Proto-oncogenes are normal genes that can lead to cancer if they are mutated or expressed at abnormally high levels. A gene is a biological unit that contains hereditary information within an organism that is necessary for producing certain proteins. An oncogene is a gene that causes cancer by causing certain cells to grow and proliferate at unmoderated rates. Normal cells eventually undergo apoptosis, or cellular death, but cancerous cells do not; they grow and proliferate until the organism containing them is dead. In many cases, a proto-oncogene must be activated by some environmental factor before it is actually able to cause cancer.
Proto-oncogenes contain genetic information that is used to produce proteins that control and moderate cellular growth and proliferation. They often contain code necessary to the signaling mechanisms responsible for cell division and for programmed cell death. This regulation is necessary for health and actually serves to prevent cancer in healthy people. Once activation occurs through some small modification of these genes, however, proto-oncogenes cease to be healthy regulatory genes and instead become tumor-causing oncogenes. The proteins and signaling mechanisms they code for no longer cause programmed cell death and proper cellular division; they instead cause cellular immortality and uncontrolled division.
There are many different mechanisms through which proto-oncogenes can be activated and turned into tumor-forming oncogenes. A simple mutation on the gene alters the structure and function of the proteins for which it codes; this has the potential to lead to cancer. In some cases, the gene itself remains unchanged, but various factors that regulate the proteins cease to function properly. Proteins that cause cell division, for example, could be far more prevalent than they are supposed to be, leading to uncontrolled cell division and tumor formation.
Another mechanism that can activate proto-oncogenes is known as a chromosomal translocation. Chromosomal translocations are genetic anomalies in which various parts of genetic information are rearranged. This may cause certain types of proteins to become active in the wrong types of cells. It may also lead to the formation of hybrid proteins, such as those that can lead to leukemia.
Proto-oncogenes are important to medical researchers because of their roles in causing cancer. Researchers try to design drugs that can specifically target proto-oncogenes and the proteins they produce. They do so with the aim of correcting the abnormalities that caused the proto-oncogenes to be activated into cancer-causing oncogenes. They may also try to inhibit the proteins produced by the genes.