Death caspase-1
Other Drosophila caspases In comparison with other caspase family members, Drosophila caspase-1 is more homologous to CPP-32 and MCH-2alpha than to ICE. It shares 37% sequence identity with both CPP-32 and MCH-2alpha, 29% identity with NEDD-2 (ICH-1), 28% homology with CED-2 and 25% homology with human ICE. This sequence similarity suggests that DCP-1 may be a member of the ced3-CPP-32 subfamily of caspases (Song, 1997).
A second Drosophila Caspase has been isolated and termed drICE. drICE is distinct from Death Caspase-1. and exhibits highest homology with the mammalian caspases, Mch2 and CPP32ß. drICE also contains a region in its putative small subunit that corresponds to the P4-specificity loop of CPP32ß. Overexpression of drICE sensitizes Drosophila cells to apoptotic stimuli; expression of an N-terminally truncated form of drICE rapidly induces apoptosis in Drosophila cells. Induction of apoptosis by reaper overexpression or by cycloheximide or etoposide treatment of Drosophila cells results in proteolytic processing of drICE. drICE is a cysteine protease that cleaves baculovirus p35 and Drosophila lamin DmO in vitro. drICE is expressed at all stages of Drosophila development at which programmed cell death can be induced. Levels are highest from 2-6 hours of embryogenesis, lower from 6-12 hours, and still lower after 12 hours of development. These results strongly argue that drICE is an apoptotic caspase that acts downstream of reaper (Fraser, 1997a).
The role of drICE was examined in in vitro apoptosis of the D. melanogaster cell line S2. Cytoplasmic lysates made from S2 cells undergoing apoptosis induced by either reaper expression or cycloheximide treatment contain a caspase activity with DEVD specificity that can cleave p35, lamin DmO, drICE and DCP-1 in vitro, one that can trigger chromatin condensation in isolated nuclei. Immunodepletion of drICE from lysates
is sufficient to remove most measurable in vitro apoptotic activity; re-addition of exogenous
drICE to such immunodepleted lysates restores apoptotic activity. It is concluded that, at least in S2
cells, drICE can be the sole caspase effector of apoptosis (Fraser 1997b).
Many members of the inhibitor of apoptosis (IAP) family inhibit cell death. Existing data suggest at
least two mechanisms of action: (1) Drosophila IAPs (D-IAP1 and D-IAP2) and a baculovirus-derived
IAP, Op-IAP, physically interact with and inhibit the anti-apoptotic activity of Reaper, HID, and Grim (three genetically defined inducers of apoptosis in Drosophila), and (2) human IAPs (c-IAP1, c-IAP2, and
X-IAP) interact with a number of different proteins including specific members of the caspase family of
cysteine proteases that are crucial in the execution of cell death. An examination was carried out to see if
insect-active IAPs could inhibit apoptosis in insect SF-21 cells induced by selected caspases, Drosophila drICE, Sf-caspase-1,
and mammalian caspase-3. D-IAP1 inhibits apoptosis induced by the active
forms of all three caspases tested and physically interacts with the active, but not the proform of
drICE. MIHA, the mouse homolog of X-IAP and an effective inhibitor of caspase-3, also interacts
with and blocks apoptosis induced by active drICE but is relatively ineffective in blocking
Sf-caspase-1. Op-IAP and D-IAP2 are unable to effectively inhibit any of the active caspases tested
and fail to interact with drICE. The Drosophila IAPs and Op-IAP, but not MIHA, block
HID-initiated activation of pro-drICE. It is concluded that D-IAP1 is capable of inhibiting the activation
of drICE as well as inhibiting apoptosis induced by the active form of drICE. In contrast, D-IAP2 and
Op-IAP are more limited in their inhibitory targets and may be limited to inhibiting the activation of
caspases (Kaiser, 1998).
Drosophila Dredd shares extensive homology with all members of the caspase gene family. Dredd includes essential residues required for catalysis and stabilization of the P1 Asp found to be absolutely conserved among all caspases thus far identified. In addition, the catalytic site for this enzyme (QACQE) is unique among the caspases, bearing a glutamic acid in a position typically occupied by a glycine. Gapped Blast analysis identifies marked similarity to caspase-8 (Mch5/FLICE/MACH) and caspase 10 (Mch4) throughout the entire protein, including significant sequence similarities within the prodomain. These similarities span regions of the prodomain in caspase-8 and-10 referred to as death effector domains, which are believed to mediate critical protein interactions required for activation of some "initiator" caspases (Chen, 1998).
Caspases play an essential role in the execution of programmed cell death in metazoans. Although 14 caspases are known in mammals, only a few have
been described in other organisms. The identification and characterization of a Drosophila caspase, DRONC, is described that contains an amino
terminal caspase recruitment domain (CARD). DRONC is the first Drosophila caspase to be identified that carries the CARD domain The putative DRONC protein consists of 450 aa residues. In vitro translation of mRNA
generated from DRONC cDNA produces a 50-kDa protein consistent with the expected size. Over the entire length of the protein, DRONC shares
25% identity (40% similarity) with caspase-2. The region downstream of the prodomain, which encodes the two subunits of DRONC, shares highest homology
(27%-28% identity, 44%-48% similarity) with all CPP32-like caspases, including caspase-3, -7, -8, -9, -10, and CED-3. Interestingly, DRONC
shares <20% identity with the three known Drosophila caspases. The putative prodomain of DRONC contains a CARD that is similar to the CARDs of
caspase-1, -2, -9, and CED-3. A unique feature of DRONC is the sequence PFCRG that encompasses the catalytic Cys (Cys-318) residue, which is
distinct from the QAC(R/Q/G)(G/E) sequence found in all other known caspases (Dorstyn, 1999a).
Ectopic expression of DRONC in cultured cells results in apoptosis, which is inhibited by the caspase inhibitors
p35 and MIHA. DRONC exhibits a substrate specificity similar to mammalian caspase-2. In some cells, DRONC protein appears to be concentrated
asymmetrically near the cellular nucleus, possibly associated with some subcellular structures. Staining of transfected cells with mitochondrial markers
suggests that DRONC does not localize to mitochondria. At 48 hr after transfection, DRONC-GFP protein is uniformly distributed in apoptotic
cells. DRONC is ubiquitously expressed in Drosophila embryos
during the early stages of development. Dronc is expressed highly in stage 1-4 syncitial embryos. Because zygotic expression does not
begin before stage 5, this early expression of DRONC represents maternally derived mRNA. In stage 8 cellularized embyros, DRONC mRNA is ubiquitously
expressed, but as development proceeds, expression levels generally are reduced. Expression of the Drosophila caspase dredd has been shown
to be up-regulated in embryonic cells undergoing programmed cell death. However, unlike dredd, dronc expression is not up-regulated in apoptotic cells in
embryos. In late third instar larvae, DRONC mRNA is dramatically up-regulated in salivary glands and midgut before histolysis of these tissues. Exposure of salivary
glands and midgut isolated from second instar larvae to ecdysone results in a massive increase in DRONC mRNA levels. These results suggest that DRONC is an
effector of steroid-mediated apoptosis during insect metamorphosis (Dorstyn, 1999a).
Low levels of dronc expression were observed throughout third
instar larval eye discs and brain lobes, which contain apoptotic cells at this stage. However, up-regulation of dronc expression is not
observed in eye disc or brain lobe cells that should be undergoing apoptosis. The cells strongly staining with dronc in the eye disc are blood cells, which often associate with imaginal discs. High expression of dronc expression in a subset of blood cells is consistent with programmed cell death also occurring in
these cells. During oogenesis in adult flies, nurse cells undergo apoptosis in stage 12 oocytes, which
is required for the deposition of nurse cell cytoplasm into the oocytes. Strong dronc expression is observed in egg chambers after stage 10, but also in earlier
stages, indicating that dronc expression precedes apoptosis during oogenesis (Dorstyn, 1999a).
The steroid hormone ecdysone has been shown to mediate apoptosis of larval tissues during pupariation. To investigate whether ecdysone also induces expression of dronc, the levels of DRONC mRNA were examined after the addition of ecdysone to second instar
larval midgut and salivary gland tissues, which normally show only low levels of DRONC mRNA. After 1 hr exposure to ecdysone there is a several-fold
increase in DRONC mRNA levels in the early second instar larval midgut tissue, indicating that ecdysone can induce dronc expression in the midgut.
However, salivary glands from early second instar larvae show no dronc induction after ecdysone treatment. Because salivary glands normally
undergo apoptosis later than midgut tissues, it is possible that the failure of ecdysone to induce dronc in salivary glands is the result of the absence of a
developmentally controlled factor required for ecdysone-induced gene expression. For this reason an examination was carried out to see whether ecdysone could induce dronc
expression in salivary glands at a later developmental stage. Salivary glands from late second instar larvae, which normally only express very low levels of dronc, are found to strongly express dronc 1 hr after ecdysone treatment. Thus, ecdysone induces dronc expression in both midgut and salivary gland
tissues. In late third instar larvae, VDVAD cleavage activity is significantly higher than in second instar larvae. This
increased VDVAD cleavage activity is likely to be attributable to DRONC activity consistent with its high expression in third instar larvae. The demonstration that
DRONC mRNA can be dramatically up-regulated by ecdysone suggests that this caspase may be the main effector in mediating programmed cell death in larval midgut
and salivary glands. The data suggest the possible transcription regulation of a caspase gene by a steroid hormone. This up-regulation may be the result of a direct
interaction between the ecdysone receptor complex and the ecdysone response elements in the dronc promoter or indirectly through an ecdysone-induced
transcription factor. Characterization of the dronc promoter region will provide information on whether dronc is directly regulated by ecdysone. Expression of dronc
in other embryonic, larval, and adult tissues suggests that DRONC also may function in other cell death pathways. Examination of dronc mutant phenotypes
will further establish the function of DRONC in developmentally programmed cell death in Drosophila (Dorstyn, 1999a).
Caspases belong to two distinct classes. Caspases with long N-terminal prodomains (the class I caspases) are believed to be
directly recruited to specific death complexes through the death effector domains (DED) or alternatively through the CARDs present in their
prodomain regions. This recruitment facilitates oligomerization and autoactivation of class I caspases. The class II
caspases have very short or no prodomain and hence they lack the ability to be recruited to specific death complexes. It is
thought that class II caspases require cleavage by upstream class I caspases for their activation. Among proapoptotic mammalian
caspases, caspase-2 and -9 contain CARD domains, whereas caspase-8 and -10 carry two copies of DEDs in their prodomain region. The C. elegans
CED-3 caspase also contains a CARD domain, whereas Drosophila DREDD contains two DEDs. The DED-containing caspases, such as
caspase-8 and -10, are activated on adaptor-mediated recruitment to death receptors, whereas the CARD containing caspase-9 requires APAF-1 (the mammalian
homolog of CED-4 and the homolog of Drosophila Apaf-1-related-killer), cytochrome c released from mitochondria, and dATP for its activation. The presence of a DED containing caspase DREDD in
Drosophila implies that a death receptor-mediated pathway may exist in the fly. The identification of DRONC as a CARD-containing Drosophila caspase
suggests that a pathway similar to CED-3/caspase-9 also may exist in Drosophila. This implies that CARD-containing adaptors such as CED-4/APAF-1, might be
required for DRONC activation. No CED-4 homologs have been reported in Drosophila to date; however, it now might be possible to identify such proteins by
using DRONC as an interacting partner (Dorstyn, 1999a).
An unusual feature of DRONC is the sequence PFCRG surrounding the catalytic Cys residue. All known mammalian caspases have a consensus QAC(R/Q/G)G
sequence, whereas Drosophila DCP-2/DREDD differs somewhat with a QACQE sequence. However, in all caspases except DRONC, the QAC
sequence is completely conserved. The variation in the sequence may reflect unique substrate specificity of DRONC. Interestingly, recombinant DRONC shows little
or no activity on caspase-1 and caspase-3 substrates, but has appreciable activity on the pentapeptide caspase-2 substrate. This suggests that, like
caspase-2, DRONC requires a minimum of a pentapeptide sequence as a substrate. It is, however, unclear at present, whether the caspase-2 substrate is the
optimal substrate for DRONC (Dorstyn, 1999a).
Dronc (Nedd2-like caspase) was isolated through its interaction with the effector caspase drICE. Ectopic
expression of Dronc induces cell death in Schizosaccharomyces pombe, mammalian fibroblasts and the developing Drosophila eye.
The caspase inhibitor p35 fails to rescue Dronc-induced cell death in vivo and is not cleaved by Dronc in vitro, making Dronc
the first identified p35-resistant caspase. The Dronc pro-domain interacts with Drosphila inhibitor of apoptosis protein 1 (Diap1: known as Thread),
and co-expression of DIAP1 in the developing Drosophila eye completely reverts the eye ablation phenotype induced by pro-Dronc
expression. In contrast, Diap1 fails to rescue eye ablation induced by Dronc lacking the pro-domain, indicating that interaction of Diap1 with the pro-domain of
Dronc is required for suppression of Dronc-mediated cell death. Heterozygosity at the Diap1 locus enhances the pro-Dronc eye phenotype, consistent with
a role for endogenous Diap1 in suppression of Dronc activation. Both heterozygosity at the Dronc locus and expression of dominant-negative Dronc mutants
suppress the eye phenotype caused by Reaper (Rpr) and Head involution defective (Hid), consistent with the idea that Dronc functions in the Rpr and Hid
pathway (Meier, 2000).
The finding that Diap1 directly binds to and inhibits cell death caused by ectopic expression of Dronc, as well as by Rpr, Grim and Hid, underscores the key
role played by Diap1 in the regulation of apoptosis in D. melanogaster and raises the possibility that Rpr, Hid or Grim may exert some, or all, of their
pro-apoptotic action through displacement of Diap1 from the pro-domain of Dronc, thereby allowing activation of the caspase and consequent cell death.
This idea is strongly supported by the successful isolation of Diap1 mutants that display greatly reduced binding for Rpr, Hid and Grim and significantly suppress Rpr, Hid and Grim cell killing. According to this model, IAPs function as 'guardians' of the apoptotic machinery: they act to suppress the chance of
spontaneous activation of the intrinsic cell death machinery by neutralizing pro-apoptotic caspases, thereby establishing a buffered threshold that must be either exceeded
or neutralized in order to initiate the destruction of a cell (Meier, 2000).
In Drosophila, four caspases have been described to date. The identification and characterization of the fifth Drosophila caspase, Decay, is described here. Decay shares a high
degree of homology with the members of the mammalian caspase-3 subfamily, particularly caspase-3 and caspase-7. Decay
lacks a long prodomain and thus appears to be a class II effector caspase. Ectopic expression of Decay in cultured cells
induces apoptosis. Recombinant Decay exhibits substrate specificity similar to the mammalian caspase-3 subfamily. Low
levels of Decay mRNA are ubiquitously expressed in Drosophila embryos during early stages of development but its expression becomes somewhat spatially
restricted in some tissues. During oogenesis Decay mRNA is detected in egg chambers of all stages consistent with a role for Decay in the apoptosis of nurse cells.
Relatively high levels of Decay mRNA are expressed in larval salivary glands and midgut, two tissues that undergo histolysis during larval/pupal metamorphosis,
suggesting that Decay may play a role in developmentally programmed cell death in Drosophila (Dorstyn, 1999b).
Properties of caspases The crystal structure at 2.5 A resolution of a recombinant human ICE-tetrapeptide
chloromethylketone complex reveals that the holoenzyme is a homodimer of catalytic domains, each of
which contains a p20 and a p10 subunit. The spatial separation of the C-terminus of p20 and the
N-terminus of p10 in each domain suggests two alternative pathways of assembly and activation in
vivo.
Conservation among members of the ICE/CED-3 family of the amino acids that form the active site
region of ICE supports the hypothesis that they share functional similarities (Walker, 1994).
In vitro
transcribed and translated Ced-3 protein (p56) undergoes rapid processing to smaller fragments.
Replacement of the predicted active site cysteine of Ced-3 with serine (C364S) prevents the
generation of smaller proteolytic fragments, suggesting that the processing might be an autocatalytic
process. Peptide aldehydes with aspartic acid at the P1 position block Ced-3 autocatalysis.
Furthermore, the protease inhibition profile of Ced-3 is similar to the profile reported for ICE. These
functional data demonstrate that Ced-3 is an Asp-dependent cysteine protease with substrate
specificity similar to that of ICE. Aurintricarboxylic acid, an inhibitor of apoptosis in mammalian cells,
blocks Ced-3 autocatalytic activity, suggesting that an aurintricarboxylic acid-sensitive
Ced-3/ICE-related protease might be involved in the apoptosis pathway(s) in mammalian cells (Hugunin, 1996).
The full-length CED-3 protein undergoes proteolytic activation to generate a CED-3
cysteine protease. CED-3 protease activity is required for killing cells by programmed cell
death in C. elegans. In its substrate preferences CED-3 is more similar to the
mammalian CPP32 protease than to mammalian ICE or NEDD2/ICH-1 protease. These results suggest
that different mammalian CED-3/ICE-like proteases may play distinct roles in mammalian apoptosis
and that CPP32 is a candidate for being a mammalian functional equivalent of CED-3 (Xue, 1996).
C. elegans caspase The C. elegans cell death gene ced-3 is most abundant during
embryogenesis, the stage during which most programmed cell deaths occur. The predicted CED-3
protein shows similarity to human and murine interleukin-1 beta-converting enzyme and to the product
of the mouse nedd-2 gene, which is expressed in the embryonic brain. The sequences of 12 ced-3
mutations as well as the sequences of ced-3 genes from two related nematode species identify sites of
potential functional importance. It is proposed that the CED-3 protein acts as a cysteine protease in the
initiation of programmed cell death in C. elegans and that cysteine proteases also function in
programmed cell death in mammals (Yuan, 1993).
Programmed cell death (PCD) is regulated by multiple evolutionarily conserved
mechanisms to ensure the survival of the cell. This study describes pvl-5,
a gene that likely regulates PCD in
Caenorhabditis elegans. In wild-type hermaphrodites at the L2
stage there are 11 Pn.p hypodermal cells in the ventral
midline arrayed along the anterior-posterior axis and 6 of these
cells become the vulval precursor cells. In pvl-5(ga87)
animals, there are fewer Pn.p cells (average of 7.0) present at
this time. Lineage analysis reveals that the missing Pn.p
cells die around the time of the L1 molt in a manner that often
resembles the programmed cell deaths that occur normally in C.
elegans development. This Pn.p cell death is suppressed by
mutations in the caspase gene ced-3 and in the bcl-2
homolog ced-9, suggesting that the Pn.p cells are dying
by PCD in pvl-5 mutants. Surprisingly, the Pn.p cell death
is not suppressed by loss of ced-4 function. ced-4
(Apaf-1) is required for all previously known apoptotic cell deaths
in C. elegans. This suggests that loss of pvl-5
function leads to the activation of a ced-3-dependent,
ced-4-independent form of PCD and that pvl-5 may
normally function to protect cells from inappropriate activation of
the apoptotic pathway (Joshi, 2004).
Temporal control of programmed cell death is necessary to ensure that cells
die at only the right time during animal development. How such temporal
regulation is achieved remains poorly understood. In some Caenorhabditis
elegans somatic cells, transcription of the egl-1/BH3-only gene
promotes cell-specific death. The EGL-1 protein inhibits the CED-9/Bcl-2
protein, resulting in the release of the caspase activator CED-4/Apaf-1.
Subsequent activation of the CED-3 caspase by CED-4 leads to cell death.
Despite the important role of egl-1 transcription in promoting CED-3
activity in cells destined to die, it remains unclear whether the temporal
control of cell death is mediated by egl-1 expression. This study show shows
that egl-1 and ced-9 play only minor roles in the death of
the C. elegans tail-spike cell, demonstrating that temporal control
of tail-spike cell death can be achieved in the absence of egl-1. The timing of the onset of tail-spike cell death is
controlled by transcriptional induction of the ced-3 caspase. The developmental expression pattern of ced-3 has been characterized; in the tail-spike cell, ced-3 expression is induced shortly
before the cell dies, and this induction is sufficient to promote the demise
of the cell. Both ced-3 expression and cell death are dependent on
the transcription factor PAL-1, the C. elegans homolog of the
mammalian tumor suppressor gene Cdx2. PAL-1 can bind to the ced-3
promoter sites that are crucial for tail-spike cell death, suggesting that it
promotes cell death by directly activating ced-3 transcription. These
results highlight a role that has not been described previously for the
transcriptional regulation of caspases in controlling the timing of cell death
onset during animal development (Maurer, 2007).
Members of the caspase family Fas/APO-1-mediated apoptosis requires the activation of a class of cysteine proteases, including
interleukin-1 beta-converting enzyme (ICE). Triggering of Fas/APO-1 rapidly stimulates
the proteolytic activity of ICE. Overexpression of ICE
strongly potentiates Fas/APO-1-mediated cell death. Inhibition of ICE activity by protease
inhibitors, as well as by transient expression of the pox virus-derived serpin inhibitor CrmA or an
antisense ICE construct, substantially suppresses Fas/APO-1-triggered cell death. It is concluded that
activation of ICE or an ICE-related protease is a critical event in Fas/APO-1-mediated cell death (Los, 1995).
Nedd2 (Caspase 3) encodes a protein similar to the mammalian interleukin-1 beta-converting enzyme (ICE) and the
product of the C. elegans cell death gene ced-3 (CED-3). Overexpression of Nedd2 in cultured fibroblast and neuroblastoma cells results in cell death
by apoptosis, which is suppressed by the expression of the human bcl-2 gene (Drosophila homolog: death executioner Bcl-2 homologue), indicating that Nedd2
is functionally similar to the ced-3 gene in C. elegans. During embryonic
development, Nedd2 is highly expressed in several types of mouse tissue undergoing high rates of
programmed cell death, such as central nervous system and kidney. This work suggests that Nedd2 is an
important component of the mammalian programmed cell death machinery (Kumar, 1994).
A novel apoptotic gene has been cloned from human Jurkat T-lymphocytes. The
32-kDa putative cysteine protease (CPP32) has significant homology to C. elegans cell
death protein Ced-3, mammalian interleukin-1 beta-converting enzyme (ICE), and the product of the
mouse nedd2 gene. The CPP32 (now known as Caspase 3) transcript is highly expressed and most abundant in cell lines of
lymphocytic origin. Overexpression of CPP32 or ICE in Sf9 insect cells results in apoptosis. In
addition, coexpression of recombinant p20 and p11 derived from the parental full-length CPP32
sequence results in apoptosis in Sf9 cells. Similar to ICE, CPP32 is made of two
subunits, p20 and p11, which form the active CPP32 complex. The apoptotic activity of CPP32 and its
high expression in lymphocytes suggest that CPP32 is an important mediator of apoptosis in the
immune system (Fernandes-Alnemri, 1994).
The enzyme apopain is the protease responsible for the cleavage of poly(ADP-ribose) polymerase, and is necessary for
apoptosis. It is composed of two
subunits of relative molecular mass 17K and 12K, derived from a common proenzyme
identified as CPP32. This proenzyme is related to interleukin-1 beta-converting enzyme (ICE) and
CED-3, the product of a gene required for programmed cell death in C. elegans. A potent
peptide aldehyde inhibitor has been developed and shown to prevent apoptotic events in vitro,
suggesting that apopain/CPP32 is important for the initiation of apoptotic cell death (Nicholson, 1995).
Neurotoxicity induced by overstimulation of N-methyl-D-aspartate (NMDA) receptors is due, in part,
to a sustained rise in intracellular Ca2+; however, little is known about the ensuing intracellular events
that ultimately result in cell death. Overstimulation of NMDA receptors by
relatively low concentrations of glutamate induces apoptosis of cultured cerebellar granule neurons
(CGNs); CGNs do not require new RNA or protein synthesis. However, glutamate-induced apoptosis of
CGNs is associated with a concentration- and time-dependent activation of the interleukin
1beta-converting enzyme (ICE)/CED-3-related protease, CPP32/Yama/apopain (now designated
caspase 3). The time course of caspase 3 activation after glutamate exposure of CGNs
parallels the development of apoptosis. Glutamate-induced apoptosis of CGNs is almost
completely blocked by the selective cell permeable tetrapeptide inhibitor of caspase 3,
Ac-DEVD-CHO, but not by the ICE (caspase 1) inhibitor, Ac-YVAD-CHO. Western blots of
cytosolic extracts from glutamate-exposed CGNs reveal both the cleavage of the caspase 3 substrate,
poly(ADP-ribose) polymerase, as well as the proteolytic processing of pro-caspase 3 to active subunits.
These data demonstrate that glutamate-induced apoptosis of CGNs is mediated by a posttranslational
activation of the ICE/CED-3-related cysteine protease caspase 3 (Du, 1997).
The cell surface receptor Fas (Apo-1/CD95) belongs to the tumor necrosis factor/nerve growth factor receptor family; it
transmits apoptotic signals by binding to its ligand. Interleukin-1beta-converting enzyme (ICE), which
shows substantial homology to the product of ced-3, the cell death gene of C. elegans, is
reported to be involved in Fas-mediated apoptosis. Using two human carcinoma-derived cell lines with
undetectable levels of ICE, it was found that an agonistic antihuman Fas antibody induces the activation of
CPP32/Yama(-like) proteases that are ICE(-like) protease family members. A tetrapeptide
inhibitor of CPP32/Yama protease, DEVD-CHO, inhibits the Fas-mediated activation of the proteases,
Fas-mediated apoptosis, and CPP32/Yama(-like) proteolytic activities in vitro. Fas-mediated apoptosis
is inhibited by the CPP32/Yama inhibitor DEVD-CHO, but not by the ICE inhibitor YVAD-CHO,
suggesting a dominant role for the CPP32/Yama(-like) proteases and not ICE itself in Fas-mediated
apoptosis of the human carcinoma cell lines (Hasegawa, 1996).
Caspases are fundamental components of the mammalian apoptotic machinery, but the precise
contribution of individual caspases is controversial. CPP32 (caspase 3) is a prototypical caspase that
becomes activated during apoptosis. A comprehensive approach was taken in this study to examining the
role of CPP32 in apoptosis using mice, embryonic stem (ES) cells, and mouse embryonic fibroblasts
(MEFs) deficient for CPP32. CPP32(ex3-/-) mice have reduced viability and, consistent with an earlier
report, display defective neuronal apoptosis and neurological defects. Inactivation of CPP32
dramatically reduces apoptosis in diverse settings, including activation-induced cell death (AICD) of
peripheral T cells, as well as chemotherapy-induced apoptosis of oncogenically transformed CPP32(-/-) MEFs. The requirement for CPP32 can be remarkably stimulus-dependent: in ES cells, CPP32 is necessary for efficient apoptosis following UV- but not gamma-irradiation. Conversely, the same stimulus can show a tissue-specific dependence on CPP32. Hence, TNFalpha treatment induces normal levels of apoptosis in CPP32 deficient thymocytes, but defective apoptosis in oncogenically transformed MEFs. In some settings, CPP32 is required for certain apoptotic events but not others. Select CPP32(ex3-/-) cell types undergoing cell death are incapable of chromatin condensation and DNA degradation, but display other hallmarks of apoptosis. Together, these results indicate that CPP32 is an essential component in apoptotic events, one that is remarkably system- and stimulus-dependent. Consequently, drugs that inhibit CPP32 may preferentially disrupt specific forms of cell death (Woo, 1998).
Caspase-2-deficient mice were generated to evaluate the requirement for this enzyme in various paradigms of apoptosis. Excess numbers of germ cells were endowed in ovaries of mutant mice and the oocytes were found to be resistant to cell death following exposure to chemotherapeutic drugs. Apoptosis mediated by granzyme B and perforin is defective in caspase-2-deficient B lymphoblasts. In contrast, cell death of motor neurons during development is accelerated in caspase-2-deficient mice. Caspase-2-deficient sympathetic neurons undergo apoptosis more effectively than wild-type neurons when deprived of NGF. Thus, caspase-2 acts both as a positive and negative cell death effector, depending upon cell lineage and stage of development (Bergeron, 1998).
Murine caspase-11, originally named Ich-3 is most homologous to human caspase-4. Expression of casp-11 is highly inducible by LPS, suggesting that casp-11 may have a regulatory role in both apoptosis and inflammatory responses. casp-11 has been inactivated by gene targeting. Like Ice-deficient mice, casp-11 mutant mice are resistant to endotoxic shock induced by lipopolysaccharide. Production of both IL-1 and IL-1ß after lipopolysaccharide stimulation (a crucial event during septic shock and an indication of ICE activation) is blocked in casp-11 mutant mice. casp-11 mutant embryonic fibroblast cells are resistant to apoptosis induced by overexpression of ICE. Pro-caspase-11 physically interacts with pro-ICE in cells; the expression of casp-11 is essential for activation of ICE. These data suggest that caspase-11 is a component of ICE complex and is required for the activation of ICE (Wang, 1998).
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