Decoding p53: the guardian against cancer

Being a tumour suppressor protein, p53 encoded by the TP53 gene plays a critical role in regulating cell division and preventing the formation of tumours. Its function in maintaining genome stability is vital in inhibiting cancer development.

Understanding p53

Located on chromosome locus 17p13.1, TP53 encodes the p53 transcription factor 1. Consisting of three domains, p53 can directly initiate or suppress the expression of 3661 different genes involved in cell cycle control and DNA repair 2. With this control, p53 can influence cell division on a massive scale. Cancer is characterised by uncontrolled cell division, which can occur due to accumulated mutations in either proto-oncogenes or tumour suppressor genes. Wild-type p53 can repair mutations in oncogenes such that they will not affect cell division. However, if p53 itself is mutated, then its ability to repair DNA and control the cell cycle is inhibited, leading to the emergence of cancer. Mutations in TP53 are actually the most prevalent genetic alterations found in patients with cancer. The mechanisms by which mutated p53 leads to cancer are manifold. One such mechanism is p53’s interaction with p21. Encoded by CDKN1A, p21 is activated by p53 and prevents cell cycle progression by inhibiting the activity of cyclin-dependent kinases (CDKs). Therefore, we can see that a non-functional p53 would lead directly to uncontrolled cell division and cancer.

Clinical significance

The importance of p53 in preventing cancer is highlighted by the fact that individuals with inherited TP53 mutations (a condition known as Li-Fraumeni syndrome or LFS) have a significantly greater risk of developing any cancer. These individuals inherit one defective TP53 allele from one parent, making them highly susceptible to losing the remaining functional TP53 allele, ultimately leading to cancer. Loss of p53 also endows cells with the ability to ignore pro-apoptotic signals such that if a cell becomes cancerous, it is far less likely to undergo programmed cell death 3. Its interactions with the apoptosis-inducing proteins Bax and Bak, are lost when mutated, thus leading to cellular apoptosis resistance.

The R337H mutation in TP53 is an example of the founder effect at work. The founder effect refers to the loss of genetic variation when a large population descends from a smaller population of fewer individuals. The descendants of the initial population are much more likely to harbour genetic variations that are less common in the species as a whole. In southern Brazil, the R337H mutation in p53 is present at an unusually high frequency 4 and is thought to have been introduced by European settlers several hundred years ago. It is responsible for a widespread incidence of early-onset breast cancers, LFS, and paediatric adrenocortical tumours. Interestingly, individuals with this mutation can trace their lineage back to the group of European settlers that set foot in Brazil hundreds of years ago.

Studying p53 has enabled us to unveil its intricate web of interactions with other proteins and molecules within the cell and unlock the secrets of cancer development and potential therapeutic strategies. By restoring or mimicking the functions of p53, we may be able to provide cancer patients with some relief from this life-changing condition.

Written by Malintha Hewa Batage