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Cell cycle-related transformation of the E2F4-p130 repressor complex

Boris Popov1, Long-Sheng Chang, Vladimir Serikov

  • 1Institute of Cytology, Russian Academy of Sciences, 4, Tikhoretsky Ave., St. Petersburg 194064, Russia. popov_478@hotmail.com

Biochemical and Biophysical Research Communications
|September 13, 2005
PubMed

Insights

The p130-E2F4 repressor complex persists through the G1/S transition in T98G cells, forming a new complex active in later cell cycle phases. This contrasts with HeLa cells under growth restriction, where the repressor complex transforms differently.

Area of Science:

  • Cell Biology
  • Molecular Biology
  • Cancer Research

Background:

  • The p130 protein, part of the pRb tumor suppressor family, typically forms a repressor complex with E2F4.
  • This complex is usually inactivated by p130 hyperphosphorylation during the G1/S phase transition.
  • The role and behavior of p130 after the G1/S transition remain largely uncharacterized.

Purpose of the Study:

  • To investigate the role and molecular behavior of the p130-E2F4 complex beyond the G1/S transition.
  • To compare the cell cycle dynamics of p130-E2F4 complexes in different cell lines (T98G and HeLa) under varying conditions.

Main Methods:

  • Analysis of nuclear and cytosolic cell fractions from T98G and HeLa cells.
  • Detection of protein complexes using immunoprecipitation and Western blotting.
  • Cell cycle phase synchronization and analysis.

Main Results:

  • The p130-E2F4-DNA repressor complex does not dissociate at G1/S in T98G cells but forms a p130-E2F4-cyclin E/A-cdk2 complex present in S and G2/M phases.
  • p130 hyperphosphorylation at G1/S correlates with decreased total p130 levels, with distinct nuclear dephosphorylation and cytosolic hyperphosphorylation.
  • Both nuclear and cytosolic fractions in T98G cells show hyperphosphorylated p130 complexed with E2F4 during S and G2/M phases.
  • In contrast, HeLa cells under growth restriction do not exhibit the transformation of the p130-E2F4-cyclin E/A-cdk2 complex into the p130-E2F4 repressor.

Conclusions:

  • The p130-E2F4 complex exhibits distinct cell cycle-dependent behavior in T98G cells, persisting and modifying its composition after G1/S.
  • Differential phosphorylation and localization of p130 occur in T98G cells throughout the cell cycle.
  • Cellular context and conditions, such as growth restriction in HeLa cells, influence the fate and function of the p130-E2F4 complex.

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