Characterization
of the mitochondrial cell death pathways in C. elegans
Mitochondrial
endonuclease G is important for apoptosis in C. elegans
JAY PARRISH*,
LILY LI , KRISTINA KLOTZ*, DUNCAN LEDWICH*, XIAODONG WANG
& DING XUE*
* Department
of Molecular, Cellular, and Developmental Biology, University of Colorado,
Boulder, Colorado 80309, USA
Howard
Hughes Medical Institute and Department of Biochemistry, University of Texas
Southwestern Medical Center, Dallas, Texas 75390, USA
Programmed
cell death (apoptosis) is a tightly regulated process of cell disassembly in
which dying cells and their nuclei shrink and fragment and the chromosomal DNA
is degraded into internucleosomal repeats. Here we report the characterization
of the cps-6 gene, which appears to function downstream of, or in parallel to,
the cell-death protease CED-3 of Caenorhabditis elegans in the DNA degradation
process during apoptosis. cps-6 encodes a homologue of human mitochondrial endonuclease G, and
its protein product similarly localizes to mitochondria in C. elegans. Reduction of cps-6 activity caused by a genetic
mutation or RNA-mediated interference (RNAi) affects normal DNA degradation, as
revealed by increased staining in a TUNEL assay, and results in delayed
appearance of cell corpses during development in C. elegans. This observation provides in
vivo
evidence that the DNA degradation process is important for proper progression
of apoptosis. CPS-6 is the first mitochondrial protein identified to be
involved in programmed cell death in C. elegans, underscoring the conserved
and important role of mitochondria in the execution of apoptosis.
Parrish, J., Li, L., Klotz, K., Ledwich, D., Wang, X.D., and
Xue, D. (2001). C. elegans mitochondrial endonuclease G is important for
apoptosis. Nature 412,
90-94. (Abstract
and PDF).
WAH-1, a C.
elegans AIF
homologue, cooperates with CPS-6/EndoG to regulates apoptotic DNA degradation.
Mechanisms
of AIF-mediated apoptotic DNA degradation in Caenorhabditis elegans
Xiaochen
Wang,1 Chonglin Yang,1 Jijie Chai,2 Yigong
Shi,2 Ding Xue1
1
Department of Molecular, Cellular and Developmental Biology, University of
Colorado,
Boulder, CO 80309, USA
2
Department of Molecular Biology, Princeton University, Princeton, NJ 08544, USA
Apoptosis-inducing
factor (AIF), a mitochondrial oxidoreductase, is released into the cytoplasm to
induce cell death in response to apoptotic signals. However, the mechanisms
underlying this process have not been resolved. We report that inactivation of
the Caenorhabditis elegans AIF homolog wah-1 by RNA interference delayed the normal
progression of apoptosis and caused a defect in apoptotic DNA degradation.
WAH-1 localized in C. elegans mitochondria and was released into the cytosol and nucleus by the
BH3-domain protein EGL-1 in a caspase (CED-3)-dependent manner. In addition, WAH-1 associated and
cooperated with the mitochondrial endonuclease CPS-6/endonuclease G (EndoG) to
promote DNA degradation and apoptosis. Thus, AIF and EndoG define a single,
mitochondria-initiated apoptotic DNA degradation pathway that is conserved
between C. elegans and mammals.
Wang, X.C., Yang, C.L., Cai, J.J., Shi, Y.G., and Xue, D. (2002). Mechanisms of AIF-mediated apoptotic DNA degradation in Caenorhabditis elegans. Science 298, 1587-1592. (Abstract and PDF).
WAH-1
also promotes phosphatidylserine externalization in apoptotic cells through
SCRM-1
C. elegans mitochondrial factor WAH-1 promotes phosphatidylserine
externalization in apoptotic cells through phospholipid scramblase SCRM-1
Xiaochen Wang1,
Jin Wang2, Keiko Gengyo-Ando3, Lichuan Gu4,
Chun-Ling Sun1, Chonglin Yang1, Yong Shi1,
Tetsuo Kobayashi3, Yigong Shi4, Shohei Mitani3,
Xiao-Song Xie2 & Ding Xue1
1
Department of Molecular, Cellular, and Developmental Biology, University of
Colorado, Boulder, CO 80309, USA.
2
McDermott Center for Human Growth and Development, University of Texas
Southwestern Medical Center, Dallas, TX 75390, USA.
3
Department of Physiology, Tokyo Women's Medical University, School of Medicine,
and CREST, JST, Tokyo, 162-8666, Japan.
4
Department of Molecular Biology, Princeton University, Princeton, NJ 08544,
USA.
Externalization
of phosphatidylserine, which is normally restricted to the inner leaflet of
plasma membrane, is a hallmark of mammalian apoptosis. It is not known what
activates and mediates the phosphatidylserine externalization process in
apoptotic cells. Here, we report the development of an annexin V-based
phosphatidylserine labelling method and show that a majority of apoptotic germ
cells in Caenorhabditis elegans have surface-exposed phosphatidylserine,
indicating that phosphatidylserine externalization is a conserved apoptotic
event in worms. Importantly, inactivation of the gene encoding either the C.
elegans apoptosis-inducing factor (AIF) homologue (WAH-1)5, a
mitochondrial apoptogenic factor, or the C. elegans phospholipid scramblase 1
(SCRM-1), a plasma membrane protein, reduces phosphatidylserine exposure on the
surface of apoptotic germ cells and compromises cell-corpse engulfment. WAH-1
associates with SCRM-1 and activates its phospholipid scrambling activity in
vitro. Thus WAH-1, after its release from mitochondria during apoptosis,
promotes plasma membrane phosphatidylserine externalization through its
downstream effector, SCRM-1.
Wang, X.C., Wang, J., Gengyo-Ando, K., Gu, L.C.,
Sun, C.L., Yang, C.L., Shi, Y., Kobayashi, T., Shi, Y.G., Mitani, S., Xie,
X.S., and Xue, D. (2007). "C. elegans
mitochondrial factor WAH-1 promotes phosphatidylserine externalization in
apoptotic cells through phospholipid scramblase SCRM-1". Nature Cell
Biology 9, 541-549. (Abstract
and PDF).
For detailed
review on mitochondrial cell death pathways and studies
Breckenridge, D. and Xue, D. (2004). Regulation of
mitochondrial membrane permeabilization by BCL-2 family proteins and caspases. Curr. Opin. Cell Biol. 16, 647-652. (Abstract
and PDF)