When tumor suppressor genes mutate, their products no longer inhibit the cell cycle or promote apoptosis (the death of cells occurs as a regular and controlled part of an organism’s growth or development). Therefore, these mutations can be called “loss-of-function,” or recessive mutations. Unlike proto-oncogenes, both copies of the tumor suppressor gene in the cell must be mutated to lose cell cycle control. In normal cells, tumor suppressor genes prevent cancer by slowing or stopping cell growth. DNA changes that inactivate tumor suppressor genes can lead to uncontrolled cell growth and cancer.
Mutation of the tumor suppressor gene Bax is a good example. Its product, the protein Bax, promotes apoptosis. When Bax mutates, Bax protein is absent, and apoptosis is less likely to occur. The Bax gene contains a line of eight consecutive G bases in its DNA. When the same base molecules are lined up in this fashion, the gene is more likely to be subject to mutation. Another tumor suppressor protein, p53, activates DNA repair enzymes. At the same time, p53 turns on genes that stop the cell cycle from proceeding. If repair is impossible, the p53 protein promotes apoptosis. Apoptosis is an essential way for carcinogenesis to be prevented. Many tumors are lacking in p53 activity. The BRCA1 gene codes for another DNA repair enzyme, one that is responsible for fixing breaks in the DNA molecule. It works very closely with the p53 protein. BRCA1 mutations prevent the body from recognizing DNA damage, allowing the cells to progress through the cell cycle unchecked. BRCA1 mutations are associated with several cancers, including breast cancer. Mutations in tumor suppressor genes cause a loss of cell cycle control. Usually, tumor suppressor genes code for a protein that inhibits the cell cycle. If mutations occur, the resulting protein loses control of the cell cycle.ChatGPT
When tumor suppressor genes undergo mutations, their products lose the ability to inhibit the cell cycle or promote apoptosis. These mutations are commonly referred to as “loss-of-function” or recessive mutations. Unlike proto-oncogenes, which only require one mutated copy to lose control over the cell cycle, both copies of the tumor suppressor gene in the cell must be mutated to lead to the loss of cell cycle control.
A notable example of this phenomenon is the tumor suppressor gene Bax. The Bax gene contains a consecutive line of eight G bases in its DNA, which makes it more prone to mutation. The Bax protein typically promotes apoptosis. However, when the Bax gene mutates, the production of the Bax protein is affected, resulting in reduced apoptosis likelihood.
Another crucial tumor suppressor protein, p53, plays a dual role. It activates DNA repair enzymes and simultaneously activates genes that halt the cell cycle when DNA damage is detected. If the DNA damage is irreparable, the p53 protein promotes apoptosis, a vital mechanism to prevent carcinogenesis. Unfortunately, many tumors lack sufficient p53 activity, allowing damaged cells to continue dividing unchecked.
The BRCA1 gene codes for a DNA repair enzyme that fixes breaks in the DNA molecule. It closely collaborates with the p53 protein. Mutations in the BRCA1 gene disrupt the body’s ability to recognize DNA damage, enabling cells to progress through the cell cycle without appropriate checks. Consequently, BRCA1 mutations are associated with various cancers, including breast cancer.
In summary, mutations in tumor suppressor genes lead to a loss of cell cycle control. Typically, these genes code for proteins that inhibit the cell cycle. When mutations occur, the resulting proteins lose their ability to regulate the cell cycle effectively. This loss of control over cell division can contribute to cancer development.
reference
https://www.facebook.com/groups/250707520782951
www.cancer.gov/about-cancer/understanding/what-is-cancer.