0.5 million liver tumor cells were crosslinked for 10 minutes using 1% formaldehyde, followed by quenching with 0.125M glycine for 10 minutes. To prepare chromatin from crosslinked cells, aliquots of cells were kept in individual eppendorf tubes for sonication to maximize the chromatin fragmentation efficiency. After purifying immunoprecipitated DNA, a TruSeq ChIP Sample Prep Kit (Illumina) was used to construct the ChIP-Seq library following the manufacturer's protocol except for amplifying the adaptor-ligated library for 15 cycles. ChIP-Seq libraries were sequenced using an Illumina HiSeq 2000 platform with single-end reads of 50 bases. Four libraries at equal molarity were pooled to aim for a sequencing depth of 20-40 million aligned reads per sample.