Effect of benzyl beta-D-xyloside on the biosynthesis of chondroitin sulphate proteoglycan in cultured human monocytes

Biosynthesis of promatrix metalloproteinase-9/chondroitin sulphate proteoglycan heteromer involves a Rottlerin-sensitive pathway

Background

Previously we have shown that a fraction of the matrix metalloproteinase-9 (MMP-9) synthesized by the macrophage cell line THP-1 was bound to a chondroitin sulphate proteoglycan (CSPG) core protein as a reduction sensitive heteromer. Several biochemical properties of the enzyme were changed when it was bound to the CSPG.

Methodology/Principal Findings

By use of affinity chromatography, zymography, and radioactive labelling, various macrophage stimulators were tested for their effect on the synthesis of the proMMP-9/CSPG heteromer and its components by THP-1 cells. Of the stimulators, only PMA largely increased the biosynthesis of the heteromer. As PMA is an activator of PKC, we determined which PKC isoenzymes were expressed by performing RT-PCR and Western Blotting. Subsequently specific inhibitors were used to investigate their involvement in the biosynthesis of the heteromer. Of the inhibitors, only Rottlerin repressed the biosynthesis of proMMP-9/CSPG and its two components. Much lower concentrations of Rottlerin were needed to reduce the amount of CSPG than what was needed to repress the synthesis of the heteromer and MMP-9. Furthermore, Rottlerin caused a minor reduction in the activation of the PKC isoenzymes δ, ε, θ and υ (PKD3) in both control and PMA exposed cells.

Conclusions/Significance

The biosynthesis of the proMMP-9/CSPG heteromer and proMMP-9 in THP-1 cells involves a Rottlerin-sensitive pathway that is different from the Rottlerin sensitive pathway involved in the CSPG biosynthesis. MMP-9 and CSPGs are known to be involved in various physiological and pathological processes. Formation of complexes may influence both the specificity and localization of the enzyme. Therefore, knowledge about biosynthetic pathways and factors involved in the formation of the MMP-9/CSPG heteromer may contribute to insight in the heteromers biological function as well as pointing to future targets for therapeutic agents.

Heparanase in primary human osteoblasts

Heparanase (HPSE) is known to be involved in fracture repair in mice, but its presence and function in human bone formation remains unclear. Our aim was to determine the expression of HPSE in human bone forming osteoblasts and to better understand its role in osteogenesis. HPSE protein expression and enzymatic activity were demonstrated in osteoblasts isolated from trabecular bone specimens of patients with osteoporosis (OP) and from healthy subjects, although the levels differed markedly. Thus, low levels of HPSE expression were observed in osteoporotic osteoblasts, including in the nucleus compared to those from healthy subjects. Notably, HPSE gene expression was associated with alkaline phosphatase (ALP) activity, the bone turnover marker. Gene profile studies demonstrated that osteogenic genes were downregulated in osteoporotic osteoblasts. We further exposed osteoblasts to exogenous HPSE and found that the level of histone H3 phosphorylation was increased. We provide evidence, for the first time, demonstrating that HPSE expresses and functions in human osteoblasts. Our data suggest that previously undescribed function of HPSE-mediated osteoblastogenesis through regulation of osteogenic gene expression and histone H3 modification. HPSE upregulation may be a novel therapeutic approach in the prevention and treatment of OP.

Stimulation of small proteoglycan synthesis by the hyaluronan synthesis inhibitor 4-methylumbelliferone in human skin fibroblasts

Human skin fibroblasts cultured with 4-methylumbelliferone (MU), a hyaluronan synthesis inhibitor, produce a hyaluronan-deficient extracellular matrix (See [9]). Our present study investigated the effects of MU on proteoglycan, which is the other main component of the extracellular matrix, and interacts with hyaluronan. Proteoglycans isolated from culture medium in the presence or absence of MU were characterized by gel-filtration chromatography, ion-exchange HPLC, electrophoresis, and immunoblotting. We found that MU had only a negligible effect on the synthesis of large proteoglycan but increased the production of small proteoglycan in comparison with cultures lacking MU. This small proteoglycan was identified by immunoblotting as decorin. The structures of decorin synthesized in the presence and absence of MU were compared by gel-filtration chromatography, and the data indicated that cells incubated with MU produced a larger decorin molecule than cells incubated without MU. Furthermore, the two decorins had galactosaminoglycan chains of different sizes. These results suggest that MU inhibits the synthesis of hyaluronan and accelerates production of the larger decorin in the extracellular matrix.

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.

The folded modules of aggrecan G3 domain exert two separable functions in glycosaminoglycan modification and product secretion

Aggrecan is the major proteoglycan in the extracellular matrix of cartilage. A notable exception is nanomelic cartilage, which lacks aggrecan in its matrix. The example of nanomelia and other evidence leads us to believe that the G3 domain plays an important role in aggrecan processing, and it has indeed been confirmed that G3 allows glycosaminoglycan (GAG) chain attachment and product secretion. However, it is not clear how G3, which contains at least a carbohydrate recognition domain (CRD) and a complement binding protein (CBP) motif, plays these two functional roles. The present study was designed to dissect the mechanisms of this phenomenon and specially 1) to determine the effects of various cysteine residues in GAG modification and product secretion as well as 2) to investigate which of the two processing events is the critical step in the product processing. Our studies demonstrated that removal of the two amino-terminal cysteines in the CRD motif and the single cysteine in the amino terminus of CBP inhibited secretion of CRD and CBP. Use of the double mutant CRD construct also allowed us to observe a deviation from the usual strict coupling of GAG modification and product secretion steps. The presence of a small chondroitin sulfate fragment overcame the secretion-inhibitory effects once the small chondroitin sulfate fragment was modified by GAG.

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.

Primers of glycosaminoglycan biosynthesis from Peruvian rain forest plants

We have developed a rapid, high throughput screening assay for compounds that alter the assembly of glycosaminoglycan chains in Chinese hamster ovary cells. The assay uses autoradiography to measure the binding of newly synthesized [35S]proteoglycans and [35S]glycosaminoglycans to a positively charged membrane. Screening over 1000 extracts from a random plant collection obtained from the Amazon rain forest yielded five plants that stimulated glycosaminoglycan assembly in both wild-type cells and a mutant cell line defective in xylosyltransferase (the first committed enzyme involved in glycosaminoglycan biosynthesis). Fractionation of an extract of Maieta guianensis by silica gel and reverse-phase chromatography yielded two pure compounds with stimulatory activity. Spectroscopic analysis by NMR and mass spectrometry revealed that the active principles were xylosides of dimethylated ellagic acid. One of the compounds also contained a galloyl group at C-3 of the xylose moiety. These findings suggest that plants and other natural products may be a source of agents that can potentially alter glycosaminoglycan and proteoglycan formation in animal cells.

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.

Activated macrophages and the blood-brain barrier: inflammation after CNS injury leads to increases in putative inhibitory molecules

The cellular responses to spinal cord or brain injury include the production of molecules that modulate wound healing. This study examined the upregulation of chondroitin sulfate proteoglycans, a family of molecules present in the wound healing matrix that may inhibit axon regeneration in the central nervous system (CNS) after trauma. We have demonstrated increases in these putative inhibitory molecules in brain and spinal cord injury models, and we observed a close correlation between the tissue distribution of their upregulation and the presence of inflammation and a compromised blood-brain barrier. We determined that the presence of degenerating and dying axons injured by direct trauma does not provide a sufficient signal to induce the increases in proteoglycans observed after injury. Activated macrophages, their products, or other serum components that cross a compromised blood-brain barrier may provide a stimulus for changes in extracellular matrix molecules after CNS injury. While gliosis is associated with increased levels of proteoglycans, not all reactive astrocytes are associated with augmented amounts of these extracellular matrix molecules, which suggests a heterogeneity among glial cells that exhibit a reactive phenotype. Chondroitin sulfate also demarcates developing cavities of secondary necrosis, implicating these types of boundary molecules in the protective response of the CNS to trauma.

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.

The effects of beta-D-xyloside on the synthesis of proteoglycans by skeletal muscle: lack of effect on decorin and differential polymerization of core protein-bound and xyloside-linked chondroitin sulfate

Developing skeletal muscle cells, as both myoblasts and myotubules, synthesize a distinctive large chondroitin sulfate proteoglycan. To probe the role of this proteoglycan in myogenesis, chick embryonic muscle cells in culture were treated with beta-D-xyloside, a compound which interferes with proteoglycan synthesis by acting as an artificial acceptor for glycosaminoglycan synthesis and thereby competing with the proteoglycan core protein. Analysis of the proteoglycans indicates that with increasing concentrations of beta-D-xyloside, synthesis of the chondroitin sulfate proteoglycan is inhibited, with concomitant massive synthesis of xyloside-linked chondroitin sulfate glycosaminoglycans. Xyloside does not appear to inhibit glycosaminoglycan attachment onto the small heparan sulfate and dermatan sulfate proteoglycans which are synthesized in the muscle cultures, even though, because of the mechanism of action of beta-xyloside, these proteoglycans should be affected. At submaximal concentrations of beta-xyloside, there is synthesis of both large chondroitin sulfate proteoglycans and xyloside-linked chondroitin sulfate. The xyloside-linked chondroitin sulfate chains have the same sulfation pattern as the core protein-bound skeletal muscle chondroitin sulfate (90% 6-sulfated isomer), but are much smaller (24,000 vs. 65,000 in molecular weight). The discrepancy in size but identify of sulfation indicates that, although sulfation takes place normally on either the core protein or the xyloside acceptor, termination of glycosylation occurs earlier for xyloside-initiated chondroitin sulfate. In spite of these dramatic effects on chondroitin sulfate proteoglycan synthesis, beta-xyloside elicits no observable effects on in vitro myogenesis. This suggests that the function served by the large chondroitin sulfate proteoglycan is not required in the more simplified environment of the muscle cultures.

Sulphation of proteochondroitin and 4-methylumbelliferyl beta-D-xyloside-chondroitin formed by mouse mastocytoma cells cultured in sulphate-deficient medium

Mouse mastocytoma cells were cultured in medium containing [3H]GlcN and concentrations of [35S]sulphate varying from 0.01 to 0.5 mM. Intracellular [35S]sulphate incorporation increased severalfold from the lowest concentrations, reaching a maximum at 0.1-0.2 mM, whereas incorporation of [3H]hexosamine remained constant at all sulphate concentrations. Proteo[3H]-chondroitin [35S]sulphate was isolated and incubated with chondroitin ABC lyase, yielding 35S-labelled and/or 3H-labelled delta Di-0S and delta Di-4S disaccharide products. The increasing percentage of delta Di-4S was consistent with the increasing sulphate incorporation at each higher [35S]sulphate concentration. Examination of proteochondroitin [35S]sulphate size by Sepharose CL-6B chromatography indicated a range consistent with various numbers of glycosaminoglycan chains on the protease-resistant serglycin core protein. Alkali-cleaved chondroitin [35S]sulphate products indicated similar size distributions at all sulphate concentrations with no indication of preferential sulphation being related to smaller or larger size. DEAE-cellulose chromatography of [3H]chondroitin [35S]sulphate glycosaminoglycans indicated a random undersulphation as [35S]sulphate concentration was lowered. Addition of 4-methylumbelliferyl beta-D-xyloside to the cultures resulted in a 2-2.5-fold stimulation of [3H]chondroitin [35S]sulphate synthesis with formation of beta-xyloside-[3H]chondroitin [35S]sulphate which was much smaller, as estimated by Sepharose CL-6B chromatography, than the decreased amount of [3H]chondroitin [35S]sulphate derived from proteo[3H]chondroitin [35S]sulphate. Much higher concentrations of sulphate were necessary to produce sulphation of the beta-xyloside-[3H]chondroitin comparable with that of proteo[3H]-chondroitin, as indicated by chondroitin ABC lyase products and DEAE-cellulose chromatography. The specific radioactivities of the [3H]GalN in the proteo[3H]chondroitin [35S]sulphate and beta-xyloside-[3H]chondroitin [35S]sulphate were calculated from the 3H and 35S c.p.m. of isolated dual-labelled delta Di-4S from each, and indicated that the presence of the beta-xyloside resulted in a dilution of the [3H]GlcN by endogenous GlcN that was 4 times higher than that of cultures lacking the beta-xyloside. The higher sulphate concentrations needed for sulphation of beta-xyloside-chondroitin suggests that the membrane-bound nature of the proteochondroitin acceptor in juxtaposition to a chondroitin sulphate-synthesizing enzyme complex effectively reduces the apparent Km for adenosine 3'-phosphate 5'-phosphosulphate.

Proliferation and transformation of cultured liver fat-storing cells (perisinusoidal lipocytes) under conditions of beta-D-xyloside-induced abrogation of proteoglycan synthesis

Fat-storing cells (perisinusoidal lipocytes, Ito cells) are the major connective tissue-producing cell type in liver. In areas of necroinflammation the cells proliferate and transform into desmin and smooth muscle alpha-actin-positive myofibroblast-like cells which synthesize a broad spectrum of significant amounts of collagens, proteoglycans, and matrix glycoproteins. Available data suggest a central role for these cells in the pathogenesis of fibrosis. Beta-D-Xyloside, an artificial initiation site for galactose-linked glycosaminoglycans, thereby uncoupling the synthesis of core protein and GAG, was used as a probe to study main cellular functions under conditions of abrogated proteoglycan synthesis. The exposure for 48 hr of fat-storing cells to p-nitrophenyl beta-D-xyloside (PNP-Xyl) increased dose-dependently the synthesis of [35S]sulfate-labeled medium GAG. Maximum stimulation of fivefold above normal was reached at 1.0 mM PNP-Xyl. Higher concentrations of PNP-Xyl progressively decreased the stimulatory effect on GAG synthesis. The relative composition of GAG in medium (60% chondroitin sulfate, 34% dermatan sulfate), at the cell surface, and intracellularly (mainly heparan sulfate) was not changed significantly by PNP-Xyl. The amounts of intracellular and cell surface-bound GAG were reduced by 40 and 30%, respectively, by PNP-Xyl leading to a depletion of heparan sulfate at the cell surface. Pulse-chase experiments revealed that xyloside-initiated GAG were secreted immediately after synthesis into the medium. GAG synthesized in the presence of 1 and 5 mM PNP-Xyl were free of core protein, and the molecular size of the GAG chains was smaller than that of GAG obtained from beta-eliminated proteoglycans synthesized in control cultures. At concentrations above 3 mM PNP-Xyl generated a dose-dependent inhibition of cell proliferation, which was at any stage of culture fully reversible upon removal of the drug. Viability and general protein synthesis were not reduced, but fat-storing cell transformation and deposition of matrix glycoproteins were retarded. Only a very small fraction of drug-treated cells (5 mM PNP-Xyl) did express on the 11th culture day smooth muscle iso-alpha-actin- and desmin-containing cytoskeletal filaments, which are important indicators of transformation into myofibroblast-like cells. Furthermore, the synthesis of hyaluronan and the expression of immunostained fibronectin, laminin, and tenascin were reduced in cultures exposed to 5 mM PNP-Xyl. The described cellular functions were not affected by exposure of fat-storing cells to p-nitrophenyl beta-D-galactoside.(ABSTRACT TRUNCATED AT 400 WORDS)

Xyloside effects on in vitro hematopoiesis: functional and biochemical studies

Xyloside supplementation of long-term bone marrow cultures (LTBMCs) has been reported to result in greatly enhanced proliferation of hematopoietic stem cells. This was presumed to be the result of xyloside-mediated perturbation of proteoglycan synthesis by marrow-derived stromal cells. To investigate this phenomenon, we first studied the effects of xyloside supplementation on proteoglycan synthesis by D2XRadII bone marrow stromal cells, which support hematopoietic stem cell proliferation in vitro. D2XRadII cells were precursor labelled with 35S-sulfate, and proteoglycans separated by ion exchange chromatography, isopyknic CsCl gradient centrifugation, and gel filtration HPLC. Xyloside-supplemented cultures showed an approximately fourfold increase in total 35S incorporation, mainly as free chondroitin-dermatan sulfate (CS/DS) glycosaminoglycan chains in the culture media. Both xyloside supplemented and nonsupplemented cultures synthesized DS1, DS2, and DS3 CS/DS proteoglycans as previously described. In contrast to previous reports, xyloside was found to inhibit hematopoietic cell growth in LTBMC. Inhibitory effects were observed both in cocultures of IL-3-dependent hematopoietic cell lines with supportive stromal cell lines and in primary murine LTBMCs. Xyloside was found to have a marked inhibitory effect on the growth of murine hematopoietic stem cells and IL-3-dependent hematopoietic cell lines in clonal assay systems and in suspension cultures. In contrast, dialyzed concentrated conditioned media from LTBMCs had no such inhibitory effects. These findings suggest that xyloside-mediated inhibition of hematopoietic cell growth in LTBMC resulted from a direct effect of xyloside on proteoglycan synthesis by hematopoietic cells.

Oligosaccharide mapping of proteoglycan-bound and xyloside-initiated dermatan sulfate from fibroblasts

The copolymeric structure of dermatan sulfate chains synthesized by skin fibroblasts has been examined. Chains initiated onto exogeneous p-nitrophenyl-beta-D-xylopyranoside or attached to protein in a large proteoglycan, PG-L, and two small proteoglycans, PG-S1 and PG-S2, have been compared by using high resolution electrophoresis and gel chromatography of oligosaccharides generated by specific enzymatic or chemical degradations. The results confirm that chains attached to PG-L are glucuronate-rich, whereas novel findings indicate that chains attached to either of the two PG-S variants yield closely similar oligosaccharide maps, have approximately equal glucuronate and iduronate content and contain over 90% 4-sulfated disaccharide repeating units. Dermatan sulfate chains built onto xyloside at concentrations of 50 microM and below have a copolymeric structure similar to that of chains from the two PG-S variants. These findings indicate that the polymer-modifying machinery can generate chains with extended iduronate-containing repeats also when the xylose primer is not linked to core protein.

Proteoglycans in haemopoietic cells

Proteoglycans are produced by all types of haemopoietic cells including mature cells and the undifferentiated stem cells. The proteinase-resistant secretory granule proteoglycan (serglycin; Ref. 14), is the most prevalent and best characterised of these proteoglycans. Although its complete pattern of distribution in the haemopoietic system is unknown, serglycin has been identified in the mast cells, basophils and NK cells, in which secretion is regulated, and in HL-60 cells and a monocytoid cell line (Kolset, S.O., unpublished data) in which secretion is constitutive. Proteinase-resistant proteoglycans have been detected in human T-lymphocytes and murine stem cells (FDCP-mix) and the core proteins may be closely related to serglycin. A variety of glycosaminoglycan chains are assembled on the serglycin protein and it is likely that this class of proteoglycan can carry out a wide variety of functions in haemopoietic cells including the regulation of immune responses, inflammatory reactions and blood coagulation. There is strong evidence that in mast cells, NK cells and platelets, the proteoglycans are complexed to basic proteins (including enzymes and cytolytic agents) and amines in secretory granules and such complexes may dissociate following secretion from the cell. The stability of the complexes may be regulated by the ambient pH which may be acidic in the granules and neutral or above in the external medium. However, proteinase-proteoglycan complexes in mast cell granules seem to remain stable after secretion and it has been proposed that the proteoglycan regulates activity of proteinases released into the pericellular domain. The functions of proteoglycans which are constitutively secreted from cells are less clear. If cells have no requirement for storage of basic proteins why do they utilise the same design of proteoglycan as cells which accumulate secretory material prior to regulated release? We should stress that the so-called constitutive secretory pathway has been identified in haemopoietic cells in culture, which are usually maintained and grown in the presence of mitogenic factors (e.g., IL-2, IL-3). the cells are therefore activated and it has not been established that continuous proteoglycan secretion occurs in quiescent cells circulating in the peripheral blood. It is possible that lymphocytes, monocytes and macrophages, in which the constitutive secretion pathway operates in vitro, may store proteoglycan in vivo unless stimulated by mitogens or other activating agents.(ABSTRACT TRUNCATED AT 400 WORDS)

The effect of beta-D-xylosides on the proliferation and proteoglycan biosynthesis of monoblastic U-937 cells

The monoblastic cell line U-937 was cultured in the presence of C-ethyl beta-D-xyloside (E-xyl), hexyl beta-D-thioxyloside (HX-xyl), p-nitrophenyl beta-D-xyloside, phenyl beta-D-xyloside or phenyl alpha-D-xyloside. All of the beta-D-xylosides inhibited proliferation, but HX-xyl was by far the most efficient, and had a maximum effect at 1 mM concentration. The inhibitory effect of HX-xyl could be reversed; after washing, the HX-xyl-treated cells proliferated with a pattern similar to that of control cells. For more detailed analysis of the effects of beta-D-xylosides on cell proliferation and chondroitin sulphate (CS)/chondroitin sulphate proteoglycan (CSPG) structure, a comparison between the effects of E-xyl and HX-xyl was made. Treating the cells with 1 mM-HX-xyl resulted in a large increase in CS synthesis, whereas 1 mM-E-xyl had only minor effects on the rate of PG/glycosaminoglycan synthesis. Sepharose CL-6B gel chromatography of medium and cell fractions from 35S-labelled cells revealed that HX-xyl treatment resulted in the expression of only free CS chains, whereas E-xyl exposure leads to the synthesis of both large and small CSPGs, as well as some free CS chains. The expression of elevated levels of free CS chains was clearly correlated to the inhibition of proliferation. The proliferation of U-937-4, a clone of U-937 synthesizing ten times more CSPG/CS than the parent line, was equally inhibited by HX-xyl treatment. With this clone, however, there was no stimulation of CS synthesis after xyloside exposure, indicating that the elevated level of CS evident after xyloside treatment of the parent cell line is not causing the inhibition of proliferation. Furthermore, the biosynthesis of hyaluronate was shown not to be implicated in the xyloside-induced decrease in proliferation. The inhibition of proliferation observed in the presence of 1 mM-HX-xyl did not lead to differentiation of the cells into macrophage-like cells, as is observed when the cells are cultured in the presence of phorbol esters, agents also known to inhibit proliferation of U-937 cells.

Effect of n-butyrate on the synthesis of sulfated glycosaminoglycans and hyaluronate by rat liver fat-storing cells (Ito cells)

The effect of naturally occurring aliphatic carboxylic acid n-butyrate on total and type-specific synthesis of sulfated proteoglycans and hyaluronic acid by rat liver fat-storing cells (Ito cells, vitamin A-storing cells), the main connective tissue producing cell type in liver, was studied. Concentrations of n-butyrate equal to and higher than 5 mM inhibited significantly in a dose-dependent manner the incorporation of [35S]sulfate and [3H]glucosamine into the carbohydrate chains of sulfated proteoglycans. Maximum inhibition of 70% was reached at 15 mM. Similarly, the formation of hyaluronic acid was impaired by n-butyrate. The synthesis profile of specific sulfated proteoglycans was not affected by the compound. beta-Xyloside, an artificial carbohydrate chain initiator, reversed only partially the inhibitory effect of n-butyrate. Thus, the mechanism of n-butyrate inhibition may involve an impairment of both proteoglycan core protein formation and glycosaminoglycan chain elongation.

Subcellular localization of the sulphation reaction of heparan sulphate synthesis and transport of the proteoglycan to the cell surface in rat liver

We report on the incorporation of radiolabelled sulphate into proteoglycan in the 'in situ'-perfused rat liver. After 5 min virtually all of the [35S]sulphate was incorporated into heparan sulphate; no partially sulphated precursors were detected. Pulse-chase experiments, followed by centrifugation in gradients of sucrose and metrizamide, showed that, at 5 min, the heparan sulphate was associated predominantly with the Golgi membranes. Over the next 20 min, intact proteoglycan appeared at the plasma membrane. At intermediate times the heparan sulphate was detected simultaneously in two distinct populations of membrane vesicles. Whether the heparan sulphate in these two populations has two different destinies (e.g. plasma membrane or secretion) is not yet clear. Subfractionation of the Golgi membranes showed that the N-sulphotransferase co-purified with the heparan [35S]sulphate and was separable from the galactosyltransferase of glycoprotein synthesis, confirming that the Golgi membrane system is functionally segregated. Subfractionation also permitted an almost 100-fold purification of the N-sulphotransferase over the homogenate: this will provide an excellent starting material for isolation and further characterization of the enzyme.

Effects of ethanol, acetaldehyde, and lactate on proteoglycan synthesis and proliferation of cultured rat liver fat-storing cells

The hypothesis that ethanol and some of its metabolites are directly involved in the process of fat-storing cell activation and stimulated proteoglycan synthesis in alcoholic liver injury was investigated. The effects of short-term (24 h) and long-term (4 days) exposure of rat liver fat-storing cells at various times of culture to ethanol, acetaldehyde, and lactate on the synthesis of proteoglycans and total protein and on the proliferation activity of the cells were studied. Ethanol and lactate did not stimulate the incorporation of [35S]sulfate into glycosaminoglycans. Acetaldehyde inhibited strongly glycosaminoglycan synthesis, reaching 50% inhibition at 330 mumol/L. The compound preferentially inhibited the synthesis of dermatan sulfate. No significant changes of glycosaminoglycan chain length or of the degree of polysaccharide sulfation were noted in acetaldehyde-treated cultures. The inhibition was reversed by the addition of beta-D-xylopyranoside (0.5 mmol/L), an artificial initiator of chain elongation, to the medium. Total protein synthesis, cell number, deoxyribonucleic acid content of the cultures, and [3H]thymidine incorporation were not affected by the compounds. The results do not support the view that ethanol, its oxidation product acetaldehyde, or lactate are directly involved in the activation of fat-storing cells and in enhanced matrix proteoglycan synthesis and secretion.