CDK5 and cancer: We have recently shown that acetylation level of APE1 increases in S-phase of the cell cycle [37], when p300 is also activated [67], and thus cell proliferation could be a trigger for enhanced APE1 acetylation in cancer Furthermore, enhanced phosphorylation of APE1 by PKC or Cdk5 which is often overexpressed in some cancers may alter the acetylation level of APE1 [22, 68].