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

Genetic and metabolic status of NGF-deprived sympathetic neurons saved by an inhibitor of ICE family proteases

Sympathetic neurons undergo programmed cell death (PCD) when deprived of NGF. We used an inhibitor to examine the function of interleukin-1 beta-converting enzyme (ICE) family proteases during sympathetic neuronal death and to assess the metabolic and genetic status of neurons saved by such inhibition. Bocaspartyl(OMe)-fluoromethylketone (BAF), a cell-permeable inhibitor of the ICE family of cysteine proteases, inhibited ICE and CPP32 (IC50 approximately 4 microM) in vitro and blocked Fas-mediated apoptosis in thymocytes (EC50 approximately 10 microM). At similar concentrations, BAF also blocked the NGF deprivation-induced death of rat sympathetic neurons in culture. Compared to NGF-maintained neurons, BAF-saved neurons had markedly smaller somas and maintained only basal levels of protein synthesis; readdition of NGF restored growth and metabolism. Although BAF blocked apoptosis in sympathetic neurons, it did not prevent the fall in protein synthesis or the increase in the expression of c-jun, c-fos, and other mRNAs that occur during neuronal PCD, implying that the ICE-family proteases function downstream of these events during PCD.NGF and BAF rescued sympathetic neurons with an identical time course, suggesting that NGF, in addition to inhibiting metabolic and genetic events associated with neuronal PCD, can act posttranslationally to abort apoptosis at a time point indistinguishable from the activation of cysteine proteases. Both poly-(ADP ribose) polymerase and pro-ICE and Ced-3 homolog-1 (ICH-1) appear to be cleaved in a BAF-inhibitable manner, although the majority of pro-CPP32 appears unchanged, suggesting that ICH-1 is activated during neuronal PCD. Potential implications of these findings for anti-apoptotic therapies are discussed.

Cold thoughts of death: the role of ICE proteases in neuronal cell death

While there has been extensive work describing the timing, location and probable signals responsible for regulating programmed cell death (PCD) in the nervous system, relatively little is known about the molecular mechanisms that mediate this process. Several investigators have demonstrated that PCD in general, and neuronal PCD in particular, can be inhibited by drugs that arrest RNA or protein synthesis. These data have been interpreted as suggesting that de novo gene expression is required for cells to commit suicide. The general picture emerging from a number of experimental systems is that a variety of proteins can mediate the coupling of extracellular signals to a resident cell-death program. In this model, some of the components required for death are more or less constitutively present in the cell and await lineage-specific signals for their activation. A recent flood of papers has presented convincing evidence that the resident program for apoptosis in numerous cell types works via a series of essential proteases belonging to the CED-3/ICE family.

Nerve growth factor induces the expression of certain cytokine genes and bcl-2 in mast cells. Potential role in survival promotion

Nerve growth factor (NGF) promotes mast cell survival in vitro (Horigome, K., Bullock, E. D., and Johnson, E. M., Jr. (1994) J. Biol. Chem. 269, 2695-2702). NGF survival promotion is cell density-dependent, and conditioned medium experiments have shown that NGF increases the production of an autocrine mast cell survival activity. Cytokines are potential candidates for autocrine survival factors. In rat peritoneal mast cells (RPMC), NGF caused an increase in the messenger RNAs for interleukin (IL)-3, IL-4, IL-10, tumor necrosis factor-alpha, and granulocyte-macrophage colony-stimulating factor. This induction was NGF dose-dependent, was blocked by NGF-neutralizing antibodies, and was not observed in the non-mast peritoneal cell population. The immunosuppressive agent, cyclosporin A, blocked both cytokine induction and NGF-activated survival promotion but not survival promotion activated by IL-3 or stem cell factor, suggesting that NGF enhanced RPMC survival by increasing cytokine production. We also examine the effects of NGF on the expression levels of some members of the bcl-2 family and the interleukin-1beta-converting enzyme-like cysteine protease families. NGF markedly increased bcl-2 expression but had little or no effect on the other genes studied. The induction of bcl-2 mRNA by NGF was not blocked by cyclosporin A. These data suggest that induced cytokine gene expression but not increased expression of bcl-2 mediates NGF-survival promotion in RPMC.

Signal transduction pathways in apoptosis

Emerging evidence indicates that apoptosis is regulated by some of the same signal transduction pathways previously implicated in other physiological cellular responses, including alterations in intracellular Ca2+ compartmentalization, activation of protein kinases and phosphatases, alteratios in pH and oxidative stress. Interestingly, signals that promote apoptosis in one model can suppress cell death in another, indicating that cellular responses are determined by the intrinsic programming of the cell in question. This review will summarize current knowledge of the signal transduction pathways regulating apoptosis and discuss how they may be coupled to components of the molecular machinery for cell death.

Functional characterization of the prodomain of interleukin-1beta-converting enzyme

Interleukin-1beta-converting enzyme (ICE) has been identified as the main protease responsible for maturation of the prodomain of interleukin-1beta. Recently, it was shown to belong to a larger gene family, members of which play an important role in programmed cell death. A common feature of the ICE family proteases is the presence of a prodomain that has been hypothesized to keep the enzyme in an inactive form. Expression analysis in yeast revealed autocatalytic degradation of p45ICE, but not of p30ICE lacking a prodomain. We further demonstrate that p45ICE, in which the critical cysteine has been mutated, is still able to dimerize in vivo. Dimerization requires the prodomain and occurs prior to autoprocessing. These results provide evidence for a regulatory role of the prodomain of ICE.

Proteases in apoptosis

The interleukin-1 beta-converting enzyme (ICE)-like family proteases have recently been identified as key enzymes in apoptotic cell death. Among these proteases one can identify specific activities which may be involved in cytokine production or in resident protein cleavage. Several factors influence the constitutive apoptotic mechanism and may provide insight into the role of protease(s) in apoptosis. Although it appears that ICE family members play a most important role in promoting apoptotic cell death, evidence has been advanced that other proteases are also involved in sequential or parallel steps of apoptosis. Activation of a particular protease can lead to processing molecules either of the same or different proteases, leading to an activation of a protease cascade. Here we attempt to summarize the current thinking concerning these proteases and their involvement in apoptosis.

Mitochondria and programmed cell death: back to the future

Programmed cell death, or apoptosis, has in the past few years undoubtedly become one of the most intensively investigated biological processes. However, fundamental questions concerning the molecular and biochemical mechanisms remain to be elucidated. The central question concerns the biochemical steps shared by the numerous death induction pathways elicited by different stimuli. Heterogeneous death signals precede a common effector phase during which cells pass a threshold of 'no return' and are engaged in a degradation phase where they acquire the typical onset of late apoptosis. Alterations in mitochondrial permeability transition linked to membrane potential disruption precede nuclear and plasma membrane changes. In vitro induction of permeability transition in isolated mitochondria provokes the release of a protein factor capable of inducing nuclear chromatin condensation and fragmentation. This permeability transition is regulated by multiple endogenous effectors, including members of the bcl-2 gene family. Inhibition of these effects prevents apoptosis.

Ceramide induces apoptosis via CPP32 activation

Although both ceramide and interleukin-1beta converting enzyme (ICE) family proteases are key molecules during apoptosis, their relationship remains to be elucidated. We report here that cell-permeable ceramide induced cleavage and activation of CPP32, a Ced-3/ICE-like protease, but not ICE. Ceramide-induced apoptosis of Jurkat cells was blocked by the CPP32-specific tetrapeptide inhibitor DEVD-CHO, but not by the ICE inhibitor YVAD-CHO. Furthermore, variant Jurkat cells with defective CPP32 activation were resistant to both anti-Fas- and ceramide-induced apoptosis. These results indicate that CPP32 activation is required for ceramide-induced apoptosis, and suggest sphingomyelin-ceramide pathway functions upstream of CPP32.

Functions of interleukin 1 receptor antagonist in gene knockout and overproducing mice

Interleukin 1 receptor antagonist (IL-1ra) is a cytokine whose only known action is competitive inhibition of the binding of interleukin 1 (IL-1) to its receptor. To investigate the physiological roles of endogenously produced IL-1ra, we generated mice that either lack IL-1ra or overproduce it under control of the endogenous promoter. Mice lacking IL-1ra have decreased body mass compared with wild-type controls. They are more susceptible than controls to lethal endotoxemia but are less susceptible to infection with Listeria monocytogenes. Conversely, IL-1ra overproducers are protected from the lethal effects of endotoxin but are more susceptible to listeriosis. Serum levels of IL-1 following an endotoxin challenge are decreased in IL-1ra nulls and increased in IL-1ra overproducers in comparison to controls. These data demonstrate critical roles for endogenously produced IL-1ra in growth, responses to infection and inflammation, and regulation of cytokine expression.

Activation of an interleukin 1 converting enzyme-dependent apoptosis pathway by granzyme B

Cytotoxic T lymphocytes (CTL) can induce apoptosis through a granzyme B-based killing mechanism. Here we show that in cells undergoing apoptosis by granzyme B, both p45 pro-interleukin 1 beta converting enzyme (ICE) and pro-CPP32 are processed. Using ICE deficient (ICE -/-) mice, embryonic fibroblasts exhibit high levels of resistance to apoptosis by granzyme B or granzyme 3, while B lymphoblasts are granzyme B-resistant, thus identifying an ICE-dependent apoptotic pathway that is activated by CTL granzymes. In contrast, an alternative ICE-independent pathway must also be activated as ICE -/- thymocytes remain susceptible to apoptosis by both granzymes. In ICE -/- B cells or HeLa cells transfected with mutant inactive ICE or Ich-1S that exhibit resistance to granzyme B, CPP32 is processed to p17 and poly(ADP-ribose) polymerase is cleaved indicating that this protease although activated was not associated with an apoptotic nuclear phenotype. Using the peptide inhibitor Ac-DEVD-CHO, apoptosis as well as p45 ICE hydrolysis are suppressed in HeLa cells, suggesting that a CPP32-like protease is upstream of ICE. In contrast, p34cdc2 kinase, which is required for granzyme B-induced apoptosis, remains inactive in ICE -/- B cells indicating it is downstream of ICE. We conclude that granzyme B activates an ICE-dependent cell death pathway in some cell types and requires a CPP32-like Ac-DEVD-CHO inhibitable protease acting upstream to initiate apoptosis.

ICE-like proteases execute the neuronal death program

The past year has witnessed significant advances in our understanding of the mechanisms that kill neurons during programmed cell death. The executioners are members of a family of proteases founded by ced-3, the product of a gene that is required for programmed cell death in the nematode Caenorhabditis elegans, and by mammalian interleukin-1 beta-converting enzyme. These proteases represent interesting novel targets for the therapy of acute and chronic pathologies of the nervous system associated with neuronal death.

Fas-induced programmed cell death is mediated by a Ras-regulated O2- synthesis

Fas induces apoptosis in lymphocytes via a poorly defined intracellular signalling cascade. Previously, we have demonstrated the involvement and significance of a signalling cascade from the Fas receptor via sphingomyelinases and ceramide to Ras in Fas-induced apoptosis. Here we demonstrate rapid and transient synthesis of reactive oxygen intermediates (ROI) via activation of Ras after Fas. Genetic inhibition of Ras by transfection of transdominant inhibitory N17Ras blocked Fas-mediated ROI synthesis and programmed cell death. Likewise, the antioxidants N-acetyl-cysteine and N-t-butyl-phenylnitrone abolished Fas-induced cell death, pointing to an important role for Ras-triggered ROI synthesis in Fas-mediated programmed cell death.

Tumour necrosis factors in immune regulation: everything that's interesting is...new!

Tumour necrosis factors have been classically studied as molecules central to the pathogenesis of infectious, inflammatory and autoimmune diseases. The recent generation of mice deficient in TNF alpha, LT alpha, or their receptors, has provided exciting new insights into the physiological role of these molecules in the development of secondary lymphoid tissues and in the organisation of the humoral immune response.

Immune and inflammatory responses in TNF alpha-deficient mice: a critical requirement for TNF alpha in the formation of primary B cell follicles, follicular dendritic cell networks and germinal centers, and in the maturation of the humoral immune response

To investigate the role of TNF alpha in the development of in vivo immune response we have generated TNF alpha-deficient mice by gene targeting. Homozygous mutant mice are viable and fertile, develop lymph nodes and Peyer's patches and show no apparent phenotypic abnormalities, indicating that TNF alpha is not required for normal mouse development. In the absence of TNF alpha mice readily succumb to L. monocytogenes infections and show reduced contact hypersensitivity responses. Furthermore, TNF alpha knockout mice are resistant to the systemic toxicity of LPS upon D-galactosamine sensitization, yet they remain sensitive to high doses of LPS alone. Most interestingly, TNF alpha knockout mice completely lack splenic primary B cell follicles and cannot form organized follicular dendritic cell (FDC) networks and germinal centers. However, despite the absence of B cell follicles, Ig class-switching can still occur, yet deregulated humoral immune responses against either thymus-dependent (TD) or thymus-independent (TI) antigens are observed. Complementation of TNF alpha functioning by the expression of either human or murine TNF alpha transgenes is sufficient to reconstitute these defects, establishing a physiological role for TNF alpha in regulating the development and organization of splenic follicular architecture and in the maturation of the humoral immune response.

Tetrapeptide DEVD-aldehyde or YVAD-chloromethylketone inhibits Fas/Apo-1(CD95)-mediated apoptosis in renal-cell-cancer cells

The apoptotic machinery has been intensively investigated, and interleukin-1-beta-converting enzyme (ICE) and its homologs directly mediate apoptosis by means of their unique protease activity. Fas/Apo1 (CD95), a member of the TNF-receptor family, mediates apoptosis by binding to its ligand, which is mainly expressed on lymphocytes. Here, we investigated the expression and function of both molecules in renal-cell cancer (RCC). The expression of Fas was examined in 6 RCC cell lines by immunoblotting and all of them expressed Fas. ICE and CPP32/YAMA were also identified among the cell lines. We earlier examined ACHN cells expressing low levels of BCL-2, as well as KRC/Y cells with high levels of BCL-2. Here, we found that the anti-Fas monoclonal antibody, CH-11, induced apoptosis in a dose-dependent fashion more remarkably in ACHN cells. Pre-incubation with the tetrapeptide YVAD-chloromethyl-ketone or DEVD-aldehyde inhibited Fas-mediated apoptosis. These findings suggest that, in RCC, apoptosis is induced by lymphocytes bearing Fas-L, and that it is achieved through the proteolytic action of CPP32/YAMA and/or ICE, or another member of the ICE/ced-3 protease family.

Stability and oligomeric equilibria of refolded interleukin-1beta converting enzyme

We report the preparation and characterization of interleukin-1beta converting enzyme (ICE) refolded from its p20 and p10 protein fragments. Refolded ICE heterodimer (p20p10) was catalytically active but unstable, and in size exclusion chromatography eluted at an apparent molecular mass of 30 kDa. The mechanisms of the observed instability were pH-dependent dissociation at low enzyme concentrations, and autolytic degradation of the p10 subunit at high concentrations. Binding and subsequent removal of a high affinity peptidic inhibitor increased the apparent molecular mass to 43 kDa (by size exclusion chromatography), and significantly increased its stability and specific activity. Chemical cross-linking and SDS-polyacrylamide gel electrophoresis analysis of the 43-kDa size exclusion chromatography conformer revealed a 60-kDa species, which was absent in the 30-kDa conformer, suggesting that inhibitor binding caused formation of a (p20p10)2 homodimer. The observation of a reversible equilibrium between ICE (p20p10) and (p20p10)2 suggests that analogous associations, possibly between ICE and ICE homologs, can occur in vivo, resulting in novel oligomeric protease species.

Cleavage of CPP32 by granzyme B represents a critical role for granzyme B in the induction of target cell DNA fragmentation

Cytotoxic T lymphocytes (CTLs) are able to recognize and destroy target cells bearing foreign antigen using one of two distinct mechanisms: granule- or Fas-mediated cytotoxicity. The exact mechanisms involved in the induction of apoptotic cell death remain elusive; however, it seems likely that a family of cysteine proteases related to interleukin-1beta converting enzyme are involved. One family member, CPP32, has been identified as an intracellular substrate for granzyme B, a CTL-specific serine protease responsible for the early induction of target cell DNA fragmentation. Here we use cytolytic cells from granzyme B-deficient mice to confirm that cleavage and activation of CPP32 represents a nonredundant role for granzyme B and that this activation plays a role in the induction of DNA fragmentation in target cells, a signature event for apoptotic cell death. A peptide inhibitor of CPP32-like proteases confirmed the function of these enzymes in fragmentation. 51Cr release was not suppressed under these conditions, suggesting that granzyme B cleavage of CPP32 is primarily involved in the induction of DNA fragmentation and not membrane damage during CTL-induced apoptosis.

ICE inhibitor YVADcmk is a potent therapeutic agent against in vivo liver apoptosis

In liver, apoptosis is a physiological process involved in the clearance of injured cells and in homeostatic control [1]. However, in patients with viral fulminant hepatitis or with nonacute liver diseases [2], dramatic liver failure or secondary cirrhosis results from the death of hepatocytes, which express the cell-surface receptor Fas, by apoptosis. To date, treatment of fulminant hepatitis relies mainly on orthotopic liver transplantation, which is limited by immunological complications and graft availability. Unravelling the molecular mechanisms that underlie acute liver failure could allow the design of an appropriate therapy. Ligand-bound Fas and tumour necrosis factor alpha (TNF-alpha) induce hepatic apoptosis in mice [3-6]. In various cell types, Fas- or TNF-alpha-induced apoptosis is blocked by viral proteins (such as p35 and CrmA) as well as by a decoy peptide (YVADcmk) [7-11], suggesting that these mechanisms of apoptosis involve ICE (interleukin-1 beta converting enzyme)-like proteases. Here, we report that, in vivo, pre-treatment of mice with YVADcmk protects them from the lethal effect of anti-Fas antibody and from liver failure induced by injection of TNF-alpha. Remarkably, YVADcmk administration is also highly effective in rescuing mice that have been pretreated with anti-Fas antibody from rapid death, despite extensive hepatic apoptosis. This dramatic curative effect could be of clinical benefit for the treatment of viral and inflammatory liver diseases.

Molecular ordering of apoptotic mammalian CED-3/ICE-like proteases

Apoptosis is executed by cysteine proteases belonging to the CED-3/ICE family, which, unlike other mammalian cysteine proteases, cleave their substrates following aspartate residues. Proteases belonging to this family exist in the cytosol as zymogens that require accurate processing at internal aspartate residues to generate the two-chain active enzymes. As such, CED-3/ICE family members are capable of activating each other in a manner analogous to the protease zymogens of the coagulation or complement cascades. At present, it is unknown whether such mutual processing exists in vivo, and if so whether it is sequential, implying an order to the death pathway. Using a cell-free apoptosis system, recombinant ICE proteases and both biochemical and morphological criteria, we demonstrate an ordering of the mammalian ICEs that are most related to the Caenorhabditis elegans death protease CED-3.

Identification and characterization of Ich-3, a member of the interleukin-1beta converting enzyme (ICE)/Ced-3 family and an upstream regulator of ICE

We report here the isolation and characterization of a new member of the ice/ced-3 family of cell death genes, named ich-3. The predicted amino acid sequence of Ich-3 protein shares 54% identity with murine interleukin-1beta converting enzyme (ICE). Overexpression of ich-3 in Rat-1 and HeLa cells induces apoptosis, which can be inhibited by CrmA and Bcl-2. The mRNA and proteins of ich-3 are dramatically induced in vivo upon stimulation with lipopolysaccharide, an inducer of septic shock. The ich-3 gene product can be cleaved by cytotoxic T cells granule serine protease granzyme B, suggesting that Ich-3 may mediate apoptosis induced by granzyme B. Ich-3 does not process proIL-1beta directly but does promote proIL-1beta processing by ICE. These results suggest that Ich-3 may play a very important role in apoptosis and inflammatory responses and may be an upstream regulator of ICE.

Bcl-2 regulates activation of apoptotic proteases in a cell-free system

BACKGROUND

Apoptosis plays an important role in the normal development and homeostasis of metazoans. Aberrations in this process have been implicated in several major human diseases, but its molecular mechanism is poorly understood. In animals as diverse as humans and nematodes, the Bcl-2 oncoprotein prevents or delays apoptosis, whereas proteases of the interleukin-1beta-converting enzyme (ICE) family are required, suggesting that they are components of a conserved mechanism controlling the onset of apoptosis.

RESULTS

A cell-free system produced from Xenopus laevis eggs reproduces nuclear events characteristic of apoptosis after a lag phase. We have used this system to define the temporal sequence of biochemical events and to examine the relationship between Bcl-2 and apoptotic proteases. Bcl-2 prevents apoptotic chromatin condensation and DNA cleavage, but only when added prior to the activation of a protease which has characteristics similar to the Ced-3 sub-family of ICE-like proteases and which cleaves poly(ADP-ribose) polymerase (PARP). Bcl-2 attenuates activation of this protease, an effect that does not require de novo protein synthesis or the presence of intact nuclei. The Ced-3-related protease CPP-32 is cleaved during the late stages of apoptosis in this system and after PARP cleavage. Generation of CPP-32-cleaving activity is inhibited by Bcl-2.

CONCLUSIONS

These experiments provide direct biochemical evidence that Bcl-2 protects against apoptosis, at least in part, by regulating the activation of a series of apoptotic proteases that cleave PARP and other substrates. This cell-free system provides a useful biochemical model for analyzing the molecular mechanism controlling the activation of these proteases.

Functional role of interleukin 1 beta (IL-1 beta) in IL-1 beta-converting enzyme-mediated apoptosis

Prointerleukin-1 beta (pro-IL-1 beta) is the only known physiologic substrate of the interleukin-1 beta (IL-1 beta)-converting enzyme (ICE), the founding member of the ICE/ced-3 cell death gene family. Since secreted mature IL-1 beta has been detected after apoptosis, we investigated whether this cytokine, when produced endogenously, plays a role in cell death. We found that hypoxia-induced apoptosis can be inhibited by either the IL-1 receptor antagonist (IL-1Ra) or by neutralizing antibodies to IL-1 or to its type 1 receptor. IL-1Ra also inhibits apoptosis induced by trophic factor deprivation in primary neurons, as well as by tumor necrosis factor alpha in fibroblasts. In addition, during the G1/S phase arrest, mature IL-1 beta induces apoptosis through a pathway independent of CrmA-sensitive gene activity. We also demonstrate that Ice, when expressed in COS cells, requires the coexpression of pro-IL-1 beta for the induction of apoptosis, which is inhibited by IL-1Ra. Interestingly, we found that mature IL-1 beta has antiapoptotic activity when added exogenously before the onset of hypoxia, which we found is caused in part by its ability to downregulate the IL-1 receptor. Our findings demonstrate that pro-IL-1 beta is a substrate of ICE relevant to cell death, and depending on the temporal cellular commitment to apoptosis, mature IL-1 beta may function as a positive or negative mediator of cell death.

Activation of the CPP32 apoptotic protease by distinct signaling pathways with differential sensitivity to Bcl-xL

In the absence of growth factors, many types of mammalian cells undergo apoptosis. We and others have shown recently that growth factors promote cell survival by activating phosphatidylinositol 3-kinase (PI 3-kinase) in several cell types. In the present study, we have compared downstream elements of the apoptotic pathways induced by PI 3-kinase inhibitors and other stimuli. In U937 cells, both PI 3-kinase inhibitors (wortmannin and LY294002) and etoposide activated the CPP32 apoptotic protease by cleavage to active p17 subunits. In contrast, treatment with tumor necrosis factor alpha (TNFalpha) resulted in the accumulation of a distinct active CPP32 subunit, p20. Furthermore, overexpression of Bcl-xL blocked DNA fragmentation, CPP32 activation and cleavage of poly(ADP-ribose) polymerase in U937 cells treated with both PI 3-kinase inhibitors and etoposide, but not in cells treated with TNFalpha. Distinct patterns of CPP32 activation and differential sensitivities to Bcl-xL thus distinguish the cell death pathways activated by PI 3-kinase inhibition and DNA damage from that activated by TNFalpha.

ICE/CED-3 proteasesin apoptosis

An expanding family of cysteine proteases, of which interleukin-1beta-converting enzyme (ICE) is the prototype, has been shown to play a key role in mammalian cell apoptosis. ICE is both a structural and functional homologue of the nematode 'death gene' ced-3. Here, Moira Whyte discusses how functional characterization of these ICE-like proteases and identification of their substrates is helping to elucidate the biochemical processes underlying the stereotyped morphology of apoptosis and to identify potential targets for therapy.

The three-dimensional structure of apopain/CPP32, a key mediator of apoptosis

Cysteine proteases related to mammalian interleukin-1 beta converting enzyme (ICE) and to its Caenorhabditis elegans homologue, CED-3, play a critical role in the biochemical events that culminate in apoptosis. We have determined the three-dimensional structure of a complex of the human CED-3 homologue CPP32/apopain with a potent tetrapeptide-aldehyde inhibitor. The protein resembles ICE in overall structure, but its S4 subsite is strikingly different in size and chemical composition. These differences account for the variation in specificity between the ICE- and CED-3-related proteases and enable the design of specific inhibitors that can probe the physiological functions of the proteins and disease states with which they are associated.

FLICE, a novel FADD-homologous ICE/CED-3-like protease, is recruited to the CD95 (Fas/APO-1) death--inducing signaling complex

To identify CAP3 and CAP4, components of the CD95 (Fas/APO-1) death-inducing signaling complex, we utilized nano-electrospray tandem mass spectrometry, a recently developed technique to sequence femtomole quantities of polyacrylamide gel-separated proteins. Interestingly, CAP4 encodes a novel 55 kDa protein, designated FLICE, which has homology to both FADD and the ICE/CED-3 family of cysteine proteases. FLICE binds to the death effector domain of FADD and upon overexpression induces apoptosis that is blocked by the ICE family inhibitors, CrmA and z-VAD-fmk. CAP3 was identified as the FLICE prodomain which likely remains bound to the receptor after proteolytic activation. Taken together, this is unique biochemical evidence to link a death receptor physically to the proapoptotic proteases of the ICE/CED-3 family.

Role of Ced-3/ICE-family proteases in staurosporine-induced programmed cell death

In the accompanying paper by Weil et al. (1996) we show that staurosporine (STS), in the presence of cycloheximide (CHX) to inhibit protein synthesis, induces apoptotic cell death in a large variety of nucleated mammalian cell types, suggesting that all nucleated mammalian cells constitutively express all of the proteins required to undergo programmed cell death (PCD). The reliability of that conclusion depends on the evidence that STS-induced, and (STS + CHS)-induced, cell deaths are bona fide examples of PCD. There is rapidly accumulating evidence that some members of the Ced-3/Interleukin-1 beta converting enzyme (ICE) family of cysteine proteases are part of the basic machinery of PCD. Here we show that Z-Val-Ala-Asp-fluoromethylketone (zVAD-fmk), a cell-permeable, irreversible, tripeptide inhibitor of some of these proteases, suppresses STS-induced and (STS + CHX)-induced cell death in a wide variety of mammalian cell types, including anucleate cytoplasts, providing strong evidence that these are all bona fide examples of PCD. We show that the Ced-3/ICE family member CPP32 becomes activated in STS-induced PCD, and that Bcl-2 inhibits this activation. Most important, we show that, in some cells at least, one or more CPP32-family members, but not ICE itself, is required for STS-induced PCD. Finally, we show that zVAD-fmk suppresses PCD in the interdigital webs in developing mouse paws and blocks the removal of web tissue during digit development, suggesting that this inhibition will be a useful tool for investigating the roles of PCD in various developmental processes.

The pathogenesis of sepsis. Factors that modulate the response to gram-negative bacterial infection

Gram-negative bacteria gain access to the bloodstream by evading host defenses. Once in circulation, lipopolysaccharide interacts with the host receptor CD14 and initiates the host's immune response. Lipolysaccharide stimulates the host to produce a cascade of mediators that activate and target leukocytes, opsonize the bacteria, and induce fever to defend against the invading bacteria. Unregulated release of these mediators, however, leads to the production of vasoactive substances, activation of the clotting cascade, and diminution of cardiac performance, which leads to the sepsis syndrome. This article discusses the pathogenic events that lead to sepsis syndrome and reviews critical steps in regulating these inflammatory mediators to allow the host to recover from gram-negative bacteremia.

Bacterial modulins: a novel class of virulence factors which cause host tissue pathology by inducing cytokine synthesis

Cytokines are a diverse group of proteins and glycoproteins which have potent and wide-ranging effects on eukaryotic cell function and are now recognized as important mediators of tissue pathology in infectious diseases. It is increasingly recognized that for many bacterial species, cytokine induction is a major virulence mechanism. Until recent years, the only bacterial component known to stimulate cytokine synthesis was lipopolysaccharide (LPS). It is only within the past decade that it has been clearly shown that many components associated with the bacterial cell wall, including proteins, glycoproteins, lipoproteins, carbohydrates, and lipids, have the capacity to stimulate mammalian cells to produce a diverse array of cytokines. It has been established that many of these cytokine-inducing molecules act by mechanisms distinct from that of LPS, and thus their activities are not due to LPS contamination. Bacteria produce a wide range of virulence factors which cause host tissue pathology, and these diverse factors have been grouped into four families: adhesins, aggressins, impedins, and invasins. We suggest that the array of bacterial cytokine-inducing molecules represents a new class of bacterial virulence factor, and, by analogy with the known virulence families, we suggest the term "modulin" to describe these molecules, because the action of cytokines is to modulate eukaryotic cell behavior. This review summarizes our current understanding of cytokine biology in relation to tissue homeostasis and disease and concisely reviews the current literature on the cytokine-inducing molecules produced by gram-negative and gram-positive bacteria, with an emphasis on the cellular mechanisms responsible for cytokine induction. We propose that modulins, by controlling the host immune and inflammatory responses, maintain the large commensal flora that all multicellular organisms support.

Activation of the native 45-kDa precursor form of interleukin-1-converting enzyme

Active interleukin-1beta-converting enzyme (ICE) is composed of 20- and 10-kDa polypeptides (p20 and p10) derived from the processing of a cytosolic 45-kDa precursor protein (p45). The cleavage and activation of the native p45 ICE precursor have been characterized by use of specific inhibitors and antibodies recognizing various regions of ICE. The processing of p45 in vitro in THP.1 monocytic cell cytoplasmic extracts is inhibited only by protease inhibitors that inhibit ICE and not by inhibitors of other protease classes. The addition of L-742,395, a biotinylated irreversible ICE inhibitor, to these extracts labels only p45 and simultaneously inhibits p45 processing, demonstrating that the p45 has catalytic activity. Following a cleavage of p45 at a site that becomes the COOH terminus of p20, a more active intermediate is formed which migrates on SDS-polyacrylamide gel electrophoresis with an molecular mass of 35 kDa (ED50 of approximately 0.1 microM L-742,395 labeling versus 5 microM for p45). This new more active ICE form serves both as an intermediate enzyme to cleave p45 as well as a substrate for the formation of the final active ICE (ED50 of 1 nM L-742,395 labeling of p20 and for p22, an NH2-terminally extended form of p20). While initial cleavage of p45 can be found at the sites corresponding to both the NH2 termini of p22 and p20, these fragments cannot be labeled by L-742,395 and are hence inactive. p45 is not processed at the site corresponding to the NH2 terminus of the p10. Less than 50% of the p45 is cleaved down to active p20 or p22 ICE as determined by band shift on SDS-polyacrylamide gel electrophoresis of the biotinylated fragments, indicating that the in vitro activation is highly inefficient. The ICE fragmentation occurs by an intermolecular process and is highly dilution sensitive. Cleavage of p45 by exogenous p20/p10 ICE differs from that of the endogenous p45 cleavage activity in that the p20/p10 activity is more salt sensitive, and it produces a different pattern of cleavage fragments, principally 35- and 12-kDa fragments. These results indicate that the nature of the ICE activity changes as p45 is processed down to the p20/p10 form of the enzyme.

Ligation of CD40 rescues Ramos-Burkitt lymphoma B cells from calcium ionophore- and antigen receptor-triggered apoptosis by inhibiting activation of the cysteine protease CPP32/Yama and cleavage of its substrate PARP

The new and growing family of interleukin-1beta-converting enzyme (ICE) cysteine proteases are now recognised to be major effectors of cellular death by apoptosis. Like other members of this family, the CPP32/Yama proform is activated by processing to its active heterodimeric enzyme or apopain when it likely contributes to the process of apoptosis by cleaving poly(ADP-ribose) polymerase (PARP) and thereby inhibiting much of its DNA repair activity. Apoptosis plays a fundamental role in the regulation of the immune system where it is involved in the selection of both T and B lymphocytes bearing antigen receptor (AgR) for non-self. Cells of the Ramos Epstein-Barr virus (EBV)-genome-negative Burkitt lymphoma (BL) B cell line (Ramos-BL) can be triggered into growth arrest and apoptosis by treating with the calcium ionophore ionomycin or by crosslinking their surface AgR with antibodies directed against immunoglobulin (Ig)M (anti-IgM). Ionomycin- and AgR-triggered growth arrest and apoptosis are arrested by signals transduced through the surface CD40 of Ramos-BL B cells. Both ionomycin and anti-IgM trigger activation of CPP32 and cleavage of PARP prior to the onset of apoptosis; this process is abrogated by treatment with anti-CD40 and is independent of Bcl-2 expression. A tripeptide inhibitor of ICE family cysteine proteases, Z-Val-Ala-Asp-fluoromethylketone (zVAD-fmk) inhibits ionomycin- and AgR-triggered CPP32 activation, PARP cleavage and apoptosis, but not growth arrest, in Ramos-BL B cells. Thus, in this report we demonstrate that in a physiological system, activation of endogenous members of the ICE family, including CPP32, and cleavage of the death substrate PARP act as major effectors of apoptotic death.

D4-GDI, a substrate of CPP32, is proteolyzed during Fas-induced apoptosis

Apoptosis (programmed cell death) is a fundamental process for normal development of multicellular organisms, and is involved in the regulation of the immune system, normal morphogenesis, and maintenance of homeostasis, ICE/CED-3 family cysteine proteases have been implicated directly in apoptosis, but relatively few of the substrates through which their action is mediated have been identified. Here we report that D4-GDI, an abundant hematopoietic cell GDP dissociation inhibitor for the Ras-related Rho family GTPases, is a substrate of the apoptosis protease CPP32/Yama/Apopain. D4-GDI was rapidly truncated to a 23-kDa fragment in Jurkat cells with kinetics that parallel the onset of apoptosis following Fas cross-linking with agonistic antibody or treatment with staurosporine. Fas- and staurosporine-induced apoptosis as well as cleavage of D4-GDI were inhibited by the ICE inhibitor, YVAD-cmk. D4-GDI was cleaved in vitro by recombinant CPP32 expressed in Escherichia coli to form a 23-kDa fragment. The CPP32-mediated cleavage of D4-GDI was completely inhibited by 1 microM DEVD-CHO, a reported selective inhibitor of CPP32. In contrast, the ICE-selective inhibitors, YVAD-CHO or YVAD-cmk, did not inhibit CPP32-mediated D4-GDI cleavage at concentrations up to 50 microM. N-terminal sequencing of the 23-kDa D4-GDI fragment demonstrated that D4-GDI was cleaved between Asp19 and Ser20 of the poly(ADP-ribose) polymerase-like cleavage sequence DELD19S. These data suggest that regulation by D4-GDI of Rho family GTPases may be disrupted during apoptosis by CPP32-mediated cleavage of the GDI protein.

Inducible nitric oxide synthase gene expression in the brain during systemic inflammation

Inducible nitric oxide synthase (iNOS) is a transcriptionally regulated enzyme that synthesizes nitric oxide from L-arginine that has a key role in the pathophysiology of systemic inflammation and sepsis. Transgenic animals with a null mutation for the iNOS gene are resistant to hypotension and death caused by Escherichia coli lipopolysaccharide (LPS). The regulation of peripheral iNOS has been well studied in sepsis, but little is known about iNOS regulation in the brain during systemic inflammation or sepsis. We know that at baseline there is no detectable iNOS gene expression in the brain, but a detailed neuroanatomical study reveals that early in the course of systemic inflammation there is a profound induction of iNOS messenger RNA in vascular, glial and neuronal structures of the rat brain, accompanied by the production of nitric oxide (NO) metabolites in brain parenchyma and cerebrospinal fluid (CSF). We propose that the spillover of nitrite into the CSF has the potential to be a diagnostic marker for systemic inflammation and sepsis. Pharmacological interventions aimed at regulating iNOS function in the brain might represent a new treatment strategy in sepsis. Brain iNOS may be relevant to the pathophysiology, diagnosis and treatment of systemic inflammation and sepsis.

Anticytokine treatment of established type II collagen-induced arthritis in DBA/1 mice. A comparative study using anti-TNF alpha, anti-IL-1 alpha/beta, and IL-1Ra

OBJECTIVE

To examine the role of tumor necrosis factor alpha (TNF alpha), interleukin-1 alpha (IL-1 alpha), and IL-1 beta in collagen-induced arthritis (CIA), immediately after onset and during the phase of established arthritis.

METHODS

Male DBA/1 mice with collagen-induced arthritis were treated with antibodies against murine TNF alpha and IL-1 alpha/beta at different time points of the disease. IL-1 receptor antagonist (IL-1Ra) was administered using Alzet osmotic minipumps. The effect of anticytokine treatment was monitored by visual scoring. Histology and cytokine reverse transcription polymerase chain reaction (RT-PCR) analyses were performed at the end of the treatment period.

RESULTS

Anti-TNF alpha treatment showed efficacy shortly after onset of the disease, but had little effect on fully established CIA. Histologic analysis after early treatment revealed that anti-TNF alpha significantly reduced joint pathology, as determined by infiltration of inflammatory cells and cartilage damage. Anti-IL-1 alpha/beta treatment ameliorated both early and full-blown CIA. This clear suppression of established arthritis was confirmed by administration of high doses of IL-1Ra. Dose-response experiments showed that a continuous supply of 1 mg/day was needed for optimal suppression. Histologic analysis showed markedly reduced cartilage destruction both in the knee and the ankle joints. Autoradiography demonstrated full recovery of chondrocyte synthetic function of articular cartilage. In addition, we found that the IL-1 beta isoform plays a dominant role in established CIA. Profound suppression of CIA was observed with anti-IL-1 beta, although elimination of both IL-1 alpha and IL-1 beta still gave better protection. Analysis of messenger RNA with RT-PCR revealed that IL-1 beta was highly upregulated in synovium and cartilage at late stages of CIA, whereas anti-IL-1 beta treatment markedly reduced IL-1 beta message in the synovium.

CONCLUSION

The present study identified different TNF alpha/IL-1 dependencies in various stages of CIA and revealed that blocking of TNF alpha does not necessarily eliminate IL-1. Continuous, high doses of IL-1Ra are needed to block CIA.

Croquemort, a novel Drosophila hemocyte/macrophage receptor that recognizes apoptotic cells

Programmed cell death is first observed at stage 11 of embryogenesis in Drosophila. The systematic removal of apoptotic cells is mediated by cells that are derived from the procephalic mesoderm and differentiate into macrophages. We describe a macrophage receptor for apoptotic cells. This receptor, croquemort (catcher of death), is a member of the CD36 superfamily. Croquemort-mediated phagocytosis represents the concept that phagocytosis evolved primarily as a cellular process for the removal of effete cells. Our findings support the idea that the primordial function of macrophages may have been in tissue modeling and that their adapted role is in host defense.

Bacterial products and the control of ingestive behavior: clinical implications

Bacterial products such as lipopolysaccharides (LPS) and muramyl peptides are delivered in the course of infections. They trigger the host's acute phase responses to bacterial infections and are probably involved in the accompanying hypophagia because LPS and muramyl dipeptide (MDP, the minimal immunologically active muramyl peptide) reduce food intake after parenteral administration in animals. LPS and MDP inhibit feeding synergistically through separate but interacting mechanisms. The hypophagic effects of LPS and MDP are presumably mediated by the combined actions of interleukin-1, tumor necrosis factor, and other cytokines. More work is required to understand the interactions between these cytokines, and between bacterial products and cytokines, before cytokine antagonists can be used for treatment of the hypophagia during bacterial infections. As the hypophagia seems to be an early mechanism of host defense, a treatment should be carefully considered. If an intervention is indicated because of a patient's poor condition, inhibitors of eicosanoid synthesis and glucocorticoids may hold more promise for therapy because such substances block LPS and MDP hypophagia. Although LPS can reduce food intake by direct action on the brain, presently available evidence indicates that systemic LPS acts primarily in the periphery to generate a neural signal that is transmitted to the brain and inhibits feeding through the vagus. The exact site where LPS acts on peripheral nerves remains to be identified. LPS hypophagia is conditionable, but conditioning cannot solely account for LPS hypophagia under most test conditions. Whether MDP hypophagia is also conditionable and mediated by vagal afferents is not yet known. All in all, the putative mediators and mechanisms of LPS and MDP hypophagia suggest some options for a treatment of the hypophagia during bacterial infection, but present knowledge about the mechanisms and interactions of the involved substances is still fragmentary and requires further investigation.

The Caenorhabditis elegans cell-death protein CED-3 is a cysteine protease with substrate specificities similar to those of the human CPP32 protease

The Caenorhabditis elegans cell-death gene ced-3 encodes a protein similar to mammalian interleukin-1beta-converting enzyme (ICE), a cysteine protease implicated in mammalian apoptosis. We show that the full-length CED-3 protein undergoes proteolytic activation to generate a CED-3 cysteine protease and that CED-3 protease activity is required for killing cells by programmed cell death in C. elegans. We developed an easy and general method for the purification of CED-3/ICE-like proteases and used this method to facilitate a comparison of the substrate specificities of four different purified cysteine proteases. We found that in its substrate preferences CED-3 was more similar to the mammalian CPP32 protease than to mammalian ICE or NEDD2/ICH-1 protease. Our results suggest that different mammalian CED-3/ICE-like proteases may have distinct roles in mammalian apoptosis and that CPP32 is a candidate for being a mammalian functional equivalent of CED-3.

The cell-death machine

Apoptosis, or programmed cell death, is the physiological process whereby individual cells are deliberately eliminated to achieve homeostasis and proper metazoan development. Numerous genes have recently been identified that are involved in apoptosis: some are believed to encode death effectors, whereas others encode positive or negative regulators of the cell-death machine. Precisely how these various proteins interact in the molecular mechanism of apoptosis remains to be discovered.

Sequential activation of ICE-like and CPP32-like proteases during Fas-mediated apoptosis

Binding of Fas ligand or an agonistic anti-Fas antibody induces apoptosis in Fas-bearing cells. The interleukin-1Beta-converting enzyme (ICE) is a cysteine protease that is involved in apoptosis induced by various stimuli, including Fas-mediated apoptosis. Several ICE homologues have been identified, and these are subdivided into three groups (ICE-, CPP32-, and Ich-1-like proteases). We show here that specific inhibitors of ICE- or CPP32-like proteases can inhibit Fas-mediated apoptosis. Transient ICE-like activity was found in the cytosolic fraction of Fas-activated cells, whereas ICE-dependent, CPP32-like activity gradually accumulated in the cytosol. Cell lysates from mouse lymphoma supplemented with either recombinant ICE or CPP32 induced apoptosis of nuclei. The CPP32 inhibitor inhibited ICE- or CPP32-induced apoptosis in the cell-free system, whereas the ICE-inhibitor only inhibited ICE-induced apoptosis. Cell extracts from thymocytes from ICE-null mice induced apoptosis in the cell-free system when it was supplemented with CPP32. These results indicate that Fas sequentially activates ICE- and CPP32-like proteases, and that downstream CPP32, together with a component(s) in the cytoplasm, causes apoptosis of nuclei.

Benzyloxycarbonyl-Val-Ala-Asp (OMe) fluoromethylketone (Z-VAD.FMK) inhibits apoptosis by blocking the processing of CPP32

Interleukin-1 beta converting enzyme (ICE)-like proteases, which are synthesized as inactive precursors, play a key role in the induction of apoptosis. We now demonstrate that benzyloxycarbonyl-Val-Ala-Asp (OMe) fluoromethylketone (Z-VAD.FMK), an ICE-like protease inhibitor, inhibits apoptosis by preventing the processing of CPP32 to its active form. These results suggest that novel inhibitors of apoptosis can be developed which prevent processing of proforms of ICE-like proteases.

Production of interleukin 1beta by human hematopoietic progenitor cells

The production of interleukin 1beta (IL-1beta) by human hematopoietic stem/progenitor cells was studied to explore the concept that these cells are not merely responders to stimuli from their microenvironment, but can themselves produce a powerful biomodulator. Cells with a CD34+ CD45RA(lo) CD71(lo) phenotype were purified from human umbilical cord blood and cultured one per well in serum-free medium with a mixture of cytokines. Cells that had divided over 2-5 d to form doublets were identified and the daughter cells were studied individually. 91% (460/506) of daughter cells had clonogenic potential. Analysis of these individual daughter cells by reverse transcription-polymerase chain reaction showed that 29% of them (14/48) were positive for IL-1beta mRNA. One of the cells that was strongly positive for IL-1beta mRNA had a sibling that generated 366,000 cells of multiple lineages after 14 d. IL-1beta converting enzyme mRNA, which is necessary to produce IL-1beta, was also detected by reverse transcription-polymerase chain reaction at the single-cell level. Moreover, enzyme immunoassay for mature secreted IL-1beta in culture supernatants demonstrated the production of IL-1beta protein by these cells. This was confirmed by fluorescent immunostaining of the cells for human IL-1beta which showed a significant portion of positive cells. Taken together, the results demonstrate the capacity of early hematopoietic cells to synthesize IL-1beta. The capacity of human hematopoietic stem/progenitor cells to produce IL-1beta may be involved in regulation of their proliferation and differentiation under certain circumstances and dysregulation of this process may be modified in leukemogenesis.

One step ahead of the game: viral immunomodulatory molecules

For decades cell biologists have relied on viruses to facilitate the study of complex cellular function. More recently, the tragedy of the AIDS epidemic has focused considerable human and financial resources on both virology and immunology, resulting in the generation of new information relating these disciplines. As the miracle of the mammalian immune system unfolds in the laboratory, the elegance of the mechanisms used by co-evolving viruses to circumvent detection and destruction by the host becomes inescapably obvious. Although many observation of virus-induced phenomena that likely contribute to the virus's escape of immune surveillance are still empirical, many other such phenomena have now been defined at the molecular level and confirmed in in vivo models. Immune modulators encoded within viral genomes include proteins that regulate antigen presentation, function as cytokines or cytokine antagonists, inhibit apoptosis, and interrupt the complement cascade. The identification of such gene products and the elucidation of their function have substantially strengthened our understanding of specific virus-host interactions and, unexpectedly, have contributed to the recognition of potent synergy between viruses, which can result in an unpredictable exacerbation of disease in co-infected individuals. Because many viral immune modulators clearly have host counterparts, viruses provide a valuable method for studying normal immune mechanisms. It is conceivable that an improved understanding of virus-encoded immunomodulators will enhance our ability to design reagents for use in therapeutic intervention in disease and in vaccine development.

Mice deficient in IL-1beta manifest impaired contact hypersensitivity to trinitrochlorobenzone

Mice rendered deficient in IL-1 beta by gene targeting in embryonic stem cells develop and grow normally in a protected laboratory environment. Endotoxin-stimulated peritoneal macrophages from IL-1beta-deficient mice showed normal synthesis and cellular release of IL-1alpha after treatment with 5 mM ATP demonstrating that IL-1beta is not necessary for expression and release of the IL-1alpha isoform. Mice deficient in IL-1beta showed unaltered sensitivity to endotoxic shock, with or without pretreatment with D-galactosamine. In contrast, IL-1beta-deficient mice showed defective contact hypersensitivity responses to topically applied trinitrochlorobenzene (TNCB). This defect could be overcome either by application of very high doses of sensitizing antigen, or by local intradermal injection of recombinant IL-1beta immediately before antigen application. These data demonstrate an essential role for IL-1beta in contact hypersensitivity and suggest that IL-1beta acts early during the sensitization phase of response. They suggest an important role for IL-1beta in initiation of the host of response at the epidermal barrier.

The molecular biology of apoptosis

All multicellular organisms have mechanisms for killing their own cells, and use physiological cell death for defence, development, homeostasis, and aging. Apoptosis is a morphologically recognizable form of cell death that is implemented by a mechanism that has been conserved throughout evolution from nematode to man. Thus homologs of the genes that implement cell death in nematodes also do so in mammals, but in mammals the process is considerably more complex, involving multiple isoforms of the components of the cell death machinery. In some circumstances this allows independent regulation of pathways that converge upon a common end point. A molecular understanding of this mechanism may allow design of therapies that either enhance or block cell death at will.

Proteolytic activation of the cell death protease Yama/CPP32 by granzyme B

The serine protease granzyme B, which is secreted by cytotoxic cells, is one of the major effectors of apoptosis in susceptible targets. To examine the apoptotic mechanism of granzyme B, we have analyzed its effect on purified proteins that are thought to be components of death pathways inherent to cells. We demonstrate that granzyme B processes interleukin 1beta-converting enzyme (ICE) and the ICE-related protease Yama (also known as CPP32 or apopain) by limited proteolysis. Processing of ICE does not lead to activation. However, processing by granzyme B leads directly to the activation of Yama, which is now able to bind inhibitors and cleave the substrate poly(ADP-ribose) polymerase whose proteolysis is a marker of apoptosis initiated by several other stimuli. Thus ICE-related proteases can be activated by serine proteases that possess the correct specificity. Activation of pro-Yama by granzyme B is within the physiologic range. Thus the cytotoxic effect of granzyme B can be explained by its activation of an endogenous protease component of a programmed cell death pathway.

Cleavage of actin by interleukin 1 beta-converting enzyme to reverse DNase I inhibition

Three of the predominant features of apoptosis are internucleosomal DNA fragmentation, plasma membrane bleb formation, and retraction of cell processes. We demonstrate that actin is a substrate for the proapoptotic cysteine protease interleukin 1beta-converting enzyme. Actin cleaved by interleukin 1beta-converting enzyme can neither inhibit DNase I nor polymerize to its filamentous form as effectively as intact actin. These findings suggest a mechanism for the coordination of the proteolytic, endonucleolytic, and morphogenetic aspects of apoptosis.

Requirement of basement membrane for the suppression of programmed cell death in mammary epithelium

Apoptosis is an active mechanism of cell death required for normal tissue homeostasis. Cells require survival signals to avoid the engagement of apoptosis. In the mammary gland, secretory epithelial cells are removed by apoptosis during involution. This cell loss coincides with matrix metalloproteinase activation and basement membrane degradation. In this paper we describe studies that confer a new role for basement membrane in the regulation of cell phenotype. We demonstrate that the first passage epithelial cells isolated from pregnant mouse mammary gland die by apoptosis in culture, but that cell death is suppressed by basement membrane. The correct type of extracellular matrix was required, since only a basement membrane, not plastic or a collagen I matrix, lowered the rate of apoptosis. Attachment to a matrix per se was not sufficient for survival, since apoptotic cells were observed when still attached to a collagen I substratum. Experiments with individually isolated cells confirmed the requirement of basement membrane for survival, and demonstrated that survival is enhanced by cell-cell contact. A function-blocking anti-beta1 integrin antibody doubled the rate of apoptosis in single cells cultured with basement membrane, indicating that integrin-mediated signals contributed to survival. We examined the cell death-associated genes bcl-2 and bax in mammary epithelia, and found that although the expression of Bcl-2 did not correlate with cell survival, increased levels of Bax were associated with apoptosis. We propose that basement membrane provides a survival stimulus for epithelial cells in vivo, and that loss of interaction with this type of matrix acts as a control point for cell deletions that occur at specific times during development, such as in mammary gland involution.

Molecular ordering of the cell death pathway. Bcl-2 and Bcl-xL function upstream of the CED-3-like apoptotic proteases

Genetic analyses of Caenorhabditis elegans has identified three genes that function in the regulation of nematode cell death. Mammalian homologs of two of these genes, ced-9 and ced-3, have been identified and comprise proteins belonging to the Bcl-2 and ICE families, respectively. To date, it is unclear where the negative regulators, ced-9 and bcl-2, function relative to the death effectors, ced-3 and the mammalian ced-3 homologs, respectively. Here, the molecular order of the cell death pathway is defined. Our results establish that Bcl-2 and Bcl-xL function upstream of two members of the ICE/CED-3 family of cysteine proteases, Yama (CPP32/apopain) and ICE-LAP3 (Mch3).