Mycobacterium tuberculosis Type VII Secreted Effector EsxH Targets Host ESCRT to Impair Trafficking

Alka Mehra,Marc Vidal,Yoshihisha Kubota,Kristen Penberthy,Victor Thompson,Christopher M Sassetti,Maura Porto,Amelie Dricot,David E Hill,Andrew J Bean,Stefan Köster,Daniel Rogan,Aleena Zahra,Ashley Wells,Natalie Sirisaengtaksin,Jennifer A Philips

doi:10.1371/journal.ppat.1003734

Abstract

Mycobacterium tuberculosis (Mtb) disrupts anti-microbial pathways of macrophages, cells that normally kill bacteria. Over 40 years ago, D'Arcy Hart showed that Mtb avoids delivery to lysosomes, but the molecular mechanisms that allow Mtb to elude lysosomal degradation are poorly understood. Specialized secretion systems are often used by bacterial pathogens to translocate effectors that target the host, and Mtb encodes type VII secretion systems (TSSSs) that enable mycobacteria to secrete proteins across their complex cell envelope; however, their cellular targets are unknown. Here, we describe a systematic strategy to identify bacterial virulence factors by looking for interactions between the Mtb secretome and host proteins using a high throughput, high stringency, yeast two-hybrid (Y2H) platform. Using this approach we identified an interaction between EsxH, which is secreted by the Esx-3 TSSS, and human hepatocyte growth factor-regulated tyrosine kinase substrate (Hgs/Hrs), a component of the endosomal sorting complex required for transport (ESCRT). ESCRT has a well-described role in directing proteins destined for lysosomal degradation into intraluminal vesicles (ILVs) of multivesicular bodies (MVBs), ensuring degradation of the sorted cargo upon MVB-lysosome fusion. Here, we show that ESCRT is required to deliver Mtb to the lysosome and to restrict intracellular bacterial growth. Further, EsxH, in complex with EsxG, disrupts ESCRT function and impairs phagosome maturation. Thus, we demonstrate a role for a TSSS and the host ESCRT machinery in one of the central features of tuberculosis pathogenesis.

Highlights

An important virulence property of Mycobacterium tuberculosis (Mtb)- the causative agent of the disease tuberculosis- is its ability to avoid delivery to the lysosome
The host immune system can’t eradicate Mtb because it grows within macrophages, cells that normally kill bacteria
In order to minimize the contribution of such proteins, we did not include open reading frames (ORFs) that were annotated in Tuberculist as being involved in lipid metabolism, information pathways, or intermediary metabolism and respiration, since most of these are likely involved in basic, intrinsic bacterial processes, and many may be misclassified

Summary

Introduction

An important virulence property of Mycobacterium tuberculosis (Mtb)- the causative agent of the disease tuberculosis- is its ability to avoid delivery to the lysosome. It has long been appreciated that Mtb alters phagosome maturation, such that internalized bacteria are not transported to the lysosome but instead reside in an early endosome-like compartment [1,2]. The Mtb-induced block in phagosome-lysosome fusion has been attributed to a wide array of lipid and protein effectors [3,4] but the mechanism remains poorly understood. The ability of Mtb to permeabilize the phagosomal membrane, which allows bacterial products and in some cases intact bacteria to access the cytosol, has been described [5,6,7,8,9]. The TSSS Esx-1 and its secreted effectors, EsxA/ESAT-6 and EsxB/CFP-10, are critical for this process. Esx-1 has been investigated intensively because its absence in the vaccine strain

Methods

Results

Discussion

Conclusion