title: Inhibiting lentiviral replication by HEXIM1, a cellular negative regulator of the CDK9/cyclin T complex.
abstract: OBJECTIVE
  Tat-dependent transcriptional elongation is crucial for the replication of HIV-1 and depends on positive transcription elongation factor b complex (P-TEFb), composed of cyclin dependent kinase 9 (CDK9) and cyclin T. Hexamethylene bisacetamide-induced protein 1 (HEXIM1) inhibits P-TEFb in cooperation with 7SK RNA, but direct evidence that this inhibition limits the replication of HIV-1 has been lacking. In the present study we examined whether the expression of FLAG-tagged HEXIM1 (HEXIM1-f) affected lentiviral replication in human T cell lines.
  
  
  METHODS
  HEXIM1-f was introduced to five human T cell lines, relevant host for HIV-1, by murine leukemia virus vector and cells expressing HEXIM1-f were collected by fluorescence activated cell sorter. The lentiviral replication kinetics in HEXIM1-f-expressing cells was compared with that in green fluorescent protein (GFP)-expressing cells.
  
  
  RESULTS
  HIV-1 and simian immunodeficiency virus replicated less efficiently in HEXIM1-f-expressing cells than in GFP-expressing cells of the five T cell lines tested. The viral revertants were not immediately selected in culture. In contrast, the replication of vaccinia virus, adenovirus, and herpes simplex virus type 1 was not limited. The quantitative PCR analyses revealed that the early phase of viral life cycle was not blocked by HEXIM1. On the other hand, Tat-dependent transcription in HEXIM1-f-expressing cells was substantially repressed as compared with that in GFP-expressing cells.
  
  
  CONCLUSIONS
  These data indicate that HEXIM1 is a host factor that negatively regulates lentiviral replication specifically. Elucidating the regulatory mechanism of HEXIM1 might lead to ways to control lentiviral replication.
authors.affiliation: AIDS Research Center, National Institute of Infectious Diseases, Tokyo, Japan.
authors.forename: Saki
authors.initials: S
authors.lastname: Shimizu
authors.forename: Emiko
authors.initials: E
authors.lastname: Urano
authors.forename: Yuko
authors.initials: Y
authors.lastname: Futahashi
authors.forename: Kosuke
authors.initials: K
authors.lastname: Miyauchi
authors.forename: Maya
authors.initials: M
authors.lastname: Isogai
authors.forename: Zene
authors.initials: Z
authors.lastname: Matsuda
authors.forename: Kyoko
authors.initials: K
authors.lastname: Nohtomi
authors.forename: Toshinari
authors.initials: T
authors.lastname: Onogi
authors.forename: Yutaka
authors.initials: Y
authors.lastname: Takebe
authors.forename: Naoki
authors.initials: N
authors.lastname: Yamamoto
authors.forename: Jun
authors.initials: J
authors.lastname: Komano
mesh_terms: D015153:Blotting, Western / Q000379:methods; D002460:Cell Line; D018076:DNA, Complementary / Q000235:genetics; D005822:Genetic Vectors; D015497:HIV-1 / Q000502:physiology; D006801:Humans; D016086:Lentivirus / Q000502:physiology*; D010957:Plasmids; D016601:RNA-Binding Proteins / Q000235:genetics / Q000502:physiology*; D020133:Reverse Transcriptase Polymerase Chain Reaction / Q000379:methods; D015302:Simian Immunodeficiency Virus / Q000502:physiology; D013601:T-Lymphocytes / Q000378:metabolism / Q000821:virology; D014157:Transcription Factors; D014162:Transfection; D014779:Virus Replication / Q000502:physiology*
chemical_list: D018076:DNA, Complementary; C476123:HEXIM1 protein, human; D016601:RNA-Binding Proteins; D014157:Transcription Factors