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Analysis of Cell Cycle Position in Mammalian Cells
12:19

Analysis of Cell Cycle Position in Mammalian Cells

Published on: January 21, 2012

IKK/NF-kappaB signaling pathway inhibits cell-cycle progression by a novel Rb-independent suppression system for E2F

K Araki1, K Kawauchi, N Tanaka

  • 1Department of Molecular Oncology, Institute of Gerontology, Nippon Medical School, Kanagawa, Japan.

Oncogene
|June 11, 2008
PubMed

Insights

The IKK/NF-kappaB pathway inhibits cell growth by suppressing E2F transcription factors, independent of Retinoblastoma proteins. This pathway offers a novel mechanism for controlling cell proliferation.

Area of Science:

  • Molecular Biology
  • Cell Biology
  • Cancer Research

Background:

  • E2F transcription factors regulate cell-cycle progression.
  • Histone acetyltransferases (HATs) and Retinoblastoma (Rb) proteins modulate E2F activity.
  • Rb proteins inhibit E2F by disrupting HAT binding and recruiting histone deacetylases.

Purpose of the Study:

  • To investigate the role of IkappaB kinases (IKKs) in regulating E2F activity and cell growth.
  • To elucidate the mechanism by which IKKs influence E2F-dependent transcription.
  • To determine if this regulation is dependent on Rb family proteins or nuclear factor (NF)-kappaB.

Main Methods:

  • Studied IKKalpha/beta activation effects on cell growth and E2F transcription in human fibroblasts.
  • Utilized cell lines with and without NF-kappaB/p65 or Rb family genes.
  • Assessed physical interactions between E2Fs, p65, HAT cofactors, and performed phosphorylation and DNA-binding assays for E2F4/p130.

Main Results:

  • IKKalpha/beta activation inhibited cell growth and E2F transcription in normal fibroblasts.
  • E2F inhibition by IKKs was dependent on NF-kappaB/p65 but independent of Rb family proteins.
  • p65 disrupted activator E2F interactions with HAT cofactors, reducing gene expression.
  • IKKalpha/beta directly phosphorylated E2F4, promoting nuclear accumulation and DNA binding of the E2F4/p130 repressor complex.

Conclusions:

  • A novel Rb-independent growth inhibitory system mediated by the IKK/NF-kappaB pathway suppresses E2Fs.
  • This pathway provides a new mechanism for controlling cell proliferation through E2F regulation.

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