Cancer-specific bivalent promoters featuring low-level H3K27me3 signals favor active transcription and govern the cancer cell state transition
Bivalent chromatin maintains genes in low-expression, poised states in embryonic stem cells (ESCs). However, bivalent promoters correlate with the transcriptional activation of oncogenic programs in malignancies, a seemingly contradiction that remains to be resolved. Here, we identify a class of cancer-specific bivalent promoters (CSBPs) through the integration of a system-level longitudinal framework. Compared with ESCs, CSBPs are characterized by lower and narrower H3K27me3 deposition alongside abundant H3K4me3, thus permitting the persistent expression of genes critical for cancer stem cell (CSC) formation and maintenance, as exemplified by SOX9. The generation of CSBPs is essentially induced by the acquisition of H3K27me3 during cell state transition, which is mediated by specific binding of PRC2.1 and the de novo recruitment of PRC2.2. Notably, disrupting the bivalency of CSBPs significantly increases H3K4me3 levels, leading to hyperactivation of CSBPs and eventually inhibiting clonal expansion of CSCs and impairing tumorigenesis. Our study not only helps explain the puzzle of transcriptionally active bivalent genes in cancer but also provides insights into the development of therapies targeting phenotypic plasticity.