Caspases are highly important proteins that are essential for the completion of apoptosis, or programmed cell death, in a wide variety of organisms. Apoptosis specifically refers to the intentional and beneficial death of cells within the body. Caspases are sometimes referred to as executioner proteins because of the particular relationship between caspases and apoptosis. There are many different types of caspases that work together to cause physiological changes within cells that lead to cell death.
Caspases are cysteine proteases, meaning that they are proteins that cleave polypeptides. In particular, they act on the amino acid cysteine, a common component in many different proteins. Though their core components are quite similar, different types of caspases with different specificities are necessary for apoptosis.
The relationship between caspases and apoptosis is highly complex and is of great interest in biomedical research. There are several different types of caspases that are necessary to bring about apoptosis. Initiator caspases, for example, cleave certain parts of effector caspases, effectively "activating" them. These activated effector caspases go on to cleave certain cellular components that are necessary for the cell's continued survival. Other proteins known as caspase inhibitors can effectively stop this process at various stages, thereby preventing apoptosis.
The regulation of caspases is necessary to ensure that the relationship between caspases and apoptosis is not harmful. Normally, apoptosis is a good thing; if it occurs at too rapid or too slow a rate, however, it can be destructive. The primary regulation of caspases occurs after translation, meaning that regulation does not occur until after genetic information has been used to produce the proteins. The caspases, then, are immediately available if needed, as the proteins themselves are inhibited or activated, not their production. If regulation occurred before translation, there would be a lag time between the need for the proteins and their actual action, as the proteins would need to be synthesized before they could act.
Caspases and apoptosis are notable in part because of their roles in cancer. One of the characteristics of cancer is that cancerous cells do not undergo apoptosis, so they are able to replicate indefinitely without succumbing to normal cellular death. Many cancerous tissue samples have been found to have very low levels of one or more caspases, so the normal pathways that lead to cellular death are not allowed to proceed to completion. Researchers are very interested in caspases and apoptosis because of the possibility of developing treatment methods based on using caspases to induce apoptosis.