The PGRMC1 Antagonist AG-205 Inhibits Synthesis of Galactosylceramide and Sulfatide.

Sulfatide synthesis in the human renal cancer cell line SMKT-R3 was strongly inhibited in the presence of low µM concentrations of AG-205, a progesterone receptor membrane component 1 (PGRMC1) antagonist. This was also the case in Chinese hamster ovary (CHO) cells stably transfected with UDP-galactose: ceramide galactosyltransferase and cerebroside sulfotransferase, the two enzymes required for sulfatide synthesis. In CHO cells synthesizing galactosylceramide but not sulfatide, galactosylceramide was also strongly reduced, suggesting an effect at the level of galactolipid synthesis. Notably, AG-205 inhibited galactosylceramide synthesis to a similar extent in wild type CHO cells and cells that lack PGRMC1 and/or PGRMC2. In vitro enzyme activity assays showed that AG-205 is an inhibitor of UDP-galactose: ceramide galactosyltransferase, but not cerebroside sulfotransferase. This study shows that PGRMC1 is only one of several targets of AG-205 and should be used with caution, especially in studies using cells synthesizing galactosylceramide and sulfatide.

Sulfatide negatively regulates the fusion process of human parainfluenza virus type 3.

Sulfatide (HSO(3)-3-galactosylceramide), which enriched in lipid rafts of plasma membranes in various epithelial cell lines, is a critical component of host cells for effective production of influenza A virus. However, the function of sulfatide in other virus infections targeting epithelial cells remains unknown. In this study, the effect of sulfatide on infection of human parainfluenza virus type 3 (hPIV3) was demonstrated by using genetically produced sulfatide-enriched cells and by treatment of hPIV3-infected cells with anti-sulfatide monoclonal antibody (GS-5) as well as by addition of sulfatide to the cells. hPIV3 was found to bind to sulfatide in a virus overlay assay and a solid-phase binding assay. Genetic expression of sulfatide in COS-7 cells defective in sulfatide suppressed initial hPIV3 infection and formation of multinucleate virus-infected cells. Treatment of virus-infected LLC-MK2 cells with GS-5 promoted formation of multinucleate cells. In contrast, exogenous addition of sulfatide to hPIV3-infected COS-7 cells and cells expressing the hPIV3-hemagglutinin-neuraminidase (HN) gene and fusion (F) gene conspicuously reduced the formation of multinucleate cells. The results suggest that sulfatide negatively regulates the fusion process of hPIV3, possibly through interaction with HN or F glycoprotein on the cell surface.

Erythrocyte membrane sulfatide plays a crucial role in the adhesion of sickle erythrocytes to endothelium.

Enhanced adhesion of sickle erythrocytes to the vascular endothelium and subendothelial matrix is fundamental to the development of vascular occlusion in sickle cell disease. Erythrocyte membrane sulfatide is implicated in the pathogenesis of vasoocclusive crises in sickle cell disease (SCD) patients. Because previous evidence linking sulfatide to cell adhesion has largely been circumstantial due to a lack of reagents that specifically target sulfatide, we used two sulfatide-specific strategies to address the role of erythrocyte membrane sulfatide in sickle cell adhesion to the vascular endothelium: a single-chain fragment variable chain (scFv) antibody against sulfatide as well as cerebroside sulfotransferase-deficient mice incapable of synthesising sulfatide. The sickle erythrocytes from mice and humans adhered at a greater extent and at higher shear stresses to activated endothelium than normal erythrocytes, and approximately 60% of the adhesion was prevented by the anti-sulfatide scFv. Similarly, the extent of adhesion of sulfatide-deficient erythrocytes was lower than normal erythrocytes. These findings suggest an important role for membrane sulfatide in sickle cell disease pathophysiology.

Selective lack of the C16:0 fatty acid isoform of sulfatide in pancreas of type II diabetic animal models.

Sulfatide (3'-sulfogalactosyl-ceramide) is a glycosphingolipid mainly located in the nervous system, but has also been found in the islets of Langerhans. Previous studies have suggested that sulfatide is involved in insulin processing and secretion. In this study, sulfatide expression and metabolism in pancreas and isolated islets of the type II diabetes models, ob/ob- and db/db mouse, was investigated using TLC-ELISA, metabolic labelling and electron microscopy. As in non-diabetic Lewis rat and human pancreas, sulfatide was located in secretory granules of the beta cells. However, the type II diabetic animal models and their background strains had an altered sulfatide expression, involving the lack of the C16:0 sulfatide fatty acid isoform, compared to non-diabetic Lewis rat, BALB/c mouse and human pancreatic tissue, in which the two dominating pancreatic sulfatide isoforms C16:0 and C24:0 are expressed. Correspondingly, in isolated ob/ob islets, sulfatide synthesis excluded the production of C16:0 sulfatide. Insulin administration to ob/ob mouse, which lowers beta cell activity, resulted in significantly increased sulfatide expression in pancreas (p=0.0003), but still no expression of the C16:0 sulfatide isoform. In vitro, the C16:0 sulfatide was shown to be the isomer involved in the preservation of insulin crystals. Thus, it is hypothesized that the selection of sulfatide isomers in pancreas might be a genetic factor contributing to disease development in type II diabetic animal models.

Antibody-mediated CNS demyelination II. Focal spinal cord lesions induced by implantation of an IgM antisulfatide-secreting hybridoma.

We showed previously that spinal cord implants of hybridoma cells (O1) that secrete an IgM antigalactocerebroside cause focal multiple-sclerosis-like plaques of demyelination followed by remyelination to form "shadow plaques" (Rosenbluth et al., 1999). The antibody in that case was directed against a glycolipid present in mature oligodendrocytes and myelin but not in precursor cells. We now report the effects of implanting a different hybridoma (O4) that secretes IgM antibodies directed against sulfatide, a constituent not only of mature myelin and oligodendrocytes but also of late precursor cells, in order to determine whether this hybridoma too would generate focal demyelination and would, in addition, block remyelination. Our results show that focal plaques of demyelination indeed appear after O4 implantation, and that remyelination does occur, but only in cases where the hybridoma cells have degenerated, probably through host rejection. The occurrence of remyelination suggests that oligodendrocyte precursor cells are capable of migrating in rapidly from adjacent areas or that early precursors, not yet expressing sulfatide, remain undamaged within the lesions. In cases where intact hybridoma cells persist at lesion sites, remyelination does not occur. Failure of remyelination in this model thus appears to result from the continuing presence of antimyelin antibodies rather than from depletion of oligodendrocyte precursors.

Dextran sulphate inhibits phospholipid and sulphatide mediated autoactivation of factor XII.

In normal plasma, high molecular mass dextran sulphate (DS500) induces formation of amidolytic activity towards the chromogenic substrate H-D-Pro-Phe-Arg-p-nitroanilide (S-2302) specific to factor XII and kallikrein. No amidolytic activity was formed when plasma deficient in prekallikrein was exposed to DS500. In contrast, factor XII amidolytic activity was formed upon exposure to sulphatide or acidic phospholipids. To assess whether DS500 interferes with the sulphatide and the acidic phospholipid in activating factor XII, plasma deficient in prekallikrein was incubated with phosphatidylinositol phosphate (PtdInsP) and sulphatide at the conditions necessary for activation with these surfaces and various concentrations of DS500. DS500 inhibited both the PtdInsP and the sulphatide-mediated autoactivation in an antithrombin III independent manner. Heparin also inhibited the PtdInsP mediated autoactivation but not that mediated by sulphatide. The heparin inhibition was due to enhancement of the antithrombin III activity, which could be partly blocked by preincubation of plasma with rabbit anti-human antithrombin III IgG.

Inhibition of the activation of Hageman factor (factor XII) by aprotinin (Trasylol)

Aprotinin (Trasylol; Bayer AG, Leverkusen, Germany), a protease inhibitor resembling or identical with Kunitz' pancreatic trypsin inhibitor, is said to have anticoagulant properties, but these are not clearly defined. The present study provides evidence that one action of aprotinin is inhibition of the activation of Hageman factor (factor XII).

The effect of beta 2-glycoprotein I on the dextran sulfate and sulfatide activation of the contact system (Hageman factor system) in the blood coagulation.

1. beta 2-Glycoprotein I, inhibits the initiation of the contact system in plasma accomplished by dextran sulfate. 2. The dextran sulfate induced activation could be inhibited both when dextran sulfate was preincubated with beta 2-glycoprotein I and when the amount of beta 2-glycoprotein I in plasma was increased. 3. The concentration of beta 2-glycoprotein I at which an inhibitory effect could be registered was dependent upon the concentration of negatively charged groups on the surface. Calculation of the molar ratios between beta 2-glycoprotein I and sulfate residues in dextran sulfate showed that beta 2-glycoprotein I had to be present in excess of a 1:1 stoichiometric ratio of the sulfate group in order to inhibit the activation. 4. beta 2-Glycoprotein I does not inhibit the initiation of the contact system in plasma accomplished by sulfatide, unless the sulfatide has been preincubated with beta 2-glycoprotein I.