 ACTIVATION AND INHIBITION OF APOPTOSIS
Douglas K. Miller, Ph.D.
Department of Immunology and Rheumatology
Merck Research Laboratories
Rahway, NJ 07065
Apoptosis Overview:
Apoptotic cell death has been characterized by a progressive series of morphological and biochemical changes ranging from the appearance on cell surfaces of phosphatidylserine, to proteolytic cleavage of numerous intracellular proteins, to nuclear condensation and fragmentation and the cleavage of DNA into nucleosomal fragments.1 Principally two mechanisms have been identified in mammalian cells for the induction of apoptosis: agents that lead to the perturbation of mitochondria, resulting in the leakage of cytochrome C and the activation of apoptosis; or agents that directly activate a family of death receptors leading to the activation of a parallel apoptotic cascade. Proapoptotic agents such as the activation of p53, growth factor withdrawal, irradiation, activated oxygen, and cytotoxic drugs induce their effects through the mitochondrial pathway.2 The mammalian proteins involved in this pathway have to a large extent been identified as homologs of the C. elegans genes originally identified as necessary for apoptotic control.3 Three proteins acted at the core of this pathway: Ced-3, Ced-4, and Ced-9. While Ced-3 was shown to be essential for the execution of apoptosis, the cytoplasmic protein Ced-4 was identified as an adapter protein that activated Ced-3.4 The mitochondrial protein Ced-9 in turn controlled the activation of Ced-4.5 Ced-3 produced the cellular cleavages necessary to induce apoptosis, and this protein was later shown to be a caspase.6 |
