The role of proteoglycan synthesis in the development of sea urchins : II. The effect of administration of exogenous proteoglycan

The role of proteoglycan synthesis in the early development of sea urchins was studied by treating the embryos with a variety of inhibitors of proteoglycan synthesis and also with proteoglycan of exogenous origin. Developmental arrest at the blastula stage caused by p-nitrophenyl-β- -xyloside (p-NP-xyl) was cancelled by the administration of proteoglycan of exogenous origin. Proteoglycan of post-gastrular origin was effective for cancellation, but proteoglycan of blastular origin was not effective. This suggests that the hindrance of development by p-NP-xyl was due to the lack of proteoglycan synthesis at the late blastula stage. On the other hand, developmental arrest caused by 2-deoxy- -glucose (deoxy-glucose) and Na-selenate was not cancelled by the administration of proteoglycan under any condition tested. Apart from the cancelling action of proteoglycan, solely administered proteoglycan caused a blockage in development at a stage corresponding to the stage from which it was extracted, indicating that proteoglycan may be characterized by a kind of stage specificity.     

Modulation of sulfated proteoglycan synthesis by bovine aortic endothelial cells during migration

The rates of 35S-sulfate incorporation into proteoglycan were compared in multi-scratch wounded and confluent cultures of bovine aortic endothelial cells to determine whether proteoglycan synthesis is altered as cells are stimulated to migrate and proliferate. Incorporation was found to be stimulated in a time-dependent manner, reaching maximal levels 44-50 h after wounding, as cells migrated into wounded areas of the culture dish. Quantitative autoradiography of 35S-sulfate-labeled single-scratch wounded cultures demonstrated a 2-4-fold increase in the number of silver grains over migrating cells near the wound edge when compared to cells remote from the wound edge. Furthermore, when cell proliferation was blocked by inhibition of DNA synthesis, the increase in 35S-sulfate incorporation into proteoglycan after wounding was unaffected. These data indicate that cell division is not required for the modulation of proteoglycan synthesis to occur after wounding. Characterization of the newly synthesized proteoglycan by ion-exchange and molecular sieve chromatography demonstrated that heparan sulfate proteoglycan constitutes approximately 80% of the labeled proteoglycan in postconfluent cultures, while after wounding, chondroitin sulfate proteoglycan and/or dermatan sulfate proteoglycan (CS/DSPG) increases to as much as 60% of the total labeled proteoglycan. These results suggest that CS/DSPG synthesis is stimulated concomitant with the stimulation of endothelial cell migration after wounding.     

Effects of glutathione depletion on the synthesis of proteoglycan and collagen in cultured chondrocytes

We studied the effect of the depletion of glutathione on the synthesis of proteoglycan and collagen in cultured chick chondrocytes. When the cultured chondrocytes were incubated with 1 mM buthionine sulfoximine (BSO), a specific inhibitor of gamma-glutamyl-cysteine synthetase, the intracellular glutathione level markedly dropped within 12 h with no loss of cell viability. Incorporation of 35SO2-4 into proteoglycan was lowered in the presence of BSO. When the 35S-labeled proteoglycans were separated into two fractions by glycerol density gradient centrifugation, the inhibitory effect of BSO on the synthesis of proteoglycan was greater in the fast-sedimenting proteoglycan fraction, which consisted mainly of cartilage specific large proteoglycan (PG-H), than in the slowly sedimenting proteoglycan fraction. The inhibition by BSO of the synthesis of core protein-free glycosaminoglycan chains primed by p-nitrophenyl-beta-D-xyloside was smaller than the inhibition of the synthesis of proteoglycan. Analysis of glycosaminoglycans labeled with [3H]glucosamine indicated that the treatment of chondrocytes with BSO resulted in a small increase in the proportion of synthesis of hyaluronic acid to the synthesis of total glycosaminoglycan. The incorporation of [3H]proline into collagen was also inhibited by BSO. Sodium dodecyl sulfate polyacrylamide gel electrophoresis of the 3H-labeled collagen showed that, in the presence of BSO, processing of Type II collagen appeared to slow down and the proportion of Type X collagen synthesis was reduced.     

An anticoagulant proteoglycan from the marine green alga, Codium pugniformis

An anticoagulant isolated from the marine green alga Codium pugniformis was composed mainly of glucose with minor amounts of arabinose and galactose. It was highly sulfated (326 μg mg^-1 polysaccharide) and contained protein(52 μg mg^-1 polysaccharide) and was thus a proteoglycan. The anticoagulant properties of the purified proteoglycan were compared with those of heparin by studying the activated partial thromboplastin time (APTT), prothrombin time (PT) and thrombin time(TT) using normal human plasma. The proteoglycan showed similar activities to heparin, but was weaker than heparin. On the other hand, the proteoglycan did not affect PT even at the concentration at which APTT and TT were prolonged. The anticoagulation mechanism of this proteoglycan was due to the direct inhibition of thrombin and the potentiation of antithrombin III. This revised version was published online in August 2006 with corrections to the Cover Date.     

Stimulation by concanavalin A of cartilage-matrix proteoglycan synthesis in chondrocyte cultures

The effect of concanavalin A on proteoglycan synthesis by rabbit costal and articular chondrocytes was examined. Chondrocytes were seeded at low density and grown to confluency in medium supplemented with 10% fetal bovine serum, and then the serum concentration was reduced to 0.3%. At the low serum concentration, chondrocytes adopted a fibroblastic morphology. Addition of concanavalin A to the culture medium induced a morphologic alteration of the fibroblastic cells to spherical chondrocytes and increased by 3- to 4-fold incorporation of [35S]sulfate and [3H]glucosamine into large chondroitin sulfate proteoglycan that was characteristically found in cartilage. The stimulation of incorporation of labeled precursors reflected real increases in proteoglycan synthesis, as chemical analyses showed a 4-fold increase in the accumulation of macromolecules containing hexuronic acid in concanavalin A-maintained cultures. Furthermore, the effect of concanavalin A on [35S]sulfate incorporation into proteoglycans was greater than that of various growth factors or hormones. However, concanavalin A had smaller effects on [35S]sulfate incorporation into small proteoglycans and [3H]glucosamine incorporation into hyaluronic acid and chondroitinase AC-resistant glycosaminoglycans. Since other lectins tested, such as wheat germ agglutinin, lentil lectin, and phytohemagglutinin, had little effect on [35S]sulfate incorporation into proteoglycans, the concanavalin A action on chondrocytes seems specific. Although concanavalin A decreased [3H]thymidine incorporation in chondrocytes, the stimulation of proteoglycan synthesis could be observed in chondrocytes exposed to the inhibitor of DNA synthesis, cytosine arabinoside. These results indicate that concanavalin A is a potent modulator of proteoglycan synthesis by chondrocytes.     

Acetylation of proteins in the course of sea urchin development

Acetate incorporation into proteins including acidic proteins and basic proteins was studied by introduction of isotopically labeled precursors during sea urchin development. At pregastrulational stages, the acetate incorporation exhibited relatively low activities, whereas a remarked enhancement was apparently observed at gastrula stage and more advanced stages. Although some amount of exogenous acetate might be metabolically converted to amino acids, the acetate incorporation into proteins appeared to be mainly attributed to acetylation of proteins that should be coupled with peptide synthesis, as indicated by the incorporation occurring on peptide-synthesizing polysomes and strong inhibition of it by administration of puromycin.     

Effect of vanadate on cartilage-matrix proteoglycan synthesis in rabbit costal chondrocyte cultures

The effect of vanadate on proteoglycan synthesis by cultured rabbit costal chondrocytes was examined. Rabbit chondrocytes were seeded at low densities and grown to confluency in medium supplemented with 10% fetal bovine serum, and then the serum concentration was reduced to 0.3%. At the low serum concentration, chondrocytes adopted a fibroblastic morphology. Addition of 4 microM vanadate to the culture medium induced a morphologic differentiation of the fibroblastic cells to spherical chondrocytes, and increased by two- to threefold incorporation of [35S]sulfate and [3H]glucosamine into large, chondroitin sulfate proteoglycans. The stimulation of incorporation of labeled precursors reflected real increases in proteoglycan synthesis, in that chemical analyses showed increases in the accumulation of macromolecules containing hexuronic acid and hexosamine in vanadate-maintained cultures. However, vanadate had only a marginal effect on [35S]sulfate incorporation into small proteoglycans and [3H]glucosamine incorporation into hyaluronic acid and chondroitinase AC-resistant material. These results provide evidence that vanadate selectively stimulates the synthesis of proteoglycans characteristically found in cartilage by rabbit costal chondrocyte cultures.     

The effects of 6-diazo-5-oxo-L-norleucine, a glutamine analogue, on the structure of the major cartilage proteoglycan synthesized by cultured chondrocytes

Incubation of embryonic chick chondrocytes with 6-diazo-5-oxo-L-norleucine (DON), a glutamine analogue, led to a dose-dependent inhibition of [35S]sulfate incorporation into proteoglycan. In the absence of exogenous L-glutamine, a maximal inhibition of 50-60% was achieved with DON concentrations greater than or equal to 1 microgram/ml (6 microM); the ED50 was approximately 0.2 microM. This inhibitory effect could be partially restored by the addition of 100-fold molar excess of either exogenous L-glutamine or M-glucosamine. The quantitative changes were due neither to inhibition of protein core synthesis nor to undersulfation of glycosaminoglycan chains. Rather, the proteoglycan synthesized in the presence of DON contained substantially fewer (approximately 50% of control) and smaller (10-15% of control, on the average) chondroitin sulfate chains as well as a paucity of keratan sulfate chains. The result of these structural changes was a proteoglycan with significantly lower molecular weight, buoyant density, and anionic charge. In spite of these modifications, the altered proteoglycan synthesized in the presence of DON was secreted normally and retained the ability to interact with exogenous hyaluronic acid and link proteins. The results of our experiments also indicate that DON substantially diminished the pool of hexosamine precursors required for glycosaminoglycan synthesis. We conclude that this decrease was responsible for the molecular alterations described above; and these, in turn, can account for the morphological changes previously seen in cartilage matrix synthesized in the presence of DON.     

Appearance of a proteoglycan in developing sea urchin embryos

It was shown that a proteoglycan is synthetized by embryos of a Japanese sea urchin, Hemicentrotus pulcherrimus. This proteoglycan appears as a single peak on sucrose density gradient ultracentrifugation throughout the development. About half of the mucopolysaccharide moiety in this proteoglycan was found to be dermatan sulphate and the rest to be chondroitinase-resistant mucopolysaccharides.Evidence is presented to show that both types of mucopolysaccharide do not exist in a free form but reside as an integral part of the proteoglycan. The linkage between mucopolysaccharide and protein moieties of the proteoglycan appeared not be an O-glucosidic bond, which is common among other proteoglycans such as proteochodroitin sulphate and proteodermatan sulphate.     

Metabolic interconversion of dolichol and dolichyl phosphate during development of the sea urchin embryo

The in vivo and in vitro synthesis and turnover of dolichol and dolichyl phosphate have been studied over the course of early development in sea urchin embryos. Synthesis of dolichol and dolichyl phosphate was studied in vivo and in vitro using [3H]acetate and [14C] isopentenylpyrophosphate, respectively, as precursors. Both the in vivo and in vitro results indicate that the principal labeled end product of de novo synthesis is the free alcohol, and that this alcohol is subsequently phosphorylated to produce dolichyl phosphate. The presence of 30 microM compactin inhibits the de novo synthesis of dolichol from [3H]acetate by greater than 90%, but has no effect on the incorporation of 32Pi into dolichyl phosphate for more than 6 h, thus suggesting that during this time interval the major source of dolichyl phosphate is preformed dolichol. The rate of turnover of the [3H]acetate-labeled polyisoprenoid backbone of dolichyl phosphate is very slow (t1/2 = 40-70 h). In contrast, the rate of loss of the [32P]phosphate headgroup is more rapid (t1/2 = 5.7-7.7 h) and increases over the course of development. Finally, dolichyl phosphate phosphatase activity has been measured in vitro. The activity of this enzyme, which can be distinguished from phosphatidic acid phosphatase, was found to increase as a function of development, in qualitative agreement with the increased turnover of 32P from dolichyl phosphate observed in vivo. These results suggest that the phosphate moiety of dolichyl phosphate is in a dynamic state, and that dolichol kinase and dolichyl phosphate phosphatase play key roles in regulating the cellular level of dolichyl phosphate.     

Phospholipid metabolism following fertilization in sea urchin eggs and embryos.

Phospholipid metabolism during early development was examined in the sea urchins Stronglyocentrotus purpuratus and Lytechinus pictus. Transport of ³H-choline was stimulated fivefold following fertilization in both species. However, the actual percent incorporation of labeled precursors into phospholipids from the TCA soluble pool did not change at fertilization. There was a slight increase in transport of ¹⁴C-ethanolamine at fertilization but again there was no change in its percent incorporation into phospholipids. When eggs were preloaded with ³H-choline or ¹⁴C-ethanolamine and fertilized, the eggs or embryos showed similar patterns of incorporation into phospholipids. There was no significant change in the percent phosphorylation of choline in fertilized or unfertilized eggs.An investigation was made of the activity of choline kinase, the first enzyme in the biosynthesis of phosphatidylcholine. This enzyme was found to have similar activities in fertilized and unfertilized eggs using a variety of homogenization media. The activity of choline kinase was found to decrease slightly in activity at fertilization and reach a maximum activity by gastrula.These results indicate that there is no activation of phospholipid synthesis at fertilization of sea urchin eggs. Apparent increased incorporation actually reflects increased transport of precursors and not de novo synthesis.     

Smad and p38 MAP kinase-mediated signaling of proteoglycan synthesis in vascular smooth muscle

Atherosclerosis is the underlying pathological process of most cardiovascular disease. A critical component of the "response to retention" hypothesis of atherogenesis is proteoglycan/low density lipoprotein (LDL) binding. Transforming growth factor beta (TGF-beta) is present in atherosclerotic lesions, regulates vascular smooth muscle cell (VSMC) proteoglycan synthesis via an unknown signaling pathway, and increases proteoglycan/LDL binding. This pathway was investigated using the activin receptor-like kinase 5 (ALK5) inhibitor SB431542 and inhibitors of p38 MAP kinase as a possible downstream or alternative mediator. TGF-beta stimulated and SB431542 inhibited the phosphorylation of Smad2/3. In human VSMC, TGF-beta increased [(35)S]sulfate incorporation into proteoglycans associated with a 19% increase in glycosaminoglycan (GAG) chain size by size exclusion chromatography. SB431542 caused a concentration-dependent decrease in TGF-beta-mediated [(35)S]sulfate incorporation with 92% inhibition at 3 mum. Two different p38 MAP kinase inhibitors, SB203580 and SB202190, but not the inactive analogue SB202474, concentration-dependently blocked TGF-beta-mediated [(35)S]sulfate incorporation. TGF-beta increased [(3)H]glucosamine incorporation into glycosaminoglycans by 180% and [(35)S]Met/Cys incorporation into proteoglycan core proteins by 35% with both effects completely inhibited by SB431542. Blocking both Smad2/3 and p38 MAP kinase pathways prevented the effect of TGF-beta to increase proteoglycan to LDL binding. TGF-beta mediates its effects on proteoglycan synthesis in VSMCs via the ALK5/Smad2/3 phosphorylation pathway as well as via the p38 MAP kinase signaling cascade. Further studies of downstream pathways controlling proteoglycan synthesis may identify potential therapeutic targets for the prevention of atherosclerosis and cardiovascular disease.     

Role of cell-wall biogenesis in the initiation of auxin-mediated growth in coleoptiles of Zea mays L.

The involvement of cell-wall polymer synthesis in auxin-mediated elongation of coleoptile segments from Zea mays L. was investigated with particular regard to the growth-limiting outer epidermis. There was no effect of indole acetic acid (IAA) on the incorporation of labeled glucose into the major polysaccharide wall fractions (cellulose, hemicellulose) within the first 2 h of IAA-induced growth. 2,6-Dichlorobenzonitrile inhibited cellulose synthesis strongly but had no effect on IAA-induced segment elongation even after a pretreatment period of 24 h, indicating that the growth response is independent of the apposition of new cellulose microfibrils at the epidermal cell wall. The incorporation of labeled leucine into total and cell-wall protein of the epidermis was promoted by IAA during the first 30 min of IAA-induced growth. Inhibition of IAA-induced growth by protein and RNA-synthesis inhibitors (cycloheximide, cordycepin) was accompanied by an inhibition of leucine incorporation into the epidermal cell wall during the first 30 min of induced growth but had no effect on the concomitant incorporation of monosaccharide precursors into the cellulose or hemicellulose fractions of this wall. It is concluded that at least one of the epidermal cell-wall proteins fulfills the criteria for a growth-limiting protein induced by IAA at the onset of the growth response. In contrast, the synthesis of the polysaccharide wall fractions cellulose and hemicellulose, as well as their transport and integration into the growing epidermal wall, appears to be independent of growth-limiting protein and these processes are therefore no part of the mechanism of growth control by IAA.Abbreviations CHI cycloheximide - COR cordycepin - DCB 2,6-dichlorobenzonitrile - GLP growth-limiting protein(s) - IAA indole-3-acetic acid     

The program of protein synthesis during the development of the micromere-primary mesenchyme cell line in the sea urchin embryo

Changes in the pattern of protein synthesis were analyzed during the in vitro development of the micromere-primary mesenchyme cell line of the sea urchin embryo. Micromeres were isolated and cultured from 16-cell stage embryos, and primary mesenchyme cells were isolated and cultured from early gastrulae. Both cell isolates developed normally in culture with about the same timing as their in situ counterparts in control embryos. Newly synthesized proteins were labeled with [³H]valine at several stages of development and were analyzed by two-dimensional polyacrylamide gel electrophoresis and fluorgraphy. The electrophoretic pattern of labeled proteins changed dramatically during development. More than half of the analyzed proteins underwent qualitative or quantitative changes in their relative rates of valine incorporation and these changes were highly specific to this cell line. Almost all of the changes were initiated prior to gastrulation and many prior to hatching. The highest frequency of changes in the micromere pattern of protein synthesis occurred between hatching and the start of gastrulation. This peak of activity coincided with the normal time of ingression of the primary mesenchyme and preceded the differentiation of spicules by more than 30 hr. Most of the observed changes were characterized as either decreases in the synthesis of proteins that showed maximum incorporation at the 16-cell stage or increases in the synthesis of proteins that showed maxima in the fully differentiated cells. Very few proteins exhibited transient synthetic maxima at intermediate stages. Thus, the program of protein synthesis associated with the development of micromeres consists largely of a switch in emphasis from early to late proteins, with the primary time of switching being between hatching and the onset of gastrulation.     

Cell movement in somite formation and development in the chick: Inhibition of segmentation

The contribution of active cell movement to somite formation (segmentation) and the later dispersal of the somite sclerotome was examined using cytochalasin D (CD). Stage 14–16 chick embryos were grown over liquid medium. After 8 hr in culture, control embryos had an average of six additional pairs of somites while CD (1–2 μg/ml dissolved in DMSO)-treated embryos had no new somites. DMSO alone had no effect on somitogenesis. CD-treated embryos transferred to drug-free medium recovered and segmentation resumed. Normal and CD-treated segmental plates were examined by SEM. Drug-treated segmental plate cells rounded up, consistent with the interaction of CD on contractile microfilaments. Embryos cultured 8 hr with or without CD were fractured through somite pair 20 and examined by SEM. In untreated embryos the sclerotome had dispersed and was migrating toward the notochord. CD stopped sclerotome dispersal. To test whether CD interfered with elaboration of extracellular matrix material associated with somite development, incorporation of [³H]glucosamine and Na₂³⁵SO₄ by somites and segmental plate was determined. There was no difference in total label incorporation. Molecular-weight profiles of proteoglycan obtained using controlled-pore glass-bead columns showed only small proteoglycans for both treated and control tissues. Therefore, the alteration of segmentation and somite morphogenesis by CD was not due to detectable changes in proteoglycan synthesis.     

Extracellular matrix metabolism by chondrocytes: VI. Concomitant depression by exogenous levels of proteoglycan of collagen and proteoglycan synthesis by chondrocytes

The synthesis of collagen and proteoglycans by cultured chondrocytes, as measured by the incorporation of L-[³H]proline into hydroxyproline and [³H]acetate into glycosaminoglycans, was shown to be depressed by 59% and 39%, respectively, by the addition of exogenous proteoglycan at a concetration of 10 mg/ml growth media. The incorporation of L-[³H]proline into acid-in-soluble protein remained unaltered in the presence of the proteoglycan. It was concluded that the effect was depressing the activity of the enzymatic steps, associated with the endoplasmic reticulum, which are responsible for the post-traslational modification of collagen and proteoglycan.     

Mechanism for the decreased biosynthesis of cartilage proteoglycan in the scorbutic guinea pig

Our previous work showed that vitamin C deficiency caused about a 70-80% decrease in the incorporation of [35S]sulfate into proteoglycan of guinea pig costal cartilage, coordinately with a decrease in collagen synthesis (Bird, T. A., Spanheimer, R. G., and Peterkofsky, B. (1986) Arch. Biochem. Biophys. 246, 42-51). We examined the mechanism for decreased proteoglycan synthesis by labeling normal and scorbutic cartilage in vitro with radioactive precursors. Proteoglycan monomers from scorbutic tissue were of a slightly smaller average hydrodynamic size than normal but there was no difference in the size of the glycosaminoglycan chains isolated after papain digestion. The type of glycosaminoglycans synthesized and the degree of sulfation were unaffected as determined by chondroitinase ABC digestion and duel labeling with [35S]sulfate and [3H]glucosamine. Conversion of [3H]glucosamine to [3H]galactosamine also was unimpaired. There was about a 40% decrease in core protein synthesis, measured by [14C]serine incorporation and sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Nevertheless, decreased incorporation of [35S]sulfate into scorbutic tissue persisted in the presence of p-nitrophenyl-beta-D-xyloside and cycloheximide, which indicated that the site of the scorbutic defect was beyond core protein synthesis and xylosylation. Galactosyltransferase activity in scorbutic cartilage decreased to about one-third the levels in control samples in parallel with the decreases in proteoglycan and collagen synthesis. Our results suggest that the step catalyzed by this enzyme activity, the addition of galactose to xylose prior to chondroitin sulfate chain elongation, is the major site of the scorbutic defect in proteoglycan synthesis. Decreased enzyme activity may be related to increased cortisol levels in scorbutic serum.     

Inhibition of proteoglycan synthesis eliminates left-right asymmetry in Xenopus laevis cardiac looping

The heart of any vertebrate is formed from an apparently symmetric cardiac tube that loops consistently in the same direction along the left-right axis of the embryo. In the amphibian Xenopus laevis, inhibition of proteoglycan synthesis by p-nitrophenyl-beta-D-xylopyranoside during a narrow period of development from late gastrula to early neurula specifically eliminated the looping of the cardiac tube. Most of the proteoglycans synthesized during this period were heparan sulfate proteoglycans. Treatment with p-nitrophenyl-alpha-D-xylopyranoside, an analogue that does not inhibit proteoglycan synthesis, did not interfere with cardiac looping. The critical period for proteoglycan synthesis was coincident with the migration of cardiac primordia to the ventral midline. The inhibition of cardiac looping was further explored in explants of cardiac primordia and anterioventral ectoderm. In recombinate embryos in which half the embryo, and thus one of the two heart primordia, was treated with p-nitrophenyl-beta-D-xylopyranoside, and the other half was untreated, cardiac looping occurred normally. It is proposed that the left-right axis in Xenopus, as reflected in cardiac looping, is established early in development, and that proteoglycan synthesis is involved in the transduction of left-right axial information to the cardiac primordia during migration.     

Pulse treatment of sea urchin embryos with A23187 blocks their hatching out

Summary Pulse treatment of sea urchin embryos with 3 µM A23187 for 2 h at 20° C, starting from 3 to 6 h of development, prevented the embryos from hatching. Many embryos thus treated with A23187 produced mesenchyme cells and underwent gastrulation while still enclosed within the fertilization membrane. The pulse treatment in this pre-hatching period exerts markedly stronger inhibitory effects on hatching than on other events in early development. Treatment beginning at times earlier than 2 h and later than 8 h of development caused only a slight delay of hatching. The activity of hatching enzyme, known to increase between 6 and 8 h after fertilization, was quite low, if present at all, in embryos in which hatching was blocked by A23187. Hatching enzyme synthesis is probably blocked by the preceding pulse treatment. However, overall protein synthesis, estimated with methionine S 35 incorporation, was somewhat augmented in embryos by the pulse treatment. The blockage of hatching and the augmentation of overall protein synthesis by A23187 were appreciably reversed by procaine, tetracaine, ruthenium red or verapamil. Probably, an artificial Ca²⁺ signal induced by A23187 activates protein synthesis but blocks the induction of hatching enzyme synthesis.     

Stimulation of human arterial smooth muscle cell chondroitin sulfate proteoglycan synthesis by transforming growth factor-beta

Summary Human platelet-derived transforming growth factor-beta (TGF-beta) is a cell-type specific promotor of proteoglycan synthesis in human adult arterial cells. Cultured human adult arterial smooth muscle cells synthesized chondroitin sulfate, dermatan sulfate, and heparan sulfate proteoglycans, and the percent composition of these three proteoglycan subclasses varied to some extent from cell strain to cell strain. However, TGF-beta consistently stimulated the synthesis of chondroitin sulfate proteoglycan. Both chondroitin 4- and chondroitin 6-sulfate were stimulated by TGF-beta to the same extent. TGF-beta had no stimulatory effect on either class of [³⁵S]sulfate-labeled proteoglycans which appeared in an approximately 1:1 and 2:1 ratio of heparan sulfate to dermatan sulfate of the medium and cell layers, respectively, of arterial endothelial cells. Human adult arterial endothelial cells synthesized little or no chondroitin sulfate proteoglycan. Pulse-chase labeling revealed that the appearance of smooth muscle cell proteoglycans into the medium over a 36-h period equaled the disappearance of labeled proteoglycans from the cell layer, independent of TGF-beta. Inhibitors of RNA synthesis blocked TGF-beta-stimulated proteoglycan synthesis in the smooth muscle cells. The incorporation of [³⁵S]methionine into chondroitin sulfate proteoglycan core proteins was stimulated by TGF-beta. Taken together, the results presented indicate that TGF-beta stimulates chondroitin sulfate proteoglycan synthesis in human adult arterial smooth muscle cells by promoting the core protein synthesis. Supported in part by grants from the Public Health Service, U.S. Department of Health and Human Services, Washington, DC (CA 37589 and HL 33842), RJR Nabisco, Inc., and Chang Gung Biomedical Research Foundation (CMRP 291).