordal space. Thus, interactions with other tissue may prescribe the pattern of neural crest cell migration in the trunk. In contrast, interactions between neural crest cells and the extracellular matrix may mediate the primary interactions controlling neural crest cells migration in the head region.

Interactions of cell-surface galactosyltransferase with immunoglobulins

Detection of the activity of beta-1,4-galactosyltransferase (beta-1,4-GT) in suspensions of viable mouse hepatocytes, the human hepatoma cell line Hep G2, the human colonic adenocarcinoma cell line HT-29, the monocyte-like cell line U937, and human splenic B and T lymphocytes suggested the presence of beta-1,4-GT, in an enzymatically active form, on plasma membranes. The presence of beta-1,4-GT on cell surfaces was also indicated from the effect of trypsinization of live cells, which significantly reduced cell surface beta-1,4-GT activity, but did not affect the activity associated with cytoplasmic membranes. Furthermore, the presence of beta-1,4-GT on the cell surface was demonstrated by indirect immunofluorescence staining of cells with anti-beta-1,4-GT antibody. The detection of radioactivity in immunoglobulins (Ig) and their component chains after incubation with suspensions of intact cells in the presence of Mn2+ and UDP-[3H]-galactose, indicated that Ig molecules were galactosylated. In the absence of UDP-[3H]-galactose, beta-1,4-GT on cell surfaces, or immobilized on Sepharose-4B, formed stable complexes with galactose acceptors, including Ig. The efficiency of binding decreased in the order: J chain > alpha chain > mu chain > polymeric IgA2 > monomeric/polymeric IgA1 > IgM > IgG. Thus, beta-1,4-GT could act as a cell-surface receptor for Ig through a cation-dependent, lectin-like association of the beta-1,4-GT with the carbohydrate moieties of the Ig. This was confirmed by indirect surface immunofluorescence and radiolabeled ligand binding assays. The binding was inhibitable by EDTA, alpha-lactalbumin (in the presence of glucose), GlcNAc, or uridine 3',5'dialdehyde. At 37 degrees C, the apparent affinity constants and association rate constants of interaction between cell surface beta-1,4-GT on glutaraldehyde-fixed HT-29 and U937 cells and alpha 2 chain or monomeric IgA1 were in the range from 7.1 x 10(7) to 4.6 x 10(8) M-1 and from 1 x 10(5) to 3 x 10(6) M-1 s-1, respectively. The dissociation rate constants and half time of dissociation calculated from these data were in the range from 2.1 x 10(-2) to 5.0 x 10(-4) s-1 and from 33 to 1380 s, respectively. The number of alpha 2 or IgA1 molecules bound per HT-29 and U937 cell were in the range from 1.9 x 10(5) to 1.3 x 10(6). The binding of IgA by the cell surface beta-1,4-GT was not associated with internalization or the catabolic degradation of the ligand.

Role of laminin carbohydrates on cellular interactions

Laminins, a family of large multidomain glycoproteins of the basal lamina, have been implicated in the development and maintenance of cellular and tissue organization. Considerable interest has arisen concerning the ways in which laminin carries out its biological functions. Previously these biologic responses have been primarily attributed to the peptide sequences of laminin, however, newer studies suggest that laminin carbohydrates may also participate in such cellular activities. Recently, a subpopulation of laminin molecules purified from EHS sarcoma by lectin affinity chromatography has been shown to contain about 25 to 30% carbohydrate. Most of the carbohydrates present are complex-type asparagine-linked oligosaccharides encompassing many different structures, some of which are unique to laminin. To date, the biological function of the carbohydrates of laminin remains somewhat unclear. They do not appear to be needed for heparin binding or to enhance proteinase stability, however, current evidence suggests they are important in cellular spreading and neurite outgrowth. It is our hypothesis that in the covalently-linked carbohydrate moieties of laminin will ultimately prove to be involved in information transfer to responsive cells. It is the purpose of this review to delineate current concepts of the structure and function of this unique glycoprotein's sugar chains.

Alpha 1 beta 1 integrin on neural crest cells recognizes some laminin substrata in a Ca(2+)-independent manner

Neural crest cells migrate along pathways containing laminin and other extracellular matrix molecules. In the present study, we functionally and biochemically identify an alpha 1 beta 1 integrin heterodimer which bears the HNK-1 epitope on neural crest cells. Using a quantitative cell adhesion assay, we find that this heterodimer mediates attachment to laminin substrata prepared in the presence of Ca2+. Interestingly, neural crest cells bind to laminin-Ca2+ substrata in the presence or absence of divalent cations in the cell attachment medium. In contrast, the attachment of neural crest cells to laminin substrata prepared in the presence of EDTA, heparin, Mg2+, or Mn2+ requires divalent cations. Interactions with these laminin substrata are mediated by a different integrin heterodimer, since antibodies against beta 1 but not alpha 1 integrins inhibit neural crest cell attachment. Thus, the type of laminin substratum appears to dictate the choice of laminin receptor used by neural crest cells. The laminin conformation is determined by the ratio of laminin to Ca2+, though incorporation of heparin during substratum polymerization alters the conformation even in the presence of Ca2+. Once polymerized, the substratum appears stable, not being altered by soaking in either EDTA or divalent cations. Our findings demonstrate: (a) that the alpha 1 beta 1 integrin can bind to some forms of laminin in the absence of soluble divalent cations; (b) that substratum preparation conditions alter the conformation of laminin such that plating laminin in the presence of Ca2+ and/or heparin modulates its configuration; and (c) that neural crest cells utilize different integrins to recognize different laminin conformations.

3T3 cell surface galactosyltransferase is a calcium-dependent adhesion molecule for collagen type IV

Cell surface galactosyltransferase (GalTase) has been previously shown to mediate cell spreading or migration on laminin matrices. This work demonstrates that 3T3 cell surface GalTase also mediates cell attachment to collagen type IV. Attachment to collagen type IV was blocked by perturbations of GalTase or substrate pregalactosylation on cells possessing only calcium-dependent mechanisms of adhesion. Cells with both calcium-dependent and calcium-independent systems were not affected by GalTase perturbation. Collagen type IV was shown to possess GalTase substrates since matrices could be galactosylated by both soluble enzyme and 3T3 cells.

A murine model for evaluating metastatic potential: characterization of a 90-110-kDa metastasis-binding protein

Reliable discriminatory tests to predict metastatic disease would clearly facilitate the management of cancer in the elderly. We have recently identified a 90-110-kilodalton (kDa) cell surface glycoprotein that is differentially expressed in benign and malignant murine adrenal carcinoma cells. In view of the proteins highly glycosylated nature, we have tested its ability to bind to a panel of agarose-bound lectins. Wheat germ agglutinin (WGA), a lectin specific for terminal sialic acid and N-acetylglucosamine (G1cNAc), had a strong affinity for the metastasis-related protein but failed to detect such a glycoprotein in nonmetastatic cells. Treatment of cells with sialidase to remove terminal sialic acids did not affect the affinity of the protein for the lectin, indicating the presence of terminal G1cNAc. We show by in situ that this metastatic binding protein (MBP) is regionally concentrated on the surface of invasive cells but absent in cells unable to invade. We postulate that MBP plays an active role in cell migration through interactions with beta-1,4 galactosytransferase and basement membrane glycoproteines.

Purification and lectin-binding properties of s-laminin, a synaptic isoform of the laminin B1 chain

The extracellular matrix (ECM) at the vertebrate neuromuscular junction is a repository of functionally important molecules, some of which can regulate the formation of synapses during regeneration. One candidate molecule is s-laminin, a 185-kDa homologue of the laminin B1 chain. Whereas several members of the laminin family are present throughout the ECM ensheathing muscle fibers, immunoreactivity for s-laminin is found selectively at synaptic sites in adult and embryonic rats, and is detectable at a time when synaptogenesis is taking place during development. We have reported previously that a rat schwannoma cell line, D6P2T, produces and releases large amounts of s-laminin in culture. We have now purified s-laminin from medium conditioned by these cells by using a simple three-step procedure. Serum-free, conditioned medium is separated by ion-exchange chromatography on DEAE-Sephacel, followed by size-exclusion chromatography on 500 HR-Sephacryl. Finally, s-laminin is dissociated from other ECM components by agarose gel electrophoresis under reducing conditions and recovered in solution by extracting slices of agarose gel. The purified preparation displays one silver-stained band that is recognized by three monoclonal antibodies known to bind to different epitopes on s-laminin. Lectin-binding studies demonstrate that s-laminin is a glycoprotein and bears many of the carbohydrate moieties present on the B1 and B2 chains of laminin. Thus, the three 185-220-kDa members of the laminin family are related in both their protein and carbohydrate domains.

Nonintegrin laminin receptors in the nervous system: evidence for lack of a relationship to P40

Laminins are extracellular matrix proteins that mediate their effects on cells through integrin and nonintegrin receptors. Two receptors of 67 and 110 kD that bind laminin with a high affinity (Kd approximately nM) have been reported in neural cells. Here, we discuss these and other nonintegrin laminin receptors that have been implicated in neural function. In addition, we report studies characterizing a 43 kD protein, (P40), immunologically related to the 67 kD laminin receptor, which may be involved in retinal development. In our studies, polyclonal antisera (anti-P-20-A) to a synthetic peptide derived from the sequence of a cDNA for a putative high-affinity laminin receptor (67 kD) detected a protein of 43 kD in immunoblots of adult rat retinas. Immunohistochemistry with this antiserum showed that the retinal immunoreactivity was predominantly localized in the ganglion cell layer of both adult chicken and rat retinas where it appeared to be intracellular. Retinal ganglion cells were shown to be immunoreactive by retrogradely labeling them from the superior colliculus with a lipophilic dye and subsequently with anti-P-20-A antisera. Consistent with the preferential localization of the P-20-A immunoreactivity in ganglion cells, there was a substantial decrease in the amounts of P40 on Western blots following optic nerve section and resulting retinal ganglion cell death. Screening of a rat (PC12 cell) cDNA library with the anti-P-20-A antiserum further confirmed the specificity of the antiserum for the rat homologue of P40. Rat P40 is 97% identical to the mouse and 87% identical to human P40 at the nucleic acid level and 98% at the protein level. Restriction mapping of the rather abundant positive clones in the library that cross-hybridized with a human cDNA probe for P40 indicated that the full-length cDNA of 1.2 kb was the major and perhaps the only cDNA in the library. In Northern blots of adult rat retina, these clones hybridized to a single 1.2-kb transcript. Electroblots of retinal homogenates probed with radioiodinated laminin demonstrated binding to a broad band at 110 kD, but none at 43 kD. Taken together these findings suggest that P40 may not be a laminin receptor and are in keeping with the hydrophilic composition of the protein, its intracellular localization, as well as other features predicted by its nucleic acid sequence.(ABSTRACT TRUNCATED AT 400 WORDS)

Mammary epithelial reorganization on extracellular matrix is mediated by cell surface galactosyltransferase

When plated at appropriate densities in serum-free media, the COMMA-D mammary epithelial cell line rapidly reorganizes into multicellular spheres on the basement membrane matrix derived from Engelbreth-Holm-Swarm murine tumor. Using time-lapse video-microscopy, four stages of reorganization were discerned during the first 24 h of culture. In the first few hours, cells attached to the matrix, elongated, migrated, and formed chains. In the next 6 h, chains of cells linked together in anastomosing networks. In the period between 8 and 18 h postplating, the networks contracted, resulting in dense cords radiating from central aggregates. During the final 6 h, the cords were drawn into the aggregates, which condensed further into spheres. The events occurring during mammary epithelial cell reorganization on the matrix were shown to be mediated by cell surface beta-1,4-galactosyltransferase (GalTase), a receptor that binds N-acetylglucosamine residues on glycosylated proteins. GalTase activity was evident at the surface of cells cultured on reconstituted matrix for 3 h but was absent from cells on glass. The protein alpha-lactalbumin (alpha-LA) inhibits the association of GalTase with N-acetylglucosamine. alpha-LA present from the beginning of culture on reconstituted matrix had no effect on cell attachment but caused concentration-dependent inhibition of the first two steps of reorganization, i.e., cell elongation and network formation, which then interfered with subsequent events. These observations were replicated using polyclonal antibodies to GalTase. Reorganization was impaired when alpha-LA was added during the first two stages but no effect was observed when it was added during the last two stages. Cells cultured on plastic, which lack surface GalTase activity, were unperturbed by incubation with alpha-LA. Thus certain events (cell elongation and network elaboration) during mammary epithelial cell reorganization on reconstituted matrix are GalTase dependent, while others (attachment, network contraction, and compaction) are not. The functional and temporal specificity of GalTase involvement indicates that GalTase mediates cell-matrix, but not cell-cell, interactions during epithelial morphogenetic events in culture.

Cell surface beta 1,4-galactosyltransferase functions during neural crest cell migration and neurulation in vivo

Mesenchymal cell migration and neurite outgrowth are mediated in part by binding of cell surface beta 1,4-galactosyltransferase (GalTase) to N-linked oligosaccharides within the E8 domain of laminin. In this study, we determined whether cell surface GalTase functions during neural crest cell migration and neural development in vivo using antibodies raised against affinity-purified chicken serum GalTase. The antibodies specifically recognized two embryonic proteins of 77 and 67 kD, both of which express GalTase activity. The antibodies also immunoprecipitated and inhibited chick embryo GalTase activity, and inhibited neural crest cell migration on laminin matrices in vitro. Anti-GalTase antibodies were microinjected into the head mesenchyme of stage 7-9 chick embryos or cranial to Henson's node of stage 6 embryos. Anti-avian GalTase IgG decreased cranial neural crest cell migration on the injected side but did not cross the embryonic midline and did not affect neural crest cell migration on the uninjected side. Anti-avian GalTase Fab crossed the embryonic midline and perturbed cranial neural crest cell migration throughout the head. Neural fold elevation and neural tube closure were also disrupted by Fab fragments. Cell surface GalTase was localized to migrating neural crest cells and to the basal surfaces of neural epithelia by indirect immunofluorescence, whereas GalTase was undetectable on neural crest cells prior to migration. These results suggest that, during early embryogenesis, cell surface GalTase participates during neural crest cell migration, perhaps by interacting with laminin, a major component of the basal lamina. Cell surface GalTase also appears to play a role in neural tube formation, possibly by mediating neural epithelial adhesion to the underlying basal lamina.

Glandular-like morphogenesis of the human submandibular tumor cell line A253 on basement membrane components

We have studied the interaction of a human tumor cell line, A253, derived from a submandibular gland carcinoma with a differentiation promoting reconstituted basement membrane extract, Matrigel. When cultured on plastic, these cells maintain a flat, cobblestone, epithelial morphology. On Matrigel, A253 cells initially form a honeycomb network of cords of cells which subsequently thickens. With time, these cords of cells become discontinuous and blunted, whereupon multilobular clusters of cells develop. These clusters possess a lumen with polarized, PAS(+) cells containing numerous desmosomes and an abundance of glycogen. Culture of the cells on laminin, the most abundant protein found in Matrigel, also induces this morphologic differentiation. Using synthetic laminin-derived peptides, the biologically active IKVAV-containing site of laminin was most active in attachment assays, as well as in inhibiting glandular-like morphogenesis when added to the media of cells cultured on Matrigel. Antibodies to the cell surface 67- and 32-kDa laminin binding proteins partially inhibited the glandular-like morphogenesis, suggesting that multiple interactions with laminin are likely required for the differentiation process. Our data demonstrate that A253 cells can undergo glandular-like morphogenesis on basement membrane and that laminin appears to be the major initiating factor.

Identification of a 110-kDa nonintegrin cell surface laminin-binding protein which recognizes an A chain neurite-promoting peptide

Laminin is a potent promoter of neurite outgrowth, and a synthetic peptide of 19 amino acids, PA22-2, from the A chain has been found to promote process formation. Using peptide affinity chromatography, we have identified a 110-kDa, cell surface ligand from both neural cells and brain which binds this sequence. This binding protein does not share immunological identity with the B1 chain of integrin, and reduction does not alter its mobility in sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Antibody to the 110-kDa protein stained cellular processes in vivo. Sequence analysis of the first 18 amino acids from the amino terminus yielded almost exact sequence identity with nucleolin, a major 110-kDa nucleolar phosphoprotein. Antibody to nucleolin, however, does not interact with the neural-derived, laminin-peptide-binding 110-kDa protein. The 110-kDa protein appears to be a ligand for a specific site on laminin.

A novel cell surface trans-sialidase of Trypanosoma cruzi generates a stage-specific epitope required for invasion of mammalian cells

When trypomastigotes of T. cruzi emerge from cells of the mammalian host, they contain little or no sialic acids on their surfaces. However, rapidly upon entering the circulation, they express a unique cell surface trans-sialidase activity. This enzyme specifically transfers alpha (2-3)-linked sialic acid from extrinsic host-derived macromolecules to parasite surface molecules, leading to the assembly of Ssp-3, a trypomastigote-specific epitope. The T. cruzi trans-sialidase does not utilize cytidine 5' monophospho-N-acetylneuraminic acid as a donor substrate, but readily transfers sialic acid from exogenously supplied alpha (2-3)-sialyllactose. Monoclonal antibodies that recognize sialic acid residues of Ssp-3 inhibit attachment of trypomastigotes to host cells, suggesting that the unusual trans-sialidase provides Ssp-3 with structural features required for target cell recognition.

Cell adhesion receptor expression during melanoma progression and metastasis

Many steps in melanoma metastasis involve cell-cell or cell-matrix adhesive interactions. The surface molecules which mediate these processes therefore play an important role in regulating melanoma dissemination and their level of expression may alter during the course of tumor progression. Human melanocyte strains and melanoma cell lines have been characterised with regard to levels of cell surface receptors of the integrin family. Increased amounts of at least two integrins, VLA-4 (alpha 4 beta 1) and VnR (alpha v beta 3), appeared to correlate with progression in this tumor, type. A novel VnR composed of an alpha v beta 1 association has been observed in one melanoma cell line and there is the possibility that heterogeneity of integrin composition could affect biological behavior of these tumors. CD44, a cell surface glycoprotein which functions as the major receptor for hyaluronate, is another molecule whose expression increases in transformed cells of the melanocytic lineage. Iterative sorting on the FACS for stable variants, of both human and murine melanomas, expressing low and high levels of CD44 established that lack of expression of this molecule correlated with impaired ability to form pulmonary tumor nodules subsequent to i.v. injection into appropriate recipient mice. These findings illustrate that an understanding of the regulation of melanoma adhesion receptors could provide insights into the process of tumor spread.