Deficiency in caspase-9 or caspase-3 induces compensatory caspase activation

Dysregulation of apoptosis contributes to the pathogenesis of many human diseases. As effectors of the apoptotic machinery, caspases are considered potential therapeutic targets. Using an established in vivo model of Fas-mediated apoptosis, we demonstrate here that elimination of certain caspases was compensated in vivo by the activation of other caspases. Hepatocyte apoptosis and mouse death induced by the Fas agonistic antibody Jo2 required proapoptotic Bcl-2 family member Bid and used a Bid-mediated mitochondrial pathway of caspase activation; deficiency in caspases essential for this pathway, caspase-9 or caspase-3, unexpectedly resulted in rapid activation of alternate caspases after injection of Jo2, and therefore failed to protect mice against Jo2 toxicity. Moreover, both ultraviolet and gamma irradiation, two established inducers of the mitochondrial caspase-activation pathway, also elicited compensatory activation of caspases in cultured caspase-3(-/-) hepatocytes, indicating that the compensatory caspase activation was mediated through the mitochondria. Our findings provide direct experimental evidence for compensatory pathways of caspase activation. This issue should therefore be considered in developing caspase inhibitors for therapeutic applications.     

DECAY, a novel Drosophila caspase related to mammalian caspase-3 and caspase-7.

Caspases are key effectors of programmed cell death in metazoans. In Drosophila, four caspases have been described so far. Here we describe the identification and characterization of the fifth Drosophila caspase, DECAY. 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 exhibited 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 was detected in egg chambers of all stages consistent with a role for DECAY in apoptosis of nurse cells. Relatively high levels of decay mRNA are expressed in larval salivary glands and midgut, two tissues which undergo histolysis during larval/pupal metamorphosis, suggesting that DECAY may play a role in developmentally programmed cell death in Drosophila.     

Engineering a dimeric caspase-9: a re-evaluation of the induced proximity model for caspase activation

Caspases are responsible for the execution of programmed cell death (apoptosis) and must undergo proteolytic activation, in response to apoptotic stimuli, to function. The mechanism of initiator caspase activation has been generalized by the induced proximity model, which is thought to drive dimerization-mediated activation of caspases. The initiator caspase, caspase-9, exists predominantly as a monomer in solution. To examine the induced proximity model, we engineered a constitutively dimeric caspase-9 by relieving steric hindrance at the dimer interface. Crystal structure of the engineered caspase-9 closely resembles that of the wild-type (WT) caspase-9, including all relevant structural details and the asymmetric nature of two monomers. Compared to the WT caspase-9, this engineered dimer exhibits a higher level of catalytic activity in vitro and induces more efficient cell death when expressed. However, the catalytic activity of the dimeric caspase-9 is only a small fraction of that for the Apaf-1-activated caspase-9. Furthermore, in contrast to the WT caspase-9, the activity of the dimeric caspase-9 can no longer be significantly enhanced in an Apaf-1-dependent manner. These findings suggest that dimerization of caspase-9 may be qualitatively different from its activation by Apaf-1, and in conjunction with other evidence, posit an induced conformation model for the activation of initiator caspases.     

N-nitrosoanilines: a new class of caspase-3 inhibitors

Caspases are a family of cysteine proteases activated during apoptosis. In cultured human endothelial cells, physiological levels of NO prevent apoptosis and interfere with the activation of the caspase cascade. Previous studies have demonstrated that NO inhibits the activity of caspase-3 by S-nitrosylation of the enzyme. In this study, the inhibitory effect of a new class of NO donors. N-nitrosoaniline derivatives, were examined against caspase-3. Initially eight small molecule inhibitors bearing N-nitroso moieties were assayed. It was found that the presence of an electron-donating group on the phenyl ring led to better inhibitory potency, a trend consistent with the results from the previous papain studies. Based on the analysis of the enzyme and substrates' structures, two peptidyl N-nitrosoaniline inhibitors [Ac-DVAD-NNO (1) and Ac-DV-AMO (2)] were designed and synthesized. Both compounds exhibited enhanced inhibitory potency against caspase-3.     

Identification of new complex for caspase-2 activation after DNA damage

Caspase-2 is reported to play an initiator role in apoptotic cell death in response to DNA damage. In this study, the mechanism of caspase-2 activation after DNA damage was investigated in human ovarian cancer cells Caov-4 treated with the chemotherapeutic agent cisplatin. To isolate the protein complex that might be involved in caspase-2 activation, a combination of gel filtration and immunoprecipitation was used. In the first step the high molecular weight complexes were separated from caspase-2 monomers by means of gel-filtration and in the second step immunoprecipitation from the high molecular weight gel-filtration fractions allowed us to isolate the complex that contains caspase-2. Interestingly, this complex did not contain the protein RAIDD that is a core component of the PIDDosome platform; the latter was shown to play an essential role in DNA damage-induced caspase-2 activation. Finally, catalytically active caspase-2 was detected in this complex, which indicates the possibility of formation of an alternative platform for caspase2 activation in DNA damage-induced apoptosis.     

Screening for caspase-3 inhibitors: a new class of potent small-molecule inhibitors of caspase-3

From the authors' 650,000 compound collection, they have selected approximately 15,000 potential small-molecule protease inhibitors, which were subjected to high-throughput screening against caspase-3. The screening yielded a series of hits that belong to 11 different scaffolds. Based on the structure of one of the hits, a new class of the small-molecule inhibitors with a double electrophilic warhead, 8-sulfonyl-pyrrolo[3,4-c]quinoline-1,3-diones (SPQ), was synthesized and tested in follow-up mechanistic and anti-apoptosis assays. Mechanistic analysis of a representative compound of this class, CD-001-0011, showed that the compound exhibited a high potency (IC (50)=130 nM), was reversible though noncompetitive, and had a broad selectivity profile to other caspases belonging to groups I to III. The compound was effective in preventing staurosporine induced apoptosis in a few cell lines and retinoic acid-induced apoptosis in zebrafish.     

Cop, a caspase recruitment domain-containing protein and inhibitor of caspase-1 activation processing.

The production of bio-active interleukin-1beta (IL-1beta), a pro-inflammatory cytokine, is mediated by activated caspase-1. One of the known molecular mechanisms underlying pro-caspase-1 processing and activation involves binding of the caspase-1 prodomain to a caspase recruitment domain (CARD)-containing serine/threonine kinase known as RIP2/CARDIAK/RICK. We have identified a novel protein, COP (CARD only protein), which has a high degree of sequence identity to the caspase-1 prodomain. COP binds to both RIP2 and the caspase-1 prodomain and inhibits RIP2-induced caspase-1 oligomerization. COP inhibits caspase- 1-induced IL-1beta secretion as well as lipopolysaccharide-induced IL-1beta secretion in transfected cells. Our data indicate that COP can regulate IL-1beta secretion, implying that COP may play a role in down-regulating inflammatory responses analogous to the CARD protein ICEBERG.     

An endoplasmic reticulum stress-specific caspase cascade in apoptosis. Cytochrome c-independent activation of caspase-9 by caspase-12

Activation of caspase-12 from procaspase-12 is specifically induced by insult to the endoplasmic reticulum (ER) (Nakagawa, T., Zhu, H., Morishima, N., Li, E., Xu, J., Yankner, B. A., and Yuan, J. (2000) Nature 403, 98-103), yet the functional consequences of caspase-12 activation have been unclear. We have shown that recombinant caspase-12 specifically cleaves and activates procaspase-9 in cytosolic extracts. The activated caspase-9 catalyzes cleavage of procaspase-3, which is inhibitable by a caspase-9-specific inhibitor. Although cytochrome c released from mitochondria has been believed to be required for caspase-9 activation during apoptosis (Zou, H., Henzel, W. J., Liu, X., Lutschg, A., and Wang, X. (1997) Cell 90, 405-413, Li, P., Nijhawan, D., Budihardjo, I., Srinivasula, S. M., Ahmad, M., Alnemri, E. S., and Wang, X. (1997) Cell 91, 479-489), caspase-9 as well as caspase-12 and -3 are activated in cytochrome c-free cytosols in murine myoblast cells under ER stress. These results suggest that caspase-12 can activate caspase-9 without involvement of cytochrome c. To examine the role of caspase-12 in the activation of downstream caspases, we used a caspase-12-binding protein, which we identified in a yeast two-hybrid screen, for regulation of caspase-12 activation. The binding protein protects procaspase-12 from processing in vitro. Stable expression of the binding protein renders procaspase-12 insensitive to ER stress, thereby suppressing apoptosis and the activation of caspase-9 and -3. These data suggest that procaspase-9 is a substrate of caspase-12 and that ER stress triggers a specific cascade involving caspase-12, -9, and -3 in a cytochrome c-independent manner.     

Function of caspase-14 in trophoblast differentiation

Background  

Within the human placenta, the cytotrophoblast consists of a proliferative pool of progenitor cells which differentiate to replenish the overlying continuous, multi-nucleated syncytiotrophoblast, which forms the barrier between the maternal and fetal tissues. Disruption to trophoblast differentiation and function may result in impaired fetal development and preeclampsia. Caspase-14 expression is limited to barrier forming tissues. It promotes keratinocyte differentiation by cleaving profilaggrin to stabilise keratin intermediate filaments, and indirectly providing hydration and UV protection. However its role in the trophoblast remains unexplored.     

Activation and substrate specificity of caspase-14

Caspase-14 is a developmentally regulated and tissue restricted member of the caspase family present in mammals. It is mainly found in epidermal keratinocytes and has been hypothesized to be involved in a tissue-specific form of cell senescence, leading to the differentiation of keratinocytes that form the cornified cell layer. However, the substrate specificity, activation mechanism, and function of this caspase have yet to be revealed. We report that caspase-14, in contrast to other caspases, is not produced in active form following expression in Escherichia coli but can be activated by high concentrations of kosmotropic salts. Moreover, proteolytic cleavage is also required since the kosmotropic salts were only effective on the cleaved enzyme. We propose that caspase-14 requires proteolytic cleavage within the catalytic domain, followed by dimerization and ordering of mobile active site loops, to generate a competent enzyme. In the presence of kosmotropic salt, we were able to determine the substrate specificities of mouse and human caspase-14. Surprisingly, the substrate preferences for the human and mouse enzyme are dissimilar. The results obtained with human caspase-14 classify this enzyme as a cytokine activator, but the mouse enzyme shows preferences similar to apical apoptotic caspases.     

Function of caspase-14 in trophoblast differentiation

Background

It has become an accepted procedure to transfer more than one embryo to the patient to achieve acceptable ongoing pregnancy rates. However, transfers of more than a single embryo increase the probability of establishing a multiple gestation. Single-embryo transfer can minimize twin pregnancies but may also lower live birth rates. This meta-analysis aimed to compare current data on single-embryo versus double-embryo transfer in fresh IVF/ICSI cycles with respect to implantation, ongoing pregnancy and live birth rates.

Methods

Search strategies included on-line surveys of databases from 1995 to 2008. Data management and analysis were conducted using the Stats Direct statistical software. The fixed-effect model was used for odds ratio (OR). Fixed-effect effectiveness was evaluated by the Mantel Haenszel method. Seven trials fulfilled the inclusion criteria.

Results

When pooling results under the fixed-effect model, the implantation rate was not significantly different between double-embryo transfer (34.5%) and single-embryo transfer group (34.7%) (P = 0.96; OR = 0.99, 95% CI 0.78, 1.25). On the other hand, double-embryo transfer produced a statistically significantly higher ongoing clinical pregnancy rate (44.5%) than single-embryo transfer (28.3%) (P < 0.0001; OR:2.06, 95% CI = 1.64,2.60). At the same time, pooling results presented a significantly higher live birth rate when double-embryo transfer (42.5%) (P < 0.001; OR: 1.87, 95% CI = 1.44,2.42) was compared with single-embryo transfer (28.4%).

Conclusion

Meta-analysis with 95% confidence showed that, despite similar implantation rates, fresh double-embryo transfer had a 1.64 to 2.60 times greater ongoing pregnancy rate and 1.44 to 2.42 times greater live birth rate than single-embryo transfer in a population suitable for ART treatment.     

Identification and cloning of a fur homologue from Neisseria meningitidis

The iron response in a number of bacterial systems is mediated by fur (f erric u ptake r egulation)-like regulatory systems. We have cloned and characterized a gene from Neisseria meningitidis that was homologous to Escherichia coli fur. This clone was capable of modulating expression from both E. coli and neisserial iron-regulated promoters in response to iron, and it produced a protein that reacted with anti-E. coli fur serum. Although the DNA and predicted amino acid sequences were very similar to those of four other published fur homologues, meningococcal fur was the most divergent of the group. Inability to construct a meningococcal fur mutant suggested that fur may be essential in this species.     

Identification and characterization of a GroEL homologue in Rhodobacter sphaeroides

A protein closely related to the Escherichia coli GroEL protein has been isolated from Rhodobacter sphaeroides. Native and SDS-polyacrylamide gel electrophoresis of this protein have shown that it is present in the cell as a multimeric complex of Mr 670,000 which is composed of a monomer of Mr 58,000. Antisera raised against the Mr 58,000 polypeptide have been shown to cross-react with GroEL and the alpha subunit of the pea plastid chaperonin. The N-terminal amino acid sequence of the Mr 58,000 polypeptide is identical to that of GroEL at 15 of 19 residues and is also closely related to the alpha subunit of the pea plastid chaperonin, though less so to the beta subunit.     

Stratum corneum-derived caspase-14 is catalytically active

Caspase-14, a cysteine protease with restricted tissue distribution, is highly expressed in differentiated epidermal keratinocytes. Here, we extracted soluble proteins from stratum corneum (SC) of human epidermis and demonstrate that the extract cleaves tetrapeptide caspase substrates. The activity decreased to below 10% when caspase-14 was removed by immunodepletion showing that caspase-14 is the predominant caspase in SC. In contrast to normal SC, where caspase-14 was present exclusively in its processed form, incompletely matured SC of parakeratotic skin from psoriasis and seborrheic dermatitis contained both procaspase-14 and caspase-14 subunits. Fractionation of extract from parakeratotic SC revealed that the peak caspase activity coeluted with processed caspase-14 but not with procaspase-14. Our results suggest that during regular terminal keratinocyte differentiation, endogenous procaspase-14 is converted to caspase-14 subunits that are catalytically active in the outermost layers of normal human skin.     

Identification and characterization of a novel mammalian caspase with proapoptotic activity

Caspases are essential proteases in programmed cell death and inflammation. Studies in murine and human cells have led to the characterization of 14 members of this enzyme family. Here we report the identification of caspase-15, a novel caspase that is expressed in various mammalian species including pig, dog, and cattle. The caspase-15 protein contains a catalytic domain with all amino acid residues critical for caspase activity and a prodomain that is predicted to fold into a pyrin domain structure, which is a unique feature among mammalian caspases. Recombinant porcine caspase-15 underwent autocatalytic processing into its subunits and cleaved both tetrapeptide caspase substrates and the apoptosis regulator protein Bid in vitro. Overexpression of caspase-15 in mammalian cells induced proenzyme maturation, cleavage of Bid, activation of caspase-3, and eventually cell death. Both the proteolytic and the pro-apoptotic activity of caspase-15 were abolished by mutation of the active site cysteine. Since a homolog of caspase-15 is absent in the human and the mouse genome, our results reveal an unexpected variability in the molecular apoptotic machinery of mammals.     

Aberrant expression of caspase-14 in epithelial tumors

Cysteine-dependent aspartate-specific proteases (caspases) are the cellular executors of apoptosis. Caspase-14 is the most divergent member of the family of mammalian caspases and displays a variety of unique characteristics. It is expressed in a limited number of tissues and has the shortest amino acid sequence within the caspase protein family. During induction of apoptosis, it is not processed, whereas terminal differentiation in skin leads to cleavage of caspase-14. Here we show that 40% of lung squamous cell carcinomas, 22% of breast cancers, and about 80% of cervical carcinomas express caspase-14. Immunohistochemistry reveals that caspase-14 is localized in areas of ongoing differentiation close to necrotic sites but is not strictly associated with the differentiation markers keratin-1/-10. Caspase-14 is neither mutated nor alternatively spliced in the tumors analyzed. Furthermore, caspase-14 is not processed into a small and large subunit, a process critical for the proteolytic activation of known effector caspases. We conclude that conditions exist in tumors leading to re-expression of this normally silent gene.     

Identification of a novel putative Ran-binding protein and its close homologue

In the process of cloning genes at the breakpoint of t(5;14) (q34;q11), a recurring translocation in acute lymphoblastic leukemia, we isolated and characterized a novel gene at 5q34, and a close human homologue (66% amino acid identity) located at 8p11-12. The presence of an importin-beta N-terminal domain at their N-terminus, their size of approximately 110 kD, their nuclear localization and the identity of the homologue to a gene of a recently submitted RanGTP binding protein (RanBP16), suggest that its protein is a novel member of the importin-beta superfamily of nuclear transport receptors, therefore called RanBP17. Northern blot analysis of human tissues revealed a ubiquitous expression pattern of the RanBP16 gene and a very restricted expression pattern of the RanBP17 gene, showing high expression in testis and pancreas. Both genes are evolutionary conserved and show a high (99 and 94%) amino acid conservation with their murine counterparts and a striking similarity (40%) to a protein product of Caenorhabditis elegans (C35A5.8).