Journal of Biological Chemistry
Volume 277, Issue 6, 8 February 2002, Pages 3878-3885
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LIPIDS AND LIPOPROTEINS
Unsaturated Fatty Acid-mediated Decreases in Sterol Regulatory Element-mediated Gene Transcription Are Linked to Cellular Sphingolipid Metabolism*

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A major physiological feedback mechanism of cholesterol in transcription of a number of lipid metabolism-related genes is mediated by sterol regulatory elements (SREs) and their binding proteins (SREBPs). Polyunsaturated free fatty acids alone, as well as synergistically with sterols, decrease SRE-mediated gene expression up to 80% in a dose-dependent manner by decreasing levels of the active transcription factor SREBP. We investigated potential mechanisms for this effect. We hypothesized that free fatty acids reduce SREBP-mediated gene transcription by increasing intracellular cholesterol content through the hydrolysis of cellular sphingomyelin, which has a high affinity for free cholesterol. We also questioned whether the lipid second messenger ceramide, a product of sphingomyelin hydrolysis, can decrease SRE-mediated gene transcription. First we investigated the effect of fatty acids on sphingomyelin hydrolysis. Incubation of [3H]choline-labeled cells with unsaturated (but not saturated) fatty acids induced hydrolysis of [3H]choline-labeled sphingomyelin. Also, incubation of cell extracts from fatty acid-treated cells with [3H]sphingomyelin increased generation of [3H]ceramide compared with control cellsin vitro. We found that addition of ceramide analogs alone and additively with fatty acids decreased SRE expression and that ceramide analogs reduced levels of the transcriptionally active forms of SREBP-1 and SREBP-2. Increasing intracellular ceramide levels by exogenous sphingomyelinase or inhibition of ceramidase decreased SRE-mediated gene expression. None of the above conditions induced apoptosis. Incubation with U18666A, a compound that inhibits intracellular cholesterol movement, increased SRE-mediated gene transcription. C2-ceramide abrogated the effect of U18666A on SRE-mediated gene transcription, suggesting cholesterol-independent regulation of SREBP. We provide evidence that sphingomyelin hydrolysis and intermediates of sphingomyelin metabolism (in addition to cholesterol and fatty acids) contribute to regulation of SRE-mediated gene transcription.

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Published, JBC Papers in Press, November 13, 2001, DOI 10.1074/jbc.M102393200

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This work was supported in part by National Institutes of Health Grant HL40404.The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

Supported in part by National Institutes of Health Training Grant T32DK07715.

Supported in part by National Institutes of Health Training Grant HL07343-22.