U2AF regulates the translation and localization of nuclear-encoded mitochondrial mRNAs.

The mechanisms underlying molecular targeting to mitochondria remain enigmatic, yet this process is crucial for normal cellular function. The RNA-binding proteins U2AF1 and U2AF2 form a heterodimer (U2AF) that shuttles between the nucleus and cytoplasm, regulating splicing in the nucleus and translation in the cytoplasm. Our study in human bronchial epithelial cells (HBECs) identifies an unexpected role for U2AF in mitochondrial function. We demonstrate that U2AF interacts with nuclear-encoded mitochondrial (NE-mt) mRNAs and proteins, inhibits translation, localizes to the mitochondria, and regulates mRNA localization to mitochondria. Moreover, an oncogenic point mutation in U2AF1(S34F) disrupts this regulation, leading to altered mitochondrial structure, increased translation, large changes in the mitochondria proteome, and oxidative phosphorylation (OXPHOS)-dependent metabolic rewiring, recapitulating changes observed in bone marrow progenitors from patients with myelodysplastic syndromes. These findings reveal a non-canonical role for U2AF, where it modulates multiple aspects of mitochondrial function by regulating the translation and mitochondrial localization of nuclear-encoded mRNAs.