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Different subcellular distribution of caspase-3 and caspase-7 following Fas-induced apoptosis in mouse liver
J M Chandler1, G M Cohen, M MacFarlane
1Medical Research Council Toxicology Unit, Hodgkin Building, University of Leicester, P. O. Box 138, Lancaster Road, Leicester LE1 9HN, United Kingdom.
Abstract:
Caspases plays a key role in the execution phase of apoptosis. "Initiator" caspases, such as caspase-8, activate "effector" caspases, such as caspase-3 and -7, which subsequently cleave cellular substrates thereby precipitating the dramatic morphological changes of apoptosis. Following treatment of mice with an agonistic anti-Fas antibody to induce massive hepatocyte apoptosis, we now demonstrate a distinct subcellular localization of the effector caspases-3 and -7. Active caspase-3 is confined primarily to the cytosol, whereas active caspase-7 is associated almost exclusively with the mitochondrial and microsomal fractions. These data suggest that caspases-3 and -7 exert their primary functions in different cellular compartments and offer a possible explanation of the presence of caspase homologs with overlapping substrate specificities. Translocation and activation of caspase-7 to the endoplasmic reticulum correlates with the proteolytic cleavage of the endoplasmic reticular-specific substrate, sterol regulatory element-binding protein 1. Liver damage, induction of apoptosis, activation and translocation of caspase-7, and proteolysis of sterol regulatory element-binding protein 1 are all blocked by the caspase inhibitor, benzyloxycarbonyl-Val-Ala-Asp fluoromethyl ketone (Z-VAD. fmk). Our data demonstrate for the first time the differential subcellular compartmentalization of specific effector caspases following the induction of apoptosis in vivo.
Insights
This study reveals that effector caspases-3 and -7 localize to different cellular compartments during apoptosis. This differential localization of caspases suggests distinct roles in the cell death process.
Area of Science:
- Cell Biology
- Molecular Biology
- Biochemistry
Background:
- Caspases are critical executioners of apoptosis, mediating programmed cell death.
- Initiator caspases activate effector caspases, leading to substrate cleavage and apoptotic morphology.
Purpose of the Study:
- To investigate the subcellular localization of effector caspases-3 and -7 during apoptosis in vivo.
- To understand the functional implications of differential caspase localization.
Main Methods:
- Induction of hepatocyte apoptosis in mice using an agonistic anti-Fas antibody.
- Analysis of subcellular fractions to determine caspase localization.
- Inhibition of caspases using benzyloxycarbonyl-Val-Ala-Asp fluoromethyl ketone (Z-VAD.fmk).
Main Results:
- Active caspase-3 was primarily found in the cytosol.
- Active caspase-7 was predominantly associated with mitochondrial and microsomal fractions.
- Caspase-7 translocation to the endoplasmic reticulum correlated with sterol regulatory element-binding protein 1 cleavage.
- Z-VAD.fmk blocked liver damage, apoptosis, caspase-7 activation/translocation, and substrate proteolysis.
Conclusions:
- Effector caspases-3 and -7 exhibit distinct subcellular compartmentalization during apoptosis.
- This differential localization suggests specialized functions in different cellular compartments.
- Findings provide insights into the roles of homologous caspases with overlapping specificities.