Induction of Glycosphingolipid GM3 Expression by Valproic Acid Suppresses Cancer Cell Growth

Identification and validation of sialyltransferase ST3Gal5 in bladder cancer through bioinformatics and experimental analysis

BACKGROUND

Bladder cancer (BLCA) is one of the top ten most common cancers in the world. Aberrant sialylation is a common feature in tumorigenesis and tumor immunity. This study seeks to explore the potential impact of sialyltransferase ST3Gal5 on BLCA.

METHODS

Initially, glycosyltransferase-related DEGs (GRDEGs) were identified using multiple bioinformatics approaches in TCGA-BLCA cohort and validated using GEO databases. Clinical prognosis integration facilitated the determination of ST3Gal5 as an independent prognostic factor in BLCA, employing univariate and multivariate Cox regression analyses. Immune cell infiltration was assessed via CIBERSORT and ssGSEA analyses, while HLA and immune checkpoint genes' levels, along with drug sensitivity, were evaluated in low- and high-ST3Gal5 groups. The TIDE and IPS scores were used to gauge the immune checkpoint blockade (ICB) response. Furthermore, functional experiments, both in vivo and in vitro, were conducted to elucidate the biological roles of ST3Gal5.

RESULTS

In agreement with bioinformatics findings, ST3Gal5 expression was down-regulated in BLCA tissues and cells, correlating with poorer prognostic outcomes. The StromalScore, ImmuneScore, and ESTIMATEScore were significantly elevated in low-ST3Gal5 group. Moreover, the levels of HLA and immune checkpoint genes were upregulated in low-ST3Gal5 group. Down-regulated ST3Gal5 promoted the proliferation, migration, and invasion of BLCA cells in vivo and in vitro.

CONCLUSION

Our findings demonstrated that low ST3Gal5 level promoted tumorigenesis and progression of BLCA, implying its potential as a predictive biomarker and therapeutic target.

Ganglioside GM3 deficiency enhances mast cell sensitivity

Mast cells are a significant source of cytokines and chemokines that play a role in pathological processes. Gangliosides, which are complex lipids with a sugar chain, are present in all eukaryotic cell membranes and comprise lipid rafts. Ganglioside GM3, the first ganglioside in the synthetic pathway, is a common precursor of the specifying derivatives and is well known for its various functions in biosystems. Mast cells contain high levels of gangliosides; however, the involvement of GM3 in mast cell sensitivity is unclear. Therefore, in this study, we elucidated the role of ganglioside GM3 in mast cells and skin inflammation. GM3 synthase (GM3S)-deficient mast cells showed cytosolic granule topological changes and hyperactivation upon IgE-DNP stimulation without affecting proliferation and differentiation. Additionally, inflammatory cytokine levels increased in GM3S-deficient bone marrow-derived mast cells (BMMC). Furthermore, GM3S-KO mice and GM3S-KO BMMC transplantation showed increased skin allergic reactions. Besides mast cell hypersensitivity caused by GM3S deficiency, membrane integrity decreased and GM3 supplementation rescued this loss of membrane integrity. Additionally, GM3S deficiency increased the phosphorylation of p38 mitogen-activated protein kinase. These results suggest that GM3 increases membrane integrity, leading to the suppression of the p38 signalling pathway in BMMC and contributing to skin allergic reaction.

Enhanced Levels of Glycosphingolipid GM3 Delay the Progression of Diabetic Nephropathy

We recently found that albuminuria levels in patients with minimal change disease (MCD) and focal segmental glomerulosclerosis (FSGS) inversely correlate with glycosphingolipid GM3 expression levels in glomerular podocytes. Moreover, we showed enhanced expression of GM3 via activation of the GM3 synthase gene upon administration of valproic acid (VPA) is effective in suppressing albuminuria and podocyte injury in mice with anti-nephrin antibody-induced podocytopathy. However, the therapeutic effect of GM3 on diabetic nephropathy, which is the most common underlying disease in patients undergoing dialysis and with podocyte injury, remains unclear. Here, we investigated the therapeutic effect of enhanced GM3 expression via VPA on podocyte injury using streptozotocin-induced diabetic nephropathy model mice. Administration of VPA clearly decreased levels of albuminuria and glomerular lesions and inhibited the loss of podocytes and expansion in the mesangial area. Furthermore, we found that albuminuria levels in patients with diabetic nephropathy inversely correlate with the expression of GM3 in podocytes. These results indicate that maintaining GM3 expression in podocytes by administration of VPA may be effective in treating not only podocyte injury, such as MCD and FSGS, but also the late stage of diabetic nephropathy.

Pathophysiological roles and applications of glycosphingolipids in the diagnosis and treatment of cancer diseases

Glycosphingolipids (GSLs) are major amphiphilic glycolipids present on the surface of living cell membranes. They have important biological functions, including maintaining plasma membrane stability, regulating signal transduction, and mediating cell recognition and adhesion. Specific GSLs and related enzymes are abnormally expressed in many cancer diseases and affect the malignant characteristics of tumors. The regulatory roles of GSLs in signaling pathways suggest that they are involved in tumor pathogenesis. GSLs have therefore been widely studied as diagnostic markers of cancer diseases and important targets of immunotherapy. This review describes the tumor-related biological functions of GSLs and systematically introduces recent progress in using diverse GSLs and related enzymes to diagnose and treat tumor diseases. Development of drugs and biomarkers for personalized cancer therapy based on GSL structure is also discussed. These advances, combined with recent progress in the preparation of GSLs derivatives through synthetic biology technologies, suggest a strong future for the use of customized GSL libraries in treating human diseases.

Valproic acid as adjuvant treatment for convulsive status epilepticus: a randomised clinical trial

BACKGROUND

Generalised convulsive status epilepticus (GCSE) is a medical emergency. Guidelines recommend a stepwise strategy of benzodiazepines followed by a second-line anti-seizure medicine (ASM). However, GCSE is uncontrolled in 20-40% patients and is associated with protracted hospitalisation, disability, and mortality. The objective was to determine whether valproic acid (VPA) as complementary treatment to the stepwise strategy improves the outcomes of patients with de novo established GCSE.

METHODS

This was a multicentre, double-blind, randomised controlled trial in 244 adults admitted to intensive care units for GCSE in 16 French hospitals between 2013 and 2018. Patients received standard care of benzodiazepine and a second-line ASM (except VPA). Intervention patients received a 30 mg/kg VPA loading dose, then a 1 mg/kg/h 12 h infusion, whilst the placebo group received an identical intravenous administration of 0.9% saline as a bolus and continuous infusion. Primary outcome was proportion of patients discharged from hospital by day 15. The secondary outcomes were seizure control, adverse events, and cognition at day 90.

RESULTS

A total of 126 (52%) and 118 (48%) patients were included in the VPA and placebo groups. 224 (93%) and 227 (93%) received a first-line and a second-line ASM before VPA or placebo infusion. There was no between-group difference for patients hospital-discharged at day 15 [VPA, 77 (61%) versus placebo, 72 (61%), adjusted relative risk 1.04; 95% confidence interval (0.89-1.19); p = 0.58]. There were no between-group differences for secondary outcomes.

CONCLUSIONS

VPA added to the recommended strategy for adult GCSE is well tolerated but did not increase the proportion of patients hospital-discharged by day 15.

TRIAL REGISTRATION NO

NCT01791868 (ClinicalTrials.gov registry), registered: 15 February 2012.

Glycosphingolipid GM3 prevents albuminuria and podocytopathy induced by anti-nephrin antibody

Podocytopathy, which is characterized by injury to podocytes, frequently causes proteinuria or nephrotic syndrome. There is currently a paucity of effective therapeutic drugs to treat proteinuric kidney disease. Recent research suggests the possibility that glycosphingolipid GM3 maintains podocyte function by acting on various molecules including nephrin, but its mechanism of action remains unknown. Here, various analyses were performed to examine the potential relationship between GM3 and nephrin, and the function of GM3 in podocytes using podocytopathy mice, GM3 synthase gene knockout mice, and nephrin injury cells. Reduced amounts of GM3 and nephrin were observed in podocytopathy mice. Intriguingly, this reduction of GM3 and nephrin, as well as albuminuria, were inhibited by administration of valproic acid. However, when the same experiment was performed using GM3 synthase gene knockout mice, valproic acid administration did not inhibit albuminuria. Equivalent results were obtained in model cells. These findings indicate that GM3 acts with nephrin in a collaborative manner in the cell membrane. Taken together, elevated levels of GM3 stabilize nephrin, which is a key molecule of the slit diaphragm, by enhancing the environment of the cell membrane and preventing albuminuria. This study provides novel insight into new drug discovery, which may offer a new therapy for kidney disease with albuminuria.

Decreased GM3 correlates with proteinuria in minimal change nephrotic syndrome and focal segmental glomerulosclerosis

BACKGROUND

Glycolipids on cell membrane rafts play various roles by interacting with glycoproteins. Recently, it was reported that the glycolipid GM3 is expressed in podocytes and may play a role in podocyte protection. In this report, we describe the correlation between changes in GM3 expression in glomeruli and proteinuria in minimal change nephrotic syndrome (MCNS) and focal segmental glomerulosclerosis (FSGS) patients.

METHODS

We performed a case-control study of the correlation between nephrin/GM3 expression levels and proteinuria in MCNS and FSGS patients who underwent renal biopsy at our institution between 2009 and 2014. Normal renal tissue sites were used from patients who had undergone nephrectomy at our institution and gave informed consent.

RESULTS

Both MCNS and FSGS had decreased GM3 and Nephrin expression compared with the normal (normal vs. MCNS, FSGS; all p < 0.01). Furthermore, in both MCNS and FSGS, GM3 expression was negatively correlated with proteinuria (MCNS: r = - 0.61, p < 0.01, FSGS: r = - 0.56, p < 0.05). However, nephrin expression had a trend to correlate with proteinuria in FSGS (MCNS: r = 0.19, p = 0.58, FSGS: r = - 0.48, p = 0.06). Furthermore, in a simple linear regression analysis, GM3 expression also correlated with proteinuric change after 12 months of treatment (MCNS: r = 0.40, p = 0.38, FSGS: r = 0. 68, p < 0.05).

CONCLUSION

We showed for the first time that decreased GM3 expression correlates with proteinuria in MCNS and FSGS patients. Further studies are needed on the podocyte-protective effects of GM3.

Glycation Interferes with the Expression of Sialyltransferases in Meningiomas

Meningiomas are the most common non-malignant intracranial tumors and prefer, like most tumors, anaerobic glycolysis for energy production (Warburg effect). This anaerobic glycolysis leads to an increased synthesis of the metabolite methylglyoxal (MGO) or glyoxal (GO), which is known to react with amino groups of proteins. This reaction is called glycation, thereby building advanced glycation end products (AGEs). In this study, we investigated the influence of glycation on sialylation in two meningioma cell lines, representing the WHO grade I (BEN-MEN-1) and the WHO grade III (IOMM-Lee). In the benign meningioma cell line, glycation led to differences in expression of sialyltransferases (ST3GAL1/2/3/5/6, ST6GAL1/2, ST6GALNAC2/6, and ST8SIA1/2), which are known to play a role in tumor progression. We could show that glycation of BEN-MEN-1 cells led to decreased expression of ST3Gal5. This resulted in decreased synthesis of the ganglioside GM3, the product of ST3Gal5. In the malignant meningioma cell line, we observed changes in expression of sialyltransferases (ST3GAL1/2/3, ST6GALNAC5, and ST8SIA1) after glycation, which correlates with less aggressive behavior.

Valproic Acid: A Promising Therapeutic Agent in Glioma Treatment

Glioma, characterized by infiltrative growth and treatment resistance, is regarded as the most prevalent intracranial malignant tumor. Due to its poor prognosis, accumulating investigation has been performed for improvement of overall survival (OS) and progression-free survival (PFS) in glioma patients. Valproic acid (VPA), one of the most common histone deacetylase inhibitors (HDACIs), has been detected to directly or synergistically exert inhibitory effects on glioma in vitro and in vivo. In this review, we generalize the latest advances of VPA in treating glioma and its underlying mechanisms and clinical implications, providing a clearer profile for clinical application of VPA as a therapeutic agent for glioma.

Endothelial ganglioside GM3 regulates angiogenesis in solid tumors

Cancer cells require oxygen and nutrients for growth, making angiogenesis one of the essential components of tumor growth. Gangliosides, constituting membrane lipid rafts, regulate intracellular signal transduction and are involved in the malignancy of cancer cells. While endothelial cells, as well as cancer cells, express vast amounts of gangliosides, the precise function of endothelial gangliosides in angiogenesis remains unclear. In this study, we focused on gangliosides of vascular endothelial cells and analyzed their functions on tumor angiogenesis. In human breast cancer, GM3 synthase was highly expressed in vascular endothelial cells as well as immune cells. Angiogenesis increased in GM3S-KO mice. In BAEC, RNA interference of GM3S showed increased cellular invasion and oxidative stress tolerance through activation of ERK. In the breast cancer model, GM3-KO mice showed an increase in tumor growth and angiogenesis. These results suggest that the endothelial ganglioside GM3 regulates tumor angiogenesis by suppressing cellular invasion and oxidative stress tolerance in endothelial cells.

DNA damage response in vascular endothelial senescence: Implication for radiation-induced cardiovascular diseases

A post-exposure cohort study in Hiroshima and Nagasaki reported that low-dose exposure to radiation heightened the risk of cardiovascular diseases (CVD), such as stroke and myocardial infarction, by 14-18% per Gy. Moreover, the risk of atherosclerosis in the coronary arteries reportedly increases with radiation therapy of the chest, including breast and lung cancer treatment. Cellular senescence of vascular endothelial cells (ECs) is believed to play an important role in radiation-induced CVDs. The molecular mechanism of age-related cellular senescence is believed to involve genomic instability and DNA damage response (DDR); the chronic inflammation associated with senescence causes cardiovascular damage. Therefore, vascular endothelial cell senescence is believed to induce the pathogenesis of CVDs after radiation exposure. The findings of several prior studies have revealed that ionizing radiation (IR) induces cellular senescence as well as cell death in ECs. We have previously reported that DDR activates endothelial nitric oxide (NO) synthase, and NO production promotes endothelial senescence. Endothelial NO synthase (eNOS) is a major isoform expressed in ECs that maintains cardiovascular homeostasis. Therefore, radiation-induced NO production, a component of the DDR in ECs, may be involved in CVDs after radiation exposure. In this article, we describe the pathology of radiation-induced CVD and the unique radio-response to radiation exposure in ECs.

Gangliosides as Signaling Regulators in Cancer

At the plasma membrane, gangliosides, a group of glycosphingolipids, are expressed along with glycosphingolipids, phospholipids, and cholesterol in so-called lipid rafts that interact with signaling receptors and related molecules. Most cancers present abnormalities in the intracellular signal transduction system involved in tumor growth, invasion, and metastasis. To date, the roles of gangliosides as regulators of signal transduction have been reported in several cancer types. Gangliosides can be expressed by the exogenous ganglioside addition, with their endogenous expression regulated at the enzymatic level by targeting specific glycosyltransferases. Accordingly, the relationship between changes in the composition of cell surface gangliosides and signal transduction has been investigated by controlling ganglioside expression. In cancer cells, several types of signaling molecules are positively or negatively regulated by ganglioside expression levels, promoting malignant properties. Moreover, antibodies against gangliosides have been shown to possess cytotoxic effects on ganglioside-expressing cancer cells. In the present review, we highlight the involvement of gangliosides in the regulation of cancer cell signaling, and we explore possible therapies targeting ganglioside-expressing cancer.

Inhibition of Ganglioside Synthesis Suppressed Liver Cancer Cell Proliferation through Targeting Kinetochore Metaphase Signaling

The incidence and mortality of liver cancer, mostly hepatocellular carcinoma (HCC), have increased during the last two decades, partly due to persistent inflammation in the lipid-rich microenvironment associated with lifestyle diseases, such as obesity. Gangliosides are sialic acid-containing glycosphingolipids known to be important in the organization of the membrane and membrane protein-mediated signal transduction. Ganglioside synthesis is increased in several types of cancers and has been proposed as a promising target for cancer therapy. Here, we provide evidence that ganglioside synthesis was increased in the livers of an animal model recapitulating the features of activation and expansion of liver progenitor-like cells and liver cancer (stem) cells. Chemical inhibition of ganglioside synthesis functionally suppressed proliferation and sphere growth of liver cancer cells, but had no impact on apoptotic and necrotic cell death. Proteome-based mechanistic analysis revealed that inhibition of ganglioside synthesis downregulated the expression of AURKA, AURKB, TTK, and NDC80 involved in the regulation of kinetochore metaphase signaling, which is essential for chromosome segregation and mitotic progression and probably under the control of activation of TP53-dependent cell cycle arrest. These data suggest that targeting ganglioside synthesis holds promise for the development of novel preventive/therapeutic strategies for HCC treatment.

Inhibition of lipogenesis and induction of apoptosis by valproic acid in prostate cancer cells via the C/EBPα/SREBP-1 pathway

Lipid metabolism reprogramming is now accepted as a new hallmark of cancer. Hence, targeting the lipogenesis pathway may be a potential avenue for cancer treatment. Valproic acid (VPA) emerges as a promising drug for cancer therapy; however, the underlying mechanisms are not yet fully understood. In this study, we aimed to investigate the effects and mechanisms of VPA on cell viability, lipogenesis, and apoptosis in human prostate cancer PC-3 and LNCaP cells. The results showed that VPA significantly reduced lipid accumulation and induced apoptosis of PC-3 and LNCaP cells. Moreover, the expression of CCAAT/enhancer-binding protein α (C/EBPα), as well as sterol regulatory element-binding protein 1 (SREBP-1) and its downstream effectors, including fatty acid synthase (FASN), acetyl CoA carboxylase 1 (ACC1), and anti-apoptotic B-cell lymphoma 2 (Bcl-2), was markedly decreased in PC-3 and LNCaP cells after VPA administration. Mechanistically, the overexpression of C/EBPα rescued the levels of SREBP-1, FASN, ACC1, and Bcl-2, enhanced lipid accumulation, and attenuated apoptosis of VPA-treated PC-3 cells. Conversely, knockdown of C/EBPα by siRNA further decreased lipid accumulation, enhanced apoptosis, and reduced the levels of SREBP-1, FASN, ACC1, and Bcl-2. In addition, SREBP-1a and 1c enhanced the expressions of FASN and ACC1, but only SREBP-1a had a significant effect on Bcl-2 expression in VPA-treated PC-3 cells. Based on the results, we concluded that VPA significantly inhibits cell viability via decreasing lipogenesis and inducing apoptosis via the C/EBPα/SREBP-1 pathway in prostate cancer cells. Therefore, VPA that targets lipid metabolism and apoptosis is a promising candidate for PCa chemotherapy.

Tumor hypoxia regulates ganglioside GM3 synthase, which contributes to oxidative stress resistance in malignant melanoma

BACKGROUND

Tumor hypoxia drastically changes cancer phenotypes, including angiogenesis, invasion, and cell death. Gangliosides are sialic acid-containing glycosphingolipids that are ubiquitously distributed on plasma membranes and are involved in many biological processes, such as the endoplasmic reticulum stress response and apoptosis. In this study, we investigated the regulation and function of glycosphingolipids, which associate with lipid raft on mammalian plasma membranes under hypoxic condition.

METHODS

B16F10 melanoma cells were subjected to chemical hypoxia and low pO2 condition, and the effect of hypoxia on expression of GM3 synthase were analyzed. Cellular resistance to oxidative stress was analyzed in GM3S-KO B16F10 cells.

RESULTS

Hypoxia treatment decreased the expression of ganglioside GM3 synthase (GM3S; ST3GAL5), which synthesizes the common substrate of ganglioside biosynthesis. RNA interference of hypoxia inducible factor 1 subunit alpha (HIF-1α) inhibited hypoxia-induced GM3S suppression. Additionally, GM3S deficiency increased cellular resistance to oxidative stress and radiation therapy via upregulation of ERK.

CONCLUSIONS

Altered synthesis of glycosphingolipids downstream of HIF-1α signaling increased the resistance of melanoma cells to oxidative stress. Furthermore, GM3 has important role on cellular adaptive response to hypoxia.

GENERAL SIGNIFICANCE

This study indicates that tumor hypoxia regulates therapy-resistance via modulation of ganglioside synthesis.

Effect of valproic acid on overall survival in patients with high-grade gliomas undergoing temozolomide: A nationwide population-based cohort study in Taiwan

High-grade gliomas (HGGs) are a rapidly progressive and highly recurrent group of primary brain tumors. Despite aggressive surgical resection with chemoradiotherapy, prognoses remained poor. Valproic acid (VPA), a histone deacetylase inhibitor has shown the potential to inhibit glioma cell growth in vitro through several diverse mechanisms. However clinical studies regarding the effect of VPA on HGGs are limited. This study aimed to investigate whether using VPA in patients with HGGs under temozolomide (TMZ) would lead to a better overall survival (OS).We used the Taiwan National Health Insurance Research database to conduct this population-based cohort study. A total of 2379 patients with HGGs under TMZ treatment were included and were further classified into VPA (n = 1212, VPA ≥ 84 defined daily dose [DDD]) and non-VPA (n = 1167, VPA < 84 DDD) groups. Each patient was followed from 1998 to 2013 or until death. A Cox proportional hazard regression was performed to evaluate the effect of VPA and OS.The VPA group had a longer mean OS time compared with the non-VPA group (OS: 50.3 ± 41.0 vs 42.0 ± 37.2 months, P < .001). In patients between 18 and 40 years old, the difference is most significant (OS: 70.5 ± 48.7 vs 55.1 ± 46.0, P = .001). The adjusted hazard ratio is 0.81 (95% confidence interval, 0.72-0.91) for the VPA group relative to the non-VPA group.VPA at over 84 DDD improved OS in HGGs TMZ treatment.

Downregulation of ST3GAL5 is associated with muscle invasion, high grade and a poor prognosis in patients with bladder cancer

In patients with bladder cancer (BC), the association between ST3 β-galactoside α-2,3-sialyltransferase 5 (ST3GAL5) expression and clinical outcomes, particularly regarding muscle-invasive disease, high tumor grade and prognosis, remain unknown. In the present study, the expression of ST3GAL5 and its association with clinical outcomes in patients with BC was analyzed using various public bioinformatics databases. The difference in ST3GAL5 expression between BC and healthy bladder tissues was also evaluated using data from the Oncomine database, The Cancer Genome Atlas and Gene Expression Omnibus database. The differences in ST3GAL5 expression between muscle invasive BC (MIBC) and non-muscle invasive BC (NMIBC), and high- and low-grade BC were also analyzed. Furthermore, genes that were positively co-expressed with ST3GAL5 in patients with BC were identified from the intersection between the Oncomine, Gene Expression Profiling Interactive Analysis 2 and UALCAN databases. Enrichment analysis by Gene Ontology, Kyoto Encyclopedia of Genes and Genomes, Reactome pathway enrichment analyses and a gene-concept network was performed using R package. Gene set enrichment analysis was also performed to assess the signaling pathways influenced by the high and low expression of ST3GAL5 in BC. The results indicated that ST3GAL5 expression was significantly lower in BC tissues compared with normal bladder tissues (P<0.05). Furthermore, ST3GAL5 expression in MIBC and high-grade BC was significantly lower compared with NMIBC and low-grade BC (P<0.05), respectively. The results from Kaplan-Meier survival analysis result demonstrated that ST3GAL5 downregulation was associated with poor survival in patients with BC (P<0.05). Taken together, these findings suggested that ST3GAL5 may be considered as an anti-oncogene in BC, could represent a potential predictive and prognostic biomarker for BC and may be a molecular target for tumor therapy.

Gangliosides generalities and role in cancer therapies

Gangliosides are located in the plasma membrane; this confers them the ability to interact with other molecules in order to participate in important cellular processes. Some gangliosides presence or absence in the cell surface is associated with either normal condition or pathologies. Particularly in cancer, gangliosides play a critical role in pathological events like cellular malignancy, tumor formation, and metastasis, defining gangliosides as good candidates to be used as cellular markers. When specific gangliosides are exhibited, immunotherapy could be applied in order to inhibit tumorigenesis or induce an immunogenic response. Novel cancer treatments such as NGcGM3/VSSP vaccines, valproic acid, BMS-345541 inhibitor of GD2 and immunotherapies using 1E10 and 14F7 monoclonal antibodies are described. On this review, there will be studied the gangliosides that allowed developing biological techniques that can give immunogenicity to cancer cells

Epigenetics and Sphingolipid Metabolism in Health and Disease

Sphingolipids represent one of the major classes of bioactive lipids. Studies of sphingolipids have intensified in the past several years, revealing their roles in nearly all cell biological processes. In addition, epigenetic regulation has gained substantial interest due to its role in controlling gene expression and activity without changing the genetic code. In this review, we first introduce a brief background on sphingolipid biology, highlighting its role in pathophysiology. We then illustrate the concept of epigenetic regulation, focusing on how it affects the metabolism of sphingolipids. We further discuss the roles of bioactive sphingolipids as epigenetic regulators themselves. Overall, a better understanding of the relationship between epigenetics and sphingolipid metabolism may help to improve the development of sphingolipid-targeted therapeutics.

Distinctive epigenomes characterize glioma stem cells and their response to differentiation cues

BACKGROUND

Glioma stem cells (GSCs) are a subpopulation of stem-like cells that contribute to glioblastoma (GBM) aggressiveness, recurrence, and resistance to radiation and chemotherapy. Therapeutically targeting the GSC population may improve patient survival, but unique vulnerabilities need to be identified.

RESULTS

We isolate GSCs from well-characterized GBM patient-derived xenografts (PDX), characterize their stemness properties using immunofluorescence staining, profile their epigenome including 5mC, 5hmC, 5fC/5caC, and two enhancer marks, and define their transcriptome. Fetal brain-derived neural stem/progenitor cells are used as a comparison to define potential unique and common molecular features between these different brain-derived cells with stem properties. Our integrative study reveals that abnormal expression of ten-eleven-translocation (TET) family members correlates with global levels of 5mC and 5fC/5caC and may be responsible for the distinct levels of these marks between glioma and neural stem cells. Heterogenous transcriptome and epigenome signatures among GSCs converge on several genes and pathways, including DNA damage response and cell proliferation, which are highly correlated with TET expression. Distinct enhancer landscapes are also strongly associated with differential gene regulation between glioma and neural stem cells; they exhibit unique co-localization patterns with DNA epigenetic mark switching events. Upon differentiation, glioma and neural stem cells exhibit distinct responses with regard to TET expression and DNA mark changes in the genome and GSCs fail to properly remodel their epigenome.

CONCLUSIONS

Our integrative epigenomic and transcriptomic characterization reveals fundamentally distinct yet potentially targetable biologic features of GSCs that result from their distinct epigenomic landscapes.

Gangliosides and Tumors

Tumor-associated gangliosides play important roles in regulation of signal transduction induced by growth-factor receptors including EGFR, FGFR, HGF and PDGFR in a specific microdomain called glycosynapse in the cancer cell membranes, and in interaction with glycan recognition molecules involved in cell adhesion and immune regulation including selectins and siglecs. As the genes involved in the synthesis and degradation of tumor-associated gangliosides were identified, biological functions became clearer from the experimental results employing forced overexpression and/or knockdown/knockout of the genes. Studies on the regulatory mechanisms for their expression also achieved great advancements. Epigenetic silencing of glycan-related genes is a dominant mechanism in glycan alteration at early stages of carcinogenesis. Development of hypoxia resistance involving activation of a transcription factor HIF, and acquisition of cancer stem cell-like characteristics through epithelial-mesenchymal transition are important mechanisms for glycan modulations in the later stages of cancer progression. In the initial stages of studies, the gangliosides which specifically appear in cancers attracted attention under the name of tumor-associated gangliosides. However, it became apparent that not only the cancer-associated gangliosides but also the normal gangliosides present in nonmalignant cells and tissues perform important biological functions, and some of them tend to disappear in cancer cells resulting in the loss of the physiological functions, and this sometimes facilitates progression of cancers.