Murine AML12 hepatocytes allow Salmonella Typhimurium T3SS1-independent invasion and intracellular fate

S Holbert,I Virlogeux-Payant,S Georgeault,J Burlaud-Gaillard,E Barilleau,P Velge,J Trotereau,A Wiedemann,S Méresse,S M Roche

doi:10.1038/s41598-021-02054-z

Abstract

Numerous studies have demonstrated the key role of the Salmonella Pathogenicity Island 1-encoded type III secretion system (T3SS1) apparatus as well as its associated effectors in the invasion and intracellular fate of Salmonella in the host cell. Several T3SS1 effectors work together to control cytoskeleton networks and induce massive membrane ruffles, allowing pathogen internalization. Salmonella resides in a vacuole whose maturation requires that the activity of T3SS1 subverts early stages of cell signaling. Recently, we identified five cell lines in which Salmonella Typhimurium enters without using its three known invasion factors: T3SS1, Rck and PagN. The present study investigated the intracellular fate of Salmonella Typhimurium in one of these models, the murine hepatocyte cell line AML12. We demonstrated that both wild-type Salmonella and T3SS1-invalidated Salmonella followed a common pathway leading to the formation of a Salmonella containing vacuole (SCV) without classical recruitment of Rho-GTPases. Maturation of the SCV continued through an acidified phase that led to Salmonella multiplication as well as the formation of a tubular network resembling Salmonella induced filaments (SIF). The fact that in the murine AML12 hepatocyte, the T3SS1 mutant induced an intracellular fate resembling to the wild-type strain highlights the fact that Salmonella Typhimurium invasion and intracellular survival can be completely independent of T3SS1.

Highlights

The main difference in the entry step between T3SS1-dependent and T3SS1-independent invasion is that T3SS1 effectors induce cell invasion by means of a trigger mechanism, while invasins mediate invasion using a zipper mechanism characterized by the interaction between a bacterial outer membrane protein and a host receptor[10]
To evaluate the intracellular multiplication of Salmonella, we quantified the number of intracellular Salmonella 16 h pi in AML12 and HeLa cells
These bacterial effectors interact with host cytoskeleton proteins allowing rearrangements in the host cell membrane

Summary

Introduction

We recently published that Salmonella invalidated for the three known invasion factors (T3SS1 apparatus, Rck and PagN) remains able to invade several non-phagocytic cell models as effectively as wild-type Salmonella[9]. Several T3SS2 effectors are implicated especially in SCV maturation, following well-described kinetics dependent on transient SCV interaction with late endosomal proteins such as Rab[7]. Among these effectors, SopD2 interacts directly with Rab[7] and inhibits vesicular transport, favoring vacuole m aturation[15,16]. Typhimurium invaded the murine hepatocyte cell line AML12 through a T3SS1-independent process and retained its ability to multiply in a mature vacuole, it had a functional T3SS1 or not

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