XIAP regulates DNA damage-induced apoptosis downstream of caspase-9 cleavage

Formal verification confirms the role of p53 protein in cell fate decision mechanism

The bio-cell cycle is controlled by a complex biochemical network of signaling pathways. Modeling such challenging networks accurately is imperative for the understanding of their detailed dynamical behavior. In this paper, we construct, analyze, and verify a hybrid Petri net (HPN) model of a complex biochemical network that captures the role of an important protein (namely p53) in deciding the fate of the cell. We model the behavior of the cell nucleus and cytoplasm as two stochastic and continuous Petri nets, respectively, combined together into a single HPN. We use simulative model checking to verify three different properties that capture the dynamical behavior of p53 protein with respect to the intensity of the ionizing radiation (IR) to which the cell is exposed. For each IR dose, 1000 simulation runs are carried out to verify each property. Our verification results showed that the fluctuations in p53, which relies on IR intensity, are compatible with the findings of the preceding simulation studies that have previously examined the role of p53 in cell fate decision.

Targeting the BIR Domains of Inhibitor of Apoptosis (IAP) Proteins in Cancer Treatment

Inhibitor of apoptosis (IAP) proteins are characterized by the presence of the conserved baculoviral IAP repeat (BIR) domain that is involved in protein-protein interactions. IAPs were initially thought to be mainly responsible for caspase inhibition, acting as negative regulators of apoptosis, but later works have shown that IAPs also control a plethora of other different cellular pathways. As X-linked IAP (XIAP), and other IAP, levels are often deregulated in cancer cells and have been shown to correlate with patients' prognosis, several approaches have been pursued to inhibit their activity in order to restore apoptosis. Many small molecules have been designed to target the BIR domains, the vast majority being inspired by the N-terminal tetrapeptide of Second Mitochondria-derived Activator of Caspases/Direct IAp Binding with Low pI (Smac/Diablo), which is the natural XIAP antagonist. These compounds are therefore usually referred to as Smac mimetics (SMs). Despite the fact that SMs were intended to specifically target XIAP, it has been shown that they also interact with cellular IAP-1 (cIAP1) and cIAP2, promoting their proteasome-dependent degradation. SMs have been tested in combination with several cytotoxic compounds and are now considered promising immune modulators which can be exploited in cancer therapy, especially in combination with immune checkpoint inhibitors. In this review, we give an overview of the structural hot-spots of BIRs, focusing on their fold and on the peculiar structural patches which characterize the diverse BIRs. These structures are exploited/exploitable for the development of specific and active IAP inhibitors.

Transcriptional activation of miR-320a by ATF2, ELK1 and YY1 induces cancer cell apoptosis under ionizing radiation conditions

MicroRNAs (miRNAs or miRs) play important roles in numerous cellular processes, including development, proliferation, tumorigenesis and apoptosis. It has been reported that miRNA expression is induced by ionizing radiation (IR) in cancer cells. However, the underlying molecular mechanisms are not yet fully understood. In this study, endogenous miR‑320a and its primary precursor (pri‑miR‑320a) were assayed by reverse transcription‑quantitative PCR (RT‑qPCR). Luciferase activities were measured using a dual‑luciferase reporter assay system. Western blot analysis was used to determine the protein expressions of upstream and downstream genes of miR‑320a. Cell apoptosis was evaluated by Annexin V apoptosis assay and cell proliferation was measured using the trypan blue exclusion method. The results revealed that miR‑320a expression increased linearly with the IR dose and treatment duration. Three transcription factors, activating transcription factor 2 (ATF2), ETS transcription factor (ELK1) and YY1 transcription factor (YY1), were activated by p38 mitogen‑activated protein kinase (MAPK) and mitogen‑activated protein kinase 8 (JNK) and by upregulated miR‑320a expression under IR conditions. In addition, it was identified that X‑linked inhibitor of apoptosis (XIAP) was an miR‑320a target gene during the IR response. By targeting XIAP, miR‑320a induced apoptosis and inhibited the proliferation of the cancer cells. On the whole, the results of this study demonstrated that miRNA‑320a, regulated by the p38 MAPK/JNK pathway, enhanced the radiosensitivity of cancer cells by inhibiting XIAP and this may thus prove to be a potential therapeutic approach with which to overcome radioresistance in cancer treatment.

Signaling by cell surface death receptors: Alterations in head and neck cancer

Cell surface death receptors are members of the tumor necrosis factor receptor (TNFR) superfamily and mediate signals leading to the induction of apoptosis or necroptosis, as well as NF-κB-mediated cell survival. These biochemical processes play key roles in cell growth, development, tissue homeostasis, and immune responses. The downstream signaling complexes activated by different death receptors can differ significantly and are subject to multiple, distinct regulatory mechanisms. Dysregulation of signaling by the TNFR superfamily contributes to a variety of pathologic conditions, including defective immune responses and cancer. Caspase-8 signaling is important for mediating death receptor signals leading to either apoptosis or NF-κB activation. By contrast, inactivation of caspase-8 or loss of caspase-8 expression shifts death receptor signaling to the necroptosis pathway. Notably, the gene encoding caspase-8 is mutated in roughly ten percent of head and neck cancers. These findings support the hypothesis that alterations in the biochemical pathways mediated by death receptors have important consequences for the development of head and neck, and possibly other, cancers.

Protective effect of N-acetylcysteine activated carbon release microcapsule on myocardial ischemia-reperfusion injury in rats

With the development of science and technology, and development of artery bypass, methods such as cardiopulmonary cerebral resuscitation have been practiced in recent years. Despite this, some methods fail to promote or recover the function of tissues and organs, and in some cases, may aggravate dysfunction and structural damage to tissues. The latter is typical of ischemia-reperfusion (IR) injury. Lipid peroxidation mediated by free radicals is an important process of myocardial IR injury. Myocardial IR has been demonstrated to induce the formation of large numbers of free radicals in rats, which promotes the peroxidation of lipids within unsaturated fatty acids in the myocardial cell membrane. Markers of lipid peroxidation include malondialdehyde, superoxide dismutase and lactic dehydrogenase. Recent studies have demonstrated that N-acetylcysteine (NAC) is able to dilate blood vessels, prevent oxidative damage, improve immunity, inhibit apoptosis and the inflammatory response and promote glutathione synthesis in cells. NAC also improves the systolic function of myocardial cells and cardiac function, prevents myocardial apoptosis, protects ventricular remodeling and vascular remodeling, reduces opiomelanocortin levels in the serum and increases the content of nitric oxide in the serum, thus improving vascular endothelial function. Therefore, NAC has potent pharmacological activity; however, the relatively fast metabolism of NAC, along with its large clinical dose and low bioavailability, limit its applications. The present study combined NAC with medicinal activated carbons, and prepared N-acetylcysteine activated carbon sustained-release microcapsules (ACNACs) to overcome the limitations of NAC. It was demonstrated that ACNACs exerted greater effective protective effects than NAC alone on myocardial IR injury in rats.

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.

ASC Induces Apoptosis via Activation of Caspase-9 by Enhancing Gap Junction-Mediated Intercellular Communication

ASC (apoptosis-associated speck-like protein containing a CARD) is a key adaptor molecule of inflammasomes that mediates inflammatory and apoptotic signals. Aberrant methylation-induced silencing of ASC has been observed in a variety of cancer cells, thus implicating ASC in tumor suppression, although this role remains incompletely defined especially in the context of closely neighboring cell proliferation. As ASC has been confirmed to be silenced by abnormal methylation in HT1080 fibrosarcoma cells as well, this cell line was investigated to characterize the precise role and mechanism of ASC in tumor progression. The effects of ASC were examined using in vitro cell cultures based on comparisons between low and high cell density conditions as well as in a xenograft murine model. ASC overexpression was established by insertion of the ASC gene into pcDNA3 and pMX-IRES-GFP vectors, the latter being packed into a retrovirus and subjected to reproducible competitive assays using parental cells as an internal control, for evaluation of cell viability. p21 and p53 were silenced using shRNA. Cell viability was suppressed in ASC-expressing transfectants as compared with control cells at high cell density conditions in in vitro culture and colony formation assays and in in vivo ectopic tumor formation trials. This suppression was not detected in low cell density conditions. Furthermore, remarkable progression of apoptosis was observed in ASC-introduced cells at a high cell density, but not at a low one. ASC-dependent apoptosis was mediated not by p21, p53, or caspase-1, but rather by cleavage of caspase-9 as well as by suppression of the NF-κB-related X-linked inhibitor-of-apoptosis protein. Caspase-9 cleavage was observed to be dependent on gap junction formation. The remarkable effect of ASC on the induction of apoptosis through caspase-9 and gap junctions revealed in this study may lead to promising new approaches in anticancer therapy.

Is there something else besides the proapoptotic AVPI-segment in the Smac/DIABLO protein?

In mammals, apoptosis is the main mechanism to eliminate unwanted cells, securing tissue homeostasis and consequently maintaining the health in the organism. Classically, apoptosis culminates with the activation of caspases, which are enzymes that display cysteine protease activity to degrade specific substrates implied in essential cellular processes. This process is highly regulated. A key regulation mechanism is mediated by the Inhibitor of Apoptosis Proteins (IAPs) family members, which inhibit the activated forms of caspases through physical interaction with them. Smac/DIABLO, a mitochondrial protein that is translocated to the cytoplasm in apoptotic conditions, derepresses the IAP-mediated caspase inhibition through physical interaction with IAPs. The first four amino acids (AVPI) of Smac/DIABLO mediate the interaction with IAPs and subsequent apoptosis induction. This interaction has lead to the creation of small molecules mimicking the AVPI segment for potential anticancer therapy. Nevertheless, several studies have pointed out the existence of AVPI-independent functions of Smac/DIABLO. The aim of this review was to provide a landscape of these underestimated AVPI-independent biological functions that have been observed using different approaches, such as the study of endogenous splice variant isoforms and truncated and mutated artificial proteins.

Procaspase-9 induces its cleavage by transnitrosylating XIAP via the Thioredoxin system during cerebral ischemia-reperfusion in rats

Transnitrosylation is an important mechanism by which nitric oxide (NO) modulates cell signaling pathways. For instance, SNO-caspase-3 can transnitrosylate the X-linked inhibitor of apoptosis (XIAP) to enhance apoptosis. XIAP is a potent antagonist of caspase apoptotic activity. Decrease in XIAP activity via nitrosylation results in SNO-XIAP-mediated caspase activation. Considering the functional liaison of procaspase-9 and XIAP, we hypothesized that procaspase-9 nitrosylates XIAP directly. Our data confirmed that cerebral ischemia-reperfusion induced XIAP nitrosylation, procaspase-9 denitrosylation and cleavage. Interestingly, the time courses of the nitrosylation of procaspase-9 and XIAP were negatively correlated, which was more prominent after cerebral ischemia-reperfusion, suggesting a direct interaction. The nitrosylation of XIAP, as well as the denitrosylation and cleavage of procaspase-9, were inhibited by DNCB, TrxR1 AS-ODNs, or TAT-AVPY treatment. Meanwhile, DNCB, TrxR1 AS-ODNs, or TAT-AVPY also inhibited the decrease in hippocampal CA1 neurons induced by ischemia-reperfusion in rats. The denitrosylation and cleavage of procaspase-9 induced by OGD/reoxygenation in SH-SY5Y cells were inhibited when cells were co-transfected with wild-type procaspase-9 and XIAP mutant (C449G). These data suggest that cerebral ischemia-reperfusion induces a transnitrosylation from procaspase-9 to XIAP via the Trx system to consequently cause apoptosis. Additionally, Cys325 is a critical S-nitrosylation site of procaspase-9.

SIAH1-induced p34SEI-1 polyubiquitination/degradation mediates p53 preferential vitamin C cytotoxicity

Vitamin C is considered as an important anticancer therapeutic agent although this view is debatable. In this study, we introduce a physiological mechanism demonstrating how vitamin C exerts anticancer activity that induces cell cycle arrest and apoptosis. Our previous and current data reveal that p53 tumor suppressor is the prerequisite factor for stronger anticancer effects of vitamin C. In addition, vitamin C-mediated cancer cell cytotoxicity appears to be achieved at least partly through the downregulation of the p34SEI-1 oncoprotein. Our previous study showed that p34SEI-1 increases the survival of various types of cancer cells by inhibiting their apoptosis. Present data suggest that vitamin C treatment decreases the p34SEI-1 expression at the protein level and therefore alleviates its anti-apoptotic activity. Of note, SIAH1, E3 ubiquitin ligase, appears to be responsible for the p34SEI-1 polyubiquitination and its subsequent degradation, which is dependent on p53. In summary, vitamin C increases cancer cell death by inducing SIAH1-mediated polyubiquitination/degradation of the p34SEI-1 oncoprotein in a p53-dependent manner.

Histone deacetylase inhibitor (HDACI) mechanisms of action: emerging insights

Initially regarded as "epigenetic modifiers" acting predominantly through chromatin remodeling via histone acetylation, HDACIs, alternatively referred to as lysine deacetylase or simply deacetylase inhibitors, have since been recognized to exert multiple cytotoxic actions in cancer cells, often through acetylation of non-histone proteins. Some well-recognized mechanisms of HDACI lethality include, in addition to relaxation of DNA and de-repression of gene transcription, interference with chaperone protein function, free radical generation, induction of DNA damage, up-regulation of endogenous inhibitors of cell cycle progression, e.g., p21, and promotion of apoptosis. Intriguingly, this class of agents is relatively selective for transformed cells, at least in pre-clinical studies. In recent years, additional mechanisms of action of these agents have been uncovered. For example, HDACIs interfere with multiple DNA repair processes, as well as disrupt cell cycle checkpoints, critical to the maintenance of genomic integrity in the face of diverse genotoxic insults. Despite their pre-clinical potential, the clinical use of HDACIs remains restricted to certain subsets of T-cell lymphoma. Currently, it appears likely that the ultimate role of these agents will lie in rational combinations, only a few of which have been pursued in the clinic to date. This review focuses on relatively recently identified mechanisms of action of HDACIs, with particular emphasis on those that relate to the DNA damage response (DDR), and discusses synergistic strategies combining HDACIs with several novel targeted agents that disrupt the DDR or antagonize anti-apoptotic proteins that could have implications for the future use of HDACIs in patients with cancer.

Stochasticity of intranuclear biochemical reaction processes controls the final decision of cell fate associated with DNA damage

A massive integrative mathematical model of DNA double-strand break (DSB) generation, DSB repair system, p53 signaling network, and apoptosis induction pathway was constructed to explore the dominant factors of unknown criteria of cell fate decision. In the proposed model, intranuclear reactions were modeled as stochastic processes and cytoplasmic reactions as deterministic processes, and both reaction sets were simulated simultaneously. The simulated results at the single-cell level showed that the model generated several sustained oscillations (pulses) of p53, Mdm2, ATM, and Wip1, and cell-to-cell variability in the number of p53 pulses depended on IR intensity. In cell populations, the model generated damped p53 oscillations, and IR intensity affected the amplitude of the first p53 oscillation. Cells were then subjected to the same IR dose exhibiting apoptosis induction variability. These simulated results are in quantitative agreement with major biological findings observed in human breast cancer epithelial MCF7, NIH3T3, and fibrosarcoma cells, demonstrating that the proposed model was concededly biologically appropriate. Statistical analysis of the simulated results shows that the generation of multiple p53 pulses is a prerequisite for apoptosis induction. Furthermore, cells exhibited considerable individual variability in p53 dynamics, which correlated with intrinsic apoptosis induction. The simulated results based on the proposed model demonstrated that the stochasticity of intranuclear biochemical reaction processes controls the final decision of cell fate associated with DNA damage. Applying stochastic simulation to an exploration of intranuclear biochemical reaction processes is indispensable in enhancing the understanding of the dynamic characteristics of biological multi-layered systems of higher organisms.

FERM domain promotes resveratrol-induced apoptosis in endothelial cells via inhibition of NO production

Focal adhesion kinase (FAK) consists of an N-terminal band 4.1; ezrin, radixin, moesin (FERM) domain; tyrosine kinase domain; and C-terminal FA targeting domain. Here we show that ectopically expressed FERM is largely located in the cytosolic fraction under quiescent conditions. We further found that this ectopically expressed FERM domain aggravates endothelial cell apoptosis triggered by 100 μM resveratrol, whereas FERM had no effect on apoptosis induced by TNF-α. We determined that resveratrol at low doses (<20 μM) promotes phosphorylation (S1177) of eNOS via an AMPK-dependent pathway. The presence of the FERM domain blocked this resveratrol-stimulated eNOS phosphorylation and NO production. Thus, the pro-apoptotic activity of cytosolic FERM domain is at least partially mediated by down-regulation of NO, a critical cell survival factor. Consistently, we found that the apoptosis induced by cytosolic FERM in the presence of resveratrol was reversed by an NO donor, SNAP. In conclusion, FERM located in the cytosolic fraction plays a pivotal role in aggravating cell apoptosis through diminishing NO production.

Resistance of cervical adenocarcinoma cells (HeLa) to venom from the scorpion Centruroides limpidus limpidus

BACKGROUND

The venom of Centruroides limpidus limpidus (Cll) is a mixture of pharmacologically active principles. The most important of these are toxic proteins that interact both selectively and specifically with different cellular targets such as ion channels. Recently, anticancer properties of the venom from other scorpion species have been described. Studies in vitro have shown that scorpion venom induces cell death, inhibits proliferation and triggers the apoptotic pathway in different cancer cell lines. Herein, after treating human cervical adenocarcinoma (HeLa) cells with Cll crude venom, their cytotoxic activity and apoptosis induction were assessed.

RESULTS

Cll crude venom induced cell death in normal macrophages in a dose-dependent manner. However, through viability assays, HeLa cells showed high survival rates after exposure to Cll venom. Also, Cll venom did not induce apoptosis after performing ethidium bromide/acridine orange assays, nor was there any evidence of chromatin condensation or DNA fragmentation.

CONCLUSIONS

Crude Cll venom exposure was not detrimental to HeLa cell cultures. This may be partially attributable to the absence of specific HeLa cell membrane targets for molecules present in the venom of Centruroides limpidus limpidus. Although these results might discourage additional studies exploring the potential of Cll venom to treat human papilloma cervical cancer, further research is required to explore positive effects of crude Cll venom on other cancer cell lines.

Caffeic acid phenethyl ester suppresses melanoma tumor growth by inhibiting PI3K/AKT/XIAP pathway

Melanoma is highly metastatic and resistant to chemotherapeutic drugs. Our previous studies have demonstrated that caffeic acid phenethyl ester (CAPE) suppresses the growth of melanoma cells and induces reactive oxygen species generation. However, the exact mechanism of the growth suppressive effects of CAPE was not clear. Here, we determined the potential mechanism of CAPE against melanoma in vivo and in vitro. Administration of 10 mg/kg/day CAPE substantially suppressed the growth of B16F0 tumor xenografts in C57BL/6 mice. Tumors from CAPE-treated mice showed reduced phosphorylation of phosphoinositide 3-kinase, AKT, mammalian target of rapamycin and protein level of X-linked inhibitor of apoptosis protein (XIAP) and enhanced the cleavage of caspase-3 and poly (ADP ribose) polymerase. In order to confirm the in vivo observations, melanoma cells were treated with CAPE. CAPE treatment suppressed the activating phosphorylation of phosphoinositide 3-kinase at Tyr 458, phosphoinositide-dependent kinase-1 at Ser 241, mammalian target of rapamycin at Ser 2448 and AKT at Ser 473 in B16F0 and SK-MEL-28 cells in a concentration and time-dependent study. Furthermore, the expression of XIAP, survivin and BCL-2 was downregulated by CAPE treatment in both cell lines. Significant apoptosis was observed by CAPE treatment as indicated by cleavage of caspase-3 and poly (ADP ribose) polymerase. AKT kinase activity was inhibited by CAPE in a concentration-dependent manner. CAPE treatment increased the nuclear translocation of XIAP, indicating increased apoptosis in melanoma cells. To confirm the involvement of reactive oxygen species in the inhibition of AKT/XIAP pathway, cells were treated with antioxidant N-acetyl-cysteine (NAC) prior to CAPE treatment. Our results indicate that NAC blocked CAPE-mediated AKT/XIAP inhibition and protected the cells from apoptosis. Because AKT regulates XIAP, their interaction was examined by immunoprecipitation studies. Our results show that CAPE treatment decreased the interaction of AKT with XIAP. To establish the involvement of AKT in the apoptosis-inducing effects of CAPE, cells were transfected with AKT. Our results revealed that AKT overexpression attenuated the decrease in XIAP and significantly blocked CAPE-mediated apoptosis. Similarly, overexpression of XIAP further decreased CAPE-induced apoptosis. Taken together, our results suggest that CAPE suppresses phosphoinositide 3-kinase/AKT/XIAP pathway leading to apoptosis in melanoma tumor cells in vitro and in vivo.

In vitro anti-cancer activity of chamaejasmenin B and neochamaejasmin C isolated from the root of Stellera chamaejasme L

AIM

To examine the anti-cancer effects of chamaejasmenin B and neochamaejasmin C, two biflavonones isolated from the root of Stellera chamaejasme L (known as the traditional Chinese herb Rui Xiang Lang Du) in vitro.

METHODS

Human liver carcinoma cell lines (HepG2 and SMMC-7721), a human non-small cell lung cancer cell line (A549), human osteosarcoma cell lines (MG63, U2OS, and KHOS), a human colon cancer cell line (HCT-116) and a human cervical cancer cell line (HeLa) were used. The anti-proliferative effects of the compounds were measured using SRB cytotoxicity assay. DNA damage was detected by immunofluorescence and Western blotting. Apoptosis and cell cycle distribution were assessed using flow cytometry analysis. The expression of the related proteins was examined with Western blotting analysis.

RESULTS

Both chamaejasmenin B and neochamaejasmin C exerted potent anti-proliferative effects in the 8 human solid tumor cell lines. Chamaejasmenin B (the IC(50) values ranged from 1.08 to 10.8 μmol/L) was slightly more potent than neochamaejasmin C (the IC(50) values ranged from 3.07 to 15.97 μmol/L). In the most sensitive A549 and KHOS cells, the mechanisms underlying the anti-proliferative effects were characterized. The two compounds induced prominent expression of the DNA damage marker γ-H2AX as well as apoptosis. Furthermore, treatment of the cells with the two compounds caused prominent G(0)/G(1) phase arrest.

CONCLUSION

Chamaejasmenin B and neochamaejasmin C are potential anti-proliferative agents in 8 human solid tumor cell lines in vitro via inducing cell cycle arrest, apoptosis and DNA damage.

Shikonin induces immunogenic cell death in tumor cells and enhances dendritic cell-based cancer vaccine

Immunogenic cell death is characterized by damage-associated molecular patterns, which can enhance the maturation and antigen uptake of dendritic cells. Shikonin, an anti-inflammatory and antitumor phytochemical, was exploited here as an adjuvant for dendritic cell-based cancer vaccines via induction of immunogenic cell death. Shikonin can effectively activate both receptor- and mitochondria-mediated apoptosis and increase the expression of all five tested damage-associated molecular patterns in the resultant tumor cell lysates. The combination treatment with damage-associated molecular patterns and LPS activates dendritic cells to a high maturation status and enhances the priming of Th1/Th17 effector cells. Shikonin-tumor cell lysate-loaded mature dendritic cells exhibit a high level of CD86 and MHC class II and activate Th1 cells. The shikonin-tumor cell lysate-loaded dendritic cell vaccines result in a strong induction of cytotoxic activity of splenocytes against target tumor cells, a retardation in tumor growth, and an increase in the survival of test mice. The much enhanced immunogenicity and efficacy of the current cancer vaccine formulation, that is, the use of shikonin-treated tumor cells as cell lysates for the pulse of dendritic cells in culture, may suggest a new ex vivo approach for developing individualized, dendritic cells-based anticancer vaccines.

Centroblastic diffuse large B cell lymphoma displays distinct expression pattern and prognostic role of apoptosis resistance related proteins

Centroblastic diffuse large B cell lymphoma (DLBCL) samples were analyzed by immunohistochemistry to evaluate the expression of p53, Bcl-2, Survivin, XIAP, and Ki-67. Survivin was the only protein which expression exhibited a trend for impact in progression-free (p = .077) and overall survival (p = .054). In the Mann-Whitney test, Survivin expression correlated with a negative overall survival (p = .045). These results appeared to be intimately related to Survivin cytoplasmic localization. Moreover, the anti-apoptotic proteins Bcl-2 and Survivin were less frequent in centroblastic DLBCL. Our results indicate that centroblastic DLBCL may be a disease with characteristic biology and clinical course and, therefore, specific prognostic factors.

A defect in cell death of macrophages is a conserved feature of nonobese diabetic mouse

Impaired apoptosis in immune effector cells such as macrophages has been implicated in the development of autoimmune disease by promoting the breakdown of self-tolerance and the sustained production of cytotoxic molecules. Macrophages from nonobese diabetic (NOD) mouse, an animal model of human autoimmune diabetes, exhibit several defects that are causally linked to the onset and progression of the disease. In this context, we investigated whether NOD macrophages have a defect in a cell death pathway, and if that is the case, the mechanism underlying such dysregulation of cell death. We found that NOD macrophages were resistant to treatment with a broad spectrum of cell death stimuli, triggering both apoptotic and non-apoptotic death. Through analysis of intracellular signaling pathways along with the expression of apoptosis-related proteins, we found that atypical resistance to cell death was associated with an elevated expression of anti-apoptotic Bcl-X(L) but not the NF-κB signaling pathway in NOD macrophages. Further, ABT-737, which can inhibit Bcl-X(L) function, sensitized NOD macrophages to apoptosis induced by diverse apoptotic stimuli, thus restoring sensitivity to cell death. Taken together, our results suggest a macrophage-intrinsic defect in cell death as a potential mechanism that promotes an immune attack towards pancreatic β-cells and the development of autoimmune diabetes in NOD mice.

Characterization of dequalinium as a XIAP antagonist that targets the BIR2 domain

Inhibitor of apoptosis proteins (IAPs) regulate the activity of caspases in apoptosis. The human X chromosome-encoded IAP (XIAP) is one of the more potent members of the IAP family and it has been described as a central regulator of apoptosis. Thus, molecules that inhibit XIAP could offer therapeutic opportunities to treat unwanted apoptosis inhibition. In the present study we have applied the selective optimization of side activities (SOSA) approach to the discovery of XIAP inhibitors. In this sense, we have identified dequalinium hydrochloride (Dq) as an inhibitor of the XIAP/caspase-3 interaction both in vitro and in cellular assays.

Long- but not short-term heat acclimation produces an apoptosis-resistant cardiac phenotype: a lesson from heat stress and ischemic/reperfusion insults

Long-term heat acclimation (AC, 30d/34 degrees C) is a phenotypic adaptation leading to increased thermotolerance during heat stress (HS, 2 h 41 degrees C). AC also renders protection against ischemic/reperfusion (I/R, 30' global ischemia/40' reperfusion) insult via cross-tolerance mechanisms. In contrast to the protected AC phenotype, the onset of acclimation (34 degrees C, AC2d) is characterized by cellular perturbations, suggesting increased susceptibility to HS and I/R insults. In this investigation, we tested the hypothesis that apoptosis resistance is part of the AC repertoire and that, at the initial phase of acclimation (AC2d), cytoprotection is impaired. TUNEL staining and caspase 3 levels in HS and I/R insulted hearts affirmed this hypothesis. To examine the role of the mitochondria in life/death decision in AC2d and 30d AC settings vs. control hearts, we studied the Bcl-2 apoptotic cascade and found increased levels of the anti-apoptotic Bcl-X(L) and decreased levels of the pro-apoptotic death promoter Bad in hearts from AC2d and AC animals. In these groups, cytochrome c (cyt c) was elevated in the mitochondria and remained unchanged in the cytosol. This adaptation was insufficient to negate apoptosis in AC2d rats. At this early acclimation phase (and in controls), increased caspase 8 activity confirmed activation of the extrinsic (Fas ligand) apoptosis pathway. In conclusion, the elevated Bcl-X(L)/Bad ratio and decreased cyt c leakage to the cytosol are insufficient to protect the heart and interactions with additional cytoprotective pathways involved in acclimation (elevated HSP70, ROS, and sarcolemmal adaptations to abolish extrinsic apoptosis pathways) are required to induce the apoptosis-resistant AC phenotype.

GDF5 and BMP2 inhibit apoptosis via activation of BMPR2 and subsequent stabilization of XIAP

GDF5 and BMP2, members of the TGF-beta superfamily of growth factors, are known to regulate apoptosis in different cell types either positively or negatively. We wanted to investigate the effects of GDF5 and BMP2 on vascular smooth muscle cells and mouse embryonic fibroblasts and disclose the mechanism by which GDF5 and BMP2 might exert anti-apoptotic effects. The effect of GDF5 and BMP2 on proliferation and/or programmed cells death was assessed in isolated human vascular smooth muscle cells and mouse embryonic fibroblasts. We demonstrate that GDF5 and BMP2 prevent apoptosis induced by serum starvation in mouse embryonic fibroblasts but not in smooth muscle cells via the BMP receptor 2 (BMPR2), which is often mutated in hereditary cases of primary pulmonary hypertension. GDF5 and BMP2 stimulate the interaction of BMPR-2 with XIAP thereby reducing the ubiquitination of XIAP, which results in enhanced protein stability. The increased concentration of XIAP counteracts apoptosis by binding and inactivating activated caspases. We conclude that the inhibition of apoptosis in mouse embryonic fibroblasts by BMP2 and GDF5 does not depend on more complex signal transduction pathways such as smad and MAPK signaling but on direct stabilization of XIAP by BMPR2.

Tetra-O-methyl nordihydroguaiaretic acid inhibits growth and induces death of leukemia cells independent of Cdc2 and survivin

Tetra-O-methyl nordihydroguaiaretic acid (M4N) was shown to induce G2 arrest and suppress human xenograft tumor growth by inhibiting Cdc2 and survivin. We examined the effect of M4N on leukemia and found that M4N inhibited growth and induced cell death in leukemic cell lines and blasts from AML patients. However, no significant changes in Cdc2 and survivin levels and G2 arrest were observed. Cell death and growth inhibition were dependent neither on XIAP, Bcl-2, and Bcl-X(L) levels nor on caspase-8. M4N did not promote cell differentiation in HL-60 cells. Interestingly, significant inhibition of AKT phosphorylation was observed in M4N treated OCI-AML3 cells. Collectively, our data showed that M4N inhibited cell growth and induced cell death in both leukemic cell lines and AML patient sample via a mechanism not mediated by Cdc2 and survivin inhibition and suggested that the extrinsic and the mitochondrial apoptotic pathways are not essential.

Inhibition of KSP by ARRY-520 induces cell cycle block and cell death via the mitochondrial pathway in AML cells

Kinesin spindle protein (KSP), a microtubule-associated motor protein essential for cell cycle progression, is overexpressed in many cancers and is a potential anti-tumor target. We found that inhibition of KSP by a selective inhibitor, ARRY-520, blocked cell cycle progression, leading to apoptosis in acute myeloid leukemia cell lines that express high levels of KSP. Knockdown of p53, overexpression of XIAP and mutation in caspase-8 did not significantly affect sensitivity to ARRY-520, suggesting that the response is independent of p53, XIAP and the extrinsic apoptotic pathway. Although ARRY-520 induced mitotic arrest in both HL-60 and Bcl-2-overexpressing HL-60Bcl-2 cells, cell death was blunted in HL-60Bcl-2 cells, suggesting that the apoptotic program is executed through the mitochondrial pathway. Accordingly, inhibition of Bcl-2 by ABT-737 was synergistic with ARRY-520 in HL-60Bcl-2 cells. Furthermore, ARRY-520 increased Bim protein levels prior to caspase activation in HL-60 cells. ARRY-520 significantly inhibited tumor growth of xenografts in SCID mice and inhibited AML blast but not normal colony formation, supporting a critical role for KSP in proliferation of leukemic progenitor cells. These results demonstrate that ARRY-520 potently induces cell cycle block and subsequent death in leukemic cells via the mitochondrial pathway and has the potential to eradicate AML progenitor cells.

Triptolide sensitizes AML cells to TRAIL-induced apoptosis via decrease of XIAP and p53-mediated increase of DR5

Acute myeloid leukemia (AML) cells are relatively resistant to tumor necrosis factor alpha-related apoptosis-inducing ligand (TRAIL). We previously reported that triptolide, a potent anticancer agent from a Chinese herb, decreases XIAP in leukemic cells. We evaluated the combination of triptolide and TRAIL and found synergistic promotion of apoptosis in AML cells. XIAP-overexpressing U937 cells (U937XIAP) were more resistant to TRAIL than U937neo cells, and inhibition of XIAP with the small-molecule inhibitor 1396-11 enhanced TRAIL-induced apoptosis, implying XIAP as a resistance factor in AML. Furthermore, triptolide increased DR5 levels in OCI-AML3, while the DR5 increase was blunted in p53-knockdown OCI-AML3 and p53-mutated U937 cells, confirming a role for p53 in the regulation of DR5. In support of this finding, disruption of MDM2-p53 binding with subsequent increase in p53 levels by nutlin3a increased DR5 levels and sensitized OCI-AML3 cells to TRAIL. The combination of 1396-11 plus nutlin3a plus TRAIL was more effective than either the 1396-11 and TRAIL or nutlin3a and TRAIL combinations in OCI-AML3 cells, further supporting the role of triptolide as a sensitizer to TRAIL-induced apoptosis in part by independent modulation of XIAP expression and p53 signaling. Thus, the combination of triptolide and TRAIL may provide a novel strategy for treating AML by overcoming critical mechanisms of apoptosis resistance.

OSU-03012, a Novel Celecoxib Derivative, Is Cytotoxic to Myeloma Cells and Acts through Multiple Mechanisms

PURPOSE

OSU-03012 is a novel celecoxib derivative, without cyclooxygenase-2 inhibitory activity, capable of inducing apoptosis in various cancer cells types, and is being developed as an anticancer drug. We investigated the in vitro activity of OSU-03012 in multiple myeloma (MM) cells.

EXPERIMENTAL DESIGN

U266, ARH-77, IM-9, and RPMI-8226, and primary myeloma cells were exposed to OSU-03012 for 6, 24, or 72 h. Cytotoxicity, caspase activation, apoptosis, and effects on intracellular signaling pathways were assessed.

RESULTS

OSU-03012 was cytotoxic to MM cells with mean LC50 3.69 +/- 0.23 and 6.25 +/- 0.86 micromol/L and at 24 h for primary MM cells and cell lines, respectively. As a known PDK-1 inhibitor, OSU-03012 inhibited the PI3K/Akt pathway with downstream effects on BAD, GSK-3beta, FoxO1a, p70S6K, and MDM-2. However, transfection of MM cells with constitutively active Akt failed to protect against cell death, indicating activity against other pathways is important. Phospho (p)-signal transducers and activators of transcription 3 and p-MAP/ERK kinase 1/2 were down-regulated, suggesting that OSU-03012 also inhibited the Janus-activated kinase 2/signal transducer and activator of transcription 3 and mitogen-activated protein kinase pathways. Although expression of Bcl-2 proteins was unchanged, OSU-03012 also down-regulated survivin and X-linked inhibitor of apoptosis (XIAP), and also induced G2 cell cycle arrest with associated reductions in cyclins A and B. Finally, although OSU-03012 induced cleavage of caspases 3, 8 and 9, caspase inhibition did not prevent cell death.

CONCLUSIONS

We conclude that OSU-03012 has potent activity against MM cells and acts via different mechanisms in addition to phosphoinositide-3-kinase/Akt pathway inhibition. These studies provide rationale for the clinical investigation of OSU-03012 in MM.

Fas Receptor Clustering and Involvement of the Death Receptor Pathway in Rituximab-Mediated Apoptosis with Concomitant Sensitization of Lymphoma B Cells to Fas-Induced Apoptosis

Ab binding to CD20 has been shown to induce apoptosis in B cells. In this study, we demonstrate that rituximab sensitizes lymphoma B cells to Fas-induced apoptosis in a caspase-8-dependent manner. To elucidate the mechanism by which Rituximab affects Fas-mediated cell death, we investigated rituximab-induced signaling and apoptosis pathways. Rituximab-induced apoptosis involved the death receptor pathway and proceeded in a caspase-8-dependent manner. Ectopic overexpression of FLIP (the physiological inhibitor of the death receptor pathway) or application of zIETD-fmk (specific inhibitor of caspase-8, the initiator-caspase of the death receptor pathway) both specifically reduced rituximab-induced apoptosis in Ramos B cells. Blocking the death receptor ligands Fas ligand or TRAIL, using neutralizing Abs, did not inhibit apoptosis, implying that a direct death receptor/ligand interaction is not involved in CD20-mediated cell death. Instead, we hypothesized that rituximab-induced apoptosis involves membrane clustering of Fas molecules that leads to formation of the death-inducing signaling complex (DISC) and downstream activation of the death receptor pathway. Indeed, Fas coimmune precipitation experiments showed that, upon CD20-cross-linking, Fas-associated death domain protein (FADD) and caspase-8 were recruited into the DISC. Additionally, rituximab induced CD20 and Fas translocation to raft-like domains on the cell surface. Further analysis revealed that, upon stimulation with rituximab, Fas, caspase-8, and FADD were found in sucrose-gradient raft fractions together with CD20. In conclusion, in this study, we present evidence for the involvement of the death receptor pathway in rituximab-induced apoptosis of Ramos B cells with concomitant sensitization of these cells to Fas-mediated apoptosis via Fas multimerization and recruitment of caspase-8 and FADD to the DISC.

MUC1 oncoprotein functions in activation of fibroblast growth factor receptor signaling

Activation of the fibroblast growth factor (FGF) receptor 3 (FGFR3) has been linked to the development of human cancers by mechanisms that are not well understood. The MUC1 oncoprotein is aberrantly overexpressed by certain hematologic malignancies and most human carcinomas. The present studies show that MUC1 associates with FGFR3. Stimulation of cells with FGF1 increased the interaction between MUC1 and FGFR3. FGF1 stimulation also induced c-Src-dependent tyrosine phosphorylation of the MUC1 cytoplasmic domain on a YEKV motif. FGF1-induced tyrosine phosphorylation of MUC1 was associated with increased binding of MUC1 to beta-catenin and targeting of MUC1 and beta-catenin to the nucleus. FGF1 also induced binding of MUC1 to the heat shock protein 90 (HSP90) chaperone by a mechanism dependent on phosphorylation of the YEKV motif. Notably, beta-catenin and HSP90 compete for binding to the MUC1 cytoplasmic domain, indicating that MUC1 forms mutually exclusive complexes with these proteins. The results also show that inhibition of HSP90 with geldanamycin or 17-(allylamino)-17-demethoxygeldanamycin attenuates FGF1-induced binding of MUC1 to HSP90 and targeting of MUC1 to the mitochondrial outer membrane. These findings indicate that FGF1 induces phosphorylation of MUC1 on YEKV and thereby activates two distinct pathways: (a) nuclear localization of MUC1 and beta-catenin and (b) delivery of MUC1 to mitochondria by HSP90.

Mathematical modeling identifies inhibitors of apoptosis as mediators of positive feedback and bistability

The intrinsic, or mitochondrial, pathway of caspase activation is essential for apoptosis induction by various stimuli including cytotoxic stress. It depends on the cellular context, whether cytochrome c released from mitochondria induces caspase activation gradually or in an all-or-none fashion, and whether caspase activation irreversibly commits cells to apoptosis. By analyzing a quantitative kinetic model, we show that inhibition of caspase-3 (Casp3) and Casp9 by inhibitors of apoptosis (IAPs) results in an implicit positive feedback, since cleaved Casp3 augments its own activation by sequestering IAPs away from Casp9. We demonstrate that this positive feedback brings about bistability (i.e., all-or-none behaviour), and that it cooperates with Casp3-mediated feedback cleavage of Casp9 to generate irreversibility in caspase activation. Our calculations also unravel how cell-specific protein expression brings about the observed qualitative differences in caspase activation (gradual versus all-or-none and reversible versus irreversible). Finally, known regulators of the pathway are shown to efficiently shift the apoptotic threshold stimulus, suggesting that the bistable caspase cascade computes multiple inputs into an all-or-none caspase output. As cellular inhibitory proteins (e.g., IAPs) frequently inhibit consecutive intermediates in cellular signaling cascades (e.g., Casp3 and Casp9), the feedback mechanism described in this paper is likely to be a widespread principle on how cells achieve ultrasensitivity, bistability, and irreversibility.

Non-steroidal anti-inflammatory drugs to potentiate chemotherapy effects: from lab to clinic

Most solid tumors express the cyclooxygenase-2 (COX-2) protein, a target of NSAIDs. COX-2 overexpression in tumorsis considered a predictor of more advanced stage disease and of worse prognosis in a number of studies investigating solid malignancies. Therefore, NSAIDs are evaluated as anti-cancer drugs. NSAIDs inhibit proliferation, invasiveness of tumors, and angiogenesis and overcome apoptosis resistance in a COX-2 dependent and independent manner. This review will focus on the rationale behind NSAIDs, including selective COX-2 inhibitors, in combination with conventional chemotherapeutic drugs or novel molecular targeted drugs. Studies investigating anti-cancer effects of NSAIDs on cell lines and xenograft models have shown modulation of the Akt, NF-kappaB, tyrosine kinase and the death receptor-mediated apoptosis pathways. COX-2 expression in tumors is not yet used as biomarker in the clinic. Despite the increased risk on cardiovascular toxicity induced by selective COX-2 inhibitors, several ongoing clinical trials are still investigating the therapeutic benefits of NSAIDs in oncology. The anti-tumor effects in these trials balanced with the side effects data will define the precise role of selective COX-2 inhibitors in the treatment of cancer patients.

Apoptotic effect of fludarabine is independent of expression of IAPs in B-cell chronic lymphocytic leukemia

Despite the efficiency of fludarabine in the induction of clinical responses in B-cell chronic lymphocytic leukemia (B-CLL) patients, resistance to this drug has been documented. The present study tested whether resistance to fludarabine is related to the expression of inhibitor of apoptosis proteins (IAPs) family members. We analyzed the expression of c-IAP1, c-IAP2 and XIAP, by immunocytochemistry, in 30 blood samples from B-CLL patients and correlated protein expression to fludarabine-induced apoptosis estimated by an annexin-V assay. Expression of c-IAP1, c-IAP2 and XIAP were found predominantly in the cytoplasm, and a wide range of staining intensities was observed among distinct samples. No correlation was found between the levels of IAPs expression and prognostic factors such as age, gender, lymphocyte doubling time, white blood cell count or previous treatment. The expression of IAPs also failed to predict the sensitivity to fludarabine-induced apoptosis. Alternative pathways of cell death may explain the independence of fludarabine-induced apoptosis from the high expression of IAPs.

Triptolide induces caspase-dependent cell death mediated via the mitochondrial pathway in leukemic cells

Triptolide, a diterpenoid isolated from the Chinese herb Tripterygium wilfordii Hook.f, has shown antitumor activities in a broad range of solid tumors. Here, we examined its effects on leukemic cells and found that, at 100 nM or less, it potently induced apoptosis in various leukemic cell lines and primary acute myeloid leukemia (AML) blasts. We then attempted to identify its mechanisms of action. Triptolide induced caspase-dependent cell death accompanied by a significant decrease in XIAP levels. Forced XIAP overexpression attenuated triptolide-induced cell death. Triptolide also decreased Mcl-1 but not Bcl-2 and Bcl-X(L) levels. Bcl-2 overexpression suppressed triptolide-induced apoptosis. Further, triptolide induced loss of the mitochondrial membrane potential and cytochrome C release. Caspase-9 knock-out cells were resistant, while caspase-8-deficient cells were sensitive to triptolide, suggesting criticality of the mitochondrial but not the death receptor pathway for triptolide-induced apoptosis. Triptolide also enhanced cell death induced by other anticancer agents. Collectively, our results demonstrate that triptolide decreases XIAP and potently induces caspase-dependent apoptosis in leukemic cells mediated through the mitochondrial pathway at low nanomolar concentrations. The potent antileukemic activity of triptolide in vitro warrants further investigation of this compound for the treatment of leukemias and other malignancies.

Potentiation of the lethality of the histone deacetylase inhibitor LAQ824 by the cyclin-dependent kinase inhibitor roscovitine in human leukemia cells

Interactions between the novel histone deacetylase inhibitor LAQ824 and the cyclin-dependent kinase inhibitor roscovitine were examined in human leukemia cells. Pretreatment (24 hours) with a subtoxic concentration of LAQ824 (30 nmol/L) followed by a minimally toxic concentration of roscovitine (10 micromol/L; 24 hours) resulted in greater than additive effects on apoptosis in U937, Jurkat, and HL-60 human leukemia cells and blasts from three patients with acute myelogenous leukemia. These events were associated with enhanced conformational changes in Bax; mitochondrial release of cytochrome c, Smac/DIABLO, and apoptosis-inducing factor; and a marked increase in caspase activation. LAQ824/roscovitine-treated cells displayed caspase-dependent down-regulation of p21(CIP1) and Mcl-1 and a pronounced caspase-independent reduction in X-linked inhibitor of apoptosis (XIAP) expression. The lethality of this regimen was significantly attenuated by ectopic expression of XIAP, a nuclear localization signal-defective p21(CIP1) mutant, Mcl-1, and Bcl-2. Combined exposure to LAQ824 and roscovitine resulted in a significant reduction in XIAP mRNA levels and diminished phosphorylation of the carboxyl-terminal domain of RNA polymerase II. Notably, roscovitine blocked LAQ824-mediated differentiation. Finally, LAQ824 and roscovitine individually and in combination triggered an increase in generation of reactive oxygen species; moreover, coadministration of the free radical scavenger N-acetylcysteine prevented LAQ824/roscovitine-mediated mitochondrial injury and apoptosis. Collectively, these findings suggest that combined treatment of human leukemia cells with LAQ824 and roscovitine disrupts maturation and synergistically induces apoptosis, lending further support for an antileukemic strategy combining novel histone deacetylase and cyclin-dependent kinase inhibitors.

Activation of caspase 8 in the pituitaries of streptozotocin-induced diabetic rats: implication in increased apoptosis of lactotrophs

Lactotroph cell death is increased in streptozotocin-induced diabetic rats. To determine the mechanism involved, cell death proteins were accessed in pituitaries of diabetic (streptozotocin at 65 mg/kg, 2 months evolution) and control male rats by Western blot analysis and double immunohistochemistry. The intact and cleaved forms of caspase 9 were increased in diabetic rat pituitaries compared with controls. Although the proforms of caspases 3, 6, and 7 were increased in diabetic rat pituitaries, their activated forms were either unchanged or decreased. Activation of these effector caspases may be blocked by the increased expression of X-chromosome-linked inhibitor of apoptosis protein (XIAP) in diabetic rat pituitaries. However, in diabetic rats, XIAP expression in lactotrophs was decreased, suggesting that this cell type is not protected. Caspase 8, p53, and nuclear factor kappaB were more highly activated in diabetic rat pituitaries, with caspase 8 colocalization in lactotrophs being increased. These results suggest that, in the pituitaries of diabetic rats, the cascades of normal cell turnover are partially inhibited, possibly via XIAP, and this may be cell specific. Furthermore, activation of the extrinsic cell-death pathway, including activation of caspase 8, may underlie the diabetes-associated increase in lactotroph death.

The histone deacetylase inhibitor LAQ824 induces human leukemia cell death through a process involving XIAP down-regulation, oxidative injury, and the acid sphingomyelinase-dependent generation of ceramide

Determinants of differentiation and apoptosis induction by the novel histone deacetylase inhibitor (HDACI) LAQ824 were examined in human leukemia cells (U937 and Jurkat). Exposure of U937 cells to a low concentration of LAQ824 (30 nM) resulted in a delayed (2 h) increase in reactive oxygen species (ROS), induction of p21(WAF1/CIP1), pRb dephosphorylation, growth arrest of cells in G(0)/G(1) phase, and differentiation. On the other hand, exposure of cells to a higher concentration of LAQ824 (75 nM) resulted in the early (30 min) generation of ROS, arrest of cells in G(2)/M phase, down-regulation of XIAP (at the transcriptional level) and Mcl-1 (through a caspase-mediated process), the acid sphingomyelinase-dependent generation of ceramide, and profound mitochondrial injury, caspase activation, and apoptosis. LAQ824-induced lethality in U937 cells did not involve the extrinsic apoptotic pathway, nor was it associated with death receptor up-regulation; instead, it was markedly inhibited by ectopic expression of Bcl-2, Bcl-x(L), XIAP, and Mcl-1. The free radical scavenger N-acetyl cysteine blocked LAQ824-mediated ROS generation, mitochondrial injury, Mcl-1 down-regulation, ceramide generation, and apoptosis, suggesting a primary role for oxidative injury in LAQ824 lethality. Together, these findings indicate that LAQ824-induced lethality represents a multifactorial process in which LAQ824-mediated ROS generation is necessary but not sufficient to induce apoptosis, and that the degree of XIAP and Mcl-1 down-regulation and ceramide generation determines whether this agent engages a maturation rather than an apoptotic program.

MUC1 oncoprotein is targeted to mitochondria by heregulin-induced activation of c-Src and the molecular chaperone HSP90

The MUC1 heterodimeric transmembrane glycoprotein is aberrantly overexpressed by most human carcinomas. The MUC1 C-terminal subunit localizes to mitochondria and blocks stress-induced activation of the intrinsic apoptotic pathway. How MUC1 is delivered to mitochondria is not known. The present studies demonstrate that MUC1 forms intracellular complexes with HSP70 and HSP90. We show that the MUC1 cytoplasmic domain binds directly to HSP70 in vitro. By contrast, binding of MUC1 to HSP90 in vitro is induced by c-Src-mediated phosphorylation of the MUC1 cytoplasmic domain. c-Src also increases binding of MUC1 to HSP90 in cells. In concert with these results, we show that heregulin (HRG), a ligand for ErbB receptors, activates c-Src and, in turn, stimulates binding of MUC1 to HSP90. We also show that inhibitors of c-Src or HSP90 block HRG-induced targeting of MUC1 to mitochondria and integration of MUC1 into the mitochondrial outer membrane. These findings indicate that MUC1 is delivered to mitochondria by a mechanism involving activation of the ErbB receptor-->c-Src pathway and transport by the molecular chaperone HSP70/HSP90 complex.

Blockade of histone deacetylase inhibitor-induced RelA/p65 acetylation and NF-kappaB activation potentiates apoptosis in leukemia cells through a process mediated by oxidative damage, XIAP downregulation, and c-Jun N-terminal kinase 1 activation

NF-kappaB activation is reciprocally regulated by RelA/p65 acetylation and deacetylation, which are mediated by histone acetyltransferases (HATs) and deacetylases (HDACs). Here we demonstrate that in leukemia cells, NF-kappaB activation by the HDAC inhibitors (HDACIs) MS-275 and suberoylanilide hydroxamic acid was associated with hyperacetylation and nuclear translocation of RelA/p65. The latter events, as well as the association of RelA/p65 with IkappaBalpha, were strikingly diminished by either coadministration of the IkappaBalpha phosphorylation inhibitor Bay 11-7082 (Bay) or transfection with an IkappaBalpha superrepressor. Inhibition of NF-kappaB by pharmacological inhibitors or genetic strategies markedly potentiated apoptosis induced by HDACIs, and this was accompanied by enhanced reactive oxygen species (ROS) generation, downregulation of Mn-superoxide dismutase and XIAP, and c-Jun N-terminal kinase 1 (JNK1) activation. Conversely, N-acetyl L-cysteine blocked apoptosis induced by Bay/HDACIs by abrogating ROS generation. Inhibition of JNK1 activation attenuated Bay/HDACI lethality without affecting NF-kappaB inactivation and ROS generation. Finally, XIAP overexpression dramatically protected cells against the Bay/HDACI regimen but failed to prevent ROS production and JNK1 activation. Together, these data suggest that HDACIs promote the accumulation of acetylated RelA/p65 in the nucleus, leading to NF-kappaB activation. Moreover, interference with these events by either pharmacological or genetic means leads to a dramatic increase in HDACI-mediated lethality through enhanced oxidative damage, downregulation of NF-kappaB-dependent antiapoptotic proteins, and stress-related JNK1 activation.

Insulin regulates cleavage of procaspase-9 via binding of X chromosome-linked inhibitor of apoptosis protein in HT-29 cells

Insulin significantly reduced tumor necrosis factor (TNF)-alpha-induced cleavage of procaspase-8, -9, and -3 and poly(ADP-ribose) polymerase when observed for up to 24 hours in a dose-dependent manner. Signaling pathways responsible for the inhibitory effects of insulin were investigated by using protein kinase inhibitors. Both phosphatidylinositol 3'-kinase (PI3K) and mitogen-activated protein kinase kinase pathways mediate the ability of insulin to decrease the TNF-alpha-induced cleavage of procaspase-8. In contrast, only the PI3K inhibitor reversed the effect of insulin on the TNF-alpha-induced cleavage of procaspase-9. Moreover, insulin decreased the apoptotic level induced by TNF-alpha, whereas the PI3K inhibitor enhanced it. The protein level of Apaf-1, an activator of procaspase-9, remained constant with the application of agents affecting the cleavage of procaspase-9. In examining another regulator of cleaved caspase-9, X chromosome-linked inhibitor of apoptosis protein (XIAP), we observed that TNF-alpha treatment induced fragmentation of XIAP, which was also enhanced by the PI3K inhibitor. In addition, XIAP was coimmunoprecipitated with procaspase-9. The treatment with TNF-alpha reduced the level of XIAP precipitated with procaspase-9, whereas insulin reversed this effect. Moreover, PI3K and Akt inhibitors, but not mammalian target of rapamycin inhibitor, inhibited the effect of insulin on the coprecipitation of procaspase-9 and XIAP. Our data suggest that insulin decreases the TNF-alpha-induced cleavage of procaspase-9 and subsequent apoptosis by regulating XIAP via the PI3K/Akt pathway.

Expression of XIAP mRNA and protein in human hepatocellular carcinoma

AIM: To study the expression of XIAP mRNA and protein in tissues of hepatocellar carcinoma (HCC), and to investigate the role of XIAP in the development of primary HCC.

METHODS: The expression of XIAP mRNA in normal liver cell line L-02, hepatoma cell lines, SMMC7721 and HepG2, and tissues of primary HCC (n = 30)as well as the corresponding adjacent tissues of HCC was detected by semi-quantitative reverse-transcription polymerase chain reaction (RT-PCR). The expression of XIAP protein was observed in preceding cell lines and tissues by immunohistochemical staining.

RESULTS: The expression level of XIAP mRNA in L-02 was lower than that in SMMC7721 and HepG2 (mean XIAP/β-actin: 0.418 ± 0.045 vs 0.719 ± 0.069, P < 0.05; 0.418 ± 0.045 vs 0.654 ± 0.055, P < 0.05 respectively). No significant difference existed in the XIAP mRNA expression between SMMC7721 and HepG2 cells. The expression of XIAP protein was significantly different among three cell lines (0.158 ± 0.016 vs 0.291 ± 0.022 vs 0.238 ± 0.011, P < 0.05). The expression of XIAP mRNA and protein in HCC tissues was higher than those in thecorresponding cancer-adjacent tissues (mRNA: 0.587 ± 0.064 vs 0.313 ± 0.059, P < 0.05; protein: 0.276 ± 0.054 vs 0.095 ± 0.014, P < 0.05). XIAP protein was mainly distributed in cytoplasm.

CONCLUSION: Overexpression of XIAP mRNA and protein may play an important role in the carcinogenesis of primary HCC.

Potent antileukemic interactions between flavopiridol and TRAIL/Apo2L involve flavopiridol-mediated XIAP downregulation

Interactions between the cyclin-dependent kinase inhibitor flavopiridol (FP) and tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL/Apo2L), were examined in human leukemia cells (U937 and Jurkat). Coexposure of cells to marginally toxic concentrations of TRAIL and FP (24 h) synergistically increased mitochondrial injury (eg, cytochrome c, AIF, Smac/DIABLO release), cytoplasmic depletion of Bax, activation of Bid as well as caspase-8 and -3, PARP cleavage, and apoptosis. Coadministration of TRAIL markedly increased FP-induced apoptosis in leukemic cells ectopically expressing Bcl-2, Bcl-x(L), or a phosphorylation loop-deleted form of Bcl-2 (DeltaBcl-2), whereas lethality was substantially attenuated in cells ectopically expressing CrmA, dominant-negative-FADD, or dominant-negative-caspase-8. TRAIL/FP induced no discernible changes in FLIP, DR4, DR5, Mcl-1, or survivin expression, modest declines in levels of DcR2 and c-IAP, but resulted in the marked transcriptional downregulation of XIAP. Moreover, cells stably expressing an XIAP-antisense construct exhibited a pronounced increase in TRAIL sensitivity comparable to degrees of apoptosis achieved with TRAIL/FP. Conversely, enforced XIAP expression significantly attenuated caspase activation and TRAIL/FP lethality. Together, these findings suggest that simultaneous activation of the intrinsic and extrinsic apoptotic pathways by TRAIL and FP synergistically induces apoptosis in human leukemia cells through a mechanism that involves FP-mediated XIAP downregulation.

Enhancement of C2-ceramide antitumor activity by small interfering RNA on X chromosome-linked inhibitor of apoptosis protein in resistant human glioma cells

OBJECT

Many human glioma cells are resistant to ceramide. In this study the authors investigated the mechanisms of that resistance and considered ways to overcome it.

METHODS

The authors first administered C2-ceramide (N-acetylsphingosine) to human glioma cells from rare cell lines susceptible to C2-ceramide (SKMG1 and U87MG) and other cell lines resistant to it (U251SP, T98G, SKAO2, and U251MG). Following this, the authors analyzed the statuses of transduction signals such as cell viability, morphological changes, caspases, mitochondrial membrane potential, apoptosis-inducing factor, oligonucleosomal DNA fragmentation, and the inhibitor of apoptosis protein (IAP) family.

CONCLUSIONS

Ceramide resistance was found to arise from the inhibition of caspase-7 induced by IAPs, especially X chromosome-linked IAP (XIAP). Small interfering RNA (siRNA) on XIAP quenched that resistance in ceramide-resistant human glioma cells (U251SP, T98G, SKAO2, U251MG), indicating that a siRNA for XIAP may be a useful tool for overcoming the resistance to ceramide in human glioma cells.

Death receptors in chemotherapy and cancer

Apoptosis, the cell's intrinsic death program, is a key regulator of tissue homeostasis. An imbalance between cell death and proliferation may result in tumor formation. Also, killing of cancer cells by cytotoxic therapies such as chemotherapy, gamma-irradiation or ligation of death receptors is predominantly mediated by triggering apoptosis in target cells. In addition to the intrinsic mitochondrial pathway, elements of death receptor signaling pathways have been implied to contribute to the efficacy of cancer therapy. Failure to undergo apoptosis in response to anticancer therapy may lead to resistance. Also, deregulated expression of death receptor pathway molecules may contribute to tumorigenesis and tumor escape from endogenous growth control. Understanding the molecular events that regulate apoptosis induced by anticancer therapy and how cancer cells evade apoptosis may provide new opportunities for pathway-based rational therapy and for drug development.

Microtubule-targeted anticancer agents and apoptosis

Over the past decade, significant progress has been made in our understanding of the biology of microtubule (MT) assembly into the mitotic spindle during mitosis and the molecular signaling and execution of the various pathways to apoptosis. In the same period, the microtubule-targeted tubulin-polymerizing agents (MTPAs), notably paclitaxel and taxotere, have come to occupy a central role in the treatment of a variety of human epithelial cancers. Following their binding to B-tubulin, MTPAs inhibit MT dynamic instability, cell cycle G2/M phase transition and mitotic arrest of cancer cells. MTPA-induced anti-MT and cell cycle effects trigger the molecular signaling for the mitochondrial pathway of apoptosis. This triggering is orchestrated through different molecular links and determined by the threshold for apoptosis that is set and controlled diversely in various cancer types. The complexity and regulatory potential of the links and the apoptosis threshold are integral to the transformed biology of the cancer cell. The emerging understanding of this biology and how it is influenced by treatment with MTPAs has highlighted novel strategies to further enhance the antitumor activity and overcome resistance to MTPA-induced apoptosis in cancer cells.

Mechanisms of apoptosis induction by nucleoside analogs

Nucleoside analogs are structurally, metabolically, and pharmacodynamically related agents that nevertheless have diverse biological actions and therapeutic consequences. This class of agents affects the structural integrity of DNA, generally after incorporation during replication or DNA excision repair synthesis, leading to stalled replication forks and chain termination. The DNA damage sensors ATM, ATR and DNA-PK recognize these events. These and other protein kinases activate checkpoint pathways that arrest cell cycle progression, and also signal for DNA repair. In addition, if these survival mechanisms are overwhelmed by the damage caused, a third function of these sensors is to activate signaling pathways that initiate apoptotic processes. A review of the spectrum of responses that are activated by clinically relevant nucleoside analogs begins to provide a mechanistic basis for diverse outcomes in cell viability. Such information, when coupled with an understanding of the intrinsic apoptotic potential of a tumor cell type may provide a rational basis for the design of therapeutic strategies.

Regulation and targeting of antiapoptotic XIAP in acute myeloid leukemia

XIAP is a member of the inhibitors-of-apoptosis family of proteins, which inhibit caspases and block cell death, with prognostic importance in AML. Here we demonstrate that cytokines regulate the expression of XIAP in leukemic cell lines and primary AML blasts. Inhibition of phosphatidylinositol-3 kinase (PI3K) with LY294002 and of the mitogen-activated protein kinase (MAPK) cascade by PD98059 resulted in decreased XIAP levels (34+/-8.7 and 23+/-5.7%, respectively). We then generated OCI-AML3 cells with constitutively phosphorylated Akt (p473-Akt) by retroviral gene transfer. Neither these nor Akt inhibitor-treated OCI-AML3 cells showed changes in XIAP levels, suggesting that XIAP expression is regulated by PI3K downstream effectors other than Akt. The induction of XIAP expression by cytokines through PI3K/MAPK pathways is consistent with its role in cell survival. Exposure of leukemic cells to chemotherapeutic agents decreased XIAP protein levels by caspase-dependent XIAP cleavage. Targeting XIAP by XIAP antisense oligonucleotide resulted in downregulation of XIAP, activation of caspases and cell death, and sensitized HL-60 cells to Ara-C. Our results suggest that XIAP is regulated by cytokines through PI3K, and to a lesser degree through MAPK pathways. Selective downregulation of XIAP expression might be of therapeutic benefit to leukemic patients.

Synergistic effects of chemotherapeutic drugs in lymphoma cells are associated with down-regulation of inhibitor of apoptosis proteins (IAPs), prostate-apoptosis-response-gene 4 (Par-4), death-associated protein (Daxx) and with enforced caspase activation

Cytotoxic drugs mediate apoptotic tumor cell death by influencing key regulator proteins of programmed cell death. In clinical practice cytotoxic drug combinations are desired to potentiate tumor cell kill and to minimize side effects. Nevertheless, the molecular mechanisms underlying synergistic and antagonistic effects on tumor cells are still poorly understood. In order to elucidate these molecular mechanisms we established models of synergistic and antagonistic drug combinations within the same lymphoma cell lines. By combination index method we demonstrated that bendamustine in combination with either doxorubicin or mitoxantrone caused antagonistic effects on disruption of mitochondrial membrane potential as well as on the rate of apoptosis. In contrast the combination of bendamustine with cladribine acted synergistically on these parameters. By using the IC(50) (dosages causing 50% rate of apoptosis) the synergistic effect of the combination of bendamustine and cladribine was associated with an enhanced mitochondrial release of cytochrome c and Smac/DIABLO, by down-regulation of x-linked inhibitor of apoptosis (XIAP), cIAP1, Par-4 and Daxx as well as by a significantly increased activation of caspases-3, -6, -7, -8 and -9. At the same rate of apoptosis (IC(50)), the antagonistic combinations did not increase the release of cytochrome c or Smac/DIABLO, nor down-regulate the expression of XIAP, cIAP1, Par-4 and Daxx, nor increase the activation of caspases. The role of down-regulation of IAPs and of enforced caspase activation for synergism in this model was supported by the observation, that broad spectrum inhibition of caspases re-established expression of XIAP. Our study is the first to outline the molecular alterations caused by synergistic and antagonistic drug combinations within the same lymphoma cell model. The above described mechanisms were already assessable at a point where the effects of synergistic or antagonistic combinations could not yet be discriminated quantitatively by the level of apoptosis rate of the lymphoma cells.