Characterization of the molecular mechanism involved in the activation of hyaluronan synthetase by platelet-derived growth factor in human mesothelial cells

Production of hyaluronan by glomerular mesangial cells in response to fibronectin and platelet-derived growth factor

The formation of the non-sulphated glycosaminoglycan hyaluronan by cells of the renal glomerulus in diabetes may contribute to altered matrix composition. We describe an increased production of hyaluronan from mesangial cell-enriched glomerular cores from diabetic animals, and further show that increased hyaluronan production follows the exposure of non-diabetic and diabetic preparations to fibronectin and to platelet-derived growth factor in vitro. Hyaluronan production appeared dependent on protein kinase C activity, and could not be shown after prolonged phorbol ester preincubation. Stimulation by fibronectin was wholly dependent on cyclooxygenase activity and prior prostaglandin production, while the effect of platelet-derived growth factor showed only a partial dependence.

Characterization of proteoglycans produced by rat pleural mesothelial cells in vitro

The mesothelial cell envelopes the surface of the parietal and visceral pleura. These cells are known to synthesize most of the protein constituents of the pleural basement membrane and interstitium. This study examined the ability of a rat pleural mesothelial cell line to synthesize proteoglycans in vitro. Cells were labeled with inorganic 35SO4 to label the glycosaminoglycan moiety of proteoglycans. The medium and combined cell membrane/extracellular matrix fractions contained 73 and 25% of the proteoglycan radioactivity, respectively. The medium contained a single chondroitin/dermatan sulfate proteoglycan of approximately 190 kDa, consistent with biglycan. As determined by Northern analysis of steady-state levels of messenger RNA, the cells contained message for biglycan. Stimulation of the cells with epidermal growth factor resulted in the appearance of a second chondroitin/dermatan sulfate proteoglycan of approximately 97 kDa, characteristic of decorin. The cell membrane/matrix contained a biglycan-like chondroitin/dermatan proteoglycan and several heparan sulfate proteoglycans. Pleural mesothelial cells in vitro are capable of synthesizing a variety of interstitial and basement membrane proteoglycans.

Stimulation of hyaluronan biosynthesis by platelet-derived growth factor-BB and transforming growth factor-beta 1 involves activation of protein kinase C

The intracellular signal transduction pathways that mediate the stimulatory effects of platelet-derived growth factor (PDGF)-BB and transforming growth factor (TGF)-beta on hyaluronan biosynthesis in human fibroblasts were investigated. The stimulatory effects of both PDGF-BB and TGF-beta 1 were dependent on protein kinase C (PKC), since the PKC inhibitor calphostin C inhibited the stimulation by the growth factors. Direct activation of PKC by phorbol 12-myristate 13-acetate (PMA) also stimulated hyaluronan production, and the combination of either PDGF-BB or TGF-beta 1 and PMA gave an increased effect. One possible mechanism for activation of PKC is via induction of phospholipase C (PLC) activity; U-17322, an inhibitor of PLC-gamma, was found to inhibit partially PDGF-BB-stimulated hyaluronan synthesis. PDGF-BB is known to activate PLC-gamma through tyrosine phosphorylation; however, a PDGF beta-receptor mutant unable to interact with and activate PLC-gamma was still able to mediate induction of hyaluronan biosynthesis, indicating that PDGF-mediated stimulation is not entirely dependent on PLC-gamma. The stimulations by PDGF-BB and TGF-beta 1 were partly dependent on protein synthesis, since parts of the effects were inhibited by cycloheximide; in contrast, the effects mediated by PMA were not. Our results indicate that PKC is involved in the transduction of the effects of growth factors on hyaluronan biosynthesis, and that the effects involve direct or indirect activation of existing hyaluronan synthetase molecules, as well as induction of new enzyme molecules.

Activation of mesangial cells by the phosphatase inhibitor vanadate. Potential implications for diabetic nephropathy

The metalion vanadate has insulin-like effects and has been advocated for use in humans as a therapeutic modality for diabetes mellitus. However, since vanadate is a tyrosine phosphatase inhibitor, it may result in undesirable activation of target cells. We studied the effect of vanadate on human mesangial cells, an important target in diabetic nephropathy. Vanadate stimulated DNA synthesis and PDGF B chain gene expression. Vanadate also inhibited total tyrosine phosphatase activity and stimulated tyrosine phosphorylation of a set of cellular proteins. Two chemically and mechanistically dissimilar tyrosine kinase inhibitors, genistein and herbimycin A, blocked DNA synthesis induced by vanadate. Vanadate also stimulated phospholipase C and protein kinase C. Downregulation of protein kinase C abolished vanadate-induced DNA synthesis. Thus, vanadate-induced mitogenesis is dependent on tyrosine kinases and protein kinase C activation. The most likely mechanism for the effect of vanadate on these diverse processes involves the inhibition of cellular phosphotyrosine phosphatases. These studies demonstrating that vanadate activates mesangial cells may have major implications for the therapeutic potential of vanadate administration in diabetes. Although vanadate exerts beneficial insulin-like effects and potentiates the effect of insulin in sensitive tissue, it may result in undesirable activation of other target cells, such as mesangial cells.

Increased hyaluronan production in the glomeruli from diabetic rats: a link between glucose-induced prostaglandin production and reduced sulphated proteoglycan

Exposure in vivo or in vitro to elevated glucose increases production of vasoactive prostaglandins by glomeruli and mesangial cells. This study aimed to determine whether this increased prostaglandin production could provide a link with later structural changes in diabetic nephropathy. Glomerular cores were prepared from control rats and streptozotocin-diabetic rats (3 weeks' duration). Over 24 h in culture hyaluronan production from diabetic glomerular cores was higher than production from control glomerular cores whether maintained in 5.6 mmol/l glucose (105.6 +/- 15.5 vs 53.6 +/- 8.5 ng hyaluronan per 250 glomerular cores, p < 0.001); in 25 mmol/l glucose (149.3 +/- 34.8 vs 62.7 +/- 7.8 ng hyaluronan per 250 glomerular cores, p < 0.01); or in 45 mmol/l glucose (176.8 +/- 23.3 vs 102.0 +/- 17.9 ng hyaluronan per 250 glomerular cores, p < 0.01). At 5.6 mmol/l glucose, exposure in vitro to prostaglandin E2 caused an increase in hyaluronan production [maximal at 10(-9) mol/l prostaglandin E2, 237 +/- 19 vs 42 +/- 4, ng hyaluronan per 250 glomerular cores, p < 0.001 (control) and 195 +/- 7 vs 103 +/- 5, ng hyaluronan per 250 glomerular cores, p < 0.001 (diabetic)]. In both control and diabetic glomerular cores hyaluronan production was reduced significantly by the cyclooxygenase inhibitor indomethacin (10(-5) mol/l) [24.7 +/- 3.33 vs. 40.25 +/- 4.11 ng hyaluronan per 250 glomerular cores, p < 0.05 (control) and 36.5 +/- 6.25 vs 118.0 +/- 22.6, p < 0.01 (diabetic)]. A direct spectrophotometric microassay was used to determine the concentration of sulphated glycosaminoglycans derived from papain-digested glomerular core proteoglycans.(ABSTRACT TRUNCATED AT 250 WORDS)

Glycosaminoglycans from two human malignant mesothelioma cell lines: determination, distribution, and effect of platelet-derived growth factor on their synthesis

The synthesis and distribution of glycosaminoglycans (GAGs) were studied in two human malignant mesothelioma cell lines: one with fibroblast-like morphology and the other with epithelial differentiation. Analyses using highly sensitive high-pressure liquid chromatography techniques and agarose gel electrophoresis showed that these cells produce not only hyaluronan (HA) but also galactosaminoglycans (GalAGs, chondroitin sulfate and (or) dermatan sulfate) and heparan sulfate (HS). In both cell lines most of the HA (87-90%) and GalAGs (57-66%) are secreted into the extracellular matrix. Although HS is mainly bound to the cell surface in fibroblast-differentiated cells (75%), in epithelial type cells only 40% occurs in the cell-associated fraction. The amounts of secreted GAGs are 6- to 8-fold higher in epithelial than in fibroblast-like mesothelioma cultures. In cells with the fibroblast phenotype, the beta-homodimer of platelet-derived growth factor (PDGF) in a concentration of 1.5 ng/mL stimulates HA and GalAG synthesis 5-fold and that of HS 10-fold, whereas higher concentrations suppress this stimulatory effect. The stimulatory effect, observed at low concentrations of this growth factor, was completely blocked by the addition of antibodies against this factor. In epithelially differentiated cells, the production of all GAGs was suppressed after addition of this factor, even at low concentrations. We therefore suggest that mesothelioma cells can produce GAGs, the synthesis of which is dependent on the presence and concentration of PDGF beta-homodimer. The differences between the two cell lines regarding the effect of this growth factor on GAG synthesis indicates that the regulation of this synthesis is complex, other factors also being important.

Transforming growth factor-beta 1 (TGF-beta 1)- and beta 2-like activities in malignant pleural effusions caused by malignant mesothelioma or primary lung cancer

We investigated the levels of TGF-beta in malignant pleural effusions (MPE) caused by malignant mesothelioma (MESO) or primary lung cancer. TGF-beta levels in MPE caused by MESO were 283.9 +/- 219.2 pm (mean +/- s.d.) and were three to six times higher than those due to primary lung cancers (P < 0.01 or P < 0.05). We also evaluated TGF-beta 1- and beta 2-like activities in MPE using specific polyclonal antibodies. Although TGF-beta 1-like activity could be detected in all cases, TGF-beta 2-like activities were detected in five of seven in MESO and in a few cases with primary lung cancer. These results demonstrate that the levels of total TGF-beta and TGF-beta 2-like activity may be clinically useful to differentiate MESO from primary lung cancer. Our data also suggest that TGF-beta may help further characterize the clinical features of MESO.

Intracellular signal transduction for serum activation of the hyaluronan synthase in eukaryotic cell lines

Hyaluronan synthase was activated in B6 cells or 3T3 fibroblasts by foetal calf serum with maximal activity after 6 h. Activation was inhibited by cycloheximide or by the protein kinase inhibitors H-7 or H-8, indicating that transcription as well as phosphorylation was required for activation. The activation by serum was markedly prolonged, when serum was added together with cholera toxin or theophylline. Without serum stimulation the hyaluronan synthase could also be activated by phorbol-12-myristate-13-acetate, by dibutyryl-c-AMP, or by forskolin. Increasing the intracellular Ca-ion concentration with a Ca-ionophore also led to an activation. The activation of the drugs was not synergistic. In isolated plasma membranes the synthase activity could be decreased by phosphatase treatment and enhanced by ATP in B6 cells and by ATP in the presence of phorbol-12-myristate-13-acetate in 3T3 fibroblasts. Stimulation correlated with increased transcription and phosphorylation of the 52 kD hyaluronan synthase at serine residues. The results led to the conclusion that hyaluronan synthase is induced by transcription and activated by phosphorylation by protein kinase C, c-AMP-dependent protein kinases, or Ca-ion-dependent protein kinases.

The source and possible significance of hyaluronan in the peritoneal cavity

The levels of hyaluronan (HA) were determined in dialysate from patients receiving CAPD. The levels found after the four hour dwell were 0.162 +/- 0.08 micrograms/ml (N = 16) in non-infected fluid and 1.69 +/- 1.12 (N = 5) during peritonitis, P < 0.0025. Similarly concentrations in overnight (8 to 10 hours) dwell dialysate were 0.384 +/- 0.22 micrograms/ml (N = 13) when uninfected and 3.17 +/- 2.28 (N = 8) during peritonitis, P < 0.0002. Following de novo catheter insertion the initial peritoneal washout yielded HA levels of 0.0032 +/- 0.0018 micrograms/ml (N = 7). In vitro human peritoneal cells synthesized HA, 90% of which was secreted into the culture medium (CM). By dissociative gel permeation chromatography on Sephacryl 1000 there were no significant differences in the molecular size of HA extracted from (a) non-infected fluid, (b) infected fluid and (c), mesothelial cell culture medium. These results indicate that the process of CAPD results in an increase in HA levels in the peritoneal cavity. During episodes of peritonitis these functions are further augmented. The likely source of HA in the dialysate is the peritoneal mesothelial cells. This response may be an initial event in wound repair.

Protein kinase C-dependent and -independent mechanisms of dense granule exocytosis by human platelets

We examined the mechanisms of ATP release by human platelets using Ro-31-7549, a specific inhibitor of protein kinase C. Ro-31-7549 almost completely inhibited TPA-induced platelet aggregation and ATP release at 5-10 microM in washed platelets and in platelet-rich plasma. However, it suppressed thrombin- and U46619-induced ATP release by only 48% and 21%, respectively, and had little effect on aggregation in washed platelet suspensions containing serum or in platelet-rich plasma. The addition of GRGDS to prevent aggregation inhibited this residual thrombin-induced release by 53% and the residual U46619 release by 100% in the presence of Ro-31-7549. In washed platelet suspensions free of serum or plasma, Ro-31-7549 almost completely inhibited the ATP release and partially suppressed the aggregation induced by these agonists. These results suggested that there are protein kinase C-dependent and -independent mechanisms for ATP release by human platelets and that activation of the latter mechanism may depend on aggregation and plasma factors.

Prostaglandin E2 stimulates cyclic AMP-mediated hyaluronan synthesis in rabbit pericardial mesothelial cells

We studied the effects of prostaglandin E2 (PGE2) on hyaluronan synthesis in rabbit pericardial mesothelial cells, and the following results were obtained. (1) PGE2 (10-1000 ng/ml) stimulated hyaluronan synthesis and the level of hyaluronan synthase activity in a dose- and time-dependent manner, but PGF2 alpha did not. (2) Cyclic AMP (cAMP) levels in the cells peaked (about a 7-fold increase) at 5-10 min after adding PGE2 (1000 ng/ml). (3) Increased hyaluronan synthesis induced by PGE2 was significantly inhibited after pretreatment with either an adenylate cyclase inhibitor (2',5'-dideoxyadenosine) or a cAMP-dependent protein kinase inhibitor (PKI 5-24), but there was no inhibition with the protein kinase C inhibitor H-7. (4) When the intracellular cAMP level was raised by manipulating the levels of dibutyryl cyclic AMP or forskolin, hyaluronan synthesis and the level of hyaluronan synthase activity were also stimulated. These results suggest that PGE2 produced by cells stimulates hyaluronan synthesis in rabbit pericardial cells and that the stimulation mechanism involves the cAMP-mediated protein kinase signal transduction process.

Ontogeny of hyaluronan secretion during early mouse development

The ontogeny of hyaluronan (HA) secretion during early mouse embryogenesis has been investigated using a biotin-labelled HA-binding complex from cartilage proteoglycan. HA is first secreted by visceral endoderm cells of the early egg cylinder on day 5.5 post coitum (p.c.), predominantly into the expanding yolk cavity. On day 6.5 p.c., HA is present in both the yolk and proamniotic cavities, but pericellular staining is restricted to the visceral endoderm and a population of embryonic ectoderm cells at the antimesometrial end of the proamniotic cavity. By the primitive streak stage, HA is secreted into the ectoplacental, exocoelomic, amniotic and yolk cavities, whilst the only cells exhibiting pericellular staining are those of the embryonic and extraembryonic mesoderm, including the allantois. Comparisons of HA-staining patterns of cultured whole blastocysts, microdissected trophectoderm fragments and immunosurgically isolated inner cell masses, revealed no trophoblast-associated HA secretion during outgrowth in vitro but significant synthetic activity by the endodermal derivatives of differentiating inner cell masses. To identify the cell lineages responsible for secretion of HA into the embryonic cavities and to investigate the origin of the HA observed around migrating mesoderm cells, day 7.5 p.c. primitive streak stage conceptuses were dissected into their various embryonic and extraembryonic cell lineages. HA secretion was observed after short-term suspension culture of mesoderm, embryonic ectoderm and embryonic endoderm, but was undetectable in fragments of ectoplacental cone, parietal yolk sac (primary giant trophoblast and parietal endoderm), extraembryonic ectoderm or extraembryonic endoderm. The level of synthesis by the HA-positive tissues was markedly enhanced by culture in medium containing serum, compared with that obtained following culture in medium supplemented with a defined serum substitute containing insulin, transferrin, selenous acid and linoleic acid. This suggests that additional growth factors, present in serum but absent from the serum substitute, are required for optimal HA synthesis by the HA-secreting tissues in vitro, and probably also in vivo. The implications of these events for implantation and the development of peri- and early post-implantation mouse embryos are discussed, and a new role for HA in the initial formation and expansion of the embryonic cavities is proposed.