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Virus-infection or 5'ppp-RNA activates antiviral signal through redistribution of IPS-1 mediated by MFN1.

Onoguchi K, Onomoto K, Takamatsu S, Jogi M, Takemura A, Morimoto S, Julkunen I, Namiki H, Yoneyama M, Fujita T - PLoS Pathog. (2010)

Bottom Line: In doing so we discovered that viral infection as well as transfection with 5'ppp-RNA resulted in the redistribution of IPS-1 to form speckle-like aggregates in cells.We further found that Mitofusin 1 (MFN1), a key regulator of mitochondrial fusion and a protein associated with IPS-1 on the outer membrane of mitochondria, positively regulates RLR-mediated innate antiviral responses.Our study suggests that mitochondria participate in the segregation of IPS-1 through their fusion processes.

View Article: PubMed Central - PubMed

Affiliation: Department of Molecular Genetics, Institute for Virus Research, Kyoto University, Kyoto, Japan.

ABSTRACT
In virus-infected cells, RIG-I-like receptor (RLR) recognizes cytoplasmic viral RNA and triggers innate immune responses including production of type I and III interferon (IFN) and the subsequent expression of IFN-inducible genes. Interferon-beta promoter stimulator 1 (IPS-1, also known as MAVS, VISA and Cardif) is a downstream molecule of RLR and is expressed on the outer membrane of mitochondria. While it is known that the location of IPS-1 is essential to its function, its underlying mechanism is unknown. Our aim in this study was to delineate the function of mitochondria so as to identify more precisely its role in innate immunity. In doing so we discovered that viral infection as well as transfection with 5'ppp-RNA resulted in the redistribution of IPS-1 to form speckle-like aggregates in cells. We further found that Mitofusin 1 (MFN1), a key regulator of mitochondrial fusion and a protein associated with IPS-1 on the outer membrane of mitochondria, positively regulates RLR-mediated innate antiviral responses. Conversely, specific knockdown of MFN1 abrogates both the virus-induced redistribution of IPS-1 and IFN production. Our study suggests that mitochondria participate in the segregation of IPS-1 through their fusion processes.

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Related in: MedlinePlus

Localization of viral nucleocapsid, RIG-I, and IPS-1.A, HeLa cells were infected with NDV for 12 h and stained with anti-RIG-I antibody (RIG-I) and anti-NP antibody (NDV NP). B and C, IPS-1-HeLa cells were infected with NDV for 12 h and stained with anti-FLAG antibody and anti-RIG-I antibody or anti-NP antibody.
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ppat-1001012-g005: Localization of viral nucleocapsid, RIG-I, and IPS-1.A, HeLa cells were infected with NDV for 12 h and stained with anti-RIG-I antibody (RIG-I) and anti-NP antibody (NDV NP). B and C, IPS-1-HeLa cells were infected with NDV for 12 h and stained with anti-FLAG antibody and anti-RIG-I antibody or anti-NP antibody.

Mentions: In order to activate RLR signaling, we used NDV to infect cells because it is available an anti-nucleocapsid protein (NP) antibody, a probe for the viral RNA-NP complex. NDV infection resulted in foci of NP in the cytoplasm and induced foci of RIG-I to form (Fig. 5A) [16]. RIG-I was evenly distributed in the cytoplasm, however some of the foci co-localized with those of NP (Fig. 5A). A similar formation of foci and co-localization with viral nucleoprotein complex was observed with other viruses (Ko.O. unpublished observations). IPS-1 accumulated on the periphery of the foci of RIG-I (Fig. 5B) and NP (Fig. 5C). We speculate that activated RIG-I recruits IPS-1, because RIG-I and IPS-1 interacted with each other through CARD-CARD interaction [7], [8]. IPS-1 did not co-localize with RIG-I nor NP presumably because mitochondria do not penetrate these foci nor is IPS-1 released from mitochondria. Immunoelectron microscopy using the anti-NP antibody clearly identified the NP foci (Fig. 6A), and anti-FLAG staining (Fig. 6B) showed that mitochondrial IPS-1 accumulated on the periphery of NP foci in NDV infected cells.


Virus-infection or 5'ppp-RNA activates antiviral signal through redistribution of IPS-1 mediated by MFN1.

Onoguchi K, Onomoto K, Takamatsu S, Jogi M, Takemura A, Morimoto S, Julkunen I, Namiki H, Yoneyama M, Fujita T - PLoS Pathog. (2010)

Localization of viral nucleocapsid, RIG-I, and IPS-1.A, HeLa cells were infected with NDV for 12 h and stained with anti-RIG-I antibody (RIG-I) and anti-NP antibody (NDV NP). B and C, IPS-1-HeLa cells were infected with NDV for 12 h and stained with anti-FLAG antibody and anti-RIG-I antibody or anti-NP antibody.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2908619&req=5

ppat-1001012-g005: Localization of viral nucleocapsid, RIG-I, and IPS-1.A, HeLa cells were infected with NDV for 12 h and stained with anti-RIG-I antibody (RIG-I) and anti-NP antibody (NDV NP). B and C, IPS-1-HeLa cells were infected with NDV for 12 h and stained with anti-FLAG antibody and anti-RIG-I antibody or anti-NP antibody.
Mentions: In order to activate RLR signaling, we used NDV to infect cells because it is available an anti-nucleocapsid protein (NP) antibody, a probe for the viral RNA-NP complex. NDV infection resulted in foci of NP in the cytoplasm and induced foci of RIG-I to form (Fig. 5A) [16]. RIG-I was evenly distributed in the cytoplasm, however some of the foci co-localized with those of NP (Fig. 5A). A similar formation of foci and co-localization with viral nucleoprotein complex was observed with other viruses (Ko.O. unpublished observations). IPS-1 accumulated on the periphery of the foci of RIG-I (Fig. 5B) and NP (Fig. 5C). We speculate that activated RIG-I recruits IPS-1, because RIG-I and IPS-1 interacted with each other through CARD-CARD interaction [7], [8]. IPS-1 did not co-localize with RIG-I nor NP presumably because mitochondria do not penetrate these foci nor is IPS-1 released from mitochondria. Immunoelectron microscopy using the anti-NP antibody clearly identified the NP foci (Fig. 6A), and anti-FLAG staining (Fig. 6B) showed that mitochondrial IPS-1 accumulated on the periphery of NP foci in NDV infected cells.

Bottom Line: In doing so we discovered that viral infection as well as transfection with 5'ppp-RNA resulted in the redistribution of IPS-1 to form speckle-like aggregates in cells.We further found that Mitofusin 1 (MFN1), a key regulator of mitochondrial fusion and a protein associated with IPS-1 on the outer membrane of mitochondria, positively regulates RLR-mediated innate antiviral responses.Our study suggests that mitochondria participate in the segregation of IPS-1 through their fusion processes.

View Article: PubMed Central - PubMed

Affiliation: Department of Molecular Genetics, Institute for Virus Research, Kyoto University, Kyoto, Japan.

ABSTRACT
In virus-infected cells, RIG-I-like receptor (RLR) recognizes cytoplasmic viral RNA and triggers innate immune responses including production of type I and III interferon (IFN) and the subsequent expression of IFN-inducible genes. Interferon-beta promoter stimulator 1 (IPS-1, also known as MAVS, VISA and Cardif) is a downstream molecule of RLR and is expressed on the outer membrane of mitochondria. While it is known that the location of IPS-1 is essential to its function, its underlying mechanism is unknown. Our aim in this study was to delineate the function of mitochondria so as to identify more precisely its role in innate immunity. In doing so we discovered that viral infection as well as transfection with 5'ppp-RNA resulted in the redistribution of IPS-1 to form speckle-like aggregates in cells. We further found that Mitofusin 1 (MFN1), a key regulator of mitochondrial fusion and a protein associated with IPS-1 on the outer membrane of mitochondria, positively regulates RLR-mediated innate antiviral responses. Conversely, specific knockdown of MFN1 abrogates both the virus-induced redistribution of IPS-1 and IFN production. Our study suggests that mitochondria participate in the segregation of IPS-1 through their fusion processes.

Show MeSH
Related in: MedlinePlus