Icm/Dot-dependent inhibition of phagocyte migration byLegionellais antagonized by a translocated Ran GTPase activator

Abstract

SummaryThe environmental bacterium Legionella pneumophila causes a severe pneumonia termed Legionnaires' disease. L. pneumophila employs a conserved mechanism to replicate within a specific vacuole in macrophages or protozoa such as the social soil amoeba Dictyostelium discoideum. Pathogen-host interactions depend on the

Beyond Rab GTPases: Legionella activates the small GTPase Ran to promote microtubule polymerization, pathogen vacuole motility, and infection

“…Realtime single-cell tracking of L. pneumophila-infected phagocytes revealed that the velocity and directionality of the cells were decreased, and cell motility as well as microtubule dynamics were impaired. 71 The above results are in agreement with the notion that LegG1 stimulates cell migration by antagonizing (unknown) Icm/Dot-translocated effectors inhibiting cell migration. L. pneumophila might benefit from the LegG1-dependent promotion of cell migration by counteracting Icm/Dot substrates, which destabilize microtubules and thus damage a number of essential cellular pathways such as phagocytosis, vesicle trafficking, cytokinesis and migration.…”

“…52 Using real-time confocal laser scanning microscopy, we analyzed the dynamics of LCV transport along microtubules in D. discoideum producing either calnexin-GFP 66 or GFP-a-tubulin. 71 Under these conditions, LCVs harboring wild-type L. pneumophila were very motile and rapidly moved along microtubules. In contrast, LCVs harboring DlegG1 mutant bacteria were stalled, and the phenotype was complemented by plasmid-encoded LegG1.…”

“…71 In under agarose assays, L. pneumophila inhibited in a dose-and T4SS-dependent manner the migration of D. discoideum amoebae toward folate, of murine RAW 264.7 macrophages toward the cytokines CCL5 and TNFa, or of primary human polymorphonuclear neutrophils (PMN) toward the peptide fMLP. L. pneumophila lacking legG1 hyper-inhibited the migration of the phagocytes, and the phenotype was reverted to an extent observed for mutant bacteria lacking a functional Icm/Dot T4SS by providing legG1 in trans.…”

The Legionella longbeachae Icm/Dot Substrate SidC Selectively Binds Phosphatidylinositol 4-Phosphate with Nanomolar Affinity and Promotes Pathogen Vacuole-Endoplasmic Reticulum Interactions

“…For L. pneumophila, more than 300 Icm/Dot substrates are known to date (21)(22)(23). A number of these effectors have been mechanistically characterized and subvert components of the endocytic, retrograde, or secretory vesicle-trafficking machinery, including small GTPases of the Arf and Rab (21,(24)(25)(26), as well as the Ran (27,28) families; the vacuolar H ϩ -ATPase (29); the autophagy machinery (30); the retromer complex (31); and phosphoinositide (PI) lipids (32,33).…”

Creating a customized intracellular niche: subversion of host cell signaling byLegionellatype IV secretion system effectors

“…LegG1 has sequence homology to the Ran GEF RCC1. Although purified LegG1 does not have direct Ran GEF activity in vitro, it induces Ran activation in infection, thus promoting LCV recruitment of the RanGTP-binding protein RanBP1, stabilization of microtubules, LCV motility, and phagocyte migration (Rothmeier et al 2013;Simon et al 2014). The advantages of keeping the LCV mobile are not fully understood; however, it might enable the LCV to leave the default "track" of phagosomes, which would otherwise efficiently ensure the encounter and fusion with endocytic vesicles.…”