Mechanisms of Autophagosome Biogenesis Rubinsztein, David C.; Shpilka, Tomer; Elazar, Zvulun
Current biology,
01/2012, Letnik:
22, Številka:
1
Journal Article
Recenzirano
Odprti dostop
Autophagy is a unique membrane trafficking process whereby newly formed membranes, termed phagophores, engulf parts of the cytoplasm leading to the production of double-membraned autophagosomes that ...get delivered to lysosomes for degradation. This catabolic pathway has been linked to numerous physiological and pathological conditions, such as development, programmed cell death, cancer, pathogen infection, neurodegenerative disorders, and myopathies. In this review, we will focus on recent studies in yeast and mammalian systems that have provided insights into two critical areas of autophagosome biogenesis — the source of the autophagosomal membranes, and the mechanisms regulating the fusion of the edges of the double-membraned phagophores to form autophagosomes.
Autophagy and Aging Rubinsztein, David C.; Mariño, Guillermo; Kroemer, Guido
Cell,
09/2011, Letnik:
146, Številka:
5
Journal Article
Recenzirano
Odprti dostop
Genetic inhibition of autophagy induces degenerative changes in mammalian tissues that resemble those associated with aging, and normal and pathological aging are often associated with a reduced ...autophagic potential. Pharmacological or genetic manipulations that increase life span in model organisms often stimulate autophagy, and its inhibition compromises the longevity-promoting effects of caloric restriction, Sirtuin 1 activation, inhibition of insulin/insulin growth factor signaling, or the administration of rapamycin, resveratrol, or spermidine. Here, we discuss the probable cause and effect relationship between perturbed autophagy and aging, as well as possible molecular mechanisms that may mediate the anti-aging effects of autophagy.
Autophagy is a catabolic process in which lysosomes degrade intracytoplasmic contents transported in double-membraned autophagosomes. Autophagosomes are formed by the elongation and fusion of ...phagophores, which can be derived from preautophagosomal structures coming from the plasma membrane and other sites like the endoplasmic reticulum and mitochondria. The mechanisms by which preautophagosomal structures elongate their membranes and mature toward fully formed autophagosomes still remain unknown. Here, we show that the maturation of the early Atg16L1 precursors requires homotypic fusion, which is essential for subsequent autophagosome formation. Atg16L1 precursor homotypic fusion depends on the SNARE protein VAMP7 together with partner SNAREs. Atg16L1 precursor homotypic fusion is a critical event in the early phases of autophagy that couples membrane acquisition and autophagosome biogenesis, as this step regulates the size of the vesicles, which in turn appears to influence their subsequent maturation into LC3-positive autophagosomes.
Display omitted
► Homotypic fusion of Atg16L1 vesicles enables their maturation into autophagosomes ► VAMP7 regulates Atg16L1 vesicle homotypic fusion and autophagosome formation ► Plasma membrane is a likely source of SNAREs required for Atg16L1 vesicle fusion ► Starvation, which induces autophagy, triggers Atg16L1 vesicle homotypic fusion
Many late-onset neurodegenerative diseases, including Parkinson's disease and Huntington's disease, are associated with the formation of intracellular aggregates by toxic proteins. It is therefore ...crucial to understand the factors that regulate the steady-state levels of these 'toxins', at both the synthetic and degradation stages. The degradation pathways acting on such aggregate-prone cytosolic proteins include the ubiquitin-proteasome system and macroautophagy. Dysfunction of the ubiquitin-proteasome or macroautophagy pathways might contribute to the pathology of various neurodegenerative conditions. However, enhancing macroautophagy with drugs such as rapamycin could offer a tractable therapeutic strategy for a number of these diseases.
Autophagy is an essential, conserved lysosomal degradation pathway that controls the quality of the cytoplasm by eliminating protein aggregates and damaged organelles. It begins when double-membraned ...autophagosomes engulf portions of the cytoplasm, which is followed by fusion of these vesicles with lysosomes and degradation of the autophagic contents. In addition to its vital homeostatic role, this degradation pathway is involved in various human disorders, including metabolic conditions, neurodegenerative diseases, cancers and infectious diseases. This article provides an overview of the mechanisms and regulation of autophagy, the role of this pathway in disease and strategies for therapeutic modulation.
Most neurodegenerative diseases that afflict humans are associated with the intracytoplasmic deposition of aggregate-prone proteins in neurons and with mitochondrial dysfunction. Autophagy is a ...powerful process for removing such proteins and for maintaining mitochondrial homeostasis. Over recent years, evidence has accumulated to demonstrate that upregulation of autophagy may protect against neurodegeneration. However, autophagy dysfunction has also been implicated in the pathogenesis of various diseases. This Review summarizes the progress that has been made in our understanding of how perturbations in autophagy are linked with neurodegenerative diseases and the potential therapeutic strategies resulting from the modulation of this process.
Autophagic protein degradation is mediated by autophagosomes that fuse with lysosomes, where their contents are degraded. The membrane origins of autophagosomes may involve multiple sources. However, ...it is unclear if and where distinct membrane sources fuse during autophagosome biogenesis. Vesicles containing mATG9, the only transmembrane autophagy protein, are seen in many sites, and fusions with other autophagic compartments have not been visualized in mammalian cells. We observed that mATG9 traffics from the plasma membrane to recycling endosomes in carriers that appear to be routed differently from ATG16L1-containing vesicles, another source of autophagosome membrane. mATG9- and ATG16L1-containing vesicles traffic to recycling endosomes, where VAMP3-dependent heterotypic fusions occur. These fusions correlate with autophagosome formation, and both processes are enhanced by perturbing membrane egress from recycling endosomes. Starvation, a primordial autophagy activator, reduces membrane recycling from recycling endosomes and enhances mATG9-ATG16L1 vesicle fusion. Thus, this mechanism may fine-tune physiological autophagic responses.
Display omitted
•mATG9 traffics from the plasma membrane to recycling endosomes•mATG9 vesicles fuse with ATG16L1 vesicles in recycling endosomes•VAMP3, Rab11, myosin Vb, and starvation regulate mATG9-ATG16L1 vesicle fusion•mATG9-ATG16L1 vesicle fusions regulate autophagosome formation
Autophagosome membranes that originate in different cellular compartments follow distinct routes to recycling endosomes, where they fuse to form autophagosome precursors.
Autophagy is an intracellular degradation process that clears long-lived proteins and organelles from the cytoplasm. It involves the formation of double-membraned structures called autophagosomes ...that can engulf portions of cytoplasm containing oligomeric protein complexes and organelles, such as mitochondria. Autophagosomes fuse with lysosomes and their contents then are degraded. Failure of autophagy in neurons can result in the accumulation of aggregate-prone proteins and neurodegeneration. Pharmacological induction of autophagy can enhance the clearance of intracytoplasmic aggregate-prone proteins, such as mutant forms of huntingtin, and ameliorate pathology in cell and animal models of neurodegenerative diseases. In this Review, the autophagic machinery and the signaling pathways that regulate the induction of autophagy are described. The ways in which dysfunctions at multiple stages in the autophagic pathways contribute to numerous neurological disorders are highlighted through the use of examples of Mendelian and complex conditions, including Alzheimer disease, Parkinson disease and forms of motor neuron disease. The different ways in which autophagic pathways might be manipulated for the therapeutic benefit of patients with neurodegenerative disorders are also considered.
Alternative cleavage and polyadenylation (APA) is emerging as an important layer of gene regulation. Factors controlling APA are largely unknown. We developed a reporter-based RNAi screen for APA and ...identified PABPN1 as a regulator of this process. Genome-wide analysis of APA in human cells showed that loss of PABPN1 resulted in extensive 3′ untranslated region shortening. Messenger RNA transcription, stability analyses, and in vitro cleavage assays indicated enhanced usage of proximal cleavage sites (CSs) as the underlying mechanism. Using Cyclin D1 as a test case, we demonstrated that enhanced usage of proximal CSs compromises microRNA-mediated repression. Triplet-repeat expansion in PABPN1 (trePABPN1) causes autosomal-dominant oculopharyngeal muscular dystrophy (OPMD). The expression of trePABPN1 in both a mouse model of OPMD and human cells elicited broad induction of proximal CS usage, linked to binding to endogenous PABPN1 and its sequestration in nuclear aggregates. Our results elucidate a novel function for PABPN1 as a suppressor of APA.
Display omitted
▸ Genetic screen identifies PABPN1 as a regulator of alternative polyadenylation ▸ PABPN1 knockdown results in global 3′ UTR shortening ▸ Global 3′ UTR shortening is observed in an OPMD mouse model expressing mutant PABPN1 ▸ PABPN1 directly suppresses cleavage at proximal alternative 3′ UTRs
The oculopharyngeal muscular dystrophy (OPMD) protein PABN1 regulates selection of alternative mRNA polyadenylation sites by binding to and suppressing the use of proximal sequences. Consequently, triplet-repeat expansion of the PABN1 gene in human OPMD results in widespread shortening of target mRNAs, contributing to pathogenesis of the disease.
PDF
