Preliminary characterization of the proteoglycans in the substrate adhesion sites of normal and virus-transformed murine cells

Characterization of a novel heparan sulfate proteoglycan found in the extracellular matrix of liver sinusoids and basement membranes

A novel heparan sulfate proteoglycan (HSPG) present in the extracellular matrix of rat liver has been partially characterized. Proteoglycans were purified from a high salt extract of total microsomes from rat liver and found to consist predominantly (approximately 90%) of HSPG. A polyclonal antiserum raised against this fraction specifically recognized HSPG by immunoprecipitation and immunoblotting. The intact, fully glycosylated HSPG migrated as a broad smear (150-300 kD) by SDS-PAGE, but after deglycosylation with trifluoromethanesulfonic acid only a single approximately 40-kD band was seen. By immunocytochemistry this HSPG was localized in the perisinusoidal space of Disse associated with irregular clumps of basement membrane-like extracellular matrix material, some of which was closely associated with the hepatocyte sinusoidal cell surface. It was also localized in biosynthetic compartments (rough ER and Golgi cisternae) of hepatocytes, suggesting that this HSPG is synthesized and deposited in the space of Disse by the hepatocyte. The anti-liver HSPG IgG also stained basement membranes of hepatic blood vessels and bile ducts as well as those of kidney and several other organs (heart, pancreas, and intestine). An antibody that recognizes the basement membrane HSPG found in the rat glomerular basement membrane did not precipitate the 150-300-kD rat liver HSPG. We conclude that the liver sinusoidal space of Disse contains a novel population of HSPG that differs in its overall size, its distribution and in the size of its core protein from other HSPG (i.e., membrane-intercalated HSPG) previously described in rat liver. It also differs in its core protein size from HSPG purified from other extracellular matrix sources. This population of HSPG appears to be a member of the basement membrane HSPG family.

Effects of glycosaminoglycans and extracellular matrix components on metastatic rat rhabdomyosarcoma tumor and myoblast cell proliferation

Experiments were performed to determine the relative effects of glycosaminoglycans and extracellular matrix components alone or in association with various substrates, including extracellular matrix, on the proliferation of rat rhabdomyosarcoma (RMS) cell lines of different metastatic potential and nontumorigenic rat myoblast L6 cells. The assays used various substrates: tissue culture plastic, type I and IV collagen, fibronectin, laminin and extracellular matrix deposited by corneal endothelial cells. In control experiments, tumor cells grew faster on fibronectin and extracellular matrix than on the other substrates, and their proliferation rate was decreased slightly by laminin. Collagens were growth-inhibitory only for the highly metastatic line. The proliferation rate of L6 myoblasts was not greatly affected by the different substrates. The addition of exogenous glycosaminoglycans to the culture medium modified cell proliferation on the various substrates. Heparin inhibited the growth of all the cell lines tested, independent of the substrate. When cultured on laminin substrate the proliferation rates of the cell lines were depressed by addition of heparan sulfate to the medium, and this effect was more pronounced in the metastatic RMS lines. Chondroitin sulfate and dermatan sulfate enhanced the growth rates of the tumorigenic cells when cultured on collagen type I surfaces. Hydrocortisone, which induces myogenic differentiation, decreased the cell proliferation rates of all the cell lines tested and intensified the inhibitory effects of heparin when added simultaneously to the culture medium. The results showed that glycosaminoglycans and other matrix components can affect the proliferation rates of rhabdomyosarcoma cell lines.

Proteoglycan synthesis by normal and neoplastic human transitional epithelial cells

Metabolically 35S-labeled proteoglycans were isolated from cell-associated matrices and media of confluent cultures of human normal transitional epithelial cells and HCV-29T transitional carcinoma cells. On Sepharose CL-4B columns, the cell-associated proteoglycans synthesized from both cell types separated into three identical size classes, termed CI, CII, and CIII. Normal epithelial cell C-fractions eluted in a 22:34:45 proportion and contained 64%, 64%, and 72% heparan sulfate, whereas corresponding HCV-29T fractions eluted in a 29:11:60 proportion, and contained 91%, 77%, and 70% heparan sulfate, respectively. Medium proteoglycans from normal cells separated into two size classes in a proportion of 6:94 and were composed of 35% and 50% heparan sulfate. HCV-29T medium contained only one size class of proteoglycans consisting of 23% heparan sulfate. The remaining percentages were accounted for by chondroitin/dermatan sulfate. On isopycnic CsCl gradients, proteoglycan fractions from normal cells had buoyant densities that were higher than the corresponding fractions from HCV-29T cells. DEAE-Sephacel chromatography showed that cell and medium associated heparan sulfate from HCV-29T cells was consistently of lower charge density (undersulfated) than that from normal epithelial cells. In contrast, the chondroitin/dermatan sulfate of HCV-29T was of a charge density similar to that of normal cells. These as well as other structural and compositional differences in the proteoglycan may account, at least in part, for the altered behavioral traits of highly invasive carcinoma cells.

Chondroitin sulfate proteoglycan synthesis and reutilization of beta-D-xyloside-initiated chondroitin/dermatan sulfate glycosaminoglycans in fetal kidney branching morphogenesis

Branching morphogenesis and chondroitin sulfate proteoglycan synthesis by explanted fetal mouse kidneys were previously shown to be inhibited by p-nitrophenyl beta-D-xylopyranoside (beta-D-xyloside) while glomerular development and heparan sulfate proteoglycan synthesis were unaffected. The metabolic fate of fetal kidney explant proteoglycans was investigated to determine whether or not recovery of proteoglycan synthesis and morphogenesis occur after exposure to beta-D-xyloside. Chondroitin sulfate proteoglycan synthesis resumed within 4 hr of removal of beta-D-xyloside and was enhanced once beta-D-xyloside-initiated chondroitin/dermatan-35SO4 glycosaminoglycans (GAGs) were released from the tissue. Radioactivity incorporated into beta-D-xyloside-initiated chondroitin/dermatan-35SO4 GAGs during labeling in the presence of beta-D-xyloside was reutilized in the synthesis of chondroitin-35SO4 proteoglycan during a 24-hr chase in nonradioactive medium without beta-D-xyloside. Further, highly purified beta-D-xyloside-initiated chondroitin/dermatan-35SO4 GAGs were taken up by kidneys more avidly than was free [35S]sulfate. These 35S-GAGs were degraded and reutilized in the synthesis of chondroitin-35SO4 proteoglycan. Ureteric bud branching resumed 48 hr after beta-D-xyloside was removed from the incubation medium. These findings support the idea that both chondroitin sulfate proteoglycan synthesis and proteoglycan processing may be involved in branching morphogenesis.

Glycosaminoglycan composition of PC12 pheochromocytoma cells: a comparison with PC12D cells, a new subline of PC12 cells

PC12D cells, a new subline of conventional PC12 cells, respond not only to nerve growth factor but also to cyclic AMP by extending their neurites. These cells are flat in shape and are similar in appearance to PC12 cells that have been treated with nerve growth factor for a few days. In both cell lines, we have characterized the glycosaminoglycans, the polysaccharide moieties of proteoglycans, which are believed to play an important role in cell adhesion and in cell morphology. Under the present culture conditions, only chondroitin sulfate was detected in the media from PC12 and PC12D cells, whereas both chondroitin sulfate and heparan sulfate were found in the cell layers. The levels of cell-associated heparan sulfate and chondroitin sulfate were about twofold and fourfold higher in PC12D cells than in PC12 cells, respectively. Compared to PC12 cells, the amounts of [35S]sulfate incorporated for 48 h into chondroitin sulfate were twofold lower but those into heparan sulfate were 35% higher in PC12D cells. The amount of chondroitin sulfate released by PC12D cells into the medium was about a half of that released by PC12 cells. The ratio of [35S]sulfate-labeled heparan sulfate to chondroitin sulfate was 6.2 in PC12D cells and 2.2 in PC12 cells. These results suggest that there may be some correlation between the increase in content of glycosaminoglycans and the change in cell morphology, which is followed by neurite outgrowth.

Distinctive populations of basement membrane and cell membrane heparan sulfate proteoglycans are produced by cultured cell lines

We have investigated the nature and distribution of different populations of heparan sulfate proteoglycans (HSPGs) in several cell lines in culture. Clone 9 hepatocytes and NRK and CHO cells were biosynthetically labeled with 35SO4, and proteoglycans were isolated by DEAE-Sephacel chromatography. Heterogeneous populations of HSPGs and chondroitin/dermatan proteoglycans (CSPGs) were found in the media and cell layer extracts of all cultures. HSPGs were further purified from the media and cell layers and separated from CSPGs by ion exchange chromatography after chondroitinase ABC digestion. In all cell types, HSPGs were found both in the cell layers (20-70% of the total) as well as the medium. When the purified HSPG fractions were further separated by octyl-Sepharose chromatography, very little HSPG in the incubation media bound to the octyl-Sepharose, whereas 40-55% of that in the cell layers bound and could be eluted with 1% Triton X-100. This hydrophobic population most likely consists of membrane-intercalated HSPGs. Basement membrane-type HSPGs were identified by immunoprecipitation as a component (30-80%) of the unbound (nonhydrophobic) HSPG fraction. By immunofluorescence, basement membrane-type HSPGs were distributed in a reticular network in Clone 9 and NRK cell monolayers; by immunoelectron microscopy, these HSPGs were localized to irregular clumps of extracellular matrix located beneath and between cells. The cells did not produce a morphologically recognizable basement membrane layer under these culture conditions. When membrane-associated HSPGs were localized by immunoelectron microscopy, they were found in a continuous layer along the cell membrane of all cell types. The results demonstrate that two antigenically distinct populations of HSPG--an extracellular matrix and a membrane-intercalated population--are found at the surface of several different cultured cells lines; these populations can be distinguished from one another by differences in their distribution in the monolayers by immunocytochemistry and can be separated by hydrophobic chromatography; and basement membrane-type HSPGs are secreted and deposited in the extracellular matrix by cultured cells even though they do not produce a bona fide basement membrane-like layer.

Isolation and characterization of basement membrane and cell proteoheparan sulphates from HR9 cells

The mouse teratocarcinoma cell line HR9 was investigated for proteoheparan sulphate production. Four species of proteoheparan sulphate molecules were isolated and purified to homogeneity. The proteoheparan sulphate isolated from the tissue-culture medium contains four heparan sulphate side-chains of 25 kDa each, and its core protein has an approximate molecular mass of 50 kDa. The proteoheparan sulphates associated with the cells were separated into three individual species: cell proteoheparan sulphate I exhibits structural characteristics which are very similar to the proteoheparan sulphate isolated from the tissue culture medium; cell proteoheparan sulphates II and III contain one heparan sulphate chain of 25 kDa and 20 kDa, and core proteins of approximately 30 kDa and 25 kDa respectively. Antisera, raised against the medium form, react specifically with basement membranes in various tissues by immunofluorescence. This staining pattern was compared to the pattern observed with an antiserum which we have obtained to a proteoheparan sulphate species isolated from the plasma membrane of bovine aortic endothelial cells. The structural and immunological data suggest that basement membrane and plasma membrane proteoheparan sulphates are different biosynthetic products and are not directly related to each other.

Conditioning of native substrates by chondroitin sulfate proteoglycans during cardiac mesenchymal cell migration

It is generally proposed that embryonic mesenchymal cells use sulfated macromolecules during in situ migration. Attempts to resolve the molecular mechanisms for this hypothesis using planar substrates have been met with limited success. In the present study, we provide evidence that the functional significance of certain sulfated macromolecules during mesenchyme migration required the presence of the endogenous migratory template; i.e., native collagen fibrils. Using three-dimensional collagen gel lattices and whole embryo culture procedures to produce metabolically labeled sulfated macromolecules in embryonic chick cardiac tissue, we show that these molecules were primarily proteoglycan (PG) in nature and that their distribution was class specific; i.e., heparan sulfate PG, the minor labeled component (15%), remained pericellular while chondroitin sulfate (CS) PG, the predominately labeled PG (85%), was associated with collagen fibrils as "trails" of 50-60-nm particles when viewed by scanning electron microscopy. Progressive "conditioning" of collagen with CS-PG inhibited the capacity of the template to support subsequent cell migration. Lastly, metabolically labeled, PG-derived CS chains were compared with respect to degree of sulfation in either the C-6 or C-4 position by chromatographic separation of chondroitinase AC digestion products. Results from temporal and regional comparisons of in situ-labeled PGs indicated a positive correlation between the presence of mesenchyme and an enrichment of disaccharide-4S relative to that from regions lacking mesenchyme (i.e., principally myocardial tissue). The suggestion of a mesenchyme-specific CS-PG was substantiated by similarly examining the PGs synthesized solely by cardiac mesenchymal cells migrating within hydrated collagen lattice in culture. These data were incorporated into a model of "substratum conditioning" which provides a molecular mechanism by which secretion of mesenchyme-specific CS-PGs not only provides for directed and sustained cell movement, but ultimately inhibits migration of the cell population as a whole.

Extracellular matrix proteoglycans and cell-substratum adhesion of human endothelial cells: the effect of methyl beta-D-xylopyranoside

The influence of methyl beta-D-xylopyranoside on human endothelial cell proteoglycans isolated from the medium and extracellular matrix was investigated. Confluent cultures of human endothelial cells incorporate significant amounts of heparan sulfate (78%), chondroitin sulfate (10%), and dermatan sulfate (12%) into the extracellular matrix. Chondroitin sulfate (35%) and dermatan sulfate (37%) were the major glycosaminoglycans present in the medium. In the presence of methyl beta-D-xylopyranoside, incorporation of labeled proteoglycans into extracellular matrix was diminished by approximately 70%. Heparan sulfate comprised the major proteoglycan present in extracellular matrix (89%) in cells grown in the presence of methyl beta-D-xylopyranoside. In contrast to the incorporation of proteoglycan into extracellular matrix, methyl beta-D-xylopyranoside stimulated the secretion of labeled glycosaminoglycan chains into the medium 2.5-fold. In the presence of methyl beta-D-xylopyranoside, secretion of chondroitin sulfate into the medium was markedly stimulated, with a slight increase in secretion of heparan sulfate. Chondroitin sulfate (62%) and heparan sulfate (34%) were the major labeled glycosaminoglycans present in medium from methyl beta-D-xylopyranoside-treated cultures. The effect of methyl beta-D-xylopyranoside on cell adhesion and detachment was investigated. Cell detachment from extracellular matrix depleted of proteoglycan was significantly faster than detachment from normal matrix. Conversely, human endothelial cells adhered faster to normal matrix than to matrix depleted of proteoglycan.

Glycosaminoglycan production in cultures of early and late passage human endothelial cells: the influence of an anionic endothelial cell growth factor and the extracellular matrix

An endothelial cell (EC) growth factor isolated from bovine brain stimulates in vitro growth of human umbilical vein endothelial cells, and permits long term serial propagation. In the presence of increasing concentrations of EC growth factor, confluent cultures of early (CPDL less than or equal to 20) and late (CPDL greater than 20) passage human endothelial cells exhibit an increased incorporation of 3H-glucosamine and Na235SO4 into the glycosaminoglycans (GAG), hyaluronic acid, chondroitin, chondroitin-4-sulfate, dermatan-4-sulfate, and chondroitin-6-sulfate. An increase in both labelled sulfated and nonsulfated GAG was observed in the cytosol, membrane, secreted and extracellular matrix fractions. In contrast, endothelial cells grown in the presence of EC growth factor contained decreased amounts of labelled heparan sulfate than cells grown without EC growth factor. Confluent cultures of early passage cells had significantly more labelled GAG but significantly less heparan sulfate than cultures of late passage cells on a per cell basis. Extracellular matrix from early passage cells contained about two- to seven-fold more labelled GAG than extracellular matrix from late passage cells, but only about half as much labelled heparan sulfate. Cell adhesion was enhanced when cells were grown in the presence of EC growth factor as compared to adhesion of cells grown without EC growth factor. Conversely, trypsin-mediated detachment of cells grown in the presence of growth factor was inhibited as compared to detachment of cells grown in medium without EC growth factor. The composition of the extracellular matrix influenced incorporation of labelled GAG into extracellular matrix. Early passage cells grown to confluence on a matrix from late passage cells incorporated significantly less labelled GAG into extracellular matrix than when grown to confluence on matrix from early passage cells. Incorporation of labelled GAG into extracellular matrix was significantly higher when late passage cells were grown on a matrix from early passage endothelial cells than when grown on matrix from late passage cells. We conclude that EC growth factor selectively stimulates incorporation of isotopic precursors into GAG in cultures of early and late passage endothelial cells but inhibits incorporation of radiolabel into heparan sulfate; early passage cells contain more GAG but less heparan sulfate than late passage cells, extracellular matrix controls the amount of GAG and heparan sulfate incorporated into matrix.(ABSTRACT TRUNCATED AT 400 WORDS)

Heparan sulfate proteoglycans are concentrated on the sinusoidal plasmalemmal domain and in intracellular organelles of hepatocytes

The distribution of cell surface heparan sulfate proteoglycans (HSPGs) was determined in rat liver by immunocytochemistry. A polyclonal antibody was raised against HSPGs purified from rat liver microsomes which specifically immunoprecipitated liver membrane HSPGs. It was shown to recognize both the heparin-releasable and membrane-intercalated form of membrane HSPGs and to recognize determinants on the core protein of these HSPGs. By immunocytochemistry membrane HSPGs were localized to hepatocytes. The distribution of HSPGs at the cell surface of the hepatocyte was restricted to the sinusoidal domain of the plasmalemma; there was little or no staining of the lateral or bile canalicular domains. Intracellularly, HSPGs were occasionally detected in cisternae of the rough endoplasmic reticulum and were regularly found in Golgi cisternae--usually distributed across the entire Golgi stack. HSPGs were also localized in some endosomes, lysosomes, and cytoplasmic vesicles of hepatocytes. We conclude that the HSPGs recognized by this antibody have a restricted distribution in rat liver: they are largely confined to the sinusoidal plasmalemmal domain and to biosynthetic and endocytic compartments of hepatocytes.

The effect of the extracellular matrix on the detachment of human endothelial cells

Human umbilical vein endothelial cells can be serially passaged by supplementing medium with a partially purified growth factor. Cell-substratum detachment of early and late passage endothelial cells was examined using trypsin, collagenase, or homocysteine. Late-passage cells detached more rapidly than early passage cells under all conditions tested. The rate of detachment was dependent upon the specific agent used. Protease-mediated detachment was most rapid, occurring over minutes, in contrast to homocysteine-induced detachment, which occurred over hours. When detached cells were collected and replated in the absence of the detaching agent, these cells reattached, spread, and continued to proliferate. No significant difference was observed in the rate of adhesion of either early or late passage cells to a gelatin matrix. When early or late-passage endothelial cells were plated and grown to confluence on a matrix synthesized by the opposite cell type, the rate of protease-mediated cell detachment resembled the cell type from which the matrix was derived. The ease of endothelial cell detachment was determined by the origin of the extracellular matrix. Examination of the extracellular matrices from early and late passage cells revealed significant differences in the amounts of glycosaminoglycans and sulfated proteins present. These studies demonstrate the importance of the endothelial cell extracellular matrix in protease-mediated cell detachment. The rate of cell detachment was controlled by the extracellular matrices are not altered by the endothelial cells.

In vitro binding of 67Ga to Ehrlich ascites tumor cells

The binding of 67Ga to Ehrlich ascites tumor cells (ETC) was studied in vitro. Acid mucopolysaccharide (AMPS) present at the cell surface of ETC was identified as heparan sulfate (HS). The extent of 67Ga binding to ETC reached a plateau (ca. 10% of the added dose) at 1-2 h after the start of incubation. The binding was higher under neutral or alkaline conditions than under acidic conditions. Heparin and heparitinase treatment both significantly decreased the extent of 67Ga binding to ETC. Mild treatment with protease, including trypsin or papain, also decreased the binding. On the contrary, the treatment with trypsin under severe conditions markedly increased the extent of 67Ga binding to ETC. These results support the hypothesis that HS plays an important role as a 67Ga receptor in the mechanism of gallium binding to ETC.

Glycosaminoglycans of human prostatic cancer

The glycosaminoglycans of normal, benign hyperplastic and cancerous prostate were studied. In both prostatic hyperplasia and cancer the chondroitin sulfate:dermatan sulfate ratio was increased. In prostatic cancer this increase correlated with both the differentiation and extent of cancer in the prostate. The percentages heparan sulfate and heparan sulfate sulfation were decreased in prostatic cancer. Hyaluronic acid increased with dedifferentiation of the cancer. Histochemically, sulfated glycosaminoglycans were concentrated in the prostatic stroma at the stromal-epithelial interface. The increased chondroitin sulfate:dermatan sulfate ratio may be a nonspecific response or requirement for epithelial growth.

Growth factors and their action in vivo and in vitro

The molecular nature and mechanism of action of several of the growth factors including epidermal growth factor, fibroblast growth factor and platelet-derived growth factor is reviewed. The ectopic production of growth factors may be important in the growth development of certain tumours. In addition, attention is directed to the importance of the extracellular matrix in controlling cell proliferation and differentiation.

Effect of thyrotropin on glycosaminoglycans synthesized by primocultured thyroid cells

The synthesis of glycosaminoglycans (GAGs) was investigated in porcine thyroid cells under the influence or not of thyrotropin. After labelling with [3H] glucosamine and [35S] SO4(2-), enriched GAG-fractions prepared from culture media, cells, and eventually substrate adhering materials, were analyzed by cellulose acetate electrophoresis combined with specific degradations. They comprised heparan sulfate and hyaluronic acid together with an unknown sulfated component labile to endo-beta-galactosidase. Whereas global labellings of newly made GAGs were not significantly modified by thyrotropin, we reproducibly observed with the hormone a substantial increase in the proportion of hyaluronic acid [3H] label and, when cells organized into follicles, of the proportion of cell-associated [3H] GAGs. This system thus offers an interesting model to study how the responsiveness to an hormone and the reorganization that follows might implicate specific glycoconjugates.

Proteoglycans from the substratum adhesion sites of MSV-transformed BALB/c 3T3 cells

Kirsten murine sarcoma virus-transformed Balb/c 3T3 cells (KiMSV) are highly tumorigenic and metastatic in the appropriate murine host, are loosely adherent to the tissue culture substratum, and can be readily detached from the substratum by ethylene glycol bis(beta-aminoethyl ether) N,N'-tetraacetic acid treatment leaving their adhesion sites as substratum-attached material. Both long-term culture-generated adhesion sites (L-SAM) of KiMSV cells and newly formed adhesion sites of reattaching cells (R-SAM) contain high levels of hyaluronate (HA) and chondroitin sulfate (CS) whereas the R-SAM of parental Balb/c 3T3 cells is enriched in heparan sulfate (HS). A sizable fraction of KiMSV L-SAM proteoglycans (PG) and a smaller fraction of R-SAM PG's aggregate into two size classes of supramolecular complexes, after extraction off the substratum with 4 M guanidine hydrochloride, as determined by chromatography on columns of Sepharose CL2B in several buffer systems. Isopycnic density gradient analyses under associative conditions of KiMSV L-SAM generated three classes of material--high-density GA1 which contained some HA but principally CS and HS; intermediate-density GA2 which contained only HA; and low-density GA3 which contained some HA and principally glycoprotein. R-SAM gradients contained no GA2 but a sizable amount of "low-density" HA in GA3. When centrifuged under dissociative conditions, most of GA1 and all of GA2 from L-SAM shifted to the top of the gradient, whereas most of the HS-PG in R-SAM remained at the bottom of dissociative gradients. Comparison of these analyses with previous analyses of Balb/c 3T3 extracts demonstrates that (a) KiMSV cells generate adhesion sites with different PG contents than 3T3 sites; (b) the PG's of KiMSV sites have a reduced potential to aggregate into high-molecular-weight complexes but do form intermediate-size complexes not apparent in material from 3T3 sites; (c) these data support the hypothesis that HA is important in detachment of cells from extracellular matrices; and (d) HS-PG's in newly formed adhesion sites of KiMSV cells are considerably different from sites which have "matured," indicating that there is metabolic activity in these sites during prolonged adherence and movement of transformed cells.

Proteoglycans in primate arteries. III. Characterization of the proteoglycans synthesized by arterial smooth muscle cells in culture

Near confluent monolayers of arterial smooth muscle cells derived from Macaca nemestrina were labeled with Na2[35S]O4 and the newly synthesized proteoglycans present in the culture medium and cell layer were extracted with either 4 M guanidine HCl (dissociative solvent) or 0.5 M guanidine HCl (associative solvent) in the presence of protease inhibitors. The proteoglycans in both compartments were further purified by cesium chloride density gradient ultracentrifugation. Two size classes of proteoglycans were observed in the medium as determined by chromatography on Sepharose CL-2B. The large population (Kav = 0.31) contained predominantly chondroitin sulfate chains with Mr = approximately 40,000. The smaller population (Kav = 0.61) contained dermatan sulfate chains of similar Mr (approximately 40,000). When tested for their ability to aggregate, only proteoglycans in the large-sized population were able to aggregate. A chondroitin sulfate containing proteoglycan with identical properties was isolated from the cell layer. In addition, the cell layer contained a dermatan sulfate component which eluted later on Sepharose CL-2B (Kav = 0.78) than the dermatan sulfate proteoglycan present in the medium. Electron microscopy of the purified proteoglycans revealed a bottlebrush structure containing a central core averaging 140 nm in length with an average of 8 to 10 side projections. The length of the side projections varied but averaged between 70 and 75 nm. Similar bottlebrush structures were observed in the intercellular matrix of the smooth muscle cell cultures after staining with Safranin 0. This culture system provides a model to investigate parameters involved in the regulation of synthesis and degradation of arterial proteoglycans.

Occurrence of fibronectin on the primary mesenchyme cell surface during migration in the sea urchin embryo

The distribution of fibronectin in situ in the sea urchin embryo was examined by using indirect immunofluorescence with an antibody raised against human plasma fibronectin. Fibronectin was detected on the surfaces of primary mesenchyme cells in the mid-mesenchyme blastula stage, when these cells are migratory. However, it was not detected on these cells at the early mesenchyme blastula or early gastrula stages. Also, it was not detected in the blastocoel nor on the basal surface of the blastular wall. The migration of the primary mesenchyme cells is therefore correlated with a stage-dependent occurrence of cell surface-associated fibronectin.

Isolation and characterization of dermatan sulphate and heparan sulphate proteoglycans from fibroblast culture

35SO42(-)- and [3H]leucine-labelled proteoglycans were isolated from the medium and cell layer of human skin fibroblast cultures. Measures were taken to avoid proteolytic modifications during isolation by adding guanidinium chloride and proteolysis inhibitors immediately after harvest. The proteoglycans were purified and fractionated by density-gradient centrifugation, followed by gel and ion-exchange chromatography. Our procedure permitted the isolation of two major proteoglycan fractions from the medium, one large, containing glucuronic acid-rich dermatan sulphate chains, and one small, containing iduronic acid-rich ones. The protein core of the latter proteoglycan had an apparent molecular weight of 47000 as determined by polyacrylamide-gel electrophoresis, whereas the protein core of the former was considerably larger. The major dermatan sulphate proteoglycan of the cell layer was similar to the large proteoglycan of the medium. Only small amounts of the iduronic acid-rich dermatan sulphate proteoglycan could be isolated from the cell layer. Instead most of the iduronic acid-rich glycans appeared as free chains. The heparan sulphate proteoglycans found in the cell culture were largely confined to the cell layer. This proteoglycan was of rather low buoyant density and seemed to contain a high proportion of protein. The major part of the heparan sulphate proteoglycan from the medium had a higher buoyant density and contained a smaller amount of protein.

Glycosaminoglycans that bind cold-insoluble globulin in cell-substratum adhesion sites of murine fibroblasts

Glycosaminoglycans (GAGs) and glycoprotein-derived glycopeptide from mouse BALB/c3T3 and simian virus 40-transformed 3T3 whole cells or their adhesion sites, which are left bound to the serum-coated tissue culture substratum after detachment of cells mediated by [ethylenebis-(oxyethylenenitrilo]tetraacetic acid (EGTA), were analyzed for specific binding to Sepharose columns derivatized with cold-insoluble globulin (CIg). CIg is the serum-contained form of fibronectin and is required for the adhesion of these fibroblasts to the substratum. Of the various GAGs present in these fractions of either cell type, only the highly N-sulfated sequences of heparan sulfate and a small subset of dermatan sulfate bind to CIg-Sepharose. There was no detectable binding of glycopeptide, undersulfated heparan sulfate, the various chondroitin species, or hyaluronate. Adhesion sites from newly attaching cells were greatly enriched in CIg-binding heparan sulfate when compared to long-term-growth adhesion sites or EGTA-detached cells. Various properties of binding were determined. The reference standard standard GAGs heparin (or heparan sulfate) and dermatan sulfate were able to displace bound radiolabeled adhesion site GAG from the column, whereas the other GAGs had no effect. CIg has been shown to be the only adhesion-promoting activity in the serum layer of this culture system. Because these fibroblast adhesion sites do not contain collagen, which could potentially mediate adhesion to the substratum-bound CIg, these data support other evidence that multivalent heparan sulfate proteoglycans mediate substratum adhesion of these cells by coordinate binding to fibronectin on the cell surface and CIg on the substratum.

Adhesion sites of murine fibroblasts on cold insoluble globulin-adsorbed substrata

The attachment and detachment behavior of three mouse fibroblast cell lines adhering to plastic tissue culture substrata coated with the serum protein cold-insoluble globulin (CIg) resembles that seen on the usual serum-coated substrata. The transformed cell line SVT2 spreads more extensively on the CIg-coated than on the serum-coated substratum, while the nontransformed Balb/c 3T3 line and concanavalin A-selected "revertant" of SVT2 are equally well spread on both substrata. In all three cases, immunofluorescence microscopy using antibodies to CIg suggests that the cells are more tightly apposed to the CIg-coated substratum than to the serum-coated substratum. Substrate-attached material (SAM), which contains cell-substratum adhesion sites and which is left after EGTA-mediated detachment of cells, is enriched for cell surface fibronectin and glycosaminoglycans (GAG). When cells are seeded onto CIg-coated substrata rather than serum-coated substrata, there is an increased deposition of GAG but a comparable deposition of cellular proteins. The protein distribution of the two types of SAM are identical as analyzed by sodium dodecyl sulfate/polyacrylamide gel electrophoresis, including fibronectin content. This indicates that substratum-bound CIg cannot functionally substitute for cell surface fibronectin in these adhesion sites. Analysis of the GAG deposited on CIg-coated substrata reveals that hyaluronate and the chondroitins are increased to a much greater extent than heparan sulfate; however, the ratio of hyaluronate to the various chondroitin species is invariant. These data provide further evidence that hyaluronate and the chondroitins are deposited in adhesion sites in well-defined stoichiometric proportions, possibly as supramolecular complexes, and that CIg may mediate adhesion of cells in the serum layer by binding to GAG-containing proteoglycans.

Role of a 16S glycoprotein complex in cellular adhesion

Myogenic cells release into their culture medium a glycoprotein complex that mediates cellular adhesion. In the absence of calcium this complex has a sedimentation value of 16S; it aggregates in the presence of calcium. The 16S material both agglutinates and increases the rate of cell-substratum adhesion of a myoblast variant and inhibits the adhesion of a nerve-like cell line to culture dishes. It is also a hemagglutinin. The 16S particle is composed of glycosaminoglycans and several proteins, including fibronectin and collagen.