Cytoplasmic NPM1 modulates autophagy and mitochondrial function
Hsin-Chieh Wu2,3,4, Caroline Berthier1,2,3,4, Hugues de Thé1,2,3,4
- Université Paris Diderot, Sorbonne Paris Cité, Hôpital St. Louis, 1 Avenue Claude Vellefaux, 75475 Paris cedex 10, France
- INSERM UMR 944, Equipe labellisée par la Ligue Nationale contre le Cancer, Institut Universitaire d'Hématologie, France
- CNRS UMR 7212, France
- Collège de France PSL research university, France
Nucleophosmin 1 (NPM1) is a nucleolar phosphoprotein that participates in various biological processes including molecular chaperoning, ribosome biogenesis, DNA repair, and genome stability. Mutations of NPM1 gene are the most frequent genetic alteration in patients with acute myeloid leukemia (AML). These mutations result in expression of a mutant protein with aberrant cytoplasmic localization, named NPMc. Among multiple cellular defects observed in NPM1c expressing cells, we showed that PML nuclear bodies are disrupted, suggesting that their tumor suppressor function may be impaired. We show that NPM1c-associated AML malignancy is associated with altered autophagy flux and mitochondria dysfunction. NPM1c is preferentially associated with ER-mitochondria associated membrane and late endosome/autophagosome. NPM1c AML cells have higher autophagy flux when compared with NPM1-WT AML cells upon autophagy induction. Blockage of autophagy flux partially restored PML-NBs and precipitated PML-NPM1c protein complex accumulation in the cytosol.
NPM1c disturbs redox balance, which contributes to clonogenic capacity of AML ex vivo. Indeed, stable expression of NPM1c in AML cells increases mitochondrial membrane potential and reactive oxygen species (ROS) production. Inhibition of ROS by N-acetyl-I-cysteine (NAC) blocks NPM1c-induced AML cell cycle progression and clonogenic ability. NPM1c causes mtDNA instability and promotes the release of mtDNA into the cytosol, where it activates the cytosolic DNA sensor cyclic GMP-AMP synthase (cGAS) and triggers type I interferon pathway. Collectively, our results provide evidence that NPM1c perturbs autophagy and mitochondria function contributing to the AML phenotype.