Site-specific acetylation of polynucleotide kinase 3’-phosphatase (PNKP) regulates its distinct role in DNA repair pathways

Abstract

Mammalian polynucleotide kinase 3’-phosphatase (PNKP) is a dual-function DNA endprocessing enzyme with 3’-phosphatase and 5’-kinase activities, which generate 3’-OH and 5’- phosphate termini respectively, as substrates for DNA polymerase and DNA ligase to complete DNA repair. PNKP is thus involved in multiple DNA repair pathways, including base excision (BER), single-strand break (SSBR), and double-strand break repair (DSBR). However, little is known as to how PNKP functions in such diverse repair processes, involving distinct sets of proteins. Here, we report that PNKP is acetylated at two lysine (K142 and K226) residues. While K142 is constitutively acetylated by p300, CBP acetylates K226 only after DSB induction. Coimmunoprecipitation analysis involving antibodies specific for PNKP peptides containing AcK142 or AcK226 of PNKP showed that AcK142-PNKP associates only with BER/SSBR and AcK226 PNKP with DSBR proteins. Although acetylation at those residues did not significantly affect the enzymatic activity of PNKP in vitro, cells expressing non-acetylable PNKP (K142R or K226R) accumulated DNA damage, specifically in transcribed genes. Intriguingly, K142, but not K226, was acetylated in striatal neuronal cells of a Huntington’s Disease (HD)-based mouse model.