Tumor Cell Apoptosis
Apoptosis is a specific type of cell death. While cells can be killed when they are either damaged or exposed to toxic agents, apoptosis is programmed cell death that usually occurs to the benefit of the organism as a whole. There are a number of specific reasons why apoptosis occurs, and a variety of set metabolic pathways that set it in motion. Tumor cells are characterized by their ability to bypass apoptosis, which is why cancer medications that induce tumor cell apoptosis are a major focus of cancer treatment research.
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Definition
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Apoptosis is a metabolic pathway that, if triggered by certain circumstances, will cause a cell to begin a series of actions that will result in its own death. Also known as PCD, or programmed cell death, a cell that is induced into apoptosis will shrink in size, develop abnormal bubbles in its cell membrane, then degrade its own DNA and organelles. Certain phospholipid compounds are exposed on the surfaces of the cell fragments that are then disposed of by white blood cells responsible for ridding the body of bacteria and foreign particles. Apoptosis is a normal part of any organism's life cycle and occurs for a number of reasons.
Reasons
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Apoptosis is beneficial to an organism. It occurs for two main reasons: as a regular part of development and as a way to prevent potentially harmful cells from hurting the organism as a whole. During development, apoptosis occurs regularly in the formation of certain intricate portions of the body, for example in the development of the fingers and toes. Additionally, cells that have become infected with viruses or have damage to their DNA are regularly triggered to begin apoptosis.
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Procedure
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A cell is triggered into apoptosis by two things: a decrease in the amount of positive growth factors it receives from other cells and an increase in the number of cell death-activating molecules that bind to its cellular membrane. These death activators include lymphotoxin and tumor necrosis factor-alpha, both of which work to trigger apoptosis.
Absence of Apoptosis in Tumor Cells
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One of the most dangerous aspects of cancer is when the cells contained within tumors have abnormalities that prevent these cells that would normally be triggered into programmed cell death from going into apoptosis. This allows these cells to continue to grow and hinder the proper function of the systems and organs they are infiltrating. Both cancers known to be caused by viruses (such as HPV, or the human papillloma virus) and other, nonviral, cancers have developed ways to prevent cell apoptosis.
Apoptosis-Inducing Tumor Treatments
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A number of cancer treatments center on triggering previously apoptosis-resistant tumor cells into entering programmed cell death. Both radiation therapy and chemotherapy are effective in causing apoptosis in certain types of cancers. Tumor cells resistant to these types of therapy -- such as certain types of leukemia -- have been found to respond to specially developed apoptosis-inducing compounds.
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