Shigella MreB promotes polar IcsA positioning for actin tail formation.

Sina Krokowski,Jeanne Salje,Damián Lobato-Márquez,Serge Mostowy,Sharanjeet Atwal,Arnaud Chastanet,Rut Carballido-López

doi:10.1242/jcs.226217

Abstract

ABSTRACTPathogenic Shigella bacteria are a paradigm to address key issues of cell and infection biology. Polar localisation of the Shigella autotransporter protein IcsA is essential for actin tail formation, which is necessary for the bacterium to travel from cell-to-cell; yet how proteins are targeted to the bacterial cell pole is poorly understood. The bacterial actin homologue MreB has been extensively studied in broth culture using model organisms including Escherichia coli, Bacillus subtilis and Caulobacter crescentus, but has never been visualised in rod-shaped pathogenic bacteria during infection of host cells. Here, using single-cell analysis of intracellular Shigella, we discover that MreB accumulates at the cell pole of bacteria forming actin tails, where it colocalises with IcsA. Pharmacological inhibition of host cell actin polymerisation and genetic deletion of IcsA is used to show, respectively, that localisation of MreB to the cell poles precedes actin tail formation and polar localisation of IcsA. Finally, by exploiting the MreB inhibitors A22 and MP265, we demonstrate that MreB polymerisation can support actin tail formation. We conclude that Shigella MreB promotes polar IcsA positioning for actin tail formation, and suggest that understanding the bacterial cytoskeleton during host–pathogen interactions can inspire development of new therapeutic regimes for infection control.This article has an associated First Person interview with the first author of the paper.

Highlights

Shigella is a Gram-negative enteroinvasive bacterium and important human pathogen leading to ∼164,000 deaths annually (Khalil et al, 2018; Kotloff et al, 2017)
MreB relocalises to the cell pole of intracellular Shigella polymerising actin tails We engineered S. flexneri M90T bearing a plasmid-encoded inducible MreB-GFPsw fusion to Journal of Cell Science (2019) 132, jcs226217. doi:10.1242/jcs
Considering that MreB-GFPsw is functional in E. coli (Ouzounov et al, 2016), and that the protein sequence of E. coli MreB and S. flexneri MreB is 100% identical (Fig. S1A), we reasoned that MreB-GFPsw would be functional in Shigella

Summary

INTRODUCTION

Shigella is a Gram-negative enteroinvasive bacterium and important human pathogen leading to ∼164,000 deaths annually (Khalil et al, 2018; Kotloff et al, 2017). Two pioneering studies artificially producing IcsA in E. coli have proposed that MreB is required for the restriction of polar material (Nilsen et al, 2005; Shih et al, 2005) In this case, genetic or pharmacologic manipulation of MreB caused IcsA to localise in multiple faint patches on the bacterial surface. We reveal that a subpopulation of intracellular S. flexneri cells remodel MreB, which helps to position IcsA at the cell pole and promotes actin tail formation.

RESULTS AND DISCUSSION

Conclusion

MATERIALS AND METHODS