Epstein-barr virus infections induce aberrant osteoclastogenesis in immune system-humanized NOD/Shi-scid/IL-2RγCnull mice.

Epstein-Barr virus (EBV) and other viral infections are possible triggers of autoimmune diseases, such as rheumatoid arthritis (RA). To analyze the causative relationship between EBV infections and RA development, we performed experiment on humanized NOD/Shi-scid/IL-2RγCnull (hu-NOG) mice reconstituted human immune system components and infected with EBV. In EBV-infected hu-NOG mice, breakdown of knee joint bones was found to be accompanied by the accumulation of receptor activator of nuclear factor-κB (NF-κB) (RANK) ligand (RANKL), a key factor in osteoclastogenesis, human CD19 and EBV-encoded small RNA (EBER)-bearing cells. Accumulation of these cells expanded in the bone marrow adjacent to the bone breakage, showing a histological feature like to that in bone marrow edema. On the other hand, human RANK/human matrix metalloprotease-9 (MMP-9) positive, osteoclast-like cells were found at broken bone portion of EBV-infected mouse knee joint. In addition, human macrophage-colony stimulating factor (M-CSF), an essential factor in development of osteoclasts, evidently expressed in spleen and bone marrow of EBV-infected humanized mice. Furthermore, RANKL and M-CSF were identified at certain period of EBV-transformed B lymphoblastoid cells (BLBCs) derived from umbilical cord blood lymphocytes. Co-culturing bone marrow cells of hu-NOG mice with EBV-transformed BLBCs resulted in the induction of a multinucleated cell population positive for tartrate-resistant acid phosphatase and human MMP-9 which indicating human osteoclast-like cells. These findings suggest that EBV-infected BLBCs induce human aberrant osteoclastogenesis, which cause erosive arthritis in the joints.

Selective involvement of UGGT variant: UGGT2 in protecting mouse embryonic fibroblasts from saturated lipid-induced ER stress.

Secretory proteins and lipids are biosynthesized in the endoplasmic reticulum (ER). The "protein quality control" system (PQC) monitors glycoprotein folding and supports the elimination of terminally misfolded polypeptides. A key component of the PQC system is Uridine diphosphate glucose:glycoprotein glucosyltransferase 1 (UGGT1). UGGT1 re-glucosylates unfolded glycoproteins, to enable the re-entry in the protein-folding cycle and impede the aggregation of misfolded glycoproteins. In contrast, a complementary "lipid quality control" (LQC) system that maintains lipid homeostasis remains elusive. Here, we demonstrate that cytotoxic phosphatidic acid derivatives with saturated fatty acyl chains are one of the physiological substrates of UGGT2, an isoform of UGGT1. UGGT2 produces lipid raft-resident phosphatidylglucoside regulating autophagy. Under the disruption of lipid metabolism and hypoxic conditions, UGGT2 inhibits PERK-ATF4-CHOP-mediated apoptosis in mouse embryonic fibroblasts. Moreover, the susceptibility of UGGT2 KO mice to high-fat diet-induced obesity is elevated. We propose that UGGT2 is an ER-localized LQC component that mitigates saturated lipid-associated ER stress via lipid glucosylation.

Are Viral Infections Key Inducers of Autoimmune Diseases? Focus on Epstein-Barr Virus.

It is generally accepted that certain viral infections can trigger the development of autoimmune diseases. However, the exact mechanisms by which these viruses induce autoimmunity are still not understood. In this review, we first describe hypothetical mechanisms by which viruses induce some representative autoimmune diseases. Then, we focus on Epstein-Barr virus (EBV) and discuss its role in the pathogenesis of rheumatoid arthritis (RA). The discussion is mainly based on our own previous findings that (A) EBV DNA and its products EBV-encoded small RNA (EBER) and latent membrane protein 1 (LMP1) are present in the synovial lesions of RA, (B) mRNA expression of the signaling lymphocytic activation molecule-associated protein (SAP)/SH2D1A gene that plays a critical role in cellular immune responses to EBV is reduced in the peripheral T cells of patients with RA, and (C) EBV infection of mice reconstituted with human immune system components (humanized mice) induced erosive arthritis that is pathologically similar to RA. Additionally, environmental factors may contribute to EBV reactivation as follows: Porphyromonas gingivalis peptidylarginine deiminase (PAD), an enzyme required for citrullination, engenders antigens leading to the production of citrullinated peptides both in the gingiva and synovium. Anti-citrullinated peptides autoantibody is an important marker for diagnosis and disease activity of RA. These findings, as well as various results obtained by other researchers, strongly suggest that EBV is directly involved in the pathogenesis of RA, a typical autoimmune disease.

Antinuclear antibodies produced in HLA-DR transgenic humanized mice developed chronic graft-versus-host disease.

BACKGROUND: Chronic graft versus host disease (GVHD) has been reported in humanized mice after the implantation of human hematopoietic stem cells (hu-HSC). As such, humanized mice have been applied to a mouse model of chronic GVHD; however, B-cell activation and autoantibody production did not occur, and the clinical features of chronic GVHD were not sufficiently reproduced. The purpose of this study was to establish an improved humanized mouse model with chronic GVHD using HLA-DR transgenic NOD/Shi-scid, IL-2RγKO (NOG) mice. METHODS: CD34-positive cells were isolated from blood extracted from HLA-DRB1∗0405-positive umbilical cords using magnetic cell isolation. Then these were transplanted into NOG-Iab KO, HLA-DR 0405 Tg mice aged 8-16 weeks. GVHD symptoms were observed 26 weeks after transplantation. Histological findings of the skin, lung, liver, and spleen were compared with those of non-humanized mice. Antinuclear antibodies (ANA) were measured by indirect immunofluorescence using sera isolated 26 weeks after transplantation. RESULTS: Although GVHD symptoms were not observed in humanized (hu-HSC) NOG-Iab KO, HLA-DR 0405 Tg mice during the observation period, histological findings of human T-cell infiltration were observed in the skin, liver, and lung, suggesting that GVDH was present; human tingible body macrophages or clusters of BCL-6-positive human B-cells were observed in the spleen. Furthermore, human IgG ANA with peripheral or homogeneous staining patterns were also detected in the sera. CONCLUSION: Hu-HSC NOG-Iab KO, HLA-DR 0405 Tg mice differed from conventional models in terms of B-cell activation and ANA production. This study is the first to report on B-cell activation and autoantibody production in humanized mice with chronic GVHD, suggesting that hu-HSC NOG-Iab KO, HLA-DR 0405 Tg mice could be applied to a new humanized mouse model of chronic GVHD.

Lysophosphatidylglucoside is a GPR55 -mediated chemotactic molecule for human monocytes and macrophages.

Neutrophils undergo spontaneous apoptosis within 24-48 h after leaving bone marrow. Apoptotic neutrophils are subsequently phagocytosed and cleared by macrophages, thereby maintaining neutrophil homeostasis. Previous studies have demonstrated involvement of lysophosphatidylglucoside (lysoPtdGlc), a degradation product of PtdGlc, in modality-specific repulsive guidance of spinal sensory axons, via its specific receptor GPR55. In the present study, using human monocytic cell line THP-1 as a model, we demonstrated that lysoPtdGlc induces monocyte/macrophage migration with typical bell-haped curve and a peak at concentration 10-9 M. Lysophosphatidylinositol (lysoPtdIns), a known GPR55 ligand, induced migration at higher concentration (10-7 M). LysoPtdGlc-treated cells had a polarized shape, whereas lysoPtdIns-treated cells had a spherical shape. In EZ-TAXIScan (chemotaxis) assay, lysoPtdGlc induced chemotactic migration activity of THP-1 cells, while lysoPtdIns induced random migration activity. GPR55 antagonist ML193 inhibited lysoPtdGlc-induced THP-1 cell migration, whereas lysoPtdIns-induced migration was inhibited by CB2-receptor inverse agonist. SiRNA experiments showed that GPR55 mediated lysoPtdGlc-induced migration, while lysoPtdIns-induced migration was mediated by CB2 receptor. Our findings, taken together, suggest that lysoPtdGlc functions as a chemotactic molecule for human monocytes/macrophages via GPR55 receptor, while lysoPtdIns induces random migration activity via CB2 receptor.

Human osteoclastogenesis in Epstein-Barr virus-induced erosive arthritis in humanized NOD/Shi-scid/IL-2Rγnull mice.

Many human viruses, including Epstein-Barr virus (EBV), do not infect mice, which is challenging for biomedical research. We have previously reported that EBV infection induces erosive arthritis, which histologically resembles rheumatoid arthritis, in humanized NOD/Shi-scid/IL-2Rγnull (hu-NOG) mice; however, the underlying mechanisms are not known. Osteoclast-like multinucleated cells were observed during bone erosion in this mouse model, and therefore, we aimed to determine whether the human or mouse immune system activated bone erosion and analyzed the characteristics and origin of the multinucleated cells in hu-NOG mice. Sections of the mice knee joint tissues were immunostained with anti-human antibodies against certain osteoclast markers, including cathepsin K and matrix metalloproteinase-9 (MMP-9). Multinucleated cells observed during bone erosion stained positively for human cathepsin K and MMP-9. These results indicate that human osteoclasts primarily induce erosive arthritis during EBV infections. Human osteoclast development from hematopoietic stem cells transplanted in hu-NOG mice remains unclear. To confirm their differentiation potential into human osteoclasts, we cultured bone marrow cells of EBV-infected hu-NOG mice and analyzed their characteristics. Multinucleated cells cultured from the bone marrow cells stained positive for human cathepsin K and human MMP-9, indicating that bone marrow cells of hu-NOG mice could differentiate from human osteoclast progenitor cells into human osteoclasts. These results indicate that the human immune response to EBV infection may induce human osteoclast activation and cause erosive arthritis in this mouse model. Moreover, this study is the first, to our knowledge, to demonstrate human osteoclastogenesis in humanized mice. We consider that this model is useful for studying associations of EBV infections with rheumatoid arthritis and human bone metabolism.

Glucocerebrosidases catalyze a transgalactosylation reaction that yields a newly-identified brain sterol metabolite, galactosylated cholesterol.

ß-Glucocerebrosidase (GBA) hydrolyzes glucosylceramide (GlcCer) to generate ceramide. Previously, we demonstrated that lysosomal GBA1 and nonlysosomal GBA2 possess not only GlcCer hydrolase activity, but also transglucosylation activity to transfer the glucose residue from GlcCer to cholesterol to form ß-cholesterylglucoside (ß-GlcChol) in vitro ß-GlcChol is a member of sterylglycosides present in diverse species. How GBA1 and GBA2 mediate ß-GlcChol metabolism in the brain is unknown. Here, we purified and characterized sterylglycosides from rodent and fish brains. Although glucose is thought to be the sole carbohydrate component of sterylglycosides in vertebrates, structural analysis of rat brain sterylglycosides revealed the presence of galactosylated cholesterol (ß-GalChol), in addition to ß-GlcChol. Analyses of brain tissues from GBA2-deficient mice and GBA1- and/or GBA2-deficient Japanese rice fish (Oryzias latipes) revealed that GBA1 and GBA2 are responsible for ß-GlcChol degradation and formation, respectively, and that both GBA1 and GBA2 are responsible for ß-GalChol formation. Liquid chromatography-tandem MS revealed that ß-GlcChol and ß-GalChol are present throughout development from embryo to adult in the mouse brain. We found that ß-GalChol expression depends on galactosylceramide (GalCer), and developmental onset of ß-GalChol biosynthesis appeared to be during myelination. We also found that ß-GlcChol and ß-GalChol are secreted from neurons and glial cells in association with exosomes. In vitro enzyme assays confirmed that GBA1 and GBA2 have transgalactosylation activity to transfer the galactose residue from GalCer to cholesterol to form ß-GalChol. This is the first report of the existence of ß-GalChol in vertebrates and how ß-GlcChol and ß-GalChol are formed in the brain.

NEURONAL DEVELOPMENT. Glycerophospholipid regulation of modality-specific sensory axon guidance in the spinal cord.

Glycerophospholipids, the structural components of cell membranes, have not been considered to be spatial cues for intercellular signaling because of their ubiquitous distribution. We identified lyso-phosphatidyl-ß-D-glucoside (LysoPtdGlc), a hydrophilic glycerophospholipid, and demonstrated its role in modality-specific repulsive guidance of spinal cord sensory axons. LysoPtdGlc is locally synthesized and released by radial glia in a patterned spatial distribution to regulate the targeting of nociceptive but not proprioceptive central axon projections. Library screening identified the G protein-coupled receptor GPR55 as a high-affinity receptor for LysoPtdGlc, and GPR55 deletion or LysoPtdGlc loss of function in vivo caused the misallocation of nociceptive axons into proprioceptive zones. These findings show that LysoPtdGlc/GPR55 is a lipid-based signaling system in glia-neuron communication for neural development.

A novel single virus infection system reveals that influenza virus preferentially infects cells in g1 phase.

BACKGROUND: Influenza virus attaches to sialic acid residues on the surface of host cells via the hemagglutinin (HA), a glycoprotein expressed on the viral envelope, and enters into the cytoplasm by receptor-mediated endocytosis. The viral genome is released and transported in to the nucleus, where transcription and replication take place. However, cellular factors affecting the influenza virus infection such as the cell cycle remain uncharacterized. METHODS/RESULTS: To resolve the influence of cell cycle on influenza virus infection, we performed a single-virus infection analysis using optical tweezers. Using this newly developed single-virus infection system, the fluorescence-labeled influenza virus was trapped on a microchip using a laser (1064 nm) at 0.6 W, transported, and released onto individual H292 human lung epithelial cells. Interestingly, the influenza virus attached selectively to cells in the G1-phase. To clarify the molecular differences between cells in G1- and S/G2/M-phase, we performed several physical and chemical assays. Results indicated that: 1) the membranes of cells in G1-phase contained greater amounts of sialic acids (glycoproteins) than the membranes of cells in S/G2/M-phase; 2) the membrane stiffness of cells in S/G2/M-phase is more rigid than those in G1-phase by measurement using optical tweezers; and 3) S/G2/M-phase cells contained higher content of Gb3, Gb4 and GlcCer than G1-phase cells by an assay for lipid composition. CONCLUSIONS: A novel single-virus infection system was developed to characterize the difference in influenza virus susceptibility between G1- and S/G2/M-phase cells. Differences in virus binding specificity were associated with alterations in the lipid composition, sialic acid content, and membrane stiffness. This single-virus infection system will be useful for studying the infection mechanisms of other viruses.

The novel neutrophil differentiation marker phosphatidylglucoside mediates neutrophil apoptosis.

A new type of glycolipid, phosphatidylglucoside (PtdGlc), was identified as a component of raft-like membrane domains of the human leukemia cell line HL-60. In this study, we show that PtdGlc forms functional domains that are different from those produced by lactosylceramide (LacCer)-enriched lipid rafts. These rafts initiate neutrophil apoptosis. Neutrophils are the only type of human peripheral blood leukocyte or monocyte-derived dendritic cell to express large amounts of PtdGlc on their cell surfaces. PtdGlc was not colocalized with LacCer. Anti-PtdGlc IgM DIM21 did not induce neutrophil chemotaxis or superoxide generation, whereas anti-LacCer IgM T5A7 induced these activities. DIM21, but not T5A7, significantly induced neutrophil apoptosis. DIM21-induced apoptosis was inhibited by specific inhibitors of cysteine-containing aspartate-specific proteases (caspases)-8, -9, and -3 but not by the Src family kinase inhibitor PP1, PIP(3) kinase inhibitor LY294002, NADPH oxidase inhibitor diphenyleneiodonium, superoxide dismutase, or catalase. PtdGlc was colocalized with Fas on the neutrophil plasma membrane. DIM21 and the agonist anti-Fas Ab DX2 induced the formation of large Fas-colocalized clusters of PtdGlc on the plasma membrane. Furthermore, the antagonistic anti-Fas Ab ZB4 significantly inhibited DIM21-induced neutrophil apoptosis. These results suggest that PtdGlc is specifically expressed on neutrophils and mediates apoptosis of these cells, and that the Fas-associated death signal may be involved in PtdGlc-mediated apoptosis.

Phosphatidylglucoside forms specific lipid domains on the outer leaflet of the plasma membrane.

Phosphatidylglucoside (PtdGlc) is a recently discovered unique glycophospholipid involved in granulocytic differentiation of human promyelocytic leukemia cell line HL60 and in astrocytic differentiation in developing rodent brains. Using a PtdGlc-specific monoclonal antibody in immunofluorescence and immunoelectron microscopy, we showed that PtdGlc forms distinct lipid domains on the outer leaflet of the plasma membrane of HL60 cells and the human alveolar epithelial cell line, A549. Similar to glycosphingolipid, glucosylceramide (GlcCer), the natural form of PtdGlc exhibited a high main phase transition temperature in differential scanning calorimetry (DSC). However, unlike GlcCer, PtdGlc did not exhibit a large difference in the main phase transition temperature between the heating and cooling scans. DSC further indicated that GlcCer, but not PtdGlc, was miscible with sphingomyelin. In addition, DSC and small-angle X-ray scattering (SAXS) experiments revealed that PtdGlc was poorly miscible with phosphatidylcholine. Our results suggest that the lack of tight intermolecular interaction excludes PtdGlc from other lipid domains on the plasma membrane.

Inhibition of HIV replication by a CD4-reactive Fab of an IgM clone isolated from a healthy HIV-seronegative individual.

HIV replication is restricted by some anti-CD4 mouse mAb in vitro and in vivo. However, a human monoclonal anti-CD4 Ab has not been isolated. We screened EBV-transformed peripheral B cells from 12 adult donors for CD4-reactive Ab production followed by functional reconstitution of Fab genes. Three independent IgM Fab clones reactive specifically to CD4 were isolated from a healthy HIV-seronegative adult (approximately 0.0013% of the peripheral B cells). The germ line combinations for the VH and VL genes were VH3-33/L6, VH3-33/L12, and VH4-4/L12, respectively, accompanied by somatic hypermutations. Genetic analysis revealed a preference for V-gene usage to develop CD4-reactive Ab. Notably, one of the CD4-reactive clones, HO538-213, with an 1 x 10(-8) M dissociation constant (Kd) to recombinant human CD4, limited the replication of R5-tropic and X4-tropic HIV-1 strains at 1-2.5 microg/mL in primary mononuclear cells. This is the first clonal genetic analysis of human monoclonal CD4-reactive Ab. A mAb against CD4 isolated from a healthy individual could be useful in the intervention of HIV/AIDS.

Preferential expression of phosphatidylglucoside along neutrophil differentiation pathway.

Phosphatidylglucoside (PtdGlc), a new type of glycolipid, was recently identified. We examined PtdGlc expression in normal blood cells and leukemic cells using an anti-PtdGlc monoclonal antibody, DIM-21. Neutrophils, monocytes, HL-60 cells and a subset of cord blood (CB) CD34(+) cells, but not erythroblasts, expressed lipid antigen. PtdGlc was preferentially expressed along the neutrophil differentiation pathway of CB CD34(+) cells treated with cytokines and HL-60 cells treated with retinoic acid. PtdGlc expression was not increased in HL-60 cells treated with phorbol ester. CB CD34(+) cells contained a population of PtdGlc(+) cells, and CB CD34(+)PtdGlc(+) cells produced mainly granulocyte-macrophage colonies and a small number of erythroid colonies. A positive correlation between PtdGlc expression and CD15 expression in leukemic cells from patients with acute myeloblastic leukemia was shown. These results indicate that increasing PtdGlc expression is seen with neutrophil maturation.

Lipid rafts enriched in phosphatidylglucoside direct astroglial differentiation by regulating tyrosine kinase activity of epidermal growth factor receptors.

Membrane lipid rafts provide a specialized microenvironment enriched with sphingolipids and phospholipids containing saturated fatty acids and serve as a platform for various intracellular signalling pathways. PtdGlc (phosphatidylglucoside) is a type of glycophospholipid localized in the outer leaflet of the plasma membrane. Owing to PtdGlc's unique fatty acid composition, exclusively composed of C(18:0) at sn-1 and C(20:0) at sn-2 of the glycerol backbone, it tends to form PGLRs (PtdGlc-enriched lipid rafts). Previously, we demonstrated that PGLRs reside on the cell surface of astroglial cells from fetal rat brain [Nagatsuka, Horibata, Yamazaki, Kinoshita, Shinoda, Hashikawa, Koshino, Nakamura and Hirabayashi (2006) Biochemistry 45, 8742-8750]. In the present study, we observed PGLRs in astroglial lineage cells at mid-embryonic to early-postnatal stages of developing mouse cortex. This suggests that PGLRs are developmentally correlated with astroglial differentiation during fetal cortical development. Our cell culture studies with multipotent neural progenitor cells prepared from fetal mouse telencephalon demonstrated that treatment with EGF (epidermal growth factor) or anti-PtdGlc antibody caused recruitment of EGFRs (EGF receptors) into lipid raft compartments, leading to activation of EGFRs. Moreover, the activation of EGFRs by antibody triggered downstream tyrosine kinase signalling and induced marked GFAP (glial fibrillary acidic protein) expression via the JAK (Janus kinase)/STAT (signal transducer and activator of transcription) signalling pathway. These findings strongly suggest that PGLRs are physiologically coupled to activated EGFRs on neural progenitor cells during fetal cortical development, and thereby play a distinct role in mediating astrogliogenesis.

Quantitative analysis of a novel glucosylated phospholipid by liquid chromatography-mass spectrometry.

Building upon the demonstrated presence of a new glyceroglycolipid, phosphatidylglucoside (PtdGlc), in rat embryonic brain tissues, we have developed a method to identify minute amounts of PtdGlc in cultured cells by using nano-flow high-performance liquid chromatography and negative-ion-mode electrospray linear-ion trap time-of-flight mass spectrometry (LC-MS). A normal-phase silica gel-based column enabled us to separate PtdGlc from other lipid classes. PtdGlc was identified from its tandem mass spectrometry spectrum and from its retention time in the column. Using an internal standard collection and LC-MS, we obtained the linearity of PtdGlc at a range of 6.3-800 fmol per injection. We applied this method to analyze quantitative changes in PtdGlc in C6 glioma cells after cellular differentiation into GFAP-positive glial cells. PtdGlc in C6 glioma cells consisted exclusively of C18:0/C20:0 fatty acyl chains. Differentiation induced by the addition of anti-PtdGlc antibody plus cAMP in culture medium significantly increased the glycolipid content.

Immunohistochemical distribution of phosphatidylglucoside using anti-phosphatidylglucoside monoclonal antibody (DIM21).

The immunohistochemical distribution of phosphatidylglucoside (PhGlc) in organs obtained from human autopsy cases was investigated using the DIM21 antibody. Immunohistochemical staining was performed on formaline-fixed, paraffin-embedded sections using the simple stain peroxidase method. The sections were then subjected to antigen retrieval by microwave irradiation in citrate buffer. PhGlc expression was observed in not only the epithelial but also the non-epithelial components of several visceral organs. Squamous and glandular epithelial cells were positive for PhGlc in several organs. The surface areas of the epithelium, particularly the squamous epithelium, were positive. Mesothelial cells were also positive in some organs. Endothelial cells, polymorphonuclear (PMN) cells are positive in several organs. Macrophage is positive in many organs. Epithelial cells of the gallbladder were positive, however, the intrahepatic bile ducts were not positive. In the brain tissue, astroglial cells, the chorioide plexus, the pituitary gland, and ependymal cells were positive. Further investigation is indispensable in order to establish a relationship between cell differentiation and PhGlc expression.

Fucoganglioside alpha-fucosyl(alpha-galactosyl)-GM1: a novel member of lipid membrane microdomain components involved in PC12 cell neuritogenesis.

In order to search for novel components of lipid membrane microdomains involved in neural signalling pathways, mAbs (monoclonal antibodies) were raised against the detergent-insoluble membrane fraction of PC12 (pheochromocytoma) cells. Among the 22 hybrid clones, mAb PR#1 specifically detected a fucoganglioside Fuc(Gal)-GM1 [a-fucosyl(a-galactosyl)-GM1], a ganglioside homologous with GM1a (II3NeuAc,GgOse4Cer), as a novel member of microdomain components with biological functions. In the presence of mAb PR#1 in the culture medium, the outgrowth of neurites was induced in PC12 cells in a dose-dependent manner, with no effects on cell proliferation, suggesting that Fuc(Gal)-GM1 is preferentially involved in PC12 cell neuritogenesis. Effects through Fuc(Gal)-GM1 were different from those through GM1a during differentiation, e.g. under PR#1 treatment on Fuc(Gal)-GM1, round cell bodies with thinner cell processes were induced, whereas treatment with CTB (cholera toxin B subunit), a specific probe for GM1a, produced flattened cell bodies with thicker pro-cesses. Molecular analysis demonstrated that the PR#1-Fuc(Gal)-GM1 pathway was associated with Fyn and Yes of the Src family of kinases, although Src itself was not involved. No association was found with TrkA (tropomyosin receptor kinase A) and ERKs (extracellular-signal-regulated kinases), which are responsible for GM1a-induced differentiation. From these findings, it is suggested that a fucoganglioside Fuc(Gal)-GM1 provides a functional platform distinct from that of GM1a for signal transduction in PC12 cell differentiation.

Establishment and characterization of a new erythroblastic leukemia cell line, EEB: phosphatidylglucoside-mediated erythroid differentiation and apoptosis.

A new erythroblastic leukemia cell line (EEB) was established from a patient with early erythroblastic leukemia. The cells had features of immature erythroblasts, including an agranular basophilic cytoplasm and CD36, CD71, CD175s (sialyl-Tn) and CD235a (glycophorin A) expression without CD41 expression, myeloperoxidase activity and platelet-peroxidase activity. The cells were confirmed to be of the erythroid lineage based on expression of the gamma-globin message. They were induced to differentiate into benzidine-positive cells by hemin and delta-amino levulinic acid (delta-ALA). An analysis of cell membrane lipids showed that EEB cells contain a type of glycerolipid, phosphatidylglucose (PhGlc), but not unbranched type 2 chains, i antigens. GL-7 which is a recombinant Fab fragment of GL-2 and binds to PhGlc, induced production of hemoglobin F (HbF) associated with accumulation of the gamma-globin (gamma-globin) message in EEB cells. The GL-7-mediated erythroid differentiation was associated with apoptosis. These results suggest that direct signaling to PhGlc mediates erythroid differentiation and apoptosis in EEB cells.

Carbohydrate-dependent signaling from the phosphatidylglucoside-based microdomain induces granulocytic differentiation of HL60 cells.

Glycosphingolipids form glycosphingolipid signaling microdomains. Here, we report an unrecognized type of phosphatidylglucoside (PhGlc)-based lipid microdomain in HL60 cells. Treatment of cells with rGL-7, which preferentially reacts with PhGlc, induced differentiation of HL60 cells. This was manifested by the appearance of nitroblue tetrazolium-positive cells together with CD38 expression and c-Myc down-regulation. We determined the molecular mechanisms underlying early stages of signal transduction. rGL-7 treatment induced rapid tyrosine phosphorylation of Src family protein kinases Lyn and Hck. Reduction of endogenous cholesterol after application of methyl-beta-cyclodextrin suppressed rGL-7-stimulated tyrosine phosphorylation. Phosphorylated proteins and PhGlc colocalized in the Triton X-100 insoluble, light buoyant density fraction after sucrose gradient ultracentrifugation of HL60 cell lysates. This suggests PhGlc-based microdomain is involved in GL-7 signaling. Ligation of known components of microdomains, such as sphingomyelin and ganglioside GM1, with corresponding antibodies failed to induce differentiation and tyrosine phosphorylation. These results show that PhGlc constitutes a previously undescribed lipid signaling domain, and the glucose residue of PhGlc is critical for organization of the carbohydrate-dependent signaling domain involved in cellular differentiation of HL60 cells.