ABSTRACT
We report here that the alternatively spliced nuclear factors associated with double-stranded RNA, NFAR-1 (90 kDa) and -2 (110 kDa), are involved in retaining cellular transcripts in intranuclear foci and can regulate the export of mRNA to the cytoplasm. Furthermore, the NFAR proteins were found to remain associated with exported ribonucleoprotein complexes. Loss of NFAR function, which was embryonic-lethal, caused an increase in protein synthesis rates, an effect augmented by the presence of the mRNA export factors TAP, p15, or Rae1. Significantly, NFAR depletion in normal murine fibroblasts rendered these cells dramatically susceptible to vesicular stomatitis virus replication. Collectively, our data demonstrate that the NFARs exert influence on mRNA trafficking and the modulation of translation rates and may constitute an innate immune translational surveillance mechanism important in host defense countermeasures against virus infection.
Subject(s)
Nuclear Factor 90 Proteins/metabolism , Protein Biosynthesis/genetics , Animals , Cells, Cultured , Gene Deletion , Humans , Mice , Nuclear Factor 90 Proteins/genetics , Nuclear Matrix-Associated Proteins/genetics , Nuclear Matrix-Associated Proteins/metabolism , Nucleocytoplasmic Transport Proteins/genetics , Nucleocytoplasmic Transport Proteins/metabolism , RNA Interference , RNA, Messenger/genetics , RNA, Small Interfering/geneticsABSTRACT
The NS1 protein of influenza A virus is a major virulence factor that is essential for pathogenesis. NS1 functions to impair innate and adaptive immunity by inhibiting host signal transduction and gene expression, but its mechanisms of action remain to be fully elucidated. We show here that NS1 forms an inhibitory complex with NXF1/TAP, p15/NXT, Rae1/mrnp41, and E1B-AP5, which are key constituents of the mRNA export machinery that interact with both mRNAs and nucleoporins to direct mRNAs through the nuclear pore complex. Increased levels of NXF1, p15, or Rae1 revert the mRNA export blockage induced by NS1. Furthermore, influenza virus down-regulates Nup98, a nucleoporin that is a docking site for mRNA export factors. Reduced expression of these mRNA export factors renders cells highly permissive to influenza virus replication, demonstrating that proper levels of key constituents of the mRNA export machinery protect against influenza virus replication. Because Nup98 and Rae1 are induced by interferons, down-regulation of this pathway is likely a viral strategy to promote viral replication. These findings demonstrate previously undescribed influenza-mediated viral-host interactions and provide insights into potential molecular therapies that may interfere with influenza infection.
Subject(s)
Influenza A virus/physiology , Nuclear Pore/metabolism , Nuclear Pore/virology , RNA, Messenger/metabolism , Active Transport, Cell Nucleus/physiology , Amino Acid Sequence , Animals , Cell Line , Down-Regulation/physiology , HeLa Cells , Humans , Influenza A virus/pathogenicity , Mice , Molecular Sequence Data , Nuclear Pore Complex Proteins/antagonists & inhibitors , Nuclear Pore Complex Proteins/metabolism , Viral Nonstructural Proteins/physiology , VirulenceABSTRACT
Viruses have been invaluable tools for discovering key pathways of nucleocytoplasmic transport. Conversely, disruption of specific nuclear transport pathways, are crucial for the productive life cycle of some viruses. The major cellular mRNA export pathway, which uses TAP (NXF1)/p15(NXT) as receptor, was discovered as a result of TAP interaction with CTE-containing RNAs from Mason-Pfizer Monkey Virus. In addition, CRM1 or exportin 1, which is a transport receptor that mediates nuclear export of proteins, snRNAs, rRNAs and a small subset of mRNAs, was discovered as an interacting partner of the Rev protein of HIV1. Viruses may disrupt the nuclear transport machinery to prevent host antiviral response. VSV Matrix (M) protein inhibits mRNA export by forming a complex with the mRNA export factor Rae1 whereas poliovirus inhibits nuclear import of proteins by probably degrading Nup62 and Nup153. Hence, this review focuses on viruses as tools and as disruptors of nucleocytoplasmic trafficking.
Subject(s)
Active Transport, Cell Nucleus/physiology , Models, Biological , Molecular Probe Techniques , Nuclear Pore/virology , Proteins/metabolism , RNA/metabolism , Virus Physiological Phenomena , Karyopherins/metabolism , Nuclear Pore/metabolismABSTRACT
Interference with nucleocytoplasmic transport is a strategy employed by certain viruses to compromise host cellular function. While it has been shown that the matrix (M) protein of the vesicular stomatitis virus (VSV) inhibits nuclear export of host cell mRNAs, the underlying mechanism has not been fully established. Here we show that VSV M protein binds the mRNA export factor Rae1/mrnp41. A mutant of M protein defective in Rae1 binding is unable to inhibit mRNA nuclear export. We further show that increased expression of Rae1 fully reverts the inhibition of mRNA export induced by M protein or following virus infection. We found that Rae1 is induced by interferon-gamma, a cytokine that plays a critical role in the immune response to viruses, such as VSV. Thus, these results demonstrate that VSV M protein blocks mRNA export by disrupting Rae1 function, which can be reverted by induction of Rae1 expression.
