Modulation of apoptosis by the widely distributed Bcl-2 homologue Bak

Identification of a caspase 3-independent role of pro-apoptotic factor Bak in TNF-α-induced apoptosis

By using our recently developed gene discovery system, we have identified Bak, a member of the Bcl-2 family, as a pro-apoptotic factor in the tumor necrosis factor (TNF)-alpha-induced apoptotic pathway in caspase 3-deficient cells. Unlike Bcl-2, Bak stimulates several apoptotic pathways, however the molecular mechanism(s) of its action remains unclear. For example, it is unclear whether Bak induces apoptosis in caspase 3-deficient cells. In this study, we examined the effects of overexpression of Bak in MCF-7 cells that lack caspase 3. We found that despite the absence of caspase 3 in MCF-7 cells, they were more sensitive to the cell death effects of Bak as compared to caspase 3-expressing HeLa S3 cells. The targeting of Bak function by ribozymes suggests that Bak is required for the TNF-alpha-induced apoptotic pathway in caspase 3-deficient cells. This study demonstrates the caspase 3-independent function of Bak in the TNF-alpha-induced apoptotic pathway.

Activated T cell death in vivo mediated by proapoptotic bcl-2 family member bim

At the end of the T cell response, the majority of the activated T cells die. We activated Vbeta8(+) T cells with staphylococcal enterotoxin B (SEB) in vivo and monitored the expansion and deletion of Vbeta8(+) T cells. We found that, in response to SEB, activated T cells died in vivo in the absence of Fas or TNF-R signaling but not when they overexpressed human Bcl-2. We also found that Vbeta8(+) T cells from Bim-deficient mice are resistant to SEB-induced deletion. While Bim levels did not change, endogenous Bcl-2 levels within Vbeta8(+) T cells decrease following SEB injection. Thus, the death of superantigen-stimulated T cells in vivo is mediated by Bim and may be modulated by a decrease in Bcl-2.

Hepatitis C virus core protein inhibits apoptosis via enhanced Bcl-xL expression

Previous studies indicated that hepatitis C virus core protein influences cellular apoptosis. However, the precise mechanisms of the effects are not fully understood. Therefore, in this study, we examined the mechanisms of the effects on cell apoptosis by core protein, using transiently transfected and magnetically collected core-producing HepG2 cells. First, to elucidate the target site of core protein in the apoptotic pathway, we examined the activation of caspases after anti-Fas antibody stimulation. Core protein inhibited the apoptotic cascade downstream from caspase 8 and upstream from caspase 3. Next, to clarify more direct mechanisms of this effect, mRNA levels of several bcl-2-related genes were examined. An RNase protection assay showed that the mRNA of bcl-xl increased in the core-producing cells. We showed that this increase was mediated by the enhancement of bcl-x promoter activity by core protein through an extracellular-regulated kinase pathway. These results suggest that core protein inhibits apoptosis at the mitochondria level through augmentation of Bcl-x expression, resulting in an inhibition of caspase 3 activation.

The expression of Bcl-2 family proteins (Bcl-2, Bcl-x, Bax, Bak and Bim) in human lymphocytes

Bcl-2 family proteins regulate programmed cell death, and may play an important role in the selection of lymphocytes. We investigated the expression of Bcl-2, Bcl-x, Bax, Bak and Bim in human lymphocytes using flow-cytometry. Bcl-2 was down-regulated in CD4(+)8(+) (DP) thymocytes and CD19(+)38(+) tonsillar lymphocytes (GC B cells). Among DP thymocytes, cells co-expressing CD69 up-regulated Bcl-2, suggesting that the role of Bcl-2 is promoting survival of positively selected DP cells. Unexpectedly, the expression level of Bcl-x was higher in DP cells than in Single Positive (SP) cells and in CD69(+) DP thymocytes it was lower than in CD69(+) DP thymocytes. Expression of Bim was low in DP thymocytes but high in a subset of GC B cells. Bim and Bax were expressed more highly in SP than in DP thymocytes. Among peripheral blood lymphocytes (PBL), CD8(+) T cells expressed an approximately ten-fold higher level of Bcl-x than CD4(+) T cells while both subsets expressed similar levels of Bcl-2. Bak expression was low and Bim expression was absent in PBL. These results suggest that not only Bcl-2 but other members of the Bcl-2 family are involved in T cell development in the thymus and affinity maturation of B cells in the germinal center.

Expression of Bcl-x, Bcl-2, Bax, and Bak in endarterectomy and atherectomy specimens

The regulation of apoptosis in atherosclerosis is not completely defined. The aim of this study was to determine the expression of Bcl-2, Bcl-x, Bax, and Bak in relation to apoptosis in advanced atherosclerotic lesions. In atherectomy (15), endarterectomy (10), and control non-atherosclerotic segments of renal (2) and of coronary and carotid (5) arteries, the extent of apoptosis was determined using TdT dUTP nick end labelling (TUNEL) and nuclear morphology (karyorrhexis/pyknosis) and expression of apoptosis regulators by immunohistochemistry and western blot analysis on paraffin-embedded material. In all specimens, the atherosclerotic involvement was advanced: grade V (n=18) and grade VI (n=7). The apoptotic index was high (mean 30%) in advanced lesions compared with controls (<2%) and smooth muscle cells (SMCs) were the predominant cell type undergoing apoptosis. In all TUNEL-positive apoptotic cells, Bax and Bak were present, while Bcl-x was absent. Bcl-2 was absent in a majority of these cells, but occasional TUNEL-positive cells expressed Bcl-2. In non-apoptotic cells, Bcl-x was present and western blot detected only the long isoform, Bcl-xL, from the plaques. In conclusion, increased Bax and Bak coupled with lack/paucity of Bcl-2 and Bcl-xL are associated with SMC apoptosis in advanced lesions. Bcl-xL in non-apoptotic cells appears to contribute to prolonged cell survival.

Differential sensitivity to apoptosis between the human small and large intestinal mucosae: linkage with segment-specific regulation of BCL-2 homologs and involvement of signaling pathways

The small and large intestines differ in their expression profiles of Bcl-2 homologs. Intestinal segment-specific Bcl-2 homolog expression profiles are acquired as early as by mid-gestation (18-20 weeks) in man. In the present study, we examined the question whether such distinctions underlie segment-specific control mechanisms of intestinal cell survival. Using mid-gestation human jejunum and colon organotypic cultures, we analyzed the impact of growth factors (namely insulin; 10 microg/ml) and pharmacological compounds that inhibit signal transduction molecules/pathways (namely tyrosine kinases, Fak, P13-K/Akt, and MEK/Erk) on cell survival and Bcl-2 homolog expression (anti-apoptotic: Bcl-2, Bcl-X(L), Mcl-1; pro-apoptotic: Bax, Bak, Bad). The relative activation levels of p125Fak, p42Erk-2, and p57Akt were analyzed as well. Herein, we report that (1) the inhibition of signal transduction molecules/pathways revealed striking differences in their impact on cell survival in the jejunum and colon (e.g., the inhibition of p125Fak induced apoptosis with a significantly greater extent in the jejunum [approximately 43%] than in the colon [approximately 24%]); (2) sharp distinctions between the two segments were noted in the modulatory effects of the various treatments on Bcl-2 homolog steady-state levels (e.g., inhibition of tyrosine kinase activities in the jejunum down-regulated all anti-apoptotics analyzed while increasing Bax, whereas the same treatment in the colon down-regulated Bcl-X(L) only and increased all pro-apoptotics); and (3) in addition to their differential impact on cell survival and Bcl-2 homolog expression, the MEK/Erk and P13-K/Akt pathways were found to be distinctively regulated in the jejunum and colon mucosae (e.g., insulin in the jejunum increased p42Erk-2 activation without affecting that of p57Akt, whereas the same treatment in the colon decreased p42Erk-2 activation while increasing that of p57Akt). Altogether, these data show that intestinal cell survival is characterized by segment-specific susceptibilities to apoptosis, which are in turn linked with segmental distinctions in the involvement of signaling pathways and the regulation of Bcl-2 homolog steady-state levels. Therefore, these indicate that cell survival is subject to segment-specific control mechanisms along the proximal-distal axis of the intestine.

The apoptosis promoting Bcl-2 homologues Bak and Nbk/Bik overcome drug resistance in Mdr-1-negative and Mdr-1-overexpressing breast cancer cell lines

We previously demonstrated that the forced expression of pro-caspase-3 can revert acquired chemoresistance in MT1-Adr breast cancer cells which show a defective activation of the mitochondrial pathway of apoptosis. We now asked whether the manipulation of mitochondrial apoptosis signaling can revert different types of drug resistance, i.e. the resistance due to impaired mitochondrial activation in the MT1-Adr cells and the resistance in MT3-Adr cells which is caused by increased expression of the Mdr-1/p-glycoprotein ABC transporter. Here we show that Bcl-2 overexpression is the underlying cause for the resistant phenotype in the MT1-Adr cells. Overexpression of the apoptosis-promoting Bax homologue Bak or the BH3 only protein Nbk/Bik reverts, as expected, acquired drug resistance in the MT1-Adr cells as recently demonstrated for pro-caspase-3. Moreover, we show that both apoptosis-promoters, Nbk/Bik and Bak, antagonize acquired chemoresistance for epirubicin-mediated apoptosis in MT3-Adr breast cancer cells. Neither drug uptake nor drug efflux were influenced by Bak or Nbk/Bik. Thus, our data show that manipulation of the downstream apoptosis signaling cascade by Bak and Nbk/Bik can overcome not only drug resistance due to mitochondrial apoptosis deficiency (in the MT1-Adr cells) but also classical, i.e. efflux-mediated, resistance for drug-induced cell death in the MT3-Adr cell line. Nbk/Bik and Bak could therefore be target genes to increase chemosensitivity and overcome different types of drug resistance.

p53-dependent apoptosis pathways

The p53 tumor suppressor limits cellular proliferation by inducing cell cycle arrest and apoptosis in response to cellular stresses such as DNA damage, hypoxia, and oncogene activation. Many apoptosis-related genes that are transcriptionally regulated by p53 have been identified. These are candidates for implementing p53 effector functions. In response to oncogene activation, p53 mediates apoptosis through a linear pathway involving bax transactivation, Bax translocation from the cytosol to membranes, cytochrome c release from mitochondria, and caspase-9 activation, followed by the activation of caspase-3, -6, and -7. p53-mediated apoptosis can be blocked at multiple death checkpoints, by inhibiting p53 activity directly, by Bcl-2 family members regulating mitochondrial function, by E1B 19K blocking caspase-9 activation, and by caspase inhibitors. Understanding the mechanisms by which p53 induces apoptosis, and the reasons why cell death is bypassed in transformed cells, is of fundamental importance in cancer research, and has great implications in the design of anticancer therapeutics.

The structure of the C-terminal domain of the pro-apoptotic protein Bak and its interaction with model membranes

Bak is a pro-apoptotic protein widely distributed in different cell types that is associated with the mitochondrial outer membrane, apparently through a C-terminal hydrophobic domain. We used infrared spectroscopy to study the secondary structure of a synthetic peptide ((+)(3)HN-(188)ILNVLVVLGVVLLGQFVVRRFFKS(211)-COO(-)) with the same sequence as the C-terminal domain of Bak. The spectrum of this peptide in D(2)O buffer shows an amide I' band with a maximum at 1636 cm(-1), which clearly indicates the predominance of an extended beta-structure in aqueous solvent. However, the peptide incorporated in multilamellar dimyristoylphosphatidylcholine (DMPC) membranes shows a different amide I' band spectrum, with a maximum at 1658 cm(-1), indicating a predominantly alpha-helical structure induced by its interaction with the membrane. It was observed that through differential scanning calorimetry the transition of the phospholipid model membrane was broadened in the presence of the peptide. Fluorescence polarization of 1,6-diphenyl-1,3,5-hexatriene (DPH) in fluid DMPC vesicles showed that increasing concentrations of the peptide produced increased polarization values, which is compatible with the peptide being inserted into the membrane. High concentrations of the peptide considerably broaden the phase transition of DMPC multilamellar vesicles, and DPH polarization increased, especially at temperatures above the T(c) transition temperature of the pure phospholipid. The addition of peptide destabilized unilamellar vesicles and released encapsulated carboxyfluorescein. These results indicate that this domain is able to insert itself into membranes, where it adopts an alpha-helical structure and considerably perturbs the physical properties of the membrane.

Expression of Bcl-2, Bcl-x, Mcl-1, Bax and Bak in human uterine leiomyomas and myometrium during the menstrual cycle and after menopause

To investigate the expression of Bcl-2, Bcl-x, Mcl-1, Bax and Bak proteins in human uterine leiomyomas and homologous myometrium during the menstrual cycle and after menopause. The expression of Bcl-2, Bcl-x, Mcl-1, Bax and Bak in leiomyomas (n=24) and myometrial samples (n=22) from women with leiomyomas was measured by immunohistochemistry and Western blot. Measured by immunohistochemistry, a significant difference between leiomyomas and myometrium was observed only for the Bax protein, in tissues obtained from women in the secretory phase of the menstrual cycle. The Bcl-2 staining was more abundant in leiomyomas than in myometrium only in tissues obtained in the proliferative phase of the cycle. Bcl-2 was more abundant in leiomyomas from women of fertile age than in leiomyomas from menopausal women. No significant differences were observed for the Bcl-x or Bak proteins, whereas the Mcl-1 protein was significantly less abundant in secretory phase leiomyomas than in leiomyomas from menopausal women. Western blot analysis based on pools of tissue extracts from the different groups essentially confirmed the data obtained by immunohistochemistry. Bcl-2 family proteins are expressed in leiomyomas and myometrium in different phases related to and influenced by gonadal steroids. These proteins are suggested to interact with each other in the regulation of programmed cell death, apoptosis, but their specific role in growth control of uterine leiomyomas remains to be investigated.

Bcl-xL expression after contusion to the rat spinal cord

After contusion-derived spinal cord injury, (SCI) there is localized tissue disruption and energy failure that results in early necrosis and delayed apoptosis, events that contribute to chronic central pain in a majority of patients. We assessed the extent of contusion-induced apoptosis of neurons in a known central pain-signaling pathway, the spinothalamic tract (STT), which may be a contributor to SCI-induced pain. We observed the loss of STT cells and localized increase of DNA fragmentation and cytoplasmic histone-DNA complexes, which suggested potential apoptotic changes among STT neurons after SCI. We also showed SCI-associated changes in the expression of the antiapoptotic protein Bcl-xL, especially among STT cells, consistent with the hypothesis that Bcl-xL regulates the extent of apoptosis after SCI. Apoptosis in the injured spinal cord correlated well with prompt decreases in Bcl-xL protein levels and Bcl-xL/Bax protein ratios at the contusion site. We interpret these results as evidence that regulation of Bcl-xL may play a role in neural sparing after spinal injury and pain-signaling function.

A role for mitochondrial Bak in apoptotic response to anticancer drugs

In the present study a clonal Jurkat cell line deficient in expression of Bak was used to analyze the role of Bak in cytochrome c release from mitochondria. The Bak-deficient T leukemic cells were resistant to apoptosis induced by UV, staurosporin, VP-16, bleomycin, or cisplatin. In contrast to wild type Jurkat cells, these Bak-deficient cells did not respond to UV or treatment with these anticancer drugs by membranous phosphatidylserine exposure, DNA breaks, activation of caspases, or release of mitochondrial cytochrome c. The block in the apoptotic cascade was in the mitochondrial mechanism for cytochrome c release because purified mitochondria from Bak-deficient cells failed to release cytochrome c or apoptosis-inducing factor in response to recombinant Bax or truncated Bid. The resistance of Bak-deficient cells to VP-16 was reversed by transduction of the Bak gene into these cells. Also, the cytochrome c releasing capability of the Bak-deficient mitochondria was restored by insertion of recombinant Bak protein into purified mitochondria. Following mitochondrial localization, low dose recombinant Bak restored the mitochondrial release of cytochrome c in response to Bax; at increased doses it induced cytochrome c release itself. The function of Bak is independent of Bid and Bax because recombinant Bak induced cytochrome c release from mitochondria purified from Bax(-/-), Bid(-/-), or Bid(-/-) Bax(-/-) mice. Together, our findings suggest that Bak plays a key role in the apoptotic machinery of cytochrome c release and thus in the chemoresistance of human T leukemic cells.

Clinical significance and prognostic value of apoptosis related proteins in superficial esophageal squamous cell carcinoma

BACKGROUND

The purpose of the present study was to examine the expression of cell cycle regulators [p53, p21WAF1/CIP1 (p21), and Rb] and apoptosis related proteins Bax and Bcl-X(L) and to evaluate the relationship between their expressions and clinicopathological findings in patients with superficial squamous cell carcinomas of the esophagus.

METHODS

We immunohistochemically investigated the expression of p53, p21, Rb, Bax, and Bcl-X(L) in 79 patients with superficial esophageal carcinoma.

RESULTS

p21 overexpression was found in mucosal carcinoma (P = 0.05) and a high Bcl-X(L) score was observed for submucosal carcinoma (P = 0.03). The patients with high Bcl-X(L) score had more frequent lymphatic invasion and lymph node metastasis than did those with low Bcl-X(L) score (P < 0.05). Univariate analysis revealed significantly shorter survival in patients with high Bcl-X(L) expression than in those with low Bcl-X(L) expression, but Bcl-X(L) expression was not identified as an independent prognostic factor by multivariate analysis.

CONCLUSIONS

Because Bcl-X(L) expression correlated well with depth of tumor invasion, lymphatic invasion, and lymph node metastasis, examination of Bcl-X(L) expression will help to estimate the properties in superficial squamous cell carcinoma of the esophagus.

Transcriptional regulation of the BCL-X gene by NF-kappaB is an element of hypoxic responses in the rat brain

Signal transduction pathways that mediate neuronal commitment to apoptosis involve the nuclear factor kappa B (NF-kappaB) transcription factor. The bcl-x gene is a member of the bcl-2 family of genes that regulate apoptosis, and gives rise to two proteins, Bcl-XL and Bcl-XS, via alternative mRNA splicing. BCl-XL protein, like Bcl-2, is a dominant inhibitor of apoptotic cell death, whereas Bcl-XS promotes apoptosis. While there is high expression of Bcl-XL in the developing and adult brain, few transcriptional control elements have been identified in the bcl-x promoter. There are two functional nuclear factor-kappa B (NF-kappaB) DNA binding sites clustered upstream of the brain-specific transcription start site in the upstream promoter region of murine bcl-x. Recombinant NF-kappaB proteins bind to these sites. Also NF-kappaB overexpression, coupled with bcl-x promoter/reporter assays using a series of murine bcl-x promoter and deletion mutants, has identified the downstream 1.1kb of the bcl-x promoter as necessary for basal promoter activity and induction by NF-kappaB in support of the hypothesis that NF-kappaB can act to enhance BCl-XL expression via highly selective interactions with the bcl-x promoter, where NF-kappaB binding and promoter activation are dependent on specific DNA binding site sequences and NF-kappaB protein dimer composition. Hypoxia induces apoptosis in the hippocampus where the NF-kappaB dimers c-Rel/p50 and p50/pS0 bind to the bcl-x promoter NF-kappaB site.

Cloning and characterization of zfBLP1, a Bcl-XL homologue from the zebrafish, Danio rerio

The importance of the Bcl-2 family proteins in normal vertebrate embryogenesis is being recognized; however, their regulatory mechanism is poorly understood. We report here the cloning and characterization of a novel zebrafish Bcl-2 family protein, zfBLP1. The zfBLP1 cDNA is 1942 nucleotides long, encoding a polypeptide of 238 amino acids. The primary sequence of zfBLP1 shares 50% identity to human Bcl-XL, and contains all four conserved BH domains of the Bcl-2 family proteins. Primary sequence analysis identified a consensus ER retention signal at the C-terminal end of zfBLP1. Northern blot analysis indicated that there were two major and two minor zfBLP1 mRNA species expressed during embryonic development. Among the two major mRNA species, the short one, approx. 3 kb in size, was expressed throughout embryonic development, while the long one, approx. 7 kb long, was not detectable until the gastrula stage. These results suggest that zfBLP1 is a novel Bcl-2 family protein under complicated regulations, and is likely to play an important role in zebrafish oogenesis and embryogenesis.

Neuron-specific Bcl-2 homology 3 domain-only splice variant of Bak is anti-apoptotic in neurons, but pro-apoptotic in non-neuronal cells

We have identified and characterized N-Bak, a neuron-specific isoform of the pro-apoptotic Bcl-2 family member Bak. N-Bak is generated by neuron-specific splicing of a novel 20-base pair exon, which changes the previously described Bak, containing Bcl-2 homology (BH) domains BH1, BH2, and BH3, into a shorter BH3-only protein. As demonstrated by reverse transcription-polymerase chain reaction and RNase protection assay, N-Bak transcripts are expressed only in central and peripheral neurons, but not in other cells, whereas the previously described Bak is expressed ubiquitously, but not in neurons. Neonatal sympathetic neurons microinjected with N-Bak resisted apoptotic death caused by nerve growth factor (NGF) removal, whereas microinjected Bak accelerated NGF deprivation-induced death. Overexpressed Bak killed sympathetic neurons in the presence of NGF, whereas N-Bak did not. N-Bak was, however, still death-promoting when overexpressed in non-neuronal cells. Thus, N-Bak is an anti-apoptotic BH3-only protein, but only in the appropriate cellular environment. This is the first example of a neuron-specific Bcl-2 family member.

Differential NF-kappa B regulation of bcl-x gene expression in hippocampus and basal forebrain in response to hypoxia

Cell death often occurs after hypoxic/ischemic injury to the central nervous system. Changes in levels of the anti-apoptotic Bcl-X(L) protein may be a determining factor in hypoxia-induced neuronal apoptosis. The transcription factor NF-kappa B regulates bcl-x gene expression. In this study, we examined the role of NF-kappa B in the regulation of bcl-x in hypoxia-induced cell death. Rat hippocampus and basal forebrain tissues were collected at different time points after hypoxia (7%O(2), 93% N(2) for 10 or 20 min). We found that 1) hypoxia induced apoptosis in the hippocampus and basal forebrain; 2) the NF-kappa B dimers c-Rel/p50 and p50/p50 bound to the bcl-x promoter NF-kappa B sequence (CS4) in the hippocampus, but only p50/p50 bound to the CS4 sequence in the basal forebrain and hypoxia-induced differential binding patterns of c-Rel/p50 and p50/p50 correlated with the bcl-x expression pattern in the hippocampus; 3) the hypoxia-induced patterns of binding of c-Rel/p50 to the bcl-x promoter CS4 sequence were different from those to the IgG-kappa B enhancer sequence, whereas those of p50/p50 were similar to both sequences; 4) nuclear protein levels of c-Rel, but not p50, correlated with the c-Rel/p50 DNA binding patterns to the bcl-x CS4 site; and 5) there were differential responses to hypoxia among the different NF-kappa B protein subunits. These results suggest that there is a tissue-specific regulation of bcl-x gene expression by NF-kappa B in hypoxia-induced cell death in the hippocampus. The absence of these regulating features in the basal forebrain may account for the early appearance of apoptosis in response to hypoxia as compared with that in hippocampus.

Heterodimerization of Bcl-2 and Bcl-X(L) with Bax and Bad in colorectal cancer

The rate of cell loss owing to apoptosis is mediated by competitive dimerization with selective pairs of cell death antagonists (Bcl-2, Bcl-X(L)) and agonists (Bax, Bad). The aim of this study was to investigate which Bcl-2 family dimers had a critical factor in colorectal cancer. We analyzed the expression of Bcl-2, Bcl-X(L), Bax, and Bad in normal-appearing mucosa and colorectal tumor tissues by Western blotting after immunoprecipitation. Compared with the ratio of Bax-Bcl-2/total Bax in normal mucosa, the ratio was significantly reduced in tumors (p = 0.02). In this series, the low ratio of Bad-Bcl-2/total Bcl-2 was associated with advanced tumor stages (p = 0.02). A reduced heterodimerization of Bax with Bcl-2 may contribute to the development of colorectal cancer. The heterodimerization of Bad with Bcl-2 may be repressed in advanced tumor tissues, and may contribute to tumor growth in colorectal cancer.

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.

Antimycin A mimics a cell-death-inducing Bcl-2 homology domain 3

The Bcl-2-related survival proteins confer cellular resistance to a wide range of agents. Bcl-xL-expressing hepatocyte cell lines are resistant to tumour necrosis factor and anti-cancer drugs, but are more sensitive than isogenic control cells to antimycin A, an inhibitor of mitochondrial electron transfer. Computational molecular docking analysis predicted that antimycin A interacts with the Bcl-2 homology domain 3 (BH3)-binding hydrophobic groove of Bcl-xL. We demonstrate that antimycin A and a Bak BH3 peptide bind competitively to recombinant Bcl-2. Antimycin A and BH3 peptide both induce mitochondrial swelling and loss of DeltaPsim on addition to mitochondria expressing Bcl-xL. The 2-methoxy derivative of antimycin A3 is inactive as an inhibitor of cellular respiration but still retains toxicity for Bcl-xL+ cells and mitochondria. Finally, antimycin A inhibits the pore-forming activity of Bcl-x L in synthetic liposomes, demonstrating that a small non-peptide ligand can directly inhibit the function of Bcl-2-related proteins.

Strategies for manipulating the p53 pathway in the treatment of human cancer

Human cancer progression is driven in part by the mutation of oncogenes and tumour-suppressor genes which, under selective environmental pressures, give rise to evolving populations of biochemically altered cells with enhanced tumorigenic and metastatic potential. Given that human cancers are biologically and pathologically quite distinct, it has been quite surprising that a common event, perturbation of the p53 pathway, occurs in most if not all types of human cancers. The central role of p53 as a tumour-suppressor protein has fuelled interest in defining its mechanism of function and regulation, determining how its inactivation facilitates cancer progression, and exploring the possibility of restoring p53 function for therapeutic benefit. This review will highlight the key biochemical properties of p53 protein that affect its tumour-suppressor function and the experimental strategies that have been developed for the re-activation of the p53 pathway in cancers.

Fas-induced apoptosis is a rare event in Sjögren's syndrome

The aim of this study was to perform a controlled in situ analysis on the incidence of apoptosis, investigate the expression of apoptosis-mediating proteins, and determine the frequency of apoptotic CD4+ and CD8+ T cells in Sjögren's syndrome (SS). The study was extended to patients with atrophy-fibrosis (AF) not related to SS, as well as to a control group. Immunohistochemistry and the terminal deoxynucleotidyl transferase mediated dUTP digoxigenin nick end labeling (TUNEL) method were applied to study the Fas and FasL expression and the incidence of apoptosis in salivary glands (SG) from patients with primary and secondary SS, AF, and controls. These methods were also combined to enable simultaneous detection of apoptotic and CD4+ or CD8+ T cells. Despite abundant expression of Fas and FasL in SS SG, apoptotic cells were not exceeding 1% in the foci of infiltrating mononuclear cells (IMC). Double staining showed that the frequency of apoptosis was low among both CD4+ and CD8+ T cells. Only a few TUNEL+ epithelial cells were found in all patient groups. Fas was expressed predominantly on SS IMC, single SS epithelial cells, and a few normal acinar cells, but not in AF SG. Although FasL was present on SS and AF IMC and epithelial cells, it was rarely detected in normal tissue. Consequently we demonstrate that Fas-induced apoptosis among SS SG is a rare event. Our findings support an earlier hypothesis indicating that IMC seem to be able to escape apoptosis, resulting in foci of inflammatory cells. Notably, however, no obvious correlation can be drawn to previous studies where a high incidence of apoptosis of epithelial cells was proposed as an important mechanism leading to decreased glandular function, which is a hallmark of SS.

The combined functions of proapoptotic Bcl-2 family members bak and bax are essential for normal development of multiple tissues

Proapoptotic Bcl-2 family members have been proposed to play a central role in regulating apoptosis. However, mice lacking bax display limited phenotypic abnormalities. As presented here, bak(-/-) mice were found to be developmentally normal and reproductively fit and failed to develop any age-related disorders. However, when Bak-deficient mice were mated to Bax-deficient mice to create mice lacking both genes, the majority of bax(-/-)bak(-/-) animals died perinatally with fewer than 10% surviving into adulthood. bax(-/-)bak(-/-) mice displayed multiple developmental defects, including persistence of interdigital webs, an imperforate vaginal canal, and accumulation of excess cells within both the central nervous and hematopoietic systems. Thus, Bax and Bak have overlapping roles in the regulation of apoptosis during mammalian development and tissue homeostasis.

Shear stress-dependent expression of apoptosis-regulating genes in endothelial cells

Laminar shear stress exerts potent anti-apoptotic effects. Therefore, we analyzed the influence of laminar shear stress on the expression of apoptosis-regulating genes in human umbilical vein endothelial cells (HUVEC). Application of high levels of laminar shear stress (15 and 30 dyn/cm(2)) decreased the susceptibility of HUVEC to undergo apoptosis, whereas low shear stress (1 dyn/cm(2)) had no effect. These diminished signs of apoptosis were accompanied by a decreased mRNA expression of apoptosis-inducing Fas receptor. Furthermore, mRNA and protein expression of anti-apoptotic, soluble Fas isoform FasExo6Del and anti-apoptotic Bcl-x(L) were induced. Surprisingly, high shear stress also elevated mRNA and protein expression of pro-apoptotic Bak. The shear stress-induced up-regulation of Bcl-x(L) and Bak mRNA can be abrogated by inhibition of the endothelial NO synthase. We propose that altered expression of Bcl-x(L) and the Fas system is involved in the protective effect of laminar shear stress against apoptosis in human endothelial cells.

Expression of bcl-2, bax, and caspase-3 in the brain of the developing rat

Naturally occurring neuronal death (NOND) is generally considered to be apoptotic. Apoptosis is an active form of cell death in which the regulation of specific proteins produces anti- or pro-apoptotic signals. Two of the protein families involved in this regulation are the bcl proteins and caspases. A quantitative immunoblotting technique was used to examine the temporal expression of bcl-2, bax, and two isoforms of caspase 3 (an active 20 kDa isoform and the inactive 32 kDa precursor) throughout the developing neuraxis. Long-Evans rat fetuses were collected on gestational day (G) 16 and G19, and pups were harvested on postnatal day (P) 0, P3, P6, P12, P21, and P30. Brains were divided into five segments: cortex, thalamus, midbrain, medulla/pons, and cerebellum. In general, the expression of bax increased and the ratio of bcl-2 expression to bax expression decreased concurrent with published data on the onset of NOND in a given area. The timing of these events was paralleled by an increase in the expression of active caspase 3. Unlike the bcl proteins, caspase 3 expression returned toward fetal levels as the brain matured. The timing of the changes in bcl protein and caspase expression show that both protein families are involved in promoting neuronal death. Reductions in caspase expression (and not bcl-2 and bax expression) are key to ending the period of NOND.

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.

Bcl-2 family gene products in cerebral ischemia and traumatic brain injury

The proto-oncogene bcl-2 plays a key role in regulating programmed cell death in neurons. The present review discusses the mechanisms by which bcl-2 family genes regulate programmed cell death, and their role in controlling cell death in cerebral ischemia and traumatic brain. Expression of several bcl-2 family members is altered in brain tissues after ischemia and trauma, suggesting that bcl-2 family genes could play a role in determining the fate of injured neurons. Furthermore, alteration of expression of bcl-2 family genes using transgenic approaches, viral vectors, or anti-sense oligonucleotides modifies neuronal cell death and neurological outcome after injury. These data suggest that the activity of bcl-2 family gene products participates in determining cellular and neurologic outcomes in ischemia and trauma. Strategies that either mimic the death-suppressor effects or inhibit the death-promoter effects of bcl-2 family gene products may improve outcome after ischemia and trauma.

Gustatory innervation and bax-dependent caspase-2: participants in the life and death pathways of mouse taste receptor cells

In the adult mouse tongue, an average of 11% of the gustatory receptor cells are replaced each day. In investigating homeostatic cell death mechanisms in gustatory renewing epithelium, we observed that taste receptor cells were selectively immunopositive for the bcl-2 family death factor, Bax, and for the protease Caspase-2 (Nedd2/Ich1). We determined that 8-10% of the taste receptor cells of the vallate papilla were Bax positive and that 11% were Caspase-2 positive. Some of these immunopositive taste cells had apoptotic morphological defects. Within the subset of vallate taste cells immunopositive for either Caspase-2 or Bax, up to 79% coexpressed both death factors. Bax and Caspase-2 first appeared in occasional vallate taste receptor cells on the same postnatal day-the day after birth. bax null mutation markedly reduced gustatory Caspase-2 immunoexpression. These observations suggest that taste cell death pathways utilize p53, Bax, and Caspase-2 to dispose of aged receptor cells. Apart from reducing Caspase-2 expression, Bax deficiency also altered taste organ development. bax(-/-) mice had a more profusely innervated vallate papilla, which grew to be 25% longer and taller, with the mean taste bud containing more than twice the normal number of taste cells. This augmentation of taste organ development with increased innervation is complementary to the well-documented reduction in taste organ development with sparse innervation. We propose that additional taste neurons survived programmed cell death in Bax-deficient mice, thereby providing an inductive boost to vallate gustatory development.

Apoptosis is rapidly triggered by antisense depletion of MCL-1 in differentiating U937 cells

Mcl-1 is a member of the Bcl-2 protein family, which has been shown to delay apoptosis in transfection and/or overexpression experiments. As yet no gene knockout mice have been engineered, and so there is little evidence to show that loss of Mcl-1 expression is sufficient to trigger apoptosis. U937 cells constitutively express the antiapoptotic protein Bcl-2; but during differentiation, in response to the phorbol ester PMA (phorbol 12 β-myristate 13 α-acetate), Mcl-1 is transiently induced. The purpose of this investigation was to determine the functional role played by Mcl-1 in this differentiation program. Mcl-1 expression was specifically disrupted by chimeric methylphosphonate/phosphodiester antisense oligodeoxynucleotides to just 5% of control levels. The depletion of Mcl-1 messenger RNA (mRNA) and protein was both rapid and specific, as indicated by the use of control oligodeoxynucleotides and analysis of the expression of otherBCL2 family members and PMA-induced tumor necrosis factor–α (TNF-α). Specific depletion of Mcl-1 mRNA and protein, in the absence of changes in cellular levels of Bcl-2, results in a rapid entry into apoptosis. Levels of the proapoptotic protein Bax remained unchanged during differentiation, while Bak expression doubled within 24 hours. Apoptosis was detected within 4 hours of Mcl-1 antisense treatment by a variety of parameters including a novel live cell imaging technique allowing correlation of antisense treatment and apoptosis in individual cells. The induction of Mcl-1 is required to prevent apoptosis during differentiation of U937 cells, and the constitutive expression of Bcl-2 is unable to compensate for the loss of Mcl-1.

Apoptosis is rapidly triggered by antisense depletion of MCL-1 in differentiating U937 cells

Mcl-1 is a member of the Bcl-2 protein family, which has been shown to delay apoptosis in transfection and/or overexpression experiments. As yet no gene knockout mice have been engineered, and so there is little evidence to show that loss of Mcl-1 expression is sufficient to trigger apoptosis. U937 cells constitutively express the antiapoptotic protein Bcl-2; but during differentiation, in response to the phorbol ester PMA (phorbol 12 β-myristate 13 α-acetate), Mcl-1 is transiently induced. The purpose of this investigation was to determine the functional role played by Mcl-1 in this differentiation program. Mcl-1 expression was specifically disrupted by chimeric methylphosphonate/phosphodiester antisense oligodeoxynucleotides to just 5% of control levels. The depletion of Mcl-1 messenger RNA (mRNA) and protein was both rapid and specific, as indicated by the use of control oligodeoxynucleotides and analysis of the expression of otherBCL2 family members and PMA-induced tumor necrosis factor–α (TNF-α). Specific depletion of Mcl-1 mRNA and protein, in the absence of changes in cellular levels of Bcl-2, results in a rapid entry into apoptosis. Levels of the proapoptotic protein Bax remained unchanged during differentiation, while Bak expression doubled within 24 hours. Apoptosis was detected within 4 hours of Mcl-1 antisense treatment by a variety of parameters including a novel live cell imaging technique allowing correlation of antisense treatment and apoptosis in individual cells. The induction of Mcl-1 is required to prevent apoptosis during differentiation of U937 cells, and the constitutive expression of Bcl-2 is unable to compensate for the loss of Mcl-1.

Susceptibility to apoptosis is restored in human leukemia HCW-2 cells following induction and stabilization of the apoptotic effector Bak

We demonstrate that treatment of HCW-2 cells, an apoptotic resistant variant of the human HL-60 promyelocytic leukemia cell line with phorbol-12-myristate acetate (PMA), induced differentiation along the monocytic lineage. During this process there was a dramatic increase in the mitochondrial levels of the apoptosis effector, Bak, due to the stabilization of bak mRNA, which was correlated with the sensitization of HCW-2 cells to respond to the apoptotic effect of staurosporine (STS). Treatment of PMA-differentiated, but not undifferentiated, HCW-2 cells induced processing of Bid, substantial efflux of cytochrome c from mitochondria to the cytosol, activation of caspase-3 and apoptosis. The biological significance of the increased mitochondrial Bak in differentiated HCW-2 cells was supported by the finding that transient transfection of a bak cDNA into HCW-2 cells conferred sensitivity to STS-triggered apoptosis, as determined by pro-caspase-3 processing, cytochrome c efflux and DNA fragmentation. Our results suggest that the induction of Bak, upon monocytic differentiation, may be a critical event that regulates the apoptotic sensitivity of differentiated HCW-2 cells. Oncogene (2000) 19, 4108 - 4116

Phytic acid in wheat bran affects colon morphology, cell differentiation and apoptosis

Wheat bran (WB) and its component phytic acid (PA) have both been shown to decrease early biomarkers of colon carcinogenesis, i.e. the PCNA labeling index of cell proliferation and certain aberrant crypt foci parameters. However, it is not known how WB and PA alter other biomarkers of colon cancer risk, such as rate of apoptosis and degree of differentiation, or how they affect colon morphology. Thus, the objectives of this study were to determine the effects of WB on these parameters, to see if PA contributes to these effects and whether there is a difference between endogenous and exogenously added PA. Five groups of azoxymethane-treated male Fischer 344 rats were fed a basal control diet (BD) or BD supplemented with either 25% wheat bran, 25% dephytinized wheat bran (DWB), 25% DWB plus 1.0% PA or 1.0% PA for 100 days. The WB, DWB and PA diets significantly increased the rate of apoptosis and cell differentiation in the whole crypt and the top 40% of the crypt. The WB, DWB and PA diets also significantly increased cell apoptosis in the bottom 60% of the crypt, while all the treatment groups significantly increased cell differentiation versus the BD group in the bottom 60% of the crypt. In addition, the WB, DWB and PA diets decreased the number of crypts per millimeter of colon, while the DWB and PA diets also decreased crypt height measured as number of cells. It is concluded that WB, partly due to its dietary fiber and endogenous PA, and exogenous PA when added to a low fiber diet can increase cell apoptosis and differentiation and favorably affect colon morphology.

Apoptosis induced by the nuclear death domain protein p84N5 is associated with caspase-6 and NF-kappa B activation

Although the mechanisms involved in responses to extracellular or mitochondrial apoptotic signals have received considerable attention, the mechanisms utilized within the nucleus to transduce apoptotic signals are not well understood. We have characterized apoptosis induced by the nuclear death domain-containing protein p84N5. Adenovirus-mediated N5 gene transfer or transfection of p84N5 expression vectors induces apoptosis in tumor cell lines with nearly 100% efficiency as indicated by cellular morphology, DNA fragmentation, and annexin V staining. Using peptide substrates and Western blotting, we have determined that N5-induced apoptosis is initially accompanied by activation of caspase-6. Activation of caspases-3 and -9 does not peak until 3 days after the peak of caspase-6 activity. Expression of p84N5 also leads to activation of NF-kappaB as indicated by nuclear translocation of p65RelA and transcriptional activation of a NF-kappaB-dependent reporter promoter. Changes in the relative expression level of Bcl-2 family proteins, including Bak and Bcl-Xs, are also observed during p84N5-induced apoptosis. Finally, we demonstrate that p84N5-induced apoptosis does not require p53 and is not inhibited by p53 coexpression. We propose that p84N5 is involved in an apoptotic pathway distinct from those triggered by death domain-containing receptors or by p53.

Upregulation of the Bcl-2 family of proteins in end stage heart failure

OBJECTIVES

To elucidate the pattern of expression of four members of the Bcl-2 family of proteins and to correlate this with terminal deoxynucleotidyl transferase [TdT]-mediated dUTP nick end labelling (TUNEL) and DNA fragmentation.

BACKGROUND

Apoptosis has been implicated as a possible mechanism in the development of heart failure. However, the mechanisms involved remain unclear.

METHODS

We have studied the expression of four members of the Bcl-2 family that are involved in the regulation of apoptosis and analyzed DNA fragmentation as a marker of apoptosis and as a biochemical criterion to distinguish between apoptosis and necrosis in dilated cardiomyopathy (DCM), ischemic heart disease (IHD) and normal donors.

RESULTS

Western blot analysis and immunocytochemistry of the proapoptotic and antiapoptotic Bcl-2 proteins demonstrated significantly higher levels of all these proteins in the diseased groups compared with normal donors. Additionally, Bax was significantly higher in the IHD group compared with DCM. Terminal deoxynucleotidyl transferase [TdT]-mediated dUTP nick end labelling analysis demonstrated a significantly higher percentage of TUNEL-positive cells in the diseased groups compared with the control. Genomic DNA extraction of ventricular myocardial tissue showed no demonstrable DNA laddering for any of the groups.

CONCLUSIONS

The significant increases in the levels of the proapoptotic proteins Bak and Bax and the higher percentage of TUNEL-positive cells in both diseased groups suggests the presence of ongoing apoptosis. However, increases in the antiapoptotic proteins, Bcl-2 and Bcl-xL, suggest a possible concomitant, compensatory antiapoptotic mechanism in patients with heart failure.

Different expression patterns of Bcl-2 family genes in breast cancer by estrogen receptor status with special reference to pro-apoptotic Bak gene

Oncogenic and anti-apoptotic Bcl-2 is expressed much less in estrogen receptor alpha (ERalpha) negative breast cancers, which show more malignant phenotypes, than ERalpha-positive, indicating that some other Bcl-2 family member(s) are involved in the apoptotic balance of the cancer cells. We first analyzed mRNA expression of pro-apoptotic Bak and Bax along with that of anti-apoptotic Bcl-2 and Bcl-xL, using breast cancer specimens of 27 patients. Bak mRNA was expressed much less in ERalpha negative breast cancers, along with reduced expression of Bcl-2. Immunostaining of sections of 108 patients confirmed the observation. Next, stable transformants of MCF-7 cells with sense Bak expression vector showed fewer colonies in soft agar compared with the parental cells, while stable introduction of antisense Bak vector enhanced colony formation at lower estradiol concentrations. The reduction of Bak may play important roles in malignant development of breast cancer to acquire estrogen independency, counteracting the reduced Bcl-2.

Expression of BCL-2, BAX and BAK in the trophoblast layer of the term human placenta: a unique model of apoptosis within a syncytium

The regulation of apoptosis in the syncytiotrophoblast is of particular interest because this is the only true syncytial epithelium in human cell biology. Nuclei characteristic of apoptotic cells have been localized to this syncytium especially in association with fibrin-containing fibrinoid deposits. The factors responsible for regulating cell death-like features in the trophoblast syncytium are unknown. We tested the hypothesis that fibrin was required for trophoblast apoptosis. TUNEL (terminal deoxynucleotidyltransferase-mediated dUTP end-labelling) staining to detect DNA fragmentation typical of apoptosis was performed in term human placentae revealing labelled nuclei associated with fibrin-type fibrinoid, as well as labelled nuclei in discrete areas of syncytiotrophoblast without fibrin. We also hypothesized that members of the BCL-2 family of apoptosis-associated proteins contribute to the regulation of syncytiotrophoblast apoptosis. To identify members of this protein family that might regulate trophoblast apoptosis, we assessed expression of three important members of the bcl-2 gene family. We used immunohistochemistry with monoclonal antisera against human BCL-2 and polyclonal antisera against human BAX and BAK to study paraffin-embedded sections of human term placentae (n=5) from uncomplicated pregnancies. The anti-apoptotic BCL-2 protein was expressed throughout the syncytium of normal villi with much less staining in cytotrophoblast. Staining was also seen adjacent to fibrin deposits and in syncytium overlying fibrin deposits. Expression of the pro-apoptotic BAX protein was undetectable in the syncytiotrophoblast, was expressed in rare cytotrophoblast and was prominent in connective tissue and perivascular cells within the villous core. Localization of a second pro-apoptotic protein, BAK, revealed immunoreactivity in isolated areas of intact syncytium of normal villi. Additionally, fibrin deposits were associated with intense BAK staining in both syncytiotrophoblast and cytotrophoblast. From these data, we speculate that modulation of BAK expression is one factor regulating apoptosis in human trophoblast.

Atypical bronchopulmonary carcinoids show a tendency toward increased apoptotic and proliferative activity

BACKGROUND

Bronchopulmonary carcinoid tumors can be divided into typical and atypical carcinoids according to their histologic and clinical features. Atypical carcinoids tend to have less predictable biologic behavior and are associated with a worse prognosis than typical carcinoids. The authors examined apoptosis and the expression of apoptosis regulating proteins Bcl-2, Bax, Bak, and Mcl-1 in 21 typical and 10 atypical bronchopulmonary carcinoid tumors. To find features distinguishing the growth of these types of tumors, the expression of p53 protein and the proliferation marker Ki-67 were also investigated. Finally, the parameters were compared with clinical follow-up data.

METHODS

Thirty-one bronchopulmonary carcinoid tumors were examined by using in situ 3'-end labeling of DNA (TUNEL) for apoptosis and immunohistochemical staining methods for Bcl-2, Bax, Bak, Mcl-1, p53, and Ki-67 in formalin fixed, paraffin embedded tissue specimens.

RESULTS

The apoptotic indices (AIs) were low in general (mean 0.18%), but higher AIs (> 0.5%) were observed significantly more often in atypical than in typical carcinoids (P < 0.008) in association with shortened survival (P < 0. 008). No relation between apoptosis and Bcl-2, Bax, Bak, or Mcl-1 expression was found. Expression of p53 protein was detected in only three atypical carcinoids, which also had significantly higher AIs than p53 negative tumors (P < 0.03). Proliferation rates measured by Ki-67 index were unusually low; the highest proliferation rates were observed in atypical carcinoids. There was a positive correlation between AI and Ki-67 indices (P < 0.01).

CONCLUSIONS

This study suggests that the extent of apoptosis in bronchopulmonary carcinoid tumors is low. This, together with a low proliferation rate and an apparent absence of p53 mutation, enables a benign growth pattern. Some atypical carcinoids with enhanced apoptosis are associated with shortened survival, clearly deviating from typical carcinoids.

Tissue-specific Bcl-2 protein partners in apoptosis: An ovarian paradigm

Apoptosis is an essential physiological process by which multicellular organisms eliminate superfluous cells. An expanding family of Bcl-2 proteins plays a pivotal role in the decision step of apoptosis, and the differential expression of Bcl-2 members and their binding proteins allows the regulation of apoptosis in a tissue-specific manner mediated by diverse extra- and intracellular signals. The Bcl-2 proteins can be divided into three subgroups: 1) antiapoptotic proteins with multiple Bcl-2 homology (BH) domains and a transmembrane region, 2) proapoptotic proteins with the same structure but missing the BH4 domain, and 3) proapoptotic ligands with only the BH3 domain. In the mammalian ovary, a high rate of follicular cell apoptosis continues during reproductive life. With the use of the yeast two-hybrid system, the characterization of ovarian Bcl-2 genes serves as a paradigm to understand apoptosis regulation in a tissue-specific manner. We identified Mcl-1 as the main ovarian antiapoptotic Bcl-2 protein, the novel Bok (Bcl-2-related ovarian killer) as the proapoptotic protein, as well as BOD (Bcl-2-related ovarian death agonist) and BAD as the proapoptotic ligands. The activity of the proapoptotic ligand BAD is regulated by upstream follicle survival factors through its binding to constitutively expressed 14-3-3 or hormone-induced P11. In contrast, the channel-forming Mcl-1 and Bok regulate cytochrome c release and, together with the recently discovered Diva/Boo, control downstream apoptosis-activating factor (Apaf)-1 homologs and caspases. Elucidation of the role of Bcl-2 members and their interacting proteins in the tissue-specific regulation of apoptosis could facilitate an understanding of normal physiology and allow the development of new therapeutic approaches for pathological states.

Activation of apoptosis and its inhibition

The induction of apoptosis, or controlled cell death, by various stimuli has been shown to activate a cascade of endoproteases, called caspases, that cleave numerous cellular proteins necessary for cellular homeostasis. This review discusses this family of proteases together with a variety of mammalian and viral regulatory proteins that act to control this activation.

Simian virus 40 large T antigen binds a novel Bcl-2 homology domain 3-containing proapoptosis protein in the cytoplasm

A 193-kDa SV40 large T antigen (T-Ag)-binding protein, designated p193, was identified and cloned. Inspection of the deduced amino acid sequence revealed the presence of a short motif similar to the Bcl-2 homology (BH) domain 3, suggesting that p193 may be a member of a family of apoptosis promoting proteins containing only BH3 motifs. In support of this, p193 expression promoted apoptosis in NIH-3T3 cells. Deletion of the BH3 motif abolished p193 apoptosis activity. p193-induced apoptosis was antagonized by co-expression of Bcl-X(L). Immune cytologic analysis indicated that p193 is localized to the cytoplasm of transfected cells. p193-induced apoptosis was also antagonized by co-expression of T-Ag, which resulted in the cytoplasmic localization of both proteins. The p193 binding site was mapped to an N-terminal region of T-Ag previously implicated in transforming activity. These results suggest that T-Ag possesses an antiapoptosis activity, independent of p53 sequestration, which is actuated by T-Ag/p193 binding in the cytoplasm.

Racial differences in prostate cancer growth: apoptosis and cell proliferation in Caucasian and African-American patients

BACKGROUND

Epidemiologic evidence reveals striking racial differences in incidence and clinical behavior of prostate cancer among American men. In this study, we assessed the incidence of apoptosis and cell proliferation in prostate cancer specimens from African-American and Caucasian patients in an attempt to identify potential differences in tumor growth determinants between the two ethnic groups.

METHODS

Apoptosis and cell proliferation were analyzed in archival paraffin-embedded prostatic tumors from 44 African-American and 35 Caucasian age-matched men who underwent radical prostatectomy for localized prostate cancer. Both groups had comparable preoperative prostate-specific antigen (PSA) levels, clinical stage, and Gleason scores, and neither group of patients received neoadjuvant therapy prior to surgery. Apoptotic status in prostate tumors was evaluated in situ, using the transferase deoxyuridine end labeling (TUNEL) assay, and the expression profile of two apoptotic proteins, bcl-2 and bax. The proliferative index was determined on the basis of Ki-67 antigen immunoreactivity.

RESULTS

Apoptosis in malignant prostate cells was significantly higher in African American than Caucasian men (11.6% vs. 4.2%, P < 0. 001). Interestingly, the rate of cell proliferation of prostate tumor cells was similar in the two ethnic groups (4.5% and 4.2%). The antiapoptotic protein bcl-2 was detected at significantly higher levels in tumors from Caucasian than African-American patients (40. 8% vs. 31.6%, P < 0.05). Expression of bax, the apoptosis promoter, was consistently high among tumor epithelial cells in specimens from both racial groups (68%).

CONCLUSIONS

These findings provide a novel insight into the molecular determinants of tumor growth that may underlie the ethnic differences in prostate cancer incidence and clinical behavior. Downregulation of bcl-2 expression may be potentially responsible for the loss of apoptotic control in prostate tumors from African-American men. This study may have significant clinical implications in the development of novel diagnostic approaches for biologically aggressive prostate cancer from diverse racial origin.

Apoptosis and the nervous system

Apoptosis is now recognized as a normal feature in the development of the nervous system and may also play a role in neurodegenerative diseases and aging. This phenomenon has been investigated intensively during the last 6-7 years, and the progress made in this field is reviewed here. Besides a few in vivo studies, a variety of neuronal preparations from various parts of the brain, the majority of which were primary cultures, and some cell lines have been investigated. Several apoptosis-inducing agents have been identified, and these include lack of neurotrophic support, neurotransmitters, neurotoxicants, modulators of protein phosphorylation and calcium homeostasis, DNA-damaging agents, oxidative stress, nitric oxide, and ceramides. The precise signaling cascade is not well established, and there are lacunae in many suggested pathways. However, it appears certain that the Bcl family of proteins is involved in the apoptotic pathway, and these proteins in turn affect the processing of interleukin-1beta converting enzyme (ICE)/caspases. The available evidence suggests that there may be several apoptotic pathways that may depend on the cell type and the inducing agent, and most of the pathways may converge at the ICE/caspases step.