Immunology and Inflammation

Apoptotic caspases cleave DRP1 to promote mitochondrial fusion and anti-viral immune responses

Yujie Fang
Zihan Guan
Xiangtao Zhu
Zhenqiong Guan
Shufen Li
Ke Peng author has email address

State Key Laboratory of Virology, Center for Antiviral Research, Center for Biosafety Mega-Science, Wuhan Institute of Virology, Chinese Academy of Sciences, Wuhan 430207, China
University of Chinese Academy of Sciences, Beijing 100049, China
Provincial Key Laboratory of Jiangxia, Wuhan, 430207, Hubei

https://doi.org/10.7554/eLife.101190.1

Open access
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Figures and data

RVFV infection leads to mitochondrial elongation.
(A) Mitochondria were visualized by immunofluorescence using confocal microscopy. THP-1^PMA, Huh7 or A549 cells were infected or mock infected with RVFV for 24 h at MOI = 5. Mitochondria were labeled with anti-Tom20 antibody (red), RVFV were labeled with anti-RVFV-NSs antibody (green) and Nuclei were stained with DAPI (blue). Scale bars, 5 μm (THP-1^PMA and Huh7 cells) or 7.5 μm (A549 cells).
(B) Sections of mock infected or RVFV-infected THP-1^PMA cells (MOI = 1) were analyzed by TEM. Black solid squares, scale bars, 1 μm. Blue dashed squares represent the magnification of regions of interest, scale bars, 250 nm. Mitochondria are circled in red shown on the right panels.
Data are representative of three experiments with similar results.

RVFV infection induces NSs-dependent DRP1 downregulation leading to mitochondrial elongation.
(A) The effects of exogenously expressed RVFV viral proteins on mitochondrial morphology in Huh7 cells was observed by confocal microscopy. Huh7 cells were transfected with empty vector or vectors expressing strep-tagged viral proteins of RVFV for 48 h. Mitochondria were labeled with anti-Tom20 antibody (red), viral proteins of RVFV were labeled with anti-strep antibody (green) and Nuclei were stained with DAPI (blue). Scale bars, 7.5 μm.
(B) Huh7 cells were mock infected or infected with the indicated virus for 24 h. Mitochondria were labeled with anti-Tom20 antibody (red), RVFV were labeled with anti-RVFV-NSs antibody (green), RVFV^EGFP△NSs were observed through detecting EGFP signal, and Nuclei were stained with DAPI (blue). Scale bars, 7.5 μm.
(C) Immunoblot analysis of the proteins that regulate mitochondrial morphology, including MFN1, MFN2, OPA1 and DRP1 in THP-1^PMA cells infected with RVFV for the indicated times.
(D) Immunoblot analysis of DRP1 protein level in Huh7 cells infected or mock infected with RVFV^WT or RVFV^EGFP△NSs for 24 h.
(E) Immunoblot analysis of DRP1 protein level in Huh7 cells transfected with the plasmids expressing the indicated proteins for 48 h.
Data are representative of three experiments with similar results.

DRP1 is cleaved by activated caspase during RVFV infection.
(A-C) Immunoblot analysis of DRP1 protein level in Huh7 cells infected or mock infected with RVFV for 2 h, followed by MG132 (5 μM) (A), CQ (10 μM) (B) or Z-VAD-FMK (20 μM) (C) treatment for 22 h.
(D) Immunoblot analysis of DRP1 protein level in THP-1^PMA cells infected or mock infected with RVFV for 2 h, followed by Z-VAD-FMK treatment with the indicted concentration for 22 h.
(E) Immunoblot analysis of DRP1 cleavage in THP-1^PMA cells infected or mock infected with RVFV for the indicted times.
(F) Immunoblot analysis of DRP1 cleavage in THP-1^PMA cells infected or mock infected with RVFV for 2 h, followed by Z-VAD-FMK treatment in the indicted concentration for 22 h.
(G) Immunoblot analysis of caspases activation in THP-1^PMA cells infected or mock infected with RVFV for 24 h.
Data are representative of three experiments with similar results.

Apoptotic caspase-3, -6, -7 and -8 cleave DRP1 at the AEAD⁵⁵⁶ and/or D⁵⁰⁰FAD⁵⁰³ motifs.
(A) Immunoblot analysis of DRP1 cleavage by the in vitro cleavage assay. The strep-tagged DRP1 protein was expressed and purified from HEK293T cells, and subjected to the in vitro cleavage assay with his-tagged caspase-1, 4, 3, 6, 7, 8 or 9 protein, followed by immunoblot analysis. Anti-strep antibody was used to determine the cleavage of DRP1. Anti-His antibody was used to identify caspases. The asterisks (*) represent non-specific bands. The blue solid rectangle represents long exposure.
(B) Immunoblot analysis of whole-cell lysates (WCL, bottom) and pull-down proteins with streptavidin magnetic beads (top) from HEK293T cells transfected with indicated plasmids for 24 h. Anti-V5 antibody was used to determine DRP1. Anti-strep antibody was used to identify EGFP or caspases.
(C) Prediction of the caspase cleavage sites for DRP1 using the CaspDB database.
(D) Immunoblot analysis of DRP1 cleavage in Huh7 cells. Cells were transfected with the DRP1- WT or DRP1-D556E mutant expressing plasmids, followed by RVFV infection or mock infection for 24 h.
(E) Immunoblot analysis of DRP1 cleavage by the in vitro cleavage assay. The strep-tagged DRP1-WT or DRP1-D556E proteins was expressed and purified from HEK293T cells, and subjected to the in vitro cleavage assay as described in (A).
(F) Immunoblot analysis of DRP1 cleavage by the in vitro cleavage assay. The strep-tagged DRP1-WT or the indicated DRP1 mutants, or his-tagged caspase-3 were expressed and purified from HEK293T cells, and incubated for the in vitro cleavage assay followed by immunoblot analysis. DRP1 fragments were detected with anti-strep antibody. Caspase-3 was detected by the anti-His antibody.
Data are representative of three experiments with similar results.

DRP1 deficiency promotes antiviral innate immunity.
(A) qPCR analysis of the indicated genes in scramble or DRP1 knockout THP-1^PMA cells infected or mock infected with RVFV for 12 h. ***P < 0.001 (Two-way ANOVA test).
(B) Immunoblot analysis of the indicated proteins in scramble or DRP1 knockout THP-1^PMA cells infected or mock infected with RVFV for 24h.
(C) Focus forming assay to determine the titer from RVFV infected scramble or DRP1 knockout THP-1^PMA cells infected for 24h. ***P < 0.001 (One-way ANOVA test).
Data are representative of three experiments with similar results.

Overexpression of DRP1 inhibits anti-viral innate immunity.
(A) qPCR analysis of the indicated genes in vector or DRP1-WT transduced THP-1^PMA cells infected or mock infected with RVFV for 12 h. ***P < 0.001 (Two-way ANOVA test).
(B) Immunoblot analysis of the indicated proteins in vector or DRP1-WT transduced THP-1^PMA cells infected or mock infected with RVFV for 24h.
(C) Focus forming assay to determine the titer from RVFV infected vector or DRP1-WT transduced THP-1^PMA cells infected with RVFV for 24h. *P < 0.05, **P < 0.01, ***P < 0.001 (Student’s t test). Data are representative of three experiments with similar results.

Caspases-mediated DRP1 cleavage promotes antiviral innate immunity.
(A) qPCR analysis of the indicated genes in DRP1-WT or DRP1-3DE transduced THP-1^PMA cells infected or mock infected with RVFV for 12 h. ***P < 0.001 (Two-way ANOVA test).
(B) Immunoblot analysis of the indicated proteins in DRP1-WT or DRP1-3DE transduced THP-1^PMA cells infected or mock infected with RVFV for 24 h.
(C) Focus forming assay to determine the titer from RVFV infected DRP1-WT or DRP1-3DE transduced THP-1^PMA cells infected with RVFV for 24 h. **P < 0.01 (Student’s t test).
(D) Immunoblot analysis of the indicated proteins in vector, DRP1-WT or DRP1-3DE transduced THP-1^PMA cells infected or mock infected with RVFV for 24 h.
Data are representative of three experiments with similar results.

Caspases-mediated DRP1 cleavage induces mitochondrial elongation to promote MAVS aggregation and immune responses.
(A) Immunofluorescence analysis of MAVS aggregation in scramble or DRP1 knockout THP-1^PMA cells. Mitochondria were labeled with anti-Tom20 antibody (red), MAVS was labeled with anti-MAVS antibody (green) and Nuclei were stained with DAPI (blue). Scale bars, 10 μm.
(B) Immunoblot analysis of caspase-8 activation, DRP1 protein level and MAVS aggregation in THP-1^PMA cells infected or mock infected with RVFV or 24 h.
(C) Immunoblot analysis of MAVS aggregation in scramble or DRP1 knockout HEK293T cells. HEK293T cells were transfected with HA-tagged MAVS (HA-MAVS) plasmid for 24 h, followed by SeV infection for 12 h.
(D) Immunoblot analysis of MAVS aggregation in scramble or DRP1 knockout THP-1^PMA cells infected or mock infected with RVFV for 24 h.
(E) Immunoblot analysis of the indicated proteins in DRP1 knockout or DRP1 and MAVS double knockout THP-1^PMA cells infected with RVFV for 24 h.
(F) Focus forming assay to determine the titer from RVFV infected DRP1 knockout or DRP1 and MAVS double knockout THP-1^PMA cells infected for 24 h. ***P < 0.001 (One-way ANOVA test). Data are representative of three experiments with similar results.

Multiple viruses trigger caspases-mediated DRP1 cleavage.
(A-C) Immunoblot analysis of caspases activation and DRP1 cleavage in THP-1^PMA cells infected or mock infected with H1N1 (A), SeV (B) or HSV-1 (C) for 24 h. The asterisks (*) represent non-specific bands.
(D) Mitochondria were visualized by immunofluorescence using confocal microscopy. THP-1^PMA cells were infected or mock infected with RVFV, H1N1, SeV or HSV-1 for 18 h, respectively. Mitochondria were labeled with anti-Tom20 (red) antibody and Nuclei were stained with DAPI (blue). Scale bars, 7.5 μm.
(E) Immunoblot analysis of DRP1 cleavage in THP-1^PMA cells infected or mock infected with H1N1 for 2 h, followed by Z-VAD-FMK treatment for 22 h.
(F) Immunoblot analysis of DRP1 cleavage in THP-1^PMA cells infected or mock infected with SeV for 2 h, followed by Z-VAD-FMK treatment for 10 h.
(G) Immunoblot analysis of DRP1 cleavage in THP-1^PMA cells infected or mock infected with HSV-1 for 2 h, followed by Z-VAD-FMK treatment for 22 h.
(H-I) Plaque assay results determining the titers from virus infected scramble or DRP1 knockout THP-1^PMA cells infected with H1N1 (H) or HSV-1 (I) for 24 h. ***P < 0.001 (One-way ANOVA test).
Data are representative of three experiments with similar results.

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