Yeast Functional Genomic Screens Lead to Identification of a Role for a Bacterial Effector in Innate Immunity Regulation

Roger W Kramer,Michael N Starnbach,Naomi L Slagowski,Ngozi A Eze,Monica F Morrison,Keri A Siggers,Kara S Giddings,Cammie F Lesser,Ralph R Isburg

doi:10.1371/journal.ppat.0030021

Roger W Kramer, Michael N Starnbach + Show 7 more

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https://doi.org/10.1371/journal.ppat.0030021

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Journal: PLoS Pathogens	Publication Date: Feb 1, 2007
Citations: 132	License type: CC BY 4.0

Affiliation: Harvard University, Massachusetts General Hospital

Abstract

Numerous bacterial pathogens manipulate host cell processes to promote infection and ultimately cause disease through the action of proteins that they directly inject into host cells. Identification of the targets and molecular mechanisms of action used by these bacterial effector proteins is critical to understanding pathogenesis. We have developed a systems biological approach using the yeast Saccharomyces cerevisiae that can expedite the identification of cellular processes targeted by bacterial effector proteins. We systematically screened the viable yeast haploid deletion strain collection for mutants hypersensitive to expression of the Shigella type III effector OspF. Statistical data mining of the results identified several cellular processes, including cell wall biogenesis, which when impaired by a deletion caused yeast to be hypersensitive to OspF expression. Microarray experiments revealed that OspF expression resulted in reversed regulation of genes regulated by the yeast cell wall integrity pathway. The yeast cell wall integrity pathway is a highly conserved mitogen-activated protein kinase (MAPK) signaling pathway, normally activated in response to cell wall perturbations. Together these results led us to hypothesize and subsequently demonstrate that OspF inhibited both yeast and mammalian MAPK signaling cascades. Furthermore, inhibition of MAPK signaling by OspF is associated with attenuation of the host innate immune response to Shigella infection in a mouse model. These studies demonstrate how yeast systems biology can facilitate functional characterization of pathogenic bacterial effector proteins.

Highlights

Bacterial pathogens have evolved numerous mechanisms to evade host cell defenses and promote infection
The yeast Saccharomyces cerevisiae has recently emerged as a model system to both identify and functionally characterize effector proteins
This inhibition of mitogen-activated protein kinase signaling is associated with attenuation of the host innate immune response

Summary

Introduction

Bacterial pathogens have evolved numerous mechanisms to evade host cell defenses and promote infection. One strategy common to many pathogens is the manipulation of host cell processes by bacterial effector proteins that are directly delivered into host cells by specialized secretion systems [1]. These effector proteins are critical to pathogenesis, relatively few are well characterized. Bacterial effectors that target conserved eukaryotic cellular processes often inhibit growth [2,3,6] and/or exhibit conserved subcellular localization patterns [3,7]. By systematically screening for yeast deletion strains hypersensitive to expression of a bacterial effector protein, cellular processes that buffer yeast against the toxicity of the effector can be identified. We applied this approach to OspF, a Shigella effector protein

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