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Hsp27 inhibits cytochrome c-mediated caspase activation by sequestering both pro-caspase-3 and cytochrome c
C G Concannon1, S Orrenius, A Samali
1Department of Biochemistry, National University of Ireland, Galway.
Abstract:
Mitochondrial cytochrome c release in response to pro-apoptotic signals leads to the formation of a cytochrome c/Apaf-1/procaspase-9 complex (the apoptosome) and resultant activation of caspase-9 and caspase-3. Here we demonstrate that the molecular chaperone, Hsp27, inhibits this cytochrome c-mediated activation of caspase-3. Immunodepeletion of Hsp27 from cytochrome c-activated cytosols resulted in decreased caspase activity. Furthermore, immunoprecipitation of Hsp27 resulted in the coprecipitation of both cytochrome c and procaspase-3. In reciprocal experiments, immunoprecipitation of both procaspase-3 and cytochrome c resulted in coprecipitation of Hsp27, indicating two independent interactions. These results point to Hsp27 mediating its inhibition of procaspase-3 activation through its ability to sequester both cytochrome c and procaspase-3, and thus prevent the correct formation/function of the apoptosome complex.
Insights
The molecular chaperone Hsp27 inhibits apoptosis by preventing the formation of the apoptosome complex. Hsp27 sequesters cytochrome c and procaspase-3, thereby blocking caspase-3 activation and cell death.
Area of Science:
- Cellular biology
- Molecular biology
- Biochemistry
Background:
- Apoptosis, or programmed cell death, is crucial for development and tissue homeostasis.
- Mitochondrial cytochrome c release initiates the apoptosome complex, activating caspase-3 and driving apoptosis.
- The role of heat shock proteins, like Hsp27, in regulating apoptosis remains an area of active investigation.
Purpose of the Study:
- To investigate the role of the molecular chaperone Hsp27 in the regulation of apoptosis.
- To elucidate the mechanism by which Hsp27 influences cytochrome c-mediated caspase activation.
Main Methods:
- Utilized immunodepletion assays to assess the impact of Hsp27 on caspase activity in cytosols.
- Employed immunoprecipitation techniques to identify molecular interactions between Hsp27, cytochrome c, and procaspase-3.
- Analyzed the formation and function of the apoptosome complex in the presence and absence of Hsp27.
Main Results:
- Hsp27 was found to inhibit cytochrome c-mediated activation of caspase-3.
- Immunodepletion of Hsp27 led to reduced caspase activity in activated cytosols.
- Hsp27 directly interacts with both cytochrome c and procaspase-3, preventing apoptosome assembly.
Conclusions:
- Hsp27 acts as a critical inhibitor of the intrinsic apoptotic pathway.
- Hsp27's mechanism involves sequestering key apoptosome components, cytochrome c and procaspase-3.
- These findings highlight Hsp27 as a potential therapeutic target for modulating apoptosis in disease.