Endocytosis blocks the vesicular secretion of exosome marker proteins.

Exosomes are secreted vesicles of ~30 to 150 nm diameter that play important roles in human health and disease. To better understand how cells release these vesicles, we examined the biogenesis of the most highly enriched human exosome marker proteins, the exosomal tetraspanins CD81, CD9, and CD63. We show here that endocytosis inhibits their vesicular secretion and, in the case of CD9 and CD81, triggers their destruction. Furthermore, we show that syntenin, a previously described exosome biogenesis factor, drives the vesicular secretion of CD63 by blocking CD63 endocytosis and that other endocytosis inhibitors also induce the plasma membrane accumulation and vesicular secretion of CD63. Finally, we show that CD63 is an expression-dependent inhibitor of endocytosis that triggers the vesicular secretion of lysosomal proteins and the clathrin adaptor AP-2 mu2. These results suggest that the vesicular secretion of exosome marker proteins in exosome-sized vesicles occurs primarily by an endocytosis-independent pathway.

Metabolic reprogramming by Syntenin-1 directs RA FLS and endothelial cell-mediated inflammation and angiogenesis.

A novel rheumatoid arthritis (RA) synovial fluid protein, Syntenin-1, and its receptor, Syndecan-1 (SDC-1), are colocalized on RA synovial tissue endothelial cells and fibroblast-like synoviocytes (FLS). Syntenin-1 exacerbates the inflammatory landscape of endothelial cells and RA FLS by upregulating transcription of IRF1/5/7/9, IL-1ß, IL-6, and CCL2 through SDC-1 ligation and HIF1α, or mTOR activation. Mechanistically, Syntenin-1 orchestrates RA FLS and endothelial cell invasion via SDC-1 and/or mTOR signaling. In Syntenin-1 reprogrammed endothelial cells, the dynamic expression of metabolic intermediates coincides with escalated glycolysis along with unchanged oxidative factors, AMPK, PGC-1α, citrate, and inactive oxidative phosphorylation. Conversely, RA FLS rewired by Syntenin-1 displayed a modest glycolytic-ATP accompanied by a robust mitochondrial-ATP capacity. The enriched mitochondrial-ATP detected in Syntenin-1 reprogrammed RA FLS was coupled with mitochondrial fusion and fission recapitulated by escalated Mitofusin-2 and DRP1 expression. We found that VEGFR1/2 and Notch1 networks are responsible for the crosstalk between Syntenin-1 rewired endothelial cells and RA FLS, which are also represented in RA explants. Similar to RA explants, morphological and transcriptome studies authenticated the importance of VEGFR1/2, Notch1, RAPTOR, and HIF1α pathways in Syntenin-1 arthritic mice and their obstruction in SDC-1 deficient animals. Consistently, dysregulation of SDC-1, mTOR, and HIF1α negated Syntenin-1 inflammatory phenotype in RA explants, while inhibition of HIF1α impaired synovial angiogenic imprint amplified by Syntenin-1. In conclusion, since the current therapies are ineffective on Syntenin-1 and SDC-1 expression in RA synovial tissue and blood, targeting this pathway and its interconnected metabolic intermediates may provide a novel therapeutic strategy.

MDA-9/Syntenin in the tumor and microenvironment defines prostate cancer bone metastasis.

Bone metastasis is a frequent and incurable consequence of advanced prostate cancer (PC). An interplay between disseminated tumor cells and heterogeneous bone resident cells in the metastatic niche initiates this process. Melanoma differentiation associated gene-9 (mda-9/Syntenin/syndecan binding protein) is a prometastatic gene expressed in multiple organs, including bone marrow-derived mesenchymal stromal cells (BM-MSCs), under both physiological and pathological conditions. We demonstrate that PDGF-AA secreted by tumor cells induces CXCL5 expression in BM-MSCs by suppressing MDA-9-dependent YAP/MST signaling. CXCL5-derived tumor cell proliferation and immune suppression are consequences of the MDA-9/CXCL5 signaling axis, promoting PC disease progression. mda-9 knockout tumor cells express less PDGF-AA and do not develop bone metastases. Our data document a previously undefined role of MDA-9/Syntenin in the tumor and microenvironment in regulating PC bone metastasis. This study provides a framework for translational strategies to ameliorate health complications and morbidity associated with advanced PC.

Downregulation of stromal syntenin sustains AML development.

The crosstalk between cancer and stromal cells plays a critical role in tumor progression. Syntenin is a small scaffold protein involved in the regulation of intercellular communication that is emerging as a target for cancer therapy. Here, we show that certain aggressive forms of acute myeloid leukemia (AML) reduce the expression of syntenin in bone marrow stromal cells (BMSC). Stromal syntenin deficiency, in turn, generates a pro-tumoral microenvironment. From serial transplantations in mice and co-culture experiments, we conclude that syntenin-deficient BMSC stimulate AML aggressiveness by promoting AML cell survival and protein synthesis. This pro-tumoral activity is supported by increased expression of endoglin, a classical marker of BMSC, which in trans stimulates AML translational activity. In short, our study reveals a vicious signaling loop potentially at the heart of AML-stroma crosstalk and unsuspected tumor-suppressive effects of syntenin that need to be considered during systemic targeting of syntenin in cancer therapy.

Heparanase promotes malignant phenotypes of human oral squamous carcinoma cells by regulating the epithelial-mesenchymal transition-related molecules and infiltrated levels of natural killer cells.

OBJECTIVES: The aim of the present study was to explore the functional role of heparanase (HPSE) and investigate the effect of HPSE on epithelial-mesenchymal transition (EMT) and Tumor-infiltrating activated natural killer cells in oral squamous cell carcinoma (OSCC). MATERIALS AND METHODS: human oral squamous carcinoma (SCC-25) cells were transfected with HPSE-specific small interfering RNA. Cell Counting Kit-8 assay was performed to examine cell proliferation, while flow cytometry was performed to analyze the cell cycle. Scratch assay was conducted to analyze cell migration, followed by Transwell assay to determine cell invasion. Real-Time Polymerase Chain Reaction and Western-blot assays were performed to measure epithelial-mesenchymal transition protein expression. RNA Sequencing analysis and tumor-infiltrating immune cells estimation were performed to elucidate the effect of HPSE on OSCC. RESULTS: Knockdown of HPSE expression decreased the proliferation rate of SCC-25 cells resulting in a significant elevation in cell percentage at the Gap phase 0/Gap phase 1 phase by suppressed cell migration and invasion. The E-cadherin messenger RNA and protein expression increased while Snail and Vimentin expression decreased. RNA Sequencing analysis performed between small interfering RNA and negative control groups identified 42 differentially expressed genes, such as syndecan binding protein, RAB11A, member RAS oncogene family, and DDB1 and CUL4 associated factor 15. CONCLUSIONS: These results indicated that knockdown of HPSE suppressed SCC-25 cell proliferation, invasion, migration, and epithelial-mesenchymal transition, possibly via syndecan binding protein and RAB11A, member RAS oncogene family. Moreover, HPSE regulates the infiltrated levels of natural killer cells activated, possibly via DDB1 and CUL4 associated factor 15.

PDZ interaction of the GABA transporter GAT1 with the syntenin-1 in Neuro-2a cells.

The GABA transporter GAT1 regulates brain inhibitory neurotransmission and it is considered a potential therapeutic target for the treatment of wide spectrum of neurological diseases including epilepsy, stroke and autism. Syntenin-1 binds to syntaxin 1A, which is known to regulate the plasma membrane insertion of several neurotransmitter transporters. Previously, a direct interaction of syntenin-1 with the glycine transporter GlyT2 was reported. Here, we show that the GABA transporter GAT1 also directly interacts with syntenin-1, involving both unidentified protein interaction interface and the GAT1 C-terminal PDZ binding motif interacting mainly with syntenin-1 PDZ domain 1. The PDZ interaction was eliminated by the mutation of GAT1 isoleucine 599 and tyrosine 598 located in PDZ positions 0 and -1, respectively. This indicates an unconventional PDZ interaction and possible regulation of the transporter PDZ motif via tyrosine phosphorylation. Whole syntenin-1 protein fused to GST protein and immobilised on glutathione resin coprecipitated intact GAT1 transporter from an extract of GAT1 transfected neuroblastoma N2a cells. This coprecipitation was inhibited by tyrosine phosphatases inhibitor pervanadate. The fluorescence tagged GAT1 and syntenin-1 colocalized upon coexpression in N2a cells. The above results show that syntenin-1 might be, in addition to GlyT2, directly involved in the trafficking of GAT1 transporter.

Melanoma differentiation associated gene-9/syndecan binding protein promotes hepatocellular carcinoma.

BACKGROUND AND AIMS: The oncogene Melanoma differentiation associated gene-9/syndecan binding protein (MDA-9/SDCBP) is overexpressed in many cancers, promoting aggressive, metastatic disease. However, the role of MDA-9 in regulating hepatocellular carcinoma (HCC) has not been well studied. APPROACH AND RESULTS: To unravel the function of MDA-9 in HCC, we generated and characterized a transgenic mouse with hepatocyte-specific overexpression of MDA-9 (Alb/MDA-9). Compared with wild-type (WT) littermates, Alb/MDA-9 mice demonstrated significantly higher incidence of N-nitrosodiethylamine/phenobarbital-induced HCC, with marked activation and infiltration of macrophages. RNA sequencing (RNA-seq) in naive WT and Alb/MDA-9 hepatocytes identified activation of signaling pathways associated with invasion, angiogenesis, and inflammation, especially NF-κB and integrin-linked kinase signaling pathways. In nonparenchymal cells purified from naive livers, single-cell RNA-seq showed activation of Kupffer cells and macrophages in Alb/MDA-9 mice versus WT mice. A robust increase in the expression of Secreted phosphoprotein 1 (Spp1/osteopontin) was observed upon overexpression of MDA-9. Inhibition of NF-κB pathway blocked MDA-9-induced Spp1 induction, and knock down of Spp1 resulted in inhibition of MDA-9-induced macrophage migration, as well as angiogenesis. CONCLUSIONS: Alb/MDA-9 is a mouse model with MDA-9 overexpression in any tissue type. Our findings unravel an HCC-promoting role of MDA-9 mediated by NF-κB and Spp1 and support the rationale of using MDA-9 inhibitors as a potential treatment for aggressive HCC.

SDCBP-AS1 destabilizes ß-catenin by regulating ubiquitination and SUMOylation of hnRNP K to suppress gastric tumorigenicity and metastasis.

BACKGROUND: Gastric cancer (GC) is among the most malignant tumors, yet the pathogenesis is not fully understood, especially the lack of detailed information about the mechanisms underlying long non-coding RNA (lncRNA)-mediated post-translational modifications. Here, the molecular mechanisms and clinical significance of the novel lncRNA syndecan-binding protein 2-antisense RNA 1 (SDCBP2-AS1) in the tumorigenesis and progression of GC were investigated. METHODS: The expression levels of SDCBP2-AS1 in 132 pairs of GC and adjacent normal tissues were compared, and the biological functions were assessed in vitro and in vivo. RNA pull-down and immunoprecipitation assays were conducted to clarify the interactions of SDCBP2-AS1 and heterogeneous nuclear ribonucleoprotein (hnRNP) K. RNA-sequencing, immunoprecipitation, immunofluorescence, and luciferase analyses were performed to investigate the functions of SDCBP2-AS1. RESULTS: SDCBP2-AS1 was significantly downregulated in GC tissues and predictive of poor patient prognosis. Silencing of SDCBP2-AS1 promoted the proliferation and migration of GC cells both in vitro and in vivo. Mechanically, SDCBP2-AS1 physically bound to hnRNP K to repress SUMOylation of hnRNP K and facilitated ubiquitination of hnRNP K and ß-catenin, thereby promoting the degradation of ß-catenin in the cytoplasm. Silencing of SDCBP2-AS1 caused SUMOylation of hnRNP K and stabilized ß-catenin activity, which altered transcription of downstream genes, resulting in tumorigenesis and metastasis of GC. Moreover, the knockdown of hnRNP K partially abrogated the effects of SDCBP2-AS1. CONCLUSIONS: SDCBP2-AS1 interacts with hnRNP K to suppress tumorigenesis and metastasis of GC and regulates post-transcriptional modifications of hnRNP K to destabilize ß-catenin. These findings suggest SDCBP2-AS1 as a potential target for the treatment of GC.

Syntenin-1-mediated small extracellular vesicles promotes cell growth, migration, and angiogenesis by increasing onco-miRNAs secretion in lung cancer cells.

Small extracellular vesicles (sEVs) play a pivotal role in tumor progression by mediating intercellular communication in the tumor microenvironment (TME). Syntenin-1 induces malignant tumor progression in various types of human cancers, including human lung cancer and regulates biogenesis of sEVs. However, the function of syntenin-1-regulated sEVs and miRNAs in sEVs remains to be elucidated. In the present study, we aimed to demonstrate the role of oncogenic Ras/syntenin-1 axis in the release of sEVs and elucidate the function of syntenin-1-mediated miRNAs in sEVs in lung cancer progression. The results revealed that oncogenic Ras promoted the release of sEVs by inducing syntenin-1 expression; disruption of syntenin-1 expression impaired the release of sEVs as well as sEV-mediated cancer cell migration and angiogenesis. Moreover, we identified three miRNAs, namely miR-181a, miR-425-5p, and miR-494-3p, as onco-miRNAs loaded into syntenin-1-dependent sEVs. Remarkably, miR-494-3p was highly abundant in sEVs and its release was triggered by syntenin-1 expression and oncogenic Ras. Ectopic expression of the miR-494-3p mimic enhanced the migration and proliferation of lung cancer cells as well as tube formation in endothelial cells; however, the miR-494-3p inhibitor blocked sEV-mediated effects by targeting tyrosine-protein phosphatase nonreceptor type 12 (PTPN12), a tumor suppressor. sEVs promoted tumor growth and angiogenesis by downregulating PTPN12 expression; however, the miR-494-3p inhibitor significantly suppressed these effects in vivo, confirming that miR-494-3p acts as a major onco-miRNA loaded into lung cancer cell-derived sEVs. Eventually, the oncogenic Ras/syntenin-1 axis may induce cancer progression by increasing miR-494-3p loading into sEVs in lung cancer cells in the TME.

Identification of immune-infiltrated hub genes as potential biomarkers of Moyamoya disease by bioinformatics analysis.

BACKGROUND: Moyamoya disease (MMD) is a rare chronic progressive cerebrovascular disease. Recent studies have shown that autoimmune inflammation may also be an important pathology in MMD but the molecular mechanisms of inflammation in this disease are still large unknown. This study was designed to identify key biomarkers and the immune infiltration in vessel tissue of MMD using bioinformatics analysis. METHODS: Raw gene expression profiles (GSE157628, GSE141024) were downloaded from the Gene Expression Omnibus (GEO) database, identified differentially expressed genes (DEGs) and performed functional enrichment analysis. The CIBERSORT deconvolution algorithm was used to analyze the proportion of immune cells between MMD and an MMD-negative control group. We screened for neutrophil-associated DEGs, constructed a protein-protein interaction network (PPI) using STRING, and clarified the gene cluster using the Cytoscape plugin MCODE analysis. The receiver operating characteristic (ROC) curve was applied to test and filter the best gene signature. RESULTS: A total of 570 DEGs were detected, including 212 downregulated and 358 up-regulated genes. Reactome and KEGG enrichment revealed that DEGs were involved in the cell cycle, molecular transport, and metabolic pathways. The immune infiltration profile demonstrated that MMD cerebrovascular tissues contained a higher proportion of neutrophils, monocytes, and natural killer cells in MMD than in controls. The PPI network and MCODE cluster identified nine DEGs (UNC13D, AZU1, PYCARD, ELANE, SDCBP, CCL11, CCL15, CCL20, and CXCL5) associated with neutrophil infiltration. ROC results showed that UNC13D has good specificity and sensitivity (AUC = 0.7846). CONCLUSIONS: The characteristics of immune infiltration in the cerebrovascular tissues of MMD patients and abnormal expression of hub genes provide new insights for understanding MMD progression. UNC13D is shows promise as a candidate molecule to determine neutrophil infiltration characteristics in MMD.

Syndecan Family Gene and Protein Expression and Their Prognostic Values for Prostate Cancer.

Prostate cancer (PCa) is the leading cause of cancer-associated mortality in men, and new biomarkers are still needed. The expression pattern and protein tissue localization of proteoglycans of the syndecan family (SDC 1-4) and syntenin-1 (SDCBP) were determined in normal and prostatic tumor tissue from two genetically engineered mouse models and human prostate tumors. Studies were validated using SDC 1-4 and SDCBP mRNA levels and patient survival data from The Cancer Genome Atlas and CamCAP databases. RNAseq showed increased expression of Sdc1 in Pb-Cre4/Ptenf/f mouse Pca and upregulation of Sdc3 expression and downregulation of Sdc2 and Sdc4 when compared to the normal prostatic tissue in Pb-Cre4/Trp53f/f-;Rb1f/f mouse tumors. These changes were confirmed by immunohistochemistry. In human PCa, SDC 1-4 and SDCBP immunostaining showed variable localization. Furthermore, Kaplan-Meier analysis showed that patients expressing SDC3 had shorter prostate-specific survival than those without SDC3 expression (log-rank test, p = 0.0047). Analysis of the MSKCC-derived expression showed that SDC1 and SDC3 overexpression is predictive of decreased biochemical recurrence-free survival (p = 0.0099 and p = 0.045, respectively), and SDC4 overexpression is predictive of increased biochemical recurrence-free survival (p = 0.035). SDC4 overexpression was associated with a better prognosis, while SDC1 and SDC3 were associated with more aggressive tumors and a worse prognosis.

Quantitative proteomics identifies the core proteome of exosomes with syntenin-1 as the highest abundant protein and a putative universal biomarker.

Exosomes are extracellular vesicles derived from the endosomal compartment that are potentially involved in intercellular communication. Here, we found that frequently used biomarkers of exosomes are heterogeneous, and do not exhibit universal utility across different cell types. To uncover ubiquitous and abundant proteins, we used an unbiased and quantitative proteomic approach based on super-stable isotope labeling with amino acids in cell culture (super-SILAC), coupled to high-resolution mass spectrometry. In total, 1,212 proteins were quantified in the proteome of exosomes, irrespective of the cellular source or isolation method. A cohort of 22 proteins was universally enriched. Fifteen proteins were consistently depleted in the proteome of exosomes compared to cells. Among the enriched proteins, we identified biogenesis-related proteins, GTPases and membrane proteins, such as CD47 and ITGB1. The cohort of depleted proteins in exosomes was predominantly composed of nuclear proteins. We identified syntenin-1 as a consistently abundant protein in exosomes from different cellular origins. Syntenin-1 is also present in exosomes across different species and biofluids, highlighting its potential use as a putative universal biomarker of exosomes. Our study provides a comprehensive quantitative atlas of core proteins ubiquitous to exosomes that can serve as a resource for the scientific community.

Pharmacological inhibition of MDA-9/Syntenin blocks breast cancer metastasis through suppression of IL-1ß.

Melanoma differentiation associated gene-9 (MDA-9), Syntenin-1, or syndecan binding protein is a differentially regulated prometastatic gene with elevated expression in advanced stages of melanoma. MDA-9/Syntenin expression positively associates with advanced disease stage in multiple histologically distinct cancers and negatively correlates with patient survival and response to chemotherapy. MDA-9/Syntenin is a highly conserved PDZ-domain scaffold protein, robustly expressed in a spectrum of diverse cancer cell lines and clinical samples. PDZ domains interact with a number of proteins, many of which are critical regulators of signaling cascades in cancer. Knockdown of MDA-9/Syntenin decreases cancer cell metastasis, sensitizing these cells to radiation. Genetic silencing of MDA-9/Syntenin or treatment with a pharmacological inhibitor of the PDZ1 domain, PDZ1i, also activates the immune system to kill cancer cells. Additionally, suppression of MDA-9/Syntenin deregulates myeloid-derived suppressor cell differentiation via the STAT3/interleukin (IL)-1ß pathway, which concomitantly promotes activation of cytotoxic T lymphocytes. Biologically, PDZ1i treatment decreases metastatic nodule formation in the lungs, resulting in significantly fewer invasive cancer cells. In summary, our observations indicate that MDA-9/Syntenin provides a direct therapeutic target for mitigating aggressive breast cancer and a small-molecule inhibitor, PDZ1i, provides a promising reagent for inhibiting advanced breast cancer pathogenesis.

Seven Novel Genes Related to Cell Proliferation and Migration of VHL-Mutated Pheochromocytoma.

Pheochromocytoma, as a neuroendocrine tumor with the highest genetic correlation in all types of tumors, has attracted extensive attention. Von Hipper Lindau (VHL) has the highest mutation frequency among the genes associated with pheochromocytoma. However, the effect of VHL on the proteome of pheochromocytoma remains to be explored. In this study, the VHL knockdown (VHL-KD) PC12 cell model was established by RNA interference (shRNA). We compared the proteomics of VHL-KD and VHL-WT PC12 cell lines. The results showed that the expression of 434 proteins (VHL shRNA/WT > 1.3) changed significantly in VHL-KD-PC12 cells. Among the 434 kinds of proteins, 83 were involved in cell proliferation, cell cycle and cell migration, and so on. More importantly, among these proteins, we found seven novel key genes, including Connective Tissue Growth Factor (CTGF), Syndecan Binding Protein (SDCBP), Cysteine Rich Protein 61 (CYR61/CCN1), Collagen Type III Alpha 1 Chain (COL3A1), Collagen Type I Alpha 1 Chain (COL1A1), Collagen Type V Alpha 2 Chain (COL5A2), and Serpin Family E Member 1 (SERPINE1), were overexpressed and simultaneously regulated cell proliferation and migration in VHL-KD PC12 cells. Furthermore, the abnormal accumulation of HIF2α caused by VHL-KD significantly increased the expression of these seven genes during hypoxia. Moreover, cell-counting, scratch, and transwell assays demonstrated that VHL-KD could promote cell proliferation and migration, and changed cell morphology. These findings indicated that inhibition of VHL expression could promote the development of pheochromocytoma by activating the expression of cell proliferation and migration associated genes.

Epstein-Barr Virus LMP1 Promotes Syntenin-1- and Hrs-Induced Extracellular Vesicle Formation for Its Own Secretion To Increase Cell Proliferation and Migration.

Extracellular vesicles (EVs) are important mediators of cell-to-cell communication that are involved in both normal processes and pathological conditions. Latent membrane protein 1 (LMP1) is a major viral oncogene that is expressed in most Epstein-Barr virus (EBV)-associated cancers and secreted in EVs. LMP1-modified EVs have the ability to influence recipient cell growth, migration, and differentiation and regulate immune cell function. Despite the significance of LMP1-modified EVs in EBV malignancies, very little is understood about how this protein hijacks the host EV pathway for secretion. Using the biotin identification (BioID) method, we identified LMP1-proximal interacting proteins that are known to play roles in EV formation and protein trafficking. Analysis of the identified LMP1-interacting proteins revealed an enrichment in the ESCRT pathway and associated proteins, including CD63, Syntenin-1, Alix, TSG101, Hrs, and charged multivesicular body proteins (CHMPs). LMP1 transcriptionally upregulated and increased the protein expression of EV biogenesis and secretion genes. Nanoparticle tracking and immunoblot analysis revealed reduced levels of LMP1 EV packaging and of vesicle production following the knockdown of Syntenin-1, Alix, Hrs, and TSG101, with altered endolysosomal trafficking observed when Syntenin-1 and Hrs expression was reduced. Knockdown of specific ESCRT-III subunits (CHMP4B, -5, and -6) impaired LMP1 packaging and secretion into EVs. Finally, we demonstrate that the efficient secretion of LMP1-modified EVs promotes cell attachment, proliferation, and migration and tumor growth. Together, these results begin to shed light on how LMP1 exploits host ESCRT machinery to direct the incorporation of the viral oncoprotein into the EV pathway for secretion to alter the tumor microenvironment.IMPORTANCE LMP1 is a notable viral protein that contributes to the modification of EV content and tumor microenvironment remodeling. LMP1-modified EVs enhance tumor proliferation, migration, and invasion potential and promote radioresistance. Currently, the mechanisms surrounding LMP1 incorporation into the host EV pathways are not well understood. This study revealed that LMP1 utilizes Hrs, Syntenin-1, and specific components of the ESCRT-III complex for release from the cell, enhancement of EV production, and metastatic properties of cancer cells. These findings begin to unravel the mechanism of LMP1 EV trafficking and may provide new targets to control EBV-associated cancers.

SDCBP/MDA-9/syntenin phosphorylation by AURKA promotes esophageal squamous cell carcinoma progression through the EGFR-PI3K-Akt signaling pathway.

SDCBP is an adapter protein containing two tandem PDZ domains mediating cell adhesion. The role and underlying molecular mechanism of SDCBP in ESCC remain obscure. Here, we report that SDCBP is frequently overexpressed in ESCC tissues and cells compared to normal controls and that its overexpression is correlated with late clinical stage and predicts poor prognosis in ESCC patients. Functionally, high expression of SDCBP is positively related to ESCC progression both in vitro and in vivo. Furthermore, mechanistic studies show that SDCBP activates the EGFR-PI3K-Akt signaling pathway by binding to EGFR and preventing EGFR internalization. Moreover, we provide evidence that AURKA binds to SDCBP and phosphorylates it at the Ser131 and Thr200 sites to inhibit ubiquitination-mediated SDCBP degradation. More importantly, the sites at which AURKA phosphorylates SDCBP are crucial for the EGFR signaling-mediated oncogenic function of SDCBP. Taken together, we propose that SDCBP phosphorylation by AURKA prevents SDCBP degradation and promotes ESCC tumor growth through the EGFR-PI3K-Akt signaling pathway. Our findings unveil a new AURKA-SDCBP-EGFR axis that is involved in ESCC progression and provide a promising therapeutic target for ESCC treatment in the clinic.

MDA-9/Syntenin/SDCBP: new insights into a unique multifunctional scaffold protein.

Tumor metastasis comprises a series of coordinated events that culminate in dissemination of cancer cells to distant sites within the body representing the greatest challenge impeding effective therapy of cancer and the leading cause of cancer-associated morbidity. Cancer cells exploit multiple genes and pathways to colonize to distant organs. These pathways are integrated and regulated at different levels by cellular- and extracellular-associated factors. Defining the genes and pathways that govern metastasis can provide new targets for therapeutic intervention. Melanoma differentiation associated gene-9 (mda-9) (also known as Syntenin-1 and SDCBP (Syndecan binding protein)) was identified by subtraction hybridization as a novel gene displaying differential temporal expression during differentiation of melanoma. MDA-9/Syntenin is an established Syndecan binding protein that functions as an adaptor protein. Expression of MDA-9/Syntenin is elevated at an RNA and protein level in a wide-range of cancers including melanoma, glioblastoma, neuroblastoma, and prostate, breast and liver cancer. Expression is increased significantly in metastatic cancer cells as compared with non-metastatic cancer cells or normal cells, which make it an attractive target in treating cancer metastasis. In this review, we focus on the role and regulation of mda-9 in cancer progression and metastasis.

The Flemmingsome reveals an ESCRT-to-membrane coupling via ALIX/syntenin/syndecan-4 required for completion of cytokinesis.

Cytokinesis requires the constriction of ESCRT-III filaments on the side of the midbody, where abscission occurs. After ESCRT recruitment at the midbody, it is not known how the ESCRT-III machinery localizes to the abscission site. To reveal actors involved in abscission, we obtained the proteome of intact, post-abscission midbodies (Flemmingsome) and identified 489 proteins enriched in this organelle. Among these proteins, we further characterized a plasma membrane-to-ESCRT module composed of the transmembrane proteoglycan syndecan-4, ALIX and syntenin, a protein that bridges ESCRT-III/ALIX to syndecans. The three proteins are highly recruited first at the midbody then at the abscission site, and their depletion delays abscission. Mechanistically, direct interactions between ALIX, syntenin and syndecan-4 are essential for proper enrichment of the ESCRT-III machinery at the abscission site, but not at the midbody. We propose that the ESCRT-III machinery must be physically coupled to a membrane protein at the cytokinetic abscission site for efficient scission, uncovering common requirements in cytokinesis, exosome formation and HIV budding.

Syntenin overexpression in human lung cancer tissue and serum is associated with poor prognosis.

BACKGROUND: Lung cancer is the major malignant tumour. The present study was conducted to determine the expression level of syntenin in lung cancer tissues and serum from lung cancer patients and to explore its clinical significance. METHODS: Syntenin expression levels were determined in paraffin-embedded lung cancer tissue specimens (n = 191) using immunohistochemistry. The mRNA expressions of syntenin in fresh lung cancer tissues and the paracancerous tissues were examined by RT-qPCR (n = 25). Syntenin and VEGF expression levels were measured in serum from patients with lung cancer (n = 60) and control subjects (n = 30) using ELISA. The associations between syntenin and the clinicopathological features or prognosis in 191 patients with lung cancer were analysed. The correlation between the syntenin and VEGF levels in serum from 60 lung cancer patients was analysed. RESULTS: The expression levels of syntenin were significantly higher in lung cancer tissues than in paracancerous tissues based on immunohistochemistry and RT-qPCR, and elevated syntenin expression was significantly associated with tumour size (P = 0.002), TNM stage (P = 0.020), tumour distant metastasis (P = 0.033), overall survival (OS) (P = 0.002) and progression-free survival (PFS) (P = 0.001). Multivariate analysis revealed that increased expression of syntenin was an independent risk factor for OS (P = 0.006) and PFS (P < 0.001) in lung cancer patients. The expression levels of syntenin and VEGF in serum from lung cancer patients were higher than those from control subjects (P < 0.001, P < 0.001, respectively), and their expression levels were positively correlated (r = 0.49, P < 0.001). CONCLUSIONS: Syntenin expression is upregulated in lung cancer patients, and its serum expression level is positively correlated with VEGF. Moreover, syntenin overexpression was correlated with poor prognosis in patients with lung cancer.

MDA-9/Syntenin (SDCBP): Novel gene and therapeutic target for cancer metastasis.

The primary cause of cancer-related death from solid tumors is metastasis. While unraveling the mechanisms of this complicated process continues, our ability to effectively target and treat it to decrease patient morbidity and mortality remains disappointing. Early detection of metastatic lesions and approaches to treat metastases (both pharmacological and genetic) are of prime importance to obstruct this process clinically. Metastasis is complex involving both genetic and epigenetic changes in the constantly evolving tumor cell. Moreover, many discrete steps have been identified in metastatic spread, including invasion, intravasation, angiogenesis, attachment at a distant site (secondary seeding), extravasation and micrometastasis and tumor dormancy development. Here, we provide an overview of the metastatic process and highlight a unique pro-metastatic gene, melanoma differentiation associated gene-9/Syntenin (MDA-9/Syntenin) also called syndecan binding protein (SDCBP), which is a major contributor to the majority of independent metastatic events. MDA-9 expression is elevated in a wide range of carcinomas and other cancers, including melanoma, glioblastoma multiforme and neuroblastoma, suggesting that it may provide an appropriate target to intervene in metastasis. Pre-clinical studies confirm that inhibiting MDA-9 either genetically or pharmacologically profoundly suppresses metastasis. An additional benefit to blocking MDA-9 in metastatic cells is sensitization of these cells to a second therapeutic agent, which converts anti-invasion effects to tumor cytocidal effects. Continued mechanistic and therapeutic insights hold promise to advance development of truly effective therapies for metastasis in the future.