The novel immunomodulator FTY720 is a synthetic structural analogue of myriocin, a metabolite of the ascomycete Isaria sinclairii 1–4 . FTY720 prolongs, with remarkable potency, the survival of solid organ grafts in ...
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The novel immunomodulator FTY720 is a synthetic structural analogue of myriocin, a metabolite of the ascomycete Isaria sinclairii 1–4 . FTY720 prolongs, with remarkable potency, the survival of solid organ grafts in animal models including non-human primates 5–15 , and prevents the development of pathology in graft-vs-host disease (GvHD) 14,16 , autoimmune type I diabetes 17 and rheumatoid arthritis (L. Feng, unpublished observations). It is now evident that FTY720 displays a novel mechanism of action that has not been observed with any other immunosuppressive agent. Unlike its structural analogue myriocin, FTY720 does not bind serine palmitoyl transferase and does not inhibit the sphingolipid pathway 18. Therapeutic doses of FTY720 do not impair lymphocyte function but instead modulate the circulation of T and B cells between the blood and the secondary lymphoid organs. In transplantation situations this leads to a sequestration of T and B cells to the lymph nodes (LNs) and Peyer's patches (PPs) 6,12 and an inhibition of T-cell infiltration into grafted organs 6,7 . Recent evidence suggests that FTY720 acts on lymphocytes via G-protein-coupled receptors (GPCRs) 19, possibly chemokine receptors, and that the drug affects the responsiveness of T and B cells to chemokines, which results in altered cell migration.
We have demonstrated that CD95-induced apoptosis in a human leukaemic T-cell line resulted in loss of glucose transporter function (Berridge ct al. 1996). To determine whether ceramide, a mediator of CD95 and tumour n...
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We have demonstrated that CD95-induced apoptosis in a human leukaemic T-cell line resulted in loss of glucose transporter function (Berridge ct al. 1996). To determine whether ceramide, a mediator of CD95 and tumour necrosis factor-a-induced apoptosis, has similar effects on glucose transport, the human leukaemic cell lines, Jurkat and U937, and human peripheral blood neutrophils were treated with ceramide or sphingomyelinase and the effects on glucose transport determined by measuring [H-3]-2-deoxyglucose uptake. We show that in U937 and Jurkat cells, the cell permeable ceramides, C-2 (N-acetylsphingosine) and C-6 (N-hexanoylsphingosine) inhibit glucose uptake within minutes of initiating ceramide treatment, 60- 70% inhibition bring observed within 2 hr. Loss of glucose transport correlated with loss of proliferative response, but metabolic activity as measured by 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide (MTT) reduction, was affected to a much lesser extent. With Jurkat and U937 cells, the inhibitory effects of ceramides on glucose transport were associated with reduced affinity of glucose transporters for glucose (K-m). Similar effects were observed with sphingomyelinase. With human peripheral blood neutrophils, C-2 and C-6-ceramides inhibited glucose uptake by 70-80% within 30 min. without affecting transporter affinity for glucose, but the maximum velocity of uptake (V-max) was reduced. These results show that acute regulation of glucose transport is an early effector mechanism of cell death induced by ceramides in human leukaemic cell lines and peripheral blood neutrophils. This is the first study which describes ceramide-induced early physiological/biochemical events leading to cell death in human cells.
The present studies tested the hypothesis that some effects of tumor necrosis factor-alpha (TNF-alpha) are mediated by activation of sphingomyelinases and the production of ceramides. Differentiated 3T3-L1 adipocytes ...
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The present studies tested the hypothesis that some effects of tumor necrosis factor-alpha (TNF-alpha) are mediated by activation of sphingomyelinases and the production of ceramides. Differentiated 3T3-L1 adipocytes were incubated with short-chain ceramide analogs, (C-2- and C-6-ceramides: N-acetyl- and N-hexanoyl-sphingosines, respectively), and this treatment increased 2-deoxyglucose uptake in the absence of insulin progressively from 2-24 h. This effect was inhibited by blocking the activations of mitogen-activated protein kinase, phosphatidylinositol 3-kinase (PI 3-kinase), and ribosomal S6 kinase which mediated an increase in GLUT1 concentrations. Long-term increases in PI 3-kinase activity associated with insulin receptor substrate-1 (IRS-1) increased the proportion of GLUT1 and GLUT4 in plasma membranes. These events explain the increases in noninsulin-dependent glucose uptake and incorporation of this glucose into the fatty acid and glycerol moieties of triacylglycerol. The mechanisms by which TNF-alpha and ceramides increase PI 3-kinase activity were investigated further by using rat2 fibroblasts. Incubation for 20 min with TNF-alpha, bacterial sphingomyelinase, or C-2-ceramides increased Pt 3-kinase activity by about fivefold, and this effect depended upon a stimulation of tyrosine kinase activity and an increase in Ras-GTP. This demonstrates the existence of a novel signaling pathway far TNF-alpha that could contribute to the effects of this cytokine in stimulating basal glucose uptake. By contrast, treating the 3T3-L1 adipocytes for 2-24 h with C-2-ceramide diminished insulin-stimulated glucose uptake by decreasing the insulin-induced translocation of GLUT1 and GLUT4 to plasma membranes. This inhibition was observed when there was no increase in basal glucose uptake, and it occurred downstream of PI 3-kinase. Our work provides further mechanisms whereby TNF-alpha and ceramides produce insulin resistance and decrease the effectiveness of insulin in stimu
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