C. elegans mitochondrial factor WAH-1 promotes phosphatidylserine externalization in apoptotic cells through phospholipid scramblase SCRM-1

Autophagosomes are double-membrane intracellular vesicles that degrade protein aggregates, intracellular organelles, and other cellular components. In the nematode Caenorhabditis elegans, 113 somatic cells undergo apoptosis during embryogenesis and are engulfed and degraded by their neighboring cells. We discovered a novel role of autophagosomes in facilitating the degradation of apoptotic cells in C. elegans embryos using a real-time imaging technique. Specifically, double-membrane autophagosomes in engulfing cells are recruited to the surfaces of phagosomes containing apoptotic cells and subsequently fuse to phagosomes, allowing the inner membrane to enter the phagosomal lumen. Mutants defective in the production of autophagosomes display significant delays in the degradation of apoptotic cells, demonstrating the important contribution of autophagosomes to this process. The signaling pathway led by the phagocytic receptor CED-1, CED-1s adaptor CED-6, and the large GTPase dynamin (DYN-1) promote the recruitment of autophagosomes to phagosomes. Moreover, the subsequent fusion of autophagosomes with phagosomes requires the functions of the small GTPase RAB-7 and the HOPS complex. Our findings reveal that, unlike the single-membrane, LC3- associated phagocytosis (LAP) vesicles reported for mammalian phagocytes, canonical autophagosomes function in the clearance of C. elegans apoptotic cells. These findings add autophagosomes to the collection of intracellular organelles that contribute to phagosome maturation, identify novel crosstalk between the autophagy and phagosome maturation pathways, and discover the upstream factors that initiate this crosstalk.

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Two Alternative Mechanisms That Regulate the Presentation of Apoptotic Cell Engulfment Signal in Caenorhabditis elegans

Molecular Biology of the Cell ◽

10.1091/mbc.e07-02-0138 ◽

2007 ◽

Vol 18 (8) ◽

pp. 3180-3192 ◽

Cited By ~ 73

Author(s):

Victor Venegas ◽

Zheng Zhou

Keyword(s):

Caenorhabditis Elegans ◽

Abc Transporter ◽

Germ Cells ◽

Mammalian Cells ◽

Developmental Stages ◽

Apoptotic Cell ◽

Somatic Cells ◽

Apoptotic Cells ◽

Phospholipid Scramblase ◽

Cell Engulfment

Phosphatidylserine exposed on the surface of apoptotic mammalian cells is considered an “eat-me” signal that attracts phagocytes. The generality of using phosphatidylserine as a clearance signal for apoptotic cells in animals and the regulation of this event remain uncertain. Using ectopically expressed mouse MFG-E8, a secreted phosphatidylserine-binding protein, we detected specific exposure of phosphatidylserine on the surface of apoptotic cells in Caenorhabditis elegans. Masking the surface phosphatidylserine inhibits apoptotic cell engulfment. CED-7, an ATP-binding cassette (ABC) transporter, is necessary for the efficient exposure of phosphatidylserine on apoptotic somatic cells, and for the recognition of these cells by phagocytic receptor CED-1. Alternatively, phosphatidylserine exposure on apoptotic germ cells is not CED-7 dependent, but instead requires phospholipid scramblase PLSC-1, a homologue of mammalian phospholipid scramblases. Moreover, deleting plsc-1 results in the accumulation of apoptotic germ cells but not apoptotic somatic cells. These observations suggest that phosphatidylserine might be recognized by CED-1 and act as a conserved eat-me signal from nematodes to mammals. Furthermore, the two different biochemical activities used in somatic cells (ABC transporter) and germ cells (phospholipid scramblase) suggest an increased complexity in the regulation of phosphatidylserine presentation in response to apoptotic signals in different tissues and during different developmental stages.

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SLI-1 Cbl Inhibits the Engulfment of Apoptotic Cells in C. elegans through a Ligase-Independent Function

PLoS Genetics ◽

10.1371/journal.pgen.1003115 ◽

2012 ◽

Vol 8 (12) ◽

pp. e1003115 ◽

Cited By ~ 6

Author(s):

Courtney Anderson ◽

Shan Zhou ◽

Emma Sawin ◽

H. Robert Horvitz ◽

Michael E. Hurwitz

Keyword(s):

Apoptotic Cells ◽

Independent Function ◽

C Elegans

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Appetizing rancidity of apoptotic cells for macrophages: oxidation, externalization, and recognition of phosphatidylserine

AJP Lung Cellular and Molecular Physiology ◽

10.1152/ajplung.00365.2002 ◽

2003 ◽

Vol 285 (1) ◽

pp. L1-L17 ◽

Cited By ~ 69

Author(s):

V. E. Kagan ◽

G. G. Borisenko ◽

B. F. Serinkan ◽

Y. Y. Tyurina ◽

V. A. Tyurin ◽

...

Keyword(s):

Oxidative Stress ◽

Cell Death ◽

Inflammatory Responses ◽

Apoptotic Cells ◽

Radical Intermediates ◽

Phosphatidylserine Externalization ◽

Phospholipid Asymmetry ◽

Lung Physiology ◽

Macrophage Receptors

Programmed cell death (apoptosis) functions as a mechanism to eliminate unwanted or irreparably damaged cells ultimately leading to their orderly phagocytosis in the absence of calamitous inflammatory responses. Recent studies have demonstrated that the generation of free radical intermediates and subsequent oxidative stress are implicated as part of the apoptotic execution process. Oxidative stress may simply be an unavoidable yet trivial byproduct of the apoptotic machinery; alternatively, intermediates or products of oxidative stress may act as essential signals for the execution of the apoptotic program. This review is focused on the specific role of oxidative stress in apoptotic signaling, which is realized via phosphatidylserine-dependent pathways leading to recognition of apoptotic cells and their effective clearance. In particular, the mechanisms involved in selective phosphatidylserine oxidation in the plasma membrane during apoptosis and its association with disturbances of phospholipid asymmetry leading to phosphatidylserine externalization and recognition by macrophage receptors are at the center of our discussion. The putative importance of this oxidative phosphatidylserine signaling in lung physiology and disease are also discussed.

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Autophagosomes fuse to phagosomes and facilitate the degradation of apoptotic cells in Caenorhabditis elegans

eLife ◽

10.7554/elife.72466 ◽

2022 ◽

Vol 11 ◽

Author(s):

Omar Peña-Ramos ◽

Lucia Chiao ◽

Xianghua Liu ◽

Xiaomeng Yu ◽

Tianyou Yao ◽

...

Keyword(s):

Caenorhabditis Elegans ◽

Apoptotic Cell ◽

Adaptor Protein ◽

Small Gtpase ◽

Apoptotic Cells ◽

Phagosome Maturation ◽

Double Membrane ◽

C Elegans ◽

Intracellular Organelles ◽

Cellular Components

Autophagosomes are double-membrane intracellular vesicles that degrade protein aggregates, intracellular organelles, and other cellular components. During the development of the nematode Caenorhabditis elegans, many somatic and germ cells undergo apoptosis. These cells are engulfed and degraded by their neighboring cells. We discovered a novel role of autophagosomes in facilitating the degradation of apoptotic cells using a real-time imaging technique. Specifically, the double-membrane autophagosomes in engulfing cells are recruited to the surfaces of phagosomes containing apoptotic cells and subsequently fuse to phagosomes, allowing the inner vesicle to enter the phagosomal lumen. Mutants defective in the production of autophagosomes display significant defects in the degradation of apoptotic cells, demonstrating the importance of autophagosomes to this process. The signaling pathway led by the phagocytic receptor CED-1, the adaptor protein CED-6, and the large GTPase dynamin (DYN-1) promotes the recruitment of autophagosomes to phagosomes. Moreover, the subsequent fusion of autophagosomes with phagosomes requires the functions of the small GTPase RAB-7 and the HOPS complex components. Further observations suggest that autophagosomes provide apoptotic cell-degradation activities in addition to and in parallel of lysosomes. Our findings reveal that, unlike the single-membrane, LC3-associated phagocytosis (LAP) vesicles reported for mammalian phagocytes, the canonical double-membrane autophagosomes facilitate the clearance of C. elegans apoptotic cells. These findings add autophagosomes to the collection of intracellular organelles that contribute to phagosome maturation, identify novel crosstalk between the autophagy and phagosome maturation pathways, and discover the upstream signaling molecules that initiate this crosstalk.

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Faculty Opinions recommendation of C. elegans Dynamin mediates the signaling of phagocytic receptor CED-1 for the engulfment and degradation of apoptotic cells.

Faculty Opinions – Post-Publication Peer Review of the Biomedical Literature ◽

10.3410/f.1032684.374474 ◽

2006 ◽

Author(s):

Barbara Conradt

Keyword(s):

Apoptotic Cells ◽

C Elegans

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The amino acid transporter SLC-36.1 cooperates with PtdIns3P 5-kinase to control phagocytic lysosome reformation

The Journal of Cell Biology ◽

10.1083/jcb.201901074 ◽

2019 ◽

Vol 218 (8) ◽

pp. 2619-2637 ◽

Cited By ~ 3

Author(s):

Qiwen Gan ◽

Xin Wang ◽

Qian Zhang ◽

Qiuyuan Yin ◽

Youli Jian ◽

...

Keyword(s):

Amino Acid ◽

Caenorhabditis Elegans ◽

Amino Acid Transporter ◽

Apoptotic Cells ◽

Phagosome Maturation ◽

Genetic Pathway ◽

C Elegans ◽

Acid Transporter ◽

Cell Corpse ◽

Cell Corpse Clearance

Phagocytic removal of apoptotic cells involves formation, maturation, and digestion of cell corpse–containing phagosomes. The retrieval of lysosomal components following phagolysosomal digestion of cell corpses remains poorly understood. Here we reveal that the amino acid transporter SLC-36.1 is essential for lysosome reformation during cell corpse clearance in Caenorhabditis elegans embryos. Loss of slc-36.1 leads to formation of phagolysosomal vacuoles arising from cell corpse–containing phagosomes. In the absence of slc-36.1, phagosome maturation is not affected, but the retrieval of lysosomal components is inhibited. Moreover, loss of PPK-3, the C. elegans homologue of the PtdIns3P 5-kinase PIKfyve, similarly causes accumulation of phagolysosomal vacuoles that are defective in phagocytic lysosome reformation. SLC-36.1 and PPK-3 function in the same genetic pathway, and they directly interact with one another. In addition, loss of slc-36.1 and ppk-3 causes strong defects in autophagic lysosome reformation in adult animals. Our findings thus suggest that the PPK-3–SLC-36.1 axis plays a central role in both phagocytic and autophagic lysosome formation.

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The lysosomal cathepsin protease CPL-1 plays a leading role in phagosomal degradation of apoptotic cells in Caenorhabditis elegans

Molecular Biology of the Cell ◽

10.1091/mbc.e14-01-0015 ◽

2014 ◽

Vol 25 (13) ◽

pp. 2071-2083 ◽

Cited By ~ 16

Author(s):

Meng Xu ◽

Yubing Liu ◽

Liyuan Zhao ◽

Qiwen Gan ◽

Xiaochen Wang ◽

...

Keyword(s):

Caenorhabditis Elegans ◽

Apoptotic Cell ◽

Cell Types ◽

Apoptotic Cells ◽

C Elegans ◽

Lysosomal Protease ◽

Leading Role ◽

Lysosomal Proteases ◽

Cell Corpse

During programmed cell death, the clearance of apoptotic cells is achieved by their phagocytosis and delivery to lysosomes for destruction in engulfing cells. However, the role of lysosomal proteases in cell corpse destruction is not understood. Here we report the identification of the lysosomal cathepsin CPL-1 as an indispensable protease for apoptotic cell removal in Caenorhabditis elegans. We find that loss of cpl-1 function leads to strong accumulation of germ cell corpses, which results from a failure in degradation rather than engulfment. CPL-1 is expressed in a variety of cell types, including engulfment cells, and its mutation does not affect the maturation of cell corpse–containing phagosomes, including phagosomal recruitment of maturation effectors and phagosome acidification. Of importance, we find that phagosomal recruitment and incorporation of CPL-1 occurs before digestion of cell corpses, which depends on factors required for phagolysosome formation. Using RNA interference, we further examine the role of other candidate lysosomal proteases in cell corpse clearance but find that they do not obviously affect this process. Collectively, these findings establish CPL-1 as the leading lysosomal protease required for elimination of apoptotic cells in C. elegans.

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