1. Human T-lymphotropic virus type 1 Tax protein complexes with P-TEFb and competes for Brd4 and 7SK snRNP/HEXIM1 binding.
- Author
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Cho WK, Jang MK, Huang K, Pise-Masison CA, and Brady JN
- Subjects
- Blotting, Western, Cell Cycle Proteins, Cell Nucleus genetics, Cell Nucleus metabolism, Chromatin Immunoprecipitation, Cyclin T genetics, Cyclin T metabolism, Flow Cytometry, Gene Products, tax genetics, HTLV-I Infections genetics, HTLV-I Infections metabolism, HTLV-I Infections virology, HeLa Cells metabolism, HeLa Cells virology, Human T-lymphotropic virus 1 pathogenicity, Humans, Molecular Weight, Nuclear Proteins genetics, Positive Transcriptional Elongation Factor B genetics, Protein Binding, RNA, Messenger genetics, RNA, Small Interfering pharmacology, RNA-Binding Proteins genetics, Reverse Transcriptase Polymerase Chain Reaction, Ribonucleoproteins, Small Nuclear genetics, Terminal Repeat Sequences genetics, Transcription Factors genetics, Transcription, Genetic, Virus Replication, gag Gene Products, Human Immunodeficiency Virus genetics, gag Gene Products, Human Immunodeficiency Virus metabolism, Gene Products, tax metabolism, Nuclear Proteins metabolism, Positive Transcriptional Elongation Factor B metabolism, RNA-Binding Proteins metabolism, Ribonucleoproteins, Small Nuclear metabolism, Transcription Factors metabolism
- Abstract
Positive transcription elongation factor b (P-TEFb) plays an important role in stimulating RNA polymerase II elongation for viral and cellular gene expression. P-TEFb is found in cells in either an active, low-molecular-weight (LMW) form or an inactive, high-molecular-weight (HMW) form. We report here that human T-lymphotropic virus type 1 (HTLV-1) Tax interacts with the cyclin T1 subunit of P-TEFb, forming a distinct Tax/P-TEFb LMW complex. We demonstrate that Tax can play a role in regulating the amount of HMW complex present in the cell by decreasing the binding of 7SK snRNP/HEXIM1 to P-TEFb. This is seen both in vitro using purified Tax protein and in vivo in cells transduced with Tax expression constructs. Further, we find that a peptide of cyclin T1 spanning the Tax binding domain inhibits the ability of Tax to disrupt HMW P-TEFb complexes. These results suggest that the direct interaction of Tax with cyclin T1 can dissociate P-TEFb from the P-TEFb/7SK snRNP/HEXIM1 complex for activation of the viral long terminal repeat (LTR). We also show that Tax competes with Brd4 for P-TEFb binding. Chromatin immunoprecipitation (ChIP) assays demonstrated that Brd4 and P-TEFb are associated with the basal HTLV-1 LTR, while Tax and P-TEFb are associated with the activated template. Furthermore, the knockdown of Brd4 by small interfering RNA (siRNA) activates the HTLV-1 LTR promoter, which results in an increase in viral expression and production. Our studies have identified Tax as a regulator of P-TEFb that is capable of affecting the balance between its association with the large inactive complex and the small active complex.
- Published
- 2010
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