Glioblastoma Stem Cells Invasion Research Articles

4,5-Dimethoxycanthin-6-one Inhibits Glioblastoma Stem Cell and Tumor Growth by Inhibiting TSPAN1 Interaction with TM4SF1.

Glioblastoma stem cells (GSCs) have been implicated in the self-renewal and treatment resistance of glioblastoma (GBM). Our previous study found that 4,5-dimethoxycanthin-6-one has the potential to inhibit GBM cell proliferation. This current study aims to elucidate the molecular mechanism underlying the effects of 4,5-dimethoxycanthin-6-one in GBM development. The effect of 4,5-dimethoxycanthin-6-one on GSC formation and differentiation was explored in human GBM cell lines U251 and U87. Subsequently, 4,5-dimethoxycanthin-6-one binding to tetraspanin 1 (TSPAN1) / transmembrane 4L six family member 1 (TM4SF1) was analyzed by molecular simulation docking. Co-immunoprecipitation (Co-IP) and immunofluorescence (IF) were used to assess the interactions between TSPAN1 and TM4SF1 in GSCs. Cell proliferation was detected by cell counting kit-8 (CCK-8) and colony formation assay. To evaluate cell migration, invasion and apoptosis, we employed wound healing assay, transwell and flow cytometry, respectively. Furthermore, subcutaneous xenograft tumor models in nude mice were constructed to evaluate the impact of 4,5-dimethoxycanthin-6-one on GSCs in vivo by examining tumor growth and histological characteristics. 4,5-Dimethoxycanthin-6-one inhibited GSC formation and promoted stem cell differentiation in a concentration-dependent manner. Molecular docking models of 4,5-dimethoxycanthin-6-one with TM4SF1 and TSPAN1 were constructed. Then, the interaction between TSPAN1 and TM4SF1 in GSC was clarified. Moreover, 4,5-dimethoxycanthin-6-one significantly inhibited the expressions of TM4SF1 and TSPAN1 in vitro and in vivo. Overexpression of TSPAN1 partially reversed the inhibitory effects of 4,5-dimethoxycanthin-6-one on GSC formation, proliferation, migration and invasion. 4,5-Dimethoxycanthin-6-one inhibited GBM progression by inhibiting TSPAN1/TM4SF1 axis. 4,5-Dimethoxycanthin-6-one might be a novel and effective drug for the treatment of GBM.

Novel terpestacin derivatives with l-amino acid residue as anticancer agents against U87MG-derived glioblastoma stem cells

Based on the natural product terpestacin, seventeen derivatives (1–17) with various l-amino acid side chains were designed and synthesized. Their anticancer activities against U87MG-derived glioblastoma stem cells (GSCs) were evaluated, and compounds 5, 11, 13 and 15 showed strong abilities to inhibit the proliferation (IC50 = 2.8–6.9 μM) and tumorsphere formation of GSCs. Besides, compounds 13 and 15 could effectively induce apoptosis and significantly inhibit the invasion of GSCs (95 and 97 % inhibition, respectively, at 2.5 μM). The levels of CD133 marker in GSCs also decreased in dose-dependent manners after the treatment of these active compounds. Compared to terpestacin and the positive control A1938, our derivatives showed stronger activities and compounds 13 and 15 are promising candidates for further development as anticancer agents by targeting GSCs.

The MAP3K1/c-JUN signaling axis regulates glioblastoma stem cell invasion and tumor progression

Glioblastoma (GBM) stem cells (GSCs) are responsible for GBM initiation, progression, infiltration, standard therapy resistance, and recurrence. However, the mechanisms underlying GSC invasion remain incompletely understood. Using public single-cell RNA-Seq data, we identified MAP3K1 as a master regulator of infiltrative GSCs through c-JUN signaling regulation. MAP3K1 knockdown significantly decreased GSC invasion capacity, proliferation, and stemness in vitro. Moreover, in an orthotopic xenograft model, knockdown of MAP3K1 prominently suppressed GSC infiltration along the corpus callosum and tumor progression and prolonged mouse survival. Mechanistically, MAP3K1 regulates GSC invasion through phosphorylation of downstream c-JUN at serine 63 and 73, as confirmed using the CPTAC phosphoproteome dataset. Furthermore, the c-JUN inhibitor JNK-IN-8 significantly decreased GSC invasion, proliferation, and stemness. Taken together, our study demonstrates that MAP3K1 regulates GSC invasion and tumor progression via activation of c-JUN signaling and indicates that the MAP3K1/c-JUN signaling axis is a therapeutic target for infiltrative GBM.

Diisothiocyanate-Derived Mercapturic Acids Are a Promising Partner for Combination Therapies in Glioblastoma.

Glioblastoma represents the most aggressive tumor of the central nervous system. Due to invasion of glioblastoma stem cells into the healthy tissue, chemoresistance, and recurrence of the tumor, it is difficult to successfully treat glioblastoma patients, which is demonstrated by the low life expectancy of patients after standard therapy treatment. Recently, we found that diisothiocyanate-derived mercapturic acids, which are isothiocyanate derivatives from plants of the Cruciferae family, provoked a decrease in glioblastoma cell viability. These findings were extended by combining diisothiocyanate-derived mercapturic acids with dinaciclib (a small-molecule inhibitor of cyclin-dependent kinases with anti-proliferative capacity) or temozolomide (TMZ, standard chemotherapeutic agent) to test whether the components have a cytotoxic effect on glioblastoma cells when the dosage is low. Here, we demonstrate that the combination of diisothiocyanate-derived mercapturic acids with dinaciclib or TMZ had an additive or even synergistic effect in the restriction of cell growth dependent on the combination of the components and the glioblastoma cell source. This strategy could be applied to inhibit glioblastoma cell growth as a therapeutic interference of glioblastoma.

Chloride intracellular channel 1 activity is not required for glioblastoma development but its inhibition dictates glioma stem cell responsivity to novel biguanide derivatives

BackgroundChloride intracellular channel-1 (CLIC1) activity controls glioblastoma proliferation. Metformin exerts antitumor effects in glioblastoma stem cells (GSCs) inhibiting CLIC1 activity, but its low potency hampers its translation in clinical settings.MethodsWe synthesized a small library of novel biguanide-based compounds that were tested as antiproliferative agents for GSCs derived from human glioblastomas, in vitro using 2D and 3D cultures and in vivo in the zebrafish model. Compounds were compared to metformin for both potency and efficacy in the inhibition of GSC proliferation in vitro (MTT, Trypan blue exclusion assays, and EdU labeling) and in vivo (zebrafish model), migration (Boyden chamber assay), invasiveness (Matrigel invasion assay), self-renewal (spherogenesis assay), and CLIC1 activity (electrophysiology recordings), as well as for the absence of off-target toxicity (effects on normal stem cells and toxicity for zebrafish and chick embryos).ResultsWe identified Q48 and Q54 as two novel CLIC1 blockers, characterized by higher antiproliferative potency than metformin in vitro, in both GSC 2D cultures and 3D spheroids. Q48 and Q54 also impaired GSC self-renewal, migration and invasion, and displayed low systemic in vivo toxicity. Q54 reduced in vivo proliferation of GSCs xenotransplanted in zebrafish hindbrain. Target specificity was confirmed by recombinant CLIC1 binding experiments using microscale thermophoresis approach. Finally, we characterized GSCs from GBMs spontaneously expressing low CLIC1 protein, demonstrating their ability to grow in vivo and to retain stem-like phenotype and functional features in vitro. In these GSCs, Q48 and Q54 displayed reduced potency and efficacy as antiproliferative agents as compared to high CLIC1-expressing tumors. However, in 3D cultures, metformin and Q48 (but not Q54) inhibited proliferation, which was dependent on the inhibition dihydrofolate reductase activity.ConclusionsThese data highlight that, while CLIC1 is dispensable for the development of a subset of glioblastomas, it acts as a booster of proliferation in the majority of these tumors and its functional expression is required for biguanide antitumor class-effects. In particular, the biguanide-based derivatives Q48 and Q54, represent the leads to develop novel compounds endowed with better pharmacological profiles than metformin, to act as CLIC1-blockers for the treatment of CLIC1-expressing glioblastomas, in a precision medicine approach.

ANO1 regulates the maintenance of stemness in glioblastoma stem cells by stabilizing EGFRvIII

Glioblastoma multiforme (GBM) or glioblastoma is the most deadly malignant brain tumor in adults. GBM is difficult to treat mainly due to the presence of glioblastoma stem cells (GSCs). Epidermal growth factor receptor variant III (EGFRvIII) has been linked to stemness and malignancy of GSCs; however, the regulatory mechanism of EGFRvIII is largely unknown. Here, we demonstrated that Anoctamin-1 (ANO1), a Ca2+-activated Cl- channel, interacts with EGFRvIII, increases its protein stability, and supports the maintenance of stemness and tumor progression in GSCs. Specifically, shRNA-mediated knockdown and pharmacological inhibition of ANO1 suppressed the self-renewal, invasion activities, and expression of EGFRvIII and related stem cell factors, including NOTCH1, nestin, and SOX2 in GSCs. Conversely, ANO1 overexpression enhanced the above phenomena. Mechanistically, ANO1 protected EGFRvIII from proteasomal degradation by directly binding to it. ANO1 knockdown significantly increased survival in mice and strongly suppressed local invasion of GSCs in an in vivo intracranial mouse model. Collectively, these results suggest that ANO1 plays a crucial role in the maintenance of stemness and invasiveness of GSCs by regulating the expression of EGFRvIII and related signaling molecules, and can be considered a promising therapeutic target for GBM treatment.

PARK7 maintains the stemness of glioblastoma stem cells by stabilizing epidermal growth factor receptor variant III.

PARK7 is involved in many key cellular processes, including cell proliferation, transcriptional regulation, cellular differentiation, oxidative stress protection, and mitochondrial function maintenance. Deregulation of PARK7 has been implicated in the pathogenesis of various human diseases, including cancer. Here, we aimed to clarify the effect of PARK7 on stemness and radioresistance of glioblastoma stem cells (GSCs). Serum differentiation and magnetic cell sorting of GSCs revealed that PARK7 was preferentially expressed in GSCs rather than differentiated GSCs. Immunohistochemical staining showed enhanced expression of PARK7 in glioma tissues compared to that in normal brain tissues. shRNA-mediated knockdown of PARK7 inhibited the self-renewal activity of GSCs in vitro, as evidenced by the results of neurosphere formation, limiting dilution, and soft-agar clonogenic assays. In addition, PARK7 knockdown suppressed GSC invasion and enhanced GSC sensitivity to ionizing radiation (IR). PARK7 knockdown suppressed expression of GSC signatures including nestin, epidermal growth factor receptor variant III (EGFRvIII), SOX2, NOTCH1, and OCT4. Contrarily, overexpression of PARK7 in CD133- non-GSCs increased self-renewal activities, migration, and IR resistance, and rescued the reduction of GSC factors under shPARK7-transfected and serum-differentiation conditions. Intriguingly, PARK7 acted as a co-chaperone of HSP90 by binding to it, protecting EGFRvIII from proteasomal degradation. Knockdown of PARK7 increased the production of reactive oxygen species, inducing partial apoptosis and enhancing IR sensitivity in GSCs. Finally, PARK7 knockdown increased mouse survival and IR sensitivity in vivo. Based on these data, we propose that PARK7 plays a pivotal role in the maintenance of stemness and therapeutic resistance in GSCs.

ANGI-13. PLEXIN-B2 FACILITATES DIFFUSE GLIOMA INVASION BY REGULATING CELL ADHESION AND ACTO-MYOSIN DYNAMICS

Abstract Diffuse invasion of glioblastoma (GBM) cells into brain tissue is a key factor for its high lethality. GBM cell migration is affected by functions of plexins, which are transmembrane receptors of semaphorins that regulate cell adhesion and cytoskeletal dynamics. Expression of Plexin-B2 is upregulated in GBM and correlates with malignancy. We show here that Plexin-B2 activity regulates biomechanical properties of GBM cells, promoting invasive growth. Plexin-B2 activity increased the capacity of GBM to invade as dispersed single cells by reducing the cell-cell adhesiveness between GBM cells, indicating that a major function of Plexin-B2 activity is to downregulate cell-cell adhesion systems. RNA-Seq analyses also revealed that GBM stem cells (GSC) with deletion of Plexin-B2 altered expression of genes related to cell adhesion and the matrisome, indicating compensatory mechanisms in cellular dynamics. Interestingly, in vivo intracranial transplant studies demonstrated that growth and invasion of Plexin-B2 mutant GSC was impaired, with mutant cells invading shorter distances and migrating mainly as groups of cells forming chains. Plexin-B2 mutant cells also were more likely to adhere to the vasculature, rather than to fiber tracts, suggesting altered biomechanical properties. This shift may be related to high stiffness of basal lamina of the vasculature, as Plexin-B2 KO cells have a preference for migration on stiff substrate in vitro. Intriguingly, the loss in Plexin-B2 expression also changed the distribution of the mechanosensor transction factor YAP, with high expression of Plexin-B2 correlating with increased nuclear YAP. Structure-function analyses revealed that the Ras-GAP domain as main signaling output of Plexin-B2. The Rap proteins are pleiotropic regulators of cell adhesion and actomysosin contractility. Our data also showed that overexpression of Plexin-B2 can lead to decreased levels of Rap1/Rap2. Thus, Plexin-B2 acts as a key regulator of the adhesion and contractility of GBM cells, thereby facilitating their diffuse invasion.

Viability of glioblastoma stem cells is effectively reduced by diisothiocyanate-derived mercapturic acids.

Glioblastoma is the most aggressive tumor of the central nervous system and is manifested by diffuse invasion of glioblastoma stem cells into the healthy tissue, chemoresistance and recurrence. Despite aggressive therapy, consisting of maximal surgical resection, radiotherapy and chemotherapy with temozolomide (Temodal®), life expectancy of patients with glioblastoma is typically less than 15 months. In general, natural isothiocyanates isolated from plants of the Cruciferae family are selectively cytotoxic to tumor cells. It has been demonstrated previously that diisothiocyanate-derived mercapturic acids are highly cytotoxic to colon cancer cells. In the present study, the application of diisothiocyanate-derived mercapturic acids led to a decrease in the viability of an established glioblastoma cell line, primary patient-derived sphere-cultured stem cell-enriched cell populations (SCs), and cells differentiated from SCs. Consequently, targeting glioblastoma cells by diisothiocyanate-derived mercapturic acids is a promising approach to restrict tumor cell growth and may be a novel therapeutic intervention for the treatment of glioblastoma.

Identification of genomic and molecular traits that present therapeutic vulnerability to HGF-targeted therapy in glioblastoma

Cancer is a complex disease with profound genomic alterations and extensive heterogeneity. Recent studies on large-scale genomics have shed light on the impact of core oncogenic pathways, which are frequently dysregulated in a wide spectrum of cancer types. Aberrant activation of the hepatocyte growth factor (HGF) signaling axis has been associated with promoting various oncogenic programs during tumor initiation, progression, and treatment resistance. As a result, HGF-targeted therapy has emerged as an attractive therapeutic approach. However, recent clinical trials involving HGF-targeted therapies have demonstrated rather disappointing results. Thus, an alternative, in-depth assessment of new patient stratification is necessary to shift the current clinical course. To address such challenges, we have evaluated the therapeutic efficacy of YYB-101, an HGF-neutralizing antibody, in a series of primary glioblastoma stem cells (GSCs) both in vitro and in vivo. Furthermore, we performed genome and transcriptome analysis to determine genetic and molecular traits that exhibit therapeutic susceptibility to HGF-mediated therapy. We have identified several differentially expressed genes, including MET, KDR, and SOX3, which are associated with tumor invasiveness, malignancy, and unfavorable prognosis in glioblastoma patients. We also demonstrated the HGF-MET signaling axis as a key molecular determinant in GSC invasion, and we discovered that a significant association in HGF expression existed between mesenchymal phenotype and immune cell recruitment. Upregulation of MET and mesenchymal cellular state are essential in generating HGF-mediated therapeutic responses. Our results provide an important framework for evaluating HGF-targeted therapy in future clinical settings.

Antibody-Antisense Oligonucleotide Conjugate Downregulates a Key Gene in Glioblastoma Stem Cells

Glioblastoma stem cells (GSCs) are invasive, treatment-resistant brain cancer cells that express downregulated in renal cell carcinoma (DRR), also called FAM107A, a genetic driver of GSC invasion. We developed antibody-antisense oligonucleotide (AON) conjugates to target and reduce DRR/FAM107A expression. Specifically, we used antibodies against antigens expressed on the GSCs, such as CD44 and EphA2, conjugated to chemically modified AONs against DRR/FAM107A, which were designed as chimeras of DNA and 2′-deoxy-2′-fluoro-beta-D-arabinonucleic acid (FANA) for increased nuclease stability and mRNA affinity. We demonstrate that these therapeutic conjugates successfully internalize, accumulate, and reduce DRR/FAM107A expression in patient-derived GSCs. This is the first example of an antibody-antisense strategy against cancer stem cells.

Knockdown of SOX2OT inhibits the malignant biological behaviors of glioblastoma stem cells via up-regulating the expression of miR-194-5p and miR-122

BackgroundAccumulating evidence has highlighted the potential role of long non-coding RNAs (lncRNAs) in the biological behaviors of glioblastoma stem cells (GSCs). Here, we elucidated the function and possible molecular mechanisms of the effect of lncRNA-SOX2OT on the biological behaviors of GSCs.ResultsReal-time PCR demonstrated that SOX2OT expression was up-regulated in glioma tissues and GSCs. Knockdown of SOX2OT inhibited the proliferation, migration and invasion of GSCs, and promoted GSCs apoptosis. MiR-194-5p and miR-122 were down-regulated in human glioma tissues and GSCs, and miR-194-5p and miR-122 respectively exerted tumor-suppressive functions by inhibiting the proliferation, migration and invasion of GSCs, while promoting GSCs apoptosis. Knockdown of SOX2OT significantly increased the expression of miR-194-5p and miR-122 in GSCs. Dual-luciferase reporter assay revealed that SOX2OT bound to both miR-194-5p and miR-122. SOX3 and TDGF-1 were up-regulated in human glioma tissues and GSCs. Knockdown of SOX3 inhibited the proliferation, migration and invasion of GSCs, promoted GSCs apoptosis, and decreased TDGF-1 mRNA and protein expression through direct binding to the TDGF-1 promoter. Over-expression of miR-194-5p and miR-122 decreased the mRNA and protein expression of SOX3 by targeting its 3’UTR. Knockdown of TDGF-1 inhibited the proliferation, migration and invasion of GSCs, promoted GSCs apoptosis, and inhibited the JAK/STAT signaling pathway. Furthermore, SOX3 knockdown also inhibited the SOX2OT expression through direct binding to the SOX2OT promoter and formed a positive feedback loop.ConclusionThis study is the first to demonstrate that the SOX2OT-miR-194-5p/miR-122-SOX3-TDGF-1 pathway forms a positive feedback loop and regulates the biological behaviors of GSCs, and these findings might provide a novel strategy for glioma treatment.

Interstitial flow differentially increases patient-derived glioblastoma stem cell invasion via CXCR4, CXCL12, and CD44-mediated mechanisms.

Glioblastoma (GBM) prognosis remains dismal due in part to the invasiveness of GBM cells. Interstitial fluid flow (IFF) has been shown to increase invasion of glioma cells in vitro through the CXCR4 receptor interacting with autologous, pericellular gradients of CXCL12 (autologous chemotaxis) or through the CD44 receptor interactions with the extracellular matrix (hyaluronan-mediated mechanotransduction). These mechanisms have not been examined together and thus we hypothesized that both mechanisms contribute to invasion in populations of cancer cells. Therefore, we examined IFF-stimulated CXCR4-, CXCL12-, and CD44-dependent invasion in patient-derived glioblastoma stem cells (GSCs). Using our 3D in vitro assay and correlative in vivo studies we demonstrated GSC lines show increased invasion with flow. This flow-stimulated invasion was reduced by blockade of CXCR4, CXCL12, and/or CD44, revealing that GSC invasion may be mediated simultaneously by both mechanisms. Characterization of CXCR4+, CXCL12+, and CD44+ populations in four GSC lines revealed different percentages of protein positive subpopulations for each line. We developed an agent-based model to identify the contributions of each subpopulation to flow-stimulated invasion and validated the model through comparisons with experimental blocking studies. Clinically relevant radiation therapy increased flow-stimulated invasion in one GSC line. Our agent-based model predicted that IFF-stimulated invasion is driven primarily by CXCR4+CXCL12+ populations, and, indeed our irradiated cells had an increase in this subpopulation. Together, these data indicate that different mechanisms govern the flow response across GSCs, but that within a single patient, there are subpopulations of GSCs that respond to flow via either CD44- or CXCR4-CXCL12 mechanisms.

Autophagy Induction by Endothelial-Monocyte Activating Polypeptide II Contributes to the Inhibition of Malignant Biological Behaviors by the Combination of EMAP II with Rapamycin in Human Glioblastoma

This study aims to investigate the effect of endothelial-monocyte activating polypeptide II (EMAP II) on human glioblastoma (GBM) cells and glioblastoma stem cells (GSCs) as well as its possible mechanisms. In this study, EMAP II inhibited the cell viability and decreased the mitochondrial membrane potential in human GBM cells and GSCs, and autophagy inhibitor 3-methyl adenine (3-MA) blocked these effects. Autophagic vacuoles were formed in these cells after EMAP II treatment and this phenomenon was blocked by 3-MA. In addition, the up-regulation of microtubule-associated protein-1 light chain-3 (LC3)-II and the down-regulation of autophagic degraded substrate p62/SQSTM1 caused by EMAP II were observed. Cells treated with EMAP-II inhibited the PI3K/Akt/mTOR signal pathway, and PI3K/Akt agonist insulin-like growth factor-1 (IGF-1) blocked the effect of EMAP II on the expression of LC3-II and p62/SQSTM1. Cells exposed to EMAP-II experienced mitophagy and ER stress. Furthermore, the inhibition of cell proliferation, migration and invasion of GBM cells and GSCs were more remarkable by the combination of EMAP II and rapamycin than either agent alone in vitro and in vivo. The current study demonstrated that the cytotoxicity of EMAP II in human GBM cells and GSCs was induced by autophagy, accompanied by the inhibition of PI3K/Akt/mTOR signal pathway, mitophagy and ER stress. The combination of EMAP II with rapamycin demonstrated the inhibitory effect on the malignant biological behaviors of human GBM cells and GSCs in vitro and in vivo.

CS-21 * EphA2 PROMOTES INFILTRATIVE INVASION OF GLIOMA STEM CELLS IN VIVO THROUGH CROSSTALK WITH Akt AND REGULATES STEM PROPERTIES

Diffuse infiltrative invasion is a major cause for the dismal prognosis of glioblastoma (GBM), but the underlying mechanisms remain incompletely understood. Using human glioblastoma stem cells (GSCs) that recapitulate the invasive propensity of primary GBM, we find that EphA2 critically regulates GBM invasion in vivo. EphA2 was expressed in all seven GSC lines examined, and overexpression of EphA2 enhanced intracranial invasion. The effects required Akt-mediated phosphorylation of EphA2 on serine 897. In vitro the Akt-EphA2 signaling axis is maintained in the absence of ephrin-A ligands and is disrupted upon ligand stimulation. To test whether ephrin-As in tumor microenvironment can regulate GSC invasion, the newly established Efna1;Efna3;Efna4 triple knockout mice (TKO) were used in an ex vivo brain slice invasion assay. We observed significantly increased GSC invasion through the brain slices of TKO mice relative to wild type littermates. Mechanistically EphA2 knockdown suppressed stem properties of GSCs, causing diminished self-renewal, reduced stem marker expression and decreased tumorigenicity. In a subset of GSCs, the reduced stem properties were associated with lower Sox2 expression. Overexpression of EphA2 promoted stem properties in a kinase-independent manner and increased Sox2 expression. In addition to suppressing invasion, disrupting Akt-EphA2 crosstalk attenuated stem marker expression and neurosphere formation while having minimal effects on tumorigenesis, suggesting that the Akt-EphA2 signaling axis contributes to the stem properties. Taken together, the results show that EphA2 endows invasiveness of GSCs in vivo in cooperation with Akt and contributes to the maintenance of stem properties.

MiR-125b Inhibitor May Enhance the Invasion-Prevention Activity of Temozolomide in Glioblastoma Stem Cells by Targeting PIAS3

Temozolomide, an alkylating agent, is a promising chemotherapeutic agent for treating glioblastoma. Although chemotherapy with temozolomide may restrain tumor growth for some months, invariable tumor recurrence suggests that cancer stem cells maintaining these tumors persist. Previous research has shown that temozolomide can inhibit the proliferation of human glioblastoma stem cells (GSCs); however, no research has focused on the invasion of GSCs, which is an important factor for glioblastoma recurrence. Accumulating evidence indicates that microRNA (miR)-125b over-expression in GSCs may increase their invasiveness. Our objective was to identify the effects and mechanism of action of an miR-125b inhibitor combined with temozolomide in the invasive pathogenesis of GSCs. We modified the levels of miR-125b expression in primary GSCs in order to observe the effect on sensitivity to temozolomide on invasion, and we further analyzed the differences in mechanism between miR-125b treatment alone and treatment with miR-125b plus temozolomide using the Cancer PathwayFinder PCR Array. Our results demonstrated that either an miR-125b inhibitor or temozolomide could modestly inhibit the invasiveness of GSCs. Furthermore, GSCs that were pre-transfected with an miR-125b inhibitor, then treated with temozolomide, showed significantly decreased invasiveness when compared with GSCs treated with an miR-125b inhibitor or temozolomide alone. Further research into the underlying mechanism demonstrated that the miR-125b inhibitor enhanced the invasion-prevention activity of temozolomide in GSCs through targeting PIAS3 (protein inhibitor of activated STAT [signal transducer and activator of transcription]), which contributed to reduced STAT3 transcriptional activity and subsequent decreased expression of matrix metalloproteinase (MMP)-2 and -9. miR-125b could play a role in the development of temozolomide resistance in GSCs. Inhibition of miR-125b expression may enhance sensitivity of GSCs to temozolomide by targeting PIAS3 on cell invasion.

ADAM17 promotes U87 glioblastoma stem cell migration and invasion

Glioblastoma stem cells (GSCs) are thought to contribute to the diffuse invasiveness of malignant gliomas. Emerging evidence supports a role for a disintegrin and metalloproteinase 17 (ADAM17) in proteolytic ectodomain shedding of several EGFR-binding ligands, which subsequently activate PI3K/AKT and MEK/ERK pathways through EGFR phosphorylation thus mediating glioma invasiveness. However, it is not clear if ADAM17 also plays important roles in promoting GSC invasion. In this study, we isolated CD133+ GSCs from the human glioblastoma cell line U87 using fluorescence-activated cell sorting and demonstrated their increased invasive potential compared with matched non-stem tumor cells. Furthermore, we showed that CD133+ GSCs expressed higher levels of ADAM17. Immunofluorescence staining revealed that high expression levels of ADAM17 at the invasive front were correlated with the presence of CD133+ GSCs in human glioblastoma specimens. Stimulation with the ADAM17 agonist chemokine phorbol myristate acetate increased migration and invasion of GSCs, which was counteracted by ADAM17 knockdown. In addition, ADAM17 also induced CD133+ GSC invasion via activation of the EGFR/PI3K/AKT signaling pathway. These findings suggest that ADAM17 is involved in U87 GSC invasive process and may provide a potential therapeutic target for glioma treatment.

Functional Differences of miR-125b on the Invasion of Primary Glioblastoma CD133-Negative Cells and CD133-Positive Cells

MicroRNAs (miRNAs) are small noncoding RNAs whose function as modulators of gene expression is crucial for the proper control of cell development, differentiation, and homeostasis. The total number and composition of miRNAs expressed per cell at different stages of development varies widely, and the same miRNA may function differently at different stages of development. In this prospective study, we evaluated the function of miR-125b at different developmental stages of glioblastoma cells, such as primary glioblastoma cells and the corresponding stem cells. CD133 is an important surface marker in glioblastoma stem cells. We found that the upregulation of miR-125b had no effects on the invasion of primary glioblastoma CD133-negative cells but that it could inhibit the invasion of corresponding CD133-positive cells; however, the downregulation of miR-125b also had no effects on the invasion of primary glioblastoma CD133-negative cells but promoted the invasion of CD133-positive cells. Further research into the underlying mechanism demonstrated that the effects of miR-125b on the invasion of glioblastoma CD133-positive cells were associated with the alteration of the expression of MMPs (MMP-2 and MMP-9) and corresponding inhibitors (RECK and TIMP3). Our results demonstrate that miR-125b expression plays an essential role in the invasion of glioblastoma CD133-positive cells but not CD133-negative cells. Therefore, miR-125b may represent a novel target for therapy targeting the invasion of glioblastoma stem cells in the future.

Platelet-derived growth factor receptors differentially inform intertumoral and intratumoral heterogeneity.

Growth factor-mediated proliferation and self-renewal maintain tissue-specific stem cells and are frequently dysregulated in cancers. Platelet-derived growth factor (PDGF) ligands and receptors (PDGFRs) are commonly overexpressed in gliomas and initiate tumors, as proven in genetically engineered models. While PDGFRα alterations inform intertumoral heterogeneity toward a proneural glioblastoma (GBM) subtype, we interrogated the role of PDGFRs in intratumoral GBM heterogeneity. We found that PDGFRα is expressed only in a subset of GBMs, while PDGFRβ is more commonly expressed in tumors but is preferentially expressed by self-renewing tumorigenic GBM stem cells (GSCs). Genetic or pharmacological targeting of PDGFRβ (but not PDGFRα) attenuated GSC self-renewal, survival, tumor growth, and invasion. PDGFRβ inhibition decreased activation of the cancer stem cell signaling node STAT3, while constitutively active STAT3 rescued the loss of GSC self-renewal caused by PDGFRβ targeting. In silico survival analysis demonstrated that PDGFRB informed poor prognosis, while PDGFRA was a positive prognostic factor. Our results may explain mixed clinical responses of anti-PDGFR-based approaches and suggest the need for integration of models of cancer as an organ system into development of cancer therapies.