Isolation of Swiss 3T3 cell variants with altered heparan sulfate

The replica filter technique has been used to isolate variants of Swiss mouse 3T3 cells which produce heparan sulfates with altered levels of sulfation. These changes in the extent of sulfation correlate with alterations in cell morphology, in the organization of cytoskeletal elements, focal contacts, and the extracellular matrix, and in the growth regulation of cells, as expressed by saturation density. An increase in the extent of heparan sulfate sulfation occurs concomitantly with a decreased saturation density and enhanced focal contact formation. In contrast, graded decreases in sulfation correlate with graded increases in saturation density and losses of cytoskeletal and extracellular matrix organization. These graded responses appear very similar to those which have been reported for the transformation of cells with fusiform mutants of Rous sarcoma virus or the adenovirus type 2 Ela transforming gene and suggest that the morphological changes observed in the transformed cells can be controlled by cellular systems.     

The effect of beta-xylosides on heparan sulfate synthesis by SV40-transformed Swiss mouse 3T3 cells.

The medium and cell surface heparan sulfates isolated from SV40-transformed Swiss mouse 3T3 cells were examined in the presence and absence of 1.0 mM p-nitrophenyl-beta-D-xyloside. Incubation of the SV3T3 cells with this beta-xyloside resulted in: (a) a 4- to 5-fold reduction in the molecular weight distribution of medium heparan sulfate, (b) a 10-fold increase in the total synthesis of medium heparan sulfate, and (c) a small reduction in cell growth. There was little, if any, change in either the total level of synthesis or the molecular weight distribution of cell surface heparan sulfate. The covalent association of the beta-xyloside to the medium heparan sulfate was demonstrated by an analysis of the medium heparan sulfate produced by cells grown in the presence of [35S]sulfate and the fluorogenic beta-xyloside, 4-methylumbelliferyl-beta-D-xyloside. Treatment of the purified radiolabeled and fluorogenic heparan sulfate with either nitrous acid or heparitinase resulted in a decrease in the molecular weight of both radiolabeled and fluorogenic material. The data presented in this paper are discussed with respect to both the structure of heparan sulfate and the putative role of heparan sulfate in cell social behavior.     

The heparan sulfates of Swiss mouse 3T3 cells. The effect of transformation

Three major pools of heparan sulfate have been isolated from cultures of Swiss mouse 3T3 and SV40-transformed 3T3 cells: cell-surface, medium, and intracellular heparan sulfates. The cell-surface heparan sulfate is a high molecular weight proteogylcan which is partially degraded by pronase. Before pronase treatment, it has a peak molecular weight (as estimated by gel filtration) of appox. 7.2 · 10⁵ in contrast to only 2.4 · 10⁵ after pronase treatment. The medium heparan sulfate appears to be similar in structure to the cell-surface heparan sulfate, since they coelute on Bio-Gel A-15m and DEAE-cellulose, and are both proteoglycans. In contrast, the intracellular heparan sulfate has a low molecular weight (6.0 · 10³) and has little if any attached protein. Both the medium and intracellular heparan sulfate exhibit the transformation-associated change in structure reported earlier for cell-surface heparan sulfate (Underhill, C.B. and Keller, J.M. (1975) Biochem. Biophys. Res. Commun. 63, 448–454). This transformation-associated change, detected by DEAE-cellulose chromatography is not the result of changes in either molecular weight or protein core. Cellulose acetate electrophoresis of the cell-surface heparan sulfate at pH 1 suggests that the transformation-associated change in structure is due to a difference in sulfate content. Both types of heparan sulfate are produced in mixed cultures ot 3T3 and SV3T3 cells, indicating that neither serum factors in the culture medium nor secreted cell products are responsible for the transformation-associated change in heparan sulfate structure. The presented date are discussed with respect to the postulated role of heparan sulfate in cell social behavior.     

The heparan sulfates of Swiss mouse 3T3 cells. The effect of transformation.

Three major pools of heparan sulfate have been isolated from cultures of Swiss mouse 3T3 and SV40-transformed 3T3 cells: cell-surface, medium, and intracellular heparan sulfates. The cell-surface heparan sulfate is a high molecular weight proteoglycan which is partially degraded by pronase. Before pronase treatment, it has a peak molecular weight (as estimated by gel filtration) of approx. 7.2 . 10(5) in contrast to only 2.4 . 10(5) after pronase treatment. The medium heparan sulfate appears to be similar in structure to the cell-surface heparan sulfate, since they coelute on Bio-Gel A-15m and DEAE-cellulose, and are both proteoglycans. In contrast, the intracellular heparan sulfate has a low molecular weight (6.0 . 10(3)) and has little if any attached protein. Both the medium and intracellular heparan sulfate exhibit the transformation-associated change in structure reported earlier for cell-surface heparan sulfate (Underhill, C.B. and Keller, J.M. )1975) Biochem. Biophys. Res. Commun. 63, 448--454). This transformation-associated change, detected by DEAE-cellulose chromatography is not the result of changes in either molecular weight or protein core. Cellulose acetate electrophoresis of the cell-surface heparan sulfate at pH 1 suggests that the transformation-associated change in structure is due to a difference in sulfate content. Both types of heparan sulfate are produced in mixed cultures of 3T3 and SV3T3 cells, indicating that neither serum factors in the culture medium nor secreted cell products are responsible for the transformation-associated change in heparan sulfate structure. The presented data are discussed with respect to the postulated role of heparan sulfate in cell social behavior.     

Heparan sulfates of mouse cells. Analysis of parent and transformed 3T3 cell lines.

Heparan sulfate from the surface of a variety of mouse cells at different cell densities was examined by ion-exchange chromatography. The results of this analysis show that: (1) The heparan sulfate from new isolates of Swiss 3T3 cells transformed by SV40 virus (a DNA tumor virus) elutes from DEAE-cellulose at a lower ionic strength than that from the parent cell type. This finding confirms our earlier observation with an established SV40-transformed cell line (Underhill and Keller, '75) and eliminates the possibility that this change is caused by extended passage in culture. (2) For both parent and transformed 3T3 cells, the heparan sulfates from low and high density cultures were the same as judged by chromatography on DEAE-cellulose. This result demonstrates that the transformation-dependent change which we have observed is independent of cell density. (3) The heparan sulfate from Balb/c 3T3 cells transformed with Kirsten murine sarcoma virus (an RNA tumor virus) elutes from DEAE-cellulose prior to that from parent Balb/c 3T3 cells. This result extends the transformation dependent change in heparan sulfate to the Balb/c 3T3 cell line and to cells transformed with an RNA virus.     

Correlation between cell substrate attachment in vitro and cell surface heparan sulfate affinity for fibronectin and collagen

Heparan sulfate glycosaminoglycan, isolated from the cell surface of nonadhering murine myeloma cells (P3X63-Ag8653), does not bind to plasma fibronectin, but binds partially to collagen type I, as assayed by affinity chromatography with proteins immobilized on cyanogen bromide-activated Sepharose 4B. Identical results were obtained when myeloma heparan sulfate was cochromatographed, on the same fibronectin and collagen columns, with cell surface heparan sulfates collagen columns, with cell surface heparan sulfates from adhering Swiss mouse 3T3 and SV3T3 cells. These latter heparan sulfates do, however, bind to both fibronectin and collagen, as reported earlier (Stamatoglou, S.C., and J.M. Keller, 1981, Biochim. Biophys. Acta., 719:90-97). Cell adhesion assays established that hydrated collagen substrata can support myeloma cell attachment, but fibronectin cannot. Saturation of the heparan sulfate binding sites on the collagen substrata with heparan sulfate or heparin, prior to cell inoculation, abolished the ability to support cell adhesion, whereas chondroitin 4 sulfate, chondroitin 6 sulfate, and hyaluronic acid had no effect.     

Cells selected for high tumorigenicity or transformed by simian virus 40 synthesize heparan sulfate with reduced degree of sulfation

Cell lines, selected from two independent clones of an established mouse embryo cell line by their ability to grow as solid tumors in immunocompetent syngeneic hosts, were found to have the same alteration in anion exchange properties as was previously reported for simian virus 40 (SV40)-transformed subclones. One tumor cell line (219CT) and one SV40-transformed subclone (215CSC) were selected for further detailed comparison with their common parent clone (210C). Cellulose acetate electrophoresis at pH 1.0 showed that 215CSC heparan sulfate had a slight overall decrease in sulfation compared with heparan sulfate from 210C; however, no gross difference in sulfation could be detected between heparan sulfate from 219CT and 210C. Analysis of the products of deaminative cleavage of heparan sulfate by nitrous acid under conditions where cleavage occurs quantitatively at N-sulfated glucosamine residues showed that, although heparan sulfate from the three cell lines gave similar yields of O-sulfated disaccharides, both 215CSC and 219CT had only about half as many O-sulfate residues in higher molecular weight oligosaccharides compared to heparan sulfate from 210C. Enzymatic degradation of heparan sulfate with a mixture of enzymes from Flavobacterium heparinum showed that this common alteration in heparan sulfate from both 215CSC and 219CT resulted from a 30% decrease in glucosamine residues bearing 6-O-sulfate groups. As this decrease in 6-O-sulfate glucosamine residues occurs in regions of the chain containing relatively few sulfate groups, it is clear that certain sequences of charged groups present in heparan sulfate frm 210C will be found only rarely in heparan sulfate from 215CSC and 219CT. It is suggested that this will result in alterations of the interaction of heparan sulfate with other molecules in the microenvironment at the cell surface which may be important in the control of such phenomena as cell growth and adhesion.     

A transformation-dependent difference in the heparan sulfate associated with the cell surface.

Glycosaminoglycans from the surface of cultured mouse cells (3T3, SV40-3T3, 3T6) were released by trypsin digestion and separated by ion-exchange chromatography into hyaluronic acid, heparan sulfate and chondroitin sulfate. Using a double label technique, the glycosaminoglycans from 3T3 cells were compared with those from SV40-3T3 and 3T6 cells. No differences were apparent in either the hyaluronic acid or chondroitin sulfate fractions, however, the heparan sulfate from 3T3 cells was found to elute from DEAE-cellulose at a higher ionic strength than that from transformed cells. This altered behavior implies a structural difference in the cell surface heparan sulfate which appears to be dependent upon transformation.     

Composition and degree of sulfation of glycosaminoglycans from tissues of different animal species: heterogeneity and tissue specificity of heparan sulfates

The composition and degree of sulfation of glycosaminoglycans (GAG) in proteoglycans from various animal tissues were studied. It was shown that sulfated GAG contain chondroitin sulfates AC and B as well as heparan sulfates. The bulk of GAG in the majority of tissues under study is represented by 2-3 types of heparan sulfate molecules differing in the degree of sulfation. According to the degree of sulfation heparan sulfates from all tissues studied can be classified into three groups. Homologous tissues of various animal species are characterized by a similar composition and the degree of sulfation The data obtained are discussed in terms of the feasible role of proteoheparan sulfates in specific cell-to-cell interactions.     

The decreased synthesis of chondroitin sulfate-containing extracellular proteoglycans by SV40 transformed Balb/c 3T3 cells.

Balb/c 3T3 cells synthesize 5--10 times more 35SO2/4- -labeled extracellular proteoglycan per cell than do Balb/c 3T3 cells transformed by SV40 (SV3T3). The extracellular 35SO2/4- -labeled proteoglycans of the Balb/c 3T3 and SV3T3 cells differ markedly in their acid mucopolysaccharide composition. Extracellular Balb/c 3T3 proteoglycans contain about 70--80% chondroitin sulfate, most of which is chondroitin 4-sulfate, and small amounts of heparan sulfate and/or heparin. On the other hand, extracellular SV3T3 proteoglycans contain 65-75% heparan sulfate and/or heparin and less than 15% chondroitin sulfate. Analysis of extracellular 35SO2/4- -labeled proteoglycan by sodium dodecyl sulfate-polyacrylamide gel electrophoresis reveals that Balb/c 3T3 alone synthesizes a class of proteoglycans capable of migrating in a 10% separating gel. This class of proteoglycans, designated as fraction C, accounts for up to 45% of the total extracellular Balb/c 3T3 35 SO2/4- -labeled proteoglycans and contains chondroitin sulfate extracellular SV3T3 proteoglycans. The absence of this and other classes of chondroitin sulfate-containing proteoglycans can account for the 5-10-fold decreased synthesis of 35SO2/4- -labeled proteoglycans by SV3T3 cells when compared to Balb/c 3T3 cells.     

Amino acid sulfur as a source of sulfate for sulfated proteoglycans produced by Swiss mouse 3T3 cells

The uptake of sulfate by Swiss mouse 3T3 cells is blocked in the presence of 1 mM 4-isothiocyano-4'-acetamido-stilbene-2,2-disulfonic acid (SITS). In the absence of an exogenous source of sulfate, glycosaminoglycans produced by cells in the presence of the inhibitor are sulfated to the same extent as those produced by cells grown in its absence. The sulfate utilized in the absence of medium sulfate has been identified as that produced by the oxidation of the sulfur present in the amino acids cysteine and methionine. This finding indicates that, under conditions of restricted exogenous sulfate, caution is needed in the interpretation of data obtained with the use of [35S]methionine and/or [35S]cysteine as a general protein label, since both tyrosine and a variety of types of protein-linked carbohydrate chains may be modified by sulfation.     

Glycosaminoglycan biosynthesis in arterial wall. Sulfation of heparan sulfate in cell membrane of aortic media-intima

Incubation of microsomal fractions with labelled 3'-phosphoadenylyl sulfate results in incorporation of [35S]sulfate into endogenous glycosaminoglycans. Specific radioactivity observed incorporated into heparan sulfate chains is 10-fold greater than that incorporated into chondro?tin sulfate chains. This is in agreement with the results obtained for glycosylation of glycosaminoglycans in arterial wall membrane fractions. Sulfation of heparan sulfate was studied since it contains N- and O-sulfate groups in contrast with the other sulfated glycosaminoglycans which contain only O-sulfate groups. Sulfation of heparan sulfate occurs rapidly, since sulfate incorporation is detected after exposure for only 0.5 min. Heparan sulfate was identified on the basis of its resistance to hyaluronidase and chondro?tin ABC lyase, its susceptibility to heparitinase, its sensitivity to nitrous acid and the presence of glucosamine as the only hexosamine. The chemical composition of the purified heparan sulfate fractions provides evidence for the high degree of sulfation of its chains. Studies into the distribution of sulfate residues on heparan sulfate at different times of sulfation indicate that N-sulfate groups are not randomly introduced into the polymer. The relationship between the processes of N- and O-sulfation was studied. The present results demonstrate that preferential N-sulfation is obtained for incorporation of labelled precursor over a short period, the O-sulfation occurring on previously N-sulfated heparan sulfate.     

Heparan sulfate D-glucosaminyl 3-O-sulfotransferase-3A sulfates N-unsubstituted glucosamine residues

3-O-Sulfation of glucosamine by heparan sulfate D-glucosaminyl 3-O-sulfotransferase (3-OST-1) is the key modification in anticoagulant heparan sulfate synthesis. However, the heparan sulfates modified by 3-OST-2 and 3-OST-3A, isoforms of 3-OST-1, do not have anticoagulant activity, although these isoforms transfer sulfate to the 3-OH position of glucosamine residues. In this study, we characterize the substrate specificity of purified 3-OST-3A at the tetrasaccharide level. The 3-OST-3A enzyme was purified from Sf9 cells infected with recombinant baculovirus containing 3-OST-3A cDNA. Two 3-OST-3A-modified tetrasaccharides were purified from the 3-O-(35)S-sulfated heparan sulfate that was digested by heparin lyases. These tetrasaccharides were analyzed using nitrous acid and enzymatic degradation combined with matrix-assisted laser desorption/ionization-mass spectrometry. Two novel tetrasaccharides were discovered with proposed structures of DeltaUA2S-GlcNS-IdoUA2S-[(35)S]GlcNH(2)3S and DeltaUA2S-GlcNS-IdoUA2S-[3-(35)S]GlcNH(2)3S6S . The results demonstrate that 3-OST-3A sulfates N-unsubstituted glucosamine residues, and the 3-OST-3A modification sites are probably located in defined oligosaccharide sequences. Our study suggests that oligosaccharides with N-unsubstituted glucosamine are precursors for sulfation by 3-OST-3A. The intriguing linkage between N-unsubstituted glucosamine and the 3-O-sulfation by 3-OST-3A may provide a clue to the potential biological functions of 3-OST-3A-modified heparan sulfate.     

An unusual heparan sulfate isolated from lobsters (Homarus americanus)

An unusual heparan sulfate was isolated from lobsters (Homarus americanus). The polysaccharide has a composition and properties intermediate to heparin and the more common heparan sulfates. The sulfate and D-glucuronic acid content is high, while anticoagulant activity is low. The major repeating unit appears to consist of D-glucuronic acid and D-glucosamine N-O-disulfate. Some N-acetyl groups are present, the content of L-iduronic acid O-sulfate is low, and monosulfated or nonsulfated disaccharide-repeating units (very common in heparan sulfates) appear to be very rare. The data obtained again emphasize the heterogeneity of heparan sulfates and the need for adequate characterization when dealing with unusual or unexplored sources.     

The decreased synthesis of chondroitin sulfate-containing extracellular proteoglycans by SV40 transformed Balb/c 3T3 cells

Balb/c 3T3 cells synthesize 5–10 times more ³⁵SO₄^2?-labeled extracellular proteoglycan per cell than do Balb/c 3T3 cells transformed by SV40 (SV3T3). The extracellular ³⁵SO₄^2?-labeled proteoglycans of the Balb/c 3T3 and SV3T3 cells differ markedly in their acid mucopolysaccharide composition. Extracellular Balb/c 3T3 proteoglycans contain about 70–80% chondroitin sulfate, most of which is chondroitin 4-sulfate, and small amounts of heparan sulfate and/or heparin. On the other hand, extracellular SV3T3 proteoglycans contain 65–75% heparan sulfate and/or heparin and less than 15% chondroitin sulfate. Analysis of extracellular ³⁵SO₄^2?-labeled proteoglycan by sodium dodecyl sulfate-polyacrylamide gel electrophoresis reveals that Balb/c 3T3 alone synthesizes a class of proteoglycans capable of migrating in a 10% separating gel. This class of proteoglycans, designated as fraction C, accounts for up to 45% of the total extracellular Balb/c 3T3 ³⁵SO₄^2?-labeled proteoglycans and contains chondroitin sulfate exclusively. It is altogether absent in the extracellular SV3T3 proteoglycans. The absence of this and other classes of chondroitin sulfate-containing proteoglycans can account for the 5–10-fold decreased synthesis of ³⁵SO₄^2?-labeled proteoglycans by SV3T3 cells when compared to Balb/c 3T3 cells.     

Modulation of cell surface heparan sulfate structure by growth of cells in the presence of chlorate

Swiss mouse 3T3 cells, when grown in the presence of 5 mM chlorate, an inhibitor of PAPS synthesis, produce heparan sulfate glycosaminoglycan chains containing only about 8% of the sulfate normally present and which have lost the ability to bind to fibronectin. These undersulfated chains are sensitive to nitrous acid at pH 4.5, indicating that many glucosaminyl residues have unsubstituted amino groups. The iduronic acid content of the heparan sulfate produced in the presence of chlorate is reduced to less than 7% as compared to the 36% in that from untreated cells. The chlorate-treated cells do not demonstrate any alterations in their growth control. However, the spreading behavior of these cells is altered to a flat rounded morphology compared to the more typical fibroblastic appearance of the untreated cell. The sulfation of chondroitin chains is also inhibited, but at a lower chlorate concentration which does not alter growth control or the spreading ability of the cells. These data indicate that (a) 3T3 cell surface heparan sulfate proteoglycan is not involved in growth control but may be involved in cell spreading, (b) the use of chlorate should be a valuable method for the study of the biosynthesis and structure/function relationships of sulfated glycosaminoglycans, and (c) the temporal sequence of the heparan sulfate chain modification reactions predicted from results of studies with cell-free extracts also operates in the cell.     

Venous and aortic porcine endothelial cells cultured under standardized conditions synthesize heparan sulfate chains which differ in charge

The identification of a specific required carbohydrate structure for the antithrombin III binding site on heparin suggests that there may be specific structures in glycosaminoglycan chains which are necessary for other vascular functions of these carbohydrates. Determining that such differences exist requires a mechanism to isolate heparan sulfates from endothelial cells of specific vascular beds. The present report indicates that cultured venous and aortic endothelial cells synthesize heparan sulfate chains differing in charge density. There are two important conclusions from this work. (i) Endothelial cells from different blood vessels (i.e., vena cava and thoracic aorta) synthesize heparan sulfates which differ in negative charge and sulfation pattern. Specifically, aortic endothelial heparan sulfates have a higher negative charge than venous heparan sulfates. Differences are also observed in the nitrous acid degradation products of the heparan sulfates. (ii) Endothelial cells in culture retain the ability to synthesize different heparan sulfates in vitro after months of subculture under defined conditions. These results indicate that it is feasible to characterize heparan sulfates using cultured endothelial cells from a variety of vascular beds.     

Transformed mouse mammary epithelial cells synthesize undersulfated basement membrane proteoglycan

Proteoglycans deposited in the basal lamina of [14C] glucosamine-labeled normal and [3H]glucosamine-labeled transformed mouse mammary epithelial cells grown on type I-collagen gels, were extracted in 4 M guanidinium chloride and cofractionated over Sepharose CL 4B. The heparan sulfate chains carried by these proteoglycans were isolated by treatment with alkaline borohydride, protease K, chondroitinase ABC, and cetylpyridinium chloride precipitation. Heparan sulfate isolated from transformed cell cultures consistently eluted from DEAE-cellulose at lower salt concentrations and was of smaller apparent Mr when chromatographed over Sepharose CL 6B, than heparan sulfate of normal cell cultures. Experiments using doubly labeled cultures ([3H]glucosamine and [35S]sulfate) demonstrated an approximately 30% reduction in the sulfate/hexosamine ratio in heparan sulfate derived from transformed cultures. Both N- and O-sulfate were decreased. The decreased Mr and decreased sulfation of heparan sulfate upon transformation appear sufficient to explain the altered heparan sulfate/chondroitin sulfate ratios previously observed in these cells. These changes may have implications for the molecular interactions in which these proteoglycans are normally engaged during basal lamina assembly, and cause the poor basal lamina formation displayed by these transformed cells.     

Structure and affinity for antithrombin of heparan sulfate chains derived from basement membrane proteoglycans

Metabolically 35S- or 3H-labeled heparan sulfate was isolated from murine Reichert's membrane, an extraembryonic basement membrane produced by parietal endoderm cells, and from the basement membrane-producing Engelbreth-Holm-Swarm mouse tumor. The polysaccharides were subjected to structural analysis involving identification of products formed on deamination of the polysaccharides with nitrous acid. The polysaccharide from Reichert's membrane contained N- and O-sulfate groups in approximately equal proportions. It bound almost quantitatively and with high affinity to antithrombin. A high proportion of antithrombin-binding sequence was also indicated by the finding that 3-O-sulfated glucosamine residues accounted for about 10% of the total O-sulfate groups. In contrast, at least 80% of the sulfate residues in the heparan sulfate isolated from the mouse tumor were N-substituents. Only a minor proportion of this polysaccharide bound with high affinity to antithrombin, and no 3-O-sulfated glucosamine residues were detected. These results are discussed in relation to the possible functional role of heparan sulfate in basement membranes.     

Density-dependent changes in the amount of sulfated glycosaminoglycans associated with mouse 3T3 cells.

The relative amount of sulfated glycosaminoglycans associated with the cell layer of parent and SV40-transformed Swiss mouse 3T3 cells was determined from the incorporation of labeled sulfate (35SO4) into macromolecular material. In cultures of SV40-transformed cells, the glycosaminoglycan content per cell was constant over a wide range of densities. In cultures of parent 3T3 cells, the glycosaminoglycan content per cell increased directly with density, the highest values being found in contact-inhibited cultures. At high cell densities, the glycosaminoglycan content of 3T3 cells was several-fold higher than that for SV40-transformed cells. Most of the density-dependent increase in glycosaminoglycans of 3T3 cells was accounted for by chondroitin sulfate (dermatan sulfate) which was over 6-fold higher in confluent cultures than in low density cultures.