Raw sequencing data were first trimmed to remove adaptors and low-quality reads using TrimGalore-0.5.0 with the following parameter settings: -q 25 --phred33 --length 35 -e 0.1 --stringency. Trimmed files were then mapped to hg19 genome utilizing Bowtie2. Sambamba_v0.6.6 was conducted for the removal of duplicates. DeepTools-3.2.1 was then performed using the function of bamCoverage to generate normalized CPM.bw files.