Biology subjects

Bennison, D. J.

Publications and source records attributed to Bennison, D. J..

5 recordsLinked to original sources

bioRxiv2025

GBP1 recruitment to actin-rich pedestals induced by extracellular Gram-negative bacteria promotes pyroptosis.

The IFN{gamma}-induced GTPase guanylate binding protein 1 (GBP1) binds to lipopolysaccharide (LPS) on cytosolic Gram-negative bacteria and promotes pyroptosis via the recruitment and activation of caspase-4 on the bacterial outer membrane. Enteropathogenic and enterohaemorrhagic Escherichia coli (EPEC and EHEC, respectively) are extracellular pathogens that also induce LPS-and caspase-4-dependent pyroptosis. However, whether GBP1 is involved in this process remains unknown. EPEC and EHEC adhere intimately to intestinal epithelial cells via avid interactions between the bacterial adhesin Intimin and Tir (Translocated intimin receptor), a type 3 secretion system effector protein. Intimin-mediated clustering of Tir triggers actin polymerisation, leading to pedestal-like structures at bacterial attachment sites. Here we show that GBP1 is recruited to actin-rich pedestals in human cells infected with EPEC and EHEC in vitro and mouse colonocytes infected with the EPEC-like murine pathogen Citrobacter rodentium in vivo. GBP1-dependent caspase-4 trafficking to these sites leads to pyroptosis and IL-18 release. GBP1 mutants defective in LPS coatomer formation also localised to EPEC pedestals, pointing to LPS-independent mobilisation of GBP1 by actin polymerisation induced by extracellular A/E pathogens. To further dissect the underlying mechanism, we engineered a chimeric receptor (Fc{gamma}R-Tir) by combining the intracellular signalling domain of Tir and the extracellular ligand-binding domain of the Fc{gamma} receptor. Clustering of Fc{gamma}R-Tir with IgG-coated beads produced sterile actin-rich pedestals that were sufficient to recruit GBP1 independently of bacteria. Our findings reveal that cytosolic GBP1 is mobilised to sites of pathogen-induced actin remodelling independently of LPS. We establish that GBP1 not only operates as a pattern-recognition receptor but also orchestrates effector-triggered immunity against pathogens that hijack the actin cytoskeleton. 175-word AbstractThe IFN{gamma}-induced GTPase guanylate binding protein 1 (GBP1) binds to lipopolysaccharide (LPS) on cytosolic Gram-negative bacteria and promotes pyroptosis via the recruitment and activation of caspase-4 on the bacterial outer membrane. Enteropathogenic and enterohaemorrhagic Escherichia coli (EPEC and EHEC, respectively) are extracellular pathogens that adhere to host cells and stimulate dense actin polymerisation underneath their attachment sites, generating structures called actin-rich pedestals. Here we show that GBP1 traffics to actin-rich pedestals in human cells infected with EPEC and EHEC in vitro and mouse colonocytes infected with the EPEC-like murine pathogen Citrobacter rodentium in vivo. GBP1 promotes caspase-4 recruitment to actin-rich pedestals, leading to pyroptosis and IL-18 release. GBP1 mutants defective in LPS coatomer formation also localised to EPEC pedestals. Our novel assay that mimics pathogenic effector activity revealed GBP1 recruitment to sterile actin polymerisation sites. We conclude that cytosolic GBP1 is mobilised to sites of pathogen-induced actin remodelling independently of LPS. Our study establishes that GBP1 not only operates as a pattern-recognition receptor but also orchestrates effector-triggered immunity against pathogens that hijack the actin cytoskeleton.

immunology↗

bioRxiv2023

Aminoglycoside heteroresistance in Enterobacter cloacae is driven by the cell envelope stress response.

Enterobacter cloacae is a Gram-negative nosocomial pathogen of the ESKAPE priority group with increasing multi-drug resistance via the acquisition of resistance plasmids. However, E. cloacae can also display phenotypic antimicrobial resistance, such as heteroresistance or persistence. Here we report that E. cloacae ATCC 13047 and six strains isolated from patients with blood infections display heteroresistance or persistence to aminoglycosides. E. cloacae heteroresistance is transient, accompanied with formation of petite colonies and increased MIC against gentamicin and other aminoglycosides used in the clinic, but not other antibiotic classes. To explore the underlying mechanisms, we performed RNA sequencing of heteroresistant bacteria, which revealed global gene-expression changes and a signature of the CpxRA cell envelope stress response. Deletion of the cpxRA two-component system abrogated aminoglycoside heteroresistance and petite colony formation, pointing to its indispensable role in phenotypic resistance. The introduction of a constitutively active allele of cpxA led to high aminoglycoside MICs, consistent with cell envelope stress driving these behaviours in E. cloacae. Cell envelope stress can be caused by environmental cues, including heavy metals. Indeed, bacterial exposure to copper increased gentamicin MIC in the wild type, but not the {Delta}cpxRA mutant. Moreover, copper exposure also elevated the gentamicin MICs of bloodstream isolates, suggesting that CpxRA- and copper-dependent aminoglycoside resistance is broadly conserved in E. cloacae strains. Altogether, we establish that E. cloacae relies on transcriptional reprogramming via the envelope stress response pathway for transient resistance to a major class of frontline antibiotic. ImportanceEnterobacter cloacae is a bacterium that belongs to the ESKAPE priority group and an increasing threat worldwide due its multidrug resistance. E. cloacae can also display phenotypic resistance to antibiotics, leading to treatment failure. We report that sensitive strains of E. cloacae, including six strains isolated from patients with bloodstream infections, show heteroresistance or persistence to aminoglycoside antibiotics. These are important frontline microbicidal drugs used against Gram-negative bacterial infections, therefore understanding how resistance develops in sensitive strains is important. We show that aminoglycoside resistance is driven by the activation of the cell envelope stress response and transcriptional reprogramming via the CpxRA two-component system. Further, heterologous activation of envelope stress via copper, typically a heavy metal with antimicrobial actions, also increased aminoglycoside MICs in all tested strains of E. cloacae. Our study suggests phenotypic aminoglycoside resistance in E. cloacae could be broadly conserved and cautions against the undesirable effects of copper.

microbiology↗

bioRxiv2022

IL-1β turnover by TRIP12 and AREL1 ubiquitin ligases and UBE2L3 limits inflammation

The cytokine interleukin-1{beta} (IL-1{beta}) has pivotal roles in antimicrobial immunity, but also incites inflammatory pathology. Bioactive IL-1{beta} is released following proteolytic maturation of the pro-IL-1{beta} precursor by caspase-1 inflammasomes. UBE2L3/UBCH7, a conserved ubiquitin conjugating enzyme, promotes pro-IL-1{beta} ubiquitylation and proteasomal disposal. However, UBE2L3 actions in vivo and ubiquitin ligases involved in this process are unknown. Here we report that deletion of Ube2l3 in mice markedly reduces pro-IL-1{beta} turnover in macrophages, leading to excessive mature IL-1{beta} production, neutrophilic inflammation and disease symptoms following inflammasome activation. A family-wide siRNA screen identified two ubiquitin ligases, TRIP12 and AREL1, which we show add K27-, K29- and K33- poly-ubiquitin chains on lysine residues in the pro domain and destabilise pro-IL-1{beta}. Mutation of ubiquitylation sites increased pro-IL-1{beta} stability, but did not affect proteolysis by caspase-1. The extent of mature IL-1{beta} production is therefore determined by precursor abundance, and UBE2L3, TRIP12 and AREL1 limit inflammation by shrinking the cellular pool of pro-IL-1{beta}. Our study has uncovered fundamental processes governing IL-1{beta} homeostasis and provided molecular insights that could be exploited to mitigate its adverse actions in disease.

immunology↗

bioRxiv2021

(p)ppGpp inhibits 70S ribosome formation in Staphylococcus aureus by impeding GTPase-ribosome interactions

During nutrient limitation, bacteria produce the alarmones (p)ppGpp as effectors of the stress signalling network termed the stringent response. Screening for (p)ppGpp-binding targets within Staphylococcus aureus identified four ribosome-associated GTPases (RA-GTPases), RsgA, RbgA, Era and HflX, each of which are cofactors in ribosome assembly, where they cycle between the ON (GTP-bound) and OFF (GDP-bound) states. Entry into the OFF-state from the ON-state occurs upon hydrolysis of GTP, with GTPase activity increasing substantially upon ribosome association. When bound to (p)ppGpp, GTPase activity is inhibited, reducing 70S ribosome assembly. Here, we sought to determine how (p)ppGpp impacts RA-GTPase-ribosome interactions by examining the affinity and kinetics of binding between RA-GTPases and ribosomes in various nucleotide-bound states. We show that RA-GTPases preferentially bind to 5'-diphosphate-containing nucleotides GDP and ppGpp over GTP, which is likely exploited as a regulatory mechanism within the cell. Binding to (p)ppGpp reduces stable association of RA-GTPases to ribosomal subunits compared to the GTP-bound state both in vitro and within bacterial cells by inducing the OFF-state conformation. We propose that in this conformation, the G2/switch I loop adopts a conformation incompatible with ribosome association. Altogether, we highlight (p)ppGpp-mediated inhibition of RA-GTPases as a major mechanism of stringent response-mediated growth control.

microbiology↗

bioRxiv2018

Stringent response-mediated control of rRNA processing via the ribosomal assembly GTPase Era

P-loop GTPases are widely conserved across all domains of life. These enzymes act as molecular switches, cycling between inactive GDP-bound, and active GTP-bound states. Our previous work identified the Staphylococcus aureus GTPase Era as a binding target for the stringent response alarmone (p)ppGpp. Here we show that, unlike in Escherichia coli, Era is not essential in S. aureus but is important for 30S ribosomal subunit assembly. We employ bacterial two-hybrid and split luciferase approaches to show that Era interacts with the endonuclease YbeY, a protein of unknown function YbeZ, and the DEAD-box RNA helicase CshA in E. coli and natively in S. aureus. We determine that both Era and CshA are cold shock proteins required for virulence and rRNA processing. Era and CshA also form direct interactions with the (p)ppGpp synthetase RSH, an interaction required for controlling (p)ppGpp levels in response to cold shock. Taken together, we conclude that Era acts as an intermediary protein, directing enzymes involved in rRNA maturation to their site of action, an activity which, under stress, is controlled by the stringent response.

microbiology↗