Autophagy

Clinical use of circulating nucleosomes

Nucleosomes, complexes of DNA and histone proteins, are released from dying and stressed cells into the blood circulation. Concentrations of circulating nucleosomes in plasma and serum are frequently found to be elevated in various cancers, and also in such acute conditions as stroke, trauma, and sepsis as well as in autoimmune diseases. The first part of this review focuses on the structural and functional properties of nucleosomes, the potential sources of nucleosome release into the circulation, the metabolism of circulating nucleosomes, and their pathophysiological role in disease. It goes on to describe the relevance of circulating nucleosomes in the diagnosis and prognosis of non-malignant conditions such as sepsis, stroke, and autoimmune disease. Finally, it describes the clinical value of nucleosomes in the diagnosis, staging, prognosis, and monitoring of therapy in cancer; in particular, their potential as a new diagnostic tool for the early estimation of response to cytotoxic cancer therapy is emphasized.

Endostatin induces autophagy in endothelial cells by modulating Beclin 1 and beta-catenin levels

Endostatin is a well-characterized endogenous inhibitor of angiogenesis that affects cell proliferation and migration by inhibiting integrin and Wnt-mediated signalling pathways. Here, we show that endothelial cells treated with native and P125A-endostatin activate autophagy. Because autophagy can either be protective or induce programmed cell death, experiments were carried out to understand the signalling pathways leading to autophagy in endothelial cells. P125A-endostatin treatment increased the levels of Beclin 1, a crucial molecule in vesicle nucleation and autophagy. The treatment also reduced the levels of Bcl-2, Bcl-x_L and β-catenin; however, progressively increasing amounts of Bcl-2 and Bcl-x_L were found to be complexed with Beclin 1. Increased β-catenin and Wnt-mediated signalling reduced Beclin 1 levels and rescued endothelial cells from endostatin-induced autophagy. Finally, knocking down Beclin 1 levels by RNA interference decreased autophagy and accelerated caspase activation in endostatin-treated cells. These studies suggest that endothelial cells may initiate autophagy as a survival response to limit the effects of angiogenesis inhibitors. Thus, interfering with autophagy can potentiate the effects of endostatin by promoting a switch to apoptosis.

Analyzing autophagy in clinical tissues of lung and vascular diseases

Autophagy, a process by which organelles and cellular proteins are encapsulated in double-membrane vesicles and subsequently degraded by lysosomes, plays a central role in cellular and tissue homeostasis. In various model systems, autophagy may be triggered by nutrient deprivation, oxidative stress, and other insults such as endoplasmic reticulum stress, hypoxia, and pathogen infection. The role of autophagy in lung physiology and homeostasis, however, has not been well studied. Even less is known of the role of autophagy in the pathogenesis of chronic lung disease. Autophagy may act essentially as a protective mechanism in lung cells, by removing dysfunctional organelles, and recycling essential nutrients. On the other hand, excessive autophagy may also contribute to cell death pathways, resulting in the depletion of critical cell populations, and thus may also contribute to the disease pathogenesis. An understanding of the cell-type specific regulation and function of autophagy in the lung may facilitate the development of therapeutic strategies for the treatment of lung pathologies. This chapter provides protocols for the isolation of distinct lung cell types, such as epithelial, endothelial, macrophages, and fibroblasts; as well as protocols for the analysis of autophagy in lung cells and tissues.

Repositioning HIV protease inhibitors as cancer therapeutics

PURPOSE OF REVIEW

Although designed to target only the HIV protease, HIV protease inhibitors induce toxicities in patients such as insulin resistance and lipodystrophy that suggest that protease inhibitors have other targets in mammalian cells. Akt controls insulin signaling and is an important target in cancer, but no Akt inhibitors are approved as cancer therapeutics. These observations have prompted the study of HIV protease inhibitors as inhibitors of Akt and possible cancer therapeutics. This review will highlight the latest advances in repositioning HIV protease inhibitors as cancer therapeutics.

RECENT FINDINGS

Although protease inhibitors can inhibit Akt activation and the proliferation of over 60 cancer cell lines, as well as improve sensitivity to radiation or chemotherapy, these effects do not always correlate with Akt inhibition. Other important processes, such as the induction of endoplasmic reticulum stress, appear critical to the biological activity of protease inhibitors. These impressive and surprising preclinical data have prompted clinical testing of nelfinavir as a lead HIV protease inhibitor in cancer patients.

SUMMARY

Although mechanisms of action for the antitumor effects of HIV protease inhibitors are complex, their broad spectrum of activity, minimal toxicity, and wide availability make protease inhibitors ideal candidates for repositioning as cancer therapeutics.

The adenovirus E4orf4 protein induces growth arrest and mitotic catastrophe in H1299 human lung carcinoma cells

The human adenovirus E4orf4 protein, when expressed alone, induces p53-independent death in a wide range of cancer cells. Earlier studies by our groups suggested that although in some cases cell death can be associated with some hallmarks of apoptosis, it is not always affected by caspase inhibitors. Thus it is unlikely that E4orf4-induced cell death occurs uniquely through apoptosis. In the present studies using H1299 human lung carcinoma cells as a model system we found that death is induced in the absence of activation of any of the caspases tested, accumulation of reactive oxygen species, or release of cytochrome c from mitochondria. E4orf4 caused a substantial change in cell morphology, including vigorous membrane blebbing, multiple nuclei in many cells and increased cell volume. Most of these characteristics are not typical of apoptosis, but they are of necrosis. FACS analysis and western blotting for cell cycle markers showed that E4orf4-expressing cells became arrested in G(2)/M and also accumulated high levels of cyclin E. The presence of significant numbers of tetraploid and polyploid cells and some cells with micronuclei suggested that E4orf4 appears to induce death in these cells through a process resulting from mitotic catastrophe.

Clinical biomarkers and imaging for radiotherapy-induced cell death

INTRODUCTION

Radiotherapy, like most anticancer treatments, achieves its therapeutic effect by inducing different types of cell death in tumors.

CELL DEATH MARKERS AND IMAGING MODALITIES

To evaluate treatment efficacy a variety of routine anatomical imaging modalities is used. However, changes in tumor physiology, metabolism and proliferation often precede these volumetric changes. Therefore, reliable biomarkers and imaging modalities that could assess treatment response more rapidly or even predict tumor responsiveness to treatment in an early phase would be very useful to identify responders and/or avoid ineffective, toxic therapies. A better understanding of cell death mechanisms following irradiation is essential for the development of such tools.

CELL DEATH AND AVAILABLE ASSAYS

In this review the most prominent types of radiation-induced cell death are discussed. In addition, the currently available assays to detect apoptosis, necrosis, mitotic catastrophe, autophagy and senescence in vitro and, if applicable, in vivo, are presented.

Autophagy upregulation by inhibitors of caspase-3 and mTOR enhances radiotherapy in a mouse model of lung cancer

Autophagy has been reported to be increased in irradiated cancer cells resistant to various apoptotic stimuli. We therefore hypothesized that induction of autophagy via mTOR inhibition could enhance radiosensitization in apoptosis-inhibited H460 lung cancer cells in vitro and in a lung cancer xenograft model. To test this hypothesis, combinations of Z-DEVD (caspase-3 inhibitor), RAD001 (mTOR inhibitor) and irradiation were tested in cell and mouse models. The combination of Z-DEVD and RAD001 more potently radiosensitized H460 cells than individual treatment alone. The enhancement in radiation response was not only evident in clonogenic survival assays, but also was demonstrated through markedly reduced tumor growth, cellular proliferation (Ki67 staining), apoptosis (TUNEL staining) and angiogenesis (vWF staining) in vivo. Additionally, upregulation of autophagy as measured by increased GFP-LC3-tagged autophagosome formation accompanied the noted radiosensitization in vitro and in vivo. The greatest induction of autophagy and associated radiation toxicity was exhibited in the tri-modality treatment group. Autophagy marker, LC-3-II, was reduced by 3-methyladenine (3-MA), a known inhibitor of autophagy, but further increased by the addition of lysosomal protease inhibitors (pepstatin A and E64d), demonstrating that there is autophagic induction through type III PI3 kinase during the combined therapy. Knocking down of ATG5 and beclin-1, two essential autophagic molecules, resulted in radiation resistance of lung cancer cells. Our report suggests that combined inhibition of apoptosis and mTOR during radiotherapy is a potential therapeutic strategy to enhance radiation therapy in patients with non-small cell lung cancer.

Class I phosphatidylinositol 3-kinase inhibitor LY294002 activates autophagy and induces apoptosis through p53 pathway in gastric cancer cell line SGC7901

We aimed to study the effects of LY294002, an inhibitor of class I phosphatidylinositol 3-kinase (PI3K), on proliferation, apoptosis, and autophagy in gastric cancer cell line SGC7901. In this study, we showed that LY294002 inhibited the viability of gastric cancer SGC7901 cells. We also showed that LY294002 increased the expression of microtubule-associated protein 1 light chain 3 (LC3), and increased monodansylcadaverine (MDC)-labeled vesicles. LY294002 activated autophagy by activating p53 and caspase-3, and induced apoptosis by up-regulating p53 and p53-up-regulated modulator of apoptosis (PUMA). Therefore, LY294002 might induce cytotoxicity in SGC7901 cells through activation of p53 and the downstream point PUMA. These findings suggest that inhibition of the class I PI3K signaling pathway is a potential strategy for managing gastric cancers.

Dynamic effects of autophagy on arsenic trioxide-induced death of human leukemia cell line HL60 cells

AIM

To evaluate the contribution of an autophagic mechanism to the As2O3- induced death of human acute myeloid leukaemia cell line HL60 cells.

METHODS

The growth inhibition of HL60 cells induced by As2O3 was assessed with 3-(4,5- dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide colorimetric assay. The activation of autophagy was determined with monodansylcadaverine labeling and transmission electron microscope. The role of autophagy in the As2O3-induced death of HL60 cells was assessed using autophagic and lysosomal inhibitors. Immunofluorescence, flow cytometry, and Western blot analysis were used to study the apoptotic and autophagic mechanisms.

RESULTS

After treatment with As2O3, the proliferation of HL60 cells was significantly inhibited and the formation of autophagosomes increased. The blockade of autophagy maturation with the autophagy-specific inhibitor 3-methyladenine (3-MA) or the lysosome-neutralizing agent NH4Cl 1 h before As2O3 potentiated the As2O3-induced death of HL60 cells. In contrast, 3-MA attenuated As2O3-induced death when administered 30 min after As2O3. 3-MA and NH4Cl also inhibited As2O3-induced upregulation of microtubule-associated protein 1 light chain 3, the protein required for autophagy in mammalian cells. Following As2O3, lysosomes were activated as indicated by increased levels of cathepsins B and L. The apoptotic response of HL60 cells to As2O3 was suggested by the collapse of mitochondrial membrane potential, release of cytochrome c from mitochondria, and the activation of caspase-3. Pretreatment with 3-MA prior to As2O3 amplified these apoptotic signals, while posttreatment with 3-MA 30 min after As2O3 attenuated the apoptotic pathways.

CONCLUSION

Autophagy plays complex roles in the As2O3-induced death of HL60 cells; it inhibits As2O3-induced apoptosis in the initiation stage, but amplifies the As2O3-mediated apoptotic program if it is persistently activated.

Nelfinavir, A lead HIV protease inhibitor, is a broad-spectrum, anticancer agent that induces endoplasmic reticulum stress, autophagy, and apoptosis in vitro and in vivo

PURPOSE

The development of new cancer drugs is slow and costly. HIV protease inhibitors are Food and Drug Administration approved for HIV patients. Because these drugs cause toxicities that can be associated with inhibition of Akt, an emerging target in cancer, we assessed the potential of HIV protease inhibitors as anticancer agents.

EXPERIMENTAL DESIGN

HIV protease inhibitors were screened in vitro using assays that measure cellular proliferation, apoptotic and nonapoptotic cell death, endoplasmic reticulum (ER) stress, autophagy, and activation of Akt. Nelfinavir was tested in non-small cell lung carcinoma (NSCLC) xenografts with biomarker assessment.

RESULTS

Three of six HIV protease inhibitors, nelfinavir, ritonavir, and saquinavir, inhibited proliferation of NSCLC cells, as well as every cell line in the NCI60 cell line panel. Nelfinavir was most potent with a mean 50% growth inhibition of 5.2 micromol/L, a concentration achievable in HIV patients. Nelfinavir caused two types of cell death, caspase-dependent apoptosis and caspase-independent death that was characterized by induction of ER stress and autophagy. Autophagy was protective because an inhibitor of autophagy increased nelfinavir-induced death. Akt was variably inhibited by HIV protease inhibitors, but nelfinavir caused the greatest inhibition of endogenous and growth factor-induced Akt activation. Nelfinavir decreased the viability of a panel of drug-resistant breast cancer cell lines and inhibited the growth of NSCLC xenografts that was associated with induction of ER stress, autophagy, and apoptosis.

CONCLUSIONS

Nelfinavir is a lead HIV protease inhibitor with pleiotropic effects in cancer cells. Given its wide spectrum of activity, oral availability, and familiarity of administration, nelfinavir is a Food and Drug Administration-approved drug that could be repositioned as a cancer therapeutic.

Kringle 5 of human plasminogen, an angiogenesis inhibitor, induces both autophagy and apoptotic death in endothelial cells

Inhibition of endothelial cell proliferation and angiogenesis is emerging as an important strategy in cancer therapeutics. Kringle 5 (K5) of human plasminogen is a potent angiogenesis inhibitor. Previous studies have shown K5 exposure promotes caspase activity and apoptosis in endothelial cells. Here we report that K5 treatment evokes an autophagic response in endothelial cells that is specific and initiated even in the absence of nutritional stress. Endothelial cells exposed to K5 up-regulated Beclin 1 levels within a few hours. Furthermore, progressively increasing amounts of antiapoptotic Bcl-2 were found to be complexed with Beclin 1, although total levels of Bcl-2 remained unchanged. Prolonged exposure to K5 ultimately led to apoptosis via mitochondrial membrane depolarization and caspase activation in endothelial cells. Knocking down Beclin 1 levels by RNA interference decreased K5 induced autophagy but accelerated K5-induced apoptosis. These studies suggest that interfering with the autophagic survival response can potentiate the antiangiogenic effects of Kringle 5 in endothelial cells.

Reactive Oxygen Species Regulate Autophagy through Redox-Sensitive Proteases

Starvation induces autophagy through a signal transduction pathway that is not fully understood. In a recent issue of The EMBO Journal, Scherz-Shouval and colleagues (Scherz-Shouval et al., 2007) show that reactive oxygen species (ROS) occurring during starvation serve as signaling molecules that initiate autophagy.

Arabidopsis AtBECLIN 1/AtAtg6/AtVps30 is essential for pollen germination and plant development

Pollen germination on the surface of compatible stigmatic tissues is an essential step for plant fertilization. Here we report that the Arabidopsis mutant bcl1 is male sterile as a result of the failure of pollen germination. We show that the bcl1 mutant allele cannot be transmitted by male gametophytes and no homozygous bcl1 mutants were obtained. Analysis of pollen developmental stages indicates that the bcl1 mutation affects pollen germination but not pollen maturation. Molecular analysis demonstrates that the failure of pollen germination was caused by the disruption of AtBECLIN 1. AtBECLIN 1 is expressed predominantly in mature pollen and encodes a protein with significant homology to Beclin1/Atg6/Vps30 required for the processes of autophagy and vacuolar protein sorting (VPS) in yeast. We also show that AtBECLIN 1 is required for normal plant development, and that genes related to autophagy, VPS and the glycosylphosphatidylinositol anchor system, were affected by the deficiency of AtBECLIN 1.

Mechanisms of cell death in oxidative stress

Reactive oxygen or nitrogen species (ROS/RNS) generated endogenously or in response to environmental stress have long been implicated in tissue injury in the context of a variety of disease states. ROS/RNS can cause cell death by nonphysiological (necrotic) or regulated pathways (apoptotic). The mechanisms by which ROS/RNS cause or regulate apoptosis typically include receptor activation, caspase activation, Bcl-2 family proteins, and mitochondrial dysfunction. Various protein kinase activities, including mitogen-activated protein kinases, protein kinases-B/C, inhibitor-of-I-kappaB kinases, and their corresponding phosphatases modulate the apoptotic program depending on cellular context. Recently, lipid-derived mediators have emerged as potential intermediates in the apoptosis pathway triggered by oxidants. Cell death mechanisms have been studied across a broad spectrum of models of oxidative stress, including H2O2, nitric oxide and derivatives, endotoxin-induced inflammation, photodynamic therapy, ultraviolet-A and ionizing radiations, and cigarette smoke. Additionally ROS generated in the lung and other organs as the result of high oxygen therapy or ischemia/reperfusion can stimulate cell death pathways associated with tissue damage. Cells have evolved numerous survival pathways to counter proapoptotic stimuli, which include activation of stress-related protein responses. Among these, the heme oxygenase-1/carbon monoxide system has emerged as a major intracellular antiapoptotic mechanism.

Mitochondrial trafficking and morphology in healthy and injured neurons

Mitochondria are the primary generators of ATP and are important regulators of intracellular calcium homeostasis. These organelles are dynamically transported along lengthy neuronal processes, presumably for appropriate distribution to cellular regions of high metabolic demand and elevated intracellular calcium, such as synapses. The removal of damaged mitochondria that produce harmful reactive oxygen species and promote apoptosis is also thought to be mediated by transport of mitochondria to autophagosomes. Mitochondrial trafficking is therefore important for maintaining neuronal and mitochondrial health while cessation of movement may lead to neuronal and mitochondrial dysfunction. Mitochondrial morphology is also dynamic and is remodeled during neuronal injury and disease. Recent studies reveal different manifestations and mechanisms of impaired mitochondrial movement and altered morphology in injured neurons. These are likely to cause varied courses toward neuronal degeneration and death. The goal of this review is to provide an appreciation of the full range of mitochondrial function, morphology and trafficking, and the critical role these parameters play in neuronal physiology and pathophysiology.

Mechanisms of programmed cell death during oogenesis in Drosophila virilis

We describe the features of programmed cell death occurring in the egg chambers of Drosophila virilis during mid-oogenesis and late oogenesis. During mid-oogenesis, the spontaneously degenerating egg chambers exhibit typical characteristics of apoptotic cell death. As revealed by propidium iodide, rhodamine-conjugated phalloidin staining, and the TUNEL assay, respectively, the nurse cells contain condensed chromatin, altered actin cytoskeleton, and fragmented DNA. In vitro caspase activity assays and immunostaining procedures demonstrate that the atretic egg chambers possess high levels of caspase activity. Features of autophagic cell death are also observed during D. virilis mid-oogenesis, as shown by monodansylcadaverine staining, together with an ultrastructural examination by transmission electron microscopy. During the late stages of oogenesis in D. virilis, once again, the two mechanisms, viz., nurse cell cluster apoptosis and autophagy, operate together, manifesting features of cell death similar to those detailed above. Moreover, an altered form of cytochrome c seems to be released from the mitochondria in the nurse cells proximal to the oocyte. We propose that apoptosis and autophagy function synergistically during oogenesis in D. virilis in order to achieve a more efficient elimination of the degenerated nurse cells and abnormal egg chambers.