Caspase-9 and APAF1 bind to each other via their respective NH2-terminal CED-3 homologous
domains in the presence of cytochrome c and dATP, an event that leads to caspase-9 activation. Activated
caspase-9 in turn cleaves and activates caspase-3.
NCBI Summary:
This gene encodes a protein which is a member of the cysteine-aspartic acid protease (caspase) family. Sequential activation of caspases plays a central role in the execution-phase of cell apoptosis. Caspases exist as inactive proenzymes which undergo proteolytic processing at conserved aspartic residues to produce 2 subunits, large and small, that dimerize to form the active enzyme. This protein is processed by caspase APAF1; this step is thought to be one of the earliest in the caspase activation cascade. Alternative splicing of this gene results in two transcript variants which encode different isoforms.
General function
Cell death/survival, Apoptosis
Comment
Cellular localization
Cytoplasmic
Comment
Ovarian function
Follicle atresia, Luteolysis
Comment
Khan SM, et al 2000 studied the role of mitochondria and caspases in induced apoptosis in human
luteinized granulosa cells
Luteinized granulosa cells isolated from in
vitro fertilization patients were treated with staurosporine. Microscopy
revealed that staurosporine treatment resulted in cells exhibiting evidence of
apoptosis, including cell detachment, loss of cell processes, membrane
shrinkage, and formation of apoptotic bodies.
Western analysis showed cleavage of
caspase-9, an initiator caspase, of caspase-3, an executioner caspase, in
staurosporine-treated cells.
Activity and expression of different members of the caspase family in the rat corpus luteum (CL) during pregnancy and postpartum. Peluffo MC et al. Studies were designed to examine the expression and activity of four caspases, which contribute to the initial (caspases-2, -8 and -9) and final (caspase-3) events in apoptosis, in the rat CL during pregnancy (days, 7, 17, 19 and 21 of gestation), postpartum (day 1 and 4) and after injection (0, 8, 16, 24 and 36 h) of the physiological luteolysin, PGF-2alpha. In addition, the temporal relationship of caspase expression/activity relative to steroid production and luteal regression was evaluated. During pregnancy, the activity of all four caspases was significantly greater on day 19, prior to a decline in CL progesterone (P) and CYP11A1 levels at day 21 of gestation. The levels of the caspase-3 active fragment (p17, measured by Western blot) also increased at day 19 and 21 of pregnancy. Immunohistochemical analyses detected specific staining for the caspases in luteal cells (large and small), as well as, in endothelial cells. However, the percentage of apoptotic cells did not increase in the CL until postpartum. Following PGF-2alpha injection, there was a significant decrease in CL P by 24 h, though the activity of all four caspases did not increase until 36 h post treatment. The active p17 fragment of caspase-3 also significantly increased at 36 h post- PGF-2alpha. These results suggest that an increase in the activity of caspase-2, -8, -9 and -3 is associated with the early events of natural luteolysis at the end of pregnancy. Also the exogenous administration of the luteolysin PGF-2alpha may regulate members of the caspase family. Key words: caspases, luteolysis, corpus luteum, pregnancy.
Expression regulated by
Comment
Ovarian localization
Oocyte, Granulosa, Luteal cells
Comment
James M. Angelastro et al 2001
identified a novel isoform of rat caspase-9 in which the C terminus of full-length
caspase-9 is replaced with an alternative peptide sequence. Casp-9-CTD (where CTD is
carboxyl-terminal divergent) is expressed in multiple tissues, with the relative highest expression
observed in ovary and heart. Casp-9-CTD was found primarily in the cytoplasm and was not
detected in the nucleus. Structural predictions suggest that in contrast to full-length caspase-9,
casp-9-CTD will not be processed. Both neuronal and
non-neuronal cell types transfected with casp-9-CTD were resistant to death evoked by trophic
factor deprivation or DNA damage. In addition, cytosolic lysates prepared from cells permanently
expressing exogenous casp-9-CTD were resistant to caspase induction by cytochrome c in
reconstitution assays. Taken together, casp-9-CTD acts as a
dominant-negative variant. Its expression in various tissues indicates a physiological role in
regulating cell death.
Follicle stages
Antral, Corpus luteum
Comment
Expression of caspase-2, -3, -8 and -9 proteins and enzyme activity in the corpus luteum of the rat at different stages during the natural estrous cycle. Peluffo MC et al. Apoptosis is associated with the regression of the corpus luteum (CL) in many species. Since caspases play a central role in apoptosis, we studied several initiators (-2, -8, and -9) and the main effector (-3) caspase in the CL during the estrous cycle of the rat. Two different populations of CL (old and new) were identified on ovaries at estrus and diestrus II (DII). Diminished (P < 0.05) luteal progesterone content and P450scc levels suggested that functional luteolysis occurred between the new CL at DII and old CL at estrus, whereas the decline (P < 0.05) in luteal weight indicated that structural regression was occurring between old CL at estrus to DII. Immunostaining for caspase-2 in luteal and endothelial cells appeared to increase as the luteal phase progressed, peaking at DII in the old CL. However, caspase-8 and -9 immunostaining showed little change with a slight increase at estrus in the old population. Notably, caspase-3 staining appeared to peak at DII in the new CL. Enzyme activity of caspase-9 increased (P < 0.05) in the new CL at DII, followed by that of caspase-2 and -3 in old CL at estrus. Caspase-8 activity did not change at any stage. The number of apoptotic cells increased at DII in the old CL. These results suggest an important role for this protease family during early events of luteolysis in the rat estrous cycle.
Phenotypes
Mutations
2 mutations
Species: mouse
Mutation name: None
type: null mutation fertility: embryonic lethal Comment:Kuida et al. (1998) created mice with a targeted disruption of the mouse homolog of the human caspase 9 gene. The
majority of caspase 9 knockout mice died perinatally with a markedly enlarged and malformed cerebrum caused by
reduced apoptosis during brain development.
Species: mouse
Mutation name: None
type: null mutation fertility: fertile Comment: Caspase 9is constitutively activated in mouse oocytes and plays a key role in oocyte elimination during meiotic prophaseprogression. Ene AC et al. In many mammalian species, more than half of the initial oocyte population is eliminated by neonatal life, thus limiting the oocyte reserve for reproduction. The cause or mechanism of this major oocyte loss remains poorly understood. We examined the apoptotic pathway involved in oocyte elimination in wild-type mouse ovaries as well as in Msh5 -/- ovaries, in which all oocytes were eliminated due to a lack of double strand break repair. Immunoblot and immunofluorescence staining showed that an initiator caspase 9and an effector caspase 7were constitutively activated in almost all oocytes in fetal ovaries regardless of their genotypes. In caspase 9 -/- ovaries, the total number of oocytes remained high while that in wild-type ovaries steadily declined during ovarian development. Therefore, the activation of caspase 9was required for but did not immediately lead to oocyte demise. We found that XIAP, an endogenous inhibitor of apoptosis, was also abundant in oocytes during meiotic prophase progression. On the other hand, a cleaved form of PARP1, a target of effector caspases, was localized to the nuclei of a limited number of oocytes, and the frequency of cleaved PARP1-positive oocyte nuclei increased significantly higher before all oocytes disappeared in Msh5 -/- ovaries. We conclude that the mitochondrial apoptotic pathway mediated by caspase 9is constitutively activated in oocytes and renders the elimination of oocytes with meiotic errors, which can be captured by the cleavage ofPARP1.