Intercellular adhesive specificity

GM2 ganglioside and pyramidal neuron dendritogenesis

GM2 ganglioside, although scarce in normal adult brain, is the predominant ganglioside accumulating in several types of lysosomal disorders, most notably Tay-Sachs disease. Pyramidal neurons of cerebral cortex in Tay-Sachs, as well as many other types of neuronal storage disorders, are known to exhibit a phenomenon believed unique to storage disorders: growth of ectopic dendrites. Recent studies have shown that a common metabolic abnormality shared by storage diseases with ectopic dendrite growth is the abnormal accumulation of GM2 ganglioside. The correlation between increased levels of GM2 and the presence of ectopic dendrites has been found in both ganglioside and nonganglioside storage disorders, the latter including sphingomyelin-cholesterol lipidosis, mucopolysaccharidosis, and alpha-mannosidosis. Quantitative HPTLC analysis has shown that increases in GM2 occur in proportion to the incidence of ectopic dendrite growth, whereas other gangliosides, including GM1, lack similar increases. Immunocytochemical studies of all nonganglioside storage diseases which exhibit ectopic dendritogenesis have revealed heightened GM2 ganglioside-immunoreactivity in the cortical pyramidal cell population, whereas nerurons in normal adult brain exhibit little or no staining for this ganglioside. Further, studies examining disease development have consistently shown that accumulation of GM2 ganglioside precedes growth of ectopic dendrites, indicating that it is not simply occurring secondary to new membrane production. These findings have prompted an examination for a similar relationship between GM2 ganglioside and dendritogenesis in cortical neurons of normal developing brain. Results show that GM2 ganglioside-immunoreactivity is consistently elevated in immature neurons during the period when they are undergoing active dendritic initiation, but this staining diminishes dramatically as the dendritic trees of these cells mature. Collectively, these studies on diseased and normal brain offer compelling evidence that GM2 ganglioside plays a pivotal role in the regulation of dendritogenesis in cortical pyramidal neurons.

Heparin-like glycosaminoglycans participate in binding of a human trophoblastic cell line (JAR) to a human uterine epithelial cell line (RL95)

In vitro studies in our laboratory have indicated that heparan sulfate proteoglycans (HSPGs) play an important role in murine embryo implantation. In order to investigate the potential function of HSPGs in human implantation, two human cell lines (RL95 and JAR) were used to model uterine epithelium and embryonal trophectoderm, respectively. A heterologous cell-cell adhesion assay was developed to determine if binding of JAR cells to RL95 cells was heparan sulfate-dependent. Labeled, single cell suspensions of JAR cells attached to confluent monolayers of RL95 cells in a dose- and time-dependent manner. Heparin-like glycosaminoglycans and JAR cell proteoglycans competitively inhibited JAR cell adhesion to RL95 cells by 50% or more. A panel of chemically modified heparins were used to demonstrate that O-sulfation and amino group substitution were critical for inhibition of cell-cell adhesion. Treatment with chlorate, an inhibitor of ATP-sulfurylase, resulted in a 56% reduction in cell-cell binding compared to untreated controls. Heparinase and chondroitinase ABC markedly inhibited JAR-RL95 binding, while chondroitinase AC had no significant effect. These observations indicated that HSPGs as well as dermatan sulfate-containing proteoglycans participated in cell-cell binding. Collectively, these results indicate that initial binding interactions between JAR and RL95 cells is mediated by cell surface glycosaminoglycans (GAGs) with heparin-like properties (i.e., heparan sulfate and dermatan sulfate). These observations are consistent with an important role for HS and heparin-like GAGs as well as their corresponding binding sites in early stages of human trophoblast-uterine epithelial cell binding.

Concentrations of fibronectin in the sera and crevicular fluid in various stages of periodontal disease

While fibronectin (FN) has previously been demonstrated to be present in gingival crevicular fluid (GCF), its quality and quantity has not been reported. Since this information is relevant for ongoing studies on the use of FN for gingival reattachment, we performed these measurements and compared plasma levels in healthy subjects, patients with gingivitis and periodontitis, and in patients undergoing maintenance therapy. Plasma and GCF samples were obtained from 4 sites in each subject using a Periotron to permit quantification of samples. FN concentrations were determined in a microELISA using hyperimmune anti-FN antibody. Purified FN served as a reference for quantification. The functional activity of each sample was assessed by examining the natural affinity of FN for gelatin. Subjects with gingivitis and those in maintenance had significantly depressed levels of plasma fibronectin. While little fibronectin could be detected in the GCF of healthy sites regardless of patient category, examination of the most diseased sites in each group revealed that the concentration of FN in the GCF was highest in health and reduced when there was gingival inflammation. In no case was GCF FN found to be biologically active.

Clinical evaluation of the use of citric acid and autologous fibronectin in periodontal surgery

This study evaluated the effects of citric acid demineralization and autologous fibronectin application in association with a modified Widman flap in the treatment of periodontitis. The study population comprised 29 patients under treatment for moderate to advanced periodontitis who reached the one-year posttherapy evaluation. After thorough scaling and root planing, a split mouth design was used in which two quadrants were treated by modified Widman flap alone, and the other two randomly assigned quadrants were treated by modified Widman flap combined with citric acid demineralization and autologous fibronectin application. Fibronectin, which had previously been isolated from the patient's own plasma, was applied with a tuberculin syringe on the citric acid demineralized root surfaces and the inner aspect of the flap. After suturing provided good flap adaptation, additional fibronectin was again applied under the flap and external pressure was applied. Patients were clinically evaluated at baseline and at one year. Statistical evaluation of the data using paired t test and Chi-square analysis indicated that both approaches, modified Widman flap alone or in combination with citric acid and fibronectin, significantly reduced probing pocket depth and increased clinical attachment. However, the changes achieved with citric acid and fibronectin were statistically greater than those obtained with the flap alone. Furthermore, the number of sites gaining 2 mm or more of clinical attachment were significantly increased. The results suggest that the use of citric acid and fibronectin holds promise in promoting reattachment after periodontal therapy.

Spheroidal aggregate culture of rat liver cells: histotypic reorganization, biomatrix deposition, and maintenance of functional activities

Liver cells isolated from newborn rats and seeded on a non-adherent plastic substratum were found to spontaneously re-aggregate and to form, within a few days, spheroidal aggregates that eventually reached a plateaued diameter of 150-175 micron. Analyses on frozen sections from these spheroids by immunofluorescence microscopy using antibodies to various cytoskeletal elements and extracellular matrix components revealed a sorting out and a histotypic reorganization of three major cell types. A first type consisted of cells that segregated out on the aggregate surface forming a monolayer cell lining; a second type was identified as hepatocytes that regrouped in small islands often defining a central lumen; and a third group of cells reorganized into bile duct-like structures. This intercellular organization in the aggregates was paralleled by the accumulation of extracellular matrix components (laminin, fibronectin, and collagen) and their deposition following a specific pattern around each cell population structure. Determinations of albumin secretion and tyrosine aminotransferase induction by dexamethasone and glucagon at various times after the initiation of the cultures revealed a maintenance of the hepatocyte-differentiated functions for at least up to 2 mo at the levels measured at 3-5 d. It is concluded that cells dispersed as single cells from newborn rat liver conserve in part the necessary information to reconstruct a proper three-dimensional cyto-architecture and that the microenvironment so generated most likely represents a basic requirement for the optimal functioning of these differentiated cells.

Dissociation and sorting out of Drosophila imaginal disc cells

Previous attempts to study sorting out of Drosophila imaginal disc cells have been hampered by an inability to thoroughly dissociate these cells and the need to use cuticular markers which require several days of in vivo culture. This study overcomes these limitations by using a new dissociation procedure and a genetic marker for undifferentiated cells, the succinate dehydrogenase8 (sdh8) mutation. Dissociated and reaggregated cells from wing and leg imaginal discs segregated or "sorted out" from one another after only 24 hr of in vivo culture. It was also found that leg cells from different body segments may sort out, but to a lesser degree than wing and leg cells. Mixtures of wing and haltere cells did not sort out, in contrast to previous reports. These results constitute the first unambiguous study of sorting out with Drosophila imaginal disc cells and indicate that dorsally situated imaginal cells share a recognition specificity which is different from that of ventral imaginal cells.

Galactosyltransferases: physical, chemical, and biological aspects

Galactosyltransferases (GTs) are one of the members of a family of enzymes called glycosyltransferases involved in the biosynthesis of complex carbohydrates. These enzymes catalyze the transfer of galactose from UDP-galactose to an acceptor (glycoprotein, glycolipid) containing terminal N-acetylglucosamine or N-acetylgalactosamine residue. GTs occur in soluble (milk, serum, effusions, etc.) and insoluble (membrane) forms. The GT activities on the outer surface of the cells have been correlated with a host of cellular interactions, including fertilization, cell migration, embryonic induction, chondrogenesis, contact inhibition of growth, cell adhesion, hemostasis, intestinal cell differentiation, and immune recognition. GTs have been purified to homogeneity using affinity chromatography. Most GTs are found active in the pH range 6 to 8 and at temperatures between 35 to 40 degrees C. Manganese is an essential co-factor for GT activity. Isoenzymes of GT have been recognized, especially in tumor tissues, malignant effusions, and sera of cancer patients using polyacrylamide gel electrophoresis in the presence and absence of SDS. Depending on the source of the enzyme, the molecular weights of GTs range between 40,000 to 80,000 daltons. Carcinoma-associated GT isoenzyme has been reported to have a higher molecular weight than the normal GT isoenzyme. Development of monoclonal antibody against the cancer-specific GT isoenzyme will provide help in the development of an immunoassay for the measurement of this isoenzyme in the sera and an aid in the radioimmunolocalization of the tumors in cancer patients.

Adhesive multiplicity in the interaction of embryonic fibroblasts and myoblasts with extracellular matrices

Neff et al. (1982, J. Cell Biol., 95:654-666) have described a monoclonal antibody, CSAT, directed against a cell surface antigen that participates in the adhesion of skeletal muscle to extracellular matrices. We used the same antibody to compare and parse the determinants of adhesion and morphology on myogenic and fibrogenic cells. We report here that the antigen is present on skeletal and cardiac muscle and on tendon, skeletal, dermal, and cardiac fibroblasts; however, its contribution to their morphology and adhesion is different. The antibody produces large alterations in the morphology and adhesion of skeletal myoblasts and tendon fibroblasts; in contrast, its effects on the cardiac fibroblasts are not readily detected. The effects of CSAT on the other cell types, i.e., dermal and skeletal fibroblasts, cardiac muscle, 5-bromodeoxyuridine-treated skeletal muscle, lie between these extremes. The effects of CSAT on the skeletal myoblasts depends on the calcium concentration in the growth medium and on the culture age. We interpret these differential responses to CSAT as revealing differences in the adhesion of the various cells to extracellular matrices. This interpretation is supported by parallel studies using quantitative assays of cell-matrix adhesion. The likely origin of these adhesive differences is the progressive display of different kinds of adhesion-related molecules and their organizational complexes on increasingly adhesive cells. The antigen to which CSAT is directed is present on all of the above cells and thus appears to be a lowest common denominator of their adhesion to extracellular matrices.

Lymphocytes express specific antigen-independent contact interaction sites upon activation

Cell contact between lymphocytes can be observed in the form of clustering in autologous cultures of rat or mouse lymph node cells. Mutual binding takes place in the absence of adherent cells and is displayed by B cells as well as by T cells, with the exception of immature (Lyt 1,2+) T cells. Contact formation is related to activation of the lymphocytes since thymidine-incorporating cells as well as plaque-forming cells are concentrated in the cluster cell fraction and the formation of clusters is greatly increased by periodate stimulation. The interaction is selective with respect to cell type (cells of other tissue origin are not bound) and differentiation (only activated lymphocytes and some of several lymphoid cell lines are able to interact). The reaction is not genetically restricted, but takes place even between different (but related) species. Neither antigen nor MHC structures are involved in contact formation. Protease treatment abolishes the ability to form clusters, but one part of the interacting receptor/acceptor structures is apparently trypsin resistant. The interaction is dependent on the presence of magnesium, whereas calcium ions have no supporting effect. Involvement of the cytoskeleton is shown by a partial inhibition of the cluster formation by cytochalasin B and azide. No indication for a lectin nature of the binding structures could be found by carbohydrate inhibition studies. The relation of this interaction mechanism to other models of physical interaction in the immune system as well as its possible function for signal exchange and local recruitment of activated cells is discussed.

Effect of concanavalin A on lymph node macrophages: stimulation of endocytic cisternae

Incubation of isolated lymph node macrophages with concanavalin A (Con A) resulted in a dense and continuous labeling of the plasmalemma and filopodia which were closely adherent to each other and the cell surface. Within a short time period (3-5 min), membranes of the closely apposed filopodia became invaginated into the cytoplasm to form numerous interconnecting cisternae. After 10 min the system of internalized membranes had migrated into the deeper cytoplasm and was closely associated with numerous actin filaments and other components of the cytoskeleton. The internalized plasmalemma remained in the cytoplasm up to 24 hr without fusing with lysosomes. Concomitant with plasmalemmal invagination and the formation of cisternae there were also changes in the Golgi apparatus. These appeared in the form of hypertrophied Golgi saccules and the accumulation of numerous vesicles around the Golgi. Treatment of isolated lymph node macrophages with either succinylated Con A, alpha-methyl-D-mannoside, or ferritin particles alone failed to produce the cisternal structures. The results suggested that the tetravalency of Con A may be responsible for the binding of adjacent Con A-labeled membranes to each other and for maintaining a crosslinking of membranes during invagination and internalization. It is suggested that this process of extensive membrane internalization represents a specialized form of endocytosis. At 24 hr after incubation with Con A, cisternal structures in close proximity to the Golgi vesicles showed signs of degradation. By 48 hr there was a breakdown of cisternal membranes with a release of Con A marker particles into large phagocytic vesicles, which also showed reaction product for acid phosphatase, suggesting a fusion with lysosomes.

Characterization of the spreading process in human T lymphocytes

Substratum-bound concanavalin A (conA) caused attachment and spreading of human T lymphocytes identified by monoclonal anti-T cell antibodies and sheep erythrocyte rosette formation. The simultaneous presence of conA in the medium increased the spreading, whereas preincubation of the cells with conA inhibited spreading. The tendency of conA to induce spreading was dependent on the concentration used, the higher the conA concentration the more pronounced was the spreading. For example, conA at 10 micrograms ml-1 triggered the formation of prominent substratum-attached filopodia with a length of 1-10 micron in 60-80% of T-enriched lymphocytes obtained from separate individuals. At the same conA dose the filopodia were, in 10-20% of the lymphocytes, accompanied by development of lamellipodia. With conA at 100 micrograms ml-1 the number of cells that underwent pronounced spreading was 55-90% in separate individuals. Observation of T-enriched cells fixed at different times after initiation of spreading induced by conA at 100 micrograms ml-1 indicated that filopodia formation represented the initial morphological alteration during the spreading process. This process thereafter proceeded with development of lamellipodia, extensive cytoplasmic spreading and flattening of the central cell mass. Quiescent and mitogen-activated cells exhibited the same sequence of changes during spreading. Spreading led to disappearance of the microvilli with a length of 0.1-0.7 micron present on lymphocytes in suspension, although some microvilli persisted over the cell center.

Induction of plasma protein secretion in a newly established human hepatoma cell line

To study the expression and the regulation of hepatocyte markers, we have undertaken to establish human hepatoma cell lines of various phenotypes. We now report the establishment of a new human hepatoma cell line, HA22T/VGH. This cell line has many of the properties of human hepatocellular carcinoma. Only 5 of 15 plasma proteins investigated were detected in the medium of a 10-day-old HA22T/VGH culture. However, when the HA22T/VGH cells and a clonal derivative, C5, were cultured in an aggregated form, all 15 plasma proteins were found in the culture medium. These results indicate that hepatoma cell lines with different phenotypes can be established, and they provide a good experimental framework to investigate differentiation of human hepatocytes.

Induction of plasma protein secretion in a newly established human hepatoma cell line

To study the expression and the regulation of hepatocyte markers, we have undertaken to establish human hepatoma cell lines of various phenotypes. We now report the establishment of a new human hepatoma cell line, HA22T/VGH. This cell line has many of the properties of human hepatocellular carcinoma. Only 5 of 15 plasma proteins investigated were detected in the medium of a 10-day-old HA22T/VGH culture. However, when the HA22T/VGH cells and a clonal derivative, C5, were cultured in an aggregated form, all 15 plasma proteins were found in the culture medium. These results indicate that hepatoma cell lines with different phenotypes can be established, and they provide a good experimental framework to investigate differentiation of human hepatocytes.

Cell surface localization and tissue distribution of a hepatocyte cell-cell adhesion glycoprotein (cell-CAM 105)

We recently identified a 105,000-dalton plasma membrane glycoprotein, denoted cell-CAM 105 (CAM, cell adhesion molecule), that is involved in intercellular adhesion of reaggregating rat hepatocytes (Ocklind, C., and B. Obrink, 1982, J. Biol. Chem., 257:6788-6795). In this communication we used a monospecific rabbit antiserum against cell-CAM 105 to localize the antigen by indirect immunofluorescence on isolated rat cells and on frozen rat tissue sections. This antiserum stained the surface of freshly isolated hepatocytes. In liver sections, however, the fluorescence seemed to be located exclusively along the bile canaliculi. In addition, cell-CAM 105 showed a very specific tissue distribution. Thus a specific fluorescence was seen only in the epithelia of the stomach, the small intestine, the large intestine, the glandular epithelium of the parotid gland, and the tubules of the kidney. No specific fluorescence was found in variety of other tissues, including cartilage, interstitial connective tissue, smooth muscle, skeletal muscle, heart muscle, eye, brain, skin, the epithelia of oesophagus, bladder, uterin mucosa, thyroid follicles, prostate gland, or collecting ducts of the kidney. In the simple epithelia of the intestine and the kidney tubules the fluorescence was confined to the apical, luminal portion. Thus, both in these epithelia and in liver, cell-CAM 105 was confined to the apical, luminal portion. Thus, both in these epithelia and in liver, cell-CAM 105 was located where the typical junctional complexes between cells are found. These findings taken together with the fact that cell-CAM 105 is involved in intercellular adhesion between hepatocytes suggest with the fac that cell-CAM 105 is involved in intercellular adhesion between hepatocytes suggest that cell-CAM 105 is a member of the junctional complexes of hepatocytes and some simple epithelia.

Redistribution of cell surface receptors induced by cell-cell contact

Cell surface lectin receptors underwent rapid redistribution after embryonic Xenopus myotomal muscle cells were manipulated into contact in culture. Soybean agglutinin (SBA) receptors became highly concentrated at the contact area and concanavalin A (Con A) and ricin receptors were depleted at the same region. The accumulation of SBA receptors was greatly reduced by the presence of SBA specific sugars in the incubating medium, by precontact binding of SBA to the surface and by lowering the temperature, but it was unaffected by prolonged treatments with metabolic inhibitors. It is culture-age dependent: older cultures showed a markedly reduced extent of accumulation, and the high accumulation resulting from contact made in younger cultures disappeared with time in culture. These findings are consistent with the notion that specific molecular interaction between the contacting surfaces results in a redistribution of preexisting rapidly diffusing surface receptors. In support of this notion, ligand-free SBA and Con A receptors were shown to be laterally mobile in the membrane, and at least a subpopulation of the SBA receptors contains physically distinct molecules from the Con A receptors. We suggest that such contact-induced redistribution of various surface components may play a role in the interaction between embryonic cells.

An assay for measuring specific adhesion of an Escherichia coli strain to tissue culture cells

Escherichia coli SS142 has been found to adhere specifically to the human epithelioid tissue culture cell line Intestine 407, but not to other tissue culture cells. This paper describes an accurate, reproducible and objective method of assessing the rate of adhesion of radiolabelled bacteria to these cellular monolayers. Adhesion was found to be linear with time for 60 min and with bacterial concentrations up to 10(9) bacteria/ml. The binding appeared to be irreversible. Adhesion was not affected by changes in the composition of the medium, its pH or ionic strength, or by the assay temperature within physiological limits, but was diminished at very high ionic strength or low temperature. It increased with increasing cell density of the monolayers. Under appropriate conditions the assay could be used for comparative determinations of the rate of adhesion of different, or differently treated bacteria.

Calcium-dependent and calcium-independent adhesive mechanisms are present during initial binding events of neural retina cells

The hypothesis that intercellular adhesion can be subdivided into two separable phenomena, an initial recognition event and a subsequent stabilization, is supported by the use of a new cell binding assay that provides a quantitative measure of intercellular binding strengths. Radioactive single cells are brought into contact with cell monolayers at 4 degrees C in sealed compartments. The compartments are inverted and a centrifugal force is then applied tending to dislodge the probe cells from the monolayers. By varying the speed of centrifugation, the force maintaining association between embryonic chick neural retina cells was determined to be on the order of 10(-5) dynes after incubation at 4 degrees C. Brief incubations at 37 degrees C resulted in significant strengthening of the intercellular bond. Using this cell binding assay, neural retina cells were shown to exhibit both a Ca++-independent and a Ca++-dependent mechanism in their initial binding to one another.

An inhibitor of animal cell growth increases cell-to-cell adhesion

The interactions of both normal and transformed cells with their environment is mediated to a large extent by the cell surface. Succinylated concanavalin A (succinyl-Con A) is a nontoxic and nonagglutinating derivative of the jack-bean lectin concanavalin A. Succinyl-Con A, presumably through an interaction with the cell surface, reversibly inhibits the growth of normal cells and restores a normal growth phenotype to transformed cells. Whereas at high cell densities migration was inhibited, it turned out that at low cell densities where cells are not in contact with each other, cell movement was not affected by succinyl-Con A. Together with some additional observations, this suggests that this lectin derivative increases cell-to-cell adhesion in culture and thereby may influence cell migration. An increase in cell-to-cell adhesion by this lectin derivative may not be brought about simply by physically linking cells together. It occurs after a lag time, possibly by inducing surface changes. The relationship between cell adhesion in culture, cell movement, and cell growth is discussed.

Intercellular recognition: quantitation of initial binding events

The hypothesis that intercellular adhesion can be subdivided into two separable phenomena--an initial recognition event and a subsequent stabilization--is supported by the use of a cell binding assay that provides a quantitative measure of intercellular binding strengths. Radioactive single cells are brought into contact with cell monolayers at 4 degrees C in sealed compartments. The compartments are inverted and a centrifugal force is then applied to dislodge the probe cells from the monolayers. By varying the speed of centrifugation, the force maintaining associations between embryonic chicken neural retina cells was determined to be on the order of 10(-5) dyne. Topographic specificities of single neural retina cells for retinal monolayers from various regions of the retina were detected with this assay and corresponded to those observed in more traditional assays at 37 degrees C. Also observed were two time- and temperature-dependent stabilization processes in which the force required for dislodgment increased. One of the stabilization processes was sensitive to dinitrophenol and was inactive at 4 degrees C; the second was still active in metabolically blocked cells. The metabolic-dependent process resulted in interactions at least 13 times as strong as the initial binding. The metabolic-independent process resulted in about a 2-fold increase in binding strength and had a temperature dependence similar to that of membrane diffusional phenomena.

Quantitative analysis of intercellular adhesive specificity in freshly explanted and cultured cells

A new method is presented for the quantitative analysis of intercellular adhesive specificity. In this assay, two cell types are mixed, one unlabeled and the other labeled with the fluorescent dye, fluorescamine [4-phenylspiro(feran-2[3H],1'-phthalan)-3,3'-dione]. The resulting aggregates are analyzed by fluorescence microscopy to determine the number of labeled and unlabeled cells per aggregate. Random (nonspecific) aggregation was characterized by a binomial distribution, and adhesive specificity was accordingly quantified by the deviation (as determined by a chi-square test) from the calculated binomial distribution. The labeling procedure was simple and rapid, and experiments with 18 different cell types showed that it did not affect cell viability, morphology, rate and extent of adhesion, plating efficiency, and the capability of myogenic cells to undergo terminal differentiation. Most important, assays with morphologically identifiable cell pairs indicated that the fluorescent label neither induced apparent nor destroyed existing adhesive specificity. The most pronounced adhesive specificities were observed with freshly explanted cells from adult tissues and also with mixtures of simian virus 40-transformed and nontransformed BALB/c 3T3 cells. A glucosamine-6-phosphate N-acetylase-deficient mutant 3T3 line (AD6), however, aggregated randomly with parental 3T3 cells. Lectin-resistant mutant Chinese hamster ovary (CHO) cells displayed marginal adhesive specificity when mixed with normal CHO cells.

Studies on cell adhesion and recognition. I. Extent and specificity of cell adhesion triggered by carbohydrate-reactive proteins (glycosidases and lectins) and by fibronectin

The extent and the specificity of the initial cell attachment induced by various proteins coated on plastic surfaces have been studied with the following results: (a) Cell adhesion on the surfaces coated with sialidase and beta-galactosidase was as strong as on concanavalin A and limulus lectin-coated surfaces and the reactions were strongly inhibited by glycosidase inhibitors or by competitive substrates. The adhesion on sialidase was inhibited by 2-deoxy-2,3-dehydro-N-acetylneuraminic acid and by polysialoganglioside (GT1b) at low concentration (0.05-0.1 mM). The cell adhesion on beta-galactosidase coat was inhibited by 1,4-D-galactonolactone and beta-methylgalactoside but not by alpha-methylgalactoside. Thus, the initiation of cell adhesion on glycosidase surfaces could be mediated through the interactions of the specific binding sites of the enzyme surface with the cell surface substrates under physiological conditions. (b) Cell adhesion on various lectins could be blocked by various competing monosaccharides at the concentrations similar to the inhibitory concentrations for binding of lectins from solution to the cells. (c) Cell adhesion on fibronectin surfaces as well as on gelatin-coated surfaces was equally inhibited by GT1b at relatively high concentrations (0.25-0.5 mM). Lower concentrations of GT1b (0.05-0.1 mM) inhibited the cell adhesion on surfaces of Limulus lectin and sialidase. It is suggested that the cell adhesion mediated by fibronectin is based on yet unknown interactions in contrast to a specific cell adhesion through glycosidases and lectins.

Studies on cell adhesion and recognition. II. The kinetics of cell adhesion and cell spreading on surfaces coated with carbohydrate-reactive proteins (glycosidases and lectins) and fibronectin

The kinetics of cell attachment and cell spreading on the coated surfaces of two classes of carbohydrate-reactive proteins, enzymes and lectins, have been compared with those on fibronectin-coated surfaces with the following results: (a) A remarkable similarity between the kinetics of cell attachment to fibronectin-coated and glycosidase-coated surfaces was found. In contrast, cell attachment kinetics induced by lectin- and galactose oxidase-coated surfaces, in general, were strikingly different from those on fibronectin and glycosidase surfaces. The distinction between fibronectin- or glycosidase- and lectin- or galactose oxidase (an enzyme with lectin-type characteristics)-coated surfaces was further supported by the finding that cytochalasin B and EDTA inhibited cell attachment to fibronectin- and glycosidase-coated surfaces but not lectin-coated surfaces. (b) Fibronectin, if labeled and added to a cell suspension, showed only low or negligible interaction with the cell surface. However, fibronectin absorbed on plastic surfaces showed a high cell-attaching activity. It is assumed that fibronectin coated on plastic surfaces may form polyvalent attachment sites in contrast to its lower valency in aqueous solution. (c) Various inhibitors of cell attachment to both fibronectin-, galactose oxidase-, and lectin-coated surfaces were effective only during the first few minutes of the adhesion assay, after which time the attached cells became insensitive to the inhibitors. It is suggested that the initial specific recognition on either lectin-type or fibronectin-type surfaces is followed by an active cell-dependent attachment process. The primary role of the adhesion surface is to stimulate the cell-dependent attachment response. (d) Cells attached on tetravalent concanavalin A (Con A) spread very rapidly and quantitatively, whereas divalent succinyl Con A and monovalent Con A were effective stimulators of cell attachment but not cell spreading. Cross-linking of succinyl Con A restored the cell spreading activity. Tetravalent Con A surfaces specifically bind soluble glycoproteins, whereas succinyl Con A has a greatly reduced ability to bind the same glycoproteins. These results suggest that cross-linking of cell surface glycoproteins by the multivalent adhesive surface may trigger the cellular reaction leading to cell spreading.

Dedifferentiated variants of a rat hepatoma: partial reversion induced by cell aggregation

Dedifferentiated rat hepatoma variant cells of clone Faof1 fail to express most of the liver-specific functions characteristic of its line or origin, H4IIEC3. When Faof1 cells are cultivated for 48 hr in the form of aggregates two cell types can be recovered from monolayer cultures established from the aggregates: the majority of cells are similar to the Faof1 parental line, but a new cell type (designated dag) that adheres only weakly to the substrate is present at a frequency of 2--12 X 10(-2). Eight dag populations and eight clones are characterized as being different from Faof1 cells by the production of serum albumin, aldolase B and in some cases activity of alcohol dehydrogenase and alanine aminotransferase. No dag cells are recovered after 18 or 24 hours of aggregation, but after 48 or 96 hrs 1--5% of the cells give rise to clones of dag cells. During aggregation cells are committed to become dag cells but their new phenotype is expressed only after 5--12 days. The fraction of dag cells in colonies that grow out from aggregates suggests that dag transformation is not a clonal event. These experiments demonstrate that a transitory change in the culture conditions of Faof1 cells can lead to a heritable modification in phenotypic expression. Since dag cells fail to express the liver-specific gluconeogenic enzymes that permit cells to grow in glucose-free medium, it is possible to select from dag populations revertants in which expression of these activities is restored. The frequency of appearance of such dag revertants is not increased by the action of EMS.

Enzymatic dissection of embryonic cell adhesive mechanisms

In this paper we describe a kinetic assay for cell adhesion which measures the formation of cell clusters. Cluster formation is dependent on both calcium and protein synthesis, two parameters essential for the formation of histotypic aggregates. We also describe modifications of the stndard method for trypsinization of tissues which result in populations of single cells that appear to bear intact and functional cell surface adhesive systems. These modifications involve the use of chymotrypsin and the inclusion of calcium during enzyme digestion of tissues with trypsin and chymotrypsin. Using the cluster formation assay and the modified tissue dissociation techniques, we demonstrate the presence of two functionally distinct adhesive systems operating among embryonic chick neural retina cells. These two systems differ in proteolytic sensitivity, protection by calcium against proteolysis, dependence on calcium for function and morphogenetic potential. Cells possessing one of these intact adhesive systems are capable of extensive morphogenetic interactions in the absence of protein synthesis.

Demonstration of fibronectin as a major extracellular protein of human gingival fibroblasts

A major extracellular protein of cultured adult human gingival fibroblasts was shown to be fibronectin by indirect immunofluorescence, lactoperoxidase catalyzed iodination and metabolic radiolabeling. Fibronectin preparations from these cells possessed the biological properties of agglutination of sheep red blood cells and promotion of cell adhesion to a collagen substrate.

The experimental production of high-level intraepidermal splits

The effects of trypsin at 37 degrees C and 4 degrees C on adhesion between keratinocytes in normal human epidermis were assessed by light and electron microscopy. The results provide evidence for the contribution of both extracellular and intracellular factors to keratinocyte adhesion and for changes in the nature of adhesion in the granular layer. Trypsinization at 4 degrees C produced a high-level intraepidermal split identical in location and intercellular route to that observed in the staphylococcal scalded skin syndrome.

The relation of temperature and lipid composition to cell adhesion

We have examined as a function of temperature the effect of changes in the composition of the fatty acid chains of membrane phospholipids on the rate of cell to cell adhesion in the neuronal cell line B103. The rate of cell to cell adhesion in this cell line is highly temperature dependent but is not influenced by changes in the fatty acid composition of the plasma membrane generated by growing the cells either in the presence of oleic acid or elaidic acid. In contrast the temperature dependence of the rate of cell to cell adhesion, measured in a monolayer adhesion assay, is highly dependent on the shear force used during the assay. A two-step model of cell to cell adhesion involving multiple adhesion ligands is presented which can be used to explain these observations.

Growth control by cell to cell contact

Control of cell growth by cell to cell contact is reviewed with particular emphasis on two systems--contact inhibition of growth observed with Swiss 3T3 cells and the mitogenic stimulation of Schwann cells by dorsal root ganglia neurites. In both cases the biological effect can be reproduced by the addition of surface membranes to the corresponding cells. In the case of contact inhibition of 3T3 cells, biological activity appears to correlate with membrane binding to the cells. An octylglucoside extract of 3T3 plasma membranes retains the biological activity (growth inhibition) of the original membranes.

A specific glycoprotein as the target site of adhesion blocking Fab in aggregating Dictyostelium cells

During the acquisition of aggregation competence a new antigen appears on the surface of Dictyostelium cells. Univalent antibody fragments (Fab) against this antigen render the cells unable to form the specific type of cell adhesion which is characteristic of aggregating cells. This membrane constituent has been purified and identified as a concanavalin A-binding glycoprotein present at about 2 X 10(5) copies per cell.