A novel assay to study autophagy: regulation of autophagosome vacuole size by amino acid deprivation

Knocking down HMGB1 using dendrimer-delivered siRNA unveils its key role in NMDA-induced autophagy in rat cortical neurons

PURPOSE

To explore the role of the High Mobility Group Box 1 (HMGB1) protein in NMDA-mediated excitotoxicity in rat cortical neurons.

METHODS

We knocked down HMGB1 using small-interfering RNA (siRNA) delivered into neurons by means of a dendrimer. We determined autophagy activation by measuring the ratio of light chain 3 protein isoforms (LC3B-I)/LC3B-II and by determining autophagolysosome labeling using the specific marker monodansyl cadaverine. Neuronal toxicity was induced by exposing the neurons to N-methyl-D-aspartate (NMDA) and it was determined by measuring Lactate dehydrogenase and MTT reduction.

RESULTS

We found that NMDA receptor stimulation induced both neuronal death and autophagy in rat cortical neurons. In addition, NMDA also caused HMGB1 translocation from the neuronal nucleus to the cytoplasm where it formed a complex with Beclin1. HMGB1 was efficiently knocked down using a specific siRNA causing a blockade of NMDA-induced autophagy and potentiating NMDA-induced neuronal death.

CONCLUSIONS

Our study demonstrates that HMGB1 plays a relevant role in neuronal autophagy regulation and suggest a protective role of autophagy during excitotoxicity. In addition, the dendrimer that we have used here is a good vector for siRNA delivery to neurons allowing lack-of-function studies.

Ablation of dihydroceramide desaturase 1, a therapeutic target for the treatment of metabolic diseases, simultaneously stimulates anabolic and catabolic signaling

The lipotoxicity hypothesis posits that obesity predisposes individuals to metabolic diseases because the oversupply of lipids to tissues not suited for fat storage leads to the accumulation of fat-derived molecules that impair tissue function. Means of combating this have been to stimulate anabolic processes to promote lipid storage or to promote catabolic ones to drive fat degradation. Herein, we demonstrate that ablating dihydroceramide desaturase 1 (Des1), an enzyme that produces ceramides, leads to the simultaneous activation of both anabolic and catabolic signaling pathways. In cells lacking Des1, the most common sphingolipids were replaced with dihydro forms lacking the double bond inserted by Des1. These cells exhibited a remarkably strong activation of the antiapoptotic and anabolic signaling pathway regulated by Akt/protein kinase B (PKB), were resistant to apoptosis, and were considerably larger than their wild-type counterparts. Paradoxically, Des1(-/-) cells exhibited high levels of autophagy. Mechanistic studies revealed that this resulted from impaired ATP synthesis due in part to decreased expression and activity of several complexes of the electron transport chain, particularly complex IV, leading to activation of AMP-activated protein kinase and its induction of the autophagosome. Thus, Des1 ablation enhanced starvation responses but dissociated them from the anabolic, prosurvival, and antiautophagic Akt/PKB pathways.

Autophagy contributes to leaf starch degradation

Transitory starch, a major photosynthetic product in the leaves of land plants, accumulates in chloroplasts during the day and is hydrolyzed to maltose and Glc at night to support respiration and metabolism. Previous studies in Arabidopsis thaliana indicated that the degradation of transitory starch only occurs in the chloroplasts. Here, we report that autophagy, a nonplastidial process, participates in leaf starch degradation. Excessive starch accumulation was observed in Nicotiana benthamiana seedlings treated with an autophagy inhibitor and in autophagy-related (ATG) gene-silenced N. benthamiana and in Arabidopsis atg mutants. Autophagic activity in the leaves responded to the dynamic starch contents during the night. Microscopy showed that a type of small starch granule-like structure (SSGL) was localized outside the chloroplast and was sequestered by autophagic bodies. Moreover, an increased number of SSGLs was observed during starch depletion, and disruption of autophagy reduced the number of vacuole-localized SSGLs. These data suggest that autophagy contributes to transitory starch degradation by sequestering SSGLs to the vacuole for their subsequent breakdown.

Three isoforms of the Atg16L1 protein contribute different autophagic properties

The mammalian Atg16L1 protein consists of a coiled-coil domain and a tryptophan-aspartic acid (WD) repeat domain and is involved in the process of autophagy. However, the mechanisms underlying the effect of the Atg16L1 isoforms on autophagy remain to be elucidated in humans. In the present study, we successfully cloned three isoforms: Atg16L1-1, which contains the complete sequence; Atg16L1-2, which lacks all of exon 8; and Atg16L1-3, which lacks the coiled-coil domain. Subsequent experiments showed that the three isoforms of Atg16L1 were colocalised with MDC within the cells. Quantitative analysis of fluorescence showed that the average number of dots of Atg16L1-1 that colocalised with MDC was higher than those of Atg16L1-2 and Atg16L1-3. The three isoforms of Atg16L1 also colocalised with the lysosome within the cells. The average number of dots of Atg16L1-1 that colocalised with the lysosome was higher than those of Atg16L1-2 and Atg16L1-3. However, although Atg16L1-1 and Atg16L1-3 colocalised with the mitochondria, Atg16L1-2 did not. Functional analysis showed that overexpression of the three isoforms of Atg16L1 had a stimulative effect on autophagy. Significant increase in the number of positive LC3-II dots per cell was observed in Atg16L1-1 (70.2 ± 2.39 dots); this number was greater than those of the other two isoforms. Atg16L1-2 appeared to have an average of 59.25 ± 2.22 LC3-II dots per cell. Atg16L1-3 appeared to have the least number of LC3-II dots per cell (48.25 ± 2.22 dots) (P < 0.001). Our results indicated that the degree of autophagy varied with different Atg16L1 isoforms. The different domains of Atg16L1 played different roles in the process of autophagy. The coiled-coil domain of Atg16L1 was involved in the process of autophagy.

Reconsider Alzheimer's disease by the 'calpain-cathepsin hypothesis'--a perspective review

Alzheimer's disease (AD) is characterized by slowly progressive neuronal death, but its molecular cascade remains elusive for over 100 years. Since accumulation of autophagic vacuoles (also called granulo-vacuolar degenerations) represents one of the pathologic hallmarks of degenerating neurons in AD, a causative connection between autophagy failure and neuronal death should be present. The aim of this perspective review is at considering such underlying mechanism of AD that age-dependent oxidative stresses may affect the autophagic-lysosomal system via carbonylation and cleavage of heat-shock protein 70.1 (Hsp70.1). AD brains exhibit gradual but continual ischemic insults that cause perturbed Ca(2+) homeostasis, calpain activation, amyloid β deposition, and oxidative stresses. Membrane lipids such as linoleic and arachidonic acids are vulnerable to the cumulative oxidative stresses, generating a toxic peroxidation product 'hydroxynonenal' that can carbonylate Hsp70.1. Recent data advocate for dual roles of Hsp70.1 as a molecular chaperone for damaged proteins and a guardian of lysosomal integrity. Accordingly, impairments of lysosomal autophagy and stabilization may be driven by the calpain-mediated cleavage of carbonylated Hsp70.1, and this causes lysosomal permeabilization and/or rupture with the resultant release of the cell degradation enzyme, cathepsins (calpain-cathepsin hypothesis). Here, the author discusses three topics; (1) how age-related decrease in lysosomal and autophagic activities has a causal connection to programmed neuronal necrosis in sporadic AD, (2) how genetic factors such as apolipoprotein E and presenilin 1 can facilitate lysosomal destabilization in the sequential molecular events, and (3) whether a single cascade can simultaneously account for implications of all players previously reported. In conclusion, Alzheimer neuronal death conceivably occurs by the similar 'calpain-hydroxynonenal-Hsp70.1-cathepsin cascade' with ischemic neuronal death. Blockade of calpain and/or extra-lysosomal cathepsins as well as scavenging of hydroxynonenal would become effective AD therapeutic approaches.

Knockdown of DEPTOR induces apoptosis, increases chemosensitivity to doxorubicin and suppresses autophagy in RPMI-8226 human multiple myeloma cells in vitro

DEP domain containing mammalian target of rapamycin (mTOR)-interacting protein (DEPTOR) is an mTOR binding protein that is overexpressed in RPMI-8226 human multiple myeloma cells, and plays an important role in maintaining cell survival. However, knowledge on the effects of DEPTOR knockdown on the biological functions of RPMI‑8226 human multiple myeloma cells, is limited. This study aimed to determine the role of DEPTOR in the proliferation, apoptosis and autophagy in these cells and to elucidate the mechanisms by which DEPTOR contributes to the chemosensitivity of myeloma cells. RNA interference was used to reduce the expression of DEPTOR. Cytotoxicity was evaluated by MTT assay. Apoptosis was examined by flow cytometry. DEPTOR mRNA and protein expression in RPMI‑8226 cells treated with DEPTOR-specific short hairpin RNA (shRNA) was evaluated by RT-PCR, quantitative PCR and western blot analysis. The expression of apoptosis‑associated proteins, autophagy‑associated proteins, and the activation of the phosphoinositide 3‑kinase (PI3K)/Akt signaling pathway were detected by western blot analysis. Autophagy was also measured by transmission electron microscopy and monodansylcadaverine (MDC). In this study, RPMI-8226 cells were transfected with the DEPTOR-specific shRNA, which resulted in the significant inhibition of the transcription and expression of DEPTOR. The downregulation of DEPTOR inhibited proliferation, enhanced the doxorubicin‑induced growth inhibitory effects on RPMI-8226 cells, and increased the expression of cleaved caspase‑3 and cleaved poly(ADP-ribose) polymerase (PARP). Moreover, the downregulation of DEPTOR suppressed autophagy and inhibited the activation of the PI3K/Akt signaling in RPMI‑8226 cells. In conclusion, our data demonstrated that the downregulation of DEPTOR induces apoptosis, increases chemosensitivity to doxorubicin, and suppresses autophagy and the activation of the PI3K/Akt signaling pathway in RPMI‑8226 human multiple myeloma cells.

AKT serine/threonine protein kinase modulates baicalin-triggered autophagy in human bladder cancer T24 cells

Baicalin is one of the major compounds in the traditional Chinese medicinal herb from Scutellaria baicalensis Georgi. We investigated the molecular mechanisms of cell autophagy induced by baicalin in human bladder cancer T24 cells. Baicalin inhibited cell survival as shown by MTT assay and increased cell death by trypan blue exclusion assay in a concentration-dependent manner. Baicalin did not induce apoptotic cell death in T24 cells by TUNEL and caspase-3 activity assay. Baicalin induced the acidic vesicular organelle cell autophagy marker, manifested by acridine orange (AO) and monodansylcadaverine (MDC) staining and cleavage of microtubule-associated protein 1 light chain 3 (LC3). The protein expression levels of the Atg 5, Atg 7, Atg 12, Beclin-1 and LC3-II were upregulated in T24 cells after baicalin treatment. Inhibition of autophagy by 3-methyl-adenine (an inhibitor of class III phosphatidylinositol-3 kinase; 3-MA) reduced the cleavage of LC3 in T24 cells after baicalin treatment. Furthermore, protein expression levels of phospho-AKT (Ser473) and enzyme activity of AKT were downregulated in T24 cells after baicalin treatment. In conclusion, baicalin triggered cell autophagy through the AKT signaling pathway in T24 cells.

The natural compounds piperovatine and piperlonguminine induce autophagic cell death on Trypanosoma cruzi

The currently available treatments for Chagas disease show limited therapeutic potential and are associated with serious side effects. Our group has been attempting to find alternative drugs isolated from natural products as a potential source of pharmacological agents against Trypanosoma cruzi. Here, we demonstrate the antitrypanosomal activity of the amides piperovatine and piperlonguminine isolated from Piper ovatum against epimastigotes and intracellular amastigotes. We also investigated the mechanisms of action of these compounds on extracellular amastigote and epimastigote forms of T. cruzi. These amides showed low toxicity to LLCMK(2) mammalian cells. By using transmission and scanning electron microscopy, we observed that the compounds caused severe alterations in T. cruzi. These alterations were mainly located in plasma membrane and mitochondria. Furthermore, the study of treated parasites labeled with Rh123, PI and MDC corroborate with our TEM data. These mitochondrial dysfunctions induced by the amides might trigger biochemical alterations that lead to cell death. Altogether, our data evidence a possible autophagic process.

Energy deprivation by silibinin in colorectal cancer cells: a double-edged sword targeting both apoptotic and autophagic machineries

Small molecules with the potential to initiate different types of programmed cell death could be useful 'adjunct therapy' where current anticancer modalities fail to generate significant activity due to a defective apoptotic machinery or resistance of cancer cells to the specific death mechanism induced by that treatment. The current study identified silibinin, for the first time, as one such natural agent, having dual efficacy against colorectal cancer (CRC) cells. First, silibinin rapidly induced oxidative stress in CRC SW480 cells due to reactive oxygen species (ROS) generation with a concomitant dissipation of mitchondrial potential (ΔΨm) and cytochrome c release leading to mild apoptosis as a biological effect. However, with increased exposure to silibinin, cytoplasmic vacuolization intensified within the cells followed by sequestration of the organelles, which inhibits the further release of cytochrome c. Interestingly, this decrease in apoptotic response correlated with increased autophagic events as evidenced by tracking the dynamics of LC3-II within the cells. Mechanistic studies revealed that silibinin strongly inhibited PIK3CA-AKT-MTOR but activated MAP2K1/2-MAPK1/3 pathways for its biological effects. Corroborating these effects, endoplasmic reticulum stress was generated and glucose uptake inhibition as well as energy restriction were induced by silibinin, thus, mimicking starvation-like conditions. Further, the cellular damage to tumor cells by silibinin was severe and irreparable due to sustained interference in essential cellular processes such as mitochondrial metabolism, phospholipid and protein synthesis, suggesting that silibinin harbors a deadly 'double-edged sword' against CRC cells thereby further advocating its clinical effectiveness against this malignancy.

Autophagic activity in the mouse urinary bladder urothelium as a response to starvation

The urinary bladder urothelium is subjected to mechanical forces during cycles of distension and contraction, and its superficial cells are constantly flushed by toxic urine. Yet, the urothelium shows a very slow turnover of cells and superficial cells are extremely long lived. Autophagy has a well-known role in tissue homeostasis and serves as a protective mechanism against cellular stress. Therefore, the presence of autophagy as one of possible processes of survival in an unpleasant environment and during long lifetime of superficial cells was examined in mouse urothelium. We detected and evaluated autophagic activity of superficial urothelial cells under normal and stress conditions, caused by short-term starvation of newborn and 24-h-starved adult mice. Immunolabeling and Western blotting of essential effectors of autophagy, LC3 and Beclin 1, showed a weak signal in superficial urothelial cells. On the other hand, ultrastructural analysis, which proved to be the most reliable method in our study, revealed the presence of autophagic vacuoles, some of them containing specific urothelial structures, fusiform vesicles. Quantitative analysis showed increased autophagy in newborn and starved mice in comparison to a low basic level of autophagy in the urothelium of normal mice. Interestingly, some superficial cells of adults and neonates exhibit intense immunoreactions against LC3 and Beclin 1 and the typical ultrastructural characteristics of autophagy-dependent cell death. We conclude that autophagy, despite low basic activity under physiological conditions, plays an important role in urothelial homeostasis and stability under stress.

Chloroquine enhances cobalt chloride-induced leukemic cell differentiation via the suppression of autophagy at the late phase

We previously reported that moderate hypoxia and hypoxia-mimetic agents including cobalt chloride (CoCl(2)) induce differentiation of human acute myeloid leukemia (AML) cells through hypoxia-inducible factor-1 α (HIF-1 α), which interacts with and enhances transcriptional activity of CCAAT-enhancer binding factor alpha and Runx1/AML1, two important transcriptional factors for hematopoietic cell differentiation. Here, we show that autophagy inhibitor chloroquine (CQ) increases HIF-1 α accumulation, thus potentiating CoCl(2)-induced growth arrest and differentiation of leukemic cells. Furthermore, the increased effect of CQ on differentiation induction is dependent of the inhibition of autophagosome maturation and degradation, since this sensitization could be mimicked by the suppression of expression of both lysosome-associated membrane proteins 1 and 2 (LAMP1 and LAMP2). These findings not only provide the evidence that CQ is a sensitizer for CoCl(2)-induced differentiation of leukemic cells but also possibly propose the new therapeutic strategy for differentiation induction of AML.

Excessive autophagy contributes to neuron death in cerebral ischemia

AIMS

To determine the extent to which autophagy contributes to neuronal death in cerebral hypoxia and ischemia.

METHODS

We performed immunocytochemistry, western blot, cell viability assay, and electron microscopy to analyze autophagy activities in vitro and in vivo.

RESULTS

In both primary cortical neurons and SH-SY5Y cells exposed to oxygen and glucose deprivation (OGD)for 6 h and reperfusion (RP) for 24, 48, and 72 h, respectively, an increase of autophagy was observed as determined by the increased ratio of LC3-II to LC3-I and Beclin-1 (BECN1) expression. Using Fluoro-Jade C and monodansylcadaverine double-staining, and electron microscopy we found the increment in autophagy after OGD/RP was accompanied by increased autophagic cell death, and this increased cell death was inhibited by the specific autophagy inhibitor, 3-methyladenine. The presence of large autolysosomes and numerous autophagosomes in cortical neurons were confirmed by electron microscopy. Autophagy activities were increased dramatically in the ischemic brains 3-7 days postinjury from a rat model of neonatal cerebral hypoxia/ischemia as shown by increased punctate LC3 staining and BECN1 expression.

CONCLUSION

Excessive activation of autophagy contributes to neuronal death in cerebral ischemia.

Innate immune responses to respiratory syncytial virus infection

The innate immune response has a critical role in the initial stages of respiratory syncytial virus (RSV) infection and provides important instructional control that determines the direction of the acquired immune response and the severity of subsequent disease. Contributions to innate immunity include responses initiated in epithelial cells, dendritic cells, and macrophages. The initiation and the intensity of the response depends upon the recognition of pathogen-associated molecular patterns (PAMPs) that activate various pattern recognition receptors (PRRs) such as toll-like receptors (TLR), RIG-I-like receptors (RLR), and NOD-like receptors (NLR), that induce innate cytokines and chemokines that promote inflammation and direct the recruitment of immune cells as well as promote anti-viral responses. In this review, we summarize the results of numerous studies that have characterized the innate immune responses that contribute to the RSV-induced responses and may be important considerations for the development of efficacious vaccine strategies.

Autophagy-independent enhancing effects of Beclin 1 on cytotoxicity of ovarian cancer cells mediated by proteasome inhibitors

Background

The ubiquitin-proteasome system and macroautophagy (hereafter referred to autophagy) are two complementary pathways for protein degradation. Emerging evidence suggests that proteasome inhibition might be a promising approach for tumor therapy. Accumulating data suggest that autophagy is activated as a compensatory mechanism upon proteasome activity is impaired.

Method

Autophagy activation was measured using acridine orange staining and LC3 transition. Cell viability and apoptosis were measured using MTT assay and flow cytometry, respectively. Beclin 1 expression vectors or shRNA against Beclin 1 (shBeclin 1) were transfected to investigate the role of Beclin 1 in autophagy activation and cytotoxicity of ovarian cancer cells induced by proteasome inhibitors.

Results

Proteasome inhibitors suppressed proliferation and induced autophagy in ovarian cancer cells. Neither phosphoinositide 3-kinase (PI3K) inhibitors nor shRNA against Beclin 1 could abolish the formation of acidic vacuoles and the processing of LC3 induced by proteasome inhibitors. Moreover, Beclin 1 overexpression enhanced anti-proliferative effects of proteasome inhibitors in ovarian cancer cells.

Conclusions

For the first time, the current study demonstrated that proteasome inhibitors induced PI3K and Beclin 1-independent autophagy in ovarian cancer cells. In addition, this study revealed autophagy-independent tumor suppressive effects of Beclin 1 in ovarian cancer cells.

Endosomes and lysosomes are involved in early steps of Tl(III)-mediated apoptosis in rat pheochromocytoma (PC12) cells

The mechanisms that mediate thallium (Tl) toxicity are still not completely understood. The exposure of rat pheochromocytoma (PC12) cells to Tl(I) or Tl(III) activates both mitochondrial (Tl(I) and Tl(III)) and extrinsic (Tl(III)) pathways of apoptosis. In this work we evaluated the hypothesis that the effects of Tl(III) may be mediated by the damage to lysosomes, where it might be incorporated following the route of iron uptake. PC12 cells exposed for 3 h to 100 μM Tl(III) presented marked endosomal acidification, effect that was absent when cells were incubated in a serum-free medium and that was fully recovered when the latter was supplemented with transferrin. After 6 h of incubation the colocalization of cathepsins D and B with the lysosomal marker Lamp-1 was decreased together with an increase in the total activity of the enzymes. A permanent damage to lysosomes after 18 h of exposure was evidenced from the impairment of acridine orange uptake. Cathepsin D caused the cleavage of pro-apoptotic protein BID that is involved in the activation of the intrinsic pathway of apoptosis. Supporting that, BID cleavage and the activation of caspase 3 by Tl(III) were fully prevented when cells were preincubated with cathepsin D inhibitor (pepstatin A) and only partially prevented when cathepsin B inhibitor (E64d) was used. None of these inhibitors affected BID cleavage or caspase 3 activation in Tl(I)-treated cells. Together, experimental results support the role of Tl(III) uptake by the acidic cell compartments and their involvement in the early steps of Tl(III)-mediated PC12 cells apoptosis.

Toll-like receptor 2 ligands promote microglial cell death by inducing autophagy

Microglial cells are phagocytes in the central nervous system (CNS) and become activated in pathological conditions, resulting in microgliosis, manifested by increased cell numbers and inflammation in the affected regions. Thus, controlling microgliosis is important to prevent pathological damage to the brain. Here, we evaluated the contribution of Toll-like receptor 2 (TLR2) to microglial survival. We observed that activation of microglial cells with peptidoglycan (PGN) from Staphylococcus aureus and other TLR2 ligands results in cell activation followed by the induction of autophagy and autophagy-dependent cell death. In C57BL/6J mice, intracerebral injection of PGN increased the autophagy of microglial cells and reduced the microglial/macrophage cell number in brain parenchyma. Our results demonstrate a novel role of TLRs in the regulation of microglial cell activation and survival, which are important for the control of microgliosis and associated inflammatory responses in the CNS.

N-Acetyl Cysteine Protects against Methamphetamine-Induced Dopaminergic Neurodegeneration via Modulation of Redox Status and Autophagy in Dopaminergic Cells

Methamphetamine- (MA-) induced neurotoxicity is associated with mitochondrial dysfunction and enhanced oxidative stress. Our previous study demonstrated that MA induces autophagy in a dopaminergic neuronal cell model (N27 cells). The cellular mechanisms underlying MA-induced autophagy and apoptosis remain poorly characterized. In the present study we sought to investigate the importance of GSH redox status in MA-induced neurotoxicity using a thiol antioxidant, N-acetylcysteine (NAC). Morphological and biochemical analysis revealed that MA-induced autophagy in N27 dopaminergic cells was associated with pronounced depletion of GSH levels. Moreover, pretreatment with NAC reduced MA-induced GSH depletion and autophagy, while depletion of GSH using L-buthionine sulfoximine (L-BSO) enhanced autophagy. Furthermore, treatment with NAC significantly attenuated MA-induced apoptotic cell death as well as oxidative stress markers, namely, 3-nitrotyrosine (3-NT) and 4-hydroxynonenal (4-HNE). Together, these results suggest that NAC exhibits significant protective effects against MA-induced dopaminergic cell death, presumably via modulation of the GSH level and autophagy. Collectively, our data provide mechanistic insights into the role of cellular GSH redox status in MA-induced autophagy and apoptotic cell death, and additional studies are needed to determine the therapeutic effectiveness of cellular redox modifiers in attenuating dopaminergic neurodegeneration in vivo.

Increased macroautophagy in the pathological process of intervertebral disc degeneration in rats

OBJECTIVE

Macroautophagy increases with age in rat intervertebral discs; however, the effect of macroautophagy on the process of intervertebral disc degeneration (IVDD) is still unclear. The aim of this study was to examine the presence of autophagosome, as well as the levels of Beclin-1 and LC3 proteins, in vivo. Additionally, in vitro evidence of macroautophagy and GRP78 and GADD153 protein levels were investigated to explore the mechanism of macroautophagy in the process of IVDD.

METHODS

Male Sprague-Dawley rats, aged 2 months, were randomly divided into six groups (three control and three model groups, n = 8 per group). At the 6-, 12-, and 18-week time points, autophagosomes in nucleus pulposus cells were detected with transmission electron microscope (TEM). Expression of Beclin-1 and LC3 protein levels within intervertebral disc was detected using Western blotting analysis. Then, the rat annulus fibrosus cells were isolated and cultured with Earle's balanced salt solution. At 1, 2, and 3 hr of culture, autophagosomes were detected using monodansylcadaverine assay, and LC3, Beclin-1, GRP78, and GADD153 protein levels were detected using Western blotting analysis.

RESULTS

Transmission electron microscopy revealed autophagosomes within nucleus pulposus cells in both the control and model groups. At 6-, 12-, and 18-week posttreatments, the levels of Beclin-1 and the LC3-II/LC3-I protein ratio in the model groups were higher than those in the control groups (p < 0.05). Compared with the control rats, amino acid starvation increased the number of monodansylcadaverine-positive cells and the LC3-II/LC3-I protein ratio in the model rats. Moreover, the in vitro levels of Beclin-1, GRP78, and GADD153 proteins were increased with the prolongation of amino acid starvation (p < 0.05).

CONCLUSIONS

Macroautophagy was present and was associated with increased pathological process of IVDD in rats. Macroautophagy of intervertebral disc cells is possibly secondary to endoplasmic reticulum stress.

Trypanocidal action of (-)-elatol involves an oxidative stress triggered by mitochondria dysfunction

Natural compounds have shown good potential for the discovery of new chemotherapeutics for the treatment of Chagas' disease. Recently, our group reported the effective trypanocidal activity of (-)-elatol, extracted from the red macroalgae Laurencia dendroidea present in the Brazilian coast against Trypanosoma cruzi. However, the mechanism of action of this compound has remained unclear. There are only hypotheses concerning its action on mitochondrial function. Here, we further investigated the mechanisms of action of (-)-elatol on trypomastigotes of T. cruzi. For this, we evaluated some biochemical alterations in trypomastigotes treated with (-)-elatol. Our results show that (-)-elatol induced depolarization of the mitochondrial membrane, an increase in the formation of mitochondrial superoxide anion and loss of cell membrane and DNA integrity. Additionally, (-)-elatol induced formation of autophagic vacuoles and a decrease in cell volume. All together, these results suggest that the trypanocidal action of (-)-elatol involves multiple events and mitochondria might be the initial target organelle. Our hypothesis is that the mitochondrial dysfunction leads to an increase of ROS production through the electron transport chain, which affects cell membrane and DNA integrity leading to different types of parasite death.

Bufalin increases sensitivity to AKT/mTOR-induced autophagic cell death in SK-HEP-1 human hepatocellular carcinoma cells

Bufalin is the major component of Chan-Su (a traditional Chinese medicine, TCM) extracts from the venom of Bufo bufo gargarizan. In the present study, we investigated the pharmacological mechanisms of cell cycle arrest and autophagic cell death induced by bufalin in SK-HEP-1 human hepatocellular carcinoma cells in vitro. Bufalin inhibited cell survival by MTT assay and increased cell death by trypan blue exclusion assay in a concentration-dependent manner. In addition, bufalin induced G2/M phase arrest by reducing CDK1 activity. Bufalin triggered DNA fragmentation and apoptotic cell death in SK-HEP-1 cells by DNA gel electrophoresis, TUNEL and caspase-3 activity assay, while bufalin induced autophagic cell death by double-membrane vacuoles (transmission electron microscopy, TEM), acidic vesicular organelles (acridine orange staining) and cleavage of microtubule-associated protein 1 light chain 3 (LC3). Protein expression levels of cyclin A and B, CDK1, phospho-CDK1 (Thr161), Cdc25c, phospho-Cdc25c (Ser198), phospho-AKT (Thr308), phospho-AKT (Ser473), phospho‑mTOR (Ser2481) were downregulated. In contrast, protein expression levels of the Chk1, Wee1, LC3-II, Beclin-1, Atg 5, Atg 7 and Atg 12 were upregulated in SK-HEP-1 cells after bufalin treatment. Inhibition of autophagy by 3-methyladenine (an inhibitor of class III phosphatidylinositol-3 kinase; 3-MA) or bafilomycin A1 (an inhibitor of the vacuolar proton pump of lysosomes and endosomes) reduced the effect of bufalin on cell viability and enhanced the effect of bufalin on apoptosis. In conclusion, bufalin triggered autophagic cell death and G2/M phase arrest through the AKT/mTOR signaling pathway in SK-HEP-1 cells. Our findings showed that bufalin may be potentially efficacious in the treatment of human hepatocellular carcinoma.

MiR-20a and miR-106b negatively regulate autophagy induced by leucine deprivation via suppression of ULK1 expression in C2C12 myoblasts

Autophagy is an evolutionarily conserved process responsible for degradation and recycling of cytoplasmic components through the lysosomal machinery. It has been proved to play pivotal roles in cellular homeostasis, cell growth and organism development. Moreover, abnormalities of autophagy have been linked to numerous human pathophysiologies. Emerging evidence has linked leucine deprivation induced protein breakdown to autophagy, but the underlying mechanisms controlling autophagic activity in this process are not fully understood. Here, we demonstrate that two members of the miR-17 microRNA family, miR-20a and miR-106b, may participate in regulating leucine deprivation induced autophagy via suppression of ULK1 expression in C2C12 myoblasts. We showed that leucine deprivation downregulated miR-20a and miR-106b expression via suppression of their transcription factor c-Myc. We discovered the essential autophagy gene ULK1 as cellular target of miR-20a and miR-106b. Treatment of C2C12 cells with the miR-20a or miR-106b mimic decreased the endogenous ULK1 protein levels. Dual luciferase reporter assay confirmed that the miRNA binding sequences in the 3' UTR of ULK1 contribute to the modulation of ULK1 expression by miR-20a and miR-106b. Furthermore, inhibition of ULK1 expression by the miR-20a or miR-106b mimic blunted activation of autophagy induced by leucine deprivation, while suppression of endogenous miR-20a or miR-106b by specific antagomir in C2C12 cells showed normal autophagic activity. Altogether, our data demonstrated that miR-20a and miR-106b regulated autophagy induced by leucine deprivation in C2C12 cells via targeting ULK1.

SD118-xanthocillin X (1), a novel marine agent extracted from Penicillium commune, induces autophagy through the inhibition of the MEK/ERK pathway

A compound named SD118-xanthocillin X (1) (C₁₈H₁₂N₂O₂), isolated from Penicillium commune in a deep-sea sediment sample, has been shown to inhibit the growth of several cancer cell lines in vitro. In the present study, we employed a growth inhibition assay and apoptotic analysis to identify the biological effect and detailed mechanism of SD118-xanthocillin X (1) in human hepatocellular carcinoma (HepG2) cells. SD118-xanthocillin X (1) demonstrated a concentration-dependent inhibitory effect on the growth of HepG2 cells and caused slight cellular apoptosis and significantly induced autophagy. Autophagy was detected as early as 12 h by the conversion of microtubule-associated protein 1 light chain 3 (LC3-I) to LC3-II, following cleavage and lipid addition to LC3-I. The pharmacological autophagy inhibitor 3-methyladenine largely attenuates the growth inhibition and autophagic effect of SD118-xanthocillin X (1) in HepG2 cells. Our data also indicated that the autophagic effect of SD118-xanthocillin X (1) occurs via the down-regulation of the MEK/ERK signaling pathway and the up-regulated class III PI3K/Beclin 1 signaling pathway.

Baculovirus infection triggers a shift from amino acid starvation-induced autophagy to apoptosis

Autophagy plays a central role in regulating important cellular functions such as cell survival during starvation and control of infectious pathogens. On the other hand, many pathogens have evolved mechanisms of inhibition of autophagy such as blockage of the formation of autophagosomes or the fusion of autophagosomes with lysosomes. Baculoviruses are important insect pathogens for pest control, and autophagy activity increases significantly during insect metamorphosis. However, it is not clear whether baculovirus infection has effects on the increased autophagy. In the present study, we investigated the effects of the Autographa californica nucleopolyhedrovirus (AcMNPV) infection on autophagy in SL-HP cell line from Spodoptera litura induced under amino acid deprivation. The results revealed that AcMNPV infection did not inhibit autophagy but triggered apoptosis under starvation pressure. In the early stage of infection under starvation, mitochondrial dysfunction was detected, suggesting the organelles might be involved in cell apoptosis. The semi-quantitative PCR assay revealed that the expression of both p35 and ie-1 genes of AcMNPV had no significant difference between the starved and unstarved SL-HP cells. The western blot analysis showed that no cleavage of endogenous Atg6 occurred during the process of apoptosis in SL-HP cells. These data demonstrated that some permissive insect cells may defend baculovirus infection via apoptosis under starvation and apoptosis is independent of the cleavage of Atg6 in SL-HP cells.

Guidelines for the use and interpretation of assays for monitoring autophagy

In 2008 we published the first set of guidelines for standardizing research in autophagy. Since then, research on this topic has continued to accelerate, and many new scientists have entered the field. Our knowledge base and relevant new technologies have also been expanding. Accordingly, it is important to update these guidelines for monitoring autophagy in different organisms. Various reviews have described the range of assays that have been used for this purpose. Nevertheless, there continues to be confusion regarding acceptable methods to measure autophagy, especially in multicellular eukaryotes. A key point that needs to be emphasized is that there is a difference between measurements that monitor the numbers or volume of autophagic elements (e.g., autophagosomes or autolysosomes) at any stage of the autophagic process vs. those that measure flux through the autophagy pathway (i.e., the complete process); thus, a block in macroautophagy that results in autophagosome accumulation needs to be differentiated from stimuli that result in increased autophagic activity, defined as increased autophagy induction coupled with increased delivery to, and degradation within, lysosomes (in most higher eukaryotes and some protists such as Dictyostelium) or the vacuole (in plants and fungi). In other words, it is especially important that investigators new to the field understand that the appearance of more autophagosomes does not necessarily equate with more autophagy. In fact, in many cases, autophagosomes accumulate because of a block in trafficking to lysosomes without a concomitant change in autophagosome biogenesis, whereas an increase in autolysosomes may reflect a reduction in degradative activity. Here, we present a set of guidelines for the selection and interpretation of methods for use by investigators who aim to examine macroautophagy and related processes, as well as for reviewers who need to provide realistic and reasonable critiques of papers that are focused on these processes. These guidelines are not meant to be a formulaic set of rules, because the appropriate assays depend in part on the question being asked and the system being used. In addition, we emphasize that no individual assay is guaranteed to be the most appropriate one in every situation, and we strongly recommend the use of multiple assays to monitor autophagy. In these guidelines, we consider these various methods of assessing autophagy and what information can, or cannot, be obtained from them. Finally, by discussing the merits and limits of particular autophagy assays, we hope to encourage technical innovation in the field.

Autophagy: a cyto-protective mechanism which prevents primary human hepatocyte apoptosis during oxidative stress

The role of autophagy in the response of human hepatocytes to oxidative stress remains unknown. Understanding this process may have important implications for the understanding of basic liver epithelial cell biology and the responses of hepatocytes during liver disease. To address this we isolated primary hepatocytes from human liver tissue and exposed them ex vivo to hypoxia and hypoxia-reoxygenation (H-R). We showed that oxidative stress increased hepatocyte autophagy in a reactive oxygen species (ROS) and class III PtdIns3K-dependent manner. Specifically, mitochondrial ROS and NADPH oxidase were found to be key regulators of autophagy. Autophagy involved the upregulation of BECN1, LC3A, Atg7, Atg5 and Atg 12 during hypoxia and H-R. Autophagy was seen to occur within the mitochondria of the hepatocyte and inhibition of autophagy resulted in the lowering a mitochondrial membrane potential and onset of cell death. Autophagic responses were primarily observed in the large peri-venular (PV) hepatocyte subpopulation. Inhibition of autophagy, using 3-methyladenine, increased apoptosis during H-R. Specifically, PV human hepatocytes were more susceptible to apoptosis after inhibition of autophagy. These findings show for the first time that during oxidative stress autophagy serves as a cell survival mechanism for primary human hepatocytes.

Fangchinoline induces autophagic cell death via p53/sestrin2/AMPK signalling in human hepatocellular carcinoma cells

BACKGROUND AND PURPOSE

Fangchinoline is a novel anti-tumour agent with little known of its cellular and molecular mechanisms of action. Here we have investigated the mode of cell death induced by fangchinoline and its underlying mechanism in two human hepatocellular carcinoma cell lines, HepG2 and PLC/PRF/5.

EXPERIMENTAL APPROACH

Apoptosis and autophagy were monitored in fangchinoline-treated HepG2 and PLC/PRF/5 cells by histological methods. The signal transduction pathways involved in activation of autophagy were examined, using immunoblotting, real-time PCR and siRNA techniques.

KEY RESULTS

Fangchinoline did not induce apoptosis in HepG2 and PLC/PRF/5 cells but triggered, dose-dependently, autophagy, an alternative mode of cell death which may contribute to fangchinoline's anti-tumour action. Nuclear translocation of p53 was involved in induction of autophagy by fangchinoline, followed by selective transactivation of the autophagy-related gene sestrin2 and initiation of the autophagic process. Signalling by the AMP-activated protein kinase was also involved as a downstream target of sestrin2 and induced mTOR-independent autophagic cell death in both cell lines. siRNA for Atg 5 or pharmacological block of p53 abolished fangchinoline-induced autophagy and inhibition of autophagy switched cell death to apoptosis in these cells, suggesting that cell death is irreversible once autophagy is induced by fangchinoline.

CONCLUSIONS AND IMPLICATIONS

Fangchinoline is a highly specific agent inducing autophagic cell death in hepatocellular carcinoma cells with a novel mechanism, which elucidates the potential of fangchinoline to potentiate programmed cell death in cancer cells.

Methamphetamine-induced neurotoxicity linked to ubiquitin-proteasome system dysfunction and autophagy-related changes that can be modulated by protein kinase C delta in dopaminergic neuronal cells

A compromised protein degradation machinery has been implicated in methamphetamine (MA)-induced neurodegeneration. However, the signaling mechanisms that induce autophagy and ubiquitin-proteasome system (UPS) dysfunction are not well understood. The present study investigates the contributions of protein kinase C delta (PKCδ)-mediated signaling events in MA-induced autophagy, UPS dysfunction, and cell death. Using an in vitro mesencephalic dopaminergic cell culture model, we demonstrate that MA-induced early induction of autophagy is associated with reduction in proteasomal function and concomitant dissipation of mitochondrial membrane potential (MMP), followed by significantly increased PKCδ activation, caspase-3 activation, accumulation of ubiquitin-positive aggregates and microtubule-associated light chain-3 (LC3-II) levels. Interestingly, siRNA-mediated knockdown of PKCδ or overexpression of cleavage-resistant mutant of PKCδ dramatically reduced MA-induced autophagy, proteasomal function, and associated accumulation of ubiquitinated protein aggregates, which closely paralleled cell survival. Importantly, when autophagy was inhibited either pharmacologically (3-MA) or genetically (siRNA-mediated silencing of LC3), the dopaminergic cells became sensitized to MA-induced apoptosis through caspase-3 activation. Conversely, overexpression of LC3 partially protected against MA-induced apoptotic cell death, suggesting a neuroprotective role for autophagy in MA-induced neurotoxicity. Notably, rat striatal tissue isolated from MA-treated rats also exhibited elevated LC3-II, ubiquitinated protein levels, and PKCδ cleavage. Taken together, our data demonstrate that MA-induced autophagy serves as an adaptive strategy for inhibiting mitochondria-mediated apoptotic cell death and degradation of aggregated proteins. Our results also suggest that the sustained activation of PKCδ leads to UPS dysfunction, resulting in the activation of caspase-3-mediated apoptotic cell death in the nigrostriatal dopaminergic system.

Autophagy regulates endoplasmic reticulum stress in ischemic preconditioning

Recent studies have suggested that autophagy plays a prosurvival role in ischemic preconditioning (IPC). This study was taken to assess the linkage between autophagy and endoplasmic reticulum (ER) stress during the process of IPC. The effects of IPC on ER stress and neuronal injury were determined by exposure of primary cultured murine cortical neurons to 30 min of OGD 24 h prior to a subsequent lethal OGD. The effects of IPC on ER stress and ischemic brain damage were evaluated in rats by a brief ischemic insult followed by permanent focal ischemia (PFI) 24 h later using the suture occlusion technique. The results showed that both IPC and lethal OGD increased the LC3-II expression and decreased p62 protein levels, but the extent of autophagy activation was varied. IPC treatment ameliorated OGD-induced cell damage in cultured cortical neurons, whereas 3-MA (5-20 mM) and bafilomycin A 1 (75-150 nM) suppressed the neuroprotection induced by IPC. 3-MA, at the dose blocking autophagy, significantly inhibited IPC-induced HSP70, HSP60 and GRP78 upregulation; meanwhile, it also aggregated the ER stress and increased activated caspase-12, caspase-3 and CHOP protein levels both in vitro and in vivo models. The ER stress inhibitor Sal (75 pmol) recovered IPC-induced neuroprotection in the presence of 3-MA. Rapamycin 50-200 nM in vitro and 35 pmol in vivo 24 h before the onset of lethal ischemia reduced ER stress and ischemia-induced neuronal damage. These results demonstrated that pre-activation of autophagy by ischemic preconditioning can boost endogenous defense mechanisms to upregulate molecular chaperones, and hence reduce excessive ER stress during fatal ischemia.

Autophagy inhibition enhances ursolic acid-induced apoptosis in PC3 cells

The phosphoinositol 3-kinase/Akt pathway plays a critical role in oncogenesis and the dysregulation of this pathway through loss of PTEN is a particularly common phenomenon in aggressive prostate cancers. Several recent studies have indicated that ursolic acid (UA), a pentacyclic triterpenoid, and its derivatives inhibit the growth of cancer cells by cell cycle arrest and the stimulation of apoptosis. In the present study, we report a novel autophagic response of UA in PTEN-deficient PC3 prostate cancer cells. As one of the major types of programmed cell death, autophagy has been observed in response to several anticancer drugs and demonstrated to be responsible for cell death. UA-induced autophagy in PC3 cells is associated with the reduced cell viability and the enhanced expression of LC3-II, an autophagosome marker in mammals, and monodansylcadaverine incorporation into autolysosomes. Furthermore, we found that UA exhibited anti-proliferative effects characterized by G1 phase arrest and autophagy at an early stage that precedes apoptosis. We also show that UA-induced autophagy in PC3 cells are mediated through the Beclin-1 and Akt/mTOR pathways. Inhibition of autophagy by either 3-methyladenine or Beclin-1/Atg5 small interfering RNA enhanced UA-induced apoptosis. Taken together, our data suggest that autophagy functions as a survival mechanism in PC3 cells against UA-induced apoptosis and a rational for the use of autophagy inhibitors in combination with UA as a novel modality of cancer therapy.

The microtubule depolymerizing agent naphthazarin induces both apoptosis and autophagy in A549 lung cancer cells

Naphthazarin (DHNQ, 5,8-dihydroxy-l,4-naphthoquinone) is a naturally available 1,4-naphthoquinone derivatives. In this study, we focused on elucidating the cytotoxic mechanism of naphthazarin in A549 non-small cell lung carcinoma cells. Naphthazarin reduced the A549 cell viability considerably with an IC(50) of 16.4 ± 1.6 μM. Naphthazarin induced cell death in a dose- and time-dependent manner by activating apoptosis and autophagy pathways. Specifically, we found naphthazarin inhibited the PI3K/Akt cell survival signalling pathway, measured by p53 and caspase-3 activation, and PARP cleavage. It also resulted in an increase in the ratio of Bax/Bcl2 protein levels, indicating activation of the mitochondrial apoptotic pathway. Similarly naphthazarin triggered LC3II expression and induced autophagic flux in A549 cells. We demonstrated further that naphthazarin is a microtubule inhibitor in cell-free system and in A549 cells. Naphthazarin treatment depolymerized interphase microtubules and disorganised spindle microtubules and the majority of cells arrested at the G(2)/M transition. Together, these data suggest that naphthazarin, a microtubule depolymerizer which activates dual cell death machineries, could be a potential novel chemotherapeutic agent.

Monitoring of autophagy in Chinese hamster ovary cells using flow cytometry

Recently, autophagy, which is a degradative process, has drawn attention as an anti-cell death engineering target in addition to apoptosis in recombinant Chinese hamster ovary (rCHO) cell cultures for enhanced production of therapeutic proteins. Appropriate autophagy monitoring methods, that are suitable for long term CHO cell cultures, are necessary in order to investigate the culture conditions that affect the autophagy pathway and to select appropriate engineering targets for autophagy control. Herein, detailed protocols for autophagy monitoring methods based on flow cytometry are provided using the GFP-LC3-overexpressing CHO DG44 host cell line or MDC-like molecules in rCHO cells grown as an adherent culture with serum-containing medium or suspension culture with serum-free medium. Furthermore, combined with the apoptosis detection based on the Annexin V-PS interaction, the simultaneous detection of autophagy and apoptosis is also described. It is anticipated that the protocols described herein will assist in the fast, high throughput monitoring of autophagy that can support other existing autophagy assays.

Dendrimer-mediated siRNA delivery knocks down Beclin 1 and potentiates NMDA-mediated toxicity in rat cortical neurons

Autophagy is an important process which plays a key role in cellular homeostasis by degrading cytoplasmic components in the lysosomes, which facilitates recycling. Alterations to normal autophagy have been linked to excitotoxicity, but the mechanisms governing its signal transduction remain unclear. The aim of this study was to explore the role of autophagy in neuronal excitotoxic death by delivering small interfering RNA (siRNA) to rat cortical neurons, using a dendrimer to silence the autophagy-related gene 6 (beclin 1) and to determine the role of autophagy in excitotoxicity. We have found that the dendrimer is very efficient to deliver siRNA to rat cortical neurons, leading to almost complete removal of the target protein Beclin 1. In addition, NMDA increases autophagy markers, such as the protein levels of Beclin 1, the microtubule-associated light chain 3 (LC3) B-II/LC3B-I ratio, and monodansylcadaverine (MDC) labeling in rat cortical neurons. Moreover, NMDA also increases the formation of autophagosomes observed under a transmission electron microscope. Silencing beclin 1 expression blocked NMDA-induced autophagy. Moreover, Beclin 1 removal potentiated NMDA-induced neuronal death indicating that autophagy plays a protective role during excitotoxicity and suggesting that targeting autophagy might be a helpful therapeutic strategy in neurodegenerative diseases.

Identification of genes involved in the regulation of 14-deoxy-11,12-didehydroandrographolide-induced toxicity in T-47D mammary cells

14-Deoxy-11,12-didehydroandrographolide is one of the principle compounds of the medicinal plant, Andrographis paniculata Nees. This study explored the mechanisms of 14-deoxy-11,12-didehydroandrographolide-induced toxicity and non-apoptotic cell death in T-47D breast carcinoma cells. Gene expression analysis revealed that 14-deoxy-11,12-didehydroandrographolide exerted its cytotoxic effects by regulating genes that inhibit the cell cycle or promote cell cycle arrest. This compound regulated genes that are known to reduce/inhibit cell proliferation, induce growth arrest and suppress cell growth. The growth suppression activities of this compound were demonstrated by a downregulation of several genes normally found to be over-expressed in cancers. Microscopic analysis revealed positive monodansylcadaverine (MDC) staining at 8h, indicating possible autophagosomes. TEM analysis revealed that the treated cells were highly vacuolated, thereby suggesting that 14-deoxy-11,12-didehydroandrographolide may cause autophagic morphology in these cells. This morphology may be correlated with the concurrent expression of genes known to affect lysosomal activity, ion transport, protein degradation and vesicle transport. Interestingly, some apoptotic-like bodies were found, and these bodies contained multiple large vacuoles, suggesting that this compound is capable of eliciting a combination of apoptotic and autophagic-like morphological characteristics.

Localization of the Arabidopsis senescence- and cell death-associated BFN1 nuclease: from the ER to fragmented nuclei

Plant senescence- or PCD-associated nucleases share significant homology with nucleases from different organisms. However, knowledge of their function is limited. Intracellular localization of the Arabidopsis senescence- and PCD-associated nuclease BFN1 was investigated. Analysis of BFN1-GFP localization in transiently transformed tobacco protoplasts revealed initial localization in filamentous structures spread throughout the cytoplasm, which then clustered around the nuclei as the protoplasts senesced. These filamentous structures were identified as being of ER origin. In BFN1-GFP-transgenic Arabidopsis plants, similar localization of BFN1-GFP was observed in young leaves, that is, in filamentous structures that reorganized around the nuclei only in senescing cells. In late senescence, BFN1-GFP was localized with fragmented nuclei in membrane-wrapped vesicles. BFN1's postulated function as a nucleic acid-degrading enzyme in senescence and PCD is supported by its localization pattern. Our results suggest the existence of a dedicated compartment mediating nucleic acid degradation in senescence and PCD processes.

PML-RARα enhances constitutive autophagic activity through inhibiting the Akt/mTOR pathway

Autophagy is a highly conserved, closely regulated homeostatic cellular activity that allows for the bulk degradation of long-lived proteins and cytoplasmic organelles. Its roles in cancer initiation and progression and in determining the response of tumor cells to anticancer therapy are complicated, and only limited investigation has been conducted on the potential significance of autophagy in the pathogenesis and therapeutic response of acute myeloid leukemia. Here we demonstrate that the inducible or transfected expression of the acute promyelocytic leukemia (APL)-specific PML-RARα, but not PLZF-RARα or NPM-RARα, fusion protein upregulates constitutive autophagy activation in leukemic and nonleukemic cells, as evaluated by hallmarks for autophagy including transmission electron microscopy. The significant increase in autophagic activity is also found in the leukemic cells-infiltrated bone marrow and spleen from PML-RARα-transplanted leukemic mice. The autophagy inhibitor 3-methyladenine significantly abrogates the autophagic events upregulated by PML-RARα, while the autophagic flux assay reveals that the fusion protein induces autophagy by increasing the on-rate of autophagic sequestration. Furthermore, this modulation of autophagy by PML-RARα is possibly mediated by a decreased activation of the Akt/mTOR pathway. Finally, we also show that autophagy contributes to the anti-apoptotic function of the PML-RARα protein. Given the critical role of the PML-RARα oncoprotein in APL pathogenesis, this study suggests an important role of autophagy in the development and treatment of this disease.

Antiproliferative activity of fucoidan was associated with the induction of apoptosis and autophagy in AGS human gastric cancer cells

Fucoidan, a sulfated polysaccharide purified from brown algae, possesses a variety of pharmacologic effects, including antiinflammatory, antioxidant, and anticancer properties; however, the underlying action mechanisms are not completely understood. This study investigated the possible mechanisms through which fucoidan exerts its antiproliferative action in cultured AGS human gastric adenocarcinoma cells. We found that fucoidan effectively inhibits the growth of AGS cells by inducing autophagy, as well as apoptosis. Apoptosis by fucoidan treatment was associated with the downregulation of antiapoptotic Bcl-2 and Bcl-xL expression, loss of mitochondrial membrane potential, activation of caspases, and concomitant degradation of poly-(ADP-ribose) polymerase protein. In addition, the morphological study indicated a characteristic finding of autophagy, such as the formation of autophagosomes in fucoidan-treated AGS cells. Furthermore, markers of autophagy, namely, the conversion of microtubule-associated protein light chain 3 (LC3)-I to LC3-II and increased beclin-1 accumulation, were observed. Overall, the present data suggest that fucoidan induces apoptotic and autophagic cell death, and both apoptotic and autophagic mechanisms contribute to the fucoidan-induced AGS cell death.