Neutral sphingomyelinase action stimulates signal transduction of tumor necrosis factor-alpha in the synthesis of cholesteryl esters in human fibroblasts.
We have investigated biochemical mechanisms of tumor necrosis factor (TNF)-alpha signaling in cultured human skin fibroblasts. We found that TNF-alpha signaling may involve activation of a cell membrane neutral sphingomyelinase (N-SMase) in that within 2.5-5 min of treatment of cells with TNF-alpha there was a 2-fold increase in the activity of N-SMase compared to control. This reaction led to the hydrolysis of sphingomyelin as evidenced by a decrease in sphingomyelin mass and in the radioactivity associated with [14C]choline-labeled sphingomyelin. This was accompanied by a 4-fold increase in the formation of cholesteryl [14C]oleate within 2.5 min of incubation with TNF-alpha. This reaction also stimulated the mobilization of cell surface-associated [3H]cholesterol and its utilization in the synthesis of [3H]cholesteryl esters via acyl coenzyme-A cholesterol acyltransferase (ACAT). Gas chromatographic analysis revealed that the cellular level of cholesteryl esters increased about 2.5-3-fold following treatment with TNF-alpha compared to control. Cholesteryl ester synthesis was compromised upon incubation of cells with antibody against N-SMase and remained unaltered with TNF-beta and fibroblast growth factor. Furthermore, TNF-alpha-mediated stimulation of cholesteryl ester synthesis was compromised by incubation of cells with an inhibitor of ACAT. These findings suggest a possible biological role of N-SMase in the signal transduction of TNF-alpha in the synthesis of cholesteryl esters in human fibroblasts.
Chatterjee
S
S
Department of Pediatrics, Johns Hopkins University, School of Medicine, Baltimore, Maryland 21287-3654.
D002478:Cells, Cultured; D002784:Cholesterol / Q000378:metabolism; D002788:Cholesterol Esters / Q000378:metabolism*; D016220:Fibroblast Growth Factor 1 / Q000494:pharmacology; D005347:Fibroblasts / Q000378:metabolism; D006801:Humans; D066298:In Vitro Techniques; D008233:Lymphotoxin-alpha / Q000494:pharmacology; D015398:Signal Transduction; D013108:Sphingomyelin Phosphodiesterase / Q000378:metabolism*; D013109:Sphingomyelins / Q000378:metabolism; D014409:Tumor Necrosis Factor-alpha / Q000502:physiology*
D002788:Cholesterol Esters; D008233:Lymphotoxin-alpha; D013109:Sphingomyelins; D014409:Tumor Necrosis Factor-alpha; D016220:Fibroblast Growth Factor 1; D002784:Cholesterol; D013108:Sphingomyelin Phosphodiesterase