Differential Effects of Glycosphingolipids n Protein Kinase C Activity in PC12D Pheochromocytoma Cells

Cancer-Associated Glycosphingolipids as Tumor Markers and Targets for Cancer Immunotherapy

Aberrant expression of glycosphingolipids is a hallmark of cancer cells and is associated with their malignant properties. Disialylated gangliosides GD2 and GD3 are considered as markers of neuroectoderm origin in tumors, whereas fucosyl-GM1 is expressed in very few normal tissues but overexpressed in a variety of cancers, especially in small cell lung carcinoma. These gangliosides are absent in most normal adult tissues, making them targets of interest in immuno-oncology. Passive and active immunotherapy strategies have been developed, and have shown promising results in clinical trials. In this review, we summarized the current knowledge on GD2, GD3, and fucosyl-GM1 expression in health and cancer, their biosynthesis pathways in the Golgi apparatus, and their biological roles. We described how their overexpression can affect intracellular signaling pathways, increasing the malignant phenotypes of cancer cells, including their metastatic potential and invasiveness. Finally, the different strategies used to target these tumor-associated gangliosides for immunotherapy were discussed, including the use and development of monoclonal antibodies, vaccines, immune system modulators, and immune effector-cell therapy, with a special focus on adoptive cellular therapy with T cells engineered to express chimeric antigen receptors.

Deletion of Gb3 Synthase in Mice Resulted in the Attenuation of Bone Formation via Decrease in Osteoblasts

Glycosphingolipids are known to play a role in developing and maintaining the integrity of various organs and tissues. Among glycosphingolipids, there are several reports on the involvement of gangliosides in bone metabolism. However, there have been no reports on the presence or absence of expression of globo-series glycosphingolipids in osteoblasts and osteoclasts, and the involvement of their glycosphingolipids in bone metabolism. In the present study, we investigated the presence or absence of globo-series glycosphingolipids such as Gb3 (globotriaosylceramide), Gb4 (globoside), and Gb5 (galactosyl globoside) in osteoblasts and osteoclasts, and the effects of genetic deletion of Gb3 synthase, which initiates the synthesis of globo-series glycosphingolipids on bone metabolism. Among Gb3, Gb4, and Gb5, only Gb4 was expressed in osteoblasts. However, these glycosphingolipids were not expressed in pre-osteoclasts and osteoclasts. Three-dimensional micro-computed tomography (3D-μCT) analysis revealed that femoral cancellous bone mass in Gb3 synthase-knockout (Gb3S KO) mice was lower than that in wild type (WT) mice. Calcein double labeling also revealed that bone formation in Gb3S KO mice was significantly lower than that in WT mice. Consistent with these results, the deficiency of Gb3 synthase in mice decreased the number of osteoblasts on the bone surface, and suppressed mRNA levels of osteogenic differentiation markers. On the other hand, osteoclast numbers on the bone surface and mRNA levels of osteoclast differentiation markers in Gb3S KO mice did not differ from WT mice. This study demonstrated that deletion of Gb3 synthase in mice decreases bone mass via attenuation of bone formation.

Lysosomal Re-acidification Prevents Lysosphingolipid-Induced Lysosomal Impairment and Cellular Toxicity

Neurodegenerative lysosomal storage disorders (LSDs) are severe and untreatable, and mechanisms underlying cellular dysfunction are poorly understood. We found that toxic lipids relevant to three different LSDs disrupt multiple lysosomal and other cellular functions. Unbiased drug discovery revealed several structurally distinct protective compounds, approved for other uses, that prevent lysosomal and cellular toxicities of these lipids. Toxic lipids and protective agents show unexpected convergence on control of lysosomal pH and re-acidification as a critical component of toxicity and protection. In twitcher mice (a model of Krabbe disease [KD]), a central nervous system (CNS)-penetrant protective agent rescued myelin and oligodendrocyte (OL) progenitors, improved motor behavior, and extended lifespan. Our studies reveal shared principles relevant to several LSDs, in which diverse cellular and biochemical disruptions appear to be secondary to disruption of lysosomal pH regulation by specific lipids. These studies also provide novel protective strategies that confer therapeutic benefits in a mouse model of a severe LSD.

Targeting sphingosine kinase 1 in carcinoma cells decreases proliferation and survival by compromising PKC activity and cytokinesis

Sphingosine kinases (SK) catalyze the phosphorylation of proapoptotic sphingosine to the prosurvival factor sphingosine 1-phosphate (S1P), thereby promoting oncogenic processes. Breast (MDA-MB-231), lung (NCI-H358), and colon (HCT 116) carcinoma cells were transduced with shRNA to downregulate SK-1 expression or treated with a pharmacologic SK-1 inhibitor. The effects of SK-1 targeting were investigated by measuring the level of intracellular sphingosine, the activity of protein kinase C (PKC) and cell cycle regulators, and the mitotic index. Functional assays included measurement of cell proliferation, colony formation, apoptosis, and cell cycle analysis. Downregulation of SK-1 or its pharmacologic inhibition increased intracellular sphingosine and decreased PKC activity as shown by reduced phosphorylation of PKC substrates. In MDA-MB-231 cells this effect was most pronounced and reduced cell proliferation and colony formation, which could be mimicked using exogenous sphingosine or the PKC inhibitor RO 31-8220. SK-1 downregulation in MDA-MB-231 cells increased the number of cells with 4N and 8N DNA content, and similar effects were observed upon treatment with sphingosine or inhibitors of SK-1 or PKC. Examination of cell cycle regulators unveiled decreased cdc2 activity and expression of Chk1, which may compromise spindle checkpoint function and cytokinesis. Indeed, SK-1 kd cells entered mitosis but failed to divide, and in the presence of taxol also failed to sustain mitotic arrest, resulting in further increased endoreduplication and apoptosis. Our findings delineate an intriguing link between SK-1, PKC and components of the cell cycle machinery, which underlines the significance of SK-1 as a target for cancer therapy.

Direct cell-cell communication: a new approach derived from recent data on the nature and self-organisation of ultradian (circahoralian) intracellular rhythms

Recent data concerning ultradian (circahoralian) intracellular rhythms are used to assess the biochemical mechanisms of direct cell-cell communication. New results and theoretical considerations suggest a fractal nature of ultradian rhythms and their self-organisation. The fundamental and innate nature of these rhythms relates to their self-similarity at different levels of cell and tissue organisation. They can be detected in cell-free systems as well as in cells and organs in vivo. Such rhythms are a means of finding an optimal state of cell function rather than achieving a state of absolute stability. As a consequence, oscillations, being irregular and numerous by the set of periods, are resilient to functional overload and injury. Recent data on the maintenance of their fractal structure and, especially on the selection of optimal periods are discussed. The positive role of chaotic dynamics is stressed. The ultradian rhythm of protein synthesis in hepatocytes in vitro was used as a marker of direct cell-cell communication. The system demonstrates cell cooperation and synchronisation throughout the cell population, and suggests that the ultradian rhythms are self-organised. These observations also led to the detection of mechanisms of direct cell-cell communication in which extracellular factors have an essential role. Experimental evidence indicated the involvement of gangliosides and/or catecholamines in this large-scale synchronisation of protein synthesis. The response of all, or a major part, of the cell population is important; after the initial trigger effect, a periodic pattern is retained for some time. The influence of Ca2+-dependent protein kinases on protein phosphorylation can be a final step in the phase modulation of rhythms during cell-cell synchronisation. The intercellular medium plays an important role in self-synchronisation of ultradian rhythms between individual cells. Low cooperative activity of hepatocytes of old rats resulted from altered composition of the intercellular medium rather than direct effects of animal and cellular ageing. Similarly, in the whole body, changes in levels of gangliosides and catecholamines in the blood serum, a natural intercellular medium, can be critical events in age-dependent changes of the serum and accordingly cell-cell synchronisation. Hepatocytes of old rats exhibit some of the properties of young cells following an increase in blood serum ganglioside level, as well as, in in vitro conditions, after the addition of gangliosides to the culture medium. Together with data on ultradian functional and metabolic rhythms, all the material reviewed here allows us to propose a mechanism of direct cell-cell cooperation via the medium in which the cells exist, that supplements the nervous and hormonal central regulation of organ functions. Ultradian intracellular rhythms may thus provide a finer framework within which the integrated dynamics of respiration, heart rate, brain activity, and even behavioural patterns, are brought to an optimal functional pattern. Innate and direct cell-cell cooperation may have been employed as a means of intercellular regulation during the course of metazoan evolution, that preceded nervous regulation and is presently retained in mammals.

Inhibition by sulfatide of 21-kDa protein phosphorylation by protein kinase C in cow mammary gland and its reversal by phosphatidylserine

The effect of sulfatide, a sulfated sphingolipid, on phosphorylation of endogenous proteins by protein kinase C (PKC) was examined in cow mammary gland. Several proteins, including 21-kDa, 43-kDa and 56-kDa proteins in the cytosolic fraction, were found to be substrates for PKC by phosphorylation in the absence or presence of the cofactors 1-oleoyl-2-acetyl-sn-glycerol (OAG), phosphatidylserine (PS) and Ca2+. Sulfatide inhibited the 21-kDa phosphorylation, whereas it enhanced the 56-kDa and 43-kDa phosphorylation. Experiments were then conducted to examine whether other sphingolipids, including sphingosine, dihydrosphingosine, ceramides, galactocerebrosides, psychosine and sphingomyelin, modulated phosphorylation of the PKC substrates. Sphingosine, dihydrosphingosine and psychosine did not inhibit the 21-kDa phosphorylation; however, they enhanced the 56-kDa and 43-kDa phosphorylation. Ceramides, galactocerebrosides and sphingomyelin did not inhibit the 21-kDa or enhance the 56-kDa and 43-kDa phosphorylation. The inhibition by sulfatide of the 21-kDa phosphorylation was reversed by excess addition of PS, but not by OAG or Ca2+; whereas the enhancement by sulfatide, as well as sphingosine, dihydrosphingosine and psychosine, of 56-kDa and 43-kDa phosphorylation was not affected by PS, OAG or Ca2+. It is suggested that sulfatide is involved in the regulation of PKC-dependent phosphorylation by modulating the association of PKC substrates, in particular the 21-kDa protein, with membrane phospholipids in cow mammary gland.

DNA vaccination using the fragment C of botulinum neurotoxin type A provided protective immunity in mice

Botulinum neurotoxin (BoNT) is one of the most toxic substances known to produce severe neuromuscular paralysis. The currently used vaccine is prepared mainly from biohazardous toxins. Thus, we studied an alternative method and demonstrated that DNA immunization provided sufficient protection against botulism in a murine model. A plasmid of pBoNT/A-Hc, which encodes the fragment C gene of type A botulinum neurotoxin, was constructed and fused with an Igkappa leader sequence under the control of a human cytomegalovirus promoter. After 10 cycles of DNA inoculation with this plasmid, mice survived lethal doses of type A botulinum neurotoxin challenges. Immunized mice also elicited cross-protection to the challenges of type E botulinum neurotoxin. This is the first study demonstrating the potential use of DNA vaccination for botulinum neurotoxins.

A non-radioactive method for inexpensive quantitative RT-PCR

We present a novel method for quantitative RT-PCR that involves direct incorporation of digoxigenin-11-dUTP (DIG-dUTP) during amplification of cDNAs, separation of RT-PCR products by agarose gel electrophoresis, Southern transfer to a nylon membrane, and chemiluminescent detection with an anti-DIG antibody. The whole procedure can be done in about a day and has the following advantages: It is highly sensitive, specificity is confirmed by monitoring the size of the RT-PCR product, it is non-radioactive, quantitative, and does not require expensive specialized equipment.

Interaction of the GM2-activator protein with phospholipid-ganglioside bilayer membranes and with monolayers at the air-water interface

Differential scanning calorimetry (DSC) and film balance measurements were performed to study the interactions of the GalNAcbeta1-->4(NeuAcalpha2-->3)Galbeta1-->4Glc1 -->1'Cer (GM2)-activator protein with phospholipid/ganglioside vesicles and monolayers. The nonglycosylated form of the GM2-activator protein, added to unilamellar lipid vesicles of different composition, causes differential effects on the gel to liquid-crystalline phase transition peaks. The phase transition temperature (Tm) of pure dimyristoylglycerophosphocholine (DMPC) bilayer is slightly decreased. When lipids which specifically bind the GM2-activator protein are incorporated into the vesicles (e.g. a sulfatide or gangliosides) a shoulder in the thermograms at higher temperatures is observed, indicating an increase of the stability of the gel phase in relation to the liquid-crystalline phase. We also studied the surface activity of a glycosylated and a nonglycosylated GM2-activator protein at the air-water interface. The glycosylated form showed a slightly lower surface activity than the GM2-activator protein without oligosaccharide moiety. When the GM2-activator protein is added to the sub-phase of a surface covered with a lipid monolayer, it can only insert into the monolayer and reach the air-water interface below a monolayer pressure of 25 mN.m-1, depending on the lipid composition, and not when the monolayers are at the bilayer equivalence pressure of 30-35 mN.m-1. Particularly for Galbeta1-->3GalNAcbeta1-->4(NeuAcalpha2-->3)Galbeta 1-->4Glc1-->1'Cer (GM1) and GM2 containing films, the critical pressures (picrit) when no additional increase in surface pressure is observed after addition of the protein into the subphase, are much lower. This leads to the conclusion that binding of the GM2 activator protein to the ganglioside headgroups prevents the protein from reaching the air-water interface. The protein is then located preferentially at the lipid-water interface and cannot penetrate into the chain region.

The role of globo-series glycolipids in neuronal cell differentiation--a review

Alterations in glycolipid composition as well as glycosyltransferase activities during cellular differentiation and growth have been well documented. However, the underlying mechanisms for the regulation of glycolipid expression remain obscure. One of the major obstacles has been the lack of a well defined model system for studying these phenomena. We have chosen PC12 pheochromocytoma cells as a model because (a) the properties of these cells have been well characterized, and (b) they respond to nerve growth factor (NGF) by differentiating into sympathetic-like neurons and are amenable to well-controlled experimentation. Thus, PC12 cells represent a suitable model for studying changes in glycolipid metabolism in relation to cellular differentiation. We have previously shown that subcloned PC12 cells accumulate a unique series of globo-series neutral glycolipids which are not expressed in parental PC12 cells. This unusual change in glycolipid distribution is accompanied by changes in the activities of specific glycosyltransferases involved in their synthesis and is correlated with neuritogenesis and/or cellular differentiation in this cell line. We have further demonstrated that changes in the glycosyltransferase activities may be modulated by the phosphorylation states of the cells via protein kinase systems. We conclude that these unique globo-series glycolipids may play a functional role in the initiation and/or maintenance of neurite outgrowth in PC12 cells.

Intravitreal injection of ganglioside GM1 after ischemia reduces retinal damage in rats

BACKGROUND AND PURPOSE

Gangliosides are normal components of cell membranes and contribute to structural rigidity and membrane function. They have been shown to protect against various insults in the brain. We have shown previously that GM1 administered intraperitoneally before the induction of retinal ischemia provides a protective effect. This study evaluates the protective effect of GM1 administered intravitreally after ischemia on retinal lesions.

METHODS

We induced retinal ischemia unilaterally in Long-Evans rats by increasing intraocular pressure to 160 mm Hg for 60 minutes. GM1 (20 microL x 10(-5) mol/L) or saline (20 microL) was injected into the vitreous 15 minutes after ischemia, and the postischemic survival time was either 8 or 15 days. The degree of retinal damage was assessed by histopathological study.

RESULTS

Retinal ischemia led to reductions in thickness and cell number, principally in the inner retinal layers (39% to 80%) and to a lesser extent in the outer retinal layers (26% to 45%). Postischemic treatment with intravitreally injected GM1 conferred significant protection against retinal ischemic damage after both 8 and 15 days of survival time. After 8 days of reperfusion, the ischemia-induced loss in overall retinal thickness was reduced by 15% and those of the inner nuclear and plexiform layers by 44% and 17%, respectively. Ischemic-induced ganglion cell and inner nuclear cell density losses were reduced by 37% and 27%, respectively. After 15 days of reperfusion, approximately the same statistically significant differences could be observed in comparison with the 15-day saline-injected group.

CONCLUSIONS

GM1 protects the rat retina from pressure-induced ischemic injury when given intravitreally after the insult. The protection provided by GM1 after initiation of retinal damage could be of therapeutic interest.