GOP-1 promotes apoptotic cell degradation by activating the small GTPase Rab2 in C. elegans

Apoptotic cells generated by programmed cell death are engulfed by phagocytes and enclosed within plasma membrane–derived phagosomes. Maturation of phagosomes involves a series of membrane-remodeling events that are governed by the sequential actions of Rab GTPases and lead to formation of phagolysosomes, where cell corpses are degraded. Here we identified gop-1 as a novel regulator of apoptotic cell clearance in Caenorhabditis elegans. Loss of gop-1 affects phagosome maturation through the RAB-5–positive stage, causing defects in phagosome acidification and phagolysosome formation, phenotypes identical to and unaffected by loss of unc-108, the C. elegans Rab2. GOP-1 transiently associates with cell corpse–containing phagosomes, and loss of its function abrogates phagosomal association of UNC-108. GOP-1 interacts with GDP-bound and nucleotide-free UNC-108/Rab2, disrupts GDI-UNC-108 complexes, and promotes activation and membrane recruitment of UNC-108/Rab2 in vitro. Loss of gop-1 also abolishes association of UNC-108 with endosomes, causing defects in endosome and dense core vesicle maturation. Thus, GOP-1 is an activator of UNC-108/Rab2 in multiple processes.

Download Full-text

RAB-35 aids apoptotic cell clearance by regulating cell corpse recognition and phagosome maturation

10.1101/298380 ◽

2018 ◽

Author(s):

Ryan C. Haley ◽

Ying Wang ◽

Zheng Zhou

Keyword(s):

Apoptotic Cell ◽

Small Gtpases ◽

Small Gtpase ◽

Apoptotic Cells ◽

Rab Gtpases ◽

Phagosome Maturation ◽

Apoptotic Cell Clearance ◽

Cell Clearance ◽

Early Endosomes ◽

Cell Corpse

AbstractIn metazoans, apoptotic cells are swiftly engulfed by phagocytes and degraded inside phagosomes. Multiple small GTPases in the Rab family are known to function in phagosome maturation by regulating vesicle trafficking. We discovered rab-35 as a new gene important for apoptotic cell clearance using an RNAi screen targeting putative Rab GTPases in Caenorhabditis elegans. We further identified TBC-10 as a putative GTPase-activating protein (GAP), and FLCN-1 and RME-4 as two putative Guanine Nucleotide Exchange Factors (GEFs), for RAB-35. RAB-35 function was found to be required for the incorporation of early endosomes to phagosomes and for the timely degradation of apoptotic cell corpses. More specifically, RAB-35 facilitates the switch of phagosomal membrane phosphatidylinositol species from PtdIns(4,5)P2 to PtdIns(3)P and promotes the recruitment of the small GTPase RAB-5 to phagosomal surfaces, processes that are essential for phagosome maturation. Interestingly, we observed that CED-1 performs these same functions, and to a much larger extent than RAB-35. Remarkably, in addition to cell corpse degradation, RAB-35 also facilitates the recognition of cell corpses independently of the CED-1 and CED-5 pathways. RAB-35 localizes to extending pseudopods and is further enriched on nascent phagosomes, consistent with its dual roles in regulating cell corpse-recognition and phagosome maturation. Epistasis analyses indicate that rab-35 represents a novel third genetic pathway that acts in parallel to both of the canonical ced-1/6/7 and ced-2/5/10/12 engulfment pathways. We propose that RAB-35 acts as a robustness factor, leading a pathway that aids the canonical pathways for the engulfment and degradation of apoptotic cells.

Download Full-text

The small GTPase RAB-35 facilitates the initiation of phagosome maturation and acts as a robustness factor for apoptotic cell clearance

Small GTPases ◽

10.1080/21541248.2019.1680066 ◽

2019 ◽

pp. 1-14

Author(s):

Ryan Haley ◽

Zheng Zhou

Keyword(s):

Apoptotic Cell ◽

Small Gtpase ◽

Phagosome Maturation ◽

Apoptotic Cell Clearance ◽

Cell Clearance

Download Full-text

Persistence of apoptotic cells without autoimmune disease or inflammation in CD14−/− mice

The Journal of Cell Biology ◽

10.1083/jcb.200410057 ◽

2004 ◽

Vol 167 (6) ◽

pp. 1161-1170 ◽

Cited By ~ 96

Author(s):

Andrew Devitt ◽

Kate G. Parker ◽

Carol Anne Ogden ◽

Ceri Oldreive ◽

Michael F. Clay ◽

...

Keyword(s):

Autoimmune Disease ◽

Apoptotic Cell ◽

Apoptotic Cells ◽

Autoantibody Production ◽

Apoptotic Cell Clearance ◽

Cell Clearance ◽

Surface Receptor ◽

Anti Inflammatory

Interaction of macrophages with apoptotic cells involves multiple steps including recognition, tethering, phagocytosis, and anti-inflammatory macrophage responses. Defective apoptotic cell clearance is associated with pathogenesis of autoimmune disease. CD14 is a surface receptor that functions in vitro in the removal of apoptotic cells by human and murine macrophages, but its mechanism of action has not been defined. Here, we demonstrate that CD14 functions as a macrophage tethering receptor for apoptotic cells. Significantly, CD14−/− macrophages in vivo are defective in clearing apoptotic cells in multiple tissues, suggesting a broad role for CD14 in the clearance process. However, the resultant persistence of apoptotic cells does not lead to inflammation or increased autoantibody production, most likely because, as we show, CD14−/− macrophages retain the ability to generate anti-inflammatory signals in response to apoptotic cells. We conclude that CD14 plays a broad tethering role in apoptotic cell clearance in vivo and that apoptotic cells can persist in the absence of proinflammatory consequences.

Download Full-text

Conserved and Distinct Elements of Phagocytosis in Human and C. elegans

International Journal of Molecular Sciences ◽

10.3390/ijms22168934 ◽

2021 ◽

Vol 22 (16) ◽

pp. 8934

Author(s):

Szilvia Lukácsi ◽

Zsolt Farkas ◽

Éva Saskői ◽

Zsuzsa Bajtay ◽

Krisztina Takács-Vellai

Keyword(s):

Apoptotic Cell ◽

Host Cells ◽

Cellular Damage ◽

Phagocytic Cells ◽

C Elegans ◽

Apoptotic Cell Clearance ◽

Vital Functions ◽

Cell Clearance ◽

Infected Cells ◽

Dying Cells

Endocytosis provides the cellular nutrition and homeostasis of organisms, but pathogens often take advantage of this entry point to infect host cells. This is counteracted by phagocytosis that plays a key role in the protection against invading microbes both during the initial engulfment of pathogens and in the clearance of infected cells. Phagocytic cells balance two vital functions: preventing the accumulation of cell corpses to avoid pathological inflammation and autoimmunity, whilst maintaining host defence. In this review, we compare elements of phagocytosis in mammals and the nematode Caenorhabditis elegans. Initial recognition of infection requires different mechanisms. In mammals, pattern recognition receptors bind pathogens directly, whereas activation of the innate immune response in the nematode rather relies on the detection of cellular damage. In contrast, molecules involved in efferocytosis—the engulfment and elimination of dying cells and cell debris—are highly conserved between the two species. Therefore, C. elegans is a powerful model to research mechanisms of the phagocytic machinery. Finally, we show that both mammalian and worm studies help to understand how the two phagocytic functions are interconnected: emerging data suggest the activation of innate immunity as a consequence of defective apoptotic cell clearance.

Download Full-text

Autophagy genes function sequentially to promote apoptotic cell corpse degradation in the engulfing cell

The Journal of Cell Biology ◽

10.1083/jcb.201111053 ◽

2012 ◽

Vol 197 (1) ◽

pp. 27-35 ◽

Cited By ~ 55

Author(s):

Wei Li ◽

Wei Zou ◽

Yihong Yang ◽

Yongping Chai ◽

Baohui Chen ◽

...

Keyword(s):

Autoimmune Disease ◽

Live Cell Imaging ◽

Cell Imaging ◽

Apoptotic Cell ◽

Imaging Techniques ◽

Time Lapse ◽

Apoptotic Cell Clearance ◽

Cell Clearance ◽

Fundamental Process ◽

Cell Corpse

Apoptotic cell degradation is a fundamental process for organism development, and impaired clearance causes inflammatory or autoimmune disease. Although autophagy genes were reported to be essential for exposing the engulfment signal on apoptotic cells, their roles in phagocytes for apoptotic cell removal are not well understood. In this paper, we develop live-cell imaging techniques to study apoptotic cell clearance in the Caenorhabditis elegans Q neuroblast lineage. We show that the autophagy proteins LGG-1/LC3, ATG-18, and EPG-5 were sequentially recruited to internalized apoptotic Q cells in the phagocyte. In atg-18 or epg-5 mutants, apoptotic Q cells were internalized but not properly degraded; this phenotype was fully rescued by the expression of autophagy genes in the phagocyte. Time-lapse analysis of autophagy mutants revealed that recruitment of the small guanosine triphosphatases RAB-5 and RAB-7 to the phagosome and the formation of phagolysosome were all significantly delayed. Thus, autophagy genes act within the phagocyte to promote apoptotic cell degradation.

Download Full-text