FIGURE 7.

Ceramide increases human GLTP promoter activity. Elevated endogenous ceramide level increases GLTP expression. A, comparison of the effects of various sphingolipids on GLTP promoter activity. HeLa cells were transfected with pGL3(−1150/+19) and then treated with different lipids. Luciferase activity was measured 24 h after lipid treatment and was normalized to Renilla luciferase activity. B, real-time PCR analyses of ceramide-induced GLTP transcript level up-regulation in vivo. Cells were grown to ∼60% confluency and then were treated with 0, 5, or 10 μm C₆-ceramide for 3, 6, or 12 h before harvesting for real-time RT-PCR analyses. GTLP mRNA levels were normalized to β-actin mRNA levels. C, effect of C₆-ceramide on endogenous ceramide levels. Cells were grown to ∼60% confluency, and then cells were treated with 10 μm C₆-ceramide for 24 h and analyzed for their ceramide species content by HPLC-MS as described under “Experimental Procedures.” Results were normalized to cell lipid phosphate. GTLP mRNA levels were normalized to β-actin mRNA levels. Cer, ceramide. Bars represent the means ± S.E. of three to six determinations, *, p < 0.05 compared with cells treated with vehicle (0.1% DMSO), respectively. **, p < 0.01.