Apoptosis

Need for apoptosis - Many organisms exhibit a process of programmed cell death called apoptosis. There are many needs for this process. During development in the growing embryo, tissues present at one stage must be removed as development proceeds - for example, the "webbing" that humans have between fingers at a certain point in fetal life. Also, in adults, damaged, imperfect, or infected cells need to be removed for the health of the organism.

Caspase cascade - The caspases are proteases that all cleave to the carboxyl side of aspartate (c-asp-ase) and are all synthesized as inactive precursors that can be activated by just such a cleavage. Thus, there is the possibility of a caspase cascade, once activation is triggered. There are a large number of potential cytoplasmic, mitochondrial, and extracellular triggers of caspases. These include interferon and tumor necrosis factor, a protein long known to inhibit tumor growth by interaction with cell surface receptors. The latter have been implicated in caspase activation. Once the caspase cascade has started, destruction is wholesale. The proteins known to be cleaved by caspases cover a wide range, from structural proteins (like actin and nuclear lamin) to transcription factors and splicing factors (see here). Nucleases are activated to digest the cell's DNA. The cell disintegrates into fragments that are recognized by phagocytes and fully destroyed.

See also: Eukaryotic DNA and Development, Oncogenes in Human Tumors (from Chapter 23), p53

INTERNET LINKS:

> 1. Apoptosis Resource Guide

> 2. Apoptosis