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At least 19 recordsLinked to original sources

PubMed2004

Distribution of syndecans 1-4 within the anterior segment of the human eye: expression of a variant syndecan-3 and matrix-associated syndecan-2.

Control of the actomyosin network plays a role in regulating the movement of aqueous humor through the anterior segment of the eye. Receptors that could control its activity are unknown. In this study, we show that all four members of the syndecan family, which can regulate the actomyosin network, are present within the anterior segment. In both sections of human anterior segments and cultures of human trabecular meshwork (HTM), Schlemm's canal (HSC) and the ciliary muscle (HCM) cells from the anterior segment, syndecans-3 and -4 were the predominant family members. They were widely distributed throughout the anterior segment. Syndecan-3 within the anterior segment was a novel, recently described variant 55 kDa form. Low levels of syndecans-1 and -2 were also observed in situ and in all three cultures. Their expression was weaker and more localized than that observed for syndecans-3 and -4. Staining for syndecan-1 in HCM cultures was variable. In HTM and HSC cultures, syndecan-2 also co-distributed with fibronectin, laminin and type IV collagen suggesting that it was shed and associated with the extracellular matrix. Western blots supported this idea and showed syndecan-2 ectodomains in lysates from anterior segments.

Adolescent↗

PubMed2005

Syndecan-2 overexpression induces osteosarcoma cell apoptosis: Implication of syndecan-2 cytoplasmic domain and JNK signaling.

Syndecans are cell surface heparan sulfate proteoglycans that serve as co-receptors and modulate the actions of a number of extracellular ligands. Syndecans thereby regulate cell adhesion, proliferation, and differentiation. Studies in cancer cells suggest that syndecans may also modulate cell viability. We previously showed that syndecan-2 controls the growth of normal human osteoblastic cells. In this study, we examined the role of syndecan-2 in osteosarcoma cell proliferation and apoptosis. To this goal, MG63 osteosarcoma cells which express low syndecan-2 levels were transfected to overexpress full-length syndecan-2 or truncated syndecan-2 lacking its cytoplasmic domain. Determination of cell growth by cell counting and 3H-thymidine incorporation showed that truncated syndecan-2 inhibited MG63 cell proliferation. Flow cytometry analysis of DNA content and colony forming test revealed that syndecan-2, but not truncated syndecan-2, induced MG63 cell death. We show that characteristic features of apoptosis such as caspase activation, PARP cleavage, cytochrome c release, increased Bax expression, and DNA fragmentation were associated with syndecan-2-induced cell death. We further show that expression of full-length or truncated syndecan-2 induced differential activation of MAPK phosphorylation in MG63 cells. Notably, syndecan-2 but not truncated syndecan-2 overexpression increased JNK phosphorylation. Moreover, SP600125, a specific inhibitor of JNK, suppressed Bax expression induced by syndecan-2 overexpression, indicating that JNK activation mediates syndecan-2-induced apoptosis. The results show that syndecan-2 induces osteoblastic cell apoptosis through the JNK/Bax apoptotic pathway and that the cytoplasmic domain of syndecan-2 is required for this action. This supports a role for syndecan-2 in the regulation of osteosarcoma cell fate and identifies one signaling pathway by which syndecan-2 induces apoptosis in osteosarcoma cells.

Anthracenes↗

PubMed1999

Regulated expression and subcellular localization of syndecan heparan sulfate proteoglycans and the syndecan-binding protein CASK/LIN-2 during rat brain development.

The syndecan family of cell surface heparan sulfate proteoglycans interacts via their cytoplasmic C-terminal tail with the PDZ domain of CASK/LIN-2, a membrane-associated guanylate kinase homolog. The syndecan-CASK interaction may be involved in intercellular signaling and/or cell adhesion. Here we show that syndecan-1 to syndecan-4 have distinctive mRNA distributions in adult rat brain by in situ hybridization, with syndecan-2 and -3 being the major syndecans expressed in neurons of the forebrain. At the protein level, syndecan-2 and -3 are differentially localized within neurons; syndecan-3 is concentrated in axons, whereas syndecan-2 is localized in synapses. The synaptic accumulation of syndecan-2 occurs late in synapse development. CASK is a cytoplasmic-binding partner for syndecans, and its subcellular distribution changes strikingly during development, shifting from a primarily axonal distribution in the first 2 postnatal weeks to a somatodendritic distribution in adult brain. This change in CASK distribution correlates temporally and spatially with the expression patterns of syndecan-3 and -2, consistent with the association of both of these syndecans with CASK in vivo. In support of this, we were able to coimmunoprecipitate a complex of CASK and syndecan-3 from brain extracts. Our results indicate that specific syndecans are differentially expressed in various cell types of the brain and are targeted to distinct subcellular compartments in neurons, where they may serve specialized functions. Moreover, CASK is appropriately expressed and localized to interact with both syndecan-2 and -3 in different compartments of the neuron throughout postnatal development.

Aging↗

PubMed2006

Expression of syndecans, a heparan sulfate proteoglycan, in malignant gliomas: participation of nuclear factor-kappaB in upregulation of syndecan-1 expression.

Invasion of tumor cells into the surrounding normal brain tissues is a prominent feature of malignant gliomas. Malignant glioma cells secrete thrombospondin-1 which participates in the motility of glioma cells and binds cell surface heparan sulfate proteoglycan. To clarify the invasion mechanism of tumor cells, expression of the syndecans (syndecan-1, -2, -3, and -4), a major cell surface heparan sulfate proteoglycan family, was analyzed in malignant gliomas. Involvement of nuclear factor-kappaB (NF-kappaB) on syndecan-1 expression was also investigated. Using reverse transcription-PCR, the authors analyzed the expression of syndecan-1, -2, -3, and -4 in 10 malignant glioma cell lines, 2 glioblastoma specimens, and 2 normal brain specimens. All malignant glioma cell lines and glioblastoma specimens expressed all types of syndecan mRNA, except in one glioma cell line that lacked syndecan-3 expression. On the other hand, normal brain specimens expressed syndecan-2, -3, and -4 mRNA, but did not syndecan-1 mRNA. Syndecan-1 protein was localized in the cell surface of all malignant glioma cell lines by flow cytometry. Various levels of active nuclear factor-kappa B (NF-kappaB) was detected in all malignant glioma cell lines using immunoblotting. The expression of active NF-kappaB and syndecan-1 increased in U251 glioma cells after tumor necrosis factor-alpha or interleukin-1beta treatment, which can activate NF-kappaB. The amplification of active NF-kappaB and syndecan-1 by tumor necrosis factor-alpha or interleukin-1beta was suppressed by an inhibitor of NF-kappaB activation (emodin). Emodin also downregulated the expression of syndecan-1 mRNA in U251 cells. These results indicate that malignant glioma cells express all types of syndecans and suggest that NF-kappaB participates in the upregulation of the syndecan-1 expression at the transcriptional level, and increased expression of syndecan-1 could associate with extracellular matrices including thrombospondin-1.

Brain Neoplasms↗

PubMed2006

Syndecan-1 and syndecan-4 are overexpressed in an estrogen receptor-negative, highly proliferative breast carcinoma subtype.

Members of the syndecan and glypican families of cell surface heparan sulfate proteoglycans (HSPGs) are modulators of growth factor signaling and cell adhesion. Both loss and gain in expression of syndecans and glypicans has been associated with malignant progression. The goal of this project was to investigate a possible relationship between expression of cell surface HSPGs (syndecan-1, syndecan-4 and glypican-1) and established prognostic factors or clinical outcome in breast carcinomas. Tissue arrays containing 207 human breast carcinoma samples in duplicate were immuno-labeled with antibodies to syndecan-1, syndecan-4, glypican-1, Ki67, E-cadherin, estrogen receptor (ER) and progesterone receptor (PR). Clinical follow-up information was available for up to 18.6 years (median follow-up 6.2 years). Syndecan-1 and syndecan-4 expression in carcinoma cells ranged from complete loss to high expression, but glypican-1 was detected only in a small subset of breast carcinomas. Expression of all three HSPGs was significantly associated with the Ki67 proliferation index (syndecan-1: p=0.0025; syndecan-4: p<0.0001; glypican-1 p=0.01). Syndecan-1 and syndecan-4 expression correlated with ER negativity, grade, and size of the primary tumors. Syndecan-1 expression (but not syndecan-4 nor glypican-1) predicted patient outcome (DFS: p=0.0054; OS: p=0.0086). However, multivariate analysis failed to identify syndecan-1 as an independent prognostic marker, which was due to its significant association with established prognostic factors. The strong association between cell surface HSPGs and the Ki67 proliferation marker would support a biologic role in carcinoma growth regulation. Furthermore, the close correlation between syndecan expression and negative ER status raises the possibility of hormonal regulation or more likely an association with an aggressive, ER-negative carcinoma phenotype.

Adult↗

PubMed1993

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↗

PubMed2001

Syndecan-1 (CD138) immunoreactivity in bone marrow biopsies of multiple myeloma: shed syndecan-1 accumulates in fibrotic regions.

Syndecan-1 (CD138) mediates myeloma cell adhesion, and loss of syndecan-1 from the cell surface may contribute to myeloma proliferation and dissemination. Flow cytometry analysis of myeloma cells in bone marrow specimens shows heterogeneity in cell surface syndecan-1 expression. It is not known whether weaker expression correlates with more aggressive disease. However, recent reports suggest that variations in syndecan-1 staining intensity on myeloma cells may be an artifact of specimen handling. In this study, we evaluate syndecan-1 expression in bone marrow biopsy sections from 28 multiple myeloma patients, to elucidate the heterogeneity of syndecan-1 expression in situ. Immunoreactivity for syndecan-1, using the antibody B-B4 (CD138), was found in more than 95% of multiple myeloma cells in 27 of 28 biopsies. However, one biopsy had more than 50% CD138-negative cells and cells with weak CD138 expression were identified in the majority of cases. Loss of syndecan-1 did not appear to relate to myeloma cell differentiation. In addition, syndecan-1 was detected on intravascular and intrasinusoidal myeloma cells suggesting that loss of syndecan-1 may not be required for extramedullary dissemination. Bone marrow biopsies from nine additional patients, with variable CD138 staining intensity on myeloma cells as determined by flow cytometry, were studied by immunohistochemistry. The heterogeneous CD138 expression was confirmed in situ, with weakly positive cells concentrated in areas of reticulin fibrosis. These cells had a disrupted pattern of membrane staining in contrast to the strong linear membrane staining seen in the other multiple myeloma cells. In addition, the fibrotic stroma stained intensely for syndecan-1. Accumulation of syndecan-1 within the extracellular matrix of the marrow likely is derived by shedding of the molecule from the surface of myeloma cells. Because syndecan-1 can act to regulate the activity of heparan-binding growth factors, these reservoirs of syndecan-1 may play a critical role in promoting myeloma pathogenesis, or in regeneration of the tumor after chemotherapy.

Biopsy↗

PubMed1994

A novel laminin-binding form of syndecan-1 (cell surface proteoglycan) produced by syndecan-1 cDNA-transfected NIH-3T3 cells.

Syndecan-1, a cell surface proteoglycan, binds many extracellular matrix components via its heparan sulfate side chains. In previous studies syndecan-1 has failed to bind laminin, although both syndecan-1 and laminin are expressed at sites of early matrix accumulation, like in basement membranes of epithelial-mesenchyma boundaries and in condensing mesenchymes during embryonic development. In order to study whether syndecan-1 regulates the adhesion of mesenchymal cells to laminin, syndecan-1 was expressed in NIH-3T3 cells by transfection. Syndecan-1-transfected cells showed increased binding to laminin in comparison to control transfected cells. We then compared the properties of syndecan-1 isolated from transfected NIH-3T3 cells and from NMuMG mammary epithelial cells. In solid-phase binding assays, syndecan-1 from NIH-3T3 cells, but not NMuMG cells, bound to laminin. NIH-3T3-derived syndecan contained more chondroitin sulfate than NMuMG-derived syndecan-1, and our results revealed that both heparan sulfate and chondroitin sulfate mediate syndecan-1 binding to laminin. E3 domain revealed highest binding for syndecan-1 among the elastase-derived fragments of laminin. These results suggest that induction of syndecan-1 in mesenchymal cells may be involved in cellular recognition of laminin during developmental processes.

3T3 Cells↗

PubMed2005

Transmembrane domain-induced oligomerization is crucial for the functions of syndecan-2 and syndecan-4.

The syndecans are known to form homologous oligomers that may be important for their functions. We have therefore determined the role of oligomerization of syndecan-2 and syndecan-4. A series of glutathione S-transferase-syndecan-2 and syndecan-4 chimeric proteins showed that all syndecan constructs containing the transmembrane domain formed SDS-resistant dimers, but not those lacking it. SDS-resistant dimer formation was hardly seen in the syndecan chimeras where each transmembrane domain was substituted with that of platelet-derived growth factor receptor (PDGFR). Increased MAPK activity was detected in HEK293T cells transfected with syndecan/PDGFR chimeras in a syndecan transmembrane domain-dependent fashion. The chimera-induced MAPK activation was independent of both ligand and extracellular domain, implying that the transmembrane domain is sufficient to induce dimerization/oligomerization in vivo. Furthermore, the syndecan chimeras were defective in syndecan-4-mediated focal adhesion formation and protein kinase Calpha activation or in syndecan-2-mediated cell migration. Taken together, these data suggest that the transmembrane domains are sufficient for inducing dimerization and that transmembrane domain-induced oligomerization is crucial for syndecan-2 and syndecan-4 functions.

Amino Acid Sequence↗

PubMed1992

Syndecan 3: a member of the syndecan family of membrane-intercalated proteoglycans that is expressed in high amounts at the onset of chicken limb cartilage differentiation.

A partial cDNA that encodes a newly discovered member of the syndecan family of integral membrane proteoglycans, which we have termed syndecan 3, has been isolated from an embryonic chicken limb bud cDNA library. Syndecan 3 is distinct from but structurally related to syndecan and fibroglycan, two previously characterized members of this family of membrane-intercalated proteoglycans. Syndecan 3 contains a cytoplasmic domain potentially associated with the cytoskeleton that is 85% identical in amino acid sequence to the cytoplasmic domain of syndecan. Syndecan 3 also possesses a hydrophobic transmembrane domain and an extracellular domain containing several clustered potential glycosaminoglycan attachment sites. Like syndecan, the ectodomain of syndecan 3 has a single dibasic protease-susceptible site adjacent to the transmembrane domain, which might be involved in shedding the ectodomain from the cell surface. A striking feature of syndecan 3 is an extensive (182 amino acid) threonine, serine, and proline (T+S+P)-rich domain that closely resembles T+S+P-rich regions in several mucin-like proteins in which O-linked oligosaccharides are bound to the threonine and serine residues. Syndecan 3 is expressed in high amounts during a critical phase of chicken limb chondrogenesis in which limb mesenchymal cells condense, round up, and interact with one another before depositing a cartilage matrix. The multiple functional domains of syndecan 3 provide potential sites for mediating the adhesive cell-matrix interactions and cytoskeletal reorganization involved in this critical condensation process.

Amino Acid Sequence↗

PubMed2001

Proximal promoter of the murine syndecan-1 gene is not sufficient for the developmental pattern of syndecan expression in B lineage cells.

Syndecan-1 (CD138) is a cell membrane proteoglycan that binds extracellular matrix components and various growth factors. The role of syndecan-1 in the control of cell growth and morphology has been illustrated by its altered expression in hematological malignancies such as multiple myeloma as well as some solid tumors. It has been reported that the expression of syndecan-1 in cells of the B lineage is developmentally regulated such that pre-B cells and plasma cells express syndecan-1 while mature B cells do not. Thus, we investigated whether the proximal promoter region of the murine syndecan-1 promoter was able to confer the observed on-off-on expression of syndecan-1 in cells of the B lineage as they develop from pre-B cells to plasma cells. Experiments carried out using deletion mutants of the proximal promoter cloned upstream of the CAT reporter gene transfected into murine cell lines, representing the above stages of B-cell development, such as BA/F3 (pro-B cell), 70Z/3 (pre-B cell), 2PK3 (late mature B cell), and MPC-11 (plasma cell), showed detectable levels of CAT expression. The WEHI-231 (mature B cell) cell lines did not show detectable levels of CAT reporter activity. The strong levels of expression were observed with a fragment of the proximal promoter spanning the region from -365 to -95 (from the translation start point). However, Northern analysis of RNA obtained from the five murine B-cell lines, representing various stages of B-cell development, showed that the 70Z/3, MPC-11 but not BA/F3, and 2PK3 cells expressed detectable levels of syndecan-1 mRNA. By FACS analysis, using a rat anti mouse syndecan-1 antibody, syndecan-1 expression on the cell surface was found to correlate with the observed mRNA expression patterns in these cell lines. Our results indicate that the proximal promoter of the murine syndecan-1 promoter is not sufficient for the observed developmental pattern of syndecan expression in B cells.

Animals↗

PubMed2004

A sandwich ELISA for the estimation of human syndecan-2 and syndecan-4 in biological samples.

Syndecans are integral membrane proteoglycans containing both chondroitin and heparan sulphate side chains. Syndecans are shed from the cell surface, and may be detected in cellular supernatant or body fluids. In this study, we wished to design ELISA methods for syndecan-2 and syndecan-4, with the future aim of analyzing syndecans in large number of patient materials. Briefly, sandwich ELISAs for human syndecan-2 and syndecan-4 were designed employing monoclonal mouse antibodies as capture and commercially available polyclonal rabbit anti-syndecan as secondary antibodies. Although no quantified standard was available, relative estimation of syndecan-2 and syndecan-4 levels was possible in a small pilot material. The paper presents the ELISA method for these proteoglycans. We suggest that this may be a useful tool in the analysis of patient materials and in the detection of syndecans during proteoglycan purification.

Animals↗

PubMed2004

Cooperation of syndecan-2 and syndecan-4 among cell surface heparan sulfate proteoglycans in the actin cytoskeletal organization of Lewis lung carcinoma cells.

Syndecan-2 cooperates with integrin alpha 5 beta 1 in cell adhesion to a fibronectin substratum and regulates actin cytoskeletal organization in an expression level-dependent manner; Lewis lung carcinoma-derived P29 cells with high expression form stress fibers, whereas the same tumor-derived low expressers, LM66-H11 cells, form cortex actin [Munesue, S., Kusano, Y., Oguri, K., Itano, N., Yoshitomi, Y., Nakanishi, H., Yamashina, I., and Okayama, M. (2002) BIOCHEM: J. 363, 201-209]. In this study we examined the participation of other cell surface heparan sulfate proteoglycans in this signaling. The two clones expressed syndecan-1, -2 and -4, and glypican-1 at similar levels except for syndecan-2. Treatment of cells with phosphatidylinositol-specific phospholipase C or immobilized anti-syndecan-1 antibodies demonstrated that neither glypican-1 nor syndecan-1 was involved in this signaling, indicating that individual cell surface heparan sulfate proteoglycans have functional specificity. Stimulation with immobilized anti-syndecan-2 or -4 antibodies induced stress fiber formation in P29 cells but not in LM66-H11 cells, despite the similar levels of syndecan-4 expression, suggesting that stress fiber formation required a threshold expression level of syndecan-2 acting downstream of syndecan-4. This was confirmed by cells in which syndecan-2 expression was artificially suppressed by antisense mRNA oligonucleotide treatment or elevated by cDNA transfection. This is the first report demonstrating that syndecan-2 and -4 cooperate in situ in actin cytoskeletal organization.

Actins↗

PubMed1997

Thrombin stimulates syndecan-1 promotor activity and expression of a form of syndecan-1 that binds antithrombin III in vascular smooth muscle cells.

Vascular smooth muscle (VSM) cells express transmembrane proteoglycans of the syndecan gene family. We reported previously that the expression of syndecans by VSM cells is regulated by mitogens such as serum, platelet-derived growth factor, and basic fibroblast growth factor and that syndecan expression is induced after balloon injury in vivo. We now show that thrombin is a potent inducer of syndecan-1 expression in VSM cells. Transient transfection experiments with a rat syndecan-1 promoter construct demonstrated that thrombin stimulates transcription of the syndecan-1 gene. Syndecan expression in response to thrombin was not inhibited by downregulation of protein kinase C. Thrombin-induced syndecan-1 expression was dependent on tyrosine kinase activity. Calcium was necessary for syndecan-1 expression, but increasing the intracellular calcium levels was not sufficient to induce syndecan-1 expression. Analysis of antithrombin III (AT III) binding activity revealed that thrombin caused an increase in the synthesis of syndecan-1 molecules that exhibited high-affinity AT III binding. These results suggest that VSM cells could play an important role in controlling local thrombus formation subsequent to vascular injury, via a feedback mechanism that involves thrombin-induced stimulation of an inhibitor of thrombin activity.

Animals↗

PubMed2000

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 OpaHSPG 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.

Amino Acid Sequence↗

PubMed2000

Syntenin-syndecan binding requires syndecan-synteny and the co-operation of both PDZ domains of syntenin.

Syntenin is an adaptor-like molecule that binds to the cytoplasmic domains of all four vertebrate syndecans. Syntenin-syndecan binding involves the C-terminal part of syntenin that contains a tandem of PDZ domains. Here we provide evidence that each PDZ domain of syntenin can interact with a syndecan. Isolated or combined mutations of the carboxylate binding lysines in the inter-betaAbetaB loops and of the alphaB1 residues in either one or both the PDZ domains of syntenin all reduce syntenin-syndecan binding in yeast two-hybrid, blot-overlay, and surface plasmon resonance assays. PDZ2 mutations have more pronounced effects on binding than PDZ1 mutations, but complete abrogation of syntenin-syndecan binding requires the combination of both the lysine and the alphaB1 mutations in both the PDZ domains of syntenin. Isothermal calorimetric titration of syntenin with syndecan peptide reveals the presence of two binding sites in syntenin. Yet, unlike a tandem of two PDZ2 domains and a reconstituted PDZ1+PDZ2 tandem, a tandem of two PDZ1 domains and isolated PDZ1 or PDZ2 domains do not interact with syndecan bait. We conclude to a co-operative binding mode whereby neither of these two PDZ domains is sufficient by itself but where PDZ2 functions as a "major" or "high affinity" syndecan binding domain, and PDZ1 functions as an "accessory" or "low affinity" syndecan binding domain. The paired, but not the isolated PDZ domains of syntenin bind also strongly to the immobilized cytoplasmic domains of neurexin and B-class ephrins. By inference, these data suggest a model whereby recruitment of syntenin to membrane surfaces requires two compatible types of bait that are in "synteny" (occurring together in location) and engages both PDZ domains of syntenin. The synteny of compatible bait may result from the assemblies and co-assemblies of syndecans and other similarly suited partners in larger supramolecular complexes. In general, an intramolecular combination of PDZ domains that are weak, taken individually, would appear to be designed to detect rather than drive the formation of specific molecular assemblies.

Amino Acid Sequence↗

PubMed1992

Regulated expression of syndecan in vascular smooth muscle cells and cloning of rat syndecan core protein cDNA.

cDNA encoding the core protein of rat syndecan was cloned from a neonatal rat aortic cDNA library by polymerase chain reaction amplification. Expression of syndecan mRNA in rat aortic vascular smooth muscle (VSM) cells was demonstrated by reverse transcriptase-linked polymerase chain reaction amplification of syndecan sequences using total RNA from rat aortic VSM cells as templates. Polyclonal antibodies against rat syndecan core protein were produced by immunizing rabbits with a recombinant fusion protein containing a fragment of the extracellular domain. The anti-syndecan antibodies immunoprecipitated a large 35SO4-labeled molecule synthesized by cultured rat aortic VSM cells. The immunoprecipitated molecule was identified as a hybrid proteoglycan, based on results of alkaline, nitrous acid, and chondroitinase ABC digestions. On immunoblots the antibodies recognized a proteoglycan of greater than 200 kDa, with a core protein size after deglycosylation of approximately 50 kDa. The anti-syndecan antibodies stained cultured rat aortic VSM cells as well as tissue sections of neonatal and adult rat aortas in the medial, smooth muscle layer. On Northern blots of RNA isolated from cultured VSM cells, a syndecan cDNA probe hybridized to a major RNA species of 2.6 kilobases. Quantitative Northern blot analysis of total RNA isolated from VSM cells harvested at different cell densities revealed a decrease in syndecan mRNA levels with increased cell density. These results demonstrate the regulated synthesis of syndecan by rat VSM cells.

Amino Acid Sequence↗

PubMed2004

Chondroitin sulfate chains on syndecan-1 and syndecan-4 from normal murine mammary gland epithelial cells are structurally and functionally distinct and cooperate with heparan sulfate chains to bind growth factors. A novel function to control binding of midkine, pleiotrophin, and basic fibroblast growth factor.

A comparative analysis was carried out of heparan sulfate (HS) and chondroitin sulfate (CS) chains of the ectodomains of hybrid type transmembrane proteoglycans, syndecan-1 and -4, synthesized simultaneously by normal murine mammary gland epithelial cells. Although the HS chains were structurally indistinguishable, intriguingly the CS chains were structurally and functionally distinct, probably reflecting the differential regulation of sulfotransferases involved in the synthesis of HS and CS. The CS chains of the two syndecans comprised nonsulfated, 4-O-, 6-O-, and 4,6-O-disulfated N-acetylgalactosamine-containing disaccharide units and were significantly different, with a higher degree of sulfation for syndecan-4. Functional analysis using a BIAcore system showed that basic fibroblast growth factor (bFGF) specifically bound only to the HS chains of both syndecans, whereas midkine (MK) and pleiotrophin (PTN) bound not only to the HS but also to the CS chains. Stronger binding of MK and PTN to the CS chains of syndecan-4 than those of syndecan-1 was revealed, supporting the structural and functional differences. Intriguingly, removal of the CS chains decreased the association and dissociation rate constants of MK, PTN, and bFGF for both syndecans, suggesting the simultaneous binding of these growth factors to both types of chains, producing a ternary complex that transfers the growth factors to the corresponding cell surface receptors more efficiently compared with the HS chains alone. The involvement of the core protein was also shown in the binding of MK and PTN to syndecan-1, suggesting the possibility of cooperation with the HS and/or CS chains in the binding of these growth factors and their delivery to the cell surface receptors.

Animals↗