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Apoptotic death sensor: an organelle's alter ego?
1MRC Toxicology Unit, Hodgkin Building, University of Leicester, PO Box 138, Lancaster Road, Leicester, UK LE1 9HN. sbb2@le.ac.uk
Abstract:
Caspases are intracellular cysteine proteases that are primarily responsible for the stereotypic morphological and biochemical changes that are associated with apoptosis. Caspases are often activated by the apoptotic protease-activating factor 1 (APAF-1) apoptosome, a complex that is formed following mitochondrial release of cytochrome c in response to many death-inducing stimuli. Both pro- and anti-apoptotic BCL-2 family members regulate apoptosis, primarily by their effects on mitochondria, whereas many inhibitor of apoptosis proteins (IAPs) regulate apoptosis by directly inhibiting distinct caspases. Exposure of cells to chemicals and radiation, as well as loss of trophic stimuli, perturb cellular homeostasis and, depending on the type of cellular stress, particular or multiple organelles appear to 'sense' the damage and signal the cell to undergo apoptosis by stimulating the formation of unique and/or common caspase-activating complexes.
Insights
Caspases, crucial proteases in apoptosis, are activated by complexes like the apoptosome following cellular stress. Various protein families regulate this programmed cell death pathway, impacting cellular homeostasis.
Area of Science:
- Molecular Biology
- Cell Biology
- Biochemistry
Background:
- Caspases are key intracellular cysteine proteases executing apoptosis.
- Apoptosis involves morphological and biochemical changes driven by caspases.
- Caspase activation is tightly regulated by various protein families.
Purpose of the Study:
- To elucidate the regulatory mechanisms of caspase activation in apoptosis.
- To understand the role of protein complexes and cellular stress in apoptosis.
- To explore the interplay between different protein families in controlling apoptosis.
Main Methods:
- Analysis of caspase activation pathways.
- Investigation of apoptosome formation and function.
- Study of BCL-2 family and inhibitor of apoptosis protein (IAP) regulation.
- Examination of cellular responses to various stress stimuli.
Main Results:
- Caspase activation is initiated by the apoptosome, often triggered by mitochondrial cytochrome c release.
- BCL-2 family proteins modulate apoptosis via mitochondrial pathways.
- Inhibitor of apoptosis proteins (IAPs) directly inhibit caspases.
- Cellular stress signals through organelles to activate caspase-dependent apoptosis.
Conclusions:
- Caspases are central executioners of apoptosis, regulated by a complex network of proteins.
- Mitochondrial integrity and cellular stress responses are critical for initiating apoptosis.
- Dysregulation of these pathways can lead to various pathologies.