Autophagy facilitates antibody-enhanced dengue virus infection in human pre-basophil/mast cells - PubMed (original) (raw)
Autophagy facilitates antibody-enhanced dengue virus infection in human pre-basophil/mast cells
Yi-Ting Fang et al. PLoS One. 2014.
Abstract
Background: Dengue virus (DENV) infection can cause severe hemorrhagic disease in humans. Although the pathogenic mechanisms underlying severe DENV disease remain unclear, one of the possible contributing factors is antibody-dependent enhancement (ADE) which occurs when sub-neutralizing antibodies derived from a previous DENV infection enhance viral infection through interaction between virus-antibody complexes and FcR-bearing cells, such as macrophages and basophil/mast cells. Although recent reports showed that DENV induces autophagy, the relationship between antibody-enhanced DENV infection and autophagy is not clear.
Methodology/principal findings: We showed that sub-neutralizing antibodies derived from dengue patient sera enhanced DENV infection and autophagy in the KU812 pre-basophil-like cell line as well as the HMC-1 immature mast cell line. Antibody-enhanced DENV infection of KU812 cells increased the number of autophagosome vesicles, LC3 punctation, LC3-II accumulation, and p62 degradation over that seen in cells infected with DENV alone. The percentages of DENV envelope (E) protein-positive cells and LC3 puncta following antibody-enhanced DENV infection of KU812 cells were reduced by the autophagy inhibitor 3-MA. Antibody-enhanced DENV infection of HMC-1 cells showed co-localization of DENV E protein and dsRNA with autophagosomes, which was inhibited by 3-MA treatment. Furthermore, DENV infection and replication were reduced when KU812 cells were transfected with the autophagy-inhibiting Atg4BC74A mutant.
Conclusions/significance: Our results demonstrate a significant induction of autophagy in antibody-enhanced DENV infection of pre-basophil-like KU812 and immature mast cell-like HMC-1 cells. Also, autophagy plays an important role in DENV infection and replication in these cells. Given the importance of ADE and FcR-bearing cells such as monocytes, macrophages and basophil/mast cells in dengue disease, the results provide insights into dengue pathogenesis and therapeutic means of control.
Conflict of interest statement
Competing Interests: The authors have declared that no competing interests exist.
Figures
Figure 1. Antibody-enhanced DENV infection and autophagosome formation in KU812 cells.
(A and B) Cells were inoculated with medium alone (Mock), with DENV alone (MOI = 1), or with DENV in the presence of a sub-neutralizing dilution (1∶10,000) of dengue patient sera at 4°C for 1.5 h. After washing, cells were resuspended in fresh medium and incubated at 37°C for 24 h. The DENV E protein (A) and NS4B protein (B) were detected by flow cytometry. Infection of UV-inactivated DENV (iDENV) was served as negative control. The means of three independent experiments ± SD are shown. (C and D) After 24 h post-infection, the culture supernatant (C) and the mixture of cell and culture supernatant (D) were collected to determine viral titers by plaque assay. The means ± SD of three independent experiments are shown. (E) After infection for 24 h, cells were fixed and observed under TEM. We analyzed five cells by TEM in each condition including mock, DENV alone, and ADE. One section per cell was obtained to quantify the autophagosome vesicles. The black square areas in the left panels were amplified (×40000) and shown in right panels. The arrowheads indicate the autophagosomes. Cy: cytoplasm; N: nucleus. (F) The quantification of autophagosome numbers in each section from (E) is shown. The means ± SD of three independent experiments are shown. **P<0.01.
Figure 2. Co-localization of DENV E protein and LC3 punctation in antibody-enhanced DENV infection of KU812 cells.
(A) KU812 cells were incubated with medium alone (Mock), with DENV alone, with DENV in the presence of sub-neutralizing dengue patient sera, sub-neutralizing dengue patient sera alone, with UV-inactivated DENV (iDENV) alone, or iDENV in the presence of sub-neutralizing dengue patient sera. After infection, cells were fixed, permeabilized, and stained with anti-DENV E protein (red), anti-LC3 (green), and DAPI (blue). Cells were then mounted and observed by confocal microscopy. The square areas are zoomed-in images and shown in the right panels (merge, zoom). Bar: 10 µm. The imaging data were repeated three times and one set of representative results is shown. (B) The quantification of E-positive cells (A, filled arrowheads) is shown. The means ± SD of three independent experiments are shown. ***P<0.005. (C) The quantification of LC3 punctation cells (A, empty arrowheads) is shown. The means ± SD of three independent experiments are shown. ***P<0.005. (D) The percentages of cells with E-positive and LC3 punctation (A, arrows) are shown. The means ± SD of three independent experiments are shown. ***P<0.005. (E) After 24 h post-infection, the protein levels of LC3, p62, and NS4B from total cell lysates were detected by Western blotting. β-actin served as internal control. NC: negative control (nutrient-rich medium); PC: positive control (starvation; Hank's balanced salt solution). (F and G) KU812 cells were pre-treated with or without 5 mM 3-MA for 1 h before incubation with medium alone (Mock), DENV alone, or DENV with sub-neutralizing dengue patient sera. 3-MA was maintained in the medium during DENV infection. After 24 h post-infection, the expression of DENV E protein (F) and NS4B protein (G) was detected by flow cytometry. The means ± SD of three independent experiments are shown. **P<0.01, ***P<0.005.
Figure 3. Sub-neutralizing anti-E monoclonal antibody enhances DENV infection and induces autophagy in KU812 cells.
KU812 cells were pretreated with or without 5 mM 3-MA for 1 h before incubation with medium alone (Mock), DENV alone, or DENV with sub-neutralizing anti-E. 3-MA was maintained in the medium during DENV infection. (A) After 24 h post-infection, the expression of DENV E protein was detected by flow cytometry. The means ± SD of three independent experiments are shown. *P<0.05, **P<0.01. (B) Cells were fixed, permeabilized, and stained with anti-DENV E protein (green), anti-LC3 (red), and DAPI (blue). Cells were then mounted and observed by confocal microscopy. The square areas are zoomed-in images and shown in the right panels (merge, zoom). Bar: 10 µm. The imaging data were repeated three times and one set of representative results is shown. (C) The quantification of LC3 punctation cells (B, empty arrowheads) is shown. The means ± SD of three independent experiments are shown. ***P<0.005.
Figure 4. Co-localization of DENV E protein and dsRNA with autophagosome in HMC-1 cells after infection with DENV alone or with enhancing antibody.
HMC-1 cells were pretreated with or without 1 mM 3-MA for 1 h. Cells were then incubated with medium alone (Mock), with DENV (MOI = 1), or with DENV in the presence of sub-neutralizing dengue patient sera with or without 0.5 mM 3-MA during the incubation periods. (A) After 24 h post-infection, cells were fixed, permeabilized, and stained with anti-E protein (red), LC3 protein (green), and DAPI (blue). The imaging data were repeated two times and one set of representative results is shown. (B) After 24 h post-infection, cells were fixed, permeabilized, and stained for anti-double strand (ds) RNA (red), LC3 protein (green), and DAPI (blue). After mounting, cells were observed by confocal microscopy. The square areas are zoomed-in images and shown in the right panels (merge, zoom). Bar: 10 µm. The imaging data were repeated three times and one set of representative results is shown.
Figure 5. Inhibition of autophagy reduces DENV infection and virus titer after DENV infection with or without enhancing antibody.
(A) KU812 cells were transfected with strawberry or strawberry-Atg4BC74A plasmids. After transfection and incubation for 48 h, strawberry- and strawberry-Atg4BC74A-expressing KU812 cells were infected with DENV or DENV with sub-neutralizing dengue patient sera. After 24 h post-infection, cells were fixed, permeabilized, stained with anti-E (green), and observed by confocal microscopy. The arrowheads indicate the strawberry- and strawberry-Atg4BC74A-expressing cells (red). The arrows (merge) indicate the cells which possess both green and red fluorescence. The visible images of total cells are shown in the right panels. The imaging data were repeated three times and one set of representative results is shown. (B) The number of E-positive cells was counted from 200 red cells from Fig. 5A. The percentage of E-positive cells from red cells was then quantified. The means ± SD of three independent experiments are shown. (C) KU812 cells were transfected with strawberry or strawberry-Atg4BC74A plasmids. After transfection and incubation for 48 h, strawberry- and strawberry-Atg4BC74A-expressing KU812 cells were infected with DENV or DENV with sub-neutralizing dengue patient sera. After 24 h post-infection, cells were fixed, permeabilized, stained with anti-NS4B, and followed by Alexa647-conjugated secondary antibody. The percentage of NS4B-positive cells in red cells was then determined by flow cytometry. The means ± SD of three independent experiments are shown. (D and E) After 24 h post-infection, the culture supernatant (D) and the mixture of cell and culture supernatant (E) were collected to detect the viral titers by plaque assay. The means ± SD of three independent experiments are shown. *P<0.05, **P<0.01, ***P<0.005.
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This work was supported by grants NSC101-2325-B-006-006 and NSC102-2325-B-006-006 from Ministry of Science and Technology, Taiwan. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
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