Modulation of the Brd4/P-TEFb interaction by the human T-lymphotropic virus type 1 tax protein.
Positive transcription elongation factor (P-TEFb), which is composed of CDK9 and cyclin T1, plays an important role in cellular and viral gene expression. Our lab has recently demonstrated that P-TEFb is required for Tax transactivation of the viral long terminal repeat (LTR). P-TEFb is found in two major complexes: the inactive form, which is associated with inhibitory subunits 7SK snRNA and HEXIM1, and the active form, which is associated with, at least in part, Brd4. In this study, we analyzed the effect of Brd4 on human T-lymphotropic virus type 1 (HTLV-1) transcription. Overexpression of Brd4 repressed Tax transactivation of the HTLV-1 LTR in a dose-dependent manner. In vitro binding studies suggest that Tax and Brd4 compete for binding to P-TEFb through direct interaction with cyclin T1. Tax interacts with cyclin T1 amino acids 426 to 533, which overlaps the region responsible for Brd4 binding. In vivo, overexpression of Tax decreased the amount of 7SK snRNA associated with P-TEFb and stimulates serine 2 phosphorylation of the RNA polymerase II carboxyl-terminal domain, suggesting that Tax regulates the functionality of P-TEFb. Our results suggest the possibility that Tax may compete and functionally substitute for Brd4 in P-TEFb regulation.
Cho
Won-Kyung
WK
Virus Tumor Biology Section, Laboratory of Cellular Oncology, Center for Cancer Research, National Cancer Institute, National Institutes of Health, 41 Medlars Dr., Bldg. 41, Rm. B201, Bethesda, MD 20892, USA.
Zhou
Meisheng
M
Jang
Moon Kyoo
MK
Huang
Keven
K
Jeong
Soo-Jin
SJ
Ozato
Keiko
K
Brady
John N
JN
D001665:Binding Sites; D001667:Binding, Competitive; D018797:Cell Cycle Proteins; D015967:Gene Expression Regulation, Viral; D016356:Gene Products, tax / Q000378:metabolism / Q000502:physiology*; D015368:Human T-lymphotropic virus 1 / Q000502:physiology*; D006801:Humans; D009687:Nuclear Proteins / Q000378:metabolism*; D042925:Positive Transcriptional Elongation Factor B / Q000378:metabolism*; D011485:Protein Binding; D020079:Terminal Repeat Sequences / Q000235:genetics; D014157:Transcription Factors / Q000378:metabolism*; D014158:Transcription, Genetic; D000092468:Bromodomain Containing Proteins
D018797:Cell Cycle Proteins; D016356:Gene Products, tax; D009687:Nuclear Proteins; D042925:Positive Transcriptional Elongation Factor B; D014157:Transcription Factors; C441289:BRD4 protein, human; D000092468:Bromodomain Containing Proteins