Sphingolipids and cellular cholesterol homeostasis. Effect of ceramide on cholesterol trafficking and HMG CoA reductase activity.
We previously showed that degradation of cellular sphingomyelin (SM) by SMase C results in a greater stimulation of cholesterol translocation to endoplasmic reticulum, compared to its degradation by SMase D. Here we investigated the hypothesis that the effect of SMase C is partly due to the generation of ceramide, rather than due to depletion of SM alone. Inhibition of hydroxymethylglutaryl CoA reductase (HMGCR) activity was used as a measure of cholesterol translocation. Treatment of fibroblasts with SMase C resulted in a 90% inhibition of HMGCR, whereas SMase D treatment inhibited it by 29%. Treatment with exogenous ceramides, or increasing the endogenous ceramide levels also inhibited HMGCR by 60-80%. Phosphorylation of HMGCR was stimulated by SMase C or exogenous ceramide. The effects of ceramide and SMase D were additive, indicating the independent effects of SM depletion and ceramide generation. These results show that ceramide regulates sterol trafficking independent of cellular SM levels.
Subbaiah
Papasani V
PV
Departments of Medicine and Biochemistry & Molecular Genetics, University of Illinois at Chicago, 1819 West Polk Street, M/C 797, Chicago, IL 60612, USA. psubbaia@uic.edu
Sowa
Jennifer M
JM
Singh
Dev K
DK
D001692:Biological Transport; D002478:Cells, Cultured; D002518:Ceramides / Q000494:pharmacology*; D002784:Cholesterol / Q000378:metabolism*; D004951:Esterification; D006706:Homeostasis; D006801:Humans; D006903:Hydroxymethylglutaryl CoA Reductases / Q000378:metabolism*; D010766:Phosphorylation; D013107:Sphingolipids / Q000378:metabolism*; D013108:Sphingomyelin Phosphodiesterase / Q000378:metabolism
D002518:Ceramides; D013107:Sphingolipids; D002784:Cholesterol; D006903:Hydroxymethylglutaryl CoA Reductases; D013108:Sphingomyelin Phosphodiesterase