Understanding p53 functions through p53 antibodies

Abstract

TP53 is the most frequently mutated gene across all cancer types. Our understanding of its functions has evolved since its discovery four decades ago. Initially thought to be an oncogene, it was later realized to be a critical tumour suppressor. A significant amount of our knowledge about p53 functions have come from the use of antibodies against its various forms. The early anti-p53 antibodies contributed to the recognition of p53 accumulation as a common feature of cancer cells and to our understanding of p53 DNA-binding and transcription activities. They led to the concept that conformational changes can facilitate p53's activity as a growth inhibitory protein. The ensuing p53 conformational-specific antibodies further underlined p53's conformational flexibility, collectively forming the basis for current efforts to generate therapeutic molecules capable of altering the conformation of mutant p53. A subsequent barrage of antibodies against post-translational modifications on p53 has clarified p53's roles further, especially with respect to the mechanistic details and context-dependence of its activity. More recently, the generation of p53 mutation-specific antibodies have highlighted the possibility to go beyond the general framework of our comprehension of mutant p53-and promises to provide insights into the specific properties of individual p53 mutants. This review summarizes our current knowledge of p53 functions derived through the major classes of anti-p53 antibodies, which could be a paradigm for understanding other molecular events in health and disease.

Keywords: antibodies; conformation; mutant; p53; post-translational modifications.

Figure 1

Schematic of the major PTMs on p53 evaluated with PTM-specific antibodies. Phosphorylation status on the specific residues at baseline and upon DNA damage, as evaluated using the respective phosphorylation-specific antibodies, are highlighted in the upper panel above the p53 cartoon. ‘+’ indicates phosphorylation. ‘+’ in black indicates activation of p53 stability/function upon phosphorylation, whereas in red indicates degradation of p53 after phosphorylation. Lower panel shows the status of acetylation (black font) and methylation (blue font) at baseline and upon DNA damage, determined using the respective PTM-specific antibodies. All acetylation events reported so far lead to p53 activation (indicated by ‘+’). However, only methylation at K372 leads to p53 activation. Methylation at the other three sites lead to inactivation of p53, represented by ‘(+)’. Amino acid residues are reflected (not to scale), together with the major p53 domains. TA, transactivation; DBD, DNA-binding domain; OD, oligomerization domain. Other PTMs on p53, such as ubiquitination and SUMOylation, are not included in this review.