title: Preventing bacterial DNA release and absent in melanoma 2 inflammasome activation by a Legionella effector functioning in membrane trafficking.
abstract: Legionella pneumophila, the causative agent of Legionnaires' pneumonia, resides in a distinct vacuole structure called Legionella-containing vacuole (LCV). The LCV resists fusion with the lysosome and permits efficient bacterial replication in host macrophages, which requires a Dot/Icm type IVB secretion system. Dot/Icm-translocated effector SdhA is critical for L. pneumophila intracellular growth and functions to prevent host cell death. Here, we show that the absence of SdhA resulted in elevated caspase-1 activation and IL-1β secretion as well as macrophage pyroptosis during Legionella infection. These inflammasome activation phenotypes were independent of the established flagellin-NAIP5-NLRC4 axis, but relied on the DNA-sensing AIM2 inflammasome. We further demonstrate that Legionella DNA was released into macrophage cytosol, and this effect was significantly exaggerated by the absence of SdhA. SdhA bears a functional Golgi-targeting GRIP domain that is required for preventing AIM2 inflammasome activation. Ectopically expressed SdhA formed a unique ring-shape membrane structure, further indicating a role in membrane trafficking and maintaining LCV membrane integrity. Our data together suggest a possible link, mediated by the function of SdhA, between LCV trafficking/maturation and suppression of host innate immune detection.
authors.affiliation: National Institute of Biological Sciences, Beijing 102206,  China.
authors.forename: Jianning
authors.initials: J
authors.lastname: Ge
authors.forename: Yi-Nan
authors.initials: YN
authors.lastname: Gong
authors.forename: Ying
authors.initials: Y
authors.lastname: Xu
authors.forename: Feng
authors.initials: F
authors.lastname: Shao
mesh_terms: D000818:Animals; D017209:Apoptosis; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D001692:Biological Transport; D020170:Caspase 1 / Q000378:metabolism; D002460:Cell Line; D004269:DNA, Bacterial / Q000235:genetics / Q000378:metabolism*; D004268:DNA-Binding Proteins; D005420:Flavoproteins / Q000235:genetics / Q000378:metabolism*; D057809:HEK293 Cells; D006367:HeLa Cells; D054884:Host-Pathogen Interactions; D006801:Humans; D015151:Immunoblotting; D058847:Inflammasomes / Q000378:metabolism*; D007425:Intracellular Membranes / Q000378:metabolism; D016952:Legionella pneumophila / Q000235:genetics / Q000378:metabolism* / Q000502:physiology; D008247:Lysosomes / Q000378:metabolism / Q000382:microbiology; D008264:Macrophages / Q000378:metabolism / Q000382:microbiology; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D008856:Microscopy, Fluorescence; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism*; D034622:RNA Interference; D020298:U937 Cells; D014617:Vacuoles / Q000378:metabolism / Q000382:microbiology
chemical_list: C540422:Aim2 protein, mouse; D001426:Bacterial Proteins; D004269:DNA, Bacterial; D004268:DNA-Binding Proteins; D005420:Flavoproteins; D058847:Inflammasomes; D009687:Nuclear Proteins; C084271:SdhA protein, Bacteria; D020170:Caspase 1