Flap endonuclease 1 repairs DNA-protein cross-links via ADP-ribosylation-dependent mechanisms.

DNA-protein cross-links (DPCs) are among the most detrimental genomic lesions. They are ubiquitously produced by formaldehyde (FA), and failure to repair FA-induced DPCs blocks chromatin-based processes, leading to neurodegeneration and cancer. The type, structure, and repair of FA-induced DPCs remain largely unknown. Here, we profiled the proteome of FA-induced DPCs and found that flap endonuclease 1 (FEN1) resolves FA-induced DPCs. We revealed that FA also damages DNA bases adjoining the DPCs, leading to DPC-conjugated 5' flap structures via the base excision repair (BER) pathway. We also found that FEN1 repairs enzymatic topoisomerase II (TOP2)-DPCs. Furthermore, we report that both FA-induced and TOP2-DPCs are adenosine diphosphate (ADP) ribosylated by poly(ADP-ribose) polymerase 1 (PARP1). PARylation of the DPCs in association with FEN1 PARylation at residue E285 is required for the recruitment of FEN1. Our work unveils the identity of proteins forming FA-induced DPCs and a previously unrecognized PARP1-FEN1 nuclease pathway repairing both FA- and TOP2-DPCs.