No energy, no autophagy-Mechanisms and therapeutic implications of autophagic response energy requirements.

Autophagy is a lysosome-mediated self-degradation process of central importance for cellular quality control. It also provides macromolecule building blocks and substrates for energy metabolism during nutrient or energy deficiency, which are the main stimuli for autophagy induction. However, like most biological processes, autophagy itself requires ATP, and there is an energy threshold for its initiation and execution. We here present the first comprehensive review of this often-overlooked aspect of autophagy research. The studies in which ATP deficiency suppressed autophagy in vitro and in vivo were classified according to the energy pathway involved (oxidative phosphorylation or glycolysis). A mechanistic insight was provided by pinpointing the critical ATP-consuming autophagic events, including transcription/translation/interaction of autophagy-related molecules, autophagosome formation/elongation, autophagosome fusion with the lysosome, and lysosome acidification. The significance of energy-dependent fine-tuning of autophagic response for preserving the cell homeostasis, and potential implications for the therapy of cancer, autoimmunity, metabolic disorders, and neurodegeneration are discussed.

The Exploitation of Lysosomes in Cancer Therapy with Graphene-Based Nanomaterials.

Graphene-based nanomaterials (GNMs), including graphene, graphene oxide, reduced graphene oxide, and graphene quantum dots, may have direct anticancer activity or be used as nanocarriers for antitumor drugs. GNMs usually enter tumor cells by endocytosis and can accumulate in lysosomes. This accumulation prevents drugs bound to GNMs from reaching their targets, suppressing their anticancer effects. A number of chemical modifications are made to GNMs to facilitate the separation of anticancer drugs from GNMs at low lysosomal pH and to enable the lysosomal escape of drugs. Lysosomal escape may be associated with oxidative stress, permeabilization of the unstable membrane of cancer cell lysosomes, release of lysosomal enzymes into the cytoplasm, and cell death. GNMs can prevent or stimulate tumor cell death by inducing protective autophagy or suppressing autolysosomal degradation, respectively. Furthermore, because GNMs prevent bound fluorescent agents from emitting light, their separation in lysosomes may enable tumor cell identification and therapy monitoring. In this review, we explain how the characteristics of the lysosomal microenvironment and the unique features of tumor cell lysosomes can be exploited for GNM-based cancer therapy.

Autophagy Receptor p62 Regulates SARS-CoV-2-Induced Inflammation in COVID-19.

As autophagy can promote or inhibit inflammation, we examined autophagy-inflammation interplay in COVID-19. Autophagy markers in the blood of 19 control subjects and 26 COVID-19 patients at hospital admission and one week later were measured by ELISA, while cytokine levels were examined by flow cytometric bead immunoassay. The antiviral IFN-α and proinflammatory TNF, IL-6, IL-8, IL-17, IL-33, and IFN-γ were elevated in COVID-19 patients at both time points, while IL-10 and IL-1ß were increased at admission and one week later, respectively. Autophagy markers LC3 and ATG5 were unaltered in COVID-19. In contrast, the concentration of autophagic cargo receptor p62 was significantly lower and positively correlated with TNF, IL-10, IL-17, and IL-33 at hospital admission, returning to normal levels after one week. The expression of SARS-CoV-2 proteins NSP5 or ORF3a in THP-1 monocytes caused an autophagy-independent decrease or autophagy-inhibition-dependent increase, respectively, of intracellular/secreted p62, as confirmed by immunoblot/ELISA. This was associated with an NSP5-mediated decrease in TNF/IL-10 mRNA and an ORF3a-mediated increase in TNF/IL-1ß/IL-6/IL-10/IL-33 mRNA levels. A genetic knockdown of p62 mimicked the immunosuppressive effect of NSP5, and a p62 increase in autophagy-deficient cells mirrored the immunostimulatory action of ORF3a. In conclusion, the proinflammatory autophagy receptor p62 is reduced inacute COVID-19, and the balance between autophagy-independent decrease and autophagy blockade-dependent increase of p62 levels could affect SARS-CoV-induced inflammation.

Combination of Ascorbic Acid and Menadione Induces Cytotoxic Autophagy in Human Glioblastoma Cells.

We investigated the ability of the ascorbic acid (AA) and menadione (MD) combination, the well-known reactive oxidative species- (ROS-) generating system, to induce autophagy in human U251 glioblastoma cells. A combination of AA and MD (AA+MD), in contrast to single treatments, induced necrosis-like cell death mediated by mitochondrial membrane depolarization and extremely high oxidative stress. AA+MD, and to a lesser extent MD alone, prompted the appearance of autophagy markers such as autophagic vacuoles, autophagosome-associated LC3-II protein, degradation of p62, and increased expression of beclin-1. While both MD and AA+MD increased phosphorylation of AMP-activated protein kinase (AMPK), the well-known autophagy promotor, only the combined treatment affected its downstream targets, mechanistic target of rapamycin complex 1 (mTORC1), Unc 51-like kinase 1 (ULK1), and increased the expression of several autophagy-related genes. Antioxidant N-acetyl cysteine reduced both MD- and AA+MD-induced autophagy, as well as changes in AMPK/mTORC1/ULK1 activity and cell death triggered by the drug combination. Pharmacological and genetic autophagy silencing abolished the toxicity of AA+MD, while autophagy upregulation enhanced the toxicity of both AA+MD and MD. Therefore, by upregulating oxidative stress, inhibiting mTORC1, and activating ULK1, AA converts MD-induced AMPK-dependent autophagy from nontoxic to cytotoxic. These results suggest that AA+MD or MD treatment in combination with autophagy inducers could be further investigated as a novel approach for glioblastoma therapy.

MAP kinase-dependent autophagy controls phorbol myristate acetate-induced macrophage differentiation of HL-60 leukemia cells.

We investigated the mechanisms and the role of autophagy in the differentiation of HL-60 human acute myeloid leukemia cells induced by protein kinase C (PKC) activator phorbol myristate acetate (PMA). PMA-triggered differentiation of HL-60 cells into macrophage-like cells was confirmed by cell-cycle arrest accompanied by elevated expression of macrophage markers CD11b, CD13, CD14, CD45, EGR1, CSF1R, and IL-8. The induction of autophagy was demonstrated by the increase in intracellular acidification, accumulation/punctuation of autophagosome marker LC3-II, and the increase in autophagic flux. PMA also increased nuclear translocation of autophagy transcription factors TFEB, FOXO1, and FOXO3, as well as the expression of several autophagy-related (ATG) genes in HL-60 cells. PMA failed to activate autophagy inducer AMP-activated protein kinase (AMPK) and inhibit autophagy suppressor mechanistic target of rapamycin complex 1 (mTORC1). On the other hand, it readily stimulated the phosphorylation of mitogen-activated protein (MAP) kinases extracellular signal-regulated kinase (ERK) and c-Jun N-terminal kinase (JNK) via a protein kinase C-dependent mechanism. Pharmacological or genetic inhibition of ERK or JNK suppressed PMA-triggered nuclear translocation of TFEB and FOXO1/3, ATG expression, dissociation of pro-autophagic beclin-1 from its inhibitor BCL2, autophagy induction, and differentiation of HL-60 cells into macrophage-like cells. Pharmacological or genetic inhibition of autophagy also blocked PMA-induced macrophage differentiation of HL-60 cells. Therefore, MAP kinases ERK and JNK control PMA-induced macrophage differentiation of HL-60 leukemia cells through AMPK/mTORC1-independent, TFEB/FOXO-mediated transcriptional and beclin-1-dependent post-translational activation of autophagy.

Graphene quantum dot antioxidant and proautophagic actions protect SH-SY5Y neuroblastoma cells from oxidative stress-mediated apoptotic death.

We investigated the ability of graphene quantum dot (GQD) nanoparticles to protect SH-SY5Y human neuroblastoma cells from oxidative/nitrosative stress induced by iron-nitrosyl complex sodium nitroprusside (SNP). GQD reduced SNP cytotoxicity by preventing mitochondrial depolarization, caspase-2 activation, and subsequent apoptotic death. Although GQD diminished the levels of nitric oxide (NO) in SNP-exposed cells, NO scavengers displayed only a slight protective effect, suggesting that NO quenching was not the main protective mechanism of GQD. GQD also reduced SNP-triggered increase in the intracellular levels of hydroxyl radical (•OH), superoxide anion (O2•-), and lipid peroxidation. Nonselective antioxidants, •OH scavenging, and iron chelators, but not superoxide dismutase, mimicked GQD cytoprotective activity, indicating that GQD protect cells by neutralizing •OH generated in the presence of SNP-released iron. Cellular internalization of GQD was required for optimal protection, since a removal of extracellular GQD by extensive washing only partly diminished their protective effect. Moreover, GQD cooperated with SNP to induce autophagy, as confirmed by the inhibition of autophagy-limiting Akt/PRAS40/mTOR signaling and increase in autophagy gene transcription, protein levels of proautophagic beclin-1 and LC3-II, formation of autophagic vesicles, and degradation of autophagic target p62. The antioxidant activity of GQD was not involved in autophagy induction, as antioxidants N-acetylcysteine and dimethyl sulfoxide failed to stimulate autophagy in SNP-exposed cells. Pharmacological inhibitors of early (wortmannin, 3-methyladenine) or late stages of autophagy (NH4Cl) efficiently reduced the protective effect of GQD. Therefore, the ability of GQD to prevent the in vitro neurotoxicity of SNP depends on both •OH/NO scavenging and induction of cytoprotective autophagy.

Modulation of Cancer Cell Autophagic Responses by Graphene-Based Nanomaterials: Molecular Mechanisms and Therapeutic Implications.

Graphene-based nanomaterials (GNM) are plausible candidates for cancer therapeutics and drug delivery systems. Pure graphene and graphene oxide nanoparticles, as well as graphene quantum dots and graphene nanofibers, were all able to trigger autophagy in cancer cells through both transcriptional and post-transcriptional mechanisms involving oxidative/endoplasmic reticulum stress, AMP-activated protein kinase, mechanistic target of rapamycin, mitogen-activated protein kinase, and Toll-like receptor signaling. This was often coupled with lysosomal dysfunction and subsequent blockade of autophagic flux, which additionally increased the accumulation of autophagy mediators that participated in apoptotic, necrotic, or necroptotic death of cancer cells and influenced the immune response against the tumor. In this review, we analyze molecular mechanisms and structure-activity relationships of GNM-mediated autophagy modulation, its consequences for cancer cell survival/death and anti-tumor immune response, and the possible implications for the use of GNM in cancer therapy.

3-Methyladenine prevents energy stress-induced necrotic death of melanoma cells through autophagy-independent mechanisms.

We investigated the effect of 3-methyladenine (3MA), a class III phosphatidylinositol 3-kinase (PI3K)-blocking autophagy inhibitor, on cancer cell death induced by simultaneous inhibition of glycolysis by 2-deoxyglucose (2DG) and mitochondrial respiration by rotenone. 2DG/rotenone reduced ATP levels and increased mitochondrial superoxide production, causing mitochondrial swelling and necrotic death in various cancer cell lines. 2DG/rotenone failed to increase proautophagic beclin-1 and autophagic flux in melanoma cells despite the activation of AMP-activated protein kinase (AMPK) and inhibition of mechanistic target of rapamycin complex 1 (mTORC1). 3MA, but not autophagy inhibition with other PI3K and lysosomal inhibitors, attenuated 2DG/rotenone-induced mitochondrial damage, oxidative stress, ATP depletion, and cell death, while antioxidant treatment mimicked its protective action. The protection was not mediated by autophagy upregulation via class I PI3K/Akt inhibition, as it was preserved in cells with genetically inhibited autophagy. 3MA increased AMPK and mTORC1 activation in energy-stressed cells, but neither AMPK nor mTORC1 inhibition reduced its cytoprotective effect. 3MA reduced JNK activation, and JNK pharmacological/genetic suppression mimicked its mitochondria-preserving and cytoprotective activity. Therefore, 3MA prevents energy stress-triggered cancer cell death through autophagy-independent mechanisms possibly involving JNK suppression and decrease of oxidative stress. Our results warrant caution when using 3MA as an autophagy inhibitor.

Dual targeting of tumor cell energy metabolism and lysosomes as an anticancer strategy.

To sustain their proliferative and metastatic capacity, tumor cells increase the activity of energy-producing pathways and lysosomal compartment, resorting to autophagolysosomal degradation when nutrients are scarce. Consequently, large fragile lysosomes and enhanced energy metabolism may serve as targets for anticancer therapy. A simultaneous induction of energy stress (by caloric restriction and inhibition of glycolysis, oxidative phosphorylation, Krebs cycle, or amino acid/fatty acid metabolism) and lysosomal stress (by lysosomotropic detergents, vacuolar ATPase inhibitors, or cationic amphiphilic drugs) is an efficient anti-cancer strategy demonstrated in a number of studies. However, the mechanisms of lysosomal/energy stress co-amplification, apart from the protective autophagy inhibition, are poorly understood. We here summarize the established and suggest potential mechanisms and candidates for anticancer therapy based on the dual targeting of lysosomes and energy metabolism.

AMP-activated protein kinase inhibits MPP+-induced oxidative stress and apoptotic death of SH-SY5Y cells through sequential stimulation of Akt and autophagy.

We investigated the interplay between the intracellular energy sensor AMP-activated protein kinase (AMPK), prosurvival kinase Akt, oxidative stress, and autophagy in the cytotoxicity of parkinsonian neurotoxin 1-methyl-4-phenyl piridinium (MPP+) towards SH-SY5Y human neuroblastoma cells. MPP+-mediated oxidative stress, mitochondrial depolarization, and apoptotic cell death were associated with rapid (within 2 h) activation of AMPK, its target Raptor, and prosurvival kinase Akt. Antioxidants N-acetylcysteine and butylated hydroxyanisole suppressed MPP+-induced cytotoxicity, AMPK, and Akt activation. A genetic or pharmacological inhibition of AMPK increased MPP+-triggered production of reactive oxygen species and cell death, and diminished Akt phosphorylation, while AMPK activation protected SH-SY5Y cells from MPP+. On the other hand, genetic or pharmacological inactivation of Akt stimulated MPP+-triggered oxidative stress and neurotoxicity, but did not affect AMPK activation. At later time-points (16-24 h), MPP+ inhibited the main autophagy repressor mammalian target of rapamycin, which coincided with the increase in the levels of autophagy marker microtubule-associated protein 1 light-chain 3B. MPP+ also increased the concentration of a selective autophagic target sequestosome-1/p62 and reduced the levels of lysosomal-associated membrane protein 1 and cytoplasmic acidification, suggesting that MPP+-induced autophagy was coupled with a decrease in autophagic flux. Nevertheless, further pharmacological inhibition of autophagy sensitized SH-SY5Y cells to MPP+-induced death. Antioxidants and AMPK knockdown reduced, whereas genetic inactivation of Akt potentiated neurotoxin-triggered autophagy. These results suggest that MPP+-induced oxidative stress stimulates AMPK, which protects SH-SY5Y cells through early activation of antioxidative Akt and late induction of cytoprotective autophagy.

Xanthone-rich extract from Gentiana dinarica transformed roots and its active component norswertianin induce autophagy and ROS-dependent differentiation of human glioblastoma cell line.

BACKGROUND: Glioblastoma multiforme (GMB) is the most malignant of all brain tumors with poor prognosis. Anticancer potential of xanthones, bioactive compounds found in Gentiana dinarica, is well-documented. Transformation of G. dinarica roots with Agrobacterium rhizogenes provides higher xanthones accumulation, which enables better exploitation of these anticancer compounds. HYPOTHESIS/PURPOSE: The aim of this study was to investigate antiglioma effect of three different G. dinarica extracts: E1-derived from untransformed roots, E2-derived from roots transformed using A. rhizogenes strain A4M70GUS, and E3-derived from roots transformed using A. rhizogenes strain 15834/PI. Further, mechanisms involved in anticancer potential of the most potent extract were examined in detail, and its active component was determined. METHODS: The cell viability was assessed using MTT and crystal violet test. Cell cycle analysis, the expression of differentiation markers, the levels of autophagy, and oxidative stress were analyzed by flow cytometry. Autophagy and related signaling pathways were assessed by immunoblotting. RESULTS: E3, in contrast to E1 and E2, strongly reduced growth of U251 human glioblastoma cells, triggered cell cycle arrest in G2/M phase, changed cellular morphology, and increased expression of markers of differentiated astrocytes (glial fibrillary acidic protein) and neurons (ß-tubulin). E3 stimulated autophagy, as demonstrated by enhanced intracellular acidification, increased microtubule-associated light chain 3B (LC3-I) conversion to autophagosome associated LC3-II, and decreased level of selective autophagy target p62. Induction of autophagy was associated with Akt-dependent inhibition of main autophagy suppressor mammalian target of rapamycin (mTOR). Both genetic and pharmacological inhibition of autophagy suppressed the expression of differentiation markers, but had no effect on cell cycle arrest in E3-treated cells. E3 stimulated oxidative stress, and antioxidants vitamin E and N-acetyl cysteine inhibited autophagy and differentiation of E3-treated U251 cells. The most prevalent compound of E3, xanthone aglycone norswertianin, also arrested glioblastoma cell proliferation in G2/M phase and induced glioblastoma cell differentiation through induction of autophagy and oxidative stress. CONCLUSION: These results indicate that E3 and its main active component norswertianin may serve as a potential candidate for differentiation therapy of glioblastoma.

Mechanisms and therapeutic significance of autophagy modulation by antipsychotic drugs.

In this review we analyze the ability of antipsychotic medications to modulate macroautophagy, a process of controlled lysosomal digestion of cellular macromolecules and organelles. We focus on its molecular mechanisms, consequences for the function/survival of neuronal and other cells, and the contribution to the beneficial and side-effects of antipsychotics in the treatment of schizophrenia, neurodegeneration, and cancer. A wide range of antipsychotics was able to induce neuronal autophagy as a part of the adaptive stress response apparently independent of mammalian target of rapamycin and dopamine receptor blockade. Autophagy induction by antipsychotics could contribute to reducing neuronal dysfunction in schizophrenia, but also to the adverse effects associated with their long-term use, such as brain volume loss and weight gain. In neurodegenerative diseases, antipsychotic-stimulated autophagy might help to increase the clearance and reduce neurotoxicity of aggregated proteotoxins. However, the possibility that some antipsychotics might block autophagic flux and potentially contribute to proteotoxin-mediated neurodegeneration must be considered. Finally, the anticancer effects of autophagy induction by antipsychotics make plausible their repurposing as adjuncts to standard cancer therapy.

Data supporting the inability of indomethacin to induce autophagy in U251 glioma cells.

Autophagy, a catabolic process involving intracellular degradation of unnecessary or dysfunctional cellular components through the lysosomal machinery, could act as a prosurvival, as well as a cytotoxic mechanism (Parzych and Klionsky, 2014) [1]. Cyclooxygenase inhibitor indomethacin inhibits proliferation of glioma cells, and has been reported to reduce the activity of the main autophagy repressor mammalian target of rapamycin (mTOR) (Pantovic et al., 2016) [2]. Here we investigated the ability of indomethacin to induce autophagy in U251 human glioma cells. We assessed the influence of indomethacin on intracellular acidification, expression of proautophagic protein beclin-1, and conversion of microtubule-associated protein light chain 3-I (LC3-I) to autophagosome-associated LC3-II, in the presence or absence of lysosomal inhibitors. The effect of genetic and pharmacological downregulation of autophagy on the cytotoxicity of indomethacin was also evaluated. The interpretation of these data can be found in "In vitro antiglioma action of indomethacin is mediated via AMP-activated protein kinase/mTOR complex 1 signaling pathway" (Pantovic et al., 2016; doi:10.1016/j.biocel.2016.12.007) [2].

In vitro antiglioma action of indomethacin is mediated via AMP-activated protein kinase/mTOR complex 1 signalling pathway.

We investigated the role of the intracellular energy-sensing AMP-activated protein kinase (AMPK)/mammalian target of rapamycin (mTOR) pathway in the in vitro antiglioma effect of the cyclooxygenase (COX) inhibitor indomethacin. Indomethacin was more potent than COX inhibitors diclofenac, naproxen, and ketoprofen in reducing the viability of U251 human glioma cells. Antiglioma effect of the drug was associated with p21 increase and G2M cell cycle arrest, as well as with oxidative stress, mitochondrial depolarization, caspase activation, and the induction of apoptosis. Indomethacin increased the phosphorylation of AMPK and its targets Raptor and acetyl-CoA carboxylase (ACC), and reduced the phosphorylation of mTOR and mTOR complex 1 (mTORC1) substrates p70S6 kinase and PRAS40 (Ser183). AMPK knockdown by RNA interference, as well as the treatment with the mTORC1 activator leucine, prevented indomethacin-mediated mTORC1 inhibition and cytotoxic action, while AMPK activators metformin and AICAR mimicked the effects of the drug. AMPK activation by indomethacin correlated with intracellular ATP depletion and increase in AMP/ATP ratio, and was apparently independent of COX inhibition or the increase in intracellular calcium. Finally, the toxicity of indomethacin towards primary human glioma cells was associated with the activation of AMPK/Raptor/ACC and subsequent suppression of mTORC1/S6K. By demonstrating the involvement of AMPK/mTORC1 pathway in the antiglioma action of indomethacin, our results support its further exploration in glioma therapy.

Synergistic Anticancer Action of Lysosomal Membrane Permeabilization and Glycolysis Inhibition.

We investigated the in vitro and in vivo anticancer effect of combining lysosomal membrane permeabilization (LMP)-inducing agent N-dodecylimidazole (NDI) with glycolytic inhibitor 2-deoxy-d-glucose (2DG). NDI-triggered LMP and 2DG-mediated glycolysis block synergized in inducing rapid ATP depletion, mitochondrial damage, and reactive oxygen species production, eventually leading to necrotic death of U251 glioma cells but not primary astrocytes. NDI/2DG-induced death of glioma cells was partly prevented by lysosomal cathepsin inhibitor E64 and antioxidant α-tocopherol, suggesting the involvement of LMP and oxidative stress in the observed cytotoxicity. LMP-inducing agent chloroquine also displayed a synergistic anticancer effect with 2DG, whereas glucose deprivation or glycolytic inhibitors iodoacetate and sodium fluoride synergistically cooperated with NDI, thus further indicating that the anticancer effect of NDI/2DG combination was indeed due to LMP and glycolysis block. The two agents synergistically induced ATP depletion, mitochondrial depolarization, oxidative stress, and necrotic death also in B16 mouse melanoma cells. Moreover, the combined oral administration of NDI and 2DG reduced in vivo melanoma growth in C57BL/6 mice by inducing necrotic death of tumor cells, without causing liver, spleen, or kidney toxicity. Based on these results, we propose that NDI-triggered LMP causes initial mitochondrial damage that is further increased by 2DG due to the lack of glycolytic ATP required to maintain mitochondrial health. This leads to a positive feedback cycle of mitochondrial dysfunction, ATP loss, and reactive oxygen species production, culminating in necrotic cell death. Therefore, the combination of LMP-inducing agents and glycolysis inhibitors seems worthy of further exploration as an anticancer strategy.

c-Jun N-terminal kinase-dependent apoptotic photocytotoxicity of solvent exchange-prepared curcumin nanoparticles.

Indian spice curcumin is known for its anticancer properties, but the anticancer mechanisms of nanoparticulate curcumin have not been completely elucidated. We here investigated the in vitro anticancer effect of blue light (470 nm, 1 W)-irradiated curcumin nanoparticles prepared by tetrahydrofuran/water solvent exchange, using U251 glioma, B16 melanoma, and H460 lung cancer cells as targets. The size of curcumin nanocrystals was approximately 250 nm, while photoexcitation induced their oxidation and partial agglomeration. Although cell membrane in the absence of light was almost impermeable to curcumin nanoparticles, photoexcitation stimulated their internalization. While irradiation with blue light (1-8 min) or nanocurcumin (1.25-10 µg/ml) alone was only marginally toxic to tumor cells, photoexcited nanocurcumin displayed a significant cytotoxicity depending both on the irradiation time and nanocurcumin concentration. Photoexcited nanocurcumin induced phosphorylation of c-Jun N-terminal kinase (JNK), mitochondrial depolarization, caspase-3 activation, and cleavage of poly (ADP-ribose) polymerase, indicating apoptotic cell death. Accordingly, pharmacologial inhibition of JNK and caspase activity rescued cancer cells from photoexcited nanocurcumin. On the other hand, antioxidant treatment did not reduce photocytotoxicity of nanocurcumin, arguing against the involvement of oxidative stress. By demonstrating the ability of photoexcited nanocurcumin to induce oxidative-stress independent, JNK- and caspase-dependent apoptosis, our results support its further investigation in cancer therapy.

Coordinated activation of AMP-activated protein kinase, extracellular signal-regulated kinase, and autophagy regulates phorbol myristate acetate-induced differentiation of SH-SY5Y neuroblastoma cells.

We explored the interplay between the intracellular energy sensor AMP-activated protein kinase (AMPK), extracellular signal-regulated kinase (ERK), and autophagy in phorbol myristate acetate (PMA)-induced neuronal differentiation of SH-SY5Y human neuroblastoma cells. PMA-triggered expression of neuronal markers (dopamine transporter, microtubule-associated protein 2, ß-tubulin) was associated with an autophagic response, measured by the conversion of microtubule-associated protein light chain 3 (LC3)-I to autophagosome-bound LC3-II, increase in autophagic flux, and expression of autophagy-related (Atg) proteins Atg7 and beclin-1. This coincided with the transient activation of AMPK and sustained activation of ERK. Pharmacological inhibition or RNA interference-mediated silencing of AMPK suppressed PMA-induced expression of neuronal markers, as well as ERK activation and autophagy. A selective pharmacological blockade of ERK prevented PMA-induced neuronal differentiation and autophagy induction without affecting AMPK phosphorylation. Conversely, the inhibition of autophagy downstream of AMPK/ERK, either by pharmacological agents or LC3 knockdown, promoted the expression of neuronal markers, thus indicating a role of autophagy in the suppression of PMA-induced differentiation of SH-SY5Y cells. Therefore, PMA-induced neuronal differentiation of SH-SY5Y cells depends on a complex interplay between AMPK, ERK, and autophagy, in which the stimulatory effects of AMPK/ERK signaling are counteracted by the coinciding autophagic response. Phorbol myristate acetate (PMA) induces the expression of dopamine transporter, microtubule-associated protein 2, and ß-tubulin, and subsequent neuronal differentiation of SH-SY5Y neuroblastoma cells through AMP-activated protein kinase (AMPK)-dependent activation of extracellular signal-regulated kinase (ERK). The activation of AMPK/ERK axis also induces the expression of beclin-1 and Atg7, and increases LC3 conversion, thereby triggering the autophagic response that counteracts differentiation process.

Idarubicin induces mTOR-dependent cytotoxic autophagy in leukemic cells.

We investigated if the antileukemic drug idarubicin induces autophagy, a process of programmed cellular self-digestion, in leukemic cell lines and primary leukemic cells. Transmission electron microscopy and acridine orange staining demonstrated the presence of autophagic vesicles and intracellular acidification, respectively, in idarubicin-treated REH leukemic cell line. Idarubicin increased punctuation/aggregation of microtubule-associated light chain 3B (LC3B), enhanced the conversion of LC3B-I to autophagosome-associated LC3B-II in the presence of proteolysis inhibitors, and promoted the degradation of the selective autophagic target p62, thus indicating the increase in autophagic flux. Idarubicin inhibited the phosphorylation of the main autophagy repressor mammalian target of rapamycin (mTOR) and its downstream target p70S6 kinase. The treatment with the mTOR activator leucine prevented idarubicin-mediated autophagy induction. Idarubicin-induced mTOR repression was associated with the activation of the mTOR inhibitor AMP-activated protein kinase and down-regulation of the mTOR activator Akt. The suppression of autophagy by pharmacological inhibitors or LC3B and beclin-1 genetic knockdown rescued REH cells from idarubicin-mediated oxidative stress, mitochondrial depolarization, caspase activation and apoptotic DNA fragmentation. Idarubicin also caused mTOR inhibition and cytotoxic autophagy in K562 leukemic cell line and leukocytes from chronic myeloid leukemia patients, but not healthy controls. By demonstrating mTOR-dependent cytotoxic autophagy in idarubicin-treated leukemic cells, our results warrant caution when considering combining idarubicin with autophagy inhibitors in leukemia therapy.

Inhibition of mTOR-dependent autophagy sensitizes leukemic cells to cytarabine-induced apoptotic death.

The present study investigated the role of autophagy, a cellular self-digestion process, in the cytotoxicity of antileukemic drug cytarabine towards human leukemic cell lines (REH, HL-60, MOLT-4) and peripheral blood mononuclear cells from leukemic patients. The induction of autophagy was confirmed by acridine orange staining of intracellular acidic vesicles, electron microscopy visualization of autophagic vacuoles, as well as by the increase in autophagic proteolysis and autophagic flux, demonstrated by immunoblot analysis of p62 downregulation and LC3-I conversion to autophagosome-associated LC3-II in the presence of proteolysis inhibitors, respectively. Moreover, the expression of autophagy-related genes Atg4, Atg5 and Atg7 was stimulated by cytarabine in REH cells. Cytarabine reduced the phosphorylation of the major negative regulator of autophagy, mammalian target of rapamycin (mTOR), and its downstream target p70S6 kinase in REH cells, which was associated with downregulation of mTOR activator Akt and activation of extracellular signal- regulated kinase. Cytarabine had no effect on the activation of mTOR inhibitor AMP-activated protein kinase. Leucine, an mTOR activator, reduced both cytarabine-induced autophagy and cytotoxicity. Accordingly, pharmacological downregulation of autophagy with bafilomycin A1 and chloroquine, or RNA interference-mediated knockdown of LC3ß or p62, markedly increased oxidative stress, mitochondrial depolarization, caspase activation and subsequent DNA fragmentation and apoptotic death in cytarabine-treated REH cells. Cytarabine also induced mTOR-dependent cytoprotective autophagy in HL-60 and MOLT-4 leukemic cell lines, as well as primary leukemic cells, but not normal leukocytes. These data suggest that the therapeutic efficiency of cytarabine in leukemic patients could be increased by the inhibition of the mTOR-dependent autophagic response.

Synthesis, characterization and cytotoxicity of a new palladium(II) complex with a coumarine-derived ligand.

The new coumarine derivative, 3-(1-(2-hydroxyethylamino)ethylidene)chroman-2,4--dione, and corresponding palladium(II) complex have been synthesized and characterized by microanalysis, infrared, (1)H and (13)C NMR spectroscopy. The proposed structure of the complex was confirmed on the basis of the X-ray structural study. The palladium(II) complex decreased viability of L929 mouse fibrosarcoma, U251 human glioma and B16 mouse melanoma cell lines in a dose dependent manner, while its ligand exhibited no significant cytotoxicity. The cytotoxic effect of the complex was comparable to that of cisplatin, and mediated by apoptosis associated with oxidative stress, mitochondrial depolarization and caspase activation. Therefore, our results indicate that newly synthesized palladium(II) complex might be a potential candidate for anticancer therapy.