Autophagy as a cell death and tumor suppressor mechanism

AAV-Mig-6 Increase the Efficacy of TAE in VX2 Rabbit Model, Is Associated With JNK Mediated Autophagy

The characterization of high recurrence rate of HCC after TAE provides insights into persistent issues surrounding the role of adjunct therapies administered with TAE. As a regulator of the HER family, Mig-6 is down-regulated in HCC and predicts the prognosis of HCC. In this study, we found up-regulation the expression of Mig-6 enhances autophagy in HCC cells. This function of Mig-6 is related to the activation of the JNK pathway. Next AAV-9 encoding Mitogen inducible gene 6 (Mig-6) was delivered into VX2 liver transplant tumor of rabbits by using hepatic artery catheter. Wild-type AAV is not associated with any human or animal disease and has very low immunogenicity. There are over 100 different AAV serotypes that vary in the amino acid sequence of their capsid protein. We also describe a novel combination therapy coupling AAV-Mig-6 and TAE in a rabbit model resulted in a growth rate decrease in tumor compared with TAE alone. Furthermore, we show that the changes of LC3b and p62, as well as the p-JNK were consistent with changes in vitro experiments. These results suggest that Mig-6 efficiently inhibits tumor progression in vivo. Our findings suggest that Mig-6 induced autophagy inhibition may become a necessary target for adjunct therapy in TAE.

Apoptosis and apoptotic body: disease message and therapeutic target potentials

Apoptosis is widely known as programmed cell death eliciting no inflammatory responses. The intricacy of apoptosis has been a focus of an array of researches, accumulating a wealth of knowledge which led to not only a better understanding of the fundamental process, but also potent therapies of diseases. The classic intrinsic and extrinsic signaling pathways of apoptosis, along with regulatory factors have been well delineated. Drugs and therapeutic measures designed based on current understanding of apoptosis have long been employed. Small-molecule apoptosis inducers have been clinically used for eliminating morbid cells and therefore treating diseases, such as cancer. Biologics with improved apoptotic efficacy and selectivity, such as recombinant proteins and antibodies, are being extensively researched and some have been approved by the FDA. Apoptosis also produces membrane-bound vesicles derived from disassembly of apoptotic cells, now known as apoptotic bodies (ApoBDs). These little sealed sacs containing information as well as substances from dying cells were previously regarded as garbage bags until they were discovered to be capable of delivering useful materials to healthy recipient cells (e.g., autoantigens). In this review, current understandings and knowledge of apoptosis were summarized and discussed with a focus on apoptosis-related therapeutic applications and ApoBDs.

Silkworm Storage Protein 1 Inhibits Autophagy-Mediated Apoptosis

Autophagy is a natural physiological process, and it induces the lysosomal degradation of intracellular components in response to environmental stresses, including nutrient starvation. Although an adequate autophagy level helps in cell survival, excessive autophagy triggered by stress such as starvation leads to autophagy-mediated apoptosis. Chinese hamster ovary (CHO) cells are widely used for producing biopharmaceuticals, including monoclonal antibodies. However, apoptosis induced by high stress levels, including nutrient deficiency, is a major problem in cell cultures grown in bioreactors, which should be overcome. Therefore, it is necessary to develop a method for suppressing excessive autophagy and for maintaining an appropriate autophagy level in cells. Therefore, we investigated the effect of silkworm storage protein 1 (SP1), an antiapoptotic protein, on autophagy-mediated apoptosis. SP1-expressing CHO cells were generated to assess the effect and molecular mechanism of SP1 in suppressing autophagy. These cells were cultured under starvation conditions by treatment with Earle’s balanced salt solution (EBSS) to induce autophagy. We observed that SP1 significantly inhibited autophagy-mediated apoptosis by suppressing caspase-3 activation and reactive oxygen species generation. In addition, SP1 suppressed EBSS-induced conversion of LC3-I to LC3-II and the expression of autophagy-related protein 7. Notably, basal Beclin-1 level was significantly low in the SP1-expressing cells, indicating that SP1 regulated upstream events in the autophagy pathway. Together, these findings suggest that SP1 offers a new strategy for overcoming severe autophagy-mediated apoptosis in mammalian cells, and it can be used widely in biopharmaceutical production.

Oncogene SRSF3 suppresses autophagy via inhibiting BECN1 expression

Autophagy is an evolutionarily conserved cellular catabolic process. Dysfunction in the autophagy pathway has been demonstrated to be associated with many human diseases, including cancer. Alternative splicing of pre-mRNA is also an evolutionarily conserved regulatory mechanism of gene expression. Dysregulation of alternative splicing is increasingly linked to cancer. However, the association between these two cellular conserved processes is unclear. Splicing factors are critical players in the regulation of alternative splicing of pre-mRNA. We analyzed the expression of 28 splicing factors during hypoxia-induced autophagy in three oral squamous cell carcinoma (OSCC) cell lines. We discovered that oncogenes SRSF3 and SRSF1 are significantly downregulated in all three cell lines. Moreover, knockdown of SRSF3 increased autophagic activity, whereas overexpression of SRSF3 inhibited hypoxia-induced autophagy. Loss-of-function and gain-of-function assays also showed that SRSF3 inhibits the expression of p65 and FoxO1 and their downstream target gene BECN1, a key regulator of autophagy. Our results demonstrated that splicing factor SRSF3 is an autophagy suppressor.

Hypoxia-induced autophagy of stellate cells inhibits expression and secretion of lumican into microenvironment of pancreatic ductal adenocarcinoma

Lumican is secreted by pancreatic stellate cells and inhibits cancer progression. Extracellular lumican inhibits cancer cell replication and restrains growth of early-stage pancreatic adenocarcinoma (PDAC) such that patients with tumors containing stromal lumican experience a three-fold longer survival after treatment. In the present study, patient tumor tissues, ex-vivo cultures of patient-derived xenografts (PDX), PDAC stellate and tumor cells were used to investigate whether hypoxia (1% O2) within the tumor microenvironment influences stromal lumican expression and secretion. We observed that hypoxia significantly reduced lumican expression and secretion from pancreatic stellate cells, but not cancer cells. Although hypoxia enhanced lactate dehydrogenase A (LDHA) expression and lactate secretion from all cells, neither hypoxia-induced nor exogenous lactate influenced lumican expression. Autophagy was induced by hypoxia in ex vivo cultures of PDX and pancreatic stellate cells, but not cancer cells cultured in 2D. Autophagic flux inhibitors, bafilomycin A1, chloroquine diphosphate salt, and ammonium chloride prevented hypoxia-mediated reduction in lumican expression in stellate cells. Furthermore, inhibition of AMP-regulated protein kinase (AMPK) phosphorylation or hypoxia-inducible factor (HIF)-1α expression within hypoxic stellate cells restored lumican expression levels. Hypoxia did not affect lumican mRNA expression, indicating that hypoxia-induced reduction of lumican occurs post-transcriptionally; in addition, AMPK inhibition prevented hypoxia-reduced phosphorylation of the mTOR/p70S6K/4EBP signaling pathway, a key contributor to protein synthesis. Taken together, these findings demonstrate that hypoxia reduces stromal lumican in PDAC through autophagy-mediated degradation and reduction in protein synthesis within pancreatic cancer stellate cells.

Role of Autophagy in Breast Cancer Development and Progression: Opposite Sides of the Same Coin

The term "autophagy", which means "self (auto) - eating (phagy)", describes a catabolic process that is evolutionarially conserved among all eukaryotes. Although autophagy is mainly accepted as a cell survival mechanism, it also modulates the process known as "type II cell death". AKT/mTOR pathway is an upstream activator of autophagy and it is tightly regulated by the ATG (autophagy-related genes) signaling cascade. In addition, wide ranging cell signaling pathways and non-coding RNAs played essential roles in the control of autophagy. Autophagy is closely related to pathological processes such as neurodegenerative diseases and cancer as well as physiological conditions. After the Nobel Prize in Physiology or Medicine 2016 was awarded to Yoshinori Ohsumi "for his discoveries of mechanisms for autophagy", there was an explosion in the field of autophagy and molecular biologists started to pay considerable attention to the mechanistic insights related to autophagy in different diseases. Since autophagy behaved dualistically, both as a cell death and a cell survival mechanism, it opened new horizons for a deeper analysis of cell type and context dependent behavior of autophagy in different types of cancers. There are numerous studies showing that the induction of autophagy mechanism will promote survival of cancer cells. Since autophagy is mainly a mechanism to keep the cells alive, it may protect breast cancer cells against stress conditions such as starvation and hypoxia. For these reasons, autophagy was noted to be instrumental in metastasis and drug resistance. In this chapter we have emphasized on role of role of autophagy in breast cancer. Additionally we have partitioned this chapter into exciting role of microRNAs in modulation of autophagy in breast cancer. We have also comprehensively summarized how TRAIL-mediated signaling and autophagy operated in breast cancer cells.

Methods to Measure Autophagy in Cancer Metabolism

Autophagy, a dynamic pathway in which intracellular membrane structures sequester portions of the cytosol for degradation, plays multiple roles in physiological and pathological processes. Autophagy may have suppressive and promotive roles in the formation and progression of cancer. A growing number of methods to identify, quantify, and manipulate autophagy have been developed. Because most of these methods are semiquantitative and have significant limitations, it is important to emphasize that a combination of these assays is recommended for the analysis of autophagy. Here, I briefly discuss the autophagic process, its role in disease, and I summarize some of the best-known and most widely used methods to study autophagy in vitro in the context of cancer, including transmission electron microscopy (TEM), detection and quantification of the autophagy protein LC3 by western blot, and the use of GFP-LC3 to quantify puncta by fluorescence microscopy and tandem labeled RFP/mCherry-GFP-LC3 fluorescence microscopy to measure autophagic flux.

Induction of autophagic cell death in human ovarian carcinoma cells by Antrodia salmonea through increased reactive oxygen species generation

We reported in our previously executed studies that the fermented culture broth of Antrodia salmonea (AS), a mushroom used in Taiwanese folk medicine induced reactive oxygen species (ROS)-mediated apoptosis in human ovarian carcinoma cells. In this study, we studied the anticancer efficacies of AS (0-240 μg/ml) by examining the key molecular events implicated in cell death associated with autophagy in SKOV-3 and A2780 human ovarian carcinoma cells and clarified the fundamental molecular mechanisms. Treatment of ovarian carcinoma cells with AS-induced autophagic cell death mediated by increased microtubule-associated protein LC3-II, GFP-LC3 puncta, and acidic vesicular organelle (AVO) formation. These events are linked with the activation of p62/SQSTM1, the inhibition of ATG4B, the expression of ATG7, and the dysregulation of Beclin-1/Bcl-2 (i.e., B-cell lymphoma 2). N-acetylcysteine inhibited AS-induced ROS generation, which in turn constricted AS-induced LC3 conversion, AVO formation, and ATG4B inhibition, indicating ROS-mediated autophagy cell death. In addition, the 3-methyladenine (3-MA) or chloroquine (CQ)-induced autophagy inhibition decreased AS-induced apoptosis. Additionally, apoptosis inhibition by Z-VAD-FMK, a pan-caspase inhibitor, substantially suppressed AS-induced autophagy. Furthermore, AS-inhibited HER-2/ neu and PI3K/AKT signaling pathways which were reversed by autophagy inhibitors 3-MA and CQ. Thus, A. salmonea is a potential chemopreventive agent that is capable of activating ROS-mediated autophagic cell death in ovarian carcinoma cells.

Plumbagin induces autophagy and apoptosis of SMMC-7721 cells in vitro and in vivo

Plumbagin (PL), an active naphthoquinone compound, has been demonstrated to be a potential anticancer agent. However, the underlying anticancer mechanism is not fully understood. In this study, the human hepatocellular carcinoma (HCC) SMMC-7721 cell line was studied in an in vitro model. The cell proliferation was inhibited by PL in a dose- and time-dependent manner. Electron microscopy, acridine orange staining, and immunofluorescence were used to evaluate autophagosome formation and LC3 protein expression in PL-treated SMMC-7721 cells. Real-time polymerase chain reaction and Western blot showed that PL treatment suppressed the expression of apoptosis and autophagy factors (LC3, Beclin1, Atg7, and Atg5), which are associated with tumor apoptosis and autophagy in SMMC-7721 cells. In the study of in vitro tumor nude mouse models, PL can inhibit tumor growth. Cell apoptosis and autophagy of the transplanted tumors were evaluated by hematoxylin and eosin staining, terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling staining, and Western blot. In addition, in the in vivo studies of HCC cells, we found that pretreatment with the autophagy inhibitor 3-methyladenine blocked the formation of apoptosis induced by PL. In contrast, administration of the apoptosis inhibitor Z-VAD did not affect PL-induced autophagy. Taken together, our findings strongly suggest that PL is a promising drug with significant antitumor activity in HCC.

GRIM-19 repressed hypoxia-induced invasion and EMT of colorectal cancer by repressing autophagy through inactivation of STAT3/HIF-1α signaling axis

Hypoxia leads to cancer progression and promotes the metastatic potential of cancer cells. Thereby, the aim of the present study was to investigate the detailed effects of gene associated with retinoid-interferon-induced mortality-19 (GRIM-19) in colorectal cancer (CRC) cell lines under hypoxia conditions and explore the potential molecular mechanisms. Here, we observed that GRIM-19 expression was downregulated in several CRC cell lines as well as in HCT116 and Caco-2 cells under a hypoxic microenvironment. Additionally, the introduction of GRIM-19 obviously suppressed cell invasive ability and epithelial-mesenchymal transition (EMT) through modulating EMT markers as reflected by the upregulation of E-cadherin along with the downregulation of vimentin and N-cadherin under hypoxic conditions. Moreover, the addition of GRIM-19 repressed hypoxia-induced autophagy through modulating autophagy associated proteins as reflected by the downregulation of LC3-II/LC3-I ratio and Beclin-1 expression, as well as the increased of p62 expression. Interestingly, overexpression of GRIM-19 markedly ameliorated the accumulation of HIF-1α triggered by hypoxia accompanied by an inhibition of vascular endothelial growth factor (VEGF) production and phospho-signal transducer and activator of transcription 3 (p-STAT3) expression. Further data demonstrated that GRIM-19 have a negative feedback effect on the expression of HIF-1α. Mechanistically, re-expression of HIF-1α completely reversed the inhibitory effects of GRIM-19 on hypoxia-induced invasion and EMT. Taken all data together, our findings established that GRIM-19 suppresses hypoxia-triggered invasion and EMT by inhibiting hypoxia-induced autophagy through inactivation HIF-1α/STAT3 signaling pathway, indicating that GRIM-19 may serve as a potential predictive factor and therapeutic target for CRC treatment.

Inhibition of autophagy by chloroquine makes chemotherapy in nasopharyngeal carcinoma more efficient

OBJECTIVES

A combination of platinum-based chemotherapy and radiotherapy is the standard treatment for nasopharyngeal carcinoma (NPC). However, the efficacy of chemotherapy has reached a plateau. Many autophagy studies suggest that autophagy can either promote or suppress to cancer progression. Thus, a role of autophagy in the acquisition of chemoradioresistance has recently been a notable event. Therefore, we examined the relationship between autophagy and chemotherapy in NPC.

METHODS

The expression of Beclin 1 and microtubule-associated protein light chain 3 (LC3), a marker of autophagy, was determined by immunohistochemistry in the biopsy samples of patients with NPC before and after the first course of chemotherapy. Additionally, to investigate in the effect of autophagy suppression in chemotherapy, NPC cell line C666-1 cells were treated with cisplatin and/or chloroquine, an inhibitor of autophagy.

RESULTS

The expression of Beclin 1 increased after chemotherapy in all patients. In NPC cell line C666-1, compared to cisplatin alone, combination therapy (cisplatin and chloroquine) reduced cell viability, and promoted cell apoptosis.

CONCLUSIONS

These results suggest that autophagy, represented by Beclin 1, is upregulated after chemotherapy in both in vitro and in vivo NPC studies. Inhibition of autophagy could therefore be new strategy for NPC treatment.

Selective inhibition of carbonic anhydrase-IX by sulphonamide derivatives induces pH and reactive oxygen species-mediated apoptosis in cervical cancer HeLa cells

Selective inhibition with sulphonamides of carbonic anhydrase (CA) IX reduces cell proliferation and induces apoptosis in human cancer cells. The effect on CA IX expression of seven previously synthesised sulphonamide inhibitors, with high affinity for CA IX, as well as their effect on the proliferation/apoptosis of cancer/normal cell lines was investigated. Two normal and three human cancer cell lines were used. Treatment resulted in dose- and time-dependent inhibition of the growth of various cancer cell lines. One compound showed remarkably high toxicity towards CA IX-positive HeLa cells. The mechanisms of apoptosis induction were determined with Annexin-V and AO/EB staining, cleaved caspases (caspase-3, caspase-8, caspase-9) and cleaved PARP activation, reactive oxygen species production (ROS), mitochondrial membrane potential (MMP), intracellular pH (pHi), extracellular pH (pHe), lactate level and cell cycle analysis. The autophagy induction mechanisms were also investigated. The modulation of apoptotic and autophagic genes (Bax, Bcl-2, caspase-3, caspase-8, caspase-9, caspase-12, Beclin and LC3) was measured using real time PCR. The positive staining using γ-H2AX and AO/EB dye, showed increased cleaved caspase-3, caspase-8, caspase-9, increased ROS production, MMP and enhanced mRNA expression of apoptotic genes, suggesting that anticancer effects are also exerted through its apoptosis-inducing properties. Our results show that such sulphonamides might have the potential as new leads for detailed investigations against CA IX-positive cervical cancers.

Programmed Cell Death, from a Cancer Perspective: An Overview

Programmed cell death (PCD) is probably the most widely discussed subject among the topics of cancer therapy. Over the last 2 decades an astonishing boost in our perception of cell death has been seen, and its role in cancer and cancer therapy has been thoroughly investigated. A number of discoveries have clarified the molecular mechanism of PCD, thus expounding the link between PCD and therapeutic tools. Even though PCD is assumed to play a major role in anticancer therapy, the clinical relevance of its induction remains uncertain. Since PCD involves multiple death programs including programmed necrosis and autophagic cell death, it has contributed to our better understanding of cancer pathogenesis and therapeutics. In this review, we discuss a brief outline of PCD types as well as their role in cancer therapeutics. Since irregularities in the cell death process are frequently found in various cancers, key proteins governing cell death type could be used as therapeutic targets for a wide range of cancer.

Secreted Phosphoprotein 1 Promotes the Development of Small Cell Lung Cancer Cells by Inhibiting Autophagy and Apoptosis

This study aimed to investigate the expression of secreted phosphoprotein 1 (SPP1) on lung cancer cells and explore its underlying mechanism on autophagy and apoptosis which effect the development of lung cancer cells. GSE19804 related to lung cancer cells was screened from Gene Expression Omnibus (GEO) database, and we screened the 47 pairs of differential expressed mRNAs in lung cancer cells and adjacent tissues using microarray analysis. The expression of the core gene SPP1 was detected by qRT-PCR and western-blot. The transfection efficiency of lung cancer cells was detected by qRT-PCR and the expression of transfected group was tested by western-blot. Cell proliferation after transfection was tested by MTT assay and plate cloning experiment. The apoptosis rate of each transfection group was detected by flow cytometry. We use western-blot to test protein expression of autophagy-related proteins Beclin-1, LC3-I, LC3-II and p62 of each transfected group. Through analysis of GSE19804,the heat map showed SPP1 was the highest expressed in tumor tissues. qRT-PCR and western-blot detected SPP1 expression in lung cancer tissues was higher than that in normal adjacent tissues and was significantly increased in lung cancer cell lines. After transfection with pcDNA3.1-SPP1 (p-SPP1 group), siRNA1-SPP1 (siRNA1 group) and siRNA2-SPP1 (siRNA2 group), showed different expression of SPP1. Up-regulation of SPP1 enhanced cell viability and promoted tumor cell proliferation, while knockdown of SPP1 inhibited tumor cell proliferation. From the results of apoptosis rate, SPP1 inhibited the tumor cell apoptosis. However, in normal lung cell, SPP1 had no effect on cell proliferation and apoptosis. And to test autophagy-related proteins, we found that overexpression of SPP1 inhibited autophagy. High expression of SPP1 inhibited autophagy and apoptosis to promote the development of small cell lung cancer cells.

Endoplasmic reticulum stress, autophagic and apoptotic cell death, and immune activation by a natural triterpenoid in human prostate cancer cells

Though the current therapies are effective at clearing an early stage prostate cancer, they often fail to treat late-stage metastatic disease. We aimed to investigate the molecular mechanisms underlying the anticancer effects of a natural triterpenoid, ganoderic acid DM (GA-DM), on two human prostate cancer cell lines: the androgen-independent prostate carcinoma (PC-3), and androgen-sensitive prostate adenocarcinoma (LNCaP). Cell viability assay showed that GA-DM was relatively more toxic to LNCaP cells than to PC-3 cells (IC₅₀ s ranged 45-55 µM for PC-3, and 20-25 µM for LNCaP), which may have occurred due to differential expression of p53. Hoechst DNA staining confirmed detectable nuclear fragmentation in both cell lines irrespective of the p53 status. GA-DM treatment decreased Bcl-2 proteins while it upregulated apoptotic Bax and autophagic Beclin-1, Atg5, and LC-3 molecules, and caused an induction of both early and late events of apoptotic cell death. Biochemical analyses of GA-DM-treated prostate cancer cells demonstrated that caspase-3 cleavage was notable in GA-DM-treated PC-3 cells. Interestingly, GA-DM treatment altered cell cycle progression in the S phase with a significant growth arrest in the G2 checkpoint and enhanced CD4 ⁺ T cell recognition of prostate tumor cells. Mechanistic study of GA-DM-treated prostate cancer cells further demonstrated that calpain activation and endoplasmic reticulum stress contributed to cell death. These findings suggest that GA-DM is a candidate for future drug design for prostate cancer as it activates multiple pathways of cell death and immune recognition.

Autophagy and liver cancer

Autophagy is a key biological phenomenon conserved from yeast to mammals. Under basal conditions, activation of autophagy leads to the protein degradation as well as damaged organelles for maintaining cellular homeostasis. Deregulation of autophagy has been identified as a key mechanism contributing to the pathogenesis and progression of several liver diseases, including hepatocellular carcinoma (HCC), one of the most common and mortal types of cancer. Currently used treatment strategies in patients with HCC result in variable success rates. Therefore, novel early diagnosis and treatment techniques should be developed. Manipulation of autophagy may improve responses of cancer cell to treatments and provide novel targeted therapy options for HCC. In this review, we summarized how our understanding of autophagy-cell death connection may have an impact on HCC therapy.

The combination of Nutlin-3 and Tanshinone IIA promotes synergistic cytotoxicity in acute leukemic cells expressing wild-type p53 by co-regulating MDM2-P53 and the AKT/mTOR pathway

P53 dysfunction has been associated with various malignant tumors, including acute leukemia. The overexpression of mouse double minute 2 (MDM2) causes the inactivation of p53 in acute leukemia. MDM2 inhibitors that activate p53 and induce apoptosis are currently being developed for potential treatment of acute leukemia. However, MDM2 inhibitors alone have limited efficacy in acute leukemia therapeutics. Combining other drugs to enhance the efficacy of MDM2 inhibitors is the thus considered as a potential treatment scheme. Here, we report that the combination of Nutlin-3 and Tanshinone IIA synergistically induces cytotoxicity, cell cycle arrest, apoptosis, and autophagic cell death, thereby imparting anti-leukemia effect in an acute leukemia cell line with wild-type p53 by effectively activating p53, inhibiting the AKT/mTOR pathway, and activating the RAF/MEK pathway. Using primary samples from acute leukemia patients, we show that the combination of Nutlin-3 plus Tanshinone IIA synergistically induces cytotoxicity by activating p53 and inhibiting the AKT/mTOR pathway. This specific combination of Nutlin-3 and Tanshinone IIA is also effective in preventing the recurrence of refractory leukemia, such as Ph+ ALL with the ABL kinase T315I mutation and AML with the FLT3-ITD mutation. Taken together, the results of this study demonstrate that the Nutlin-3 plus Tanshinone IIA combination exerts synergistic anti-leukemia effects by regulating the p53 and AKT/mTOR pathways, although further investigation is warranted. Small-molecule MDM2 antagonists plus Tanshinone IIA may thus be a promising strategy for the treatment of acute leukemia.

MITF-MIR211 axis is a novel autophagy amplifier system during cellular stress

Macroautophagy (autophagy) is an evolutionarily conserved recycling and stress response mechanism. Active at basal levels in eukaryotes, autophagy is upregulated under stress providing cells with building blocks such as amino acids. A lysosome-integrated sensor system composed of RRAG GTPases and MTOR complex 1 (MTORC1) regulates lysosome biogenesis and autophagy in response to amino acid availability. Stress-mediated inhibition of MTORC1 results in the dephosphorylation and nuclear translocation of the TFE/MITF family of transcriptional factors, and triggers an autophagy- and lysosomal-related gene transcription program. The role of family members TFEB and TFE3 have been studied in detail, but the importance of MITF proteins in autophagy regulation is not clear so far. Here we introduce for the first time a specific role for MITF in autophagy control that involves upregulation of MIR211. We show that, under stress conditions including starvation and MTOR inhibition, a MITF-MIR211 axis constitutes a novel feed-forward loop that controls autophagic activity in cells. Direct targeting of the MTORC2 component RICTOR by MIR211 led to the inhibition of the MTORC1 pathway, further stimulating MITF translocation to the nucleus and completing an autophagy amplification loop. In line with a ubiquitous function, MITF and MIR211 were co-expressed in all tested cell lines and human tissues, and the effects on autophagy were observed in a cell-type independent manner. Thus, our study provides direct evidence that MITF has rate-limiting and specific functions in autophagy regulation. Collectively, the MITF-MIR211 axis constitutes a novel and universal autophagy amplification system that sustains autophagic activity under stress conditions. Abbreviations: ACTB: actin beta; AKT: AKT serine/threonine kinase; AKT1S1/PRAS40: AKT1 substrate 1; AMPK: AMP-activated protein kinase; ATG: autophagy-related; BECN1: beclin 1; DEPTOR: DEP domain containing MTOR interacting protein; GABARAP: GABA type A receptor-associated protein; HIF1A: hypoxia inducible factor 1 subunit alpha; LAMP1: lysosomal associated membrane protein 1; MAP1LC3B/LC3B: microtubule associated protein 1 light chain 3 beta; MAPKAP1/SIN1: mitogen-activated protein kinase associated protein 1; MITF: melanogenesis associated transcription factor; MLST8: MTOR associated protein, LST8 homolog; MRE: miRNA response element; MTOR: mechanistic target of rapamycin kinase; MTORC1: MTOR complex 1; MTORC2: MTOR complex 2; PRR5/Protor 1: proline rich 5; PRR5L/Protor 2: proline rich 5 like; RACK1: receptor for activated C kinase 1; RPTOR: regulatory associated protein of MTOR complex 1; RICTOR: RPTOR independent companion of MTOR complex 2; RPS6KB/p70S6K: ribosomal protein S6 kinase; RT-qPCR: quantitative reverse transcription-polymerase chain reaction; SQSTM1: sequestosome 1; STK11/LKB1: serine/threonine kinase 11; TFE3: transcription factor binding to IGHM enhancer 3; TFEB: transcription factor EB; TSC1/2: TSC complex subunit 1/2; ULK1: unc-51 like autophagy activating kinase 1; UVRAG: UV radiation resistance associated; VIM: vimentin; VPS11: VPS11, CORVET/HOPS core subunit; VPS18: VPS18, CORVET/HOPS core subunit; WIPI1: WD repeat domain, phosphoinositide interacting 1.

The multifaceted role of autophagy in cancer and the microenvironment

Autophagy is a crucial recycling process that is increasingly being recognized as an important factor in cancer initiation, cancer (stem) cell maintenance as well as the development of resistance to cancer therapy in both solid and hematological malignancies. Furthermore, it is being recognized that autophagy also plays a crucial and sometimes opposing role in the complex cancer microenvironment. For instance, autophagy in stromal cells such as fibroblasts contributes to tumorigenesis by generating and supplying nutrients to cancerous cells. Reversely, autophagy in immune cells appears to contribute to tumor‐localized immune responses and among others regulates antigen presentation to and by immune cells. Autophagy also directly regulates T and natural killer cell activity and is required for mounting T‐cell memory responses. Thus, within the tumor microenvironment autophagy has a multifaceted role that, depending on the context, may help drive tumorigenesis or may help to support anticancer immune responses. This multifaceted role should be taken into account when designing autophagy‐based cancer therapeutics. In this review, we provide an overview of the diverse facets of autophagy in cancer cells and nonmalignant cells in the cancer microenvironment. Second, we will attempt to integrate and provide a unified view of how these various aspects can be therapeutically exploited for cancer therapy.

Molecular Targets Modulated by Fangchinoline in Tumor Cells and Preclinical Models

Despite tremendous progress made during the last few decades in the treatment options for cancer, compounds isolated from Mother Nature remain the mainstay for therapy of various malignancies. Fangchinoline, initially isolated from the dried root of Stephaniae tetrandrine, has been found to exhibit diverse pharmacological effects including significant anticancer activities both in tumor cell lines and selected preclinical models. This alkaloid appears to act by modulating the activation of various important oncogenic molecules involved in tumorigenesis leading to a significant decrease in aberrant proliferation, survival and metastasis of tumor cells. This mini-review briefly describes the potential effects of fangchinoline on important hallmarks of cancer and highlights the molecular targets modulated by this alkaloid in various tumor cell lines and preclinical models.

Functional characterization of lysosomal interaction of Akt with VRK2

Serine-threonine kinase Akt (also known as PKB, protein kinase B), a core intracellular mediator of cell survival, is involved in various human cancers and has been suggested to play an important role in the regulation of autophagy in mammalian cells. Nonetheless, the physiological function of Akt in the lysosomes is currently unknown. We have reported previously that PtdIns(3)P-dependent lysosomal accumulation of the Akt-Phafin2 complex is a critical step for autophagy induction. Here, to characterize the molecular function of activated Akt in the lysosomes in the process of autophagy, we searched for the molecules that interact with the Akt complex at the lysosomes after induction of autophagy. By time-of-flight-mass spectrometry (TOF/MS) analysis, kinases of the VRK family, a unique serine-threonine family of kinases in the human kinome, were identified. VRK2 interacts with Akt1 and Akt2, but not with Akt3; the C terminus of Akt and the N terminus of VRK2 facilitate the interaction of Akt and VRK2 in mammalian cells. The kinase-dead form of VRK2A (KD VRK2A) failed to interact with Akt in coimmunoprecipitation assays. Bimolecular fluorescence complementation (BiFC) experiments showed that, in the lysosomes, Akt interacted with VRK2A but not with VRK2B or KD VRK2A. Immunofluorescent assays revealed that VRK2 and phosphorylated Akt accumulated in the lysosomes after autophagy induction. WT VRK2A, but not KD VRK2A or VRK2B, facilitated accumulation of phosphorylated Akt in the lysosomes. Downregulation of VRK2 abrogated the lysosomal accumulation of phosphorylated Akt and impaired nuclear localization of TFEB; these events coincided to inhibition of autophagy induction. The VRK2-Akt complex is required for control of lysosomal size, acidification, bacterial degradation, and for viral replication. Moreover, lysosomal VRK2-Akt controls cellular proliferation and mitochondrial outer-membrane stabilization. Given the roles of autophagy in the pathogenesis of human cancer, the current study provides a novel insight into the oncogenic activity of VRK2-Akt complexes in the lysosomes via modulation of autophagy.

Natural pyrethrins induce autophagy of HepG2 cells through the activation of AMPK/mTOR pathway

Natural pyrethrins, one kind of insects' neural toxin, have been used worldwide for the control of pests of crops, livestock, and human beings. However, their specific mechanisms of action are incompletely understood and hence further investigation is required. Here we used a series of experiments including colony formation, fluorescent staining, western blotting, enzyme activity detection, immunofluorescence analysis, and real-time quantitative PCR (QPCR) to investigate whether natural pyrethrins (0-40 μg/mL) are able to modulate autophagy process through AMPK/mTOR signaling pathway, in order to reveal their cytotoxic mechanisms. The results showed that natural pyrethrins markedly inhibited the proliferation of HepG2 cells in both concentration- and time-dependent manners. Particularly, natural pyrethrins could induce the resulting autophagosome, and the intensification of LC3-II formation and translocation, the accumulation of Beclin-1 and the reduction of p62 and thus autophagy. We clarified that natural pyrethrins induced the abnormal level of oxidation reduction metabolism, leading to mitochondrial permeability transition pore (mPTP) opening, ATP depletion and mitochondria eliminating by autophagy. Moreover, the phosphorylation levels of AMPK were significantly enhanced, and the mTOR and p70s6k phosphorylation were drastically decreased. These results showed that natural pyrethrins induced autophagy of HepG2 cells and activation of the AMPK/mTOR signaling pathway might have potential risk to human health.

Loperamide, pimozide, and STF-62247 trigger autophagy-dependent cell death in glioblastoma cells

Autophagy is a well-described degradation mechanism that promotes cell survival upon nutrient starvation and other forms of cellular stresses. In addition, there is growing evidence showing that autophagy can exert a lethal function via autophagic cell death (ACD). As ACD has been implicated in apoptosis-resistant glioblastoma (GBM), there is a high medical need for identifying novel ACD-inducing drugs. Therefore, we screened a library containing 70 autophagy-inducing compounds to induce ATG5-dependent cell death in human MZ-54 GBM cells. Here, we identified three compounds, i.e. loperamide, pimozide, and STF-62247 that significantly induce cell death in several GBM cell lines compared to CRISPR/Cas9-generated ATG5- or ATG7-deficient cells, pointing to a death-promoting role of autophagy. Further cell death analyses conducted using pharmacological inhibitors revealed that apoptosis, ferroptosis, and necroptosis only play minor roles in loperamide-, pimozide- or STF-62247-induced cell death. Intriguingly, these three compounds induce massive lipidation of the autophagy marker protein LC3B as well as the formation of LC3B puncta, which are characteristic of autophagy. Furthermore, loperamide, pimozide, and STF-62247 enhance the autophagic flux in parental MZ-54 cells, but not in ATG5 or ATG7 knockout (KO) MZ-54 cells. In addition, loperamide- and pimozide-treated cells display a massive formation of autophagosomes and autolysosomes at the ultrastructural level. Finally, stimulation of autophagy by all three compounds is accompanied by dephosphorylation of mammalian target of rapamycin complex 1 (mTORC1), a well-known negative regulator of autophagy. In summary, our results indicate that loperamide, pimozide, and STF-62247 induce ATG5- and ATG7-dependent cell death in GBM cells, which is preceded by a massive induction of autophagy. These findings emphasize the lethal function and potential clinical relevance of hyperactivated autophagy in GBM.

Mir223 restrains autophagy and promotes CNS inflammation by targeting ATG16L1

Microglia are innate immune cells in the central nervous system (CNS), that supplies neurons with key factors for executing autophagosomal/lysosomal functions. Macroautophagy/autophagy is a cellular catabolic process that maintains cell balance in response to stress-related stimulation. Abnormal autophagy occurs with many pathologies, such as cancer, and autoimmune and neurodegenerative diseases. Hence, clarification of the mechanisms of autophagy regulation is of utmost importance. Recently, researchers presented microRNAs (miRNAs) as novel and potent modulators of autophagic activity. Here, we found that Mir223 deficiency significantly ameliorated CNS inflammation, demyelination and the clinical symptoms of experimental autoimmune encephalomyelitis (EAE) and increased resting microglia and autophagy in brain microglial cells. In contrast, the autophagy inhibitor 3-methylademine (3-MA) aggravated the clinical symptoms of EAE in wild-type (WT) and Mir223-deficienct mice. Furthermore, it was confirmed that Mir223 deficiency in mice increased the protein expression of ATG16L1 (autophagy related 16-like 1 [S. cerevisiae]) and LC3-II in bone marrow-derived macrophage cells compared with cells from WT mice. Indeed, the cellular level of Atg16l1 was decreased in BV2 cells upon Mir223 overexpression and increased following the introduction of antagomirs. We also showed that the 3’ UTR of Atg16l1 contained functional Mir223-responsive sequences and that overexpression of ATG16L1 returned autophagy to normal levels even in the presence of Mir223 mimics. Collectively, these data indicate that Mir223 is a novel and important regulator of autophagy and that Atg16l1 is a Mir223 target in this process, which may have implications for improving our understanding of the neuroinflammatory process of EAE.

Abbreviations: 3-MA: 3-methylademine; ACTB/β-actin: actin, beta; ATG: autophagy related; ATG16L1: autophagy related 16-like 1 (S. cerevisiae); BECN1: beclin 1, autophagy related; CNR2: cannabinoid receptor 2 (macrophage); CNS: central nervous system; CQ: chloroquine; EAE: experimental autoimmune encephalomyelitis; FOXO3: forkhead box O3; GAPDH: glyceraldehyde-3-phosphate dehydrogenase; H&E: hematoxylin and eosin; ITGAM: integrin alpha M; LPS: lipoplysaccharide; MAP1LC3/LC3: microtubule-associated protein 1 light chain 3; miRNAs: microRNAs; MS: multiple sclerosis; PPARG: peroxisome proliferator activated receptor gamma; PTPRC: protein tyrosine phosphatase, receptor type, C; RA: rheumatoid arthritis; SQSTM1: sequestosome 1; TB: tuberculosis; TIMM23: translocase of inner mitochondrial membrane 23; TLR: toll-like receptor.

Silencing of cadherin-17 enhances apoptosis and inhibits autophagy in colorectal cancer cells

Cadherin-17 (CDH17), a structurally unique member of the non-classical cadherin family, is associated with poor survival, cell proliferation, and metastasis in colorectal cancer. However, the role of CDH17 in the apoptosis and autophagy of colorectal cancer cells remains unclear. Here, we aimed to investigate the effect of CDH17 knockdown on autophagy and apoptosis in colorectal cancer cells. We inhibited CDH17 expression in KM12SM and KM12C colorectal cancer cells by RNA interference and found that silencing of CDH17 significantly inhibited cell viability and increased apoptosis in KM12SM and KM12C cells. In addition, silencing of CDH17 significantly increased the expression of cleaved caspase-3 and Bax and decreased the expression of Bcl-2. Concurrently, silencing of CDH17 significantly inhibited the conversion of LC3-I to LC3-II and decreased the formation of LC3⁺ autophagic vacuoles and the accumulation of acidic vesicular organelles, indicating that autophagy was significantly inhibited in KM12SM and KM12C cells. Additionally, treatment with the autophagy-specific activator rapamycin attenuated apoptosis in CDH17-knockdown cells and as indicated by decreased caspase-3 activity, decreased expression of cleaved caspase-3 and Bax, and increased expression of Bcl-2. In conclusion, CDH17 silencing induced apoptosis and inhibited autophagy in KM12SM and KM12C cells, and this autophagy protected the cells from apoptotic cell death.

Autophagy-disrupted LC3 abundance leads to death of supporting cells of human oocytes

Autophagic recycling of cell parts is generally termed as the opposite of cell death. Here, we explored the relation between cell death and autophagy by examining granulosa cell layers that control oocyte quality, which is important for the success of fertilization. Granulosa cell layers were collected from infertile women and morphologically divided into four types, viz., mature (MCCs), immature (ICCs), and dysmature cumulus cells (DCCs), and mural granulosa cells (MGCs). Microtubule-associated protein light chain 3 (LC3), which is involved in autophagosome formation, was expressed excessively in DCCs and MGCs, and their chromosomal DNA was highly fragmented. However, autophagy initiation was limited to MGCs, as indicated by the expression of membrane-bound LC3-II and autophagy-related protein 7 (ATG7), an enzyme that converts LC3-I to LC3-II. Although pro-LC3 was accumulated, autophagy was disabled in DCCs, resulting in cell death. Our results suggest the possibility that autophagy-independent accumulation of pro-LC3 proteins leads to the death of human granulosa cells surrounding the oocytes and presumably reduces oocyte quality and female fertility.

Anticancer activity of tetrandrine by inducing pro-death apoptosis and autophagy in human gastric cancer cells

OBJECTIVES

To investigate the antitumour property of tetrandrine by inducing autophagy and apoptosis in human gastric cancer cells, and to explore the potential molecular mechanisms.

METHODS

The antitumour activity of tetrandrine was assessed through MTT assay. Apoptosis was measured by flow cytometry and microscopic examination of cellular morphology. The mitochondrial membrane potential was detected by staining with Rh-123. Induction of autophagy was monitored by transmission electron microscopy observation, using GFP-LC3 transfection.

KEY FINDINGS

The results revealed that tetrandrine exhibits significant antitumour activity against gastric human cancer cell and the antigastric tumour activity was depended on inducing autophagy and apoptosis through upregulating the apoptosis-related protein (cleaved PARP, cleaved caspase-3 and cleaved caspase-9) and autophagy-related protein (Beclin-1, LC3-II and p62), and decreasing the phosphorylation of AKT/mTOR, PS6K and P-4EBP1. Adding the inhibitor of autophagy, 3-MA or Baf-A1, increased the viability of tetrandrine-exposed gastric cancer cells, which confirmed the role of autophagy played in the gastric cancer cell death induced by tetrandrine.

CONCLUSIONS

These results demonstrated that the antitumour effects of tetrandrine by inducing autophagy and apoptosis involving Akt/mTOR pathway. Thus, tetrandrine may be a promising lead compound to be further developed in future for cancer therapy.

Cell-specific pattern of berberine pleiotropic effects on different human cell lines

The natural alkaloid berberine has several pharmacological properties and recently received attention as a potential anticancer agent. In this work, we investigated the molecular mechanisms underlying the anti-tumor effect of berberine on glioblastoma U343 and pancreatic carcinoma MIA PaCa-2 cells. Human dermal fibroblasts (HDF) were used as non-cancer cells. We show that berberine differentially affects cell viability, displaying a higher cytotoxicity on the two cancer cell lines than on HDF. Berberine also affects cell cycle progression, senescence, caspase-3 activity, autophagy and migration in a cell-specific manner. In particular, in HDF it induces cell cycle arrest in G2 and senescence, but not autophagy; in the U343 cells, berberine leads to cell cycle arrest in G2 and induces both senescence and autophagy; in MIA PaCa-2 cells, the alkaloid induces arrest in G1, senescence, autophagy, it increases caspase-3 activity and impairs migration/invasion. As demonstrated by decreased citrate synthase activity, the three cell lines show mitochondrial dysfunction following berberine exposure. Finally, we observed that berberine modulates the expression profile of genes involved in different pathways of tumorigenesis in a cell line-specific manner. These findings have valuable implications for understanding the complex functional interactions between berberine and specific cell types.

Ailanthone induces autophagic and apoptotic cell death in human promyelocytic leukemia HL-60 cells

Ailanthone, which is extracted from the traditional Chinese medicinal plant Ailanthus altissima, has been thoroughly demonstrated to have anti-tumor, anti-HIV, anti-inflammatory, anti-malarial, anti-allergic and anti-microbial activities. However, the anti-proliferative effects of ailanthone on HL-60 cells and potential mechanisms underlying those effects have not been reported. In the present study, we demonstrated the potent cytotoxicity of ailanthone against HL-60 cells. Annexin V-APC/7-ADD staining assay indicated that ailanthone increased the number of apoptotic cells in a dose-dependent manner. PI staining showed that ailanthone increased the percentage of G0/G1-phase cells in a dose-dependent manner. Acridine orange staining suggested that ailanthone induced the formation of acidic vesicular organelles in HL-60 cells and pretreatment with BaF-A1 could attenuate this process. Western blotting showed that ailanthone up-regulated the protein expression levels of beclin-1 and LC3-II and down-regulated those of LC3-I and p62 in a dose-dependent manner. Use of BaF-A1 showed that the anti-proliferative effects of ailanthone on HL-60 cells may be partly attributable to the induction of autophagy-mediated apoptosis by MTT assay and annexin V-APC/7-ADD staining assay.

Chronic restraint stress induces hippocampal memory deficits by impairing insulin signaling

Chronic stress is a psychologically significant factor that impairs learning and memory in the hippocampus. Insulin signaling is important for the development and cognitive function of the hippocampus. However, the relation between chronic stress and insulin signaling at the molecular level is poorly understood. Here, we show that chronic stress impairs insulin signaling in vitro and in vivo, and thereby induces deficits in hippocampal spatial working memory and neurobehavior. Corticosterone treatment of mouse hippocampal neurons in vitro caused neurotoxicity with an increase in the markers of autophagy but not apoptosis. Corticosterone treatment impaired insulin signaling from early time points. As an in vivo model of stress, mice were subjected to chronic restraint stress. The chronic restraint stress group showed downregulated insulin signaling and suffered deficits in spatial working memory and nesting behavior. Intranasal insulin delivery restored insulin signaling and rescued hippocampal deficits. Our data suggest that psychological stress impairs insulin signaling and results in hippocampal deficits, and these effects can be prevented by intranasal insulin delivery.

Autophagy Suppresses Invasiveness of Endometrial Cells through Reduction of Fascin-1

OBJECTIVE

Autophagy has been reported to be involved in the development of various disorders such as neurodegenerative and metabolic diseases and tumors. Autophagy activators and inhibitors are also potential therapeutics for these diseases. However, the mechanism of autophagic involvement in different diseases is not the same, and the role of autophagy in endometriosis (EM) has not yet been elucidated. This research investigated the mechanism by which autophagy acts in EM, with the aim of establishing a theoretical basis for its prevention and treatment through the targeted interference with autophagy.

METHODS

We used an RNA interference fragment targeting ATG5, the autophagy activator rapamycin, and the autophagy inhibitor 3-MA or overexpression of filopodia-related protein fascin-1, in conjunction with clonogenic assays, growth curves, and scratch assay to investigate the influence of autophagy on cellular growth, proliferation, and invasiveness. We collected specimens from 20 clinical cases of EM and investigated the protein expression of the autophagic marker LC3-II, the autophagic substrate p62, and fascin-1.

RESULTS

Rapamycin was able to inhibit the proliferation and colony formation of the endometriotic cell line CRL-7566, whereas the autophagy inhibitor 3-MA as well as the interference with the autophagy-related gene ATG5 had the opposite effect. More importantly, the autophagy activator rapamycin was able to inhibit the growth of filopodia in the endometriotic cells, and the overexpression of the fascin-1 restored the rapamycin-induced decrease of invasiveness. We found that the expression of the autophagy marker LC3-II was significantly reduced among the clinical EM specimens compared to the control group, while the expressions of fascin-1 and autophagic substrate p62 were increased.

CONCLUSION

Our results indicate that the inhibition of autophagy and exogenous expression of fascin-1 may promote the invasiveness of endometrial cells. As a corollary, autophagy represents a potential target for the treatment of EM.

The gastric mucosal protective effects of astragaloside IV in mnng-induced GPL rats

Gastric Cancer is one of the most common types of cancer. And the occurrence of gastric carcinoma is an evolutionary histopathological stage. As a result, further research of GPL, which is a borderline of gastric cancer, is indispensable for preventing the formation and development of gastric carcinoma. Several studies have demonstrated a correlation between the expression of autophagy, apoptosis and Gastric cancer (GC). However, the effects of autophagy and apoptosis on human gastric cancer progression, particularly on gastric precancerous lesions (GPL), have not totally been investigated. At present, Astragaloside IV(AS-IV) is a saponin purified from Astragalus membranaceous Bge, a traditional Chinese herb that has been widely used for more than 2000 y in the treatment of cancer, cardiovascular and immune disorders. This study was designed to investigate the mechanism of AS-IV protecting gastric mucosa in N-methyl-N'-nitro-N-nitrosoguanidine (MNNG)-induced GPL rats. The lesions of GIM and GED were significantly ameliorated compared with the model rats, especially crowded tubular glandular and back-to-back tubular structure, which were the dangerous borderline between GPL and GC. Western Blot analysis showed that the ratio of Bcl-2/Bax and the protein expression of Bcl-XL, p53, Beclin1, p62, ATG5 and ATG12 were decreased and the level of Caspase3 was increased in the group of AS-IV compared with the model group; RT-PCR analysis showed that the gene expression Ambra1, Beclin1, ATG5, LC3 and p62 were decreased in the group of AS-IV compared with the model group. This research manifested that the occurrence of gastric cancer was preceded by a prolonged precancerous stage, which could be ameliorated by the AS-IV. Meanwhile, the mild and moderate stage of precancerous lesions is similar with gastric adenocarcinoma in critical biological processes, including inflammation, cell proliferation, differentiation. But this lesion is very different from cancer, because it does not appear obvious invasion and malignant lesions in this pathologic stag. Further, AS-IV could regulate p53 expression to activate the Ambra1/Beclin1 complex in GPL, and it will protect the gastric mucosal injury, prevent and cure gastric mucosal atrophy, intestinal metaplasia and atypical hyperplastic lesions. It provided a potential therapeutic strategy in reversing intestinal metaplasia and dysplasia of gastric precancerous lesions and protecting the gastric mucosa in GPL rats.

Cold PSM, but not TRAIL, triggers autophagic cell death: A therapeutic advantage of PSM over TRAIL

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) and cold plasma-stimulated medium (PSM) are promising novel anticancer tools due to their strong anticancer activities and high tumor-selectivity. The present study demonstrated that PSM and TRAIL may trigger autophagy in human malignant melanoma and osteosarcoma cells. Live-cell imaging revealed that even under nutritional and stress-free conditions, these cells possessed a substantial level of autophagosomes, which were localized in the cytoplasm separately from tubular mitochondria. In response to cytotoxic levels of PSM, the mitochondria became highly fragmented, and aggregated and colocalized with the autophagosomes. The cytotoxic effects of PSM were suppressed in response to various pharmacological autophagy inhibitors, including 3-methyladenine (3-MA) and bafilomycin A1, thus indicating the induction of autophagic cell death (ACD). Lethal levels of PSM also resulted in non-apoptotic, non-autophagic cell death in a reactive oxygen species-dependent manner under certain circumstances. Furthermore, TRAIL exhibited only a modest cytotoxicity toward these tumor cells, and did not induce ACD and mitochondrial aberration. The combined use of TRAIL and subtoxic concentrations of 3-MA resulted in decreased basal autophagy, increased mitochondrial aberration, colocalization with autophagosomes and apoptosis. These results indicated that PSM may induce ACD, whereas TRAIL may trigger cytoprotective autophagy that compromises apoptosis. To the best of our knowledge, the present study is the first to demonstrate that PSM can induce ACD in human cancer cells. These findings provide a rationale for the advantage of PSM over TRAIL in the destruction of apoptosis-resistant melanoma and osteosarcoma cells.

Dual Suppression Effect of Magnetic Induction Heating and Microencapsulation on Ice Crystallization Enables Low-Cryoprotectant Vitrification of Stem Cell-Alginate Hydrogel Constructs

Stem cells microencapsulated in hydrogel as stem cell-hydrogel constructs have wide applications in the burgeoning cell-based medicine. Due to their short shelf life at ambient temperature, long-term storage or banking of the constructs is essential to the "off-the-shelf" ready availability needed for their widespread applications. As a high-efficiency, easy-to-operate, low-toxicity, and low-cost method for long-term storage of the constructs, low-cryoprotectant (CPA) vitrification has attracted tremendous attention recently. However, we found many cells in the stem cell-alginate constructs (∼500 μm in diameter) could not attach to the substrate post low-CPA vitrification with ∼2 M penetrating CPAs. To address this problem, we introduced nanowarming via magnetic induction heating (MIH) of Fe3O4 nanoparticles to minimize recrystallization and devitrification during the warming step of the low-CPA vitrification procedure. Our results indicate that high-quality stem cell-alginate hydrogel constructs with an intact microstructure, high immediate cell survival (>80%), and greatly improved attachment efficiency (by nearly three times, 68% versus 24%) of the encapsulated cells could be obtained post-cryopreservation with nanowarming. Moreover, the cells encapsulated in the cell-hydrogel constructs post-cryopreservation maintained normal proliferation under 3D culture and retained intact biological function of multilineage differentiation. This novel low-CPA vitrification approach for cell cryopreservation enabled by the combined use of alginate hydrogel microencapsulation and Fe3O4 nanoparticles-mediated nanowarming may be valuable in facilitating the widespread application of stem cells in the clinic.

Atg7 inhibits Warburg effect by suppressing PKM2 phosphorylation resulting reduced epithelial-mesenchymal transition

Metabolic reprogramming is a distinct hallmark in tumorigenesis. Autophagy can rewire cell metabolism by regulating intracellular homeostasis. Warburg effect is a specific energy metabolic process that allows tumor cells to metabolize glucose via glycolysis into lactate even in the presence of oxygen. Although both autophagy and Warburg effect are involved in the stress response to energy crisis in tumor cells, their molecular relationship has remained largely elusive. We found that Atg7, a key molecule involved in autophagy, inhibits the Warburg effect. Mechanistically, Atg7 binds PKM2 and prevents its Tyr-105 phosphorylation by FGFR1. Furthermore, the hyperphosphorylation of PKM2 and its induced Warburg effect due to Atg7 deficiency promote epithelial-mesenchymal transition (EMT). Conversely, overexpression of Atg7 inhibits PKM2 phosphorylation and the Warburg effect, thereby inhibiting EMT of tumor cells. Our work reveals a molecular link between Atg7 and the Warburg effect, which may provide insight into novel strategies for cancer treatment.

Crosstalk between the Warburg effect, redox regulation and autophagy induction in tumourigenesis

Tumourigenic tissue uses modified metabolic signalling pathways in order to support hyperproliferation and survival. Cancer-associated aerobic glycolysis resulting in lactic acid production was described nearly 100 years ago. Furthermore, increased reactive oxygen species (ROS) and lactate quantities increase metabolic, survival and proliferation signalling, resulting in increased tumourigenesis. In order to maintain redox balance, the cell possesses innate antioxidant defence systems such as superoxide dismutase, catalase and glutathione. Several stimuli including cells deprived of nutrients or failure of antioxidant systems result in oxidative stress and cell death induction. Among the cell death machinery is autophagy, a compensatory mechanism whereby energy is produced from damaged and/or redundant organelles and proteins, which prevents the accumulation of waste products, thereby maintaining homeostasis. Furthermore, autophagy is maintained by several pathways including phosphoinositol 3 kinases, the mitogen-activated protein kinase family, hypoxia-inducible factor, avian myelocytomatosis viral oncogene homolog and protein kinase receptor-like endoplasmic reticulum kinase. The persistent potential of cancer metabolism, redox regulation and the crosstalk with autophagy in scientific investigation pertains to its ability to uncover essential aspects of tumourigenic transformation. This may result in clinical translational possibilities to exploit tumourigenic oxidative status and autophagy to advance our capabilities to diagnose, monitor and treat cancer.

Autophagy induced by cardamonin is associated with mTORC1 inhibition in SKOV3 cells

BACKGROUND

The mammalian target of rapamycin (mTOR) integrates energy level to modulate cell proliferation and autophagy. Cardamonin exhibits anti-proliferative activity through inhibiting mTOR. In this study, the effect of cardamonin on autophagy and its mechanism on mTOR inhibition were investigated.

METHODS

Cell viability and proliferation were measured by MTT assay and BrdU incorporation, respectively. Cell apoptosis was assayed by flow cytometry and cell autophagy was detected by electron microscopy and GFP-LC3 fluorescence. The mechanism of cardamonin on mTORC1 inhibition was investigated by Raptor siRNA and Raptor over-expression.

RESULTS

The cell viability and proliferation were inhibited by cardamonin. The autophagosomes and the protein level of LC3-II were increased by cardamonin. Cell apoptosis and the levels of cleaved PARP and Caspase-3 were increased by cardamonin. Cardamonin inhibited the phosphorylation of mTOR and ribosome S6 protein kinase 1 (S6K1) as well as the protein level of regulatory associated protein of mTOR (Raptor). However, cardamonin had no effect on the component of mTORC2 and its downstream substrate Akt. The inhibitory effect of cardamonin on the phosphorylation of mTOR and S6K1 was eliminated by Raptor knockdown with siRNA, whereas this effect of cardamonin was stronger than that of rapamycin and AZD8055 in Raptor over-expression cells. Cell viability was inhibited by cardamonin in both Raptor knockdown and Raptor over-expression cells, which was consistent with the inhibitory effect of cardamonin on mTOR.

CONCLUSION

These findings demonstrated that the autophagy induced by cardamonin was associated with mTORC1 inhibition through decreasing the protein level of Raptor in SKOV3 cells.

PP242 Counteracts Glioblastoma Cell Proliferation, Migration, Invasiveness and Stemness Properties by Inhibiting mTORC2/AKT

Glioblastoma multiforme (GBM) is the most malignant brain tumor and is associated with poor prognosis due to its thorny localization, lack of efficacious therapies and complex biology. Among the numerous pathways driving GBM biology studied so far, PTEN/phosphatidylinositol-4,5-bisphosphate 3-kinase (PI3K)/AKT/mechanistic target of rapamycin (mTOR) signaling plays a pivotal role, as it controls cell survival, proliferation and metabolism and is involved in stem cell maintenance. In front of recent and numerous evidences highlighting mTOR upregulation in GBM, all the strategies developed to inhibit this pathway have been substantially unsuccessful. Our study focused on mTOR complex 2 (mTORC2) to understand its involvement in GBM cell growth, proliferation, migration and invasiveness. We utilized an in vitro model, characterized by various genetic alterations (i.e., GL15, U257, U87MG and U118MG cell lines) in order to achieve the clonal heterogeneity observed in vivo. Additionally, being the U87MG cell line endowed with glioblastoma stem cells (GSCs), we also investigated the role of the PTEN/PI3K/AKT/mTOR pathway in this specific cell population, which is responsible for GBM relapse. We provide further insights that explain the reasons for the failure of numerous clinical trials conducted to date targeting PI3K or mTOR complex 1 (mTORC1) with rapamycin and its analogs. Additionally, we show that mTORC2 might represent a potential clinically valuable target for GBM treatment, as proliferation, migration and GSC maintenance appear to be mTORC2-dependent. In this context, we demonstrate that the novel ATP-competitive mTOR inhibitor PP242 effectively targets both mTORC1 and mTORC2 activation and counteracts cell proliferation via the induction of high autophagy levels, besides reducing cell migration, invasiveness and stemness properties.

The TLR7 agonist imiquimod induces anti-cancer effects via autophagic cell death and enhances anti-tumoral and systemic immunity during radiotherapy for melanoma

Toll-like receptor (TLR) ligands are strongly considered immune-adjuvants for cancer immunotherapy and have been shown to exert direct anti-cancer effects. This study was performed to evaluate the synergistic anti-cancer and anti-metastatic effects of the TLR7 agonist imiquimod (IMQ) during radiotherapy for melanoma. The pretreatment of B16F10 or B16F1 cells with IMQ combined with γ-ionizing radiation (IR) led to enhanced cell death via autophagy, as demonstrated by increased expression levels of autophagy-related genes, and an increased number of autophagosomes in both cell lines. The results also confirmed that the autophagy process was accelerated via the reactive oxygen species (ROS)-mediated MAPK and NF-κB signaling pathway in the cells pretreated with IMQ combined with IR. Mice subcutaneously injected with melanoma cells showed a reduced tumor growth rate after treatment with IMQ and IR. Treatment with 3-methyladenine (3-MA), ameliorated the anti-cancer effect of IMQ combined with IR. Additionally, the combination therapy enhanced anti-cancer immunity, as demonstrated by an increased number of CD8⁺ T cells and decreased numbers of regulatory T cells (Treg) and myeloid-derived suppressor cells (MDSCs) in the tumor lesions. Moreover, the combination therapy decreased the number of metastatic nodules in the lungs of mice that were injected with B16F10 cells via the tail vein. In addition, the combination therapy enhanced systemic anti-cancer immunity by increasing the abundances of T cell populations expressing IFN-γ and TNF-α. Therefore, these findings suggest that IMQ could serve as a radiosensitizer and immune booster during radiotherapy for melanoma patients.

CK1α suppresses lung tumour growth by stabilizing PTEN and inducing autophagy

The contribution of autophagy to cancer development remains controversial, largely owing to the fact that autophagy can be tumour suppressive or oncogenic in different biological contexts. Here, we show that in non-small-cell lung cancer (NSCLC), casein kinase 1 alpha 1 (CK1α) suppresses tumour growth by functioning as an autophagy inducer to activate an autophagy-regulating, tumour-suppressive PTEN/AKT/FOXO3a/Atg7 axis. Specifically, CK1α bound the C-terminal tail of PTEN and enhanced both PTEN stability and activity by competitively antagonizing NEDD4-1-induced PTEN polyubiquitination and abrogating PTEN phosphorylation, thereby inhibiting AKT activity and activating FOXO3a-induced transcription of Atg7. Notably, blocking CK1α-induced Atg7-dependent autophagy cooperates with oncogenic HRasV12 to initiate tumorigenesis of lung epithelial cells. An association of a CK1α-modulated autophagic program with the anti-neoplastic activities of the CK1α/PTEN/FOXO3a/Atg7 axis was demonstrated in xenografted tumour models and human NSCLC specimens. This provides insights into the biological and potentially clinical significance of autophagy in NSCLC.

TRAP1 regulates autophagy in lung cancer cells

BACKGROUND

Expression of TRAP1, a member of the HSP90 chaperone family, has been implicated in tumour protective effects, based on its differential mitochondrial localization and function.

DESIGN

This work was designed to provide new insights into the pathways involved in TRAP1-provided cytoprotection on NSCLC. For this, TRAP1-depleted A549 human NSCLC cells and MRC-5 normal lung fibroblasts were produced using a siRNA approach and main cellular quality control mechanisms were investigated.

RESULTS

TRAP1-depleted A549 cells displayed decreased cell viability likely due to impaired mitochondrial function including decreased ATP/AMP ratio, oxygen consumption and membrane potential, as well as increased apoptotic indicators. Furthermore, the negative impact of TRAP1 depletion on mitochondrial function was not observed in normal MRC-5 lung cells, which might be due to the differential intracellular localization of the chaperone in tumour versus normal cells. Additionally, A549 TRAP1-depleted cells showed increased autophagic flux. Functionally, autophagy inhibition resulted in decreased cell viability in both TRAP1-expressing and TRAP1-depleted tumour cells with minor effects on MRC-5 cells. Conversely, autophagy stimulation decreased cell viability of both A549 and MRC-5 TRAP1-expressing cells while in A549 TRAP1-depleted cells, increased autophagy augmented viability.

CONCLUSIONS

Our results show that even though TRAP1 depletion affects both normal MRC-5 and tumour A549 cell proliferation, inhibition of autophagy per se led to a decrease in tumour cell mass, while having a reduced effect on the normal cell line. The strategy of targeting TRAP1 in NSCLC shows future potential therapeutic applications.

Anti-cancerous effect of cis-khellactone from Angelica amurensis through the induction of three programmed cell deaths

Angelica amurensis has traditionally been used to treat various medical problems. In this report, we introduce cis-khellactone as a new anti-cancer agent, which was isolated from the chloroform soluble fraction of the rhizomes of Angelica amurensis. Its anti-cancerous effect was at first tested in MCF7 and MDA-MB-231 breast cell lines, in which MCF7 is well known to be resistant to many anti-cancer drugs; MCF10A normal breast cell line was used as a control. In vitro experiments showed that cis-khellactone suppressed cell growth and proliferation at a relatively low concentrations (<5 μg/ml) and decreased cell viability at high concentrations (>10 μg/ml) in both cancer cell lines in a time- and concentration-dependent manner. This anti-cancerous effect was also checked in additional 16 different types of normal and cancer cell lines. Cis-khellactone treatment significantly suppressed cell proliferation and enhanced cell death in all tested cancer cell lines. Furthermore, Western blot analysis showed that cis-khellactone induced three types of programmed cell death (PCD): apoptosis, autophagy-mediated cell death, and necrosis/necroptosis. Cis-khellactone concentration-dependently decreased cell viability by increasing the level of reactive oxygen species (ROS) and decreasing mitochondrial membrane potential (MMP), which are related to all three types of PCD. Mitochondrial fractionation data revealed that cis-khellactone induced the translocation of BAX and BAK into mitochondria as well as the overexpression of VDAC1, which probably accelerates MMP disruption and finally cell death. Importantly, our extended in vivo studies with xenograft model further confirmed these findings of anti-cancerous effects and showed no harmful effects in normal tissues, suggesting that there would be no side effects in humans.

Sodium butyrate induces cell death by autophagy and reactivates a tumor suppressor gene DIRAS1 in renal cell carcinoma cell line UOK146

Sodium butyrate (SB), a histone deacetylase inhibitor, is emerging as a potent anti-cancer drug for different types of cancers. In the present study, anti-cancer activity of SB in Xp11.2 (TFE3) translocated renal cell carcinoma cell line UOK146 was studied. Anti-proliferative effect of SB in renal cell carcinoma (RCC) cell line UOK146 was evaluated by MTT assay and morphological characteristics were observed by phase contrast microscopy which displayed the cell death after SB treatment. SB induces DNA fragmentation and change in nuclear morphology observed by increased sub-G1 region cell population and nuclear blebbings. Cell cycle arrest at G2/M phase was found after SB treatment. UOK146 cell line shows autophagy mode of cell death as displayed by acridine orange staining and flow cytometry analysis. LC3-II, a protein marker of autophagy, was also found to be upregulated after SB treatment. A tumor suppressor gene DIRAS1 was upregulated after SB treatment, displaying its anti-cancer potential at molecular level. These findings suggest that SB could serve as a novel regulator of tumor suppressors and lead to the discovery of novel therapeutics with better and enhanced anti-cancer activity.

Silencing Livin improved the sensitivity of colon cancer cells to 5-fluorouracil by regulating crosstalk between apoptosis and autophagy

Colorectal cancer (CRC) is the third most common cause of cancer-associated mortality worldwide. Currently, 5-fluorouracil (5-FU) remains a widely used chemotherapeutic drug in the treatment of CRC; however, 5-FU resistance during treatment has become a common problem. Livin, a member of the inhibitor of apoptosis protein family, is considered to be associated with tumor resistance to chemotherapy. In the present study, Livin-silenced cells were generated by introducing a lentivirus into HCT116 and SW620 colon cancer cell lines. Acridine orange/ethidium bromide staining was used as an indicator of cell death. Western blot analysis was performed to detect protein expression levels, and transmission electron microscopy was used to assess autophagy. The half-maximal inhibitory concentration of 5-FU in colon cancer cells was evaluated using a Cell Counting Kit-8 assay. The results of the present study confirmed that silencing Livin significantly enhanced colon cancer cell death in the presence of 5-FU, increased expression levels of various apoptosis- and autophagy-associated proteins and augmented chemotherapeutic sensitivity to 5-FU. Furthermore, the present study demonstrated that this effect may be reversed when autophagy or apoptosis was inhibited, indicating that apoptosis and autophagy were involved in this process. The protein kinase B signaling pathway and B-cell lymphoma-2 expression levels significantly decreased following Livin knockdown, suggesting they may contribute to the regulation of apoptosis and autophagy crosstalk, which caused the Livin knockdown-induced cell death observed.

Isoliquiritigenin induces apoptosis and autophagy and inhibits endometrial cancer growth in mice

Endometrial cancer is the most common cancer in women, typically with onset after menopause. Isoliquiritigenin (ISL), a licorice flavonoid, was previously shown to have anti-oxidant, anti-inflammatory, and tumor suppression effects. In this study, we investigated the anti-tumor effect of ISL on human endometrial cancer both in vitro and in vivo. We used telomerase-immortalized human endometrial stromal cells (T-HESCs) and human endometrial cancer cell lines (Ishikawa, HEC-1A, and RL95-2 cells) as targets. The effects of ISL on cell proliferation, cell cycle regulation, and apoptosis or autophagy-related protein expression were examined. In addition, we conducted in vivo experiments to confirm the inhibitory effects of ISL on cancer cells. ISL significantly inhibited the viability of cancer cells in a dose- and time-dependent manner but with little toxicity on normal cells. In addition, flow cytometry analysis indicated that ISL induced sub-G1 or G2/M phase arrest. ISL treatment activated the extracellular signal regulated kinase signaling pathway to enhance the protein expression of caspase-7/LC3BII associated with apoptosis/autophagy. Furthermore, ISL suppressed xenograft tumor growth in vivo. Taken together, these findings suggest that ISL may induce apoptosis, autophagy, and cell growth inhibition, indicating its potential as a therapeutic agent for human endometrial cancer.