Opposing regulatory roles of phosphorylation and acetylation in DNA mispair processing by thymine DNA glycosylase

CpG dinucleotides are mutational hotspots associated with cancer and genetic diseases. Thymine DNA glycosylase (TDG) plays an integral role in CpG maintenance by excising mispaired thymine and uracil in a CpG context and also participates in transcriptional regulation via gene-specific CpG demethylation and functional interactions with the transcription machinery. Here, we report that protein kinase C alpha (PKCalpha) interacts with TDG and phosphorylates amino-terminal serine residues adjacent to lysines acetylated by CREB-binding protein (CBP) and p300 (CBP/p300). We establish that acetylation and phosphorylation are mutually exclusive, and their interplay dramatically alters the DNA mispair-processing functions of TDG. Remarkably, acetylation of the amino-terminal region abrogates high-affinity DNA binding and selectively prevents processing of G:T mispairs. In contrast, phosphorylation does not markedly alter DNA interactions, but may preserve G:T processing in vivo by preventing CBP-mediated acetylation. Mutational analysis suggests that the acetyl-acceptor lysines are not directly involved in contacting DNA, but may constitute a conformationally sensitive interface that modulates DNA interactions. These findings reveal opposing roles of CBP/p300 and PKCalpha in regulating the DNA repair functions of TDG and suggest that the interplay of these modifications in vivo may be critically important in the maintenance of CpG dinucleotides and epigenetic regulation.