Rapid Nutritional Remodeling of the Host Cell upon Attachment of Legionella pneumophila

Abstract

Upon entry of Legionella pneumophila into amoebas and macrophages, host-mediated farnesylation of the AnkB effector enables its anchoring to the Legionella-containing vacuole (LCV) membrane. On the LCV, AnkB triggers docking of K 48 -linked polyubiquitinated proteins that are degraded by the host proteasomes to elevate cellular levels of amino acids needed for intracellular proliferation. Interference with AnkB function triggers L. pneumophila to exhibit a starvation response and differentiate into the nonreplicative phase in response to the basal levels of cellular amino acids that are not sufficient to power intracellular proliferation of L. pneumophila. Therefore, we have determined whether the biological function of AnkB is temporally and spatially triggered upon bacterial attachment to the host cell to circumvent a counterproductive bacterial differentiation into the nonreplicative phase upon bacterial entry. Here, we show that upon attachment of L. pneumophila to human monocyte-derived macrophages (hMDMs), the host farnesylation and ubiquitination machineries are recruited by the Dot/Icm system to the plasma membrane exclusively beneath sites of bacterial attachment. Transcription and injection of ankB is triggered by attached extracellular bacteria followed by rapid farnesylation and anchoring of AnkB to the cytosolic side of the plasma membrane beneath bacterial attachment, where K 48 -linked polyubiquitinated proteins are assembled and degraded by the proteasomes, leading to a rapid rise in the cellular levels of amino acids. Our data represent a novel strategy by an intracellular pathogen that triggers rapid nutritional remodeling of the host cell upon attachment to the plasma membrane, and as a result, a gratuitous surplus of cellular amino acids is generated to support proliferation of the incoming pathogen.

Nutrient generation and retrieval from the host cell cytosol by intra-vacuolar Legionella pneumophila

“…On the LCV membrane, AnkB interacts with the host SCF1 ubiquitin ligase (Figure 1) (Bruckert et al, 2014). As a bona fide F-box effector (Ensminger and Isberg, 2010; Lomma et al, 2010; Price and Abu Kwaik, 2010), AnkB triggers decoration of the LCV with Lys 48 -linked polyubiquitinated proteins that are targeted for proteasomal degradation (Figure 1) (Price et al, 2011).…”

Lysine 11 -Linked Polyubiquitination of the AnkB F-Box Effector of Legionella pneumophila

“…Following its translocation, AnkB is anchored to the cytosolic face of the LCV membrane through host-mediated farnesylation (16), where it triggers polyubiquitination of the LCV (14,17). The F-box domain of AnkB interacts directly with the SCF1 (SKP1/CUL1/F-box) E3 ubiquitin ligase complex, which is acquired by the LCV (18). The interaction with the SCF1 complex results in AnkB-mediated decoration of the LCV with lysine 48 -linked polyubiquitinated proteins, which are subjected to host-mediated proteasomal degradation (19).…”

Bacterial Metabolism Shapes the Host–Pathogen Interface

“…AnkB is also injected into the host cell directly after bacterial attachment and localized to the plasma membrane. This allows rapid polyubiquitination and degradation of host proteins and generates a nutrient-rich environment for the establishment of the LCV (111). Not surprisingly, the Legionella AnkB mutant has a severe growth defect for intravacuolar replication in macrophages and has a reduced ability to cause pulmonary disease in mice.…”