GM1 and Tumor Necrosis Factor-α, Overexpressed in Renal Cell Carcinoma, Synergize to Induce T-Cell Apoptosis

The cancer glycocode as a family of diagnostic biomarkers, exemplified by tumor-associated gangliosides

One unexploited family of cancer biomarkers comprise glycoproteins, carbohydrates, and glycolipids (the Tumor Glycocode).A class of glycolipid cancer biomarkers, the tumor-marker gangliosides (TMGs) are presented here as potential diagnostics for detecting cancer, especially at early stages, as the biological function of TMGs makes them etiological. We propose that a quantitative matrix of the Cancer Biomarker Glycocode and artificial intelligence-driven algorithms will expand the menu of validated cancer biomarkers as a step to resolve some of the challenges in cancer diagnosis, and yield a combination that can identify a specific cancer, in a tissue-agnostic manner especially at early stages, to enable early intervention. Diagnosis is critical to reducing cancer mortality but many cancers lack efficient and effective diagnostic tests, especially for early stage disease. Ideal diagnostic biomarkers are etiological, samples are preferably obtained via non-invasive methods (e.g. liquid biopsy of blood or urine), and are quantitated using assays that yield high diagnostic sensitivity and specificity for efficient diagnosis, prognosis, or predicting response to therapy. Validated biomarkers with these features are rare. While the advent of proteomics and genomics has led to the identification of a multitude of proteins and nucleic acid sequences as cancer biomarkers, relatively few have been approved for clinical use. The use of multiplex arrays and artificial intelligence-driven algorithms offer the option of combining data of known biomarkers; however, for most, the sensitivity and the specificity are below acceptable criteria, and clinical validation has proven difficult. One strategic solution to this problem is to expand the biomarker families beyond those currently exploited. One unexploited family of cancer biomarkers comprise glycoproteins, carbohydrates, and glycolipids (the Tumor Glycocode). Here, we focus on a family of glycolipid cancer biomarkers, the tumor-marker gangliosides (TMGs). We discuss the diagnostic potential of TMGs for detecting cancer, especially at early stages. We include prior studies from the literature to summarize findings for ganglioside quantification, expression, detection, and biological function and its role in various cancers. We highlight the examples of TMGs exhibiting ideal properties of cancer diagnostic biomarkers, and the application of GD2 and GD3 for diagnosis of early stage cancers with high sensitivity and specificity. We propose that a quantitative matrix of the Cancer Biomarker Glycocode and artificial intelligence-driven algorithms will expand the menu of validated cancer biomarkers as a step to resolve some of the challenges in cancer diagnosis, and yield a combination that can identify a specific cancer, in a tissue-agnostic manner especially at early stages, to enable early intervention.

Lysolipids regulate raft size distribution

The lipid matrix of cellular membranes, directly and indirectly, regulates many vital functions of the cell. The diversity of lipids in membranes leads to the formation of ordered domains called rafts, which play a crucial role in signal transduction, protein sorting and other cellular processes. Rafts are believed to impact the development of different neurodegenerative diseases, such as Alzheimer’s, Parkinson’s, Huntington’s ones, amyotrophic lateral sclerosis, some types of cancer, etc. These diseases correlate with the change in the membrane lipid composition resulting from an oxidative stress, age-related processes, dysfunction of proteins, and many others. In particular, a lot of studies report a significant rise in the level of lysolipids. Physicochemical properties of rafts are determined by membrane composition, in particular, by the content of lysolipids. Lysolipids may thus regulate raft-involving processes. However, the exact mechanism of such regulation is unknown. Although studying rafts in vivo still seems to be rather complicated, liquid-ordered domains are well observed in model systems. In the present study, we used atomic force microscopy (AFM) to examine how lysophospholipids influence the liquid-ordered domains in model ternary membranes. We demonstrated that even a small amount of lysolipids in a membrane significantly impacts domain size depending on the saturation of the lysolipid hydrocarbon tails and the amount of cholesterol. The mixture with the bigger relative fraction of cholesterol was more susceptible to the action of lysolipids. This data helped us to generalize our previous theoretical model of the domain size regulation by lipids with particular molecular shape expanding it to the case of lysolipids and dioleoylglycerol.

Aiming for the Sweet Spot: Glyco-Immune Checkpoints and γδ T Cells in Targeted Immunotherapy

Though a healthy immune system is capable of recognizing and eliminating emergent cancerous cells, an established tumor is adept at escaping immune surveillance. Altered and tumor-specific expression of immunosuppressive cell surface carbohydrates, also termed the “tumor glycocode,” is a prominent mechanism by which tumors can escape anti-tumor immunity. Given their persistent and homogeneous expression, tumor-associated glycans are promising targets to be exploited as biomarkers and therapeutic targets. However, the exploitation of these glycans has been a challenge due to their low immunogenicity, immunosuppressive properties, and the inefficient presentation of glycolipids in a conventional major histocompatibility complex (MHC)-restricted manner. Despite this, a subset of T-cells expressing the gamma and delta chains of the T-cell receptor (γδ T cells) exist with a capacity for MHC-unrestricted antigen recognition and potent inherent anti-tumor properties. In this review, we discuss the role of tumor-associated glycans in anti-tumor immunity, with an emphasis on the potential of γδ T cells to target the tumor glycocode. Understanding the many facets of this interaction holds the potential to unlock new ways to use both tumor-associated glycans and γδ T cells in novel therapeutic interventions.

Host membrane glycosphingolipids and lipid microdomains facilitate Histoplasma capsulatum internalisation by macrophages

Recognition and internalisation of intracellular pathogens by host cells is a multifactorial process, involving both stable and transient interactions. The plasticity of the host cell plasma membrane is fundamental in this infectious process. Here, the participation of macrophage lipid microdomains during adhesion and internalisation of the fungal pathogen Histoplasma capsulatum (Hc) was investigated. An increase in membrane lateral organisation, which is a characteristic of lipid microdomains, was observed during the first steps of Hc-macrophage interaction. Cholesterol enrichment in macrophage membranes around Hc contact regions and reduced levels of Hc-macrophage association after cholesterol removal also suggested the participation of lipid microdomains during Hc-macrophage interaction. Using optical tweezers to study cell-to-cell interactions, we showed that cholesterol depletion increased the time required for Hc adhesion. Additionally, fungal internalisation was significantly reduced under these conditions. Moreover, macrophages treated with the ceramide-glucosyltransferase inhibitor (P4r) and macrophages with altered ganglioside synthesis (from B4galnt1^-/- mice) showed a deficient ability to interact with Hc. Coincubation of oligo-GM1 and treatment with Cholera toxin Subunit B, which recognises the ganglioside GM1, also reduced Hc association. Although purified GM1 did not alter Hc binding, treatment with P4 significantly increased the time required for Hc binding to macrophages. The content of CD18 was displaced from lipid microdomains in B4galnt1^-/- macrophages. In addition, macrophages with reduced CD18 expression (CD18^low ) were associated with Hc at levels similar to wild-type cells. Finally, CD11b and CD18 colocalised with GM1 during Hc-macrophage interaction. Our results indicate that lipid rafts and particularly complex gangliosides that reside in lipid rafts stabilise Hc-macrophage adhesion and mediate efficient internalisation during histoplasmosis.

Hypertension and Circulating Cytokines and Angiogenic Factors in Patients With Advanced Non-Clear Cell Renal Cell Carcinoma Treated With Sunitinib: Results From a Phase II Trial

BACKGROUND

We evaluated the significance of hypertension developing during vascular endothelial growth factor (VEGF) receptor tyrosine kinase inhibitor (VEGFR-TKI) treatment and a group of cytokines and angiogenic factors (CAFs) in advanced non-clear cell renal cell carcinoma (nccRCC) patients treated with sunitinib in a phase II study.

MATERIALS AND METHODS

Using multiplex assays, we analyzed the levels of 38 CAFs in plasma at baseline and after 4 weeks of sunitinib therapy. Sunitinib benefit was defined as a partial response or stable disease using the Response Evaluation Criteria in Solid Tumors lasting ≥4 months. Cox proportional hazards regression models were used to assess the associations among hypertension, CAFs, and progression-free (PFS) and overall survival (OS).

RESULTS

Fifty-seven patients were evaluable; 53 had baseline CAF levels available. The median PFS and OS were 2.9 months (95% confidence interval [CI], 1.4-5.5) and 16.8 months (95% CI, 10.7-27.4), respectively. Sunitinib benefit was observed in 21 patients (37%). However, 33 patients (60%) developed hypertension during treatment, although no association was found with survival or response. Elevated baseline soluble tumor necrosis factor (TNF) receptor I, interleukin-8, growth-regulated oncogene, transforming growth factor-α, and VEGFR-2 levels were associated with an increased risk of death on multivariate analysis.

CONCLUSION

We found no association between the development of hypertension and survival or sunitinib benefit in advanced nccRCC. TNF and angiogenic/immunomodulatory mediators were identified for evaluation as markers of prognosis and VEGFR-TKI benefit in future studies.

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.

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.

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.

PPARγ-dependent anti-tumor and immunomodulatory actions of pioglitazone

Peroxisome proliferator-activated receptor-γ (PPARγ) has been reported to play important roles in carcinogenesis. The current study was carried out to assess the possible anti-tumor effects of pioglitazone (PIO), a PPARγ agonist, in a mouse mammary carcinoma model, i.e. a solid Ehrlich carcinoma (SEC). Effects of PIO on tumor-induced immune dysfunction, and the possibility that PIO may modulate the anti-tumor and immunomodulatory effects of doxorubicin (DOX) were also studied. The effects in tumor-bearing hosts of several doses of PIO (100 mg/kg, per os), with and without the added presence of DOX (2 mg/kg, IP), was investigated in vivo; end-points evaluated included assessment of tumor volume, splenic lymphocyte profiles/functionality, tumor necrosis factor (TNF)-α content, as well as apoptosis and expression of nuclear factor-κB (NF-κB) among the tumor cells. The data indicate that PIO induced significant anti-tumor activity against the SEC. PIO treatments also significantly mitigated both tumor- and doxorubicin-induced declines in immune parameters assessed here. Moreover, PIO led to decreased NF-κB nuclear expression, and, in doing so, appeared to chemo-sensitize these tumor cells to DOX-induced apoptosis. All pioglitazone-studied effects were antagonized by GW9662, a selective PPARγ antagonist.

ROS-PIASγ cross talk channelizes ATM signaling from resistance to apoptosis during chemosensitization of resistant tumors

With the existing knowledge of ATM's role in therapeutic resistance, the present study aimed at identifying the molecular mechanisms that influence ATM to oscillate between chemoresistance and chemosensitivity. We observed that the redox status of tumors functions as a major determinant of ATM-dependent ‘resistance-to-apoptosis' molecular switch. At a low reactive oxygen species (ROS) condition during genotoxic insult, the ATM/sumoylated-IKKγ interaction induced NFκB activation that resisted JNK-mediated apoptosis, whereas increasing cellular ROS restored ATM/JNK apoptotic signaling. A search for the upstream missing link revealed that high ROS induces oxidation and ubiquitin-mediated degradation of PIASγ, thereby disrupting PIASγ-IKKγ cross talk, a pre-requisite for IKKγ sumoylation and subsequent NFκB activation. Interruption in the PIASγ-mediated resistance pathway channels ATM signaling toward ATM/JNK pro-death circuitry. These in vitro results also translated to sensitive and resistant tumor allograft mouse models in which low ROS-induced resistance was over-ruled in PIASγ knockout tumors, while its overexpression inhibited high ROS-dependent apoptotic cues. Cumulatively, our findings identified an unappreciated yet critical combinatorial function of cellular ROS and PIASγ in regulating ATM-mediated chemosensitization of resistant tumors. Thus, therapeutic strategies employing ROS upregulation to inhibit PIASγ during genotoxic therapy may, in future, help to eliminate the problems of NFκB-mediated tumor drug resistance.

Calcarea carbonica induces apoptosis in cancer cells in p53-dependent manner via an immuno-modulatory circuit

BACKGROUND

Complementary medicines, including homeopathy, are used by many patients with cancer, usually alongside with conventional treatment. However, the molecular mechanisms underneath the anti-cancer effect, if any, of these medicines have still remained unexplored. To this end we attempted to evaluate the efficacy of calcarea carbonica, a homeopathic medicine, as an anti-cancer agent and to delineate the detail molecular mechanism(s) underlying calcerea carbonica-induced tumor regression.

METHODS

To investigate and delineate the underlying mechanisms of calcarea carbonica-induced tumor regression, Trypan blue dye-exclusion test, flow cytometric, Western blot and reverse transcriptase-PCR techniques were employed. Further, siRNA transfections and inhibitor studies were used to validate the involvement of p53 pathway in calcarea carbonica-induced apoptosis in cancer cells.

RESULTS

Interestingly, although calcarea carbonica administration to Ehrlich's ascites carcinoma (EAC)- and Sarcoma-180 (S-180)-bearing Swiss albino mice resulted in 30-35% tumor cell apoptosis, it failed to induce any significant cell death in ex vivo conditions. These results prompted us to examine whether calcarea carbonica employs the immuno-modulatory circuit in asserting its anti-tumor effects. Calcarea carbonica prevented tumor-induced loss of effector T cell repertoire, reversed type-2 cytokine bias and attenuated tumor-induced inhibition of T cell proliferation in tumor-bearing host. To confirm the role of immune system in calcarea carbonica-induced cancer cell death, a battery of cancer cells were co-cultured with calcarea carbonica-primed T cells. Our results indicated a "two-step" mechanism of the induction of apoptosis in tumor cells by calcarea carbonica i.e., (1) activation of the immune system of the host; and (2) induction of cancer cell apoptosis via immuno-modulatory circuit in p53-dependent manner by down-regulating Bcl-2:Bax ratio. Bax up-regulation resulted in mitochondrial transmembrane potential loss and cytochrome c release followed by activation of caspase cascade. Knocking out of p53 by RNA-interference inhibited calcarea carbonica-induced apoptosis thereby confirming the contribution of p53.

CONCLUSION

These observations delineate the significance of immuno-modulatory circuit during calcarea carbonica-mediated tumor apoptosis. The molecular mechanism identified may serve as a platform for involving calcarea carbonica into immunotherapeutic strategies for effective tumor regression.

Nifetepimine, a dihydropyrimidone, ensures CD4+ T cell survival in a tumor microenvironment by maneuvering sarco(endo)plasmic reticulum Ca2+ ATPase (SERCA)

Multiple mechanisms have been proposed by which tumors induce T cell apoptosis to circumvent tumor immune-surveillance. Although sarco/endoplasmic reticulum Ca(2+)-ATPase (SERCA) have long been known to regulate intracellular Ca(2+) homeostasis, few studies have examined the role of SERCA in processes of T lymphocyte survival and activation. In this context it remains largely unexplored as to how tumors jeopardize SERCA function to disable T cell-mediated anti-tumor immunity. Here, we show that human CD4(+) T cells in the presence of tumor conditions manifested an up-regulation of SERCA3 expression that resulted in development of endoplasmic reticulum stress leading to CD4(+) T cell apoptosis. Prostaglandin E(2) produced by the tumor cell plays a critical role in up-regulating SERCA3 by enhancing the binding of its transcription factor Sp1. Gene manipulation and pharmacological approaches further established that an increase in SERCA expression also resulted in subsequent inhibition of PKCα and -θ and retention of NFκB in the cytosol; however, down-modulation of SERCA3 expression by a dihydropyrimidone derivative, ethyl-4-(3-nitro)-phenyl-6-methyl-2-oxo-1,2,3,4-tetrahydropyrimidine-5 carboxylate (nifetepimine), protected the CD4(+) T cells from tumor-induced apoptosis. In fact, nifetepimine-mediated restoration of PKC activity resulted in nuclear translocation of p65NFκB, thereby ensuring its survival. Studies further undertaken in a tumor-bearing mice model revalidated the immunoprotective role of nifetepimine. Our present study thus strongly suggests that imbalance in cellular calcium homeostasis is an important factor leading to CD4(+) T cell death during cancer and holds promise that nifetepimine may have the potential to be used as an immunorestoring agent in cancer bearers.

Curcumin enhances the efficacy of chemotherapy by tailoring p65NFκB-p300 cross-talk in favor of p53-p300 in breast cancer

Breast cancer cells often develop multiple mechanisms of drug resistance during tumor progression, which is the major reason for the failure of breast cancer therapy. High constitutive activation of NFκB has been found in different cancers, creating an environment conducive for chemotherapeutic resistance. Here we report that doxorubicin-induced SMAR1-dependent transcriptional repression and SMAR1-independent degradation of IkBα resulted in nuclear translocation of p65NFκB and its association with p300 histone acetylase and subsequent transcription of Bcl-2 to impart protective response in drug-resistant cells. Consistently SMAR1-silenced drug-resistant cells exhibited IkBα-mediated inhibition of p65NFκB and induction of p53-dependent apoptosis. Interestingly, curcumin pretreatment of drug-resistant cells alleviated SMAR1-mediated p65NFκB activation and hence restored doxorubicin sensitivity. Under such anti-survival condition, induction of p53-p300 cross-talk enhanced the transcriptional activity of p53 and intrinsic death cascade. Importantly, promyelocyte leukemia-mediated SMAR1 sequestration that relieved the repression of apoptosis-inducing genes was indispensable for such chemo-sensitizing ability of curcumin. A simultaneous decrease in drug-induced systemic toxicity by curcumin might also have enhanced the efficacy of doxorubicin by improving the intrinsic defense machineries of the tumor-bearer. Overall, the findings of this preclinical study clearly demonstrate the effectiveness of curcumin to combat doxorubicin-resistance. We, therefore, suggest curcumin as a potent chemo-sensitizer to improve the therapeutic index of this widely used anti-cancer drug. Taken together, these results suggest that curcumin can be developed into an adjuvant chemotherapeutic drug.

Restoration of tumor suppressor p53 by differentially regulating pro- and anti-p53 networks in HPV-18-infected cervical cancer cells

Abrogation of functional p53 is responsible for malignant cell transformation and maintenance of human papilloma virus (HPV)-infected cancer cells. Restoration of p53 has, therefore, been regarded as an important strategy for molecular intervention of HPV-associated malignancies. Here we report that differential regulation of pro- and anti-p53 setups not only upregulates p53 transcription but also stabilizes and activates p53 protein to ensure p53-induced apoptosis in HPV-18-infected cervical cancer. Functional restoration of p53 can be achieved by non-steroidal anti-inflammatory drug celecoxib via multiple molecular mechanisms: (i) inhibition of p53 degradation by suppressing viral oncoprotein E6 expression, (ii) promoting p53 transcription by downmodulating cycloxygenase-2 (Cox-2) and simultaneously retrieving p53 from Cox-2 association and (iii) activation of p53 via ataxia telangiectasia mutated-/p38 mitogen-activated protein kinase-mediated phosphorylations at serine-15/-46 residues. That restored p53 is functional has been confirmed by its ability of transactivating Bax and p53-upregulated modulator of apoptosis, which in turn switch on the apoptotic machinery in these cells. Studies undertaken in biopsy samples of cervical carcinoma further validated celecoxib effect. Our approaches involving gene manipulation and pharmacological interference finally highlight that celecoxib alters pro- and anti-p53 networks, not in isolation but in concert, to rejuvenate p53-dependent apoptotic program in HPV-infected cervical cancer cells.

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.

Ganglioside-exposed dendritic cells inhibit T-cell effector function by promoting regulatory cell activity

Tumour pathogenesis is characterized by an immunosuppressive microenvironment that limits the development of effective tumour-specific immune responses. This is in part the result of tumour-dependent recruitment and activation of regulatory cells, such as myeloid-derived suppressor cells and regulatory T cells in the tumour microenvironment and draining lymph nodes. Shedding of gangliosides by tumour cells has immunomodulatory properties, suggesting that gangliosides may be a critical factor in initiating an immunosuppressive microenvironment. To better define the immunomodulatory properties of gangliosides on antigen-specific T-cell activation and development we have developed an in vitro system using ganglioside-treated murine bone-marrow-derived dendritic cells to prime and activate antigen-specific CD4(+) T cells from AND T-cell receptor transgenic mice. Using this system, ganglioside treatment promotes the development of a dendritic cell population characterized by decreased CD86 (B7-2) expression, and decreased interleukin-12 and interleukin-6 production. When these cells are used as antigen-presenting cells, CD4 T cells are primed to proliferate normally, but have a defect in T helper (Th) effector cell development. This defect in Th effector cell responses is associated with the development of regulatory T-cell activity that can suppress the activation of previously primed Th effector cells in a contact-dependent manner. In total, these data suggest that ganglioside-exposed dendritic cells promote regulatory T-cell activity that may have long-lasting effects on the development of tumour-specific immune responses.

Curcumin reverses T cell-mediated adaptive immune dysfunctions in tumor-bearing hosts

Immune dysfunction is well documented during tumor progression and likely contributes to tumor immune evasion. CD8(+) cytotoxic T lymphocytes (CTLs) are involved in antigen-specific tumor destruction and CD4(+) T cells are essential for helping this CD8(+) T cell-dependent tumor eradication. Tumors often target and inhibit T-cell function to escape from immune surveillance. This dysfunction includes loss of effector and memory T cells, bias towards type 2 cytokines and expansion of T regulatory (Treg) cells. Curcumin has previously been shown to have antitumor activity and some research has addressed the immunoprotective potential of this plant-derived polyphenol in tumor-bearing hosts. Here we examined the role of curcumin in the prevention of tumor-induced dysfunction of T cell-based immune responses. We observed severe loss of both effector and memory T-cell populations, downregulation of type 1 and upregulation of type 2 immune responses and decreased proliferation of effector T cells in the presence of tumors. Curcumin, in turn, prevented this loss of T cells, expanded central memory T cell (T(CM))/effector memory T cell (T(EM)) populations, reversed the type 2 immune bias and attenuated the tumor-induced inhibition of T-cell proliferation in tumor-bearing hosts. Further investigation revealed that tumor burden upregulated Treg cell populations and stimulated the production of the immunosuppressive cytokines transforming growth factor (TGF)-beta and IL-10 in these cells. Curcumin, however, inhibited the suppressive activity of Treg cells by downregulating the production of TGF-beta and IL-10 in these cells. More importantly, curcumin treatment enhanced the ability of effector T cells to kill cancer cells. Overall, our observations suggest that the unique properties of curcumin may be exploited for successful attenuation of tumor-induced suppression of cell-mediated immune responses.

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

Increased expression of gangliosides by different tumor types including renal cell carcinoma (RCC) is thought to contribute to the immune suppression observed in cancer patients. In this study, we report an increase in apoptotic T cells from RCC patients compared with T cells from normal donors that coincided with the detection of T cells staining positive for GM2 and that the apoptosis was predominantly observed in the GM2(+) but not the GM2(-) T cell population. Ganglioside shedding from tumor rather than endogenous production accounts for GM2(+) T cells since there was no detectable level of mRNA for GM2 synthase in RCC patient T cells and in T cells from normal healthy donors after incubation with either purified GM2 or supernatant from RCC cell lines despite their staining positive for GM2. Moreover, reactive oxygen species as well as activated caspase 3, 8, and 9 were predominantly elevated in GM2(+) but not GM2(-) T cells. Similarly, increased staining for GD2 and GD3 but not GD1a was detected with patient T cells with elevated levels of apoptosis in the GD2(+) and GD3(+) cells. These findings suggest that GM2, GD2, and GD3 play a significant role in immune dysfunction observed in RCC patient T cells.

Tumor-shed PGE(2) impairs IL2Rgammac-signaling to inhibit CD4 T cell survival: regulation by theaflavins

Background

Many tumors are associated with decreased cellular immunity and elevated levels of prostaglandin E2 (PGE2), a known inhibitor of CD4+ T cell activation and inducer of type-2 cytokine bias. However, the role of this immunomodulator in the survival of T helper cells remained unclear. Since CD4+ T cells play critical roles in cell-mediated immunity, detail knowledge of the effect tumor-derived PGE2 might have on CD4+ T cell survival and the underlying mechanism may, therefore, help to overcome the overall immune deviation in cancer.

Methodology/Principal Findings

By culturing purified human peripheral CD4+ T cells or Jurkat cells with spent media of theaflavin- or celecoxib-pre-treated MCF-7 cells, we show that tumor-shed PGE2 severely impairs interleukin 2 receptor γc (IL2Rγc)-mediated survival signaling in CD4+ T cells. Indeed, tumor-shed PGE2 down-regulates IL2Rγc expression, reduces phosphorylation as well as activation of Janus kinase 3 (Jak-3)/signal transducer and activator of transcription 5 (Stat-5) and decreases Bcl-2/Bax ratio thereby leading to activation of intrinsic apoptotic pathway. Constitutively active Stat-5A (Stat-5A1*6) over-expression efficiently elevates Bcl-2 levels in CD4+ T cells and protects them from tumor-induced death while dominant-negative Stat-5A over-expression fails to do so, indicating the importance of Stat-5A-signaling in CD4+ T cell survival. Further support towards the involvement of PGE2 comes from the results that (a) purified synthetic PGE2 induces CD4+ T cell apoptosis, and (b) when knocked out by small interfering RNA, cyclooxygenase-2 (Cox-2)-defective tumor cells fail to initiate death. Interestingly, the entire phenomena could be reverted back by theaflavins that restore cytokine-dependent IL2Rγc/Jak-3/Stat-5A signaling in CD4+ T cells thereby protecting them from tumor-shed PGE2-induced apoptosis.

Conclusions/Significance

These data strongly suggest that tumor-shed PGE2 is an important factor leading to CD4+ T cell apoptosis during cancer and raise the possibility that theaflavins may have the potential as an effective immunorestorer in cancer-bearer.

GD3, an overexpressed tumor-derived ganglioside, mediates the apoptosis of activated but not resting T cells

We previously elucidated an important role for gangliosides in renal cell carcinoma-mediated T lymphocyte apoptosis, although the mechanism by which they mediated lymphocyte death remained unclear. Here, we show that when added in purified form, GD3 is internalized by activated T cells, initiating a series of proapoptotic events, including the induction of reactive oxygen species (ROS), an enhancement of p53 and Bax accumulation, an increase in mitochondrial permeability, cytochrome c release, and the activation of caspase-9. GD3-induced apoptosis of activated T cells was dose dependent and inhibitable by pretreating the lymphocytes with N-acetylcysteine, cyclosporin A, or bongkrekic acid, emphasizing the essential role of ROS and mitochondrial permeability to the process. Ganglioside-induced T-cell killing was associated with the caspase-dependent degradation of nuclear factor-kappaB-inducible, antiapoptotic proteins, including RelA; this suggests that their loss is initiated only after the cascade is activated and that their disappearance amplifies but not triggers GD3 susceptibility. Resting T cells did not internalize appreciable levels of GD3 and did not undergo any of the proapoptotic changes that characterize activated T lymphocytes exposed to the ganglioside. RelA overexpression endows Jurkat cells with resistance to GD3-mediated apoptosis, verifying the role of the intact transcription factor in mediating protection from the ganglioside.