PCNA acetylation by CBP/p300 links its degradation to DNA repair synthesis

PCNA protein serves as a molecular platform recruiting and coordinating the activity of factors involved in several DNA transactions. PCNA functions appears to be regulated by different post-translational modifications, such as ubiquitination, phosphorylation and acetylation. Among these, the mechanism responsible for PCNA acetylation has been not yet clarified. In this study we have identified CREB-binding protein (CBP), as another acetyltransferase (p300 homolog) interacting with PCNA. In particular, we have found that PCNA is acetylated after UV-induced DNA damage, and that CBP interacts with PCNA after DNA damage. In vitro, CBP acetylates PCNA more efficiently than p300. MS/MS analysis has shown that acetylation of recombinant PCNA involves lysine (Lys) residues Lys13,14,77 and 80. Expression of PCNA mutated in these residues, resulted in impaired DNA replication and repair, enhanced sensitivity to UV radiation, and activated a DNA damage response (histone H2AX phosphorylation). The same mutations prevented proteolytic degradation of PCNA after DNA damage. Depletion of CBP/p300 in normnal fibroblasts, or failure to load PCNA on DNA in nucleotide excision repair deficient XPA cells, prevented PCNA acetylation and degradation, while proteasome inhibition resulted in accumulation of acetylated PCNA. Our results suggest that CBP/p300 acetylate PCNA in order to link DNA repair synthesis with degradation of PCNA after DNA damage, and provide a novel mechanism to avoid excessive retention of PCNA on chromatin, that is dangerous for genome stability.