Regulation of autophagy by kinases

Glioblastoma, hypoxia and autophagy: a survival-prone 'ménage-à-trois'

Glioblastoma multiforme is the most common and the most aggressive primary brain tumor. It is characterized by a high degree of hypoxia and also by a remarkable resistance to therapy because of its adaptation capabilities that include autophagy. This degradation process allows the recycling of cellular components, leading to the formation of metabolic precursors and production of adenosine triphosphate. Hypoxia can induce autophagy through the activation of several autophagy-related proteins such as BNIP3, AMPK, REDD1, PML, and the unfolded protein response-related transcription factors ATF4 and CHOP. This review summarizes the most recent data about induction of autophagy under hypoxic condition and the role of autophagy in glioblastoma.

Crosstalk between autophagy and intracellular radiation response (Review)

Autophagy induced by radiation is critical to cell fate decision. Evidence now sheds light on the importance of autophagy induced by cancer radiotherapy. Traditional view considers radiation can directly or indirectly damage DNA which can activate DNA damage the repair signaling pathway, a large number of proteins participating in DNA damage repair signaling pathway such as p53, ATM, PARP1, FOXO3a, mTOR and SIRT1 involved in autophagy regulation. However, emerging recent evidence suggests radiation can also cause injury to extranuclear targets such as plasma membrane, mitochondria and endoplasmic reticulum (ER) and induce accumulation of ceramide, ROS, and Ca2+ concentration which activate many signaling pathways to modulate autophagy. Herein we review the role of autophagy in radiation therapy and the potent intracellular autophagic triggers induced by radiation. We aim to provide a more theoretical basis of radiation-induced autophagy, and provide novel targets for developing cytotoxic drugs to increase radiosensitivity.

May autophagy be a novel biomarker and antitumor target in colorectal cancer?

Autophagy is a catabolic process associated with intracellular self-digestion of damaged organelles or redundant proteins enabling maintenance of cell homeostasis. It is accepted that impaired autophagy is closely linked to cancer development and has been extensively studied in a variety of malignancies including colorectal cancer (CRC) to elucidate its influence on carcinogenesis, metastasis and antitumor therapy response. CRC remains a great epidemiological problem because of poor 5-year survival and treatment resistance. Many studies concerning autophagy in CRC gave inconsistent and contradictory results, illustrating a multifaceted nature of this process. In this review, we focus on current knowledge of autophagy in CRC development to determinate its role as a potential prognostic and predictive biomarker as well as target in antitumor therapy.

Herpesvirus-Associated Lymphadenitis Distorts Fibroblastic Reticular Cell Microarchitecture and Attenuates CD8 T Cell Responses to Neurotropic Infection in Mice Lacking the STING-IFNα/β Defense Pathways

Type I IFN (IFN-α/β)-driven immune responses to acute viral infection are critical to counter replication and prevent dissemination. However, the mechanisms underlying host resistance to HSV type 1 (HSV-1) are incompletely understood. In this study, we show that mice with deficiencies in IFN-α/β signaling or stimulator of IFN genes (STING) exhibit exacerbated neurovirulence and atypical lymphotropic dissemination of HSV-1 following ocular infection. Synergy between IFN-α/β signaling and efficacy of early adaptive immune responses to HSV-1 were dissected using bone marrow chimeras and adoptive cell transfer approaches to profile clonal expansion, effector function, and recruitment of HSV-specific CD8(+) T cells. Lymphotropic viral dissemination was commensurate with abrogated CD8(+) T cell responses and pathological alterations of fibroblastic reticular cell networks in the draining lymph nodes. Our results show that resistance to HSV-1 in the trigeminal ganglia during acute infection is conferred in part by STING and IFN-α/β signaling in both bone marrow-derived and -resident cells, which coalesce to support a robust HSV-1-specific CD8(+) T cell response.

Autophagy regulates Selumetinib (AZD6244) induced-apoptosis in colorectal cancer cells

OBJECTIVE

As Selumetinib is a MEK1/2 inhibitor that has gained interest as an anti-tumor agent, the present study was designed to investigate autophagy involvement on Selumetinib-induced apoptosis in colorectal cancer (CRC) cells.

METHODS

CRC cells death and cycle studies were assessed by AnnexinV-FITC and PI staining, respectively. Autophagy flux was analysed by Western Blot (LC3II and p62 protein levels) and retroviral infection of SW480 cells for siBecn1 RNA interference experiments. Confocal microscopy was used to determine mCherry-EGFP-LC3 distribution.

KEY FINDINGS

The Selumetinib effects were concentration-dependent in SW480 cell line. Whereas 1 μM exerted an arrest in the cell cycle (G1 phase), higher concentrations (10 μM) induced cell death, which was accompanied by autophagy blockage in its last stages. Autophagy induction by Rapamycin (RAPA) increased cell survival, whereas pharmacology autophagy inhibition by Bafilomycin A1 (BAF), Chloroquine (CQ) or 3-Methyladenine (3-MA) increased Selumetinib-induced CRC cells death.

CONCLUSIONS

Altogether, these results suggest that autophagy plays a fundamental role in CRC cells response to Selumetinib. In addition, the combination of Selumetinib with autophagy inhibitors may be a useful therapeutic strategy to enhance its activity against colorectal tumours.

Melatonin Suppresses Autophagy Induced by Clinostat in Preosteoblast MC3T3-E1 Cells

Microgravity exposure can cause cardiovascular and immune disorders, muscle atrophy, osteoporosis, and loss of blood and plasma volume. A clinostat device is an effective ground-based tool for simulating microgravity. This study investigated how melatonin suppresses autophagy caused by simulated microgravity in preosteoblast MC3T3-E1 cells. In preosteoblast MC3T3-E1 cells, clinostat rotation induced a significant time-dependent increase in the levels of the autophagosomal marker microtubule-associated protein light chain (LC3), suggesting that autophagy is induced by clinostat rotation in these cells. Melatonin treatment (100, 200 nM) significantly attenuated the clinostat-induced increases in LC3 II protein, and immunofluorescence staining revealed decreased levels of both LC3 and lysosomal-associated membrane protein 2 (Lamp2), indicating a decrease in autophagosomes. The levels of phosphorylation of mammalian target of rapamycin (p-mTOR) (Ser2448), phosphorylation of extracellular signal-regulated kinase (p-ERK), and phosphorylation of serine-threonine protein kinase (p-Akt) (Ser473) were significantly reduced by clinostat rotation. However, their expression levels were significantly recovered by melatonin treatment. Also, expression of the Bcl-2, truncated Bid, Cu/Zn- superoxide dismutase (SOD), and Mn-SOD proteins were significantly increased by melatonin treatment, whereas levels of Bax and catalase were decreased. The endoplasmic reticulum (ER) stress marker GRP78/BiP, IRE1α, and p-PERK proteins were significantly reduced by melatonin treatment. Treatment with the competitive melatonin receptor antagonist luzindole blocked melatonin-induced decreases in LC3 II levels. These results demonstrate that melatonin suppresses clinostat-induced autophagy through increasing the phosphorylation of the ERK/Akt/mTOR proteins. Consequently, melatonin appears to be a potential therapeutic agent for regulating microgravity-related bone loss or osteoporosis.

Inhibition of autophagic flux by ROS promotes apoptosis during DTT-induced ER/oxidative stress in HeLa cells

As targets for cancer therapy, endoplasmic reticulum (ER) stress and autophagy are closely linked. However, the signaling pathways responsible for induction of autophagy in response to ER stress and its cellular consequences appear to vary with cell type and stimulus. In the present study, we showed that dithiothreitol (DTT) induced ER stress in HeLa cells in a time- and dose-dependent fashion. With increased ER stress, reactive oxygen species (ROS) production increased and autophagy flux, assessed by intracellular accumulation of LC3B-II and p62, was inhibited. N-acetyl-L-cysteine (NAC), a classic antioxidant, exacerbated cell death induced by 3.2 mM of DTT, but attenuated that induced by 6.4 mM DTT. Low cytotoxic doses of DTT transiently activated c-JNU N-terminal kinase (JNK) and p38, whereas high dose of DTT persistently activated JNK and p38 and simultaneously reduced extracellular signal-regulated kinase (ERK) activity. Combined treatment with DTT and U0126, an inhibitor of ERK upstream activators mitogen-activated protein kinase (MAPK) kinase 1 and 2 (MEK1/2), blocked autophagy flux in HeLa cells. This effect was similar to that caused by a combination of DTT and chloroquine (CQ). These data suggested that insufficient autophagy was accompanied by increased ROS production during DTT-induced ER stress. ROS appeared to regulate MAPK signaling, switching from a pro-survival to a pro-apoptotic signal as ER stress increased. ERK inhibition by ROS during severe ER stress blocked autophagic flux. Impaired autophagic flux, in turn, aggravated ER stress, ultimately leading to cell death. Taken together, our data provide the first reported evidence that ROS may control cell fate through regulating the MAPK pathways and autophagic flux during DTT-induced ER/oxidative stress.

Oxysterols and mechanisms of survival signaling

Oxysterols, a family of oxidation products of cholesterol, are increasingly drawing attention of scientists to their multifaceted biochemical properties, several of them of clear relevance to human pathophysiology. Taken up by cells through both vesicular and non-vesicular ways or often generated intracellularly, oxysterols contribute to modulate not only the inflammatory and immunological response but also cell viability, metabolism and function by modulating several signaling pathways. Moreover, they have been recognized as elective ligands for the most important nuclear receptors. The outcome of such a complex network of intracellular reactions promoted by these cholesterol oxidation products appears to be largely dependent not only on the type of cells, the dynamic conditions of the cellular and tissue environment but also on the concentration of the oxysterols. Here focus has been given to the cascade of molecular events exerted by relatively low concentrations of certain oxysterols that elicit survival and functional signals in the cells, with the aim to contribute to further expand the knowledge about the biological and physiological potential of the biochemical reactions triggered and modulated by oxysterols.

BRAF associated autophagy exploitation: BRAF and autophagy inhibitors synergise to efficiently overcome resistance of BRAF mutant colorectal cancer cells

Autophagy is the basic catabolic mechanism that involves cell degradation of unnecessary or dysfunctional cellular components. Autophagy has a controversial role in cancer--both in protecting against tumor progression by isolation of damaged organelles, or by potentially contributing to cancer growth. The impact of autophagy in RAS induced transformation still remains to be further analyzed based on the differential effect of RAS isoforms and tumor cell context. In the present study, the effect of KRAS/BRAF/PIK3CA oncogenic pathways on the autophagic cell properties and on main components of the autophagic machinery like p62 (SQSTM1), Beclin-1 (BECN1) and MAP1LC3 (LC3) in colon cancer cells was investigated. This study provides evidence that BRAF oncogene induces the expression of key autophagic markers, like LC3 and BECN1 in colorectal tumor cells. Herein, PI3K/AKT/MTOR inhibitors induce autophagic tumor properties, whereas RAF/MEK/ERK signalling inhibitors reduce expression of autophagic markers. Based on the ineffectiveness of BRAFV600E inhibitors in BRAFV600E bearing colorectal tumors, the BRAF related autophagic properties in colorectal cancer cells are further exploited, by novel combinatorial anti-cancer protocols. Strong evidence is provided here that pre-treatment of autophagy inhibitor 3-MA followed by its combination with BRAFV600E targeting drug PLX4720 can synergistically sensitize resistant colorectal tumors. Notably, colorectal cancer cells are very sensitive to mono-treatments of another autophagy inhibitor, Bafilomycin A1. The findings of this study are expected to provide novel efficient protocols for treatment of otherwise resistant colorectal tumors bearing BRAFV600E, by exploiting the autophagic properties induced by BRAF oncogene.

Clearance of Damaged Mitochondria Through PINK1 Stabilization by JNK and ERK MAPK Signaling in Chlorpyrifos-Treated Neuroblastoma Cells

Mitochondrial quality control and clearance of damaged mitochondria through mitophagy are important cellular activities. Studies have shown that PTEN-induced putative protein kinase 1 (PINK1) and Parkin play central roles in triggering mitophagy; however, little is known regarding the mechanism by which PINK1 modulates mitophagy in response to reactive oxygen species (ROS)-induced stress. In this study, chlorpyrifos (CPF)-induced ROS caused mitochondrial damage and subsequent engulfing of mitochondria in double-membrane autophagic vesicles, indicating that clearance of damaged mitochondria is due to mitophagy. CPF treatment resulted in PINK1 stabilization on the outer mitochondrial membrane and subsequently increased Parkin recruitment from the cytosol to the abnormal mitochondria. We found that PINK1 physically interacts with Parkin in the mitochondria of CPF-treated cells. Furthermore, a knockdown of PINK1 strongly inhibited the LC3-II protein level by blocking Parkin recruitment. This indicates that CPF-induced mitophagy is due to PINK1 stabilization in mitochondria. We observed that PINK1 stabilization was selectively regulated by ROS-mediated c-Jun N-terminal kinase (JNK) and extracellular signal-regulated kinase 1/2 (ERK1/2) signaling activation but not p38 signaling. In the mitochondria of CPF-exposed cells, pretreatment with specific inhibitors of JNK and ERK1/2 significantly decreased PINK1 stabilization and Parkin recruitment and blocked the LC3-II protein level. Specifically, JNK and ERK1/2 inhibition also dramatically blocked the interaction between PINK1 and Parkin. Our results demonstrated that PINK1 regulation plays a critical role in CPF-induced mitophagy. The simple interpretation of these results is that JNK and ERK1/2 signaling regulates PINK1/Parkin-dependent mitophagy in the mitochondria of CPF-treated cells. Overall, this study proposes a novel molecular regulatory mechanism of PINK1 stabilization under CPF exposure.

Zapotin (5,6,2',6'-tetramethoxyflavone) Modulates the Crosstalk Between Autophagy and Apoptosis Pathways in Cancer Cells with Overexpressed Constitutively Active PKCϵ

Autophagy is important in the regulation of survival and death signaling pathways in cancer. PKCϵ revealed high transforming potential and the ability to increase cell migration, invasion, and metastasis. Zapotin (5,6,2',6'-tetramethoxyflavone), a natural flavonoid, showed chemopreventive and anticancer properties. Previously, we reported that downmodulation of induced PKCϵ level by zapotin was associated with decreased migration and increased apoptosis in HeLa cell line containing doxycycline-inducible constitutively active PKCϵ (PKCϵA/E, Ala(159) → Glu). Depending on the genetic and environmental content of cells, autophagy may either precede apoptosis or occur simultaneously. The purpose of this study was to assess the effect of zapotin on autophagy. Increasing concentration of zapotin (from 7.5 µM to 30 µM) caused an inhibition of the formation of autophagosomes and a decline in microtubule-associated protein 1 light chain 3 (LC3) protein levels. The gene expression level of major negative regulator of autophagy was noticeably increased. Moreover, the expression of the pivotal autophagy genes was decreased. These changes were accompanied by alternation in autophagy-related protein levels. In conclusion, our results implied that both the antiautophagic and the proapoptosis effect of zapotin in HeLaPKCϵA/E cells are associated with the protein kinase C epsilon signaling pathway and lead to programmed cell death.

c-Jun N-terminal kinase activation by nitrobenzoxadiazoles leads to late-stage autophagy inhibition

BACKGROUND

Nitrobenzoxadiazole derivatives (NBDs), including NBDHEX and the recently developed MC3181, are promising anticancer agents able to target glutathione transferase and inhibit both its catalytic activity and ability to sequester TNF-receptor associated factor 2 (TRAF2) and c-Jun N-terminal kinase (JNK). NBDs have been shown to impair the growth and survival of a broad-spectrum of tumor types, in vitro and in vivo. Herein, we evaluated the effects of the new compound MC3181 on U-2OS osteosarcoma cells and investigated the impact of both NBDHEX and MC3181 on autophagy.

METHODS

Cell viability was evaluated by sulforhodamine B assay. The dissociation of the TRAF2-GSTP1-1 complex was detected by proximity ligation assay, while the phospho-activation of JNK was assessed by western blotting. The effects of NBDs on autophagy were evaluated by GFP-LC3 puncta formation, western blotting for LC3-II and p62, and LC3 turnover assay in the presence of bafilomycin A1. The role of JNK in the reduction of autophagic flux caused by NBDs was investigated using JNK1 shRNA-transfected cells. Fluorogenic caspase activity assay and flow cytometric analysis of DNA content were used to determine the cytotoxic effects of NBDs on JNK1-silenced cells.

RESULTS

Similar to NBDHEX, MC3181 reduced viability and activated TRAF2/JNK signaling in U-2OS cells. Moreover, NBDs induced the accumulation of autophagic vesicles and LC3-II while reducing both basal and nutritional stress-induced autophagic flux. Furthermore, increased levels of both LC3-II and the autophagy selective substrate p62 were observed in different tumor cell lines treated with NBDs, the concurrent increase of these markers being consistent with an impairment of autophagosome clearance. Autophagy inhibition by NBDs required JNK activity: NBDs caused autophagy inhibition and caspase-3 activation in JNK-positive U-2OS, but no autophagic flux inhibition or caspase-3 activation in JNK-silenced cells.

CONCLUSIONS

Our demonstration that NBDs can act as late-phase autophagy inhibitors opens new opportunities to fully exploit their therapeutic potential. This may not rely solely on their effectiveness in inducing cell cycle arrest and apoptosis, but also on their ability to weaken the capacity of tumor cells to endure stress conditions via autophagy. In addition, this study provides evidence that JNK can participate in impairing autophagy.

MytiLec, a Mussel R-Type Lectin, Interacts with Surface Glycan Gb3 on Burkitt's Lymphoma Cells to Trigger Apoptosis through Multiple Pathways

MytiLec; a novel lectin isolated from the Mediterranean mussel (Mytilus galloprovincialis); shows strong binding affinity to globotriose (Gb3: Galα1-4Galβ1-4Glc). MytiLec revealed β-trefoil folding as also found in the ricin B-subunit type (R-type) lectin family, although the amino acid sequences were quite different. Classification of R-type lectin family members therefore needs to be based on conformation as well as on primary structure. MytiLec specifically killed Burkitt's lymphoma Ramos cells, which express Gb3. Fluorescein-labeling assay revealed that MytiLec was incorporated inside the cells. MytiLec treatment of Ramos cells resulted in activation of both classical MAPK/ extracellular signal-regulated kinase and extracellular signal-regulated kinase (MEK-ERK) and stress-activated (p38 kinase and JNK) Mitogen-activated protein kinases (MAPK) pathways. In the cells, MytiLec treatment triggered expression of tumor necrosis factor (TNF)-α (a ligand of death receptor-dependent apoptosis) and activation of mitochondria-controlling caspase-9 (initiator caspase) and caspase-3 (activator caspase). Experiments using the specific MEK inhibitor U0126 showed that MytiLec-induced phosphorylation of the MEK-ERK pathway up-regulated expression of the cyclin-dependent kinase inhibitor p21, leading to cell cycle arrest and TNF-α production. Activation of caspase-3 by MytiLec appeared to be regulated by multiple different pathways. Our findings, taken together, indicate that the novel R-type lectin MytiLec initiates programmed cell death of Burkitt's lymphoma cells through multiple pathways (MAPK cascade, death receptor signaling; caspase activation) based on interaction of the lectin with Gb3-containing glycosphingolipid-enriched microdomains on the cell surface.

The synthetic β-nitrostyrene derivative CYT-Rx20 induces breast cancer cell death and autophagy via ROS-mediated MEK/ERK pathway

The β-nitrostyrene family has been shown to suppress cancer cell proliferation and induce programmed cell death. However, mechanisms underlying β-nitrostyrenes remain less evaluated. Here, we synthesized a β-nitrostyrene derivative, CYT-Rx20, and characterized its anticancer effect and involving mechanisms in breast cancer. We found that CYT-Rx20 arrested breast cancer cells at G2/M phase and decreased cell viability by activating the caspase cascade, accompanying with increases of poly (ADP-ribose) polymerase (PARP) cleavage and γ-H2AX expression. On the other hand, up-regulation of Beclin-1, ATG5, and LC-3 was observed in CYT-Rx20-induced autophagy, which was evidently shown by transmission electron microscopy. In addition to these, CYT-Rx20-induced breast cancer cell death, intracellular reactive oxygen species (ROS) formation and expression of phospho-ERK1/2, Beclin-1, and LC-3 were significantly reversed in the presence of N-acetyl-l-cysteine (NAC), a thiol antioxidant. Furthermore, the cytotoxicity of CYT-Rx20 was enhanced by co-treatment with the autophagy inhibitor chloroquine or bafilomycin A1, suggesting that an incomplete autophagy process could deteriorate CYT-Rx20-induced cytotoxicity. In nude mice xenograft study, CYT-Rx20 significantly reduced orthotopic tumor growth. Immunohistochemical analysis revealed elevated expression of phospho-ERK1/2 and LC-3 in tumor tissues of the mice treated with CYT-Rx20. Together, we propose that CYT-Rx20 may have potential to be further developed into a β-nitrostyrene-based anticancer compound for the treatment of breast cancer.

The autophagic- lysosomal pathway determines the fate of glial cells under manganese- induced oxidative stress conditions

Manganese (Mn) overexposure is frequently associated with the development of a neurodegenerative disorder known as Manganism. The Mn-mediated generation of reactive oxygen species (ROS) promotes cellular damage, finally leading to apoptotic cell death in rat astrocytoma C6 cells. In this scenario, the autophagic pathway could play an important role in preventing cytotoxicity. In the present study, we found that Mn induced an increase in the amount and total volume of acidic vesicular organelles (AVOs), a process usually related to the activation of the autophagic pathway. Particularly, the generation of enlarged AVOs was a ROS- dependent event. In this report we demonstrated for the first time that Mn induces autophagy in glial cells. This conclusion emerged from the results obtained employing a battery of autophagy markers: a) the increase in LC3-II expression levels, b) the formation of autophagic vesicles labeled with monodansylcadaverine (MDC) or LC3 and, c) the increase in Beclin 1/ Bcl-2 and Beclin 1/ Bcl-X(L) ratio. Autophagy inhibition employing 3-MA and mAtg5(K130R) resulted in decreased cell viability indicating that this event plays a protective role in Mn- induced cell death. In addition, mitophagy was demonstrated by an increase in LC3 and TOM-20 colocalization. On the other hand, we proposed the occurrence of lysosomal membrane permeabilization (LMP) based in the fact that cathepsins B and D activities are essential for cell death. Both cathepsin B inhibitor (Ca-074 Me) or cathepsin D inhibitor (Pepstatin A) completely prevented Mn- induced cytotoxicity. In addition, low dose of Bafilomycin A1 showed a similar effect, a finding that adds evidence about the lysosomal role in Mn cytotoxicity. Finally, in vivo experiments demonstrated that Mn induces injury and alters LC3 expression levels in rat striatal astrocytes. In summary, our results demonstrated that autophagy is activated to counteract the harmful effect caused by Mn. These data is valuable to be considered in future research concerning Manganism therapies.

Dehydroepiandrosterone prevents linoleic acid-induced endothelial cell senescence by increasing autophagy

BACKGROUND

Autophagy has emerged as a potentially important factor in the pathogenesis of atherosclerosis. Dehydroepiandrosterone (DHEA) is an adrenal steroid of great recent interest due to its anti-aging and anti-atherogenic effects; however, little is known about its role in autophagy and endothelial senescence.

OBJECTIVE

The aim of this study was to investigate whether DHEA prevents linoleic acid (LA)-induced endothelial senescence by enhancing autophagy.

MATERIALS/METHODS

After pre-treatement with or without DHEA prior to LA treatment in human aortic endothelial cells (HAECs), the level of senescence was compared by senescence-associated acidic β-galactosidase (SA-β-Gal) staining and hyperphosphorylated pRB (ppRB) protein level. Autophagy was detected by LC3 conversion and measuring the level of p62/SQSTM1 (sequestosome 1), a protein degraded by autophagy. The fusion of autophagosome and lysosome was confirmed by fluorescence microscopy.

RESULTS

Pre-treatment with DHEA inhibited LA-induced endothelial senescence. DHEA increased the conversion of LC3-I to LC3-II and decreased the level of p62 in a time- and dose-dependent manner. Although both DHEA and LA treatment increased the conversion of LC3-I to LC3-II, treatment of LA increased p62 and decreased fusion of autophagosome and lysosome, which reflected decreased autophagic flux. However, pre-treatment with DHEA restored autophagic flux inhibited by LA. When we evaluated signaling pathways, we found that JNK activation involved in LC3 conversion induced by DHEA.

CONCLUSION

DHEA prevents LA-induced endothelial senescence by restoring autophagy and autophagic flux through JNK activation.

Rhus coriaria induces senescence and autophagic cell death in breast cancer cells through a mechanism involving p38 and ERK1/2 activation

Here, we investigated the anticancer effect of Rhus coriaria on three breast cancer cell lines. We demonstrated that Rhus coriaria ethanolic extract (RCE) inhibits the proliferation of these cell lines in a time- and concentration-dependent manner. RCE induced senescence and cell cycle arrest at G1 phase. These changes were concomitant with upregulation of p21, downregulation of cyclin D1, p27, PCNA, c-myc, phospho-RB and expression of senescence-associated β-galactosidase activity. No proliferative recovery was detected after RCE removal. Annexin V staining and PARP cleavage analysis revealed a minimal induction of apoptosis in MDA-MB-231 cells. Electron microscopy revealed the presence of autophagic vacuoles in RCE-treated cells. Interestingly, blocking autophagy by 3-methyladenine (3-MA) or chloroquine (CQ) reduced RCE-induced cell death and senescence. RCE was also found to activate p38 and ERK1/2 signaling pathways which coincided with induction of autophagy. Furthermore, we found that while both autophagy inhibitors abolished p38 phosphorylation, only CQ led to significant decrease in pERK1/2. Finally, RCE induced DNA damage and reduced mutant p53, two events that preceded autophagy. Our findings provide strong evidence that R. coriaria possesses strong anti-breast cancer activity through induction of senescence and autophagic cell death, making it a promising alternative or adjunct therapeutic candidate against breast cancer.

The Novel Anticancer Drug Hydroxytriolein Inhibits Lung Cancer Cell Proliferation via a Protein Kinase Cα- and Extracellular Signal-Regulated Kinase 1/2-Dependent Mechanism

Membrane lipid therapy is a novel approach to rationally design or discover therapeutic molecules that target membrane lipids. This strategy has been used to design synthetic fatty acid analogs that are currently under study in clinical trials for the treatment of cancer. In this context, and with the aim of controlling tumor cell growth, we have designed and synthesized a hydroxylated analog of triolein, hydroxytriolein (HTO). Both triolein and HTO regulate the biophysical properties of model membranes, and they inhibit the growth of non-small-cell lung cancer (NSCLC) cell lines in vitro. The molecular mechanism underlying the antiproliferative effect of HTO involves regulation of the lipid membrane structure, protein kinase C-α and extracellular signal-regulated kinase activation, the production of reactive oxygen species, and autophagy. In vivo studies on a mouse model of NSCLC showed that HTO, but not triolein, impairs tumor growth, which could be associated with the relative resistance of HTO to enzymatic degradation. The data presented explain in part why olive oil (whose main component is the triacylglycerol triolein) is preventive but not therapeutic, and they demonstrate a potent effect of HTO against cancer. HTO shows a good safety profile, it can be administered orally, and it does not induce nontumor cell (fibroblast) death in vitro or side effects in mice, reflecting its specificity for cancer cells. For these reasons, HTO is a good candidate as a drug to combat cancer that acts by regulating lipid structure and function in the cancer cell membrane.

Naringin induces autophagy-mediated growth inhibition by downregulating the PI3K/Akt/mTOR cascade via activation of MAPK pathways in AGS cancer cells

Naringin, one of the major bioflavonoid of Citrus, has been demonstrated as potential anticancer agent. However, the underlying anticancer mechanism still needs to be explored further. This study investigated the inhibitory effect of Naringin on human AGS cancer cells. AGS cell proliferation was inhibited by Naringin in a dose- and time-dependent manner. Naringin did not induce apoptotic cell death, determined by no DNA fragmentation and the reduced Bax/Bcl-xL ratio. Growth inhibitory role of Naringin was observed by western blot analysis demonstrating downregulation of PI3K/Akt/mTOR cascade with an upregulated p21CIPI/WAFI. Formation of cytoplasmic vacuoles and autophagosomes were observed in Naringin-treated AGS cells, further confirmed by the activation of autophagic proteins Beclin 1 and LC3B with a significant phosphorylation of mitogen activated protein kinases (MAPKs). Collectively, our observed results determined that anti-proliferative activity of Naringin in AGS cancer cells is due to suppression of PI3K/Akt/mTOR cascade via induction of autophagy with activated MAPKs. Thus, the present finding suggests that Naringin induced autophagy- mediated growth inhibition shows potential as an alternative therapeutic agent for human gastric carcinoma.

MiR-26a enhances autophagy to protect against ethanol-induced acute liver injury

Abstract

Autophagy is a process for the turnover of intracellular organelles and molecules during stress responses. microRNAs (miRNAs) are small, non-coding endogenous RNAs that may regulate almost every cellular process. However, the roles of miRNAs in autophagy are still poorly understood. In this study, we show that miR-26a enhances autophagy in both culture cells and the mouse liver. Hepatic overexpression of miR-26a in mice alleviated ethanol-induced hepatic steatosis and liver injury. Overexpression of miR-26a increased the expression of the autophagy mediator Beclin-1, which is regulated by mitogen-activated protein kinases (MAPKs). We identified DUSP4 and DUSP5, two MAPKs inhibitors, as direct targets of miR-26a. We further demonstrated that miR-26a targeted the 3′-UTRs of several other negative regulators of autophagy. Our results thus identify a novel miRNA-mediated mechanism that enhances cytoprotective autophagy in the liver.

Key messages

• miR-26a enhances autophagy in liver cells.

• Hepatic overexpression of miR-26a in mice alleviates ethanol-induced liver injury.

• Overexpression of miR-26a increases the expression of autophagy mediator Beclin-1.

• DUSP4 and DUSP5, two MAPKs inhibitors, were identified as direct targets of miR-26a.

Electronic supplementary material

The online version of this article (doi:10.1007/s00109-015-1282-2) contains supplementary material, which is available to authorized users.

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, β-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 β-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.

PKC theta and p38 MAPK activate the EBV lytic cycle through autophagy induction

PKC activation by combining TPA with sodium butyrate (T/B) represents the most effective and widely used strategy to induce the Epstein-Barr virus (EBV) lytic cycle. The results obtained in this study show that novel PKCθ is involved in such process and that it acts through the activation of p38 MAPK and autophagy induction. Autophagy, a mechanism of cellular defense in stressful conditions, is manipulated by EBV to enhance viral replication. Besides promoting the EBV lytic cycle, the activation of p38 and autophagy resulted in a pro-survival effect, as indicated by p38 or ATG5 knocking down experiments. However, this pro-survival role was counteracted by a pro-death activity of PKCθ, due to the dephosphorylation of AKT. In conclusion, this study reports, for the first time, that T/B activates a PKCθ-p38 MAPK axis in EBV infected B cells, that promotes the viral lytic cycle and cell survival and dephosphorylates AKT, balancing cell life and cell death.

[D-Lys3]-GHRP-6 exhibits pro-autophagic effects on skeletal muscle

[D-Lys3]-GHRP-6 is regarded as a highly selective growth-hormone secretagogue receptor (GHSR) antagonist and has been widely used to investigate the dependency of GHSR-1a signalling mediated by acylated ghrelin. However, [D-Lys3]-GHRP-6 has been reported to influence other cellular processes which are unrelated to GHSR-1a. This study aimed to examine the effects of [D-Lys3]-GHRP-6 on autophagic and apoptotic cellular signalling in skeletal muscle. [D-Lys3]-GHRP-6 enhanced the autophagic signalling demonstrated by the increases in protein abundances of beclin-1 and LC3 II-to-LC3 1 ratio in both normal muscle and doxorubicin-injured muscle. [D-Lys3]-GHRP-6 reduced the activation of muscle apoptosis induced by doxorubicin. No histological abnormalities were observed in the [D-Lys3]-GHRP-6-treated muscle. Intriguingly, the doxorubicin-induced increase in centronucleated muscle fibres was not observed in muscle treated with [D-Lys3]-GHRP-6, suggesting the myoprotective effects of [D-Lys3]-GHRP-6 against doxorubicin injury. The [D-Lys3]-GHRP-6-induced activation of autophagy was found to be abolished by the co-treatment of CXCR4 antagonist, suggesting that the pro-autophagic effects of [D-Lys3]-GHRP-6 might be mediated through CXCR4. In conclusion, [D-Lys3]-GHRP-6 exhibits pro-autophagic effects on skeletal muscle under both normal and doxorubicin-injured conditions.

Transcription factors and cognate signalling cascades in the regulation of autophagy

Autophagy is a process that maintains the equilibrium between biosynthesis and the recycling of cellular constituents; it is critical for avoiding the pathophysiology that results from imbalance in cellular homeostasis. Recent reports indicate the need for the design of high-throughput screening assays to identify targets and small molecules for autophagy modulation. For such screening, however, a better understanding of the regulation of autophagy is essential. In addition to regulation by various signalling cascades, regulation of gene expression by transcription factors is also critical. This review focuses on the various transcription factors as well as the corresponding signalling molecules that act together to translate the stimuli to effector molecules that up- or downregulate autophagy. This review rationalizes the importance of these transcription factors functioning in tandem with cognate signalling molecules and their interfaces as possible therapeutic targets for more specific pharmacological interventions.

Regulation of the Tumor-Suppressor Function of the Class III Phosphatidylinositol 3-Kinase Complex by Ubiquitin and SUMO

The occurrence of cancer is often associated with a dysfunction in one of the three central membrane-involution processes—autophagy, endocytosis or cytokinesis. Interestingly, all three pathways are controlled by the same central signaling module: the class III phosphatidylinositol 3-kinase (PI3K-III) complex and its catalytic product, the phosphorylated lipid phosphatidylinositol 3-phosphate (PtdIns3P). The activity of the catalytic subunit of the PI3K-III complex, the lipid-kinase VPS34, requires the presence of the membrane-targeting factor VPS15 as well as the adaptor protein Beclin 1. Furthermore, a growing list of regulatory proteins associates with VPS34 via Beclin 1. These accessory factors define distinct subunit compositions and thereby guide the PI3K-III complex to its different cellular and physiological roles. Here we discuss the regulation of the PI3K-III complex components by ubiquitination and SUMOylation. Especially Beclin 1 has emerged as a highly regulated protein, which can be modified with Lys11-, Lys48- or Lys63-linked polyubiquitin chains catalyzed by distinct E3 ligases from the RING-, HECT-, RBR- or Cullin-type. We also point out other cross-links of these ligases with autophagy in order to discuss how these data might be merged into a general concept.

Regulation of autophagic activation by Rta of Epstein-Barr virus via the extracellular signal-regulated kinase pathway

Autophagy is an intracellular degradation pathway that provides a host defense mechanism against intracellular pathogens. However, many viruses exploit this mechanism to promote their replication. This study shows that lytic induction of Epstein-Barr virus (EBV) increases the membrane-bound form of LC3 (LC3-II) and LC3-containing punctate structures in EBV-positive cells. Transfecting 293T cells with a plasmid that expresses Rta also induces autophagy, revealing that Rta is responsible for autophagic activation. The activation involves Atg5, a key component of autophagy, but not the mTOR pathway. The expression of Rta also activates the transcription of the genes that participate in the formation of autophagosomes, including LC3A, LC3B, and ATG9B genes, as well as those that are involved in the regulation of autophagy, including the genes TNF, IRGM, and TRAIL. Additionally, treatment with U0126 inhibits the Rta-induced autophagy and the expression of autophagy genes, indicating that the autophagic activation is caused by the activation of extracellular signal-regulated kinase (ERK) signaling by Rta. Finally, the inhibition of autophagic activity by an autophagy inhibitor, 3-methyladenine, or Atg5 small interfering RNA, reduces the expression of EBV lytic proteins and the production of viral particles, revealing that autophagy is critical to EBV lytic progression. This investigation reveals how an EBV-encoded transcription factor promotes autophagy to affect viral lytic development.

Monepantel induces autophagy in human ovarian cancer cells through disruption of the mTOR/p70S6K signalling pathway

We have recently shown that the novel anthelmintic drug monepantel (MPL) inhibits growth, proliferation and colony formation, arrests the cell cycle and induces cleavage of PARP-1 in ovarian cancer cell lines. Here we report on the mechanism behind the anticancer properties of MPL. The cytotoxic effect of MPL on ovarian cancer cells (OVCAR-3 and A2780) was investigated employing a panel of tests used for the detection of apoptosis and autophagy. Apoptosis and autophagy were defined by caspase activity, DNA-laddering, Annexin-V and acridine orange (AO) staining. Autophagy markers such as LC3B, SQSTM1/p62 and mammalian target of rapamycin (mTOR) pathway related proteins were assessed by western blotting and ELISA techniques. MPL did not activate caspases 3 or 8, nor did it alter the percentage of Annexin V positive stained cells. Failure to cause DNA laddering and the inability of z-VAD-fmk to block the MPL antiproliferative effects led to the ruling out of apoptosis as the mechanism behind MPL-induced cell death. On the other hand, accumulation of acidic vacuoles with distinct chromatin morphology and an increase in punctuate localization of green fluorescent protein-LC3B, and MPL-induced changes in the expression of SQSTM1/p62 were all indicative of MPL-induced autophagy. Consistent with this, we found inhibition of mTOR phosphorylation leading to suppression of the mTOR/p70S6K signalling pathway. Our findings provide the first evidence to show that MPL triggers autophagy through the deactivation of mTOR/p70S6K signalling pathway.

Oleanolic acid inhibits proliferation and invasiveness of Kras-transformed cells via autophagy

Oleanolic acid (OA) has been widely studied because of its pleiotropic therapeutic and preventive effect on various diseases. However, the mechanisms of OA's action are still not clear yet, especially its suppressing effect on transformed cells. In this work, we found that OA induced autophagy in normal tissue-derived cells without cytotoxicity. OA-induced autophagy was shown to decrease the proliferation of KRAS-transformed normal cells and to impair their invasion and anchorage-independent growth. Interrupting autophagy rescued OA's effect on the transformed cells. Mouse model experiments also demonstrated that OA suppressed the growth of KRAS-transformed breast epithelial cell MCF10A-derived tumor xenograft by inducing autophagy. Finally, we identified that OA induced autophagy in normal cells by inhibiting the activation of Akt/mTOR/S6K signaling. In conclusions, we found that OA treatment permitted normal cells to undergo autophagy. The induced autophagy was required for OA to prevent or delay the growth of transformed normal cells.

Itraconazole suppresses the growth of glioblastoma through induction of autophagy: involvement of abnormal cholesterol trafficking

Glioblastoma is one of the most aggressive human cancers with poor prognosis, and therefore a critical need exists for novel therapeutic strategies for management of glioblastoma patients. Itraconazole, a traditional antifungal drug, has been identified as a novel potential anticancer agent due to its inhibitory effects on cell proliferation and tumor angiogenesis; however, the molecular mechanisms involved are still unclear. Here, we show that itraconazole inhibits the proliferation of glioblastoma cells both in vitro and in vivo. Notably, we demonstrate that treatment with itraconazole induces autophagic progression in glioblastoma cells, while blockage of autophagy markedly reverses the antiproliferative activities of itraconazole, suggesting an antitumor effect of autophagy in response to itraconazole treatment. Functional studies revealed that itraconazole retarded the trafficking of cholesterol from late endosomes and lysosomes to the plasma membrane by reducing the levels of SCP2, resulting in repression of AKT1-MTOR signaling, induction of autophagy, and finally inhibition of cell proliferation. Together, our studies provide new insights into the molecular mechanisms regarding the antitumor activities of itraconazole, and may further assist both the pharmacological investigation and rational use of itraconazole in potential clinical applications.

Acylated and unacylated ghrelin inhibit doxorubicin-induced apoptosis in skeletal muscle

AIM

Doxorubicin, a potent chemotherapeutic drug, has been demonstrated previously as an inducer of apoptosis in muscle cells. Extensive induction of apoptosis may cause excessive loss of muscle cells and subsequent functional decline in skeletal muscle. This study examined the effects of acylated ghrelin, a potential agent for treating cancer cachexia, on inhibiting apoptotic signalling in doxorubicin-treated skeletal muscle. Unacylated ghrelin, a form of ghrelin that does not bind to GHSR-1a, is also employed in this study to examine the GHSR-1a signalling dependency of the effects of ghrelin.

METHODS

Adult C57BL/6 mice were randomly assigned to saline control (CON), doxorubicin (DOX), doxorubicin with treatment of acylated ghrelin (DOX+Acylated Ghrelin) and doxorubicin with treatment of unacylated ghrelin (DOX+Unacylated Ghrelin). Mice in all groups that involved DOX were intraperitoneally injected with 15 mg of doxorubicin per kg body weight, whereas mice in CON group received saline as placebo. Gastrocnemius muscle tissues were harvested after the experimental period for analysis.

RESULTS

The elevation of apoptotic DNA fragmentation and number of TUNEL-positive nuclei were accompanied with the upregulation of Bax in muscle after exposure to doxorubicin, but all these changes were neither seen in the muscle treated with acylated ghrelin nor unacylated ghrelin after doxorubicin exposure. Protein abundances of autophagic markers including LC3 II-to-LC3 I ratio, Atg12-5 complex, Atg5 and Beclin-1 were not altered by doxorubicin but were upregulated by the treatment of either acylated or unacyated ghrelin. Histological analysis revealed that the amount of centronucleated myofibres was elevated in doxorubicin-treated muscle while muscle of others groups showed normal histology.

CONCLUSIONS

Collectively, our data demonstrated that acylated ghrelin administration suppresses the doxorubicin-induced activation of apoptosis and enhances the cellular signalling of autophagy. The treatment of unacylated ghrelin has similar effects as acylated ghrelin on apoptotic and autophagic signalling, suggesting that the effects of ghrelin are probably mediated through a signalling pathway that is independent of GHSR-1a. These findings were consistent with the hypothesis that acylated ghrelin inhibits doxorubicin-induced upregulation of apoptosis in skeletal muscle while treatment of unacylated ghrelin can achieve similar effects as the treatment of acylated ghrelin. The inhibition of apoptosis and enhancement of autophagy induced by acylated and unacylated ghrelin might exert myoprotective effects on doxorubicin-induced toxicity in skeletal muscle.

Metformin aggravates immune-mediated liver injury in mice

Hepatotoxicity of the antidiabetic drug metformin has been reported, but the underlying mechanisms remain unclear. We here investigated the effect of metformin in immune-mediated liver damage. While not hepatotoxic alone, metformin (200 mg/kg) aggravated concanavalin A (Con A, 12 mg/kg)-induced hepatitis, an experimental model of T cell-mediated liver injury, in both relatively resistant BALB/c and highly susceptible C57Bl/6 mice. Metformin + Con A-treated mice had elevated serum levels of pro-inflammatory cytokines TNF-α and IFN-γ, accompanied by a massive mononuclear cell infiltration in the liver. This was associated with the higher numbers of CD4(+) T cells producing TNF-α, IFN-γ and IL-17, CD4(+) T cells expressing chemokine receptor CXCR3 and activation marker CD27, CD4(+)CD62L(-)CCR7(-) and CD8(+)CD62L(-)CCR7(-) effector memory cells, IFN-γ producing NK cells, IL-4 and IL-17 producing NKT cells and IL-12 producing macrophages/dendritic cells. The percentage of CD4(+)CXCR3(+)Tbet(+)IL-10(+) and CD4(+)CD69(+)CD25(-) regulatory T cells was reduced. Metformin stimulated inducible nitric oxide synthase (iNOS) expression in the liver and spleen, and genetic deletion of iNOS attenuated the hepatotoxicity of metformin. Metformin increased the autophagic light chain 3 conversion and mRNA expression of important autophagy-inducing (beclin-1, Atg5 and GABARAP) and pro-apoptotic (p21, p27, Puma, Noxa, Bax, Bad, Bak1, Bim and Apaf1), but not anti-apoptotic molecules (Bcl-xL, survivin and XIAP), which correlated with the apoptotic caspase-3/PARP cleavage in the liver. The autophagy inhibitor chloroquine (20 mg/kg) prevented liver injury and apoptotic changes induced by metformin. Therefore, metformin aggravates immune-mediated hepatitis by promoting autophagy and activation of immune cells, affecting effector, as well as liver-specific regulatory T cells and iNOS expression.

Methamphetamine induces autophagy as a pro-survival response against apoptotic endothelial cell death through the Kappa opioid receptor

Methamphetamine (METH) is a psychostimulant with high abuse potential and severe neurotoxicity. Recent studies in animal models have indicated that METH can impair the blood-brain barrier (BBB), suggesting that some of the neurotoxic effects resulting from METH abuse could be due to barrier disruption. We report here that while chronic exposure to METH disrupts barrier function of primary human brain microvascular endothelial cells (HBMECs) and human umbilical vein endothelial cells (HUVECs), an early pro-survival response is observed following acute exposure by induction of autophagic mechanisms. Acute METH exposure induces an early increase in Beclin1 and LC3 recruitment. This is mediated through inactivation of the protein kinase B (Akt)/mammalian target of rapamycin (mTOR)/p70S6K pathway, and upregulation of the ERK1/2. Blockade of Kappa opioid receptor (KOR), and treatment with autophagic inhibitors accelerated METH-induced apoptosis, suggesting that the early autophagic response is a survival mechanism for endothelial cells and is mediated through the kappa opioid receptor. Our studies indicate that kappa opioid receptor can be therapeutically exploited for attenuating METH-induced BBB dysfunction.

Correction of glycogen storage disease type III with rapamycin in a canine model

Recently, we reported that progression of liver fibrosis and skeletal myopathy caused by extensive accumulation of cytoplasmic glycogen at advanced age is the major feature of a canine model of glycogen storage disease (GSD) IIIa. Here, we aim to investigate whether rapamycin, a specific inhibitor of mTOR, is an effective therapy for GSD III. Our data show that rapamycin significantly reduced glycogen content in primary muscle cells from human patients with GSD IIIa by suppressing the expression of glycogen synthase and glucose transporter 1. To test the treatment efficacy in vivo, rapamycin was daily administered to GSD IIIa dogs starting from age 2 (early-treatment group) or 8 months (late-treatment group), and liver and skeletal muscle biopsies were performed at age 12 and 16 months. In both treatment groups, muscle glycogen accumulation was not affected at age 12 months but significantly inhibited at 16 months. Liver glycogen content was reduced in the early-treatment group but not in the late-treatment group at age 12 months. Both treatments effectively reduced liver fibrosis at age 16 months, consistent with markedly inhibited transition of hepatic stellate cells into myofibroblasts, the central event in the process of liver fibrosis. Our results suggest a potential useful therapy for GSD III.

KEY MESSAGES

Rapamycin inhibited glycogen accumulation in GSD IIIa patient muscle cells. Rapamycin reduced muscle glycogen content in GSD IIIa dogs at advanced age. Rapamycin effectively prevented progression of liver fibrosis in GSD IIIa dogs. Our results suggest rapamycin as potential useful therapy for patients with GSD III.

Role of PI3K/Akt/mTOR and MEK/ERK pathway in Concanavalin A induced autophagy in HeLa cells

Concanavalin A (Con A), a mannose or glucose specific legume lectin, is well known for its anti-proliferative and cytotoxic effect on different types of cancer cells, through its binding to the membrane receptors leading to a major stimulus for the induction of distinct metabolic responses. Recently it has been also been proved that, Con A induces autophagy in hepatoma cells through internalization and mitochondria mediated pathway involving a mitochondrial interacting protein named Bcl2/E1B-19kDa protein-interacting protein 3 (BNIP3). Through this current endeavor, we propose a membrane associated pathway involved in Con A induced autophagy, taking Human cervical cancer (HeLa) cell as a cancer model. Here, we deciphered the role of membrane mediated phosphatidylinositol 3 kinase (PI3K)/Akt/mTOR (mammalian target of rapamycin) and MEK/Extracellular signal-regulated kinases (ERK) pathway in Con A induced autophagy in HeLa cells. Subsequently, we found that Con A treatment suppresses the PI3K/Akt/mTOR and up regulates the MEK/ERK pathway leading to the activation of autophagy. This study will further help us to understand the mechanism behind the autophagic pathway induced by Con A and simultaneously it will strengthen its effective use as a prospective cancer chemo-therapeutic.

Samsoeum, a traditional herbal medicine, elicits apoptotic and autophagic cell death by inhibiting Akt/mTOR and activating the JNK pathway in cancer cells

Background

Samsoeum (SSE), a traditional herbal formula, has been widely used to treat cough, fever, congestion, and emesis for centuries. Recent studies have demonstrated that SSE retains potent pharmacological efficiency in anti-allergic and anti-inflammatory reactions. However, the anti-cancer activity of SSE and its underlying mechanisms have not been studied. Thus, the present study was designed to determine the effect of SSE on cell death and elucidate its detailed mechanism.

Methods

Following SSE treatment, cell growth and cell death were measured using an MTT assay and trypan blue exclusion assay, respectively. Cell cycle arrest and YO-PRO-1 uptake were assayed using flow cytometry, and LC3 redistribution was observed using confocal microscope. The mechanisms of anti-cancer effect of SSE were investigated through western blot analysis.

Results

We initially found that SSE caused dose- and time-dependent cell death in cancer cells but not in normal primary hepatocytes. In addition, during early SSE treatment (6–12 h), cells were arrested in G₂/M phase concomitant with up-regulation of p21 and p27 and down-regulation of cyclin D1 and cyclin B1, followed by an increase in apoptotic YO-PRO-1 (+) cells. SSE also induced autophagy via up-regulation of Beclin-1 expression, conversion of microtubule-associated protein light chain 3 (LC3) I to LC3-II, and re-distribution of LC3, indicating autophagosome formation. Moreover, the level of B-cell lymphoma 2 (Bcl-2), which is critical for cross-talk between apoptosis and autophagy, was significantly reduced in SSE-treated cells. Phosphorylation of adenosine monophosphate-activated protein kinase (AMPK) was increased, followed by suppression of the protein kinase B/mammalian target of rapamycin (Akt/mTOR) pathway, and phosphorylation of mitogen-activated protein kinases (MAPKs) in response to SSE treatment. In particular, among MAPKs inhibitors, only the c-Jun N-terminal kinase (JNK)-specific inhibitor SP600125 nearly blocked SSE-induced increases in Beclin-1, LC3-II, and Bax expression and decreases in Bcl-2 expression, indicating that JNK activation plays critical role in cell death caused by SSE.

Conclusions

These findings suggest that SSE efficiently induces cancer cell death via apoptosis as well as autophagy through modification of the Akt/mTOR and JNK signaling pathways. SSE may be as a potent traditional herbal medicine for treating malignancies.

Autophagy in breast cancer and its implications for therapy

Autophagy is an evolutionarily conserved process of cellular self-digestion that serves as a mechanism to clear damaged organelles and recycle nutrients. Since autophagy can promote cell survival as well as cell death, it has been linked to different human pathologies, including cancer. Although mono-allelic deletion of autophagy-related gene BECN1 in breast tumors originally indicated a tumor suppressive role for autophagy in breast cancer, the intense research during the last decade suggests a role for autophagy in tumor progression. It is now recognized that tumor cells often utilize autophagy to survive various stresses, such as oncogene-induced transformation, hypoxia, endoplasmic reticulum (ER) stress and extracellular matrix detachment. Induction of autophagy by tumor cells may also contribute to tumor dormancy and resistance to anticancer therapies, thus making autophagy inhibitors promising drug candidates for breast cancer treatment. The scientific endeavors continue to define a precise role for autophagy in breast cancer. In this article, we review the current literature on the role of autophagy during the development and progression of breast cancer, and discuss the potential of autophagy modulators for breast cancer treatment.

Insulin receptor substrate-1 prevents autophagy-dependent cell death caused by oxidative stress in mouse NIH/3T3 cells

Background

Insulin receptor substrate (IRS)-1 is associated with tumorigenesis; its levels are elevated in several human cancers. IRS-1 protein binds to several oncogene proteins. Oxidative stress and reactive oxygen species (ROS) are involved in the initiation and progression of cancers. Cancer cells produce greater levels of ROS than normal cells do because of increased metabolic stresses. However, excessive production of ROS kills cancer cells. Autophagy usually serves as a survival mechanism in response to stress conditions, but excessive induction of autophagy results in cell death. In addition to inducing necrosis and apoptosis, ROS induces autophagic cell death. ROS inactivates IRS-1 mediated signaling and reduces intracellular IRS-1 concentrations. Thus, there is a complex relationship between IRS-1, ROS, autophagy, and cancer. It is not fully understood how cancer cells grow rapidly and survive in the presence of high ROS levels.

Methods and results

In this study, we established mouse NIH/3T3 cells that overexpressed IRS-1, so mimicking cancers with increased IRS-1 expression levels; we found that the IRS-1 overexpressing cells grow more rapidly than control cells do. Treatment of cells with glucose oxidase (GO) provided a continuous source of ROS; low dosages of GO promoted cell growth, while high doses induced cell death. Evidence for GO induced autophagy includes increased levels of isoform B-II microtubule-associated protein 1 light chain 3 (LC3), aggregation of green fluorescence protein-tagged LC3, and increased numbers of autophagic vacuoles in cells. Overexpression of IRS-1 resulted in inhibition of basal autophagy, and reduced oxidative stress-induced autophagy and cell death. ROS decreased the mammalian target of rapamycin (mTOR)/p70 ribosomal protein S6 kinase signaling, while overexpression of IRS-1 attenuated this inhibition. Knockdown of autophagy-related gene 5 inhibited basal autophagy and diminished oxidative stress-induced autophagy and cell death.

Conclusion

Our results suggest that overexpression of IRS-1 promotes cells growth, inhibits basal autophagy, reduces oxidative stress-induced autophagy, and diminishes oxidative stress-mediated autophagy-dependent cell death. ROS-mediated autophagy may occur via inhibition of IRS-1/phosphatidylinositol 3-kinase/mTOR signaling. Our data afford a plausible explanation for IRS-1 involvement in tumor initiation and progression.