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Infect Immun. 2017 Nov 6. pii: IAI.00596-17. doi: 10.1128/IAI.00596-17. [Epub ahead of print]

Orientia tsutsugamushi modulates endoplasmic reticulum-associated degradation to benefit its growth.

Author information

1
Department of Microbiology and Immunology, Virginia Commonwealth University School of Medicine, Richmond, Virginia, 23298-0678, USA.
2
Viral and Rickettsial Diseases Department, Naval Medical Research Center, Silver Spring, Maryland, 20910, USA.
3
Department of Microbiology and Immunology, Virginia Commonwealth University School of Medicine, Richmond, Virginia, 23298-0678, USA jason.carlyon@vcuhealth.org.

Abstract

Orientia tsutsugamushi, an obligate intracellular bacterium that is auxotrophic for the aromatic amino acids and histidine, causes scrub typhus, a potentially deadly infection that threatens one billion people. O. tsutsugamushi growth is minimal during the first 24 to 48 h of infection, but becomes logarithmic thereafter. How the pathogen modulates cellular functions to support its growth is poorly understood. The unfolded protein response (UPR) is a cytoprotective pathway that relieves endoplasmic reticulum (ER) stress by promoting ER-associated degradation (ERAD) of misfolded proteins. Here we show that O. tsutsugamushi invokes the UPR in the first 48 h and benefits from ER stress in an amino acid-dependent manner. O. tsutsugamushi also impedes ERAD during this time period. By 72 h, ER stress is alleviated and ERAD proceeds unhindered. Sustained inhibition of ERAD using RNA interference results in an O. tsutsugamushi growth defect at 72 h that can be rescued by amino acid supplementation. Thus, O. tsutsugamushi temporally stalls ERAD until ERAD-derived amino acids are needed to support its growth. The O. tsutsugamushi effector, Ank4, is linked to this phenomenon. Ank4 interacts with Bat3, a eukaryotic chaperone that is essential for ERAD, and is transiently expressed by O. tsutsugamushi during the infection period when it inhibits ERAD. Ectopically expressed Ank4 blocks ERAD to phenocopy O. tsutsugamushi infection. Our data reveal a novel mechanism by which an obligate intracellular bacterial pathogen modulates ERAD to satisfy its nutritional virulence requirements.

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