Macroautophagy (autophagy) is a conserved lysosomal degradation process essential for cellular homeostasis and adaption to stress. Accumulating evidence indicates that autophagy declines with age and ...that impaired autophagy predisposes individuals to age-related diseases, whereas interventions that stimulate autophagy often promote longevity. In this Review, we examine how the autophagy pathway restricts cellular damage and degeneration, and the impact of these functions towards tissue health and organismal lifespan.
•EVs are enriched with specific biomolecules indicating regulated mechanisms of loading.•Multiple cellular machineries sort molecules into distinct EV subpopulations.•Methods such as ...proximity-dependent biotinylation have revealed EV loading pathways.•Understanding of EV loading is critical to leveraging EVs for diagnosis/treatment.
Extracellular vesicles (EVs) are small membrane-bound organelles naturally released from cells and potentially function as vehicles of intercellular communication. Cells release numerous sub-species of EVs, including exosomes and microvesicles, which are formed via distinct cellular pathways and molecular machineries and contain specific proteins, RNAs and lipids. Accumulating evidence indicates that the repertoire of molecules packaged into EVs is shaped by both the physiological state of the cell and the EV biogenesis pathway involved. Although these observations intimate that precisely regulated pathways sort molecules into EVs, the underlying molecular mechanisms that direct molecules for secretion remain poorly defined. Recently, with the advancement of mass spectrometry, next-generation sequencing techniques and molecular biology tools, several mechanisms contributing to EV cargo selection are beginning to be unraveled. This review examines strategies employed to reveal how specific proteins, RNAs and lipids are directed for secretion via EVs.
Beyond Autophagy: The Expanding Roles of ATG8 Proteins Nieto-Torres, Jose L.; Leidal, Andrew M.; Debnath, Jayanta ...
Trends in biochemical sciences (Amsterdam. Regular ed.),
08/2021, Letnik:
46, Številka:
8
Journal Article
Recenzirano
Odprti dostop
The ATG8 family proteins are critical players in autophagy, a cytoprotective process that mediates degradation of cytosolic cargo. During autophagy, ATG8s conjugate to autophagosome membranes to ...facilitate cargo recruitment, autophagosome biogenesis, transport, and fusion with lysosomes, for cargo degradation. In addition to these canonical functions, recent reports demonstrate that ATG8s are also delivered to single-membrane organelles, which leads to highly divergent degradative or secretory fates, vesicle maturation, and cargo specification. The association of ATG8s with different vesicles involves complex regulatory mechanisms still to be fully elucidated. Whether individual ATG8 family members play unique canonical or non-canonical roles, also remains unclear. This review summarizes the many open molecular questions regarding ATG8s that are only beginning to be unraveled.
Macroautophagy is a conserved cytoprotective process, that facilitates the degradation of damaged or unwanted cellular components and pathogens, collectively termed cargo.ATG8 proteins play key functions during macroautophagy, upon conjugation to double-membrane vesicles, termed autophagosomes, which sequester cargo for lysosomal degradation.In addition to their canonical functions in macroautophagy, ATG8s also function in non-canonical pathways that do not involve autophagosome formation, and in such cases, ATG8s can be targeted to single-membrane vesicles with roles in divergent processes including cargo degradation and secretion.The canonical and non-canonical functions of ATG8 proteins are regulated, at least in part, by the autophagy conjugation machinery, and possibly the unique interactome that ATG8s have at distinct cellular locations.
Although autophagy is being pursued as a therapeutic target in clinical oncology trials, its effects on metastasis, the principal cause of cancer mortality, remain unclear. Here, we utilize mammary ...cancer models to temporally delete essential autophagy regulators during carcinoma progression. Though genetic ablation of autophagy strongly attenuates primary mammary tumor growth, impaired autophagy promotes spontaneous metastasis and enables the outgrowth of disseminated tumor cells into overt macro-metastases. Transcriptomic analysis reveals that autophagy deficiency elicits a subpopulation of otherwise luminal tumor cells exhibiting basal differentiation traits, which is reversed upon preventing accumulation of the autophagy cargo receptor, Neighbor to BRCA1 (NBR1). Furthermore, pharmacological and genetic induction of autophagy suppresses pro-metastatic differentiation and metastatic outgrowth. Analysis of human breast cancer data reveal that autophagy gene expression inversely correlates with pro-metastatic differentiation signatures and predicts overall and distant metastasis-free survival. Overall, these findings highlight autophagy-dependent control of NBR1 as a key determinant of metastatic progression.
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•Autophagy promotes primary tumor growth, yet suppresses metastatic outgrowth•Autophagy deficiency elicits a pro-metastatic basal tumor cell subpopulation•NBR1 accumulation mediates the effects of autophagy inhibition on metastasis•Enforced autophagy induction prevents the outgrowth of disseminated tumor cells
Autophagy is a therapeutic target in cancer, but its role during metastasis remains incompletely understood. In mammary cancer models, Marsh et al. demonstrate that autophagic degradation of NBR1 suppresses metastatic outgrowth by restricting an aggressive, basal subpopulation of tumor cells. Enforced autophagy is a potential therapeutic approach to prevent metastases.
The tumor-promoting functions of autophagy are primarily attributed to its ability to promote cancer cell survival. However, emerging evidence suggests that autophagy plays other roles during ...tumorigenesis. Here, we uncover that autophagy promotes oncogenic RAS-driven invasion. In epithelial cells transformed with oncogenic RAS, depletion of autophagy-related genes suppresses invasion in three-dimensional culture, decreases cell motility, and reduces pulmonary metastases in vivo. Treatment with conditioned media from autophagy-competent cells rescues the invasive capacity of autophagy-deficient cells, indicating that these cells fail to secrete factors required for RAS-driven invasion. Reduced autophagy diminishes the secretion of the promigratory cytokine interleukin-6 (IL-6), which is necessary to restore invasion of autophagy-deficient cells. Moreover, autophagy-deficient cells exhibit reduced levels of matrix metalloproteinase 2 and WNT5A. These results support a previously unrecognized function for autophagy in promoting cancer cell invasion via the coordinate production of multiple secreted factors.
Our results delineate a previously unrecognized function for autophagy in facilitating oncogenic RAS-driven invasion. We demonstrate that an intact autophagy pathway is required for the elaboration of multiple secreted factors favoring invasion, including IL-6.
Autophagy traditionally sustains metabolism in stressed cells by promoting intracellular catabolism and nutrient recycling. Here, we demonstrate that in response to stresses requiring increased ...glycolytic demand, the core autophagy machinery also facilitates glucose uptake and glycolytic flux by promoting cell surface expression of the glucose transporter GLUT1/Slc2a1. During metabolic stress, LC3+ autophagic compartments bind and sequester the RabGAP protein TBC1D5 away from its inhibitory interactions with the retromer complex, thereby enabling retromer recruitment to endosome membranes and GLUT1 plasma membrane translocation. In contrast, TBC1D5 inhibitory interactions with the retromer are maintained in autophagy-deficient cells, leading to GLUT1 mis-sorting into endolysosomal compartments. Furthermore, TBC1D5 depletion in autophagy-deficient cells rescues retromer recruitment to endosomal membranes and GLUT1 surface recycling. Hence, TBC1D5 shuttling to autophagosomes during metabolic stress facilitates retromer-dependent GLUT1 trafficking. Overall, our results illuminate key interconnections between the autophagy and endosomal pathways dictating GLUT1 trafficking and extracellular nutrient uptake.
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•Autophagy facilitates glucose uptake by promoting GLUT 1 cell surface expression•Autophagy enables retromer-driven translocation of GLUT1 to the plasma membrane•Autophagy deficiency causes GLUT1 mis-sorting into endolysosomal compartments•Shuttling of TBC1D5 into LC3+ autophagosomes relieves inhibition of the retromer
Roy et al. demonstrate that in response to increased glycolytic demand, autophagy induction coordinates glucose uptake from the extracellular milieu by promoting the retromer-dependent cell surface trafficking of the key nutrient transporter, GLUT1.
Accumulating evidence implicates various autophagy-related (ATG) proteins in cellular secretion. Recently, we identified a new secretory autophagy pathway in which components of LC3 conjugation ...machinery specify the incorporation of RNA binding proteins (RBPs) and small non-coding RNAs into extracellular vesicles (EVs), resulting in their secretion outside of cells. We term this process
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ecretion (LDELS). Importantly, LDELS is distinct from classical macroautophagy/autophagy because it requires components of the LC3 conjugation machinery, but not other ATGs involved in autophagosome formation. Because EVs have emerged as mediators of intracellular communication, our results provide new insight into how the autophagy machinery may influence the non-cell autonomous exchange of information between cells.
Both macroautophagy/autophagy and extracellular vesicle (EV) secretion pathways converge upon the endolysosome system. Although lysosome impairment leads to defects in autophagic degradation, the ...impact of such dysfunction on EV secretion remains poorly understood. Recently, we uncovered a novel secretory autophagy pathway that employs EVs and nanoparticles (EVPs) for the secretion of autophagy cargo receptors outside the cell when either autophagosome maturation or lysosomal function is blocked. We term this process secretory autophagy during lysosome inhibition (SALI). SALI functionally requires multiple steps in classical autophagosome formation and the small GTPase RAB27A. Because the intracellular accumulation of autophagy cargo receptors perturbs cell signaling and quality control pathways, we propose that SALI functions as a failsafe mechanism to preserve protein and cellular homeostasis when autophagic or lysosomal degradation is impaired.
Autophagy classically functions to maintain cell health during stressful conditions by targeting cytosolic components for degradation and recycling via lysosomal pathways. However, accumulating ...evidence also supports roles for autophagy‐related genes (ATGs) in non‐degradative processes including cellular secretion. Here, we review emerging roles for the autophagy machinery in regulating extracellular vesicle loading and secretion and discuss how functional coupling of these pathways may impact normal physiology and disease.
The endolysosome system plays central roles in both autophagic degradation and secretory pathways, including the release of extracellular vesicles and particles (EVPs). Although previous work reveals ...important interconnections between autophagy and EVP-mediated secretion, our understanding of these secretory events during endolysosome inhibition remains incomplete. Here, we delineate a secretory autophagy pathway upregulated in response to endolysosomal inhibition, which mediates EVP-associated release of autophagic cargo receptors, including p62/SQSTM1. This secretion is highly regulated and dependent on multiple ATGs required for autophagosome formation, as well as the small GTPase Rab27a. Furthermore, disrupting autophagosome maturation, either via genetic inhibition of autophagosome-to-autolysosome fusion or expression of SARS-CoV-2 ORF3a, is sufficient to induce EVP secretion of autophagy cargo receptors. Finally, ATG-dependent EVP secretion buffers against the intracellular accumulation of autophagy cargo receptors when classical autophagic degradation is impaired. Thus, we propose secretory autophagy via EVPs functions as an alternate route to clear sequestered material and maintain proteostasis during endolysosomal dysfunction or impaired autophagosome maturation.
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