BOD (Bcl-2-related ovarian death gene) is an ovarian BH3 domain-containing proapoptotic Bcl-2 protein capable of dimerization with diverse antiapoptotic Bcl-2 members

Epstein-Barr virus interactions with the Bcl-2 protein family and apoptosis in human tumor cells

Epstein-Barr virus (EBV), a human gammaherpesvirus carried by more than 90% of the world's population, is associated with malignant tumors such as Burkitt's lymphoma (BL), Hodgkin lymphoma, post-transplant lymphoma, extra-nodal natural killer/T cell lymphoma, and nasopharyngeal and gastric carcinomas in immune-compromised patients. In the process of infection, EBV faces challenges: the host cell environment is harsh, and the survival and apoptosis of host cells are precisely regulated. Only when host cells receive sufficient survival signals may they immortalize. To establish efficiently a lytic or long-term latent infection, EBV must escape the host cell immunologic mechanism and resist host cell apoptosis by interfering with multiple signaling pathways. This review details the apoptotic pathway disrupted by EBV in EBV-infected cells and describes the interactions of EBV gene products with host cellular factors as well as the function of these factors, which decide the fate of the host cell. The relationships between other EBV-encoded genes and proteins of the B-cell leukemia/lymphoma (Bcl) family are unknown. Still, EBV seems to contribute to establishing its own latency and the formation of tumors by modifying events that impact cell survival and proliferation as well as the immune response of the infected host. We discuss potential therapeutic drugs to provide a foundation for further studies of tumor pathogenesis aimed at exploiting novel therapeutic strategies for EBV-associated diseases.

Role of T cell death in maintaining immune tolerance during persistent viral hepatitis

Virus-specific T cells play an important role in the resolution of hepatic infection. However, during chronic hepatitis infection these cells lack their effector functions and fail to control the virus. Hepatitis B virus and hepatitis C virus have developed several mechanisms to generate immune tolerance. One of these strategies is the depletion of virus-specific T cells by apoptosis. The immunotolerogenic liver has unique property to retain and activate naïve T cell to avoid the over reactivation of immune response against antigens which is exploited by hepatotropic viruses to persist. The deletion of the virus-specific T cells occurs by intrinsic (passive) apoptotic mechanism. The pro-apoptotic molecule Bcl-2 interacting mediator (Bim) has attracted increasing attention as a pivotal involvement in apoptosis, as a regulator of tissue homeostasis and an enhancer for the viral persistence. Here, we reviewed our current knowledge on the evidence showing critical role of Bim in viral-specific T cell death by apoptotic pathways and helps in the immune tolerance.

BHLH transcription factor DEC2 regulates pro-apoptotic factor Bim in human oral cancer HSC-3 cells

DEC1 (BHLHE40/Stra13/Sharp2) and DEC2 (BHLHE41/Sharp1) are basic helix-loop-helix (bHLH) transcription factors that are involved in the regulation of apoptosis, cell proliferation, circadian rhythms and the response to hypoxia. We previously showed the functional effects of DEC1 and DEC2 on apoptosis in human breast cancer MCF-7 cells. However, the roles of DEC1 and DEC2 in oral cancer are poorly understood. We examined whether DEC1 and DEC2 are involved in the regulation of apoptosis in human oral cancer HSC-3 and CA9-22 cells. The expression of DEC2 was upregulated by cis-diamminedichloroplatinum (II) (cisplatin: CDDP) treatment in HSC-3 cells, whereas CDDP treatment had little effects on the expression of DEC2 in CA9-22 cells. We showed that DEC2 overexpression inhibits pro-apoptotic factor Bim and inhibits apoptosis induced by CDDP in HSC-3 cells, whereas it had little effects on apoptosis in CA9-22 cells. DEC1 overexpression had little effects on apoptosis induced by CDDP in these cells. We also found that CDDP upregulated the amounts of DEC2 in the nucleus in HSC-3 cells. These results suggest that DEC2 has anti-apoptotic effects on apoptosis induced by CDDP in HSC-3 cells.

The proapoptotic Bcl-2 family member Bim plays a central role during the development of virus-induced hepatitis

The proapoptotic Bcl-2 homolog Bim was shown to control the apoptosis of both T cells and hepatocytes. This dual role of Bim might be particularly relevant for the development of viral hepatitis, in which both the sensitivity of hepatocytes to apoptosis stimuli and the persistence of cytotoxic T cells are essential factors for the outcome of the disease. The relevance of Bim in regulating survival of cytotoxic T cells or induction of hepatocyte death has only been investigated in separate systems, and their relative contributions to the pathogenesis of T cell-mediated hepatitis remain unclear. Using the highly dynamic model system of lymphocytic choriomeningitis virus-mediated hepatitis and bone marrow chimeras, we found that Bim has a dual role in the development of lymphocytic choriomeningitis virus-induced, T cell-mediated hepatitis. Although the absence of Bim in parenchymal cells led to markedly attenuated liver damage, loss of Bim in the lymphoid compartment moderately enhanced hepatitis. However, when both effects were combined in Bim(-/-) mice, the effect of Bim deficiency in the lymphoid compartment was overcompensated for by the reduced sensitivity of Bim(-/-) hepatocytes to T cell-induced apoptosis, resulting in the protection of Bim(-/-) mice from hepatitis.

The emerging role of matrix metalloproteases of the ADAM family in male germ cell apoptosis

Constitutive germ cell apoptosis during mammalian spermatogenesis is a key process for controlling sperm output and to eliminate damaged or unwanted cells. An increase or decrease in the apoptosis rate has deleterious consequences and leads to low sperm production. Apoptosis in spermatogenesis has been widely studied, but the mechanism by which it is induced under physiological or pathological conditions has not been clarified. We have recently identified the metalloprotease ADAM17 (TACE) as a putative physiological inducer of germ cell apoptosis. The mechanisms involved in regulating the shedding of the ADAM17 extracellular domain are still far from being understood, although they are important in order to understand cell-cell communications. Here, we review the available data regarding apoptosis during mammalian spermatogenesis and the localization of ADAM proteins in the male reproductive tract. We propose an integrative working model where ADAM17, p38 MAPK, protein kinase C (PKC) and the tyrosine kinase c-Abl participate in the physiological signalling cascade inducing apoptosis in germ cells. In our model, we also propose a role for the Sertoli cell in regulating the Fas/FasL system in order to induce the extrinsic pathway of apoptosis in germ cells. This working model could be applied to further understand constitutive apoptosis in spermatogenesis and in pathological conditions (e.g., varicocele) or following environmental toxicants exposure (e.g., genotoxicity or xenoestrogens).

Update on the chemopreventive effects of ginger and its phytochemicals

The rhizomes of Zingiber officinale Roscoe (Zingiberaceae), commonly known as ginger, is one of the most widely used spice and condiment. It is also an integral part of many traditional medicines and has been extensively used in Chinese, Ayurvedic, Tibb-Unani, Srilankan, Arabic, and African traditional medicines, since antiquity, for many unrelated human ailments including common colds, fever, sore throats, vomiting, motion sickness, gastrointestinal complications, indigestion, constipation, arthritis, rheumatism, sprains, muscular aches, pains, cramps, hypertension, dementia, fever, infectious diseases, and helminthiasis. The putative active compounds are nonvolatile pungent principles, namely gingerols, shogaols, paradols, and zingerone. These compounds are some of the extensively studied phytochemicals and account for the antioxidant, anti-inflammatory, antiemetic, and gastroprotective activities. A number of preclinical investigations with a wide variety of assay systems and carcinogens have shown that ginger and its compounds possess chemopreventive and antineoplastic effects. A number of mechanisms have been observed to be involved in the chemopreventive effects of ginger. The cancer preventive activities of ginger are supposed to be mainly due to free radical scavenging, antioxidant pathways, alteration of gene expressions, and induction of apoptosis, all of which contribute towards decrease in tumor initiation, promotion, and progression. This review provides concise information from preclinical studies with both cell culture models and relevant animal studies by focusing on the mechanisms responsible for the chemopreventive action. The conclusion describes directions for future research to establish its activity and utility as a human cancer preventive and therapeutic drug. The above-mentioned mechanisms of ginger seem to be promising for cancer prevention; however, further clinical studies are warranted to assess the efficacy and safety of ginger.

Bim: guardian of tissue homeostasis and critical regulator of the immune system, tumorigenesis and bone biology

One of the most important roles of apoptosis is the maintenance of tissue homeostasis. Impairment of apoptosis leads to a number of pathological conditions. In response to apoptotic signals, various proteins are activated in a pathway and signal-specific manner. Recently, the pro-apoptotic molecule Bim has attracted increasing attention as a pivotal regulator of tissue homeostasis. The Bim expression level is strictly controlled in both transcriptional and post-transcriptional levels. This control is dependent on cell, tissue and apoptotic stimuli. The phenotype of Bim-deficient mice is a systemic lupus erythematosus-like autoimmune disease with an abnormal accumulation of hematopoietic cells. Bim is thus a critical regulator of hematopoietic cells and immune system. Further studies have revealed the critical roles of Bim in various normal and pathological conditions, including bone homeostasis and tumorigenesis. The current understanding of Bim signaling and roles in the maintenance of tissue homeostasis is reviewed in this paper, focusing on the immune system, bone biology and tumorigenesis to illustrate the diversified role of Bim.

Cyclin D1, cdk4, and Bim are involved in thrombin-induced apoptosis in cultured cortical neurons

Thrombin, a multifunctional serine protease, is neurotoxic in vitro and in vivo. Thrombin has been shown to be increased in Alzheimer's disease (AD) and other neuropathological conditions and could be a mediator of pathological neuronal cell death in the brain. The mechanisms of thrombin-induced neuronal cell death are incompletely understood. The objective of this study is to explore mechanisms that contribute to thrombin-induced neuronal apoptosis focusing on the role of cell cycle regulators and the pro-apoptotic protein Bim (Bcl-2-interacting mediator of cell death) in this process. Our data show that thrombin treatment of primary cerebral cortical cultures results in dose-dependent apoptotic cell death. Exposure of neuronal cultures to thrombin leads to induction of cell cycle proteins cyclin D1 and cyclin E, at both mRNA and protein levels. In addition, thrombin treatment causes the appearance of cyclin-dependent kinase 4 (cdk4) and expression of the pro-apoptotic protein Bim. Inhibition of cdk4 prevents both induction of Bim expression and thrombin-induced neuronal apoptosis. These data demonstrate that thrombin-induced apoptosis proceeds via cell cycle activation involving cdk4 resulting in induction of Bim. Thus, cell cycle proteins could be therapeutic targets in diseases such as AD where thrombin has been implicated.

BCL2 family of apoptosis-related genes: functions and clinical implications in cancer

One of the most effective ways to combat different types of cancer is through early diagnosis and administration of effective treatment, followed by efficient monitoring that will allow physicians to detect relapsing disease and treat it at the earliest possible time. Apoptosis, a normal physiological form of cell death, is critically involved in the regulation of cellular homeostasis. Dysregulation of programmed cell death mechanisms plays an important role in the pathogenesis and progression of cancer as well as in the responses of tumours to therapeutic interventions. Many members of the BCL2 (B-cell CLL/lymphoma 2; Bcl-2) family of apoptosis-related genes have been found to be differentially expressed in various malignancies, and some are useful prognostic cancer biomarkers. We have recently cloned a new member of this family, BCL2L12, which was found to be differentially expressed in many tumours. Most of the BCL2 family genes have been found to play a central regulatory role in apoptosis induction. Results have made it clear that a number of coordinating alterations in the BCL2 family of genes must occur to inhibit apoptosis and provoke carcinogenesis in a wide variety of cancers. However, more research is required to increase our understanding of the extent to which and the mechanisms by which they are involved in cancer development, providing the basis for earlier and more accurate cancer diagnosis, prognosis and therapeutic intervention that targets the apoptosis pathways. In the present review, we describe current knowledge of the function and molecular characteristics of a series of classic but also newly discovered genes of the BCL2 family as well as their implications in cancer development, prognosis and treatment.

Distinct mechanisms of neuronal apoptosis are triggered by antagonism of Bcl-2/Bcl-x(L) versus induction of the BH3-only protein Bim

Primary cerebellar granule neurons (CGNs) require depolarizing extracellular potassium for their survival. Removal of depolarizing potassium triggers CGN apoptosis that requires induction of Bim, a BH3-only Bcl-2 family member. Bim is classically thought to promote apoptosis by neutralizing pro-survival Bcl-2 proteins. To determine if this is the principal function of Bim in CGNs, we contrasted Bim-mediated apoptosis to neuronal death induced by HA14-1, a BH3-domain mimetic that antagonizes Bcl-2 and Bcl-x(L). HA14-1 elicited CGN apoptosis characterized by caspase 3 and 9 activation, cytochrome c release, conformational activation of Bax, and mitochondrial depolarization. HA14-1 provoked CGN apoptosis in the absence of Bim induction and negative regulators of Bim transcription did not prevent HA14-1-induced cell death. However, the antioxidant glutathione and its precursor, N-acetyl-l-cysteine, suppressed HA14-1-induced apoptosis. Similarly, apoptosis induced by either a structurally distinct Bcl-2/Bcl-x(L) inhibitor (compound 6) or Bcl-2 antisense oligonucleotides was diminished by glutathione. In contrast, antioxidants had no effect on CGN apoptosis provoked by either removal of depolarizing potassium or overexpression of a GFP-Bim fusion protein, two models of Bim-dependent death. These data show that antagonism of Bcl-2/Bcl-x(L) function elicits oxidative stress-dependent CGN apoptosis that is mechanistically distinct from Bim-mediated cell death. These results further indicate that, although Bcl-2/Bcl-x(L) antagonism is sufficient to induce neuronal apoptosis, Bim likely promotes neuronal death by interacting with additional proteins besides Bcl-2/Bcl-x(L).

Modulation and function of caspase pathways in B lymphocytes

During their development, B-lineage cells are selected to mature, to die, to divide, or to survive and wait, ready to respond to external signals. The homeostatic balance between growth, death, and survival is mediated by signaling pathways through the B-cell antigen receptor (BCR) complex, cytokine and chemokine receptors or cell-cell coreceptor interactions. The BCR complex is a master regulator essential at key checkpoints during development. These checkpoints involve various processes, including negative selection (deletion), anergy, receptor editing, and positive selection. Without BCRs or downstream BCR-signaling components, B-lineage cells arrest during development. Removal of BCRs from mature B cells leads to their death. Here, we discuss signaling pathways in B cells that activate members of the caspase family of cysteine proteases. In some B-cell subsets, BCR signaling activates caspases, which in turn induce a program leading to cell death. However, in other contexts, caspases are involved in the proliferation of B cells. The outcome depends in part on the presence or absence of modifiers that affect signaling thresholds and on which caspases are activated. These mechanisms allow the coordinated regulation of proliferation and apoptosis that is essential for lymphoid homeostasis.

Over-expression of Bim α3, a novel isoform of human Bim, result in cell apoptosis

Bim proteins are essential factors of apoptosis. Nine isoforms of Bim have been submitted to GenBank database. In order to improve the understanding of the regulation of Bims' proapoptotic activity, we screened a multiple tissue cDNA panels for Bim isoforms and tested their proapoptotic activity by over-expression. Two novel cDNA isoforms of Bim family are generated by alternative splicing. One isoform encodes a 79 residue putative protein with a BH3 domain, named Bim alpha3. There is not any significant ORF found in another isoform, named Bim beta5. Subcellular localized analysis of EGFP-Bim fusion protein suggests Bim alpha3 distributed to both plasma and nucleus of HEK 293 cell. HEK 293 cells transfected with pcDNA-Bim alpha3 presented a similar proapoptotic activity (32.05 +/- 6.42%) with Bim alpha2 (30.14 +/- 2.66%). The proapoptotic activity of Bim alpha3 was obviously weaker than that of Bim S (46.52 +/- 5.07%) and Bim L (55.53 +/- 1.99%). Anti-sense over-expression of Bim in HEK 293 cells results in a weak down-regulated proapoptotic level. Expression pattern analysis reveals that both the novel cDNAs are expressed widely in normal tissue just like the other reported isoforms. The expression pattern of Bim isoforms shows tissue specific obviously. The results suggest that BH3 domain is sufficiency for proapoptotic activity of Bim proteins. The functional state of Bims might be regulated both in the transcript and post transcript process.

Lovastatin-induced up-regulation of the BH3-only protein, Bim, and cell death in glioblastoma cells

The mechanism of lovastatin-induced cell death was examined in three established human glioblastoma cell lines; U87, U251, and U138. Changes in potential modifiers of apoptosis, including Bcl-2 family proteins and MAP kinase targets after such lovastatin treatment, were evaluated. Lovastatin (5 microm) treatment causes extensive cell death in two of the cell lines, U87 and U251; but only minimal in a third, U138. Lovastatin-induced death occurs in correlation with significantly increased levels of the BH3-only protein, Bim. The up-regulation of Bim levels was directly associated with an increased incidence of apoptosis. Lovastatin treatment in U87 cells results in activation of targets of three major mitogen-activating protein kinase cascades including Erk1/2, JNK and p38. Changes in levels of Bim, as well as increase phosphorylation of Erk1/2, c-jun, and p38 are all prevented by co-incubation of lovastatin and the isoprenylation metabolite, geranylgeranyl pyrophosphate. Inhibition of the MAP kinase pathways failed to block the increased expression of Bim expression or cell death. Further elucidation of the mechanisms of lovastatin-induced up-regulation of Bim and apoptosis in glioblastoma cells are important in determining a potential role for lovastatin as a chemotherapy agent.

Regulation of cell death in the lymphoid system by Bcl-2 family proteins

Programmed cell death is an ordered process that is essential for the normal development and homeostasis of an organism. Dysregulation of this programmed pathway, resulting in either excess cell numbers or unscheduled cell death, underlies a number of disease states. Bcl-2 family proteins play a key role in regulating cell death and survival, and a number of studies have demonstrated their role as important regulators of cell fate in the lymphoid system. Mice that are genetically deficient or overexpress various Bcl-2 family proteins have provided important clues regarding their roles in lymphocyte development, progression of lymphoid tumors and analogous human disorders. In addition, lymphotropic viruses may trigger cell proliferation and inhibit cell death with the help of their own Bcl-2 homologues. Comparing the shared and distinct functions of viral and cellular Bcl-2-related proteins yields new insight into their fundamental mechanisms.

Rat retinal ganglion cells upregulate the pro-apoptotic BH3-only protein Bim after optic nerve transection

Increased expression of Bim, a pro-apoptotic member of the Bcl-2 family, has been shown to be critical for neuronal apoptosis. To study the involvement of Bim in injury-induced cell death in retina, Bim expression was studied in normal rat retina and in retina after optic nerve transection using quantitative RT-PCR and immunohistochemistry. As a complement to this, the apoptotic regulators Bax, Bcl-2, caspase-3 and phosphorylated c-jun were studied. The relative levels of Bim mRNA in retina were significantly higher 4 days after optic nerve transection and below normal levels at 14 days after transection. A parallel increase in the number of Bim-immunoreactive cells in the retinal ganglion cell layer could be seen. Bim-immunoreactivity localized to retrogradely True Blue-labeled retinal ganglion cells. The relative mRNA levels for both Bax and Bcl-2 were higher at 4 days after transection when compared to normal. Immunoreactivity for Bax, Bcl-2 as well as for caspase-3 and phosphorylated c-jun, indicative of cell death, localized to True Blue-identified retinal ganglion cells 4 days after injury. Bcl-2 immunoreactivity was also seen on other cells, most likely Müller glia cells. In addition, optic nerve transection caused an increase in Bim, Bax, and Bcl-2 mRNA levels in optic nerve and superior colliculus. Our results suggest that Bim is involved in injury-induced retinal ganglion cell death and indicate that the increase in Bim and Bax expression promote cell death of axotomized retinal ganglion cells whereas the elevation in Bcl-2 in retina may contribute to the control of the extent of apoptosis after the optic nerve transection.

Expression of apoptosis related proteins in brains of patients with Alzheimer's disease

An increasing number of proteins are implicated in apoptosis and several of them have been shown to be altered in Alzheimer's disease (AD) brain. Because of this apoptosis is thought to be the underlying mechanism of neuronal cell loss in AD. To further substantiate this hypothesis we investigated the expression of a recently identified apoptosis related proteins and other apoptosis regulators in frontal cortex and cerebellum of AD by Western blot and enzyme-linked immunsorbent assay technique. Quantitative analysis revealed unaltered levels of Bax and RAIDD (Receptor interacting protein associated ICH-1 (caspase-2)/CED-3 (Caenorhabditis elegans death protease-3)-homologous protein with death domain) in both regions. ZIP (Zipper interacting protein) kinase, Bim/BOD (Bcl-2 interacting mediator of cell death/Bcl-2 related ovarian death gene) and p21 were significantly increased only in AD frontal cortex (P < 0.05, in all cases). Cerebellar Bcl-2 levels were significantly increased in AD (P < 0.01) while in AD frontal cortex, although the levels tended to increase did not reach significance level. The results indicate that apoptosis indeed account for the neuronal loss in AD. However, it does not seem to involve Bax and RAIDD.

Apoptosis signaling

Apoptosis, a physiological process for killing cells, is critical for the normal development and function of multicellular organisms. Abnormalities in cell death control can contribute to a variety of diseases, including cancer, autoimmunity, and degenerative disorders. Signaling for apoptosis occurs through multiple independent pathways that are initiated either from triggering events within the cell or from outside the cell, for instance, by ligation of death receptors. All apoptosis signaling pathways converge on a common machinery of cell destruction that is activated by a family of cysteine proteases (caspases) that cleave proteins at aspartate residues. Dismantling and removal of doomed cells is accomplished by proteolysis of vital cellular constituents, DNA degradation, and phagocytosis by neighboring cells. This article reviews current knowledge of apoptosis signaling, lists several pressing questions, and presents a novel model to explain the biochemical and functional interactions between components of the cell death regulatory machinery.

Mechanisms underlying hypoxia-induced neuronal apoptosis

In vivo models of cerebral hypoxia-ischemia have shown that neuronal death may occur via necrosis or apoptosis. Necrosis is, in general, a rapidly occurring form of cell death that has been attributed, in part, to alterations in ionic homeostasis. In contrast, apoptosis is a delayed form of cell death that occurs as the result of activation of a genetic program. In the past decade, we have learned considerably about the mechanisms underlying apoptotic neuronal death following cerebral hypoxia-ischemia. With this growth in knowledge, we are coming to the realization that apoptosis and necrosis, although morphologically distinct, are likely part of a continuum of cell death with similar operative mechanisms. For example, following hypoxia-ischemia, excitatory amino acid release and alterations in ionic homeostasis contribute to both necrotic and apoptotic neuronal death. However, apoptosis is distinguished from necrosis in that gene activation is the predominant mechanism regulating cell survival. Following hypoxic-ischemic episodes in the brain, genes that promote as well as inhibit apoptosis are activated. It is the balance in the expression of pro- and anti-apoptotic genes that likely determines the fate of neurons exposed to hypoxia. The balance in expression of pro- and anti-apoptotic genes may also account for the regional differences in vulnerability to hypoxic insults. In this review, we will examine the known mechanisms underlying apoptosis in neurons exposed to hypoxia and hypoxia-ischemia.

Crosstalk Among Multiple Signaling Pathways Controlling Ovarian Cell Death

Ovarian cell death is an essential process for the homeostasis of ovarian function in human and other mammalian species. It ensures the selection of the dominant follicle and the demise of excess follicles. In turn, this process minimizes the possibility of multiple embryo development during pregnancy and assures the development of few but healthy embryos. Degeneration of the old corpora lutea in each estrous/menstrual cycle by programmed cell death is essential to maintain the normal cyclicity of ovarian steroidogenesis. Although there are multiple pathways that can determine cell death or survival, crosstalk among endocrine, paracrine and autocrine factors, as well as among protooncogenes, tumor suppressor genes, survival genes and death genes, plays an important role in determining the fate of ovarian somatic and germ cells. The establishment of immortalized rat and human steroidogenic granulosa cell lines and the investigation of pure populations of primary granulosa cells allows systematic studies of the mechanisms that control steroidogenesis and apoptosis of granulosa cells. These cells are the most abundant type of somatic follicular cell. Moreover, crosstalk between p53 and extracellular matrix components such as laminin, fibronectin and basic fibroblast growth factor, between cAMP- and p53-generated signals and between steroid hormones and Bcl-2, can explain some of the fine tuning that controls ovarian steroidogenesis and apoptosis. Further study of the mechanisms of ovarian cell death will lead to a better understanding of the processes involved and permit the formulation of novel strategies for the treatment of ovarian malfunctions, such as polycystic ovarian syndrome and ovarian cancer.

Deciphering the pathways of life and death

Caspase recruitment and oligomerization mediated by adaptor proteins constitute a basic mechanism of caspase activation. The complex phenotypes of the caspase knockout mice indicate that multiple mechanisms of caspase activation operate in parallel and that death signal transduction pathways are both cell-type and stimulus specific. The BH3-domain- containing pro-apototic members of Bcl-2 family may be one of the critical links between the initial death signals and the central machinery of apoptosis.