The Bromodomain Protein Brd4 Is a Positive Regulatory Component of P-TEFb and Stimulates RNA Polymerase II-dependent Transcription

Mol Cell. 2005 Aug 19;19(4):523-34. doi: 10.1016/j.molcel.2005.06.027.

Abstract

Brd4 is a mammalian bromodomain protein that binds to acetylated chromatin. Proteomic analysis revealed that Brd4 interacts with cyclinT1 and Cdk9 that constitutes core positive transcription elongation factor b (P-TEFb). Brd4 interacted with P-TEFb in the living nucleus through its bromodomain. About half of P-TEFb was bound to the inhibitory subunit and functionally inactive. Brd4 interacted with P-TEFb that was free of the inhibitory subunit. An increase in Brd4 expression led to increased P-TEFb-dependent phosphorylation of RNA polymerase II (RNAPII) CTD and stimulation of transcription from promoters in vivo. Conversely, a reduction in Brd4 expression by siRNA reduced CTD phosphorylation and transcription, revealing that Brd4 is a positive regulatory component of P-TEFb. In chromatin immunoprecipitation (ChIP) assays, the recruitment of P-TEFb to a promoter was dependent on Brd4 and was enhanced by an increase in chromatin acetylation. Together, P-TEFb alternately interacts with Brd4 and the inhibitory subunit to maintain functional equilibrium in the cell.

MeSH terms

  • Animals
  • Cyclin-Dependent Kinase 9 / genetics
  • Cyclin-Dependent Kinase 9 / metabolism*
  • DNA, Complementary / metabolism
  • Mice
  • Nuclear Proteins
  • Oncogene Proteins, Fusion / genetics
  • Oncogene Proteins, Fusion / physiology*
  • Positive Transcriptional Elongation Factor B / metabolism*
  • Promoter Regions, Genetic
  • RNA Polymerase II / genetics
  • RNA Polymerase II / metabolism*
  • RNA, Small Nuclear / genetics
  • RNA, Small Nuclear / metabolism
  • Transcription Factors
  • Transcription, Genetic / physiology*

Substances

  • Brd4 protein, mouse
  • DNA, Complementary
  • Nuclear Proteins
  • Oncogene Proteins, Fusion
  • RNA, Small Nuclear
  • Transcription Factors
  • Positive Transcriptional Elongation Factor B
  • Cdk9 protein, mouse
  • Cyclin-Dependent Kinase 9
  • RNA Polymerase II