MDA-9/syntenin is a key regulator of glioma pathogenesis

Impact of Radiation on Invasion and Migration of Glioma In Vitro and In Vivo

Glioblastoma (GBM) constitutes the most common primary brain tumor and it remains incurable despite therapeutic advances. The high infiltration/invasion potential of GBM cells is considered to be one of the reasons for the inevitable recurrence of the disease. Radiotherapy (RT) is part of the standard care for patients with GBM, and its benefits on overall survival are extensively reported. However, numerous preclinical studies show that X-ray irradiation can enhance the motility of GBM cells. In the present review, we bring together state-of-the-art research on the impact of radiation on GBM cell motility. The mechanisms through which irradiation impacts the brain tumor microenvironment and the tumor cells themselves, leading to more aggressive/invasive tumors, are described. Finally, we summarize potential pharmacological strategies to overcome this problem. Clinical data validating the occurrence of these processes are urgently needed as they could be of great value for patient outcomes. With this comprehensive review, we expect to highlight the need for methods which allow for monitoring the post-irradiation invasive behavior of GBM in patients.

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.

The Multifunctional Protein Syntenin-1: Regulator of Exosome Biogenesis, Cellular Function, and Tumor Progression

Syntenin acts as an adaptor and scaffold protein through its two PSD-95, Dlg, and ZO-1 (PDZ) domains, participating in multiple signaling pathways and modulating cellular physiology. It has been identified as an oncogene, promoting cancer development, metastasis, and angiogenesis in various carcinomas. Syntenin-1 is also associated with the production and release of exosomes, small extracellular vesicles that play a significant role in intercellular communication by containing bioactive molecules such as proteins, lipids, and nucleic acids. The trafficking of exosomes involves a complex interplay of various regulatory proteins, including syntenin-1, which interacts with its binding partners, syndecan and activated leukocyte cell adhesion molecule (ALIX). Exosomal transfer of microRNAs, a key cargo, can regulate the expression of various cancer-related genes, including syntenin-1. Targeting the mechanism involving the regulation of exosomes by syntenin-1 and microRNAs may provide a novel treatment strategy for cancer. This review highlights the current understanding of syntenin-1's role in regulating exosome trafficking and its associated cellular signaling pathways.

Biological Role and Aberrant Overexpression of Syntenin-1 in Cancer: Potential Role as a Biomarker and Therapeutic Target

Syntenin-1 is a 298 amino acid protein codified by the melanoma differentiation-associated gene-9 (MDA-9). Structurally, it is composed of four domains: N-terminal, PDZ1, PDZ2, and C-terminal. The PDZ domains of syntenin-1 are involved in the stability and interaction with other molecules such as proteins, glycoproteins, and lipids. Domains are also associated with several biological functions such as the activation of signaling pathways related to cell-to-cell adhesion, signaling translation, and the traffic of intracellular lipids, among others. The overexpression of syntenin-1 has been reported in glioblastoma, colorectal, melanoma, lung, prostate, and breast cancer, which promotes tumorigenesis by regulating cell migration, invasion, proliferation, angiogenesis, apoptosis, and immune response evasion, and metastasis. The overexpression of syntenin-1 in samples has been associated with worst prognostic and recurrence, whereas the use of inhibitors such as shRNA, siRNA, and PDZli showed a diminution of the tumor size and reduction in metastasis and invasion. Syntenin-1 has been suggested as a potential biomarker and therapeutic target in cancer for developing more effective diagnostic/prognostic tests or passive/active immunotherapies.

Huaier Inhibits Gastric Cancer Growth and Hepatic Metastasis by Reducing Syntenin Expression and STAT3 Phosphorylation

Gastric cancer (GC) is a common malignant tumor worldwide and poses a serious threat to human health. As a traditional Chinese medicine, Huaier (Trametes robiniophila Murr.) has been used in the clinical treatment of GC. However, the mechanism underlying the anticancer effect of Huaier remains poorly understood. In this study, we used in vivo imaging technology to determine the anticancer effect of the Huaier n-butanol extract (HBE) on orthotopic and hepatic metastasis of GC mouse models. We found that HBE suppressed tumor growth and metastasis without causing apparent host toxicity. Proteomic analysis of GC cells before and after HBE intervention revealed syntenin to be one of the most significantly downregulated proteins after HBE intervention. We further demonstrated that HBE suppressed the growth and metastasis of GC by reducing the expression of syntenin and the phosphorylation of STAT3 at Y705 and reversing the epithelial-mesenchymal transition (EMT). In addition, we confirmed that syntenin was highly expressed in GC tissue and correlated with metastasis and poor prognosis. In conclusion, our results suggest that Huaier, a clinically used anticancer drug, may inhibit the growth and liver metastasis of GC by inhibiting the syntenin/STAT3 signaling pathway and reversing EMT.

Unconventional Protein Secretion in Brain Tumors Biology: Enlightening the Mechanisms for Tumor Survival and Progression

Non-canonical secretion pathways, collectively known as unconventional protein secretion (UPS), are alternative secretory mechanisms usually associated with stress-inducing conditions. UPS allows proteins that lack a signal peptide to be secreted, avoiding the conventional endoplasmic reticulum-Golgi complex secretory pathway. Molecules that generally rely on the canonical pathway to be secreted may also use the Golgi bypass, one of the unconventional routes, to reach the extracellular space. UPS studies have been increasingly growing in the literature, including its implication in the biology of several diseases. Intercellular communication between brain tumor cells and the tumor microenvironment is orchestrated by various molecules, including canonical and non-canonical secreted proteins that modulate tumor growth, proliferation, and invasion. Adult brain tumors such as gliomas, which are aggressive and fatal cancers with a dismal prognosis, could exploit UPS mechanisms to communicate with their microenvironment. Herein, we provide functional insights into the UPS machinery in the context of tumor biology, with a particular focus on the secreted proteins by alternative routes as key regulators in the maintenance of brain tumors.

Targeting PDZ domains as potential treatment for viral infections, neurodegeneration and cancer

The interaction between proteins is a fundamental event for cellular life that is generally mediated by specialized protein domains or modules. PDZ domains are the largest class of protein-protein interaction modules, involved in several cellular pathways such as signal transduction, cell-cell junctions, cell polarity and adhesion, and protein trafficking. Because of that, dysregulation of PDZ domain function often causes the onset of pathologies, thus making this family of domains an interesting pharmaceutical target. In this review article we provide an overview of the structural and functional features of PDZ domains and their involvement in the cellular and molecular pathways at the basis of different human pathologies. We also discuss some of the strategies that have been developed with the final goal to hijack or inhibit the interaction of PDZ domains with their ligands. Because of the generally low binding selectivity of PDZ domain and the scarce efficiency of small molecules in inhibiting PDZ binding, this task resulted particularly difficult to pursue and still demands increasing experimental efforts in order to become completely feasible and successful in vivo.

Overview of the molecular mechanisms of migration and invasion in glioblastoma multiforme

Glioblastoma (GBM) is one of the most devastating cancers, with an approximate median survival of only 16 months. Although some new insights into the fantastic heterogeneity of this kind of brain tumor have been revealed in recent studies, all subclasses of GBM still demonstrate highly aggressive invasion properties to the surrounding parenchyma. This behavior has become the main obstruction to current curative therapies as invasive GBM cells migrate away from these foci after surgical therapies. Therefore, this review aimed to provide a relatively comprehensive study of GBM invasion mechanisms, which contains an intricate network of interactions and signaling pathways with the extracellular matrix (ECM). Among these related molecules, TGF-β, the ECM, Akt, and microRNAs are most significant in terms of cellular procedures related to GBM motility and invasion. Moreover, we also review data indicating that Musashi-1 (MSI1), a neural RNA-binding protein (RBP), regulates GBM motility and invasion, maintains stem cell populations in GBM, and promotes drug-resistant GBM phenotypes by stimulating necessary oncogenic signaling pathways through binding and regulating mRNA stability. Importantly, these necessary oncogenic signaling pathways have a close connection with TGF-β, ECM, and Akt. Thus, it appears promising to find MSI-specific inhibitors or RNA interference-based treatments to prevent the actions of these molecules despite using RBPs, which are known as hard therapeutic targets. In summary, this review aims to provide a better understanding of these signaling pathways to help in developing novel therapeutic approaches with better outcomes in preclinical studies.

A Key Pathway to Cancer Resilience: The Role of Autophagy in Glioblastomas

There are no effective strategies for the successful treatment of glioblastomas (GBM). Current therapeutic modalities effectively target bulk tumor cells but leave behind marginal GBM cells that escape from the surgical margins and radiotherapy field, exhibiting high migratory phenotype and resistance to all available anti-glioma therapies. Drug resistance is mostly driven by tumor cell plasticity: a concept associated with reactivating transcriptional programs in response to adverse and dynamic conditions from the tumor microenvironment. Autophagy, or "self-eating", pathway is an emerging target for cancer therapy and has been regarded as one of the key drivers of cell plasticity in response to energy demanding stress conditions. Many studies shed light on the importance of autophagy as an adaptive mechanism, protecting GBM cells from unfavorable conditions, while others recognize that autophagy can kill those cells by triggering a non-apoptotic cell death program, called 'autophagy cell death' (ACD). In this review, we carefully analyzed literature data and conclude that there is no clear evidence indicating the presence of ACD under pathophysiological settings in GBM disease. It seems to be exclusively induced by excessive (supra-physiological) stress signals, mostly from in vitro cell culture studies. Instead, pre-clinical and clinical data indicate that autophagy is an emblematic example of the 'dark-side' of a rescue pathway that contributes profoundly to a pro-tumoral adaptive response. From a standpoint of treating the real human disease, only combinatorial therapy targeting autophagy with cytotoxic drugs in the adjuvant setting for GBM patients, associated with the development of less toxic and more specific autophagy inhibitors, may inhibit adaptive response and enhance the sensibility of glioma cells to conventional therapies.

What Are the Potential Roles of Nuclear Perlecan and Other Heparan Sulphate Proteoglycans in the Normal and Malignant Phenotype

The recent discovery of nuclear and perinuclear perlecan in annulus fibrosus and nucleus pulposus cells and its known matrix stabilizing properties in tissues introduces the possibility that perlecan may also have intracellular stabilizing or regulatory roles through interactions with nuclear envelope or cytoskeletal proteins or roles in nucleosomal-chromatin organization that may regulate transcriptional factors and modulate gene expression. The nucleus is a mechano-sensor organelle, and sophisticated dynamic mechanoresponsive cytoskeletal and nuclear envelope components support and protect the nucleus, allowing it to perceive and respond to mechano-stimulation. This review speculates on the potential roles of perlecan in the nucleus based on what is already known about nuclear heparan sulphate proteoglycans. Perlecan is frequently found in the nuclei of tumour cells; however, its specific role in these diseased tissues is largely unknown. The aim of this review is to highlight probable roles for this intriguing interactive regulatory proteoglycan in the nucleus of normal and malignant cell types.

CRISPR activation screen in mice identifies novel membrane proteins enhancing pulmonary metastatic colonisation

Melanoma represents ~5% of all cutaneous malignancies, yet accounts for the majority of skin cancer deaths due to its propensity to metastasise. To develop new therapies, novel target molecules must to be identified and the accessibility of cell surface proteins makes them attractive targets. Using CRISPR activation technology, we screened a library of guide RNAs targeting membrane protein-encoding genes to identify cell surface molecules whose upregulation enhances the metastatic pulmonary colonisation capabilities of tumour cells in vivo. We show that upregulated expression of the cell surface protein LRRN4CL led to increased pulmonary metastases in mice. Critically, LRRN4CL expression was elevated in melanoma patient samples, with high expression levels correlating with decreased survival. Collectively, our findings uncover an unappreciated role for LRRN4CL in the outcome of melanoma patients and identifies a potential therapeutic target and biomarker.

A High-Affinity Peptide Ligand Targeting Syntenin Inhibits Glioblastoma

Despite the recent advances in cancer therapeutics, highly aggressive cancer forms, such as glioblastoma (GBM), still have very low survival rates. The intracellular scaffold protein syntenin, comprising two postsynaptic density protein-95/discs-large/zona occludens-1 (PDZ) domains, has emerged as a novel therapeutic target in highly malignant phenotypes including GBM. Here, we report the development of a novel, highly potent, and metabolically stable peptide inhibitor of syntenin, KSL-128114, which binds the PDZ1 domain of syntenin with nanomolar affinity. KSL-128114 is resistant toward degradation in human plasma and mouse hepatic microsomes and displays a global PDZ domain selectivity for syntenin. An X-ray crystal structure reveals that KSL-128114 interacts with syntenin PDZ1 in an extended noncanonical binding mode. Treatment with KSL-128114 shows an inhibitory effect on primary GBM cell viability and significantly extends survival time in a patient-derived xenograft mouse model. Thus, KSL-128114 is a novel promising candidate with therapeutic potential for highly aggressive tumors, such as GBM.

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.

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.

Lumefantrine, an antimalarial drug, reverses radiation and temozolomide resistance in glioblastoma

Glioblastoma multiforme (GBM) is an aggressive cancer without currently effective therapies. Radiation and temozolomide (radio/TMZ) resistance are major contributors to cancer recurrence and failed GBM therapy. Heat shock proteins (HSPs), through regulation of extracellular matrix (ECM) remodeling and epithelial mesenchymal transition (EMT), provide mechanistic pathways contributing to the development of GBM and radio/TMZ-resistant GBM. The Friend leukemia integration 1 (Fli-1) signaling network has been implicated in oncogenesis in GBM, making it an appealing target for advancing novel therapeutics. Fli-1 is linked to oncogenic transformation with up-regulation in radio/TMZ-resistant GBM, transcriptionally regulating HSPB1. This link led us to search for targeted molecules that inhibit Fli-1. Expression screening for Fli-1 inhibitors identified lumefantrine, an antimalarial drug, as a probable Fli-1 inhibitor. Docking and isothermal calorimetry titration confirmed interaction between lumefantrine and Fli-1. Lumefantrine promoted growth suppression and apoptosis in vitro in parental and radio/TMZ-resistant GBM and inhibited tumor growth without toxicity in vivo in U87MG GBM and radio/TMZ-resistant GBM orthotopic tumor models. These data reveal that lumefantrine, an FDA-approved drug, represents a potential GBM therapeutic that functions through inhibition of the Fli-1/HSPB1/EMT/ECM remodeling protein networks.

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.

Transcriptional regulation of HSPB1 by Friend leukemia integration-1 factor modulates radiation and temozolomide resistance in glioblastoma

Glioblastoma (GBM) is the most common primary brain tumor and is invariably fatal. Heat shock proteins (HSPs) provide protein signatures/biomarkers for GBM that afford potential as targets for developing anti-GBM drugs. In GBM, elevated expression of hypoxia inducible factors under the influence of Ets family proteins significantly promotes the expression of HSPs. RNAseq analysis identified HSPB1 as a prominent upregulated HSP in GBM and in radiation resistant/temozolomide resistant (radio/TMZR) GBM. Here, we established friend leukemia integration 1 (Fli-1), a member of Ets family to be playing a transcriptional regulatory role on the HSPB1 gene. Fli-1 binds to nucleotide residues GGAA at binding sites 3, 6 and 7 in the 5-kb upstream region of HSPB1. Fli-1 has been linked to oncogenic transformation with upregulation in radio/TMZR GBM. Overexpression of Fli-1 in GBM promotes resistance, whereas Fli-1 knockdown in radio/TMZR GBM cells suppresses resistance. We identify the underlying molecular mechanisms of Fli-1-mediated regulation of HSPB1 that drive extracellular matrix remodeling and epithelial to mesenchymal transition in radio/TMZR GBM cells. This study uncovers Fli-1 as a potential therapeutic target for combating radiation and temozolomide resistance in GBM.

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.

Lung Adenocarcinoma Syndecan-2 Potentiates Cell Invasiveness

Altered expression of syndecan-2 (SDC2), a heparan sulfate proteoglycan, has been associated with diverse types of human cancers. However, the mechanisms by which SDC2 may contribute to the pathobiology of lung adenocarcinoma have not been previously explored. SDC2 levels were measured in human lung adenocarcinoma samples and lung cancer tissue microarrays using immunohistochemistry and real-time PCR. To understand the role of SDC2 in vitro, SDC2 was silenced or overexpressed in A549 lung adenocarcinoma cells. The invasive capacity of cells was assessed using Matrigel invasion assays and measuring matrix metalloproteinase (MMP) 9 expression. Finally, we assessed tumor growth and metastasis of SDC2-deficient A549 cells in a xenograft tumor model. SDC2 expression was upregulated in malignant epithelial cells and macrophages obtained from human lung adenocarcinomas. Silencing of SDC2 decreased MMP9 expression and attenuated the invasive capacity of A549 lung adenocarcinoma cells. The inhibitory effect of SDC2 silencing on MMP9 expression and cell invasion was reversed by overexpression of MMP9 and syntenin-1. SDC2 silencing attenuated NF-κB p65 subunit nuclear translocation and its binding to the MMP9 promoter, which were restored by overexpression of syntenin-1. SDC2 silencing in vivo reduced tumor mass volume and metastasis. These findings suggest that SDC2 plays an important role in the invasive properties of lung adenocarcinoma cells and that its effects are mediated by syntenin-1. Thus, inhibiting SDC2 expression or activity could serve as a potential therapeutic target to treat lung adenocarcinoma.

MDA-9/Syntenin (SDCBP) Is a Critical Regulator of Chemoresistance, Survival and Stemness in Prostate Cancer Stem Cells

Despite some progress, treating advanced prostate cancer remains a major clinical challenge. Recent studies have shown that prostate cancer can originate from undifferentiated, rare, stem cell-like populations within the heterogeneous tumor mass, which play seminal roles in tumor formation, maintenance of tumor homeostasis and initiation of metastases. These cells possess enhanced propensity toward chemoresistance and may serve as a prognostic factor for prostate cancer recurrence. Despite extensive studies, selective targeted therapies against these stem cell-like populations are limited and more detailed experiments are required to develop novel targeted therapeutics. We now show that MDA-9/Syntenin/SDCBP (MDA-9) is a critical regulator of survival, stemness and chemoresistance in prostate cancer stem cells (PCSCs). MDA-9 regulates the expression of multiple stem-regulatory genes and loss of MDA-9 causes a complete collapse of the stem-regulatory network in PCSCs. Loss of MDA-9 also sensitizes PCSCs to multiple chemotherapeutics with different modes of action, such as docetaxel and trichostatin-A, suggesting that MDA-9 may regulate multiple drug resistance. Mechanistically, MDA-9-mediated multiple drug resistance, stemness and survival are regulated in PCSCs through activation of STAT3. Activated STAT3 regulates chemoresistance in PCSCs through protective autophagy as well as regulation of MDR1 on the surface of the PCSCs. We now demonstrate that MDA-9 is a critical regulator of PCSC survival and stemness via exploiting the inter-connected STAT3 and c-myc pathways.

Syntenin: PDZ Protein Regulating Signaling Pathways and Cellular Functions

Syntenin is an adaptor-like molecule that has two adjacent tandem postsynaptic density protein 95/Discs large protein/Zonula occludens 1 (PDZ) domains. The PDZ domains of syntenin recognize multiple peptide motifs with low to moderate affinity. Many reports have indicated interactions between syntenin and a plethora of proteins. Through interactions with various proteins, syntenin regulates the architecture of the cell membrane. As a result, increases in syntenin levels induce the metastasis of tumor cells, protrusion along the neurite in neuronal cells, and exosome biogenesis in various cell types. Here, we review the updated data that support various roles for syntenin in the regulation of neuronal synapses, tumor cell invasion, and exosome control.

Regulation of neuroblastoma migration, invasion, and in vivo metastasis by genetic and pharmacological manipulation of MDA-9/Syntenin

Despite multi-modality treatments, prognosis for advanced stage neuroblastoma (NB) remains challenging with residual long-term disabilities in survivors. Advanced stage NB is metastatic, which is a principal cause of cancer-related deaths. We presently document a primary role of MDA-9 in NB progression and define the molecular mechanisms by which MDA-9 promotes transformed phenotypes. NB cell lines and clinical samples display elevated MDA-9 expression and bioinformatic analysis supports an association between elevated MDA-9 and bone metastasis and poor prognosis. Genetic (shmda-9, mda-9 siRNA) or pharmacological (small molecule inhibitor of protein-protein interactions; PDZ1i) blockade of MDA-9 decreases NB migration, invasion, and metastasis. Blocking mda-9 expression or disrupting MDA-9 partner protein interactions downregulates integrin α6 and β4, diminishing Src activity and suppressing Rho-Rac-Cdc42 activity. These signaling changes inhibit cofilin and matrix metalloproteinases reducing in vitro and in vivo NB cell migration. Overexpression of integrin α6 and β4 rescues the invasion phenotype and increases Src activity, supporting integrins as essential regulators of MDA-9-mediated NB migration and invasion. We identify MDA-9 as a key contributor to NB pathogenesis and show that genetic or pharmacological inhibition suppresses NB pathogenesis by an integrin-mediated Src-disruption pathway.

Suppression of Prostate Cancer Pathogenesis Using an MDA-9/Syntenin (SDCBP) PDZ1 Small-Molecule Inhibitor

Metastasis is the primary determinant of death in patients with diverse solid tumors and MDA-9/Syntenin (SDCBP), a pro-metastatic and pro-angiogenic gene, contributes to this process. Recently, we documented that by physically interacting with IGF-1R, MDA-9/Syntenin activates STAT3 and regulates prostate cancer pathogenesis. These observations firmly established MDA-9/Syntenin as a potential molecular target in prostate cancer. MDA-9/Syntenin contains two highly homologous PDZ domains predicted to interact with a plethora of proteins, many of which are central to the cancerous process. An MDA-9/Syntenin PDZ1 domain-targeted small molecule (PDZ1i) was previously developed using fragment-based drug discovery (FBDD) guided by NMR spectroscopy and was found to be well-tolerated in vivo, had significant half-life (t _1/2 = 9 hours) and displayed substantial anti-prostate cancer preclinical in vivo activity. PDZ1i blocked tumor cell invasion and migration in vitro, and metastasis in vivo Hence, we demonstrate that PDZ1i an MDA-9/Syntenin PDZ1 target-specific small-molecule inhibitor displays therapeutic potential for prostate and potentially other cancers expressing elevated levels of MDA-9/Syntenin.

MDA-9/Syntenin: An emerging global molecular target regulating cancer invasion and metastasis

With few exceptions, metastasis is the terminal stage of cancer with limited therapeutic options. Metastasis consists of numerous phenotypic and genotypic alterations of cells that are directly and indirectly induced by multiple intrinsic (cellular) and extrinsic (micro-environmental) factors. To metastasize, a cancer cell often transitions from an epithelial to mesenchymal morphology (EMT), modifies the extracellular matrix, forms emboli and survives in the circulation, escapes immune surveillance, adheres to sites distant from the initial tumor and finally develops a blood supply (angiogenesis) and colonizes in a secondary niche (a micrometastasis). Scientific advances have greatly enhanced our understanding of the precise molecular and genetic changes, operating independently or collectively, that lead to metastasis. This review focuses on a unique gene, melanoma differentiation associated gene-9 (also known as Syntenin-1; Syndecan Binding Protein (sdcbp); mda-9/syntenin), initially cloned and characterized from metastatic human melanoma and shown to be a pro-metastatic gene. In the last two decades, our comprehension of the diversity of actions of MDA-9/Syntenin on cellular phenotype has emerged. MDA-9/Sytenin plays pivotal regulatory roles in multiple signaling cascades and orchestrates both metastatic and non-metastatic events. Considering the relevance of this gene in controlling cancer invasion and metastasis, approaches have been developed to uniquely and selectively target this gene. We also provide recent updates on strategies that have been successfully employed in targeting MDA-9/Syntenin resulting in profound pre-clinical anti-cancer activity.

Rethinking Glioblastoma Therapy: MDA-9/Syntenin Targeted Small Molecule

Effective therapies for glioblastoma multiforme (GBM) are not currently available. A small molecule has been identified using fragment-based drug-discovery guided by NMR that targets important protein-protein interactions controlling GBM invasion and pathogenicity. This first generation drug displays excellent pharmacokinetic properties, passes through the blood-brain barrier and is effective in preclinical animal models of GBM, particularly when combined with radiation therapy.

Ultrasensitive Immunoprofiling of Plasma Extracellular Vesicles Identifies Syndecan-1 as a Potential Tool for Minimally Invasive Diagnosis of Glioma

PURPOSE

Liquid biopsy has great potential to improve the management of brain tumor patients at high risk of surgery-associated complications. Here, the aim was to explore plasma extracellular vesicle (plEV) immunoprofiling as a tool for noninvasive diagnosis of glioma.

EXPERIMENTAL DESIGN

PlEV isolation and analysis were optimized using advanced mass spectrometry, nanoparticle tracking analysis, and electron microscopy. We then established a new procedure that combines size exclusion chromatography isolation and proximity extension assay-based ultrasensitive immunoprofiling of plEV proteins that was applied on a well-defined glioma study cohort (n = 82).

RESULTS

Among potential candidates, we for the first time identify syndecan-1 (SDC1) as a plEV constituent that can discriminate between high-grade glioblastoma multiforme (GBM, WHO grade IV) and low-grade glioma [LGG, WHO grade II; area under the ROC curve (AUC): 0.81; sensitivity: 71%; specificity: 91%]. These findings were independently validated by ELISA. Tumor SDC1 mRNA expression similarly discriminated between GBM and LGG in an independent glioma patient population from The Cancer Genome Atlas cohort (AUC: 0.91; sensitivity: 79%; specificity: 91%). In experimental studies with GBM cells, we show that SDC1 is efficiently sorted to secreted EVs. Importantly, we found strong support of plEV^SDC1 originating from GBM tumors, as plEV^SDC1 correlated with SDC1 protein expression in matched patient tumors, and plEV^SDC1 was decreased postoperatively depending on the extent of surgery.

CONCLUSIONS

Our studies support the concept of circulating plEVs as a tool for noninvasive diagnosis and monitoring of gliomas and should move this field closer to the goal of improving the management of cancer patients.

A PDZ Protein MDA-9/Syntenin: As a Target for Cancer Therapy

Melanoma differentiation-associated gene 9 (MDA-9)/Syntenin is a multidomain PDZ protein and identified as a key oncogene in melanoma initially. This protein contains a unique tandem PDZ domain architecture (PDZ1 and PDZ2 spaced by a 4-amino acid linker), an N-terminal domain (NTD) that is structurally uncharacterized and a short C-terminal domain (CTD). The PDZ1 domain is regarded as the PDZ signaling domain while PDZ2 served as the PDZ superfamily domain. It has various cellular roles by regulating many of major signaling pathways in numerous cancertypes. Through the use of novel drug design methods, such as dimerization and unnatural amino acid substitution of inhibitors in our group, the protein may provide a valuable therapeutic target. The objective of this review is to provide a current perspective on the cancer-specific role of MDA-9/Syntenin in order to explore its potential for cancer drug discovery and cancer therapy.

MiRNA-139-3p inhibits the proliferation, invasion, and migration of human glioma cells by targeting MDA-9/syntenin

Gliomas are the most common primary malignant brain tumor in adults. Although these tumors are aggressive and frequently lethal, there are currently few therapeutic approaches available to prolong patient survival. MicroRNAs play important roles in regulating the expression of genes that control diverse cellular processes. Here, we investigated the expression and function of miR-139-3p in gliomas using clinical specimens, cultured cells, and a mouse xenograft tumor model. We found that miR-139-3p expression is markedly lower in human glioma tissues than in normal brain tissues. We identified melanoma differentiation-associated gene-9 (MDA-9)/syntenin, an adaptor protein implicated in tumor metastasis, as a novel direct target of miR-139-3p and showed that syntenin mRNA and miR-139-3p levels were inversely correlated in clinical specimens (r = -0.6817, P = 0.0002). Overexpression of miR-139-3p in human glioma cell lines inhibited cell proliferation, migration, and invasion, and these effects were rescued by co-transfection with syntenin. Our results indicate that miR-139-3p plays a significant role in controlling behaviors associated with the malignant progression of gliomas, and we identify the miR-139-3p-syntenin axis as a potential therapeutic target for glioma.

MDA-9/Syntenin regulates protective autophagy in anoikis-resistant glioma stem cells

Glioma stem cells (GSCs) comprise a small subpopulation of glioblastoma multiforme cells that contribute to therapy resistance, poor prognosis, and tumor recurrence. Protective autophagy promotes resistance of GSCs to anoikis, a form of programmed cell death occurring when anchorage-dependent cells detach from the extracellular matrix. In nonadherent conditions, GSCs display protective autophagy and anoikis-resistance, which correlates with expression of melanoma differentiation associated gene-9/Syntenin (MDA-9) (syndecan binding protein; SDCBP). When MDA-9 is suppressed, GSCs undergo autophagic death supporting the hypothesis that MDA-9 regulates protective autophagy in GSCs under anoikis conditions. MDA-9 maintains protective autophagy through phosphorylation of BCL2 and by suppressing high levels of autophagy through EGFR signaling. MDA-9 promotes these changes by modifying FAK and PKC signaling. Gain-of-function and loss-of-function genetic approaches demonstrate that MDA-9 regulates pEGFR and pBCL2 expression through FAK and pPKC. EGFR signaling inhibits autophagy markers (ATG5, Lamp1, LC3B), helping to maintain protective autophagy, and along with pBCL2 maintain survival of GSCs. In the absence of MDA-9, this protective mechanism is deregulated; EGFR no longer maintains protective autophagy, leading to highly elevated and sustained levels of autophagy and consequently decreased cell survival. In addition, pBCL2 is down-regulated in the absence of MDA-9, leading to cell death in GSCs under conditions of anoikis. Our studies confirm a functional link between MDA-9 expression and protective autophagy in GSCs and show that inhibition of MDA-9 reverses protective autophagy and induces anoikis and cell death in GSCs.

Syndecan-1 knockdown inhibits glioma cell proliferation and invasion by deregulating a c-src/FAK-associated signaling pathway

Recent studies have shown that increased syndecan-1 (SDC1) expression in human glioma is associated with higher tumor grades and poor prognoses, but its oncogenic functions and the underlying molecular mechanisms remain unknown. Here, we examined SDC1 expression in datasets from The Cancer Genome Atlas and the National Center for Biotechnology Information Gene Expression Omnibus. Elevated SDC1 expression in glioma was closely associated with increases in tumor progression and shorter survival. We also examined SDC1 expression and evaluated the effects of stable SDC1 knockdown in glioma cell lines. SDC1 knockdown attenuated proliferation and invasion by glioma cells and markedly decreased PCNA and MMP-9 mRNA and protein expression. In a xenograft model, SDC1 knockdown suppressed the tumorigenic effects of U87 cells in vivo. SDC1 knockdown decreased phosphorylation of the c-src/FAK complex and its downstream signaling molecules, Erk, Akt and p38 MAPK. These results suggest that SDC1 may be a novel therapeutic target in the treatment of glioma.

Syntenin promotes VEGF-induced VEGFR2 endocytosis and angiogenesis by increasing ephrin-B2 function in endothelial cells

Syntenin, a tandem PDZ-domain-containing scaffold protein, is involved in the regulation of diverse biological functions, including protein trafficking, exosome biogenesis, and cancer metastasis. Here, we present the first study to explore the significance of syntenin in endothelial cells. Syntenin knockdown in human umbilical vein endothelial cells (HUVECs) impaired vascular endothelial growth factor (VEGF)-mediated proliferation, migration, invasion, vascular permeability, and nitric oxide (NO) production. Syntenin knockdown also suppressed expression of the VEGFR2 target genes VEGF, MMP2, and Nurr77 as well as VEGF-induced angiogenesis in vitro and in vivo. And it decreased cell-surface levels of ephrin-B2. Biochemical analyses revealed that syntenin exists in complex with VEGFR2 and ephrin-B2. Syntenin knockdown abolished the association between VEGFR2 and ephrin-B2, suggesting syntenin functions as a scaffold protein facilitating their association in HUVECs. Consistent with these observations, knocking down syntenin or ephrin-B2 abolished VEGF-induced endocytosis and VEGFR2 phosphorylation and activation of its downstream signaling molecules. Treatment with MG132, a proteasome inhibitor, rescued the downregulation of ephrin-B2 and VEGFR2 signaling induced by syntenin knockdown. These findings demonstrate that syntenin promotes VEGF signaling and, through its PDZ-dependent interaction with ephrin-B2, enhances VEGF-mediated VEGFR2 endocytosis and subsequent downstream signaling and angiogenesis in endothelial cells.

The MDA-9/Syntenin/IGF1R/STAT3 Axis Directs Prostate Cancer Invasion

Although prostate cancer is clinically manageable during several stages of progression, survival is severely compromised once cells invade and metastasize to distant organs. Comprehending the pathobiology of invasion is required for developing efficacious targeted therapies against metastasis. Based on bioinformatics data, we predicted an association of melanoma differentiation-associated gene-9 [syntenin, or syndecan binding protein (SDCBP)] in prostate cancer progression. Using tissue samples from various Gleason stage prostate cancer patients with adjacent normal tissue, a series of normal prostate and prostate cancer cell lines (with differing tumorigenic/metastatic properties), mda-9/syntenin-manipulated variants (including loss-of-function and gain-of-function cell lines), and CRISPR/Cas9 stable MDA-9/Syntenin knockout cells, we now confirm the relevance of and dependence on MDA-9/syntenin in prostate cancer invasion. MDA-9/Syntenin physically interacted with insulin-like growth factor-1 receptor following treatment with insulin-like growth factor binding protein-2 (IGFBP2), regulating downstream signaling processes that enabled STAT3 phosphorylation. This activation enhanced expression of MMP2 and MMP9, two established enzymes that positively regulate invasion. In addition, MDA-9/syntenin-mediated upregulation of proangiogenic factors including IGFBP2, IL6, IL8, and VEGFA also facilitated migration of prostate cancer cells. Collectively, our results draw attention to MDA-9/Syntenin as a positive regulator of prostate cancer metastasis, and the potential application of targeting this molecule to inhibit invasion and metastasis in prostate cancer and potentially other cancers.Significance: This study provides new mechanistic insight into the proinvasive role of MDA-9/Syntenin in prostate cancer and has potential for therapeutic application to prevent prostate cancer metastasis. Cancer Res; 78(11); 2852-63. ©2018 AACR.

MDA-9/Syntenin (SDCBP) modulates small GTPases RhoA and Cdc42 via transforming growth factor β1 to enhance epithelial-mesenchymal transition in breast cancer

Epithelial-mesenchymal transition (EMT) is one of the decisive steps regulating cancer invasion and metastasis. However, the molecular mechanisms underlying this transition require further clarification. MDA-9/syntenin (SDCBP) expression is elevated in breast cancer patient samples as well as cultured breast cancer cells. Silencing expression of MDA-9 in mesenchymal metastatic breast cancer cells triggered a change in cell morphology in both 2D- and 3D-cultures to a more epithelial-like phenotype, along with changes in EMT markers, cytoskeletal rearrangement and decreased invasion. Conversely, over expressing MDA-9 in epithelial non-metastatic breast cancer cells instigated a change in morphology to a more mesenchymal phenotype with corresponding changes in EMT markers, cytoskeletal rearrangement and an increase in invasion. We also found that MDA-9 upregulated active levels of known modulators of EMT, the small GTPases RhoA and Cdc42, via TGFβ1. Reintroducing TGFβ1 in MDA-9 silenced cells restored active RhoA and cdc42 levels, modulated cytoskeletal rearrangement and increased invasion. We further determined that MDA-9 interacts with TGFβ1 via its PDZ1 domain. Finally, in vivo studies demonstrated that silencing the expression of MDA-9 resulted in decreased lung metastasis and TGFβ1 re-expression partially restored lung metastases. Our findings provide evidence for the relevance of MDA-9 in mediating EMT in breast cancer and support the potential of MDA-9 as a therapeutic target against metastatic disease.

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.

IL-6 increases SDCBP expression, cell proliferation, and cell invasion by activating JAK2/STAT3 in human glioma cells

Syndecan-binding protein (SDCBP), which is induced by tumor necrosis factor-α and interferon-γ, controls the proliferation and invasion of several different types of cancer cells. Interleukin-6 (IL-6) is known to play an important role in the glioma cell growth and invasion. The present study aimed to investigate the relationship between IL-6 and SDCBP in glioma cells. SDCBP expression was knocked down in two glioma cell lines (T98G and U87) by small interfering RNA (siRNA) transfection. Cell proliferation and invasion were significantly repressed following SDCBP knockdown, and there was a positive correlation between SDCBP and IL-6 expression levels in glioma tissues. IL-6 stimulation dose- and time-dependently induced SDCBP expression at both mRNA and protein levels. Furthermore, pre-treatment with the Janus kinase 2 (JAK2) inhibitor AG490 abolished the IL-6-induced SDCBP expression, suggesting that the effect of IL-6 on SDCBP transcription is dependent on JAK2/signal transducer and activator of transcription 3 (STAT3) signaling. Finally, IL-6 did not stimulate glioma cell growth or invasion when SDCBP expression was suppressed. In summary, our results suggest that IL-6 promotes glioma cell proliferation and invasion by inducing SDCBP expression, which is mediated by JAK2/STAT3 signaling.

Effects of syndecan-1 on the expression of syntenin and the migration of U251 glioma cells

Glioma is the most frequently occuring primary brain tumor. Syndecan-1 (SDC1) expression is related to poor prognosis of numerous human malignancies including glioma. Syndecan binding protein (SDCBP) is an important partner for SDC1. The present study investigated whether SDC1 and SDCBP are expressed in glioma and their functions on glioma cell migration. An immunohistochemical assay revealed that SDC1 and SDCBP were expressed and were positively related to malignant level of glioma (SDC1, r_s=0.576, P=0.001; SDCBP, r_s=0.661, P<0.001). Moreover, the protein levels of SDC1 were positively correlated with those of SDCBP in glioma tissues (r_s=0.628, P=0.001). In U251 glioma cells, protein levels of SDC1 and SDCBP were both upregulated in U251 cells with SDC1 overexpression, while downregulated with SDC1 knockdown. Transwell assay and scratch-wound healing assay showed that SDC1 overexpression significantly increased U251 cell migration, while SDC1 knockdown had the opposite effects. Rac1 activity, signal transducer and activator of transcription 3 (STAT3) phosphorylation, as well as expression of matrix metalloproteinase 2 (MMP2) and MMP9 was significantly increased by SDC1 overexpression, while was decreased by SDC1 knockdown. In conclusion, SDC1 overexpression upregulated SDCBP expression, and promoted glioma cell migration via Rac1 activation.

Inhibition of radiation-induced glioblastoma invasion by genetic and pharmacological targeting of MDA-9/Syntenin

Glioblastoma multiforme (GBM) is an intractable tumor despite therapeutic advances, principally because of its invasive properties. Radiation is a staple in therapeutic regimens, although cells surviving radiation can become more aggressive and invasive. Subtraction hybridization identified melanoma differentiation-associated gene 9 [MDA-9/Syntenin; syndecan-binding protein (SDCBP)] as a differentially regulated gene associated with aggressive cancer phenotypes in melanoma. MDA-9/Syntenin, a highly conserved double-PDZ domain-containing scaffolding protein, is robustly expressed in human-derived GBM cell lines and patient samples, with expression increasing with tumor grade and correlating with shorter survival times and poorer response to radiotherapy. Knockdown of MDA-9/Syntenin sensitizes GBM cells to radiation, reducing postradiation invasion gains. Radiation induces Src and EGFRvIII signaling, which is abrogated through MDA-9/Syntenin down-regulation. A specific inhibitor of MDA-9/Syntenin activity, PDZ1i (113B7), identified through NMR-guided fragment-based drug design, inhibited MDA-9/Syntenin binding to EGFRvIII, which increased following radiation. Both genetic (shmda-9) and pharmacological (PDZ1i) targeting of MDA-9/Syntenin reduced invasion gains in GBM cells following radiation. Although not affecting normal astrocyte survival when combined with radiation, PDZ1i radiosensitized GBM cells. PDZ1i inhibited crucial GBM signaling involving FAK and mutant EGFR, EGFRvIII, and abrogated gains in secreted proteases, MMP-2 and MMP-9, following radiation. In an in vivo glioma model, PDZ1i resulted in smaller, less invasive tumors and enhanced survival. When combined with radiation, survival gains exceeded radiotherapy alone. MDA-9/Syntenin (SDCBP) provides a direct target for therapy of aggressive cancers such as GBM, and defined small-molecule inhibitors such as PDZ1i hold promise to advance targeted brain cancer therapy.

MDA-9/Syntenin-Slug transcriptional complex promote epithelial-mesenchymal transition and invasion/metastasis in lung adenocarcinoma

Melanoma differentiation-associated gene-9 (MDA-9)/Syntenin is a novel therapeutic target because it plays critical roles in cancer progression and exosome biogenesis. Here we show that Slug, a key epithelial-mesenchymal-transition (EMT) regulator, is a MDA-9/Syntenin downstream target. Mitogen EGF stimulation increases Slug expression and MDA-9/Syntenin nuclear translocation. MDA-9/Syntenin uses its PDZ1 domain to bind with Slug, and this interaction further leads to HDAC1 recruitment, up-regulation of Slug transcriptional repressor activity, enhanced Slug-mediated EMT, and promotion of cancer invasion and metastasis. The PDZ domains and nuclear localization of MDA-9/Syntenin are both required for promoting Slug-mediated cancer invasion. Clinically, patients with high MDA-9/Syntenin and high Slug expressions were associated with poor overall survival compared to those with low expression in lung adenocarcinomas. Our findings provide evidence that MDA-9/Syntenin acts as a pivotal adaptor of Slug and it transcriptionally enhances Slug-mediated EMT to promote cancer invasion and metastasis.

miR-216b suppresses breast cancer growth and metastasis by targeting SDCBP

Breast cancer is the most deadly cancer among women and the second leading cause of cancer death worldwide. Treatment effectiveness is complicated with tumor invasiveness/drug resistance. To tailor treatments more effectively to individual patients, it is important to define tumor growth and metastasis at molecular levels. SDCBP is highly overexpressed and associated with a strikingly poor prognosis in breast cancer. However the post transcriptional regulation of SDCBP overexpression remains to be an unexplored area. Our study reveals that miR-216b directly regulates SDCBP expression by binding to its 3'UTR region. miR-216b is a tumor suppressive miRNA and it is underexpressed during metastatic breast cancer. Consequently, overexpression of miR-216b resulted in decreased proliferation, migration and invasion in BC cell lines by modulating the expression of SDCBP. Inhibition of miR-216b divergent the tumor suppressive role by inducing the growth proliferation, migration and invasion in vitro. There is therefore a negative correlation between the expression of miR-216b and its target gene SDCBP in the BC tissue samples as well as cell lines. Simultaneous expression of miR-216b and SDCBP rescued the growth, migration and invasion effect suggesting that tumor suppressive action of miR-216b may be directly mediated by SDCBP. In summary, the study identifies miR-216b as a regulator of SDCBP expression in breast cancer which can potentially be targeted for developing newer therapies for the effective treatment of this killer disease.

The Genetic Architecture of Murine Glutathione Transferases

Glutathione S-transferase (GST) genes play a protective role against oxidative stress and may influence disease risk and drug pharmacokinetics. In this study, massive multiscalar trait profiling across a large population of mice derived from a cross between C57BL/6J (B6) and DBA2/J (D2)—the BXD family—was combined with linkage and bioinformatic analyses to characterize mechanisms controlling GST expression and to identify downstream consequences of this variation. Similar to humans, mice show a wide range in expression of GST family members. Variation in the expression of Gsta4, Gstt2, Gstz1, Gsto1, and Mgst3 is modulated by local expression QTLs (eQTLs) in several tissues. Higher expression of Gsto1 in brain and liver of BXD strains is strongly associated (P < 0.01) with inheritance of the B6 parental allele whereas higher expression of Gsta4 and Mgst3 in brain and liver, and Gstt2 and Gstz1 in brain is strongly associated with inheritance of the D2 parental allele. Allele-specific assays confirmed that expression of Gsto1, Gsta4, and Mgst3 are modulated by sequence variants within or near each gene locus. We exploited this endogenous variation to identify coexpression networks and downstream targets in mouse and human. Through a combined systems genetics approach, we provide new insight into the biological role of naturally occurring variants in GST genes.

Evolving Strategies for Therapeutically Targeting Cancer Stem Cells

Cancer is a multifactor and multistep process that is affected intrinsically by the genetic and epigenetic makeup of tumor cells and extrinsically by the host microenvironment and immune system. A key component of cancer involves a unique subpopulation of highly malignant cancerous cells referred to as cancer stem cells (CSCs). CSCs are positioned at the apex of the tumor hierarchy with an ability to both self-renew and also generate non-CSC/differentiated progeny, which contribute to the majority of the tumor mass. CSCs undergo functional changes and show plasticity that is stimulated by specific microenvironmental cues and interactions in the tumor niche, which contribute to the complexity and heterogeneity of the CSC population. The prognostic value of CSCs in the clinic is evident since there are many examples in which CSCs serve as markers for poor patient prognosis. CSCs are innately resistant to many standard therapies and they display anoikis resistance, immune evasion, tumor dormancy, and field cancerization, which may result in metastasis and relapse. Many academic laboratories and biotechnology companies are currently focusing on strategies that target CSCs. Combination therapies, epigenetic modifiers, stemness inhibitors, CSC surface marker-based therapies, and immunotherapy-based CSC-targeting drugs are currently undergoing clinical trials. Potential new targets/strategies in CSC-targeted therapy include MDA-9/Syntenin (SDCBP), Patched (PTCH), epigenetic targets, noncoding RNAs, and differentiation induction. Defining ways of targeting and destroying CSCs holds potential to impact significantly on cancer therapy, including prevention of metastasis and cancer recurrence.

Syntenin controls migration, growth, proliferation, and cell cycle progression in cancer cells

The scaffold protein syntenin abounds during fetal life where it is important for developmental movements. In human adulthood, syntenin gain-of-function is increasingly associated with various cancers and poor prognosis. Depending on the cancer model analyzed, syntenin affects various signaling pathways. We previously have shown that syntenin allows syndecan heparan sulfate proteoglycans to escape degradation. This indicates that syntenin has the potential to support sustained signaling of a plethora of growth factors and adhesion molecules. Here, we aim to clarify the impact of syntenin loss-of-function on cancer cell migration, growth, and proliferation, using cells from various cancer types and syntenin shRNA and siRNA silencing approaches. We observed decreased migration, growth, and proliferation of the mouse melanoma cell line B16F10, the human colon cancer cell line HT29 and the human breast cancer cell line MCF7. We further documented that syntenin controls the presence of active β1 integrin at the cell membrane and G1/S cell cycle transition as well as the expression levels of CDK4, Cyclin D2, and Retinoblastoma proteins. These data confirm that syntenin supports the migration and growth of tumor cells, independently of their origin, and further highlight the attractiveness of syntenin as potential therapeutic target.

MDA-9/Syntenin Control

MDA-9/Syntenin is a small PDZ domain containing scaffolding protein with diverse array of functions regulating membrane trafficking, cell adhesion, neural, and synaptic development, ubiquitination, and exosome biogenesis. An appreciable number of studies also established a pivotal role of MDA-9/Syntenin in cancer development and progression. In this review, we will discuss the dynamic role of MDA-9/Syntenin in regulating normal and abnormal fate of various cellular processes.

CRM197 in Combination With shRNA Interference of VCAM-1 Displays Enhanced Inhibitory Effects on Human Glioblastoma Cells

CRM197 is a naturally nontoxic diphtheria toxin mutant that binds and inhibits heparin-binding epidermal growth factor-like growth factor. CRM197 serves as carrier protein for vaccine and other therapeutic agents. CRM197 also inhibits the growth, migration, invasion, and induces apoptosis in various tumors. Vascular cell adhesion molecule-1 (VCAM-1) is an important cell surface adhesion molecule associated with malignancy of gliomas. In this work, we aimed to investigate the role and mechanism of CRM197 combined with shRNA interference of VCAM-1 (shRNA-VCAM-1) on the migration, invasion, and apoptosis of glioblastoma cells. U87 and U251 human glioblastoma cells were treated with CRM197 (10 µg/ml) and shRNA interfering technology was employed to silence VCAM-1 expression. Cell viability, migration, invasiveness, and apoptosis were assessed with CCK8, Transwell and Annexin V-PE/7-AAD staining. Activation of cleaved caspase-3, 8, and 9, activity of matrix metalloproteinase-2/9 (MMP-2/9), and expression of phosphorylated Akt (p-Akt) were also checked. Results showed that CRM197 and shRNA-VCAM-1 not only significantly inhibited the cell proliferation, migration, invasion, but also promoted the apoptosis of U87 and U251 cells. Combined treatment of both displayed enhanced inhibitory effects on the malignant biological behavior of glioma cells. The activation of cleaved caspase-3, 8, 9 was promoted, activity of MMP-2 and MMP-9 and expression of p-Akt were inhibited significantly by the treatment of CRM197 and shRNA-VCAM-1 alone or in combination, indicating that the combination of CRM197 with shRNA-VCAM-1 additively inhibited the malignant behavior of human glioblastoma cells via activating caspase-3, 8, 9 as well as inhibiting MMP-2, MMP-9, and Akt pathway.

Glioma invasion mediated by the p75 neurotrophin receptor (p75(NTR)/CD271) requires regulated interaction with PDLIM1

The invasive nature of glioblastoma renders them incurable by current therapeutic interventions. Using a novel invasive human glioma model, we previously identified the neurotrophin receptor p75^NTR (aka CD271) as a mediator of glioma invasion. Herein, we provide evidence that preventing phosphorylation of p75^NTR on S303 by pharmacological inhibition of PKA, or by a mutational strategy (S303G), cripples p75^NTR-mediated glioma invasion resulting in serine phosphorylation within the C-terminal PDZ-binding motif (SPV) of p75^NTR. Consistent with this, deletion (ΔSPV) or mutation (SPM) of the PDZ motif results in abrogation of p75^NTR-mediated invasion. Using a peptide-based strategy, we identified PDLIM1 as a novel signaling adaptor for p75^NTR and provide the first evidence for a regulated interaction via S425 phosphorylation. Importantly, PDLIM1 was shown to interact with p75^NTR in highly invasive patient-derived glioma stem cells/tumor-initiating cells and shRNA knockdown of PDLIM1 in vitro and in vivo results in complete ablation of p75^NTR-mediated invasion. Collectively, these data demonstrate a requirement for a regulated interaction of p75^NTR with PDLIM1 and suggest that targeting either the PDZ domain interactions and/or the phosphorylation of p75^NTR by PKA could provide therapeutic strategies for patients with glioblastoma.

Examination of Epigenetic and other Molecular Factors Associated with mda-9/Syntenin Dysregulation in Cancer Through Integrated Analyses of Public Genomic Datasets

mda-9/Syntenin (melanoma differentiation-associated gene 9) is a PDZ domain containing, cancer invasion-related protein. In this study, we employed multiple integrated bioinformatic approaches to identify the probable epigenetic factors, molecular pathways, and functionalities associated with mda-9 dysregulation during cancer progression. Analyses of publicly available genomic data (e.g., expression, copy number, methylation) from TCGA, GEO, ENCODE, and Human Protein Atlas projects led to the following observations: (a) mda-9 expression correlates with both copy number and methylation level of an intronic CpG site (cg1719774) located downstream of the CpG island, (b) cg1719774 methylation is a likely prognostic marker in glioma, (c) among 22 cancer types, melanoma exhibits the highest mda-9 level, and lowest level of methylation at cg1719774, (d) cg1719774 hypomethylation is also associated with histone modifications (at the mda-9 locus) indicative of more active transcription, (e) using Gene Set Enrichment Analysis (GSEA), and the Virtual Gene Overexpression or Repression (VIGOR) analytical scheme, we were able to predict mda-9's association with extracellular matrix organization (e.g., MMPs, collagen, integrins), IGFBP2 and NF-κB signaling pathways, phospholipid metabolism, cytokines (e.g., interleukins), CTLA-4, and components of complement cascade pathways. Indeed, previous publications have shown that many of the aforementioned genes and pathways are associated with mda-9's functionality.

Syntenin regulates TGF-β1-induced Smad activation and the epithelial-to-mesenchymal transition by inhibiting caveolin-mediated TGF-β type I receptor internalization

Syntenin, a tandem PDZ domain containing scaffold protein, functions as a positive regulator of cancer cell progression in several human cancers. We report here that syntenin positively regulates transforming growth factor (TGF)-β1-mediated Smad activation and the epithelial-to-mesenchymal transition (EMT) by preventing caveolin-1-mediated internalization of TGF-β type I receptor (TβRI). Knockdown of syntenin suppressed TGF-β1-mediated cell migration, transcriptional responses and Smad2/3 activation in various types of cells; however, overexpression of syntenin facilitated TGF-β1-mediated responses. In particular, syntenin knockdown abolished both the basal and TGF-β1-mediated repression of E-cadherin expression, as well as induction of vimentin expression along with Snail and Slug upregulation; thus, blocking the TGF-β1-induced EMT in A549 cells. In contrast, overexpression of syntenin exhibited the opposite effect. Knockdown of syntenin-induced ubiquitination and degradation of TβRI, but not TGF-β type II receptor, leading to decreased TβRI expression at the plasma membrane. Syntenin associated with TβRI at its C-terminal domain and a syntenin mutant lacking C-terminal domain failed to increase TGF-β1-induced responses. Biochemical analyzes revealed that syntenin inhibited the interaction between caveolin-1 and TβRI and knockdown of syntenin induced a massive internalization of TβRI and caveolin-1 from lipid rafts, indicating that syntenin may increase TGF-β signaling by inhibiting caveolin-1-dependent internalization of TβRI. Moreover, a positive correlation between syntenin expression and phospho-Smad2 levels is observed in human lung tumors. Taken together, these findings demonstrate that syntenin may act as an important positive regulator of TGF-β signaling by regulating caveolin-1-mediated internalization of TβRI; thus, providing a novel function for syntenin that is linked to cancer progression.

In vivo modeling of malignant glioma: the road to effective therapy

Despite an increased emphasis on developing new therapies for malignant gliomas, they remain among the most intractable tumors faced today as they demonstrate a remarkable ability to evade current treatment strategies. Numerous candidate treatments fail at late stages, often after showing promising preclinical results. This disconnect highlights the continued need for improved animal models of glioma, which can be used to both screen potential targets and authentically recapitulate the human condition. This review examines recent developments in the animal modeling of glioma, from more established rat models to intriguing new systems using Drosophila and zebrafish that set the stage for higher throughput studies of potentially useful targets. It also addresses the versatility of mouse modeling using newly developed techniques recreating human protocols and sophisticated genetically engineered approaches that aim to characterize the biology of gliomagenesis. The use of these and future models will elucidate both new targets and effective combination therapies that will impact on disease management.

Targeting tumor invasion: the roles of MDA-9/Syntenin

INTRODUCTION

Melanoma differentiation-associated gene - 9 (MDA-9)/Syntenin has become an increasingly popular focus for investigation in numerous cancertypes. Originally implicated in melanoma metastasis, it has diverse cellular roles and is consistently identified as a regulator of tumor invasion and angiogenesis. As a potential target for inhibiting some of the most lethal aspects of cancer progression, further insight into the function of MDA-9/Syntenin is mandatory.

AREAS COVERED

Recent literature and seminal articles were reviewed to summarize the latest collective understanding of MDA-9/Syntenin's role in normal and cancerous settings. Insights into its participation in developmental processes are included, as is the functional significance of the N- and C-terminals and PDZ domains of MDA-9/Syntenin. Current reports highlight the clinical significance of MDA-9/Syntenin expression level in a variety of cancers, often correlating directly with reduced patient survival. Also presented are assessments of roles of MDA-9/Syntenin in cancer progression as well as its functions as an intracellular adapter molecule.

EXPERT OPINION

Multiple studies demonstrate the importance of MDA-9/Syntenin in tumor invasion and progression. Through the use of novel drug design approaches, this protein may provide a worthwhile therapeutic target. As many conventional therapies do not address, or even enhance, tumor invasion, an anti-invasive approach would be a worthwhile addition in cancer therapy.