Whole-genome doubling drives oncogenic loss of chromatin segregation.

Whole-genome doubling (WGD) is a recurrent event in human cancers and it promotes chromosomal instability and acquisition of aneuploidies1-8. However, the three-dimensional organization of chromatin in WGD cells and its contribution to oncogenic phenotypes are currently unknown. Here we show that in p53-deficient cells, WGD induces loss of chromatin segregation (LCS). This event is characterized by reduced segregation between short and long chromosomes, A and B subcompartments and adjacent chromatin domains. LCS is driven by the downregulation of CTCF and H3K9me3 in cells that bypassed activation of the tetraploid checkpoint. Longitudinal analyses revealed that LCS primes genomic regions for subcompartment repositioning in WGD cells. This results in chromatin and epigenetic changes associated with oncogene activation in tumours ensuing from WGD cells. Notably, subcompartment repositioning events were largely independent of chromosomal alterations, which indicates that these were complementary mechanisms contributing to tumour development and progression. Overall, LCS initiates chromatin conformation changes that ultimately result in oncogenic epigenetic and transcriptional modifications, which suggests that chromatin evolution is a hallmark of WGD-driven cancer.

Systematic dissection of transcriptional regulatory networks by genome-scale and single-cell CRISPR screens.

Millions of putative transcriptional regulatory elements (TREs) have been cataloged in the human genome, yet their functional relevance in specific pathophysiological settings remains to be determined. This is critical to understand how oncogenic transcription factors (TFs) engage specific TREs to impose transcriptional programs underlying malignant phenotypes. Here, we combine cutting edge CRISPR screens and epigenomic profiling to functionally survey ≈15,000 TREs engaged by estrogen receptor (ER). We show that ER exerts its oncogenic role in breast cancer by engaging TREs enriched in GATA3, TFAP2C, and H3K27Ac signal. These TREs control critical downstream TFs, among which TFAP2C plays an essential role in ER-driven cell proliferation. Together, our work reveals novel insights into a critical oncogenic transcription program and provides a framework to map regulatory networks, enabling to dissect the function of the noncoding genome of cancer cells.

SHRED Is a Regulatory Cascade that Reprograms Ubr1 Substrate Specificity for Enhanced Protein Quality Control during Stress.

When faced with proteotoxic stress, cells mount adaptive responses to eliminate aberrant proteins. Adaptive responses increase the expression of protein folding and degradation factors to enhance the cellular quality control machinery. However, it is unclear whether and how this augmented machinery acquires new activities during stress. Here, we uncover a regulatory cascade in budding yeast that consists of the hydrophilin protein Roq1/Yjl144w, the HtrA-type protease Ynm3/Nma111, and the ubiquitin ligase Ubr1. Various stresses stimulate ROQ1 transcription. The Roq1 protein is cleaved by Ynm3. Cleaved Roq1 interacts with Ubr1, transforming its substrate specificity. Altered substrate recognition by Ubr1 accelerates proteasomal degradation of misfolded as well as native proteins at the endoplasmic reticulum membrane and in the cytosol. We term this pathway stress-induced homeostatically regulated protein degradation (SHRED) and propose that it promotes physiological adaptation by reprogramming a key component of the quality control machinery.