Disparate leukemia mutations converge on nuclear phase-separated condensates.

During cancer development, mutations promote changes in gene expression that cause transformation. Leukemia associated with aberrant HOXA expression is driven by translocations of nucleoporin genes or KMT2A as well as mutations in NPM1. The mechanistic convergence of these disparate mutations remains elusive. Here, we demonstrate that mutant nucleophosmin 1 (NPM1c) forms nuclear condensates in human cell lines, mouse models, and primary patient samples. We show NPM1c phase separation is necessary and sufficient to recruit NUP98 and KMT2A to condensates. Through extensive mutagenesis and pharmacological destabilization of phase separation, we find that NPM1c condensates are necessary for regulating gene expression, promoting in vivo leukemic expansion, and maintaining the undifferentiated leukemic state. Finally, we show that nucleoporin and KMT2A fusion proteins form condensates that are biophysically indistinguishable from NPM1c condensates. Together, these data define a new condensate that we term the coordinating body (C-body) and establish C-bodies as a therapeutic vulnerability in leukemia.