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Nature Reviews. Molecular Cell Biology Nov 2021Autophagy is a versatile degradation system for maintaining cellular homeostasis whereby cytosolic materials are sequestered in a double-membrane autophagosome and... (Review)
Review
Autophagy is a versatile degradation system for maintaining cellular homeostasis whereby cytosolic materials are sequestered in a double-membrane autophagosome and subsequently delivered to lysosomes, where they are broken down. In multicellular organisms, newly formed autophagosomes undergo a process called 'maturation', in which they fuse with vesicles originating from endolysosomal compartments, including early/late endosomes and lysosomes, to form amphisomes, which eventually become degradative autolysosomes. This fusion process requires the concerted actions of multiple regulators of membrane dynamics, including SNAREs, tethering proteins and RAB GTPases, and also transport of autophagosomes and late endosomes/lysosomes towards each other. Multiple mechanisms modulate autophagosome maturation, including post-translational modification of key components, spatial distribution of phosphoinositide lipid species on membranes, RAB protein dynamics, and biogenesis and function of lysosomes. Nutrient status and various stresses integrate into the autophagosome maturation machinery to coordinate the progression of autophagic flux. Impaired autophagosome maturation is linked to the pathogenesis of various human diseases, including neurodegenerative disorders, cancer and myopathies. Furthermore, invading pathogens exploit various strategies to block autophagosome maturation, thus evading destruction and even subverting autophagic vacuoles (autophagosomes, amphisomes and autolysosomes) for survival, growth and/or release. Here, we discuss the recent progress in our understanding of the machinery and regulation of autophagosome maturation, the relevance of these mechanisms to human pathophysiology and how they are harnessed by pathogens for their benefit. We also provide perspectives on targeting autophagosome maturation therapeutically.
Topics: Autophagosomes; Autophagy; Endosomes; Humans; Lysosomes; Neurodegenerative Diseases; Phagosomes; Protein Processing, Post-Translational; SNARE Proteins; Transport Vesicles; rab GTP-Binding Proteins
PubMed: 34302147
DOI: 10.1038/s41580-021-00392-4 -
Nature Reviews. Molecular Cell Biology Jan 2020Cellular membranes can form two principally different involutions, which either exclude or contain cytosol. The 'classical' budding reactions, such as those occurring... (Review)
Review
Cellular membranes can form two principally different involutions, which either exclude or contain cytosol. The 'classical' budding reactions, such as those occurring during endocytosis or formation of exocytic vesicles, involve proteins that assemble on the cytosol-excluding face of the bud neck. Inverse membrane involution occurs in a wide range of cellular processes, supporting cytokinesis, endosome maturation, autophagy, membrane repair and many other processes. Such inverse membrane remodelling is mediated by a heteromultimeric protein machinery known as endosomal sorting complex required for transport (ESCRT). ESCRT proteins assemble on the cytosolic (or nucleoplasmic) face of the neck of the forming involution and cooperate with the ATPase VPS4 to drive membrane scission or sealing. Here, we review similarities and differences of various ESCRT-dependent processes, with special emphasis on mechanisms of ESCRT recruitment.
Topics: Animals; Cell Membrane; Cytokinesis; Endosomal Sorting Complexes Required for Transport; Endosomes; Exosomes; Host-Pathogen Interactions; Humans; Neurons; Nuclear Envelope; Phagosomes; Protein Transport; Spastin; Virus Replication
PubMed: 31705132
DOI: 10.1038/s41580-019-0177-4 -
Nature Reviews. Molecular Cell Biology Aug 2020Autophagosomes are double-membrane vesicles newly formed during autophagy to engulf a wide range of intracellular material and transport this autophagic cargo to... (Review)
Review
Autophagosomes are double-membrane vesicles newly formed during autophagy to engulf a wide range of intracellular material and transport this autophagic cargo to lysosomes (or vacuoles in yeasts and plants) for subsequent degradation. Autophagosome biogenesis responds to a plethora of signals and involves unique and dynamic membrane processes. Autophagy is an important cellular mechanism allowing the cell to meet various demands, and its disruption compromises homeostasis and leads to various diseases, including metabolic disorders, neurodegeneration and cancer. Thus, not surprisingly, the elucidation of the molecular mechanisms governing autophagosome biogenesis has attracted considerable interest. Key molecules and organelles involved in autophagosome biogenesis, including autophagy-related (ATG) proteins and the endoplasmic reticulum, have been discovered, and their roles and relationships have been investigated intensely. However, several fundamental questions, such as what supplies membranes/lipids to build the autophagosome and how the membrane nucleates, expands, bends into a spherical shape and finally closes, have proven difficult to address. Nonetheless, owing to recent studies with new approaches and technologies, we have begun to unveil the mechanisms underlying these processes on a molecular level. We now know that autophagosome biogenesis is a highly complex process, in which multiple proteins and lipids from various membrane sources, supported by the formation of membrane contact sites, cooperate with biophysical phenomena, including membrane shaping and liquid-liquid phase separation, to ensure seamless segregation of the autophagic cargo. Together, these studies pave the way to obtaining a holistic view of autophagosome biogenesis.
Topics: Animals; Autophagosomes; Autophagy; Autophagy-Related Proteins; Cell Membrane; Endoplasmic Reticulum; Humans; Lysosomes; Macroautophagy; Protein Transport
PubMed: 32372019
DOI: 10.1038/s41580-020-0241-0 -
Frontiers in Immunology 2020Phagocytosis is a cellular process for ingesting and eliminating particles larger than 0.5 μm in diameter, including microorganisms, foreign substances, and apoptotic... (Review)
Review
Phagocytosis is a cellular process for ingesting and eliminating particles larger than 0.5 μm in diameter, including microorganisms, foreign substances, and apoptotic cells. Phagocytosis is found in many types of cells and it is, in consequence an essential process for tissue homeostasis. However, only specialized cells termed professional phagocytes accomplish phagocytosis with high efficiency. Macrophages, neutrophils, monocytes, dendritic cells, and osteoclasts are among these dedicated cells. These professional phagocytes express several phagocytic receptors that activate signaling pathways resulting in phagocytosis. The process of phagocytosis involves several phases: i) detection of the particle to be ingested, ii) activation of the internalization process, iii) formation of a specialized vacuole called phagosome, and iv) maturation of the phagosome to transform it into a phagolysosome. In this review, we present a general view of our current understanding on cells, phagocytic receptors and phases involved in phagocytosis.
Topics: Apoptosis; Humans; Models, Immunological; Pathogen-Associated Molecular Pattern Molecules; Phagocytes; Phagocytosis; Phagosomes; Receptors, Complement; Receptors, IgG; Receptors, Immunologic; Receptors, Pattern Recognition; Signal Transduction
PubMed: 32582172
DOI: 10.3389/fimmu.2020.01066 -
Protein & Cell Sep 2023Lipophagy, the selective engulfment of lipid droplets (LDs) by autophagosomes for lysosomal degradation, is critical to lipid and energy homeostasis. Here we show that...
Lipophagy, the selective engulfment of lipid droplets (LDs) by autophagosomes for lysosomal degradation, is critical to lipid and energy homeostasis. Here we show that the lipid transfer protein ORP8 is located on LDs and mediates the encapsulation of LDs by autophagosomal membranes. This function of ORP8 is independent of its lipid transporter activity and is achieved through direct interaction with phagophore-anchored LC3/GABARAPs. Upon lipophagy induction, ORP8 has increased localization on LDs and is phosphorylated by AMPK, thereby enhancing its affinity for LC3/GABARAPs. Deletion of ORP8 or interruption of ORP8-LC3/GABARAP interaction results in accumulation of LDs and increased intracellular triglyceride. Overexpression of ORP8 alleviates LD and triglyceride deposition in the liver of ob/ob mice, and Osbpl8-/- mice exhibit liver lipid clearance defects. Our results suggest that ORP8 is a lipophagy receptor that plays a key role in cellular lipid metabolism.
Topics: Animals; Mice; Lipid Droplets; Autophagy; Autophagosomes; Homeostasis; Triglycerides
PubMed: 37707322
DOI: 10.1093/procel/pwac063 -
Science (New York, N.Y.) Oct 2019The nucleotide oligomerization domain (NOD)-like receptors 1 and 2 (NOD1/2) are intracellular pattern-recognition proteins that activate immune signaling pathways in...
The nucleotide oligomerization domain (NOD)-like receptors 1 and 2 (NOD1/2) are intracellular pattern-recognition proteins that activate immune signaling pathways in response to peptidoglycans associated with microorganisms. Recruitment to bacteria-containing endosomes and other intracellular membranes is required for NOD1/2 signaling, and NOD1/2 mutations that disrupt membrane localization are associated with inflammatory bowel disease and other inflammatory conditions. However, little is known about this recruitment process. We found that NOD1/2 S-palmitoylation is required for membrane recruitment and immune signaling. ZDHHC5 was identified as the palmitoyltransferase responsible for this critical posttranslational modification, and several disease-associated mutations in NOD2 were found to be associated with defective S-palmitoylation. Thus, ZDHHC5-mediated S-palmitoylation of NOD1/2 is critical for their ability to respond to peptidoglycans and to mount an effective immune response.
Topics: Acyltransferases; Animals; Cysteine; HCT116 Cells; HEK293 Cells; Humans; Lipoylation; Macrophages; Mice; Mice, Inbred C57BL; Mice, Knockout; Nod1 Signaling Adaptor Protein; Nod2 Signaling Adaptor Protein; Peptidoglycan; Phagosomes; Protein Processing, Post-Translational; RAW 264.7 Cells; Salmonella typhimurium; Signal Transduction
PubMed: 31649195
DOI: 10.1126/science.aau6391 -
Immunity Aug 2023STING (stimulator of interferon genes) exerts protective cellular responses to viral infection via induction of interferon production and autophagy. Here, we report the...
STING (stimulator of interferon genes) exerts protective cellular responses to viral infection via induction of interferon production and autophagy. Here, we report the role of STING in modulating the immune responses toward fungal infection. Upon Candida albicans stimulation, STING transited alongside the endoplasmic reticulum (ER) to the phagosomes. In phagosomes, STING directly bound with Src via the N-terminal 18 amino acids of STING, and this binding prevented Src from recruiting and phosphorylating Syk. Consistently, Syk-associated signaling and production of pro-inflammatory cytokines and chemokines were increased in mouse BMDCs (bone-marrow-derived dendritic cells) lacking STING with fungal treatment. STING deficiency improved anti-fungal immunity in systemic C. albicans infection. Importantly, administration of the N-terminal 18-aa (amino acid) peptide of STING improved host outcomes in disseminated fungal infection. Overall, our study identifies a previously unrecognized function of STING in negatively regulating anti-fungal immune responses and offers a potential therapeutic strategy for controlling C. albicans infection.
Topics: Animals; Mice; Cytokines; Immunity, Innate; Interferons; Nucleotides; Phagosomes; Signal Transduction
PubMed: 37379835
DOI: 10.1016/j.immuni.2023.06.002 -
Methods in Molecular Biology (Clifton,... 2024One hundred years have passed since the death of Élie Metchnikoff (1845-1916). He was the first to observe the uptake of particles by cells and realized the importance... (Review)
Review
One hundred years have passed since the death of Élie Metchnikoff (1845-1916). He was the first to observe the uptake of particles by cells and realized the importance of this process, named phagocytosis, for the host response to injury and infection. He also was a strong advocate of the role of phagocytosis in cellular immunity, and with this, he gave us the basis for our modern understanding of inflammation and the innate immune response. Phagocytosis is an elegant but complex process for the ingestion and elimination of pathogens, but it is also important for the elimination of apoptotic cells and hence fundamental for tissue homeostasis. Phagocytosis can be divided into four main steps: (i) recognition of the target particle, (ii) signaling to activate the internalization machinery, (iii) phagosome formation, and (iv) phagolysosome maturation. In this chapter, we present a general view of our current knowledge on phagocytosis performed mainly by professional phagocytes through antibody and complement receptors and discuss aspects that remain incompletely understood.
Topics: Phagocytosis; Humans; Animals; Phagosomes; Phagocytes; Signal Transduction; Immunity, Innate
PubMed: 38888769
DOI: 10.1007/978-1-0716-3890-3_3 -
Cells Dec 2021Mitochondria are multifunctional subcellular organelles essential for cellular energy homeostasis and apoptotic cell death. It is, therefore, crucial to maintain... (Review)
Review
Mitochondria are multifunctional subcellular organelles essential for cellular energy homeostasis and apoptotic cell death. It is, therefore, crucial to maintain mitochondrial fitness. Mitophagy, the selective removal of dysfunctional mitochondria by autophagy, is critical for regulating mitochondrial quality control in many physiological processes, including cell development and differentiation. On the other hand, both impaired and excessive mitophagy are involved in the pathogenesis of different ageing-associated diseases such as neurodegeneration, cancer, myocardial injury, liver disease, sarcopenia and diabetes. The best-characterized mitophagy pathway is the PTEN-induced putative kinase 1 (PINK1)/Parkin-dependent pathway. However, other Parkin-independent pathways are also reported to mediate the tethering of mitochondria to the autophagy apparatuses, directly activating mitophagy (mitophagy receptors and other E3 ligases). In addition, the existence of molecular mechanisms other than PINK1-mediated phosphorylation for Parkin activation was proposed. The adenosine5'-monophosphate (AMP)-activated protein kinase (AMPK) is emerging as a key player in mitochondrial metabolism and mitophagy. Beyond its involvement in mitochondrial fission and autophagosomal engulfment, its interplay with the PINK1-Parkin pathway is also reported. Here, we review the recent advances in elucidating the canonical molecular mechanisms and signaling pathways that regulate mitophagy, focusing on the early role and spatial specificity of the AMPK/ULK1 axis.
Topics: AMP-Activated Protein Kinases; Animals; Autophagy-Related Protein-1 Homolog; Humans; Mitophagy; Models, Biological; Phagosomes; Ubiquitin-Protein Ligases
PubMed: 35011593
DOI: 10.3390/cells11010030 -
Nature Immunology Feb 2021Type 1 conventional dendritic (cDC1) cells are necessary for cross-presentation of many viral and tumor antigens to CD8 T cells. cDC1 cells can be identified in mice and...
Type 1 conventional dendritic (cDC1) cells are necessary for cross-presentation of many viral and tumor antigens to CD8 T cells. cDC1 cells can be identified in mice and humans by high expression of DNGR-1 (also known as CLEC9A), a receptor that binds dead-cell debris and facilitates XP of corpse-associated antigens. Here, we show that DNGR-1 is a dedicated XP receptor that signals upon ligand engagement to promote phagosomal rupture. This allows escape of phagosomal contents into the cytosol, where they access the endogenous major histocompatibility complex class I antigen processing pathway. The activity of DNGR-1 maps to its signaling domain, which activates SYK and NADPH oxidase to cause phagosomal damage even when spliced into a heterologous receptor and expressed in heterologous cells. Our data reveal the existence of innate immune receptors that couple ligand binding to endocytic vesicle damage to permit MHC class I antigen presentation of exogenous antigens and to regulate adaptive immunity.
Topics: Animals; Antigen Presentation; Cell Death; Coculture Techniques; Cross-Priming; Dendritic Cells; HEK293 Cells; Histocompatibility Antigens Class I; Humans; Lectins, C-Type; Ligands; Mice; NADPH Oxidases; Phagosomes; Phosphorylation; RAW 264.7 Cells; Reactive Oxygen Species; Receptors, Immunologic; Receptors, Mitogen; Signal Transduction; Syk Kinase; T-Lymphocytes
PubMed: 33349708
DOI: 10.1038/s41590-020-00824-x