The Legionella Kinase LegK2 Targets the ARP2/3 Complex To Inhibit Actin Nucleation on Phagosomes and Allow Bacterial Evasion of the Late Endocytic Pathway

Abstract

Legionella pneumophila, the etiological agent of legionellosis, replicates within phagocytic cells. Crucial to biogenesis of the replicative vacuole is the Dot/Icm type 4 secretion system, which translocates a large number of effectors into the host cell cytosol. Among them is LegK2, a protein kinase that plays a key role in Legionella infection. Here, we identified the actin nucleator ARP2/3 complex as a target of LegK2. LegK2 phosphorylates the ARPC1B and ARP3 subunits of the ARP2/3 complex. LegK2-dependent ARP2/3 phosphorylation triggers global actin cytoskeleton remodeling in cells, and it impairs actin tail formation by Listeria monocytogenes, a well-known ARP2/3-dependent process. During infection, LegK2 is addressed to the Legionella-containing vacuole surface and inhibits actin polymerization on the phagosome, as revealed by legK2 gene inactivation. Consequently, LegK2 prevents late endosome/lysosome association with the phagosome and finally contributes to remodeling of the bacterium-containing phagosome into a replicative niche. The inhibition of actin polymerization by LegK2 and its effect on endosome trafficking are ARP2/3 dependent since it can be phenocopied by a specific chemical inhibitor of the ARP2/3 complex. Thus, LegK2-ARP2/3 interplay highlights an original mechanism of bacterial virulence with an unexpected role in local actin remodeling that allows bacteria to control vesicle trafficking in order to escape host defenses.

Right on Q: Genetics begin to Unravel Coxiella Burnetii host cell Interactions

“…Apoptosis and inflammasome inhibition are clearly strategies to sustain the macrophage host for Coxiella's lengthy infectious cycle, with subversion of several vesicular trafficking pathways providing the CCV membrane and nutrients. However, the complex effector pool of Coxiella undoubtedly modulates additional eukaryotic systems for pathogen benefit such as the cytoskeleton [146], ubiquitination [147] and nuclear processes via the activity of an emerging class of effectors known as nucleomodulins [148,149]. Elucidating signal transduction events that trigger effector translocation, the temporal reliance on effector groups during infection and whether effector-effector regulation occurs [150,151], are of much interest to the field.…”

The Legionella pneumophila effector Ceg4 is a phosphotyrosine phosphatase that attenuates activation of eukaryotic MAPK pathways

“…Studies into the function of bacterial effectors suggested that these pathogenic factors demonstrate unparalleled abilities to manipulate a wide spectrum of host cell's processes including facilitating alterations in cytoskeletal rearrangement (17,18), vesicular trafficking (19,20), signal transduction (21,22) and transcription regulation (23,24). To achieve these effects, effectors are often involved in posttranslational modification (PTM) of specific host proteins.…”

Comparative Genomics of the Zoonotic Pathogen Ehrlichia chaffeensis Reveals Candidate Type IV Effectors and Putative Host Cell Targets

“…ATM/MKA14 regulatory networks have also been shown to regulate cytoplasmic targets, resulting in extensive cytoskeletal rearrangements (Pines et al, 2011). Acting on these cascades could favor the maturation of Ehrlichia -containing vacuoles, as shown for L. pneumophila which controls vesicle trafficking to escape host defenses and counteract the endocytic pathway (Michard et al, 2015). Finally, some candidate T4Es could affect metabolic proteins, like SYVN1, which acts as an E3 ubiquitin-protein ligase.…”