Proteoglycans in human malignant mesothelioma. Stimulation of their synthesis induced by epidermal, insulin and platelet-derived growth factors involves receptors with tyrosine kinase activity.

Identification of proteoglycans in two human malignant mesothelioma cell lines, one with epithelial differentiation and the other with fibroblast-like phenotype, and the effects of epidermal (EGF), insulin-like (IGF-I) and platelet-derived (PDGF-BB) growth factors on the synthesis of hyaluronan (HA) and proteoglycans (PGs) were studied. Both cell lines synthesize HA and PGs: these last were recovered both as secreted and cell-associated compounds. Chondroitin sulfate (CS) containing PGs are mainly organized as versican in the extracellular medium and as thrombomodulin and syndecan in the cell membrane. Heparan sulfate (HS) containing PGs are mainly in the form of perlecan in the culture medium, whereas cell-associated HSPGs were recovered mainly as syndecan-1, -2 and -4. Receptors for EGF, IGF-I and PDGF-BB were identified in both cell lines. In addition to cell proliferation, these growth factors stimulated the synthesis of HA and PGs, the pattern of stimulation being unique for each of them and depending on the cell phenotype. EGF increased the synthesis of HA and PGs. IGF-I showed similar stimulatory effects on the synthesis of CSPGs, whereas higher amounts were needed to influence the synthesis of HA and HSPGs, the latter only being stimulated in the epithelial cell line. PDGF-BB stimulated the synthesis of HA, HSPGs and CSPGs at low concentrations, while the stimulatory effect was abolished at higher levels. Incubation with genistein inhibited the HA and PG synthesis induced by growth factors in a mode depending on both growth factor and genistein concentrations. The results clearly suggest that the stimulatory effects of EGF, IGF-I and PDGF-BB on matrix synthesis, expressed as proteoglycan synthesis, are mediated via receptor-growth factor complexes and the protein tyrosine kinase intracellular pathway.     

Immunoreactivity to cell surface syndecans in cytoplasm and nucleus: tubulin-dependent rearrangements

Syndecans are transmembrane proteoglycans implicated in the regulation of cell growth and differentiation, by interacting with growth factors. Although syndecans play a major role in regulating cell morphology, little is known about their subcellular distribution and in vivo association with the cytoskeleton. To address this question, we investigated the subcellular distribution and dynamic rearrangement of syndecans-1, -2, and -4, using confocal laser microscopy. Furthermore, we monitored the spatial relation of syndecans to tubulin in both mitotic and interphase cells. Initially, the reactivity to syndecans was confined to the cytoplasm, staining of the cell membranes appearing later. Syndecan-1 also seems to translocate to the nucleus in a time-dependent manner. The mitotic spindle shows unexpectedly more syndecans than that found in interphase cells. After vinblastine treatment, both syndecan-1 and tubulin were recovered as paracrystalline occlusion bodies, and the nuclear reactivity to syndecan-1 disappeared, suggesting tubulin-mediated nuclear transport of this proteoglycan. Plasma membrane staining reappeared in the postmitotic cells. Nuclear translocation predominantly affected syndecan-1, whereas syndecan-2 and -4 remained in cytoplasm and cell membrane. This is the first report on regulated nuclear translocation and the presence of syndecan-1 in the mitotic spindle, where it may stabilize the mitotic machinery. The syndecan-1/tubulin complex may also act as a vehicle for the transport of protein growth factors to the cell nucleus.     

Syndecan-2 expression in colorectal cancer-derived HT-29 M6 epithelial cells induces a migratory phenotype

Members of the heparan sulfate proteoglycan family, the syndecans have emerged as integrators of extracellular signals, such as ECM components or growth factors, that activate cytoplasmic signaling cascades and regulate cytoskeletal functions. Specifically, syndecan-2 has been implicated in various cellular processes, from differentiation to migration, including its participation in cell-cell and cell-matrix adhesion. Here, we focused on the involvement of syndecan-2 in epithelial versus mesenchymal differentiation. Colorectal cancer-derived HT-29 M6 epithelial cells were stably transfected with full-length syndecan-2 cDNA, and the effect on cell morphology, adhesion, and mobility was evaluated. Characteristic features of migratory cells such as loss of intercellular contacts, flatter shape and multiple membrane projections were observed in syndecan-2 transfectants. Western blot analysis of the major component of epithelial adherens junctions, E-cadherin, revealed decreased expression levels. Furthermore, syndecan-2 induced stronger adhesion to collagen type I, specifically inhibited by heparin. This was correlated with an increased ability for migration, as demonstrated by wound healing experiments and transwell assays, without affecting their growth rate. These results indicate that syndecan-2 expression in mucus-secreting HT-29 M6 cells induces differentiation toward a migratory mesenchymal-like phenotype.     

A Disintegrin and Metalloproteinase 17 (ADAM17) Mediates Inflammation-induced Shedding of Syndecan-1 and -4 by Lung Epithelial Cells

Syndecans are cell surface proteoglycans that bind and modulate various proinflammatory mediators and can be proteolytically shed from the cell surface. Within the lung, syndecan-1 and -4 are expressed as transmembrane proteins on epithelial cells and released in the bronchoalveolar fluid during inflammation. We here characterize the mechanism leading to the generation of soluble syndecan-1 and -4 in cultured epithelial cells and murine lung tissue. We show that the bladder carcinoma epithelial cell line ECV304, the lung epithelial cell line A459 and primary alveolar epithelial cells express and constitutively release syndecan-1 and -4. This release involves the activity of the disintegrin-like metalloproteinase ADAM17 as demonstrated by use of specific inhibitors and lentivirally transduced shRNA. Stimulation of epithelial cells with PMA, thrombin, or proinflammatory cytokines (TNFα/IFNγ) led to the down-regulation of surface-expressed syndecan-1 and -4, which was associated with a significant increase of soluble syndecans and cell-associated cleavage fragments. The enhanced syndecan release was not related to gene induction of syndecans or ADAM17, but rather due to increased ADAM17 activity. Soluble syndecan-1 and -4 were also released into the bronchoalveolar fluid of mice. Treatment with TNFα/IFNγ increased ADAM17 activity and syndecan release in murine lungs. Both constitutive and induced syndecan shedding was prevented by the ADAM17 inhibitor. ADAM17 may therefore be an important regulator of syndecan functions on inflamed lung epithelium.     

Syndecan-3 and syndecan-4 specifically mark skeletal muscle satellite cells and are implicated in satellite cell maintenance and muscle regeneration.

Myogenesis in the embryo and the adult mammal consists of a highly organized and regulated sequence of cellular processes to form or repair muscle tissue that include cell proliferation, migration, and differentiation. Data from cell culture and in vivo experiments implicate both FGFs and HGF as critical regulators of these processes. Both factors require heparan sulfate glycosaminoglycans for signaling from their respective receptors. Since syndecans, a family of cell-surface transmembrane heparan sulfate proteoglycans (HSPGs) are implicated in FGF signaling and skeletal muscle differentiation, we examined the expression of syndecans 1-4 in embryonic, fetal, postnatal, and adult muscle tissue, as well as on primary adult muscle fiber cultures. We show that syndecan-1, -3, and -4 are expressed in developing skeletal muscle tissue and that syndecan-3 and -4 expression is highly restricted in adult skeletal muscle to cells retaining myogenic capacity. These two HSPGs appear to be expressed exclusively and universally on quiescent adult satellite cells in adult skeletal muscle tissue, suggesting a role for HSPGs in satellite cell maintenance or activation. Once activated, all satellite cells maintain expression of syndecan-3 and syndecan-4 for at least 96 h, also implicating these HSPGs in muscle regeneration. Inhibition of HSPG sulfation by treatment of intact myofibers with chlorate results in delayed proliferation and altered MyoD expression, demonstrating that heparan sulfate is required for proper progression of the early satellite cell myogenic program. These data suggest that, in addition to providing potentially useful new markers for satellite cells, syndecan-3 and syndecan-4 may play important regulatory roles in satellite cell maintenance, activation, proliferation, and differentiation during skeletal muscle regeneration.     

Syndecan expressions in the human amnion and chorionic plate

The syndecan family consists of four distinct membrane glycoproteins in mammals. Syndecans control cell proliferation, differentiation, adhesion and migration through participation in cell-cell interactions, anchorage of cells to the extracellular environment, and modulation of multiple growth factors. Therefore, syndecans may play a pivotal role in the regulation of cell behaviour depending on the cellular microenvironment. Here, we demonstrate that syndecan-1, syndecan-2 and syndecan-4 are expressed in fetal membrane tissue with different immunolocalizations. Syndecan-1 is expressed in the amniotic epithelium, localizing at basolateral cell surfaces. Syndecan-2 and syndecan-4, in contrast, are mostly localized in intracellular compartments, in the extravillous cytotrophoblastic cells and in some fibroblasts of the chorionic plate as well as in the amniotic epithelial cells. In the latter, syndecan-4 is mainly localized in the apical part of the cells. Our results strongly suggest a key role of syndecan-1, syndecan-2 and syndecan-4 in the determination of structural and functional characteristics of human amnion and chorionic plate. Since the solute exchanges between fetus and mother take place in fetal membranes, our data suggest that syndecans are important players in the placenta for the establishment of the fetal-maternal inter-communication.     

Syndecan-1 and Syndecan-4 Are Independent Indicators in Breast Carcinoma

Syndecan proteoglycans may be key regulators of tumor invasion and metastasis because this four-member family of transmembrane receptors regulates cell adhesion, proliferation, and differentiation. Their expression can also serve as prognostic markers. In breast carcinomas, syndecan-1 overexpression correlates with poor prognosis and aggressive phenotype. Syndecan-4 is expressed in most breast carcinoma cell lines, but its role in malignancy is unclear. A possible relationship between syndecan-1 and syndecan-4 expression and established prognostic factors in breast carcinomas was examined. Duplicate samples of 114 benign and malignant breast disease cases were stained for the two syndecans. Clinicopathological information was available for all cases. Syndecan-1 was detected in 72.8% of cases, with significant association between its expression and histological tumor type (p<0.05) and high grade tumors (p<0.05). Syndecan-4 was expressed in 66.7% of cases; expression correlated significantly with positive estrogen (p<0.01) and progesterone (p<0.01) receptor status. Independent expression of the two syndecans was noted from an analysis of single and double positive cases. There was a statistical relationship between syndecan-1 presence in high-grade tumors and absence of syndecan-4, whereas syndecan-4 presence in cases positive for estrogen and progesterone receptor associated with syndecan-1 absence. These syndecans may, therefore, have distinct roles in regulating breast carcinoma cell behavior.     

Syndecan-1 expression in epithelial cells is induced by transforming growth factor beta through a PKA-dependent pathway

Syndecans comprise a major family of cell surface heparan sulfate proteoglycans (HSPGs). Syndecans bind and modulate a wide variety of biological molecules through their heparan sulfate (HS) moiety. Although all syndecans contain the ligand binding HS chains, they likely perform specific functions in vivo because their temporal and spatial expression patterns are different. However, how syndecan expression is regulated has yet to be clearly defined. In this study, we examined how syndecan-1 expression is regulated in epithelial cells. Our results showed that among several bioactive agents tested, only forskolin and three isoforms of TGFbeta (TGFbeta1-TGFbeta3) significantly induced syndecan-1, but not syndecan-4, expression on various epithelial cells. Steady-state syndecan-1 mRNA was not increased by TGFbeta treatment and cycloheximide did not inhibit syndecan-1 induction by TGFbeta, indicating that TGFbeta induces syndecan-1 in a post-translational manner. However, TGFbeta induction of syndecan-1 was inhibited by transient expression of a dominant-negative construct of protein kinase A (PKA) and by specific inhibitors of PKA. Further (i) syndecan-1 cytoplasmic domains were Ser-phosphorylated when cells were treated with TGFbeta and this was inhibited by a PKA inhibitor, (ii) PKA was co-immunoprecipitated from cell lysates by anti-syndecan-1 antibodies, (iii) PKA phosphorylated recombinant syndecan-1 cytoplasmic domains in vitro, and (iv) expression of a syndecan-1 construct with its invariant Ser(286) replaced with a Gly was not induced by TGFbeta. Together, these findings define a regulatory mechanism where TGFbeta signals through PKA to phosphorylate the syndecan-1 cytoplasmic domain and increases syndecan-1 expression on epithelial cells.     

Upregulation of 9 genes, including that for thioredoxin, during epithelial differentiation of mesothelioma cells

Malignant mesothelioma is a tumour originating from mesothelial cells, and it exhibits epithelial, fibrous, or biphasic differentiation. This tumour is highly resistant to therapy, and presence of a sarcomatous growth pattern has been associated with worse prognosis. A mesothelioma cell line with retained ability to differentiate into either epithelial or fibroblast-like phenotype was subjected to subtractive hybridisation in order to identify the genes coupled to tumour cell differentiation. Nine genes were found to be selectively overexpressed in the epithelial sub-line, compared to only two genes in the fibroblast-like phenotype. This may support the idea that the sarcomatous phenotype represents a less differentiated tumour. One of the genes that is differentially expressed by the epithelial cells was thioredoxin, a small redox-active protein associated with cell-growth and differentiation. This overexpression was accompanied by increased protein levels both intracellularly and in the medium. Thioredoxin is reduced by the selenoprotein thioredoxin reductase and NADPH. The activity of this enzyme was high in both cell sub-lines but induced 2-fold in the epithelially-differentiated cells. Overexpression of thioredoxin might be a factor behind the poor prognosis and reduced responsiveness to therapy of mesotheliomas. Epithelial differentiation in this cell line has previously been linked to increased synthesis of heparan sulphate proteoglycans. The possible formation of complexes including thioredoxin, thioredoxin reductase, and heparan sulphate proteoglycans might play a role in the local control of cell growth and differentiation.     

Syndecan-1 and syndecan-4 can mediate the invasion of OpaHSPG-expressing Neisseria gonorrhoeae into epithelial cells

Neisseria gonorrhoeae ( Ngo ) expressing the outer membrane protein Opa_HSPG can adhere to and invade epithelial cells via binding to heparan sulphate proteoglycan (HSPG) receptors. In this study, we have investigated the role of syndecan-1 and syndecan-4, two members of the HSPG family, in the uptake of Ngo by epithelial cells. When overexpressed in HeLa cells, both syndecans co-localize with adherent Ngo on the host cell surface. This overexpression of syndecan-1 and syndecan-4 leads to a three- and sevenfold increase in Ngo invasion respectively. In contrast, transfection with the syndecan-1 and syndecan-4 mutant constructs lacking the intracellular domain results in an abrogation of the invasion process, characteristic of a dominant-negative mode of action. A concomitant loss of the capacity to mediate Ngo uptake was also observed with syndecan-4 mutant constructs carrying lesions in the dimerization motif necessary for the binding of protein kinase C (PKC) and phosphatidylinositol 4,5-bisphosphate (PIP₂), and mutants that are deficient in a C-terminal EFYA amino acid motif responsible for binding to syntenin or CASK. We conclude that syndecan-1 and syndecan-4 can both mediate Ngo uptake into epithelial cells, and that their intracellular domains play a crucial role in this process, perhaps by mediating signal transduction or anchorage to the cytoskeleton.     

Syndecan-1 and -4 differentially regulate oncogenic K-ras dependent cell invasion into collagen through α2β1 integrin and MT1-MMP

Syndecans function as co-receptors for integrins on different matrixes. Recently, syndecan-1 has been shown to be important for α2β1 integrin-mediated adhesion to collagen in tumor cells by regulating cell adhesion and migration on two-dimensional collagen. However, the function of syndecans in supporting α2β1 integrin interactions with three-dimensional (3D) collagen is less well studied. Using loss-of-function and overexpression experiments we show that in 3D collagen syndecan-4 supports α2β1-mediated collagen matrix contraction. Cell invasion through type I collagen containing 3D extracellular matrix (ECM) is driven by α2β1 integrin and membrane type-1 matrix metalloproteinase (MT1-MMP). Here we show that mutational activation of K-ras correlates with increased expression of α2β1 integrin, MT1-MMP, syndecan-1, and syndecan-4. While K-ras-induced α2β1 integrin and MT1-MMP are positive regulators of invasion, silencing and overexpression of syndecans demonstrate that these proteins inhibit cell invasion into collagen. Taken together, these data demonstrate the existence of a complex interplay between integrin α2β1, MT1-MMP, and syndecans in the invasion of K-ras mutant cells in 3D collagen that may represent a mechanism by which tumor cells become more invasive and metastatic.     

Syndecan-4 distribution during the differentiation of satellite cells isolated from soleus muscle treated by phorbol ester and calphostin C

It was shown that syndecans have a potential role in muscle development. We focused this study on the role of syndecan-4 distribution and phosphorylation during the differentiation of satellite cells isolated from Soleus muscle. Syndecans are cell surface heparan sulfate proteoglycans (HSPGs) that bind numerous ligands through their HS glycosaminoglycan chains (GAG). They play a role in cell-extracellular matrix and cell-cell adhesion, signal transduction and the targeting of growth factors and other molecules to the cell surface. Syndecan-4 acts as a co-receptor or, along with integrins, is localized to the cell membrane of focal contacts. Syndecan-4 participates in the organization of the structure of focal contacts reacting with extracellular matrix molecules. The interaction of syndecan-4 with protein kinase C (PKC) isoforms is the main mechanism regulating its distribution in cells. Our current study focused on the role of the distribution of syndecan-4, and its interactions with PKC isoforms during the differentiation of activated satellite cells. We used the PKC activator TPA (12-O-tetradecanoyl phorbol 13-acetate) and the PKC inhibitor Calphostin C (Cal C). We concluded that syndecan-4 was important not only in the activation of satellite cells, but also in myoblast differentiation. During our research, we observed the presence of syndecan-4 and changes in its location over the course of that process. We also showed that TPA and Cal C treatment had an influence on the subcellular distribution of syndecan-4, but there was no influence on myoblast differentiation. We speculated that the reason for changes after TPA treatment was the interactions with activated PKC alpha, which provoked syndecan-4/PKC alpha complex translocation to integrins. We also supposed that Cal C treatment inhibited PKC delta activity and probably induced PKC lpha association to syndecan-4, and syndecan-4 translocation to integrins.     

Fibroblast growth factor-2 modulates melanoma adhesion and migration through a syndecan-4-dependent mechanism

Fibroblast growth factor-2 (FGF-2), the most abundant growth factor produced by melanoma cells but not by normal melanocytes, is an important regulator of cell proliferation, migration and differentiation. In this study we show that M5 human metastatic melanoma cells’ ability to migrate is significantly enhanced by exogenously added FGF-2 while, neutralization of endogenous FGF-2 stimulates their adhesion. Previously, we have demonstrated that FGF-2 distinctly modulates the synthesis of individual glycosaminoglycans/proteoglycans (GAGs/PGs) subclasses, changing both their amounts and distribution in M5 cells. Here, treatment with FGF-2 strongly reduces the expression levels of the heparan sulfate-containing proteoglycan, syndecan-4. Syndecan-4 is a focal adhesion component in a range of cell types, adherent to several different matrix molecules, including fibronectin (FN). The reduction in syndecan-4 expression by utilizing specific siRNA discriminately increased melanoma cell motility and decreased their attachment on FN, demonstrating a regulatory role of syndecan-4 on these cell functions. Syndecan-4 has previously been demonstrated to regulate focal adhesion kinase (FAK) phosphorylation. In this study FGF-2 was shown to downregulate FAK Y397-phosphorylation during FN-mediated M5 cell adhesion, promoting their migration. The observed decrease in FAK Y397 activation was correlated to syndecan-4 expression levels. Thus, a balance in syndecan-4 expression perpetrated by FGF-2 may be required for optimal M5 cell migration.These results suggest that essential in melanoma progression FGF-2, specifically regulates melanoma cell ability to migrate through a syndecan-4-dependent mechanism.     

Differential expression and regulation of cyclooxygenase isozymes in thymic stromal cells

Prostaglandins (PGs) are lipid-derived mediators of rapid and localized cellular responses. Given the role of PG in supporting thymic T cell development, we investigated the expression of the PG synthases, also known as cyclooxygenases (COX)-1 and -2, in the biosynthesis of PGs in thymic stromal cell lines. The predominant isozyme expressed in cortical thymic epithelial cells was COX-1, while COX-2 predominated in the medulla. IFN-gamma up-regulated expression and activity of COX-2 in medullary cells, in which COX-2 was expressed constitutively. In contrast, IFN-gamma down-regulated COX-1 activity, but not expression, in cortical cells. Stromal cells support T cell development in the thymus, although the mediators of this effect are unknown. Selective inhibition of COX-2, but not COX-1, blocked the adhesion of CD4+CD8+ and CD4+CD8- thymocytes to medullary cell lines. No effect of the inhibitors was observed on the interactions of thymocytes with cortical epithelial lines. These data further support the differential regulation of COX-1 and COX-2 expression and function in thymic stromal cells. PGs produced by COX-2 in the medullary thymic stroma may regulate the development of thymocytes by modulating their interaction with stromal cells.     

Establishment of a human malignant fibrous mesothelioma cell line and the biological characteristics compared with malignant epithelial mesothelioma cell line

Two human malignant mesothelioma cell lines, which we designated "epithelial mesothelioma cells" and "fibrous mesothelioma cells", were established from the pleural fluid containing malignant mesothelial cells of a 72-year-old Japanese man. These cell lines were separated by the colonial techniques from the initiation of the primary cultures and grew well without interruption for 12 years. They were characterized as producing hyaluronic acid. These cell lines displayed different biological characteristics, including morphology, heterotransplantability and genetics using with BAC array CGH. The epithelial mesothelioma cells were epithelial in shape and transplantable into the subcutis of nude mice, while the cells of the fibrous mesothelioma line were fibroblast-like and transplantable into the submucosa of Hamster's cheek pouches but not into the subcutis of nude mice. The mesotheliomas are classified into three types: epithelial mesothelioma, fibrous mesothelioma and mixed type. The gene copy number losses observed on 9p21.3, 9p21.2, 9p21.1, among others may be a major mechanism of malignant mesothelioma carcinogenesis. We considered and supported the combination theory for the histogenesis of malignant mesothelioma.