727
A very common and the best understood of the mechanisms of physiological cell death is apoptosis, resulting from the activation, through either of two primary pathways, of
site-specific proteases called caspases. There are, however, many other routes to cell death, prominently including autophagy and proteasomal degradation of critical constituents of cells. These routes are frequently seen in experimental situations in which initiator or effector caspases are inhibited or blocked through genetic means, but they are also encountered during normal physiological and pathological processes. Most frequently, autophagic or proteasomal degradation is used to eliminate massive cytoplasm of very large cells, especially
post-mitotic cells, and these pathways are prominent even though caspase genes, messages, and pro-enzymes are found in the cells. These forms of cell death are fully physiological and not simply a default pathway for a defective cell; and they are distinct from necrosis. We do not yet understand the extent to which the pathways are linked, what mechanisms trigger the caspase-independent deaths, and how the choices are made. Addresses
*Department of Biological Sciences, St. John’s University, 8000Utopia Parkway, Jamaica, NY 11439, USA; *e-mail: lockshin@https://www.doczj.com/doc/ef10792613.html,
?Department of Biology, Queens College and Graduate Center of the City University of New Y ork, 65-30 Kissena Boulevard, Flushing,
NY11367, USA; #e-mail: Zahra_zakeri@https://www.doczj.com/doc/ef10792613.html,
Current Opinion in Cell Biology2002, 14:727–733
0955-0674/02/$ — see front matter
? 2002 Elsevier Science Ltd. All rights reserved.
DOI 10.1016/S0955-0674(02)00383-6
Abbreviations
MMP matrix metalloproteinase
zVAD.fmk benzyloxycarbonyl valyl alanyl aspartate
fluoromethylketone
Introduction
The discovery of caspases and the elucidation of the role of these enzymes in apoptosis have been a brilliant chapter in cell biology. However, as is the case with virtually all major developments, the situation is more complex. In the sense of the more trivial interpretation of a quotation from the Ethics of the Fathers, ‘Despise no one and do not discard anything, for there is no one whose hour does not come and no thing without its place’, it is now time to note that caspases do not represent the unique effectors of cell death. Indeed, many ideas are returning to haunt us from the past, including the roles of lysosomal and serine proteases. This earlier literature has been reviewed in recent publications [1?,2?].
T wo sources of confusion are reflected in many publications, and it is important at the outset to recognize them. First, it should be obvious, but often is not, that inhibition of one or more caspases will not prevent the death of a severely compromised cell. This statement is the equiv-alent of stating that providing water to a starving individual will prevent death by dehydration but not eventual death. It is therefore not surprising that caspase inhibition does not prevent the death of cells deprived of growth factors or those exposed to strong metabolic toxins or to physiological killing agents such as glucocorticoids. The second source of confusion is failure to acknowledge a continuum between apoptosis and necrosis. Necrosis, narrowly defined, results from rapid or massive loss of control of energy resources or membrane barriers, and is typified by osmotic swelling of the cell and organelles (commonly mitochondria), lysis, and extraction of cyto-plasmic contents. There are, however, controlled forms of death, most commonly autophagic deaths, in which much of the cytoplasm is destroyed by lysosomal or proteasomal proteases. These are often confused with necrosis. In this sense, it is important to remember that some forms of necrosis may be artefacts. Thus, massive toxic insult to an animal may overwhelm macrophages, so that apoptotic cells are never scavenged and ultimately become necrotic. In vitro, the absence of phagocytes may lead to the same end. These comments therefore address the narrower issue of caspase-independent cell deaths of physiological interest. Autophagy and proteasomal digestion are frequently seen in physiological or programmed cell death, and we focus on this here. The idea that death, once induced, may occur through any of several pathways is illustrated in Figure 1. Caspase dependence of apoptosis
Caspases are highly conserved in animals from hydra [3] to mammals, including Drosophila[4,5,6] but are not found in yeast, Dictyostelium(although it does undergo a programmed cell death [7?,8,9]), or plants [10]. These organisms may contain similar genes. Yeast, and perhaps other organisms, have metacaspases, which resemble caspases but have no currently known function [11]. Cell deaths in these organisms do not closely resemble classical apoptosis, reinforcing the idea that apoptotic morphology results from activation of the caspase cascade. Apoptosis-like and other types of programmed cell death
Efforts to classify cell deaths as either apoptosis or necrosis have been a bit overzealous. During insect metamorphosis for instance, earlier literature in the 1960s and 1970s, and more recent literature [12]has demonstrated that the death of large, cytoplasm-rich cells such as muscle and labial gland consists of a prolonged period of cytoplasmic destruction, and concludes with a final conversion to apop-totic morphology of the cell and nucleus. In mammalian cells, the territory between classical apoptosis and classical
Caspase-independent cell deaths Richard A Lockshin*and Zahra Zakeri?
necrosis is filled with many intermediates in which blebbing may be more or less prominent, and there are varying degrees of chromatin condensation and margination. Proteases other than caspases may account for the apoptosis-like appearance of the nucleus [13??,14]. As more investi-gators identify cell death in different systems or under different conditions, we find more variations to the classical theme of apoptosis versus necrosis. It is likely that we will need to recognize a near continuum of types of cell death.Death of cells in the presence of caspase inhibitors or in knockouts
Transgenic models
With the advent of transgenic models, we have gained great knowledge about the function of many genes. However, they have often forced new questions rather than providing answers. Knockouts and inhibitors produce problems of their own. With knockouts of caspases or other genes, a primary problem is redundancy, such that overexpression of compensatory enzymes eventually yields a normal phenotype, although the dynamics of the development of the phenotype may be modestly altered [15]. A secondary problem is that the knockout may produce unintended and misunderstood consequences. For instance, individual knockout of each of several caspases does not seriously disrupt early embryonic development [15] but knockout of caspase-9 is lethal, owing to massive overgrowth of the forebrain, leading to exencephaly [16??,17]. This result was originally interpreted to indicate excess cell number deriving from failure of apoptosis; however, an extra round of mitosis could double the number of neurons and create a similar phenotype. Oppenheim and colleagues [16??,18] explored this possibility, noting that the spinal cord, in which embryonic neuronal cell death is equally common as in the brain, appeared to be normal. They found that cell deaths in the brain and spinal cord were normal, but that the cells did not look apoptotic. Thus, the cause of the overgrowth remains unexplained; and more importantly, loss of caspase-9 altered the morphology but not the frequency of cell death.
As is noted in the Introduction, once a cell has lost its primary supporting mechanisms, any of several paths can lead to its death. If the caspase sequence is inhibited, death domain receptors can still initiate a necrotic signaling pathway [19]. Similarly, Apaf1 (apoptotic protease inhibiting factor 1) knockout mice die during embryonic development due to brain overgrowth. There is also a delay in cell death in the limb, leading to prolonged webbing of the digits. However, the interdigital cells die, and this type of cell death does not appear to be classical apoptosis either [20].
Caspase inhibitors
Most other studies purporting to demonstrate the require-ment for caspase control of cell death are based on the use of inhibitors, primarily chloromethylketone (cmk) or fluoromethylketone (fmk) derivatives of substrate peptides. The most popular are zVAD.fmk (benzyloxycarbonyl valyl alanyl aspartate fluoromethylketone), considered to be a relatively non-specific caspase inhibitor, and DEVD.fmk (aspartic glutamic valyl aspartate fluoromethylketone), a caspase-8 inhibitor. In many experiments, application of these inhibitors has a substantial impact on the phenomenon under investigation. However, researchers tend to use the inhibitors at around 50 μM. In our hands, this concentration of zVAD.fmk will seriously disrupt development of the mammalian pre-implantation embryo. However, at the
728Cell division, growth and death
concentrations these inhibitors also completely inhibit the lysosomal acid proteases cathepsins B and H. In vitro, the ID50of zVAD.fmk against cathepsin B is closer to 8 μM, and 1 μM is sufficient to inhibit purified cathepsin B; [21??,22.) This is often missed because cathepsin B does not hydrolyze the caspase-1 substrate Ac-YVAD.amc (acetyl lysyl valyl alanyl aspartate aminomethylcoumarin) and barely hydrolyzes the caspase-3 substrate Ac-DEVD.amc (acetyl aspartic glutamic valyl apartate aminomethyl-coumarin) [22]. Alternatively, caspases may play roles other than those obviously related to cell death. Inhibition of caspases (although possibly also cathepsins) can lead to activation of dormant HIV in a cell [23].
Other proteases activated in dying cells
In situations such as attack by granzymes (not discussed here), cell death may or may not proceed through a caspase cascade [24,25], and in several other situations, such as degeneration of insect muscle, other proteolytic machinery, such as proteasomes, plays a substantial role. Ubiquitination of cytoplasmic substrates, and their delivery to the proteasome, is an important aspect of the removal of cytoplasm from muscle and other large cells [26]; but proteasomes play a much more complex role in the regulation of apoptosis. When apoptosis is invoked in response to a signal, pro-apoptotic proteins (e.g. Bax [Bcl-associated X protein] and caspases) may be activated, synthesized or translocated, or anti-apoptotic proteins (e.g.AIF [apoptosis-inhibiting factor] or Bcl-2 [B-cell lymphoma 2]) inactivated or destroyed. The proteasome is deeply involved in this process, being able to degrade Bcl-2family members, BAG1 (Bcl-2-binding athanogene 1), p53, TRAF2 (tumor necrosis factor receptor associated factor 2), IκB (inhibitor of NF-κB) and IAPs (inhibitor of apoptosis proteins) [27]. Furthermore, the IAPs themselves have ubiquitin ligase activity, and proteasomal cleavage may activate several growth and death factors, including JNK (c-Jun amino-terminal kinase) and NFκB [28]. Overall, the proteasomal protease is well placed to modulate the decision as to whether or not to undergo apoptosis, as both pro- and anti-apoptotic proteins may be consumed by the proteasome. The amount of ubiquiti-nation or the number of proteasomes may be the deciding factor [29], and inhibition of proteasomal proteolysis may have a greater impact on cell death than does inhibition of caspases [30]. Distelhorst suggests that proteasomes may, by degrading pro- or anti-apoptotic proteins, determine the apparent mechanism of death.
Matrix metalloproteinases (MMPs), first detected in a classic case of developmental cell death (tadpole metamorphosis), are another type of protease influential in cell death, in that they can free cells from their attachments and lead cells to apoptosis via anoikis (death by isolation from normal cell-substratum contact) [31]. First documented in amphibia, these enzymes perform similar functions in mammals, and they play a substantial role in a much wider variety of diseases than can be addressed here[32,33].
Autophagic cell death
Lysosomes
By far the potentially most studied of the caspase-independent cell deaths are the autophagic cell deaths. Long before caspases were discovered, a substantial amount literature focused on the role of lysosomes in cell death [34] and studies of models that were later taken to represent classic apoptosis, such as hormone-deprived prostate and post-lactational mammary gland, emphasized the role of lysosomes in the death of the cells. In many situations under modern investigation, including lymphocytes exposed to glucocorticoids [35], inhibition of cathepsin B or proteasomal proteases interferes with cell death or apoptosis more effectively Caspase-independent cell deaths Lockshin and Zakeri 729
than does inhibition of caspase-3. Apparently similar lymphocytes may show considerable variance in dying,because metabolic or historical differences tip the balance of fate in different directions.
Lysosome-mediated deaths are often ‘apoptosis-like’, to use Leist and J??ttel?’s [13??]term, and the options open to cells often cover the complete spectrum from autophagic (meaning that the cytoplasm is actively destroyed long before nuclear changes become apparent [Figure 2]) to classically apoptotic (meaning that the chromatin marginates and the cell and nucleus fragment before morphological changes are seen in intracellular organelles [36]). What happens to a cell is often a matter of dose, timing, and duration of the noxious as opposed to supportive stimuli.Very little is known about the controls of these processes.The early literature on insect metamorphosis had remarked the regulation of autophagy, such that specific organelles such as mitochondria were often removed in a precisely timed wave of autophagy [37?]. Xue et al. [38?]reported more recently that when apoptosis is blocked in neurons or HeLa cells, the failure of the cells to survive is linked to an autophagic clearance of mitochondria from the damaged cells. This leads to the intriguing possibility that in metamorphosing insects (and perhaps other situations in which autophagy predominates), the triggering mecha-nisms reflect the same mitochondrial depolarization that leads to activation of caspase-9, but in the absence of caspase-9 it diverts to an autophagic route.
Cells may, of course, atrophy without dying, as is well known for muscles and hormone-dependent tissues,and it is also true that axons of neurons may wither or otherwise deteriorate independently of the fate of the cell body. Although the mechanism of axonal deterioration is not known, it apparently is independent of caspase activity, even though the nerve cell body may die by true apoptosis [39?].
Distinguishing among proteases
Distinguishing among the different proteases, unfortunately,is less precise than we would wish. Proteases are often activated rather than synthesized for cell death. In most cases, therefore, measurement of mRNA or protein levels is of limited value. Thus, most laboratories rely on measure-ment of activity of proteases. For at least mammalian caspases, antibodies are available from several sources that specifically identify the active form of the enzyme.Otherwise, identification is usually through the use of site-specific substrates (small peptides from which a fluorogenic moiety or caged fluor is released, available for both biochemical and intracellular use; or proteins such as PARP that are cleaved at known sites) or site-specific inhibitors that covalently link to the active site and contain a fluorescent or other tag. However, the substrates and especially the inhibitors (which are often used at concentra-tions two to three orders of magnitude over their inhibiting level) display overlapping activity (T ables 1 and 2) and may not accurately identify the protease (T able 3). Protein inhibitors, such as the viral inhibitors of caspases,appear to be relatively specific. Since caspases are typically active in cytoplasm or nucleus, while cathepsins usually appear to be active in lysosomes or autophagosomes and MMPs may be extracellular, cell fractionation or histo-logical identification may help resolve ambiguities. In appropriate situations, lysosomal activity may be blocked by 5-methyladenine. The development of degradome chips, in which specific proteases are identified by antibody, active site or activity, will permit researchers to screen many proteases simultaneously [40,41]. Otherwise,researchers should be circumspect in their conclusions.
Absence of caspase activation
T o state that caspase-type genes exist in the genome of an organism, or even that activation of caspases can lead to the death of cells in culture, does not resolve the question of how they function in the organism. Caspases function in
730Cell division, growth and death
Table 1
Specificity profile of protease inhibitors.Inhibitor Specificity
Caspase-3
Cathepsin B Calpain
zVAD.fmk
Pan- caspase
0.158>100
DEVD.CHO Caspase-3<0.150>100CA-074-Me Cathepsin B >1000.5>100Pepstatin Cathepsin D >100>100>100TPCK Serine protease
>10050>100
ALLN Calpain >100<0.1 1.2
Apparent IC 50 in M. DEVD.CHO, aspartic glutamic valyl aspartate aldehyde; CA-074-Me, cathepsin B inhibitor IV (L-3-trans -[Polycarbamoyl]oxirane-2-carbonyl)-L-isoleucyl-L-proline methyl ester) from Calbiochem-Novabiochem Corp., La Jolla, CA; TPCK,tocyl-L-phenyl chloromethylketone; ALLN, N -acetyl leucyl leucyl norleucyl aldehyde. Data is reproduced, with permission, from
Schotte et al . (1999) [22]. zVAD.fmk inhibits several caspases and is considered a pan-caspase inhibitor.
Table 2
Effect of fluorometylketones inhibitors on cathepsin B in vitro and in tissue culture.Condition
Control
zVAD.fmk
Ac-YVAD.fmk
z-DEVD.fmk
z-FA.fmk
Purified enzyme, 1 M inhibitor 600060000Cultured cells, 50 M inhibitor 8502525
Activity of cathepsin B in F/min = increase in fluorescence/minute. Ac-YVAD.fmk, acetyl lysyl valyl alanyl aspartate fluoromethylketone;z-DEVD.fmk, benzyloxycarbonyl aspartic glutamic valyl aspartate fluoromethylketone; z-FA.fmk, benzyloxycarbonyl phenyl alanyl fluoromethylketone. Data is reproduced, with permission, from Schotte et al . (1999) [22].
several other physiological situations, including the activation of interleukin, and perhaps in the pre-implantation embryo and elsewhere. The caspases evolved from a substantial family of proteases, which undoubtedly had other functions, including perhaps the destruction of host cells by parasites [42,43]. Caspase-1 is overexpressed in at least one situation not obviously associated with apoptosis [44], and other caspases may be involved in cell differentiation and stimulatory responses [45]. Thus, roles for caspases other than in cell death should be explored. Several caspase-type genes have been documented for Drosophila and their activity demonstrated in cultured cells, in affecting the phenotype of the Bar mutant, in which the number of ommatidia in the eye is reduced because of loss of cells; manipulating the activity of the Hid, Reaper, Grim and Scythe genes can affect the penetrance of the mutation (particularly those of more recent evolu-tionary origin [46]) and ommatidium development [6,47,48]. However, involution at metamorphosis of the salivary gland in Drosophila and other insects has long been con-sidered to be autophagic in style [49,50,51]. In both Drosophila and Manduca(Lepidoptera), the appearance of characteristics of apoptosis occurs only in the last 10% of the period of involution. During this period, we find evidence for the activation of cathepsin B and calpain, a calcium-activated protease, but no evidence for activation of any caspase (COB Facey and RA Lockshin, unpublished data). These results are fully consistent with the argument that destruction of cytoplasm is often achieved without caspases, and they beg the issue of the role of caspases in these large post-mitotic cells.
Why does it appear that caspase-driven apoptosis is the mode of death in an insect embryo but not a metamor-phosing adult? The answer to this question potentially can tell us a lot about the decisions to activate caspases or other routes to cell death.
Conclusions
The caspase cascades represent a major mechanism of
cell loss, but they do not define the entire story. First, in many situations prevention of caspase enzymatic activity may block the appearance of an apoptotic morphology or degradation of DNA but fail to maintain the cell. Second, in many cells — particularly large, cytoplasm-rich or post-mitotic cells — removal of the cytoplasm by lysosomal (autophagic) or proteasomal means often occurs much earlier than activation of caspases or appearance of classical apoptotic morphology. In other cases, the remnants of the reduced cell may be removed by phagocytes without appearing apoptotic. Third, many claims for the primacy of caspases are based on the use of inhibitors under circumstances where the inhibitors are likely to act non-specifically.
There is a broad range of styles of cell death, most of which reflect a physiological control. In evaluating cell death,researchers should keep in mind that cells have several options to die under control, each of which may be characterized by different manifestations. How these autophagic and proteasomal mechanisms are controlled, and whether they are influenced by regulators of apoptosis, remains a fruitful subject of study. Acknowledgements
This review was written while the authors were supported by a National Institutes of Health grant (1R15 GM/AG 1057614 to RA Lockshin). References and recommended reading
Papers of particular interest, published within the annual period of review, have been highlighted as:
?of special interest
??of outstanding interest
1.Vaux DL: Apoptosis timeline.Cell Death Differ2002,
?9:349-354.
See annotation for Lockshin and Zakeri (2001) [2?].
Caspase-independent cell deaths Lockshin and Zakeri 731
Table 3
Peptide sequences of some commonly used substrates or inhibitors for proteases (generally used at 1–100 ).
Enzyme
Substrate or
inhibitor peptides Comments
Caspase-1WEHD, YVKD,YVAD can inhibit
YVAD* caspase-4
Caspase-2VDVAD*
Caspase-3ESMD, IETD,
DMQD?
DEVD*?Also has inhibitory
activity with
caspase-7
Caspase-4LEVD?
Caspase-6VEID*
Caspase-8IETD, IEPD,IETD also for
AEVD*? caspase-3
Caspase-9LEHD*
Caspase-10AEVD*
Caspase-11(I/L/V/P)EHD*
Caspase-13LEED*
Cathepsin B RR, ARR?
substrates
Cathepsin B
inhibitors
FA, LVW, LLR??
FG Also cathepsin L and
S, papain
LLM Also cathepsin L,
calpain
LL Also cathepsin L, D
and I
Cathepsin B RR, ARR?
substrates
Cathepsin D
inhibitors
LVF, pepstatin?
Cathepsin D RGFFP?
substrates
Cathepsin L
inhibitors
FF/Y?
Cathepsin L
substrates
FR?
Manufacturers for the protease substrates and inhibitors: *R&D (Minneapolis); ?Bachem (Pennsylvania); ?Calbiochem (La Jolla).
2.Lockshin RA, Zakeri Z: Programmed cell death and apoptosis: ?origins of the theory.Nat Rev Mol Cell Biol2001, 2:545-550.
The authors of this paper and the preceding paper (Vaux [2002] [1?]) describe the earlier history of apoptosis, noting the variant types of cell death encountered.
3.Cikala M, Wilm B, Hobmayer E, Bottger A, David CN: Identification
of caspases and apoptosis in the simple metazoan Hydra.
Curr Biol1999, 9:959-962.
4.Dorstyn L, Read SH, Quinn LM, Richardson H, Kumar S: DECAY, a
novel Drosophila caspase related to mammalian caspase-3 and
caspase-7.J Biol Chem1999, 274:30778-30783.
5.Dorstyn L, Colussi PA, Quinn LM, Richardson H, Kumar S: DRONC,
an ecdysone-inducible Drosophila caspase.Proc Natl Acad Sci
USA1999, 96:4307-4312.
6.Shigenaga A, Kimura K, Kobayakawa Y, Tsujimoto Y, Tanimura T:
Cell ablation by ectopic expression of cell death genes,
ced-3 and Ice, in Drosophila.Dev Growth Differ1997,
39:429-436.
7.Arnoult D, Tatischeff I, Estaquier J, Girard M, Sureau F, Tissier JP, ?Grodet A, Dellinger M, Traincard F, Kahn A et al.: On the evolutionary conservation of the cell death pathway: mitochondrial release of an apoptosis-inducing factor during Dictyostelium discoideum
cell death. Mol Biol Cell2001, 12:3016-3030.
One of the shorter of several articles speculating on the origin of apoptosis. There is a longer discussion by several authors in Cell Death and Differentiation, volume 9(4), April 2002.
8.Cornillon S, Foa C, Davoust J, Buonavista N, Gross JD, Golstein P:
Programmed cell death in Dictyostelium.J Cell Sci1994,
107:2691-2704.
9.Olie RA, Durrieu F, Cornillon S, Loughran G, Gross J, Earnshaw WC,
Golstein P: Apparent caspase independence of programmed cell death in Dictyostelium.Curr Biol1998, 8:955-958.
https://www.doczj.com/doc/ef10792613.html,m E, del Pozo O: Caspase-like protease involvement in the
control of plant cell death.Plant Mol Biol2000, 44:417-428.
11.Madeo F, Herker E, Maldener C, Wissing S, Lachelt S, Herlan M,
Fehr M, Lauber K, Sigrist SJ, Wesselborg S, Frohlich KU:
A caspase-related protease regulates apoptosis in yeast.Mol
Cell2002, 9:911-917.
12.Jochová J, Zakeri Z, Lockshin RA: Rearrangement of the tubulin and
actin cytoskeleton during programmed cell death in Drosophila
salivary glands.Cell Death Differ1997, 4:140-149.
13.Leist M, Jaattela M: Four deaths and a funeral: from caspases ??to alternative mechanisms.Nat Rev Mol Cell Biol2001, 2:589-598.
An excellent summary of the range of physiological cell death types, from apoptosis and autophagic deaths through types that are similar to necrosis.
14.Leist M, Jaattela M: Triggering of apoptosis by cathepsins.Cell
Death Differ2001, 8:324-326.
15.Pampfer S, Donnay I: Apoptosis at the time of embryo implantation
in mouse and rat.Cell Death Differ1999, 6:533-545.
16.Oppenheim RW, Flavell RA, Vinsant S, Prevette D, Kuan CY, ??Rakic P: Programmed cell death of developing mammalian neurons after genetic deletion of caspases.J Neurosci2001,
21:4752-4760.
This work illustrates clearly the problem of measuring cell death using techniques that inherently depend on caspase activation, such as in caspase knockout mice. It is an interesting comparison study to that by Zheng et al. (1999) [17].
17.Zheng TS, Hunot S, Kuida K, Flavell RA: Caspase knockouts:
matters of life and death.Cell Death Differ1999,
6:1043-1053.
18.Yaginuma H, Shiraiwa N, Shimada T, Nishiyama K, Hong J, Wang S,
Momoi T, Uchiyama Y, Oppenheim RW: Caspase activity is
involved in, but is dispensable for, early motoneuron death in the chick embryo cervical spinal cord.Mol Cell Neurosci2001,
18:168-182.
19.Denecker G, Vercammen D, Declercq W, Vandenabeele P: Apoptotic
and necrotic cell death induced by death domain receptors.Cell
Mol Life Sci2001, 58:356-370.
20.Chautan M, Chazal G, Cecconi F, Gruss P, Golstein P: Interdigital
cell death can occur through a necrotic and caspase-independent pathway. Curr Biol1999, 9:967-970.21.Foghsgaard L, Wissing D, Mauch D, Lademann U, Bastholm L, ??Boes M, Elling F, Leist M, Jaattela M: Cathepsin B acts as a dominant execution protease in tumor cell apoptosis induced by
tumor necrosis factor.J Cell Biol2001, 153:999-1010.
This is one of the few articles that contains a direct assessment, with a table, of the specificity and lack of specificity of commonly used inhibitors of proteases.
22.Schotte P, Declercq W, Van Huffel S, Vandenabeele P, Beyaert R:
Non-specific effects of methyl ketone peptide inhibitors of
caspases.FEBS Lett1999, 442:117-121.
23.Scheller C, Sopper S, Chen P, Flory E, Koutsilieri E, Racek T,
Ludwig S, Ter M, V, Jassoy C:Caspase inhibition activates HIV in
latently infected cells. Role of tumor necrosis factor receptor 1
and CD95.J Biol Chem2002, 277:15459-15464.
24.Hengartner MO: The biochemistry of apoptosis.Nature2000,
407:770-776.
25.Krammer PH: CD95’s deadly mission in the immune system.
Nature2000, 407:789-795.
26.Jesenberger V, Jentsch S: Deadly encounter: ubiquitin meets
apoptosis.Nat Rev Mol Cell Biol2002, 3:112-121.
27.Distelhorst CW: Recent insights into the mechanism of
glucocorticosteroid-induced apoptosis. Cell Death Differ2002,
9:6-19.
28.Orlowski RZ: The role of the ubiquitin-proteasome pathway in
apoptosis.Cell Death Differ1999, 6:303-313.
29.Lin KI, Baraban JM, Ratan RR: Inhibition versus induction of
apoptosis by proteasome inhibitors depends on concentration.
Cell Death Differ1998, 5:577-583.
30.Distelhorst CW: Recent insights into the mechanism of
glucocorticosteroid-induced apoptosis. Cell Death Differ2002,
9:6-19.
31.Tidball JG, Albrecht DE: Regulation of apoptosis by cellular
interactions with the extracellular matrix. In When Cells Die:
a Comprehensive Evaluation of Apoptosis and Programmed Cell
Death.Edited by RA Lockshin et al.New Y ork: Wiley–Liss;
1998:411-428.
32.Damjanovski S, Amano T, Li Q, Ueda S, Shi YB, Ishizuya-Oka A:
Role of ECM remodeling in thyroid hormone-dependent
apoptosis during anuran metamorphosis.Ann NY Acad Sci2000, 926:180-191.
33.Ishizuya-Oka A, Li Q, Amano T, Damjanovski S, Ueda S, Shi YB:
Requirement for matrix metalloproteinase stromelysin-3 in cell
migration and apoptosis during tissue remodeling in Xenopus
laevis.J Cell Biol2000, 150:1177-1188.
34.Zakeri Z, Bursch W, Tenniswood M, Lockshin RA: Cell death.
Programmed, apoptosis, necrosis, or other.Cell Death Differ
1995, 2:87-96.
35.Distelhorst CW: Recent insights into the mechanism of
glucocorticosteroid-induced apoptosis. Cell Death Differ2002,
9:6-19.
36.Bursch W: The autophagosomal–lysosomal compartment in
programmed cell death.Cell Death Differ2001, 8:569-581.
37.Lockshin RA, Zakeri Z: Programmed cell death and apoptosis: ?origins of the theory.Nat Rev Mol Cell Biol2001, 2:545-550.
The early work of Zakeri et al. (1995) [34], which attempted to distinguish between different types of cell death, is updated and expanded in this study.
38.Xue L, Fletcher GC, Tolkovsky AM: Mitochondria are selectively ?eliminated from eukaryotic cells after blockade of caspases during apoptosis.Curr Biol2001, 11:361-365.
A thoughtful examination of the idea that autophagocytosis can compromise the function of a cell to such a degree that it will undergo necrosis or apoptosis.
39.Raff MC, Whitmore AV, Finn JT: Axonal self-destruction and ?neurodegeneration.Science2002, 296:868-871.
Raff et al.explored the idea of death of an axon versus death of the entire cell.
40.Greenbaum D, Baruch A, Hayrapetian L, Darula Z, Burlingame A,
Medzihradszky KF, Bogyo M: Chemical approaches for functionally probing the proteome.Mol Cell Proteomics2002, 1:60-68.
41.Lopez-Otin C, Overall CM: Protease degradomics: a new challenge
for proteomics.Nat Rev Mol Cell Biol2002, 3:509-519.
42.Koonin EV, Aravind L: Origin and evolution of eukaryotic apoptosis:
the bacterial connection.Cell Death Differ2002, 9:394-404.
732Cell division, growth and death
43.Frade JM, Michaelidis TM: Origin of eukaryotic programmed cell
death: a consequence of aerobic metabolism? Bioessays1997,
19:827-832.
44.Ramadani M, Gansauge F, Schlosser S, Yang Y, Beger HG,
Gansauge S: Overexpression of caspase-1 in pancreatic
disorders: implications for a function besides apoptosis.
J Gastrointest Surg2001, 5:352-358.
45.Sadowski-Debbing K, Coy JF, Mier W, Hug H, Los M: Caspases —
their role in apoptosis and other physiological processes as revealed by knock-out studies.Arch Immunol Ther Exp 2002, 50:19-34.
46.Nassif C, Daniel A, Lengyel JA, Hartenstein V: The role of
morphogenetic cell death during Drosophila embryonic head
development.Dev Biol1998, 197:170-186.
47.Hay BA: Understanding IAP function and regulation: a view from
Drosophila.Cell Death Differ2000, 7:1045-1056.48.Wang SL, Hawkins CJ, Y oo SJ, Muller HA, Hay BA: The Drosophila
caspase inhibitor DIAP1 is essential for cell survival and is
negatively regulated by HID. Cell1999, 98:453-463.
49.Beaulaton J, Lockshin RA: Ultrastructural study of the normal
degeneration of the intersegmental muscles of Antheraea
polyphemus and Manduca sexta(Insecta, Lepidoptera) with
particular reference to cellular autophagy.J Morphol1977,
154:39-58.
50.Jochová J, Quaglino D, Zakeri Z, Woo K, Sikorska M, Weaver VM,
Lockshin RA: Protein synthesis, DNA degradation, and
morphological changes during programmed cell death
in labial glands of Manduca sexta.Devel Genet1997,
21:249-257.
51.Zakeri ZF, Quaglino D, Latham T, Lockshin RA: Delayed
internucleosomal DNA fragmentation in programmed cell death.
FASEB J1993, 7:470-478.
Caspase-independent cell deaths Lockshin and Zakeri 733