Syntenin-knock out reduces exosome turnover and viral transduction.

Exosomal transfers represent an important mode of intercellular communication. Syntenin is a small scaffold protein that, when binding ALIX, can direct endocytosed syndecans and syndecan cargo to budding endosomal membranes, supporting the formation of intraluminal vesicles that compose the source of a major class of exosomes. Syntenin, however, can also support the recycling of these same components to the cell surface. Here, by studying mice and cells with syntenin-knock out, we identify syntenin as part of dedicated machinery that integrates both the production and the uptake of secreted vesicles, supporting viral/exosomal exchanges. This study significantly extends the emerging role of heparan sulfate proteoglycans and syntenin as key components for macromolecular cargo internalization into cells.

Syntenin-1 promotes colorectal cancer stem cell expansion and chemoresistance by regulating prostaglandin E2 receptor.

BACKGROUND: The protein syntenin-1 is expressed by a variety of cell types, and is upregulated in various malignancies, including melanoma, breast cancer and glioma. Although the mechanism by which elevated syntenin-1 expression contributes to cancer has been described, the exact pathway has not been elucidated. METHODS: To investigate the involvement of syntenin-1 in colorectal cancer (CRC), we performed immunohistochemical analysis of 139 CRC surgical specimens. We also examined syntenin-1 knockdown in CRC cell lines. RESULTS: High syntenin-1 expression was associated with less differentiated histologic grade and poor prognosis, and was an independent prognostic indicator in CRC. Syntenin-1 knockdown in CRC cells reduced the presence of cancer stem cells (CSCs), oxaliplatin chemoresistance and migration. DNA microarray analysis and quantitative real-time polymerase chain reaction showed decreased prostaglandin E2 receptor 2 (PTGER2) expression in syntenin-1-knockdown cells. PTGER2 knockdown in CRC cells yielded the same phenotype as syntenin-1 knockdown. Celecoxib, which has anti-inflammatory effects by targeting cyclooxygenase-2, reduced CSCs and decreased chemoresistance, while prostaglandin E2 (PGE2) had the opposite effect. CONCLUSIONS: Our findings suggested that syntenin-1 enhanced CSC expansion, oxaliplatin chemoresistance and migration capability through regulation of PTGER2 expression. Syntenin-1 may be a promising new prognostic factor and target for anti-cancer therapies.

New structural insight of C-terminal region of Syntenin-1, enhancing the molecular dimerization and inhibitory function related on Syndecan-4 signaling.

The PDZ domain-containing scaffold protein, syntenin-1, binds to the transmembrane proteoglycan, syndecan-4, but the molecular mechanism/function of this interaction are unknown. Crystal structure analysis of syntenin-1/syndecan-4 cytoplasmic domains revealed that syntenin-1 forms a symmetrical pair of dimers anchored by a syndecan-4 dimer. The syndecan-4 cytoplasmic domain is a compact intertwined dimer with a symmetrical clamp shape and two antiparallel strands forming a cavity within the dimeric twist. The PDZ2 domain of syntenin-1 forms a direct antiparallel interaction with the syndecan-4 cytoplasmic domain, inhibiting the functions of syndecan-4 such as focal adhesion formation. Moreover, C-terminal region of syntenin-1 reveals an essential role for enhancing the molecular homodimerization. Mutation of key syntenin-1 residues involved in the syndecan-4 interaction or homodimer formation abolishes the inhibitory function of syntenin-1, as does deletion of the homodimerization-related syntenin-1 C-terminal domain. Syntenin-1, but not dimer-formation-incompetent mutants, rescued the syndecan-4-mediated inhibition of migration and pulmonary metastasis by B16F10 cells. Therefore, we conclude that syntenin-1 negatively regulates syndecan-4 function via oligomerization and/or syndecan-4 interaction, impacting cytoskeletal organization and cell migration.

Novel function of MDA-9/Syntenin (SDCBP) as a regulator of survival and stemness in glioma stem cells.

Glioblastoma multiforme (GBM) is an aggressive cancer with current therapies only marginally impacting on patient survival. Glioma stem cells (GSCs), a subpopulation of highly tumorigenic cells, are considered major contributors to glioma progression and play seminal roles in therapy resistance, immune evasion and increased invasion. Despite clinical relevance, effective/selective therapeutic targeting strategies for GSCs do not exist, potentially due to the lack of a definitive understanding of key regulators of GSCs. Consequently, there is a pressing need to identify therapeutic targets and novel options to effectively target this therapy-resistant cell population. The precise roles of GSCs in governing GBM development, progression and prognosis are under intense scrutiny, but key upstream regulatory genes remain speculative. MDA-9/Syntenin (SDCBP), a scaffold protein, regulates tumor pathogenesis in multiple cancers. Highly aggressive cancers like GBM express elevated levels of MDA-9 and contain increased populations of GSCs. We now uncover a unique function of MDA-9 as a facilitator and determinant of glioma stemness and survival. Mechanistically, MDA-9 regulates multiple stemness genes (Nanog, Oct4 and Sox2) through activation of STAT3. MDA-9 controls survival of GSCs by activating the NOTCH1 pathway through phospho-Src and DLL1. Once activated, cleaved NOTCH1 regulates C-Myc expression through RBPJK, thereby facilitating GSC growth and proliferation. Knockdown of MDA-9 affects the NOTCH1/C-Myc and p-STAT3/Nanog pathways causing a loss of stemness and initiation of apoptosis in GSCs. Our data uncover a previously unidentified relationship between MDA-9 and GSCs, reinforcing relevance of this gene as a potential therapeutic target in GBM.

Phosphoinositides and PDZ domain scaffolds.

The discovery that PSD-95/Discs large/ZO-1 (PDZ) domains can function as lipid-binding modules, in particular interacting with phosphoinositides (PIs), was made more than 10 years ago (Mol Cell 9(6): 1215-1225, 2002). Confirmatory studies and a series of functional follow-ups established PDZ domains as dual specificity modules displaying both peptide and lipid binding, and prompted a rethinking of the mode of action of PDZ domains in the control of cell signaling. In this chapter, after introducing PDZ domains, PIs and methods for studying protein-lipid interactions, we focus on (i) the prevalence and the specificity of PDZ-PIs interactions, (ii) the molecular determinants of PDZ-PIs interactions, (iii) the integration of lipid and peptide binding by PDZ domains, (iv) the common features of PIs interacting PDZ domains and (v) the regulation and functional significance of PDZ-PIs interactions.

MDA-9/syntenin: a positive gatekeeper of melanoma metastasis.

Melanoma differentiation associated gene-9 (MDA-9), synonymous with syntenin, is an adapter protein that provides a central role in regulating cell-cell and cell-matrix adhesion. MDA-9/syntenin transduces signals from the cell-surface to the interior through its interaction with a plethora of additional proteins and actively participates in intracellular trafficking and cell-surface targeting, synaptic transmission, and axonal outgrowth. Recent studies demarcate a seminal role of MDA-9/syntenin in cancer metastasis. In the context of melanoma, MDA-9/syntenin functions as a positive regulator of melanoma progression and metastasis through interactions with c-Src and promotes the formation of an active FAK/c-Src signaling complex leading to NF-k B and matrix metalloproteinase (MMP) activation. The present review provides a current perspective of our understanding of the important features of MDA-9/syntenin and its significant role in tumor cell metastasis with special focus on molecular mechanism of action.

mda-9/Syntenin promotes metastasis in human melanoma cells by activating c-Src.

The scaffold PDZ-domain containing protein mda-9/syntenin functions as a positive regulator of cancer cell progression in human melanoma and other tumors. mda-9/Syntenin regulates cell motility and invasion by altering defined biochemical and signaling pathways, including focal adhesion kinase (FAK), p38 mitogen-activated protein kinase (MAPK) and NF-kappaB, but precisely how mda-9/syntenin organizes these multiprotein signaling complexes is not well understood. Using a clinically relevant human melanoma model, we demonstrate that mda-9/syntenin physically interacts with c-Src and this communication correlates with an increase in FAK/c-Src complex formation and c-Src activation. Inhibiting mda-9/syntenin, using an adenovirus expressing antisense mda-9/syntenin or addition of c-Src siRNA, suppresses melanoma cell migration, anchorage-independent growth, and spontaneous tumor cell dissemination in vivo in a human melanoma animal metastasis model. These data are compatible with a model wherein interaction of MDA-9/syntenin with c-Src promotes the formation of an active FAK/c-Src signaling complex, leading to enhanced tumor cell invasion and metastatic spread. These provocative findings highlight mda-9/syntenin and its interacting partners as promising therapeutic targets for intervention of metastasis.

mda-9/Syntenin: more than just a simple adapter protein when it comes to cancer metastasis.

Cancer is a progressive disease that, in many instances, if untreated, can culminate in metastatic spread of primary tumor cells to distant sites in the body. Metastasis frequently confers virulence and therapy resistance to cancer cells, and defining the molecular events that control metastasis will be mandatory to develop rational, targeted therapies for effective intervention, prevention of recurrence, and the "holy grail" of engendering a cure. Adapter proteins are physiologically pertinent molecules that, through interactions with key regulatory proteins via specific conserved domains, control important cellular events. Melanoma differentiation associated gene-9 (mda-9), also known as syntenin, is a PDZ domain-containing adapter protein that is involved in organization of protein complexes in the plasma membranes, regulation of B-cell development, intracellular trafficking and cell-surface targeting, synaptic transmission, and axonal outgrowth. Recent studies now define a seminal role for mda-9/syntenin in cancer metastasis. The present review provides a current perspective of our understanding of this important aspect of mda-9/syntenin, suggesting that this gene and its encoded protein and interacting protein partners may provide viable targets for intervening in the final and invariably the most lethal stage of cancer progression, namely, cancer metastasis.