An Atg1/Atg13 Complex with Multiple Roles in TOR-mediated Autophagy Regulation

The TOR kinases are conserved negative regulators of autophagy in response to nutrient conditions, but the signaling mechanisms are poorly understood. Here we describe a complex containing the protein kinase Atg1 and the phosphoprotein Atg13 that functions as a critical component of this regulation in Drosophila. We show that knockout of Atg1 or Atg13 results in a similar, selective defect in autophagy in response to TOR inactivation. Atg1 physically interacts with TOR and Atg13 in vivo, and both Atg1 and Atg13 are phosphorylated in a nutrient-, TOR- and Atg1 kinase-dependent manner. In contrast to yeast, phosphorylation of Atg13 is greatest under autophagic conditions and does not preclude Atg1-Atg13 association. Atg13 stimulates both the autophagic activity of Atg1 and its inhibition of cell growth and TOR signaling, in part by disrupting the normal trafficking of TOR. In contrast to the effects of normal Atg13 levels, increased expression of Atg13 inhibits autophagosome expansion and recruitment of Atg8/LC3, potentially by decreasing the stability of Atg1 and facilitating its inhibitory phosphorylation by TOR. Atg1-Atg13 complexes thus function at multiple levels to mediate and adjust nutrient-dependent autophagic signaling.     

The Roles of Autophagy in Cerebral Ischemia

Recent studies indicate the existence of autophagy in cerebral ischemia, but the functions of autophagy in this setting remain unclear. Here we discuss the role of autophagy in cerebral ischemia based on our own publication and the literature on this subject. We propose that oxidative and endoplasmic reticulum (ER) stresses in cerebral ischemia-hypoxia are potent stimuli of autophagy in neurons. We also reviewed evidence suggesting autophagosomes may have a shorter half-life in neurons and that a fraction of LC3 protein is degraded within autolysosomes, leading to a smaller detectable amount of LC3-II in the brain while there are clear indications of on-going autophagy. Finally, we suggest autophagy is an important modifier of cell death and survival, interacting with necrosis and apoptosis in determining the outcomes and final morphology of deceased neurons.     

Crucial Roles of microRNA-Mediated Autophagy in Urologic Malignancies

Urologic oncologies are major public health problems worldwide. Both microRNA and autophagy, separately or concurrently, are involved in a variety of the cellular and molecular processes of multiple cancers, including urologic malignancies. In this review, we have summarized the related studies and found that microRNA-mediated autophagy acted as carcinogenic factors or suppressors in prostate cancer, kidney cancer, and bladder cancer. MiRNAs, targeted genes, and the different signaling pathways constitute a complex network that orchestrates autophagy regulation, militating the oncogenic and tumor-suppressive effects in urologic malignancies. Aberrant expression of miRNAs may induce the dysregulation of the autophagy process, resulting in tumorigenesis, progression, and resistance to anticancer therapies. Targeting specific miRNAs for autophagy modulation may present as reliable diagnostic and prognostic biomarkers or promising therapeutic strategies for urologic oncologies.     

细胞自噬在植物细胞程序性死亡中的作用

细胞自噬是真核生物中一种由液泡或溶酶体介导的, 对细胞内物质进行周转的重要代谢机制。在植物中, 细胞自噬作为一种重要的降解手段, 参与营养物质的重新分配、受损蛋白和细胞器的清除及生物和非生物胁迫的响应等过程。此外, 细胞自噬在各种程序性细胞死亡中也起着重要作用, 该文主要综述了近几年来在此方面的研究进展。     

雷帕霉素靶蛋白与自噬在衰老中的交互作用

衰老是一个非常复杂的过程,与细胞和组织中累积的各种大分子（DNA、蛋白质和脂质）损伤密不可分,并且是由细胞中不同的信号通道共同调控的结果,而雷帕霉素靶标途径就是其中的一种。该途径整合了各种来自细胞内外的信号以调控细胞的生长、增殖和代谢。越来越多证据表明,雷帕霉素靶蛋白（target of rapamycin,TOR）控制着细胞和组织老化的速度,影响着整个机体衰老过程。另外TOR参与调控自噬的发生,而自噬能使生物大分子和细胞器降解并回收重复利用。多种生物模型研究发现,衰老其实是与自噬的不足有关联。本文对TOR和自噬在衰老过程中的作用和相互关系进行综述,为发展与老年疾病相关的新型治疗方法提供思路。     

Multiple Roles for Cysteine Cathepsins in Cancer

Cysteine cathepsins are a family of proteases that have recently emerged as important players in cancer, and have variously been reported to be involved in apoptosis, angiogenesis, cell proliferation, and invasion. In normal cells, cysteine cathepsins are typically localized in lysosomes and other intracellular compartments, and are involved in protein degradation and processing. However, in certain tumors, cathepsins are translocated from their intracellular compartments to the cell surface, and can even be secreted. In addition, the expression and activity levels of some cysteine cathepsins are upregulated in human and mouse cancers. Understanding which cathepsins are critically involved, what their substrates are, and how they may be mediating these complex roles in cancer are important questions to address. We highlight recent results that begin to answer some of these questions, illustrating in particular the lessons from studying a mouse model of multistage carcinogenesis, which suggests distinctive roles for individual cysteine cathepsins in tumor progression.     

金属离子对细胞自噬的诱导作用

自噬是真核生物普遍存在的重要生理过程,通过溶酶体降解错误折叠的蛋白质、异常的细胞器从而循环利用自身内含物。细胞自噬广泛参与多种病理和生理过程,是当前生物医学领域研究的热点之一。自噬的分子机制能够揭示自噬本质,不仅有利于理解自噬的生理意义,也有利于寻找新的药物靶点,为治疗疾病提供理论基础。金属离子能通过不同的信号通路诱导自噬,其研究对药物开发和疾病治疗具有重要的意义。主要从自噬的分子机制、金属离子的诱导作用两方面进行阐述。     

Investigation of Peroxisome Biogenesis Revealed Possible New Roles for Autophagy Components

Precursor aminopeptidase I oligomerizes in the cytosol and is imported into the vacuole as a dodecamer via the cytoplasm-to-vacuole targeting (Cvt) pathway or autophagy. However, this is not the only example for the import of oligomeric protein complexes into an organelle. During peroxisome biogenesis folded and oligomeric proteins can be imported into the lumen of the organelle. The mechanism of this transport is still unknown. In this article, we point out mechanistic parallels between peroxisome biogenesis and the Cvt pathway or autophagy. Furthermore, we summarize our recently published investigation on a possible overlap between these pathways. Our investigation revealed new insights into autophagy and the Cvt pathway and possible new functions of Cvt4p, Cvt8p and Atg14p in organelle biogenesis or stability.

Addendum to:

Topogenesis of peroxisomal proteins does not require a functional cytoplasm-to-vacuole transport

Ines Heiland and Ralph Erdmann

Eur J Cell Biol 2005; 84:799-807     

Multiple Tissue-specific Roles for the O-GlcNAc Post-translational Modification in the Induction of and Complications Arising from Type II Diabetes

In this minireview, we will highlight work in the last 30 years that has clearly demonstrated that the O-GlcNAc modification is nutrient-responsive and plays multiple roles in metabolic regulation of signaling and gene expression. Further, we will examine recent studies that have investigated the impact of O-GlcNAc in a variety of glucose- and insulin-responsive tissues and the roles attributed to O-GlcNAc in the induction of insulin resistance and glucose toxicity, the hallmarks of type II diabetes mellitus. We will also summarize potential causal roles for the O-GlcNAc modification in complications associated with diabetes.     

细胞自噬对酒精诱导的肝细胞毒性的保护作用

目的：研究细胞自噬对酒精诱导的人肝细胞系（CL-1）的保护作用。方法：培养正常肝细胞系CL-1细胞,80mmol／L酒精常规处理24小时,采用CCK-8法观察酒精对细胞活力的影响;流式细胞技术观察酒精对细胞凋亡的影响;免疫蛋白印迹及转染GFP-LC3法检测细胞自噬水平;选用rapamycin和3-MA调节细胞自噬,观察酒精处理后细胞活力及凋亡的变化。结果：酒精处理体外培养的CL-1细胞,实验组较对照组细胞活力下降（P〈0．05）;实验组细胞46．2％发生凋亡,显著高于对照组8．4％;LC3II及Beclinl水平显著高于对照组;GFP-LC3荧光数显著高于对照组（P〈0．05）;调节细胞自噬水平,rapamycin组细胞活性增加（P〈0．01）,31．1％（46．2％）细胞发生凋亡;3-MA组细胞活性降低（P〈0．05）,54．1％（46．2％）细胞发生凋亡。结论：酒精处理降低CL-1细胞活性,促进凋亡,提高自噬水平;提高或降低细胞自噬水平,细胞凋亡及活力随之降低和增加;细胞自噬能够对抗酒精诱导的肝细胞凋亡。     

Protective Roles of CNS Mitochondria

Mitochondria benefit their host cells by generating ATP, detoxifying oxygen, maintaining cellular redox potential, and detoxifying reactive oxygen species and xenobiotics. These beneficial roles are in stark contrast to mitochondrial participation in both necrotic and apoptotic degenerative pathways. However, cellular stresses do not always result in deleterious mitochondrial changes. Decreases in the calcium sensitivity of the permeability transition may be initial mitochondrial responses to stress that act to preserve mitochondrial function and prolong normal functioning of the host cell.     

细胞自噬在个体发育和肿瘤发生中的作用

细胞自噬是一种广泛存在于真核生物细胞中的代谢过程,参与调控胞内物质合成、降解和重新利用之间的代谢平衡。自噬体与溶酶体的有效融合能有效地保障胞内多余物质的降解及其再利用,是真核细胞所特有的一种自我保护机制。细胞自噬近年来受到广泛的关注,其不仅能充当胞内一个合格的质检员,有效地降解胞内受损的蛋白质成分和细胞器,进而阻止细胞损伤和凋亡,也与肿瘤发生、衰老、神经退行性疾病、人体自身免疫性疾病、肥胖症和糖尿病等多种疾病的发生及发展密切相关。本文旨在对细胞自噬过程和其调控机制进行介绍,并侧重对自噬在生长发育和肿瘤发生中的作用进行综述,为预防与治疗多种人类重大疾病提供理论依据。     

Multiple Roles of Peroxiredoxins in Inflammation

Inflammation is a pathophysiological response to infection or tissue damage during which high levels of reactive oxygen and nitrogen species are produced by phagocytes to kill microorganisms. Reactive oxygen and nitrogen species serve also in the complex regulation of inflammatory processes. Recently, it has been proposed that peroxiredoxins may play key roles in innate immunity and inflammation. Indeed, peroxiredoxins are evolutionarily conserved peroxidases able to reduce, with high rate constants, hydrogen peroxide, alkyl hydroperoxides and peroxynitrite which are generated during inflammation. In this minireview, we point out different possible roles of peroxiredoxins during inflammatory processes such as cytoprotective enzymes against oxidative stress, modulators of redox signaling, and extracellular pathogen- or damage-associated molecular patterns. A better understanding of peroxiredoxin functions in inflammation could lead to the discovery of new therapeutic targets.     

Autophagy: a Novel Protective Mechanism in Chronic Ischemia

During the search for cardioprotective mechanisms in a porcine model of chronic myocardial ischemia and hibernating myocardium, we discovered evidence for autophagy, which could be involved in the protection against apoptosis. Autophagy is a cellular degradation process responsible for the turnover of unnecessary or dysfunctional organelles and cytoplasmic proteins, which become sequestered in a double-membrane-bound vesicle, termed autophagosome, and subsequently degrade upon fusion with lysosomes. The dauer phase in C. elegans shares similarities with the induction of autophagy in chronically ischemic (hibernating) myocardium. In this sense, autophagy is an essential mechanism for survival which is activated by environmental stresses and confers stress resistance to the organism. Our study provided insight into understanding of the protective mechanism of autophagy in chronic ischemia.     

Induction of Autophagy by Amino Acid Starvation in Fish Cells

Autophagy is well established as a starvation-induced process in yeast and mammalian cells and tissues. To elucidate the cellular mechanisms induced by starvation in fish, we characterized the induction of autophagy in cultured zebrafish cells under starvation conditions. As an autophagic marker protein, the microtubule-associated protein 1-light chain 3B protein (MAP1-LC3B) was cloned from the fish cells, and its expression and localization were characterized. In zebrafish embryonic (ZE) cells, posttranslational modifications produced two distinct forms of MAP1-LC3B, i.e., a cytosolic form and a membrane-bound form (types I and II, respectively). Immunofluorescence microscopy revealed fluorescently labeled autophagosomes in cells stably transfected with a green fluorescent protein (GFP)–MAP1-LC3B fusion protein and showed that this protein accumulated in punctate dots in a time-dependent manner in response to amino acid starvation. Starvation also induced the degradation of long-lived proteins. Treatment with 3-methyladenine and wortmannin, two class-III inhibitors of phosphoinositide 3-kinase (PI3K), repressed autophagy under starvation conditions, indicating that the PI3K class-III pathway regulates starvation-induced autophagy in fish.     

Hidden Behind Autophagy: The Unconventional Roles of ATG Proteins

Macroautophagy (hereafter referred to as autophagy) is an evolutionarily conserved intracellular catabolic transport route that generally allows the lysosomal degradation of cytoplasmic components, including bulk cytosol, protein aggregates, damaged or superfluous organelles and invading microbes. Target structures are sequestered by double‐membrane vesicles called autophagosomes, which are formed through the concerted action of the autophagy (ATG)‐related proteins. Until recently it was assumed that ATG proteins were exclusively involved in autophagy. A growing number of studies, however, have attributed functions to some of them that are distinct from their classical role in autophagosome biogenesis. Autophagy‐independent roles of the ATG proteins include the maintenance of cellular homeostasis and resistance to pathogens. For example, they assist and enhance the turnover of dead cells and microbes upon their phagocytic engulfment, and inhibit murine norovirus replication. Moreover, bone resorption by osteoclasts, innate immune regulation triggered by cytoplasmic DNA and the ER‐associated degradation regulation all have in common the requirement of a subset of ATG proteins. Microorganisms such as coronaviruses, Chlamydia trachomatis or Brucella abortus have even evolved ways to manipulate autophagy‐independent functions of ATG proteins in order to ensure the completion of their intracellular life cycle. Taken together these novel mechanisms add to the repertoire of functions and extend the number of cellular processes involving the ATG proteins.