Bromodomain analysis of Brd2-dependent transcriptional activation of cyclin A

Biochem J. 2005 Apr 1;387(Pt 1):257-69. doi: 10.1042/BJ20041793.

Abstract

Cyclin A is regulated primarily through transcription control during the mammalian cell cycle. A dual mechanism of cyclin A transcriptional repression involves, on the one hand, promoter-bound inhibitory complexes of E2F transcription factors and RB (retinoblastoma) family proteins, and on the other, chromatin-directed histone deacetylase activity that is recruited to the cyclin A promoter early in the cell cycle in association with these RB proteins. This dual regulation maintains transcriptional silence of the cyclin A locus until its transcription is required in S-phase. At that time, RB family members dissociate from E2F proteins and nucleosomal restructuring of the locus takes place, to permit transcriptional activation and resultant S-phase progression to proceed. We have identified a double bromo-domain-containing protein Brd2, which exhibits apparent 'scaffold' or transcriptional adapter functions and mediates recruitment of both E2F transcription factors and chromatin-remodelling activity to the cyclin A promoter. We have shown previously that Brd2-containing nuclear, multiprotein complexes contain E2F-1 and -2. In the present study, we show that, in S-phase, they also contain histone H4-directed acetylase activity. Overexpression of Brd2 in fibroblasts accelerates the cell cycle through increased expression of cyclin A and its associated cyclin-dependent kinase activity. Chromatin immunoprecipitation studies show that Brd2 is physically present at the cyclin A promoter and its overexpression promotes increased histone H4 acetylation at the promoter as it becomes transcriptionally active, suggesting a new model for the dual regulation of cyclin A.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Acetyltransferases / metabolism
  • Animals
  • Cell Cycle / physiology
  • Cell Cycle Proteins / physiology
  • Cell Line
  • Cell Proliferation
  • Chromatin Immunoprecipitation / methods
  • Chromosomal Proteins, Non-Histone
  • Cyclin A / metabolism*
  • DNA-Binding Proteins / deficiency
  • DNA-Binding Proteins / physiology
  • E2F Transcription Factors
  • E2F1 Transcription Factor
  • Histone Acetyltransferases
  • Humans
  • Kidney / cytology
  • Kidney / embryology
  • Kidney / enzymology
  • Mice
  • NIH 3T3 Cells
  • Phosphotransferases / metabolism
  • Promoter Regions, Genetic / physiology
  • Protein Serine-Threonine Kinases / biosynthesis
  • Protein Serine-Threonine Kinases / physiology*
  • Retinoblastoma Protein / deficiency
  • Retinoblastoma Protein / physiology
  • Transcription Factors / deficiency
  • Transcription Factors / physiology
  • Transcriptional Activation / physiology*

Substances

  • Brd2 protein, mouse
  • Cell Cycle Proteins
  • Chromosomal Proteins, Non-Histone
  • Cyclin A
  • DNA-Binding Proteins
  • E2F Transcription Factors
  • E2F1 Transcription Factor
  • E2F1 protein, human
  • E2f1 protein, mouse
  • Retinoblastoma Protein
  • Transcription Factors
  • Acetyltransferases
  • Histone Acetyltransferases
  • Phosphotransferases
  • Protein Serine-Threonine Kinases