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Published on: April 2, 2013
Host Cells Upregulate Phosphate Transporter PIT1 to Inhibit Ehrlichia chaffeensis Intracellular Growth
Meifang Li1,2, Nan Yang1,2, Xiaoxiao Li1,2
1The Key Laboratory of Molecular Microbiology and Technology, Ministry of Education, Nankai University, Tianjin 300071, China.
Abstract:
Ehrlichia chaffeensis infects and proliferates inside monocytes or macrophages and causes human monocytic ehrlichiosis (HME), an emerging life-threatening tick-borne zoonosis. After internalization, E. chaffeensis resides in specialized membrane-bound inclusions, E. chaffeensis-containing vesicles (ECVs), to evade from host cell innate immune responses and obtain nutrients. However, mechanisms exploited by host cells to inhibit E. chaffeensis growth in ECVs are still largely unknown. Here we demonstrate that host cells recognize E. chaffeensis Ech_1067, a penicillin-binding protein, and then upregulate the expression of PIT1, which is a phosphate transporter and transports phosphate from ECVs to the cytosol to inhibit bacterial growth. We found that host cells upregulate the PIT1 expression upon E. chaffeensis infection using transcriptome sequencing, qRT-PCR and Western blotting, and PIT1 is localized on the ECV membrane in infected THP-1 cells using confocal microscopy. Silence of PIT1 using shRNA enhances E. chaffeensis intracellular growth. Finally, we found that E. chaffeensis Ech_1067 induces the upregulation of PIT1 expression through the MyD88-NF-κB pathway using recombinant protein for stimulation and siRNA for silence. Our findings deepen the understanding of the innate immune responses of host cells to inhibit bacterial intracellular growth and facilitate the development of new therapeutics for HME.
Insights
Host cells combat Ehrlichia chaffeensis by upregulating phosphate transporter PIT1, which limits bacterial growth within vesicles. This innate immune response is triggered by the bacterial protein Ech_1067 via the MyD88-NF-κB pathway.
Area of Science:
- Infectious Diseases
- Immunology
- Microbiology
Background:
- Human monocytic ehrlichiosis (HME) is a severe tick-borne zoonosis caused by Ehrlichia chaffeensis.
- E. chaffeensis resides in host cell inclusions (ECVs) to evade immune responses and acquire nutrients.
- Mechanisms by which host cells inhibit intracellular bacterial growth remain largely unknown.
Purpose of the Study:
- To elucidate host cell mechanisms that restrict Ehrlichia chaffeensis proliferation.
- To identify host factors involved in innate immunity against E. chaffeensis infection.
- To understand the signaling pathway triggered by E. chaffeensis that modulates host defenses.
Main Methods:
- Transcriptome sequencing, qRT-PCR, and Western blotting to identify host gene expression changes.
- Confocal microscopy to determine the localization of PIT1 in infected cells.
- RNA interference (shRNA and siRNA) and recombinant protein stimulation to investigate molecular pathways.
Main Results:
- Host cells upregulate the phosphate transporter PIT1 upon E. chaffeensis infection.
- PIT1 localizes to the ECV membrane and its depletion enhances bacterial growth.
- E. chaffeensis Ech_1067 protein induces PIT1 upregulation via the MyD88-NF-κB pathway.
Conclusions:
- Host cells utilize PIT1 to limit intracellular E. chaffeensis growth, representing a novel innate immune mechanism.
- The bacterial protein Ech_1067 activates the MyD88-NF-κB pathway to induce PIT1 expression.
- Findings provide insights into HME pathogenesis and potential therapeutic targets.
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