Mice deficient in IL-1 beta-converting enzyme are defective in production of mature IL-1 beta and resistant to endotoxic shock

Cleavage of PITSLRE kinases by ICE/CASP-1 and CPP32/CASP-3 during apoptosis induced by tumor necrosis factor

Emerging evidence suggests that multiple aspartate-specific cysteine proteases (caspases (CASPs)) play a crucial role in programmed cell death. Many cellular proteins have been identified as their substrates and serve as markers to assay the activation of CASPs during the death process. However, no substrate has yet been unambiguously identified as an effector molecule in apoptosis. PITSLRE kinases are a superfamily of Cdc2-like kinases that have been implicated in apoptotic signaling and tumorigenesis. In this paper we report that tumor necrosis factor (TNF)-mediated apoptosis is associated with a CrmA- and Bcl-2-inhibitable cleavage of PITSLRE kinases, indicating a role for CASPs. Testing of seven murine CASPs for their ability to cleave p110 PITSLRE kinase alpha2-1 in vitro revealed that only CASP-1 (ICE (interleukin-1beta-converting enzyme)) and CASP-3 (CPP32) were able to produce the same 43-kDa cleavage product as observed in cells undergoing TNF-induced apoptosis. Mutational analysis revealed that cleavage of p110 PITSLRE kinase alpha2-1 occurred at Asp393 within the sequence YVPDS, which is similar to that involved in the CASP-1-mediated cleavage of prointerleukin-1beta. TNF-induced proteolysis of PITSLRE kinases was still observed in fibroblasts from CASP-1(0/0) mice. These data implicate CASP-3 as a potentially important CASP family protease responsible for the cleavage of PITSLRE kinases during TNF-induced apoptosis.

Selective activation of the JNK/AP-1 pathway in Fas-mediated apoptosis of rheumatoid arthritis synoviocytes

OBJECTIVE

To evaluate the Fas-dependent signaling pathway, we examined the involvement of protein tyrosine phosphorylation and the DNA binding activity of AP-1 in rheumatoid arthritis (RA) cultured synovial cells.

METHODS

The number of dead cells was counted after treatment with anti-Fas antibody in the presence of protein tyrosine kinase or phosphatase inhibitor. Protein tyrosine phosphorylation in synoviocytes after Fas ligation was examined by immunoblot and immunoprecipitation analyses. The DNA binding activity of AP-1 was examined by electrophoretic mobility shift assay.

RESULTS

Treatment with the protein tyrosine phosphatase inhibitor, orthovanadate, significantly enhanced the apoptosis of RA synoviocytes after Fas ligation. Ligation of the Fas molecule on RA synoviocytes induced a rapid tyrosine phosphorylation of JNK (c-Jun amino-terminal kinase) and formation of the AP-1 transcription factor.

CONCLUSION

Our results strongly suggest that the JNK/AP-1 signaling pathway is activated during the process of Fas-mediated apoptosis of RA synovial cells.

Up-regulation of the Nedd2 gene encoding an ICE/Ced-3-like cysteine protease in the gerbil brain after transient global ischemia

We assessed the expression of several genes encoding pro-apoptotic cysteine proteases similar to interleukin-1 beta converting enzyme (ICE) and nematode Ced-3 in association with delayed neuronal death (DND) after transient forebrain ischemia in Mongolian gerbil. The levels of the two species of Nedd2 mRNA concomitantly increased about two-fold in the whole forebrain at 3-6 h after 10-min ischemia and declined to the basal level by 24 h. In situ hybridization revealed that the Nedd2 gene was up-regulated in some neuronal populations in CA1 and CA3 regions of the hippocampus. In contrast, expression of ICE, CPP32/Yama/Apopain, and TX/ICErelll did not change within 48 h. These observations raise the possibility that up-regulation of Nedd2 in the vulnerable neurons may contribute to the proteolytic processes preceding the manifestation of apoptosis and/or necrosis after ischemic insult.

T-cell receptor ligation by peptide/MHC induces activation of a caspase in immature thymocytes: the molecular basis of negative selection

T-cell receptors (TCRs) are created by a stochastic gene rearrangement process during thymocyte development, generating thymocytes bearing useful, as well as unwanted, specificities. Within the latter group, autoreactive thymocytes arise which are subsequently eliminated via a thymocyte-specific apoptotic mechanism, termed negative selection. The molecular basis of this deletion is unknown. Here, we show that TCR triggering by peptide/MHC ligands activates a caspase in double-positive (DP) CD4+ CD8+ thymocytes, resulting in their death. Inhibition of this enzymatic activity prevents antigen-induced death of DP thymocytes in fetal thymic organ culture (FTOC) from TCR transgenic mice as well as apoptosis induced by anti-CD3epsilon monoclonal antibody and corticosteroids in FTOC of normal C57BL/6 mice. Hence, a common caspase mediates immature thymocyte susceptibility to cell death.

Cleavage of caspase family members by granzyme B: a comparative study in vitro

The aspartase granzyme B is one of the major components of the granules involved in cell killing by cytotoxic T lymphocytes. Granzyme B has been shown to activate the apoptotic death pathway in the target cell, and this involves activation of members of the caspase (CASP) protein family. Therefore, activational cleavage of mouse (m) CASP proforms by granzyme B was examined in vitro. CASP can be subdivided in the CASP-1 (interleukin-1 beta-converting enzyme; ICE) subfamily, the CASP-2 (Ich1) subfamily, and the CASP-3 (CPP32) subfamily. Our results reveal that the proforms of the CASP-3 subfamily members mCASP-3 and mCASP-7 are hydrolyzed by granzyme B, while proforms of CASP-2 and CASP-1 subfamily members are not directly cleaved. Only one CASP-3 subfamily member, pro-mCASP-6, was not proteolytically cleaved by granzyme B. These results indicate that two members of the CASP-3 subfamily, but no others, become activated by granzyme B.

Molecular cloning of the interleukin-1 gene cluster: construction of an integrated YAC/PAC contig and a partial transcriptional map in the region of chromosome 2q13

Genes of the interleukin-1 (IL-1) gene cluster localized on chromosome 2q13 are implicated in many physiological and pathophysiological processes. We present here a high-resolution physical map of this region between markers D2S2008 and D2S4/PAX8. An integrated YAC/PAC contig and a partial transcriptional map were constructed by STS-constent mapping using the CEPH YAC library and three PAC libraries. A total of 3 YACs, 34 PACs, and 56 STSs were integrated: 33 newly generated probes to PAC end sequences, 9 polymorphic and 4 nonpolymorphic markers, 5 known genes, 4 expressed sequence tags, and 1 pseudogene. Within the map, a complete PAC contig of > 1 Mb encompasses the IL-1 gene cluster and PAX8, a paired-box-containing gene. This allowed us to define the transcriptional orientation of GLVR1, IL1B, and IL1RN and to show that PAX8 is localized outside the IL-1 gene cluster. FISH analysis localized PAC clones containing the IL-1 gene cluster to 2q12-q13. The data provide the basis for further characterization of the IL-1 gene cluster and for the construction of a sequence-ready PAC contig of this region.

Processing/activation of at least four interleukin-1beta converting enzyme-like proteases occurs during the execution phase of apoptosis in human monocytic tumor cells

Identification of the processing/activation of multiple interleukin-1beta converting enzyme (ICE)-like proteases and their target substrates in the intact cell is critical to our understanding of the apoptotic process. In this study we demonstrate processing/activation of at least four ICE-like proteases during the execution phase of apoptosis in human monocytic tumor THP.1 cells. Apoptosis was accompanied by processing of Ich-1, CPP32, and Mch3alpha to their catalytically active subunits, and lysates from these cells displayed a proteolytic activity with kinetics, characteristic of CPP32/Mch3alpha but not of ICE. Fluorescence-activated cell sorting was used to obtain pure populations of normal and apoptotic cells. In apoptotic cells, extensive cleavage of Ich-1, CPP32, and Mch3alpha. was observed together with proteolysis of the ICE-like protease substrates, poly (ADP-ribose) polymerase (PARP), the 70-kD protein component of U1 small nuclear ribonucleoprotein (U1-70K), and lamins A/B. In contrast, no cleavage of CPP32, Mch3alpha or the substrates was observed in normal cells. In cells exposed to an apoptotic stimulus, some processing of Ich-1 was detected in morphologically normal cells, suggesting that cleavage of Ich-1 may occur early in the apoptotic process. The ICE-like protease inhibitor, benzyloxycarbonyl-Val-Ala-Asp (OMe) fluoromethyl ketone (Z-VAD.FMK), inhibited apoptosis and cleavage of Ich-1, CPP32, Mch3alpha, Mch2alpha, PARP, U1-70K, and lamins. These results suggest that Z-VAD.FMK inhibits apoptosis by inhibiting a key effector protease upstream of Ich-1, CPP32, Mch3alpha, and Mch2alpha. Together these observations demonstrate that processing/activation of Ich-1, CPP32, Mch3alpha, and Mch2alpha accompanies the execution phase of apoptosis in THP.1 cells. This is the first demonstration of the activation of at least four ICE-like proteases in apoptotic cells, providing further evidence for a requirement for the activation of multiple ICE-like proteases during apoptosis.

Substrate specificities of caspase family proteases

The caspase family represents a new class of intracellular cysteine proteases with known or suspected roles in cytokine maturation and apoptosis. These enzymes display a preference for Asp in the P1 position of substrates. To clarify differences in the biological roles of the interleukin-1beta converting enzyme (ICE) family proteases, we have examined in detail the specificities beyond the P1 position of caspase-1, -2, -3, -4, -6, and -7 toward minimal length peptide substrates in vitro. We find differences and similarities between the enzymes that suggest a functional subgrouping of the family different from that based on overall sequence alignment. The primary specificities of ICE homologs explain many observed enzyme preferences for macromolecular substrates and can be used to support predictions of their natural function(s). The results also suggest the design of optimal peptidic substrates and inhibitors.

Caspase-1 processes IFN-gamma-inducing factor and regulates LPS-induced IFN-gamma production

Interferon-gamma-inducing factor (IGIF, interleukin-18) is a recently described cytokine that shares structural features with the interleukin-1 (IL-1) family of proteins and functional properties with IL-12. Like IL-12, IGIF is a potent inducer of interferon (IFN)-gamma from T cells and natural killer cells. IGIF is synthesized as a biologically inactive precursor molecule (proIGIF). The cellular production of IL-1beta, a cytokine implicated in a variety of inflammatory diseases, requires cleavage of its precursor (proIL-1beta) at an Asp-X site by interleukin-1beta-converting enzyme (ICE, recently termed caspase-1). The Asp-X sequence at the putative processing site in proIGIF suggests that a protease such as caspase-1 might be involved in the maturation of IGIF. Here we demonstrate that caspase-1 processes proIGIF and proIL-1beta with equivalent efficiencies in vitro. A selective caspase-1 inhibitor blocks both lipopolysaccharide-induced IL-1beta and IFN-gamma production from human mononuclear cells. Furthermore, caspase-1-deficient mice are defective in lipopolysaccharide-induced IFN-gamma production. Our results thus implicate caspase-1 in the physiological production of IGIF and demonstrate that it plays a critical role in the regulation of multiple proinflammatory cytokines. Specific caspase-1 inhibitors would provide a new class of anti-inflammatory drugs with multipotent action.

Antiapoptotic effect of benzyloxycarbonyl-aspartyl-(beta-tertier-butyl ester)-bromomethylketone (Z-D(OtBu)-Bmk), an intermediate of interleukin-1 beta converting enzyme inhibitors

The effect of several interleukin-1 beta converting enzyme (ICE) inhibitors on apoptosis was examined. The ICE inhibitors tested were peptide aldehydes such as ethyloxycarbonyl-Ala-Tyr-Val-Ala-Asp-aldehyde (Etoco-AYVAD-CHO), acetyl-Tyr-Val-Ala-Asp-aldehyde (Ac-YVAD-CHO), benzyloxycarbonyl-Val-His-Asp-aldehyde (Z-VHD-CHO), a tetrapeptide chloromethylketone, acetyl-Tyr-Val-Ala-Asp-chloromethylketone (Ac-YVAD-Cmk) and their common intermediate benzyloxycarbonyl-Asp-(beta-tertier-butyl ester)-bromomethylketone (Z-D(OtBu)-Bmk). Apoptosis was induced with several chemical agents conventionally used for this purpose in THP-1, L929, NB-41A3 cell lines and mouse thymocytes. DNA fragmentation during apoptosis was measured by conventional gel electrophoresis and ELISA. The cell morphology was examined by hematoxylin/eosin staining method. Cell viability was also monitored by MTT assay. Contrary to expectations, the peptide aldehydes listed above and Ac-YVAD-Cmk, known as highly specific ICE inhibitors, did not inhibit the apoptosis of these cell types. However, Z-D(OtBu)-Bmk, which had no relevant inhibitory activity on ICE, potently blocked the DNA fragmentation in THP-1 cells and thymocytes whichever of the inducing agents was used. In the other two cell lines Z-D(OtBu)-Bmk was inactive. The apoptotic cell morphology was also inhibited by Z-D(OtBu)-Bmk. Nevertheless, Z-D(OtBu)-Bmk failed to prevent the loss of mitochondrial activity and the cell destruction in the late phase of apoptosis. These data suggest that ICE is not involved in the apoptotic cell death induced by chemical agents. Thus, Z-D(OtBu)-Bmk, a common intermediate of some ICE inhibitors, may be a useful antiapoptotic agent for studying the early events of apoptosis in some cell types.

Cloning and expression of a rat brain interleukin-1beta-converting enzyme (ICE)-related protease (IRP) and its possible role in apoptosis of cultured cerebellar granule neurons

Several members of the IL-1beta-converting enzyme (ICE) family of proteases recently have been implicated in the intracellular cascade mediating the apoptotic death of various cell types. It is unclear, however, whether ICE-related proteases are involved in apoptosis of mammalian neurons and, if so, how they are activated. Here we report the cloning of an ICE-related protease (IRP) from rat brain, which displays strong sequence identity to human CPP32. In situ hybridization histochemistry reveals that this IRP mRNA is expressed in neuron-enriched regions of the developing and adult rat brain but is profoundly downregulated in the adult (compared with developing) brain. To investigate whether this IRP is involved in the death of neurons in the developing brain, we studied IRP expression in cultured cerebellar granule neurons. In cultured cerebellar granule neurons, reduction of extracellular K+ reliably induces apoptosis and stimulates overexpression of IRP mRNA. The latter is especially prominent 4 hr after switching from high K+ to low K+ medium. The expression of IRP mRNA was maintained at this level for at least 8 hr and was followed by apoptotic death of these neurons. Induction of IRP mRNA and cell death are blocked completely by adding depolarizing concentrations of K+ </=90 min after switching to low K+ medium (i.e., before the commitment point for apoptosis) and partially blocked by brain-derived neurotrophic factor (BDNF), which also partially rescues granule neurons from low K+-induced apoptosis. In addition, overexpression of IRP cDNA in HeLa cells results in cell death accompanied by strong internucleosomal cleavage of DNA, a typical feature of apoptosis. Finally, we detected cleavage of the putative death substrate poly (ADP-ribose) polymerase (PARP), beginning 8 hr after changing from high K+ to low K+ medium, coinciding with the time course of induced expression of the IRP gene. Our data suggest that transcriptional activation of IRP could be one of the mechanisms involved in the apoptotic death of cerebellar granule neurons.

Target protease specificity of the viral serpin CrmA. Analysis of five caspases

When ectopically expressed in animal cells, cytokine response modifier A (CrmA), a product of the cowpox virus, prevents programmed cell death initiated by a variety of stimuli. Since CrmA is a proteinase inhibitor, its target is probably a protease that promotes cell death. The identification of this target is crucial in delineating essential regulation points that modulate the apoptotic program. We have compared the kinetics of interaction of CrmA with five proteases that may play a role in apoptosis. Four of the proteases, all members of the caspase family, are inhibited with widely different rates and affinities ranging over 5 orders of magnitude. One is not inhibited at all under the experimental conditions. CrmA is quite selective in its ability to inhibit caspases, showing the highest affinity for interleukin-1beta-converting enzyme and the second highest for the caspase FLICE (Ki = 0.95 nM), identified as a component of the intracellular signaling complex recruited by ligation of the death receptor Fas. On the basis of comparative inhibitor kinetics, we propose that CrmA is unlikely to inhibit the caspases Yama, Mch2, or LAP3 in vivo but that its inhibition of FLICE is of a magnitude for this protease to be a key target of CrmA during Fas-mediated apoptosis. Therefore, our results support the hypothesis that FLICE catalyzes a crucial step in the promotion of cell death.

Hyperresponsive febrile reactions to interleukin (IL) 1alpha and IL-1beta, and altered brain cytokine mRNA and serum cytokine levels, in IL-1beta-deficient mice

IL-1beta is an endogenous pyrogen that is induced during systemic lipopolysaccharide (LPS)- or IL-1-induced fever. We have examined the fever and cytokine responses following i.p. injection of IL-1 agonists, IL-1alpha and IL-1beta, and compared these with response to LPS (i.p.) in wild-type and IL-1beta-deficient mice. The IL-1beta deficient mice appear to have elevated body temperature but exhibit a normal circadian temperature cycle. Exogenously injected IL-1beta, IL-1alpha, or LPS induced hyperresponsive fevers in the IL-1beta-deficient mice. We also observed phenotypic differences between wild-type and IL-1beta-deficient mice in hypothalamic basal mRNA levels for IL-1alpha and IL-6, but not for IL-1beta-converting enzyme or IL-1 receptor type I or type II. The IL-1alpha mRNA levels were down-regulated, whereas the IL-6 mRNA levels were up-regulated in the hypothalamus of IL-1beta-deficient mice as compared with wild-type mice. The IL-1beta-deficient mice also responded to LPS challenge with significantly higher serum corticosterone and with lower serum tumor necrosis factor type alpha levels than the wild-type mice. The data suggest that, in the redundant cascade of proinflammatory cytokines, IL-1beta plays an important but not obligatory role in fever induction by LPS or IL-1alpha, as well as in the induction of serum tumor necrosis factor type alpha and corticosterone responses either by LPS or by IL-1alpha or IL-1beta.

Granzyme B (GraB) autonomously crosses the cell membrane and perforin initiates apoptosis and GraB nuclear localization

Granzyme B (GraB) induces apoptosis in the presence of perforin. Perforin polymerizes in the cell membrane to form a nonspecific ion pore, but it is not known where GraB acts to initiate the events that ultimately lead to apoptosis. It has been hypothesized that GraB enters the target cell through a perforin channel and then initiates apoptosis by cleaving and activating members of the ICE/Ced-3 family of cell death proteases. To determine if GraB can enter the cell, we treated YAC-1 or HeLa cells with FITC-labeled GraB and measured intracellular fluorescence with a high sensitivity CCD camera and image analyzer. GraB was internalized and found diffusely dispersed in the cell cytoplasm within 10 min. Uptake was inhibited at low temperature (4 degrees C) and by pretreatment with metabolic inhibitors, NaF and DNP, or cytochalasin B, a drug that both blocks microfilament formation, and FITC-GraB remained on the cell membrane localized in patches. With the simultaneous addition of perforin and FITC-GraB, no significant increase in cytoplasmic fluorescence was observed over that found in cells treated only with FITC-GraB. However, FITC-GraB was now detected in the nucleus of apoptotic cells labeling apoptotic bodies and localized areas within and along the nuclear membrane. The ability of GraB to enter cells in the absence of perforin was reexamined using anti-GraB antibody immunogold staining of ultrathin cryosections of cells incubated with GraB. Within 15 min, gold particles were detected both on the plasma membrane and in the cytoplasm of cells with some gold staining adjacent to the nuclear envelope but not in the nucleus. Cells internalizing GraB in the absence of perforin appeared morphologically normal by Hoechst staining and electron microscopy. GraB directly microinjected into the cytoplasm of B16 melanoma cells induced transient plasma membrane blebbing and nuclear coarsening but the cells did not become frankly apoptotic unless perforin was added. We conclude that GraB can enter cells autonomously but that perforin initiates the apoptotic process and the entry of GraB into the nucleus.

Expression of a dominant negative mutant of interleukin-1 beta converting enzyme in transgenic mice prevents neuronal cell death induced by trophic factor withdrawal and ischemic brain injury

To explore the role of the interleukin (IL)-1 beta converting enzyme (ICE) in neuronal apoptosis, we designed a mutant ICE gene (C285G) that acts as a dominant negative ICE inhibitor. Microinjection of the mutant ICE gene into embryonal chicken dorsal root ganglial neurons inhibits trophic factor withdrawal-induced apoptosis. Transgenic mice expressing the fused mutant ICE-lacZ gene under the control of the neuron specific enolase promoter appeared neurologically normal. These mice are deficient in processing pro-IL-1 beta, indicating that mutant ICEC285G blocks ICE function. Dorsal root ganglial neurons isolated from transgenic mice were resistant to trophic factor withdrawal-induced apoptosis. In addition, the neurons isolated from newborn ICE knockout mice are similarly resistant to trophic factor withdrawal-induced apoptosis. After permanent focal ischemia by middle cerebral artery occlusion, the mutant ICEC285G transgenic mice show significantly reduced brain injury as well as less behavioral deficits when compared to the wild-type controls. Since ICE is the only enzyme with IL-1 beta convertase activity in mice, our data indicates that the mutant ICEC285G inhibits ICE, and hence mature IL-1 beta production, and through this mechanism, at least in part, inhibits apoptosis. Our data suggest that genetic manipulation using ICE family dominant negative inhibitors can ameliorate the extent of ischemia-induced brain injury and preserve neurological function.

Impact of knockout mice in toxicology

Knockout mice obtained by homologous recombination technology may be valuable tools for in vivo investigations in toxicopathogenesis. A short review is given on the phenotype of mice with distinct deletions of cytokines and related genes. The application of these mice in pharmacological and toxicological research is discussed, with emphasis in endotoxic shock, hepatic toxicity, and myelotoxicity. The use of such knockout mice will be valuable for mechanistic studies in toxicology.

Interleukin-1beta is differentially expressed by human dermal papilla cells in response to PKC activation and is a potent inhibitor of human hair follicle growth in organ culture

The dermal papilla plays an important role in the regulation of hair follicle matrix cell proliferation and hair fiber production, at least in part through mesenchymal-epithelial interactions. In the present study, we have investigated the regulation of interleukin-1 (IL-1) production by protein kinase C in cultured human dermal papilla cells. Treatment of dermal papilla cells with 12-O-tetradecanoylphorbol-13-acetate (TPA) elicited the rapid and transient production of mature (17 kDa) cytosolic IL-1beta protein, but not IL-1alpha, with maximal levels achieved after 12 h. Rapid secretion of IL-1beta into the medium occurred subsequent to increased intracellular cytokine levels, after which medium IL-1beta protein levels were stable for 4 days. Northern blot analysis showed that TPA treatment elicited a transient induction of IL-1beta mRNA expression, maximal after 12 h, indicating that TPA regulates dermal papilla cell IL-1beta production at the transcriptional level. Pretreatment of dermal papilla cells with Ro 31-7549, a selective protein kinase C inhibitor, dose dependently and completely reversed phorbol-induced IL-1beta protein production. In addition, we demonstrated that IL-1beta is a highly potent inhibitor of the growth of human hair follicles in whole-organ culture, with an IC50 value of approximately 5 pg/ml. These findings, taken together with a previous report that follicular matrix cells express type I IL-1 receptors but dermal papilla cells do not, raise the possibility that dermal papilla cell-derived IL-1beta may act as a negative paracrine factor in the regulation of matrix cell proliferation.

Kinase cascades regulating entry into apoptosis

All cells are constantly exposed to conflicting environment cues that signal cell survival or cell death. Survival signals are delivered by autocrine or paracrine factors that actively suppress a default death pathway. In addition to survival factor withdrawal, cell death can be triggered by environmental stresses such as heat, UV light, and hyperosmolarity or by dedicated death receptors (e.g., FAS/APO-1 and tumor necrosis factor [TNF] receptors) that are counterparts of growth factor or survival receptors at the cell surface. One of the ways that cells integrate conflicting exogenous stimuli is by phosphorylation (or dephosphorylation) of cellular constituents by interacting cascades of serine/threonine and tyrosine protein kinases (and phosphatases). Survival factors (e.g., growth factors and mitogens) activate receptor tyrosine kinases and selected mitogen-activated, cyclin-dependent, lipid-activated, nucleic acid-dependent, and cyclic AMP-dependent kinases to promote cell survival and proliferation, whereas environmental stress (or death factors such as FAS/APO-1 ligand and TNF-alpha) activates different members of these kinase families to inhibit cell growth and, under some circumstances, promote apoptotic cell death. Because individual kinase cascades can interact with one another, they are able to integrate conflicting exogenous stimuli and provide a link between cell surface receptors and the biochemical pathways leading to cell proliferation or cell death.

Inhibition of ICE-related proteases (caspases) and nuclear apoptosis by phenylarsine oxide

Biochemical analyses of nuclear apoptosis in vitro have revealed the existence of multiple active interleukin-1beta-converting enzyme-related proteases (caspases) with distinct substrate recognition properties in extracts of preapoptotic chicken DU249 cells (S/M extracts). Previously we demonstrated that the activity of a caspase that cleaves lamins is required for the disintegration of nuclei in the late stages of apoptosis, despite the presence of a second active caspase that cleaves poly(ADP-ribose) polymerase (PARP). One simple explanation for this observation was that the lamin-cleaving caspase is sufficient to drive the nuclear events of apoptotic execution. Here, we report that phenylarsine oxide (PAO) inhibits the protease activities of recombinant human caspases as well as endogenous chicken caspases that are active in S/M extracts. PAO at 100 microM blocks the morphological changes of nuclear apoptosis in vitro and internucleosomal DNA fragmentation in S/M extracts without interfering with PARP or lamin A cleavage. Thus, lamin cleavage is not sufficient to drive the changes in nuclear morphology characteristic of apoptosis. Affinity labeling with YV(bio)KD-aomk shows that the degree of sensitivity to PAO differs among active caspases in S/M extracts. These results suggest that a PAO-sensitive caspase that is distinct from the PARP- or lamin-cleaving enzymes is required for the initiation of apoptotic morphological changes and for the activation of endonuclease(s). Taken together, our results suggest that two or more caspases are required for proteolytic events that are essential for the initiation and completion of nuclear apoptotic changes. The observation that PAO is an inhibitor of caspases and nuclear apoptotic events should be useful for the biochemical dissection of apoptosis in vitro and in vivo.

Specific expression of CPP32 in sensory neurons of mouse embryos and activation of CPP32 in the apoptosis induced by a withdrawal of NGF

We isolated mouse CPP32/apopain cDNA, a mammalian homologue most closely related to Ced-3 in C. elegans, and examined the involvement of CPP32 in the apoptosis of nervous system during development. CPP32 is specifically expressed in the trigeminal (V) ganglia, facio-acoustic (VII-VIII) ganglion complex, and dorsal root ganglia (DRGs) of mouse 10.5-day embryos. CPP32-like proteases are activated during apoptosis of DRG neurons induced by deprivation of NGF and serum. Ac-DEVD-CHO, an inhibitor for CPP32-like proteases, prevents apoptosis of DRG neurons, but Ac-YVAD-CHO, an inhibitor for ICE-like proteases, does not. These results suggest that CPP32 or CPP32-like proteases play a role as central mediator in the apoptosis of DRG neurons induced by lack of neurotrophin signals.

Identification and mapping of Casp7, a cysteine protease resembling CPP32 beta, interleukin-1 beta converting enzyme, and CED-3

Cloning of interleukin-1 beta converting enzyme (ICE) and Caenorhabditis elegans death protein CED-3 revealed the structural and functional homology between these two proteases. It also suggested the involvement of ICE-like cysteine proteases in apoptosis. Several CED-3- and ICE-like cysteine proteases have been described, including Nedd2/Ich-1, CPP32 beta, Tx, ICErel3, and Mch2. We have previously described a mouse ortholog of cysteine protease CPP32 beta that shares strong homology with ICE and CED-3. Here, we describe the cloning of mouse and human Casp7, another member of this family of cysteine proteases. Mouse Casp7 encodes a putative 340-amino-acid polypeptide that contains all the known conserved residues required for protease function, including the QACRG sequence, aspartic acid residues for internal cleavage sites, and the residues required for substrate binding. Three RNA variants of human Casp7 were also cloned. Amino acid sequence analysis indicated that Casp7 shared high homology with CPP32 beta/Casp3 and Mch2/Casp6. Northern blot analysis demonstrated that a 2.6-kb Casp7 mRNA was expressed in various tissues except brain. Mouse interspecific backcross mapping allowed localization of Casp7 to the distal region of mouse chromosome 19, linked to Mxi1, Adra2a, and Aop1.

Activation of the cell death program by inhibition of proteasome function

Activation of proteolytic enzymes, including cysteine proteases of the ced-3/ICE family, is a characteristic feature of the apoptotic program. In contrast, the role of the proteasome as the major nonlysosomal machinery to degrade or process proteins by ATP/ubiquitin-dependent proteolysis in this process is less clear. In human leukemic HL60 cells, inhibition of proteasome-mediated proteolysis by specific proteasomal inhibitors leads to the rapid induction of apoptosis as judged by morphological changes as well as by nuclear condensation and DNA fragmentation. HL60 apoptosis is due to activation of CPP32, a member of the ced-3/ICE family of cysteine proteases, and appears to occur independently from ICE activity. HL60 apoptosis is accompanied by an increase in the concentration of the cyclin-dependent kinase inhibitor p27Kip1. Labeling of the cells by the TUNEL technique demonstrates that HL60 cells undergoing apoptosis are primarily in the G1 phase of the cell cycle. Proteasomal activity therefore appears to be required in proliferating, but not in quiescent, HL60 cells for cell survival as well as normal progression through the cell cycle.

Role of interleukin-1 beta converting enzyme (ICE) in acute myelogenous leukemia cell proliferation and programmed cell death

The proinflammatory cytokine interleukin (IL)-1 has been shown to play a pivotal role in stimulating acute myelogenous leukemia (AML) cell proliferation. The gene for its prominent IL-1 beta form produces a 31-kDa precursor protein (pro-IL-1 beta) that is biologically inactive unless cleaved to its mature form by a cytoplasmic cysteine protease termed Il- 1 beta converting enzyme (ICE). Although ICE was first thought to be a unique enzyme with a single biologic activity, several investigators have demonstrated that ICE shares sequence homology with the protein product of ced-3, the gene for cell death of the nematode Caenorhabditis elegans, and induces apoptosis in different experimental models. It was therefore hypothesized that ICE may either augment the production of mature IL-1 beta and stimulate the proliferation of cells, in which IL-1 beta acts as an autocrine growth factor, or induce apoptosis. Recent data indicate that ICE is a member of an increasingly recognized family of cysteine proteases. Unlike ICE, the other members of this family do not cleave pro-IL-1 beta but are effective inducers of apoptotic cell death, whereas ICE acts primarily as an IL-1 beta converting enzyme. Because IL-1 beta serves as either an autocrine or paracrine growth factor in AML, we recently investigated the effect of ICE inhibition on AML colony growth and found that ICE inhibition reduced the production of mature IL-1 beta and suppressed AML progenitor proliferation. Our data suggest that ICE does not function as an apoptosis gene in AML but rather increases mature Il-1 beta production and AML cell proliferation. It is possible, therefore, that ICE inhibitors may be beneficial in AML therapy.

A combinatorial approach for determining protease specificities: application to interleukin-1beta converting enzyme (ICE)

BACKGROUND

Interleukin-1beta converting enzyme (ICE/caspase-1) is the protease responsible for interleukin-1beta (IL-1beta) production in monocytes. It was the first member of a new cysteine protease family to be identified. Members of this family have functions in both inflammation and apoptosis.

RESULTS

A novel method for identifying protease specificity, employing a positional-scanning substrate library, was used to determine the amino-acid preferences of ICE. Using this method, the complete specificity of a protease can be mapped in the time required to perform one assay. The results indicate that the optimal tetrapeptide recognition sequence for ICE is WEHD, not YVAD, as previously believed, and this led to the synthesis of an unusually potent aldehyde inhibitor, Ac-WEHD-CHO (Ki = 56 pM). The structural basis for this potent inhibition was determined by X-ray crystallography.

CONCLUSIONS

The results presented in this study establish a positional-scanning library as a powerful tool for rapidly and accurately assessing protease specificity. The preferred sequence for ICE (WEHD) differs significantly from that found in human pro-interleukin-1beta (YVHD), which suggests that this protease may have additional endogenous substrates, consistent with evidence linking it to apoptosis and IL-1alpha production.

DCP-1, a Drosophila cell death protease essential for development

Apoptosis, a form of cellular suicide, involves the activation of CED-3-related cysteine proteases (caspases). The regulation of caspases by apoptotic signals and the precise mechanism by which they kill the cell remain unknown. In Drosophila, different death-inducing stimuli induce the expression of the apoptotic activator reaper. Cell killing by reaper and two genetically linked apoptotic activators, hid and grim, requires caspase activity. A Drosophila caspase, named Drosophila caspase-1 (DCP-1), was identified and found to be structurally and biochemically similar to Caenorhabditis elegans CED-3. Loss of zygotic DCP-1 function in Drosophila caused larval lethality and melanotic tumors, showing that this gene is essential for normal development.

Reduced incidence and severity of antigen-induced autoimmune diseases in mice lacking interferon regulatory factor-1

Interferon regulatory factor-1 (IRF-1) is a transcription factor that regulates interferon-induced genes and type I interferons. Recently, studies of IRF-l-deficient mice have revealed that IRF-I regulates the induction of molecules that play important roles in inflammation, such as inducible nitric oxide synthase (iNOS) and interleukin-l beta-converting enzyme (ICE). To study the role of IRF-1 in autoimmunity, we investigated type II collagen-induced arthritis (CIA), and experimental allergic encephalomyelitis (EAE), in mice lacking IRF-1. The incidence and severity of CIA were significantly decreased in IRF-1-/- mice compared with IRF-l +/- mice, as was the production of interferon (IFN)-gamma in lymph node cells. Both IRF-l+/- and IRF-1-/- mice exhibited mild and transient disease after adoptive transfer of a type II collagen (CII)-specific T cell line together with sera from arthritic mice, but the IRF-1-/- mice were less severely affected than the IRF-1+/- mice. In addition, the incidence of EAE in IRF-1-/- mice was decreased as compared with IRF-1 +/- mice. Reverse transcription polymerase chain reaction showed that IRF-1 mRNA was constitutively expressed in the spinal cords of IRF-1+/- mice, and was upregulated in mice with clinical EAE. Expression of iNOS was also detected in inflamed spinal cords. These results suggest that IRF-I plays a key role in promoting inflammation and autoimmunity in CIA and EAE animal models.

A Cysteine Protease Inhibitor Prevents Activation-Induced T-Cell Apoptosis and Death of Peripheral Blood Cells From Human Immunodeficiency Virus-Infected Individuals by Inhibiting Upregulation of Fas Ligand

Activation of T-cell hybridomas, preactivated normal T cells, and peripheral blood lymphocytes (PBL) from human immunodeficiency virus (HIV)-infected individuals results in apoptosis. In the first two cases, apoptosis is caused by the upregulation of Fas ligand (FasL) and its subsequent interaction with Fas; the mechanism for the spontaneous and activation-induced death of lymph node cells and PBL from HIV+ blood is not known. A number of protease inhibitors have been shown to prevent T-cell apoptosis under all of these circumstances, but the mechanism of action has not been determined. Here we show that the cysteine protease inhibitor E64d prevents activation-induced T hybridoma cell death by inhibiting the upregulation of FasL. Quantitative polymerase chain reaction (PCR) demonstrated that mRNA for FasL is expressed at low levels in fresh PBL from HIV-infected blood, but increases in cultured PBL from both uninfected and HIV-infected donors. The ex vivo apoptosis of PBL from HIV+ donors was prevented by adding the soluble extracellular domain of Fas, demonstrating a requisite role for Fas/FasL interactions in this form of cell death. Furthermore, while having no effect on the death of PBL from HIV-infected blood stimulated directly via Fas, E64d inhibited FasL upregulation. Thus, aberrant apoptosis of cultured PBL from HIV-infected individuals is mediated by FasL and Fas, and E64d blocks this apoptosis by inhibiting the upregulation of FasL. These results are consistent with the hypothesis that the abnormal expression of Fas and the inducible expression of FasL contributes to the immunodeficiency of patients with acquired immune deficiency syndrome and suggest that modulation of FasL expression could be an effective target for therapeutic intervention.

Activation of interferon-gamma inducing factor mediated by interleukin-1beta converting enzyme

The interleukin-1beta (IL-1beta) converting enzyme (ICE) processes the inactive IL-1beta precursor to the proinflammatory cytokine. ICE was also shown to cleave the precursor of interferon-gamma inducing factor (IGIF) at the authentic processing site with high efficiency, thereby activating IGIF and facilitating its export. Lipopolysaccharide-activated ICE-deficient (ICE-/-) Kupffer cells synthesized the IGIF precursor but failed to process it into the active form. Interferon-gamma and IGIF were diminished in the sera of ICE-/- mice exposed to Propionibacterium acnes and lipopolysaccharide. The lack of multiple proinflammatory cytokines in ICE-/- mice may account for their protection from septic shock.

Interleukin (IL) 1beta, IL-1 receptor antagonist, IL-10, and IL-13 gene expression in the central nervous system and anterior pituitary during systemic inflammation: pathophysiological implications

The pathophysiology of systemic inflammation and sepsis involves peripheral organs, causing gastrointestinal, renal, and cardiovascular alterations, as well as the central nervous system (CNS), affecting sleep, temperature regulation, behavior, and neuroendocrine function. The molecular basis of the CNS effects of systemic inflammation are not fully elucidated. Here we show that the CNS responds to systemic inflammation with pronounced IL-1beta gene expression and limited IL-1 receptor antagonist (IL-1ra), IL-10, and IL-13 gene expression. This pattern occurs throughout the CNS, including areas such as the subfornical organ, pineal gland, neurohypophysis, and hypothalamus. In contrast, in the anterior pituitary, we found limited IL-1beta gene expression but marked induction of the mRNA encoding for the secreted isoform of IL-1ra, secreted IL-1ra. We conclude that the central manifestations of peripheral inflammation are mediated by endogenous brain IL-1beta synthesized during systemic inflammation in the context of limited central cytokine counter regulation of IL-1. As IL-1beta is a potent stimulus for inducible nitric oxide synthase expression and activity, these findings explain our previous observation that systemic inflammation promotes inducible nitric oxide synthase gene expression in the brain and the spillover of NO metabolites into cerebrospinal fluid. The CNS transcription of the HIV-1 replication factor IL-1beta in the context of limited transcription of the IL-1 replication inhibitors IL-1ra, IL-10, and IL-13 might help explain the negative impact of systemic inflammation on the clinical course of AIDS. In addition, we propose that IL-1ra may be secreted by the anterior pituitary as a systemic anti-inflammatory hormone that is released in response to IL-1beta originated from multiple sources.

Macromolecular substrates for the ICE-like proteases during apoptosis

The interleukin-1 beta-converting enzyme (ICE) family of proteases is an important component of the mechanism of the apoptotic process, but the physiologic roles of the different homologs during apoptosis remain unclear. Significant information about the roles of proteolysis in apoptosis will be gained through identification of the distal substrates through which these proteases achieve their pro-apoptotic effects. Identification of these substrates therefore remains an important challenge. A subset of autoantibodies from patients with systemic lupus erythematosus (SLE) recognize molecules that are specifically cleaved early during apoptosis. Several of the identified autoantigens are nuclear proteins (PARP, U1-70 kDa, and DNA-PKcs) that are substrates for CPP32 in vitro and in apoptotic cells. Of note, these substrates are catalytic proteins involved in homeostatic pathways, suggesting that abolition of homeostasis is one fundamental feature ensuring the rapid irreversibility of the apoptotic process. Identification of the other substrates for this protease family will provide the tools to assess the roles of the different proteases in apoptotic death.

Apoptosis: its role in the development of malignancies and its potential as a novel therapeutic target

OBJECTIVE

To review the current literature regarding the role of apoptosis in the development of malignant cells and how the induction of this pathway could be used in cancer therapy.

DATA SOURCE

A MEDLINE search of basic science articles pertinent to the understanding of the normal physiologic process of apoptosis was conducted.

STUDY SELECTION

Because of the rapidly growing literature regarding apoptosis, only articles describing key processes in the biology of the cell and the genetic control of apoptosis were included.

DATA SYNTHESIS

Apoptosis is imperative for host survival since it discards unwanted, damaged, and atypical cells. The process is therefore implicated in the continuous regulation of development, differentiation, and homeostasis. Furthermore, apoptosis is a response to physiologic and pathologic stresses that disrupt the balanced rates of cell generation and elimination. In a disease such as cancer, there is a lack of equilibrium between the rates of cell division and cell death; agents that promote or suppress apoptosis can manipulate these rates, influencing the anomalous accumulation of neoplastic cells. Pharmacologic manipulation of apoptosis can manipulate these rates, influencing the anomalous accumulation represents a novel approach in targeting malignant cells and has far-reaching implications for new directions in cancer therapy.

CONCLUSIONS

Apoptosis is a highly organized physiologic mechanism of destroying injured and abnormal cells as well as maintaining homeostasis in multicellular organisms. Both the activation and inhibition of apoptosis are tightly controlled. Pharmacologic manipulation of this pathway is a novel therapeutic target in cancer therapy.

Central nervous system cytokines and their relevance for neurotoxicity and apoptosis

Cytokines are molecules that are synthesized not only by the immune system, but also by cells in the central nervous system, including neurons, glia, and brain vascular cells. In the brain, cytokines can be neuroprotective or they can contribute to neurodegeneration. The role of cytokines in the regulation of normal and abnormal brain function represents a rapidly growing frontier in neuroscience. Cytokines are pleiotropic and redundant, and they can modulate the effects of neurotransmitters and neuropeptides; thus, in order to understand the effects of brain cytokines on apoptosis and toxicity, it is necessary to study the temporal and spatial expression of complex networks of cytokines, growth factors, neuropeptides, and neurotransmitters. This effort is currently in progress in many centers. Modulation of cytokine function in the central nervous system represents a new therapeutic strategy for neurodegeneration.

Characterization of mice deficient in interleukin-1 beta converting enzyme

Interleukin-1 beta converting enzyme (ICE) processes the inactive prolL-1 beta to the proinflammatory mature IL-1 beta. ICE belongs to a family of cysteine proteases that have been implicated in apoptosis. To address the biological functions of ICE, we generated ICE-deficient mice through gene targeting technology. ICE-deficient mice developed normally, appeared healthy, and were fertile. Peritoneal macrophages from ICE-deficient mice underwent apoptosis normally upon ATP treatment. Thymocytes from young ICE-deficient mice also underwent apoptosis when triggered by dexamethasone, gamma irradiation, or aging. ICE-deficient mice had a major defect in the production of mature IL-1 beta and had impaired IL-1 alpha production on LPS stimulation in vitro and in vivo. ICE-deficient mice were resistant to LPS-induced endotoxic shock.

Caspase inhibition selectively reduces the apoptotic component of oxygen-glucose deprivation-induced cortical neuronal cell death

Cultured mouse cortical neurons undergo apoptosis when exposed to staurosporine. The cell-permeable caspase inhibitor Z-Val-Ala-Asp fluoromethylketone (Z-VAD.FMK) attenuated this death, without altering overall protein synthesis. Z-VAD.FMK also attenuated cortical neuronal apoptosis induced by removal of serum. However, Z-VAD.FMK did not attenuate the excitotoxic necrosis induced by 5-min exposure to 100 microM NMDA, 24-h exposure to 100 microM kainate, or 90-min exposure to oxygen-glucose deprivation. We have previously shown that blockade of the excitotoxic component of oxygen-glucose deprivation-induced neuronal death with glutamate antagonists unmasks an apoptotic death. Treatment with Z-VAD.FMK, but not the cathepsin-B protease inhibitor Z-Phe-Ala fluoromethylketone (Z-FA.FMK), also attenuated this oxygen-glucose deprivation-induced neuronal apoptosis. These data support the idea that brain caspases mediate the apoptotic component of oxygen-glucose deprivation-induced neuronal death and raise the possibility that combining caspase inhibitors with glutamate antagonists might attenuate brain damage induced by hypoxic-ischemic insults in vivo.

Apoptosis and disease: regulation and clinical relevance of programmed cell death

Regulation of the homeostatic balance between cell proliferation and cell death is essential for development and maintenance of multicellular organisms. Physiologic, or programmed, cell death is dependent on a genetically encoded and evolutionarily conserved pathway that induces a form of cellular suicide known as apoptosis. In the past decade, it has become clear that the regulatory mechanisms controlling programmed cell death are as fundamental, and as complex, as those regulating cell proliferation. Perturbation of the signaling cascades regulating apoptosis, whether by extracellular triggers, acquired or germline genetic mutations, or viral mimicry of signaling molecules, can result in a wide variety of human diseases. Analysis of these regulatory pathways has led to a better understanding of the etiology and pathogenesis of many human diseases, notably cancers, infectious diseases including AIDS, autoimmune diseases, and neurodegenerative/neurodevelopmental diseases. Our understanding of the regulation of programmed cell death in health and disease is far from complete, and the challenge of converting that understanding into new therapeutic modalities has only begun to be approached.

Structure and function of interleukin-1 beta converting enzyme

An overwhelming body of evidence has shown that IL-1 beta is a major mediator of inflammatory disease (Tocci and Schmidt, 1996). The discovery of ICE, a unique processing enzyme involved in the production of active IL-1 beta, has provided a new approach to specifically block the production of this potent cytokine. Consequently, the discovery and development of inhibitors against the enzyme could hold great promise therapeutically. Potent inhibitors of the enzyme would be useful in the treatment of a number of important inflammatory diseases and potentially in the management of leukemia (Arend, 1993b; Estrov and Talpaz, 1996). A number of key questions must be answered before the therapeutic potential of such inhibitors can be realized. The development of a pharmaceutically acceptable cysteine proteinase inhibitor will almost certainly involve new chemical strategies gauged at safely inactivating the enzyme. For such inhibitors, it will be necessary to achieve selectivity for ICE from among the growing number of ICE family members while retaining potency. It will also be important to establish the level of inhibition of IL-1 beta required to achieve therapeutic efficacy. The studies comparing IL-1 beta- and ICE-deficient mice suggest that complete abrogation of IL-1 beta is required to achieve efficacy in models of inflammation. It is not known if this is the case in humans. Understanding the source of the residual IL-1 beta produced in ICE-deficient mice will be important in order to ascertain if a similar mechanism could generate active IL-1 beta in patients receiving if a ICE inhibitor. As for ICE itself, a number of formidable questions remain regarding its regulation and mechanism of activation. Answering these questions experimentally will present a major challenge due to the extremely low levels of enzyme present in cells. Studies on other family members may provide easier access to some of these questions and provide clues that can be applied to ICE. The components of the pathway involved in IL-1 trafficking and secretion are unknown, as are the mechanisms of ICE activation and regulation. Clearly other cellular proteins that have yet to be discovered will be involved in each of these processes, opening up new avenues of research in this field.

Mammalian cell death proteases: a family of highly conserved aspartate specific cysteine proteases

So far nine human aspartate-specific cysteine proteases (ASCPs) have been identified and cloned in our lab and others. Their sequence and structural homology to the nematode Ced-3 implicated them in the cell death pathway of mammalian cells. Recent evidence suggests that ASCPs initiate apoptosis by acting at or near the cell death effector level. However, it is not clear whether the activity of one or several of these enzymes is necessary for execution of apoptosis. In addition, it is not yet clear how the proenzymes of ASCPs are activated or what triggers their activation. Execution of apoptosis in higher eukaryotes is apparently more complicated than in nematodes. It is most likely that in mammalian cells this process involves the coordinated action of multiple ASCPs and multiple redundant proteolytic pathways.

Increased expression of IL-1beta converting enzyme in hippocampus after ischemia: selective localization in microglia

Although the interleukin-1beta converting enzyme (ICE)/CED-3 family of proteases has been implicated recently in neuronal cell death in vitro and in ovo, the role of specific genes belonging to this family in cell death in the nervous system remains unknown. To address this question, we examined the in vivo expression of one of these genes, Ice, after global forebrain ischemia in gerbils. Using RT-PCR and Western immunoblot techniques, we detected an increase in the mRNA and protein expression of ICE in hippocampus during a period of 4 d after ischemia. Chromatin condensation was observed in CA1 neurons within 2 d after ischemia. Internucleosomal DNA fragmentation and apoptotic bodies were observed between 3 and 4 d after ischemia, a period during which CA1 neuronal death is maximal. In nonischemic brains, ICE-like immunoreactivity was relatively low in CA1 pyramidal neurons but high in scattered hippocampal interneurons. After ischemia, ICE-like immunoreactivity was not altered in these neurons. ICE-like immunoreactivity, however, was observed in microglial cells in the regions adjacent to the CA1 layer as early as 2 d after ischemic insult. The increase in ICE-like immunoreactivity was robust at 4 d after ischemia, a period that correlates with the DNA fragmentation observed in hippocampal homogenates of ischemic brains. These results provide the first evidence for the localization and induction of ICE expression in vivo after ischemia and suggest an indirect role for ICE in ischemic damage through mediation of an inflammatory response.

Molecular ordering of the Fas-apoptotic pathway: the Fas/APO-1 protease Mch5 is a CrmA-inhibitable protease that activates multiple Ced-3/ICE-like cysteine proteases

The Fas/APO-1-receptor associated cysteine protease Mch5 (MACH/FLICE) is believed to be the enzyme responsible for activating a protease cascade after Fas-receptor ligation, leading to cell death. The Fas-apoptotic pathway is potently inhibited by the cowpox serpin CrmA, suggesting that Mch5 could be the target of this serpin. Bacterial expression of proMch5 generated a mature enzyme composed of two subunits, which are derived from the pre-cursor proenzyme by processing at Asp-227, Asp-233, Asp-391, and Asp-401. We demonstrate that recombinant Mch5 is able to process/activate all known ICE/Ced-3-like cysteine proteases and is potently inhibited by CrmA. This contrasts with the observation that Mch4, the second FADD-related cysteine protease that is also able to process/activate all known ICE/Ced-3-like cysteine proteases, is poorly inhibited by CrmA. These data suggest that Mch5 is the most upstream protease that receives the activation signal from the Fas-receptor to initiate the apoptotic protease cascade that leads to activation of ICE-like proteases (TX, ICE, and ICE-relIII), Ced-3-like proteases (CPP32, Mch2, Mch3, Mch4, and Mch6), and the ICH-1 protease. On the other hand, Mch4 could be a second upstream protease that is responsible for activation of the same protease cascade in CrmA-insensitive apoptotic pathways.

Lamin proteolysis facilitates nuclear events during apoptosis

Expression of the adenovirus E1A oncogene stimulates both cell proliferation and p53-dependent apoptosis in rodent cells. p53 implements apoptosis in all or in part through transcriptional activation of bax, the product of which promotes cell death. The adenovirus E1B 19K product is homologous in sequence and in function to Bcl-2, both of which bind to and inhibit the activity of Bax and thereby suppress apoptosis. The E1B 19K protein also interacts with the nuclear lamins, but the role of this interaction in the regulation of apoptosis is not known. Lamins are, however, substrates for members of the interleukin-1 beta-converting enzyme (ICE) family of cysteine proteases that are activated during apoptosis and function downstream of Bcl-2 in the cell death pathway. lamins are degraded during E1A-induced p53-dependent apoptosis. Lamin A and C are cleaved into 47- and 37-kD fragments, respectively, and the site of proteolysis is mapped to a conserved aspartic acid residue at position 230. The cleavage of lamins during apoptosis is consistent with the activation of an ICE-related cysteine protease down-stream of p53. No lamin protease activity was detected in cells expressing the E1B 19K protein, indicating that 19K functions upstream of protease activation in inhibiting apoptosis. Substitution of the aspartic acid at the cleavage site produced a mutant lamin protein that was resistant to proteolysis both in vitro and in vivo. Expression of uncleavable mutant lamin A or B attenuated apoptosis, delaying cell death and the associated DNA fragmentation by 12 h. Mutant lamin expressing cells failed to show the signs of chromatin condensation and nuclear shrinkage typical of cell death by apoptosis. Instead, the nuclear envelope collapsed and the nuclear lamina remained intact. However, the late stage of apoptosis was morphologically unaltered and formation of apoptotic bodies was evident. Thus, lamin breakdown by proteolytic degradation facilitates the nuclear events of apoptosis perhaps by facilitating nuclear breakdown.