ATAC-seq for cell lines was performed based on Omni-ATAC-seq protocol (Corces et al., 2017) with 50,000 cells. Nuclear pellet was subjected to transposition with Nextera DNA Sample Preparation Kit (Illumina, no. FC-121-1030) in the presence of 0.01% digitonin and 0.1% Tween-20 at 37 degree for 30 minutes.  The reaction was then cleaned up by DNA Clean and Concentrator-5 Kit (Zymo, no. D4014) and PCR amplified with NEBNext High-Fidelity 2X PCR Master Mix (NEB, no. M0541L) and Nextera Index kit (Illumina, no. 15055289). The resulting libraries were pooled and sequenced on Illumina NextSeq500, according to validated standard operating procedures established by the University of Virginia Genome And Technology Core, RRID: SCR_018883.