HDAC1 and neoplasm: Because p300 primarily acetylates APE1 in cells [14], and both classical histone deacetylase HDAC1 and NAD+-dependent deacetylase SIRT1 are involved in APE1 deacetylation in cells [14, 39], deregulation of the fine balance between acetyl transferase p300 and HDAC1/SIRT1 deacetylase activity in tumor may elevate APE1 acetylation during tumorigenesis.