Legionella para-effectors target chromatin and promote bacterial replication

The role of HDAC6 in enhancing macrophage autophagy via the autophagolysosomal pathway to alleviate legionella pneumophila-induced pneumonia

Legionella pneumophila (L. pneumophila) is a prevalent pathogenic bacterium responsible for significant global health concerns. Nonetheless, the precise pathogenic mechanisms of L. pneumophila have still remained elusive. Autophagy, a direct cellular response to L. pneumophila infection and other pathogens, involves the recognition and degradation of these invaders in lysosomes. Histone deacetylase 6 (HDAC6), a distinctive member of the histone deacetylase family, plays a multifaceted role in autophagy regulation. This study aimed to investigate the role of HDAC6 in macrophage autophagy via the autophagolysosomal pathway, leading to alleviate L. pneumophila-induced pneumonia. The results revealed a substantial upregulation of HDAC6 expression level in murine lung tissues infected by L. pneumophila. Notably, mice lacking HDAC6 exhibited a protective response against L. pneumophila-induced pulmonary tissue inflammation, which was characterized by the reduced bacterial load and diminished release of pro-inflammatory cytokines. Transcriptomic analysis has shed light on the regulatory role of HDAC6 in L. pneumophila infection in mice, particularly through the autophagy pathway of macrophages. Validation using L. pneumophila-induced macrophages from mice with HDAC6 gene knockout demonstrated a decrease in cellular bacterial load, activation of the autophagolysosomal pathway, and enhancement of cellular autophagic flux. In summary, the findings indicated that HDAC6 knockout could lead to the upregulation of p-ULK1 expression level, promoting the autophagy-lysosomal pathway, increasing autophagic flux, and ultimately strengthening the bactericidal capacity of macrophages. This contributes to the alleviation of L. pneumophila-induced pneumonia.

Host-bacteria interactions: ecological and evolutionary insights from ancient, professional endosymbionts

Interactions between eukaryotic hosts and their bacterial symbionts drive key ecological and evolutionary processes, from regulating ecosystems to the evolution of complex molecular machines and processes. Over time, endosymbionts generally evolve reduced genomes, and their relationship with their host tends to stabilize. However, host-bacteria relationships may be heavily influenced by environmental changes. Here, we review these effects on one of the most ancient and diverse endosymbiotic groups, formed by-among others-Legionellales, Francisellaceae, and Piscirickettsiaceae. This group is referred to as Deep-branching Intracellular Gammaproteobacteria (DIG), whose last common ancestor presumably emerged about 2 Ga ago. We show that DIGs are globally distributed, but generally at very low abundance, and are mainly identified in aquatic biomes. Most DIGs harbour a type IVB secretion system, critical for host-adaptation, but its structure and composition vary. Finally, we review the different types of microbial interactions that can occur in diverse environments, with direct or indirect effects on DIG populations. The increased use of omics technologies on environmental samples will allow a better understanding of host-bacterial interactions and help unravel the definition of DIGs as a group from an ecological, molecular, and evolutionary perspective.

Cross-family small GTPase ubiquitination by the intracellular pathogen Legionella pneumophila

The intracellular bacterial pathogen Legionella pneumophila (L.p.) manipulates eukaryotic host ubiquitination machinery to form its replicative vacuole. While nearly 10% of L.p.'s ∼330 secreted effector proteins are ubiquitin ligases or deubiquitinases, a comprehensive measure of temporally resolved changes in the endogenous host ubiquitinome during infection has not been undertaken. To elucidate how L.p. hijacks host cell ubiquitin signaling, we generated a proteome-wide analysis of changes in protein ubiquitination during infection. We discover that L.p. infection increases ubiquitination of host regulators of subcellular trafficking and membrane dynamics, most notably ∼40% of mammalian Ras superfamily small GTPases. We determine that these small GTPases undergo nondegradative ubiquitination at the Legionella-containing vacuole (LCV) membrane. Finally, we find that the bacterial effectors SidC/SdcA play a central role in cross-family small GTPase ubiquitination, and that these effectors function upstream of SidE family ligases in the polyubiquitination and retention of GTPases in the LCV membrane. This work highlights the extensive reconfiguration of host ubiquitin signaling by bacterial effectors during infection and establishes simultaneous ubiquitination of small GTPases across the Ras superfamily as a novel consequence of L.p. infection. Our findings position L.p. as a tool to better understand how small GTPases can be regulated by ubiquitination in uninfected contexts.

Cross-family small GTPase ubiquitination by the intracellular pathogen Legionella pneumophila

The intracellular bacterial pathogen Legionella pneumophila (L.p.) manipulates eukaryotic host ubiquitination machinery to form its replicative vacuole. While nearly 10% of L.p.'s arsenal of ~330 secreted effector proteins have been biochemically characterized as ubiquitin ligases or deubiquitinases, a comprehensive measure of temporally resolved changes in the endogenous host ubiquitinome during infection has not been undertaken. To elucidate how L.p hijacks ubiquitin signaling within the host cell, we undertook a proteome-wide analysis of changes in protein ubiquitination during infection. We discover that L.p. infection results in increased ubiquitination of host proteins regulating subcellular trafficking and membrane dynamics, most notably 63 of ~160 mammalian Ras superfamily small GTPases. We determine that these small GTPases predominantly undergo non-degradative monoubiquitination, and link ubiquitination to recruitment to the Legionella-containing vacuole membrane. Finally, we find that the bacterial effectors SidC/SdcA play a central, but likely indirect, role in cross-family small GTPase ubiquitination. This work highlights the extensive reconfiguration of host ubiquitin signaling by bacterial effectors during infection and establishes simultaneous ubiquitination of small GTPases across the Ras superfamily as a novel consequence of L.p. infection. This work positions L.p. as a tool to better understand how small GTPases can be regulated by ubiquitination in uninfected contexts.