A NOTCH feed-forward loop drives reprogramming from adrenergic to mesenchymal state in neuroblastoma.

Transition between differentiation states in development occurs swift but the mechanisms leading to epigenetic and transcriptional reprogramming are poorly understood. The pediatric cancer neuroblastoma includes adrenergic (ADRN) and mesenchymal (MES) tumor cell types, which differ in phenotype, super-enhancers (SEs) and core regulatory circuitries. These cell types can spontaneously interconvert, but the mechanism remains largely unknown. Here, we unravel how a NOTCH3 intracellular domain reprogrammed the ADRN transcriptional landscape towards a MES state. A transcriptional feed-forward circuitry of NOTCH-family transcription factors amplifies the NOTCH signaling levels, explaining the swift transition between two semi-stable cellular states. This transition induces genome-wide remodeling of the H3K27ac landscape and a switch from ADRN SEs to MES SEs. Once established, the NOTCH feed-forward loop maintains the induced MES state. In vivo reprogramming of ADRN cells shows that MES and ADRN cells are equally oncogenic. Our results elucidate a swift transdifferentiation between two semi-stable epigenetic cellular states. Overall design: Cultured cells were fixed with 1% formaldehyde. Nuclei were isolated and the DNA was sheared to 200 to 300 bp fragments. Histon-bound DNA was precipitated using antibodies H3K27Ac (#4729, Abcam) . De-crosslinked DNA was purified using Qiagen PCR purification kit (Qiagen) and quantified with Quant-IT Picogreen (Invitrogen). The DNA was used to generate sequencing libraries according to the manufactures procedure (Life Technologies): The DNA was end-polished, dA-tailed and adaptors with barcodes were ligated. The fragments were amplified (8 cycles) and quantified with a Bioanalyzer (Agilent). The libraries were prepped with the 5500W Flowchip v2 kit (Life Technologies) and sequenced on the SOLiD Wildfire (Illumina) resulting in 50 bp reads. Alternatively, the libraries were sequenced using the HiSeq PE cluster kit v4 (Illumina) with the HiSeq2500 (Illumina) resulting in 125 bp reads.