Studies thread: Ebola VP24 & STAT1

[Vibrant62]

Elucidation of the Ebola Virus VP24 Cellular Interactome and Disruption of Virus Biology through Targeted Inhibition of Host-Cell Protein Function

http://pubs.acs.org/doi/full/10.1021/pr500556d

Publication Date (Web): August 26, 2014

Abstract

Viral pathogenesis in the infected cell is a balance between antiviral responses and subversion of host-cell processes. Many viral proteins specifically interact with host-cell proteins to promote virus biology. Understanding these interactions can lead to knowledge gains about infection and provide potential targets for antiviral therapy. One such virus is Ebola, which has profound consequences for human health and causes viral hemorrhagic fever where case fatality rates can approach 90%. The Ebola virus VP24 protein plays a critical role in the evasion of the host immune response and is likely to interact with multiple cellular proteins. To map these interactions and better understand the potential functions of VP24, label-free quantitative proteomics was used to identify cellular proteins that had a high probability of forming the VP24 cellular interactome. Several known interactions were confirmed, thus placing confidence in the technique, but new interactions were also discovered including one with ATP1A1, which is involved in osmoregulation and cell signaling. Disrupting the activity of ATP1A1 in Ebola-virus-infected cells with a small molecule inhibitor resulted in a decrease in progeny virus, thus illustrating how quantitative proteomics can be used to identify potential therapeutic targets.

Keywords:
Ebola virus; VP24 protein; label free proteomics; proteomics; virus; antiviral; inhibitor; interactome

 

[Vibrant62]

Re: Studies thread: Ebola VP24

Re: Studies thread: Ebola VP24

Ebola Virus VP24 Targets a Unique NLS Binding Site on Karyopherin Alpha 5 to Selectively Compete with Nuclear Import of Phosphorylated STAT1

http://www.cell.com/cell-host-microbe/fulltext/S1931-3128(14)00263-7

Volume 16, Issue 2, p187?200, 13 August 2014

Highlights

?Structure of Ebola virus VP24 bound to the C terminus of karyopherin alpha 5 (KPNA5)
?VP24 binds a unique nonclassical NLS binding site in KPNA5
?VP24 and phosphorylated STAT1 share a common binding site on KPNA5 binding
?VP24 competes with nuclear import of phosphorylated STAT1 to counter STAT signaling

Summary

During antiviral defense, interferon (IFN) signaling triggers nuclear transport of tyrosine-phosphorylated STAT1 (PY-STAT1), which occurs via a subset of karyopherin alpha (KPNA) nuclear transporters. Many viruses, including Ebola virus, actively antagonize STAT1 signaling to counteract the antiviral effects of IFN. Ebola virus VP24 protein (eVP24) binds KPNA to inhibit PY-STAT1 nuclear transport and render cells refractory to IFNs. We describe the structure of human KPNA5 C terminus in complex with eVP24. In the complex, eVP24 recognizes a unique nonclassical nuclear localization signal (NLS) binding site on KPNA5 that is necessary for efficient PY-STAT1 nuclear transport. eVP24 binds KPNA5 with very high affinity to effectively compete with and inhibit PY-STAT1 nuclear transport. In contrast, eVP24 binding does not affect the transport of classical NLS cargo. Thus, eVP24 counters cell-intrinsic innate immunity by selectively targeting PY-STAT1 nuclear import while leaving the transport of other cargo that may be required for viral replication unaffected.

 

[Vibrant62]

Re: Studies thread: Ebola VP24

Re: Studies thread: Ebola VP24

How a Virus Blocks a Cellular Emergency Access Lane to the Nucleus, STAT!

Volume 16, Issue 2, p150?152, 13 August 2014

http://www.cell.com/cell-host-microbe/abstract/S1931-3128(14)00268-6

Early in viral infection, the STAT1 transcription factor is rapidly transported into the nucleus using a nonconventional import mechanism to establish an antiviral state. In this issue, Xu et al. (2014) show how the Ebola virus VP24 protein precisely blocks specialized STAT1 import while leaving other cellular import processes intact.

 

[Vibrant62]

Re: Studies thread: Ebola VP24 & STAT1

How Ebola Shuts Down Antiviral Signaling

Sci. Signal., 19 August 2014
Vol. 7, Issue 339, p. ec216

http://stke.sciencemag.org/content/7/339/ec216.abstract?intcmp=collection-ebola

Interferons are the main effectors of the antiviral immune response and are released from virus-infected cells to stimulate the transcription of antiviral genes by triggering phosphorylation, dimerization, and nuclear import of signal transducer and activator of transcription 1 (STAT1) and STAT2. Because Ebola virus blocks the interferon-mediated antiviral response, the virus replicates extremely rapidly and interferon treatment is ineffective. Most proteins imported into the nucleus contain a classical nuclear localization signal (cNLS) sequence that is recognized by members of the karyopherin-α (also known as KPNA or importin-α) family and mediates their nuclear import. However, STATs do not contain a cNLS. Instead, they rely on a largely uncharacterized nonclassical NLS (ncNLS) that is formed through the dimerization of phosphorylated STATs and recognized by KPNA1, KPNA5, and KPNA6, a subset of the KPNA family of nuclear cargo receptors. The VP24 protein of Ebola virus (eVP24) binds to KPNA1, KPNA5, and KPNA6 to block the nuclear import of phosphorylated STAT1 (pSTAT1). Xu et al. solved the crystal structure of eVP24 bound to the C-terminal portion of KPNA5, shedding light not only on how the virus blocks the host antiviral response but also on how KPNAs recognize ncNLS-containing proteins. The structure showed that eVP24 bound to domains of KPNA5 distinct from the domains through which KPNA5 binds to cNLS-containing proteins. The residues of KPNA5 that mediated binding to eVP24 were conserved in KPNA1 and KPNA6 but not conserved in KPNAs that bind only cNLS-containing proteins. These eVP24-binding residues also mediated pSTAT1 binding to KPNA5 in vitro. Mutating residues of eVP24 that contacted KPNA5 reduced nuclear accumulation of pSTAT1 and compromised the ability of eVP24 to inhibit expression of an interferon-inducible reporter gene. Coimmunoprecipitation experiments indicated that eVP24 competed with pSTAT1 for binding to KPNA5 in cells, but eVP24 did not compete with a cNLS peptide for binding to KPNA5, implying that eVP24 does not interfere with the nuclear trafficking of viral or host proteins that rely on a cNLS for nuclear import. Marburg virus, another filovirus closely related to Ebola virus, does not antagonize interferon signaling. Structural and sequence comparisons showed that Marburg virus VP24 (mVP24) differed from eVP24 in regions that mediated binding of eVP24 to KPNA5. Commentary by Daugherty and Malik notes that ncNLS-mediated nuclear import of STATs may have evolved to ensure that during viral infection STAT1 nuclear import and cNLS-dependent nuclear import mechanisms do not compete.