The retinoblastoma protein binds the promoter of the survival gene bcl-2 and regulates its transcription in epithelial cells through transcription factor AP-2

Mol Cell Biol. 2002 Nov;22(22):7877-88. doi: 10.1128/MCB.22.22.7877-7888.2002.

Abstract

The retinoblastoma (RB) gene product has been shown to restrict cell proliferation, promote cell differentiation, and inhibit apoptosis. Loss of RB function can induce both p53-dependent apoptosis and p53-independent apoptosis; little is known about the mechanisms of RB-regulated p53-independent apoptosis. Here we show that RB specifically activates transcription of the survival gene bcl-2 in epithelial cells but not in NIH 3T3 mesenchymal cells. This transcriptional activity is mediated by the transcription factor AP-2. By monitoring protein-DNA interactions in living cells using formaldehyde cross-linking and chromatin immunoprecipitation, we show that endogenous RB and AP-2 both bind to the same bcl-2 promoter sequence. In addition, we demonstrate that RB and AP-2 also bind to the E-cadherin gene promoter in vivo, consistent with regulation of this promoter by both AP-2 and RB in epithelial cells. This study provides evidence that RB activates bcl-2 and E-cadherin by binding directly to the respective promoter sequences and not indirectly by repressing an inhibitor. This recruitment is mediated by a transcription factor, in this case AP-2. For the first time, our results suggest a direct molecular mechanism by which RB might inhibit apoptosis independently of p53. The results are discussed in a context where RB and Bcl-2 contribute under nonpathological conditions to the maintenance of cell viability in association with a differentiated phenotype, contributing to the tumor suppressor function of RB and playing important roles in normal development.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Acetylation
  • Cadherins / genetics
  • Cell Line
  • Chromatin / metabolism
  • DNA-Binding Proteins / metabolism*
  • Epithelial Cells / cytology
  • Epithelial Cells / physiology*
  • Gene Expression Regulation
  • Genes, Reporter
  • Histones / metabolism
  • Humans
  • Models, Genetic
  • Promoter Regions, Genetic*
  • Protein Binding
  • Proto-Oncogene Proteins c-bcl-2 / genetics*
  • Proto-Oncogene Proteins c-bcl-2 / metabolism
  • Recombinant Fusion Proteins / genetics
  • Recombinant Fusion Proteins / metabolism
  • Retinoblastoma Protein / metabolism*
  • Transcription Factor AP-2
  • Transcription Factors / metabolism*
  • Transcriptional Activation*

Substances

  • Cadherins
  • Chromatin
  • DNA-Binding Proteins
  • Histones
  • Proto-Oncogene Proteins c-bcl-2
  • Recombinant Fusion Proteins
  • Retinoblastoma Protein
  • Transcription Factor AP-2
  • Transcription Factors