Ribosome biogenesis is a downstream effector of the oncogenic U2AF1-S34F mutation

U2AF1 forms a heterodimeric complex with U2AF2 that is primarily responsible for 3 splice site selection. U2AF1 mutations have been identified in most cancers but are prevalent in Myelodysplastic Syndrome and Acute Myeloid Leukemia, and the most common mutation is a missense substitution of serine-34 to phenylalanine (S34F). However, the U2AF heterodimer also has a non-canonical function as a translational regulator. Here, we report that the U2AF1 S34F mutation results in specific mis-regulation of the translation initiation and ribosome biogenesis machinery, with the potential for widespread translational changes. The net result is a global increase in mRNA translation at the single cell level. Among the translationally upregulated targets of U2AF1-S34F are Nucleophosmin1 (NPM1), which is a major driver of myeloid malignancy. Depletion of NPM1 impairs the viability of wt/S34F cells and causes rRNA processing defects, thus indicating an unanticipated synthetic interaction between U2AF1, NPM1 and ribosome biogenesis. Our results establish a unique molecular phenotype for the U2AF1 mutation which recapitulates translational mis-regulation in myeloid disease.