DIABLO promotes apoptosis by removing MIHA/XIAP from processed caspase 9

Mechanisms of Biological Effects of Ionic Liquids: From Single Cells to Multicellular Organisms

The review presents a detailed discussion of the evolving field studying interactions between ionic liquids (ILs) and biological systems. Originating from molten salt electrolytes to present multiapplication substances, ILs have found usage across various fields due to their exceptional physicochemical properties, including excellent tunability. However, their interactions with biological systems and potential influence on living organisms remain largely unexplored. This review examines the cytotoxic effects of ILs on cell cultures, biomolecules, and vertebrate and invertebrate organisms. Our understanding of IL toxicity, while growing in recent years, is yet nascent. The established findings include correlations between harmful effects of ILs and their ability to disturb cellular membranes, their potential to trigger oxidative stress in cells, and their ability to cause cell death via apoptosis. Future research directions proposed in the review include studying the distribution of various ILs within cellular compartments and organelles, investigating metabolic transformations of ILs in cells and organisms, detailed analysis of IL effects on proteins involved in oxidative stress and apoptosis, correlation studies between IL doses, exposure times and resulting adverse effects, and examination of effects of subtoxic concentrations of ILs on various biological objects. This review aims to serve as a critical analysis of the current body of knowledge on IL-related toxicity mechanisms. Furthermore, it can guide researchers toward the design of less toxic ILs and the informed use of ILs in drug development and medicine.

In vitroSodium Fluoride Treatment Significantly Affects Apoptosis and Proliferation in the Liver of Embryonic Chickens

Sodium fluoride (NaF), although helpful in preventing dental decay, may negatively affect the body. The aim of this study was to examine the effects of a 6-h in vitro treatment of livers isolated from 14-day-old chicken embryos with NaF at doses of 1.7 (D1), 3.5 (D2), 7.1 (D3) and 14.2 mM (D4), with regard to apoptosis, cell proliferation and tissue structure. The mRNA expression of the apoptosis regulators CYCS, APAF1, BCL2, CASP3, CASP9 and TMBIM1 was analysed by the qPCR method. Apoptotic cells were detected by a TUNEL assay. The tissue and DNA structure were also analysed by histological staining (H&E, Feulgen). The number of proliferating cells was determined and the apoptosis regulatory proteins were localised by the immunohistochemical staining of PCNA, CASP3 and APAF1. The results showed that the mRNA expression of CYCS, BCL2, CASP3, CASP9 and APAF1 increased significantly in the D1 group, as did that of CASP9 in the D3 group and of BCL2 and APAF1 in the D4 group. The number of apoptotic cells increased significantly in the D4 group, where they increased from 18% to 49%. On the other hand, the number of proliferating cells decreased gradually, in a dose-dependent manner, from 84% in the control group to 5.5% in the D4 group. The expression of apoptosis-regulating factors also increased: in the D3 and D4 groups, the CASP3 immunopositive reaction was more intensive in single cells in the embryonic livers, whereas that of APAF1 increased in the hepatocytes as well as in the hepatic blood vessel walls. The mechanism of the effect of NaF on apoptosis in the embryonic liver is very complex. In the groups exposed to higher doses of NaF, apoptosis was significantly stimulated, while proliferation was inhibited and the tissue structure was damaged. The expression of apoptosis regulators at the mRNA and protein levels increased, but the mRNA expression did not depend on the NaF dose. These results reveal that NaF, by changing the balance between apoptosis and the proliferation of hepatocytes, may disturb the development and function of the liver in embryonic chickens. Therefore, the risk of exposure to NaF should be considered when determining the standards for human and animal exposure to this compound.

Fluoxetine in the environment may interfere with the neurotransmission or endocrine systems of aquatic animals

Antidepressants are extensively used to treat the symptoms of depression in humans, and the environmentally discharged drugs potentially threaten aquatic organisms. In this study, the acute toxic effects of fluoxetine (FLX) were investigated in two aquatic organisms, the freshwater polyp (Hydra magnipapillata) and Javanese medaka (Oryzias javanicus). The median lethal concentration (LC₅₀) of FLX in H. magnipapillata was 3.678, 3.082, and 2.901 mg/L after 24, 48, and 72 h, respectively. Morphological observations of the FLX-exposed H. magnipapillata showed that 1.5 mg/L FLX induced the contraction of the tentacles and body column. The LC₅₀ of FLX in O. javanicus was 2.046, 1.936, 1.532, and 1.237 mg/L after 24, 48, 72, and 96 h, respectively. Observation of the behavior of the FLX-exposed fish showed that FLX reduced their swimming performance at a minimum concentration of 10 µg/L. The half-maximal effective concentration (EC₅₀) of FLX for swimming behavior in O. javanicus was 0.135, 0.108, and 0.011 mg/L after 12, 24, and 96 h, respectively. Transcriptomic analyses indicated that FLX affects various physiological and metabolic processes in both species. FLX exposure induced oxidative stress, reproductive deficiency, abnormal pattern formation, DNA damage, and neurotransmission disturbance in H. magnipapillata, whereas it adversely affected O. javanicus by inducing oxidative stress, DNA damage, endoplasmic reticulum stress, and mRNA instability. Neurotransmission-based behavioral changes and endocrine disruption were strongly suspected in the FLX-exposed fish. These results suggest that FLX affects the behavior and metabolic regulation of aquatic organisms.

BH3-mimetics: recent developments in cancer therapy

The hopeful outcomes from 30 years of research in BH3-mimetics have indeed served a number of solid paradigms for targeting intermediates from the apoptosis pathway in a variety of diseased states. Not only have such rational approaches in drug design yielded several key therapeutics, such outputs have also offered insights into the integrated mechanistic aspects of basic and clinical research at the genetics level for the future. In no other area of medical research have the effects of such work been felt, than in cancer research, through targeting the BAX-Bcl-2 protein-protein interactions. With these promising outputs in mind, several mimetics, and their potential therapeutic applications, have also been developed for several other pathological conditions, such as cardiovascular disease and tissue fibrosis, thus highlighting the universal importance of the intrinsic arm of the apoptosis pathway and its input to general tissue homeostasis. Considering such recent developments, and in a field that has generated so much scientific interest, we take stock of how the broadening area of BH3-mimetics has developed and diversified, with a focus on their uses in single and combined cancer treatment regimens and recently explored therapeutic delivery methods that may aid the development of future therapeutics of this nature.

Oxidative and Non-Oxidative Antimicrobial Activities of the Granzymes

Cell-mediated cytotoxicity is an essential immune defense mechanism to fight against viral, bacterial or parasitic infections. Upon recognition of an infected target cell, killer lymphocytes form an immunological synapse to release the content of their cytotoxic granules. Cytotoxic granules of humans contain two membrane-disrupting proteins, perforin and granulysin, as well as a homologous family of five death-inducing serine proteases, the granzymes. The granzymes, after delivery into infected host cells by the membrane disrupting proteins, may contribute to the clearance of microbial pathogens through different mechanisms. The granzymes can induce host cell apoptosis, which deprives intracellular pathogens of their protective niche, therefore limiting their replication. However, many obligate intracellular pathogens have evolved mechanisms to inhibit programed cells death. To overcome these limitations, the granzymes can exert non-cytolytic antimicrobial activities by directly degrading microbial substrates or hijacked host proteins crucial for the replication or survival of the pathogens. The granzymes may also attack factors that mediate microbial virulence, therefore directly affecting their pathogenicity. Many mechanisms applied by the granzymes to eliminate infected cells and microbial pathogens rely on the induction of reactive oxygen species. These reactive oxygen species may be directly cytotoxic or enhance death programs triggered by the granzymes. Here, in the light of the latest advances, we review the antimicrobial activities of the granzymes in regards to their cytolytic and non-cytolytic activities to inhibit pathogen replication and invasion. We also discuss how reactive oxygen species contribute to the various antimicrobial mechanisms exerted by the granzymes.

IAP-Mediated Protein Ubiquitination in Regulating Cell Signaling

Over the last decade, the E3-ubiquitine ligases from IAP (Inhibitor of Apoptosis) family have emerged as potent regulators of immune response. In immune cells, they control signaling pathways driving differentiation and inflammation in response to stimulation of tumor necrosis factor receptor (TNFR) family, pattern-recognition receptors (PRRs), and some cytokine receptors. They are able to control the activity, the cellular fate, or the stability of actors of signaling pathways, acting at different levels from components of receptor-associated multiprotein complexes to signaling effectors and transcription factors, as well as cytoskeleton regulators. Much less is known about ubiquitination substrates involved in non-immune signaling pathways. This review aimed to present IAP ubiquitination substrates and the role of IAP-mediated ubiquitination in regulating signaling pathways.

Future Therapeutic Directions for Smac-Mimetics

It is well accepted that the ability of cancer cells to circumvent the cell death program that untransformed cells are subject to helps promote tumor growth. Strategies designed to reinstate the cell death program in cancer cells have therefore been investigated for decades. Overexpression of members of the Inhibitor of APoptosis (IAP) protein family is one possible mechanism hindering the death of cancer cells. To promote cell death, drugs that mimic natural IAP antagonists, such as second mitochondria-derived activator of caspases (Smac/DIABLO) were developed. Smac-Mimetics (SMs) have entered clinical trials for hematological and solid cancers, unfortunately with variable and limited results so far. This review explores the use of SMs for the treatment of cancer, their potential to synergize with up-coming treatments and, finally, discusses the challenges and optimism facing this strategy.

In vitro effects of PNP and PNMC on apoptosis and proliferation in the hen ovarian stroma and prehierarchal follicles

This study aimed to examine the mRNA expression, activity, and immunolocalisation of apoptosis/proliferation regulating factors following in vitro exposure of the stroma, white (WFs), and yellowish (YFs) follicles of the chicken ovary to 4-nitrophenol (PNP) or 3-methyl-4-nitrophenol (PNMC). PNMC increased the mRNA expression of caspase-3, -8, Apaf-1, and cytochrome c in the ovarian stroma. The activity of caspase-3, -8, and -9 decreased in WFs in both nitrophenol-treated groups. PNP reduced the number of caspase-3-positive cells in the stromal connective tissue (CT) and the theca interna and externa layers of WFs. In the stroma, the proliferating index decreased in the wall of primary follicles in both nitrophenol-treated groups, however, in the CT, the effect of PNMC was opposite. In the theca interna of WFs, PNP diminished the proliferating index. These results suggest that nitrophenols might impact the development of chicken ovarian follicles by affecting cell death and proliferation.

In Vitro Pro-apoptotic and Anti-migratory Effects of Ficus deltoidea L. Plant Extracts on the Human Prostate Cancer Cell Lines PC3

This study aims to evaluate the in vitro cytotoxic and anti-migratory effects of Ficus deltoidea L. on prostate cancer cells, identify the active compound/s and characterize their mechanism of actions. Two farmed varieties were studied, var. angustifolia (FD1) and var. deltoidea (FD2). Their crude methanolic extracts were partitioned into n-hexane (FD1h, FD2h) chloroform (FD1c, FD2c) and aqueous extracts (FD1a, FD2a). Antiproliferative fractions (IC50 < 30 μg/mL, SRB staining of PC3 cells) were further fractionated. Active compound/s were dereplicated using spectroscopic methods. In vitro mechanistic studies on PC3 and/or LNCaP cells included: annexin V-FITC staining, MMP depolarization measurements, activity of caspases 3 and 7, nuclear DNA fragmentation and cell cycle analysis, modulation of Bax, Bcl-2, Smac/Diablo, and Alox-5 mRNA gene expression by RT-PCR. Effects of cytotoxic fractions on 2D migration and 3D invasion were tested by exclusion assays and modified Boyden chamber, respectively. Their mechanisms of action on these tests were further studied by measuring the expression VEGF-A, CXCR4, and CXCL12 in PC3 cells by RT-PCR. FD1c and FD2c extracts induced cell death (P < 0.05) via apoptosis as evidenced by nuclear DNA fragmentation. This was accompanied by an increase in MMP depolarization (P < 0.05), activation of caspases 3 and 7 (P < 0.05) in both PC3 and LNCaP cell lines. All active plant extracts up-regulated Bax and Smac/DIABLO, down-regulated Bcl-2 (P < 0.05). Both FD1c and FD2c were not cytotoxic against normal human fibroblast cells (HDFa) at the tested concentrations. Both plant extracts inhibited both migration and invasion of PC3 cells (P < 0.05). These effects were accompanied by down-regulation of both VEGF-A and CXCL-12 gene expressions (P < 0.001). LC–MS dereplication using taxonomy filters and molecular networking databases identified isovitexin in FD1c; and oleanolic acid, moretenol, betulin, lupenone, and lupeol in FD2c. In conclusion, FD1c and FD2c were able to overcome three main hallmarks of cancer in PC3 cells: (1) apoptosis by activating of the intrinsic pathway, (2) inhibition of both migration and invasion by modulating the CXCL12-CXCR4 axis, and (3) inhibiting angiogenesis by modulating VEGF-A expression. Moreover, isovitexin is here reported for the first time as an antiproliferative principle (IC50 = 43 μg/mL, SRB staining of PC3 cells).

Stress-induced hyperacetylation of microtubule enhances mitochondrial fission and modulates the phosphorylation of Drp1 at 616Ser

Mitochondria dynamics results from fission and fusion events that may be unbalanced in favor of mitochondrial fragmentation upon cell stress. During oxidative stress, microtubules are hyperacetylated in a mitochondria-dependent manner. In this study, we show that under stress conditions, most of the mitochondria form foci with microtubule domains that carry Drp1. We also demonstrate that stress-induced hyperacetylation of microtubules is required for the effective induction of Drp1 phosphorylation at ⁶¹⁶Ser, in a kinesin-1- and c-Jun N-terminal kinase-dependent manner. Furthermore, hyperacetylation of microtubules contributes to the recruitment of total Drp1 to mitochondria to enhance fission. These results highlight a new way of interaction between microtubules and mitochondria dynamics.

Inducing death in tumor cells: roles of the inhibitor of apoptosis proteins

The heterogeneous group of diseases collectively termed cancer results not just from aberrant cellular proliferation but also from a lack of accompanying homeostatic cell death. Indeed, cancer cells regularly acquire resistance to programmed cell death, or apoptosis, which not only supports cancer progression but also leads to resistance to therapeutic agents. Thus, various approaches have been undertaken in order to induce apoptosis in tumor cells for therapeutic purposes. Here, we will focus our discussion on agents that directly affect the apoptotic machinery itself rather than on drugs that induce apoptosis in tumor cells indirectly, such as by DNA damage or kinase dependency inhibition. As the roles of the Bcl-2 family have been extensively studied and reviewed recently, we will focus in this review specifically on the inhibitor of apoptosis protein (IAP) family. IAPs are a disparate group of proteins that all contain a baculovirus IAP repeat domain, which is important for the inhibition of apoptosis in some, but not all, family members. We describe each of the family members with respect to their structural and functional similarities and differences and their respective roles in cancer. Finally, we also review the current state of IAPs as targets for anti-cancer therapeutics and discuss the current clinical state of IAP antagonists.

The activator of apoptosis Smac-DIABLO acts as a tetramer in solution

Smac-DIABLO in its mature form (20.8 kDa) binds to baculoviral IAP repeat (BIR) domains of inhibitor of apoptosis proteins (IAPs) releasing their inhibitory effects on caspases, thus promoting cell death. Despite its apparent molecular mass (∼100 kDa), Smac-DIABLO was held to be a dimer in solution, simultaneously targeting two distinct BIR domains. We report an extensive biophysical characterization of the protein alone and in complex with the X-linked IAP (XIAP)-BIR2-BIR3 domains. Our data show that Smac-DIABLO adopts a tetrameric assembly in solution and that the tetramer is able to bind two BIR2-BIR3 pairs of domains. Our small-angle x-ray scattering-based tetrameric model of Smac-DIABLO/BIR2-BIR3 highlights some conformational freedom of the complex that may be related to optimization of IAPs binding.

Localization of apoptotic and proliferating cells and mRNA expression of caspases and Bcl-2 in gonads of chicken embryos

The aim of the present study was to analyze participation of apoptosis and proliferation in gonadal development in the chicken embryo by: (1) localization of apoptotic (TUNEL) and proliferating (PCNA immunoassay) cells in male and female gonads and (2) examination of mRNA expression (RT-PCR) of caspase-3, caspase-6 and Bcl-2 in the ovary and testis during the second half of embryogenesis and in newly hatched chickens. Apoptotic cells were found in gonads of both sexes. At E18 the percentage of apoptotic cells (the apoptotic index, AI) in the ovarian medulla and the testis was lower (p<0.05) than in the ovarian cortex. In the ovarian medulla, the AI at E18 was lower (p<0.05) than on E12. In the testis, the AI was significantly lower (p<0.05) at E18 than at E15 and 1D. The percentage of proliferating cells (the proliferation index: PI) within the ovary significantly increased from E15 to 1D in the cortex, while proliferating cells in the medulla were detected only at E15. In the testis, the PI gradually increased from E12 to 1D. The mRNA expression of caspase-3 and -6 as well as Bcl-2 was detected in male and female gonads at days 12 (E12), 15 (E15) and 18 (E18) of embryogenesis and the day after hatching (1D). The expression of all analyzed genes on E12 was significantly higher (p<0.05) in female than in male gonads. This difference was also observed at E15 and E18, but only for the caspase-6. The results obtained showed tissue- and sex-dependent differences in the number of apoptotic and proliferating cells as well as mRNA expression of caspase-3, -6 and Bcl-2 genes in the gonads of chicken embryos. Significant increase in the number of proliferating cells in the ovarian cortex and lack of these cells in the ovarian medulla (stages E12, E18, 1D) simultaneous with decrease in the intensity of apoptosis only in the medulla indicates that proliferation is the dominant process involved in the cortical development, which constitutes the majority of the functional structure of the fully developed ovary. No pronounced changes in the expression of apoptosis-related genes found during embryogenesis suggest that they cannot be considered as important indicators of gonad development. The molecular mechanisms of the regulation of balance between apoptosis and proliferation in developing avian gonads need to be further investigated.

Prenatal exposure to chromium induces early reproductive senescence by increasing germ cell apoptosis and advancing germ cell cyst breakdown in the F1 offspring

Hexavalent chromium (CrVI), one of the more toxic heavy metals, is widely used in more than 50 industries such as chrome plating, welding, wood processing and tanneries. As one of the world's leading producers of chromium compounds, the U.S. is facing growing challenges in protecting human health against multiple adverse effects of CrVI. CrVI is rapidly converted to CrIII intracellularly, and can induce apoptosis through different mechanisms. Our previous studies demonstrated postnatal exposure to CrVI results in a delay or arrest in follicle development and puberty. Pregnant rats were treated with 25 ppm potassium dichromate (CrVI) from gestational day (GD) 9.5 to 14.5 through drinking water, placentae were removed on GD 20, and total Cr was estimated in the placentae; ovaries were removed from the F1 offspring on postnatal day (PND)-1 and various analyses were performed. Our results show that gestational exposure to CrVI resulted in (i) increased Cr concentration in the placenta, (ii) increased germ cell apoptosis by up-regulating p53/p27-Bax-caspase-3 proteins and by increasing p53-SOD-2 co-localization; (iii) accelerated germ cell cyst (GCC) breakdown; (iv) advanced primordial follicle assembly and primary follicle transition and (v) down regulation of p-AKT, p-ERK and XIAP. As a result of the above events, CrVI induced early reproductive senescence and decrease in litter size in F1 female progeny.

Mitochondrial and postmitochondrial survival signaling in cancer

Cancer cells are resistant to conventional chemotherapy and radiotherapy, however, the molecular mechanisms of resistance to therapy remain unclear. Cellular survival machinery protects mitochondrial integrity against endogenous or exogenous stresses. Prodeath molecules orchestrate around mitochondria to initiate and execute cell death in cancer, and also play an underappreciated role in survival of cancer cells. Prosurvival mechanisms can operate at mitochondrial and postmitochondrial levels to attenuate core apoptotic death program. It is intriguing to explore how prosurvival and prodeath molecules crosstalk to regulate mitochondrial functions leading to increased cancer cell survival. This review describes some putative survival mechanisms at mitochondria, which may play a role in designing effective agents for cancer prevention and therapy. These survival pathways may also have significance in understanding other human pathophysiological conditions including diabetes, cardiovascular, autoimmune, and neurodegenerative diseases.

Identification of BIRC6 as a novel intervention target for neuroblastoma therapy

BACKGROUND

Neuroblastoma are pediatric tumors of the sympathetic nervous system with a poor prognosis. Apoptosis is often deregulated in cancer cells, but only a few defects in apoptotic routes have been identified in neuroblastoma.

METHODS

Here we investigated genomic aberrations affecting genes of the intrinsic apoptotic pathway in neuroblastoma. We analyzed DNA profiling data (CGH and SNP arrays) and mRNA expression data of 31 genes of the intrinsic apoptotic pathway in a dataset of 88 neuroblastoma tumors using the R2 bioinformatic platform ( http://r2.amc.nl). BIRC6 was selected for further analysis as a tumor driving gene. Knockdown experiments were performed using BIRC6 lentiviral shRNA and phenotype responses were analyzed by Western blot and MTT-assays. In addition, DIABLO levels and interactions were investigated with immunofluorescence and co-immunoprecipitation.

RESULTS

We observed frequent gain of the BIRC6 gene on chromosome 2, which resulted in increased mRNA expression. BIRC6 is an inhibitor of apoptosis protein (IAP), that can bind and degrade the cytoplasmic fraction of the pro-apoptotic protein DIABLO. DIABLO mRNA expression was exceptionally high in neuroblastoma but the protein was only detected in the mitochondria. Upon silencing of BIRC6 by shRNA, DIABLO protein levels increased and cells went into apoptosis. Co-immunoprecipitation confirmed direct interaction between DIABLO and BIRC6 in neuroblastoma cell lines.

CONCLUSION

Our findings indicate that BIRC6 may have a potential oncogenic role in neuroblastoma by inactivating cytoplasmic DIABLO. BIRC6 inhibition may therefore provide a means for therapeutic intervention in neuroblastoma.

Apoptotic signaling in mouse odontogenesis

Apoptosis is an important morphogenetic event in embryogenesis as well as during postnatal life. In the last 2 decades, apoptosis in tooth development (odontogenesis) has been investigated with gradually increasing focus on the mechanisms and signaling pathways involved. The molecular machinery responsible for apoptosis exhibits a high degree of conservation but also organ and tissue specific patterns. This review aims to discuss recent knowledge about apoptotic signaling networks during odontogenesis, concentrating on the mouse, which is often used as a model organism for human dentistry. Apoptosis accompanies the entire development of the tooth and corresponding remodeling of the surrounding bony tissue. It is most evident in its role in the elimination of signaling centers within developing teeth, removal of vestigal tooth germs, and in odontoblast and ameloblast organization during tooth mineralization. Dental apoptosis is caspase dependent and proceeds via mitochondrial mediated cell death with possible amplification by Fas-FasL signaling modulated by Bcl-2 family members.

Effect of smoking status on seminal parameters and apoptotic markers in infertile men

PURPOSE

We assessed semen parameters, sperm apoptotic markers and seminal plasma cotinine in infertile smokers.

MATERIALS AND METHODS

A total of 160 men were divided into 4 equal groups, including fertile smokers, fertile nonsmokers, infertile smokers and infertile nonsmokers. Smoking was classified as mild--fewer than 10, moderate--10 to 20 or heavy--more than 20 cigarettes daily. All men underwent semen analysis, and assessment of sperm caspase-9, Smac/DIABLO, DNA fragmentation and seminal plasma cotinine.

RESULTS

Infertile men, particularly smokers, have significantly lower semen variables and significantly higher sperm Smac/DIABLO, caspase-9 activity, the percent of DNA fragmentation and seminal plasma cotinine. The mean number of cigarettes smoked daily and smoking duration significantly correlated positively with sperm Smac/DIABLO, caspase-9 activity, the percent of DNA fragmentation and seminal plasma cotinine, and significantly correlated negatively with tested semen variables. Heavy smoking was associated with a significant increase in sperm Smac/DIABLO, caspase-9 activity and seminal plasma cotinine, and with a significant decrease in tested semen variables compared with those in moderate or mild smokers.

CONCLUSIONS

Smoking has a negative impact on semen variables. It is associated with increased sperm caspase-9, Smac/DIABLO and the percent of DNA fragmentation, especially in infertile heavy smokers.

Sensitization of human bladder tumor cells to TNF-related apoptosis-inducing ligand (TRAIL)-induced apoptosis with a small molecule IAP antagonist

Urothelial carcinoma of the bladder accounts for approximately 5% of all cancer deaths in humans. The large majority of bladder tumors are non-muscle invasive at diagnosis, but even after local surgical therapy there is a high rate of local tumor recurrence and progression. Current treatments extend time to recurrence but do not significantly alter disease survival. The objective of the present study was to investigate the tumoricidal potential of combining the apoptosis-inducing protein TNF-related apoptosis-inducing ligand (TRAIL) with a small molecule inhibitor of apoptosis proteins (IAP) antagonist to interfere with intracellular regulators of apoptosis in human bladder tumor cells. Our results demonstrate that the IAP antagonist Compound A exhibits high binding affinity to the XIAP BIR3 domain. When Compound A was used at nontoxic concentrations in combination with TRAIL, there was a significant increase in the sensitivity of TRAIL-sensitive and TRAIL-resistant bladder tumor lines to TRAIL-mediated apoptosis. In addition, modulation of TRAIL sensitivity in the TRAIL-resistant bladder tumor cell line T24 with Compound A was reciprocated by XIAP small interfering RNA-mediated suppression of XIAP expression, suggesting the importance of XIAP-mediated resistance to TRAIL in these cells. These results suggest the potential of combining Compound A with TRAIL as an alternative therapy for bladder cancer.

Pharmacological interventions for spinal cord injury: where do we stand? How might we step forward?

Despite numerous studies reporting some measures of efficacy in the animal literature, there are currently no effective therapies for the treatment of traumatic spinal cord injuries (SCI) in humans. The purpose of this review is to delineate key pathophysiological processes that contribute to neurological deficits after SCI, as well as to describe examples of pharmacological approaches that are currently being tested in clinical trials, or nearing clinical translation, for the therapeutic management of SCI. In particular, we will describe the mechanistic rationale to promote neuroprotection and/or functional recovery based on theoretical, yet targeted pathological events. Finally, we will consider the clinical relevancy for emerging evidence that pharmacologically targeting mitochondrial dysfunction following injury may hold the greatest potential for increasing tissue sparing and, consequently, the extent of functional recovery following traumatic SCI.

Mono- or double-site phosphorylation distinctly regulates the proapoptotic function of Bax

Bax is the major multidomain proapoptotic molecule that is required for apoptosis. It has been reported that phosphorylation of Bax at serine(S) 163 or S184 activates or inactivates its proapoptotic function, respectively. To uncover the mechanism(s) by which phosphorylation regulates the proapoptotic function of Bax, a series of serine (S)→ alanine/glutamate (A/E) Bax mutants, including S163A, S184A, S163E, S184E, S163E/S184A (EA), S163A/S184E (AE), S163A/S184A (AA) and S163E/S184E (EE), were created to abrogate or mimic, respectively, either single or double-site phosphorylation. The compound Bax mutants (i.e. EA and AE) can flesh out the functional contribution of individual phosphorylation site(s). WT and each of these Bax mutants were overexpressed in Bax^−/− MEF or lung cancer H157 cells and the proapoptotic activities were compared. Intriguingly, expression of any of Bax mutants containing the mutation S→A at S184 (i.e. S184A, EA or AA) represents more potent proapoptotic activity as compared to WT Bax in association with increased 6A7 epitope conformational change, mitochondrial localization/insertion and prolonged half-life. In contrast, all Bax mutants containing the mutation S→E at S184 (i.e. S184E, AE or EE) have a mobility-shift and fail to insert into mitochondrial membranes with decreased protein stability and less apoptotic activity. Unexpectedly, mutation either S→A or S→E at S163 site does not significantly affect the proapoptotic activity of Bax. These findings indicate that S184 but not S163 is the major phosphorylation site for functional regulation of Bax's activity. Therefore, manipulation of the phosphorylation status of Bax at S184 may represent a novel strategy for cancer treatment.

Apoptogenic factors released from mitochondria

When cells kill themselves, they usually do so by activating mechanisms that have evolved specifically for that purpose. These mechanisms, which are broadly conserved throughout the metazoa, involve two processes: activation in the cytosol of latent cysteine proteases (termed caspases), and disruption of mitochondrial functions. These processes are linked in a number of different ways. While active caspases can cleave proteins in the mitochondrial outer membrane, and cleave and thereby activate certain pro-apoptotic members of the Bcl-2 family, proteins released from the mitochondria can trigger caspase activation and antagonise IAP family proteins. This review will focus on the pro-apoptotic molecules that are released from the mitochondria of cells endeavouring to kill themselves. This article is part of a Special Issue entitled Mitochondria: the deadly organelle.

Smac/DIABLO release from mitochondria and XIAP inhibition are essential to limit clonogenicity of Type I tumor cells after TRAIL receptor stimulation

Death receptors, such as Fas/CD95 and TRAIL receptors, engage the extrinsic pathway for caspase activation, but also couple to the intrinsic mitochondrial route. In so-called Type II cells, death receptors require the mitochondrial pathway for apoptotic execution, whereas in Type I cells they reportedly do not. For established tumor cell lines, the Type I/Type II distinction is based on short-term apoptosis assays. We report here that the mitochondrial pathway is essential for apoptotic execution of Type I tumor cells by death receptors, when long-term clonogenicity is taken into account. A blockade of the mitochondrial pathway in Type I tumor cells - by RNA interference for Bid or Bcl-2 overexpression - reduced effector caspase activity and mediated significant clonogenic resistance to TRAIL. Downstream from the mitochondria, Caspase-9 did not contribute to clonogenic death of TRAIL-treated Type I cells. Rather, the release of Smac/DIABLO and the inhibition of XIAP activity proved to be crucial for full effector caspase activity and clonogenic execution. Thus, in Type I cells the intrinsic pathway downstream from death receptors is not redundant, but limits clonogenicity by virtue of Smac/DIABLO release and XIAP inhibition. This finding is relevant for cancer therapy using death receptor agonists.

Identification of an Xiap-like pseudogene on mouse chromosome 7

The most thoroughly characterized mammalian IAP is XIAP/BIRC4, which can inhibit caspases 9, 3 and 7, but may also regulate apoptosis through interactions with other proteins such as Smac/DIABLO, HtrA2/Omi, XAF1, TAK1, cIAP1, and cIAP2.

High throughput sequencing of the mouse genome revealed the existence of a gene resembling Xiap/Birc4 on mouse chromosome 7. To confirm the existence of this gene, and to determine its functional significance, we performed Southern and Northern blot analysis. This showed the presence of the Xiap-like gene in both wild-type and Xiap gene knock-out mice, but the corresponding mRNA was not detected in any tissues examined by Northern blot. Analysis of the gene sequence in all three possible reading frames predicts that expression of this gene would not give rise to a full-length protein, but only non-functional truncated polypeptides. Because its nucleotide sequence is 92% identical to Xiap, but it has no introns corresponding to those of Xiap, we conclude that Xiap-ps1 is a pseudogene generated by retro-transposition of a spliced Xiap message to chromosome 7.

Etoposide induces protein kinase Cdelta- and caspase-3-dependent apoptosis in neuroblastoma cancer cells

In this report, we reveal that etoposide inhibits the proliferation of SK-N-AS neuroblastoma cancer cells and promotes protein kinase Cdelta (PKCdelta)- and caspase-dependent apoptosis. Etoposide induces the caspase-3-dependent cleavage of PKCdelta to its active p40 fragment, and active PKCdelta triggers the processing of caspase-3 by a positive-feedback mechanism. Treatment of cells with the caspase-3-specific inhibitor N-benzyloxycarbonyl-Asp-Glu-Val-Asp-fluoromethyl ketone or caspase-3-specific small interacting RNA (siRNA) prevented the etoposide-induced activation of caspase-8 and inhibited apoptosis. The silencing of the caspase-2 or caspase-8 genes using siRNAs did not affect the etoposide-induced processing of caspase-3, indicating that these caspases lie downstream of caspase-3 in this signaling pathway. Furthermore, the etoposide-induced processing of caspase-2 required the expression of caspase-8, and the etoposide-mediated processing of caspase-8 required the expression of caspase-2, indicating that these two caspases activate each other after etoposide treatment. We also observed that etoposide-mediated apoptosis was decreased by treating the cells with the caspase-6-specific inhibitor benzyloxycarbonyl-Val-Glu(OMe)-Ile-Asp-(OMe)-fluoromethyl ketone and that caspase-6 was activated by a caspase-8-dependent mechanism. Finally, we show that rottlerin blocks etoposide-induced apoptosis by inhibiting the PKCdelta-mediated activation of caspase-3 and by degrading caspase-2, which prevents caspase-8 activation. Our results add important insights into how etoposide mediates apoptotic signaling and how targeting these pathways may lead to the development of novel therapeutics for the treatment of neuroblastomas.

Expression of the apoptosis inducer gene head involution defective in primordial germ cells of the Drosophila embryo requires eiger, p53, and loki function

Nanos (Nos) is an evolutionarily conserved protein essential for the maintenance of primordial germ cells (PGCs). In Drosophila, the PGCs or pole cells express head involution defective (hid), which is required for caspase activation, but its translation is repressed by maternal Nos. In the absence of Nos activity, translation of hid mRNA into protein induces apoptosis in pole cells. However, it remains unclear how hid mRNA is regulated in pole cells. Here, we report that hid expression requires eiger (egr), a tumor necrosis factor ligand (TNF) homologue, which is induced in pole cells by decapentaplegic (dpp). In addition, we demonstrate that p53 and loki (lok), a damage-activated kinase known to be required for p53 phosphorylation, are both required for hid expression in pole cells. Since maternal lok mRNA is enriched in pole cells, it is possible that ubiquitously distributed p53 is activated in pole cells by maternal Lok. We propose that hid expression is activated in a pole cell-specific manner by loki/p53 and dpp/egr during embryogenesis.

Granulocyte-colony stimulating factor inhibits neuronal apoptosis in a rat model of diabetic cerebral ischemia

Incidence of cerebral vascular disease (CVD) is higher in patients with diabetes mellitus (DM) than that in individuals without DM, and neuronal apoptosis determines the severity of cerebral infarction. However, there is no effective therapy for CVD. Granulocyte-colony stimulating factor (G-CSF), a potent hematopoietic factor, could inhibit apoptosis of hematopoietic progenitor cells. However, its effect on neuronal cells is still unclear. In this study, we investigated the anti-apoptosis properties of G-CSF in neurons following focal cerebral ischemia in diabetic rats. The diabetic condition was generated in rats by intravenous injection of streptozotocin. After 6 weeks, diabetic rats underwent middle cerebral artery occlusion (MCAO) and received subcutaneous administration of G-CSF (50 microg/kg) daily for 7, 14 or 21 days. We analyzed the changes in neurological severity scores, infarct volume, number of apoptotic neurons, and the expression of G-CSF receptor, phosphorylated signal transducer and activator of transcription 3 (pSTAT3), cellular inhibitor of apoptosis protein 2 (cIAP2), Bcl-2, and Bax in the brain tissue. Bax is a pro-apoptotic member of the Bcl-2 protein family. The DM rats treated with G-CSF not only showed the reduced infarct volume and decreased apoptosis cell number, but also presented improved neurological scores. The G-CSF also increased the expression of pSTAT3, Bcl-2, and cIAP2 proteins as well as Bcl-2 mRNA, but inhibited Bax protein expression in the brain. These results indicate that G-CSF partially increases neuronal survival by affecting apoptosis pathways. G-CSF provides a potential treatment for stroke and other neurological dysfunction accompanied by neuronal apoptosis.

Effects of imatinib mesylate on normal bone marrow cells from chronic myeloid leukemia patients in complete cytogenetic response

Information on the effects of imatinib mesylate (IM) on the non-clonal bone marrow (BM) cell compartment is scanty. We have analyzed the gene expression profile of BM hematopoietic cells after IM therapy in 20 patients with chronic myeloid leukaemia (CML) in complete cytogenetic response (CCyR) and compared it with that of normal volunteer donors by oligonucleotide microarrays. In CCyR CML samples, IM induces a decrease in proliferation as well as increase in apoptosis and ubiquitination in residual non-clonal BM cells. In addition, IM diminishes cell-to-cell adhesion and downregulates the expression of the erythropoietin (EPO) receptor gene. The latter was confirmed by RT-PCR.

c-Myc and caspase-2 are involved in activating Bax during cytotoxic drug-induced apoptosis

Activation of Bax following diverse cytotoxic stress has been shown to be an essential gateway to mitochondrial dysfunction and activation of the intrinsic apoptotic pathway characterized by cytochrome c release with caspase-9/-3 activation. Interestingly, c-Myc has been reported to promote apoptosis by destabilizing mitochondrial integrity in a Bax-dependent manner. Stress-induced activation of caspase-2 may also induce permeabilization of mitochondria with activation of the intrinsic death pathway. To test whether c-Myc and caspase-2 cooperate to activate Bax and thereby mediate intrinsic apoptosis, small interfering RNA was used to efficiently knock down the expression of c-Myc, caspase-2, and Apaf-1, an activating component in the apoptosome, in two human cancer cell lines, lung adenocarcinoma A-549 and osteosarcoma U2-OS cells. Under conditions when the expression of endogenous c-Myc, caspase-2, or Apaf-1 is reduced 80-90%, cisplatin (or etoposide)-induced apoptosis is significantly decreased. Biochemical studies reveal that the expression of c-Myc and caspase-2 is crucial for cytochrome c release from mitochondria during cytotoxic stress and that Apaf-1 is only required following cytochrome c release to activate caspases-9/-3. Although knockdown of c-Myc or caspase-2 does not affect Bax expression, caspase-2 is important for cytosolic Bax to integrate into the outer mitochondrial membrane, and c-Myc is critical for oligomerization of Bax once integrated into the membrane.

SMAC-expression in denervated human skeletal muscle as a potential inhibitor of coexpressed inhibitor-of-apoptosis proteins

In multinucleated skeletal muscle fibers, apoptotic muscle fiber loss is mediated by a consecutive disassembly of single fiber segments. During this period of time, proapoptotic and antiapoptotic factors compete for promotion or inhibition of apoptotic fiber degradation. In 16 patients with a neurogenic muscular atrophy, we studied the immunohistochemical expression of the inhibitor-of-apoptosis proteins (IAP) survivin, cIAP1, and XIAP and also of second mitochondria-derived activator of caspase (SMAC), which is released during apoptosis and binds to IAPs to prevent them from inhibiting caspases. Although normal control muscle fibers show no expression of SMAC and IAPs, there was a distinct sarcoplasmic expression of SMAC (12.0%+/-3.5%), survivin (10.2%+/-4.0%), cIAP1 (9.0%+/-3.1%), and XIAP (11.0%+/-4.6%) in varying numbers of muscle fibers in neurogenic muscular atrophy. Coexpression of SMAC and IAPs varied. Some denervated muscle fibers displayed up-regulation of either SMAC or IAPs. Other groups of atrophic muscle fibers showed coexpression of SMAC and IAPs. All factors were exclusively up-regulated in atrophic muscle fibers. These findings indicate that IAPs may inhibit apoptotic degradation of denervated muscle fibers. However, IAPs are finally insufficient to counterbalance and prevent muscle fiber apoptosis, as up-regulated expression of SMAC can antagonize this antiapoptotic potential and promote apoptotic muscle fiber disassembly and loss. The interplay between IAPs and SMAC may represent a threshold for muscle fiber-degrading caspase activities. If this bears a therapeutic potential in the prevention of loss of denervated muscle fibers, it remains highly speculative.

Apoptosis and Cell Death: Relevance to Lung

In multicellular organisms, cell death plays an important role in development, morphogenesis, control of cell numbers, and removal of infected, mutated, or damaged cells. The term apoptosis was first coined in 1972 by Kerr et al.1 to describe the morphologic features of a type of cell death that is distinct from necrosis and is today considered to represent programmed cell death. In fact, the evidence that a genetic program existed for physiologic cell death came from the developmental studies of the nematode Caenorhabditis elegans.2 As time has progressed, however, apoptotic cell death has been shown to occur in many cell types under a variety of physiologic and pathologic conditions. Cells dying by apoptosis exhibit several characteristic morphologic features that include cell shrinkage, nuclear condensation, membrane blebbing, nuclear and cellular fragmentation into membrane-bound apoptotic bodies, and eventual phagocytosis of the fragmented cell (Figure 4.1). Figure 4.1

Inhibition of NF-kappaB activation reduces the tissue effects of transgenic IL-13

IL-13 is a major Th2 cytokine that is capable of inducing inflammation, excessive mucus production, airway hyperresponsiveness, alveolar remodeling, and fibrosis in the murine lung. Although IL-13 through its binding to IL-4Ralpha/IL-13Ralpha1 uses the canonical STAT6-signaling pathway to mediate these tissue responses, recent studies have demonstrated that other signaling pathways may also be involved. Previous studies from our laboratory demonstrated that IL-13 mediates its tissue effects by inducing a wide variety of downstream genes many of which are known to be regulated by NF-kappaB. As a result, we hypothesized that NF-kappaB activation plays a critical role in the pathogenesis of IL-13-induced tissue alterations. To test this hypothesis, we compared the effects of transgenic IL-13 in mice with normal and diminished levels of NF-kappaB activity. Three pharmacologic approaches were used to inhibit NF-kappaB including 1) PS1145, a small molecule inhibitor of IkappaBalpha kinase (IKK2), 2) antennapedia-linked NF-kappaB essential modulator-binding domain (NBD) peptide (wild-type NBD), and 3) an adenoviral construct expressing a dominant-negative version of IKK2. We also crossed IL-13-transgenic mice with mice with null mutations of p50 to generate mice that overproduced IL-13 in the presence and absence of this NF-kappaB component. These studies demonstrate that all these interventions reduced IL-13-induced tissue inflammation, fibrosis and alveolar remodeling. In addition, we show that both PS1145 and wild-type NBD inhibit lung inflammatory and structural cell apoptosis. PS1145 inhibits caspase activation and up-regulates inhibitor of apoptosis protein cellular-inhibitor of apoptosis protein 1 (c-IAP-1). Therefore, NF-kappaB is an attractive target for immunotherapy of IL-13-mediated diseases.

Commitment to apoptosis in CD4(+) T lymphocytes productively infected with human immunodeficiency virus type 1 is initiated by lysosomal membrane permeabilization, itself induced by the isolated expression of the viral protein Nef

Primary CD4(+) T lymphocytes, supporting in vitro human immunodeficiency virus type 1 (HIV-1) replication, are destined to die by apoptosis. We explored the initial molecular events that act upstream from mitochondrial dysfunction in CD4(+) T lymphocytes exposed to the HIV-1(LAI) strain. We tracked by immunofluorescence the cells expressing the p24 viral antigen and used Percoll density gradients to isolate a nonapoptotic CD4(+) T-cell subset with a high inner mitochondrial transmembrane potential (DeltaPsim) but no outer mitochondrial membrane (OMM) rupture. In most p24(+) (but not bystander p24(-)) cells of this subset, the lysosomes were undergoing limited membrane permeabilization, allowing the lysosomal efflux of cathepsins (Cat) to the cytosol. This was also induced by HIV-1 isolates from infected patients. Using pepstatin A to inhibit Cat-D enzymatic activity and Cat-D small interfering RNA to silence the Cat-D gene, we demonstrate that once released into the cytosol, Cat-D induces the conformational change of Bax and its insertion into the OMM. Inhibition of Cat-D activity/expression also conferred a transient survival advantage upon productively HIV-1-infected cells, indicating that Cat-D is an early death factor. The transfection of activated CD4(+) T lymphocytes with a Nef expression vector rapidly induced the permeabilization of lysosomes and the release of Cat-D, with these two events preceding OMM rupture. These results reveal a previously undocumented mechanism in which Nef acts as an internal cytopathic factor and strongly suggest that this viral protein may behave similarly in the context of productive HIV-1 infection in CD4(+) T lymphocytes.

Structure–activity based study of the Smac-binding pocket within the BIR3 domain of XIAP

A small series of peptide mimics was designed and synthesized to contain a heterocyclic ring in place of the potentially labile N-terminal peptide bond of the tetrapeptide containing the Smac-XIAP-binding motif. Two Smac mimics were shown to bind to the BIR3 domain of XIAP with moderate affinity and one displayed increased activity in cells relative to the Smac peptides. The structures of BIR3-XIAP in complex with a Smac peptide and a peptide mimic were solved and analyzed to elucidate the structure-activity relationship surrounding the Smac-binding domain within BIR3-XIAP.

The equilibrium of XIAP and Smac/DIABLO expression is gradually deranged during the development and progression of testicular germ cell tumours

Overexpression of the inhibitor of apoptosis protein (IAP) XIAP (BIRC4) and downregulation of its antagonist Smac/DIABLO (DIABLO) are associated with the onset and progression of various malignancies. In this study, real-time RT-PCR was used to quantify the mRNA expression of XIAP and Smac/DIABLO in normal testicular tissue (n = 19), testicular carcinoma in situ (CIS; n = 4), testicular seminomas (n = 64) and non-seminomatous germ cell tumours (NSGCT; n = 35). XIAP and Smac/DIABLO were commonly expressed in normal and malignant testicular tissue with no apparent differences in XIAP mRNA levels among the histologic subgroups. Smac/DIABLO levels, on the other hand, gradually decreased from normal testicular tissue to CIS and seminomas and finally to NSGCT (p < 0.001). An inverse trend was observed when calculating the XIAP-to-Smac/DIABLO ratio (p < 0.001). This ratio differed when comparing normal testicular tissue with CIS (p = 0.014), seminomas (p < 0.001) and NSGCT (p < 0.001) and when comparing seminomas with NSGCT (p = 0.002), whereas no such difference was observed between CIS and seminomas (p = 0.302). TGCT patients dichotomized by the overall median XIAP-to-Smac/DIABLO ratio were more likely to present with a high ratio in clinical stage (CS) III than in CS I or II (p = 0.034). These data indicate that the balance of mRNA expression between XIAP and Smac/DIABLO is altered in favour of antiapoptotic XIAP during the development and progression of TGCT. Thus the expression of proapoptotic Smac/DIABLO is lowest in NSGCT and stage III tumours.

Apoptosis induced by cAMP requires Smac/DIABLO transcriptional upregulation

Smac/DIABLO is a mitochondrial protein that participates in apoptotic cell death by means of sequestering several members of the inhibitor of apoptosis protein family. This action allows caspase activation, cleavage of key cellular substrates and death. Release from mitochondria is considered the main regulatory step of Smac/DIABLO activity. Nevertheless, the fact that at least one isoform, Smac-beta, does not reside in this organelle implies that transcriptional regulation could also be important. cAMP is a well known second messenger with important apoptotic effects. To analyze if cAMP could be involved in Smac/DIABLO gene regulation, we analyzed 2903 base pairs upstream of the coding sequence and characterized the minimal promoter, which contains a consensus CRE site. We found that cAMP/PKA/CREB pathway is indeed an important regulator of Smac/DIABLO transcription, since exposure to the cAMP analog 8-CPT-cAMP, the adenylyl cyclase activator forskolin, the inhibitor of phosphodiesterase isobutylmethylxanthine or by hindering PKA activation with H89, regulated the promoter activity, as shown by gene reporter and RT-PCR assays. Additionally, the results of site-directed mutagenesis revealed that the consensus CRE site was biologically functional and required for cAMP-induced promoter activity in human HeLa cells. Supporting these results, a negative dominant version of the protein kinase A responsive factor, KCREB, reduced basal Smac/DIABLO expression and rendered the promoter unresponsive to cAMP. Reducing Smac expression using an antisense approach blocked the apoptosis effects of cAMP in cervical cancer cells. These results show that cAMP is an important modulator of the apoptotic threshold in cancer cell by means of regulating Smac/DIABLO expression.

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.

Therapy-induced apoptosis in primary tumors

An enormous body of literature has accumulated over the past 15 years implicating apoptosis (programmed cell death) in breast cancer cell death induced by conventional and investigational cancer therapies in preclinical models. As a result, new therapeutic approaches that directly target key components of apoptotic pathways are either entering or will soon enter clinical trials in patients, raising hopes that the information gained from the preclinical studies can be translated to improve patient care. However, there is a new appreciation for the fact that apoptosis is not the only relevant pathway that mediates physiological cell death, and many investigators are challenging the notion that targeting apoptosis is the best means of optimizing therapeutic efficacy in primary tumors. Here I will review some of the basic concepts that have emerged from the study of apoptosis in preclinical models, the evidence that apoptosis does or does not mediate the effects of current front line therapies in patients, and the new strategies that are emerging that are designed to more directly target apoptotic pathways.

Design, synthesis, and evaluation of a potent, cell-permeable, conformationally constrained second mitochondria derived activator of caspase (Smac) mimetic

A potent, cell-permeable, conformationally constrained second mitochondria derived activator of caspase mimetic (SM-131, 2) has been designed, synthesized, and evaluated. Compound 2 binds to X-linked inhibitors of apoptosis proteins (XIAP) with a Ki of 61 nM in a competitive binding assay and directly antagonizes the XIAP inhibition of caspase-9 activity in a cell-free functional assay. Compound 2 achieves an IC50 of 100 nM in inhibition of cell growth and effectively induces cell death in the MDA-MB-231 human breast cancer cell line.