Search results for: ASAH2 Blocking Peptide
#11457826 
2001/07/16
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Interleukin-1beta induces chronic activation and de novo synthesis of neutral ceramidase in renal mesangial cells.
The lipid signaling molecule ceramide is formed by the action of acid and neutral sphingomyelinases and degraded by acid and neutral ceramidases. Short-term stimulation of mesangial cells with the pro-inflammatory cytokine interleukin-1beta (IL-1beta) leads to a rapid and transient increase in neutral sphingomyelinase activity (Kaszkin, M., Huwiler, A., Scholz, K., van den Bosch, H., and Pfeilschifter, J. (1998) FEBS Lett. 440, 163-166). In this study, we report on a second delayed peak of activation occurring after hours of IL-1beta treatment. This second phase of activation was first detectable after 2 h of treatment and steadily increased over the next 2 h, reaching maximal values after 4 h. In parallel, a pronounced increase in neutral ceramidase activity was observed, accounting for a constant or even decreased level of ceramide after long-term IL-1beta treatment, despite continuous sphingomyelinase activation. The increase in neutral ceramidase activity was due to expressional up-regulation, as detected by an increase in mRNA levels and enhanced de novo protein synthesis. The increase in neutral ceramidase protein levels and activity could be blocked dose- dependently by the p38 MAPK inhibitor SB 202190, whereas the classical MAPK pathway inhibitor U0126 and the protein kinase C inhibitor Ro 318220 were ineffective. Moreover, cotreatment of cells for 24 h with IL-1beta and SB 202190 led to an increase in ceramide formation. Interestingly, IL-1beta-stimulated neutral ceramidase activation was not reduced in mesangial cells isolated from mice deficient in MAPK-activated protein kinase-2, which is a downstream substrate of p38 MAPK, thus suggesting that the p38 MAPK-mediated induction of neutral ceramidase occurs independently of the MAPK-activated protein kinase-2 pathway. In summary, our results suggest a biphasic regulation of sphingomyelin hydrolysis in cytokine-treated mesangial cells with delayed de novo synthesis of neutral ceramidase counteracting sphingomyelinase activity and apoptosis. Neutral ceramidase may thus represent a novel cytoprotective enzyme for mesangial cells exposed to inflammatory stress conditions.R Franzen, A Pautz, L Bräutigam, G Geisslinger, J Pfeilschifter, A Huwiler
1221 related Products with: Interleukin-1beta induces chronic activation and de novo synthesis of neutral ceramidase in renal mesangial cells.
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Bimodal regulation of ceramidase by interleukin-1beta. Implications for the regulation of cytochrome p450 2C11.
Interleukin 1beta (IL-1beta) induces the hydrolysis of sphingomyelin (SM) to ceramide (Cer) in primary cultures of rat hepatocytes, and Cer has been proposed to play a role in the down-regulation of cytochrome P450 2C11 (CYP2C11) and induction of alpha1-acid glycoprotein (AGP) by this cytokine (Chen, J., Nikolova-Karakashian, M., Merrill, A. H. & Morgan, E. T. (1995) J. Biol. Chem. 270, 25233-25238). Nonetheless, some of the features of the down-regulation of CYP2C11 do not fit a simple model of Cer as a second messenger as follows: N-acetylsphinganine (C2-DHCer) is as potent as N-acetylsphingosine (C2-Cer) in suppression of CYP2C11; the IL-1beta concentration dependence for SM turnover is different from that for the increase in Cer; and the increase in Cer mass is not equivalent to the amount of SM hydrolyzed nor the time course of SM hydrolysis. In this article, we report that these discrepancies are due to activation of ceramidase by the low concentrations of IL-1beta ( approximately 2.5 ng/ml) that maximally down-regulate CYP2C11 expression, whereas higher IL-1beta concentrations (that induce AGP) do not activate ceramidase and allow Cer accumulation. This bimodal concentration dependence is demonstrated both by in vitro ceramidase assays and in intact hepatocytes using a fluorescence Cer analog, 6-((N-(7-nitrobenz-2-oxa-1, 3-diazol-4-yl)amino)-Cer (NBD-Cer), and following release of the NBD-fatty acid. IL-1beta increases both acid and neutral ceramidase activities, which appear to be regulated by tyrosine phosphorylation because pretreatment of hepatocytes with sodium vanadate increases (and 25 microM genistein reduces) the basal and IL-1beta-stimulated ceramidase activities. Since these findings suggested that sphingosine (and, possibly, subsequent metabolites) is the primary mediator of the down-regulation of CYP2C11 by IL-1beta, the effects of exogenous sphingosine and C2-Cer on expression of this gene were compared. Sphingosine was more potent than C2-Cer in down-regulation of CYP2C11 when added alone or with fumonisin B1 to block acylation of the exogenous sphingosine. Furthermore, the suppression of CYP2C11 by C2-Cer (and C2-DHCer) is probably mediated by free sphingoid bases, rather than the short chain Cer directly, because both are hydrolyzed by hepatocytes and increase cellular levels of sphingosine and sphinganine. From these observations we conclude that sphingosine, possibly via sphingosine 1-phosphate, is a mediator of the regulation of CYP2C11 by IL-1beta in rat hepatocytes and that ceramidase activation provides a "switch" that determines which sphingolipids are elevated by this cytokine to produce multiple intracellular responses.M Nikolova-Karakashian, E T Morgan, C Alexander, D C Liotta, A H Merrill