Human JARID2 blocking peptide

Recruitment of the Polycomb repressive complexes PRC1 and PRC2 by Xist RNA is an important paradigm for chromatin regulation by long noncoding RNAs. Here, we show that the noncanonical Polycomb group RING finger 3/5 (PCGF3/5)-PRC1 complex initiates recruitment of both PRC1 and PRC2 in response to Xist RNA expression. PCGF3/5-PRC1-mediated ubiquitylation of histone H2A signals recruitment of other noncanonical PRC1 complexes and of PRC2, the latter leading to deposition of histone H3 lysine 27 methylation chromosome-wide. Pcgf3/5 gene knockout results in female-specific embryo lethality and abrogates Xist-mediated gene repression, highlighting a key role for Polycomb in Xist-dependent chromosome silencing. Our findings overturn existing models for Polycomb recruitment by Xist RNA and establish precedence for H2AK119u1 in initiating Polycomb domain formation in a physiological context.

How specific genetic lesions contribute to transformation of non-malignant myeloproliferative neoplasms (MPNs) and myelodysplastic syndromes (MDSs) to secondary acute myeloid leukemia (sAML) are poorly understood. JARID2 is lost by chromosomal deletions in a proportion of MPN/MDS cases that progress to sAML. In this study, genetic mouse models and patient-derived xenografts demonstrated that JARID2 acts as a tumor suppressor in chronic myeloid disorders. Genetic deletion of Jarid2 either reduced overall survival of animals with MPNs or drove transformation to sAML, depending on the timing and context of co-operating mutations. Mechanistically, JARID2 recruits PRC2 to epigenetically repress self-renewal pathways in hematopoietic progenitor cells. These studies establish JARID2 as a bona fide hematopoietic tumor suppressor and highlight potential therapeutic targets.