Chromatin immunoprecipitation (ChIP) assay

ChIP assay was performed using ChIP-IT Express kit (Active Motif, Carlsbad, CA, USA) in accordance with the manufacturer’s protocols. Briefly, the chromatin was extracted from 1 × 10⁷ formalin-fixed cells and chromatin including 15 μg DNA was immunoprecipitated using 2 μg anti-DNMT1 antibody or anti-DNMT3A antibody. For negative control, mouse non-specific IgG was used. The amount of precipitated DNA was measured using NanoDrop 1000 (Thermo Fisher Scientific).