transcriptional control of the core cell-death machinery

Transcriptional control of the corecell-death machinerySharad Kumar and Dimitrios Cakouros

Hanson Institute, IMVS, PO Box 14, Rundle Mall, Adelaide 5000, Australia

Developmental and physiological cues, as well as signals

in response to cell damage, initiate a cell suicide program

that is often referred to as apoptosis or programmed cell

death (PCD). PCD is mediated by the core cell-death

machinery consisting of proteins that mediate and con-

trol the activation of caspases – enzymes that dismantle

cellular architecture during apoptosis. Because com-

ponents of the caspase-activation apparatus are constitu-

tively present in most cells, most studies during the last

decade have focused on the posttranslational regulation

of this preexisting machinery. However, accumulating

evidence suggests that, in many contexts, transcriptional

regulation also plays a crucial role in the activation of the

physiological cell-death program.

Programmed cell death (PCD) is an essential processrequired to delete harmful or superfluous cells and maintainhomeostasis [1]. The process of PCD is executed by caspases,cysteine proteases that cleave several hundred proteinsin dying cells [2]. The evolutionarily conserved protein-signaling network that causes caspase activation and itsregulation is termed the core cell-death machinery. Theprototypic apoptotic machinery was first defined in thenematode Caenorhabditis elegans, where it consists of fourmain proteins [3]. Three of these, EGL-1, CED-3 and CED-4,are required for PCD execution, whereas the fourth, CED-9,is essential for cell survival by preventing CED-4-dependentactivation of the caspase CED-3 [3]. All these proteins areconserved in mammals, and the homologs CED-3, CED-4and CED-9 have also been identified in Drosophilamelanogaster (Figure 1). The mammalian homologs ofCED-9 include both death antagonists (e.g. Bcl-2, Bcl-XL

and Bcl-w) and death agonists (e.g. Bax, Bak and Bok) [2,3].EGL-1 is similar to proteins that contain a single Bcl-2homology (BH) domain, BH3 [2–5]. These proteins (e.g. Bid,Bim, Noxa, Puma and Bmf) are commonly known as theBH3-only proteins [4]. Caspases are CED-3 homologs andhave 13 members in mammals [2,3]. The only CED-4-likeprotein identified in mammals is Apaf-1, which is requiredfor caspase-9 activation [6]. In addition to the four conservedproteins that are involved in most stress-mediated apoptoticpathways, mammals also have caspase-activation machin-eries initiated either by the ligation of death receptors or atthe level of endoplasmic reticulum [2,7]. Although the initialactivation of caspases can occur in several cellular com-partments, there is substantial crosstalk between various

pathways. The inhibitor of apoptosis (IAP) family of proteinskeep caspases in check, whereas several proteins, such asSmac and Diablo in mammals and Reaper (Rpr), Hid andGrim in Drosophila, antagonize the functions of IAPs, thuspromoting caspase activation [2,3,8]. Although much of thecontrol of caspase activation is mediated by the preexistingcellular machinery, transcription also plays a substantialrole in this process. This article focuses on what is currentlyknown about this emerging concept of transcriptionalcontrol of the cell-death machinery.

Activation of caspases

Caspase activation is fundamental to the execution ofapoptosis [2,3]. The initial activation of caspasesrequires the recruitment of the upstream caspases, suchas caspase-8 and -9, to specific death complexes throughadaptors such as FADD (Fas-associating death domain-containing protein) and Apaf-1 [2,3]. Similarly, the initi-ator caspases in C. elegans (CED-3) and Drosophila(DRONC) bind to their adaptors CED-4 and DARK,respectively [2,3,9]. The homophilic interactions betweeninitiator caspases and their respective adaptors are medi-ated by the protein–protein interaction motifs found incaspases and adaptors. In the death-receptor pathwaysthat are mediated by the tumor necrosis factor (TNF)family of cell surface receptors, ligation of the receptorsleads to the recruitment of FADD through death domains[3,7]. FADD, in turn, recruits caspase-8 through death-effector domains (DEDs), forming the death-inducingsignaling complex (Figure 1). The stress-induced deathpathway involves the recruitment of caspase-9 to an Apaf-1apoptosome (a caspase-activating complex) through cas-pase recruitment domains (CARDs), although, in some celltypes, apoptosis can occur in the absence of Apaf-1 andcaspase-9 [10]. In both cases, the recruitment of initiatorcaspases results in their activation by a proximity-induceddimerization mechanism [11,12]. Once active, caspase-8and -9 activate downstream effector caspases that lackDEDs or CARDs (e.g. caspase-3 and -7) by processing theeffector caspase precursors into two subunits that form atetrameric enzyme. Activated effector caspases then medi-ate the cleavage of over 300 substrates to cause thecharacteristic changes that occur in apoptotic cells [13].

Regulation of apoptotic initiation

Activation of the cell-death machinery can occur in manyways. For example, removal or sequestration of antiapop-totic molecules, upregulation or activation of proapoptoticCorresponding author: Sharad Kumar ([email protected]).

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molecules or translocation of a proapoptotic molecule to aspecific cellular compartment can all result in caspaseactivation. Thus, although most cells constitutively con-tain both prosurvival and proapoptotic components of thecore cell-death machinery, an alteration in the balancebetween pro and antideath factors is crucial in theregulation of apoptosis. Various signals, such as cytotoxicinsults, hormones and growth factors, regulate the acti-vation of the death program by controlling the balancebetween pro and antideath factors. Recent evidencesuggests that BH3-only proteins play a key role in theactivation of cell-death machinery by interfering with theprosurvival Bcl-2 family members [2,4]. The members ofthe BH3-only proteins can be regulated by different meanssuch as sequestration to the cytoskeleton, posttransla-tional modification by phosphorylation or cleavage andtranscriptional upregulation [4]. However, besides theseproteins, much less is known about the transcriptionalregulation of other factors that control PCD in variousways. Although rapid activation of a preexisting cell-deathmachinery is important for the removal of a cell damagedby cytotoxic insults, the coordinated removal of specificcells in a tissue, or synchronous removal of a large numberof cells during development, metamorphosis or tissueremodeling, is also regulated at the level of transcription ofthe key components of the cell-death machinery. Emergingdata, some summarized here, suggest that regulation of theexpression of genes involved in the cell-death ‘execution’machinery plays a direct role in various cell survival andapoptotic signaling pathways. Figure 2 shows various

cell-survival and -death genes that are transcriptionallyregulated in response to different signaling pathways.

Transcriptional regulation of developmental PCD

Most knowledge of transcriptional control of developmentalcell death is derived from nonmammalian models such asC. elegans and Drosophila. The BH3-only proteins, whichlink apoptotic signaling to the execution machinery, areoften transcriptionally controlled. One example is theapoptosis of neurosecretory motor neurons (NSM) ‘sister’cells in C. elegans. During embryogenesis, the NSM cellsdifferentiate intoneurons,whereas their sistercells undergoEGL-1-dependent PCD [14]. Mutation of the genes encodingCES-1,asnail familyof zinc-fingertranscriptionfactors,andCES-2, abZIP transcription factor, interferes with the deathof the NSM sister cells [15]. The egl-1 promoter contains asnailbinding-site,whichoverlapswiththebindingsiteof thebHLH transcription factors HLH-2 and 3. These factorstranscriptionally activate egl-1, whereas CES-1 competesfor the binding site of egl-1, repressing transcription andpromoting survival [15]. In the ventral cord PAG-3, a zinc-finger transcription factor, similar to CES-1, determinesneuroblast fate in C. elegans by regulating differentiationand PCD [16]. Interestingly, the mammalian homolog ofPAG-3, Gfi1, controls cell survival by directly repressingtranscription of the proapoptotic Bcl-2 family member Baxin cultured lymphocytes [17].

In Drosophila, the apoptotic activators Rpr and Hid aretranscriptionally controlled to orchestrate temporal andspatial PCD during development. These proteins act by

Figure 1. Conserved components of the cell-death machinery. The Caenorhabditis elegans, Drosophila and mammalian proteins that constitute the core caspase activation

and regulation arm of the apoptotic pathways are illustrated. Analogous colors represent homologs. For Drosophila and mammals, only the representative examples of the

family members are shown. In Drosophila and mammals, the two main pathways of caspase activation are induced by cellular stress or damage and the tumor necrosis fac-

tor (TNF) family of receptors (TNFRs), also called the death receptors. Although, in C. elegans, CED-9 directly binds to CED-4 to prevent CED-3 activation, there is no evi-

dence for Bcl-2 family members directly interacting with the CED-4 homologs in Drosophila and in mammals. Nevertheless, in Drosophila and mammals, Bcl-2 homologs

act upstream of caspase activation. Until now, an EGL-1 homolog (BH3-only protein) has not been reported in Drosophila. The death-receptor pathway in Drosophila con-

sists of a TNF-like molecule (Eiger) and its receptor (Wengen). Induction of apoptosis by this pathway depends on the activation of the JNK pathway, DARK and DRONC

[74]. In mammals, the TNFR-mediated cell death proceeds through a distinct adaptor (FADD) and caspase (caspase-8) complex. Many of the components of cell-death

machinery shown here are regulated at the level of transcription.

Ti BS

EGL-1

CED-9

CED-4

CED-3

? BH3 only

BUFFY Bcl-2

DARK Apaf-1

DRONC Caspase-9

TNFRfamily

FADD

Caspase-8

Caspase-3, -7DRICE

C. elegans Drosophila Mammals

DEBCL Bax

TNFR

JNK

Diap1

Rpr, Hid, Grim

IAPs

Diablo

FLIP

Stresspathway

Death-receptorpathway

Stresspathway

Death-receptorpathway


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neutralizing Diap1, allowing caspase activation [18].Diverse apoptotic signals converge on Rpr, Hid and Grimand are relayed to the core cell-death machinery (Figure 3).The survival of a subset of midline glia cells in Drosophiladepends upon suppression of Hid through the EGF-receptor–RAS–MAPK pathway [19,20]. The Hox genedeformed (Dfd), expressed in the maxillary and mandib-ular segments, is necessary for the morphological featuresof the head segments, and Dfd-null mutants showabnormalities of the mandibular and maxillary lobesbecause of an excess of cell populations in these regions[21]. Dfd is a direct transcriptional activator of rpr geneand Rpr-mediated apoptosis is necessary to maintain themaxillary–mandibular boundary [22]. The Hox familymember Abdominal B also induces cell death at theboundaries between abdominal segments through theactivation of rpr [22]. Abdominal A was recently found tocontrol proliferation of neuroblasts by determining thetiming of PCD and therefore the amount of progenyproduced by each neuroblast [23].

Hox-dependent regulation of apoptosis seems to bea conserved mechanism during animal development.Although some Hox genes are necessary for PCD, othersare required for cell survival. In amniotes, for example, limbformation is accompanied by cell death in the interdigitalmesenchymal tissue, eliminating cells located between thedifferentiating cartilages and thereby ‘sculpting’ the limbshape [24]. In Hoxa13 heterozygous mice, reduced apoptosisin the interdigital regions leads to the fusion of digits II andIII [25]. In addition, DLX-7, a divergent homeobox geneexpressedinnormalbonemarrow, isrequiredforcellsurvival[26]. Although many Hox genes are implicated in the controlof PCD, their relevant targets remain largely unknown.

Hormone-regulated PCD

The key roles of nuclear hormones in development,morphogenesis and tissue regression are well known.

The sculpting of shape in the developing limb and theregression of tail in frog tadpoles, both mediated by steroidhormones, have served as classical models of PCD [27].Frog metamorphosis is controlled by thyroid hormone

Figure 2. Transcriptional control of cell-death genes occurs in various different pathways. Some examples of cell-survival and -death pathways that are regulated at the

level of transcription are shown. These pathways use different groups of transcription factors to regulate apoptotic (red) or antiapoptotic (green) genes, altering the balance

between death versus survival signalling. Many hormones and cytokines primarily act as survival factors and their removal could activate the expression of apoptotic

genes and/or repress the genes that are required for keeping the death machinery inactive.

Ti BS

Developmentalsignals, hormones

HOX proteins(Dfd, AbdB, Hoxa13, DLX-7),Nuclear hormone receptors

RprHidDarkBimcaspases

Cytokine withdrawal(e.g.IL-2, -3, -6, GM-CSF, NGF)

FOXO, CREB, NFκB,JNK, Jaks and Stats

BimBcl-xsCD95L

Cytotoxic damage byUV or stress

E2F, Rb, p53

RprNoxaPumaBidBaxApaf-1CaspasesCD95L

Mcl-1Bcl-2Bcl-xL

Mcl-1Bcl-2Bcl-xLXIAPFLIPA1

Diap1Diap2Bcl-2Bcl-xL

Figure 3. Transcriptional control of pro- and anti-death factors regulates caspase

activation in Drosophila. This diagram provides an example of how transcription

regulates the balance between apoptotic and antiapoptotic (survival) genes to con-

trol caspase activation in Drosophila cells. The caspase inhibitor Diap1 is essential

for survival of most Drosophila cells and its removal is sufficient to induce the acti-

vation of the initiator caspase DRONC. Death inducers Rpr and Hid bind to and pro-

mote Diap1 degradation that allows DRONC activation through binding to its

adaptor DARK. In cells destined to die, Rpr and Hid are upregulated in response to

various death signals by transcription factors such as Dfd and Dmp53, whereas in

healthy cells, Hid is kept in check. The expression of dronc and dark is also upregu-

lated in response to specific death signals, presumably to overcome effects of

Diap1 inhibition.

Ti BS

Rpr Hid

Dmp53

Ecdysone

Dfd Ras/MAPK

DRONCDARK Ecdysone

DNA damage

Diap1

Review TRENDS in Biochemical Sciences Vol.29 No.4 April 2004 195



(TH) as individual tissues undergo distinct changes atdifferent stages of development [28,29]. These changesinclude formation of the limb, tail resorption and drasticremodeling events in the brain and the intestine. TheTH target-genes include transcription factors, signalingmolecules, caspases and matrix metalloproteases [29].Although many steroid hormones, including estrogen,androgen and progesteron, are known to regulate cellsurvival [30], the best-studied models of steroid-regulatedPCD are glucocorticoid-mediated thymocyte apoptosis inmammals and ecdysone-mediated PCD during larval–pupal metamorphosis in Drosophila [31,32]. Glucocorti-coids repress the activity of prosurvival transcriptionfactors such as NFkB, and AP-1 [31]; however, recentmicroarray data suggest that bim is upregulated byglucocorticoids, thereby linking the effects of glucocorti-coids to the activation of the apoptosis effector machinery[33]. The upregulation of bim by glucocorticoids isprobably indirect and might involve forkhead (FOXO)transcription factor (FKHRL1) [33].

In Drosophila, the steroid hormone 20-hydroxyecdy-sone (commonly known as ecdysone) regulates differen-tiation, morphogenesis and PCD to remove obsolete larvaltissues [1,34–36]. An increase in ecdysone titer at the endof the third larval instar triggers metamorphosis and thedestruction of the larval midgut and anterior muscles.Twelve hours following puparium formation, a second risein ecdysone triggers salivary glands to undergo PCD[34–36]. Ecdysone binds to its heterodimeric receptorEcR–Usp, directly activating a set of early genes many ofwhich encode transcription factors including Broad–Complex (BR–C), E74A and E93 (Figure 4). Studiesinvolving the salivary gland and in vitro PCD modelsindicate that these transcription factors upregulate keycell-death genes, including rpr, hid, dark and dronc,and downregulate death inhibitors diap1 and diap2(Figures 3 and 4) [34–37]. EcR–Usp and ecdysone-induced transcription factors could also play a role in thetemporal and spatial regulation of gene expressionassociated with PCD. For example, BR–C and E93 regu-late temporal expression of the caspase dronc, whereasdirect binding of EcR–Usp to the dronc promoter isimportant for spatial expression of this caspase [36–38].Numerous other genetic, cellular and biochemical studieshave clearly established the fundamental role of hormone-mediated transcription in directly activating the core cell-death machinery [1,30,31,34].

Transcriptional control of stress-induced apoptosis

Cellular stress, caused by DNA-damaging agents, cytokinewithdrawal or UV irradiation, triggers the apoptoticresponse as a safeguard to remove harmful cells fromthe organism. Cytokine withdrawal also plays a key role indeleting unwanted cells during embryonic and adultdevelopment. Increasing evidence in various model sys-tems indicates that, in many cases, the regulation ofstress-induced PCD occurs through transcriptional con-trol of proteins of the core cell-death machinery, especi-ally BH3-only proteins and Bcl-2 family members. TheBH3-only protein Bim is required for both cytokine-withdrawal-induced cell death and homeostasis in the

immune and haemopoietic compartments [39,40]. In pro Band T cells, deprivation of the survival cytokine IL-3results in the dephosphorylation of FKHRL1, whichtranslocates to the nucleus and activates Bim expression[41]. IL-2-mediated T-cell survival pathway involves theactivation of serine/threonine kinase PKB and/or Akt,which inhibits transcriptional activation of FOXO3 [42].IL-2 withdrawal results in rapid dephosphorylation ofFOXO3 and upregulation of Bim, suggesting thatIL-2-mediated T-cell survival occurs through FOXO3inactivation and hence the suppression of Bim expression.GM-CSF and IL-3 are key survival cytokines for haemo-poietic cells and their effects are mediated by the phos-phoinositide 3-kinase (PtdIns 3-kinase) pathway [43].Mcl-1, a member of Bcl-2 family, is induced early in manymyeloid leukemia cells and its overexpression delaysapoptosis induced by the withdrawal of growth factor[44]. In IL-3-stimulated cells, the transcription factorCREB binds to a CRE-2-binding site in the Mcl-1 promoterand mediates Mcl-1 expression [45].

Recent findings suggest that Bim regulation is alsocrucial for neuronal survival and apoptosis [46–49]. Forexample, in sympathetic neurons, the survival of whichdepends on nerve growth factor (NGF), NGF withdrawalresults in upregulation of Bim through FKHRL1 [48]. Theinsulin-like growth factor-1 (IGF-1) exerts its neuro-protective effects through the PtdIns 3-kinase pathway[49]. Interestingly, when NGF is withdrawn IGF-1completely blocks FKHRL1 dephosphorylation and Bim

Figure 4. An ecdysone-induced hierarchy of genes controls programmed cell

death (PCD) in the salivary glands of Drosophila. During larval–pupal metamor-

phosis, a prepupal pulse of ecdysone initiates PCD. The timing of the ecdysone

pulse in relation of the prepupal–pupal development is crucial for temporal regu-

lation of PCD. The blue line shows the separation of the prepupal and pupal

stages. Ecdysone binds to its heterodimeric receptor consisting of EcR and Usp

proteins and promotes the expression of various transcription factors including

E74A, BR–C and E93. These factors then upregulate transcription of several genes

of the core cell-death machinery. EcR–Usp can also directly activates rpr and

dronc promoters, which probably contributes to temporal and spatial control of

gene expression. EcR–Usp represses the nuclear receptor bFTZ-F1, which acts as a

competence factor to facilitate the expression of ecdysone-induced transcription

factors, presumably to provide temporal control of ecdysone action.

Ti BS

EcR/Usp

BR–C

Prepupa Pupa

Ecdysone pulse

E74A E93

rprdronc

hiddrice

hiddarkdroncdricestrica

rprhiddroncdrice

βFTZ-F1




transcriptional upregulation in neurons [49], emphasizingthat cell-death signals converge on FOXO activation ofBim. In PC12 cells, the withdrawal of NGF upregulatesantiapoptotic isoform of Bcl-x (Bcl-xs) and Bax [50];however, how these proteins are regulated at the levelsof transcription is unknown.

DNA-damage-induced apoptosis involves two maintranscription factors, p53 and E2F-1, which have beenimplicated in various apoptotic pathways and play acrucial role in cancer development [51]. These transcrip-tion factors control the expression of several cell-death and-survival genes (Figure 5). In Drosophila embryos, UVinduces expression of dark and rpr (Figure 3) [52,53]. AnE2F-binding site in the dark promoter appears to regulateits UV-induced transcription [52]. In addition, the bindingof p53 directly regulates rpr promoter [53]. Similar toDrosophila dark, E2F-1 can directly bind to and regulateApaf-1 promoter in mammals [54]. In neurons, p53 alsodirectly induces Apaf-1 [55]. Although E2F-1 partly medi-ates apoptosis through p53, in cells lacking p53, E2F-1 caninduce apoptosis through the transcription of p73, amember of p53 family that shares some of its targetswith p53 [56]. Retinoblastoma (Rb) restrains proliferationpartly by suppressing E2F-1-mediated transcription [57].In quiescent cells, Rb interacts with E2F-1, and as cellsprogress into the cell cycle, phosphorylation of Rb bycyclin-dependent kinases frees E2F-1, allowing it toactivate genes required for the entry into the S phase[57]. Consequently, loss of Rb or enforced E2F expressioncan result in apoptosis. Recent data show that, indeed,deregulation of E2F-1 by adenovirus E1A, loss of Rb orforced E2F-1 expression results in direct transcriptionalupregulation of several caspases [58]. Transcriptionalrepression by E2F-1 is also equally important for initiatingapoptosis as seen with Mcl-1, which is repressed inresponse to E2F-1 expression [59]. Although Rb repressesE2F-1, it can also act as an activator of transcription insome cell types. In epithelial cells, for example, inacti-vation of Rb by the large T antigen of SV40 induces

massive apoptosis [60]. This could simply be because ofeither increased caspase expression by E2F-1 or Bcl-2downregulation in the absence of Rb, because Rb regulatesBcl-2 through the epithelial transcription factor AP-2 [61].

The BH3-only proteins Noxa and PUMA are directlyregulated by p53, and according to recent knockout data,are both important for p53-mediated cell death [62–66].PUMA loss causes a partial resistance to apoptosisinduced by cytokine withdrawal, PMA and glucocorticoids[64,65]. PUMA can also be induced by signals that mediatep53-independent cell death, and antiapoptotic growthfactors, such as IGF-1 or epidermal growth factor, stronglyinhibit PUMA expression [67]. Dexamethasone and serumdeprivation potently upregulate PUMA [67]; however, thetranscription factors involved in these responses have notbeen identified.

Transcriptional regulation of death receptor pathways

Apoptosis induced by TNF family of death receptors(TNFRs) proceeds through the recruitment of the FADDadaptor and caspase-8 to the activated receptor complex(Figure 1) [7,68]. Several components of the death receptorpathways are also regulated by transcription to controlapoptosis. One of these regulators is FLICE-inhibitoryprotein (FLIP), a caspase-8-like protein that lacks cata-lytic activity [69]. PKB promotes FLIP expression and cellsurvival in endothelial and tumor cells through FOXO3a[70]. NFkB also regulates FLIP expression during B-cellsurvival [71]. An additional target for NFkB is A1, which isa member of Bcl-2 family [72]. The TNF family memberFas-ligand–CD95L acts through its receptor Fas–CD95 toinduce apoptosis in many cell types [68]. In the immunesystem, CD95L–CD95-mediated apoptosis is crucialfor homeostasis. Several signaling pathways regulateCD95L expression. These include: antigen stimulation ofT cells by crosslinking of TCR and/or CD3, engagement ofCD28 on the Tcells by the B7 family of receptors expressedon the antigen-presenting cells, cytotoxic drug-inducedstress and IFN-g-receptor-mediated signaling involving

Figure 5. Regulation of the core cell-death machinery by E2F-1 and the p53 family. E2F-1 can regulate apoptosis in many ways. It can induce cell death by stabilizing the

levels of p53 through activating the ARF tumor suppressor, which suppresses Mdm2, a negative regulator of p53. The p53 protein regulates the transcription of several cell-

death genes including BH3-only proteins, proapoptotic Bcl-2 protein Bax and the caspase-9 adaptor Apaf-1. In cells lacking p53, E2F-1 can act through p73, a member of

p53 family that activates some of the same target genes as p53. E2F-1 can also directly regulate the transcription of several different caspases and suppress cell survival

pathways by suppressing Mcl-1 expression or by inhibiting NFkB-mediated antiapoptotic signaling.

Ti BS

BaxApaf-1 PumaNoxa

Caspases (2, 3, 7, 8, 9)

Apoptosis

Rb E2F-1

NFκB

ARF p53Mdm2

p73Mcl-1




phosphorylation of STAT1 through the activation of theJAK1 and JAK2 [68]. The promoter of the gene encodingCD95L is highly complex and is directly or indirectlyregulated by a large number of transcription factors,such as NF-AT, Egr, NFkB, HIV-1 Tat, AP-1, cMyc, Nur77,IFN-regulatory factors (IRFs), viral IRFs, SP-1, ALG-4and CIITA [68]. Caspase-8, which is the initiator caspasefor all TNFR-mediated death pathways, is also transcrip-tionally induced in some cases and its promoter contains ap53-responsive element [73].

Concluding remarks – future perspectives

This article summarizes some recent developments in thefield of transcriptional regulation of apoptotic genes inresponse to specific death signals. Despite the intenseeffort to identify and study the basic cell-death machineryin the past decade, little attention has been paid to the factthat varying concentrations of the core components of thedeath machinery can mediate apoptosis. The emergingconcept that, the survival–death switch is turned on oroff by transcription factors through either upregulatingproapoptotic genes or downregulating antiapoptotic genes,is well established in various contexts of PCD, includingcytotoxic stress, nuclear hormones, death ligands anddevelopmental cues. Importantly, studies from nonmam-malian systems indicate that the temporal and spatialregulation of PCD during development is primarilyregulated by controlling the expression of cell-deathexecution machinery, and many transcription factorsthat regulate PCD are also involved in other pathways.One key question that is to be addressed is whethertemporal and spatial control of PCD during mammaliandevelopment is also orchestrated at the transcriptionallevel. For instance, temporally and spatially controlledupregulation of specific BH3-only proteins might play akey role in deleting specific cells or tissues during tissueand organ modelling, and this might, in turn, be regulatedby specific hormones, cytokines and retinoids. The scene isnow set for more detailed mechanistic studies to under-stand and exploit the transcriptional machinery involvedin various PCD pathways. As aberrant expression of celldeath and survival regulators can result in humanpathologies, the transcription factors that specificallycontrol apoptotic execution machinery are potentiallynovel targets for therapeutic intervention.

AcknowledgementsWe thank Andreas Strasser and the members of our laboratory for helpfulcomments. The work in our laboratory is supported by the National Healthand Medical Research Council of Australia. We apologize to colleagueswhose work could not be included in this review owing to spaceconstraints.

References

1 Baehrecke, E.H. (2002) How death shapes life during development.Nat. Rev. Mol. Cell Biol. 3, 779–787

2 Adams, J.M. (2003) Ways of dying: multiple pathways to apoptosis.Genes Dev. 17, 2481–2495

3 Hengartner, M.O. (2000) The biochemistry of apoptosis. Nature 407,770–776

4 Puthalakath, H. and Strasser, A. (2002) Keeping killers on a tightleash: transcriptional and post translational control of the pro-apoptotic activity of BH3-only proteins. Cell Death Differ. 9, 505–512

5 Adams, J.M. and Cory, S. (2001) Life-or-death decisions by the Bcl-2protein family. Trends Biochem. Sci. 26, 61–66

6 Zou, H. et al. (1997) Apaf-1, a human protein homologous to C. elegansCED-4 participates in cyt c dependent activation of caspase-3. Cell 90,405–413

7 Aggarwal, B.B. (2003) Signalling pathways of the TNF superfamily: adouble-edged sword. Nat. Rev. Immunol. 3, 745–756

8 Vaux, D.L. and Silke, J. (2003) Mammalian mitochondrial IAP bindingproteins. Biochem. Biophys. Res. Commun. 304, 499–504

9 Dorstyn, L. et al. (2002) The role of cytochrome c in caspase activationin Drosophila melanogaster cells. J. Cell Biol. 156, 1089–1098

10 Marsden, V.S. et al. (2002) Apoptosis initiated by Bcl-2-regulatedcaspase activation independently of the cytochrome c/Apaf-1/caspase-9apoptosome. Nature 419, 634–637

11 Shi, Y. (2002) Mechanisms of caspase activation and inhibition duringapoptosis. Mol. Cell 9, 459–470

12 Boatright, K.M. et al. (2003) A unified model for apical caspaseactivation. Mol. Cell 11, 529–541

13 Fischer, U. et al. (2003) Many cuts to ruin: a comprehensive update ofcaspase substrates. Cell Death Differ. 10, 76–100

14 Metzstein, M.M. and Horvitz, H.R. (1999) The C. elegans cell deathspecification gene ces-1 encodes a snail family zinc finger protein. Mol.Cell 4, 309–319

15 Thellmann, M. et al. (2003) The Snail-like CES-1 protein of C.eleganscan block the expression of the BH3-only cell death activator gene egl-1by antagonizing the function of bHLH proteins. Development 130,4057–4071

16 Cameron, S. et al. (2002) PAG-3, a Zn-finger transcription factor,determines neuroblast fate in C. elegans. Development 129, 1763–1774

17 Grimes, H.L. et al. (1996) The Gfi-1 protoncoprotein represses Baxexpression and inhibits T-cell death. Proc. Natl. Acad. Sci. U. S. A. 93,14569–14573

18 Martin, S.J. (2002) Destabilizing influences in apoptosis: sowing theseeds of IAP destruction. Cell 109, 793–796

19 Bergmann, A. et al. (1998) The Drosophila gene hid is a directmolecular target of Ras-dependent survival signaling. Cell 95,331–341

20 Kurada, P. and White, K. (1998) Ras promotes cell survival inDrosophila by downregulating hid expression. Cell 95, 319–329

21 Mc Ginnis, W. et al. (1990) Establishment and maintenance of position-specific expression of the Drosophila homeotic selector gene Deformed.Adv. Genet. 27, 363–402

22 Lohmann, I. et al. (2002) The Drosophila hox gene deformed sculptshead morphology via direct regulation of the apoptosis activatorreaper. Cell 110, 457–466

23 Bello, B.C. et al. (2003) A pulse of the Drosophila Hox proteinAbdominal-A schedules the end of neural proliferation via neuroblastapoptosis. Neuron 37, 209–219

24 Hurle, J.M. et al. (1996) Morphology and significance of programmedcell death in the developing limb bud of the vertebrate embryo.Microsc. Res. Tech. 34, 236–246

25 Stadler, H.S. et al. (2001) Loss of Eph-receptor expression correlateswith loss of cell adhesion and chondrogenic capacity in Hoxa13 mutantlimbs. Development 128, 4177–4188

26 Shimamoto, T. et al. (1997) Inhibition of DLX-7 homeobox gene causesdecreased expression of GATA-1 and c-myc genes and apoptosis. Proc.Natl. Acad. Sci. U. S. A. 94, 3245–3249

27 Dodd, M.H.I. and Dodd, J.M. (1976) The Biology of Metamorphosis,Academic Press, 467–599

28 Tata, J.R. (1966) Requirement for RNA and protein synthesis forinduced regression of the tadpole tail in organ culture. Dev. Biol. 13,77–94

29 Shi, Y.B. (1999) Amphibian Metamorphosis: From Morphology toMolecular Biology, John Wiley & Sons, Inc

30 Kucharova, S. and Farkas, R. (2002) Hormone nuclear receptors andtheir ligands: role in programmed cell death. Endocr. Regul. 36, 37–60

31 Distelhorst, C.W. (2002) Recent insights into the mechanism ofglucocorticosteroid-induced apoptosis. Cell Death Differ. 9, 6–19

32 Jiang, C. et al. (1997) Steroid regulated programmed cell death duringDrosophila metamorphosis. Development 124, 4673–4683

33 Wang, Z. et al. (2003) Microarray analysis uncovers the induction ofthe proapoptotic BH3-only protein Bim in multiple models ofglucocorticoid-induced apoptosis. J. Biol. Chem. 278, 23861–23867




34 Thummel, C.S. (1996) Flies on steroids: Drosophila metamorphosisand the mechanisms of hormone action. Trends Genet. 12, 306–310

35 Lee, C-Y. et al. (2000) E93 directs steroid-triggered programmed celldeath in Drosophila. Mol. Cell 6, 433–443

36 Jiang, C. et al. (2000) A steroid-triggered transcriptional hierarchycontrols salivary gland cell death during Drosophila metamorphosis.Mol. Cell 5, 445–455

37 Cakouros, D. et al. (2002) Ecdysone-induced expression of the caspaseDRONC during hormone-dependent programmed cell death inDrosophila is regulated by Broad–Complex. J. Cell Biol. 157, 985–995

38 Daish, T. et al. (2003) Distinct promoter regions regulate spatial andtemporal expression of the Drosophila caspase dronc. Cell Death Differ.10, 1348–1356

39 Bouillet, P. et al. (1999) Proapoptotic Bcl-2 relative Bim required forcertain apoptotic responses, leukocyte homeostasis and to procludeautoimmunity. Science 286, 1735–1738

40 Strasser, A. and Bouillet, P. (2003) The control of apoptosis inlymphocyte selection. Immunol. Rev. 193, 82–92

41 Dijkers, P.F. et al. (2000) Expression of the proapoptotic BCl-2 familymember Bim is regulated by the forkhead transcription factorFKHRL1. Curr. Biol. 10, 1201–1204

42 Stahl, M. et al. (2002) The Forkhead transcription factor FOXOregulates transcription of p27kip1 and Bim in response to IL-2.J. Immunol. 168, 5024–5031

43 Arai, K. et al. (1990) Cytokines: coordinators of immune andinflammatory responses. Annu. Rev. Biochem. 59, 783–836

44 Zhou, P. et al. (1997) Mcl-1, a Bcl-2 family member delays the death ofhaemopoeitc cells under a variety of apoptosis-inducing conditions.Blood 89, 630–643

45 Wang, J. et al. (1999) The Antiapoptotic gene mcl-1 is upregulated bythe phosphatidylinositol 3-kinase/Akt signaling pathway through atranscription factor complex containing CREB. Mol. Cell. Biol. 19,6195–6206

46 Harris, C.A. and Johnson, E.M. (2001) BH3-only BCl-2 familymembers are coordinately regulated by the JNK pathway and requireBax to induce apoptosis in neurons. J. Biol. Chem. 276, 37754–37760

47 Whitfield, J. et al. (2001) Dominant negative c-jun promotes neuronalsurvival by reducing BIM expression and inhibiting mitochondrialcytochrome c release. Neuron 29, 629–643

48 Gilley, J. et al. (2003) FOXO transcription factors directly activate bimexpression and promoter apoptosis in sympathetic neurons. J. CellBiol. 162, 613–622

49 Linseman, D.A. et al. (2002) Insulin-like growth factor-I blocks Bcl-2interacting mediator of cell death (Bim) induction and intrinsic deathsignaling in cerebellar granule neurons. J. Neurosci. 22, 9287–9297

50 Rong, P. et al. (1999) Nerve growth factor determines survival anddeath of PC12 cells by regulation of the bcl-x, bax and caspase-3 genes.J. Neurochem. 72, 2294–2300

51 Evan, G.I. and Vousden, K.H. (2001) Proliferation, cell cycle andapoptosis in cancer. Nature 411, 342–348

52 Sogame, N. et al. (2003) Drosophila p53 preserves genomic stability byregulating cell death. Proc. Natl. Acad. Sci. U. S. A. 100, 4696–4701

53 Zhou, L. and Steller, H. (2003) Distinct pathways mediate UV-inducedapoptosis in Drosophila embryos. Dev. Cell 4, 599–605

54 Moroni, M.C. et al. (2001) Apaf-1 is a transcriptional target for E2F andp53. Nat. Cell Biol. 3, 552–558

55 Fortin, A. et al. (2001) APAF1 is a key transcriptional target for p53 inthe regulation of neuronal cell death. J. Cell Biol. 155, 207–216

56 Irwin, M. et al. (2000) Role for the p53 homologue p73 in E2F-1-inducedapoptosis. Nature 407, 645–648

57 Harbour, J.W. and Dean, D.C. (2000) Rb function in cell cycleregulation and apoptosis. Nat. Cell Biol. 2, E65–E67

58 Nahle, Z. et al. (2002) Direct coupling of the cell cycle and cell deathmachinery by E2F. Nat. Cell Biol. 4, 859–864

59 Croxton, R. et al. (2002) Direct repression of the Mcl-1 promoter byE2F1. Oncogene 21, 1359–1369

60 Martel, C. et al. (1997) Inactivation of retinoblastoma familyproteins by SV40 T antigen results in creation of a hepatocyte growthfactor/scatter factor autocrine loop associated with an epithelial–fibroblastoid conversion and invasiveness. Cell Growth Differ. 8,165–178

61 Decary, S. et al. (2002) The retinoblastoma protein binds the promoterof the survival gene bcl-2 and regulates its transcription in epithelialcells through transcription factor AP-2. Mol. Cell. Biol. 22, 7877–7888

62 Oda, E. et al. (2000) Noxa, a BH3-only member of the Bcl-2 family andcandidate mediator of p53-induced apoptosis. Science 288, 1053–1058

63 Nakano, K. and Vousden, K.H. (2001) PUMA, a novel proapoptoticgene, is induced by p53. Mol. Cell 7, 683–694

64 Villunger, A. et al. (2003) p53 and drug-induced apoptotic responsesmediated by BH3-only proteins Puma and Noxa. Science 302,1036–1038

65 Jeffers, J.R. et al. (2003) Puma is an essential mediator of p53-dependentand -independent apoptotic pathways. Cancer Cell 4, 321–328

66 Shibue, T. et al. (2003) Integral role of Noxa in p53-mediated apoptoticresponse. Genes Dev. 17, 2233–2238

67 Han, J. et al. (2001) Expression of bbc3, a pro-apoptotic BH3-only gene,is regulated by diverse cell death and survival signals. Proc. Natl.Acad. Sci. U. S. A. 98, 11318–11323

68 Li-Weber, M. and Krammer, P.H. (2003) Function and regulation of theCD95 (APO-1/Fas) ligand in the immune system. Semin. Immunol. 15,145–157

69 Lakhani, S. and Flavell, R.A. (2003) Caspases and T lymphocytes: a flipof the coin? Immunol. Rev. 193, 22–30

70 Skurk, C. et al. (2003) The Akt-regulated forkhead transcription factorFOXO3a controls endothelial cell viability through modulation of thecaspase-8 inhibitor FLIP. J. Biol. Chem. 279, 1513–1525

71 Gerondakis, S. and Strasser, A. (2003) The role of Rel/NF-kappaBtranscription factors in B lymphocyte survival. Semin. Immunol. 15,159–166

72 Wang, C.Y. et al. (1999) NF-kappaB induces expression of the Bcl-2homologue A1/Bfl-1 to preferentially suppress chemotherapy-inducedapoptosis. Mol. Cell. Biol. 19, 5923–5929

73 Liedtke, C. et al. (2003) The human caspase-8 promoter sustains basalactivity through SP1 and ETS-like transcription factors and can be up-regulated by a p53-dependent mechanism. J. Biol. Chem. 278,27593–27604

74 Moreno, E. et al. (2002) Evolution of TNF signaling mechanisms:JNK-dependent apoptosis triggered by Eiger, the Drosophilahomolog of the TNF superfamily. Curr. Biol. 12, 1263–1268

PSM final submission date: 28 May 2004

Owing to decreasing downloads, citations and biological impact of the Protein Sequence Motif section of the journal, the PSMcolumn is being closed down. TiBS has decided to focus exclusively on its core strengths, providing content in the form of Reviews,

Opinions and Research Focus articles only. The last submission date for this section of the journal will be 28 May 2004.




transcriptional control of the core cell-death machinery

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