Inhibiting lentiviral replication by HEXIM1, a cellular negative regulator of the CDK9/cyclin T complex.
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.
Shimizu
Saki
S
AIDS Research Center, National Institute of Infectious Diseases, Tokyo, Japan.
Urano
Emiko
E
Futahashi
Yuko
Y
Miyauchi
Kosuke
K
Isogai
Maya
M
Matsuda
Zene
Z
Nohtomi
Kyoko
K
Onogi
Toshinari
T
Takebe
Yutaka
Y
Yamamoto
Naoki
N
Komano
Jun
J
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*
D018076:DNA, Complementary; C476123:HEXIM1 protein, human; D016601:RNA-Binding Proteins; D014157:Transcription Factors