Identification of a SOX2-dependent subset of tumor- and sphere-forming glioblastoma cells with a distinct tyrosine kinase inhibitor sensitivity profile

Rapamycin inhibited the function of lung CSCs via SOX2

The presence of cancer stem cells (CSCs) is the source of occurrence, aggravation, and recurrence of lung cancer. Accordingly, targeting killing the lung CSCs has been suggested to be an effective approach for lung cancer treatment. In this study, we showed that rapamycin inhibited the mammalian target of rapamycin (mTOR) signal transduction in A549 cells and improved the sensitivity to cisplatin (DDP). The mechanisms involve inhibition of the SOX2 expression, cell proliferation, epithelial-mesenchymal transition (EMT) phenotype, and sphere formation. Interestingly, knocked down SOX2 was a similar effect with rapamycin in A549 sphere. Furthermore, we showed that ectopic expression of Sox2 in A549 cells was sufficient to render them more resistant to rapamycin treatment in vitro. These data suggested that rapamycin inhibited the function of lung CSCs via SOX2. It will be of great interest to further explore the therapeutic strategies of lung cancer.

Profiling gene promoter occupancy of Sox2 in two phenotypically distinct breast cancer cell subsets using chromatin immunoprecipitation and genome-wide promoter microarrays

Introduction

Aberrant expression of the embryonic stem cell marker Sox2 has been reported in breast cancer (BC). We previously identified two phenotypically distinct BC cell subsets separated based on their differential response to a Sox2 transcription activity reporter, namely the reporter-unresponsive (RU) and the more tumorigenic reporter-responsive (RR) cells. We hypothesized that Sox2, as a transcription factor, contributes to their phenotypic differences by mediating differential gene expression in these two cell subsets.

Methods

We used chromatin immunoprecipitation and a human genome-wide promoter microarray (ChIP-chip) to determine the promoter occupancies of Sox2 in the MCF7 RU and RR breast cancer cell populations. We validated our findings with conventional chromatin immunoprecipitation, quantitative reverse transcription polymerase chain reaction (qPCR), and western blotting using cell lines, and also performed qPCR using patient RU and RR samples.

Results

We found a largely mutually exclusive profile of gene promoters bound by Sox2 between RU and RR cells derived from MCF7 (1830 and 456 genes, respectively, with only 62 overlapping genes). Sox2 was bound to stem cell- and cancer-associated genes in RR cells. Using quantitative RT-PCR, we confirmed that 15 such genes, including PROM1 (CD133), BMI1, GPR49 (LGR5), and MUC15, were expressed significantly higher in RR cells. Using siRNA knockdown or enforced expression of Sox2, we found that Sox2 directly contributes to the higher expression of these genes in RR cells. Mucin-15, a novel Sox2 downstream target in BC, contributes to the mammosphere formation of BC cells. Parallel findings were observed in the RU and RR cells derived from patient samples.

Conclusions

In conclusion, our data supports the model that the Sox2 induces differential gene expression in the two distinct cell subsets in BC, and contributes to their phenotypic differences.

Electronic supplementary material

The online version of this article (doi:10.1186/s13058-014-0470-2) contains supplementary material, which is available to authorized users.

Platelet-derived growth factor in glioblastoma-driver or biomarker?

The platelet-derived growth factor (PDGF) family of mitogens exerts vital functions during embryonal development, e.g. in the central nervous system, where PDGF drives the proliferation of oligodendrocyte precursors. PDGF and PDGF receptors are co-expressed in human glioblastoma (GBM). Whether an aberrant activation of the PDGF receptor pathway is a driving force in glioma development has remained an open question. In experimental animals, overexpression of PDGF has convincingly been shown to induce tumors, both in wild-type animals (marmoset, rat, mouse) and in mice with targeted deletions of suppressor genes, e.g. Tp53 or Ink4A. Targeting the PDGF receptor in tumor-bearing mice leads to growth inhibition and reversion of the transformed phenotype. Findings of PDGF receptor amplification or mutations in human GBM are strong indicators of a causative role of the PDGF receptor pathway. However, clinical trials using PDGF receptor antagonists have been disappointing. In conclusion, a PDGF receptor profile may be a biomarker for a subgroup of GBM originating from a PDGF receptor-responsive cell. Although compelling experimental and clinical evidence supports the notion that the PDGF receptor pathway is a driver in GBM, formal proof is still missing.

Role of SOX family of transcription factors in central nervous system tumors

SOX genes are developmental regulators with functions in the instruction of cell fate and maintenance of progenitor's identity during embryogenesis. They play additional roles during tissue homeostasis and regeneration in adults particularly in the Central Nervous System (CNS). In the last years a growing number of evidences has shown that mutations and dysfunction of SOX factors are implicated in several human diseases, including a variety of cancers. In this review, we will summarize the current knowledge about SOX family in CNS tumors and their role in the origin and maintenance of the subpopulation of cancer stem cells in these tumors.

SOX2 expression is an early event in a murine model of EGFR mutant lung cancer and promotes proliferation of a subset of EGFR mutant lung adenocarcinoma cell lines

OBJECTIVES

Primary and acquired resistance to EGFR TKIs in EGFR mutant lung cancer occurs primarily through secondary mutations in EGFR or Met amplification. Drug resistance can also be mediated by expression of pluripotency transcription factors, such as OCT4, SOX2 and NANOG that decrease terminal differentiation. In this study, we investigated the expression and role of SOX2 in model systems of EGFR mutant tumors.

MATERIALS AND METHODS

Immunoblotting or immunohistochemistry was used to assess expression of pluripotency transcription factors in lungs of transgenic mice or in human NSCLC cell lines. Expression of SOX2 was reduced by shRNA knockdown, and response to erlotinib and cellular proliferation were assessed.

RESULTS AND CONCLUSION

Induction of mutant EGFR in transgenic CCSP-rtTA/TetO-EGFR(L858R/T790M) mice correlated with increased OCT4 and SOX2 expression in lung tissue prior to tumor development. Established lung tumors retained SOX2 expression. To assess a role for SOX2 in tumorigenesis, a panel of NSCLC cell lines with activating EGFR mutations was assessed for SOX2 expression. Two of six cell lines with mutant EGFR showed detectable SOX2 levels, suggesting SOX2 expression did not correlate with EGFR mutation status. To assess the role of SOX2 in these cell lines, HCC827 and H1975 cells were infected with lentivirus containing SOX2 shRNA. Knockdown of SOX2 decreased proliferation in both cell lines and increased sensitivity to erlotinib in HCC827 cells. Because constitutive activation of the PI3K/Akt pathway is associated with EGFR TKI resistance, cells were treated with PI3K/AKT inhibitors and expression of SOX2 was examined. PI3K/Akt inhibitors decreased SOX2 expression in a time-dependent manner. These data suggest targeting SOX2 may provide therapeutic benefit in the subset of EGFR-mutant tumors with high constitutive levels of SOX2, and that until more direct means of inhibiting SOX2 are developed, PI3K/Akt inhibitors might be useful to inhibit SOX2 in EGFR TKI resistant tumors.

FoxG1 interacts with Bmi1 to regulate self-renewal and tumorigenicity of medulloblastoma stem cells

Brain tumors represent the leading cause of childhood cancer mortality, of which medulloblastoma (MB) is the most frequent malignant tumor. Recent studies have demonstrated the presence of several MB molecular subgroups, each distinct in terms of prognosis and predicted therapeutic response. Groups 1 and 2 are characterized by relatively good clinical outcomes and activation of the Wnt and Shh pathways, respectively. In contrast, groups 3 and 4 ("non-Shh/Wnt MBs") are distinguished by metastatic disease, poor patient outcome, and lack a molecular pathway phenotype. Current gene expression platforms have not detected brain tumor-initiating cell (BTIC) self-renewal genes in groups 3 and 4 MBs as BTICs typically comprise a minority of tumor cells and may therefore go undetected on bulk tumor analyses. Since increasing BTIC frequency has been associated with increasing tumor aggressiveness and poor patient outcome, we investigated the subgroup-specific gene expression profile of candidate stem cell genes within 251 primary human MBs from four nonoverlapping MB transcriptional databases (Amsterdam, Memphis, Toronto, Boston) and 74 NanoString-subgrouped MBs (Vancouver). We assessed the functional relevance of two genes, FoxG1 and Bmi1, which were significantly enriched in non-Shh/Wnt MBs and showed these genes to mediate MB stem cell self-renewal and tumor initiation in mice. We also identified their transcriptional regulation through reciprocal promoter occupancy in CD15+ MB stem cells. Our work demonstrates the application of stem cell data gathered from genomic platforms to guide functional BTIC assays, which may then be used to develop novel BTIC self-renewal mechanisms amenable to therapeutic targeting.

YB-1 regulates Sox2 to coordinately sustain stemness and tumorigenic properties in a phenotypically distinct subset of breast cancer cells

BACKGROUND

Sox2, a transcription factor and an embryonic stem cell marker, has been implicated in the pathogenesis of breast cancer (BC). YB-1 is another transcription factor that has been shown to promote stemness in BC cells.

METHODS

Western blotting, quantitative PCR, and siRNAs were used to query the regulatory relationships between YB-1, Sox2, and their downstream targets. Chromatin immunoprecipitation was used to detect YB-1 interactions at the Sox2 promoter. Mammosphere and soft agar assays were used to assess the phenotypic consequences of YB-1 knockdown.

RESULTS

Here, we report that YB-1 regulates Sox2. YB-1 was found to bind to the SOX2 promoter and down-regulate its expression in MCF7 and ZR751. The regulatory interaction between YB-1 and Sox2 was drastically different between the two phenotypically distinct cell subsets, purified based on their differential response to a Sox2 reporter. They are referred to as the reporter unresponsive (RU) cells and the reporter responsive (RR) cells. Upon siRNA knockdown of YB-1, RU cells showed an increase in Sox2 expression but no change in Sox2 reporter activity; in contrast, RR cells exhibited increased expression and reporter activity of Sox2. Correlating with these findings, YB-1 knockdown induced a differential response in the expression of genes known to be regulated by both Sox2 and YB-1 (e.g. CCND1 and ITGA6). For instance, in response to YB-1 knockdown, CCND1 and ITGA6 expression were decreased or unchanged in RU cells but paradoxically increased in RR cells. Compared to RU cells, RR cells were significantly more resistant to the suppression of mammosphere formation due to YB-1 knockdown. Importantly, mammospheres derived from parental MCF7 cells treated with YB-1 siRNA knockdown exhibited higher expression levels of SOX2 and its downstream targets.

CONCLUSIONS

To conclude, in a subset of BC cells, namely RR cells, YB-1 regulates Sox2 to coordinately maintain stemness and tumorigenic properties.

Sox2 promotes malignancy in glioblastoma by regulating plasticity and astrocytic differentiation

The high-mobility group-box transcription factor sex-determining region Y-box 2 (Sox2) is essential for the maintenance of stem cells from early development to adult tissues. Sox2 can reprogram differentiated cells into pluripotent cells in concert with other factors and is overexpressed in various cancers. In glioblastoma (GBM), Sox2 is a marker of cancer stemlike cells (CSCs) in neurosphere cultures and is associated with the proneural molecular subtype. Here, we report that Sox2 expression pattern in GBM tumors and patient-derived mouse xenografts is not restricted to a small percentage of cells and is coexpressed with various lineage markers, suggesting that its expression extends beyond CSCs to encompass more differentiated neoplastic cells across molecular subtypes. Employing a CSC derived from a patient with GBM and isogenic differentiated cell model, we show that Sox2 knockdown in the differentiated state abolished dedifferentiation and acquisition of CSC phenotype. Furthermore, Sox2 deficiency specifically impaired the astrocytic component of a biphasic gliosarcoma xenograft model while allowing the formation of tumors with sarcomatous phenotype. The expression of genes associated with stem cells and malignancy were commonly downregulated in both CSCs and serum-differentiated cells on Sox2 knockdown. Genes previously shown to be associated with pluripontency and CSCs were only affected in the CSC state, whereas embryonic stem cell self-renewal genes and cytokine signaling were downregulated, and the Wnt pathway activated in differentiated Sox2-deficient cells. Our results indicate that Sox2 regulates the expression of key genes and pathways involved in GBM malignancy, in both cancer stemlike and differentiated cells, and maintains plasticity for bidirectional conversion between the two states, with significant clinical implications.

Glioblastoma development in mouse brain: general reduction of OCTs and mislocalization of OCT3 transporter and subsequent uptake of ASP+ substrate to the nuclei

Organic cation transporters (OCTs) were first found and then isolated from cultured glioma cells. When glioma cells are implanted into brain the fate of OCTs varies with time after implantation and transporter type. Here we report that OCT1, OCT2 and OCT3 immunofluorescence is significantly reduced over time in implanted GL261 glioma cells, during tumor development in the brain. By day 21 after glioma implantation, OCT1, OCT2 and OCT3 immunofluorescence was reduced more than 10-fold in the cytoplasm of glioma cells, while OCT3 immunofluorescence became concentrated in the nucleus. The well-known fluorescent substrate for OCT transporters, 4-(4-(dimethylamino)-styryl)-N-methylpyridinium iodide (ASP⁺), previously shown to accumulate in glioma-cell cytoplasm in in vivo slices, began to accumulate in the nucleus of these cells, but not in cytoplasm, after 21 days post-implantation. Considering this mislocalization phenomenon, and other literature on similar nuclear mislocalization of different transporters, receptors and channels in glioma cells, we suggest that it is one of the "omens" preceding the motility and aggressivity changes in glioma behavior.

LIN28 is involved in glioma carcinogenesis and predicts outcomes of glioblastoma multiforme patients

LIN28, an evolutionarily conversed RNA binding protein which can bind to the terminal loops of let-7 family microRNA precursors and block their processing to maturation, is highly expressed in several subsets of tumors that carry poor prognoses, such as ovarian carcinoma, hepatocellular carcinoma, colon carcinoma and germ cell carcinoma. However, there has been no study on the expression of LIN28 in glioma tissues or their importance as a prognostic predictor of glioma patients. This study aimed to examine the expression of LIN28 in glioma and correlate the results to patient outcome. We found that LIN28 expression was significantly higher in the group of patients with a poor prognosis compared to patients with a good prognosis by gene microarray. Log-rank analysis showed patients with higher LIN28 expression level in tumor had a shorter progression-free survival and overall survival times compared to those with lower LIN28 expression level. Similar results were also obtained from the tissue microarray analysis. Univariate and multivariate analyses showed high LIN28 expression was an independent prognostic factor for a shorter progression-free survival and overall survival in GBM patients. Furthermore in vitro experiments showed that down-regulation of LIN28 in U251 and U373 cells caused cell cycle arrest in the G1 phase, delayed cell proliferation, increased apoptosis, and resulted in fewer colonies compared to controls. Summarily, our data provides a potential target for cancer therapy as an approach to overcome the poor options currently available for GBM patients.

Disrupting the CXCL12/CXCR4 axis disturbs the characteristics of glioblastoma stem-like cells of rat RG2 glioblastoma

BACKGROUND

Glioblastoma stem-like cells (GSC) have been shown to promote tumor growth, tumor-associated neovascularization, therapeutic resistance, and metastasis. CXCR4 receptors have been found involved in the proliferation, metastasis, angiogenesis, and drug-resistant characteristics of glioblastoma. However, the role of CXCR4 in modulating the stem-like cell properties of rat glioblastoma remains ambiguous.

METHODS

To explore the role of the CXCL12/CXCR4 axis in maintaining rat GSC properties, we disrupted the CXCR4 signaling by using small hairpin interfering RNA (shRNA). To investigate the role of the CXCL12/CXCR4 axis in maintaining rat GSC properties, we used a spheroid formation assay to assess the stem cell self-renewal properties. A western blot analysis and PCR arrays were used to examine the genes involved in proliferation, self-renewal, and cancer drug resistance. Finally, DNA content and flow cytometry, an immunohistochemical analysis, and methylcellulose colony formation, in vitro invasive and intracranial injection xenograft assays were employed to examine the disruptive effect of CXCR4 on the characteristics of GSCs of the RG2 cell line.

RESULTS

Disrupting CXCR4 inhibited the proliferation of RG2 cells both in vitro and in vivo. The spheroid formation assay indicated that CXCR4 was vital for the self-renewal of RG2 GSCs. Disrupting the CXCL12/CXCR4 pathway also reduced the expression of GSC cell markers, including Nestin, ABCG2, and musashi (Msi), and the expression of genes involved in regulating stem cell properties, including Oct4, Nanog, maternal embryonic leucine zipper kinase (MELK), MGMT, VEGF, MMP2, and MMP9.

CONCLUSION

The chemokine receptor CXCR4 is crucial for maintaining the self-renewal, proliferation, therapeutic resistance, and angiogenesis of GSCs of rat RG2 glioblastoma.

Correlation of Nrf2 and HIF-1α in glioblastoma and their relationships to clinicopathologic features and survival

OBJECTIVES

Glioblastoma (GB) is the most common, aggressive, and proliferative among all brain tumors. The prognosis of GB is still far from satisfactory currently, thus demanding great modification and enhancement, which may be acquired by the help of the molecular target therapy. Nuclear factor E2-related factor 2 (Nrf2), a pivotal transcriptional factor of cellular responses to oxidative stress, was observed to function remarkably in cancer pathobiology. In the current study, we analyzed the correlation between Nrf2 and Hypoxia-inducible factor-1alpha (HIF-1alpha) in GB, together with their association to the features and survival of clinicopathology.

METHODS

We examined the expression of Nrf2 and HIF-1alpha in 68 specimens of GB by tissue microarray and immunohistochemistry, and correlated this investigation to the outcome of GB patients.

RESULTS

Nrf2 and HIF-1alpha were overexpressed in GB tissues. There was significant correlation between the high level of Nrf2 and tumor necrosis on MRI and 1-year survival. There was significant correlation between HIF-1alpha level and Nrf2 status (r = 0·294, P = 0·015). Kaplan-Meier analysis showed that high Nrf2 expression was significantly associated with shorter overall survival (OS) (log-rank test, P = 0·006), and was identified as an independent prognostic factor in multivariate analysis (P = 0·034). HIF-1alpha was another independent factor for both OS and progression-free survival by Cox regression analysis (P = 0·048 and P = 0·032, respectively).

DISCUSSION

Mutual association between Nrf2 and HIF-1alpha was found in GB: higher Nrf2 expression and poorer outcome of GB patients. Nrf2 would therefore be a new molecular marker for the targeted treatment of GB.

Brain tumor stem cells: Molecular characteristics and their impact on therapy

Glioblastoma (GBM) is the most prevalent primary brain tumor and ranks among the most lethal of human cancers with conventional therapy offering only palliation. Great strides have been made in understanding brain cancer genetics and modeling these tumors with new targeted therapies being tested, but these advances have not translated into substantially improved patient outcomes. Multiple chemotherapeutic agents, including temozolomide, the first-line treatment for glioblastoma, have been developed to kill cancer cells. However, the response to temozolomide in GBM is modest. Radiation is also moderately effective but this approach is plagued by limitations due to collateral radiation damage to healthy brain tissue and development of radioresistance. Therapeutic resistance is attributed at least in part to a cell population within the tumor that possesses stem-like characteristics and tumor propagating capabilities, referred to as cancer stem cells. Within GBM, the intratumoral heterogeneity is derived from a combination of regional genetic variance and a cellular hierarchy often regulated by distinct cancer stem cell niches, most notably perivascular and hypoxic regions. With the recent emergence as a key player in tumor biology, cancer stem cells have symbiotic relationships with the tumor microenvironment, oncogenic signaling pathways, and epigenetic modifications. The origins of cancer stem cells and their contributions to brain tumor growth and therapeutic resistance are under active investigation with novel anti-cancer stem cell therapies offering potential new hope for this lethal disease.

The differentiation of pancreatic tumor-initiating cells by vitronectin can be blocked by cilengitide

OBJECTIVE

Pancreatic cancer is a leading cancer type and its molecular pathology is poorly understood. The only potentially curative therapeutic option available is complete surgical resection; however, this is inadequate as most of the patients are diagnosed at an advanced or metastatic stage. Tumor-initiating cells (TICs) constitute a subpopulation of cells within a solid tumor that sustain tumor growth, metastasis, and chemo/radioresistance. Within pancreatic cancer, TICs have been identified based on the expression of specific cell surface markers.

METHODS

We use a sphere formation assay to enrich putative TICs and use human serum as a driver of differentiation. We demonstrate by using specific blocking reagents that we can inhibit the differentiation process and maintain TIC-associated markers and genes.

RESULTS

We can induce differentiation of pancreatospheres with the addition of human serum, and we identified vitronectin as an inducer of differentiation. We inhibit differentiation by human serum using an arginine-glycine-aspartate-specific peptide, which is Cilengitide; hence, demonstrating this differentiation is mediated via specific integrin receptors.

CONCLUSIONS

Overall, our studies further the definition of pancreatic TICs and provide further insight into both the maintenance and differentiation of this lethal population.

Visualization of implanted GL261 glioma cells in living mouse brain slices using fluorescent 4-(4-(dimethylamino)-styryl)-N-methylpyridinium iodide (ASP+)

Here we describe a new method of glioma cell visualization in living brain slices that can be used for evaluation of tumor size or visualization of internal tumor structures. Glial cells, as well as glioma cells of glial origin, express high levels of organic cation transporters. We demonstrate that application of a fluorescent substrate for these transporters 4-(4-(dimethylamino)-styryl)-N-methylpyridinium iodide (ASP+) to the incubation medium leads to quick accumulation of fluorescence in glioma cells during early developmental stages and in astrocytes, but not in neurons. Stained brain slices can be immediately investigated using confocal or fluorescence microscopy. Glioma and glial cells can be discriminated from each other because of their different morphology. The method described has the advantage of staining living tissue and is simple to perform.

Sox21 inhibits glioma progression in vivo by forming complexes with Sox2 and stimulating aberrant differentiation

Sox2 is a transcription factor in neural stem cells and keeps the cells immature and proliferative. Sox2 is expressed in primary human glioma such as glioblastoma multiforme (GBM), primary glioma cells and glioma cell lines and is implicated in signaling pathways in glioma connected to malignancy. Sox21, the counteracting partner of Sox2, has the same expression pattern as Sox2 in glioma but in general induces opposite effects. In this study, Sox21 was overexpressed by using a tetracycline-regulated expression system (tet-on) in glioma cells. The glioma cells were injected subcutaneously into immunodeficient mice. The control tumors were highly proliferative, contained microvascular proliferation and large necrotic areas typical of human GBM. Induction of Sox21 in the tumor cells resulted in a significant smaller tumor size, and the effect correlated with the onset of treatment, where earlier treatment gave smaller tumors. Mice injected with glioma cells orthotopically into the brain survived significantly longer when Sox21 expression was induced. Tumors originating from glioma cells with an induced expression of Sox21 exhibited an increased formation of Sox2:Sox21 complexes and an upregulation of S100β, CNPase and Tuj1. Sox21 appears to decrease the stem-like cell properties of the tumor cells and initiate aberrant differentiation of glioma cells in vivo. Taken together our results indicate that Sox21 can function as a tumor suppressor during gliomagenesis mediated by a shift in the balance between Sox2 and Sox21. The wide distribution of Sox2 and Sox21 in GBM makes the Sox2/Sox21 axis a very interesting target for novel therapy of gliomas.

The multiple roles for Sox2 in stem cell maintenance and tumorigenesis

The Sry-containing protein Sox2 initially was known to regulate the self-renewal of the mouse and human embryonic stem cells (ESCs). It is also important for the maintenance of stem cells in multiple adult tissues including the brain and trachea, and it is one of the key transcription factors for establishing induced pluripotent stem cells. Recently, overexpression and gene amplification of Sox2 have been associated with the development of squamous cell carcinoma in multiple tissues such as the lung and esophagus. These different roles for Sox2 involve a complicated regulatory networks consisting of microRNAs, kinases and signaling molecules. While the levels of Sox2 are modulated transcriptionally and translationally, post-translational modification is also important for the various functions of Sox2. In clinics, high levels of Sox2 are correlated with poor prognosis and increased proliferation of cancer stem cells. Therefore targeting Sox2 can be potentially explored for a new therapeutic avenue to treat cancers. This review will focus on the different roles for Sox2 in stem cell maintenance and its oncogenic roles in the context of signal transcription and microRNA regulation. We will also review the main upstream and downstream targets of Sox2, which can be potentially used as therapeutic measures to treat cancer with abnormal levels of Sox2.

Overexpression of Golgi phosphoprotein-3 (GOLPH3) in glioblastoma multiforme is associated with worse prognosis

Golgi phosphoprotein-3 (GOLPH3), an important protein in mammalian target of rapamycin (mTOR) signaling, is overexpressed in and correlates with the pathological grade of glioma. However, the potential correlation between GOLPH3 and clinical outcome in patients with glioblastoma multiforme (GBM) remains unknown. In this study, we examined GOLPH3 expression in GBM by tissue microarray and correlated this measure to patient outcome. GOLPH3 expression in tumor tissue from 97 primary GBM patients was examined by tissue microarray and immunohistochemistry. Potential effects of GOLPH3 on tumor growth were also examined in representative cell lines (U251 and U87) by downregulating GOLPH3 with RNA interference. For this cohort, the median overall survival (OS) was 12 months [95 % confidence interval (CI): 10.31-13.69 months], and the median progression-free survival (PFS) was 10 months (95 % CI: 7.33-12.67 months). Tissue microarray analysis revealed high GOLPH3 expression in 40 patients (40/97, 41.2 %) and low GOLPH3 expression in the remaining 57 patients (57/97, 58.8 %). Log-rank test showed that patients with low GOLPH3 expression had significantly longer median OS (15 versus 10 months in patients with high GOLPH3 expression, p = 0.009) and median PFS (12 versus 7 months, p = 0.015). Univariate and Cox analysis indicated that GOLPH3 was an independent prognostic factor for OS and PFS. In in vitro experiments, GOLPH3 downregulation by small interfering RNA (siRNA) suppressed proliferation and clonogenic growth in cultured cell lines. These findings demonstrate that high GOLPH3 expression is associated with poor outcome of GBM patients.

The quest for self-identity: not all cancer stem cells are the same

A central critique of the cancer stem cell (CSC) hypothesis involves the robustness of CSC markers. Zorniak and colleagues suggest that different progenitor marker profiles can classify CSCs, and improved modeling of cellular hierarchies can be achieved by incorporating inter- and intratumoral diversity.

PDGF and PDGF receptors in glioma

The family of platelet-derived growth factors (PDGFs) plays a number of critical roles in normal embryonic development, cellular differentiation, and response to tissue damage. Not surprisingly, as it is a multi-faceted regulatory system, numerous pathological conditions are associated with aberrant activity of the PDGFs and their receptors. As we and others have shown, human gliomas, especially glioblastoma, express all PDGF ligands and both the two cell surface receptors, PDGFR-α and -β. The cellular distribution of these proteins in tumors indicates that glial tumor cells are stimulated via PDGF/PDGFR-α autocrine and paracrine loops, while tumor vessels are stimulated via the PDGFR-β. Here we summarize the initial discoveries on the role of PDGF and PDGF receptors in gliomas and provide a brief overview of what is known in this field.