Sulfated glycoproteins and extracellular matrix of cultured human pulmonary endothelial cells

Extracellular matrix heparan sulfate proteoglycans modulate the mitogenic capacity of acidic fibroblast growth factor

Confluent cultures of human endothelial cells deposit into extracellular matrix (ECM) distinct heparan sulfate proteoglycans (HSPG) which modulate acidic fibroblast growth factor's (aFGF) ability to stimulate human endothelial cell mitogenic capacity. Extracellular matrix 35S-HSPG were isolated from cultures metabolically labelled with Na235SO4 by DEAE-Sepharose, Sepharose CL-4B, and aFGF-Affi-Gel 15 column chromatography and identified by resistance to chondroitinase ABC and sensitivity to nitrous acid. Fifty to sixty percent of the 35S-HSPG deposited into ECM do not bind aFGF. The bound 35S-HSGP (40-50% of the total counts applied) eluted from the aFGF-Affi-Gel column after the addition of buffer containing 2 M NaCl. aFGF-binding and aFGF-nonbinding 35S-HSPG were individually pooled and further purified by Sepharose CL-4B column chromatography. 35S-HSPG which bind aFGF, designated HSPGP, were 100-fold superior to heparin in augmenting the mitogenic efficacy of aFGF in sparse proliferating cultures. In contrast, however, 35S-HSPG, which did not bind aFGF, designated HSPG1, inhibited aFGF-stimulated proliferation in both sparse and subconfluent endothelial cell cultures. The majority of the biological activity of both aFGF-potentiating HSPGP and aFGF-inhibitory HSPG1 was contained in the glycosaminoglycan chains released by alkaline borohydride treatment of intact HSPGP or HSPG1, respectively. 3H-Core protein derived from HSPGP or HSPG1 contained only minor biological activity. The ability of heparitinase or heparinase (Flavobacterium heparinum) to abolish biological activity differed, depending upon the HSPG tested, also suggested that these are two distinct HSPGs.

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)

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.

Enzymatic sulfation of N-glycosidically linked oligosaccharides by endothelial cell membranes

Homogenates of human vascular endothelial cells catalyze the transfer of 35SO4 from 3'-phosphoadenosine 5'-phospho[35S]sulfate into macromolecular endogenous acceptors with properties of both glycoproteins and glycosaminoglycans. Analysis of the 35S-glycoprotein products by both DEAE-cellulose chromatography and sodium dodecyl sulfate-polyacrylamide gel electrophoresis indicates that these 35S-glycoproteins correspond to the major sulfated glycoproteins observed when endothelial cell cultures were labeled with 35SO4 [A. Heifetz, C. Watson, A. R. Johnson, and M. K. Roberts (1982) J. Biol. Chem. 257, 13581-13586]. The pH optimum of the glycoprotein sulfotransferase is 7.0-7.5, which is distinctly different than that of endothelial glycosaminoglycan sulfotransferase(s), whose pH optimum is 6.0. The 35S-glycoprotein products were characterized as sialated, triantenary-branched, N-linked 35SO4-oligosaccharides containing an endo-beta-N-acetylglucosaminidase D-sensitive site. The site of sulfation was characterized as the GlcNAc residue on the reducing end of the N-linked oligosaccharide. Thus, these sulfotransferases in a cell-free homogenate appear to preferentially add sulfate moieties to a specific class of glycoprotein acceptors at a specific site on sialated oligosaccharides.

Glycosaminoglycan: cell interactions; their role in lipoprotein lipase secretion from isolated cardiac muscle cells

When cardiac muscle cells from mature rats were incubated in vitro in the presence of heparin (8.7 nmole ml-1) lipoprotein lipase activity appeared in the incubation medium. The intracellular activity of the enzyme remained unchanged. Other glycosaminoglycans (heparan sulphate, dermatan sulphate, keratan sulphate and chrondroitin 6-sulphate) at the same or higher concentrations were totally ineffective in producing any enzyme redistribution between cells and medium. The release seen in the presence of heparin was blocked by the presence of cycloheximide. Cycloheximide by contrast had no effect on the release observed in the presence of dexamethasone, The action of endogenous glycosaminoglycans are unlikely therefore to have a significant role to play in the movement of lipoprotein lipase in heart tissue in vivo.

Biosynthesis of cell surface sulfated glycoproteins by cultured vascular endothelial cells

Cultured vascular endothelial cells incorporate 35SO4 into a class of oligosaccharides which are N-glycosidically linked to cell-surface or extracellular proteins. This type of sulfated oligosaccharide was not synthesized by smooth muscle cell cultures and may represent sulfation of vascular tissue glycoproteins which are unique to endothelial cells. These endothelial cell 35S-labeled oligosaccharides are not released from the polypeptides under alkaline conditions that cleave O-glycosidically linked chains. The incorporation of both [3H]hexosamine and 35SO4 into these oligosaccharides is inhibited by tunicamycin, an antibiotic which inhibits protein N-glycosylation. 35S-Labeled oligosaccharides, isolated as glycopeptides, were resistant to a variety of chemical and enzymatic treatments which degraded vascular cell sulfated glycosaminoglycans but appear to contain terminal sialic acid residues. Endothelial cell sulfated oligosaccharide chains could also be distinguished from sulfated glycosaminoglycans by the apparent size and charge. Endothelial cells released or secreted 35S-labeled glycoproteins into the culture medium. These soluble 35S-labeled glycoproteins were partially purified by DEAE-cellulose chromatography and separated from the 35S-labeled proteoglycans, which are also released into the medium. The major 35S-labeled glycoproteins released from the cells had apparent molecular weights of 24 000--66 000. The cell-associated 35S-labeled glycoproteins, released with ethylenediaminetetraacetate or extracted with 0.5% octyl glucoside, were partially purified on DEAE-cellulose and had apparent molecular weights of 45 000--250 000.