tumor protein p53
The TP53 gene provides instructions for making a protein called tumor protein p53 (or p53). This protein acts as a tumor suppressor, which means that it regulates cell division by keeping cells from growing and dividing too fast or in an uncontrolled way.
The p53 protein is located in the nucleus of cells throughout the body, where it attaches (binds) directly to DNA. When the DNA in a cell becomes damaged by agents such as toxic chemicals, radiation, or ultraviolet (UV) rays from sunlight, this protein plays a critical role in determining whether the DNA will be repaired or the damaged cell will self-destruct (undergo apoptosis). If the DNA can be repaired, p53 activates other genes to fix the damage. If the DNA cannot be repaired, this protein prevents the cell from dividing and signals it to undergo apoptosis. By stopping cells with mutated or damaged DNA from dividing, p53 helps prevent the development of tumors.
Because p53 is essential for regulating cell division and preventing tumor formation, it has been nicknamed the "guardian of the genome."
Somatic TP53 gene mutations have been found in some cases of bladder cancer. Most of these mutations change single amino acids in p53. The altered protein cannot bind to DNA, preventing it from effectively regulating cell growth and division. As a result, DNA damage accumulates in cells, which can allow them to grow and divide in an uncontrolled way to form a cancerous tumor. Mutations in the TP53 gene may help predict whether bladder cancer will progress and spread to nearby tissues, and whether the disease will recur after treatment.
Inherited changes in the TP53 gene greatly increase the risk of developing breast cancer, as well as several other forms of cancer, as part of a rare cancer syndrome called Li-Fraumeni syndrome (described below). These mutations are thought to account for only a small fraction of all breast cancer cases.
Noninherited (somatic) mutations in the TP53 gene are much more common than inherited mutations, occurring in 20 to 40 percent of all breast cancers. These somatic mutations are acquired during a person's lifetime and are present only in cells that become cancerous. The cancers associated with somatic mutations do not occur as part of a cancer syndrome. Most of these mutations change single protein building blocks (amino acids) in the p53 protein, which reduces or eliminates the protein's tumor suppressor function. Because the altered protein is less able to regulate cell growth and division, DNA damage can accumulate. This damage may contribute to the development of a cancerous tumor by allowing cells to grow and divide in an uncontrolled way.
Compared with breast cancers without TP53 gene mutations, tumors with these genetic changes tend to have a poorer prognosis. They are more likely to be aggressive, to be resistant to treatment with certain anti-cancer drugs and radiation, and to come back (recur) after treatment.
Somatic mutations in the TP53 gene have been found in nearly half of all head and neck squamous cell carcinomas (HNSCC). This type of cancerous tumor occurs in the moist lining of the mouth, nose, and throat. Most of the TP53 gene mutations involved in HNSCC change single amino acids in p53; these changes impair the protein's function. Without functioning p53, DNA damage builds up in cells, and they can continue to divide without control, leading to tumor formation.
Although somatic mutations in the TP53 gene are found in many types of cancer, Li-Fraumeni syndrome appears to be the only cancer syndrome associated with inherited mutations in this gene. This condition greatly increases the risk of developing several types of cancer, particularly in children and young adults. At least 140 different mutations in the TP53 gene have been identified in individuals with Li-Fraumeni syndrome.
Many of the mutations associated with Li-Fraumeni syndrome change single amino acids in the part of the p53 protein that binds to DNA. Other mutations delete small amounts of DNA from the gene. Mutations in the TP53 gene lead to a version of p53 that cannot regulate cell growth and division effectively. Specifically, the altered protein is unable to trigger apoptosis in cells with mutated or damaged DNA. As a result, DNA damage can accumulate in cells. Such cells may continue to divide in an uncontrolled way, leading to the growth of tumors.
Somatic TP53 gene mutations are common in ovarian cancer, occurring in almost half of ovarian tumors. These mutations result in a p53 protein that is less able to control cell growth and division, contributing to the development of a cancerous tumor.
Somatic mutations in the TP53 gene are the most common genetic changes found in human cancer, occurring in about half of all cancers. In addition to the cancers described above, somatic TP53 gene mutations have been identified in several types of brain tumor, colorectal cancer, liver cancer, lung cancer, a type of bone cancer called osteosarcoma, a cancer of muscle tissue called rhabdomyocarcinoma, and a cancer called adrenocortical carcinoma that affects the outer layer of the adrenal glands (small hormone-producing glands on top of each kidney).
Most TP53 mutations change single amino acids in the p53 protein, which leads to the production of an altered version of the protein that cannot control cell growth and division effectively. As a result, cells can grow and divide in an unregulated way, which can lead to cancerous tumors.
- antigen NY-CO-13
- cellular tumor antigen p53
- P53 tumor suppressor
- phosphoprotein p53
- transformation-related protein 53
- tumor protein p53 (Li-Fraumeni syndrome)
- tumor suppressor p53
- Molecular Biology of the Cell (fourth edition, 2002): Cell-Cycle Progression is Blocked by DNA Damage and p53: DNA Damage Checkpoints
- Molecular Cell Biology (fourth edition, 2000): Mutations in p53 Abolish G1 Checkpoint Control
- National Cancer Institute: Genetics of Breast and Gynecologic Cancers (PDQ)