Bimodal regulation of ceramidase by interleukin-1β. Implications for the regulation of cytochrome P450 2C11 (CYP2C11)

Mariana Nikolova-Karakashian, Edward T. Morgan, Christopher Alexander, Dennis C. Liotta, Alfred H. Merrill

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144 Scopus citations


Interleukin 1β (IL-1β) 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 α1-acid glycoprotein (AGP) by this cytokine (Chen, J., Nikolova-Karakashian, M., Merrill, A. H. and 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-1β 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-1β (~2.5 ng/ml) that maximally down-regulate CYP2C 11 expression, whereas higher IL-1β 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-1β 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 μM genistein reduces) the basal and IL-1β-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-1β, 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-1β in rat hepatocytes and that ceramidase activation provides a 'switch' that determines which sphingolipids are elevated by this cytokine to produce multiple intracellular responses.

Original languageEnglish
Pages (from-to)18718-18724
Number of pages7
JournalJournal of Biological Chemistry
Issue number30
StatePublished - 1997

ASJC Scopus subject areas

  • Biochemistry
  • Molecular Biology
  • Cell Biology


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