Apoptosis

Programmed Cell Death

Cancer Cell Apoptosis
This colored scanning electron micrograph (SEM) shows a cancer cell undergoing programmed cell death, or apoptosis. Credit: Steve Gschmeissner/Science Photo Library/Getty Images

What Is Apoptosis?

Apoptosis, or programmed cell death, is a naturally occurring process in the body. It involves a controlled sequence of steps in which cells signal self-termination. Apoptosis works to keep the body's natural cell division process of mitosis in check.

Why Cells Undergo Apoptosis

There are several instances in which cells may need to self-destruct. Cells may need to be removed to ensure proper development.

For instance, the natural process of menstruation involves the breakdown and removal of tissue from the uterus. Cells may also become damaged or undergo some type of infection. One way to remove these cells without causing harm to other cells is through apoptosis.

What Happens During Apoptosis?

Apoptosis is a complex process that involves many pathways. During apoptosis, a cell triggers a process from within that will allow it to commit suicide. If a cell experiences some type of significant stress, such as DNA damage, signals are released which cause mitochondria to release apoptosis-inducing proteins. As a result, the cell undergoes a reduction in size as its cellular components and organelles break down and condense. Bubble shaped balls called blebs appear on the surface of the cell membrane. The cell then breaks down into smaller fragments called apoptotic bodies. These fragments are enclosed in membranes so as not to harm nearby cells.

Then phagocytic cells, such as macrophages, engulf and destroy the apoptotic bodies without causing an inflammatory reaction. Apoptosis can also be triggered externally by chemical substances that bind to specific receptors on the cell surface. This is the pathway used by certain white blood cells to activate apoptosis in infected cells.

Apoptosis and Cancer

Some types of cancers persist as a result of a cell's inability to undergo apoptosis. Tumor viruses change cells by integrating their genetic material with the host cell's DNA. This is a permanent insertion in that the genetic material is never removed. These viruses initiate the production of proteins that stop apoptosis from occurring. An example of this can be seen with papilloma viruses, which have been linked with cervical cancer. Cancer cells that do not develop from viral infection can also produce substances that inhibit apoptosis and promote uncontrolled growth. Radiation and chemical therapies have been used to induce apoptosis in some types of cancers.