Elevated levels of select gangliosides in T cells from renal cell carcinoma patients is associated with T cell dysfunction

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.

The biological role and immunotherapy of gangliosides and GD3 synthase in cancers

Gangliosides are a large subfamily of glycosphingolipids that broadly exist in the nervous system and interact with signaling molecules in the lipid rafts. GD3 and GD2 are two types of disialogangliosides (GDs) that include two sialic acid residues. The expression of GD3 and GD2 in various cancers is mostly upregulated and is involved in tumor proliferation, invasion, metastasis, and immune responses. GD3 synthase (GD3S, ST8SiaI), a subclass of sialyltransferases, regulates the biosynthesis of GD3 and GD2. GD3S is also upregulated in most tumors and plays an important role in the development and progression of tumors. Many clinical trials targeting GD2 are ongoing and various immunotherapy studies targeting gangliosides and GD3S are gradually attracting much interest and attention. This review summarizes the function, molecular mechanisms, and ongoing clinical applications of GD3, GD2, and GD3S in abundant types of tumors, which aims to provide novel targets for future cancer therapy.

Lipids as Targets for Renal Cell Carcinoma Therapy

Kidney cancer is among the top ten most common cancers to date. Within the kidney, renal cell carcinoma (RCC) is the most common solid lesion occurring. While various risk factors are suspected, including unhealthy lifestyle, age, and ethnicity, genetic mutations seem to be a key risk factor. In particular, mutations in the von Hippel-Lindau gene (Vhl) have attracted a lot of interest since this gene regulates the hypoxia inducible transcription factors HIF-1α and HIF-2α, which in turn drive the transcription of many genes that are important for renal cancer growth and progression, including genes involved in lipid metabolism and signaling. Recent data suggest that HIF-1/2 are themselves regulated by bioactive lipids which make the connection between lipids and renal cancer obvious. This review will summarize the effects and contributions of the different classes of bioactive lipids, including sphingolipids, glycosphingolipids, eicosanoids, free fatty acids, cannabinoids, and cholesterol to renal carcinoma progression. Novel pharmacological strategies interfering with lipid signaling to treat renal cancer will be highlighted.

Glycosylation in Renal Cell Carcinoma: Mechanisms and Clinical Implications

Renal cell carcinoma (RCC) is one of the most prevalent malignant tumors of the urinary system, accounting for around 2% of all cancer diagnoses and deaths worldwide. Clear cell RCC (ccRCC) is the most prevalent and aggressive histology with an unfavorable prognosis and inadequate treatment. Patients' progression-free survival is considerably improved by surgery; however, 30% of patients develop metastases following surgery. Identifying novel targets and molecular markers for RCC prognostic detection is crucial for more accurate clinical diagnosis and therapy. Glycosylation is a critical post-translational modification (PMT) for cancer cell growth, migration, and invasion, involving the transfer of glycosyl moieties to specific amino acid residues in proteins to form glycosidic bonds through the activity of glycosyltransferases. Most cancers, including RCC, undergo glycosylation changes such as branching, sialylation, and fucosylation. In this review, we discuss the latest findings on the significance of aberrant glycans in the initiation, development, and progression of RCC. The potential biomarkers of altered glycans for the diagnosis and their implications in RCC have been further highlighted.

Identifying an Immune-Related Gene ST8SIA1 as a Novel Target in Patients With Clear-Cell Renal Cell Carcinoma

Clear-cell renal cell carcinoma (ccRCC) is one of the most common urological cancers. The tumor microenvironment plays an important role in tumor development. The present study was conducted to identify novel immune-related biomarkers. The differentially expressed genes were identified using the ESTIMATE algorithm base on GEO and TCGA databases. The Kaplan–Meier survival curve and univariate and multivariate analyses were performed. The association between ST8SIA1 and the immune system was explored. The gene set enrichment analysis (GSEA) and online databases were used for functional annotation. ST8SIA1 was identified as a potential prognostic gene. Elevated ST8SIA1 was observed in the tumor tissues compared with adjacent normal tissues and associated with higher T stage and advanced TNM stage (all p < 0.05). The mRNA and protein levels of ST8SIA1 in cancer tissues and cells are also upregulated. The Kaplan–Meier survival curve and univariate and multivariate analyses showed that higher expression of ST8SIA1 was associated with worse OS (all p < 0.05). ST8SIA1 expression levels were negatively correlated with tumor purity and positively associated with infiltrated immune cells and expression of immune checkpoint genes. Function analysis also revealed that ST8SIA1 was significantly associated with immune-related pathways. In conclusion, ST8SIA1 was identified as an immune-related gene and a potential target in ccRCC patients. Further relevant studies are required to validate our findings.

Structure and function of glycosphingolipids on small extracellular vesicles

Extracellular vesicles (EVs) are membrane-delineated particles secreted by most types of cells under both normal and pathophysiological conditions. EVs are believed to mediate intercellular communication by serving as carriers of different bioactive ingredients, including proteins, nucleic acids and lipids. Glycoconjugates are complex molecules consisting of covalently linked carbohydrate with proteins or lipids. These glycoconjugates play essential roles in the sorting of vesicular protein and the uptake of small extracellular vesicles (30–100 nm, sEVs) into recipient cells. Glycosphingolipids (GSLs), one subtype of glycolipids, which are ubiquitous membrane components in almost all living organisms, are also commonly distributed on sEVs. However, the study of functional roles of GSLs on sEVs are far behind than other functional cargos. The purpose of this review is to highlight the importance of GSLs on sEVs. Initially, we described classification and structure of GSLs. Then, we briefly introduced the essential functions of GSLs, which are able to interact with functional membrane proteins, such as growth factor receptors, integrins and tetraspanins, to modulate cell growth, adhesion and cell motility. In addition, we discussed analytical methods for studying GSLs on sEVs. Finally, we focused on the function of GSLs on sEVs, including regulating the aggregation of extracellular α-synuclein (α-syn) or extracellular amyloid-β (Aβ) and influencing tumor cell malignancy.

Role of Globotriaosylceramide in Physiology and Pathology

At first glance, the biological function of globoside (Gb) clusters appears to be that of glycosphingolipid (GSL) receptors for bacterial toxins that mediate host-pathogen interaction. Indeed, certain bacterial toxin families have been evolutionarily arranged so that they can enter eukaryotic cells through GSL receptors. A closer look reveals this molecular arrangement allocated on a variety of eukaryotic cell membranes, with its role revolving around physiological regulation and pathological processes. What makes Gb such a ubiquitous functional arrangement? Perhaps its peculiarity is underpinned by the molecular structure itself, the nature of Gb-bound ligands, or the intracellular trafficking unleashed by those ligands. Moreover, Gb biological conspicuousness may not lie on intrinsic properties or on its enzymatic synthesis/degradation pathways. The present review traverses these biological aspects, focusing mainly on globotriaosylceramide (Gb3), a GSL molecule present in cell membranes of distinct cell types, and proposes a wrap-up discussion with a phylogenetic view and the physiological and pathological functional alternatives.

The role of Globo H and SSEA-4 in the development and progression of cancer, and their potential as therapeutic targets

Glycans, chains of sugar molecules found conjugated to cell proteins and lipids, contribute to their growth, movement and differentiation. Aberrant glycosylation is a hallmark of several medical conditions including tumorigenesis. Glycosphingolipids (GSLs), consisting of glycans conjugated to a lipid (ceramide) core, are found in the lipid bilayer of eukaryotic cell membranes. GSLs, play an active role in cell processes. Several GSLs are expressed by human embryonic stem cells and have been found to be overexpressed in several types of cancer. In this review, we discuss the data, hypotheses and perspectives related to the GSLs Globo H and SSEA-4.

Targeting glycosphingolipids for cancer immunotherapy

Aberrant expression of glycosphingolipids (GSLs) is a unique feature of cancer and stromal cells in tumor microenvironments. Although the impact of GSLs on tumor progression remains largely unclear, anticancer immunotherapies directed against GSLs are attracting growing attention. Here, we focus on GD2, a disialoganglioside expressed in tumors of neuroectodermal origin, and Globo H ceramide (GHCer), the most prevalent cancer-associated GSL overexpressed in a variety of epithelial cancers. We first summarize recent advances on our understanding of GD2 and GHCer biology and then discuss the clinical development of the first immunotherapeutic agent targeting a glycolipid, the GD2-specific antibody dinutuximab, its approved indications, and new strategies to improve its efficacy for neuroblastoma. Next, we review ongoing clinical trials on Globo H-targeted immunotherapeutics. We end with highlighting how these studies provide sound scientific rationales for targeting GSLs in cancer and may facilitate a rational design of new GSL-targeted anticancer therapeutics.

Effects of Gangliosides on Spermatozoa, Oocytes, and Preimplantation Embryos

Gangliosides are sialic acid-containing glycosphingolipids, which are the most abundant family of glycolipids in eukaryotes. Gangliosides have been suggested to be important lipid molecules required for the control of cellular procedures, such as cell differentiation, proliferation, and signaling. GD1a is expressed in interstitial cells during ovarian maturation in mice and exogenous GD1a is important to oocyte maturation, monospermic fertilization, and embryonic development. In this context, GM1 is known to influence signaling pathways in cells and is important in sperm-oocyte interactions and sperm maturation processes, such as capacitation. GM3 is expressed in the vertebrate oocyte cytoplasm, and exogenously added GM3 induces apoptosis and DNA injury during in vitro oocyte maturation and embryogenesis. As a consequence of this, ganglioside GT1b and GM1 decrease DNA fragmentation and act as H2O2 inhibitors on germ cells and preimplantation embryos. This review describes the functional roles of gangliosides in spermatozoa, oocytes, and early embryonic development.

Stage-specific embryonic antigen-4 is a histological marker reflecting the malignant behavior of prostate cancer

Stage-specific embryonic antigen-4 (SSEA-4), a specific marker for pluripotent stem cells, plays an important role in the malignant behavior of several cancers. Here, SSEA-4 expression was evaluated by immunohistochemistry using monoclonal antibody RM1 specific to SSEA-4 in 181 and 117 prostate cancer (PC) specimens obtained by biopsy and radical prostatectomy (RP), respectively. The relationships between SSEA-4 expression in cancer cells or the presence of SSEA-4-positive tumor-infiltrating immune cells (TICs) and clinicopathological parameters were analyzed. SSEA-4 expression in cancer cells was significantly associated with Gleason score, local progression, and lymph node and distant metastasis. In RP specimens, high SSEA-4 expression in cancer cells and the presence of SSEA-4-positive TICs were significant predictors of pT3, i.e., invasion and worse biochemical recurrence (BCR) after RP, respectively, in univariate analysis. In contrast, combination of high SSEA-4 expression in cancer cells and the presence of SSEA-4-positive TICs was an independent predictor for pT3 and BCR in multivariate analysis. Biologically this combination was also independently associated with suppression of apoptosis. Thus, the co-expression of SSEA-4 in cancer cells and TICs may have crucial roles in the malignant aggressiveness and prognosis of PC. Invasive potential and suppression of apoptosis may be linked to SSEA-4 expression.

The Role of Glycosphingolipids in Immune Cell Functions

Glycosphingolipids (GSLs) exhibit a variety of functions in cellular differentiation and interaction. Also, they are known to play a role as receptors in pathogen invasion. A less well-explored feature is the role of GSLs in immune cell function which is the subject of this review article. Here we summarize knowledge on GSL expression patterns in different immune cells. We review the changes in GSL expression during immune cell development and differentiation, maturation, and activation. Furthermore, we review how immune cell GSLs impact membrane organization, molecular signaling, and trans-interactions in cellular cross-talk. Another aspect covered is the role of GSLs as targets of antibody-based immunity in cancer. We expect that recent advances in analytical and genome editing technologies will help in the coming years to further our knowledge on the role of GSLs as modulators of immune cell function.

Elevated histone H3 acetylation and loss of the Sp1-HDAC1 complex de-repress the GM2-synthase gene in renal cell carcinoma

GM2-synthase produces sialic acid-containing glycosphingolipids called gangliosides, and its mRNA overexpression and the gangliosides it generates are linked to tumor progression, migration, and suppression of tumor-specific host immune responses. However, the mechanism underlying GM2-synthase de-repression in renal cell carcinoma (RCC) is poorly understood. Here, we demonstrate that higher GM2-synthase mRNA expression levels in various cancer cells and in human RCC tumors correlate with higher histone acetylation levels (H3K9, H3K14, or both) at region +38/+187 relative to the transcription start site (TSS) of the GM2-synthase gene than in normal kidney epithelial (NKE) cells or healthy adjacent tissues. An increase in GM2-synthase mRNA expression in cells treated with a histone deacetylase (HDAC) inhibitor was accompanied by increased histone acetylation levels at this promoter region. DNA methylation around the TSS was absent in both RCC cell lines and NKE cells. Of note, both the transcription factor Sp1 and corepressor HDAC1 associated with the +38/+187 region when the GM2-synthase gene was repressed in NKE and tumor-adjacent tissues, indicating plausible site-specific repressive roles of HDAC1 and Sp1 in GM2-synthase mRNA expression. Site-directed mutagenesis of the Sp1-binding site within the +38/+187 region relieved repressed luciferase activity of this region by limiting HDAC1 recruitment. Moreover, Sp1 or HDAC1 knock down increased GM2-synthase transcription, and butyrate-mediated activation of GM2-synthase mRNA expression in SK-RC-45 cells was accompanied by Sp1 and HDAC1 loss from the +38/+187 region. Taken together, we have identified an epigenetic mechanism for the de-repression of the GM2-synthase gene in RCC.

Sialic Acid-Dependent Inhibition of T Cells by Exosomal Ganglioside GD3 in Ovarian Tumor Microenvironments

The tumor microenvironment is rendered immunosuppressive by a variety of cellular and acellular factors that represent potential cancer therapeutic targets. Although exosomes isolated from ovarian tumor ascites fluids have been previously reported to induce a rapid and reversible T cell arrest, the factors present on or within exosomes that contribute to immunosuppression have not been fully defined. In this study, we establish that GD3, a ganglioside expressed on the surface of exosomes isolated from human ovarian tumor ascites fluids, is causally linked to the functional arrest of T cells activated through their TCR. This arrest is inhibited by Ab blockade of exosomal GD3 or by the removal of GD3⁺ exosomes. Empty liposomes expressing GD3 on the surface also inhibit the activation of T cells, establishing that GD3 contributes to the functional arrest of T cells independent of factors present in exosomes. Finally, we demonstrate that the GD3-mediated arrest of the TCR activation is dependent upon sialic acid groups, because their enzymatic removal from exosomes or liposomes results in a loss of inhibitory capacity. Collectively, these data define GD3 as a potential immunotherapeutic target.

Ganglioside GD3 synthase (GD3S), a novel cancer drug target

Gangliosides are a class of important glycosphingolipids containing sialic acid that are widely distributed on the outer surface of cells and are abundantly distributed in brain tissue. Disialoganglioside with three glycosyl groups (GD3) and disialoganglioside with two glycosyl groups (GD2) are markedly increased in pathological conditions such as cancers and neurodegenerative diseases. GD3 and GD2 were found to play important roles in cancers by mediating cell proliferation, migration, invasion, adhesion, angiogenesis and in preventing immunosuppression of tumors. GD3 synthase (GD3S) is the regulatory enzyme of GD3 and GD2 synthesis, and is important in tumorigenesis and the development of cancers. The study of GD3S as a drug target may be of great significance for the discovery of new drugs for cancer treatment. This review will describe the gangliosides and their roles in physiological and pathological conditions; the roles of GD3 and GD2 in cancers; the expression, functions and mechanisms of GD3S, and its potential as a drug target in cancers.

Live cell superresolution-structured illumination microscopy imaging analysis of the intercellular transport of microvesicles and costimulatory proteins via nanotubes between immune cells

Membrane nanotubes are transient long-distance connections between cells that can facilitate intercellular communication. These tethers can form spontaneously between many cell types, including cells of the immune and nervous systems. Traffic of viral proteins, vesicles, calcium ions, mRNA, miRNA, mitochondria, lysosomes and membrane proteins/raft domains have all been reported so far via the open ended tunneling nanotubes (TNTs). Recently we reported on existence of plasma membrane derived GM₁/GM₃ ganglioside enriched microvesicles and costimulatory proteins in nanotubes connecting B lymphocytes, the way they are formed and transported across TNTs, however, still remained unclear. Here, using live cell confocal and Structured Illumination (SR-SIM) superresolution imaging, we show that B cells respond to bacterial (Cholera) toxin challenge by their subsequent internalization followed by rapid formation of intracellular microvesicles (MVs). These MVs are then transported between adjacent B cells via nanotubes. Selective transport-inhibition analysis of two abundant motor proteins in these cell types demonstrated that actin-based non-muscle myosin 2A dominantly mediates intercellular MV-transport via TNTs, in contrast to the microtubule-based dynein, as shown by the unchanged transport after inhibition of the latter. As suggested by SR-SIM images of GFP-CD86 transfected macrophages, these costimulatory molecules may be transferred by unusually shaped MVs through thick TNTs connecting macrophages. In contrast, in B cell cultures the same GFP-CD86 is dominantly transported along the membrane wall of TNTs. Such intercellular molecule-exchange can consequently improve the efficiency of antigen-dependent T cell activation, especially in macrophages with weak costimulator expression and T cell activation capacity. Such improved T cell activating potential of these two cell types may result in a more efficient cellular immune response and formation of immunological memory. The results also highlight the power of superresolution microscopy to uncover so far hidden structural details of biological processes, such as microvesicle formation and transport.

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.

Ganglioside GM2 mediates migration of tumor cells by interacting with integrin and modulating the downstream signaling pathway

The definitive role of ganglioside GM2 in mediating tumor-induced growth and progression is still unknown. Here we report a novel role of ganglioside GM2 in mediating tumor cell migration and uncovered its mechanism. Data shows differential expression levels of GM2-synthase as well as GM2 in different human cancer cells. siRNA mediated knockdown of GM2-synthase in CCF52, A549 and SK-RC-26B cells resulted in significant inhibition of tumor cell migration as well as invasion in vitro without affecting cellular proliferation. Over-expression of GM2-synthase in low-GM2 expressing SK-RC-45 cells resulted in a consequent increase in migration thus confirming the potential role GM2 and its downstream partners play in tumor cell migration and motility. Further, treatment of SK-RC-45 cells with exogenous GM2 resulted in a dramatic increase in migratory and invasive capacity with no change in proliferative capacity, thereby confirming the role of GM2 in tumorigenesis specifically by mediating tumor migration and invasion. Gene expression profiling of GM2-synthase silenced cells revealed altered expression of several genes involved in cell migration primarily those controlling the integrin mediated signaling. GM2-synthase knockdown resulted in decreased phosphorylation of FAK, Src as well as Erk, while over-expression and/or exogenous GM2 treatment caused increased FAK and Erk phosphorylation respectively. Again, GM2 mediated invasion and Erk phosphorylation is blocked in integrin knockdown SK-RC-45 cells, thus confirming that GM2 mediated migration and phosphorylation of Erk is integrin dependent. Finally, confocal microscopy suggested co-localization while co-immunoprecipitation and surface plasmon resonance (SPR) confirmed direct interaction of membrane bound ganglioside, GM2 with the integrin receptor.

Dysregulated Expression of Glycolipids in Tumor Cells: From Negative Modulator of Anti-tumor Immunity to Promising Targets for Developing Therapeutic Agents

Glycolipids are complex molecules consisting of a ceramide lipid moiety linked to a glycan chain of variable length and structure. Among these are found the gangliosides, which are sialylated glycolipids ubiquitously distributed on the outer layer of vertebrate plasma membranes. Changes in the expression of certain species of gangliosides have been described to occur during cell proliferation, differentiation, and ontogenesis. However, the aberrant and elevated expression of gangliosides has been also observed in different types of cancer cells, thereby promoting tumor survival. Moreover, gangliosides are actively released from the membrane of tumor cells, having a strong impact on impairing anti-tumor immunity. Beyond the undesirable effects of gangliosides in cancer cells, a substantial number of cancer immunotherapies have been developed in recent years that have used gangliosides as the main target. This has resulted in successful immune cell- or antibody-responses against glycolipids, with promising results having been obtained in clinical trials. In this review, we provide a general overview on the metabolism of glycolipids, both in normal and tumor cells, as well as examining glycolipid-mediated immune modulation and the main successes achieved in immunotherapies using gangliosides as molecular targets.

GBM Derived Gangliosides Induce T Cell Apoptosis through Activation of the Caspase Cascade Involving Both the Extrinsic and the Intrinsic Pathway

Previously we demonstrated that human glioblastoma cell lines induce apoptosis in peripheral blood T cells through partial involvement of secreted gangliosides. Here we show that GBM-derived gangliosides induce apoptosis through involvement of the TNF receptor and activation of the caspase cascade. Culturing T lymphocytes with GBM cell line derived gangliosides (10-20μg/ml) demonstrated increased ROS production as early as 18 hrs as indicated by increased uptake of the dye H₂DCFDA while western blotting demonstrated mitochondrial damage as evident by cleavage of Bid to t-Bid and by the release of cytochrome-c into the cytosol. Within 48-72 hrs apoptosis was evident by nuclear blebbing, trypan blue positivity and annexinV/7AAD staining. GBM-ganglioside induced activation of the effector caspase-3 along with both initiator caspases (-9 and -8) in T cells while both the caspase-8 and -9 inhibitors were equally effective in blocking apoptosis (60% protection) confirming the role of caspases in the apoptotic process. Ganglioside-induced T cell apoptosis did not involve production of TNF-α since anti-human TNFα antibody was unable to protect T cells from nuclear blebbing and subsequent cell death. However, confocal microscopy demonstrated co-localization of GM2 ganglioside with the TNF receptor and co-immunoprecipitation experiments showed recruitment of death domains FADD and TRADD with the TNF receptor post ganglioside treatment, suggesting direct interaction of gangliosides with the TNF receptor. Further confirmation of the interaction between GM2 and TNFR1 was obtained from confocal microscopy data with wild type and TNFR1 KO (TALEN mediated) Jurkat cells, which clearly demonstrated co-localization of GM2 and TNFR1 in the wild type cells but not in the TNFR1 KO clones. Thus, GBM-ganglioside can mediate T cell apoptosis by interacting with the TNF receptor followed by activation of both the extrinsic and the intrinsic pathway of caspases.

Extracellular Vesicles Present in Human Ovarian Tumor Microenvironments Induce a Phosphatidylserine-Dependent Arrest in the T-cell Signaling Cascade

The identification of immunosuppressive factors within human tumor microenvironments, and the ability to block these factors, would be expected to enhance patients' antitumor immune responses. We previously established that an unidentified factor, or factors, present in ovarian tumor ascites fluids reversibly inhibited the activation of T cells by arresting the T-cell signaling cascade. Ultracentrifugation of the tumor ascites fluid has now revealed a pellet that contains small extracellular vesicles (EV) with an average diameter of 80 nm. The T-cell arrest was determined to be causally linked to phosphatidylserine (PS) that is present on the outer leaflet of the vesicle bilayer, as a depletion of PS-expressing EV or a blockade of PS with anti-PS antibody significantly inhibits the vesicle-induced signaling arrest. The inhibitory EV were also isolated from solid tumor tissues. The presence of immunosuppressive vesicles in the microenvironments of ovarian tumors and our ability to block their inhibition of T-cell function represent a potential therapeutic target for patients with ovarian cancer.

Reprogramming the tumor microenvironment: tumor-induced immunosuppressive factors paralyze T cells

It has become evident that tumor-induced immuno-suppressive factors in the tumor microenvironment play a major role in suppressing normal functions of effector T cells. These factors serve as hurdles that limit the therapeutic potential of cancer immunotherapies. This review focuses on illustrating the molecular mechanisms of immunosuppression in the tumor microenvironment, including evasion of T-cell recognition, interference with T-cell trafficking, metabolism, and functions, induction of resistance to T-cell killing, and apoptosis of T cells. A better understanding of these mechanisms may help in the development of strategies to enhance the effectiveness of cancer immunotherapies.

TALEN mediated targeted editing of GM2/GD2-synthase gene modulates anchorage independent growth by reducing anoikis resistance in mouse tumor cells

Complex ganglioside expression is highly deregulated in several tumors which is further dependent on specific ganglioside synthase genes. Here, we designed and constructed a pair of highly specific transcription-activator like effector endonuclease (TALENs) to disrupt a particular genomic locus of mouse GM2-synthase, a region conserved in coding sequence of all four transcript variants of mouse GM2-synthase. Our designed TALENs effectively work in different mouse cell lines and TALEN induced mutation rate is over 45%. Clonal selection strategy is undertaken to generate stable GM2-synthase knockout cell line. We have also demonstrated non-homologous end joining (NHEJ) mediated integration of neomycin cassette into the TALEN targeted GM2-synthase locus. Functionally, clonally selected GM2-synthase knockout clones show reduced anchorage-independent growth (AIG), reduction in tumor growth and higher cellular adhesion as compared to wild type Renca-v cells. Insight into the mechanism shows that, reduced AIG is due to loss in anoikis resistance, as both knockout clones show increased sensitivity to detachment induced apoptosis. Therefore, TALEN mediated precise genome editing at GM2-synthase locus not only helps us in understanding the function of GM2-synthase gene and complex gangliosides in tumorigenicity but also holds tremendous potential to use TALENs in translational cancer research and therapeutics.

Disialoganglioside GD2 as a therapeutic target for human diseases

INTRODUCTION

Ganglioside GD2 is found in vertebrates and invertebrates, overexpressed among pediatric and adult solid tumors, including neuroblastoma, glioma, retinoblastoma, Ewing's family of tumors, rhabdomyosarcoma, osteosarcoma, leiomyosarcoma, liposarcoma, fibrosarcoma, small cell lung cancer and melanoma. It is also found on stem cells, neurons, some nerve fibers and basal layer of the skin.

AREAS COVERED

GD2 provides a promising clinical target for radiolabeled antibodies, bispecific antibodies, chimeric antigen receptor (CAR)-modified T cells, drug conjugates, nanoparticles and vaccines. Here, we review its biochemistry, normal physiology, role in tumorigenesis, important characteristics as a target, as well as anti-GD2-targeted strategies.

EXPERT OPINION

Bridging the knowledge gaps in understanding the interactions of GD2 with signaling molecules within the glycosynapses, and the regulation of its cellular expression should improve therapeutic strategies targeting this ganglioside. In addition to anti-GD2 IgG mAbs, their drug conjugates, radiolabeled forms especially when genetically engineered to improve therapeutic index and novel bispecific forms or CARs to retarget T-cells are promising candidates for treating metastatic cancers.

CD1d expression in renal cell carcinoma is associated with higher relapse rates, poorer cancer-specific and overall survival

Aims

We hypothesised that CD1d expression in renal cell carcinoma (RCC) may play a role in modifying the host immune response. Our aims were to investigate the expression of CD1d and to correlate this with histopathology and clinical outcomes in a cohort study of patients with RCC.

Methods

Gene expression and tissue microarray studies on a panel of RCC tissue were performed. Clinicopathological correlation was analysed using χ²/Fisher's exact test. Relapse-free survival, cancer-specific survival and overall survival were calculated for both CD1d high and low expressors. Survival outcomes were estimated with the Kaplan–Meier method and compared using Cox regression analysis.

Results

Gene expression microarray showed significant expression of CD1d in RCC versus normal renal tissue. By immunohistochemistry, we found that CD1d expression significantly associated with tumour stage/grade, higher relapse rates, poorer cancer-specific and overall survival.

Conclusions

CD1d expression on RCC correlated with aggressive disease and poorer clinical outcomes.

The plasma membrane sialidase NEU3 regulates the malignancy of renal carcinoma cells by controlling β1 integrin internalization and recycling

The human plasma membrane sialidase NEU3 is a key enzyme in the catabolism of membrane gangliosides, is crucial in the regulation of cell surface processes, and has been demonstrated to be significantly up-regulated in renal cell carcinomas (RCCs). In this report, we show that NEU3 regulates β1 integrin trafficking in RCC cells by controlling β1 integrin recycling to the plasma membrane and controlling activation of the epidermal growth factor receptor (EGFR) and focal adhesion kinase (FAK)/protein kinase B (AKT) signaling. NEU3 silencing in RCC cells increased the membrane ganglioside content, in particular the GD1a content, and changed the expression of key regulators of the integrin recycling pathway. In addition, NEU3 silencing up-regulated the Ras-related protein RAB25, which directs internalized integrins to lysosomes, and down-regulated the chloride intracellular channel protein 3 (CLIC3), which induces the recycling of internalized integrins to the plasma membrane. In this manner, NEU3 silencing enhanced the caveolar endocytosis of β1 integrin, blocked its recycling and reduced its levels at the plasma membrane, and, consequently, inhibited EGFR and FAK/AKT. These events had the following effects on the behavior of RCC cells: they (a) decreased drug resistance mediated by the block of autophagy and the induction of apoptosis; (b) decreased metastatic potential mediated by down-regulation of the metalloproteinases MMP1 and MMP7; and (c) decreased adhesion to collagen and fibronectin. Therefore, our data identify NEU3 as a key regulator of the β1 integrin-recycling pathway and FAK/AKT signaling and demonstrate its crucial role in RCC malignancy.

Ganglioside inhibition of CD8+ T cell cytotoxicity: interference with lytic granule trafficking and exocytosis

Granule exocytosis-mediated cytotoxicity by CD8(+) CTL plays a crucial role in adaptive immunity to tumors and to intracellular pathogens. This T cell effector function has been shown to be defective in various murine tumor models and in human cancer. However, factors and their mechanisms that cause inhibition of CD8(+) T cell lytic function in tumor-bearing hosts remain to be fully defined. We postulate that gangliosides, highly expressed on tumor cell membranes, actively shed into the tumor microenvironment, and having well-established immunosuppressive properties, may be such a factor. We exposed primary mouse CD8(+) CTL to gangliosides derived from three sources (tumors and normal brain). This significantly inhibited cytotoxicity-mediated by granule exocytosis, that is, cytotoxicity of alloantigen-specific and polyclonal CD8(+) CTL in vitro. These molecules did not interfere with the interaction of CD8(+) T cells with their cognate targets. Rather, they inhibited lytic granule release in response both to TCR engagement and to stimuli that induce granule release in a nonpolarized manner. At the subcellular level, confocal microscopic imaging identified inhibition of polarization of lytic granules to the immunological synapse upon target cell recognition. Thus, tumor-shed gangliosides suppress lytic activity of CD8(+) T cells by a novel mechanism, that is, inhibition of trafficking of lytic granules in response to TCR engagement, as well as by interfering with the process of granule exocytosis in CD8(+) T cells.

Elevation of GM2 ganglioside during ethanol-induced apoptotic neurodegeneration in the developing mouse brain

GM2 ganglioside in the brain increased during ethanol-induced acute apoptotic neurodegeneration in 7-day-old mice. A small but a significant increase observed 2 h after ethanol exposure was followed by a marked increase around 24 h. Subcellular fractionation of the brain 24 h after ethanol treatment indicated that GM2 increased in synaptic and non-synaptic mitochondrial fractions as well as in a lysosome-enriched fraction characteristic to the ethanol-exposed brain. Immunohistochemical staining of GM2 in the ethanol-treated brain showed strong punctate staining mainly in activated microglia, in which it partially overlapped with staining for LAMP1, a late endosomal/lysosomal marker. Also, there was weaker neuronal staining, which partially co-localized with complex IV, a mitochondrial marker, and was augmented in cleaved caspase 3-positive neurons. In contrast, the control brain showed only faint and diffuse GM2 staining in neurons. Incubation of isolated brain mitochondria with GM2 in vitro induced cytochrome c release in a manner similar to that of GD3 ganglioside. Because ethanol is known to trigger mitochondria-mediated apoptosis with cytochrome c release and caspase 3 activation in the 7-day-old mouse brain, the GM2 elevation in mitochondria may be relevant to neuroapoptosis. Subsequently, activated microglia accumulated GM2, indicating a close relationship between GM2 and ethanol-induced neurodegeneration.

Adoptive T cell therapy promotes the emergence of genomically altered tumor escape variants

Adoptive T cell therapy has been proven effective against melanoma in mice and humans. However, because most responses are incomplete or transient, cures remain rare. To maximize the efficacy of this therapy, it will be essential to gain a better understanding of the processes which result in tumor relapse. We studied these processes using B16ova murine melanoma and adoptive transfer of OT-I T cells. Transfer of T cells as a single therapy provided a significant survival benefit for mice with established subcutaneous tumors. However, tumors which initially regressed often recurred. By analyzing tumors which emerged in the presence of a potent OT-I response, we identified a novel tumor escape mechanism in which tumor cells evaded T cell pressure by undergoing major genomic changes involving loss of the gene encoding the target tumor antigen. Furthermore, we show that these in vivo processes can be recapitulated in vitro using T cell/tumor cell co-cultures. A single round of in vitro co-culture led to significant loss of the ova gene and a tumor cell population with rapidly induced and diverse karyotypic changes. Although these current studies focus on the model OVA antigen, the finding that T cells can directly promote genomic instability has important implications for the development of adoptive T cell therapies.

Accumulation of long-chain glycosphingolipids during aging is prevented by caloric restriction

Background

Chronic kidney disease and end-stage renal disease are major causes of morbidity and mortality that are seen far more commonly in the aged population. Interestingly, kidney function declines during aging even in the absence of underlying renal disease. Declining renal function has been associated with age-related cellular damage and dysfunction with reports of increased levels of apoptosis, necrosis, and inflammation in the aged kidney. Bioactive sphingolipids have been shown to regulate these same cellular processes, and have also been suggested to play a role in aging and cellular senescence.

Methodology/Principal Findings

We hypothesized that alterations in kidney sphingolipids play a role in the declining kidney function that occurs during aging. To begin to address this, the sphingolipid profile was measured in young (3 mo), middle aged (9 mo) and old (17 mo) C57BL/6 male mice. Interestingly, while modest changes in ceramides and sphingoid bases were evident in kidneys from older mice, the most dramatic elevations were seen in long-chain hexosylceramides (HexCer) and lactosylceramides (LacCer), with C14- and C16-lactosylceramides elevated as much as 8 and 12-fold, respectively. Increases in long-chain LacCers during aging are not exclusive to the kidney, as they also occur in the liver and brain. Importantly, caloric restriction, previously shown to prevent the declining kidney function seen in aging, inhibits accumulation of long-chain HexCer/LacCers and prevents the age-associated elevation of enzymes involved in their synthesis. Additionally, long-chain LacCers are also significantly elevated in human fibroblasts isolated from elderly individuals.

Conclusion/Significance

This study demonstrates accumulation of the glycosphingolipids HexCer and LacCer in several different organs in rodents and humans during aging. In addition, data demonstrate that HexCer and LacCer metabolism is regulated by caloric restriction. Taken together, data suggest that HexCer/LacCers are important mediators of cellular processes fundamental to mammalian aging.