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

Glycosylation of Nα-lauryl-O-(β-D-xylopyranosyl)-L-serinamide as a saccharide primer in cells

N(α)-Lauryl-O-(β-D-xylopyranosyl)-L-serinamide (Xyl-Ser-C12) was synthesized as a saccharide primer to obtain oligosaccharides of glycosaminoglycan using the glycan biosynthetic potential of mouse osteosarcoma FBJ-S1 cells and Chinese hamster ovary (CHO) cells. The glycosylated products secreted into the culture medium were collected and analyzed by liquid chromatography-mass spectrometry and glycosidase digestion. The structure of the Xyl-Ser-C12 derivatives was investigated. Several glycosaminoglycan-type oligosaccharides, such as GalNAc-(GlcA-GlcNAc)(n)-GlcA-Gal-Gal-Xyl-Ser-C12, were detected, and identified as intermediates of the biosynthesis of heparan sulfate glycosaminoglycans. Xyl-Ser-C12 exhibited greater acceptor activity for the glycosylation of glycosaminoglycan-type oligosaccharides than p-nitrophenyl-β-D-xylopyranoside.

In vivo mechanisms of vaccine-induced protection against HPV infection

Using a human papillomavirus (HPV) cervicovaginal murine challenge model, we microscopically examined the in vivo mechanisms of L1 virus-like particle (VLP) and L2 vaccine-induced inhibition of infection. In vivo HPV infection requires an initial association with the acellular basement membrane (BM) to induce conformational changes in the virion that permit its association with the keratinocyte cell surface. By passive transfer of immune serum, we determined that anti-L1 antibodies can interfere with infection at two stages. Similarly to active VLP immunization, transfer of high L1 antibody concentrations prevented BM binding. However, in the presence of low concentrations of anti-L1, virions associated with the BM, but to the epithelial cell surface was not detected. Regardless of the concentration, L2 vaccine-induced antibodies allow BM association but prevent association with the cell surface. Thus, we have revealed distinct mechanisms of vaccine-induced inhibition of virus infection in vivo.

Identification of a heparin binding site and the biological activities of the laminin alpha1 chain carboxy-terminal globular domain

The carboxy-terminal globular domain (G-domain) of the laminin alpha1 chain has been shown to promote heparin binding, cell adhesion, and neurite outgrowth. In this study, we defined the potential sequences originating from the G-domain of laminin alpha1 chain which possess these functional activities. A series of peptides were synthesized from the G-domain, termed LG peptides (LG-1 to LG-6) and were tested for their various biological activities. In the direct [3H] heparin binding assays, LG-6 (residues 2,335-2,348: KDFLSIELVRGRVK) mediated high levels of [3H]heparin binding, and this peptide also directly promoted cell adhesion and spreading, including B16F10, M2, HT1080, and PC12 cells. The peptide LG-6 also promoted the neurite outgrowth of PC12 cells, mouse granule cells, and chick telencephalic cells. An anti-peptide LG-6 antibody inhibited laminin-1 and peptide LG-6-mediated cell adhesion and neurite outgrowth. Furthermore, an anti-integrin alpha2 antibody also inhibited the cell adhesion activity. These results suggest that peptide LG-6 plays a functional role as a heparin binding site in the G-domain of the laminin alpha1 chain, and this sequence was thus concluded to play a crucial role in regulating cell adhesion and spreading and neurite out-growth which is related to integrin alpha2.

High glucose modifies heparansulphate synthesis by mouse glomerular epithelial cells

BACKGROUND

Alterations in proteoglycan metabolism are involved in the pathogenesis of diabetic nephropathy. The aim of this study is to evaluate the effects of high glucose on proteoglycan production and to find a reliable in vitro model for the study of diabetic nephropathy.

METHODS

A clone of mouse glomerular epithelial cells was cultured in media containing elevated (30 mmol) and physiological (5 mmol) glucose, or iso-osmolar (30 mmol) mannitol concentrations. We evaluated the synthesis of 35SO4-labeled molecules and the amount of proteoglycans by Sepharose CL6B and DEAE-Sephacel chromatographies.

RESULTS

A clear decrease (56%) in total cell-layer proteoglycan synthesis was induced by 30 mmol glucose, in comparison with normal glucose. A reduction of 25% in medium associated proteoglycan synthesis was observed in high glucose cultured cells. After Sepharose CL6B, in cells cultured in high glucose, cell layer heparansulphate proteoglycan-I (Kav 6B 0. 04) synthesis was reduced by about 81%, heparansulphate proteoglycan-II (Kav 6B 0.21) by about 87% and heparansulphate glycosaminoglycan (Kav 0.4-0.8) by about 91%, respectively. In mannitol-incubated cells the reductions observed were less evident and not significantly different from those in normal glucose.

CONCLUSIONS

These results indicate that (1) glomerular epithelial cells play a central role in proteoglycan synthesis, (2) high glucose modifies the amount and influences the different species production of these macromolecules, while osmotic forces seem to be only partially involved in these effects, and (3) this cellular clone of glomerular epithelial cells can represent a reliable in vitro model for the study of the mechanisms involved in diabetic nephropathy.

Calcium oxalate crystallizing properties of polyanions elaborated by cultured renal proximal tubular cells

To study the influence of renal polyanions on crystallization of urinary calcium oxalate, we recovered polyanionic macromolecules from media conditioned by primary cultures of renal proximal tubular epithelial cells of rats in serum-free, hormonally defined medium. Cells cultured on microporous supports showed a higher degree of morphological and functional proximal differentiation into a polarized monolayer than those on plastic impervious substrata. Papainization of the polyanions yielded the glycosaminoglycans chondroitin/dermatan sulphate and heparan sulphate. These accounted respectively for 60% and 80% of the crystal nucleation-promoting activities of polyanions recovered from the apical and basal media conditioned by polarized cultures on microporous supports. Similar relative activities were observed among the urinary glycosaminoglycans and polyanions similarly tested. Primary cultures of polarized proximal tubular epithelial cells are useful then as an in vitro model to study the crystallizing activities of polyanionic macromolecules produced by renal cells.

Acidic pH of the lateral intercellular spaces of MDCK cells cultured on permeable supports

The pH of the lateral intercellular space (LIS) of Madin-Darby canine kidney (MDCK) cell monolayers grown on permeable supports was investigated by microspectrofluorimetry using BCECF (2',7'-bis(carboxyethyl)-5,6-carboxyfluorescein). The permeability of the support was selectively reduced by growing Zn-Al-silicate crystals inside its pores. The diffusion of BCECF across the filter was sufficiently retarded to allow measurements of fluorescence in the LIS. The LIS pH and intracellular pH of the cells surrounding them were determined in HEPES-buffered solutions. When the perfusate pH was 7.4, the LIS pH was more acidic (7.06 +/- 0.02) and equaled the cytoplasmic pH (7.08 +/- 0.05). When perfusate was changed to pH 7.0 or 7.8, the LIS changed linearly by about half the magnitude of the perfusate pH. Intracellular pH followed LIS pH variations between perfusate pH 7.0 and 7.4 but was significantly higher when perfusate pH was 7.8. Tight junctional H+ permeability was undetectably low. The low steady-state pH in the LIS was not altered by inhibitors of acid transport or low temperature. Rapid perturbations of pH in the LIS showed that protons were not immobilized in the LIS. The acidic microenvironment within the LIS may be the result of buffering by the cell surface proteins.

An induced extracellular matrix protein reverses the polarity of band 3 in intercalated epithelial cells

The intercalated epithelial cell exists in two interconvertible forms in vivo, one where band 3 protein is apical and the other where it is basolateral. We seeded an immortalized clone of these cells at low density and found that band 3 was apical at confluence. There was little or no apical endocytosis. But when the cells were plated at high density, band 3 was basolateral, and there was vigorous apical endocytosis. Extracellular matrix produced by high density cells was able to retarget band 3 in low density cells and to induce apical endocytosis, as did a 230 kd protein partially purified from this matrix. Therefore, polarized targeting of some proteins is determined by external cues that might determine their polarity by reorganizing the cytoplasm.

Cardiac sarcoplasmic reticulum calcium ATPase, an autoimmune antigen in experimental cardiomyopathy

BACKGROUND

Various myocardial cell surface and intracellular antigens have been associated with autoimmune myocarditis. Since sarcoplasmic calcium overload is a recognized pathobiochemical finding in cardiomyopathy, we reasoned that there might be a causal relation between inhibition of sarcoplasmic calcium exclusion and pathogenesis of the disease and that immunization with sarcoplasmic reticulum calcium ATPase (SR-ATPase) or antibody specific for SR-ATPase, which can interfere with the regulation of the intracellular calcium content and the myocardial contractility, should lead to the development of cardiomyopathy and possibly myocarditis.

METHODS AND RESULTS

Monoclonal antibody 4C11-20.21 (IgM class) specific for canine cardiac SR-ATPase (M(r) approximately 110 kD) was generated by immunization of CAF1/J mice with dog heart sarcoplasmic reticulum. Antibody 4C11-20.21 inhibits 75% of the enzymatic activity of the cardiac SR-ATPase. This antibody also cross-reacts with the higher M(r) subunit of canine skeletal SR-ATPase, but the skeletal muscle SR-ATPase activity is unaffected. This antibody does not cross-react with sarcolemmal calcium ATPase (134 kD). Antibody 4C11-20.21 was used for affinity purification of cardiac muscle SR-ATPase, which did not contain sarcolemmal calcium ATPase antigen. Nine of 11 CAF1/J mice injected with purified canine cardiac SR-ATPase protein demonstrated myocardial lesions: 3 of 4 mice had occasional perivascular and/or interstitial mononuclear cell infiltrates after 3 weeks, 3 of 4 had borderline myocarditis after 6 weeks, and 3 of 3 had focal myocarditis after 12 weeks. No mononuclear infiltrates were seen in any other organ. To identify the independent effect of 4C11-20.21 antibody on cardiac muscle, 2 x 10(6) hybridoma cells producing the antibody were injected intraperitoneally into 12 severe combined immunodeficiency (SCID) mice. Eleven of 12 SCID mice showed variable cardiac myocyte degeneration without cellular infiltration between 8 and 19 days. Three control SCID mice, which received equivalent injections of hybridoma cells producing IgM anti-myosin light chain antibody, did not show any pathological lesions. Immunoperoxidase staining and/or immunoperoxidase transmission electron microscopy for detection of in vivo localization of 4C11-20.21 demonstrated staining of the subsarcolemmal myotubular system and focal staining of immediately adjacent sarcolemma in animals that received either 4C11-20.21 hybridoma cells or purified canine cardiac SR-ATPase antigen but not in controls. Immunofluorescence staining with goat anti-mouse C3 antibody revealed focal deposition of complement in the cardiac myocytes.

CONCLUSIONS

The time-dependent association between immunization with SR-ATPase antigen and the development of myocarditis in mice suggests that cardiac SR-ATPase constitutes one of several autoimmunogens capable of inducing autoimmune myocarditis. Besides antigenic specificity, since antibody to cardiac SR-ATPase also inhibits energy-dependent processes in the myocardium, it is reasonable to associate the pathological evidence of myonecrosis with the interference of calcium regulation, which controls myocardial contractility.

A quantitative method for analysis of radiolabelled proteoglycans synthesized by cultured human arterial smooth muscle cells

1. Sulphate labelled proteoglycans (PG) synthesized by cultured human arterial smooth muscle cell have been quantified using an improved method based on a combination of specific enzymes and ethanol precipitation. 2. The present method gives quantitative data of PGs and subclasses allowing batchwise analysis of a large number of samples. 3. Approximately 81% +/- 1.7% (mean +/- SD, n = 6) of total PGs synthesized by human arterial smooth muscle cells accumulated in medium. 4. In cell layer and medium chondroitin sulphate proteoglycan constituted 65.0% +/- 0.3% and 75.8% +/- 0.7% (mean +/- SD, n = 3), respectively of sulphated PGs. 5. Heparan sulphate proteoglycan accounted for 26.8% +/- 0.6% in cell layer and 22.6% +/- 0.5% (mean +/- SD, n = 3) in medium of sulphated PGs.

Proteoglycans of basement membranes

Proteoglycans carrying either heparan sulfate and/or chondroitin sulfate side chains are typical constituents of basement membranes. The most prominent proteoglycan (perlecan) consists of a 400-500 kDa core protein and three heparan sulfate chains. Electron microscopy and cDNA sequencing show a complex and elongated domain structure for the core protein which in part is homologous to that of the laminin A chain. This structure may be varied by alternative splicing and proteolysis. Integration into basement membranes probably occurs by heparan sulfate binding to laminin and collagen IV, core protein binding to nidogen and by limited self assembly. The proteoglycan is in addition a cell-adhesive protein which is recognized by beta 1 integrins. Several more proteoglycans with smaller core proteins (10-160 kDa) apparently exist in basement membranes but are less well characterized. Biological functions include control of filtration through basement membranes and binding of growth factors and protease inhibitors.

Calcium-dependent heparin-like ligands for L-selectin in nonlymphoid endothelial cells

L-Selectin is a calcium-dependent mammalian lectin that mediates lymphocyte trafficking by recognizing sialylated ligands on high endothelial venules in lymph nodes. Although L-selectin probably mediates neutrophil extravasation into nonlymphoid tissues, no corresponding ligand has been characterized. Staining of cultured endothelial cells with an L-selectin chimera (LS-Rg) showed an internal pool of ligands. Metabolic labeling with sulfur-35-labeled sulfate revealed heparin lyase-sensitive ligands that bound LS-Rg in a calcium-dependent, sialic acid-independent manner. A fraction of commercial heparin bound to LS-Rg and LS-Rg bound to heparin-agarose, both in a calcium-dependent manner. Thus, L-selectin recognizes endothelial heparin-like chains, which could be physiological ligands mediating leucocyte trafficking.

Proteoglycans of basement membranes

Proteoglycans carrying either heparan sulfate and/or chondroitin sulfate side chains are typical constituents of basement membranes. The most prominent proteoglycan (perlecan) consists of a 400-500 kDa core protein and three heparan sulfate chains. Electron microscopy and cDNA sequencing show a complex and elongated domain structure for the core protein which in part is homologous to that of the laminin A chain. This structure may be varied by alternative splicing and proteolysis. Integration into basement membranes probably occurs by heparan sulfate binding to laminin and collagen IV, core protein binding to nidogen and by limited self assembly. The proteoglycan is in addition a cell-adhesive protein which is recognized by beta 1 integrins. Several more proteoglycans with smaller core proteins (10-160 kDa) apparently exist in basement membranes but are less well characterized. Biological functions include control of filtration through basement membranes and binding of growth factors and protease inhibitors.

Major influence of cell differentiation status on characteristics of proteoglycans synthesized by cultured rabbit renal proximal tubule cells: role of insulin and dexamethasone

To analyze the influence of epithelial cell differentiation and the effects of hormones on the characteristics of cell-associated and secreted proteoglycans (PGs), we studied their distribution, synthesis, and biochemical features in a model of renal proximal tubule cells in primary culture in which cell differentiation could be controlled by medium composition. In cells cultured in serum-free, hormonally defined medium supplemented with insulin and dexamethasone that exhibited a high degree of morphological and functional proximal differentiation (Ronco et al., 1990), cell-associated PGs were similar to those extracted in vivo by their size estimated by Sepharose CL-6B chromatography (Kav = 0.27, vs. 0.26), composition (heparan-sulfate), and localization in a continuous basal layer of extra-cellular matrix (ECM). In contrast, major quantitative and qualitative anomalies of cell-associated PGs were observed in poorly differentiated cells grown in 1% fetal calf serum-supplemented medium (FCS). PGs alterations included: (1) reduced and irregular expression of PGs at the cell basal pole, (2) a 2.8-fold decrease in [35S]-sulfate incorporation into cell-associated PGs, (3) a 3.1-fold increase in trypsin-releasable PGs, and (4) the emergence of a high MW PG composed exclusively of chondroitin-sulfate (CS) (Kav = 0.09 on Sepharose CL-6B) as well as of putative free CS-glycosaminoglycan (GAG) chains (Kav = 0.49 on Sepharose CL-6B). The same alterations were identified in the basal defined medium devoid of hormones but were partially or totally abolished by addition of insulin and dexamethasone, respectively. At variance with cell-associated PGs, production and biochemical features of secreted PGs were not influenced by cell differentiation status and medium composition.

Structural differences between heparan sulphates of proteoglycan involved in the formation of basement membranes in vivo by Lewis-lung-carcinoma-derived cloned cells with different metastatic potentials

This study addresses the characterization of heparan sulphates of the basement-membrane proteoglycans in tumour formed after the subcutaneous implantation of Lewis-lung-carcinoma-derived different metastatic clones (P29, LM12-3 and LM60-D6 clones with low, medium and high metastatic potentials respectively). Heparan sulphate proteoglycans (125-158 micrograms of hexuronate/g dry weight of tissue) were isolated from chondroitin ABC lyase digests of a proteoglycan fraction obtained after DEAE-Sephacel chromatography of tissue extracts. The proteoglycans were separated into three molecular species by Sepharose CL-4B chromatography followed by CsCl-density-gradient centrifugation: large proteoglycans with an estimated M(r) of 820,000-130,000, which consisted of two components with low (< 1.34 g/ml; PGII-M) and high (> 1.37 g/ml; PGII-B) density, and a small proteoglycan with an M(r) of less than 80,000 (PGIII). Of these, only the PGII-M proteoglycan (34-37 micrograms of hexuronate/g dry weight) reacted with the antiserum against proteoglycan of Engelbreth-Holm-Swarm-tumour basement membrane, and represented, therefore, a basement-membrane proteoglycan. Digestion with heparan sulphate lyases I and II of the heparan sulphates (M(r) 36,000) from the PGII-M proteoglycan of the three tumours resulted in almost complete depolymerization to give six unsaturated disaccharides identified as 2-acetamido-2-deoxy-4-O-(4-deoxy-alpha-L-threo-hex-4-enopyranosyluron ic acid)-D-glucose, 2-acetamido-2-deoxy-4-O-(4-deoxy-alpha-L-threo-hex-4-enopyranosyluron ic acid)-6-O-sulpho-D-glucose, 2-deoxy-2-sulphamino-4-O-(4-deoxy-alpha-L-threo-hex-4-enopyrano syluronic acid)-D-glucose, 2-deoxy-2-sulphamino-4-O-(4-deoxy-alpha-L-threo-hex-4-enopyrano syluronic acid)-6-O-sulpho-D-glucose, 2-deoxy-2-sulphamino-4-O-(4-deoxy-2-O-sulpho-alpha-L-threo-hex-4- enopyranosyluronic acid)-D-glucose and 2-deoxy-2-sulphamino-4-O-(4-deoxy-2-O-sulpho-alpha-L-threo-hex-4- enopyranosyluronic acid)-6-O-sulpho-D-glucose. Comparison of the relative amounts of these disaccharides produced from the three tumour-derived heparan sulphates demonstrated that the degree of sulphation of the heparan sulphates correlated with the degree of morphological organization of the tumour basement membranes; the heparan sulphate from the more highly metastatic tumour with more highly organized basement membrane exhibited a higher degree of overall sulphation along the glycosaminoglycan chains, which was due to an increased content of the three repeating disaccharides having 6-O-sulphated glucosamine residues.

Immunolocalization of laminin, heparan-sulfate proteoglycan, entactin and type IV collagen in the rat anterior pituitary. II. An in vitro study on primary cultures

The distribution of four basement membrane components: laminin (LAM), type IV collagen (Coll. IV), heparan-sulfate proteoglycan (HSPG), and entactin (ENT), was studied by immunocytochemistry in primary cultures of adult rat anterior pituitaries. In such cultures, the pituitary cells are deprived of their normal environment of adjacent cells and basement membranes (BM), and of the connectivo-vascular system of the hypophysis. In this dissociated system, pituitary cells grow as small clusters upon a monolayer of fibroblasts. LAM was found highly expressed in endocrine and in folliculo-stellate cells. Very small amounts of Coll. IV, but neither HSPG nor ENT, could be detected in endocrine cells. In contrast, in fibroblasts, very large amounts of Coll. IV, HSPG, and ENT, and a lower quantity of LAM were detected. At the ultrastructural level, the immunoreactive components present within the cells were located in the subcellular compartments involved in the elaboration of exported products. In addition to that intracellular distribution, the four constituents were observed in an extracellular matrix which appeared between the cultured cells, either as an amorphous material, or as a more or less dense reticular network, weakly stained with anti-LAM, but strongly stained with the other antibodies. Thus, the present immunocytochemical data support the implication of pituitary endocrine cells, at least for LAM secretion, in the elaboration of a novel extracellular matrix in primary cultures. In addition, a cooperation with non-endocrine cells seemed to be required for the production of the four BM components.

Identification of a 200-kD, brefeldin-sensitive protein on Golgi membranes

A mAb AD7, raised against canine liver Golgi membranes, recognizes a novel, 200-kD protein (p200) which is found in a wide variety of cultured cell lines. Immunofluorescence staining of cultured cells with the AD7 antibody produced intense staining of p200 in the juxtanuclear Golgi complex and more diffuse staining of p200 in the cytoplasm. The p200 protein in the Golgi complex was colocalized with other Golgi proteins, including mannosidase II and beta-COP, a coatomer protein. Localization of p200 by immunoperoxidase staining at the electron microscopic level revealed concentrations of p200 at the dilated rims of Golgi cisternae. Biochemical studies showed that p200 is a peripheral membrane protein which partitions to the aqueous phase of Triton X-114 solutions and is phosphorylated. The p200 protein is located on the cytoplasmic face of membranes, since it was accessible to trypsin digestion in microsomal preparations, and is recovered in approximately equal amounts in membrane pellets and in the cytosol of homogenized cells. Immunofluorescence staining of normal rat kidney cells exposed to the toxin brefeldin A (BFA), showed that there was very rapid redistribution of p200, which was dissociated from Golgi membranes in the presence of this drug. The effect of BFA was reversible, since upon removal of the toxin, AD7 rapidly reassociated with the Golgi complex. In the BFA-resistant cell line PtK1, BFA failed to cause redistribution of p200 from Golgi membranes. Taken together, these results indicate that the p200 Golgi membrane-associated protein has many properties in common with the coatomer protein, beta-COP.

Heparin releasable and nonreleasable forms of heparan sulfate proteoglycan are found on the surfaces of cultured porcine aortic endothelial cells

Evidence suggests that endothelial cell layer heparan sulfate proteoglycans include a variety of different sized molecules which most likely contain different protein cores. In the present report, approximately half of endothelial cell surface associated heparan sulfate proteoglycan is shown to be releasable with soluble heparin. The remaining cell surface heparan sulfate proteoglycan, as well as extracellular matrix heparan sulfate proteoglycan, cannot be removed from the cells with heparin. The heparin nonreleasable cell surface proteoglycan can be released by membrane disrupting agents and is able to intercalate into liposomes. When the heparin releasable and nonreleasable cell surface heparan sulfate proteoglycans are compared, differences in proteoglycan size are also evident. Furthermore, the intact heparin releasable heparan sulfate proteoglycan is closer in size to proteoglycans isolated from the extracellular matrix and from growth medium than to that which is heparin nonreleasable. These data indicate that cultured porcine aortic endothelial cells contain at least two distinct types of cell surface heparan sulfate proteoglycans, one of which appears to be associated with the cells through its glycosaminoglycan chains. The other (which is more tightly associated) is probably linked via a membrane intercalated protein core.

Agrin mediates cell contact-induced acetylcholine receptor clustering

One of the important events in synapse formation is the accumulation of neurotransmitter receptors beneath the presynaptic nerve terminal. Agrin is a component of the synaptic basal lamina that induces the clustering of acetylcholine receptors when bath-applied to muscle fibers in culture. When a cDNA encoding a putative agrin protein is transfected into cells, the molecule is secreted and concentrated on the extracellular surface. Coculture of transfected cells with muscle fibers induces the formation of receptor patches at contact sites. These results demonstrate that expression of a single gene encoding agrin confers receptor clustering that is restricted to specific sites of cell-muscle contact.

Synthetic peptides from the carboxy-terminal globular domain of the A chain of laminin: their ability to promote cell adhesion and neurite outgrowth, and interact with heparin and the beta 1 integrin subunit

The large carboxy-terminal globular domain (G domain; residues 2,110-3,060) of the A chain of murine-derived laminin has been shown to promote heparin binding, cell adhesion, and neurite outgrowth. This study was conducted to define the potential sequence(s) originating from the G domain of laminin with any of these functional activities. A series of peptides were synthesized from the G domain, termed GD peptides, each approximately 20 amino acids long and containing multiple positively charged amino acids. In direct 3H-heparin binding assays, peptides GD-1 and GD-2 bound high levels of 3H-heparin, while peptides GD-3 and GD-4 bound lower levels of 3H-heparin, and GD-5 bound essentially no 3H-heparin. The binding of 3H-heparin to peptides GD-1 and GD-2 appeared to be of high affinity, since significant binding of 3H-heparin to these two peptides was still observed even when the NaCl concentration was raised to 1.0 M. Four of the peptides, GD-1, GD-2, GD-3, and GD-4, directly promoted the adhesion and spreading of HT-1080 human fibrosarcoma cells as well as the outgrowth of neurites from chick spinal cord and dorsal root ganglia neurons. In addition, solutions of these peptides or antibodies generated against these peptides inhibited laminin-mediated HT-1080 cell adhesion. Antibodies against the beta 1 integrin subunit inhibited HT-1080 cell adhesion and neurite outgrowth on surfaces adsorbed with peptides GD-3 and GD-4. Therefore, laminin appears to have multiple, independent sequences in the G domain that serve a similar cell adhesion promoting function for different cell types. Furthermore, these results suggest that the sequences comprising peptides GD-3 and GD-4 use an integrin as a receptor, of which the beta 1 integrin subunit is a component for these various cell types.

A heterotrimeric G protein, G alpha i-3, on Golgi membranes regulates the secretion of a heparan sulfate proteoglycan in LLC-PK1 epithelial cells

A heterotrimeric G alpha i subunit, alpha i-3, is localized on Golgi membranes in LLC-PK1 and NRK epithelial cells where it colocalizes with mannosidase II by immunofluorescence. The alpha i-3 was found to be localized on the cytoplasmic face of Golgi cisternae and it was distributed across the whole Golgi stack. The alpha i-3 subunit is found on isolated rat liver Golgi membranes by Western blotting and G alpha i-3 on the Golgi apparatus is ADP ribosylated by pertussis toxin. LLC-PK1 cells were stably transfected with G alpha i-3 on an MT-1, inducible promoter in order to overexpress alpha i-3 on Golgi membranes. The intracellular processing and constitutive secretion of the basement membrane heparan sulfate proteoglycan (HSPG) was measured in LLC-PK1 cells. Overexpression of alpha i-3 on Golgi membranes in transfected cells retarded the secretion of HSPG and accumulated precursors in the medial-trans-Golgi. This effect was reversed by treatment of cells with pertussis toxin which results in ADP-ribosylation and functional uncoupling of G alpha i-3 on Golgi membranes. These results provide evidence for a novel role for the pertussis toxin sensitive G alpha i-3 protein in Golgi trafficking of a constitutively secreted protein in epithelial 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.

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.

Age-related changes in the plasma membrane proteoglycans of rat kidney glomerular cells

In a previous in vivo study, we showed that the glomerular cells of rat kidney synthesize both peripheral and integral plasma membrane proteoglycans. The present work focuses on the age-related changes in these cell membrane proteoglycans. The peripheral proteoglycans in "adult control" rats aged 3 months were found to be heparan sulfate, dermatan sulfate, and chondroitin sulfate, with heparan sulfate being the main glycosaminoglycan. The integral membrane proteoglycans contained mainly dermatan sulfate plus less amounts of heparan sulfate. The relative proportions of the glycosaminoglycans in the integral membrane proteoglycans changed between 1 and 3 months. In addition, the degree of sulfation increased in both families of proteoglycans, and this was associated with an increase in glycosaminoglycan synthesis in the peripheral proteoglycans. The nature and relative proportions of the glycosaminoglycans forming the proteoglycans, did not change with age, after 10 months, and neither did the amount of glycosaminoglycans. But, the degree of sulfation of both peripheral and integral membrane proteoglycans decreased. De novo synthesized proteoglycans from 24-month-old rats had a higher overall charge than did those at other ages, owing to the presence of sulfate and carboxylic groups. We conclude that, as for glomerular basement membrane proteoglycans, biochemical alterations affect the glomerular cell membrane proteoglycans with aging.

Human glomerular epithelial cell proteoglycans

Proteoglycans synthesized by cultures of human glomerular epithelial cells have been isolated and characterized. Three types of heparan sulfate were detected. Heparan sulfate proteoglycan I (HSPG-I; Kav 6B 0.04) was found in the cell layer and medium and accounted for 12% of the total proteoglycans synthesized. HSPG-II (Kav 6B 0.25) accounted for 18% of the proteoglycans and was located in the medium and cell layer. A third population (9% of the proteoglycan population), heparan sulfate glycosaminoglycan (HS-GAG; Kav 6B 0.4-0.8), had properties consistent with single glycosaminoglycan chains or their fragments and was found only in the cell layer. HSPG-I and HSPG-II from the cell layer had hydrophobic properties; they were released from the cell layer by mild trypsin treatment. HS-GAG lacked these properties, consisted of low-molecular-mass heparan sulfate oligosaccharides, and were intracellular. HSPG-I and -II released to the medium lacked hydrophobic properties. The cells also produced three distinct types of chondroitin sulfates. The major species, chondroitin sulfate proteoglycan I (CSPG-I) eluted in the excluded volume of a Sepharose CL-6B column, accounted for 30% of the proteoglycans detected, and was found in both the cell layer and medium. Cell layer CSPG-I bound to octyl-Sepharose. It was released from the cell layer by mild trypsin treatment. CSPG-II (Kav 6B 0.1-0.23) accounted for 10% of the total 35S-labeled macromolecules and was found predominantly in the culture medium. A small amount of CS-GAG (Kav 6B 0.25-0.6) is present in the cell extract and like HS-GAG is intracellular. Pulse-chase experiments indicated that HSPG-I and -II and CSPG-I and -II are lost from the cell layer either by direct release into the medium or by internalization where they are metabolized to single glycosaminoglycan chains and subsequently to inorganic sulfate.

Partial characterization of proteoglycans synthesized by human glomerular epithelial cells in culture

Confluent adult and fetal human glomerular epithelial cells were incubated for 24 h in the presence of [3H]-amino acids and [35S]sulfate. Two heparan-35SO4 proteoglycans were released into the culture medium. These 35S-labeled proteoglycans eluted as a single peak from anion exchange chromatographic columns, but were separable by gel filtration on Sepharose CL-6B columns. The larger heparan-35SO4 proteoglycan eluted with the column void volume and at a Kav of 0.26 from Sepharose CL-4B columns. The most abundant medium heparan-35SO4 proteoglycan was a high buoyant density proteoglycan similar in hydrodynamic size (Sepharose CL-6B Kav 0.23) to those previously described in glomerular basement membranes and isolated glomeruli. Heparan-35SO4 chains from both proteoglycans were 36 kDa. A smaller proportion of Sepharose CL-6B excluded dermatan-35SO4 proteoglycan was also synthesized by these cells. The predominant protein cores of both medium heparan-35SO4 proteoglycans were approximately 230 and 180 kDa. A hybrid chondroitin/dermatan-heparan-35SO4 proteoglycan with an 80-kDa protein core copurified with the smaller medium heparan-35SO4 proteoglycan. This 35S-labeled proteoglycan appeared as a diffuse, chondroitinase ABC sensitive 155-kDa fluorographic band in sodium dodecyl sulfate-polyacrylamide gels after the Sepharose CL-6B Kav 0.23 35S-labeled proteoglycan fraction was digested with heparitinase. The heparitinase generated heparan sulfate proteoglycan protein cores and the 155-kDa hybrid proteoglycan fragment had molecular weights similar to those previously identified in rat glomerular basement membrane and glomeruli using antibodies against a basement membrane tumor proteoglycan precursor (Klein et al. J. Cell Biol. 106, 963-970, 1988). Thus, human glomerular epithelial cells in culture are capable of synthesizing, processing, and releasing heparan sulfate proteoglycans which are similar to those synthesized in vivo and found in the glomerular basement membrane. These proteoglycans may belong to a family of related basement membrane proteoglycans.

Comparison of heparan sulfate proteoglycans from equine and human glomerular basement membranes

1. Proteoglycans extracted from human and equine glomerular basement membranes (GBM) were purified by ion-exchange chromatography and gel filtration. 2. The glycoconjugates had an apparent molecular mass of 200-400 kDa and consisted of 75% protein and 25% glycosaminoglycan. Glycosidase and HNO2 treatment and the amino sugar and sulfate composition of both proteoglycan preparations identified heparan sulfate (HS) as the predominant saccharide chain. 3. Hydrolysis with trifluoromethanesulfonic acid yielded comparable core proteins with molecular masses of ca 160 and 120 kDa. 4. The HS chains had an apparent molecular mass of 18 kDa. Results of heparitinase digestion and HNO2-treatment indicated a clustering of sulfate groups in the distal part of the HS side chains. 5. Peptide mapping after trypsin, clostripain or V8 protease digestion of radiolabeled human and equine heparan sulfate proteoglycans (HSPG) preparations with three different separation techniques showed large differences. 6. Polyclonal antisera raised against the HSPGs reacted against the core proteins. Both HSPG preparations and their antisera showed ca 40% cross-reactivity. About 50% of monoclonal antisera elicited against one HSPG preparation showed reaction with both HSPG preparations. 7. Polyclonal antisera stained all basement membranes in an intense linear fashion in indirect immunofluorescence studies of kidney sections from horse, man and various mammalian species. 8. Biochemical and immunological data indicate that HSPGs from equine and human GBM have a comparable structure, but the core proteins differ considerably.

Matrix-associated heparan sulfate proteoglycan: core protein-specific monoclonal antibodies decorate the pericellular matrix of connective tissue cells and the stromal side of basement membranes

Cultured human lung fibroblasts produce a large, nonhydrophobic heparan sulfate proteoglycan that accumulates in the extracellular matrix of the monolayer (Heremans, A., J. J. Cassiman, H. Van den Berghe, and G. David. 1988. J. Biol. Chem. 263: 4731-4739). A panel of four monoclonal antibodies, specific for four distinct epitopes on the 400-kD core protein of this extracellular matrix heparan sulfate proteoglycan, detects similar proteoglycans in human epithelial cell cultures. Immunohistochemistry of human tissues with the monoclonal antibodies reveals that these proteoglycans are concentrated at cell-matrix interfaces. Immunogold labeling of ultracryosections of human skin indicates that the proteoglycan epitopes are nonhomogeneously distributed over the width of the basement membrane. Immunochemical investigations and amino acid sequence analysis indicate that the proteoglycan from the fibroblast matrix shares several structural features with the large, low density heparan sulfate proteoglycan isolated from the Engelbreth-Holm-Swarm sarcoma. Thus, both epithelial cell sheets and individual mesenchymal cells accumulate a large heparan sulfate proteoglycan(s) at the interface with the interstitial matrix, where the proteoglycan may adopt a specific topological orientation with respect to this matrix.

Basement membrane heparan sulfate proteoglycan is the main proteoglycan synthesized by glomerular epithelial cells in culture

The production and distribution of basement membrane-type heparan sulfate proteoglycans (BM HSPG) were investigated in a mouse glomerular epithelial cell line. Confluent cell monolayers were radiolabeled with [35S]sulfate or [35S]cysteine. Proteoglycans were isolated from the medium and cell layers by ion exchange chromatography and their nature determined by enzyme digestion (chondroitinase ABC) or degradative treatment (nitrous acid). It was found that more than 80% of the proteoglycans in both the cell layer and medium were heparan sulfate proteoglycans (HSPG) based on their susceptibility to nitrous acid degradation. More than half of the HSPG in the cell layer could be precipitated with an antiserum that specifically recognizes BM HSPG; only 10% of those released into the medium were precipitated with this antiserum. When immunoprecipitates of [35S] sulfate-labeled proteoglycans were analyzed by SDS-PAGE, the mature proteoglycans ran as a broad band at the top of the gel. When immunoprecipitates of [35S]cysteine-labeled proteoglycans were similarly analyzed, a 250 kd precursor core protein band was seen in addition to the mature proteoglycan. When BM HSPG were localized by immunofluorescence and immunoelectron microscopy (immunoperoxidase), they were found intracellularly in biosynthetic compartments (ER and Golgi cisternae) and extracellularly in deposits of basement membrane-like matrix located beneath and between the cells. These results indicate that l) BM HSPG are the predominant type of proteoglycans made by glomerular epithelial cells in culture; 2) these HSPG are assembled into a loosely organized matrix that is deposited beneath and between the cells; and 3) this cell type produces a higher proportion of BM HSPG than other cultured epithelial cells studied previously.

Mammalian tissue distribution of a large heparan sulfate proteoglycan detected by monoclonal antibodies

A panel of nine monoclonal antibodies has been characterized, all of which have reactivity with the core protein of a large heparan sulfate proteoglycan derived from the murine EHS tumor matrix. These rat monoclonal antibodies stained mouse basement membranes intensely, including those of all muscle, endothelia, peripheral nerve fibers and epithelia so far examined. In addition, two of the monoclonal antibodies show cross-species reactivity, staining bovine and human basement membranes, and immunoprecipitating proteoglycans from human endothelial cell cultures. These antibodies do not, however, cross-react with avian tissues. These results show the ubiquitous distribution of a heparan sulfate proteoglycan in mammalian tissues, which will be useful in vitro and in vivo for studies on the biology of basement membrane proteoglycans and investigations of possible roles of these molecules in human disease processes.

Cell biology of arterial proteoglycans

Although proteoglycans constitute a minor component of vascular tissue, these molecules have been shown to influence a number of arterial properties such as viscoelasticity, permeability, lipid metabolism, hemostasis, and thrombosis. A hallmark of early and late atherosclerosis is the accumulation of proteoglycans in the intimal lesions. Yet, it is not clear why this accumulation occurs. This article reviews the classes of proteoglycans synthesized by the two major cell types of the arterial wall--the endothelial and smooth muscle cell. Detailed consideration is then given to the modulation of proteoglycan metabolism and the role that proteoglycans play in a number of cellular events such as adhesion, migration, and proliferation--important processes in both the development and the pathogenesis of blood vessels. Last, the involvement of proteoglycans in two critical vascular wall processes--hemostasis and lipid metabolism--is reviewed, because these events pertain to atherogenesis. This review emphasizes the importance of proteoglycans in regulating several key events in normal and pathophysiological processes in the vascular tissue.

Analysis of heparan sulfate from the Engelbreth-Holm-Swarm (EHS) tumor

The size of the heparan sulfate chains from the Engelbreth-Holm-Swarm (EHS) tumor heparan sulfate proteoglycan (PG) was measured by several techniques in order to resolve uncertainty about their size and the chains were chemically characterized for comparison with other basement membrane heparan sulfate PGs. Heparan sulfate size was determined by gel filtration (Mr = 5.5 - 6.0 x 10(4], by equilibrium sedimentation centrifugation (Mw = 6.8 x 10(4], and by end group analysis (Mn = 7.1 x 10(4]. A higher molecular weight (HMW) (Mw = 2.13 x 10(5] calculated from scattering measurements may reflect chain-chain interactions. Forty percent of newly synthesized chains eluted on gel filtration as a lower molecular weight (LMW) shoulder and in vivo turned over faster than the larger species. A large heparan sulfate PG was present after 4 hours of in vivo 35SO4 labeling in both a low density form and a high density, slightly smaller form with large heparan sulfate chains (Mr approximately 8.0 x 10(4]. Heparan sulfate PG of intermediate size (Kav = 0.3-0.65, Sepharose CL-4B) and of smaller size (Kav = 0.75, CL-4B) were found predominantly as high density species. These PGs contained chains (Mr = 3.5 x 10(4) and Mr = 1.2 x 10(4), respectively) which were partially sensitive to chondroitinase ABC (CABC) and may include a hybrid heparan sulfate/chondroitin sulfate PG. Heparan sulfate chains, possibly intracellular degradation products, were also found. Heparan sulfate chains were normal in N-sulfation (58% of hexosamine residues) and in iduronate content (approximately 30%). N-sulfation started within two disaccharides of the linkage region. The EHS heparan sulfate was unusually low in O-sulfation (10% of the total sulfation) and no 6-O sulfated, N-acetylated glucosamine residues adjacent to N-sulfated block regions were found.

A novel synthetic peptide from the B1 chain of laminin with heparin-binding and cell adhesion-promoting activities

Recent studies using solid-phase-binding assays and electron microscopy suggested the presence of a heparin-binding domain between the inner globule of a lateral short arm and the cross region of laminin. Using the information from the amino acid sequence of the B1 chain of laminin, several peptides were synthesized from areas with a low hydropathy index and a high density of lysines and/or arginines. One of these, peptide F-9 (RYVVLPRPVCFEKGMNYTVR), which is derived from the inner globular domain of the lateral short arm, demonstrated specific binding to heparin. This was tested in direct solid-phase binding assays by coating the peptide either on nitrocellulose or on polystyrene and in indirect competition assays where the peptide was in solution and either laminin or heparin was immobilized on a solid support. The binding of [3H]heparin to peptide F-9 was dramatically reduced when heparin but not other glycosaminoglycans other than heparin (dextran sulfate, dermatan sulfate) were used in competition assays. Modification of the free amino groups of peptide F-9 by acetylation abolished its ability to inhibit the binding of [3H]heparin to laminin on polystyrene surfaces. Peptide F-9 promoted the adhesion of various cell lines (melanoma, fibrosarcoma, glioma, pheochromocytoma) and of aortic endothelial cells. Furthermore, when peptide F-9 was present in solution, it inhibited the adhesion of melanoma cells to laminin-coated substrates. These findings suggest that peptide F-9 defines a novel heparin-binding and cell adhesion-promoting site on laminin.

Evidence for independent metabolism and cell surface localization of cell surface localization of cellular proteoglycans and glycosaminoglycan free chains

The synthesis and turnover of metabolically labeled proteoglycans from medium, cell layer, and substratum-associated compartments were characterized in four cell lines of fibroblastic origin, including a fibrosarcoma line, and in the murine melanoma cell type, B16.F10. Substantial differences were apparent between the various cell types with regard to quantities, hydrodynamic sizes, and compartmentalization of labeled product. Such variations were greater between the different cell lines than between separately labeled cultures of the same cell type. Greater than 85% of cell-associated proteoglycans were accessible to glycosaminoglycan-degrading enzymes added to the medium of monolayer cultures, demonstrating their principal location to be external to the cell membrane. Apparent glycosaminoglycan free chains, determined by a lack of change in hydrodynamic size following alkaline elimination, were among the products from each cell line and were similarly found to be in a principally pericellular location. Results from label-chase studies demonstrated apparent independent kinetics for proteoglycans and glycosaminoglycan free chains, with little conclusive evidence for precursor-product relationships. Also, their processing by the cells was different, since the proteoglycans were shed largely unchanged into the medium for the three cell lines evaluated, whereas the free chains were not recoverable from the medium in significant amounts. The latter observation suggests the internalization of cell surface-associated free chains and their depolymerization at an intracellular site. The results, which indicate that the content, cellular disposition, and turnover of proteoglycans are quite variable between the cell lines studied, may reflect fundamental cell type-specific specialization in the metabolism of these complex substances. Furthermore, the data raise the interesting possibility that glycosaminoglycan free chains may have biological functions at the cellular level, independent of proteoglycans.

Structural characterization of heparan sulfate proteoglycan subclasses isolated from bovine aortic endothelial cell cultures

Labeled heparan sulfate proteoglycans (HSPG) were isolated from wounded and confluent cultures of bovine aortic endothelial cells by nondegradative extraction with 4 M guanidine hydrochloride and detergent. HSPG were separated from more highly charged chondroitin or dermatan sulfate proteoglycans by ion-exchange chromatography, and subclasses of different hydrodynamic size were isolated by gel filtration. Three major subclasses of HSPG were characterized structurally with respect to the presence and relative size of protein core, the presence and amount of nonsulfated oligosaccharide, and size and structure of heparan sulfate (HS) chains. The largest (600-800-kDa) HSPG subclass (I), isolated from cell layers and media of confluent cultures, bears 38-kDa HS chains on an apparently heterogeneous class of relatively large glycoprotein cores. HSPG II (150-200 kDa), isolated from cell layer or media, has 22-kDa HS chains and smaller core glycoproteins (less than 50 kDa). HSPG III, the subclass of smallest hydrodynamic size, has 13-kDa HS chains and a glycopeptide core of less than 15 kDa. All subclasses bear varying proportions of non-sulfated oligosaccharides of similar sizes. Comparisons of HS chain structure indicated that the different subclasses have similar proportions (49-55%) of N-sulfate, with both O-sulfate and highly N-sulfated blocks of disaccharide distributed similarly along HS chains. In addition, HS chains from subclasses II and III contain sequences that are insensitive to periodate oxidation or heparitinase digestion, suggesting that they contain increased proportions of iduronate.(ABSTRACT TRUNCATED AT 250 WORDS)

Mouse mammary epithelial cells produce basement membrane and cell surface heparan sulfate proteoglycans containing distinct core proteins

Cultured mouse mammary (NMuMG) cells produce heparan sulfate-rich proteoglycans that are found at the cell surface, in the culture medium, and beneath the monolayer. The cell surface proteoglycan consists of a lipophilic membrane-associated domain and an extracellular domain, or ectodomain, that contains both heparan and chondroitin sulfate chains. During culture, the cells release into the medium a soluble proteoglycan that is indistinguishable from the ectodomain released from the cells by trypsin treatment. This medium ectodomain was isolated, purified, and used as an antigen to prepare an affinity-purified serum antibody from rabbits. The antibody recognizes polypeptide determinants on the core protein of the ectodomain of the cell surface proteoglycan. The reactivity of this antibody was compared with that of a serum antibody (BM-1) directed against the low density basement membrane proteoglycan of the Englebarth-Holm-Swarm tumor (Hassell, J. R., W. C. Leyshon, S. R. Ledbetter, B. Tyree, S. Suzuki, M. Kato, K. Kimata, and H. Kleinman. 1985. J. Biol. Chem. 250:8098-8105). The BM-1 antibody recognized a large, low density heparan sulfate-rich proteoglycan in the cells and in the basal extracellular materials beneath the monolayer where it accumulated in patchy deposits. The affinity-purified anti-ectodomain antibody recognized the cell surface proteoglycan on the cells, where it is seen on apical cell surfaces in subconfluent cultures and in fine filamentous arrays at the basal cell surface in confluent cultures, but detected no proteoglycan in the basal extracellular materials beneath the monolayer. The amino acid composition of the purified medium ectodomain was substantially different from that reported for the basement membrane proteoglycan. Thus, NMuMG cells produce at least two heparan sulfate-rich proteoglycans that contain distinct core proteins, a cell surface proteoglycan, and a basement membrane proteoglycan. In newborn mouse skin, these proteoglycans localize to distinct sites; the basement membrane proteoglycan is seen solely at the dermal-epidermal boundary and the cell surface proteoglycan is seen solely at the surfaces of keratinocytes in the basal, spinous, and granular cell layers. These results suggest that although heparan sulfate-rich proteoglycans may have similar glycosaminoglycan chains, they are sorted by the epithelial cells to different sites on the basis of differences in their core proteins.

Heparan sulfate proteoglycan from human and equine glomeruli and tubules

1. Proteoglycans were isolated from human and equine glomeruli or tubules by guanidine extraction and anion exchange chromatography. 2. These proteoglycan preparations contained about equal amounts of heparan sulfate and chondroitin sulfates. 3. During the preparation of glomerular or tubular basement membranes the main part of proteoglycans (greater than 50%) was extracted in the salt extract. Chondroitin sulfate proteoglycan was mainly found in the water and salt extracts of glomeruli and tubules, heparan sulfate proteoglycan in the deoxycholate extracts and the basement membranes. 4. The glomerular basement membrane (GBM) contains about 12% (human) or 20% (equine) of the proteoglycans of the total glomerulus. They consist of greater than 70% (equine) or 80% (human) of heparan sulfate. 5. Heparan sulfate proteoglycan was isolated from the proteoglycan preparations of human or equine glomeruli and tubules by additional treatment with nucleases and chondroitinase ABC followed by CsCl gradient centrifugation. 6. Protein accounts for about 40% (dry weight) of the heparan sulfate proteoglycans. Their amino acid composition is characterized by a high content of glycine, but 3-hydroxyproline, 4-hydroxyproline and hydroxylysine are lacking. 7. The biochemical characteristics of the heparan sulfate proteoglycan of human or equine glomeruli or tubules differ from that isolated from rat glomeruli by their higher protein content and their amino acid composition. The significance of these differences is discussed.