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

Inhibition of autophagy by 3-MA enhances the effect of 5-FU-induced apoptosis in colon cancer cells

BACKGROUND

5-fluorouracil-(5-FU)-based adjuvant chemotherapy is widely used for the treatment of colorectal cancer. However, 5-FU resistance in the course of treatment has become more common. Therefore, new therapeutic strategies and/or new adjuvant drugs still need to be explored.

METHODS

Two colon-cancer-derived cell lines, colon26 and HT29, were used to investigate the effect of 5-FU, 3-methyladenine (3-MA, an autophagy inhibitor), or their combination on apoptotic cell death and autophagy. MTT assay, Hochest plus propidium iodide (PI) staining, and DNA fragmentation assay were used to observe apoptosis. Meanwhile, monodansylcadaverine (MDC) was used to detect autophagy. Finally, immunoblotting assay was used to explore the molecular change that occurred.

RESULTS

We observed the apoptosis induced by 5-FU in colon cancer cells. Meanwhile, autophagy was also stimulated. The combination treatment of 3-MA and 5-FU significantly increased the apoptotic cell death. By isolating the subcellular fractions of mitochondria and cytosol, we observed that the release of cytochrome c was increased in combination-treated cells. Cytochrome c resulted in the activation of caspase-3, thus activating PARP. Moreover, the anti-apoptotic protein, Bcl-xL, was significantly downregulated by 3-MA.

CONCLUSIONS

Our results suggest that 5-FU-induced apoptosis in colon cancer cells can be enhanced by the inhibitor of autophagy, 3-MA. Autophagy might play a role as a self-defense mechanism in 5-FU-treated colon cancer cells, and its inhibition could be a promising strategy for the adjuvant chemotherapy of colon cancer.

Endolysosomal phospholipidosis and cytosolic lipid droplet storage and release in macrophages

This review summarizes the current knowledge of endolysosomal and cytoplasmic lipid storage in macrophages induced by oxidized LDL (Ox-LDL), enzymatically degraded LDL (E-LDL) and other atherogenic lipoprotein modifications, and their relation to the adapter protein 3 (AP-3) dependent ABCA1 and ABCG1 cellular lipid efflux pathways. We compare endolysosomal lipid storage caused either through drug induced phospholipidosis, inheritable endolysosomal and cytosolic lipid storage disorders and Ox-LDL or E-LDL induced phagosomal uptake and cytosolic lipid droplet storage in macrophages. Ox-LDL is resistant to rapid endolysosomal hydrolysis and is trapped within the endolysosomal compartment generating lamellar bodies which resemble the characteristics of phospholipidosis. Various inherited lysosomal storage diseases including sphingolipidosis, glycosphingolipidosis and cholesterylester storage diseases also present a phospholipidosis phenotype. In contrast E-LDL resembling coreless unesterified cholesterol enriched LDL-particles, with a multilamellar, liposome-like structure, lead to rapid phagosomal degradation and cytosolic lipid droplet accumulation. As a consequence the uptake of E-LDL through type I and type II phagocytosis leads to increased lipid droplet formation and moderate upregulation of ABCA1 and ABCG1 while uptake of Ox-LDL leads to a rapid expansion of the lysosomal compartment and a pronounced upregulation of the ABCA1/ABCG1/AP-3 lipid efflux pathway.

The Bax/Bak ortholog in Drosophila, Debcl, exerts limited control over programmed cell death

Bcl-2 family members are pivotal regulators of programmed cell death (PCD). In mammals, pro-apoptotic Bcl-2 family members initiate early apoptotic signals by causing the release of cytochrome c from the mitochondria, a step necessary for the initiation of the caspase cascade. Worms and flies do not show a requirement for cytochrome c during apoptosis, but both model systems express pro- and anti-apoptotic Bcl-2 family members. Drosophila encodes two Bcl-2 family members, Debcl (pro-apoptotic) and Buffy (anti-apoptotic). To understand the role of Debcl in Drosophila apoptosis, we produced authentic null alleles at this locus. Although gross development and lifespans were unaffected, we found that Debcl was required for pruning cells in the developing central nervous system. debcl genetically interacted with the ced-4/Apaf1 counterpart dark, but was not required for killing by RHG (Reaper, Hid, Grim) proteins. We found that debcl(KO) mutants were unaffected for mitochondrial density or volume but, surprisingly, in a model of caspase-independent cell death, heterologous killing by murine Bax required debcl to exert its pro-apoptotic activity. Therefore, although debcl functions as a limited effector of PCD during normal Drosophila development, it can be effectively recruited for killing by mammalian members of the Bcl-2 gene family.

Autophagy and autophagic cell death are next targets for elimination of the resistance to tyrosine kinase inhibitors

Autophagy, a cellular degradation system has been demonstrated in some hematopoietic malignant cell lines, but there is much still remaining to be known about its role and the mechanisms. We observed the excessive autophagy in chronic myelogenous leukemia (CML) cell line, K562, associated with treatment of 12-O-tetradecanoyl-phorbol-13-acetate (TPA), which can induce K562 cells to differentiate into megakaryocytic lineage. Confocal microscopic analysis demonstrated that autophagic cells did not express a megakaryocyte marker, the CD41 molecule, indicating that the autophagy was independent of megakaryocytic differentiation. After remarkable autophagic degradation, the cells finally underwent autophagic cell death (APCD). On the other hand, a block of TPA-induced autophagy by chloroquine rapidly promoted cell death that was not APCD. This result suggested that autophagy regulated two mechanisms in K562 cells: both the cell survival system and APCD. To confirm that autophagy regulates the cell survival system in K562 cells, imatinib was used to induce cell death in K562 cells. Autophagy has not been considered during imatinib treatment; nonetheless, co-treatment with imatinib and chloroquine markedly enhanced imatinib-induced cell death, compared to K562 cells treated only with imatinib. Furthermore, imatinib-resistant cell lines, BaF3/T315I and BaF3/E255K, also underwent cell death by co-treatment with imatinib and chloroquine. From these data, we concluded that autophagy is deeply related to the cell survival system and that inhibition of autophagy accelerates TPA- or imatinib-induced cell death. The block of autophagy could be a new strategy in the treatment of CML.

A role for macroautophagy in protection against 4-hydroxytamoxifen-induced cell death and the development of antiestrogen resistance

This study identifies macroautophagy as a key mechanism of cell survival in estrogen receptor-positive (ER+) breast cancer cells undergoing treatment with 4-hydroxytamoxifen (4-OHT). This selective ER modifier is an active metabolite of tamoxifen commonly used for the treatment of breast cancer. Our study provides the following key findings: (a) only 20% to 25% of breast cancer cells treated with 4-OHT in vitro die via caspase-dependent cell death; more typically, the antiestrogen-treated ER+ breast cancer cells express increased levels of macroautophagy and are viable; (b) 4-OHT-induced cell death, but not 4-OHT-induced macroautophagy, can be blocked by the pan-caspase inhibitor z-VAD-fmk, providing strong evidence that these two outcomes of antiestrogen treatment are not linked in an obligatory manner; (c) 4-OHT-resistant cells selected from ER+ breast cancer cells show an increased ability to undergo antiestrogen-induced macroautophagy without induction of caspase-dependent cell death; and (d) 4-OHT, when used in combination with inhibitors of autophagosome function, induces robust, caspase-dependent apoptosis of ER+, 4-OHT-resistant breast cancer cells. To our knowledge, these studies provide the first evidence that macroautophagy plays a critical role in the development of antiestrogen resistance. We propose that targeting autophagosome function will improve the efficacy of hormonal treatment of ER+ breast cancer.

Akt induces apoptosis in neuroblastoma cells expressing a C98X vasopressin mutant following autophagy suppression

Mutations in the arginine vasopressin (AVP)-neurophysin II (NP-II) gene that affect the folding and transport of the prohormone result in loss of secretion of the anti-diuretic hormone AVP from pituitary nerve terminals and cause autosomal dominant familial neurohypophyseal diabetes insipidus (adFNDI). One such mutation consists of the replacement of a Cys residue at position 98 with a stop codon (C98X) in the AVP precursor (corresponding to C67X in NP domain). In neuroblastoma cells over-expressing this truncated AVP precursor autophagy, a macromolecular degradation process, was shown to be essential for assuring cell survival. In the present study, we investigated the role of the Akt pro-survival signalling in the regulation of autophagy and of apoptosis linked with the handling of C98X AVP. Impairing autophagy-lysosomal sequestration or cathepsin D (CD)-mediated proteolysis triggered the activation of the intrinsic death pathway of apoptosis in C98X-expressing cells, but not in the wild-type -AVP-expressing cells. This was shown by the expression of a Vps34 dominant negative, which down-regulates the PI3k class III-dependent signalling needed for autophagosome (APH) formation, by genetic silencing as a result of RNA interference (RNAi) of Lamp2, a protein indispensable for the fusion of APHs with lysosomes, and by RNAi silencing of the lysosomal protease CD. Ectopic expression of either the wild-type or the mutated C98X AVP altered neither the expression nor the phosphorylation of the pro-survival signalling molecule Akt. Strikingly, the ectopic adenoviral-directed expression of a constitutively active Akt, instead of preserving cell survival, resulted in the suppression of autophagy, and precipitated Bax-mediated cell death. The present data demonstrate the need for autophagy-mediated degradation of mutated C98X peptides, which otherwise become toxic to the cell, and suggest that, in the presence of mis-folded proteins, the stimulation of the Akt signalling counteracts the beneficial effects of autophagy and precipitates cell death. It follows that growth factors impinging on the Akt pathway may have deleterious effect in neurones expressing mutant neuropeptides. This can provide an explanation for the late onset and progressive neuronal cell loss observed in hypothalamic magnocellular neurones of adFNDI patients.

Characterization of a serine proteinase mediating encystation of Acanthamoeba

Members of the genus Acanthamoeba, amphizoic protozoan parasites, are causative agents of granulomatous amoebic encephalitis and amoebic keratitis. Proteinases play a role in various biologic actions in Acanthamoeba, including host tissue destruction, pathogenesis, and digestion of phagocytosed food. Interestingly, we found that encystation of Acanthamoeba was inhibited by the serine proteinase inhibitor phenylmethanesulfonyl fluoride. In this study, we characterize a serine proteinase that is involved in mediating the encystation of Acanthamoeba. This encystation-mediating serine proteinase (EMSP) is shown to be highly expressed during encystation by real-time PCR and Western blot analysis. Chemically synthesized small interfering RNA against EMSP inhibited the expression of EMSP mRNA and significantly reduced the encystation efficiency of Acanthamoeba. An EMSP-enhanced green fluorescent protein fusion protein localized to vesicle-like structures within the amoeba. Using LysoTracker analysis, these vesicular structures were confirmed to be lysosomes. After incubation of the transfected amoeba in encystment media, small fluorescent vesicle-like structures gathered and formed ball-like structures, which were identified as colocalizing with the autophagosome. Taken together, these results indicate that EMSP plays an important role in the differentiation of Acanthamoeba by promoting autolysis.

Septins stabilize mitochondria in Tetrahymena thermophila

We describe phylogenetic and functional studies of three septins in the free-living ciliate Tetrahymena thermophila. Both deletion and overproduction of septins led to vacuolization of mitochondria, destabilization of the nuclear envelope, and increased autophagy. All three green fluorescent protein-tagged septins localized to mitochondria. Specific septins localized to the outer mitochondrial membrane, to septa formed during mitochondrial scission, or to the mitochondrion-associated endoplasmic reticulum. The only other septins known to localize to mitochondria are human ARTS and murine M-septin, both alternatively spliced forms of Sep4 (S. Larisch, Cell Cycle 3:1021-1023, 2004; S. Takahashi, R. Inatome, H. Yamamura, and S. Yanagi, Genes Cells 8:81-93, 2003). It therefore appears that septins have been recruited to mitochondrial functions independently in at least two eukaryotic lineages and in both cases are involved in apoptotic events.

Oridonin induced autophagy in human cervical carcinoma HeLa cells through Ras, JNK, and P38 regulation

In this study, we investigated autophagy induced by oridonin in HeLa cells. HeLa cells were exposed to oridonin, and the fluorescent changes, autophagic levels, and protein expressions were evaluated. Oridonin induced autophagy in HeLa cells in vitro in a dose- and time-dependent manner. Oridonin-treated HeLa cells, which had been prelabeled with the autophagosome-specific dye monodansylcadervarine (MDC), recruited more MDC-positive particles and had a significantly higher fluorescent density; and simultaneously, expressions of autophagy-related proteins, MAP-LC3 and Beclin 1, were increased by oridonin. In oridonin-induced Hela cells, pretreatment with 3-methyladenine (3-MA, the specific inhibitor of autophagy) dose-dependently decreased the autophagic ratio accompanied with downregulation of the protein expressions of MAP-LC3 and Beclin 1. Furthermore, when a Ras inhibitor was applied, the autophagic levels were augmented, whereas P38 and JNK inhibitors decreased the autophagic ratio significantly, indicating that this oridonin-induced autophagic process was negatively regulated by Ras, but positively regulated by P38 and JNK MAPKs. Raf-1 and ERK1/2 had no obvious correlation to these signaling pathways.

Inhibition of histone deacetylase1 induces autophagy

Autophagy is a process where cytoplasmic materials are degraded by lysosomal machinery. Histone deacetylase (HDAC) inhibitors induce autophagy, and HDAC6, one of class II HDAC isotypes, is directly involved in autophagic degradation in the cell. However, it is unclear if class I HDAC isotype such as HDCA1 is involved in this process. To investigate if class I HDAC isotype is involved in autophagy, a specific class I HDAC inhibitor and an siRNA of HDAC1 were used to treat HeLa cells. Autophagic markers were then investigated. Both inhibition and genetic knock-down of HDAC1 in the cells significantly induced autophagic vacuole formation and lysosome function. Moreover, disruption of HDAC1 leads to the conversion of LC3-I to LC3-II. Together, these results demonstrate that HDAC1 could play a role in autophagy and specific inhibition of HDAC1 can induce autophagy.

The roles of therapy-induced autophagy and necrosis in cancer treatment

Metabolic and therapeutic stresses activate several signal transduction pathways that regulate cell death and cell survival in cancer cells. Although decades of research unraveled the pathways that regulate apoptosis and allowed the development of novel diagnostic and therapeutic modalities in cancer treatment, only recently has the regulation and significance of tumor cell autophagy and necrosis become the focus of investigations. Necrosis is an irreversible inflammatory form of cell death. In contrast, autophagy is a reversible process that can contribute both to tumor cell death and survival. This review describes recent advances in understanding the regulation of autophagy and necrosis and their implications for cancer therapy. Currently available methods to measure autophagy and necrosis are highlighted. The effect of tumor cell autophagy and necrosis on host immunity is explored. Finally, therapeutic approaches that target autophagy and necrosis in cancer are described.

Lithium delays progression of amyotrophic lateral sclerosis

ALS is a devastating neurodegenerative disorder with no effective treatment. In the present study, we found that daily doses of lithium, leading to plasma levels ranging from 0.4 to 0.8 mEq/liter, delay disease progression in human patients affected by ALS. None of the patients treated with lithium died during the 15 months of the follow-up, and disease progression was markedly attenuated when compared with age-, disease duration-, and sex-matched control patients treated with riluzole for the same amount of time. In a parallel study on a genetic ALS animal model, the G93A mouse, we found a marked neuroprotection by lithium, which delayed disease onset and duration and augmented the life span. These effects were concomitant with activation of autophagy and an increase in the number of the mitochondria in motor neurons and suppressed reactive astrogliosis. Again, lithium reduced the slow necrosis characterized by mitochondrial vacuolization and increased the number of neurons counted in lamina VII that were severely affected in saline-treated G93A mice. After lithium administration in G93A mice, the number of these neurons was higher even when compared with saline-treated WT. All these mechanisms may contribute to the effects of lithium, and these results offer a promising perspective for the treatment of human patients affected by ALS.

Capsular polysaccharides galactoxylomannan and glucuronoxylomannan from Cryptococcus neoformans induce macrophage apoptosis mediated by Fas ligand

The effects of capsular polysaccharides, galactoxylomannan (GalXM) and glucuronoxylomannan (GXM), from acapsular (GXM negative) and encapsulate strains of Cryptococcus neoformans were investigated in RAW 264.7 and peritoneal macrophages. Here, we demonstrate that GalXM and GXM induced different cytokines profiles in RAW 264.7 macrophages. GalXM induced production of TNF-alpha, NO and iNOS expression, while GXM predominantly induced TGF-beta secretion. Both GalXM and GXM induced early morphological changes identified as autophagy and late macrophages apoptosis mediated by Fas/FasL interaction, a previously unidentified mechanism of virulence. GalXM was more potent than GXM at induction of Fas/FasL expression and apoptosis on macrophages in vitro and in vivo. These findings uncover a mechanism by which capsular polysaccharides from C. neoformans might compromise host immune responses.

Macroautophagy inhibition sensitizes tamoxifen-resistant breast cancer cells and enhances mitochondrial depolarization

Macroautophagy (autophagy), a process for lysosomal degradation of organelles and long-lived proteins, has been linked to various pathologies including cancer and to the cellular response to anticancer therapies. In the human estrogen receptor positive MCF7 breast adenocarcinoma cell line, treatment with the endocrine therapeutic tamoxifen was shown previously to induce cell cycle arrest, cell death, and autophagy. To investigate specifically the role of autophagy in tamoxifen treated breast cancer cell lines, we used a siRNA approach, targeting three different autophagy genes, Atg5, Beclin-1, and Atg7. We found that knockdown of autophagy, in combination with tamoxifen in MCF7 cells, results in decreased cell viability concomitant with increased mitochondrial-mediated apoptosis. The combination of autophagy knockdown and tamoxifen treatment similarly resulted in reduced cell viability in the breast cancer cell lines, estrogen receptor positive T-47D and tamoxifen-resistant MCF7-HER2. Together, these results indicate that autophagy has a primary pro-survival role following tamoxifen treatment, and suggest that autophagy knockdown may be useful in a combination therapy setting to sensitize breast cancer cells, including tamoxifen-resistant breast cancer cells, to tamoxifen therapy.

Plasmodium falciparum: erythrocytic stages die by autophagic-like cell death under drug pressure

It has been reported that an apoptotic cell death process can occur with protozoans, but no consensus on Plasmodium susceptibility to apoptosis was reached till now. Thus, we evaluated if Plasmodium falciparum blood forms undergo apoptosis after in vitro pressure with chloroquine, S-nitroso-N-acetyl-penicillamine (SNAP) or staurosporine. Inhibition of parasite growth and loss of viability were observed in treated cultures by both light microscopy and flow cytometry. When DNA fragmentation was verified, only a small number of TUNEL-positive parasites was detected in treated cultures and pretreatment of parasite with a general caspase inhibitor was not able to prevent parasite death. Considering the lack of apoptotic characteristics and the observation of parasites with cytoplasmatic vacuolization by electron microscopy, we conclude that P. falciparum parasites under chloroquine, SNAP or staurosporine pressures do not die by apoptosis but by a process similar to autophagy. The autophagic pathway could be explored as an alternative target for the development of new antimalarial drugs.

Induction of autophagy promotes fusion of multivesicular bodies with autophagic vacuoles in k562 cells

Morphological and biochemical studies have shown that autophagosomes fuse with endosomes forming the so-called amphisomes, a prelysosomal hybrid organelle. In the present report, we have analyzed this process in K562 cells, an erythroleukemic cell line that generates multivesicular bodies (MVBs) and releases the internal vesicles known as exosomes into the extracellular medium. We have previously shown that in K562 cells, Rab11 decorates MVBs. Therefore, to study at the molecular level the interaction of MVBs with the autophagic pathway, we have examined by confocal microscopy the fate of MVBs in cells overexpressing green fluorescent protein (GFP)-Rab11 and the autophagosomal protein red fluorescent protein-light chain 3 (LC3). Autophagy inducers such as starvation or rapamycin caused an enlargement of the vacuoles decorated with GFP-Rab11 and a remarkable colocalization with LC3. This convergence was abrogated by a Rab11 dominant negative mutant, indicating that a functional Rab11 is involved in the interaction between MVBs and the autophagic pathway. Interestingly, we presented evidence that autophagy induction caused calcium accumulation in autophagic compartments. Furthermore, the convergence between the endosomal and the autophagic pathways was attenuated by the Ca2+ chelator acetoxymethyl ester (AM) of the calcium chelator 1,2-bis(o-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid (BAPTA), indicating that fusion of MVBs with the autophagosome compartment is a calcium-dependent event. In addition, autophagy induction or overexpression of LC3 inhibited exosome release, suggesting that under conditions that stimulates autophagy, MVBs are directed to the autophagic pathway with consequent inhibition in exosome release.

Chemical inhibition of acetyl-CoA carboxylase induces growth arrest and cytotoxicity selectively in cancer cells

Development and progression of cancer is accompanied by marked changes in the expression and activity of enzymes involved in the cellular homeostasis of fatty acids. One class of enzymes that play a particularly important role in this process are the acetyl-CoA carboxylases (ACC). ACCs produce malonyl-CoA, an intermediate metabolite that functions as substrate for fatty acid synthesis and as negative regulator of fatty acid oxidation. Here, using the potent ACC inhibitor soraphen A, a macrocyclic polyketide from myxobacteria, we show that ACC activity in cancer cells is essential for proliferation and survival. Even at nanomolar concentrations, soraphen A can block fatty acid synthesis and stimulate fatty acid oxidation in LNCaP and PC-3M prostate cancer cells. As a result, the phospholipid content of cancer cells decreased, and cells stopped proliferating and ultimately died. LNCaP cells predominantly died through apoptosis, whereas PC-3M cells showed signs of autophagy. Supplementation of the culture medium with exogenous palmitic acid completely abolished the effects of soraphen A and rescued the cells from cell death. Interestingly, when added to cultures of premalignant BPH-1 cells, soraphen A only slightly affected cell proliferation and did not induce cell death. Together, these findings indicate that cancer cells have become dependent on ACC activity to provide the cell with a sufficient supply of fatty acids to permit proliferation and survival, introducing the concept of using small-molecule ACC inhibitors as therapeutic agents for cancer.

Eupalinin A isolated from Eupatorium chinense L. induces autophagocytosis in human leukemia HL60 cells

Eupalinin A, a natural phytoalexin included in Eupatorium chinense L., exhibited a marked inhibitory effect on cell growth in HL60 cells. The morphological aspects of eupalinin A-treated cells evaluated by Hoechst 33342 nuclear staining indicated cell death, only a small part of which showed a typical apoptosis with nuclear fragmentation and condensation. To determine what type of cell death is caused by eupalinin A, we examined the contribution of caspases, Bcl-2 family proteins, MAP kinase, and PI3K/Akt, and mitochondrial membrane potential to this cell death. As a result, most part of the cell death was not associated with apoptosis because of caspase independence and no death factor released from mitochondria. Electron microscopic study indicated a characteristic finding of autophagy such as the formation of autophagosomes. Furthermore, the level of microctubule-associated-protein light chain 3 (LC3) II protein and monodancylcanaverin (MDC) incorporation were gradually increased with reduction of mitochondrial membrane potential by the accumulation of intracellular ROS after eupalinin A treatment. From these results, we can conclude that eupalinin A-induced cell death was mainly due to autophagy, which was initiated by increased ROS, resulting in the perturbation of mitochondrial membrane potential. Since the class III PI3K inhibitor such as 3-MA or LY294002 did not inhibit the eupalinin A-induced type II programmed cell death (PCD II), it was suggested that the PCD II was executed by Beclin-1 independent pathway of damage-induced mitochondrial autophagy (mitophagy).

Characterization of cocaine-elicited cell vacuolation: the involvement of calcium/calmodulin in organelle deregulation

The sizes of organelles are tightly regulated in the cells. However, little is known on how cells maintain the homeostasis of these intracellular compartments. Using cocaine as a model compound, we have characterized the mechanism of deregulated vacuolation in cultured rat liver epithelial Clone 9 cells. The vacuoles were observed as early as 10 min following cocaine treatment. Removal of cocaine led to vacuole degeneration, indicating vacuolation is a reversible process. The vacuoles could devour intracellular materials and the vacuoles originated from late endosome/lysosome as indicated by immunofluorescence studies. Instant calcium influx and calmodulin were required for the initiation of vacuole formation. The unique properties of these late endosome/lysosome-derived vacuoles were further discussed. In summary, cocaine elicited a new type of deregulated vacuole and the involvement of calcium/calmodulin in vacuolation could shed light on prevention or treatment of cocaine-induced cytotoxicity.

Cell survival under nutrient stress is dependent on metabolic conditions regulated by Akt and not by autophagic vacuoles

Akt activation assists tumor cell survival and promotes resistance to chemotherapy. Here we show that constitutively active Akt (CA-Akt) cells are highly sensitized to cell death induced by nutrient and growth factor deprivation, whereas dominant-negative Akt (DN-Akt) cells have a high rate of survival. The content of autophagosomes in starved CA-Akt cells was high, while DN-Akt cells expressed autophagic vacuoles constitutively, independently of nutrition conditions. Thus Akt down-regulation and downstream events can induce autophagosomes which were not directly determinants of cell death. Biochemical analysis in Akt-mutated cells show that (i) Akt and mTOR proteins were degraded more rapidly than the housekeeping proteins, (ii) mTOR phosphorylation at position Thr(2446) was relatively high in DN-Akt and low in CA-Akt cells, induced by starvation in mock cells only, which suggests reduced autoregulation of these pathways in Akt-mutated cells, (iii) both protein synthesis and protein degradation were significantly higher in starved CA-Akt cells than in starved DN-Akt cells or mock cells. In conclusion, constitutively active Akt, unable to control synthesis and wasting of proteins, accelerates the death of starved cells.

Augmentation of oridonin-induced apoptosis observed with reduced autophagy

Our previous studies showed that oridonin could induce apoptosis in HeLa cells; and in this study, we further investigated autophagy induced by oridonin in HeLa cells and the relationship between apoptosis and autophagy. HeLa cells were exposed with oridonin after 3-methyladenine (3-MA) pre-culture, and we evaluated the growth inhibitory ratio, morphologic changes, DNA fragmentation, proteins expression as well as autophagic and apoptotic levels. Oridonin inhibited the proliferation of HeLa cells in vitro and induced autophagy. Oligonucleosomal fragementation of DNA as well as increased activities of Bax proteins were induced by oridonin, but the expression of p-Bcl-2 protein was reduced. In the condition of oridonin-treatment, when the inhibitor of phosphoinositide 3-kinase (PI3K), wortmannin, was applied, the autophagic level was significantly decreased, while the apoptotic level was increased, indicating that PI3K is a key regulator of both autophagy and apoptosis. Akt, down-stream factor of PI3K, was activated in autophagic process but suppressed in apoptosis in this study. In addition, when autophagy was blocked by 3-MA, the expression of SIRT-1 was decreased, indicating SIRT-1 contributed to autophagy. Taken together, oridonin simultaneously induced HeLa cell both apoptosis and autophagy in HeLa cells, and inhibition of autophagy contributes to upregulation of apoptosis.

A transporter associated with antigen-processing independent vacuolar pathway for the MHC class I-mediated presentation of endogenous transmembrane proteins

MHC class I molecules present peptides derived from the ectodomains of endogenous transmembrane proteins; however, the processing of these Ags is incompletely understood. As model transmembrane Ags we investigated the processing of MHC-I-derived fusion proteins containing the N-terminally extended K(b)-restricted OVA epitope SIINFEKL in the extracytoplasmic domain. In TAP-deficient, nonprofessional APCs, the epitope was cleaved out of various sequence contexts and presented to T cells. Ag presentation was inhibited by acidophilic amines and inhibitors of the vacuolar proton pump, indicating processing in endosomes. Endosomal aspartic-type cathepsins, and to some extent also the trans-Golgi network protease furin, were involved in processing. Clathrin-dependent and independent internalization from the cell surface targeted MHC-I fusion proteins to early and late endosomes, where SIINFEKL/K(b) complexes were detected by immunofluorescence microscopy. Targeting of MHC-I fusion proteins to processing compartments was independent of sequence motifs in the cytoplasmic tail. Not only TAP-deficient cells, but also TAP-competent APCs used the vacuolar pathway for processing of MHC-I fusion proteins. Thus, endosomal processing of internalized endogenous transmembrane proteins represents a novel alternate pathway for the generation of MHC-I-binding peptides.

Tumor suppressor 101F6 and ascorbate synergistically and selectively inhibit non-small cell lung cancer growth by caspase-independent apoptosis and autophagy

101F6 is a candidate tumor suppressor gene harbored on chromosome 3p21.3, a region with frequent and early allele loss and genetic alterations in many human cancers. We previously showed that enforced expression of wild-type 101F6 by adenoviral vector-mediated gene transfer significantly inhibited tumor cell growth in 3p21.3-deficient non-small cell lung cancer (NSCLC) cells in vitro and in vivo. The molecular mechanism of 101F6-mediated tumor suppression is largely unknown. A computer-aided structural and functional model predicts the 101F6 protein to be a member of the cytochrome b561 protein family that is involved in the regeneration of the antioxidant ascorbate. 101F6 protein is expressed in normal lung bronchial epithelial cells and fibroblasts but is lost in most lung cancers. Treatment with 101F6 nanoparticle-mediated gene transfer in combination with a subpharmacologic dose (200-500 micromol/L) of ascorbate synergistically and selectively inhibited lung cancer cell growth in vitro. Systemic injection of 101F6 nanoparticles plus the i.p. injection of ascorbate synergistically inhibited both tumor formation and growth in human NSCLC H322 orthotopic lung cancer mouse models (P<0.001). Furthermore, exogenous expression of 101F6 enhanced intracellular uptake of ascorbate, leading to an accumulation of cytotoxic H(2)O(2) and a synergistic killing of tumor cells through caspase-independent apoptotic and autophagic pathways. The antitumor synergism showed by the combination treatment with systemic administration of 101F6 nanoparticles and ascorbate on lung cancer offers an attractive therapeutic strategy for future clinical trials in cancer prevention and treatment.

Regulation of various proteolytic pathways by insulin and amino acids in human fibroblasts

Intracellular protein degradation is a regulated process with several proteolytic pathways. Although regulation of macroautophagy has been investigated in some detail in hepatocytes and in few other cells, less is known on this regulation in other cells and proteolytic pathways. We show that in human fibroblasts insulin and amino acids reduce protein degradation by different signalling pathways and that this inhibition proceeds in part via the mammalian target of rapamycin, especially with amino acids, which probably increase lysosomal pH. Moreover, the regulatory amino acids (Phe, Arg, Met, Tyr, Trp and Cys) are partially different from other cells. Finally, and in addition to macroautophagy, insulin and amino acids modify, to different extents and sometimes in opposite directions, the activities of other proteolytic pathways.

Human WIPI-1 puncta-formation: a novel assay to assess mammalian autophagy

Autophagy depends on the activity of phosphoinositide-3 kinase class III to generate PI(3)P. We identified the human WIPI protein family of PI(3)P-binding factors and showed that WIPI-1 (Atg18) is linked to autophagy in human cells. Induction of autophagy by rapamycin, gleevec, thapsigargin and amino acid deprivation led to an accumulation of WIPI-1 at LC3-positive membrane structures (WIPI-1 puncta-formation), suggested to represent autophagosomal isolation membranes. WIPI-1 puncta-formation is inhibited by wortmannin and LY294002, and PI(3)P-binding-deficient WIPI-1 is puncta-formation-incompetent. Quantification of WIPI-1 puncta should be suitable to assay mammalian autophagy.

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.

TMEM166, a novel transmembrane protein, regulates cell autophagy and apoptosis

Programmed cell death can be divided into apoptosis and autophagic cell death. We describe the biological activities of TMEM166 (transmembrane protein 166, also known as FLJ13391), which is a novel lysosome and endoplasmic reticulum-associated membrane protein containing a putative TM domain. Overexpression of TMEM166 markedly inhibited colony formation in HeLa cells. Simultaneously, typical morphological characteristics consistent with autophagy were observed by transmission electron microscopy, including extensive autophagic vacuolization and enclosure of cell organelles by double-membrane structures. Further experiments confirmed that the overexpression of TMEM166 increased the punctate distribution of MDC staining and GFP-LC3 in HeLa cells, as well as the LC3-II/LC3-I proportion. On the other hand, TMEM166-transfected HeLa and 293T cells succumbed to cell death with hallmarks of apoptosis including phosphatidylserine externalization, loss of mitochondrial transmembrane potential, caspase activation and chromatin condensation. Kinetic analysis revealed that the appearance of autophagy-related biochemical parameters preceded the nuclear changes typical of apoptosis in TMEM166-transfected HeLa cells. Suppression of TMEM166 expression by small interference RNA inhibited starvation-induced autophagy in HeLa cells. These findings show for the first time that TMEM166 is a novel regulator involved in both autophagy and apoptosis.

Autophagy in Niemann-Pick C disease is dependent upon Beclin-1 and responsive to lipid trafficking defects

Niemann-Pick C (NPC) disease is an autosomal recessive lipid storage disorder characterized by a disruption of sphingolipid and cholesterol trafficking that produces cognitive impairment, ataxia and death, often in childhood. Most cases are caused by loss of function mutations in the Npc1 gene, which encodes a protein that localizes to late endosomes and functions in lipid sorting and vesicle trafficking. Here, we demonstrate that NPC1-deficient primary human fibroblasts, like npc1(-/-) mice fibroblasts, showed increased autophagy as evidenced by elevated LC3-II levels, numerous autophagic vacuoles and enhanced degradation of long-lived proteins. Autophagy because of NPC1 deficiency was associated with increased expression of Beclin-1 rather than activation of the Akt-mTOR-p70 S6K signaling pathway, and siRNA knockdown of Beclin-1 decreased long-lived protein degradation. Induction of cholesterol trafficking defects in wild-type fibroblasts by treatment with U18666A increased Beclin-1 and LC3-II expression, whereas treatment of NPC1-deficient fibroblasts with sphingolipid-lowering compound NB-DGJ failed to alter the expression of either Beclin-1 or LC3-II. Primary fibroblasts from patients with two other sphingolipid storage diseases, NPC2 deficiency and Sandhoff disease, characterized by sphingolipid trafficking defects also showed elevation in Beclin-1 and LC3-II levels. In contrast, Gaucher disease fibroblasts, which traffic sphingolipids normally, showed wild-type levels of Beclin-1 and LC3-II. Our data define a critical role for Beclin-1 in the activation of autophagy because of NPC1 deficiency, and reveal an unexpected role for lipid trafficking in the regulation of this pathway in patients with several sphingolipid storage diseases.

The role of autophagy in the death of L1210 leukemia cells initiated by the new antitumor agents, XK469 and SH80

The phenoxypropionic acid derivative 2-{4-[(7-chloro-2-quinoxalinyl)oxy]phenoxy}propionic acid (XK469) and an analogue termed 2-{4-[(7-bromo-2-quinalinyl)oxy]phenoxy}propionic acid (SH80) can eradicate malignant cell types resistant to many common antitumor agents. Colony formation assays indicated that a 24 h exposure of L1210 cells to XK469 or SH80 inhibited clonogenic growth with CI(90) values of 10 and 13 micromol/L, respectively. This effect was associated with G(2)-M arrest and the absence of any detectable markers of apoptosis (i.e., plasma membrane blebbing, procaspase 3 activation, loss of mitochondrial membrane potential, and formation of condensed chromatin). Drug-treated cells increased in size and eventually exhibited the characteristics of autophagy (i.e., appearance of autophagosomes and conversion of microtubule-associated protein light chain 3-I to 3-II). The absence of apoptosis was not related to an inhibition of the apoptotic program. Cultures treated with XK469 or SH80 readily underwent apoptosis upon exposure to the Bcl-2/Bcl-x(L) antagonist ethyl 2-amino-6-bromo-4-(1-cyano-2-ethoxy-2-oxoethyl)-4H-chromene-3-carboxylate. Continued incubation of drug-treated cells led to a reciprocal loss of large autophagic cells and the appearance of smaller cells that could not be stained with Höechst dye HO33342, had a chaotic morphology, were trypan blue-permeable, and lacked mitochondrial membrane potential. L1210 cells cotreated with the phosphatidylinositol-3-kinase inhibitor wortmannin, or having reduced Atg7 protein content, underwent G(2)-M arrest, but not autophagy, following XK469 treatment. Hence, the therapeutic actions of XK469/SH80 with L1210 cultures reflect both the initiation of a cell cycle arrest as well as the initiation of autophagy.

Protective role of autophagy against Vibrio cholerae cytolysin, a pore-forming toxin from V. cholerae

Autophagy is the unique, regulated mechanism for the degradation of organelles. This intracellular process acts as a prosurvival pathway during cell starvation or stress and is also involved in cellular response against specific bacterial infections. Vibrio cholerae is a noninvasive intestinal pathogen that has been studied extensively as the causative agent of the human disease cholera. V. cholerae illness is produced primarily through the expression of a potent toxin (cholera toxin) within the human intestine. Besides cholera toxin, this bacterium secretes a hemolytic exotoxin termed V. cholerae cytolysin (VCC) that causes extensive vacuolation in epithelial cells. In this work, we explored the relationship between the vacuolation caused by VCC and the autophagic pathway. Treatment of cells with VCC increased the punctate distribution of LC3, a feature indicative of autophagosome formation. Moreover, VCC-induced vacuoles colocalized with LC3 in several cell lines, including human intestinal Caco-2 cells, indicating the interaction of the large vacuoles with autophagic vesicles. Electron microscopy analysis confirmed that the vacuoles caused by VCC presented hallmarks of autophagosomes. Additionally, biochemical evidence demonstrated the degradative nature of the VCC-generated vacuoles. Interestingly, autophagy inhibition resulted in decreased survival of Caco-2 cells upon VCC intoxication. Also, VCC failed to induce vacuolization in Atg5-/- cells, and the survival response of these cells against the toxin was dramatically impaired. These results demonstrate that autophagy acts as a cellular defense pathway against secreted bacterial toxins.

Regulation of autophagy by extracellular signal-regulated protein kinases during 1-methyl-4-phenylpyridinium-induced cell death

Increased autophagic vacuoles (AVs) occur in injured or degenerating neurons, under both developmental and pathological situations. Although regulation of starvation-induced autophagy has been extensively studied, less is known about autophagic responses to pathological damage. The neurotoxin 1-methyl-4-phenylpyridinium (MPP(+)) produces mitochondria-targeted injury, which contributes to parkinsonism induced by 1-methyl-4-phenyl-1,2,3,6-tetrahydro-pyridine in mammals. Here, we demonstrate that MPP(+) elicited increased autophagy in SH-SY5Y cells, as assessed by electron microscopy, immunofluorescence for the autophagy protein LC3/Atg8, LC3 electrophoretic mobility shift, mitochondrial degradation, and monodansylcadaverine staining for late AVs/autolysosomes. During nutrient deprivation, class III phosphatidylinositol-3 kinase (PI3K) stimulates autophagy in concert with the autophagy-regulatory protein beclin 1/Atg6. Although PI3K inhibitors and RNA interference knockdown of beclin 1 effectively inhibited autophagy elicited by amino acid deprivation, neither reduced MPP+-induced autophagic stress. In contrast, inhibition of mitogen-activated protein kinase/extracellular signal-regulated protein kinase kinase reduced AV content, mitochondrial degradation, and cell death in MPP+-treated cells. RNA interference studies targeting core Atg proteins also reduced AV content and cell death. Likewise, in primary midbrain dopaminergic neurons, MPP+ elicited increased AV content, which was reversed by inhibition of mitogen-activated protein kinase/extracellular signal-regulated protein kinase kinase but not PI3K. These results implicate a role for extracellular signal-regulated protein kinase (ERK) signaling upstream of MPP+-elicited autophagic stress. Moreover, pathological stimulation of beclin 1-independent autophagy is associated with neuronal cell death.

Plumbagin induces G2-M arrest and autophagy by inhibiting the AKT/mammalian target of rapamycin pathway in breast cancer cells

This study is the first to investigate the anticancer effect of plumbagin in human breast cancer cells. Plumbagin exhibited cell proliferation inhibition by inducing cells to undergo G2-M arrest and autophagic cell death. Blockade of the cell cycle was associated with increased p21/WAF1 expression and Chk2 activation, and reduced amounts of cyclin B1, cyclin A, Cdc2, and Cdc25C. Plumbagin also reduced Cdc2 function by increasing the association of p21/WAF1/Cdc2 complex and the levels of inactivated phospho-Cdc2 and phospho-Cdc25C by Chk2 activation. Plumbagin triggered autophagic cell death but not predominantly apoptosis. Pretreatment of cells with autophagy inhibitor bafilomycin suppressed plumbagin-mediated cell death. We also found that plumbagin inhibited survival signaling through the phosphatidylinositol 3-kinase/AKT signaling pathway by blocking the activation of AKT and downstream targets, including the mammalian target of rapamycin, forkhead transcription factors, and glycogen synthase kinase 3beta. Phosphorylation of both of mammalian target of rapamycin downstream targets, p70 ribosomal protein S6 kinase and 4E-BP1, was also diminished. Overexpression of AKT by AKT cDNA transfection decreased plumbagin-mediated autophagic cell death, whereas reduction of AKT expression by small interfering RNA potentiated the effect of plumbagin, supporting the inhibition of AKT being beneficial to autophagy. Furthermore, suppression of AKT by plumbagin enhanced the activation of Chk2, resulting in increased inactive phosphorylation of Cdc25C and Cdc2. Further investigation revealed that plumbagin inhibition of cell growth was also evident in a nude mouse model. Taken together, these results imply a critical role for AKT inhibition in plumbagin-induced G2-M arrest and autophagy of human breast cancer cells.

Amino acid starvation induced autophagic cell death in PC-12 cells: evidence for activation of caspase-3 but not calpain-1

While the apoptotic and necrotic cell death pathways have been well studied, there lacks a comprehensive understanding of the molecular events involving autophagic cell death. We examined the potential roles of the apoptosis-linked caspase-3 and the necrosis/apoptosis-linked calpain-1 after autophagy induction under prolonged amino acid (AA) starvation conditions in PC-12 cells. Autophagy induction was observed as early as three hours following amino acid withdrawal. Cell death, measured by lactate dehydrogenase (LDH) and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assays occurred within 24 h following starvation and was accompanied by an upregulation in caspase-3 activity but not calpain-1. The cell death that occurred following AA starvation was significantly alleviated by treatment with the autophagy inhibitor 3-methyl adenine but not with the broad spectrum caspase inhibitors. Thus, this study demonstrates that 3-methyladenine-sensitive autophagic cell death due to AA starvation in PC-12 cells is mechanistically and biochemically similar to, yet distinct from, classic caspase dependent apoptosis.

The formation of peripheral myelin protein 22 aggregates is hindered by the enhancement of autophagy and expression of cytoplasmic chaperones

The accumulation of misfolded proteins is associated with various neurodegenerative conditions. Peripheral myelin protein 22 (PMP22) is a hereditary neuropathy-linked, short-lived molecule that forms aggresomes when the proteasome is inhibited or the protein is mutated. We previously showed that the removal of pre-existing PMP22 aggregates is assisted by autophagy. Here we examined whether the accumulation of such aggregates could be suppressed by experimental induction of autophagy and/or chaperones. Enhancement of autophagy during proteasome inhibition hinders protein aggregate formation and correlates with a reduction in accumulated proteasome substrates. Conversely, simultaneous inhibition of autophagy and the proteasome augments the formation of aggregates. An increase of heat shock protein levels by geldanamycin treatment or heat shock preconditioning similarly hampers aggresome formation. The beneficial effects of autophagy and chaperones in preventing the accumulation of misfolded PMP22 are additive and provide a potential avenue for therapeutic approaches in hereditary neuropathies linked to PMP22 mutations.

AMP-activated protein kinase and the regulation of autophagic proteolysis

Interruption of mTOR-dependent signaling by rapamycin is known to stimulate autophagy, both in mammalian cells and in yeast. Because activation of AMPK also inhibits mTOR-dependent signaling one would expect stimulation of autophagy by AMPK activation. According to the literature, this is true for yeast but, unexpectedly, not for mammalian cells on the basis of the use of AICAR, a pharmacological activator of AMPK. In the present study, carried out with hepatocytes, HT-29 cells, and HeLa cells, we have reexamined the possible role of AMPK in the control of mammalian autophagy. Inhibition of AMPK activity by compound C or by transfection with a dominant negative form of AMPK almost completely inhibited autophagy. These results suggest that the inhibition of autophagy by AICAR is not related to its ability to activate AMPK. We conclude that in mammalian cells, as in yeast, AMPK is required for autophagy.

mTOR inhibition induces endothelial progenitor cell death

Immunosuppressants are necessary to prevent graft rejection after solid organ transplantation. However, they are also known to have significant side effects, including endothelial toxicity. Endothelial progenitor cells originate in the bone marrow and are recognized by their angiogenic and endothelial reparative properties. The effects of the immunosuppressants cyclosporine A (CyA), tacrolimus and rapamycin were analyzed on endothelial progenitor-like cells. Rapamycin induced rapid cell death, even at concentrations much lower than those used clinically, in peripheral blood mononuclear cells (PBMC) cultured to favor outgrowth of endothelial progenitors. Cyclosporine A and tacrolimus had no significant effects at clinical concentrations. The effect of rapamycin was specific to endothelial progenitor cells, in particular to the early stages of differentiation, as a lesser effect was observed in late outgrowth endothelial progenitors, mature aortic endothelial cells, and macrophages derived from the same PBMCs. The mechanism of cell death appeared to be apoptosis; however, its induction was probably multifactorial and did not depend on caspase or cathepsin activation. In conclusion, rapamycin induces endothelial progenitor cell death, possibly because it blocks survival signals given by growth factors critically required by these cells.

Vacuolar and plasma membrane stripping and autophagic elimination of Toxoplasma gondii in primed effector macrophages

Apicomplexan protozoan pathogens avoid destruction and establish a replicative niche within host cells by forming a nonfusogenic parasitophorous vacuole (PV). Here we present evidence for lysosome-mediated degradation of Toxoplasma gondii after invasion of macrophages activated in vivo. Pathogen elimination was dependent on the interferon γ inducible-p47 GTPase, IGTP, required PI3K activity, and was preceded by PV membrane indentation, vesiculation, disruption, and, surprisingly, stripping of the parasite plasma membrane. Denuded parasites were enveloped in autophagosome-like vacuoles, which ultimately fused with lysosomes. These observations outline a series of mechanisms used by effector cells to redirect the fate of a classically nonfusogenic intracellular pathogen toward a path of immune elimination.

Akt and Mammalian Target of Rapamycin Regulate Separate Systems of Proteolysis in Renal Tubular Cells

EGF suppresses proteolysis via class 1 phosphatidylinositol 3-kinase (PI3K) in renal tubular cells. EGF also increases the abundance of glycolytic enzymes (e.g., glyceraldehyde-3-phosphate dehydrogenase [GAPDH]) and transcription factors (e.g., pax2) that are degraded by the lysosomal pathway of chaperone-mediated autophagy. To determine if EGF regulates chaperone-mediated autophagy through PI3K signaling, this study examined the effect of inhibiting PI3K and its downstream mediators Akt and the mammalian target of rapamycin (mTOR). Inhibition of PI3K with LY294002 prevented EGF-induced increases in GAPDH and pax2 abundance in NRK-52E renal tubular cells. Similar results were seen with an adenovirus encoding a dominant negative Akt (DN Akt). Expression of a constitutively active Akt increased GAPDH and pax2 abundance. An mTOR inhibitor, rapamycin, did not prevent EGF-induced increases in these proteins. Neither DN Akt nor rapamycin alone had an effect on total cell protein degradation, but both partially reversed EGF-induced suppression of proteolysis. DN Akt no longer affected proteolysis after treatment with a lysosomal inhibitor, methylamine. In contrast, methylamine or the inhibitor of macroautophagy, 3-methyladenine, did not prevent rapamycin from partially reversing the effect of EGF on proteolysis. Notably, rapamycin did not increase autophagasomes detected by monodansylcadaverine staining. Blocking the proteasomal pathway with either MG132 or lactacystin prevented rapamycin from partially reversing the effect of EGF on proteolysis. It is concluded that EGF regulates pax2 and GAPDH abundance and proteolysis through a PI3K/Akt-sensitive pathway that does not involve mTOR. Rapamycin has a novel effect of regulating proteasomal proteolysis in cells that are stimulated with EGF.

Cysteine peptidases CPA and CPB are vital for autophagy and differentiation in Leishmania mexicana

In the past, ultrastructural investigations of Leishmania mexicana amastigotes revealed structures that were tentatively identified as autophagosomes. This study has now provided definitive data that autophagy occurs in the parasite during differentiation both to metacyclic promastigotes and to amastigotes, autophagosomes being particularly numerous during metacyclic to amastigote form transformation. Moreover, the results demonstrate that inhibiting two major lysosomal cysteine peptidases (CPA and CPB) or removing their genes not only interferes with the autophagy pathway but also prevents metacyclogenesis and transformation to amastigotes, thus adding support to the hypothesis that autophagy is required for cell differentiation. The study suggests that L. mexicana CPA and CPB perform similar roles to the aspartic peptidase PEP4 and the serine peptidase PRB1 in Saccharomyces cerevisiae. The results also provide an explanation for why L. mexicana CPA/CPB-deficient mutants transform to amastigotes very poorly and lack virulence in macrophages and mice.

Dipeptidyl peptidase II and leukocyte cell death

Dipeptidyl peptidase (DPP) II (E.C. 3.4.14.2) is an intracellular protease that releases, preferably at acidic pH, N-terminal dipeptides from oligopeptides with Pro or Ala in the penultimate position. The natural substrates and the physiological role of DPPII remain unclear. The aim of the present study was to investigate the involvement of DPPII activity in different forms of cell death (apoptosis, necrosis and autophagy) in human leukocytes. We determined specific DPP activities in leukocytes. Compared to other subpopulations of peripheral blood mononuclear cells (PBMC), we observed relatively high DPPII specific activity in monocytic cells, opening new perspectives for further investigation of the DPPII functions. A second intriguing finding was that DPPII specific activity increased during necrosis, whereas induction of apoptosis or autophagy did not affect any of the dipeptidyl peptidase activities. Finally, we showed that inhibition of DPPII (>90%) using the in vitro applicable, highly potent (K(i) of 0.082+/-0.048 nM) and selective DPPII inhibitor UAMC00039, did not induce any form of cell death in leukocytes. These data are of importance for a more precise interpretation of the in vitro and in vivo effects of other dipeptidyl peptidase inhibitors.

Non-apoptotic programmed cell death induced by a copper(II) complex in human fibrosarcoma cells

A0, a Cu(II) thioxotriazole complex, produces severe cytotoxic effects on HT1080 human fibrosarcoma cells with a potency comparable to that exhibited by cisplatin. A0 induced a characteristic series of changes, hallmarked by the formation of eosin- and Sudan Black-B-negative vacuoles. No evidence of nuclear fragmentation or caspase-3 activation was detected in cells treated with A0 which, rather, inhibited cisplatin-stimulated caspase-3 activity. Membrane functional integrity, assessed with calcein and propidium iodide, was spared until the late stages of the death process induced by the copper complex. Vacuoles were negative to the autophagy marker monodansylcadaverine and their formation was not blocked by 3-methyladenine, an inhibitor of autophagic processes. Negativity to the extracellular marker pyranine excluded vacuole derivation from the extracellular fluid. Ultrastructural analysis indicated that A0 caused the appearance of many electronlight cytoplasmic vesicles, possibly related to the endoplasmic reticulum, which progressively enlarge and coalesce to form large vacuolar structures that eventually fill the cytoplasm. It is concluded that A0 triggers a non-apoptotic, type 3B programmed cell death (Clarke in Anat Embryol (Berl) 181:195-213, 1990), characterized by an extensive cytoplasmic vacuolization. This peculiar cytotoxicity pattern may render the employment of A0 to be of particular interest in apoptosis-resistant cell models.

Proteasomal proteolysis in anoxia-reoxygenation, preconditioning and postconditioning of isolated cardiomyocytes

The role of proteasomal proteolysis in the pathogenesis of ischemia-reperfusion is being actively studied. To evaluate the participation of the proteasome in the preconditioning and postconditioning phenomena we used primary culture of neonatal cardiomyocytes. This culture was undergone 30min of anoxia followed by 60min of reoxygenation. Preconditioning was modeled by three cycles of 3min anoxia followed by 3min reoxygenation. Postconditioning was modeled by three cycles of 1min reoxygenation followed by 1min anoxia, respectively. Clasto-lactacystin beta-lactone, a specific proteasome inhibitor, was added to the culture medium right before the cycles of preconditioning or postconditioning in the dose that does not cause cell death (2.5muM). Percentages of living, necrotic, and apoptotic cells were determined by staining with bisbenzimide and propidium iodide. Autophagy was demonstrated by staining vacuolar structures with monodansyl cadaverine. Proteasomal activity was determined by cleavage intensity of specific fluorogenic substrates. Trypsin-like, chymotrypsin-like and peptidyl-glutamyl peptide-hydrolyzing (PGPH) activities were decreased after anoxia. Reoxygenation has led to the increase in trypsin-like and chymotrypsin-like activities comparing to anoxia, but these parameters have never reached the control levels. PGPH activity has been restored up to the initial level. Preconditioning and postconditioning increased numbers of living cells and decreased that of necrotic, apoptotic and autophagic cells. Paradoxically, it was established that proteasome inhibitors prevented the necrotic and apoptotic cell death of cardiomyocytes in anoxia-reoxygenation, but in the same concentration abolished the effects of preconditioning and postconditioning. Low doses of proteasome inhibitors, particularly the ones used in our experiments, resulted in the abolishing of preconditioning and postconditioning phenomena, but at the same time led to the increase of the population of living cells in anoxia-reoxygenation, and can be considered as potential pharmacological agents of preconditioning and postconditioning.

The Crohn's disease-associated adherent-invasive Escherichia coli strain LF82 replicates in mature phagolysosomes within J774 macrophages

Adherent-invasive Escherichia coli (AIEC) bacteria isolated from Crohn's disease patients are able to extensively replicate within macrophages in large vacuoles. The mechanism by which AIEC bacteria survive within phagocytic cells is unknown. This report describes the maturation of AIEC LF82-containing phagosomes within J774 macrophages. LF82-containing phagosomes traffic through the endocytic pathway as shown by the sequential acquisition and loss of EEA1 and Rab7 and by accumulation of Lamp-1, Lamp-2 and cathepsin D. We demonstrated that AIEC LF82-containing phagosomes mature into active phagolysosomes where bacteria are exposed to low pH and to the degradative activity of cathepsin D. Finally, we showed that an acidic environment is necessary for replication of AIEC LF82 bacteria within J774 macrophages. Thus, evidence is provided that AIEC LF82 bacteria do not escape from the endocytic pathway but undergo normal interaction with host endomembrane organelles and replicate within acidic and cathepsin D-positive vacuolar phagolysosomes.