The mitochondrial nature of the DNA repair protein APE1

APE1 is a multifunctional protein with a fundamental role in repairing nuclear and mitochondrial DNA lesions caused by oxidative and alkylating agents. Unfortunately, comprehensions of the mechanisms regulating APE1 intracellular trafficking are still fragmentary and contrasting. Recent data demonstrate that APE1 interacts with the mitochondrial import and assembly protein Mia40 suggesting the involvement of a redox-assisted mechanism, dependent on the disulfide transfer system, to be responsible of APE1 trafficking into the mitochondria. The MIA pathway is an import machinery that uses a redox system for cysteine enriched proteins to drive them in this compartment. It is composed by two main proteins: Mia40 is the oxidoreductase that catalyzes the formation of the disulfide bonds in the substrate, while ALR reoxidizes Mia40 after the import. In this study, we demonstrated that: (i) APE1 and Mia40 interact through disulfide bond formation; and (ii) Mia40 expression levels directly affect APE1's mitochondrial translocation and, consequently, play a role in the maintenance of mitochondrial DNA integrity. In summary, our data strongly support the hypothesis of a redox-assisted mechanism, dependent on Mia40, in controlling APE1 translocation into the mitochondrial inner membrane space and thus highlight the role of this protein transport pathway in the maintenance of mitochondrial DNA stability and cell survival. Apart from its canonical activities, recent studies have demonstrated that APE1 is also enzymatically active on RNA molecules. The present study unveils for the first time a new role of APE1 in the metabolism of RNA in mitochondria. Our data demonstrate that APE1 binds and exerts endoribonuclease activity on abasic mitochondrial messenger RNA. Loss of APE1 determines the accumulation of damaged mitochondrial mRNA species determining impairment in protein translation and reduced expression of mitochondrial encoded proteins, finally leading to less efficient mitochondrial respiration. All these effects are rescued by the expression of a recombinant mitochondrial targeted form of APE1 protein. Altogether, our data demonstrate that APE1 has an active role in the degradation of the mitochondrial mRNAs and a profound impact on mitochondria well-being.