The cells were harvested, fixed with 1% formaldehyde (Thermo Fisher Scientific, MA, USA) for 10 min, washed twice with cold PBS and frozen at -80C. The chromatin was sonicated to generate fragments of 200-500bp in length, followed by incubation with rabbit polyclonal p50 (#3035, Cell Signaling, Danvers, MA, USA) and p65 (ab16502, Abcam, Cambridge, UK) antibodies overnight. Precipitated chromatin was washed, de-crosslinked and DNA extraction was carried out using phenol-chloroform (Sigma). ChIP DNA was prepared for high throughput sequencing using Accel-NGS 2S Plus DNA library kit (Swift Biosciences) as per manufacturer's protocol. DNA libraries were sequenced on an Illumina Hiseq4000 with a paired-end 75bp run (CAT, UCSF).