细胞自噬与凋亡的交互作用

细胞自唾又称Ⅱ型程序性细胞死亡,参与了多种疾病的发生和发展。自唆与凋亡之间存在着复杂的交互调控——二者能被多种应激刺激共同激活、共享多个调节分子,甚至互相协调转化等。全面深入研究自噬与凋亡之间的交互作用机制,将为肿瘤等疾病的认知及治疗带来突破性进展。     

Ultrastructure of autophagy in plant cells

Just as with yeasts and animal cells, plant cells show several types of autophagy. Microautophagy is the uptake of cellular constituents by the vacuolar membrane. Although microautophagy seems frequent in plants it is not yet fully proven to occur. Macroautophagy occurs farther away from the vacuole. In plants it is performed by autolysosomes, which are considerably different from the autophagosomes found in yeasts and animal cells, as in plants these organelles contain hydrolases from the onset of their formation. Another type of autophagy in plant cells (called mega-autophagy or mega-autolysis) is the massive degradation of the cell at the end of one type of programmed cell death (PCD). Furthermore, evidence has been found for autophagy during degradation of specific proteins, and during the internal degeneration of chloroplasts. This paper gives a brief overview of the present knowledge on the ultrastructure of autophagic processes in plants.     

Berberine as a potential autophagy modulator

Today, pharmacognosy is considered a valuable science in the prevention and treatment of diseases. Among herbals, Berberine is an isoquinoline alkaloid found in the Berberis species. Surprisingly, it shows antimicrobial, antiviral, antidiarrheal, antipyretic, and anti-inflammatory potential. Furthermore, it diminishes drug resistance in cancer therapy and enhances tumor suppression in part through autophagy and cell cycle arrest mechanisms. In the present review, we discuss the effect of berberine on diverse cellular pathways and describe how berberine acts as an autophagy modulator to adjust physiologic and pathologic conditions and diminishes drug resistance in cancer therapy.     

昆虫细胞自噬的生物学意义和自噬体膜的来源

细胞自噬(autophagy)是生物体广泛存在的细胞内自主降解过程。该过程通过自我吞噬细胞质成分和细胞器形成具有双层膜结构的自噬体, 与溶酶体融合实现细胞内物质的循环利用。细胞自噬在饥饿、 缺氧、 内质网胁迫、 病原入侵、 蛋白聚集等不良环境条件下实现自我挽救, 而细胞自噬的大量发生也是程序性细胞死亡(PCD)的启动和执行者之一。目前人们对自噬体分子组装和自噬发生的分子通路已有较深入的了解, 但仍然在很多重要问题上难以达成共识。本文结合我们的研究进展, 对昆虫细胞自噬的生物学意义和自噬体膜的来源问题进行综述和探讨。昆虫在营养相对匮乏的情况下发生低水平自噬(常态自噬), 用于维持细胞内的新陈代谢和继续生存的需要。昆虫在摄食阶段受到过度饥饿的刺激, 在变态发育时期受到蜕皮激素(20E)的诱导, 幼虫组织细胞发生高水平自噬和凋亡(apoptosis), 细胞表现为不可逆死亡, 过度饥饿导致幼虫发育迟缓或者死亡, 而20E导致幼虫蜕皮和幼虫组织退化或消亡。不同于酵母和高等动物细胞中的深入研究, 病原入侵是否和如何诱导昆虫细胞发生自噬, 目前尚缺乏足够的文献依据, 值得深入探讨。几乎所有的细胞器(内质网、 高尔基体、 线粒体)膜都可能是自噬体膜的来源, 这一问题在昆虫中也有待进一步诠释。     

Curcumin: A naturally occurring autophagy modulator

Autophagy is a self-degradative process that plays a pivotal role in several medical conditions associated with infection, cancer, neurodegeneration, aging, and metabolic disorders. Its interplay with cancer development and treatment resistance is complicated and paramount for drug design since an autophagic response can lead to tumor suppression by enhancing cellular integrity and tumorigenesis by improving tumor cell survival. In addition, autophagy denotes the cellular ability of adapting to stress though it may end up in apoptosis activation when cells are exposed to a very powerful stress. Induction of autophagy is a therapeutic option in cancer and many anticancer drugs have been developed to this aim. Curcumin as a hydrophobic polyphenol compound extracted from the known spice turmeric has different pharmacological effects in both in vitro and in vivo models. Many reports exist reporting that curcumin is capable of triggering autophagy in several cancer cells. In this review, we will focus on how curcumin can target autophagy in different cellular settings that may extend our understanding of new pharmacological agents to overcome relevant diseases.     

Programmed cell death of follicular epithelium during the late developmental stages of oogenesis in the fruit flies Bactrocera oleae and Ceratitis capitata (Diptera, Tephritidae) is mediated by autophagy

In the present study, we describe the features of programmed cell death of ovarian follicle cells, occurring during the late developmental stages of oogenesis in the olive fruit fly, Bactrocera oleae and the medfly, Ceratitis capitata. During stage 14, the follicle cells contain autophagic vacuoles, and they do not exhibit caspase activity in all parts of the egg chamber. Their nuclei are characterized by condensed chromatin, accompanied with high- but not low-molecular weight DNA fragmentation events exclusively detected in distinct cells of the anterior pole. These data argue for the presence of an autophagy-mediated cell death program in the ovarian follicle cell layer in both species. The above results are likely associated with the abundant phagocytosis observed at the entry of the lateral oviducts, where numerous cell bodies are massively engulfed by epithelial cells. We strongly believe that during the termination of the above Dipteran oogenesis, an efficient mechanism of absorption of the degenerated follicle cells is selectively activated, in order to prevent the blockage of the ovarioles and thus robustly support the physiological completion of the ovulation process.     

Sphingolipids: regulators of crosstalk between apoptosis and autophagy

Apoptosis and autophagy are two evolutionarily conserved processes that maintain homeostasis during stress. Although the two pathways utilize fundamentally distinct machinery, apoptosis and autophagy are highly interconnected and share many key regulators. The crosstalk between apoptosis and autophagy is complex, as autophagy can function to promote cell survival or cell death under various cellular conditions. The molecular mechanisms of crosstalk are beginning to be elucidated and have critical implications for the treatment of various diseases, such as cancer. Sphingolipids are a class of bioactive lipids that mediate many key cellular processes, including apoptosis and autophagy. By targeting several of the shared regulators, sphingolipid metabolites differentially regulate the induction of apoptosis and autophagy. Importantly, individual sphingolipid species appear to “switch” autophagy toward cell survival (e.g., sphingosine-1-phosphate) or cell death (e.g., ceramide, gangliosides). This review assesses the current understanding of sphingolipid-induced apoptosis and autophagy to address how sphingolipids mediate the “switch” between the cell survival and cell death. As sphingolipid metabolism is frequently dysregulated in cancer, sphingolipid-modulating agents, or sphingomimetics, have emerged as a novel chemotherapeutic strategy. Ultimately, a greater understanding of sphingolipid-mediated crosstalk between apoptosis and autophagy may be critical for enhancing the chemotherapeutic efficacy of these agents.     

Dual inhibition of BDNF/TrkB and autophagy: a promising therapeutic approach for colorectal cancer

Colorectal cancer (CRC) is the most common digestive cancer in the Western world. Despite effective therapies, resistance and/or recurrence frequently occur. The present study investigated the impact of two survival pathways—neurotrophic factors (TrkB/BDNF) and autophagy—on cell fate and tumour evolution. In vitro studies were performed on two CRC cell lines, SW480 (primary tumour) and SW620 (lymph node invasion), which were also used for subcutaneous xenografts on a nude mouse model. In addition, the presence of neurotrophic factors (NTs) and autophagy markers were assessed in tissue samples representative of different stages. On the basis of our previous study (which demonstrated that TrkB overexpression is associated with prosurvival signaling in CRC cells), we pharmacologically inhibited NTs pathways with K252a. As expected, an inactivation of the PI3K/AKT pathway was observed and CRC cells initiated autophagy. Conversely, blocking the autophagic flux with chloroquine or with ATG5‐siRNA overactivated TrkB/BDNF signaling. In vitro, dual inhibition improved the effectiveness of single treatment by significantly reducing metabolic activity and enhancing apoptotic cell death. These findings were accentuated in vivo, in which dual inhibition induced a spectacular reduction in tumour volume following long‐term treatment (21 days for K252a and 12 days for CQ). Finally, significant amounts of phospho‐TrkB and LC3II were found in the patients’ tissues, highlighting their relevance in CRC tumour biology. Taken together, our results show that targeting NTs and autophagy pathways potentially constitutes a new therapeutic approach for CRC.     

Dihydroceramide accumulation mediates cytotoxic autophagy of cancer cells via autolysosome destabilization

Autophagy is considered primarily a cell survival process, although it can also lead to cell death. However, the factors that dictate the shift between these 2 opposite outcomes remain largely unknown. In this work, we used Δ⁹-tetrahydrocannabinol (THC, the main active component of marijuana, a compound that triggers autophagy-mediated cancer cell death) and nutrient deprivation (an autophagic stimulus that triggers cytoprotective autophagy) to investigate the precise molecular mechanisms responsible for the activation of cytotoxic autophagy in cancer cells. By using a wide array of experimental approaches we show that THC (but not nutrient deprivation) increases the dihydroceramide:ceramide ratio in the endoplasmic reticulum of glioma cells, and this alteration is directed to autophagosomes and autolysosomes to promote lysosomal membrane permeabilization, cathepsin release and the subsequent activation of apoptotic cell death. These findings pave the way to clarify the regulatory mechanisms that determine the selective activation of autophagy-mediated cancer cell death.     

TAK1 activates AMPK‐dependent cytoprotective autophagy in TRAIL‐treated epithelial cells

The capacity of tumour necrosis factor‐related apoptosis‐inducing ligand (TRAIL) to trigger apoptosis preferentially in cancer cells, although sparing normal cells, has motivated clinical development of TRAIL receptor agonists as anti‐cancer therapeutics. The molecular mechanisms responsible for the differential TRAIL sensitivity of normal and cancer cells are, however, poorly understood. Here, we show a novel signalling pathway that activates cytoprotective autophagy in untransformed human epithelial cells treated with TRAIL. TRAIL‐induced autophagy is mediated by the AMP‐activated protein kinase (AMPK) that inhibits mammalian target of rapamycin complex 1, a potent inhibitor of autophagy. Interestingly, the TRAIL‐induced AMPK activation is refractory to the depletion of the two known AMPK‐activating kinases, LKB1 and Ca(2+)/calmodulin‐dependent kinase kinase‐β, but depends on transforming growth factor‐β‐activating kinase 1 (TAK1) and TAK1‐binding subunit 2. As TAK1 and AMPK are ubiquitously expressed kinases activated by numerous cytokines and developmental cues, these data are most likely to have broad implications for our understanding of cellular control of energy homoeostasis as well as the resistance of untransformed cells against TRAIL‐induced apoptosis.     

On the role of autophagy in human diseases: a gender perspective

Cytopathological features of cells from males and females, i.e. XX and XY isolated cells, have been demonstrated to represent a key variable in the mechanism underlying gender disparity in human diseases. Major insights came from the studies of gender differences in cell fate, e.g. in apoptotic susceptibility. We report here some novel insights recently emerged from literature that are referred as to a cytoprotection mechanism by which cells recycle cytoplasm and dispose of excess or defective organelles, i.e. autophagy. Autophagy and related genes have first been identified in yeast. Orthologue genes have subsequently been found in other organisms, including human beings. This stimulated the research in the field and, thanks to the use of molecular genetics and cell biology in different model systems, autophagy gained the attention of several research groups operating to analyse the pathogenetic mechanisms of human diseases. It remains unclear, however, whether autophagy can exert a protective effect or instead contribute to the pathogenesis of important human diseases. On the basis of the growing importance of sex/gender as key determinant of human pathology and of the known differences between males and females in the onset, progression, drug susceptibility and outcome of a plethora of diseases, the idea that autophagy could represent key and critical factor should be taken into account. In the review, we summarize our current knowledge about the role of autophagy in some paradigmatic human diseases (cancer, neurodegenerative, autoimmune, cardiovascular) and the role of 'cell sex' differences in this context.     

Plant Bax Inhibitor-1 interacts with ATG6 to regulate autophagy and programmed cell death

Autophagy is an evolutionarily conserved catabolic process and is involved in the regulation of programmed cell death during the plant immune response. However, mechanisms regulating autophagy and cell death are incompletely understood. Here, we demonstrate that plant Bax inhibitor-1 (BI-1), a highly conserved cell death regulator, interacts with ATG6, a core autophagy-related protein. Silencing of BI-1 reduced the autophagic activity induced by both N gene-mediated resistance to Tobacco mosaic virus (TMV) and methyl viologen (MV), and enhanced N gene-mediated cell death. In contrast, overexpression of plant BI-1 increased autophagic activity and surprisingly caused autophagy-dependent cell death. These results suggest that plant BI-1 has both prosurvival and prodeath effects in different physiological contexts and both depend on autophagic activity.     

Relationship between growth arrest and autophagy in midgut programmed cell death in Drosophila

Autophagy has been implicated in both cell survival and programmed cell death (PCD), and this may explain the apparently complex role of this catabolic process in tumourigenesis. Our previous studies have shown that caspases have little influence on Drosophila larval midgut PCD, whereas inhibition of autophagy severely delays midgut removal. To assess upstream signals that regulate autophagy and larval midgut degradation, we have examined the requirement of growth signalling pathways. Inhibition of the class I phosphoinositide-3-kinase (PI3K) pathway prevents midgut growth, whereas ectopic PI3K and Ras signalling results in larger cells with decreased autophagy and delayed midgut degradation. Furthermore, premature induction of autophagy is sufficient to induce early midgut degradation. These data indicate that autophagy and the growth regulatory pathways have an important relationship during midgut PCD. Despite the roles of autophagy in both survival and death, our findings suggest that autophagy induction occurs in response to similar signals in both scenarios.     

自噬在细胞存活和死亡中的作用

自噬是亚细胞膜结构发生动态变化并经溶酶体介导对细胞内蛋白质和细胞器降解的过程.通过平衡细胞合成和分解代谢,自噬稳定细胞内环境,维持细胞的存活.然而,过度自噬可导致细胞发生Ⅱ型程序性细胞死亡.自噬与凋亡在细胞死亡过程中的关系十分密切.本文对自噬的过程及其在细胞存活和死亡中的作用作一综述.     

Corilagin inhibits breast cancer growth via reactive oxygen species‐dependent apoptosis and autophagy

Corilagin is a component of Phyllanthus urinaria extract and has been found of possessing anti‐inflammatory, anti‐oxidative, and anti‐tumour properties in clinic treatments. However, the underlying mechanisms in anti‐cancer particularly of its induction of cell death in human breast cancer remain undefined. Our research found that corilagin‐induced apoptotic and autophagic cell death depending on reactive oxygen species (ROS) in human breast cancer cell, and it occurred in human breast cancer cell (MCF‐7) only comparing with normal cells. The expression of procaspase‐8, procaspase‐3, PARP, Bcl‐2 and procaspase‐9 was down‐regulated while caspase‐8, cleaved PARP, caspase‐9 and Bax were up‐regulated after corilagin treatment, indicating apoptosis mediated by extrinsic and mitochondrial pathways occurred in MCF‐7 cell. Meanwhile, autophagy mediated by suppressing Akt/mTOR/p70S6K pathway was detected with an increase in autophagic vacuoles and LC3‐II conversion. More significantly, inhibition of autophagy by chloroquine diphosphate salt (CQ) remarkably enhanced apoptosis, while the caspase inhibitor z‐VAD‐fmk failed in affecting autophagy, suggesting that corilagin‐induced autophagy functioned as a survival mechanism in MCF‐7 cells. In addition, corilagin induced intracellular reactive oxygen species (ROS) generation, when reduced by ROS scavenger NAC, apoptosis and autophagy were both down‐regulated. Nevertheless, in SK‐BR3 cell which expressed RIP3, necroptosis inhibitor Nec‐1 could not alleviate cell death induced by corilagin, indicating necroptosis was not triggered. Subcutaneous tumour growth in nude mice was attenuated by corilagin, consisting with the results in vitro. These results imply that corilagin inhibits cancer cell proliferation through inducing apoptosis and autophagy which regulated by ROS release.     

The interplay between autophagy and tumorigenesis: exploiting autophagy as a means of anticancer therapy

In wild‐type cells, autophagy represents a tumour‐suppressor mechanism, and dysfunction of the autophagy machinery increases genomic instability, DNA damage, oxidative stress and stem/progenitor expansion, which are events associated with cancer onset. Autophagy occurs at a basal level in all cells depending on cell type and cellular microenvironment. However, the role of autophagy in cancer is diverse and can promote different outcomes even in a single tumour. For example, in hypoxic tumour regions, autophagy emerges as a protective mechanism and allows cancer cell survival. By contrast, in cancer cells surrounding the tumour mass, the induction of autophagy by radio‐ or chemotherapy promotes cell death and significantly reduces the tumour mass. Importantly, inhibition of autophagy compromises tumorigenesis by mechanisms that are not entirely understood. The aim of this review is to explain the apparently contradictory role of autophagy as a mechanism that both promotes and inhibits tumorigenesis using different models. The induction/inhibition of autophagy as a mechanism for cancer treatment is also discussed.     

Dual inhibition of autophagy and the AKT pathway in prostate cancer

Genetic inactivation of PTEN through either gene deletion or mutation is common in metastatic prostate cancer, leading to activation of the phosphoinositide 3-kinase (PI3K-AKT) pathway, which is associated with poor clinical outcomes. The PI3K-AKT pathway plays a central role in various cellular processes supporting cell growth and survival of tumor cells. To date, therapeutic approaches to develop inhibitors targeting the PI3K-AKT pathway have failed in both pre-clinical and clinical trials. We showed that a novel AKT inhibitor, AZD5363, inhibits the AKT downstream pathway by reducing p-MTOR and p-RPS6KB/p70S6K. We specifically reported that AZD5363 monotherapy induces G2 growth arrest and autophagy, but fails to induce significant apoptosis in PC-3 and DU145 prostate cancer cell lines. Blocking autophagy using pharmacological inhibitors (3-methyladenine, chloroquine and bafilomycin A₁) or genetic inhibitors (siRNA targeting ATG3 and ATG7) enhances cell death induced by AZD5363 in these prostate cancer cells. Importantly, the combination of AZD5363 with chloroquine significantly reduces tumor volume compared with the control group, and compared with either drug alone in prostate tumor xenograft models. Taken together, these data demonstrate that AKT inhibitor AZD5363, synergizes with the lysosomotropic inhibitor of autophagy, chloroquine, to induce apoptosis and delay tumor progression in prostate cancer models that are resistant to monotherapy, with AZD5363 providing a new therapeutic approach potentially translatable to patients.     

Regulation of autophagy and chloroquine sensitivity by oncogenic RAS in vitro is context-dependent

Chloroquine (CQ) is an antimalarial drug and late-stage inhibitor of autophagy currently FDA-approved for use in the treatment of rheumatoid arthritis and other autoimmune diseases. Based primarily on its ability to inhibit autophagy, CQ and its derivative, hydroxychloroquine, are currently being investigated as primary or adjuvant therapy in multiple clinical trials for cancer treatment. Oncogenic RAS has previously been shown to regulate autophagic flux, and cancers with high incidence of RAS mutations, such as pancreatic cancer, have been described in the literature as being particularly susceptible to CQ treatment, leading to the hypothesis that oncogenic RAS makes cancer cells dependent on autophagy. This autophagy “addiction” suggests that the mutation status of RAS in tumors could identify patients who would be more likely to benefit from CQ therapy. Here we show that RAS mutation status itself is unlikely to be beneficial in such a patient selection because oncogenic RAS does not always promote autophagy addiction. Moreover, oncogenic RAS can have opposite effects on both autophagic flux and CQ sensitivity in different cells. Finally, for any given cell type, the positive or negative effect of oncogenic RAS on autophagy does not necessarily predict whether RAS will promote or inhibit CQ-mediated toxicity. Thus, although our results confirm that different tumor cell lines display marked differences in how they respond to autophagy inhibition, these differences can occur irrespective of RAS mutation status and, in different contexts, can either promote or reduce chloroquine sensitivity of tumor cells.     

Regulation of autophagy and chloroquine sensitivity by oncogenic RAS in vitro is context-dependent

Chloroquine (CQ) is an antimalarial drug and late-stage inhibitor of autophagy currently FDA-approved for use in the treatment of rheumatoid arthritis and other autoimmune diseases. Based primarily on its ability to inhibit autophagy, CQ and its derivative, hydroxychloroquine, are currently being investigated as primary or adjuvant therapy in multiple clinical trials for cancer treatment. Oncogenic RAS has previously been shown to regulate autophagic flux, and cancers with high incidence of RAS mutations, such as pancreatic cancer, have been described in the literature as being particularly susceptible to CQ treatment, leading to the hypothesis that oncogenic RAS makes cancer cells dependent on autophagy. This autophagy “addiction” suggests that the mutation status of RAS in tumors could identify patients who would be more likely to benefit from CQ therapy. Here we show that RAS mutation status itself is unlikely to be beneficial in such a patient selection because oncogenic RAS does not always promote autophagy addiction. Moreover, oncogenic RAS can have opposite effects on both autophagic flux and CQ sensitivity in different cells. Finally, for any given cell type, the positive or negative effect of oncogenic RAS on autophagy does not necessarily predict whether RAS will promote or inhibit CQ-mediated toxicity. Thus, although our results confirm that different tumor cell lines display marked differences in how they respond to autophagy inhibition, these differences can occur irrespective of RAS mutation status and, in different contexts, can either promote or reduce chloroquine sensitivity of tumor cells.