Regulation of Phagosome Maturation by Signals from Toll-Like Receptors

Blander, J. Magarian; Medzhitov, Ruslan

doi:10.1126/science.1096158

Cited by 889 publications

(828 citation statements)

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“…Apoptotic cells are not trafficked into MHC class II-containing phagosomes 32 , and the inability to properly degrade apoptotic cells has also been linked to autoimmune disease. This opens the possibility that blocking corpse degradation via the ÃstandardÃ pathway results in inappropriate presentation of antigens derived from apoptotic cells 4 .…”

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

“…How these candidates coordinately function in phagosome maturation and processing remains to be determined. It is also unknown to what degree proteins identified in these screens would overlap with those containing apoptotic cells, which engage different signaling pathways for internalization and can produce different immunological outcomes 32,33 .Here, we use C. elegans as a model system to identify a novel pathway for the maturation of internalized apoptotic cell corpses. First, we show that the GTPases RAB-5 and RAB-7 are required for efficient corpse degradation following internalization, and that RAB-5 and RAB-7 are recruited to phagosomes containing apoptotic cells in a temporally distinct manner.…”

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A pathway for phagosome maturation during engulfment of apoptotic cells

et al. 2008

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The efficient removal of apoptotic cells is critical for the physiological well-being of the organism 1 Ã 4 ; defects in corpse removal have been linked to autoimmune disease 4,5 . While several players regulating the early steps of corpse recognition and internalization have been characterized 6 , the molecules and mechanisms relevant to the subsequent processing of the internalized corpses are poorly understood. Here, we identify a novel pathway for the processing of internalized apoptotic cells in C. elegans and in mammals. First, we show that RAB-5 and RAB-7 are sequentially recruited to phagosomes containing apoptotic corpses as they mature within phagocytes, and that both proteins are required for efficient corpse clearance. We then used targeted genetic screens to identify players regulating the recruitment and/or retention of Rab5 and Rab7 to phagosomes. Seven members of the HOPS complex (a Rab7 activator/effector complex) were required for Rab7 localization or retention on phagosomes. In an effort to identify factors that regulate Rab5 recruitment, we undertook an unbiased reverse genetic screen and identified 61 genes potentially required for corpse removal. In-depth analysis of two candidate genes, vps-34 and dyn-1/ dynamin, showed accumulation of internalized, but undegraded corpses within abnormal phagosomes that are defective in RAB-5 recruitment. Using a series of genetic and biochemical experiments in worms and mammalian cells, we ordered these proteins in a pathway, with DYN-1 functioning upstream of VPS-34, in the recruitment/retention of Rab5 to the nascent phagosome. Further, we identified a novel biochemical complex containing Vps34, dynamin and Rab5 GDP , providing a mechanism for Rab5 recruitment to the nascent phagosome.Removal of apoptotic cells (engulfment) is an essential process that occurs throughout life in multi-cellular animals as part of development, homeostasis, and wound healing1Ã4 , 7 , 8. Engulfment) can be broken down into a series of steps, comprising recognition, internalization, phagosome maturation and finally lysosomal degradation of the apoptotic cell by the phagocyte. In mammals, impaired clearance of apoptotic cell corpses can lead to exposure of autoantigens, resulting in onset of autoimmune diseases, such as systemic lupus erythematosus 4,9,10 . Modulation of the engulfment process is therefore a potential therapeutic target in these conditions. One of the fundamental challenges in understanding how defects in engulfment of apoptotic cells translates into diseased states is the identification of critical players involved in corpse removal and how these proteins orchestrate the different stages of engulfment.The nematode C. elegans represents a powerful genetic tool for the study of programmed cell death 11,12 . Large numbers of cells are induced to die during two periods in the life of a worm: during embryonic and larval morphogenesis and during germ cell development 13 . Genetic studies have identified two evolutionarily conserved signaling pathways invol...

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

mentioning

confidence: 99%

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A pathway for phagosome maturation during engulfment of apoptotic cells

et al. 2008

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“…Impaired phagosome maturation in the absence of MyD88 or TLR4/TLR2 has been shown to impair phagocytosis of bacteria e.g. Escherichia coli, Staphylococcus aureus, and Salmonella typhimurium due to impaired phagosome maturation [6]. Therefore, the bovine mammary epithelial cells possess the capability of dealing with excess bacterial load by up-regulating the necessary mediators of apoptosis.…”

Section: Discussionmentioning

confidence: 99%

Bacterial lipopolysaccharide induces increased expression of toll-like receptor (TLR) 4 and downstream TLR signaling molecules in bovine mammary epithelial cells

et al. 2007

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-Bovine mammary epithelial cells contribute to the innate immune response to intramammary infections by recognizing pathogens through specialized pattern recognition receptors. Toll-like receptor 4 (TLR4) is one such receptor that binds and is activated by lipopolysaccharide (LPS), a component of the outer envelope of Gram-negative bacteria. In this study, MAC-T cells (a bovine mammary epithelial cell line) were incubated in the presence or absence of increasing concentrations of LPS for 24 h. Expression of TLR2 and TLR4 were analyzed at both mRNA and protein levels by quantitative real-time PCR (qPCR) and flow cytometry, respectively. The mRNA of both receptors were up-regulated by all concentrations of LPS used (P < 0.01). Similarly, flow cytometry with specific antibodies against TLR2 and TLR4 detected increased surface expression of these proteins. Furthermore, expression of downstream TLR4 signaling molecules was examined by qPCR following varying exposure times to 1 μg/mL of LPS. Results demonstrate that the required adaptor molecules and transcription factors were up-regulated in a time-dependent manner. Both the MyD88 dependent and independent pathways in TLR4 signaling were activated in MAC-T cells. Expression of TOLLIP increased in response to LPS as did the pro-apoptotic protease, CASP8. These results suggest that the bovine mammary epithelium possesses the necessary immune repertoires required to achieve a robust defense against E. coli. The current findings, coupled with previous findings that S. aureus ligands induce up-regulation of TLR4, may indicate a positive adaptation by mammary epithelial cells to effectively respond to different types of mastitis pathogens.lipopolysaccharide / TLR4 and TLR2 / signal transduction / bovine mammary epithelial cells / mastitis

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“…Signaling through TLRs has been shown to activate macrophages including enhanced bacterial phagocytosis and phagosome maturation, nucleus translocation of NF-κB and proinflammatory cytokine production [28]. To determine the role of TLR4 in Brucella invasion, uptake of smooth and rough B. abortus was evaluated in BMDMs from C3H/HeJ and C3H/HeOuJ mice.…”

Section: Tlr4 Is Important For Smooth Brucella Uptake In Murine Bmdmmentioning

confidence: 99%

Evidence of Brucella abortus OPS dictating uptake and restricting NF-κB activation in murine macrophages

Pei

Turse

Ficht

2008

Microbes and Infection

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Smooth Brucella abortus S2308 is virulent while rough derivatives are attenuated. Intracellular killing is often blamed for these differences. In the studies described, uptake kinetics and interaction of S2308 and S2308 manBA::Tn5 (CA180) rough mutants with macrophages were investigated. The results revealed that smooth B. abortus was rapidly internalized, achieving a maximum level in less than 5 minutes without additional uptake over the next 30 minutes. In contrast, continued uptake of the rough mutant was observed and only achieves a maximum level after 30 minutes. The results were confirmed by the differences in F-actin polymerization, lipid raft staining, early endosome colocalization and electron microscopic observations after smooth and rough Brucella infection. We also demonstrated for the first time that uptake of S2308, but not rough mutant CA180 was PI3-kinase and toll-like receptor 4 (TLR4) dependent. Differences in uptake were associated with differences in macrophage activation with regard to NF-κB translocation and cytokine production. These results provide evidence that the presence of B. abortus OPS dictates the interactions between Brucella and specific cell surface receptors minimizing macrophage activation and enhancing Brucella survival and/or persistence.

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Regulation of Phagosome Maturation by Signals from Toll-Like Receptors

Cited by 889 publications

References 21 publications

A pathway for phagosome maturation during engulfment of apoptotic cells

A pathway for phagosome maturation during engulfment of apoptotic cells

Bacterial lipopolysaccharide induces increased expression of toll-like receptor (TLR) 4 and downstream TLR signaling molecules in bovine mammary epithelial cells

Evidence of Brucella abortus OPS dictating uptake and restricting NF-κB activation in murine macrophages

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