Combinational SNARE Proteins VAMP8 and Vti1b Mediate Fusion of Antimicrobial and Canonical Autophagosomes with Lysosomes

Department of Oral Frontier Biology, Osaka University Graduate School of Dentistry, Suita-Osaka 565-0871, Japan.
Molecular biology of the cell (Impact Factor: 4.47). 03/2010; 21(6):1001-10. DOI: 10.1091/mbc.E09-08-0693
Source: PubMed


Autophagy plays a crucial role in host defense, termed antimicrobial autophagy (xenophagy), as it functions to degrade intracellular foreign microbial invaders such as group A Streptococcus (GAS). Xenophagosomes undergo a stepwise maturation process consisting of a fusion event with lysosomes, after which the cargoes are degraded. However, the molecular mechanism underlying xenophagosome/lysosome fusion remains unclear. We examined the involvement of endocytic soluble N-ethylmaleimide-sensitive factor attachment protein receptors (SNAREs) in xenophagosome/lysosome fusion. Confocal microscopic analysis showed that SNAREs, including vesicle-associated membrane protein (VAMP)7, VAMP8, and vesicle transport through interaction with t-SNAREs homologue 1B (Vti1b), colocalized with green fluorescent protein-LC3 in xenophagosomes. Knockdown of Vti1b and VAMP8 with small interfering RNAs disturbed the colocalization of LC3 with lysosomal membrane protein (LAMP)1. The invasive efficiency of GAS into cells was not altered by knockdown of VAMP8 or Vti1b, whereas cellular bactericidal efficiency was significantly diminished, indicating that antimicrobial autophagy was functionally impaired. Knockdown of Vti1b and VAMP8 also disturbed colocalization of LC3 with LAMP1 in canonical autophagy, in which LC3-II proteins were negligibly degraded. In contrast, knockdown of Syntaxin 7 and Syntaxin 8 showed little effect on the autophagic fusion event. These findings strongly suggest that the combinational SNARE proteins VAMP8 and Vti1b mediate the fusion of antimicrobial and canonical autophagosomes with lysosomes, an essential event for autophagic degradation.

Download full-text


Available from: Atsuo Amano,
  • Source
    • "The autophagosomal membranes assemble around cargo, encapsulating it in a vesicle that subsequently fuses with a lysosome, generating an auto-lysosome. A number of SNARE proteins , including VAMP8 and Vti1B, are believed to be involved in regulating heterotypic fusion between autophagosomes and the lysosomal compartment [38]. The contents are then degraded by lysosomal enzymes and the lysosomal permeases release the breakdown products into the cytosol, where they are available for synthetic and metabolic pathways [4] "
    [Show abstract] [Hide abstract]
    ABSTRACT: In its classical form, autophagy is an essential, homeostatic process by which cytoplasmic components are degraded in a double-membrane-bound autophagosome in response to starvation. Paradoxically, although autophagy is primarily a protective process for the cell, it can also play a role in cell death. The roles of autophagy bridge both the innate and adaptive immune systems and autophagic dysfunction is associated with inflammation, infection, neurodegeneration and cancer. In this review, we discuss the contribution of autophagy to inflammatory, infectious and neurodegenerative diseases, as well as cancer.
    International immunopharmacology 11/2013; 18(1). DOI:10.1016/j.intimp.2013.11.001 · 2.47 Impact Factor
  • Source
    • "This is distinct from the autophagy initiation step: UVRAG-Beclin1- mediated autophagosome formation (Liang et al., 2008). Recent studies have identified the SNARE machinery, including vesicle-associated membrane protein (VAMP) 3, VAMP7, and VAMP9, as key molecules involved in the fusion step (Fader et al., 2009; Furuta et al., 2010). Moreover, it was recently shown that the autophagosomal SNARE syntaxin 17, which is found in the outer membrane of completed autophagosomes, is required for autophagosome-lysosome fusion via an interaction with SNAP29 and another SNARE: VAMP8 (Itakura et al., 2012). "
    [Show abstract] [Hide abstract]
    ABSTRACT: A variety of cellular stresses activate the autophagy pathway, which is fundamentally important in protection against injurious stimuli. Defects in the autophagy process are associated with a variety of human diseases, including inflammatory and metabolic diseases. The inflammasomes are emerging as key signaling platforms directing the maturation and secretion of interleukin-1 family cytokines in response to pathogenic and sterile stimuli. Recent studies have identified the critical role of inflammasome activation in host defense and inflammation. Delineation of the relationship between autophagy and inflammasome activation is now being greatly facilitated by the use of mice models of autophagy gene deficiency and clinical studies. We surveyed the recent research regarding the contribution of autophagy to the control of inflammation, in particular the association between autophagy and inflammasomes. Understanding the mechanisms by which autophagy balances inflammation might facilitate the development of autophagy-based therapeutic modalities for infectious and inflammatory diseases.
    Moleculer Cells 11/2013; 36(5). DOI:10.1007/s10059-013-0298-0 · 2.09 Impact Factor
  • Source
    • "Vti1b were all suggested to be involved in autophagosomal fusion events (Fader et al., 2009; Furuta et al., 2010). The accumulation of both autophagosomes and autolysosomes in Vti1b knockout mice indicates that this gene product is likely to function in later steps of autophagy (Atlashkin et al., 2003). "
    [Show abstract] [Hide abstract]
    ABSTRACT: During autophagy, phagophores capture portions of cytoplasm and form double-membrane autophagosomes to deliver cargo for lysosomal degradation. How autophagosomes gain competence to fuse with late endosomes and lysosomes is not known. In this paper, we show that Syntaxin17 is recruited to the outer membrane of autophagosomes to mediate fusion through its interactions with ubisnap (SNAP-29) and VAMP7 in Drosophila melanogaster. Loss of these genes results in accumulation of autophagosomes and a block of autolysosomal degradation during basal, starvation-induced, and developmental autophagy. Viable Syntaxin17 mutant adults show large-scale accumulation of autophagosomes in neurons, severe locomotion defects, and premature death. These mutant phenotypes cannot be rescued by neuron-specific inhibition of caspases, suggesting that caspase activation and cell death do not play a major role in brain dysfunction. Our findings reveal the molecular mechanism underlying autophagosomal fusion events and show that lysosomal degradation and recycling of sequestered autophagosome content is crucial to maintain proper functioning of the nervous system.
    The Journal of Cell Biology 05/2013; 201(4):531-9. DOI:10.1083/jcb.201211160 · 9.83 Impact Factor
Show more