title: Caspase-2 resides in the mitochondria and mediates apoptosis directly from the mitochondrial compartment.
abstract: Caspase-2 plays an important role in apoptosis induced by several stimuli, including oxidative stress. However, the subcellular localization of caspase-2, particularly its presence in the mitochondria, is unclear. It is also not known if cytosolic caspase-2 translocates to the mitochondria to trigger the intrinsic pathway of apoptosis or if caspase-2 is constitutively present in the mitochondria that then selectively mediates this apoptotic effect. Here, we demonstrate the presence of caspase-2 in purified mitochondrial fractions fromin vitro-cultured cells and in liver hepatocytes using immunoblots and confocal microscopy. We show that mitochondrial caspase-2 is functionally active by performing fluorescence resonance energy transfer analyses using a mitochondrially targeted substrate flanked by donor and acceptor fluorophores. Cell-free apoptotic assays involving recombination of nuclear, cytosolic and mitochondrial fractions from the livers of wild type andCasp2-/-mice clearly point to a direct functional role for mitochondrial caspase-2 in apoptosis. Furthermore, cytochromecrelease fromCasp2-/-cells is decreased as compared with controls upon treatment with agents inducing mitochondrial dysfunction. Finally, we show thatCasp2-/-primary skin fibroblasts are protected from oxidants that target the mitochondrial electron transport chain. Taken together, our results demonstrate that caspase-2 exists in the mitochondria and that it is essential for mitochondrial oxidative stress-induced apoptosis.
authors.affiliation: Department of Cellular and Structural Biology, The University of Texas Health Science Center at San Antonio, 7703 Floyd Curl Drive, MED 238D.2, San Antonio, TX 78229-3900, USA.
authors.forename: M
authors.initials: M
authors.lastname: Lopez-Cruzan
authors.affiliation: Department of Cellular and Structural Biology, The University of Texas Health Science Center at San Antonio, 7703 Floyd Curl Drive, MED 238D.2, San Antonio, TX 78229-3900, USA.
authors.forename: R
authors.initials: R
authors.lastname: Sharma
authors.affiliation: Department of Cellular and Structural Biology, The University of Texas Health Science Center at San Antonio, 7703 Floyd Curl Drive, MED 238D.2, San Antonio, TX 78229-3900, USA.
authors.forename: M
authors.initials: M
authors.lastname: Tiwari
authors.affiliation: Department of Cellular and Structural Biology, The University of Texas Health Science Center at San Antonio, 7703 Floyd Curl Drive, MED 238D.2, San Antonio, TX 78229-3900, USA.
authors.forename: S
authors.initials: S
authors.lastname: Karbach
authors.affiliation: Department of Cellular and Structural Biology, The University of Texas Health Science Center at San Antonio, 7703 Floyd Curl Drive, MED 238D.2, San Antonio, TX 78229-3900, USA.
authors.forename: D
authors.initials: D
authors.lastname: Holstein
authors.affiliation: Department of Cellular and Structural Biology, The University of Texas Health Science Center at San Antonio, 7703 Floyd Curl Drive, MED 238D.2, San Antonio, TX 78229-3900, USA.
authors.forename: C R
authors.initials: CR
authors.lastname: Martin
authors.affiliation: Department of Cellular and Structural Biology, The University of Texas Health Science Center at San Antonio, 7703 Floyd Curl Drive, MED 238D.2, San Antonio, TX 78229-3900, USA; Center for Biomedical Neuroscience, University of Texas Health Science Center at San Antonio, San Antonio, TX 78229, USA.
authors.forename: J D
authors.initials: JD
authors.lastname: Lechleiter
authors.affiliation: Department of Cellular and Structural Biology, The University of Texas Health Science Center at San Antonio, 7703 Floyd Curl Drive, MED 238D.2, San Antonio, TX 78229-3900, USA.
authors.forename: B
authors.initials: B
authors.lastname: Herman