Bcl-XL interacts with Apaf-1 and inhibits Apaf-1-dependent caspase-9 activation

A tetracycline-regulated adenovirus encoding dominant-negative caspase-9 is regulated in rat brain and protects against neurotoxin-induced cell death in vitro, but not in vivo

Caspase-9 is a critical downstream effector molecule involved in apoptosis, a cell death process thought to be involved in the demise of dopamine (DA) neurons in the substantia nigra (SN) affected by Parkinson's disease (PD). In this study, we determined that a tetracycline-regulated adenovirus harboring a dominant-negative form of caspase-9 (Casp9DN) and the marker gene, enhanced green fluorescent protein (EGFP), under the control of a bidirectional promoter could each be regulated in vitro and in vivo by doxycycline. We next observed that Casp9DN gene delivery significantly protected against TNFalpha and cycloheximide-induced chromatin condensation in HeLa cells and prevented chromatin condensation and the appearance of the early apoptotic marker annexin V in 6-hydroxydopamine (6-OHDA) treated MN9D cells, a dopaminergic cell line. Effects of Casp9DN on DA neurons in vivo were also assessed. DA neurons were retrogradely labeled with fluorogold (FG) and transduced with Casp9DN and EGFP or EGFP alone. A progressive lesion of DA neurons was induced by striatal injection of 6-OHDA 1 week later. At 2 weeks post-lesion, a morphometric analysis of FG+ neurons in the SN revealed that the mean cell diameter of FG labeled neurons in the Casp9DN group was 8% and 21% larger than the EGFP and PBS groups, respectively (P <0.05). However, there was no difference among the treatment groups in the number of neurons remaining in the lesioned SN. These results suggest that while inhibiting apoptosis at the level of caspase-9 is protective in vitro, it is not protective against 6-OHDA-induced cell death in vivo.

Nuclear localization of apoptosis protease activating factor-1 predicts survival after tumor resection in early-stage non-small cell lung cancer

The proapoptotic protein apoptosis protein activating factor-1 (Apaf-1), which is normally located in the cytoplasm, can translocate to the nucleus before non-small cell lung carcinoma (NSCLC) cells manifest signs of apoptosis such as mitochondrial damage, caspase activation, or chromatin condensation. This may indicate a stage of imminent apoptosis. Importantly, we found that 24% (15 of 62) of resected stage I NSCLC (T(1)N(0)M(0) or T(2)N(0)M(0)), manifested a marked nuclear localization of Apaf-1 (Apaf-1(Nuc)), as compared with the mostly cytoplasmic localization of Apaf-1 found in the remaining tumors (Apaf-1(Cyt)). After a median follow-up of 6.31 years, the actuarial 5-year overall survival rates were 89% (56-98%) in the Apaf-1(Nuc) group and 54% (36-71%) in the Apaf-1(Cyt) group (P = 0.039). No correlation between the subcellular localization of Apaf-1 and that of p53 and Hsp70 could be established. Thus, the subcellular location of Apaf-1 (but not that of p53 or Hsp70) constitutes an accurate prognostic factor for overall survival in NSCLC.

Cytotoxic effects of mansonone E and F isolated from Ulmus pumila

Two sesquiterpenoids, mansonone E (ME) and mansonone F (MF) were first isolated from the dried root bark of Ulmus pumila (shironire in Japanese), and their antiproliferative activities on human tumor cells were evaluated in vitro. ME had more potent cytotoxic effects on four tumor cell lines, human cervical cancer HeLa, human malignant melanoma A375-S2, human breast cancer MCF-7, and human histiocytic lymphoma U937, than those of MF. The results showed that ME induced oligonucleosomal fragmentation of DNA in HeLa cells and activated caspase-3, followed by the degradation of the inhibitor of caspase-activated DNase, decreased the expression of anti-apoptotic mitochondrial proteins Bcl-2 and Bcl-(XL), and increased that of proapoptotic Bax.

The kinder side of killer proteases: caspase activation contributes to neuroprotection and CNS remodeling

Caspases are a family of cysteine proteases that are expressed as inactive zymogens and undergo proteolytic maturation in a sequential manner in which initiator caspases cleave and activate the effector caspases 3, 6 and 7. Effector caspases cleave structural proteins, signaling molecules, DNA repair enzymes and proteins which inhibit apoptosis. Activation of effector, or executioner, caspases has historically been viewed as a terminal event in the process of programmed cell death. Emerging evidence now suggests a broader role for activated caspases in cellular maturation, differentiation and other non-lethal events. The importance of activated caspases in normal cell development and signaling has recently been extended to the CNS where these proteases have been shown to contribute to axon guidance, synaptic plasticity and neuroprotection. This review will focus on the adaptive roles activated caspases in maintaining viability, the mechanisms by which caspases are held in check so as not produce apoptotic cell death and the ramifications of these observations in the treatment of neurological disorders.

Dracorhodin perchlorate induces apoptosis via activation of caspases and generation of reactive oxygen species

Dracorhodin perchlorate inhibited proliferation of several tumor cell lines. The drug induced oligonucleosomal fragmentation of DNA in HeLa cells and increased caspase-3, -8, -9 activities followed by the degradation of caspase-3 substrates, inhibitor of caspase-dependent DNase, and poly-(ADP-ribose) polymerase. It also increased caspase-1 activity and a caspase-1 inhibitor, Ac-YVAD-cmk, and a caspase-10 inhibitor z-AEVD-fmk, also reduced dracorhodin-perchlorate-induced HeLa cell death. Dracorhodin perchlorate decreased the expression of anti-apoptotic mitochondrial protein, Bcl-X(L), but not Bcl-2; and it increased the expression of pro-apoptotic protein, Bax. Dracorhodin perchlorate induced a sustained generation of reactive oxygen species (ROS) in HeLa cells; caspase-1 inhibitor, Ac-YVAD-cmk, and caspase-3 inhibitor, z-DEVD-fmk, attenuated the generation of ROS. Taken together, our results indicate that dracorhodin perchlorate alters the intracellular redox status, changed the balance of Bcl-X(L) and Bax protein expression, and induces apoptosis through caspase pathways in HeLa cells.

Changing picture of cellular drug resistance in human leukemia

A relatively well documented and seemingly firm overall picture of mechanisms involved in leukemia-cell drug resistance has evolved since the 1970s, where mechanisms involved in multidrug resistance towards anti-leukemia chemotherapeutic compounds were first described. At that time, based on available data, resistance associated with overexpression of the cell-surface transmembrane ATPase P-glycoprotein (P-170, P-gp, the product of the MDR1 gene) was described as "the" cause of multidrug resistance in cancer cells. However, during the 1980s and later on other mechanisms were described as candidate causes of multidrug resistance in human leukemia. Moreover, research of the past decade has provided us with an enormous increase in the amount of data and knowledge on the cell-biological and--to an even higher extent--the molecular-genetic processes governing cell survival and death in cancer cells. This, in turn, has improved the possibilities of designing and developing better drugs and drug combinations in leukemia. Along this line, based on rational drug design, imatinib, a 2-phenylaminopyrimidine derivative, has very recently been introduced and found to be an efficient inhibitor of the altered tyrosine kinase, which arises as a product of the BCR-ABL fusion transcript in Philadelphia chromosome positive (Ph+) cases of CML. This new compound appears to be the first of a (hopefully) large family of small organic molecules with a more specific inhibiting activity against the pathogenetic defects in leukemia as well as cancer. With this novel compound, as with all other known individual drugs and classes of chemotherapeutic drugs, drug resistance is seen. To what extent drug resistance towards this novel compound (and its successors) will follow patterns of drug resistance that are already known or entirely new mechanisms of drug resistance is yet to be seen.

Aven and Bcl-xL enhance protection against apoptosis for mammalian cells exposed to various culture conditions

A balance between proliferation and cell death is critical for achieving desirable high cell densities in mammalian cell culture. In this study, we evaluate a recently discovered anti-apoptotic gene, aven, and examine its effectiveness alone and in combination with a member of the Bcl-2 family, bcl-xL. The commercially popular cell line, Chinese hamster ovary (CHO), was genetically modified to constitutively express aven, bcl-xL, and the two genes in combination. Cells were exposed to several model insults that simulate severe bioreactor environments, including serum deprivation, spent medium, and Sindbis virus infection, as well as staurosporine, a known chemical inducer of apoptosis. CHO cells exhibited DNA fragmentation, a hallmark of apoptosis, after exposure to these model insults. After exposure to serum deprivation, 4- and 5-day spent medium, and staurosporine, cells expressing Aven provided limited protection against cell death when compared with the protection afforded by cells expressing Bcl-xL alone. However, the highest survival levels for all insults were achieved when Aven was expressed in combination with Bcl-xL. In fact, Aven appeared to act synergistically to enhance the protective function of Bcl-xL for several insults, because the protective function of the two genes expressed together in one cell line often exceeded the additive protective levels of each anti-apoptosis gene expressed alone. Surprisingly, Aven expression provided a mildly pro-apoptotic response in CHO isolates infected with Sindbis virus. However, CHO cells expressing both Bcl-xL and Aven showed protection against Sindbis virus infection due to the inhibitory properties of the bcl-xL anti-apoptosis gene. This study shows that combinatorial anti-apoptosis cell engineering strategies may be the most effective mechanisms for providing extended protection against cell death in mammalian cell culture.

Trichomonas vaginalis-induced apoptosis in RAW264.7 cells is regulated through Bcl-xL, but not Bcl-2

The purpose of this study was to determine whether anti-apoptotic proteins of the Bcl-2 family such as Bcl-2 and Bcl-x(L), proteins that confer resistance to apoptotic death from some stimuli, block apoptotic cell death in RAW264.7 cells upon treatment with Trichomonas vaginalis. In this study, the expression level of Bcl-2 was unchanged throughout the course of apoptotic cell death, and overexpressed Bcl-2 did not prevent release of cytochrome c, the significant change of the membrane potential, activation of caspases, and PARP cleavage in T. vaginalis-treated RAW264.7 cells. On the other hand, Bcl-x(L)expression was decreased after T. vaginalis treatment accompanied with Bax activation. Furthermore, we showed that release of mitochondrial cytochrome c, cleavage of caspase-9 and PARP during apoptosis in T. vaginalis-treated RAW264.7 cells were considerably diminished by transfection with overexpressed Bcl-x(L), and overexpressed Bcl-x(L)could inhibit T. vaginalis-induced apoptosis in RAW264.7 cells. In addition, interestingly, pre-treatment with caspase inhibitors, Boc-D-FMK and Z-DEVD-FMK, significantly abolished T. vaginalis-induced down-regulation of Bcl-x(L), suggesting that caspase-3 may play a pivotal role in the process of apoptosis as well as the down-regulation of Bcl-x(L)by T. vaginalis. Therefore, these results suggest that T. vaginalis-induced apoptosis in RAW264.7 cells can occur via a Bcl-x(L)-dependent apoptotic mechanism.

Adult neuron survival strategies--slamming on the brakes

Developing neurons are programmed to die by an apoptotic pathway unless they are rescued by extrinsic growth factors that generate an anti-apoptotic response. By contrast, adult neurons need to survive for the lifetime of the organism, and their premature death can cause irreversible functional deficits. The default apoptotic pathway is shut down when development is complete, and consequently growth factors are no longer required to prevent death. To protect against accidental apoptotic cell death, anti-apoptotic mechanisms are activated in mature neurons in response to stress. Loss or reduced activity of these intrinsic anti-apoptotic 'brakes' might contribute to or accelerate neurodegeneration, whereas their activation might rescue neurons from injury or genetic abnormalities.

Chemical-induced apoptosis: formation of the Apaf-1 apoptosome

Many environmental and therapeutic agents initiate apoptotic cell death by inducing the release of cytochrome c from the mitochondria, which activates Apaf-1 (apoptotic protease-activating factor-1). This large (approximately 130kD) protein is a mammalian homologue of CED-4, an essential protein involved in programmed cell death in the nematode C. elegans. Cytochrome c activates Apaf-1, which oligomerizes to form an approximately 700-1400-kDa caspase-activating complex known as the Apaf-1 apoptosome. Caspase-9, an initiator caspase, is then recruited to the complex by binding to Apaf-1 through CARD-CARD (caspase recruitment domain) interactions to form a holoenzyme complex. Subsequently, the Apaf-1/caspase-9 holoenzyme complex recruits the effector caspase-3 via an interaction between the active site cysteine in caspase-9 and the critical aspartate, which is the cleavage site for generating the large and small subunits of caspase-3 that constitute the activated form of caspase-3. This initiates the caspase cascade that is responsible for the execution phase of apoptosis. Intracellular levels of K+, XIAP an inhibitor of apoptosis protein, and at least two mitochondrial released proteins, Smac/DIABLO and Omi/Htra 2 a serine protease, tightly regulate formation and function of the apoptosome. Thus, a number of physiological mechanisms ensure that the apoptosome complex is only fully assembled and functional when the cell is irrevocably committed to die. It is interesting that more recent studies show that a variety of small molecules can directly activate or inhibit caspase activation by interfering with the formation and function of the apoptosome complex. The cytotoxicity of many conventional chemotherapeutic drugs rests on their ability to induce apoptosome formation and apoptosis. Defects in this pathway can result in drug resistance, and the discovery that small molecules can directly activate or inhibit the apoptosome may provide new alternative treatments for cancer.

Bcl-2 homodimerization involves two distinct binding surfaces, a topographic arrangement that provides an effective mechanism for Bcl-2 to capture activated Bax

The homo- and heterodimerization of Bcl-2 family proteins is important for transduction and integration of apoptotic signals and control of the permeability of mitochondria and endoplasmic reticulum membranes. Here we mapped the interface of the Bcl-2 homodimer in a cell-free system using site-specific photocross-linking. Bcl-2 homodimer-specific photoadducts were detected from 11 of 17 sites studied. When modeled into the structure of Bcl-2 core, the interface is composed of two distinct surfaces: an acceptor surface that includes the hydrophobic groove made by helices 2 and 8 and the loop connecting helices 4 and 5 and a donor surface that is made by helices 1-4 and the loop connecting helices 2 and 3. The two binding surfaces are on separate faces of the three-dimensional structure, explaining the formation of Bcl-2 homodimers, homo-oligomers, and Bcl-2/Bax hetero-oligomers. We show that in vitro the Bcl-2 dimer can still interact with activated Bax as a larger oligomer. However, formation of a Bax/Bcl-2 heterodimer is favored, since this interaction inhibits Bcl-2 homodimerization. Our data support a simple model mechanism by which Bcl-2 interacts with activated Bax during apoptosis in an effective manner to neutralize the proapoptotic activity of Bax.

Apoptotic pathways in ischemic acute renal failure

The study of cell death has emerged as an important and exciting area of research in cell biology. Although two kinds of cell death, apoptosis and necrosis, are recognized, one of the major advances in our understanding of cell death has been the recognition that the pathways traditionally associated with apoptosis may be very critical in the form of cell injury associated with necrosis. Renal tubular epithelial cell injury from ischemia has been generally regarded as a result of necrotic form of cell death. We briefly describe recent evidence indicating that pathways generally associated with apoptosis, including endonuclease activation, role of mitochondria and caspases, are important in renal tubular injury. It is likely that the cascades that lead to apoptotic or necrotic mode of cell death are activated almost simultaneously and may share some common pathways.

ATP and cytochrome c-dependent inhibition of caspase-9 activity in the cerebral cortex of newborn piglets

The present study investigates the mechanism of activation of caspase-9 during hypoxia and tests the hypothesis that ATP and cytochrome c regulate the activity of caspase-9 in the cerebral cortex of newborn piglets. Cerebral tissue hypoxia was documented by decreased levels of high energy phosphates, ATP and phosphocreatine (PCr). Cytosolic fractions were prepared from cerebral cortices and passed through a G50 column, to remove endogenous ATP and cytochrome c. Caspase-9 activity was determined spectrofluorometrically using a specific fluorogenic substrate for caspase-9 at increasing concentrations of ATP (0-1.0 mM) or cytochrome c (0-3.0 microM). Caspase-9 activity (nmol/mg protein/h) was 1.26 +/- 0.15 in the normoxic and 2.13 +/- 0.14 in the hypoxic group (P < 0.05). The enzyme activity was inhibited by ATP or cytochrome c in both normoxic and hypoxic groups. The IC50 for ATP and cytochrome c increased 5-fold and 1.5-fold, respectively, following hypoxia, suggesting a hypoxia-induced modification of the ATP and cytochrome binding sites. The data demonstrate that ATP (1 mM) and cytochrome c (3.0 microM) inhibit caspase-9 activity by approximately 70%. On the basis of these observations, we propose a new and novel concept that the caspase-9 activity remains inhibited under the normoxic conditions and during hypoxia the decrease in ATP and decreases in the affinity for ATP and cytochrome c release the inhibitory block to activate the enzyme. Results of ATP- and cytochrome c-dependent inhibition of purified caspase-9 human recombinant show that the inhibitory effect by ATP and cytochrome c does not require Apaf-1. To our knowledge, this is a completely new concept and a new mechanism of regulation of caspase-9 activity that may lead to hypoxia-induced programmed cell death.

Multiple gene differential expression patterns in human ischemic liver: Safe limit of warm ischemic time

AIM: To investigate the multiple gene differential expression patterns in human ischemic liver and to produce the evidence about the hepatic ischemic safety time.

METHODS: The responses of cells to hepatic ischemia and hypoxia at hepatic ischemia were analyzed by cDNA microarrary representing 4000 different human genes containing 200 apoptotic correlative genes.

RESULTS: There were lower or normal expression levels of apoptotic correlative genes during the periods of hepatic ischemia for 0-15 min, the maintenance homostatic genes were expressed significantly higher at the same time. But at the hepatic ischemia for 30 min, the expression levels of maintenance homeostatic genes were down-regulated, the expressions of many apoptotic correlative genes and nuclear transcription factors were activated and up-regulated.

CONCLUSION: HIF-1, APAF-1, PCDC10, FBX5, DFF40, DFFA XIAP, survivin may be regarded as the signal genes to judge the degree of hepatic ischemic-hypoxic injure, and the apoptotic liver cell injury due to ischemia in different time limits. The safe limit of human hepatic warm ischemic time appears to be generally less then 30 min.

Ochratoxin A Induces Apoptosis in Human Lymphocytes through Down Regulation of Bcl-xL

Ochratoxin A (OTA) is a widespread mycotoxin contaminating feed and food. Besides its potent nephrotoxicity, OTA also affects the immune system. We demonstrate here a role for Bcl-x(L) in OTA-induced apoptosis in human lymphocytes. In particular, human peripheral blood lymphocytes and the human lymphoid T cell line, Kit 225 cells, underwent apoptosis in a time- and dose-dependent manner. This apoptosis was inhibited by z-VAD.fmk, suggesting that caspases were responsible for the induction of apoptosis. Moreover, OTA triggered mitochondrial transmembrane potential (Deltachim) loss and caspase-9 and caspase-3 activation. Interestingly, Bcl-x(L) protein expression was decreased by OTA treatment, whereas Bcl-2 protein level was not affected. Down-regulation of bcl-x(L) mRNA was not observed in cells treated with OTA. Overexpression of Bcl-x(L) in Kit 225 cells protected them against mitochondrial perturbation and retarded the appearance of apoptotic cells. Taken together, our data indicate that mitochondria are a central component in OTA-induced apoptosis and that the loss of Bcl-x(L) may participate in OTA-induced cell death.

Excess Bcl-XL increases the intrinsic growth potential of adult CNS neurons in vitro

The regenerative potential of adult mammalian CNS neurons is limited. Recent data suggest that inactivation of major growth inhibitors may not suffice to induce robust regeneration from mature neurons unless the intrinsic growth state is modulated. To investigate a possible role of Bcl-XL for axon regeneration in the adult mammalian CNS, Bcl-XL was adenovirally overexpressed in severed rat RGCs. Bcl-XL overexpression in mature axotomized RGCs in vivo increased both numbers [3.10-fold (+/-0.20)] and cumulative length [6.72-fold (+/-0.47)] of neurites regenerated from retinal explants, and this effect was further pronounced in the central retina where specific and dense axoplasmatic transduction occurs. Similarly, delayed Bcl-XL gene transfer to explanted retinae 12-13 days after lesion increased the numbers and length of emanating neurites by a factor of 5.22 (+/-0.41) and 8.29 (+/-0.69), respectively. In vivo, intraretinal sprouting of unmyelinated RGC axons into the nerve fiber layer was increased. However, fiber ingrowth into the optic nerve remained sparse, likely due to myelin inhibitors and scar components. Therefore, Bcl-XL overexpression may enhance, but may not be sufficient to, restitute functional regeneration in the adult CNS. As assessed by cell quantification analysis, Bcl-XL overexpression rescued a higher proportion of RGCs in vivo than in vitro. Therefore, Bcl-XL is capable to induce both neuronal survival and axon regeneration, but these two processes appear to be differentially modified by distinct pathways in vivo.

The role of Bcl-2 family members in tumorigenesis

The Bcl-2 family consists of about 20 homologues of important pro- and anti-apoptotic regulators of programmed cell death. The established mode of function of the individual members is to either preserve or disturb mitochondrial integrity, thereby inducing or preventing release of apoptogenic factors like Cytochrome c (Cyt c) from mitochondria. Recent findings also indicate further Bcl-2-controlled mitochondria-independent apoptosis pathways. Bcl-2 represents the founding member of the new and growing class of cell death inhibiting oncoproteins. In this review, we try to briefly summarize current models of Bcl-2 family function and to outline the work demonstrating the influence of deregulated Bcl-2 family member expression on tumorigenesis and cancer therapy. Since several Bcl-2 homologues, in addition to influencing apoptotic behaviour, also impinge on cell cycle progression, we discuss possible implications of this additional role for the expression of Bcl-2 family members in tumor cells.

Apoptosis defects and chemotherapy resistance: molecular interaction maps and networks

Intrinsic (innate) and acquired (adaptive) resistance to chemotherapy critically limits the outcome of cancer treatments. For many years, it was assumed that the interaction of a drug with its molecular target would yield a lethal lesion, and that determinants of intrinsic drug resistance should therefore be sought either at the target level (quantitative changes or/and mutations) or upstream of this interaction, in drug metabolism or drug transport mechanisms. It is now apparent that independent of the factors above, cellular responses to a molecular lesion can determine the outcome of therapy. This review will focus on programmed cell death (apoptosis) and on survival pathways (Bcl-2, Apaf-1, AKT, NF-kappaB) involved in multidrug resistance. We will present our molecular interaction mapping conventions to summarize the AKT and IkappaB/NF-kappaB networks. They complement the p53, Chk2 and c-Abl maps published recently. We will also introduce the 'permissive apoptosis-resistance' model for the selection of multidrug-resistant cells.

Bcl-xES, a BH4- and BH2-containing antiapoptotic protein, delays Bax oligomer formation and binds Apaf-1, blocking procaspase-9 activation

Bcl-2 family members either negatively or positively regulate the apoptotic threshold of cells. Bcl-xES (extra short), a novel Bcl-x member, possesses a unique combination of BH4 and BH2 domains as well as a COOH-terminal hydrophobic transmembrane anchor domain. Bcl-xES contains sequences of hydrophobic alpha-6 helices but lacks sequences of alpha-5 helices, suggesting that it does not have pore channel-forming activity but functions uniquely as a trapping protein. mRNA expression analysis by reverse transcriptase-polymerase chain reaction and RNase protection assay reveal that Bcl-xES is expressed in a variety of human cancer cell lines and human tumors, including bone marrow from patients with acute lymphoblastic leukemia. Bcl-xES expression is much less pronounced in some specimens of normal human tissues, including the breast, ovary, testis and lung. Stable, transfected human B lymphoma Namalwa variant cells expressing Bcl-xES were derived to investigate its role in apoptosis. Bcl-xES had a preventive effect on cell death induced by tumor necrosis factor-alpha and various concentrations of anticancer drugs, including camptothecin, etoposide and cisplatin. Its protective action on cell death was correlated with the inhibition of mitochondrial cytochrome c release and caspase activation. In a yeast two-hybrid system, Bcl-xES interacted with most Bcl-2 family members, including those containing only a BH3 domain, and with the Ced-4 homolog Apaf-1. Co-immunoprecipitation and gel filtration chromatography experiments suggest that Bcl-xES delays drug-induced apoptosis by disturbing the formation of Bax oligomers and preventing cytochrome c release, but also by interacting with Apaf-1 and inhibiting procaspase-9 activation, thus averting the apoptogenic proteolytic caspase cascade and cell death.

Resistance of pancreatic cancer to gemcitabine treatment is dependent on mitochondria-mediated apoptosis

Palliative chemotherapy with gemcitabine, a common mode of treatment of pancreatic cancer, has little influence on patients' survival. We investigated the impact of anti-apoptotic Bcl-xL protein and its antagonist Bax on gemcitabine-induced apoptosis in human pancreatic carcinoma cells in vitro and in vivo. The level of Bcl-xL and Bax expression was determined in 3 established pancreatic cancer cell lines that differ in their sensitivity to gemcitabine-mediated apoptosis. Bcl-xL and Bax genes were transduced into Colo357 cells by retroviral infection. In addition, cells were transfected with c-FLIP to assess involvement of CD95 and caspase-8. The impact of Bax/Bcl-xL expression on gemcitabine-sensitivity in vivo was evaluated in orthotopic Colo357 tumors in SCID mice. The apoptotic index revealed a strong inverse correlation between Bcl-xL expression and gemcitabine-induced apoptosis in the pancreatic carcinoma cell lines tested. Caspase-8 and Bid were cleaved in Colo357 cells exposed to gemcitabine, and there was no correlation with either Bcl-xL or with Bax expression. In contrast, the lack of mitochondrial transmembrane potential transition, release of cytochrome-c and absence of caspase-9- and PARP-cleavage showed a strong correlation with Bcl-xL expression. Expression of c-FLIP significantly increased the resistance towards gemcitabine. Orthotopically growing Colo357-bcl-xl tumors in SCID mice were refractory to gemcitabine treatment, and in contrast to the in vitro data, Colo357-bax tumors exhibited a 12-fold greater tumor regression than Colo357-wild-type tumors in the control group. Gemcitabine-induced apoptosis involves the mitochondria-mediated signaling pathway. A functional restoration of this pathway appears to be essential to overcome the resistance mechanisms of pancreatic tumor cells and to improve the response to therapy as demonstrated by Bax overexpression in a clinically relevant tumor model.

Chemotherapy-induced Apoptosis of S-type Neuroblastoma Cells Requires Caspase-9 and Is Augmented by CD95/Fas Stimulation

Stromal or S-type tumor cells are a distinct lineage found in neuroblastoma tumors and have an important role in the biology of this disease. Anticancer agents induce apoptosis through death receptor- and mitochondria-initiated pathways. The object of this work was to determine the involvement of these pathways in the response to doxorubicin (Dox) and cisplatin (CDDP) in S-type neuroblastoma cells. Both drugs activated caspase-9 and caspase-3 but not caspase-8. Caspase-9-specific inhibition blocked S-type cell death induced by Dox. SH-EP1 cells transfected to express dominant negative mutant caspase-9, but not those expressing DN caspase-8, were resistant to Dox- and CDDP-induced apoptosis. The lack of caspase-8 involvement in chemotherapy-induced death was not the result of an intrinsic inability of these cells to activate this enzyme because when they were treated with tumor necrosis factor-related apoptosis-inducing ligand, caspase-8 was activated. We also found that both drugs up-regulated CD95/Fas expression but that CD95/Fas signaling was not necessary for cell killing. Experiments testing the response of chemotherapy-treated cells to agonists of the CD95/Fas receptor established that Dox and CDDP treatment sensitizes cells to CD95/Fas killing. Together, these results are consistent with a model in which caspase-9 is of central importance in the death mechanism utilized by these drugs in S-type cells. Although the death response is not dependent on CD95/Fas, concomitant stimulation of this receptor amplifies the death response in drug-treated cells.

The myelodysplastic syndromes: a matter of life or death

Apoptosis is upregulated in early myelodysplastic syndromes (MDS) and may contribute to the peripheral cytopenias commonly observed. Conversely, leukemic progression is associated with abrogation of programmed cell death (PCD). The stage of hematopoietic cell maturation at which defects in PCD arise and the underlying causes of apoptosis dysregulation remain unknown. This paper outlines the apoptotic process in normal hematopoietic cells and summarizes current data regarding the role, potential causes and clinical implications of altered apoptosis in MDS.

Synthetic retinoids as inducers of apoptosis in ovarian carcinoma cell lines

Apoptosis is also known as programmed cell death. Apoptosis plays an essential role in maintaining normal tissue and cell physiology in multicellular organisms. Clearance of aberrant or pre-cancerous cells occurs through the induction of apoptosis. It has been reported that many tumors and tumor cell lines have dysfunctional apoptosis signaling, causing these tumors to escape immune monitoring and internal cellular control mechanisms. One potential cause of this dysfunctional apoptosis is the tumor suppressor p53, an important regulator of growth arrest and apoptosis that is mutated in over 50% of all cancers. Retinoids have great potential in the areas of cancer therapy and chemoprevention. While some tumor cells are sensitive to the growth inhibitory effects of natural retinoids such as all-trans-retinoic acid (ATRA), many ovarian tumor cells are not. 6-[3-(1-Admantyl)]-4-hydroxyphenyl]-2-naphthalene carboxylic acid (CD437) and fenretinide N-[4-hydroxyphenyl] retinamide (4-HPR) are conformationally restricted synthetic retinoids that induce growth arrest and apoptosis in both ATRA-sensitive and ATRA-resistant ovarian tumor cell lines. Recently, we have identified the molecular pathways of apoptosis induced by treatment of ovarian carcinoma cells with mutated p53 by CD437 and 4-HPR.

UV-induced apoptosis is mediated independent of caspase-9 in MCF-7 cells: a model for cytochrome c resistance

The importance of the mitochondria in UV-induced apoptosis has become increasingly apparent. Following DNA damage cytochrome c and other pro-apoptotic factors are released from the mitochondria, allowing for formation of the apoptosome and subsequent cleavage and activation of caspase-9. Active caspase-9 then activates downstream caspases-3 and/or -7, which in turn cleave poly(ADP)-ribose polymerase (PARP) and other down-stream targets, resulting in apoptosis. In an effort to understand the mechanisms of Akt-mediated cell survival in breast cancer, we studied the effects of insulin-like growth factor (IGF)-I treatment on UV-treated MCF-7 human breast cancer cells. Apoptosis was induced in MCF-7 cells after UV treatment, as measured by caspase-7 and PARP cleavage, and IGF-I co-treatment protected against this response. Surprisingly caspase-9 cleavage was unchanged with UV and/or IGF-I treatment. Using MCF-7 cells overexpressing caspase-3 we have shown that resistance of caspase-9 to cleavage was not altered by the expression of caspase-3. Furthermore, overexpression of caspase-9 did not enhance PARP or caspase-7 cleavage after UV treatment. Because caspase-8 was activated with UV treatment alone, we believe that UV-induced apoptosis in MCF-7 cells occurs independently of cytochrome c and caspase-9, supporting the existence of a cytoplasmic inhibitor of cytochrome c in MCF-7 cells. We anticipate that such inhibitors may be overexpressed in cancer cells, allowing for treatment resistance.

Retroactive pathway involving mitochondria in electroloaded cytochrome c-induced apoptosis. Protective properties of Bcl-2 and Bcl-XL

Cytochrome c release is thought to play an important role in the initiation of apoptosis. The nature of the control exerted by Bcl-2 and Bcl-XL on such a pathway is not precisely known. We addressed this issue by square-wave pulse electroloading of exogenous cytochrome c into Jurkat cells. Three hours after cytochrome c loading into the cells, characteristic phenotypes of apoptosis were observed. However, a significant drop in the mitochondrial membrane potential (Deltapsim) was also observed, while cytochrome c was generally considered to act downstream from the mitochondria. Related to the Deltapsim drop, there was a release of proapoptotic proteins such as AIF and Smac from the mitochondria. This release, as well as NAD(P)H and cardiolipids oxidation, are linked to previous caspase activation. Cytochrome c-linked caspase activation also led to potassium efflux out of the cell. Overexpression of Bcl-2 and Bcl-XL or N-acetyl-DEVD-aldehyde treatment not only prevented the mitochondrial membrane potential decrease, but also protected cells from the apoptosis directly induced by cytochrome c electroloading. Bcl-2 and Bcl-XL protection is based on the inhibition of the caspase-dependent retroactive pathway affecting the mitochondrial compartment.

The gene that encodes the herpes simplex virus type 1 latency-associated transcript influences the accumulation of transcripts (Bcl-x(L) and Bcl-x(S)) that encode apoptotic regulatory proteins

The herpes simplex virus type 1 latency-associated transcript (LAT) inhibits apoptosis. We demonstrate here that LAT influences the accumulation of the Bcl-x(L) transcript versus the Bcl-x(S) transcript in Neuro-2A cells. Bcl-x(L) encodes an antiapoptotic protein, whereas Bcl-x(S) encodes a proapoptotic protein. Promoting the accumulation of Bcl-x(L) in neurons may inhibit apoptosis, thus enhancing the latency-reactivation cycle.

Smac3, a novel Smac/DIABLO splicing variant, attenuates the stability and apoptosis-inhibiting activity of X-linked inhibitor of apoptosis protein

X-linked inhibitor of apoptosis protein (XIAP), the most potent member of the inhibitor of apoptosis protein (IAP) family, plays a crucial role in the regulation of apoptosis. XIAP is structurally characterized by three baculovirus IAP repeat (BIR) domains that mediate binding to and inhibition of caspases and a RING domain that confers ubiquitin ligase activity. The caspase inhibitory activity of XIAP can be eliminated by the second mitochondria-derived activator of caspases (Smac)/direct IAP-binding protein with low pI (DIABLO) during apoptosis. Here we report the identification and characterization of a novel isoform of Smac/DIABLO named Smac3, which is generated by alternative splicing of exon 4. Smac3 contains an NH2-terminal mitochondrial targeting sequence required for mitochondrial targeting of Smac3 and an IAP-binding motif essential for Smac3 binding to XIAP. Smac3 is released from mitochondria into the cytosol in response to apoptotic stimuli, where it interacts with the second and third BIR domains of XIAP. Smac3 disrupts processed caspase-9 binding to XIAP, promotes caspase-3 activation, and potentiates apoptosis. Strikingly, Smac3, but not Smac/DIABLO, accelerates XIAP auto-ubiquitination and destruction. Smac3-stimulated XIAP ubiquitination is contingent upon the physical association of XIAP with Smac3 and an intact RING domain of XIAP. Smac3-accelerated XIAP destabilization is, at least in part, attributed to its ability to enhance XIAP ubiquitination. Our study demonstrates that Smac3 is functionally additive to, but independent of, Smac/DIABLO.

Identification of a Bcl-XL binding region within the ATPase domain of Apaf-1

CED-4, a pro-apoptotic factor in Caenorhabditis elegans, activates the cell death protease CED-3. CED-9 directly binds to CED-4 and represses this. However, it has remained unclear whether a mammalian CED-9 homologue, Bcl-XL, inhibits the function of the mammalian CED-4 homologue, Apaf-1, by direct binding. To analyze the interaction, we adopted a yeast two-hybrid system. Since Bcl-XL and the CED-4-like portion of Apaf-1 failed to exhibit a positive result in the assay, we prepared "fragment libraries" of bcl-XL or apaf-1 cDNA. By screening of the apaf-1 "fragment library," we obtained nine clones interacting with Bcl-XL, all containing the same region within the ATPase domain, designated BBR: the Bcl-XL binding region. Binding of BBR to Bcl-XL was also confirmed by immunoprecipitation assays. Bcl-2, Bcl-w, A1/Bfl-1, and Boo/Diva failed to show the same capacity for binding to BBR as Bcl-XL. These results indicate that Bcl-XL directly binds to a specific region in Apaf-1.

Beta-irradiation used for systemic radioimmunotherapy induces apoptosis and activates apoptosis pathways in leukaemia cells

Beta-irradiation used for systemic radioimmunotherapy (RIT) is a promising treatment approach for high-risk leukaemia and lymphoma. In bone marrow-selective radioimmunotherapy, beta-irradiation is applied using iodine-131, yttrium-90 or rhenium-188 labelled radioimmunoconjugates. However, the mechanisms by which beta-irradiation induces cell death are not understood at the molecular level. Here, we report that beta-irradiation induced apoptosis and activated apoptosis pathways in leukaemia cells depending on doses, time points and dose rates. After beta-irradiation, upregulation of CD95 ligand and CD95 receptor was detected and activation of caspases resulting in apoptosis was found. These effects were completely blocked by the broad-range caspase inhibitor zVAD-fmk. In addition, irradiation-mediated mitochondrial damage resulted in perturbation of mitochondrial membrane potential, caspase-9 activation and cytochrome c release. Bax, a death-promoting protein, was upregulated and Bcl-x(L), a death-inhibiting protein, was downregulated. We also found higher apoptosis rates and earlier activation of apoptosis pathways after gamma-irradiation in comparison to beta-irradiation at the same dose rate. Furthermore, irradiation-resistant cells were cross-resistant to CD95 and CD95-resistant cells were cross-resistant to irradiation, indicating that CD95 and irradiation used, at least in part, identical effector pathways. These findings demonstrate that beta-irradiation induces apoptosis and activates apoptosis pathways in leukaemia cells using both mitochondrial and death receptor pathways. Understanding the timing, sequence and molecular pathways of beta-irradiation-mediated apoptosis may allow rational adjustment of chemo- and radiotherapeutic strategies.

Transforming growth factor-beta and tumor necrosis factor-alpha cooperate to induce apoptosis in the oligodendroglial cell line OLI-neu

As shown previously, transforming growth factor-beta (TGF-beta) plays an important role during the period of developmental cell death in the nervous system. As with neurons, oligodendrocytes are generated in excess and eliminated by apoptosis. The present study was aimed at investigating the possible interaction of TGF-beta with tumor necrosis factor-alpha (TNF-alpha) in the regulation of cell death in oligodendroglial precursor cells and analyzing the underlying signaling mechanisms. We show that both factors induce apoptosis independently, but cooperate when applied together. The investigation of the signaling events revealed an important role of the JNK pathway during induction of apoptosis. TGF-beta seemed to be more efficient at inducing a release in cytochrome c from mitochondria than TNF-alpha. This might be the consequence of decreased Bcl-xL levels observed in cells treated with TGF-beta but not with TNF-alpha. Both factors stimulated caspase-3 activity, which could be inhibited by caspase-8 or caspase-9 inhibitors. Therefore, we conclude that TNF-alpha and TGF-beta affect partially common pathways but also regulate different steps in the apoptotic cascade.

Necrotic cell death in response to oxidant stress involves the activation of the apoptogenic caspase-8/bid pathway

Human epithelial (A549) cells exposed to hyperoxia die by cellular necrosis. In the current study, we demonstrated the involvement of apoptogenic factors in epithelial cell necrosis in response to hyperoxia, including the formation of the Fas-related death-inducing signaling complex and initiation of mitochondria-dependent apoptotic pathways. We showed increased activation of both Bid and Bax in A549 cells subjected to hyperoxia. Bax activation involved a Bid-assisted conformational change. We discovered that the response to hyperoxia in vivo predominantly involved the activation of the Bid/caspase-8 pathway without apparent increases in Bax expression. Disruption of the Bid pathway by gene deletion protected against cell death in vivo and in vitro. Likewise, inhibition of caspase-8 by Flip also protected against cell death. Taken together, we have demonstrated the involvement of apoptogenic factors in epithelial cell responses to hyperoxia, despite a final outcome of cellular necrosis. We have, for the first time, identified a predominant role for the caspase-8/Bid pathway in signaling associated with hyperoxic lung injury and cell death in vivo and in vitro.

Cytochrome c, released from cerebellar granule cells undergoing apoptosis or excytotoxic death, can generate protonmotive force and drive ATP synthesis in isolated mitochondria

In rat cerebellar granule cells, cytochrome c release takes place during glutamate toxicity and apoptosis due to deprivation of depolarising levels of potassium. We show that, as in necrosis, the released cytochrome c present in the cytosolic fraction obtained from cerebellar granule cells undergoing apoptosis can operate as a reactive oxygen species (ROS) scavenger and as a respiratory substrate. The capability of the cytosolic fraction containing cytochrome c, obtained from cerebellar granule cells undergoing either necrosis or apoptosis, to energise coupled mitochondria isolated by the same cells is also investigated. We show that, in both cases, the cytosolic fraction containing cytochrome c, added to mitochondria, can cause proton ejection, and membrane potential generation and can drive ATP synthesis and export in the extramitochondrial phase, as photometrically measured via the ATP detecting system. Cytochrome c, separated immunologically from the cytosolic fraction of apoptotic cells when added to mitochondria, is found to cause proton ejection to generate membrane potential and to drive ATP synthesis and export in a manner not sensitive to the further addition of the cytosolic fraction depleted of cytochrome c, which failed to do this. In the light of these findings we propose that in apoptosis the released cytochrome c can contribute to provide ATP required for the cell programmed death to occur.

Oxidized low density lipoprotein inhibits macrophage apoptosis by blocking ceramide generation, thereby maintaining protein kinase B activation and Bcl-XL levels

Macrophages play a central role in the development and progression of atherosclerotic lesions. It is well known that oxidized low density lipoprotein (ox-LDL) promotes the recruitment of monocytes (which differentiate to macrophages) into the intima. We reported recently that ox-LDL blocks apoptosis in bone marrow-derived macrophages deprived of macrophage colony-stimulating factor (M-CSF) by a mechanism involving protein kinase B (PKB) (Hundal, R., Salh, B., Schrader, J., Gómez-Muñoz, A., Duronio, V., and Steinbrecher, U. (2001) J. Lipid Res. 42, 1483-1491). The aims of the present study were 1) to define the apoptotic pathway involved in the pro-survival effect of ox-LDL; 2) to determine which PKB target mediated this effect; and 3) to identify mechanisms responsible for PKB activation by ox-LDL. Apoptosis following M-CSF withdrawal was accompanied by activation of the caspase 9-caspase 3 cascade and cytochrome c release from mitochondria, but the caspase 8 pathway was unaffected. M-CSF withdrawal resulted in a marked and selective reduction in Bcl-XL protein and mRNA levels, and this decrease was prevented by ox-LDL. The ability of ox-LDL to preserve Bcl-XL levels was blocked by NFkappaB antagonists, thereby implicating IkappaB kinase as a key PKB target. M-CSF deprivation resulted in activation of acid sphingomyelinase and an increase in ceramide levels. Desipramine (a sphingomyelinase inhibitor) prevented the increase in ceramide and inhibited apoptosis after M-CSF deprivation. Ox-LDL completely blocked the increase in acid sphingomyelinase activity as well as the increase in ceramide after M-CSF deprivation. Pretreatment of macrophages with C2-ceramide reversed the effect of ox-LDL on PKB and macrophage survival. These results indicate that ox-LDL prevents apoptosis in M-CSF-deprived macrophages at least in part by inhibiting acid sphingomyelinase. This in turn prevents ceramide-induced down-regulation of PKB, the activity of which is required to maintain production of Bcl-XL.

Contribution of caspase-8 to apoptosis of axotomized rat retinal ganglion cells in vivo

We have investigated the role of caspase-8 and its mode of activation during apoptosis of adult rat retinal ganglion cells (RGCs) in vivo. Retinal pro-caspase-8 expression was almost completely restricted to RGCs. Although caspase-8 is known to be involved in death-receptor-dependent apoptosis, measurable caspase-8 activity or even RGC death could be induced by neither tumor necrosis factor-alpha nor Fas ligand injections into unlesioned eyes. However, substantial caspase-8 activation could be detected after optic nerve transection as shown by a fluorogenic activity assay and Western blot analysis. Intravitreal injection of caspase-8 inhibitors significantly attenuated degeneration of RGCs and reduced the number of RGCs showing caspase-3 activation. A late peak of caspase-8 activity and additive protective effects of caspase-8 and -9 inhibition on axotomized RGCs place caspase-8 in our model rather late in the apoptosis cascade, possibly after the onset of mitochondrial dysfunction.

Myocardial apoptosis after cardioplegic arrest in the neonatal lamb

OBJECTIVE

Myocardial apoptosis is observed after various cardiac injuries and is also a normal part of fetal cardiac development and early postnatal maturation. Cardioplegic arrest and reperfusion result in ischemic injury and oxidative stress, known triggers of apoptosis. Because the neonatal heart is in a proapoptotic state, we hypothesize that apoptosis is triggered after cardioplegic arrest in neonatal myocardium.

METHODS

We started neonatal lambs (6-8 days old, n = 5) on cardiopulmonary bypass and administered cold crystalloid cardioplegia at 20-minute intervals. Total crossclamp time was 70 minutes, and bypass time was 90 minutes. After a six-hour recovery period, the hearts were excised and examined by using TdT-mediated dUTP nick-end labeling; radiolabeled DNA electrophoresis; fluorimetric caspase 3, 8, and 9 activity assay; mRNA microarray; and Western immunoblotting. Control lambs were anesthetized but did not undergo operation (n = 5) or were started on cardiopulmonary bypass for 90 minutes but not arrested (n = 5).

RESULTS

Lambs subjected to cardioplegia had 5-fold more TdT-mediated dUTP nick-end labeling-positive nuclei compared with that seen in unoperated control animals (P =.007) and bypass-only control animals (P =.008). DNA laddering was present in all postcardioplegia hearts but absent among control hearts. Bad and Bcl-X mRNA transcription increased significantly. Caspase 3, 8, and 9 activities were slightly greater than those seen in control animals, but the differences were not significant. No change was detected in Bcl-2, Bax, or Bcl-xL proteins.

CONCLUSIONS

In a clinically relevant model of neonatal cardioplegic arrest, increased apoptotic cell death is present 6 hours after reperfusion, and both proapoptotic and antiapoptotic responses are triggered. The clinical implications of apoptosis after cardioplegic arrest remain undetermined.

Deletion of the BH1 domain of Bcl-2 accelerates apoptosis by acting in a dominant negative fashion

To investigate the exact biochemical functions by which Bcl-2 regulates apoptosis, we established a stable human small cell lung carcinoma cell line, Ms-1, overexpressing wild-type human Bcl-2 or various deletion and point mutants thereof, and examined the effect of these Bcl-2 mutants on apoptosis induced by antitumor drugs such as camptothecin. Cytochrome c release, caspase-3-(-like) protease activation, and apoptosis induced by antitumor drugs were accelerated by overexpression of Bcl-2 lacking a Bcl-2 homology (BH) 1 domain (Bcl-2/ DeltaBH1), but not by that of BH2, BH3, or BH4 domain-deleted Bcl-2. A similar result was obtained upon the substitution of glycine 145 with alanine in the BH1 domain (Bcl-2/G145A), which failed to interact with either Bax or Bak. Pro-apoptotic Bax and Bak have been known to be activated in response to antitumor drugs, and Bcl-2/G145A as well as Bcl-2/DeltaBH1 also accelerated Bax- or Bak-induced apoptosis in HEK293T cells. These two mutants still retained the ability to interact with wild-type Bcl-2 and Bcl-xL, and abrogated the inhibitory effect of wild-type Bcl-2 or Bcl-xL on Bax- or Bak-induced apoptosis. In addition, immunoprecipitation studies revealed that Bcl-2/DeltaBH1 and Bcl-2/G145A interrupted the association between wild-type Bcl-2 and Bax/Bak. Taken together, our results demonstrate that Bcl-2/DeltaBH1 or Bcl-2/G145A acts as a dominant negative of endogenous anti-apoptotic proteins such as Bcl-2 and Bcl-xL, thereby enhancing antitumor drug-induced apoptosis, and that this dominant negative activity requires both a failure of interaction with Bax and Bak through the BH1 domain of Bcl-2 and retention of the ability to interact with Bcl-2 and Bcl-xL.

Apoptosis in uterine epithelium and decidua in response to implantation: evidence for two different pathways

During the initial steps of implantation, the mouse uterine epithelium of the implantation chamber undergoes apoptosis in response to the interacting blastocyst. With progressing implantation, regression of the decidual cells allows a restricted and coordinated invasion of trophoblast cells into the maternal compartment. In order to investigate pathways of apoptosis in mouse uterine epithelium and decidua during early pregnancy (day 4.5-7.0 post coitum), we have investigated different proteins such as TNFalpha, TNF receptor1, Fas ligand, Fas receptor1, Bax and Bcl2 as well as caspase-9 and caspase-3 using immunohistochemistry. To detect cells undergoing apoptosis the Tunel assay was performed. Immunoreactivity for TNFalpha as well as for TNF receptor1 was observed exclusively in the epithelium of the implantation chamber and the adjacent luminal epithelium from day 4.5 post coitum onwards. In the developing decidua the Fas ligand, but not the Fas receptor, was expressed. Bax and Bcl2 revealed a complementary expression pattern with Bax in the primary and Bcl2 in the adjacent decidual zone. Strong immunolabelling for the initiator caspase-9 was restricted to the decidual compartment, whereas caspase-3 expression characterized the apoptotic uterine epithelium. Only some caspase-3 positive decidual cells were found around the embryo which correlated to the pattern of Tunel staining. Taken together, the apoptotic degeneration of the uterine epithelium seems to be mediated by TNF receptor1 followed by caspase-3, whereas the very moderate regression of the decidua did not show the investigated death receptor, but Bax and Blc2 instead and in addition caspase-9, which indicates a different regulation for epithelial versus decidual apoptosis.

JNK-dependent release of mitochondrial protein, Smac, during apoptosis in multiple myeloma (MM) cells

Smac, second mitochondria-derived activator of caspases, promotes apoptosis via activation of caspases. Previous studies have shown that c-Jun NH(2)-terminal kinase (JNK) is involved in regulating another mitochondrial protein, cytochrome c during apoptosis; however, the role of JNK in the release of mitochondrial Smac is unknown. Here we show that induction of apoptosis in multiple myeloma (MM) cells is associated with activation of JNK, translocation of JNK from cytosol to mitochondria, and release of Smac from mitochondria to cytosol. Blocking JNK either by dominant-negative mutant (DN-JNK) or cotreatment with a specific JNK inhibitor, SP600125, abrogates both stress-induced release of Smac and induction of apoptosis. These findings demonstrate that activation of JNK is an obligatory event for the release of Smac during stress-induced apoptosis in MM cells.

Apoptosis and plastic surgery

Apoptosis, or programmed cell death, is a phenomenon that is integral to development and cellular homeostasis. In the last decade, many of the essential molecules and pathways that control this phenomenon have been elucidated. Because apoptosis is involved in almost all physiologic and pathologic processes, the understanding of its regulation has significant clinical ramifications. This article reviews the basic understanding of programmed cell death in terms of the effector molecules and pathways. Areas of interest to plastic surgeons are reviewed as they pertain to apoptosis. These areas include allotransplantation, craniofacial and limb development, flap survival, wound healing, stem cell science, and physiologic aging. These topics have not yet been studied extensively in the context of cell death. In this review article, other related and more comprehensively studied scientific areas are used to extrapolate their relevance to apoptosis. Apoptosis is an increasingly better understood process. With the knowledge of how programmed cell death is controlled, combined with the improved ability to effectively perform genetic manipulation and to design specific chemical approaches, apoptosis is gaining clinical relevance. In the next few years, practical clinical breakthroughs will help the medical community to understand the phenomenon of apoptosis and how it relates to the needs of patients.

Natural cellular inhibitors of caspases

The crucial role of cell death in many diseases is obvious and has spurred intense research to understand the regulation of apoptotic pathways. Caspase activation is central to many of the apoptotic pathways. In recent years, the study of the regulation of caspase activation and activity in various cell lines and in diseases has revealed highly complex mechanisms regulating cell survival or cell death. In this review, the major natural cellular anticaspase factors are described with particular attention to the inhibitors that prevent active caspases from committing the cell to irreversible destruction. The major group of caspase inhibitors known is the inhibitor of apoptosis proteins (IAP) and this review describes the characteristics of IAP, regulation of IAP expression, and mechanisms of action of IAP. However, other proteins including Bcl-2 family members, heat shock proteins, caspase-like decoy, calpains and proteases, and lipid moieties in the form of phosphoinositides also can function as caspase inhibitors. The current knowledge of the inhibition of these non-IAP factors is described herein.

Caspase inhibitors as anti-inflammatory and antiapoptotic agents

The striking efficacy of Z-VAD-fmk in the various animal models presented above may reflect its ability to inhibit multiple enzymes including caspases. In accord with this, more selective, reversible inhibitors usually show low efficacy in multifactorial models such as ischaemia, but may offer some protection against NMDA-induced excitotoxicity and hepatitis. Importantly, caspase inhibitors may exhibit significant activity in vivo even when they are applied post insult. As far as the CNS is concerned, the first systemically active inhibitors have emerged. Functional recovery could be achieved in some ischaemia models, but long-term protection by caspase inhibitors is still being questioned. Recent developments in drug design enabled the first caspase inhibitors to enter the clinic. Although initially directed towards peripheral indications such as rheumatoid arthritis, caspase inhibitors will no doubt eventually be used to target CNS disorders. For this purpose the peptidic character of current inhibitors will have to be further reduced. Small molecule, nonpeptidic caspase inhibitors, which have appeared recently, indicate that this goal can be accomplished. Unfortunately, many fundamental questions still remain to be addressed. In particular, the necessary spectrum of inhibitory activity required to achieve the desired effect needs to be determined. There is also a safety aspect associated with prolonged administration. Therefore, the next therapeutic areas for broader-range caspase inhibitors are likely to involve acute treatment. Recent results with synergistic effects between MK-801 and caspase inhibitors in ischaemia suggest that caspase inhibitors may need to be used in conjunction with other drugs. It can be expected that, in the near future, research on caspases and their inhibitors will remain a rapidly developing area of biology and medicinal chemistry. More time, however, may be needed for the first caspase inhibitors to appear on the market.

Apoptosis induced by cryo-injury in human colorectal cancer cells is associated with mitochondrial dysfunction

Cryotherapy, a method of in situ ablation, is used in the treatment of colorectal liver metastases with variable results. During the treatment, the central area of treated tumor undergoes necrotic destruction by lethal cryo-injury; however, the cellular response of tumor exposed to sublethal cryo-injury at the peripheral zone is unclear. In our study, we have identified the induction of apoptosis by cryo-injury at -10 degrees C in 4 colorectal cancer cell lines (HT29, HCT116, KM12C and KM12SM). The apoptosis was characterized by chromatin condensation, transferase-mediated dUTP nick end-labeling (TUNEL) staining, proteolytic cleavage of poly(ADP-ribose) polymerase (PARP) and cytokeratin 18, and activation of caspase-3. The occurrence and intensity of cryo-induced apoptosis did not correlate with the functional status of p53 in the cell lines studied. The expression of anti-apoptotic proteins (Bcl-2, Bcl-X(L)) and pro-apoptotic proteins (Bax, Bcl-X(S), Bad, and Bak) in response to cryo-injury varied in this cell line panel. The basal level of Bcl-2/Bax protein ratio correlated inversely to the apoptotic rate. We further demonstrated that Bax level decreased in cytosol and increased in mitochondria, followed by a loss of mitochondrial membrane potential after cryo-injury in HT29 cells. These findings indicate that cryo-injury induces apoptosis in colorectal cancer cells via disruption of mitochondrial integrity. The cryo-induced apoptosis was also identified in a nude mouse tumor xenograft model. Our elucidation of the apoptosis pathway induced by cryo-injury implies that synergistic combination of cryosurgery with pharmacological agents that augment of apoptosis induction may have clinical relevance in treating colorectal liver metastasis.

Apoptosis: targets in pancreatic cancer

Pancreatic adenocarcinoma is characterized by poor prognosis, because of late diagnosis and lack of response to chemo- and/or radiation therapies. Resistance to apoptosis mainly causes this insensitivity to conventional therapies. Apoptosis or programmed cell death is a central regulator of tissue homeostasis. Certain genetic disturbances of apoptotic signaling pathways have been found in carcinomas leading to tumor development and progression. In the past few years, the knowledge about the complex pathways of apoptosis has strongly increased and new therapeutic approaches based on this knowledge are being developed. This review will focus on the role of apoptotic proteins contributing to pancreatic cancer development and progression and will demonstrate possible targets to influence this deadly disease.

Apoptosomes: engines for caspase activation

Activation of the caspases that initiate apoptosis typically requires cognate scaffold proteins, including CED-4 in Caenorhabditis elegans, Apaf-1 in mammals and Dark in Drosophila. Each scaffold protein oligomerizes procaspases into a complex called the apoptosome, but the regulation and biological roles of the scaffolds differ. Whereas CED-4 is restrained by the Bcl-2 homologue CED-9, Apaf-1 is inhibited by its WD40 repeat region, until it is activated by cytochrome c, derived from damaged mitochondria. Although Dark also has a WD40 region, its activation does not seem to involve cytochrome c. CED-4 is essential for apoptosis in the worm and Dark for many apoptotic responses in the fly, but the Apaf-1/caspase-9 system probably amplifies rather than initiates the mammalian caspase cascade.

IKK beta is required for Bcl-2-mediated NF-kappa B activation in ventricular myocytes

The transcription factor nuclear factor kappa B (NF-kappa B) is regulated by cytoplasmic inhibitor I kappa B alpha. An integral step in the activation of NF-kappa B involves the phosphorylation and degradation of I kappa B alpha. We have previously reported that I kappa B alpha activity is diminished in ventricular myocytes expressing Bcl-2 (de Moissac, D., Zheng, H., and Kirshenbaum, L. A. (1999) J. Biol. Chem. 274, 29505-29509). The underlying mechanism by which Bcl-2 activates NF-kappa B is undefined. In view of growing evidence that the I kappa B kinases (IKKs), notably IKK beta, are involved in signal induced phosphorylation of I kappa B alpha, we ascertained whether IKK beta is necessary and sufficient for Bcl-2 mediated NF-kappa B activation. Here we demonstrate that expression of Bcl-2 in ventricular myocytes resulted in an increase in NF-kappa B-dependent DNA binding, NF-kappa B gene transcription and reduced I kappa B alpha levels. An increase in the IKK beta kinase activity was observed in cells expressing full-length Bcl-2 but not in cells expressing the BH4 deletion mutant of Bcl-2 (Delta BH4; residues 10-30). Catalytically inactive mutants of IKK beta, but not IKK alpha, suppressed Bcl-2-mediated I kappa B alpha phosphorylation and NF-kappa B activation. Transfection of human embryonic 293 cells with a kinase-defective Raf-1 or a kinase-defective mitogen-activated protein kinase/extracellular signal-regulated kinase kinase-1 (MEKK-1) suppressed Bcl-2-mediated IKK beta activity and NF-kappa B activation. Further, Bcl-2-mediated NF-kappa B activity was impaired in nullizygous mouse embryonic fibroblasts deficient for IKK beta. In this report, we provide the first direct evidence that Bcl-2 activates NF-kappa B by a signaling mechanism that involves Raf-1/MEKK-1 mediated activation of IKK beta.

TGF-beta induces cell death in the oligodendroglial cell line OLI-neu

We have shown that TGF-beta plays an important role during the period of developmental cell death in the nervous system. Immunoneutralization of TGF-beta prevents ontogenetic neuron death in vivo. Like neurons, oligodendrocytes are generated in excess and eliminated by apoptosis. It has been shown that oligodendrocyte progenitors and newly formed oligodendrocytes are especially susceptible to apoptosis. We choose the oligodendrocyte precursor cell line OLI-neu to address the question if TGF-beta could play a role for the control of oligodendrocyte proliferation and cell death. Flow cytometric analysis revealed that OLI-neu cells arrested in the G1 phase of the cell cycle underwent apoptosis in response to TGF-beta. TUNEL assays, apoptosis ELISA, and caspase assays substantiated the finding that OLI-neu cells died after TGF-beta treatment. Cell death could be inhibited by application of pan-caspase or caspase 8 and 9 inhibitors, whereas the inhibition of calpain was unaffected. Furthermore, we found a reduction of bcl-X(L) at the protein as well as at the mRNA level, while p27 was upregulated. The Smad cascade was activated while TGF-beta reduced the activity of the p42/p44 MAP kinase pathway. Together, these data show that TGF-beta induced apoptotic cell death in cells of oligodendroglial origin, whereby the signaling cascade involved the downregulation of antiapoptotic signaling such as bcl-X(L) leading to the activation of caspases.

Differential regulation of doxorubicin-induced mitochondrial dysfunction and apoptosis by Bcl-2 in mammary adenocarcinoma (MTLn3) cells

Various anticancer drugs cause mitochondrial perturbations in association with apoptosis. Here we investigated the involvement of caspase- and Bcl-2-dependent pathways in doxorubicin-induced mitochondrial perturbations and apoptosis. For this purpose, we set up a novel three-color flow cytometric assay using rhodamine 123, annexin V-allophycocyanin, and propidium iodide to assess the involvement of the mitochondria in apoptosis caused by doxorubicin in the breast cancer cell line MTLn3. Doxorubicin-induced apoptosis was preceded by up-regulation of CD95 and CD95L and a collapse of mitochondrial membrane potential (Deltapsi) occurring prior to phosphatidylserine externalization. This drop in Deltapsi was independent of caspase activity, since benzyloxycarbonyl-Val-Ala-dl-Asp-fluoromethylketone did not inhibit it. Benzyloxycarbonyl-Val-Ala-dl-Asp-fluoromethylketone also blocked activation of caspase-8, thus excluding an involvement of the death receptor pathway in Deltapsi dissipation. Furthermore, although overexpression of Bcl-2 in MTLn3 cells inhibited apoptosis, dissipation of Deltapsi was still observed. No decrease in Deltapsi was observed in cells undergoing etoposide-induced apoptosis. Immunofluorescent analysis of Deltapsi and cytochrome c localization on a cell-to-cell basis indicates that the collapse of Deltapsi and cytochrome c release are mutually independent in both normal and Bcl-2-overexpressing cells. Together, these data indicate that doxorubicin-induced dissipation of the mitochondrial membrane potential precedes phosphatidylserine externalization and is independent of a caspase- or Bcl-2-controlled checkpoint.