The p53 Protein: Mutations, Cancer & Cell Signalling

This article contains an overview of the p53 protein, including its function and signalling pathway. It also looks at p53 protein domains, p53 target genes and the relationship between p53 mutations and cancer.  

What is p53?

P53 is a protein that helps to regulate the cell cycle and prevent genome mutations. It is found in the nucleus of cells and works to repair damaged DNA. The protein is made up of 53 amino acids. If p53 is not functioning properly, it can lead to cancer. It is encoded by a gene called TP53, which is located on chromosome 17. The main difference between p53 and tp53 is that p53 is a protein, while tp53 is a gene. TP53 is one of the most important tumor suppressor genes in humans. p53 is a protein that is essential for the regulation of cell growth and division.



Schematic of p53 and its relevant areas

Example p53 standard curve

How is p53 measured?

Cell technology can be used to measure p53 protein levels. Cell-based ELISA or western blotting are most commonly used to measure the total amount of p53 protein in a cell. In addition, immunofluorescence or immunohistochemistry can be used to detect p53 protein in specific cell types or in cells that are actively undergoing apoptosis. ELISA (enzyme-linked immunosorbent assay) is a type of immunoassay that is used to detect and measure p53 protein levels in a sample. ELISA can be used to measure both the total amount of p53 protein and the amount of active, or phosphorylated, p53 protein.

p53 Signalling Pathway

The p53 signalling pathway is a stress response pathway that is activated in response to stress signals. These stress signals can be caused by DNA damage, UV radiation, or other cellular stresses. The p53 signalling pathway leads to the activation of p53, which then regulates the cell cycle and prevents genome mutations.

Input signals :

- DNA damage

- UV radiation

- Other cellular stresses

Activation of p53 :

- Regulation of cell cycle

- Prevention of genome mutations

The p53 signalling pathway is important for the maintenance of genomic stability and the prevention of cancer.

As mentioned, the p53 signalling pathway is activated by stress signals and they can cause the release of p53 from its inhibitor, MDM2. Once released, p53 binds to DNA and promotes the transcription of genes that lead to cell cycle arrest or apoptosis. Cell cycle arrest allows damaged cells to repair their DNA before replicating. Apoptosis is a process of programmed cell death that prevents damaged cells from replicating and spreading mutations.

p53 is a key regulator of senescence, a process by which cells stop dividing and enter a state of permanent growth arrest. Senescent cells are thought to play an important role in the aging process and in the development of age-related diseases.

p53 is also involved in the regulation of cell proliferation. In response to stress signals, p53 can induce cell cycle arrest or apoptosis. However, under normal conditions, p53 actually promotes cell proliferation by inhibiting senescence. This ensures that cells can continue to divide and proliferate in response to growth signals.

p53 Protein Domains

p53 is a 53 amino acid protein that is encoded by the TP53 gene. The protein contains several important domains including a transcriptional activation domain, a sequence specific DNA binding domain, and a tetramerization domain.

The transcriptional activation domain allows p53 to bind to promoters of genes and activate their transcription. The sequence specific DNA binding domain enables p53 to bind to specific sequences of DNA. The tetramerization domain allows p53 to form dimers and tetramers, which is important for its function.

Schematic of p53 known protein domains

p53 protein levels are regulated by several mechanisms including transcription, translation, post-translational modification, and degradation.

Transcription of the TP53 gene is regulated by several transcription factors including p53, E2F1, and MYC. Translation of the TP53 mRNA is regulated by the mTOR pathway. Post-translational modification of p53 protein can occur through phosphorylation, acetylation, or ubiquitination.

Phosphorylation of p53 protein by kinases such as ATM, ATR, or MAPK can lead to its activation. Acetylation of p53 protein by acetyltransferases such as p300 or CBP can also lead to its activation. Ubiquitination of p53 protein by ubiquitin ligases such as MDM2 or CHIP can lead to its degradation.

p53 Target Genes

Genes that are regulated by p53 include:

  • BAX: pro-apoptotic protein
  • MDM2: inhibitor of p53
  • P21: cell cycle regulator
  • PUMA: pro-apoptotic protein
  • NOXA: pro-apoptotic protein
  • BIRC5: anti-apoptotic protein
  • CyclinB1: cell cycle regulator

Functions of these genes include:

  • cell cycle regulation
  • DNA repair
  • apoptosis

The p53 protein regulates the expression of these genes in response to stress signals. Under normal conditions, p53 levels are low and these genes are expressed at low levels. However, when DNA is damaged or other stress signals are present, p53 levels increase and this leads to the increased expression of these genes. The proteins encoded by these genes then mediate the cell's response to the stress. This can lead to cell cycle arrest, DNA repair, or apoptosis.

p53 Related Products

Product Name Reactivity Sample Types


Serum, Plasma, Cell lysate

Human, Mouse, Rat


Human, Mouse

Nuclear or Cell Lysates

Human, Mouse, Rat


p53 Mutations and Cancer

Mutations are changes in the DNA that can lead to cancer. Mutations in TP53 are are thought to be involved in more than half of all human cancers including breast cancer, lung cancer, and colorectal cancer. p53 is sometimes called the "guardian of the genome" because of its important role in preventing mutations. p53 helps to prevent these mutations by causing cells with damaged DNA to either repair themselves or die (apoptosis). p53 protein levels are normally very low. When DNA is damaged, p53 levels increase. Some chemotherapy drugs work by damaging DNA and increasing p53 levels. This can cause cancer cells to undergo apoptosis. However, it is still not clear how these mutations lead to cancer. One possibility is that they cause a loss of function of the protein. Another possibility is that they cause the protein to become overly active. More research is needed to understand how p53 mutations contribute to cancer.

Why is a mutation in the p53 gene so important?

p53 mutations are often found in tumors that have developed resistance to chemotherapy. This is because the drugs that are used to treat cancer work by damaging DNA and increasing p53 levels. However, in tumors with p53 mutations, the protein does not function properly and these drugs are not as effective.

There are several ways to detect p53 mutations. One way is to look for changes in the DNA sequence. Another way is to look for changes in the structure of the protein. The most common method is to look for changes in the expression of p53 target genes.

p53 mutations are important not only for their role in cancer, but also for their potential as targets for new cancer treatments. There are several drugs that are being developed that target p53 mutations. These drugs work by either restoring the function of the protein or by preventing the protein from becoming overly active. More research is needed to determine if these drugs are effective in humans.

p53 Future Research

There is still much that is unknown about p53. More research is needed to understand how p53 mutations lead to cancer and to develop more effective treatments for cancer. Additionally, more research is needed to understand the role of p53 in normal cell physiology and how its function is regulated.

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26th Jul 2022 Niamh Murphy MSc

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