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Cell May 2021Damaged mitochondria need to be cleared to maintain the quality of the mitochondrial pool. Here, we report mitocytosis, a migrasome-mediated mitochondrial...
Damaged mitochondria need to be cleared to maintain the quality of the mitochondrial pool. Here, we report mitocytosis, a migrasome-mediated mitochondrial quality-control process. We found that, upon exposure to mild mitochondrial stresses, damaged mitochondria are transported into migrasomes and subsequently disposed of from migrating cells. Mechanistically, mitocytosis requires positioning of damaged mitochondria at the cell periphery, which occurs because damaged mitochondria avoid binding to inward motor proteins. Functionally, mitocytosis plays an important role in maintaining mitochondrial quality. Enhanced mitocytosis protects cells from mitochondrial stressor-induced loss of mitochondrial membrane potential (MMP) and mitochondrial respiration; conversely, blocking mitocytosis causes loss of MMP and mitochondrial respiration under normal conditions. Physiologically, we demonstrate that mitocytosis is required for maintaining MMP and viability in neutrophils in vivo. We propose that mitocytosis is an important mitochondrial quality-control process in migrating cells, which couples mitochondrial homeostasis with cell migration.
Topics: Animals; Biological Transport; Cell Line; Cell Movement; Cytoplasm; Exocytosis; Female; Homeostasis; Male; Membrane Potential, Mitochondrial; Mice; Mice, Inbred C57BL; Microscopy, Electron, Transmission; Mitochondria; Mitochondrial Membranes; Organelles
PubMed: 34048705
DOI: 10.1016/j.cell.2021.04.027 -
Biochimica Et Biophysica Acta.... Jan 2021Stress granules (SGs) are membrane-less ribonucleoprotein (RNP)-based cellular compartments that form in the cytoplasm of a cell upon exposure to various environmental... (Review)
Review
Stress granules (SGs) are membrane-less ribonucleoprotein (RNP)-based cellular compartments that form in the cytoplasm of a cell upon exposure to various environmental stressors. SGs contain a large set of proteins, as well as mRNAs that have been stalled in translation as a result of stress-induced polysome disassembly. Despite the fact that SGs have been extensively studied for many years, their function is still not clear. They presumably help the cell to cope with the encountered stress, and facilitate the recovery process after stress removal upon which SGs disassemble. Aberrant formation of SGs and impaired SG disassembly majorly contribute to various pathological phenomena in cancer, viral infections, and neurodegeneration. The assembly of SGs is largely driven by liquid-liquid phase separation (LLPS), however, the molecular mechanisms behind that are not fully understood. Recent studies have proposed a novel mechanism for SG formation that involves the interplay of a large interaction network of mRNAs and proteins. Here, we review this novel concept of SG assembly, and discuss the current insights into SG disassembly.
Topics: Cell Compartmentation; Cell Membrane; Cytoplasm; Cytoplasmic Granules; Humans; Liquid Phase Microextraction; Polyribosomes; RNA, Messenger; Ribonucleoproteins; Stress, Physiological
PubMed: 33007331
DOI: 10.1016/j.bbamcr.2020.118876 -
Trends in Biochemical Sciences Mar 2020Members of the mitochondrial carrier family (SLC25) provide the transport steps for amino acids, carboxylic acids, fatty acids, cofactors, inorganic ions, and... (Review)
Review
Members of the mitochondrial carrier family (SLC25) provide the transport steps for amino acids, carboxylic acids, fatty acids, cofactors, inorganic ions, and nucleotides across the mitochondrial inner membrane and are crucial for many cellular processes. Here, we use new insights into the transport mechanism of the mitochondrial ADP/ATP carrier to examine the structure and function of other mitochondrial carriers. They all have a single substrate-binding site and two gates, which are present on either side of the membrane and involve salt-bridge networks. Transport is likely to occur by a common mechanism, in which the coordinated movement of six structural elements leads to the alternating opening and closing of the matrix or cytoplasmic side of the carriers.
Topics: Animals; Biological Transport; Cytoplasm; Humans; Mitochondria; Mitochondrial ADP, ATP Translocases
PubMed: 31787485
DOI: 10.1016/j.tibs.2019.11.001 -
Molecular Cell Jun 2022Virus infection modulates both host immunity and host genomic stability. Poly(ADP-ribose) polymerase 1 (PARP1) is a key nuclear sensor of DNA damage, which maintains...
Virus infection modulates both host immunity and host genomic stability. Poly(ADP-ribose) polymerase 1 (PARP1) is a key nuclear sensor of DNA damage, which maintains genomic integrity, and the successful application of PARP1 inhibitors for clinical anti-cancer therapy has lasted for decades. However, precisely how PARP1 gains access to cytoplasm and regulates antiviral immunity remains unknown. Here, we report that DNA virus induces a reactive nitrogen species (RNS)-dependent DNA damage and activates DNA-dependent protein kinase (DNA-PK). Activated DNA-PK phosphorylates PARP1 on Thr, thus facilitating the cytoplasmic translocation of PARP1 to inhibit the antiviral immunity both in vitro and in vivo. Mechanistically, cytoplasmic PARP1 interacts with and directly PARylates cyclic GMP-AMP synthase (cGAS) on Asp to inhibit its DNA-binding ability. Together, our findings uncover an essential role of PARP1 in linking virus-induced genome instability with inhibition of host immunity, which is of relevance to cancer, autoinflammation, and other diseases.
Topics: Antiviral Agents; Cytoplasm; DNA; DNA Damage; Genomic Instability; Humans; Nucleotidyltransferases; Poly (ADP-Ribose) Polymerase-1
PubMed: 35460603
DOI: 10.1016/j.molcel.2022.03.034 -
Cells Feb 2023Autophagy-the lysosomal degradation of cytoplasm-plays a central role in cellular homeostasis and protects cells from potentially harmful agents that may accumulate in... (Review)
Review
Autophagy-the lysosomal degradation of cytoplasm-plays a central role in cellular homeostasis and protects cells from potentially harmful agents that may accumulate in the cytoplasm, including pathogens, protein aggregates, and dysfunctional organelles. This process is initiated by the formation of a phagophore membrane, which wraps around a portion of cytoplasm or cargo and closes to form a double-membrane autophagosome. Upon the fusion of the autophagosome with a lysosome, the sequestered material is degraded by lysosomal hydrolases in the resulting autolysosome. Several alternative membrane sources of autophagosomes have been proposed, including the plasma membrane, endosomes, mitochondria, endoplasmic reticulum, lipid droplets, hybrid organelles, and de novo synthesis. Here, we review recent progress in our understanding of how the autophagosome is formed and highlight the proposed role of vesicles that contain the lipid scramblase ATG9 as potential seeds for phagophore biogenesis. We also discuss how the phagophore is sealed by the action of the endosomal sorting complex required for transport (ESCRT) proteins.
Topics: Autophagosomes; Macroautophagy; Autophagy; Endosomes; Cell Membrane
PubMed: 36831335
DOI: 10.3390/cells12040668 -
Cells Oct 2020Filamentous fungi typically grow as interconnected multinucleate syncytia that can be microscopic to many hectares in size. Mechanistic details and rules that govern the... (Review)
Review
Filamentous fungi typically grow as interconnected multinucleate syncytia that can be microscopic to many hectares in size. Mechanistic details and rules that govern the formation and function of these multinucleate syncytia are largely unexplored, including details on syncytial morphology and the regulatory controls of cellular and molecular processes. Recent discoveries have revealed various adaptations that enable fungal syncytia to accomplish coordinated behaviors, including cell growth, nuclear division, secretion, communication, and adaptation of the hyphal network for mixing nuclear and cytoplasmic organelles. In this review, we highlight recent studies using advanced technologies to define rules that govern organizing principles of hyphal and colony differentiation, including various aspects of nuclear and mitochondrial cooperation versus competition. We place these findings into context with previous foundational literature and present still unanswered questions on mechanistic aspects, function, and morphological diversity of fungal syncytia across the fungal kingdom.
Topics: Cell Nucleus; Cytoplasm; Fungi; Giant Cells; Mitochondria
PubMed: 33050028
DOI: 10.3390/cells9102255 -
Nature Jul 2021Liquid-liquid phase separation is a major mechanism of subcellular compartmentalization. Although the segregation of RNA into phase-separated condensates broadly affects...
Liquid-liquid phase separation is a major mechanism of subcellular compartmentalization. Although the segregation of RNA into phase-separated condensates broadly affects RNA metabolism, whether and how specific RNAs use phase separation to regulate interacting factors such as RNA-binding proteins (RBPs), and the phenotypic consequences of such regulatory interactions, are poorly understood. Here we show that RNA-driven phase separation is a key mechanism through which a long noncoding RNA (lncRNA) controls the activity of RBPs and maintains genomic stability in mammalian cells. The lncRNA NORAD prevents aberrant mitosis by inhibiting Pumilio (PUM) proteins. We show that NORAD can out-compete thousands of other PUM-binding transcripts to inhibit PUM by nucleating the formation of phase-separated PUM condensates, termed NP bodies. Dual mechanisms of PUM recruitment, involving multivalent PUM-NORAD and PUM-PUM interactions, enable NORAD to competitively sequester a super-stoichiometric amount of PUM in NP bodies. Disruption of NORAD-driven PUM phase separation leads to PUM hyperactivity and genome instability that is rescued by synthetic RNAs that induce the formation of PUM condensates. These results reveal a mechanism by which RNA-driven phase separation can regulate RBP activity and identify an essential role for this process in genome maintenance. The repetitive sequence architecture of NORAD and other lncRNAs suggests that phase separation may be a widely used mechanism of lncRNA-mediated regulation.
Topics: Cell Line; Cytoplasm; Genomic Instability; Humans; Phase Transition; RNA; RNA, Long Noncoding; RNA-Binding Proteins; Transcription Factors
PubMed: 34108682
DOI: 10.1038/s41586-021-03633-w -
Current Biology : CB Jul 2019In 1955, the biologist and Nobel Prize laureate Christian de Duve discovered that cells possess specialized organelles filled with hydrolytic enzymes and he called these...
In 1955, the biologist and Nobel Prize laureate Christian de Duve discovered that cells possess specialized organelles filled with hydrolytic enzymes and he called these organelles lysosomes. At the same time, electron microscopy studies by Novikoff and colleagues showed that intracellular dense bodies, which later turned out to be lysosomes, contain cytoplasmic components. Together, these groundbreaking observations revealed that cells can deliver cytoplasmic components to lysosomes for degradation. The hallmark of this degradative process, which de Duve called autophagy, is the formation of double-membrane-limited vesicles. Further morphological characterization of these vesicles (autophagosomes) revealed that they mainly contain bulk cytoplasm. Although this suggested that autophagy leads to a non-selective degradation of cytoplasmic material, de Duve anticipated that a regulated and selective type of this pathway must also exist. Today we know that, under normal conditions, macroautophagy is a highly selective pathway that sequesters damaged or superfluous material from the cytoplasm through the formation of double-membrane-limited autophagosomes. Upon fusion with lysosomes, the content of autophagosomes is degraded and the resulting building blocks are released into the cytoplasm. However, in response to cytotoxic stress or starvation, cells start to produce autophagosomes that capture bulk cytoplasm non-selectively. This stress response is essential for cells to survive adverse environmental conditions, whereas the selective sequestration of cargo is important to maintain cellular homeostasis.
Topics: Autophagosomes; Autophagy; Cytosol; Lysosomes; Macroautophagy
PubMed: 31336079
DOI: 10.1016/j.cub.2019.06.014 -
Cell Apr 2020Liquid-liquid phase separation (LLPS) mediates formation of membraneless condensates such as those associated with RNA processing, but the rules that dictate their...
Liquid-liquid phase separation (LLPS) mediates formation of membraneless condensates such as those associated with RNA processing, but the rules that dictate their assembly, substructure, and coexistence with other liquid-like compartments remain elusive. Here, we address the biophysical mechanism of this multiphase organization using quantitative reconstitution of cytoplasmic stress granules (SGs) with attached P-bodies in human cells. Protein-interaction networks can be viewed as interconnected complexes (nodes) of RNA-binding domains (RBDs), whose integrated RNA-binding capacity determines whether LLPS occurs upon RNA influx. Surprisingly, both RBD-RNA specificity and disordered segments of key proteins are non-essential, but modulate multiphase condensation. Instead, stoichiometry-dependent competition between protein networks for connecting nodes determines SG and P-body composition and miscibility, while competitive binding of unconnected proteins disengages networks and prevents LLPS. Inspired by patchy colloid theory, we propose a general framework by which competing networks give rise to compositionally specific and tunable condensates, while relative linkage between nodes underlies multiphase organization.
Topics: Biophysical Phenomena; Cell Line, Tumor; Cytoplasm; Cytoplasmic Granules; Cytoplasmic Structures; Humans; Intrinsically Disordered Proteins; Liquid-Liquid Extraction; Organelles; Protein Interaction Maps; RNA; RNA Recognition Motif Proteins
PubMed: 32302570
DOI: 10.1016/j.cell.2020.03.050 -
Developmental Cell Jan 2021Cytoplasm is a gel-like crowded environment composed of various macromolecules, organelles, cytoskeletal networks, and cytosol. The structure of the cytoplasm is highly... (Review)
Review
Cytoplasm is a gel-like crowded environment composed of various macromolecules, organelles, cytoskeletal networks, and cytosol. The structure of the cytoplasm is highly organized and heterogeneous due to the crowding of its constituents and their effective compartmentalization. In such an environment, the diffusive dynamics of the molecules are restricted, an effect that is further amplified by clustering and anchoring of molecules. Despite the crowded nature of the cytoplasm at the microscopic scale, large-scale reorganization of the cytoplasm is essential for important cellular functions, such as cell division and polarization. How such mesoscale reorganization of the cytoplasm is achieved, especially for large cells such as oocytes or syncytial tissues that can span hundreds of micrometers in size, is only beginning to be understood. In this review, we will discuss recent advances in elucidating the molecular, cellular, and biophysical mechanisms by which the cytoskeleton drives cytoplasmic reorganization across different scales, structures, and species.
Topics: Animals; Cytoplasm; Cytoskeleton; Cytosol; Humans; Mechanotransduction, Cellular; Multiprotein Complexes; Organelles
PubMed: 33321104
DOI: 10.1016/j.devcel.2020.12.002