Effect of IFN-β on methylation dynamics of xaf1 promoter. Cells were exposed to 500 U/mL of IFN-β in culture medium for 0 hour, 24 hours, 48 hours or 5 days. (A) The methylation status of xaf1 promoter region in HeLa and SK-N-AS cells was determined based on the analysis of 8 CpG sites, by methylation-sensitive PCR as described previously in Figure 1. (B) HeLa and (C) SK-N-AS cells were treated for 5 days, and then were subsequently sub-cultured on medium lacking IFN-β for 7 days. Genomic DNA was harvested and subjected to sodium bisulphite treatment and PCR using primers MS2 and MS3. Results represent average methylation for 10 independent clones at 8 representative CpG sites for each cell line. After 5 days of continuous exposure to IFN-β there is a significant overall drop (p < 0.05) in methylation within the xaf1 promoter region.