Netrin-4 promotes glioblastoma cell proliferation through integrin β4 signaling

IGF2BP2 inhibits invasion and migration of clear cell renal cell carcinoma via targeting Netrin-4 in an m6A-dependent manner

Clear cell renal cell carcinoma (ccRCC), the most common subtype of renal cell carcinoma, often leads to a poor prognosis due to metastasis. The investigation of N6-methyladenosine (m6A) methylation, a crucial RNA modification, and its role in ccRCC, particularly through the m6A reader insulin-like growth factor 2 mRNA-binding protein 2 (IGF2BP2), revealed significant insights. We found that IGF2BP2 was notably downregulated in ccRCC, which correlated with tumor aggressiveness and poor prognosis. Thus, IGFBP2 has emerged as an independent prognostic factor of ccRCC. Moreover, a strong positive correlation was observed between the expression of IGF2BP2 and Netrin-4. Netrin-4 was also downregulated in ccRCC, and its lower levels were associated with increased malignancy and poor prognosis. Overexpression of IGF2BP2 and Netrin-4 suppressed the invasion and migration of ccRCC cells, while Netrin-4 knockdown reversed these effects in ccRCC cell lines. RNA immunoprecipitation (RIP)-quantitative polymerase chain reaction validated the robust enrichment of Netrin-4 mRNA in anti-IGF2BP2 antibody immunoprecipitates. MeRlP showed significantly increased Netrin4 m6A levels after lGF2BP2 overexpression. Moreover, we found that IGF2BP2 recognized and bound to the m6A site within the coding sequence of Netrin-4, enhancing its mRNA stability. Collectively, these results showed that IGF2BP2 plays a suppressive role in the invasion and migration of ccRCC cells by targeting Netrin-4 in an m6A-dependent manner. These findings underscore the potential of IGF2BP2/Netrin-4 as a promising prognostic biomarker and therapeutic target in patients with ccRCC metastasis.

EXOSC5 maintains cancer stem cell activity in endometrial cancer by regulating the NTN4/integrin β1 signalling axis

Endometrial carcinoma (EC) is a common type of uterine cancer in developed countries, originating from the uterine epithelium. The incidence rate of EC in Taiwan has doubled from 2005. Cancer stem cells (CSCs) are a subpopulation of cancer cells that have high tumorigenicity and play a crucial role in the malignant processes of cancer. Targeting molecules associated with CSCs is essential for effective cancer treatments. This study delves into the role of Exosome component 5 (EXOSC5) in EC. Data from The Cancer Genome Atlas suggests a correlation between high EXOSC5 mRNA expression and unfavorable EC prognosis. EXOSC5 knockdown diminished EC-CSC self-renewal and reduced expression of key cancer stemness proteins, including c-MYC and SOX2. Intriguingly, this knockdown significantly curtailed tumorigenicity and CSC frequency in EC tumor spheres. A mechanistic examination revealed a reduction in netrin4 (NTN4) levels in EXOSC5-depleted EC cells. Moreover, NTN4 treatment amplified EC cell CSC activity and, when secreted, NTN4 partnered with integrin β1, subsequently triggering the FAK/SRC axis to elevate c-MYC activity. A clear positive relation between EXOSC5 and NTN4 was evident in 93 EC tissues. In conclusion, EXOSC5 augments NTN4 expression, activating c-MYC via the integrin β1/FAK/SRC pathway, offering potential avenues for EC diagnosis and treatment.

Netrin-4 synthesized in satellite cell-derived myoblasts stimulates autonomous fusion

Satellite cells are indispensable for skeletal muscle regeneration and hypertrophy by forming nascent myofibers (myotubes). They synthesize multi-potent modulator netrins (secreted subtypes: netrin-1, -3, and -4), originally found as classical neural axon guidance molecules. While netrin-1 and -3 have key roles in myogenic differentiation, the physiological significance of netrin-4 is still unclear. This study examined whether netrin-4 regulates myofiber type commitment and myotube formation. Initially, the expression profiles indicated that satellite cells isolated from the extensor digitorum longus muscle (EDL muscle: fast-twitch myofiber-abundant) expressed slightly more netrin-4 than the soleus muscle (slow-type abundant) cells. As netrin-4 knockdown inhibited both slow- and fast-type myotube formation, netrin-4 may not directly regulate myofiber type commitment. However, netrin-4 knockdown in satellite cell-derived myoblasts reduced the myotube fusion index, while exogenous netrin-4 promoted myotube formation, even though netrin-4 expression level was maximum during the initiation stage of myogenic differentiation. Furthermore, netrin-4 knockdown also inhibited MyoD (a master transcriptional factor of myogenesis) and Myomixer (a myoblast fusogenic molecule) expression. These data suggest that satellite cells synthesize netrin-4 during myogenic differentiation initiation to promote their own fusion, stimulating the MyoD-Myomixer signaling axis.

Netrin Family Genes as Prognostic Markers and Therapeutic Targets for Clear Cell Renal Cell Carcinoma: Netrin-4 Acts through the Wnt/β-Catenin Signaling Pathway

Clear cell renal cell carcinoma (ccRCC, or KIRC) is the most common type of kidney cancer, originating within the renal cortex. The current outcomes for early diagnosis and late treatment of ccRCC are unsatisfactory. Therefore, it is important to explore tumor biomarkers and therapeutic opportunities for ccRCC. In this study, we used bioinformatics methods to systematically evaluate the expression and prognostic value of Netrin family genes in ccRCC. Through our analysis, three potential biomarkers for ccRCC were identified, namely NTNG1, NTNG2, and NTN4. Moreover, we performed in vitro and in vivo experiments to explore the possible biological roles of NTN4 and found that NTN4 could regulate ccRCC development through Wnt/β-catenin signaling. We elucidate the molecular mechanism by which NTN4 modulates β-catenin expression and nuclear translocation to inhibit ccRCC progression, providing a new theoretical basis for developing therapeutic targets for ccRCC. Thus, we suggest that Netrin-related studies may offer new directions for the diagnosis, treatment, and prognosis of ccRCC patients.

Regulation of Kinase Signaling Pathways by α6β4-Integrins and Plectin in Prostate Cancer

Hemidesmosomes (HDs) are adhesive structures that ensure stable anchorage of cells to the basement membrane. They are formed by α6β4-integrin heterodimers and linked to intermediate filaments via plectin. It has been reported that one of the most common events during the pathogenesis of prostate cancer (PCa) is the loss of HD organization. While the expression levels of β4-integrins are strongly reduced, the expression levels of α6-integrins and plectin are maintained or even elevated, and seem to promote tumorigenic properties of PCa cells, such as proliferation, invasion, metastasis, apoptosis- and drug-resistance. In this review, we discuss the potential mechanisms of how HD components might contribute to various cellular signaling pathways to promote prostate carcinogenesis. Moreover, we summarize the current knowledge on the involvement of α6β4-integrins and plectin in PCa initiation and progression.

Fate mapping of neural stem cell niches reveals distinct origins of human cortical astrocytes

Progenitors of the developing human neocortex reside in the ventricular and outer subventricular zones (VZ and OSVZ, respectively). However, whether cells derived from these niches have similar developmental fates is unknown. By performing fate mapping in primary human tissue, we demonstrate that astrocytes derived from these niches populate anatomically distinct layers. Cortical plate astrocytes emerge from VZ progenitors and proliferate locally, while putative white matter astrocytes are morphologically heterogeneous and emerge from both VZ and OSVZ progenitors. Furthermore, via single-cell sequencing of morphologically defined astrocyte subtypes using Patch-seq, we identify molecular distinctions between VZ-derived cortical plate astrocytes and OSVZ-derived white matter astrocytes that persist into adulthood. Together, our study highlights a complex role for cell lineage in the diversification of human neocortical astrocytes.

The risk variant rs11836367 contributes to breast cancer onset and metastasis by attenuating Wnt signaling via regulating NTN4 expression

Most genome-wide association study (GWAS)-identified breast cancer-associated causal variants remain uncharacterized. To provide a framework of understanding GWAS-identified variants to function, we performed a comprehensive study of noncoding regulatory variants at the NTN4 locus (12q22) and NTN4 gene in breast cancer etiology. We find that rs11836367 is the more likely causal variant, disrupting enhancer activity in both enhancer reporter assays and endogenous genome editing experiments. The protective T allele of rs11837367 increases the binding of GATA3 to the distal enhancer and up-regulates NTN4 expression. In addition, we demonstrate that loss of NTN4 gene in mice leads to tumor earlier onset, progression, and metastasis. We discover that NTN4, as a tumor suppressor, can attenuate the Wnt signaling pathway by directly binding to Wnt ligands. Our findings bridge the gaps among breast cancer-associated single-nucleotide polymorphisms, transcriptional regulation of NTN4, and breast cancer biology, which provides previously unidentified insights into breast cancer prediction and prevention.

Elevated RGMA Expression Predicts Poor Prognosis in Patients with Glioblastoma

Background

Glioblastoma (GBM) is the most aggressive type of human brain tumor with a poor prognosis and a low survival rate. Secreted proteins from tumors are recently considered as important modulators to promote tumorigenesis by communicating with microenvironments. Repulsive guidance molecule A (RGMA) was initially characterized as an axon guidance molecule after secretion in the brain during embryogenesis but has not been studied in GBM. In this study, we investigated secreted gene expression patterns and the correlation between RGMA expression and prognosis in GBM using in silico analysis.

Methods

RGMA mRNA levels in normal human astrocyte (NHA), human glioma cells, and GBM patient-derived glioma stem cells (GSCs) were assessed by qRT‐PCR. Patient survival analysis was performed with the Kaplan–Meier curve and univariate and multivariate analyses using publicly available datasets. The predictive roles of RGMA in progressive malignancy were evaluated using Gene Ontology (GO), Kyoto Encyclopedia of Genes and Genomes (KEGG), and Gene Set Enrichment Analysis (GSEA).

Results

RGMA mRNA expression was elevated in glioma cells and GSCs compared with NHA and correlated with unfavorable prognosis in glioma patients. Thus, RGMA could serve as an independent predictive factor for GBM. Furthermore, the increased levels of RGMA expression and its putative receptor, neogenin (NEO1), were associated with poor patient survival rates in GBM.

Conclusion

We identified RGMA as an independent prognostic biomarker for progressive malignancy in glioblastoma and address the possibilities to develop novel therapeutic strategies against glioblastoma.

Integrin β4 as a Potential Diagnostic and Therapeutic Tumor Marker

Integrin β4 (ITGβ4) is a class of transmembrane adhesion molecules composed of hemidesmosomes (HDs). Its unique long intracellular domain provides intricate signal transduction functions. These signal transduction effects are especially prominent in tumors. Many recent studies have shown that integrin β4 is differentially expressed in various tumors, and it plays a vital role in tumor invasion, proliferation, epithelial–mesenchymal transition, and angiogenesis. Therefore, we categorize the research related to integrin β4, starting from its structure and function in tumor tissues, and provide a basic description. Based on its structure and function, we believe that integrin β4 can be used as a tumor marker. In clinical practice, it is described as a diagnostic marker for the targeted treatment of cancer and will be helpful in the clinical diagnosis and treatment of tumors.

Transcriptomics-Based Phenotypic Screening Supports Drug Discovery in Human Glioblastoma Cells

Simple Summary

Glioblastoma (GBM) remains a particularly challenging cancer, with an aggressive phenotype and few promising treatment options. Future therapy will rely heavily on diagnosing and targeting aggressive GBM cellular phenotypes, both before and after drug treatment, as part of personalized therapy programs. Here, we use a genome-wide drug-induced gene expression (DIGEX) approach to define the cellular drug response phenotypes associated with two clinical drug candidates, the phosphodiesterase 10A inhibitor Mardepodect and the multi-kinase inhibitor Regorafenib. We identify genes encoding specific drug targets, some of which we validate as effective antiproliferative agents and combination therapies in human GBM cell models, including HMGCoA reductase (HMGCR), salt-inducible kinase 1 (SIK1), bradykinin receptor subtype B2 (BDKRB2), and Janus kinase isoform 2 (JAK2). Individual, personalized treatments will be essential if we are to address and overcome the pharmacological plasticity that GBM exhibits, and DIGEX will play a central role in validating future drugs, diagnostics, and possibly vaccine candidates for this challenging cancer.

Abstract

We have used three established human glioblastoma (GBM) cell lines—U87MG, A172, and T98G—as cellular systems to examine the plasticity of the drug-induced GBM cell phenotype, focusing on two clinical drugs, the phosphodiesterase PDE10A inhibitor Mardepodect and the multi-kinase inhibitor Regorafenib, using genome-wide drug-induced gene expression (DIGEX) to examine the drug response. Both drugs upregulate genes encoding specific growth factors, transcription factors, cellular signaling molecules, and cell surface proteins, while downregulating a broad range of targetable cell cycle and apoptosis-associated genes. A few upregulated genes encode therapeutic targets already addressed by FDA approved drugs, but the majority encode targets for which there are no approved drugs. Amongst the latter, we identify many novel druggable targets that could qualify for chemistry-led drug discovery campaigns. We also observe several highly upregulated transmembrane proteins suitable for combined drug, immunotherapy, and RNA vaccine approaches. DIGEX is a powerful way of visualizing the complex drug response networks emerging during GBM drug treatment, defining a phenotypic landscape which offers many new diagnostic and therapeutic opportunities. Nevertheless, the extreme heterogeneity we observe within drug-treated cells using this technique suggests that effective pan-GBM drug treatment will remain a significant challenge for many years to come.

Basement membrane stiffness determines metastases formation

The basement membrane (BM) is a special type of extracellular matrix and presents the major barrier cancer cells have to overcome multiple times to form metastases. Here we show that BM stiffness is a major determinant of metastases formation in several tissues and identify netrin-4 (Net4) as a key regulator of BM stiffness. Mechanistically, our biophysical and functional analyses in combination with mathematical simulations show that Net4 softens the mechanical properties of native BMs by opening laminin node complexes, decreasing cancer cell potential to transmigrate this barrier despite creating bigger pores. Our results therefore reveal that BM stiffness is dominant over pore size, and that the mechanical properties of 'normal' BMs determine metastases formation and patient survival independent of cancer-mediated alterations. Thus, identifying individual Net4 protein levels within native BMs in major metastatic organs may have the potential to define patient survival even before tumour formation. The ratio of Net4 to laminin molecules determines BM stiffness, such that the more Net4, the softer the BM, thereby decreasing cancer cell invasion activity.

Expression Profiling of Glioblastoma Cell Lines Reveals Novel Extracellular Matrix-Receptor Genes Correlated With the Responsiveness of Glioma Patients to Ionizing Radiation

Glioblastoma (GBM) is the most lethal and frequent type of brain tumor, leading patients to death in approximately 14 months after diagnosis. GBM treatment consists in surgical removal followed by radio and chemotherapy. However, tumors commonly relapse and the treatment promotes only a slight increase in patient survival. Thus, uncovering the cellular mechanisms involved in GBM resistance is of utmost interest, and the use of cell lines has been shown to be an extremely important tool. In this work, the exploration of RNAseq data from different GBM cell lines revealed different expression signatures, distinctly correlated with the behavior of GBM cell lines regarding proliferation indexes and radio-resistance. U87MG and U138MG cells, which presented expressively reduced proliferation and increased radio-resistance, showed a particular expression signature encompassing enrichment in many extracellular matrix (ECM) and receptor genes. Contrasting, U251MG and T98G cells, that presented higher proliferation and sensibility to radiation, exhibited distinct signatures revealing consistent enrichments for DNA repair processes and although several genes from the ECM-receptor pathway showed up-regulation, enrichments for this pathway were not detected. The ECM-receptor is a master regulatory pathway that is known to impact several cellular processes including: survival, proliferation, migration, invasion, and DNA damage signaling and repair, corroborating the associations we found. Furthermore, searches to The Cancer Genome Atlas (TCGA) repository revealed prognostic correlations with glioma patients for the majority of genes highlighted in the signatures and led to the identification of 31 ECM-receptor genes individually correlated with radiation responsiveness. Interestingly, we observed an association between the number of upregulated genes and survivability greater than 5 years after diagnosis, where almost all the patients that presented 21 or more upregulated genes were deceased before 5 years. Altogether our findings suggest the clinical relevance of ECM-receptor genes signature found here for radiotherapy decision and as biomarkers of glioma prognosis.

Rapid 3D Bioprinting of Glioblastoma Model Mimicking Native Biophysical Heterogeneity

Glioblastoma multiforme (GBM) is the most lethal primary brain tumor characterized by high cellular and molecular heterogeneity, hypervascularization, and innate drug resistance. Cellular components and extracellular matrix (ECM) are the two primary sources of heterogeneity in GBM. Here, biomimetic tri-regional GBM models with tumor regions, acellular ECM regions, and an endothelial region with regional stiffnesses patterned corresponding to the GBM stroma, pathological or normal brain parenchyma, and brain capillaries, are developed. Patient-derived GBM cells, human endothelial cells, and hyaluronic acid derivatives are used to generate a species-matched and biochemically relevant microenvironment. This in vitro study demonstrates that biophysical cues are involved in various tumor cell behaviors and angiogenic potentials and promote different molecular subtypes of GBM. The stiff models are enriched in the mesenchymal subtype, exhibit diffuse invasion of tumor cells, and induce protruding angiogenesis and higher drug resistance to temozolomide. Meanwhile, the soft models demonstrate enrichment in the classical subtype and support expansive cell growth. The three-dimensional bioprinting technology utilized in this study enables rapid, flexible, and reproducible patient-specific GBM modeling with biophysical heterogeneity that can be employed by future studies as a tunable system to interrogate GBM disease mechanisms and screen drug compounds.

Involvement of Netrins and Their Receptors in Neuronal Migration in the Cerebral Cortex

In mammals, excitatory cortical neurons develop from the proliferative epithelium and progenitor cells in the ventricular zone and subventricular zone, and migrate radially to the cortical plate, whereas inhibitory GABAergic interneurons are born in the ganglionic eminence and migrate tangentially. The migration of newly born cortical neurons is tightly regulated by both extracellular and intracellular signaling to ensure proper positioning and projections. Non-cell-autonomous extracellular molecules, such as growth factors, axon guidance molecules, extracellular matrix, and other ligands, play a role in cortical migration, either by acting as attractants or repellents. In this article, we review the guidance molecules that act as cell-cell recognition molecules for the regulation of neuronal migration, with a focus on netrin family proteins, their receptors, and related molecules, including neogenin, repulsive guidance molecules (RGMs), Down syndrome cell adhesion molecule (DSCAM), fibronectin leucine-rich repeat transmembrane proteins (FLRTs), and draxin. Netrin proteins induce attractive and repulsive signals depending on their receptors. For example, binding of netrin-1 to deleted in colorectal cancer (DCC), possibly together with Unc5, repels migrating GABAergic neurons from the ventricular zone of the ganglionic eminence, whereas binding to α3β1 integrin promotes cortical interneuron migration. Human genetic disorders associated with these and related guidance molecules, such as congenital mirror movements, schizophrenia, and bipolar disorder, are also discussed.

The pan-cancer landscape of netrin family reveals potential oncogenic biomarkers

Recent cancer studies have found that the netrin family of proteins plays vital roles in the development of some cancers. However, the functions of the many variants of these proteins in cancer remain incompletely understood. In this work, we used the most comprehensive database available, including more than 10000 samples across more than 30 tumor types, to analyze the six members of the netrin family. We performed comprehensive analysis of genetic change and expression of the netrin genes and analyzed epigenetic and pathway relationships, as well as the correlation of expression of these proteins with drug sensitivity. Although the mutation rate of the netrin family is low in pan-cancer, among the tumor patients with netrin mutations, the highest number are Uterine Corpus Endometrial Carcinoma patients, accounting for 13.6% of cases (54 of 397). Interestingly, the highest mutation rate of a netrin family member is 38% for NTNG1 (152 of 397). Netrin proteins may participate in the development of endocrine-related tumors and sex hormone-targeting organ tumors. Additionally, the participation of NTNG1 and NTNG2 in various cancers shows their potential for use as new tumor markers and therapeutic targets. This analysis provides a broad molecular perspective of this protein family and suggests some new directions for the treatment of cancer.

Ischemia-induced Netrin-4 promotes neovascularization through endothelial progenitor cell activation via Unc-5 Netrin receptor B

Endothelial progenitor cells (EPCs) promote neovascularization and tissue repair by migrating to vascular injury sites; therefore, factors that enhance EPC homing to damaged tissues are of interest. Here, we provide evidence of the prominent role of the Netrin-4 (NTN4)-Unc-5 Netrin receptor B (UNC5B) axis in EPC-specific promotion of ischemic neovascularization. Our results showed that NTN4 promoted the proliferation, chemotactic migration, and paracrine effects of small EPCs (SEPCs) and significantly increased the incorporation of large EPCs (LEPCs) into tubule networks. Additionally, NTN4 prominently augmented neovascularization in mice with hindlimb ischemia by increasing the homing of exogenously transplanted EPCs to the ischemic limb and incorporating EPCs into vessels. Moreover, silencing of UNC5B, an NTN4 receptor, abrogated the NTN4-induced cellular activities of SEPCs in vitro and blood-flow recovery and neovascularization in vivo in ischemic muscle by reducing EPC homing and incorporation. These findings suggest NTN4 as an EPC-based therapy for treating angiogenesis-dependent diseases.

Netrin Family: Role for Protein Isoforms in Cancer

Netrins form a family of secreted and membrane-associated proteins. Netrins are involved in processes for axonal guidance, morphogenesis, and angiogenesis by regulating cell migration and survival. These processes are of special interest in tumor biology. From the netrin genes various isoforms are translated and regulated by alternative splicing. We review here the diversity of isoforms of the netrin family members and their known and potential roles in cancer.

EGF/EGFR upregulates and cooperates with Netrin-4 to protect glioblastoma cells from DNA damage-induced senescence

BACKGROUND

Glioblastoma multiforme (GBM) is the most malignant central nervous system tumor. Alkylating agent, temozolomide (TMZ), is currently the first-line chemotherapeutic agent for GBM. However, the sensitivity of GBM cells to TMZ is affected by many factors. And, several clinic trials, including co-administration of TMZ with other drugs, have failed in successful treatment of GBM. We have previously reported that Netrin-4 (NTN4), a laminin-like axon guidance protein, plays a protective role in GBM cell senescence upon TMZ-triggered DNA damage. However, the master regulator of NTN4 needs further elucidation. Epidermal growth factor/Epidermal growth factor receptor (EGF/EGFR) can modulate the expression of various extracellular matrix related molecules, and prevent DNA damage in GBM cells. In this study, we investigated the relationship between EGF/EGFR signaling and NTN4, and explored their effect on therapeutic efficacy in GBM cells upon TMZ treatment.

METHODS

Co-expression analysis were performed by using the RNA sequencing data from NIH 934 cell lines and from single cell RNA sequencing data of GBM tumor. The co-expressing genes were used for GO enrichment and signaling pathway enrichment. mRNA expression of the target genes were quantified by qPCR, and cell senescence were investigated by Senescence-Associated Beta-Galactosidase Staining. Protein phosphorylation were observed and analyzed by immunoblotting. The RNA sequencing data and clinical information of TMZ treated patients were extracted from TCGA-glioblastoma project, and then used for Kaplan-Meier survival analysis.

RESULTS

Analysis of RNA sequencing data revealed a potential co-expression relationship between NTN4 and EGFR. GO enrichment of EGFR-correlated genes indicated that EGFR regulates GBM cells in a manner similar to that in central nervous system development and neural cell differentiation. Pathway analysis suggested that EGFR and its related genes contribute to cell adhesion, extracellular matrix (ECM) organization and caspase related signaling. We also show that EGF stimulates NTN4 expression in GBM cells and cooperates with NTN4 to attenuate GBM cell senescence induced by DNA damage, possibly via AKT and ERK. Clinical analysis showed that co-expression of EGFR and NTN4 significantly predicts poor survival in TMZ-treated GBM patients.

CONCLUSIONS

This study indicates that EGF/EGFR regulates and cooperates with NTN4 in DNA damage resistance in GBM. Therefore, our findings provide a potential therapeutic target for GBM.

The Netrin-4/ Neogenin-1 axis promotes neuroblastoma cell survival and migration

Neogenin-1 (NEO1) is a transmembrane receptor involved in axonal guidance, angiogenesis, neuronal cell migration and cell death, during both embryonic development and adult homeostasis. It has been described as a dependence receptor, because it promotes cell death in the absence of its ligands (Netrin and Repulsive Guidance Molecule (RGM) families) and cell survival when they are present. Although NEO1 and its ligands are involved in tumor progression, their precise role in tumor cell survival and migration remain unclear. Public databases contain extensive information regarding the expression of NEO1 and its ligands Netrin-1 (NTN1) and Netrin-4 (NTN4) in primary neuroblastoma (NB) tumors. Analysis of this data revealed that patients with high expression levels of both NEO1 and NTN4 have a poor survival rate. Accordingly, our analyses in NB cell lines with different genetic backgrounds revealed that knocking-down NEO1 reduces cell migration, whereas silencing of endogenous NTN4 induced cell death. Conversely, overexpression of NEO1 resulted in higher cell migration in the presence of NTN4, and increased apoptosis in the absence of ligand. Increased apoptosis was prevented when utilizing physiological concentrations of exogenous Netrin-4. Likewise, cell death induced after NTN4 knock-down was rescued when NEO1 was transiently silenced, thus revealing an important role for NEO1 in NB cell survival. In vivo analysis, using the chicken embryo chorioallantoic membrane (CAM) model, showed that NEO1 and endogenous NTN4 are involved in tumor extravasation and metastasis. Our data collectively demonstrate that endogenous NTN4/NEO1 maintain NB growth via both pro-survival and pro-migratory molecular signaling.

Identifying and targeting determinants of melanoma cellular invasion

Epithelial-to-mesenchymal transition is a critical process that increases the malignant potential of melanoma by facilitating invasion and dissemination of tumor cells. This study identified genes involved in the regulation of cellular invasion and evaluated whether they can be targeted to inhibit melanoma invasion. We identified Peroxidasin (PXDN), Netrin 4 (NTN4) and GLIS Family Zinc Finger 3 (GLIS3) genes consistently elevated in invasive mesenchymal-like melanoma cells. These genes and proteins were highly expressed in metastatic melanoma tumors, and gene silencing led to reduced melanoma invasion in vitro. Furthermore, migration of PXDN, NTN4 or GLIS3 siRNA transfected melanoma cells was inhibited following transplantation into the embryonic chicken neural tube compared to control siRNA transfected melanoma cells. Our study suggests that PXDN, NTN4 and GLIS3 play a functional role in promoting melanoma cellular invasion, and therapeutic approaches directed toward inhibiting the action of these proteins may reduce the incidence or progression of metastasis in melanoma patients.

SEC-induced activation of ANXA7 GTPase suppresses prostate cancer metastasis

Annexin A7 (ANXA7) is a suppressor of tumorigenesis and metastasis in prostate cancer. Activated ANXA7 GTPase promotes prostate cancer cell apoptosis. However, the role and underlying mechanism of ANXA7 GTPase in prostate cancer metastasis have not been established. RKIP is a metastatic suppressor and downregulated in prostate cancer metastases. The binding of RKIP and its target proteins could inhibit the activation of its interactive partners. However, the effect of RKIP on ANXA7 GTPase activation is not clear. Here, we report that activation of ANXA7 GTPase by a small molecule SEC ((S)-ethyl 1-(3-(4-chlorophenoxy)-2-hydroxypropyl)-3- (4-methoxyphenyl)-1H-pyrazole-5-carboxylate) effectively inhibited prostate cancer metastasis. Mechanistically, activated ANXA7 promoted AMPK phosphorylation, leading to decreased mTORC1 activity, suppressed STAT3 nuclear translocation, and downregulation of pro-metastatic genes, including CCL2, APLN, and IL6ST. Conversely, RKIP interacted with ANXA7 and impaired activation of ANXA7 GTPase by SEC and its downstream signaling pathway. Notably, SEC treatment suppressed metastasis of prostate cancer cells in in vivo orthotopic analysis. Together, our findings provide a novel insight into how metastasis of prostate cancer with low RKIP expression is suppressed by SEC-induced activation of ANXA7 GTPase via the AMPK/mTORC1/STAT3 signaling pathway.

Molecular characterization of pro-metastatic functions of β4-integrin in colorectal cancer

The β4-integrin subunit has been implicated in development and progression of several epithelial tumor types. However, its role in metastases of colorectal cancer (CRC) remains elusive. To study CRC metastasis, we generated a highly invasive, metastatic cell line MC38-LM10 (LM10) by passaging mouse CRC MC38 cells ten times, using a splenic injection model of liver metastasis. Affymetrix microarray analyses of LM10 and MC38 cell lines and their corresponding liver metastases generated a gene signature for CRC metastasis. This signature shows strong upregulation of β4-integrin in LM10 cells and corresponding metastases. Upregulation of β4-integrin in highly aggressive LM10 cells is associated with increased migration, invasion, and liver metastases. Furthermore, stable knockdown of β4-integrin in human CRC SW620 cells reduces Bcl-2 expression, increases apoptosis, and decreases invasion, tumorigenicity, and liver metastasis, thus resulting in significantly increased survival of mice (hazard ratio = 0.32, 95% confidence interval = 0.15-0.66, P<0.01). Patients with CRC tumors display higher β4-integrin levels in stages 1-4 and significantly lower survival rate. Collectively, β4-integrin plays a critical role in CRC progression, invasion, and metastasis, suggesting that it could be a potential therapeutic target for CRC patients.

Interest of integrins targeting in glioblastoma according to tumor heterogeneity and cancer stem cell paradigm: an update

Glioblastomas are malignant brain tumors with dismal prognosis despite standard treatment with surgery and radio/chemotherapy. These tumors are defined by an important cellular heterogeneity and notably contain a particular subpopulation of Glioblastoma-initiating cells, which recapitulate the heterogeneity of the original Glioblastoma. In order to classify these heterogeneous tumors, genomic profiling has also been undertaken to classify these heterogeneous tumors into several subtypes. Current research focuses on developing therapies, which could take into account this cellular and genomic heterogeneity. Among these targets, integrins are the subject of numerous studies since these extracellular matrix transmembrane receptors notably controls tumor invasion and progression. Moreover, some of these integrins are considered as membrane markers for the Glioblastoma-initiating cells subpopulation. We reviewed here integrin expression according to glioblastoma molecular subtypes and cell heterogeneity. We discussed their roles in glioblastoma invasion, angiogenesis, therapeutic resistance, stemness and microenvironment modulations, and provide an overview of clinical trials investigating integrins in glioblastomas. This review highlights that specific integrins could be identified as selective glioblastoma cells markers and that their targeting represents new diagnostic and/or therapeutic strategies.

Netrin-1 promotes gastric cancer cell proliferation and invasion via the receptor neogenin through PI3K/AKT signaling pathway

Netrin-1 is a laminin-related protein found to promote proliferation and invasion in multiple types of cancers. Recent studies have identified the function role of netrin-1 in several cancers; however, the influence of netrin-1 in human gastric cancer(GC) remains largely unknown. In this study, we found netrin-1 was upregulated in human GC tissues, where its expression correlated inversely with cancer stage and lymph node metastasis. We detected netrin-1 and its receptor knockdown significantly suppressed GC cells proliferation and invasion, while overexpression netrin-1 reversed these effects. Xenografted analyses using GC cells displayed significantly inhibition of tumor growth and metastasis by netrin-1 depletion. Furthermore, we identified that netrin-1 as a regulator of PI3K/AKT pathway to modulate GC cells proliferation and invasion abilities via its receptor neogenin. Taken together, our findings argued that netrin-1 and its receptor neogenin might act synergistically in promoting GC cells proliferation and invasion through the PI3K/AKT signaling pathway. It is conceivable that netrin-1 could be new therapeutic target to GC therapy.

Netrin-4 as a biomarker promotes cell proliferation and invasion in gastric cancer

Gastric cancer (GC) is the second most common cause of cancer-related death with limited serum biomarkers for diagnosis and prognosis. Netrin-4 (Ntn4) is a laminin-related secreted molecule found to regulate tumor progression and metastasis. However, it is completely unknown whether Ntn4 has roles in GC development. Here, we first reported Ntn4 knockdown significantly suppressed cell proliferation and motility, while overexpression or addition of exogenous Ntn4 reversed these effects. In addition, Ntn4 receptor, neogenin (Neo) was also found highly expressed in GC cells and mediated the Ntn4-induced cell proliferation and invasion. Moreover, Ntn4 or Neo silencing decreased the phosphorylation of Stat3, ERK, Akt and p38, indicating multi-oncogenic pathways (Jak/Stat, PI3K/Akt, and ERK/MAPK) were involved in Ntn4-induced effects on the GC cells. Importantly, Ntn4 level was significantly increased in 82 tumor tissues (p = 0.001) and 52 serum samples (p < 0.0001) from GC patients and positively correlated with Neo expression (p = 0.003). Ntn4 expression was negatively correlated with the survival period (p = 0.038), and positively associated with the severity of pathological stages of the tumors (p = 0.008). Taken together, Ntn4 promoted the proliferation and motility of GC cells which was mediated by its receptor Neo and through further activation of multi-oncogenic pathways. Elevated Ntn4 was detected in both tumor tissues and serum samples of GC patients and suggested a relatively poor survival, indicating Ntn4 may be used as a potential non-invasive biomarker for diagnosis and prognosis of GC.

Bone morphogenetic protein signaling promotes tumorigenesis in a murine model of high-grade glioma

BACKGROUND

Improved therapies for high-grade glioma (HGG) are urgently needed as the median survival for grade IV gliomas is only 15 months. Bone morphogenetic protein (BMP) signaling plays critical and complex roles in many types of cancer, including glioma, with most of the recently published work focusing on BMP-mediated regulation of glioma stem cells (GSCs). We hypothesized that BMP signaling may be an important modulator of tumorigenic properties in glioma cells outside of the GSC compartment.

METHODS

We used a human HGG tissue microarray and performed immunohistochemistry for phospho-Smads1,5,8. To examine the role of BMP signaling in tumorigenic astrocytes, transgenic mice were used to delete the BMP type IA receptor (Bmpr1a) and generate astrocytes transformed with oncogenic Ras and homozygous deletion of p53. The cells were transplanted orthotopically into immunocompetent adult host mice.

RESULTS

First we established that BMP signaling is active within the vast majority of HGG tumor cells. Mice implanted with BMPR1a-knockout transformed astrocytes showed an increase in median survival compared with mice that received BMPR1a-intact transformed astrocytes (52.5 vs 16 days). In vitro analysis showed that deletion of BMPR1a in oncogenic astrocytes resulted in decreased proliferation, decreased invasion, decreased migration, and increased expression of stemness markers. In addition, inhibition of BMP signaling in murine cells and astrocytoma cells with a small molecule BMP receptor kinase inhibitor resulted in similar tumor suppressive effects in vitro.

CONCLUSION

BMP inhibition may represent a viable therapeutic approach in adult HGG.

Collaboration of 3D context and extracellular matrix in the development of glioma stemness in a 3D model

A hierarchy of cellular stemness exists in certain cancers, and any successful strategy to treat such cancers would have to eliminate the self-renewing tumor-initiating cells at the apex of the hierarchy. The cellular microenvironment, in particular the extracellular matrix (ECM), is believed to have a role in regulating stemness. In this work, U251 glioblastoma cells are cultured on electrospun polystyrene (ESPS) scaffolds coated with an array of 7 laminin isoforms to provide a 3D model for stem cell-related genes and proteins expression studies. We observed collaboration between 3D context and laminins in promoting glioma stemness. Depending on the laminin isoform presented, U251 cells cultured on ESPS scaffolds (3D) exhibited increased expression of stemness markers compared to those cultured on tissue culture polystyrene (2D). Our results indicate the influence of 3D (versus 2D) context on integrin expression, specifically, the upregulation of the laminin-binding integrins alpha 6 and beta 4. By a colony forming assay, we showed enhanced clonogenicity of cells grown on ESPS scaffolds in collaboration with laminins 411, 421, 511 and 521. Evaluation of patient glioma databases demonstrated significant enrichment of integrin and ECM pathway networks in tumors of worse prognosis, consistent with our observations. The present results demonstrate how 3D versus 2D context profoundly affects ECM signaling, leading to stemness.

MiR-320a acts as a prognostic factor and Inhibits metastasis of salivary adenoid cystic carcinoma by targeting ITGB3

BACKGROUND

Salivary Adenoid cystic carcinoma (SACC) patients with local invasion and lung metastasis are often resistant to conventional therapy such as operation, chemotherapy and radiotherapy. To explore the underling mechanisms, we studied the roles of miRNA in regulating invasiveness of SACC cells.

METHODS

MicroRNA profiling was done in SACC cells with microarray. MiRNA mimics or antisense oligonucleotide was transfected and invasiveness of SACC cells was evaluated by adhesion assay and transwell assay. The target gene of miRNA was identified by luciferase reporter assay and "rescue" experiment. Tumor metastasis was evaluated by BALB/c-nu mice xenografts. MiRNA and its target gene expression were identified by in-situ hybridization and immunohistochemistry respectively, in 302 patients from affiliated hospitals of Sun Yat-sen University and in 148 patients from affiliated hospitals of Central South University, and correlated to the clinicopathological status of the patients.

RESULTS

MiR-320a was down-regulated in high lung metastatic ACCM and SACC-LM cells compared with the corresponding low metastatic ACC2 and SACC-83 cells, and inhibited adhesion, invasion and migration of SACC cells by targeting integrin beta 3 (ITGB3). In vivo, enforced miR-320a expression suppressed metastasis of SACC xenografts. In the two independent sets, miR-320a was downregulated in primary SACCs with metastasis compared to those without metastasis, and low expression of this miRNA predicts poor patient survival and rapid metastasis. Multivariate analysis showed that miR-320a expression was an independent indicator of lung metastasis.

CONCLUSIONS

MiR-320a inhibits metastasis in SACCs by targeting ITGB3 and may serve as a therapeutic target and prognostic marker in salivary cancers.

Netrin-5 is highly expressed in neurogenic regions of the adult brain

Mammalian netrin family proteins are involved in targeting of axons, neuronal migration, and angiogenesis and act as repulsive and attractive guidance molecules. Netrin-5 is a new member of the netrin family with homology to the C345C domain of netrin-1. Unlike other netrin proteins, murine netrin-5 consists of two EGF motifs of the laminin V domain (LE) and the C345C domain, but lacks the N-terminal laminin VI domain and one of the three LE motifs. We generated a specific antibody against netrin-5 to investigate its expression pattern in the rodent adult brain. Strong netrin-5 expression was observed in the olfactory bulb (OB), rostral migrate stream (RMS), the subventricular zone (SVZ), and the subgranular zone (SGZ) of the dentate gyrus in the hippocampus, where neurogenesis occurs in the adult brain. In the SVZ and RMS, netrin-5 expression was observed in Mash1-positive transit-amplifying cells and in Doublecortin (DCX)-positive neuroblasts, but not in GFAP-positive astrocytes. In the OB, netrin-5 expression was maintained in neuroblasts, but its level was decreased in NeuN-positive mature neurons. In the hippocampal SGZ, netrin-5 was observed in Mash1-positive cells and in DCX-positive neuroblasts, but not in GFAP-positive astrocytes, suggesting that netrin-5 expression occurs from type 2a to type 3 cells. These data suggest that netrin-5 is produced by both transit-amplifying cells and neuroblasts to control neurogenesis in the adult brain.

Therapeutic effects of topical netrin-4 inhibits corneal neovascularization in alkali-burn rats

Netrins are secreted molecules involved in axon guidance and angiogenesis. However, the role of netrins in the vasculature remains unclear. Netrin-4 and netrin-1 have been found to be either pro- or antiangiogenic factors. Previously, we found that netrin-1 acts as an anti-angiogenic factor in rats by inhibiting alkali burn-induced corneal neovascularization. Here, we further investigate the effects of netrin-4, another member of the same netrin family, on neovascularization in vitro and in vivo. We found that netrin-4 functions similarly as netrin-1 in angiogenesis. In vitro angiogenesis assay shows that netrin-4 affected human umbilical vein endothelial cell (HUVEC) tube formation, viability and proliferation, apoptosis, migration, and invasion in a dose-dependent manner. Netrin-4 was topically applied in vivo to alkali-burned rat corneas on day 0 (immediately after injury) and/or day 10 post-injury. Netrin-4 subsequently suppressed and reversed corneal neovascularization. Netrin-4 inhibited corneal epithelial and stromal cell apoptosis, inhibited vascular endothelial growth factor (VEGF), but promoted pigment epithelium-derived factor (PEDF) expression, decreased NK-KB p65 expression, and inhibits neutrophil and macrophage infiltration. These results indicate that netrin-4 shed new light on its potential roles in treatmenting for angiogenic diseases that affect the ocular surface, as well as other tissues.

Laminins: Roles and Utility in Wound Repair

Significance: Laminins are complex extracellular macromolecules that are major players in the control of a variety of core cell processes, including regulating rates of cell proliferation, differentiation, adhesion, and migration. Laminins, and related extracellular matrix components, have essential roles in tissue homeostasis; however, during wound healing, the same proteins are critical players in re-epithelialization and angiogenesis. Understanding how these proteins influence cell behavior in these different conditions holds great potential in identifying new strategies to enhance normal wound closure or to treat chronic/nonhealing wounds. Recent Advances: Laminin-derived bioactive peptides and, more recently, laminin-peptide conjugated scaffolds, have been designed to improve tissue regeneration after injuries. These peptides have been shown to be effective in decreasing inflammation and granulation tissue, and in promoting re-epithelialization, angiogenesis, and cell migration. Critical Issues: Although there is now a wealth of knowledge concerning laminin form and function, there are still areas of some controversy. These include the relative contribution of two laminin-based adhesive devices (focal contacts and hemidesmosomes) to the re-epithelialization process, the impact and implications of laminin proteolytic processing, and the importance of laminin polymer formation on cell behavior. In addition, the roles in wound healing of the laminin-related proteins, netrins, and LaNts are still to be fully defined. Future Directions: The future of laminin-based therapeutics potentially lies in the bioengineering of specific substrates to support laminin deposition for ex vivo expansion of autologous cells for graft formation and transplantation. Significant recent advances suggest that this goal is within sight.

Cancer subclonal genetic architecture as a key to personalized medicine

The future of personalized oncological therapy will likely rely on evidence-based medicine to integrate all of the available evidence to delineate the most efficacious treatment option for the patient. To undertake evidence-based medicine through use of targeted therapy regimens, identification of the specific underlying causative mutation(s) driving growth and progression of a patient's tumor is imperative. Although molecular subtyping is important for planning and treatment, intraclonal genetic diversity has been recently highlighted as having significant implications for biopsy-based prognosis. Overall, delineation of the clonal architecture of a patient's cancer and how this will impact on the selection of the most efficacious therapy remain a topic of intense interest.

Gene markers of cellular aging in human multipotent stromal cells in culture

Introduction

Human multipotent stromal cells (MSCs) isolated from bone marrow or other tissue sources have great potential to treat a wide range of injuries and disorders in the field of regenerative medicine and tissue engineering. In particular, MSCs have inherent characteristics to suppress the immune system and are being studied in clinical studies to prevent graft-versus-host disease. MSCs can be expanded in vitro and have potential for differentiation into multiple cell lineages. However, the impact of cell passaging on gene expression and function of the cells has not been determined.

Methods

Commercially available human MSCs derived from bone marrow from six different donors, grown under identical culture conditions and harvested at cell passages 3, 5, and 7, were analyzed with gene-expression profiling by using microarray technology.

Results

The phenotype of these cells did not change as reported previously; however, a statistical analysis revealed a set of 78 significant genes that were distinguishable in expression between passages 3 and 7. None of these significant genes corresponded to the markers established by the International Society for Cellular Therapy (ISCT) for MSC identification. When the significant gene lists were analyzed through pathway analysis, these genes were involved in the top-scoring networks of cellular growth and proliferation and cellular development. A meta-analysis of the literature for significant genes revealed that the MSCs seem to be undergoing differentiation into a senescent cell type when cultured extensively. Consistent with the differences in gene expression at passage 3 and 7, MSCs exhibited a significantly greater potential for cell division at passage 3 in comparison to passage 7.

Conclusions

Our results identified specific gene markers that distinguish aging MSCs grown in cell culture. Confirmatory studies are needed to correlate these molecular markers with biologic attributes that may facilitate the development of assays to test the quality of MSCs before clinical use.

Netrin-4 promotes mural cell adhesion and recruitment to endothelial cells

Netrins are secreted molecules involved in axon guidance and angiogenesis. We previously showed that Netrin-4 acts as an anti-angiogenic factor by inhibiting endothelial cell (EC) functions. In this study, we investigated the effects of Netrin-4 on vascular smooth muscle cell (VSMC) activity in vitro and in vivo. We show that exogenous Netrin-4 stimulated VSMC adhesion and migration, and increased their coverage on EC tubes (grown on a Matrigel substrate). siRNA knock-down of endogenous Netrin-4 expression in VSMC decreased their recruitment to EC tubes. VSMC expressed Netrin-4 and three of the six Netrin-1 cognate receptors: DCC, Neogenin, and Unc5B. Silencing of these receptors reduced Netrin-4 adhesion to VSMC, strongly suggesting that these receptors were involved in the recruitment process. We previously showed that Netrin-4 overexpression in PC3 cancer cells delayed tumor growth in a model of subcutaneous xenograft by reducing tumor vessel density. Here, we show that Netrin-4 overexpression improved tumor blood vessel structure and increased VSMC coverage. Thus, Netrin-4 induced mural cell recruitment may play a role in the inhibition of tumor growth. Our data suggest that Netrin-4 is important for blood vessel normalization through the regulation of both endothelial and perivascular cells.

NETRIN-4 protects glioblastoma cells FROM temozolomide induced senescence

Glioblastoma multiforme is the most common primary tumor of the central nervous system. The drug temozolomide (TMZ) prolongs lifespan in many glioblastoma patients. The sensitivity of glioblastoma cells to TMZ is interfered by many factors, such as the expression of O-6-methylguanine-DNA methyltransferase (MGMT) and activation of AKT signaling. We have recently identified the interaction between netrin-4 (NTN4) and integrin beta-4 (ITGB4), which promotes glioblastoma cell proliferation via activating AKT-mTOR signaling pathway. In the current work we have explored the effect of NTN4/ITGB4 interaction on TMZ induced glioblastoma cell senescence. We report here that the suppression of either ITGB4 or NTN4 in glioblastoma cell lines significantly enhances cellular senescence. The sensitivity of GBM cells to TMZ was primarily determined by the expression of MGMT. To omit the effect of MGMT, we concentrated on the cell lines devoid of expression of MGMT. NTN4 partially inhibited TMZ induced cell senescence and rescued AKT from dephosphorylation in U251MG cells, a cell line bearing decent levels of ITGB4. However, addition of exogenous NTN4 displayed no significant effect on TMZ induced senescence rescue or AKT activation in U87MG cells, which expressed ITGB4 at low levels. Furthermore, overexpression of ITGB4 combined with exogenous NTN4 significantly attenuated U87MG cell senescence induced by TMZ. These data suggest that NTN4 protects glioblastoma cells from TMZ induced senescence, probably via rescuing TMZ triggered ITGB4 dependent AKT dephosphorylation. This suggests that interfering the interaction between NTN4 and ITGB4 or concomitant use of the inhibitors of the AKT pathway may improve the therapeutic efficiency of TMZ.

Overcoming intratumor heterogeneity of polygenic cancer drug resistance with improved biomarker integration

Improvements in technology and resources are helping to advance our understanding of cancer-initiating events as well as factors involved with tumor progression, adaptation, and evasion of therapy. Tumors are well known to contain diverse cell populations and intratumor heterogeneity affords neoplasms with a diverse set of biologic characteristics that can be used to evolve and adapt. Intratumor heterogeneity has emerged as a major hindrance to improving cancer patient care. Polygenic cancer drug resistance necessitates reconsidering drug designs to include polypharmacology in pursuit of novel combinatorial agents having multitarget activity to overcome the diverse and compensatory signaling pathways in which cancer cells use to survive and evade therapy. Advances will require integration of different biomarkers such as genomics and imaging to provide for more adequate elucidation of the spatially varying location, type, and extent of diverse intratumor signaling molecules to provide for a rationale-based personalized cancer medicine strategy.

Ephrin-As, Eph receptors and integrin α3 interact and colocalise at membrane protrusions of U251MG glioblastoma cells

Glioblastoma is the most common brain cancer. Ephrins and their Eph receptors play important roles in the development of central nervous system and the regulation of cancer cell migration and invasion. In a search for the Eph receptor complexes, we used tandem affinity purification based interaction screening with tagged ephrins A1, A3 and A4 combined with protein identification by mass-spectrometry in U251MG glioblastoma cells. Ephrins bound to Eph receptors, mainly to EphA2 in these cells. Integrin α3 was identified in protein complexes with ephrin-As. Soluble ephrin-A1 colocalised with integrin α3 at the cell surface, and was rapidly endocytosed by the cells. However, integrin α3 did not colocalise with internalised ephrin-A1, whereas EphA2 receptor did. In U251MG cells, integrin α3 colocalised with EphA2 receptor at the cell edges and protrusions. Sites of EphA2-integrin α3 colocalisation were positive for vinculin, focal adhesion kinase and phosphotyrosine, that is, markers for cell adhesion and active signalling. The interaction between ephrin-As, Eph receptors and integrin α3 is plausibly important for the crosstalk between Eph and integrin signalling pathways at the membrane protrusions and in the migration of brain cancer cells.

Netrin-1-induced activation of Notch signaling mediates glioblastoma cell invasion

Glioblastoma multiforme is an aggressively invasive human brain cancer, which lacks effective treatment. The axonal guidance protein, netrin-1, is overexpressed in glioblastoma tumor biopsies. In Matrigel invasion assays we observed that experimental overexpression of netrin-1 increased cell invasiveness and its downregulation decreased invasiveness. Using tandem affinity purification and mass spectrometry protein identification we found that netrin-1 forms a complex with both Notch2 and Jagged1. Recombinant netrin-1 colocalized with Jagged1 and Notch2 at the cell surface and was also present in the intracellular vesicles with Jagged1, but not with Notch2. Netrin-1 activated Notch signaling and subsequent glioblastoma cell invasion. Interestingly, the recombinant central domain of netrin-1 counteracted the effects of the full-length netrin-1: it inhibited glioblastoma cell invasion and Notch activation by retaining the Notch signaling complex at the cell surface. This finding may give rise to therapeutic applications. These results reveal a new mechanism leading to glioblastoma cell invasion, in which netrin-1 activates Notch signaling.