The target promoter sequence (1000 bp upstream of exon) was retrieved from the NCBI database (https://www.ncbi.nlm.nih.gov/) and synthesized with 5' biotin modification (FITGENE, China). Tumor cells were lysed under two conditions: (1) SDS lysis buffer with sonication (strong condition) or (2) IP lysis buffer (mild condition). Lysates were centrifuged (14,000g, 10 min, 4 °C), then incubated overnight at 4 °C with biotinylated DNA, followed by streptavidin magnetic bead capture (30 min, RT). Bound proteins were eluted in 4× Laemmli buffer (95°C, 7 min), resolved on 10% Omni-PAGE™ Hepes Plus gels, and processed for LC-MS/MS proteomic analysis.