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Journal of Virology, October 2007, p. 11179-11186, Vol. 81, No. 20
0022-538X/07/$08.00+0     doi:10.1128/JVI.00408-07
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

Modulation of the Brd4/P-TEFb Interaction by the Human T-Lymphotropic Virus Type 1 Tax Protein{triangledown}

Won-Kyung Cho,1 Meisheng Zhou,1 Moon Kyoo Jang,2 Keven Huang,1 Soo-Jin Jeong,1 Keiko Ozato,2 and John N. Brady1*

Virus Tumor Biology Section, Laboratory of Cellular Oncology, Center for Cancer Research, National Cancer Institute,1 Laboratory of Molecular Growth Regulation, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland 208922

Received 26 February 2007/ Accepted 26 July 2007

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.

* Corresponding author. Mailing address: 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. Phone: (301) 496-0986. Fax: (301) 496-4951. E-mail: bradyj{at}mail.nih.gov

{triangledown} Published ahead of print on 8 August 2007.

Journal of Virology, October 2007, p. 11179-11186, Vol. 81, No. 20
0022-538X/07/$08.00+0     doi:10.1128/JVI.00408-07
Copyright © 2007, American Society for Microbiology. All Rights Reserved.



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