title: Interplay between HIV entry and transportin-SR2 dependency.
abstract: BACKGROUND
  Transportin-SR2 (TRN-SR2, TNPO3, transportin 3) was previously identified as an interaction partner of human immunodeficiency virus type 1 (HIV-1) integrase and functions as a nuclear import factor of HIV-1. A possible role of capsid in transportin-SR2-mediated nuclear import was recently suggested by the findings that a chimeric HIV virus, carrying the murine leukemia virus (MLV) capsid and matrix proteins, displayed a transportin-SR2 independent phenotype, and that the HIV-1 N74D capsid mutant proved insensitive to transportin-SR2 knockdown.
  
  
  RESULTS
  Our present analysis of viral specificity reveals that TRN-SR2 is not used to the same extent by all lentiviruses. The DNA flap does not determine the TRN-SR2 requirement of HIV-1. We corroborate the TRN-SR2 independent phenotype of the chimeric HIV virus carrying the MLV capsid and matrix proteins. We reanalyzed the HIV-1 N74D capsid mutant in cells transiently or stably depleted of transportin-SR2 and confirm that the N74D capsid mutant is independent of TRN-SR2 when pseudotyped with the vesicular stomatitis virus glycoprotein (VSV-G). Remarkably, although somewhat less dependent on TRN-SR2 than wild type virus, the N74D capsid mutant carrying the wild type HIV-1 envelope required TRN-SR2 for efficient replication. By pseudotyping with envelopes that mediate pH-independent viral uptake including HIV-1, measles virus and amphotropic MLV envelopes, we demonstrate that HIV-1 N74D capsid mutant viruses retain partial dependency on TRN-SR2. However, this dependency on TRN-SR2 is lost when the HIV N74D capsid mutant is pseudotyped with envelopes mediating pH-dependent endocytosis, such as the VSV-G and Ebola virus envelopes.
  
  
  CONCLUSIONS
  Here we discover a link between the viral entry of HIV and its interaction with TRN-SR2. Our data confirm the importance of TRN-SR2 in HIV-1 replication and argue for careful interpretation of experiments performed with VSV-G pseudotyped viruses in studies on early steps of HIV replication including the role of capsid therein.
authors.affiliation: Laboratory of Molecular Virology and Gene Therapy, Katholieke Universiteit Leuven, Kapucijnenvoer 33, VCTB+5, B-3000 Leuven, Flanders, Belgium.
authors.forename: Wannes
authors.initials: W
authors.lastname: Thys
authors.forename: Stéphanie
authors.initials: S
authors.lastname: De Houwer
authors.forename: Jonas
authors.initials: J
authors.lastname: Demeulemeester
authors.forename: Oliver
authors.initials: O
authors.lastname: Taltynov
authors.forename: Renée
authors.initials: R
authors.lastname: Vancraenenbroeck
authors.forename: Melanie
authors.initials: M
authors.lastname: Gérard
authors.forename: Jan
authors.initials: J
authors.lastname: De Rijck
authors.forename: Rik
authors.initials: R
authors.lastname: Gijsbers
authors.forename: Frauke
authors.initials: F
authors.lastname: Christ
authors.forename: Zeger
authors.initials: Z
authors.lastname: Debyser
mesh_terms: D002460:Cell Line; D015497:HIV-1 / Q000502:physiology*; D006801:Humans; D053586:Virus Internalization; D028961:beta Karyopherins / Q000378:metabolism*
chemical_list: D028961:beta Karyopherins; C424165:transportin SR2