NPM1 and APE1: nucleolar teamwork in controlling base excision DNA repair

Abstract

Apurinic/apyrimidinic endonuclease 1 (APE1), the main abasic endonuclease in base excision repair (BER) acting on oxidative and alkylation DNA lesions, is a promising target for anticancer therapy. In nucleoli, APE1 interacts through N‐terminal lysine residues with nucleophosmin 1 (NPM1). We used a reconstitution strategy to address the impact of the NPM1‐APE1 interaction on resistance to genotoxic damage. Lysine‐mutated APE1 proteins were expressed while endogenous APE1 was silenced by siRNA to address the role of APE1 acetylation during cell response to DNA damage and a NPM1 knock‐out system to determine its role in modulating APE1 in BER pathway. We demonstrated that APE1 acetylation at lysines 27, 31, 32 and 35, enhanced by genotoxic stress, inhibited binding to NPM1 and promoted re‐localization of APE1 from nucleoli to the nucleoplasm. Interestingly, NPM1 stimulated APE1 BER activity in vivo, since cells lacking NPM1 were more sensitive to bleomycin or alkylating agents and displayed impaired DNA repair. These results highlight an unexpected role for NPM1 and the nucleolus in coordinating APE1 and BER pathways, and point to acetylation at critical lysine residues for controlling subnuclear protein trafficking during DNA repair.This work is supported by grants from AIRC and FIRB.