Regeneration of the surface glycoproteins of a transplantable mouse tumor cell after treatment with neuraminidase

UDP-GlcNAc 2-Epimerase/ManNAc Kinase (GNE): A Master Regulator of Sialic Acid Synthesis

UDP-N-acetylglucosamine 2-epimerase/N-acetylmannosamine kinase is the key enzyme of sialic acid biosynthesis in vertebrates. It catalyzes the first two steps of the cytosolic formation of CMP-N-acetylneuraminic acid from UDP-N-acetylglucosamine. In this review we give an overview of structure, biochemistry, and genetics of the bifunctional enzyme and its complex regulation. Furthermore, we will focus on diseases related to UDP-N-acetylglucosamine 2-epimerase/N-acetylmannosamine kinase.

Establishment of transplantable porcine tumor cell lines derived from MHC-inbred miniature swine

The lack of transplantable tumors has limited assessment of graft-versus-tumor effects following hematopoietic cell transplantation in clinically relevant large-animal models. We describe the derivation and characterization of porcine tumor cell lines with initial efforts of tumor transplantation using immunocompromised mice and highly inbred sublines of Massachusetts General Hospital major histocompatibility complex (MHC)-inbred miniature swine. Autopsies were performed routinely on swine that died unexpectedly or had suspicion of malignancy based on clinical symptoms or peripheral blood analysis. Tissue samples were obtained for pathology, phenotyped by flow cytometry, and placed in culture. Based on growth, lines were selected for passage into nonobese diabetic/severe combined immunodeficient (NOD/SCID) mice and miniature swine. Porcine tumor recipients were preconditioned with total body irradiation from 0 to 500 cGy or with a 30-day course of oral cyclosporine. We identified 19 cases of hematologic tumors. Nine distinct tumor cell lines were established from 8 of these cases, including 3 derived from highly inbred sublines. In vivo tumor growth and serial transfer were observed in immunocompromised mice for one tumor cell line and in miniature swine for 1 of 2 tumor cell lines expanded for this purpose. These results suggest the possibility of developing a transplantable tumor model in this large-animal system.

Establishment of transplantable porcine tumor cell lines derived from MHC-inbred miniature swine

The lack of transplantable tumors has limited assessment of graft-versus-tumor effects following hematopoietic cell transplantation in clinically relevant large-animal models. We describe the derivation and characterization of porcine tumor cell lines with initial efforts of tumor transplantation using immunocompromised mice and highly inbred sublines of Massachusetts General Hospital major histocompatibility complex (MHC)-inbred miniature swine. Autopsies were performed routinely on swine that died unexpectedly or had suspicion of malignancy based on clinical symptoms or peripheral blood analysis. Tissue samples were obtained for pathology, phenotyped by flow cytometry, and placed in culture. Based on growth, lines were selected for passage into nonobese diabetic/severe combined immunodeficient (NOD/SCID) mice and miniature swine. Porcine tumor recipients were preconditioned with total body irradiation from 0 to 500 cGy or with a 30-day course of oral cyclosporine. We identified 19 cases of hematologic tumors. Nine distinct tumor cell lines were established from 8 of these cases, including 3 derived from highly inbred sublines. In vivo tumor growth and serial transfer were observed in immunocompromised mice for one tumor cell line and in miniature swine for 1 of 2 tumor cell lines expanded for this purpose. These results suggest the possibility of developing a transplantable tumor model in this large-animal system.

Studies of mammary carcinoma metastasis in a mouse model system. II: Lectin binding properties of cells in relation to the incidence and organ distribution of metastases

A panel of fluorescein-conjugated lectins was used to investigate the cell surface carbohydrates of cell lines isolated from a mouse mammary adenocarcinoma which differ markedly in their morphological and metastatic properties. The lectin-binding profiles of the cells showed them to express generally similar cell surface characteristics; however, two minor differences were evident. Galactose moieties recognized by peanut lectin were expressed on all highly metastatic fusiform cell types examined, but only on 50-60 per cent of the polygonal cells of limited metastatic capacity. Similarly, N-acetylgalactosamine moieties were demonstrated on fusiform cell types by soya bean lectin binding but were not expressed on intact polygonal cells. In both cases pretreatment of polygonal cells with neuraminidase allowed lectin binding comparable with that of fusiform cells suggesting that Gal and GalNAc sugars were abundantly present but masked by sialic acid residues. Using a novel technique in which tumour cells were incubated on cryostat sections of normal tissues, it was found that the cell lines exhibited different adhesion patterns which to some extent reflected their preferential sites for spontaneous metastasis and organ colonization in vivo. Thus the adherence of fusiform cells to liver was five times as great as that of polygonal cells, whereas the latter bound preferentially to lung tissue. Prior treatment of polygonal cells with neuraminidase doubled their frequency of attachment to liver sections, but had no effect on their binding to other tissues. Also, the presence of 100 mM N-acetylgalactosamine during incubation specifically inhibited the adherence of fusiform cells to liver tissues, but did not significantly influence other cell-tissue interactions. The data suggest that the expression of galactosyl or N-acetylated galactosyl groups on the fusiform cells facilitates their attachment to lectin-like receptors on liver cells and contributes to their superior capacity, compared with polygonal cells, for growth and metastasis in this organ.

Therapeutic effectiveness of neuraminidase-treated allogeneic myeloblasts as immunogen in acute myelocytic leukemia

Our chemoimmunotherapy study shows significantly longer remission and survival in acute myelocytic leukemia (AML) patients who have been immunized with neuraminidase-treated allogeneic myeloblasts as compared to patients who received chemotherapy alone or neuraminidase-treated myeloblasts plus MER. MER impairs the immunotherapeutic effectiveness of neuraminidase-treated allogeneic myeloblasts in AML patients. The in vivo and in vitro immunologic status in each arm of the protocol correlate well with the duration of remission and survival of the patient.

Inhibition of in vitro biosynthesis of N-acetylneuraminic acid by N-acyl- and N-alkyl-2-amino-2-deoxyhexoses

The biosynthesis of N-acetylneuraminic acid is markedly inhibited by 2-deoxy-2-propionamido-D-glucose (GlcNProp) and to a much lesser extent by 2-deoxy-2-propionamido-D-mannose (ManNProp), but not by 2-deoxy-2-propionamido-D-galactose and N-methylated derivatives of 2-amino-2-deoxy-D-glucose. 2-Deoxy-2-trimethylamino-D-glucose is a weak inhibitor of 2-acetamido-2-deoxy-D-mannose metabolism. When incubated in a cell-free system from rat liver, GlcNProp gives the 6-phosphate, which is converted into N-propionylneuraminic acid. Evidence is presented which shows that it is the metabolites GlcNProp-6-P and ManNProp-6-P which are the competitive inhibitors, and not GlcNProp itself.

Correlation of glycosphingolipids and sialic acid in YAC-1 lymphoma variants with their sensitivity to natural killer-cell-mediated lysis

Sialoglycoconjugates and glycosphingolipids were quantitated in a series of variants derived from the YAC-1 lymphoma, known to be highly sensitive to natural killer (NK)-cell-mediated lysis. The variants, which had widely diverging sensitivities to NK cells, were obtained by a number of methods, including selection in the presence of NK cells, antibody to H-2, or antibody to the murine leukemia-virus-induced antigen, and by fusion of sensitive cells with an NK-resistant cell line, A9HT. The sensitivities of these cells to NK-cell-mediated lysis did not correlate with their sensitivities to anti-H-2a cytotoxic T cells. While no correlation could be made between the NK-sensitivity of these variants and their total cellular sialic acid, a statistically significant inverse correlation was observed between the levels of percentage neuraminidase releasable surface sialic acid of total labelled sialyl components and sensitivity to NK cells. This correlation with cell surface sialic acid was observed with either endogenous or lymphocytic choriomeningitis virus-induced activated NK cells as effectors. Neuraminidase treatment of insensitive target cells caused a moderate increase in sensitivity but failed to render the resistant targets as sensitive as YAC-1. Analysis of glycosphingolipids among the variants revealed a strong positive correlation between the total cell neutral glycolipid with chromatographic migration of asialo-GM2 and sensitivity to endogenous or activated NK-cell-mediated lysis. Significant correlations were not found with any other neutral glycolipids. However, ganglioside homologues with chromatographic mobility of GM1, GD1a, GD1b, And GT also showed a positive correlation with both endogenous and activated NK-cell-mediated lysis. The ratio of asialo-GM2 to GM2 had a highly significant positive correlation with sensitivity. These correlative results suggest that asialo-GM2 and certain gangliosides could be involved in binding or lytic events in NK cell:target cell interactions, and that high levels of sialic acid and sialylation on the surface may inhibit and/or modify such interactions. Further studies with these YAC variants should be useful for examining the biochemical bases of target cell-effector cell interactions in the NK-system.

Lectin receptors as markers for Trypanosoma cruzi. Developmental stages and a study of the interaction of wheat germ agglutinin with sialic acid residues on epimastigote cells

Trypanosoma cruzi at various stages of maturation and differentiation have been isolated by conventional cellular fractionation procedures and characterized by cell surface markers using 30 highly purified lectins encompassing all known sugar specificities. Cell surface carbohydrates of the various T. cruzi stages were analyzed by agglutination and lectin-binding assays. Specific receptors for wheat germ agglutinin (WGA), Helix pomatia, Sophora japonica, and Bandeiraea simplicifolia lectin II were found only in culture epimastigotes, whereas peanut agglutinin (PNA) sites were present exclusively in amastigotes, those for Phaseolus vulgaris in bloodstream trypomastigotes and amastigotes, and for Wistaria floribunda hemagglutinin predominantly in culture forms of T. cruzi. The N-acetylgalactosamine (DGalNAc)-binding lectin from Bauhinia purpurea agglutinated and inhibited the movement of epimastigotes and bloodstream trypomastigotes, but it only inhibited--without agglutinating--culture trypomastigotes. Because both the agglutination and inhibition of movement were reversed by specific sugar haptens, Bauhinia purpurea sites were present in all the flagellated parasites. On the other hand, PNA sites were detectable on epimastigotes after the cells were treated with sialidase, whereas, at the same time, WGA receptors were completely removed and those for the other sialic acid-binding proteins, Aaptos papillata lectin II and Limulus polyphemus, were partially eliminated; moreover, the activity of Wistaria floribunda hemagglutinin, a DGalNAc-binding lectin, increased 4,000 times. Trypsinization and lyzozyme treatment of epimastigote cells did not significantly affect lectin agglutination or lectin binding. WGA reacted solely with sialic acid residues on epimastigote cell surface with an apparent association constant of 2 x 10(6) M-1, each epimastigote having an estimated average of 3 x 10(6) WGA sites, as determined by binding experiments and a minimum of 7.7 x 10(6) sialic acid residues, as calculated by colorimetric method after sialidase digestion. Evidences are presented that the sialyl residues are rapidly regenerated (in approximately 4 h) and that they, at least for the most part, are not adsorbed from the culture medium. The receptor for the D-mannose-binding lectins (concanavalin A [Con A] and Lens culinaris) must either be on the same carbohydrate moiety having the WGA site, or, if in a distinct molecule, both carrier molecules of Con A and WGA sites must be located close to each other in the plasma membrane of the parasite.

Photochemical damage to skin fibroblasts caused by protoporphyrin and violet light

Foreskin fibroblasts cultured in a medium containing protoporphyrin and exposed to violet light lose the capacity to proliferate. This phenomenon can be assessed on the basis of the ability of the irradiated cells to form colonies. Potentially lethal injuries can, however, be repaired during postirradiation incubation under optimal growth conditions. We investigated the photodynamically induced transformations of certain molecular targets in the irradiated cells. Biochemical analysis showed that only traces of unsaturated fatty acids were oxidized, but SH groups of both the membranes and the cytosol appeared to be very sensitive targets. Of the tryptophan content, 20% was damaged during irradiation. Recovery was observed during post-irradiation incubation. The tryptophan content and the SH groups recovered to some extent, and these results showed a good correlation with the regeneration of surviving cells.

Covalent attachment of enzyme as a membrane-label for viable eucaryotic cells

An enzyme, beta-D-galactosidase, was covalently coupled to mammalian cells by means of a bifunctional reagent. The coupling procedure did not cause appreciable loss of cell viability (less than 6%) as measured by plating efficiently and membrane integrity. After 24 h in culture, the cells exhibited an average of 2.6 x 10(4) molecules of beta-D-galactosidase per cell. Histological evidence indicated that the enzyme was localized on the cell surface and distributed uniformly among the cell population. Considerations for choosing enzyme-label include sensitivity of assay by enzymatic, immunologic and histochemical methods, and the possibility of isolating labeled membrane components by enzyme-specific affinity chromatography.

Studies on the attachment of herpes simplex virus. Effect of trypsin treatment

The adsorption of herpes simplex virus (HSV) to monolayers of trypsinized and mock-treated GMK-AH1 cells was studied by means of a microplaque technique. Plaque formation was nearly abolished for c:a 20 minutes and full sensitivity regained at 6--8 hours post trypsinization. The return of sensitivity to HSV was inhibited by cycloheximide and incubation at 4 degrees C. The sum of PFU in the supernatant and PFU successe modifying agents were without effect on the adsorption of HSV.

Ehrlich ascites tumor cell surface labeling and kinetics of glycocalyx release

Ehrlich ascites tumor cells spontaneously release cell surface material (glycocalyx) into isotonic saline medium. Exposure of these cells to tritium-labeled 4,4'-diisothiocyano-1,2-diphenylethane-2,2'-disulfonic acid (3H2DIDS) at 4 degrees C leads to preferential labeling of the cell surface coat. We have combined studies of the kinetics of 3H2DIDS-label release, the effects of enzymatic treatment, and cell electrophoretic mobility to characterize the 3H2DIDS-labeled components of the cell surface. Approximately 73% of the cell-associated radioactivity is spontaneously released from the cells after 5 h at 23 degrees C. The kinetics of release is consistent with the first-order loss of two fractions; a slow (tau 1/2 = 360 min) component representing 33% of the radioactivity and a fast (tau 1/2 = 20 min) component representing 26%. The remaining 14% of the labile binding may reflect mechanically induced surface release. Trypsin (1 microgram/ml) also removes approximately 73% of the labeled material within 30 min and converts the kinetics of release to that of a single component (tau 1/2 = 5.5 min). The specific activity (SA) of material released by trypsin immediately after labeling is 83% of the SA of the material spontaneously lost in 1 h. However, trypsinization following a 2-h period of spontaneous release yields material of reduced (43%) SA. Neither 3H2DIDS labeling nor the initial spontaneous loss of labeled material alters cell electrophoretic mobility. However, extended spontaneous release is accompanied by a significant decrease in surface charge density. Trypsinization immediately following labeling or after spontaneous release (2 h) reduces mobility by 32%. We have tentatively identified the slowly released compartment as contributing to cell surface negativity.

Effects of neuraminidase on lectin binding by wild-type and ricin-resistant strains of hamster fibroblasts

The nature of cell surface receptors for ricin on wild-type and ricin-resistant variants of baby hamster kidney fibroblasts has been studied. Neuraminidase stimulated ricin binding threefold by wild-type cells, and increased their susceptibility to ricin toxicity as measured by inhibition of [3H]leucine uptake (LD30 fell from 5.0 to 0.5 microgram/mL). Basal ricin binding by ricin-resistant variants (10-300% that of wild type) was also stimulated (2- to 17-fold) by neuraminidase in all seven clonal strains examined; susceptibility to ricin was greatly increased by neuraminidase in these variants. Neuraminidase did not affect the binding of concanavalin A by wild type or a ricin-resistant variant, but decreased the binding of wheat-germ agglutinin by 90% in both cell types. The trivial binding of peanut agglutinin by wild type and a ricin-resistant variant was markedly enhanced (14- to 22-fold) by neuraminidase. Neither collagenase (50 U/mL) nor Pronase (0.0001%) affected ricin binding by wild type or a ricin-resistant variant. These data suggest the existence of "exposed" and "cryptic" oligosaccharide receptors for ricin on the cell membrane glycoproteins of baby hamster kidney fibroblasts. The cryptic ricin receptors probably include at least the sequence D-galactosyl-beta-(1 replaced by 3)-N-acetylhexosamine substituted by sialic acid residues. Exposed and cryptic ricin receptors appear to be different and under separate genetic control.

Specific immunotherapy with neuraminidase-modified leukemic cells: experimental and clinical trials

The data presented establish the therapeutic effectiveness of immunotherapy with neuraminidase-treated allogeneic myeloblasts in combination with sustaining chemotherapy in patients with acute myelocytic leukemia. The in vivo and in vitro immunologic tests indicate normal immunocompetence in patients receiving immunotherapy versus control patients treated with chemotherapy alone. These findings correlate well with the improved duration of remission as the direct result of the immunotherapy.

Neuraminidase and tumor immunotherapy

Preliminary results of first clinical studies with the enzyme neuraminidase call attention to a new kind of cancer treatment. This promising approach to tumor immunotherapy was entered into the clinical phase as a consequence of successful experimental studies in tumor-bearing mice, rats and dogs. In this review, the presently known and essential results of experimental and clinical studies on tumor immunotherapy by means of neuraminidase are presented as well as some necessary and critical considerations in this context. Moreover, out of a broad variety of results of biochemical and biological in vitro studies, it was attempted to select the more essential knowledge which could contribute to a better understanding of the still rather unclear in vivo mode of action of the enzyme neuraminidase. In a first brief paragraph (1.0), the biochemically characteristic data of the enzyme neuraminidase is presented. In the second section (2.0), the basic knowledge about the effects of neuraminidase on cell behavior is rather amply contained. Here, on the one hand, the biophysical and biochemical alterations are mentioned, the so-called ""unmasking'' effects are reconsidered and, on the other hand, the effects on the immunologically responding cell are discussed. In a third section (3.0), the diverse findings from animal experiments using neuraminidase-treated tumor cells are confronted, whereby tumor transplantation experiments and tumor therapy experiments are dealt with separately. The last section (4.0) reports about the first clinical studies with neuraminidase-treated autologous as well as homologous tumor cells, which partly brought about rather surprising and astonishing success. On the basis of recent findings by the study group of the authors, the more prior and sometimes discrepant results of various groups are critically considered. The problems of alteration of antigenicity and of other properties of cells through splitting off membrane-bound neuraminic acid, the facts of adjuvanticity of neuraminidase itself, the relation of successful therapy to dose dependency as well as the relation of undesirable methods for tumor mass reduction to the immunological responsiveness of the tumor bearer were especially looked into.

The repair of the surface structure of animal cells

Experiments were performed to determine if animal cells in culture possess specific mechanisms to repair surface molecules damaged by enzymes. The surface membranes of a primary cell culture, chick fibroblasts, a permanent hamster cell line, BHK21/C13, and its virally transformed counterpart, C13/B4 were damaged by exposure to trypsin or to neuraminidase. Following digestion with trypsin, the incorporation of radioactive amino acids or sugars into purified surface membrane of cells was monitored. No differences were noted in rates of incorporation when control and trypsin-damaged cells were compared. Neuraminidase damage to the surface of BHK21/C13 and C13/B4 cells was evidenced by altered gel filtration profiles of surface glycopeptides, i.e., delayed elution because of reduction in size. By labelling cells with 14C-L-fucose prior to neuraminidase treatment and following the incorporation of 3H-L-fucose into cell surface glycopeptides after neuraminidase digestion, we were able to monitor the synthesis and turnover of fucose-containing glycopeptides in the same cells. Gel filtration profiles indicated that little or no desialylated glycoproteins were resialylated (repaired) by specific replacement of sialic acid. Comparing neuraminidase-digested and control cells we observed no difference in rates of 3H-L-fucose incorporation or of 14C-L-fucose loss from these cells; nor did we find differences in the rate of incorporation of isotopic glucosamine into sialic acid. Neuraminidase treatment failed to alter the rate of cell growth or the pattern of isotopic incorporation into various cell surface components. These results support the suggestion that return of sialic acid (repair) was effected by turnover which serves as a non-specific repair mechanism to replace damaged cell surface molecules (Warren and Glick '68; Warren, '69).

Isolation of retina-specific cell-aggregating factor from membranes of embryonic neural retina tissue

There is increasing evidence that developmental associations among embryonic cells are mediated by specific components of the cell surface. Earlier work has indicated that such components are extruded into the medium of primary monolayer cultures of embryonic cells, and that they represent the active constituents of the tissue-spedific cell-aggregating factors isolated fro- the supernatant medium of such cultures. We presently report that tissue-specific cell-aggregating factors can be obtained directly from embryonic tissues, and describe the isolation and partial purification of retina-spedific factor from a cell-membrane preparation derived from retina tissue of the chick embryo. Extraction of the purified membrane preparation with 1-butanol yielded an activity in the aqueous phase which resides in a protein probably a glycoprotein, with an estimated molecular weight of 50,000 in solution. This material could be obtained from retinas of embryos not older than 13 days, and only pre-13-day cells responded to its cell-aggregating activity. By these characteristics, this membrane-derived retina factor closely resembles the retina cell-aggregating glycoprotein previously purified from the supernatant medium of retina cell cultures. It is of special interest that the cell-aggregating protein is obtainable from cellular membranes during those stages of development when retina cells are most actively engaged in histological organization. Work in progress indicates that, by the procedures described herein, tissue-specific cell-aggregating factors can also be obtained from membrane preparations of other embryonic tissues.

Reappearance in vivo of neuraminidase-sensitive sialic acid in L 5222 rat leukemia cells

Cell electrophoretic data and quantitative sialic acid determination show that, 16 to 20 h after i.p. implantation of neuraminidase-treated L 5222 rat leukemia cells, the original sialic acid content at the cell periphery is reconstituted.

Possible limitation of growth in human fibroblast cultures by diffusion

Secondary cultures of human diploid fibroblasts which demonstrated density dependent inhibition of cell growth (DDI) were used to study the possible limitation of growth in cell cultures by diffusion. An oscillating platform system is described which insures constant mixing of the medium during the culturing period. Using this system, it was found that a greater number of cells in density inhibited cultures, grown to confluence for four days after initial seeding, could be stimulated to resume growth by a fresh medium change if the cultures were incubated on the oscillating platform than if the cultures were left undisturbed. This greater stimulation on the platform was probably not due to mechanical alterations on the surface of the cells due to motion of the medium as judged by TCA precipitable material released into the medium from cells prelabeled with glucosamine-3H. In spite of this greater stimulation after a single treatment with fresh medium, refeeding the cells on the platform every other day was a 12-day period did not affect the final saturation density achieved in the cultures. The results indicate that diffusion limitation of growth might occur under certain circumstances but that it cannot account entirely for the phenomenon of DDI.

Lens glycoproteins: biosynthesis in cultured epithelial cells of bovine lens

1. Radioactivity from [3H]glucosamine is rapidly incorporated into cellular fractions of lens epithelial cells cultured in vitro. The incorporated isotope appears largely in glycoproteins of the cell surface that are exposed to trypsin and are released into a soluble form by proteolysis of intact cells. Glycoproteins are also secreted by cultured cells and can be recovered in the culture fluids. Sodium dodecysulphate-polyacrylamide gell electrophoresis shows that a range of glycoproteins with apparent molecular weights from approximately 14000 to 120000 are present. The relationships of these glycoproteins to collagen and the non-collagenous glycoproteins of lens basement membranes are discussed. 2. A plasma membrane fraction obtained from non-trypsinised lens epithelial cells contains one major glycoprotein of apparent molecular weight 120000. A major non-glycosylated polypeptide of molecular weight about 38000 detectable by Bloemendal et al. (1972) in plasma membranes of differentiated lens fibre cells was not prominent in lens epithelial cell membranes. 3. Examination of lens basement membranes extracted in various ways failed to reveal major glycoproteins of low molecular weight. Higher molecular weight glycoproteins, some of them related to collagen, were present.

Externally disposed plasma membrane proteins. II. Metabolic fate of iodinated polypeptides of mouse L cells

The fate of the L-cell plasma membrane proteins labeled by enzymatic iodination was studied. The disappearance of label from growing cells exhibits a biphasic behavior, with 5-20% lost rapidly (t1/2 similar to 2 h) and 80-90% lost relatively slowly (t1/2 similar to 25-33 h). The loss is temperature dependent and serum independent, and is accompanied by the appearance of 51% (125-I)monoiodotyrosine (MIT) in the medium by 47 h. A variable amount (1-14%) of acid-insoluble label can be recovered in the medium over 47 h. Sodium dodecyl sulfate (SDS)-polyacrylamide gel labeling patterns from cells cultured up to 48 h after iodination reveal no change in the relative distribution of radioactivity, indicating similar rates of degradation for most of the labeled membrane proteins. The fate of the labeled membrane proteins was studied at various times after phagocytosis of nondigestible polystyrene particles. Iodinated L cells phagocytose sufficient 1.1 mum latex beads in 60 min to interiorize 15-30% of the total cell surface area. Electron microscope autoradiography confirmed that labeled membrane is internalized during phagocytosis. The latex-containing phagocytic vacuoles are isolated by flotation in a discontinuous sucrose gradient. 15-30% of the total incorporated label and a comparable percentage of alkaline phosphodiesterase I activity (PDase, a plasma membrane enzyme marker) are recovered in the phagocytic vacuole fraction. Lysosomal enzyme activities are found in the latex vacuole fraction, indicating formation of phagolysosomes. SDS gel analyses reveal that all of the radioactive proteins initially present on the intact cell's surface are interiorized to the same relative extent. Incorporated label and PDase activity disappear much more rapidly from the phagolysosomes than from the whole cell. In the phagolysosomal compartment, greater than 70% of the TCA-precipitable labeled proteins and all of the PDase activity are lost rapidly (t1/2 equals 1-2 h) but similar 30% of the labeled proteins in this compartment are degraded with a 17-20 h half-life. The slowly degraded label is due to specific long-lived polypeptides, of 85,000 and 8,000-15,000 daltons, which remain in the phagolysosomal membrane up to 40 h after phagocytosis.

Characterization of the external proteins of hamster fibroblasts

The results of metabolic labeling studies and enzymatic treatments followed by analysis on polyacrylamide gels show that the external proteins of hamster fibroblast cell lines, which have been identified by lactoperoxidase-catalyzed iodination, do not contain sulphated mucopolysaccharides or hyaluronic acid and are probably unrelated to collagen. Several of the iodinated species comigrate with carbohydrate-containing molecules. In particular, the major iodine-labeled polypeptide of normal fibroblasts appears to be a glycoprotein. This glycoprotein is absent or much reduced in virus-transformed cells, as detected both by iodination and by metabolic labeling. We conclude that the major iodinated polypeptide is not detected on transformed cells because it is absent rather than because it is masked. Approximate molecular weights of the external proteins are also reported.

In vivo release of glycoprotein I from the Ha subline of TA3 murine tumor into ascites fluid and serum

Previous studies have demonstrated that a unique glycoprotein can be cleaved by trypsin from the plasma membrane of the Ha, but not the St, subline of the TA(3) murine mammary adenocarcinoma. Using an automated quantitative method for measurement of trypsincleaved fragments (glycoprotein fraction I) by inhibition of Vicia graminea lectin hemagglutination, we find evidence that glycoprotein fraction I-like molecules appear in the ascites fluid and serum of the Ha-bearing, but not the St-bearing, syngeneic mice. These molecules were shown by gel filtration to be larger than the trypsincleaved glycoprotein fraction I but have a carbohydrate composition very similar to glycoprotein fraction I. It is likely that these ascites and serum glycoproteins have been released in vivo from the membranes of the viable Ha tumor cells. In view of the ability of the Ha, but not the St, cells to grow in allogeneic recipients, it is possible that these circulating membrane-derived molecules may be playing a blocking role in the immune response to the tumor.

A study on the mechanism of intercellular adhesion. Effects of neuraminidase, calcium, and trypsin on the aggregation of suspended HeLa cells

Aggregation of suspended HeLa cells is increased on removal of cell surface sialic acid. Calcium ions promote aggregation whereas magnesium ions have no effect. The calcium effect is abolished by previous treatment of the cells with neuraminidase. Trypsinization of the HeLa cells followed by thorough washing diminishes the rate of mutual cell aggregation. Subsequent incubation with neuraminidase restores the aggregation rate to the original value before trypsin treatment. Cells which had acquired a greater tendency for aggregation after removal of peripheral sialic acid lose this property when subsequently treated with trypsin. Calcium ions have no aggregative effect on trypsinized cells. In contrast to HeLa cells, aggregation of human erythrocytes was not increased after treatment with neuraminidase or on addition of calcium. The results with HeLa cells are interpreted as follows: (a) Trypsin-releasable material confers adhesiveness upon the cells. (b) The adhesive property of this material is counteracted by the presence of cell surface sialic acids. (c) Calcium ions exert their effect by attenuating the adverse effect of sialic acid.

Migration of glycoprotein from the Golgi apparatus to the surface of various cell types as shown by radioautography after labelled fucose injection into rats

A single intravenous injection of L-[(3)H]fucose, a specific glycoprotein precursor, was given to young 35-45 g rats which were sacrificed at times varying between 2 min and 30 h later. Radioautography of over 50 cell types, including renewing and nonrenewing cells, was carried out for light and electron microscope study. At early time intervals (2-10 min after injection), light microscope radioautography showed a reaction over nearly all cells investigated in the form of a discrete clump of silver grains over the Golgi region. This reaction varied in intensity and duration from cell type to cell type. Electron microscope radioautographs of duodenal villus columnar cells and kidney proximal and distal tubule cells at early time intervals revealed that the silver grains were restricted to Golgi saccules. These observations are interpreted to mean that glycoproteins undergoing synthesis incorporate fucose in the saccules of the Golgi apparatus. Since fucose occurs as a terminal residue in the carbohydrate side chains of glycoproteins, the Golgi saccules would be the site of completion of synthesis of these side chains. At later time intervals, light and electron microscope radioautography demonstrated a decrease in the reaction intensity of the Golgi region, while reactions appeared over other parts of the cells: lysosomes, secretory material, and plasma membrane. The intensity of the reactions observed over the plasma membrane varied considerably in various cell types; furthermore the reactions were restricted to the apical surface in some types, but extended to the whole surface in others. Since the plasma membrane is covered by a "cell coat" composed of the carbohydrate-rich portions of membrane glycoproteins, it is concluded that newly formed glycoproteins, after acquiring fucose in the Golgi apparatus, migrate to the cell surface to contribute to the cell coat. This contribution implies turnover of cell coat glycoproteins, at least in nonrenewing cell types, such as those of kidney tubules. In the young cells of renewing populations, e.g. those of gastro-intestinal epithelia, the new glycoproteins seem to contribute to the growth as well as the turnover of the cell coat. The differences in reactivity among different cell types and cell surfaces imply considerable differences in the turnover rates of the cell coats.

Cell-surface interactions: differential inhibition by proflavine of embryonic cell aggregation and production of specific cell-aggregating factor

Cell recognition and morphogenetic aggregation of embryonic cells into tissues are mediated by specific macromolecules in the cell surface (cell-aggregating factors). A factor specific for embryonic neural retina cells was demonstrated; its synthesis is required for histotypic reaggregation of retina cell suspensions. We show that proflavine (3,6-diaminoacridine) preferentially and reversibly suppresses production of the cell-aggregating factor and thereby inhibits normal cell reaggregation. If such proflavine-treated retina cells are exogenously supplied with the retina-specific factor, they reaggregate. The selectivity of these effects supports the postulated significance of specific cell-surface components in cell association into tissues; the results indicate that proflavine may be a useful molecular probe for studying formation of specific cell-surface components and their role in various cell interactions.

Hormone secretion by cells dissociated from rat anterior pituitaries

A new procedure has been developed for dissociating anterior pituitary tissue and producing a viable suspension of single cells. The procedure involves incubation of small tissue blocks in 1 mg/ml trypsin (15 min), followed by incubation in 8 microg/ml neuraminidase and 1 mM EDTA (15 min), followed by mechanical dispersion. Cell yields are approximately 55%, based on recovered DNA. By electron microscopy five types of secretory cells (somatotrophs, mammotrophs, thyrotrophs, gonadotrophs, and corticotrophs) plus endothelial and follicular cells can be identified and are morphologically well preserved up to 20 h after dissociation. Throughout this period, the cells incorporate linearly [(3)H]leucine into protein for up to 4 h at a rate 90% greater than hemipituitaries, and they synthesize, transport intracellularly, and release the two major pituitary secretory products, growth hormone and prolactin. Immediately after dissociation the cells' ability to respond to secretogogues (high K(+) and dibutyryl cyclic AMP) is impaired, but after a 6-12-h culture period, the cells apparently recover and discharge 24% and 52%, respectively, of their content of prelabeled growth hormone over a 3-h period in response to these two secretogogues. This represents a stimulation of 109% and 470% over that released by cells incubated in control medium. The results demonstrate that function and morphologic integrity are preserved in this cell system. Therefore it is suitable for the study of various aspects of pituitary secretion and its control.

Requirement for alpha-L-fucose on the macrophage membrane receptor for MIF

alpha-L-fucose abolishes the activity of guinea pig migration inhibitory factor (MIF) on the macrophages. Other sugars such as alpha-D-glucose, beta-D-galactose, alpha-L-rhamnose, methyl-alpha-D-mannoside, and N-acetyl-beta-D-glucosamine had no effect. Theabolition of MIF activity by alpha-L-fucose was reversible. When macrophages were incubated with alpha-L-fucosidase, a glycosidase which splits terminal alpha-L-fucose from oligosaccharides, the macrophages no longer responded to MIF. On the other hand, MIF incubated with alpha-L-fucosidase was still active. These experiments strongly suggest that alpha-L-fucose comprises an essential part of a macrophage membrane receptor for MIF.

Change in cell-surface glycoproteins of mouse embryos before implantation

The early biochemical ontogeny of the mammalian cell surface has been examined in mouse embryos. After in vitro incubation of embryos in D-[(3)H]- or D-[(14)C]glucosamine, the cell-surface glycopeptides were removed by trypsinization, digested with Pronase, and fractionated by gel filtration on Sephadex G-50; radioactivity was determined in the fractions by scintillation counting. Cochromatography of digests from the surfaces of embryos of two age groups yielded markedly different elution patterns. The labeled surface material from embryos in or near the blastocyst stage, when the outermost cells are differentiating into trophoblast, was substantially enriched, as compared with material from cleavage-stage embryos, in relatively more rapidly eluted components of presumed higher molecular weight. A similar change has previously been reported by others in cultured mammalian cell lines after viral transformation, in comparison with corresponding untransformed cells. This similarity between blastocysts and transformed cells suggests that the early biochemical differentiation of the surface, as the embryo passes into the blastocyst stage, may be responsible for the stage-specific capacity of the outermost cells to attach to the uterine wall in response to an implantation-initiating stimulus and to become invasive.

Comparative studies on the carbohydrate-containing membrane components of normal and adenosine 3':5'-cyclic monophosphate-treated Chinese hamster ovary cells

1. We investigated some of the changes in plasma-membrane composition that accompany the alteration in cell growth and morphology induced by treating Chinese-hamster ovary cells with dibutyryladenosine 3':5'-cyclic monophosphate (dibutyryl cyclic AMP). 2. A double-labelling technique was employed in which normal cells were given (14)C-labelled precursor, and those treated with dibutyryl cyclic AMP were given (3)H label. l-Leucine, d-glucosamine, and l-fucose were used to label the membranes. 3. After 3 days growth, the two populations of cells were harvested by trypsin treatment, the cells were pooled, and plasma membranes isolated. Proteins and glycoproteins of the membranes were separated by electrophoresis on sodium dodecyl sulphate-polyacrylamide gels, and the radioactive profiles for (14)C and (3)H and the staining patterns with Amido Black were compared. 4. Although certain components of the membrane from treated cells showed marked quantitative changes, there was neither major addition nor major deletions of components. 5. Complete proteolysis of the mixed membranes, of the material released from the cell surface by trypsin, and of the glycoproteins released from the cells into the medium, gave a series of radioactive glycopeptides when either fucose or glucosamine was employed as precursor. 6. After such glycopeptides were fractionated on columns of Sephadex G-50, marked differences in the elution profiles of (3)H and (14)C were noted. Dibutyryl cyclic AMP evidently causes alterations in the overall composition of the carbohydrate components of the cell surface. It was not possible to decide whether this was solely the result of the same glycoproteins being formed but in different proportions, or the result of modifications of oligosaccharide side chains on some of the glycoproteins. 7. Some of the changes were not unlike the reverse of those that accompany the transformation of fibroblasts by oncogenic viruses, and our results lend credence to the idea that the lowered amount of cyclic AMP noted in transformed cells is responsible for their altered surface properties.

Studies on the turnover of protein and glycoprotein components in rabbit kidney brush borders

The kinetics of incorporation of [(3)H]lysine and [(14)C]glucosamine into kidney brush borders were studied in vivo. The patterns of incorporation and loss of radioactivity from the brush borders were similar for both radioactively labelled precursors. Maximal labelling occurred 15-20h after injection of the precursors, and then the radioactivity declined rapidly until 50h. The radioactivity of brush borders then remained constant until 120h and thereafter declined slowly. These results are interpreted as indicating that two processes contribute to the turnover of brush-border components, pinocytosis and a slower turnover of the components of the microvilli. Studies of the distribution of radioactivity among glycoprotein components of the brush borders, separated by polyacrylamide-gel electrophoresis, indicated that the membrane components turned over in unison.

Antigen-induced stimulation of glucosamine incorporation by guinea pig peritoneal macrophages in delayed hypersensitivity

The interaction between sensitized lymphocytes and specific antigen occurring in delayed hypersensitivity causes bystander macrophages to undergo a variety of light-microscopic, ultrastructural, and biochemical changes, which are reflected in alterations in cell movement and intercellular contacts. Since such alterations involve functions of the cell periphery, we postulated that metabolic changes in this polysaccharide-rich zone would accompany the expression of delayed hypersensitivity. We here demonstrate that the incorporation of radioactive glucosamine by peritoneal macrophages into TCA-precipitable, membrane-associated material is regularly enhanced when these are cultured in the presence of specific antigen and nonadherent cells (lymphocytes) primed for delayed hypersensitivity. Lymphocytes from unsensitized animals, or from animals immunized so as to form antibody but not delayed hypersensitivity, do not stimulate such incorporation. Antigen-induced glucosamine incorporation is maximal at 2 or 3 days of culture and is not observed earlier; it may be elicited with as little as 0.1 microg/ml PPD, and affords an exceedingly reproducible and sensitive index of delayed hypersensitivity. Radioautographic studies indicate that nearly all plastic adherent cells (90% macrophages) incorporate glucosamine and that grains are concentrated in the regions of the perinuclear zone and cell membrane. Subcellular fractionation indicates that nearly 30% of counts and the highest specific activity are associated with the membrane-rich microsomal fraction; the microsomal distribution of counts increases in both absolute and relative terms when macrophages are cultured in the presence of specific antigen and sensitized lymphocytes. Taken together, these data indicate that a sizable fraction of incorporated glucosamine is localized to the vicinity of the cell periphery but lack sufficient resolution to determine whether this material is associated with the cell membrane itself or with the extramembranous cell coat. This last possibility is of particular interest since we have previously shown that macrophage cell coat material is lost or altered as a consequence of an interaction between sensitized lymphocytes and specific antigen.

Regeneration of cation-transport capacity in HeLa cell membranes after specific blockade by ouabain

The cardiac glycoside, ouabain, inhibits alkali-cation transport in HeLa cells. It binds to 0.75 x 10(6) sites per cell, and the half-time for its dissociation is 16 hr. After partial blockade by ouabain, the cell generates new ouabain-binding sites, with total restoration of transport in 10% of a cell cycle( approximately 3 hr). This recovery requires protein synthesis and appears to be a response to altered cell-electrolyte content, since growth of cells in media with low K(+) concentration enhances the titer of the transport enzyme in a fashion similar to the effect of ouabain. Totally blocked cells do not recover.