Chromatin immunoprecipitation (ChIP)

ChIP assay was performed using a One-Day Chromatin Immunoprecipitation kit (EMD Millipore) according to the manufacturer's protocol. ChIP was performed using anti-MBD2 (1:50; cat. no. AB38646; Abcam), BMI1 (1:50; cat. no. 5856; Cell Signalling Technology, Inc.) and EZH2 antibodies (1:25; cat. no. 4905; Cell Signalling Technology, Inc.) for 12 h at 4˚C, with normal rabbit IgG (cat. no. LK2001; 1:1,000; Sungene Biotech, Ltd.) serving as a control. DNA fragments isolated from chromatin were subjected to 40 cycles of RT-qPCR (cat. no. CW2627; CoWin Biosciences) at 95˚C for 10 sec followed by annealing at 60˚C for 60 sec and extension at 95˚C for 15 sec. The enrichment of marks on the target regions was quantified relative to the input amounts. The region of the SFRP1 promoters analysed for methylation by ChIP are presented in Fig. S1B.