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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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MFN1 is involved in antiviral signaling.A, Schematic representation of the MFN1 domain. B, L929 cells were transfected with a virus-responsive reporter gene (p-125 Luc) and either an empty vector (Empty), an expression vector for MFN1, or an expression vector for MFN2 as indicated. 48 h after the transfection, cells were mock-treated or infected with NDV. Luciferase activity was determined at 12 h after infection. C and D, L929 cells were transfected with a virus-responsive reporter gene (p-125 Luc) and either an empty vector (Empty) or an expression vector for MFN1 or its mutant (MFN1 T109A) as indicated. At 48 h after transfection, cells were mock-treated, infected with NDV, or transfected with 5′OH-RNA or 5′ppp-RNA. Luciferase activity was determined at 12 h (C) or 9 h (D) after induction. E, L929 cells were transfected with a virus-responsive reporter gene (p-125 Luc) and combinations of the indicated vectors. 48 h after the transfection, cells were mock-treated or infected with NDV. Luciferase activity was determined 12 h after infection.
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ppat-1001012-g008: MFN1 is involved in antiviral signaling.A, Schematic representation of the MFN1 domain. B, L929 cells were transfected with a virus-responsive reporter gene (p-125 Luc) and either an empty vector (Empty), an expression vector for MFN1, or an expression vector for MFN2 as indicated. 48 h after the transfection, cells were mock-treated or infected with NDV. Luciferase activity was determined at 12 h after infection. C and D, L929 cells were transfected with a virus-responsive reporter gene (p-125 Luc) and either an empty vector (Empty) or an expression vector for MFN1 or its mutant (MFN1 T109A) as indicated. At 48 h after transfection, cells were mock-treated, infected with NDV, or transfected with 5′OH-RNA or 5′ppp-RNA. Luciferase activity was determined at 12 h (C) or 9 h (D) after induction. E, L929 cells were transfected with a virus-responsive reporter gene (p-125 Luc) and combinations of the indicated vectors. 48 h after the transfection, cells were mock-treated or infected with NDV. Luciferase activity was determined 12 h after infection.

Mentions: RIG-I was originally identified by screening an expression cDNA library [17]. In addition to the cDNA encoding RIG-I, there were several other candidate cDNA clones which enhance virus-responsive reporter activity. Two of the independent clones encoded a full-length protein, Mitofusin 1 (MFN1). Human MFN1 is composed of 741 amino acids and domains of GTPase and transmembranes (Fig. 8A). MFN1 together with its related protein Mitofusin 2 (MFN2) is expressed on the outer membrane of mitochondria and regulates mitochondrial dynamics [18], [19]. Hyper- and hypo-functioning of either MFN1 or MFN2 result in elongated/aggregated and fragmented mitochondria, respectively. GTPase activity was previously shown to be essential for mitochondrial morphological change, particularly the fragmentation of mitochondria induced by a GTP-binding-deficient mutant of MFN1 (MFN1 T109A) [18].


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)

MFN1 is involved in antiviral signaling.A, Schematic representation of the MFN1 domain. B, L929 cells were transfected with a virus-responsive reporter gene (p-125 Luc) and either an empty vector (Empty), an expression vector for MFN1, or an expression vector for MFN2 as indicated. 48 h after the transfection, cells were mock-treated or infected with NDV. Luciferase activity was determined at 12 h after infection. C and D, L929 cells were transfected with a virus-responsive reporter gene (p-125 Luc) and either an empty vector (Empty) or an expression vector for MFN1 or its mutant (MFN1 T109A) as indicated. At 48 h after transfection, cells were mock-treated, infected with NDV, or transfected with 5′OH-RNA or 5′ppp-RNA. Luciferase activity was determined at 12 h (C) or 9 h (D) after induction. E, L929 cells were transfected with a virus-responsive reporter gene (p-125 Luc) and combinations of the indicated vectors. 48 h after the transfection, cells were mock-treated or infected with NDV. Luciferase activity was determined 12 h after infection.
© Copyright Policy
Related In: Results  -  Collection

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

ppat-1001012-g008: MFN1 is involved in antiviral signaling.A, Schematic representation of the MFN1 domain. B, L929 cells were transfected with a virus-responsive reporter gene (p-125 Luc) and either an empty vector (Empty), an expression vector for MFN1, or an expression vector for MFN2 as indicated. 48 h after the transfection, cells were mock-treated or infected with NDV. Luciferase activity was determined at 12 h after infection. C and D, L929 cells were transfected with a virus-responsive reporter gene (p-125 Luc) and either an empty vector (Empty) or an expression vector for MFN1 or its mutant (MFN1 T109A) as indicated. At 48 h after transfection, cells were mock-treated, infected with NDV, or transfected with 5′OH-RNA or 5′ppp-RNA. Luciferase activity was determined at 12 h (C) or 9 h (D) after induction. E, L929 cells were transfected with a virus-responsive reporter gene (p-125 Luc) and combinations of the indicated vectors. 48 h after the transfection, cells were mock-treated or infected with NDV. Luciferase activity was determined 12 h after infection.
Mentions: RIG-I was originally identified by screening an expression cDNA library [17]. In addition to the cDNA encoding RIG-I, there were several other candidate cDNA clones which enhance virus-responsive reporter activity. Two of the independent clones encoded a full-length protein, Mitofusin 1 (MFN1). Human MFN1 is composed of 741 amino acids and domains of GTPase and transmembranes (Fig. 8A). MFN1 together with its related protein Mitofusin 2 (MFN2) is expressed on the outer membrane of mitochondria and regulates mitochondrial dynamics [18], [19]. Hyper- and hypo-functioning of either MFN1 or MFN2 result in elongated/aggregated and fragmented mitochondria, respectively. GTPase activity was previously shown to be essential for mitochondrial morphological change, particularly the fragmentation of mitochondria induced by a GTP-binding-deficient mutant of MFN1 (MFN1 T109A) [18].

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