FIGURE 1.

TNFα promoter is hypermethylated in endotoxin-tolerant THP-1 cells. A, a schematic diagram representing the proximal promoter region of the human TNFα gene analyzed by bisulfite sequencing. The eight CpG dinucleotides located in this region are represented by vertical lines with open circles, and their locations relative to the transcription start site are indicated. B, bisulfite sequencing results. Endotoxin tolerance was induced by pretreatment with 1 μg/ml LPS for 16 h. Endotoxin responsive and tolerant cells were then stimulated with 1 μg/ml LPS for the indicated times. Genomic DNA was extracted and subjected to sodium bisulfite conversion, followed by PCR amplification and sequencing. The total numbers of methylated CpGs in responsive untreated cells (0 h) was set at 100%, and all other values were calculated relative to this value. The data represent the mean ± S.E. of at least three independent experiments. *, significant difference (p < 0.05) between responsive versus tolerant cells.