Sox2 is translationally activated by eukaryotic initiation factor 4E in human glioma-initiating cells

Boric Acid Suppresses Glioblastoma Cellular Survival by Regulating Ferroptosis via SOX10/GPx4/ACSL4 Signalling and Iron Metabolism

Ferroptosis, a distinct form of regulated cell death, plays a role in glioma pathogenesis. SRY-box (SOX) transcription factors are key regulators of cancer progression. In this study, we investigated the role of SOX10 in ferroptosis induction in U87 cells following boric acid treatment. First, the cytotoxic effects of boric acid on HMC3 and U87 cells were assessed using CCK8 and BrdU incorporation assays. Subsequently, SOX10, GPX4, ACSL4, GSH, MDA, total ROS, Fe2+, and TFR levels were analysed using ELISA, Western blot, and RT-PCR techniques. Additionally, DAPI staining was performed to evaluate nuclear abnormalities. According to the CCK8 analysis, the IC50 value for boric acid was determined to be 3.12 mM for HMC3 cells and 532 μM for U87 cells, a finding further supported by BrdU incorporation analysis, which indicated that U87 cells were more sensitive to boric acid. Western blot and RT-PCR analyses revealed that SOX10 expression was significantly higher in U87 cells compared to HMC3 cells. Boric acid treatment led to a reduction in GSH, GPX4, and SOX10 levels in U87 cells, while inducing an increase in MDA, total ROS, ACSL4, Fe2+, and TFR levels. Moreover, microscopic analysis demonstrated that boric acid treatment induced both morphological and nuclear abnormalities in U87 cells. In conclusion, our findings demonstrate that SOX10 is involved in the ferroptosis signalling pathway and that boric acid effectively suppresses U87 cell viability by targeting the SOX10/GPX4/ACSL4 axis.

N7-methylguanosin regulators-mediated methylation modification patterns and characterization of the immune microenvironment in lower-grade glioma

N7-methylguanosine (m7G) modification signature has recently emerged as a crucial regulator of tumor progression and treatment in cancer. However, there is limited information available on the genomic profile of lower-grade gliomas (LGGs) related to m7G methylation modification genes' function in tumorigenesis and progression. In this study, we employed bioinformatics methods to characterize m7G modifications in individuals with LGG from The Chinese Glioma Genome Atlas (CGGA) and The Cancer Genome Atlas (TCGA). We used gene set enrichment analysis (GSEA), single sample GSEA (ssGSEA), CIBERSORT algorithm, ESTIMATE algorithm, and TIDE to evaluate the association between m7G modification patterns, tumor microenvironment (TME) cell infiltration properties, and immune infiltration markers. The m7G scoring scheme using principal component analysis (PCA) was employed to investigate the m7G modification patterns quantitatively. We examined the m7G modification hub genes' expression levels in normal samples, refractory epilepsy samples, and LGG samples using immunohistochemistry, western-blotting, and qRT-PCR. Our findings revealed that individuals with LGG could be categorized into two groups based on m7G scores (high and low) according to the properties of m7G. Moreover, we observed that high m7G score was associated with significant clinical benefit and prolonged survival duration in the anti-PD-1 cohort, while low m7G score was associated with improved prognostic outcomes and increased likelihood of complete or partial response in the anti-PD-L1 cohort. Different m7G subtypes also showed varying Tumor Mutational Burden (TMB) and immune profiles and might have distinct responses to immunotherapy. Furthermore, we identified five potential genetic markers that were highly correlated with the m7G score signature index. These findings provide insight into the features and classification associated with m7G methylation modifications and may aid in improving the clinical outcome of LGG.

Crosstalk between SOX Genes and Long Non-Coding RNAs in Glioblastoma

Glioblastoma (GBM) continues to be the most devastating primary brain malignancy. Despite significant advancements in understanding basic GBM biology and enormous efforts in developing new therapeutic approaches, the prognosis for most GBM patients remains poor with a median survival time of 15 months. Recently, the interplay between the SOX (SRY-related HMG-box) genes and lncRNAs (long non-coding RNAs) has become the focus of GBM research. Both classes of molecules have an aberrant expression in GBM and play essential roles in tumor initiation, progression, therapy resistance, and recurrence. In GBM, SOX and lncRNAs crosstalk through numerous functional axes, some of which are part of the complex transcriptional and epigenetic regulatory mechanisms. This review provides a systematic summary of current literature data on the complex interplay between SOX genes and lncRNAs and represents an effort to underscore the effects of SOX/lncRNA crosstalk on the malignant properties of GBM cells. Furthermore, we highlight the significance of this crosstalk in searching for new biomarkers and therapeutic approaches in GBM treatment.

The dark side of mRNA translation and the translation machinery in glioblastoma

Among the different types of cancer affecting the central nervous system (CNS), glioblastoma (GB) is classified by the World Health Organization (WHO) as the most common and aggressive CNS cancer in adults. GB incidence is more frequent among persons aged 45–55 years old. GB treatments are based on tumor resection, radiation, and chemotherapies. The current development of novel molecular biomarkers (MB) has led to a more accurate prediction of GB progression. Moreover, clinical, epidemiological, and experimental studies have established genetic variants consistently associated with the risk of suffering GB. However, despite the advances in these fields, the survival expectancy of GB patients is still shorter than 2 years. Thus, fundamental processes inducing tumor onset and progression remain to be elucidated. In recent years, mRNA translation has been in the spotlight, as its dysregulation is emerging as a key cause of GB. In particular, the initiation phase of translation is most involved in this process. Among the crucial events, the machinery performing this phase undergoes a reconfiguration under the hypoxic conditions in the tumor microenvironment. In addition, ribosomal proteins (RPs) have been reported to play translation-independent roles in GB development. This review focuses on the research elucidating the tight relationship between translation initiation, the translation machinery, and GB. We also summarize the state-of-the-art drugs targeting the translation machinery to improve patients’ survival. Overall, the recent advances in this field are shedding new light on the dark side of translation in GB.

Glioblastoma as a Novel Drug Repositioning Target: Updated State

Glioblastoma multiforme (GBM) is an aggressive form of adult brain tumor that can arise from a low-grade astrocytoma. In recent decades, several new conventional therapies have been developed that have significantly improved the prognosis of patients with GBM. Nevertheless, most patients have a limited long-term response to these treatments and survive < 1 year. Therefore, innovative anti-cancer drugs that can be rapidly approved for patient use are urgently needed. One way to achieve accelerated approval is drug repositioning, extending the use of existing drugs for new therapeutic purposes, as it takes less time to validate their biological activity as well as their safety in preclinical models. In this review, a comprehensive analysis of the literature search was performed to list drugs with antiviral, antiparasitic, and antidepressant properties that may be effective in GBM and their putative anti-tumor mechanisms in GBM cells.

Machine learning-based identification of SOX10 as an immune regulator of macrophage in gliomas

Gliomas, originating from the glial cells, are the most lethal type of primary tumors in the central nervous system. Standard treatments like surgery have not significantly improved the prognosis of glioblastoma patients. Recently, immune therapy has become a novel and effective option. As a conserved group of transcriptional regulators, the Sry-type HMG box (SOX) family has been proved to have a correlation with numerous diseases. Based on the large-scale machine learning, we found that the SOX family, with significant immune characteristics and genomic profiles, can be divided into two distinct clusters in gliomas, among which SOX10 was identified as an excellent immune regulator of macrophage in gliomas. The high expression of SOX10 is related to a shorter OS in LGG, HGG, and pan-cancer groups but benefited from the immunotherapy. It turned out in single-cell sequencing that SOX10 is high in neurons, M1 macrophages, and neural stem cells. Also, macrophages are found to be elevated in the SOX10 high-expression group. SOX10 has a positive correlation with macrophage cytokine production and negative regulation of macrophages' chemotaxis and migration. In conclusion, our study demonstrates the outstanding cluster ability of the SOX family, indicating that SOX10 is an immune regulator of macrophage in gliomas, which can be an effective target for glioma immunotherapy.

Molecular Pathways and Genomic Landscape of Glioblastoma Stem Cells: Opportunities for Targeted Therapy

Glioblastoma (GBM) is an aggressive tumor of the central nervous system categorized by the World Health Organization as a Grade 4 astrocytoma. Despite treatment with surgical resection, adjuvant chemotherapy, and radiation therapy, outcomes remain poor, with a median survival of only 14-16 months. Although tumor regression is often observed initially after treatment, long-term recurrence or progression invariably occurs. Tumor growth, invasion, and recurrence is mediated by a unique population of glioblastoma stem cells (GSCs). Their high mutation rate and dysregulated transcriptional landscape augment their resistance to conventional chemotherapy and radiation therapy, explaining the poor outcomes observed in patients. Consequently, GSCs have emerged as targets of interest in new treatment paradigms. Here, we review the unique properties of GSCs, including their interactions with the hypoxic microenvironment that drives their proliferation. We discuss vital signaling pathways in GSCs that mediate stemness, self-renewal, proliferation, and invasion, including the Notch, epidermal growth factor receptor, phosphatidylinositol 3-kinase/Akt, sonic hedgehog, transforming growth factor beta, Wnt, signal transducer and activator of transcription 3, and inhibitors of differentiation pathways. We also review epigenomic changes in GSCs that influence their transcriptional state, including DNA methylation, histone methylation and acetylation, and miRNA expression. The constituent molecular components of the signaling pathways and epigenomic regulators represent potential sites for targeted therapy, and representative examples of inhibitory molecules and pharmaceuticals are discussed. Continued investigation into the molecular pathways of GSCs and candidate therapeutics is needed to discover new effective treatments for GBM and improve survival.

Long Noncoding RNA PVT1 Promotes Stemness and Temozolomide Resistance through miR-365/ELF4/SOX2 Axis in Glioma

Long non-coding RNA (lncRNA) are a class of non-coding RNAs demonstrated to play pivotal roles in regulating tumor progression. Therefore, deciphering the regulatory role of lncRNA in the development of glioma may offer a promising therapeutic target for treatment of glioma. We performed RT-qPCR analysis on the expression of lncRNA plasmacytoma variant translocation 1 (PVT1) and miR-365 in glioma tissues and cell lines. Cell proliferation and viability was assessed with CCK8 assay. Cell migration was assessed by wound healing assay. Transwell assay was used to assess cell invasion capacity. Expression of CD133+ cells was detected by flow cytometry. Western blot assay was used to detection the expression of ELF4 and stemness-related protein SOX2, Oct4 and Nanog. Bioinformatics and dual-luciferase assay were used to predict and validate the interaction between PVT1 and miR-365. Elevated PVT1 expression was observed in glioma tissues and cells. Knockdown of PVT1 and overexpression of miR-365 inhibited proliferation, migration, invasion and promoted stemness and Temozolomide (TMZ) resistance of glioma cells. PVT1 regulated ELF4 expression by competitively binds to miR-365. PVT1 regulated the stemness and sensitivity of TMZ of glioma cells through miR-365/ELF4/SOX2 axis. This study identified that PVT1 promoted glioma stemness through miR-365/ELF4/SOX2 axis.

Relevance of Translation Initiation in Diffuse Glioma Biology and its Therapeutic Potential

Cancer cells are continually exposed to environmental stressors forcing them to adapt their protein production to survive. The translational machinery can be recruited by malignant cells to synthesize proteins required to promote their survival, even in times of high physiological and pathological stress. This phenomenon has been described in several cancers including in gliomas. Abnormal regulation of translation has encouraged the development of new therapeutics targeting the protein synthesis pathway. This approach could be meaningful for glioma given the fact that the median survival following diagnosis of the highest grade of glioma remains short despite current therapy. The identification of new targets for the development of novel therapeutics is therefore needed in order to improve this devastating overall survival rate. This review discusses current literature on translation in gliomas with a focus on the initiation step covering both the cap-dependent and cap-independent modes of initiation. The different translation initiation protagonists will be described in normal conditions and then in gliomas. In addition, their gene expression in gliomas will systematically be examined using two freely available datasets. Finally, we will discuss different pathways regulating translation initiation and current drugs targeting the translational machinery and their potential for the treatment of gliomas.

Transcription factors in SOX family: Potent regulators for cancer initiation and development in the human body

Transcription factors (TFs) have a key role in controlling the gene regulatory network that sustains explicit cell states in humans. However, an uncontrolled regulation of these genes potentially results in a wide range of diseases, including cancer. Genes of the SOX family are indeed crucial as deregulation of SOX family TFs can potentially lead to changes in cell fate as well as irregular cell growth. SOX TFs are a conserved group of transcriptional regulators that mediate DNA binding through a highly conserved high-mobility group (HMG) domain. Accumulating evidence demonstrates that cell fate and differentiation in major developmental processes are controlled by SOX TFs. Besides; numerous reports indicate that both up- and down-regulation of SOX TFs may induce cancer progression. In this review, we discuss the involvement of key TFs of SOX family in human cancers.

The role of SOX family members in solid tumours and metastasis

Cancer is a heavy burden for humans across the world with high morbidity and mortality. Transcription factors including sex determining region Y (SRY)-related high-mobility group (HMG) box (SOX) proteins are thought to be involved in the regulation of specific biological processes. The deregulation of gene expression programs can lead to cancer development. Here, we review the role of the SOX family in breast cancer, prostate cancer, renal cell carcinoma, thyroid cancer, brain tumours, gastrointestinal and lung tumours as well as the entailing therapeutic implications. The SOX family consists of more than 20 members that mediate DNA binding by the HMG domain and have regulatory functions in development, cell-fate decision, and differentiation. SOX2, SOX4, SOX5, SOX8, SOX9, and SOX18 are up-regulated in different cancer types and have been found to be associated with poor prognosis, while the up-regulation of SOX11 and SOX30 appears to be favourable for the outcome in other cancer types. SOX2, SOX4, SOX5 and other SOX members are involved in tumorigenesis, e.g. SOX2 is markedly up-regulated in chemotherapy resistant cells. The SoxF family (SOX7, SOX17, SOX18) plays an important role in angio- and lymphangiogenesis, with SOX18 seemingly being an attractive target for anti-angiogenic therapy and the treatment of metastatic disease in cancer. In summary, SOX transcription factors play an important role in cancer progression, including tumorigenesis, changes in the tumour microenvironment, and metastasis. Certain SOX proteins are potential molecular markers for cancer prognosis and putative potential therapeutic targets, but further investigations are required to understand their physiological functions.

O-GlcNAc transferase activates stem-like cell potential in hepatocarcinoma through O-GlcNAcylation of eukaryotic initiation factor 4E

O-GlcNAcylation catalysed by O-GlcNAc transferase (OGT) is a reversible post-translational modification. O-GlcNAcylation participates in transcription, epigenetic regulation, and intracellular signalling. Dysregulation of O-GlcNAcylation in response to high glucose or OGT expression has been implicated in metabolic diseases and cancer. However, the underlying mechanisms by which OGT regulates hepatoma development remain largely unknown. Here, we employed the lentiviral shRNA-based system to knockdown OGT to analyse the contribution of OGT in hepatoma cell proliferation and stem-like cell potential. The sphere-forming assay and western blot analysis of stem-related gene expression were used to evaluate stem-like cell potential of hepatoma cell. We found that the level of total O-GlcNAcylation or OGT protein was increased in hepatocellular carcinoma. OGT activated stem-like cell potential in hepatoma through eukaryotic initiation factor 4E (eIF4E) which bound to stem-related gene Sox2 5'-untranslated region. O-GlcNAcylation of eIF4E at threonine 168 and threonine 177 protected it from degradation through proteasome pathway. Expression of eIF4E in hepatoma was determined by immunostaining in 232 HCC patients, and Kaplan-Meier survival analysis was used to determine the correlation of eIF4E expression with prognosis. High glucose promoted stem-like cell potential of hepatoma cell through OGT-eIF4E axis. Collectively, our findings indicate that OGT promotes the stem-like cell potential of hepatoma cell through O-GlcNAcylation of eIF4E. These results provide a mechanism of HCC development and a cue between the pathogenesis of HCC and high glucose condition.

ER stress inducer tunicamycin suppresses the self-renewal of glioma-initiating cell partly through inhibiting Sox2 translation

Glioma-initiating cells possess tumor-initiating potential and are relatively resistant to conventional chemotherapy and irradiation. Therefore, their elimination is an essential factor for the development of efficient therapy. Here, we report that endoplasmic reticulum (ER) stress inducer tunicamycin inhibits glioma-initiating cell self-renewal as determined by neurosphere formation assay. Moreover, tunicamycin decreases the efficiency of glioma-initiating cell to initiate tumor formation. Although tunicamycin induces glioma-initiating cell apoptosis, apoptosis inhibitor z-VAD-fmk only partly abrogates the reduction in glioma-initiating cell self-renewal induced by tunicamycin. Indeed, tunicamycin reduces the expression of self-renewal regulator Sox2 at translation level. Overexpression of Sox2 obviously abrogates the reduction in glioma-initiating cell self-renewal induced by tunicamycin. Taken together, tunicamycin suppresses the self-renewal and tumorigenic potential of glioma-initiating cell partly through reducing Sox2 translation. This finding provides a cue to potential effective treatment of glioblastoma through controlling stem cells.

β1,4-Galactosyltransferase V activates Notch1 signaling in glioma stem-like cells and promotes their transdifferentiation into endothelial cells

Malignant glioblastoma multiforme is one of the most aggressive human cancers, with very low survival rates. Recent studies have reported that glioma stem-like cells transdifferentiate into endothelial cells, indicating a new mechanism for tumor angiogenesis and potentially providing new therapeutic options for glioblastoma treatment. Glioma malignancy is strongly associated with altered expression of N-linked oligosaccharide structures on the cell surface. We have previously reported that β1,4-galactosyltransferase V (β1,4GalTV), which galactosylates the GlcNAcβ1-6Man arm of the branched N-glycans, is highly expressed in glioma and promotes glioma cell growth in vitro and in vivo However, the mechanism by which β1,4GalTV stimulates glioma growth is unknown. Here we demonstrate that short hairpin RNA-mediated β1,4GalTV knockdown inhibits the tumorigenesis of glioma stem-like cells and reduces their transdifferentiation into endothelial cells. We also found that β1,4GalTV overexpression increased glioma stem-like cell transdifferentiation into endothelial cells and that this effect required β1,4GalTV galactosylation activity. Moreover, β1,4GalTV promoted β1,4-galactosylation of Notch1 and increased Notch1 protein levels. Of note, ectopic expression of activated Notch1 rescued the inhibitory effect of β1,4GalTV depletion on glioma stem-like cell transdifferentiation. In summary, our findings indicate that β1,4GalTV stimulates transdifferentiation of glioma stem-like cells into endothelial cells by activating Notch1 signaling. These detailed insights shed important light on the mechanisms regulating glioma angiogenesis.

PIM2 regulates stemness through phosphorylation of 4E-BP1

Embryonic stem cells (ESCs) can undergo unlimited self-renewal and maintain pluripotency to differentiate into any cell type of the three germ layers. Extensive studies have shown ESC identity is regulated by transcription factors, epigenetic regulators and multiple signal transduction pathways. However, the kinase regulation of pluripotency is not well understood. Here we show that the serine/threonine kinase PIM2, which is highly expressed in ESCs but not in somatic cells, functions as a crucial stemness regulator in ESCs. Knockout of Pim2 inhibits the self-renewal and differentiation capability of ESCs. Mechanistic studies identified that PIM2 can directly phosphorylate 4E-BP1, leading to release of eIF4E which facilitates the translation of pluripotent genes in ESCs. Our study highlights a novel kinase cascade pathway for ESC identity maintenance.

Glioma Stem Cells and Their Microenvironments: Providers of Challenging Therapeutic Targets

Malignant gliomas are aggressive brain tumors with limited therapeutic options, possibly because of highly tumorigenic subpopulations of glioma stem cells. These cells require specific microenvironments to maintain their “stemness,” described as perivascular and hypoxic niches. Each of those niches induces particular signatures in glioma stem cells (e.g., activation of Notch signaling, secretion of VEGF, bFGF, SDF1 for the vascular niche, activation of HIF2α, and metabolic reprogramming for hypoxic niche). Recently, accumulated knowledge on tumor-associated macrophages, possibly delineating a third niche, has underlined the role of immune cells in glioma progression, via specific chemoattractant factors and cytokines, such as macrophage-colony stimulation factor (M-CSF). The local or myeloid origin of this new component of glioma stem cells niche is yet to be determined. Such niches are being increasingly recognized as key regulators involved in multiple stages of disease progression, therapy resistance, immune-escaping, and distant metastasis, thereby substantially impacting the future development of frontline interventions in clinical oncology. This review focuses on the microenvironment impact on the glioma stem cell biology, emphasizing GSCs cross talk with hypoxic, perivascular, and immune niches and their potential use as targeted therapy.

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.

Multifaceted regulation of somatic cell reprogramming by mRNA translational control

Translational control plays a pivotal role in the regulation of the pluripotency network in embryonic stem cells, but its effect on reprogramming somatic cells to pluripotency has not been explored. Here, we show that eukaryotic translation initiation factor 4E (eIF4E) binding proteins (4E-BPs), which are translational repressors, have a multifaceted effect on the reprogramming of mouse embryonic fibroblasts (MEFs) into induced pluripotent stem cells (iPSCs). Loss of 4E-BP expression attenuates the induction of iPSCs at least in part through increased translation of p21, a known inhibitor of somatic cell reprogramming. However, MEFs lacking both p53 and 4E-BPs show greatly enhanced reprogramming resulting from a combination of reduced p21 transcription and enhanced translation of endogenous mRNAs such as Sox2 and Myc and can be reprogrammed through the expression of only exogenous Oct4. Thus, 4E-BPs exert both positive and negative effects on reprogramming, highlighting the key role that translational control plays in regulating this process.

The RNA binding protein ESRP1 fine-tunes the expression of pluripotency-related factors in mouse embryonic stem cells

In pluripotent stem cells, there is increasing evidence for crosstalk between post-transcriptional and transcriptional networks, offering multifold steps at which pluripotency can be controlled. In addition to well-studied transcription factors, chromatin modifiers and miRNAs, RNA-binding proteins are emerging as fundamental players in pluripotency regulation. Here, we report a new role for the RNA-binding protein ESRP1 in the control of pluripotency. Knockdown of Esrp1 in mouse embryonic stem cells induces, other than the well-documented epithelial to mesenchymal-like state, also an increase in expression of the core transcription factors Oct4, Nanog and Sox2, thereby enhancing self-renewal of these cells. Esrp1-depleted embryonic stem cells displayed impaired early differentiation in vitro and formed larger teratomas in vivo when compared to control embryonic stem cells. We also show that ESRP1 binds to Oct4 and Sox2 mRNAs and decreases their polysomal loading. ESRP1 thus acts as a physiological regulator of the finely-tuned balance between self-renewal and commitment to a restricted developmental fate. Importantly, both mouse and human epithelial stem cells highly express ESRP1, pinpointing the importance of this RNA-binding protein in stem cell biology.

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.

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.

Overcoming resistance to rapalogs in gliomas by combinatory therapies

Glioblastoma is the most common and aggressive brain tumor type, with a mean patient survival of approximately 1year. Many previous analyses of the glioma kinome have identified key deregulated pathways that converge and activate mammalian target of rapamycin (mTOR). Following the identification and characterization of mTOR-promoting activity in gliomagenesis, data from preclinical studies suggested the targeting of mTOR by rapamycin or its analogs (rapalogs) as a promising therapeutic approach. However, clinical trials with rapalogs have shown very limited efficacy on glioma due to the development of resistance mechanisms. Analysis of rapalog-insensitive glioma cells has revealed increased activity of growth and survival pathways compensating for mTOR inhibition by rapalogs that are suitable for therapeutic intervention. In addition, recently developed mTOR inhibitors show high anti-glioma activity. In this review, we recapitulate the regulation of mTOR signaling and its involvement in gliomagenesis, discuss mechanisms resulting in resistance to rapalogs, and speculate on strategies to overcome resistance. This article is part of a Special Issue entitled: Inhibitors of Protein Kinases (2012).

Post-transcriptional regulation in cancer progression : Microenvironmental control of alternative splicing and translation

The microenvironment acts as a conduit for cellular communication, delivering signals that direct development and sustain tissue homeostasis. In pathologies such as cancer, this integral function of the microenvironment is hijacked to support tumor growth and progression. Cells sense the microenvironment via signal transduction pathways culminating in altered gene expression. In addition to induced transcriptional changes, the microenvironment exerts its effect on the cell through regulation of post-transcriptional processes including alternative splicing and translational control. Here we describe how alternative splicing and protein translation are controlled by microenvironmental parameters such as oxygen availability. We also emphasize how these pathways can be utilized to support processes that are hallmarks of cancer such as angiogenesis, proliferation, and cell migration. We stress that cancer cells respond to their microenvironment through an integrated regulation of gene expression at multiple levels that collectively contribute to disease progression.

Cord blood stem cells revert glioma stem cell EMT by down regulating transcriptional activation of Sox2 and Twist1

The dynamic nature of cancer stem cells that underlie metastasis or their ability to switch between different cellular identities, as in EMT and MET, has profound implications for cancer therapy. The functional relationship between molecules involved in cancer cell stemness and metastasis is not clear. In this regard, our studies on hGBM tissue grade IV specimens showed significant expression of Twist1 and Sox2, known mesenchymal and stemness related markers, respectively, indicating their association with glial tumor genesis and metastasis. The glioma stem cells obtained from CD133⁺ cells demonstrated increased expression of Twist1 and Sox2 accompanied by significant increase in the mesenchymal markers such as N-cadherin, vimentin and β-catenin. Our studies on glioma stem cells treatment with human umbilical cord blood derived- mesenchymal stem cells, showed down regulation of Twist1 and Sox2 proteins, apart from other mesenchymal stem cell markers. Based on the in vitro experiments and in vivo intracranial xenograft mouse model studies, we elucidated the potential therapeutic role of hUCBSC in suppressing glioma cancer stemness by the induction of MET.

Cryptotanshinone induces cell cycle arrest and apoptosis of multidrug resistant human chronic myeloid leukemia cells by inhibiting the activity of eukaryotic initiation factor 4E

Cryptotanshinone (CPT), a diterpene quinone isolated from Salvia miltiorrhiza, is recently reported to have obvious anticancer activities against diverse cancer cells. However, the effect and regulatory mechanism of CPT remain unclear in human chronic myeloid leukemia (CML) cells. In this study, we investigated the antiproliferative activity of CPT on the multidrug resistant CML cells K562/ADM. Our results demonstrated that CPT decreased the cell viability of K562/ADM cells by inducing cell cycle arrest and apoptosis through suppressing the expression of cyclin D1 and Bcl-2. Further studies indicated that CPT mainly functions at post-transcriptional levels, suggesting the involvement of eukaryotic initiation factor 4E (eIF4E). CPT significantly reduced the expression and activity of eIF4E in K562/ADM cells. Overexpression of eIF4E obvious conferred resistance to the CPT antiproliferation and proapoptotic activity as well as the cyclin D1 and Bcl-2 expressions. Knockdown of eIF4E significantly reduced the inhibitory effect of CPT in K562/ADM, confirming the participation of eIF4E during CPT function process. More importantly, the relative inhibitory efficiency of CPT positively correlated with the reductions on eIF4E in primary CML specimens. These results demonstrated that CPT played antitumor roles in K562/ADM cells by inhibiting the eIF4E regulatory system. Our results provide a novel anticancer mechanism of CPT in human CML cells.

Activation of neural and pluripotent stem cell signatures correlates with increased malignancy in human glioma

The presence of stem cell characteristics in glioma cells raises the possibility that mechanisms promoting the maintenance and self-renewal of tissue specific stem cells have a similar function in tumor cells. Here we characterized human gliomas of various malignancy grades for the expression of stem cell regulatory proteins. We show that cells in high grade glioma co-express an array of markers defining neural stem cells (NSCs) and that these proteins can fulfill similar functions in tumor cells as in NSCs. However, in contrast to NSCs glioma cells co-express neural proteins together with pluripotent stem cell markers, including the transcription factors Oct4, Sox2, Nanog and Klf4. In line with this finding, in high grade gliomas mesodermal- and endodermal-specific transcription factors were detected together with neural proteins, a combination of lineage markers not normally present in the central nervous system. Persistent presence of pluripotent stem cell traits could only be detected in solid tumors, and observations based on in vitro studies and xenograft transplantations in mice imply that this presence is dependent on the combined activity of intrinsic and extrinsic regulatory cues. Together these results demonstrate a general deregulated expression of neural and pluripotent stem cell traits in malignant human gliomas, and indicate that stem cell regulatory factors may provide significant targets for therapeutic strategies.