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The functional interactome of PYHIN immune regulators reveals IFIX is a sensor of viral DNA.

Diner BA, Li T, Greco TM, Crow MS, Fuesler JA, Wang J, Cristea IM - Mol. Syst. Biol. (2015)

Bottom Line: We discover that IFIX detects viral DNA in both the nucleus and cytoplasm, binding foreign DNA via its HIN domain in a sequence-non-specific manner.Furthermore, IFIX contributes to the induction of interferon response.Our results highlight the value of integrative proteomics in deducing protein function and establish IFIX as an antiviral DNA sensor important for mounting immune responses.

View Article: PubMed Central - PubMed

Affiliation: Department of Molecular Biology, Lewis Thomas Laboratory, Princeton University, Princeton, NJ, USA.

No MeSH data available.


Related in: MedlinePlus

Model for IFIX-mediated intrinsic and innate immune functionsIFIX functions as a previously unrecognized viral DNA sensor. IFIX binds viral DNA in the cytoplasm through its HIN200 domain. This initiates innate immunity via induction of interferon-β expression. During HSV-1 infection, IFIX recognizes and binds viral DNA within the nucleus. This IFIX function may be mediated by its association with sub-nuclear PML bodies. To inhibit PML body-mediated intrinsic defenses, HSV-1 E3 ubiquitin ligase ICP0 is known to target PML for its proteasome-dependent degradation, dispersing PML bodies and relieving the imposed repression.
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fig07: Model for IFIX-mediated intrinsic and innate immune functionsIFIX functions as a previously unrecognized viral DNA sensor. IFIX binds viral DNA in the cytoplasm through its HIN200 domain. This initiates innate immunity via induction of interferon-β expression. During HSV-1 infection, IFIX recognizes and binds viral DNA within the nucleus. This IFIX function may be mediated by its association with sub-nuclear PML bodies. To inhibit PML body-mediated intrinsic defenses, HSV-1 E3 ubiquitin ligase ICP0 is known to target PML for its proteasome-dependent degradation, dispersing PML bodies and relieving the imposed repression.

Mentions: Among the PYHIN interactions identified in this study, those between IFIX and the components of PML bodies were some of the most striking and unexpected. These sub-nuclear proteinaceous foci are scaffolded via self-association of the integral protein PML. Since their discovery, PML bodies have been demonstrated to play central roles in regulating apoptosis, DNA damage repair, transcription, and viral infection. For instance, a PML-associated ATRX-DAXX complex has been demonstrated to chromatinize and transcriptionally repress herpesviruses during infection, while a HIRA-UBN1 complex is thought to coordinate senescence-associated heterochromatinization (Banumathy et al, 2009). In fact, given their prominence in antiviral defenses, PML body components are commonly targeted and inhibited by viral proteins. Furthermore, DNA damage pathways are known to be induced during infections with nuclear-replicating DNA viruses (Schwartz et al, 2009; Lilley et al, 2011). The functions of PML bodies and DDR factors in host defense are further intertwined. For instance, the MRN complex elicits both DNA damage and dsDNA-dependent IFN responses (Kondo et al, 2013) and localizes to PML bodies (Lombard & Guarente, 2000; Mirzoeva & Petrini, 2001). Our observed IFIX interactions with PML bodies, Ku70/80, and MRN complexes led us to hypothesize that these proteins may act cooperatively in antiviral response upon deposition of viral genome, and we went on to more closely investigate these possible IFIX functions. Overexpression of IFIX significantly hindered the ability of HSV-1 to replicate in HEK293 cells (Fig5E). Reciprocally, knockdown of IFIX in primary fibroblasts increased HSV-1 titers to an extent comparable to that of a PML knockdown in the same cell type. Therefore, we sought to investigate the mechanism by which IFIX exerts antiviral activities. Using in vitro and in vivo DNA-binding assays, we demonstrated that IFIX binds foreign dsDNA through its HIN200 domain (model in Fig7). This physical interaction with DNA is not dependent on DNA ends (unlike the IFIX-associated MRN and Ku70/80 complexes we identified) and is not sequence specific (Fig6B and C). Furthermore, we showed that IFIX contributes to the induction of type I IFNs in response to transfection with vaccinia virus dsDNA. Thus, IFIX possesses both characteristics ubiquitous among all currently established DNA sensors: (i) an ability to bind foreign dsDNA in a sequence-independent manner and (ii) a contribution to the induction of innate immune signaling in response to dsDNA.


The functional interactome of PYHIN immune regulators reveals IFIX is a sensor of viral DNA.

Diner BA, Li T, Greco TM, Crow MS, Fuesler JA, Wang J, Cristea IM - Mol. Syst. Biol. (2015)

Model for IFIX-mediated intrinsic and innate immune functionsIFIX functions as a previously unrecognized viral DNA sensor. IFIX binds viral DNA in the cytoplasm through its HIN200 domain. This initiates innate immunity via induction of interferon-β expression. During HSV-1 infection, IFIX recognizes and binds viral DNA within the nucleus. This IFIX function may be mediated by its association with sub-nuclear PML bodies. To inhibit PML body-mediated intrinsic defenses, HSV-1 E3 ubiquitin ligase ICP0 is known to target PML for its proteasome-dependent degradation, dispersing PML bodies and relieving the imposed repression.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
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getmorefigures.php?uid=PMC4358659&req=5

fig07: Model for IFIX-mediated intrinsic and innate immune functionsIFIX functions as a previously unrecognized viral DNA sensor. IFIX binds viral DNA in the cytoplasm through its HIN200 domain. This initiates innate immunity via induction of interferon-β expression. During HSV-1 infection, IFIX recognizes and binds viral DNA within the nucleus. This IFIX function may be mediated by its association with sub-nuclear PML bodies. To inhibit PML body-mediated intrinsic defenses, HSV-1 E3 ubiquitin ligase ICP0 is known to target PML for its proteasome-dependent degradation, dispersing PML bodies and relieving the imposed repression.
Mentions: Among the PYHIN interactions identified in this study, those between IFIX and the components of PML bodies were some of the most striking and unexpected. These sub-nuclear proteinaceous foci are scaffolded via self-association of the integral protein PML. Since their discovery, PML bodies have been demonstrated to play central roles in regulating apoptosis, DNA damage repair, transcription, and viral infection. For instance, a PML-associated ATRX-DAXX complex has been demonstrated to chromatinize and transcriptionally repress herpesviruses during infection, while a HIRA-UBN1 complex is thought to coordinate senescence-associated heterochromatinization (Banumathy et al, 2009). In fact, given their prominence in antiviral defenses, PML body components are commonly targeted and inhibited by viral proteins. Furthermore, DNA damage pathways are known to be induced during infections with nuclear-replicating DNA viruses (Schwartz et al, 2009; Lilley et al, 2011). The functions of PML bodies and DDR factors in host defense are further intertwined. For instance, the MRN complex elicits both DNA damage and dsDNA-dependent IFN responses (Kondo et al, 2013) and localizes to PML bodies (Lombard & Guarente, 2000; Mirzoeva & Petrini, 2001). Our observed IFIX interactions with PML bodies, Ku70/80, and MRN complexes led us to hypothesize that these proteins may act cooperatively in antiviral response upon deposition of viral genome, and we went on to more closely investigate these possible IFIX functions. Overexpression of IFIX significantly hindered the ability of HSV-1 to replicate in HEK293 cells (Fig5E). Reciprocally, knockdown of IFIX in primary fibroblasts increased HSV-1 titers to an extent comparable to that of a PML knockdown in the same cell type. Therefore, we sought to investigate the mechanism by which IFIX exerts antiviral activities. Using in vitro and in vivo DNA-binding assays, we demonstrated that IFIX binds foreign dsDNA through its HIN200 domain (model in Fig7). This physical interaction with DNA is not dependent on DNA ends (unlike the IFIX-associated MRN and Ku70/80 complexes we identified) and is not sequence specific (Fig6B and C). Furthermore, we showed that IFIX contributes to the induction of type I IFNs in response to transfection with vaccinia virus dsDNA. Thus, IFIX possesses both characteristics ubiquitous among all currently established DNA sensors: (i) an ability to bind foreign dsDNA in a sequence-independent manner and (ii) a contribution to the induction of innate immune signaling in response to dsDNA.

Bottom Line: We discover that IFIX detects viral DNA in both the nucleus and cytoplasm, binding foreign DNA via its HIN domain in a sequence-non-specific manner.Furthermore, IFIX contributes to the induction of interferon response.Our results highlight the value of integrative proteomics in deducing protein function and establish IFIX as an antiviral DNA sensor important for mounting immune responses.

View Article: PubMed Central - PubMed

Affiliation: Department of Molecular Biology, Lewis Thomas Laboratory, Princeton University, Princeton, NJ, USA.

No MeSH data available.


Related in: MedlinePlus