DDX3 Participates in Translational Control of Inflammation Induced by Infections and Injuries

ABSTRACT

Recent studies have suggested that DDX3 functions in antiviral innate immunity, but the underlying mechanism remains elusive. We previously identified target mRNAs whose translation is controlled by DDX3. Pathway enrichment analysis of these targets indicated that DDX3 is involved in various infections and inflammation. Using immunoblotting, we confirmed that PACT, STAT1, GNB2, Rac1, TAK1, and p38 mitogen-activated protein kinase (MAPK) proteins are downregulated by DDX3 knockdown in human monocytic THP-1 cells and epithelial HeLa cells. Polysome profiling revealed that DDX3 knockdown reduces the translational efficiency of target mRNAs. We further demonstrated DDX3-mediated translational control of target mRNAs by luciferase reporter assays. To examine the effects of DDX3 knockdown on macrophage migration and phagocytosis, we performed in vitro cell migration assay and flow cytometry analysis of the uptake of green fluorescent protein-expressing Escherichia coli in THP-1 cells. The DDX3 knockdown cells exhibited impaired macrophage migration and phagocytosis. Moreover, we used a human cytokine antibody array to identify the cytokines affected by DDX3 knockdown. Several chemokines were decreased considerably in DDX3 knockdown THP-1 cells after lipopolysaccharide or poly(I·C) stimulation. Lastly, we demonstrated that DDX3 is crucial for the recruitment of phagocytes to the site of inflammation in transgenic zebrafish.

KEYWORDS:

• DEAD-box RNA helicase
• inflammation
• innate immunity
• phagocytosis
• translational control

ACKNOWLEDGMENTS

We thank Ching-Yu Lin (Graduate Institute of Biomedical Sciences, Chang Gung University) and Chuan-Sheng Lin (Department of Medical Biotechnology and Laboratory Science, Chang Gung University) for technical assistance in microinjection of zebrafish embryos and flow cytometry analysis, respectively. The manuscript was edited by Wallace Academic Editing.

This work was supported by grants from Ministry of Science and Technology, Taiwan (MOST 107-2320-B-182-031), and Chang Gung Memorial Hospital, Taiwan (CMRPD3E0013, CMRPD1H0051, and CMRPG3F0181).