Ganglioside GD1a suppresses TNFalpha expression via Pkn1 at the transcriptional level in mouse osteosarcoma-derived FBJ cells

Linking genetic variation with epigenetic profiles in Sjögren's syndrome

DNA methylation represents an important regulatory event governing gene expression that is dysregulated in Sjögren's syndrome (SjS) and a number of autoimmune/inflammatory diseases. As disease-associated single-nucleotide polymorphisms (SNPs) have relevance in controlling DNA methylation, 94 non-HLA SjS-SNPs were investigated, among them 57 (60.6%) with widespread effects on 197 individual DNA methylation quantitative trait loci (meQTL) were selected. Typically, these SNPs are intronic, possess an active promoter histone mark, and control cis-meQTLs located around transcription start sites. Interplay is independent of the physical distance between SNPs and meQTLs. Using epigenome-wide association study datasets, SjS-meQTLs were characterized (41 genes and 13 DNA methylation CpG motifs) and for the most part map to a pro-inflammatory cytokine pathway, which is important for the control of DNA methylation in autoimmune diseases. In conclusion, exploring meQTLs represents a valuable tool to predict and investigate downstream effects of genetic factors in complex diseases such as SjS.

Vitamin K Deficiency Induced by Warfarin Is Associated With Cognitive and Behavioral Perturbations, and Alterations in Brain Sphingolipids in Rats

Initially discovered for its role in blood coagulation, there is now convincing evidence that vitamin K (VK) has important actions in the nervous system. In brain, VK is present in the form of menaquinone-4 (MK-4), a byproduct of the main dietary source, phylloquinone. It contributes to the biological activation of various proteins (i.e., Gas6), and participates in the synthesis of sphingolipids, a class of lipids widely present in brain cell membranes with important cell signaling functions. In a previous study, we reported that lifetime consumption of a low VK diet resulted in mild cognitive impairment in aged rats, a finding associated with an alteration of the sphingolipid profile. To confirm the role of VK as it relates to sphingolipids, cognition, and behavior outside the context of aging, we conducted a study of acute VK deficiency using a pharmacological model of VK deficiency in brain. In this procedure, rats (8 weeks) are maintained on a ratio of warfarin (a VK antagonist) to VK whereby coagulation is maintained while inducing VK deficiency in extrahepatic tissues. After 10 weeks of treatment, rats who were subjected to the warfarin plus phylloquinone protocol (WVK) exhibited longer latencies in the Morris water maze test as well as lower locomotor activity and exploratory behavior in the open field test, when compared to control rats. The WVK treatment resulted in a dramatic decrease in MK-4 level in all brain regions despite the presence of high local concentrations of phylloquinone, which suggests an inhibition of the biosynthetic MK-4 pathway in the presence of warfarin. Additionally, WVK treatment affected sphingolipid concentrations in key brain regions, notably those of the ganglioside family. Finally, brain MK-4 was correlated with performances in the open field test. This study confirms the modulatory role of VK in cognition and behavior and the implication of sphingolipids, notably those of the ganglioside family.

Ganglioside GD1a promotes oocyte maturation, furthers preimplantation development, and increases blastocyst quality in pigs

Gangliosides are key lipid molecules required for the regulation of cellular processes such as proliferation, differentiation, and cell signaling, including signaling of epidermal growth factor receptor (EGFR). Epidermal growth factor (EGF) has long been considered a potential regulator of meiotic and cytoplasmic maturation in mammalian oocytes. However, there is no report on the direct effect of ganglioside GD1a in porcine oocyte maturation. In this study, we first investigated a functional link between GD1a and meiotic maturation during in vitro maturation (IVM) of porcine embryos. Moreover, we confirmed the effect of exogenous GD1a treatment on blastocyst development, quality, and fertilization rate in early embryonic development. First, we observed that the protein level of ST3GAL2, a GD1a synthesizing enzyme, significantly increased (P < 0.01) in cumulus-oocyte-complexes (COCs) during IVM progress. The proportion of arrested germinal vesicles (GV) increased in oocytes treated with EGF+GD1a (41.6 ± 1.5%) at the IVM I stage. Upon completion of meiotic maturation, the proportion of metaphase II (M II) was significantly higher (P < 0.05) in the EGF+GD1a (89.9 ± 3.6%) treated group. After IVF, the percentage of penetrated oocytes was significantly higher (P < 0.05) in the EGF+GD1a (89.1 ± 2.3%) treated group than in the control group. Furthermore, exogenous GD1a treatment improved the developmental competence and quality of blastocysts during preimplantation embryo development stage. These results suggest that ganglioside GD1a may play an important role in IVM mechanisms of porcine maturation capacity. Furthermore, our findings will be helpful for better promoting the embryo development and blastocyst quality in pigs.

Glycosphingolipids: synthesis and functions

Glycosphingolipids (GSLs) comprise a heterogeneous group of membrane lipids formed by a ceramide backbone covalently linked to a glycan moiety. Hundreds of different glycans can be linked to tens of different ceramide molecules, giving rise to an astonishing variety of structurally different compounds, each of which has the potential for a specific biological function. GSLs have been suggested to modulate membrane-protein function and to contribute to cell-cell communication. Although GSLs are dispensable for cellular life, they are indeed collectively required for the development of multicellular organisms, and are thus considered to be key molecules in 'cell sociology'. Consequently, the GSL make-up of individual cells is highly dynamic and is strictly linked to the cellular developmental and environmental state. In the present review, we discuss some of the available knowledge, open questions and future perspectives relating to the study of GSL biology.

Calcium regulates caveolin-1 expression at the transcriptional level

Caveolin-1, an indispensable component of caveolae serving as a transformation suppressor protein, is highly expressed in poorly metastatic mouse osteosarcoma FBJ-S1 cells while highly metastatic FBJ-LL cells express low levels of caveolin-1. Calcium concentration is higher in FBJ-S1 cells than in FBJ-LL cells; therefore, we investigated the possibility that calcium signaling positively regulates caveolin-1 in mouse FBJ-S1 cells. When cells were treated with the calcium channel blocker nifedipine, cyclosporin A (a calcineurin inhibitor), or INCA-6 (a nuclear factor of activated T-cells [NFAT] inhibitor), caveolin-1 expression at the mRNA and protein levels decreased. RNA silencing of voltage-dependent L-type calcium channel subunit alpha-1C resulted in suppression of caveolin-1 expression. This novel caveolin-1 regulation pathway was also identified in mouse NIH 3T3 cells and Lewis lung carcinoma cells. These results indicate that caveolin-1 is positively regulated at the transcriptional level through a novel calcium signaling pathway mediated by L-type calcium channel/Ca(2+)/calcineurin/NFAT.

Role of metabolism in the effects of genistein and its phase II conjugates on the growth of human breast cell lines

Genistein has been investigated for several decades for its potential role in breast cancer prevention. Previous researches have shown that glucuronide and sulfate conjugates are the major species circulating in the blood after genistein ingestion. It was hypothesized that enzymes (UDP-glucuronosyltransferases, sulphotransferases, β-glucuronidases, and sulphatases) present in breast tissues would catalyze the inter-conversion between the aglycone and the conjugates in situ. Therefore, our aim was to investigate how genistein, genistein-7-glucuronide (G-7-G), genistein-7-sulfate (G-7-S), and 4'-sulfate (G-4'-S) were metabolized in mammary cells and to determine the effects of metabolism on their proliferative actions using cultured breast cell lines. As expected, genistein stimulated the cell growth of breast cancer cells (MCF-7 and T47D) concentration-dependently at lower concentrations but inhibited their growth at higher concentration. It showed low activities in a non-tumorigenic cell line (MCF-10A) due to the absence of ERα. Genistein was extensively metabolized to glucuronides by MCF-7 and to sulfates by T47D, while it was poorly metabolized by MCF-10A. G-7-G displayed weak stimulation activity in breast cancer cells. G-7-G underwent extensive metabolism in T47D and MCF-10A but not in MCF-7. The proliferative effects of G-7-G on MCF-7 and T47D were associated with its hydrolysis to genistein in these cells. In contrast, G-7-S and G-4'-S were not metabolized by these three cells and had no effects on their growth. In conclusion, production of phase II metabolites did not affect the proliferation effect of genistein on MCF-7 and T47D. Deconjugation was correlated to the apparent proliferative effects of G-7-G in breast cancer cells.

GM3 suppresses anchorage-independent growth via Rho GDP dissociation inhibitor beta in melanoma B16 cells

Ly-GDI, Rho GTPase dissociation inhibitor beta, was found to be expressed parallel to the GM3 level in mouse B16 cells whose GM3 contents were modified by B4galt6 sense, B4galt6 antisense cDNA, or St3galt5 siRNA transfection. Ly-GDI expression was increased on GM3 addition to these cells and decreased with D-PDMP treatment, a glucosylceramide synthesis inhibitor. Suppression of GM3 or Ly-GDI by RNAi was concomitantly associated with an increase in anchorage-independent growth in soft agar. These results clearly indicate that GM3 suppresses anchorage-independent growth through Ly-GDI. GM3 signals regulating Ly-GDI expression was inhibited by LY294002, siRNA against Akt1 and Akt2 and rapamycin, showing that GM3 signals are transduced via the PI3K/Akt/mTOR pathway. Either siRNA towards Rictor or Raptor suppressed Ly-GDI expression. The Raptor siRNA suppressed the effects of GM3 on Ly-GDI expression and Akt phosphorylation at Thr(308) , suggesting GM3 signals to be transduced to mTOR-Raptor and Akt-Thr(308) , leading to Ly-GDI stimulation. siRNA targeting Pdpk1 reduced Akt phosphorylation at Thr(308) and rendered the cells insensitive to GM3 stimulation, indicating that Akt-Thr(308) plays a critical role in the pathway. The components aligned in this pathway showed similar effects on anchorage-independent growth as GM3 and Ly-GDI. Taken together, GM3 signals are transduced in B16 cells through PI3K, Pdpk1, Akt(Thr308) and the mTOR/Raptor pathway, leading to enhanced expression of Ly-GDI mRNA, which in turn suppresses anchorage-independent growth in melanoma B16 cells.

Induction of GM1a/GD1b synthase triggers complex ganglioside expression and alters neuroblastoma cell behavior; a new tumor cell model of ganglioside function

Neuroblastoma is the most common extracranial solid tumor in children and tumor ganglioside composition has been linked to its biological and clinical behavior. We recently found that high expression of complex gangliosides that are products of the enzyme GM1a/GD1b synthase predicts a more favorable outcome in human neuroblastoma, and others have shown that complex gangliosides such as GD1a inhibit metastasis of murine tumors. To determine how a switch from structurally simple to structurally complex ganglioside expression affects neuroblastoma cell behavior, we engineered IMR32 human neuroblastoma cells, which contain almost exclusively (89%) the simple gangliosides (SG) GM2, GD2, GM3, and GD3, to overexpress the complex gangliosides (CG) GM1, GD1a, GD1b and GT1b, by stable retroviral-mediated transduction of the cDNA encoding GM1a/GD1b synthase. This strikingly altered cellular ganglioside composition without affecting total ganglioside content: There was a 23-fold increase in the ratio of complex to simple gangliosides in GM1a/GD1b synthase-transduced cells (IMR32-CG) vs. wild type (IMR32) or vector-transfected (IMR32-V) cells with essentially no expression of the clinical neuroblastoma marker, GD2, confirming effectiveness of this molecular switch from simple to complex ganglioside synthesis. Probing for consequences of the switch, we found that among functional properties of IMR32-CG cells, cell migration was inhibited and Rho/Rac1 activities were altered, while proliferation kinetics and cell differentiation were unaffected. These findings further implicate cellular ganglioside composition in determining cell migration characteristics of tumor cells. This IMR32 model system should be useful in delineating the impact of ganglioside composition on tumor cell function.

Sphingolipids and expression regulation of genes in cancer

Sphingolipids including glycosphingolipids have myriad effects on cell functions and affect cancer in aspects of tumorigenesis, metastasis and tumor response to treatments. Bioactive ones like ceramide, sphingosine 1-phosphate and globotriaosylceramide initiate and process cellular signaling to alter cell behaviors immediately responding to oncogenic stress or treatment challenges. Recent studies pinpoint that sphingolipid-mediated gene expression has long and profound impacts on cancer cells, and these play crucial roles in tumor progression and in treatment outcome. More than 10 sphingolipids and glycosphingolipids selectively mediate expressions of approximately 50 genes including c-myc, p21, c-fos, telomerase reverse transcriptase, caspase-9, Bcl-x, cyclooxygenase-2, matrix metalloproteinases, integrins, Oct-4, glucosylceramide synthase and multidrug-resistant gene 1. By diverse functions of these genes, sphingolipids enduringly affect cellular processes of mitosis, apoptosis, migration, stemness of cancer stem cells and cellular resistance to therapies. Mechanistic studies indicate that sphingolipids regulate particular gene expression by modulating phosphorylation and acetylation of proteins that serve as transcription factors (β-catenin, Sp1), repressor of transcription (histone H3), and regulators (SRp30a) in RNA splicing. Disclosing molecular mechanisms by which sphingolipids selectively regulate particular gene expression, instead of other relevant ones, requires understanding of the exact roles of individual lipid instead of a group, the signaling pathways that are implicated in and interaction with proteins or other lipids in details. These studies not only expand our knowledge of sphingolipids, but can also suggest novel targets for cancer treatments.