Explain the difference between a proto-oncogene and an oncogene, and the relevance of gain-of-function mutations in these genes. Give an example of an oncogene that is common to many cancers.
A proto-oncogene is a normal gene that can become an oncogene, a gene that promotes the development of cancer, through mutations. Gain-of-function mutations in proto-oncogenes result in the production of an overactive oncogene protein, leading to uncontrolled cell growth and division.
An example of an oncogene that is common to many cancers is the RAS gene, which is involved in signaling pathways that regulate cell growth and division. Mutations in RAS genes can lead to the production of an overactive RAS protein, resulting in uncontrolled cell growth and the development of various types of cancers, including colon, pancreatic, and lung cancers.
P53 is a tumor suppressor gene that plays a crucial role in preventing cancer. It regulates the cell cycle and acts as a checkpoint to ensure that damaged DNA is repaired before cell division takes place. If DNA damage cannot be repaired, p53 triggers cellular processes that either repair the damage or cause the cell to undergo programmed cell death (apoptosis). When p53 is mutated or otherwise nonfunctional, it can no longer perform its tumor suppressor function, allowing damaged cells to divide and potentially leading to the development of cancer. Mutations in the p53 gene are present in over 50% of all human cancers.