Ebb-and-Flow of Macroautophagy and Chaperone-Mediated Autophagy in Raji Cells Induced by Starvation and Arsenic Trioxide

Autophagy is crucial in the maintenance of homeostasis and regenerated energy of mammalian cells.Macroautophagy and chaperone-mediated autophagy(CMA) are the two best-identified pathways. Recentresearch has found that in normal cells, decline of macroautophagy is appropriately parallel with activationof CMA. However, whether it is also true in cancer cells has been poorly studied. Here we focused on crosstalkand conversion between macroautophagy and CMA in cultured Burkitt lymphoma Raji cells whenfacing serum deprivation and exposure to a toxic compound, arsenic trioxide. The results showed that bothmacroautophagy and CMA were activated sequentially instead of simultaneously in starvation-induced Raji cells,and macroautophagy was quickly activated and peaked during the first hours of nutrition deprivation, and thengradually decreased to near baseline. With nutrient deprivation persisted, CMA progressively increased alongwith the decline of macroautophagy. On the other hand, in arsenic trioxide-treated Raji cells, macroautophagyactivity was also significantly increased, but CMA activity was not rapidly enhanced until macroautophagy wasinhibited by 3-methyladenine, an inhibitor. Together, we conclude that cancer cells exhibit differential responsesto diverse stressor-induced damage by autophagy. The sequential switch of the first-aider macroautophagyto the homeostasis-stabilizer CMA, whether active or passive, might be conducive to the adaption of cancercells to miscellaneous intracellular or extracellular stressors. These findings must be helpful to understand thecharacteristics, compensatory mechanisms and answer modes of different autophagic pathways in cancer cells,which might be very important and promising to the development of potential targeting interventions for cancertherapies via regulation of autophagic pathways.     

自噬在菌群相关肿瘤中的研究进展

自噬是真核生物中高度保守的分解代谢过程,其实质是溶酶体依赖的蛋白质降解途径。自噬调节异常与许多肿瘤的发生发展密切相关,其既能促进肿瘤存活,亦能促进肿瘤消亡。研究表明菌群失调可通过促进黏膜炎症或引起全身疾病直接或间接导致肿瘤发生发展,并在调节免疫系统对肿瘤的反应中发挥作用。菌群失衡和自噬过程可通过多种分子机制联系在一起并通过这些途径影响肿瘤进展。本文旨在对自噬在菌群相关肿瘤中的关键作用进行综述,并探讨了自噬调节这一复杂生物学过程的分子机制;此外,本文还分析了以菌群/自噬生物轴为靶点的多种分子药物治疗肿瘤的可能性,对以自噬或菌群为靶点的临床试验进行总结并针对其作为抗癌策略的治疗潜力进行评价。      

Targeting autophagic pathways for cancer drug discovery

Autophagy , an evolutionarily conserved lysosomal degradation process , has drawn an increasing amount of attention in recent years for its role in a variety of human diseases, such as cancer. Notably, autophagy plays an important role in regulating several survival and death signaling pathways that determine cell fate in cancer. To date, substantial evidence has demonstrated that some key autophagic mediators, such as autophagy-related genes (ATGs), PI3K, mTOR, p53, and Beclin-1, may play crucial roles in modulating autophagic activity in cancer initiation and progression. Because autophagy-modulating agents such as rapamycin and chloroquine have already been used clinically to treat cancer, it is conceivable that targeting autophagic pathways may provide a new opportunity for discovery and development of more novel cancer therapeutics. With a deeper understanding of the regulatory mechanisms governing autophagy, we will have a better opportunity to facilitate the exploitation of autophagy as a target for therapeutic intervention in cancer. This review discusses the current status of targeting autophagic pathways as a potential cancer therapy.     

Beclin-1-independent autophagy mediates programmed cancer cell death through interplays with endoplasmic reticulum and/or mitochondria in colbat chloride-induced hypoxia

Autophagy has dual functions in cell survival and death. However, the effects of autophagy on cancer cell survival or death remain controversial. In this study, we show that Autophagy can mediate programmed cell death (PCD) of cancer cells in responding to cobalt chloride (CoCl₂)-induced hypoxia in a Beclin-1-independent but autophagy protein 5 (ATG5)-dependent manner. Although ATG5 is not directly induced by CoCl₂, its constitutive expression is essential for CoCl₂-induced PCD. The ATG5-mediated autophagic PCD requires interplays with endoplasmic reticulum (ER) and/or mitochondria. In this process, ATG5 plays a central role in regulating ER stress protein CCAAT/enhancer-binding protein (C/EBP) homologous protein (CHOP) and mitochondrial protein second mitochondria derived activator of caspases (Smac). Two pathways for autophagic PCD in cancer cells responding to hypoxia have been identified: ATG5/CHOP/Smac pathway and ATG5/Smac pathway, which are probably dependent on the context of cell lines. The former is more potent than the latter for the induction of PCD at the early stage of hypoxia, although the ultimate efficiency of both pathways is comparable. In addition, both pathways may require ATG5-mediated conversion of LC3-I into LC3-II. Therefore, we have defined two autophagy-mediated pathways for the PCD of cancer cells in hypoxia, which are dependent on ATG5, interplayed with ER and mitochondria and tightly regulated by hypoxic status. The findings provide a new evidence that autophagy may inhibit tumor cell proliferation through trigger of PCD, facilitating the development of novel anti-cancer drugs.     

Autophagic tumor stroma: Mechanisms and roles in tumor growth and progression

Macroautophagy (hereafter autophagy) is a cellular homeostatic mechanism that involves protein and organelle degradation, and has a number of connections to human physiology and diseases. Autophagy in tumor parenchyma acts as either a tumor‐promoting role or a tumor‐inhibiting role depending on the types and stages of tumors. In recent years, attention to autophagy in tumor stroma that is referred as “autophagic tumor stroma” has created a new paradigm to understand the role of autophagy in cancer. Here we propose that the autophagic tumor stroma is a phenomenon of adaptation at a certain stage of tumor development, and has a prominent role in tumor growth, progression and spread of tumors. This idea is supported by recent studies: (i) Autophagic tumor stroma is activated by hypoxia and cancer cells induced oxidative stress, when tumors grow to a certain stage; (ii) Autophagic tumor stroma aids in providing essential nutrients to malignant cells, remodeling the tumor microenvironment, increasing DNA damage, genetic instability and stemness in cancer cells, and decreasing the apoptotic sensitivity of cancer cells. The autophagic tumor stroma is therefore a significant determinant in tumor growth and progression and implicates an important target for cancer therapies.     

Targeting autophagy using natural compounds for cancer prevention and therapy

Autophagy, also known as macroautophagy, is a tightly regulated process involved in the stress responses, such as starvation. It is a vacuolar, lysosomal pathway for the degradation of damaged proteins and organelles in eukaryotic cells. Autophagy also plays a key role in various tissue processes and immune responses and in the regulation of inflammation. Over the past decade, three levels of autophagy regulation have been identified in mammalian cells: 1) signaling, 2) autophagosome formation, and 3) autophagosome maturation and lysosomal degradation. Any deregulation of the autophagy processes can lead to the development of diverse chronic diseases, such as diabetes, obesity, cardiovascular disease, neurodegenerative disease, and malignancies. However, the potential role of autophagy in cancer is rather complex and has been associated with both the induction and the inhibition of neoplasia. Several synthetic autophagy modulators have been identified as promising candidates for cancer therapy. In addition, diverse phytochemicals derived from natural sources, such as curcumin, ursolic acid, resveratrol, thymoquinone, and γ-tocotrienol, also have attracted attention as promising autophagy modulators with minimal side effects. In this review, the authors discuss the importance of autophagy regulators and various natural compounds that induce and/or inhibit autophagy in the prevention and therapy of cancer.     

自噬在恶性肿瘤治疗中的进展及影像学应用前景

自噬是在营养缺乏条件下维持细胞代谢的主要途径。这使其成为肿瘤研究的新热点,调控自噬信号通路的机制已经很明确,越来越多的研究发现机体细胞自噬活性变化对肿瘤治疗的效果具有巨大影响。但缺乏能够重复比较或靶向定位自噬活性的测量技术。正电子示踪剂PET等影像手段通过将相关自噬的信号通路蛋白标记放射性核素进行显像似乎具有解决这些问题的潜力。在本文中,我们综述自噬在肿瘤治疗中的应用,并展望医学影像技术协助自噬治疗肿瘤的前景。     

Autophagy as a cell death and tumor suppressor mechanism

Autophagy is characterized by sequestration of bulk cytoplasm and organelles in double or multimembrane autophagic vesicles, and their delivery to and subsequent degradation by the cell's own lysosomal system. Autophagy has multiple physiological functions in multicellular organisms, including protein degradation and organelle turnover. Genes and proteins that constitute the basic machinery of the autophagic process were first identified in the yeast system and some of their mammalian orthologues have been characterized as well. Increasing lines of evidence indicate that these molecular mechanisms may be recruited by an alternative, caspase-independent form of programmed cell death, named autophagic type II cell death. In some settings, autophagy and apoptosis seem to be interconnected positively or negatively, introducing the concept of 'molecular switches' between them. Additionally, mitochondria may be central organelles integrating the two types of cell death. Malignant transformation is frequently associated with suppression of autophagy. The recent implication of tumor suppressors like Beclin 1, DAP-kinase and PTEN in autophagic pathways indicates a causative role for autophagy deficiencies in cancer formation. Autophagic cell death induction by some anticancer agents underlines the potential utility of its induction as a new cancer treatment modality.     

Tumor cell autophagy as an adaptive response mediating resistance to treatments such as antiangiogenic therapy

Autophagy is a lysosomal degradation pathway that can sequester cytosolic material, including organelles, nonspecifically in a process called nonselective macroautophagy, or target specific protein aggregates designated for destruction in a process called selective autophagy. Autophagy is one mechanism that enables tumor cells to survive stressors in the tumor microenvironment, as well as injuries caused by treatments such as chemotherapy and radiation therapy. The complexity of the role of autophagy in cancer is underscored by evidence that autophagy can allow premalignant cells to escape the genotoxic stress and inflammation that promote tumorigenesis, and that some tumor cells exhibit loss of autophagy capacity altogether through molecular mechanisms that have not yet been defined. Efforts to understand and modulate the autophagy pathway will be crucial to maximize the full therapeutic potential of cancer therapies that are currently hindered by tumor cell autophagy as a resistance mechanism. Cancer Res; 72(17); 4294-9. ?2012 AACR.     

Mechanisms for autophagy modulation by isoprenoid biosynthetic pathway inhibitors in multiple myeloma cells

Multiple myeloma (MM) is characterized by the production of monoclonal protein (MP). We have shown previously that disruption of the isoprenoid biosynthetic pathway (IBP) causes a block in MP secretion through a disruption of Rab GTPase activity, leading to an enhanced unfolded protein response and subsequent apoptosis in MM cells. Autophagy is induced by cellular stressors including nutrient deprivation and ER stress. IBP inhibitors have been shown to have disparate effects on autophagy. Here we define the mechanisms underlying the differential effects of IBP inhibitors on autophagic flux in MM cells utilizing specific pharmacological inhibitors. We demonstrate that IBP inhibition induces a net increase in autophagy as a consequence of disruption of isoprenoid biosynthesis which is not recapitulated by direct geranylgeranyl transferase inhibition. IBP inhibitor-induced autophagy is a cellular defense mechanism as treatment with the autophagy inhibitor bafilomycin A1 enhances the cytotoxic effects of GGPP depletion, but not geranylgeranyl transferase inhibition. Immunofluorescence microscopy studies revealed that IBP inhibitors disrupt ER to Golgi trafficking of monoclonal light chain protein and that this protein is not a substrate for alternative degradative pathways such as aggresomes and autophagosomes. These studies support further development of specific GGTase II inhibitors as anti-myeloma agents.     

肿瘤抑制基因p53与自噬

近年来研究表明,p53是一种抑癌基因,作为一种重要的转录因子,其在细胞周期阻滞、凋亡中都发挥着重要作用。自噬是在细胞营养物质匮乏条件下蛋白质动态降解的过程,自噬性细胞死亡是不同于细胞凋亡的另一种细胞程序性死亡模式,被称之为II型程序性死亡,细胞凋亡为I型程序性死亡。研究表明,肿瘤的发生发展与自噬性细胞死亡相关,作为肿瘤抑制基因p53也参与了自噬活性的调节。本文对此做一简要概述。     

The significance of autophagy in cancer

Autophagy, a vacuolar process of cytoplasmic degradation, is implicated in a form of programmed cell death distinct from apoptosis. The regulation of autophagy is complex and signalling pathways such as the target of rapamycin (Tor) kinase pathway, play important roles in tumourigenesis. Beclin 1, an autophagic protein, has been found to be a tumour suppressor. Conversely, cancer cells may exploit autophagy as a means to adapt to hypoxic and nutrient-limiting environments. The relative importance of autophagic cell death and apoptosis in carcinogenesis remains to be established, and the Bcl-2 family of proteins may be instrumental in coordinating the two pathways of programmed cell death.     

A systems biology analysis of autophagy in cancer therapy

Autophagy, which degrades redundant or damaged cellular constituents, is intricately relevant to a variety of human diseases, most notably cancer. Autophagy exerts distinct effects on cancer initiation and progression, due to the intrinsic overlapping of autophagic and cancer signalling pathways. However, due to the complexity of cancer as a systemic disease, the fate of cancer cells is not decided by any one signalling pathway. Numerous autophagic inter-connectivity and cross-talk pathways need to be further clarified at a systems level. In this review, we propose a systems biology perspective for the comprehensive analysis of the autophagy–cancer network, focusing on systems biology analysis in autophagy and cancer therapy. Together, these analyses may not only improve our understanding on autophagy–cancer relationships, but also facilitate cancer drug discovery.     

Modulation of the autophagy pathway by human tumor viruses

Autophagy is a highly conserved and regulated process in eukaryotic cells by which components of the cytoplasm, such as damaged organelles and foreign pathogens, become enveloped into double-membrane autophagosome vesicles that fuse with the lysosome for degradation. Viruses are adept at subverting host cellular pathways for their replication and survival. The human tumor viruses, Epstein-Barr virus (EBV), Kaposi's Sarcoma-Associated Herpesvirus (KSHV), Hepatitis B virus (HBV), and Hepatitis C virus (HCV), have evolved novel ways of modulating autophagy during productive and latent stages of the virus life cycle. This review will discuss how the autophagy pathway becomes activated upon viral infection and the role of viral proteins in regulating the autophagy pathway. Specifically, we will examine how virus-encoded homologs of autophagy proteins evade autophagy-mediated degradation by blocking the induction, elongation, or maturation steps in the autophagy pathway. We will also discuss how certain viruses enhance autophagy induction or usurp autophagic machinery for their own replication. A comprehensive understanding of the autophagic response to tumor viruses may enable the discovery of novel antiviral and/or anticancer drug therapies.     

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.     

氯喹促进顺铂诱导胃癌SGC7901细胞凋亡及其机制

  目的  研究自噬对顺铂（cisplatin,DDP）诱导的胃癌SGC7901细胞凋亡的影响,并初步探讨其可能机制。  方法  DDP和（或）氯喹处理胃癌SGC7901细胞,MTT法检测细胞增殖,流式细胞术检测细胞凋亡,MDC染色后荧光显微镜观察自噬囊泡,West. ern Blot检测自噬和凋亡相关蛋白。  结果  5 mg/L的顺铂作用于胃癌SGC7901细胞24 h,细胞凋亡率为21.07%±2.12%,同时观测到自噬囊泡增多和LC3-Ⅱ蛋白表达升高;氯喹特异性抑制自噬活性后,提高了顺铂诱导的细胞凋亡率（30.16%±3.54%,P < 0.05）;检测到凋亡相关蛋白Caspase-3和P53表达增加,Bcl-2蛋白表达下降。  结论  自噬在顺铂诱导胃癌SGC7901细胞凋亡的过程中起保护作用,氯喹抑制自噬后,可能通过激活P53蛋白及灭活Bcl-2蛋白的表达来促进细胞凋亡,联合应用顺铂和氯喹有望成为胃癌治疗的新策略。      

细胞自噬及其在乳腺癌中的研究进展

自噬是一种在生物进化过程中发生的细胞分解代谢过程,细胞内膜结构、蛋白质复合物和溶酶体形成自噬溶酶体用于降解和更新细胞成分.自噬是为细胞内稳态以及适应压力而发生的生理性调节,自噬机制发生改变会导致不同的病理条件.在肿瘤中自噬是复杂的,并且具有双面效应.在多种乳腺癌类型中,自噬有希望成为一种新的靶向治疗策略.本文旨在总结在肿瘤转移中自噬参与调节的主要分子机制,以及在肿瘤治疗中自噬所起的作用.     

Autophagy induced by valproic acid is associated with oxidative stress in glioma cell lines

Autophagy represents an alternative tumor-suppressing mechanism that overcomes the dramatic resistance of malignant gliomas to radiotherapy and proapoptotic-related chemotherapy. This study reports that valproic acid (VPA), a widely used anti-epilepsy drug, induces autophagy in glioma cells. Autophagy, crucial for VPA-induced cell death, is independent of apoptosis, even though apoptotic machinery is proficient. Oxidative stress induced by VPA occurs upstream of autophagy. Oxidative stress also activates the extracellular signal-regulated kinase 1/2 (ERK1/2) pathway, whereas blocking this pathway inhibits autophagy and induces apoptosis. VPA-induced autophagy cannot be alleviated by inositol, suggesting a mechanism different from that for lithium. Moreover, VPA potentiates autophagic cell death, but not apoptosis, when combined with other autophagy inducers such as rapamycin, {"type":"entrez-nucleotide","attrs":{"text":"Ly294002","term_id":"1257998346","term_text":"LY294002"}}Ly294002, and temozolomide in glioma cells both in vitro and in vivo, which may warrant further investigation toward possible clinical application in patients with malignant gliomas.