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Inhibition of p53 transcriptional activity by Bcl-2 requires its membrane-anchoring domain

B A Froesch1, C Aimé-Sempé, B Leber

  • 1Burnham Institute, La Jolla, California 92037, USA.

The Journal of Biological Chemistry
|February 26, 1999
PubMed

Insights

The anti-apoptosis protein Bcl-2 inhibits p53 transcriptional activity, a function dependent on its membrane-anchoring domain. This suggests Bcl-2 interferes with p53 target gene expression, potentially by sequestering a necessary factor.

Area of Science:

  • Molecular Biology
  • Cell Biology
  • Cancer Research

Background:

  • The p53 protein is a critical tumor suppressor involved in apoptosis and cell cycle arrest.
  • Bcl-2 is an anti-apoptotic protein that regulates cell death.
  • The interplay between Bcl-2 and p53 function is not fully understood.

Purpose of the Study:

  • To investigate the effect of Bcl-2 on p53-dependent transcriptional activation.
  • To determine if the membrane-anchoring domain of Bcl-2 is required for this function.
  • To explore the mechanism by which Bcl-2 might interfere with p53 activity.

Main Methods:

  • Reporter gene co-transfection assays in human embryonic kidney 293 and MCF7 cells.
  • Generation and use of Bcl-2 mutants lacking the transmembrane domain (Bcl-2(DeltaTM)).
  • Stable expression of Bcl-2 and its mutants in MCF7 cells.
  • Treatment with DNA-damaging agents (doxorubicin, UV radiation).
  • Analysis of p53 nuclear accumulation, p53-responsive promoter activity, and p21(CIP1/WAF1) expression.

Main Results:

  • Bcl-2 potently inhibited p53-dependent transcriptional activation without affecting p53 nuclear accumulation.
  • Bcl-2 lacking its transmembrane domain (Bcl-2(DeltaTM)) did not inhibit p53 activity.
  • In cells treated with DNA damage, Bcl-2 expression reduced p53-responsive promoter activity and p21 expression, while Bcl-2(DeltaTM) did not.
  • Chimeric Bcl-2 proteins with heterologous transmembrane domains mimicked wild-type Bcl-2's inhibitory function.

Conclusions:

  • Bcl-2 interferes with the transcriptional activation of p53 target genes, in addition to suppressing apoptosis.
  • Membrane anchoring of Bcl-2 is essential for its ability to inhibit p53 transcriptional activity.
  • Membrane-anchored Bcl-2 may sequester an unknown factor required for p53 transcriptional function.

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