Active repression of alternative cell fates by PROX1 safeguards hepatocyte identity and prevents liver tumorigenesis [Cut&Run]
Cell fate induction and maintenance require activation of lineage-specific programs and silencing of alternative identities. While single master regulators can bind and activate cell type-specific genes, the suppression of numerous unwanted fates by a limited number of available repressors is poorly understood. Here, we identify master repressor candidates that can silence many non-lineage-specific regulators to safeguard the desired cell identity. We validated hepatocyte-specific candidates using cell reprogramming, revealing that PROX1 enhances hepatocyte identity and suppresses several alternate cell identities. Mechanistically, direct repression of PROX1 target genes, including alternate fate master regulators Prrx1 and Pparg, promoted hepatocyte fate. Deleting Prox1 impaired hepatocyte formation and caused alternate fate marker induction. In line with cancer patient data, Prox1 depletion caused hepatocyte fate loss, while overexpression prevented neoplastic transformation during mouse liver tumorigenesis. Our findings support a model where individual cell type-specific safeguard repressors actively suppress many alternative fates to safeguard lineage choice and prevent cell fate plasticity and disease. Overall design: CUT&RUN of MEFs, and MEFs reprogrammed with 4in1 towards induced hepatocytes ± Prox1 ovexpression, harvested after two days.