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cDNA cloning, genomic organization, and in vivo expression of rat N-syndecan.

The amino acid sequence of rat N-syndecan core protein was deduced from the cloned cDNA sequence. The sequence predicts a core protein of 442 amino acids with six structural domains: an NH2-terminal signal peptide, a membrane distal glycosaminoglycan attachment domain, a mucin homology domain, a membrane proximal glycosaminoglycan attachment domain, a single transmembrane domain, and a noncatalytic COOH-terminal cytoplasmic domain. Transfection of human 293 cells resulted in the expression of N-syndecan that was modified by heparan sulfate chain addition. Heparitinase digestion of the expressed proteoglycan produced a core protein that migrated on SDS-polyacrylamide gels at an apparent molecular weight of 120, 000, identical to N-syndecan synthesized by neonatal rat brain or Schwann cells. Rat genomic DNA coding for N-syndecan was isolated by hybridization screening. The rat N-syndecan gene is comprised of five exons. Each exon corresponds to a specific core protein structural domain, with the exception of the fifth exon, which contains the coding information for both the transmembrane and cytoplasmic domains as well as the 3'-untranslated region of the mRNA. The first intron is large, with a length of 22 kilobases. The expression of N-syndecan was investigated in late embryonic, neonatal, and adult rats by immunoblotting and Northern blotting analysis. Among the tissues and developmental stages studied, high levels of N-syndecan expression were restricted to the early postnatal nervous system. N-syndecan was expressed in all regions of the nervous system, including cortex, midbrain, spinal cord, and peripheral nerve. Immunohistochemical staining revealed high levels of N-syndecan expression in all brain regions and fiber tract areas.

Amino Acid Sequence↗

Syndecan 3 intramembrane proteolysis is presenilin/gamma-secretase-dependent and modulates cytosolic signaling.

The syndecans play critical roles in several signal transduction pathways. The core proteins of these heparan sulfate proteoglycans are characterized by highly conserved transmembrane and intracellular domains which are required for signaling across the membrane and for interaction with cytosolic proteins. However, regulatory mechanisms controlling these functions remain largely unknown. Here we show that, upon ligand-induced primary proteolytic cleavage within the ectodomain, the intracellular domain of syndecan 3 is released by regulated intramembrane proteolysis. The cleavage is mediated by presenilin/gamma-secretase complex and negatively regulates the plasma membrane targeting of the transcriptional cofactor CASK.

Amino Acid Sequence↗

HB-GAM/Pleiotrophin and Midkine are differently expressed and distributed during retinoic acid-induced neural differentiation of P19 cells.

HB-GAM/Pleiotrophin and Midkine (MK) are developmentally-regulated proteins with putative functions during cell growth and differentiation. Using the P19 cell which is a model to study the events associated with early development, we examined the expression and cellular localization of HB-GAM and MK during neural differentiation of P19 cells induced by retinoic acid (RA). The temporal expressions of HB-GAM and MK transcripts and both the levels and cellular localizations of the corresponding proteins appeared dramatically different. MK mRNA, already expressed in untreated P19 cells, was transiently increased by exposure to RA and then largely down regulated. More interestingly, HB-GAM which was not detected in untreated P19 cells was strongly expressed after 2 days of RA treatment and this expression persists throughout the duration of the culture suggesting that it could be involved in different aspects of this differentiation process.

Animals↗

Osteoblast recruitment and bone formation enhanced by cell matrix-associated heparin-binding growth-associated molecule (HB-GAM).

Bone has an enormous capacity for growth, regeneration, and remodeling. This capacity is largely due to induction of osteoblasts that are recruited to the site of bone formation. The recruitment of osteoblasts has not been fully elucidated, though the immediate environment of the cells is likely to play a role via cell- matrix interactions. We show here that heparin-binding growth-associated molecule (HB-GAM), an extracellular matrix-associated protein that enhances migratory responses in neurons, is prominently expressed in the cell matrices that act as target substrates for bone formation. Intriguingly, N-syndecan, which acts as a receptor for HB-GAM, is expressed by osteoblasts/osteoblast precursors, whose ultrastructural phenotypes suggest active cell motility. The hypothesis that HB-GAM/N-syndecan interaction mediates osteoblast recruitment, as inferred from developmental studies, was tested using osteoblast-type cells that express N-syndecan abundantly. These cells migrate rapidly to HB-GAM in a haptotactic transfilter assay and in a migration assay where HB-GAM patterns were created on culture wells. The mechanism of migration is similar to that previously described for the HB-GAM-induced migratory response of neurons. Our hypothesis that HB-GAM/N-syndecan interaction participates in regulation of osteoblast recruitment was tested using two different in vivo models: an adjuvant-induced arthritic model and a transgenic model. In the adjuvant-induced injury model, the expression of HB-GAM and of N-syndecan is strongly upregulated in the periosteum accompanying the regenerative response of bone. In the transgenic model, the HB-GAM expression is maintained in mesenchymal tissues with the highest expression in the periosteum. The HB-GAM transgenic mice develop a phenotype characterized by an increased bone thickness. HB-GAM may thus play an important role in bone formation, probably by mediating recruitment and attachment of osteoblasts/osteoblast precursors to the appropriate substrates for deposition of new bone.

Animals↗

Nitric oxide mediates interleukin-1-induced gene expression of matrix metalloproteinases and basic fibroblast growth factor in cultured rabbit articular chondrocytes.

We recently reported that nitric oxide (NO), which is produced by chondrocytes treated with interleukin-1beta (IL-1), releases basic fibroblast growth factor (bFGF) stored in the matrix of articular chondrocytes. To clarify the mechanism of the IL-1-induced bFGF release, we investigated the production and gene expression of bFGF, matrix metalloproteinases (MMPs), syndecan 3, and inducible NO synthase (iNOS) by IL-1-treated rabbit articular chondrocytes. IL-1 stimulated not only the release of bFGF but also the production of it. Gelatin and casein zymography revealed that IL-1 stimulated the production of not only MMP-9 but also MMP-3. The increase in the production of these MMPs preceded the IL-1-stimulated bFGF release. An MMP inhibitor partially suppressed the release of bFGF, indicating that matrix degradation is at least partially involved in the IL-1-stimulated bFGF release even if increased production of bFGF is related to the release. IL-1 sequentially stimulated mRNA expression of iNOS, membrane type 1-MMP, MMP-9 and -3, and bFGF, in that order. NG-Monomethyl-L-arginine, an inhibitor of NO production, inhibited gene expression of MMP-9 and bFGF. These findings suggest that elevation of the NO level via iNOS mRNA expression stimulated by IL-1 mediates gene expression and production of MMPs and bFGF, resulting in the release of bFGF, and also reveal molecular mechanisms implicating the degradation of articular cartilage followed by angiogenesis in the synovium in arthritic joints.

Animals↗

Normal labor associated with changes in uterine heparan sulfate proteoglycan expression and localization.

HYPOTHESIS: Proteoglycans are well-known modulators of intercellular communication and signaling. Remodeling of the proteoglycans in the human uterus occurs throughout pregnancy, and during labor. We therefore hypothesize that heparan sulfate proteoglycans (HSPGs) play an important role in establishing normal labor. In this study HSPGs were characterized and localized in human uterine tissue. METHODS: Uterine biopsies were obtained from four nonpregnant women, four women during elective cesarean section and four during emergency cesarean section. The biopsies were extracted using 4 m guanidinium hydrochloride (GuHCL). HSPGs were then purified by repeated ion-exchange chromatography on dehydroepiandrosterone (DEAE)-cellulose after digestion with chondroitinase ABC and finally precipitated with Alcian blue. HSPGs were identified by agarose gel electrophoresis and Western blotting. Controlled degradation of the heparan sulfate (HS) side-chains was performed using heparitinase or deglycosylation with trifluoromethanesulfonic acid (TFMS). The resulting core proteins were separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and visualized by Coomassie staining. HSPGs were localized in uterine tissue by immunohistochemistry. RESULTS: SDS-PAGE after deglycosylation indicated the presence of multiple distinct core proteins tentatively identified as syndecans 1-4 and glypican 1. Western blots confirmed the presence of these proteoglycans and also perlecan. Immunohistochemistry revealed that the HSPGs were localized mainly in the smooth muscle with few in the extracellular matrix (ECM). Syndecan 3, the dominant proteoglycan, showed the most pronounced changes during pregnancy and labor. CONCLUSION: For the first time several heparan sulfate proteoglycans have been identified and localized in the human uterus and shown to vary in expression during pregnancy and labor. Syndecan 3 had the most outstanding features in this respect.

Adult↗

Distribution and clinical significance of heparan sulfate proteoglycans in ovarian cancer.

PURPOSE: Heparan sulfate proteoglycans have been implicated in cancer cell growth, invasion, metastasis, and angiogenesis. This study was designed to compare their expression in normal ovary and ovarian tumors and then to examine their prognostic significance in ovarian cancer. EXPERIMENTAL DESIGN: The expression of syndecan-1, -2, -3, and -4, glypican-1, and perlecan was assessed by immunohistochemistry in 147 biopsies that included normal ovary and benign, borderline, and malignant ovarian tumors. Clinical data, including tumor stage, performance status, treatment, and survival, were collected. Univariate and multivariate analyses were performed to evaluate prognostic significance. RESULTS: The expression patterns of syndecan-1 and perlecan were altered in ovarian tumors compared with normal ovary. Syndecan-1 was not detected in normal ovary but was present in the epithelial and stromal cells of benign and borderline tumors and in ovarian adenocarcinomas. Perlecan expression was decreased in basement membranes that were disrupted by cancer cells but maintained in the basement membranes of blood vessels. Syndecan-2, -3, and -4, and glypican-1 were expressed in normal ovary and benign and malignant ovarian tumors. Stromal expression of syndecan-1 and glypican-1 were poor prognostic factors for survival in univariate analysis. CONCLUSION: We report for the first time distinct patterns of expression of cell surface and extracellular matrix heparan sulfate proteoglycans in normal ovary compared with ovarian tumors. These data reinforce the role of the tumor stroma in ovarian adenocarcinoma and suggest that stromal induction of syndecan-1 contributes to the pathogenesis of this malignancy.

Adult↗

Human nasal polyp microenvironment maintained in viable and functional states as xenografts in SCID mice.

OBJECTIVES: We undertook to maintain human nasal polyp tissue in a viable and functional state in SCID (severe combined immunodeficiency) mice. METHODS: Small, nondisrupted pieces of human nasal polyp tissues were subcutaneously implanted into SCID mice depleted of natural killer cells. The resulting xenografts were examined histologically, and the sera were evaluated for the presence of human protein. RESULTS: The original histologic architecture of the polyp was maintained in the xenografts. The tissues, including pseudostratified columnar epithelial-lined polyps and subepithelial stroma, remained viable, and goblet cells continued to produce mucin for up to 26 weeks after engraftment. Human inflammatory leukocytes, including CD3+ T cells, CD20+ B cells, CD138+ plasma cells, and CD68+ monocytes and/or macrophages, were present. Identification of human immunoglobulin and human interferon-gamma in the sera of xenograft-bearing mice indicated that the B cells or plasma cells and T cells within the xenografts remained functional for 2 weeks after engraftment. CONCLUSIONS: The ability to engraft and maintain nasal polyps provides an in vivo human/mouse chimeric model with which to investigate the role of inflammatory leukocytes and stromal cells in the maintenance and progression of polyposis and to determine how exogenous cytokines may alter the interaction of inflammatory cells, stromal cells, and epithelial cells in the polyp.

Animals↗

Prolonged labour associated with lower expression of syndecan 3 and connexin 43 in human uterine tissue.

BACKGROUND: Prolonged labour is associated with greater morbidity and mortality for mother and child. Connexin 43 is a major myometrial gap junction protein found in human myometrium. Syndecan 3 seems to prevail in the human uterus among heparan sulphate proteoglycans, showing the most significant increase during labour. The aims of the present study were to investigate syndecan 3 and connexin 43 mRNA expressions and protein distributions in human uterine tissue during normal and prolonged labour. METHODS: Uterine isthmic biopsies were collected from non-pregnant (n = 7), term pregnant women not in labour (n = 14), in normal labour (n = 7) and in prolonged labour (n = 7). mRNA levels of syndecan 3 and connexin 43 were determined by real time RT-PCR. The localization and expression were demonstrated by immunohistochemistry and confocal microscopy. RESULTS: In women with prolonged labour, the mRNA expressions of syndecan 3 and Connexin 43 were considerably lower than the expression level at normal labour (p < 0.05). In term-pregnant tissue, the expression of syndecan 3 and connexin 43 did not differ significantly compared to non-pregnant and normal labour. The immunoreactivity of syndecan 3 was strong at normal labour, in contrast to prolonged labour, where both a weaker expression and an irregular distribution were detected. The immunoreactivity of connexin 43 increased until term and further stronger staining occurred at normal labour. At prolonged labour, the immunoreactivity was weaker and more unevenly distributed. At labour, a co-localization of syndecan 3 and connexin 43 could be demonstrated in the smooth muscle by confocal microscopy. CONCLUSION: The high expression of syndecan 3 and connexin 43 and their co-localization to the smooth muscle bundles during normal labour, together with the significant reduction in prolonged labour, may indicate a role for these proteins in the co-ordination of myometrial contractility.

Adult↗

Positive association of obesity with single nucleotide polymorphisms of syndecan 3 in the Korean population.

CONTEXT: Very recently the unforeseen role of syndecan 3 (SDC3), a family of membrane-bound heparin sulfate proteoglycans, in the regulation of energy balance has been discovered in the Sdc3 null female mice. OBJECTIVE: The objective of the study was to test the hypothesis that single nucleotide polymorphisms (SNPs) in SDC3 are associated with obesity in the Korean population. DESIGN/SETTING/SUBJECTS: We conducted a population-based cohort study consisting of 229 control and 245 study subjects and a second independent study consisting of 192 control and 115 study subjects. MAIN OUTCOME MEASUREMENT: Body mass index (BMI) was measured. RESULTS: First, Sdc3 mRNA expression in the brain of ob/ob mice was profoundly increased, compared with control mice. Next, all three nonsynonymous SNPs [T271I (rs2282440, C>T), D245N (rs4949184, C>T), and V150I (rs2491132, C>T)] in the SDC3 gene in control female subjects (BMI < 23, n = 229) and obese female subjects (BMI > 30, n = 245) were genotyped. We demonstrated the presence of clear ethnic differences in three nonsynonymous SDC3 SNPs among African-Americans, Chinese, Europeans, and Koreans. Of three SNPs in SDC3, rs4949184 was not associated with obesity and the other two SNPs (rs2282440 and rs2491132) were strongly associated with obesity (P < 0.0001), and the results were confirmed in the second independent study group. Haplotype analysis also revealed strong association with obesity (chi2 = 76.92, P < 0.000001). CONCLUSIONS: There are ethnic differences in the SDC3 polymorphisms, and the polymorphisms are strongly associated with obesity.

Adult↗

Regulation of mRNA localization by transmembrane signalling: local interaction of HB-GAM (heparin-binding growth-associated molecule) with the cell surface localizes beta-actin mRNA.

Localization of mRNAs is currently thought to be partially responsible for molecular sorting to specific compartments within the cell. In mammalian cells the best-studied example is the beta-actin mRNA that is localized to the cell processes, and its localization is necessary in migratory responses of cells. It is reasonable to assume that mRNA localization within cells is coupled to transmembrane signalling due to extracellular factors, but little is known about such putative mechanisms. We show here that HB-GAM, an extracellular matrix-associated factor that enhances migratory responses in cells, is able to localize beta-actin mRNA when locally applied to cells via microbeads. The HB-GAM-induced mRNA localization is specifically inhibited by low concentrations of heparin and by heparitinase treatment of cells, showing that cell-surface heparin-type glycans are required for the effect. The finding that soluble N-syndecan is also inhibitory suggests that the transmembrane proteoglycan N-syndecan, previously identified as an HB-GAM receptor, is involved in the mRNA-localizing effect of HB-GAM. Inhibition of the mRNA localization by the src-kinase inhibitor PP1 is compatible with an N-syndecan-mediated effect since the receptor function of N-syndecan has been recently found to depend on the src-kinase signalling pathway. The mRNA-localizing activity of N-syndecan is also suggested by the finding that affinity-purified anti-N-syndecan antibodies coated on microbeads are able to localize beta-actin mRNA.

Actins↗

Bipartite interaction between neurofibromatosis type I protein (neurofibromin) and syndecan transmembrane heparan sulfate proteoglycans.

The neurofibromatosis type 1 (NF1) gene encodes a large tumor suppressor protein (neurofibromin). Although it is known to possess Ras GTPase-activating protein (GAP) activity, the cellular role of neurofibromin remains unclear. Here we used yeast two-hybrid screening to identify neurofibromin-interacting proteins. Syndecan-2, a transmembrane heparan sulfate proteoglycan (HSPG), was isolated as a binding partner for two distinct regions of the neurofibromin protein. We subsequently found that neurofibromin can bind all four mammalian syndecans. NF1 interaction requires the transmembrane domain and a membrane-proximal region of the cytoplasmic tail of syndecan, but not the C terminus of syndecan known to bind to CASK, a membrane-associated guanylate kinase (MAGUK). Neurofibromin, syndecans, and CASK have overlapping subcellular distributions in axons and synapses of neurons, as shown by biochemical fractionation and immunostaining. Moreover, neurofibromin exists in a complex with syndecan and CASK in vivo, as evidenced by their coimmunoprecipitation from rat brain. Our findings suggest that interaction with different members of the syndecan family may be a mechanism for localizing neurofibromin to specialized domains of the plasma membrane.

Animals↗

Spatiotemporal expression patterns of N-syndecan, a transmembrane heparan sulfate proteoglycan, in developing retina.

PURPOSE: N-syndecan is a transmembrane heparan sulfate proteoglycan, that is highly expressed in neural tissues. In the current study, changes in N-syndecan expression during retinal development were examined. METHODS: Localization of N-syndecan in developing rat retina was examined by immunohistochemistry and in situ hybridization. The amount of the core protein was evaluated by immunoblot analysis, using retinal homogenates at various developmental stages. In addition, mRNA expression was semiquantified by reverse transcription-polymerase chain reaction (RT-PCR). To understand better the localization of N-syndecan in retinal neuronal cells, we performed immunocytochemistry using retinal ganglion cells in culture. RESULTS: N-syndecan is highly expressed in nerve fiber-rich layers of the retina at early postnatal stages (between postnatal day [P]0 and P14). In contrast, immunoreactivity was faint during embryonic stages and late postnatal stages. In addition, in retinal flatmounted sections, N-syndecan immunoreactivity was observed on the axons of retinal ganglion cells. Intense signals were observed in the ganglion cell layer during in situ hybridization. Immunoblot analyses demonstrated that the amount of N-syndecan core protein reached a peak at approximately P14. The RT-PCR analyses using N-syndecan primers showed that an intense amplified band was observed in the cDNA derived from P14 retinas, whereas only faint bands were detected in the embryonic day (E)16 and P42 retinas. In retinal ganglion cells in culture, N-syndecan was located on the long, extended neurites. CONCLUSIONS: The data show that N-syndecan is transiently expressed, primarily in retinal neural fibers, during retinal development, indicating that it may be involved in formation of the retinal neural network.

Animals↗

N-syndecan (syndecan 3) from neonatal rat brain binds basic fibroblast growth factor.

The cell surface proteoglycan N-syndecan (syndecan 3) was isolated from neonatal rat brain. Purified brain N-syndecan had biochemical properties very similar to N-syndecan previously identified in Schwann cells: it contained mainly, if not exclusively, heparan sulfate glycosaminoglycan chains and had a core protein with an apparent molecular mass of 120 kDa by sodium dodecyl sulfate-gel electrophoresis. We examined the interactions between purified N-syndecan and extracellular ligands using a solid phase binding assay. It was found that among all proteins tested, including a variety growth factors and extracellular matrix molecules, only basic fibroblast growth factor (bFGF) exhibited significant N-syndecan binding. N-syndecan binding to bFGF was saturable and exhibited a KD = 0.5 nM. Soluble bFGF effectively competed with immobilized bFGF for binding to N-syndecan, indicating that these two proteins also interact in solution. Heparin and heparan sulfate, but not chondroitin sulfate, inhibited N-syndecan-bFGF binding. Isolated N-syndecan core protein did not exhibit significant binding to bFGF. Thus, the heparan sulfate chains of N-syndecan, rather than its core protein, appear to be responsible for binding to bFGF. Interestingly, acidic fibroblast growth factor, which is structurally similar to bFGF, did not exhibit significant N-syndecan binding. N-syndecan also did not bind to several other heparin-binding proteins used in this study, indicating a high degree of specificity for the N-syndecan-bFGF interaction. Both N-syndecan and bFGF are abundant in neonatal brain, suggesting that N-syndecan may function as a co-receptor for bFGF during nerve tissue development.

Animals↗

N-syndecan: structure and function of a transmembrane heparan sulfate proteoglycan.

N-syndecan is a member of the syndecan family of transmembrane heparan sulfate proteoglycans that was cloned initially from neonatal rat Schwann cells and is the principal syndecan expressed during early postnatal development in the central and peripheral nervous systems. Purified N-syndecan binds in vitro with high affinity to several extracellular regulatory ligands, including basic fibroblast growth factor, the secreted adhesive protein heparin binding growth-associated molecule, and a novel collagen-like protein secreted by Schwann cells. These extracellular ligands utilize the heparan sulfate chains of N-syndecan for binding. Based on the striking amino acid sequence homology of the cytoplasmic domain of N-syndecan to syndecan-1, it is proposed that N-syndecan associates with the actin-based cytoskeleton. N-syndecan core proteins self associate by means of an unusual dimerization motif comprised of the transmembrane domain and a short flanking sequence in the ectodomain. Similar to other single transmembrane domain receptor proteins, it is suggested that ligand-regulated dimerization of N-syndecan represents a mechanism for regulating downstream signaling activities. In rat brain tissue a significant fraction of the N-syndecan molecules are present in a soluble form, presumably as a result of proteolytic membrane shedding. A model is presented for morphoregulatory activity of N-syndecan in which extracellular ligand-induced clustering of N-syndecan molecules on the cell surface promotes cytoskeletal association and reorganization. Membrane shedding separates the functional domains of the proteoglycan and terminates this activity.

Animals↗