Syndecan-4 is a maestro of gastric cancer cell invasion and communication that underscores poor survival.

Gastric cancer is a dominating cause of cancer-associated mortality with limited therapeutic options. Here, we show that syndecan-4 (SDC4), a transmembrane proteoglycan, is highly expressed in intestinal subtype gastric tumors and that this signature associates with patient poor survival. Further, we mechanistically demonstrate that SDC4 is a master regulator of gastric cancer cell motility and invasion. We also find that SDC4 decorated with heparan sulfate is efficiently sorted in extracellular vesicles (EVs). Interestingly, SDC4 in EVs regulates gastric cancer cell-derived EV organ distribution, uptake, and functional effects in recipient cells. Specifically, we show that SDC4 knockout disrupts the tropism of EVs for the common gastric cancer metastatic sites. Our findings set the basis for the molecular implications of SDC4 expression in gastric cancer cells and provide broader perspectives on the development of therapeutic strategies targeting the glycan-EV axis to limit tumor progression.

Effects of syndecan-4 silencing on the extracellular matrix remodeling in anoikis-resistant endothelial cells.

Anoikis is a process of programmed cell death induced by the loss of cell/matrix interactions. In previous work, we have shown that the acquisition of anoikis resistance upregulates syndecan-4 (SDC4) expression in endothelial cells. In addition, SDC4 gene silencing by microRNA interference reverses the transformed phenotype of anoikis-resistant endothelial cells. Due to this role of SDC4 in regulating the behavior of anoikis-resistant endothelial cells, we have evaluated that the functional consequences of SDC4 silencing in the extracellular matrix (ECM) remodeling in anoikis-resistant rabbit aortic endothelial cells submitted to SDC4 gene silencing (miR-Syn4-Adh-1-EC). For this, we evaluated the expression of adhesive proteins, ECM receptors, nonreceptor protein-tyrosine kinases, and ECM-degrading enzymes and their inhibitors. Altered cell behavior was monitored by adhesion, migration, and tube formation assays. We found that SDC4 silencing led to a decrease in migration and angiogenic capacity of anoikis-resistant endothelial cells; this was accompanied by an increase in adhesion to fibronectin. Furthermore, after SDC4 silencing, we observed an increase in the expression of fibronectin, collagen IV, and vitronectin, and a decrease in the expression of integrin α5ß1 and αvß3, besides that, silenced cells show an increase in Src and FAK expression. Quantitative polymerase chain reaction and Western blot analysis demonstrated that SDC4 silencing leads to altered gene and protein expression of MMP2, MMP9, and HSPE. Compared with parental cells, SDC4 silenced cells showed a decrease in nitric oxide production and eNOS expression. In conclusion, these data demonstrate that SDC4 plays an important role in ECM remodeling. In addition, our findings represent an important step toward understanding the mechanism by which SDC4 can reverse the transformed phenotype of anoikis-resistant endothelial cells.

Syndecan-4 is required for early-stage repair responses during zebrafish heart regeneration.

BACKGROUND: The healing process after a myocardial infarction (MI) in humans involves complex events that replace damaged tissue with a fibrotic scar. The affected cardiac tissue may lose its function permanently. In contrast, zebrafish display a remarkable capacity for scar-free heart regeneration. Previous studies have revealed that syndecan-4 (SDC4) regulates inflammatory response and fibroblast activity following cardiac injury in higher vertebrates. However, whether and how Sdc4 regulates heart regeneration in highly regenerative zebrafish remains unknown. METHODS AND RESULTS: This study showed that sdc4 expression was differentially regulated during zebrafish heart regeneration by transcriptional analysis. Specifically, sdc4 expression increased rapidly and transiently in the early regeneration phase upon ventricular cryoinjury. Moreover, the knockdown of sdc4 led to a significant reduction in extracellular matrix protein deposition, immune cell accumulation, and cell proliferation at the lesion site. The expression of tgfb1a and col1a1a, as well as the protein expression of Fibronectin, were all down-regulated under sdc4 knockdown. In addition, we verified that sdc4 expression was required for cardiac repair in zebrafish via in vivo electrocardiogram analysis. Loss of sdc4 expression caused an apparent pathological Q wave and ST elevation, which are signs of human MI patients. CONCLUSIONS: Our findings support that Sdc4 is required to mediate pleiotropic repair responses in the early stage of zebrafish heart regeneration.

Low dose cadmium inhibits syndecan-4 expression in glycocalyx of glomerular endothelial cells.

Cadmium (Cd) is one of the most polluting heavy metal in the environment. Cd exposure has been elucidated to cause dysfunction of the glomerular filtration barrier (GFB). However, the underlying mechanism remains unclear. C57BL/6J male mice were administered with 2.28 mg/kg cadmium chloride (CdCl2) dissolved in distilled water by oral gavage for 14 days. The expression of SDC4 in the kidney tissues was detected. Human renal glomerular endothelial cells (HRGECs) were exposed to varying concentrations of CdCl2 for 24 h. The mRNA levels of SDC4, along with matrix metalloproteinase (MMP)-2 and 9, were analyzed by quantitative PCR. Additionally, the protein expression levels of SDC4, MMP-2/9, and both total and phosphorylated forms of Smad2/3 (P-Smad2/3) were detected by western blot. The extravasation rate of fluorescein isothiocyanate-dextran through the Transwell was used to evaluate the permeability of HRGECs. SB431542 was used as an inhibitor of transforming growth factor (TGF)-ß signaling pathway to further investigate the role of TGF-ß. Cd reduced SDC4 expression in both mouse kidney tissues and HRGECs. In addition, Cd exposure increased permeability and upregulated P-Smad2/3 levels in HRGECs. SB431542 treatment inhibited the phosphorylation of Smad2/3, Cd-induced SDC4 downregulation, and hyperpermeability. MMP-2/9 levels increased by Cd exposure was also blocked by SB431542, demonstrating the involvement of TGF-ß/Smad pathway in low-dose Cd-induced SDC4 reduction in HRGECs. Given that SDC4 is an essential component of glycocalyx, protection or repair of endothelial glycocalyx is a potential strategy for preventing or treating kidney diseases associated with environmental Cd exposure.

Syndecan-4 inhibition attenuates cartilage degeneration in temporomandibular joint osteoarthritis.

BACKGROUND: Syndecan 4 (SDC4), a type I transmembrane proteoglycan, serves as a critical link between chondrocytes and the extracellular matrix. OBJECTIVE: This study aimed to explore the role of SDC4 in cartilage degeneration of temporomandibular joint osteoathritis (TMJOA). METHODS: Condylar chondrocytes were stimulated with varying concentrations of recombinant rat interleukin-1ß (rrIL-1ß) and SDC4 small interfering RNA (si-SDC4). Anti-SDC4 ectodomain-specific antibodies or IgG were intra-articularly administrated in a TMJOA model rats. SDC4 conditional knockout (SDC4-cKO) and Sdc4flox/flox mice were induced TMJOA. Cartilage degeneration was assessed using haematoxylin & eosin (H&E) and safranin O (SO) staining. Protein levels of SDC4, matrix metalloproteinases (MMPs), a disintegrin and metalloproteinase with a thrombospondin motifs 5 (ADAMTS5), tumour necrosis factor α (TNFα), type II collagen (Col-II), aggrecan (ACAN), cleaved caspase 3 (CASP3), Ki67 and related pathways in condylar cartilage were evaluated by immunohistochemical (IHC) staining or western blot assays. RESULTS: SDC4 expression was evidently increased in MIA-model animals compared to control groups. rrIL-1ß stimulation increased the expression of SDC4, MMP3 and ADAMTS5 expression in chondrocytes, while decreasing the expression of Col-II. These effects were reversed by si-SDC4 in vitro. In vivo, SDC4 blockade reduced the death of chondrocytes and the loss of cartilage matrix, which was evidenced by increased expression of Col-II and ACAN, and a decrease in SDC4, MMP13 and cleaved-CASP3-positive cells. Furthermore, the protein levels of ACAN and Ki67 were elevated, and the ERK1/2 and P38 signalling pathways were activated following SDC4 inhibition. CONCLUSIONS: SDC4 inhibition significantly ameliorates condylar cartilage degeneration, which was mediated, at least partly, through P38 and ERK1/2 signalling. Inhibition of SDC4 may be of great value for the treatment of TMJOA.

Syndecan-4 affects myogenesis via Rac1-mediated actin remodeling and exhibits copy-number amplification and increased expression in human rhabdomyosarcoma tumors.

Skeletal muscle demonstrates a high degree of regenerative capacity repeating the embryonic myogenic program under strict control. Rhabdomyosarcoma is the most common sarcoma in childhood and is characterized by impaired muscle differentiation. In this study, we observed that silencing the expression of syndecan-4, the ubiquitously expressed transmembrane heparan sulfate proteoglycan, significantly enhanced myoblast differentiation, and fusion. During muscle differentiation, the gradually decreasing expression of syndecan-4 allows the activation of Rac1, thereby mediating myoblast fusion. Single-molecule localized superresolution direct stochastic optical reconstruction microscopy (dSTORM) imaging revealed nanoscale changes in actin cytoskeletal architecture, and atomic force microscopy showed reduced elasticity of syndecan-4-knockdown cells during fusion. Syndecan-4 copy-number amplification was observed in 28% of human fusion-negative rhabdomyosarcoma tumors and was accompanied by increased syndecan-4 expression based on RNA sequencing data. Our study suggests that syndecan-4 can serve as a tumor driver gene in promoting rabdomyosarcoma tumor development. Our results contribute to the understanding of the role of syndecan-4 in skeletal muscle development, regeneration, and tumorigenesis.

Unravelling the Effects of Syndecan-4 Knockdown on Skeletal Muscle Functions.

The remodelling of the extracellular matrix plays an important role in skeletal muscle development and regeneration. Syndecan-4 is a cell surface proteoglycan crucial for muscle differentiation. Syndecan-4-/- mice have been reported to be unable to regenerate following muscle damage. To investigate the consequences of the decreased expression of Syndecan-4, we have studied the in vivo and in vitro muscle performance and the excitation-contraction coupling machinery in young and aged Syndecan-4+/- (SDC4) mice. In vivo grip force was decreased significantly as well as the average and maximal speed of voluntary running in SDC4 mice, regardless of their age. The maximal in vitro twitch force was reduced in both EDL and soleus muscles from young and aged SDC4 mice. Ca2+ release from the sarcoplasmic reticulum decreased significantly in the FDB fibres of young SDC4 mice, while its voltage dependence was unchanged regardless of age. These findings were present in muscles from young and aged mice as well. On C2C12 murine skeletal muscle cells, we have also found altered calcium homeostasis upon Syndecan-4 silencing. The decreased expression of Syndecan-4 leads to reduced skeletal muscle performance in mice and altered motility in C2C12 myoblasts via altered calcium homeostasis. The altered muscle force performance develops at an early age and is maintained throughout the life course of the animal until old age.

NMR Structural Study of Syndecan-4 Transmembrane Domain with Cytoplasmic Region.

Syndecan-4 (SDC4) consists of transmembrane heparan sulfate proteoglycan (HSPG) belonging to the syndecan family. It is present in most cell types of Mammalia. Its structure contains a heparan-sulfate-modified extracellular domain, a single transmembrane domain, and a short C-terminal cytoplasmic domain. Regarding the overall cellular function of SDC4, other cells or ligands can bind to its ecto-domain. In addition, 4,5-bisphosphate phosphatidylinositol (PIP2) or protein kinase Cα can bind to its cyto-domain to activate downstream signaling pathways. To understand the signal transduction mechanism of syndecan, it is important to know the interactions between their actual structure and function in vivo. Therefore, it is important to identify the structure of SDC4 to understand the ligand binding behavior of SDC4. In this study, expression and purification were performed to reveal structures of the short ecto-domain, the transmembrane domain, and the cytoplasmic domain of Syd4-eTC (SDC4). Solution-state NMR spectroscopy and solid-state NMR spectroscopy were used to study the structure of Syd4-eTC in membrane environments and to demonstrate the interaction between Syd4-eTC and PIP2.

Role of syndecan-4 in breast cancer pathophysiology.

Expression of the cell surface heparan sulfate proteoglycan syndecan-4 is dysregulated in breast cancer, the most frequent malignancy in women. High expression of syndecan-4 correlates with a worse survival in the subgroup of estrogen receptor negative and estrogen/progesterone-receptor negative patients. Aberrant expression of syndecan-4 in breast cancer involves both transcriptional and posttranscriptional mechanisms, including estrogen- and growth factor-dependent regulation, mutations in GAPVD1, NUP153, PDE4DIP, and RREB1, as well as targeting by microRNAs. At the functional level, syndecan-4 plays an important role in various stages of breast cancer progression by interacting with ligands as diverse as plasma proteins, extracellular matrix proteins, growth factors, and surface receptors, as well as members of the integrin family. Mechanisms including integrin recycling, ectodomain shedding, and crosstalk with other syndecans expand the repertoire of syndecan-4 function. Through these interactions, syndecan-4 regulates cellular processes such as adhesion, migration, and invasion. Additional possible functions of syndecan-4 in cells of the microenvironment contribute to the complexity of its pathophysiology. Notably, syndecan-4 expression is modulated by drugs used in breast cancer treatment, such as trastuzumab and zoledronate. Overall, these findings mark syndecan-4 as a novel pathogenesis factor and promising target for therapeutic interventions in breast cancer.

A reduction of Syndecan-4 in macrophages promotes atherosclerosis by aggravating the proinflammatory capacity of macrophages.

BACKGROUND: Cardiovascular diseases (CVDs) are a significant cause of mortality worldwide and are characterized by severe atherosclerosis (AS) in patients. However, the molecular mechanism of AS formation remains elusive. In the present study, we investigated the role of syndecan-4 (SDC4), a member of the syndecan family, in atherogenesis. METHODS AND RESULTS: The expression of SDC4 decreased in mouse severe AS models. Moreover, knockout of SDC4 accelerated high-cholesterol diets (HCD)-induced AS in ApoE-/- mice. Mechanistically, the decrease of SDC4 increased macrophage proinflammatory capacity may be through the PKCα-ABCA1/ABCG1 signaling pathway. CONCLUSION: These findings provide evidence that SDC4 reduction links macrophages and inflammation to AS and that SDC4 in macrophages provides a therapeutic target for preventing AS formation.

Tenascin-C promotes bladder cancer progression and its action depends on syndecan-4 and involves NF-κB signaling activation.

BACKGROUND: Bladder Cancer (BCa) is a severe genitourinary tract disease with an uncertain pathology. Increasing evidence indicates that the tumor microenvironment plays a decisive role with respect to cancer progression, and that this is driven by tumor cell interactions with stromal components. Tenascin-C (TN-C) is an important extracellular matrix (ECM) component, which has been reported to be involved in other types of cancer, such as breast cancer. The expression of TN-C in BCa tissue has been reported to be positively associated with the BCa pathological grade, yet the presence of urine TN-C is considered as an independent risk factor for BCa. However, the role of TN-C in BCa progression is still unknow. Thus, the object of the present investigation is to determine the role of TN-C in BCa progression and the involved mechanism. METHODS: In this study, expression of TN-C in BCa tissue of Chinese local people was determined by IHC. Patients corresponding to tumor specimens were flowed up by telephone call to get their prognostic data and analyzed by using SPSS 19.0 statistic package. In vitro mechanistic investigation was demonstrated by QT-qPCR, Western Blot, Plasmid transfection to establishment of high/low TN-C-expression stable cell line, Boyden Chamber Assay, BrdU incorporation, Wound Healing, laser scanning confocal microscopy (LSCM) and ELISA. RESULTS: TN-C expression in BCa tissue increases with tumor grade and is an independent risk factor for BCa patient. The in vitro investigation suggested that TN-C enhances BCa cell migration, invasion, proliferation and contributes to the elevated expression of EMT-related markers by activating NF-κB signaling, the mechanism of which involving in syndecan-4. CONCLUSIONS: Expression of TN-C in BCa tissues of Chinese local people is increased according to tumor grade and is an independent risk factor. TN-C mediates BCa cell malignant behavior via syndecan-4 and NF-κB signaling. Although the mechanisms through which syndecan-4 is associated with the activation of NF-κB signaling are unclear, the data presented herein provide a foundation for future investigations into the role of TN-C in BCa progression.

Altered Distribution and Expression of Syndecan-1 and -4 as an Additional Hallmark in Psoriasis.

Syndecans act as independent co-receptors to exert biological activities and their altered function is associated with many pathophysiological conditions. Here, syndecan-1 and -4 were examined in lesional skin of patients with psoriasis. Immunohistochemical staining confirmed altered syndecan-1 distribution and revealed absence of syndecan-4 expression in the epidermis. Fibronectin (FN)-known to influence inflammation and keratinocyte hyperproliferation via α5ß1 integrin in psoriasis-was also decreased. Syndecan-1 and -4 expression was analyzed in freshly isolated lesional psoriatic human keratinocytes (PHK) characterized based on their proliferation and differentiation properties. mRNA levels of syndecan-1 were similar between healthy and PHK, while syndecan-4 was significantly decreased. Cell growth and release of the pro-inflammatory Tumor Necrosis Factor-alpha (TNFα) were selectively and significantly induced in PHKs plated on FN. Results from co-culture of healthy keratinocytes and psoriatic fibroblasts led to the speculation that at least one factor released by fibroblasts down-regulate syndecan-1 expression in PHK plated on FN. To assay if biological treatments for psoriasis target keratinocyte proliferation, gelatin-based patches enriched with inteleukin (IL)-17α or TNFα blockers were prepared and tested using a full-thickness healthy epidermal model (Phenion®). Immunohistochemistry analysis showed that both blockers impacted the localisation of syndecan-1 within the refined epidermis. These results provide evidence that syndecans expression are modified in psoriasis, suggesting that they may represent markers of interest in this pathology.

Mesoglycan exerts its fibrinolytic effect through the activation of annexin A2.

Mesoglycan is a drug based on a mixture of glycosaminoglycans mainly used for the treatment of blood vessel diseases acting as antithrombotic and profibrinolytic drugs. Besides the numerous clinical studies, there is no information about its function on the fibrinolytic cascade. Here, we have elucidated the mechanism of action by which mesoglycan induces the activation of plasmin from endothelial cells. Surprisingly, by a proteomic analysis, we found that, following mesoglycan treatment, these cells show a notable amount of annexin A2 (ANXA2) at the plasma membrane. This protein has been widely associated with fibrinolysis and appears able to move to the membrane when phosphorylated. In our model, this translocation has proven to enhance cell migration, invasion, and angiogenesis. Furthermore, the interaction of mesoglycan with syndecan 4 (SDC4), a coreceptor belonging to the class of heparan sulfate proteoglycans, represents the upstream event of the ANXA2 behavior. Indeed, the activation of SDC4 triggers the motility of endothelial cells culminating in angiogenesis. Interestingly, mesoglycan can induce the release of plasmin in endothelial cell supernatants only in the presence of ANXA2. This evaluation suggests that mesoglycan triggers the formation of a chain mechanism starting from the activation of SDC4, and the related cascade of events, including src complex and PKCα activation, promoting the phosphorylation of ANXA2 and its translocation to plasma membrane. This indicates a connection among mesoglycan, SDC4-(PKCα-src), and ANXA2 which, in turn, links the tissue plasminogen activator bringing it closer to plasminogen. This latter is so cleaved to release the plasmin and degrade fibrin sleeves.

microRNA-140-3p modulates invasiveness, motility, and extracellular matrix adhesion of breast cancer cells by targeting syndecan-4.

Syndecan-4, a predicted target of the microRNA miR-140-3p, plays an important role in multiple steps of tumor progression and is the second most abundant heparan sulfate proteoglycan produced by breast carcinoma cell lines. To investigate the potential functional relationship of miR-140-3p and syndecan-4, MDA-MB-231, SKBR3, and MCF-7 breast cancer (BC) cells were transiently transfected with pre-miR-140-3p, syndecan-4 small interfering RNAJ, or control reagents, respectively. Altered cell behavior was monitored by adhesion, migration, and invasion chamber assays. Moreover, the prognostic value of syndecan-4 was assessed by Kaplan-Maier Plotter analysis of gene expression data from tumor samples of 4929 patients. High expression of syndecan-4 was associated with better relapse-free survival in the whole collective of BC patients, but correlated with a worse survival in the subgroup of estrogen receptor negative and estrogen/progesterone-receptor negative patients. miR-140-3p expression was associated with improved survival irrespective of hormone receptor status. miR-140-3p overexpression induced posttranscriptional downregulation of syndecan-4, as demonstrated by quantitative real-time PCR (qPCR), flow cytometry, and luciferase assays, resulting in decreased BC cell migration and matrigel invasiveness. Furthermore, miR-140-3p overexpression and syndecan-4 silencing increased the adhesion of BC to fibronectin and laminin. qPCR analysis demonstrated that syndecan-4 silencing leads to altered gene expression of adhesion-related molecules, such as fibronectin and focal adhesion kinase, as well as in the gene expression of the proinvasive factors matrix metalloproteinase 2 and heparanase (also known as HPSE). We conclude that syndecan-4 is a novel target of miR-140-3p that regulates BC cell invasiveness and cell-matrix interactions in the tumor microenvironment.

Syndecan-3 contributes to the regulation of the microenvironment at the node of Ranvier following end-to­side neurorrhaphy: sodium image analysis.

Syndecan-3 (SDC3) and Syndecan-4 (SDC4) are distributed throughout the nervous system (NS) and are favourable factors in motor neuron development. They are also essential for regulation of neurite outgrowth in the CNS. However, their roles in the reconstruction of the nodes of Ranvier after peripheral nerve injury (PNI) are still unclear. Present study used an in vivo model of end-to-side neurorrhaphy (ESN) for 1-3 months. The recovery of neuromuscular function was evaluated by grooming test. Expression and co-localization of SDC3, SDC4, and Nav1.6 channel (Nav1.6) at regenerating axons were detected by proximity ligation assay and confocal microscopy after ESN. Time-of-flight secondary ion mass spectrometry was used for imaging ions distribution on tissue. Our data showed that the re-clustering of sodium and Nav1.6 at nodal regions of the regenerating nerve corresponded to the distribution of SDC3 after ESN. Furthermore, the re-establishment of sodium and Nav1.6 correlated with the recovery of muscle power 3 months after ESN. This study suggested syndecans may involve in stabilizing Nav1.6 and further modulate the distribution of sodium at nodal regions after remyelination. The efficiency of sodium re-clustering was improved by the assistance of anionic syndecan, resulting in a better functional repair of PNI.

MMP-9 mediated Syndecan-4 shedding correlates with osteoarthritis severity.

OBJECTIVE: Osteoarthritis (OA) is a degenerative joint disease inducing the degradation of the articular cartilage. Syndecan-4 (Sdc4) is a heparan sulfate proteoglycan, expressed under inflammatory conditions and by chondrocytes during OA. Little is known about Sdc4 shedding and its regulation in OA. Therefore, we investigated the regulation of Sdc4 shedding and underlying shedding mechanisms under OA conditions. DESIGN: Articular cartilage, serum, synovial fluid and synovial membrane from OA patients with different radiological severity were analyzed. ELISA, RT-qPCR and IHC for Sdc4, MMP-2 and -9 were performed. MMP inhibitors and siRNA were evaluated for their effect on Sdc4 shedding by ELISA and on IL-1 signaling by western blot (pERK/ERK). RESULTS: Shed Sdc4 was increased in synovial fluid of OA patients, but not in the serum and is a good predictor (AUC = 0.72) for OA severity with a sensitivity of 67.5% and specificity 65.2%. MMP-9, but not MMP-2, was increased in cartilage and synovial membrane at mRNA levels and in the synovial fluid at protein levels. Shed Sdc4 correlated with the amount of MMP-9 in synovial fluid. Further, the inhibition and knock-down of MMP-9 decreased the amount of shed Sdc4 in vitro. Increased Sdc4 shedding resulted in less phosphorylation of ERK upon IL-1ß stimulation. CONCLUSION: Shed Sdc4 might be a good prognostic biomarker for OA mediated cartilage degradation. MMP-9 seems to be the relevant sheddase for Sdc4 under OA conditions, desensitizing chondrocytes towards IL-1 signaling.

PKC (Protein Kinase C)-δ Modulates AT (Antithrombin) Signaling in Vascular Endothelial Cells.

OBJECTIVE: Native and latent conformers of AT (antithrombin) induce anti-inflammatory and proapoptotic signaling activities, respectively, in vascular endothelial cells by unknown mechanisms. Synd-4 (syndecan-4) has been identified as a receptor that is involved in transmitting signaling activities of AT in endothelial cells. Approach and Results: In this study, we used flow cytometry, signaling assays, immunoblotting and confocal immunofluorescence microscopy to investigate the mechanism of the paradoxical signaling activities of high-affinity heparin (native) and low-affinity heparin (latent) conformers of AT in endothelial cells. We discovered that native AT binds to glycosaminoglycans on vascular endothelial cells via its heparin-binding D-helix to induce anti-inflammatory signaling responses by recruiting PKC (protein kinase C)-δ to the plasma membrane and promoting phosphorylation of the Synd-4 cytoplasmic domain at Ser179. By contrast, the binding of latent AT to endothelial cells to a site(s), which is not competed by the native AT, induces a proapoptotic effect by localizing PKC-δ to the perinuclear/nuclear compartment in endothelial cells. Overexpression of a dominant-negative form of PKC-δ resulted in inhibition of anti-inflammatory and proapoptotic signaling activities of both native and latent AT. CONCLUSIONS: These results indicate that the native and latent conformers of AT may exert their distinct intracellular signaling effects through differentially modulating the subcellular localization of PKC-δ in endothelial cells.

The effects of YKL-40 on angiogenic potential of HUVECs are partly mediated by syndecan-4.

Background: YKL-40, a secreted glycoprotein, has a role in promoting tumor angiogenesis through syndecan-1 receptor. Syndecan-4 is a member of syndecan family. However, the effects of YKL-40 on migration and tube formation of human umbilical vein cells (HUVECs) mediated by syndecan-4 receptor are unknown. Materials and methods: HUVECs were transfected with lentivirus encoding syndecan-4 short hairpin (sh) RNAs (lenti-synd4 shRNAs) and the efficiency of transfection was measured using qRT-PCR and western blotting. The effects of recombinant protein of YKL-40 on migration and angiogenesis of HUVECs adjusted by syndecan-4 were determined by wound healing and tube formation assay. The expressions of protein kinase Cα (PKCα) and extracellular signal regulated kinases (ERKs) 1 and 2 (ERK1/2) in HUVECs were measured using western blotting. Results: The mRNA and protein expression of syndecan-4 were significantly decreased in HUVECs successfully transfected with lenti-synd4 shRNAs. Lenti-synd4 shRNAs remarkably inhibited the migration and tube formation of HUVECs stimulated by recombinant protein of YKL-40. The levels of PKCα and ratio of p-ERK1/2 to ERK1/2 in HUVECs were also decreased by down-regulating syndecan-4. Conclusion: The effects of YKL-40 on migration and tube formation of HUVECs are partly inhibited by knock-downing syndecan-4 through suppressing PKCα and ERK1/2 signaling pathways.

The cardiac syndecan-4 interactome reveals a role for syndecan-4 in nuclear translocation of muscle LIM protein (MLP).

Costameres are signaling hubs at the sarcolemma and important contact points between the extracellular matrix and cell interior, sensing and transducing biomechanical signals into a cellular response. The transmembrane proteoglycan syndecan-4 localizes to these attachment points and has been shown to be important in the initial stages of cardiac remodeling, but its mechanistic function in the heart remains insufficiently understood. Here, we sought to map the cardiac interactome of syndecan-4 to better understand its function and downstream signaling mechanisms. By combining two different affinity purification methods with MS analysis, we found that the cardiac syndecan-4 interactome consists of 21 novel and 29 previously described interaction partners. Nine of the novel partners were further validated to bind syndecan-4 in HEK293 cells (i.e. CAVIN1/PTRF, CCT5, CDK9, EIF2S1, EIF4B, MPP7, PARVB, PFKM, and RASIP). We also found that 19 of the 50 interactome partners bind differently to syndecan-4 in the left ventricle lysate from aortic-banded heart failure (ABHF) rats compared with SHAM-operated animals. One of these partners was the well-known mechanotransducer muscle LIM protein (MLP), which showed direct and increased binding to syndecan-4 in ABHF. Nuclear translocation is important in MLP-mediated signaling, and we found less MLP in the nuclear-enriched fractions from syndecan-4-/- mouse left ventricles but increased nuclear MLP when syndecan-4 was overexpressed in a cardiomyocyte cell line. In the presence of a cell-permeable syndecan-4-MLP disruptor peptide, the nuclear MLP level was reduced. These findings suggest that syndecan-4 mediates nuclear translocation of MLP in the heart.

Syndecan-4 involves in the pathogenesis of rheumatoid arthritis by regulating the inflammatory response and apoptosis of fibroblast-like synoviocytes.

Rheumatoid arthritis (RA) is a chronic autoimmune inflammatory disease, and the pathogenesis of RA is still unknown. Rheumatoid arthritis fibroblast-like synoviocytes (RA-FLSs) are of significance in the pathogenesis of RA. In this study, three microarray profiles (GSE55457, GSE55584, and GSE55235) of human joint FLSs from 33 RA patients and 20 normal controls were extracted from the Gene Expression Omnibus Dataset and analyzed to investigate the underlying pathogenesis of RA. As analyzed by the differently expressed genes, gene ontology, Kyoto Encyclopedia of Genes and Genomes pathway enrichment, and protein-protein interaction network analysis, syndecan-4 (SDC4), a receptor of multiple cytokines and chemokines, which played a key role in the regulation of inflammatory response, was found to be an essential regulator in RA. To further validate these results, the levels of SDC4, reactive oxygen species (ROS), nitric oxide (NO), inflammation, and apoptosis in RA-FLSs were examined. SDC4-silenced RA-FLSs were also used. The results demonstrated that SDC4 and the level of ROS, NO, and inflammation were highly expressed while the apoptosis was decreased in RA-FLSs compared with normal FLSs. SDC4 silencing significantly suppressed the levels of ROS, NO, and inflammation; elevated the expression of nuclear factor erythroid 2-related factor 2; and promoted the apoptosis of RA-FLSs. Collectively, our results demonstrated a new mechanism of SDC4 in initiating the inflammation and inhibiting the apoptosis of RA-FLSs and that a potential target for the diagnosis and treatment of RA in the clinic might be developed.