Area Around My Mole Hurts To Touch

Introduction to Apoptosis (Part Three)

By: Lionel Perez Valenzuela

Mechanism of apoptosis

Most cells need to survive a continuous stimulation of other cells, and many of them also need to be attached to the extracellular matrix.

Some of survival signals (positive signals) are:

a) growth factors and hormones.

b) Interleukin-2 (IL-2), which is essential for mitosis of lymphocytes.

Moreover cells also receive a steady stream of negative signals (signs of death), related in many cases aging cells or exposed to radiation or toxic chemicals, among them we can mention:

a) High levels of oxidants within the cell

b) Damage to DNA by oxidants or other agents such as ultraviolet light, x-rays, drugs, mutagenic

c) Accumulation of protein that fail to fold, so its tertiary structure is incorrect

Other death signals are mediated by certain molecules (ligands) that bind to specific receptors on the cell surface, to start the apoptotic program . That is, certain cell types undergo a selection according to their characteristics, some cells survive, whereas others were ordered activate the apoptotic program. These factors of death include:

- tumor necrosis factor alpha (TNF-alpha) that binds to TNF.

- The lymphotoxin (also known as TNF-beta) that also binds to TNF receptor.

- Fas ligand (Fas L), a molecule that binds to surface receptor known as Fas (also known as CD95).

For example in the immune system to eliminate autoreactive cells (ie that can attack the body itself) through apoptosis, and allows cells to survive that distinguish self from foreign. They were also directed to transformed cells (tumor), activate the apoptotic program. During maturation of the nervous system, a large number of neurons undergoing apoptosis, not receiving appropriate survival stimuli, did not form correct synapses.

Therefore the survival of the cell is determined by a balance between the positive signs of survival (presence or absence) and the receipt of negative signals.

Molecular mechanisms of apoptosis

There are basically two major molecular mechanisms by which a cell commits apoptosis.

1) Via intrinsic or mitochondrial pathway : death signals that occur within the cell.

2) extrinsic or death receptor : death-activating signals arriving from abroad. These signals binds to receptors on the cell surface.

In the next article we will see in detail, how they act at the molecular level the intrinsic (mitochondrial) and extrinsic (receptor demuerte).