Frameshift mutations of autophagy-related genes ATG2B, ATG5, ATG9B and ATG12 in gastric and colorectal cancers with microsatellite instability

The mitochondrial permeability transition pore and cancer: molecular mechanisms involved in cell death

Since its discovery in the 1970s, the mitochondrial permeability transition (MPT) has been proposed to be a strategic regulator of cell death. Intense research efforts have focused on elucidating the molecular components of the MPT because this knowledge may help to better understand and treat various pathologies ranging from neurodegenerative and cardiac diseases to cancer. In the case of cancer, several studies have revealed alterations in the activity of the mitochondrial permeability transition pore (mPTP) and have determined its regulatory mechanism; these studies have also suggested that suppression of the activity of the mPTP, rather than its inactivation, commonly occurs in solid neoplasms. This review focuses on the most recent advances in understanding mPTP regulation in cancer and highlights the ability of the mPTP to impede the mechanisms of cell death.

Dicer expression and microRNA dysregulation associate with aggressive features in thyroid cancer

BACKGROUND

Altered miRNA expression and down-regulation of Dicer has been shown in various cancers. We investigated Dicer expression and global miRNA environment in correlation with malignant features of thyroid tumors.

METHODS

Dicer gene expression was assessed for 22 normal thyroids, 16 follicular adenomas, 28 papillary thyroid cancers (PTCs), 10 tall-cell variants of PTC, 11 follicular variants of PTC, as well as the four thyroid cell lines BCPAP, TPC1, KTC1, and TAD2 via quantitative polymerase chain reaction. BRAF((V600E)) mutation screening was completed for 31 neoplasms. Next-generation sequencing was performed on a subset of PTC and normal thyroid. Protein levels were assessed via Western blotting and immunohistochemistry.

RESULTS

Dicer mRNA was down-regulated in malignant thyroid samples and cell lines compared with normal tissues, benign neoplasms, and the fetal cell line TAD2. Decreased Dicer gene expression in malignant tissues was correlated greatly with aggressive features: extrathyroidal extension, angiolymphatic invasion, multifocality, lymph node and distant metastasis, recurrence, and BRAF((V600E)) mutation. Conversely, increased levels of Dicer protein were observed in malignant tissues and cell lines. Sequencing yielded 19 differentially expressed miRNAs. Eight samples had a nonsignificant a global down-regulation in malignant tissues.

CONCLUSION

Dysregulation of Dicer and possibly altered expression of miRNAs are associated with aggressive features in thyroid cancers. These findings suggest that disruption in normal miRNA processing involving Dicer may play a role in thyroid cancer progression.

The oncogenic polycomb histone methyltransferase EZH2 methylates lysine 120 on histone H2B and competes ubiquitination

The histone methyltransferase enhancer of zeste 2 (EZH2) is known to be a polycomb protein homologous to Drosophila enhancer of zeste and catalyzes the addition of methyl groups to histone H3 at lysine 27 (H3K27). We previously reported that EZH2 was overexpressed in various types of cancer and plays a crucial role in the cell cycle regulation of cancer cells. In the present study, we demonstrated that EZH2 has the function to monomethylate lysine 120 on histone H2B (H2BK120). EZH2-dependent H2BK120 methylation in cancer cells was confirmed with an H2BK120 methylation-specific antibody. Overexpression of EZH2 significantly attenuated the ubiquitination of H2BK120, a key posttranslational modification of histones for transcriptional regulation. Concordantly, knockdown of EZH2 increased the ubiquitination level of H2BK120, suggesting that the methylation of H2BK120 by EZH2 may competitively inhibit the ubiquitination of H2BK120. Subsequent chromatin immunoprecipitation-Seq and microarray analyses identified downstream candidate genes regulated by EZH2 through the methylation of H2BK120. This is the first report to describe a novel substrate of EZH2, H2BK120, unveiling a new aspect of EZH2 functions in human carcinogenesis.

Chloroquine and hydroxychloroquine for cancer therapy

Macroautophagy (herein referred to as autophagy) is a highly conserved mechanism for the lysosomal degradation of cytoplasmic components. Autophagy is critical for the maintenance of intracellular homeostasis, both in baseline conditions and in the context of adaptive responses to stress. In line with this notion, defects in the autophagic machinery have been etiologically associated with various human disorders including infectious, inflammatory and neoplastic conditions. Once tumors are established, however, autophagy sustains the survival of malignant cells, hence representing an appealing target for the design of novel anticancer regimens. Accordingly, inhibitors of autophagy including chloroquine and hydroxychloroquine have been shown to mediate substantial antineoplastic effects in preclinical models, especially when combined with chemo- or radiotherapeutic interventions. The pharmacological profile of chloroquine and hydroxychloroquine, however, appear to involve mechanisms other than autophagy inhibition. Here, we discuss the dual role of autophagy in oncogenesis and tumor progression, and summarize the results or design of clinical studies recently completed or initiated to evaluate the therapeutic activity of chloroquine derivatives in cancer patients.

Xenophagy in Helicobacter pylori- and Epstein-Barr virus-induced gastric cancer

Helicobacter pylori and Epstein-Barr virus (EBV) account for roughly 80% and 10%, respectively, of gastric carcinomas worldwide. Autophagy is an evolutionarily conserved and intricately regulated cellular process that involves the sequestration of cytoplasmic proteins and organelles into double-membrane autophagosomes that eventually fuse with lysosomes for degradation of the engulfed content. Emerging evidence indicates that xenophagy, a form of selective autophagy, plays a crucial role in the pathogenesis of H. pylori- and EBV-induced gastric cancer. Xenophagy specifically recognizes intracellular H. pylori and EBV and physically targets these pathogens to the autophagosomal-lysosomal pathway for degradation. In this connection, H. pylori or EBV-induced dysregulation of autophagy may be causally linked to gastric tumourigenesis and therefore can be exploited as therapeutic targets. This review will discuss how H. pylori and EBV infection activate autophagy and how these pathogens evade recognition and degradation by the autophagic pathway. Elucidating the molecular aspects of H. pylori- and EBV-induced autophagy will help us better understand the pathogenesis of gastric cancer and promote the development of autophagy modulators as antimicrobial agents.

Methylation silencing of ULK2, an autophagy gene, is essential for astrocyte transformation and tumor growth

Glioblastoma (GBM) is the most aggressive type of brain tumor and shows very poor prognosis. Here, using genome-wide methylation analysis, we show that G-CIMP+ and G-CIMP-subtypes enrich distinct classes of biological processes. One of the hypermethylated genes in GBM, ULK2, an upstream autophagy inducer, was found to be down-regulated in GBM. Promoter hypermethylation of ULK2 was confirmed by bisulfite sequencing. GBM and glioma cell lines had low levels of ULK2 transcripts, which could be reversed upon methylation inhibitor treatment. ULK2 promoter methylation and transcript levels showed significant negative correlation. Ectopic overexpression of ULK2-induced autophagy, which further enhanced upon nutrient starvation or temozolomide chemotherapy. ULK2 also inhibited the growth of glioma cells, which required autophagy induction as kinase mutant of ULK2 failed to induce autophagy and inhibit growth. Furthermore, ULK2 induced autophagy and inhibited growth in Ras-transformed immortalized Baby Mouse Kidney (iBMK) ATG5(+/+) but not in autophagy-deficient ATG5(-/-) cells. Growth inhibition due to ULK2 induced high levels of autophagy under starvation or chemotherapy utilized apoptotic cell death but not at low levels of autophagy. Growth inhibition by ULK2 also appears to involve catalase degradation and reactive oxygen species generation. ULK2 overexpression inhibited anchorage independent growth, inhibited astrocyte transformation in vitro and tumor growth in vivo. Of all autophagy genes, we found ULK2 and its homologue ULK1 were only down-regulated in all grades of glioma. Thus these results altogether suggest that inhibition of autophagy by ULK1/2 down-regulation is essential for glioma development.

Autophagy--a key player in cellular and body metabolism

Knowledge gained over the past 10 years about the mechanisms that underpin autophagy has provided a universal framework for studies of diverse physiological and pathological processes. Of particular interest is the emerging role of autophagy in the maintenance of energy homeostasis, both at the cellular level and within the organism as a whole. Dysregulation of autophagy might contribute to the development of metabolic disorders, including insulin resistance, diabetes mellitus, obesity, atherosclerosis and osteoporosis. The authors of this Review highlight research findings on the regulation of cellular autophagy by nutrients. They also describe the role of autophagy in various tissues in the regulation of energy metabolism and the development of diseases related to altered metabolism. Finally, the potential of pharmacological modulation of autophagy as a treatment for human metabolic disorders is discussed.

Unravelling the multifaceted roles of Atg proteins to improve cancer therapy

Autophagy follows a lysosomal degradation pathway in which a cell digests its own components. It is highly regulated by a limited number of autophagy-related genes (Atg) and the proteins they encode, that are crucial for cells to undergo the process via modulating autophagsome formation. Recently, accumulating evidence has revealed the core molecular machinery of autophagy; however, intricate relationships between autophagy and cancer remain an enigma. Several studies have shown that Atgs can play an important role in carcinogenesis, by which Atgs may modulate a series of oncogenic and tumour suppressive pathways, implicating microRNA (miRNA) involvement. In this review, we will present the key role of Atgs in deciding the fate of cancer cells, discuss some representative Atgs and their proteins such as ULK, Beclin-1, and Atg8/LC3-Atg4, which can also be regulated by miRNAs. Thus, Atgs can be considered to be targets for cancer treatment, which may illuminate the future of cancer therapy.

QSOX1 inhibits autophagic flux in breast cancer cells

The QSOX1 protein (Quiescin Sulfhydryl oxidase 1) catalyzes the formation of disulfide bonds and is involved in the folding and stability of proteins. More recently, QSOX1 has been associated with tumorigenesis and protection against cellular stress. It has been demonstrated in our laboratory that QSOX1 reduces proliferation, migration and invasion of breast cancer cells in vitro and reduces tumor growth in vivo. In addition, QSOX1 expression has been shown to be induced by oxidative or ER stress and to prevent cell death linked to these stressors. Given the function of QSOX1 in these two processes, which have been previously linked to autophagy, we wondered whether QSOX1 might be regulated by autophagy inducers and play a role in this catabolic process. To answer this question, we used in vitro models of breast cancer cells in which QSOX1 was overexpressed (MCF-7) or extinguished (MDA-MB-231). We first showed that QSOX1 expression is induced following amino acid starvation and maintains cellular homeostasis. Our results also indicated that QSOX1 inhibits autophagy through the inhibition of autophagosome/lysosome fusion. Moreover, we demonstrated that inhibitors of autophagy mimic the effect of QSOX1 on cell invasion, suggesting that its role in this process is linked to the autophagy pathway. Previously published data demonstrated that extinction of QSOX1 promotes tumor growth in NOG mice. In this study, we further demonstrated that QSOX1 null tumors present lower levels of the p62 protein. Altogether, our results demonstrate for the first time a role of QSOX1 in autophagy in breast cancer cells and tumors.

Manipulation of autophagy in cancer cells: an innovative strategy to fight drug resistance

Autophagy is a catabolic process activated by stress conditions and nutrient deprivation, to which it reacts by promoting the degradation of damaged organelles and misfolded/aggregated proteins, as well as generating new energetic pools. Paradoxically, in cancer cells, which signal the dangerous microenvironment occurring during clinical therapies, autophagy could promote their proliferation and sustain drug resistance. Special attention is given to autophagy manipulation in order to counteract drug resistance of cancer cells. This article describes the basic properties of autophagy and focuses on the strategies of manipulating it.

Modulation of autophagy by Helicobacter pylori and its role in gastric carcinogenesis

Helicobacter pylori infection represents the strongest known risk factor for the development of gastric cancer. The vacuolating cytotoxin (VacA) plays a key role in disease pathogenesis by exerting pleiotrophic effects on the host. One effect of acute VacA exposure is the induction of autophagy. However, prolonged exposure to the toxin disrupts autophagy by preventing maturation of the autolysosome. Novel insights into the mechanism and consequences of this phenomenon have emerged, but many aspects remain largely unknown. Current evidence supports a scenario in which H. pylori-suppressed autophagy facilitates intracellular survival and persistence of the pathogen, while also generating an environment favoring carcinogenesis.

Autophagy and genomic integrity

DNA lesions, constantly produced by endogenous and exogenous sources, activate the DNA damage response (DDR), which involves detection, signaling and repair of the damage. Autophagy, a lysosome-dependent degradation pathway that is activated by stressful situations such as starvation and oxidative stress, regulates cell fate after DNA damage and also has a pivotal role in the maintenance of nuclear and mitochondrial genomic integrity. Here, we review important evidence regarding the role played by autophagy in preventing genomic instability and tumorigenesis, as well as in micronuclei degradation. Several pathways governing autophagy activation after DNA injury and the influence of autophagy upon the processing of genomic lesions are also discussed herein. In this line, the mechanisms by which several proteins participate in both DDR and autophagy, and the importance of this crosstalk in cancer and neurodegeneration will be presented in an integrated fashion. At last, we present a hypothetical model of the role played by autophagy in dictating cell fate after genotoxic stress.

XIAP inhibits autophagy via XIAP-Mdm2-p53 signalling

The primary role of autophagy is adaption to starvation. However, increasing evidence suggests that autophagy inhibition also plays an important role in tumorigenesis. Upregulation of X-linked inhibitor of apoptosis (XIAP) has been associated to a variety of human cancers, yet the underlying mechanisms remain obscure. Here, we report that XIAP suppresses autophagy by exerting a previously unidentified ubiquitin E3 ligase activity towards Mdm2, which is a negative regulator of p53. XIAP controls serum starvation-induced autophagy downstream of the PI3K/Akt pathway. In mouse models, inhibition of autophagy by XIAP promotes tumorigenecity of HCT116 cells. XIAP-mediated autophagy inhibition is also largely validated in clinical tumour samples. These findings reveal a novel XIAP-Mdm2-p53 pathway that mediates the inhibition of autophagy, by which XIAP may contribute to tumorigenesis.

Nilotinib induces autophagy in hepatocellular carcinoma through AMPK activation

Hepatocellular carcinoma (HCC) is the most common liver cancer and the third-leading cause of cancer death worldwide. Nilotinib is an orally available receptor tyrosine kinase inhibitor approved for chronic myelogenous leukemia. This study investigated the effect of nilotinib on HCC. Nilotinib did not induce cellular apoptosis. Instead, staining with acridine orange and microtubule-associated protein 1 light chain 3 revealed that nilotinib induced autophagy in a dose- and time-dependent manner in HCC cell lines, including PLC5, Huh-7, and Hep3B. Moreover, nilotinib up-regulated the phosphryaltion of AMP-activated kinase (AMPK) and protein phosphatase PP2A inactivation were detected after nilotinib treatment. Up-regulating PP2A activity suppressed nilotinib-induced AMPK phosphorylation and autophagy, suggesting that PP2A mediates the effect of nilotinib on AMPK phosphorylation and autophagy. Our data indicate that nilotinib-induced AMPK activation is mediated by PP2A, and AMPK activation and subsequent autophagy might be a major mechanism of action of nilotinib. Growth of PLC5 tumor xenografts in BALB/c nude mice was inhibited by daily oral treatment with nilotinib. Western blot analysis showed both increased phospho-AMPK expression and decreased PP2A activity in vivo. Together, our results reveal that nilotinib induces autophagy, but not apoptosis in HCC, and that the autophagy-inducing activity is associated with PP2A-regulated AMPK phosphorylation.

Autophagy modulation as a target for anticancer drug discovery

Autophagy, an evolutionarily conserved catabolic process involving the engulfment and degradation of non-essential or abnormal cellular organelles and proteins, is crucial for homeostatic maintenance in living cells. This highly regulated, multi-step process has been implicated in diverse diseases including cancer. Autophagy can function as either a promoter or a suppressor of cancer, which makes it a promising and challenging therapeutic target. Herein, we overview the regulatory mechanisms and dual roles of autophagy in cancer. We also describe some of the representative agents that exert their anticancer effects by regulating autophagy. Additionally, some emerging strategies aimed at modulating autophagy are discussed as having the potential for future anticancer drug discovery. In summary, these findings will provide valuable information to better utilize autophagy in the future development of anticancer therapeutics that meet clinical requirements.

Autophagy in ageing and ageing-associated diseases

Autophagy is a cell self-digestion process via lysosomes that clears “cellular waste”, including aberrantly modified proteins or protein aggregates and damaged organelles. Therefore, autophagy is considered a protein and organelle quality control mechanism that maintains normal cellular homeostasis. Dysfunctional autophagy has been observed in ageing tissues and several ageing-associated diseases. Lifespan of model organisms such as yeast, worms, flies, and mice can be extended through promoting autophagy, either by genetic manipulations such as over-expression of Sirtuin 1, or by administrations of rapamycin, resveratrol or spermidine. The evidence supports that autophagy may play an important role in delaying ageing or extending lifespan. In this review, we summarize the current knowledge about autophagy and its regulation, outline recent developments ie the genetic and pharmacological manipulations of autophagy that affects the lifespan, and discuss the role of autophagy in the ageing-related diseases.

Small-molecule regulators of autophagy and their potential therapeutic applications

Autophagy is a highly conserved process in which damaged proteins and organelles are sequestered in double-membrane autophagosomes and delivered to lysosomes for degradation and recycling. As an efficient response to cellular stress, autophagy is essential for the maintenance of cellular homeostasis. Defective autophagy is associated with a variety of diseases, including cancer. This article summarizes current knowledge about the molecular mechanism of autophagy and its role in tumorigenesis. Particular focus is placed on the development of small-molecule regulators of autophagy and their potential application as anticancer therapeutic agents.

A novel and functional variant within the ATG5 gene promoter in sporadic Parkinson's disease

Parkinson's disease (PD) is one of the most common neurodegenerative diseases. Majority of PD are sporadic, for which genetic causes remain largely unknown. Alpha-synuclein, the main component of Lewy bodies, plays a central role in the PD pathogenesis. Macroautophagy is a highly conserved cellular process that digests dysfunctional macromolecules and damaged organelles. Accumulating evidence indicates that macroautophagy (hereafter referred to as autophagy) is involved in alpha-synuclein degradation. Dysregulation of autophagy has been observed in the brain tissues from PD patients and animal models. We hypothesized that change expression levels of autophagy-related genes (ATG), including ATG5, may contribute to PD. In this study, we genetically and functionally analyzed the ATG5 gene promoter in groups of sporadic PD patients and ethnic-matched healthy controls. A novel heterozygous variant, 106774459T>A, was identified in one female patient, but in none of controls, which significantly enhanced transcriptional activities of the ATG5 gene promoter. Furthermore, ATG5 gene expression level in the PD patient was significantly elevated than that in controls. Four novel heterozygous variants, 106774423C>A, 106774418C>A, 106774382C>A and 106774206G>A, were only found in controls. The variant, 106774464C>T, and SNP-106774030A>G (rs510432) were found in PD patients and controls with similar frequencies. Collectively, the variant identified in PD patient may change ATG5 protein levels and alter autophagy activities, contributing to PD onset as a risk factor.

Modulating autophagy: a strategy for cancer therapy

Autophagy is a process in which long-lived proteins, damaged cell organelles, and other cellular particles are sequestered and degraded. This process is important for maintaining the cellular microenvironment when the cell is under stress. Many studies have shown that autophagy plays a complex role in human diseases, especially in cancer, where it is known to have paradoxical effects. Namely, autophagy provides the energy for metabolism and tumor growth and leads to cell death that promotes tumor suppression. The link between autophagy and cancer is also evident in that some of the genes that regulate Carcinogenesis, oncogenes and tumor suppressor genes, participate in or impact the autophagy process. Therefore, modulating autophagy will be a valuable topic for cancer therapy. Many studies have shown that autophagy can inhibit the tumor growth when autophagy modulators are combined with radiotherapy and/or chemotherapy. These findings suggest that autophagy may be a potent target for cancer therapy.

Role of autophagy in cancer prevention, development and therapy

Autophagy is a process that takes place in all mammalian cells and ensures homoeostasis and quality control. The term autophagy [self (auto)-eating (phagy)] was first introduced in 1963 by Christian de Duve, who discovered the involvement of lysosomes in the autophagy process. Since then, substantial progress has been made in understanding the molecular mechanism and signalling regulation of autophagy and several reviews have been published that comprehensively summarize these findings. The role of autophagy in cancer has received a lot of attention in the last few years and autophagy modulators are now being tested in several clinical trials. In the present chapter we aim to give a brief overview of recent findings regarding the mechanism and key regulators of autophagy and discuss the important physiological role of mammalian autophagy in health and disease. Particular focus is given to the role of autophagy in cancer prevention, development and in response to anticancer therapy. In this regard, we also give an updated list and discuss current clinical trials that aim to modulate autophagy, alone or in combination with radio-, chemo- or targeted therapy, for enhanced anticancer intervention.

New frontiers in promoting tumour cell death: targeting apoptosis, necroptosis and autophagy

Cancer is a multifaceted disease comprising a combination of genetic, metabolic and signalling aberrations, which severely disrupt the normal homeostasis of cell growth and death. Many oncogenic events while promoting tumour development also increase the sensitivity of cells to cell death stimuli including chemotherapeutic drugs. As a result, tumour cells often acquire the ability to evade death by inactivating cell death pathways that normally function to eliminate damaged and harmful cells. The impairment of cell death function is also often the reason for the development of chemotherapeutic resistance encountered during treatment. It is therefore necessary to achieve a comprehensive understanding of existing cell death pathways and the relevant regulatory components involved, with the intention of identifying new strategies to kill cancer cells. This review provides an insightful overview of the common forms of cell death signalling pathways, the interactions between these pathways and the ways in which these pathways are deregulated in cancer. We also discuss the emerging therapies targeted at activating or restoring cell death pathways to induce tumour cell death, which are currently being tested in clinical trials.

Autophagy Mechanism, Regulation, Functions, and Disorders

Autophagy is a self-digesting mechanism responsible for removal of damaged organelles, malformed proteins during biosynthesis, and nonfunctional long-lived proteins by lysosome. Autophagy has been divided into three general types depending on the mechanism by which intracellular materials are delivered into lysosome for degradation that is, microautophagy, chaperone-mediated autophagy (CMA), and macroautophagy. In microautophagy cytoplasm material is sequestered through direct invagination to the lysosomal membrane. Whereas in CMA proteins flagged with pentapeptide motif (KFERQ) were selectively degraded through direct translocation into lysosome. Macroautophagy involves the formation of subcellular double-membrane-bound structures called autophagosomes that contain degradable contents of cytoplasm materials and deliver them into lysosomes for breakdown by lysosomal enzymes. The molecular mechanism of autophagy involves several conserved Atg (autophagy-related) proteins. Systems produce modified complexes Atg8-PE and Atg5-Atg12-Atg16 as autophagy regulators. Autophagy is activated in response to diverse stress and physiological conditions. For example, food deprivation, hyperthermia, and hypoxia are mediated by factors like insulin/IGF-1, m-TOR signaling, FOXO transcription factors, and chaperones. The perturbance in autophagy may lead to several types of cancers, myopathies, and neuromuscular disorders. Several autophagy inducers and inhibitors like 3-methyladenine (3-MA), bafilomycin A1, LY294002 (LY), and Velcade have been used to treat disease is an intense field of study.

Autophagy and cancer

Autophagy is a housekeeping survival mechanism with a protective function against stress conditions. However, when stress severity or duration increases, it may promote cell death. Paradoxically, autophagy favors cancer development, since cancer cells could enhance their proliferation potential (thus becoming able to resist anticancer therapy) thanks to the energetic supply provided by organelle degradation typically driven by autophagy following a stepwise pathway. The main actors of the autophagic machinery as well as the features shared with apoptosis will be described. Special attention will be paid to the effects of autophagy manipulation.

Analysis of macroautophagy by immunohistochemistry

(Macro)Autophagy is a phylogenetically conserved membrane-trafficking process that functions to deliver cytoplasmic cargoes to lysosomes for digestion. The process is a major mechanism for turnover of cellular constituents and is therefore critical for maintaining cellular homeostasis. Macroautophagy is characteristically distinct from other forms of autophagy due to the formation of double-membraned vesicles termed autophagosomes which encapsulate cargoes prior to fusion with lysosomes. Autophagosomes contain an integral membrane-bound form (LC3-II) of the microtubule-associated protein 1 light chain 3 β (MAP1LC3B), which has become a gold-standard marker to detect accumulation of autophagosomes and thereby changes in macroautophagy. Due to the role played by macroautophagy in various diseases, the detection of autophagosomes in tissue sections is frequently desired. To date, however, the detection of endogenous LC3-II on paraffin-embedded tissue sections has proved problematic. We report here a simple, optimized and validated method for the detection of LC3-II by immunohistochemistry in human and mouse tissue samples that we believe will be a useful resource for those wishing to study macroautophagy ex vivo.

Autophagy and cancer--issues we need to digest

Autophagy is an evolutionarily conserved catabolic pathway that has multiple roles in carcinogenesis and cancer therapy. It can inhibit the initiation of tumorigenesis through limiting cytoplasmic damage, genomic instability and inflammation, and the loss of certain autophagy genes can lead to cancer. Conversely, autophagy can also assist cells in dealing with stressful metabolic environments, thereby promoting cancer cell survival. In fact, some cancers rely on autophagy to survive and progress. Furthermore, tumour cells can exploit autophagy to cope with the cytotoxicity of certain anticancer drugs. By contrast, it appears that certain therapeutics require autophagy for the effective killing of cancer cells. Despite these dichotomies, it is clear that autophagy has an important, if complex, role in cancer. This is further exemplified by the fact that autophagy is connected with major cancer networks, including those driven by p53, mammalian target of rapamycin (mTOR), RAS and glutamine metabolism. In this Commentary, we highlight recent advances in our understanding of the role that autophagy has in cancer and discuss current strategies for targeting autophagy for therapeutic gain.

Autophagy in tumorigenesis and cancer therapy: Dr. Jekyll or Mr. Hyde?

Autophagy is an evolutionarily conserved mechanism for intracellular substance degradation, responsible for the recycling of metabolic substances and the maintenance of intracellular stability. It has early been demonstrated to play a significant role in tumorigenesis, but whether it acts as a promoter or a suppressor during tumorigenesis seems to be context-specific. Moreover, autophagy is also implicated in promoting chemoresistance of cancer cells so as to attenuate therapeutic efficacy of chemotherapy. On the contrary, other reports highlight a tumor-killing role of autophagy during cancer treatment. Herein, this review aims to revisit the key features of autophagy, summarize the seemingly contradictory roles of autophagy during both tumorigenesis and cancer chemotherapy, and evaluate the feasibility of altering the level of cellular autophagy as part of cancer adjuvant treatment.

miRNA-130a targets ATG2B and DICER1 to inhibit autophagy and trigger killing of chronic lymphocytic leukemia cells

Toxicity and relapses from the immunochemotherapy used to treat chronic lymphocytic leukemia (CLL) prompt continued interest in gentle but effective targeted treatment options for the mainly elderly population suffering from this disease. Here, we report the definition of critical CLL cell survival pathways that can be targeted by ectopic reexpression of the miRNA genes miR-130a and miR-143 which are widely downregulated in CLL. Notably, miR-130a inhibited autophagy by reducing autophagosome formation, an effect mediated by downregulation of the genes ATG2B and DICER1, the latter of which is a major component of the miRNA silencing machinery. In support of the concept of a fundamental connection between miRNA disregulation and altered autophagic flux in this cancer, we showed that RNA interference-mediated knockdown of DICER1 expression was sufficient to reduce autophagy in primary or established cultures of CLL cells. Together, our findings show that miR-130a modulates cell survival programs by regulating autophagic flux, and they define roles for miR-130a and Dicer1 in a regulatory feedback loop that mediates CLL cell survival.

Autophagy in tumor suppression and cancer therapy

Autophagy is a stress-induced cell survival program whereby cells under metabolic, proteotoxic, or other stress remove dysfunctional organelles and/or misfolded/polyubiquitylated proteins by shuttling them via specialized structures called autophagosomes to the lysosome for degradation. The end result is the release of free amino acids and metabolites for use in cell survival. For tumor cells, autophagy is a double-edged sword: autophagy genes are frequently mono-allelically deleted, silenced, or mutated in human tumors, resulting in an environment of increased oxidative stress that is conducive to DNA damage, genomic instability, and tumor progression. As such, autophagy is tumor suppressive. In contrast, it is important to note that although tumor cells have reduced levels of autophagy, they do not eliminate this pathway completely. Furthermore, the exposure of tumor cells to an environment of increased metabolic and other stresses renders them reliant on basal autophagy for survival. Therefore, autophagy inhibition is an active avenue for the identification of novel anti-cancer therapies. Not surprisingly, the field of autophagy and cancer has experienced an explosion of research in the past 10 years. This review covers the basic mechanisms of autophagy, discusses its role in tumor suppression and cancer therapy, and posits emerging questions for the future.

Here, there be dragons: charting autophagy-related alterations in human tumors

Macroautophagy (or autophagy) is a catabolic cellular process that is both homeostatic and stress adaptive. Normal cells rely on basal levels of autophagy to maintain cellular integrity (via turnover of long-lived proteins and damaged organelles) and increased levels of autophagy to buoy cell survival during various metabolic stresses (via nutrient and energy provision through lysosomal degradation of cytoplasmic components). Autophagy can function in both tumor suppression and tumor progression, and is under investigation in clinical trials as a novel target for anticancer therapy. However, its role in cancer pathogenesis has yet to be fully explored. In particular, it remains unknown whether in vitro observations will be applicable to human cancer patients. Another outstanding question is whether there exists tumor-specific selection for alterations in autophagy function. In this review, we survey reported mutations in autophagy genes and key autophagy regulators identified in human tumor samples and summarize the literature regarding expression levels of autophagy genes and proteins in various cancer tissues. Although it is too early to draw inferences from this collection of in vivo studies of autophagy-related alterations in human cancers, their results highlight the challenges that must be overcome before we can accurately assess the scope of autophagy's predicted role in tumorigenesis.

Autophagy in brain tumors: a new target for therapeutic intervention

The role of autophagy, traditionally considered a cellular homeostatic and recycling mechanism, has expanded dramatically to include an involvement in discrete stages of tumor initiation and development. Gliomas are the most aggressive and also the most common brain malignancies. Current treatment modalities have only a modest effect on patient outcomes. Resistance to apoptosis, a hallmark of most cancers, has driven the search for novel targets in cancer therapy. The autophagy lysosomal pathway is one such target that is being explored in multiple cancers including gliomas and is a promising avenue for further therapeutic development. This review summarizes our current understanding of the autophagic process and its potential utility as a target for glioma therapy.

Autophagy: for better or for worse

Autophagy is a lysosomal degradation pathway that degrades damaged or superfluous cell components into basic biomolecules, which are then recycled back into the cytosol. In this respect, autophagy drives a flow of biomolecules in a continuous degradation-regeneration cycle. Autophagy is generally considered a pro-survival mechanism protecting cells under stress or poor nutrient conditions. Current research clearly shows that autophagy fulfills numerous functions in vital biological processes. It is implicated in development, differentiation, innate and adaptive immunity, ageing and cell death. In addition, accumulating evidence demonstrates interesting links between autophagy and several human diseases and tumor development. Therefore, autophagy seems to be an important player in the life and death of cells and organisms. Despite the mounting knowledge about autophagy, the mechanisms through which the autophagic machinery regulates these diverse processes are not entirely understood. In this review, we give a comprehensive overview of the autophagic signaling pathway, its role in general cellular processes and its connection to cell death. In addition, we present a brief overview of the possible contribution of defective autophagic signaling to disease.

Autophagy and cancer

(Macro)autophagy is a cellular membrane trafficking process that serves to deliver cytoplasmic constituents to lysosomes for degradation. At basal levels, it is critical for maintaining cytoplasmic as well as genomic integrity and is therefore key to maintaining cellular homeostasis. Autophagy is also highly adaptable and can be modified to digest specific cargoes to bring about selective effects in response to numerous forms of intracellular and extracellular stress. It is not a surprise, therefore, that autophagy has a fundamental role in cancer and that perturbations in autophagy can contribute to malignant disease. We review here the roles of autophagy in various aspects of tumor suppression including the response of cells to nutrient and hypoxic stress, the control of programmed cell death, and the connection to tumor-associated immune responses.

Depletion of tissue factor suppresses hepatic metastasis and tumor growth in colorectal cancer via the downregulation of MMPs and the induction of autophagy and apoptosis

Tissue factor (TF) is a significant risk factor for hepatic metastasis in patients with colorectal cancer (CRC). However, the mechanism by which TF promotes hepatic metastasis in CRC remains elusive. In this study, we first confirmed that TF expression was significantly correlated with lymph node metastasis, hepatic metastasis and TNM staging in clinical CRC samples, and found that TF expression in colon cancer cell lines was correlated with the invasion ability. Next, by employing TF-overexpressing LOVO cell line as a model we demonstrated that lentivirus mediated knockdown of TF suppressed the migration and invasion of LOVO cells in vitro, and hepatic metastasis of colorectal cancer in nude mice orthotopic model. Mechanistically, we found that TF knockdown decreases colony formation ability and induced autophagy and apoptosis of LOVO cells, and this was at least partly mediated by the activation of unfolded protein response/PERK signaling. In conclusion, our data provide new insight into hepatic metastasis of CRC. Agents targeting TF should be developed as adjuvant therapeutics for CRC metastasis.

Expressional and mutational analyses of ATG5 gene in prostate cancers

Autophagy is an evolutionarily conserved mechanism that plays important roles in both cell death and cell survival. ATG5 is an essential constituent for autophagosome formation, which sequesters cytoplasmic materials before lysosomal delivery. Although both cell death and survival are important in cancer development, the role of autophagy in prostate cancer development remains unclear. The aim of this study was to see whether alterations of ATG5 protein expression and somatic mutations of the ATG5 gene are found in prostate cancers. In the present study, we analyzed ATG5 protein expression in 107 prostate carcinomas by immunohistochemistry; additionally, we assayed the presence of ATG5 somatic mutations in 45 prostate carcinomas by single-strand conformation polymorphism. Immunostaining of ATG5 in normal prostate cells was observed in 44.9% of the cases, whereas in prostate intraepithelial neoplasm (PIN) and prostate cancer cells, ATG5 was observed in 100% and 89.7% of the cases, respectively. Cytoplasmic expression of ATG5 that might be related to autophagy was seen in PIN (100%) and cancers (83.2%), but not in normal cells (0%). ATG5 expression was not associated with any of the pathologic characteristics, including size of the cancers, age, Gleason score, and stage. As for the ATG5 gene, we found no somatic mutations in the prostate cancers. In this study, we analyzed ATG5 expression and mutation in prostate cancers, and found that ATG5 expression was altered in prostate cancers. The expression of ATG5, especially in the cytoplasm, in the prostate cancers compared with normal prostate cells suggested that overexpression of this protein may be related to autophagy and might play a role in prostate tumorigenesis.

The multifaceted roles of autophagy in tumors-implications for breast cancer

Autophagy is an evolutionarily conserved lysosomal degradation process that is crucial for adaptation to stress as well as in cellular homeostasis. In cancer, our current understanding has uncovered multifaceted roles for autophagy in tumor initiation and progression. Although genetic evidence corroborates a critical role for autophagy as a tumor suppressor mechanism, autophagy can also promote the survival and fitness of advanced tumors subject to stress, which has important implications during breast cancer progression and metastasis. Here, I discuss the mechanisms and the evidence underlying these diverse roles for autophagy in cancer and speculate on specific circumstances in which autophagy can be most effectively targeted for breast cancer treatment.

Molecular machinery of macroautophagy and its deregulation in diseases

Macroautophagy maintains cellular homeostasis through targeting cytoplasmic contents and organelles into autophagosomes for degradation. This process begins with the assembly of protein complexes on isolation membrane to initiate the formation of autophagosome, followed by its nucleation, elongation and maturation. Fusion of autophagosomes with lysosomes then leads to degradation of the cargo. In the past decade, significant advances have been made on the identification of molecular players that are implicated in various stages of macroautophagy. Post-translational modifications of macroautophagy regulators have also been demonstrated to be critical for the selective targeting of cytoplasmic contents into autophagosomes. In addition, recent demonstration of distinct macroautophagy regulators has led to the identification of different subtypes of macroautophagy. Since deregulation of macroautophagy is implicated in diseases including neurodegenerative disorders, cancers and inflammatory disorders, understanding the molecular machinery of macroautophagy is crucial for elucidating the mechanisms by which macroautophagy is deregulated in these diseases, thereby revealing new potential therapeutic targets and strategies. Here we summarize current knowledge on the regulation of mammalian macroautophagy machineries and their disease-associated deregulation.

The autophagic paradox in cancer therapy

Autophagy, hallmarked by the formation of double-membrane bound organelles known as autophagosomes, is a lysosome-dependent pathway for protein degradation. The role of autophagy in carcinogenesis is context dependent. As a tumor-suppressing mechanism in early-stage carcinogenesis, autophagy inhibits inflammation and promotes genomic stability. Moreover, disruption of autophagy-related genes accelerates tumorigenesis in animals. However, autophagy may also act as a pro-survival mechanism to protect cancer cells from various forms of cellular stress. In cancer therapy, adaptive autophagy in cancer cells sustains tumor growth and survival in face of the toxicity of cancer therapy. To this end, inhibition of autophagy may sensitize cancer cells to chemotherapeutic agents and ionizing radiation. Nevertheless, in certain circumstances, autophagy mediates the therapeutic effects of some anticancer agents. Data from recent studies are beginning to unveil the apparently paradoxical nature of autophagy as a cell-fate decision machinery. Taken together, modulation of autophagy is a novel approach for enhancing the efficacy of existing cancer therapy, but its Janus-faced nature may complicate the clinical development of autophagy modulators as anticancer therapeutics.

The multiple roles of autophagy in cancer

Autophagy is an evolutionarily conserved, catabolic process that involves the entrapment of cytoplasmic components within characteristic vesicles for their delivery to and degradation within lysosomes. Autophagy is regulated via a group of genes called AuTophaGy-related genes and is executed at basal levels in virtually all cells as a homeostatic mechanism for maintaining cellular integrity. The levels and cargos of autophagy can be modulated in response to a variety of intra- and extracellular cues to bring about specific and selective events. Autophagy is a multifaceted process and alterations in autophagic signalling pathways are frequently found in cancer and many other diseases. During tumour development and in cancer therapy, autophagy has paradoxically been reported to have roles in promoting both cell survival and cell death. In addition, autophagy has been reported to control other processes relevant to the aetiology of malignant disease, including oxidative stress, inflammation and both innate and acquired immunity. It is the aim of this review to describe the molecular basis and the signalling events that control autophagy in mammalian cells and to summarize the cellular functions that contribute to tumourigenesis when autophagy is perturbed.

Mutational and expressional analyses of ATG5, an autophagy-related gene, in gastrointestinal cancers

There is mounting evidence that alterations of cell death processes are involved in cancer pathogenesis. ATG5 is a key regulator of autophagic and apoptotic cell death. The aim of this study was to see whether alterations of ATG5 protein expression and somatic mutation of ATG5 gene are features of human gastrointestinal cancers. In this study, we analyzed ATG5 somatic mutation in 45 gastric, 45 colorectal, and 45 hepatocellular carcinomas by single-strand conformation polymorphism (SSCP). Also, we analyzed ATG5 protein expression in 100 gastric, as well as in 95 colorectal and hepatocellular carcinomas using immunohistochemistry. Overall, we detected two somatic missense mutations of ATG5 gene in the coding sequences p.Leu112Phe and p.His41Tyr. The mutations were observed in one gastric and one hepatocellular carcinoma. Immunohistochemically, ATG5 protein was well expressed in normal stomach, colon, and liver epithelial cells, while it was lost in 21 (21%) of the gastric carcinomas, in 22 (23%) of the colorectal carcinomas, and in 5 (10%) of the hepatocellular carcinomas. Our data suggest that ATG5 gene could be altered in gastrointestinal cancers at the mutational or expressional level. Despite the low incidences of the alterations, our data led us to conclude that somatic mutation and loss of expression of ATG5 gene might play a role in gastrointestinal cancer pathogenesis by altering autophagic and apoptotic cell death.

Autophagy in the pathogenesis of myelodysplastic syndrome and acute myeloid leukemia

Autophagy is a conserved cellular pathway responsible for the sequestration of spent organelles and protein aggregates from the cytoplasm and their delivery into lysosomes for degradation. Autophagy plays an important role in adaptation to starvation, in cell survival, immunity, development and cancer. Recent evidence in mice suggests that autophagic defects in hematopoietic stem cells (HSCs) may be implicated in leukemia. Indeed, mice lacking Atg7 in HSCs develop an atypical myeloproliferation resembling human myelodysplastic syndrome (MDS) progressing to acute myeloid leukemia (AML). Studies suggest that accumulation of damaged mitochondria and reactive oxygen species result in cell death of the majority of progenitor cells and, possibly, concomitant transformation of some surviving ones. Interestingly, bone marrow cells from MDS patients are characterized by mitochondrial abnormalities and increased cell death. A role for autophagy in the transformation to cancer has been proposed in other cancer types. This review focuses on autophagy in human MDS development and progression to AML within the context of the role of mitochondria, apoptosis and reactive oxygen species (ROS) in its pathogenesis.

Tumour-infiltrating T-cell subsets, molecular changes in colorectal cancer, and prognosis: cohort study and literature review

The abundance of tumour-infiltrating T-cells has been associated with microsatellite instability (MSI) and a favourable prognosis in colorectal cancer. However, numerous molecular alterations have been associated with clinical outcome, and potentially confounding the biological and prognostic significance of tumour-infiltrating T-cells. We utilized a database of clinically and molecularly-annotated colon and rectal carcinoma cases (N = 768; stage I-IV) in two prospective cohort studies (the Nurses' Health Study and the Health Professionals Follow-up Study) and quantified the densities of CD3(+), CD8(+), CD45RO(+) (PTPRC), and FOXP3(+) cells within neoplastic epithelial areas using an Ariol image analysis system and tissue microarray. We used Cox proportional hazard models to compute the mortality hazard ratio, adjusting for clinical and molecular features including KRAS, BRAF, and PIK3CA mutations, MSI, CIMP, and LINE-1 hypomethylation. The densities of CD8(+), CD45RO(+), and FOXP3(+) cells were significantly associated with patient survival in univariate analyses (P(trend) < 0.007). In the multivariate model, tumour-infiltrating CD45RO(+)-cell density, but not CD3(+), CD8(+) or FOXP3(+)-cell density, was significantly associated with survival (p = 0.0032). In multivariate linear regression analysis, MSI-high (p < 0.0001) and high-level tumour LINE-1 methylation (p = 0.0013) were independently associated with higher CD45RO(+)-cell density. The survival benefit associated with CD45RO(+) cells was independent of MSI and LINE-1 status. In conclusion, tumour-infiltrating CD45RO(+)-cell density is a prognostic biomarker associated with longer survival of colorectal cancer patients, independent of clinical, pathological, and molecular features. In addition, MSI-high and tumour LINE-1 methylation level are independent predictors of CD45RO(+)-cell density. Our data offer a possible mechanism by which MSI confers an improved clinical outcome and support efforts to augment the host immune response in the tumour microenvironment as a strategy of targeted immunotherapy.

Somatic frameshift mutations of bone morphogenic protein receptor 2 gene in gastric and colorectal cancers with microsatellite instability

Mounting evidence exists that perturbation of bone morphogenic protein (BMP) signaling is involved in cancer development, especially in gastrointestinal cancers. However, somatic mutations of the genes encoding BMP and BMP receptors have not yet been discovered in human cancer tissues. By analyzing a public database, we found that BMP receptor 2 (BMPR2) and BMP1 genes had mononucleotide repeats in their coding sequences that could be mutation targets in cancers with microsatellite instability (MSI). In this study, we analyzed the mutation of BMPR2 and BMP1 genes in gastric (GC) and colorectal cancers (CRC) with MSI [31 GC with high MSI (MSI-H), 13 GC with low MSI (MSI-L), 38 CRC with MSI-H and 15 CRC with MSI-L] by single-strand conformation polymorphism analysis and DNA sequencing. Overall, we found seven frameshift mutations in the BMPR2 gene, but not in the BMP1 gene. The mutations were an identical deletion mutation of one base in the repeats (c.1748delA) that would result in premature stops of the amino acid synthesis (p.Asn583ThrfsX44). The BMPR2 mutations were detected in 6.5% of GC and 13.2% of CRC with MSI-H. All the cancers with the BMPR2 mutation showed loss of BMPR2 expression. Our data indicate that frameshift mutation of BMPR2 gene occurs in GC and CRC with MSI-H, and suggest that the BMPR2 mutation might contribute to cancer pathogenesis by inactivating BMPR2-mediated BMP signaling.