 include pollutants in the air, such as cigarette smoke, too much ultraviolet radiation (such as excessive sun tanning or tanning booths), or other pollutants in the water or food. Such causes of mutation are called mutagens. Avoiding mutagens is an important strategy for avoiding cancer in the long term.
7. Another important proto-oncogene is called p53. p53 is also called the guardian of the cell, because it helps to ensure that DNA replication finishes properly before cell division occurs. It works as follows. When DNA replication occurs properly, p53 signals to the cell to continue to divide. On the other hand, if DNA replication has a problem and can't finish, p53 stops the cell in its tracks and stimulates the synthesis of proteins that help to repair damaged DNA. If the proteins can repair the damage, then p53 signals the cell to divide. If the proteins can't fix the damage, then p53 signals the cell to commit suicide.
8. Cellular suicide (called apoptosis) is important for a multicellular organism. If cells do not commit suicide when they are damaged, they may turn cancerous and kill the organism. Not surprisingly, p53 is found to be mutated in many cancers. A mutated p53 can't stimulate suicide when cells need to do so, allowing the cancer to get established.
9. DNA repair proteins are very important in preventing cancer too. BRC-A is an important DNA repair protein that is often found mutated in breast cancer.
10. Treating cancers involves several strategies, including radiation (damaging the DNA) and chemicals (chemotherapy) targeted at killing cancer cells. The search for a "magic bullet" is aimed at finding something that will kill cancer cells without negatively affecting normal cells.
11. One interesting approach to a "magic bullet" is that of the anti-cancer drug called gleevec. Gleevec is designed to kill cells that have an unusual protein in them called bcr-abl. Bcr-abl arises in cells when the coding region of the bcr gene fuses with part of the coding region of the abl gene. This fusion gives rise to a type of leukemia called CML. Normal cells do not have bcr-abl, but CML cells have it. Gleevec targets these cancer cells fairly effectively and has few side effects.