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Ehrlichia chaffeensis Etf-3 Induces Host RAB15 Upregulation for Bacterial Intracellular Growth
Nan Yang1,2, Meifang Li1,2, Shanhua Qin1,2
1The Key Laboratory of Molecular Microbiology and Technology, Ministry of Education, Nankai University, Tianjin 300071, China.
Abstract:
Ehrlichia chaffeensis infects human monocytes or macrophages and causes human monocytic ehrlichiosis (HME), an emerging life-threatening zoonosis. After internalization, E. chaffeensis resides in membrane-bound inclusions, E. chaffeensis-containing vesicles (ECVs), which have early endosome-like characteristics and fuse with early autophagosomes but not lysosomes, to evade host innate immune microbicidal mechanisms and obtain nutrients for bacterial intracellular growth. The mechanisms exploited by E. chaffeensis to modulate intracellular vesicle trafficking in host cells have not been comprehensively studied. Here, we demonstrate that E. chaffeensis type IV secretion system (T4SS) effector Etf-3 induces RAB15 upregulation in host cells and that RAB15, which is localized on ECVs, inhibits ECV fusion with lysosomes and induces autophagy. We found that E. chaffeensis infection upregulated RAB15 expression using qRT-PCR, and RAB15 was colocalized with E. chaffeensis using confocal microscopy. Silence of RAB15 using siRNA enhanced ECV maturation to late endosomes and fusion with lysosomes, as well as inhibited host cell autophagy. Overexpression of Etf-3 in host cells specifically induced RAB15 upregulation and autophagy. Our findings deepen the understanding of E. chaffeensis pathogenesis and adaptation in hosts as well as the function of RAB15 and facilitate the development of new therapeutics for HME.
Insights
Ehrlichia chaffeensis manipulates host cells using the Etf-3 effector to upregulate RAB15. This protein prevents bacterial vesicle fusion with lysosomes, promoting pathogen survival and autophagy, crucial for understanding human monocytic ehrlichiosis.
Area of Science:
- Microbiology
- Cell Biology
- Immunology
Background:
- * *Ehrlichia chaffeensis* causes human monocytic ehrlichiosis (HME), a serious zoonotic disease, by residing in host monocytes/macrophages.
- * *E. chaffeensis*-containing vesicles (ECVs) mimic early endosomes, fuse with autophagosomes, and avoid lysosomes to evade immune defenses and acquire nutrients.
- * Mechanisms by which *E. chaffeensis* manipulates host vesicle trafficking remain incompletely understood.
Purpose of the Study:
- * To investigate the role of *E. chaffeensis* type IV secretion system (T4SS) effectors in modulating host intracellular vesicle trafficking.
- * To elucidate the function of RAB15 in the intracellular lifestyle of *E. chaffeensis*.
Main Methods:
- * Quantitative reverse transcription PCR (qRT-PCR) to measure *RAB15* gene expression.
- * Confocal microscopy to visualize the colocalization of RAB15 with *E. chaffeensis*.
- * Small interfering RNA (siRNA) to silence RAB15 expression and assess its impact on ECV maturation and autophagy.
- * Overexpression of the Etf-3 effector to study its effect on RAB15 and autophagy.
Main Results:
- * *E. chaffeensis* infection and Etf-3 effector activity significantly upregulate *RAB15* expression in host cells.
- * RAB15 localizes to ECVs, inhibiting their fusion with lysosomes and promoting autophagy.
- * Silencing RAB15 restores ECV maturation to late endosomes, facilitates lysosomal fusion, and suppresses autophagy.
- * Etf-3 overexpression specifically induces RAB15 upregulation and autophagy.
Conclusions:
- * The *E. chaffeensis* T4SS effector Etf-3 hijacks host cell machinery by inducing RAB15.
- * RAB15 plays a critical role in *E. chaffeensis* pathogenesis by preventing lysosomal degradation and promoting bacterial survival via autophagy.
- * These findings offer insights into *E. chaffeensis* adaptation and potential therapeutic targets for HME.
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