title: MLV requires Tap/NXF1-dependent pathway to export its unspliced RNA to the cytoplasm and to express both spliced and unspliced RNAs.
abstract: BACKGROUND
  Eukaryotic cells have evolved stringent proofreading mechanisms to ensure that intron-containing mRNAs do not leave the nucleus. However, all retroviruses must bypass this checkpoint for replication. Indeed, their primary polycistronic transcript (Full-Length) must reach the cytoplasm to be either translated or packaged as genomic RNA in progeny viruses.Murine leukemia virus (MLV) is a prototype of simple retroviruses with only two well-regulated splicing events that directly influence viral leukemogenic properties in mice. Several cis-elements have been identified in the FL RNA that regulate its cytoplasmic accumulation. However, their connection with an export mechanism is yet unknown. Our goal was to identify the cellular pathway used by MLV to export its RNAs into the cytoplasm of the host cells.
  
  
  RESULTS
  Since other retroviruses use the CRM1 and/or the Tap/NXF1 pathways to export their unspliced RNA from the nucleus, we investigated the role of these two pathways in MLV replication by using specific inhibitors. The effects of export inhibition on MLV protein synthesis, RNA levels and RNA localization were studied by Western blotting, RT-qPCR, fluorescence microscopy and ribonucleoprotein immunoprecipitation assays. Taken together, our results show for the first time that MLV requires the Tap/NXF1-mediated export pathway, and not the CRM1 pathway, for the expression of its spliced and unspliced RNAs and for FL RNA nuclear export.
  
  
  CONCLUSIONS
  By contrast to HIV-1, MLV recruits the same pathway for the cytoplasmic expression of its spliced and unspliced RNAs. Thus, MLV RNA expression depends upon coordinated splicing/export processes. In addition, FL RNA translation relies on Tap/NXF1-dependent export, raising the critical question of whether the pool of FL RNA to be packaged is also exported by Tap/NXF1.
authors.forename: Lucie
authors.initials: L
authors.lastname: Pessel-Vivares
authors.forename: Mireia
authors.initials: M
authors.lastname: Ferrer
authors.affiliation: UMR5236 CNRS, UM1, UM2, CPBS, 1919 Route de Mende, Montpellier, France. sebastien.laine@cpbs.cnrs.fr.
authors.forename: Sébastien
authors.initials: S
authors.lastname: Lainé
authors.forename: Marylène
authors.initials: M
authors.lastname: Mougel
mesh_terms: D021581:Active Transport, Cell Nucleus; D000818:Animals; D000950:Antigens, Ly / Q000378:metabolism*; D015153:Blotting, Western; D002460:Cell Line; D003593:Cytoplasm / Q000378:metabolism; D015870:Gene Expression; D009052:Leukemia Virus, Murine / Q000235:genetics / Q000502:physiology*; D008565:Membrane Proteins / Q000378:metabolism*; D051379:Mice; D029543:Nucleocytoplasmic Transport Proteins / Q000378:metabolism*; D012333:RNA, Messenger / Q000378:metabolism*; D012367:RNA, Viral / Q000378:metabolism*; D060888:Real-Time Polymerase Chain Reaction; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014764:Viral Proteins / Q000096:biosynthesis
chemical_list: D000950:Antigens, Ly; C074650:Ly6a protein, mouse; D008565:Membrane Proteins; C569386:NXF1 protein, mouse; D029543:Nucleocytoplasmic Transport Proteins; D012333:RNA, Messenger; D012367:RNA, Viral; D014764:Viral Proteins