TP63 mediates the generation of tumour-specific chromatin loops that underlie MYC activation in radiation-induced tumorigenesis

Alterations in 3D chromatin conformation may disrupt the interplay between promoters and distal enhancers. How gene regulatory circuits are reshaped during ionizing radiation-induced tumorigenesis remains unclear, and little is known about the mediators that drive these processes. To decipher the chromatin alterations in radiation-induced lung cancer, we performed ATAC-seq, RNA-seq and Hi-C analyses of human bronchial epithelial cells and corresponding radiation-induced malignantly transformed cell lines. We found that this malignant transformation is accompanied by chromatin switching from the inactive B compartment to the active A compartment, an increased number of TADs and gained ATAC-seq peaks that mediate new distal chromatin contacts. We identified tumour protein 63 (TP63) as a mediator of new chromatin-accessible sites that anchor tumour-specific chromatin contacts in radiation-induced tumour cells. A TP63-mediated accessible chromatin site anchors a tumour-specific TAD boundary and multiple tumour-specific chromatin loops, which might underlie MYC oncogene activation during malignant transformation.