Cloning of a bcl-2 homologue by interaction with adenovirus E1B 19K

Release of cytochrome c from mitochondria precedes Bax translocation/activation in Triton X-100-induced apoptosis

The precise mechanisms by which sublytic concentrations of detergents induce apoptosis remain unclear. Recent studies reported the ability of nonionic detergents such as Triton X-100 to induce conformational change of Bax to the active form in vitro. Here we investigated whether activation of Bax might play a role in Triton X-100-induced apoptosis in cells. Although Bax translocation/activation was inhibited by caspase inhibitors, cytochrome c release from mitochondria was not affected in Triton X-100-induced apoptosis in U-937 cells. These results demonstrate that translocation/activation of Bax occurs downstream of cytochrome c release and caspase activation in Triton X-100-induced apoptosis.

Effect of hypoxia on expression of apoptotic proteins in nuclear, mitochondrial and cytosolic fractions of the cerebral cortex of newborn piglets: the role of nuclear Ca++ -influx

We have shown that hypoxia results in increased influx of nuclear Ca++ and increased expression of nuclear apoptotic proteins. The present study tests the hypothesis that hypoxia alters the distribution of pro-apoptotic proteins Bad and Bax, and the anti-apoptotic proteins Bcl-xl, and Bcl-2 in the nuclear, mitochondrial and cytosolic compartments of the cerebral cortex of newborn piglets and the administration of Clonidine, an inhibitor of high affinity nuclear Ca++ -ATPase, will prevent the hypoxia-induced increase in apoptotic proteins' expression. Studies were conducted in 19 newborn piglets, 6 normoxic (Nx), 7 hypoxic and 6 Clonidine-treated hypoxic (Hx-Clo). Tissue hypoxia was documented biochemically by measuring cerebral tissue ATP and phosphocreatine (PCr) levels. Bax and Bad protein expression increased in all the three compartments during hypoxia, while there was no significant change in the expression of anti-apoptotic proteins Bcl-2 and Bcl-xl. In Clonidine pretreated hypoxic group, the hypoxia-induced increased expression of pro-apoptotic proteins Bad and Bax was prevented in all the three fractions. We conclude that hypoxia results in increased expression of pro-apoptotic proteins in nuclear, mitochondrial and cytosolic compartments and that the increased expression of pro-apoptotic proteins during hypoxia is nuclear Ca++ -influx-dependent. We propose that during hypoxia the increased ratio of (pro-apoptotic Bad and Bax/anti-apoptotic Bcl-xl and Bcl-2) in all the three compartments, will lead to altered mitochondrial and nuclear membrane permeability as well as caspase-9 activation in the cytosolic compartment.

Anti-apoptotic genes Aven and E1B-19K enhance performance of BHK cells engineered to express recombinant factor VIII in batch and low perfusion cell culture

The engineering of production cell lines to express anti-apoptotic genes has been pursued in recent years due to potential process benefits, including enhanced cell survival, increased protein expression, and improved product quality. In this study, a baby hamster kidney cell line secreting recombinant factor VIII (BHK-FVIII) was engineered to express the anti-apoptotic genes Aven and E1B-19K. In high cell density shake flask culture evaluation, 11 clonal cell lines expressing either E1B-19K or a combination of Aven and E1B-19K showed improved survival compared to both parental and blank vector cell line controls. These cell lines exhibited lower caspase-3 activation and reduced Annexin-V binding compared to the controls. Parental and blank vector cell lines were less than 50% viable after 48 h of exposure to thapsigargin while cell lines expressing E1B-19K with or without Aven maintained viabilities approaching 90%. Subsequently, the best Aven-E1B-19K candidate cell line was compared to the parental cell line in 12-L perfusion bioreactor studies. Choosing the appropriate perfusion rates in bioreactors is a bioprocess optimization issue, so the bioreactors were operated at sequentially lower specific perfusion rates, while maintaining a cell density of 2 x 10(7) viable cells/mL. The viability of the parental cell line declined from nearly 100% at a perfusion rate of 0.5 nL/cell/day to below 80% viability, with caspase-3 activity exceeding 15%, at its lower perfusion limit of 0.15 nL/cell/day. In contrast, the Aven-E1B-19K cell line maintained an average viability of 94% and a maximum caspase-3 activity of 2.5% even when subjected to a lower perfusion minimum of 0.1 nL/cell/day. Factor VIII productivity, specific growth rate, and cell size decreased for both cell lines at lower perfusion rates, but the drop in all cases was larger for the parental cell line. Specific consumption of glucose and glutamine and production of lactate were consistently lower for the Aven-E1B-19K culture. Furthermore, the yield of ammonia from glutamine increased for the Aven-E1B-19K cell line relative to the parent to suggest altered metabolic pathways following anti-apoptosis engineering. These results demonstrate that expression of anti-apoptotic genes Aven and E1B-19K can increase the stability and robustness of an industrially relevant BHK-FVIII mammalian cell line over a wide range of perfusion rates.

p53 initiates apoptosis by transcriptionally targeting the antiapoptotic protein ARC

p53 plays an important role in regulating apoptosis. However, the molecular mechanism by which it initiates the apoptotic program still remains to be fully understood. Here, we report that p53 can transcriptionally target the antiapoptotic protein, apoptosis repressor with caspase recruitment domain (ARC). Our results show that reactive oxygen species and anoxia lead to the up-regulation of p53 expression. Concomitantly, ARC is down-regulated at both the protein and mRNA levels. Knockdown of p53 expression can attenuate the decreases in ARC protein and mRNA levels, indicating that ARC down-regulation is a consequence of p53 activation. Strikingly, p53-induced ARC repression occurs in a transcription-dependent manner. We further demonstrate that the p53 up-regulated modulator of apoptosis (PUMA) and Bad are up-regulated in response to the stimulation with reactive oxygen species or anoxia, and p53 is responsible for their up-regulation. ARC can interact with PUMA or Bad via its N terminus. Such an interaction displaces the association of PUMA or Bad with Bcl-2. ARC repression by p53 leads to its failure to counteract the proapoptotic activity of PUMA and Bad. Thus, our data reveal a novel p53 apoptotic pathway in which it initiates apoptosis by transcriptionally repressing ARC.

Interaction of the C-terminal domain of Bcl-2 family proteins with model membranes

Bcl-2 family proteins are involved in the cell homeostasis by regulating programmed cell death. Some of these proteins promote apoptosis, while others inhibit the same process. The C-terminal hydrophobic domain of some of these proteins is predicted to be involved in anchoring them to a variety of cell membranes, such as mitochondrial, endoplasmic reticulum and nuclear membranes. We have used five synthetic peptides imitating the C-terminal domain from both anti-apoptotic (Bcl-2) and pro-apoptotic members (Bak, Bax, and two mutants of this last protein) of this family to study their interaction with model membranes. Some differences were detected in the interaction with these peptides. The addition of all the peptides to large unilamellar vesicles destabilized them and released encapsulated carboxyfluorescein to different degrees, so that fluidity and the increase in negative curvature favoured the extent in the release of carboxyfluorescein. Bcl-2-C and Bax-C peptides produced the highest release levels in most cases, while BaxS184K-C was the least efficient in this respect. These results indicate that these C-terminal domains are able to insert themselves in the membranes, each in a different way that is probably related with their different way which can be related to their differing locations within the cell and their different roles in regulating apoptosis.

Fowlpox virus encodes a Bcl-2 homologue that protects cells from apoptotic death through interaction with the proapoptotic protein Bak

Poxviruses are renowned for encoding numerous immunomodulatory proteins capable of undermining potent immune defenses. One effective barrier against infection is apoptosis, a process controlled at the mitochondria by pro- and antiapoptotic members of the highly conserved Bcl-2 family of proteins. Although poxviruses are known to encode an array of effective inhibitors of apoptosis, members of the Avipoxvirus genus, which includes fowlpox virus, encode proteins with Bcl-2 homology. Here, we show that FPV039, a fowlpox virus protein with limited Bcl-2 homology, inhibited apoptosis in response to a variety of cytotoxic stimuli, including virus infection itself. Similar to other antiapoptotic Bcl-2 proteins, FPV039 localized predominantly to the mitochondria in both human and chicken cells and protected human cells from tumor necrosis factor alpha-induced loss of the mitochondrial membrane potential. In addition, coimmunoprecipitation revealed that FPV039 interacted constitutively with the proapoptotic Bcl-2 protein, Bak, in both human and chicken cells. Concordantly, FPV039 also inhibited apoptosis induced by the transient overexpression of Bak. To confirm these results in the context of virus infection, we generated a recombinant vaccinia virus lacking F1L, the endogenous apoptotic inhibitor in vaccinia virus, and expressing FPV039. In the context of vaccinia virus infection, FPV039 retained the ability to localize to the mitochondria and interacted with Bak. Moreover, FPV039 prevented the activation of Bak and protected infected cells from apoptosis induced by staurosporine and virus infection. Together, our data indicate that FPV039 is a functional Bcl-2 homologue that inhibits apoptosis by neutralizing the proapoptotic Bcl-2 family member Bak.

Curcumin as chemosensitizer

This overview presents curcumin as a significant chemosensitizer in cancer chemotherapy. Although the review focuses on curcumin and its analogues on multidrug resistance (MDR) reversal, the relevance of curcumin as a nuclear factor (NF)-KB blocker and sensitizer of many chemoresistant cancer cell lines to chemotherapeutic agents will also be discussed. One of the major mechanisms of MDR is the enhanced ability of tumor cells to actively efflux drugs, leading to a decrease in cellular drug accumulation below toxic levels. Active drug efflux is mediated by several members of the ATP-binding cassette (ABC) superfamily of membrane transporters, which have now been subdivided into seven families designated A through G. Among these ABC families, the classical MDR is attributed to the elevated expression of ABCB1 (Pgp), ABCC1 (MRP1), and ABCG2 (MXR). The clinical importance of Pgp, MRP1, and MXR for MDR and cancer treatment has led to the investigation of the inhibiting properties of several compounds on these transporters. At present, due in part to the disappointing results associated with the many side effects of synthetic modulators that have been used in clinical trials, current research efforts are directed toward the identification of novel compounds, with attention to dietary natural products. The advantage is that they exhibit little or virtually no side effects and do not further increase the patient's medication burden.

Apoptotic gene expression in Alzheimer's disease hippocampal tissue

Alzheimer's disease (AD) is the major cause of dementia, accounting for 50% to 70% of the late-onset patients, with 17 to 20 million affected. It is characterized by neurofibrillary tangles, neuronal loss, and amyloid plaques in tissues of the cortex, hippocampus, and amygdala. Apoptosis or programmed cell death appears in the progression of AD. In this study, we investigated the gene expression of 14 apoptotic genes (E2F1, p21/WAF, ICE-LAP3, Fas Antigen, CPP-32, GADD153, ICE-beta, c-Fos, c-Jun, Bax-alpha, Bcl-2, Bcl-(x)L, BAK, and p53) in 5 normal and 6 AD human hippocampal tissues, using reverse transcription-polymerase chain reaction. Our results show an upregulation of gene expression in AD patients for c-Fos and BAK. ICE-beta, c-Jun, Bax-alpha, Bcl-x(L), p53, and GADD153 were found to be upregulated in some AD samples but were not detected or downregulated in other AD or normal samples. No gene expression was found for E2F1 , p21/WAF, ICE-LAP3, Fas Antigen, CPP32, or Bcl-2. These results indicate significant increases in c-Fos , c-Jun, and Bak; therefore, we suggest that these genes may be critical in the apoptotic cascades of AD.

DNA-damage response network at the crossroads of cell-cycle checkpoints, cellular senescence and apoptosis

Tissue homeostasis requires a carefully-orchestrated balance between cell proliferation, cellular senescence and cell death. Cells proliferate through a cell cycle that is tightly regulated by cyclin-dependent kinase activities. Cellular senescence is a safeguard program limiting the proliferative competence of cells in living organisms. Apoptosis eliminates unwanted cells by the coordinated activity of gene products that regulate and effect cell death. The intimate link between the cell cycle, cellular senescence, apoptosis regulation, cancer development and tumor responses to cancer treatment has become eminently apparent. Extensive research on tumor suppressor genes, oncogenes, the cell cycle and apoptosis regulatory genes has revealed how the DNA damage-sensing and -signaling pathways, referred to as the DNA-damage response network, are tied to cell proliferation, cell-cycle arrest, cellular senescence and apoptosis. DNA-damage responses are complex, involving "sensor" proteins that sense the damage, and transmit signals to "transducer" proteins, which, in turn, convey the signals to numerous "effector" proteins implicated in specific cellular pathways, including DNA repair mechanisms, cell-cycle checkpoints, cellular senescence and apoptosis. The Bcl-2 family of proteins stands among the most crucial regulators of apoptosis and performs vital functions in deciding whether a cell will live or die after cancer chemotherapy and irradiation. In addition, several studies have now revealed that members of the Bcl-2 family also interface with the cell cycle, DNA repair/recombination and cellular senescence, effects that are generally distinct from their function in apoptosis. In this review, we report progress in understanding the molecular networks that regulate cell-cycle checkpoints, cellular senescence and apoptosis after DNA damage, and discuss the influence of some Bcl-2 family members on cell-cycle checkpoint regulation.

Enhanced cell culture performance using inducible anti-apoptotic genes E1B-19K and Aven in the production of a monoclonal antibody with Chinese hamster ovary cells

Mammalian cells are used for the production of numerous biologics including monoclonal antibodies. Unfortunately, mammalian cells can lose viability at later stages in the cell culture process. In this study, the effects of expressing the anti-apoptosis genes, E1B-19K and Aven, separately and in combination on cell growth, survival, and monoclonal antibody (MAb) production were investigated for a commercial Chinese Hamster Ovary (CHO) mammalian cell line. CHO cells were observed to undergo apoptosis following a model insult, glucose deprivation, and at later stages of batch cell culture. The CHO cell line was then genetically modified to express the anti-apoptotic proteins E1B-19K and/or Aven using an ecdysone-inducible expression system. Stable transfected pools induced to express Aven or E1B-19K alone were found to survive 1-2 days longer than the parent cell line following glucose deprivation while the expression of both genes in concert increased cell survival by 3 days. In spinner flask batch studies, a clonal isolate engineered to express both anti-apoptosis genes exhibited a longer operating lifetime and higher final MAb titer as a result of higher viable cell densities and viabilities. Interestingly, survival was increased in the absence of an inducer, most likely as a result of leaky expression of the anti-apoptosis genes confirmed in subsequent PCR studies. In fed-batch bioreactors, the expression of both anti-apoptosis genes resulted in higher growth rates and cell densities in the exponential phase and significantly higher viable cell densities, viabilities, and extended survival during the post-exponential phase. As a result, the integral of viable cells (IVC) was between 40 and 100% higher for cell lines engineered to express both Aven and E1B-19K in concert, and the operational lifetime of the fed-batch bioreactors was increased from 2 to 5 days. The maximum titers of MAb were also increased by 40-55% for bioreactors containing cells expressing Aven and E1B-19K. These increases in volumetric productivity arose primarily from enhancements in viable cell density over the course of the fed-batch culture period since the specific productivities for the cells expressing anti-apoptosis genes were comparable or slightly lower than the parental hosts. These results demonstrate that expression of anti-apoptosis genes can enhance culture performance and increase MAb titers for mammalian CHO cell cultures especially under conditions such as extended fed-batch bioreactor operation.

Molecular targets in cerebral ischemia for developing novel therapeutics

Cerebral ischemia (stroke) triggers a complex series of biochemical and molecular mechanisms that impairs the neurologic functions through breakdown of cellular integrity mediated by excitotoxic glutamatergic signalling, ionic imbalance, free-radical reactions, etc. These intricate processes lead to activation of signalling mechanisms involving calcium/calmodulin-dependent kinases (CaMKs) and mitogen-activated protein kinases (MAPKs) such as extracellular signal-regulated kinase (ERK), p38, and c-Jun N-terminal kinase (JNK). The distribution of these transducers bring them in contact with appropriate molecular targets leading to altered gene expression, e.g. ERK and JNK mediated early gene induction, responsible for activation of cell survival/damaging mechanisms. Moreover, inflammatory reactions initiated at the neurovascular interface and alterations in the dynamic communication between the endothelial cells, astrocytes and neurons are thought to substantially contribute to the pathogenesis of the disease. The damaging mechanisms may proceed through rapid nonspecific cell lysis (necrosis) or by active form of cell demise (apoptosis or necroptosis), depending upon the severity and duration of the ischemic insult. A systematic understanding of these molecular mechanisms with prospect of modulating the chain of events leading to cellular survival/damage may help to generate the potential strategies for neuroprotection. This review briefly covers the current status on the molecular mechanisms of stroke pathophysiology with an endeavour to identify potential molecular targets such as targeting postsynaptic density-95 (PSD-95)/N-methyl-d-aspartate (NMDA) receptor interaction, certain key proteins involved in oxidative stress, CaMKs and MAPKs (ERK, p38 and JNK) signalling, inflammation (cytokines, adhesion molecules, etc.) and cell death pathways (caspases, Bcl-2 family proteins, poly (ADP-ribose) polymerase-1 (PARP-1), apoptosis-inducing factor (AIF), inhibitors of apoptosis proteins (IAPs), heat shock protein 70 (HSP70), receptor interacting protein (RIP), etc., besides targeting directly the genes itself. However, selecting promising targets from various signalling cascades, for drug discovery and development is very challenging, nevertheless such novel approaches may lead to the emergence of new avenues for therapeutic intervention in cerebral ischemia.

Bcl-2 Expression as a Predictive Marker of Hormone-Refractory Prostate Cancer Treated with Taxane-Based Chemotherapy

PURPOSE

Bcl-2 inhibits apoptosis, and its overexpression is associated with hormone refractory prostate cancer (HRPC). Bak and Bax are in the Bcl-2 family and counteract the antiapoptotic function of Bcl-2. Taxane-induced (paclitaxel and its analogue docetaxel) phosphorylation of Bcl-2 abolishes the potential antiapoptotic effect of Bcl-2. We hypothesized that (a) survival benefit in HRPC patients treated with taxanes is determined by the presence of Bcl-2 protein and (b) altered expression of Bak and Bax protein caused by genetic mutation is associated with biological aggressiveness of prostate cancer.

EXPERIMENTAL DESIGN

Forty localized prostate cancer and 30 HRPC cases were used in this study. Surgical specimens of localized prostate cancer and biopsy specimens of HRPC were used for immunostaining of Bcl-2, Bak, and Bax as well as DNA extraction. Mutations in the Bak and Bax genes were screened by single-strand conformational polymorphism, and confirmed by direct DNA sequencing.

RESULTS

Bcl-2-positive HRPC showed longer cause-specific survival in comparison with the counterparts. Multivariate analysis revealed that the level of Bcl-2 expression before treatment with taxane-based chemotherapy was an independent predictor for cause-specific survival (P < 0.01) and baseline prostate-specific antigen level was an independent predictor for progression-free survival (P < 0.01). Bax gene mutation was found in only one HRPC specimen.

CONCLUSIONS

Bcl-2 expression in addition to prostate-specific antigen measurement before treatment could identify HRPC patients who may benefit from taxane-based chemotherapy. Mutation of the Bak and Bax genes is a rare event in prostate cancer.

RNAi suppression of Bax and Bak enhances viability in fed-batch cultures of CHO cells

Bcl-2 family proteins play a crucial role in the regulation of the mitochondrial pathway that leads to apoptosis. Members of the Bcl-2 family can be divided into the anti-apoptotic proteins such as Bcl-2 and Bcl-X(L), and the pro-apoptotic proteins such as Bax and Bak and the BH3-only proteins. In this study, siRNA constructs to silence the Bax and Bak genes in Chinese hamster ovary (CHO) cells were generated. Stable CHO cell lines in which the expression of Bax and Bak were significantly knocked down were screened by Western blot analysis and confirmed by RT-PCR. CHO cells with both Bax and Bak knocked down showed a clear resistance against cytotoxic lectins and UV irradiation-induced apoptosis. Compared to original CHO-K1 cells, these cells also survived longer when cultured under extreme conditions such as complete nutrient depletion or in high-osmolality medium. CHO cells with both Bax and Bak genes knocked down displayed an extended lifespan as well as higher viable cell densities in fed-batch cultures, both in adherent form on microcarrier beads and in suspension. The IFN-gamma productivity by a rCHO IFN-gamma cell line in which both Bak and Bax were knocked down increased by 35% compared to the control cells. These results indicate that the genetic inactivation of Bax and Bak in recombinant CHO cells can be an effective strategy in delaying the onset of apoptosis in batch and fed-batch cultures.

Mechanisms of apoptosis regulation by viral oncogenes in infection and tumorigenesis

Apoptosis mediated by the proapoptotic BCL-2 family members BCL-2-associated X-protein (BAX) and BCL-2 antagonist/killer (BAK) is part of the antiviral response at the cellular level to limit virus replication. Viruses, in turn, have evolved to encode antiapoptotic BCL-2 homologs (v-BCL-2s) to prevent the premature death of the infected host cell to sustain virus replication. These same v-BCL-2 proteins cooperate with loss of retinoblastoma protein and p53 tumor suppressor function, by inactivating the BAX and BAK apoptotic pathway to promote epithelial solid tumor growth and resistance to chemotherapy. Analogously to infected cells, failure of apoptosis in tumors permits the survival of abnormal, damaged cells displaying chromosome instability that may further promote tumor progression. Thus, both infected cells and tumor cells require inhibition of the apoptotic host defense mechanism, the insights from which can be exploited for therapy development.

Accelerated degradation of FADD and procaspase 8 in cells expressing human papilloma virus 16 E6 impairs TRAIL-mediated apoptosis

Viruses have developed sophisticated strategies to evade host defenses and facilitate the production and spread of progeny. In this study, we show that transfection of the human papillomavirus (HPV) 16 E6 oncogene into HCT116 cells provides protection from tumor necrosis factor-related apoptosis inducing ligand (TRAIL)-mediated apoptosis. Additionally, we demonstrate that the protection provided by E6 is dose-dependent because higher levels of E6 provide greater protection. The mechanism underlying this protection involves a rapid reduction in the protein levels of both Fas-associated death domain (FADD) and procaspase 8, which results in suppression of the activation of caspases 8, 3 and 2. Interestingly, E6 does not interfere with the mitochondrial apoptotic pathway even though HCT116 cells have been classified as type II cells with regard to TRAIL signaling. These findings demonstrate that E6 has a more generalized effect on signaling by death ligands than was previously thought and support the notion that E6 can utilize p53-independent mechanisms to modulate cell survival.

A new description of cellular quiescence

Cellular quiescence, defined as reversible growth/proliferation arrest, is thought to represent a homogenous state induced by diverse anti-mitogenic signals. We used transcriptional profiling to characterize human diploid fibroblasts that exited the cell cycle after exposure to three independent signals—mitogen withdrawal, contact inhibition, and loss of adhesion. We show here that each signal caused regulation of a unique set of genes known to be important for cessation of growth and division. Therefore, contrary to expectation, cells enter different quiescent states that are determined by the initiating signal. However, underlying this diversity we discovered a set of genes whose specific expression in non-dividing cells was signal-independent, and therefore representative of quiescence per se, rather than the signal that induced it. This fibroblast “quiescence program” contained genes that enforced the non-dividing state, and ensured the reversibility of the cell cycle arrest. We further demonstrate that one mechanism by which the reversibility of quiescence is insured is the suppression of terminal differentiation. Expression of the quiescence program was not simply a downstream consequence of exit from the cell cycle, because key parts, including those involved in suppressing differentiation, were not recapitulated during the cell cycle arrest caused by direct inhibition of cyclin-dependent kinases. These studies form a basis for understanding the normal biology of cellular quiescence.

Transcriptional profiling of fibroblasts induced to exit the cell cycle by distinct signals reveals distinctions and commonalities in the pathways to cellular quiescence.

Over-expression of p53/BAK in aseptic loosening after total hip replacement

Particle-induced osteolysis is a major cause of aseptic loosening after total joint replacement. The possible induction of apoptosis has not been addressed in great detail. Thus far, it has been shown that ceramic and polyethylene particles can induce apoptosis of macrophages in vitro. The purpose of this study was to test the hypothesis that wears debris generated from total hip arthroplasty could induce cellular damage and apoptosis in vivo. We therefore determined by immunohistochemical methods if increased expression of p53, an important transcription factor, and BAK and Bcl-2, two important regulators of apoptosis, can be found in interface membranes and capsules of hips with aseptically loose implants. Strongly positive immunohistochemical staining for p53 and BAK was found in peri-implant tissues from patients with aseptic hip implant loosening. Differentiation of various cell types showed that macrophages stained positive for p53 in all capsule and interface specimens. p53 was frequently detected in giant cells. Positive staining of BAK in macrophages and giant cells was seen in all specimens. Some positive reactions were observed in fibroblasts, only two of 19 cases stained for p53 and three cases for BAK within synovial cells. Positive macrophages and giant cells were localized around polyethylene particles. While T-lymphocytes showed a regular BAK-staining, the other leukocytes were negative. Statistical analyses showed significant positive correlations (p < 0.001) between the presence of polyethylene and metal debris and the expression of BAK and p53. Polyethylene particles were surrounded by more positive macrophages and giant cells than were metal particles, indicating that polyethylene debris may be a stronger inductor of cell cycle arrest and apoptosis than metal debris. In this study apoptosis of macrophages, giant cells and T-lymphocytes in capsules and interface membranes of patients with aseptic hip implant loosening has been demonstrated in vivo. It is possible that the apoptotic cascade could evolve as a novel therapeutic target to prevent particle-induced osteolysis.

Induction of thymocyte apoptosis by systemic administration of concanavalin A in mice: role of TNF-alpha, IFN-gamma and glucocorticoids

Administration of concanavalin A (Con A) is a well-established model of acute immune-mediated hepatitis. Here, we demonstrate that intravenous injection of Con A in mice induces profound thymic atrophy. Compared to liver damage, the kinetics of Con A-induced thymic atrophy is slower and more prolonged; the nadir in thymocyte number is reached 4 days after Con A injection, whereas peak transaminase levels are observed at 12-24 h. Marked alterations in the ratio of CD4+ and CD8+cells in the thymus and spleen and significantly increased rates of thymocyte and splenocyte apoptosis are observed. Neutralization of the cytokines TNF-alpha or IFN-gamma, which protects mice from Con A-induced hepatitis, prevents thymic atrophy as well as alterations in CD4+ and CD8+ cell numbers and apoptosis rates. However, neither TNF-alpha nor IFN-gamma are detectable in thymocyte lysates after Con A injection, whereas both cytokines are present in liver, spleen and serum. Administration of the glucocorticoid receptor antagonist mifepristone does not prevent thymic atrophy, thus ruling out a possible contribution of endogenous glucocorticoids. Con A-induced thymic atrophy is accompanied by down-regulation of Bcl-2 expression in the thymus, which is prevented by neutralization of TNF-alpha or IFN-gamma. These data demonstrate that the thymus is a critical target organ of Con A-induced inflammation; the effects of Con A on the thymus are mediated by extrathymic production of TNF-alpha and IFN-gamma, but not by glucocorticoids.

The role of apoptosis in the development and function of T lymphocytes

Apoptosis plays an essential role in T cell biology. Thymocytes expressing nonfunctional or autoreactive TCRs are eliminated by apoptosis during development. Apoptosis also leads to the deletion of expanded effector T cells during immune responses. The dysregulation of apoptosis in the immune system results in autoimmunity, tumorogenesis and immunodeficiency. Two major pathways lead to apoptosis: the intrinsic cell death pathway controlled by Bcl-2 family members and the extrinsic cell death pathway controlled by death receptor signaling. These two pathways work together to regulate T lymphocyte development and function.

Biological function of the vaccinia virus Z-DNA-binding protein E3L: gene transactivation and antiapoptotic activity in HeLa cells

The vaccinia virus (VV) E3L protein is essential for virulence and has anti-apoptotic activity. In mice, Z-DNA-binding activity of the N-terminal domain of E3L (Z alpha) is necessary for viral lethality. Here, we report that inhibition of hygromycin-B-induced apoptosis in HeLa cells depends on Z-DNA binding of the E3L Z alpha domain. Z-DNA-binding domains of other proteins are equally effective in blocking apoptosis. Using a transient reporter assay, we demonstrate transactivation of human IL-6, nuclear factor of activated T cells (NF-AT), and p53 genes by E3L. This activation also requires Z-DNA binding of the N-terminal domain of E3L. Overall, this work suggests that the important role of E3L in VV pathogenesis involves modulating expression of host cellular genes at the transcriptional level and inhibiting apoptosis of host cells through Z-DNA binding.

Mitochondrial localization of p53 during adenovirus infection and regulation of its activity by E1B-19K

Recent results have revealed that the p53 tumor suppressor protein possesses a direct transcription-independent apoptotic activity. During apoptosis induced by genotoxic stress, a small fraction of p53 is targeted to mitochondria where it initiates apoptosis by causing mitochondrial dysfunction. In adenovirus-infected cells, the expression of E1A protein enhances the accumulation of p53 during early phases of infection and during late times after infection, it is targeted for degradation by the combined action of E1B-55K and E4-orf6 proteins. The functional significance of E1A-mediated accumulation of p53 during early phases of viral replication is not known. Our studies with isogenic epithelial cell lines that differ only on the status of p53 indicate that Ad infection induces apoptosis by p53-dependent and -independent pathways and both pathways are suppressed by E1B-19K. We show that during early phase of Ad infection, a fraction of p53 is targeted to the mitochondria. In virus infected cells, a large fraction of the viral antiapoptosis protein E1B-19K is also localized in mitochondria during early and late phases of infection. Coimmunoprecipitation analysis has revealed that p53 and E1B-19K form a complex in mitochondria. The interaction of 19K involves two noncontiguous regions located around amino-acid residues 14-15 and 123-124. On p53, the mutations within the DNA-binding domain reduce interaction with E1B-19K. Our studies also suggest that 19K may additionally complex with the multidomain mitochondrial proapoptotic protein BAK, thereby reducing the level of p53 interaction with BAK. We suggest that p53-induced apoptosis may be important for efficient cell lysis and viral spread and that E1B-19K may neutralize the apoptotic activity of p53 at multiple levels.

The mitochondrial death pathway and cardiac myocyte apoptosis

Apoptosis has been causally linked to the pathogenesis of myocardial infarction and heart failure in rodent models. This death process is mediated by two central pathways, an extrinsic pathway involving cell surface receptors and an intrinsic pathway using mitochondria and the endoplasmic reticulum. Each of these pathways has been implicated in myocardial pathology. In this review, we summarize recent advances in the understanding of the intrinsic pathway and how it relates to cardiac myocyte death and heart disease.

Proapoptotic Bak is sequestered by Mcl-1 and Bcl-xL, but not Bcl-2, until displaced by BH3-only proteins

Commitment of cells to apoptosis is governed largely by the interaction between members of the Bcl-2 protein family. Its three subfamilies have distinct roles: The BH3-only proteins trigger apoptosis by binding via their BH3 domain to prosurvival relatives, while the proapoptotic Bax and Bak have an essential downstream role involving permeabilization of organellar membranes and induction of caspase activation. We have investigated the regulation of Bak and find that, in healthy cells, Bak associates with Mcl-1 and Bcl-x(L) but surprisingly not Bcl-2, Bcl-w, or A1. These interactions require the Bak BH3 domain, which is also necessary for Bak dimerization and killing activity. When cytotoxic signals activate BH3-only proteins that can engage both Mcl-1 and Bcl-x(L) (such as Noxa plus Bad), Bak is displaced and induces cell death. Accordingly, the BH3-only protein Noxa could bind to Mcl-1, displace Bak, and promote Mcl-1 degradation, but Bak-mediated cell death also required neutralization of Bcl-x(L) by other BH3-only proteins. The results indicate that Bak is held in check solely by Mcl-1 and Bcl-x(L) and induces apoptosis only if freed from both. The finding that different prosurvival proteins have selective roles has notable implications for the design of anti-cancer drugs that target the Bcl-2 family.

Mitochondria as Functional Targets of Proteins Coded by Human Tumor Viruses

Molecular analyses of tumor virus-host cell interactions have provided key insights into the genes and pathways involved in neoplastic transformation. Recent studies have revealed that the human tumor viruses Epstein-Barr virus (EBV), Kaposi's sarcoma-associated herpesvirus (KSHV), human papillomavirus (HPV), hepatitis B virus (HBV), hepatitis C virus (HCV), and human T-cell leukemia virus type 1 (HTLV-1) express proteins that are targeted to mitochondria. The list of these viral proteins includes BCL-2 homologues (BHRF1 of EBV; KSBCL-2 of KSHV), an inhibitor of apoptosis (IAP) resembling Survivin (KSHV K7), proteins that alter mitochondrial ion permeability and/or membrane potential (HBV HBx, HPV E[wedge]14, HCV p7, and HTLV-1 p13(II)), and K15 of KSHV, a protein with undefined function. Consistent with the central role of mitochondria in energy production, cell death, calcium homeostasis, and redox balance, experimental evidence indicates that these proteins have profound effects on host cell physiology. In particular, the viral BCL-2 homologues BHRF1 and KSBCL-2 inhibit apoptosis triggered by a variety of stimuli. HBx, p7, E1[wedge]4, and p13(II) exert powerful effects on mitochondria either directly due to their channel-forming activity or indirectly through interactions with endogenous channels. Further investigation of these proteins and their interactions with mitochondria will provide important insights into the mechanisms of viral replication and tumorigenesis and could aid in the discovery of new targets for anti-tumor therapy.

The Bcl-2 protein family and its role in the development of neoplastic disease

Programmed cell death is the physiological process responsible for shaping organs during embryogenesis, maintaining tissue homeostasis and allowing controlled deletion of potentially harmful cells within the adult organism. The genetics of apoptosis are well conserved in all metazoans and although the evolution of humans and worms separated more than 600 million years ago, basic signaling concepts in apoptosis are highly related in both species. More crucial to humans than worms is the fact that abnormalities in cell death control can contribute to the development of cancer. While C.elegans can easily survive with additional somatic cells that should normally be deleted during development humans may suffer pathological consequences, ranging from tumorigenesis to autoimmunity, as a result of mutations in cell death regulatory genes. Despite the high degree of evolutionary conservation in cell death control, apoptosis signaling in mammals is much more complex than in C.elegans. In mammalian cells, programmed cell death can be induced either by ligand-mediated activation of certain members of the tumor necrosis factor receptor family--so-called 'death receptors'--such as Fas (CD95/Apo-1) and TRAIL or it can be induced in a cell autonomous manner in response to certain stress signals by pro-apoptotic members of the Bcl-2 family. In this review, we focus on general concepts of how the Bcl-2 protein family regulates cell death and how deregulation of this 'intrinsic' apoptotic signaling pathway impinges on the pathogenesis of malignant disease, the major cause of death in the aging population.

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.

Overexpression of adenovirus E3-11.6K protein induces cell killing by both caspase-dependent and caspase-independent mechanisms

Recent studies have shown enhanced antitumor efficacy with adenoviruses that either lack E1B-19K or overexpress E3-11.6K (also known as adenoviral death protein). E1B-19K is a well-characterized anti-apoptotic protein, and viruses with E1B-19K deletions show increased cytopathicity. However, the mechanism of cell killing by E3-11.6K, which plays an important role in killing infected cells and virion release, is not well characterized. To understand the mechanism of cell killing following E3-11.6K overexpression, we constructed a recombinant adenovirus, Ad-ME, by introducing viral major late promoter upstream of the E3-11.6K sequence. Similar to the E1B-19K-deleted virus, E1B/19K-, Ad-ME induced cell death to a greater extent than the wild-type virus. Cell shrinkage, membrane blebbing, activation of caspases 3 and 9, cleavage of poly(ADP-ribose)polymerase (PARP), DNA degradation, and ratio of ADP to ATP in Ad-ME-infected cells indicated that apoptosis contributes to cell death following E3-11.6K overexpression. However, the levels of activation of caspases 3 and 9 were lower in cells infected with Ad-ME compared to those infected with E1B/19K-. Furthermore, cell killing by Ad-ME was not effectively inhibited by Z-VAD-FMK, a general caspase inhibitor. Taken together, our results suggest both caspase-dependent and caspase-independent mechanisms of cell killing due to overexpression of E3-11.6K.

Lactoferrin modifies apoptosis-related gene expression in the colon of the azoxymethane-treated rat

Lactoferrin, an iron-binding glycoprotein, exhibits suppressive effects on development of azoxymethane (AOM)-induced tumors in the rat colon, but the mechanisms are largely unknown. In this study, we investigated the effect of lactoferrin on the gene expression of 10 apoptosis-related molecules in colon mucosa of AOM-treated rats during early and late stages of colon carcinogenesis by reverse transcription PCR. Here we document that a death-inducing receptor, Fas, and a pro-apoptotic Bcl-2 family member, Bid, are increased in the colon mucosa in proportion to decreases in AOM-induced aberrant crypt foci by lactoferrin. Similarly, increased expression of the pro-apoptotic Bcl-2 family member, Bax, was also observed in AOM-induced tumors in rats fed by lactoferrin. These results indicate that Fas and pro-apoptotic Bcl-2 members participate in the lactoferrin action and may contribute to suppressive effects on tumor development in the rat colon.

BAK overexpression mediates p53-independent apoptosis inducing effects on human gastric cancer cells

Background

BAK (Bcl-2 homologous antagonist/killer) is a novel pro-apoptotic gene of the Bcl-2 family. It has been reported that gastric tumors have reduced BAK levels when compared with the normal mucosa. Moreover, mutations of the BAK gene have been identified in human gastrointestinal cancers, suggesting that a perturbation of BAK-mediated apoptosis may contribute to the pathogenesis of gastric cancer. In this study, we explored the therapeutic effects of gene transfer mediated elevations in BAK expression on human gastric cancer cells in vitro.

Methods

Eukaryotic expression vector for the BAK gene was constructed and transferred into gastric cancer cell lines, MKN-45 (wild-type p53) and MKN-28 (mutant-type p53). RT-PCR and Western Blotting detected cellular BAK gene expression. Cell growth activities were detected by MTT colorimetry and flow cytometry, while apoptosis was assayed by electronic microscopy and TUNEL. Western Blotting and colorimetry investigated cellular caspase-3 activities.

Results

BAK gene transfer could result in significant BAK overexpression, decreased in vitro growth, cell cycle G₀/G₁ arrest, and induced apoptosis in gastric cancer cells. In transferred cells, inactive caspase-3 precursor was cleaved into the active subunits p20 and p17, during BAK overexpression-induced apoptosis. In addition, this process occurred equally well in p53 wild-type (MKN-45), or in p53 mutant-type (MKN-28) gastric cancer cells.

Conclusions

The data presented suggests that overexpression of the BAK gene can lead to apoptosis of gastric cancer cells in vitro, which does not appear to be dependent on p53 status. The action mechanism of BAK mediated apoptosis correlates with activation of caspase-3. This could be served as a potential strategy for further development of gastric cancer therapies.

Cytomegalovirus cell death suppressor vMIA blocks Bax- but not Bak-mediated apoptosis by binding and sequestering Bax at mitochondria

We report that the cytomegalovirus-encoded cell death suppressor vMIA binds Bax and prevents Bax-mediated mitochondrial membrane permeabilization by sequestering Bax at mitochondria in the form of a vMIA-Bax complex. vMIA mutants with a defective mitochondria-targeting domain retain their Bax-binding function but not their ability to suppress mitochondrial membrane permeabilization or cell death. vMIA does not seem to either specifically associate with Bak or suppress Bak-mediated mitochondrial membrane permeabilization. Recent evidence suggests that the contribution of Bax and Bak in the mitochondrial apoptotic signaling pathway depends on the distinct phenotypes of cells, and it appears from our data that vMIA is capable of suppressing apoptosis in cells in which this pathway is dominated by Bax, but not in cells where Bak also plays a role.

Viral Bcl-2 homologs and their role in virus replication and associated diseases

Cellular Bcl-2 family proteins regulate a critical step in the mammalian programmed cell death pathway by modulating mitochondrial permeability and function. Bcl-2 family proteins are also encoded by several large DNA viruses, including all known gamma herpesviruses, adenoviruses, and several other unrelated viruses. Viral Bcl-2 proteins can prevent cell death but often escape cellular regulatory mechanisms that govern their cellular counterparts. By evading the "altruistic" suicide of infected cells, viruses can ensure replication and propagation in the infected host, but sometimes in surprising ways. Many human cancers and other disorders are associated with viruses that encode Bcl-2 homologs. Here we consider the available mechanistic data for viral compared to cellular Bcl-2 protein function along with relevance to the virus life cycle and human disease states.

Enhanced apoptosis by a novel gene, Bak-like, that lacks the BH3 domain

In a variety of physiological settings, cells are eliminated by apoptosis-a genetically encoded process of cellular suicide. Bak, a member of the Bcl-2 protein family, accelerates apoptosis by an unknown mechanism. We have found a novel cDNA encoding a 101-amino acid protein that possesses a Bak-like sequence in our full-length cDNA bank and termed it Bak-like. This protein shares the conserved domains BH1 and BH2 with other pro-apoptotic proteins, but lacks the BH3 domain. Database searches identified this gene on chromosome 6, which could account for the cloned bak and bak-like transcripts by alternative splicing. Bak-like is expressed in a wide variety of tissues. Bak-like is different from bak by Southern blots using probes with or without homology to bak. Despite the loss of the BH3 sequence, bak-like did enhance apoptosis, but was less potent than bak. Confocal microscopy of HeLa cells revealed that EGFP-Bak-like was located diffusely throughout the cytosol. However, upon induction of apoptosis, EGFP-Bak-like redistributed into a punctuate pattern, colocalizing with mitochondria. Like bak, the bak-like gene product directly enhanced apoptotic cell death following an appropriate stimulus.

Bcl-2 family regulation of neuronal development and neurodegeneration

Neuronal cell death is a key feature of both normal nervous system development and neuropathological conditions. The Bcl-2 family, via its regulation of both caspase-dependent and caspase-independent cell death pathways, is uniquely positioned to critically control neuronal cell survival. Targeted gene disruptions of specific bcl-2 family members and the generation of transgenic mice overexpressing anti- or pro-apoptotic Bcl-2 family members have confirmed the importance of the Bcl-2 family in the nervous system. Data from studies of human brain tissue and experimental animal models of neuropathological conditions support the hypothesis that the Bcl-2 family regulates cell death in the mature nervous system and suggest that pharmacological manipulation of Bcl-2 family action could prove beneficial in the treatment of human neurological conditions such as stroke and neurodegenerative diseases.

Replicating Adenoviruses in Cancer Therapy

The potential use of adenoviruses in therapy against cancer has evoked a rapidly moving field of research. Unlike conventional gene therapy vectors, oncolytic adenoviruses retain the ability to replicate. However, replication is restricted as much as possible to tumor cells, with the aim of eliminating these cells through viral cytotoxicity. The two key issues are to improve the efficiency of virus replication and cell killing while ensuring the specificity of these activities for tumor cells. Wild-type adenoviruses as such may already be usable for cancer therapy. Strategies to further improve efficiency and specificity include the partial or complete removal of viral genes. The idea is that functions carried out by the corresponding gene products are not required for replication in tumor cells, but are needed in normal cells. Accordingly, the removal of genes encoding E1B-55 kDa or E1B-19 kDa, or the mutation of E1A may improve the selective killing of tumor cells. On the other hand, the overexpression of the adenovirus death protein (ADP) may enhance viral spread and oncolytic efficiency. Other strategies to improve the specific oncolytic activity of replicating adenoviruses have been pursued. For instance, some promoters are active specifically in tumor cells, and these promoters were introduced into the viral genome, to regulate essential viral genes. Moreover, replicating viruses were engineered to express toxic proteins or drug converters. A number of these viruses have been tested successfully using tumor xenografts in nude mice as a model system. An oncolytic adenovirus lacking the E1B-55 kDa gene product, termed dl1520 or ONYX015, was injected into squamous cell carcinomas of head and neck in phase II clinical trials, and the results were encouraging when chemotherapy was applied in parallel. In the future, further progress might be achieved on the level of virus constructs, but also by refining and adjusting simultaneous conventional therapies, and by standardizing the assessment of the clinical outcome. Recent progress has been made towards the use of replicating virus constructs in cancer therapy. The goal of these developments is to remove cancerous cells from patients with the help of viruses that selectively replicate in these cells. These viruses are generally termed oncolytic viruses. Some convenient properties of adenovirus make this virus particularly useful for this purpose. It infects a large number of human cell types, especially epithelial cells, which give rise to the vast majority of human malignancies. It can be grown easily and to high titers, and the creation of virus recombinants is well established. Finally, a large body of basic research has already been carried out on this virus, facilitating its manipulation. Various approaches to use adenovirus as a cancer drug have been reviewed (Alemany et al. 1999a, 2000; Curiel 2000; Galanis et al. 2001b; Gromeier 2001; Heise and Kirn 2000; Kirn 2000a; Kirn et al. 2001; Kirn and McCormick 1996; Smith and Chiocca 2000; Sunamura 2000; Wells 2000; Wodarz 2001). The aim of this chapter is to provide an integrated overview of these strategies.

Cell transformation by human adenoviruses

The last 40 years of molecular biological investigations into human adenoviruses have contributed enormously to our understanding of the basic principles of normal and malignant cell growth. Much of this knowledge stems from analyses of their productive infection cycle in permissive host cells. Also, initial observations concerning the carcinogenic potential of human adenoviruses subsequently revealed decisive insights into the molecular mechanisms of the origins of cancer, and established adenoviruses as a model system for explaining virus-mediated transformation processes. Today it is well established that cell transformation by human adenoviruses is a multistep process involving several gene products encoded in early transcription units 1A (E1A) and 1B (E1B). Moreover, a large body of evidence now indicates that alternative or additional mechanisms are engaged in adenovirus-mediated oncogenic transformation involving gene products encoded in early region 4 (E4) as well as epigenetic changes resulting from viral DNA integration. In particular, detailed studies on the tumorigenic potential of subgroup D adenovirus type 9 (Ad9) E4 have now revealed a new pathway that points to a novel, general mechanism of virus-mediated oncogenesis. In this chapter, we summarize the current state of knowledge about the oncogenes and oncogene products of human adenoviruses, focusing particularly on recent findings concerning the transforming and oncogenic properties of viral proteins encoded in the E1B and E4 transcription units.

Bcl-2 as a target for overcoming chemoresistance in small-cell lung cancer

Small-cell lung cancer (SCLC) is an aggressive malignancy that is frequently metastatic at presentation and has a poor prognosis. Although initially sensitive to primary therapy, acquisition of apoptosis resistance is typical, resulting in failure of secondary chemotherapy following relapse. Expression of the antiapoptosis protein Bcl-2 is prevalent in SCLC. The understanding of this oncoprotein's function has increased dramatically over the past decade. In vitro and in vivo evidence supports a role for overexpression of Bcl-2 in SCLC and supports the notion that it is a major factor contributing to apoptosis resistance. Targeting Bcl-2 may provide a novel therapeutic approach to overcoming chemoresistance in SCLC. This article discusses the relevance of Bcl-2 to apoptosis susceptibility in SCLC and its exploitation using gene silencing to improve the clinical outcome in this disease.

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.

DNA damage response and MCL-1 destruction initiate apoptosis in adenovirus-infected cells

Expression of adenovirus E1A deregulates cell proliferation to facilitate viral DNA replication, prompting the initiation of apoptosis signaled primarily through proapoptotic BAK in productively infected cells. We demonstrate here that in uninfected cells, BAK is complexed with the anti-apoptotic BCL-2 family member Myeloid Cell Leukemia 1 (MCL-1). E1A expression during infection resulted in the specific down-regulation of MCL-1 through destabilization of the protein and loss of the mRNA. Upon loss of the MCL-1-BAK complex, BAK complexed with either BAX in proapoptotic E1B mutant adenovirus-infected cells, or with the adenovirus BCL-2 homolog E1B 19K in cells infected with the wild-type virus in which apoptosis is inhibited. Loss of MCL-1 was required to initiate the apoptotic pathway in infected cells as restoration of MCL-1 expression rescued infected cells from E1A-induced apoptosis. Analogous to E1A expression, DNA damage down-regulates MCL-1, and adenovirus infection resulted in the accumulation of phosphorylated H2AX and ataxia-telangiectasia mutant protein (ATM), hallmarks of DNA double-strand breaks. Thus, MCL-1 may function by maintaining BAK in an inactive state, and the loss of MCL-1 upon activation of the DNA damage response, perhaps through replication stress induced in virus infected cells, may be required to initiate the apoptotic response.

Control of apoptosis in the immune system: Bcl-2, BH3-only proteins and more

Apoptotic cell death plays a critical role in the development and functioning of the immune system. During differentiation, apoptosis weeds out lymphocytes lacking useful antigen receptors and those expressing dangerous ones. Lymphocyte death is also involved in limiting the magnitude and duration of immune responses to infection. In this review, we describe the role of the Bcl-2 protein family, and to a lesser extent that of death receptors (members of the tumor necrosis factor receptor family with a death domain), in the control of lymphoid and myeloid cell survival. We also consider the pathogenic consequences of failure of apoptosis in the immune system.

Intrinsic and extrinsic pathways signaling during HIV-1 mediated cell death

Infection with human immunodeficiency virus (HIV) is characterized by the gradual depletion of CD4+ T lymphocytes. The incorporation of the concept of apoptosis as a rationale to explain progressive T cell depletion has led to growing research in this field during the last 10 years. In parallel, the biochemical pathways implicated in programmed cell death have been extensively studied. Thus, the influence of mitochondrial control in the two major apoptotic pathways-the extrinsic and intrinsic pathways-is now well admitted. In this review, we summarized our current knowledge of the different pathways involved in the death of T cells in the course of HIV infection.

Diabetes induced erectile dysfunction and apoptosis in penile crura are recovered by insulin treatment in rats

PURPOSE

We hypothesized that apoptosis is a downstream event in erectile dysfunction, and pro-apoptotic (Bak and Bax) and anti-apoptotic (Bcl-2 and Bcl-x) factors are involved in the etiology of diabetes induced erectile dysfunction. To test this hypothesis the intracavernous pressure of diabetic and insulin treated rats was measured to assess erectile function. Molecular and immunohistochemical analyses for apoptosis were then performed in rat crura to assess their role in diabetes induced erectile dysfunction and insulin treatment.

MATERIALS AND METHODS

A total of 70, 6-month-old male Sprague-Dawley rats were divided into 2 groups, including a diabetic (50) and a healthy control (20) group. The diabetic group received intraperitoneal injection of streptozotocin (STZ) (Sigma-Aldrich Co., St. Louis, Missouri) to induce diabetes. Subcutaneous injection of insulin was administered daily to 9 diabetic rats 4 and 8 weeks after STZ injections for 4 and 8 weeks, respectively. Functional studies were performed in 9 diabetic rats each 4, 8 and 12 weeks after STZ injections, in 6 age matched control rats and in insulin treated rats at the termination of therapy. After the completion of functional study the penile crura were collected from rats for molecular and immunohistochemical studies.

RESULTS

Mean intracavernous pressure of diabetic rats was significantly lower than in control rats and the decrease in intracavernous pressure was significantly recovered by insulin treatment. Gene expressions of pro-apoptotic and anti-apoptotic factors were present in control, diabetic and insulin treated rat crura. However, anti-apoptotic protein expression was lacking in diabetic rat crura and pro-apoptotic protein expression was lost in insulin treated rat crura. The apoptotic index of diabetic rat crura was significantly higher than that of control rat crura and this index was significantly decreased in insulin treated rat crura.

CONCLUSIONS

There was a significant correlation between the decrease and recovery in intracavernous pressure, and protein expression of apoptotic factors in diabetic and insulin treated rat crura. To our knowledge this is the first report demonstrating that the relief of diabetes associated erectile dysfunction by insulin treatment is due to alterations in the protein expression of apoptotic factors in rat crura.

Mitochondrial membrane permeabilisation by Bax/Bak

Recent studies on cells derived from mice deficient in both multi-domain pro-apoptotic genes of the Bcl-2 family, Bax and Bak, suggest that one or other of these proteins are required for the release of apoptogens such as cytochrome c from mitochondria. In addition BH-3 only proteins of this family such as Bid are suggested to act as critical death inducing ligands via interactions with pro- and anti-apoptotic Bcl-2 family proteins with Bax or Bak at the mitochondrial surface. Despite this increase in knowledge it remains unclear precisely how Bak and Bax promote outer mitochondrial membrane (OMM) permeabilisation. We suggest that Bax and Bak may not operate in precisely the same manner and evaluate the current models for their function. We also consider the emerging information that lipid-protein interactions may be crucial to the actions of Bax and Bak.

EGR2 induces apoptosis in various cancer cell lines by direct transactivation of BNIP3L and BAK

EGR2 plays a key role in the PTEN-induced apoptotic pathway. Using adenovirus-mediated gene transfer to 39 cancer cell lines, we found that EGR2 could induce apoptosis in a large proportion of these lines by altering the permeability of mitochondrial membranes, releasing cytochrome c and activating caspase-3, -8, and -9. Analysis by cDNA microarray and subsequent functional studies revealed that EGR2 directly transactivates expression of BNIP3L and BAK. Our results helped to clarify the molecular mechanism of the apoptotic pathway induced by PTEN-EGR2, and suggested that EGR2 may be an excellent target molecule for gene therapy to treat a variety of cancers.

The Bcl-2 protein family: sensors and checkpoints for life-or-death decisions

Members of the Bcl-2 family are crucial integrators of survival and death signals in higher eukaryotes. Although recent studies have provided novel and quite unexpected insights into the mechanisms by which these proteins might issue life permits or death sentences in cells, we are still on the way to fully understand their modes of action. This review provides a snapshot on where we are on this journey and how we may exploit our knowledge on this family of proteins to unveil the mysteries of immune regulation.

Pleural mesothelial cells modulate polymorphonuclear leukocyte apoptosis in empyema

In bacterial empyema, the recruited polymorphonuclear leukocytes (PMN) represent important phagocytic cells involved in antibacterial defense. In this study we demonstrate that pleural fluids (PF) obtained from patients with empyema (EMP) contains significantly higher levels of granulocyte colony stimulating factor (GM-CSF), and PMN incubated in empyema (EMP) pleural fluid (PF) showed significantly less apoptosis than congestive heart failure (CHF) PF. Staphylococcus aureus-stimulated PMC released significantly (P < 0.001) higher levels of GM-CSF than resting PMC. Staphylococcus aureus-stimulated PMC (SPMC)-CM significantly (P < 0.001) inhibited PMN apoptosis. In SPMC-CM-incubated PMN the antiapoptotic gene Bcl-xL mRNA and protein expression was up-regulated; Bak mRNA and protein expression was down-regulated compared to control PMN. The active caspases activity significantly decreased. When SPMC-CM and EMP PF were immunodepleted with GM-CSF antibody, PMN apoptosis was significantly higher. The delay in apoptosis of PMN is in part attributable to the release of cytokine GM-CSF by activated PMC. These findings suggest that S. aureus-activated PMC extend PMN life span by modulating Bcl-xL and Bak gene expression and active caspases activity during acute inflammation and empyema.

Distribution of apoptotic cells and apoptosis-related molecules in the developing murine palatine rugae

Distribution of apoptotic cells and expression of the apoptosis-related factors p53, bcl-2 and bad during morphogenesis of the murine palatine rugae (PR) were examined histochemically using the terminal deoxynucleotidyl transferase-mediated UTP nick end-labeling (TUNEL) technique and specific antibodies against apoptosis and cell cycle-related molecules. Formation of the PR rudiment was controlled by cell proliferation and apoptosis in the palatal epithelium. TUNEL-positive cells were detected only at the epithelial placode area at 12.5-13.5 days post coitus (dpc), but only a few cells were positive at the protruding PR area at 14.5-16.5 dpc. Bcl-2 protein was expressed mainly in the areas outside of those containing TUNEL-positive cells at 15.5 -6.5 dpc. P53 protein was not detected throughout gestation. Bad was detected in the epithelial layer at 13.5 and 15.5 dpc and overlapping the apoptotic area at 13.5-15.5 dpc. Apoptosis of palatal epithelial cells might therefore involve spatiotemporally regulated expression of bad during murine PR development.

Loss of anti-apoptotic genes in aging rat crura

PURPOSE

Erectile dysfunction is a common problem in aging men. The molecular mechanisms associated with aging erectile dysfunction are not completely understood. We hypothesized that apoptosis is a downstream event in erectile dysfunction, and pro-apoptotic (Bak and Bax) and anti-apoptotic (Bcl-2 and Bcl-x) factors are involved in the etiology of aging erectile dysfunction. To test this hypothesis intracavernous pressure in aging rats was measured to assess erectile function. Gene and protein expression of pro-apoptotic and anti-apoptotic factors was then analyzed in aging rat crura to assess its role in aging erectile dysfunction.

MATERIALS AND METHODS

A total of 25 male Sprague-Dawley rats divided into 5 groups of 5 each based on age (6, 12, 18, 24 and 28 months old, respectively) were used in functional and apoptotic studies. In addition, 5, 3-month-old male Sprague-Dawley rats were used in the apoptotic study. The rats were anesthetized with pentobarbital. Erectile function was assessed by measuring intracavernous pressure after electrostimulation of the cavernous nerves. After completion of the functional study the penile crura were immediately harvested for histochemical and molecular studies. Gene expression of pro-apoptotic (Bak and Bax) and anti-apoptotic (Bcl-2 and Bcl-x) factors were then analyzed by reverse transcription-polymerase chain reaction. Protein expressions of these apoptotic factors were also analyzed by immunohistochemistry using specific antibodies.

RESULTS

Mean intracavernous pressure plus or minus SD in 18, 24 and 28-month-old rats was significantly lower than in 6-month-old rats (101.6 +/- 24.8, 77.7 +/- 24.5 and 45.7 +/- 7.3 versus 136.7 +/- 11.4 cm. water, respectively; p <0.05). The reduction in intracavernous pressure was an age dependent phenomenon. Gene and protein expression of the pro-apoptotic genes Bak and Bax was detected in the crura of all age groups but there was no significant difference in young and old rat crura. The anti-apoptotic Bcl-2 and Bcl-x genes were expressed in 3, 6 and 12-month-old crura, whereas this expression was lost at 18, 24 and 28 months. Anti-apoptotic Bcl-2 and Bcl-x proteins were also expressed in young rat crura, whereas this expression was lost in old rat crura.

CONCLUSIONS

The decline in intracavernous pressure correlated significantly with a loss of anti-apoptotic genes in aging rat crura. To our knowledge this is the first report to show the loss of anti-apoptotic factors in aging rat crura and suggest their role in the pathogenesis of aging erectile dysfunction.