Chromatin immunoprecipitation (ChIP) was performed with the SimpleChIP Enzymatic Chromatin IP Kit (Magnetic Beads) (#9003, Cell Signaling Technology, Danvers, MA) according to the manufacturer's instructions. Briefly, cells were cross‐linked with 1% formaldehyde (Sigma‐Aldrich) and lysed. Chromatin was digested with micrococcal nuclease into 150-900bp DNA/protein fragments. The fragments were immunoprecipitated with antibodies against H3K4me3 (C42D8, Cell Signaling Technology), H3K27me3 (C36B11, Cell Signaling Technology), or normal rabbit IgG with protein G magnetic beads. Cross-links were reversed, and purified DNAs were then subjected to next-generation sequencing (NovaSeq 6000 System).