TNFalpha signaling primes chromatin for NF-kappaB binding and induces rapid and widespread nucleosome repositioning

Background The rearrangement of nucleosomes along the DNA fiber profoundly affects gene expression, but little is known about how signaling reshapes the chromatin landscape, in 3D space and over time, to allow the establishment of new transcriptional programs. Results Using micrococcal nuclease treatment and high-throughput sequencing, we map genome-wide changes in nucleosome positioning in primary human endothelial cells stimulated with tumour necrosis factor alpha (TNFalpha) - a proinflammatory cytokine that signals through nuclear factor kappaB (NF-kappaB). Within 10 minutes, nucleosomes reposition at regions both proximal and distal to NF-kappaB binding sites, before the transcription factor quantitatively binds thereon. Similarly, in long TNFalpha-responsive genes, repositioning precedes transcription by pioneering elongating polymerases and appears to nucleate from intragenic enhancer clusters resembling super-enhancers. By 30 minutes, widespread repositioning occurs throughout Mbp-long chromosomal segments, with consequential effects on 3D structure, detected using chromosome conformation capture. Conclusions Whilst nucleosome repositioning is viewed as a local phenomenon, our results point to effects occurring over multiple scales. Here, we present data in support of a TNFalpha-induced priming mechanism, mostly independent of NF-kappaB binding and/or elongating RNA polymerases, leading to a plastic network of interactions that affects DNA accessibility over large domains. Overall design: MNase-Seq of HUVEC cells after stimulation with TNFa for 0, 10 or 30 min. Biological replicates for 0 and 30 min.