Regulating p53-mediated apoptosis by modulating DNA-binding domain acetylation

The tumor suppressor gene TP53, is the most commonly mutated gene in human cancer. This gene encodes the p53 protein, which antagonizes tumorigenesis by preventing the accumulation and propagation of gene mutations. In unstressed cells, the p53 tumor suppressor is unstable. Cellular stresses rapidly stabilize and activate p53, a process linked to a complex array of post-translational modifications dynamically deposited onto p53. These modifications orchestrate multiple p53 functions. Specifically, acetylation of p53 at lysine 120 (K120), a DNA-binding domain residue, is essential for triggering apoptosis. The first aim of this study was to identify the cellular stress pathways that can activate acetylation of p53 at K120. Here we identify that both the DNA-damage response and oncogene/p14 ARF pathways stabilize p53 and facilitate the accumulation of K120 acetylation. Defining the enzymatic machinery that regulates the stress-induced modification of p53 at single residue resolution is essential to our understanding of the biochemical mechanisms that control this critical tumor suppressor. We find that K120 acetylation accumulates in response to DNA-damage which also leads to an increase in the activity of the K120 acetyltransferase hMOF. Additionally HDAC1 is found to deacetylate this site on p53. Given the oncogenic properties of deacetylases and the progress of deacetylase inhibitors as potential anti-cancer agents, the deacetylation of K120 was investigated using pharmacologic and genetic approaches. This analysis revealed that HDAC1 is predominantly responsible for the deacetylation of K120 and that this activity requires KAP1 and the NuRD co-repressor complex. Furthermore, treatment with clinically-relevant HDAC inhibitors enhances K120 acetylation, an event that is mechanistically linked to their apoptotic effects. Cancer cells carry inherent genetic damage, but avoid arrest and apoptosis often by inactivating p53 via direct mutation within the DNA-binding domain. The final aim of the study was to evaluate acetylation of K120 on common cancer-derived mutant forms of p53. It appears that the specific type of mutation dictates the ability of p53 to be acetylated at K120. These data expand our understanding of the mechanisms controlling p53 function and suggest that regulation of p53 modification status by targeted therapeutics, can selectively alter p53 pathway function.