Synthesis of a fluorogenic mucopolysaccharide by chondrocytes in cell culture with 4-methylumbelliferyl beta-D-xyloside

Chemistry of xylopyranosides

Xylose is one of the few monosaccharidic building blocks that are used by mammalian cells. In comparison with other monosaccharides, xylose is rather unusual and, so far, only found in two different mammalian structures, i.e. in the Notch receptor and as the linker between protein and glycosaminoglycan (GAG) chains in proteoglycans. Interestingly, simple soluble xylopyranosides can not only initiate the biosynthesis of soluble GAG chains but also function as inhibitors of important enzymes in the biosynthesis of proteoglycans. Furthermore, xylose is a major constituent of hemicellulosic xylans and thus one of the most abundant carbohydrates on Earth. Altogether, this has spurred a strong interest in xylose chemistry. The scope of this review is to describe synthesis of xylopyranosyl donors, as well as protective group chemistry, modifications, and conformational analysis of xylose.

Exploration of the active site of β4GalT7: modifications of the aglycon of aromatic xylosides

Proteoglycans (PGs) are macromolecules that consist of long linear polysaccharides, glycosaminoglycan (GAG) chains, covalently attached to a core protein by the carbohydrate xylose. The biosynthesis of GAG chains is initiated by xylosylation of the core protein followed by galactosylation by the galactosyltransferase β4GalT7. Some β-d-xylosides, such as 2-naphthyl β-d-xylopyranoside, can induce GAG synthesis by serving as acceptor substrates for β4GalT7 and by that also compete with the GAG synthesis on core proteins. Here we present structure-activity relationships for β4GalT7 and xylosides with modifications of the aromatic aglycon, using enzymatic assays, cell studies, and molecular docking simulations. The results show that the aglycons reside on the outside of the active site of the enzyme and that quite bulky aglycons are accepted. By separating the aromatic aglycon from the xylose moiety by linkers, a trend towards increased galactosylation with increased linker length is observed. The galactosylation is influenced by the identity and position of substituents in the aromatic framework, and generally, only xylosides with β-glycosidic linkages function as good substrates for β4GalT7. We also show that the galactosylation ability of a xyloside is increased by replacing the anomeric oxygen with sulfur, but decreased by replacing it with carbon. Finally, we propose that reaction kinetics of galactosylation by β4GalT7 is dependent on subtle differences in orientation of the xylose moiety.

Synthesis of fluorophore-tagged xylosides that prime glycosaminoglycan chains

Biosynthesis and functions of glycosaminoglycan (GAG) chains are complex and remain elusive. To better understand the factors that regulate the biosynthesis and functions, fluorophore-tagged xylosides carrying two different linkages between fluorophore and xylose residue were synthesized and evaluated for their ability to prime GAG chains such as heparan sulfate (HS), chondroitin sulfate (CS), and dermatan sulfate (DS) in various cell lines. These in vitro studies resulted in the identification of fluorophore-tagged xylosides that prime high molecular weight GAG chains. Primed GAG chains carrying a fluorophore group has several advantages for studying the factors that regulate the biosynthesis, analyzing intact fine structures at low detection limits, and setting the stage for studying structure-function relations of GAG chains of cellular origin.

Opposing functions of chondroitin sulfate and heparan sulfate during early neuronal polarization

Axon-dendrite polarity of neurons is essential for information processing in the nervous system. Here we studied the functions of chondroitin sulfate (CS) and heparan sulfate (HS) in neuronal polarization using cultured dissociated hippocampal neurons. Immunohistochemical analyses of early cultured neurons indicated the distribution of these glycosaminoglycans to be quite different. While CS epitopes were accumulated in the focal contacts present in axons and cell bodies, those of HS were detected ubiquitously on the cell surface including on dendrites and axons. Treatment with chondroitinase (CHase) ABC, which degrades CS, and knockdown of a CS sulfotransferase, N-acetylgalactosamine 4-sulfate 6-O-sulfotransferase (4,6-ST), which is involved in the biosynthesis of oversulfated structures, induced the formation of multiple axons in hippocampal neurons. Time-lapse recordings revealed the multiple axons of CHase ABC-treated neurons to be highly unstable, extending and retracting, repeatedly. CHase ABC-treatments suggested that CS is involved in the formation of phosphorylated focal adhesion kinase-positive focal contacts. Thus, CS may enhance integrin signaling in the nascent axons, supporting axon specification. On the other hand, when neurons were treated with heparitinases that specifically degrade HS, neurons with a single axon increased. The axons of HSase-treated neurons extended steadily and showed almost no retraction. These results suggest that CS stabilizes and HS destabilizes the growth of axons in an opposing manner, contributing to early neuronal polarization.

HNK-1-Reactive oligosaccharide, sulfate-O-3GlcAbeta1-4Xylbeta1-MU, synthesized by cultured human colorectal cancer cells

Human colorectal cancer cells were incubated with medium containing 4-methylumbelliferyl-beta-D-xyloside (Xyl-MU). The cells synthesized Xyl-MU-derivatives which were detected in the culture medium by gel-filtration high-performance liquid chromatography. These included a Xyl-MU-induced glycosaminoglycan and its biosynthetic intermediates, Galbeta1-4Xylbeta1-MU and Galbeta1-3Galbeta1-4Xylbeta1-MU, and other Xyl-MU-induced oligosaccharides, not related to Xyl-MU-induced glycosaminoglycan, were also synthesized. One of these oligosaccharides, sulfate-O-3GlcAbeta1-4Xylbeta1-MU, reacted with HNK-1, a mouse monoclonal antibody raised against human natural killer cells. Human neural cells and skin fibroblasts have also been reported to synthesize HNK-1-reactive sugar chains. Since HNK-1-reactive sugar chains are known to be involved in cell adhesion in the nervous system, the present results suggest that epithelium-derived colorectal cancer cells might also be able to utilize them in cell adhesion.

A sulfated proteoglycan is necessary for storage of exocrine secretory proteins in the rat parotid gland

Sulfated proteoglycans have been proposed to play a role in the sorting and storage of secretory proteins in exocrine secretory granules. Rat parotid acinar cells expressed a 40- to 60-kDa proteoglycan that was stored in secretory granules. Treatment of the tissue with the proteoglycan synthesis inhibitor paranitrophenyl xyloside resulted in the complete abrogation of the sulfated proteoglycan. Pulse-chase experiments in the presence of the xyloside analog showed a significant reduction in the stimulated secretion and granule storage of the newly synthesized regulated secretory proteins amylase and parotid secretory protein. Inhibition of proteoglycan sulfation by chlorate did not affect the sorting of these proteins. The effect of proteoglycan synthesis inhibition on protein sorting was completely reversed upon treatment with a weak acid. These results suggest that the sulfated proteoglycan is necessary for sorting and storage of regulated secretory proteins in the exocrine parotid gland. Preliminary evidence suggests that the mechanism involves the modulation of granule pH by the proteoglycan rather than a direct interaction with other granule components.

Growth factors and epithelial-stromal interactions in prostate cancer development

Epithelial-stromal interactions are important not only in growth, development, and functional cytodifferentiation of the prostate but also in derangements of prostate gland such as BPH and prostate carcinoma. This chapter explores the roles of epithelium and stroma during this delicate process and highlights the role and mutual influence of each on the other. It also examines the importance of ECM in mediating the effects of androgens and drawn attention to estrogen and genetic factors in the process. During this process of epithelial-stromal interaction, growth factors play a central role in mediating the interactions. This chapter focuses on the role of several growth factors including epidermal growth factor, fibroblast growth factor, transforming growth factor alpha, transforming growth factor beta, insulin-like growth factor-1, vascular endothelial growth factor, nerve growth factor, platelet-derived growth factor, and hepatocyte growth factor. This chapter emphasizes the importance of epithelial-stromal interactions in tumorigenesis and highlights the switch of paracrine to autocrine mode during the process of carcinogenesis.

A novel 4-methylumbelliferyl-beta-D-xyloside derivative, sulfate-O-3-xylosylbeta1-(4-methylumbelliferone), isolated from culture medium of human skin fibroblasts, and its role in methylumbelliferone-initiated glycosaminoglycan biosynthesis

Human skin fibroblasts were incubated in the presence of 4-methylumbelliferyl-beta-D-xyloside (Xyl-MU). The culture medium was recovered and Xyl-MU derivatives which were initiated by the Xyl-MU acting as a primer were purified. As a result, a novel Xyl-MU derivative was isolated, in addition to previously reported Xyl-MU derivatives such as glycosaminoglycan-MU, Gal-Gal-Xyl-MU, Gal-Xyl-MU, SA-Gal-Xyl-MU, Xyl-Xyl-MU, GlcA-Xyl-MU, and sulfate-GlcA-Xyl-MU. This Xyl-MU derivative was subjected to carbohydrate composition analysis, enzyme digestion, ion-spray mass spectrometric analysis, and Smith degradation. The results indicated that it was sulfate- O -3-Xyl-MU. When Xyl-MU was incubated with [35S]PAPS using a homogenate prepared from the same cultured skin fibroblasts, [35S]sulfate- O -3-Xyl-MU was produced. Moreover, when Xyl-MU was incubated with UDP-[3H]Gal, [3H]galactose was transferred to Xyl-MU, but when sulfate- O -3-Xyl-MU was incubated with UDP-[3H]Gal, [3H]galactose was not transferred. These results indicate that chain elongation from Xyl-MU is inhibited by sulfation of Xyl-MU, and that Xyl-MU sulfation is involved in the control of Xyl-MU-initiated glycosaminoglycan biosynthesis.

Characterization of beta-D-xyloside-initiated glycosaminoglycan synthesized by human skin fibroblasts in the presence of tunicamycin

Human skin fibroblasts were incubated with a fluorogenic xyloside, 4-methylumbelliferyl-beta-D-xyloside (Xyl-MU), in the presence or absence of tunicamycin. The xyloside-initiated glycosaminoglycans (GAG-MUs) were isolated from the culture medium, and their structures characterized. When the cells were incubated with Xyl-MU in the presence of 0.2 microg ml(-1) tunicamycin, the synthesis of GAG-MU was increased about three fold, compared with the control value in the absence of tunicamycin (cells exposed to Xyl-MU alone). The structures of GAG-MUs synthesized in the presence or absence of tunicamycin were compared by HPLC analysis using gel-filtration and ion-exchange columns, enzymatic digestion, and unsaturated disaccharide composition analysis. The data indicated that cells incubated with tunicamycin produced more undersulfated and shorter GAG-MUs than cells without tynicamycin. These results suggest that tunicamycin inhibits the elongation and sulfation of glycosaminoglycan (GAG) chains and that, as a result, GAG-MUs with shorter chains and undersulfated residues, but possessing a large number of GAG chains, are synthesized in the presence of tunicamycin.

Effects of dietary manganese on arterial glycosaminoglycan metabolism in Sprague-Dawley rats

The objectives of this study were to determine whether dietary manganese deficiency alters total glycosaminoglycan (GAG) concentration and composition and glycosyltransferase activity in rat aortas. Sprague-Dawley rats were fed either a manganese-deficient or a manganese-sufficient diet. Arterial GAGs were isolated and quantified by measuring uronic acid content. The individual GAGs were separated and quantified with cellulose acetate electrophoresis. The activity of the enzyme galactosyltransferase I was measured using a 100,000 g particulate fraction and 4-methylumbelliferylxyloside (Xyl-MU) as an acceptor. There was a significant decrease (p < or = 0.05) in uronic acid content in the manganese-deficient (1.18 +/- 0.08 mg/g) rat aortas as compared with the manganese-sufficient (1.59 +/- 0.10 mg/g) ones. Chondroitin sulfate and heparan sulfate concentrations were decreased by 38% (p < or = 0.01) and 36% (p < or = 0.05), respectively, in the manganese-deficient rat aortas. The incorporation of UDP-galactose to acceptors by the manganese-deficient rat aorta preparations was increased by 28% as compared to the manganese-sufficient preparations. These results indicate that manganese is involved in arterial GAG metabolism by affecting the enzyme galactosyltransferase and that changes in GAG concentration and composition with manganese deficiency may ultimately affect arterial wall integrity and subsequently cardiovascular health. This is the first work to demonstrate that manganese nutrition is important in arterial GAG metabolism.

HNK-1-reactive novel oligosaccharide, sulfate-O-3GlcA beta 1-4Xyl beta 1-(4-methylumbelliferone), synthesized by cultured human skin fibroblasts

4-Methylumbelliferyl-beta-D-xyloside (Xyl-MU) was added to the medium of cultured human skin fibroblasts. After incubation, the culture medium was pooled, and the Xyl-MU-induced oligosaccharides in the medium were purified by gel filtration chromatography. A novel Xyl-MU derivative was obtained, in addition to the previously reported Xyl-MU derivatives such as Gal-Gal-Xyl-MU, Gal-Xyl-MU, Sia-Gal-Xyl-MU, GlcA-Xyl-MU, and Xyl-Xyl-MU. The novel Xyl-MU derivative was purified using gel-filtration chromatography and high performance liquid chromatography and then subjected to carbohydrate composition analysis, enzymic digestion, Smith degradation, and ion spray mass spectrometric analysis. The results indicated that it was sulfate-O-3GlcA beta 1-4Xyl beta 1-MU. The structure of the nonreducing terminal of this Xyl-MU-induced oligosaccharide was the same as that of the oligosaccharide chain of a human peripheral nerve-derived glycolipid, reactive with the mouse monoclonal antibody HNK-1, and this Xyl-MU-induced oligosaccharide also reacted with HNK-1. These results suggest that the oligosaccharide, which is structurally identical to that of human peripheral nerve-derived glycolipid synthesized by nervous tissue and related to cell adhesion, is synthesized also by mesenchymal cells.

A novel oligosaccharide, GlcA beta 1-4Xyl beta 1-(4-methylumbelliferone), synthesized by human cultured skin fibroblasts

Human skin fibroblasts were cultured in the presence of 4-methylumbelliferyl-beta-D-xyloside (Xyl-MU) using a mass-culture system with a microcarrier. The structures of Xyl-MU-induced sugars purified from the dialysable fraction of the incubation medium were investigated. In addition to glycosaminoglycans the elongation of which initiated by Xyl-MU has already been reported, and oligosaccharides similarly initiated by Xyl-MU, such as Gal-Gal-Xyl-MU, Gal-Xyl-MU and SA-Gal-Xyl-MU, a novel Xyl-MU-induced oligosaccharide was detected. This oligosaccharide was identified as GlcA beta 1-4Xyl beta 1-(4-methylumbelliferone) using sugar composition analysis, enzyme digestion, mass spectrometry and Smith degradation. Using this culture system, the amount of the new oligosaccharide produced increased with the incubation time, even after the production of glycosaminoglycan initiated by Xyl-MU and Gal-Xyl-MU had reached a plateau. These results suggest that this oligosaccharide may be involved in terminating the elongation of glycosaminoglycan chains that is initiated by Xyl-MU.

A method for determination of galactosyltransferase I activity synthesizing the proteoglycan linkage region

An assay method was devised for measuring the activity of galactosyltransferase I (UDP-D-galactose:D-xylose galactosyltransferase), which is one of the enzymes synthesizing the linkage region between the core protein and glycosaminoglycan chains of proteoglycan. For this method, the reaction mixture contained a fluorescent substrate, 4-methylumbelliferyl-beta-D-xyloside as an acceptor, UDP-galactose as a donor and D-galactal as a competitive inhibitor of endogenous beta-galactosidase in the enzyme solution. The reaction mixture was incubated at 37 degrees C with enzyme solution prepared from an extract of cultured cells, and galactosyl-xylosyl-4-methylumbelliferone was produced as a reaction product. Measurement of galactosyltransferase I activity was performed by separation and quantitative analysis of this reaction product using high-performance liquid chromatography. Utilizing this method, easier and more sensitive detection of galactosyltransferase I activity in a cell-free system became possible. Application of the method revealed that cultured human skin fibroblasts contained galactosyltransferase I activity.

Simple measurement of glycosaminoglycan produced by cultured fibroblasts using 4-methylumbelliferyl beta-D-xyloside

A simple and rapid method was devised for measurement of glycosaminoglycan produced by cultured cells. 4-Methylumbelliferyl-beta-D-xyloside was added to the medium of the cultured cells. After incubation, glycosaminoglycan, which was produced from 4-methylumbelliferyl-beta-D-xyloside as a primer and secreted into the medium, was separated by proteinase digestion, trichloroacetic acid treatment and ethanol precipitation. The glycosaminoglycan, bearing a fluorescent moiety at the reducing terminal, was electrophoresed on cellulose acetate membrane, and then the fluorescent band visible on the membrane was extracted. The fluorescence of the band was measured, and from this the amount of glycosaminoglycan was estimated. Using this method, it was possible to quantify a very small amount of glycosaminoglycan with relatively high sensitivity without employing a radioisotope. This method was applied for determination of glycosaminoglycan produced by cultured fibroblasts from human uterine cervix, and also the effect of a hormone on glycosaminoglycan production. It was found that uterine cervical fibroblasts produced twice as much glycosaminoglycan as skin fibroblasts.

Effects of p-nitrophenyl-beta-D-xylopyranoside (beta-D-xyloside) on the androgen-induced growth of the lateral prostate of the prepubertally castrated guinea pig

The aim of this study was to examine the effects of beta-D-xyloside (XYL), a compound which interferes with stromal proteoglycan (PG) synthesis, on androgen induced growth of the lateral prostate (LP). Young male guinea pigs were castrated at 3 weeks of age and divided into three groups 6 weeks after castration. In group one, the animals were injected subcutaneously daily with 80 mg/kg of XYL, followed 3 days later by a daily dose of 10 mg/kg of dihydrotestosterone (DHT) for 2 more weeks. The second group served as control and received DHT only. In the third group, animals were treated first with XYL, like those in group one, and then followed by DHT alone for 2 weeks to check reversibility of the XYL effect. At the end of the experiment, the lateral prostate was removed and processed for morphological and cytochemical examination. The results showed that XYL inhibited the DHT stimulated growth of the lateral prostate. The fibroblasts showed a dilated granular endoplasmic reticulum filled with granular substances. In the interstitial spaces, there was a drastic increase in Cuprolinic Blue (CB) positive filaments and polygonal granules believed to be PGs or glycosaminoglycans (GAGs). Their number was much greater than the control. The distribution and density of the collagen fibers appeared similar to the control. The secretory alveoli were lined by epithelium with few secretory granules of low electron density and a larger number of clear vesicles. There was a slight reduction in glycoconjugate reactivities in the epithelial cells. The lectin binding patterns and the structural features were comparable between the control and recovery groups, indicating the XYL effects were reversible. The results suggest that stromal PG biosynthesis may play a role in epithelial function and an altered stromal matrix would hamper the effects of DHT on the target organ.

Questioning the reliability of p-nitrophenyl-beta-D-xyloside as probe to study the metabolic effects of abrogated proteoglycan synthesis in cultured cells

p-Nitrophenyl-beta-D-xylopyranoside (PNP-Xyl) and similar aglycone derivatives of xylosides are proposed selective inhibitors of proteoglycan synthesis which are used frequently to analyse the metabolic and cellular effects of abrogated proteoglycan formation and, hence, tentatively, the functions of these complex molecules. Using rat liver fat storing cell (FSC) cultures as a model, the possibility was tested that p-nitrophenol (PNP), which might be generated by the enzymatic hydrolysis of PNP-Xyl, could mediate some of those effects ascribed previously to PNP-Xyl induced inhibition of proteoglycan synthesis. PNP-Xyl and PNP inhibited dose-dependently the proliferation of FSC reaching 50% inhibition at about 1.9 and 0.6 mM, respectively. The inhibition of proliferation was not accompanied by signs of toxic cell damage and was fully reversible after withdrawal of the drugs. After an initial 4-fold stimulation of the formation of [35S]sulfate-labeled medium glycosaminoglycans (GAG) by PNP-Xyl at 0.1 mM, higher concentrations of this compound (about 0.5 mM) but also PNP decreased progressively the synthesis of sulfated medium GAG. A proliferation inhibiting concentration of PNP (0.75 mM) induced disorganization and reduced the expression of desmin- and smooth muscle iso-alpha-actin containing cytoskeletal filaments. These effects were similar to related effects reported previously for PNP-Xyl. Incubation of FSC with 5 mM PNP-Xyl resulted in a time-dependent increase of PNP in medium and cells; intracellular concentrations of PNP were reached sufficient to inhibit the mitotic activity of FSC. In lysates of FSC 0.65 nmol PNP/hr/micrograms DNA or 1 x 10(5) cells were generated from PNP-Xyl (5 mM) added as substrate. Exemplified with PNP-Xyl-treated FSC cultures, the results suggest for other cell and organ systems also that PNP, which is enzymatically cleaved from PNP-Xyl, might mediate at least some of the major effects attributed previously to the inhibition of proteoglycan synthesis. The aglycone may interfere with the effects of PNP-Xyl on proteoglycan metabolism and, therefore, could complicate in an unpredictable manner the interpretation of metabolic inhibitory studies using these compounds.

Heparitinase treatment of rat embryos during cranial neurulation

Heparan sulphate has been reported to be present in rat embryos. It is covalently linked to a core protein as heparan sulphate proteoglycan (HSPG). Heparitinase specifically degrades heparan sulphate, thus treatment of rat embryos with this enzyme in vitro should result in the perturbation of any tissue interactions which involve heparan sulphate proteoglycan. In this study heparitinase was either added to the culture medium or microinjected directly into the amniotic cavity. Heparitinase treatment resulted in abnormal development of the whole embryo, but the earliest effects were observed in the cranial region. Forebrain development was grossly abnormal: the neural folds remained widely open, with beak-like outgrowths rostrally. Optic sulci failed to develop. The midbrain and rostral hindbrain neural folds also remained widely open. In the trunk, where the pattern of neurulation is less complex than in the cranial region, rostral neural tube closure did occur although the morphology of the closed region was far from normal. These results suggest that heparan sulphate proteoglycan is essential for normal neurulation. Epithelial somite formation was perturbed, but neural crest cell emigration, otic pit formation and pharyngeal arch formation, all important morphogenetic events which occur during this period of development, were not inhibited by heparitinase treatment. Prolonged (44 h) exposure to the enzyme resulted in the conversion of the embryonic structure to a much simpler form: mesenchymal cells (stellate or spindle-shaped) enclosed within a simple epithelial coating.

Preparation and application of a fluorogenic substrate for endo-beta-xylosidase

The present paper describes a fluorometric assay for galactosaminoglycan-degrading endo-beta-xylosidase, utilizing glycosaminoglycan chains bearing a 4-methylumbelliferyl group at the reducing terminus as a substrate. This fluorogenic substrate is synthesized by human skin fibroblasts cultured in the presence of a fluorogenic xyloside, 4-methylumbelliferyl-beta-D-xyloside. The assay is based on measurement of the fluorescence of 4-methylumbelliferone, enzymatically liberated from the synthetic substrate by endo-beta-xylosidase. We examined the applicability of the assay for analysis of endo-beta-xylosidase activity.

Correlations between heparan sulfate metabolism and hepatoma growth

A rat hepatoma cell line (Gershenson et al., Science, 170:859-861, 1970) contains a dynamic steady-state pool of free heparan sulfate (HS) chains in the nucleus that increases in amount when growing cells reach confluence (Fedarko and Conrad, J. Cell Biol., 102:587-599, 1986). In logarithmically growing cells labeled with 35SO4(2-) steady-state levels of [35SO4]HS in the nucleus are altered by a variety of culture conditions. Rapidly dividing cells (doubling time = 18-22 h) growing under optimized conditions had steady-state levels of nuclear HS within the range of 40-50 pmol 35SO4 in nuclear HS/10(6) cells. The steady-state levels of nuclear HS were lowered by several changes in culture conditions, including 1) additions of 1 mM p-nitrophenyl-beta-D-xyloside, 0.25-0.5 mM (+)-catechin, 0.5 ng/ml transforming growth factor beta, 20 ng/ml phorbol-12-myristate-13-acetate, 1 mM dibutyryl cAMP, or 1 mM inositol-2-PO4; 2) decreased levels of D-glucose; or 3) deletions of serum, insulin, or inositol. In all cases lowering of the nuclear HS level was accompanied by an increase in the cell doubling times, suggesting a correlation in which nuclear HS levels must be optimized for maximal growth rates. When cells cultured under optimal growth conditions reached confluence, the level of nuclear HS increased threefold and the cells stopped dividing. The same culture conditions that lowered the steady-state levels of HS in the logarithmically growing cells prevented this rise in the nuclear HS as the cells reached confluence and resulted in loss of contact inhibition and overgrowth of the confluent cultures. These observations suggest a second correlation in which elevated nuclear HS levels are found when cell growth is inhibited at confluence; prevention of this rise results in continued growth. Consistent with this correlation between elevated nuclear HS and reduced growth rates, it was observed that addition of either 0.5 microgram/ml hydrocortisone or 0.05 microgram/ml retinoic acid to the culture medium of logarithmically growing cultures resulted in increases in steady-state levels of nuclear HS that were accompanied by increased cell doubling times. The two agents that increased the levels of nuclear HS in logarithmically growing cultures had little effect on levels of nuclear HS in confluent cells or on contact inhibition.(ABSTRACT TRUNCATED AT 400 WORDS)

beta-D-xylosides and their analogues as artificial initiators of glycosaminoglycan chain synthesis. Aglycone-related variation in their effectiveness in vitro and in ovo

A series of aryl and alkyl O-beta-D-xylosides and their analogues with S, NH or CH2 in the glycosidic linkage were prepared and examined for their ability to act as artificial chain initiators of chondroitin (dermatan) sulphate synthesis in embryonic chick cartilage, foetal rat skin and 6-week-old-rat aorta under conditions where normal protein-core synthesis was inhibited by cycloheximide. For all these tissues in culture, phenyl O-beta-D-xyloside and phenyl beta-D-thioxyloside were clearly more effective than the corresponding N-xyloside and homo-C-xyloside. Introduction of a carboxy group to the para position of their aglycone yielded derivatives with far lower initiator activity. In a concentration range lower than 0.1 mM, the effectiveness of alkyl beta-D-thioxyloside was greatly influenced by the carbon number (n) of the alkyl group and was at a maximum at n = 7 or 8 for the cartilage, at n = 5 for the skin and at n = 4 for the aorta. In the beta-xyloside-treated cartilages, the average length of newly formed chondroitin sulphate chains reflected the chain-initiator activity of added xyloside, i.e. the higher the initiator activity, the shorter the average chain length. In the skin and aorta, none of the drugs could relieve the inhibition of heparan sulphate synthesis caused by cycloheximide. Fertilized hens' eggs were each injected on day 9 with 9.2 mumol of beta-xyloside and the skeletal systems of embryos were examined a week later. The embryos treated with beta-xylosides of relatively high initiator activity showed a 30-40% decrease in the overall growth rate of skeletons, whereas those treated with beta-xylosides of low initiator activity showed little or no decrease in the growth rate. The results are consistent with the notion that the observed change in skeletal morphology results mainly, if not completely, from beta-xyloside-induced synthesis of core-protein-free chondroitin sulphate, and further suggest that a procedure employing a series of beta-xyloside homologues with various initiator activities will furnish an easily applied criterion on which to test the specificity of xyloside action on biological processes.

Inhibition of cell migration in sea urchin embryos by beta-D-xyloside

This investigation examines the effect of exogenous xylosides on primary mesenchyme cell behavior in Strongylocentrotus purpuratus embryos. In confirmation of studies in some other species the addition of 2 mM p-nitrophenyl-beta-D-xylopyranoside blocks the migration but not the initial ingression of primary mesenchyme cells. The blastocoel matrix of treated embryos appears deficient in a 15- to 30-nm-diameter granular component that is observed extensively on the basal lamina and on filopodia of migrating primary mesenchyme cells in untreated embryos. Other blastocoel components appear unaffected by ultrastructural criteria. The incorporation of 35SO4(2-) per embryo into ethanol precipitates of isolated blastocoel matrices was reduced significantly after xyloside treatment but the distribution of 35SO4(2-) after polyacrylamide gel electrophoresis or the glycosaminoglycan composition was unaffected. Chromatography on Sepharose CL-2B demonstrates a reduction in size of sulfated components of the blastocoel. While over 60% of the 35S-labeled material from the blastocoel of normal mesenchyme blastulae is voided from a Sepharose CL-2B column run in a dissociative solvent, only 10% from xyloside treated embryos is voided. Instead, there is a large included peak with Kav of 0.33. This material is acid soluble but cetylpyridinium chloride precipitable. It apparently consists largely of free glycosaminoglycan chains. Based on analysis of chondroitinase ABC digestion products this material consists of 41% chondroitin-6-sulfate and 58% dermatan sulfate. These results are consistent with a role in cell migration for intact chondroitin sulfate/dermatan sulfate proteoglycans in the sea urchin blastocoel matrix.

Initiation of chondroitin sulphate synthesis by beta-D-galactosides. Substrates for galactosyltransferase II

beta-Galactosides were found to initiate chondroitin sulphate chain synthesis in chick-embryo cartilage in vitro and thereby relieve inhibition by cycloheximide of [3H]-acetate incorporation into chondroitin sulphate. beta-Galactosides with an apolar aglycan group such as phenyl O-beta-galactoside were active, whereas those with a charged or polar aglycan group such as pyridine 3-O-beta-galactoside or those with sulphur instead of oxygen in the glycosidic linkage (phenyl beta-thiogalactoside) were not. beta-Galactosides also serve as substrates for microsomal galactosyltransferase activity from chick-embryo cartilage. Phenyl O-beta-galactoside and pyridine 3-O-beta-galactoside were effective substrates for this enzyme, but phenyl S-beta-thiogalactoside and pyridine 2-S-beta-thiogalactoside were only slightly active. This galactosyltransferase was shown to be a separate enzyme from galactosyltransferase I, which catalyses transfer of galactose from UDP-galactose to beta-xylosides. It is proposed that the enzyme catalysing this reaction is galactosyltransferase II, responsible for transfer of the second galactose residue of the chondroitin sulphate linkage oligosaccharide. No transfer of glucuronic acid from UDP-glucuronic acid to beta-galactosides, catalysed by the microsomal preparation could be detected.

Development of the biochemical and morphological changes induced by administration of a beta-xyloside to chick embryos

4-Methylumbelliferyl beta-D-xyloside was administered to 9-day-old chick embryos, and the morphological and chemical changes in the embryo were followed daily. Increases in wet weight, Na and Cl content, and visible edema were detectable at 10 days and fully apparent at 11 days. Dry weight increased to the same extent in control and treated embryos for four days, but then diverged. The degree of sulfation of chondroitin sulfate was slightly less in treated than control embryos at 10 days, and reached a steady low value at 11 days. Analysis of glycosaminoglycans in skin, muscle, and aorta showed an increase in chondroitin and its sulfates in the two former tissues but not the latter. In muscle and aorta, the degree of sulfation of chondroitin sulfate was markedly reduced; but in skin the results suggested a more complex picture in which the normal metabolism of glycosaminoglycans was altered. A possible physiological role is suggested for chondroitin sulfate in embryonic soft tissues.

Fluid and glycosaminoglycan excretion by chick embryos treated with a beta-D-xyloside

Wet weights and glycosaminoglycan content were determined for embryo, amnion, and allantois of control chick embryos and embryos injected with 4-methylumbelliferyl beta-D-xyloside at nine days of age. There was an immediate increase in total uronic acid content, but not in uronic acid concentration, in the embryo. No difference could be detected either in fluid volume, nor in content or type of glycosaminoglycan, in the amnion of the two groups. The fluid content of the allantois fo control eggs increased steadily between nine and 14 days, but in treated embryos the fluid content of the allantois remained low for at least a week. Less than 2 mg of uronic acid was present in allantoic fluid of control 16-day-old embryos, while treated embryos had accumulated more than 8 mg. More than 95% of the latter uronic acid was accounted for as chondroitin sulfate linked to methylumbelliferone and with a degree of sulfation of 50-60%. Thus beta-xyloside-treated embryos excrete large amounts of chondroitin sulfate and very little fluid.

Control of chondroitin sulphate biosynthesis. beta-D-Xylopyranosides as substrates for UDP-galactose: D-xylose transferase from embryonic-chicken cartilage

Embryonic-chicken epiphyseal cartilage was incubated in vitro with a variety of beta-xylosides and the amount of [3H]acetate incorporation into chondroitin sulphate was determined under conditions when normal protein core production was inhibited by cycloheximide. The ability of the different beta-xylosides to relieve thea cycloheximide-mediated inhibition of chondroitin sulphate synthesis was influenced by the nature of the aglycan group of te xyloside. beta-Xylosides with apolar and uncharged aglycan groups were most effective and produced a severalfold stimulation of chondroitin sulphate biosynthesis. beta-Xylosides with charged aglycan groups were less effective initiators of chondroitin sulphate synthesis. The rate of galactose transfer from UDP-galactose to each of the beta-xylosides, catalysed by a cell-free microsomal preparation from embryonic cartilage, was measured. This study showed that the nature of the aglycan group of the beta-xyloside was a factor determining the capacity of the xyloside to act as an acceptor for galactosyltransferase I, the enzyme that catalyses the first galactose transfer reaction of chondroitin sulphate synthesis. The aglycan group of the xyloside also appeared to influence other steps leading to chondroitin sulphate chain initiation in vitro.

Chondroitinase-resistant sulfated glycosaminoglycans synthesized by cartilages of chick embryos and of newborn chickens and rats

Biosynthesis of chondroitinase-resistant glycosaminoglycans as minor components was studied in the cartilages of chick embryos and of newborn chickens and rats. Sternal and knee cartilages were labeled in vitro with 35SO42-, and then 35S-labeled glycosaminoglycans were analyzed. In rats up to 2 weeks old, only one glycosaminoglycan could be detected as heparan sulfate. In the chick embryos and the newborn chickens, however, keratan sulfate as well as heparan sulfate could be detected. As chondroitinase-sensitive glycosaminoglycans, large amounts of both chrondroitin 4- and 6-sulfates were synthesized in the chick cartilage, but the synthesis of chondroitin 6-sulfate could scarcely be seen in the rat cartilage. The results seem to indicate that the biosynthesis of keratan sulfate has some relation to that of chondroitin 6-sulfate.

Changes in chemical composition of chick embryos treated with a beta-xyloside and a lathyrogen

Nine-day chick embryos were treated with 4-methylumbelliferyl beta-D-xyloside or beta-aminopropionitrile fumarate, and their gross chemical composition was examined one week later. Total DNA was 10--20% less in embryos treated with either drug than it was in control embryos. Xyloside-treated embryos showed marked increases in percent wet weight and in sodium/DNA and chloride/DNA ratios, and small decreases in protein/DNA, hydroxyproline/DNA and sulfate/DNA. None of these parameters was affected in embryos treated with beta-aminopropionitrile. Approximately 85% of the uronic acid of control embryos was present as chondroitin sulfate, with a degree of sulfation of 80% and charge density of 1.8; all of this chondroitin sulfate was covalently linked to peptide and had a number-average molecular weight of 29,300. In embryos treated with beta-xyloside, 90% of the uronic acid was present as chondroitin sulfate, with a degree of sulfation of 40% and charge density ranging from 1 to 2; 27% of this chondroitin sulfate, with an average molecular weight of 25,400, was peptide linked, while 73% was linked to 4-methylumbelliferone and had an average molecular weight of 22,900. The chemical differences between embryos treated with the xyloside and embryos treated with the lathyrogen reinforce the conclusion on morphological grounds that these are distinct syndromes involving different aspects of the extracellular matrix.

The mode of action of 4-methylumbelliferyl beta-D-xyloside on the synthesis of chondroitin sulphate in embryonic-chicken sternum

1. Embryonic-chicken sterna, incubated in medium containing 0.1mm-4-methylumbelliferyl beta-d-xyloside (4-methylcoumarin 7-beta-d-xyloside), synthesize proteochondroitin sulphate that is significantly undersulphated and shorter than usual [Gibson, Segen & Audhya (1977) Biochem. J.162, 217-233]. 2. Neither the beta-d-galactoside nor the beta-d-glucuronide of 4-methylumbelliferone, nor 4-methylumbelliferone itself, produced the effects. The only metabolites of 4-methylumbelliferone that were detected in cartilages exposed to 4-methylumbelliferyl beta-d-xyloside were unchanged xyloside and chondroitin sulphate covalently attached to 4-methylumbelliferone. 3. Gel filtration of salt extracts of sterna incubated in medium containing the xyloside showed that there were two pools of chondroitin sulphate in the tissue. One pool was identified, on the basis of its elution pattern and the linear kinetics of incorporation of sulphate into it, as proteochondroitin sulphate. Incorporation into the other pool, whose properties suggested that it was methylumbelliferyl-chondroitin sulphate, indicated that it underwent partial turnover. The molecular weight of this chondroitin sulphate was about 19000, and it appeared to be about 70% sulphated. 4. When sterna were incubated in medium containing the xyloside, there was a very large incorporation of sulphate and glucose into glycosaminoglycans that were released into the incubation medium. This contrasts with incubations of sterna in the absence of the xyloside, in which less than 5% of the sulphate incorporated could be recovered from the medium. The glycosaminoglycan released into the medium was 4-methylumbelliferyl-chondroitin sulphate, whose average molecular weight was 7000-8000 and degree of sulphation more than 95%. 5. Incorporation of sulphate into proteochondroitin sulphate was stimulated more than 3-fold by addition of 20% (v/v) human serum and 10nm-l-3,3',5-tri-iodothyronine. Incorporation into methylumbelliferyl-chondroitin sulphate, in either the tissue or the medium, was not significantly altered. 6. The decrease in chain length and degree of sulphation of proteochondroitin sulphate is explained in terms of competition between peptide-linked primers and methylumbelliferone-containing primers at the intracellular sites of polysaccharidechain elongation and sulphation. The implications of the results for the mechanism of stimulation of proteoglycan synthesis by serum factors are discussed.

The effect of beta-D-xylosides on chondroitin sulphate biosynthesis in embryonic chicken cartilage in the absence of protein synthesis inhibitors

Incorporation of [35S]]sulphate, [3H]glucose and [3H]serine into glycosaminoglycans and proteoglycans of embryonic-chicken sternum was measured in vitro in incubation medium containing 4-methylumbelliferyl beta-D-xyloside or p-nitrophenyl beta-D-xyloside at low concentrations, and in the absence of inhibitors of protein synthesis. Incorporation of sulphate was decreased by 80% in incubations in which 1mM-4-methylumbelliferyl beta-xyloside or 2.5 mM-p-nitrophenyl beta-xyloside was present; under these conditions, serum factors stimulated incorporation to only a small extent. When the concentration of the xyloside was decreased tenfold, incorporation of sulphate was inhibited by 60-70%, but when normal human serum or L-3,3',5-tri-iodothyronine or both were also added to the incubation medium, incorporation was markedly stimulated. Experiments in which [35S]sulphate and [3H]glucose were incorporated simultaneously, and enzymic analysis of glycosaminoglycans formed in such experiments, indicated that chondroitin sulphate formed in the presence of 0.1 mM-4-methylumbelliferyl beta-xyloside contained 30-40% less sulphate than did chondrotin sulphate synthesized in the absence of xylosides. Similar experiments, with [3H]serine instead of [3H]glucose, suggested also a 20-30% decrease in chain length of the chondroitin sulphate; this was confirmed by direct gel filtration of labelled glycosaminoglycans on a calibrated column. Incorporation of [3H]glucose or [3H]serine was stimulated by serum and tri-iodothyronine in parallel with incorporation of sulphate. The changes seen in the total chondroitin sulphate were mirrored in the major proteoglycan fraction, purified by isopycnic centrifugation of salt-extracted proteoglycans. The labelling pattern of chondroitin sulphate from this proteoglycan indicated that decreased sulphation of chondroitin sulphate was largely due to the inferior ability of short polysaccharide chains to accept sulphate, with some direct interference with transfer of sulphate to all chains. The results also suggested that the action of serum factors on synthesis of proteochondroitin sulphate is exercised at the level of either protein synthesis or transport to the sites of initiation of polysaccharide synthesis.