Covalent PARylation of DNA base excision repair proteins regulates DNA demethylation

Poly(ADP-ribose) polymerases (PARP1 and PARP2) contribute to DNA base excision repair (BER) and DNA demethylation and has been implicated in epigenetic programming in early mammalian development. Recently, proteomic analyses identified BER proteins to be covalently poly-ADP-ribosylated by PARPs. The role of this posttranslational modification in the BER process is unknown. Here, we show that PARP1 senses AP-sites and SSBs generated during TET-TDG mediated active DNA demethylation and covalently attaches PAR to each BER protein engaged. Covalent PARylation dissociates BER proteins from DNA, which accelerates completion of the repair process. Consistently, inhibition of PARylation in mESC resulted both in reduced locus specific TET-TDG-targeted DNA demethylation, and in reduced general repair of random DNA damage. Our findings establish a critical function of covalent protein PARylation in coordinating molecular processes associated with dynamic DNA methylation. Single-strand break sequencing of 2i-cultivated murine embryonic stem cells (+/- TDG), treated with PARP-inhibitor Talazoparib